HMOX1 and retinal disorder: To elucidate mechanisms mediating the beneficial effect of linagliptin, expressions of genes with an impact on retinopathy were analyzed, including the pro-inflammatory factors interleukin 1 beta (Il1b) [26] and intercellular adhesion molecule 1 (Icam1) [27], the pro-angiogenic SDF-1a receptor C-X-C motif chemokine receptor 4 (Cxcr4) [28], the antioxidative catalase (Cat) [29], and the vaso- and neuroprotective heme oxygenase 1 (Ho-1) [30].