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Investigating the Mechanisms of Neuropathic Pain: An Interview With Margarita Calvo

2 June 2020

PRF Interviews


Margarita Calvo, MD, PhD, is an associate professor in the Department of Physiology at Pontifical Catholic University of Chile, Santiago. After completing her medical training there, she undertook her PhD in David Bennett’s laboratory at King’s College London, UK. Calvo returned to her alma mater in 2013, where she set up her own lab. Her research follows two lines of investigation: painful small-fiber neuropathy in skin conditions, and the role of voltage-gated potassium channels in counterbalancing hyperexcitability in neuropathic pain. Calvo took time to talk with Lincoln Tracy, a research fellow at Monash University, Melbourne, Australia, and a freelance writer, to discuss her research, the pain landscape in Chile, her scientific heroes, and more. Below is an edited transcript of their conversation.


What was your path to pain research?


It’s hard to say exactly how I got here. I was working clinically and had started my anesthesiology training while working in a pain clinic. I loved the practical, hands-on aspects of anesthesiology, but I found pain to be very interesting. So I went to England to do a master's degree in pain. This is how I learned about IASP and the Neuropathic Pain Special Interest Group, NeuPSIG. I can’t remember who invited me, but since presenting my master's thesis at my first IASP meeting, I haven’t missed a World Congress or a NeuPSIG congress since!


I never ended up completing my anesthesiology training, as I went on to complete a PhD in neuroscience with David Bennett instead. But since I returned to Chile I have been working clinically and doing research as well. I feel that having a mix of clinical and research experience is important; seeing patients with neuropathic pain helps guide my research, and I can act as a bit of a bridge between science and the clinic.


What is the aim of your research?


My research aims to understand the mechanisms behind neuropathic pain. There are two lines of research within the lab that work toward this aim. The first is more clinical, where we study different skin conditions that produce small-fiber neuropathies, which can lead to chronic pain or itch. We have been working with patients with epidermolysis bullosa, a condition where patients develop blisters in the skin and mucous membranes. In epidermolysis bullosa the nerve fibers are either missing or non-functional, but the end result is neuropathic pain and itch. We are also looking at other chronic skin conditions where patients complain of itch more than pain, such as lichen simplex or atopic dermatitis. The itch experienced by these patients could be neuropathic as well.


The second line of research focuses on potassium channels and how they counteract the spontaneous activity and hyperexcitability that occurs after you cut a nerve. We know that after cutting a nerve there is an overexpression of Kv1 channels, which are voltage-gated potassium channels. These channels can decrease the sensitivity of the fibers. We see this as a natural mechanism that mammals use to counterbalance the hyperexcitability in chronic pain. We are interested in seeing how this happens from a basic science perspective, and whether we can mimic it in patients with chronic pain.


The potassium channel work sounds fascinating. Can you elaborate on that further?


This line of work started when we observed that when you do any kind of nerve lesion in a rat, they display hypersensitivity for the first few days. But if you look at the same animals about a month later, many of them have recovered. We were curious to figure out what was going on in these animals.


We didn’t know where to start, but we knew that the myelinated fibers maintain spontaneous activity after the lesion. We set up a neuroma model in rats, where we would cut the sciatic nerve and fix the end of the nerve to the skin. This would allow us to poke the neuroma to test its sensitivity.


We continued along this line of work and discovered that Kv1.2 channels disappear from the nerve in the initial stages after injury. We also found that the rats were expressing another potassium channel around the time they recovered from the hypersensitivity, Kv1.6.


What are you currently working on?


We are currently running a randomized clinical trial where we are testing whether pregabalin can reduce neuropathic pain in patients with epidermolysis bullosa. The Epidermolysis Bullosa Research Partnership provided funding for this work. We started with two centers because epidermolysis bullosa is a very rare genetic condition. It took a while to sort out protocols and ethical applications, but we are now recruiting from our unit in Chile and from the Hospital for Sick Children in Toronto, Canada, with Elena Pope and Irene Lara-Corrales.


Because epidermolysis bullosa is rare, recruitment is slow. We have also been challenged by newly introduced clinical trial regulations in Chile. In January, before COVID-19, we were in discussions with other clinicians from Argentina and Mexico about joining our collaboration.


We are also investigating the mechanisms underlying the neuropathy we have observed in patients with epidermolysis bullosa, especially the neurotrophic factors secreted in their skin. For this line of work, we are using in vitro models, animal models, and patient samples. We are also looking at other skin conditions involving neuropathic pain or itch in the clinic. And, of course, we are continuing our work on Kv1 channels.


Your work involves both animal models and patients in the clinic. Why is taking a translational approach to neuropathic pain research so important?


It’s important because it allows you to look at things you can’t look at in humans. If you have questions in patients, you can go back, look at the animal models, and then bring what you have learned back to the patients. While we acknowledge that the mice we work with are different from humans, there are lots of similarities with respect to proteins and the structure of the nervous system. It is important to keep the animal models and the patient work close together.


For example, in my clinic, we start with the epidermolysis bullosa patients and see the problems they have with pain and itch. We know that this is a peripheral neuropathy, but we want to see what is going on in the rest of the somatosensory system. But we need animal models to investigate the pathophysiological events that occur in the central nervous system, as samples are not easily obtained from patients.


So we went back to the animal model. This was very challenging because the animal colonies were difficult to breed and maintain because of their massive blisters. But we persevered, and we eventually learned that these animals are like diabetic animal models, where there isn’t a lot of neuroinflammation occurring. Their condition is closer to a secondary neuropathy.


We also learned that the animal models have degeneration of nerve fibers in their skin, and that there is a lack of regeneration; the fibers are not growing back after injury. This led us to look at neurotrophic factors and how the lack of these factors in patients prevents the axons from growing back.


Now that we know how our epidermolysis bullosa patients respond after injury, our next step is to see what happens if we treat them. Giving nerve growth factor, NGF, to patients is painful, so we have gone back to the animal model to see if applying NGF locally can somehow increase nerve regeneration in the skin and prevent these neuropathies.


Last year you published a review article looking at recent developments in harnessing different resources to understand the mechanisms driving neuropathic pain. How did you find working on a paper like this?


This paper came about after a joint meeting between NeuPSIG and the IASP Genetics and Pain SIG in 2018. This meeting generated a lot of active discussion about neuropathic pain, some of which was a bit controversial because of differing opinions. It was challenging to review so much of the literature and to pull it all together in a balanced, coherent manner. But it was an interesting process because so many of us were working together.


There are lots of new things coming up in genetics, animal models, and population-based studies. There is a lot of interesting work being done on ion channels in C. elegans and zebrafish. This is important because we don’t know much about the mechanisms of sensitivity. But population-based studies are also important, so approaching the problem from both ends teaches us a lot about genetics and pain.


It’s hard to say how well the paper has been received by the rest of the community. I’ve received several emails with positive feedback about the review and its balance of the different aspects of the research we discuss. It takes a while for reviews to have an impact, and for people to start citing it in their own work. But at the end of the day I’m proud of it because it encourages discussion. People might not agree with what we have written, but it opens a dialogue about it.


What keeps you motivated to do research?


My motivation comes from how much I enjoy my work – I really like it! There are always new questions to ask or new things to learn, and I think that’s amazing. I admit that any work you do repetitively can get boring, but having two different yet complementary areas of work keeps you entertained throughout the year – and busy. Working with patients makes you have clinically relevant questions that you can answer with basic science in the lab.


What is the pain landscape like in Chile?


We have an IASP chapter in Chile, the Chilean Chapter for the Study of Pain, but it has a strong clinical focus, and there is not a lot of emphasis on research. However, at the last meeting we managed to secure a research day in between all the clinical lectures. There are several very good people undertaking research, mostly in the molecular biology space. There is less clinical research going on now; it’s challenging.


The first challenge for clinical research was that we had to create a pain unit. Although I work in a pain unit, they are a new concept here. It took us about two years to set up our clinic and have it running properly. I have started pushing for more research, but this is taking longer than anticipated because health workers are under great pressure on the wards and there is little time protected for research.


Despite this, funding opportunities exist for clinical research. We are in the process of applying for collaborative research funding; hopefully we will be successful this year. It is an interesting opportunity because it makes you collaborate with colleagues that you otherwise wouldn’t see.


Who are some of your scientific heroes?


I would say Rita Levi-Montalcini, the Italian Nobel Laureate who discovered NGF. I relate to her as a woman and as someone who works with NGF. She had to work in very difficult times during the war. She is a real hero of neuroscience, as well as of pain, because neurotrophic factors are so important to our work in these fields. There are so many other people who I would like to be like when I’m older, but it’s a bit embarrassing to put in an interview [laughs]. But if I could have a dinner party with anyone from history, I’d pick Rita to start with.


Thank you for your time. It’s been fascinating to talk to you.


Thank you, it’s been fun!


Lincoln Tracy is a research fellow and freelance writer based in Melbourne, Australia. You can follow him on Twitter @lincolntracy.

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