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Altered aromatic amine metabolism in epileptic patients treated with phenobarbital
H Wallin1, P L Skipper, S R Tannenbaum
1Danish Cancer Society, Division of Cancer Epidemiology, Copenhagen, Denmark.
Abstract:
The fate of carcinogens differs among individuals who have different activities of drug-metabolizing enzymes that are important in activating and detoxifying carcinogens. A drug that profoundly alters the metabolism of the drugs and carcinogens is the anticonvulsive agent phenobarbital. To investigate why epileptic patients appear to have a low risk of cancer of the urinary bladder, and on the basis of the observation that levels of aromatic amine-hemoglobin adducts are strongly associated with various risk factors for cancer at that site, we determined aromatic amine-hemoglobin adducts in 62 epileptic patients as a surrogate measure of the reaction of carcinogenic metabolites with DNA in target tissue. Although adducts were detected in all subjects, the levels were proportional to daily tobacco consumption. When the subjects were stratified into groups smoking 20 g tobacco/day or more, smoking <20 g/day, and not smoking, an effect of medication was detected. Epileptic patients treated chronically with phenobarbital or primidone, which is effectively metabolized to phenobarbital, were found to have lower levels of 4-aminobiphenyl adducts than patients on the other treatment (P = 0.02; ANOVA). In nonsmokers, no effect of medication could be demonstrated above background variation; however, an increasing effect was seen with tobacco consumption with only one-half the increase in adducts per g of tobacco smoked as epileptic patients on other treatment. The difference in the increases (slopes of regression lines) was highly significant statistically. This reduction in the level of hemoglobin-aromatic amine adducts is probably due to induction of detoxification enzymes in the patients treated with phenobarbital.
Insights
Phenobarbital medication in epileptic patients significantly reduces aromatic amine-hemoglobin adducts, a marker for carcinogen exposure. This suggests phenobarbital may lower cancer risk by enhancing carcinogen detoxification.
Area of Science:
- Pharmacology
- Toxicology
- Oncology
Background:
- Individual differences in drug-metabolizing enzyme activity influence carcinogen fate.
- Anticonvulsant phenobarbital alters drug and carcinogen metabolism.
- Epileptic patients show a lower risk of urinary bladder cancer.
Purpose of the Study:
- Investigate the reduced urinary bladder cancer risk in epileptic patients.
- Assess aromatic amine-hemoglobin adducts as a surrogate for carcinogenic metabolite-DNA reactions.
- Determine the effect of phenobarbital on carcinogen adduct levels.
Main Methods:
- Measured aromatic amine-hemoglobin adducts in 62 epileptic patients.
- Stratified subjects by tobacco consumption (≥20g/day, <20g/day, non-smokers).
- Compared adduct levels between patients on phenobarbital/primidone and other treatments using ANOVA.
Main Results:
- Adduct levels correlated with tobacco consumption.
- Patients on phenobarbital/primidone had significantly lower 4-aminobiphenyl adducts (P=0.02).
- Phenobarbital showed a dose-dependent reduction in adducts with increasing tobacco use.
Conclusions:
- Chronic phenobarbital treatment in epileptic patients reduces hemoglobin-aromatic amine adducts.
- This reduction is likely due to phenobarbital-induced detoxification enzymes.
- Findings suggest a mechanism for reduced cancer risk in patients treated with phenobarbital.