Life span extension and cancer risk: myths and reality

A significant increase in the number of old people in the populations of de veloped countries was followed by an increase in morbidity and mortality re sulting from main age-related diseases cardiovascular, cancer, neurodegener ative, diabetes mellitus, decrease in resistance to infections. Obviously, the development of the means of prevention of the premature aging of humans is crucial for the realization of this program. However, data available on such kind of means are rather scarce, contradictory and are often not reli able from the points of view of the adequacy of the experiments to current scientific requirements as well as the interpretation of the results and sa fety. Data available on the increase in life span and the adverse effects o f the following geroprotectors were critically analyzed: antioxidants, chel ate agents and lathyrogens, succinate, adaptogens and herbs, neurotropic dr ugs, inhibitors of monoamine oxidase, glucocorticoids, dehydroepiandrostero ne, sex and growth hormones, melatonin, pineal peptide preparations, protei n inhibitors, antidiabetic biguanides, thymic hormones and peptides, immuno modulators, enteroadsorbents, lypofuscin inhibitors, as well as calorie int ake restriction and special diets. Most of the available results were insuf ficient and could not provide convincing evidence for the life span extensi on and the safety of the suggested geroprotectors. Drugs and means prolongi ng the life span could be subdivided into three groups: (a) geroprotectors prolonging the life span equally in all the members of the population: thes e postponed the beginning of the population's aging; (b) geroprotectors dec reasing the mortality rate in a long-lived subpopulation, which raised thei r maximal Life span: these slowed down the population's aging rate; (c) ger oprotectors increasing the survival rate in a short-lived subpopulation wit hout changes in the maximal life span: in this case, the aging rate increas ed. There was a high positive correlation between the type of geroprotector -induced aging delay and the pattern of tumour development in the same popu lation of animals. The first type of geroprotectors did not influence the i ncidence of tumour but increased tumour latency. The second type of geropro tectors was effective both in the inhibition of spontaneous carcinogenesis and the increase in tumour latency. Certain drugs of the third type raised tumour incidence in the exposed populations. According to the multistage mo del, geroprotectors either inhibit or accelerate the passage of carcinogen- exposed cells form one stage to another. Thus, the efficacy of geroprotecto rs as preventive means of cancer development will decrease with respect to the age of exposure onset. Recommendations of the available drugs and means of life span increase should be carefully reconsidered under the internati onal scientific control. (C) 2001 Elsevier Science Inc. All rights reserved .