Anti-aging and aging factors in life. The role of free radicals☆

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Abstract

The present review deals with some factors determining the anti-aging as well as the aging process. In order to get a deeper insight in the subject matter, firstly some less known spectroscopic and kinetic data of antioxidant vitamins (C, E, β-carotene) acting as anti-aging factors by electron transfer are briefly discussed. The generation of oxygen transients (OH, ROOradical dot, 1O2, ozone radicals, etc.) by sunlight, ultrasonic and microwave radiation are causing "oxygen stress" and contribute to early ageing is also reviewed. Particular attention is paid to external environmental aging factors. Their action is based on the incorporation of various pollutants contained in water and air in the human organism. In this respect the polycyclic aromatic hydrocarbons (PAHs) play an essential role by initiating DNA-mutation, leading to an accelerate aging, carcinogenesis and diseases.

Introduction

The aging is a very complex biological process. In addition to individual genetic factors also external influences, such as nutrition, smoking, alcohol, environmental conditions, etc. can strongly contribute to its anticipated appearance. A particular attention in this respect has been paid to the biological action of free radicals, especially to oxygen species (OH, peroxyl, ozone and other oxidizing species), which are causing "oxidative stress" (Stocker and Frei, 1991). It appears that these transients in addition to the nitrogen oxides are one of the major factors for a forced aging, DNA-damage, carcinogenesis and for initiation of a number of diseases.
It might be mentioned that the oxidizing and reducing free radicals generated in the human organism can also be produced by ionizing radiation in aqueous media. In such case it is possible to obtain each desired kind of transients, such as OH (hydroxyl), ROradical dot (alkoxyl), ROOradical dot (peroxyl), NOradical dot (nitric oxide), ONOO− (peroxynitrite) as well as radical cations, radical anions, ozonides, etc. in wanted concentration in a given media. Consequently, using radiation, more precise studies can be performed on model systems for a better understanding of involved mechanisms and for development of preventive anti-aging measures.
Based on these premises a brief overview is presented on less known formation and characterization of the most important free radicals resulting from the antioxidant vitamins (β-carotene, E and C), which are involved in the anti-aging process. The antioxidant properties of flavonoides, polyphenols, etc. are also mentioned. The "oxidative stress" initiated by uv-light: formation and scavenging of singlet oxygen (1O2) and other reactive oxygen species, which are leading to an accelerated skin aging and carcinogenesis, plays nowadays a particular role for the population, is also briefly discussed (Kaiser et al., 1990; Lang et al., 2006). The involved reaction mechanisms and some protection measures are reviewed.

Section snippets

Water radiolysis and primary products

The living systems consists of more than 70% of water. By treatment of aqueous media with ionizing radiation the water is radiolyzed to reducing (eaq-, H) and oxidizing (OH) free radicals, as well as molecular products (H2, H2O2).
For better understanding of the subject matter, the formation of primary products of water radiolysis, their yields (G-values) and some common transformation reactions are compiled in Table 1. Thereby the "solvated electrons" (eaq-) represent the second form of the

Antioxidant vitamins

The vitamin C (ascorbate AH−), E (α-tocopherol) and β-carotene were taken as representatives of this group and some of their somewhat less known behaviors are briefly discussed. The antioxidant effect is based on the vitamin's ability to act as electron donor in various biological processes. After the electron ejection, β-carotene results in an oxidizing radical cation (β-carradical dot+). The same is valid for vitamin E, yielding (vit.Eradical dot+), whereas ascorbate converts into a neutral free radical (AHradical dot).

Protection of cell membrane damage by antioxidant vitamins

In general the biological cell membrane consists of lipoproteins, where also enzymes and 3–5% antioxidant vitamins (β-carotene, vitamin E and C) are also contained. Based on the above briefly mentioned spectroscopic and kinetic data of vitamins, an attempt was made to investigate their effect on the membrane protection. The studies concerned the electron transfer between them in airfree DMSO solutions. It was established a cascade electron transfer process with the following pathway: β-carotene

The nature of antioxidants. General considerations

Early investigations showed that the structure of a molecule, having substituents like –OH, –O−, –OPO3H−, –COO−, –NH2, –NH3CH3, –N(CH3)2, etc. can act as electron donor, that means they have antioxidant properties. This fact has been demonstrated by studies on formate (Zechner and Getoff, 1974), phenol and related compounds (Zechner et al., 1976; Grabner et al., 1977), aromatic amines (Köhler et al., 1977), flavines (Getoff et al., 1978), etc. In the last decades it was stated that the above

Formation of peroxyl radicals and action of antioxidant vitamins

The most reactive oxidizing species are the OH radicals. They can split off an H-atom or electron of an organic molecule. However, their preferred reaction sites are the double bonds. In the case of aromatic compounds, the OH-species react on various ring positions, where the ortho- and para-sites are the preferred ones. All resulting transients can subsequently add O2, resulting into peroxyl radicals. For illustration of the reaction mechanisms the absorption spectra and kinetics of

Effect of sunlight: generation of oxygen transients and ozone

The sunlight reaching the earth surface (λ ⩾ 315 nm) has a manifold effect on all life systems. Since oxygen in the atmosphere is in excited triplet state (3O2), it can be activated to the very reactive singlet state (1O2), where organic compounds, like chlorophyll, flavines, various phyto-dye-stuffs, etc. as well as inorganic materials, e.g. dust particles can act as sensitizer. Such substances can mediate energy or/and electron transfer, which can initiate cell damage.
Some basic sunlight

Ultrasonic radiation

Electromagnetic radiation with a frequency in the range of ×ばつ105 to about 108 Hz is indicated as ultrasonic radiation. It can lead to sonolysis of water, meaning water splitting to H and OH radicals, whereby in the presence of air peroxyl radicals are formed (El’Piner, 1964; Getoff, 1995): H+O2→HO2 (k=×ばつ1010 L mol−1 s−1),HO2⇌H++O2- (pK=4.8).
It might be noted that under certain conditions ultrasonic treatment of nutrients can evoke chemical changes, which consequently may contribute to the aging

Microwave radiation

It covers the electromagnetic radiation range from about ×ばつ108 up to 1012 Hz and is partly overlapping with the far infrared. It has broad practical application, e.g. as microwave oven for quick cooking (×ばつ109 Hz).
The heat results by excitation of dipoles of molecules with polar structure, e.g. water, amino acids, proteins and ions. In the last case the absorbed microwave radiation causes very intense motions and frictions, leading also to heat.
Microwave radiation can produce singlet oxygen (1O

Environmental influences

The strong development of various industries and the rapid growth of the world population in the last decades led to a rather heavy pollutant-overloading of the atmosphere and water resources. The combustion of fossil fuels (coal, oil, gas) in the industry and in caloric plants, as well as in private households are associated not only with the emission of NOx, SO2/SO3 (acid rain precursors) in addition to CO2 in the atmosphere (green house effect and damaging of the world climate), but also

Conclusion

In the present review some anti-aging as well as aging factors are very briefly discussed. Basic data characterizing vitamins (C, E, β-carotene), acting as anti-aging compounds and their protecting action of the cell membrane are reviewed. The production of reactive oxygen transients (OH, ROOradical dot, 1O2, ozone species, etc.) by sunlight, as well as by ionizing, ultrasonic and microwave radiation are leading to "oxygen stress". All these factors contribute to a forced aging. Finally, the PAH

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    ☆
    Presented in part at the First European Congress of Anti-Aging Medicine and Congress on Menopause Andropause Anti-Aging, October 18–21, 2006, Vienna, Austria.
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