Improvement and Evaluation of a Staining Method for Measuring Sperm Lactate Dehydrogenase C4 Activity

Background: This study sought to improve and evaluate a 2-hydroxyvaleric acid based staining method for detection of lactate dehydrogenase C4 (LDH-C4) activity in human spermatozoa. Methods: A staining method for measuring sperm LDH-C4 activity with the substrate 2-hydroxyvaleric acid was improved. Expression level of LDH-C4 was assessed by Western blotting. The diagnostic performance was evaluated by plotting the receiver operating characteristic (ROC) curve. Results: The positive products were black purple lumps concentrated in the neck segment of spermatozoa. Expression level of LDH-C4 was significantly reduced in the low activity infertile cases as compared to the matched contrasts. Decreased LDH-C4 level was significantly correlated with the declined enzyme activity (r = 0.702, p = 0.000). The ROC curve allowed for the discrimination between low and normal LDH-C4 activity cases with a sensitivity of 0.912 and specificity of 0.895, corresponding to an area under curve (AUC) of 0.941. Conclusions: The improved method hallmarks a promising accuracy in evaluating sperm LDH-C4 activity. Down regulated LDH-C4 level is a culprit for the decreased LDH-C4 activity in spermatozoa.