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.