Effects of factors prolonging life span on carcinogenesis

Aging, increasing genomic entropy, and neurodegenerative disease

The genome, as biologic information, can be conceptualized in terms of entropy. The second law of thermodynamics dictates that entropy must increase over time. Consequently, aging can be viewed as increasing genomic entropy. Genetic instability is the biophysical correlate of increasing genomic entropy. Rates of increasing genomic entropy can be determined from age-specific mortality rate dynamics (e.g., Parkinson's disease and amyotrophic lateral sclerosis). These observations are consistent with a model of neurodegenerative disease as a manifestation of increasing genomic entropy with aging.

Aging, genomic entropy and carcinogenesis: implications derived from longitudinal age-specific colon cancer mortality rate dynamics

Many types of cancer are intrinsically linked to the process of aging. Aging, from the perspective of the second law of thermodynamics, can be viewed as associated with the inevitable and natural increase in informational entropy of the genome. The molecular biologic basis of increasing genetic informational entropy is the inherent and variable instability of different regions of genome. Colon cancer cells have been shown to have characteristic acquired genetic abnormalities, most commonly, deletions in presumed tumor suppressor genes. Age-specific colon cancer mortality rates in the US from 1958 to 1988 were subjected to longitudinal Gompertzian analysis, a method that may identify and distinguish among genetic, environmental and competitive influences upon mortality. The Strehler-Mildvan modification of the Gompertz relationship between aging and mortality can be used to determine a relative measure of the rate of increase in informational entropy (a reflection of genetic instability) for those genetic factors that are involved in the pathogenesis of colon cancer.

Carcinogenesis induced by a single administration of 1,2-diethylhydrazine in female rats of various ages

Three- or fourteen-month-old female L10 rats were exposed to a single intravenous injection of 1,2-diethylhydrazine (SDEH) at 150 mg/kg of body weight. At the 95th week after carcinogen treatment when the experiment was stopped, 30.7% and 4.5% of rats from the younger and older groups survived, respectively. Total tumor incidences were 68.8% and 84.6%, respectively, in rats treated with SDEH at the age of 3 or 14 months vs. 18.2% and 34.5% in corresponding young and old controls (P < 0.01). Leukemias, thyroid adenomas, uterine tumors and mammary malignancies developed more frequently in animals exposed to carcinogens than in control groups. No age-related differences in tumor incidence or localization between rats exposed to SDEH at various ages were observed, but tumors developed earlier in older groups than in younger groups. The results supported the suggestion that the accumulation of initiated cells in some tissues during natural aging is a cause of the age-related increase in cancer incidence.

Effect of neonatal exposure to 5-bromo-2'-deoxyuridine on life span, estrus function and tumor development in rats--an argument in favor of the mutation theory of aging?

Outbred LIO rats were exposed to subcutaneous injections (3.2 mg) of a synthetic analogue of thymidine, 5-bromo-2'-deoxyuridine (BrdUrd), on days 1 and 3, or days 1, 3, 7 and 21 of postnatal life. The mean life span decreased by 31% and 38% in male and by 14% and 27% in female rats that received 2 and 4 injections of BrdUrd, respectively, in comparison to untreated controls. The opening of the vagina was delayed, whereas age-related changes in the length of the estrous cycle and in the incidence of persistent estrus and/or anestrus were observed earlier in BrdUrd-injected female rats than in untreated ones. Inhibition of compensatory ovarian hypertrophy induced by hemiovariectomy at the age of 3 months was found in females exposed neonatally to BrdUrd as compared to untreated rats, while the uterus weight increase induced by the administration of human chorionic gonadotropin was similar in both control and BrdUrd-treated infantile rats. These data suggest that exposure to BrdUrd in early life impairs pituitary gonadotropic function in female rats. It was also shown that neonatal administration of BrdUrd to rats doubles the incidence of chromosome aberrations in peripheral blood lymphocytes in comparison to controls and is followed by a dose-related increase in tumor incidence. Our observations on the decrease in mean and maximum life span, acceleration of age-related changes in reproductive system function, increase in chromosome aberration and tumor incidence and decrease in tumor latency in rats exposed to BrdUrd in early life suggest that this model could be used as a model of accelerated aging and that some of the results can be interpreted as arguments in favor of the mutation theory of aging.