The role of nitric oxide synthase isoforms and arginase in the pathogenesis of diabetic foot ulcers: possible modulatory effects by transforming growth factor beta 1

Abstract

Aims/hypothesis. l-arginine, an amino acid involved in wound healing, is metabolised by one of two pathways; nitric oxide synthase and arginase. If metabolised by nitric oxide synthase, this can result in tissue destruction, or matrix deposition if metabolised by arginase. The aim therefore was to investigate the role of these enzymes in the pathogenesis of diabetic foot ulcers. Methods. The activity, proteins by Western blot analysis and cellular distribution (using immunocytochemistry) of these enzymes were measured in diabetic foot ulcers, diabetic skin and normal skin. Results. Total and inducible nitric oxide synthase (p < 0.001) and endothelial nitric oxide synthase were increased in diabetic ulcers compared with diabetic and normal skin and were associated with increased plasma nitrite concentrations in diabetic ulcers (p < 0.05). Inducible nitric oxide synthase was the major isoform, with the macrophage being the predominant cellular source. Similarly arginase activity was increased (p < 0.01) in diabetic ulcers. The protein levels corroborated with the activity data, with the fibroblast being the major cellular source. The spatial and cellular distribution of the two enzyme systems was distinct. Transforming growth factor-beta1 was decreased in diabetic ulcers in comparison with diabetic skin and normal skin. Conclusion/interpretation. Increased nitric oxide synthase activity in diabetic foot ulcers may be responsible for the impaired healing in this disease. Furthermore, the increased activity of arginase could account for the characteristic callus formation around these ulcers. In addition, the lower concentrations of transforming growth factor-beta1 in diabetic ulcers may explain the raised concentrations of nitric oxide in this condition. [Diabetologia (1999) 42: 748–757]