Sperm caspases become more activated in infertility patients than in healthy donors during cryopreservation.

The programmed cell death (PCD, the apoptosis) is associated with the activation of the "death enzymes" caspases and very likely plays a role in the decrease of sperm vitality during cryopreservation. The activation of pan-caspases was examined in fresh and cryostored sperm by fluorescence microscopy applying a cell permeable and noncytotoxic carboxy-fluorescein labelled caspase inhibitor. Cryopreservation increased significantly the percentage of spermatozoa with activated pan-caspases (aCP) from 21 +/- 2.6 to 47 +/- 5.8 % (mean +/- SEM). Quantitative Western blot analyses confirmed the activation of caspase-1, -8, and -9 in detail on protein level after cryopreservation, whereas, the caspases of sperm of infertility patients showed a higher activation status than donors' sperm. This effect raised with increasing glycerol concentration from 7-14 %. The higher level in activation of caspases in cryostored spermatozoa of infertility patients may indicate that these cells have a lower cryotolerance and a higher susceptibility to caspase activation than does the sperm of donors.