NQO1 and type 2 diabetes mellitus: Another antioxidant enzyme studied with regards to a potential role in the development of T2DM complications is NAD(P)H dehydrogenase, quinone 1 (NQO1), a cytoplasmic enzyme that catalyzes the reduction of quinones to hydroquinones by using NADH as an electron donor, thus, increasing intracellular NAD+ levels.