Age-related changes in carcinogen metabolism

[Epidemiological, pathological and prognostic characteristics of bladder cancer in elderly patients]

AIM

To define and present explanations for the epidemiological, pathological and prognostic differences in bladder cancer in elderly patients.

METHOD

Bibliographical search was performed from the Medline bibliographic database (NLM Pubmed tool) and Embase focused on: bladder cancer, carcinogenesis, elderly, epidemiology, prognosis.

RESULTS

Bladder cancer is a growing concern for the elderly first and foremost and with an impact, mainly those who are consumers or former users of tobacco, whose therefore frequently have comorbidities associated with this consumption. The initiated carcinogenesis extends with the life length of patients, increasing the prevalence of bladder cancer. Aging promotes carcinogenesis by both potentiating its genetic abnormalities and reducing the immune system performance of the aged host to destroy cancer cells. The delay in the diagnosis of bladder cancer in elderly patients is explained and make up for the time could improve the prognosis.

CONCLUSION

Regardless of variations in therapeutic effect and morbidity and mortality of treatments, aging promotes the occurrence and aggressiveness of bladder cancer. The incentive to stop exposure to carcinogens and the search for bladder cancer in patients with hematuria should not reduce with advanced age but instead be promoted in order to improve the prognosis.

My Winding Road: From Microbiology to Toxicology and Environmental Health

I would certainly never have predicted that I would become the director of the National Institute of Environmental Health Sciences (NIEHS) and the National Toxicology Program (NTP) when I was a Jewish girl growing up in Teaneck, New Jersey. My family stressed the importance of education. Yet for a girl there were many not-so-subtle suggestions that the appropriate careers were in teaching or nursing, and the most important thing was to be a wife and mother. Well, I can't disagree with the latter, although I would have to add grandmother to that list of achievements. My parents were both college graduates, but my mom only taught high school English for one year before leaving the field to start our family. My dad returned from World War II and joined his brother in accounting. After my first sister was born, my father joined my mother's family jewelry business and helped to open a second retail store. My mother helped my dad out during the busy times—Christmas and wedding season—but otherwise focused on our growing family of three girls and one boy. This became increasingly challenging when it became clear that my little brother was severely retarded and would require extra care.

Use of physiologically based pharmacokinetic modeling to investigate individual versus population risk

Because of the heterogeneity of the human population, it is generally expected that there will be a broad range of observed susceptibilities to the biological effects of exposure to chemicals or drugs. Often it is possible to distinguish specific classes of individuals, such as infants or the elderly, who appear to be more susceptible to a specific effect. Non-cancer risk assessment often address this variability by dividing the experimentally determined acceptable exposure level by an uncertainty factor of 10 to protect sensitive individuals; cancer risk assessments typically do not address this issue in any quantitative fashion. Physiologically based pharmacokinetic (PBPK) modeling provides the capability to quantitatively describe the potential impact of pharmacokinetic factors on the variability of individual risk. In particular, PBPK models can be used to determine the impact of differences in key metabolism enzymes, whether due to multiple genotypic expression, such as cytochrome P450 polymorphisms, or just due to normal variation in enzyme activities within the general population. Other potential modulators of sensitivity which can be addressed quantitatively with a PBPK model include physical condition, level of activity, disease states, age, hormonal status, and interactions with other chemicals and drugs. In each case, the PBPK model provides a quantitative structure for determining the effect of these various factors on the relationship between the external (environmental) exposure and the internal (biologically effective) target tissue exposure. When coupled with Monte Carlo analysis, the PBPK model provides a method to assess the quantitative impact of these sources of variability on individual risk (as opposed to average population risk) by comparing model-predicted risks over the distribution of individual parameter values.

Biology of aging as related to cancer

The relationship of the biology of aging to cancer in older patients is of importance at several levels. The striking increase of cancer incidence with age may be related to a number of biologic factors. Potential age-related etiologic factors include decreased immune surveillance, longer duration of carcinogenic exposure, increased susceptibility of cells to carcinogens, decreased DNA repair, oncogene activation or amplification, and defects in tumor-suppressor genes. Moreover, at the cellular level, the uncontrolled proliferation characteristic of cancer and the reduced proliferation characteristic of senescence may be "opposite sides of the coin," governed by similar mechanisms of gene regulation. The biologic behavior of neoplasma, once initiated, may vary in different age groups depending on tumor type, immune system status, and alterations in other regulatory factors such as angiogenesis. In the clinical approach to the older cancer patient, attention to age-related biologic changes leading to decreased homeostatic reserve, especially in such areas as the hematopoietic, renal, immune, and cardiovascular systems, is essential to the designing of successful therapies.

Age- and gender-related changes in the hepatic metabolism of 2-methylpropene and relationship to epoxide metabolizing enzymes

The effect of age and gender on the in vitro biotransformation of 2-methylpropene, an alkene metabolized to 2-methyl-1,2-epoxypropane, was studied. The epoxide concentration and the epoxide metabolizing enzymatic activities were investigated in male and female Brown Norway rats of different ages. Liver tissue of senescent rats was exposed to smaller 2-methyl-1,2-epoxypropane concentrations than that of young animals, although changes during ageing were rather modest. With advancing age a feminization of male glutathione S-transferase and cytosolic epoxide hydrolase activities was found, as well as a significant decline of the female microsomal epoxide hydrolase activity and an increase of the cytochrome P-450 content in the oldest female rats.

Effects of caloric restriction on rodent drug and carcinogen metabolizing enzymes: implications for mutagenesis and cancer

Caloric restriction in rodents results in increased longevity and a decreased rate of spontaneous and chemically induced neoplasia. The low rates of spontaneous neoplasia and other pathologies have made calorically restricted rodents attractive for use in chronic bioassays. However, caloric restriction also alters hepatic drug metabolizing enzyme (DME) expression and so may also alter the biotransformation rates of test chemicals. These alterations in DME expression may be divided into two types: (1) those that are the direct result of caloric restriction itself and are detectable from shortly after the restriction is initiated; (2) those which are the result of pathological conditions that are delayed by caloric restriction. These latter alterations do not usually become apparent until late in the life of the organism. In rats, the largest direct effect of caloric restriction on liver DMEs is an apparent de-differentiation of sex-specific enzyme expression. This includes a 40-70% decrease in cytochrome P450 2C11 (CYP2C11) expression in males and a 20-30% reduction of corticosterone sulfotransferase activity in females. Changes in DME activities that occur late in life in calorically restricted rats include a stimulation of CYP2E1-dependent 4-nitrophenol hydroxylase activity and a delay in the disappearance of male-specific enzyme activities in senescent males. It is probable that altered DME expression is associated with altered metabolic activation of chemical carcinogens. For example the relative expression of hepatic CYP2C11 in ad libitum-fed or calorically restricted rats of different ages is closely correlated with the amount of genetic damage in 2-acetylaminofluorene- or aflatoxin B1-pretreated hepatocytes isolated from rats of the same age and caloric intake. This suggests that altered hepatic drug and carcinogen metabolism in calorically restricted rats can influence the carcinogenicity of test chemicals.

Human acetylator genotype: relationship to colorectal cancer incidence and arylamine N-acetyltransferase expression in colon cytosol

Polymorphic expression of arylamine N-acetyltransferase (EC 2.3.1.5) may be a differential risk factor in metabolic activation of arylamine carcinogens and susceptibility to cancers related to arylamine exposures. Human epidemiological studies suggest that rapid acetylator phenotype may be associated with higher incidences of colorectal cancer. We used restriction fragment length polymorphism analysis to determine acetylator genotypes of 44 subjects with colorectal cancer and 28 non-cancer subjects of similar ethnic background (i.e., approximately 25% Black and 75% White). The polymorphic N-acetyltransferase gene (NAT2) was amplified by the polymerase chain reaction from DNA templates derived from human colons of colorectal and non-cancer subjects. No significant differences in NAT2 allelic frequencies (i.e., WT, M1, M2, M3 alleles) or in acetylator genotypes were found between the colorectal cancer and non-cancer groups. No significant differences in NAT2 allelic frequencies were observed between Whites and Blacks or between males and females. Cytosolic preparations from the human colons were tested for expression of arylamine N-acetyltransferase activity. Although N-acetyltransferase activity was expressed for each of the arylamines tested (i. e., p-aminobenzoic acid, 4-aminobiphenyl, 2-aminofluorene, beta-naphthylamine), no correlation was observed between acetylator genotype and expression of human colon arylamine N-acetyltransferase activity. Similarly, no correlation was observed between subject age and expression of human colon arylamine N-acetyltransferase activity. These results suggest that arylamine N-acetyltransferase activity expressed in human colon is catalyzed predominantly by NAT1, an arylamine N-acetyltransferase that is not regulated by NAT2 acetylator genotype.(ABSTRACT TRUNCATED AT 250 WORDS)

Age-related changes in biotransformation of azoxymethane and methylazoxymethanol in vitro

1. Age-related changes in hepatic hydroxylation of azoxymethane (AZO) to methylazoxymethanol (MAM), as well as colonic phase I metabolism of MAM by alcohol dehydrogenase (ADH) were examined in young (2-4 months), middle-aged (12-14 months), and old (22-24 months) male Fischer 344 rats. In addition, the possibility that colonic glucuronyltransferase might be involved in the biotransformation of MAM was also investigated. 2. A significant decrease in hepatic conversion of AZO to MAM was found in old vs young rats, concomitant with a decrease in hepatic cytochrome P-450 content, while no age-related difference was found in the colonic metabolism of MAM by ADH. MAM inhibition of colonic 4-methylumbelliferone glucuronyltransferase was non-competitive, suggesting indirectly that colonic glucuronyltransferase is not involved in conjugation of MAM. 3. It is concluded that ageing in the male Fischer 344 rat results in alternations of AZO and MAM biotransformation which indicate that AZO may be less carcinogenic in older rats.