Upregulation of acyl-CoA: cholesterol acyltransferase in chronic renal failure

Atorvastatin Improves Hepatic Lipid Metabolism and Protects Renal Damage in Adenine-Induced Chronic Kidney Disease in Sprague-Dawley Rats

Objective

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 largely due to the dysregulation of lipoprotein metabolism which further aggravates the progression of kidney disease. The present study sought to determine the efficacy of atorvastatin treatment on hepatic lipid metabolism and renal tissue damage in CKD rats.

Methods

Serum, hepatic and faecal lipid contents and the expression and enzyme activity of molecules involved in cholesterol and triglyceride metabolism, along with kidney function, were determined in untreated adenine-induced CKD, atorvastatin-treated CKD (10 mg/kg/day oral for 24 days) and control rats.

Key Findings

CKD resulted in metabolic dyslipidaemia, renal insufficiency, hepatic lipid accumulation, upregulation of 3-hydroxy-3-methyl-glutaryl-coenzyme A (HMG-CoA) reductase, acyl-CoA cholesterol acyltransferase-2 (ACAT2) and the downregulation of LDL receptor protein, VLDL receptor, hepatic lipase, lipoprotein lipase (LPL), lecithin–cholesterol acyltransferase (LCAT) and scavenger receptor class B type 1 (SR-B1). CKD also resulted in increased enzymatic activity of HMG-CoA reductase and ACAT2 together with decreased enzyme activity of lipase and LCAT. Atorvastatin therapy attenuated dyslipidaemia, renal insufficiency, reduced hepatic lipids, HMG-CoA reductase and ACAT2 protein abundance and raised LDL receptor and lipase protein expression. Atorvastatin therapy decreased the enzymatic activity of HMG-CoA reductase and increased enzymatic activity of lipase and LCAT.

Conclusions

Atorvastatin improved hepatic tissue lipid metabolism and renal function in adenine-induced CKD rats.

Impaired Delivery of Cholesterol Effluxed From Macrophages to Hepatocytes by Serum From CKD Patients May Underlie Increased Cardiovascular Disease Risk

Introduction

Although chronic kidney disease (CKD) is associated with increased risk for coronary artery disease (CAD), the underlying mechanisms are not completely defined. In the present study, we tested the hypothesis that flux of cholesterol from macrophage foam cells to liver is impaired in subjects with CKD.

Methods

Consecutive healthy patients, patients with at least 1 CAD risk factor, patients with established CAD, and patients with CKD stages G3 to G5 (n ≥ 15/group) were recruited prospectively. The ability of total patient serum without any modifications to (i) facilitate efflux of cholesterol from human THP1-macrophage foam cells under physiological conditions (cholesterol efflux capacity [CEC]) and (ii) to deliver this effluxed cholesterol to primary hepatocytes with physiological expression of high-density lipoprotein (HDL) receptor SR-BI (capacity to deliver cholesterol to hepatocytes [CDCH]) was evaluated.

Results

Although healthy patients, patients with at least 1 CAD risk factor, and patients with established CAD all showed similar CEC, patients with CKD showed significantly higher CEC. CDCH was significantly lower in all groups compared with the healthy patients; however, when corrected for higher CEC, CDCH in patients with CKD was significantly lower than in patients with CAD. CDCH correlated with age, body mass index, metabolic parameters, inflammatory markers, and kidney function markers (estimated glomerular filtration rate [eGFR], serum creatinine, and serum cystatin C).

Conclusions

These results suggest that aberrations in delivery of cholesterol effluxed from macrophage foam cells to liver for final elimination or the last step of reverse cholesterol transport, may underlie the increased risk of CAD in patients with CKD.

ESRD-induced dyslipidemia-Should management of lipid disorders differ in dialysis patients?

Cardiovascular disease (CVD) is a major cause of morbidity and mortality worldwide. Although numerous modifiable risk factors in the pathogenesis of CVD and its associated mortality have been identified, dyslipidemia remains to be a key focus for therapy. In this regard, significant progress has been made in reducing cardiovascular mortality via the use of lipid-lowering agents such as HMG CoA reductase inhibitors (statins). Yet, despite the disproportionate risk of CVD and mortality in patients with advanced chronic and end stage renal disease (ESRD), treatment of dyslipidemia in this patient population has not been associated with a notable improvement in outcomes. Furthermore, observational studies have not consistently found an association between dyslipidemia and poor outcomes in patients with ESRD. However, it is imperative that examination of dyslipidemia and its association with outcomes take place in the context of the many factors that are unique to kidney disease and may contribute to the abnormalities in lipid metabolism in patients with ESRD. Understanding these intricacies and distinct features will be vital not only to the interpretation of the available clinical data in regards to outcomes, but also to the individualization of lipid therapy in ESRD. In this review, we will examine the nature and underlying mechanisms responsible for dyslipidemia, the association of serum lipids and lipoprotein concentrations with outcomes and the results of major trials targeting cholesterol (mainly statins) in patients with ESRD.

Increments in serum high-density lipoprotein cholesterol over time are not associated with improved outcomes in incident hemodialysis patients

BACKGROUND

Elevated serum high-density lipoprotein cholesterol (HDL-C) has not been associated with better cardiovascular (CV) and all-cause mortality in hemodialysis patients. However, the association between change in HDL over time and mortality has not been fully examined.

OBJECTIVE

In a nationally representative cohort of incident hemodialysis patients who had available HDL data at baseline and 6 months after dialysis initiation, we studied the association of change in HDL-C during the first 6 months of dialysis with all-cause and CV mortality.

METHODS

Associations between HDL-C change and mortality were determined in Cox proportional hazard regression models with adjustment for multiple variables.

RESULTS

In case-mix models, there was a J-shaped association between change in HDL-C and mortality, such that quartiles 1 (<-5 mg/dL) and 4 (≥7 mg/dL) were each associated with higher all-cause (hazard ratio, 1.32 [95% confidence interval, 1.21-1.45] and 1.09 [1.01-1.18]) and CV (1.28 [1.06-1.55] and 1.23 [1.04-1.45]) death risk, respectively. In fully adjusted models that included indices of malnutrition and inflammation, the higher death risk observed in the lowest quartile was attenuated, whereas the highest quartile continued to demonstrate significantly higher all-cause (1.11 [1.02-1.20]) and CV mortality (1.15 [1.00-1.32]). These associations persisted across various subgroups.

CONCLUSIONS

Although malnutrition and inflammation may explain the increased risk for mortality in patients with decreasing serum HDL-C concentrations over time, these indices do not mitigate the elevated risk in patients with rising serum HDL-C. We found that increasing serum HDL-C over time is paradoxically associated with worse outcomes in incident hemodialysis patients.

Plasma metabolite profiles, cellular cholesterol efflux, and non-traditional cardiovascular risk in patients with CKD

BACKGROUND

Patients with chronic kidney disease (CKD) experience high rates of atherosclerotic cardiovascular disease and death that are not fully explained by traditional risk factors. In animal studies, defective cellular cholesterol efflux pathways which are mediated by the ATP binding cassette transporters ABCA1 and ABCG1 are associated with accelerated atherosclerosis. We hypothesized that cholesterol efflux in humans would vary in terms of cellular components, with potential implications for cardiovascular disease.

METHODS

We recruited 120 CKD patients (eGFR<30mL/min/1.73m²) and 120 control subjects (eGFR ≥60mL/min/1.73m²) in order to measure cholesterol efflux using either patients' HDL and THP-1 macrophages or patients' monocytes and a flow cytometry based cholesterol efflux assay. We also measured cell-surface levels of the common β subunit of the IL-3/GM-CSF receptor (IL-3Rβ) which has been linked to defective cholesterol homeostasis and may promote monocytosis. In addition, we measured plasma inflammatory cytokines and plasma metabolite profiles.

RESULTS

There was a strong positive correlation between cell-surface IL-3Rβ levels and monocyte counts in CKD (P<0.001). ABCA1 mRNA was reduced in CKD vs. control monocytes (P<0.05), across various etiologies of CKD. Cholesterol efflux to apolipoprotein A1 was impaired in monocytes from CKD patients with diabetic nephropathy (P<0.05), but we found no evidence for a circulating HDL-mediated defect in cholesterol efflux in CKD. Profiling of plasma metabolites showed that medium-chain acylcarnitines were both independently associated with lower levels of cholesterol transporter mRNA in CKD monocytes at baseline (P<0.05), and with cardiovascular events in CKD patients after median 2.6years of follow-up.

CONCLUSIONS

Cholesterol efflux in humans varies in terms of cellular components. We report a cellular defect in ABCA1-mediated cholesterol efflux in monocytes from CKD patients with diabetic nephropathy. Unlike several traditional risk factors for atherosclerotic cardiovascular disease, plasma metabolites inversely associated with endogenous cholesterol transporters predicted cardiovascular events in CKD patients. (Funded by the National Institute of Diabetes and Digestive and Kidney DiseasesK23DK097288 and others.).

Modified Lipids and Lipoproteins in Chronic Kidney Disease: A New Class of Uremic Toxins

Chronic kidney disease (CKD) is associated with an enhanced oxidative stress and deep modifications in lipid and lipoprotein metabolism. First, many oxidized lipids accumulate in CKD and were shown to exert toxic effects on cells and tissues. These lipids are known to interfere with many cell functions and to be pro-apoptotic and pro-inflammatory, especially in the cardiovascular system. Some, like F2-isoprostanes, are directly correlated with CKD progression. Their accumulation, added to their noxious effects, rendered their nomination as uremic toxins credible. Similarly, lipoproteins are deeply altered by CKD modifications, either in their metabolism or composition. These impairments lead to impaired effects of HDL on their normal effectors and may strongly participate in accelerated atherosclerosis and failure of statins in end-stage renal disease patients. This review describes the impact of oxidized lipids and other modifications in the natural history of CKD and its complications. Moreover, this review focuses on the modifications of lipoproteins and their impact on the emergence of cardiovascular diseases in CKD as well as the appropriateness of considering them as actual mediators of uremic toxicity.

Worsening of lipid metabolism after successful treatment of primary aldosteronism

Primary aldosteronism (PA) describes the most frequent cause of secondary arterial hypertension. Recently, deterioration of lipid metabolism after adrenalectomy (ADX) for aldosterone-producing adenoma (APA) has been described. We analysed longitudinal changes in lipid profiles in a large prospective cohort of PA patients. Data of 215 consecutive PA patients with APA (n = 144) or bilateral idiopathic adrenal hyperplasia (IHA, n = 71) were extracted from the database of the German Conn's Registry. Patients were investigated before and 1 year after successful treatment by ADX or by mineralocorticoid receptor antagonists (MRA). Glomerular filtration rate (GFR), fasting plasma glucose and components of lipid metabolism including triglycerides (TG), total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C) and high-density lipoprotein cholesterol (HDL-C) were determined at 8.00 after a 12-h fasting period. One year after initiation of treatment mean serum potassium levels and blood pressure normalized in the patients. HDL-C and TG developed inversely with decreasing HDL-C levels in patients with APA (p = .046) and IHA (p = .004) and increasing TG levels (APA p = .000; IHA p = .020). BMI remained unchanged and fasting plasma glucose improved in patients with APA (p = .004). Furthermore, there was a significant decrease of GFR in both subgroups at follow-up (p = .000). Changes in HDL-C and TG correlated with decrease in GFR in multivariate analysis (p = .024). Treatment of PA is associated with a deterioration of lipid parameters despite stable BMI and improved fasting plasma glucose and blood pressure. This effect can be explained by renal dysfunction following ADX or MRA therapy.

HDL Cholesterol Efflux Does Not Predict Cardiovascular Risk in Hemodialysis Patients

The cardioprotective effect of HDL is thought to be largely determined by its cholesterol efflux capacity, which was shown to inversely correlate with atherosclerotic cardiovascular disease in populations with normal kidney function. Patients with ESRD suffer an exceptionally high cardiovascular risk not fully explained by traditional risk factors. Here, in a post hoc analysis in 1147 patients with type 2 diabetes mellitus on hemodialysis who participated in the German Diabetes Dialysis Study (4D Study), we investigated whether the HDL cholesterol efflux capacity is predictive for cardiovascular risk. Efflux capacity was quantified by incubating human macrophage foam cells with apoB-depleted serum. During a median follow-up of 4.1 years, 423 patients reached the combined primary end point (composite of cardiac death, nonfatal myocardial infarction, and stroke), 410 patients experienced cardiac events, and 561 patients died. Notably, in Cox regression analyses, we found no association of efflux capacity with the combined primary end point (hazard ratio [HR], 0.96; 95% confidence interval [95% CI], 0.88 to 1.06; P=0.42), cardiac events (HR, 0.92; 95% CI, 0.83 to 1.02; P=0.11), or all-cause mortality (HR, 0.96; 95% CI, 0.88 to 1.05; P=0.39). In conclusion, HDL cholesterol efflux capacity is not a prognostic cardiovascular risk marker in this cohort of patients with diabetes on hemodialysis.

HDL abnormalities in nephrotic syndrome and chronic kidney disease

Normal HDL activity confers cardiovascular and overall protection by mediating reverse cholesterol transport and through its potent anti-inflammatory, antioxidant, and antithrombotic functions. Serum lipid profile, as well as various aspects of HDL metabolism, structure, and function can be profoundly altered in patients with nephrotic range proteinuria or chronic kidney disease (CKD). These abnormalities can, in turn, contribute to the progression of cardiovascular complications and various other comorbidities, such as foam cell formation, atherosclerosis, and/or glomerulosclerosis, in affected patients. The presence and severity of proteinuria and renal insufficiency, as well as dietary and drug regimens, pre-existing genetic disorders of lipid metabolism, and renal replacement therapies (including haemodialysis, peritoneal dialysis, and renal transplantation) determine the natural history of lipid disorders in patients with kidney disease. Despite the adverse effects associated with dysregulated reverse cholesterol transport and advances in our understanding of the underlying mechanisms, safe and effective therapeutic interventions are currently lacking. This Review provides an overview of HDL metabolism under normal conditions, and discusses the features, mechanisms, and consequences of HDL abnormalities in patients with nephrotic syndrome or advanced CKD.

Role of dyslipidemia in impairment of energy metabolism, oxidative stress, inflammation and cardiovascular disease in chronic kidney disease

Advanced chronic kidney disease (CKD) results in a constellation of dysregulation of lipid metabolism, oxidative stress, and inflammation which are causally interconnected and participate in a vicious cycle. The CKD-associated lipid disorders are marked by impaired clearance of very low density lipoprotein and chylomicrons, hypertriglyceridemia, formation of small dense low-density lipoprotein (LDL), oxidative modification of LDL, intermediate density lipoprotein and chylomicron remnants, and high-density lipoprotein deficiency and dysfunction. This review provides a brief overview of the role of CKD-induced lipid disorders in the pathogenesis of oxidative stress, inflammation, cardiovascular disease, impaired exercise capacity, cachexia and wasting syndrome.

Post-transcriptional nature of uremia-induced downregulation of hepatic apolipoprotein A-I production

Chronic kidney disease is associated with premature death from cardiovascular disease, which is, in part, driven by high density lipoprotein deficiency and dysfunction. One of the main causes of high density lipoprotein deficiency in chronic kidney disease is diminished plasma apolipoprotein (Apo)A-I level. Plasma ApoA-I is reduced in dialysis patients and hepatic ApoA-I messenger RNA (mRNA) is decreased in the uremic rats. This study explored the mechanism of uremia-induced downregulation of ApoA-I. Human hepatoma derived cells were incubated in media containing whole plasma or plasma subfractionation from normal subjects and patients with end stage renal disease pre- and posthemodialysis. Cells and culture media were isolated to measure ApoA-I protein and mRNA. ApoA-I promoter activity was measured using transfection with a luciferase promoter construct containing the -2096 to +293 segment of ApoA-I gene. Finally, effect of uremic and control plasma was assessed on ApoA-I RNA stability. Exposure to uremic plasma significantly reduced ApoA-I mRNA expression and ApoA-I protein production. These effects were reversed by replacing uremic plasma with normal plasma. Although no difference in ApoA-I promoter activity was found between cells exposed to uremic and normal plasma, uremic plasma significantly reduced ApoA-I RNA stability. Experiments using plasma subfractions revealed that the inhibitory effect of uremic plasma on ApoA-I mRNA expression resides in fractions containing molecules larger but not smaller than 30 kd. The pre- and postdialysis plasma exerted an equally potent inhibitory effect on ApoA-I mRNA abundance. Uremia lowers ApoA-I production by reducing its RNA stability. The inhibitory effect of uremic milieu on ApoA-I mRNA expression is mediated by non-dialyzable molecule(s) larger than 30 kd.

Reasons for the lack of salutary effects of cholesterol-lowering interventions in end-stage renal disease populations

Cardiovascular disease (CVD) is the main cause of premature death in patients with chronic kidney disease (CKD). The underlying mechanisms of CVD in patients with mild to moderate CKD are different from those with end-stage renal disease (ESRD). While serum cholesterol is frequently elevated and contributes to atherosclerosis in many CKD patients, particularly those with nephrotic proteinuria, it is usually normal, even subnormal, in most ESRD patients receiving hemodialysis. CVD in the ESRD population is primarily driven by oxidative stress, inflammation, accumulation of the oxidation-prone intermediate-density lipoproteins, chylomicron remnants and small dense low-density lipoprotein particles as well as high-density lipoprotein deficiency and dysfunction, hypertension, vascular calcification, and arrhythmias. Only a minority of hemodialysis patients have hypercholesterolemia which is most likely due to genetic or unrelated factors. In addition, due to peritoneal losses of proteins which simulate nephrotic syndrome, peritoneal dialysis patients often exhibit hypercholesterolemia. Clearly when present, hypercholesterolemia contributes to CVD in the CKD and ESRD population and justifies cholesterol-lowering therapy. However, the majority of ESRD patients and a subpopulation of CKD patients with minimal proteinuria have normal or subnormal serum cholesterol levels and do not benefit from and can be potentially harmed by statin therapy. In fact the lack of efficacy of statins in hemodialysis patients has been demonstrated in several randomized clinical trials. This review is intended to provide an overview of the mechanisms responsible for the failure of statins to reduce cardiovascular morbidity and mortality in most ESRD patients and to advocate the adoption of individualized care principles in the management of dyslipidemia in this population.

Dysregulation of hepatic fatty acid metabolism in chronic kidney disease

BACKGROUND

Chronic kidney disease (CKD) results in hypertriglyceridemia which is largely due to impaired clearance of triglyceride-rich lipoproteins occasioned by downregulation of lipoprotein lipase and very low-density lipoprotein (LDL) receptor in the skeletal muscle and adipose tissue and of hepatic lipase and LDL receptor-related protein in the liver. However, data on the effect of CKD on fatty acid metabolism in the liver is limited and was investigated here.

METHODS

Male Sprague-Dawley rats were randomized to undergo 5/6 nephrectomy (CRF) or sham operation (control) and observed for 12 weeks. The animals were then euthanized and their liver tissue tested for nuclear translocation (activation) of carbohydrate-responsive element binding protein (ChREBP) and sterol-responsive element binding protein-1 (SREBP-1) which independently regulate the expression of key enzyme in fatty acid synthesis, i.e. fatty acid synthase (FAS) and acyl-CoA carboxylase (ACC) as well as nuclear Peroxisome proliferator-activated receptor alpha (PPARα) which regulates the expression of enzymes involved in fatty acid oxidation and transport, i.e. L-FABP and CPT1A. In addition, the expression of ATP synthase α, ATP synthase β, glycogen synthase and diglyceride acyltransferase 1 (DGAT1) and DGAT2 were determined.

RESULTS

Compared with controls, the CKD rats exhibited hypertriglyceridemia, elevated plasma and liver tissue free fatty acids, increased nuclear ChREBP and reduced nuclear SREBP-1 and PPARα, upregulation of ACC and FAS and downregulation of L-FABP, CPT1A, ATP synthase α, glycogen synthase and DGAT in the liver tissue.

CONCLUSION

Liver in animals with advanced CKD exhibits ChREBP-mediated upregulation of enzymes involved in fatty acid synthesis, downregulation of PPARα-regulated fatty acid oxidation system and reduction of DGAT resulting in reduced fatty acid incorporation in triglyceride.

Statins in the management of dyslipidemia associated with chronic kidney disease

The cause of death in the majority of patients with chronic kidney disease (CKD) and end-stage renal disease (ESRD) is accelerated cardiovascular disease and not renal failure per se, suggesting a role for statin therapy in this setting. During the past 6 years three large, randomized, placebo-controlled studies of three different statins have been conducted in the dialysis population-but two of these studies did not demonstrate any benefits of statin therapy, and the third study showed only marginally positive results. To understand why statins have failed to reduce cardiovascular events in patients with ESRD, the basic mechanisms underlying the pathogenesis of dyslipidemia in CKD must be critically examined. The observed negative results in the clinical trials of statin therapy might also reflect the biomarkers and targets that were chosen to be evaluated. The characteristics of dyslipidemia in patients with CKD not yet requiring dialysis treatment differ markedly from those of individuals with established ESRD and form the basis for therapeutic recommendations. The potential adverse effects associated with statin therapy are important to consider in the management of dyslipidemia in patients with CKD.

Salutary effects of hemodialysis on low-density lipoprotein proinflammatory and high-density lipoprotein anti-inflammatory properties in patient with end-stage renal disease

End-stage renal disease (ESRD) causes oxidative stress, inflammation, low-density lipoprotein (LDL) oxidation, high-density lipoprotein (HDL) deficiency and accelerated atherosclerosis. Uptake of oxidized LDL by macrophages results in foam cell and plaque formation. HDL mitigates atherosclerosis via reverse cholesterol transport and inhibition of LDL oxidation. ESRD heightens LDL inflammatory activity and suppresses HDL anti-inflammatory activity. The effect of hemodialysis on the LDL and HDL inflammatory properties is unknown. By removing the potential pro-oxidant/proinflammatory uremic toxins, dialysis may attenuate LDL inflammatory and HDL anti-inflammatory properties. Conversely, exposure to dialyzer membrane and tubing and influx of impurities from dialysate can intensify LDL and HDL inflammatory activities. This study examined the effect of hemodialysis on LDL and HDL inflammatory activities. Plasma samples were obtained from 12 normal control and 26 ESRD patients before and after hemodialysis with (16 patients) or without (10 patients) heparinization. HDL and LDL were isolated and tested for monocyte chemotactic activity in cultured endothelial cells. ESRD patients had increased LDL chemotactic activity, reduced HDL anti-inflammatory activity, paraoxonase and glutathione peroxidase levels, and elevated plasma IL-6 before dialysis. Hemodialysis partially improved LDL inflammatory and HDL anti-inflammatory activities and enhanced patients' HDL ability to suppress their LDL inflammatory activity. The salutary effect on LDL inflammatory activity was significantly greater in patients dialyzed with than those without heparin. ESRD heightens LDL inflammatory and impairs HDL anti-inflammatory activities. Hemodialysis partially improves LDL and HDL inflammatory activities. The salutary effects of hemodialysis are in part mediated by heparin, which is known to possess lipolytic and antioxidant properties.

Lipotoxicity and impaired high density lipoprotein-mediated reverse cholesterol transport in chronic kidney disease

Chronic kidney disease (CKD) is associated with a high risk of death from cardiovascular disease. Inflammation, oxidative stress, and dyslipidemia, which are common consequences of CKD, contribute to the pathogenesis of atherosclerosis and cardiovascular disease in this population. Dyslipidemia of CKD is characterized by diminished plasma high density lipoprotein (HDL) concentration, impaired HDL anti-oxidant and anti-inflammatory activities, and elevated plasma triglyceride, very low density lipoprotein (VLDL), intermediate density lipoprotein, chylomicron remnants, and oxidized lipids and lipoproteins. The constellation of inflammation, HDL deficiency, and oxidative modification of lipoproteins can cause atherosclerosis and progression of renal disease. We have recently found lipid accumulation in the remnant kidney and the wall of aorta in rats with CKD induced by 5/6 nephrectomy. This was mediated by up-regulation of scavenger receptors involved in the influx of oxidized lipids or lipoproteins, tubular reabsorption of lipid binding proteins through megalin-cubilin complexes, upregulation of fatty acid synthesis, and downregulation of fatty acid oxidation pathways. The combination of increased lipid influx, elevated production and reduced catabolism of lipids, and impaired HDL-mediated reverse cholesterol transport can promote atherosclerosis, glomerulosclerosis, and tubulointerstitial damage. Although statins can be effective in slowing CKD progression in patients with mild-to-moderate CKD, they have consistently failed to mitigate oxidative stress, inflammation, HDL deficiency, or cardiovascular mortality in the end-stage renal disease populations. Similarly, high doses of antioxidant vitamins have failed to either ameliorate oxidative stress, inflammation, or improve overall mortality in end-stage renal disease. This article is intended to provide a brief review of the effects of CKD on HDL structure and function and pathways of lipid influx, efflux, synthesis, and catabolism in the artery wall and the diseased kidney.

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.

HDL metabolism and activity in chronic kidney disease

Chronic kidney disease (CKD) is associated with development of atherosclerosis and premature death from cardiovascular disease. The predisposition of patients with CKD to atherosclerosis is driven by inflammation, oxidative stress and dyslipidemia, all of which are common features of this condition. Markers of dyslipidemia in patients with advanced CKD are impaired clearance and heightened oxidation of apolipoprotein-B-containing lipoproteins and their atherogenic remnants, and a reduction of the plasma concentration, antioxidant, and anti-inflammatory properties of high-density lipoprotein (HDL). Studies in animal models of CKD indicate that the disease promotes lipid accumulation in the artery wall and kidney, leading to atherosclerosis, glomerulosclerosis and tubulointerstitial injury. These effects seem to be mediated by an increased cellular influx of lipids, elevated cellular production and reduced cellular catabolism of fatty acids, and impaired antioxidant, anti-inflammatory and reverse lipid transport properties of HDL. Available pharmacological therapies have been largely ineffective in ameliorating oxidative stress, inflammation, HDL deficiency and/or dysfunction, and the associated atherosclerosis and cardiovascular disease in patients with end-stage renal disease. This Review aims to provide an overview of the mechanisms and consequences of CKD-induced HDL deficiency and dysfunction.

Niacin improves renal lipid metabolism and slows progression in chronic kidney disease

BACKGROUND

Mounting evidence points to lipid accumulation in the diseased kidney and its contribution to progression of nephropathy. We recently found heavy lipid accumulation and marked dysregulation of lipid metabolism in the remnant kidneys of rats with chronic renal failure (CRF). Present study sought to determine efficacy of niacin supplementation on renal tissue lipid metabolism in CRF.

METHODS

Kidney function, lipid content, and expression of molecules involved in cholesterol and fatty acid metabolism were determined in untreated CRF (5/6 nephrectomized), niacin-treated CRF (50 mg/kg/day in drinking water for 12 weeks) and control rats.

RESULTS

CRF resulted in hypertension, proteinuria, renal tissue lipid accumulation, up-regulation of scavenger receptor A1 (SR-A1), acyl-CoA cholesterol acyltransferase-1 (ACAT1), carbohydrate-responsive element binding protein (ChREBP), fatty acid synthase (FAS), acyl-CoA carboxylase (ACC), liver X receptor (LXR), ATP binding cassette (ABC) A-1, ABCG-1, and SR-B1 and down-regulation of sterol responsive element binding protein-1 (SREBP-1), SREBP-2, HMG-CoA reductase, PPAR-alpha, fatty acid binding protein (L-FABP), and CPT1A. Niacin therapy attenuated hypertension, proteinuria, and tubulo-interstitial injury, reduced renal tissue lipids, CD36, ChREBP, LXR, ABCA-1, ABCG-1, and SR-B1 abundance and raised PPAR-alpha and L-FABP.

CONCLUSIONS AND GENERAL SIGNIFICANCE

Niacin administration improves renal tissue lipid metabolism and renal function and structure in experimental CRF.

The genetics of neutral lipid biosynthesis: an evolutionary perspective

The storage of fatty acids and fatty alcohols in the form of neutral lipids such as triacylglycerol (TAG), cholesteryl ester (CE), and wax ester (WE) serves to provide reservoirs for membrane formation and maintenance, lipoprotein trafficking, lipid detoxification, evaporation barriers, and fuel in times of stress or nutrient deprivation. This ancient process likely originated in actinomycetes and has persisted in eukaryotes, albeit by different molecular mechanisms. A surfeit of neutral lipids is strongly, perhaps causally, related to several human diseases such as diabetes mellitus, obesity, atherosclerosis and nonalcoholic fatty liver disease. Therefore, understanding the metabolic pathways of neutral lipid synthesis and the roles of the enzymes involved may facilitate the development of new therapeutic interventions for these syndromes.

Feedback inhibition of cholesterol biosynthesis by dietary cholesterol in experimental chronic renal failure

OBJECTIVE

Enhanced liver cholesterol synthesis is present in experimental chronic renal failure (CRF), even though cholesterol concentrations in blood and liver are increased, suggesting that CRF results in disturbed cholesterolegenesis feedback regulation.

DESIGN

This study sought to elucidate whether dietary cholesterol exerts inhibitory effects on liver cholesterologenesis in CRF rats.

METHODS

Male Wistar rats were used. Experimental CRF was achieved by a 5/6 nephrectomy model. Cholesterologenesis was measured (1) in vivo by tritiated water incorporation into cholesterol, and (2) in vitro (using liver slices) by [(14)C]-acetate and [(3)H]-mevalonate incorporation into cholesterol. In addition, the mRNA abundance of 3-hydroxy-3-methylglutaryl-CoA reductase, a rate-limiting enzyme in cholesterologenesis pathway, as well as its activity, was determined. Finally, the mRNA level of liver sterol regulatory element-binding protein-2, a nuclear transcription factor engaged in intracellular cholesterol homeostasis, was measured.

RESULTS

Experimental CRF was associated with significantly increased concentrations of serum and liver cholesterol. In vitro and in vivo cholesterologenesis was enhanced in CRF rats. A cholesterol-enriched diet resulted in a significant decrease in (1) in vivo and in vitro cholesterol synthesis, (2) 3-hydroxy-3-methylglutaryl-CoA reductase gene expression, and (3) the level of liver sterol regulatory element-binding protein-2 mRNA in CRF rats.

CONCLUSIONS

Despite elevated plasma and liver cholesterol concentrations, cholesterologenesis is increased in CRF rats. It is, however, inhibited by dietary cholesterol. These results suggest that a feedback inhibition of cholesterologenesis by dietary cholesterol is preserved in experimental CRF.

Decreased peroxisome proliferator-activated receptor alpha gene expression is associated with dyslipidemia in a rat model of chronic renal failure

The transcription factor peroxisome proliferator-activated receptor (PPAR) alpha plays an important role in lipid homeostasis. In this study, we examined whether the down-regulation of PPAR-alpha gene expression is associated with dyslipidemia in a rat model of chronic renal failure (CRF). Rats with laboratory-induced uremia by 5/6 nephrectomy were bled at 2 weeks and 10 weeks after the nephrectomy to produce conditions. For the sake of convenience, the rats observed at postoperative week 2 were defined as acute renal failure (ARF) and those observed at week 10 were defined as CRF. Lipids in lipoprotein fractions were measured by high-performance liquid chromatography. The abundance of PPAR-alpha messenger RNA (mRNA) in the liver was measured by reverse transcriptase-polymerase chain reaction. Serum creatinine and blood urea nitrogen levels rose with the progression of renal failure, but the total protein levels remained constant. Serum triglyceride in ARF rats remained unchanged from the level in sham-operated control rats, whereas that in CRF rats was 66% higher than the control level. Serum cholesterol was elevated 1.5-fold in ARF rats and 2-fold in CRF rats compared with the sham-operated counterparts. As with triglyceride, very low-density lipoprotein remained unchanged in ARF rats but rose substantially in CRF rats. All of the major lipoprotein fractions were elevated in CRF rats. These lipid and lipoprotein changes were significantly associated with creatinine and blood urea nitrogen levels. The PPAR-alpha mRNA expression in the liver was unchanged in ARF rats but was 44% lower in CRF rats. The PPAR-alpha mRNA expression was inversely correlated with serum creatinine and lipids in the overall rats. Our results indicate that PPAR-alpha mRNA expression is down-regulated in the liver of CRF rats and that this down-regulation may play a crucial role in the development of dyslipidemia.

Gender differences in mRNA expression of ATP-binding cassette efflux and bile acid transporters in kidney, liver, and intestine of 5/6 nephrectomized rats

ATP-binding cassette (ABC) transporters including multidrug resistance proteins (Mdr), multidrug resistance-associated proteins (Mrp), and breast cancer resistance protein (Bcrp/Abcg2) play major roles in tissue defense. Abcg5/g8 is essential in cholesterol efflux. The present study was aimed at elucidating alteration in expression of these transporters and bile-acid transporters during chronic kidney disease (CKD) and underlying molecular mechanisms. Seven weeks after 5/6 nephrectomy (Nx), mRNA expression of 16 aforementioned transporters in kidney, liver, jejunum, and large intestine of male and female Nx rats was quantified with the branched DNA signal amplification assay. In Nx males, intestinal expression of all the transporters remained unchanged; hepatic expression of most transporters was not altered, except increases in Mdr1a, Mrp3, and Abcg8. In male remnant kidneys, kidney-predominant transporter Abcg2 decreased and correlated with CKD severity, whereas Mdr1b, Mrp3, and ileal bile-acid transporter increased and correlated with CKD severity. Such changes were largely absent in Nx females. Renal alterations of these transporters correlated with increases of cytokines and/or decreases of nuclear receptors such as estrogen receptor alpha and glucocorticoid receptor. Renal protein expression of Mrp2 increased, whereas that of Mrp4 remained unchanged in both genders of Nx rats. Treatment of rat proximal tubule NRK-52E cells with interleukin (IL)-1beta and IL-6 increased Mrp3 mRNA expression. In conclusion, during CKD, renal expression of many ABC transporters was altered at the transcriptional level, whereas hepatic mRNA expression of most ABC transporters remained unchanged. Down-regulation of steroid hormone receptors and increase of inflammatory cytokines may contribute to alteration of transporter gene expression in kidney during CKD.

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.

The time-dependent effect of gluconasturtiin and phenethyl isothiocyanate on metabolic and antioxidative parameters in rats

The effect of gluconasturtiin (GNST) and phenethyl isothiocyanate (PEITC) on some metabolic changes and antioxidative parameters in the rat was tested using different doses of PEITC and duration of GNST or PEITC ingestion. Their effect on antioxidative processes was previously observed, however, their influence on metabolic changes is still poorly characterized. In the performed experiment, the effect of GNST (0.5 mg/kg BW) and PEITC (0.1 mg/kg BW or 0.3 mg/kg BW) administered intragastrically after 4 h or 14 days to growing male rats was studied. PEITC at both doses after 4 h of its administration caused a considerable increase in liver cholesterol and triglyceride content with a concomitant drop in the amount of glycogen. Blood glucose, free fatty acids, phospholipids and total, free, esterified cholesterol as well as cholesterol in high-density lipoprotein were not altered. GNST, at its short-time ingestion, augmented significantly the concentration of triglycerides in blood serum. The compounds tested had no influence on metabolic changes after a longer period of action with the exception of glycogen values in liver, which were substantially augmented by PEITC at both doses. Our trial revealed a lack of GNST and PEITC influence on the content of liver sulphhydryl groups and on glutathione peroxidase and glutathione-S-transferase activities. The only distinct change in the content of malonodialdehyde was observed after short-time action of lower dose of PEITC. Our research showed that the short-term PEITC action constituted a significant factor interfering with liver metabolism. Although PEITC has been repeatedly advocated as very promising anticancer agent, in our experiment, the lower dose of PEITC was revealed as a pro-oxidative substance. These inconsistent properties seem to depend on its dose and time of action.

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.

Mycophenolate mofetil ameliorates nephropathy in the obese Zucker rat

BACKGROUND

The obese Zucker rat has metabolic condition resembling type II diabetes, including hyperlipidemia, obesity, insulin resistance, and hyperglycemia. With advancing age, the obese Zucker rat develops glomerulosclerosis, proteinuria, and renal failure. Since immune cells play a central role in the development of chronic renal injury, we evaluated the potential benefit of mycophenolate mofetil (MMF), alone and in combination with angiotensin receptor type 1 blockade (ARB) in the obese Zucker rat.

METHODS

Thirteen-week-old male obese Zucker rats (fa/fa) were randomly assigned to four experimental groups (five rats each) that received the following treatments for 3 months: (1) losartan (100 mg/L in the drinking water), (2) MMF (20 mg/kg/day), (3) MMF and losartan, and (4) placebo. Lean Zucker rats (N = 5) were included as normal controls. Renal function, biochemical parameters, renal histology, and immunohistology were evaluated.

RESULTS

The placebo-treated obese Zucker rats exhibited proteinuria and significant glomerular and tubulointerstitial injury in association with renal immune cell infiltration. Proteinuria, histologic damage, and renal immune cell infiltration were all reduced by MMF treatment alone or in combination with ARB. The improvement of proteinuria and structural damage was more pronounced in the group that received the combination of MMF and losartan.

CONCLUSION

MMF treatment alone, and especially in combination with ARB, improves nephropathy in the obese Zucker rat.

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.

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.

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.

Downregulation of hepatic acyl-CoA:diglycerol acyltransferase in chronic renal failure

Chronic renal failure (CRF) is associated with hypertriglyceridemia and elevated plasma VLDL and IDL concentrations. These events can be due to either increased production or depressed catabolism of triglyceride-rich lipoproteins. Several studies have documented downregulation of lipoprotein lipase, hepatic triglyceride lipase, and the VLDL receptor, leading to depressed clearance and elevated plasma concentration of triglyceride-rich lipoproteins and their remnants in CRF. However, the effect of CRF on the triglyceride biosynthetic pathway has not been explored. Diglycerol acyltransferase (DGAT) is a microsomal enzyme that joins acyl-CoA to 1,2 diacylglycerol and, as such, constitutes the final step in triglyceride biosynthesis. Two distinct forms of DGAT (DGAT-1 and -2) have thus far been identified. The present study was undertaken to examine the effect of CRF on DGAT gene expression and activity in the liver, which is the source of endogenous triglycerides in the circulation. Male Sprague-Dawley rats were studied 8 wk after 5/6 nephrectomy (CRF) or sham operation. DGAT-1 and DGAT-2 mRNA abundance and DGAT activity were quantified. The CRF group showed reduced creatinine clearance, elevated plasma triglycerides, and VLDL concentrations. This was accompanied by significant reductions in hepatic DGAT-2 mRNA abundance (P < 0.01) and total DGAT activity (P < 0.1), pointing to diminished hepatic triglyceride production capacity in CRF animals. In conclusion, CRF results in significant downregulation of hepatic DGAT gene expression and activity. Given the critical role of DGAT in triglyceride biosynthesis, the present study points to diminished, not increased, hepatic triglyceride synthetic capacity in CRF rats.

Increased calcium intake reduces plasma cholesterol and improves vasorelaxation in experimental renal failure

Chronic renal failure (CRF) is associated with abnormal lipid metabolism and high prevalence of vascular complications. Calcium salts are commonly used in CRF as phosphate binders. Increased calcium intake may also lower plasma cholesterol and beneficially influence vascular tone. Therefore, we investigated the influence of increasing dietary calcium from 0.3% to 3.0% for 8 wk after 5/6 nephrectomy (NTX) on plasma cholesterol and mesenteric resistance vessel tone in male Sprague-Dawley rats. The groups were Sham, Sham-Calcium, NTX, and NTX-Calcium ( n = 10–11). Blood pressure was modestly elevated after NTX, whereas the plasma creatinine, urea nitrogen, phosphate, and parathyroid hormone levels were clearly increased. The high-calcium diet suppressed plasma phosphate and parathyroid hormone but was without effect on blood pressure. The NTX resulted in 1.6-fold elevation in plasma total cholesterol and 40% reduction in high density-to-low density lipoprotein ratio (HDL/LDL). However, the lipid profile in NTX rats on the high-calcium diet did not differ from sham-operated controls. The endothelium-mediated relaxations induced by acetylcholine were impaired in NTX rats, whereas the response was normalized by a high-calcium diet. No differences in vasorelaxations by the endothelium-independent vasodilator nitroprusside were detected. In conclusion, improved vasorelaxation after a high-calcium diet could be due to reduced plasma total cholesterol and ameliorated HDL/LDL ratio, although decreased plasma phosphate and parathyroid hormone may also play a significant role in the vascular effects of increased calcium intake.

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.