Free radicals in skin aging processes

Under the mysterious name “free radicals” is the most important cause of accelerated aging of the skin, the entire body and also the cause of many diseases.

Every organism and tissue ages. The natural process of intrinsic (endogenous) aging is the result of the predominance of destruction processes over regeneration of the body that occurs with age. We have limited influence on these processes, largely dependent on genes and predisposition. The greater challenge responsible for accelerating these processes is extrinsic (exogenous) aging. Tissues, enzymes, the body’s regenerative systems, genetic material are damaged and mutations occur. In the skin, this manifests itself as a reduction in the total thickness of the epidermis, though thickening of its stratum corneum, damage to collagen and elastin structures. Discoloration and telangiectasias also appear. The skin becomes gray, dry, with an uneven color, its elasticity decreases and wrinkles form.

Exogenous aging is caused by environmental factors and the most important culprit is free radicals. UV radiation is mainly responsible for their formation, but also other physical and chemical factors, such as smoking.

UV radiation carries energy and affects the functioning of organisms.

The type of this impact and interactions on the tissue is strongly related to the energy of the radiation. This energy is greater the shorter the electromagnetic wavelength (higher frequency). Light is such an electromagnetic wave.

Visible light (400 – 800nm) activates many processes essential for life. UVA and UVB radiation (280-400nm) can cause adverse changes in biological structures, while UVC radiation (100-280nm) destroys proteins and nucleic acids.

This radiation can reflect off matter, scatter, but also be absorbed (absorbed) acting on the tissue. The mechanisms for this are varied, sometimes quite complex.

All photochemical processes start with excitation – M + hn = M*

The excited molecule undergoes a transformation so that the energy can be passed on somewhere. There may be fluorescence (light emission), deactivation with heat generation or a change in the energy of the molecule (energy transition). Primary reactions such as isomerization of the molecule may also occur.

The products of these transformations undergo further secondary reactions such as fluorescence or deactivation.

Primary reactions, on the other hand, can lead to the formation of free radicals

The excited molecule undergoes homolytic disintegration, that is, some chemical bond between atoms is symmetrically broken) Different bonds require different energy to break. The bond between O-O oxygen atoms is the easiest to break, O-H the hardest.

After the molecule is broken into 2 fragments, the excess energy is divided into 2 parts. At each remains an electron that is part of the broken bond. A molecule with such an unpaired electron is called a radical. He has excess energy that he needs to give away somewhere.

A chain reaction occurs and free radicals undergo secondary reactions.

R.+ A = R + A.

A.+ B = A + B. …….

A.= C + energy

A.+ B.= C

The oxygen molecule also undergoes these reactions.

“Ordinary” oxygen is two-atom O2. There may also be “aggressive” two-atom oxygen (singlet oxygen) 1 O2

It is formed in the atmosphere from tropospheric ozone under the influence of UV radiation. It can also be formed in the skin from “ordinary” oxygen, but it doesn’t happen so easily, and in addition to UV radiation, you need a sensitizer, a compound that easily absorbs UV radiation. In the atmosphere, it’s oxygen (ozone) and pollutants such as nitrogen oxides.

In the skin, on the other hand, it’s oxygen, some endogenous compounds (porphyrins), drugs, cosmetic ingredients, fragrances, etc. Strong sensitizers are, for example, sulfonamides, anti-inflammatory drugs,antibiotics, dyes in cosmetics, plant products (St. John’s wort, citrus oils, etc.) The more sensitizers there are, the more dangerous UV radiation is in its effects.

The sensitizer initially undergoes excitation under the influence of absorbed energy and then the bond in its molecule breaks down, resulting in the formation of radicals.

Ozone in the upper atmosphere is useful, absorbing UVC radiation without allowing it to reach the ground. In the lower layers of the atmosphere, it is formed by the action of solar radiation on environmental pollutants and is a source of very active, harmful singlet oxygen. Nitrogen oxides are an indirect source.

NO2 + hn = NO* + O*

O2 + O* = O3

The final result is singlet oxygen.

The result of these processes is the formation of photosmogs. Car exhaust (hydrocarbons + nitrogen oxides) under bright sunlight causes radical oxidation of nitrogen compounds. In addition to the formation of ozone, reactions with olefins take place – nitroolefins are formed. The pollution profile changes over time. In the morning there is a preponderance of hydrocarbons and NO contained in the exhaust gas, while in the afternoon the content of oxidation products increases.

The radical reactions that occur under UV radiation are very destructive to the body. Free radicals accelerate aging, destroy intercellular cement lipids, cell walls, damage enzymes, destroy collagen, elastin and glcosaminoglycans. They cause changes in the structure of nucleic acids resulting in the inability to continue DNA replication but also mutations and carcinogenesis resulting in skin cancer.

Reactions triggered by free radicals cause damage to stratum corneum lipids, inflammation of the epidermis. The correct structure of lipid structures is determined by the presence of linoleic acid. Other unsaturated acids are essential for the synthesis of tissue hormones – eicosanoids – and are particularly sensitive to UV exposure. Undergo isomerization and oxidation which damages the epidermal barrier structure. The skin becomes excessively dry.

Anti-free radicals and UV radiation inhibit the effects of exogenous aging factors. It is necessary to protect against UV radiation through filters and sunscreens. Use substances that neutralize free radicals, such as vitamins C, E, beta carotene and flavonoids. The body also has its own protective mechanisms. Such factors include melanin, enzymes (SOD, catalase), glutathione and other natural anti-radicals, metal complexes such as copper. An unhelpful effect of the body’s protective processes is excessive keratinization and melanogenesis in the skin.

Free radicals are a factor whose role is crucial to understanding and counteracting skin aging.

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