A cell culture system was employed to test a large number of samples of human serum for the ability to stimulate the efflux of cell cholesterol. The extent of efflux obtained with each specimen was correlated with the serum concentrations of cholesterol, triglycerides, apoprotein (apo) B, apo A-I, apo A-II, and lipoprotein subfractions (ie, high-density lipoprotein 2 [HDL 2 ], HDL 3 , lipoprotein [Lp] A-I, and LpA-I:A-II). In addition, the subsequent esterification of the released cholesterol and the distribution of the synthesized exogenous cholesteryl esters between HDL and low-density lipoprotein/ very-low-density lipoprotein provided estimates of the lecithin:cholesterol acyltransferase (LCAT) and cholesteryl ester transfer protein (CETP) activities of each serum. The values for these activities were analyzed for correlations with cell efflux and the various serum parameters. Cell cholesterol efflux best correlated with serum total HDL cholesterol values. HDL 2 and HDL 3 correlated about equally well with efflux, whereas LpA-I demonstrated a much greater association with T he process by which cholesterol in peripheral tissues is transported back to the liver for excretion has been termed reverse cholesterol transport (RCT). While the importance of high-density lipoprotein (HDL) in RCT is now universally accepted, it is not known which specific fractions of HDL are most important. Most in vitro studies have used either native lipoproteins, particularly subclasses of HDL, or reconstituted particles containing apolipoproteins and phospholipids to study cholesterol efflux, which is the first step in RCT. The difficulties in clearly identifying the specific lipoprotein in serum or interstitial fluid that plays the primary role in cholesterol efflux are due to several facts. First, there is a wide variety of particles within the HDL class of lipoproteins, and no single class of particles appears to be uniquely responsible for cholesterol efflux. 1 -2 Second, depending on the method of separation, two subclasses of HDL have been pro- Studies with whole serum have been limited, and it is not known if the quantification of a single serum parameter, or even combinations of parameters, is sufficient to allow the prediction of how individual samples of human serum will influence cellular cholesterol efflux.Cholesterol efflux studies using whole sera are best represented by the investigations of Fielding and colleagues. 68 The initial studies using fibroblasts as the cholesterol donor cell clearly established that sera from individuals differed in their ability to produce changes in net cellular cholesterol efflux. These differences were correlated to a number of clinical conditions that are known to influence serum lipoprotein patterns, such as by guest on May 9, 2018 http://atvb.ahajournals.org/ Downloaded from

Abstract-The incremental elastic modulus of the common carotid and radial arteries is increased in patients with end-stage renal disease (ESRD), independently of blood pressure, wall stress, and the presence of atherosclerotic alterations. Whether biochemical factors may be involved in the arterial changes and related to renal dysfunction remain largely ignored. To assess this question, we measured aortic (carotid-femoral), upper-limb (carotid-radial), and lower-limb (femoral-tibial) pulse wave velocity (PWV) in 74 ESRD patients undergoing hemodialysis in comparison with 57 control subjects similar in age, sex ratio, and mean blood pressure. We evaluated arterial blood presure by sphygmomanometry, aortic calcifications and cardiac mass by echography, and routine biochemical parameters, total plasma homocysteine, and plasma endothelin levels by standard techniques. In the population of patients with ESRD, on the basis of multiple stepwise regression analysis, aortic PWV was positively and independently correlated with systolic blood pressure (PϽ.0001), age (PϽ.0001), prevalence of aortic calcification (Pϭ.0004), and the prevalence of diabetes mellitus (Pϭ.0043). Upper-limb PWV was influenced exclusively by mean blood pressure (PϽ.0001). Lower-limb PWV was positively and independently correlated with plasma total homocysteine (Pϭ.0004) and plasma endothelin (Pϭ.0187) only. At any vascular site, PWV was not independently correlated with tobacco consumption; plasma levels of cholesterol, triglyceride, fibrinogen, or hemoglobin; body mass index; or the presence of bilateral nephrectomy. Finally, plasma homocysteine was independently correlated with cardiac mass (Pϭ.0022). This study provides evidence that in ESRD patients, the stiffness of the arterial wall and cardiac mass are strongly influenced by biochemical factors related to the kidney alterations and are independent of age and blood pressure level. Increased plasma endothelin and homocysteine may be specifically involved in the vascular damage of lower limbs. (Arterioscler Thromb Vasc Biol. 1998;18:535-541.)

The relationships of cell cholesterol efflux to HDL phospholipid (PL) content and composition in human serum were analyzed in two groups of subjects selected on the basis of their HDL cholesterol (HDL-C) levels: a norm-HDL group (1.10 mmol/L < HDL-C < 1.50 mmol/L) and a high-HDL group (HDL-C > 1.75 mmol/L). In the high-HDL group, the relative fractional efflux was significantly higher than in the norm-HDL group, and in both groups, fractional efflux was correlated with a number of lipoprotein parameters, the best correlation and the only one that remained significant after multivariate analysis being with HDL phospholipid (HDL-PL). Analysis of the HDL-PL subclasses revealed that HDL in the high-HDL sera was enriched with phosphatidylethanolamine (HDL-PE) and relatively deficient in sphingomyelin (HDL-SM) compared with norm-HDL sera. Moreover, the fractional efflux values in the high-HDL group were negatively correlated with the proportion of HDL-PE (r = -.64, P < .0001) and positively correlated with the proportion of HDL-SM (r = .43, P < .01). Thus, this study provides evidence that HDL-PL concentration can be used to predict the capacity of serum to accept cellular cholesterol. Among the differences described between norm-HDL and high-HDL sera, the variability in PE to SM ratio might reflect changes in serum cholesterol acceptors that modulate the first step of reverse cholesterol transport.