Ochnaflavone inhibits TNF-α-induced human VSMC proliferation via regulation of cell cycle, ERK1/2, and MMP-9

Ochnaflavone (c-3 of apigenin-0-c-4 of apigenin; OC), a biflavonoid present in the human diet, is known to inhibit angiotensin II-induced hypertrophy and serum-induced smooth muscle cell proliferation. OC is known to have anti-fungal and anti-inflammatory activities. However, it is not known whether OC exerts similar cardioprotective effects in cells treated with tumor necrosis factor (TNF)-α. In this study, we isolated OC from Lonicera japonica and studied its effect on matrix metalloproteinase-9 (MMP-9) gene expression in human aortic smooth muscle cells (HASMC). Furthermore, we investigated whether OC exerts the multiple suppressive effects on cytokine TNF-α-induced HASMC. Treatment of OC showed its potent inhibitory effects on DNA synthesis of cultured HASMC in the presence of TNF-α. These inhibitory effects were associated with reduced extracellular signal-regulated kinase 1/2 (ERK1/2) activity and G1 cell cycle arrest. Treatment of OC, which induced a cell cycle block in G1-phase, induced downregulation of cyclins and CDKs and upregulation of the CDK inhibitor p21^waf1 expression, whereas upregulation of p27 or p53 by OC was not observed. Because anti-atherogenic effects need not be limited to anti-proliferation, we decided to examine whether OC exerts inhibitory effects on MMP-9 activity in TNF-α-induced HASMC. OC inhibited TNF-α-induced MMP-9 secretion on HASMC in a dose-dependent manner. This inhibition was characterized by downregulation of MMP-9, which was transcriptionally regulated at nuclear factor (NF)-κB site and activation protein (AP)-1 site in the MMP-9 promoter. These findings indicate the efficacy of OC in inhibiting cell proliferation, G1 to S-phase cell cycle progress, and MMP-9 expression through the transcription factors NF-κB and AP-1 on TNF-α-induced HASMC. The findings of the present study may provide a potential mechanism that explains the anti-atherogenic activity of OC.