Clustered binary logistic regression in teratology data using a finite mixture distribution.

The beta-binomial distribution introduced by Skellam has been applied in many teratology problems for modelling the litter effect. Recently, Morel and Nagaraj proposed a new distribution for modelling cluster multinomial data when the clustering is believed to be caused by clumped sampling. It turns out that the distribution is a mixture of two binomial distributions and accommodates the estimation of an additional parameter to account for intra-litter effect. The new distribution arises from a cluster mechanism in which some individuals within a cluster exhibit the same behaviour while the remaining individuals from the cluster react independently of each other. Such a mechanism is a natural model in teratology problems, where typically a genetic trait is passed with a certain probability to the foetuses of the same litter. In this article, we use the new distribution to model binary responses with logistic regression. We analyse data from a teratology experiment to demonstrate that the new model provides a useful addition to current methodology. The experiment investigates the synergistic effect of the anticonvulsant phenytoin and trichloropopene oxide on the prenatal development of inbred mice. In a simulation study we investigate the type I error rate and the power of the maximum likelihood ratio test when the data follow a finite mixture distribution.

Evaluation of the generation of genotoxic and cytotoxic metabolites of benzo[a]pyrene, aflatoxin B1, naphthalene and tamoxifen using human liver microsomes and human lymphocytes.

1. The ability of model stable epoxides and metabolites generated by human liver microsomes from benzo[a]pyrene, aflatoxin B1, naphthalene and tamoxifen to produce cytotoxicity and genotoxicity in human peripheral lymphocytes has been investigated. 2. The stable epoxides 1,1,1 trichloropropene-2,3-oxide (100 microM) and trans stilbene oxide (100 microM) as well as metabolites generated from aflatoxin B1 (30 microM) and naphthalene (100 microM) by an extracellular metabolising system were toxic to isolated resting mononuclear leucocytes (MNLs), whereas glycidol (100 microM), benzo[a]pyrene (100 microM) and tamoxifen (50 microM) were not. 3. The stable epoxides 1,1,1 trichloropropene-2,3-oxide (100 microM) and trans stilbene oxide (100 microM) but not glycidol (100 microM) were toxic to dividing lymphocytes only after a 72-h exposure. Tamoxifen (30 microM), aflatoxin B1 (30 microM) and their metabolites were also toxic to dividing lymphocytes. Benzo[a]pyrene (100 microM) and naphthalene (100 microM) were not toxic either in the absence or presence of the extracellular metabolising system. 4. Benzo[a]pyrene (100 microM) and aflatoxin B1 (30 microM) were directly genotoxic to lymphocytes, this genotoxicity was significantly enhanced by the presence of the extracellular metabolising system. This indicates that both intracellular and extracellular bioactivation of these two compounds can produce genotoxicity. In contrast, naphthalene and tamoxifen were non-genotoxic.

Chromosomal aberrations in mouse lymphocytes exposed in vivo and in vitro to aliphatic epoxides.

Mouse lymphocytes in vivo or in vitro were exposed for 24 h to 4 aliphatic epoxides, glycidyl 1-naphthyl ether, glycidyl 4-nitrophenyl ether, 1-naphthyl-propylene oxide and trichloropropylene oxide (TCPO), and tested for the induction of chromosomal aberrations (CA). These epoxides were among the most genotoxic aliphatic epoxides in our previous studies. With the exception of TCPO, the test epoxides caused significant increases in CA in vivo compared to a negative control. There were concentration related increases in CA for all 4 epoxides in vitro and TCPO produced the greatest cellular toxicity and genotoxic effects towards cultured lymphocytes. The difference in the order of genotoxicity for the two test systems can be explained on the basis of a much shorter half-life for TCPO than for the other epoxides.

Genotoxicity characteristics of reverse diol-epoxides of chrysene.

Trans-3,4-dihydroxy-3,4-dihydrochrysene (chrysene-3,4-diol), a major metabolite of chrysene, is further metabolized by rat liver enzymes to products which effectively revert the his- Salmonella typhimurium strain TA98 to histidine prototrophy, but are only weakly mutagenic in strain TA100 and in Chinese hamster V79 cells (acquisition of resistance to 6-thioguanine). The liver enzyme mediated mutagenicity of chrysene-3,4-diol is substantially enhanced in the presence of 1,1,1-trichloropropene 2,3-oxide, an inhibitor of microsomal epoxide hydrolase. The predominant metabolites of chrysene-3,4-diol, namely the anti- and syn-isomers of its 1,2-oxide (termed reverse diol-epoxides), proved to be extraordinarily effective mutagens in S.typhimurium strain TA98, but were only moderately active in strains TA100 and TA104, and in the SOS induction in Escherichia coli PQ37. These genotoxicity spectra in bacteria are completely different from those observed with the bay-region diol-epoxides of chrysene and 3-hydroxychrysene. In V79 cells, the reverse diol-epoxides formed low levels of DNA adducts and were very weak inducers of gene mutations. In M2 mouse prostate cells, however, high numbers of transformed foci were induced by chrysene-3,4-diol and its diastereomeric 1,2-oxides. Chrysene-3,4-diol was somewhat more potent than chrysene-1,2-diol. The potency of both reverse diol-epoxides was similar to that of the syn-diastereomers of the bay-region diol-epoxides of chrysene and 3-hydroxychrysene, but lower than that of their anti-diastereomers. The reverse diol-epoxides of chrysene, unlike the bay-region diol-epoxides, were inactivated by purified microsomal epoxide hydrolase. Noteworthy findings were also made with regard to the chemical stability of the diol-epoxides in buffer, determined from the decline in mutagenicity after preincubation in the absence of the target cells. Despite its lower delta Edeloc/beta value for the formation of the benzylic carbocation, anti-chrysene-3,4-diol 1,2-oxide was shorter-lived (t1/2 = 46 min) than anti-chrysene-1,2-diol 3,4-oxide (t1/2 = 74 min). Unlike other investigated diastereomeric pairs of diol-epoxides, it was also shorter-lived than its syn-diastereomer (t1/2 = 340 min).

Base-pair mutations caused by six aliphatic epoxides in Salmonella typhimurium TA100, TA104, TA4001, and TA4006.

Salmonella typhimurium strains TA100, TA104, TA4001, and TA4006 were used to detect the base-pair mutations caused by six aliphatic epoxides: chloropropylene oxide, glycidyl 1-naphthyl ether, glycidyl 4-nitrophenyl ether, 1-naphthyl-propylene oxide, styrene oxide, and trichloropropylene oxide. Dose-mutagenicity relationships could be established for all six epoxides in strains TA100 and TA104 but not in strains TA4001 and TA4006. These results, together with the lack of sensitivity of the TA100 revertants to DL-1,2,4-triazole-3-alanine, indicate CG-->TA transitions and/or CG-->AT transversions are of major importance for mutations induced by these epoxides in Salmonella TA100 and possibly TA104. In addition, since the reproducibility of the effect of the triazole on TA104 reversions was poor, TA-->AT transversions were not eliminated as also contributing to the mutagenicity of these epoxides in this Salmonella strain.

Genetic toxicology of propylene oxide and trichloropropylene oxide--a review.

Aliphatic epoxides are a group of compounds extensively used in industry and as laboratory reagents, and can be produced as metabolic intermediates. An important aliphatic epoxide is propylene oxide, extensively used in the production of propylene glycol and polyols used in the manufacture of polyurethane polymers. The widespread human exposure to propylene oxide is of great health concern. In this review an attempt has been made to evaluate and update the genotoxic effects of propylene oxide and trichloropropylene oxide based on the available literature.