**1. Introduction**

Aerobic metabolism results reactive oxygen species (ROS) as its by-product. ROS is comprised of both radical and non-radical species. Distinctively, superoxide anion (O2 -•), hydroxyl radical (•OH), and hydrogen peroxide (H2O2) exhibit properties which discuss its involvement in biological targets. ROS possesses two faces; physiological levels support redox biology and pathological levels are explained via oxidative stress. At normal physiological amounts, ROS contributes to the activation of signaling pathways hence initiate biological processes, though oxidative stress damage cellular components including macromolecules such as DNA, lipids, and proteins [1,2]. The e ffect of ROS elevated levels is counterbalanced with a variety of antioxidants which are divided into two categories namely enzymatic and non-enzymatic. Superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GTPx), and glutathione transferase (GST) are foremost components of enzymatic antioxidants. Non-enzymatic

antioxidants include compounds with a low molecular weight—such as ascorbic acid (vitamin C), α-tocopherol (vitamin E), glutathione, and β-carotene [3]. However, excessive ROS accumulation makes way to countless pathologies such as inflammation, cancer, and abnormal aging. With regard, supplementary antioxidants are beneficial. Such synthetic antioxidants are butylated hydroxytoluene (BHT), and butylated hydroxyanisole (BHA) [4]. However, given its synthetic nature, the human body is vulnerable to side e ffects. Thus, research endeavors complying with natural antioxidants from sustainable sources have received much attention.

Seaweeds are a source of bioactive components, capable of producing a myriad of secondary metabolites. Previous literature covers antioxidant, anti-fungal, anti-inflammatory, and anti-tumor potential of compounds from vivid algal species. Though seaweeds undergo harsh environmental conditions, such as high intense light and oxygen concentrations, which support the formation of oxidizing components, they manage to prevail without any serious damage. This fact suggests possession of protective compounds and mechanisms among seaweeds [5,6].

Different species of the genus *Padina* have been subjected to experiments. A range of phytochemicals and their bioactivities were analyzed in *Padina tetrastromatica* [7]. *Padina pavonica* was extensively studied for its sulfated hetero-polysaccharides [8,9]. Inhibition of hyaluronidase activity of the *Padina pavonica* was assessed in its water extract [10].

Polysaccharides are one of the major components of the natural sources available in marine algae. These were reported as e ffective and non-toxic components with comparatively higher in yield and rather easy to extract, having pharmacological importance [11]. Sulfated polysaccharides inherit distinct attention among other types of polysaccharides due to its numerous bioactivities. Anti-inflammatory [11,12], anti-coagulant [13], anti-proliferative, and antioxidant [14] properties of polysaccharides purified from seaweed species have been studied previously.

This study focuses on the extraction of polysaccharides from brown algae *Padina boryana* collected from the Maldives. Antioxidant potential of the polysaccharides from *P. boryana* has not been reported yet, to the best of our knowledge. Hence, the above properties of the polysaccharides are evaluated in vitro (Vero cells) and in vivo (zebrafish) scale.
