CORRESPONDENCE
Author disclosures are available with the text of this letter at www.atsjournals.org. Shamsah Kazani, M.D. Elliot Israel, M.D. Brigham and Women’s Hospital Boston, Massachusetts
References 1. Short PM, Williamson PA, Anderson WJ, Lipworth BJ. Randomized placebo-controlled trial to evaluate chronic dosing effects of propranolol in asthma. Am J Respir Crit Care Med 2013;187:1308–1314. 2. Kazani S, Israel E. What doesn’t kill may not make you stronger: b-blockers for asthma [editorial]. Am J Respir Crit Care Med 2013;187:1281–1286. 3. Nguyen LP, Lin R, Parra S, Omoluabi O, Hanania NA, Tuvim MJ, Knoll BJ, Dickey BF, Bond RA. b2-Adrenoceptor signaling is required for the development of an asthma phenotype in a murine model. Proc Natl Acad Sci USA 2009;106:2435–2440. 4. Thanawala VJ, Forkuo GS, Al-Sawalha N, Azzegagh Z, Nguyen LP, Eriksen JL, Tuvim MJ, Lowder TW, Dickey BF, Knoll BJ, et al. b2-Adrenoceptor agonists are required for development of the asthma phenotype in a murine model. Am J Respir Cell Mol Biol 2013;48:220–229.
Copyright © 2014 by the American Thoracic Society
Rationale for Anticoagulant Therapy of Pulmonary Fibrosis To the Editor: We read with interest the article regarding warfarin in idiopathic pulmonary fibrosis by Noth and colleagues (1). Despite an overall negative result, the value of the data collected is very high because it leads to a very important conclusion: namely, that the general inhibition of the coagulation cascade is not a good strategy for the treatment of pulmonary fibrosis. Our laboratory has investigated the profibrotic effects of thrombin for more than a decade. Based on our work, we have come to a very similar conclusion with important implications for potential therapy for idiopathic pulmonary fibrosis (IPF) and other fibrosing lung diseases, which is that there is no need to inhibit the coagulation cascade to inhibit the profibrotic effects of thrombin. Activation of thrombin is one of the earliest events after tissue injury. Thrombin promotes differentiation of fibroblasts to a myofibroblast phenotype, increases fibroblast proliferation, and enhances the proliferative effect of fibrinogen on fibroblasts. Thrombin is also a potent inducer of fibrogenic cytokines, including transforming growth factor-b, connective tissue growth factor, platelet-derived growth factor (PDGF), as well as various chemokines and extracellular matrix proteins like collagen, fibronectin, and tenascin (reviewed in Reference 2). There is Supported by the South Carolina Clinical and Translational Research (SCTR) Institute, with an academic home at the Medical University of South Carolina, through National Institutes of Health (NIH) grants UL1 RR029882 and UL1 TR000062, a grant from the Tarr Family “Young Investigator’s Program” and the SC SmartState “Center for Inflammation and Fibrosis Research” (G.S.B.), a grant from the Scleroderma Foundation (R.M.S.), and a grant P60 AR062755 from the NIH (G.S.B., P.J.N., and R.M.S.).
362
compelling evidence that thrombin is an important mediator of interstitial lung diseases, including both IPF and sclerodermaassociated interstitial lung disease (SSc-ILD). Our laboratory and others have demonstrated dramatically increased levels of thrombin in bronchoalveolar lavage fluid (BALF) from patients with SSc-ILD and other fibrosing lung diseases (3, 4). BALF samples from normal subjects have a low level of thrombin activity, while BALF samples from patients with SSc-ILD express up to 100-fold higher thrombin activity. Elevated thrombin activity is also observed in the bleomycin rodent model of pulmonary fibrosis. In this setting, highly concentrated thrombin binds to the proteaseactivated receptor 1 and initiates profibrotic signaling. We recently demonstrated that inhibition of thrombin using dabigatran etexilate has marked antiinflammatory and antifibrotic effects in the bleomycin pulmonary fibrosis model (5). Importantly, the antifibrotic effects of dabigatran etexilate were achieved without inhibition of the coagulation cascade. Thrombin activity in BALF was significantly reduced in bleomycin-treated mice receiving dabigatran etexilate as compared with bleomycin-treated mice receiving placebo, but not significantly different compared with saline-treated control mice receiving placebo. We have not observed any hemorrhagic side effects during our studies of dabigatran etexilate in this rodent model of ILD, suggesting that levels of dabigatran in mouse plasma are not sufficient to perturb the normal hemostatic process, yet were sufficient to ameliorate thrombin-induced and protease-activated receptor 1–mediated lung inflammation and fibrosis. The study published by Noth and coworkers was not designed to address the molecular mechanisms involved in the respiratory worsening (exacerbation or progression) associated with warfarin treatment (1). One obvious explanation for the respiratory worsening and higher mortality rate of warfarin-treated patients with IPF is inhibition of vitamin K–dependent synthesis of protein C, known to already be at a very low level in patients with IPF. Activated protein C plays a protective role in lung tissue repair and remodeling. Yasui and colleagues demonstrated that intratracheal administration of activated protein C inhibits bleomycin-induced lung fibrosis (6). In contrast to warfarin, dabigatran etexilate does not interfere with protein C synthesis; therefore, the protective effect of protein C on lung tissue should remain intact even when dabigatran etexilate is administered. We suggest that thrombin inhibition as a strategy to treat fibrosing lung diseases needs to be explored and not abandoned based on studies employing warfarin as an anticoagulant, particularly since lung fibrosis may be ameliorated with doses of a thrombin inhibitor not sufficient to cause significant perturbation of hemostasis. n Author disclosures are available with the text of this letter at www.atsjournals.org. Galina S. Bogatkevich, M.D., Ph.D. Paul J. Nietert, Ph.D. Richard M. Silver, M.D. Medical University of South Carolina Charleston, South Carolina Kristin B. Highland, M.D., M.S.C.R. Cleveland Clinic Cleveland, Ohio
American Journal of Respiratory and Critical Care Medicine Volume 189 Number 3 | February 1 2014
CORRESPONDENCE References 1. Noth I, Anstrom KJ, Calvert SB, de Andrade J, Flaherty KR, Glazer C, Kaner RJ, Olman MA; Idiopathic Pulmonary Fibrosis Clinical Research Network (IPFnet). A placebo-controlled randomized trial of warfarin in idiopathic pulmonary fibrosis. Am J Respir Crit Care Med 2012;186:88–95. 2. Chambers RC. Procoagulant signalling mechanisms in lung inflammation and fibrosis: novel opportunities for pharmacological intervention? Br J Pharmacol 2008;153:S367–S378. 3. Ohba T, McDonald JK, Silver RM, Strange C, LeRoy EC, Ludwicka A. Scleroderma BAL fluid contains thrombin, a mediator of human lung fibroblast proliferation via induction of the PDGF-alpha receptor. Am J Respir Cell Mol Biol 1994;10:405–412. ´ıguez NA, Cambrey AD, Harrison NK, Chambers RC, Gray 4. Hernandez-Rodr ´ AJ, Southcott AM, duBois RM, Black CM, Scully MF, McAnulty RJ, et al. Role of thrombin in pulmonary fibrosis. Lancet 1995;346:1071–1073. 5. Bogatkevich GS, Ludwicka-Bradley A, Nietert PJ, Akter T, van Ryn J, Silver RM. Antiinflammatory and antifibrotic effects of the oral direct thrombin inhibitor dabigatran etexilate in a murine model of interstitial lung disease. Arthritis Rheum 2011;63:1416–1425. 6. Yasui H, Gabazza EC, Tamaki S, Kobayashi T, Hataji O, Yuda H, Shimizu S, Suzuki K, Adachi Y, Taguchi O. Intratracheal administration of activated protein C inhibits bleomycin-induced lung fibrosis in the mouse. Am J Respir Crit Care Med 2001;163:1660–1668.
Copyright © 2014 by the American Thoracic Society
Reply From the Authors: We appreciate the insightful letter by Bogatkevich and colleagues, and strongly concur with their conclusions to carefully consider the potential unique antifibrotic effects of inhibiting individual components of the coagulation cascade, especially thrombin. Indeed, the unique effects of individual members of the coagulation cascade, compared with the cascade as a whole, deserve additional respect in light of the unsuccessful AntiCoagulant Effective in Idiopathic Pulmonary Fibrosis (ACE-IPF) trial (1, 2). At the time of our trial development, we were charged with designing a trial using available, FDA-approved, therapeutic interventions for pathways involved in fibrosis. We believe the ACE trial does demonstrate that the coagulation cascade (or other vitamin K–dependent proteins) plays a role in IPF, in that use of warfarin did lead to worsened outcomes (2). The notion of a more selective blockade of thrombin activity is an attractive idea. Our understanding of thrombin activity and protease-activated receptor (PAR)-mediated lung inflammation and fibrosis is growing rapidly. The authors of the letter to the editor have contributed significantly to this understanding through their findings that the thrombin inhibitor, dabigatran, has antifibrotic effects on lung fibroblasts and in a murine lung fibrosis model (3, 4). Moreover, Wygrecka and colleagues demonstrate that knockdown of PAR-1 and PAR-3 together, rather than PAR-1 alone, was necessary to inhibit thrombin-mediated epithelial to mesenchymal transition (5). The PARs remain an interesting antifibrotic target, and understanding their complex biological effects may be critical in the selection of a successful therapy. Given the availability of dabigatran etexilate, we would fully support a clinical trial to evaluate its activity. We hope that a validation of the biological effect on the correct target in vivo, would be a key part of any such clinical outcome trial in IPF, so that we can further advance this promising field. n Correspondence
Author disclosures are available with the text of this letter at www.atsjournals.org. Imre Noth, M.D. University of Chicago Chicago, Illinois Mitchell A. Olman, M.A., M.D. Cleveland Clinic Cleveland, Ohio
References 1. Chambers RC, Scotton CJ. Coagulation cascade proteinases in lung injury and fibrosis. Proc Am Thorac Soc 2012;9:96–101. 2. Noth I, Anstrom KJ, Calvert SB, de Andrade J, Flaherty KR, Glazer C, Kaner RJ, Olman MA; Idiopathic Pulmonary Fibrosis Clinical Research Network (IPFnet). A placebo-controlled randomized trial of warfarin in idiopathic pulmonary fibrosis. Am J Respir Crit Care Med 2012;186: 88–95. 3. Bogatkevich GS, Ludwicka-Bradley A, Silver RM. Dabigatran, a direct thrombin inhibitor, demonstrates antifibrotic effects on lung fibroblasts. Arthritis Rheum 2009;60:3455–3464. 4. Bogatkevich GS, Ludwicka-Bradley A, Nietert PJ, Akter T, van Ryn J, Silver RM. Antiinflammatory and antifibrotic effects of the oral direct thrombin inhibitor dabigatran etexilate in a murine model of interstitial lung disease. Arthritis Rheum 2011;63:1416–1425. 5. Wygrecka M, Didiasova M, Berscheid S, Piskulak K, Taborski B, Zakrzewicz D, Kwapiszewska G, Preissner KT, Markart P. Proteaseactivated receptors (PAR)-1 and -3 drive epithelial-mesenchymal transition of alveolar epithelial cells - potential role in lung fibrosis. Thromb Haemost 2013;110:295–307.
Copyright © 2014 by the American Thoracic Society
Mesenchymal Stromal (Stem) Cell Therapy: An Emerging Immunomodulatory Strategy for the Adjunctive Treatment of Sepsis To the Editor: We read with considerable interest the Critical Care Perspective by Leentjens and colleagues regarding immunotherapy for the adjunctive treatment of sepsis (1). We were surprised that this perspective failed to include discussion of mesenchymal stromal (stem) cell (MSC) therapy as an emerging and innovative potential adjunctive treatment strategy for sepsis and its associated major end-organ complications, including the acute respiratory distress syndrome (ARDS), when administered in either a prophylactic (preventative) or treatment (importantly, after the onset of experimental sepsis) strategy (2–6). Although sepsis has traditionally been regarded as a syndrome characterized by an overwhelming proinflammatory host immune response, Leentjens and colleagues presented evidence that secondary infections (usually bacterial) occurring in the postinflammatory immunosuppressive or immunoparalysis stage of illness may play a more important role in ultimate clinical outcome of critically ill patients with sepsis than previously recognized. The authors argued that previous antiinflammatory strategies may have failed to 363
Author disclosures are available with the text of this letter at www.atsjournals.org. Shamsah Kazani, M.D. Elliot Israel, M.D. Brigham and Women’s Hospital Boston, Massachusetts
References 1. Short PM, Williamson PA, Anderson WJ, Lipworth BJ. Randomized placebo-controlled trial to evaluate chronic dosing effects of propranolol in asthma. Am J Respir Crit Care Med 2013;187:1308–1314. 2. Kazani S, Israel E. What doesn’t kill may not make you stronger: b-blockers for asthma [editorial]. Am J Respir Crit Care Med 2013;187:1281–1286. 3. Nguyen LP, Lin R, Parra S, Omoluabi O, Hanania NA, Tuvim MJ, Knoll BJ, Dickey BF, Bond RA. b2-Adrenoceptor signaling is required for the development of an asthma phenotype in a murine model. Proc Natl Acad Sci USA 2009;106:2435–2440. 4. Thanawala VJ, Forkuo GS, Al-Sawalha N, Azzegagh Z, Nguyen LP, Eriksen JL, Tuvim MJ, Lowder TW, Dickey BF, Knoll BJ, et al. b2-Adrenoceptor agonists are required for development of the asthma phenotype in a murine model. Am J Respir Cell Mol Biol 2013;48:220–229.
Copyright © 2014 by the American Thoracic Society
Rationale for Anticoagulant Therapy of Pulmonary Fibrosis To the Editor: We read with interest the article regarding warfarin in idiopathic pulmonary fibrosis by Noth and colleagues (1). Despite an overall negative result, the value of the data collected is very high because it leads to a very important conclusion: namely, that the general inhibition of the coagulation cascade is not a good strategy for the treatment of pulmonary fibrosis. Our laboratory has investigated the profibrotic effects of thrombin for more than a decade. Based on our work, we have come to a very similar conclusion with important implications for potential therapy for idiopathic pulmonary fibrosis (IPF) and other fibrosing lung diseases, which is that there is no need to inhibit the coagulation cascade to inhibit the profibrotic effects of thrombin. Activation of thrombin is one of the earliest events after tissue injury. Thrombin promotes differentiation of fibroblasts to a myofibroblast phenotype, increases fibroblast proliferation, and enhances the proliferative effect of fibrinogen on fibroblasts. Thrombin is also a potent inducer of fibrogenic cytokines, including transforming growth factor-b, connective tissue growth factor, platelet-derived growth factor (PDGF), as well as various chemokines and extracellular matrix proteins like collagen, fibronectin, and tenascin (reviewed in Reference 2). There is Supported by the South Carolina Clinical and Translational Research (SCTR) Institute, with an academic home at the Medical University of South Carolina, through National Institutes of Health (NIH) grants UL1 RR029882 and UL1 TR000062, a grant from the Tarr Family “Young Investigator’s Program” and the SC SmartState “Center for Inflammation and Fibrosis Research” (G.S.B.), a grant from the Scleroderma Foundation (R.M.S.), and a grant P60 AR062755 from the NIH (G.S.B., P.J.N., and R.M.S.).
362
compelling evidence that thrombin is an important mediator of interstitial lung diseases, including both IPF and sclerodermaassociated interstitial lung disease (SSc-ILD). Our laboratory and others have demonstrated dramatically increased levels of thrombin in bronchoalveolar lavage fluid (BALF) from patients with SSc-ILD and other fibrosing lung diseases (3, 4). BALF samples from normal subjects have a low level of thrombin activity, while BALF samples from patients with SSc-ILD express up to 100-fold higher thrombin activity. Elevated thrombin activity is also observed in the bleomycin rodent model of pulmonary fibrosis. In this setting, highly concentrated thrombin binds to the proteaseactivated receptor 1 and initiates profibrotic signaling. We recently demonstrated that inhibition of thrombin using dabigatran etexilate has marked antiinflammatory and antifibrotic effects in the bleomycin pulmonary fibrosis model (5). Importantly, the antifibrotic effects of dabigatran etexilate were achieved without inhibition of the coagulation cascade. Thrombin activity in BALF was significantly reduced in bleomycin-treated mice receiving dabigatran etexilate as compared with bleomycin-treated mice receiving placebo, but not significantly different compared with saline-treated control mice receiving placebo. We have not observed any hemorrhagic side effects during our studies of dabigatran etexilate in this rodent model of ILD, suggesting that levels of dabigatran in mouse plasma are not sufficient to perturb the normal hemostatic process, yet were sufficient to ameliorate thrombin-induced and protease-activated receptor 1–mediated lung inflammation and fibrosis. The study published by Noth and coworkers was not designed to address the molecular mechanisms involved in the respiratory worsening (exacerbation or progression) associated with warfarin treatment (1). One obvious explanation for the respiratory worsening and higher mortality rate of warfarin-treated patients with IPF is inhibition of vitamin K–dependent synthesis of protein C, known to already be at a very low level in patients with IPF. Activated protein C plays a protective role in lung tissue repair and remodeling. Yasui and colleagues demonstrated that intratracheal administration of activated protein C inhibits bleomycin-induced lung fibrosis (6). In contrast to warfarin, dabigatran etexilate does not interfere with protein C synthesis; therefore, the protective effect of protein C on lung tissue should remain intact even when dabigatran etexilate is administered. We suggest that thrombin inhibition as a strategy to treat fibrosing lung diseases needs to be explored and not abandoned based on studies employing warfarin as an anticoagulant, particularly since lung fibrosis may be ameliorated with doses of a thrombin inhibitor not sufficient to cause significant perturbation of hemostasis. n Author disclosures are available with the text of this letter at www.atsjournals.org. Galina S. Bogatkevich, M.D., Ph.D. Paul J. Nietert, Ph.D. Richard M. Silver, M.D. Medical University of South Carolina Charleston, South Carolina Kristin B. Highland, M.D., M.S.C.R. Cleveland Clinic Cleveland, Ohio
American Journal of Respiratory and Critical Care Medicine Volume 189 Number 3 | February 1 2014
CORRESPONDENCE References 1. Noth I, Anstrom KJ, Calvert SB, de Andrade J, Flaherty KR, Glazer C, Kaner RJ, Olman MA; Idiopathic Pulmonary Fibrosis Clinical Research Network (IPFnet). A placebo-controlled randomized trial of warfarin in idiopathic pulmonary fibrosis. Am J Respir Crit Care Med 2012;186:88–95. 2. Chambers RC. Procoagulant signalling mechanisms in lung inflammation and fibrosis: novel opportunities for pharmacological intervention? Br J Pharmacol 2008;153:S367–S378. 3. Ohba T, McDonald JK, Silver RM, Strange C, LeRoy EC, Ludwicka A. Scleroderma BAL fluid contains thrombin, a mediator of human lung fibroblast proliferation via induction of the PDGF-alpha receptor. Am J Respir Cell Mol Biol 1994;10:405–412. ´ıguez NA, Cambrey AD, Harrison NK, Chambers RC, Gray 4. Hernandez-Rodr ´ AJ, Southcott AM, duBois RM, Black CM, Scully MF, McAnulty RJ, et al. Role of thrombin in pulmonary fibrosis. Lancet 1995;346:1071–1073. 5. Bogatkevich GS, Ludwicka-Bradley A, Nietert PJ, Akter T, van Ryn J, Silver RM. Antiinflammatory and antifibrotic effects of the oral direct thrombin inhibitor dabigatran etexilate in a murine model of interstitial lung disease. Arthritis Rheum 2011;63:1416–1425. 6. Yasui H, Gabazza EC, Tamaki S, Kobayashi T, Hataji O, Yuda H, Shimizu S, Suzuki K, Adachi Y, Taguchi O. Intratracheal administration of activated protein C inhibits bleomycin-induced lung fibrosis in the mouse. Am J Respir Crit Care Med 2001;163:1660–1668.
Copyright © 2014 by the American Thoracic Society
Reply From the Authors: We appreciate the insightful letter by Bogatkevich and colleagues, and strongly concur with their conclusions to carefully consider the potential unique antifibrotic effects of inhibiting individual components of the coagulation cascade, especially thrombin. Indeed, the unique effects of individual members of the coagulation cascade, compared with the cascade as a whole, deserve additional respect in light of the unsuccessful AntiCoagulant Effective in Idiopathic Pulmonary Fibrosis (ACE-IPF) trial (1, 2). At the time of our trial development, we were charged with designing a trial using available, FDA-approved, therapeutic interventions for pathways involved in fibrosis. We believe the ACE trial does demonstrate that the coagulation cascade (or other vitamin K–dependent proteins) plays a role in IPF, in that use of warfarin did lead to worsened outcomes (2). The notion of a more selective blockade of thrombin activity is an attractive idea. Our understanding of thrombin activity and protease-activated receptor (PAR)-mediated lung inflammation and fibrosis is growing rapidly. The authors of the letter to the editor have contributed significantly to this understanding through their findings that the thrombin inhibitor, dabigatran, has antifibrotic effects on lung fibroblasts and in a murine lung fibrosis model (3, 4). Moreover, Wygrecka and colleagues demonstrate that knockdown of PAR-1 and PAR-3 together, rather than PAR-1 alone, was necessary to inhibit thrombin-mediated epithelial to mesenchymal transition (5). The PARs remain an interesting antifibrotic target, and understanding their complex biological effects may be critical in the selection of a successful therapy. Given the availability of dabigatran etexilate, we would fully support a clinical trial to evaluate its activity. We hope that a validation of the biological effect on the correct target in vivo, would be a key part of any such clinical outcome trial in IPF, so that we can further advance this promising field. n Correspondence
Author disclosures are available with the text of this letter at www.atsjournals.org. Imre Noth, M.D. University of Chicago Chicago, Illinois Mitchell A. Olman, M.A., M.D. Cleveland Clinic Cleveland, Ohio
References 1. Chambers RC, Scotton CJ. Coagulation cascade proteinases in lung injury and fibrosis. Proc Am Thorac Soc 2012;9:96–101. 2. Noth I, Anstrom KJ, Calvert SB, de Andrade J, Flaherty KR, Glazer C, Kaner RJ, Olman MA; Idiopathic Pulmonary Fibrosis Clinical Research Network (IPFnet). A placebo-controlled randomized trial of warfarin in idiopathic pulmonary fibrosis. Am J Respir Crit Care Med 2012;186: 88–95. 3. Bogatkevich GS, Ludwicka-Bradley A, Silver RM. Dabigatran, a direct thrombin inhibitor, demonstrates antifibrotic effects on lung fibroblasts. Arthritis Rheum 2009;60:3455–3464. 4. Bogatkevich GS, Ludwicka-Bradley A, Nietert PJ, Akter T, van Ryn J, Silver RM. Antiinflammatory and antifibrotic effects of the oral direct thrombin inhibitor dabigatran etexilate in a murine model of interstitial lung disease. Arthritis Rheum 2011;63:1416–1425. 5. Wygrecka M, Didiasova M, Berscheid S, Piskulak K, Taborski B, Zakrzewicz D, Kwapiszewska G, Preissner KT, Markart P. Proteaseactivated receptors (PAR)-1 and -3 drive epithelial-mesenchymal transition of alveolar epithelial cells - potential role in lung fibrosis. Thromb Haemost 2013;110:295–307.
Copyright © 2014 by the American Thoracic Society
Mesenchymal Stromal (Stem) Cell Therapy: An Emerging Immunomodulatory Strategy for the Adjunctive Treatment of Sepsis To the Editor: We read with considerable interest the Critical Care Perspective by Leentjens and colleagues regarding immunotherapy for the adjunctive treatment of sepsis (1). We were surprised that this perspective failed to include discussion of mesenchymal stromal (stem) cell (MSC) therapy as an emerging and innovative potential adjunctive treatment strategy for sepsis and its associated major end-organ complications, including the acute respiratory distress syndrome (ARDS), when administered in either a prophylactic (preventative) or treatment (importantly, after the onset of experimental sepsis) strategy (2–6). Although sepsis has traditionally been regarded as a syndrome characterized by an overwhelming proinflammatory host immune response, Leentjens and colleagues presented evidence that secondary infections (usually bacterial) occurring in the postinflammatory immunosuppressive or immunoparalysis stage of illness may play a more important role in ultimate clinical outcome of critically ill patients with sepsis than previously recognized. The authors argued that previous antiinflammatory strategies may have failed to 363
