Effect of carboxymethylated pyridoindoles on free radical-induced haemolysis of rat erythrocytes in vitro.

Recently novel carboxymethylated pyridoindoles, analogues of the efficient chain-breaking antioxidant stobadine, have been designed, synthesised and characterised as bifunctional compounds with joint antioxidant/aldose reductase inhibitory activities with the potential of preventing diabetic complications. The critical property for the efficacy of the novel aldose reductase inhibitors in vivo is their ability to penetrate into target tissues. In this study, the issue was addressed by measuring the antioxidant activity of compounds 1 [(2-benzyl-2,3,4,5-tetrahydro-1H-pyrido[4,3-b]indole-8-yl)-acetic acid] and 2 [(+/-)-2-benzyl-(4a,9b)-cis-1,2,3,4,4a,9b-hexahydro-1H-pyrido[4,3-b] indole-8-yl acetic acid] in the cellular system of intact erythrocytes exposed to peroxyl radicals generated by thermal degradation of the azoinitiator 2,2'-azobis(2-amidinopropane) hydrochloride (AAPH) in vitro. Isolated washed rat erythrocytes were incubated in the presence of the azoinitiator AAPH and the compounds tested for increasing periods of time up to 4 h at 37 degrees C. The degree of haemolysis was determined by absorbance of the haemoglobin released. The onset of AAPH-induced haemolysis was found to be shifted from the starting zero point by the time interval assigned as a lag period. In the presence of the compounds studied the lag period was prolonged significantly. The free radical-initiated haemolysis was retarded by the compounds studied with decreasing efficiency: stobadine > compound 1 ~ Trolox > compound 2. The results have demonstrated an antioxidant activity of the novel carboxymethylated pyridoindoles developed as potential agents for multitarget pharmacology of diabetic complications.

Carboxymethylated tetrahydropyridoindoles as aldose reductase inhibitors: in vitro selectivity study in intact rat erythrocytes in relation to glycolytic pathway.

Oxidative stress and polyol pathway hypotheses are generally accepted in the etiology of diabetic complications. Recently, novel carboxymethylated pyridoindoles, structural analogues of the efficient chain-breaking antioxidant stobadine, were designed, synthesised and characterised as prospective aldose reductase inhibitors endowed with antioxidant activity. Of them (2-benzyl-2,3,4,5-tetrahydro-1H-pyrido[4,3-b]indole-8-yl)-acetic acid (compound 1) and (2-phenethyl-2,3,4,5-tetrahydro-1H-pyrido[4,3-b]indole-8-yl)-acetic acid (compound 2) were found to be the most efficient inhibitors of aldose reductase with the corresponding IC50 values in a micromolar region. The aim of this work was to study cellular uptake of the novel pyridoindole derivatives and their effect on the complex metabolism of glucose in isolated rat erythrocytes under euglycaemic conditions. Glycolysis was shown to be the sole process responsible for the observed clearance of glucose. The compounds studied were avidly taken up by the cells, yet they did not significantly affect glucose consumption and lactate production nor did they affect osmotic fragility of the erythrocytes. On balance, the present experimental findings indicate that compounds 1 and 2, efficient inhibitors of aldose reductase, are selective in relation to the glycolytic pathway of glucose elimination. This conclusion supports current preclinical development of novel carboxymethylated tetrahydropyridoindoles as promising aldose reductase inhibitors for pharmacological prevention and treatment of diabetic complications.

Electrophoretic analysis of oxidatively modified eye lens proteins in vitro: implications for diabetic cataract.

Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) profiles of eye lens proteins showed that both progression of diabetic cataract in rats in vivo and precipitation of soluble eye lens proteins stressed by free radicals in vitro were accompanied by significant protein cross-linking. There was a noticeable contribution of disulfide bridges to protein cross-linking in diabetic eye lens in vivo. In contrast, under conditions in vitro, when eye lens proteins were exposed to hydroxyl or peroxyl radicals, we showed that the participation of reducible disulfide linkages in the formation of high molecular mass products was markedly lower. These in vivo--in vitro differences indicate that the generally accepted role of reactive oxygen species in diabetic cataractogenesis may be overestimated in connection with the processes of protein cross-linking.