# Antioxidant Activity of _Panax ginseng_ to Regulate ROS in Various Chronic Diseases
## 3 ROS, Oxidative Stress, and Antioxidants  
Reactive oxygen species (ROS) including hydrogen peroxide (H\({}_{2}\)O\({}_{2}\)), superoxide (O\({}_{2}\)'), and hydroxyl (HO-) radicals were initially recognized as potentially hazardous byproducts; they are now acknowledged to serve significant roles as secondary messengers in numerous intercellular pathways [21]. ROS are produced during ATP production by the electron transport chain and NADPH (nicotinamide adenine dinucleotide phosphate) oxidase system [22]. Moreover, our bodies usually produce huge amounts of ROS due to our daily lifestyles including extended working circumstances, sitting for a long time, wearing restrictive clothing, using illicit substances often, eating unhealthily, and smoking or drinking too much alcohol [23]. ROS positively impact on immunological activity and intracellular signaling at mild to moderate levels [24]. A higher concentration of ROS can cause oxidative stress, DNA damage, redox homeostasis, tumor progression, and drug resistance which are related to the development of various diseases. ROS play a crucial role in cell proliferation, differentiation, and the control of signal transduction at certain levels (Figure 1) [22]. According to [PERSON] (1985), \"Oxidative stress is defined as the imbalance of pro-oxidant and the antioxidant protective capacity that promotes ROS or RNS which might cause potential damage\" [25]. Undeniably, oxidative stress is associated with more than 100 diseases as a source or outcome [26,27]. It is well known that oxidative stress leads to cell death by damaging important bio-compounds such as proteins, DNA, and lipids [28]. Oxidative stress acts as a contributor to many chronic diseases such as cancer, neuro-generative disease, inflammation, cardiovascular disease, etc. [29]. On the other hand, an antioxidant is a compound that reduces or scavenges reactive species or blocks the oxidation in cells [30]. In other words, antioxidants have the power to stop or delay the oxidation reaction to regulate the excessive production of oxidants [31]. Thiols and polyphenols are common examples of antioxidants for their reducing behavior [32]. Plants and animals consist of two types of antioxidants: non-enzymatic (vitamin E, C, carotenoids, lipoic acid, and others) and enzymatic (catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx), Glutathione-S-Transferase (GST), Glutathione reductase (GR), etc.). These enzymatic antioxidants have important functions in regulating cell homeostasis [33]. In a nutshell, the antioxidant mechanisms are (a) inhibiting the production of reactive species, (b) scavenging oxidants, (c) restoring the damaged molecule, (d) blocking the formation of harmful secondary metabolites and inflammation mediators, and (e) developing and boosting the natural antioxidant defense system. These defensive mechanisms work together to prevent oxidative stress in the body [34]. However, in redox biology, superoxide dismutase quickly turns into H\({}_{2}\)O\({}_{2}\) and O\({}_{2}\) via the SOD enzyme. The Fenton reaction can decrease metal ions to produce OH- from H\({}_{2}\)O\({}_{2}\), which is issued in systemic inflammation [35; 36]. OH- are reactive and so damages macromolecules. Antioxidant enzymes (catalase, glutathione peroxidase) can detoxify H\({}_{2}\)O\({}_{2}\) to avoid the production of OH (Figure 2). Natural antioxidants have numerous biological effects including preventing ROS production and inhibiting free radicals [37]. The administration of natural sources of an antioxidant such as ginseng, pomegranate, curcumin, sesame, garlic, peppermint, and olive leaves demonstrated beneficial effects on ROS-mediated diseases in both animal and human studies [38; 39]. Figure 1: In normal cells, the balance between antioxidants and ROS remain at equilibrium due to the chemical reactions of antioxidant enzymes (SOD, CAT, GPx, and GST). However, the overproduction or scavenging of ROS breaks this equilibrium system.