TNF and type 2 diabetes mellitus: Lastly, a cross sectional study that evaluated TNF-α, HO-1, and Nrf2 levels in β-cells of normal glucose tolerant, prediabetic and T2DM patients found that while TNF-α levels increased with progressing DM, HO-1 and Nrf2 levels decreased, indicating an impaired antioxidative system in DM conditions [34].