The influence of 6-mercaptopurine on rat placenta and fetus

Microarray analysis of 6-mercaptopurine-induced-toxicity-related genes and microRNAs in the rat placenta

MicroRNAs (miRNAs) are small single-stranded RNAs of 19-25 nucleotides and are important in posttranscriptional regulation of genes. Recently, the role of miRNAs in toxicity incidence is reported to be a regulator of key-stopper of gene expression, however the detailed mechanism of miRNAs is not well known yet. 6-Mercaptopurine (6-MP), the anti-leukemic and immunosuppressive drug, produced teratogenicity and pregnancy loss. We focused on the placenta to evaluate toxicity in embryo/fetal development produced by 6-MP treatment. MiRNA expression in the placenta was analyzed by miRNA microarray. Fifteen miRNAs were upregulated on GD13 and 5 miRNAs were downregulated on GD15 in 6-MP treatment rat placentas. Some miRNAs may have functions in apoptosis (miR-195, miR-21, miR-29c and miR-34a), inflammation (miR-146b), and ischemia (miR-144 and miR-451). In the maternal plasma, expression of miR-144 was significantly reduced by 6-MP treatment when examined by real-time RT-PCR. We determined toxicity-related gene expression in the rat placenta. Gene expression analysis was carried out by DNA oligo microarray using rat placenta total RNAs. Compared between predicted targets of miRNAs and microarray data in 6-MP-treated rat placenta, expressions of hormone receptor genes (estrogen receptor 1; Esr1, progesterone receptor; Pgr, and prolactin receptor; Prlr), xanthine oxidase (Xdh), Slc38a5 and Phlda2 genes were changed. The histopathologically found increase in trophoblastic giant cells and reduced placental growth by 6-MP treatment were well correlated to these gene expressions. These data suggest that some miRNAs may link to toxicological reactions in 6-MP-induced placental toxicity.

6-Mercaptopurine-induced histopathological changes and xanthine oxidase expression in rat placenta

The placenta secures the embryo and fetus to the endometrium and releases a variety of steroid and peptide hormones that convert the physiology of a female to that of a pregnant female. Chemical-induced alteration or deviation of placental function in the maternal and extraembryonic tissue can ultimately lead to pregnancy loss, congenital malformation and fetal death. The 6-mercaptopurine (6-MP), an anti-leukemic drug, is known to produce undesired effects on some organs, then the placenta/embryo toxicity of 6-MP was investigated in pregnant rats given 60 mg/kg with two intraperitoneal injections on gestation days (GD) 11 and 12. The rats were sacrificed and their placentas were collected on GD13 or 15. On GD15 small and limb-defected embryos were found in the 6-MP-treated rats. Placental weights were significantly reduced on GD15, as well as a reduced number of cells was detected in the labyrinth zone with both the labyrinth and basal zones having thinned. Cleaved caspase-3-positive cells increased in number in the labyrinth zone, while in the basal zone, glycogen cells reduced with cytolysis. The number of spongiotrophoblasts and trophoblastic giant cells also increased by 6-MP treatment. The 6-MP-treatment resulted in the increased xanthine oxidase (Xdh) expression in the placenta, which gene is related to the ischemic condition of tissues. These data suggest that apoptosis of the labyrinth zone cells may lead to decreased materno-fetal exchange. Moreover, subsequent ischemia in the placental tissue may occur and induce Xdh expression.

Effect of 6-mercaptopurine on rat placenta

In order to investigate the toxic effects of 6-mercaptopurine (6-MP) on placental development, we examined sequential morphology in the placentas from rats exposed to 6-MP. 6-MP was intraperitoneally administered at 60 mg/kg during gestation days (GDs) 11 to 12, and the placentas were sampled on GD 13, 15 or 21. In the 6-MP-treated group, maternal body weight suppression, increased death embryo/fetus ratio and some malformations were observed. The placenta weights were decreased on GDs 15 and 21. Macroscopically, placentas on GD 21 were small, brittle and thin with a white peripheral rim. Histopathologically, in the labyrinth zone, 6-MP treatment mainly evoked decreased mitosis on GDs 13 and 15, increased apoptotic cell on GDs 13, 15 and 21 and thinning on GDs 15 and 21. In the basal zone, 6-MP evoked decreased mitosis on GDs 13, and PAS-positive material in the spongiotrophoblasts was still detected on GD 15. Thickening of the basal zone was observed with cytolysis of glycogen cells, apoptosis and an increased number of composed cells on GD 21. In conclusion, 6-MP administration in pregnant rats induced growth arrest of the labyrinth zone and developmental delay in the basal zone, leading to small placentas. The fetotoxicity of 6-MP may be responsible for its direct anti-proliferative effects and resulting placental dysfunction.

Attenuating effect of zinc on abnormal placental morphology in 6-mercaptopurine treated rats

Pregnant Sprague-Dawley rats were fed diets containing 9 (marginal level), 100 (control level), or 1,000 (very high level) ppm zinc and were given a single intraperitoneal injection of 6-mercaptopurine (6-MP, 55 mg/kg) or an equivalent volume of carboxymethylcellulose on day 11 of gestation. Live young and their placentas were recovered at surgery on day 21 of gestation: they were weighed, measured, and placentas were examined histologically. Placentas from drug treated animals were smaller in diameter and lighter in weight than controls; however, the placentas of animals fed the 1,000 ppm zinc diet were significantly heavier than those of the other drug-treated groups. Histologically, the placentas of the 6-MP treated dams showed a highly disproportionate reduction in the labyrinthine layer with larger, less subdivided maternal sinuses than in controls, reduction of fetal vasculature, vesiculation of trophoblast nuclei, deposition of PAS positive material in the septal wall, and fibrinous degeneration of trophoblast cells. These morphological changes were reduced in placental tissues of drug treated rats given 1,000 ppm of zinc. In contrast, no placental abnormalities were observed in rats not treated with 6-MP.

Relationship of dietary zinc to 6-mercaptopurine teratogenesis and DNA metabolism in the rat

The possible interaction between the level of maternal dietary zinc and the teratogenic activity of 6-mercaptopurine was investigated. Pregnant Sprague-Dawley rats were fed diets containing 9,100 or 1,000 ppm zinc from day zero of pregnancy and were given a single intraperitoneal injection of 6-MP (55mg/kg) on day 11. At term, females in the group fed 1,000 ppm zinc (a high intake) showed less pronounced effects on reproduction and embryogenesis than did those fed 9 ppm (marginally deficient) or 100 ppm (normal) zinc. Embryos examined on day 12 of gestation had similar concentrations of protein and RNA; however, the DNA content was lower and the incorporation of 3H-thymidine was greater in the drug treated groups than in non-drug treated controls. These results indicate that 6-mercaptopurine is acting to alter embryonic DNA metabolism and that high levesl of dietary zinc may ameliorate some of the deleterious effects of this drug on embryonic and maternal toxicity.