Activation of perivascular mast cells (MCs) and subsequent release of their abundant inflammatory mediators have been well documented to induce excessive inflammation and subsequent rupture of atherosclerotic plaques. Previous studies have suggested that rosiglitazone affects the stability of plaques, although the precise mechanism of action is not clearly understood. In this study, we evaluated the effects of rosiglitazone on MCs in vivo and in vitro. Apolipoprotein E-deficient (ApoE(-/-)) mice were fed a high-fat diet (HFD), with or without rosiglitazone supplemented in the drinking water (1.5 mg/kg/day). Compared with the HFD group, rosiglitazone did not affect blood glucose levels, but it attenuated serum levels of tumor necrosis factor alpha (TNF alpha) and interleukin-6 (IL-6), ameliorated plaque lipid accumulation and the expression of matrix metalloproteinases-2 and -9, increased the collagen content of plaques, and inhibited perivascular MC degranulation and chymase expression. The in vitro experiments showed that rosiglitazone treatment repressed the expression of TNF alpha and IL-6 induced by antigenchallenged RBL-2H3 cells in a peroxisome proliferator-activated receptor gamma (PPAR gamma)-independent manner, which was related to the repression of protein kinase C (PKC)-beta 1 activation. Combined, these results suggest that the plaque-stabilizing effect of rosiglitazone is attributable to its ability to inhibit the activation of perivascular MCs. (C) 2019 Elsevier Inc. All rights reserved.