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Keywords:

  • NADPH oxidase;
  • oxidative stress;
  • renal disease;
  • unilateral ureteric obstruction

Summary

  1. Top of page
  2. Summary
  3. Introduction
  4. Inflammation in UUO
  5. TGF-β-BMP superfamily involvement
  6. Oxidative stress in UUO
  7. NADPH oxidases
  8. NADPH oxidases and renal injury
  9. NADPH oxidase inhibitors
  10. New therapies in UUO
  11. Conclusion
  12. References

Unilateral ureteric obstruction (UUO) is one of the most commonly applied rodent models to study the pathophysiology of renal fibrosis. This model reflects important aspects of inflammation and fibrosis that are prominent in human kidney diseases. In this review, we present an overview of the factors contributing to the pathophysiology of UUO, highlighting the role of oxidative stress.


Introduction

  1. Top of page
  2. Summary
  3. Introduction
  4. Inflammation in UUO
  5. TGF-β-BMP superfamily involvement
  6. Oxidative stress in UUO
  7. NADPH oxidases
  8. NADPH oxidases and renal injury
  9. NADPH oxidase inhibitors
  10. New therapies in UUO
  11. Conclusion
  12. References

Unilateral ureteral obstruction (UUO) is an experimental rodent model of renal injury that mimics the complex pathophysiology of chronic obstructive nephropathy in an accelerated manner. The hydrostatic pressure ensuing from the obstruction triggers tubular cell death by apoptosis and necrosis (Cachat et al. 2003), interstitial inflammatory infiltration (Schreiner et al. 1988), capillary rarefaction (Rouschop et al. 2006), and progressive fibrosis with loss of renal parenchyma, myofibroblast activation and extracellular matrix deposition (Nagle et al. 1973; Sharma et al. 1993; Vaughan et al. 2004). The characteristics of UUO are highlighted in Figure 1. Despite this relatively severe picture in the obstructed kidney, the animal remains healthy due to the presence of a functional contralateral kidney. As such, there is no uremia in this model, as is the case in renal ablation models (Liu et al. 2003). The UUO model is thus very convenient for study of the histopathology and molecular changes of tubulointerstitial damage, a process closely resembling deterioration of renal function in human chronic kidney disease (Mackensen-Haen et al. 1981). UUO is applied in rats and mice, and there are also reports on its use in rabbits (Nagle et al. 1973) and guinea pigs (Chevalier 1990).

image

Figure 1.  Characteristics of the UUO model in mice. (a) PAS-staining of an obstructed kidney showing inflammatory infiltrates (thin arrow) and dilated tubules (thick arrow). (b) Higher magnification of PAS-stain depicting atrophic tubules characterized by flattened epithelium, cast formation (pink luminal material), basement membrane thickening (arrow) and widened interstitial compartments. (c) Immunohistochemistry for the mouse macrophage antigen F4/80 on frozen sections showing diffuse infiltration of macrophages around the tubules. (d) Immunofluorescence for CD45 highlighting interstitial macrophages and lymphocytic infiltrates. (e) Sirius red staining depicting interstitial matrix deposition. Collagen bundles stain dark red (arrow). (f) Western blot for the modified amino acid 3-nitrotyrosine showing dark bands in obstructed kidneys (UUO) as compared to contralateral kidneys (CON), for equal protein loading.

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In this review, we mainly focus on the contribution of oxidative stress to the pathogenesis of renal fibrosis in UUO. Current evidence for the benefits of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase blockade by apocynin in renal disease is summarized.

Inflammation in UUO

  1. Top of page
  2. Summary
  3. Introduction
  4. Inflammation in UUO
  5. TGF-β-BMP superfamily involvement
  6. Oxidative stress in UUO
  7. NADPH oxidases
  8. NADPH oxidases and renal injury
  9. NADPH oxidase inhibitors
  10. New therapies in UUO
  11. Conclusion
  12. References

Already within the first week of induction, a network of inflammatory, vasoactive and apoptotic processes results in the appearance of signs of tubular atrophy and features of tubulointerstitial fibrosis (Chevalier et al. 2009). Tubulointerstitial infiltration of leucocytes is a particularly early, prominent, and crucial event at the onset of UUO (Schreiner et al. 1988), helping to lay the foundation for all subsequent developments. Increased numbers of macrophages are observed as early as four hours after UUO in rats (Schreiner et al. 1988; Klahr & Morrissey 2002). Leucocyte recruitment after UUO involves increased expression of chemokines, chemokine receptors (Vielhauer et al. 2001; Anders et al. 2002), and adhesion molecules like osteopontin (Ophascharoensuk et al. 1999; Bascands & Schanstra 2005), galectin-3 (Henderson et al. 2008) and selectins (Bascands & Schanstra 2005). Other induced molecules include platelet-derived growth factor-D (PDGF-D) (Taneda et al. 2003), and macrophage-colony stimulating factor (M-CSF). The latter supports both systemic recruitment and local proliferation of macrophages (Le Meur et al. 2002; Lenda et al. 2003).

Upon recruitment and stimulation, infiltrating inflammatory cells themselves produce numerous cytokines and vasoactive agents that sustain and enhance inflammation, and contribute to stimulation of fibrogenic, apoptotic and gene regulatory signalling pathways involving among other mechanisms, the renin–angiotensin system, transforming growth factor-β (TGF-β), nuclear factor-kappa B (NF-κB) (Chevalier et al. 2009) and the MAPK pathways (Ma et al. 2007). During obstruction, leucocyte infiltration was found to correlate in time with decline of glomerular filtration rate (Schreiner et al. 1988). Within six days after induction of UUO, relief of obstruction resulted in slow but remarkably complete resolution of tubulointerstitial infiltration (Schreiner et al. 1988). Without relief of obstruction, atrophy and fibrotic processes continued to progressive tissue loss, massive deposition of extracellular matrix, and irreversible loss of function in association with hydronephrosis.

TGF-β-BMP superfamily involvement

  1. Top of page
  2. Summary
  3. Introduction
  4. Inflammation in UUO
  5. TGF-β-BMP superfamily involvement
  6. Oxidative stress in UUO
  7. NADPH oxidases
  8. NADPH oxidases and renal injury
  9. NADPH oxidase inhibitors
  10. New therapies in UUO
  11. Conclusion
  12. References

TGF-β is a cytokine playing a crucial role in the inflammation and tissue damage that characterize obstructive nephropathy (Klahr & Morrissey 2003).

Biologic actions of TGF-β are mediated via activation of their transmembrane receptor serine/threonine kinases. Downstream signal transduction is through Smad proteins, which are TGF-β-responsive transcription factors. Smads 1, 2, 3, 4 and 5 variously work together as transcriptional regulators of target genes to effect TGF-β-mediated actions, while Smads 6 and 7 are regarded as intracellular antagonists of TGF-β signalling (Schiller et al. 2004). When stimulated during UUO, TGF-β signalling favours fibrosis; thus Smad3 deficiency ameliorates inflammation and fibrosis after UUO (Sato et al. 2003; Inazaki et al. 2004) while Smad7 downregulation contributes to fibrosis (Fukasawa et al. 2004; Chung et al. 2009). Apart from the canonical, Smad-mediated transduction pathway, TGF-β also signals via various branches of the MAP kinase and pAkt pathways (Zhang 2009).

The complex downstream signalling cascade of TGF-β presents multiple opportunities for pharmacological blockade. However, TGF-β is also crucial for immunocompetence, presenting a major obstacle for pharmacological intervention (Liu 2006; Leask 2008).

In UUO research, there is currently much interest in the role of bone morphogenetic proteins (BMPs), a large subgroup of the TGF-β superfamily. Although BMPs have their own distinct receptors, they share broadly similar signalling pathways with TGF-β, including transduction via Smad proteins (Blitz & Cho 2009). BMPs are known to also signal through non-Smad pathways involving JNK and p38 MAP kinase (Zwijsen et al. 2003; Miyazono et al. 2005). BMPs are multifunctional proteins that exert complicated biological activities in diverse organ systems. The various BMPs differ in their receptor binding properties, which dictate their biologic effects. BMP signalling behaviour is complex, and involves cross-talk with TGF-β within the Smad network that is not yet fully elucidated (Zwijsen et al. 2003). In the kidney, effects of BMP-7 counteract those of TGF-β. BMP-7 (also known as osteogenic protein-1, OP-1) has shown an impressive ability to inhibit UUO-induced tubulointerstitial fibrosis (Hruska et al. 2000), via inhibition of apoptosis and epithelial–mesenchymal transdifferentiation (Klahr & Morrissey 2003); and to accelerate the restoration of renal function following relief of obstruction (Klahr 2003). BMP-7 also relieved tubulointerstitial injury in other renal injury models (Zeisberg 2006), which are known to be associated with increased oxidant stress. There is much less information about the renal effects of other BMPs, particularly BMP-6, which bears similarity to BMP-7 in terms of amino acid sequence (Kawabata et al. 1998) and ALK2 receptor binding (Zwijsen et al. 2003).

Oxidative stress in UUO

  1. Top of page
  2. Summary
  3. Introduction
  4. Inflammation in UUO
  5. TGF-β-BMP superfamily involvement
  6. Oxidative stress in UUO
  7. NADPH oxidases
  8. NADPH oxidases and renal injury
  9. NADPH oxidase inhibitors
  10. New therapies in UUO
  11. Conclusion
  12. References

Oxidative stress contributes importantly to the pathogenesis of UUO (Kinter et al. 1999). Various markers of oxidative stress are increased in UUO kidneys, such as the oxidatively damaged protein product Nε-carboxymethyl-lysine (CML) (Kawada et al. 1999); the modified amino acid 3-nitrotyrosine (Rabbani et al. 2007); the marker of DNA oxidant damage, 8-hydroxy-2′-deoxyguanosine (8-OHdG) (Pat et al. 2005); and lipid peroxidation markers such as malondialdehyde (MDA) (Lin et al. 1998; Saborio et al. 2000), 8-iso prostaglandin F2α (8-iPGF2α) (Moriyama et al. 2000), and 4-HNE or 4-HHE (Sugiyama et al. 2005). Oxidant stress response molecules like heat shock protein-70 (HSP-70) (Lin et al. 1998), heat-shock protein-27 and heme oxygenase-1 (HO-1) (Pat et al. 2005; Kamijo-Ikemori et al. 2006) are strongly expressed after UUO. Among other pathways, oxidative stress has been shown to promote epithelial-to-mesenchymal transition by influencing expression of the basement membrane component TINag (Xie et al. 2009). Mice that are genetically deficient in the protective endogenous antioxidant enzyme catalase are more susceptible to UUO-induced renal injury than normal wild type mice (Sunami et al. 2004; Sugiyama et al. 2005). Furthermore, increased renal concentrations of reactive oxygen species (ROS) have been observed in obstructed kidneys (Manucha et al. 2005), together with decreased activities of the major protective antioxidant enzymes superoxide dismutase (SOD), catalase and glutathione peroxidase (Manucha et al. 2005; Sugiyama et al. 2005).

Although the effects of nitric oxide (NO) on renal oxidative status are complex (Modlinger et al. 2004), anti-apoptotic effects of nitric oxide play a protective role in UUO. Apoptosis, mediated by caspases (Truong et al. 2001), is a prominent feature of injury in this model. To study the role of NO in apoptosis during UUO, Felsen and colleagues subjected cultured tubular epithelial cells to mechanical stretch as an in vitro replication of UUO-induced tubular cellular stress (Miyajima et al. 2001). Mechanical stretch-induced apoptosis was aggravated by the non-specific NO synthase (NOS) inhibitor l-NAME but inhibited by both the NO precursor l-arginine and the NO donor agent SNAP. In the same study, inducible NOS (iNOS) knockout mice (iNOS-/-) were compared with wild type mice. iNOS-/- mice expressed significantly less NOS activity, and developed more severe UUO-induced tubular apoptosis than their wild type counterparts. l-NAME further aggravated apoptosis in iNOS-/- mice, indicating the importance of other NOS isoforms. In contrast, l-arginine supplementation during UUO helps to preserve renal function after relief of temporary obstruction (Frokiaer 2005; Ito et al. 2005). Liposome-mediated iNOS gene transfer was proposed as an elegant NO delivery technique into obstructed kidneys (Chevalier 2004; Ito et al. 2004). Besides NO, low dose CO might also have protective effects on renal obstruction, probably acting downstream of HO-1 (Wang et al. 2008).

Despite the appreciable evidence of oxidant stress involvement in UUO, little is known about the possible source(s) of such increased stress. Because oxidant stress mechanisms vary between models, it is important to identify specific ROS sources that may be potential treatment targets. Various ROS sources implicated in other renal injury models include the mitochondrial respiratory chain (Brownlee 2001, 2005), NADPH oxidase (Vaziri et al. 2003), xanthine oxidase, cyclooxygenase, lipoxygenase (Paravicini & Touyz 2008) and uncoupled NOS (Satoh et al. 2005). Interestingly, mRNA and proteins of the NADPH oxidase components p22-, p47-, and p67-phox were all found to be upregulated in UUO kidneys (Sugiyama et al. 2005), raising the possibility that this enzyme is a major source of oxidative stress in obstructive nephropathy. The recent finding that TGF-β activates myofibroblasts via Smad3-mediated NADPH oxidase activation underscores the role of NADPH oxidases in renal fibrogenesis (Bondi et al. 2010).

There is currently limited information about whether direct antioxidant therapy can reduce inflammation or ameliorate other nephropathic changes that follow UUO. The general antioxidant agent, α-tocopherol, did not convincingly reduce kidney tissue MDA (Saborio et al. 2000), and neither NAC nor vitamin E substantially relieved renal injury induced by UUO (Pat et al. 2005). There is a report that soybean lecithin extract ameliorates injury accompanied by a reduction in renal oxidant levels and a rise in antioxidant enzyme activity (Akin et al. 2007). Although the mechanism of effect was not clearly unraveled, melatonin seemed to reduce tissue MDA levels and restore gluthatione levels when administered before and during UUO (Ozbek et al. 2009).

Statins demonstrated benefits that appear to stem from reduction of oxidant stress. Simvastatin reduced markers of renal inflammation and fibrosis (Vieira et al. 2005). Fluvastatin attenuated 8-OHdG expression along with fibronectin and α-smooth muscle actin (α-SMA) (Pat et al. 2005). In another study, fluvastatin similarly alleviated UUO-induced expression of α-SMA, and significantly reduced interstitial fibrosis. These benefits were accompanied by signs of relief of oxidant stress, shown by reduction in UUO-induced expression of advanced glycation end-products (AGE) (Moriyama et al. 2000). Zhou et al. linked renoprotection by statins to an increase in NO availability (Zhou et al. 2008). However, it is not clear whether their beneficial effects were mediated only via antioxidant mechanisms. The same holds true for the water-soluble small peptide SS-31, which decreased inflammation and apoptosis in concert with decreased 8-OHdG and HO-1 expression in UUO, by an unclear mechanism (Mizuguchi et al. 2008).

NADPH oxidases

  1. Top of page
  2. Summary
  3. Introduction
  4. Inflammation in UUO
  5. TGF-β-BMP superfamily involvement
  6. Oxidative stress in UUO
  7. NADPH oxidases
  8. NADPH oxidases and renal injury
  9. NADPH oxidase inhibitors
  10. New therapies in UUO
  11. Conclusion
  12. References

NADPH oxidase catalyses the production of the superoxide anion through the reaction of NADPH and oxygen. In functional terms, there are two forms of the enzyme. The first form is leucocyte NADPH oxidase, which catalyses the production of large amounts of superoxide to facilitate leucocyte phagocytic function. The second form of NADPH oxidase is not simply a single entity but a group of closely related oxidases that are found in non-phagocytic cells. The physiologic function of these enzymes is to generate limited amounts of superoxide for normal cellular functions, such as oxygen sensing and signal transduction (Babior 1999, 2004). Under pathophysiological circumstances, however, these oxidases are responsible for excessive production of superoxide, with attendant increase in downstream conversion to other ROS. If the tissue antioxidant defensive mechanisms are overwhelmed by excess radicals, a state of oxidant stress ensues, with numerous possible deleterious effects. Non-phagocyte forms of NADPH oxidase occur in a variety of tissue types, including the kidney. NADPH oxidases have a complex structure, comprising multiple sub-units that are either membrane-bound or located in the cytoplasm in the resting state. Upon stimulation, various cytosolic components migrate to link up with the membrane-bound subunits, resulting in the fully assembled, biologically active enzyme (Griendling et al. 2000). Non-phagocytic NADPH oxidases differ in the details of sub-unit expression, and they are named according to the specific g91phox homologue (or Nox) they possess, e.g. Nox 1, 2, 3, or 4 (Paravicini & Touyz 2008).

NADPH oxidases and renal injury

  1. Top of page
  2. Summary
  3. Introduction
  4. Inflammation in UUO
  5. TGF-β-BMP superfamily involvement
  6. Oxidative stress in UUO
  7. NADPH oxidases
  8. NADPH oxidases and renal injury
  9. NADPH oxidase inhibitors
  10. New therapies in UUO
  11. Conclusion
  12. References

Various NADPH oxidase subunits have been found expressed in the kidney (Chabrashvili et al. 2002), including Renox (renal NADPH oxidase) alias Nox4 (Geiszt et al. 2000; Block et al. 2008), which, as yet, appears to be uniquely expressed in renal tissue. Functionally, both tubular and glomerular NADPH oxidase activities have been demonstrated (Gwinner et al. 1998). Therefore, in pathophysiological conditions that involve increased oxidant stress in the kidney, NADPH oxidase is always considered a possible source of oxidant stress. NADPH oxidase is implicated in a wide range of specific renal disease models, such as 5/6 subtotal nephrectomy (Vaziri et al. 2003), anti-Thy 1.1 nephritis (Gaertner et al. 2002), angiotensin II-induced renal damage (Wolak et al. 2009), renovascular hypertension (Oliveira-Sales et al. 2008; Salguero et al. 2008), transplant nephropathy (Djamali et al. 2009), nephrolithiasis (Li et al. 2009) and NOS inhibition (Bapat et al. 2002). Moreover, in diabetic nephropathy, NAPDH oxidase is present in the cortex, in mesangial cells as well as in podocytes, where it mediates apoptosis (Satoh et al. 2005; Thallas-Bonke et al. 2008; Yang et al. 2010). Normalizing Nox4 in db/db mice by pitavastatin ameliorated albuminuria and mesangial sclerosis (Fujii et al. 2007). Furthermore, NADPH oxidases may account for increased ROS production in the aging kidney (Adler et al. 2004), and their effect can be reverted by the anti-aging gene Klotho (Wang & Sun 2009). NADPH oxidase subunits are also expressed more in UUO (Sugiyama et al. 2005), and they might be mediators of TGF-β-induced myofibroblast activation (Bondi et al. 2010). In type 1 diabetes, medullary superoxide accumulation is caused by PKC-dependent NADPH oxidase activation (Yang et al. 2010). Further evidence of NADPH oxidase contribution to tissue injury is derived from observations in NADPH oxidase-deficient mice, developed by genetic knockout of crucial enzyme subunits such as gp91phox homologs (Nox family) or p47phox (Liu et al. 2006; Chen & Stinnett 2008; Haque & Majid 2008). For example, the p47phox–/– mice are protected against atherosclerosis and renovascular hypertension revealing the enzyme's crucial role in vascular pathophysiology (Chen & Stinnett 2008). The drawback with these genetically modified animals is that they are immunodeficient due to severe loss of normal leucocyte function (Jackson et al. 1995; Pollock et al. 1995). Additionally, it is crucial to note that this complex enzyme family is sometimes hard to study in isolation, for instance, in a Nox-1 KO model, blood pressure was elevated despite decreased NADPH oxidase activity in chronic Ang II-dependent hypertension (Yogi et al. 2008).

NADPH oxidase inhibitors

  1. Top of page
  2. Summary
  3. Introduction
  4. Inflammation in UUO
  5. TGF-β-BMP superfamily involvement
  6. Oxidative stress in UUO
  7. NADPH oxidases
  8. NADPH oxidases and renal injury
  9. NADPH oxidase inhibitors
  10. New therapies in UUO
  11. Conclusion
  12. References

Another major difficulty with assessing the functional role of NADPH oxidase is that specific blockers are still missing. The iodonium compound, diphenylene iodonium (DPI) has been widely applied in the role of NADPH oxidase inhibitor (Babior 1999; Griendling et al. 2000; Griendling & Harrison 2001). Of importance, however, DPI is also an efficient inhibitor of other ROS-producing enzymes, including xanthine oxidase, NOS, and other flavin-containing oxidases (Moulton et al. 2000). Furthermore, DPI is also recognised as a powerful mitochondrial ROS inhibitor (Li & Trush 1998). Because of this non-specificity, data derived from experiments based on the use of DPI can only yield preliminary conclusions about the role of NADPH oxidase. Apocynin is an aromatic ketone that presumably acts by preventing the assembly of NADPH oxidase subunits at the cellular membrane, thereby blocking enzyme activity (Stolk et al. 1994). Also, by curtailing the amounts of superoxide available for reacting with NO, apocynin indirectly provides the benefit of suppressing pro-oxidant peroxynitrite formation (Muijsers et al. 2000). Interestingly, apocynin has also been shown to induce nitric oxide synthesis via increased iNOS activity (Riganti et al. 2008). This induction was accompanied by peroxide formation and ROS generation suggesting a paradoxal pro-oxidative effect of apocynin.

In spite of the uncertainty regarding its exact mechanism of action, apocynin is still considered an appropriate candidate for effective suppression of oxidative stress and inflammation by means of its NADPH blocking activity, and there is evidence to show that it does indeed possess the potential for such effects. Apocynin can conveniently be administered in vivo orally, and is well tolerated by rodents without adversely affecting humoral or cellular immunity (Hart et al. 1992). Some reported in vivo beneficial benefits of apocynin treatment are listed in Table 1.

Table 1.   Examples of beneficial in vivo effects of apocynin in rodent models
 Effect of apocyninReference
  1. ACTH, adrenocorticotropic hormone; AOPP, advanced oxidation protein products; BMP-4, bone morphogenetic protein-4; DOCA, deoxycorticosteron acetate; PAN, puromycin aminonucleoside-induced nephrosis.

Angiotensin II infusion (mice)Relief of renal NO depletion and sodium retentionLópez et al. (2003)
Dexamethasone hypertension (rats)Prevention and reversal of hypertensionHu et al. (2006)
ACTH hypertension (rats)Prevention and reversal of hypertensionZhang et al. (2005)
Leptin-induced hypertension (rats)Prevention of hypertensionBeltowski et al. (2005)
BMP-4 treatment (mice)Alleviation of hypertensionMiriyala et al. (2006)
Dopamine D5 receptor null miceAlleviation of hypertensionYang et al. (2006)
Spontaneously hypertensive ratsAlleviation of hypertensionIliescu et al. (2007)
DOCA-salt ratsAlleviation of hypertensionJin et al. (2006)
Kidney androgen-regulated protein transgenic miceAlleviation of hypertensionTornavaca et al. (2009)
Dahl salt-sensitive ratsAlleviation of hypertension and tubulointerstitial injuryTaylor et al. (2006), Tian et al. (2008)
Cisplatinum toxicity (rats)Prevention of tubular injury and renal dysfunctionChirino et al. (2008)
Angiotensinogen overexpressing miceRelief of tubulointerstitial apoptosis and fibrosisLiu et al. (2009)
Cyclosporine-induced nephrotoxicity (mice)Relief of tubular necrosisLaSpina et al. (2008)
Renovascular hypertension (rats)Relief of proteinuria and glomerular injuryCosta et al. (2009)
Diabetic nephropathy (rats)Relief of proteinuria and glomerular injuryAsaba et al. (2005), Nam et al. (2009), Thallas-Bonke et al. (2008)
Diabetic nephropathy+AOPP infusion (rats)Relief of proteinuria and glomerular injuryShi et al. (2008)
Hyperhomocysteinaemia (rats)Relief of proteinuria and glomerular injuryYi et al. (2006)
PAN ratsReduction of proteinuria and podocyte effacementWang et al. (2009)

New therapies in UUO

  1. Top of page
  2. Summary
  3. Introduction
  4. Inflammation in UUO
  5. TGF-β-BMP superfamily involvement
  6. Oxidative stress in UUO
  7. NADPH oxidases
  8. NADPH oxidases and renal injury
  9. NADPH oxidase inhibitors
  10. New therapies in UUO
  11. Conclusion
  12. References

The crucial role of the renin-angiotensin-system in renal inflammation (Esteban et al. 2004) and fibrosis (Chevalier et al. 2009) has been underscored by studies involving genetic or pharmacological interventions such as angiotensinogen knockout (Fern et al. 1999), vector-mediated angiotensinogen inhibition (Shin et al. 2005), angiotensin converting enzyme (ACE) inhibition (Kaneto et al. 1994), Ang II type 1 (AT1) receptor inhibition (Manucha et al. 2005), AT1a receptor gene knockout (Satoh et al. 2001) or inhibition of chymase-mediated angiotensin formation (Fan et al. 2009), which have all shown considerable benefits in reducing UUO-induced renal fibrosis.

However, many other molecular pathways leading to inflammation and fibrosis have been identified. In the past few years, innovative therapeutic approaches aimed at abrogating profibrotic signalling have been investigated, with varying degrees of relief of UUO-induced injury. Such approaches include drugs targeted at injury-mediating signal transduction pathways, like the p38 mitogen-activated protein kinase (MAPK) inhibitors NPC 31169 and FR167653 (Stambe et al. 2004; Nishida et al. 2008), or even a locally delivered inhibitor ALK5/p38 inhibitor (LY364947) by means of a drug targeting approach (Prakash et al. 2008). In other studies, chemokine receptors (e.g. CCR1) are targeted by non-peptide antagonists such as BX471 (Anders et al. 2002). Also, channel-blocking has been identified as a novel approach for anti-fibrotic therapy. For instance, abrogation of Ras/Raf/MEK/ERK induced fibroblast proliferation has been achieved by blocking membrane-bound calcium-activated potassium channels (Grgic et al. 2009). Other studies have explored immunological techniques, such as the use of the anti-c-fms antibody to inhibit M-CSF (Le Meur et al. 2002). Finally, molecular methods have been exploited, such as antisense oligonucleotide treatment to reduce connective tissue growth factor (CTGF) (Yokoi et al. 2004) or siRNA administration targeting heat-shock protein Hsp-47 (Xia et al. 2008). Gene therapy is yet another option, and favorable results have been reported of hydrodynamic-based gene transfer for the antifibrotic hepatocyte-growth factor (HGF) (Gao et al. 2002). Although potentially promising, experience with these approaches remains still rather limited.

Conclusion

  1. Top of page
  2. Summary
  3. Introduction
  4. Inflammation in UUO
  5. TGF-β-BMP superfamily involvement
  6. Oxidative stress in UUO
  7. NADPH oxidases
  8. NADPH oxidases and renal injury
  9. NADPH oxidase inhibitors
  10. New therapies in UUO
  11. Conclusion
  12. References

UUO-induced leucocyte infiltration and myofibroblast activation can result from collective effects of multiple mechanisms operating in concert. Among these, oxidative stress, at least partially generated by NADPH oxidase, contributes significantly to inflammatory activity and dysregulation of growth factor expression. This makes NADPH oxidases attractive potential targets for pharmacological intervention, especially when combined with existing or novel therapies addressing the intricately associated inflammatory, fibrotic and apoptotic pathways underlying tubulointerstitial damage in UUO.

References

  1. Top of page
  2. Summary
  3. Introduction
  4. Inflammation in UUO
  5. TGF-β-BMP superfamily involvement
  6. Oxidative stress in UUO
  7. NADPH oxidases
  8. NADPH oxidases and renal injury
  9. NADPH oxidase inhibitors
  10. New therapies in UUO
  11. Conclusion
  12. References