Occurrence of D-aspartic acid in human seminal plasma and spermatozoa: Possible role in reproduction

Objective: To determine D-aspartic acid (D-Asp) in human seminal plasma and spermatozoa in fertile and infertile donors. Designs: Prospective observation study. Setting: Department of Pathophysiology for Human Reproduction, Hospital "S. Luca" Salerno Italy, and Department of Neurobiology and Comparative Physiology, Zoological Station "A Dohrn," Naples, Italy. Patient(s): Ten normospermic, 10 oligoasthenoteratospermic, and 10 azoospermic (nonobstructive) men. Intervention(s): D-aspartic acid was determined by a specific enzymatic high-performance liquid chromatography method on purified seminal plasma and on isolated spermatozoa and by an immunohistochemical method using light and electronic microscopic techniques. Main Outcome Measure(s): Concentration of D-Asp in seminal plasma and in isolated spermatozoa; subcellular localization of D-Asp in the acrosome and nucleus. Result(s): The concentration of D-Asp in seminal plasma and in spermatozoa was significantly reduced in oligoasthenoteratospermic donors. In the seminal fluid of normospermic donors, D-Asp occurs at a concentration of 80 +/- 12 nmol/mL semen (10.4 +/- 1.5 mu g/ml), whereas 26 +/- 6 nmol/mL semen were found in oligoasthenoteratospermic donors, and 12 +/- 1.5 nmol/mL semen were found in azoospermic donors. In spermatozoa from normospermic donors, D-Asp occured at a concentration of 130 +/- 15 fmol per spermatozoa (17.0 +/- 1.96 ng per spermatozoa), vs. 60.5 +/- 5.0 fmol per spermatozoa from oligoasthenoteratospermic subjects. Other D-amino acids analyzed were not present in seminal plasma or in spermatozoa in a significant concentration compared with D-Asp. Conclusion(s): D-aspartic acid occurs in human seminal plasma and spermatozoa and is implicated in male fertility.