Rocío Núñez Calonge
Scientific Director of the UR International Group and Coordinator of the Ethics Group of the Spanish Fertility Society
One of the main problems in cases of male infertility is asthenozoospermia, that is, the lack of sperm mobility. Especially when the cause is unknown. To solve this, assisted reproduction techniques such as ICSI are used, where only one mobile sperm is needed to introduce it into the oocyte.
The authors present a study with a novel method to improve and even induce the mobility of immobile sperm. For this, they use a microfluidic droplet platform, where they individually introduce sperm and subject them to ultrasound. By isolating the sperm within the droplets, although acoustic transmission causes some movement of the droplets and there is flow within them, individual cells can be easily identified before and after exposure.
The study is well-designed and the conclusions are supported by solid data. The results show that sperm with low initial mobility are those that experience the greatest change in mobility after ultrasound exposure (at 800 mW and 40 MHz). The percentage of non-progressive sperm in a sample is reduced from 36% to only 10% after 20 seconds of ultrasound treatment. This increase in motility is even more profound when it comes to immobile sperm, as it causes 34% of live immobile sperm to become mobile after exposure.
It is known that the lack of sperm mobility is associated with a disturbance in mitochondria, which is like the "engine" of sperm, which requires energy. In this work, to elucidate the underlying mechanism behind the increased mobility caused by ultrasound, the regulation of mitochondrial function was evaluated by controlling mitochondrial membrane potential levels, or in other words, verifying energy supply within the cell, which can affect mobility. The results demonstrated that ultrasound application improved this potential.
The real significance of this work lies in its potential application in cases of patients with completely immobile sperm or in testicular biopsy samples. In these cases, techniques have been applied, as they themselves describe, such as pentoxifylline, a substance that, when applied to sperm, induces movement. However, its safety is not proven, and it is not useful in many cases. Therefore, being able to use a technique that is non-invasive for sperm, without the need for staining or chemical treatment, offers tremendous potential for improving clinical outcomes through ICSI.
Despite accurately describing the results, the press release does not highlight this utility, which is the most important aspect of the study.