Diagnosing and Monitoring Chronic Wounds
Matt McGowan: Hello and welcome to Short Talks From the Hill, a podcast of the University of Arkansas. I’m Matt McGowan, science writer at the University, and today I’m talking to Kyle Quinn, assistant professor of biomedical engineering. Welcome Kyle and thanks for being here.
Kyle Quinn: Thanks for having me.
MM: Kyle in your work you use something called multiphoton microscopy. What is multiphoton microscopy? How is it… maybe how is it different than just a regular microscope? How does it work? How do you use it?
KQ: So one of the major differences between a regular microscope and multiphoton microscopy is the fact that we can image in 3D, so when you put a standard, thick sample under a standard microscope, you’re going to see something. It’s a fairly blurry. And with multiphoton microscopy, we have this intrinsic optical sectioning ability, so we basically can move the microscope objective lens up or down and measure the images at different depths. And so this is very advantageous in that we can image a very thick sample, like an entire piece of tissue or an entire animal or human, potentially. So we can just bring an objective down onto the skin and image cells and tissue and characterize its organization. There’s a number of advantages with multiphoton microscopy as well. Because we use near-infrared light rather than visible light or UV light, we can image deeper than your standard microscopes or a lot of the standard microscopes that you find in in research labs as well, and it’s also less damaging because we’re using near-infrared light to basically do the same amount of work that UV light would normally do and as many people may know UV light can be particularly damaging to skin and tissue as well, if you sit out in the sun too long. With these advantages in an optical an intrinsic optical sectioning ability, minimal photo damage and the deeper imaging penetration, we explore a lot of techniques where we can image the outer layer of skin and organs, and in addition, there’s a number of molecules in the body that are naturally fluorescent that we can pick up through multiphoton microscopy.
MM: And multiphoton microscopy enables something called autofluorescence, which is central to your work. What is autofluorescence imaging?
KQ: So when we talk about autofluorescence, we’re talking about really anything that is naturally fluorescent. So we don’t take a molecule or protein with any fluorescent dye. And there’s a number of things in the body, in our cells, that are naturally fluorescent. Two of those are NADH and FAD. These are metabolic cofactors involved in metabolism. And we can take a ratio of the fluorescence intensity of these, something we call an optical redox ratio, to assess cell metabolism. And we can do this on a cell by cell basis, and we can follow cells or tissues over time.
MM: What our chronic skin wounds? Can you tell us what causes them and why they’re a problem?
KQ: So skin wound healing is a really complex problem. You have multiple cell types that have to come in and reform tissue. You have a number of different cell types with different metabolic demands, and they have to coordinate to reform the tissue. And at any point you could have a certain group of cells that may no longer respond as expected, and this causes some ensuing dysfunction in the healing process. And healing can either be impaired or it can slow down or can it can stop. There can be a number of reasons for this. You can have problems with the cardiovascular system. Diabetes is a major problem. Hyperglycemia and complications associated with diabetes can cause some delays and some problems. Certainly the neuropathy becomes a problem in that sometimes patients don’t even know that they injured their foot. For example, they could step on a nail and not even realize it. And then you can have things like infection, causing a delay. You have some sustained inflammation as a result of that. And even… certainly as we get older, our skin doesn’t heal as well. So there’s a number of causes for delays or problems in the wound healing process that cause specific problems with specific types of cells.
Multiphoton microscopy imaging shows tissue section with wound bed (light blue).
MM: What are some examples of chronic skin wounds?
KQ: So chronic skin wounds can take many forms, including diabetic foot ulcers, pressure sores, or bed sores, as they’re often known, venous stasis ulcers, you know, there’s a number of different types of forms, but the underlying issue is there’s non-healing, there’s a lack of healing.
MM: Well, just for a little bit of context here, about how many people suffer with chronic skin wounds?
KQ: So chronic wounds are a major societal problem. You have millions of them a of Americans that that suffer from non-healing wounds and it costs billions of dollars. There’s a number of advanced wound care products out there. And so there’s all kinds of things being tried in the clinic, really with variable efficacy. And so part of the problem is we don’t have a number of good measurements of delayed healing.
MM: So, sort of attacking this problem, you have conducted an animal study. So you looked at chronic skin wounds on mice, and these were mice models that were… both control models and those with diabetes. Tell us what you found in this study and why it’s important to study chronic skin wounds on the diabetic models.
KQ: Right, so to study diabetic wounds, we use an animal model. We induced diabetes in mice, and that’s a standard preclinical model for delayed healings used in the development of a number of wound-healing products. And so we wanted to demonstrate, using this standard preclinical model, how our optical redox ratio, this measure of cell metabolism, may be used to predict delayed healing. So we monitored mice for 10 days following wounding at multiple time points and found some interesting changes in the optical redox ratio. So we found the redox ratio would drop initially and then rebound back up, and we found that this dynamic change corresponded to differences in the cell function. So as the redox ratio decreased, we had an increase in the number of cells proliferating. So the number of cells growing and dividing, and then as it rebounded back up, that corresponded to the migration of the cells over the wound. And what we found were diabetic wounds had a lower optical redox ratio when they should be migrating. Instead they were just sitting there continuing to proliferate, so we were sensitive to that delayed wound closure that we see in diabetic wounds.
MM: So for the diabetic models the cells were sort of remaining in kind of a stasis at the edge of the wound?
KQ: With the diabetic mice, they seemed to remain at the edge of the wound, like you said, continuing to proliferate and not migrate over the wound and reform that protective barrier that we need.
MM: Your most recent study used NADH fluorescence only to study metabolic changes to mitochondria. Can you talk about this study and why it’s important first? Why don’t you tell us what remind us what mitochondria is?
KQ: So yeah, mitochondria are these organelles in our cells. So there are these compartments in our cells that are really responsible for generating energy. And so they’re the major energy producers, the powerhouses of the cells, if you will. And we can get these beautiful images of NADH autofluorescence. And with our studies that we performed looking at an optical redox ratio of NADH and FAD, there are different patterns within the cell of the NADH autofluorescence, and this corresponds to the organization of the mitochondria. So we’ve developed a technique to rapidly quantify and characterize the patterns that we see within the cells just using that NADH autofluorescence image. And that’s particularly important because a number of the number of microscopes and certainly the clinically… The clinical multiphoton microscopes available are really only utilizing and capable of measuring NADH autofluorescence, as well as some collagen organization, but they can’t measure FAD autofluorescence, something that we’ve typically used and others used to assess metabolism. So, using this technique where we can characterize the changes in the mitochondrial patterns, using just NADH, we can characterize changes in metabolism that are occurring just using that NADH image.
MM: Well, Kyle, I’d like to thank you again for visiting with us today, and we look forward to learning more about your research in the coming months and years.
KQ: Thanks for having me here.
MM: Music for Short Talks From the Hill was written and performed by Ben Harris, guitar instructor at the University of Arkansas. For more information and additional podcasts, go to KUAF.com or researchfrontiers.uark.edu, the home of research news at the University of Arkansas.