Modification of the teratogenicity and mutagenicity of cyclophosphamide with thiol compounds

Abstract

Cyclophosphamide must be metabolized to have either therapeutic or toxic effects; many of the major metabolites of cyclophosphamide interact with thiol compounds. To characterize the relationship between the teratogenic and mutagenic metabolites of cyclophosphamide, the effect of thiol compounds on the teratogenicity and mutagenicity of this drug was studied. The effect on teratogenicity was assessed in vivo by treatment of rats with thiol compounds or thiol‐depleting agents prior to administration to cyclophosphamide on day 13 of gestation. The effect on mutagenicity was measured in vitro with a bacterial mutagenicity test using Salmonella typhimurium TA 1535. The administration of thiol compounds (glutathione or cysteine) decreased the teratogenicity of cyclophosphamide, whereas the administration of a thiol‐depleting agent (diethyl maleate) increased its teratogenicity. Low concentrations of glutathione (0.1–1.0 mM) increased the mutagenicity of cyclophosphamide; this effect was not observed with S‐methylglutathione or other thiol compounds. Higher concentrations of glutathione (10 mM, reduced or oxidized) and cystine, but not cysteine, decreased the mutagenicity of cyclophosphamide. Reduced dithiothreitol also decreased the mutagenicity of cyclophosphamide but was toxic in experiments in vivo so its effect on teratogenicity could not be evaluated. Thus, thiol compounds modify both the teratogenic and mutagenic effects of cyclophosphamide. Low concentrations of glutathione (the addition of glutathione in mutagenicity experiments or the depletion of endogenous glutathione in teratogenicity experiments) increased both the mutagenicity and the teratogenicity of cyclophosphamide, whereas high concentrations of this or other thiol compounds decreased these toxic effects. It may be possible to exploit the protective effect of thiol compounds clinically by using thiols to protect pregnant women from the teratogenic effects of inadvertent or intentional administration of cyclophosphamide.

Preventive effect of piperonyl butoxide on cyclophosphamide‐induced teratogenesis in rats

“…Since the present study is presumably the first report to show that PBO decreases CYP2B activity by suppressing the expression of its mRNA, an additional study to clarify the direct effect of PBO, including the reversible or irreversible manner of inhibition, on this enzyme activity is warranted. On the other hand, previous reports have indicated that oxidative stress is a significant factor contributing to cyclophosphamide-induced fetal malformations, which are substantially attenuated by antioxidants, such as glutathione, cysteine, and indole-3-carbinol, but exacerbated by glutathione depletion (Hales, 1981;Slott and Hales, 1987;Han et al, 1995;Bailey et al, 2005). Recently, we demonstrated that butylated hydroxyanisole, a synthetic antioxidant food additive, markedly reduced the incidence and severity of fetal defects induced by cyclophosphamide in rats and mice (Kang et al, 2003;Kim et al, 2003).…”

PCR‐RFLP to detect codon 248 mutation in exon 7 of p53 tumor suppressor gene

“…In another model, pregnant rats are dosed on gestation day 13 with 12.5 mg/kg of CPA (morning of plug=0). Remarkably, in this paradigm such treatments induce encephalocele at a rate of 96% despite the neural tube having closed on approximately gestation 11 (Zhao et al, 2010). This observation contradicts our previous concept about windows of susceptibility, which posit that such neural tube defects should no longer occur after the neural tube has closed.…”

“…In contrast, the intervention treatment plus CPA had the opposite effects on the number of cells expressing Blc‐2 and Bax. Based upon literature reports and maternal NOT embryonic measures of oxidative stress, Zhao et al (2010) suggest the amelioration of CPA's effects are the result of the antioxidant properties of soy isoflavones and folic acid. It is the reviewer's opinion that there may be another explanation.…”

Licorice extract increases cyclophosphamide teratogenicity by upregulating the expression of cytochrome P‐450 2B mRNA

“…On the other hand, oxidative stress is also a significant factor contributing to cyclophosphamide‐induced fetal malformations. This is substantially attenuated by antioxidants, such as glutathione, cysteine, and indole‐3‐carbinol, but exacerbated by glutathione depletion (Hales, 1981; Slott and Hales, 1987; Han et al, 1995; Bailey et al, 2005). We demonstrated that butylated hydroxyanisole, a synthetic antioxidant food additive, markedly reduced the incidence and severity of fetal defects induced by cyclophosphamide in rats and mice (Kang et al, 2003; Kim et al, 2003).…”