Effects of intravenous apolipoprotein A-I/phosphatidylcholine discs on paraoxonase and platelet-activating factor acetylhydrolase in human plasma and tissue fluid.

We have previously shown that intravenous apolipoprotein (apo) A-I/phosphatidylcholine (apo A-I/PC) discs increase plasma high-density lipoprotein (HDL) concentration in humans. We have now studied the associated changes in two enzymes, paraoxonase (PON) and platelet-activating factor acetylhydrolase (PAF-AH) that are carried in whole or in part by HDLs, and are thought to influence atherogenesis by hydrolyzing oxidized phospholipids in lipoproteins. Apo A-I/PC discs (40 mg/kg over 4 h) were infused into eight healthy males. Although plasma apo A-I and HDL cholesterol increased on average by 178 and 158%, respectively, plasma total PON and total PAF-AH concentrations did not rise. By the end of the infusion, HDL-associated PAF-AH had increased by 0.56 +/- 0.14 microg/mL (mean +/- S.D., P < 0.01), and nonHDL-associated PAF-AH had decreased by 0.84 +/- 0.11 microg/mL (P < 0.05). These changes were accompanied by an increase in the HDL-associated PAF-AH/apo A-I ratio from 0.19 to 0.35 (P < 0.05), and by a decrease in the nonHDL-associated PAF-AH/apo B ratio from 2.1 to 1.4 (P < 0.05). No changes in PON or PAF-AH concentrations were detected in prenodal lymph (tissue fluid), collected continuously from the leg. Our results show that the total concentrations of PON and PAF-AH in plasma are uninfluenced by plasma HDL concentration. PAF-AH transfers readily between HDLs and LDLs in vivo, and its distribution between them is determined partly by their relative concentrations and partly by HDL composition.

Variations in lipid and apolipoprotein concentrations in human leg lymph: effects of posture and physical exercise.

We studied the variations in the concentrations of cholesterol, triglycerides, phospholipids, apolipoproteins (apos) (A-I, A-II, B, C-III, E), free glycerol and albumin in human prenodal leg lymph during the 24 h cycle. Lymph was collected continuously for up to 96 h from nine healthy males on a low-fat isocaloric diet. In three free-living subjects, all lipid and apolipoprotein concentrations underwent synchronous variations, rising during the night and decreasing during the day. In three subjects who remained in supine rest for 48 h, the amplitude of circadian variation was much smaller. In three who alternated periods of supine rest with upright exercise, the highest concentrations occurred during rest. Lipid, apolipoprotein and albumin concentrations were inversely related to lymph flow rate. Free glycerol, much of which in tissue fluid is derived from local adipocytes, did not follow this pattern. On multiple regression, concentrations in lymph were related independently to the corresponding concentration in plasma (positive) and to lymph flow rate (negative) or lymph albumin concentration (positive). These results show that lipoprotein concentrations in human tissue fluid are determined only partly by their concentrations in plasma. They are also strongly affected by hemodynamic factors via their effects on fluid transport.

Association of coronary heart disease with pre-beta-HDL concentrations in Japanese men.

BACKGROUND: In individuals heterozygous for ABCA1 transporter mutations, defective reverse cholesterol transport (RCT) causes low HDL-cholesterol and premature coronary heart disease (CHD). However, the extent to which impaired RCT underlies premature CHD in others with low HDL-cholesterol is not known. The primary acceptors of cell cholesterol are a minor subclass of lipid-poor pre-beta-HDLs. These are generated during remodeling of alpha-HDLs, which account for almost all HDL-cholesterol. We studied the strength of the association of CHD with pre-beta-HDL concentrations in Japanese men. METHODS: Blood was collected from 42 men with clinical CHD and 44 healthy controls 40-70 years of age. Pre-beta-HDL was assayed by crossed immunoelectrophoresis. RESULTS: Cases had lower HDL-cholesterol (-23%), total apolipoprotein A-I (-26%), and pre-beta-HDL (-55%; all P <0.001) concentrations; lower pre-beta-HDL:alpha-HDL ratios (-45%; P <0.001); and higher plasma triglycerides (20%; P <0.03) than the controls. On stepwise logistic regression, CHD was associated most strongly with pre-beta-HDL concentrations. On ROC analysis, pre-beta-HDL concentration discriminated between cases and controls better than any other lipoprotein measurement. When plasma was incubated for 16 h at 37 degrees C, mean (SD) pre-beta-HDL increased by 47 (36)% in controls, but was unchanged in cases (group difference, P <0.001). CONCLUSIONS: Our results suggest that inefficient RCT, secondary to a low pre-beta-HDL concentration and production rate in plasma, contributes to premature CHD in Japanese men with low HDL-cholesterol.

Effects of intravenous apolipoprotein A-I/phosphatidylcholine discs on LCAT, PLTP, and CETP in plasma and peripheral lymph in humans.

OBJECTIVE: We have previously shown that intravenous apolipoprotein A-I/phosphatidylcholine (apoA-I/PC) discs increase plasma pre-beta HDL concentration and stimulate reverse cholesterol transport (RCT) in humans. We have now investigated the associated changes in the following 3 HDL components that play key roles in RCT: lecithin:cholesterol acyltransferase (LCAT), cholesteryl ester transfer protein (CETP), and phospholipid transfer protein (PLTP). METHODS AND RESULTS: apoA-I/PC discs (40 mg/kg over 4 hours) were infused into 8 healthy men. Samples of blood and prenodal peripheral lymph were collected for 24 to 48 hours. At 12 hours, plasma LCAT concentration had increased by 0.40+/-0.90 mg/L (+7.8%; mean+/-SD; P<0.05), plasma cholesterol esterification rate by 29.0+/-9.0 nmol/mL per h (+69.5%; P<0.01), plasma CETP concentration by 0.5+/-0.2 mg/L (+29.7%; P<0.01), and plasma PLTP activity by 1.45+/-0.67 micromol/mL per h (+23.9%; P<0.01). In contrast, plasma PLTP concentration had decreased by 4.4+/-2.7 mg/L (-44.8%; P<0.01). The changes in PLTP were accompanied by alterations in the relative proportions of large lipoproteins containing inactive PLTP and small particles containing PLTP of high specific activity. No changes were detected in peripheral lymph. CONCLUSIONS: Nascent HDL secretion may induce changes in PLTP, LCAT, and CETP that promote RCT by catalyzing pre-beta HDL production, cholesterol esterification in HDLs, and cholesteryl ester transfer from HDLs to other lipoproteins.

Altered distribution of plasma PAF-AH between HDLs and other lipoproteins in hyperlipidemia and diabetes mellitus.

Platelet-activating factor acetylhydrolase (PAF-AH) is a phospholipase A2 associated with lipoproteins that hydrolyzes platelet-activating factor (PAF) and oxidized phospholipids. We have developed an ELISA for PAF-AH that is more sensitive than previous methods, and have quantified HDL-associated and non-HDL-associated PAF-AH in healthy, hyperlipidemic, and diabetic subjects. In healthy subjects, plasma total PAF-AH concentration was positively correlated with PAF-AH activity and with plasma total cholesterol, triacylglycerol, LDL cholesterol and apolipoprotein B (apoB) concentrations (all P < 0.01). HDL-associated PAF-AH concentration was correlated positively with plasma apoA-I and HDL cholesterol. Subjects with hyperlipidemia (n = 73) and diabetes mellitus (n = 87) had higher HDL-associated PAF-AH concentrations than did controls (P < 0.01). Non-HDL-associated PAF-AH concentration was lower in diabetic subjects than in controls (P < 0.01). Both hyperlipidemic and diabetic subjects had lower ratios of PAF-AH to apoB (P < 0.01) and higher ratios of PAF-AH to apoA-I (P < 0.01) than did controls. Our results show that the distribution of PAF-AH mass between HDLs and LDLs is determined partly by the concentrations of the lipoproteins and partly by the mass of enzyme per lipoprotein particle, which is disturbed in hyperlipidemia and diabetes mellitus.

Long-term low-dose treatment with reserpine of cholesterol-fed rabbits reduces cholesterol in plasma, non-high density lipoproteins and arterial walls.

The effects of long-term low-dose treatment with reserpine on plasma lipoproteins and arterial cholesterol were determined in cholesterol-fed rabbits. Hepatic low-density lipoprotein (LDL) receptors; uptake of LDL by liver, heart, and kidneys; plasma fibrinogen; blood pressure; and heart rate were also determined. Reserpine at 43 microg/kg. d was continuously infused subcutaneously via implanted minipumps for 6 weeks into conscious unrestrained male New Zealand White rabbits (n = 5) fed a 0.2% cholesterol-enriched diet. Compared with controls, reserpine (n = 4) significantly reduced the elevated levels of plasma total cholesterol and esterified and unesterified cholesterol throughout the study, and at 6 weeks of treatment these reductions were 42, 41, and 49%, respectively. The increased cholesterol in the aortic walls (n = 5) produced by the atherogenic diet was reduced by 73% (p < 0.004) and 125I-tyramine cellobiose-labeled LDL by 67 to 86% (0.05 < p <0.004), respectively. The aortic intimal-medial thickness ratio was reduced by 70%. The decrease in elevated plasma total cholesterol was mainly due to cholesterol reductions in both LDL (41%) and non-high density lipoprotein (HDL) of density < 1.019 g/ml (51%). HDL cholesterol and triglyceride levels were unchanged. Reserpine had no significant effects on the clearance of 125I-tyramine cellobiose-LDL from plasma and there was a trend towards an increase in hepatic LDL receptor expression. Heart rate was decreased by 28%. There were no significant effects on blood pressure, liver and heart lipids, hematocrit, or plasma fibrinogen. The results suggest that treatment of cholesterol-fed rabbits with reserpine at a low dose over a long period prevents increases in plasma atherogenic lipoproteins. Reserpine decreases the cholesterol in aortic walls and the intima-media thickness ratio. This anti-atherosclerotic effect of reserpine may have therapeutic implication.