NOS2 and diabetes mellitus: In addition, a variety of inflammatory mediators on the retina can be upregulated in the early stage of diabetes, including intercellular adhesion molecule-1 (ICAM-1), VEGF, nuclear factor kappa B (NF-κB), inducible nitric oxide synthase (iNOS), tumor necrosis factor (TNF)-α, CD18, and local inflammatory response playing an important role in the occurrence and development of DR [4, 5].