Changes in glucose transporter expression and nitric oxide production are associated with liver injury in diabetes

Abstract

In diabetes mellitus (DM), both hyperglycaemia and hyperlipidaemia can initiate accumulation of fat in the liver, which might be further mediated by inducible nitric oxide synthase. We have studied changes in GLUT1, nitric oxide (NO(·)) concentration and liver damage in two rat DM models. STZ model was induced by strepozotocin 50 mg/kg. HS model was induced by high-fat diet and 30 mg/kg streptozotocin. GLUT1 expression was studied by means of real-time RT-PCR and immunohistochemistry. Production of NO(·) was monitored by means of erythrocyte sedimentation rate spectroscopy of Fe-DETC-NO complex. Liver damage was assessed using histological activity index (HAI). NO(·) concentration was increased in the liver of STZ rats, but it did not change in HS rats (control 36.8 ± 10.3; STZ 142.1 ± 31.1; HS 35.4 ± 9.8 ng/g). Liver HAI was higher in STZ group, 8.6 ± 0.17 versus HS 4.7 ± 0.31, p < 0.05. GLUT1 protein expression was elevated only in STZ group, 16 ± 3 cells/mm(2) versus Control 5 ± 2 cells/mm(2), p = 0.007. Hyperglycaemia sooner causes severe liver damage in rat models of DM, compared with hyperlipidaemia, and is associated with increased NO(·) production. GLUT1 transporter expression might be involved in toxic effects of glucose in the liver. We have obtained novel data about association of GLUT1 expression and NO(·) metabolism in the pathogenesis of liver injury in DM. Increased GLUT1 expression was observed together with overproduction of NO(·) and pronounced liver injury in severely hyperglycaemic rats. On the contrary, moderately hyperglycaemic hyperlipidaemic rats developed only moderate liver steatosis and no increase in GLUT1 and NO(·). GLUT1 overexpression might be implicated in the toxic effects of glucose in the liver. Glycotoxicity is associated with oxidative stress and NO(·) hyperproduction. GLUT1 and NO(·) metabolism might become novel therapeutic targets in liver steatosis.