Effect of ultra-violet radiations in health and diseases

The term UV is described “beyond violet” according to light spectra and is of three different types: UVC, UVB and UVA. UV radiations act as strong environmental mutagen due to their property of ionisation and inducing chemical reactions and are capable of forming skin diseases like cancer. Skin with its larger surface area comes in direct contact with the environment and becomes the most vulnerable organ system.

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The epidemiological demonstrations have shown that sunlight plays a role in malignant melanomas. There have been found significant genetic factors in human skin cancer from UV radiation which is characterized by hyper-susceptibility. The phenotypic characters associated with skin cancers are fair complexion, light eye colour, light original hair colour, poor ability to tan and frequent sunburn. Skin plays an important interface between humans and their physical, chemical and biological environment. It becomes essential to understand the physiological and biochemical aspects of percutaneous absorption and the factors which enhance cutaneous penetration and pathological patterns in response to environmental injury.

When UV radiations strike the skin, its ionising energy can be absorbed. DNA is one of the major UV-absorbing molecules resulting in accumulation of genetic mutations and eventually the malignant transformation of the cell. The skin has its adaptive immune system with APCs, Langerhans cells and T-cell receptors including CLA, CCR4 and CCR6. Keratinocytes on activation act as a component of cutaneous immune system secretes cytokines, chemokines, and ICAM-1 and MHC-II expressions. UV activates the cutaneous immune system by producing an inflammatory response. The first defence against radiation injury is melanin produced by melanocytes, serves as protective agent. Melanin synthesis is started with tyrosine in presence of copper-protein complex tyrosinase and oxygen which is transformed to dihydroxyphenylalanine or dopa.

UV radiations lead to various forms of skin cancers, melanomas are the most common skin cancers. Melanomas are formed by short wave UVR. At molecular level UV leads to CC>TT double base substitutions and C>T substitution at di pyrimidines associated with p53 mutations. UV also causes ROS generation leading to DNA damage. A defect in effector proteins of NER pathway leads cancer resistance. MC1R is involved in pigmentation, adaptive tanning response and skin cancer susceptibility. It’s signaling leads to PKA activation which increases the melanogenic enzyme activity and enhancing melanin production by melanocytes. MC1R mutations commonly referred as RHC variants are associated with up to four-fold increased risk of melanoma and skin cancers.

Despite with side effects, UV is associated with several health benefits. According to ITA a base tan can act as “body’s natural protection against sunburn”. UV induced tan produces SPF of 3-4 and plays role in UV induced photo-protection. Pre-vitamin D3 generation is induced by UVB radiations. Low level of vitamin D increases the risk of several types of cancers, heart diseases and bone diseases. A daily amount of sun exposure produces enough percutaneous vitamin D3 to meet day-to-day requirements. UV is also useful in photo-therapies, a radiation based treatments for skin diseases. PUVA is the most common photo-therapy and response to any immune-mediated skin disease including cutaneous T-cell lymphoma.

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