Mutagenic outcome of the urinary carcinogen 4-aminobiphenyl is increased in acidic pH

Non-innocuous Consequences of Metabolic Oxidation of Alkyls on Arenes

Reactive metabolite (RM) formation is widely accepted as playing a pivotal role in causing adverse idiosyncratic drug reactions, with most attention paid to drug-induced liver injury. Mechanisms of RM formation are determined by the drug's properties in relation to human enzymes transforming the drug. This Perspective focuses on enzymatic oxidation of alkyl groups on aromatics leading to quinone methides and benzylic alcohol sulfates as RMs, a topic that has not received very much attention. Unlike previous overviews, we will include in our Perspective several fulvene-like methides such as 3-methyleneindole. We also speculate that a few older drugs may form non-reported methides of this class. In addition, we report a few guiding DFT calculations of changes in free energy on going from a benzylic alcohol to the corresponding methide. Particularly facile reactions of 2-aminothiazole-5-methanol and 4-aminobenzyl alcohol are noted.

Evaluation of biomarkers of exposure in adult cigarette smokers using Marlboro snus

INTRODUCTION

It has been reported that adult smokers (AS) may be considering smokeless tobacco products as an alternative to smoking. The objective of this study was to evaluate the change in exposure in AS using Marlboro snus (MSNUS) (a tobacco pouch product in test market in June 2007).

METHODS

AS were randomized into the following groups--CS: subjects (n = 30) continue smoking their own brand; DU: subjects (n = 60) reduced their daily cigarette consumption by >or=50% and were allowed to use MSNUS; SN: subjects (n = 15) stopped smoking their cigarettes but were allowed to use MSNUS; NT: subjects (n = 15) were not allowed to use any tobacco products for the entire duration of the 8-day study. Biomarkers of smoke exposure (BOE) measured at baseline and postbaseline were 24-hr urinary excretion of metabolites of N-nitrosamines, nicotine (urine and plasma), aromatic amines, benzene, and polycyclic aromatic hydrocarbon; urine mutagenicity; and carboxyhemoglobin at various timepoints.

RESULTS

Statistically significant (p < .05) reductions in all the urinary BOE were observed in the DU group compared with the CS group. After correcting for the residual effect, a proportionate reduction (approximately 50%) in most of the biomarkers was observed. Even larger reductions, similar to the NT group, were observed in the SN group.

DISCUSSION

The proportionate reduction in exposure when reducing the number of cigarettes by 50% and using MSNUS, under the consumption patterns observed, suggest that the AS did not appear to alter their smoking behavior. The added exposure from MSNUS usage in this group was minimal. The AS sustained substantial reductions in exposure when using MSNUS exclusively.

4-Aminobiphenyl and DNA Reactivity: Case Study Within the Context of the 2006 IPCS Human Relevance Framework for Analysis of a Cancer Mode of Action for Humans

The IPCS Human Relevance Framework was evaluated for a DNA-reactive (genotoxic) carcinogen, 4-aminobiphenyl, based on a wealth of data in animals and humans. The mode of action involves metabolic activation by N-hydroxylation, followed by N-esterification leading to the formation of a reactive electrophile, which binds covalently to DNA, principally to deoxyguanosine, leading to an increased rate of DNA mutations and ultimately to the development of cancer. In humans and dogs, the urinary bladder urothelium is the target organ, whereas in mice it is the bladder and liver; in other species, other tissues can be involved. Differences in organ specificity are thought to be due to differences in metabolic activation versus inactivation. Based on qualitative and quantitative considerations, the mode of action is possible in humans. Other biological processes, such as toxicity and regenerative proliferation, can significantly influence the dose response of 4-aminobiphenyl-induced tumors. Based on the IPCS Human Relevance Framework, 4-aminobiphenyl would be predicted to be a carcinogen in humans, and this is corroborated by extensive epidemiologic evidence. The IPCA Human Relevance Framework is useful in evaluating DNA-reactive carcinogens.

Effect of pH on mutagenicity of urine from smokers and nonsmokers

Cigarette smoking is a major risk factor for bladder cancer. Some chemicals from cigarette smoke e.g. aromatic amines, are metabolized in the liver and excreted in urine as either glucuronide or acetyl conjugates. These metabolites undergo pH mediated activation to reactive nitreneum ions that may lead to DNA adducts, initiating bladder tumorigenesis in some smokers. We hypothesize that changing the pH of smokers urine will impact the mutagenic outcome of these metabolites. Overnight samples were collected from smokers (n=11) and nonsmokers (n=11) and stored at -70°C. Each urine sample was adjusted to neutral (7.0), basic (8.2) and acidic (5.5) pH. Mutagenic activity was assessed with the Ames test utilizing the Salmonella Typhimurium strain YG1024 microsuspension assay. Urine from smokers was significantly mutagenic compared with nonsmokers (P<0.001). In both the groups, there was no difference between urine adjusted at different pH (P>0.05). We conclude that changing the pH of smokers urine might not affect their subsequent risk for bladder cancer.