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Keywords:

  • Apoptosis. Cell death;
  • morphology;
  • mechanisms;
  • clinical implications;
  • Multiple organ dysfunction syndrome

Abstract

  1. Top of page
  2. Abstract
  3. History
  4. Definitions
  5. Pathophysiology
  6. Clinical relevance of apoptosis
  7. Therapeutic possibilities and future directions
  8. Conclusion
  9. References

The balance between cell survival and death is under tight genetic control. A multiplicity of extracellular signals and intracellular mediators is involved in maintaining this balance. When the cell is exposed to physical, biochemical or biological injury, or deprived of necessary substances, it activates a series of stress-response genes. With minimal insults, the cell may recover. With greater insults, single cell death, or apoptosis, results; the cell dies and is recycled to its neighbours. If the insult overwhelms a large number of cells then necrosis ensues, with an accompanying inflammatory response. Dysregulation of the controlling mechanisms of this system results in disease. Deficient apoptosis is associated with cancer, auto-immunity and viral infections. Excessive apoptosis is associated with ischaemic heart disease, stroke, neurodegenerative disease, sepsis and multiple organ dysfunction syndrome. There are myriad therapeutic options unfolding as understanding is gained of apoptosis and its control.

Cell death, a tightly controlled, finely orchestrated event, may be described either as apoptosis or nonapoptotic cell death, traditionally called ‘necrosis’[1]. Apoptosis is a process of cell suicide, the mechanisms of which are encoded in the chromosomes of all nucleated cells. Physiological cell death that removes unwanted cells plays an important role in development, tissue homeostasis and defence against viral infection and mutation. Apoptosis is regulated by complex molecular signalling systems. Tissue ischaemia and reperfusion activate these molecular systems, which therefore represent a therapeutic target for novel treatment to preserve cellular integrity in critical organs such as the brain and heart. Apoptotic cells undergo orderly, energy-dependent enzymatic breakdown into characteristic molecular fragments, deoxyribonucleic acid (DNA), lipids and other macromolecules, which are packaged into small vesicles that may be phagocytosed and reused. The cells involute and die with minimal harm to nearby cells [2]. In contrast ‘necrotic’ cell death is characterised by inflammation and widespread damage.

Apoptosis has a central role in the pathogenesis of human disease when the genes controlling the apoptotic process are suppressed, overexpressed or altered by mutation [3]. Disordered apoptosis is implicated in a variety of human diseases (Table 1). Research into apoptosis is proceeding at a fast pace and this has led to the possibility of new therapeutic approaches to some intractable human diseases [4].

Table 1.  Human diseases associated with disordered apoptosis.
Increased apoptosis 
 Central nervous systemDegenerative diseases (Alzheimer's and Parkinson's disease)
 Cerebral ischaemia
 MyocardiumPeri-infarct border zones
 LymphocytesLymphocyte depletion in sepsis and HIV infection
 MacrophagesBacillary dysentery (Shigella dysenteriae)
Decreased apoptosis 
 Epithelial tissuesCarcinogenesis
 Blood vesselsIntimal hyperplasia
 LymphocytesAutoimmune disorders
 Haemopoietic systemLeukaemia, lymphoma

The purpose of this review is to provide a background to the molecular components that activate apoptosis and the relevance of these to a variety of human diseases, and to discuss the potential for novel therapies based on our understanding of them. An understanding of the role of cell injury and death in the pathophysiology of organ dysfunction is relevant to anaesthetists and intensivists particularly in the management of ischaemic and reperfusion injury, and multiple organ dysfunction syndrome (MODS).

History

  1. Top of page
  2. Abstract
  3. History
  4. Definitions
  5. Pathophysiology
  6. Clinical relevance of apoptosis
  7. Therapeutic possibilities and future directions
  8. Conclusion
  9. References

In the 1880s Weigert & Cohnheim described the microscopic appearance of cell death in necrotic tissue as coagulation necrosis [5]. In 1885, Flemming described the process of ‘chromatolysis’ in which the nuclei of mammalian ovarian follicles broke up and ultimately disappeared in spontaneous cell death [6–8].

In the early 1970s, Kerr described the electron microscopic appearance of singe-cell death in the livers of animals [9, 10] treated with toxins (heliotrine and albitocin) and ischaemia (by ligation of a large branch of the portal vein) and called it ‘shrinkage necrosis’[11]. ‘Single cell death’ in carcinogen-treated rat adrenal cortex [12] and in tumour cells treated with actinomycin D, mitomycin C, cytosine arabinose and cycloheximide [13] was also observed. In 1971, Wyllie found that single cell death in the adrenal gland was induced by hypophysectomy, and suggested a common pathway for cell death initiated by hormone regulation and carcinogen-induced injury [14, 15]. In a landmark paper in 1972, Kerr et al. described the characteristic sequential changes occurring in cell structure during the death process in healthy tissues, normal development, tumour regression, atrophy and involution [1]. The term ‘apoptosis’ (derived from the Greek word for ‘falling off’, a reference to the falling of leaves from trees in autumn in response to the impending threat of freezing and damage in winter) was coined [1].

Further momentum was gained in the mid-1980s when Horvitz reported specific cell death during the development of the nematode Caenorhabditis elegans and cloned the C. elegans death genes (ced genes) responsible [16]. The nematode anti-apoptotic gene ced-9 shared homology with the mammalian proto-oncogene, Bcl-2[17], and was shown to preserve B lymphocytes [18, 19]. During the 1990s, the molecular mechanisms that keep apoptosis in check and the molecular events involved in disordered apoptosis were unravelled. Rodent fibroblast tumours expressing human c-myc genes had high rates of apoptosis [20], suggesting that cancer can occur when a mutation results in dysfunctional apoptosis [21].

Definitions

  1. Top of page
  2. Abstract
  3. History
  4. Definitions
  5. Pathophysiology
  6. Clinical relevance of apoptosis
  7. Therapeutic possibilities and future directions
  8. Conclusion
  9. References

Apoptosis specifically refers to an energy-dependent, asynchronous, genetically controlled process by which unnecessary or damaged single cells self-destruct when the apoptosis genes are activated [22, 23]. Briefly, the cell shrinks and detaches from neighbouring cells and the nucleus is broken down. The nuclear fragments and organelles condense and are ultimately packaged in membrane-bound vesicles, exocytosed and ingested by surrounding cells. Membrane integrity is preserved and dyes are only taken up late in the process. The absence of inflammation differentiates apoptosis from necrosis. The differences between apoptotic and necrotic cell deaths are summarised in Table 2.

Table 2.  Differences between apoptosis and necrosis.
ApoptosisNecrosis
Physiological or pathologicalAlways pathological
Asynchronous process in single cellsOccurs synchronously in multiple cells
Genetically controlledCaused by overwhelming noxious stimuli
Late loss of membrane integrityEarly loss of membrane integrity
Cell shrinkageGeneralised cell and nucleus swelling
Condensation of nuclear contents (‘ladder’ formation of chromatin)Nuclear chromatin disintegration
No inflammatory reactionInflammatory reaction

Ischaemic and accidental (caused by toxins) cell death are characterised by cell swelling or ‘oncosis’ (from the Greek word ‘onkos’ meaning swelling), resulting in cytoplasmic and nuclear swelling and karyolysis (loss of affinity for basic dyes). After either oncosis or apoptosis, cells reach the stage of necrosis where phagocytosis occurs, and in the case of oncosis, this is accompanied by inflammation. Apoptosis and oncosis/necrosis are part of an overlapping spectrum [5, 8, 24–26]. Cells exposed to an overwhelming noxious stimulus, such as ischaemia or toxins, undergo oncosis and necrosis [27]. Programmed cell death (PCD) refers to cell suicide occurring during normal embryological development of an immature organism and the maturation of tissues or organs [28, 29] and does not require de novo gene expression [30].

Pathophysiology

  1. Top of page
  2. Abstract
  3. History
  4. Definitions
  5. Pathophysiology
  6. Clinical relevance of apoptosis
  7. Therapeutic possibilities and future directions
  8. Conclusion
  9. References

Morphological features

There are three distinct phases of apoptosis [31]. During the first phase, the cell detaches from its substratum and adjacent cells with a loss of microvilli and junctional complexes or desmosomes [32]. The DNA is digested by specific endonucleases into fragments and ultimately packed into vesicles. The changes in DNA include strand breakage (karyorhexis) and condensation of nuclear chromatin (pyknosis). This pyknotic chromatin appears as characteristic crescent-shaped ‘caps’ under light microscopy. The endoplasmic reticulum swells and exocytoses its contents. The cell becomes denser as the cytoplasm shrinks and involutes. In the second phase, the cell produces pseudopodia (budding) which contain organelles or nuclear fragments, and these break off into multiple membrane-bound vesicles. The remaining cell becomes a round, smooth membrane-bound remnant (apoptotic body) [3, 4, 32]. In the third phase, the cell membrane becomes permeable to dyes such as Tryphan Blue. The apoptotic body and membrane-bound buds may then be phagocytosed by macrophages, epithelial cells, vascular endothelium or tumour cells. The entire process occurs may take only 15 min, and therefore may be undetectable on tissue sections [5, 23, 33].

In contrast, oncosis is characterised by cellular and organelle swelling with late nuclear fragmentation and breakdown by lysosomal enzymes. The swelling is caused by a deficit in adenosine triphosphate (ATP) production that leads to membrane ionic pump failure and increased plasma membrane permeability. This results in bleb (blister-like, fluid-filled structures) formation of the plasma membrane and ultimate rupture [5]. There is an influx of neutrophils and macrophages in the surrounding tissues, leading to generalised inflammation.

Techniques to identify and quantify apoptosis include staining with nuclear stains such as Hoechst 33258 that allow visualisation of nuclear chromatin clumping. Modern video microscopy allows visualisation of the temporal sequence of events that occur over 15–60 min to 24 h [23, 34, 35].

Fluorescent microscopy using acridine orange allows characteristic chromatin clumping to be observed soon after staining. A further refinement is the comet assay, which shows up DNA degradation [2]. More accurate identification of apoptosis is achieved with methods that specifically target the characteristic DNA cleavages [36]. Agarose gel electrophoresis of extracted DNA fragments yields a characteristic ‘ladder’ pattern which can be used as a marker for apoptosis. A lesser extent of DNA degradation produces hexameric structures called ‘rosettes’[4]. Necrotic cells leave a nondescript smear [3]. The terminal transferase deoxyuridine nick-end labelling of DNA breaking points (TUNEL) method [37], which labels the uridine residues of the nuclear DNA fragments, can be applied to tissue sections and cell cultures to quantify apoptosis. Flow cytometry assays [38–40] may prove to be most accurate in quantifying apoptosis.

Mechanism of cell death

Following an appropriate stimulus, the first stage or ‘decision phase’ of apoptosis is the genetic control point of cell death. This is followed by the second stage or ‘execution’ phase, which is responsible for the morphological changes of apoptosis.

There are four main groups of stimuli for apoptosis [4, 30, 32, 34, 41–45]. A wide variety of physiological and pathological stimuli can initiate apoptosis and these stimuli are summarised in Table 3. The first group of stimuli causes DNA damage and include ionising radiation and alkylating anticancer drugs. The second group induces apoptosis via receptor mechanisms, either by receptor activation mediated by glucocorticoids (acting on the thymus) [34], tumour necrosis factor-α (TNF-α), or by withdrawal of growth factors (nerve growth factor and interleukin (IL)-3) [41, 42]. The third group comprises biochemical agents that enhance the downstream components of the apoptotic pathway and includes phosphatases [30] and kinase inhibitors (e.g. calphostin C, staurosporine). The fourth group comprises agents that cause direct cell membrane damage and includes heat, ultraviolet light and oxidising agents (superoxide anion, hydrogen peroxide). Excessive production of reactive oxygen species (ROS), such as superoxide, hydrogen peroxide and the hydroxyl radicals, produces free radicals that damage lipid membranes, proteins, nucleic acids and extracellular matrix glycosaminoglycans. Many of these stimuli cause necrosis in larger doses. Injury to cell membranes induces apoptosis by activating acid sphingomyelinase that generates the second messenger ceramide from membrane lipids [43, 44].

Table 3.  Stimuli for apoptosis.
  1. DNA, deoxyribonucleic acid; TNF, tumour necrosis factor; IL-3, interleukin-3.

DNA (genome) damageIonising radiation
Anti-cancer drugs (e.g. alkylating agents)
Activation of death receptorsBinding of ‘death receptors’ (e.g. Fas receptor, TNF receptor)
Withdrawal of growth factors (e.g. nerve growth factor, IL-3)
Stimulation of apoptotic pathwayPhosphatases, kinase inhibitors
Direct physical cell damageHeat, ultraviolet light, oxygen free radicals, hydrogen peroxide

The signal that initiates apoptosis may result from binding of a cell-surface ‘death’ receptor or from damage to the genome. Death receptors that initiate apoptosis include the Fas receptor and the TNF receptor system [41]. The Fas receptor, initially known as CD95 or APO-1, is a transmembrane glycoprotein death receptor that is activated by binding of Fas ligand (Fas-L) to cell membranes [41]. Intracellular molecules known as Fas-associated death domain (FADD) are produced. Fas receptors are found in epithelial tissues, tumours and haemopoietic tissues, and may be induced in other tissues that do not express them. The Fas pathway is important in controlling the immune response. Cytotoxic T lymphocytes expressing Fas ligands activate cells bearing Fas receptors and induce apoptosis.

The TNF receptor system mediates different biochemical pathways [41, 42]. A TNF-related apoptosis-inducing ligand (TRAIL) has been discovered. Cancer cells are susceptible to TRAIL-induced apoptosis. Following binding of the TNF receptor, intracellular molecules called ‘death domains’ are produced. A TNF receptor associated death domain (TRADD) has been identified. Tumour necrosis factor may suppress apoptosis by binding to the receptor, TNFR2, which activates a protein known as Nuclear Factor κB (NF-κB), classed as an inhibitor of apoptosis protein (IAP) that prevents the execution phase of apoptosis [43]. It is a DNA binding protein that regulates many pro-inflammatory genes for the production of cytokines and other pro-inflammatory molecules. There is increasing evidence that NF-κB is important in the pathogenesis of systemic inflammatory response syndrome (SIRS), MODS and acute respiratory distress syndrome (ARDS) [28].

Decision phase (genetic control)

Apoptosis is controlled genetically and two genes, Bcl-2 and p53 are important. The first, Bcl-2, is a family of genes that regulates apoptosis [46–49]; found on the mitochondrial membrane, endoplasmic reticulum it may control calcium channels. It is now recognised that there is a family of mammalian proteins similar to Bcl-2 that promotes or inhibits apoptosis [50, 51]. Proteins such as Bcl-2 and Bcl-xL prevent apoptosis, whereas Bcl-2 associated x proteins (Bax) such as Bax, Bad, Bak and Bcl-xS promote apoptosis [30, 52, 53].

The gene p53 is a 53-kDa nuclear phospho-protein that binds to DNA to act as a transcription factor, and controls cell proliferation and DNA repair [54]. Mutations of p53 have been found in > 50% of human cancers (e.g. colon carcinoma) and are associated with resistance to treatment [55]. The gene c-myc is a proto-oncogene that encodes a sequence-specific DNA-binding protein that acts as a transcription factor and induces apoptosis in the presence of p53. The c-myc protein is elevated in many tumours [4].

Mutation of the gene for neuronal apoptosis inhibitory protein (NAIP) occurs in people with spinal muscular atrophy [56]. NAIP protects various cells from apoptosis caused by TNF-α, free radicals and growth factor deprivation.

Execution phase

The central events in apoptosis are proteolysis and mitochondrial inactivation. Cellular disruption results from activation of a family of cysteine proteases called caspases (CASP) [30, 32, 43, 57–59]. Caspases are proenzymes that have been conserved from nematodes to humans. Ten human caspases (CASP 1–10) have been described. Early molecular studies on apoptosis focused on the nematode C. elegans and the gene required for the execution of apoptosis, called ced-3, has been identified and coded. There are two subfamilies of caspases, the ced-3 subfamily (produced by ced-3 gene) and the ICE (IL-1β-converting enzyme) subfamily [60, 61]. Caspase 1, which is related to ICE, is mainly involved in inflammation [60, 61]. The ced-3 caspases are important effectors of apoptosis. Caspase 8 or FADD-like interleukin converting enzyme (FLICE) is the most important enzyme of the ced-3 subfamily [61, 62]. The actions of the caspases are varied; some are endonucleases that cleave DNA, some cleave cytoskeletal proteins and others cause a loss of cell adhesion.

The integrity of the plasma membrane of the apoptotic cell is maintained initially, although ‘budding’ of the cell membrane can occur later. There is no leakage of lysosomal enzymes that can damage nearby cells or elicit immune responses [63]. The apoptotic cell expresses membrane signals that induce phagocytosis [64]. Macrophages can recognise neutrophils undergoing apoptosis via complexes involving thrombospondin receptors (CD36) and the αvβ3 integrin [65–67].

Clinical relevance of apoptosis

  1. Top of page
  2. Abstract
  3. History
  4. Definitions
  5. Pathophysiology
  6. Clinical relevance of apoptosis
  7. Therapeutic possibilities and future directions
  8. Conclusion
  9. References

Central nervous system

In the developing organism there is a specialised form of cell death previously called apoptosis but now known as ‘programmed cell death’ (PCD) [30]. During embryonic development of the nervous system a surplus of cells is produced. PCD eliminates those neurons whose axons fail to reach the target. It occurs with the withdrawal of trophic substances, such as nerve growth factor, or with a loss of synaptic contact or afferent input. Cytokines (e.g. TNF-α) and ROS may trigger PCD [68].

Oxidative stress, glutamate excitotoxicity and calcium influx can induce apoptosis in the mature central nervous system. Excessive production of ROS causes ‘oxidative stress’, damaging lipid membranes, proteins, nucleic acids and extracellular matrix glycosaminoglycans. At low levels of ROS or depletion of antioxidants (e.g. superoxide dismutase, catalase, glutathione peroxidase) apoptosis occurs. At high levels ROS produce more damage and cause necrosis [30].

Glutamate receptor-mediated neuronal injury is an important cause of ‘excitotoxic‘ neuronal death following ischaemia, trauma, epileptic seizures or neurodegeneration [30]. Glutamate produces either necrosis associated with influx of Na+, Cl and water leading to cell swelling or delayed neuronal death (DND) which appears to be apoptotic, occurring several hours after exposure and associated with calcium influx via channels linked to glutamate receptors [69–71].

Calcium is an important second messenger, instrumental in inducing apoptosis by stimulating neurotransmitter release, gene induction and the activation of enzymes (proteases, phosphatases, protein kinases, endonucleases, phospholipases and nitric oxide synthase) [72]. Phospholipase A2 produces superoxide anion, and nitric oxide synthase produces nitric oxide, both of which can cause oxidative stress leading to apoptosis.

Increased apoptosis caused by excessive intracellular Ca2+ has been implicated in cerebral ischaemia, traumatic brain injury, epilepsy and neurodegenerative disease. Cerebral ischaemia results in both necrosis and DND. Cells undergoing DND as a result of less severe insult are seen on the periphery of the infarct within the penumbra. There is accumulating evidence that apoptosis plays a role in DND [30]. Gene transfer using herpes simplex viruses containing a Bcl-2 vector may offer neuroprotection against ischaemia [73]. In traumatic brain injury apoptosis occurs in ≈ 10% of dying neurons, peaking 24–48 h after injury [74]. With severe trauma, the proportion of necrotic cell death increases and antiapoptotic agents may minimise cell death following trauma [73].

Enhanced apoptosis is implicated in several neurodegenerative diseases. In Alzheimer’s disease accumulation of β-amyloid peptide in plaques in the brain and cerebral vasculature causes apoptosis of cortical neurones [75], possibly via nitric oxide (NO) [76]. Parkinson's disease is associated with the loss of dopaminergic neurones in the substantia nigra, and dopamine is thought to cause apoptosis in exposed neurons [30]. Some forms of familial amyotrophic lateral sclerosis may be caused by a mutant gene coding for the antioxidant superoxide dismutase resulting in motor neuron loss via apoptosis. Future therapy may involve the use of growth factors or inhibitors of macromolecular synthesis to block apoptosis [56].

Defective apoptosis caused by mutant apoptotic genes may contribute to the development of neural tumours. Mutated p53 is seen in astrocytic tumours [77, 78]. Protein kinase C inhibitors (e.g. hypericin and calphostin) can cause apoptosis in glioma cell lines. Gene transfer techniques have also been used to introduce Bcl-xs into neuroblastoma cells and ICE retrovirus into gliosarcoma cells with induction of apoptosis in these tumours [79, 80].

Cardiovascular system

Recently it has been shown that myocyte death with cardiac disease occurs by both apoptosis and necrosis in response to hypoxia and ischaemia [45]. Apoptosis has been documented in myocardial ischaemia, reperfusion and infarction, heart failure induced by rapid ventricular pacing or coronary microemboli, several models of pressure overload hypertrophy (by passive load on papillary muscle, aortic banding) [42] and ageing [53].

Hypoxia, nutritional deficiency and toxins (e.g. chemotherapy) that can cause necrosis may induce apoptosis at lower doses [45, 52]. Infarcted areas have a central area of necrosis with surrounding apoptosis in the peri-infarct border zone [42]. Autopsy studies of myocardial infarction have found apoptotic cells scattered between the necrotic cells centrally and the normal cells around the periphery. Coronary artery ligation induces marked increases in proto-oncogenes (Bcl-2 and Fas) in myocytes. The initial event during the early hours of ischaemia appears to be apoptosis. As myocardial cells are overwhelmed by severe ischaemia, apoptotic genes can no longer be expressed and necrosis supervenes [81]. In in vivo reperfusion studies in rabbit models, apoptosis was seen predominantly in reperfused hearts, whereas necrosis was seen mainly with persistent occlusion [82]. Reperfusion increases free radical production and intracellular calcium, which are potent inducers of apoptosis.

Apoptosis in vascular smooth muscle cells in atherosclerotic plaques in coronary arteries may be involved in plaque destabilisation and rupture [83]. Apoptosis is increased by 43% in primary atherosclerotic lesions and 93% in restenoses [84, 85]. It may be triggered by NO and is associated with the expression of caspase 1 [84].

Arrhythmias may be associated with deficient apoptosis during cardiac development. Normally after birth there is apoptosis of the small round pacemaker cells in the central and lower part of the AV node. Delay or failure of apoptosis in these cells may lead to life-threatening arrhythmias that may resolve spontaneously. Excessive apoptosis can lead to bradyarrhythmias and sudden death [45]. Patients with long QT syndrome have increased rates of apoptosis in the sinus node [85].

A common end-stage pathway of various cardiovascular diseases results in deteriorating function and cardiac failure associated with dilated cardiomyopathy [45, 46]. Myocardial hypertrophy may be an initial compensatory response to overloading of adult myocytes. This is associated with c-myc, c-fos, and transforming growth factor, which are also involved in initiating apoptosis. Dilated cardiomyopathy can be induced by chronic infusion of TNF-α, which causes apoptosis [43]. A progressive decline in function in end-stage cardiac failure may be due to apoptosis and this is supported by the finding of increased levels of Bcl-2 in the myocytes of patients with cardiac failure. Although apoptosis itself is irreversible, minimising it with growth factors and cytokines may prevent the progressive decline in left ventricular function [45].

Arrhythmogenic right ventricular dysplasia is a cardiomyopathy associated with sudden death. It is postulated that repetitive episodes of ischaemia and reperfusion associated with ventricular arrhythmias produce apoptosis, which is found in myocardial biopsies in these patients [45].

Immune system

Dysfunction of the apoptotic pathway causes autoimmune disease, immunodeficiencies and lymphoid malignancies. During development large numbers of precursor cells from the bone marrow migrate to the thymus. The majority (90–95%) fail to produce T-cell receptor (TCR) and die via the apoptotic pathway [86]. Thymocyte apoptosis can be induced by endogenously produced glucocorticoids and a lack of TCR [87, 88]. Death of a cell clone (clonal deletion) due to TCR-induced apoptosis takes place in immature B cells that produce antiself antibodies in the fetal liver and later in the bone marrow [89, 90]. Animal studies indicate that autoimmune diseases, such as rheumatoid arthritis, systemic lupus erythematosis, inflammatory bowel disease and insulin-dependent diabetes, may be caused by dysfunctional apoptosis [91, 92]. There is evidence that cytotoxic T cells kill their target cells by the induction of apoptosis in the target [93]. Activated peripheral cytotoxic T cells and peripheral B cells are removed by apoptosis [89].

Granulocyte apoptosis is also important for the resolution of the inflammatory response. Inflammatory agents such as lipopolysaccharide (LPS) and granulocyte colony-stimulating factor (G-CSF) inhibit neutrophil apoptosis. During apoptosis induced by TNF-α and NO donors the neutrophil loses its ability to degranulate, thus limiting the inflammation. Intact senescent neutrophils are engulfed by macrophages and degraded within minutes, with no release of pro-inflammatory mediators. When necrotic granulocytes are ingested, the macrophages release mediators leading to inflammation [94].

Haematological diseases, such as myelodysplastic syndromes, aplastic anaemia, chronic neutropenia or severe β-thalassaemia, are associated with increased apoptosis within the bone marrow [95].

Viral infection

Many viruses inhibit apoptosis in their target cells to prolong host cell life and permit viral replication. Viruses may encode anti-apoptotic proteins, such as the baculovirus IAPs, the baculovirus p35 and cowpox serpin protein crmA, to promote the development of certain cancers [96]. DNA viruses also contain anti-apoptotic genes. For example, the papilloma virus and adenovirus can encode a p53 inhibitor. Ribonucleic acid (RNA) viruses may also contain anti-apoptotic genes [97].

Human immunodeficiency virus (HIV) infection is characterised by a decreased proliferation of T cells with loss of CD4+ cells initially, and loss of CD8+ cells, natural killer cells and neurons later. Inappropriate induction of apoptosis in HIV-infected CD4+ cells is triggered by the virus [98]. Another viral product, the HIV-1 transactivating protein, Tat, is produced by infected cells and taken up by uninfected T cells. It enhances apoptosis by reducing intracellular antioxidant levels, producing oxidative stress [99].

Sepsis and multiple organ dysfunction syndrome

Sepsis is often accompanied by MODS, which may caused by apoptosis [100]. Systemic release of cytokines such as TNF-α and IL-1β by bacterial LPS, resulting in increased intracellular calcium and enhanced production of oxygen free radicals, is thought to produce apoptosis in various organs [101–104]. TNF-α may act by causing macrophage release of IL-1β[105]. In a murine model of septic shock, direct application of TNF-α caused apoptosis in hepatocytes [106]. Further support for the role of apoptosis in endotoxic shock is provided by the finding that mice deficient in ICE have a marked resistance to septic shock [107]. It is postulated that apoptotic (as opposed to necrotic) cell death may confer advantages to the septic organism by limiting the inflammatory response [28]. Apoptosis is an important cause of death of lymphocytes in the immune system (thymus, lymph nodes and spleen) during bacterial and viral infections [101, 108–113]. Furthermore, apoptotic cell death has been shown in the lung, ileum, colon and skeletal muscle during sepsis [109]. Apoptosis may be an important regulator of a balance between pro- and anti-inflammatory factors and this balance is achieved through widespread lymphocyte apoptosis and subsequently diminished cytokine load [114].

Trauma patients with and without septic complications show decreased neutrophil apoptosis associated with increased tyrosine phosphorylation leading to excessive tissue damage [115, 116]. Patients with SIRS and following major elective aortic surgery also show decreased neutrophil apoptosis, possibly due to circulating pro-inflammatory anti-apoptotic factors such as LPS, TNF-α, interferon (IFN)-γ, G-CSF and granulocyte/monocyte colony-stimulating factor [117]. The persistence of neutrophils in such conditions may contribute to the pathophysiology of MODS through the excessive release of toxic granule components and ROS leading to tissue destruction. Apoptosis can be partially restored by the addition of anti-TNF antibody and IL-10 [118]. Macrophages show increased rates of apoptosis in polymicrobial sepsis, associated with NO and caspase activation, leading to loss of phagocytic function [119].

Cancer

There is evidence that a failure to initiate apoptosis following DNA damage may cause cancer. Elevated levels of c-myc are found in many tumours [120–122]. In human follicular lymphoma, translocation of chromosomes 14 and 18 causes up-regulation of Bcl-2‘oncogene’ expression [48, 123]. Levels of Bcl-2 are elevated in various other human cancers, for example lymphomas, leukaemias, adenocarcinomas, renal and lung cancers, neuroblastomas and melanomas [123–126].

Other mutations may also be involved in carcinogenesis. A notable example involves the tumour suppressor p53 that represses Bcl-2 expression. The p53 gene is deficient in over half of human cancers [127–130]. For example, in Wilm's tumour p53 mutations occur in anaplastic areas.

Renal system

Embryological development of the kidney involves periods of growth and apoptosis which are reflected by the levels of Bcl-2 present [131]. Mice deficient in Bcl-2 develop polycystic kidney disease [132] whereas, Bcl-2 levels are high in all renal tumours [133].

Gastrointestinal system

Gastrointestinal diseases may be associated with excessive or defective apoptosis. Shigella dysenteriae causes excessive apoptosis of macrophages in the lamina propria of the intestine by the release of IL-1β. Mice expressing a mutant nonfunctional N-cadherin in intestinal villi develop changes similar to Crohn's disease and show increased rates of apoptosis in both villi and crypts, as well as higher rates of adenomas.

Progressive inhibition of apoptosis appears to be involved in the pathogenesis of gastrointestinal neoplasia, in particular colorectal cancer [134]. Genes that regulate apoptosis are mutant in colonic and gastric cancers. Wild-type p53, when introduced into human colon cancer cell lines, inhibits cell growth and induces apoptosis [135]. However, p53 expression is associated with a poorer prognosis in both colorectal and gastric cancers [4] possibly owing to mutant or nonfunctional p53 that fails to induce the usual apoptosis. The Bcl-2 protein can also be detected in human cancers and is highest in adenomas [136].

Hepatic cells develop apoptosis when infected with viruses as in chronic hepatitis [137]. Abnormal activation of cytotoxic T cells may be involved in human fulminant hepatitis [95]. Paracetamol stimulates increases in intracellular calcium which activates Ca2+-dependent nucleases [138]. Apoptosis also appears to mediate allograft rejection in a model of liver transplantation [139].

Reproductive system

Apoptosis is continually inhibited in many tissues of the reproductive system owing to the presence of trophic hormones from the pituitary, gonads and uterus. When the hormones are removed, the tissues undergo atrophy. Ovarian follicles undergo growth or atresia in response to cyclic changes in luteinizing hormone and follicle stimulating hormone; the endometrium, breast and prostate are dependent on the steroid hormones and regress when these are removed [140].

Therapeutic possibilities and future directions

  1. Top of page
  2. Abstract
  3. History
  4. Definitions
  5. Pathophysiology
  6. Clinical relevance of apoptosis
  7. Therapeutic possibilities and future directions
  8. Conclusion
  9. References

The widespread involvement of apoptosis in the pathophysiology of disease lends itself to therapeutic intervention. In diseases caused by increased cell loss, such as viral hepatitis and neurodegenerative disease, the aim will be to minimise apoptosis by modifying the signals which trigger the response (e.g. Ca2+, ROS) or interfering with the effectors (e.g. caspases and endonucleases). However, inhibition of apoptosis may be deleterious because new tumours may arise when damaged cells are prevented from committing suicide. In diseases caused by deficient apoptosis, such as cancer, viral latency and autoimmunity, methods of producing selective apoptosis are being sought.

Agents targeting receptors or regulatory molecules and agents targeting the final common pathway are attractive possibilities. The soluble form of Fas could prove useful for increasing apoptosis (e.g. in tumours). Antibodies to Fas or Fas ligand may be useful in preventing apoptosis (e.g. in neurodegenerative disease). Preliminary successes in treating chronic inflammatory diseases, such as rheumatoid arthritis and ulcerative colitis, with TNF-α inhibitors have been reported, but these therapies have proved disappointing in sepsis [141].

The regulatory molecule Bcl-2 may protect normal cells from death induced by cytotoxic agents [142]. In contrast, decreasing Bcl-2 in cancer cells can reinstate chemo- and radio-sensitivity. This can be achieved by treatment with synthetic short DNA single strands called antisense oligonucleotides, which bind to specific messenger RNA sequences and prevent production of the offending protein [143].

The caspases are of interest from a therapeutic point of view as specific inhibitors exist. Tetrapeptide aldehydes are potent inhibitors of ICE but are toxic [4]. They act by specifically binding to the protease and preventing cleavage of the target proteins. Inhibitors of ICE can inhibit apoptosis in a number of cell systems. They may have a role in sepsis and chronic inflammatory and neurodegenerative disease [144].

Cancer

Kerr et al. [145] found that anticancer agents induce apoptosis in tumours. Chemotherapeutic agents reported to induce apoptosis include the alkylating agents (cyclophosphamide, mitomycin C, nitrogen mustard), topoisomerase II inhibitors (daunorubicin, adriamycin), dexamethasone, antimetabolites (methotrexate, 5-fluorouracil, 5-azacytidine), cisplatin, microtubule disrupters (vincristine, vinblastine, taxol), cycloheximide, bleomycin, cisplatin, tamoxifen and cytosine arabinose [30, 90]. Irradiation and cytotoxic agents produce DNA damage which predisposes to p53 enhancement of apoptosis. If p53 is defective, then resistance to chemotherapy may result [129]. The activation of the p53 pathway in neoplasms to regain chemosensitivity is a potentially powerful therapeutic tool that can render the tumour apoptotic. This may be possible through p53 gene-specific therapy. Such therapy has been attempted using retrovirally introduced wild-type p53 on non-small cell-lung cancer with encouraging results [129]. Nicotine has been shown to suppress apoptosis in lung cancer in humans [146].

Inflammatory disease

Corticosteroids induce eosinophil apoptosis but inhibit neutrophil apoptosis. The treatment of asthmatic patients with corticosteroids can cause eosinophil death and macrophage engulfment [147]. The detection of this process in airway secretions of asthmatic patients is associated with clinical improvement [148].

Ischaemia and reperfusion

Apoptosis has been demonstrated in areas of brief ischaemia and reperfusion in the brain, heart, liver and kidney [11, 82]. Further understanding of the molecular mechanisms should allow novel protective strategies to be developed.

Gastrointestinal tract

Cytotoxic drugs induce apoptosis in studies of human gastrointestinal cancer cells as well as normal mouse intestine, which may account for their therapeutic action. Chronic ingestion of nonsteroidal anti-inflammatory drugs may be useful in preventing colonic cancer, possibly by induction of apoptosis. Cyclo-oxygenase-2 (COX-2) may enhance formation of cancer by changes in cellular adhesion and by inhibition of apoptosis via enhanced Bcl-2 expression [4, 134]. Non-steroidal anti-inflammatory drugs, which inhibit COX-1 and COX-2, can prevent up-regulation of Bcl-2 by prostaglandins and prevent colorectal carcinoma. The protective effects of dietary fibre may be via its fermentation by bacteria in the colon to form short-chain fatty acids (e.g. butyrate) which promote apoptosis [4].

Conclusion

  1. Top of page
  2. Abstract
  3. History
  4. Definitions
  5. Pathophysiology
  6. Clinical relevance of apoptosis
  7. Therapeutic possibilities and future directions
  8. Conclusion
  9. References

Cell injury, as a result of physical, biochemical or biological insults, or from a deficiency of vital substances, induces expression of adaptive stress response genes. The interactions of the acute phase, heat shock and oxidative stress responses appear to determine the fate of the cell. The intracellular response to injury leads to distinct genetic expression that mediates the cellular changes which are usually specific to cell type and injury. These cellular responses are usually cytoprotective but can precipitate apoptosis. Reducing agents, antioxidants, anti-TNF antibodies, steroid antagonists and inhibitors of protein synthesis can modulate apoptosis. Novel gene-directed treatment for various disease states, such as multiple organ dysfunction syndrome and some cancers, may be available as the understanding of the impact and mechanism of stress gene responses to injury are elucidated.

References

  1. Top of page
  2. Abstract
  3. History
  4. Definitions
  5. Pathophysiology
  6. Clinical relevance of apoptosis
  7. Therapeutic possibilities and future directions
  8. Conclusion
  9. References
  • 1
    Kerr JFR, Wyllie AH & Currie AR. Apoptosis: a basic biological phenomenon with wide-ranging implications in tissue kinetics. British Journal of Cancer 1972; 26: 23957.
  • 2
    Bär PR. Apoptosis – the cell's silent exit. Life Science 1996; 59: 36978.
  • 3
    Thatte U & Dahanukar S. Apoptosis – clinical relevance and pharmacological manipulation. Drugs 1997; 54: 51132.
  • 4
    Pritchard DM & Watson AJM. Apoptosis and gastrointestinal pharmacology. Pharmacological Therapeutics 1996; 72: 14969.
  • 5
    Majno G & Joris I. Apoptosis, oncosis and necrosis – an overview of cell death. American Journal of Pathology 1995; 146: 315.
  • 6
    Gräper L. Eine neue Anschauung über physiologische Zellausschaltung. Archive Zellforsch 1914; 12: 37394.
  • 7
    Glücksmann A. Cell deaths in normal vertebrate ontogeny. Biological Reviews of the Cambridge Philosophical Society 1951; 26: 5986.
  • 8
    Farber E. Programmed cell death: necrosis versus apoptosis. Modern Pathology 1994; 7: 6059.
  • 9
    Kerr JFR. An electron-microscope study of liver cell necrosis due to Heliotrine. Journal of Pathology 1969; 97: 55762.
  • 10
    Kerr JFR. An electron-microscope study of liver cell necrosis due to Albitocin. Pathology 1970; 2: 2519.
  • 11
    Kerr JFR. Shrinkage necrosis: a distinct mode of cellular death. Journal of Pathology 1971; 105: 1320.
  • 12
    Wyllie AH, Kerr JFR & Currie AR. Cell death in the normal neonatal rat adrenal cortex. Journal of Pathology 1973; 111: 25561.
  • 13
    Searle J, Lawson TA, Abbott PJ, Harmon B & Kerr JF. An electron microscope study of the mode of cell death induced by cancer-chemotherapeutic agents in populations of proliferating normal and neoplastic cells. Journal of Pathology 1975; 116: 12938.
  • 14
    Wyllie AH, Kerr JFR, Macaskill IAM & Currie AR. Adrenocortical cell deletion: the role of ACTH. Journal of Pathology 1973; 111: 8594.
  • 15
    Wyllie AH, Beattie GJ & Hargreaves AD. Chromatin changes in apoptosis. Histochemistry Journal 1981; 13: 68192.
  • 16
    Ellis EM & Horvitz HR. Genetic control of programmed cell death in the nematode Caenorhabditis elegans. Cell 1986; 4: 81729.
  • 17
    Korsmeyer SJ. Bcl-2 initiates a new category of oncogenes: regulators of cell death. Blood 1992; 80: 87986.
  • 18
    Vaux DL, Cory S & Adams JM. Bcl-2 gene promotes haemopoetic cell survival and cooperates with C-myc to immortalize pre-B cells. Nature 1988; 335: 4402.
  • 19
    Nagata S & Goldstein P. The Fas death factor. Science 1995; 267: 144956.
  • 20
    Wyllie AH, Rose KA, Morris RG, Stell CM, Forster E & Spandidis DA. Rodent fibroblast tumours expressing human myc and ras genes: growth, metastasis and endogenous oncogene expression. British Journal of Cancer 1987; 56: 2519.
  • 21
    Evan GI, Wyllie AH & Gilbert CS, et al. Induction of apoptosis in fibroblasts by C-myc protein. Cell 1992; 69: 11928.
  • 22
    Martin SJ. Apoptosis: suicide, execution or murder? Trends in Cell Biology 1993; 3: 1414.
  • 23
    Earnshaw WC. Nuclear changes in apoptosis. Current Opinions in Cell Biology 1995; 7: 33743.
  • 24
    Farber E. Chemical carcinogenesis. New England Journal of Medicine 1981; 305: 137989.
  • 25
    Hockenbery D. Defining apoptosis. American Journal of Pathology 1995; 146: 1619.
  • 26
    Kane AB. Redefining cell death. American Journal of Pathology 1995; 146: 12.
  • 27
    Lennon SV, Martin SJ & Cotter TG. Dose-dependent induction of apoptosis in human tumour cell lines by widely divergent stimuli. Cell Proliferation 1991; 24: 20314.
  • 28
    Cobb JP, Hotchkiss RS, Karl IE & Buchman TG. Mechanisms of cell injury and death. British Journal of Anaesthesia 1996; 77: 310.
  • 29
    Sulston JE & Horvitz HR. Post-embryonic cell lineages of the nematode C. elegans. Developmental Biology 1977; 82: 11056.
  • 30
    Savitz SI, Daniel BA & Rosenbaum MD. Apoptosis in neurological disease. Neurosurgery 1998; 42: 55572.
  • 31
    Arends MJ & Wyllie AH. Apoptosis: mechanisms and roles in pathology. International Reviews of Experimental Pathology 1991; 32: 22354.
  • 32
    Wyllie AH. Apoptosis: an overview. British Medical Bulletin 1997; 53: 45165.
  • 33
    Weedon D, Searle J & Kerr JFR. Apoptosis: its nature and implications for dermatopathology. American Journal of Dermatopathology 1979; 1: 13344.
  • 34
    Wyllie A. Glucocorticoid-induced thymocyte apoptosis is associated with endogenous endonuclease activation. Nature 1980; 284: 5556.
  • 35
    Kontogeorgos G & Kovacs K. Apoptosis in endocrine glands. Endocrine Pathology 1995; 6: 25765.
  • 36
    Bortner CD, Oldenburg NBS & Cedlowski JA. The role of DNA fragmentation in apoptosis. Trends in Cell Biology 1995; 5: 216.
  • 37
    Gavrieli Y, Sherman Y & Benasson SA. Identification of programmed cell death in situ via special labelling of nuclear DNA fragments. Journal of Cell Biology 1992; 119: 493501.
  • 38
    Hamel W, Dazin P & Israel M. Adaptation of a simple flow cytometric assay to identify different stages during apoptosis. Cytometry 1996; 25: 17381.
  • 39
    Dive C, Gregory CD, Phipps DJ, Evans DL, Milner AE & Wyllie AH. Analysis and discrimination of necrosis and apoptosis (programmed cell death) by multiparameter flow cytometry. Biochemica et Biophysica Acta 1992; 1133: 27585.
  • 40
    Gong J, Traganos F & Darsynkiewicz Z. A selective procedure for DNA extracting form apoptotic cells applicable for gel electrophoresis and flow cytometry. Analytical Biochemistry 1994; 218: 31419.
  • 41
    Rudin CM & Thompson CB. Apoptosis and disease: regulation and clinical relevance of programmed cell death. Annual Review of Medicine 1997; 48: 26781.
  • 42
    MacLellan WR & Schneider MD. Death by design – programmed cell death in cardiovascular biology and disease. Circulation Research 1997; 81: 13744.
  • 43
    Haimovitz-Friedman A, Kan C & Enleiter D, et al. Ionizing radiation acts on cellular membranes to generate ceramide and initiate apoptosis. Journal of Experimental Medicine 1994; 180: 52535.
  • 44
    Santana P, Peña LA & Haimovitz-Friedman A, et al. Acid sphingomyelinase deficient lymphoblasts and mice are defective in radiation-induced apoptosis. Cell 1996; 86: 18999.
  • 45
    Narula J, Kharbanda S & Khaw B-A. Apoptosis and the heart. Chest 1997; 112: 135862.
  • 46
    Vaux DL, Weissman IL & Kim SK. Prevention of programmed cell death in Caenorhabditis elegans by human Bcl-2. Science 1992; 258: 19557.
  • 47
    Brown R. The Bcl-2 family of proteins. British Medical Bulletin 1996; 53: 46677.
  • 48
    Tsujimoto Y, Cossman J, Jaffe E & Croce C. Involvement of the Bcl-2 gene in human follicular lymphoma. Science 1985; 228: 14403.
  • 49
    Cleary ML, Smith SD & Sklar J. Cloning and structural analysis of cDNAs for Bcl-2 and a hybrid Bcl-2 immunoglobulin transcript resulting from the T (14; 18) translocation. Cell 1986; 47: 1928.
  • 50
    Hockenbery D, Oltavi Z, Yin X, Milliman C & Kersmeyer B. Bcl-2 functions in an antioxidant pathway to prevent apoptosis. Cell 1993; 75: 24151.
  • 51
    Yang J, Liu X & Bhalla K, et al. Prevention of apoptosis by Bcl-2: release of cytochrome C from mitochondria blocked. Science 1997; 275: 112932.
  • 52
    Haunstetter A & Izumo S. Apoptosis – basic mechanisms and implications for cardiovascular disease. Circulation Research 1998; 82: 111129.
  • 53
    Olivetti G, Abbi R & Quaini F, et al. Apoptosis in the failing human heart. New England Journal of Medicine 1997; 336: 113141.
  • 54
    Miyashita T & Reed JC. Tumour suppressor p53 is a direct transcriptional activator of the human bax gene. Cell 1995; 80: 2939.
  • 55
    Donehower LA, Harvey M & Slagle BL, et al. Mice deficient for p53 are developmentally normal but susceptible to spontaneous tumours. Nature 1992; 356: 21521.
  • 56
    Roy N, Mahadevan MS & McLean M, et al. The gene for neuronal apoptosis inhibitory protein is partially deleted in individuals with spinal muscular atrophy. Cell 1995; 80: 16778.
  • 57
    Oberhammer F, Wilson JW & Dive C, et al. Apoptotic death in epithelial cells: cleavage of DNA to 300 and/or 50kb fragments prior to or in the absence of internucleosomal fragmentation. EMBO Journal 1993; 12: 367984.
  • 58
    Whyte M. ICE/CED-3 proteases in apoptosis. Trends in Cell Biology 1996; 6: 2458.
  • 59
    Thornberry NA, Rosen A & Nicholson DW. Control of apoptosis by proteases. Advances in Pharmacology 1997; 41: 15577.
  • 60
    Enari M, Hug H & Nagata S. Involvement of an ICE-like protease in Fas-mediated apoptosis. Nature 1995; 375: 7881.
  • 61
    Thornberry NA. The caspase family of cysteine proteases. British Medical Bulletin 1996; 53: 47890.
  • 62
    Knight CR, Ress RC & Griffin M. Apoptosis: a potential role for cytosolic transglutaminase and its importance in tumour progression. Biochemica et Biophysica Acta 1991; 1096: 31218.
  • 63
    Savill J. Recognition and phagocytosis of cells undergoing apoptosis. British Medical Bulletin 1997; 53: 491508.
  • 64
    Savill J. Phagocytic docking without shocking. Nature 1998; 392: 4423.
  • 65
    Savill J & Haslett C. Granulocyte clearance by apoptosis in the resolution of inflammation. Seminars in Cell Biology 1995; 6: 38593.
  • 66
    Savill J, Hogg N, Ren Y & Haslett C. Thrombospondin cooperates with CD36 and the vitronectin receptor in macrophage recognition of neutrophils undergoing apoptosis. Journal of Clinical Investigation 1992; 90: 151322.
  • 67
    Devitt A, Moffatt OD, Raykundalia C, Capra JD, Simmons DL & Gregory CD. Human CD14 mediates recognition and phagocytosis of apoptotic cells. Nature 1998; 392: 5058.
  • 68
    Louis J, Magal E, Takayama S & Varon S. CNTF protection of oligodendrocytes against natural and tumour necrosis factor-induces death. Science 1993; 259: 68992.
  • 69
    Choi DW. Ionic dependence of glutamate neurotoxicity in cortical cell culture. Journal of Neuroscience 1987; 7: 36989.
  • 70
    Choi DW, Malucci-Gedde M & Kriegstein SR. Glutamate neurotoxicity in cortical cell culture. Journal of Neuroscience 1987; 7: 35768.
  • 71
    Kure S, Tominaga T, Yoshimoto T, Tada K & Narisawa K. Glutamate triggers internucleosomal DNA cleavage in neuronal cells. Biochemistry and Biophysics Research Communications (New York) 1991; 179: 3945.
  • 72
    Tymianski M & Tator CH. Normal and abnormal calcium homeostasis in neurones: a basis for the pathophysiology of traumatic and ischaemic central nervous system injury. Neurosurgery 1996; 38: 117695.
  • 73
    Linnick MD, Zahos P, Geschwind MD & Fedoroff HJ. Expression of bcl-2 from a defective herpes simplex virus-1 vector limits neuronal death in focal cerebral ischaemia. Stroke 1995; 26: 16705.
  • 74
    Rink A, Fung KM, Trojanowski JQ, Lee VM, Neugebauer E & McIntosh TK. Evidence of apoptotic cell death after experimental traumatic brain injury in the rat. American Journal of Pathology 1995; 147: 157583.
  • 75
    Loo D, Copani A, Pike C, Whittemore E, Walencewicz A & Cotman C. Apoptosis is induced by Β-amyloid in cultured central nervous system neurones. Proceedings of the National Academy of Sciences of the USA 1993; 90: 79515.
  • 76
    Lee WD, Colom LV, Xie WJ, Smith RG, Alexianu M & Appel SH. Cell death induced by Β-amyloid 1–40 in MES 23.5 hybrid clone: the role of nitric oxide and NMDA-gated channel attraction leading to apoptosis. Brain Research 1995; 686: 4960.
  • 77
    Wu JYeZ & Darras B. Frequency of p53 tumor suppressor gene mutations in human primary brain tumors. Neurosurgery 1993 33: 82430.
  • 78
    Bogler O, Huang HJ, Kleihues P & Cavenee WK. The p53 gene and its role in human brain tumors. Glia 1995; 15: 30827.
  • 79
    Clarke MF, Apel IJ & Benedict MA, et al. A recombinant bcl-xs adenovirus selectively induces apoptosis in cancer cells but not in normal bone marrow cells. Proceedings of the National Academy of Sciences of the USA 1995; 92: 110248.
  • 80
    Yu J, Sena-Esteves M, Paulus W, Breakfield X & Reeve DS. Retroviral delivery and tetracycline-dependent expression of IL-1β-converting enzyme (ICE) in a rat glioma model provides controlled induction of apoptotic death in tumor cells. Cancer Research 1996; 56: 54237.
  • 81
    Tanaka M, Ito H & Adachi S, et al. Hypoxia induces apoptosis with enhanced expression of Fas antigen messenger RNA in cultured neonatal rat cardiomyocytes. Circulation Research 1994; 75: 42633.
  • 82
    Gottlieb RA, Burleson KO, Kloner RA, Babior BM & Engler RA. Reperfusion injury induced apoptosis in rabbit cardiomyocytes. Journal of Clinical Investigation 1994; 94: 16218.
  • 83
    Bennett MR, Evan GI & Schwartz SM. Apoptosis of human vascular smooth muscle cells derived from normal vessels and coronary atherosclerotic plaques. Journal of Clinical Investigation 1995; 95: 226674.
  • 84
    Isner JM, Kearney M, Bortram S & Passeri J. Apoptosis in human atherosclerosis and restenosis. Circulation 1995; 91: 270311.
  • 85
    James TN. Normal and abnormal consequences of apoptosis in the human heart: from postnatal morphogenesis to paroxysmal arrhythmias. Transactions of the American Clinical and Climatological Association 1993; 105: 14577.
  • 86
    Surh CD & Sprent J. T-cell apoptosis detected in situ during positive and negative selection in the thymus. Nature 1994; 372: 1003.
  • 87
    Zacharchuk CM, Mercep M & Ashwell JD. Programmed T lymphocyte death: cell activation- and steroid-induced pathways are mutually antagonistic. Journal of Immunology 1990; 145: 403745.
  • 88
    Iwata M, Hanaoka S & Sato K. Rescue of thymocytes and T cell hybridomas from glucocorticoid-induced apoptosis by stimulation via the T cell receptor/CD3 complex: a possible in vitro model for positive selection of the T cell repertoire. European Journal of Immunology 1991; 21: 6438.
  • 89
    Osborne BA. Apoptosis and the maintenance of homeostasis in the immune system. Current Opinion in Immunology 1996; 8: 24554.
  • 90
    McConkey DJ, Zhivotovsky B & Orrenius S. Apoptosis – molecular mechanisms and biomedical implications. Molecular Aspects of Medicine 1996; 17: 1110.
  • 91
    Elkon KB. Mechanisms of autoantibody production and their role in disease. Mount Sinai Journal of Medicine 1994; 61: 28390.
  • 92
    Emlen W, Niebur J & Kadera R. Accelerated in vitro apoptosis of lymphocytes from patients with systemic lupus erythematosis. Journal of Immunology 1994; 152: 368592.
  • 93
    Eckert PG & Vaux DL. Apoptosis and the immune system. British Medical Bulletin 1997; 53: 591603.
  • 94
    Haslett C. Granulocyte apoptosis and inflammatory disease. British Medical Bulletin 1997; 53: 66983.
  • 95
    Solary E, Dubrez L & Eymin B. The role of apoptosis in the pathogenesis and treatment of diseases. European Respiratory Journal 1996; 9: 1293305.
  • 96
    Clem RJ, Hardwick JM & Miller LK. Anti-apoptotic genes of baculovirus. Cell Death 1996; 3: 916.
  • 97
    Young LS, Dawson CW & Eliopoulos A. Viruses and apoptosis. British medical Bulletin 1997; 53: 50921.
  • 98
    Terai C, Kornbluth TS, Pauza CD, Richman DD & Carson AD. Apoptosis as a mechanism of cell death in cultured T lymphoblasts acutely infected with HIV-1. Journal of Clinical Investigation 1991; 87: 171015.
  • 99
    Peter ME, Ehret A, Berndt C & Krammer PH. AIDS and the death receptors. British Medical Bulletin 1997; 53: 60416.
  • 100
    Carrico CJ, Meakins JL, Marshall JC, Fry D & Maier RV. Multiple organ failure syndrome. Archives of Surgery 1986; 121: 196208.
  • 101
    Ayala A, Herdon C, Lehman D, DeMaso CM, Ayala CA & Chaudry IH. The induction of accelerated thymic programmed cell death during polymicrobial sepsis: control by corticosteroids but not tumor necrosis factor. Shock 1995; 3: 25967.
  • 102
    Zaloga GP, Washburn D, Black KW & Prielipp R. Human sepsis increases lymphocyte intracellular calcium. Critical Care Medicine 1993; 21: 196202.
  • 103
    Bautista AP, Meszaros K, Bojta J & Spitzer J. Superoxide anion generation in the liver during the early stage of endotoxaemia in rats. Journal of Leukemia Biology 1990; 48: 1238.
  • 104
    Vassali P. The pathophysiology of tumor necrosis factors. Annual Review of Immunology 1992; 10: 41152.
  • 105
    Dinarello CA. The biological properties of interleukin-1. European Cytokine Network 1994; 5: 51731.
  • 106
    Leist M, Gantner F, Jilg S & Wendel A. Activation of the 55 kDa TNF receptor is necessary and sufficient for TNF-induced liver failure, hepatocyte apoptosis, and nitrite release. Journal of Immunology 1995; 154: 130716.
  • 107
    Li P, Allen H & Banerjee S. Mice deficient in IL-1β-converting enzyme are defective in production of mature IL-1β and resistant to endotoxic shock. Cell 1995; 80: 40111.
  • 108
    Ayala A, Herdon C, Lehman D, Ayala CA & Chaudry IH. Differential induction of apoptosis in lymphoid tissues during sepsis: variation in onset, frequency and nature of the mediators. Blood 1996; 87: 426175.
  • 109
    Hotchkiss RS, Swanson PE, Cobb JP, Jacobson A, Buchman TG & Karl IE. Apoptosis in lymphoid and parenchymal cells during sepsis: findings in normal and T- and B-cell deficient mice. Critical Care Medicine 1997; 25: 1298307.
  • 110
    Wang SD, Huang KJ, Lin YS & Lei HY. Sepsis-induced apoptosis of the thymocytes in mice. Journal of Immunology 1994; 152: 501421.
  • 111
    Barke RA, Roy S, Chapin RB & Charboneau R. The role of programmed cell death (apoptosis) in thymic involution following sepsis. Archives of Surgery 1994; 129: 125662.
  • 112
    Zhang XM, Morikawa A & Takahashi K, et al. Localization of apoptosis (programmed cell death) in mice by administration of lipopolysaccharide. Microbiology and Immunology 1994; 38: 66971.
  • 113
    Rogers HW, Callery MP, Deck B & Unanue ER. Listeria monocytogenes induce apoptosis of infected hepatocytes. Journal of Immunology 1996; 156: 67986.
  • 114
    Bone RC. Sir Isaac Newton, sepsis. SIRS and CARS. Critical Care Medicine 1996; 24: 11259.
  • 115
    Ertel W, Keel M, Infanger M, Ungethum U, Steckholzer U & Trentz O. Circulating mediators in serum of injured patients with septic complications inhibit neutrophil apoptosis through up-regulation of protein–tyrosine phosphorylation. Journal of Trauma 1998; 44: 76775.
  • 116
    Ertel W, Keel M, Ungethum U & Trentz O. Pro-inflammatory cytokines regulate apoptosis of granulocytes during systemic inflammation. Langenbecks Archive Fur Chirugie 1997; 114: 6279.
  • 117
    Jimenez MF, Watson RW & Parodo J, et al. Dysregulated expression of neutrophil apoptosis in the systemic inflammatory response syndrome. Archives of Surgery 1997; 132: 12639.
  • 118
    Keel M, Ungethum U & Steckholzer U, et al. Interleukin-10 counter-regulates proinflammatory cytokine-induced inhibition of neutrophil apoptosis during severe sepsis. Blood 1997; 90: 335663.
  • 119
    Williams TE, Ayala A & Chaudry IH. Inducible macrophage apoptosis following sepsis is mediated by cysteine protease activation and nitric oxide release. Journal of Surgical Research 1997; 70: 11318.
  • 120
    Spencer CA & Groudine M. Control of C-myc regulation in normal and neoplastic cells. Advances in Cancer Research 1991; 56: 148.
  • 121
    Loke SL, Stein C, Zhang X, Avigan M, Cohen J & Neckers LM. Delivery of C-myc antisense phosphorothioate oligodeoxynucleotides to haematopoietic cells in culture by liposome fusion: specific reduction in C-myc protein expression correlates with inhibition of cell growth and DNA synthesis. Current Topics in Microbiology and Immunology 1988; 141: 2829.
  • 122
    Bennet M, Anglin A, McEwan J, Jagoe R, Newby A & Evan G. Inhibition of vascular smooth muscle cell proliferation in vitro and in vivo by C-myc antisense oligonucleotides. Journal of Clinical Investigation 1993; 93: 8208.
  • 123
    Reed JC. Bcl-2 and the regulation of cell death. Journal of Cell Biology 1994; 124: 16.
  • 124
    Allsop TE, Wyatt S, Paterson HF & Davies AM. The proto-oncogene bcl-2 can selectively rescue neurotrophic factor-dependent neurons from apoptosis. Cell 1993; 73: 295307.
  • 125
    Levine B, Huang Q, Isaacs JT, Reed JC, Griffin DE & Hardwick JM. Conversion of lytic to persistent alphavirus infection by the bcl-2 cellular oncogene. Nature 1993; 361: 73942.
  • 126
    Miyashita T & Reed JC. Bcl-2 oncoprotein blocks chemotherapy-induced apoptosis in a human leukemia cell line. Blood 1993; 81: 1517.
  • 127
    Harris CC & Holstein M. Clinical implications of the p53 tumor suppressor gene. New England Journal of Medicine 1993; 329: 131827.
  • 128
    Lowe SW, Jacks T, Housman DE & Ruley HE. Abrogation of oncogene-associated apoptosis allows transformation of p53-deficient cells. Proceedings of the National Academy of Sciences of the USA 1994; 91: 202630.
  • 129
    Bellamy CO. P53 and apoptosis. British Medical Bulletin 1997; 53: 52238.
  • 130
    Strand S, Hoffman WJ & Hug H, et al. Lymphocyte apoptosis induced by CD 45 (APO-1/fas) ligand-expressing tumour cells – a mechanism of immune-evasion? Nature Medicine 1996; 2: 13616.
  • 131
    Savill J. Apoptosis and the kidney. Journal of the American Society of Nephrology 1994; 5: 1221.
  • 132
    Veis DJ, Sorenson CM, Shutter JR & Korsmeyer SJ. Bcl-2-deficient mice demonstrate fulminant lymphoid apoptosis, polycystic kidneys, and hypopigmented hair. Cell 1993; 75: 22940.
  • 133
    Chandler D, El-Naggar AK, Brisbay S, Redline RW & McDonnel TJ. Apoptosis and expression of the Bcl-2 proto-oncogene in the fetal and adult human kidney: evidence for the contribution of bcl-2 expression to renal carcinogenesis. Human Pathology 1994; 25: 78996.
  • 134
    Bedi A, Pasricha PJ & Akhtar AJ, et al. Inhibition of apoptosis during development of colorectal cancer. Cancer Research 1995; 55: 181116.
  • 135
    Shaw P, Bovey R, Tardy S, Sahli R, Sordat B & Costa J. Induction of apoptosis by wild-type p53 in a human colon tumour-derived cell line. Proceedings of the National Academy of Sciences of the USA 1992; 89: 44959.
  • 136
    Bosari S, Moneghini L & Graziani D, et al. Bcl-2 oncoprotein in colorectal hyperplastic polyps, adenomas, and adenocarcinomas. Human Pathology 1995; 26: 53440.
  • 137
    Hiramatsu N, Hayashi N & Katayama K, et al. Immunohistochemical detection of Fas antigen in liver tissue of patients with chronic hepatitis C. Hepatology 1994; 19: 13549.
  • 138
    Ray SD, Kamendulis LM, Gurule MW, Yorkin RD & Corcoran GB. Ca2+ antagonists inhibit DNA fragmentation and toxic cell death induced by acetaminophen. FASEB Journal 1993; 7: 45363.
  • 139
    Krams SM, Egawa H, Quinn MB, Villanueva JC, Garcia-Kennedy R & Martinez OM. Apoptosis as a mechanism of cell death in liver allograft rejection. Transplantation 1995; 59: 6215.
  • 140
    Gosden R & Spears N. Programmed cell death in the reproductive system. British Medical Bulletin 1997; 53: 64461.
  • 141
    Natanson C, Hoffman WD, Suffredini AF, Eichacker PQ & Danner RL. Selected treatment strategies for septic shock based on proposed mechanisms of pathogenesis. Annals of Internal Medicine 1994; 120: 77183.
  • 142
    Kondo S, Takeuchi J, Morimura T, Oda Y & Kikuchi H. Bcl-2 gene enables rescue from in vitro myelosupression (bone marrow cell death) induced by chemotherapy. British Journal of Cancer 1994; 70: 4216.
  • 143
    Campos L, Sabido O, Rouault JP & Guyotat D. Effects of Bcl-2 antisense oligonucleotides on in vitro proliferation and survival of normal bone marrow progenitors and leukemic cells. Blood 1994; 84: 595600.
  • 144
    Livinston DJ. In vitro and in vivo studies of ICE inhibitors. Journal of Cell Biochemistry 1997; 64: 1926.
  • 145
    Kerr J, Witerford C & Harmon B. Apoptosis: its significance in cancer and cancer therapy. Cancer 1994; 73: 201326.
  • 146
    Maneckgee R & Minna JD. Opioids induce while nicotine suppresses apoptosis in human lung cancer cells. Cell Growth and Differentiation 1994; 5: 103340.
  • 147
    Meagher L, Cousin JM, Seckl JR & Haslett C. Opposing effects of glucocorticoids on the rate of apoptosis in neutrophilic and eosinophilic granulocytes. Journal of Immunology 1996; 156: 44228.
  • 148
    Wooley KL, Gibson PG, Carty K, Wilson AJ, Twaddel SH & Wooley MJ. Eosinophil apoptosis and the resolution of airway inflammation in asthma. American Journal of Respiratory and Critical Care Medicine 1996; 154: 23743.