Trans-ancestry genome-wide association study identifies 12 genetic loci influencing blood pressure and implicates a role for DNA methylation

We carried out a trans-ancestry genome-wide association and replication study of blood pressure phenotypes among up to 320,251 individuals of East Asian, European and South Asian ancestry. We find genetic variants at 12 new loci to be associated with blood pressure (P = 3.9 × 10-11 to 5.0 × 10-21). The sentinel blood pressure SNPs are enriched for association with DNA methylation at multiple nearby CpG sites, suggesting that, at some of the loci identified, DNA methylation may lie on the regulatory pathway linking sequence variation to blood pressure. The sentinel SNPs at the 12 new loci point to genes involved in vascular smooth muscle (IGFBP3, KCNK3, PDE3A and PRDM6) and renal (ARHGAP24, OSR1, SLC22A7 and TBX2) function. The new and known genetic variants predict increased left ventricular mass, circulating levels of NT-proBNP, and cardiovascular and all-cause mortality (P = 0.04 to 8.6 × 10-6). Our results provide new evidence for the role of DNA methylation in blood pressure regulation

DNA adducts, mutant frequencies and mutation spectra in λlacZ transgenic mice treated with N-nitrosodimethylamine

Groups of λlacZ transgenic mice were treated i.p. with N-nitrosodimethylamine (NDMA) as single doses of 5 mg/kg or 10 mg/kg or as 10 daily doses of 1 mg/kg and changes in DNA N7- or O6-methylguanine or the repair enzyme O6-alkylguanine-DNA alkyltransferase (AGT) were followed for up to 14 days in various tissues. Adduct induction in the liver exceeded by at least one order of magnitude than observed in the next nearest target tissue (lung), and was approximately linearly related to dose, except for O6-methylguanine after the first dose of 1 mg/kg which was lower than expected. Substantial induction of λlacZ mutagenesis was observed only in the liver, where the mutant frequency was already maximal within 7 days after 5 mg/kg NDMA and remained unchanged thereafter up to 49 days. Small but marginally significant increases in mutant frequency were consistently observed in the spleen after all three modes of treatment. A lack of proportionality between mutation induction and the administered dose or the corresponding adduct levels was observed, probably reflecting the importance of toxicity-related cell proliferation caused by NDMA at higher doses. Twenty eight days after a dose of 10 mg/kg (causing a 3.6-fold increase in mutant frequency), NDMA was found to increase the frequency of GC→AT mutations (with a concomitant shift of their preferential location from CpG sites to GpG sites), which made up ~ 60% of the induced mutations. Surprisingly, NDMA also caused a significant increase in deletions of a few (up to 11) base-pairs (22%)

Induction of somatic mutations but not methylated DNA adducts in λlacZ transgenic mice by dichlorvos

In order to examine the in vivo genotoxic activity of dichlorvos, λlacZ transgenic mice (Muta(TM)Mouse) were treated i.p. with single (4.4 or 11 mg/kg) or multiple (5x11 mg/kg) doses of this agent and sacrificed 4 h or 14 days post-treatment for DNA adduct measurement or mutant frequency analysis, respectively. Neither methylated DNA adducts nor an increase in mutant frequency were detected in the bone marrow, white blood cells, liver, spleen, lung, brain and sperm cells after the single doses. However, following multiple dosing a statistically significant 3-fold increase in mutant frequency was observed in the liver, while a non-statistically significant increase was observed in the bone marrow. In contrast, dimethylsulphate, a model methylating agent, gave rise to detectable DNA adducts but no increase in mutant frequency following i.p. administration of single (30 mg/kg) or multiple (10x6 mg/kg) doses. Copyright (C) 1999 Elsevier Science Ireland Ltd

Methyl bromide causes DNA methylation in rats and mice but fails to induce somatic mutations in λlacZ transgenic mice

Following single or multiple oral treatments of rats or λlacZ transgenic mice with methyl bromide, methylated DNA adducts (N7- and/or O6-methylguanine) were found at comparable levels in various tissues, including among others the glandular stomach, the forestomach and the liver. Multiple rat treatment resulted in substantial decreases in the repair enzyme O6-alkylguanine-DNA alkyltransferase which were probably due in part to direct interaction of the enzyme with methyl bromide. However, no induction of mutagenesis in the lacZ transgene could be detected in any tissue 14 days after single treatments of up to 50 mg/kg or after multiple treatments of as many as 10 daily treatments of 25 mg/kg MeBr. Copyright (C) 1998 Elsevier Science Ireland Ltd

Monitoring for DNA damage of humans occupationally exposed to methyl bromide

Monitoring for DNA damage of humans occupationally exposed to methyl bromide. Pletsa V, Steenwinkel MJ, Stoikidou M, van Delft JH, Baan RA, Katsouyanni K, Kyrtopoulos SA. Laboratory of Chemical Carcinogenesis, Institute of Biological Research and Biotechnology, National Hellenic Research Foundation, Athens, Greece. [email protected] BACKGROUND: Methyl bromide (MeBr) is a methylating agent, weak mutagen and possible animal carcinogen. A molecular epidemiological study to examine human exposure to, and consequent DNA damage by MeBr was conducted in an area where this agent is used extensively for soil sterilisation in greenhouses. MATERIALS AND METHODS: During the first part of the study, blood samples were collected from 21 persons within 24 hours after use of MeBr for greenhouse sterilisation, as well as from 19 non-exposed subjects. Personal air sampling was also carried out, indicating mean air concentrations for different subjects in the range 11-78 mg/m3. In the second part of the study, an attempt was made to examine professional applicators of MeBr who suffered particularly high exposures (mean exposures, based on personal monitoring 23-165 mg/m3). The levels of N7-methylguanine and O6-methylguanine, two DNA adducts known to be induced by MeBr, were assessed in blood leukocyte DNA. RESULTS: Concerning the first part, two subjects (one exposed and one control) were found to be positive for N7-methylguanine, while none of the blood samples analysed had detectable levels of O6-methylguanine. Among 6 such persons examined during the second part, 2 were found positive for N7-methylguanine while none was positive for O6-methylguanine. CONCLUSION: Within the detection power of this limited study, no significant evidence of induction of DNA damage in blood leukocyte DNA by MeBr was found

Progressive changes in chromatin structure and DNA damage response signals in bone marrow and peripheral blood during myelomagenesis

The molecular pathways implicated in multiple myeloma (MM) development are rather unknown. We studied epigenetic and DNA damage response (DDR) signals at selected model loci (N-ras, p53, d-globin) in bone marrow plasma cells and peripheral blood mononuclear cells (PBMCs) from patients with monoclonal gammopathy of undetermined significance (MGUS; n=20), smoldering/asymptomatic MM (SMM; n=29) and MM (n=18), as well as in healthy control-derived PBMCs (n=20). In both tissues analyzed, a progressive, significant increase in the looseness of local chromatin structure, gene expression levels and DNA repair efficiency from MGUS to SMM and finally to MM was observed (all P<0.002). Following ex vivo treatment with melphalan, a gradual suppression of the apoptotic pathway occurred in samples collected at different stages of myelomagenesis, with the severity and duration of the inhibition of RNA synthesis, p53 phosphorylation at serine15 and induction of apoptosis being higher in MGUS than SMM and lowest in MM patients (all P<0.0103). Interestingly, for all endpoints analyzed, a strong correlation between plasma cells and corresponding PBMCs was observed (all P<0.0003). We conclude that progressive changes in chromatin structure, transcriptional activity and DDR pathways during myelomagenesis occur in malignant plasma cells and that these changes are also reflected in PBMCs. © 2014 Macmillan Publishers Limited. All rights reserved

N7-methylguanine and O6-methylguanine levels in DNA of white blood cells from cancer patients treated with dacarbazine

Methyl-DNA adducts are induced by a number of lifestyle, environmental and occupational carcinogens, however knowledge about their kinetics is scarce. Here, N7-methylguanine (N7-MeGua) and O6-methylguanine (O6-MeGua) levels were determined in the DNA of white blood cells from eight cancer patients treated iv with the antitumour drug dacarbazine (DTIC). Five of the patients were treated with the drug as a single agent (a single dose of 800 mg m-2) and three on three successive days with dacarbazine (225 mg m-2 day-1) in combination with other drugs. The data indicate that maximum adduct levels are reached at 4-8 h after treatment and that the amount of N7-MeGua is at least 20-fold higher than that of O6-MeGua. The half-life of N7-MeGua is 40-96 h and that of O6-MeGua 25-27 h. Following treatment on three consecutive days, an accumulation of N7-MeGua was observed but not of O6-MeGua. The data show substantial interindividual differences in adduct levels but not in the ratio of N7/O6-MeGua. This may reflect differences in the metabolism of dacarbazine or in repair capacities. © 1996 Taylor & Francis Ltd