From a Mushroom in the Woods to a Medicinal Compound: A Chemical Approach
A Day with Dr. Rich Tehan
This article is an exploration into a new evolution of this publication. As we continue to learn weekly about mushrooms, I also want to learn more about the people who are passionate about mushrooms. The mushroom people. The hope is not only to improve our understanding of mycology and the natural world, but also realize the impacts mushrooms have on humanity.
From a Mushroom in the Woods to a Medicinal Compound: A Chemical Approach
They say there’s no place like Utica in December. That’s exactly what I had in mind when I met Dr. Rich Tehan on a sunny Sunday morning at Marcy Town Park where the car thermometer clocked in at 19 degrees Fahrenheit. We walked for just over an hour, found a modest seven species (limited by the snow-covered ground and the majority of our attention devoted to conversation), and then headed down to his lab at Utica University.
I first caught wind of Rich at the Adirondack Experience’s Mushroom Mania where he gave a presentation on some of his research with the entomopathogenic (insect-infecting) Paraisaria fungus. The depth of the research coupled with the potential applications gave me goosebumps, and I felt like this was something that should be shared beyond those fortunate folks in the auditorium that day. Thankfully, Rich was open to the idea and gave me basically a whole day of his time to talk about his research, show me the lab, and even butter me up with a succulent Indian lunch buffet.
Rich is a chemist, and keeping up with him was phenomenal mental exercise for someone who failed organic chemistry the first go-round and got a gentlemanly C on the second run through (a B- in the lab portion for those keeping score at home).
Rich fell in love with fungi back on July 4th, 2011. After a prodigiously rainy start to the year, Rich went fishing in the Adirondacks but became captivated by all the mushrooms that were growing in the wet woods. As a sophomore chemistry student at Utica College, he figured he was well-positioned to further study these mushrooms and the natural compounds they produce. He went on to do eight years of graduate and post-doc work at Oregon State University before the opportunity to return to his alma mater, now Utica University, presented itself just a couple years ago.
Within the wide world of chemistry, Rich now has a narrow niche as a natural products chemist. “Natural products” are chemical compounds produced by living organisms. We’re all familiar with the refined outcomes of natural products chemistry, whether its penicillin derived from the Penicillium fungus, or aspirin derived from willow bark.
Rich focuses on the natural products produced by fungi. These natural products are also known as secondary metabolites, compounds produced by the organism that are not involved with the critical functioning of cells. Examples of a secondary metabolite we are all familiar with is caffeine, which plants can produce as an anti-herbivory compound, but caffeine is not essential to the vital functioning of the plant.
Rich has isolated myriad secondary metabolites, but today we will learn about his work with the aforementioned Paraisaria and (hopefully) get a better understanding of all the work required to go from a mushroom to a medicinal compound.
Paraisaria (pair-uh-ih-sair-ee-uh) and the Paraisariamides
Back in 2021, Rich received a peculiar entomopathogenic fungus in need of identification from a mycologist down in Arkansas. On it’s own this is not a novel phenomenon as many people send Rich entomopathogenic fungi for him to take a closer look at, but this mushroom was different.
As he does with all the mushrooms he receives, he began to culture the parasitic fungus in a petri dish in the lab. Fungi can exist in different states at different points in their life, and this fungus can both infect an insect or grow as a mold in a lab setting. One of the most iconic parasitic mushrooms, Ophiocordyceps sinensis, can exist as an endophyte (living inside grass) and as a parasite (digesting and growing out of the host caterpillar).
At the time, this large entomopathogenic fungus didn’t appear like any that were familiar to Rich, and the possibility of a new species was at hand. Now, before you can describe a new species you have to do the proper due diligence to make sure the species isn’t already described. This requires a great amount of fine combing through herbarium archives and data.
The fine combing came to a head when a 142-year old specimen that was stored in the Kew Gardens herbarium in London, named Ophiocordyceps insignis, was described to look like Tolypocladium capitatum (similar to the Tolypocladium I wrote about here). Rich also had the thought that his mystery specimen looked like T. capitatum, and that was enough for him to loan the 142-year specimen from Kew to see if this mystery mushroom was Ophiocordyceps insignis.
As you can imagine, it can be rather difficult to get DNA off a tiny (albeit relatively large by Cordyceps standards), desiccated mushroom that has been sitting in an herbarium for 142 years. That’s where Rich’s chemistry background proved helpful. Instead of sampling DNA, he was able to use Liquid Chromatography Mass Spectrometry (LCMS) to determine that the mystery mushroom and the old O. insignis had the exact same chemical profile, including a specific set of compounds which he named paraisariamides. With further inspection, he was able to determine that the fungus produces these paraisariamides in the host. The last two sentences took years of work.
This work allowed Rich and colleagues to publish research that reclassified the 142-year old Ophiocordyceps insignis to Paraisaria insignis (Reference 2), but the story is far from over.
Isolating Paraisariamides
Rich uses two routes for new molecule discovery:
Bioassays. You run a crude extract of the fungus through a bioassay on cancer and bacterial cells. This is a test to see if fungal compounds inhibit cancer cells or possess antimicrobial activity. If you get a hit, something like ~50% inhibition, then you go find out which individual compound is responsible. That entails whittling down from crude extract to chromatograph fractions, from chromatograph fractions to refined fractions, and finally from refined fractions to pure compounds. When you have pure compounds, you can then see which is responsible for the hit.
You can profile the fungus on the LCMS. Through LCMS you can identify known compounds or find new compounds.
It should be noted these tests are on the lab-grown cultures of the wild mushroom, not the original specimen. Interestingly, and perhaps not surprisingly, the fungus will produce different secondary metabolites based on the substrate they consume. For Rich, those substrates are cheerios or potato dextrose. As Rich said, “every fungus we grow is a shot on goal for finding a new compound”.
Regardless of which method you use to isolate compounds, it’s a lot of lab work and it’s costly. In the case of the paraisariamides, Rich had 95% of the structure elucidated overnight, but it took two years to get the last 5% and determine the definitive compounds. You typically need to have a reason to do this, and one of those reasons is if these compounds could potentially be used as medicine.
It just so happens that was the case with the paraisariamides. They produced a hit when run through anti-cancer assays. Further research at the cancer lab at Oregon State, where Rich still maintains a working relationship, determined that these paraisariamides inhibit translation of RNA into peptides in cancer cells. All that to say they have potential as a cancer drug, but whether they’re doing it better than any current cancer drugs - and would therefore be a useful pharmaceutical - is still an open question.
Natural Products Chemistry and Medicinal Mushrooms aren’t Synonyms
It’s important to note that isolating potentially medicinal compounds differs from the general idea of medicinal mushrooms - your Reishi teas and Lion’s Mane coffees. The former isolates compounds that can be replicated and used for pharmaceutical medicine, whereas the latter may provide benefit through consumption of entire mushroom parts/extracts. Most medicinal mushroom products involve broadband uptake of the fungal cell wall components and all the secondary metabolites, not just one isolated compound.
One mechanism of how medicinal mushrooms can work is that the polysaccharides (the components of the fungal cell wall) become soluble when boiled and can be recognized by immune cells. The body responds to them the same way as it responds to a fungal infection, which is to boost immune cells. However, this is not the same as one secondary metabolite binding to a receptor or other cellular target to activate or antagonize protein synthesis (as is the case with the paraisariamides).
A Case from Across the Pacific
Now the story of the paraisariamides doesn’t necessarily end there. They are not only toxic to cancer cells, but to healthy human cells as well. Let’s travel across the Pacific where a 2017 study out of Vietnam looked at 60 documented cases of people who suffered adverse effects from the consumption of a “cicada flower” - a cicada nymph infected by a cordyceps fungus. They determined the cause of the illness was ibotenic acid (a psychoactive compound also found in Amanita muscaria) produced by the parasitic fungus Ophiocordyceps heteropoda.
Well, as it goes with fungal taxonomy, that fungus has since been reclassified to Paraisaria heteropoda and it’s possible the poisonings could have been caused by the cytotoxic paraisariamides. They’re incredibly stable compounds that don’t degrade with heat (i.e. when they’re cooked) nor with time (sitting in the herbarium). Rich has continued to look for paraisariamides in different species of Paraisaria he finds, and he continues to find these compounds produced in the host. It’s possible they were the culprit in the Vietnamese poisonings.
Why Does the Fungus Produce Paraisariamides?
So why does the fungus produce these protein synthesis inhibitors in the host? Well, Rich has a handful of hypotheses:
Host virulence factor. They’re found in the host so the thinking might be that paraisariamides are used to overcome the host’s natural defenses and kill the insect.
Preservation of the host. These cordyceps are found in the spring, and in the case of some Paraisaria, right after the snowmelts. Likely, the fungus is not infecting the host that spring but has been overwintering with the host. It’s possible that they’re acting as a preservative to fend off other fungi, nematodes, or insects that might want to munch on the tasty package of protein.
Self-protection. Hyperparasites are parasites that infect other parasites, and in this instance, there are other fungi that infect Paraisaria, specifically one called Pleurocordyceps. We’re talking about a fungus on a fungus on an insect, folks. These Pleurocordyceps are commonly found on Ophiocordyceps, a very close relative to Paraisaria, but not on Paraisaria. Perhaps Paraisaria makes these paraisariamides as a defense against Pleurocordyceps or other hyperparasites.
They all could be true. There’s no reason why 1-3 would be mutually exclusive.
Alright, Wrap it Up
While we were just introduced to a lot of chemical terms and Latin names, the process can be boiled down to: you find a mushroom, get the fungus to grow in a lab, find the compounds produced, and see if these compounds have antibacterial or anti-cancer capabilities. The research is discovery driven, not hypotheses driven. You take a lot of shots (cultivate a lot of fungi) and see where you get hits.
Throughout my Mushroom Monday profiles, many of the mushrooms we look at have some array of antibacterial, antioxidant, and/or anti-cancer properties. Rich, his colleagues, and students are the scientists that are distilling and discovering these compounds. That’s just to see what these compounds do in humans, what these natural products do for the fungus is a whole different ballgame and is just as intriguing.
The best part of mushroom festivals may be looking for mushrooms in the woods, but a more subtle appeal is the ability to interact with people whose passion for mushrooms manifests into their daily lives and occupations. I hope you enjoyed this thorough foray into this fascinating research. This was both fun and challenging, and I hope you learned something.
Acknowledgements
I want to thank Rich for his incredible generosity with both his time and his knowledge. We hung out for over five hours and he helped me reconnect some of the chemistry neurons in my brain (although if you looked at my orgo track record you might ask if there were any there to begin with). He patiently walked me through many of these difficult concepts and even broke out the molecule models to demonstrate chirality. He also took the time to proofread the article because I wanted to make sure that I had all the information presented correctly. Thank you, Rich.
References
1. Tehan, Richard M. Drug Discovery and Chemical Ecology Investigations of Specialized Metabolism In Tolypocladium and Paraisaria. : Oregon State University, 2022. Access: https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/3f462d70r
2. Tehan RM, Dooley CB, Barge EG, McPhail KL, Spatafora JW. New species and new combinations in the genus Paraisaria (Hypocreales, Ophiocordycipitaceae) from the U.S.A., supported by polyphasic analysis. MycoKeys. 2023 Nov 13;100:69-94. doi: 10.3897/mycokeys.100.110959. PMID: 38025585; PMCID: PMC10660154.
3. Doan, Uyenvy & Mendez Rojas, Bomar & Kirby, Ralph. (2017). Unintentional ingestion of Cordyceps fungus-infected cicada nymphs causing ibotenic acid poisoning in Southern Vietnam. Clinical Toxicology. 55. 1-4. 10.1080/15563650.2017.1319066.
Excited to see the shift into a mushroom and mushroom-people oriented exploration. It's true, our world imprints on us as much as we imprint on the world.
He's got a sick Chasm shirt on too. \m/