Summary of findings
For a glossary of terms used in this review please refer to the appendices (Appendix 1).
Description of the condition
Sickle cell disease (SCD) is a group of disorders characterized by the deformation of erythrocytes, due to a synthesis of an abnormal form of hemoglobin (HbS). Either a mutation in β-globin, where glutamic acid (GAG) is substituted into valine (GTG) in codon 6 of the gene (designated Glu6Val (Driss 2009)) or a compound heterozygosity for Glu6Val and another β-globin mutation, causes the formation of HbS (Steinberg 2006). The erythrocytes have a markedly short life span, leading to hemolytic anemia and release of free hemoglobin into the circulatory system which binds to and inactivates nitric oxide (NO) with consequent vaso-occlusion. Reduced endothelial bioavailability of NO impairs its downstream homeostatic vascular functions which skews the vasoconstriction-vasodilation balance towards vasoconstriction, which in turn increases the possibility of sickle vaso-occlusion (Kato 2007; Kotiah 2009; Pawloski 2005).
Epidemiologically, SCD predominantly affects populations originating from Sub-Saharan Africa, the Mediterranean basin and Latin America. The disorder is most prevalent in African countries with approximately 200,000 babies born with sickle cell anemia every year (Diallo 2002). In the United Arab Emirates, the overall incidence of SCD among 22,200 screened neonates was 1 in 2500, while the incidence of sickle cell trait was 1.1% overall (Al Hosani 2005). In Latin America, a recent large population study involving more than 1.8 million Brazillian newborns revealed an incidence of 1 in 1300 live births (Fernandes 2010). Sickle cell disease is the most common inherited blood disorder in the USA. It is responsible for approximately 113,000 hospitalizations and USD 488 million in hospitalization costs annually (Steiner 2006). Population estimates, with mortality adjusted by age and sickle-cell type, yielded an estimate for 2005 of 89,079 people with SCD in the USA, of which 80,151 were black and 8928 Hispanic (Brousseau 2009). In the UK there are approximately 12,500 people with the disease (National Screening Committee for SC and Thal 2006).
Disease manifestations in SCD can be roughly attributed to two phenomena: hemolysis (such as dilated cardiomyopathy, jaundice and pigmented gallstones); and vaso-occlusion (such as painful crisis, acute chest syndrome, renal dysfunction, and hyposplenism) (Schnog 2004). Although bone marrow transplantation may substantially reduce disease manifestations, choices of curative therapy are limited. Several factors determine the prognosis of affected individuals, including the frequency, severity, and nature of specific complications. The survival of young children with SCD has improved, especially those living in western industrialized countries. Most children with sickle cell anemia (93.9%) and nearly all children with milder forms of SCD (98.4%) now live to become adults (Quinn 2010).
Renal complications in SCD
Renal damage is a frequent complication in SCD as a result of long-standing anemia and disturbed circulation through the renal medullary capillaries (Serjeant 1992). Risk for the development of renal disease is influenced by genetic factors, severity of anemia, and overall disease severity, as well as the sickling process and compensatory mechanisms such as prostaglandin-mediated increases in vascular flow and angiotensin-mediated glomerular hyperperfusion (Powars 1991; Scheinman 2009; Schnog 2004). Renal insufficiency is reported to affect 4% to 18% of adult sickle cell patients (Ataga 2000; Pham 2000; Powars 1991; Steinberg 1999). Renal complications in SCD are typically preceded by microalbuminuria or proteinuria ahead of renal failure. Microalbuminuria or proteinuria affects 16% to 28% of pediatric patients with SCD (Becton 2010).
Proteinuria was noted to be a strong predictor of subsequent renal failure (Powars 1991). Increase of albumin and immunoglobulin G (IgG) excretion were noted to be the earliest clinically detectable features of glomerular injury in patients with sickle cell anemia (Guasch 1996). Recent studies have also associated proteinuria and albuminuria with pulmonary hypertension in adults (Ataga 2010) and children (Forrest 2012). However, there are no long-term data to demonstrate that the reduction of proteinuria slows or prevents progression to chronic renal insufficiency and renal failure (Lottenberg 2005).
The underlying mechanisms of renal failure in SCD are thought to begin with hyperfiltration, or an increase in glomerular filtration rate (GFR) (Etteldorf 1952; Ware 2010; Wigfall 2000). This is followed by glomerular hypertension (Falk 1992), chronic hypoxia, renal medullary ischemias, and increased prostaglandin secretion that leads to glomerular hypertrophy (Falk 1994), increased glomerular permeability (Guasch 1997), and proteinuria (Guasch 1999). These events then progress to a decrease in GFR which eventually results in chronic renal failure. Furthermore, the hyperosmolar milieu of the medulla, a condition favouring HbS polymerisation and resulting in increased blood viscosity within the renal medullary capillaries, leads to loss of concentrating capacity, urinary acidification, and decreased potassium excretion (Falk 1994; Guasch 1997; Guasch 1999; Serjeant 1992). In the American Cooperative Study of Sickle Cell Disease, almost 9% of SCD patients who died due to disease complications manifested overt renal failure, which was identified as the major cause of death in adult patients with SCD (Platt 1994).
Description of the intervention
As there is no proven treatment for sickle cell nephropathy, every attempt should be made to slow its rate of progression (NIH-NHLBI 2002). There is extensive experience and evidence with angiotensin-converting enzyme (ACE) inhibitors over many years in a variety of clinical situations for patients who do not have sickle cell disease. What is unknown is the effect of ACE inhibitors in patients with SCD. Yet, administration of angiotensin-converting enzyme (ACE) inhibitors for such purpose has been commonly practiced due to their renoprotective properties (Lerma 2010; Saborio 1999; Scheinman 2009). Angiotensin blockade appears to effectively control proteinuria and stabilize kidney function in children with non-diabetic proteinuric kidney disease (Chandar 2007).
The ACE inhibitors competitively inhibit the activity of the angiotensin-converting enzyme to prevent the formation of the active octapeptide angiotensin II from its inactive precursor, angiotensin I. All ACE inhibitor drugs are bound to tissues and plasma proteins and this gives rise to a characteristic concentration-time profile whereby any free drug is relatively rapidly eliminated from the kidney, predominantly by glomerular filtration (Reid 2006). The ACE inhibitors are different from the angiotensin II receptor blockers (ARBs), which act specifically to block the AT1 receptor in order to prevent its binding with angiotensin II.
Most ACE inhibitors are given as prodrugs, because the active forms are water soluble and poorly absorbed from the gut (Waller 2005). The initial dosage of ACE inhibitor therapy must be individualized, mainly due to the risk of hypotension (Reid 2006; Rxmed 1999). There are known interactions with various drugs such as diuretics, agents increasing serum potassium, allopurinol, alpha-blocking agents, iron, lithium, non-steroidal anti-inflammatory drugs (NSAIDs), and tetracycline (Rxmed 1999).
How the intervention might work
It has been suggested that destruction of the renal medulla results in the release of vasodilating substances which subsequently triggers glomerular hyperfiltration followed by glomerular hypertension. These events, which consequently lead to glomerulosclerosis, a decrease in GFR and subsequent proteinuria or microalbuminuria, are pathogenic factors in sickle cell nephropathy (Falk 1992; Guasch 1996; McKie 2007; Wesson 2002; Wigfall 2000). Proteinuria and microalbuminuria are mostly attributed to vaso-occlusive events (Schnog 2004), which happen as a result of a skewed vasoconstriction-vasodilation balance towards vasoconstriction (Kato 2007; Kotiah 2009; Pawloski 2005).
It has been observed that ACE inhibitors dilate the efferent glomerular arterioles, leading to a fall in the intra-glomerular pressure and a decrease in the glomerular permeability to albumin. These events lead to amelioration of pathological changes like perihilar focal segmental glomerulosclerosis with consequent decrease of urinary protein excretion (Anderson 1986; Powars 1991). In fact, experimental studies have shown that ACE inhibitors prevent the occurrence of albuminuria and glomerulosclerosis in diabetic rats (Zatz 1986).
For more than a decade ACE inhibitors and angiotensin II receptor blockers (ARB) are known to have pronounced antiproteinuric and renoprotective properties, independently from their primary antihypertensive effect. Several large studies confirmed the pronounced antiproteinuric and renoprotective effects of ACE inhibitors, which were associated with a major reduction of proteinuria, slower GFR decline and reduced risk of doubling serum creatinine or reduced rate of progression to end-stage renal disease (ESRD) (Appendix 1) (Kolesnyk 2010).
Why it is important to do this review
Due to the improvement in life expectancy of people with SCD (Quinn 2010), there is a corresponding significant increase in the incidence of renal complications. Previous studies have shown the potential clinical application of ACE inhibitors to reduce proteinuria in SCD (Lerma 2010; Powars 1991; Saborio 1999). As such, administration of ACE inhibitors has been commonly practised for the treatment of SCD-related proteinuria (Scheinman 2009). This review aims to bring together clinical trials in this area to establish the clinical value of this pharmaceutical approach.
To determine the effectiveness of ACE inhibitor administration in people with SCD for preserving renal function by decreasing intraglomerular pressure and proteinuria thus maintaining current GFR or slowing the decline in GFR. A secondary objective is to assess the safety of ACE inhibitors as pertains to their side effects (hyperkalemia, hypotension, etc.).
Criteria for considering studies for this review
Types of studies
Randomized or quasi-randomized trials. Trials in which quasi-randomized methods, such as alternation, are used will be included in future updates if there is sufficient evidence that the treatment and control groups were similar at baseline.
Types of participants
People with known SCD (SS, SC, Sβ+ thal and Sβ
Types of interventions
Any ACE inhibitors designed to reduce proteinuria in patients with SCD compared to either placebo or a standard treatment regimen.
Types of outcome measures
- Urinary protein or albumin excretion (over 24 hours or first morning void (FMV))
- Serum creatinine
- Electrolyte levels
- Chromium-ethylenediaminetetraacetic acid (EDTA) GFR or estimated GFR (eGFR)
- Blood pressure
- Hemoglobin concentration
- Comprehensive metabolic panel (CMP) excluding electrolytes and proteins parameters
- Number of dialysis events
- Occurence of kidney transplantation
- Any reported adverse effect or toxicity (e.g. hypotension, hyperkalemia, maculopapular rash, hematologic reactions, etc.)
Search methods for identification of studies
The authors identified relevant studies from the Cystic Fibrosis and Genetic Disorders Group's Haemoglobinopathies Trials Register using the terms: sickle cell AND (proteinuria OR microalbuminuria).
The Haemoglobinopathies Trials Register is compiled from electronic searches of the Cochrane Central Register of Controlled Trials (CENTRAL) (updated each new issue of The Cochrane Library) and quarterly searches of MEDLINE. Unpublished work is identified by searching the abstract books of five major conferences: the European Haematology Association conference; the American Society of Hematology conference; the British Society for Haematology Annual Scientific Meeting; the Caribbean Health Research Council Meetings; and the National Sickle Cell Disease Program Annual Meeting. For full details of all searching activities for the register, please see the relevant section of the Cochrane Cystic Fibrosis and Genetic Disorders Group Module.
Date of the last search: 05 July 2012.
Please refer to a PRISMA diagram illustrating study selection (Figure 1).
|Figure 1. Study flow diagram.|
Searching other resources
The bibliographic references of all retrieved literature were reviewed for additional reports of studies. Experts will be contacted if the need arises for future updates.
Data collection and analysis
Selection of studies
Three authors independently applied the inclusion criteria in order to select studies for inclusion in the review. No disagreements arose, but if for future updates any disagreements do arise on the suitability of a study for inclusion in the review, the authors will aim to reach consensus by discussion.
Data extraction and management
Two authors (THS and SN) independently extracted the data using the standard acquisition forms. One author (SKB) verified the data collection. No disagreements arose, but if for future updates any disagreements do arise on the suitability of a study for inclusion in the review, the authors will aim to reach consensus by discussion. The authors will contact study investigators whenever necessary. The eligible time period for endpoint analysis were at least one month after ACE inhibitor treatment. The authors excluded studies from analysis if the only time period reported is less than one month. Authors analysed data in three blocks of time: one to three months; over three months to six months; and longer than six months.
Assessment of risk of bias in included studies
Two authors (THS and SN) assessed the risk of bias of each study. One author (SKB) verified the assessment. Authors generated a risk of bias table as described in the Cochrane Handbook of Systematic Reviews of Interventions 5.1 (Higgins 2011). In particular, the authors examined details of the following components in each study:
- sequence generation (e.g. whether randomization was adequate);
- allocation concealment (e.g. whether the allocation was adequately concealed);
- blinding of participants, personnel and outcome assessors (e.g. whether the the participants, personnel and outcome assessors were blinded);
- incomplete outcome data (e.g. whether attrition and exclusion were reported);
- selective outcome reporting (e.g. whether the study was free from selective outcome reporting);
- other sources of bias (will be specified during the assessment).
Authors assessed all components as having either a low risk of bias, an unclear risk of bias, or a high risk of bias.
Measures of treatment effect
The authors recorded continuous data such as urinary protein excretion and GFR or eGFR as either mean change from baseline for each group or mean post-treatment values and standard deviation (SD) for each group. The authors used the mean difference (MD) for the urinary protein excretion outcome, however, the standardized mean difference (SMD) may be used for future versions of the review if there are studies with data included which report on both 24-hour urinary excretion and first morning void (FMV). The 24-hour urinary protein excretion and FMV would be on the same scale with different mean and SD summaries, hence requiring standardization.
The authors recorded dichotomous outcomes, e.g. dialysis or no dialysis, as present or absent. For binary outcomes, the authors calculated the odds ratio (OR) based on the ratio of an outcome among treatment-allocated participants to that amongst controls. The authors aimed to calculate a pooled estimate of the treatment effect for each outcome across studies by determining the OR or SMD.
Unit of analysis issues
The authors will only include cross-over studies in this review if they consider there to be a sufficient washout period between the treatment arms. The authors will analyze any data from such trials using paired analysis as described by Elbourne (Elbourne 2002). For cluster randomized studies, the authors will calculate the effective sample size and monitor and analyze them based on the method described by Donner (Donner 2002). The authors will analyze any such trials separately. The authors aim to address the risk of unit of analysis error caused by repeated observations on participants based on the information provided in the Cochrane Handbook of Systematic Reviews of Interventions (Higgins 2011).
Dealing with missing data
For future updates the review authors will contact the trial authors of the included study regarding outcomes where no exact value was indicated in the study manuscript (Foucan 1998). For any further trials included, the review authors will seek full reports from trial investigators where studies have been published in abstract form, presented at meetings or reported to the authors. Where information is missing or unclear, the authors will contact the primary investigator. In order to allow an intention-to-treat analysis, the authors will group data by allocated treatment groups, irrespective of later exclusion (regardless of cause) or loss to follow-up.
Assessment of heterogeneity
In future updates of the review, when more studies are included, the authors plan to test for heterogeneity between studies using a standard chi-squared test and I
- 0% to 40%: might not be important;
- 30% to 60%: may represent moderate heterogeneity;
- 50% to 90%: may represent substantial heterogeneity;
- 75% to 100%: considerable heterogeneity.
Assessment of reporting biases
The authors compared the 'Methods' section of the full published paper to the 'Results' section to ensure that all outcomes which were measured, were reported. The authors could not obtain the protocol of the included study from trials registers. In future updates, the authors will try to obtain protocols from trials registers in order to identify any potential reporting bias.
The authors employed a fixed-effect analysis in the review. In future updates of the review, when more trials are included, where the value of I
Subgroup analysis and investigation of heterogeneity
For future updates, if the authors find heterogeneity between studies, examination of subgroups, such as: age of participants (0 years to 10 years, over 10 years to 20 years, over 20 years); type of SCD (SS, SC, Sβ+ thal and Sβ
If a range of studies are included in the review the authors plan to test the robustness of their results with the following sensitivity analyses:
- studies where quasi-randomisation methods are used;
- studies where there are variations among one or more inclusion criteria (such as different definitions for hypertension);
- studies of different designs (e.g. cross-over and cluster randomized studies).
In addition, the authors plan to undertake a sensitivity analysis to investigate the effects of combining endpoint analysis across all time-periods.
Description of studies
Results of the search
Five studies were identified from the searches. Four of them were non-randomized, observational studies and did not use any control groups (Aoki 1995; Falk 1992; Fitzhugh 2005; McKie 2007). These studies were therefore excluded from this review. One study was eligible for inclusion in the review (Foucan 1998).
The Foucan study was described as a double-blind, randomized, placebo-controlled trial. It was carried out in a single center in France. The participants were treated for six months with a median length of follow-up of three months (Foucan 1998).
The Foucan study randomized 22 patients (7 males and 15 females) having proteinuria or microalbuminuria with SCD. There were 12 patients in the treatment group and 10 in the placebo group. This study included the patients if they were 18 years or older (Foucan 1998).
The Foucan study compared captopril and placebo. The captopril dose varied over time: 6.25 mg per day (¼ of a tablet of 25 mg once a day) during the first month; 12.5 mg per day (¼ of a tablet twice a day) during the second and the third months; and 25 mg per day (½ of a tablet twice a day) after the third month (Foucan 1998).
The Foucan study reported the effect of captopril on albumin excretion, serum creatinine, potassium, blood pressure and hemoglobin concentration. Sodium level was not reported, although it was measured. Adverse effects were reported (Foucan 1998).
Risk of bias in included studies
The Foucan study was judged to have an unclear risk of bias for the generation of allocation sequence (Foucan 1998). Although this study was described as using random assignment to generate allocation, the process was not described.
In addition, allocation concealment was not reported. Therefore, this study was judged to also have unclear risk of bias for this criterion (Foucan 1998).
Participants, treating physicians and outcome assessors were blinded in the included study (Foucan 1998). Therefore, the authors judged this study to have low risk of bias for this criterion.
Incomplete outcome data
Two patients were withdrawn from the trial: one in the ACE inhibitor group had an unusual pain in the shoulder and discontinued treatment on the sixth day; and one in the placebo group was unavailable for follow-up after the first month. These patients were included in the intention-to-treat analysis (Foucan 1998). In this regard, this study was therefore judged to have a low risk of bias.
Sodium level was not reported in the results section of the included study, although the methods section mentioned that it was measured (Foucan 1998). In addition, the exact serum creatinine level and hemoglobin concentration were not reported. The authors therefore judged there to be high risk of bias from selective reporting.
Other potential sources of bias
Baseline characteristics between the captopril group and placebo group in Foucan study were not systematically different. There was no significant difference in the mean age, body mass index, blood pressure, hemoglobin concentration, serum creatinine, urine albumin excretion and creatinine clearance (Foucan 1998). The authors therefore judged this study to have low risk for these potential sources of bias.
Effects of interventions
1. Urinary protein or albumin excretion
In the Foucan study, urinary albumin excretion was examined at one month, three months and six months (Foucan 1998). At one month, it was reported that no significant changes were noted, although the report did not mention the exact level of excretion. At three months, it was reported that the urinary albumin excretion decreased from baseline in the treatment group and increased in the placebo group. The authors could not assess whether there was a statistically significant difference since exact levels of excretion were not reported. At six months, the study reported no significant difference in per-hour urinary albumin excretion between the captopril group and the placebo group, although the urinary albumin excretion in the captopril group was lower by a MD of -49.00 (95% CI -124.10 to 26.10) compared to placebo ( Analysis 1.1). However, our analyses on the absolute change score showed significant changes between the two groups by a MD of -63.00 (95% CI -93.78 to -32.22) ( Analysis 1.1). The captopril group was noted to decrease by a mean (SD) of 45 (23) mg/day and the placebo group was noted to increase by 18 (45) mg/day, when the albumin excretion was compared between that of the baseline and at six months.
Note: The authors planned to report on this outcome at over 24 hours or first morning void (FMV), however, only per hour data were available for the included trial.
2. Serum creatinine
The Foucan study reported that serum creatinine was constant throughout the study within both the captopril and placebo groups (Foucan 1998). However, no statistical calculation could be made as the exact serum creatinine levels were not reported.
3. Electrolyte levels
Two electrolyte levels were examined in the Foucan study, sodium and potassium. However, only the potassium level was reported; this was constant throughout the study within each group. No statistical calculation can be carried out as the exact potassium level was not reported (Foucan 1998).
1. Chromium-ethylenediaminetetraacetic acid (EDTA) GFR or estimated GFR (eGFR)
this outcome was not measured in the Foucan study (Foucan 1998).
2. Blood pressure
In general, the Foucan study recorded a decrease in blood pressure among patients within captopril group and constant blood pressure among patients within placebo group (Foucan 1998). A decrease of 5 mmHg was recorded for mean blood pressure and diastolic blood pressure. A decrease of 8 mmHg was recorded for systolic blood pressure.
3. Hemoglobin concentration
Hemoglobin concentration was reported to be constant throughout the study within each group (Foucan 1998). No statistical calculation can be carried out as the exact concentration was not reported.
4. Comprehensive metabolic panel (CMP) excluding electrolytes and proteins parameters
This outcome was not measured in the Foucan study (Foucan 1998).
5. Number of dialysis events
No events were reported in the Foucan study (Foucan 1998) .
6. Occurence of kidney transplantation
No occurrences were reported in the Foucan study (Foucan 1998).
7. Any reported adverse effect or toxicity
No significant differences between groups were found for any adverse effect (Foucan 1998). The Foucan study reported dry cough at the end of the sixth month in one of the patients within the captopril group, RR 2.54 (95% CI 0.11 to 56.25) ( Analysis 1.2). Another patient in the captopril group reported unusual pain in the shoulder and discontinued treatment on the sixth day, RR 2.54 (95% CI 0.11 to 56.25) ( Analysis 1.2). One patient in the placebo group progressed to clinical proteinuria (urinary albumin excretion greater than 300 mg/day) during the third month, RR 0.28 (95% CI 0.01 to 6.25) ( Analysis 1.2).
Summary of main results
In this review the authors could only identify one study which fulfilled the review criteria. The study included six-month urinary protein excretion as the primary outcome measure (Foucan 1998). Although other outcome measures were reported, none were detailed enough to allow statistical analysis ( Summary of findings for the main comparison).
The authors noted that the mean urinary albumin excretion was lower in the captopril group compared to the control group at six months of treatment. However, our systematic review found that different analyses resulted in different levels of significance. There was a non-significant difference in mean urinary albumin excretion between groups, MD -49.00 (95% CI -124.10 to 26.10); however, the change score for mean albumin excretion between groups was significant, MD -63.00 (95% CI -93.78 to 32.22). In the treatment group this decreased by 45 ± 23 mg/day and in the control group increased by 18 ± 45 mg/day. Under some circumstances, a change score can be more efficient because it can remove some between-person variability from the measurement. The confidence interval widths for the former and the latter analyses are 150.20 and 61.60, respectively. However, one could argue that the latter analysis is less efficient for difficult measurements that cannot be recorded precisely and perhaps more relevant for skewed distribution.
Serum creatinine and potassium levels were reported constant throughout the study. The potential for inducing hypotension should be highlighted; the study reported a decrease of 8 mmHg in systolic pressure and 5 mmHg in diastolic and mean blood pressure. Other reported events which were thought as due to the intervention were difficult to assess as there was no clear evidence of what they signify.
Overall completeness and applicability of evidence
Although reported only in very limited details, the authors admit that the included study has addressed the primary outcome measures in this review. However, there is no report of GFR, which could also indicate the level of glomerular damage. Relevant types of participants, interventions and outcomes were investigated in the study. Participants involved were all homozygous for hemoglobin SS, aged over 18 years and had urinary albumin excretion between 30 mg and 300 mg per 24 hours on three different occasions in the six months prior to the study. Captopril was used as an ACE inhibitor intervention and appropriately compared to placebo. Relevant primary and secondary outcome measures were reported, although not all that were proposed in this review.
Previous studies have mentioned the common practice of administering ACE inhibitors for the treatment of microalbuminuria and proteinuria in people with SCD (Lerma 2010; Saborio 1999; Scheinman 2009). Although there are no published guidelines on the administration of ACE inhibitors for proteinuria, it has been recommended that ACE inhibitors can be started once the urinary protein to creatinine ratio is persistently above 100 mg/umol (Sharpe 2011).
Quality of the evidence
While the only included study was small (22 participants), the overall quality of the outcomes reported was high, since most aspects that may contribute to bias were regarded to be of low risk (Risk of bias in included studies), although allocation concealment was not reported (Foucan 1998). There may be selective reporting on sodium level, but other electrolyte levels were reported. Nevertheless, the amount of data with detailed descriptions has allowed only limited analysis in this review.
Potential biases in the review process
No potential biases were identified in the current review process.
Agreements and disagreements with other studies or reviews
Four observational, non-randomized studies of enalapril (an ACE inhibitor) did not employ a control group (Aoki 1995; Falk 1992; Fitzhugh 2005; McKie 2007). The Falk study prospectively reported enalapril treatment in 10 patients, the length of treatment was only two weeks (Falk 1992).This study concluded that enalapril reduced the degree of proteinuria, since the rate of urinary protein excretion decreased in all 10 patients at the end of the two-week treatment period (P <0.001), with a reduction of 57% from baseline.
The Aoki study included eight SCD patients with a urinary albumin excretion above 30 mg/day (Aoki 1995). In six of these urinary albumin excretion returned to normal after six months of treatment. One patient had a 70% reduction and another had a level beyond that observable. Electrolyte levels and creatinine clearance level did not change significantly throughout the study; but mean arterial pressure was significantly decreased by 8.1 mmHg (P < 0.05) (Aoki 1995).
The Fitzhugh study retrospectively reported on three patients, receiving enalapril alone followed by enalapril with hydroxyurea, using their medical records as the main source of data (Fitzhugh 2005). Length of sole enalapril administration was 38.7 ± 15.3 months. All patients experience a reduction in urinary protein and creatinine ratio: before treatment 6.9 ± 3.7; and after treatment 2.2 ± 1.8. Although the difference is not statistically significant, a substantial reduction of 4.7 in the urinary protein to creatinine ratio was noted. This study concluded that enalapril therapy for children with sickle nephropathy reduces urinary protein excretion.
The McKie study retrospectively reported on nine patients, using their medical records as the main source of data; for three of the patients in this study enalapril treatment was subsequently switched to a longer-acting lisinopril (McKie 2007). Length of treatment was 42 ± 19.2 months. In five of the patients proteinuria or microalbuminuria improved and the study summarized that these conditions may be amenable to ACE inhibitor treatment, although a further efficacy study is warranted.
None of the above studies have been reviewed systematically and presented different results, it is therefore difficult to determine agreement or disagreement among these four studies and the Foucan study. Although all studies showed reduction in urinary protein excretion, the statistical significance of the reduction was not noted in all of them.
Implications for practice
There is not enough evidence that ACE inhibitors are associated with a reduction of microalbuminuria and proteinuria in people with SCD. This was observed through analyses on the effect of ACE inhibitors for decreasing urinary albumin excretion in people with SCD. There is also no evidence of other potential adverse effects on the administration of ACE inhibitor for people with sickle nephropathy. The use of ACE inhibitors for reducing proteinuria and microalbuminuria in people with SCD may not be indicated until further evidence is obtained, especially in light of a potential hypotensive effect.
Implications for research
The potential for ACE inhibitors to decrease microalbuminuria and proteinuria in people with SCD has been observed and randomized controlled studies are warranted. As microalbuminuria may develop during childhood (McKie 2007), randomized controlled studies in this group of participant should be conducted, with emphasis on investigating the long-term effectiveness and safety in preventing clinical proteinuria and chronic kidney disease. Longer-term studies involving larger cohorts from multiple centers should be carried out to investigate if the findings reported previously are sustained and consistent.
Detailed reporting of each outcome measure is necessary to allow a clear cut interpretation in a systematic review. One of the difficulties encountered in this review is lack of detailed data reported in the included study.
The authors would like to thank Tracey Remmington for her assistance throughout the preparation of this manuscript. This work was partly supported by Research Universiti Grants No. 304/PPSP/812072 and 304/PPSP/812048 from Universiti Sains Malaysia.
Data and analyses
- Top of page
- Summary of findings [Explanations]
- Authors' conclusions
- Data and analyses
- Contributions of authors
- Declarations of interest
- Sources of support
- Index terms
Appendix 1. Glossary
Contributions of authors
THS, SN and SKB independently applied the inclusion criteria for including studies into this review. THS and SN independently assessed the study quality and extracted data. SN verified the data. THS drafted the review text, SKB and SN provided reviews and suggestions to the draft.
Declarations of interest
Sources of support
- Universiti Sains Malaysia (USM) Research University (RU) Grant, Malaysia.USM RU Grants No. 1001/PPSP/812048 and No. 1001/PPSP/812072 for Dr. Teguh Haryo Sasongko.
- No sources of support supplied
Medical Subject Headings (MeSH)
Albuminuria [*drug therapy]; Anemia, Sickle Cell [*complications; urine]; Angiotensin-Converting Enzyme Inhibitors [*therapeutic use]; Captopril [*therapeutic use]; Creatinine [blood]; Potassium [blood]; Proteinuria [*drug therapy]; Randomized Controlled Trials as Topic; Renal Insufficiency [prevention & control]
MeSH check words
Female; Humans; Male