spermNMR published paper #1: 1 H MRS can detect metabolite differences in live human sperm
3 May 2017
The first results from our work have just been published in ‘Molecular Human Reproduction’, a scientific journal for those interested in the science of reproductive medicine.
In our article we asked the question:
Can 1H Magnetic Resonance Spectroscopy (MRS) be used to obtain information about the molecules and metabolites in live human spermatozoa?
This was because current methods to examine sperm are either limited in their value (eg semen analysis) or are destructive (eg sperm DNA testing). A few studies have previously used MRS to examine sperm, but these have either looked at seminal fluid from men with different ejaculate qualities or at the molecules present in pooled samples of sperm that had their contents removed. To our knowledge our work is the first to directly examine live sperm.
An important part of our work is ensuring that the MRS spectrum we observed was from the sperm and not seminal fluid that makes up 95% of the ejaculate. Therefore, we tested different techniques for ‘washing’ sperm to remove seminal fluid. We found that a method called density gradient centrifugation (to which we added an additional washing step) was capable of cleaning sperm to an acceptable level.
Once we had established our experimental method, we then examined sperm from both healthy volunteers, as well as men attending the Andrology Laboratory in the Jessop Wing for fertility investigations.
Our enhanced sperm washing methods allowed us to show that MRS could detect that the molecules choline, glycerophosphocholine, citrate, acetylcarnitine and unsaturated lipid were associated with sperm. Additionally, we could detect MRS signals from sperm at very low concentration, 3 million per millilitre – thereby making the technique suitable to be used on sperm samples from men with very low sperm counts (oligozoospermia).
Density centrifugation separates sperm into two populations: one with high and the other with low motility. This is the method used by assisted conception units to obtain the best swimming sperm for in vitro fertilisation (IVF).
Typically, in IVF, the higher motility fraction is used. However, since our project is about understanding the metabolism of sperm with poor motility, the ability to compare these two populations allows us to see if there are any differences between them by MRS. Interestingly, we found that they differed in terms of the amount of choline, glycerophosphocholine and lipids. These molecules are often associated with the outer membrane of sperm and therefore could reflect differences in sperm structure.
Moreover, we also found a difference in the MRS spectrum for lactate. This is interesting because lactate is an indicator of energy metabolism and could suggest difference in chemical fuel consumption.
In summary, our first paper shows 1H MRS can provide information about the molecules present in live human sperm and may therefore permit the study of the underlying functional biology or metabolomics of live sperm to be investigated further.
Given the relatively low concentration of sperm required to obtain a suitable MRS signal, this could be carried out on sperm from men with very poor quality sperm (eg oligo-, astheno- or teratozoospermia). This may lead to the development of new diagnostic tests or ultimately novel treatments for male factor infertility.
Below are three 1H MRS spectra showing some of the molecules we have identified from our work.