Sink or Swim

How did you investigate this?

We initially used a rapid urine screening test to measure 11-nor-9-carboxy-ΔTHC (THCCOOH; the primary metabolite of cannabis) and then verified the results using an enzyme immunoassay. Measurements for THC and other cannabinoids were performed using ultra performance liquid chromatography/tandem mass spectrometry (UPLC-MS/MS) and by enzyme immunoassay (EIA). Our findings indicate that cannabis use (in humans) and THC exposure (in rats) are associated with changes in DNA methylation, meaning changes in the way genes are being regulated.

What made you think THC might affect sperm?

We had previously found that newborns of obese fathers had methylation changes in growth regulatory genes, and hypothesized that this might be epigenetic and transmitted through the sperm. In another study we examined the relationship between obesity and sperm DNA methylation, finding that there were indeed methylation differences at these growth regulatory genes relative to normal BMI controls in their sperm DNA. Cannabis was just beginning to be legalized, and we wanted to know if cannabis use could impact the sperm epigenome. No one had previously examined this, but there was evidence of intergenerational effects from animal studies, suggesting that epigenetics could be responsible.

What did you expect to find?

I truly did not know what to expect. For quite a few genes, there were relatively large changes in methylation between the user and control groups. For a substantial number of genes, we also saw multiple regions of the gene that were affected, bolstering the credibility of the results. Also surprising was the significance in the overlap of the genes identified in sperm from THC-exposed male rats and the same genes identified by an independent group as having altered methylation in the brains of rat offspring (not themselves exposed to THC) born to parents who were both exposed to THC during their own adolescence. This suggests potential for inheritance of effects from the parents via the gametes, but we need more definitive evidence.

Do you anticipate there being any evidence of epigenetic changes in the offspring?

This remains an open question. Until a few years ago, the inheritance of such effects from the paternal germline was thought to be improbable since DNA methylation in sperm is largely erased in the early embryo, just after fertilization. However, there is now evidence that there are thousands of regions of the genome that are not erased, providing a potential mechanism for transmission of these alterations. We don’t know as yet if any of the changes we have identified are in these regions. We are also working on determining whether the changes we see are happening at different regions in all of the sperm and are thus distributed throughout the entire sperm population, or if the changes are only present in a subset of the sperm population. This requires being able to analyze DNA methylation in single sperm cells, which is technically quite challenging!

What does this mean for potential fathers who use cannabis?

It is too early to make definitive recommendations other than to err on the side of caution. The findings need to be replicated in a larger study, and we need to determine if the changes we observed in sperm can be “washed out” with abstinence from cannabis use. This may be possible if the changes are happening only during the maturation process of the sperm cells. – but if the changes are affecting the sperm stem cell population (the spermatogonial stem cells), then the changes may be permanent. We also need to determine if the changes we see in sperm are able to be carried forward to the next generation.