Quick histochemical staining method for measuring lactate dehydrogenase C4 activity in human spermatozoa

The enzyme activity of lactate dehydrogenase C4 (LDH-C4, due to tetrameric nature of C-subunit) has been proposed as an important parameter in evaluating sperm motility and semen quality. A novel histochemical staining method for detecting LDH-C4 activity in human spermatozoa is described in this report. The staining working solution comprises sodium 2-hydroxybutyrate (an affinity substrate of LDH-C4), nitrotetrazolium blue chloride (NBT), nicotinamide adenine dinucleotide (NAD) and naphthol blue. The positive products were purple black lumps concentrated in the neck segment of the spermatozoa and weakly in the middle piece. A normal reference range for the integral enzyme activity was constructed from 120 healthy males based upon the scoring criteria. The study further compared the staining method with the routine spectrophotometry technique in terms of the results of 96 cases with infertile status. Moreover, we found the down-regulated LDH-C4 expression was significantly correlated with the lowered enzyme activity (r = 0.865, P = 0.000). Our data suggest that the histochemical staining method hallmarks a relatively high accuracy and may be a better alternative for measuring LDH-C4 activity in human spermatozoa.