Altered molecular dynamics and antioxidant status in the spermatozoa in testosterone-induced oligospermia in mouse

Though supraphysiological doses testosterone (T) and its derivatives are known to suppress spermatogenesis in mammals by interfering with the hypothalamus-pituitary axis leading to oligozoospermia, no study has been performed to evaluate the integrity of the sperm cells produced by such individuals. In T-induced oligozoospermia in the mouse, the spermatozoa showed suppressed zona-binding ability though the motility and viability remained unchanged. In order to assess whether this decreased zona-binding ability is due to perturbations in the mechanical properties of the sperm membranes, we attempted to examine the molecular dynamics employing a lipophilic spin label (16-doxyl stearate) and a protein-binding label (Mal-Net) in two sets of independent experiments. The results showed that the rotational freedom of lipophilic molecules reduced significantly within the first week of T-treatment. During weeks 1 through 4, the protein rotation was found to be retarded significantly. We observed a sharp increase in the ascorbyl radical associated with the cauda epididymal spermatozoa and epididymal fluid of testosterone-treated mice. Moreover, the glutathione (GSH) content in the spermatozoa and the epididymal fluid increased significantly after testosterone-treatment. Further, there was a elevation in the superoxide dismutase (SOD) activity and suppression in the superoxide anion radical generated by the cauda epididymal spermatozoa of testosterone-treated animals. A change in the mechanical properties of a bilayer could modify both the mechanical properties and the function of incorporated proteins. In many instances, a liquid-crystalline bilayer is necessary for protein function. It is likely that the change in the physical properties of sperm membranes might cause the inhibition of enzymes associated with spermatozoa after T-treatment. The alterations in the sperm membrane structure and the antioxidant potentials of both the spermatozoa and the cauda epididymal fluid could also account for the decrease in the zona-binding index of the spermatozoa in T-treated animals. Thus, this study demonstrates for the first time that supraphysiological doses of testosterone could modify the mechano-dynamic properties of sperm membranes and could perturb the redox status of both spermatozoa and the epididymal fluid.