Decamethylcyclopentasiloxane affects estradiol production in female rats but not H295R cells.

Sex hormones, such as androgens and estrogens, are predominantly produced in the gonads (ovaries and testes) and adrenal cortex. Endocrine-disrupting chemicals (EDCs) are substances that mimic, block, or interfere with hormones in the endocrine systems of humans and organisms. EDCs mainly act via nuclear receptors and steroidogenesis-related enzymes. In the OECD conceptual framework for testing and assessment of EDCs, several well-known assays are used to identify the potential disruption of nuclear receptors both in vivo and in vitro, whereas the H295R steroidogenesis assay is the only assay that detects the disruption of steroidogenesis. Forskolin and prochloraz are often used as positive controls in the H295R steroidogenesis assay. Decamethylcyclopentasiloxane (D5) was suspected one of EDCs, but the effects of D5 on steroidogenesis remain unclear. To establish a short-term in vivo screening method that detects the disruption of steroidogenesis, rats in the present study were fed a diet containing forskolin, prochloraz, or D5 for 14 days. Forskolin increased plasma levels of 17ß-estradiol (E2) and testosterone as well as the mRNA level of Cyp19 in both the adrenal glands and ovaries. Prochloraz induced the loss of cyclicity in the sexual cycle and decreased plasma levels of E2 and testosterone. D5 increased E2 levels and shortened the estrous cycle in a dose-dependent manner; however, potential endocrine disruption was not detected in the H295R steroidogenesis assay. These results demonstrate the importance of comprehensively assessing the endocrine-disrupting effects of chemicals on steroidogenesis in vivo.

Evaluation of the in vivo mutagenicity of melamine by the RBC Pig-a assay and PIGRET assay.

The Pig-a assay is a new in vivo genotoxicity test for detecting mutagens in the bodies of animals, using the endogenous Pig-a gene as the target. There are two types of Pig-a assays: the red blood cell (RBC) Pig-a assay, which uses RBCs, and the PIGRET assay, which uses reticulocytes. The Japanese Environmental Mutagen Society-Mammalian Mutagenicity Study Group collaborative study of the Pig-a assay was carried out to investigate the usefulness of the PIGRET assay. The mutagenicity of melamine was evaluated as part of this study. Eight-week-old male Crl:CD (SD) rats were administered a single gavage dose of melamine as a non-genotoxic bladder carcinogen. Blood samples were collected at the first, second and fourth weeks after administration, and the RBC Pig-a assay and PIGRET assays were conducted using these samples. Three dose levels were used in the study: the highest dose was 2000mg/kg, which is generally used as the maximum dose in in vivo genotoxicity testing, and 1000 and 500mg/kg were also used. As a positive control, a group of rats was administered a single dose of N-nitroso-N-ethylurea (ENU) by gavage at 40mg/kg. The Pig-a mutant frequencies (Pig-a MFs) did not increase in any of the melamine groups throughout the experimental period in either the RBC Pig-a assay or the PIGRET assay. Both the RBC Pig-a and PIGRET assays revealed significant increases in the Pig-a MFs in the ENU group, starting at day 7 after a single administration. Therefore, these two assays, when evaluated after a single administration, can be used to determine that melamine is non-mutagenic.