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Nature’s Way
Research by Dr. Gabor Huszar and his co-workers at the Yale University School of Medicine has shown that during spermiogenesis sperm develop the ability to bind to hyaluronan. And, in fact, he has shown that hyaluronan binding is a simple, direct indicator of sperm maturity (1-4).
This is important because only mature sperm are able to interact normally with the oocyte’s hyaluronan-rich outer cumulus oophorus layer and the inner egg boundary, the zona pellucida, leading to normal fertilization (3-6).
It appears that these critical sperm-hyaluronan interactions constitute a natural selection mechanism for mature sperm during normal conception (3,7,8).
Sperm-Hyaluronan Binding and DNA Integrity
Mature, hyaluronan-binding sperm are also known to have a higher frequency of normal chromosome complement and better DNA integrity than immature sperm (4-6,8).
Huszar and co-workers found a four to six fold lower frequency of mistakes in chromosomal complement (aneuploidy) in sperm selected for hyaluronan (HA) binding compared to their unselected brothers (3).
Yagci et al studied DNA integrity and found that more than 99% of HA-binding sperm had high DNA integrity compared to about 55% in the unselected sperm (8).
Clinical Practice - The ICSI Procedure
In the IVF procedure known as ICSI (Intra Cytoplasmic Sperm Injection) a sperm is injected into an egg to produce conception. ICSI therefore bypasses many normal sperm-oocyte interactions such as those with the cumulus and the zona pellucida that constitute a natural selection for mature sperm. In consequence, ICSI conceptions carry an increased risk of failure due to the possibility that immature sperm are used.
Until now, the only means to assess an individual sperm’s suitability for ICSI has been evaluation of motility and sperm size and shape. With the advent of sperm selection by HA-binding, it is now possible to select for sperm maturity as well.
A recent clinical study (7) has indicated the magnitude of this problem and the improvement achievable by selection of HA-binding sperm. The study, presented by Dr. Kathryn Worrilow at the 2007 meeting of the American Society for Reproductive Medicine, found that about one-third of patient couples presenting as candidates for ICSI had a low frequency of HA-binding sperm. When these patients had these less-frequent HA-binding sperm selected for use during their ICSI procedure, the clinical pregnancy rate that resulted increased about 20% compared to couples using sperm unselected for HA-binding. A multi-center trial will begin in the fall of 2008 intended to confirm these preliminary findings.
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