Effects of Exposure to Extreme Artificial Light at Night on Liver Oxidative Damage and Gut Microbiota During Pregnancy and Lactation in Mice

Chronic exposure to artificial light at night (ALAN) is increasingly recognized as an environmental risk factor that disrupts circadian regulation of endocrine and metabolic systems. In this study, we investigated the effects of extreme ALAN on oxidative stress and gut microbiota composition in mice using two complementary experiments. In Experiment 1, adult female mice were maintained under either as a standard 12 h light/12 h dark cycle (12 h group) or continuous 24 h light exposure (24 h group) throughout pregnancy and lactation. In Experiment 2, the offspring from the 12 h group were maintained under the same photoperiod, whereas offspring from the 24 h group were divided into a 12 h light/12 h dark group or a continuous 24 h light group, with treatments initiated on postnatal day 19 and continued until 2 months of age. For all 12 h groups, light exposure occurred from 8:00 to 20:00. Compared with dams in the 12 h group, dams exposed to continuous light exhibited significantly increased catalase activity, while their offspring maintained under the 12 h photoperiod showed elevated glutathione levels. No significant changes were detected in immune organ indices. These results suggest that extreme ALAN modulates antioxidant defenses, potentially reflecting adaptive responses to oxidative stress. Moreover, offspring exposed early to extreme ALAN showed significantly reduced gut microbial α-diversity, accompanied by decreased abundances of Firmicutes, Bacteroidota, Campylobacterota, and Desulfobacterota, and an increase in Proteobacteria. Notably, Verrucomicrobiota and Akkermansia failed to recover following photoperiod normalization, indicating persistent microbiota dysbiosis. Overall, these findings demonstrate that extreme ALAN induces oxidative stress and long-lasting alterations in gut microbiota composition, highlighting potential health risks associated with night-time light pollution.