Extender-dependent effects of reduced glutathione on post-thaw boar sperm quality: A systematic review and meta-analysis.
Supplementation of reduced glutathione (GSH) in freezing media has been proposed to improve post-thaw boar sperm quality, although reported findings remain inconsistent. This study aimed to quantitatively evaluate the effects of reduced glutathione on post-thaw sperm quality through a systematic review and meta-analysis. The study followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Scopus, PubMed, CAB Direct, EBSCOhost, and Google Scholar were systematically searched. Based on predefined inclusion and exclusion criteria, 15 in vitro studies comprising 19 experiments were included. Four outcomes were analyzed: total motility, progressive motility, viability, and acrosome integrity. Standardized mean differences (SMD) were calculated using random-effects models. Heterogeneity was assessed using Cochran's Q test, and the I2 statistic. Publication bias was evaluated using funnel plots, Egger's test, and trim-and-fill analysis, while sensitivity analyses were performed using Baujat plots and leave-one-out analysis. Reduced glutathione was positively associated with total motility (SMD = 0.74; 95% CI: 0.42-1.05; P<0.001), progressive motility (SMD = 0.90; 95% CI: 0.21-1.58; P=0.014), viability (SMD = 0.67; 95% CI: 0.11-1.23; P=0.022), and acrosome integrity (SMD = 0.72; 95% CI: 0.32-1.12; P=0.002). Low to high heterogeneity was observed across outcomes, indicating variability in the estimated effects across studies. Significant subgroup differences were identified according to GSH concentration, freezing media, and thawing media. Overall, the available evidence suggests a possible positive association between GSH supplementation and several post-thaw sperm quality parameters, although these subgroup findings are exploratory and require confirmation in well-standardized experimental studies.