Nutr Clin Pract. Feb;10(1) Role of antioxidants in health maintenance. Sardesai VM. Free radicals are produced in the body as by products of. Antioxidants neutralise the effects of free radicals, substances that damage the body`s cells, and have a role in disease prevention. Antioxidants are nature's way of protecting the body and cells from damaging free radicals. Free radicals are unstable molecules that are generated by sun.
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Lass A, Sohal RS. Melanin, the pigment deposited by melanocytes, is the first line of defense against DNA damage at the surface of the skin, but it cannot totally prevent skin damage. A second category of defense is repair processes, which remove the damaged biomolecules before they can accumulate and before their presence results in altered cell metabolism.
Additional UV protection includes avoidance of sun exposure, usage of sunscreens, protective clothes, and antioxidant supplements. Ultraviolet radiation UVR is an essential risk factor for the development of premalignant skin lesions as well as of melanoma and nonmelanoma skin cancer. Skin cancer generally develops in the epidermis the outermost layer of skin , so a tumor is usually clearly visible, which makes it easier to detect.
There are various types of skin cancer. One main class is formed by the cutaneous melanocytes—melanoma. The other main types are basal cell carcinoma and squamous cell carcinoma, cancers of the epithelial cells. While exposure to UVR is the risk factor most closely linked to the development of skin cancer, other environmental factors such as ionizing radiation, chronic arsenic ingestion, and immunosuppression and genetic factors such as family history, skin type, and genetic syndromes also potentially contribute to carcinogenesis.
UVR exposure appears to promote the induction of skin cancer by two mechanisms. The first involves direct mutagenesis of epidermal DNA, which promotes the induction of neoplasia. The second is associated with immune suppression, which allows the developing tumor to escape immune surveillance and grow progressively [ 1 ]. It is known that UVR exposure results in photochemical modification of the genetic material DNA , but most of this damage is accurately and efficiently repaired by the cell.
However, if the amount of damage is too great, some of the alterations to the DNA may remain as permanent mutations. Most of the DNA breakages are repaired by proteins present in the cell nucleus, but unrepaired genetic damage of the DNA can lead to skin cancers. As already mentioned previously, solar UVR induces a variety of photoproducts in DNA, including cyclobutane-type pyrimidine dimers, pyrimidine-pyrimidone 6—4 photoproducts, thymine glycols, cytosine damage, purine damage, DNA strand breaks, and DNA-protein crosslinks.
It has been proposed that if unrepaired damage occurs to regulatory genes e. In this context, mutations to and activation of genes may be important. Other responses likely to result from UVR exposure of cells include increased cellular proliferation, which could have a tumor-promoting effect on genetically altered cells, as well as changes in components of the immune system present in the skin [ 2 ].
Solar radiation was tested for carcinogenicity in a series of exceptional studies in mice and rats. Large numbers of animals were studied, and well-characterized benign and malignant skin tumors developed in most of the surviving animals. Although the reports are deficient in quantitative details, the results provide convincing evidence that sunlight is carcinogenic for the skin of animals [ 3 ].
Although DNA damage due to reactive oxygen species formation is not a rare event since it is estimated that human cell sustains an average of 10 5 oxidative hits per day due to cellular oxidative metabolism [ 4 ], DNA is functionally very stable, so that the incidence of cancer is much lower than one would expect, taking into account the high frequency of oxidative hits.
It seems that in rapidly dividing epithelium, such as the epidermis, nuclear damage triggered by some xenobiotics may not be so important because of the constant introduction of new healthy cells, whereas a DNA mutation has a much higher probability to become fixed to a transformed phenotype in tissues e. This may explain at least in part why the absolute number of clinically well-recognizedhuman skin carcinogens is so small.
The specific mutations needed to activate an oncogene would be rarer. However, clonal expansion increases by 1,fold the number of targets for the next mutation and increases the probability of tumor formation. It is widely believed that cancer development inhumans and laboratory animals is caused by sequential mutations and clonal outgrowth of somatic cells. Most important oxidative damage prevention mechanisms include antioxidative enzymatic and nonenzymatic defenses as well as repair processes.
But the problem arises with age, when endogenous antioxidative mechanisms and repair processes do not work anymore in the effective way. The identification of free radical reactions as initiators and promoters of the cancer process implies that interventions aimed at limiting or inhibiting these factors should be able to reduce the rate of cancer incidence.
There still remains the answer regarding controversial data on the use of synthetic antioxidants in cancer prevention and treatment. Although the skin possesses an elaborate antioxidant defense system to deal with oxidative stress, excessive and chronic exposure to UV light or other oxidizing agents e.
A biological antioxidant has been defined as any substance that when present at low concentrations compared to those of an oxidizable substrate significantly delays or prevents oxidation of that substrate [ 6 ].
Antioxidant functions are associated with lowering oxidative stress, DNA damage, malignant transformation, and other parameters of cell damage in vitro as well as epidemiologically with lowered incidence of certain types of cancer and degenerative diseases. However, increased or prolonged free radical action can overwhelm ROS defense mechanisms, contributing to the development of cutaneous diseases, disorders, and skin cancer. The two main categories of antioxidant defenses are those whose role is to prevent the generation of ROS and those that intercept any radicals that are generated [ 7 ].
The defense system exists in aqueous and membrane compartments of cells and can be enzymatic and nonenzymatic. A second category of natural antioxidants are repair processes, which remove the damaged biomolecules before they accumulate to cause altered cell metabolism or viability [ 7 ]. The skin is equipped with a network of protective antioxidants. They include enzymatic antioxidants such as glutathione peroxidase, superoxide dismutase and catalase, and nonenzymatic low-molecular-weight antioxidants such as vitamin E isoforms, vitamin C, glutathione GSH , uric acid, and ubiquinol [ 8 ].
Various other components present in skin are potent antioxidants including ascorbate, uric acid, carotenoids, and sulfhydrils. Water-soluble antioxidants in plasma include glucose, pyruvate, uric acid, ascorbic acid, bilirubin, and glutathione. Lipid-soluble antioxidants include alpha-tocopherol, ubiquinol, lycopene, -carotene, lutein, zeaxanthin, and alpha-carotene. In general, the outer part of the skin, the epidermis, contains higher concentrations of antioxidants than the dermis [ 9 , 10 ].
In the lipophilic phase, -tocopherol is the most prominent antioxidant, while vitamin C and GSH have the highest abundance in the cytosol. On molar basis, hydrophilic nonenzymatic antioxidants including L-ascorbic acid, GSH, and uric acid appear to be the predominant antioxidants in human skin [ 11 ]. Their overall dermal and epidermal concentration are more than to fold greater than those found for vitamin E or ubiquinol.
The antioxidant capacity of the human epidermis is far greater than that of dermis. This was demonstrated in the studies by Shindo et al.
The role of vitamins, antioxidants
The cell damage will cause the release of free radicals. These free radicals will play an important role in any bioactive process of the cells. Chapter 1. The Role of Antioxidants in Human Health. Saikat Sen* and Raja Chakraborty. Creative Educational Society's College of Pharmacy, Kurnool, Andhra. Oxidative stress initiates structure and function alterations of key biomolecules. •. The oxidant/antioxidant unbalance activates factors.