The role of lipids and antioxidative factors for development of atherosclerosis. The Probucol Quantitative Regression Swedish Trial (PQRST).

The effect of probucol on the development of atherosclerosis is being investigated in the Probucol Quantitative Regression Swedish Trial (PQRST). Hypercholesterolemic patients are randomized to receive either probucol 0.5 g twice daily or placebo in a double-blind manner, in combination with dietary therapy and cholestyramine 8-16 g daily for a 3-year period. The primary endpoint of the trial is the change in atheroma volume, assessed by annual quantitative angiography involving 20-cm segments of the femoral artery. Data from the open diet and prerandomization phase indicate that probucol added to dietary intervention plus cholestyramine produced highly significant reductions in total (-17%), low-density lipoprotein (LDL; -10%), and high-density lipoprotein (-30%) cholesterol. From a subpopulation, LDL levels were isolated during different stages of the prerandomization phase. LDL was exposed to the oxidant Cu2+ and binding to fibroblasts as well as degradation by macrophages was measured. The generation of thiobarbituric acid-reactive substances (TBARS) was also measured. Probucol prevented degradation of copper-exposed LDL by macrophages and also reduced the formation of TBARS, indicating that probucol protected LDL from oxidation. After the trial concludes in December 1992, statistical models will be used to investigate how much of the change in atherosclerosis is explained by changes in lipoprotein concentrations and how much is explained by probucol's antioxidative effects. Thus, other metabolic factors such as dietary intake and circulating levels of lipid soluble vitamins and fatty acids that may modify the possible antioxidative effects of probucol are also measured and will be related to change in atherosclerosis.