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Antioxidant properties of aqueous and ethanolic extract of propolis and their polyphenolic/flavonoid compaunds in diabetes-induced oxidative stress

Chronic hyperglycemia in diabetes leads to chronic oxidative stress in all tissues because glucose in high concentrations forms reactive oxygen species.1 Therefore, antioxidant properties of aqueous (AEP) and ethanolic (EEP) extract of propolis as well as of several flavonoids (quercetin, naringenin and chrysin) were investigated. Antioxidant activity in vitro was established using several methods. In addition, lipid peroxidation in liver, kidney, spleen, brain and plasma of mice with alloxan-induced diabetes was measured. Effects of EEP, AEP and flavonoids on diabetic nephropathy and liver toxicity were examined histopathologicaly. Results were compared using t-test and ANOVA with Dunett's post-hoc test (p < 0.05). EEP was richer in total phenols, flavonoids and phenolic acids than AEP. Extracts and investigated flavonoids showed notable antioxidant properties in vitro. For example, quercetin and EEP were as effective DPPH radical scavengers as butylated hidroxianisol (BHA), while chrisin was as efficient Fe2+ ion chelator as EDTA. Furthermore, EEP and AEP inhibited heat induced -carotene-linoleic acid degradation as effectively as BHA. Antioxidant activity in vivo, however, did not entirely reflect the results obtained in vitro. For example, contrary to considerable antioxidant properties in vitro, EEP increased the level of lipid peroxidation in spleen and brain of mice. On the other hand some of the investigated samples were able to inhibit lipid preoxidation in liver (quercetin, chrisin, AEP and EEP), brain (naringenin, chrisin) and plasma (naringenin). Histopathological observation of the liver sections of diabetic mice showed several lesions including cellular vacuolization, cytoplasmic eosinophilia and lymphocyte infiltrations. Treatment of diabetic mice with propolis extracts or flavonoids resulted in decreased degree of vacuolization. These findings suggest that propolis treatment may be able to improve the impairment of fatty acid metabolism in diabetes. Renal histology showed corpuscular, tubular and interstitial changes in untreated diabetic mice. Test components, however, did not improve renal histopathology. It seems that antioxidant properties of propolis extracts are not a result of action of one sole principle but rather interplay between several constituents and mechanisms of action.

propolis; diabetes

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