Effects of Cold Storage Prior to Freezing on Superoxide Dismutase, Glutathione Peroxidase Activities, Level of Total Reactive Oxygen Species and Sperm Quality in Dogs

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Abstract
Reactive oxygen species (ROS) are one of several crucial factors that cause mammalian sperm damage during handling and preservation. Their deleterious effects can be restricted by the action of antioxidants. The present study aimed at investigating: (i) effects of cold storage prior to freezing on activities of enzymatic antioxidants (superoxide dismutase; SOD and glutathione peroxidase; GPx) and level of total reactive oxygen species (tROS); and (ii) effects of SOD or SOD plus GPx supplementation to chilled (3 and 96 h) and frozen-thawed semen. Six privately owned dogs were included. Experiment I: Each pooled semen was divided into three equal aliquots, which were subjected to chilled storage for 3, 24 or 96 h prior to freezing (n = 7). The activities of SOD and GPx in sperm cells and tROS level in chilled and frozen-thawed semen were measured. Experiment II: Pooled semen was divided to be cold stored for 3 or 96 h in three different extenders; (i) Uppsala Equex extender (control), (ii) Uppsala Equex extender supplemented SOD, or (iii) Uppsala Equex extender supplemented with SOD plus GPx. Sperm motility, viability and integrity of acrosome and DNA was evaluated after cold storage and frozen-thawed. The cold storage from 24 h prior to freezing resulted in a decrease in the SOD activity in the frozen-thawed sperm cells whereas the GPx activity and tROS levels were not affected. In addition, the supplementation of SOD plus GPx enhanced the percentage of sperm viability and DNA integrity after cold stored and frozen-thawed. In sum, the SOD activity is compromised by cold storage prior to freezing of dog semen. Addition of GPx is suggested to assist SOD to complete the enzymatic ROS scavenging system in the dog sperm.

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