Effect of antihypertensive therapy on the kidney in patients with diabetes: a meta-regression analysis

OBJECTIVE

To assess the relative effect of different antihypertensive agents on proteinuria and renal function in patients with diabetes.

DATA SOURCES

We used MEDLINE and bibliographies in recent articles to identify studies of the effects of antihypertensive agents on renal function in patients with diabetes.

STUDY SELECTION

We selected 100 controlled and uncontrolled studies that provided data on renal function, proteinuria, or both, before and after treatment with an antihypertensive agent.

DATA EXTRACTION

Data on blood pressure, renal function, proteinuria, patient characteristics (for example, age, sex, and type of diabetes), and study design (for example, random allocation and the use of a placebo) were extracted from selected studies.

DATA SYNTHESIS

Multiple linear regression analysis indicated that angiotensin-converting enzyme (ACE) inhibitors decreased proteinuria independent of changes in blood pressure, treatment duration, and the type of diabetes or stage of nephropathy, as well as study design (P < 0.0001). Reductions in proteinuria from other antihypertensive agents could be entirely explained by changes in blood pressure. Blood pressure reduction in itself was associated with a relative increase in glomerular filtration rate (regression coefficient [+/- SE], 3.70 +/- .92 mL/min for each reduction of 10 mm Hg in mean arterial pressure; P = 0.0002); however, compared with other agents, ACE inhibitors had an additional favorable effect on glomerular filtration rate that was independent of blood pressure changes (3.41 +/- 1.71 mL/min; P = 0.05).

CONCLUSION

Angiotensin-converting enzyme inhibitors can decrease proteinuria and preserve glomerular filtration rate in patients with diabetes. These effects occur independent of changes in systemic blood pressure.

Lovastatin inhibits proliferation of rat mesangial cells

Products of intracellular mevalonate metabolism are essential for cell growth and proliferation. Lovastatin, an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase, blocks the formation of mevalonate and its metabolites, and has been shown to inhibit proliferation of several cell types. In vivo, lovastatin has reduced mesangial cellularity and glomerular injury in experimental renal disease. In this study, we investigated the effects of lovastatin on DNA replication and proliferation in rat glomerular mesangial cells. Growth-arrested mesangial cells were exposed to medium containing 10% fetal bovine serum to stimulate mitogenesis. Lovastatin (1-20 microM) caused a significant (P < 0.05) dose-dependent reduction in DNA synthesis ([3H]thymidine incorporation) which was completely prevented in the presence of exogenous mevalonate (100 microM). Lovastatin (1 microM) inhibited cell proliferation by 90% over a 5-d period, and this was largely overcome by added mevalonate. Exogenous low density lipoprotein (100 micrograms/ml) did not prevent lovastatin inhibition of DNA synthesis. The isoprenoid end product isopentenyl adenine (5 or 50 microM) had little effect on DNA synthesis and cell proliferation in lovastatin-blocked cells. By contrast, the isoprenoid farnesol (5 microM) largely prevented lovastatin inhibition of DNA synthesis. We conclude that mevalonate metabolism is essential for mesangial cell proliferation, possibly through the production of the isoprenoid farnesol. Moreover, the action of lovastatin to reduce experimental glomerular injury may involve a direct effect on mesangial cells.

Lovastatin but not enalapril reduces glomerular injury in Dahl salt-sensitive rats

Dahl salt-sensitive (S) rats fed a high salt diet develop hypertension, hyperlipidemia, and progressive renal disease. Previous studies have suggested that lipids may be important in the pathogenesis of glomerulosclerosis in Dahl S rats. To investigate this possibility, Dahl S rats fed 4% NaCl chow were treated chronically with the cholesterol synthesis inhibitor lovastatin. After 22 weeks, lovastatin-treated rats had a 38% reduction in serum cholesterol, a 76% reduction in urine albumin excretion, and one-sixth the incidence of focal glomerulosclerosis compared with vehicle-treated control rats. Blood pressure in lovastatin-treated rats was significantly (p < 0.05) lower than that in vehicle-treated rats both early in the study (4 weeks of treatment) and at the end of the protocol. Lovastatin had no effect on glomerular filtration rate or glomerular ultrafiltration dynamics. The efficacy of angiotensin converting enzyme inhibitors in attenuating proteinuria and experimental glomerular disease may be dependent on sodium intake. Thus, we also investigated the effects of long-term enalapril treatment on glomerular injury in Dahl S rats fed high salt chow. Enalapril treatment (50 or 200 mg/l drinking water) significantly lowered blood pressure in Dahl S rats, but did not significantly affect albuminuria or glomerulosclerosis. Enalapril also had no effect on glomerular hemodynamics. These results suggest that lipids may be important in the development of both glomerular disease and hypertension in Dahl S rats and that angiotensin converting enzyme inhibition may not affect the course of renal disease in a setting of high salt intake.

Is the aggressive management of hyperlipidemia in nephrotic syndrome mandatory?

The development of the nephrotic syndrome is associated with a lipid profile characterized by increased total and low density lipoprotein cholesterol. Although total high density lipoprotein (HDL) values may be in the normal range, there is frequently abnormalities of HDL subclasses, with reduction of the mature HDL2 subfraction. While these lipid changes may be considered a risk for atherosclerosis, they revert to normal with remission of the nephrotic syndrome. However, with chronic nephrotic range proteinuria, these abnormalities persist and may also be associated with increased levels of lipoprotein (a), increased levels of very light density lipoprotein and further reductions in HDL. These factors could all contribute to greater risk for atherosclerosis. Although coronary artery disease is frequently seen in patients with end-stage renal disease, and many uncontrolled studies in patients with chronic nephrotic syndrome have suggested an increased prevalence of cardiovascular disease, no prospective studies to evaluate relationship between lipid abnormalities and cardiac disease have been performed in patients with the nephrotic syndrome. Recent experimental data have also suggested a relationship between hyperlipidemia and progressive renal injury. Unfortunately, human epidemiological data are incomplete in correlating lipid changes with renal disease in patients with chronic nephrotic syndrome. No therapeutic trials have tested whether or not pharmacologic interventions will benefit either the cardiac or renal disease that ensues in patients with chronic persistent nephrotic syndrome. Thus, considerably more data are needed to help clarify this important area.

Transient reductions in serum cholesterol after renal transplantation

Declines in serum cholesterol have been reported in patients with altered immune system activity. However, the frequency and clinical significance of transient reductions in serum cholesterol after renal transplantation are unknown. In the present retrospective study, we examined the frequency and clinical setting of reduced serum cholesterol (< or = 4.40 mmol/L [170 mg/dL]) in patients who each had 28 +/- 7 (total, 1,110) cholesterol determinations during the first year posttransplant. Reduced cholesterol was found on at least one occasion in 26 of 40 (65%) patients. Ninety-two percent (119/129) of the reduced cholesterol values occurred in one of three clinical settings: (1) within 10 days after transplantation, (2) within 6 weeks before or after the onset of acute rejection, or (3) within 6 weeks before or after the onset of a cytomegalovirus infection (CMV). Multiple linear regression analysis showed that the relationship between reductions in cholesterol associated with acute rejection was independent of CMV and the type of immunosuppression (one half of the patients were treated with cyclosporine [CSA]). The fact that serum albumin was reduced during CMV, but not during acute rejection, suggested that reduced cholesterol associated with rejection was relatively specific, and was not caused by a generalized leak of plasma proteins or by poor nutrition. Thus, during the first year posttransplant, reductions in serum cholesterol are most often associated with acute rejection episodes and/or CMV.(ABSTRACT TRUNCATED AT 250 WORDS)

Renal injury in obese Zucker rats: glomerular hemodynamic alterations and effects of enalapril

Angiotensin-converting enzyme inhibitors may ameliorate experimental glomerular injury by either hemodynamic or nonhemodynamic mechanisms. In a long-term study, we examined the effects of 30 wk of enalapril treatment on the development of glomerular disease in obese Zucker rats (OZR). Enalapril significantly (P less than 0.05) lowered blood pressure, fasting serum cholesterol, and urine albumin excretion in OZR throughout the experimental period. At 38 wk of age, enalapril-treated OZR had a sixfold reduction in the percent glomeruli exhibiting focal glomerulosclerosis and a 20-30% reduction in kidney weight and glomerular area. A separate micropuncture study in 22- to 26-wk-old rats revealed that untreated OZR with albuminuria and increased blood pressure had elevated glomerular capillary pressure (Pgc). Enalapril-treated OZR had less albuminuria and lower blood pressure, but Pgc was not reduced. The value of the transcapillary hydraulic pressure difference (delta P) in enalapril-treated OZR was intermediate between values in untreated OZR and lean Zucker rats. Thus enalapril markedly attenuated the development of glomerular injury in OZR. The salutary effects of enalapril may have involved a reduction in delta P coupled to a nonhemodynamic action, possibly restriction of glomerular growth or lowering of serum cholesterol.

Patients with a low income have reduced renal allograft survival

The impact of socioeconomic factors on long-term outcome after renal transplantation is unknown. We examined the effects of family income among 202 patients transplanted between 1976 and 1982 who had an allograft that functioned for at least 1 year. Compared with patients with an adequate income, recipients of medical assistance at the time of transplantation were more likely to return to dialysis after 1 year (16/45 [36%] v 26/157 [17%], P less than 0.01), or after 5 years of graft function (10/38 [26%] v 12/116 [10%], P less than 0.01). Patients who complied with fewer than 85% of visits during the first 2 years were also more likely to return to dialysis after 1 year (17/49 [35%] v 25/153 [16%], P less than 0.01), or after 5 years (8/31 [26%] v 14/123 [11%], P less than 0.05) than were more compliant patients. However, noncompliance was not different in patients with and without a low income (37/157 [24%] v 12/45 [27%], P greater than 0.05). The relative risk for returning to dialysis after 5 years was 2.4 (P less than 0.05) for low income and 3.0 (P less than 0.05) for less than 85% compliance using a Cox proportional hazards model. These effects were independent of prior transplantation, mismatches, pre-formed antibodies, delayed graft function, age, sex, diabetes, alcohol or drug abuse, education, race, distance from the transplant center, and living in an urban environment (relative risk = 2.5, P less than 0.05). Neither income nor compliance could be linked to death.(ABSTRACT TRUNCATED AT 250 WORDS)

Patient and renal allograft survival in the late posttransplant period

Finding the proper balance between too much and not enough immunosuppression is just as important in the late posttransplant period as it is during the first year after transplantation. In general, too much immunosuppression leads to an increase in patient mortality, whereas inadequate immunosuppression can lead to an inordinately high rate of allograft failure (Fig 5). In the late posttransplant period, patient and allograft survival are both critically dependent on the degree of immunosuppression and on the long-term side effects of the agents used to achieve this immunosuppression. Adequate immunosuppression is important in treating and preventing the acute allograft rejection episodes that are common during the first year after transplantation (Fig 6). Some data suggest that the severity of early acute rejection episodes may influence the development of chronic rejection, the most common cause of graft failure in the late posttransplant period. Otherwise, the role of immunosuppression in treating and preventing chronic rejection is unclear. The discontinuation of immunosuppression by noncompliant patients is a major cause of late graft failure. Whether the nephrotoxicity of CsA will also result in graft failure in the very late posttransplant period is still unknown. The agents used to achieve immunosuppression, along with decreased graft function and proteinuria, contribute to hypercholesterolemia, hypertension, and hyperglycemia. These and other risk factors have a negative impact on both graft and patient survival. Thus, immunosuppression is directly, or indirectly linked to most of the common causes of death and graft failure after renal transplantation. Although potent new immunosuppression protocols have increased the rate of short-term patient and allograft survival after renal transplantation, future advances in long-term survival after renal transplantation will depend on improvements that are effective in the late posttransplant period. Currently, the best approach to preventing complications in the late posttransplant period is to maintain a vigilant, comprehensive program of on-going medical care. The minimal amount of immunosuppression required to prevent allograft rejection should be used, while adhering to the principle that it is better to lose the graft than to lose the patient.

The Zucker rat model of obesity, insulin resistance, hyperlipidemia, and renal injury

Although the pathogenesis of obesity in OZR is unknown, the association among hyperinsulinemia, insulin resistance, and hyperlipidemia suggests that investigations using OZR may help define how a number of vascular disease risk factors interact to cause end-organ damage. Like other rat strains, OZR do not develop atherosclerosis spontaneously. Nevertheless, in an endothelial injury model, atherosclerosis was worse in OZR than in LZR. Perhaps more intriguing is the fact that OZR develop spontaneous glomerular injury. Although the mechanisms important in the development and progression of glomerular injury in OZR remain to be clarified, both lipid abnormalities and glomerular hemodynamic alterations could play a role.

Histopathologic findings associated with a chronic, progressive decline in renal allograft function

The relationship between specific histopathologic findings of chronic rejection (CR) and the clinical course of renal transplant recipients with a chronic progressive decline in allograft function (CPDAF) is unknown. We used one or two hinged regression lines, fitted by least-squares to serial creatinine clearances, to define the onset and clinical course of CPDAF. Biopsies (N = 100) from patients transplanted from 1978 to 1982 were studied retrospectively. Interstitial fibrosis, tubular atrophy, and fibrointimal arterial narrowing were more pronounced in biopsies obtained after, but not before the onset of CPDAF. Interstitial hemorrhage, an infrequent finding in acute vascular rejection, preceded the onset of CPDAF, but the more common histologic findings of acute cellular rejection did not. The severity of histologic features of CR (as reflected by a score combining fibrointimal arterial narrowing, interstitial fibrosis, tubular atrophy, glomerular sclerosis, glomerular mesangial expansion, and glomerular basement membrane reduplication) correlated with the duration of subsequent allograft survival (r = -0.65, P less than 0.001). Glomerular size increased after transplantation, but was not different in patients with or without CPDAF, suggesting that mechanisms related to compensatory hypertrophy did not play a major role in the pathogenesis of CR. In summary, the histologic findings of CR did not predict the onset of CPDAF, did not distinguish whether the pathogenesis was mediated by immune or nonimmune events, but did correlate with the duration of subsequent allograft survival.

Glomerular hemodynamic effects of dietary polyunsaturated fatty acid supplementation

Dietary supplementation with polyunsaturated fatty acids (PUFAs) has been shown to alter the course of experimental renal disease. Although hemodynamic factors such as glomerular hypertension are felt to be important in the progression of renal disease, the effects of dietary PUFA supplementation on glomerular hemodynamics are unknown. The present investigation, therefore, was designed to evaluate the glomerular hemodynamic effects of dietary PUFA supplementation in normal rats. Male Sprague-Dawley rats were fed standard chow supplemented with either 20% (wt/wt) fish oil (FO) as a source of omega-3 PUFAs, 20% sunflower oil (SO) as a source of omega-6 PUFAs, or 20% coconut oil (CO) as a control diet. Micropuncture studies were performed after 4 to 6 weeks of dietary supplementation. Compared with CO rats, SO rats did not demonstrate any changes in glomerular hemodynamics. However, rats supplemented with FO demonstrated significant (p less than 0.05) increases in both single nephron glomerular filtration rate and single nephron plasma flow. These hemodynamic changes were not associated with alterations in glomerular capillary hydraulic pressure or the glomerular ultrafiltration coefficient. The increase in SNPF was primarily the consequence of a 37% reduction (p less than 0.05) in efferent arteriolar resistance. Thus dietary FO supplementation resulted in glomerular hyperfiltration and hyperperfusion. These hemodynamic actions may have important consequences in determining the effect of omega-3 PUFAs on the course of experimental and clinical renal disease.

The adverse impact of cyclosporine on serum lipids in renal transplant recipients

The extent to which cyclosporine (CsA) directly, or indirectly, influences serum lipid levels in renal transplant patients treated with multiple-drug immunosuppression protocols is unclear. Indeed, patients treated with CsA have reduced corticosteroid requirements, fewer acute rejection episodes, and other differences from patients receiving conventional immunosuppression that may reduce serum lipid levels. We studied patients treated with low-dose CsA, corticosteroids, azathioprine, and Minnesota antilymphocyte globulin ([ALG] n = 205) versus conventional (three-drug) immunosuppression (n = 368) and evaluated the impact of CsA, acute rejection episodes, and other clinical parameters on serum lipids. Fasting serum lipid levels from stable patients transplanted between 1976 to 1989 were studied at 3 (n = 573), 12 (n = 565), 26 (n = 55), and 52 (n = 521) weeks posttransplant using multivariate, linear regression analysis. The incidence of acute rejection episodes was reduced by CsA, but patients with fewer acute rejection episodes in the early posttransplant period had higher serum total cholesterol (increased by .33 +/- .12 mmol/L [13 +/- 5 mg/dL] and .27 +/- .12 mmol/L [10 +/- 5 mg/dL], P less than 0.05, at 3 and 12 weeks, respectively) and low-density lipoprotein (LDL) (increased by .23 +/- .11 mmol/L [9 +/- 4 mg/dL] and .23 +/- .11 mmol/L [9 +/- 4 mg/dL], P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Impact of dietary fatty acid supplementation on renal injury in obese Zucker rats

We previously reported that renal injury in hyperlipidemic, obese Zucker rats was associated with a relative deficiency of tissue polyunsaturated fatty acids (PUFA). In the present study 10-week-old obese Zucker rats were pair fed regular chow or chow containing either 20% sunflower oil rich in n-6 PUFA, fish oil rich in n-3 PUFA, coconut oil medium-chain saturated fatty acid, or beef tallow long-chain saturated fatty acid. At 34 weeks of age there were comparable reductions in albuminuria, mesangial matrix expansion, and glomerulosclerosis in the fish oil and sunflower oil groups. While both fish oil and sunflower oil reduced serum triglycerides, and improved the composition of triglyceride-enriched lipoproteins, only fish oil decreased serum cholesterol. The effect of the dietary fatty acid supplementation on fatty acid profiles were similar in isolated glomeruli and cortical tissue. In general, the amelioration in injury in the fish oil and sunflower oil fed rats was most closely linked to glomerular levels of PUFA, either n-6 or n-3. These data suggest that hyperlipidemia and abnormalities in tissue FA are closely linked, and that dietary supplementation with PUFA may ameliorate chronic, progressive renal injury.

Role of lipid peroxidation in the inhibition of mononuclear cell proliferation by normal lipoproteins

Stimulated peripheral blood mononuclear cells (PBMC) can oxidize normal lipoproteins, and sufficiently oxidized lipoproteins are cytotoxic. However, the role of lipid peroxidation in the inhibition of mitogen-stimulated PBMC proliferation by physiologic concentrations of normal lipoproteins is unclear. In the present investigation, normal low density lipoprotein (LDL) and very low density lipoprotein (VLDL) suppressed [3H]thymidine incorporation and gamma interferon production in concanavalin A-stimulated PBMC without causing cell death. This suppression was accompanied by parallel increases in lipid peroxidation products measured as thiobarbituric acid reactive substances (TBARS). In contrast, high density lipoprotein (HDL) failed to inhibit PBMC and TBARS remains low. Differences between the PBMC suppression from LDL, VLDL, and HDL were best accounted for by normalizing the lipoprotein concentrations by their total lipid content. Moreover, the antioxidants superoxide dismutase and butylated hydroxytoluene each substantially ameliorated the inhibition of PBMC caused by LDL, and reduced the levels of lipid peroxidation products that were generated. Altogether, these results suggest that reactive oxygen species generated by stimulated PMBC may cause oxidative alterations of normal lipoproteins that may, in turn, account for much of the previously reported inhibition of PBMC by normal lipoproteins.

Hyperlipidemia and progressive renal disease

Experimental studies have suggested an important role for abnormal lipid metabolism as an integral factor in modulating progressive renal damage. Dietary induced hypercholesterolemia induced relatively modest glomerular injury. However, in the presence of reduced nephron population or in the presence of underlying renal diseases, such as diabetes, nephrotic syndrome, and hypertension, nephron injury can be markedly exaggerated. These experimental results suggest that an important interaction may occur between renal disease and the occurrence of abnormalities of lipid metabolism. Additional support for the role of lipids in progressive renal injury can be obtained from studies in which pharmacological interventions reduced circulating lipids and this led to decreased glomerular damage. The mechanisms whereby lipids may amplify glomerular injury are not completely understood but may include an interaction with macrophages, alteration in vascular and mesangial functions, changes in production of mediator substances or alterations in membrane fluidity. Local glomerular modification of lipoproteins could also occur and contribute to the development of glomerular pathologic changes. Clinically, few data are available that provide insights into the potential role of renal-related lipid abnormalities in the progression of human renal disease.

Variability in the morphological spectrum and clinical outcome of chronic liver disease in hepatitis B-positive and B-negative renal transplant recipients

The impact of hepatitis B infection on the clinical outcome of renal transplantation has been controversial. Some investigators reported excess mortality from hepatic failure and/or concurrent sepsis while others found no such detrimental effect. Since the clinical or biochemical data do not reflect the severity or the course of liver disease in these immunosuppressed patients, we performed percutaneous liver biopsies and systematically analyzed the histological findings in 68 patients who had clinical evidence of chronic liver disease in the posttransplant period. Twenty-six of these patients were HBs Ag-positive and 42 were HBs Ag-negative. There were no significant differences in the demographic data, biochemical variables, or the mean follow-up between the two groups.

RESULTS

HBs Ag-positive patients had more severe histological forms of liver disease, i.e., chronic persistent hepatitis (CPH) (38%) and chronic active hepatitis (CAH) (38%), compared with 17% CPH and 14% CAH in HBs Ag-negative patients (CPH, P = 0.08; CAH, P = 0.04). The incidence of cirrhosis was also higher in the HBs Ag-positive patients (42% vs. 19%, P = 0.07). During a mean follow-up of 82 +/- 58 months from the onset of hepatitis, 54% of hepatitis B-positive patients died from liver failure compared with 12% of the B-negative group, who were followed for a mean period of 74 +/- 47 months from the onset of hepatitis. The difference in mortality rate was highly significant (P = 0.002). Comparison of initial histology with a follow-up specimen in 25 patients (13 HBs Ag-positive, 12 HBs Ag-negative) also showed a trend towards higher frequency of liver cirrhosis in the B-positive patients compared with the B-negative group (P = NS). Our observations, based on liver histology, confirm earlier reports that hepatitis B infection is associated with a bad prognosis in renal allograft recipients, who have clinical evidence of chronic liver disease.

Lipids and the progression of renal disease

The mechanisms involved in progressive renal injury have been the subject of intense investigation during the past decade. Hemodynamic and nonhemodynamic factors have been implicated in progressive renal damage, including abnormalities of lipid metabolism. The idea that abnormal lipid metabolism may be important in the development and progression of renal injury has intrigued investigators for over 100 years. Studies in models of progressive renal insufficiency have demonstrated that abnormalities in lipid metabolism may participate in the development of glomerular and tubular alterations leading to nephron destruction. This concept has been supported by the demonstration that pharmacologic intervention with different classes of lipid-lowering agents is associated with a reduction in the extent and severity of glomerular and tubular injury. The mechanism whereby hyperlipidemia contributes to renal injury are at present unknown. Morphologically, marked expansion of the mesangial matrix, prior to the development of glomerulosclerosis, suggests the possibility that altered production of mesangial matrix proteins may contribute to glomerular injury. Increased numbers of glomerular monocyte-derived macrophages and foam cells in hyperlipidemic rats have been described. The role that these cells may play in the development of proteinuria and glomerular damage has not been clarified. Biochemically, increased renal tissue content of cholesterol esters and reduced concentrations of essential fatty acids have been described. Whether these changes in tissue lipids contribute to renal injury is also unknown. In addition, persistent hyperlipidemia, particularly hypercholesterolemia, may also lead to glomerular hypertension, possibly through alterations in eicosanoid metabolism. Finally, preliminary data have suggested that oxidized lipoproteins may contribute to the hemodynamic and structural changes described in lipid-induced renal injury. The roles of altered platelet function and other lipid-derived inflammatory mediators are yet to be explored. In conclusion, experimental studies have indicated that hyperlipidemia is an important modulator of nephron damage and may contribute to the progression of renal disease. Whether alterations in lipid metabolism participate in progressive renal insufficiency in humans remains to be determined.