Association of hypoglutathionemia with reduced Na+/K+ ATPase activity in type 2 diabetes and microangiopathy.

Abstract

OBJECTIVE: Although recent studies link altered cellular redox state to protein dysfunction in various disease-states, such associations are least studied in clinical diabetes. Therefore, this study assessed the levels of reduced glutathione (GSH) and Na(+)/K(+) ATPase activities in type 2 diabetic patients with and without microangiopathy. METHODS: The study group comprised of a total of 160 subjects, which included non-diabetic healthy controls (n = 40) and type 2 diabetic patients without (n = 60) and with microangiopathy (n = 60), defined as presence of retinopathy with or without nephropathy. Erythrocyte Na(+)/K(+) ATPase activity and GSH levels were estimated spectrophotometrically and fluorometry was used to determine the plasma thiobarbituric acid reactive substances (TBARS) and serum advanced glycation end products (AGEs). RESULTS: GSH levels in diabetic subjects without (4.8+/- 0.15 mumol/g Hb) and with microangiopathy (5.2+/- 0.14 micromol/g Hb) were significantly lower (p < 0.001) compared to control subjects (6.3 +/- 0.14 mumol/g Hb). Erythrocyte Na(+)/K(+) ATPase activity was significantly reduced (p < 0.001) in diabetes subjects with (272 +/- 7 nmol Pi/mg protein/h) and without microangiopathy (304 +/- 8) compared to control (374 +/- 6) subjects. TBARS were significantly higher (p < 0.001) in diabetes subjects with (10.65 +/- 0.81 nM/ml) and without microangiopathy (9.90 +/- 0.5 nM/ml) compared to control subjects (5.18 +/- 0.18 nM/ml). Advanced glycation end product levels were also significantly (p < 0.001) elevated in diabetic subjects with microangiopathy (8.2+/- 1.8 AU) when compared to diabetes subjects without microangiopathy (7.0 +/- 2.0 AU) and control subjects (4.6 +/- 1.9 AU). On multivariate regression analysis, GSH levels showed a positive association with the Na(+)/K(+) ATPase activity and negative association with TBARS and AGE levels. CONCLUSION: Hypoglutathionemia and increased oxidative stress appears to be early biochemical aberrations in diabetes, and through protein alterations, oxidative stress and redox modifications may contribute to pathogenesis of diabetic microangiopathy.