Effect of ethanol dose on low density lipoproteins and high density lipoprotein subfractions

Low ethanol consumption induces enhancement of insulin sensitivity in liver of normal rats

Moderate amounts of alcohol intake have been reported to have a protective effect on the cardiovascular system and this may involve enhanced insulin sensitivity. We established an animal model of increased insulin sensitivity by low ethanol consumption and here we investigated metabolic parameters and molecular mechanisms potentially involved in this phenomenon. For that, Wistar rats have received drinking water either without (control) or with 3% ethanol for four weeks. The effect of ethanol intake on insulin sensitivity was analyzed by insulin resistance index (HOMA-IR), intravenous insulin tolerance test (IVITT) and lipid profile. The role of liver was investigated by the analysis of insulin signaling pathway, GLUT2 gene expression and tissue glycogen content. Rats consuming 3% ethanol showed lower values of HOMA-IR and plasma free fatty acids (FFA) levels and higher hepatic glycogen content and glucose disappearance constant during the IVITT. Neither the phosphorylation of insulin receptor (IR) and insulin receptor substrate-1 (IRS-1), nor its association with phosphatidylinositol-3-kinase (PI3-kinase), was affected by ethanol. However, ethanol consumption enhanced liver IRS-2 and protein kinase B (Akt) phosphorylation (3 times, P<0.05), which can be involved in the 2-fold increased (P<0.05) hepatic glycogen content. The GLUT2 protein content was unchanged. Our findings point out that liver plays a role in enhanced insulin sensitivity induced by low ethanol consumption.

Alterations in brain levels of atrial and C-type natriuretic peptides after chronic moderate ethanol consumption in spontaneously hypertensive rats

Atrial (ANP) and C-type (CNP) natriuretic peptides have been found in brain regions associated with fluid homeostasis and blood pressure. Since chronic moderate ethanol consumption has been shown to prevent the age-dependent increase in blood pressure in experimental animals, the objective of the present studies was to investigate the effect of ethanol (20% (v/v) for 8 months) on the total content and concentration of ANP and CNP in the brain of spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats. Ethanol increased the content and concentration of both ANP and CNP in the hypothalamus, pons and medulla of SHR rats. In contrast, in the WKY rats ethanol had no effect on the levels of ANP in any of the brain regions studies, but enhanced the concentration of CNP in the hypothalamus and medulla. Thus, ethanol induced changes in the content of natriuretic peptides in distinct brain regions associated with control of cardiovascular activity. Such changes may be partially responsible for the effect of chronic moderate ethanol consumption on blood pressure.

Effect of chronic moderate ethanol consumption on heart brain natriuretic peptide

There is experimental evidence indicating that chronic moderate ethanol consumption delays the age-dependent increase in blood pressure. Since the brain natriuretic peptide (BNP) is a potent hypotensive hormone, the effect of chronic ethanol treatment on the heart BNP system was investigated, using spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats. Chronic moderate ethanol consumption resulted in significantly lower circulating BNP levels for both SHR (206.9 +/- 18.5 vs. 306.9 +/- 28.1 pg/ml, n = 12, P < or = 0.05) and WKY rats (131.3 +/- 20.7 vs. 220.6 +/- 25.0 pg/ml, n = 12, P < or = 0.05). Left and right atrial BNP content and concentration in WKY rats and left atrial BNP content and concentration in SHR rats were augmented by the ethanol treatment, but not atrial BNP mRNA. In ventricular tissue, alcohol had no effect on total BNP content of either SHR or WKY rats, but it induced a significant elevation in ventricular BNP concentration (microgram/mg protein) and BNP mRNA in SHR, but not WKY rats. Thus, chronic ethanol treatment resulted in specific alterations in the activity of the heart BNP system.

Effect of ethanol on hepatic apolipoprotein B synthesis and secretion in vitro

The effect of ethanol on hepatic lipoprotein secretion is not fully understood. This study shows that exposure of HepG2 cells to ethanol significantly increases intracellular apolipoprotein B, apo B mRNA and secreted apolipoprotein B. No other agent has been shown to produce such an increase in apolipoprotein B synthesis or apolipoprotein B mRNA levels.

Effect of ethanol on lipoprotein secretion in two human hepatoma cell lines, HepG2 and Hep3B

The two human hepatoma cell lines, HepG2 and Hep3B, have been demonstrated to metabolize ethanol efficiently even in the absence of alcohol dehydrogenase. By using specific metabolic inhibitors, it was found that the microsomal ethanol-oxidizing system (MEOS) plays a significant role in ethanol metabolism in these two cell lines. There is a strong positive correlation between the rates of ethanol metabolism and the total cytochrome P-450 levels in the hepatoma cells. The involvement of the cytochrome P-450 system was further supported by the induction of aniline p-hydroxylase activity after ethanol treatment. However, the 3- to 4-fold elevation in aniline p-hydroxylase activity was not accompanied by an increase in cytochrome P450IIE1 mRNA level. Exposure of HepG2 and Hep3B cells to ethanol resulted in an increase of accumulation of apoA-I (15%-45% over control) in a dose-dependent manner (from 5 to 50 mM) of ethanol over a 24-hr period. All other major apolipoproteins which included apo CII, apo CIII and apoE, with the exception of apoB, were not affected by these treatments. At a concentration of ethanol of 25 mM or greater, accumulation of apoB, VLDL and LDL triglyceride were increased by 20% to 25% over the control level. Elevation of HDL cholesterol (40%-70% over control) was observed when the cells were exposed to an ethanol concentration of > or = 10 mM. Metyrapone, which inhibited the MEOS, was capable of blocking the induction of apoAI caused by ethanol treatment.

Alcohol delays clearance of lipoproteins from the circulation

Long-term (18-month) consumption of high-dose ethanol ([EtOH] 24% of total calories) by squirrel monkeys results in marked elevations in plasma antiatherogenic high-density lipoprotein (HDL) cholesterol and apolipoprotein (apo) A-1, and atherogenic low-density lipoprotein (LDL) cholesterol and apo B. In an effort to determine whether alterations in lipoprotein turnover could explain the above findings, 131I-HDL apo A-1 and 125I-LDL apo B were injected into EtOH and control animals, following which in-vivo catabolic and production rates were determined. For both lipoproteins, synthetic rates were unaltered, while fractional catabolic rates (FCR) were significantly reduced in EtOH monkeys. Results from this study implicate EtOH-induced changes in hepatic metabolism as the basis for delayed lipoprotein clearance and hence elevated plasma apolipoprotein levels.

Alcohol dose and low density lipoprotein heterogeneity in squirrel monkeys (Saimiri sciureus)

The present study was designed to determine whether normolipidemic male squirrel monkeys (Saimiri sciureus) exhibit low density lipoprotein (LDL) heterogeneity similar to that observed in humans and if present, whether LDL subfractions are altered by consumption of low vs. high dose ethanol (EtOH). Primates were divided into three groups designated control, low, and high EtOH and fed isocaloric liquid diets containing 0%, 12% and 24% of calories as EtOH, respectively, for 6 months. The 12% EtOH caloric level resulted in a modest, non-significant increase in high density lipoprotein (HDL) cholesterol and no change in LDL cholesterol or plasma apolipoprotein B (apo B), while the 24% dose produced significant elevations in plasma, LDL and HDL cholesterol and apo B. Using a single-spin density gradient ultracentrifugation procedure developed for humans, three distinct LDL subclasses designated LDL1a (d = 1.031 g/ml), LDL1b (d = 1.038 g/ml) and LDL 2 (d = 1.046 g/ml) were isolated from all three treatment groups. Monkey LDL subfractions were nearly identical to very light, light and heavy LDL subspecies isolated from human plasma in terms of their: (1) isopycnic densities following ultracentrifugation; (2) co-migration as single bands with beta-electrophoretic mobility in cellulose acetate and agarose electrophoretic gels; (3) size-dependent migration pattern in polyacrylamide gradient electrophoretic gels; (4) co-migration as a single band corresponding to apo B-100, following SDS polyacrylamide gel electrophoresis; and (5) decrease in total cholesterol/protein ratios with increasing LDL subclass density. Although there were no treatment differences in LDL particle size, within each treatment group, mean particle size for each LDL subfraction was significantly different from every other subfraction. Low (12%) dose alcohol had no effect on LDL subfraction mass relative to controls while high alcohol consumption resulted in marked increases in all lipid (except triglyceride) and protein of the larger, buoyant LDL subspecies (LDL1a and LDL1b). Moreover, the best correlation between plasma apo B and LDL subfraction total mass was demonstrated with LDL1b (r = 0.735). Since neither the lipid nor the protein concentration of the small, dense, purportedly more atherogenic, LDL2 changed with the 24% EtOH dose, we propose that the LDL subfraction alterations associated with high alcohol intake in squirrel monkeys (increased LDL1a, increased LDL1b, LDL2 no effect) may represent a compensatory response to modulate the overall atherogenic lipoprotein profile associated with elevations in total LDL cholesterol and plasma apolipoprotein B.

Effect of ethanol on low density lipoprotein and platelet composition

The present study was designed to investigate the effect of ethanol (EtOH) dose on low density lipoprotein (LDL) and platelet composition. Male squirrel monkeys were divided into three groups designated Control, Low, and High EtOH, and fed isocaloric liquid diets containing 0%, 12%, and 24% of calories as EtOH, respectively. After four months of treatment, monkeys fed the 12% alcohol dose had LDL and platelet cholesterol concentrations similar to Controls. By contrast, platelet membranes from High EtOH animals contained significantly more cholesterol which was associated with higher levels of plasma LDL cholesterol and apolipoprotein B. Blood platelet count, size, and mass were similar for all groups and circulating platelet aggregates were absent in the two alcohol cohorts. Despite elevations in platelet cholesterol mass and thromboxane A2 (TXA2) precursor, phospholipid arachidonate, platelet responsiveness, measured as thromboxane formed in response to a collagen challenge in vitro, and the cholesterol/phospholipid molar ratio, were not significantly altered by high dose alcohol. Normal platelet activity in High EtOH monkeys may have resulted from a significant increase in the platelet phospholipid polyunsaturated/saturated fatty acid ratio and a non-significant increase in platelet phospholipid mass, both of which would have a fluidizing effect on platelet membranes. Our data indicate that low EtOH intake has no effect on platelet composition and function while unfavorable platelet cholesterol enrichment following consumption of high dose ethanol may arise from elevations in plasma LDL.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of chronic ethanol feeding on high density lipoprotein subfractions in rats

We have reported previously that chronic alcohol consumption in the rat produced elevated total serum high density lipoprotein (HDL) fraction, but HDL particles of the alcohol-fed rat were deficient in apolipoprotein (apo) E. In that report, serum HDL particles were prepared by successive ultracentrifugation method and there were concerns that the apo E deficiency in HDL particles was artificially produced by centrifugal forces. In the present report, apo Al affinity column chromatography was used instead of successive ultracentrifugation and it likewise yielded HDL particles from alcohol-fed rats that exhibited lower apo E: apo Al ratio than HDL from control rats (0.185 +/- 0.016 vs. 0.303 +/- 0.017, respectively). When the total serum lipoprotein fraction (d less than 1.21) was analyzed by high performance liquid chromatography (HPLC), both HDL and VLDL peaks were higher in alcohol-fed rats than controls. The size of apo E deficient HDL particles from alcohol-fed rats determined by HPLC did not differ from that of normal HDL particles. When HDL (1.063 less than d less than 1.21) was subfractionated into HDL2 (1.063 less than d less than 1.125) and HDL3 (1.125 less than d less than 1.21), only HDL2 of alcohol-fed rats showed lowered apo E: apo Al ratio when compared with same HDL subfraction of control animals. Therefore, the molecular structure of only HDL2 (but not HDL3) was affected by alcohol-feeding. Another HDL subpopulation which is enriched with apo E, i.e. HDL1 (1.054 less than d less than 1.063), was also prepared.(ABSTRACT TRUNCATED AT 250 WORDS)