The effect of diphenylhydantoin on the frequency of micronuclei in bone-marrow polychromatic erythrocytes of mice

Phenytoin - An anti-seizure drug: Overview of its chemistry, pharmacology and toxicology

Phenytoin is a long-standing, anti-seizure drug widely used in clinical practice. It has also been evaluated in the context of many other illnesses in addition to its original epilepsy indication. The narrow therapeutic index of phenytoin and its ubiquitous daily use pose a high risk of poisoning. This review article focuses on the chemistry, pharmacokinetics, and toxicology of phenytoin, with a special focus on its mutagenicity, carcinogenicity, and teratogenicity. The side effects on human health associated with phenytoin use are thoroughly described. In particular, DRESS syndrome and cerebellar atrophy are addressed. This review will help in further understanding the benefits phenytoin use in the treatment of epilepsy.

Genotoxic and mutagenic studies of teratogens in developing rat and mouse

In this review, genotoxic and mutagenic effects of teratogenic chemical agents in both rat and mouse have been reviewed. Of these chemicals, 97 are drugs and 33 are pesticides or belong to other groups. Large literature searches were conducted to determine the effects of chemicals on chromosome abnormalities, sister chromatid exchanges, and micronucleus formation in experimental animals such as rats and mice. In addition, studies that include unscheduled DNA synthesis, DNA adduct formations, and gene mutations, which help to determine the genotoxicity or mutagenicity of chemicals, have been reviewed. It has been estimated that 46.87% of teratogenic drugs and 48.48% of teratogenic pesticides are positive in all tests. So, all of the teratogens involved in this group have genotoxic and mutagenic effects. On the other hand, 36.45% of the drugs and 21.21% of the pesticides have been found to give negative results in at least one test, with the majority of the tests giving positive results. However, only 4.16% of the drugs and 18.18% of the pesticides were determined to give negative results in the majority of the tests. Among tests with major negative results, 12.50% of the teratogenic drugs and 12.12% of the teratogenic pesticides were negative in all conducted tests.

Effect of polyunsaturated fatty acids on diphenyl hydantoin-induced genetic damage in vitro and in vivo

Phenytoin sodium/diphenyl hydantoin (DPH) is used by a major segment of epileptics and neuro surgery patients with head injury to prevent seizures. DPH is a known mutagen, carcinogen, and teratogen. Essential fatty acids (EFAs) are critical for various tissues and were reported to act as anti-mutagenic agents. In the present study we assessed the effect of five EFAs on DPH-induced genetic damage both in vitro and in vivo. DPH induced significant genetic damage. Of all the EFAs (linoleic acid, alpha-linolenic acid, gamma-linolenic acid, arachidonic acid, dihomo-gamma-linolenic acid, and eicosapentaenoic acid) studied, all except eicosapentaenoic acid showed significant decrease in DPH induced genetic damage as assessed by micronucleus (MN) test. However, gamma-linolenic acid (GLA) was found to be the most effective in reducing the number of MN containing lymphocytes both in vitro and in vivo to control values. EFAs when tested alone produced insignificant increase in the amount of genetic damage but when tested in combination with DPH the number of micronuclei containing lymphocytes was reduced; but the DNA ladder pattern, an indication of DNA damage, was increased. This apparently paradoxical action of EFAs, especially of GLA, suggests that, in all probability, fatty acids induce apoptosis of cells that harbor significant DNA damage. Based on these results we suggest that GLA functions as a unique endogenous molecule that protects cells from accumulating genetic damage.

Genetic toxicities of human teratogens

Birth defects cause a myriad of societal problems and place tremendous anguish on the affected individual and his or her family. Current estimates categorize about 3% of all newborn infants as having some form of birth defect or congenital anomaly. As more precise means of detecting subtle anomalies become available this estimate, no doubt, will increase. Even though birth defects have been observed in newborns throughout history, our knowledge about the causes and mechanisms through which these defects are manifested is limited. For example, it has been estimated that around 20% of all birth defects are due to gene mutations, 5-10% to chromosomal abnormalities, and another 5-10% to exposure to a known teratogenic agent or maternal factor [D.A. Beckman, R.L. Brent, Mechanisms of teratogenesis. Ann. Rev. Pharmacol. Toxicol. 24 (1984) 483-500; K. Nelson, L.B. Holmes Malformations due to presumed spontaneous mutations in newborn infants, N. Engl. J. Med. 320 (1989) 19-23.]. Together, these percentages account for only 30-40%, leaving the etiology of more than half of all human birth defects unexplained. It has been speculated that environmental factors account for no more than one-tenth of all congenital anomalies [D.A. Beckman, R.L. Brent, Mechanisms of teratogenesis, Ann. Rev. Pharmacol. Toxicol. 24 (1984) 483-500]. Furthermore, since there is no evidence in humans that the exposure of an individual to any mutagen measurably increases the risk of congenital anomalies in his or her offspring' [J.F. Crow, C. Denniston, Mutation in human populations, Adv. Human Genet. 14 (1985) 59-121; J.M. Friedman, J.E. Polifka, Teratogenic Effects of Drugs: A Resource for Clinicians (TERIS). The John Hopkins University Press, Baltimore, 1994], the mutagenic activity of environmental agents and drugs as a factor in teratogenesis has been given very little attention. Epigenetic activity has also been given only limited consideration as a mechanism for teratogenesis. As new molecular methods are developed for assessing processes associated with teratogenesis, especially those with a genetic or an epigenetic basis, additional environmental factors may be identified. These are especially important because they are potentially preventable. This paper examines the relationships between chemicals identified as human teratogens (agents that cause birth defects) and their mutagenic activity as evaluated in one or more of the established short-term bioassays currently used to measure such damage. Those agents lacking mutagenic activity but with published evidence that they may otherwise alter the expressions or regulate interactions of the genetic material, i.e. exhibit epigenetic activity, have likewise been identified. The information used in making these comparisons comes from the published literature as well as from unpublished data of the U.S. National Toxicology Program (NTP).

Bone marrow micronucleus assay: a review of the mouse stocks used and their published mean spontaneous micronucleus frequencies

We have examined published negative control data from 581 papers on micronucleated bone marrow polychromatic erythrocytes (mnPCE) for differences in mean frequency and the frequency distribution profile among the mouse stocks used with the bone marrow micronucleus assay. For the 55 mouse stocks with published micronucleus assay data, the overall mean frequency is 1.95 mnPCE/1,000 PCE (1.95 mnPCE/1,000); for the 13 stocks most commonly used in the assay, it is 1.88 mnPCE/1,000. During the last 5 years, the mnPCE rate for these 13 major stocks has been 1.74 mnPCE/1,000. This current mean frequency is a substantial decrease from the mean of 3.07 mnPCE/1,000 observed for these 13 stocks for data published prior to 1981. Of the major stocks, the highest mean mnPCE negative control frequencies were observed for MS/Ae > BALB/c > C57Bl/6, and the lowest for CD-1 < Swiss Webster. We note that hybrid mouse stocks appear to have lower and less variable negative control frequencies than either of their parent strains and that the negative control frequency for some progeny stocks have diverged significantly from that of the parent stocks. Overall mean negative control frequencies appear to be correlated with breadth of the frequency distribution profile of published mean negative control values. Furthermore, a possible correlation between negative control frequency in the micronucleus assay and sensitivity to clastogens of different mouse strains may be indicated. The databases generated here allow us to define a range of norms for both the historical mean frequency and individual experimental mean frequencies for most stocks, but in particular, for the more commonly used mouse stocks. Our analysis, for the most part, bears out the recommendation of the first Gene-Tox Report on the micronucleus assay that the historical negative control frequency for a mouse stock should fall between 1 and 3 mnPCE/1,000. Eighty-six percent of the most commonly used mouse stocks have historical mean frequencies within this range. Though individual experimental mean values would not necessarily be expected to fall within the 1-3.00 mnPCE/1,000 range, 65.3% of the 2,327 published negative control values do, and 83.5% are < 3 mnPCE/1,000. The frequency with which an individual experimental mean value lies outside the 1.00 to 3.00 mnPCE/1,000 range differs among stocks and appears related to the mouse mean frequency. We suggest that the recommended range for historical mean frequency be extended slightly, to approximately 3.4 mnPCE/1,000, to accommodate some commonly used strains with overall mean negative control frequencies just above 3.00 mnPCE/1,000.(ABSTRACT TRUNCATED AT 400 WORDS)

Diphenylhydantoin is not genotoxic in a battery of short-term cytogenetic assays

5,5-Diphenylhydantoin (DPH) is an antiepileptic drug associated with an increase in malformations in infants born to women taking DPH during pregnancy. Positive and negative results have been reported by various investigators for in vivo and in vitro chromosome aberration (CAB) assays, in vivo and in vitro sister chromatid exchange (SCE) assays, and in vivo micronucleus tests (MNT). In this laboratory, DPH was tested in an in vitro CAB assay using Chinese hamster ovary cells with and without an S-9 activation system, an in vivo SCE assay in female CD-1 mice, an in vivo MNT, using both male and female CD-1 mice, and a transplacental micronucleus test. The results from this comprehensive battery of cytogenetic tests were uniformly negative and support a conclusion that the known teratogen, DPH, is not clastogenic.

In vivo cytogenetic activity of diphenylhydantoin in mice

Diphenylhydantoin was tested in vivo in mice using a variety of cytogenetic endpoints to evaluate its genotoxicity. Injected doses of 125, 250 and 500 mg/kg failed to increase the number of chromosome aberrations in marrow cells at 17 h post-treatment, and 37.5, 75 and 150 mg/kg doses were likewise ineffective at 36 h. SCEs were significantly increased by doses of 125 mg/kg (but not 250 mg) after 23 h and modestly, in relation to dose, at 42 h. No increase in the number of micronuclei among marrow PCEs was seen following single i.v. injections ranging from 0.1 to 20 mg/kg. Three daily i.p. injections of doses up to 70 mg/kg also failed to increase the number of micronuclei in either marrow or peripheral blood PCEs. Some cytotoxic effect was evident following relatively high doses.

The in vivo micronucleus assay in mammalian bone marrow and peripheral blood. A report of the U.S. Environmental Protection Agency Gene-Tox Program

The protocol recommended for the micronucleus assay in mammalian bone marrow has been revised and simplified. The number of sample times has been reduced to one or two, depending upon the dosing protocol. The minimum number of cells to be scored per treatment group has been increased to 20,000 to increase the ability of the assay to detect a doubling of the control micronucleus frequency. Use of both male and female animals is recommended. Scoring of micronuclei in polychromatic erythrocytes of peripheral blood is included as a variation of the bone marrow assay. Published data on chemicals tested by the micronucleus assay have been reviewed and are summarized.

Correlations between embryotoxic and genotoxic effects of phenytoin in mice

The anticonvulsant drug phenytoin (DPH) has been suspected to produce embryotoxicity through an arene oxide intermediate. This drug was also found to be a genotoxic agent. These hypotheses were tested in pregnant mice modulating the phases I and II metabolizing enzymes. DPH was studied by assessing embryotoxicity, teratogenicity, and genotoxicity, the latter by the micronucleus test on the polychromatic erythrocytes of dams and fetuses. DPH embryotoxicity was potentiated by inhibiting both cytochrome P-450 and epoxide hydrase and decreased by inducing cytochrome P-450. Equivocal results were obtained by modulating cytochrome P-448. The main DPH metabolite, p-hydroxyphenytoin (HPPH), was ineffective both per se and after cytochrome induction or epoxide hydrase inhibition. DPH did not exert genotoxicity on the maternal organism, no matter which modulating agent was used. In the fetus, however, weak genotoxic effects were observed. These effects significantly increased with inhibition of epoxide hydrase; they disappeared with induction of both cytochromes P-448 and P-450 or with inhibition of the latter. No genotoxicity was exerted by HPPH, even when the enzymatic pattern was modulated. It is concluded that the major role in DPH embryotoxicity is played by the unchanged drug, while the presence of the arene oxide is determinant for genotoxic effects.