Therapeutic and nutraceutical potentials of a brown seaweed Sargassum fusiforme

Abstract Sargassum fusiforme, also known as Yangqicai (羊栖菜) in Chinese and Hijiki in Japanese, is a brown seaweed that grows abundantly along the rocky coastlines of Asian countries such as Japan, Korea, and China. The first use of S. fusiforme as a traditional Chinese medicinal plant was recorded in the Shennong Bencao Jing, dated 200 AD. It was referred to as Haizao (seaweed), renowned for treating Yinglu (tumor‐like induration), dysuria, and edema. Currently, it is commonly used in traditional cuisine as it is rich in dietary fiber and minerals such as calcium, iron, and magnesium. Owing to its health benefits, S. fusiforme remains popular in China, Korea, and Japan, as well as in the UK and in North America. Currently, there is a lack of research on S. fusiforme; thus, we review the therapeutic effects of S. fusiforme, such as anticancer, antiangiogenic, and antiviral effects, in vitro and in vivo as reported during the past two decades. This review may promote further research on the therapeutic uses of S. fusiforme. Furthermore, we discuss the processes and considerations involved in using drugs produced from marine sources.


| INTRODUC TI ON
Marine macroalgae (also referred to as seaweeds) belong to three major classes or phyla: Chlorophyceae (green algae), Rhodophyceae (red algae), and Phaeophyceae (brown algae). Each phylum comprises thousands of species, and vast chemodiversity has been described within and between these major algal groups (Baurain et al., 2010;Shannon & Abu, 2019). According to the Food and Agriculture Organization (FAO) database (2020), global aquaculture production of marine algae has more than tripled, from 10.6 million tons in 2000 to 32.4 million tons in 2018 (FAO, 2020). Since ancient times, seaweeds have been used as food products and as traditional medical agents, especially in Asian countries. Currently, there is interest in expanding the use of seaweeds and particularly in adding value to extracted components for a wide range of uses. Apart from its usage as a food source, seaweeds are also an excellent source of structurally diverse bioactive compounds with considerable pharmaceutical and biomedical potential for developing functional materials such as nutraceuticals and cosmeceuticals (Gupta & Abu, 2011). Over the past few years, seaweeds have been gaining considerable interest as sources of valuable functional metabolites. Every year, a substantial number of novel bioactive secondary metabolites are isolated from seaweeds, and these compounds are typically tested using various biological assays to assess their potential as anticancer, anti-inflammatory, antiviral, antihypertensive, antibacterial, and antidiabetic agents (Fernando, Sanjeewa, Kim, Lee, & Jeon, 2018;Wijesekara, Pangestuti, & Kim, 2011;Wijesinghe & Jeon, 2012). Future efforts in the seaweed industry will help develop high-value markets for functional foods, cosmeceuticals, nutraceuticals, and pharmaceuticals (Hafting et al., 2015).
Various natural products can be obtained from plants, animals, and microorganisms. Owing to the diversity of these products and lack of effective natural compounds from terrestrial sources, scientists began focusing their attention on developing drugs from marine sources (Senthilkumar, Manivasagan, Venkatesan, and Kim (2013)).
Sargassum fusiforme (also referred to as Hizikia or Hijiki) is a macroalgal seaweed belonging to the class Phaeophyceae of the order Fucales (Cleveland, 2008). This species is typically distributed along the coastal areas of China, Korea, and Japan (Cong, Xiao, Liao, Dong, & Ding, 2014;Li, Fu, Duan, Xu, & Gao, 2018a). The market demand for S. fusiforme remains high because of its nutritional potential and its economic value in the pharmaceutical and manufacturing fields . Metabolites of S. fusiforme have been shown to possess antitumor (Chen, Nie, Yu, et al., 2012), antiviral (Sun et al., 2019), antiaging (Chen, He, et al., 2016), and anticoagulant properties (Sun et al., 2018). The unique characteristics of polysaccharides and bioactive low-molecule compounds in this seaweed species are of particular interest, thus emphasizing the importance of further research in this area. Therefore, exploring the therapeutic and nutraceutic potential of this seaweed is required to increase public awareness and to efficiently utilize this sustainable natural resource. Usage of the bioactive metabolites of S. fusiforme in various applications as a source of functional ingredients is worthy of consideration. Hence, the objective of this review was to present current literature on S. fusiforme, highlighting its functional properties that may be important for promoting further use of this seaweed.

| CHAR AC TERIZ ATI ON OF S . FUSIFORME P OLYSACCHARIDE S
Most studies on S. fusiforme have focused on polysaccharides, especially fucoidans; thus, we present data on sources, extraction methods, and analytical methods of fucoidans before describing their usage in in vitro and in vivo studies (Table 1). Fucoidans are associated with several bioactivities of S. fusiforme. Different methods of extraction and analysis of fucoidans have been reported.
Fucoidan is one of the most pharmacologically significant active compounds produced by S. fusiforme. The considerable heterogeneity of fucoidans entails that their molecular weight cannot be discretely determined; instead, they are characterized by a range of molecular weights, typically referred to as a scope, or by the "numerical average" or median peak weight (Fitton et al., 2015).

Summary of the literature
According to evidence gathered so far, Sargassum fusiforme appears to have some therapeutic potential. This review highlights the in vivo and in vitro findings supporting the therapeutic potential of S. fusiforme Section 1 (Introduction) provides general facts on S. fusiforme. Section 2 focuses on the characteristics and composition of S. fusiforme polysaccharides. Section 3 summarizes reports on apoptosis-inducing and anticancer effects of S. fusiforme. Angiogenesis has been implicated in diseases such as cancer; hence, Section 4 summarizes the antiangiogenic effects of S. fusiforme. Currently, only few drugs are available that protect from UV radiation-induced damage, which frequently causes skin cancer; thus, Section 5 describes the protective effects of this seaweed against UV radiation. Section 6 summarizes studies on intestinal homeostasis in conjunction with gut microbiota composition, which has become a research hotspot in recent times.
However, the solution behavior and molecular conformation of S. fusiforme polysaccharides remain unclear. Using scanning electron microscopy, a recent study demonstrated that fucoidan extracts of S. fusiforme exhibited an inhomogeneous texture with a flaky or villiand powder-like structure (Liu et al., 2020).
Taken together, examining the relationship between chemical structure, chain conformation, and biological activity of S. fusiforme polysaccharides is of great importance for drawing further conclusions. The general relationship between the bioactivity and structure of S. fusiforme polysaccharides remains unclear, even though the bioactivity of SFPS has been extensively explored in the past decade.

| AP OP TOS IS INDUC TI ON AND ANTI C AN CER AC TIVIT Y
Apoptosis-mediated cell death has become an extensively researched topic. Understanding disease-associated apoptosis is essential as it can provide fundamental information regarding the etiology of the disease and may aid in choosing the optimal treatment. For example, cancer involves an imbalance between cell division and cell death, where cells that are supposed to die fail to receive the corresponding signals. Such processes can arise at any stage of the apoptotic pathway. Downregulation of the tumor suppressor gene p53 leads to reduced apoptosis and enhanced growth and development of tumor cells (Bauer & Helfand, 2006), and inactivation of p53, regardless of the mechanism, has been associated with a number of human cancers (Iacopetta, 2003;Morton et al., 2010). The ability of malignant cells to evade apoptosis is a hallmark of cancer (Hanahan & Weinberg, 2011). Cancer cells show multiple characteristics; for example, they can evade cell cycle checkpoints and withstand exposure to cytotoxic agents (Letai, 2008). Therefore, causing targeted apoptosis is therapeutically important for treating cancers (Plati, Bucur, & Khosravi, 2011).
A study on the antitumor effects of SFPSs (299 kDa) on liver cancer was conducted by Fan et al. (2017) who used SFPSs that were mainly composed of d-fucose, l-xylose, d-mannose, and d-galactose, with a relative molar ratio of 5.9:1.0:2.3:2.2. Additionally, SFPSs contained 10.74% ester sulfate and 6.48% uronic acid. In this study, different dosages of S. fusiforme were orally administered to mice inoculated with human hepatocellular carcinoma cells HepG2.
Their results showed antitumor effects of S. fusiforme when admin-

| ANTIANG IOG ENIC AC TIVIT Y
Angiogenesis is typically defined as growth from pre-existing vasculature. Several preclinical and related studies have shown that angiogenesis plays a vital role in oncogenesis and metastasis; consequently, suppression of angiogenesis in tumor tissue may hold considerable treatment potential (Gimbrone, Leapman, Cotran, & Folkman, 1972;Graham, Rivers, Kerbel, Stankiewicz, & White, 1994).
Paracrine stimulation of tumor cells is considered the main promotor of angiogenesis. Endothelial cells, once activated by this stimulus, will proliferate and migrate to form new vessels and blood flow. This process involves a variety of biomolecules. VEGF is one of the most effective and prominent angiogenic factors in tumor-induced angiogenesis (Claffey & Robinson, 1996), and it was initially recognized for its capacity to initiate vascular permeability and induce growth of endothelial cells.
SFPSs also inhibited the expression of VEGF-A in cancer cells and of VEGFR2, its receptor, in human umbilical vein endothelial cells.
In addition, Chen, Cong, et al. (2016) observed that signaling pathways such as EGFR2, Erk, and VEGF may be blocked by FP08S2 in human microvascular endothelial cells-1, thereby preventing growth and microvascular generation in a xenograft model of A549 cancer cells in nude rats. FP08S2 is a sulfated fucoidan of S. fusiforme, and owing to its remarkable antiangiogenic activity, it may indeed be the preeminent compound that inhibits lung cancer cell growth . Future studies should focus on following up previous research in this field to determine whether therapeutic avenues employing such polysaccharides can help cure malignant tumors or related growths that might eventually become malignant.

| U V PROTEC TI ON
The skin is the largest and most visible organ and is heavily affected by environmental factors; the skin, therefore, is the obvious choice for studying long-term effects of UV-induced aging and damage and the efficacy of protective measures (Ranadive, Menon, Shirwadkar, & Persad, 1989).
Human skin is continuously exposed to diverse environmental stimuli including air, environmental pollutants, and solar UV radiation. UV radiation can cause physical changes, immunological changes such as inflammation and impaired wound healing, and DNA damage, thereby promoting cellular senescence and carcinogenesis (Dunaway et al., 2018).
Sargassum fusiforme reduce water loss through the skin and protect skin structure as well as immune organs, as observed in an in vivo mouse study by Ye et al. (2018), which demonstrated structural properties and protective effects of SFPSs against UV-B radiation in hairless Kunming mice. The polysaccharide was composed of 58.10% ± 2.12% carbohydrate components, 1.01% ± 0.15% protein components, 9.85% ± 0.96% sulfate groups, and 17.66% ± 0.54% glucuronic acid, with an average molecular weight of 224 kDa. The monosaccharide composition of the SFPS was 43.2% l-fucose, 3.5% rhamnose, 18.4% galactose, 1.5% glucose, 18.5% fructose, 5.9% xylose, and 9.0% mannose. This SFPS also alleviated UV-B-induced oxidative stress by increasing the activity of catalase and superoxide dismutase and reducing the levels of malondialdehyde, an end product of lipid peroxidation. Additionally, the levels of MMP-1 and MMP-9 were also suppressed as a consequence of the SFPS treatment. These results suggest that S. fusiforme can be used as a functional food supplement to achieve skin protection. Current climatic changes such as global warming may affect human skin health, thereby aggravating pre-existing skin conditions. The above-mentioned study provides an innovative perspective on skin protection and may contribute to the prevention of skin cancer. Another interesting finding of this study is that degradation of skin collagen and wrinkle formation were suppressed by the SFPS in the model group; this finding might be of significance to the cosmetics and beauty therapy industries.

| INTE S TINAL HOMEOS TA S IS
The

| ANTI OXIDANT B I OAC TIVIT Y
Antioxidants are molecules that are sufficiently stable for donating electrons to aggressive free radicals, thereby neutralizing them and reducing potential damage. Antioxidants can delay and ameliorate cell damage, mainly by means of their free radical scavenging properties (Lü, Lin, Yao, & Chen, 2010). Such low-molecular weight antioxidants can safely interact with free radicals and consequently terminate oxidative chain reactions before damage to essential structures occurs. Examples of antioxidants include glutathione, ubiquinol, and uric acid, which are produced during normal metabolism (Shi, Noguchi, & Niki, 1999). Other kinds of antioxidants are absorbed from the diet. A wide variety of enzymes in the body are responsible for scavenging free radicals; however, the standard micronutrient (vitamin) antioxidants-vitamin E (α-tocopherol), vitamin C (ascorbic acid), and β-carotene-cannot be synthesized in the human body and must therefore be supplied through the diet (Levine, Rumsey, Daruwala, Park, & Wang, 1999).

An in vitro antioxidant evaluation on carboxymethylated and
hydroxamated degraded SFPSs demonstrated significant radical scavenging abilities and high total antioxidant activity of these polysaccharides . Chen, He, et al. (2016)) observed that SFPSs exert strong antioxidant activity in vivo, and SFPSs pro-

| NEUROPROTEC TIVE EFFEC TS
Natural or "alternative" remedies for treating physical and psychiatric disorders have gained worldwide popularity. Further studies are required before these remedies can be accredited as safe and effective alternatives, particularly regarding neuropharmacology (Mischoulon, 2009

| ANTI -OS TEOARTHRITI C EFFEC TS
Numerous elderly people have from osteoarthritis, which is a degenerative disease that has been associated with chronic health conditions and is one of the predominant causes of disability and pain in adults (Allen & Golightly, 2015). Osteoarthritis, a type of inflammation that affects the synovium and cartilage and leads to subchondral bone tissue degradation, is the most common form of arthritis (Cross et al., 2014), resulting in pain, stiffness, and complete failure of affected joints (Barve et al., 2007;Henrotin & Kurz, 2007;Krasnokutsky, Attur, Palmer, Samuels, & Abramson, 2008).
Numerous studies indicated that joint degeneration due to osteoarthritis results from a combination of biochemical factors and mechanical stresses (Henrotin & Kurz, 2007;Krasnokutsky et al., 2008;Lee et al., 2015). Therefore, expression of tumor necrosis factor (TNF)-α and inflammatory factors such as interleukin (IL)-1β by chondrocytes as well as synovial cells occurs at advanced stages of osteoarthritis, and consequently, the levels of MMPs and some proinflammatory factors such as prostaglandin E2 (PGE2), IL-8, IL-6, and nitric oxide increase (Krasnokutsky et al., 2008).
Sargassum fusiforme extracts have shown inhibitory effects on degenerative diseases such as osteoarthritis in vitro and in vivo.
Primary cultures of rat chondrocytes and a rat model of osteoarthritis induced by monosodium iodoacetate were used by Lee et al. (2015) who showed that S. fusiforme extract (20% EtOH) increased cell sur-

| ANTIVIR AL AC TIVIT Y
The treatment of human immunodeficiency virus (HIV) type 1 presents major challenges for antiviral therapies, including treatment complications, drug toxicity and resistance, and high costs. Hence, novel compounds which may help overcome such limitations are urgently needed (Wu, Attele, Zhang, & Yuan, 2001). Paskaleva et al. (2006) found that an S. fusiforme extract prevented HIV replication during a postentry event in the virus' life cycle, that is, when infected macrophages serve as a bridge between the central and the peripheral nervous system through spreading HIV-1 infection to microglia and astrocytes in the central nervous system (Imam, 2005).
Treatment with 1 mg/ml S. fusiforme extract inhibited active replication of the microglial cell cultures and R5-tropic viruses by 90% in primary human macrophages. In primary human astrocytes, the S. fusiforme extract significantly inhibited independent entry of infection in VSV/NL4-3 cells . In a different study, palmitic acid was isolated from S. fusiforme and was found to be a bioactive compound that can inhibit both X4-and R5-tropic HIV entry into CD4 T cells (Paskaleva et al., 2008). Furthermore, bioactivity-guided fractionation of an S. fusiforme mixture yielded the bioactive compound SP4-2, which at 8 μg/ml was found to inhibit HIV-1 infection by 86.9%, with an IC 50 value of 3.7 μg/ml. This represents a 230-fold enhancement of antiretroviral potency, compared to the whole extract (Paskaleva et al., 2008). Western medicine is predominant in the search for drugs to treat HIV infection; however, traditional Chinese medicine may also help identify candidate drugs for HIV treatment, including S. fusiforme compounds, which broadens the perspective on potential future cures .

| ANTIBAC TERIAL AB ILIT Y
Seaweed has been shown to produce bioactive components which can inhibit growth of a variety of Gram-positive and Gramnegative bacteria, including pathogens (Liu, Heinrich, Myers, & Dworjanyn, 2012). Seaweed extracts have been employed as antibiotics, anthelmintics, remedies for cough, hypertension, and diarrhea, for treating cancer, and for prophylaxis (Siddhanata, Ramavat, & Chauhan, 1991

| IMMUNOMODUL ATORY EFFEC TS
Clinical medicine focuses on treating malignant diseases by using chemotherapeutic drugs. However, such drugs are immunosuppressive, that is, the drugs weaken the patient's immune responses even though the intention is to improve the chance of survival (Corper & Rensch, 1921). Hence, there is a need for immunomodulators or other therapeutic alternatives to assist with ameliorating such adverse effects of chemotherapy (Harris, Sengar, Stewart, & Hyslop, 1976). These alternatives should also accelerate recovery in terms of boosting the immune system after chemotherapeutic treatment. In light of this, a group of scientists started to assess the efficacy of S. fusiforme as an immunomodulator (Hu et al., 2014).
Immunomodulators are intrinsic and extrinsic substances that regulate or modify the scope, type, duration, or capacity of the immune response (Rasmussen & Arvin, 1982). Diet may affect maintenance of immune homeostasis (Burns & Goodwin, 2004;Derhovanessian, Solana, Larbi, & Pawelec, 2008;Gardner & Murasko, 2002;Gorczynski & Terzioglu, 2008;Lebish & Moraski, 1987). Chen, Nie, Fan, et al. (2012)) reported that S. fusiforme can be an efficacious immune-potentiating supplement and that it can be used as an alternative to reduce immunosuppression induced by chemotherapy; therefore, it may be used as an immunostimulant in food and pharmaceutical industries. This conclusion was supported by results indicating that SFPSs promoted proliferation of splenic lymphocytes and secretion of cell factors (IFN-γ, IL-2, and IL-6) in immunocompromised mice treated with cyclophosphamide. SFPSs significantly increased the spleen index.
In line with a previous study (Wang et al., 2013)

| CON CLUS I ON S AND FUTURE PER S PEC TIVE S
Increasing scientific research on marine algae as potential drugs suggests that natural products from seaweeds are a precious resource of bioactive ingredient. Sargassum fusiforme shows various bioactivities including antitumor, immunomodulatory, antiviral, and antioxidant effects. Although extensive biological activities of its compounds have been demonstrated with promising preclinical results, applications in clinical practice remain limited. Important questions in this field are yet to be answered; thus, it is necessary to progress from correlation studies to causation studies and from animal to human studies. As revealed in many studies, S. fusiforme produces various remarkable active metabolites. Among the compounds isolated from S. fusiforme, polysaccharides have received considerable attention in the scientific community due to their potential health-promoting effects. Nevertheless, the relationship between structural features, solution behavior, space conformation, and bioactivity is still unclear. In future studies, structure-function relationships of SFPSs need to be systematically examined in depth. Furthermore, relationships between biological activities of SFPSs and their effects on gut microbiota are of considerable interest.
In the present review, we focused on bioactive properties of polysaccharides isolated from S. fusiforme in relation to their health-promoting effects and to update bioactive properties of bioactive low-molecular weight compounds isolated from this seaweed.
Therefore, our review may help increase awareness of bioactive properties of S. fusiforme to utilize it as a valuable source for therapeutic and nutraceutical applications.

ACK N OWLED G M ENTS
We gratefully acknowledge the support of the South African

Department of Higher Education and Training (DHET) and the China
Study Abroad Commission (CSC), and a Golden Seed Project Grant funded by Ministry of Oceans and Fisheries (213008-05-4-SB910).

CO N FLI C T O F I NTE R E S T
The authors declare no conflict of interest.