16 The complexity of PLTP is illustrated further by the increased secretion of VLDL, but with no change in plasma VLDL levels and with falling levels of HDL, which was reported in transgenic mice with elevated plasma phospholipid

transfer protein.17 In this issue of HEPATOLOGY, the study by Yazdanyar and Jiang18 provides relevant data that bring new support to the hypothesis that liver PLTP plays a role in promoting VLDL production. Elegantly, these investigators re-expressed the endogenous mouse PLTP gene in a PLTP-null background with a low level of PLTP activity in the circulation. It was found to produce dramatic increases in the liver production and circulating level of apoB-containing Angiogenesis inhibitor lipoproteins, but with no effect on the production of apoAI-containing lipoproteins and no substantial effect on circulating HDL, which retained the same features and the same level whether animals expressed the PLTP gene

or not. Noticeably, and in addition to the liver, selleck chemicals llc a number of peripheral tissues are known to make significant amounts of PLTP in humans, thus contributing significantly to circulating levels of PLTP in human plasma. In addition, like rabbits but unlike rats and mice, humans produce apoB100-containing VLDL in the liver and express a functional plasma cholesteryl ester transfer protein (CETP), which is currently recognized as a major factor in regulating the distribution of cholesteryl esters between HDL and apoB-containing

lipoproteins. This raises an important question as to the prominent function of PLTP in vivo: Is PLTP, in a human-like situation, chiefly involved in the production of apoB100-containing lipoproteins in the liver or in the metabolism of HDL in blood and peripheral MCE公司 tissues? In recent rabbit studies, a human PLTP transgene was placed under the control of the human eF1-α gene promoter, which, in contrast to the study by Yazdanyar and Jiang,18 resulted in widespread expression in various tissues (with substantial levels of human PLTP messenger RNAs detected not only in the liver, but also in adipose tissue, the pancreas, kidney, lung, brain, heart, and spleen of human PLTP transgenic rabbits).19 It resulted in increased plasma PLTP activity, increased cholesterol content of plasma apoB-containing lipoproteins, and increased formation of aortic fatty streaks in animals fed a cholesterol-rich diet, but with no significant change in plasma HDL cholesterol levels. It suggests further that the prominent and final consequence of PLTP expression on circulating apoB-containing lipoproteins versus HDL could actually be governed by the predominance of one lipoprotein class over the other. When VLDL and LDL predominate, as it is the case in humans and rabbits, PLTP expression would accentuate cholesterol accumulation in these lipoproteins only, with no major effect on HDL.