How does blood pressure affect the kidneys?

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Joe Rutkowski, PhD, an assistant professor in the Texas A&M College of Medicine, explains his research on blood pressure and its effect on the kidneys...and vice versa.

Episode Transcript

Christina Sumners: Welcome to Science Sound Off, I’m Christina Sumners.

Tim Schnettler: And I’m Tim Schnettler.

Christina Sumners: Our guest today is Dr. Joe Rutkowski, an assistant professor of medical physiology at Texas A&M College of Medicine. Welcome, Dr. Rutkowski.

Joe Rutkowski: Thank you for having me.

Christina Sumners: So you and some of your fellow researchers have recently received a couple of major grants to study the interaction of renal lymphatics and blood pressure. Could you tell me a little bit about what you guys are up to?

Joe Rutkowski: So the lymphatic system is really underappreciated by most in the medical field. It’s part, it closes the circulatory loop, and it’s responsible for the clearance of fluid, macromolecules, and immune cells from peripheral tissues and bringing them back into central circulation. As such, it plays a critical role in inflammation and immunity. And work over the last decade in many labs has identified that hypertension is in part a disease of chronic inflammation in the kidney. And so we hypothesized that changes in the kidney’s lymphatic architecture would play a role in regulating blood pressure.

Christina Sumners: Interesting. So you studied the renal lymphatic system, so that’s the kidneys. Why are kidneys, let’s just kinda go back to basics, why are kidneys important in the body?

Joe Rutkowski: Well, kidneys are, you can think of them as the filter organ of the body in a sense, in that they’re filtering unwanted metabolic waste products from your blood, also drugs and other things, are going out through your urine. As such, they help to regulate fluid balance in the body, and so they are actually the organ that probably is most responsible for maintaining blood pressure in the sense that they’re maintaining the blood volume, as well as secreting a host of hormones that regulate vascular tone and help to regulate blood pressure in that way as well. So common anti-hypertension medications are just simply diuretics to reduce your fluid volume so that you urinate more, so it reduces your blood volume, your blood pressure goes down.

Christina Sumners: So how can high blood pressure affect your kidneys, or does it affect your kidneys in any way?

Joe Rutkowski: Well there is a negative feedback on the kidneys in that, because your kidney is a filter organ, if you imagine if you increase the pressure on the side of the filter, you enforce more product across there, and so you can result in proteinuria, or protein appearance in your urine. Over time, when you have increased protein load in the initial urine, the kidney works harder to try to reclaim it. It’s not supposed to have been filtered out, and over time, that causes a condition very much like a chronic kidney disease, in that you start losing some of the filtering, so the epithelial cells of the kidney, and that causes interstitial fibrosis. So there’s fibrosis of the kidney and immune response and so it’s kind of a feed forward mechanism. And so those interested in hypertension, or the American Heart Association who has graciously funded one of the projects is very interested in a cardiorenal aspect of that with now roughly 50 percent of Americans being diagnosed as hypertensive with the new guidelines, it’s a major area.

Tim Schnettler: So tell me about these new guidelines. Suddenly, a bunch more people were, had high blood pressure or hypertensive?

Joe Rutkowski: Yeah they, so, blood pressure, like many of those things, like getting your vitamin D measured or anything, is what the normal homeostatic level is, is often difficult to judge until you’ve sampled however many hundreds and thousands of people. And even then, is it normal or not? You know, Americans have the worst diet than perhaps other places or our different lifestyles. And so if you look at correlative evidence of co-pathologies of hypertension, including risk for stroke, chronic kidney disease, they’ve just pushed the guidelines down for what would be considered to be elevated blood pressure, at least. So what are blood pressure ranges that increase your risk for these comorbidities? And that then makes roughly 50 percent of adults hypertensive. So it used to be about a third, which wasn’t good, but then if you lower that number, now we’re down to half of us, so that’s all. But guys, you know, diet, exercise, those things are always good to maintain it, but at least for what is something to watch out for, particularly as you get older in your lives, and you become a little more sedentary. These are things to at least put on your radar screen.

Tim Schnettler: So let’s talk a little bit about renal lymphatics and the immune system, as that’s part of what you’re studying with the American Heart Association grant. So how does, or do we know how the role of lymphatics in the immune system, does it increase inflammation, or-

Joe Rutkowski: Well, in other tissues, lymphatics are critical for the resolution of inflammation. And so when you sprain your ankle, alright, you do damage to the tissue, and the blood vasculature, the blood capillaries leak more, that’s how the fluid gets there in the first place. But over a couple days, that swelling resolves and that is, in part, there’s less fluid coming out of the blood vasculature, but it’s because you have a functional lymphatic network there, and the lymphatics are responsible for draining that excess fluid, and they have a pretty dynamic range, and they can increase their ability to clear if you have an increased burden. An inflammation, there’s an increased burden. So any time there’s, you get a bee sting or a cut, or some other bacterial infection, there’s an increased load of fluid in the tissue, there’s an increased immune cell accumulation that tissue. The only route for that fluid to really be resorbed from the tissue space and definitely the only route for the immune cells to then clear out of that tissue space is through lymphatic vessels. And so in many pre-clinical models and genetic models where we can manipulate these things, models of acute and chronic inflammation, if you block the expansion of lymphatics during that process, the inflammation is prolonged. So lymphatics expand naturally during inflammation, the immune cells that come in as well as tissue damage, secrete factors that cause an expansion of the lymphatic network. That lymphatic expansion, or lymph angiogenesis, is, appears to be necessary for the resolution of inflammation. Now it could resolve over some period of time, but helping it out was part of our hypothesis. So if we augment, or we increase, the lymphatic density, in an inflammatory event, would that help to resolve inflammation? So in the kidneys, kidneys, most of the kidney tissue does not have a lymphatic vessel network. The lymphatics are in the kidney, are for the most part track along the larger arteries and arterials of the kidney. As we call it, the interlobular arteries in the corticomedullary junction. So fluid balance in the kidney is a little bit strange because, compared to other tissues, just because you’re creating urine, so if you increase the hydrostatic, or the fluid pressure forces in it, you kinda force some of that fluid to go into the urine, and the kidney functions differently. The kidney’s also odd in that it wants to concentrate solutes. So the salt that you eat gets concentrated in the tissue space of the kidney. That allows the kidney to work less, to resorb water. So you wanna maintain your water balance, and so having a high salt content in the tissue allows some of the water to just effectively suck back out of the urine to concentrate your urine. So that’s part why they don’t have lymphatics but that leaves the kidney highly susceptible to prolonged information, because immune cells can accumulate which has been shown in hypertension.

Christina Sumners: Tell me a little bit about your pre-clinical models to study this information in the, in the kidneys.

Joe Rutkowski: So, our labs as well as others, have identified that in pre-clinical models of hypertension that there is immune cell accumulation in the kidney. Various other laboratories have tackled this by targeting one of the immune cell population. So, targeting the macrophage population or targeting a t-cell population. And they’ve demonstrated pretty consistently across the board, that using these anti-immune therapies that hypertension in these models is reduced. And so, that’s tackling, again, that immune accumulation aspect of inflammation, but the role of the lymphatics is to help clear those immune cells. So, getting tissue sections, actually this is how the study originally started, from these various labs that had these models we labeled them for markers of lymphatic endothelial cells or lymphatic vessels. And we were able to quantify that lymphatic density was increased in these inflammatory hypertensive events. So, my laboratory had developed a model in which we can increase the lymphatic density, like significantly. Far beyond what happens biologically. And so, we tested that model and two different types of hypertension, one that’s just simply drug induced, and one that’s a high sodium diet induced. And in both models, they were highly resistant to increased blood pressure. So, literally 20, 30 millimeters of mercury less than their same controls.

Christina Sumners: So would this have implications for new drugs for humans, eventually down the line?

Joe Rutkowski: Well targeting lymphatic vasculature has been a dream of the labs that first identified the growth factors that regulate it. So, it’s been tried, and it’s in clinical trials in a few conditions. Most notably there seems to be an effect on cardi, on heart attack, so myocardial infarction, the damaged tissue of the heart. So there are some clinical trials in Finland using an adenoviral delivery of a lymphatic growth factor, so that the heart would express a lymphatic growth factor, is being applied in those models. Pre-clinical models it seems to work out very well. The most noteworthy condition in the United States and in the western world, where lymphatic expansion seems to be necessary, is in the case of lymphedema. So, in breast cancer patients often have the sentinel lymph nodes, the axillary lymph nodes from the arm pit removed, that lymph node-ectomy disrupts the lymphatic architecture and roughly a third of, 20 to 30 percent of women who have the lymph nodes removed experience lymphedema in their arm. So the swelling of the arm can be shortly after surgery, it can be years following the surgery. Sometimes it’s anecdotally associated with scratch, some inflammation in the tissue, but the lymphatic insufficiency in that tissue then leads to swelling over time. That limb is more prone to inflammation and infection because immune cells cannot clear from the tissue correctly. And so, in that case, one of the therapies they are trying is to re-grow that lymphatic tree. That’s mostly through a stem cell like transplant or a transplant of a lymph node from another place in the body to try to provide lymphatic endothelial cells to grow. The growth factor therapies there, have not to date, been tried, I don’t believe, in humans. For the kidney and for targeting this for blood pressure, I myself am very interested in renal emphatic density as being an indicator of susceptibility to these things. So could we use it as a biomarker? The nephrology community has long sought for some time of urinary biomarker to dictate who progresses from acute kidney injury on to chronic kidney disease. It seems to happen, if you suffer an acute kidney injury, you are multiple likely to have chronic kidney disease longer term. Is lymphatic density and how that inflammation resolves, somehow regulate that. For hypertension, we are developing some, I believe, it’s part of one of the grant aims, that to develop some, in collaboration with the College of Pharmacy, some type of delivery method to increase them pharmacologically.

Tim Schnettler: So how did you get involved in all of this? I mean a lot of times a researcher will say; well, I had a family member who suffered from something. What drew your interest to this particular subject?

Joe Rutkowski: The hypertension? Or the lymphatic physiology?

Tim Schnettler: The lymphatic. Either one.

Joe Rutkowski: So, lymphatic physiology, that one, that’s a longer story. But, that’s essentially one, I joined for my doctoral studies, I started a Northwestern University in Melody Swartz’s lab. I wanted to work in her laboratory. She was a young and up and coming scientist at the time and just by serendipity, I suppose, I had worked with pre-clinical models before and so with, as a new graduate student, having experience with that, she just said hey, we have this project on lymph angiogenesis or the growth of new lymphatic vessels following a wound healing response. Would you be interested in taking this on? That wasn’t the reason why I joined the lab but that project seemed like it was bearing the most fruit at the time. So, as the new student in the group I said sure, let’s do that. At the time the lymphatic research community was kind of new. It had long been, sort of the realm of lymphology, is what it’s called, is those who study or treat lymphatic diseases. It was kind of a small specialty in the medical community. And it wasn’t until the late 90s, early 2000s, when specific proteins that labeled lymphatic endothelial cells were identified. And the growth factors that caused lymphatic expansion were identified. And so really, that was 2000, I’m dating myself 2003, when I joined the lab. This was a new thing, and so a lot of these antibodies weren’t even commercially available yet. You would get them from the labs that generated them, but the lymphatic research was really able to take off and expand. So people have been doing, folks like, particularly here at Texas A&M. Historically it was very strong in the physiology of the system, but it was really the identification of these markers that allowed the biology of the cells and of the lymphatic vasculature to really be studied. So, I was in some ways an early person in the field. Like, I was a graduate student, but there weren’t that many faculty in it. And so, many of us who were graduate students or post docs at the time, now have laboratories that are based on lymphatic vessel research. So it was kind of a new field, but was able to carve my own, I guess, spot in it, as far as lymph angiogenesis. And so, one of my goals from the last decade or so was to develop models in which we could manipulate the biology of the lymphatic system to study how that impacted their function. And so we developed a model where we could expand the lymphatic vasculature. It’s dictated on a lymphatic specific growth factor and we have targeted that in the lung and in adipose tissue for metabolic syndrome and in the kidney. And when we first developed the kidney model we almost knew right away that it was going to have a blood pressure phenotype. Cause it seemed pretty clear just from the phenotype of animals. So, once I started at Texas A&M, Dr. Mitchell’s lab had been studying hypertension for years. He had recently joined our department through a merger with another department. And our department of medical physiology has long been a lymphatic research. In fact, when I started my graduate studies, I met many of the other faculty here, Drs. Muthuchamy, Zawieja, and Gashev, as like early mentors in the field. They were all nice people. So, strangely over 15 years later, I then join the department. So, Dr. Mitchell kind of was, once joining medical physiology, was like, you know Brett, you should look at lymphatics, was basically what a lot of the folks were saying. Like, you’re looking at inflammatory hypertension, he had, Dr. Mitchell had already been studying inflammation in the context of pre-eclampsia and in these other hypertensive models. And so, let’s look at lymphatics. And so, pretty much from day one, when I started, it was like, I have a model that was going to have a hypertensive phenotype, or a phenotype in blood pressure, so let’s look at that. And then we started accumulating these sections and tissues from other researchers to look at their models as well.

So, lymphatics, one of the interesting aspects of them because they regulate the immune system, so it’s not just passive immune cell transport. Immune cells enter lymphatic capillaries in the periphery and they travel downstream to the lymph node that’s draining that tissue and an immune response is mounted. So immunologists long thought of the lymphatics as this passive sewer system that essentially existed for immune cells to traffic. Studies over the last 15 years from my doctoral lab as well as many others have found that it’s not just immune cell trafficking. So if you get your flu vaccine, you have that antigen, or what has been put in for your vaccination, that travels with the fluid, downstream to the lymph node. It gets taken up by an antigen presenting cell which presents to the b and t cells to have a specific response against that antigen. There’s also antigen presenting cells in the periphery that take that up locally and migrate down. But, more work has been showing that the lymphatic endothelial cells themselves are able to perhaps take up that antigen and present it to immune cells. And so they’re playing an active role. It’s not just the walls of a pipe anymore. The pipe is actively sampling what’s going on. And that the interaction of lymphatic endothelial cells with antigen presenting cells or t cells can regulate their maturity and function both in the periphery as well as the lymph node. So having a lymphatic vascular network in a tissue appears to help regulate it’s immunity. So in conditions of auto immunity, lymphatic vascular just seems to play a pretty critical role. We had published years ago that in a model where lymphatic vasculature was lacking in the skin that auto antibodies against its own skin were actually generated over time. So, every time you have tissue remodeling processes, your own self antigen, or proteins from yourself, are traffic being taken up by these cells and being sampled by the lymphatics. And that is then regulated to identify, to not attack self. So in conditions of auto immunity, so you could consider something like psoriasis, or lupus, or perhaps even multiple sclerosis, the role that lymphatics play in regulating that immune response is becoming increasingly important. And so, the kidney, is one of my interests as well. The kidney is an organ that is highly susceptible to auto immune disease. I believe that’s in part because there is not a dense lymphatic network in the tissue otherwise. So due to it’s physiologic roles, it lacks lymphatics but that sets it up for iga nephropathy, lupus nephritis. And also, then it’s critically important for renal transplant rejection.

Christina Sumners: What is the coolest part of your research? What gets you excited in the morning?

Joe Rutkowski: Well, I think what’s always most interesting to that, in that for me is, the translatability of that condition. So, I started studying the kidney years ago during my post doc to look at, like, mineral balance in the kidney. So just learning how the kidney functions and how that can impacts health and disease. And then what role my research plays in that. So studying the lymphatic vasculature and really gaining a new appreciation or new understanding of what may be happening in chronic kidney disease. In really a way, in the way that we’re targeting this is an angle that clinicians really haven’t thought about and even the research community hasn’t really thought about. And so, to kind of, it’s always nice to be able to do and try new things, but that the research is actually when, when you find something and your result has an immediate, like, oh, I can see how this would impact a patient, is something that’s always fun to have. So it’s always great when the experiment works but when it working has an obvious implication I guess is the most exciting part of the work.

Christina Sumners: So tell me a little bit about what you and your lab will be doing for these grants.

Joe Rutkowski: So far to date, we’ve been able to demonstrate that during inflammatory hypertension, there is a small but significant increase in the native lymphatic vasculature of the kidney. We’ve been able to demonstrate that if we significantly enhance this, it’s actually increasing it multiple fold, that in the models, they’re resistant to hypertension. And so far we’ve tested that in models that are somewhat artificial, but yet one of them is a sodium, or a high salt induced hypertension. So with that as our base data, we’re pretty confident that it’ll work but we wanna demonstrate it in a few other models. And so, that is part of the proposed research going forward. So we have a few pre-clinical models that are genetically pre-disposed to hypertension, in which we will be testing this out. We have, we’re going to be, we were just recently discussing yesterday, that we’re going to be starting a sort of American diet induced model of it. So, a high fat diet and feeding. So with obesity that causes hypertension. So that’s obviously very relevant translational model so if it works there. But in each of these models, we are concurrently testing whether or not there is changes in the native vasculature as well within the hope of augmenting. Or, you to do a, to block it as well to more convincingly show that you need to have some degree of expansion and that increasing this will be helpful. Other goals of the grants are to characterize better how the immunology is effected. You know, what immune cells specifically are we increasing the trafficking of and what role they play. And then also how hypertension or some causes of hypertension, such as high sodium, directly impact the biology of the native lymphatic vasculature of the kidney. So, are they functioning normally under these conditions? And so, some of the kidney regulatory hormones that regulate the blood vasculature, in regulating blood pressure, do they also impact lymphatic vasculature as well? And regulate lymphatic vessel contractility and function. Those are some of the planned studies in a very general overview sort of way.

Christina Sumners: Interesting. I’m not sure we really talked about how blood vessels and lymphatic vessels interact throughout the body.

Joe Rutkowski: So in vascularized tissues, a fraction of the fluid from within the blood, exits the blood. The term is extravasation. That is, you can think of it is almost filtration but it’s caused by the pressure difference between the blood and the tissue space. So there’s a pressure driving force for fluid transfer, so that’s the typical filtration that you would think of, of forcing water through a filter membrane. But there’s also an osmolarity difference. So if the salt concentration is higher or greater one way, you’ll force both salt or water has to exchange. So it works that way with most proteins. So the interstitial space, or the space that is within the actual tissue itself. So if you think of your muscles. Once you’re outside the blood vasculature, you’re in the interstitial space. And most cells of the body exist in an interstitial space. So all of their, everything from their oxygen to all of the nutrients they receive, leave the blood this way. The lymphatic vessels, in vascular tissue are responsible for then clearing that excess fluid to maintain that fluid balance. So that they maintain the driving force. If you just cut the lymphatics off, as in the case with lymphedema, the tissue will swell because there’s no way to remove that fluid. It’s also the way that the immune cells, which lead the blood vasculature return back to circulation and move downstream to the lymph nodes. So many factors that influence the blood side also impact the lymphatic side, as well. So, if you were to look at lymphatic function or how lymphatics are draining fluid, it is in part due to the amount of fluid leaving the blood vasculature as well, so. It’s, it closes the circulatory loop, basically. So you have liters a day of lymph are generating, it’s not as much as the blood, but it’s really responsible for maintaining any tissue homeostasis.

Christina Sumners: So you had mentioned lymphedema is a problem in breast cancer, why is that?

Joe Rutkowski: So I had said both before about the time when we were able to identify markers for lymphatic system. So oncologists have long known that lymph node metastasis were a problem and that was very indicative of an advancing cancer. So with now these lymphatic markers in hand, pathologists were able to label tissue sections and identify that in fact lymphatic expansion or tumor lymph angiogenesis was highly predictive of downstream lymphatic metastasis. So one of the identification of the growth factors that led to lymphatic expansion was really based on early 2000s, the tumor biology at the time. So trials were in place, I think, to block the lymphatic expansion, as a means to inhibit metastasis but unfortunately they’ve never really panned out as well in the human studies as they did in the pre-clinical models. Probably in large part that once the tumor advances to a certain point there’s a whole host of growth factors. So much like blocking the blood angiogenesis with the bevacizumab, which is used in breast cancer, colon cancer, and there’s only a limited efficacy once the tumor has advanced to a certain point that you’re not gonna stop the process.

Christina Sumners: And lymph nodes can also be used to determine whether the cancer has metastasized?

Joe Rutkowski: Yeah, so they’ll biopsy the lymph nodes to look for tumor cells that have progressed downstream. So in order to do that, a good surgeon might, so part of the problem in breast cancer was they know where they are but humans have a network of lymph nodes, it’s not just one lymph node. So, they’ll often take out multiple lymph nodes in order to be sure they got any potentially metastasizing cells. In order to do that, you can identify them, you can see them fine, but sometimes surgeons will inject a dye or some type of a contrast agent near the site of the tumor and watch where’d the dye close and then identify those lymph nodes.

Christina Sumners: And then they can remove just those lymph nodes that the dye is…

Joe Rutkowski: Yeah, that’s the idea. And so one of the best, if most effective treatments for lymphedema is really to minimize the lymphatic destruction that occurs during the time of the initial surgery. So like, lymph node sparing is the idea. So try to minimize what is taken will reduce the likelihood that lymphedema will develop in the future.

Christina Sumners: Are there any treatments if lymphedema does develop?

Joe Rutkowski: Most treatments for lymphedema right now, are treating the symptoms, and so that is compression. So patients wear a compression garment. Massage, or decongestive therapy, and so you get a, it’s a very thorough massage, not just like what you’d go to a spa for, to really help to move the interstitial fluid. So with absinthial lymphatics you have to manually try to remove the fluid, so it’s literally forcing with, you know, it’s very much like a deep tissue massage to try to move the fluid from the effected limb. That, and compression, and anti-inflammatories are right now in trials to help reduce the inflammation in the tissue. But, there’s currently no cure, per say for it. It’s just prevention is just the best way.

Christina Sumners: So all you can do is try to minimize the number of lymph nodes you have to…

Joe Rutkowski: Yeah, like I said it’s, a lymph node transfer has been tried. And there was a panel on lymphedema treatment a few, back probably about six months ago, or so. And part of the recommendations are of course, prevent it in the first place by using surgical intervention as minimally as possible. But the subsequent treatments for it are really limited to kind of experimental lymph node transfer. There’s a lympho-venus anastomosis where small lymphatic vessels can be tied into smaller veins to help to drain the fluid. You’re limited there due to the pressure differences in the system, so you can’t put into a larger vein because the venous pressure would be too high and cause backflow, and you don’t want blood backflow into the tissue. But that does work on limited cases, so not in advanced. And then unfortunately for cosmetic therapy, it’s really only a liposuction and tissue resection. And so adipose tissue, or the fat tissue expansion is characteristic of lymphedema. The only real way to resolve that is to just surgically remove the tissue. So we want to prevent it as much as possible.

Christina Sumners: Well thank you so much for joining us today, Dr. Rutkowski. And congratulations again on these grants and best of luck in your future research.

Joe Rutkowski: Thank you. It was nice to talk about our work. It’s always great to have people interested in lymphatics.

Christina Sumners: And thanks for listening, and we’ll see you next time.