Correlation between the seasonal variations in phlorotannin content and the antiallergic effects of the brown alga Ecklonia cava subsp. stolonifera

Abstract

Here, we investigated the antiallergic effects of brown algae (Ecklonia cava subsp. stolonifera) harvested on the coast of Nishinoshima Town, Oki Islands, Shimane Prefecture, Japan. Specifically, we investigated whether the active components of E. cava ssp. stolonifera vary seasonally and whether such variation correlates with seasonal variation in the antiallergic effects of the algae. High-performance liquid chromatography, liquid chromatography–mass spectrometry, and nuclear magnetic resonance spectra were used to analyze 80% methanol (80M) extract from E. cava ssp. stolonifera and to isolate eckol, 6,6′-bieckol, 8,8′-bieckol, dieckol, and phlorofucofuroeckol-A as the major active compounds in the species' phlorotannins. Monthly measurements of phlorotannin content and the isolated phlorotannins in the 80M extract showed that the crude phlorotannin and isolated phlorotannin content was higher in the summer–autumn period than in the winter–spring period. The antiallergic effects of the monthly 80M extracts and the isolated phlorotannins were confirmed by measuring inhibition of inflammation-related enzymatic activity, suppression of degranulation in rat basophile leukemia-2H3 cells, and effects on allergic inflammation in Institute of Cancer Research strain mice. There was partial seasonal variation in the effect of 80M extract in combination with the amount of isolated phlorotannin and the antiallergic effects. When phlorotannin was removed from the extracts using polyvinylpolypyrrolidone, the antiallergic effects were no longer observed; thus, phlorotannins are the active components. Overall, these results show that correlations exist between the seasonal variations in the suppressive effect of 80M extract on enzymatic activities, allergic inflammation in mice, and the amount of isolated phlorotannins.