Natural metabolites with antioxidant activity from micro-and macro-algae

In humans, excess accumulation of reactive oxygen species (ROS) produces oxidative stress, resulting in cell and tissue damage, and eventually, leading to variety of diseases. Excess ROS can be eliminated, and its detrimental repercussions avoided by combining endogenous and exogenous antioxidants. A plant-based diet and dietary supplements are a major source of exogenous antioxidants; however, fungi, bacteria, lichens, insects, and algae (macroalgae and microalgae) are also deemed as potential sources for exogenous antioxidants. For example, algal biomass and extracts can be directly consumed or their purified metabolites can be used as antioxidants. Furthermore, some exogenous antioxidant molecules can be synthesized only by algae but not by other organisms. Antioxidant molecules derived from algae, include a variety of polysaccharides, pigments (carotenoids, phycobiliproteins etc), mycosporins-like amino acids, phytosterols, phenolic compounds (phenolic acids, bromophenols, phlorotannins, flavonoids etc), fatty acids, and alkaloids. They exhibit potent antioxidant activities confirmed by in vitro scavenging assays (DPPH, ABTS, hydroxyl, superoxide, hydrogen peroxide and nitric oxide radicals) and/or by reducing or chelating metal ions. In addition, algal-derived antioxidants have also been tested in in vivo models and have demonstrated high antioxidant activities achieved by upregulation of antioxidant enzymes (catalase, superoxide dismutase and glutathione peroxidase) and inhibition of lipid peroxidation. This review study focuses on the antioxidant potential of different natural compounds obtained from different algal groups (macroalgae, eukaryotic microalgae and prokaryotic microalgae). This review is based primarily on research and review articles published in the last five years (2019-2023) and written in English.