Avaliação do efeito citoprotetor do extrato bruto das folhas de Eugenia uniflora L. (Pintanga) e de compostos bioativos isolados em células secretoras de insulina

Abstract

Surinam cherry leaves are popularly used as an alternative treatment for diabetes mellitus. They are rich in phenolic compounds which have antioxidant properties. Besides, it is well known that reactive species influence in the progression of diabetes. The aim of this study was to evaluate the antioxidant, cytotoxic and cytoprotective activity of the crude leaf extracts of Eugenia uniflora L. and some major components of the extracts, quercetin (QE) and myricetin (MI); and the effect of these substances on the functionality of RINm5f cells. The methodologies performed were: Folin- Ciocalteau method, MTT reduction, DPPH method, hematoxylin-eosin stain, radioimmunoassay and Western Blot analyses. The total phenolic content obtained for the extracts was 440.27 g/mL and 37.83Yg/mL catechin equivalent/mg of aqueous extract (AE) and ethanol extract (EE), respectively. In the DPPH essay, the IC50 of AE was 321.50 g/mL, MI was 152.63 g/mL and QE was 110.278 g/mL. The EE didn’t show significant antioxidant activity. The AE and the EE are not cytotoxic in the concentrations between 12.5 - 75 g/mL and 31.25 - 500Yg/mL, respectively. QE and MI are not cytotoxic in the concentrations between 3.13 – .25 g/mL and 3.13 – 12.5 g/mL, respectively. Most of the compounds didn’t interfere in insulin secretion, except for EE, which increased at least 3 times insulin secretion and MI which decreased insulin secretion in its lower concentration tested. Hydrogen peroxide (H2O2) induced a reduction of 33% of cell viability in acute assay and 45% in chronic assay. The AE had a cytoprotective effect mainly in the chronic assay and in its higher concentrations. The EE had a similar effect only when chronically tested. QE showed a dose-dependent result (6.5 > 3.13 g/mL) in the acute assay and prevented 100% of the damage caused by H2O2 in the chronic assay. One possible cytoprotective mechanism for these compounds and extracts is the inhibition of the activation of NF-κB. Besides that, H2O2 altered intercellular adhesion with intense modification of cellular morphology. The cells presented a round shape, with the formation of folds in the membrane and reduction of cytoplasm basophily. Both extracts and isolated compounds also prevented changes in morphology caused by H2O2, suggesting prevention of lipid peroxidation. There was no variation in the expression of the proteins superoxide dismutase (SOD), Bax, disulfide isomerase (PDI) and GRP94 (glucoseregulated protein), however, the increased protein content of GRP78 was an indicative of reticular stress. These results are an evidence that Eugenia uniflora L. can be used as an alternative treatment for diabetes mellitus.