Lipids and the kidney

Resistance to remnant nephropathy in the Wistar-Furth rat

The Wistar-Furth rat, an inbred strain resistant to actions of mineralocorticoids, was used to study the concept that mineralocorticoids contribute to progressive renal injury. It was postulated that if chronic nephropathy depends on aldosterone and if Wistar-Furth rats are resistant to aldosterone, remnant nephropathy would be attenuated in Wistar-Furth rats. Wistar-Furth rats and control Wistar rats were subjected to 5/6 nephrectomy or a sham procedure and then followed for 4 wk. Renal ablation resulted in hypertension at 4 wk in both strains (164+/-5 [Wistar-Furth] versus 184+/-7 [Wistar] mm Hg mean arterial pressure), with sham animals remaining normotensive (134+/-6 mm Hg). Renal damage in response to 5/6 nephrectomy was greatly decreased in Wistar-Furth rats compared with Wistar rats. Albuminuria was markedly less in Wistar-Furth rats (12.7+/-4.2 [Wistar-Furth] versus 97.4+/-22.6 [Wistar] mg/d per 100 g body wt, P<0.01). Glomerular damage, consisting of mesangial proliferation, mesangial lysis, and segmental necrosis, was observed in 42% of glomeruli from Wistar rats but in 0% of glomeruli from Wistar-Furth rats (P<0.01). To address the possibility that higher BP in partially nephrectomized Wistar rats mediated the greater renal damage, the study was repeated, with Wistar rats (not Wistar-Furth rats) being treated with a hydralazine-reserpine-hydrochlorothiazide regimen. Although this antihypertensive regimen equalized BP (conscious systolic) (144+/-8 mm Hg [Wistar] versus 157+/-7 mm Hg [Wistar-Furth] at 4 wk), albuminuria remained more than 10-fold greater in Wistar rats. In summary, renal damage upon 5/6 nephrectomy was markedly reduced in Wistar-Furth rats, a finding not attributable to reduced systemic BP. Since Wistar-Furth rats have been shown previously to be resistant to the actions of mineralocorticoids, the data from the present study support the hypothesis that aldosterone mediates, at least in part, the renal injury attendant to renal mass reduction.

Management of chronic renal insufficiency in lupus nephritis: role of proteinuria, hypertension and dyslipidemia in the progression of renal disease

Non-immune mechanisms appear to be important in the majority of patients with lupus nephritis and progressive renal injury. Proteinuria, hypertension and dyslipidemia are associated non-immune risk factors often implicated in the deterioration of kidney function. There is ample animal experimental evidence that they are independent risk factors for progressive renal injury and their treatment results in amelioration of renal function. Proteinuria and hypertension, unlike dyslipidemia, have been shown to be independent risk factors for progressive renal injury in patients with lupus nephritis. Treatment of hypertension and proteinuria in the diabetic and non-diabetic progressive renal disease population results in stabilization of kidney function. Response to treatment should target both blood pressure of 120/80 and significant reductions in protein excretion. If protein excretion rate is unaltered by use of an angiotensin-converting enzyme inhibitor and salt restriction, one might resort to the use of an angiotensin II antagonist. Treatment of the dyslipidemia following good control of proteinuria, blood pressure and dietary change may not alter renal progression but should provide similar protection from accelerated vascular disease to the non-renal dyslipidemia population.

Identification of oxidized low density lipoprotein in human renal biopsies

BACKGROUND

Intraglomerular lipid deposition is frequently observed in routine renal biopsies, and it has been suggested that lipid peroxidation of low density lipoprotein (LDL) may be implicated in the pathogenesis of progressive glomerulosclerosis. We have examined whether oxidized LDL (Ox-LDL) is present in the glomeruli of patients with renal disease and whether intrinsic human glomerular cells express NADPH-oxidase (a superoxide-generating enzyme found in professional phagocytes).

METHODS

Immunocytochemical study was performed on 939 renal biopsy specimens, using monoclonal antibodies (mAbs) OL-10, 48 and 449, and polyclonal antibody against human apolipoprotein (apo) B. Mouse mAb OL-10 recognizes malondialdehyde (MDA)-modified peptide epitope, and mAbs 48 and 449 react with alpha and beta subunits of cytochrome b558, an essential component of NADPH-oxidase.

RESULTS

Sixty-two (6.6%) of the 939 patients with renal disease exhibited a staining for MDA-altered protein or Ox-LDL in the glomeruli, mainly in the sclerotic segments or mesangial areas. Group 1 patients with heavy Ox-LDL deposition mainly in the sclerotic segments showed a higher frequency of renal insufficiency and heavy proteinuria and a greater degree of glomerulosclerosis, compared to those in group 2 with mesangial Ox-LDL staining. The distribution of MDA protein epitopes, in general, paralleled the deposition of apo B epitopes. Immunoelectron microscopy of ultrathin frozen sections showed the presence of immunogold particles for mAbs 48 and 449 in the cytoplasm of resident glomerular cells of both normal and diseased kidneys. When immunoblotted with mAb OL-10, one band from the IgA nephropathy and focal segmental glomerulosclerosis groups at approximately 260 kD was labeled, whereas immunostaining of normal control samples revealed no staining.

CONCLUSIONS

These results indicate that Ox-LDL is present mainly in the lesions of glomerulosclerosis and mesangial areas in human renal biopsies. They also suggest that patients with heavy Ox-LDL accumulation in the sclerotic segments of glomeruli have more advanced renal disease than those with mesangial Ox-LDL and that resident glomerular cells generate cytochrome b558, the potential of which may not suffice to induce peroxidation of LDL in the diseased glomeruli.

Oxidative stress and lipid abnormalities in renal transplant recipients with or without chronic rejection

BACKGROUND

The histological picture of chronic rejection with endothelial lesions and vascular hyperplasia resembles the early arteriosclerotic lesions. As increasing evidence suggests a role for oxidative stress in arteriosclerosis, we examined whether chronic rejection in renal transplant recipients was associated with increased oxidative stress markers.

METHODS

We investigated lipid metabolism and oxidative stress in 77 renal transplant recipients. Group I patients (n=34; 48+/-2 years old, 12 women, 22 men) had no clinical or histological signs of chronic rejection, whereas group II patients (n=43; 47+/-3 years old, 15 women, 28 men) had histologically proven chronic rejection. All patients were treated with cyclosporine and steroids. Lipid metabolism was evaluated by determining total cholesterol, triglycerides, high-density lipoprotein cholesterol, apolipoproteins AI and B, and lipoprotein (a). Oxidative stress was evaluated by determining: (i) the end product of lipid peroxidation, malonyldialdehyde (MDA), and erythrocyte polyunsaturated fatty acids; (ii) the nonenzymatic antioxidant system: erythrocyte alpha-tocopherol and glutathione; and (iii) the enzymatic antioxidant system: erythrocyte superoxide dismutase and plasma glutathione peroxidase. Results were compared with those of a control group (38 healthy volunteers).

RESULTS

Compared with controls, renal transplant recipients had significantly increased total cholesterol, triglyceride, and apolipoprotein B levels; they also had, in association with these lipid abnormalities, a significant increase in MDA and a significant decrease in erythrocyte polyunsaturated fatty acids, as well as a significant decrease in enzymatic and nonenzymatic antioxidant defense mechanisms. In contrast to lipid disturbances, where no difference was observed between groups I and II, markers of oxidative stress were significantly higher in group II compared with group I (MDA: 1.87+/-0.43 and 1.62+/-0.31 nmol/ml, respectively, P<0.05). The red blood cell antioxidative defense mechanisms were significantly decreased in group II compared with controls (erythrocyte alpha-tocopherol: 0.61+/-0.38 and 1.08+/-0.31 mg/L, respectively, P<0.01; superoxide dismutase: 1.08+/-0.2 and 1.32+/-0.31 U/mg Hb, respectively, P<0.01).

CONCLUSION

Our data show that oxidative stress with a decrease in antioxidant defenses is associated with kidney transplantation. In addition, oxidative stress markers are particularly increased in transplant recipients with chronic rejection, which suggests that oxidative stress may participate in the development and/or progression of vascular lesions observed in these patients.

Interstitial fibrosis in hypercholesterolemic rats: role of oxidation, matrix synthesis, and proteolytic cascades

Uninephrectomized rats with diet-induced hypercholesterolemia develop interstitial inflammation and fibrosis after 8 to 12 weeks. Fibrosis has been associated with the accumulation of lipid peroxidation products within the tubulointerstitium, along with increased renal mRNA levels for transforming growth factor beta-1 (TCF-beta 1), some matrix proteins, and the tissue inhibitor of metalloproteinases (TIMP-1). However, mRNA levels for urokinase-type plasminogen activator (uPA) have been found to be decreased. The purpose of the present study was to determine whether antioxidant therapy could attenuate interstitial fibrosis in hypercholesterolemic rats and to determine changes in the pattern of renal gene expression induced by antioxidant therapy. Three groups of uninephrectomized rats were studied after 12 weeks of feeding standard rat chow, an atherogenic diet (standard chow plus 4% cholesterol/1% cholic acid), or an atherogenic diet supplemented with high doses of the antioxidants probucol and vitamin E. Rats fed the atherogenic diet developed hypercholesterolemia and a 56% increase in total kidney collagen compared with rats fed standard chow. In comparison, the hypercholesterolemic rats treated with antioxidants had normal levels of renal lipid peroxidation products and a normal kidney collagen content. In contrast, there were no significant differences in urinary albumin excretion rates or the number of interstitial macrophages between the two hypercholesterolemic groups. Compared with the untreated hypercholesterolemic group, antioxidant therapy induced significant reductions in renal mRNA levels for procollagen III (to 60% of untreated levels), collagen IV (60%), and TIMP-1 (20%), while uPA levels were significantly increased (to 210%). Paradoxically, antioxidant therapy was associated with a significant increase in renal TGF-beta 1 mRNA levels (to 150%), although TGF-beta 1 protein expression shifted from interstitial to tubular epithelial cells in predominance. The results of the present study demonstrate the efficiency of antioxidant therapy in preventing renal interstitial fibrosis in hypercholesterolemic rats with a single kidney. Based on changes in renal gene expression at the mRNA level, impaired matrix protein synthesis and increased intrarenal activity of the metalloproteinases and uPA/plasmin may play a role in the attenuation of fibrosis.

Estrogen induces glomerulosclerosis in analbuminemic rats

Progression of chronic renal disease is usually more rapid in males, both in humans and in experimental animals. Estrogen-replacement studies indicate that this may be related to the beneficial effects of estrogen on the lipoprotein profile. However, in hyperlipidemic analbuminemic rats (NAR), females are more prone to develop renal injury than males, and ovariectomy tends to decrease triglyceride levels and prevent renal disease. Therefore, we studied the effects of estrogen administration on lipoproteins, and the induction of renal injury in uninephrectomized female and male NAR. Ovariectomized and orchidectomized uninephrectomized NAR were treated with estradiol implants for 24 weeks. In an additional group of ovariectomized rats, the implant was removed after 12 weeks. Both in ovariectomized and orchidectomized NAR, estradiol caused severe hypercholesterolemia (9 to 12 mmol/liter) and hypertriglyceridemia (6 to 8 mmol/liter) after six weeks. Subsequently, these rats developed severe proteinuria, reaching 209 +/- 25 and 95 +/- 43 mg/day, respectively, after 24 weeks. At this point there was severe glomerular sclerosis, with a respective score of 107 +/- 21 and 61 +/- 33. In terminal blood samples the most pronounced increase in lipid levels were observed in very low density lipoproteins (VLDL), intermediate density lipoproteins (IDL) and low density lipoproteins (LDL). In contrast, ovariectomized NAR and orchidectomized NAR without exogenous estrogen had much lower lipid levels (cholesterol 5 to 7 mmol/liter and triglycerides 1 to 2 mmol/liter) after six weeks. These rats, or ovariectomized NAR where the estrogen treatment had been withdrawn, had practically no proteinuria (4 +/- 1, 19 +/- 11, and 13 +/- 4 mg/day, respectively) or renal damage (glomerulosclerosis score 1 +/- 0.4, 5 +/- 3 and 3 +/- 1, respectively) after 24 weeks. Thus, in hypertriglyceridemic analbuminemic rats, estrogen-treatment causes further increases in both triglycerides and cholesterol. Most probably these changes contribute to the development of renal injury by estrogen in this model. This effect of estrogen, which has also been observed in the Zucker rat, is unique for the hypertriglyceridemic state and deserves further study.

Increased VLDL in nephrotic patients results from a decreased catabolism while increased LDL results from increased synthesis

Increased very low density lipoprotein (VLDL) in nephrotic patients results from a decreased catabolism while increased low density lipoprotein (LDL) results from increased synthesis. Hyperlipidemia is a hallmark of nephrotic syndrome that has been associated with increased risk for ischemic heart disease as well as a loss of renal function in these patients. The hyperlipidemia usually is characterized by increased cholesterol levels, although hypertriglyceridemia may be present as well. The factors that determine the phenotype of nephrotic dyslipidemia are not understood, nor has the primary stimulus for nephrotic hyperlipidemia been identified. One hypothesis is that nephrotic hyperlipidemia is the result of a coordinate increase in synthesis of proteins by the liver. To address these issues we simultaneously measured the in vivo rate of VLDL apolipoprotein B100 (apo B100) secretion, LDL apo B100 synthesis and albumin synthesis in patients with a nephrotic syndrome (N = 8) and compared them with a control group (N = 7) using a primed/continuous infusion of the stable isotope L-[1-13C] valine for six hours. Kinetic data were analyzed by multicompartmental analysis. Patients studied had combined hyperlipidemia as reflected by an significant increase in both VLDL and LDL apo B100 pool sizes. In contrast, the albumin pool size was significantly decreased. VLDL apo B100 levels were primarily increased as a consequence of a decrease in fractional catabolic rate (FCR) rather than from an increase in the absolute synthesis rate (ASR). Both VLDL apo B100 and triglycerides were inversely related to the fractional catabolism (FCR) of VLDL apo B100 (r2 = 0.708; P = 0.0088) while neither had any relationship to the ASR of VLDL apo B100. In contrast to VLDL, increased LDL apo B100 was not a consequence of decreased catabolism. The LDL apo B100 ASR was significantly increased (P = 0.001) in the nephrotic patients compared to controls. Low density lipoprotein apo B100 ASR was greater than that of VLDL apo B100 in some patients, suggesting that LDL in these patients was not only derived from VLDL delipidation, but also by an alternative secretory pathway. There was no clear relationship between the ASR of VLDL apo B100 and the ASR of albumin within the current study population. Our data indicate that increased VLDL in nephrotic patients results from a decreased catabolism, while increased LDL results from increased synthesis.

Reduction of insulin and triglycerides delays glomerulosclerosis in obese Zucker rats

To evaluate the effect of insulin and/or triglycerides on the pathogenesis of glomerulosclerosis, acarbose (BAYg5421), an inhibitor of intestinal alpha-glucosidases, was administered as a dietary admix (40 mg/100 g chow) to Zucker obese rats (ZOA), from 1.5 months until sacrifice at 1.5, 5, 8, 10 and 15 months. Obese (ZO) and lean (ZL) rats served as controls. Despite a similar food intake, ZOA weighed less than ZO at all ages. Acarbose reduced serum triglycerides at all ages, and insulin until 10 months. Glycemia remained normal in all groups. Proteinuria developed with age and to a greater degree in ZO than in ZOA rats. In ZL, a faint proteinuria appeared only in the oldest animals. Glomerulosclerosis, tubular and interstitial lesions rapidly affected ZO kidneys. These lesions were reduced in ZOA until 10 months. Acarbose did not modify the hypertrophy of the glomeruli that developed after three months, but slowed down the expansion of the mesangial domain seen in ZO. Thus, by reducing the amount of ingested glucose, acarbose yielded a normal glycemia with a lesser production of insulin and reduced renal impairment. Therefore, insulin could be a key factor involved in the pathogenesis of glomerulosclerosis, either directly or through a control of triglyceride concentrations.

Effect of lipoproteins on cultured human mesangial cells

It was recently reported that low-density lipoprotein (LDL) promotes mesangial cell proliferation, and oxidized LDL is cytotoxic for mesangial cells. However, there have been few studies about the effects of other lipoproteins on mesangial cells. Accordingly, we investigated the effect of various lipoproteins on cultured human mesangial cells using 3H-thymidine (3H-TdR) incorporation and cell counting assays. We also investigated the levels of several cytokines in mesangial cell culture supernatants after stimulation by the lipoproteins. Addition of very-low-density lipoprotein (VLDL) at concentrations up to 100 micrograms/mL, intermediate-density lipoprotein (IDL) at up to 50 micrograms/mL, and LDL at up to 50 micrograms/mL induced the proliferation of cultured human mesangial cells, whereas cell growth was inhibited at higher concentrations. Oxidized LDL caused a concentration-dependent decrease of 3H-TdR incorporation. High-density lipoprotein (HDL) had no proliferative effective effect at any concentration. Exposure to VLDL, IDL, LDL, or a high concentration of HDL enhanced the secretion of interleukin-6, platelet-derived growth factor, and transforming growth factor-beta by mesangial cells, whereas tumor necrosis factor-alpha secretion was stimulated by oxidized LDL. These finding indicate that triglyceride (TG)-rich lipoproteins (VLDL and IDL) promote mesangial cell proliferation as well as LDL, whereas oxidized LDL has the reverse effect. These effects of lipoproteins may be related to modulation of various cytokines. Accordingly, TG-rich lipoproteins, LDL, and oxidized LDL may be involved in mesangial cell proliferation and injury in patients with mesangial proliferative glomerulonephritis.

Dietary antioxidant inhibits lipoprotein oxidation and renal injury in experimental focal segmental glomerulosclerosis

Lipid peroxidation may be involved in the pathogenesis of focal segmental glomerulosclerosis (FSGS). In the present study we examined whether lipid-soluble antioxidants, probucol and vitamin E, could inhibit renal injury in rats with chronic puromycin aminonucleoside (PA) nephrosis and dietary hypercholesterolemia by protecting lipoproteins from oxidation. Male Sprague-Dawley rats received six intraperitoneal injections of PA over a 10 week period and were fed a high cholesterol (HC) diet (PA-HC) or the same diet supplemented with either 1% probucol or vitamin E (100 IU/kg) for 32 weeks. For comparison, a group of rats received PA injections and a normal diet (PA-normal) with or without probucol or vitamin E. Another group rats received saline injections instead of PA and were fed a HC diet (Sal-HC) with or without probucol or vitamin E. At the end of the experiment, proteinuria, FSGS and tubulointerstitial lesions were present in the untreated rats with PA-HC or PA-normal. The magnitude of these lesions was significantly greater in the PA-HC rats than the PA-normal. In contrast to the PA-HC group with hypercholesterolemia, the PA-normal group did not show hypercholesterolemia from week 16 onwards. The rats with PA-HC alone showed significantly higher renal cortical malondialdehyde (MDA) levels and greater susceptibility of plasma very low density lipoprotein (VLDL) + low density lipoprotein (LDL) to the copper-mediated oxidation than the rats with PA-normal or Sal-HC alone. The administration of probucol or vitamin E in the rats with PA-HC significantly reduced the susceptibility of plasma VLDL + LDL to in vitro oxidation, renal cortical MDA level, proteinuria, mesangial volume density and magnitude of FSGS and interstitial lesions. Immunohistochemical staining of renal tissue showed focal segmental distribution of oxidized LDL (Ox-LDL) in the glomeruli of rats with PA-HC. Administration of probucol or vitamin E reduced the intensity of Ox-LDL staining. The staining with ED1 demonstrated that infiltrating glomerular macrophages were significantly more prevalent in the untreated rats with PA-HC than PA-normal or Sal-HC. Treatment with probucol or vitamin E significantly reduced the number of glomerular macrophages in the rats with PA-HC. These results suggest that alimentary hypercholesterolemia aggravates the renal damage in association with increased renal lipid peroxides in chronic PA nephrosis, and that dietary probucol or vitamin E attenuates renal injury in rats with PA-HC possibly by making lipoproteins resistant to oxidation and by inhibiting intraglomerular macrophage infiltration.

Management of hyperlipidemia in children with refractory nephrotic syndrome: the effect of statin therapy

The efficacy and safety of hydroxymethylglutaric coenzyme A reductase inhibitor (statins) in the treatment of hyperlipidemia were evaluated in 12 infants and children with steroid-resistant nephrotic syndrome followed prospectively for 1 to 5 years. All patients experienced a hypolipidemic response with a marked reduction in their total cholesterol (40%), low-density lipoprotein cholesterol (44%), and triglyceride levels (33%), but no appreciable change in high-density lipoprotein cholesterol. Statin therapy was well tolerated without clinical or laboratory adverse effects. In spite of a significant hypolipidemic response to statin therapy there were no changes observed in the degree of proteinuria, hypoalbuminemia, or in the rate of progression to chronic renal failure. Long-term controlled studies with statin therapy are needed to further document or negate their renoprotective role in refractory nephrotic syndrome.

Fluvastatin (Lescol) treatment of hyperlipidaemia in patients with renal transplants

Hyperlipidaemia of 18 male and 20 female patients following successful renal transplantation was treated with daily 20 mg fluvastatin (Lescol) for 12 weeks. The patients were several months after transplantation, and their total cholesterol levels exceeded 6.5 mmol/l following an 8-week diet. The effect of fluvastatin on the levels of total cholesterol, HDL, LDL, triglyceride, Apo A1 and Apo B, as well as of lipoprotein(a) was examined. Furthermore, changes of the renal function (GFR-urea, creatinine, uric acid) and hepatic function (bilirubin, GOT, GPT, CPK, ALP) were followed up, together with the body weight and blood pressure. The results of the examinations are summarized as follows: Fluvastatin may be administered effectively and without side effects in a daily dose of 20 mg in appropriately selected renal transplant patients. The average total cholesterol values, which were 7.91 mmol/l in men and 7.78 mmol/l in women following the diet, were reduced by 22-25% (p < 0.001) after 6 and 12 weeks, respectively, of fluvastatin treatment. The levels of LDL also decreased significantly (p < 0.001): in response to a 20 mg evening dosage, reduction of more than 25% was observed in 78% of men and 65% of women. Reductions of the Apo B levels were more pronounced in the females (18.3% men vs. 21.2% women). The ratio C/HDL-C decreased both in men (from 5.49 to 4.19) and in women (from 4.83 to 4.02). The ratio Apo B/Apo A1 also decreased (men: from 0.86 to 0.73, women: from 0.73 to 0.66). The concentrations of HDL and Apo A1 did not increase significantly, the reductions in the levels of triglyceride and lipoprotein(a) were not considerable either. An increase in the levels of hepatic enzymes and CPK was not encountered during the administration of fluvastatin. In two patients the levels of serum bilirubin increased by 2-4 micromol/l. Three patients complained about temporary myalgias of the sacroiliac or lumbar region which, however, were not accompanied by elevated CPK levels. The monitored levels of cyclosporine, urea and creatinine did not increase significantly during the 12 weeks of treatment. Two patients had temporary gastric complaints.

Proteinuria and albumin homeostasis in the nephrotic syndrome: effect of dietary protein intake

Nephrotic syndrome is analyzed in the light of interventions designed to decrease proteinuria and renal injury. The effect of dietary protein intake on urinary protein losses and albumin homeostasis are discussed on the basis of the pathophysiologic mechanisms known to account for changes in renal function of nephrotic patients. In addition, the effect of angiotensin-converting enzyme inhibitors for reduction of proteinuria is discussed in terms of the modulation of glomerular permselectivity and hemodynamics.

The benefits of ACE inhibitors and calcium antagonists in slowing progressive renal failure: focus on fixed-dose combination antihypertensive therapy

During the past two decades, major investigative interest has been focused on the determinants of chronic renal disease and interventions to retard the inexorable progression to end-stage renal disease. Recent studies have provided a theoretic framework for anticipating that angiotensin-converting enzyme (ACE) inhibitors, and possibly calcium antagonists, may preferentially retard the progression of renal disease. Whereas the majority of available clinical trials have assessed the effects of ACE inhibitors in patients with insulin-dependent diabetes mellitus (IDDM), there are relatively few long-term studies that have evaluated the renal protective effects of ACE inhibitors and calcium antagonists in patients with nondiabetic renal disease. Although clinical trials have been initiated using both of these drug classes as monotherapy, theoretical considerations suggest that fixed-dose combinations of an ACE inhibitor and a calcium antagonist might be appealing as renal protective agents. Several lines of evidence suggest that the renal microcirculatory effects of coadministration of both agents should be complementary. Similarly, recent observations suggest that the two classes may act in a complementary manner to countervail pathogenetic mechanisms at the level of the mesangium. A recent study in type II diabetic patients demonstrated that combination therapy with an ACE inhibitor and a calcium antagonist induced the greatest reduction in proteinuria, and reduced the rate of decline in glomerular filtration rate (GFR) more than did either agent alone at the same level of blood pressure reduction. Based on such considerations, recent randomized prospective studies have been initiated to compare the renal protective effects of combination calcium antagonist-ACE inhibitor therapy versus monotherapy with agents of either of these two antihypertensive classes.

Involvement of oxidation in LDL-induced collagen gene regulation in mesangial cells

Oxidized low-density lipoprotein (Ox-LDL) is present in the lesions of focal segmental glomerulosclerosis (FSGS), but the role of Ox-LDL in the disease process is not clear. Recent studies have shown that LDL stimulates the type IV collagen mRNA expression in cultured mesangial cells. Thus, we examined whether oxidative stress is responsible for the stimulation of LDL-induced collagen gene expression in cultured human mesangial cells (HMCs). When quiescent HMCs were exposed to serum-free media containing LDL for 48 hours, peroxidation of LDL was induced as shown by the increased production of thiobarbituric acid-reactive substances (TBARS). LDL stimulated the alpha 1 (I), alpha 1 (III), and alpha 1 (IV) mRNA expression in a dose-dependent manner. At a concentration of 200 micrograms/ml, LDL enhanced the levels of alpha 1 (I), alpha 1 (III), and alpha 1 (IV) mRNA by 3.7-, 3.8- and 3.2-fold, respectively, over the levels in the control cells. These transcripts were further increased 5.4-, 6.7-, and 5.9-fold, respectively, by the addition of 500 micrograms/ml of LDL. Cu(2+)-catalyzed Ox-LDL at a concentration of 200 micrograms/ml also stimulated the alpha 1 (I), alpha 1 (III), and alpha 1 (IV) mRNA expression 4.4-, 5.9-, and 2.8-fold, respectively, compared with the control cells. The addition of monoclonal antibody (mAb) OL-10, which recognizes the malondialdehyde (MDA)-modified peptide epitope, or vitamin E (50 microM) to cultured HMC exposed to LDL markedly inhibited the stimulation of collagen gene expression. When HMCs were incubated with MDA (200 microM), alpha 1 (I), alpha 1 (III), and alpha 1 (IV) mRNA levels increased by two- to threefold compared to control cells. Immunohistochemical staining utilizing mAb OL-10 demonstrated the presence of MDA-modified proteins in the cytoplasm of HMC exposed to either LDL or MDA. These results suggest that peroxidative products of LDL stimulate collagen gene expression possibly via modification of proteins, which are responsible for the expression of collagen genes in cultured HMCs. Given that, lipid peroxidation of LDL may be implicated in the development of glomerulosclerosis by facilitating excessive mesangial matrix generation.

Interstitial inflammation and fibrosis in rats with diet-induced hypercholesterolemia

Abnormalities in lipid metabolism appear to play a pathogenic role in progressive renal disease. To elucidate the cellular and molecular basis of renal interstitial fibrosis in uninephrectomized rats with diet-induced hypercholesterolemia, we fed experimental rats with standard rat chow supplemented with 4% cholesterol and 1% cholic acid. Control rats were fed an isocaloric diet. Groups of 7 control and 7 experimental rats were killed after 4, 8, and 12 weeks. Hypercholesterolemic rats developed albuminuria; serum creatinine was elevated at 12 weeks. By 12 weeks numerous oil red O-positive cells were present throughout the interstitium and to a lesser extent in tubules. Total renal lipid-peroxidation products were significantly increased (172 +/- 15, 198 +/- 28, and 197 +/- 13 mmol malondialdehyde/kidney at 4, 8, and 12 weeks vs. 123 +/- 17, 144 +/- 6, and 125 +/- 10 mmol in controls). Immunostaining revealed oxidatively modified lipoproteins within tubular and interstitial cells. The interstitial disease was characterized by an interstitial infiltrate of monocytes. Significant increases were detected in renal cortical mRNA levels for monocyte chemoattractant protein-1 (MCP-1), osteopontin, and vascular cell adhesion molecule-1 (VCAM-1), associated with changes in the pattern of immunostaining for each encoded proteins. Total kidney collagen was significantly increased at 12 weeks (9.8 +/- 0.9 mg/kidney vs. 7.8 +/- 0.9 mg in controls). At 12 weeks there was a significant increase in interstitial immunostaining for collagen I, collagen III, collagen IV, fibronectin and tenascin. A significant threefold increase in renal cortical mRNA levels for transforming growth factor beta-1 (TGF-beta 1) at 4 and 12 weeks was associated with the appearance of TGF-beta 1-positive interstitial cells. Renal matrix protein mRNA levels were measured at 4, 8, and 12 weeks. The only statistically significant elevations were procollagen alpha 1(I) and procollagen alpha 1(III) at weeks 8 and 12. In contrast, renal cortical mRNA levels for the tissue inhibitor of metalloproteinases-1 (TIMP-1) were significantly increased at 4, 8 and 12 weeks (1.4 +/- 0.5, 2.7 +/- 0.9 and 2.7 +/- 1.4 arbitrary densitometric units, respectively, vs. 1.0 +/- 0.4, 1.0 +/- 0.5 and 1.0 +/- 0.4 units for controls), and urokinase-type plasminogen activator (muPA) mRNA levels were significantly decreased at 4, 8, and 12 weeks (0.4 +/- 0.1 arbitrary densitometric units for all three experimental groups vs. 1.0 +/- 0.4, 1.0 +/- 0.3, and 1.0 +/- 0.4 units for the control groups). In summary, rats with diet-induced hypercholesterolemia develop renal interstitial fibrosis over several weeks. Following the accumulation of lipids within tubulointerstitial cells, interstitial nephritis develops. The fibrotic phase is characterized by modest changes in matrix protein mRNA levels, up-regulated TIMP-1, and down-regulated muPA levels, suggesting that altered matrix degradation plays a role in the interstitial fibrogenesis in this model.

Apolipoprotein B independently predicts progression of very-low-level albuminuria in insulin-dependent diabetes mellitus

The purpose of the study was to examine the contribution of alterations in lipoprotein metabolism to the progression of very-low-level albuminuria in insulin-dependent diabetes mellitus (IDDM). We measured serum concentrations of lipids, lipoproteins, and apolipoproteins in 53 normoalbuminuric diabetic patients without overt hypertension, whom we restudied after 10 years. Albuminuria was measured as the urinary albumin to creatinine ratio (UA/UC) in repeated early-morning samples. Over 10 years, UA/UC increased significantly (P < .001), and five patients (9.4%) progressed to microalbuminuria. The increase in albuminuria was significantly and positively related to the baseline serum concentrations of total cholesterol (P < .05), low-density lipoprotein (LDL) cholesterol (P = .05), non-high-density lipoprotein (HDL) cholesterol (P < .05), and apolipoprotein (apo) B (P < .001), but no significant associations were found with triglycerides, HDL cholesterol, apo A-1, or lipoprotein(a) [Lp(a)]. The relative risk of developing microalbuminuria for a serum apo B concentration more than 1.1 g/L was 3.8 (95% confidence interval [CI], 1.9 to 7.7). In multiple linear regression analysis, serum apo B (P < .05) and glycated hemoglobin ([HbA] P < .05) at baseline were significant independent predictors of the increase in albuminuria, with no significant associations found for sex, smoking, duration of diabetes, mean arterial blood pressure (BP), or family history of cardiovascular disease and hypertension; the regression model predicted 42% of the variation in UA/UC at 10 years. The findings suggest that an abnormality in the metabolism of apo B may be independently associated with progression of very-low-level albuminuria and possibly with the development of early nephropathy in IDDM patients.

Dyslipidaemia and hyperlipidaemia following renal transplantation

The lipid metabolism of 93 patients with renal transplantation was prospectively studied. It was characterized by the serum levels of cholesterol, HDL, LDL, triglyceride, apolipoprotein Al, Apo B and lipoprotein (a) as well as by lipid electrophoresis. In addition to the examination of lipid concentrations, the authors looked for correlations with other metabolic changes, immunosuppressive treatment and the changes of body weight and hypertension following transplantation. Their conclusion is that hyperlipidaemic and dyslipidaemic changes, as reflected by the levels of total cholesterol, LDL and Apo B, are more considerable in women than in men. The levels of pre-beta and beta lipoprotein were not significantly lower in men than in women. With the passing of time after transplantation and with the reduction of the doses of cyclosporine and corticosteroids, the values of hypertension, hyperlipidaemia and dyslipidaemia decreased. According to the follow-up results, the lipid values measured in the winter and autumn months are higher than those found in the summer. The importance of early and follow-up examinations and of the reduction of pathological metabolic alterations is emphasized.

Lipids, lipoproteins, antioxidants and glomerular and tubular dysfunction in type 1 diabetes

We aimed to examine the relationship of serum lipids, lipoproteins, apolipoproteins and antioxidants with renal dysfunction as measured by urinary excretion of albumin and of retinol binding protein (RBP) in insulin-dependent diabetes mellitus (IDDM). We studied 121 patients with IDDM. Glomerular function was assessed as the urinary albumin/creatinine ratio (UA/UC), and tubular function as the urinary retinol-binding protein/creatinine ratio (UR/UC), both measured in three early morning spot urine samples. The mean (range) UA/UC was 1.95 mg/mmol (0.3-476.5) and UR/UC was 17.5 micrograms/mmol (1.0-1853.8). 17% of the patients had a UA/UC > 3 mg/mmol and 33% had a UR/UC > 20 micrograms/mmol. Significant positive correlations were observed between both UA/UC and UR/UC and the following: serum total cholesterol (P < 0.005); triglycerides (P < 0.001); apolipoproteins A-I (P < 0.05), A-II (P < 0.02) and B (P < 0.002); glycated haemoglobin (P < 0.002). No significant associations were found with serum vitamin E, beta-carotene or total antioxidant activity. In multiple regression, only UA/UC was independently associated with serum apo B and cholesterol concentrations. In conclusion, in IDDM glomerular dysfunction, as measured by UA/UC, is associated with elevated serum cholesterol, triglycerides, apo B, apo A-I and apo A-II, but not with HDL cholesterol or antioxidant status. Tubular dysfunction tends to occur with increasing albuminuria, but it is not independently associated with serum lipid, lipoprotein, apolipoprotein or antioxidant levels.

Lovastatin ameliorates depressed intraglomerular proteolytic activities in experimental nephrotic syndrome

Lipid abnormalities have been implicated in the pathogenesis of glomerulosclerosis in experimental models of kidney disease. In previous studies it has been shown that Adriamycin-induced nephropathy is associated with reduced activities of glomerular proteinases. This observation led to the hypothesis that reduced proteolytic activities may be responsible for mesangial protein accumulation, which ultimately leads to global sclerosis of the glomerular tuft. The aim of the present study was to investigate whether lovastatin treatment, which prevents progressive glomerulosclerosis in experimental nephrotic syndrome, would also have an effect on glomerular proteinase activities. Adriamycin administration resulted in a persistent nephrotic syndrome with gross proteinuria (377 +/- 26 mg/24 h), hypoalbuminemia (2.1 +/- 0.12 vs. 2.8 +/- 0.02 g/dl), hypercholesterolemia (575 +/- 74 vs. 68 +/- 1.5 mg/dl) and elevated triglyceride levels (1,155 +/- 78 vs. 57 +/- 8 mg/dl). Glomerular azocaseinolytic activities both at pH 5.4 (-21%) and 7.4 (-37%) were significantly reduced. In contrast to human subjects, nephrotic rats that were treated with lovastatin displayed reduced triglyceride levels (767 +/- 134 mg/dl); their serum cholesterol, however, remained unchanged. In terms of glomerular proteolytic enzyme activities, the decline in azocaseinolysis at both pH values was, at least partly, prevented by lovastatin. On the basis of these data, it appears that the beneficial effect of lovastatin on the evolution of glomerulosclerosis in the nephrotic rat is associated with the conservation of glomerular proteolytic activities.