This new technique of sperm selection using magnetic activated cell sorting is able to remove spermatozoa with apoptosis markers. This is an improvement on the success rates of assisted reproductive technology (ART) for those couples in which the male factor is significant.
Success of assisted reproductive technology depends significantly on sperm quality, since it has a direct impact on early and late embryo development. This has been highlighted on several studies, although surprisingly there was also a time when it was subject of controversy.
The emergence of the Intracytoplasmic Sperm Injection (ICSI) in the 1990s revolutionised the ARTs and removed the seriousness of the male factor, since it is considered that almost every spermatozoon is able to fertilise an egg by means of ICSI (Palermo et al., 1995). Subsequent studies on molecular biology conducted a deeper exploration on disorders affecting male gametes, and highlighted their importance and impact on assisted reproductive technology (Chemes and Rawe, 2003-2006).
So far, sperm selection before the microinjection was performed on the basis of the classic parameters of motility and morphology. Techniques such as density gradient centrifugation (a.k.a. Percoll method) or swim-up select the sperm according to motility.
There are also other interesting parameters to bear in mind which are known thanks to development in the field of molecular biology. The presence of apoptotic sperm, for instance, may be an important factor causing a low fertilisation and implantation rate (Boe-Hansen et al., 2006, Avendaño et al. 2008).
Apoptotic sperm in the ejaculate
Since it was highlighted, several therapeutic attempts have been performed in order to fight against apoptotic sperm in semen samples. Some of them are, for example, oral antioxidants –according to some researchers, they do not mean a great improvement for the results of ICSI– or sperm retrieval with testicular biopsy –in that case, results showed a great improvement, but it is a rather invasive method.
Annexin columns or MACS (magnetic-activated cell sorting) use the presence in sperm membranes of certain apoptosis markers in order to select and remove them from the semen sample, obtaining this way a fraction free from apoptosis markers and, thus, of better-quality. It is a rather innovative methodology which has been proved to be efficient in several studies as well as safe for human beings.
How do annexin columns work?
The presence or, conversely, absence of a membrane on certain molecular markers is an excellent indicator for their health status and quality. For example, phosphatidylserine (PS) is associated with apoptotic status. Its presence on the outer membrane of the spermatozoon correlates to a high level of apoptosis. Thus, there is a direct relationship between PS and viability.
The technique is based on the use of magnetic colloidal particles of approximately 50 mm diameter (microbeads) together with annexin V and specific phosphatidylserine antibodies. This will allow altered sperm presenting such translocation on their membrane to join specifically to these microspheres. By using a strong magnetic field, marked sperm would stay trapped by its union to the microspheres in the matrix of the column, taking thus place the physical division of the sperm.
Every study carried out to date show that this is an effective technique for reducing the amount of pre-apoptotic and fragmented spermatozoa. The number of spermatozoa retrieved after being subjected to annexin columns show normal levels of DNA fragmentation. In addition, its use on normal samples enriches the amount of spermatozoa.