18.02.2013 Views

Tobacco and Public Health - TCSC Indonesia

Tobacco and Public Health - TCSC Indonesia

Tobacco and Public Health - TCSC Indonesia

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

Steps to carcinogenesis<br />

Exposure to smoke<br />

MICHAEL MURPHY ET AL.<br />

The harmful consequences of smoking are well known. The smoking of tobacco is an<br />

efficient method of delivering nicotine to the brain where it elicits rewarding effects.<br />

However tobacco smoke also carries more than 50 carcinogens direct to the lungs,<br />

including polycyclic aromatic hydrocarbons (PAHs) such as benzo[a]pyrene <strong>and</strong> several<br />

nitrosamine-based compounds that are specific to tobacco. Actual doses of<br />

nicotine, carcinogens, <strong>and</strong> toxins will vary, depending on an individual’s intensity <strong>and</strong><br />

method of smoking <strong>and</strong> also on the smoking device. Genetic predisposition to nicotine<br />

addiction (discussed previously) will also contribute to risk via modulation of both<br />

amount smoked <strong>and</strong> ability to stop smoking.<br />

Activation of procarcinogens<br />

<strong>Tobacco</strong> carcinogens are metabolized by complex enzyme systems <strong>and</strong> involve both<br />

activation <strong>and</strong> detoxification. Phase 1 enzymes such as those from the cytochrome P450<br />

family are primarily responsible for the activation (via oxidation) of procarcinogens.<br />

Many genes encoding CYP enzymes are polymorphic <strong>and</strong> this inherited variation will<br />

influence the activity of specific CYP isozymes, resulting in individual differences in<br />

exposure to activated carcinogens. CYP1A1 (on chromosome 2, see gene map earlier in<br />

chapter) is the principal enzyme that metabolizes PAHs <strong>and</strong> possessing polymorphic<br />

variant alleles seems to confer elevated risk of lung cancer, in certain ethnic<br />

populations (Vineis et al. 1999).<br />

Adduct formation<br />

Smoking-related DNA adducts (long-lasting aggregates of tobacco carcinogens <strong>and</strong><br />

genetic material) have been detected by a variety of analytical methods in respiratory<br />

tract, bladder, cervix. DNA adducts are found at higher levels in tissues of smokers<br />

compared to non-smokers (Perera et al. 1987). Biomarker data provide convincing<br />

evidence that carcinogen uptake, activation, <strong>and</strong> binding to cellular macromolecules<br />

(including DNA) are higher in smokers than non-smokers (R<strong>and</strong>erath <strong>and</strong> R<strong>and</strong>erath<br />

1993).<br />

Failure of DNA repair<br />

DNA repair plays a crucial role in maintenance of genome stability by removing these<br />

kinds of lesions, thus diminished DNA repair capacity may increase susceptibility to<br />

smoking-related cancers. Reduced DNA repair has been shown in lymphocytes from<br />

lung cancer patients in vitro compared to age-matched controls (Wei et al. 2000),<br />

although poor repair is thought to be independent of smoking status. Whilst DNA<br />

repair is undertaken, cell cycle checkpoints will arrest the growth of the cell,<br />

635

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!