It has been previously shown that human spermatozoa produce nitric oxide (NO), a short-lived free radical synthesised by three isoforms of NO synthase (NOS): endothelial (eNOS), neuronal (nNOS), and inducible (iNOS), which are responsible for the conversion of L-arginine to L-citrulline and NO. Spermatozoa of fertile men express both eNOS and nNOS. The specific roles of NOS isoforms in gametes are not well understood, even if iNOS seems to negatively affect sperm function through the production of large amounts of NO. NO plays a relevant role in sperm physiology, although at high concentrations it could combine with superoxide to produce peroxynitrite, which can rapidly react with proteins, lipids, and nucleic acids. In the present study we aimed to assess the immunohistochemical expression of NOS isoforms in human spermatozoa isolated from normospermic fertile donors and infertile subjects affected by idiopathic asthenozoospermia. In addition we evaluated the immunoexpression of citrulline, to achieve the microscopic visualisation of NOS catalytic activity, and nitrotyrosine, since ample evidence supports the tyrosine nitration of proteins in vivo in different pathological conditions.
Our results show that constitutive NOS expression was greater in spermatozoa isolated from normospermic fertile donors. On the contrary, the immunohistochemical expression of inducible iNOS and nitrotyrosine was higher in asthenozoospermic samples. Our data concerning citrulline indicated an enhanced NOS activity in sperms from idiopathic asthenozoospermic patients.
In conclusion, our study strongly support the hypothesis that an increased NOS activity, and consequently an excess of tyrosine nitration are involved in the pathogenesis of idiopathic asthenozoospermia that causes male infertility, furthering the development of new therapeutic strategies in the near future.
Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.
Funding: This research did not receive any specific grant from any funding agency in the public, commercial or not-for-profit sector.
05 - 09 May 2012
European Society of Endocrinology