Human sperm testicular angiotensin-converting enzyme helps determine human embryo quality

Abstract

Angiotensin-converting enzyme functions in the male reproductive system, but the extent of its function in reproduction is not fully understood. The primary objective of this work was to investigate the relationship between the testicular isoform of angiotensin-converting enzyme present in human spermatozoa and semen parameters, human embryo quality, and assisted reproduction success. A total of 81 semen samples and 635 embryos from couples undergoing oocyte donation cycles at the IVI Bilbao Clinic were analyzed. Semen parameters, embryos quality, and blastocyst development were examined according to the World Health Organization standards and the Spanish Association of Reproduction Biology Studies criteria. The percentage of testicular angiotensin-converting enzyme-positive spermatozoa and the number of molecules per spermatozoon were analyzed by flow cytometry. Both parameters were inversely correlated with human sperm motility. Higher percentages of testicular angiotensin-converting enzyme-positive spermatozoa together with fewer enzyme molecules per spermatozoon were positively correlated with better embryo quality and development. Our results suggest that embryos with a higher implantation potential come from semen samples with higher percentages of testicular angiotensin-converting enzyme-positive cells and fewer enzyme molecules per spermatozoon. Based on these findings, we propose that testicular angiotensin-converting enzyme could be used to aid embryologists in selecting better semen samples for obtaining high-quality blastocysts during in vitro fertilization procedures.

Keywords: ART; angiotensin-converting enzyme; embryonic development; human sperm; male fertility.

Figure 1

Graphic representation of the scoring of the early embryo quality on days 2 and 3 and the association with sperm tACE. Number of tACE molecules per spermatozoon on (a) day 2, and (b) day 3; and percentage of tACE-positive spermatozoa on (c) day 2, and (d) day 3. Box-plot graph shows the median values as lines across the box. Lower and upper box lines indicate the 25^th–75^th percentile. Whiskers represent the maximum and minimum values. ^*P < 0.05 and ^**P < 0.01. tACE: testicular angiotensin-converting enzyme.

Figure 2

Graphic representation of embryo quality on day 5 and its association with sperm tACE. Embryo development phase at the blastocyst stage and the association with tACE. (a) Number of tACE molecules per spermatozoon and (b) percentage of tACE-positive spermatozoa. Blastocyst viability on day 5 of development and association with tACE: (c) number of tACE molecules per spermatozoon and (d) percentage of tACE-positive spermatozoa. MC: compact morula stage; BT: early blastocyst; BC: expanding blastocyst; BE: expanded blastocyst; BHi: hatching/hatched blastocyst; BD: blocked or degenerated embryos; V: viable blastocyst; NV: non-viable blastocyst. Box-plot graph shows the median values as lines across the box. Lower and upper box lines indicate the 25^th–75^th percentile. Whiskers represent the maximum and minimum values. ^*P < 0.05 and ^**P < 0.01. tACE: testicular angiotensin-converting enzyme.