Oligossacarídeos sulfatados de Solieria filiformis: obtenção, caracterização estrutural e atividade antioxidante in vitro como estratégia para potencial aplicação na neuroproteção

Abstract

Oxidative stress can lead to free radical release and the oxidation of cell membrane components, causing neurodegenerative diseases. Therefore, agents that reduce this effect are a growing target for research. Some species of red seaweed are rich in iota-carrageenan, a sulfated polysaccharide (SP) with pharmaceutical and biotechnological potential. This study utilized the red seaweed Solieria filiformis, a source of iota-carrageenans, a high-molecular-weight galactan, whose acid hydrolysis products originate low-viscosity oligosaccharides (OS), showing promise for the investigation of antioxidant effects with potential neuroprotective activity. This study aimed to characterize the chemical structure of OS from the SP of S. filiformis and investigate its in vitro antioxidant activity. The red seaweed was cultivated at Flecheiras beach, Trairi-CE, and after cleaning and drying, was milled and subjected to proteolytic extraction with papain (20 mL - 30 mg/mL) and incubated at 60°C for 6h. The obtained SP were hydrolyzed with 0.2 M HCl (10 mg:mL) at 60°C for 4h, followed by dialysis against distilled water in 12 kDa membranes and lyophilization. The contents of total carbohydrates, free sulfates, proteins, and reducing sugars, as well as the molecular weight, functional groups, and antioxidant potential at OS concentrations of 0.5, 1, 2, and 4 mg/mL were determined. The yields of PS extraction and hydrolysis were 21.01 ± 4.23% based on dry mass and 29.23 ± 4.92% based on the mass of PS used. The total carbohydrate contents of SP and their OS were: 60.89 ± 4.19% and 34.96 ± 1.02%, free sulfates: 16.2 ± 0.4% and 16.10 ± 0.21%, reducing sugars: 0.59% and 23.26 ± 0.5%, and proteins: 0.6 ± 0.1% and 1.6 ± 0.4%, respectively. The molecular weights of PS and OS were 300 kDa and 4.58 kDa, respectively, and the functional groups hydroxyl (–OH), carbonyl (C=O), sulfate (S=O), pyranosidic ring, glycosidic bonds, carbon–oxygen (C–O) linkage, 3,6-anhydrogalactose, and galactopyranose-4-sulfate (G4S) were preserved. OS showed higher activity at a concentration of 4 mg/mL, reaching 26.59 ± 1.78%. The hydroxyl radical scavenging assay showed no activity at any tested concentration. These findings demonstrate the effectiveness of acid hydrolysis in obtaining sulfated oligosaccharides and preserving the functional groups essential for their biological properties. Moreover, an antioxidant effect was observed in OS; however, the subsequent application of complementary methodologies and higher concentrations is required for a more comprehensive characterization of their activity and potential future applications in neuroprotection studies.