Proteinuria, not altered albumin metabolism, affects hyperlipidemia in the nephrotic rat

Albumin is an interface between blood plasma and cell membrane, and not just a sponge

Albumin is the most abundant protein in blood plasma and acts as a carrier for many circulating molecules. Hypoalbuminaemia, mostly caused by either renal or liver disease or malnutrition, can perturb vascular homeostasis and is involved in the development of multiple diseases. Here we review four functions of albumin and the consequences of hypoalbuminaemia on vascular homeostasis. (i) Albumin is the main determinant of plasma colloid osmotic pressure. Hypoalbuminaemia was therefore thought to be the main mechanism for oedema in nephrotic syndrome (NS), however, experimental studies showed that intrarenal mechanisms rather than hypoalbuminaemia determine formation and, in particular, maintenance of oedema. (ii) Albumin functions as an interface between lysophosphatidylcholine (LPC) and circulating factors (lipoproteins and erythrocytes) and the endothelium. Consequently, hypoalbuminaemia results in higher LPC levels in lipoproteins and erythrocyte membrane, thereby increasing atherosclerotic properties of low-density lipoprotein and blood viscosity, respectively. Furthermore, albumin dose-dependently restores LPC-induced inhibition of vasodilation. (iii) Hypoalbuminaemia impacts on vascular nitric oxide (NO) signalling by directly increasing NO production in endothelial cells, leading to reduced NO sensitivity of vascular smooth muscle cells. (iv) Lastly, albumin binds free fatty acids (FFAs). FFAs can induce vascular smooth muscle cell apoptosis, uncouple endothelial NO synthase and decrease endothelium-dependent vasodilation. Unbound FFAs can increase the formation of reactive oxygen species by mitochondrial uncoupling in multiple cell types and induce hypertriglyceridemia in NS. In conclusion, albumin acts as an interface in the circulation and hypoalbuminaemia impairs multiple aspects of vascular function that may underlie the association of hypoalbuminaemia with adverse outcomes. However, hypoalbuminaemia is not a key to oedema in NS. These insights have therapeutic implications.

Kidney-derived PCSK9-a new driver of hyperlipidemia in nephrotic syndrome?

Increased plasma concentrations of proprotein convertase subtilisin/kexin type 9 or PCSK9, which reduces hepatic uptake of low-density lipoprotein by downregulation of the low-density lipoprotein receptor, have been reported in nephrotic patients and might contribute to hyperlipidemia in nephrotic syndrome. The results of the study by Molina-Jijon et al. found that renal PCSK9 expression was upregulated in the collecting duct of nephrotic patients and animals, suggesting that the kidney might be a major source for plasma PCSK9 in nephrotic syndrome.

Kidney Lipidomics by Mass Spectrometry Imaging: A Focus on the Glomerulus

Lipid disorders have been associated with glomerulopathies, a distinct type of renal pathologies, such as nephrotic syndrome. Global analyses targeting kidney lipids in this pathophysiologic context have been extensively performed, but most often regardless of the architectural and functional complexity of the kidney. The new developments in mass spectrometry imaging technologies have opened a promising field in localized lipidomic studies focused on this organ. In this article, we revisit the main works having employed the Matrix Assisted Laser Desorption Ionization Time of Flight (MALDI-TOF) technology, and the few reports on the use of TOF-Secondary Ion Mass Spectrometry (TOF-SIMS). We also present a first analysis of mouse kidney cortex sections by cluster TOF-SIMS. The latter represents a good option for high resolution lipid imaging when frozen unfixed histological samples are available. The advantages and drawbacks of this developing field are discussed.

Dyslipidaemia in nephrotic syndrome: mechanisms and treatment

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

Lipid-Lowering Therapy in CKD: Should We Use It and in Which Patients

BACKGROUND

Chronic kidney disease is associated with a 15-fold increase in the risk of death and a 30-fold increase in the risk of cardiovascular events even prior to dialysis initiation, and this situation remains unchanged following the initiation of the dialysis procedure. Lipoprotein structure and function, especially the anti-oxidative properties of high-density lipoprotein, are altered. In this study, the effectiveness of lipid-lowering therapy on mortality and cardiovascular outcomes is explored.

SUMMARY

Mortality is inversely associated with the cholesterol level. The degree of inflammation and wasting is a stronger predictor of mortality than are cholesterol levels. Treatment with statins reduces the risk of death and cardiovascular outcomes among patients not yet requiring renal replacement therapy, but is not effective once dialysis is initiated, most likely because other processes, such as inflammation, not affected by lipid-lowering therapy, dominate in the causal pathway leading to adverse outcomes. Fenofibrate is also useful in reducing cardiovascular outcomes and the progression of renal disease among patients with type 2 diabetes not yet requiring dialysis. While the lipid-lowering therapy is effective in patients with the nephrotic syndrome, no long-term outcome studies regarding hard outcomes are available.

KEY POINTS

The great increase in cardiovascular outcomes in patients with kidney disease is likely due to a consequence of properties that are unresponsive to the lipid-lowering therapy, most likely inflammation. The lipid-lowering therapy is useful in patients who are not yet in need of dialysis but does not reduce mortality in dialysis patients.

Treatment of Hyperlipidemia Changes With Level of Kidney Function-Rationale

Lipoprotein abnormalities such as low levels of high-density lipoprotein (HDL) and high triglycerides (TGs), associated with the metabolic syndrome, are also associated with subsequent decline in kidney function. Patients with end-stage kidney disease also exhibit low HDL and high TGs and a modest reduction in low-density lipoprotein (LDL), although the mechanisms responsible for these changes differ when patients with end-stage kidney disease are compared with those having metabolic syndrome with normal kidney function, as do lipoprotein structures. Among dialysis patients, oxidized LDL, levels of TG-rich intermediate-density lipoprotein, and low HDL are associated with aortic pulsewave velocity and other markers of atherosclerosis. Statins are effective in reducing LDL and do decrease risk of cardiovascular events in patients with CKD not requiring dialysis but have no significant effect on outcomes, including all-cause mortality among dialysis patients. Similarly gemfibrozil and other fibrates lower TGs, increase HDL, and reduce cardiovascular events, but not mortality, among patients with CKD not requiring dialysis but have no significant effect on cardiovascular outcomes in dialysis patients. There is potential clinical benefit in treating elevated LDL, TGs, and low HDL in patients with CKD using statins or fibrates in those not yet requiring dialysis.

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.

Hepatic fatty acid and cholesterol metabolism in nephrotic syndrome

Heavy proteinuria (nephrotic syndrome) is associated with hypercholesterolemia, hypertriglyceridemia and a high risk of atherosclerosis. Hypertriglyceridemia in nephrotic syndrome (NS) is partly due to increased TG and TG-rich lipoprotein production. However, data on the effect of NS on fatty acid production and catabolic machinery are limited. NS was induced in male Sprague Dawley rats by IP injection of puromycin aminonucleoside. Six weeks after the second injection the animals were euthanized, liver was harvested and processed. The NS group exhibited heavy proteinuria, hypercholesterolemia, hypertriglyceridemia, activation of SREBP-1 and LXR α/β, up-regulation of FAS, ACC and HMG CoA reductase. In contrast hepatic tissue ChREBP activity was reduced in NS excluding its role in upregulation of FA synthetic pathway. Despite increased expression and nuclear translocation of PPARα, expression of ACO and abundance of CPT and L-FABP, were decreased in the liver of nephrotic animals. Therefore, NS results in upregulation of FA production machinery. Increased hepatic fatty acid production capacity in NS is compounded by reduced FA catabolism, events that contribute to the associated hypertiglyceridemia.

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.

Lack of plasma albumin impairs intravascular lipolysis and explains the associated free fatty acids deficiency and hypertriglyceridemia

BACKGROUND

Abnormalities in lipid metabolism and transport are hallmarks in analbuminemic Nagase rats (NAR) and humans. Triglyceridemia is nearly 3- to 5-fold higher in female NAR than in control Sprague-Dawley rats (SDR). Also, NAR present with a severe plasma free fatty acid (FFA) deficit. There are conflicting results regarding the mechanisms underlying NAR hypertriglyceridemia.

OBJECTIVE

We aimed at investigating whether liver lipogenesis and triglyceride secretion rates into the plasma contribute to the hypertriglyceridemia in NAR. We also studied whether heparin or albumin administration would release the hypothesized lipolysis inhibition in NAR.

METHODS

The incorporation of tritiated water into lipids and the linear accumulation rate of plasma triglycerides after Triton WR1339 injection were the measures of liver lipogenesis and triglyceride secretion rates.

RESULTS

Lipogenesis (596 ± 40 vs. 929 ± 124 μmol 3H2O/g/h) and triglyceride (4.25 ± 1.00 vs. 7.04 ± 1.68 mg/dL/min) secretion rates were slower (P ≤ 0.05) in fasted NAR than in control SDR. The injection of either heparin or albumin elicited an increase in NAR plasma FFA levels over time. FFA levels reached control levels 90 min after the albumin administration, increasing from 0.36 ± 0.05 to 1.34 ± 0.16 mEq/L (P ≤ 0.05). These results indicate that the lack of plasma albumin inhibits intravascular lipolysis and causes the FFA deficit observed in NAR.

CONCLUSION

NAR hepatic triglyceride synthesis and output do not contribute to NAR hypertriglyceridemia. We propose that the lack of albumin diminishes intravascular lipolysis which reduces the plasma triglyceride removal rate and explain both NAR hypertriglyceridemia and FFA deficiency.

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.

Endothelial bound lipoprotein lipase (LpL) depletion in hypoalbuminemia results from decreased endothelial binding, not decreased secretion

Hypertriglyceridemia in nephrotic (NS) and Nagase analbuminemic rats (Analb) results from reduced triglyceride clearance. NS and Analb have reduced or absent albumin, reduced plasma oncotic pressure (pi), but Analb lack proteinuria. The heparin releasable lipoprotein lipase (LpL) pool in both models is greatly reduced, suggesting reduced LpL is related to low albumin or pi and not proteinuria. To determine the cause of endothelial LpL reduction, we studied effectors of endothelial LpL (eLpL) levels from gene expression, to delivery and endothelial binding. eLpL was measured as heparin releasable activity. eLpL and secretion rate was measured in isolated hearts perfused with heparin. mRNA levels were measured in rat hearts by kinetic RT-PCR. Finally, binding of (125)I-LpL by competition assays rat endothelial cells measured serum-induced changes in affinity. eLpL in vivo was reduced in nephrotic and Analb rats. While the eLpL pool was reduced in isolated perfused hearts, neither LpL secretion by isolated hearts nor myocardial mRNA was reduced in NS or Analb. Binding of LpL to RAEC preincubated with serum from either NS or Analb was reduced compared to control. LpL mRNA levels and release rate was not altered in hearts from NS rats, while eLpL is depleted, suggesting that reduced eLpL in NS is not the result of reduced delivery. The finding that NS serum alters LpL binding to RAEC suggests LpL depletion results from decreased binding rather than defective delivery. This in turn is a consequence of reduced serum albumin or pi but does not require proteinuria.

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.

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

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

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.

Regulation of Epithelial Sodium Channel in Puromycin Aminonucleoside-Induced Unilateral Experimental Nephrotic Syndrome in Normal and Analbuminemic Nagase Rats

BACKGROUND

Nephrotic syndrome (NS) is characterized by renal sodium retention and edema formation. In nephrotic rats the site of enhanced sodium retention has been localized in the cortical collecting duct (CCD). The epithelial sodium channel (ENaC) is the rate-limiting constituent of sodium transport in CCD. Amiloride, an ENaC-blocking drug, corrects the abnormal rate of sodium transport in isolated perfused CCD from puromycin aminonucleoside (PAN)-treated rats. Therefore, we hypothesized that ENaC functional expression is increased in NS.

METHODS

Unilateral NS was induced by PAN in Wistar rats and analbuminemic Nagase rats (NAR). Urinary protein excretion, renal abundance of mRNA and protein of ENaC subunits, as well as the ENaC regulatory serum glucocorticoid-inducible kinase (Sgk1) and Nedd4-2, were assessed.

RESULTS

Proteinuria appeared at day 2 in the Wistar rats and NAR. Surprisingly a downregulation rather than the expected upregulation of alpha-, beta- and gamma-ENaC mRNA abundance was observed in both Wistar rats and NAR, when the treated kidney was compared with the untreated kidney. The amount of protein of alpha-, beta- and gamma-ENaC was not affected by the NS. Sgk1 mRNA expression did not change and Nedd4-2 protein expression was only decreased at days 1 and 2 in Wistar rats.

CONCLUSION

ENaC mRNA and protein expression are not increased in the early phase of unilateral PAN-induced NS. Sgk1, Nedd4-2 and analbuminemia are not important regulatory factors of ENaC protein expression in experimental NS.

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

BACKGROUND

Binding of very low-density lipoprotein (VLDL) isolated from serum of nephrotic rats VLDL to endothelial cells is defective. This defect is conferred on normal VLDL by prior incubation with high-density lipoprotein (HDL) from nephrotic, but not control rats. It is not known whether the defect is present in nascent VLDL (nVLDL) or is acquired after secretion. We test the hypothesis that VLDL is normal at the time of secretion from the liver and the defect in binding to endothelium is conferred following secretion through interaction with HDL.

METHODS

nVLDL was synthesized by and collected from isolated perfused livers from either control or nephrotic rats. nVLDL was labeled with 3H-oleate to measure binding and 35S methionine to evaluate apolipoprotein exchange and composition. To test whether HDL conferred a binding defect, nVLDL was incubated with HDL obtained either from control or nephrotic rats prior to measurement of binding. To distinguish the effects of proteinuria from reduced albumin concentration we additionally incubated nVLDL with HDL obtained from rats with hereditary analbuminemia. Both HDL and VLDL were reisolated by centrifugation prior to subsequent binding and lipolysis determination. Exchange of 35S-labeled apolipoprotein E (apoE) among the subsequent VLDL and HDL fractions was determined. To determine the effect of HDL on lipolysis, HDL-treated VLDL was exposed to lipoprotein lipase-coated 96-well plates and 3H-oleate release measured. To establish whether differences in apoE content could explain the differences in binding and lipolysis, apoE was restored to nephrotic VLDL and lipolysis and binding were subsequently measured.

RESULTS

Binding of nephrotic nVLDL was greater than control nVLDL (0.58 +/- 0.13 vs. 0.75 +/- 0.07 ng protein bound/mg cell protein) (P= 0.04, N= 6). Lipolysis was similarly elevated (0.091 +/- 0.010 vs 0.064 +/- 0.002 nmol NEFA released/well/hour) (P < 0.05). Prior incubation with nephrotic HDL reduced binding of nVLDL obtained from either nephrotic or control livers (P= 0.02, N= 6). Treatment with nephrotic (vs. control) HDL reduced both binding (control nVLDL + control HDL, 0.64 +/- 0.02; control + nephrotic, 0.43 +/- 0.06; nephrotic + control, 0.69 +/- 0.05; and nephrotic + nephrotic, 0.62 +/- 0.04 mg VLDL protein/mg cell protein) and lipolysis (control nVLDL + control HDL, 0.053 +/- 0.004; control + nephrotic, 0.038 +/- 0.004; nephrotic + control, 0.069 +/- 0.004; and nephrotic + nephrotic, 0.062 +/- 0.004 nmol NEFA/well/hour) (P < 0.05 vs. nVLDL + control HDL) of nVLDL from either source. The apoE content of nVLDL coincubated with control HDL or analbuminemic HDL was increased compared nVLDL incubated with either no HDL or nephrotic HDL (P < 0.05). Similarly, the apoE/apoA-I ratio was reduced in HDL from nephrotic rats but not in HDL from controls (P < 0.05). Reintroduction of apoE to nephrotic VLDL resulted in increased binding.

CONCLUSION

Unlike circulating VLDL, binding of nVLDL from isolated livers from nephrotic rats to endothelial cells is greater and its lipolysis is increased compared to control nVLDL. Decreased binding and lipolysis is conferred following incubation with HDL isolated from control, but not nephrotic rats and binding can be restored by reintroduction of apoE. Thus both defects are conferred on VLDL by exposure to HDL obtained from nephrotic animals, possibly a consequence of a failure of nephrotic HDL to enrich VLDL with apoE during clearance.

Effect of Lovastatin on lipid peroxidation and total antioxidant concentrations in hemodialysis patients

BACKGROUND

Atherosclerosis is the main cause of mortality and morbidity in end stage renal diseases (ESRD), especially in hemodialysis (HD) patients. In addition the classic risk factors for atherosclerosis, non classical risk factors, such as high lipid peroxidation and low antioxidants, also, are culprit in the pathogenesis.

METHOD

We tested lipid peroxidation and total antioxidant levels in forty five stable hyperlipidemic HD males (age range 40-60 years) before, after 45 and 90 days of prescription of 20 mg/day Lovastatin for three months. Malondialdehyde (MDA), as prototype of lipid peroxidation, and total antioxidants (TA) were measured by flourimetric and spectrophotometric assays, respectively.

RESULTS

Serum triglyceride (Tg) (213.7 +/- 112.4 mg/dl vs. 153.4 +/- 54.8 mg/dl p = 0.003), serum cholesterol (C) (185.8 +/- 48.3 mg/dl vs. 149.3 +/- 37.8 mg/dl, p = 0.014), LDL-C (120.1 mg/dl +/- 48.9 vs. 84.8 +/- 43.7 mg/d, p = 0.001), VLDL-C (40.7 +/- 18.9 mg/dl vs. 30.7 +/- 10.9 mg/dl, p = 0.025), MDA (13.1 +/- 3.5 nmol/ml vs. 1.27 +/- 1 nmol/ml, p = 0.00), TA (0.98 +/- 0.17 mmol/l vs. 1.28 +/- 0.27 mmol/l, p = 0.001) and HDL (24.9+11.1 mg/dl vs. 31.4 +/- 7.7 mg/dl, p = 0.007) significantly were changed by 3 months of Lovastatin therapy. These changes for HDL, VLDL and Tg after the 3 months were more obvious than 45 days of Lovastatin therapy.

CONCLUSION

In HD patients serum lipids and their oxidations are increased. Both of them, quantitatively and qualitatively, are improved by using of Lovastatin. The later would be due to enhance of TA activity.

Pathobiochemistry of nephrotic syndrome

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

Comorbidity and cardiovascular risk factors in patients with chronic kidney disease

The mortality rate among dialysis patients is high. Although guidelines have been in place to improve outcomes in dialysis patients, new emphasis is being placed on better management of patients who are pre-end-stage renal disease (pre-ESRD)-patients with chronic kidney disease (CKD). Spearheaded by the National Kidney Foundation, the National Institute of Health, and the nephrology community at large, an effort is underway to improve the care of patients with kidney disease. We hope that improvement in health and outcomes of patients with kidney disease will be optimized through attention to care before the development of advanced renal disease. Cardiovascular disease (CVD) is an important comorbidity of chronic kidney disease, and reducing cardiovascular events in this population is an important goal for the people who care for chronic kidney disease patients. In this article, we review the available literature regarding certain risk factors for cardiovascular disease: proteinuria, hyperglycemia, hypertension, homocysteine, hyperlipidemia, and inflammation. When possible, recommendations for treatment are provided based on the information reviewed.

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.

Plasma protein synthesis in patients with low-grade nephrotic proteinuria

Overt nephrotic syndrome is characterized by albumin and fibrinogen hyperproduction and reduced very low density lipoprotein apolipoprotein B-100 (VLDL apoB-100) clearance. Whether similar changes also occur in low-grade proteinuria is not known. Thus we measured albumin, fibrinogen, and VLDL apoB-100 kinetics in six patients with modest proteinuria and normal creatinine clearance (P) and in ten control subjects (C) by leucine tracer infusion and precursor-product relationships. In P, plasma albumin concentration was decreased (P < 0.003), whereas concentrations of fibrinogen and VLDL apoB-100 were increased (P < 0.001). In P, albumin fractional secretion rate (FSR) was increased (P < 0.01), fibrinogen FSR was normal, and VLDL apoB-100 FSR was decreased (P < 0.03). As a result, in P, absolute secretion rates (ASR) of albumin and fibrinogen were increased (P < 0.03), whereas VLDL apoB-100 ASR was normal. Albumin FSR was inversely correlated to oncotic pressure in P but not in C. These findings suggest that low-grade nephrotic proteinuria is characterized by simultaneous multiple alterations in turnover rates of albumin, fibrinogen, and VLDL apoB-100. Their pathogenesis, however, appears to be multifactorial.

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.

Proteinuria and plasma compositional changes contribute to defective lipoprotein catabolism in the nephrotic syndrome by separate mechanisms

Triglyceride (TG)-rich lipoproteins are primarily increased in the nephrotic syndrome (NS) as a result of decreased catabolism. Lipoprotein lipase (LpL) is the rate limiting enzyme for lipolysis of TG. The biologically active endothelial bound LpL pool is reduced in NS providing one mechanism for decreased clearance of very low density lipoprotein (VLDL). LpL, however, is also reduced in the Nagase Analbuminemic Rat (NAR) to the same extent as in NS, suggesting that other factors contribute to decreased VLDL clearance. Hyperlipidemia worsens with the onset of proteinuria and is reduced when proteinuria abates. We established that while VLDL from NS rats bind poorly to bovine aortic endothelial cells (BAEC) in the presence of saturating LpL while, VLDL from NAR bind more avidly than control. We then established that rat aortic endothelial cells (RAEC) incubated with serum from NAR or from NS rats bind significantly less exogenous LpL. Thus decreased clearance of VLDL in NS results from: 1) reduced endothelial bound LpL; an effect of serum from animals with reduced oncotic pressure (pi) that makes cells unable to bind LpL; and 2) an alteration in VLDL binding to endothelial bound LpL. The former has no relationship to proteinuria while the latter occurs as a consequence of proteinuria. These effects combine to suppress VLDL clearance.

Estrogen effects on triglyceride metabolism in analbuminemic rats

BACKGROUND

Triglyceride (TG) levels are normally lower in female rats, while the opposite is the case in the Nagase analbuminemic rats (NAR). Increased TG levels in normal males are caused by a testosterone-mediated decrease in postheparin (PH) lipoprotein lipase (LpL). Castration of males reduces TG, while castration of females is without effect. TG levels are reduced by castration of the female NAR, suggesting that estrogen rather than testosterone causes hypertriglyceridemia in this strain. The mechanism for this increase is unknown.

METHODS

We measured secretion of very-low density lipoprotein (VLDL) TG using Triton WR 1339 clearance as the disappearance from blood of 3H-trioleate and 14C-cholesterol-labeled chylomicrons (CM), and the activity of the PH lipases: LpL and hepatic lipase (HL). All were determined in Sprague-Dawley (SD) and NAR female, male, and ovariectomized (OVX) rats.

RESULTS

TG levels were significantly greater in female NAR in comparison to all other groups. Ovariectomy of NAR significantly ameliorated hypertriglyceridemia. VLDL TG secretion was significantly greater in intact female NAR compared with all other groups. There were no other differences in VLDL TG secretion among the other groups. The clearance of CM was greatest in female SD rats, and OVX had no effect. NAR cleared CM less well than did SD rats (P < 0.001), but among NAR, clearance was greatest in OVX NAR and male NAR (P < 0. 002). Both PH LpL activity and HL activity were lowest in female NAR (P < 0.05). Ovariectomy partially corrected the defect in HL (P < 0. 05).

CONCLUSION

TG levels in female NAR are in part a result of increased VLDL-TG secretion, an effect mediated by estrogen. The presence of an estrogen-mediated catabolic defect that was alleviated by OVX was also observed. This catabolic defect is likely a result of an estrogen-mediated decrease both in LpL and HL expressed only in the presence of analbuminemia.

Early mechanisms of renal injury in hypercholesterolemic or hypertriglyceridemic rats

Hyperlipidemia in conjunction with uninephrectomy leads to renal injury in rats. It is unknown whether this is due to mesangial cell or podocyte injury and whether the injuries induced by hypercholesterolemia and hypertriglyceridemia share a similar pathogenesis. Therefore, renal effects of hypercholesterolemia were studied in male rats with dietary hypercholesterolemia compared with rats on a regular diet. Renal effects of hypertriglyceridemia were studied in female Nagase analbuminemic rats (NAR). Hypertriglyceridemia was reduced in NAR by ovariectomy. Both models were studied after uninephrectomy or sham operation. Dietary hypercholesterolemia had little effect on plasma triglycerides, whereas ovariectomy in the NAR had no effect on plasma cholesterol. However, an increase in intermediate density lipoprotein cholesterol was common to both models. Dietary hypercholesterolemia and uninephrectomy separately induced a similar increase in proteinuria after 13 wk, which was additive when these interventions were combined. At this stage, only a minimal increase was present in glomerular alpha-smooth muscle actin staining, a marker of mesangial cell activation, or in mesangial matrix expansion. Moreover, platelet-derived growth factor-B chain, a marker of mesangial cell proliferation, was not increased. However, podocyte injury was prominent as evidenced by podocytic de novo expression of desmin and ultrastructural changes. Glomerular macrophage counts were increased by hypercholesterolemia but not by uninephrectomy, and were not related to the level of proteinuria. Hypertriglyceridemia and uninephrectomy in female NAR induced an increase in proteinuria after 24 wk, which was also associated with an increase in podocyte desmin expression without any mesangial activation and proliferation or matrix accumulation. Hypertriglyceridemia, proteinuria, and the increase in desmin staining were largely prevented by ovariectomy. Interstitial myofibroblast activation and tubulointerstitial injury accompanied proteinuria in both models. These findings indicate that both hypercholesterolemia and hypertriglyceridemia aggravate renal injury primarily via podocyte rather than via mesangial cell damage. Such podocyte injury is accompanied by tubulointerstitial cell activation and injury.

Lipopheresis in the nephrotic syndrome

BACKGROUND

Experimental models have established a role for lipoproteins in the pathogenesis of progressive renal failure. However, conventional treatment rarely normalizes the high serum cholesterol of the nephrotic syndrome. The removal of low-density lipoprotein by lipopheresis is discussed.

METHODS

Lipopheresis may be beneficial in nephrotic patients with focal segmental glomerulosclerosis. The authors studied the long-term effects of low-density lipoprotein cholesterol (LDL-C) removal using the Kaneka Liposorber system, which binds LDL-C to dextran sulfate in a controlled trial in 20 nephrotic patients with different renal diseases.

RESULTS

A 21-month clamp of plasma total cholesterol at 6.0 mmol/liter or below was significantly lower than controls (chi 2 = 84.3, P < 0.001), followed 12 aphereses over 6 to 12 weeks in all but three apheresed patients. 1/Cr slopes were unchanged when the 50-day average period of lipopheresis treatments was excluded from analysis. Proteinuria was not reduced, but serum albumin tended to rise (NS). Fibrinogen fell by 29.8%; high-density lipoprotein, apoA1, and Lp(a) were unchanged. Two apheresed patients had a prolonged remission with a reduction of proteinuria to less than 250 mg/24 hr. The reasons for prolonged reduction of total cholesterol include depletion of tissue cholesterol, an improved fractional catabolic rate of very low density lipoprotein (VLDL), increased hepatocyte LDL turnover, and the maintenance of statin therapy.

CONCLUSION

Lipopheresis is a safe and effective method for the control of LDL in nephrotic syndrome. Early clamping of total cholesterol in the normal range resulted in a prolonged and significant reduction of LDL compared with controls.

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.

Lipid-lowering therapy in membranous nephropathy

Membranous nephropathy (MN) is a very common cause of nephrotic syndrome in adults, and lipid abnormalities are, therefore, frequently found in these subjects. Although efficient lipid-lowering therapy is available, almost nothing is known about the contribution of hyperlipidemia in the pathogenesis of progressive renal failure in MN. Studies in an experimental animal model of human MN, Heymann nephritis, have shown that lipids play an essential role in the pathogenesis of proteinuria. Local production of reactive oxygen species after subepithelial immune complex deposition leads to the formation of lipid peroxidation (LPO) adducts, which ultimately alter the composition of the glomerular basement membrane. As the magnitude of urinary protein excretion is associated with the long-term prognosis, a normalization of glomerular permselective properties has been used as a surrogate parameter for the beneficial effects of treatment. Probucol, a drug with LPO inhibitor potential, is able to reduce urinary protein excretion in rats with passive Heymann nephritis. In humans with MN, preliminary data also support this observation. It remains to be determined, however, if this intervention, which does not interfere with immune complex formation, will reduce the number of the patients reaching end-stage renal failure because of MN. In conclusion, lipids may contribute to glomerular injury in MN, as LPO might be an especially important factor, opening the possibility for new therapeutic interventions, thereby avoiding the side-effects of the currently used treatment regimen.

Apolipoprotein(a) phenotypes and lipoprotein(a) concentrations in patients with renal failure

Patients with renal failure have an increased incidence of atherosclerotic disease. Numerous studies have shown that these patients show increased serum lipoprotein(a) [Lp(a)] concentrations compared with the control population. However, variable alleles at the apolipoprotein(a) [apo(a)] gene locus determine to a large extent the Lp(a) concentration in the general population. We therefore undertook the present study to evaluate apo(a) phenotypes and Lp(a) serum concentrations in a large number of patients with renal disease. Seventy-nine patients treated by hemodialysis (HD), 47 patients treated by continuous ambulatory peritoneal dialysis (CAPD), 68 patients with mild/moderate chronic renal failure (CRF) and serum creatinine levels of 1.8 to 8 mg/dL, and 73 healthy controls were studied. All patients showed significantly elevated median serum Lp(a) concentrations in comparison with controls: HD patients, 15.7 mg/dL (P < 0.01); CAPD patients, 20 mg/dL (P < 0. 005); CRF patients, 15.1 mg/dL (P < 0.01) versus controls, 7 mg/dL. The greater Lp(a) values in all groups were not explained by differences in isoform frequencies, whereas their increase was apo(a)-type specific. Thus, patients in all groups with high-molecular-weight (HMW) apo(a) isoforms showed a significant elevation of Lp(a) levels, whereas serum Lp(a) concentrations in patients with low-molecular-weight (LMW) isoforms were not significantly different from controls, except for CAPD patients, who presented increased serum Lp(a) concentrations. We conclude that in patients with renal failure, even of mild/moderate degree, as well as in patients with end-stage renal disease undergoing HD or CAPD, elevated Lp(a) concentrations are mainly observed in those with HMW apo(a) phenotypes.

The full induction of human apoprotein A-I gene expression by the experimental nephrotic syndrome in transgenic mice depends on cis-acting elements in the proximal 256 base-pair promoter region and the trans-acting factor early growth response factor 1

To identify molecular factors regulating apo A-I production in vivo, we induced in transgenic mice the experimental nephrotic syndrome, which results in elevated levels of HDL cholesterol (HDL-C), plasma apo A-I, and hepatic apo A-I mRNA. Human (h) apo A-I transgenic mice with different length 5' flanking sequences (5.5 or 0.256 kb, the core promoter for hepatic-specific basal expression) were injected with nephrotoxic (NTS) or control serum. With nephrosis, there were comparable (greater than twofold) increases in both lines of HDL-C, h-apo A-I, and hepatic h-apo A-I mRNA, suggesting that cis-acting elements regulating induced apo A-I gene expression were within its core promoter. Hepatic nuclear extracts from control and nephrotic mice footprinted the core promoter similarly, implying that the same elements regulated basal and induced expression. Hepatic mRNA levels for hepatocyte nuclear factor (HNF) 4 and early growth response factor (EGR) 1, trans-acting factors that bind to the core promoter, were measured: HNF4 mRNA was not affected, but that of EGR-1 was elevated approximately fivefold in the nephrotic group. EGR-1 knockout (EGR1-KO) mice or mice expressing EGR-1 were injected with either NTS or control serum. Levels of HDL-C, apo A-I, and hepatic apo A-I mRNA were lowest in nonnephrotic EGR1-KO mice and highest in nephrotic mice expressing EGR-1. Although in EGR1-KO mice HDL-C, apo A-I, and apo A-I mRNA levels also increased after NTS injection, they were approximately half of those in the nephrotic EGR-1-expressing mice. We conclude that in this model, basal and induced apo A-I gene expression in vivo are regulated by the trans-acting factor EGR-1 and require the same cis-acting elements in the core promoter.

Increased VLDL in nephrotic patients results from a decreased catabolism while increased LDL results from increased synthesis

Increased very low density lipoprotein (VLDL) in nephrotic patients results from a decreased catabolism while increased low density lipoprotein (LDL) results from increased synthesis. Hyperlipidemia is a hallmark of nephrotic syndrome that has been associated with increased risk for ischemic heart disease as well as a loss of renal function in these patients. The hyperlipidemia usually is characterized by increased cholesterol levels, although hypertriglyceridemia may be present as well. The factors that determine the phenotype of nephrotic dyslipidemia are not understood, nor has the primary stimulus for nephrotic hyperlipidemia been identified. One hypothesis is that nephrotic hyperlipidemia is the result of a coordinate increase in synthesis of proteins by the liver. To address these issues we simultaneously measured the in vivo rate of VLDL apolipoprotein B100 (apo B100) secretion, LDL apo B100 synthesis and albumin synthesis in patients with a nephrotic syndrome (N = 8) and compared them with a control group (N = 7) using a primed/continuous infusion of the stable isotope L-[1-13C] valine for six hours. Kinetic data were analyzed by multicompartmental analysis. Patients studied had combined hyperlipidemia as reflected by an significant increase in both VLDL and LDL apo B100 pool sizes. In contrast, the albumin pool size was significantly decreased. VLDL apo B100 levels were primarily increased as a consequence of a decrease in fractional catabolic rate (FCR) rather than from an increase in the absolute synthesis rate (ASR). Both VLDL apo B100 and triglycerides were inversely related to the fractional catabolism (FCR) of VLDL apo B100 (r2 = 0.708; P = 0.0088) while neither had any relationship to the ASR of VLDL apo B100. In contrast to VLDL, increased LDL apo B100 was not a consequence of decreased catabolism. The LDL apo B100 ASR was significantly increased (P = 0.001) in the nephrotic patients compared to controls. Low density lipoprotein apo B100 ASR was greater than that of VLDL apo B100 in some patients, suggesting that LDL in these patients was not only derived from VLDL delipidation, but also by an alternative secretory pathway. There was no clear relationship between the ASR of VLDL apo B100 and the ASR of albumin within the current study population. Our data indicate that increased VLDL in nephrotic patients results from a decreased catabolism, while increased LDL results from increased synthesis.

Role of lipoprotein-bound NEFAs in enhancing the specific activity of plasma CETP in the nephrotic syndrome

Plasma cholesteryl ester transfer protein (CETP) activity, evaluated by the transfer of radiolabeled cholesteryl esters from a tracer dose of tritiated HDL to the plasma apolipoprotein B-containing lipoproteins, was significantly higher in patients with untreated idiopathic nephrotic syndrome (n = 15) than in normolipidemic control subjects (n = 22) (81.5 +/- 8.4 versus 43.1 +/- 3.1 micrograms CE.mL-1.h-1, respectively; P < .001). The increased CETP activity in nephrotic plasma was explained by a significant rise in both the CETP mass concentration (3.2 +/- 0.2 versus 2.1 +/- 0.1 mg/L; P < .001), and the specific CETP activity, calculated as the ratio of CETP activity to CETP mass (25.3 +/- 1.7 versus 20.4 +/- 1.6 micrograms CE.mg-1.h-1; P < .05). Elevated CETP activity in nephrotic patients was shown to be associated with a significant decrease in the mean size of LDL (24.4 +/- 0.5 versus 26.3 +/- 0.5 nm; P < .0001) as well as in the relative abundance of HDL2a (29.6 +/- 1.6% versus 34.8 +/- 1.1%; P < .05). The nephrotic syndrome was characterized by a significant increase in the relative proportion of lipoprotein-bound nonesterified fatty acids (NEFAs) (35.4 +/- 7.7% versus 7.6 +/- 3.0% of total; P < .01), leading to a significant increase in the electronegative charge of LDL (-4.3 +/- 0.1 versus -3.9 +/- 0.1 mV; P < .05) and HDL (-11.5 +/- 0.1 versus -11.1 +/- 0.2 mV; P < .05). Compared with native, non-supplemented plasma, removal of lipoprotein-bound NEFAs by addition of fatty acid-poor albumin to total plasma from nephrotic patients or control subjects significantly decreased CETP activity and specific CETP activity. Specific CETP activity no longer differed between nephrotic and control groups after albumin supplementation (19.7 +/- 1.5 versus 17.7 +/- 1.5 micrograms CE.mg-1.h-1; NS). It is concluded that, in addition to elevated CETP mass concentration, lipoprotein-bound NEFAs, by increasing the negative electrostatic charge of nephrotic lipoproteins, can facilitate the CETP-mediated neutral-lipid transfer reaction in total plasma from nephrotic patients.

Effect of increasing serum albumin on serum lipoprotein(a) concentration in patients receiving CAPD

Lipoprotein(a) [Lp(a)], an independent risk factor for atherosclerotic cardiovascular disease in the general population, is known to be elevated in patients with renal disease accompanied by hypoalbuminemia such as nephrotic syndrome and end-stage renal disease. In this study, the role of hypoalbuminemia in the elevation of serum Lp(a) was investigated in 20 continuous ambulatory peritoneal dialysis (CAPD) patients with serum albumin below 3.5 g/dL. The patients were divided into two groups. In group 1 (n = 10), fasting serum Lp(a) and albumin were measured before, after repeated infusion of 20% albumin 100 mL three times per week for 2 weeks, and 4 weeks after withdrawal of albumin infusion. In group 2 (n = 10), serum albumin and Lp(a) were measured similarly without albumin infusion. C-reactive protein was monitored in both group as an indicator of acute-phase reactant. Serum Lp(a) was also measured in 20 age- and sex-matched normal controls. Apolipoprotein(a) [apo(a)] phenotype was determined in all the subjects. CAPD patients as a whole (n = 20; median, 70.2 mg/dL; interquartile range, 45.0 to 86.2 mg/dL) had higher serum Lp(a) than normal controls (n = 20; median, 9.9 mg/dL; interquartile range, 2.4 to 24.3 mg/dL) (P < 0.0001), although the distribution of apo(a) phenotype was similar. Serum albumin in group 1 increased from 2.6+/-0.5 g/dL to 3.5+/-0.6 g/dL (P < 0.0005) at the end of repeated infusion of albumin, whereas serum Lp(a) decreased from 73.7 mg/dL (range, 43.2 to 89.0 mg/dL) to 25.6 mg/dL (range, 10.7 to 71.7 mg/dL) (P < 0.01). Four weeks after withdrawal of albumin infusion, serum albumin decreased again to 2.9+/-0.5 g/dL (P < 0.001), whereas serum Lp(a) increased to 65.2 mg/dL (range, 43.3 to 106.0 mg/dL) (P < 0.05). Serum albumin in group 2 was 2.8+/-0.6 g/dL, 3.0+/-0.4 g/dL, and 2.9+/-0.7 g/dL, respectively. The change of serum Lp(a) was not significant (67.0 mg/dL [range, 46.8 to 84.8 mg/dL], 62.8 mg/dL [range, 45.1 to 81.0 mg/dL], and 63.0 mg/dL [range, 44.7 to 74.0 mg/dL]). C-reactive protein was stable during the study period in both groups. These findings support the hypothesis that hypoalbuminemia is one of the important trigger factors in the elevation of serum Lp(a) in CAPD patients.

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.

Hypoalbuminemia causes high blood viscosity by increasing red cell lysophosphatidylcholine

Albumin deficiency is accompanied by a reduction in red cell deformability and blood hyperviscosity. Albumin deficiency increases plasma fibrinogen and triglyceride levels and may alter red cell membrane lipid composition. These options, which could all contribute to reduced red cell deformability (RCD) and hyperviscosity, were studied in the Nagase analbuminemic rat (NAR), a mutant Sprague Dawley rat (CON), characterized by normal total protein levels, with an absolute deficiency of albumin, but elevated levels of non-albumin proteins and hyperlipidemia. Plasma protein-binding of the polar phopholipid lysophosphatidylcholine (LPC) was markedly decreased. LPC comprised only 26 +/- 1% of total plasma phospholipids as compared to 42 +/- 2% in CON. NAR red cells in CON plasma had a viscosity that was similar to CON red cells in CON plasma. Conversely, CON red cells in NAR plasma show an increased viscosity as compared to CON red cells in CON plasma. The maximum deformation index of both NAR and CON red cells was markedly decreased in NAR plasma as compared to either NAR or CON cells in CON plasma (0.04 +/- 0.03 and 0.02 +/- 0.02 vs. 0.22 +/- 0.06 and 0.15 +/- 0.04, respectively; P < 0.05). Thus, plasma composition causes hyperviscosity and reduced RCD in NAR. Fibrinogen is not responsible since red cells in serum and red cells in plasma had a similar viscosity and differences in viscosity and RCD between NAR and CON were maintained. Plasma triglycerides are also not responsible since the viscosity of red cells in serum with a 50% reduction in triglycerides was not reduced. LPC levels in red cells were increased in NAR (8.7 +/- 0.2 vs. 5.5 +/- 0.3% of total phospholipids; P < 0.01). Adding albumin to NAR blood dose-dependently decreased whole blood viscosity, despite marked increases in plasma viscosity, and increased RCD of NAR cells (from 0.04 +/- 0.03 to 0.21 +/- 0.01; P < 0.05). There was also some effect on CON RCD of similar albumin addition to CON blood (from 0.15 +/- 0.04 to 0.29 +/- 0.03; P < 0.05). Adding albumin to NAR blood reduced red cell LPC content and increased plasma LPC content in a dose-dependent fashion, whereas there were only slight effects of adding albumin to CON blood. There was a reciprocal relation between red cell LPC and the other polar phospholipids in the red cell membrane, probably indicating exchange. The maximum deformability index of either NAR or CON cells was not affected much by adding LPC to CON plasma (NAR, from 0.22 +/- 0.06 to 0.18 +/- 0.10; CON, from 0.15 +/- 0.04 to 0.12 +/- 0.05; NS), whereas adding LPC to NAR plasma caused the red cells to become rigid. Adding LPC to CON red cells in NAR plasma caused a much stronger increase in relative LPC content (from 6.6 +/- 0.7 to 10.9 +/- 0.9%; P < 0.05) than adding LPC to CON red cells in CON plasma (from 5.6 +/- 0.4 to 6.4 +/- 0.8%; NS). Thus, in the absence of albumin, LPC in red blood cells is increased. As a consequence of the latter, RCD is decreased and whole blood viscosity increased. Alterations in red cell phospholipids are far more important than increases in plasma fibrinogen or triglycerides in determining hyperviscosity of blood and reduced RCD in NAR.

Lipoprotein kinetics in patients with analbuminemia. Evidence for the role of serum albumin in controlling lipoprotein metabolism

In vitro data suggested that albumin is a key factor controlling apolipoprotein (apo) synthesis by hepatocytes. Studies in analbuminemic rats have shown an increase in secretion of apoB-containing lipoprotein from the liver. We studied the kinetic aspects of apoB- and apoAI-containing lipoprotein metabolism in two sisters with analbuminemia using a constant 14-hour infusion of leucine labeled with stable isotopes. Compared with control subjects, total cholesterol was higher in the two patients (432 and 461 versus 155 +/- 14 mg/dL), as was apoB (257 and 230 versus 72 +/- 7 mg/dL). Triglycerides were slightly increased (134 and 105 versus 89 +/- 9 mg/dL), whereas apoAI was lower (109 and 105 versus 124 +/- 6 mg/dL). VLDL-apoB production was higher, as was the production of IDL-apoB and LDL-apoB (32.8 and 36.0 versus 24.8 +/- 5.9, 32.1 and 27.2 versus 16.4 +/- 2.3, and 14.1 and 17.6 versus 10.3 +/- 1.2 mg.kg-1.d-1, respectively). The fractional catabolic rate of all the apoB-containing lipoproteins was decreased (0.23 and 0.37 versus 0.48 +/- 0.05, 0.27 and 0.28 versus 0.62 +/- 0.08, and 0.012 and 0.009 versus 0.022 +/- 0.002.h-1, respectively). A similar mechanism could explain the dyslipidemia observed in other conditions associated with low albumin levels, such as nephrotic syndrome.

Plasma protein abnormalities in nephrotic syndrome: effect on plasma colloid osmotic pressure and viscosity

The concentrations of 25 plasma proteins were measured in 22 patients with membranous nephropathy. For some large proteins, the plasma concentrations were increased; there were also large proteins with low plasma concentrations, but small or medium-sized proteins showed uniformly lower plasma concentration than the controls. Plasma colloid osmotic pressure (π) and viscosity (η) were not interrelated but showed positive and significant correlations with plasma concentrations of small and medium-sized proteins (π) and plasma concentrations of large proteins (η), respectively. Nephrotic plasma is not efficient in maintaining plasma π but highly efficient in maintaining plasma η. High plasma fibrinogen concentrations and low antithrombin III concentrations may predispose to thrombosis, and low IgG concentrations may account for the higher predisposition to bacterial infection. The relative composition of nephrotic plasma is heavily dependent on the size of the different proteins. Plasma π and η are also maintained by the relative preponderance of different plasma proteins.

The influence of hypoalbuminemia in the generation of nephrotic hyperlipidemia

Lipoprotein measurements in a group of 29 patients with massive proteinuria and without hypoalbuminemia, were compared with those observed in matched controls and patients with overt nephrotic syndrome to assess the influence of plasma albumin concentration and proteinuria in modulating blood lipid levels. Plasma apoprotein B and apo B containing lipoproteins were not increased in proteinuric normoalbuminemic patients. There was a good correlation between plasma albumin and oncotic pressure (r = 0.937; P < 0.001). Plasma oncotic pressure was inversely correlated with plasma apoprotein B in nephrotic patients (r = -0.44, P = 0.017) but not in normoalbuminemics (r = 0.17, P = 0.369), suggesting that plasma albumin affects apoprotein B secretion. Other findings, however, indicate that multiple processes are ocurring simultaneously in these patients. There was an accumulation of very low- and intermediate density lipoproteins in normoalbuminemics, suggesting a residual defect in the lipoprotein removal. Also, raised (P < 0.05) lipoprotein(a) levels respect to controls (median, 0.15 g/l) were noted in both, normoalbuminemics (median, 0.72 g/l) and hypoalbuminemics (median, 0.84 g/l) with similar degree of proteinuria (6.4 vs. 6.6 g/24 h), suggesting that other mechanisms may be operative in lipoprotein(a) derangements. Our findings suggest that there is no unique mechanism in the pathogenesis of nephrotic hyperlipidemia but that both hypoalbuminemia and proteinuria can have a distinct contribution, individually or in combination.

The serum lathosterol to cholesterol ratio, an index of cholesterol synthesis, is not elevated in patients with glomerular proteinuria and is not associated with improvement of hyperlipidemia in response to antiproteinuric treatment

The hypothesis that increased cholesterol synthesis provides a mechanism that contributes to nephrotic syndrome-associated hyperlipidemia is mainly based on experimental evidence. The serum level of the cholesterol precursor, lathosterol (expressed per millimole cholesterol), is a reliable marker of whole-body cholesterol synthesis in normocholesterolemia and primary hypercholesterolemia. Serum lathosterol and lipoprotein levels were measured in 11 moderately hyperlipidemic patients with nephrotic-range proteinuria and 22 matched controls. The proteinuric patients were evaluated before and during three antiproteinuric treatment periods with angiotensin-converting enzyme (ACE) inhibition therapy (n = 6) or a low-protein diet (n = 5) alone, in combination, and again as a single treatment. In untreated patients, serum total cholesterol, very-low-density (VLDL) and low-density (LDL) lipoprotein cholesterol, apolipoprotein B (apo B), and lipoprotein (a) [Lp(a)] levels were higher than in controls (P < .01 to P < .001), but the lathosterol to cholesterol ratio tended to be lower in patients (0.99 +/- 0.43 micromol/mmol) as compared with controls (1.29 +/- 0.41 micromol/mmol, P < .10). During combined antiproteinuric treatment, total and VLDL + LDL cholesterol, apo B, and Lp(a) decreased (P < .02 to P < .01), but remained higher than levels in controls. Yet the serum lathosterol to cholesterol ratio changed little and was even lower (P < .05) in treated patients than in controls. Serum total cholesterol (r = -.82, P < .01) and apo B (r = -.84, P < .01) were inversely correlated with serum albumin in untreated patients, whereas the serum lathosterol to cholesterol ratio was not (r = -.01, NS). In the patient group, multiple regression analysis showed that changes in the lathosterol to cholesterol ratio during the study were only related to changes in the dietary polyunsaturated to saturated fatty acids ratio (P:S) coinciding with the low-protein diet (P < .01). In contrast, the decrease of VLDL + LDL cholesterol, apo B, and Lp(a) was independently related to reduction of proteinuria (P < .02 to P < .001), but not to changes in the lathosterol to cholesterol ratio. In conclusion, the present data, based on the serum lathosterol to cholesterol ratio, do not support the concept that increased cholesterol synthesis plays an important role in the maintenance of human nephrotic syndrome-associated hypercholesterolemia. Moreover, it appears unlikely that the decrease of apo B-containing lipoproteins with antiproteinuric treatment is attributable to inhibition of cholesterogenesis. These findings warrant further documentation of cholesterol synthesis in human nephrotic syndrome by direct methods.

Ovariectomy decreases plasma triglyceride levels in analbuminaemic rats by lowering hepatic triglyceride secretion

In mutant analbuminaemic rats (NAR), females demonstrate a more marked hypertriglyceridaemia than males. Ovariectomy decreases triglyceride levels in female NAR. We measured triglyceride secretion rates in vivo as well as the activity of acetyl CoA carboxylase (ACC) and fatty acid synthase (FAS) in hepatic cytosol obtained from female control Sprague-Dawley (SD) rats and NAR with or without ovariectomy. NAR were severely hyperlipidaemic, and triglyceride, cholesterol, apolipoprotein A-I and plasma protein concentrations levels were decreased (all P < 0.01) by ovariectomy. Only triglyceride levels were decreased by ovariectomy in the SD rats (P < 0.05). Oestradiol treatment in ovariectomized NAR restored plasma protein and triglyceride concentrations to levels similar to those observed in intact female NAR and caused a marked increase in plasma cholesterol. Ovariectomy in NAR reduced lipoprotein triglycerides and cholesterol in VLDL, IDL and LDL1, but had little effect on the triglyceride-cholesterol ratio of these particles. Both ACC and FAS activities were markedly increased in NAR vs. SD rats (P < 0.01). This increase was partially corrected by ovariectomy. There was no significant effect of ovariectomy on ACC or FAS activity in the SD rats. Triglyceride secretion rates were significantly increased in NAR vs. SD rats (135 +/- 10 vs. 103 +/- 12 nmol/min per 100 g body weight; P < 0.05). Ovariectomy markedly decreased triglyceride secretion rate in NAR to 69 +/- 6 (P < 0.01), but not in SD rats (92 +/- 8 nmol/min per 100 g body weight, NS). Oestradiol treatment in ovariectomized SD rats restored triglyceride levels but had no significant effect on triglyceride secretion rate (106 +/- 23 nmol/min per 100 g).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of oncotic pressure on apolipoprotein A-I metabolism in the rat

The nephrotic syndrome is characterized by reduced plasma albumin and colloid osmotic pressure (pi), urinary protein loss and hyperlipidemia. High-density lipoprotein (HDL) and the level of apo A-I, the principal apolipoprotein in HDL, is increased in nephrotic rats and rats with hereditary analbuminemia (NAR)--animals with virtually no albumin in plasma and reduced plasma pi, but without proteinuria, suggesting that urinary protein loss is not responsible for increased plasma apo A-I levels. We conducted these studies to determine the mechanism responsible for increased plasma apo A-I levels in the nephrotic syndrome and NAR and to determine whether reduced plasma pi or albumin was responsible for increased apo A-I. We first measured the clearance of 125I apo A-I HDL in NAR and rats with passive Heymann nephritis (HN) compared with normal Sprague Dawley (SD) control. Both the clearance of apo A-I and fractional apo A-I turnover rate (FTR) were significantly reduced both in HN (7.40 +/- 2.18% plasma pool/hr) and NAR (5.63 +/- 1.12) compared with SD (9.87 +/- 0.75). Total apo A-I turnover rate, which in steady state equals apo A-I synthesis rate, was also significantly increased in both HN (487 +/- 127 micrograms/100 g body weight/hr) and NAR (253 +/- 16), compared with SD (216 +/- 19). Thus decreased apo A-I catabolism and increased synthesis both contributed to increased apo A-I levels in HN and NAR. We then infused either f3p4roncotic human albumin or ficoll into two additional groups of HN for days in quantities sufficient to maintain plasma pi within the normal range.(ABSTRACT TRUNCATED AT 250 WORDS)