R.W.L. Godschalk

Modulation of DNA and protein adducts in smokers by genetic polymorphisms in GSTM1,GSTT1, NAT1 and NAT2.

The formation of DNA and protein adducts by environmental pollutants is modulated by host polymorphisms in genes that encode metabolizing enzymes. In our study on 67 smokers, aromatic-DNA adduct levels were examined by nuclease P1 enriched 32P-postlabelling in mononuclear blood cells (MNC) and 4-aminobiphenyl-haemoglobin adducts (4-ABP-Hb) by gas chromatography-mass spectroscopy. Genetic polymorphisms in glutathione S-transferase M1 (GSTM1), T1 (GSTT1) and N-acetyl-transferase 1 (NAT1) and 2 (NAT2) were assessed by polymerase chain reaction-based methods. DNA adduct levels, adjusted for the amount of cigarettes smoked per day, were higher in GSTM1(-/-) individuals (1.30 +/- 0.57 adducts per 108 nucleotides) than in GSTM1(+) subjects (1.03 +/- 0.56, P = 0.05), higher in NAT1 slow acetylators (1.58 +/- 0.54) than in NAT1 fast acetylators (1.11 +/- 0.58, P = 0.05) and were also found to be associated with the NAT2 acetylator status (1.29 +/- 0.64 and 1.03 +/- 0.46, respectively, for slow and fast acetylators, P = 0.06). An effect of GSTT1 was only found in combination with the NAT2 genotype; individuals with the GSTT1(-/-) and NAT2-slow genotype contained higher adduct levels (1.80 +/- 0.68) compared to GSTT1(+)/NAT2 fast individuals (0.96 +/- 0.36). Highest DNA adduct levels were observed in slow acetylators for both NAT1 and NAT2 also lacking the GSTM1 gene (2.03 +/- 0.17), and lowest in GSTM1(+) subjects with the fast acetylator genotype for both NAT1 and NAT2 (0.91 +/- 0.45, P = 0.01). No overall effects of genotypes were observed on 4-ABP-Hb levels. However, in subjects smoking less than 25 cigarettes per day, 4-ABP-Hb levels were higher in NAT2 slow acetylators (0.23 +/- 0.10 ng/g Hb) compared to fast acetylators (0.15 +/- 0.07, P = 0.03). These results provide further evidence for the combined effects of genetic polymorphisms in GSTM1, GSTT1, NAT1 and NAT2 on DNA and protein adduct formation in smoking individuals and indicate that, due to the complex carcinogen exposure, simultaneous assessment of multiple genotypes may identify individuals at higher cancer risk.

Pulmonary Inflammation Impacts on CYP1A1- Mediated Respiratory Tract DNA Damage Induced by the Carcinogenic Air Pollutant Benzo(a)pyrene

Pulmonary inflammation can contribute to the development of lung cancer in humans. We investigated whether pulmonary inflammation alters the genotoxicity of polycyclic aromatic hydrocarbons (PAHs) in the lungs of mice and what mechanisms are involved. To model nonallergic acute inflammation, mice were exposed intranasally to lipopolysaccharide (LPS; 20u2009µg/mouse) and then instilled intratracheally with benzo[a]pyrene (BaP; 0.5u2009mg/mouse). BaP-DNA adduct levels, measured by 32P-postlabeling analysis, were approximately 3-fold higher in the lungs of LPS/BaP-treated mice than in mice treated with BaP alone. Pulmonary Cyp1a1 enzyme activity was decreased in LPS/BaP-treated mice relative to BaP-treated mice suggesting that pulmonary inflammation impacted on BaP-induced Cyp1a1 activity in the lung. Our results showed that Cyp1a1 appears to be important for BaP detoxification in vivo and that the decrease of pulmonary Cyp1a1 activity in LPS/BaP-treated mice results in a decrease of pulmonary BaP detoxification, thereby enhancing BaP genotoxicity (ie, DNA adduct formation) in the lung. Because less BaP was detoxified by Cyp1a1 in the lungs of LPS/BaP-treated mice, more BaP circulated via the blood to extrapulmonary tissues relative to mice treated with BaP only. Indeed, we observed higher BaP-DNA adduct levels in livers of LPS/BaP-treated mice compared with BaP-treated mice. Our results indicate that pulmonary inflammation could be a critical determinant in the induction of genotoxicity in the lung by PAHs like BaP. Cyp1a1 appears to be involved in both BaP bioactivation and detoxification although the contribution of other enzymes to BaP-DNA adduct formation in lung and liver under inflammatory conditions remains to be explored.

Incomplete protection of genetic integrity of mature spermatozoa against oxidative stress.

Although DNA damage in human spermatozoa is associated with adverse health effects, its origin is not fully understood. Therefore, we assessed biomarkers in ejaculates that retrospectively reflect processes that occurred in the epididymis or testis. Smoking increased the amount of DNA strand breaks (P<0.01), and enhanced the presence of vitamin C radicals in seminal plasma. In vitro, vitamin C protected mature spermatozoa against DNA damage, but this protection appeared to be insufficient in vivo. CAT and DDIT4 expression in spermatozoa were higher in smokers than in nonsmokers, but were not related to DNA damage. CAT and DDIT4 expression were inversely related with sperm count (P=0.039 and 0.024 resp.), but no effect was observed for SOD2 expression. These data indicate that spermatozoa of smokers encounter higher levels of oxidative stress. Expression of antioxidant enzymes and seminal vitamin C were insufficient to provide full protection of spermatozoa against DNA damage.

The impact of p53 on DNA damage and metabolic activation of the environmental carcinogen benzo[a]pyrene : effects in Trp53(+/+), Trp53(+/-) and Trp53(-/-) mice

The tumour suppressor p53 is one of the most important cancer genes. Previous findings have shown that p53 expression can influence DNA adduct formation of the environmental carcinogen benzo[a]pyrene (BaP) in human cells, indicating a role for p53 in the cytochrome P450 (CYP) 1A1-mediated biotransformation of BaP in vitro. We investigated the potential role of p53 in xenobiotic metabolism in vivo by treating Trp53(+/+), Trp53(+/–) and Trp53(−/−) mice with BaP. BaP-DNA adduct levels, as measured by 32P-postlabelling analysis, were significantly higher in liver and kidney of Trp53(−/−) mice than of Trp53(+/+) mice. Complementarily, significantly higher amounts of BaP metabolites were also formed ex vivo in hepatic microsomes from BaP-pretreated Trp53(−/−) mice. Bypass of the need for metabolic activation by treating mice with BaP-7,8-dihydrodiol-9,10-epoxide resulted in similar adduct levels in liver and kidney in all mouse lines, confirming that the influence of p53 is on the biotransformation of the parent compound. Higher BaP-DNA adduct levels in the livers of Trp53(−/−) mice correlated with higher CYP1A protein levels and increased CYP1A enzyme activity in these animals. Our study demonstrates a role for p53 in the metabolism of BaP in vivo, confirming previous in vitro results on a novel role for p53 in CYP1A1-mediated BaP metabolism. However, our results also suggest that the mechanisms involved in the altered expression and activity of the CYP1A1 enzyme by p53 in vitro and in vivo are different.

Impact of GSTM1 on aromatic-DNA adducts and p53 accumulation in human skin and lymphocytes.

The cellular response to DNA damage is often a p53-mediated cell cycle arrest to provide time for DNA repair or to direct damaged cells into apoptosis. In this study, the impact of glutathione-S-transferase M1 (GSTM1) on DNA damage and subsequent p53-protein accumulation was examined in lymphocytes of healthy volunteers in vitro exposed to benzo[a]pyrene-diol-epoxide (BPDE) and in skin of atopic eczema patients topically treated with coal tar. DNA adducts were determined by immunocytochemical staining (ICC) and 32P-postlabelling, p53 accumulation was studied by ICC and the GSTM1 genotype was assessed by polymerase chain reaction. In cultured lymphocytes treated with 2.5 microM BPDE for 18 h, increased levels of p53 were found, which were positively related to BPDE-DNA adduct levels assessed by ICC (rs = 0.66, P < 0.001) and 32P-postlabelling (rs = 0.56, P < 0.001) and appeared to be higher in GSTM1(-/-) than in GSTM1(+) subjects (P = 0.003). In skin biopsies of coal tar treated eczema patients, p53 levels were elevated in 7/10 patients and a correlation was observed between p53 and DNA adduct levels (rs = 0.50, P = 0.029). GSTM1(-/-) subjects contained higher levels of p53 in the stratum basale than GSTM1(+) individuals (P = 0.026), but no influence of GSTM1 on DNA adduct levels was observed. Thus, p53 accumulates in human skin and lymphocytes as a protective mechanism against polycyclic aromatic hydrocarbon induced DNA damage, and this is more pronounced in GSTM1(-/-) compared to GSTM1(+) individuals.

Polymorphisms in genes of the renin-angiotensin-aldosterone system and renal cell cancer risk: Interplay with hypertension and intakes of sodium, potassium and fluid

Hypertension is an established risk factor for renal cell cancer (RCC). The renin‐angiotensin‐aldosterone system (RAAS) regulates blood pressure and is closely linked to hypertension. RAAS additionally influences homeostasis of electrolytes (e.g. sodium and potassium) and fluid. We investigated single nucleotide polymorphisms (SNPs) in RAAS and their interactions with hypertension and intakes of sodium, potassium and fluid regarding RCC risk in the Netherlands Cohort Study (NLCS), which was initiated in 1986 and included 120,852 participants aged 55 to 69 years. Diet and lifestyle were assessed by questionnaires and toenail clippings were collected. Genotyping of toenail DNA was performed using the SEQUENOM® MassARRAY® platform for a literature‐based selection of 13 candidate SNPs in seven key RAAS genes. After 20.3 years of follow‐up, Cox regression analyses were conducted using a case‐cohort approach including 3,583 subcohort members and 503 RCC cases. Two SNPs in AGTR1 were associated with RCC risk. AGTR1_rs1492078 (AA vs. GG) decreased RCC risk [hazard ratio (HR) (95% confidence interval (CI)): 0.70(0.49–1.00)], whereas AGTR1_rs5186 (CC vs. AA) increased RCC risk [HR(95%CI): 1.49(1.08–2.05)]. Associations were stronger in participants with hypertension. The RCC risk for AGT_rs3889728 (AG + AA vs. GG) was modified by hypertension (p interaction = 0.039). SNP‐diet interactions were not significant, although HRs suggested interaction between SNPs in ACE and sodium intake. SNPs in AGTR1 and AGT influenced RCC susceptibility, and their effects were modified by hypertension. Sodium intake was differentially associated with RCC risk across genotypes of several SNPs, yet some analyses had probably inadequate power to show significant interaction. Results suggest that RAAS may be a candidate pathway in RCC etiology.

Decreased nucleotide excision repair in steatotic livers associates with myeloperoxidase-immunoreactivity.

Chronic inflammation is characterized by the influx of neutrophils and is associated with an increased production of reactive oxygen species that can damage DNA. Oxidative DNA damage is generally thought to be involved in the increased risk of cancer in inflamed tissues. We previously demonstrated that activated neutrophil mediated oxidative stress results in a reduction in nucleotide excision repair (NER) capacity, which could further enhance mutagenesis. Inflammation and oxidative stress are critical factors in the progression of nonalcoholic fatty liver disease that is linked with enhanced liver cancer risk. In this report, we therefore evaluated the role of neutrophils and the associated oxidative stress in damage recognition and DNA repair in steatotic livers of 35 severely obese subjects with either nonalcoholic steatohepatitis (NASH) (n=17) or steatosis alone (n=18). The neutrophilic influx in liver was assessed by myeloperoxidase (MPO) staining and the amount of oxidative DNA damage by measuring M(1)dG adducts. No differences in M(1)dG adduct levels were observed between patients with or without NASH and also not between individuals with high or low MPO immunoreactivity. However, we found that high expression of MPO in the liver, irrespective of disease status, reduced the damage recognition capacity as determined by staining for histone 2AX phosphorylation (γH2AX). This reduction in γH2AX formation in individuals with high MPO immunoreactivity was paralleled by a significant decrease in NER capacity as assessed by a functional repair assay, and was not related to cell proliferation. Thus, the observed reduction in NER capacity upon hepatic inflammation is associated with and may be a consequence of reduced damage recognition. These findings suggest a novel mechanism of liver cancer development in patients with nonalcoholic fatty liver disease.

DNA from Nails for Genetic Analyses in Large-Scale Epidemiologic Studies

Background: Nails contain genomic DNA that can be used for genetic analyses, which is attractive for large epidemiologic studies that have collected or are planning to collect nail clippings. Study participants will more readily participate in a study when asked to provide nail samples than when asked to provide a blood sample. In addition, nails are easy and cheap to obtain and store compared with other tissues. Methods: We describe our findings on toenail DNA in terms of yield, quality, genotyping a limited set of SNPs with the Sequenom MassARRAY iPLEX platform and high-density genotyping with the Illumina HumanCytoSNP_FFPE-12 DNA array (>262,000 markers). We discuss our findings together with other studies on nail DNA and we compare nails and other frequently used tissue samples as DNA sources. Results: Although nail DNA is considerably degraded, genotyping a limited set of SNPs with the Sequenom MassARRAY iPLEX platform (average sample call rate, 97.1%) and high-density genotyping with the Illumina HumanCytoSNP_FFPE chip (average sample call rate, 93.8%) were successful. Conclusions: Nails are a suitable source of DNA for genotyping in large-scale epidemiologic studies, provided that methods are used that are suitable or optimized for degraded DNA. For genotyping through (next generation) sequencing where DNA degradation is less of an issue, nails may be an even more attractive DNA source, because it surpasses other sources in terms of ease and costs of obtaining and storing the samples. Impact: It is worthwhile to consider nails as a source of DNA for genotyping in large-scale epidemiologic studies. See all the articles in this CEBP Focus section, “Biomarkers, Biospecimens, and New Technologies in Molecular Epidemiology.” Cancer Epidemiol Biomarkers Prev; 23(12); 2703–12. ©2014 AACR.