The influence of donor age on renal function in transplant recipients

To the extent that age-related declines in kidney function are caused by intrarenal alterations, donor age should affect glomerular filtration rate (GFR) after renal transplantation. Although some investigations have suggested that transplantation of aging kidneys may cause an increased incidence of primary allograft failure, the effects of donor age on GFR are unknown. In the present study, 201 patients who had allografts that survived for at least 24 months were investigated. The age range of the donors was 7 to 61 years. Multivariate regression analysis demonstrated that both donor and recipient age had significant, independent effects on creatinine clearance at 1 year, and at last follow-up, 5.0 +/- 1.9 years (mean +/- SD) after transplantation. The effect of donor age on renal function could not be attributed to differences in the number of rejection episodes, the frequency or duration of posttransplant acute tubular necrosis, age of the recipient, or other factors. Donor age had no effect on allograft survival, and did not affect the rate of decline in creatinine clearance between 1 year and last follow-up. Thus, these results suggest that donor age is associated with intrarenal alterations that lead to reductions in renal function after transplantation, but donor age may not affect long-term prognosis or allograft survival in the late posttransplant period.

Pharmacologic treatment of hyperlipidemia reduces glomerular injury in rat 5/6 nephrectomy model of chronic renal failure

The role of lipid abnormalities in the pathogenesis of focal glomerulosclerosis was investigated in the rat remnant kidney model of chronic renal failure. Rats subjected to right nephrectomy and two-thirds segmental infarction of the left kidney (5/6 nephrectomy) were treated for 10 weeks with the lipid-lowering agent clofibric acid. Both serum cholesterol and urine albumin excretion were significantly reduced by clofibric acid. At 10 weeks, the percent of glomeruli with focal glomerulosclerosis was 5 +/- 2% in clofibric acid-treated and 24 +/- 5% in untreated 5/6 nephrectomy rats (p less than 0.01). Inulin clearance was greater in clofibric acid-treated than in untreated 5/6 nephrectomy rats (0.28 +/- 0.02 versus 0.22 +/- 0.02 ml/min 100 g body wt, p less than 0.05). Body weight, kidney weight, and systemic blood pressure were not significantly altered by clofibric acid. Micropuncture studies, performed in separate groups of clofibric acid-treated and untreated 5/6 nephrectomy rats, demonstrated elevated single nephron glomerular filtration rates and glomerular capillary pressures 4 weeks after surgery. However, clofibric acid did not significantly alter single nephron glomerular filtration rates (95 +/- 2.1 nl/min in treated versus 97.0 +/- 6.2 nl/min in untreated, p greater than 0.05) or glomerular capillary pressures (56.6 +/- 1.5 mm Hg in treated versus 57.8 +/- 0.8 mm Hg in untreated, p greater than 0.05) in 5/6 nephrectomy rats. In a separate set of experiments, 5/6 nephrectomy rats were treated with the specific cholesterol synthesis inhibitor, mevinolin. Mevinolin improved serum lipid levels and reduced albuminuria in 5/6 nephrectomy rats without causing significant alterations in blood pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Hyperlipidemia and the progression of renal disease

Focal glomerulosclerosis (FGS) is commonly seen in human and in experimental models of chronic renal disease. Although considerable experimental data suggest that hypertension is important in progressive nephron damage, recent studies also have indicated that abnormal lipid metabolism may be an independent risk factor in the pathogenesis of FGS. Indeed, the synergistic impact of hypertension and hyperlipidemia in the pathogenesis of FGS may be analogous to the role of these factors in the pathogenesis of atherosclerosis. This review focuses on some of the recent and pertinent data that support a role of lipid-mediated glomerular injury in the pathogenesis of progressive renal disease.

Direct effects of altered temperature on renal structure and function

Although marked alterations in temperature often accompany ischemic, acute renal failure (ARF), the effects of altered temperature on renal structure and function have received little attention. In the present investigation, isolated rat kidneys perfused at 41 degrees C had extensive tubular damage and decreased function compared to kidneys perfused at 37 degrees C. In contrast, kidneys perfused at 30 degrees C had less tubular damage, and better function, than kidneys perfused at 37 degrees C. Increased temperature caused a 50% reduction in renal ATP (0.46 +/- 0.04 microM/100 mg tissue protein. 37 degrees C vs. 0.26 +/- 0.03 microM/100 mg tissue protein, 41 degrees C; p less than 0.05). The decreased ATP occurred despite reduced sodium reabsorption (129 +/- 8 microM/min/g, 37 degrees C vs. 65 +/- 12 microM/min/g, 41 degrees C, p less than 0.05) and normal renal oxygen consumption (QO2). These results suggest that increased temperature may cause an uncoupling of QO2 and sodium chloride transport, and an increase in nontransport mediated, basal metabolic rate may result in depleted cellular ATP levels and renal tubular cell death.

Possible causes and consequences of hypertension in stable renal transplant patients

Previous epidemiologic studies of hypertension in renal transplant patients have produced contradictory results. Therefore, the incidence and clinical setting of chronic hypertension were examined in 201 stable renal transplant patients using a multivariate approach. Hypertension was present in 52.7% of patients at one year, and in 46.3% at the time of last follow-up, 5.0 +/- 1.9 years (mean +/- SD) after transplantation. Among possible causative factors, discriminant analysis demonstrated that body weight, the presence of native kidneys, and variables linked to allograft function were most closely associated with hypertension at both one year and last follow-up. One year after transplantation, age, sex, pretransplant hypertensive nephrosclerosis, and diabetes were also independently associated with hypertension. However, renal function declined to a greater degree in hypertensive patients, and only body weight, the presence of native kidneys, and variables linked to allograft function were associated with hypertension at last follow-up. Results also demonstrated that hypertension was associated with elevated serum lipid levels and an increased likelihood of dying or returning to dialysis. Thus, these results suggested several important risk factors for hypertension and its consequences in renal transplant patients.

Persistent hyperlipidemia in renal transplant patients

The exact nature and significance of posttransplant hyperlipidemia is controversial. In the present study, serum lipids were examined in 201 clinically stable renal transplant recipients before, 1 year after, and at the time of the last follow-up, 5.0 +/- 0.1 yr after transplantation. Hypertriglyceridemia, present in 36% of patients treated with dialysis before transplantation, occurred in 23% 1 year after successful transplantation. At last follow-up, 29% had elevated triglyceride levels. Hypercholesterolemia, present in only 8% of patients before transplantation, was found in 27% 1 year after receiving a renal allograft. At the time of last follow-up, 30% had elevated cholesterol levels. HDL cholesterol levels were normal 1 year after transplantation, and increased significantly during the posttransplant follow-up period. Multivariate stepwise linear regression analysis was used to determine factors independently associated with serum lipid levels. Age, body weight, pretransplant serum lipids, and variables linked to allograft function (urine protein excretion, serum creatinine, and the use of loop diuretics) were independently associated with posttransplant cholesterol and triglycerides. Diabetes, the use of alternate day steroids, beta-adrenergic-blocking antihypertensive medications, and thiazide diuretics were not linked to hyperlipidemia. In addition, changes in variables associated with renal function helped to explain why different factors were associated with lipid levels at 1 year than at the time of last follow-up. Thus, the results of this study suggest that hyperlipidemia is a frequent and persistent complication in clinically stable renal transplant recipients. Multiple factors, including several associated with declining allograft function, appear to be involved in the pathogenesis of posttransplant hyperlipidemia.

Effects of cyclosporine on the isolated perfused rat kidney

Although cyclosporine (CsA) has been shown to cause decreased renal function in humans, the mechanisms important in cyclosporine nephrotoxicity are not well understood. Investigations of cyclosporine nephrotoxicity in animal models have been complicated by systemic toxic effects not seen in humans. In the present study, the direct renal effects of cyclosporine were investigated in the isolated perfused rat kidney (IPRK) model. Cyclosporine delivered by nontoxic liposomes had no effect on IPRK resistance, perfusate flow, inulin clearance, or fractional reabsorption of sodium, despite marked tissue accumulation of CsA (55.1 +/- 7.2 micrograms/g kidney tissue). In contrast, a 63% decrease in inulin clearance was observed following the administration of intravenous cyclosporine (0.1 ml). However, similar changes in IPRK function were seen after the administration of 0.1 ml of the intravenous cyclosporine vehicle, cremophor, suggesting that the alterations in function were secondary to the vehicle. All together, these findings suggest that cyclosporine nephrotoxicity may be secondary to renal innervation, toxic metabolites, or other systemic effects of cyclosporine not present in the IPRK.

Relationship between vascular disease and age-associated changes in the human kidney

To investigate the relationship between atherosclerotic vascular disease and age-associated changes in the normal human kidney, autopsy findings and renal histology from 57 individuals with mild systemic atherosclerosis (group I), were compared to 57 sex- and age-matched individuals with moderate-to-severe atherosclerosis (group II). Age, sex, body build, the presence or absence of hypertension, semiquantitative aorta and coronary-artery atherosclerosis scores, organ weights, and the percent of globally sclerotic glomeruli were determined in each. Glomerular area, arcuate/interlobular arteries, and percent interstitial fibrosis were measured using standard morphometric techniques. Group I individuals had a 8.3 +/- 7.0% incidence of sclerotic glomeruli, compared to 15.4 +/- 16.3% in group II (mean +/- SD, P less than 0.01). Relative intrarenal arterial wall area was increased in group II (60 +/- 12%) compared to group I (55 +/- 11%, P less than 0.05). The mean glomerular area of nonsclerotic glomeruli was greater in group II (23,700 +/- 6,000 sq mu) than in group I (19,600 +/- 3,700 sq mu, P less than 0.01), suggesting that there were compensatory increases in glomerular size in group II. Interstitial fibrosis was similar in both groups. The relative impact of age, sex, body build, hypertension, systemic atherosclerosis, intrarenal vascular disease and interstitial fibrosis on glomerulosclerosis and glomerular size was investigated using multiple linear regression. Both age and intrarenal vascular disease exhibited highly significant, independent associations with glomerulosclerosis. Glomerular area was positively correlated with heart weight and coronary artery atherosclerosis. In contrast, there was no independent correlation between glomerular area and glomerulosclerosis.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of lipids in progressive glomerular disease

The role of lipids in the pathogenesis of focal glomerulosclerosis (FGS) was evaluated using two chemically different lipid lowering agents, clofibric acid and mevinolin. Pharmacologically, these two agents have different mechanisms of action. Clofibric acid affects both cholesterol and triglyceride metabolism, while mevinolin inhibits 3-hydroxy-3 methyl-glutaryl coenzyme A reductase, the rate limiting enzyme in cellular cholesterol synthesis. In two different models of FGS in which hyperlipidemia occurs, the obese Zucker rat and the 5/6 nephrectomy model, both agents significantly reduced FGS and albuminuria. Since glomerular hemodynamic function is normal in obese Zucker rats, these results suggested that lipids are an independent factor in the pathogenesis of FGS. Moreover, in the 5/6 nephrectomy model, the beneficial effects on glomerular structure of reducing serum lipids occurred despite persistent systemic and glomerular hypertension. Thus, we postulated that a synergistic interaction between lipids and hypertension might exist in the pathogenesis of FGS.

Renal effects of angiotensin II: modulation by calcium and cyclooxygenase products

Modulation of angiotensin II effects on renal function by extracellular calcium levels and cyclooxygenase products was evaluated using the isolated perfused rat kidney. Kidneys from normal male Sprague-Dawley rats were perfused at constant pressure. After base-line assessment of function, angiotensin II was administered as a bolus and constant infusion; group 1 with normal ionized calcium and 1.2 ng/min angiotensin II, group 2 with normal ionized calcium and 0.6 ng/min angiotensin II, group 3 with low ionized calcium and 1.2 ng/min angiotensin II, and group 4 with indomethacin, low ionized calcium, and 1.2 ng/min angiotensin II. Angiotensin II caused a marked fall in inulin clearance (CIn) in groups 1 and 2. With low ionized calcium (group 3), angiotensin II increased resistance to the same degree as in group 2, but in contrast to group 2, CIn was unchanged. Kidneys perfused with indomethacin (group 4) had marked angiotensin II-induced declines in CIn that rapidly returned to base line despite persistently elevated resistance. Thus the results demonstrated that both calcium and cyclooxygenase products may directly modulate the effects of angiotensin II on renal function. These effects involve more than modulation of angiotensin II-induced vasoconstriction.

Effects of nephron loss on glomerular hemodynamics and morphology in diabetic rats

Loss of renal mass in rats with experimental diabetes mellitus leads to exaggerated hypertrophy of remaining nephrons and accelerated diabetic glomerulopathy. To examine factors responsible for glomerular injury in this setting, rats with preexisting diabetes were subjected to unilateral nephrectomy. Micropuncture studies and evaluation of glomerular morphology were performed 2-3 mo later. Nephrectomized diabetic rats demonstrated significant increases in kidney weight, superficial nephron glomerular filtration rate, and superficial nephron plasma flow compared with two-kidney diabetic rats and nephrectomized nondiabetic controls. Glomerular capillary hydraulic pressure was comparable in two-kidney and nephrectomized diabetic rats and was significantly reduced compared with nephrectomized nondiabetic controls. Nephrectomized diabetic rats demonstrated significant albuminuria, mesangial matrix expansion, and focal glomerulosclerosis, whereas two-kidney diabetic rats and nephrectomized nondiabetic controls showed only minimal alterations in glomerular morphology. It is concluded that diabetic rats can undergo glomerular functional compensation in response to nephron loss. Moreover, accelerated glomerular injury caused by nephron loss in diabetic rats could not be attributed to increased glomerular capillary pressure.

Effects of carbohydrate restriction on renal injury in the obese Zucker rat

The obese Zucker rat model of nonimmune-mediated, spontaneous focal glomerulosclerosis is ideally suited to study the influence of diet on the initiation and progression of glomerular injury. Young (6 wk) and old (33 wk) lean and obese female Zucker rats were fed a carbohydrate-restricted diet intermittently for 27 wk. Carbohydrate restriction resulted in lower body weight (460 +/- 16 versus 310 +/- 7 g, p less than 0.025), kidney weight (1.26 +/- 0.04 versus 1.07 +/- 0.05 g, p less than 0.025), and glomerular area (6930 +/- 290 versus 5780 +/- 230 micron2, p less than 0.025) in young obese Zucker rats compared to ad libitum-fed rats. Although urine-albumin excretion was substantially reduced by carbohydrate restriction in young obese Zucker rats (41.1 +/- 12.3 versus 6.9 +/- 2.9 mg/24 h, p less than 0.01), glomerular injury was not significantly altered. In old obese rats, carbohydrate restriction did not significantly reduce albuminuria or prevent the progression of glomerular injury. Thus, intermittent carbohydrate restriction failed to alter significantly either the initiation of glomerular injury in young, or the progression of nephron damage in old, obese Zucker rats.

Renal disease in patients with massive obesity

During a four-year period, 17 massively obese patients without clinically apparent systemic disease underwent renal biopsy for marked proteinuria. Clinical information and biopsy results were compared with those in 34 normal-body-weight controls matched for age, sex, and similar presentation. Histopathologic changes characteristic of focal glomerulosclerosis were found in nine (53%) of the obese patients and two (6%) of the controls. In addition, five (29%) of the obese patients had occult diabetic nephropathy, while no diabetic changes were seen in controls. Clinically, obese patients resembled controls in most respects. Serum albumin level, however, was higher than in controls (3.5 +/- 0.2 vs 2.5 +/- 0.1 g/dL). Indeed, obese patients with focal glomerulosclerosis had normal serum albumin levels (4.0 +/- 0.1 g/dL). Thus, primary renal disease in massively obese patients with marked proteinuria differed in several important respects from that seen in normal-body-weight patients with a similar degree of proteinuria.

The influence of age, sex, race, and body habitus on kidney weight in humans

The impact of age, sex, race, and body build on kidney weight was examined in 357 normal individuals who died suddenly. Mulivariate, stepwise linear-regression analysis demonstrated that kidney weight was best predicted by body surface area. Age, sex, and race had no additional impact on kidney weight once differences in body build were taken into account. Similar results were obtained with heart and liver weights. These findings were confirmed using a second, independent paired sample of 16 lean and 16 massively obese adults. Body build-associated changes in kidney weight were paralleled by changes in both glomerular and tubulointerstitial areas. Body build is the major determinant of kidney weight and nephron size in normal humans.

Effects of genetic obesity on renal structure and function in the Zucker rat. II. Micropuncture studies

The obese Zucker rat is a model of nonimmune glomerular disease characterized by spontaneous proteinuria and focal glomerulosclerosis. Mechanisms important in the pathogenesis of glomerular injury in obese Zucker rats are unknown, but may involve hemodynamic and metabolic factors. Micropuncture studies of superficial nephron function were performed prior to the development of FGS in male obese Zucker rats and lean littermates 9 to 13 weeks of age. Compared with lean littermates, obese Zucker rats demonstrated small increases in superficial nephron glomerular filtration rate (32.3 +/- 2.3 nl/min vs. 27.8 +/- 2.0, P greater than 0.05) and plasma flow (87.1 +/- 7.2 nl/min vs. 79.0 +/- 5.1, P greater than 0.05). Intraglomerular hydraulic pressures were not significantly different between groups. Despite similarities in superficial nephron glomerular function, obese Zucker rats displayed increases in glomerular area and mesangial matrix. These morphologic changes occurred in both superficial and deep nephrons. We conclude that increases in glomerular pressures and flows are not a prerequisite for the initiation of glomerular injury in the obese Zucker rat.

Age is a determinant of the glomerular morphologic and functional responses to chronic nephron loss

Loss of renal mass results in a compensatory increase in growth and function of remaining nephrons. Renal ablation also accelerates the expansion of mesangial matrix and the development of focal glomerulosclerosis (FGS) associated with aging. To determine whether age at the time of nephron loss influences the compensatory changes in function and the severity of subsequent glomerular lesions, immature rats (group I) and adult rats (group II) underwent right unilateral nephrectomy (Nx). Four weeks after Nx, compensatory renal growth and single nephron function showed a similar pattern in both groups. Five months after Nx, however, group I displayed significantly greater compensatory growth than group II, although both groups exhibited similar single nephron function. Moreover, group II demonstrated a significant increase in mean transcapillary hydraulic pressure difference (delta P) of approximately 5 mm Hg. Although both groups experienced accelerated expansion of mesangial matrix, significant FGS was detectable only in group I. Thus glomerular injury after Nx may result from factors other than alterations in glomerular hemodynamics.

Glucose-induced increases in renal hemodynamic function. Possible modulation by renal prostaglandins

Increased glomerular filtration rate and kidney size early in the course of experimental and human diabetes may be important in the pathogenesis of diabetic nephropathy. Factors causing these renal functional changes are unknown. The isolated, perfused rat kidney (IPRK) was used to study the effects of elevated glucose levels on kidneys from normal and diabetic rats in the absence of complex systemic effects of in vivo hyperglycemia. It was found that acute increases in perfusate glucose levels caused sustained dose-dependent vasodilatation in both normal and diabetic isolated kidneys. Furthermore, in normal kidneys, raising perfusate glucose to levels seen in moderately severe diabetes caused increased inulin clearance (Cln). In contrast, equal osmolar concentrations of mannitol caused sustained vasoconstriction and a slight decrease in Cln. Prostaglandin synthetase inhibitors reduced glucose-induced vasodilatation by 50% and prevented the increase in Cln that followed the addition of glucose to normal kidneys. Thus, these studies demonstrated that elevated glucose levels caused significant vasodilatation and increased Cln in the IPRK, and these glucose-induced hemodynamic changes were attenuated by prostaglandin synthetase inhibitors. It is possible that these glucose-induced effects may be important determinants of increased glomerular function in early diabetes.

Glomerular sclerosis in patients with massive obesity

In animals with reduced renal mass increased glomerular filtration is associated with accelerated glomerular sclerosis. Whether hyperfiltration causes glomerular damage in humans is unknown. Since increased glomerular filtration occurs in obesity, the amount of glomerular sclerosis found in renal autopsy tissue from 46 patients with massive obesity was compared to that found in 46 normal body weight controls. Despite increased kidney weight and glomerular size, obese patients had the same proportion of completely sclerosed glomeruli as controls. In addition, no focal segmental glomerular sclerosis was seen in the obese group. It is concluded that patients with massive obesity have increased kidney weight and nephron size consistent with hyperfiltration. Nevertheless, massively obese patients do not appear to have increased glomerular sclerosis.