Retinoic Acid Effects on Endothelial Cell Function: Interaction with Interleukin 1

Abstract

Blood vessel angiogenesis is an important component of chronic synovitis, and its regulation may be mediated through local production and effects of certain inflammatory cytokines, including interleukin-1 (IL-1). Retinoic acid (RA) can alter the progression of some inflammatory arthritic diseases, presumably through effects on fibroblast collagenase and PGE 2 production. To explore alternate hypotheses, we examined the interaction of retinoic acid and IL-1 on endothelial cell (EC) function and found that RA directly affects and modifies the effects of IL-1 on EC proliferation, prostacyclin production, and plasminogen activator inhibitor capacity (PAI-1). With respect to EC proliferation, cis- and trans-retinoic acid and retinol induced a dosedependent increase of [ 3H]TdR uptake by cultured ECs, independent of the effects of serum or eicosanoid production. This effect was blocked by IL-1. With respect to EC prostacyclin production, although retinoic acid alone had no effect, cis and trans -retinoic acid and retinol all induced a dose-dependent increase in IL-1-mediated prostacyclin production, which was most marked at higher concentrations (20 U/ml) of IL-1. This effect was mediated through effects independent of cyclooxygenase (COX) production. With respect to plasminogen activator inhibitor capacity, both IL-1 and retinoic acid stimulated EC PAI-1 synthesis, but the individual effects were additive, with RA augmenting the known IL-1 effects on EC PAI-1 production. The interaction between RA and IL-1 on the endothelium, described in this study, may play a role in the fashion through which retinoic acid alters the expression of synovitis in certain types of experimental inflammatory arthritis.