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.     

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.     

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.     

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.     

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.     

Cholesterol metabolism in alloxan-induced diabetic rabbits

The effect of diabetes control on the activities of hydroxymethylglutaryl-CoA reductase (HMG-CoA reductase), cholesterol acyltransferase (ACAT), and phenol 2-monooxygenase, the major enzymes regulating cholesterol metabolism, was determined in alloxan-induced diabetic rabbits, and the results obtained were correlated with lipid and lipoprotein levels. Although intestinal HMG-CoA reductase activity was significantly increased (P less than 0.001) in poorly controlled compared with moderately controlled diabetic rabbits, there was a significant reduction in the activities of intestinal ACAT (P less than 0.01), hepatic HMG-CoA reductase (P less than 0.05) and ACAT (P less than 0.001), and phenol 2-monooxygenase (P less than 0.01). The poorly controlled animals were hypercholesterolemic (P less than 0.01), and this was reflected in the very-low-density and high-density lipoprotein fractions. Serum cholesterol levels in the nondiabetic and moderately controlled diabetic groups were similar. This increase in intestinal HMG-CoA reductase activity in the poorly controlled diabetic animals occurred in the absence of hyperphagia. Although abnormalities in cellular cholesterol metabolism could be partly responsible for the alterations in serum cholesterol levels in diabetes, the precise mechanisms underlying these enzymatic changes have yet to be elucidated.     

Disorders in high-density metabolism with insulin resistance and chronic kidney disease.

Cardiovascular risk increases with each decrement in renal function. Low-density lipoprotein (LDL) cholesterol levels are not associated with increased mortality, but high-density lipoprotein (HDL) levels are inversely associated with cardiovascular risk. Lipoprotein composition with increased abundance of small dense LDL and HDL and reduced levels of more buoyant isoforms is similar to what is found in states of insulin resistance and in the metabolic syndrome (MS). In both cases, high triglyceride levels are associated with reduced HDL levels. Chronic kidney disease (CKD) is itself associated with increasing insulin resistance as renal function fails. In both instances, decreased levels of apo A-I and apo A-II are a consequence of increased fractional catabolic rate (FCR), resulting from a predominance of small HDL particles. HDL maturation is impaired in CKD through decreased activity of lecithin:cholesterol acyltransferase (LCAT), and increased cholesterol ester transfer protein (CETP) activity in MS shuttles triglycerides back into HDL, thereby destabilizing it. Whether insulin resistance is entirely responsible for disorders of HDL metabolism in CKD, or whether the process is a result of unrelated pathophysiology, is currently unknown.     

Down-regulation of hepatic lecithin:cholesterol acyltransferase gene expression in chronic renal failure

BACKGROUND: Chronic renal failure (CRF) is associated with premature arteriosclerosis, impaired high-density lipoprotein (HDL) maturation, increased pre-beta HDL (a lipid-poor HDL species), reduced HDL/total cholesterol ratio, hypertriglyceridemia, and depressed lipolytic activity. The latter has been, in part, attributed to elevated pre-beta HDL, which is a potent inhibitor of lipoprotein lipase (LPL). Accumulation of cholesterol in the arterial wall is a critical step in atherogenesis, and HDL-mediated cholesterol removal from peripheral tissues mitigates atherosclerosis. Lecithin:cholesterol acyltransferase (LCAT) is essential for maturation of HDL and cholesterol removal by HDL from peripheral tissues. Earlier studies have revealed depressed plasma LCAT enzymatic activity in patients with CRF. This study was conducted to determine whether impaired LCAT activity can be confirmed in CRF animals and if so whether it is due to down-regulation of hepatic LCAT expression. METHODS: Hepatic tissue LCAT mRNA and plasma LCAT enzymatic activity were measured in male Sprague-Dawley rats six weeks after excisional 5/6 nephrectomy or sham operation. RESULTS: Compared with the controls, the CRF group exhibited a significant reduction of hepatic tissue LCAT mRNA abundance. The reduction in hepatic LCAT mRNA was accompanied by a marked reduction of plasma LCAT activity and elevation of serum-free cholesterol in the CRF animals. LCAT activity correlated positively with the HDL/total cholesterol ratio and inversely with free cholesterol and triglyceride concentrations. CONCLUSIONS: CRF leads to a marked down-regulation of hepatic LCAT mRNA expression and plasma LCAT activity. This abnormality can impair HDL-mediated cholesterol uptake from the vascular tissue and contribute to cardiovascular disease. In addition, LCAT deficiency can, in part, account for elevated serum-free cholesterol, reduced HDL/total cholesterol, and elevated pre-beta HDL in CRF. The latter can, in turn, depress lipolytic activity and hinder triglyceride-rich lipoprotein clearance in CRF.     

Plasma lipids and acyltransferase activities in experimental nephrotic syndrome

Lecithin:cholesterol acyltransferase (LCAT) and lysolecithin acyltransferase (LAT) are two activities carried out by the same plasma enzyme, but require different apoprotein activators. The LCAT reaction takes place primarily on high density lipoproteins (HDL) and is activated by serum albumin, whereas LAT takes place on low density lipoproteins (LDL) and is inhibited by albumin. In nephrotic syndrome (NS), the levels of serum albumin are reduced, whereas the LDL levels are increased, and therefore, the ratio of LAT/LCAT activities should be increased. To test this hypothesis, we estimated the lipid levels and the two enzyme activities in experimental NS induced in rats by the injection of anti-Fx1A antibody (passive Heymann nephritis). As found in other nephrotic conditions, the plasma lipid levels rose progressively as the proteinuria increased and the serum albumin concentration declined. In addition, the ratio of LAT/LCAT activities increased by about fourfold after nine days of induction of nephritis. The LCAT activity correlated positively and the LAT activity negatively with serum albumin levels. The esterified cholesterol correlated positively with LCAT activity in normal rats but negatively in nephrotic animals, indicating that most of the cholesteryl esters in NS may be non-LCAT derived. The free cholesterol/lecithin ratio, a known risk factor for atherosclerosis, increased significantly in nephrotic rats. Furthermore, since the increase in the LAT activity produces more disaturated lecithins, another putative risk factor, the cumulative risk of coronary heart disease may be increased in long-term NS.     

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.     

Short–and Long–Term Effects on Serum Lipoproteins by Three Different Techniques of Apheresis

Abstract: Low–density lipoprotein (LDL) apheresis is applied in patients with coronary heart disease because of severe inherited forms of hypercholesterolemia, for which dietary and combined drug treatment cannot lower LDL cholesterol concentrations less than 130 mg/dl. The following article describes the changes in lipoprotein levels in a total of 19 patients undergoing weekly LDL apheresis. Immunoadsorption, operating with polyclonal antibodies against apolipoprotein B–100, was used in 6 patients. Five patients were put on heparin–induced extracorporeal LDL precipitation (HELP) therapy; 6 received dextran sulfate adsorption treatments. Under steady–state conditions a single treatment reduced LDL cholesterol by 149 ± 3 m/dl with immunoadsorption, 122 ± 2 mg/dl with HELP, and 124 ± 18 mg/dl with dextran sulfate adsorption. Lipoprotein (a) (Lp[a]) declined by 52 to 65%. Very low density lipoprotein (VLDL) cholesterol and VLDL triglycerides declined by 45 to 55% because of the activation of lipoprotein lipase and precipitation during the HELP procedure. In all procedures, there was a small reduction in the different high–density lipoprotein fractions, which had returned to normal after 24 h. The long–term HDL3 cholesterol levels increased significantly. During all procedures there was a decrease in the molar esterification rate of lecithin cholesterol acyltrans–ferase activity. All changes in lipid fractions were paralleled by changes in the corresponding apolipoprotein levels. It is concluded that all three techniques described are powerful tools capable of lowering LDL cholesterol in severe hereditary forms of hypercholesterolemia. In HELP and dextran sulfate adsorption, the amount of plasma is limited by the elimination of other plasma constituents. Immunoadsorption may thus be preferred in very severe forms of hypercholesterolemia.     

Downregulation of high-density lipoprotein receptor in human fibroblasts by insulin and IGF-I

High-density lipoprotein (HDL3) particles bind to a cell surface receptor, thereby promoting the efflux of cholesterol from extrahepatic nonsteroidogenic cells. This receptor appears to be upregulated by increased cell cholesterol content and also may be responsive to the growth state of cells. Because insulin can be mitogenic, the effect of insulin on HDL-receptor function was tested. HDL-receptor activity of cholesterol-loaded fibroblasts was inhibited by insulin treatment. Insulin decreased HDL binding in a log-dose fashion (-25% at 67 nM insulin) in association with increases in [3H]thymidine incorporation into DNA. HDL-mediated cholesterol efflux from cholesterol-loaded cells was diminished by insulin treatment of cells in parallel with decreased HDL binding. Insulin induced reciprocal changes in HDL- and low-density lipoprotein (LDL)-receptor activity. In cells in which these receptors were upregulated by varying cell cholesterol content, insulin increased LDL binding (+88%) and decreased HDL binding (-24%). Insulin-like growth factor I (IGF-I, 100 ng/ml) also significantly decreased HDL binding and HDL-mediated cholesterol efflux to a comparable degree. Pooled human serum similarly induced a reduction in HDL binding to its receptor. These results are consistent with the hypothesis that growth factors in general, and insulin and IGF-I in particular, decrease HDL-receptor activity, possibly to promote retention of cholesterol needed for new membrane synthesis during cell proliferation. Such a mechanism could be partly responsible for accumulation of cholesteryl esters in arterial wall cells during atherogenesis in diabetes mellitus.     

Lovastatin therapy in nephrotic hyperlipidemia: effects on lipoprotein metabolism

The nephrotic syndrome is characterized by proteinuria, hypoalbuminemia, and hypercholesterolemia. Hypertriglyceridemia often is present as well. In this study, the kinetics of plasma lipoproteins were investigated in four patients with nephrotic hyperlipidemia, and repeat studies were carried out in three of these patients during therapy with lovastatin. Before lovastatin therapy, the patients had an extremely delayed catabolism of very low density lipoproteins (VLDL) without evidence of overproduction of lipoproteins in this fraction. Three of four patients had elevated levels of low density lipoprotein (LDL) that were due mainly to increased production rates for LDL. In the three patients treated with lovastatin, the drug therapy lowered plasma concentrations of total cholesterol, triglycerides, VLDL-cholesterol, and LDL-cholesterol, and raised high density lipoprotein (HDL)-cholesterol. Lovastatin therapy decreased VLDL-triglycerides primarily by enhancing their catabolism, and lowered LDL-cholesterol levels mainly by reducing input rates for LDL. Overall, lovastatin appears to be an effective drug for the treatment of hyperlipidemia in the nephrotic syndrome.     

Early Postoperative Changes of HDL Subfraction Profile and HDL-Associated Enzymes After Laparoscopic Sleeve Gastrectomy

This study aimed to determine early postoperative changes of LDL/HDL subfraction profile and HDL-associated enzymes following laparoscopic sleeve gastrectomy (LSG). Thirteen obese patients (mean body mass index (BMI) 52.74?±?10.97 kg/m²) underwent LSG and normal weight control patients (mean BMI 23.56?±?1.92 kg/m²) underwent laparoscopic abdominal surgery. Fasting blood samples were collected prior to surgery, at day 1 after surgery, and after postoperation oral feeding. LDL and HDL subfraction analysis was done by continuous disk polyacrylamide gel electrophoresis. Plasma levels of cholesteryl ester transfer protein (CETP), lecithin–cholesterol acyltransferase (LCAT), and apolipoprotein A-1 (apoA-I) were determined by enzyme-linked immunosorbent assay. Measurement of CETP and LCAT activity was performed via fluorometric analysis. LDL subfraction profile showed no change in both LSG and control group patients. No significant difference was observed in HDL cholesterol, HDL-subfraction distribution, and apoA-I levels in the control group. LSG patients showed a significant increase in HDL-large and a significant decrease in HDL-small fractions at postoperation day 1 compared to preoperation. HDL cholesterol significantly decreased and apoA-I significantly increased in LSG patients after postoperation oral feeding compared to both preoperation and postoperation day 1. Changes in HDL subfraction profile at postoperation day 1 after LSG were accompanied by a significant decrease in CETP protein, LCAT protein, and LCAT activity as compared to preoperation levels. Early changes in HDL subfraction profile and HDL-associated enzymes following LSG suggest that the surgical procedure, irrespective of changes in body weight, affects reverse cholesterol transport.     

Gene expression of LDL receptor, HMG-CoA reductase, and cholesterol-7 alpha-hydroxylase in chronic renal failure

BACKGROUND: Chronic renal failure (CRF) is associated with an atherogenic lipid profile and an increased risk of ischaemic cardiovascular disease. The associated hyperlipidaemia is reportedly ameliorated by erythropoietin (Epo) therapy. According to a recent report, rats studied 3 weeks after 5/6 nephrectomy and fed a high- protein diet exhibited increased activities of hepatic HMG-CoA reductase (HMG-CoAR) and cholesterol 7 alpha-hydroxylase (Ch-7 alpha- H), despite normal corresponding mRNA values. DESIGN AND METHODS: This study was designed to examine the effects of naturally progressing CRF of longer duration as well as those of Epo therapy on gene expressions of the key factors involved in hepatic cholesterol metabolism, i.e., LDL receptor (LDLR), HMG-CoAR, and Ch-7 alpha-H. Sprague-Dawley rats were randomized to the CRF group (5/6 nephrectomy), Epo-treated CRF group (given Epo 150 U/kg/twice weekly) and sham-operated, placebo- treated normal controls. They were allowed free access to regular rat chow and studied 6 weeks after surgery. Liver mRNAs and protein mass or activities of the above factors were studied. RESULTS: Plasma cholesterol concentration was significantly increased in the CRF group (P < 0.001) and was modestly lowered (P < 0.05) by Epo therapy. However, microsomal cholesterol concentration and LDLR, HMG-CoAR, and Ch-7 alpha-H mRNA as well as HMG-CoAR activity, and Ch-7 alpha-H and LDLR protein mass measurements were virtually identical in the three groups. Thus, hepatic LDLR, HMG-CoAR, and Ch-7 alpha-H mRNA and protein measurements in rats with CRF were similar to those of the normal control group representing an inappropriate response to the associated hypercholesterolemia. Epo therapy led to partial amelioration of CRF- associated hypercholesterolaemia with no discernible effect on hepatic tissue expression of the above factors.      

Effect of a soy protein diet on serum lipids of renal transplant patients.

OBJECTIVE: The aim of the present study was to evaluate the effect of a soy-protein diet on plasma lipid levels of renal transplant recipients with moderate hypercholesterolemia. DESIGN: Dietary intervention case-control observational study. SETTING: Renal transplantation outpatient clinic. PATIENTS: Fifteen stable patients who had renal transplantation (serum creatinine < 2 mg/dL) with moderate hypercholesterolemia (low-density lipoprotein [LDL] cholesterol > 140 mg/dL). INTERVENTION: After a baseline dietary interview, dietary counseling was given individually with the goal of substituting 25 g of animal protein with 25 g of soy protein for a 5-week period, using commercially available soy foods, according to each patient's own preference.Main outcome measures Before and after the soy-diet period, plasma lipid profiles including total, LDL, and high-density lipoprotein (HDL) cholesterol, triglycerides, apolipoprotein A1 and B were determined. Protein catabolic rate was assumed as a measure of dietary protein intake. RESULTS: Two patients dropped out. After the soy diet, total cholesterol (254 +/- 22 to 231 +/- 31 mg/dL, P <.05) and LDL cholesterol (165 +/- 20 versus 143 +/- 20 mg/dL, P <.01) decreased significantly. No significant changes were observed regarding HDL cholesterol and triglycerides. Dietary protein intake did not differ at baseline (73.2 +/- 22.9 g/day) and during the soy diet (72.6 +/- 15.6 g/day), when the reported actual soy protein intake resulted 26 +/- 8 g/day. CONCLUSIONS: This study shows that soy proteins given as part of the daily protein intake have beneficial effects on serum LDL cholesterol levels of renal transplant recipients with moderate hypercholesterolemia. Soy proteins could be of use in the nutritional management of renal transplant recipients.     

Nephrotic livers secrete normal VLDL that acquire structural and functional defects following interaction with HDL

BACKGROUND: Binding of very low-density lipoprotein (VLDL) isolated from serum of nephrotic rats VLDL to endothelial cells is defective. This defect is conferred on normal VLDL by prior incubation with high-density lipoprotein (HDL) from nephrotic, but not control rats. It is not known whether the defect is present in nascent VLDL (nVLDL) or is acquired after secretion. We test the hypothesis that VLDL is normal at the time of secretion from the liver and the defect in binding to endothelium is conferred following secretion through interaction with HDL. METHODS: nVLDL was synthesized by and collected from isolated perfused livers from either control or nephrotic rats. nVLDL was labeled with 3H-oleate to measure binding and 35S methionine to evaluate apolipoprotein exchange and composition. To test whether HDL conferred a binding defect, nVLDL was incubated with HDL obtained either from control or nephrotic rats prior to measurement of binding. To distinguish the effects of proteinuria from reduced albumin concentration we additionally incubated nVLDL with HDL obtained from rats with hereditary analbuminemia. Both HDL and VLDL were reisolated by centrifugation prior to subsequent binding and lipolysis determination. Exchange of 35S-labeled apolipoprotein E (apoE) among the subsequent VLDL and HDL fractions was determined. To determine the effect of HDL on lipolysis, HDL-treated VLDL was exposed to lipoprotein lipase-coated 96-well plates and 3H-oleate release measured. To establish whether differences in apoE content could explain the differences in binding and lipolysis, apoE was restored to nephrotic VLDL and lipolysis and binding were subsequently measured. RESULTS: Binding of nephrotic nVLDL was greater than control nVLDL (0.58 +/- 0.13 vs. 0.75 +/- 0.07 ng protein bound/mg cell protein) (P= 0.04, N= 6). Lipolysis was similarly elevated (0.091 +/- 0.010 vs 0.064 +/- 0.002 nmol NEFA released/well/hour) (P < 0.05). Prior incubation with nephrotic HDL reduced binding of nVLDL obtained from either nephrotic or control livers (P= 0.02, N= 6). Treatment with nephrotic (vs. control) HDL reduced both binding (control nVLDL + control HDL, 0.64 +/- 0.02; control + nephrotic, 0.43 +/- 0.06; nephrotic + control, 0.69 +/- 0.05; and nephrotic + nephrotic, 0.62 +/- 0.04 mg VLDL protein/mg cell protein) and lipolysis (control nVLDL + control HDL, 0.053 +/- 0.004; control + nephrotic, 0.038 +/- 0.004; nephrotic + control, 0.069 +/- 0.004; and nephrotic + nephrotic, 0.062 +/- 0.004 nmol NEFA/well/hour) (P < 0.05 vs. nVLDL + control HDL) of nVLDL from either source. The apoE content of nVLDL coincubated with control HDL or analbuminemic HDL was increased compared nVLDL incubated with either no HDL or nephrotic HDL (P < 0.05). Similarly, the apoE/apoA-I ratio was reduced in HDL from nephrotic rats but not in HDL from controls (P < 0.05). Reintroduction of apoE to nephrotic VLDL resulted in increased binding. CONCLUSION: Unlike circulating VLDL, binding of nVLDL from isolated livers from nephrotic rats to endothelial cells is greater and its lipolysis is increased compared to control nVLDL. Decreased binding and lipolysis is conferred following incubation with HDL isolated from control, but not nephrotic rats and binding can be restored by reintroduction of apoE. Thus both defects are conferred on VLDL by exposure to HDL obtained from nephrotic animals, possibly a consequence of a failure of nephrotic HDL to enrich VLDL with apoE during clearance.     

肾移植患者的血脂改变

目的 研究肾移植患者的血脂变化。方法 对上海市8家医院174例肾移植的资料进行调查分析。结果 与正常对照组相比，肾移植患者术前血胆固醇（Tch)、低密度脂蛋白胆固醇（LDL－ch)显著增高，血甘油三酯（TG）、高密度脂蛋白胆固醇（HDL－ch)、极低密度脂蛋白胆固醇（VLDL－ch)与正常对照组的差异无显著性；载脂蛋白Al(Apo A1)及卵磷脂胆固醇酰基转移酶（LCAT）均低于正常对照组，脂蛋白（a)[Lp(a)]的水平显著高于正常对照组；肾移植患者手术前后上述各指标的变化不显著。结论 肾移植患者脂质紊乱相当常见，应高度重视。     

Treatment of the hyperlipidemia of the nephrotic syndrome: a controlled trial

The hyperlipidemia of the nephrotic syndrome is often associated with elevated total and low-density lipoprotein (LDL) cholesterol levels and low or normal high-density lipoprotein (HDL) cholesterol levels. This pattern of hyperlipidemia has been associated with an increased risk of accelerated atherosclerosis in other populations. Despite extensive studies of diet and drug therapy in other populations, few such therapeutic studies exist in patients with the nephrotic syndrome. To investigate the effect of diet and lipid-lowering drugs on the lipoprotein-lipid profile of patients with unremitting nephrotic syndrome and marked hyperlipidemia, we conducted a controlled trial using two such drugs: colestipol and probucol. Colestipol lowered the mean total fasting plasma cholesterol of seven patients from 397 +/- 27 to 317 +/- 37 mg/dL, a 20.2% decrease, and lowered the LDL cholesterol from 398 +/- 28 to 203 +/- 18 mg/dL, a 31.9% decrease. It did not affect the HDL cholesterol level, and thus lowered the LDL-to-HDL cholesterol ratio. Probucol lowered the mean total cholesterol from 439 +/- 72 to 339 +/- 60 mg/dL, a 22.6% decrease, and the LDL cholesterol from 282 +/- 43 to 215 +/- 26 mg/dL, a 23.8% decrease. Although the HDL cholesterol was lowered from 49 +/- 9 to 43 +/- 7 mg/dL by probucol, a 12.2% decrease, the LDL-to-HDL cholesterol ratio still declined. Both drugs were well tolerated and proved safe in this short-term trial. Antihyperlipidemic therapy may well be indicated in certain patients with unremitting nephrotic syndrome.     

酰基辅酶A胆固醇酰基转移酶抑制剂对人系膜细胞细胞内脂质稳态的影响

目的 研究酰基辅酶A胆固醇酰基转移酶抑制剂（ACATI，58-035）对脂质负荷人系膜细胞系（HMCL）细胞内脂质稳态的影响。 方法 油红O染色观察细胞内脂滴变化。偶氮四唑盐（MTT）法了解细胞增殖。高效液相色谱法（HPLC）测定细胞内游离胆固醇(FC)和胆固醇酯（CE）。Western印迹法检测ACATI对HMCL ACAT1和腺苷三磷酸结合盒转运体A1(ABCA1)的蛋白表达。荧光实时定量PCR检测ACATI对HMCL ACAT1、ABCA1和低密度脂蛋白（LDL）受体的影响。瞬时转染检测ACATI对HMCL ACAT1 p1启动子的影响。 结果 100 mg/L LDL明显增加HMCL内脂滴和CE含量。10 mg/L ACATI 58-035没有细胞毒性，且能显著抑制LDL导致的脂滴形成和CE含量增加(相对对照比值，分别是1.91±0.36和1.07±0.30,P < 0.01)。100 mg/L LDL主要在蛋白水平增加ACAT1表达（为对照1.27倍），在10 mg/L ACATI 58-035共同作用时，ACAT1蛋白表达进一步增加（为对照1.77倍）；100 mg/L LDL明显上调HMCL ABCA1 mRNA表达[为对照（2.97±0.39）倍，P < 0.01]，明显下调LDL受体mRNA表达[为对照（0.08±0.02）倍, P < 0.01]，在10 mg/L ACATI 58-035共同作用时，HMCL ABCA1的蛋白和mRNA表达进一步上调[为对照（4.41±1.27）倍，与LDL作用组比较，P < 0.05]，LDL受体mRNA表达进一步下调[为对照（0.04±0.005）倍，与LDL作用组比较，P < 0.01]。 结论 脂质负荷HMCL在一定剂量ACATI作用下，细胞内CE含量明显减少，FC并没有明显增加，这与HMCL上调ABCA1蛋白和mRNA表达、下调LDL受体mRNA表达有关。脂质负荷主要引起HMCL ACAT1蛋白表达增加。