By Kimberly McGhee
Illustrations by Linda Nye
Cover image licensed from sciencesource.com
It has been estimated that some 45% of all deaths in developed countries are due to organ dysfunction resulting from fibrosis.1 It is implicated in diseases that take a heavy toll on our society, including cardiovascular disease, pulmonary fibrosis, liver cirrhosis, and chronic kidney failure. Virtually every organ in the body is vulnerable; the affected organ shrinks, hardens, and ceases to function properly, leaving little treatment recourse for patients other than transplant.
“Fibrosis is the final common denominator in all those who require a transplant,” explains Kenneth D. Chavin, M.D., Ph.D., Surgical Director of Liver Transplant at MUSC, “and it rears its head as part of the process of chronic rejection as well.”
Although the specific factors leading to fibrosis may vary slightly by body compartment, all organ systems are thought to share a common final pathway to fibrosis (i.e., the excessive production of collagen). Thus, an anti-fibrotic agent shown to have efficacy in one fibrotic disease could hold promise for others. Despite the overwhelming need, few agents with anti-fibrotic effects have made it to the market in the U.S., leaving millions of patients with very limited treatment options.
That could be changing, as 2014 is proving to be a watershed year for advancing anti-fibrotic therapies. Positive findings were reported from important clinical trials of anti-fibrotic agents for idiopathic pulmonary fibrosis2,3 and heart failure.4 Trials are also under way in fibrotic diseases of the liver and kidneys.
What have been the obstacles to advancing anti-fibrotic agents through clinical trials and into the clinic? For many years, pharmaceutical industry interest has been faint for a number of reasons. The underlying mechanisms of fibrosis were poorly understood. There were few biomarkers for fibrotic disease, and so invasive biopsies were necessary to assess outcomes. Fibrosis and the chronic diseases with which it is associated take years to do their damage, making them poor fits for typical clinical trials that follow patients for restricted periods of time.
As the mechanisms underlying fibrosis are becoming better elucidated and as more and more biomarkers of disease are being identified, pharmaceutical interest in developing anti-fibrotic agents has been growing. According to Karen Lackey, the new Director of the South Carolina Center for Therapeutic Discovery and Development, “Within the last few years, there have been significant breakthroughs in our understanding of the pathophysiology of these diseases and the role of relevant biochemical pathways, and perhaps most importantly, there are now examples of drugs that seem to work (i.e., pirfenidone). These advances make it highly likely that effective therapeutic agents to treat diseases like idiopathic pulmonary fibrosis, scleroderma, diabetic kidney disease, and even liver fibrosis can be created.” A number of leading pharmaceutical companies (e.g., Bristol Myers Squibb, Biogen Idex, Gilead Sciences, Pfizer, Sanofi, GlaxoSmithKline) have anti-fibrotic agents in their drug pipelines or are working to develop them.
Challenges, of course, remain. Perhaps one of the most serious is preventing off-target effects of anti-fibrotic agents. The flip side of the good news that an anti-fibrotic agent might be effective across a number of organ systems is that it could target not only pathological, but also normal, fibrosis. Impairing normal fibrosis could limit the ability of the body to heal itself and make healthy connective tissue. As with anti-cancer therapies, efforts are being made to better target anti-fibrotic therapies. Taking a page from the playbook for personalized cancer treatment, researchers are working to develop better biomarkers that will predict which patients might benefit from a particular therapy. Pharmaceutical companies are taking care to develop diagnostic tools to accompany each targeted therapeutic agent to ensure proper patient selection.
After injury, organs in the body undergo a wound-healing response, intended to create new connective tissue that provides structure to the organ. This process is extremely complicated and involves a wide variety of cells, molecules, and signaling pathways. A critical cell in the process is the fibroblast, which both produces extracellular matrix (ECM) and governs its resorption.
In pathological fibrosis, the balance is lost between normal production of ECM (scar tissue) and its resorption. With progressive fibrosis, the tissue becomes less elastic and pliable and more fibrous, stringy, and tough. These changes in tissue architecture alter organ function and can ultimately lead to organ failure.
Effective anti-fibrotic therapeutics will require an understanding of all of the cells involved in fibrosis. According to Lynn M. Schnapp, M.D., Director of the Division of Pulmonary and Critical Care, who is seeking to identify myofibroblast precursors implicated in pathological fibrosis: “If you are going to develop additional therapies to target collagen synthesis, you need to identify each of those cells that are potential collagen producers. Each could have its own distinctive cell markers, its own cell surface profile, that could be targeted by a therapeutic.” Fibroblasts and the smooth muscle–like myofibroblasts into which they differentiate are prolific producers of ECM. However, it is still debated whether fibroblasts residing in an organ compartment are activated by injury to produce excess ECM or whether fibrocytes in the bone marrow are recruited to the area of injury, where they then differentiate into fibroblasts/myofibroblasts. Pericytes, which typically form a sheath around blood vessels and regulate vascular stability, are another group of fibrogenic cells in which there is growing research interest. Schnapp has shown that pericytes are major contributors to the myofibroblast population in a mouse model of pulmonary fibrosis.5 Finally, epithelial-mesenchymal transition (EMT), in which epithelial cells differentiate into mesenchymal cells, is thought to create an environment conducive to fibrosis. The contribution of EMT to collagen synthesis remains hotly debated.
Pathological fibrosis in any given organ system likely involves more than one of these myofibroblast precursors, suggesting that combination regimens of anti-fibrotic agents, each targeting a different precursor, might be necessary for successful therapy, as is often the case with cancer and chronic conditions such as hypertension. Such combination regimens would use lower doses of more than one anti-fibrotic agent to improve efficacy and mitigate side effects.
The role of inflammation in the development of fibrosis is another hotly debated topic. In many organ systems, acute or chronic inflammation precedes fibrosis; however, inflammation has not been found to play a role in idiopathic pulmonary fibrosis. Proponents of inflammation as the driver of fibrosis argue that damaged epithelial or endothelial cells secrete inflammatory mediators such as cytokines and chemokines that recruit lymphocytes, macrophages, and other inflammatory cells to the site of injury. These cells and their secretions then activate effector cells–typically fibroblasts and myofibroblasts–to make ECM and lead to fibrosis and scarring.
Collectively, MUSC researchers are investigating almost all of the molecular pathways associated with fibrosis, including peptides, cytokines, and growth factors (Don C. Rockey, M.D.; Galina S. Bogatkevich, M.D., Ph.D.), TGF-β (Lynn M. Schnapp, M.D.), the caveolin-1 signaling pathway (Stanley R. Hoffman, Ph.D.; Elena V. Tourkina, Ph.D.); and integrin and matrix pathways (Amy D. Bradshaw, PhD).
In many ways, systemic sclerosis, the systemic form of scleroderma, is the fibrotic disease. Scleroderma, which translates literally as “hard skin,” is characterized by deposition of excessive collagen in the skin of the face, extremities, and trunk as well as injury to the capillaries. However, according to Richard M. Silver, M.D., FACP, FACR, Director of the the Division of Rheumatology and Immunology: “In many cases, it’s more than skin deep and affects the gastrointestinal tract, the lungs, the heart, the kidneys, and the blood vessels, so it is a model for many other more prevalent diseases. Whereas there may be 300,000 Americans with scleroderma, millions of others suffer from fibrosis of the kidneys, the liver, the lungs, the heart, and the blood vessels.” If an anti-fibrotic agent is demonstrated to be efficacious in systemic sclerosis, that could mean that it holds promise for treating fibrotic diseases that are more confined to particular organ compartments.
In addition to leading and participating in clinical trials of breakthrough anti-fibrotic therapies (for more detail on these trials, see the organ-specific articles that follow), MUSC’s impressive cadre of fibrosis researchers engage in translational research that is laying the foundation for the breakthrough therapies of tomorrow. A number of researchers have identified and patented promising anti-fibrotic agents and hope to partner with industry to carry them forward toward clinical trials.
Stanley R. Hoffman, Ph.D., Professor in the Division of Rheumatology and Immunology, and Elena V. Tourkina, Ph.D., Associate Professor in the Division of Rheumatology and Immunology, have characterized a mouse model of systemic sclerosis, in which mini-osmotic pumps emitting bleomycin, known to cause fibrosis, are inserted under the skin.6 These mice, like humans with scleroderma, have been shown to be deficient in the protein caveolin-1. Underexpression of caveolin-1 promotes the differentiation of monocytes in the bone marrow into fibrocytes and their migration via the circulatory system to sites of injury, where they further differentiate into fibroblasts and make collagen. Administered caveolin-1 scaffolding domain (CSD) peptide substitutes for the lost caveolin-1 and prevents fibrosis.7 Mice implanted with the bleomycin pump showed a significant thickening of the skin (along with other systemic symptoms), whereas those receiving both bleomycin and CSD did not. Hoffman and Tourkina are inventors on an issued U.S. patent for the use of CSD as an anti-fibrotic treatment and, on the basis of promising results in small animal studies, are now working to optimize the peptide for drug development and planning other studies that must be performed before the initiation of clinical trials. They are also assessing whether CSD, currently delivered as an injection or via a mini-pump, could be administered orally, as oral agents are generally better tolerated by patients.
Galina S. Bogatkevich, M.D., Ph.D., Associate Professor in the Division of Rheumatology and Immunology, and Yuichiro Shirai, PhD, a postdoctoral research fellow in the Division of Rheumatology and Immunology, have also identified a potentially anti-fibrotic peptide that could help protect against scleroderma-associated interstitial lung disease, and the MUSC Foundation for Research Development has filed a provisional patent application for it. When purified, the peptide has been shown in preliminary studies to reduce collagen and other ECM proteins in scleroderma lung fibroblasts (unpublished data).
Silver is also investigating the role of thrombin, which is important for blood coagulation and clotting, in fibrosis. The lung fluid of patients with systemic sclerosis has very high levels of thrombin. Using dabigatran to block thrombin in bleomycin mouse models of scleroderma reduces the severity of fibrosis compared with controls.8 Silver and colleagues at MUSC have applied for NIH funding and are planning a pilot study of dabigatran in patients with scleroderma to establish the safety of proposed doses. Once the doses have been shown to be safe, Silver would like to conduct a much larger trial to assess efficacy.
In October 2013, MUSC recruited Carol A. Feghali-Bostwick, Ph.D., a noted fibrosis researcher, as the Kitty Trask Holt Endowed SmartState Chair in Scleroderma Research. She joined MUSC from the University of Pittsburgh, where she was instrumental in developing a promising anti-fibrotic peptide, E4, that is derived from endostatin.9 The peptide showed efficacy in bleomycin animal models, but results of animal trials are not always predictive of clinical success. Feghali-Bostwick and her colleagues went a step further and showed that the peptide was effective in a human skin organ model of fibrosis, a novel methodology that she developed.10 Fibrosis was induced in cultured human skin cells by administration of TGF-β and, two days later after fibrosis had become established, E4 was added. These studies showed that addition of E4 significantly reduced the thickness of the cultured skin, suggesting that it could reverse ongoing fibrosis. On the basis of these promising results, the peptide was licensed by iBio, Inc, a small biotechnology company, which is planning on taking the plant-manufactured peptide into clinical trials in early 2015. Because of Feghali-Bostwick’s involvement in the development of the peptide, MUSC will be one of the first sites in the nation to enroll patients in these trials.
The pages that follow highlight the damage done by fibrosis to several key organ compartments—the lungs, the heart, the liver, and the kidneys—and summarize recently reported clinical trial results that presage likely FDA approval of novel anti-fibrotic agents for pulmonary and cardiac fibrosis. Ongoing clinical trials of anti-fibrotic agents in other organ systems are also briefly discussed.
“Idiopathic pulmonary fibrosis (IPF) is an aggressive, relentless scarring of the lung that will ultimately lead to a person’s death,” notes Timothy P.M. Whelan, M.D., Medical Director of MUSC’s Lung Transplant Program. Of the interstitial lung diseases (ILDs), IPF, which affects approximately 500,000 people in the U.S. and Europe, has the worst prognosis, worse indeed than most cancers. On average, patients with IPF survive only three to five years after diagnosis.
For eligible patients, lung transplant is the last recourse and has been shown to confer a clear survival benefit.11 However, most IPF patients do not qualify for lung transplant and have few treatment options available other than supportive care. With the publication of the results of the ASCEND2 and INPULSIS3 clinical trials in the New England Journal of Medicine in May 2014, that will be changing.
Previous clinical trials in IPF have yielded disappointing results. Both anti-inflammatory agents and IFN-γ were eventually shown to be of little efficacy, and the former were actually found to do harm to clinical trial participants, leading the National Heart, Lung, and Blood Institute to recommend against their use in patients with IPF.
Such past disappointments made the news of the positive results of the ASCEND (NCT01366209) and INPULSIS trials (INPULSIS-1: NCT01335464 and INPULSIS 2: NCT01335477) even more welcome. “There is a lot of excitement in the pulmonary fibrosis community. These are the first drugs that have shown promise in clinical trials and so everyone is almost giddy,” says Lynn M. Schnapp, M.D., Director of the Division of Pulmonary and Critical Care at MUSC. These trials showed that the characteristic decline in forced vital capacity (FVC) seen in patients with IPF was slowed by both pirfenidone (ASCEND), an anti-fibrotic agent already approved in Europe on the basis of the results of the earlier CAPACITY trials, and nintedanib, a tyrosine kinase inhibitor (INPULSIS). Side effects (rash and gastrointestinal upset for pirfenidone and diarrhea for nintedanib) were mild and were tolerated by most patients at a full or a slightly reduced dose.
“These trials mark an important turning point for the treatment of IPF,” says J. Terrill Huggins, M.D., Associate Professor in the Division of Pulmonary and Critical Care, who served as the principal investigator for the MUSC site in both studies. “We have clearly reached a point where we can slow progression. This was a black box ten years ago, and now we have two drugs that will likely be approved by the FDA.” MUSC was among the top-enrolling sites for both trials.
On the basis of the results of these two trials, which showed efficacy for a clinically relevant endpoint in a fatal disease, the FDA granted Breakthrough Therapies designation to both agents in July 2014. This designation is intended to speed the translation of innovative therapies into the clinic where they are urgently needed. It ensures that the review of these agents by the FDA will be fast-tracked (six-month priority review), that FDA managers will be involved, and that the review will be cross-disciplinary. By early next year the FDA should weigh in on whether these drugs can be used as standard therapy for the treatment of IPF.
As good as this news is, there is still much more work to be done. The drugs slowed decline in FVC but did not reverse disease, and the patients were carefully selected, meaning that results may not be generalizable to patients with other types of pulmonary fibrosis. “People are excited because these are the only drugs we have, but by no means are they the cure. We still need much more research on pulmonary fibrosis,” cautions Schnapp.
Because most novel therapies are likely to have maximal effect in patients with early-stage IPF, clinical biomarkers that could help to identify those patients even before symptom onset are an area of active research at MUSC and nationwide. The Division of Pulmonary and Critical Care is participating in a prospective outcomes registry with Boehringer Ingelheim to help track how IPF is diagnosed and managed in these patients and with what results and to analyze blood samples from these patients to identify possible biomarkers for IPF. It is also applying through the Pulmonary Fibrosis Foundation to participate in its Patient Care Network and Patient Registry, which seek to track outcomes and identify biomarkers in patients with IPF as well as to standardize the treatment for IPF by establishing regional centers following best practices where these patients can be referred.
With two pharmacological therapies for IPF likely to be approved by the FDA in the next few months, correctly identifying patients with IPF is crucial. Too often, patients with IPF go years after onset of symptoms (shortness of breath, dry cough, fatigue, sometimes finger or toenail clubbing) without an accurate diagnosis, are mistakenly believed to have chronic obstructive pulmonary disease (COPD) or another lung disease, and receive inappropriate treatment.
|Currently Recruiting Clinical Trials of Anti-Fibrotic Agents at MUSC|
Expanded Access Program
J. Terrill Huggins, M.D./
Michael R. Zile, M.D
Ruth C. Campbell, M.D./
IPF = idiopathic pulmonary fibrosis; HFpEF = heart failure with preserved ejection fraction.
Patients with suspected ILD or with COPD or other lung disease that does not improve with treatment should be seen in a tertiary care center such as MUSC with a high volume of patients with IPF and access to the latest clinical trials. “At MUSC, we see on average eight to ten patients with IPF per week who are on active clinical trials,” says Huggins. Because of its participation in the ASCEND and INPULSIS trials, MUSC is the only institution in the state to be approved to participate in the expanded-access trial for the former and expects to receive approval for the latter shortly. These expanded-access trials provide appropriate patients with continued access to the drugs while the final FDA ruling is awaited. Patients with more serious disease can be screened for a lung transplant. Patients who are diagnosed with an ILD other than IPF can benefit from MUSC’s expertise in scleroderma and sarcoidosis and in treating all of the affected organ compartments.
“There are a lot of things we can offer proactively for patients with IPF. Even though we may not have a potential cure for IPF, we have made significant progress. Having patients active in clinical trials may allow us to get to the summit of cure down the road,” says Huggins.
Patient participation in clinical trials is the best way to ensure that a cure for IPF will one day be found. To refer a patient for a pulmonary clinical trial, including several for IPF, and to find contact information for study coordinators, visit the pulmonary clinical trials page on MUSC.edu
More than 20 million people in the U.S. and Europe are thought to have heart failure. Approximately half of those patients have chronic heart failure with reduced ejection fraction (HFrEF), meaning that the heart’s forward pumping capacity is compromised and it cannot send adequate blood and oxygen to the organs. In the other half of patients with chronic heart failure, the ejection fraction is preserved, meaning the heart is able to pump effectively but cannot relax and fill rapidly and completely due a ventricle that is stiffened by fibrosis.
Angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers are the mainstay of treatment for patients with HFrEF and have helped prolong the lives of these patients, though many are still frequently hospitalized. In contrast, no pharmacological option has been available for patients with HFpEF. According to Michael R. Zile, M.D., the Charles Ezra Daniel Chair in Cardiology and Director of the SmartState Center for Molecular Proteomics in Cardiovascular Disease and Prevention at MUSC, “The most important unmet need in cardiology today is a treatment for heart failure with preserved ejection fraction.”
According to Zile, 60% of patients with heart failure with preserved ejection fraction (HFpEF) will not survive beyond five years, and 50% of those hospitalized are likely to be readmitted within six months. Like HFrEF, HFpEF has a devastating effect on quality of life. “HFpEF is very common, very lethal, and it causes an unbelievable burden on our patients. To date, zero clinical trials have demonstrated that you can improve morbidity and mortality in HFpEF,” says Zile.
Recent results from the PARADIGM-HF trial (NCT01035255),4 the largest heart failure clinical trial ever conducted (8,436 patients), has important implications for both populations of patients, according to Zile, who served on the steering committee of the trial.
For patients with HFrEF, it could mean improved outcomes and a new standard of care. The PARADIGM-HF trial was stopped early because it compellingly showed that 200 mg of a twice-a-day investigational, first-in-class agent with anti-fibrotic effects (LCZ696, Novartis Pharmaceuticals) reduced cardiovascular death more than did 10 mg twice daily of the ACE inhibitor enalapril. If the FDA approves LCZ696 (an angiotensin receptor neprilysin inhibitor), as it is expected to do based on the results of the PARADIGM study, it “will replace ACEs and ARBs as the cornerstone of therapy for patients with HFrEF,” says Zile.
For patients with HFpEF, the PARADIGM-HF trial could help clear the way for an important future therapy. On the basis of its compelling results, Novartis is opening a second five-year study of the same investigational agent in patients with HFpEF—the PARAGON-HF trial (NCT01920711). Zile plans on MUSC being among the first institutions in the world to enroll a patient in this trial.
The trials also herald the coming of age for anti-fibrotic therapy for heart failure. Fibrotic pathways play a role in both types of heart failure. The stiffness of the ventricular wall depends largely on the total quantity of collagen, the relative proportion of collagen type I, and the degree of cross-linking between collagen fibers. Continual turnover of collagen is necessary in highly stressful environments such as the heart and lungs to ensure that the extracellular matrix (ECM) stays pliable and new and does not become cross-linked and thus more resistant to turnover. The two types of heart failure represent two ways in which such a healthy homeostasis can be lost. In HFrEF, the degradation of the ECM occurs too quickly, leading to thinner walls in and dilation of the ventricles. Such dilated cardiomyopathy impairs the heart’s ability to contract. In contrast, in HFpEF, the degradation of the ECM occurs too slowly, allowing cross-linking to occur and resulting in the thickening and stiffening of ventricular and blood vessel walls. The stiffer left ventricle is unable to relax, so it cannot adequately and rapidly fill with fluid. In addition to a lethargic turnover rate for the ECM, HFpEF is also typically characterized by increased collagen deposition. The resulting stiffness and inelasticity can wreak havoc in a dynamic environment like the heart.
Amy Bradshaw, PhD, Associate Professor in the Division of Cardiology, who works with Zile to elucidate the anti-fibrotic pathways underlying HFpEF, sums it up as follows: “It is not only important to break down but to make new stuff—you want to keep ECM young—particularly in tissues, such as cardiac tissues, that require high rates of turnover.”
Although fibrotic pathways are implicated in both types of heart failure, many, such as Zile, think that they are more profoundly involved in HFpEF, and thus hypothesize that the new anti-fibrotic drug found efficacious in HFrEF could hold even greater promise among patients with HFpEF.
Zile and Bradshaw have studied the fibrotic pathways that underlie HFpEF. Zile’s laboratory recently completed a study of biopsy samples from healthy patients, those with high blood pressure, and those with HFpEF (unpublished data). Zile and his colleagues demonstrated greater left ventricular stiffness in patients with HFpEF by using a special device to stretch biopsy samples, measure stiffness, and monitor the effects on the individual sarcomeres. They also helped identify biomarkers that could be useful in assessing the severity or aggressiveness of a patient’s disease by analyzing blood samples taken from the same patients from which biopsy samples were obtained (unpublished data).
“At MUSC, we are involved in the discovery of the basic mechanisms of HFpEF, in proving that the basic mechanisms we identify in animal models are relevant to human models, and in developing novel therapeutic strategies to treat these patients,” notes Zile.
“If injured, the liver, like any other organ, will become fibrotic,” says Don C. Rockey, M.D., a noted investigator of fibrosis in the liver and Chair of the Department of Medicine at MUSC. The liver responds to any injury—whether caused by fatty liver disease, a viral infection, alcohol, or any of a variety of chronic hepatic diseases—with a wound-healing response. In some patients, that healthy response can become exaggerated, leading to fibrosis and eventually to cirrhosis. The fact that such a wide variety of inciting factors culminate in the same outcome—cirrhosis—has fueled speculation that there is a final common pathway to fibrosis in the liver. An anti-fibrotic agent targeting that final pathway could help prevent or delay cirrhosis and the catastrophic complications with which it is associated, including portal hypertension, ascites, variceal bleeding, and liver failure.
Fibrosis in the liver, more so than in perhaps any other organ, is associated with inflammation. When the infection is treated, the fibrosis begins to resolve, providing the best evidence to date that fibrosis can be reversed.
The cellular and molecular mechanisms underlying fibrosis are perhaps better delineated in the liver than in any other organ. Injury and inflammation activate resident hepatic stellate cells, the principal effector cells in the liver, causing them to transform into myofibroblast-producing extracellular matrix and deposit the scar and fibrous tissue typical of cirrhosis. Fibrocytes recruited from the bone marrow and other cells also contribute to matrix synthesis in the liver. A variety of growth factors, integrins, and other factors such as chemokines and vasoactive peptides are produced by stellate cells, and these help create an environment conducive to fibrosis. As the liver becomes more fibrotic, it loses functionality and shrinks from an average of three pounds to one and a half.
Clinical trials in fibrotic liver disease have been hampered by the lack of biomarkers to measure liver fibrosis. Although more such biomarkers have been identified for the liver than for most other organ compartments, too often invasive liver biopsies are necessary to assess disease severity during a clinical trial. Rockey’s laboratory is working to elucidate the basic molecular and cellular mechanisms underlying liver fibrosis in order to establish more serum markers of fibrosis.
The Rockey laboratory is also elucidating how fibrosis affects the vasculature of the liver.12 Fibrosis damages the endothelial cells lining the blood vessels that supply the liver. Portal hypertension can develop when blood flow is blocked by scar tissue or by stellate cells that have become contractile. Serhan Karvar, M.D., Songling Liu, M.D., and Zengdun Shi, M.D., members of the Rockey laboratory, have developed a robust technique for isolating hepatic stellate cells and endothelial cells and are examining interactions and cross-talk among the epithelial, endothelial, and mesenchymal cells of the liver.
Rockey’s group also collaborates with industry partners to examine the effect of the latest and most promising anti-fibrotic drugs. MUSC is among the nation’s top enrollers for a Gilead trial of GS-6624, a novel anti-fibrotic agent. This monoclonal antibody targeting lysyl oxidase-like 2 (LOXL2) is being tested in patients with liver fibrosis secondary to non-alcoholic steatohepatitis (NASH or fatty liver disease) to determine whether it can delay or prevent disease progression. The same compound is also being trialed in patients with IPF (Principal Investigator: Timothy Whelan, M.D.) and has been studied in patients with a variety of adenocarcinomas.
In the kidneys, as in other organ systems, fibrosis represents a final common pathway for a variety of diseases. That pathway can lead to organ failure (e.g., end-stage renal disease [ESRD]) and leaves patients little recourse beyond dialysis or transplant.
As with fibrosis of the heart, fibrosis of the kidneys is closely associated with hypertension and diabetes. Each kidney is composed of a filtering unit known as the glomerulus and a series of tubules that perform the final processing of urine. The glomerulus, which has a rich supply of blood vessels by which it receives oxygen and delivers it to the tubules, is very susceptible to high blood pressure and is destroyed by long-term exposure to such stresses. The clinical manifestation of this damage is a reduced glomerular filtration rate. As the glomerulus becomes fibrotic and shuts down, it blocks blood flow, resulting in a hypoxic state in all surrounding tissues that further promotes fibrosis. Thus, even primary glomerular disease often has marked tubular manifestations due to restrictions in blood flow. In addition, multiple other stressors associated with chronic disease such as production of reactive oxygen species and immune system dysregulation can lead to fibrosis. The mechanisms by which diabetes damages the kidneys is less well understood, but high blood glucose levels are thought to directly damage the glomerular filtration unit and the tubular structures.
As opposed to fibrosis in organs such as the liver, fibrosis in the kidneys is not thought to be reversible. This is especially true of the glomerulus, which is very susceptible to scarring and permanent damage. There is some evidence that fibrosis in the tubules can be reversed, but to a lesser degree than is seen in the liver.
Fibrosis does not result solely from chronic diseases such as hypertension and diabetes. Fibrosis of the kidneys can also be caused by certain genetic diseases, such as polycystic kidney disease. The laboratory of P. Darwin Bell, PhD, Professor in the Division of Nephrology, is seeking to understand the pathways underlying cyst formation and fibrosis in these patients, particularly the mTOR (mammalian target of rapamycin) pathway.
Researchers are also investigating biomarkers of fibrosis in the kidneys. John M. Arthur, M.D., PhD, Professor in the Division of Nephrology and Director of the Renal Disease Biomarkers SmartState Program, is seeking to identify biomarkers for a number of kidney diseases. He notes that, so far, the biomarkers for fibrosis have been indirect, indicating the presence of an underlying injury process that causes fibrosis rather than the fibrosis itself. The Bell laboratory is working to identify serum biomarkers of polycystic kidney disease.
Bell’s laboratory has also explored the renin-angiotensin system (RAS) in relation to fibrosis. For instance, although angiotensin-2 is a necessary hormone, an excess of it can promote fibrosis through cytokine-signaling pathways such as TGF-ß. Indeed, RAS inhibitors have proven the most effective agents for treating fibrosis-inducing diseases such as hypertension and diabetes. It is not yet known whether they act directly on the fibrotic tissue or only on the underlying disease (i.e., hypertension, diabetes) that leads to fibrosis.
RAS inhibitors, which decrease albuminuria and slow progression to ESRD, have been the only agents shown to be effective against diabetic nephropathy, However, adjunctive therapies may be necessary to further slow or reverse disease progression. One agent being investigated as possible adjunctive therapy for patients with diabetic nephropathy is atrasentan, an endothelin A receptor antagonist. Ruth C. Campbell, M.D., Associate Professor in the Division of Nephrology, is the principal investigator for the MUSC site of the Study Of Diabetic Nephropathy With Atrasentan (SONAR; NCT01858532), a double-blind, parallel, placebo-controlled trial of the effects of atrasentan on renal outcomes in patients with type 2 diabetes and nephropathy. The study seeks to evaluate whether atrasentan can delay the time to the doubling of serum creatinine levels or the onset of ESRD compared with placebo in patients who are receiving the maximum dose of a RAS inhibitor. The study is currently recruiting patients. For more information on enrolling a patient in the SONAR trial, contact Vickie Hunt at 843-792-7852 or firstname.lastname@example.org.
1 Wynn TA. Cellular and molecular mechanisms of fibrosis. J. Pathol. 2008;214:199–210.
2 King TE, et al, for the ASCEND Study Group. A phase 3 trial of pirfenidone in patients with idiopathic pulmonary fibrosis. N Engl J Med. 2014 May 29;370(22):2083-2092
3 Richeldi L, et al, for the INPULSIS Trial Investigators. Efficacy and safety of nintedanib in idiopathic pulmonary fibrosis. N Engl J Med. 2014 May 29;370(22):2071-2082.
4 McMurray JJ, Packer M, Desai AS, Gong J, Lefkowitz MP, Rizkala AR, Rouleau JL, Shi VC, Solomon SD, Swedberg K, Zile MR; for the PARADIGM-HF Investigators and Committees. Angiotensin–neprilysin inhibition versus enalapril in heart failure. N Engl J Med. August 30, 2014 (Epub ahead of print). Available at http://dx.doi.org/10.1056/NEJMoa1409077.
5 Hung C, Linn G, Chow YH, Kobayashi A, Mittelsteadt K, Altemeier WA, Gharib SA, Schnapp LM, Duffield JS. Role of lung pericytes and resident fibroblasts in the pathogenesis of pulmonary fibrosis. Am J Respir Crit Care Med. 2013 Oct 1;188(7):820-830.
6 Lee R, Reese C, Bonner M, Tourkina E, Hajdu Z, Riemer EC, Silver RM, Visconti RP, Hoffman S. Bleomycin delivery by osmotic minipump: similarity to human scleroderma interstitial lung disease. Am J Physiol Lung Cell Mol Physiol. 2014 Apr 15;306(8):736-748.
7 Lee R, Perry B, Heywood J, Reese C, Bonner M, Hartfield CM, Silver RM, Visconti RP, Hoffman S, Tourkina E. Caveolin-1 regulates chemokine receptor 5-mediated contribution of bone marrow-derived cells to dermal fibrosis. Front Pharmacol June 11 2014; 5:140.
8 Bogatkevich GS, Ludwicka-Bradley A, Silver RM. Dabigatran, a direct thrombin inhibitor, demonstrates antifibrotic effects on lung fibroblasts. Arthritis Rheum. 2009 Nov;60(11):3455-3464.
9 Yamaguchi Y, Takihara T, Chambers RA, Veraldi KL, Larregina AT, Feghali-Bostwick CA. A peptide derived from endostatin ameliorates organ fibrosis. Sci Transl Med 2012;4(136): 136ra71
10 Yasuoka H, Larregina AT, Yamaguchi Y, Feghali-Bostwick CA. Human skin culture as an ex vivo model for assessing the fibrotic effects of insulin-like growth factor binding proteins. Open Rheumatol J. 2008;2:17-22.
11 Thabut G, et al. Survival benefit of lung transplantation for patients with idiopathic pulmonary fibrosis. J Thorac Cardiovasc Surg. 2003 Aug;126(2):469-475.
12 Iwakiri Y, Shah V, Rockey DC. Vascular pathobiology in chronic liver disease and cirrhosis - Current status and future directions. J Hepatol. June 6, 2014 (Epub ahead of print). In press.
Current Issue of Progressnotes
View the PDF