Protective Effect of l-Theanine on Cyclophosphamide-Induced Testicular Toxicity in Mice

l-Theanine is the most abundant free amino acid present in tea. Several tea components have been studied for their impact on male fertility, but little is known about the effects of l-theanine. Cyclophosphamide (CP) is an antineoplastic and immunosuppressive agent that reduces fertility in males. In the present study, we evaluated the effect of l-theanine on CP-induced testicular toxicity in male mice. A single dosage of 50 mg/kg saline or CP was administered intraperitoneally over the course of 5 days. Mice were administered l-theanine (80 mg/kg) or saline by gavage for 30 days. Animals were euthanized 24 h after the last l-theanine administration, and the testes were removed for histopathological and transmission electron microscopy analysis. Histological evaluation and transmission electron microscopy showed that administration of l-theanine alleviated CP-induced damage to the testicles, including spermatogonial cells, epithelial cells, seminiferous tubules, and basement membrane. An integrated proteomics and metabolomics investigation of testes revealed that l-theanine therapy substantially affected the quantity of 719 proteins (395 upregulated and 324 downregulated) and 196 metabolites (75 upregulated and 111 downregulated). The top three enriched Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways for these proteins and metabolites were purine metabolism, choline metabolism in cancer, and arachidonic acid metabolism. This is the first study to reveal the protective effect of l-theanine on CP-induced testicular toxicity. l-Theanine could be a potential natural active substance for resistance to the testis toxicity induced by CP.