Bulky DNA adduct levels in normal-appearing colon mucosa, and the prevalence of colorectal adenomas.

PURPOSE: Examine the association between bulky DNA adduct levels in colon mucosa and colorectal adenoma prevalence, and explore the correlation between adduct levels in leukocytes and colon tissue. METHODS: Bulky DNA adduct levels were measured using 32P-postlabelling in biopsies of normal-appearing colon tissue and blood donated by 202 patients. Multivariable logistic regression was used to examine associations between DNA adducts, and interactions of DNA adduct-DNA repair polymorphisms, with the prevalence of colorectal adenomas. Correlation between blood and tissue levels of DNA adducts was evaluated using Spearman's correlation coefficient. RESULTS: An interaction between bulky DNA adduct levels and XPA rs1800975 on prevalence of colorectal adenoma was observed. Among individuals with lower DNA repair activity, increased DNA adduct levels were associated with increased colorectal adenoma prevalence (OR = 1.41 per SD increase, 95%CI: 0.92-2.18). Conversely, among individuals with normal DNA activity, an inverse association was observed (OR = 0.60 per SD increase, 95%CI: 0.34-1.07). Blood and colon DNA adduct levels were inversely correlated (ρ = -0.20). CONCLUSIONS: Among genetically susceptible individuals, higher bulky DNA adducts in the colon was associated with the prevalence of colorectal adenomas. The inverse correlation between blood and colon tissue measures demonstrates the importance of quantifying biomarkers in target tissues.

Effect of 8-oxoguanine glycosylase deficiency on aflatoxin B1 tumourigenicity in mice.

The mycotoxin aflatoxin B1 (AFB1) may initiate cancer by causing oxidatively damaged DNA, specifically by causing 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) lesions. Base excision repair removes these lesions, with 8-oxoguanine glycosylase (OGG1) being the rate-limiting enzyme. The aim of this study was to determine the effect of ogg1 deficiency on AFB1-induced oxidatively damaged DNA and tumourigenesis. Female wild-type, heterozygous and homozygous ogg1 null mice were given a single dose of 50mg/kg AFB1 or 40 µl dimethyl sulfoxide (DMSO) ip. Neither ogg1 genotype nor AFB1 treatment affected levels of oxidised guanine in lung or liver 2h post-treatment. AFB1-treated ogg1 null mice showed exacerbated weight loss and mortality relative to DMSO-treated ogg1 null mice, but AFB1 treatment did not significantly increase lung or liver tumour incidence compared with controls, regardless of ogg1 genotype. Suspect lung masses from three of the AFB1-treated mice were adenomas, and masses from two of the mice were osteosarcomas. No osteosarcomas were observed in DMSO-treated mice. All liver masses from AFB1-treated mice were adenomas, and one also contained a hepatocellular carcinoma. In DNA from the lung tumours, the K-ras mutation pattern was inconsistent with initiation by AFB1. In conclusion, ogg1 status did not have a significant effect on AFB1-induced oxidatively damaged DNA or tumourigenesis, but deletion of one or both alleles of ogg1 did increase susceptibility to other aspects of AFB1 toxicity.

Up-regulation of nucleotide excision repair in mouse lung and liver following chronic exposure to aflatoxin B1 and its dependence on p53 genotype.

Aflatoxin B1(AFB1) is biotransformed in vivo into an epoxide metabolite that forms DNA adducts that may induce cancer if not repaired. p53 is a tumor suppressor gene implicated in the regulation of global nucleotide excision repair (NER). Male heterozygous p53 knockout (B6.129-Trp53(tm1Brd)N5, Taconic) and wild-type mice were exposed to 0, 0.2 or 1.0 ppm AFB1 for 26 weeks. NER activity was assessed with an in vitro assay, using AFB1-epoxide adducted plasmid DNA as a substrate. For wild-type mice, repair of AFB1-N7-Gua adducts was 124% and 96% greater in lung extracts from mice exposed to 0.2 ppm and 1.0 ppm AFB1respectively, and 224% greater in liver extracts from mice exposed to 0.2 ppm AFB1( p<0.05). In heterozygous p53 knockout mice, repair of AFB1-N7-Gua was only 45% greater in lung extracts from mice exposed to 0.2 ppm AFB1 (p<0.05), and no effect was observed in lung extracts from mice treated with 1.0 ppm AFB1or in liver extracts from mice treated with either AFB1concentration. p53 genotype did not affect basal levels of repair. AFB1exposure did not alter repair of AFB1-derived formamidopyrimidine adducts in lung or liver extracts of either mouse genotype nor did it affect XPA or XPB protein levels. In summary, chronic exposure to AFB1increased NER activity in wild-type mice, and this response was diminished in heterozygous p53 knockout mice, indicating that loss of one allele of p53 limits the ability of NER to be up-regulated in response to DNA damage.

Relationships among biomarkers of one-carbon metabolism.

One-carbon metabolism is a network of metabolic pathways, disruption of which has been associated with cancer and other pathological conditions. Biomarkers of these pathways include homocysteine (HCY), S-adenosylmethionine (SAM), and S-adenosylhomocysteine (SAH). A better understanding of the relationships between these biomarkers is needed for their utilization in research. This study investigated the relationships between fasting concentrations of plasma HCY, SAM, SAH and the ratio of SAM:SAH, and serum folate, vitamin B(12) and creatinine in a healthy adult population. A cross-sectional study recruited 678 volunteers; only subjects with complete data (n = 581) were included in this analysis. Correlations were used to examine bivariate relationships among the biomarkers and multivariate linear regression determined independent relationships with HCY, SAM and SAH treated as dependent variables in separate models. Multivariate logistic regression examined determinants of a low SAM:SAH ratio (defined as having a SAM:SAH ratio in the bottom quartile and SAH value in the top quartile). HCY correlated inversely with folate and vitamin B(12) and weakly correlated with SAH and creatinine. Both SAM and SAH correlated with creatinine but were independent of serum folate and vitamin B(12). In multivariate analyses, folate, vitamin B(12), creatinine, sex and age were associated with HCY; age and creatinine were determinants of SAM, and sex and creatinine determinants of SAH. Finally, male sex and increasing creatinine levels were associated with having a low SAM:SAH ratio. Findings suggest that HCY, SAM and SAH are relatively independent parameters and reflect distinct aspects of one-carbon metabolism.

Deuterated Drugs and Biomarkers in the COVID-19 Pandemic.

Coronavirus disease 2019 (COVID-19) is a highly contagious disease caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Initially identified in Wuhan (China) in December 2019, COVID-19 rapidly spread globally, resulting in the COVID-19 pandemic. Carriers of the SARS-CoV-2 can experience symptoms ranging from mild to severe (or no symptoms whatsoever). Although vaccination provides extra immunity toward SARS-CoV-2, there has been an urgent need to develop treatments for COVID-19 to alleviate symptoms for carriers of the disease. In seeking a potential treatment, deuterated compounds have played a critical role either as therapeutic agents or as internal MS standards for studying the pharmacological properties of new drugs by quantifying the parent compounds and metabolites. We have identified >70 examples of deuterium-labeled compounds associated with treatment of COVID-19. Of these, we found 9 repurposed drugs and >20 novel drugs studied for potential therapeutic roles along with a total of 38 compounds (drugs, biomarkers, and lipids) explored as internal mass spectrometry standards. This review details the synthetic pathways and modes of action of these compounds (if known), and a brief analysis of each study.

Mechanisms of amiodarone and desethylamiodarone cytotoxicity in nontransformed human peripheral lung epithelial cells.

Amiodarone (AM) is a potent antidysrhythmic agent that can cause potentially life-threatening pulmonary fibrosis, and N-desethylamiodarone (DEA), an AM metabolite, may contribute to AM toxicity. Apoptotic cell death in nontransformed human peripheral lung epithelial 1A (HPL1A) cells was assessed by annexin V-fluorescein isothiocyanate (ann-V) staining and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL), and necrotic cell death was assessed by propidium iodide (PI) staining. The percentage of cells that were PI-positive increased more than six times with 20 µM AM and approximately doubled with 3.5 µM DEA, relative to control. The percentage of cells that were ann-V-positive decreased by more than 80% after 24-h exposure to 10 µM AM but more than doubled after 24-h incubation with 3.5 µM DEA. Incubation for 24 h with 5.0 µM DEA increased the percentage of cells that were TUNEL-positive more than six times. Incubation with AM (2.5 µM) or DEA (1-2 µM) for 24 h did not significantly alter angiotensinogen mRNA levels. Furthermore, angiotensin II (100 pM-1 µM) alone or in combination with AM or DEA did not alter cytotoxicity, and pretreatment with the angiotensin-converting enzyme inhibitor and antioxidant captopril (3-6 µM) did not protect against AM or DEA cytotoxicity. In conclusion, AM activates primarily necrotic pathways, whereas DEA activates both necrotic and apoptotic pathways, and the renin-angiotensin system does not seem to be involved in AM or DEA cytotoxicity in HPL1A cells.

Thymidylate synthase gene polymorphisms and markers of DNA methylation capacity.

BACKGROUND: DNA methylation plays a critical role in gene regulation and has been implicated in the etiology of chronic disease including atherosclerosis, neural degeneration and cancer. One-carbon metabolism serves two critically important functions: one concerning the production of purines and thymidine for DNA synthesis and the other related to the provision of methyl groups through the metabolism of methionine. Critical intermediates of methionine metabolism relevant to DNA methylation include S-adenosylmethionine (SAM), a universal methyl donor, and S-adenosylhomocysteine (SAH), a potent inhibitor of most methylation reactions. Thymidine synthesis, catalyzed by the crucial enzyme thymidylate synthase (TS), competes with methionine metabolism for a common substrate. Three functional polymorphisms in the TS gene have been identified including: (i) the thymidylate synthase enhancer region (TSER) tandem repeat polymorphism and (ii) the G to C single nucleotide polymorphism (G/C SNP) both of which occur in the 5'untranslated region (UTR) of the TS gene; and (iii) the 6-bp deletion at base pair 1494 (TS1494del6) located in the 3'UTR. PURPOSE: The purpose of this research was to investigate the relationship between TS polymorphisms and concentrations of SAM and SAH, markers of DNA methylation capacity. METHODS: The study population consisted of 395 healthy male and female volunteers from Kingston, Ontario and Halifax, Nova Scotia, Canada between 2006 and 2008. The effect of each TS polymorphism on SAM and SAH concentrations was investigated, and further analyses were conducted on categorization of polymorphisms based on 5' or 3'UTR. The combined effect of TS polymorphisms on SAM and SAH concentrations was also investigated, in addition to interactions between polymorphisms in TS and MTHFR 677C>T and interactions between TS polymorphisms and serum folate and vitamin B(12) status. RESULTS: No associations were observed between TS polymorphisms and concentrations of SAM and SAH. Analysis of interaction between TS and MTHFR polymorphisms on SAH levels revealed a significant interaction with TS 3'polymorphism and MTHFR C677T (p=0.03). As well, interactions between TS 3'polymorphism and serum folate (p=0.03) and the combined effect of TS polymorphisms and serum folate on SAH levels (p=0.04) were found. CONCLUSIONS: The findings of this research provide evidence that SAH, a marker of methylation capacity, is influenced by genetic and environmental factors and their interactions.

Effects of in vivo treatment of mice with sulforaphane on repair of DNA pyridyloxylbutylation.

The phytochemical sulforaphane (SF) has gained interest for its apparent association with reduced cancer risk and other cytoprotective properties, at least some of which are attributed to activation of the transcription factor Nrf2. Repair of bulky DNA adducts is important for mitigating carcinogenesis from exogenous DNA damaging agents, but it is unknown whether in vivo treatment with SF affects adduct repair. At 12 h following a single oral dose of 100 mg/kg SF, an almost doubling in activity for repair of pyridyloxobutylated DNA was observed in CD-1 mouse liver nuclear extracts, but not in lung extracts. This change at 12 h in repair activity was preceded by the induction of Nrf2-regulated genes but not accompanied by changes in levels of the specific nucleotide excision repair (NER) proteins XPC, XPA, XPB and p53 or in binding of hepatic XPC, XPA and XPB to damaged DNA. SF also did not significantly alter histone deacetylase activity as measured by acetylated histone H3 levels, or stimulate formation of γ-H2A.X, a marker of DNA damage. A significant reduction in oxidative DNA damage, as measured by 8-OHdG (a biomarker of oxidative DNA damage), was observed only in DNA from the lungs of SF-treated mice 3 h post-dosing. These results suggest that the ability of SF to increase bulky adduct repair activity is organ-selective and is consistent with activation of the Nrf2 signaling pathway.

Influence of thymidylate synthase gene polymorphisms on total plasma homocysteine concentrations.

BACKGROUND: Thymidylate synthase (TS) is a key enzyme that regulates the production of nucleotide synthesis by catalyzing the conversion of deoxyuridylate to thymidylate. Three functional polymorphisms in the TS gene have been identified including: (i) the thymidylate synthase enhancer region (TSER) tandem repeat polymorphism and (ii) the G to C single nucleotide polymorphism (G/C SNP) both of which occur in the 5'untranslated region (UTR) of the TS gene; and (iii) the 6 base pair deletion at base pair 1494 (TS1494del6) located in the 3'UTR. PURPOSE: The purpose of this research was to investigate the relationship between TS polymorphisms and total plasma homocysteine (tHcy) levels. METHODS: The study population consisted of 396 healthy male and female volunteers from Kingston, Ontario and Halifax, Nova Scotia, Canada between 2006 and 2008. The effect of each TS polymorphism on tHcy concentrations was investigated and further analyses were conducted on categorization of polymorphisms based on 5' or 3'UTR. The combined effect of TS polymorphisms on tHcy concentration was also investigated, in addition to interactions between polymorphisms in TS and MTHFR 677C>T and interactions between TS polymorphisms and serum folate and vitamin B(12) status. RESULTS: An association between TS 5'polymorphisms and tHcy concentration was observed (p=0.05). The combined effect of the TS polymorphisms was also found to be associated with tHcy concentration (p=0.05). Additionally, an antagonistic interaction was observed between TS 5'polymorphism and MTHFR 677C>T on tHcy concentrations (p=0.04). CONCLUSIONS: The findings of this research provide evidence of an association between TS polymorphisms and tHcy concentrations.

In vivo treatment with 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) induces organ-specific alterations in in vitro repair of DNA pyridyloxobutylation.

To investigate the mechanisms responsible for inter-organ differences in susceptibility to 4-methylnitrosamino-1-(3-pyridyl)-1-butanone (NNK)-induced carcinogenesis, the objectives were to compare DNA repair activities of extracts from mouse lung and liver towards NNK-induced pyridyloxobutyl (POB) damage to plasmid DNA, and to determine if and the mechanism by which in vivo NNK treatment of mice alters DNA repair. Repair activity of POB adducts was three times greater in mouse liver than in mouse lung (P<0.05). Repair activities of lung extracts from mice 4 or 24 h post-NNK treatment were 30-45% those of control (P<0.05). Conversely, POB adduct repair was 2-3 times higher in liver extracts from NNK treated mice than in controls (4 h, 24 h, P<0.05). NNK treatment also decreased incision of POB adducts by 92% (4 h, P<0.05) in lung and increased incision by 169% (24 h, P<0.05) in liver. NNK decreased immunoreactive levels of the incision protein RPA in lung (P<0.05) 4 h post-treatment but increased immunoreactive lung RPA and XPB after 24 h (P<0.05). In liver, levels of immunoreactive proteins, XPA, XPB and ERCC1 were increased after NNK treatment (24 h, P<0.05). Binding of XPA and XPB from liver extracts to POB adducts increased following NNK treatment, while binding of XPA and XPB from lung decreased (4 h, 24 h). These results suggest that lower incision activity of nucleotide excision repair and NNK-mediated alterations in levels and activities of key incision proteins contribute to the relative susceptibility of mouse lung to NNK-induced carcinogenesis.

Repair of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone-induced DNA pyridyloxobutylation by nucleotide excision repair.

The tobacco-specific lung carcinogen, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) forms DNA methylating and pyridyloxobutylating species. In this study, the involvement of nucleotide excision repair (NER) in the repair of pyridyloxobutyl adducts was assessed using an in vitro NER assay with pyridyloxobutylated plasmid DNA. Nuclear extracts from NER-deficient xeroderma pigmentosum (XP) cells, XPA and XPC, were less active at repairing pyridyloxobutyl adducts than were extracts from normal cells, while combining NER-deficient extracts reconstituted activity. Also, NER-deficient cells were more susceptible to NNKOAc-induced cytotoxicity than were normal cells. Results demonstrate a role for NER in the repair of NNK-induced pyridyloxobutylation.

Telomere length in the colon is related to colorectal adenoma prevalence.

Telomere length has been associated with risk of several cancers. However, studies of the relationship between telomere length and colorectal cancer risk have been inconsistent. This study examined the relationship between telomere length in normal colon tissue and the prevalence of colorectal adenoma, a precursor to colorectal cancer. This nested case-control study consisted of 85 patients aged 40 to 65 undergoing a screening colonoscopy: 40 cases with adenoma(s) detected at colonoscopy and 45 controls with normal colonoscopy. During the colonoscopy, two pinch biopsies of healthy, normal appearing mucosa were obtained from the descending colon. Relative telomere length (rTL) was quantified in DNA extracted from colon mucosa using quantitative real-time PCR. Logistic regression was used to assess the relationship between telomere length and adenoma prevalence and estimate odds ratios and 95% confidence intervals. rTL was significantly longer in colon tissue of individuals with adenomas compared to healthy individuals (p = 0.008). When rTL was categorized into quartiles according to the distribution of rTL among controls, individuals with the longest telomeres had increased odds of adenoma when compared to individuals with shortest telomeres (OR = 4.58, 95% CI: 1.19, 17.7). This study suggests that long telomeres in normal colon tissue are associated with increased colorectal cancer risk.

Elevation of 8-hydroxydeoxyguanosine in DNA from isolated mouse lung cells following in vivo treatment with aflatoxin B(1).

Aflatoxin B(1) (AFB(1)) is a mycotoxin produced by some strains of Aspergillus and is a recognized pulmonary and hepatic carcinogen. The most widely accepted mechanism of AFB(1) carcinogenicity involves bioactivation to AFB(1)-8,9-exo-epoxide and binding to DNA to form AFB(1)-N(7)-guanine. Another potential cause of DNA damage is AFB(1)-mediated stimulation of reactive oxygen species formation, leading to oxidation of DNA bases. The objective of this study was to determine the ability of AFB(1) to cause oxidative DNA damage in lung cell types of the A/J mouse. The formation of 8-hydroxy-2'-deoxyguanosine (8-OHdG) in freshly isolated mouse lung alveolar macrophages, alveolar type II cells, and nonciliated bronchial epithelial (Clara) cells was assessed by high-performance liquid chromatography with electrochemical detection. An approximately 3-fold increase in 8-OHdG formation occurred in both alveolar macrophage and Clara cell preparations isolated from A/J mice 2 h following treatment with a single tumorigenic dose of 50 mg/kg AFB(1) ip (n = 3, p < 0.05). Prior treatment with 300 kU/kg polyethylene glycol-conjugated catalase prevented the AFB(1)-induced increase in 8-OHdG levels in all mouse lung cell preparations (n = 3, p < 0.05). These results support the possibility that oxidative DNA damage in mouse lung cells contributes to AFB(1) carcinogenicity.

Susceptibility to aflatoxin B1-induced carcinogenesis correlates with tissue-specific differences in DNA repair activity in mouse and in rat.

To investigate the mechanisms responsible for species- and tissue-specific differences in susceptibility to aflatoxin B(1) (AFB(1))-induced carcinogenesis, DNA repair activities of nuclear extracts from whole mouse lung and liver and rat liver were compared, and the ability of in vivo treatment of mice with AFB(1) to alter repair of AFB(1)-DNA damage was determined. Plasmid DNA containing AFB(1)-N(7)-guanine or AFB(1)-formamidopyrimidine adducts were used as substrates for the in vitro determination of DNA repair synthesis activity, detected as incorporation of radiolabeled nucleotides. Liver extracts from CD-1 mice repaired AFB(1)-N(7)-guanine and AFB(1)-formamidopyrimidine adducts 5- and 30-fold more effectively than did mouse lung, and approximately 6- and 4-fold more effectively than did liver extracts from Sprague-Dawley rats. The susceptibility of mouse lung and rat liver to AFB(1)-induced carcinogenesis correlated with lower DNA repair activity of these tissues relative to mouse liver. Lung extracts prepared from mice treated with a single tumorigenic dose of 50 mg/kg AFB(1) i.p. and euthanized 2 hours post-dosing showed minimal incision and repair synthesis activities relative to extracts from vehicle-treated mice. Conversely, repair activity towards AFB(1)-N(7)-guanine damage was approximately 3.5-fold higher in liver of AFB(1)-treated mice relative to control. This is the first study to show that in vivo treatment with AFB(1) can lead to a tissue-specific induction in DNA repair. The results suggest that lower DNA repair activity, sensitivity of mouse lung to inhibition by AFB(1), and selective induction of repair in liver contribute to the susceptibility of mice to AFB(1)-induced lung tumorigenesis relative to hepatocarcinogenesis.

Exposure to meat-derived carcinogens and bulky DNA adduct levels in normal-appearing colon mucosa.

INTRODUCTION: Meat consumption is a risk factor for colorectal cancer. This research investigated the relationship between meat-derived carcinogen exposure and bulky DNA adduct levels, a biomarker of DNA damage, in colon mucosa. METHODS: Least squares regression was used to examine the relationship between meat-derived carcinogen exposure (PhIP and meat mutagenicity) and bulky DNA adduct levels in normal-appearing colon tissue measured using 32P-postlabelling among 202 patients undergoing a screening colonoscopy. Gene-diet interactions between carcinogen exposure and genetic factors relevant to biotransformation and DNA repair were also examined. Genotyping was conducting using the MassARRAY® iPLEX® Gold SNP Genotyping assay. RESULTS: PhIP and higher meat mutagenicity exposures were not associated with levels of bulky DNA adducts in colon mucosa. The XPC polymorphism (rs2228001) was found to associate with bulky DNA adduct levels, whereby genotypes conferring lower DNA repair activity were associated with higher DNA adduct levels than the normal activity genotype. Among individuals with genotypes associated with lower DNA repair (XPD, rs13181 and rs1799179) or detoxification activity (GSTP1, rs1695), higher PhIP or meat mutagenicity exposures were associated with higher DNA adduct levels. Significant interactions between the XPC polymorphism (rs2228000) and both dietary PhIP and meat mutagenicity on DNA adduct levels was observed, but associations were inconsistent with the a priori hypothesized direction of effect. CONCLUSION: Exposure to meat-derived carcinogens may be associated with increased DNA damage occurring directly in the colon among genetically susceptible individuals.

Aflatoxin B1-induced DNA damage and its repair.

Aflatoxin B(1) (AFB(1))-N(7)-guanine is the predominant adduct formed upon the reaction of AFB(1)-8,9-exo-epoxide with guanine residues in DNA. AFB(1)-N(7)-guanine can convert to the ring-opened formamidopyrimidine, or the adducted strand can undergo depurination. AFB(1)-N(7)-guanine and AFB(1)-formamidopyrimidine are thought to be predominantly repaired by nucleotide excision repair in bacteria, yeast and mammals. Although AFB(1)-formamidopyrimidine is removed less efficiently than AFB(1)-N(7)-guanine in mammals, both lesions are repaired with equal efficiencies in bacteria, reflecting differences in damage recognition between bacterial and mammalian repair systems. Furthermore, DNA repair activity and modulation of repair by AFB(1) seem to be major determinants of susceptibility to AFB(1)-induced carcinogenesis.

The Influence of Alcohol Consumption, Cigarette Smoking, and Physical Activity on Leukocyte Telomere Length.

BACKGROUND: Telomeres protect from DNA degradation and maintain chromosomal stability. Short telomeres have been associated with an increased risk of cancer at several sites. However, there is limited knowledge about the lifestyle determinants of telomere length. We aimed to determine the effect of three factors, known to be important in cancer etiology, on relative leukocyte telomere length (rLTL): alcohol consumption, smoking, and physical activity. METHODS: This cross-sectional study included 477 healthy volunteers ages 20 to 50 years who completed a questionnaire and provided a fasting blood sample. Multiplex quantitative real-time PCR (qPCR) was used to measure rLTL. Regression coefficients were calculated using multiple linear regression while controlling for important covariates. RESULTS: There was no association between alcohol consumption and rLTL. Daily smokers and those in the middle and lower tertile of pack-years smoking had shorter rLTL than never daily smokers (P = 0.02). Data were suggestive of a linear trend with total physical activity (P = 0.06). Compared with the lowest quartile, the highest quartile of vigorous physical activity was associated with longer rLTL. A significant linear trend of increasing rLTL with increasing vigorous physical activity was observed (P = 0.02). CONCLUSIONS: Cigarette smoking and vigorous physical activity have an impact on telomere length. Smoking was related to shorter telomere length while vigorous physical activity was related to longer telomeres. IMPACT: The findings from this study suggest that lifestyle may play an important role in telomere dynamics and also suggest that engaging in healthy behaviors may mitigate the effect of harmful behaviors on telomere length.

Carcinogen-specific targeting of chromosome 12 for loss of heterozygosity in mouse lung adenocarcinomas: implications for chromosome instability and tumor progression.

Genotoxic carcinogens exert their tumorigenic effects in part by inducing genomic instability. We recently showed that loss of heterozygosity (LOH) on chromosome 12 associates significantly with the induction of chromosome instability (CIN) by the likely human lung carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and vinyl carbamate (VC) during mouse lung carcinogenesis. Here, we demonstrate the carcinogen specificity of this event and its effect on lung tumor evolution. LOH on chromosome 12 was observed in 45% of NNK-induced, 59% of VC-induced, 58% of aflatoxin B1 (AFB1)-induced, 14% of N-ethyl-N-nitrosourea (ENU)-induced and 12% of spontaneous lung adenocarcinomas. The frequency of LOH in each of the carcinogen-induced groups, except ENU, was significantly higher than in the spontaneous group (P<0.001). Deletion mapping revealed four potential candidate regions of 1-4 centiMorgans suspected to contain targeted tumor suppressor genes, with at least one expected to have a role in CIN. The relationship between LOH on chromosome 12 and additional chromosomal alterations occurring during lung tumor progression was also examined. LOH on chromosomes 1 and 14 were moderately frequent during malignant progression in tumors from all treatment groups, occurring in 21-35 and 18-33% of tumors. However, these alterations showed significant concurrence with LOH on chromosome 12 in VC-, NNK- and AFB1-induced tumors (P<0.05). The results suggest that a carcinogen-selective mechanism of lung cancer induction involves the frequent inactivation of genes on chromosome 12, including a stability gene that evidently promotes the evolutionary selection of additional chromosomal alterations during malignant progression.

The impact of chronic Aflatoxin B1 exposure and p53 genotype on base excision repair in mouse lung and liver.

Aflatoxin B1 (AFB1) is produced by species of Aspergillus, and is a known human carcinogen. AFB1-induced oxidative DNA damage, specifically 8-hydroxy-2-deoxyguanosine (8-OHdG) lesions, has been demonstrated in both animal models and in humans, and is repaired by base excision repair (BER). The tumour suppressor gene p53 is implicated in the regulation of DNA repair, and heterozygous p53 knockouts have an attenuated nucleotide excision repair response to AFB1. Male heterozygous p53 knockout mice and their wild-type controls were exposed to 0, 0.2 or 1.0ppm AFB1 for 26 weeks in their diet. BER activity of lung and liver was assessed with an in vitro assay, using 8-OHdG-damaged plasmid DNA as a substrate. BER activity did not differ between livers or lungs from untreated wild-type versus heterozygous p53 knockout mice. In wild-type mice, repair was 65% lower in liver extracts from mice exposed to 1.0ppm AFB1 than in liver extracts from mice exposed to 0.2ppm AFB1 (p<0.05), but not significantly lower than that in liver extracts from control mice. AFB1 did not affect BER in lung extracts from wild-type mice, or in lung and liver extracts from heterozygous p53 knockout mice. In liver and lung, AFB1 exposure did not alter levels of 8-oxoguanine glycosylase protein, a key enzyme in the repair of 8-OHdG, and did not cause hepatotoxicity, as indicated by plasma alanine aminotransferase levels. In conclusion, chronic exposure to AFB1 did not affect BER in lungs or livers of heterozygous p53 knockout mice. BER activity was lower in livers from p53 wild type mice exposed to 1.0ppm AFB1 versus those exposed to 0.2ppm AFB1, an effect that was not attributable to liver cell death or altered levels of 8-oxoguanine glycosylase.

Gene-diet interactions in exposure to heterocyclic aromatic amines and bulky DNA adduct levels in blood leukocytes.

Heterocyclic aromatic amines (HAAs), carcinogens produced in meat when cooked at high temperatures, are an emerging biologic explanation for the meat-colorectal cancer relationship. HAAs form DNA adducts; left unrepaired, adducts can induce mutations, which may initiate/promote carcinogenesis. The purpose of this research was to investigate the relationship between dietary HAAs, genetic susceptibility and bulky DNA adduct levels. Least squares regression was used to examine the relationship between dietary HAA exposure and bulky DNA adduct levels in blood measured using (32)P-postlabeling among 99 healthy volunteers. Gene-diet interactions between dietary HAAs and genetic factors relevant to the biotransformation of HAAs and DNA repair were also examined. No main effects of dietary HAAs on bulky DNA adduct levels was found. However, those with the putative NAT1 rapid acetylator phenotype had lower adduct levels than those with the slow acetylator phenotype (P = 0.02). Furthermore, having five or more 'at-risk' genotypes was associated with higher bulky DNA adduct levels (P = 0.03). Gene-diet interactions were observed between NAT1 polymorphisms and dietary HAAs (P < 0.05); among the slow acetylator phenotype, higher intakes of HAAs were associated with an increase in DNA adduct levels compared to lower intakes. This study provides evidence of a biologic relationship between dietary HAAs, genetic susceptibility and bulky DNA adduct formation. However, the lack of a strong main effect of HAAs suggests that dietary HAAs are not a large contributor to bulky DNA adducts in this population; future studies should consider relevant gene-diet interactions to clarify the role of HAAs in carcinogenesis.