Effects of the antioxidants dihydrolipoic acid (DHLA) and probucol on xenobiotic-mediated methaemoglobin formation in diabetic and non-diabetic humanerythrocytes in vitro

The antioxidant effects of dihydrolipoic acid (DHLA) and probucol were inve stigated in a human erythrocytic in-vitro model of diabetic oxidative stres s, where xenobiotics were used to form methaemoglobin. 4-Aminophenol mediat ed haemoglobin oxidation in non-diabetic erythrocytes was not affected by t he presence of either DHLA or probucol. However, with diabetic cells, there were significant increases (P < 0.01) in 4-aminophenol-mediated haemoglobi n oxidation in the presence of DHLA. Methaemoglobin formed by nitrite in no n-diabetic and diabetic cells was not altered by either DHLA or probucol ex cept at one time point in diabetic cells. In non-diabetic as well as diabet ic cells, methaemoglobin formed by MADDS-NHOH was significantly reduced at all three time points in the presence of DHLA (P < 0.0001) but unaffected b y probucol. In the presence of DHLA only, methaemoglobin formed by the prod ucts of rat microsomal oxidation of both 4-aminopropiophenone and benzocain e was markedly reduced for both xenobiotics in diabetic and non-diabetic ce lls (P <less than> 0.0001) compared with cells incubated in the absence of DHLA. There were no significant differences between total cellular thiol le vels determined between diabetic and non-diabetic erythrocytes, nor did DHL A or probucol affect resting thiol levels. MADDS-NHOH caused a significant thiol depletion in diabetic cells, which was restored in the presence of DH LA. A further study is required to determine how DHLA attenuates the potent REDOX reactions that occur during hydroxylamine-mediated methaemoglobin fo rmation. (C) 2001 Elsevier Science B.V. All rights reserved.