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Alkylation, DNA leads to Increase, Mutations
Key Event Relationship Overview
AOPs Referencing Relationship
|AOP Name||Adjacency||Weight of Evidence||Quantitative Understanding||Point of Contact||Author Status||OECD Status|
|Alkylation of DNA in male pre-meiotic germ cells leading to heritable mutations||non-adjacent||High||Moderate||Carole Yauk (send email)||Open for citation & comment||WPHA/WNT Endorsed|
|Alkylation of DNA leading to cancer 1||non-adjacent||High||Moderate||Carole Yauk (send email)||Open for adoption|
Life Stage Applicability
Key Event Relationship Description
Alkylated DNA may be ‘misread’ during DNA replication, leading to insertion of incorrect nucleotides. Upon replication, these changes become fixed as mutations. Subsequent replication propagates these mutations to daughter cells. Mutations in stem cells are of the greatest concern, as these will persist throughout the organism’s lifetime. Thus, increased mutations will be found in the cells of organisms that possess alkylated DNA.
Evidence Collection Strategy
Evidence Supporting this KER
Alkylating agents can cause a variety of adducts and DNA damage (e.g., alkali labile sites, DNA strand breaks, etc.) that are potentially mutagenic and clastogenic. This KER focuses on the probability that an alkyl DNA adduct will lead to a mutation.
Not all adducts are equally mutagenic. Very generally, chemicals that preferentially cause O-alkylation in DNA induce DNA sequence changes, whereas chemicals that cause N-alkylation of DNA are more efficient inducers of structural chromosomal aberrations (reviewed in Beranek 1990). Indeed, a review of the biological significance of N7 alkyl-guanine adducts concluded that these adducts simply be used to confirm exposure to target tissue (Boysen et al., 2009), because the vast majority of studies shows that these adducts do not cause mispairing. A variety of work has demonstrated that N7-alkylguanine adducts can be bypassed essentially error free (e.g., Philippin et al., 2014; Shrivastav et al., 2010). Moreover, alkylation can involve modification with different sizes of alkylation groups (e.g., methyl, ethyl, propyl). Although response to these is qualitatively similar with respect to the key events, in general, larger alkylating groups tend to be more mutagenic (Beranek, 1990). It is widely known that chemicals that preferentially cause O-alkylation in DNA induce mutations. ENU (N-ethyl-N-nitrosourea) is a prototypical O-alkylating agent and the most studied male germ cell mutagen.
Alkylating agents are prototypical somatic and male germ cell mutagens.
Uncertainties and Inconsistencies
As described above, not all alkyl adducts are mutagenic. The proportion of oxygen-alkylation and the type of mutation (with ethylation > methylation) will govern mutagenicity, but there are few empirical data to support this. There are no inconsistencies or uncertainties for ENU or iPMS; other alkylating agents (EMS, MMS) have yielded some discrepancies in the transgenic rodent mutation assay. However, the experimental protocols applied were sub-standard (the OECD TG for this analysis was revised and published in 2013). Overall, more work is needed on alkylating agents other than ENU to fill important data gaps.
Known modulating factors
Known Feedforward/Feedback loops influencing this KER
Domain of Applicability
Alkylating agents are well-established to cause mutation in virtually any cell type in any organism.
Beranek, D.T. (1990), "Distribution of methyl and ethyl adducts following alkylation with monofunctional alkylating agents", Mutation Research, 231(1): 11-30.
Boysena, G., B.F. Pachkowski, J. Nakamura and J.A. Swenberg (2009), "The formation and biological significance of N7-guanine adducts", Mutation Research, 678: 76–94.
Brooks, T.M. and S.W. Dean (1997), "The detection of gene mutation in the tubular sperm of Muta Mice following a single intraperitoneal treatment with methyl methanesulphonate or ethylnitrosourea", Mutat. Res., 388(2-3): 219-222.
Douglas, G.R., J. Jiao, J.D. Gingerich, J.A. Gossen and L.M. Soper (1995), "Temporal and molecular characteristics of mutations induced by ethylnitrosourea in germ cells isolated from seminiferous tubules and in spermatozoa of lacZ transgenic mice", Proc. Natl. Acad. Sci. USA, 92(16): 7485-7489.
Katoh, M., N. Horiya and R.P. Valdivia (1997), "Mutations induced in male germ cells after treatment of transgenic mice with ethylnitrosourea", Mutat Res. 1997 Feb 14;388(2-3):229-37.
Katoh, M., T. Inomata, N. Horiya, F. Suzuki, T. Shida, K. Ishioka and T. Shibuya (1997), "Studies on mutations in male germ cells of transgenic mice following exposure to isopropyl methanesulfonate, ethylnitrosourea or X-ray", Mutat. Res., 388(2-3):213-8.
Liegibel, U.M. and P. Schmezer (1994), "Detection of the two germ cell mutagens ENU and iPMS using the LacZ/transgenic mouse mutation assay" Mutat. Res., 341(1):17-28.
Mattison, J.D., L.B. Penrose and B. Burlinson (1997), "Preliminary results of ethylnitrosourea, isopropyl methanesulphonate and methyl methanesulphonate activity in the testis and epididymal spermatozoa of Muta Mice", Mutat. Res. 388(2-3): 123-7.
Mientjes, E.J., K. Hochleitner, A. Luiten-Schuite, J.H. van Delft, J. Thomale, F. Berends, M.F. Rajewsky, P.H. Lohman and R.A. Baan (1996), "Formation and persistence of O6-ethylguanine in genomic and transgene DNA in liver and brain of lambda(lacZ) transgenic mice treated with N-ethyl-N-nitrosourea", Carcinogenesis, 17(11): 2449-2454.
Mientjes, E.J., A. Luiten-Schuite, E. van der Wolf, Y. Borsboom, A. Bergmans, F. Berends, P.H. Lohman, R.A. Baan RA, J.H. van Delft (1998), "DNA adducts, mutant frequencies, and mutation spectra in various organs of lambda lacZ mice exposed to ethylating agents", Environ. Mol. Mutagen., 31(1): 18-31
Norris, M.B. and R.N. Winn (2010), "Isolated spermatozoa as indicators of mutations transmitted to progeny", Mutat. Res., 688(1-2): 36–40.
Labib, S., C. Yauk, A. Williams, V.M. Arlt, D.H. Phillips, P.A. White and S. Halappanavar (2012)," Subchronic oral exposure to benzo(a)pyrene leads to distinct transcriptomic changes in the lungs that are related to carcinogenesis. Toxicol Sci 129(1):213-224.
Malik, A.I., A. Williams, C.L. Lemieux, P.A. White and C.L. Yauk (2012), "Hepatic mRNA, microRNA, and miR-34a-target responses in mice after 28 days exposure to doses of benzo(a)pyrene that elicit DNA damage and mutation", Environ. Mol. Mutagen., 53(1): 10-21.
Malik, A.I., A. Rowan-Carroll, A. Williams, C.L. Lemieux, A.S. Long, V.M. Arlt, D.H. Phillips, P.A. White and C.L. Yauk (2013), "Hepatic genotoxicity and toxicogenomic responses in MutaMouse males treated with dibenz[a,h]anthracene", Mutagenesis, 28(5): 543-554.
O'Brien, J.M., M.A. Beal, J.D. Gingerich, L. Soper L, G.R. Douglas, C.L. Yauk and F. Marchetti (2014), "Transgenic rodent assay for quantifying male germ cell mutant frequency", J. Vis. Exp., (90): e51576.
O’Brien, J.M., M. Walker, A. Sivathayalan, G.R. Douglas, C.L. Yauk and F. Marchetti (2015), "Sublinear response in lacZ mutant frequency of Muta™ Mouse spermatogonial stem cells after low dose subchronic exposure to N-ethyl-N-nitrosourea", Environ. Mol. Mutagen., 56(4): 347-55.
Renault, D., D. Brault and V. Thybaud (1997), "Effect of ethylnitrosourea and methyl methanesulfonate on mutation frequency in MutaMouse germ cells (seminiferous tubule cells and epididymis spermatozoa)", Mutat. Res., 388(2-3): 145-153.
Shrivastav, N., D. Li and J.M. Essigmann (2010), "Chemical biology of mutagenesis and DNA repair: cellular responses to DNA alkylation", Carcinogenesis, 31(1): 59-70.
Skopek, T.R., K.L. Kort, D.R. Marino, L.V. Mittal, D.R. Umbenhauer, G.M. Laws and S.P. Adams (1996), "Mutagenic response of the endogenous hprt gene and lacI transgene in benzo[a]pyrene-treated Big Blue B6C3F1 mice", Environ. Mol. Mutagen., 28(4): 376-384.
Suzuki, T., S. Itoh, N. Takemoto, N. Yajima, M. Miura, M. Hayashi, H. Shimada and T. Sofuni (1997), "Ethyl nitrosourea and methyl methanesulfonate mutagenicity in sperm and testicular germ cells of lacZ transgenic mice (Muta Mouse)", Mutat. Res., 388(2-3): 155-163.
Swenberg, J.A., E. Fryar-Tita, Y. Jeong, G. Boysen, T. Starr, V.E. Walker and R.J. Albertini (2008), "Biomarkers in toxicology and risk assessment: informing critical dose-response relationships", Chem. Res. Toxicol., 21(1): 253-265.
Swayne, B.G., A. Kawata, N.A. Behan, A. Williams, M.G. Wade, A.J. Macfarlane and C.L. Yauk (2012), "Investigating the effects of dietary folic acid on sperm count, DNA damage and mutation in Balb/c mice", Mutat. Res., 737(1-2): 1-7.
Tinwell, H., P. Lefevre, C.V. Williams and J. Ashby (1997), "The activity of ENU, iPMS and MMS in male mouse germ cells using the Muta Mouse positive selection transgenic mutation assay", Mutat. Res., 388(2-3): 179-185.
van Delft J.H., A. Bergmans and R.A. Baan RA (1997), "Germ-cell mutagenesis in lambda lacZ transgenic mice treated with ethylating and methylating agents: comparison with specific-locus test", Mutat. Res., 388(2-3): 165-173.
van Delft, J.H. and R.A. Baan (1995), "Germ cell mutagenesis in lambda lacZ transgenic mice treated with ethylnitrosourea; comparison with specific-locus test", Mutagenesis, 10(3): 209-214.
van Zeeland, A.A., A. de Groot and A. Neuhäuser-Klaus (1990), "DNA adduct formation in mouse testis by ethylating agents: a comparison with germ-cell mutagenesis", Mutat. Res., 231(1):55-62.