br Materials and methods br Results and discussion

Materials and methods
Results and discussion
Conclusion
Introduction Free radicals produced by normal oxidative metabolism in the human body can cause chain oxidation of food, accelerate food deterioration and cause serious problems of food safety (Choe & Min, 2006). Excess free radicals can lead to cancer, atherosclerosis, cardiovascular disease, Parkinson’s disease and Cytidine 5-triphosphate (Fearon & Faux, 2009). Reactive oxygen species (ROS) and reactive nitrogen species (RNS) play critical roles in modulating numerous biochemical processes (Tsukagoshi, Busch, & Benfey, 2010). High levels of ROS or RNS can damage DNA, proteins and lipids, generating liver disorders, coronary heart disease, and many other health issues (Ward, Prosser, & Lederer, 2014). ROS are highly reactive non-specific molecules, including hydrogen peroxide and other species, such as oxygen free radicals and singlet oxygen derived from the metabolism of oxygen (Liu et al., 2014). Oxidative stress ensues when ROS and free radicals overwhelm the regulatory ability of the body (Sies, 2015), and such a dynamic imbalance between ROS production and elimination can be counteracted by various enzymes and antioxidants. Nowadays, synthetic antioxidants are widely used in food and pharmaceutical products, but their use is often accompanied by toxic and other side effects. For example, butylated hydroxytoluene (BHT), butyl hydroxy anisole (BHA) and tertiary butylhydroquinone (TBHQ) are commonly used in the food industry, and all have some toxic and carcinogenetic effects (Carocho & Ferreira, 2012). Thus, safer and more effective antioxidants containing natural compounds from food, fruit or plants are needed. Many phenolics, flavonoids and benzophenones from fruit, vegetables and plants are good exogenous antioxidants with chemopreventive effects (Hua and Rong, 2016, Wu et al., 2014). In addition, these bioactive compounds can reinforce biological defence systems by regulating the activities of antioxidant enzymes such as superoxide dismutase, catalase and glutathione peroxidase (Kong et al., 2016). The purple mangosteen Garcinia. mangostana L. is a promising source of both novel biologically active substances and compounds essential for human nutrition (Zarena et al., 2012, Zadernowski et al., 2009). Isogarcinol (Fig. S1) is a bioactive polyisoprenylated benzophenone derivative isolated from G. mangostana L. and exists in other Guttiferae plants that are widespread in tropical rain forests (Liu et al., 2015). The review showed that the prenylation of aromatic compounds and a variety of subsequent tailoring reactions, including oxidation, reduction and cyclisation, give rise to a plethora of ‘hybrid’ natural products that exhibit diverse biological properties. In particular, the introduction of prenyl moieties often increases the lipophilicity of these compounds, enhancing their interactions with biological membranes (Chen et al., 2017). Simultaneously, many reports have also demonstrated that natural benzophenones, most with polyisoprenylated benzophenone skeletons, exhibit a range of biological activities, including antifungal, anti-HIV, antimicrobial, antioxidant, antiviral and cytotoxic activities (Wu et al., 2014). Additionally, the hydroxylation pattern on the phenyl rings is an important structural feature for their antioxidant activity, with greater numbers of hydroxyl groups resulting in more antioxidant activity (Wu et al., 2014). It has been proved that isogarcinol has a variety of biological activities, including anti-bacterial and anti-plasmodial activities (Marti, Eparvier, Litaudon, Grellier, & Guéritte, 2010). It also has therapeutic effects in experimental autoimmune encephalomyelitis (Wang et al., 2016) and is a powerful and low-toxicity immunosuppressant (Cen et al., 2013, Li et al., 2015) with desirable anti-inflammatory effects (Fu, Zhou, Wang, Cen, & Wei, 2014). Moreover it is less toxic to liver and kidney function than is cyclosporin A (CsA) in experimental animals (Cen et al., 2013). Stark, Salger, and Frank (2015) reported that isogarcinol had some anti-oxidative activity, but obtained no evidence of its biological relevance in their study, which only involved chemical experiments.