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Antioxidants Description and Overview Essay

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Updated: Jun 23rd, 2022

Pomegranate is a fruit crop belonging to the order Myrtales and the genus Punica. There are two species of pomegranate, the Punica granatum, and Punica protopunica. P. granatum originates from Yemen (Socotra Island) and is believed to be crucial in the ancestry of the present cultivated form of pomegranate. On the other hand, there has been controversy revolving around the family to which P. granatum L. belongs. Early morphological studies suggest that the species should be classified under the Lythraceae family; nevertheless, its distinct features, including the presence of pulpy seeds with edible sarcotesta, fruits with lethargy pericarp, the unicellular archesporium, and ovules with multilayers of the outer integument, indicate that P. granatum L. differs from typical plants found within the genera. As a result, it was categorized under a different family, Punicaceae. The word “punica” dates back to the 18th century and was given by C. Laneus. In Leighman terms, P. granatum L. is often referred to as the “seeded apple” or “granular apple”. Pomegranate has been a popular fruit crop since the 18th century due to its ability to withstand drought conditions, therefore, cultivated in arid areas.

The peroxidation of lipids entails three steps which consist of initiation, propagation, and termination. The initiation phase is triggered by the reaction of an activated oxygen species with a lipid substrate (allylic hydrogen), forming a carbon-centered lipid radical. This is followed by the propagation phase, in which the lipid radical reacts with oxygen to form a lipid peroxy radical (LOO). The LOO abstracts a hydrogen atom from other lipid molecules creating a lipid hydroperoxide (LOOH). The activity of antioxidants manifests in the termination phase; it is at this stage that the antioxidants, for instance, vitamin E, donate a hydrogen atom to LOOH, forming a corresponding antioxidant radical that reacts with another to create non-radical products. As a result, it is evident that antioxidants are crucial for reducing the reactive oxygen species resulting from lipid peroxidation, thereby preventing oxidative stress. It is essential to note that the initiation of lipid peroxidation has to reach termination.

Vitamin A also referred to as retinoic acid, is obtained from both plant and animal sources. All-trans retinol, the parent compound, is regarded as the most abundant dietary form of vitamin A. On the other hand, retinoic acid and retinal are minor dietary components. Although it is not a popular antioxidant, research has illustrated its efficacy in disrupting the etiology of several diseases, including inhibiting viral hepatitis and hepatocellular carcinoma. All-trans-retinol plays a crucial role in the inhibition of hepatic stellate cells, which is central in the occurrence of hepatocellular carcinoma. Its mechanism of action, especially that of all-trans-retinol, is centered on inducing glutathione transferase and superoxide dismutase activities while reducing malondialdehyde and reactive oxygen species, thereby enhancing antioxidant enzyme activity.

Vitamin C, also known as ascorbic acid, is the most efficacious antioxidant. It is located in the aqueous phase of cells, which is the cytosol. It protects biomembranes from lipid peroxidation injury through the elimination of peroxy radicals in the aqueous phase prior to the initiation of peroxidation. It also prevents lipid peroxidation by preventing the formation of nitrosamine that produces the reactive nitrogen species. In addition to its hydroxyl radical scavenger and superoxide, ascorbic acid acts as a co-factor. It has been noted to boost the antioxidant properties of vitamin E, which also helps in controlling lipid peroxidation occurring within the cellular membranes and nuclear materials. Nevertheless, it is essential to note that it can also act as a pro-oxidant in specific conditions, which contrasts with its antioxidant properties. When in high concentration, vitamin C induces reactive oxygen species production inside cells, bringing about injuries to the mitochondrial membrane. Due to this characteristic, it has been proposed to kill cancer cells as it induces a pro-oxidant effect selectively.

Vitamin E is the primary antioxidant vitamin that protects tissues against free radical damage by neutralizing free radicals and preventing the oxidation of lipids within membranes. Vitamin E is a fat-soluble antioxidant that exists as either a-tocopherol or tocotrienol, which occurs in the alpha, beta, gamma, and delta forms. Alpha-tocopherol is the main form of vitamin E with potent antioxidant and immune functions. It has been revealed to be a more inhibitor of exercise-induced oxidative stress. Furthermore, it protects the cell membranes from lipid peroxidation resulting from lipid peroxyl free radical scavenging and superoxide radical anion. Lastly, alpha-tocopherol disrupts oxidative stress caused by high toxic metal concentrations in the body, for instance, lead and BPA. Gamma-tocopherols have excellent antioxidant activity and have been shown to reduce inflammation and oxidative stress.

Catalase exists in most animal cells as a protective enzyme. It is an enzyme responsible for the degradation of hydrogen peroxide (H2O2), produced from the beta-oxidation of fatty acids, purine catabolism, respiration, and water and molecular oxygen. This biological reaction has to occur in the presence of a co-factor that comprises iron or manganese. Catalase activity is abundant in cells located in the kidney, liver, and red blood cells. It is located in peroxisomes and absent in mitochondria; as a result, hydrogen peroxide degradation in the mitochondria is performed by another enzyme, glutathione peroxidase. Catalase reacts with hydrogen donors, such as ethanol, methanol, formic acid, or phenols, with peroxidase activity. The mechanism of action of the enzyme occurs in two steps. First, a hydrogen peroxide molecule oxidizes a heme group to form an oxyferryl species. At the same time, one oxidation equivalent is removed from the iron in the heme compound, creating a porphyrin ring. In the second phase, the other H2O2 molecule acts as a reducing agent by regenerating the resting state enzyme to water and oxygen. At a normal level, H2O2 helps regulate a variety of cellular activities, such as cell proliferation and activation. However, at high levels, it is associated with damaging effects. Therefore, this insinuates that the capacity of catalase to maintain hydrogen peroxide levels within the normal standards is crucial for physiological processes.

Glutathione peroxidase is an antioxidant that is located in almost every cell in the body. It usually plays a role in the detoxification of drugs and xenobiotics. It is an essential intracellular enzyme that degenerates hydrogen peroxide into water and lipid peroxides into their corresponding alcohols. This process often takes place in the cytosol and mitochondria. There are two types of glutathione in the body, namely, the reduced and oxidized glutathione. Either of the types can be readily converted into another. However, it is often present in its reduced state in normal conditions, with only a little concentration being found in its fully oxidized form. It functions as a co-factor for several enzymes consisting of glutathione transferase, glutathione reductase, and GPx. Reduced glutathione acts as a hydrogen donor in the degradation of H2O2. It can either be formed in the body naturally or be introduced into the body as a dietary supplement.

As a dietary supplement, the enzyme is associated with the prevention in the progression of several complex diseases. This has been noted in its capabilities to improve liver abnormalities, improve diabetic complications, protect from viral infections, and anti-tumor activity. Its synthetic version is even administered in the treatment of autism. Furthermore, it is essential to note that its synthetic components have not been associated with any adverse reactions; therefore, the drug can be classified as non-toxic. In addition, it has been noted even to neutralize the detrimental effects resulting from excessive intake of other amino acids. Glutathione oxidase has exhibited antimelanogenic properties that comprise stimulating pheomelanin synthesis instead of the darker eumelanin and inhibiting the intracellular transportation of melanogenic enzymes. It is essential to note that the physiological distinction between the two forms of enzymes is unclear, particularly when it comes to melanogenesis.

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