A new study published in the journal Cell outlines researchers' development of reptile organoids; specifically, organoids of the venom glands of the Cape coral snake (Aspidelaps lubricus cowlesi).1 What's more, these organoids are capable of producing venom in vitro.
What is an organoid?
Over recent years, organoids have become a valuable resource in clinical research, particularly for studying the molecular mechanisms of certain diseases and in the testing of pharmaceutical compounds.
In case you're unfamiliar, an organoid is a 3D multicellular in vitro construct that mimics an in vivo organ and can be therefore utilized to study how the organ works at the molecular level in a dish within the laboratory.2
Want to learn more about organoids? Download our infographic.
Snake venom – a source of potent therapeutics
Statistics suggest that between 81,000 and 138,000 people die annually as a result of snake bites. Multiply this figure by three and you have a rough estimation of the number of amputations caused by snake bites every year.
Methods for manufacturing antivenom haven't adapted or changed significantly since the 19th century. Hans Clevers from the Hubrecht Institute for Developmental Biology and Stem Cell Research at Utrecht University, senior author of the study, says, "It's clear there is a huge unmet medical need for new treatments."
Clevers' laboratory usually focuses on research adopting mammalian organoids. So what inspired them to create reptile organoids?
"We wanted to go down the evolutionary tree to see if it would be possible to grow organs from other non-mammals. We thought we could also use such cultures to learn about the biology of that animal," Yorick Post, PhD student at the Hubrecht Institute and one author of the study, told Technology Networks.
Post continues, "An iconic reptile that drew most of our attention was the snake that carries adapted salivary glands that produce venom. Snake bites kill over 100,000 people a year, but the venom also contains many molecules which could be potent therapeutics. The snake venom gland organoid would – besides being the first reptilian organoid – be a useful system to start fighting snakebite or bioprospecting venom."
Organoids successfully produce biologically active venom
Jens Puschhof, PhD student at the Hubrecht Institute told Technology Networks that the first challenge in this study was acquiring venom gland material. "In collaboration with the Dutch Reptile Zoo in Rijswijk and local snake breeders, we were able to acquire eggs of the Cape Coral snake, Aspidelaps lubricus, from which we could perform our first attempts to establish organoid cultures," said Puschhof.
He continues, "We quickly found a successful culture condition, inspired by the pancreatic organoid medium used for mammals, while reducing the growth temperature from 37 degrees Celsius to 32 degrees Celsius. This lowering of the temperature was essential to acquire growth and is consistent with the average body temperature of a cold-blooded animal such as the snake."
The venom gland organoids grew more quickly than the scientists expected and after one week they were able to break them apart and replate them.
Another hurdle that the scientists encountered was the fact that none of the snake organoids that they were working with had annotated genomes. Post remarks, "Currently only a couple of dozen reptile genomes have been annotated, which is an expensive, complicated and lengthy process. Considering that more than 500 venomous snakes exists, only a few of those are annotated."
In collaboration with the Dutch company Baseclear in Leiden, the scientists built a de novo transcriptome of the flagship snake used in this study. "This allowed us to perform detailed molecular analyses and enabled us to validate toxin expression in our organoid cultures and prove these accurately match actual tissue," Post continues.
At least four different cell types could be distinguished from the venom gland organoids, and these cells were found to produce biologically active venom peptides.
Creating next generation antivenoms
The speed at which the organoids divided holds promise for the future of antivenom manufacturing. Joep Beumer, PhD student and one of the authors of the study, told Technology Networks: "Together with increasing knowledge of the key venom components, we think organoids can serve as a tool to selectively express these most relevant toxins. This control over venom expression and the ability to produce large batches of standardized venom could indeed help with next generation antivenoms."
Towards a "biobank" of potent drugs?
"We are currently expanding our repertoire of venomous organoids in collaboration with Freek Vonk (Naturalis), a Dutch snake expert. Together, we intend to build a biobank of 50 venomous reptiles that are most relevant to humans. These would for example include the most lethal snakes, but also the lizard Gila monster which is a source a potent diabetes drug (Exendin-4). We hope such biobank could work as a platform to study the regulation of venom products, as well as providing a cellular source to start bioprospecting," Beumer said.
A key component of scientific research is of course reproducibility. It's encouraging to see that the work of Clevers’ laboratory has inspired other scientists across the globe to successfully produce snake venom organoids. Puschhof told Technology Networks, "Other groups, among them Sean B. Carroll and Christopher Chen in the USA, have successfully established snake venom gland organoids following our protocol. They are further developing these tools for epigenetic studies and biotechnological applications, respectively."
Yorick Post, Jens Puschhof and Joep Beumer, PhD students at Hubrecht University, were speaking with Molly Campbell, Science Writer, Technology Networks.
1. Post et al. (2020). Snake Venom Gland Organoids. Cell. DOI: https://doi.org/10.1016/j.cell.2019.11.038.
2. De Souza. (2018). Organoids. Nature Methods. DOI: https://doi.org/10.1038/nmeth.4576.