Hyperlipoproteinemia in Nagase analbuminemic rats: effects of pravastatin on plasma (apo)lipoproteins and lecithin:cholesterol acyltransferase activity

Can blood proteome diversity among fish species help explain perfluoroalkyl acid trophodynamics in aquatic food webs?

Per- and polyfluoroalkyl substances (PFAS) are a diverse family of industrially significant synthetic chemicals infamous for extreme environmental persistence and global environmental distribution. Many PFAS are bioaccumulative and biologically active mainly due to their tendency to bind with various proteins. These protein interactions are important in determining the accumulation potential and tissue distribution of individual PFAS. Trophodynamics studies including aquatic food webs present inconsistent evidence for PFAS biomagnification. This study strives to identify whether the observed variability in PFAS bioaccumulation potential among species could correspond with interspecies protein composition differences. Specifically, this work compares the perfluorooctane sulfonate (PFOS) serum protein binding potential and the tissue distribution of ten perfluoroalkyl acids (PFAAs) detected in alewife (Alosa pseudoharengus), deepwater sculpin (Myoxocephalus thompsonii), and lake trout (Salvelinus namaycush) of the Lake Ontario aquatic piscivorous food web. These three fish sera and fetal bovine reference serum all had unique total serum protein concentrations. Serum protein-PFOS binding experiments showed divergent patterns between fetal bovine serum and fish sera, suggesting potentially two different PFOS binding mechanisms. To identify interspecies differences in PFAS-binding serum proteins, fish sera were pre-equilibrated with PFOS, fractionated by serial molecular weight cut-off filter fractionation, followed by liquid chromatography-tandem mass spectrometry analysis of the tryptic protein digests and the PFOS extracts of each fraction. This workflow identified similar serum proteins for all fish species. However, serum albumin was only identified in lake trout, suggesting apolipoproteins are likely the primary PFAA transporters in alewife and deepwater sculpin sera. PFAA tissue distribution analysis provided supporting evidence for interspecies variations in lipid transport and storage, which may also contribute to the varied PFAA accumulation in these species. Proteomics data are available via ProteomeXchange with identifier PXD039145.

A triglyceride-rich lipoprotein environment exacerbates renal injury in the accelerated nephrotoxic nephritis model

Hyperlipidaemia accompanies chronic renal disease either as a consequence of the renal dysfunction or as part of generalized metabolic derangements. Under both situations, the lipid profile is characterized by accumulation of triglyceride-rich lipoproteins (TGRLs). This lipid profile is recognized as a risk factor for cardiovascular complications. Whether it may pose a risk for renal injury as well remains unclear. A hyper-TGRL state was generated in C57BL/6 mice using poloxamer-407 (P-407) and immune complex-mediated renal injury was triggered using the accelerated nephrotoxic nephritis (ANTN) model. The hyper-TGRL animals were hypersensitive to ANTN demonstrated by greater haematuria and glomerular cellularity. These changes were accompanied by increased glomerular accumulation of CD68⁺ macrophages. The hypersensitive response to ANTN was not seen in low-density lipoprotein receptor knock-out mice fed with a high fat diet, where triglyceride levels were lower but cholesterol levels comparable to those obtained using P-407. These data indicate that a hyper-TGRL state might be more detrimental to the kidneys than low-density lipoprotein-driven hypercholesterolaemia during immune complex-mediated nephritis. We speculate that the hyper-TGRL environment primes the kidney to exacerbated renal damage following an inflammatory insult with increased accumulation of macrophages that may play a key role in mediating the injurious effects.

Pravastatin attenuates hypertension, oxidative stress, and angiogenic imbalance in rat model of placental ischemia-induced hypertension

Preeclampsia is a pregnancy-specific condition characterized by an imbalance of circulating angiogenic factors and new-onset hypertension. Although current treatment options are limited, recent studies suggest that pravastatin may improve angiogenic profile and reduce blood pressure in preeclampsia. We hypothesized pravastatin would restore angiogenic balance and reduce mean arterial pressure (MAP) in rats with reduced utero-placental perfusion pressure (RUPP)-induced hypertension. Pravastatin was administered intraperitoneally (1 mg/kg per day) in RUPP (RUPP+P) and normal pregnant rats (NP+P) from day 14 to 19 of pregnancy. On day 19, MAP was measured via catheter, conceptus data were recorded, and tissues collected. MAP was increased (P<0.05) in RUPP compared with NP dams, and pravastatin ameliorated this difference. Pravastatin attenuated decreased fetal weight and plasma vascular endothelial growth factor and the RUPP-induced increased soluble fms-like tyrosine kinase-1 when compared with NP dams. Pravastatin treatment did not improve angiogenic potential in RUPP serum and decreased (P<0.05) endothelial tube formation in NP rats. RUPP rats presented with indices of oxidative stress, such as increased placental catalase activity and plasma thiobarbituric acid reactive substances along with decreased plasma total antioxidant capacity compared with NP controls, and pravastatin attenuated these effects. MAP, fetal weight, plasma vascular endothelial growth factor, and plasma soluble fms-like tyrosine kinase-1 were unchanged in NP+P compared with NP controls. The present data indicate that treatment with pravastatin attenuates oxidative stress and lowers MAP in placental ischemia-induced hypertension, but may have negative effects on circulating angiogenic potential during pregnancy. Further studies are needed to determine whether there are long-term deleterious effects on maternal or fetal health after pravastatin treatment during pregnancy-induced hypertension or preeclampsia.

The higher susceptibility of congenital analbuminemic rats to Ca2+-induced mitochondrial permeability transition is associated with the increased expression of cyclophilin D and nitrosothiol depletion

Congenital analbuminemia is a rare autosomal recessive disorder characterized by a trace level of albumin in blood plasma and mild clinical symptoms. Analbuminemic patients generally present associated abnormalities, among which dyslipidemia is a hallmark. In this study, we show that mitochondria isolated from different tissues (liver, heart and brain) from 3-month-old analbuminemic rats (NAR) present a higher susceptibility to Ca(2+)-induced mitochondrial permeability transition (MPT), as assessed by either Ca(2+)-induced mitochondrial swelling, dissipation of membrane potential or mitochondrial Ca(2+) release. The Ca(2+) retention capacity of the liver mitochondria isolated from 3-month-old NAR was about 50% that of the control. Interestingly, the assessment of this variable in 21-day-old NAR indicated that the mitochondrial Ca(2+) retention capacity was preserved at this age, as compared to age-matched controls, which indicates that a reduced capacity for mitochondrial Ca(2+) retention is not a constitutive feature. The search for putative mediators of MPT sensitization in NAR revealed a 20% decrease in mitochondrial nitrosothiol content and a 30% increase in cyclophilin D expression. However, the evaluation of other variables related to mitochondrial redox status showed similar results between the controls and NAR, i.e., namely the contents of reduced mitochondrial membrane protein thiol groups and total glutathione, H(2)O(2) release rate, and NAD(P)H reduced state. We conclude that the higher expression of cyclophilin D, a major component of the MPT pore, and decreased nitrosothiol content in NAR mitochondria may underlie MPT sensitization in these animals.

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.

Diminished macrophage cholesterol removal rate by the altered HDL metabolism in the Nagase analbuminemic rat

Dyslipoproteinemia of the Nagase analbuminemic rat (NAR) is characterized by elevated concentrations of VLDL and LDL attributed to increased rates of liver lipoprotein synthesis. Increased lysophosphatidylcholine (LPC) in NAR HDL has been attributed to high plasma LCAT activity. We show here that, as compared with Sprague-Dawley rats (SDR), NAR plasma triacylglycerol (TAG), total cholesterol (TC), HDL TAG, protein, total phospholipids (PL), LPC, and PS are increased. These alterations rendered the NAR HDL particle more susceptible to the activity of the enzyme hepatic lipoprotein lipase (HL), which otherwise was unaltered in our study. Fractional catabolic rates in blood of the autologous 125I-apoHDL (median and lower quartile values), were, respectively, 0.231 and 1.645 (n = 10) in NAR as compared with 0.140 and 0.109 (n = 10) in SDR (P = 0.012), corresponding to synthesis rates of HDL protein of 89.8 +/- 33.7 mg/d in NAR and 17.4 +/- 6.5 mg/d in SDR (P = 0.0122). Furthermore, Swiss mouse macrophage free-cholesterol (FC) efflux rates, measured as the percent [14C]-cholesterol efflux/6 h, were 8.2 +/- 2.3 (n = 9) in NAR HDL and 11.2 +/- 3.2 (n = 10) in SDR HDL (P = 0.03). Therefore, in NAR the modification of the HDL composition slows down the cell FC efflux rate, and together with the increased rate of plasma HDL metabolism influences the reverse cholesterol transport system.

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.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Male gender increases sensitivity to renal injury in response to cholesterol loading

Males are at greater risk for renal injury than females. This may relate to nitric oxide (NO) availability, because female rats have higher renal endothelial NO synthase (NOS) levels. Previously, our laboratory found susceptibility to proteinuria induced by NOS inhibition in male compared with female rats. Dyslipidemia and hypercholesterolemia dose dependently decreased renal NOS activity and caused renal injury in female rats. We hypothesized that exposure of male rats to hypercholesterolemia would lead to more renal injury in male than in female rats due to an a priori lower renal NO system. Female and male rats were fed no, low-dose, or high-dose cholesterol for 24 wk. Cholesterol feeding dose dependently increased proteinuria in both female and male rats, but male rats developed more proteinuria at similar plasma cholesterol (P < 0.001). Control males had lower renal NOS activity than control females (4.44 +/- 0.18 vs. 7.46 +/- 0.37 pmol. min(-1). mg protein(-1); P < 0.05), and cholesterol feeding decreased renal NOS activity in males and in females (P < 0.05). Cholesterol-fed males developed significantly more vascular, glomerular, and tubulointerstitial monocyte/macrophage influx and injury than females. Thus under baseline conditions, male rats have lower renal NOS activity than female rats. This may explain why male rats are more sensitive to renal injury by factors that decrease NO availability, such as hypercholesterolemia.

Proteinuria is preceded by decreased nitric oxide synthesis and prevented by a NO donor in cholesterol-fed rats

BACKGROUND

Hypercholesterolemia decreases nitric oxide (NO) availability in the circulation and induces podocyte activation and renal injury in rats. It is unknown whether hypercholesterolemia decreases renal NO availability. To dissociate the injury-independent effect of hypercholesterolemia on renal NO availability from secondary effects of proteinuria, increasing concentrations of cholesterol were administered. To determine whether podocyte activation and renal injury were associated with NO deficiency, molsidomine, an exogenous NO donor, was administered to hypercholesterolemic rats.

METHODS

Female rats were fed 0, 0.5, 1, or 2% cholesterol for 24 weeks. Rats fed 2% cholesterol were also studied for two weeks. In addition rats fed 0 or 1% cholesterol received 120 mg molsidomine/L drinking water. Renal NO availability was determined by measuring renal NO synthesis and superoxide activity. Podocyte activation was monitored by desmin staining.

RESULTS

Hypercholesterolemia dose-dependently increased proteinuria. In the absence of proteinuria, hypercholesterolemia decreased renal NO synthesis (4.2 +/- 0.5 in 0.5% cholesterol vs. 6.8 +/- 0.6 pmol/min/mg protein in controls; P < 0.05). With the exception of neuronal nitric oxide synthase (nNOS), renal NOS protein mass remained unaffected. Renal superoxide activity was dose-dependently increased, thus further lowering renal NO availability. Podocyte injury was dose-dependently increased even in the absence of proteinuria (score, 40 +/- 4 in 0.5% cholesterol vs. 9 +/- 4 in controls; P < 0.05). After two weeks, hypercholesterolemia caused no proteinuria, but did cause some podocyte injury. Renal NOS activity was decreased, but glomerular endothelial NOS (eNOS) staining was unchanged. Molsidomine prevented proteinuria, podocyte activation, and all further renal injury.

CONCLUSIONS

Hypercholesterolemia decreases renal NO synthesis, and induces podocyte activation before proteinuria appears. Renal superoxide activity is increased once rats are proteinuric, further lowering renal NO availability. All of these changes can be prevented by a NO donor.

Apolipoprotein A-II/A-I ratio is a key determinant in vivo of HDL concentration and formation of pre-beta HDL containing apolipoprotein A-II

Overexpression of human apolipoprotein A-II (apo A-II) in mice induced postprandial hypertriglyceridemia and marked reduction in plasma HDL concentration and particle size [Boisfer et al. (1999) J. Biol. Chem. 274, 11564-11572]. We presently compared lipoprotein metabolism in three transgenic lines displaying plasma concentrations of human apo A-II ranging from normal to 4 times higher, under ad libitum feeding and after an overnight fast. Fasting dramatically decreased VLDL and lowered circulating human apo A-II in transgenic mice; conversely, plasma HDL levels increased in all genotypes. The apo A-I content of HDL was inversely related to the expression of human apo A-II, probably reflecting displacement of apo A-I by an excess of apo A-II. Thus, the molar ratios of apo A-II/A-I in HDL were significantly higher in fed as compared with fasted animals of the same transgenic line, while endogenous LCAT activity concomitantly decreased. The number and size of HDL particles decreased in direct proportion to the level of human apo A-II expression. Apo A-II was abundantly present in all HDL particles, in contrast to apo A-I mainly present in large ones. Two novel findings were the presence of pre-beta migrating HDL transporting only human apo A-II in the higher-expressing mice and the increase of plasma HDL concentrations by fasting in control and transgenic mice. These findings highlight the reciprocal modifications of VLDL and HDL induced by the feeding-fasting transition and the key role of the molar ratio of apo A-II/A-I as a determinant of HDL particle metabolism and pre-beta HDL formation.

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.

Substrate specificity of lysophospholipase D which produces bioactive lysophosphatidic acids in rat plasma

Previously we reported that lysophospholipase D in rat plasma hydrolyzes endogenous unsaturated lysophosphatidylcholines (LPCs) preferentially to saturated LPCs to lysophosphatidic acids with growth factor-like and hormone-like activities. In this study, we examined the possibility that association of LPCs with different proteins in rat plasma has an effect on the preference of lysophospholipase D for unsaturated LPCs. Large portions of various LPCs were found to be recovered in the lipoprotein-poor bottom fraction. Furthermore, the percentages of LPCs associated with albumin isolated from rat plasma were shown not to be consistent with their percentage conversions to lysophosphatidic acids by lysophospholipase D on incubation of rat plasma at 37 degrees C. These results indicate that distinct distributions of LPCs in the plasma protein fractions are not critical factors for the substrate specificity of lysophospholipase D. Experiments with Nagase analbuminemic rats suggested that albumin-LPC complexes are not necessarily required for the hydrolysis by lysophospholipase D; lipoprotein-associate LPCs appeared to be good substrates for the phospholipase. We found that both saturated and unsaturated LPCs are present mainly as 1-acyl isomers in rat plasma. This result indicates that the preference of lysophospholipase D for unsaturated LPCs is not attributable to a difference in position of the acyl group attached to the glycerol backbone of LPC. In addition, lysophospholipase D was also found to attack choline phospholipids with a long chain group and a short chain alkyl group, although their percentage hydrolyses were low. Taken altogether, these results suggest that lysophospholipase D shows higher affinities for free forms of unsaturated acyl type LPCs equilibrated with albumin-bound and lipoprotein-associated forms, than for free forms of saturated acyl type LPCs and analogs of platelet-activating factor.

Estrogen induces glomerulosclerosis in analbuminemic rats

Progression of chronic renal disease is usually more rapid in males, both in humans and in experimental animals. Estrogen-replacement studies indicate that this may be related to the beneficial effects of estrogen on the lipoprotein profile. However, in hyperlipidemic analbuminemic rats (NAR), females are more prone to develop renal injury than males, and ovariectomy tends to decrease triglyceride levels and prevent renal disease. Therefore, we studied the effects of estrogen administration on lipoproteins, and the induction of renal injury in uninephrectomized female and male NAR. Ovariectomized and orchidectomized uninephrectomized NAR were treated with estradiol implants for 24 weeks. In an additional group of ovariectomized rats, the implant was removed after 12 weeks. Both in ovariectomized and orchidectomized NAR, estradiol caused severe hypercholesterolemia (9 to 12 mmol/liter) and hypertriglyceridemia (6 to 8 mmol/liter) after six weeks. Subsequently, these rats developed severe proteinuria, reaching 209 +/- 25 and 95 +/- 43 mg/day, respectively, after 24 weeks. At this point there was severe glomerular sclerosis, with a respective score of 107 +/- 21 and 61 +/- 33. In terminal blood samples the most pronounced increase in lipid levels were observed in very low density lipoproteins (VLDL), intermediate density lipoproteins (IDL) and low density lipoproteins (LDL). In contrast, ovariectomized NAR and orchidectomized NAR without exogenous estrogen had much lower lipid levels (cholesterol 5 to 7 mmol/liter and triglycerides 1 to 2 mmol/liter) after six weeks. These rats, or ovariectomized NAR where the estrogen treatment had been withdrawn, had practically no proteinuria (4 +/- 1, 19 +/- 11, and 13 +/- 4 mg/day, respectively) or renal damage (glomerulosclerosis score 1 +/- 0.4, 5 +/- 3 and 3 +/- 1, respectively) after 24 weeks. Thus, in hypertriglyceridemic analbuminemic rats, estrogen-treatment causes further increases in both triglycerides and cholesterol. Most probably these changes contribute to the development of renal injury by estrogen in this model. This effect of estrogen, which has also been observed in the Zucker rat, is unique for the hypertriglyceridemic state and deserves further study.

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.

Toxicity of amphotericin B to analbuminemic rats

Nagase analbuminemic rats (NAR), a strain derived from Sprague Dawley rats (SDR), are suitable to determine the in vivo effect of hyperlipidemia and analbuminemia on the toxicity of the antifungal agent amphotericin B (AB). Cholesterol content was increased in all plasma lipoprotein fractions when SDR serum was compared with NAR serum. Incubation of AB with plasma from animals of both strains and further isolation of plasma lipoprotein by ultracentrifugation, showed that, while in SDR approximately 40% of the injected AB was in the lipoprotein fraction, in NAR almost all (approximately 80%) AB was associated with lipoproteins, especially in the low density lipoprotein fraction. AB spectrophotometry showed differences in the extent of AB aggregation between SDR and NAR plasma fractions. The lack of albumin results in aggregation of the AB present in the infranatant fraction. In vivo, a strong reduction in lethality was observed for NAR when compared to SDR (LD 50% of 6.4 and 1.9 mg/kg respectively). The preferential distribution of AB in the plasma lipoprotein fraction seems to affect pharmacological parameters, with a consequent reduction of toxicity.

Serum albumin is a significant intermediate in cholesterol transfer between cells and lipoproteins

The function of albumin in the movement of cholesterol into and out of non-cholesterol-loaded fibroblasts has been investigated. Cholesterol efflux from cholesterol labeled normal human skin fibroblasts to fatty acid-free human serum albumin (HSA) is biphasic with a rapid first phase that plateaus at about 15 min followed by a nearly linear phase up to 90 min, the longest incubation in this study. Saturation of efflux is observed at about 10 mg of albumin/mL. Efflux is specific to albumin since other molecules, such as ovalbumin or gelatin, do not induce efflux. The ability of HSA to induce cellular cholesterol efflux is low compared to reconstituted discoidal lipoprotein A-I (LpA-I). HSA at 2 mg/mL produces a rate of cholesterol efflux similar to that of LpA-I at 45 micrograms of protein/mL; however, these concentrations are within the physiological range for both HSA and apolipoprotein A-I (apoA-I). The efflux to the medium containing both LpA-I and HSA is greater than that to each of them alone but does not show complete additivity, indicating a competition between HSA and LpA-I. The HSA-mediated cholesterol movement is bidirectional as demonstrated by the transfer of cholesterol from HSA-(3H)- cholesterol complexes to fibroblasts; moreover, the HSA-mediated transfer is much faster than that from cholesterol-containing LpA-I (0.8 versus 0.2 pmol (micrograms of cell protein)-1 (90 min)-1. However, the presence of either low-density lipoprotein (LDL) or LpA-I in the incubation medium significantly inhibits the transfer of cholesterol from HSA-(3H)-cholesterol complexes to fibroblasts, thus allowing the bidirectional transfer of cholesterol between HSA and cells to possibly operate as a net efflux. In conclusion, albumin plays a significant role in cholesterol transfer between cells and lipoproteins.

Increased cholesteryl ester transfer activity in plasma from analbuminemic patients

Hypercholesterolemia associated with analbuminemia, an inherited disease manifesting low plasma albumin concentration, is characterized by enhanced LDL cholesterol levels and reduced HDL cholesterol levels. In addition, compared with normal counterparts, the esterified cholesterol:triglyceride ratio tends to be higher in analbuminemic apoB-containing lipoproteins and lower in analbuminemic HDL. The aim of the present study was to investigate the mechanism that may account for the association of a hypoalbuminemic state with alterations in the concentration and composition of plasma lipoprotein fractions. To this end, endogenous cholesterol esterification activity, phospholipid transfer activity, and cholesteryl ester transfer activity were measured in total plasma from three analbuminemic patients and five control subjects. Whereas endogenous cholesterol esterification and phospholipid transfer rates were not significantly affected in analbuminemia, the transfer of radiolabeled cholesteryl esters from HDL toward apoB-containing lipoproteins was constantly higher in analbuminemic plasmas than in normal control plasma (473.6+/-107.3% x h(-1) x mL(-1) versus 227.5+/-84.0% x h(-1) x mL(-1), respectively; P=.036). The rise in cholesteryl ester transfer protein (CETP) activity in analbuminemic plasma was due to a significant increase in the transfer of radiolabeled cholesteryl esters toward LDL but not toward the triglyceride-rich lipoproteins. The CETP mass was higher in analbuminemic patients than in control subjects, but the difference did not reach the significance level (5.18+/-0.82 mg/L versus 3.13+/-1.19 mg/L respectively; P=.07). Since abnormally elevated nonesterified fatty acid (NEFA) levels were shown to be associated with analbuminemic lipoproteins, mostly LDL, the direct role of lipoprotein-bound NEFA in enhancing CETP activity was suspected. In support of this view, supplementation of total plasmas with fatty acid-poor albumin was shown to reduce CETP activity to a significantly greater extent in analbuminemic plasmas than in normal control plasma. It is concluded that hyperlipidemia associated with the hypoalbuminemic state can relate, at least in part, to the combined effect of CETP and NEFA in promoting the transfer of cholesteryl esters from the antiatherogenic HDL toward the proatherogenic apoB-containing lipoproteins.

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)

Proteinuria, lipoproteins and renal apolipoprotein deposits in uninephrectomized female analbuminemic rats

To elucidate the pathogenetic role of hyperlipidemia per se in the development of glomerulosclerosis, severely hyperlipidemic female analbuminemic rats (NAR) and mildly hyperlipidemic male NAR were studied for a period of 37 weeks after uninephrectomy (UNX). Plasma cholesterol increased from 6.3 +/- 0.4 (week 4) to 11.9 +/- 0.6 mmol/liter (week 37) in the female NAR, and from 4.3 +/- 0.1 to 6.4 +/- 0.5 mmol/liter in the male NAR in the same period. Plasma protein concentration was also consistently higher in female NAR (60 +/- 1 g/liter) as compared to male NAR (52 +/- 1 g/liter). Plasma viscosity was higher in female NAR than in male NAR, but there were no differences in blood viscosity. Proteinuria increased progressively in the UNX female NAR from 25 weeks after surgery, reaching a final value of 141 +/- 37 mg/day. No proteinuria occurred in the UNX male NAR (final value 15 +/- 2 mg/day). Glomerular capillary pressure, measured prior to the onset of proteinuria, was not significantly different in UNX female NAR and UNX male NAR. At the end of the study glomerulosclerosis and lipid deposition was only found in the UNX female NAR. Throughout the study hyperfiltration and hyperperfusion, relative to the one-kidney clearances of the sham-operated (2K) animals, were not different in UNX male and female NAR. No differences were observed in blood pressure. Hypertrophy, evaluated by glomerular diameters, was less pronounced in UNX female NAR (174 +/- 3 microns) than in UNX male NAR (190 +/- 7 microns). Glomerular diameters in 2K female and male NAR were similar (respectively 158 +/- 2 and 157 +/- 4 microns). Plasma apo B levels were similar (2K female NAR: 204 +/- 8 U; 2K male NAR 204 +/- 13 U), but cholesterol and triglyceride content of apo B-containing lipoproteins, namely VLDL, IDL and LDL, was increased twofold in the female NAR as compared to the male NAR, implying a larger particle size in the female NAR. Deposition of apo B and apo E was observed in the glomerular mesangium of UNX female NAR, particularly in sclerotic lesions. Glomerular apo A-I deposits were localized primarily in visceral epithelial cells and were not associated with sclerotic lesions. The development of proteinuria and glomerulosclerosis after UNX in female NAR but not in male NAR may depend upon differences in plasma lipoprotein composition, but is apparently not related to differences in whole kidney hyperfiltration and hyperperfusion, glomerular capillary pressure, or blood viscosity.

Plasma triglyceride levels are higher in nephrotic than in analbuminemic rats despite a similar increase in hepatic triglyceride secretion

The relative contributions of increased hepatic secretion of triglyceride (TG) and decreased TG catabolism to hypertriglyceridemia in the nephrotic syndrome, and their relationship to urinary protein loss and reduced plasma colloid osmotic pressure (pi) remain unclear. We measured the activity of acetyl-CoA carboxylase (ACC) and fatty acid synthase (FAS), two key enzymes of fatty acid synthesis in hepatic cytosol, in fed control rats, in rats with congenital analbuminemia (NA) that are free of proteinuria, and in rats with adriamycin-induced nephrotic syndrome (ADR). Both NA and ADR rats had decreased pi (respectively 13.2 +/- 0.3 and 10.7 +/- 0.4 mm Hg vs. control rats 18.3 +/- 0.7 mm Hg, P < 0.05), but only ADR rats had increased plasma TG (5.8 +/- 2.6 mmol/liter vs. 1.5 +/- 0.2 mmol/liter in both control and NA rats, P < 0.05), and were proteinuric: 811 +/- 45 mg/day, P < 0.01 versus control and NA rats. Total cytosolic ACC activity, expressed per g body weight, was increased in both NA and ADR rats by 45% and 39%, respectively (P < 0.05). Total FAS activity was increased by 65% and 115% in NA and ADR rats, respectively (P < 0.05). Thus low pi was consistently associated with an increase in total ACC and FAS activities in the livers of fed rats. However, low pi was consistently associated with an increase in plasma TG only in ADR rats. Hepatic TG secretion rates, measured in vivo after blocking lipolysis with Triton WR-1339 in fasting animals, were increased by 33% in both ADR and NA rats as compared to controls (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Abnormal acyltransferase activities and accelerated cholesteryl ester transfer in patients with nephrotic syndrome

To determine the effects of the nephrotic syndrome (NS) on atherogenic risk, we studied the lipoprotein composition and the activities of lecithin-cholesterol acyltransferase (LCAT), lysolecithin acyltransferase (LAT), and cholesteryl ester transfer (CET) in the plasma of 11 NS patients and 10 control subjects. NS plasma had lower ratios of high-density lipoprotein (HDL) to low-density lipoprotein (LDL) and HDL2/HDL3 and an elevated free cholesterol (FC) to phosphatidyl choline (PC) ratio (1.09 +/- 0.27 in NS and 0.72 +/- 0.21 in controls, P < .02), all of which indicate an increased atherogenic potential. LCAT activity was normal in NS plasma when assayed with an exogenous substrate, but was 40% lower than in control plasma when assayed with the endogenous substrates. However, in vitro addition of serum albumin to NS plasma failed to normalize the LCAT activity. The LAT reaction, which is catalyzed by LCAT protein in the presence of LDL, was 60% to 80% higher in NS plasma, and consequently the ratio of LAT/LCAT activities was increased twofold. CET activity was significantly increased (+160% of control), and this abnormality was attributable to changes in both the acceptor (very-low-density lipoprotein [VLDL] + LDL) and donor (HDL) lipoproteins and possibly in CET protein. These results suggest that the NS may increase the risk of atherosclerosis not only by adversely affecting the concentrations of lipoproteins, but also by altering their composition and function.

Lipoprotein phospholipid composition and LCAT activity in nephrotic and analbuminemic rats

Albumin is an acceptor of lysophosphatidylcholine (LPC), product of the lecithin:cholesterol acyl transferase (LCAT) reaction, and it has been suggested that low LCAT activity and reduced cholesterol esterification rate in patients with the nephrotic syndrome may be linked to depletion of albumin. Effects of low plasma albumin levels on LCAT activity, cholesterol esterification rates and LPC-binding were therefore studied in hyperlipidemic nephrotic (NS) and analbuminemic (NAR) rats. LPC-binding was also measured in normoalbuminemic rats with dietary hypercholesterolemia. Remarkably, LCAT activity, measured with excess exogenous substrate, was not decreased but increased in both NAR and NS rats. Molar esterification rates with endogenous substrate were increased in NAR but normal in NS rats. In normoalbuminemic rats, with or without hypercholesterolemia, LPC was primarily found in the lipoprotein-deficient plasma and the HDL3 fraction. In NAR and NS rats LPC levels were increased in lipoproteins (notably in LDL and HDL2), but, in marked contrast to normoalbuminemic rats, decreased in lipoprotein-deficient plasma. Phosphatidylcholine, quantitatively the major phospholipid, was distributed proportionally over the lipoproteins in NS, NAR and control rats. Therefore, in hypoalbuminemia and analbuminemia LPC is mainly bound to lipoproteins, which is in contrast to the paucity of LPC in these particles in normoalbuminemic rats. Cholesterol esterification in nephrotic plasma is thus not impaired by lack of an acceptor for LPC-binding. The absence of an increase in molar cholesterol esterification in conjunction with increased LCAT activity points to a possible defect of the substrate for this reaction in nephrotic plasma. Increased LPC levels in LDL, a characteristic of oxidized LDL, may be a hitherto unrecognized atherosclerotic risk factor in the nephrotic syndrome.

Nagase analbuminemic rats have faster plasma triacylglycerol and VLDL synthesis rates

Serum triacylglycerol (TG) concentration is markedly elevated in Nagase analbuminemic rats (NAR) as compared to Sprague-Dawley rats (SDR) and reflects a high level of mainly VLDL. Hepatic production of triacylglycerol, as measured by the Triton-WR1339 infusion technique of impairing TG removal from blood, and plasma metabolic rate of pulse-infused [125I]apo VLDL, were higher in NAR. However, contrary to previous reports, this elevated TG production could not be controlled by previous treatment of NAR with (i) bovine albumin infused intra-arterially or into the peritoneal cavity, or with (ii) dextran (Mol.wt. 73,500) injected intraperitoneally. Albumin administration expanded the plasma volume and could explain the apparent reduction of blood lipids found by others. Nonetheless, intraperitoneal dextran, as compared to saline, reduced the plasma cholesterol concentration regardless of the variation in the hematocrit level and thus, by raising the osmotic pressure of blood might regulate the metabolism of cholesterol-rich lipoproteins such as LDL and HDL in NAR.

In vivo regulation of hepatic lipase activity and mRNA levels by diets which modify cholesterol influx to the liver

The aim of this study was to assess whether diets enriched in cholesterol, sodium cholate and drugs known to modify liver cholesterol biosynthesis can modulate hepatic lipase (H-TGL) expression and activity in vivo. Female lean Zucker rats, known to be good responders to cholesterol, were fed for 7 days with a control C diet or the C diet supplemented (w/w) with either 2% cholesterol, 0.5% sodium cholate, 2% cholestyramine or simvastatin (0.1%) added to the cholestyramine diet or given by gavage (10 mg/rat) for 3 days. H-TGL activity decreased by 34% with cholesterol, and by 27% when both cholesterol and cholate were administered to the rats. Under these conditions, H-TGL mRNA decreased by 34% and 87%, respectively. The sharp decrease in H-TGL expression was associated with a strong increase in cholesteryl ester in total liver and in the liver microsome fraction. H-TGL activity decreased by 33% with cholestyramine and the mRNA level decreased by 47%. Simvastatin lowered H-TGL activity by 55% when added to the cholestyramine diet, probably because of a reduction in food intake. When administrated by gavage, simvastatin increased both the H-TGL activity (by 28%) and mRNA (by 23%). These variations may be linked to the availability of mevalonate-derived sterol and non-sterol products.

Effect of simvastatin treatment on plasma apolipoproteins and hepatic apolipoprotein mRNA levels in the genetically hypercholesterolemic rat (RICO)

The effects of long-term treatment with simvastatin on plasma lipoproteins, plasma apolipoproteins, and on hepatic apolipoprotein gene expression were evaluated in genetically hypercholesterolemic (RICO) rats. Simvastatin administration caused a decrease in plasma triglyceride and phospholipid concentrations. Plasma cholesterol concentration was not changed by simvastatin, but cholesterol distribution among plasma lipoproteins was altered. Plasma apo B, apo A-I, and apo A-IV concentrations were lowered by simvastatin treatment whereas plasma apo E concentration was not affected by this drug. In the liver, simvastatin treatment induced a significant decrease of apo E mRNA level but had no effect on apo B, apo A-I, and apo A-IV mRNA abundances. It appears that simvastatin may modify plasma apolipoprotein concentrations by influencing their hepatic synthesis at both pre- and posttranscriptional levels.

Role of elevated lecithin: cholesterol acyltransferase and cholesteryl ester transfer protein activities in abnormal lipoproteins from proteinuric patients

Lecithin:cholesterol acyltransferase (LCAT) and cholesteryl ester transfer protein (CETP) are key factors in the esterification of free cholesterol, and the distribution of cholesteryl ester among lipoproteins in plasma. Alterations in these processes may play a role in the lipoprotein abnormalities associated with glomerular proteinuria. The activities of LCAT and CETP were measured using excess exogenous substrate assays in nine patients with nephrotic-range proteinuria and in 18 matched controls. The proteinuria-lowering effect of four weeks of angiotensin converting enzyme (ACE) inhibition with enalapril was also studied. Plasma very low lipoprotein and low density lipoprotein (VLDL and LDL) cholesterol, triacylglycerol and apolipoprotein B levels were significantly elevated in the patients compared with controls. High density lipoprotein (HDL) total cholesterol, free cholesterol, cholesteryl ester and the free cholesterol/cholesteryl ester ratio in HDL were lower. Total plasma apolipoprotein A1 was normal. Plasma LCAT and CETP activities were elevated in the patients by 30% (P < 0.01) and by 39% (P < 0.01), respectively, and were both inversely related to serum albumin. VLDL and LDL cholesterol levels were positively related to LCAT and CETP activities, whereas the HDL free cholesterol content was inversely related to LCAT activity. ACE inhibition resulted in a 40% reduction of proteinuria, a partial normalization of LCAT activity, and a decrease in VLDL and LDL cholesterol. In conclusion, elevated activities of LCAT and CETP may provide a mechanism that contributes to the low proportion of cholesterol in HDL relative to that in VLDL and LDL, as well as to the compositional changes of HDL seen in glomerular proteinuria.(ABSTRACT TRUNCATED AT 250 WORDS)