Down-regulation of hepatic lipase expression in experimental nephrotic syndrome

HDL and chronic kidney disease

Low HDL-cholesterol (HDL-C) concentrations are a typical trait of the dyslipidemia associated with chronic kidney disease (CKD). In this condition, plasma HDLs are characterized by alterations in structure and function, and these particles can lose their atheroprotective functions, e.g., the ability to promote cholesterol efflux from peripheral cells, anti-oxidant and anti-inflammatory proprieties and they can even become dysfunctional, i.e., exactly damaging. The reduction in plasma HDL-C levels appears to be the only lipid alteration clearly linked to the progression of renal disease in CKD patients. The association between the HDL system and CKD development and progression is also supported by the presence of genetic kidney alterations linked to HDL metabolism, including mutations in the APOA1, APOE, APOL and LCAT genes. Among these, renal disease associated with LCAT deficiency is well characterized and lipid abnormalities detected in LCAT deficiency carriers mirror the ones observed in CKD patients, being present also in acquired LCAT deficiency. This review summarizes the major alterations in HDL structure and function in CKD and how genetic alterations in HDL metabolism can be linked to kidney dysfunction. Finally, the possibility of targeting the HDL system as possible strategy to slow CKD progression is reviewed.

Lipoprotein Abnormalities in Chronic Kidney Disease and Renal Transplantation

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

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

Background

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

Methods

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

Results

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

Conclusion

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

Cachexia induced by cancer and chemotherapy yield distinct perturbations to energy metabolism

BACKGROUND

Cancer cachexia is a metabolic disorder involving perturbed energy balance and altered mitochondrial function. Chemotherapy is a primary treatment option for many types of cancer, but there is substantial evidence that some chemotherapeutic agents can also lead to the development and progression of cachexia. In this study, we apply a comprehensive and systems level metabolomics approach to characterize the metabolic perturbations in murine models of cancer-induced and chemotherapy-induced cachexia. Knowledge of the unique pathways through which cancer and chemotherapy drive cachexia is necessary in order to develop effective treatments.

METHODS

The murine Colon26 (C26) adenocarcinoma xenograft model was used to study the metabolic derangements associated with cancer-induced cachexia. In vivo administration of Folfiri (5-fluorouracil, irinotecan, and leucovorin) was used to model chemotherapy-induced cachexia. Comprehensive metabolic profiling was carried out using both nuclear magnetic resonance-based and mass spectrometry-based platforms. Analyses included plasma, muscle, and liver tissue to provide a systems level profiling.

RESULTS

The study involved four groups of CD2F1 male mice (n = 4-5), including vehicle treated (V), C26 tumour hosts (CC), Folfiri treated (F), and C26 tumour hosts treated with Folfiri (CCF). Significant weight loss including skeletal muscle was observed for each of the experimental groups with the tumour hosts showing the most dramatic change (-3.74 g vs. initial body weight in the CC group). Skeletal muscle loss was evident in all experimental groups compared with V, with the CCF combination resulting in the most severe depletion of quadriceps mass (-38% vs. V; P < 0.001). All experimental groups were characterized by an increased systemic glucose demand as evidenced by decreased levels of circulating glucose (-47% in CC vs. V; P < 0.001) and depletion of liver glucose (-51% in CC vs. V; P < 0.001) and glycogen (-74% in CC vs. V; P < 0.001). The cancer-induced and chemotherapy-induced cachexia models displayed unique alterations in flux through the tricarboxylic acid cycle and β-oxidation pathways. Cancer-induced cachexia was uniquely characterized by a dramatic elevation in low-density lipoprotein particles (+6.9-fold vs. V; P < 0.001) and a significant increase in the inflammatory marker, GlycA (+33% vs. V; P < 0.001).

CONCLUSIONS

The results of this study demonstrated for the first time that cancer-induced and chemotherapy-induced cachexia is characterized by a number of distinct metabolic derangements. Effective therapeutic interventions for cancer-induced and chemotherapy-induced cachexia must take into account the specific metabolic defects imposed by the pathological or pharmacological drivers of cachexia.

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.

Disorders of lipid metabolism in nephrotic syndrome: mechanisms and consequences

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

Proteinuria and lipoprotein lipase activity in Miniature Schnauzer dogs with and without hypertriglyceridemia

Spontaneous hyperlipidemia in rats causes glomerular disease. Idiopathic hypertriglyceridemia (HTG) is prevalent in Miniature Schnauzers, but its relationship with proteinuria is unknown. Decreased activity of major lipid metabolism enzymes, lipoprotein lipase (LPL) and hepatic lipase (HL), may play a role in the cyclic relationship between hyperlipidemia and proteinuria. These enzymes have also not been previously investigated in Miniature Schnauzers. The aims of this study were to determine the relationship between HTG and proteinuria in Miniature Schnauzers and to measure LPL and HL activities in a subset of dogs. Fifty-seven Miniature Schnauzers were recruited (34 with and 23 without HTG). Fasting serum triglyceride concentrations and urine protein-to-creatinine ratios (UPC) were measured in all dogs, and LPL and HL activities were determined in 17 dogs (8 with and 9 without HTG). There was a strong positive correlation between triglyceride concentration and UPC (r = 0.77-0.83, P < 0.001). Proteinuria (UPC ≥ 0.5) was present in 60% of dogs with HTG and absent from all dogs without HTG (P < 0.001). Proteinuric dogs were not azotemic or hypoalbuminemic. Dogs with HTG had a 65% reduction in LPL activity relative to dogs without HTG (P < 0.001); HL activity did not differ. Proteinuria occurs with HTG in Miniature Schnauzers and could be due to lipid-induced glomerular injury. Reduced LPL activity may contribute to the severity of HTG, but further assay validation is required.

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.

Residual Cardiovascular Risk in Chronic Kidney Disease: Role of High-density Lipoprotein

Although reducing low-density lipoprotein-cholesterol (LDL-C) levels with lipid-lowering agents (statins) decreases cardiovascular disease (CVD) risk, a substantial residual risk (up to 70% of baseline) remains after treatment in most patient populations. High-density lipoprotein (HDL) is a potential contributor to residual risk, and low HDL-cholesterol (HDL-C) is an established risk factor for CVD. However, in contrast to conventional lipid-lowering therapies, recent studies show that pharmacologic increases in HDL-C levels do not bring about clinical benefits. These observations have given rise to the concept of dysfunctional HDL where increases in serum HDL-C may not be beneficial because HDL loss of function is not corrected by or even intensified by the therapy. Chronic kidney disease (CKD) increases CVD risk, and patients whose CKD progresses to end-stage renal disease (ESRD) requiring dialysis are at the highest CVD risk of any patient type studied. The ESRD population is also unique in its lack of significant benefit from standard lipid-lowering interventions. Recent studies indicate that HDL-C levels do not predict CVD in the CKD population. Moreover, CKD profoundly alters metabolism and composition of HDL particles and impairs their protective effects on functions such as cellular cholesterol efflux, endothelial protection, and control of inflammation and oxidation. Thus, CKD-induced perturbations in HDL may contribute to the excess CVD in CKD patients. Understanding the mechanisms of vascular protection in renal disease can present new therapeutic targets for intervention in this population.

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.

High-density lipoprotein in uremic patients: metabolism, impairment, and therapy

Several studies have shown that HDL has altered antioxidant and anti-inflammatory effects in chronic uremia, either by the reduction in its antioxidant enzymes or by the impairment of their activity. Systemic oxidative stress, which is highly prevalent in chronic kidney disease (CKD) patients, has been shown to decrease antioxidant and anti-inflammatory effects of HDL and even transform it into a pro-oxidant and pro-inflammatory agent. For this reason, we believe that the propensity for accelerated cardiovascular disease in CKD is facilitated by a few key features of this disease, namely, oxidative stress, inflammation, hypertension, and disorders of lipid metabolism. In a nutshell, oxidative stress and inflammation enhance atherosclerosis leading to increased cardiovascular mortality and morbidity in this population. In this detailed review, we highlight the current knowledge on HDL dysfunction and impairment in chronic kidney disease as well as the available therapy.

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.

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

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

Proteinuria decreases tissue lipoprotein receptor levels resulting in altered lipoprotein structure and increasing lipid levels

Rats with nephrotic syndrome (NS) have a fivefold increase in lipids and a similar decrease in triglyceride-rich lipoprotein (TRL) clearance. Lipoprotein lipase (LPL) is reduced both in NS and in the Nagase analbuminemic rat. These rats have nearly normal triglyceride levels and TRL clearance, suggesting that reduction in LPL alone is insufficient to cause increased TRL levels. Apolipoprotein E (apoE) was decreased in lipoprotein fractions in NS, but not in analbuminemia. Here we tested whether decreased apoE binding to lipoproteins in NS contributes to hyperlipidemia by decreasing their affinity for lipoprotein receptors. Plasma apoE was increased 60% in both NS and analbuminemia compared with control (CTRL) as a result of a 60% decreased apoE clearance. Very-low-density lipoprotein and high-density lipoprotein in NS had significantly less apoE per mole of phospholipid compared with analbuminemia or CTRL and significantly greater lipid content; however, apoE binding did not differ by lipoprotein class or group. There was a significant reduction of receptors for lipoproteins in nearly all tissues in NS compared with CTRL and analbuminemia. Thus, apoE within lipoprotein fractions was reduced by dilution resulting from expansion of the lipid fraction due to decreased lipolysis and not to differing affinity for apoE. Decreased lipoprotein receptors result from proteinuria and contribute to hyperlipidemia in NS.

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.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

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.

Longitudinal examination of lipid profiles in pediatric systemic lupus erythematosus

OBJECTIVE

Lipid abnormalities in patients with systemic lupus erythematosus (SLE) are common and are likely to be one of the causes of premature atherosclerosis in these patients. This study was undertaken to serially examine the lipid profile in pediatric patients with SLE to determine the roles of active disease and therapy in altering lipid levels.

METHODS

Serial lipid measurements were obtained in an inception cohort of 139 pediatric patients with SLE at the time of treatment with either a constant dose or differing doses of prednisone, and annually. The levels of cholesterol, triglycerides, low-density lipoprotein (LDL), and high-density lipoprotein (HDL) were correlated with measures of disease activity and prednisone dose.

RESULTS

At the time of SLE diagnosis in this pediatric cohort, the mean values for all lipids were abnormal. With each reduction in prednisone dose, there was a statistically significant decrease in cholesterol and triglyceride levels (P < 0.001) but not HDL or LDL levels. Nephrotic-range proteinuria was associated with altered cholesterol, triglyceride, and LDL levels, whereas changes in HDL were more commonly associated with active nephritis. In the absence of nephrotic-range proteinuria, increases in prednisone dose were associated with increased levels of all lipids, including HDL.

CONCLUSION

Active SLE leads to a proatherogenic lipid profile. Levels of cholesterol and LDL were mainly associated with the dose of prednisone, and were abnormal only during very high disease activity. Triglyceride levels were mainly associated with proteinuria, while changes in HDL were associated with active SLE and a high dose of prednisone. Our results suggest that the lipid profile in pediatric SLE is the result of a complex interaction of disease manifestations and the effects of prednisone therapy.

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.

Skeletal muscle dysfunction in chronic renal failure: effects of exercise

A number of chronic illnesses such as renal failure (CRF), obstructive pulmonary disease, and congestive heart failure result in a significant decrease in exercise tolerance. There is an increasing awareness that prescribed exercise, designed to restore some level of physical performance and quality of life, can be beneficial in these conditions. In CRF patients, muscle function can be affected by a number of direct and indirect mechanisms caused by renal disease as well as various treatment modalities. The aims of this review are twofold: first, to briefly discuss the mechanisms by which CRF negatively impacts skeletal muscle and, therefore, exercise capacity, and, second, to discuss the available data on the effects of programmed exercise on muscle function, exercise capacity, and various other parameters in CRF.

Statins in nephrotic syndrome: a new weapon against tissue injury

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

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

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

Dyslipidemia and nephrotic syndrome: Recent advances

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

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

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

OBJECTIVE

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

DATA SOURCES

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

STUDY SELECTION AND DATA EXTRACTION

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

DATA SYNTHESIS

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

CONCLUSIONS

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

Upregulation of lipogenic enzymes genes expression in white adipose tissue of rats with chronic renal failure is associated with higher level of sterol regulatory element binding protein-1

Chronic renal failure (CRF) frequently results in hypertriglyceridemia and elevated plasma concentration of very-low-density lipoprotein (VLDL). These abnormalities are thought to be primarily due to depressed lipoprotein lipase and hepatic lipase activities, as well as impaired clearance of plasma lipoproteins. Some results suggest that not only lipoproteins catabolism but also their overproduction might contribute to hypertriglyceridemia in CRF. Because sterol regulatory element binding protein (SREBP) plays an important role in the regulation of lipid homeostasis, increased level of this transcription factor might be involved in modulating lipid metabolism in CRF. The purpose of the present study is to determine whether there is an altered regulation of the SREBP-1 in CRF rats and whether the altered regulation of SREBP-1 is associated with the upregulation of lipogenic enzymes genes expression in CRF rats. In the white adipose tissue (WAT) of CRF rats, marked increases in the microsomal (precursor) and nuclear (mature) forms of SREBP-1 have been found. The increase in SREBP-1 was associated with an increased level of lipogenic enzymes (acetyl-coenzyme A [CoA] carboxylase [ACC], adenosine triphosphate-citrate lyase [ACL], fatty acid synthase [FAS], glucose 6-phosphate dehydrogenase [G6PDH], 6-phosphogluconate dehydrogenase [6PGDH], and malic enzyme [ME]) genes expression. In turn, this was associated with an increased rate of fatty acids synthesis in WAT and a significant increase in plasma triacylglycerol (TAG) and VLDL concentration. Our study indicates that WAT SREBP-1 expression is increased in CRF rats and that SREBP-1 may play an important role in the increased fatty acid synthesis. These results reveal another facet of disturbed lipid metabolism in CRF.

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

BACKGROUND

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

METHODS AND RESULTS

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

CONCLUSIONS

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

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.

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.

Endothelial chylomicron binding is altered by interaction with high-density lipoprotein in Heymann's nephritis

Very-low-density lipoprotein (VLDL) catabolism is impaired in the nephrotic syndrome, partly as a result of structural changes that impair endothelial binding in the presence of lipoprotein lipase. Previous results suggested that postsynthetic modification of VLDL by high-density lipoprotein (HDL) in nephrotic syndrome rats causes their failure to bind endothelia normally. It is unknown (1) whether the structure of secreted lipoproteins is normal before exposure to nephrotic syndrome serum and (2) whether the same structural or functional defects are imparted to chylomicrons (CMs) through their interaction with HDL from nephrotic syndrome rats. CMs were isolated from thoracic duct lymph from rats with passive Heymann's nephritis (HN) and normal controls. CMs from control rats were incubated with HDL from either HN or control rats and reisolated, and apolipoprotein E (apo E) content and endothelial binding were determined. We found that CMs secreted by HN and control rats had similar apo E/B-48 ratios. HDL from HN rats had significantly lower apo E/A-I ratios than controls. Incubation of nascent control CMs with control HDL resulted in a 4-fold increase in CM apo E content, but binding was unaffected. Incubation with HDL from HN resulted in only a 50% increase in CM apo E content but reduced binding of these treated CMs by 50% compared either with nascent control CMs or with CMs incubated with control HDL. HDL from rats with HN alters CM binding to lipoprotein lipase by a mechanism that does not involve reducing the content of apo E already present on CMs at the time of secretion.

Acquired lecithin-cholesterol acyltransferase deficiency in nephrotic syndrome

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

Hypoalbuminemia and proteinuria contribute separately to reduced lipoprotein catabolism in the nephrotic syndrome

BACKGROUND

Hypertriglyceridemia is a result of reduced triglyceride (TG)-rich lipoprotein (TRL) catabolism and occurs in rats with nephrotic syndrome (NS) and in Nagase analbuminemic rats (NARs). While the heparin-releasable lipoprotein lipase (LpL) pool in NAR and in NS is similar, TG levels are significantly greater in NS, suggesting that factors other than reduced LpL alone act in NS but not in NARs. Furthermore, clearance of chylomicrons (CM) and very low-density lipoprotein (VLDL) is normal in vivo in NAR despite low LpL levels. We tested the hypotheses that impaired binding of VLDL and impaired VLDL-high density lipoprotein (HDL) interactions contribute to hyperlipidemia in NS.

METHODS

TG and apoB secretion was measured using Triton WR 1339. Clearance of CMs by perfused hearts from NS and NAR was determined. Binding of VLDL from control, NS and NAR to rat aortic endothelial cells (RAECs) was measured prior to and following incubation with HDL from NS, NARs, and control. ApoE, protein, and TG content was determined.

RESULTS

TG levels were greatest in NS (516 +/- 95 mg/dL), intermediate in NAR (193 +/- 20), and least in control (97 +/- 16, P = 0.05), while in contrast, TG secretion was least in NS (178 +/- 33 mg/dL/hour) versus 212 +/- 17 in NAR and 294 +/- 15 in control (P < 0.001 vs. NS). Clearance of CMs by NS and NAR hearts was the same and significantly reduced versus control (P < 0.005). Binding of NS-VLDL to endothelial cells was reduced, while NAR-VLDL binding was increased versus control (P < 0.001). Incubation of NS-VLDL with control or NAR HDL increased VLDL binding compared with binding following incubation with NS HDL (P < 0.001).

CONCLUSION

Increased TG levels in both NS and NAR are the result of decreased TRL clearance. TG levels are greater in NS because of the presence of a combined defect: (1) a decrease in endothelial-bound LpL that occurs as a consequence of reduced serum albumin concentration, and (2) a defect in VLDL binding to endothelial-bound LpL. This latter defect occurs only in the presence of proteinuria and is conferred by HDL.

Effect of the lipoprotein lipase activator NO-1886 on adriamycin-induced nephrotic syndrome in rats

Hyperlipidemia associated with nephrotic syndrome may play a role in the deterioration of renal function. Tsutsumi et al have previously reported that the novel compound NO-1886 increases lipoprotein lipase (LPL) activity, resulting in a reduction of plasma triglycerides and an elevation of high-density lipoprotein (HDL) cholesterol in normal rats. The aim of this study was to ascertain whether NO-1886 suppresses the renal injury by treatment of the hyperlipidemia in an Adriamycin (Kyowa Hakko Kogyo, Tokyo, Japan) induced nephrosis rat model fed a high-protein diet that induced renal dysfunction and tubulointerstitial injury. Administration of Adriamycin caused hyperlipidemia, proteinuria, and edema with ascites in rats in 4 weeks. Furthermore, a combination of Adriamycin and a high-protein diet increased plasma creatinine and blood urea nitrogen (BUN) and decreased plasma albumin. Histologically, in Adriamycin-treated rats, marked interstitial cellular infiltration, tubular lumen dilation, and tubular cast formation in the kidney were observed. NO-1886 decreased plasma triglyceride and increased HDL cholesterol in Adriamycin-induced nephrotic rats. NO-1886 treatment reduced plasma creatinine and BUN levels and increased plasma albumin in Adriamycin-treated rats; it also ameliorated the ascites and proteinuria. Histologically, NO-1886-treated rats showed a quantitatively significant preservation of tubulointerstitial lesions. These data suggest that NO-1886 may have a protective effect against Adriamycin-induced nephrosis with tubulointerstitial nephritis in rats by a modification of the plasma lipid disorder.

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.

New insights into lipid metabolism in the nephrotic syndrome

Hyperlipidemia in the nephrotic syndrome results from increased synthesis and decreased catabolism of lipoproteins. The contribution of each to establishing blood lipid levels is unknown. Increased triglyceride rich lipoprotein concentration, very low density lipoprotein (VLDL) and intermediate density lipoprotein (IDL) primarily results from decreased clearance. This defect is due in part to reduced lipoprotein lipase (LPL) on the vascular endothelium resulting either from decreased synthesis or inadequate binding of this enzyme to endothelial surfaces. In contrast, both low density lipoprotein (LDL) and lipoprotein(a) [Lp(a)] concentrations are increased. Unlike the case of albumin or transferrin, or apoA-I in the rat, LDL apoB 100 synthesis is not related to that of albumin, suggesting a different mechanism of regulation or a response to a stimulus that is not the same as that augmenting the synthesis of nonlipoproteins. Evidence is presented for synthesis of LDL through a mechanism that bypasses the normal delipidation pathway that requires a VLDL precursor for LDL formation. HDL concentration is normal but maturation is impaired leading to a shift from the larger HDL2 to the smaller HDL3, a variant that is less effective as a transporter of the LPL cofactor apolipoprotein C II.

Hepatic lipase

Hepatic lipase (HL) is an important enzyme that is involved in the metabolism of chylomicrons, intermediate density lipoproteins, and high density lipoproteins. HL may affect the liver uptake of remnant lipoproteins by modifying their compositions. HL also participates in the reverse cholesterol transport, thereby influencing the process of atherosclerosis. Several new functions of HL have recently been revealed. In this article, we review some of the recent progress based on studies using transgenic animals, with an emphasis on HL functions in remnant metabolism and atherosclerosis.

Bile acid metabolism in analbuminemic rats

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

Gene expression of lipoprotein lipase in experimental nephrosis

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