Investigation of comet assays under conditions mimicking ocular instillation administration in a three-dimensional reconstructed human corneal epithelial model

Purpose: A comet assay is one of the genotoxicity methods for evaluating the potential of chemicals to induce DNA strand breaks. To investigate the usefulness of comet assays for evaluating the genotoxic potential of ophthalmic solutions, a three-dimensional (3D) reconstructed human corneal epithelial model (3D corneal model) was exposed to conditions mimicking topical ocular instillation administration. Methods: The 3D corneal model was exposed to acridine orange, ethidium bromide, hydrogen peroxide, 1,1'-dimethyl-4,4'-bipyridinium dichloride (paraquat), 4-nitroquinoline 1-oxide (4-NQO), acrylamide and methyl methanesulfonate (MMS). To mimic the ocular surface condition to which ophthalmic solutions are administered, the exposure time was set to 1 minute. Likewise, human corneal epithelial (HCE-T) cells, as monolayer cultured cells, were exposed to the same chemicals, for comparison. Results: In the 3D corneal model, the amount of DNA fragments was statistically significantly increased in cells treated with each of the test chemicals except acrylamide. In HCE-T cells, the amount of DNA fragments was statistically significantly increased in acridine orange-, ethidium bromide-, hydrogen peroxide-, 4-NQO- and MMS-treated cells but not in paraquat- or acrylamide-treated cells. In the 3D corneal model, the lowest concentrations at which we observed DNA damage were about 100 times higher than the concentrations in HCE-T cells. Since the 3D corneal model is morphologically similar to human corneal tissue, form a multilayer and having tight junctions, it may be that the test chemicals only permeated about 1% into the 3D corneal model. Conclusion: These results suggest that the comet assay using 3D cell culture models may reflect in vivo conditions better than do monolayer cultured cells, and that the comet assay may be useful for the evaluation of genotoxic potential of topical ophthalmic solution.

The contribution of efficient production of monozygotic twins to beef cattle breeding

Production of sires with high breeding potential is indispensable for prompt and reliable breeding using their semen in the cattle industry. Currently, in Japan, we aim to further the production of Japanese black sires via a new breeding system that uses genetically homologous monozygotic twins so that better growth performance and carcass traits can be translated to the increased production of beef with higher economic value. Several studies have reported that monozygotic twins are produced by embryo bisection. On the other hand, with the evolution and stabilization of in vitro fertilization technology, it has become possible to produce multiple monozygotic twin calves from blastomeres separated from a cleavage-stage embryo. This review attempts to clarify breeding practices through revalidation of the factors that affect the production efficiency of monozygotic twin calves by embryo bisection. Furthermore, the establishment of a system for monozygotic twin embryo production via the simplified technique of blastomere separation is reviewed while showing data from our previously performed studies.

Genotoxicity assessment of reactive and disperse textile dyes using human dermal equivalent (3D cell culture system)

Thousands of dyes are marketed daily for different purposes, including textile dyeing. However, there are several studies reporting attributing to dyes deleterious human effects such as DNA damage. Humans may be exposed to toxic dyes through either ingestion of contaminated waters or dermal contact with colored garments. With respect to dermal exposure, human skin equivalents are promising tools to assess in vitro genotoxicity of dermally applied chemicals using a three-dimensional (3D) model to mimic tissue behavior. This study investigated the sensitivity of an in-house human dermal equivalent (DE) for detecting genotoxicity of textile dyes. Two azo (reactive green 19 [RG19] and disperse red 1[DR1]) dyes and one anthraquinone (reactive blue 2 [RB2]) dye were analyzed. RG19 was genotoxic for DE in a dose-responsive manner, whereas RB2 and DR1 were nongenotoxic under the conditions tested. These findings are not in agreement with previous genotoxicological assessment of these dyes carried out using two-dimensional (2D) cell cultures, which showed that DR1 was genotoxic in human hepatoma cells (HepG2) and RG19 was nongenotoxic for normal human dermal fibroblasts (NHDF). These discrepant results probably may be due to differences between metabolic activities of each cell type (organ-specific genotoxicity, HepG2 and fibroblasts) and the test setup systems used in each study (fibroblasts cultured at 2D and three-dimensional [3D] culture systems). Genotoxicological assessment of textile dyes in context of organ-specific genotoxicity and using in vitro models that more closely resemble in vivo tissue architecture and physiology may provide more reliable estimates of genotoxic potential of these chemicals.