Kinetics of inhibition of sperm beta-acrosin activity by suramin

Soybean lecithin-based extender preserves spermatozoa membrane integrity and fertilizing potential during goat semen cryopreservation

Soybean lecithin may represent a suitable alternative to egg yolk for semen cryopreservation in livestock species. However, additional studies are needed to elucidate its effects on spermatozoa functional properties. Semen collected from five Sarda bucks was cryopreserved in Tris-based extender and glycerol (4% v:v) with different supplementations. In a preliminary experiment, different soybean lecithin concentrations were tested (1%-6% wt/vol) and results in terms of viability, percentages of progressive motile and rapid spermatozoa, and DNA integrity after thawing showed that the most effective concentration was 1%. In the second experiment, semen was frozen in a Tris-based extender with no supplementation (EXT), with 1% lecithin (EXT LC), and 20% egg yolk (EXT EY). The effectiveness of these extenders was also compared with a commercial extender. The EXT EY led to the highest viability and motility parameters after freezing and thawing (P < 0.0001). No significant differences were observed in intracellular ATP concentrations. Additional molecular features revealed that sperm functionality was affected in EXT EY, as demonstrated by lower DNA and acrosome integrity (P < 0.05), and higher lipid peroxidation compared with spermatozoa cryopreserved in EXT LC (P < 0.0001). Results obtained in the heterologous in vitro fertilization test showed that EXT LC better preserved spermatozoa functionality, as demonstrated by the higher fertilization rates compared with the other media (66.2 ± 4.5% for EXT LC vs. 32.7 ± 4.5%, 38.7 ± 4.5%, 39.6 ± 5.2% for EXT, EXT EY, and commercial extender; P < 0.01). The present study demonstrated that lecithin can be considered as a suitable alternative to egg yolk in goat semen cryopreservation, because it ensures higher fertilization rates and a better protection from membrane damage by cold shock.

Study of the proacrosin-acrosin system in epididymal, ejaculated and in vitro capacitated boar spermatozoa

The present study aimed to develop a set of sensitive assays to evaluate the presence of different isoforms, the activity degree, and the immunolocalisation of proacrosin-acrosin in sexually mature boars. The goal was to determine the proacrosin-acrosin status of boar spermatozoa throughout epididymal maturation, during ejaculation and after in vitro capacitation. In epididymal samples, proacrosin expression was high in all regions studied. In contrast, α- and β-acrosin expression was low in the caput region, and increased progressively during maturation and in vitro capacitation. In in vitro capacitated samples, the acrosin activity was 2.25 times higher than in the ejaculated samples and immunolocalisation analyses showed redistribution of proacrosin-acrosin at the apical ridge of the head. This study provides relevant data about the expression, localisation and activity of the proacrosin-acrosin system in healthy adult boars that can be used as a base to analyse changes in the proacrosin-acrosin system under pathological conditions.

Binding of sperm proacrosin/β-acrosin to zona pellucida glycoproteins is sulfate and stereodependent. Synthesis of a novel fertilization inhibitor

Specific binding of spermatozoa to the zona pellucida that surrounds mammalian eggs is a key step in the fertilization process. However, the sperm proteins that recognise zona pellucida receptors remain contentious despite longstanding research efforts to identify them. Here we present evidence that proacrosin, a tissue-specific protein found within the acrosomal vesicle of all mammalian spermatozoa, is a multifunctional protein that mediates binding of acrosome-reacted spermatozoa to zona glycoproteins via a stereospecific polysulfate recognition mechanism. Using sulfated versus non-sulfated forms of chemically defined compounds in binding assays employing native proteins in their normal cellular location or conjugated to FluoSpheres, we have attempted to identify the sulfation "code" required for recognition. Results show that protein conformation is important for specificity and that at least 2 sulfate groups are required to cross-link spatially separated docking sites on proacrosin. The consistently most effective inhibitory compounds were suramin and quercetin-3beta-d-glucoside sulfate. The results support our hypothesis that proacrosin is one of several proteins in the acrosomal matrix that retain acrosome reacted spermatozoa on the zona surface prior to penetration. They also establish, as a proof-of-principle, the feasibility of synthesising sulfated compounds of high specificity as antifertility agents for human or animal use.

Proacrosin/acrosin quantification as an indicator of acrosomal integrity in fresh and frozen dog spermatozoa

The scope of the present study was to evaluate the presence and activation of proacrosin/acrosin as a tool to determine the acrosomal status of fresh and frozen/thawed dog spermatozoa. Monoclonal antibody C5F11, directed against human acrosin, cross-reacted with dog spermatozoa and labeled the acrosome of both fresh and frozen/thawed dog spermatozoa. Frozen/thawed spermatozoa had a lesser proportion of labeled spermatozoa than fresh spermatozoa (P<0.05). When live spermatozoa were labeled with soybean trypsin inhibitor conjugated with Alexa 488 (SBTI-Alexa 488), the proportion of acrosome-labeled fresh spermatozoa was less than frozen/thawed spermatozoa (P<0.05). By using Western blots and enzymatic activity, frozen/thawed spermatozoa had a greater proportion of active acrosin than fresh spermatozoa. In addition, beta 1,4-galactosyl-transferase (GalT), a plasma membrane bound protein, remained attached to frozen/thawed spermatozoa. Proacrosin is activated during freezing/thawing of dog spermatozoa, and that proacrosin/acrosin may be a good indicator of acrosomal integrity of frozen/thawed spermatozoa.

Inhibition of Myotoxic Activity of Bothrops asper Myotoxin II by the Anti-trypanosomal Drug Suramin

Suramin, a synthetic polysulfonated compound, developed initially for the treatment of African trypanosomiasis and onchocerciasis, is currently used for the treatment of several medically relevant disorders. Suramin, heparin, and other polyanions inhibit the myotoxic activity of Lys49 phospholipase A2 analogues both in vitro and in vivo, and are thus of potential importance as therapeutic agents in the treatment of viperid snake bites. Due to its conformational flexibility around the single bonds that link the central phenyl rings to the secondary amide backbone, the symmetrical suramin molecule binds by an induced-fit mechanism complementing the hydrophobic surfaces of the dimer and adopts a novel conformation that lacks C2 symmetry in the dimeric crystal structure of the suramin-Bothrops asper myotoxin II complex. The simultaneous binding of suramin at the surfaces of the two monomers partially restricts access to the nominal active sites and significantly changes the overall charge of the interfacial recognition face of the protein, resulting in the inhibition of myotoxicity.