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DNA adducts in human breast tissue: association with N-acetyltransferase-2 (NAT2) and NAT1 genotypes
W Pfau1, E M Stone, U Brockstedt
1Department of Toxicology and Environmental Medicine of the Fraunhofer Society, Hamburg University Medical School, Germany.
Abstract:
The etiology of human breast cancer is poorly understood, but circumstantial evidence points toward exogenous genotoxins as causative agents; they are believed to exert their carcinogenic action by binding to DNA. Because this binding is often preceded by metabolic activation, it is dependent on the expression and activities of metabolic enzymes of the host. Human mammary tissue samples from 42 women undergoing surgery for breast cancer or reduction mammoplasty were analyzed for DNA adducts by 32P-postlabeling analysis. With the butanol extraction method of DNA adduct enrichment, adduct levels were determined to be 0-414.6 adducts per 10(9) nucleotides, with considerable interindividual variation. To characterize the DNA adducts, we reanalyzed the adduct spots by reversed-phase high-performance liquid chromatography. Of two major adduct spots detected on TLC that accounted for up to 70% of the DNA modification, one eluted as a single peak on high-performance liquid chromatography, whereas the other was resolved into two distinct peaks of radioactivity. These major adducts were highly lipophilic in character. The N-acetyltransferase-1 (NAT1) and NAT2 genes were analyzed for common mutations using random RFLP analysis. An association between NAT2 acetylator status and adduct levels was observed; significantly elevated adduct levels occurred in the mammary DNA from women who were designated slow acetylators for NAT2 [median adduct level = 83.0 adducts per 10(9) nucleotides (range, 9.0-414.6)], as compared with the levels in individuals designated rapid acetylators for NAT2 [median adduct level = 39.7 adducts per 10(9) nucleotides (range, 0-91.0; P = 0.0053)]. On the other hand, NAT1 genotypes were not significantly associated with adduct levels. Although the agents responsible for the DNA modifications in the human breast are not known, this pilot study supports the hypothesis that DNA adduct formation in the human breast may be influenced by the NAT2 genotype.
Insights
Human breast cancer may be linked to DNA damage influenced by genetic factors. Specifically, the NAT2 genotype, affecting how the body processes toxins, was associated with higher levels of DNA adducts in breast tissue.
Area of Science:
- Environmental Health
- Molecular Biology
- Oncology
Background:
- The exact causes of human breast cancer remain unclear, but environmental toxins (genotoxins) are suspected culprits.
- Genotoxins are thought to cause cancer by damaging DNA, a process often requiring metabolic activation by host enzymes.
Purpose of the Study:
- To investigate the presence and levels of DNA adducts in human breast tissue.
- To explore the potential association between DNA adducts and genetic variations in metabolic enzymes, specifically N-acetyltransferase (NAT) genes.
Main Methods:
- DNA adducts in mammary tissue samples from 42 women were quantified using 32P-postlabeling analysis.
- High-performance liquid chromatography (HPLC) was used to characterize the detected DNA adducts.
- N-acetyltransferase-1 (NAT1) and NAT2 genes were analyzed for common mutations using RFLP analysis.
Main Results:
- DNA adducts were detected in all analyzed breast tissue samples, with levels varying significantly among individuals (0-414.6 adducts per 10(9) nucleotides).
- Two major, lipophilic DNA adducts were identified.
- A significant association was found between slow acetylator status for the NAT2 gene and elevated DNA adduct levels (P = 0.0053).
Conclusions:
- This study provides evidence that DNA adduct formation in human breast tissue may be influenced by an individual's NAT2 genotype.
- While the specific genotoxins remain unidentified, the findings support a role for host metabolic enzyme variations in breast cancer etiology.