Protective effect of BN 52021, a specific antagonist of platelet-activating factor (PAF-acether) against diet-induced cholesteryl ester deposition in rabbit aorta.

Platelet-activating factor (PAF-acether), a phospholipid mediator involved in inflammatory reactions, has been reported to induce endovascular surface lesions. We investigated the possible involvement of PAF-acether in the mechanism of arterial cholesterol deposition. Rabbits fed a normal or hypercholesterolic diet were treated orally for 1 month with BN 52021 (20 mg/kg per day), a specific PAF-acether antagonist, and killed at the end of treatment. Cholesterol feeding resulted in a marked (50-fold) increase in plasma cholesterol. However, the drug had no significant effect on the diet-induced hypercholesterolemia. Free and esterified cholesterol were markedly increased (635%) in the aorta of animals receiving the atherogenic diet. This accumulation was reduced by 36% upon simultaneous administration of BN 52021 (P less than 0.02, n = 15). This decrease essentially affected the esterified cholesterol content. Conversely, BN 52021 showed no effect on the cellular cholesterol esterification, since liver acyl-CoA: cholesterol acyltransferase activity remained unchanged. This study indicates that BN 52021 is effective in reducing cholesterol accumulation in rabbit atherosclerotic aorta, without changing the plasma cholesterol levels.

Effect of PCR 4099 on ADP-induced calcium movements and phosphatidic acid production in rat platelets.

Antiplatelet activity of PCR 4099, an analogue of ticlopidine, resides in its specific effect against exogenous as well as released ADP. This study investigated in rat platelets the effects of the drug on ADP-induced shape change, elevation of cytosolic free Ca2+ concentration ([Ca2+]i) and hydrolysis of inositol phospholipids, monitored as [32P]phosphatidic acid formation. Shape change and influx of Ca2+ ions across the plasma membrane were not modified after PCR 4099 administration using aspirin-treated platelets. On the other hand, phosphatidic acid formation and calcium mobilization from internal stores were strongly inhibited. These results suggest that PCR 4099 leaves intact the machinery involved in ADP-induced platelet shape change and influx of calcium ions, but inhibits an early step in the ADP-response coupling leading to inositol phospholipid hydrolysis and aggregation.

Broad spectrum anti-platelet activity of ticlopidine and PCR 4099 involves the suppression of the effects of released ADP.

Aggregation and serotonin secretion were studied in washed rat platelets after oral administration of ticlopidine or its more potent analog PCR 4099. Besides a complete suppression of the ADP-induced aggregation, the two drugs significantly inhibited aggregation and secretion induced by three protein kinase C activators (1-oleoyl-2-acetyl-sn-glycerol, OAG; 12-0-tetradecanoyl phorbol-13-acetate, TPA; phospholipase C), by the calcium ionophore A 23187 and by thrombin. The highest inhibition was observed at low stimuli concentrations but could be partly or almost completely overcome by increasing their concentrations. The combination of aspirin (ASA) with the ADP scavenging system, creatine phosphate/creatine phosphokinase (CP/CPK) in vitro resulted in an inhibition similar to that observed ex vivo after ticlopidine or PCR 4099 treatment. Moreover, these in vitro and ex vivo treatments were not additive. As identical results were obtained with CP/CPK alone but not with ASA, it is concluded that ticlopidine and PCR 4099 do not interfere with protein kinase C or calcium movements but specifically inhibit the effects of released ADP, which might explain the broad spectrum anti-platelet activity of these drugs.

Effects of inhaled HF on lipid metabolism in guinea pigs.

Guinea pigs were exposed to hydrogen fluoride (10 mg/m3) for 84 hr. Plasma triglyceride and cholesterol levels were significantly increased in the treated animals with respect to the controls. An increase in triglyceride levels was also observed in the liver. The metabolism of plasma and hepatic lipids was studied using incorporation of [1-14C]acetate. Compared to the control group, triglyceride synthesis was accelerated in the liver of the fluoride group. Extrahepatic lipoprotein lipase activity however was decreased in the fluoride group; this could be related to the decrease in apoprotein C.

Irradiation-induced free cholesterol accumulation in very-low-density lipoproteins. Role of lipoprotein lipase deficiency.

Irradiation of rabbits induced an accumulation of free cholesterol in VLDL fraction. In the present study, an attempt was made to explain the abnormal free cholesterol enhancement. The study demonstrated that lecithin:cholesterol acyltransferase activity was normal in irradiated rabbits. In addition, electron microscopy examination of HDL revealed no changes after irradiation: spherical particles were present. On the other hand, ACAT activity was increased while neutral and acidic cholesteryl esterases were strongly decreased. Moreover, HMG-CoA reductase was 3-fold reduced after irradiation. These results show that neither cholesterol esterification nor cholesterol ester hydrolysis nor cholesterol biosynthesis are responsible for this increase of free cholesterol in VLDL. In contrast, we have shown that extra-hepatic lipoprotein lipase was deficient in irradiated rabbit plasma although synthesis in the adipocytes is normal. To investigate a hypothetical deficiency of VLDL catabolism, we performed experiments with injection of heparin and with labeled VLDL. These experiments show that, in irradiated rabbits, VLDL were not catabolized, since the radioactivity was recovered only in the VLDL fraction. This impaired VLDL removal was compatible with the deficiency of extra-hepatic lipoprotein lipase activity.

Effects of threonine-poor apolipoproteins on post-heparin plasma hepatic triacylglycerol lipase and lipoprotein lipase.

Whole-irradiated rabbit pre-heparin plasma had an important inhibitory effect on hepatic triacylglycerol lipase and lipoprotein lipase activities, whereas control rabbit pre-heparin plasma slightly inhibited hepatic triacylglycerol lipase activity at a high concentration and enhanced lipoprotein lipase activity. As some apolipoproteins were known to modulate these two lipolytic enzymes, the inhibitory effects of irradiated rabbit plasma were investigated in apolipoproteins. Three apolipoproteins, with isoelectric points of about 6.58, 6.44 and 6.12, characterized by their low content in threonine (threonine-poor apolipoproteins) were produced in high concentrations in rabbit VLDL and HDL after irradiation. The effects of these apolipoproteins on control rabbit post-heparin plasma hepatic triacylglycerol lipase and extrahepatic lipoprotein lipase were studied. Threonine-poor apolipoproteins substantially inhibited the hepatic triacylglycerol lipase activity and enhanced the apolipoprotein C-II-stimulated activity of lipoprotein lipase. The amounts of these apolipoproteins in triacylglycerol-rich lipoprotein particles may determine the lipolytic activity of lipoprotein lipase and hepatic triacylglycerol lipase in triacylglycerol hydrolysis. The existence of another inhibitor of lipoprotein lipase remains to be determined.