Lipids and progressive glomerulosclerosis. A model analogous to atherosclerosis

Effects of sirolimus on mesangial cell cholesterol homeostasis: a novel mechanism for its action against lipid-mediated injury in renal allografts

Lipoprotein abnormalities are present in a high proportion of renal transplant patients. It is accepted that dyslipidemia is associated with atherosclerosis and in the progression of renal disease. Lipid abnormalities may also play a significant role in the development of chronic allograft nephropathy. Sirolimus was found to have an antiatherosclerotic effect in the apolipoprotein E-knockout mice model of hyperlipidemia through its antiproliferative effects. As lipid-mediated renal injury is important in the pathogenesis of glomerulosclerosis which shares common pathogenic mechanisms with atherosclerosis, in this study we have tested the hypothesis that sirolimus prevents lipid-mediated renal injury through the modulation of cholesterol homeostasis of mesangial cells and its anti-inflammatory effects on macrophages. We demonstrated that sirolimus reduced lipid accumulation, as measured by oil red O staining in human mesangial cells (HMCs). Using real-time PCR, we screened the mRNA expression of lipoprotein receptors. Sirolimus significantly suppressed LDL and VLDL receptors and CD36 gene expression. It also increased cholesterol efflux from HMCs by increasing peroxisome proliferator-activated receptor-α (PPARα), PPARγ, liver X receptor-α, and ATP binding cassette A1 (ABCA1) gene expression. Sirolimus overrode the suppression of cholesterol efflux and ABCA1 gene expression induced by the inflammatory cytokine IL-1β. Furthermore, sirolimus significantly inhibited inflammatory cytokines IL-6 and TNF-α production in macrophages. These data suggest that sirolimus may prevent cellular cholesterol accumulation even in the presence of hyperlipidemia and inflammation, by regulating both cholesterol homeostasis and inflammatory responses.

Kidney in early atherosclerosis

Atherosclerosis represents one of the major causes of premature death in the United States today, and it is frequently associated with, exacerbates, and is aggravated by chronic kidney disease (CKD). Atherosclerosis integrates the response to a number of insults, and consequently, the accelerated atherosclerosis found in CKD patients is associated with activation of a variety of humoral and tissue mechanisms. Hypertension, diabetes, dyslipidemia, obesity, metabolic syndrome, and additional nontraditional risk factors can damage the kidney directly and by promoting intrarenal atherogenesis, even in the absence of obstructive lesions in the renal artery. Evidence indicates that increased oxidative stress and inflammation may mediate a large part of the effects of risk factors on the kidney. In turn, progressive deterioration of renal function in CKD may lead to dyslipidemia or accumulation of uremic toxins, which can induce production of free radicals and activate proinflammatory and fibrogenic factors, leading to vascular endothelial cell dysfunction and injury, and favoring development of atherosclerosis. Therefore, the kidney can be a villain or a victim during atherogenesis. The purpose of this review is to provide new insights into the mechanisms by which atherogenic factors may instigate early renal injury.

Evidence for low-density lipoprotein–induced expression of connective tissue growth factor in mesangial cells

BACKGROUND

Although hyperlipidemia is a risk factor for the progression of renal damage, the relationship between increased plasma lipoproteins and glomerular injury is poorly defined. Connective tissue growth factor (CTGF) is emerging as a key determinant of progressive fibrotic diseases and its expression is up-regulated by diabetes. To define the mechanisms through which low-density lipoproteins (LDLs) promote glomerular injury, we evaluated whether LDL can modulate the expression of CTGF and collagen I.

METHODS

The effects of LDL on CTGF and collagen I expression were carried out in rat mesangial cells.

RESULTS

Treatment of mesangial cells with LDL for 24 hours produced a significant increase in the protein levels of CTGF and collagen I compared to unstimulated controls. To explore if CTGF and collagen I are downstream targets for regulation by transforming growth factor-beta (TGF-beta), mesangial cells were treated with various concentration of TGF-beta for 24 hours. TGF-beta produced a concentration-dependent increase in the protein levels of CTGF and collagen I. The increase in CTGF and collagen I induced by LDL was significantly inhibited by neutralizing anti-TGF-beta antibodies. Inhibition of p38(mapk) or p42/44(mapk) activities did not affect LDL-induced TGF-beta1, CTGF, and collagen I expression, whereas inhibition of c-Jun NH2-terminal kinase (JNK) suppressed LDL-induced TGF-beta, CTGF, and collagen I expression.

CONCLUSION

These findings implicate JNK pathway and TGF-beta1 as key players in LDL signaling leading to CTGF and collagen I expression in mesangial cells. The data also point to a potential mechanistic pathway through which lipoproteins may promote glomerular injury.

Effects of statin therapy on the progression of chronic kidney disease

Statins are lipid-lowering agents that specifically, competitively, and reversibly inhibit 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, the enzyme that catalyzes the conversion of HMG-CoA to mevalonic acid, the rate-limiting step in the formation of cholesterol. A large body of evidence from numerous, well-controlled, randomized trials demonstrates that statins significantly reduce fatal and nonfatal cardiovascular events in the general population. Cardiovascular benefits of statins have been conventionally attributed to reduction in levels of low-density lipoprotein cholesterol. More recently, subanalyses of large clinical trials suggest that statins may also prove beneficial in ameliorating the progression of kidney disease through their cholesterol-dependent and/or cholesterol-independent (pleiotropic) effects. This review focuses on the role of statin therapy in the progression of chronic kidney disease, the published trials that study the effect of antilipidemic agents on nephropathy, and the emerging pleiotropic effects of statins on the kidneys.

Liver X receptor-α mediates cholesterol efflux in glomerular mesangial cells

Lipid-mediated injury plays an important role in the pathogenesis of many renal diseases including diabetic nephropathy. Liver X receptor-α (LXRα) is an intracellular sterol sensor that regulates expression of genes controlling cholesterol absorption, excretion, catabolism, and cellular efflux. The present study was aimed at examining the role of LXRα in cholesterol metabolism in glomerular mesangial cells. A 1,561-bp fragment of full-length rabbit LXR cDNA was cloned. The deduced protein sequence exhibited 92.4 and 89.2% identity to human and mouse LXRα, respectively. Tissue distribution studies showed that rabbit LXRα was expressed in the liver, spleen, and kidney. In situ hybridization and RT-PCR assays further indicated that LXRα mRNA was widely expressed in the kidney and present in every nephron segment including the glomeruli. To determine intrarenal regulation of LXRα, rabbits were treated with thiazolidinedione (TZD) peroxisome proliferator-activated receptor-γ (PPARγ) agonists, which have been previously shown to enhance LXRα expression via PPARγ and increase cholesterol efflux in macrophages. The results showed that glomerular LXRα expression was markedly induced by TZDs. In cultured rabbit mesangial cells, LXRα mRNA and protein were detected by RT-PCR and immunoblotting. Treatment of mesangial cells with a specific LXRα agonist, TO-901317, significantly increased basal and apolipoprotein AI-mediated cholesterol efflux and markedly enhanced the promoter activity of an LXRα target gene, ATP-binding cassette transporter A1 (ABCA1). In conclusion, LXRα is expressed in renal glomeruli and functionally present in mesangial cells where its activation mediates cholesterol efflux via ABCA1. These data suggest that LXRα may be a potential therapeutic target for treating lipid-related renal glomerular disease.

The leaf extract of Ginkgo Biloba L. suppresses oxidized LDL-stimulated fibronectin production through an antioxidant action in rat mesangial cells

1 The leaf extract of Ginkgo Biloba L. exhibits a variety of pharmacological effects through an antioxidant action. We examined the effects of the leaf extract (Ginkgolon-24) on the production of fibronectin induced by oxidized low-density lipoprotein (oxLDL) in rat mesangial cells. 2 Stimulation with oxLDL accelerated the production of fibronectin with the preceding generation of reactive oxygen species (ROS). Pretreatment with Ginkgolon-24 inhibited the oxLDL-induced fibronectin production as well as ROS generation. 3 oxLDL also elicited the activation of SP-1, nuclear factor-kappaB, and cAMP response element-binding protein, which are transcription factors involved in the fibronectin production. Among these activated transcription factors, Ginkgolon-24 inhibited the activation of SP-1 only. 4 Furthermore, 7-ketocholesterol, an oxidized lipid in oxLDL particles, induced the production of fibronectin and the activation of SP-1, which were also suppressed by Ginkgolon-24. 5 These results suggest that the leaf extract of Ginkgo Biloba L. inhibits the oxLDL-induced production of fibronectin probably through inhibitory effects on ROS generation and SP-1 activation in rat mesangial cells.

Apolipoprotein E and renal disease

Apolipoprotein E (ApoE) is a major constituent of plasma lipoproteins with many biological actions of great significance. Beyond the known influence of ApoE polymorphisms on serum lipid profile, the pathogenesis of atherosclerosis, and the development of neurodegenerative disorders, ApoE also has a major role in the pathogenesis and progression of a variety of renal diseases, as well as in the atherosclerotic complications associated with them. Briefly, the polymorphisms of ApoE are major determinants of plasma lipid levels in uremic patients. They may affect the risk for cardiovascular disease in this population, predispose to the development of diabetic nephropathy, influence the severity of certain glomerulopathies, and regulate mesangial and glomerular functions locally in the kidney microenvironment. Finally, certain mutations of the ApoE gene are associated with a recently described nephropathy, termed lipoprotein glomerulopathy.

Association of atherosclerotic coronary artery disease and pulse pressure with renal disease progression

BACKGROUND

This study was performed to identify the association of atherosclerotic coronary artery disease (CAD) and pulse pressure with renal disease progression in patients with mild chronic renal disease.

METHODS

Eligibility criteria for enrollment in this study included age 18 to 70 years, mild chronic renal disease (CRD), undergoing thallium SPECT and echocardiography and followed longer than three years. Mild CRD was defined as serum creatinine level of 1.5 to 3.0 mg/dL in men and 1.4 to 3.0 mg/dL in women. Patients with serious illness, history of kidney transplantation, ejection fraction less than 40% on echocardiography and development of acute renal failure during follow-up were excluded.

RESULTS

A total of 87 patients were included in this study. The underlying renal disease included diabetic nephropathy in 51 patients. Forty-five patients showed positive findings on thallium SPECT and they were classified as having CAD. Coronary angiography showed significant stenosis in 41 of 42 patients studied. Median duration of follow-up was 56 months. During the follow-up period, 40 patients required chronic dialysis therapy and 16 patients showed a doubling of baseline serum creatinine in three years. These 56 patients were classified as progressors. Comparison of clinical and laboratory parameters between progressors and nonprogressors showed a difference in the presence of diabetic nephropathy, mean arterial pressure, 24-h urine protein (p < 0.001), pulse pressure (p < 0.01), total cholesterol and presence of CAD (p < 0.05). There was no association between the progression of CRD and the results of CAD or treatment of CAD. Multivariate logistic regression analysis showed that the presence of diabetic nephropathy and mean arterial pressure > 100 mm Hg were independent predictors of CRD progression.

CONCLUSION

Atherosclerotic coronary artery disease and pulse pressure were associated with renal disease progression.

Involvement of reactive oxygen species and SP-1 in fibronectin production by oxidized LDL

We examined the mechanisms responsible for the production of fibronectin induced by oxidized low-density lipoprotein (oxLDL) in rat mesangial cells. oxLDL accelerated the production of fibronectin with the preceding generation of reactive oxygen species (ROS). Pretreatment with N-acetylcysteine suppressed the oxLDL-induced fibronectin production as well as ROS generation. oxLDL also elicited the activation of SP-1, nuclear factor-kappaB, and cAMP response element-binding protein, but not activator protein-1. Among these activated transcription factors, N-acetylcysteine inhibited the activation of SP-1 only. 7-Ketocholesterol, an oxidized lipid in oxLDL particles, induced the production of fibronectin and the activation of SP-1, those which were suppressed by N-acetylcysteine. Furthermore, mithramycin A, an inhibitor of SP-1, also suppressed the oxLDL- and 7-ketocholesterol-stimulated production of fibronectin. These results suggest that oxLDL stimulates fibronectin production, at least in part, through the ROS-dependent activation of SP-1 in rat mesangial cells, and further that the ROS-dependent cellular responses may be elicited by 7-ketocholesterol.

Cholesterol and the risk of renal dysfunction in apparently healthy men

Despite extensive knowledge about abnormal lipid patterns in patients with end-stage renal disease, the association between cholesterol and the development of renal dysfunction is unclear. We evaluated this association in a prospective cohort study among 4,483 initially healthy men participating in the Physicians' Health Study who provided blood samples in 1982 and 1996. Main outcome measures were elevated creatinine, defined as >/= 1.5 mg/dl (133 micromol/L), and reduced estimated creatinine clearance, defined as </=55 ml/min. Cholesterol parameters included total cholesterol (<200, 200 to 239, and >/= 240 mg/dl), HDL (<40 or >/= 40 mg/dl), total non-HDL cholesterol, and the ratio of total cholesterol to HDL. We used logistic regression to calculate age- and multivariable adjusted odds ratios as a measure for the relative risk. After 14 yr, 134 men (3.0%) had elevated creatinine and 244 (5.4%) had reduced creatinine clearance. The multivariable relative risk for elevated creatinine was 1.77 (95% confidence interval [CI], 1.10 to 2.86) for total cholesterol >/= 240 mg/dl, 2.16 (95% CI, 1.42 to 3.27) for HDL <40 mg/dl, 2.34 (95% CI, 1.34 to 4.07) for the highest quartile of total cholesterol/HDL ratio (>/= >6.8), and 2.16 (95% CI, 1.22 to 3.80) for the highest quartile of non-HDL cholesterol (>/= 196.1). Similar although smaller associations were observed between cholesterol parameters and reduced creatinine clearance. Elevated total cholesterol, high non-HDL cholesterol, a high ratio of total cholesterol/HDL, and low HDL in particular were significantly associated with an increased risk of developing renal dysfunction in men with an initial creatinine <1.5 mg/dl.

Apolipoprotein E gene polymorphism, hypercholesterolemia and glomerular filtration rate in type 2 diabetic subjects: a 9-year follow-up study

OBJECTIVE

To study the association between apolipoprotein E (apoE) genotype and the rate of decline in glomerular filtration rate (GFR) in type 2 diabetic patients in a 9-year prospective study.

METHODS

GFR was determined in 84 type 2 diabetic patients by plasma clearance of (51)Cr-EDTA at baseline and after 9 years of follow-up. ApoE genotypes were determined by polymerase chain reaction and restriction enzyme HHAI digestion and designated as epsilon4 allele group (apoE4/2, 4/3 and 4/4 genotypes; n = 20) and non-epsilon4 allele group (apoE3/3 and E3/2 genotypes; n = 64). We focused our analysis on those patients who were more likely to progress to diabetic renal disease, i.e. whose GFR fell more than expected in the normal course of ageing [1 ml x min(-1) x (1.73 m(2))(-1) per year].

RESULTS

In the whole population, the decline in the GFR did not differ statistically significantly between the apoE genotype groups [p = 0.65 with analysis of variance for repeated variables (RANOVA) for interaction between apoE genotype group and time point]. However, among patients whose GFR changed more than 9 ml x min(-1) x (1.73 m(2))(-1), GFR showed a statistically significantly greater decline in the epsilon4 allele group (n = 11) than in the non-epsilon4 allele group (n = 43) [from 116 +/- 36 to 80 +/- 29 ml x min(-1) x (1.73 m(2))(-1) vs. from 119 +/- 20 to 96 +/- 18 ml x min(-1) x (1.73 m(2))(-1); p = 0.005 with RANOVA].

CONCLUSION

ApoE allele epsilon4 may speed up the rate of decline of the GFR in patients with progressive diabetic renal disease.

Hypercholesterolemia is a prerequisite for puromycin inducible damage in mouse kidney

BACKGROUND

The mouse, as opposed to the rat, is relatively resistant to the experimental nephrosis induced by puromycin aminonucleoside. The reason for this species specificity is not known. Apolipoprotein E (apoE)-deficient mice were used to determine whether hypercholesterolemia plays a role in inducing proteinuria.

METHODS

Thirty-two mice were divided into normal and high cholesterol diet groups and then divided further into four subgroups: puromycin, puromycin+probucol, probucol and control. Urinary albumin of these mice was analyzed by nephelometry. The lipid peroxidation (LPO) end products malonyldialdehyde (MDA) and 4-hydroxynonenal (4-HNE) were detected by immunohistochemistry, and the expression level of the glomerular slit diaphragm protein, nephrin, was studied by immunohistochemistry and real time RT-PCR.

RESULTS

Overt proteinuria was induced by puromycin only in the apoE knockout mice ingesting the high cholesterol diet. The staining intensities of MDA and 4-HNE were stronger in the glomeruli of proteinuric mice compared to glomeruli of non-proteinuric mice. When serum cholesterol levels were reduced by probucol, proteinuria decreased and fewer LPO end products were seen immunohistochemically. Three and eight days after puromycin injection the level of nephrin mRNA in the kidneys of proteinuric mice decreased in comparison to the controls. Puromycin-treated mice kidneys demonstrated a clearly reduced reactivity to the nephrin antibodies.

CONCLUSIONS

Hypercholesterolemia, possibly via LPO, is a prerequisite for puromycin-inducible glomerular damage in the mouse. Furthermore, nephrin protein and mRNA levels appear to be candidate markers of glomerular damage in the mouse.

Serum C-reactive protein and leptin as predictors of kidney disease progression in the Modification of Diet in Renal Disease Study

BACKGROUND

In vitro and in vivo data suggest that markers of inflammation and nutritional status may be risk factors for the progression of chronic kidney disease.

METHODS

We investigated whether higher levels of C-reactive protein (CRP) and leptin were risk factors for progression of chronic kidney disease in the Modification of Diet in Renal Disease (MDRD) Study. Frozen samples were assayed for high sensitivity C-reactive protein (CRP) or leptin in 804 patients. CRP and leptin were then evaluated as risk factors for glomerular filtration rate (GFR) decline using univariate and multivariable analyses.

RESULTS

At baseline, the mean (median) CRP in Study A (GFR between 25 and 55 mL/min/1.73 m2) and Study B (GFR between 13 and 24 mL/min/1.73 m2) were 0.48 (0.25) and 0.46 (0.20) mg/dL, respectively, while the mean (median) leptin in Study A and Study B were 15.2 (9.80) and 15.1 (7.80) ng/mL, respectively. Mean follow-up time was 2.2 years. The mean GFR decline was -4.33 and -3.65 mL/min/year in Study A and B, respectively. There was no significant association between the rate of GFR decline with the level of CRP or leptin in multivariable analysis in Study A [0.08 (-0.14, 0.30) mL/min/year slower GFR decline per twofold increase in CRP level; and 0.14 (-0.13, 0.40) mL/min/year slower GFR decline per twofold increase in leptin level], or in multivariable analysis in Study B [-0.05 (-0.28, 0.18) mL/min/year faster GFR decline per twofold increase in CRP level; and -0.12 (-0.42, 0.19) mL/min/year faster GFR decline per twofold increase in leptin level].

CONCLUSIONS

Higher serum levels of CRP and leptin are not independent risk factors for progression of non-diabetic kidney disease.

Homocysteine, cysteine, and B vitamins as predictors of kidney disease progression

BACKGROUND

Pathological similarities between atherosclerosis and glomerulosclerosis suggest that risk factors for the two processes may be similar. Elevated total homocysteine (tHcy) levels and low B vitamin levels are risk factors for atherosclerosis, but have not been evaluated sufficiently as risk factors for the progression of kidney disease.

METHODS

Frozen samples from the Modification of Diet in Renal Disease Study were assayed for serum tHcy, cysteine, pyridoxal 5-phosphate (PLP), folate, and vitamin B12 levels in 804 participants. These factors were evaluated in both continuous and categorical analyses as risk factors for glomerular filtration rate (GFR) decline by using univariate and multivariable analyses.

RESULTS

At baseline, mean tHcy levels in study A (GFR, 25 to 55 mL/min/1.73 m2) and study B (GFR, 13 to 24 mL/min/1.73 m2) were 16.9 micromol/L (median, 15.6 micromol/L) and 23.0 micromol/L (median, 20.5 micromol/L), respectively. Mean follow-up was 2.2 years. Mean GFR declines were -4.35 and -3.65 mL/min/y in studies A and B, respectively. There was no significant association between change in GFR with baseline level of tHcy in univariate (-0.26 mL/min/y per 1-SD unit increase in tHcy level; 95% confidence interval [CI], -0.67 to 0.15) or multivariable (-0.18 mL/min/y per 1-SD unit increase in tHcy level; 95% CI, -0.53 to 0.17) analysis in study A or univariate (0.07 mL/min/y per 1-SD unit increase in tHcy level; 95% CI, -0.36 to 0.51) or multivariable (0.24 mL/min/y per 1-SD unit increase in tHcy level; 95% CI, -0.16 to 0.64) analysis in study B. Similarly, higher cysteine levels and lower B vitamin levels were not associated with faster rates of GFR decline in multivariable analysis in either study.

CONCLUSION

Higher tHcy or cysteine levels and lower folate, PLP, and vitamin B12 levels are not independent risk factors for progression of nondiabetic kidney disease.

IGF-1-induced lipid accumulation impairs mesangial cell migration and contractile function

BACKGROUND

Chronic treatment of mesangial cells with insulin-like growth factor-1 (IGF-1) results in intracellular lipid accumulation. These mesangial cells resemble foam cells.

METHODS

To determine whether this phenotype affects cell function, lipid-laden mesangial cells were tested for their ability to migrate in response to IGF-binding protein-5 (IGFBP-5) and to contract in response to angiotensin II (Ang II). IGFBP-5 binding and subsequent activation of the signal transduction cascade for migration were examined. To confirm that lipid accumulation was responsible for impaired contractility, lipid was removed from lipid-laden mesangial cells and the cells were re-tested for contractile response to Ang II.

RESULTS

In comparison to control mesangial cells, lipid-laden cells failed to migrate in response to IGFBP-5. Although cellular binding of IGFBP-5 was not altered by lipid accumulation, IGFBP-5 failed to activate cdc42, a Rho GTPase required for IGFBP-5-mediated mesangial cell migration. These data indicate that lipid accumulation within the mesangial cell interferes with the signal transduction response to IGFBP-5. In addition, mesangial cells treated with IGF-1 had reduced contraction to Ang II. When lipid accumulation was exaggerated by adding cholesteryl esters to the culture medium, mesangial cells failed to contract in response to Ang II. Following removal of excess lipid from these mesangial cells, the contractile response to Ang II was restored.

CONCLUSIONS

IGF-1 induces lipid accumulation in mesangial cells, which impairs their ability to respond to specific migratory and contractile stimuli. These observations are relevant to understanding functional abnormalities in diseases where mesangial foam cells occur, such as focal and segmental glomerulosclerosis and diabetic nephropathy.

Apolipoprotein E genetic polymorphism, remnant lipoproteins, and nephropathy in type 2 diabetic patients

BACKGROUND

We previously showed that the apolipoprotein (apo) Eepsilon2 allele is associated with the progression of diabetic nephropathy. The aim of the present study is to further investigate the association between apo E genetic polymorphism, plasma lipid levels (particularly remnant lipoproteins), and diabetic nephropathy.

SUBJECTS AND METHODS

One hundred fifty-eight patients with type 2 diabetes who had a duration of diabetes longer than 10 years were divided into the three apo E groups: apo E2 (n = 22), E3/3 (n = 102), and E4 (n = 34). Plasma levels of lipids and remnant lipoproteins were measured. The effect of apo E2 triglyceride (TG)-rich lipoproteins, including remnant lipoproteins, on the accumulation of cholesteryl esters by human mesangial cells (HMCs) was estimated by measuring the stimulation of radioactive carbon-labeled oleate incorporation into cholesteryl esters.

RESULTS

The frequency of overt nephropathy was significantly greater in apo E2 patients with diabetes (59.1%) than apo E3/3 (34.3%) or apo E4 patients (8.8%), and the frequency of normoalbuminuria was significantly greater in apo E4 patients with diabetes (67.6%) than apo E3/3 (34.3%) or apo E2 patients (4.5%). Logistical regression analysis showed that odds ratios of apo E2 and apo E4 genotypes for the presence of overt nephropathy were 10.179 (P = 0.0349) and 0.129 (P = 0.0028), respectively. Plasma TG and remnant-like lipoprotein particle cholesterol levels were significantly greater in apo E2 patients and significantly lower in apo E4 patients than apo E3/3 patients. Apo E2 TG-rich lipoproteins stimulated the accumulation of cholesteryl esters by HMCs significantly more than apo E3/3 or apo E4 TG-rich lipoproteins.

CONCLUSION

Apo E2 is a positive factor and apo E4 is a negative factor for diabetic nephropathy. Apo E2 TG-rich lipoproteins, including remnant lipoproteins, affected HMCs. Remnant lipoproteins may have an important role in the progression of diabetic nephropathy.

Effects of antioxidants on kidney disease

Kidney mesangial cells (MCs) and vascular smooth muscle cells (VSMCs) are closely related in terms of origin, microscopic anatomy, histochemistry, and contractility. This relationship suggests a similarity between kidney glomerular sclerosis and atherosclerosis. Vitamin E appears beneficial in the prevention and treatment of coronary disease and also inhibits the proliferation of VSMCs in vitro. We used vitamin E and probucol to treat glomerular sclerosis and MC-proliferative glomerulonephritis (GN) in two animal models of glomerular disease. Using rats, a remnant kidney model accelerated with hyperlipidemia was employed to reflect progressive glomerular sclerosis leading to chronic renal failure, and an anti-thymocyte serum treatment was used to model acute MC-proliferative GN. Supplemental dietary antioxidants suppress MC proliferation and glomerular sclerosis in models of glomerular disease in rats. These results suggest that treatment with antioxidants may be a promising intervention to prevent progression of kidney disease.

Fluvastatin improves lipid abnormalities in patients with moderate to advanced chronic renal insufficiency

Chronic renal insufficiency is characterized by specific abnormalities in lipoprotein metabolism, affecting both apolipoprotein A (apo A)- and apo B-containing lipoproteins. To evaluate the effects of fluvastatin, a synthetic 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor, on renal dyslipoproteinemia, we performed a randomized, double-blind, placebo-controlled, two-way, period cross-over study. Study patients were administered fluvastatin, 40 mg/d, or placebo during 8 weeks in randomized order. Forty-five nonnephrotic patients (28 men, 17 women) without diabetes with moderate to advanced chronic renal insufficiency participated in the study. Their mean age was 56.4 +/- 11.0 years. Glomerular filtration rate ranged from 12 to 44 mL/min/1.73 m2 of body surface area (mean, 27.5 +/- 10.5 mL/min/1.73 m2). Fluvastatin treatment resulted in significant reductions in the primary outcome variables low-density lipoprotein cholesterol (LDL-C; -26%; P < 0.001), apo B (-21%; P < 0.001), and lipoprotein B complex (Lp-Bc) (-14%; P < 0.01). There were statistically significant differences between fluvastatin and placebo treatment for the secondary outcome variables total cholesterol (-19%), triglycerides (TGs; -13%), VLDL-C (-13%), apo E (-13%), and Lp-B (-22%). There was no treatment effect on high-density lipoprotein cholesterol or lipoprotein(a). Fluvastatin treatment was well tolerated, with no serious adverse events during the study. In conclusion, fluvastatin treatment was well tolerated in patients with moderately advanced renal insufficiency and led to a significant reduction in cholesterol-rich, but to a lesser extent in TG-rich, apo B-containing lipoproteins. It remains to be clarified whether these positive changes in lipoprotein profile also will result in attenuation of the atherosclerotic process in these patients, as well as beneficially affect the progression of chronic renal failure.

Dysregulation of LDL receptor under the influence of inflammatory cytokines: a new pathway for foam cell formation

BACKGROUND

Lipid-mediated renal injury is an important component of glomerulosclerosis and its similarity to atherosclerosis is well described. This study focused on the relationship between lipid-mediated injury and inflammation by examining the role of inflammatory cytokines in the regulation of human mesangial cell low-density lipoprotein (LDL) receptors.

METHODS

A human mesangial cell line (HMCL) was used to study the effects of tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) on the regulation of LDL receptor mRNA and protein in the presence of a high concentration of native LDL (250 microg/mL).

RESULTS

Native LDL caused foam cell formation in HMCL in the presence of antioxidants, TNF-alpha and IL-1beta. Both cytokines overrode LDL receptor suppression induced by a high concentration of LDL and increased LDL uptake by enhancing receptor expression. These cytokines also caused increased expression of SCAP [sterol responsive element binding protein (SREBP) cleavage activation protein], and an increase in the nuclear translocation of SREBP, which induces LDL receptor expression.

CONCLUSION

These observations demonstrate that inflammatory cytokines can modify cholesterol-mediated LDL receptor regulation in mesangial cells, permitting unregulated intracellular accumulation of unmodified LDL and causing foam cell formation. These findings suggest that inflammatory cytokines contribute to lipid-mediated renal damage, and also may have wider implications for the study of inflammation in the atherosclerotic process.

Paradoxical increase in nitric oxide synthase activity in hypercholesterolaemic rats with impaired renal function and decreased activity of nitric oxide

BACKGROUND

We have shown that acute exposure of oxidized low-density lipoprotein (OX-LDL) induces vasoconstriction in renal vessels and reduces glomerular filtration rate (GFR) in an isolated perfused rat kidney model by decreasing the activity of nitric oxide (NO). L-arginine has a protective role against OX-LDl-induced vasoconstriction. Micropuncture studies have demonstrated that short-term diet-induced hypercholesterolaemia is associated with decreased GFR and renal blood flow and increased glomerular capillary pressure. This may be mediated by decreased activity of NO.

METHODS

Rats were made hypercholesterolaemic by supplementing the standard chow with 4% cholesterol and 1% sodium cholate. A group of rats on hypercholesterolaemic diet also received L-arginine in the drinking water. After 4 and 6 weeks, blood samples and 24-h urine samples were collected for the measurement of biochemical parameters. After 6 weeks, all rats were subjected to isolated perfusion of kidneys at a constant pressure of 100 mmHg. During isolated perfusion, the unused contralateral kidney was taken for morphological studies and for assessing the activity of nitric oxide synthase enzyme by beta-NADPH diaphorase histochemistry.

RESULTS

Rats fed a high-cholesterol diet had LDL levels 3-6 times greater than the rats fed standard chow. Rats that received L-arginine in the drinking water had serum L-arginine levels 5-6 times greater than control rats. At 6 weeks, creatinine clearance was significantly lower in the rats on the high-cholesterol diet compared to the rats on standard chow and rats on high-cholesterol diet plus L-arginine. Twenty-four-hour urinary total nitrate and nitrite excretion in the hypercholesterolaemic rats was 1.5-2 times greater than that of control rats. Twenty-four-hour urinary cGMP excretion was significantly lower in the rats on a high-cholesterol diet, but in the rats on high-cholesterol diet and L-arginine, 24-h urinary cGMP excretion was not significantly different from that of control rats. During isolated perfusion of kidneys, renal perfusate flow was found to be significantly reduced in the kidneys taken from the rats on a high-fat diet compared to controls. L-arginine supplementation in the drinking water almost completely reversed the effect of a high-fat diet. Inulin clearance was also significantly reduced in kidneys on a high-fat diet in contrast to controls but not in kidneys on high fat-diet and L-arginine. Basal cGMP excretion in urine was significantly lower in the kidneys taken from the rats on a high-fat diet compared to controls. L-arginine supplementation restored the basal cGMP excretion in these kidneys. NO synthase (NOS) enzyme activity as assessed by NADPH diaphorase activity showed that kidney sections taken from the rats on a high-fat diet showed more intense staining, indicating increased activity compared to the kidney sections taken from the rats on a normal diet.

CONCLUSION

Though activity of NO is diminished in hypercholesterolaemic rats with impaired renal function, there is a paradoxical increase in NO production and NOS activity. L-arginine reverses the effects of a high-fat diet.

Genetic polymorphism in paraoxonase is a risk factor for childhood focal segmental glomerulosclerosis

Focal segmental glomerulosclerosis (FSGS) is an important cause of end-stage renal failure (ESRF) in children. Our previous studies have shown that Arab children in Israel have a worse prognosis compared with Jewish patients despite similar clinical presentation and management. Progression of proteinuric glomerular diseases has been associated with alterations in lipid metabolism, and similarities have been drawn between the mechanisms underlying atherosclerosis and glomerulosclerosis. Paraoxonase (PON) is a high-density lipoprotein (HDL)-associated enzyme involved in preventing the oxidation of low-density lipoprotein (LDL), and an association has been shown between two genetic polymorphisms in PON1 and the risk of coronary artery disease. The aim of this study was to determine the frequency of these genetic polymorphisms in PON1 in Arab and Jewish children with FSGS and to determine any association with severity of outcome. Forty-seven children (21 Arab and 26 Jewish) with biopsy-proven FSGS and 274 healthy controls of matching ethnic origin were studied. The glutamine (A)-192-arginine (B) and the methionine (M)-55-leucine (L) polymorphisms were analyzed. The frequency of the A allele was similar in patients and controls (0.68 versus 0.71), as was that of the L allele (0.63 versus 0.6). When subgroups were analyzed, the prevalence of the LL genotype in Arab patients was significantly greater than in Jewish patients (57.1% versus 26.9%, P: < 0.05) and Arab controls (57.1% versus 28.9%, P: < 0.03). A trend in association was found between homozygosity for the L allele and progression of renal disease in Arab children. Homozygosity for the L allele is a risk factor for developing FSGS in Arab children and may be associated with a worse prognosis.

Aortic atheromatous lesions developed in APA hamsters with streptozotocin induced diabetes: a new animal model for diabetic atherosclerosis. 1. Histopathological studies

To develop an adequate animal model for atherosclerosis in large vessels of patients with diabetes, i.e. diabetic macroangiopathy, we induced diabetes in APA hamsters with a single injection of streptozotocin (SZ) and examined the aorta histopathologically and immunohistochemically. As a result, hyperglycemia and hyperlipidemia were continuously observed for 26 weeks after the SZ injection (WAI) in APA hamsters. Fatty streaks characterized by a subendothelial accumulation of many foam cells were observed, limited to the aortic arches as early as 6 WAI. In addition to larger fatty streaks developing with the duration of diabetes, fibrous plaques and plaques containing calcium deposits or cholesterol clefts developed at 26 WAI. These lesions are generally similar to the atheromatous lesions developed in humans. Moreover, depositions of apolipoprotein E and advanced glycation end-products immunohistochemically detected in the lesions were very similar to those found in humans. The diabetic APA hamster is therefore considered to be a useful model for studying the formation of atheromatous lesions in diabetic patients.

Characteristics of progressive renal disease

Virtually all renal diseases progress to terminal renal failure relatively independently of the initial disease. Arresting the rate of the deterioration of kidney failure has a great impact on reducing the number of patients reaching the stage of expensive renal replacement therapy. Understanding the mechanisms of the progression of kidney disease has greatly been improved during recent years. The nature of the progressive renal damage with various etiologies includes various well-known factors where hemodynamics, renin-angiotensin system (RAS) and progressive proteinuria play the central roles. Proteinuria has to be shown as an independent risk factor for renal disease progression. Also, disturbances in lipid metabolism as well as the later structural lesions contribute to the progression. Various modalities have been used for the prevention of progressive renal disease, e.g. low-protein diet, antihypertensive therapy, antifibrotic therapy. Many recent experimental and clinical studies have shown that besides the systemic blood pressure lowering effect, RAS blocking agents provide renal protective effects via direct, hemodynamic, and indirect, non-hemodynamic, pathways: (1) lowering intraglomerular capillary hydraulic pressure, and increasing the glomerular ultrafiltration coefficient; (2) lowering proteinuria; (3) lowering hyperlipidemia; (4) diminishing kidney growth; (5) diminishing infiltration of macrophages; (6) downregulation of proinflammatory cytokines. Therefore, RAS blocking agents are widely prescribed not only for antihypertensive but also for renoprotective purposes in diabetic and non-diabetic nephropathies.

Inhibitory effect of Cordyceps sinensis and Cordyceps militaris on human glomerular mesangial cell proliferation induced by native LDL

Native LDL, in low concentrations, promotes proliferation of cultured human glomerular mesangial cells. LDL stimulated [(3)H]-thymidine incorporation into DNA of human glomerular mesangial cells. Increased concentrations of LDL led to increased [(3)H]-thymidine incorporation. When LDL concentrations were 5, 10 and 50 microg ml(-1), [(3)H]-thymidine incorporation was 919.5+/-216, 1106+/-132, and 1200+/-210, respectively. When Cordyceps sinensis 100, 200, 300, 400 microg ml(-1) plus LDL 10 microg ml(-1) were added, [(3)H]-thymidine incorporation was 99+/-19 and 53+/-8, respectively, P<0.01 compared with controls. With Cordyceps militaris at similar concentrations plus LDL 10 microg ml(-1), [(3)H]-thymidine incorporation was respectively 192+/-75, 168+/-66, 145+/-53 and 72+/-16, P<0.01 compared with controls. The data suggest that LDL may play a critical role in mediating mesangial cell hypertrophy or proliferation involved in the development of glomerulosclerosis. Cordyceps sinensis and Cordyceps militaris inhibited, to a certain degree, proliferation of cultured human glomerular mesangial cell induced by LDL.

Plasminogen activator inhibitor-1 and apolipoprotein E gene polymorphisms and diabetic angiopathy

BACKGROUND

A point mutation in the plasminogen activator inhibitor-1 (PAI-1) gene and a three-allelic variation in the apolipoprotein-E (ApoE) gene have been suggested as risk factors for the development of diabetic micro- and macrovascular complications.

METHODS

We studied 198 type 1 diabetic patients with diabetic nephropathy [121 men, age (mean+/-SD) 41+/-10 years, diabetes duration 28+/-8 years] and 192 patients with persistent normoalbuminuria (118 men, age 43+/-10 years, diabetes duration 27+/-9 years).

RESULTS

Male patients with nephropathy had elevated plasma PAI-1 levels [geometric mean (95% CI)], 70 (62-79) ng/ml, compared with normoalbuminuric men, 43 (38-47) ng/ml, P<0.001. Even though nephropathic patients with the 4G4G genotype tended to have higher plasma PAI-1 levels, P=0.06, no difference in allele frequency (4G/5G) was seen between patients with and without nephropathy: 0.538/0.462 vs 0.539/0.461, respectively. Nor did ApoE allele frequencies (epsilon2/epsilon3/epsilon4) differ between nephropathic and normoalbuminuric patients: 0.099/0.749/0. 152 vs 0.081/0.745/0.174, respectively. Genotype distributions were also similar, n.s. Coronary heart disease was more prevalent (36%) among nephropathic patients carrying the atherogenic epsilon4-allele compared with 12% in patients with the epsilon3,epsilon3 genotype, P<0.001. No associations between diabetic retinopathy and PAI-1 or ApoE polymorphisms were observed, n.s.

CONCLUSIONS

The ApoE polymorphism may accelerate the development of coronary heart disease often seen in Caucasian patients with type 1 diabetes and diabetic nephropathy, a condition characterized by elevated plasma PAI-1 in men. Neither the PAI-1 nor the ApoE gene polymorphism contributes to the genetic susceptibility to diabetic nephropathy or retinopathy.

Hypertriglyceridaemia and hyperuricaemia are risk factors for progression of IgA nephropathy

BACKGROUND

The prognosis of IgA nephropathy (IgAN) is variable and about 10-20% of patients progress to end-stage renal disease (ESRD) in 10 years. Hypertension, proteinuria and renal insufficiency at the time of diagnosis are risk factors associated with poor prognosis. Lipid abnormalities may have a role in the progression of glomerulonephritides, and glomerulosclerosis and atherosclerosis may have similar pathophysiological mechanisms. We therefore evaluated factors associated with cardiovascular diseases, especially hypercholesterolaemia, hypertriglyceridaemia, and hyperuricaemia, as predictors of the progression of IgAN.

METHODS

A total of 223 patients with IgAN (141 men, 82 women; median age 41 years, range 8-78 years) were studied. The following parameters were recorded at the time of renal biopsy: presence of hypertension or diabetes, smoking habits, body mass index (BMI), serum creatinine, total and HDL-cholesterol, triglycerides, and urate and 24-h urinary protein excretion. The patients were followed up for 0.2-17 years (median 10 years) with respect to progression of renal disease defined as elevation of serum creatinine above 125 micromol/l in men or 105 micromol/l in women, and over 20% elevation from baseline.

RESULTS

Forty-one patients (18%) showed progression. Hypertriglyceridaemia and hyperuricaemia were significantly more common at the time of renal biopsy in patients with progressive than in those with stable disease. In patients with normal renal function at the time of diagnosis initial hypertriglyceridaemia, hyperuricaemia, hypertension and proteinuria were independent risk factors for progression of IgAN in the Cox regression hazard model.

CONCLUSIONS

Our results show that hypertriglyceridaemia and hyperuricaemia at the time of diagnosis are important, previously underestimated predictors of poor outcome in IgAN, although causality between these factors and progression cannot be inferred from the present study.

Quantitation of allograft fibrosis and chronic allograft nephropathy

Despite improvements in the prevention and treatment of acute renal allograft rejection, the long-term survival of renal transplants has not increased. Immunologic and non-immunologic factors contribute to the gradual deterioration of graft function and to the histologic lesion characterized by vascular and interstitial fibrosis ('chronic rejection'). Quantitation of this process has been attempted using various invasive and non-invasive methods. These methods, performed at different times post-transplant, are reviewed in this article. In particular, pathology scoring systems and the potential of using computerized image analysis of biopsy material are discussed.

Brief periods of hyperphagia cause renal injury in the obese Zucker rat

BACKGROUND

Female obese (fa/fa) Zucker rats are maximally hyperphagic from the beginning of access to solid food until 20 weeks of age and die primarily from renal failure. We documented that urinary albumin excretion (UAE) rises early in obese rats during this time of greatest hyperphagia. This study was conducted to examine if this early surge of hyperphagia is critical to the initiation of glomerular damage.

METHODS

Three groups of six-week-old rats were used: (a) obese females fed ad libitum (AL-obese), (b) obese females pair fed to lean controls until 21 weeks and then allowed to eat ad libitum until 57 weeks (PF. AL-obese), (c) lean (Fa/Fa) Zucker rats fed ad libitum (AL-lean). Cohorts of AL-obese and PF.AL-obese rats were allowed to continue to death or 57 weeks of age, and the rest were terminated at 21 weeks for renal histology.

RESULTS

At 21 weeks, neither PF.AL-obese nor AL-lean rats had elevated UAE or glomerular histopathology. In contrast, glomerular injury was severe in AL-obese rats. UAE increased by 10 and 29 weeks in AL- and PF.AL-obese rats, respectively. Plasma triglycerides increased prior to UAE in both PF. AL- and AL-obese rats.

CONCLUSIONS

In obese rats fed ad libitum, hyperphagia is followed within a few weeks by hypertriglyceridemia and then by glomerular injury regardless of when ad libitum feeding is initiated. These events do not occur in lean rats or in obese rats pair fed to lean rats. Protective effects of pair feeding did not extend into the period of ad libitum feeding for PF.AL-obese rats. Hyperphagia quickly initiates glomerular injury in obese female Zucker rats.

Chronic allograft nephropathy: An update

Chronic allograft nephropathy is the most prevalent cause of renal transplant failure in the first post-transplant decade, but its pathogenesis has remained elusive. Clinically, it is characterized by a slow but variable loss of function, often in combination with proteinuria and hypertension. The histopathology is also not specific, but transplant glomerulopathy and multilayering of the peritubular capillaries are highly characteristic. Several risk factors have been identified, such as advanced donor age, delayed graft function, repeated acute rejection episodes, vascular rejection episodes, and rejections that occur late after transplantation. A common feature of chronic allograft nephropathy is that it develops in grafts that have undergone previous damage, although the mechanism(s) responsible for the progressive fibrosis and tissue remodeling has not yet been defined. Hypotheses to explain chronic allograft nephropathy include the immunolymphatic theory, the cytokine excess theory, the loss of supporting architecture theory, and the premature senescence theory. The most effective option to prevent chronic allograft nephropathy is to avoid graft injury from both immune and nonimmune mechanisms.

Association between apolipoprotein E polymorphism and macroalbuminuria in patients with non-insulin dependent diabetes mellitus

OBJECTIVES

Apolipoprotein E (apo E) is known to play an important role in lipoprotein metabolism through its ability to bind to the receptors as a ligand. Three different apo E alleles (epsilon2, epsilon3 and epsilon4) produce six apo E genotypes (epsilon2/2, epsilon2/3, epsilon2/4, epsilon3/3, epsilon3/4 and epsilon4/4). The objective of this study was to investigate an association between apo E gene polymorphism and macroalbuminuria in 167 Korean patients with non-insulin dependent diabetes mellitus (NIDDM).

METHODS

The patients in the macroalbuminuria group (n = 74) represent those in whom 24 h urinary albumin excretion was above 300 mg. The patients in the normoalbuminuria group (n = 93) represent those in whom 24 h urinary albumin excretion was below 30 mg and serum creatinine levels were less than 1.2 mg/dl. The duration of diabetes in all patients was at least 8 years.

RESULTS

There were no significant differences in terms of age, sex, body mass index, HbA1c, total cholesterol, triglyceride, HDL-cholesterol and LDL-cholesterol between the two groups. In the macroalbuminuria group, the distribution of apo E genotypes revealed epsilon2/2 2 (2.7%), epsilon2/3 14 (18.9%), epsilon2/4 0 (0%), epsilon3/3 47 (63.5%), epsilon3/4 11 (14.9%) and epsilon4/4 0 (0%). In the normoalbuminuria group, the distribution of apo E genotypes revealed epsilon2/2 0 (0%), epsilon2/3 7 (7.5%), epsilon2/4 1 (1.1%), epsilon3/3 72 (77.4%), epsilon3/4 12 (12.9%) and epsilon4/4 1 (1.1%). There was no significant difference in the distribution of apo E genotypes between the two groups. However, there was a significant difference in the allele frequencies, epsilon2 frequency was significantly higher in macroalbuminuria group compared to normoalbuminuria group (12.2% vs 4.3%, P<0.05). Also, we compared apo E carrier frequencies between the two groups. Epsilon2 carrier frequency was significantly higher in macroalbuminuria group compared to normoalbuminuria group (21.6% vs 7.6%, P<0.05). In each group, there was no significant difference in the degree of lipid abnormalities between apo epsilon2 carrier (epsilon2/2, epsilon2/3 genotypes), epsilon3 carrier (epsilon3/3 genotype) and epsilon4 carrier (epsilon3/4, epsilon4/4 genotype).

CONCLUSION

Apo epsilon2 allele and epsilon2 carrier frequencies were significantly higher in macroalbuminuria group. These results suggest that epsilon2 allele may be associated with the development of clinical albuminuria in Korean patients with NIDDM.

Effect of dietary fish oil, vitamin E, and probucol on renal injury in the rat

Dietary fish oil, vitamin E, and probucol have been considered in a variety of human and experimental models of kidney disease. Using subtotal nephrectomized cholesterol-fed rats as a model for progressive kidney disease, we examined the effect of 5% dietary fish oil, or a combination of 5% dietary fish oil with 500 IU vitamin E/kg diet or 1% probucol on renal injury. Three-month-old Sprague Dawley rats were fed a control diet (C group) or a cholesterol supplemented (2%) diet (Ch group) containing either fish oil (FO group) or fish oil plus vitamin E (FO+E group) or fish oil plus probucol (FO+P group). After 4 weeks of dietary treatment, the right kidney was electrocoagulated and the left kidney nephrectomized. After 8 weeks, 24-hour urine was collected before sacrifice. No effect of the dietary treatments was noted on serum creatinine, blood urea nitrogen, or proteinuria, except that proteinuria was highest in FO+P group. Rats receiving the cholesterol diets had higher serum low density lipoprotein (LDL) + very low density lipoprotein (VLDL) cholesterol (P < 0.05). In contrast, rats in the FO+P group had the lowest serum total cholesterol and LDL+VLDL cholesterol among all groups. The FO group had 26% lower kidney alpha-tocopherol concentrations than the C group. However, inclusion of vitamin E in the diet (FO+E group) increased the kidney alpha-tocopherol status to a level comparable to that in the C group, whereas inclusion of probucol in fish oil diet (FO+P group) did not improve the kidney alpha-tocopherol status. Rats fed the cholesterol diet had a 2.5-fold higher glomerular segmental sclerosis (GSS) score and 1.5-fold higher glomerular macrophage (GM) subpopulation than the C group. These effects of the cholesterol diet were ameliorated by a fish oil diet (FO group: GSS by 30%, GM by 24%). The inclusion of vitamin E in the fish oil diet (FO+E group) did not further improve the GSS score or GM subpopulation. However, inclusion of probucol in fish oil diet (FO+P group) lowered the GSS score by 73% and reduced GM subpopulation by 83% compared with the Ch group. These remarkable changes can be attributed to the powerful hypocholesterolemic activity of probucol. Our findings indicate that progression of glomerular sclerosis in the rat remnant kidney model of progressive kidney disease can be significantly modulated with fish oil treatment.

Human mesangial cells express inducible macrophage scavenger receptor

BACKGROUND

Type A scavenger receptors (Scr) mediate the uptake of modified low-density lipoproteins by macrophages. The accumulation of lipids via this process is thought to lead to foam cell formation in atherosclerotic plaques. Human mesangial cells (HMCs) have not been previously shown to express Scr in normal culture. We therefore investigated whether there is an inducible form of Scr in a human mesangial cell line (HMCL).

METHODS

Scr activity was analyzed by cellular uptake of fluorescently labeled acetylated low-density lipoprotein using a flow cytometer. Scr mRNA expression was examined using reverse transcription-polymerase chain reaction, followed by Southern blotting. To investigate the molecular mechanism of Scr expression, several reporter gene constructs were designed. The first contained a full Scr promoter, the second a part of the Scr promoter that has both AP-1 and ets transcription factor binding sites. Other constructs were identical to the second, except that they contained either AP-1 or ets motif mutations.

RESULTS

Phorbol 12-Myristate 13-acetate (PMA) and angiotensin II (Ang II) increased both the percentage of Scr-positive cells and the Scr mean fluorescence intensity. PMA and Ang II also increased Scr mRNA and promoter activity in a time- and dose-responsive manner. Protein kinase C and calmodulin transduction pathways were involved in Scr up-regulation induced by PMA and Ang II. Additionally, a serine/threonine kinase was involved in PMA stimulation. Functional analysis showed that both AP-1 and ets motifs were specific response elements to PMA stimulation in HMCLs.

CONCLUSIONS

This study suggests that HMCs may express an inducible Scr, by which cells can acquire lipids and convert to foam cells in developing glomerulosclerosis.

Atherogenic lipoproteins and tyrosine kinase mitogenic signaling in mesangial cells

BACKGROUND

Mesangial hypercellularity is a critical early histopathological finding seen in human and experimental glomerular diseases. Hyperlipidemia and the glomerular deposition of atherogenic lipoproteins [for example, low-density lipoprotein (LDL) and its oxidized variants, minimally oxidized/modified LDL (mm-LDL)] are commonly associated with mesangial hypercellularity and the development of glomerular disease. This article reviews signal transduction pathways involved in cell proliferation and provides evidence for the participation of atherogenic lipoproteins in intracellular signaling pathways for mesangial cell proliferation. The mitogenic intracellular signaling pathways are regulated by the activation of a series of transmembrane and cytoplasmic protein tyrosine kinases that converge into the activation of Ras and downstream mitogen-activated protein (MAP) kinase. Activated MAP kinase, through translocating into the nucleus and the activation of various transcription factors and proto-oncogenes, regulates cellular proliferation.

METHODS

Murine mesangial cells were stimulated with LDL and mm-LDL and were analyzed for the tyrosine kinase activity, phosphorylation of membrane proteins, activation of Ras and MAP kinase, and cell proliferation.

RESULTS

The results indicated that the stimulation of mesangial cells with LDL and, with greater activity, mm-LDL induced the phosphorylation of membrane platelet-derived growth factor (PDGF) and epidermal growth factor (EGF) receptors, activated Ras, and resulted in sustained (up to 24 hr) activation of MAP kinase. LDL/mm-LDL-mediated mesangial cell proliferation and MAP kinase activation were dependent on the activation of tyrosine kinases.

CONCLUSIONS

We suggest that the accumulation of LDL and more potently its oxidized forms within the glomerulus, through the activation of membrane receptor tyrosine kinases, activate the Ras and MAP kinase signaling cascade leading to DNA synthesis and subsequent cell proliferation.

Effect of inhibition of cholesterol synthetic pathway on the activation of Ras and MAP kinase in mesangial cells

Intermediary metabolites of cholesterol synthetic pathway are involved in cell proliferation. Lovastatin, an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase, blocks mevalonate synthesis, and has been shown to inhibit mesangial cell proliferation associated with diverse glomerular diseases. Since inhibition of farnesylation and plasma membrane anchorage of the Ras proteins is one suggested mechanism by which lovastatin prevents cellular proliferation, we investigated the effect of lovastatin and key mevalonate metabolites on the activation of mitogen-activated protein kinase (MAP kinase) and Ras in murine glomerular mesangial cells. The preincubation of mesangial cells with lovastatin inhibited the activation of MAP kinase stimulated by either FBS, PDGF, or EGF. Mevalonic acid and farnesyl-pyrophosphate, but not cholesterol or LDL, significantly prevented lovastatin-induced inhibition of agonist-stimulated MAP kinase. Lovastatin inhibited agonist-induced activation of Ras, and mevalonic acid and farnesylpyrophosphate antagonized this effect. Parallel to the MAP kinase and Ras data, lovastatin suppressed cell growth stimulated by serum, and mevalonic acid and farnesylpyrophosphate prevented lovastatin-mediated inhibition of cellular growth. These results suggest that lovastatin, by inhibiting the synthesis of farnesol, a key isoprenoid metabolite of mevalonate, modulates Ras-mediated cell signaling events associated with mesangial cell proliferation.

Effects of multidisciplinary case management in patients with chronic renal insufficiency

PURPOSE

Though case management has been recommended to improve the outcomes of patients with costly or morbid conditions, it has seldom been studied in controlled trials. We performed a randomized, controlled clinical trial of an intensive, multidisciplinary case management program for patients with chronic renal insufficiency and followed patients for 5 years.

PATIENTS AND METHODS

We enrolled 437 primary-care patients (73% of those eligible) with chronic renal insufficiency (estimated creatinine clearance consistently < 50 mL/min with the last serum creatinine level > 1.4 mg/dL) who were attending an urban academic general internal medicine practice. The intensive case management, administered during the first 2 years after enrollment, consisted of mandatory repeated consultations in a nephrology case management clinic staffed by two nephrologists, a renal nurse, a renal dietitian, and a social worker. Control patients received usual care. Primary outcome measurements included serum creatinine level, estimated creatinine clearance, health services use, and mortality in the 5 years after enrollment. Secondary measures included use of renal sparing and potentially nephrotoxic drugs.

RESULTS

There were no differences in renal function, health services use, or mortality in the first, second, or third through fifth years after enrollment. There were significantly more outpatient visits among intervention patients, mainly because of the added visits to the nephrology case management clinic. There were also no significant differences in the use of renal sparing or selected potentially nephrotoxic drugs. The annual direct costs of the intervention were $89,355 ($484 per intervention patient).

CONCLUSION

This intensive, multidisciplinary case-management intervention had no effect on the outcomes of care among primary-care patients with established chronic renal insufficiency. Such expensive and intrusive interventions, despite representing state-of-the-art care, should be tested prospectively before being widely introduced into practice.

Role of dyslipidemia in the progression of chronic renal disease

The connection between lipids and the rate of progression of chronic renal disease was retrospectively examined in 70 patients who were divided into 2 groups according to their baseline creatinine clearance (CCr): Group 1 (Gp1) contained 30 patients with CCr 60-40 mL/min followed for 40.0 +/- 13.3 months; Group 2 (G2) contained 40 patients with CCr 39-15 mL/min followed for 39.0 +/- 18.2 months. The following parameters were considered: basal and final CCr proteinuria per unit of CCr (UProt/CCr); the difference between final and basal UProt/CCr (delta UProt/CCr); the change in CCr/month (delta CCr); baseline triglycerides (TG), total (TC), HDL (HDLC) and LDL (LDLC) cholesterol, Apo AI, Apo B, Lp(a). Besides in basal CCr the 2 groups significantly differed in the final CCr, final UProt/CCr, delta UProt/CCr, delta CCr. No differences were observed concerning lipid parameters except for Lp(a) (G1 14.8 +/- 13.6, G2 28.7 +/- 27.4 mg/dL; p < 0.05). Baseline TG (G1 184.1 +/- 61.3, G2 187.5 +/- 72.1 mg/dL) and Apo B (only G2 1.05 +/- 0.32 g/L) were significantly higher than normal subjects and the Apo AI/Apo B ratio (G1 1.42 +/- 0.43, G2 1.33 +/- 0.45) were significantly lower than in normal subjects. delta CCr, while inversely correlated in both groups with delta UProt/CCr (p < 0.01), only in G2 did it correlate directly with the Apo AI/Apo B ratio (p < 0.05) and inversely with Apo B and LDLC (p < 0.05). Although a correlation between Lp(a) and delta CCr was not found, 20/22 patients (3/5 G1, 17/17 G2) with a level > 30 mg% ran a progressive course. A natural progression of CRI, heralded by an increasing UProt, is highly frequent when baseline CCr is < 40 mL/min; only then lipids seem to add a burden to the renal damage.

Uptake and metabolism of lipoprotein-X in mesangial cells

Progressive glomerulosclerosis is a major complication in patients with familial lecithin:cholesterol acyltransferase (LCAT) deficiency. The lack of LCAT activity results in the accumulation of an abnormal lipoprotein, lipoprotein-X (Lp-X), in the plasma of these patients. Lipoprotein-X contains high levels of unesterified cholesterol and phosphatidylcholine. Lp-X may play a role in the accumulation of lipids in the kidney, which in turn may lead to glomerulosclerosis. The objective of this study is to examine the uptake and metabolism of Lp-X by rat mesangial cells. Our results suggest that Lp-X is taken up by mesangial cells and that the lipids in Lp-X are metabolized. Lysosomes containing unesterified cholesterol and phosphatidylcholine, in a molar ratio similar to Lp-X, were synthesized to investigate the roles individual apolipoproteins (apo CI, II, III and E) play in the uptake of Lp-X. Both apo CI and CIII inhibited its uptake while apo CII (1.5 fold) and E (4 fold) stimulated the uptake of Lp-X. Very low density lipoprotein (VLDL) and low density lipoprotein (LDL) inhibited Lp-X uptake by mesangial cells. However, at higher concentrations of high density lipoprotein (HDL), the uptake of Lp-X was stimulated. Proteoglycans have an important role in regulating the uptake of Lp-X, while cytoskeleton-dependent phagocytosis and the scavenger receptor do not appear to be involved.

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.

Abnormal lipid metabolism and renal disorders

Abnormal renal diseases including nephrotic syndrome and chronic renal failure are associated with hyperlipidemia, significance of abnormal lipid metabolism has been thought to be limited in some inherited renal diseases. However, recent studies have postulated that glomerulosclerosis is induced by hyperlipidemia and is in common with atherosclerosis. This involvement is found in the progressive renal disorders, e.g., focal glomerular sclerosis, diabetic nephropathy and glycogen storage disease. Interaction between macrophages and mesangial cells may play an important role in such conditions. This evidence is supported by experimental models with hyperlipidemia. On the other hand, discovery and new hereditary metabolic disorders, such as type III hyperlipoproteinemia and lipoprotein glomerulopathy, shows that apolipoprotein (apo) E abnormalities are responsible for the glomerular lesions. Especially, lipoprotein glomerulopathy has specific features different from those of lipid-induced renal diseases. In this disease, apo E Sendai which results from new substitution (Arginine 145-->Proline) may induce intraglomerular lipoprotein thrombi characteristic of lipoprotein glomerulopathy.

Antihypertensive drug treatment in chronic renal allograft rejection in the rat. Effect on structure and function

To gain insight into the contribution of immunologic and hemodynamic factors in the progressive demise of structure and function in chronic renal allograft dysfunction, we studied the histological changes, the immunostainable glomerular anionic sites, and glomerular capillary hydrostatic pressures of rat renal allografts with chronic rejection. Recipient animals were left untreated, received 8 weeks of treatment with the immunosuppressive drug cyclosporine, or received antihypertensive drugs consisting of the combination of reserpine, hydralazine and hydrochlorothiazide, the angiotensin-converting enzyme inhibitor cilazapril, or the angiotensin II receptor blocker L-158,809. Grafts in untreated recipients developed chronic interstitial inflammation, as well as vascular and glomerular lesions consistent with chronic rejection. These lesions were associated with immunohistochemical loss of the negatively charged heparan sulfate proteoglycan side chain. All treatment regimens decreased the systemic and glomerular capillary pressures and were associated with no loss of function, decreased proteinuria, and a tendency to improved graft function. Cyclosporine prevented all histological manifestations of rejection, and antihypertensive drugs decreased the extent of glomerular mesangiolysis and glomerulosclerosis; L-158,809 and cilazapril also inhibited graft atherosclerosis and tubular atrophy. We conclude that chronic rejection is primarily an immune-mediated process, but hemodynamic and angiotensin II-mediated effects may play a pivotal role in the expression of immune-mediated lesions.

ACTH lowers serum lipids in steroid-treated hyperlipemic patients with kidney disease

The mechanisms behind secondary hyperlipidemia in patients with various chronic inflammatory diseases are not known in detail. We have recently demonstrated that ACTH exerts strong hypolipidemic effects in healthy volunteers. To test the clinical relevance of this finding, we administrated ACTH during three weeks to nine hyperlipidemic steroid-treated patients with kidney disease. Before administration of ACTH 1-24, plasma ACTH concentrations were low. Treatment with ACTH led to 20 to 50% reductions in serum concentrations of triglycerides, cholesterol, LDL cholesterol and Apo B as well as of Lp(a). HDL cholesterol and Apo A1 concentrations increased by 10 to 25%. HL activity in postheparin plasma decreased by about 40% and LPL activity, which was initially low, increased by about 140%. The effects of ACTH were similar in kidney transplant recipients and in patients with inflammatory kidney disease. Our results indicate that hyperlipidemia in steroid treated patients with kidney disease may at least partly be due to iatrogenic ACTH deficiency.

The changing course of diabetic nephropathy: low-density lipoprotein cholesterol and blood pressure correlate with regression of proteinuria

Diabetic nephropathy (DN) as manifested by persistent and clinically evident proteinuria, has long been considered an irreversible process that predicts a rapid decline in renal function. The observation of reversal of DN in several individuals enrolled in a prospective study of the natural course of diabetes complications challenged this view and led to the current investigation into the correlates of such regression of proteinuria. DN was defined as a median albumin excretion rate (AER) over 200 microg/min in two or three urine collections obtained at baseline, and again at 2 and 4 years of follow-up. Among 658 individuals with childhood-onset insulin-dependent diabetes mellitus (IDDM), 146 had DN at baseline. Nine subsequently died without renal failure, and 13 were lost to follow-up. Of the 124 subjects with at least survey follow-up data, 32 (24%) developed renal failure, and 78 of the remaining 92 provided full quantitative data. AER decreased by > or = 10-fold into the microalbuminuric (20 to 200 microg/min) or normal range (<20 microg/min) in 7 of these individuals and are called "regressors of proteinuria." Compared with the remaining 71 subjects, the strongest correlate of regression of proteinuria was an improvement in fasting plasma low-density lipoprotein cholesterol (LDL-C) in the 7 regressors (P < 0.008). Improved glycemic control was not a significant predictor of improved AER. Five of the 7 individuals with improved AER had a baseline median AER below 500 microg/min. When the 7 regressors of proteinuria were combined with an additional 38 individuals who also experienced smaller decreases in median AER, such improvement was associated with a more favorable systolic (or diastolic) blood pressure (BP) change (P < 0.01), and a decrease in plasma LDL-C level (P = 0.01). These data suggest that proteinuria in DN may substantially regress in approximately 6% and improve in at least 34% of individuals with IDDM over a 4-year period, often in association with a decrease in plasma LDL-C concentration or stabilization or improvement in BP. Furthermore, the data suggest that the nonreversibility threshold for diabetic nephropathy may be higher (500 mg/min) than previously reported (200 microg/min).

The role of proteinuria in the progression of chronic renal failure

The cause of the relentless progression of chronic renal failure of diverse origins remains unknown and is likely to be multifactorial. Numerous studies have now demonstrated a correlation between the degree of proteinuria and the rate progression of renal failure, which has led to the hypothesis that proteinuria may be an independent mediator of progression rather than simply being a marker of glomerular dysfunction. This article reviews the evidence underlying this hypothesis and the mechanisms by which particular proteins may cause renal pathology. The abnormal filtration of proteins across the glomerular basement membrane will bring them into contact with the mesangium and with the tubular cells. There is evidence to support a role of lipoproteins on mesangial cell function, which ultimately could contribute to glomerular sclerosis. The proximal tubular cells reabsorb proteins from the tubular fluid, which leaves them particularly vulnerable to any adverse effects proteins may have. It has been postulated that the sheer amount of protein to be metabolized by these cells may overwhelm the lysosomes and result in leakage of cytotoxic enzymes into the cells. In addition, the increased metabolism of proteins may result in production of ammonia, which can mediate inflammation through activation of complement. Specific proteins that have been shown to be cytotoxic are transferrin/iron, low-density lipoprotein, and complement components, all of which appear in the urine in proteinuric states. Other specific proteins have been shown to stimulate production of cytokines, chemoattractants, and matrix proteins by tubular cells and thus may stimulate interstitial inflammation and scarring. The mechanisms by which the presence of proteins in the tubular fluid alters tubular cell biology is yet to be determined.

Regulation of mesangial chloride channels by insulin and glucose: role in diabetic nephropathy

1. In response to vasoactive peptides (e.g. angiotensin II (AngII), vasopressin, endothelin-1, platelet-activating factor), glomerular mesangial cell contraction is mediated through activation of a Ca2+-dependent Cl- conductance that, in turn, promotes membrane depolarization and voltage-activated Ca2+ entry. 2. Using patch clamp technology, our laboratory was the first to characterize a candidate Ca2+-dependent, 4 pS Cl- channel that is stimulated by vasoactive peptides in cultured rat mesangial cells. In the absence of extracellular insulin, the activation of Cl- channels by AngII is abolished. We find that Cl- channel sensitivity to intracellular Ca2+ and the membrane density of AngII receptors is also dependent on the presence of insulin. 3. Our studies also show that high extracellular glucose interferes with mesangial cell IP3 generation and Cl- channel stimulation. Importantly, we find that the insulin-dependency of Cl- channels occurs within the range of plasma insulin concentrations observed in normal, obese, hypertensive and diabetic humans (i.e. 1-100 mu U/mL). Similarly, normal regulation of Cl- channel activity is also modulated by glucose concentrations commonly observed in the plasma of diabetic humans (5-30 mmol/L). 4. There is substantial evidence, both in diabetic humans and animal models, that the provision of insulin and improved glycaemic control corrects or prevents glomerular hyperfiltration. The requirement for normal insulin and glucose levels, for the proper regulation of the 4 pS Cl- channel, provides a mechanism for impaired Ca2+ uptake and contraction observed in glomerular mesangial cells in association with insulin deficiency and hyperglocaemia.

Chronic renal transplant loss

Chronic rejection results from recurrent episodes of subclinical or clinically evident acute rejection, with or without involvement of chronic rejection-specific allogeneic immune mechanisms. The tissue damage occurs over a prolonged period of time, which allows the emergence of antigen-independent tissue repair mechanisms and intrarenal adaptations in response to progressive loss of renal mass (Fig. 1). The combination of these mechanisms leads, very likely, to the tissue remodeling of chronic rejection. The heterogeneous expression of chronic rejection may result from different types and specificities of allogeneic immune reactions as well as different contributions of antigen-independent factors that modulate the antigen-dependent tissue responses to injury. The extent to which these mechanisms participate in the overall picture is presently unknown as immunological parameters are not measured routinely in the follow-up of patients with chronic graft dysfunction. Furthermore, some grafts may undergo tissue remodeling as a consequence of predominantly antigen-independent mechanisms. Therefore, the term chronic allograft dysfunction may clinically be preferable over chronic rejection to describe the gradual decline in graft function months or years after transplantation in the absence of a well-defined mechanism or an accepted treatment.