(1) Background: Many studies have shown that microgravity experienced by astronauts or long-term bedridden patients results in increased oxidative stress and bone loss. Low-molecular-weight chondroitin sulfates (LMWCSs) prepared from intact chondroitin sulfate (CS) have been demonstrated to possess good antioxidant and osteogenic activities in vitro. This study aimed to assess the antioxidant activity of the LMWCSs in vivo and evaluate their potential in preventing microgravity-induced bone loss. (2) Methods: we used hind limb suspension (HLS) mice to simulate microgravity in vivo. We investigated the effects of LMWCSs against oxidative stress damage and bone loss in HLS mice and compared the findings with those of CS and a non-treatment group. (3) Results: LMWCSs reduced the HLS-induced oxidative stress level, prevented HLS-induced alterations in bone microstructure and mechanical strength, and reversed changes in bone metabolism indicators in HLS mice. Additionally, LMWCSs downregulated the mRNA expression levels of antioxidant enzyme- and osteogenic-related genes in HLS mice. The results showed that overall effect of LMWCSs was better than that of CS. (4) Conclusions: LMWCSs protect against the bone loss caused by simulated microgravity, which may be related to their ability to reduce oxidative stress. LMWCSs can be envisaged as potential antioxidants and bone loss protective agents in microgravity.

Pefloxacin (PFLX) is a type of fluoroquinolone (FQ) that has been widely used in aquaculture and animal husbandry. It is also a new kind of pseudo-persistent pollutant, which has some toxic effects. In this study, zebrafish (Danio rerio) embryos were used as exposure models to analyze the toxicity of PFLX. The results showed that PFLX was absorbed on the outer membrane surface at the beginning, and then a few PFLX slowly entered the cytoplasm. The adsorption complied with the Langmuir isotherm adsorption model. The surface morphology of the embryonic membrane was changed. PFLX exposure had no effect on fetal autonomous movement, but it significantly inhibited the embryo hatching rate. After PFLX exposure, the embryo and larval survival rates showed a clear dose–effect relationship. Though PFLX exposure did not cause teratogenic toxicity, it still affected cardiovascular function. The potential toxicity mechanism and developmental toxicity of PFLX to zebrafish were revealed. These results could be important for studies concerning FQ toxicology.