Oxidative stress is believed to be an important cause of sperm damage during freezing. l-Carnitine (LC) may have the potential to improve sperm quality after frozen-thawed process. The present study aimed to investigate the effect of LC supplementation in cryoprotectant media of mouse epididymal sperm on post-thaw sperm quality and expression of apoptosis-related genes. Male BALB/cJ mice spermatozoa were cryopreserved in a cryoprotectant medium containing 2.5 or 5 mM LC. The untreated group was cryopreserved with the cryoprotectant medium only. Six months following cryopreservation, the samples were thawed and sperm quality parameters, chromatin and acrosome integrity, reactive oxygen species (ROS) and glutathione (GSH) levels, mitochondrial activity, and mRNA expression of Bax and Bcl-2 were assessed. The results demonstrated that the concentration of 5 mM LC in cryoprotectant media exhibited higher values for the sperm quality parameters and integrity of chromatin and acrosome in post-thaw spermatozoa than those of the untreated group. Furthermore, sperm ROS levels decreased while GSH and mitochondrial activity levels increased in 5 mM LC group compared to those in the untreated group (P < 0.01). In 5 mM LC-treated group, Bax was down-regulated (P < 0.05) while Bcl-2 was up-regulated (P < 0.001) compared to the untreated group. Collectively, LC supplementation of cryoprotectant medium improved the quality of frozen-thawed mouse epididymal spermatozoa, as showed reduced ROS level and Bax expression as well as increased GSH, mitochondrial activity, and Bcl-2 expression.

中文翻译：

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左旋肉碱处理冻存小鼠附睾精子的顶体和染色质完整性、氧化应激和凋亡相关基因的表达

氧化应激被认为是冷冻过程中精子损伤的一个重要原因。左旋肉碱 (LC) 可能具有改善冻融过程后精子质量的潜力。本研究旨在研究在小鼠附睾精子冷冻保护培养基中添加 LC 对解冻后精子质量和凋亡相关基因表达的影响。将雄性 BALB/cJ 小鼠的精子冷冻保存在含有 2.5 或 5 mM LC 的冷冻保护剂培养基中。未处理组仅用冷冻保护剂培养基冷冻保存。冷冻保存 6 个月后，将样品解冻，并评估精子质量参数、染色质和顶体完整性、活性氧 (ROS) 和谷胱甘肽 (GSH) 水平、线粒体活性以及 Bax 和 Bcl-2 的 mRNA 表达。结果表明，与未处理组相比，冷冻保护剂培养基中 5 mM LC 的浓度在精子质量参数以及染色质和顶体的完整性方面表现出更高的值。此外，与未处理组相比，5 mM LC 组精子 ROS 水平降低，而 GSH 和线粒体活性水平增加（P < 0.01）。在 5 mM LC 治疗组中，与未治疗组相比，Bax 下调（P < 0.05）而 Bcl-2 上调（P < 0.001）。总的来说，冷冻保护培养基的 LC 补充改善了冻融小鼠附睾精子的质量，表现为 ROS 水平和 Bax 表达降低以及 GSH、线粒体活性和 Bcl-2 表达增加。