In Vitro Effects of Lipopolysaccharide on Rabbit Sperm: Toll-like Receptor 4 Expression, Motility, and Oxidative Status

Lipopolysaccharide (LPS)-induced inflammation impairs sperm function; how- ever, its impact on ejaculated rabbit sperm remains unexplored. This dose-response study aims to determine the LPS concentration that negatively affects sperm motility in vitro, while also providing the first identification of TLR4 localization on rabbit spermatozoa. Additionally, it evaluates malondialdehyde (MDA) levels in seminal plasma as an indicator of oxidative stress. Sperm motility was analyzed using computer-assisted sperm analysis (CASA) after incubation with increasing LPS concentrations (0, 50, 100, 200, 400, 600, and 800 μg/mL) at multiple time points (0, 1, 2, and 4 h). LPS doses ≥ 400 μg/mL signifi- cantly reduced progressive and non-progressive motility, as well as curvilinear velocity (all p < 0.001), while increasing the proportion of static spermatozoa (p < 0.05). Receiver operating characteristic (ROC) analysis identified 300 μg/mL as the threshold dose for motility decline. Immunofluorescence revealed TLR4 localization in the midpiece of sperm tails, with weak labeling in control samples and a marked increase after 4 h of incubation with 400 μg/mL LPS. MDA levels were assessed using the thiobarbituric acid reactive substances (TBARS) assay with a colorimetric kit, showing no significant effect of LPS treatment. No correlation was found between MDA and other semen parameters. ccThese findings identify TLR4 on rabbit sperm for the first time and establish a threshold LPS dose for future in vitro studies.