Effects of visible light and other environmental factors on the production of oxygen radicals by hamster embryos

Abstract

Previous studies have demonstrated that developing hamster embryos are very sensitive to visible light. In order to elucidate why visible light exerts a toxic effect on hamster embryos, we examined the effect of visible light on the production of hydrogen peroxide (H 2O 2) within individual embryos, using a fluorimetric method. In addition, we examined the H 2O 2 generating capacity of other factors which are known to be related to the in vitro developmental capacity of hamster embryos. One-cell hamster embryos were cultured with 2′,7′-dichlorodihydrofluorescin diacetate, and the fluorescence emissions of the H 2O 2-dependent oxidative product in the embryos were measured using an Olympus microscopic photometry system. When embryos were exposed to visible light (14,000 lux) for a specified period (0, 0.5, 1, 2 or 3 min) prior to measurement, the fluorescence emissions from embryos increased with the time of exposure to visible light. An exposure of even 0.5 min resulted in a significant increase in hydrogen peroxide. This increase was more rapid in embryos cultured under 20% O 2 than in those cultured under 5% O 2, and the response was quicker than that observed in mouse embryos. The fluorescence emissions from embryos cultured under 5% O 2 were significantly (P<0.001) lower than those from embryos cultured under 20% O 2 in TLP medium. However, the effects of different oxygen tensions on fluorescence emissions were medium-dependent, and were not significant in embryos cultured in HECM-1 medium. The addition of L-cysteine to or elimination of phenol red from the media decreased the fluorescence emissions from embryos (P<0.001), but glucose and phosphate did not affect them. These results suggest that the toxic effect of visible light on the in vitro development of hamster embryos might be due to increased generation of reactive oxygen species, induced by the visible light. This could be one of the explanations for the strict conditions required for overcoming the in vitro developmental block. It is also suggested that the promotive effects of low oxygen culture and L-cysteine on embryo development seem to be derived from their ability to reduce reactive oxygen species.