Lipid profiles of plasma lipoproteins of fasted and fed normal and choline‐deficient rats

Abstract

Three major density classes of lipoproteins and a residual protein (d greater than 1.21) were isolated by ultracentrifugation from plasma of fasted, fed normal, and choline-deficient rats. Lipid extracts were obtained from total plasma and the various density classes of lipoproteins, and each extract was examined in detail by thin layer and gas chromatographies. The results indicated essentially identical compositions of molecular species of phosphatidyl choline, which suggested their rapid equilibration among the different plasma lipoprotein classes. In contrast, the molecular species of the triacylglycerols and cholesteryl esters showed significant differences among the chylomicrons, very low and low, and high density lipoproteins, which excluded the possibility of their ready equilibration in vivo. Omission of choline from diet resulted in a sharp and statistically significant decrease in all lipid components of the very low and low density lipoproteins with 2 days. After 10 days of choline deficiency, the lipid levels of chylomicrons and very low and low density lipoproteins were ca. one-half the levels found in the choline supplemented animals, and there were discernible distortions in their lipid composition. Reintroduction of choline led to a prompt return to normal levels and lipid composition of both chylomicron and very low and low density lipoprotein fractions. The lack of equilibration of the triacylglycerols among the lipoprotein classes under normal conditions and in choline deficiency demonstrates an as yet unrecgnized source of compartmentation of plasma lipids.

Dietary methyl-consuming compounds and metabolic syndrome

“…Methyl depletion as a consequence of niacin toxicity has been confirmed by the observations that hepatic toxicity can be prevented by choline and betaine supplements. 30,55 It is known that methyl deficiency may limit the formation of very low density lipoprotein and low density lipoprotein in the liver due to decreased phosphatidylcholine synthesis, which may result in a decrease in the levels of plasma very low density lipoprotein and low density lipoprotein, as demonstrated in rats by Mookerjea et al 56 On the other hand, the decreased transport of fat from the liver may lead to an accumulation of fat in the liver, and as a result, fatty liver and steatosis may occur. 57 Moreover, adequate phosphatidylcholine is also required for the formation and clearance of chylomicrons from the intestinal mucosa.…”

“…Similarly, choline deficiency has been demonstrated to lower the level of plasma chylomicrons. 56 Interestingly, niacin has been found to induce both lipid-lowering effect 52 and adverse hepatic outcomes. 46,52,54,55 Thus, it seems that the lipidlowering effect of niacin may be mediated by methyl depletion, which, although improving cardiovascular outcomes, may increase the risk of adverse hepatic outcomes.…”

A Choline-deficient Diet in Mice Inhibits neither the CDP-choline Pathway for Phosphatidylcholine Synthesis in Hepatocytes nor Apolipoprotein B Secretion

“…Although choline deficiency reduces plasma TG in both male and female rats, the response is more pronounced in males (26). These observations led to the widely held view that the development of fatty livers in animals fed a CD diet is the result of an impaired hepatic secretion of TG into plasma lipoproteins, primarily VLDLs, because of inhibition of PC synthesis from choline (24,25,27,28,30,31).To determine whether the reduction in plasma TG induced by choline deficiency in rats was the result of impaired lipoprotein secretion, rather than increased removal of TGs from plasma, Yao and Vance (17, 32) examined VLDL secretion by CD and CS primary rat hepatocytes. The hepatocytes were isolated from rats fed a CD diet for 3 days and subsequently incubated in medium containing or lacking choline and methionine.…”

“…Although choline deficiency reduces plasma TG in both male and female rats, the response is more pronounced in males (26). These observations led to the widely held view that the development of fatty livers in animals fed a CD diet is the result of an impaired hepatic secretion of TG into plasma lipoproteins, primarily VLDLs, because of inhibition of PC synthesis from choline (24, 25,27,28,30,31).…”

The Hypocholesterolemic Action ofLentinus edodesIs Evoked through Alteration of Phospholipid Composition of Liver Microsomes in Rats

“…1) might be evoked through the alteration of hepatic phospholipid composition, e.g., a decrease in the ratio of phosphatidylcholine (PC) to phosphatidylethanolamine (PE), in rats fed on a cholesterol-free diet. Choline defici ency 12,13) and dietary supplementation with PE 14) or ethanolamine 15 ) are also shown to reduce plasma cholesterol with a concomitant decrease in the PC/PE ratio of the rat liver. Further, Mogami-Nishimaki et al 16 ) have recently demonstrated that some hypocholesterolemic drugs such as clofibrate and bezafibrate could decrease the PC/PE ratio of cultured rat hepatocytes and thereby reduce the secretion of very low-density lipoprotein (VLDL) from the cells.…”