Clinical correlates to chronic renal allograft rejection

Chronic rejection is a clinical syndrome characterized by a progressive decline in renal allograft function and nonspecific histologic findings of interstitial fibrosis, glomerulosclerosis, and fibrointimal proliferation of intrarenal arteries. Most late allograft failure that is not due to death with a functioning allograft is caused by chronic rejection. Although the pathogenesis and treatment of chronic rejection are unknown, a number of epidemiological studies have examined clinical correlates for possible clues to its pathogenesis. Clinical correlates for chronic renal allograft rejection can be classified in two broad categories: immune (alloantigen-dependent) and non-immune (alloantigen-independent). The strongest evidence that chronic rejection is immune mediated comes from its association with acute rejection and the degree of histocompatibility mismatching. However, not all acute rejection leads to chronic rejection, and there is little evidence that newer immunosuppression regimens which effectively prevent acute rejection have reduced the incidence and severity of chronic rejection. Therefore, many clinical investigators have also looked for potential non-immune causes of chronic rejection. Putative non-immune risk factors include donor source (living-related vs. cadaveric), cold ischemia time, delayed graft function, size mismatching, donor age, donor and recipient gender, recipient race, hyperlipidemia, and hypertension. Although there is little evidence supporting a cause and effect relationship between any immune or non-immune risk factor and chronic rejection, these clinical associations suggest a number of potentially important areas for further study.

A randomized trial comparing cyclosporine induction with sequential therapy in renal transplant recipients

Calcium antagonists may reduce the nephrotoxicity of cyclosporine (CsA), allowing CsA to be introduced immediately after renal transplantation and thereby obviating the need for sequential induction therapy with a monoclonal or polyclonal antibody. To test this hypothesis, in a pilot feasibility trial 100 cadaveric or one-haplotype-mismatched living-related renal transplant recipients were randomized to either (1) sequential therapy with anti-thymocyte globulin (ATG) (ATGAM; Upjohn, Kalamazoo, MI) 20 mg/kg/d for 7 to 14 days until renal function was established and CsA (Sandimmune; Sandoz, East Hanover, NJ) was started, or (2) CsA 8 mg/kg/d begun immediately before surgery with diltiazem (Cardizem; Marion Merrell Dow, Kansas City, MO) 60 mg sustained release twice daily. Acute rejection episodes during the first 90 days were not different with ATG versus CsA induction (42% v 28%; P = 0.142 by chi-square analysis). Graft failures (10% v 16%; P = 0.372) and the incidence of delayed graft function (28% v 34%; P = 0.516) were also similar with ATG compared with CsA. ATG caused lower platelet counts (138 +/- 59 x 10(3) v 197 +/- 75 x 10(3) at 7 days; P < 0.001) and lower white blood cell counts (9.6 +/- 4.6 x 10(3) v 12.3 +/- 4.9 x 10(3) at 7 days; P = 0.003). Diltiazem reduced the dose of CsA required to maintain target blood levels (479 +/- 189 mg/d v 576 +/- 178 mg/d at 14 days; P = 0.015). There were no statistically significant differences between the groups in serum creatinine levels at days 1, 3, 5, 7, 14, 28, 60, or 90. The results of this pilot feasibility trial suggest that prophylactic treatment with CsA and diltiazem may be equally effective and less toxic than ATG induction after renal transplantation.

Use of urine specific gravity to improve screening for albuminuria

The albumin to creatinine ratio (ACR) can be used to measure urine albumin excretion rates, but is inconvenient and expensive. More rapid and less expensive screening methods estimate only albumin concentration and are subject to errors caused by variation in urine volume. We examined whether urine specific gravity could be used in place of urine creatinine to correct albumin concentration for differences in urine volume in 50 patients. Urine specific gravity accurately estimated urine creatinine concentration (r = 0.79, P < 0.001). The albumin estimated-creatinine ratio (ACestR) in random spot urine sample correlated with urine albumin excretion measured in a 24-hour urine collection (r = 0.98, P < 0.001), as did the ACR (r = 0.95, P < 0.001). For determining microalbuminuria, the sensitivity (0.88) and specificity (0.93) of the ACestR were similar to those of ACR (0.89 and 0.93, respectively). Unfortunately, the sensitivity (0.63) of the Micral-Test was relatively poor, and was only slightly improved by correcting for urine specific gravity (0.69) in this small sample of patients. Nevertheless, these results suggest that as rapid methods for measuring urine albumin concentration improve, combining them with urine specific gravity might produce a less expensive and more convenient alternative to the ACR.

Risk factors for nephropathy and cardiovascular disease in diabetic Northern Minnesota American Indians

Although complications of diabetes are common among Southwest American Indians, little is known about diabetes and associated risk factors for nephropathy and cardiovascular disease in other genetically distinct tribes. We conducted a retrospective analysis of 665 diabetic patients at two Chippewa Indian reservations in northern Minnesota to evaluate the prevalence of risk factors for diabetic nephropathy and cardiovascular disease. In 79 patients, a more detailed study was carried out, including an assessment of renal function and urinary albumin excretion (UAE). The overall prevalences of proteinuria and hypertension were 47.9% and 62.6%, respectively. Proteinuria was observed more often in hypertensive than in non-hypertensive patients (55.2% vs 44.4%, p < 0.05), and in patients with diabetes for longer than 10 years (57% vs 40% for diabetes less than 10 years, p < 0.05). Although hypercholesterolemia (total cholesterol > or = 200 mg/dl) was observed in 54% of patients, there was no relationship between hypercholesterolemia and proteinuria. In the 79 patients studied in more detail, UAE was greater in hypertensive patients compared to non-hypertensive patients (606 +/- 15600 mg/24h vs 101 +/- 157 mg/24 h, p < 0.05), and in patients with diabetes for 10 years or longer compared to patients in the first decade of disease (748 +/- 1732 mg/24 h vs 96 +/- 171 mg/24 h, p < 0.05). Hypercholesterolemia and elevated LDL-cholesterol (> 130 mg/dl) were observed in 56% and 49% of patients, respectively, but were not associated with increased UAE. In contrast, hypertriglyceridemia (> 250 mg/dl) was associated with an elevated UAE (932 +/- 2150 mg/24 h vs 245 +/- 735 mg/24h, p < 0.05). Increased lipoprotein(a) was found in patients with overt albuminuria. In summary, the prevalence of risk factors for diabetic nephropathy and associated cardiovascular disease is high in Chippewa American Indians in northern Minnesota. Although detecting abnormal UAE may be useful in identifying high-risk patients who may benefit from early intervention, traditional risk factors such as hypercholesterolemia may not explain the risk associated with increased UAE.

Post-transplant hyperlipidemia: mechanisms and management

Hyperlipidemia is common after renal transplantation. In recent years, much progress has been made in understanding the causes and treatment of lipid abnormalities in renal transplant patients. Recently, short-term studies have shown that newer antilipemic agents appear to be safe and effective in treating hyperlipidemia in this population. Despite the absence of large, controlled clinical trials examining the effect of lipid-lowering strategies on cardiovascular disease and chronic renal allograft rejection, therapy appears to be warranted in renal transplant patients with an atherogenic lipid profile and multiple risk factors.

Lovastatin inhibits lipopolysaccharide-induced NF-kappaB activation in human mesangial cells

BACKGROUND

HMG-CoA reductase inhibitors have been shown to reduce glomerular injury in different models of progressive renal damage. The transcription factor NF-kappaB plays a major role in the induced expression of genes involved in cellular proliferation and inflammatory responses that could be important in the pathogenesis of glomerular injury. We therefore examined the effects of the HMG-CoA reductase inhibitor lovastatin on NFkappaB activation in human mesangial cells.

METHODS

Cultured human mesangial cells were stimulated with bacterial lipopolysaccharide (LPS) in the presence or absence of lovastatin. NF-kappaB activity was measured by electrophoretic mobility shift assay (EMSA).

RESULTS

LPS-stimulated mesangial cells exhibited an NF-kappaB-like activity as assessed by EMSA competition assays, and supershift assays with antibodies against the p50 and p65 subunits of NF-kappaB. Treatment of mesangial cells with lovstatin in the presence of exogenous cholesterol resulted in a significant reduction of the LPS-induced NF-kappaB activity. In the presence of either mevalonate or the mevalonate metabolite farnesyl pyrophosphate, the lovastatin inhibition of NF-kappaB activation was substantially reversed, supporting a role for mevalonate metabolites in LPS-induced mesangial cell NF-kappaB activation.

CONCLUSIONS

These data suggest an additional mechanism by which HMG-CoA reductase inhibitors may reduce glomerular injury, namely, by inhibiting NF-kappaB activation and the subsequent proliferative and inflammatory responses.

Hyperlipidemia and its management in renal disease

Dyslipidemia is common in patients with renal disease, may contribute to the high incidence of cardiovascular disease, and may play a role in progressive renal injury. Recent studies have shown that newer antilipemic agents appear to be safe and effective in patients with renal disease. This should make it possible to conduct large, controlled clinical trials examining the effect of lipid-lowering strategies on cardiovascular disease, and on renal disease progression.

Chronic renal allograft rejection: immunologic and nonimmunologic risk factors

The pathogenesis of chronic renal allograft rejection is unknown. It is also unclear why cyclosporine has failed to prevent chronic rejection. We examined possible risk factors for graft loss to chronic rejection among 706 renal transplants using the Cox proportional hazards model with fixed and time-dependent covariates. Both the number and the severity of acute rejection episodes were independent risk factors for chronic rejection [relative risk (95% confidence interval) 2.31 (2.04 to 2.60) and 1.53 (1.27 to 1.84), respectively]. Cyclosporine and cyclosporine withdrawal had no effect on chronic rejection. Acute rejections occurring within the first three months after transplantation, when cyclosporine most effectively prevented acute rejection, also had no effect on chronic rejection. Risk factors that were independent of acute rejection and not clearly attributable to immune mechanisms included serum albumin [0.20 (0.10 to 0.38) for each g/dl], proteinuria [1.42 (1.29 to 1.57) for each g/24 hr], and serum triglycerides -1.09 (1.03 to 1.16) for each 100 mg/dl-. These results suggest that the reduction in acute rejection episodes from cyclosporine has failed to reduce graft failure from chronic rejection, possibly because the early (within the first 3 months) and mild acute rejection episodes that are most effectively prevented by cyclosporine do not cause chronic rejection. In addition, the results suggest that there may be a number of nonimmunologic risk factors for chronic rejection.

Determination of residual renal function with iohexol clearance in hemodialysis patients

Residual renal function (RRF) may contribute significantly to the total dialysis prescription. Conventional quantitation of RRF in hemodialysis (HD) patients is measured by urea clearance and requires a 24-hour urine collection which is often difficult to perform and inaccurate. The renal clearance of iohexol was evaluated as an alternative method for RRF assessment (iohexol-derived RRF) in hemodialysis patients. An intravenous bolus of iohexol (12 ml; 300 mg iodine/ml) was administered to 42 hemodialysis patients following routine HD. A single blood sample was obtained approximately 44 hours later (pre-HD) to determine the plasma clearance of iohexol using x-ray fluorescence methods. Total body clearance of iohexol (CTBio) and non-renal clearance of iohexol (CNRio) 2.87 +/- 0.3 ml/min (mean +/SEM) were used to calculate iohexol-derived RRF (CTBio-CNRio). Iohexol-derived RRF determinations were then compared to urea clearance-derived RRF measurements. The RRF contribution to the dialysis prescription was also calculated utilizing iohexol-derived RRF compared to urea-derived RRF. Iohexol-derived RRF did not differ from urea-derived RRF (2.48 +/- 0.3 vs. 2.64 +/- 0.4 ml/min, P = 0.21). The RRF contribution to the weekly dialysis prescription (Kt/V) did not differ when iohexol-derived RRF was compared to urea-derived RRF (0.94 +/- 0.1 vs. 0.93 +/- 0.1, P = 0.9). Additionally, the effect of iohexol on RRF was assessed in 17 HD patients. Urea-derived RRF determinations one week after iohexol exposure did not differ from those measured one week prior to iohexol exposure (3.17 +/- 0.6 vs. 2.91 +/- 0.5 ml/min, respectively). Thus, renal clearance of iohexol can be an accurate and safe measure of RRF in HD patients and potentially simplify delivery of the dialysis prescription.

Serum albumin and mortality after renal transplantation

The incidence, causes, and consequences of hypoalbuminemia after renal transplantation are not well defined. We examined clinical correlates of serum albumin measured at 3 months, 6 months, 1 year, and annually thereafter in 706 renal transplant recipients who survived at least 6 months with a functioning allograft. Follow-up was 7.0 +/- 4.2 years. Hypoalbuminemia (< or = 3.5 g/dL) was most common at 3 months (31%, n = 692), least common at 1 year (12%, n = 656), and then became increasingly common among survivors, for example, 14% (n = 466) at 4 years, 20% (n = 204) at 8 years, and 29% (n = 77) at 12 years after transplantation. By multiple linear regression, variables that correlated (P < 0.05) with lower serum albumin at 3, 6, 12, and 24 months included age, diabetes, proteinuria, and cytomegalovirus infection. Other independent correlates on at least one of these occasions included renal function and chronic disease (malignancy, liver disease, and cardiovascular disease). Serum albumin, as a time-averaged and time-dependent covariate, was a strong independent risk factor for death using Cox proportional hazards analysis (relative risk for each g/dL increment, 0.26; 95% confidence interval, 0.16 to 0.44 [1.00 = no risk]). The effects of albumin on mortality were independent of age, diabetes, serum lipids, renal function, chronic liver disease, malignancies, and cardiovascular disease. The effects of albumin on mortality were evident even when the analysis was restricted to patients dying several years after albumin was measured. Thus, hypoalbuminemia is common and serum albumin is a strong independent risk factor for all-cause mortality after renal transplantation.

Cardiovascular disease after renal transplantation

Although cardiovascular disease is a major cause of morbidity and mortality after renal transplantation, its pathogenesis and treatment are poorly understood. We conducted separate analyses of risk factors for ischemic heart disease, cerebral, and peripheral vascular disease after 706 renal transplants, all of which functioned for at least 6 months. We used Cox proportional hazards analysis to examine the effects of multiple pretransplant and posttransplant risk factors and included time-dependent variables measured at 3, 6, and 12 months, and annually to last follow-up at 7.0 +/- 4.2 yr. The independent relative risk (RR) of diabetes was 3.25 for ischemic heart disease, 3.21 for cerebral vascular disease, and 28.18 peripheral vascular disease (P < 0.05). The RR of each acute rejection episode was 1.40 for ischemic heart disease and 1.24 for cerebral vascular disease. Among serum lipid levels, high-density lipoprotein cholesterol was the best predictor of ischemic heart disease (RR = 0.80 for each 10 mg/dL). Posttransplant ischemic heart disease was strongly predictive of cerebral (5.80) and peripheral vascular disease (5.22), whereas ischemic heart disease was predicted by posttransplant cerebral (8.25) and peripheral vascular disease (4.58). Other risk factors for vascular disease included age, gender, cigarette smoking, pretransplant splenectomy, and serum albumin. Hypertension and low-density lipoprotein cholesterol had no effect, perhaps because of aggressive pharmacologic treatment. Thus, the incidence of cardiovascular disease continues to be high after renal transplantation, and multiple risk factors suggest a number of possible strategies for more effective treatment and prevention.

Clinical predictors of chronic renal allograft rejection

Among both immune and nonimmune factors implicated in the pathogenesis of chronic renal allograft rejection, acute rejection episodes represent a strong and consistent predictor. However, all acute rejection episodes are not equally predictive of chronic renal allograft rejection. Early and mild acute rejection episodes do not usually cause chronic renal allograft rejection. On the other hand, late and severe acute rejection episodes occurring more than one year after transplantation are particularly strong predictors of chronic renal allograft rejection. The number of HLA mismatches is a risk factor, but its influence may not be independent of acute rejection and other risk factors. Proteinuria and recently hypoalbuminemia are also independent risk factors for chronic renal allograft rejection. However, whether these nonimmune factors are merely the result of chronic renal allograft rejection, or whether they contribute to the pathogenesis of renal injury in chronic renal allograft rejection is yet unclear. Better HLA matching, new strategies to decrease the severity of acute rejection, and measures to prevent late acute rejection, as well as prospective evaluation of the therapies to reduce proteinuria and other nonimmune risk factors for chronic renal allograft rejection are needed.

Isoprenoids and Ras: potential role in chronic rejection

Protein prenylation, the post-translational attachment of isoprenoids to certain cellular proteins, increases protein hydrophobicity and promotes protein-membrane interactions. Of the many cellular proteins that undergo protein prenylation, particular attention has been paid to the protooncogene product Ras. Prenylated Ras protein localizes to the inner cell membrane and appears to function as a "molecular switch" through which peptide growth factors such as PDGF, IGF-1, and FGF, and cytokines such as IL-2, IL-6, and GM-CSF stimulate intracellular events. Binding of these substances to their respective receptors on target cells can activate Ras, triggering intracellular signaling cascades which culminate in processes such as cell proliferation, differentiation, and T-cell activation. Protein prenylation inhibitors block Ras prenylation, prevent membrane localization of Ras, and inhibit growth and proliferation of a variety of cell types. Recent studies in our laboratory have begun to examine the possible role of Ras in chronic allograft rejection. Abdominal aorta segments from donor Lewis rats were transplanted into Buffalo recipient rats. Recipients treated with the HMG-CoA reductase inhibitor lovastatin, which inhibits isoprenoid production, showed significantly decreased allograft intimal area after 12 weeks, when compared with untreated recipients. In a separate study, recipients treated with the agent leflunomide, which inhibits growth factor receptor tyrosine kinases that can activate Ras, had significantly decreased allograft intimal area after 12 weeks. These results suggest that Ras may be important in chronic allograft rejection, and that agents that interfere with Ras protein prenylation or activation by growth factor receptors may ameliorate chronic rejection.

Chronic renal allograft rejection and clinical trial design

Both the choice of endpoints and the selection of patients will be critical study design features in randomized controlled trials needed to test the effectiveness of treatments for chronic renal allograft rejection. We examined the feasibility of carrying out clinical trials with different endpoints and patient inclusion criteria by analyzing data from a population of 627 cadaveric kidney transplant recipients who survived with a functioning allograft for at least six months. Among those who lost grafts to chronic rejection, decreases in renal function of 30% and 60% preceded graft loss by a median of only 1.1 and 0.7 years, respectively, suggesting that little would be gained in a clinical trial that used a predetermined reduction in renal function as a surrogate endpoint. Less clear is whether histologic changes could be used as a surrogate endpoint. At present, graft loss to chronic rejection and graft failure from any cause are the most reliable endpoints. Unfortunately, large numbers of patients are needed to demonstrate clinically relevant therapeutic effects on these endpoints. Limiting enrollment to patients who are at high risk for developing chronic rejection, by selecting patients who already have a decline in renal function, for example, may reduce the number of patients needed in a clinical trial. On the other hand, selecting patients with disease that is too advanced may diminish the effectiveness of therapy. In any case, it is impossible to accurately determine the number of patients needed for a definitive clinical trial without preliminary data demonstrating the expected magnitude of the treatment effect. Thus, well-designed pilot studies are needed to measure possible treatment effects before conducting large-scale clinical trials for chronic renal allograft rejection.

Clinical correlation between renal allograft failure and hyperlipidemia

Chronic rejection is the leading cause of late allograft failure, but its pathogenesis is poorly understood. The prominence of the vascular lesions and certain similarities with the pathological features of atherosclerosis suggest that lipids may be involved in the pathogenesis of chronic rejection. Studies have reported an association between different lipid abnormalities and several indicators of chronic renal allograft damage. However, other potential risk factors for the development of chronic rejection were present in most cases, and an independent association between lipids and chronic rejection has not been convincingly demonstrated. In our series of 706 consecutive renal transplants with long-term follow-up, increased post-transplant serum triglycerides, but not total cholesterol, were strong predictors of graft loss to chronic rejection. This effect was independent of other risk factors for chronic rejection such as age, acute rejections, proteinuria and hypoalbuminemia. These results add to existing evidence suggesting that lipid abnormalities may be involved in the pathogenesis of chronic renal allograft rejection.

The angiotensin II receptor antagonist losartan reduces blood pressure but not renal injury in obese Zucker rats

Agents that interfere with the renin-angiotensin system (RAS) may ameliorate progressive renal injury, particularly in a setting where intrarenal RAS activity appears to be elevated. Whether RAS antagonists affect renal disease progression when intrarenal RAS activity is not increased is unclear. In this study, therefore, the effects of the angiotensin II receptor antagonist losartan on glomerular and tubulointerstitial injury were investigated in obese Zucker rats (OZR), an experimental model of progressive renal disease characterized by reduced intrarenal renin content and reduced plasma renin activity. Losartan (100 or 200 mg/L of drinking water) was administered to OZR beginning at 26 wk of age, when renal disease was established. At 38 and 44 wk of age, losartan-treated OZR demonstrated significant (P < 0.05) dose-related decreases in systolic blood pressure, compared with blood pressures in untreated, control OZR. Despite the reductions in blood pressure, losartan had no significant effects on albuminuria or glomerular or tubulointerstitial injury. At 44 wk of age, the percentage (mean +/- SE) of glomeruli with sclerosis was 51 +/- 11, 49 +/- 9, and 39 +/- 14% in control OZR, low-dose (100 mg/L) losartan-treated OZR, and high-dose (200 mg/L) losartan-treated OZR, respectively (P > 0.05). Similarly, the tubulointerstitial injury score (range, 0 to 4) in the three groups was, respectively, 1.7 +/- 0.4, 1.6 +/- 0.3, and 1.5 +/- 0.3 (P > 0.05). It was concluded that in a setting of chronic renal failure where intrarenal RAS activity does not appear to be increased, angiotensin II receptor antagonism may not be nephroprotective despite a reduction in blood pressure.