In vitro and in vivo investigation for biological activities of neoagarooligosaccharides prepared by hydrolyzing agar with beta-agarase

Abstract

Our study investigated the biological functions of three neoagarooligosaccharides (NAOs), neoagarobiose (NA2), neoagarotetraose (NA4), and neoagarohexaose (NA6). NAOs were prepared by hydrolyzing agar with the recombinant beta-agarases, DagA and DagB, from Streptomyces coelicolor A3(2). An in vitro DPPH (diphenyl-2,4,6-trinitrophenyliminoazanium) radical scavenging assay revealed that none of the NAOs had any significant antioxidative activity. We also assessed the antibacterial activity of each NAO against several gram-negative and gram-positive bacteria. This revealed weak effects against four of the seven tested strains. NAO treatment resulted in significant inhibition of alpha-glucosidase, with the strongest effect observed in a NA4 and NA6 mixture, and a decreasing effect was observed in the order NA2 > NA4 > NA6. Little inhibition was observed against alpha-amylase, with an effect significantly lower than that of acarbose. No observable cytotoxicity was found in immortalized Melan-a mouse melanocytes by NAO treatment up to a concentration of 2,000 mu g/mL. However, melanin synthesis was significantly reduced by NAO treatment, with the strongest effect observed in a NA4 and NA6 mixture and decreasing effects observed in the order NA6 > NA4 > NA2. The tyrosinase activity of Melan-a cells was also consistently decreased by NAO treatment. Among the tested factors, treatment of NA4 and NA6 mixture showed the highest inhibition effects against alpha-glucosidase and tyrosinase, and melanin biosynthesis. Further in vivo study to investigate the role of NAO in these biological functions will be necessary for future biotechnological applications.