3Rs Stimulus Fund: studying pain in a dish

Willemen does not use laboratory animals for this project; her pain studies use Petri dishes. She received a grant from the 3Rs Stimulus Fund for this research. We asked her to tell us a bit more about her work.

“One in five people suffer from chronic pain. That’s a lot! Often there is no real appropriate medication: either a substance doesn’t work well, or it has unpleasant side effects like addiction. Also, some therapies turn out to cause a lot of pain. For example, a patient’s chemotherapy dosage may have to be lowered, or even stopped completely, because it causes them too much pain. Isn’t that tragic? It astonished me that there is so little interest in chronic pain. We’re currently the only group in the Netherlands doing fundamental research in this area."

What are you trying to find out?

To begin with, we want to know how chronic pain arises. Let’s take rheumatoid arthritis. You know that an inflammation can cause pain, but even after the inflammation has been properly treated, 20 to 30 percent of patients still have pain. The same goes for osteoarthritis: patients may get a new hip or knee, but for many of them the pain doesn’t go away. How does this happen? There may be some change in the sensory neurons at the molecular level that causes pain. This is something we’d like to understand so that we can develop pain relievers that target that.”

Do you use animals in your experiments?

“Pain is complex; it can originate in your toe, and pass through the nerves in your leg and spinal cord to get to your brain. Pain can be regulated at all of those spots. So you need a whole organism to study pain. Usually it’s done with behavioural research on animals. You might give a mouse a mild inflammation in the sole of its paw. Then you hold a nylon filament or a heat ray to it and see at what point the mouse withdraws its paw, either at a certain thickness of filament or duration of the heat.

Do you find it difficult to do that kind of experiment?

“When I first came to work here, I wasn’t really open to animal testing, but once I knew more about why and how it’s done, I was completely behind it. Given that pain is such a huge public-health problem, and a problem for animals too, it’s really important that we understand it better and develop new pain medications. We make sure that we measure the animals’ pain as soon, and as quickly, as we can. And it’s precisely because we do these pain measurements that we know really well how the mice are doing.

Thus, although animal experiments are still necessary, we’re also looking at whether we can simulate the whole pain system in a Petri dish, for example with human stem cells that have been reprogrammed  into sensory neurons. We stimulate these cells with an extract of hot pepper, menthol or mustard oil, then we test how the sensory neurons respond to those compounds. We hope that more and more of this research process can be done with cells in Petri dishes.  Moreover, the huge advantage of working with human cells is that the research comes a lot closer to what we want to know about the human body.”

Are you making progress?

“We’ve used stem-cell-derived human sensory neurons and investigated whether they express important “pain receptors”. However, some of the receptors were missing. That was a setback. But a little later on, cells that colleagues at the UMC Utrecht had developed did turn out to have the right pain receptors. We’ve tested a number of substances that usually elicit a pain response, and with most of them, we did see a response in the sensory neurons.

In the next step we made the cells more sensitive to pain stimuli, since that seems to be what’s going on with these patients. They experience pain much more intensely. Imagine taking a shower when you have burns on your skin: you won’t be able to cope with hot water the way you normally can. We can simulate this kind of hypersensitivity by adding inflammation-promoting substances to the cells. Then we introduce the substances that normally elicit a pain response again. And indeed, we saw that the response from the cells was much more intense.”

How do you then arrive at a good remedy for chronic pain?

“We’ve already been working on new pain medications for some time, and we test them now on the hyper-sensitised stem-cell-derived human sensory neurons. And we’re planning another intriguing move. Osteoarthritis patients have painful joints. For example, when it involves the knee, there’s fluid surrounding the joint. Doctors remove this fluid from the knee, so it can be studied, with the patient’s permission of course. What happens if you administer this fluid to our home-grown sensory neurons? Do these cells react differently if the patient had more pain, or are the sensory neurons long-lasting activated? If we can pinpoint the differences between joint fluids in patients with and without persistent pain, then we can use that fluid of a given patient to predict over the long term whether they will develop chronic pain. Then you can intervene at a much earlier stage.”

What is your dream?

“I’d really like to do something meaningful for patients with chronic pain. The fund is helping me, but we’re aiming to apply as a group for an even larger grant to identify and document everything even better. There are also things like experimental cell systems that simulate reality even better. Then you have greater distance between different cell compartments in the bottles and dishes, more like the distance between your toe and your spinal cord. What I’d like to do is build in that distance. This can help us to better understand how sensory neurons detect pain, and how they can transfer signals over a longer distance.

It would also be interesting to use these systems in combination with other cells, so that we can find out if these cells can regulate the sensitivity and activity of sensory neurons. And of course we want to study our new home-made pain medications even more: whether they work well, and if we can test them using our method with stem-cell-derived human sensory neuron in a dish.

In the long term, it would be great to be able to work with stem-cell-derived human sensory neurons grown from fibroblasts of an individual patient. Then you could test a whole range of painkillers on that patient’s cells, in order to know what works best for that specific person. But that’s still a long way off.”