Assessment of antioxidant activity of seaweed extracts from the Sea of Japan in vitro and in vivo

Abstract

Seaweeds are a source of important biologically active substances: lipids, amino acids, phenolic compounds, polycarbohydrates, etc. Polyphenolic compounds are one of the perspective groups of constituents of marine origin with high antioxidant activity; those play a key role in the life of marine macrophytes, allowing them to quickly respond to external stress and to perform protective functions. At the same time, the multicomponent composition of the phenolic fraction of the seaweed extract provides a wide spectrum of its pharmacological activity, inter alia a regulatory effect on numerous homeostasis disorders occurring during pathological processes in humans and animals. Wherein, the available opportunities for the practical use of seaweed extracts have not yet been depleted, and this is of undoubted interest for modern science. The aim of the work was to carry out a comparative assessment of the antioxidant activity of hydroalcoholic extracts isolated from the thalli of three classes of algae [brown (Sargassum pallidum), green (Ulva lactuca), and red (Ahnfeltia fastigiata var. tobuchiensis)] and to analyze their effect on indices of the endogenous antioxidant system of liver and blood in mice under experimental stress. Seaweeds were sampled in summer in the coastal waters of the Peter the Great Bay (the Sea of Japan). Sampled seaweeds were dried at a temperature of about +50 °C, grinded in a laboratory mill to particles 0.5–1 mm in size, and extracted with 70% ethanol via repercolation. In the extract of the brown alga S. pallidum, the highest content of polyphenols was recorded – (218.2 ± 20.3) mg-Eq GA·g−1 dry weight. In the extract of the green alga U. lactuca, the value was (16.2 ± 1.8) mg-Eq GA·g−1 dry weight; in the extract of the red alga A. fastigiata var. tobuchiensis, (9.1 ± 1.6) mg-Eq GA·g−1 dry weight. Accordingly, the antiradical activity of S. pallidum extract towards the cation radical ABTS+ and the alkyl peroxyl radical was significantly higher than that of U. lactuca and A. fastigiata var. tobuchiensis extracts. The effect of these seaweed extracts on the antioxidant defense indices of liver and plasma in mice under acute stress was studied experimentally. Weight indicators (weight of animals and weight coefficients of their internal organs) and biochemical indices (level of antiradical activity, malondialdehyde and reduced glutathione content, and activity of antioxidant enzymes) were established. The experiment was carried out on white outbred male mice (weight of 20–30 g). To model conditions of acute stress, mice were fixed vertically by the dorsal neck crease for 24 h. Alcohol-free seaweed extracts were injected into mice stomachs as an aqueous suspension (a dose of 100 mg of total polyphenols per kg of body weight) through a tube twice: right before vertical fixation and in 6 h. Into stomachs of the animals of the control and the “stress” groups, distilled water was injected in a volume equal to that of the injected extracts. In this model, all the attributes of stress manifested themselves: adrenal hypertrophy, involution of the thymus and spleen, and ulceration of the gastric and intestinal mucosa. Moreover, disturbances of the antioxidant defense system were recorded: a decrease of antioxidant enzymes activity in blood plasma, a drop in reduced glutathione content in liver, and an increase of the malondialdehyde level. Under the effect of the extracts, in all the groups of animals under stress, a tendency to stabilization of the studied antioxidant defense indices was observed. Interestingly, the values in mice receiving U. lactuca and A. fastigiata var. tobuchiensis extracts were inferior to those in the group of animals receiving S. pallidum extract. In the latter group of mice, there were no significant differences from the control values in terms of antioxidant defense indices. This is due to the fact the main components of the polyphenolic fractions of green and red algae are monomeric flavonoids, while brown algae contain high molecular weight phlorotannins. The latter ones are characterized by higher antioxidant activity than low molecular weight polyphenolic fractions of green and red algae.

Keywords

• seaweeds
• polyphenols
• antioxidant activity
• stress
• mice