Technique may make the assessment of male fertility more accurate, says study

The flow cytometry technique, already adopted by specialists in animal reproduction, can also be used to analyze human sperm and predict male fertility potential more accurately than traditional methods. That’s what a new study published in the scientific journal Reproductive Toxicology points out.

At the Botucatu campus of the Universidade Estadual Paulista (Unesp), researchers successfully tested flow cytometry for performing functional analyzes of spermatozoa. According to the authors, this type of analysis with human cells is unprecedented in the scientific literature.

The experts used an optical-electronic detection apparatus equipped with lasers. Lasers are able to excite specific proteins called fluorophores, while filters detect this fluorescence emission in different colors.

The technology makes it possible to evaluate different characteristics of cells linked to fertility. It was possible to observe points such as the integrity and stability of the sperm plasma membrane, fundamental for its survival in the female genital environment and connection with the woman’s reproductive cells.

The researchers also evaluated the status of the acrosome, a structure present in the sperm that helps it penetrate the oocyte (as the female gamete is called before fertilization) during the fertilization process. The technique also highlights the mitochondrial potential, which generates the energy used to beat the flagellum as it passes through the female genital system – all with just one sample.

In continuous decline in recent decades, sperm counts have influenced the decline in the number of births. The clinical evaluation of these cells is essential both to identify cases of infertility and to work with reproduction biotechniques, such as in vitro fertilization and ISCI (intracytoplasmic sperm injection), a fertilization method in which the selected male gamete is injected directly into the mature oocyte with a fine needle.

This evaluation is usually performed using microscopy techniques, but there is an obstacle: the impossibility of testing several attributes simultaneously in a single cell, which impairs its analytical precision.

In the most recent manual (2021) for examination and processing of human semen from the World Health Organization (WHO), conventional sperm evaluation performed in clinical laboratories (spermogram) was classified as unable to accurately predict a man’s fertile potential and , therefore, many cases remain as idiopathic (without a defined cause).

“In the microscope, we manage to count a small number of cells – around 100 or 200 per sample –, while in a flow cytometer this goes up to at least 20 thousand cells”, says Josiane de Lima Rosa, who shares with researcher Camila Paula Freitas Dell’Aqua was the first author of the study, conducted with support from the São Paulo Research Foundation (FAPESP).

“This allows us to observe more than one part of the sperm at the same time, ensuring much greater accuracy in the examination and referral to more specific and assertive treatments.”

According to Camila, the results of this study, added to the previous experience in veterinary medicine in centers that work with bovine semen, present a new possibility of applying flow cytometry also in human reproduction laboratories.

To enable the developed analysis protocol to be used more widely, the researchers used two types of cytometers in the study – a more robust one, with three lasers (red, blue and violet), and a simpler one, with two lasers.

new partnerships

In addition to enabling the use of a more effective technique for fertility analysis, the researchers’ idea is that the work encourages approximation and the exchange of information between medical and veterinary professionals, enabling the development of new procedures.

“As it requires less bioethical rigor in obtaining samples, veterinarians find it easier to perform new tests and look for alternatives in other tools, and this can be transferred translationally to human medicine”, says Fabiana Ferreira de Souza, professor at the Department of Veterinary Surgery and Animal Reproduction of the School of Veterinary Medicine and Animal Science at Unesp. “The union between the two areas is essential for us to achieve progress.”