# Phytosterols in Seaweeds: An Overview on Biosynthesis to Biomedical Applications
## 4 Health Benefits and Biomedical Applications of Phytosterols
### Phytosterols as Antioxidative Agents  
Reactive oxygen species (ROS) and free radicals are perpetually generated and their implications in pathobiology are associated with various diseases, including cancer, neurodegenerative and cardiac diseases [62]. The human body is endogenously equipped with enzymatic antioxidants, such as superoxide dismutase (SOD), glutathione peroxidase (GPx), glutathione reductase (GR), and catalase (CAT), to counteract the effects of oxidation. A transcriptional regulator, nuclear erythroid 2-related factor 2 (Nrf2), mediates the expression of antioxidant response elements during oxidative stress [63]. In addition, non-enzymatic antioxidants are shown to boost the antioxidant defense mechanisms and thereby aid in ROS elimination. The antioxidant supplements from seaweeds are reported to reduce the risk of cancer, cardiovascular, and other degenerative diseases in humans [63; 64; 65]. Particularly, toxicrels from brown seaweed are gaining interest due to their exceptional antioxidant properties. Studies have suggested several mechanisms for the antioxidant activity of fucosterol, including increased activities of free radical scavenging enzymes such as GPx, CAT and SOD [61], inhibition of ROS generation by suppressing iNOS (Inducible nitric oxide synthase) and COX-2 (cyclooxygenase-2) [66; 67], and inhibitory activities against biomarkers (\(\beta\)-secretase, acetylcholinesterase) and butylcholinesteraseterase (AChE) of [PERSON]'s disease [68]. The general antioxidant mechanism of action of phytosterol is illustrated in Figure 4.  
Figure 3: Biological properties and biomedical applications of phytosterols. Phaeophyta, a brown seaweed, with higher amounts of fucosterol, exhibited considerable antioxidant activity in the 2, 2-diphenyl-1-picrylhydrazyl (DPPH) assay [48]. Fucosterol, one of the major components of the brown seaweed _Padina gymnospora_ ethyl acetate extract, exhibited promising antioxidant activity in \(\beta\)-carotene bleaching (BCB) and total reducing activity (TRA) assays [69]. [PERSON] et al. [70] have reported that fucosterol (from brown seaweed _S. binder_) treatment in HaCaT keratinocytes and HDF fibroblasts cells significantly decreased intracellular ROS levels and increased cell viability during exposure to particulate matter (PM). In another study by [PERSON] et al. [71], fucosterol increased the level of enzymatic antioxidants, such as SOD, CAT, and HO-1, as well as the transcriptional regulator Nrf2 in A549 cells in the nucleus. Similarly, [PERSON] et al. [72] reported that fucosterol, obtained from _E. stolonifera_ and _Eisenia bicyclis_, hugely inhibited the generation of intracellular ROS and ameliorated the levels of glutathione in tert-butyl hydroperoxide and tacrine-treated HepG2 cells. [PERSON] et al. [73] reported the dose-dependent intensification of intracellular ROS in a fucosterol-treated HeLa cervical cancer cell line. Fucosterol from _S. horneri_ showed strong free radical scavenging activities in DPPH and 2,2 azino-bis3-ethylbethiazol-6-sulfonic acid (ABTS) assays. In addition, fucosterol attenuated the oxidative actions in HT22 and BV2 cells by enhancing the HO-1 and Nrf2 levels in the cytoplasm and nucleus, respectively [74]. Similarly, fucosterol from _P. boryana_, a brown seaweed, significantly upregulated the antioxidant proteins such as Nrf2, and HO-1 and downregulated the Kelch-like ECH-associated protein-1 (Keap1) in the RAW 264.7 macrophage cell line induced with PM [67], in addition to anti-inflammatory activity. Remarkably, [PERSON] et al. [75] revealed the antioxidant property of sterol hydrocarbon, obtained from brown seaweed _Taonia atomaria_, through DPPH, ABTS, and total antioxidant capacity (TAC) assays. The study also unveiled the anti-inflammatory and anticancer (against human liver, breast, ovarian, and colon cancer cell lines) activities of _T. atomaria_  
Figure 4: Schematic diagram representing the antioxidant mechanism of fucosterol.