Hepatic HMG-CoA reductase gene expression during the course of puromycin-induced nephrosis

A proximity labeling strategy enables proteomic analysis of inter-organelle membrane contacts

Inter-organelle membrane contacts are highly dynamic and act as central hubs for many biological processes, but the protein compositions remain largely unknown due to the lack of efficient tools. Here, we developed BiFCPL to analyze the contact proteome in living cells by a bimolecular fluorescence complementation (BiFC)-based proximity labeling (PL) strategy. BiFCPL was applied to study mitochondria-endoplasmic reticulum contacts (MERCs) and mitochondria-lipid droplet (LD) contacts. We identified 403 highly confident MERC proteins, including many transiently resident proteins and potential tethers. Moreover, we demonstrated that mitochondria-LD contacts are sensitive to nutrient status. A comparative proteomic analysis revealed that 60 proteins are up- or downregulated at contact sites under metabolic challenge. We verified that SQLE, an enzyme for cholesterol synthesis, accumulates at mitochondria-LD contact sites probably to utilize local ATP for cholesterol synthesis. This work provides an efficient method to identify key proteins at inter-organelle membrane contacts in living cells.

Does pathological type of primary nephrotic syndrome affect serum concentrations of proprotein convertase subtilisin/kexin type 9?

Background

Dyslipidemia is a common finding in primary nephrotic syndrome (PNS). Serum PCSK9 level is also increased in PNS and is the main cause of dyslipidemia in such patients. There is a paucity of data on the relation between dyslipidemia and pathological types of PNS. We hypothesized that severity of dyslipidemia varies across different types of PNS, and this variation is due to differences in serum PCSK9 levels.

Methods

Fifty patients recently diagnosed with PNS were included in this cross-sectional study. Serum PCSK9, albumin, creatinine, total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), very low-density lipoprotein cholesterol (VLDL-C), triglycerides (TG), and 24-h urine protein were measured. Comparison of patients’ characteristics between pathological types of PNS and correlations between serum PCSK9 and other parameters were assessed.

Results

Serum PCSK9 levels were significantly higher in PNS patients compared with healthy individuals (314.58 ± 73.83 vs 253.42 ± 36.66 ng/ml, p < 0.001). No differences found between PNS types regarding serum levels of PCSK9 (p = 0.571), TC (p = 0.806), LDL-C (p = 0.950), HDL-C (p = 0.844), VLDL-C (p = 0.472), and TG (p = 0.969). Serum PCSK9 levels correlated significantly with TC (p < 0.001), LDL-C (p < 0.001), HDL-C (p = 0.003), VLDL-C (p = 0.008), TG (p = 0.005), 24-h urine protein (p = 0.005), and male sex (p = 0.014).

Conclusion

The pathological type of PNS does not affect serum levels of PCSK9 and components of lipid profile.

Lipoprotein Abnormalities in Chronic Kidney Disease and Renal Transplantation

Chronic kidney disease (CKD) is one of the most important risk factors for cardiovascular disease (CVD). Despite the kidney having no direct implications for lipoproteins metabolism, advanced CKD dyslipidemia is usually present in patients with CKD, and the frequent lipid and lipoprotein alterations occurring in these patients play a role of primary importance in the development of CVD. Although hypertriglyceridemia is the main disorder, a number of lipoprotein abnormalities occur in these patients. Different enzymes pathways and proteins involved in lipoprotein metabolism are impaired in CKD. In addition, treatment of uremia may modify the expression of lipoprotein pattern as well as determine acute changes. In renal transplantation recipients, the main lipid alteration is hypercholesterolemia, while hypertriglyceridemia is less pronounced. In this review we have analyzed lipid and lipoprotein disturbances in CKD and also their relationship with progression of renal disease. Hypolipidemic treatments may also change the natural history of CVD in CKD patients and may represent important strategies in the management of CKD patients.

Secretion of the epithelial sodium channel chaperone PCSK9 from the cortical collecting duct links sodium retention with hypercholesterolemia in nephrotic syndrome

The proprotein PCSK9 functions as a chaperone for the epithelial sodium channel in the cortical collecting duct (CCD), is highly expressed in the liver, and plays a significant role in the pathogenesis of hypercholesterolemia. Lower levels of PCSK9 expression also occur in the normal kidney and intestine. Here, we found increased PCSK9 expression in the CCD of biopsies of patients with primary glomerular disease and explored a possible relationship with hypercholesterolemia of nephrotic syndrome. Significantly elevated serum PCSK9 and cholesterol levels were noted in two models of focal and segmental glomerulosclerosis, the Rrm2b-/- mouse and the Buffalo/Mna rat. Increased expression of PCSK9 in the kidney occurred when liver expression was reduced in both models. The impact of reduced or increased PCSK9 in the CCD on hypercholesterolemia in nephrotic syndrome was next studied. Mice with selective deficiency of PCSK9 expression in the collecting duct failed to develop hypercholesterolemia after injection of nephrotoxic serum. Blocking epithelial sodium channel activity with Amiloride in Rrm2b-/- mice resulted in increased expression of its chaperone PCSK9 in the CCD, followed by elevated plasma levels and worsening hypercholesterolemia. Thus, our data suggest that PCSK9 in the kidney plays a role in the initiation of hypercholesterolemia in nephrotic syndrome and make a case for depletion of PCSK9 early in patients with nephrotic syndrome to prevent the development of hypercholesterolemia.

IL-13-driven alterations in hepatic cholesterol handling contributes to hypercholesterolemia in a rat model of minimal change disease

Circulating factors have been implicated in the pathogenesis of minimal change disease (MCD), and may have direct effects on cholesterol metabolism. This study investigated the pathogenesis of hypercholesterolemia in an IL-13 overexpression rat model of MCD prior to the onset of proteinuria, so as to establish the direct contribution of IL-13, especially with regard to hepatic cholesterol handling. In this model of MCD, the temporal relationship between hypercholesterolemia and proteinuria was first identified. Plasma proprotein convertase subtilisin/kexin type 9 (Pcsk9) and liver ATP-binding cassette sub-family G member 5 (Abcg5) were measured using ELISA. Liver Ldlr and liver X receptor alpha (Lxra) were quantified with Western blot. Abcg5-mediated cholesterol efflux in IL-13-stimulated rat primary hepatocytes was measured using taurocholate as cholesterol acceptor. The role of Lxra was validated using a luciferase assay in Lxre-luciferase-transfected IL-13-stimulated hepatocytes. IL-13-transfected rats developed hypercholesterolemia prior to proteinuria, with 35% of rats hypercholesterolemic but only 11% proteinuric by Day 20 (P = 0.04). These pre-proteinuric hypercholesterolemic rats showed elevations in total and LDL-cholesterol, but not hypertriglyceridemia or hepatic steatosis. The hypercholesterolemia was associated with increased hepatic Pcsk9 synthesis and enhanced circulating Pcsk9 levels, which correlated strongly with plasma total cholesterol (r = 0.73, P&lt;0.001). The hypercholesterolemia was also contributed by decreased Abcg5 expression and activity, due to reduced Lxra expression. Lxra expression correlated with plasma total cholesterol levels (r = −0.52, P = 0.01), and overexpression of pLxra in rat hepatocytes abrogated the IL-13-mediated down-regulation of Lxre-driven gene expression. In conclusion, we have shown that IL-13 induced changes in hepatic cholesterol handling in a cytokine-induced rat model of MCD, resulting in hypercholesterolemia which can precede the onset of proteinuria.

Chronic treatment of curcumin improves hepatic lipid metabolism and alleviates the renal damage in adenine-induced chronic kidney disease in Sprague-Dawley rats

Background

Chronic kidney disease (CKD), including nephrotic syndrome, is a major cause of cardiovascular morbidity and mortality. The literature indicates that CKD is associated with profound lipid disorders due to the dysregulation of lipoprotein metabolism which progresses kidney disease. The objective of this study is to evaluate the protective effects of curcumin on dyslipidaemia associated with adenine-induced chronic kidney disease in rats.

Methods

Male SD rats (n = 29) were divided into 5 groups for 24 days: normal control (n = 5, normal diet), CKD control (n = 6, 0.75% w/w adenine-supplemented diet), CUR 50 (n = 6, 50 mg/kg/day curcumin + 0.75% w/w adenine-supplemented diet), CUR 100 (n = 6, 100 mg/kg/day curcumin + 0.75% w/w adenine-supplemented diet), and CUR 150 (n = 6, 150 mg/kg/day curcumin + 0.75% w/w adenine-supplemented diet). The serum and tissue lipid profile, as well as the kidney function test, were measured using commercial diagnostic kits.

Results

The marked rise in total cholesterol, low-density lipoprotein (LDL) cholesterol, very low-density lipoprotein (VLDL) cholesterol, triglycerides and free fatty acids in serum, as well as hepatic cholesterol, triglyceride and free fatty acids of CKD control rats were significantly protected by curcumin co-treatment (at the dose of 50, 100 and 150 mg/kg). Furthermore, curcumin significantly increased the serum high-density lipoprotein (HDL) cholesterol compared to the CKD control rats but did not attenuate the CKD-induced weight retardation. Mathematical computational analysis revealed that curcumin significantly reduced indicators for the risk of atherosclerotic lesions (atherogenic index) and coronary atherogenesis (coronary risk index). In addition, curcumin improved kidney function as shown by the reduction in proteinuria and improvement in creatinine clearance.

Conclusion

The results provide new scientific evidence for the use of curcumin in CKD-associated dyslipidaemia and substantiates the traditional use of curcumin in preventing kidney damage.

Compound α-keto acid tablet supplementation alleviates chronic kidney disease progression via inhibition of the NF-kB and MAPK pathways

Background

Keto-analogues administration plays an important role in clinical chronic kidney disease (CKD) adjunctive therapy, however previous studies on their reno-protective effect mainly focused on kidney pathological changes induced by nephrectomy. This study was designed to explore the currently understudied alternative mechanisms by which compound α-ketoacid tablets (KA) influenced ischemia–reperfusion (IR) induced murine renal injury, and to probe the current status of KA administration on staving CKD progression in Chinese CKD patients at different stages.

Methods

In animal experiment, IR surgery was performed to mimic progressive chronic kidney injury, while KA was administrated orally. For clinical research, a retrospective cohort study was conducted to delineate the usage and effects of KA on attenuating CKD exacerbation. End-point CKD event was defined as 50% reduction of initial estimated glomerular filtration rate (eGFR). Kaplan–Meier analysis and COX proportional hazard regression model were adopted to calculate the cumulative probability to reach the end-point and hazard ratio of renal function deterioration.

Results

In animal study, KA presented a protective effect on IR induced renal injury and fibrosis by attenuating inflammatory infiltration and apoptosis via inhibition of nuclear factor-kappa B (NF-κB) and mitogen-activated protein kinase (MAPK) pathways. In clinical research, after adjusting basic demographic factors, patients at stages 4 and 5 in KA group presented a much delayed and slower incidence of eGFR decrease compared to those in No-KA group (hazard ratio (HR) = 0.115, 95% confidence interval (CI) 0.021–0.639, p = 0.0134), demonstrating a positive effect of KA on staving CKD progression.

Conclusion

KA improved IR induced chronic renal injury and fibrosis, and seemed to be a prospective protective factor in end stage renal disease.

Dyslipidaemia in nephrotic syndrome: mechanisms and treatment

Nephrotic syndrome is a highly prevalent disease that is associated with high morbidity despite notable advances in its treatment. Many of the complications of nephrotic syndrome, including the increased risk of atherosclerosis and thromboembolism, can be linked to dysregulated lipid metabolism and dyslipidaemia. These abnormalities include elevated plasma levels of cholesterol, triglycerides and the apolipoprotein B-containing lipoproteins VLDL and IDL; decreased lipoprotein lipase activity in the endothelium, muscle and adipose tissues; decreased hepatic lipase activity; and increased levels of the enzyme PCSK9. In addition, there is an increase in the plasma levels of immature HDL particles and reduced cholesterol efflux. Studies from the past few years have markedly improved our understanding of the molecular pathogenesis of nephrotic syndrome-associated dyslipidaemia, and also heightened our awareness of the associated exacerbated risks of cardiovascular complications, progressive kidney disease and thromboembolism. Despite the absence of clear guidelines regarding treatment, various strategies are being increasingly utilized, including statins, bile acid sequestrants, fibrates, nicotinic acid and ezetimibe, as well as lipid apheresis, which seem to also induce partial or complete clinical remission of nephrotic syndrome in a substantial percentage of patients. Future potential treatments will likely also include inhibition of PCSK9 using recently-developed anti-PCSK9 monoclonal antibodies and small inhibitory RNAs, as well as targeting newly identified molecular regulators of lipid metabolism that are dysregulated in nephrotic syndrome.

The Role of Proprotein Convertase Subtilisin/Kexin Type 9 in Nephrotic Syndrome-Associated Hypercholesterolemia

BACKGROUND

In nephrotic syndrome, damage to the podocytes of the kidney produces severe hypercholesterolemia for which novel treatments are urgently needed. PCSK9 (proprotein convertase subtilisin/kexin type 9) has emerged as an important regulator of plasma cholesterol levels and therapeutic target. Here, we tested the role of PCSK9 in mediating the hypercholesterolemia of nephrotic syndrome.

METHODS

PCSK9 and plasma lipids were studied in nephrotic syndrome patients before and after remission of disease, mice with genetic ablation of the podocyte (Podocyte Apoptosis Through Targeted Activation of Caspase-8, Pod-ATTAC mice) and mice treated with nephrotoxic serum (NTS), which triggers immune-mediated podocyte damage. In addition, mice with hepatic deletion of Pcsk9 were treated with NTS to determine the contribution of PCSK9 to the dyslipidemia of nephrotic syndrome.

RESULTS

Patients with nephrotic syndrome showed a decrease in plasma cholesterol and plasma PCSK9 on remission of their disease (P<0.05, n=47-50). Conversely, Pod-ATTAC mice and NTS-treated mice showed hypercholesterolemia and a 7- to 24-fold induction in plasma PCSK9. The induction of plasma PCSK9 appeared to be attributable to increased secretion of PCSK9 from the hepatocyte coupled with decreased clearance. Interestingly, knockout of Pcsk9ameliorated the effects of NTS on plasma lipids. Thus, in the presence of NTS, mice lacking hepatic Pcsk9 showed a 40% to 50% decrease in plasma cholesterol and triglycerides. Moreover, the ability of NTS treatment to increase the percentage of low-density lipoprotein-associated cholesterol (from 9% in vehicle-treated Flox mice to 47% after NTS treatment), was lost in mice with hepatic deletion of Pcsk9 (5% in both the presence and absence of NTS).

CONCLUSIONS

Podocyte damage triggers marked inductions in plasma PCSK9, and knockout of Pcsk9 ameliorates dyslipidemia in a mouse model of nephrotic syndrome. These data suggest that PCSK9 inhibitors may be beneficial in patients with nephrotic syndrome-associated hypercholesterolemia.

Disorders of lipid metabolism in nephrotic syndrome: mechanisms and consequences

Nephrotic syndrome results in hyperlipidemia and profound alterations in lipid and lipoprotein metabolism. Serum cholesterol, triglycerides, apolipoprotein B (apoB)-containing lipoproteins (very low-density lipoprotein [VLDL], immediate-density lipoprotein [IDL], and low-density lipoprotein [LDL]), lipoprotein(a) (Lp[a]), and the total cholesterol/high-density lipoprotein (HDL) cholesterol ratio are increased in nephrotic syndrome. This is accompanied by significant changes in the composition of various lipoproteins including their cholesterol-to-triglyceride, free cholesterol-to-cholesterol ester, and phospholipid-to-protein ratios. These abnormalities are mediated by changes in the expression and activities of the key proteins involved in the biosynthesis, transport, remodeling, and catabolism of lipids and lipoproteins including apoproteins A, B, C, and E; 3-hydroxy-3-methylglutaryl-coenzyme A reductase; fatty acid synthase; LDL receptor; lecithin cholesteryl ester acyltransferase; acyl coenzyme A cholesterol acyltransferase; HDL docking receptor (scavenger receptor class B, type 1 [SR-B1]); HDL endocytic receptor; lipoprotein lipase; and hepatic lipase, among others. The disorders of lipid and lipoprotein metabolism in nephrotic syndrome contribute to the development and progression of cardiovascular and kidney disease. In addition, by limiting delivery of lipid fuel to the muscles for generation of energy and to the adipose tissues for storage of energy, changes in lipid metabolism contribute to the reduction of body mass and impaired exercise capacity. This article provides an overview of the mechanisms, consequences, and treatment of lipid disorders in nephrotic syndrome.

Cholesterol Metabolism in CKD

Patients with chronic kidney disease (CKD) have a substantial risk of developing coronary artery disease. Traditional cardiovascular disease (CVD) risk factors such as hypertension and hyperlipidemia do not adequately explain the high prevalence of CVD in CKD. Both CVD and CKD are inflammatory states and inflammation adversely affects lipid balance. Dyslipidemia in CKD is characterized by elevated triglyceride levels and high-density lipoprotein levels that are both decreased and dysfunctional. This dysfunctional high-density lipoprotein becomes proinflammatory and loses its atheroprotective ability to promote cholesterol efflux from cells, including lipid-overloaded macrophages in the arterial wall. Elevated triglyceride levels result primarily from defective clearance. The weak association between low-density lipoprotein cholesterol level and coronary risk in CKD has led to controversy over the usefulness of statin therapy. This review examines disrupted cholesterol transport in CKD, presenting both clinical and preclinical evidence of the effect of the uremic environment on vascular lipid accumulation. Preventative and treatment strategies are explored.

Role of PCSK9 and IDOL in the pathogenesis of acquired LDL receptor deficiency and hypercholesterolemia in nephrotic syndrome

BACKGROUND

Nephrotic syndrome (NS) leads to elevation of serum total and LDL cholesterol. This is largely due to impaired LDL clearance, which is caused by hepatic LDL receptor (LDLR) deficiency despite normal LDLR mRNA expression, pointing to a post-transcriptional process. The mechanism(s) by which NS causes LDLR deficiency is not known. By promoting degradation of LDLR, Proprotein Convertase Subtilisin/Kexin type 9 (PCSK9) and inducible degrader of the LDL receptor (IDOL) play a major role in post-translational regulation of LDLR. We, therefore, tested the hypothesis that LDLR deficiency despite its normal gene expression in NS may be due to upregulation of hepatic PCSK9 and IDOL.

METHODS

LDLR, IDOL and PCSK9 expressions and nuclear translocation of liver X receptor (LXR) that regulates IDOL expression were determined in the liver of rats with puromycin-induced NS and control (CTL) rats.

RESULTS

Compared with the CTLs, the NS rats showed marked elevation of serum total and LDL cholesterol and a significant reduction in hepatic LDLR protein expression. This was accompanied by marked upregulation of hepatic PCSK9 and IDOL expressions and heightened LXR activation.

CONCLUSIONS

LDLR deficiency, hypercholesterolemia and elevated plasma LDL in NS are associated with upregulation of PCSK9 and IDOL. Interventions targeting these pathways may be effective in the management of hypercholesterolemia and the associated cardiovascular and other complications of NS.

Lipid abnormalities in patients with chronic kidney disease: implications for the pathophysiology of atherosclerosis

Cardiovascular disease is increased in patients with chronic kidney disease (CKD) and is the principle cause of morbidity and mortality in these patients. In patients with stage 5 CKD, structural changes in the myocardium have been implicated as the principle cardiovascular processes leading to this increase in morbidity and mortality, while atherosclerotic events including acute myocardial infarction and strokes are responsible for approximately 10-15% of cardiovascular deaths. Dyslipidemia is common in CKD patients and is usually not characterized by elevated cholesterol levels, except in patients with marked proteinuria. Increased triglyceride levels in conjunction with decreased high-density lipoprotein levels are the commonest qualitative abnormality. Characteristically, abnormalities in the metabolism of apolipoprotein (apo) B-containing lipoproteins have been described, including both gut derived (apoB-48) as well as those produced by hepatic synthesis (apoB-100). A decrease in enzymatic delipidation as well as reduced receptor removal of these lipoproteins both contribute to the increased levels of these apo-B-containing particles and their remnants (which are believed to be highly atherogenic). Abnormalities in the metabolism of apoA-containing lipoproteins are also present and these changes contribute to the lower levels of HDL seen. Qualitative abnormalities of these HDL particles may be associated with cellular oxidative injury and contribute to a pro-inflammatory, pro-thrombotic milieu that is frequently present in CKD patients.

Nephrotic syndrome causes upregulation of HDL endocytic receptor and PDZK-1-dependent downregulation of HDL docking receptor

BACKGROUND

Nephrotic syndrome (NS) is associated with dysregulation of lipid/lipoprotein metabolism and impaired high-density lipoprotein (HDL)-mediated reverse cholesterol transport and atherosclerosis. HDL serves as vehicle for transport of surplus lipids from the peripheral tissues for disposal in the liver via two receptors: (i) scavenger receptor class B type I (SR-BI) which serves as a docking receptor, enabling HDL to unload its lipid cargo and return to circulation to repeat the cycle, and (ii) beta chain ATP synthase which serves as the endocytic receptor mediating removal and catabolism of lipid-poor HDL. SR-BI abundance is regulated by PDZ-containing kidney protein 1 (PDZK1), a multifunctional protein, which prevents SRB-1 degradation at the post-translational level. This study explored the effect of NS on hepatic expression of these important molecules.

METHODS

Gene expression, protein abundance and immunohistological appearance of the above proteins were measured in the liver of rats with puromycin-induced NS and control rats.

RESULTS

The nephrotic animals exhibited severe proteinuria, hypoalbuminemia, hypercholesterolemia, hypertriglyceridemia, reduced HDL/total cholesterol ratio, normal glomerular filtration rate, significant upregulation of the endocytic HDL receptor messenger RNA (mRNA) and protein (P < 0.005) and significant reduction of SR-BI protein (P < 0.002) despite its normal mRNA abundance. The reduction in SR-BI protein abundance in NS animals was accompanied by parallel reductions in PDZK1 mRNA (P = 0.02) and protein abundance (P = 0.012).

CONCLUSIONS

NS results in elevation of hepatic HDL endocytic receptor and deficiency of HDL docking receptor. The latter is associated with and, in part, mediated by downregulation of PDZK1. Together, these abnormalities can increase catabolism and diminish recycling of HDL and contribute to the defective reverse cholesterol/lipid transport in NS.

Dyslipidemia associated with chronic kidney disease

Cardiovascular disease is a major cause of morbidity and mortality in patients with impaired renal function. Dyslipidemia has been established as a well-known traditional risk factor for cardiovascular disease (CVD) in the general population and it is well known that patients with chronic kidney disease (CKD) exhibit significant alterations in lipoprotein metabolism. In this review, the pathogenesis and treatment of CKD-induced dyslipidemia are discussed. Studies on lipid abnormalities in predialysis, hemodialysis and peritoneal dialysis patients are analyzed. In addition, the results of the studies that tested the effects of the hypolipidemic drugs on cardiovascular morbidity and mortality in patients with CKD are reported.

Improvement of dyslipidemia in OLETF rats by the prostaglandin I(2) analog beraprost sodium

The Otsuka Long-Evans Tokushima Fatty (OLETF) rat was established as an animal model of human type 2 diabetes. Improvement of dyslipidemia by BPS has been confirmed in OLETF rats. The aim of this report is to clarify the mechanisms associated with improvement of dyslipidemia by BPS in OLETF rats. We divided male OLETF rats into three groups; 400microg/kg BPS treated (Group H), 200microg/kg BPS treated (Group L), and untreated control (Group C). After sacrifice, using the quantitative real-time PCR, we assayed the transcription levels of the HMG-CoA reductase (Hmgcr) for cholesterol biosynthesis, monoacylglycerol O-acyltransferase 1 (Mogat1) as TG synthetase, hepatic triglyceride lipase (Lipc) and lipoprotein lipase (Lpl) as triglycerides (TG) reductase in the liver. The mRNA expression of transketolase (Tkt) for pentose phosphate pathway (PPP) enzyme was also evaluated in the liver and kidney. Hmgcr and Mogat1 RNA expression levels were reduced in the livers and those of Tkt were increased in the kidney of BPS treated rats compared with those in untreated rats. The protein expressions of transketolase (Tkt) of BPS treated rats were similarly increased both in the kidney and liver. These results suggest that dyslipidemia was not improved by the acceleration of TG metabolism but by the suppression of activated cholesterol and TG biosyntheses in OLETF rats treated with BPS. High activity of Tkt induced by BPS may be involved in the suppression of such synthetic mechanisms.

Causes of dysregulation of lipid metabolism in chronic renal failure

End-stage renal disease (ESRD) is associated with accelerated atherosclerosis and premature death from cardiovascular disease. These events are driven by oxidative stress inflammation and lipid disorders. ESRD-induced lipid abnormalities primarily stem from dysregulation of high-density lipoprotein (HDL), triglyceride-rich lipoprotein metabolism, and oxidative modification of lipoproteins. In this context, production and plasma concentration of Apo-I and Apo-II are reduced, HDL maturation is impaired, HDL composition is altered, HDL antioxidant and anti-inflammatory functions are depressed, clearance of triglyceride-rich lipoproteins and their atherogenic remnants is impaired, their composition is altered, and their plasma concentration is elevated in ESRD. The associated defect in HDL maturation is largely caused by acquired lecithin-cholesterol acyltransferase deficiency while its triglyceride enrichment is due to hepatic lipase deficiency. Hypertriglyceridemia, abnormal composition, and impaired clearance of triglyceride-rich lipoproteins and their remnants are mediated by down-regulation of lipoprotein lipase, hepatic lipase, very low-density lipoprotein (VLDL) receptor, and LDL receptor-related protein, relative reduction in ApoC-II/ApoC-III ratio, up-regulation of acyl-CoA cholesterol acyltransferase, and elevated plasma level of cholesterol ester-poor prebeta HDL. Impaired clearance and accumulation of oxidation-prone VLDL and chylomicron remnants and abnormal LDL composition in the face of oxidative stress and inflammation favors their uptake by macrophages and resident cells in the artery wall. The effect of heightened influx of lipids is compounded by impaired HDL-mediated reverse cholesterol transport leading to foam cell formation which is the central event in atherosclerosis plaque formation and subsequent plaque rupture, thrombosis, and tissue damage.

Expression profiling of hepatic genes associated with lipid metabolism in nephrotic rats

Hyperlipidemia is one of the major features of nephrotic syndrome (NS). Although many factors have been implicated in the pathogenesis of NS-related dyslipidemia, the underlying mechanisms remain largely uncharacterized. The present study was designed to examine the gene profile associated with lipid metabolism in the livers of nephrotic rats. NS was created in male Sprague-Dawley rats (n = 6) receiving sequential intraperitoneal injections of puromycin aminonucleoside. Analysis by Affymetrix assay, quantitative RT-PCR, and Northern and Western blotting revealed 21 genes associated with cholesterol and fatty acid metabolism. Eight genes involved in cholesterol metabolism, Apo A-I, Acly, Acat, Mpd, Fdps, Ss, Lss, and Nsdhl, were significantly upregulated under NS. Four genes involved in fatty acid biosynthesis, Acc, FAS, ELOVL 2, and ELOVL6, and three critical for triglyceride biosynthesis, Gpam, Agpat 3, and Dgat 1, were significantly upregulated, whereas two genes involved in fatty acid oxidation, Dci and MCAD, were downregulated. Expression of several genes in sterol-regulatory element-binding protein (SREBP)-1 activation was also aberrantly altered in nephrotic livers. The expression and transcriptional activity of SREBP-1 but not SREBP-2 were increased in nephrotic rats as assessed by real-time PCR, immunoblotting, and gel shift assays. The upregulation of hepatic genes involved in cholesterol biosynthesis may play an important role in the pathogenesis of hypercholesterolemia, whereas upregulation of genes participating in hepatic fatty acid and triglyceride biosynthesis and downregulation of genes involved in hepatic fatty acid oxidation may contribute to hypertriglyceridemia in nephrotic rats. Activation of SREBP-1 transcription factor may represent an underlying molecular mechanism of hyperlipidemia in NS.

Dyslipidaemia and cardiorenal disease: mechanisms, therapeutic opportunities and clinical trials

Dyslipidaemia is an important risk factor for the development of chronic kidney disease (CKD) and cardiovascular disease (CVD). CKD generates an atherogenic lipid profile, characterised by high triglycerides, low high-density lipoprotein (HDL) cholesterol and accumulation of small dense low-density lipoprotein (LDL) particles, comparable to that in the metabolic syndrome. These changes are due specifically to the effects of CKD on key enzymes, transfer proteins and receptors involved in lipid metabolism. Dyslipidaemia is further compounded by dialysis, immunosuppressive drugs, and concomitant diseases such as diabetes mellitus. Post hoc analyses from large intervention trials suggest the benefit of statins in patients with early CKD, but prospective clinical trials in haemodialysis (HD) and renal transplant recipients have not conclusively shown improvements in hard cardiovascular end-points. The lack of efficacy of statins in late-stage CKD could be a consequence of other disease processes, such as calcific arteriopathy and insulin resistance, which are not modified by lipid-lowering agents. Despite uncertainty and pending the results of ongoing statin trials such as Study of Heart and Renal Protection (SHARP) and AURORA (A study to evaluate the Use of Rosuvastatin in subjects On Regular haemodialysis: an Assessment of survival and cardiovascular events), major international guidelines continue to support statin therapy in CKD and renal transplant patients to reduce cardiovascular risk burden. Because of increased risk of toxicity, particularly myopathy, statins and other lipid-regulating agents should be used cautiously in CKD and renal transplant recipients.

Hepatic tissue sterol regulatory element binding protein 2 and low-density lipoprotein receptor in nephrotic syndrome

Hypercholesterolemia is a main feature of nephrotic syndrome (NS) and is, in part, caused by acquired low-density lipoprotein (LDL) receptor deficiency. The LDL receptor deficiency in NS is accompanied by normal hepatic LDL receptor messenger RNA (mRNA) abundance. Expression of LDL receptor, 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, and several other cholesterol-regulatory factors is regulated by sterol regulatory element binding protein 2 (SREBP-2). This study tested the hypothesis that nephrotic hypercholesterolemia may be associated with dysregulation of hepatic tissue SREBP-2 abundance or activity. Protein and mRNA abundance of SREBP-2, LDL receptor, and HMG-CoA reductase was determined in the livers of rats with chronic puromycin-induced NS and of control rats. The nephrotic group showed heavy proteinuria, hypoalbuminemia, severe hypercholesterolemia, and normal liver tissue total and free cholesterol concentrations. Despite severe hypercholesterolemia, the inactive microsomal and the active nuclear SREBP-2 levels were unchanged in the liver of the nephrotic animals. This was associated with a marked reduction in LDL receptor protein abundance. In confirmation of our earlier studies, LDL receptor and HMG-CoA reductase mRNA levels were unchanged in nephrotic animals. Hepatic SREBP-2 abundance and activity in hypercholesterolemic nephrotic rats were similar to those found in the normocholesterolemic control animals, representing a maladaptive response. This paradox may be, in part, due to acquired LDL receptor deficiency that helps sustain SREBP-2 expression/activity and maintain hypercholesterolemia by limiting hepatic cholesterol uptake. This is because SREBP-2 expression and activity are, in part, regulated by intracellular as opposed to plasma cholesterol.

Mechanisms of dyslipidemia of chronic renal failure

Chronic renal failure is associated with profound dysregulation of lipid metabolism and marked abnormalities of plasma lipid profile. This review is intended to provide an overview of the molecular basis of lipid disorders in chronic renal failure and explore their potential impact on cardiovascular disease and energy metabolism.

Statins in nephrotic syndrome: a new weapon against tissue injury

The nephrotic syndrome is characterized by metabolic disorders leading to an increase in circulating lipoproteins levels. Hypertriglyceridemia and hypercholesterolemia in this case may depend on a reduction in triglyceride-rich lipoproteins catabolism and on an increase in hepatic synthesis of Apo B-containing lipoproteins. These alterations are the starting point of a self-maintaining mechanism, which can accelerate the progression of chronic renal failure. Indeed, hyperlipidemia can affect renal function, increase proteinuria and speed glomerulosclerosis, thus determining a higher risk of progression to dialysis. 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase is the rate-limiting enzyme in cholesterol synthesis from mevalonate and its inhibitors, or statins, can therefore interfere with the above-mentioned consequences of hyperlipidemia. Statins are already well known for their effectiveness on primary cardiovascular prevention, which cannot be explained only through their hypolipemic effect. As far as kidney diseases are concerned, statin therapy has been shown to prevent creatinine clearance decline and to slow renal function loss, particularly in case of proteinuria, and its favorable effect may depend only partially on the attenuation of hyperlipidemia. Statins may therefore confer tissue protection through lipid-independent mechanisms, which can be triggered by other mediators, such as angiotensin receptor blockers. Possible pathways for the protective action of statins, other than any hypocholesterolemic effect, are: cellular apoptosis/proliferation balance, inflammatory cytokines production, and signal transduction regulation. Statins also play a role in the regulation of the inflammatory and immune response, coagulation process, bone turnover, neovascularization, vascular tone, and arterial pressure. In this study, we would like to provide scientific evidences for the pleiotropic effects of statins, which could be the starting point for the development of new therapeutical strategies in different clinical areas.

Dyslipidemia of chronic renal failure: the nature, mechanisms, and potential consequences

Chronic renal failure (CRF) results in profound lipid disorders, which stem largely from dysregulation of high-density lipoprotein (HDL) and triglyceride-rich lipoprotein metabolism. Specifically, maturation of HDL is impaired and its composition is altered in CRF. In addition, clearance of triglyceride-rich lipoproteins and their atherogenic remnants is impaired, their composition is altered, and their plasma concentrations are elevated in CRF. Impaired maturation of HDL in CRF is primarily due to downregulation of lecithin-cholesterol acyltransferase (LCAT) and, to a lesser extent, increased plasma cholesteryl ester transfer protein (CETP). Triglyceride enrichment of HDL in CRF is primarily due to hepatic lipase deficiency and elevated CETP activity. The CRF-induced hypertriglyceridemia, abnormal composition, and impaired clearance of triglyceride-rich lipoproteins and their remnants are primarily due to downregulation of lipoprotein lipase, hepatic lipase, and the very-low-density lipoprotein receptor, as well as, upregulation of hepatic acyl-CoA cholesterol acyltransferase (ACAT). In addition, impaired HDL metabolism contributes to the disturbances of triglyceride-rich lipoprotein metabolism. These abnormalities are compounded by downregulation of apolipoproteins apoA-I, apoA-II, and apoC-II in CRF. Together, these abnormalities may contribute to the risk of arteriosclerotic cardiovascular disease and may adversely affect progression of renal disease and energy metabolism in CRF.

Effects of gender on hepatic HMG-CoA reductase, cholesterol 7alpha-hydroxylase, and LDL receptor in hereditary analbuminemia

Hypoalbuminemia is accompanied by hypercholesterolemia in both nephrotic syndrome and hereditary analbuminemia. Hypercholesterolemia is more severe in the female than in the male Nagase analbuminemic rats (NAR). The sex difference in plasma cholesterol diminishes after ovariectomy (OVX) and reappears after estrogen replacement in the NAR. The molecular mechanism responsible for the sex difference in severity of hypercholesterolemia in NAR is not known and was investigated here. To this end, hepatic hydroxylmethylglutaryl (HMG)-CoA reductase, cholesterol 7alpha-hydroxylase, and LDL receptor were determined in male, female, and OVX female NAR and Sprague-Dawley (SD) rats. Plasma cholesterol, triglycerides, and hepatic HMG-CoA reductase activities were greater in both female and male NAR than in SD rats. This was coupled with upregulation of cholesterol 7alpha-hydroxylase in both male and female NAR compared with SD controls. LDL receptor in male NAR was similar to that in male SD rats but was significantly reduced in female NAR. OVX partially, but significantly, reduced plasma cholesterol and triglyceride levels in female NAR. This was coupled with a significant rise in hepatic cholesterol 7alpha-hydroxylase and a modest increase in hepatic LDL receptor. In contrast, OVX resulted in a mild elevation of plasma cholesterol and no significant changes in total hepatic HMG-CoA reductase, cholesterol 7alpha-hydroxylase, or LDL receptor in female SD rats. Thus the greater severity of hypercholesterolemia in the female NAR appears to be due, in part, to a combination of the constrained compensatory upregulation of cholesterol 7alpha-hydroxylase and LDL receptor deficiency.

Upregulation of hepatic LDL receptor-related protein in nephrotic syndrome: response to statin therapy

Nephrotic syndrome (N-S) is associated with elevated plasma concentration and impaired clearance of VLDL, chylomicrons (CM), and their atherogenic remnants. These abnormalities are largely due to lipoprotein lipase, hepatic triglyceride lipase, and VLDL receptor deficiencies and impaired HDL-mediated shuttling of apoE and apoC between the nascent and remnant VLDL and CM. LRP is a multifaceted endocytic receptor that is heavily expressed in the liver. LRP recognizes at least 30 different ligands including VLDL and CM remnants. These observations prompted the present study to discern the effect of N-S on hepatic LRP gene and protein expressions. The study further sought to explore the effect of lipid-lowering therapy on LRP expression in N-S. Sprague-Dawley rats were randomized to the N-S (given ip injections of puromycin aminonucleoside; 130 mg/kg on day 1, 60 mg/kg on day 14) and placebo-injected control groups. On day 14, animals were subdivided into statin-treated (rosuvastatin; 20 mg x kg(-1) x day(-1) mixed with powdered chow) and untreated groups and studied on day 28. The untreated N-S group exhibited severe proteinuria, hypoalbuminemia, hypercholesterolemia, hypertriglyceridemia, and marked elevation of hepatic tissue LRP mRNA and protein abundance. Statin administration for 2 wk resulted in significant improvements of plasma lipid profile, proteinuria, and hypoalbuminemia as well as hepatic LRP mRNA and protein abundance. In contrast, statin administration had no significant effect on either plasma lipids or hepatic LRP levels in the normal control rats. In conclusion, N-S results in marked upregulation of hepatic LRP expression that is partly reversed with statin administration. These findings exclude depressed hepatic LRP expression as the primary cause of elevated plasma lipoprotein remnants in N-S.

Dyslipidemia and nephrotic syndrome: Recent advances

Patients with nephrotic syndrome (NS) have one of the most pronounced secondary changes in lipoprotein metabolism known, and the magnitude of the changes correlates with the severity of the disease. These changes are of a quantitative as well as a qualitative nature. All apolipoprotein B (apo B)-containing lipoproteins, such as very-low-density lipoproteins (VLDL), intermediate-density lipoproteins (IDL), low-density lipoproteins (LDL), and lipoprotein(a) [Lp(a)], are elevated in nephrotic syndrome. High-density lipoproteins (HDL) are reported to be unchanged or reduced. In addition to these quantitative changes, the lipoprotein composition is markedly changed, with a higher ratio of cholesterol to triglycerides in the apo B-containing lipoproteins and an increase in the proportion of cholesterol, cholesterol ester, and phospholipids compared with proteins. Also apolipoproteins show major changes, with an increase in apolipoprotein A-I, A-IV, B, C, and E. Particularly the changes in apo C-II, which is an activator of the enzyme lipoprotein lipase (LPL), and apo C-III, an inhibitor of LPL, with an increase of the C-III to C-II ratio, might contribute to the impaired lipoprotein catabolism in NS. The mechanisms for these changes in lipoprotein metabolism are discussed in this review as far as they are known. Furthermore, the tremendous elevations of Lp(a) in nephrotic syndrome and its primary and secondary causes are reviewed. Primary causes became recently apparent by a significantly higher frequency of low-molecular-weight apo(a) phenotypes in patients compared with controls. The secondary causes were shown by an increase of Lp(a) in all apo(a) isoform groups. Because Lp(a) is an LDL-like particle that is usually included in the measured or calculated LDL cholesterol fraction, the influence of the extremely high Lp(a) levels in NS on the measurement of LDL cholesterol is discussed.

HMG-CoA reductase inhibition reverses LCAT and LDL receptor deficiencies and improves HDL in rats with chronic renal failure

Dyslipidemia is a prominent feature of chronic renal failure (CRF) and a major risk factor for atherosclerosis and the progression of renal disease. CRF-induced dyslipidemia is marked by hypertriglyceridemia and a shift in plasma cholesterol from HDL to the ApoB-containing lipoproteins. Several studies have demonstrated a favorable response to administration of 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase inhibitors (statins) in CRF. This study was intended to explore the effect of statin therapy on key enzymes and receptors involved in cholesterol metabolism. Accordingly, CRF ( nephrectomized) and sham-operated rats were randomized to untreated and statin-treated (rosuvastatin 20 mg·kg−1·day−1) groups and observed for 6 wk. The untreated CRF rats exhibited increased total cholesterol-to-HDL cholesterol ratio, diminished plasma lecithin:cholesterol acyltransferase (LCAT) and the hepatic LDL receptor, elevated hepatic acyl-CoA:cholesterol acyltransferase (ACAT), and no change in hepatic HMG-CoA reductase, cholesterol 7α-hydroxylase, or HDL receptor (SRB-1). Statin administration lowered HMG-CoA reductase activity, normalized plasma LCAT, total cholesterol-to-HDL cholesterol ratio, and hepatic LDL receptor but did not significantly change either plasma total cholesterol, hepatic cholesterol 7α-hydroxylase, total ACAT activity, or SRB-1 in the CRF animals. Statin administration to the normal control rats led to significant increases in plasma LCAT and hepatic LDL receptor, significant reductions of total cholesterol-to-HDL cholesterol ratio, hepatic HMG-CoA reductase activity, and cholesterol 7α-hydroxylase abundance with virtually no change in plasma cholesterol concentration. Thus administration of rosuvastatin reversed LCAT and LDL receptor deficiencies and promoted a shift in plasma cholesterol from ApoB-containing lipoproteins to HDL in CRF rats.

Up-regulation of hepatic Acyl CoA: Diacylglycerol acyltransferase-1 (DGAT-1) expression in nephrotic syndrome

BACKGROUND

Nephrotic syndrome is associated with hypercholesterolemia, hypertriglyceridemia, and marked elevations of plasma low-density lipoprotein (LDL) and very low-density lipoprotein (VLDL). Hypertriglyceridemia in nephrotic syndrome is accompanied by increased hepatic fatty acid synthesis, elevated triglyceride secretion, as well as lipoprotein lipase, VLDL-receptor, and hepatic triglyceride lipase deficiencies, which lead to impaired clearance of triglyceride-rich lipoproteins. Acyl CoA: diacylglycerol acyltransferase (DGAT) is a microsomal enzyme that joins acyl CoA to 1, 2-diacylglycerol to form triglyceride. Two distinct DGATs (DGAT-1 and DGAT2) have recently been identified in the liver and other tissues. The present study tested the hypothesis that the reported increase in hepatic triglyceride secretion in nephrotic syndrome may be caused by up-regulation of DGAT.

METHODS

Male Sprague-Dawley rats were rendered nephrotic by two sequential injections of puromycin aminonucleoside (130 mg/kg on day 1 and 60 mg/kg on day 14) and studied on day 30. Placebo-treated rats served as controls. Hepatic DGAT-1 and DGAT-2 mRNA abundance and enzymatic activity were measured.

RESULTS

The nephrotic group exhibited heavy proteinuria, hypoalbuminemia, hypercholesterolemia, hypertriglyceridemia, and marked elevation of VLDL concentration. Hepatic DGAT-1 mRNA, DGAT-1, and total DGAT activity were significantly increased, whereas DGAT-2 mRNA abundance and activity were unchanged in the nephrotic rats compared to the control animals. The functional significance of elevation of DGAT activity was illustrated by the reduction in microsomal free fatty acid concentration in the liver of nephrotic animals.

CONCLUSION

Nephrotic syndrome results in up-regulation of hepatic DGAT-1 expression and activity, which can potentially contribute to the associated hypertriglyceridemia by enhancing triglyceride synthesis. Thus, it appears that both depressed catabolism and increased synthetic capacity contribute to hypertriglyceridemia of nephrotic syndrome.

Effects of HMG-CoA reductase inhibition on hepatic expression of key cholesterol-regulatory enzymes and receptors in nephrotic syndrome

BACKGROUND

Hypercholesterolemia is one of the major manifestations of nephrotic syndrome. We have previously shown that nephrotic hypercholesterolemia is associated with and, in part, due to dysregulation of hepatic HMG-CoA reductase, acyl-CoA:cholesterol acyltransferase (ACAT) and cholesterol 7alpha-hydroxylase, as well as lecithin:cholesterol acyltransferase (LCAT), low-density lipoprotein (LDL) receptor and high-density lipoprotein (HDL) receptor deficiencies. This study was carried out to discern the effect of inhibition of HMG-CoA reductase on expression of the key enzymes and receptors involved in cholesterol metabolism in the liver.

METHODS

Rats with puromycin-induced nephrotic syndrome were treated with either a statin (rosuvastatin 20 mg/kg/day) or placebo for 2 weeks. Placebo-treated normal rats served as controls. Gene expression, protein abundance and/or activities of relevant receptors and enzymes were quantified.

RESULTS

The untreated nephrotic rats showed heavy proteinuria, hypoalbuminemia, hypercholesterolemia, elevated total cholesterol:HDL cholesterol ratio and normal creatinine clearance. This was associated with severe reductions in hepatic LDL receptor, hepatic HDL receptor and plasma LCAT concentration, marked upregulation of hepatic ACAT, and unchanged cholesterol 7alpha-hydroxylase (rate-limiting step in cholesterol catabolism). Statin administration for 2 weeks ameliorated hepatic LDL receptor and HDL receptor deficiencies and significantly lowered plasma cholesterol, LDL cholesterol, total cholesterol:HDL cholesterol ratio and proteinuria.

CONCLUSIONS

HMG-CoA reductase inhibition improved hepatic LDL and HDL receptor deficiencies, and ameliorated the associated hyperlipidemia in the nephrotic rats.

AT-1 receptor blockade prevents proteinuria, renal failure, hyperlipidemia, and glomerulosclerosis in the Imai rat

BACKGROUND

The Imai rat is a model of spontaneous focal glomerulosclerosis which leads to nephrotic syndrome, hyperlipidemia, hypertension, and progressive renal failure. We evaluated the effects of angiotensin II receptor type 1 (AT-1)blockade, and compared the results with the effects of the administration of hypolipidemic treatment with a 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor. All treatments were started at 10 weeks of age when the rats were already proteinuric and continued for 6 months when rats were sacrificed.

METHODS

The following groups (N= 6 each) were studied: (1) control Sprague-Dawley rats, 34 weeks old; (2) Imai group that received vehicle; (3) Imai + angiotensin II receptor blockade (ARB) group that received olmesartan (10 mg/kg/day by gastric gavage); (4) Imai + prava group, that received pravastatin (20 mg/kg/day by gastric gavage); and (5) Imai + ARB + prava group that received both ARB and pravastatin. Lipid profile, renal function, and structure were assessed at 6 months.

RESULTS

As expected, the untreated Imai rats exhibited heavy proteinuria, hypoalbuminemia, hypertension, renal insufficiency, marked glomerulosclerosis, tubulointerstitial inflammation, and profound hyperlipidemia. Pravastatin treatment alone led to a significant, but partial improvement of hyperlipidemia and renal disease. The ARB treatment alone or in combination with pravastatin resulted in normalization of the blood pressure, urinary protein excretion, plasma cholesterol, triglycerides, low-density lipoproteins (LDLs), very low-density lipoproteins (VLDLs), and albumin concentrations and renal function. Significant glomerulosclerosis was prevented and tubulointerstitial injury and immune cell infiltration were reduced by long-term AT-1 blockade.

CONCLUSION

The study revealed that long-term AT-1 blockade corrects proteinuria, hyperlipidemia, and nephropathy in this model of spontaneous glomerulosclerosis.

The Potential Role of HMG-CoA Reductase Inhibitors in Pediatric Nephrotic Syndrome

OBJECTIVE

To evaluate the safety and efficacy of the hydroxymethylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) as a potential treatment option for the dyslipidemia associated with childhood nephrotic syndrome.

DATA SOURCES

Searches of MEDLINE (1966–April 2004), Cochrane Library, International Pharmaceutical Abstracts (1977–April 2004), and an extensive manual review of journals were performed using the key search terms nephrotic syndrome, familial hypercholesterolemia, dyslipidemia, and HMG-CoA reductase inhibitor.

STUDY SELECTION AND DATA EXTRACTION

Two prospective uncontrolled studies evaluating the safety and efficacy of statin therapy in pediatric nephrotic syndrome were included.

DATA SYNTHESIS

While an extensive amount of data is available in adult nephrotic syndrome in which statin therapy decreases total plasma cholesterol 22–39%, low-density lipoprotein cholesterol (LDL-C) 27–47%, and total plasma triglycerides 13–38%, only 2 small uncontrolled studies have been conducted evaluating the utility of these agents in pediatric nephrotic syndrome. These studies indicate that statins are capable of safely reducing total cholesterol up to 42%, LDL-C up to 46%, and triglyceride levels up to 44%.

CONCLUSIONS

Lowering cholesterol levels during childhood may reduce the risk for atherosclerotic changes and may thus be of benefit in certain patients with nephrotic syndrome. Statins have demonstrated short-term safety and efficacy in the pediatric nephrotic syndrome population. Implementing pharmacologic therapy with statins in children with nephrotic syndrome must be done with care until controlled studies are conducted in this population.

HMG-CoA reductase, cholesterol 7alpha-hydroxylase, LDL receptor, SR-B1, and ACAT in diet-induced syndrome X

BACKGROUND

Long-term consumption of Western diets can lead to acquired syndrome X, which presents with obesity, insulin resistance, hypertension, hyperlipidemia, and risk of atherosclerotic cardiovascular disease. While plasma lipid abnormalities in syndrome X have been well characterized, their molecular basis remains unclear. This study explored potential mechanisms of hypercholesterolemia in diet-induced syndrome X.

METHODS

Female Fischer rats were fed a high-fat, refined-carbohydrate (sucrose) diet (HFS) or standard rat chow (low-fat, complex carbohydrate, LFCC) for 20 months. Plasma lipids and hepatic tissue mRNA, protein, and/or activities of the key enzymes and receptors involved in cholesterol metabolism were determined.

RESULTS

The HFS group exhibited hypertension, hyperlipidemia, insulin resistance, obesity, significant down-regulation of hepatic cholesterol 7alpha-hydroxylase (the rate-limiting step in cholesterol catabolism) and low-density lipoprotein (LDL) receptor (LDL-R, the primary pathway of LDL clearance). In contrast, hepatic tissue acyl-coenzyme A:cholesterol acyltransferase (ACAT-2, the primary enzyme involved in intracellular esterification of cholesterol) and scavenger-receptor class B, type 1 (SR-B1 or HDL receptor) were up-regulated. While 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase mRNA expression was increased, its protein abundance and activity were unchanged, and HMG-CoA reductase-to-cholesterol 7alpha-hydroxylase ratio was increased in HFS-fed animals.

CONCLUSION

Hypercholesterolemia in diet-induced syndrome X is associated with depressed cholesterol 7alpha-hydroxylase, diminished LDL-R, elevated ACAT, and increased HMG-CoA reductase-to-cholesterol 7alpha-hydroxylase ratio. These findings point to impaired hepatic catabolism and uptake of cholesterol and inappropriate cholesterol production capacity as the underlying causes of hypercholesterolemia in rats with diet-induced syndrome X.

Acyl-coenzyme A:cholesterol acyltransferase inhibition ameliorates proteinuria, hyperlipidemia, lecithin-cholesterol acyltransferase, SRB-1, and low-denisty lipoprotein receptor deficiencies in nephrotic syndrome

BACKGROUND

Nephrotic syndrome (NS) is associated with hyperlipidemia, altered lipid regulatory enzymes and receptors, and increased risk of progressive renal and cardiovascular diseases. Acyl-coenzyme A:cholesterol acyltransferase (ACAT) catalyzes intracellular esterification of cholesterol and plays an important role in production of apolipoprotein B-containing lipoproteins, regulation of cholesterol-responsive proteins, and formation of foam cells. Because hepatic ACAT-2 is markedly upregulated in NS, we tested the hypothesis that inhibition of ACAT may improve cholesterol metabolism in NS.

METHODS AND RESULTS

Rats with puromycin-induced NS were treated with either the ACAT inhibitor CI-976 or placebo for 2 weeks. Normal rats served as controls. Plasma lipids, renal function, and key lipid regulatory factors were measured. Untreated NS rats showed heavy proteinuria; hypoalbuminemia; elevated plasma cholesterol, triglyceride, LDL, VLDL, and total cholesterol-to-HDL cholesterol ratio; increased hepatic ACAT activity, ACAT-2 mRNA, and ACAT-2 protein; and reduced LDL receptor, HDL receptor, otherwise known as scavenger receptor B-1 (SRB-1) and plasma lecithin-cholesterol acyltransferase (LCAT). ACAT inhibitor reduced plasma cholesterol and triglycerides, normalized total cholesterol-to-HDL cholesterol ratio, and lowered hepatic ACAT activity without changing ACAT-2 mRNA or protein. This was accompanied by near normalizations of plasma LCAT, hepatic SRB-1, and LDL receptor and a significant amelioration of proteinuria and hypoalbuminemia.

CONCLUSIONS

Pharmacological inhibition of ACAT reverses NS-induced LDL receptor, HDL receptor, and LCAT deficiencies; improves plasma lipid profile; and ameliorates proteinuria in nephrotic animals. Further studies are needed to explore the effect of ACAT inhibition in nephrotic humans.

ACAT inhibition reverses LCAT deficiency and improves plasma HDL in chronic renal failure

Chronic renal failure (CRF) is associated with increased risk of arteriosclerotic cardiovascular disease and profound alteration of plasma lipid profile. Uremic dyslipidemia is marked by increased plasma concentration of ApoB-containing lipoproteins and impaired high-density lipoprotein (HDL)-mediated reverse cholesterol transport. These abnormalities are, in part, due to acquired LCAT deficiency and upregulation of hepatic acyl-CoA:cholesterol acyltransferase (ACAT). ACAT catalyzes intracellular esterification of cholesterol, thereby promoting hepatic production of ApoB-containing lipoproteins and constraining HDL-mediated cholesterol uptake in the peripheral tissues. In view of the above considerations, we tested the hypothesis that pharmacological inhibition of ACAT may ameliorate CRF-induced dyslipidemia. 5/6 Nephrectomized rats were treated with either ACAT inhibitor IC-976 (30 mg.kg(-1).day(-1)) or placebo for 6 wk. Sham-operated rats served as controls. Key cholesterol-regulating enzymes, plasma lipids, and creatinine clearance were measured. The untreated CRF rats exhibited increased plasma low-density lipoprotein (LDL) and very LDL (VLDL) cholesterol, unchanged plasma HDL cholesterol, elevated total cholesterol-to-HDL cholesterol ratio, reduced liver microsomal free cholesterol, and diminished creatinine clearance. This was accompanied by reduced plasma LCAT, increased hepatic ACAT-2 mRNA, ACAT-2 protein and ACAT activity, and unchanged hepatic HMG-CoA reductase and cholesterol 7alpha-hydroxylase. ACAT inhibitor raised plasma HDL cholesterol, lowered LDL and VLDL cholesterol, and normalized total cholesterol-to-HDL cholesterol ratio without changing total cholesterol concentration (hence, a shift from ApoB-containing lipoproteins to HDL). This was accompanied by normalizations of hepatic ACAT activity and plasma LCAT. In conclusion, inhibition of ACAT reversed LCAT deficiency and improved plasma HDL level in CRF rats. Future studies are needed to explore the efficacy of ACAT inhibition in humans with CRF.

Protein restriction and AST-120 improve lipoprotein lipase and VLDL receptor in focal glomerulosclerosis

BACKGROUND

Imai rats exhibit spontaneous focal glomerulosclerosis (FGS) with progressive proteinuria and hyperlipidemia leading to renal insufficiency by age 34 weeks. Recently, we reported marked down-regulations of skeletal muscle and adipose tissue lipoprotein lipase (LPL) and very low-density lipoprotein (VLDL) receptor in male Imai rats at 32 weeks of age. Dietary protein restriction and oral adsorbent AST-120 (AST) have been shown to slow progression of renal disease and attenuate hyperlipidemia in the Imai rats. This study tested the hypothesis that amelioration of proteinuria by protein restriction or use of oral adsorbent AST-120 beginning at 10 weeks of age may improve renal disease and LPL and VLDL receptor deficiencies in Imai rats.

METHODS

Ten-week-old male Imai rats were randomly assigned to those fed either a regular diet, low protein diet (LPD), or regular diet containing the adsorbent preparation, AST-120. Ten-week-old male Sprague-Dawley rats served as controls. The animals were observed for 24 weeks. Six rats were included in each group. All diets were prepared in powder form.

RESULTS

The untreated 34-week-old Imai rats showed severe proteinuria, hypoalbuminemia, 50% reduction in creatinine clearance, hypercholesterolemia, hypertriglyceridemia, and elevated plasma VLDL concentration. This was associated with significant reductions in plasma post-heparin LPL activity, hepatic lipase activity, as well as adipose tissue and skeletal muscle immunodetectable LPL and VLDL receptor proteins. Protein restriction mitigated the decline in creatinine clearance, ameliorated proteinuria, hypoalbuminemia, hypertension, and hypercholesterolemia, lowered plasma VLDL, and improved plasma postheparin LPL activity, hepatic lipase activity, LPL, and VLDL receptor proteins in skeletal muscle and adipose tissue. Similar improvements were observed in all parameters with AST administration.

CONCLUSION

Moderate protein restriction and use of oral adsorbent can slow progression of renal disease and, thereby, ameliorate LPL, hepatic lipase, and VLDL receptor deficiencies and the associated hyperlipidemia in rats with spontaneous FGS.

Pathobiochemistry of nephrotic syndrome

Nephrotic syndrome is a clinical and laboratory syndrome caused by the increased permeability of the glomerular capillary wall for macromolecules. Nephrotic syndrome is a potentially life-threatening state and persistent nephrotic syndrome has a poor prognosis with a high risk of progression to end-stage renal failure and a high risk of cardiovascular complications due to severe hyperlipidemia. Pathogenesis of increased glomerular permeability in different glomerular diseases has not been fully elucidated. Recently, identification of the mutated genes for some podocyte proteins (nephrin, podocin, alpha-actinin-4) in rare familial forms of nephrotic syndrome shed has new light on the molecular mechanisms of glomerular permselectivity. Gradually it becomes apparent that sporadic mutations of podocyte proteins (e.g., podocin) may be present even in some patients with acquired nephrotic syndrome. Expression of other podocyte proteins may change during the course of experimental nephrotic syndrome, possibly as a response to podocyte damage resulting either in apoptosis or stimulation of proliferation and some form of repair, including glomerular sclerosis. Better understanding of these mechanisms could clearly also have therapeutic implications. Glomerular permeability factors are believed to play a role in some noninflammatory glomerular diseases, mainly minimal change disease and focal segmental glomerulosclerosis, but their molecular identification remains elusive, possibly due to the nonhomogeneous nature of the underlying diseases. As an example, focal segmental glomerulosclerosis possibly can be caused by the sporadic mutation of some genes for podocyte proteins, increased production of glomerular permeability factor (possibly by T lymphocytes), or the loss of inhibitors of glomerular permeability factors in nephrotic urine. Clearly the factors causing increased glomerular permeability and factors perpetuating glomerular sclerosis are not necessarily the same. Proteinuria does not seem to be only the consequence of glomerular damage, but it may possibly cause tubular damage and initiate interstitial fibrosis and thus contribute to the progression of chronic renal failure in proteinuric renal diseases. Recent insights into the mechanisms of tubular protein reabsorption may give new tools for preventing the progression of chronic renal disease. Cubilin inhibitors could potentially ameliorate tubular and interstitial damage in patients with heavy proteinuria refractory to treatment. Nephrotic hyperlipidemia is accompanied with increased risk of cardiovascular complications and should be treated in all patients with persistent nephrotic syndrome. The putative positive effect of hypolipidemic drugs (namely statins) on the cardiovascular risk and potentially also on the rate of progression of chronic renal failure remains to be demonstrated in prospective controlled studies. Recent progress in understanding podocyte biology in rare inherited glomerular diseases gives the chance to understand in the near future the molecular pathogenesis of increased glomerular permeability in the much more common acquired forms of nephrotic syndrome.

HMG-CoA reductase, cholesterol 7alpha-hydroxylase, LCAT, ACAT, LDL receptor, and SRB-1 in hereditary analbuminemia

BACKGROUND

Hereditary analbuminemia is associated with hypercholesterolemia, which has been shown to be primarily caused by increased extrahepatic production of cholesterol. Nagase rats with hereditary analbuminemia (NAR) have been used as a model to dissect the effect of primary hypoalbuminemia from that caused by proteinuria in nephrotic syndrome. The present study was undertaken to explore the effect of hereditary analbuminemia on protein expression of the key factors involved in cholesterol metabolism.

METHODS

Hepatic tissue protein abundance of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, cholesterol 7alpha-hydroxylase (a rate-limiting enzyme in cholesterol catabolism), low density lipoprotein (LDL) receptor, high density lipoprotein (HDL) receptor (SRB-1), acyl-coA cholesterol acyltransferase-2 (ACAT-2), and plasma concentration of lecithin cholesterol acyltransferase (LCAT), as well as HMG-CoA reductase, ACAT, and LCAT activities were determined in fasting male NAR and Sprague-Dawley control rats.

RESULTS

The NAR group exhibited significant up-regulation of HMG-CoA reductase protein abundance but normal HMG-CoA reductase enzymatic activity. This was coupled with a significant up-regulation of cholesterol 7alpha-hydroxylase and a mild up-regulation of ACAT protein abundance and activity. However, hepatic LDL receptor and HDL receptor and plasma LCAT protein concentration and activity were normal in NAR.

CONCLUSION

Hypercholesterolemia in NAR is associated with elevated hepatic HMG-CoA reductase protein abundance, but normal HMG-CoA reductase activity. These findings point to post-translational regulation of this enzyme and favor an extrahepatic origin of hypercholesterolemia in NAR. The observed up-regulation of cholesterol 7alpha-hydroxylase represents a compensatory response to the associated hypercholesterolemia. Unlike nephrotic syndrome, which causes severe LDL receptor, HDL receptor, and LCAT deficiencies, hereditary analbuminemia does not affect these proteins.

Molecular mechanisms of altered cholesterol metabolism in rats with spontaneous focal glomerulosclerosis

BACKGROUND

Imai rats exhibit spontaneous focal glomerulosclerosis (FGS), which is marked by heavy proteinuria, severe hyperlipidemia, and progressive renal insufficiency beginning at 8 to 10 weeks of age. In an earlier study, we reported severe skeletal muscle and adipose tissue lipoprotein lipase, and very low-density lipoprotein (VLDL) receptor deficiencies, which account for elevated plasma VLDL and triglycerides in Imai rats at 34 weeks of age. In this study, we investigated key factors involved in cholesterol metabolism.

METHODS

Male Imai and Sprague-Dawley control rats were fed a regular rat chow and observed from age 8 through 34 weeks. Hepatic 3-hydroxy-3 methylglutaryl coenzyme A (HMG-CoA) reductase, cholesterol 7alpha-hydroxylase, low-density lipoprotein (LDL) receptor and acyl Co A:cholesterol acyltransferase (ACAT) were measured by Western blot and plasma lecithin:cholesterol acyltransferase (LCAT) protein was measured by enzyme-linked immunosorbent assay (ELISA).

RESULTS

At 34 weeks of age, the Imai rats showed severe proteinuria, hypoalbuminemia, 60% reduction in glomerular filtration rate (GFR), elevated plasma total and LDL cholesterol and LDL/high-density lipoprotein (HDL) ratio. Imai rats showed a twofold elevation of hepatic HMG-CoA reductase, the rate-limiting step in cholesterol biosynthesis, but no significant change in cholesterol 7alpha-hydroxylase, the rate-limiting enzyme in cholesterol catabolism to bile acids. This was accompanied by and largely due to a threefold down-regulation of hepatic LDL receptor, which limits hepatic uptake of LDL; and a threefold up-regulation of hepatic ACAT (P < 0.01), which augments esterification of hepatocyte free cholesterol, thus, limiting cholesterol-mediated feedback regulation of cholesterol synthesis and catabolism. Moreover, plasma LCAT concentration was severely depressed (by fourfold) in Imai rats. This abnormality can impair HDL-mediated cholesterol transport from extrahepatic tissues to the liver.

CONCLUSION

The study revealed marked abnormalities of the key proteins involved in regulation of hepatic cholesterol metabolism. These abnormalities can account for severe dysregulation of cholesterol metabolism in Imai rats with spontaneous FGS, which closely resembles FGS in humans.

Up-regulation of acyl-coenzyme A:cholesterol acyltransferase (ACAT) in nephrotic syndrome

BACKGROUND

We have previously demonstrated that hypercholesterolemia in rats with puromycin-induced nephrotic syndrome (NS) is associated with up-regulation of hepatic 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase and relative down-regulation of cholesterol 7alpha-hydroxylase (Ch-7alpha), which represent the rate-limiting steps in cholesterol biosynthesis and catabolism. Expression of HMG-CoA reductase is inhibited and Ch-7alpha is augmented by intracellular free cholesterol, which is avidly esterified by acyl-CoA:cholesterol acyltransferase (ACAT). Therefore, we hypothesized that NS may result in up-regulation of hepatic ACAT.

METHODS

Hepatic tissue ACAT mRNA (Northern blot), protein (Western blot) and enzymatic activity were determined in rats with puromycin-induced NS, placebo-treated control rats and Nagase hypoalbuminemic (NAG) rats.

RESULTS

The NS group exhibited heavy proteinuria, hypoalbuminemia, normal creatinine clearance, severe hypercholesterolemia and hypertriglyceridemia. Despite severe hypoalbuminemia, NAG rats with inherited hypoalbuminemia exhibited only a mild elevation of plasma cholesterol and triglycerides. Severe hypercholesterolemia in the NS group was coupled with depressed liver tissue free cholesterol concentration and marked increases in hepatic ACAT mRNA, protein and enzymatic activity. In contrast, ACAT mRNA and protein contents of the liver were normal and ACAT activity was mildly elevated in the NAG group.

CONCLUSIONS

NS results in marked up-regulation of hepatic ACAT, which is primarily due to proteinuria and not hypoalbuminemia, since the latter alone, as seen in NAG rats, does not significantly impact ACAT expression. Elevated ACAT in NS can contribute to dysregulation of cholesterol biosynthesis and catabolism by limiting the normal cholesterol signaling involved in regulation of these processes.

Acquired lecithin-cholesterol acyltransferase deficiency in nephrotic syndrome

Lecithin-cholesterol acetyltransferase (LCAT) is involved in the synthesis of plasma cholesteryl esters and is pivotal in the maturation of plasma high-density lipoprotein (HDL) and conversion of HDL3 to HDL2. In nephrotic syndrome (NS), the ratio of HDL2 to HDL3 is low even though the total concentration of HDL is generally normal. We hypothesize that the reduced HDL2/HDL3 ratio in NS is due to urinary losses of LCAT, leading to plasma LCAT deficiency. To test this hypothesis, Sprague-Dawley rats were randomized to NS (given 130 mg puromycin aminonucleoside on day 1 and 60 mg ip on day 14) or control groups and were studied on day 30. To dissect the effect of proteinuria from hypoalbuminemia, a group of Nagase rats with inherited hypoalbuminemia was included. Hepatic LCAT and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) mRNA abundance and plasma and urine LCAT activity were measured. The NS group showed a fourfold rise in serum cholesterol and triglycerides, a fivefold rise in free cholesterol, and a fourfold fall in the HDL-to-total cholesterol ratio. Despite severe hypoalbuminemia, the Nagase rats showed only a mild elevation of serum cholesterol and triglycerides with a normal serum free cholesterol and HDL-to-total cholesterol ratio. The NS group exhibited a normal hepatic LCAT-to-GAPDH mRNA ratio, a marked reduction in plasma LCAT activity, and a significant increase in urinary LCAT excretion. LCAT/GAPDH mRNA and plasma and urine LCAT were normal in Nagase rats. Thus NS led to heavy urinary losses and reduced plasma concentration of LCAT, despite normal hepatic LCAT mRNA abundance. However, hypoalbuminemia, per se, without proteinuria as seen in the Nagase rats had no effect on plasma LCAT or the HDL-to-total cholesterol ratio. Therefore, proteinuria, not hypoalbuminemia, causes LCAT deficiency and a depressed HDL-to-total cholesterol ratio in NS.

Down-regulation of hepatic high-density lipoprotein receptor, SR-B1, in nephrotic syndrome

BACKGROUND

Nephrotic syndrome (NS) is a prototype of acquired hypercholesterolemia. Hepatic synthesis and removal of cholesterol play major roles in the regulation of plasma concentration of this sterol. Low-density lipoprotein (LDL) and high-density lipoprotein (HDL) particles are the primary vehicles for cholesterol transport to the liver. We have recently demonstrated that NS results in acquired hepatic LDL receptor deficiency in rats. This study was undertaken to determine the effect of NS on hepatic expression of the newly discovered, long-sought HDL receptor.

METHODS

Hepatic HDL receptor and apolipoprotein A-I (apo A-I) expressions were studied in rats with puromycin-induced NS. The results were compared with those obtained in placebo-treated, normal controls.

RESULTS

The NS group exhibited a marked reduction in hepatic tissue HDL receptor protein abundance when compared with the control group. In contrast, hepatic HDL receptor mRNA abundance in the NS group was similar to that of the control group. As expected, the NS group showed a marked increase in hepatic apo A-I mRNA abundance.

CONCLUSIONS

The study explored the effect of experimental NS on hepatic HDL receptor expression, and the results revealed a marked down-regulation of HDL receptor in rats with NS. In contrast, hepatic expression of Apo A-I, the principal protein constituent of HDL, was markedly increased in NS rats. The HDL receptor deficiency shown here can potentially limit the efficiency of HDL as the primary vehicle for reverse cholesterol transport in NS.

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.

Hepatic cholesterol metabolism in experimental nephrotic syndrome

Hypercholesterolemia is a consistent feature of the nephrotic syndrome. However, the mechanisms underlying this perturbation are unclear. In the present work, we have investigated different factors that influence hepatic cholesterol metabolism using the nephrotic rat as a model. The induction of nephrosis resulted in a severe and sustained hypercholesterolemia. However, no effect on the rate-limiting enzyme in cholesterol synthesis, 3-hydroxy-3-methylglutaryl CoA reductase, could be detected. Further, plasma lathosterol/cholesterol ratio, a measure of cholesterol synthesis, was not altered. Also, plasma levels of mevalonate, both a substrate for cholesterogenesis beyond the rate-limiting step and a marker for cholesterol synthesis, did not differ between control rats and those with established hypercholesterolemia. There was no detectable change in the expression of low density lipoprotein (LDL) receptor between the two experimental groups. We conclude that the early increase in cholesterol synthesis reported after the induction of nephrosis is not necessary for the maintenance of hypercholesterolemia. Established hypercholesterolemia of the nephrotic syndrome seems to represent a steady state in which neither enhanced hepatic cholesterol synthesis nor retarded LDL cholesterol clearance is of major importance.

Bile acid metabolism in analbuminemic rats

The bile acid concentrations in the serum, liver, bile, intestines, and feces of 3- and 19-mon-old male and female Nagase analbuminemic (NA) rats were compared with those in Sprague-Dawley (SD) rats. There was no significant difference in the bile acid levels between NA and SD rats. However, increased biosynthesis and pool size of cholic acid (CD) derivatives and decreased levels of chenodeoxycholic acid (CDCA) derivatives (increased CA/CDCA ratio) were detected in male NA rats as compared to SD rats. The CA/CDCA ratio in female NA rats was not different from that in their SD counterparts. There were no significant differences between NA and SD rats in the biliary bile flow, bile acid levels in the small and large intestines, fecal bile acid excretion, bile acid concentration in the portal and systemic circulation, and in the pool size of bile acids. The blood lipid concentrations were significantly higher in the NA rats than in the SD rats. The hepatic levels of lipids were not significantly different between the two rat strains. In conclusion, this study showed that metabolism of bile acids in NA rats is not significantly affected, and that the hypercholesterolemia observed in these strains is not related to abnormalities of bile acid metabolism.

Gene expression of lipoprotein lipase in experimental nephrosis

Nephrotic syndrome (NS) is commonly associated with marked hypertriglyceridemia, impaired triglyceride-laden lipoprotein clearance, and reduced peripheral tissue uptake of triglycerides from chylomicrons. Lipoprotein lipase (LPL) is the rate-limiting step in triglyceride-rich lipoprotein metabolism. Earlier studies have demonstrated a marked reduction of plasma post-heparin lipolytic activity and LPL protein in NS. However, the effect of NS on gene expression of LPL has not been elucidated. We studied rats with puromycin aminonucleoside-induced NS and the placebo-injected control animals. Heart, soleus muscle, and fat body LPL activity, protein mass, and mRNA were measured and plasma lipid levels were quantitated. The NS group exhibited marked proteinuria, hypoalbuminemia, and hypertriglyceridemia. This was associated with significant reductions of LPL activity and immunodetectable protein in the heart, adipose tissue, and soleus muscle in the NS group. The reduction in LPL protein mass in the tissues tested was accompanied by a parallel reduction in LPL mRNA of the heart but not of either adipose tissue or skeletal muscle, suggesting translational or posttranslational modifications. A negative correlation was found between plasma triglyceride concentration and the LPL, activities of the tissues tested in the study population. Thus this study has revealed a significant down-regulation of tissue LPL protein in experimental NS. This phenomenon can, in part, account for hypertriglyceridemia, impaired catabolism of chylomicrons, and very low-density lipoprotein by peripheral tissues and decreased postheparin lipolytic activity in NS.

Acquired VLDL receptor deficiency in experimental nephrosis

Nephrotic syndrome (NS) is commonly associated with elevation of plasma very low density lipoprotein (VLDL) and triglyceride concentrations. VLDL receptor (VLDL-R) is a novel protein that specifically binds and internalizes VLDL particles and is primarily distributed in heart, skeletal muscle, brain and adipose tissue. Based on these properties, VLDL-R is thought to play a role in VLDL and triglyceride metabolism. The present study was undertaken to test the hypothesis that elevation of plasma VLDL in NS may be, in part, related to VLDL-R deficiency. To this end, heart and skeletal muscle VLDL-R protein (Western blot) and mRNA (Northern blot) were measured at various points in the course of puromycin-induced NS in rats. The results were compared with those obtained in the placebo-treated normal control animals. The NS group showed a significant decline in VLDL-R protein (relative to total plasma membrane protein mass) in the heart and skeletal muscle paralleling the rise in plasma VLDL and triglyceride concentrations. The fall in VLDL-R protein was accompanied by a parallel decline in VLDL-R mRNA in the heart but not skeletal muscle. VLDL-R protein was directly related to proteinuria and inversely related to plasma VLDL and triglyceride concentrations. In conclusion, puromycin-induced NS in rats is associated with profound reduction in heart and skeletal muscle VLDL receptor protein. Acquired VLDL-R deficiency, shown for the first time here, may contribute to elevation of plasma concentration of triglyceride-rich VLDL in the nephrotic rat. Recognition of this abnormality reveals another dimension of the complex dysregulation of lipid metabolism in NS. The precise mechanism responsible for NS-induced VLDL-R deficiency in this model is not clear and awaits further investigation.