Troglitazone Upregulates Nitric Oxide Synthesis in Vascular Smooth Muscle Cells

Abstract

Abstract-We investigated the effects of troglitazone on cytokine-stimulated nitric oxide (NO) production in cultured rat vascular smooth muscle cells (VSMC). The increase in NO formation caused by interleukin-1␣ (IL-1) was enhanced by troglitazone in a concentration-dependent manner. Bacterial lipopolysaccharide-stimulated NO synthesis was also increased by troglitazone. The combinations of IL-1, tumor necrosis factor-␣, or lipopolysaccharide with interferon-␥ (IFN) were strong stimuli for induction of NO synthesis in VSMC, which were further potentiated by the presence of troglitazone. When troglitazone was added at increasing intervals after the stimulation of VSMC with IL-1, the enhancement in NO production decreased as the interval lengthened, suggesting that troglitazone alters NO synthase (NOS) expression by VSMC rather than having a direct affect on VSMC NOS activity. Troglitazone had no effect on IL-1-elicited or IL-1/IFN-elicited nuclear factor-B activity in VSMC. Troglitazone inhibited the degradation of cytokine-induced NOS mRNA. Thus troglitazone appears to enhance IL-1-induced NOS mRNA levels by prolonging its half-life rather than activating its transcription, which is nuclear factor -B-dependent. No expression of peroxisome proliferator-activated receptor-␥ (PPAR␥) was detected in VSMC, and 15-deoxy-D 12,14 prostaglandin J 2 , the natural ligand for the PPAR␥, did not resemble the effect of troglitazone on IL-1-induced NO synthesis. These results indicate that troglitazone upregulates cytokine-stimulated NO synthesis in VSMC through PPAR␥-independent mechanisms. Considering its inhibitory effects on the action of numerous growth factors on VSMC, the direct vascular effects of troglitazone shown in this study may have important implications for prevention of restenosis and possibly atherosclerosis. (Hypertension. 1999;33:943-948.) Key Words: troglitazone Ⅲ nitric oxide Ⅲ peroxisome proliferator-activated receptor-␥ Ⅲ cytokines Ⅲ muscle, smooth, vascular T he thiazolidinediones are novel insulin-sensitizing agents that have been shown to significantly reduce hyperinsulinemia in insulin-resistant animals and humans and to reduce hyperglycemia in diabetic models, including humans. [1][2][3] Migration and proliferation of vascular smooth muscle cells (VSMC) are critical events in the development of restenosis and in the progression of atherosclerosis. 4 A previous study demonstrated that the thiazolidinedione analogue pioglitazone inhibited insulin, epidermal growth factor, and serum-induced growth of cultured arterial VSMC. 5 The effect of troglitazone has been investigated on intimal hyperplasia after balloon injury of the vessel wall, a situation in which platelet-derived growth factor (PDGF) and basic fibroblast growth factor (bFGF) are induced and regulate these VSMC activities. Troglitazone inhibited both bFGF-induced VSMC growth and PDGF-induced VSMC migration as well as VSMC intimal hyperplasia after endothelial injury in rats. 6 In animal models of restenosis after balloon angioplasty, endogen...

Troglitazone Induces GLUT4 Translocation in L6 Myotubes

“…It has been suggested that cytokines/LPS exposure significantly increased GLUT1 transporter protein levels but decreased GLUT4 transporter protein levels by inducing iNOS expression and NO production in L6 cells. Another study (53) found that TGZ upregulated cytokine-stimulated NO synthase in vascular smooth muscle cells, but TGZ alone did not stimulate it. In our study, L6 myotubes were not exposed to cytokines.…”

Expression of NAG-1, a Transforming Growth Factor-β Superfamily Member, by Troglitazone Requires the Early Growth Response Gene EGR-1

“…Furthermore, TGZ and PGJ 2 affect several pathways in a PPAR␥-independent manner. TGZ up-regulates nitric oxide synthesis (19), induces the p53 pathway (20), inhibits cholesterol biosynthesis (21), and has antioxidant function (22), whereas PGJ 2 induces apoptosis (23) and affects signaling pathways that utilize ERK1/2 or NF-B (24) independent of PPAR␥. In addition, we have recently demonstrated that TGZ induces the early growth response gene EGR-1 independently of the PPAR␥ transcription factor (25).…”

Troglitazone administration limits infarct size by reduced phosphorylation of canine myocardial connexin43 proteins

“…Thus inhibition of troglitazone-induced InsP 3 release can contribute to limited Ca 2ϩ overload during reperfusion. Besides, we cannot exclude the possibility that other mechanisms of troglitazone may be involved via a non-free radical-mediated mechanism such as inhibition of the Na/H exchange (11) and calcium channel blocker (35), increased nitric oxide (24), activated peroxisome proliferator activated receptor-␥ (51), attenuated sympathetic discharge (43), and increased lactate uptake (52), actions that may be protective during myocardial ischemia and reperfusion. Previous studies have demonstrated that troglitazone can act as an inhibitor of Na/H exchange, which provided a cardioprotection by reducing intracellular calcium load (29) and attenuated neutrophil accumulation during ischemia-reperfusion (21).…”

“…Previous studies have demonstrated that troglitazone can act as an inhibitor of Na/H exchange, which provided a cardioprotection by reducing intracellular calcium load (29) and attenuated neutrophil accumulation during ischemia-reperfusion (21). Troglitazone at the concentrations (10 M) can enhance synthesis of nitric oxide (24) and act as a calcium channel blocker (35) in vitro, which concentrations can be attained used here. Increased nitric oxide has been found to attenuate reperfusion-induced sarcolemmal fragility and reduced formation of contraction band necrosis (36).…”