Antioxidative Mechanism of Plant Extract

Posted by Tylor Keller on December 11th, 2018

Because people often come into contact with the outside world, normal breathing, external pollution and radiation exposure can cause free radicals in the human body. Excessive free radicals can cause aging or other diseases of the human body, and free radical antioxidants can effectively overcome these hazards. Therefore, antioxidant has become one of the main research topics in the health care products and cosmetics market. Different plant extracts have different active ingredients. Similarly, plant extracts with antioxidant effects also have many different components, and their mechanism of action is also different. This article describes the antioxidative mechanism of plant extracts.

1 Acting on free radical-related enzymes

The enzymes related to free radicals are divided into two types: oxidase and antioxidant enzymes. The antioxidant activity of plant extracts is reflected in the inhibition of the activities of related oxidases and the enhancement of antioxidant enzyme activities.

1.1 Inhibition of oxidase activity

There are many oxidases in the organism, such as P-450 enzyme, xanthine oxidase (XOD), lipoxygenase, myeloperoxidase(MPO) and cyclooxygenase, which are related to the generation of free radicals. Studies have shown that many plant extracts have inhibitory effects on various oxidases described above, inhibiting free radical generation from the source. For example, quercetin and curcumin in flavonoids can inhibit the activity of iNOS during ischemia-reperfusion injury, thereby exerting an antioxidant effect.

1.2 Enhancement of antioxidant enzyme activity

The body has antioxidant enzymes that can remove and repair excess free radicals, such as catalase (CAT), glutathione peroxidase (GSH-Px), superoxide dismutase (SOD), and peroxidase and the like. Many studies have shown that antioxidants in plant extracts not only protect antioxidant enzymes in the body, but also enhance the activity of antioxidant enzymes in the body. For example, quercetin in flavonoids can reduce the oxidative damage of islet β cells, and it can also restore the activity of SOD, GSH-Px and CAT in animals with Fe2+-induced renal cell injury. Saponins have little effect on oxygen free radicals, but most of them can increase the activity of antioxidant enzymes such as SOD and CAT in vivo, thus enhancing the anti-oxidation function of body.

2 Complementarity and synergy between antioxidant components

There is a complementary and synergetic relationship between the antioxidant components of plant extracts, which exert antioxidant effects by transferring electrons and/or protons in the human body, acting on oxidases and antioxidant enzymes, chelating and inactivating transition metal ions. Study have found that there were significant synergistic effects between different concentrations of tea polyphenols and American ginseng, and the synergistic effects increased with the increase of concentrations.

3 Direct removal or inhibition of free radicals

Plant extracts can directly remove or inhibit free radicals by providing hydrogen protons or electrons, terminating the chain reaction of free radicals, and exerting antioxidant functions.

3.1 Providing protons

Most of the antioxidants are oxygen radical scavengers such as polyphenols, sterols, VE. One of the reasons is that it can release small hydrogen protons to capture high-potential, active free radicals, and convert them into an inactive or relatively stable compound, while transforming themselves into more stable substances than the radicals generated by the oxidative chain reaction, thereby interrupting or delaying the chain reaction.

3.2 Providing electronics

Another reason why plant extracts exert antioxidant effects is that they can scavenge free radicals by directly giving electrons by electron transfer. Such plant extracts include polyphenols, plant polysaccharides, vitamins and the like. β-carotene has good antioxidant properties and can suppress the generation of reactive oxygen by providing electrons, thereby achieving the purpose of scavenging free radicals. VC is converted into semi-dehydroascorbic acid and dehydroascorbic acid by supplying electrons step by step to achieve the purpose of scavenging active oxygen radicals.

4 Chelation and passivation of transition metal ions

Transition metal ions, such as Fe2+ and Cu2+, are necessary in the oxygen radical generation process. For example, Fe2+ can both mediate lipid peroxidation and it is also a catalyst for the generation of free radicals. The flavonoids in the plant extract have 4-keto group, 5-hydroxyl molecular structure, and the vicinal hydroxyl group at the 3' and 4' positions of the B ring contains a lone pair of electrons, so that they can chelate metal ions. The antioxidant components capable of chelation and passivation of transition metal ions by electron coordination include tannins, polysaccharides, active peptides, phytic acid, citric acid, and so on.