The rat, a useful animal model for pharmacological studies on apolipoprotein E

Apolipoprotein E is a major protein component of lipoproteins and plays an important role in cholesterol transport. The structure of the gene and the polymorphism of apolipoprotein E have been studied in human and rat, which show similar structures of apolipoprotein E. The wide tissue distribution of this apolipoprotein suggests diverse functions like cholesterol distribution between cells, intracellular cholesterol trafficking and tissue reparation. Nevertheless, the presence of apolipoprotein E in atherosclerotic plaques and amyloid deposits in brains of Alzheimer's disease patients also indicate pathologic functions staying misunderstood. The aim of this paper is to review the present knowledge on the distribution of apolipoprotein E between the different organs with the related functions and to make an overview of the implications of this apolipoprotein is physiological events and pathological states in the rat. The rat is widely used for drug metabolism studies. Its serum levels are 5-10 times higher than in human and thus this animal provides an useful pharmacological model to elucidate the functions of apo E.

The effect of a thromboxane A2 synthase inhibitor on the dyslipoproteinemia of an inbred rat strain with spontaneous age-related nephrotic syndrome

We have previously shown that the administration of a thromboxane A2 (TXA2) synthase inhibitor (FCE 22178) reduced the progression of glomerular lesions and proteinuria in MNS rats, an inbred strain which develops an age-related nephrotic syndrome. In the present study we investigated the effect of FCE 22178 on the plasma lipoproteins of MNS rats at 28 weeks of age (with mild proteinuria and moderate dyslipoproteinemia) and at 48 weeks of age (with heavy proteinuria and severe dyslipoproteinemia). Drug treatment reduced proteinuria (by 70% and 36% at 28 and 48 weeks of age, respectively) plasma cholesterol (by 36% and 27% at 28 and 48 weeks of age, respectively) and prevented the decrease of plasma albumin observed in untreated rats (C-MNS) 48 weeks old. In treated rats (T-MNS), the decrease of proteinuria was positively correlated with that of plasma cholesterol. FCE 22178 reduced the elevation in plasma HDL1 (by 17.4%) and HDL2 levels (by 30%), a key feature of nephrotic dyslipoproteinemia in the rat. From 28 to 48 weeks of age plasma apo A-I and apo E increased 217% and 128%, respectively, in C-MNS rats and 191% and 121%, respectively, in T-MNS rats. A significant increase of apo A-I/apo E ratio was found in C-MNS rats from 28 (2.28 +/- 0.36) to 48 weeks of age (3.84 +/- 0.9) but not in T-MNS rats. FCE 22178 altered the lipid composition of VLDL and HDL2 by reducing the content of cholesteryl esters and increasing that of free cholesterol and phospholipids. These findings suggest that the beneficial effect of FCE 22178 on the dyslipoproteinemia of nephrotic MNS rats is secondary to the amelioration in kidney function and to the reduction of proteinuria produced by this drug.

Effect of ascorbic acid administration on B and E apoproteins in rats fed a cholesterol enriched diet

The effect of ascorbic acid on cholesterol metabolism is very well documented; it is ascribed to the activation of this vitamin on cholesterol 7 alpha-hydroxylase (EC 1.14) that activates the catabolism of cholesterol. In this paper we have studied the effect of the administration of ascorbic acid on B and E apoproteins of rats fed a diet enriched with 1.5% of cholesterol. The results obtained show that ascorbic acid is able to affect cholesterol metabolism by modifying the serum levels of apo B in total serum and in lipoprotein classes of density less than 1.050 g/ml. Moreover the ascorbic acid treatment reduced the amount of cholesterol and triglycerides in all lipoprotein classes examined. No significant change of total serum apo E was observed following ascorbic acid administration.

Norethindrone alters apolipoprotein E concentration and isoform expression in rat plasma high-density lipoproteins

The administration of norethindrone, a synthetic progestin, to female rats caused marked decreases in the cholesterol and protein contents of high-density lipoproteins (HDL). A 84% decrease in the total apolipoprotein (apo) E of HDL was associated with a 80% decrease in the proportions of apoE isoforms E1 and E2, whereas E3 and E4 were unchanged. This appears to be the first demonstration of hormonally-induced modification of the apoE phenotype.

Effects of dietary fats and cholesterol on liver lipid content and hepatic apolipoprotein A-I, B, and E and LDL receptor mRNA levels in cebus monkeys

The effects of the long-term administration of the dietary fats coconut oil and corn oil at 31% of calories with or without 0.1% (wt/wt) dietary cholesterol on plasma lipoproteins, apolipoproteins (apo), hepatic lipid content, and hepatic apoA-I, apoB, apoE, and low density lipoprotein (LDL) receptor mRNA abundance were examined in 27 cebus monkeys. Relative to the corn oil-fed animals, no significant differences were noted in any of the parameters of the corn oil plus cholesterol-fed group. In animals fed coconut oil without cholesterol, significantly higher (P less than 0.05) plasma total cholesterol (145%), very low density lipoprotein (VLDL) + LDL (201%) and high density lipoprotein (HDL) (123%) cholesterol, apoA-I (103%), apoB (61%), and liver cholesteryl ester (263%) and triglyceride (325%) levels were noted, with no significant differences in mRNA levels relative to the corn oil only group. In animals fed coconut oil plus cholesterol, all plasma parameters were significantly higher (P less than 0.05), as were hepatic triglyceride (563%) and liver apoA-I (123%) and apoB (87%) mRNA levels relative to the corn oil only group, while hepatic LDL receptor mRNA (-29%) levels were significantly lower (P less than 0.05). Correlation coefficient analyses performed on pooled data demonstrated that liver triglyceride content was positively associated (P less than 0.05) with liver apoA-I and apoB mRNA levels and negatively associated (P less than 0.01) with hepatic LDL receptor mRNA levels. Liver free and esterified cholesterol levels were positively correlated (P less than 0.05) with liver apoE mRNA levels and negatively correlated (P less than 0.025) with liver LDL receptor mRNA levels. Interestingly, while a significant correlation (P less than 0.01) was noted between hepatic apoA-I mRNA abundance and plasma apoA-I levels, no such relationship was observed between liver apoB mRNA and plasma apoB levels, suggesting that the hepatic mRNA of apoA-I, but not that of apoB, is a major determinant of the circulating levels of the respective apolipoprotein. Our data indicate that a diet high in saturated fat and cholesterol may increase the accumulation of triglyceride and cholesterol in the liver, each resulting in the suppression of hepatic LDL receptor mRNA levels. We hypothesize that such elevations in hepatic lipid content differentially alter hepatic apoprotein mRNA levels, with triglyceride increasing hepatic mRNA concentrations for apoA-I and B and cholesterol elevating hepatic apoE mRNA abundance.