spermNMR published paper #3: A spoonful of sugar

12 February 2019

It’s not just a certain nanny that said a ‘a spoonful of sugar helps…’, in our latest published paper we fed sperm not just sugar but a whole range of different molecules to see which ones they could metabolise and how this related to their motility.

Sugar is a name of a range of sweet tasting carbohydrate molecules. We tested two of these, glucose and fructose, that can also be found in both semen and the female reproductive system. Each was readily consumed by sperm at similar rates and both of these sugars were processed into lactate (the metabolite that makes your muscles sore when exercising).

Conversion of glucose or fructose to lactate is a quick way to make ATP through a process called glycolysis that is inefficient but works without oxygen.

Interestingly, a more efficient but oxygen dependent process (Oxidative Phosphorylation) was only seen occasionally in our experiments, which was a surprise.

To observe sperm feeding on molecules like glucose or fructose we have to put a tracer into them by using a carbon-13 atom. This doesn’t change them chemically, to the sperm they are the same molecules, but it makes them visible to a technique called Magnetic Resonance Spectroscopy (MRS).

We can then track the progress of the carbon-13 atom as the molecules it is contained within are metabolised. This is done by measuring the size of the peaks in the MRS spectrum.

Of the molecules we tested glucose, fructose, pyruvate, lactate and 3-D-hydroxybutyrate were consistently metabolised by sperm and all are associated with energy production. Some of the others were occasionally metabolised by sperm to much lower levels.

Armed with this knowledge we then separated sperm into higher and lower motility fractions to see if they metabolised differently. Our findings showed that only glucose metabolism was different between low and high motility sperm.

However, the results showed something else which we weren’t quite expecting. It appears that sperm with lower motility produce more lactate, and so generate more energy, than higher motility sperm. This is quite counterintuitive and it may be that more efficient sperm swim better than non-moving sperm.

So sugars appear to have an important role in sperm swimming but don’t go reaching for the sweets just yet. Too much sugar metabolism by sperm may damage them. Plus sugar is bad for your teeth.

As we expand our knowledge of how sperm make energy, we hope to discover the causes of poor sperm motility and suggest new approaches for novel treatments or therapies.