Study finds cannabis is harmful to zebrafish embryos

EDMONTON—An researcher from Edmonton says women who are pregnant should be careful with cannabis, after a study showed the plant’s compounds have harmful effects on developing zebrafish embryos.

The study finds cannabis is harmful to zebrafish embryos and may have similar effects to human embryos. The study led by Declan Ali, a professor in the University of Alberta’s biological sciences department, exposed fish embryos to tetrahydrocannabinol (THC) and cannabidiol (CBD), which are the main chemicals in cannabis that affect endocannabinoid receptors in the brain and body.

Zebrafish embryos similar to human embryos

Researchers briefly put the fish eggs in water with varying concentrations of CBD and THC during gastrulation, the phase early in the embryonic development of most animals, and then washed them and put them back in uncontaminated water for the rest of their development.

What they found was that fewer of the exposed eggs hatched and fewer fish survived, compared to embryos that were not exposed to the compounds. High concentrations of THC led to a small decrease in survivals, but high concentrations of CBD showed a significant decrease.

“We use concentrations for these compounds that we believe are physiologically relevant given what’s been measured in human blood plasma after smoking marijuana,” Ali said.

Both compounds showed reductions in heart rate and in communication between motor neurons and muscle fibres.

Some of the fish also tended to be shorter in length, and some exhibited malformations like cardiac edema, swelling of the heart, and curvature of the back and trunk.

“I hesitate to translate it directly to humans. However, the proteins that we are looking at, the receptors for these compounds, the way that our bodies work, are very, very similar,” Ali said.

He explained human and fish both have an endocannabinoid system that naturally makes compounds similar to THC and CBD.

Pregnant women cautious with consumption

When organisms are exposed to those compounds, the functioning of their endocannabinoid system is potentially being altered.

“Other research has shown that when you do alter those systems, you get aberrant growth and development of neurons and cells in a very similar way to what we’ve seen,” he said.

Ali said he is aware of three longitudinal studies done on humans to test the effects of cannabis exposure during pregnancy, in 1978, 1982 and 2002.

While some results were inconsistent, he said the studies tended to link exposure to cannabis with aberrant behaviours in newborns, cognitive deficits in children, and impairments in inhibitory control and impulsivity.

He said those results seem to be in line with his study, which suggests we should be more careful when consuming marijuana, especially with legalization looming in Canada.

“It does have clear uses for medicinal purposes,” Ali said.

“But I think if you are thinking of becoming pregnant, maybe just take a step back and just rethink your use and consumption of these compounds during the time of pregnancy, in a very similar way that you would for alcohol.”

Ali plans to continue his research by monitoring the fish through adulthood and studying potential effects on their offspring.

His findings were published in nature research journal Scientific Reports.

The Canadian Press