Purification and characterization of a novel acrosin-like enzyme from boar cauda epididymal sperm

A critical assessment of the effect of serine protease inhibitors on porcine fertilization and quality parameters of porcine spermatozoa in vitro

Proteases play an important role during mammalian fertilization. Their function is frequently investigated using specific inhibitors. We analyzed four serine protease inhibitors [4-(2-aminoethyl) benzene sulfonyl fluoride hydrochloride (AEBSF), soybean trypsin inhibitor from glycine max (STI), Nα-tosyl-L-lysine-chloromethyl ketone hydrochloride (TLCK) and N(p)-tosyl-L-phenylalanine-chloromethyl ketone (TPCK)] for their in vitro effect on fertilization and sperm quality in pigs. Inhibitor concentrations were chosen based on the reduction of fertilization rate during preliminary dose-response experiments with cryopreserved epididymal spermatozoa. The inhibitor effects on in vitro fertilization (IVF) and sperm parameters (membrane and acrosomal integrity, motility and mitochondrial membrane potential - MMP) were evaluated using diluted fresh semen. AEBSF (100 μM), TLCK (100 μM) and TPCK (100 μM) decreased total fertilization and polyspermy rates by at least 50%. STI (5 μM) lowered total fertilization rates but not the level of polyspermy. AEBSF and TPCK reduced fertilization parameters to a similar degree using cryopreserved epididymal spermatozoa (dose-response experiment) or diluted fresh semen. Inhibition by STI was more pronounced using cryopreserved epididymal spermatozoa, whereas TLCK inhibited IVF only with diluted fresh semen. AEBSF and STI had no effect on sperm parameters, and TLCK significantly reduced motility. TPCK diminished MMP and motility and affected membrane and acrosomal integrity in a negative way. In summary, serine protease inhibitors differed in the way they reduce the fertilization rate. These results emphasize the necessity of inhibitor testing before they can be applied in fertilization studies. AEBSF and STI can be used in the future IVF studies without compromising sperm quality.

Discovery of substituted isoxazolecarbaldehydes as potent spermicides, acrosin inhibitors and mild anti-fungal agents

BACKGROUND

The continued endeavour to design novel, non-detergent molecules that can be useful as topical, prophylactic contraceptives has led to the discovery of substituted isoxazolecarbaldehydes as a new class of compounds exhibiting both spermicidal and acrosin inhibitory activities simultaneously.

METHODS

Normal human semen samples were used to detect the spermicidal and acrosin inhibitory activities of the new compounds. Lactobacillus, HeLa and Candida cultures were used to determine the safety of compounds towards normal vaginal flora, their cytotoxicity and anti-fungal activity. Supravital staining and the hypo-osmotic swelling test (HOST) were used to detect the effect on sperm membrane integrity. Nonoxynol-9 (N-9) was used as a reference standard.

RESULTS

The 5- and 3-substituted isoxazolecarbaldehydes showed significant spermicidal [minimum effective concentration (MEC)=0.005-2.5%] and acrosin inhibitory (IC50=3.9-58 x 10(-4) mol/l) activities in several molecules along with weak fungicidal activity against Candida albicans. Lineweaver-Burk and Dixon plot analysis of a representative structure showed non-competitive inhibition of human acrosin enzyme, and the most potent acrosin inhibitors also considerably diminished the induction of the acrosome reaction by Ca2+ ionophore. Some compounds were found to be significantly safer than N-9 towards Lactobacillus acidophilus in vitro at their respective spermicidal MECs. In the cytotoxicity assay, the IC50 of these compounds towards the HeLa cell line was of the same order as N-9 (0.9-0.1 mmol/l); however, in contrast, the compounds exhibited only a moderate effect on sperm membrane integrity.

CONCLUSIONS

This study indicates that 5- and 3-substituted isoxazolecarbaldehydes are 'first generation' multifunctional, spermicidal molecules that hold promise for development as topical contraceptives with useful associated activities that can add considerably to their effectiveness, safety and prophylaxis.

BSp66 protease is widespread in the acrosomal region of sperm from several mammalian species

Fertilization in mammals comprises a sequence of events leading to the fusion of sperm and oocyte membranes. Although proteases are known to be involved in this process, their role in fertilization is controversial. There is extensive work on the characterization of proteolytic systems, including serine proteases, which demonstrates that acrosomal proteases can be distinguished among the sperm of different mammalian species on the basis of the gelatin-hydrolyzing activity on SDS-PAGE by the quantity and variety of the enzymes. In this report, we investigated the occurrence and activity of the serine protease BSp66, previously characterized in bovine spermatozoa, in various mammalian sperm. A protein with a molecular mass of 66 kDa cross-reacted with heterologous antibodies against bovine BSp66 when sperm extracts of several mammalian species were analyzed by Western blot. In agreement, proteolytic activity corresponding to the molecular mass of BSp66 was detected by gelatin zymography in all the species analyzed. This protein was located on the acrosomal region of sperm cells by immunofluorescence methods. We concluded that BSp66 is widespread in mammalian sperm, with a conserved location in the acrosomal region.

Immunolocalization of proacrosin/acrosin in bovine sperm and sperm penetration through the zona pellucida

The aim of the present work was to immunolocalize acrosin in bull spermatozoa incubated for up to 6 h in capacitating culture medium (TALP-heparin), in order to study the kinetics of its release during the acrosome reaction and in vitro sperm penetration. Six replicates from semen of one bull were used. Acrosin was localized by the silver-enhanced immunogold technique using anti-bovine acrosin monoclonal antibody ACRO-C2E5. Spermatozoa thus showed the presence of acrosin only at the acrosomal region. Four different patterns were seen: (1) no labeling: (2) intense labeling on the rim of the portion of the acrosome; (3) diffuse label over the entire acrosomal region; and (4) intense label over the entire acrosomal region. Spermatozoa incubated in capacitating medium for 4 h showed that unlabeled (pattern 1) spermatozoa decreased from 72% to 28% difference that was found to be significant (p<0.05). Patterns 3 and 4 increased from about 10% to 20-29%, (p<0.05). With further incubation (4-6 h), pattern 1 increased while patterns 3 and 4 decreased differences were not significant (p0.05). The incidence of pattern 2 did not change through the whole incubation period. Sperm penetration through the zona pellucida of in vitro matured bovine oocytes (57%) or empty zonae pellucida (70.5%) increased (p<0.05) as a function of sperm incubation time in capacitating medium. The presence of acrosin, as determined by the silver-enhanced immunogold technique, was highly correlated with sperm penetration of in vitro mature bovine oocyte (r=0.98) and cryopreserved zonae pellucidae (r=0.93) (p<0.01).