3H-1,2-Dithiole-3-thione Suppresses LPS-induced Proinflammatory Responses in Macrophages: Potential Involvement of Antioxidant Induction, NF-κB, and Nrf2

Previously, we reported that 3H-1,2-dithiole-3-thione (D3T), an Nrf2 activator, acted as a potential chemoprotectant against lipopolysaccharide (LPS)-induced mortality in mice. In view of the critical involvement of macrophages in the pathogenesis of LPS-induced endotoxemia, in the present study, we investigated the protective effects of D3T on LPS-induced proinflammatory responses in cultured murine RAW 264.7 macrophage cell line and primary peritoneal macrophages and the potential involvement of antioxidant induction, NF-κB, and Nrf2. We showed that treatment with D3T resulted in increased levels of a series of antioxidants in RAW 264.7 cells in a concentration-dependent manner. These included the reduced form of glutathione (GSH), glutathione peroxidase, glutathione reductase, glutathione S-transferase, and NADPH:quinone oxidoreductase 1. Catalase was also potently induced by D3T which, however, did not show a concentration dependency. Concurrent with the ability to induce the above cellular antioxidants, D3T pretreatment of RAW 264.7 cells also led to a concentration-dependent suppression of LPS-induced interleukin-1beta (IL-1β) production and nitric oxide release. LPS-stimulated tumor necrosis factor-alpha (TNF-α) production was also suppressed by D3T, but to a much lesser extent. Using NF-κB reporter gene-expressing RAW 264.7 cells, we further showed that D3T pretreatment also suppressed LPS-induced NF-κB activation. To investigate the potential involvement of Nrf2, a chief regulator of cellular antioxidant genes, we used peritoneal macrophages isolated from Nrf2(+/+) and Nrf2(−/−) mice. Our results showed that D3T pretreatment suppressed LPS-induced proinflammatory responses in Nrf2(+/+) macrophages, and this inhibitory effect of D3T was completely lost in Nrf2(−/−) macrophages. Collectively, the results of the present study demonstrated that D3T acted as a potent suppressor of LPS-induced proinflammatory responses in macrophages. Antioxidant induction, NF-κB suppression, and Nrf2 activation appeared to contribute to the anti-proinflammatory activity of D3T in macrophages.