Biological activity and chemical composition of organic extracts from three Guatemalan mangrove trees

Abstract

Introduction: Mangroves are trees or shrubs that are able to grow in brackish water along tropical and sub-tropical coasts around the world, representing an important ecological conservation system. They have a long tradition of medicinal use and are rich in secondary metabolites. The aim of this research was to evaluate the biological activity and chemical composition of three mangrove species, Avicennia germinans, Conocarpus erectus and Laguncularia racemose, from a natural reserve from Guatemala. Methods: Leaf, bark and root were organically extracted; secondary metabolites were identified by macro and semi-micro tests and TLC, and evaluated for flavonoid and tannin content. Antioxidant activity was evaluated by DPPH, FRAP, TPC and ABTS methods, and antimicrobial activity against seven bacteria. By established protocols it was investigated the larvicidal activity against Anopheles and Aedes, cytotoxicity against Artemia salina and anti-tyrosinase activity by TLC. Results: The best yields were obtained with ethanol in leaves (5.43-26.65%); the highest essential oil yields also in leaves (0.02-0.13%), in both cases A. germinans. Main secondary metabolites were flavonoids, tannins, coumarins, saponins and alkaloids, except C. erectus leaf and bark and A. germinans root. The highest amount of chlorogenic acid was found in A. germinans bark (15.6%), the highest percentage of tannins in L. racemosa root (7.2%), the highest antioxidant activity by DPPH (IC50 0.2-5.6 mg/mL) in C. erectus leaves, and FRAP (1.2-4.5 g Fe+2/g of extract) and ABTS (IC50 0.2-11.6 mg/mL) in the bark. Antioxidant activity correlated with TPC, the highest amount in A. germinans bark (149.40-291.39 μg of gallic acid/g extract). None of the species showed larvicidal activity, nor cytotoxicity. Only L. racemosa root showed antibacterial activity against all strains (IC50 0.62 mg/mL). The ethyl acetate and ethanol extracts exhibited mild anti-tyrosinase activity. Conclusion: Mangroves are a promising potential source of antioxidants and antibacterial compounds