Oxidation of low density lipoprotein by mesangial cells may promote glomerular injury

New potentials for 3-hydroxy-3-methyl-glutaryl-coenzymeA reductase inhibitors: Possible applications in retarding diabetic complications

The prevalence of diabetes mellitus is increasing all over the world and it is apparent that treatment of diabetic complications has the same importance as primary diabetes treatment and glycemic control. Diabetic complications occur as a result of prolonged hyperglycemia and its consequences, such as advanced glycation end products and reactive oxygen species. Impairment of lipid profile is also contributed to worsening diabetic complications. Therefore, it seems that the application of lipid-lowering agents may have positive effects on reversing diabetic complications besides glycemic control. Statins, a group of lipid-lowering compounds, have been shown to exert antioxidant, immunomodulatory, anti-inflammatory, and antiproliferative properties beyond their lipid-lowering effects. Furthermore, they have been reported to improve diabetic complications with different pathways. In this review, we will discuss the clinical importance, molecular biology of the most important microvascular/macrovascular diabetic complications, possible application of statins and their mechanism of action in retarding these complications.

Osteopontin deficiency reduces kidney damage from hypercholesterolemia in Apolipoprotein E-deficient mice

Hypercholesterolemia is a well-established risk factor for kidney injury, which can lead to chronic kidney disease (CKD). Osteopontin (OPN) has been implicated in the pathology of several renal conditions. This study was to evaluate the effects of OPN on hypercholesterolemia induced renal dysfunction. Eight-week-old male mice were divided into 4 groups: apolipoprotein E knockout (ApoE^−/−) and ApoE/OPN knockout (ApoE^−/−/OPN^−/−) mice fed a normal diet (ND) or high cholesterol diet (HD). After 4 weeks, Periodic acid-Schiff (PAS) and oil red O staining revealed excessive lipid deposition in the glomeruli of ApoE^−/−HD mice, however, significantly suppressed in ApoE^−/−/OPN^−/−HD mice. Lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) expression was lower in the glomeruli of ApoE^−/−/OPN^−/−HD mice than ApoE^−/−HD mice. In vitro study, primary mesangial cells were incubated with recombinant mouse OPN (rmOPN). RmOPN induced LOX-1 mRNA and protein expression in primary mesangial cells. Pre-treatment with an ERK inhibitor suppressed the LOX-1 gene expression induced by rmOPN. These results indicate that OPN contributes to kidney damage in hypercholesterolemia and suggest that inhibition of OPN may provide a potential therapeutic target for the prevention of hypercholesterolemia.

High levels of oxidized LDL in circulating immune complexes are associated with increased odds of developing abnormal albuminuria in Type 1 diabetes

BACKGROUND

Modified low-density lipoprotein (LDL) immune complexes (IC) have proinflammatory properties and play a role in albuminuria development.

METHODS

We measured oxidized LDL (oxLDL) and advanced glycation end-product (AGE)-LDL in IC isolated from sera of Type 1 diabetic subjects followed for 14-20 years and studied their association with abnormal albuminuria. Patients with albumin excretion rates (AER)<40 mg/24 h at baseline and follow-up (n=302) were deemed resistant to developing abnormal albuminuria. Patients with AER<40 mg/24 h at baseline whose AER levels progressed to >40 mg/24 h were considered prone to abnormal albuminuria (n=185), those who progress to AER>299 mg/24 h were considered as having macroalbuminuria (n=57). The odds of developing abnormal albuminuria were estimated by logistic regression based on natural log-transformed levels of oxLDL and AGE-LDL in IC and stratified by baseline AER decile.

RESULTS

OxLDL and AGE-LDL were significantly higher in IC isolated from patients progressing to abnormal albuminuria. In unadjusted conditional logistic analysis, an increase of 1 SD in oxLDL and AGE-LDL levels in IC significantly increased the odds ratio (OR) for development of macroalbuminuria, respectively, by a factor of 2.5 and 1.8 (P<0.001, P=0.008). The increased odds of developing macroalbuminuria remained significant when adjusted for treatment group, diabetes duration, retinopathy, baseline hemoglobin A1c and LDL (OR=2.5 and 1.8, respectively, P<0.01).

CONCLUSION

Higher levels of oxLDL and AGE-LDL in circulating IC were associated with increased odds to develop abnormal albuminuria.

Interleukin-1β enhances the intracellular accumulation of cholesterol by up-regulating the expression of low-density lipoprotein receptor and 3-hydroxy-3-methylglutaryl coenzyme A reductase in podocytes

The aim of this article is to investigate whether interleukin-1β (IL-1β) could regulate the intracellular accumulation of cholesterol and the expression of lipid-metabolism-related regulators in podocytes in vitro and the potential mechanisms. Podocytes were treated with 200 μg/ml of low-density protein (LDL), 20 ng/ml of IL-1β, or 200 μg/ml of LDL plus 5-20 ng/ml of IL-1β for 24 h in vitro. The contents of intracellular cholesterol were determined by enzymatic assays and Oil Red O staining. The levels of LDL receptor (LDLr), 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, sterol regulatory element binding protein 2 (SREBP-2), SREBP cleavage activating protein (SCAP), and insulin-induced gene-1 (Insig-1) expression were characterized by real-time polymerase chain reaction (RT-PCR) and Western blot assays. Treatment with IL-1β or LDL alone increased the contents of intracellular cholesterol (P < 0.05 for both) and lipid droplets, and treatment with both IL-1β and LDL further increased the accumulation of intracellular cholesterol in podocytes (P < 0.05 vs. LDL alone). While loading with LDL significantly inhibited the expression of LDLr, HMG-CoA reductase, nuclear SREBP-2 (nSREBP-2), SCAP, and Insig-1 by 40-62% treatment with IL-1β enhanced the expression of LDLr, HMG-CoA reductase and nSREBP-2, but not Insig-1, in podocytes (P < 0.05 vs. control). Treatment with both LDL and IL-1β significantly increased the levels of LDLr and HMG-CoA reductase expression and the ratio of SCAP to Insig-1, as compared with that in the LDL-treated podocytes (P < 0.05 vs. LDL alone). Our data indicated that IL-1β mitigated the LDL-triggered SCAP-SREBP-2-mediated feedback inhibition on the expression of LDLr and HMG-CoA reductase, leading to the intracellular accumulation of LDL-cholesterol in podocytes in vitro.

Citrus bergamia Risso & Poiteau juice protects against renal injury of diet-induced hypercholesterolemia in rats

The present study was designed to evaluate the protective effect of treatment with Citrus bergamia juice (1 mL/day, for 30 days) against hypercholesterolemic diet-induced renal injury in rat.C. bergamia juice provoked a significant reduction in the plasma levels of cholesterol, triglycerides and LDL, and an increase in HDL levels, versus hyperlipidemic controls (p < 0.05). Plasma creatinine levels, measured to assess renal glomerular function, did not change compared with hyperlipidemic controls (0.37 +/- 0.11 mg/dL and 0.32 +/- 0.10 mg/dL, respectively). Moreover, in vivo lipid peroxidation was measured in kidney homogenate; C. bergamia juice administration significantly decreased MDA levels elevations compared with hyperlipidemic controls (4.10 +/- 0.10 nmol/mg protein and 4.78 +/- 0.15 nmol/mg protein, respectively).Histological observations of the kidney supported the biochemical data and indicated a protective effect of C. bergamia juice on the development of renal damage in hypercholesterolemic rats.The antioxidant potential of C. bergamia juice was examined in two in vitro systems: in the DPPH test the juice showed a noticeable effect on scavenging free radicals (IC(50) = 25.01 +/- 0.70 +/-L); in the reducing power assay it showed a strong activity, too (1.44 +/- 0.01 ASE/mL).These findings suggest that C. bergamia juice has a protective role in hypercholesterolemic diet-induced renal damage, which may be attributed to its antioxidant properties.

CXCL16 and oxLDL are induced in the onset of diabetic nephropathy

Diabetic nephropathy (DN) is a major cause of end-stage renal failure worldwide. Oxidative stress has been reported to be a major culprit of the disease and increased oxidized low density lipoprotein (oxLDL) immune complexes were found in patients with DN. In this study we present evidence, that CXCL16 is the main receptor in human podocytes mediating the uptake of oxLDL. In contrast, in primary tubular cells CD36 was mainly involved in the uptake of oxLDL. We further demonstrate that oxLDL down-regulated alpha(3)-integrin expression and increased the production of fibronectin in human podocytes. In addition, oxLDL uptake induced the production of reactive oxygen species (ROS) in human podocytes. Inhibition of oxLDL uptake by CXCL16 blocking antibodies abrogated the fibronectin and ROS production and restored alpha(3) integrin expression in human podocytes. Furthermore we present evidence that hyperglycaemic conditions increased CXCL16 and reduced ADAM10 expression in podocytes. Importantly, in streptozotocin-induced diabetic mice an early induction of CXCL16 was accompanied by higher levels of oxLDL. Finally immunofluorescence analysis in biopsies of patients with DN revealed increased glomerular CXCL16 expression, which was paralleled by high levels of oxLDL. In summary, regulation of CXCL16, ADAM10 and oxLDL expression may be an early event in the onset of DN and therefore all three proteins may represent potential new targets for diagnosis and therapeutic intervention in DN.

Glucose regulation of beta-defensin-1 mRNA in human renal cells

We previously showed that beta-defensin-1 (BD-1), an anti-microbial peptide, is up-regulated during progressive hyperglycemia in the kidneys of the GK rat [R.A. Page, C.A. Morris, J.D. Williams, C.J. von Ruhland, A.N. Malik, Isolation of diabetes-associated kidney genes using differential display, Biochem. Biophys. Res. Commun. 232 (1997) 49-53, R.A. Page, A.N. Malik, Elevated levels of beta-defensin-1 mRNA in diabetic kidneys of GK rats, Biochem. Biophys. Res. Commun. 310 (2003) 513-521]. In this paper, we show that human beta-defensin-1 (hBD-1) mRNA is directly up-regulated by glucose in cultured human renal cells. hBD-1 mRNA levels increased by approximately 7-fold and approximately 4-fold in human embryonic kidney (HEK) cells and human mesangial cells (HMC) grown in 25mM glucose for four days, as determined by quantitative real-time PCR. Immunofluorescence showed that the hBD1 protein is located in the cytoplasm of HEK cells and transfected HMCs. The highest levels of hBD-1 mRNA were found in the kidney compared with 21 other human tissues. The increased expression of hBD-1 mRNA in cultured HMCs in high glucose suggests a role for hBD-1 in the molecular pathways induced during hyperglycemia.

Antioxidants in the Prevention of Renal Disease

Reactive oxygen species (ROS) play a key role in the pathophysiological processes of renal diseases. The cellular damage is mediated by an alteration in the antioxidant status, which increases the concentration of ROS in the stationary state (oxidative stress). Oxidative stress mediates a wide range of renal impairments, from acute renal failure, rhabdomyolysis, obstructive nephropathy, hyperlipidemia, and glomerular damage to chronic renal failure and hemodialysis. Therefore, interventions favoring the scavenging and/or depuration of ROS (dietary and pharmacological antioxidants) should attenuate or prevent the oxidative stress, thereby mitigating against the subsequent renal damage.

Group IVA phospholipase A2-mediated production of fibronectin by oxidized LDL in mesangial cells

The deposition of atherogenic lipoproteins such as oxidized low-density lipoprotein (oxLDL) within the mesangium is involved in the overproduction of extracellular matrix proteins, a key event in the progression of glomerular diseases including glomerulosclerosis. To clarify the mechanisms underlying the oxLDL-induced production of extracellular matrix proteins, we examined the possible involvement of group IVA phospholipase A(2) (PLA(2)) using human mesangial cells and group IVA PLA(2)-deficient mouse mesangial cells. oxLDL accelerated the production of fibronectin and collagen (type IV), components of extracellular matrix proteins, with the preceding release of arachidonic acid. Methyl arachidonyl fluorophosphonate (MAFP), known as an inhibitor of group IVA PLA(2), markedly suppressed the oxLDL-induced production of fibronectin as well as the release of arachidonic acid, whereas it did not inhibit the production of collagen. The inhibitory effect of MAFP on the production of fibronectin was reversed by adding arachidonic acid and 12-hydroxyeicosatetraenoic acid. Furthermore, we found that in group IVA PLA(2)-deficient mouse mesangial cells, the production of fibronectin in response to oxLDL was weak as compared with that in wild-type cells. However, the production by oxLDL of collagen was not suppressed in the group IVA PLA(2)-deficient cells. These findings suggest that group IVA PLA(2) is involved in the production of fibronectin in oxLDL-stimulated mesangial cells.

Management of Dyslipidemia in Special Populations

Dyslipidemia is a significant contributor to morbidity and mortality in the industrialized world. Because it is often intertwined with other medical conditions, its management is becoming progressively more complex. Populations that pose a particular challenge to clinicians include diabetic patients, children and adolescents, elderly persons, transplant patients, patients with the human immunodeficiency virus, and patients with chronic kidney disease. When establishing lipid goals, it is imperative to have a thorough understanding of the evidence, or lack thereof, supporting the use of lipid-lowering agents among these patients. To maximize the benefits and minimize the risks of pharmacological intervention, clinicians must consider not only the unique alterations in the lipid profile of the aforementioned populations but also individual changes in patients' pharmacokinetic and pharmacodynamic parameters, as well as the potential for drug-drug and drug-disease interactions.

Oxidative stress and protective effects of polyphenols: comparative studies in human and rodent kidney. A review

Reactive oxygen species (ROS) play a key role in the pathophysiological processes of a wide range of renal diseases. Thus, antioxidants are expected to decrease the vulnerability of the kidney to oxidative challenges. Polyphenols, particularly abundant in red wine, could act as ROS scavengers, iron chelators and enzyme modulators. In addition, chronic exposure to moderate amounts of ethanol results in increased activity of the renal antioxidant enzymes, further supporting a renoprotective effect of red wine based on its antioxidant properties. An enhancement of plasma antioxidant capacity following red wine consumption has been reported both in man and rodents, thereby providing a contributory factor to its renoprotective effect because the kidney is a highly perfused organ. Although phenol concentration of red wine does not influence the activity of antioxidant enzymes of the kidney, the concentration of these compounds is negatively correlated with tissue lipid peroxidation, assessed by thiobarbituric acid reactive substances, and positively correlated with the antioxidant capacity of plasma. Moreover, amelioration of myoglobinuric renal damage was found in rats following chronic exposure to flavonol-rich red wine. Also, pretreatment with resveratrol, or other red wine polyphenols, decreased kidney damage caused by ischaemia-reperfusion. The aim of the present review is to examine the pathophysiological basis of the renoprotective effect of red wine in man and rodents, based on functional, biochemical and ultrastructural evidence.

The role of statins in chronic kidney disease

Chronic kidney disease is associated with cardiovascular event rates that are at least as high as in patients with established atherosclerotic cardiovascular disease or in those with diabetes mellitus. Chronic kidney disease is therefore considered a cardiovascular disease risk equivalent. Treatment of dyslipidemia, which is very common in this population and reflects the pattern seen in the metabolic syndrome, reduces cardiovascular events in patients with chronic kidney disease. Thus, patients with chronic kidney disease should be evaluated and treated for dyslipidemia. Dyslipidemia is a risk factor for the development of impaired kidney function. Dyslipidemia is also associated with progressive renal disease in subjects with no overt renal disease, as well as those with diabetic and nondiabetic kidney disease. Although definitive randomized controlled trials are lacking, the collective evidence suggests that treatment of dyslipidemia is associated with less decline in renal function. The use of potent statins in high doses can lead to transient proteinuria via impairment of proximal tubular receptor--mediated endocytosis, in a dose-dependent manner. Over the long term, however, the use of statins results in a reduction in proteinuria and in the rate of decline of renal function. Several large definitive trials that are currently underway to examine the safety and efficacy of statins in cardiovascular and renal protection should provide more definitive answers on the role of these drugs in this very high risk population.

9HODE stimulates cell proliferation and extracellular matrix synthesis in human mesangial cells via PPARgamma

Plasma oxidized low-density lipoprotein (OX-LDL) levels are elevated in patients with renal diseases, including diabetic nephropathy. We examined effects of OX-LDL on cell proliferation and extracellular matrix (ECM) production by using normal human mesangial cells. Furthermore, we examined possible involvement of peroxisome proliferator-activated receptor gamma (PPARgamma). Mesangial cell proliferation with OX-LDL, 9-hydroxy-10,12-octadecadienoic acid (9HODE), and 13-hydroxy-9,11-octadecadienoic acid (13HODE), the major components of OX-LDL, were determined by 5-bromo-2'-deoxyuridine (BrdU) or 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyl tetrazolium bromide (MTT) incorporation. The effect of OX-LDL on mesangial cell proliferation with PD98059 pretreatment was determined by BrdU incorporation. Type IV collagen, fibronectin, and PPARgamma expression with OX-LDL or 9HODE or 13HODE was determined by Western blotting. Type IV collagen expression with antisense oligonucleotide against PPARgamma pretreatment was also determined by Western blotting. The effect of PD98059 pretreatment on PPARgamma expression was determined by Western blotting. In mesangial cells exposed to isolated OX-LDL from human plasma, BrdU incorporation was increased, and this increase was deleted by PD98059. Type IV collagen expression was significantly increased by OX-LDL. 9HODE and 13HODE increased BrdU and MTT incorporation into mesangial cells and also increased expressions of Type IV collagen and fibronection, the major components of ECM. PPARgamma expression in mesangial cells was stimulated by 9HODE. The reduction of PPARgamma synthesis by pretreatment of antisense oligonucleotide against PPARgamma remarkably attenuated Type IV collagen synthesis induced by 9HODE. PPARgamma expression induced by 9HODE was also reduced by PD98059 pretreatment. These findings demonstrate that 9HODE, the major component of OX-LDL, stimulates cell proliferation and ECM production of human mesangial cells. In addition, the stimulatory effects are, at least in part, mediated by PPARgamma, which may exist in downstream of ERK1/2 pathway.

Hyperlipidemia aggravates renal disease in B6.ROP Os/+ mice

INTRODUCTION

Reduction of renal mass is frequently associated with progressive loss of kidney function. We examined the effects of hyperlipidemia on renal pathology and mediators of tissue damage in B6.ROP Os/+ mice, a model of reduced renal mass.

METHODS

C57BL/6 control mice and B6.ROP Os/+ mice were fed normal rodent chow or a high fat, high cholesterol (HFHC) diet for 12 weeks. Kidney function and renal pathology were assessed.

RESULTS

Hyperlipidemia led to a decline in kidney function in C57BL/6 mice. Renal pathology was characterized by an increase in glomerular matrix and cellularity, glomerular and tubulointerstitial macrophage influx, and increased tubular epithelial cell turnover. Chow-fed B6.ROP Os/+ animals demonstrated glomerular hypertrophy with an increase in mesangial matrix and cellularity that was characterized by macrophage influx and increased proliferation. The tubulointerstitium showed increased macrophages as well as tubular atrophy and dilation. Renal pathology was accompanied by an increase in blood urea nitrogen (BUN) and proteinuria. Hyperlipidemia in B6.ROP Os/+ mice resulted in increased plasma BUN compared to chow-fed B6.ROP Os/+ animals and aggravated renal pathology by further increasing glomerular matrix and glomerular hypercellularity. Glomerular hypercellularity was associated with increased expression of platelet-derived growth factor-B (PDGF B) and its receptor beta. Glomerular transforming growth factor-beta (TGF-beta) mRNA expression was increased in B6.ROP Os/+ mice, hyperlipidemic C57BL/6 mice and hyperlipidemic B6.ROP Os/+ animals compared to controls and correlated with the amount of mesangial matrix.

CONCLUSION

This study demonstrates that hyperlipidemia worsens renal pathology in B6.ROP Os/+ mice with a decline in renal function mediated at least in part through increased renal expression of the cytokines PDGF B and TGF-beta.

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.

End-stage renal failure and cardiac mortality after heart transplantation

BACKGROUND

Coronary artery disease (CAD) is the leading cause of mortality after the first year of heart transplantation. End-stage renal failure (ESRF) is more frequent because of long-term survival. Impact of ESRF on cardiac mortality in heart transplant patients is unappreciated. The hypothesis of accelerated CAD in uremic patients has been suggested.

METHODS

In Pitié La Salpêtrière hospital, 1211 heart transplants have been performed between 1982 and 2001. Thirty-three patients have reached ESRF. A case-control study was performed to identify risk factors responsible for ESRF and to appreciate the impact of ESRF on cardiac mortality.

RESULTS

In cases at 6 months, serum creatinine tended to be higher (159 +/- 31 micromol/L vs. 141 +/- 44 micromol/L, p = 0.06) and cyclosporine (CSA) dosage (mg/kg) was significantly lower (5.4 +/- 1.8 mg/kg vs. 7.7 +/- 2.7 mg/ kg, p = 0.002). Mean triglyceride level after transplantation until dialysis was significantly lower in cases (2.18 +/- 0.82 mmol/L vs. 1.48 +/- 0.62 mmol/L, p = 0.002). In cases and controls, cardiac mortality was responsible for 67% (10 of 15) and 38% (three of eight) of all deaths, respectively. High triglyceride level (> or = 2 mmol/L) was associated with cardiac mortality [p < 0.03, hazard ratio (HR) = 3.89]. Kaplan Meier cardiac free survival rates were significantly lower in cases than in controls (p < 0.03).

CONCLUSION

These data suggest that CSA nephrotoxicity could result from individually determined susceptibility and that hypertriglyceridemia may have a negative impact on renal function and cardiac mortality. The risk of cardiac mortality is increased in heart transplant patients with ESRF. The hypothesis of accelerated atherosclerosis in ESRF patients after heart transplantation leading to higher cardiac mortality incidence needs further study.

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.

Monocyte adhesion to mesangial matrix modulates cytokine and metalloproteinase production

BACKGROUND

Monocytes migrate into the glomerular mesangium during acute inflammatory renal disease, differentiate into macrophages, and may play a key role in the development and progression of glomerular scarring. Treatment strategies that inhibit monocyte infiltration ameliorate glomerular injury in animal models. Mesangial matrix contains several potential monocyte-binding domains that may contribute to monocyte entrapment and modulate cell activation.

METHODS

Adhesion of peripheral blood-derived monocytes to matrix synthesized by human mesangial cells and to individual matrix proteins was assessed by colorimetry of nuclear staining with crystal violet. Monoclonal antibodies were used to identify the cell-surface integrins and matrix ligands involved. Monocyte proliferation was assessed by 3H-thymidine incorporation and cytokine production using enzyme-linked immunosorbent assay (ELISA). Secretion of metalloproteinases and their inhibitors was determined by zymography and ELISA, respectively.

RESULTS

Monocytes bound to matrix synthesized by mesangial cells. Prestimulation of mesangial cells with tumor necrosis factor-alpha (TNF-alpha) and transforming growth factor-beta (TGF-beta) enhanced matrix fibronectin content (P < 0.001) and monocyte binding (P < 0.001). Blocking antibodies to fibronectin, as well as to the integrins very late antigen-4 (VLA-4) and VLA-5, reduced monocyte adhesion to mesangial matrix by approximately 50%. Incubation of monocytes with matrix, fibronectin, laminin and collagen IV enhanced production of interleukin-1beta (IL-1beta), interleukin-6 (IL-6), TNF-alpha and metalloproteinase-9 (MMP-9) when compared to cells incubated in plastic wells. However, there was no apparent difference in proliferation rate and no change in production of metalloproteinase inhibitors.

CONCLUSION

Monocyte activation within the glomerulus may be mediated by binding to mesangial matrix components, particularly fibronectin. Matrix-mediated activation enhances production of inflammatory cytokines and matrix-degrading enzymes.

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.

Renal damage mediated by oxidative stress: a hypothesis of protective effects of red wine

Over the last decade, oxidative stress has been implicated in the pathogenesis of a wide variety of seemingly unrelated renal diseases. Epidemiological studies have documented an association of moderate wine consumption with a decreased risk of cardiovascular and neurological diseases; however, similar studies in the kidney are still lacking. The kidney is an organ highly vulnerable to damage caused by reactive oxygen species (ROS), likely due to the abundance of polyunsaturated fatty acids in the composition of renal lipids. ROS are involved in the pathogenic mechanism of conditions such as glomerulosclerosis and tubulointerstitial fibrosis. The health benefits of moderate consumption of red wine can be partly attributed to its antioxidant properties. Indeed, the kidney antioxidant defense system is enhanced after chronic exposure to moderate amounts of wine, a response arising from the combined effects of ethanol and the nonalcoholic components, mainly polyphenols. Polyphenols behave as potent ROS scavengers and metal chelators; ethanol, in turn, modulates the activity of antioxidant enzymes. Therefore, a hypothesis that red wine causes a decreased vulnerability of the kidney to the oxidative challenges could be proposed. This view is partly supported by direct evidences indicating that wine and antioxidants isolated from red wine, as well as other antioxidants, significantly attenuate or prevent the oxidative damage to the kidney. The present hypothesis paper provides a collective body of evidence suggesting a protective role of moderate wine consumption against the production and progression of renal diseases, based on the existing concepts on the pathophysiology of kidney injury mediated by oxidative stress.

Exposure to oxidized low-density lipoprotein reduces activable Ras protein in vascular endothelial cells

Oxidized low-density lipoprotein (ox-LDL) has been shown to alter the migratory and proliferative activities of the vascular endothelial cells (EC) in response to serum and growth factors. The mechanism underlying the antiproliferative effect of ox-LDL on vascular EC has not been fully elucidated. In this report, we show that exposure of vascular EC to ox-LDL results in a marked reduction of the membrane-associated Ras protein. Further study shows that in ox-LDL-treated EC, reduction of the membrane-associated Ras protein is correlated with a reduced amount of active Ras (Ras-guanosine triphosphate), indicating that the Ras signaling pathway is attenuated. The attenuation of the Ras signaling pathway in ox-LDL-treated EC may thus be responsible for the retarded response to the mitogenic stimulation of serum and growth factors.

Renal protective effect of candesartan cilexetil in spontaneously hypercholesterolemic rats

Spontaneously hypercholesterolemic (SHC) rats exhibit hypercholesterolemia, proteinuria and focal glomerulosclerosis with age, and they finally die as a result of renal failure. In this study, the renoprotective effects of candesartan cilexetil, an angiotensin II type 1 receptor antagonist, and enalapril, an angiotensin I converting enzyme inhibitor, were examined in SHC rats. Candesartan cilexetil (0.1 and 1 mg /kg) and enalapril (10 mg/kg) were administered orally to 10-week-old SHC rats for a 6-week period. Candesartan cilexetil (1 mg/kg) and enalapril (10 mg/kg) significantly inhibited proteinuria and hypercholesterolemia to a similar extent. In untreated 16-week-old SHC rats, glomerulosclerosis, basophilic change, cast formation and interstitial mononuclear cell infiltration were observed. Candesartan cilexetil (1 mg/kg) inhibited all of these histological changes. Enalapril inhibited glomerulosclerosis and cast formation. These results show that candesartan cilexetil and enalapril have renal protective effects in SHC rats. Thus, angiotensin II might play an important role in renal pathogenesis in a model of focal glomerulosclerosis with hypercholesterolemia.

IGF-1 induces foam cell formation in rat glomerular mesangial cells

When rat glomerular mesangial cells (MCs) are cultured with IGF-1 they accumulate intracellular lipid and take on foam cell morphology. These changes were characterized by electron microscopy and Nile red staining. To define the mechanism responsible for IGF-1-mediated lipid uptake, MCs were evaluated for endocytosis, scavenger receptor activity, and receptor-mediated uptake by the LDL receptor. Lipid accumulation was markedly increased when MCs were cultured with IGF. The primary route of uptake was through enhanced endocytosis. Lipid-laden MCs have decreased phagocytic capacity and disrupted cytoskeletons. These data show that IGF-1 induces MC to take on a foam cell morphology and that lipid-laden MCs have impaired phagocytic function.

Serum lipid metabolism abnormalities and change in lipoprotein contents in patients with advanced-stage renal disease

BACKGROUND

Arteriosclerosis is the major cause of death in patients with chronic renal failure. There is much interest in the lipid metabolism of patients treated with hemodialysis.

METHODS

We analyzed low-density lipoproteins (LDL) and high-density lipoproteins (HDL) in chronic renal failure (CRF) patients according to patients on hemodialysis (HD), patients with diabetic nephropathy before initiation of dialysis (DN), and patients with chronic glomerulonephritis in the conservative stage (CGN); and compared the lipid metabolic abnormalities in patients on hemodialysis and those not yet on hemodialysis. We also analyzed the qualitative abnormalities of LDL and HDL and their relationship with the pathological stages.

RESULTS

Electrophoretic patterns identified small LDL particles and small HDL particles in the three groups, and the degree of denaturation was more enhanced in CRF patients in the conservative stage than in HD patients. For LDL susceptibility to oxidation LDL (oxLDL) by addition of Cu(2+), the lag time was approximately 57 min in healthy controls and CGN patients, but was prolonged to approximately 75 min in HD and DN patients. For HDL susceptibility to oxidation HDL (oxHDL), HD, DN and CGN patients showed lag times shorter than those found in healthy control subjects. These results showed that LDL and HDL in the serum of CRF patients were in a state of enhanced susceptibility to oxidative modification. In Western blot analysis using anti-human-denatured LDL and anti-human-oxidized HDL monoclonal antibodies, bands of low molecular oxLDL at 150-197 kDa were detected in all CRF patients, with marked tailing in CGN patients. Similarly, bands of small oxHDL particles at 110 and 120 kDa were found in HD, DN and CGN patients.

CONCLUSIONS

Oxidative modification of both LDL and HDL occurs in patients with advanced CRF resulting in small lipoproteins. Increased production of oxLDL and oxHDL is the main cause of lipid metabolic abnormality in CRF patients.

Achieving maximal renal protection in nondiabetic chronic renal disease

A rapid global increase in the number of patients requiring renal replacement therapy necessitates that effective strategies for renal protection are developed and applied widely. We review the experimental and clinical evidence in support of individual renoprotective interventions, including angiotensin-converting enzyme therapy, control of systemic hypertension, dietary protein restriction, reduction of proteinuria, treatment of hyperlipidemia, and smoking cessation. We also consider potential future renoprotective therapies. To achieve maximal renal protection, a comprehensive strategy employing all of these elements is required. This strategy should be directed at normalizing clinical markers of renal disease to induce a state of remission.

Conjugated dienes: a critical trait of lipoprotein oxidizability in renal fibrosis

BACKGROUND

We assessed whether a differential oxidizability of apolipoprotein B (apo B)-containing lipoproteins (LDL and VLDL) may explain the oxidative stress that we had observed at the onset of renal fibrosis in Zucker obese (ZO) rats (Nephrol Dial Transplant 2000, 15: 467--476).

METHODS

Ex vivo copper-induced oxidation of lipoproteins was performed in 1-, 3-, and 9-month-old ZO and age-matched lean (ZL) rats. LDL/VLDL oxidizability was determined by spectrophotometry at 234 nm by monitoring the formation of conjugated diene hydroperoxides.

RESULTS

A significant increase in lag time (reflecting the resistance to oxidation) was observed in ZO rats at 3 months while the maximal diene production (reflecting the amount of hydroperoxides formed during oxidation) was higher in ZO than in ZL rats as early as 1 month. Lipoproteins were larger in ZO than in ZL rats, as shown by their core to surface component ratio. Furthermore, ZO lipoproteins had increased vitamin E and polyunsaturated fatty acid (PUFA) content, with no change in vitamin E/PUFA ratio.

CONCLUSIONS

Rather than oxidizability of apo B-containing lipoproteins, the ability of these molecules to produce high levels of conjugated dienes, which can act as toxic tissue messengers, appears to be a critical trait in the development of renal fibrosis in this rat model of obesity and renal fibrosis.

Evolving strategies for renoprotection: non-diabetic chronic renal disease

Experimental and clinical studies over the past two decades have identified several interventions for slowing the progression of chronic renal disease towards end-stage renal failure. In this paper we review the experimental and clinical evidence in support of dietary protein restriction, angiotensin-converting enzyme inhibitor therapy, control of systemic hypertension, reduction of proteinuria, treatment of hyperlipidemia and smoking cessation. We also consider potential future renoprotective therapies. Finally we propose a comprehensive strategy for achieving maximal renoprotection with available interventions and monitoring.

Induction of hyaluronan metabolism after mechanical injury of human peritoneal mesothelial cells in vitro

BACKGROUND

Hyaluronan (HA) is an important extracellular matrix component that is involved in cell movement and tissue repair. In vertebrates, HA synthase genes (HAS 1, HAS 2, and HAS 3) that control the synthesis of HA have been identified. In this article, we investigated HA synthesis in the response of human peritoneal mesothelial cells (HPMCs) to injury.

METHODS

The expression of HAS 1, HAS 2, and HAS 3 mRNA and the synthesis of [(3)H]-labeled HA were examined in an in vitro model of peritoneal mesothelial cell damage. The staining for uridine diphosphoglucose dehydrogenase, a key enzyme in the synthesis of HA, and biotinylated HA-binding protein was used to determine the cellular location of HA synthesis and its site of deposition.

RESULTS

Growth-arrested human HPMCs expressed low levels of mRNA for HAS 2 and HAS 3 but not HAS 1. Following injury to the monolayer, HAS 2 was up-regulated by 6 hours, reaching maximal expression between 12 and 24 hours. In contrast, the expression of HAS 3 was down-regulated. During the same time period, synthesis of HA was increased in the injured monolayer. This synthetic activity appeared to be restricted to cells at the edge of the wound and to cells entering the wound. In a separate series of experiments, the addition of HA to the injured monolayer at a concentration range found in peritoneal fluid (50 to 3300 ng/mL) increased the migration of cells into the wound in a dose-dependent manner.

CONCLUSIONS

These studies provide evidence that HA is an important component of peritoneal mesothelial cell migration. The results also suggest that in this process, there is differential regulation of HAS gene expression and that the synthesis of HA is limited to cells located at the leading edge of the wound.

Effects of the new hydroxy-3-methylglutaryl coenzyme a reductase inhibitor fluvastatin on anti-oxidant enzyme activities and renal function in streptozotocin-induced diabetic rats

1. The effects of 11 week treatments with the new hydroxy3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor fluvastatin on renal intrinsic anti-oxidant enzyme (AOE) activities and renal function were evaluated in streptozotocin (STZ)-induced diabetic rats. 2. Renal intrinsic AOE activities, creatinine clearance and urinary albumin excretion were examined in STZ-induced diabetic rats. The levels of total cholesterol (TC), triglyceride (TG) and phospholipid (PL) were also examined. 3. In general, renal AOE activities and function were lower in diabetic rats than in non-diabetic Sprague-Dawley rats. 4. Decreases in TC, TG and PL levels and urinary albumin excretion by the HMG-CoA reductase inhibitor fluvastatin improved renal function and produced a non-uniform alteration in renal AOE; only glutathione peroxidase (GSH-Px) activity increased significantly with fluvastatin treatment. 5. It appears that the improvement in renal function and albuminuria may be related to increases in GSH-Px activity, but there was no correlation between changes in renal function and changes in the activity of Mn-superoxide dismutase or catalase.

Regulation of cell growth by oxidized LDL

The first reports of the influences of oxidized LDL (oxLDL) on cell function pertained to negative effects on cell growth-growth arrest, injury, and toxicity. Since these studies, it has become apparent that sublethal levels of oxLDL cause some, but not all, cells to proliferate. This review highlights the growth-promoting effects of oxLDL rather than its inhibitory or injurious effects. Smooth muscle cells (SMCs) and monocyte-macrophages proliferate after exposure to oxLDL; endothelial cells do not. Scavenger receptors are involved in the proliferative effects on monocyte-macrophages, whereas the effects of oxLDL on SMCs appear to be receptor independent. Lysophosphatidylcholine (lysoPC), and structurally related lipids are among the growth-promoting constituents of oxLDL. OxLDL exerts at least a part of its effects by inducing expression or causing the release of growth factors. OxLDL (or lysoPC) can cause the release of basic fibroblast growth factor (bFGF) from SMCs; oxLDL (or lysoPC) can induce heparin binding EGF-like growth factor (HB-EGF) synthesis and release from macrophages. An imposing array of changes in cytokine and growth factor expression and/or release can be imposed by oxLDL on a wide variety of cell types. These effects and the studies probing the cell signaling events leading to them are described.

Oxidative stress occurs in absence of hyperglycaemia and inflammation in the onset of kidney lesions in normotensive obese rats

BACKGROUND

Several factors favour the development of kidney lesions. We examined the role of oxidative stress in the onset of renal alterations that occur in Zucker obese (ZO) fa/fa rats.

METHODS

Kidney structure, biological data, glycation parameters, advanced glycation end products (AGE), thiobarbituric acid-reactive substances (TBARS), circulating antibodies anti-malondialdehyde (MDA)-modified low-density lipoprotein (LDL), antioxidant defenses (Cu/Zn and Mn superoxide dismutase (SOD), catalase, glutathione peroxidase (GPx) activities, glutathione level), were determined in plasma and/or kidney of young and old ZO rats and lean (ZL) Fa/fa littermates.

RESULTS

Renal lesions and functional decline appeared at 3 months in hyperlipidaemic, hyperinsulinaemic, normotensive ZO rats, independently of any macrophage-ED(1)(+)-cell infiltration. At 6 months and thereafter, kidney lesions and functional impairment worsened while numerous ED(1)(+)-cells invaded the interstitium. At 3 and 9 months, TBARS level in the LDL/very low-density lipoprotein fraction and in the kidney was higher in ZO than in ZL rats. Anti-MDA-LDL antibodies were increased in ZO rats. At 3 months, renal activity of Cu/Zn SOD was higher, and activities of catalase and GPx lower in ZO than in ZL rats, leading to an accumulation of hydrogen peroxide (H(2)O(2)). At 9 months, a decrease in Cu/Zn SOD activity and an increase in glutathione level were observed. Blood glucose and glycated proteins, as well as AGE in kidney, remained similar in both ZL and ZO rats, whatever their age.

CONCLUSION

These data suggest that oxidative stress triggers, at an early age, the onset of kidney lesions and functional impairment in ZO rats, in absence of hyperglycaemia, hypertension and inflammation.

Reactive oxygen species enhances endothelin-1 production of diabetic rat glomeruli in vitro and in vivo

Both reactive oxygen species (ROS) and endothelin-1 (ET- 1) have been implicated in the pathophysiology of diabetic nephropathy. The interrelationship between them, however, has not been documented in this disease. To determine whether ROS regulates ET-1 production in diabetic kidneys, we examined the in vitro and in vivo effects of ROS donors and scavengers on ET-1 production of diabetic rat glomeruli. For in vitro study, the glomeruli were isolated with a sieving method from streptozotocin-induced diabetic rats and killed at 1 week, 1 month, and 3 months, respectively. Superoxide was measured by a spectrophotometer, and ET-1 was measured by radioimmunoassay. The results demonstrated that the basal production levels of superoxide and ET-1 were higher in diabetic glomeruli than in normal glomeruli in vitro. There was a positive correlation between the production of superoxide and ET-1 in diabetic glomeruli. The basal ET-1 production was markedly attenuated by ROS scavengers including superoxide dismutase, catalase, dimethyl sulfoxide, and deferoxamine in diabetic glomeruli. Exogenous ROS generated by xanthine/xanthine oxidase significantly enhanced ET-1 generation by both diabetic and normal glomeruli. A high glucose concentration (500 mg/dL) in vitro increased ET-1 production by normal glomeruli but not diabetic glomeruli, and insulin partly suppressed ET- 1 production by diabetic glomeruli. The in vivo study demonstrated that when diabetic rats were injected daily with superoxide dismutase or catalase after diabetes was induced, the basal production of ET-1 was markedly attenuated after 1 week and 1 month, respectively. These results indicate that exogenously or endogenously derived ROS can enhance ET-1 production by diabetic rat glomeruli and that ROS scavengers suppress ET- 1 production both in vitro and in vivo. The effects of ROS on ET-1 production of diabetic glomeruli may be partly caused by the effect of hyperglycemia or insulin deficiency.

Low-density lipoprotein stimulates mesangial cell proteoglycan and hyaluronan synthesis

BACKGROUND

Hyperlipidaemia leads to glomerulosclerosis in small mammals and may contribute to progressive renal disease in man. One prominent feature of lipid-induced glomerular injury in animal models is the accumulation of mesangial matrix. These studies were designed to investigate whether low-density lipoprotein (LDL) enhanced mesangial cell (MC) matrix deposition by modulating the production of proteoglycans (PG) and hyaluronan (HA).

METHODS

Growth arrested human MC were metabolically labelled with either 50 microCi/ml Na(2)[(35)S]sulphate or 25 microCi/ml [(3)H]glucosamine and stimulated with LDL (10-100 microg/ml). The radiolabelled PG and HA extracted from the cell layer and the culture medium were isolated, quantified and characterized. Comparison of the PG core proteins synthesized by MC was carried out using Western blot analysis.

RESULTS

LDL stimulation led to a dose- and time-dependent increase in [(35)S]sulphate incorporation into PG in the culture medium and to a lesser extent in the cell layer. Analysis of the glycosaminoglycan (GAG) chains showed no difference in either their size or charge. Enzyme digestion studies demonstrated that the synthesis of both chondroitin sulphate PG (CSPG) and heparan sulphate PG (HSPG) was enhanced as was the production of the core proteins of versican (a large CSPG), perlecan (a basement membrane HSPG) and to a lesser extent decorin (a small dermatan sulphate PG (DSPG)). An increase in HA synthesis was also demonstrated in [(3)H]glucosamine labelled cells following LDL stimulation.

CONCLUSION

LDL selectively enhances the synthesis of specific PG and HA by mesangial cells. Such effects may contribute to the expansion of the mesangial matrix and modify cell-matrix interactions in lipid-induced renal damage.

Oxidized LDL, glomerular mesangial cells and collagen

Lipid deposits, foam cell collection and accumulation of mesangial matrix components are recognized as early events in the development of focal segmental glomerulosclerosis (FSGS). Studies have suggested that oxidative stress is increased in uremic patients. Oxidized low-density lipoprotein (Ox-LDL) has been identified in the lesions of FSGS. Dietary antioxidants reduced not only the staining intensity of Ox-LDL but also the severity of renal injury in rats with experimental FSGS possibly by making lipoproteins resistant to oxidation. In vitro studies showed that LDL during its incubation with human mesangial cells (HMC) was peroxidatively modified and stimulated alpha1(I), alpha1(III), and alpha1(IV) collagen mRNA expression. Vitamin E, an antioxidant, and antibody against Ox-LDL caused a marked reduction in collagen mRNA stimulated by LDL. These findings suggest that LDL deposited and oxidized in the glomeruli may be implicated in the development of glomerulosclerosis by facilitating excessive mesangial matrix generation.

Effect of protein A immunoadsorption in nephrotic syndrome of various etiologies

Protein A immunoadsorption (IA) has proved effective in reducing proteinuria in patients with nephrotic syndrome after recurrence of focal and segmental glomerulosclerosis (FSGS) in kidney transplants. The effect of IA in nephrotic syndrome of other etiologies remains unknown. Nine patients with nephrotic syndrome secondary to membranous nephropathy (four cases), diabetes mellitus (one case), IgA nephropathy (two cases), and amyloidosis (two cases) had three to five IA of 2.5 plasma volumes over 4 to 8 d. Patients received no concomitant immunosuppressive treatment, and antihypertensive drugs were left unchanged. Proteinuria decreased from 12.64 +/- 5.49 to 3.35 +/- 2.2 g/24 h (mean +/- SD) in all patients after three to five IA. Hematocrit decreased from 37.32 to 32.64% (12.5% hemodilution) and serum albumin from 25.43 to 18.6 g/L (26.4% decrease). Proteinuria returned to baseline levels within 1 mo, as described in recurrent FSGS following transplantation. When serum albumin balance was controlled by albumin infusion after IA in two patients, comparable decreases in proteinuria were observed. Therefore, IA is effective in producing short-term reduction of proteinuria in nephrotic syndromes related not only to FSGS but also to membranous and IgA nephropathies, diabetes mellitus, and amyloidosis, which suggests that IA removes a nonspecific circulating hemodynamic-altering or permeability-increasing factor.

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.

Vascular cell adhesion molecule-1 expression in the renal interstitium of diabetic KKAy mice

To investigate the mechanism of interstitial inflammation in diabetic nephropathy, we used spontaneously diabetic KKAy mice. Twelve KKAy mice were divided into two groups; six mice were fed standard mouse chow ad libitum and six mice were placed on a diet (i.e. they received the same amount of chow as six control C57BL mice). Diabetic KKAy mice developed hypercholesterolemia and albuminuria. Animals were killed at 16 weeks of age and renal tissues were immunostained for vascular cell adhesion molecule-1 (VCAM-1). In diabetic KKAy mice, the renal interstitium was infiltrated by monocytes, lymphocytes, plasma cells, and other cells. The walls of venules near the infiltrating cells were more intensely stained for VCAM-1 when compared with other sites. In contrast, the VCAM-1 staining of arterioles and peritubular capillaries was not significantly increased. There was weak VCAM-1 staining of the infiltrating cells, including lymphocytes, monocytes, and other cells. Electron microscopy demonstrated immunolabeling for VCAM-1 on the cell surface and in the cytoplasm of both infiltrating cells and vascular endothelial cells. In KKAy mice placed on a diet, there was less staining for VCAM-1 and cellular infiltration was also decreased. Thus, increased expression of VCAM-1 by the endothelial cells of venules and VCAM-1 expression by infiltrating cells were demonstrated in the interstitium of kidneys from diabetic mice. These results suggest that increased expression of VCAM-1 by endothelial cells and infiltrating cells contributes to interstitial inflammation in diabetic nephropathy.

Fibronectin augments monocyte adhesion to low-density lipoprotein-stimulated mesangial cells

BACKGROUND

Glomerular monocyte infiltration is an early feature of lipid-mediated renal injury in animal models. Interactions between mesangial and infiltrating mononuclear cells may contribute to the development of glomerular scarring.

METHODS

Adherence of U-937 monocytes to low-density lipoprotein (LDL)- or tumor necrosis factor alpha (TNFalpha)-prestimulated human mesangial cells was assessed by colorimetry of nuclear staining with crystal violet. Blocking antibodies were added to examine the mechanisms of binding. Adhesion molecule expression and fibronectin synthesis were measured by ELISA.

RESULTS

Preincubation of mesangial cells for 24 hours with LDL (100 micrograms/ml) or mildly oxidized (minimally modified) LDL (MM-LDL) increased monocyte adhesion by 207% and 240%, respectively, compared with control nonstimulated cells (100%). TNFalpha (100 U/ml) enhanced binding by 335% and up-regulated intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) expression by 505% and 179%, respectively, as compared with MM-LDL (120% and 116%) and LDL, which had no effect. Blocking antibodies to these adhesion molecules inhibited monocyte binding to TNFalpha- and, to a lesser extent, MM-LDL-primed mesangial cells, but had no effect after LDL pretreatment. In contrast to TNFalpha, MM-LDL and LDL increased mesangial cell-associated fibronectin, whereas antibodies to fibronectin inhibited monocyte binding to lipoprotein-stimulated but not TNFalpha-stimulated cells.

CONCLUSIONS

Although enhanced monocyte adhesion to TNFalpha- and, to a lesser extent, MM-LDL-stimulated mesangial cells is mediated by changes in ICAM-1 and VCAM-1 expression, both LDL and MM-LDL promote similar cellular interactions as a result of increased fibronectin production.

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.

Oxidized low-density lipoprotein decreases the induced nitric oxide synthesis in rat mesangial cells

Recently, the close relation between oxidized low density lipoprotein (Ox-LDL) and the progression of glomerular injury has been demonstrated. The nitric oxide (NO) pathway in glomerular mesangial cells may be a potential target for the adverse effects of Ox-LDL in the development of glomerular injury. In this study, we treated cultured rat mesangial cells (RMC) with Fe(2+)-oxidized LDL and then stimulated the cells with lipopolysacharride (LPS, 10 micrograms ml-1). The LPS-induced NO production, assessed by NO2-concentrations in cultured supernatants, decreased from 7.83 nmol per 10(6) cells in control to 4.00 nmol per 10(6) cells and 1.67 nmol per 10(6) cells in RMC preincubated with Ox-LDL at 20 micrograms ml-1 and 40 micrograms ml-1, respectively (P < 0.01). Native LDL had no significant effects on LPS-induced NO production. Using the reverse transcription-polymerase chain reaction (RT-PCR) technique, we could not detect significant alteration of inducible NO synthase (iNOS) mRNA levels in RMC preincubated with Ox-LDL. Our results suggest that Ox-LDL decreases induced NO production in RMC, which may contribute to the adverse effects of Ox-LDL in progressive glomerular injury. The mechanisms of this decrease may not involve changes of iNOS genic transcription.

Statins and the kidney

Experience to date suggests that 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors or statins can be used relatively safely and effectively to treat dyslipidaemia complicating renal disease. Recent studies suggest that in addition to lowering plasma lipid levels, these drugs modify other factors that contribute to vascular injury. Furthermore, statins could slow the progression of chronic renal failure and may augment the action of immunosuppressive therapy after renal transplantation. Such newly defined actions, some of which could be unrelated to lipid lowering, are likely to extend the applications of statins in nephrology.

Atherogenic lipoproteins enhance mesangial cell expression of platelet-derived growth factor: role of protein tyrosine kinase and cyclic AMP-dependent protein kinase A

Mesangial cell proliferation and extracellular matrix accumulation are fundamental in the pathogenesis of glomerulosclerosis. Platelet-derived growth factor (PDGF) is a major cytokine involved in mesangial cell proliferation, and its increased expression is seen in glomerular injury. Atherogenic lipoproteins stimulate mesangial cell proliferation and induce glomerular injury in experimental animals. We examined the effect of low-density lipoprotein (LDL) and its more atherogenic oxidized forms, minimally modified LDL (mm-LDL) and oxidized LDL (ox-LDL) on mesangial cell PDGF mRNA expression. Incubation with 2.5 to 25 microg/ml LDL or mm-LDL for 1 to 4 hours stimulated mesangial cell PDGF mRNA expression (mm-LDL 2 to 3 times greater than LDL); ox-LDL had no effect. Similarly, both LDL and mm-LDL induced mesangial cell DNA synthesis (mm-LDL 1.5 to 2 times greater). In further studies evaluating key associated intracellular signal transduction mechanisms, the protein tyrosine kinase (PTK) inhibitors herbimycin and genistein markedly decreased basal and lipoprotein-induced PDGF mRNA expression. Both pertussis toxin and isoproterenol, cyclic AMP-generating substances, stimulated PDGF mRNA expression. Preincubation with H-8 or H-89, cyclic AMP-dependent protein kinase A (PKA) inhibitors, blocked the lipoprotein-induced PDGF message, whereas preincubation with calphostin C, a protein kinase C inhibitor, did not alter LDL- or mm-LDL-mediated PDGF mRNA expression. These data suggest that the accumulation of atherogenic lipoproteins and their endogenous oxidized forms within the glomerulus may regulate mesangial cell PDGF expression and related cellular responses. These events appear to be modulated by signal transduction pathways involving PTK and PKA.

Differential ability of cells to promote oxidation of low density lipoproteins in vitro

Atherosclerosis and focal segmental glomerulosclerosis share some common histological features and it is speculated that they result from similar pathobiological mechanisms. There is strong evidence that oxidation of low density lipoprotein (LDL) may be an initiating event in atherogenesis and that oxidised LDL may also be involved in the glomerulosclerotic process. In vitro studies have demonstrated that cells present in the arterial intima and kidney-derived cells promote LDL oxidation. The aim of this study was to compare LDL oxidation by kidney-derived human mesangial cells and proximal tubular cells, with human umbilical vein endothelial cells and the human monocyte cell line THP-1. We used the thiobarbituric acid assay and agarose gel electrophoresis to measure the extent of LDL oxidation. Our results demonstrate that all of the cell types used had the ability to oxidise LDL significantly more than cell-free controls and that endothelial cells induced the highest degree of oxidative modification of LDL under our experimental conditions.

Do E-series prostaglandins and their metabolites influence oxidation of native and glycated low-density lipoproteins?

Oxidation of lipoproteins, and, in particular, low-density lipoproteins (LDL), has been shown to play a significant role in the pathogenesis of atherosclerosis. Oxidized LDL are endocytosed via scavenger receptors to form lipid-laden foam cells. The non-enzymatic reaction of glucose with proteins and lipoproteins results in a modified LDL involved in the pathogenesis of late complications in diabetes mellitus. In the present paper, the influence of various E-series prostaglandins (PGE1; 13,14-dihydro PGE1; 13,14-dihydro 15-keto PGE1; and PGE2) on oxidation of native and glycated LDL was investigated. The effect of these agents in the concentration range from 1 pg/mL to 1.6 micrograms/mL on copper-induced oxidation of native and glycated LDL was tested. The concentration of each agent causing the maximal effect on oxidation of native LDL, as measured by the formation of thiobarbituric acid-reacting substances, was chosen to estimate the effect on 2, 4, 8, and 24 h oxidation of glycated LDL. The study was performed with LDL isolated by sequential ultracentrifugation from normolipidemic individuals. LDL (0.25 mg protein/mL) was oxidatively modified with 5 microM CuSO4. The glycosylation of LDL was performed by incubation of LDL with 500 mM glucose for varying periods of time ranging from 10 to 31 days. Our results show that only 13,14-dihydro PGE1 significantly inhibits copper-induced oxidation of native LDL, while the other examined E-series prostaglandins in vitro are ineffective as reducing agents in LDL-oxidation.

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.