Exposure of human keratinocytes to ischemia, hyperglycemia and their combination induces oxidative stress via the enzymes inducible nitric oxide synthase and xanthine oxidase.

BACKGROUND: Diabetes mellitus is characterized by a chronic hyperglycemia and might cause skin pathologies resulting from an ischemic insult. A variety of mechanisms have been suggested for the damage provided by ischemia-reperfusion injury (IRI) or for hyperglycemic conditions. Yet, the association between IRI and hyperglycemia together in skin has been poorly investigated even thought they are both present in diabetic patients.
OBJECTIVE: To examine the effect of a dual stress combining IRI and hyperglycemia on human keratinocytes-its ability to cause oxidative damage and inflammatory response via the enzymes xanthine oxidase (XO) and inducible nitric oxide synthase (iNOS).
METHODS: HaCaT cells were used as a model to induce IRI and hyperglycemia. In order to assess the oxidative damage, total antioxidant scavenging capacity (TSC) and GSH/GSSG ratio were evaluated. iNOS expression was evaluated and its metabolite nitric oxide was estimated by measuring nitrite levels. XO activity was assessed by uric acid quantification and by superoxide radical formation. Inflammatory response was determined through interleukin-6 secretion.
RESULTS: Our observations demonstrate different responses of the cells exposed to single stress (IRI) compared to dual stress combining also hyperglycemia. However, cells response exhibited similarity during reperfusion, by enhancing iNOS expression as well as superoxide levels. While ischemia led to changes in TSC and redox state, reperfusion restored them to basal levels. IRI also caused the enhancement of secreted IL-6 and uric acid levels.
CONCLUSION: iNOS and XO play a major role in IRI and hyperglycemia. Inhibition of one of these enzymes may be beneficial to skin cells under these conditions.