As cannabis legalization expands across the United States, researchers are working to understand how exposure to chemicals within cannabis products may affect human health. One such researcher is Duke Environment’s Susan K. Murphy, an established scientist in the fields of ovarian cancer and epigenetics.
As the principal investigator of Duke’s CIPHERS Project, Murphy and her team have organized multiple research projects to explore cannabis-induced effects on sperm. CIPHERS, which stands for “Cannabis-Induced Potential Heritability of Epigenetic Revision in Sperm,” has one human research component, one rat component and one epigenetics component. Each of these projects have specific goals designed to answer critical questions about the impact of cannabis on sperm quality, DNA changes and the potential for effects to be inherited by future generations.
In a recent study published in the journal Epigenetics, Murphy and her team recruited both cannabis-using and non-using males of reproductive age (18-40 years old) to determine how cannabis exposure affected semen and sperm quality. They found that cannabis users and non-users produced a similar volume of semen per ejaculation and had similar sperm quality, with respect to motility and morphology. However, they observed that cannabis-users had significantly lower numbers of sperm per ejaculation than non-cannabis users.
Susan Murphy answers some of the questions I had after reading the study:
Why focus on males?
This study focused on how cannabis-use affects males because males generally report a higher frequency of cannabis use than females. In addition, we have published on other environmental effects on the sperm methylome, including the effects of obesity and of flame retardant exposure (with Heather Stapleton). Our results, and those from other studies, raise the question about how the preconceptional environment might impact the fidelity of epigenetic programming, and if the shifts in the epigenome can be transmitted to the next generation. Of course, it helps considerably that sperm are a bit easier to obtain than eggs.
How does route of cannabis intake affect sperm (i.e. smoking vs. edibles)?
We have only started to look at this, and at least for one of the genes we have examined in the rat studies, there does seem to be a difference by route of exposure. In this case, the gene was significantly altered in sperm when the rats were dosed with THC orally, but not when rats were injected with THC. We do not yet know if and how this might differ in humans by route of exposure.
Does removal of affected sperm help reduce effects?
One way we are trying to determine the answer to this is by recruiting men who use cannabis and asking them to stop using for a little longer than the duration of a spermatogenic cycle, which is 74 days in humans. They have to come in for drug testing every week and have to provide a semen specimen before and after the period of cannabis abstinence. We also have a control group who are not cannabis users. We are still in the recruiting phase of this study. If we do not see any differences in the before and after specimens, then it is likely that the spermatogonia (the sperm progenitor cells) are affected by the cannabis and that it might not be possible to “clear out” the affected sperm. If we do see an improvement in the methylation profiles of the sperm, then this would suggest that the cannabis effects are altering the sperm that are actively undergoing maturation, and that it may indeed be possible for cessation of use to improve sperm quality.