EFFECT OF PROBUCOL TREATMENT ON GENE-EXPRESSION OF VCAM-1, MCP-1, ANDM-CSF IN THE AORTIC-WALL OF LDL RECEPTOR-DEFICIENT RABBITS DURING EARLY ATHEROGENESIS

Probucol is a potent inhibitor of atherosclerosis in animal models. Ho wever, the mechanism of its antiatherogenic effect is not known. To in vestigate the effects of probucol on gene expression of VCAM-1, MCP-1, and M-CSF in vivo during the early stages of atherogenesis, we determ ined gene expression in 12 control WHHL rabbits and 12 WHHL rabbits fe d 1% probucol from age 3 weeks. Three animals from each group were kil led at 6, 9, 12, and 18 weeks of age. Two intimal/medial segments of t he thoracic aorta, each comprising the orifices of a pair of intercost al arteries, were analyzed by semiquantitative RT-PCR using GAPDH as a n internal standard. A third segment located between these two segment s was studied by immunocytochemistry. A basal level of VCAM-1 gene exp ression was observed in lesion-free aortas of both treated and untreat ed WHHL rabbits (and in normal NZW aortas). Immunocytochemistry showed some VCAM-1 protein in normal arteries and confirmed that VCAM-1 prot ein expression generally correlated with gene expression. In the untre ated WHHL rabbits, a marked upregulation of VCAM-1 expression was obse rved at 18 weeks. To correlate gene expression with intimal monocyte/m acrophages in each animal, the macrophage area was determined by morph ometry of immunostained sections. In addition, a scoring system of les ions was used. VCAM-1 expression showed a highly significant correlati on with the extent of intimal macrophage presence (P<.001). A lesser d egree of correlation between gene expression and macrophage accumulati on was also seen for MCP-1. In contrast, M-CSF expression remained con stant over the entire study period and showed no correlation with the intimal macrophage accumulation. Probucol treatment completely prevent ed lesion formation in all animals up to 18 weeks of age. Probucol red uced the level of basal VCAM-1 expression and prevented its upregulati on. MCP-1 expression was not affected by probucol treatment, whereas M -CSF expression was significantly lowered by probucol. Our results sup port the idea that VCAM-1 plays an important role in early atherogenes is and suggest that the antiatherogenic effect of probucol may in parr be due to a downregulation of VCAM-1. Reduction of the basal level of M-CSF gene expression by probucol treatment may also contribute to it s ability to inhibit atherogenesis.