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 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 oC. 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.
In pancreatic β-cells, although H2O2 is a metabolic signal for glucose stimulated insulin secretion, it may induce injury in the presence of increased oxidative stress (OS) as in the case of diabetic chronic hyperglycemia. Olea europea L. (olive) leaves contain polyphenolic compounds that may protect insulin-secreting cells against OS. The major polyphenolic compound in ethanolic olive leaf extract (OLE) is oleuropein (about 20 %), thus we compared the effects of OLE with the effects of standard oleuropein on INS-1 cells. The cells were incubated with increasing concentrations of OLE or oleuropein for 24 h followed by exposure to H2O2 (0.035 mM) for 45 min. H2O2 alone resulted in a significantly decreased viability (MTT assay), depressed glucose-stimulated insulin secretion, increased apoptotic and necrotic cell death (AO/EB staining), inhibited glutathione peroxidase activity (GPx) and stimulated catalase activity that were associated with increased intracellular generation of reactive oxygen species (ROS) (fluorescence DCF). OLE and oleuropein partly improved the viability, attenuated necrotic and apoptotic death, inhibited the ROS generation and improved insulin secretion in H2O2-exposed cells. The effects of oleuropein on insulin secretion were more pronounced than those of OLE, while OLE exerted a stronger anti-cytotoxic effect than oleuropein. Unlike OLE, oleuropein had no significant preserving effect on GPx; however, both compounds stimulated the activity of catalase in H2O2-exposed cells. These findings indicate different modulatory roles of polyphenolic constituents of olive leaves on redox homeostasis that may have a role in the maintenance of β-cell physiology against OS.
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