Estrutura e atividade antidiarreica de polissacarídeos da alga marinha vermelha Bryothamnion triquetrum S. G. Gmelin

Abstract

Marine algae (seaweeds) are source of several molecules with biological activities, such as sulfated polysaccharides which have aroused a great interest in biomedical sciences. The aim of this study was to characterize chemically and structurally the total sulfated polysaccharides (TSP) from the red seaweed Bryothamnion triquetrum and to evaluate its antidiarrheal potential. The TSP were obtained through enzymatic extraction with papain, its molecular mass and sulfate and carbon content were determined by gel permeation chromatography and elemental microanalysis, respectively. Acute diarrhea in mice was induced by Castor oil and the antidiarrheal effects of the TSP were evaluated through the total amount of stool and diarrheal stools, intestinal fluid secretion (enteropooling) and intestinal motility using charcoal meal. The effects of the TSP on secretory diarrhea induced by cholera toxin were analyzed by fluid secretion and absorption in intestinal closed loops and through interactions with the ganglioside GM1, utilizing ELISA method. The TSP yield from dry seaweed was 7.2% and its molecular mass estimated at 61.41 kDa. Structural analyses have shown that this compound consisted of an agar-type galactan, containing mainly 3,6-anhydro-L- galactose and β-D-galactose-6-O-methyl. Sulfate groups are present in small amounts, in the form of α-L-galactose-6-sulfate, with sulfation degree of 0.28%, corresponding to 2.1% of the atoms present in TSP. Doses of 1, 3, 10 and 30 mg/Kg of TSP (v.o.) were tested against acute diarrhea and the dose of 10 mg/Kg has shown the best results, reducing the total amount of stool and diarrheal stools in 90.24% and 93.98%, respectively. Hence, it was used as the standard dose for subsequent experiments. Enteropooling and intestinal motility were decreased by TSP in 54.26% and 45.35%, respectively. In secretory diarrhea, TSP have inhibited intestinal fluid secretion in 20.00% reversing the secretory state induced by the cholera toxin, however, it had no effect on the intestinal absorption. The results also showed that TSP were interacting with GM1 receptors and/or cholera toxin, blocking toxin binding to its receptor and preventing the onset of the disease. These results confirm the potential use of the TSP obtained from the red seaweed B. triquetrum as an antidiarrheal compound.