Determinative role of peroxidized low-density lipoprotein in myocardial thromboxane synthesis during pacing-induced ischaemia in humans

Gemfibrozil treatment potentiates oxidative resistance of high-density lipoprotein in hypertriglyceridemic patients

BACKGROUND

Studies suggest that both oxidized low and high density lipoprotein (LDL and HDL) play a role in the pathogenesis of atherosclerosis. Gemfibrozil is widely used and is reported to increase cholesterol of LDL and HDL in hypertriglyceridemic patients. The aim of this study was to investigate the effect of gemfibrozil treatment on the oxidative status of lipoprotein particles in Fredrickson phenotype IV hypertriglyceridemic patients.

METHODS

Twenty-two patients, aged 38-64 years, with fasting plasma triglyceride concentrations between 2.90 and 8.97 mmol L(-1), were recruited and were given gemfibrozil 300 mg three times daily for 12 weeks. Venous blood samples were collected before gemfibrozil treatment, after 4, 8, or 12 weeks of treatment, and 4 weeks after termination of treatment, and used to analyse the plasma lipid profile, isolate lipoproteins, and analyse the chemical composition and in vitro oxidation of lipoprotein particles.

RESULTS

Gemfibrozil treatment resulted in a decrease in plasma total triglyceride levels and the triglyceride content of all lipoproteins. Plasma total cholesterol levels were decreased as a result of a decrease in very low density lipoprotein (VLDL) cholesterol levels. A slight increase in LDL cholesterol levels was observed, whereas the thiobarbituric acid-reactive substances (TBARS) of LDL were decreased and the lag and peak time of LDL to oxidation were unchanged and maximal diene production was decreased. Plasma HDL cholesterol levels, the surface-to-core ratio of HDL particles, and the resistance of HDL to oxidation were increased.

CONCLUSION

The decreased TBARS and diene production of LDL, increased HDL cholesterol levels, and increased resistance of HDL to oxidation may, in part, explain why gemfibrozil treatment was found to be generally beneficial in terms of protection against coronary heart disease.

Exercise shifts the platelet aggregation modulatory role from native to mildly oxidized low-density lipoprotein

PURPOSE

The role of low-density lipoprotein (LDL) lipid peroxides in strenuous exercise-induced changes in platelet function was studied in 30 patients (male/female = 22/8) aged 30-62 yr (mean +/- SD = 508).

METHODS

All subjects were subjected to a treadmill exercise test, using the standard Bruce protocol. Blood samples were collected pre-, peak, and 10 min postexercise to assess hematological and biochemical parameters and platelet aggregation. Ex vivo whole blood platelet aggregation during treadmill exercise was assessed in 10 subjects by adding mildly oxidized LDL.

RESULTS

Preexercise, a correlation existed between plasma thromboxane (TX) levels and plasma LDL cholesterol or beta-thromboglobulin (beta-TG) levels (r = 0.48, P < 0.05: r = 0.47, P < 0.05, respectively), whereas, at peak exercise, TX and beta-TG levels increased, but no correlation was seen. At peak exercise, platelets showed hyperaggregability in terms of maximal amplitude and reaction slope (P < 0.001 and P < 0.01, respectively). In contrast to the increase in plasma lipid peroxide levels seen during peak exercise (P < 0.05), LDL lipid peroxides decreased during exercise, this decrease reaching a statistical significance at 10 min postexercise (P < 0.05). In addition, the ex vivo addition of mildly oxidized LDL (10 mg protein x L(-1)) to peak exercise blood resulted in a significant attenuation of platelet aggregation and a decrease in TX release. At 10 min postexercise, a correlation was seen between LDL lipid peroxides and TX levels (r = 0.78, P < 0.001) or beta-TG levels (r = 0.68, P < 0.005).

CONCLUSION

These results suggest that LDL lipid peroxides play a role in modulating and attenuating platelet aggregation during strenuous exercise.