Avaliação da atividade do alginato conjugado com ácido gálico como agente antioxidante e modulador da formação de cristais de oxalato de cálcio

Abstract

Alginate or alginic acid is a carboxylated polysaccharide that can be extracted from marine seaweeds (Phaeophyceae) or bacteria. It is composed by two monosaccharides, manuronic acids and guluronic acid. The alginate has already been widely used in the food, textile, and pharmaceutical industries such as biofilm constituent for food coating, as an emulsifier, in the composition of paint and medication coatings. Therefore, among other properties, it is non-toxic compound and presents good bioavailability. However, the alginate does not present other desired characteristics, for example, is not a good antioxidant agent. Another commercial interesting molecule is gallic acid. This is a phenolic compound with low toxicity, easy to obtain, can be found in various food sources, and presents various biological activities, including antioxidant. However, the antioxidant activity of in vivo gallic acid is not as prominent due its low bioavailability. Since when it is ingested, it needs a large amount for its performance and even in large quantity, it has an easy degradation, which makes it difficult its action. It was observed that this compound can combine some other molecules, which is interesting, since this conjugation can improve its activity/bioavailability. The idea of the present Thesis was to link gallic acid to alginate, thus favoring a better antioxidant activity of the alginate, potentiating it and improving the bioavailability of gallic acid, since the alginate aid in the availability of gallic acid in a higher period. In view of this objective, it was carried out the combination of gallic acid to alginate, a compound called alg-GA. To verify the effectiveness of this conjugation tests such as high efficiency liquid chromatography (HPLC) and infrared spectroscopy were performed. With respect to the apparent molecular mass, it was verified that the mass of the the alg-GA was around 33.28 kDa. In vitro antioxidant tests alg-GA has exhibited high activity as iron and cooper chelating, and as hydrogen peroxide scavenger. Cytotoxicity of these compounds (300 μm) is not detected into African green monkey cells (Vero CCL-81). When these cells were exposed, the oxidative stress induced by H2O2 (2 mm) it was observed that alg-GA (300 μm) protected cells (~ 70%) of cell damage. About modulation of calcium oxalate crystal formation, alginate, at low concentrations (100 and 300 μm) induces the highest formation of crystals and at high concentrations (600 μm) induces the formation of COD crystals. alg-GA has induced only the formation of COD crystals independent of the concentrations evaluated (from 300 μm to 1.5 mm). Regarding the size of the crystals, a proportional decrease in the size of the COD was observed with the increase in the concentration of the alg-GA used, which was not observed with the alg. The data obtained indicated that the conjugation of the alginate with gallic acid promoted the synthesis of a compound with greater antioxidant activity than the alginate and that it promotes the formation of COD crystals, which are related to half people. In future studies it is intended to evaluate the activity of alg-GA in vivo to indicate its possible use in various applicability.