Reproductive implication of d-aspartic acid in human pre-ovulatory follicular fluid

BACKGROUND In the present study, we report that d-aspartic acid (d-Asp) occurs in human ovarian follicular fluid and that a relationship may exist between the concentration of this amino acid and oocyte quality. METHODS Samples of pre-ovulatory follicle fluid were obtained from 20 patients undergoing an IVF programme. The concentration of d-Asp was measured by using specific high-performance liquid chromatography (HPLC) combined with a d-aspartate oxidase. RESULTS d-Asp occurs in human follicular fluid at a mean concentration of 14.98 ± 4.51 nmol/ml. A significant difference in the content of this amino acid in the follicular fluid in relation to patient’s age exists. In younger women aged 22–34 years (group A), d-Asp was found at a concentration of 19.11 ± 1.91 nmol/ml, whereas in patients aged 35–40 years (group B), it decreased to 10.86 ± 1.22 nmol/ml (P < 0.01). In addition, this amino acid was linked to oocyte quality; a relationship exists between d-Asp follicular concentration and the percentage of good quality metaphase II oocytes (P < 0.01), as well as the fertilization rate. CONCLUSIONS In human follicular fluid, d-Asp is present at a relatively higher concentration in younger women than in older patients and there appears to be a relationship between the concentration of d-Asp and fertility outcome parameters. These findings suggest that follicular d-Asp concentration may be considered as an alternative or additional biochemical marker for oocyte quality in patients undergoing IVF programmes.