Pirfenidone inhibits lung allograft fibrosis through L-arginine-arginase pathway

Pirfenidone use in fibrotic diseases: What do we know so far?

BACKGROUND

Pirfenidone has demonstrated significant anti-inflammatory and antifibrotic effects in both animal models and some clinical trials. Its potential for antifibrotic activity positions it as a promising candidate for the treatment of various fibrotic diseases. Pirfenidone exerts several pleiotropic and anti-inflammatory effects through different molecular pathways, attenuating multiple inflammatory processes, including the secretion of pro-inflammatory cytokines, apoptosis, and fibroblast activation.

OBJECTIVE

To present the current evidence of pirfenidone's effects on several fibrotic diseases, with a focus on its potential as a therapeutic option for managing chronic fibrotic conditions.

FINDINGS

Pirfenidone has been extensively studied for idiopathic pulmonary fibrosis, showing a favorable impact and forming part of the current treatment regimen for this disease. Additionally, pirfenidone appears to have beneficial effects on similar fibrotic diseases such as interstitial lung disease, myocardial fibrosis, glomerulopathies, aberrant skin scarring, chronic liver disease, and other fibrotic disorders.

CONCLUSION

Given the increasing incidence of chronic fibrotic conditions, pirfenidone emerges as a potential therapeutic option for these patients. However, further clinical trials are necessary to confirm its therapeutic efficacy in various fibrotic diseases. This review aims to highlight the current evidence of pirfenidone's effects in multiple fibrotic conditions.

Trichodelphinine A alleviates pulmonary fibrosis by inhibiting collagen synthesis via NOX4-ARG1/TGF-β signaling pathway

BACKGROUND

Pulmonary fibrosis, a progressive and fatal lung disease with no effective treatment medication, is characterized by lung remodeling and fibroblastic foci caused by an oxidative imbalance with an overloading deposition of collagen. Trichodelphinine A, a hetisine-type C20-diterpenoid alkaloid, was found anti-fibrotic activity in vitro, but its effect and mechanism on pulmonary fibrosis still unknown.

PURPOSE

Our study aimed to investigate and validate the anti-fibrotic properties of trichodelphinine A in pulmonary fibrosis animals induced by bleomycin (BLM), and its mechanism whether via NOX4-ARG1/TGF-β signaling pathway.

METHODS

The anti-fibrotic effects of trichodelphinine A were evaluated using BLM-induced rats through indicators of lung histopathology and collagen synthesis. Dynamic metabolomics evaluated the metabolic disorder and therapeutic effect of trichodelphinine A. The interaction between trichodelphinine A and NOX4 receptor was confirmed using CETSA and molecular dynamics experiments. Molecular biology experiments were conducted in NOX4 gene knockout mice to investigate the intervention effect of trichodelphinine A.

RESULTS

Trichodelphinine A could suppress histopathologic changes, collagen deposition and proinflammatory cytokine release pulmonary fibrosis in bleomycin induced rats. Dynamic metabolomics studies revealed that trichodelphinine A could correct endogenous metabolic disorders of arachidonic acid, arginine and proline during fibrosis development, which revealed that the regulation of oxidative stress and amino acid metabolism targeting NOX4 and ARG1 may be the main pharmacological mechanisms of trichodelphinine A on pulmonary fibrosis. We further determined that trichodelphinine A inhibited over oxidative stress and collagen deposition by suppressing Nrf2-keap1 and ARG1-OAT signaling pathways, respectively. Molecular dynamics studies showed that trichodelphinine A was directly binds with NOX4, in which PHE354 and THR355 residues of NOX4 are critical binding sites for trichodelphinine A. Mechanistic validation in cells or mice with NOX4 knockout or silencing suggested that the anti-fibrotic effects of trichodelphinine A depended on inhibition of NOX4 to suppress ARG1/OAT activation and TGF-β/Smads signaling pathway.

CONCLUSION

Collectively, our findings indicate a powerful anti-fibrotic function of trichodelphinine A in pulmonary fibrosis via targeting NOX4. NOX4 mediates the activation of ARG1/OAT to regulate arginase-proline metabolism, and promotes TGF-β/Smads signaling pathway, thereby affecting the collagen synthesis in pulmonary fibrosis, which is a novel finding and indicates that inhibition of NOX4 is a novel therapeutic strategy for pulmonary fibrosis.

Metformin attenuates chronic lung allograft dysfunction: evidence in rat models

BACKGROUND

Chronic lung allograft dysfunction (CLAD) directly causes an abysmal long-term prognosis after lung transplantation (LTx), but effective and safe drugs are not available. Metformin exhibits high therapeutic potential due to its antifibrotic and immunomodulatory effects; however, it is unclear whether metformin exerts a therapeutic effect in CLAD. We sought to investigate the effect of metformin on CLAD based on rat models.

METHODS

Allogeneic LTx rats were treated with Cyclosporin A (CsA) in the first week, followed by metformin, CsA, or vehicle treatment. Syngeneic LTx rats received only vehicles. All rats were sacrificed on post-transplant week 4. Pathology of lung graft, spleen, and thymus, extent of lung fibrosis, activity of profibrotic cytokines and signaling pathway, adaptive immunity, and AMPK activity were then studied.

RESULTS

Allogeneic recipients without maintenance CsA treatment manifested CLAD pathological characteristics, but these changes were not observed in rats treated with metformin. For the antifibrotic effect, metformin suppressed the fibrosis extent and profibrotic cytokine expression in lung grafts. Regarding immunomodulatory effect, metformin reduced T- and B-cell infiltration in lung grafts, spleen and thymus weights, the T- and B-cell zone areas in the spleen, and the thymic medullary area. In addition, metformin activated AMPK in lung allografts and in α-SMA⁺ cells and T cells in the lung grafts.

CONCLUSIONS

Metformin attenuates CLAD in rat models, which could be attributed to the antifibrotic and immunomodulatory effects. AMPK activation suggests the potential molecular mechanism. Our study provides an experimental rationale for further clinical trials.

Integrated proteomics and metabolomics reveal variations in pulmonary fibrosis development and the potential therapeutic effect of Shuangshen Pingfei formula

ETHNOPHARMACOLOGICAL RELEVANCE

Shuangshen Pingfei formula (SSPF), a Chinese medicine prescription, has been prescribed to alleviate PF. However, little is known about the molecular mechanism underlying PF progression and the regulatory mechanism in SSPF.

AIMS OF THE STUDY

To discriminate the molecular alterations underlying the development of pulmonary fibrosis (PF) and reveal the regulatory mechanism of Shuangshen Pingfei formula (SSPF).

MATERIALS AND METHODS

An integrated analysis of a time-course pathology combined with proteomics and metabolomics was performed to investigate changes in body weight, survival rate, lung coefficient, histopathology, proteins, and metabolites of lung tissues at different time points upon bleomycin (BLM) exposure and SSPF treatment.

RESULTS

The results showed that PF progression was characterized by gradually aggravated fibrosis accompanied by inflammation with extended exposure (7, 14, and 21 days). SSPF significantly attenuated lung fibrosis, as evidenced by increased weight, and reduced lung coefficients and fibrosis scores. Moreover, 368 common differentially expressed proteins (DEPs) were identified, and 102 DEPs were continuously and monotonically upregulated via proteomics among the three BLM treatments. The DEPs were principally involved in extracellular matrix (ECM) remodeling and arginine and proline (AP) metabolic reprogramming. Additionally, metabolomics analyses revealed that BLM exposure mainly affected six metabolism pathways, including 34 differentially regulated metabolites (DRMs). Furthermore, correlation analysis found that several DEPs and DRMs, including L-ornithine, S-adenosyl-L-methionine, ARG, and AOC1, were associated with arginine and proline metabolism, and 8,9-EET, 8,9-DHET, CYP2B, etc., were involved in arachidonic acid (AA) metabolism, suggesting that these two pathways play a critical role in the development of fibrosis. After SSPF treatment, the related protein expression and metabolic disorders were regulated, implying that SSPF provides potential solutions to target these pathways for benefit in the treatment of PF.

CONCLUSION

Our data suggest that ECM remodeling, and metabolic reprogramming of AP and AA are distinctive features of PF development. Simultaneously, we confirmed that SSPF could effectively regulate metabolic disorders, indicating its potential clinical application for PF therapy. Our findings using multiple approaches provide a molecular-scale perspective on the mechanisms of PF progression and the amelioration of SSPF.

Inhibition of CEMIP potentiates the effect of sorafenib on metastatic hepatocellular carcinoma by reducing the stiffness of lung metastases

Hepatocellular carcinoma (HCC) with lung metastasis is associated with poor prognosis and poor therapeutic outcomes. Studies have demonstrated that stiffened stroma can promote metastasis in various tumors. However, how the lung mechanical microenvironment favors circulating tumor cells remains unclear in metastatic HCC. Here, we found that the expression of cell migration-inducing hyaluronan-binding protein (CEMIP) was closely associated with lung metastasis and can promote pre-metastatic niche formation by increasing lung matrix stiffness. Furthermore, upregulated serum CEMIP was indicative of lung fibrotic changes severity in patients with HCC lung metastasis. By directly targeting CEMIP, pirfenidone can inhibit CEMIP/TGF-β1/Smad signaling pathway and reduce lung metastases stiffening, demonstrating promising antitumor activity. Pirfenidone in combination with sorafenib can more effectively suppress the incidence of lung metastasis compared with sorafenib alone. This study is the first attempt to modulate the mechanical microenvironment for HCC therapy and highlights CEMIP as a potential target for the prevention and treatment of HCC lung metastasis. CEMIP mediating an HCC-permissive microenvironment through controlling matrix stiffness. Meanwhile, Pirfenidone could reduce metastasis stiffness and increases the anti-angiogenic effect of Sorafenib by directly targeting CEMIP.

Macrophages-microenvironment crosstalk in fibrostenotic inflammatory bowel disease: from basic mechanisms to clinical applications

INTRODUCTION

Intestinal fibrosis is a common complication of Inflammatory Bowel Disease (IBD) with no available drugs. The current therapeutic principle is surgical intervention as the core. Intestinal macrophages contribute to both the progression of inflammation and fibrosis. Understanding the role of macrophages in the intestinal microenvironment could bring new hope for fibrosis prevention or even reversal.

AREAS COVERED

This article reviewed the most relevant reports on macrophage in the field of intestinal fibrosis. The authors discussed current opinions about how intestinal macrophages function and interact with surrounding mediators during inflammation resolution and fibrostenotic IBD. Based on biological mechanisms findings, authors summarized related clinical trial outcomes.

EXPERT OPINION

The plasticity of intestinal macrophages allows them to undergo dramatic alterations in their phenotypes or functions when exposed to gastrointestinal environmental stimuli. They exhibit distinct metabolic characteristics, secrete various cytokines, express unique surface markers, and transmit different signals. Nevertheless, the specific mechanism through which the intestinal macrophages contribute to intestinal fibrosis remains unclear. It should further elucidate a novel therapeutic approach by targeting macrophages, especially distinct mechanisms in specific subgroups of macrophages involved in the progression of fibrogenesis in IBD.

Regulation of Extracellular Matrix Production in Activated Fibroblasts: Roles of Amino Acid Metabolism in Collagen Synthesis

Cancer associated fibroblasts (CAFs) are a major component of the tumour microenvironment in most tumours, and are key mediators of the response to tissue damage caused by tumour growth and invasion, contributing to the observation that tumours behave as 'wounds that do not heal'. CAFs have been shown to play a supporting role in all stages of tumour progression, and this is dependent on the highly secretory phenotype CAFs develop upon activation, of which extracellular matrix (ECM) production is a key element. A collagen rich, stromal ECM has been shown to influence tumour growth and metastasis, exclude immune cells and impede drug delivery, and is associated with poor prognosis in many cancers. CAFs also extensively remodel their metabolism to support cancer cells, however, it is becoming clear that metabolic rewiring also supports intrinsic functions of activated fibroblasts, such as increased ECM production. In this review, we summarise how fibroblasts metabolically regulate ECM production, focussing on collagen production, at the transcriptional, translational and post-translational level, and discuss how this can provide possible strategies for effectively targeting CAF activation and formation of a tumour-promoting stroma.

Antifibrotic drugs in lung transplantation and chronic lung allograft dysfunction: a review

This review aims to provide an overview of pre-transplant antifibrotic therapy on peri-transplant outcomes and to address the possible role of antifibrotics in lung transplant recipients with chronic lung allograft dysfunction.Lung transplantation is an established treatment modality for patients with various end-stage lung diseases, of which idiopathic pulmonary fibrosis and other progressive fibrosing interstitial lung diseases are growing indications. Theoretically, widespread use of antifibrotics prior to lung transplantation may increase the risk of bronchial anastomotic complications and impaired wound healing.Long-term graft and patient survival are still hampered by development of chronic lung allograft dysfunction, on which antifibrotics may have a beneficial impact.Antifibrotics until the moment of lung transplantation proved to be safe, without increasing peri-transplant complications. Currently, best practice is to continue antifibrotics until time of transplantation. In a large multicentre randomised trial, pirfenidone did not appear to have a beneficial effect on lung function decline in established bronchiolitis obliterans syndrome. The results of antifibrotic therapy in restrictive allograft syndrome are eagerly awaited, but nonrandomised data from small case reports/series are promising.

Tianlongkechuanling Inhibits Pulmonary Fibrosis Through Down-Regulation of Arginase-Ornithine Pathway

Background: Pulmonary Fibrosis (PF) is an interstitial lung disease characterized by excessive accumulation of extracellular matrix in the lungs, which disrupts the structure and gas exchange of the alveoli. There are only two approved therapies for PF, nintedanib (Nib) and pirfenidone. Therefore, the use of Chinese medicine for PF is attracting attention. Tianlongkechuanling (TL) is an effective Chinese formula that has been applied clinically to alleviate PF, which can enhance lung function and quality of life.

Purpose: The potential effects and specific mechanisms of TL have not been fully explored, yet. In the present study, proteomics was performed to explore the therapeutic protein targets of TL on Bleomycin (BLM)-induced Pulmonary Fibrosis.

Method: BLM-induced PF mice models were established. Hematoxylineosin staining and Masson staining were used to analyze histopathological changes and collagen deposition. To screen the differential proteins expression between the Control, BLM, BLM + TL and BLM + Nib (BLM + nintedanib) groups, quantitative proteomics was performed using tandem mass tag (TMT) labeling with nanoLC-MS/MS [nano liquid chromatographymass spectrometry]). Changes in the profiles of the expressed proteins were analyzed using the bioinformatics tools Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG). The protein–protein interactions (PPI) were established by STRING. Expressions of α-smooth muscle actin (α-SMA), Collagen I (Col1a1), Fibronectin (Fn1) and enzymes in arginase-ornithine pathway were detected by Western blot or RT-PCR.

Result: TL treatments significantly ameliorated BLM-induced collagen deposition in lung tissues. Moreover, TL can inhibit the protein expressions of α-SMA and the mRNA expressions of Col1a1 and Fn1. Using TMT technology, we observed 253 differentially expressed proteins related to PPI networks and involved different KEGG pathways. Arginase-ornithine pathway is highly significant. The expression of arginase1 (Arg1), carbamoyltransferase (OTC), carbamoy-phosphate synthase (CPS1), argininosuccinate synthase (ASS1), ornithine aminotransferase (OAT) argininosuccinate lyase (ASL) and inducible nitric oxide synthase (iNOS) was significantly decreased after TL treatments.

Conclusion: Administration of TL in BLM-induced mice resulted in decreasing pulmonary fibrosis. Our findings propose that the down regulation of arginase-ornithine pathway expression with the reduction of arginase biosynthesis is a central mechanism and potential treatment for pulmonary fibrosis with the prevention of TL.

Regulatory Immune Cells in Idiopathic Pulmonary Fibrosis: Friends or Foes?

The immune system is receiving increasing attention for interstitial lung diseases, as knowledge on its role in fibrosis development and response to therapies is expanding. Uncontrolled immune responses and unbalanced injury-inflammation-repair processes drive the initiation and progression of idiopathic pulmonary fibrosis. The regulatory immune system plays important roles in controlling pathogenic immune responses, regulating inflammation and modulating the transition of inflammation to fibrosis. This review aims to summarize and critically discuss the current knowledge on the potential role of regulatory immune cells, including mesenchymal stromal/stem cells, regulatory T cells, regulatory B cells, macrophages, dendritic cells and myeloid-derived suppressor cells in idiopathic pulmonary fibrosis. Furthermore, we review the emerging role of regulatory immune cells in anti-fibrotic therapy and lung transplantation. A comprehensive understanding of immune regulation could pave the way towards new therapeutic or preventive approaches in idiopathic pulmonary fibrosis.

Pirfenidone: Molecular Mechanisms and Potential Clinical Applications in Lung Disease

Pirfenidone (PFD) is a pharmacological compound with therapeutic efficacy in idiopathic pulmonary fibrosis. It has been chiefly characterized as an antifibrotic agent, although it was initially developed as an antiinflammatory compound because of its ability to diminish the accumulation of inflammatory cells and cytokines. Despite recent studies that have elucidated key mechanisms, the precise molecular activities of PFD remain incompletely understood. PFD modulates fibrogenic growth factors, thereby attenuating fibroblast proliferation, myofibroblast differentiation, collagen and fibronectin synthesis, and deposition of extracellular matrix. This effect is mediated by suppression of TGF-β1 (transforming growth factor-β1) and other growth factors. Here, we appraise the impact of PFD on TGF-β1 production and its downstream pathways. Accumulating evidence indicates that PFD also downregulates inflammatory pathways and therefore has considerable potential as a viable and innovative antiinflammatory compound. We examine the effects of PFD on inflammatory cells and the production of pro- and antiinflammatory cytokines in the lung. In this context, recent evidence that PFD can target inflammasome pathways and ensuing lung inflammation is highlighted. Finally, the antioxidant properties of PFD, such as its ability to inhibit redox reactions and regulate oxidative stress-related genes and enzymes, are detailed. In summary, this narrative review examines molecular mechanisms underpinning PFD and its recognized benefits in lung fibrosis. We highlight preclinical data that demonstrate the potential of PFD as a nonsteroidal antiinflammatory agent and outline areas for future research.

Increased Arginase Expression and Decreased Nitric Oxide in Pig Donor Lungs after Normothermic Ex Vivo Lung Perfusion

An established pig lung transplantation model was used to study the effects of cold ischemia time, normothermic acellular ex vivo lung perfusion (EVLP) and reperfusion after lung transplantation on l-arginine/NO metabolism in lung tissue. Lung tissue homogenates were analyzed for NO metabolite (NOx) concentrations by chemiluminescent NO-analyzer technique, and l-arginine, l-ornithine, l-citrulline and asymmetric dimethylarginine (ADMA) quantified using liquid chromatography-mass spectrometry (LC-MS/MS). The expression of arginase and nitric oxide synthase (NOS) isoforms in lung was measured by real-time polymerase chain reaction. EVLP preservation resulted in a significant decrease in concentrations of NOx and l-citrulline, both products of NOS, at the end of EVLP and after reperfusion following transplantation, compared to control, respectively. The ratio of l-ornithine over l-citrulline, a marker of the balance between l-arginine metabolizing enzymes, was increased in the EVLP group prior to reperfusion. The expression of both arginase isoforms was increased from baseline 1 h post reperfusion in EVLP but not in the no-EVLP group. These data suggest that EVLP results in a shift of the l-arginine balance towards arginase, leading to NO deficiency in the lung. The arginase/NOS balance may, therefore, represent a therapeutic target to improve lung quality during EVLP and, subsequently, transplant outcomes.

Idiopathic Pulmonary Fibrosis and Antifibrotic Treatments: Focus on Experimental Studies

Context.—

Idiopathic pulmonary fibrosis (IPF) is a progressive fatal disease that up to now has been associated with a poor outcome. Some advances have been made in understanding the multiple interrelated pathogenic pathways underlying IPF. The disease is now believed to result from complex interactions among genetic, epigenetic, transcriptional, posttranscriptional, metabolic, and environmental factors. The discovery and validation of theranostic biomarkers are necessary to enable a more precise and earlier diagnosis of IPF and to improve the prediction of future disease behavior. Two drugs recently approved by the US Food and Drug Administration, pirfenidone and nintedanib, have shown the ability to reduce the progression of the disease, although survival benefits are only minimal and neither drug prevents or reverses the disease.

Objective.—

To provide a critical overview of the main experimental studies carried out for testing the principal effects of pirfenidone and nintedanib on IPF.

Data Sources.—

Experimental (animal and in vitro) studies concerning both drugs were used.

Conclusions.—

Pirfenidone has a longer history of preclinical experimental studies than nintedanib. Many studies have been reported more recently (after 2014) and some of them evaluated the association of both drugs, thus suggesting their combination in future therapeutic approaches. Future investigations focusing on targets at molecular, cellular, and tissue levels are necessary to have a better in-depth knowledge of the properties of these drugs and to explore the potential efficacy of both or other drug combinations.

Purinergic P2X4 receptors and mitochondrial ATP production regulate T cell migration

T cells must migrate in order to encounter antigen-presenting cells (APCs) and to execute their varied functions in immune defense and inflammation. ATP release and autocrine signaling through purinergic receptors contribute to T cell activation at the immune synapse that T cells form with APCs. Here, we show that T cells also require ATP release and purinergic signaling for their migration to APCs. We found that the chemokine stromal-derived factor-1α (SDF-1α) triggered mitochondrial ATP production, rapid bursts of ATP release, and increased migration of primary human CD4+ T cells. This process depended on pannexin-1 ATP release channels and autocrine stimulation of P2X4 receptors. SDF-1α stimulation caused localized accumulation of mitochondria with P2X4 receptors near the front of cells, resulting in a feed-forward signaling mechanism that promotes cellular Ca2+ influx and sustains mitochondrial ATP synthesis at levels needed for pseudopod protrusion, T cell polarization, and cell migration. Inhibition of P2X4 receptors blocked the activation and migration of T cells in vitro. In a mouse lung transplant model, P2X4 receptor antagonist treatment prevented the recruitment of T cells into allograft tissue and the rejection of lung transplants. Our findings suggest that P2X4 receptors are therapeutic targets for immunomodulation in transplantation and inflammatory diseases.

Tissue metabolic changes for effects of pirfenidone in rats of acute paraquat poisoning by GC-MS

We developed a metabolomic method to evaluate the effect of pirfenidone on rats with acute paraquat (PQ) poisoning, through the analysis of various tissues (lung, liver, kidney, and heart), by gas chromatography–mass spectrometry (GC-MS). Thirty-eight rats were randomly divided into a control group, an acute PQ (20 mg kg−1) poisoning group, a pirfenidone (20 mg kg−1) treatment group, and a pirfenidone (40 mg kg−1) treatment group. Partial least squares-discriminate analysis (PLS-DA) revealed metabolic alterations in rat tissue samples from the two pirfenidone treatment groups after acute PQ poisoning. The PLS-DA 3D score chart showed that the rats in the acute PQ poisoning group were clearly distinguished from the rats in the control group. Also, the two pirfenidone treatment groups were distinguished from the acute PQ poisoning group and control group. Additionally, the pirfenidone (40 mg kg−1) treatment group was separated farther than the pirfenidone (20 mg kg−1) treatment group from the acute PQ poisoning group. Evaluation of the pathological changes in the rat tissues revealed that treatment with pirfenidone appeared to decrease pulmonary fibrosis in the acute PQ poisoning rats. The results indicate that pirfenidone induced beneficial metabolic alterations in the tissues of rats with acute PQ poisoning. Rats with acute PQ poisoning exhibited a certain reduction in biochemical indicators after treatment with pirfenidone, indicating that pirfenidone could protect liver and kidney function. Accordingly, the developed metabolomic approach proved to be useful to elucidate the effect of pirfenidone in rats of acute PQ poisoning.

Pirfenidone ameliorates murine chronic GVHD through inhibition of macrophage infiltration and TGF-β production

Allogeneic hematopoietic stem cell transplantation is hampered by chronic graft-versus-host disease (cGVHD), resulting in multiorgan fibrosis and diminished function. Fibrosis in lung and skin leads to progressive bronchiolitis obliterans (BO) and scleroderma, respectively, for which new treatments are needed. We evaluated pirfenidone, a Food and Drug Administration (FDA)-approved drug for idiopathic pulmonary fibrosis, for its therapeutic effect in cGVHD mouse models with distinct pathophysiology. In a full major histocompatibility complex (MHC)-mismatched, multiorgan system model with BO, donor T-cell responses that support pathogenic antibody production are required for cGVHD development. Pirfenidone treatment beginning one month post-transplant restored pulmonary function and reversed lung fibrosis, which was associated with reduced macrophage infiltration and transforming growth factor-β production. Pirfenidone dampened splenic germinal center B-cell and T-follicular helper cell frequencies that collaborate to produce antibody. In both a minor histocompatibility antigen-mismatched as well as a MHC-haploidentical model of sclerodermatous cGVHD, pirfenidone significantly reduced macrophages in the skin, although clinical improvement of scleroderma was only seen in one model. In vitro chemotaxis assays demonstrated that pirfenidone impaired macrophage migration to monocyte chemoattractant protein-1 (MCP-1) as well as IL-17A, which has been linked to cGVHD generation. Taken together, our data suggest that pirfenidone is a potential therapeutic agent to ameliorate fibrosis in cGVHD.

Update on Chronic Lung Allograft Dysfunction

Chronic lung allograft dysfunction (CLAD) encompasses a range of pathologies that cause a transplanted lung to not achieve or maintain normal function. CLAD manifests as airflow restriction and/or obstruction and is predominantly a result of chronic rejection. Three distinct phenotypes of chronic rejection are now recognized: bronchiolitis obliterans, neutrophilic reversible allograft dysfunction, and restrictive allograft syndrome. Recent investigations have revealed that each phenotype has a unique pathology and histopathological findings, suggesting that treatment regimens should be tailored to the underlying etiology. CLAD is poorly responsive to treatment once diagnosed, and therefore the prevention of the factors that predispose a patient to develop CLAD is critically important. Small and large animal models have contributed significantly to our understanding of CLAD and more studies are needed to develop treatment regimens that are effective in humans.

Therapeutic lymphangiogenesis ameliorates established acute lung allograft rejection

Lung transplantation is the only viable option for patients suffering from otherwise incurable end-stage pulmonary diseases such as chronic obstructive pulmonary disease and idiopathic pulmonary fibrosis. Despite aggressive immunosuppression, acute rejection of the lung allograft occurs in over half of transplant recipients, and the factors that promote lung acceptance are poorly understood. The contribution of lymphatic vessels to transplant pathophysiology remains controversial, and data that directly address the exact roles of lymphatic vessels in lung allograft function and survival are limited. Here, we have shown that there is a marked decline in the density of lymphatic vessels, accompanied by accumulation of low-MW hyaluronan (HA) in mouse orthotopic allografts undergoing rejection. We found that stimulation of lymphangiogenesis with VEGF-C156S, a mutant form of VEGF-C with selective VEGFR-3 binding, alleviates an established rejection response and improves clearance of HA from the lung allograft. Longitudinal analysis of transbronchial biopsies from human lung transplant recipients demonstrated an association between resolution of acute lung rejection and decreased HA in the graft tissue. Taken together, these results indicate that lymphatic vessel formation after lung transplantation mediates HA drainage and suggest that treatments to stimulate lymphangiogenesis have promise for improving graft outcomes.

IPF Care: a support program for patients with idiopathic pulmonary fibrosis treated with pirfenidone in Europe

Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive, and irreversible fibrotic lung disease that requires long-term treatment. Given the importance of adherence to treatment and management of adverse events (AEs), patients with IPF need long-term, high-quality support in living with their condition, and adhering to therapy so they can derive maximum benefit. The IPF Care Patient Support Program (IPF Care) provides support, education, and empowerment to patients receiving pirfenidone for the treatment of IPF in Europe, through the provision of frequent, patient-managed discussions with specialist IPF nurses. In this review, we describe the structure of IPF Care in the United Kingdom (UK) and Austria, two of the longest-running IPF Care programs to date, and describe the benefits that these programs provide to patients with IPF. Analysis of results demonstrates a low rate of discontinuation from the program, and provides insight into the questions and concerns that patients express, not only with respect to pirfenidone (the only approved treatment for IPF at the time of analysis), but also in relation to other aspects of living with IPF. Pirfenidone dose modifications are common in patients in IPF Care and AEs most commonly occur early in treatment, with the majority of affected patients continuing on a stable maintenance dose. This highlights the value of the advice and support that patients receive in IPF Care regarding management of AEs and staying on treatment. Patient satisfaction was high in a survey of the UK program, with patients reporting high scores regarding ‘feeling in control of their condition’, ‘knowing what to expect from treatment’, and ‘feeling confident about how their disease is managed’. IPF Care in Europe will continue to evolve over time, striving to provide individually tailored support and patient-friendly information to improve treatment outcomes and quality of life for patients living with IPF.

Arginase inhibition prevents bleomycin-induced pulmonary hypertension, vascular remodeling, and collagen deposition in neonatal rat lungs

Arginase is an enzyme that limits substrate L-arginine bioavailability for the production of nitric oxide by the nitric oxide synthases and produces L-ornithine, which is a precursor for collagen formation and tissue remodeling. We studied the pulmonary vascular effects of arginase inhibition in an established model of repeated systemic bleomycin sulfate administration in neonatal rats that results in pulmonary hypertension and lung injury mimicking the characteristics typical of bronchopulmonary dysplasia. We report that arginase expression is increased in the lungs of bleomycin-exposed neonatal rats and that treatment with the arginase inhibitor amino-2-borono-6-hexanoic acid prevented the bleomycin-induced development of pulmonary hypertension and deposition of collagen. Arginase inhibition resulted in increased L-arginine and L-arginine bioavailability and increased pulmonary nitric oxide production. Arginase inhibition also normalized the expression of inducible nitric oxide synthase, and reduced bleomycin-induced nitrative stress while having no effect on bleomycin-induced inflammation. Our data suggest that arginase is a promising target for therapeutic interventions in neonates aimed at preventing lung vascular remodeling and pulmonary hypertension.

Pirfenidone in idiopathic pulmonary fibrosis: expert panel discussion on the management of drug-related adverse events

Pirfenidone is currently the only approved therapy for idiopathic pulmonary fibrosis, following studies demonstrating that treatment reduces the decline in lung function and improves progression-free survival. Although generally well tolerated, a minority of patients discontinue therapy due to gastrointestinal and skin-related adverse events (AEs). This review summarizes recommendations based on existing guidelines, research evidence, and consensus opinions of expert authors, with the aim of providing practicing physicians with the specific clinical information needed to educate the patient and better manage pirfenidone-related AEs with continued pirfenidone treatment. The main recommendations to help prevent and/or mitigate gastrointestinal and skin-related AEs include taking pirfenidone during (or after) a meal, avoiding sun exposure, wearing protective clothing, and applying a broad-spectrum sunscreen with high ultraviolet (UV) A and UVB protection. These measures can help optimize AE management, which is key to maintaining patients on an optimal treatment dose.

Arginase inhibition prevents inflammation and remodeling in a guinea pig model of chronic obstructive pulmonary disease

Airway inflammation and remodeling are major features of chronic obstructive pulmonary disease (COPD), whereas pulmonary hypertension is a common comorbidity associated with a poor disease prognosis. Recent studies in animal models have indicated that increased arginase activity contributes to features of asthma, including allergen-induced airway eosinophilia and mucus hypersecretion. Although cigarette smoke and lipopolysaccharide (LPS), major risk factors for COPD, may increase arginase expression, the role of arginase in COPD is unknown. This study aimed to investigate the role of arginase in pulmonary inflammation and remodeling using an animal model of COPD. Guinea pigs were instilled intranasally with LPS or saline twice weekly for 12 weeks and pretreated by inhalation of the arginase inhibitor 2(S)-amino-6-boronohexanoic acid (ABH) or vehicle. Repeated LPS exposure increased lung arginase activity, resulting in increased l-ornithine/l-arginine and l-ornithine/l-citrulline ratios. Both ratios were reversed by ABH. ABH inhibited the LPS-induced increases in pulmonary IL-8, neutrophils, and goblet cells as well as airway fibrosis. Remarkably, LPS-induced right ventricular hypertrophy, indicative of pulmonary hypertension, was prevented by ABH. Strong correlations were found between arginase activity and inflammation, airway remodeling, and right ventricular hypertrophy. Increased arginase activity contributes to pulmonary inflammation, airway remodeling, and right ventricular hypertrophy in a guinea pig model of COPD, indicating therapeutic potential for arginase inhibitors in this disease.

Single- and Multiple-Dose Pharmacokinetics of Pirfenidone, an Antifibrotic Agent, in Healthy Chinese Volunteers

A randomized, dose-escalating study evaluated the pharmacokinetics of single and multiple oral doses of pirfenidone, a promising antifibrotic agent, in 48 healthy Chinese volunteers. The effects of sex and food on the pharmacokinetics of pirfenidone were also evaluated. Pharmacokinetics was determined from serial blood samples obtained up to 12 hours after administration of single 200-, 400-, or 600-mg doses of pirfenidone and after multiple doses of 400 mg administrated 3 times daily (tid). Plasma levels of pirfenidone and areas under the curve were found to be proportional to dose. Pirfenidone was rapidly absorbed (t(max) = 0.33-1 hours) and cleared (t((1/2)) = 2-2.5 hours). Pharmacokinetic parameters after multiple doses were similar to those after single doses. Food had a significant effect (P < .01) on the extent of absorption (AUC(0-infinity) = 37.4 +/- 15.4 mg x h/L [fed] vs 46.6 +/- 16.8 mg x h/L [fasted]), rate of absorption was considerably (P < .001) prolonged (t(max) = 1.5 +/- 0.4 hours [fed] vs 0.7 +/- 0.2 hours [fasted]), and peak concentrations were significantly (P < .001) decreased (C(max) = 9.2 +/- 2.9 mg/L [fed] vs 13.0 +/- 1.8 mg/L [fasted]). No significant sex differences were noted for pharmacokinetic variables. Pirfenidone was well tolerated. These results support a tid regimen of pirfenidone for the management of idiopathic pulmonary fibrosis. Concomitant intake of food will reduce the rate and extent (about 20%) of absorption, which is associated with better tolerability of pirfenidone.

Role of arginase in asthma: potential clinical applications

Allergic asthma is a chronic disease with significant morbidity and mortality. It affects 300 million people worldwide and absorbs a significant amount of the healthcare budget. The predisposition to asthma is dictated by complex genetic regulation, and the asthmatic inflammation itself is characterized by the interplay of various local cells of the bronchial tree and invading inflammatory immune cells. The clinical problems of asthma are owing to intermittent airway hyper-responsiveness that can become chronic in the course of the disease. Histopathologically, infiltration with a variety of inflammatory cells, smooth muscle cell hyperplasia and hypertrophy, goblet cell hyperplasia and subepithelial fibrosis are found in asthmatic inflammatory tissue. This special report sets out to review data on the role of the enzyme arginase and L-arginine metabolism as a unifying element of asthma pathophysiology and as a potential target for future clinical asthma treatment.

Inhibitory effects of pirfenidone on dendritic cells and lung allograft rejection

BACKGROUND

Pirfenidone (PFD) is an antifibrotic agent with beneficial effects on proinflammatory disorders. In this study, we further investigated PFD and long-acting form, "deuterated PFD," immune-modulating properties by evaluating their effects on mouse dendritic cells (DCs).

METHODS

The effects of PFD on DCs were examined in vivo using an orthotopic mouse lung transplant model and in vitro using isolated bone marrow-derived DCs in response to lipopolysaccharide and allogeneic stimulation.

RESULTS

In mouse lung transplants, PFD and deuterated PFD treatment improved allograft lung function based on peak airway pressure, less infiltrates/consolidation on micro-computed tomography scan imaging, and reduced lung rejection/injury. DC activation from lung allografts was suppressed with PFD, and there seemed to be a greater effect of PFD on CD11c(+)CD11b(-)CD103(+) lung DCs. In addition, PFD reduced the expression of several proinflammatory cytokines/chemokines from lung allografts. In vitro, DCs treated with PFD showed decreased expression of major histocompatibility complex class II and costimulatory molecules and the capacity of these DCs to stimulate T-cell activation was impaired, although antigen uptake was preserved. PFD directly inhibited the release of inflammatory cytokines from isolated DCs, was associated with a reduction of stress protein kinases, and attenuated lipopolysaccharide-dependent mitogen-activated protein kinase p38 phosphorylation.

CONCLUSIONS

PFD has lung allograft protective properties, and in addition to its known effects on T-cell biology, PFD immune-modulating activities encompass inhibitory effects on DC activation and function.

Arginase and arginine dysregulation in asthma

In recent years, evidence has accumulated indicating that the enzyme arginase, which converts L-arginine into L-ornithine and urea, plays a key role in the pathogenesis of pulmonary disorders such as asthma through dysregulation of L-arginine metabolism and modulation of nitric oxide (NO) homeostasis. Allergic asthma is characterized by airway hyperresponsiveness, inflammation, and remodeling. Through substrate competition, arginase decreases bioavailability of L-arginine for nitric oxide synthase (NOS), thereby limiting NO production with subsequent effects on airway tone and inflammation. By decreasing L-arginine bioavailability, arginase may also contribute to the uncoupling of NOS and the formation of the proinflammatory oxidant peroxynitrite in the airways. Finally, arginase may play a role in the development of chronic airway remodeling through formation of L-ornithine with downstream production of polyamines and L-proline, which are involved in processes of cellular proliferation and collagen deposition. Further research on modulation of arginase activity and L-arginine bioavailability may reveal promising novel therapeutic strategies for asthma.

Simvastatin inhibits goblet cell hyperplasia and lung arginase in a mouse model of allergic asthma: a novel treatment for airway remodeling?

Airway remodeling in asthma contributes to airway hyperreactivity, loss of lung function, and persistent symptoms. Current therapies do not adequately treat the structural airway changes associated with asthma. The statins are cholesterol-lowering drugs that inhibit the enzyme 3-hydroxy-3-methyl-glutaryl-CoA reductase, which is the rate-limiting step of cholesterol biosynthesis in the mevalonate (MA) pathway. These drugs have been associated with improved respiratory health, and ongoing clinical trials are testing their therapeutic potential in asthma. We hypothesized that simvastatin treatment of ovalbumin (OVA)-exposed mice would attenuate early features of airway remodeling by a mevalonate-dependent mechanism. BALB/c mice initially were sensitized to OVA and then exposed to 1% OVA aerosol for 2 weeks after sensitization for 6 exposures. Simvastatin (40 mg/kg) or simvastatin plus MA (20 mg/kg) were injected intraperitoneally before each OVA exposure. Treatment with simvastatin attenuated goblet cell hyperplasia, arginase-1 protein expression, and total arginase enzyme activity, but it did not alter airway hydroxyproline content or transforming growth factor-β1. Inhibition of goblet cell hyperplasia by simvastatin was mevalonate-dependent. No appreciable changes to airway smooth muscle cells were observed in any control or treatment groups. In conclusion, in an acute mouse model of allergic asthma, simvastatin inhibited early hallmarks of airway remodeling, which are indicators that can lead to airway thickening and fibrosis. Statins are potentially novel treatments for airway remodeling in asthma. Additional studies using subchronic or chronic allergen exposure models are needed to extend these initial findings.

The multifaceted role of pirfenidone and its novel targets

BACKGROUND

Pirfenidone (PFD) is a molecule that exhibits antifibrotic properties in a variety of in vitro and animal models of lung, liver and renal fibrosis. These pathologies share many fibrogenic pathways with an abnormal fibrous wound-healing process; consequently, tissue repair and tissue regeneration-regulating mechanisms are altered.

OBJECTIVE

To investigate the usefulness of PFD as an antifibrotic agent in clinical and experimental models of fibrotic disease.

CONCLUSIONS

There is a growing understanding of the molecular effects of PFD on the wound healing mechanism, leading to novel approaches for the management of fibrosis in lung, liver and renal tissues. Although the optimum treatment for fibrosis remains undefined, it is possible that combined therapeutic regimens that include this wide-application molecule, pirfenidone, could offer a useful treatment for fibrotic disease.

Arginase 1 and arginase 2 variations associate with asthma, asthma severity and beta2 agonist and steroid response

RATIONALE

Arginase probably plays an important role in asthma development, severity and progression. Polymorphisms in arginase 1 and arginase 2 genes have been associated with childhood asthma and FEV1 reversibility to beta2 agonists.

OBJECTIVES

We investigated the association between arginase 1 and arginase 2 polymorphisms and adult asthma, asthma severity and treatment response in a longitudinal cohort of 200 asthma patients.

METHODS

Patients were studied during 1962-1975 and reexamined during 1990-1999, together with their families. Longitudinal data on lung function and treatment were extracted from medical records. Associations between haplotype-tagging polymorphisms in arginase 1 (n=3) and arginase 2 (n=8) and asthma, asthma severity, acute response to bronchodilators and chronic response to inhaled corticosteroids were analyzed.

MEASUREMENTS AND MAIN RESULTS

Two polymorphisms in arginase 2 (rs17249437 and rs3742879) were associated with asthma and with more severe airway obstruction. Increased airway hyperresponsiveness and lower beta2 agonist reversibility, but not anticholinergic reversibility, were associated with both arginase 1 and arginase 2. Inhaled corticosteroids slowed down the annual FEV1 decline, which was significantly less effective in homozygote carriers of the C-allele of the arginase 1 polymorphism, rs2781667.

CONCLUSION

We show that previously reported associations between arginase polymorphisms and childhood asthma are also present in adult asthma and the previously found associations with lower reversibility are specific for beta2 agonists. Furthermore, we identified associations of arginase 1 and arginase 2 genes with asthma severity, as reflected by a lower lung function, more severe airway hyperresponsiveness, and less long-term response to inhaled corticosteroids. Studies on the functionality of the polymorphisms are warranted to further unravel the complex mechanisms underlying these observations.

Abnormal expression of IGF-binding proteins, an initiating event in idiopathic pulmonary fibrosis?

For significant improvements to occur in the survival of patients with idiopathic pulmonary fibrosis (IPF), it is necessary to develop novel and more precisely targeted therapies. The selection of future appropriate regimens must critically depend on improved characterization of the molecules driving the pathogenesis of IPF. It is well defined that IPF is characterized by the expression of genes indicating an active tissue remodeling program, including extracellular matrix (ECM) and basement membrane components, as well as myofibroblast-associated and epithelial cell-related genes. A few recent advances are worth mentioning. Pulmonary research demonstrates abnormal expression of insulin-like growth factor (IGF) binding proteins (IGFBPs) in IPF, including human IPF bronchoalveolar lavage (BAL) cells and BAL fluids, human IPF fibroblasts, as well as fibrotic lung tissues of bleomycin-induced mice and IPF patients, analyzed by microarray, reverse transcription-polymerase chain reaction (RT-PCR), ribonuclease protection assay (RPA), Western blot, immunohistochemistry, or enzyme-linked immunosorbent assay (ELISA). Simultaneously, in vitro and in vivo studies indicate the involvement of IGFBPs in the initiation and development of the fibrosis process, including fibroblast activation and transdifferentiation to a myofibroblast phenotype, epithelial-mesenchymal transition (EMT), increased ECM production, and decreased ECM degradation, possibly contributing to the final lung fibrosis. These observations suggest that dysregulation of IGFBPs may be a key factor responsible for the initiation and perpetuation of IPF. Such efforts could lead to potential candidate molecules being exploited for therapeutic manipulation.

Fibrogenesis in kidney transplantation: potential targets for prevention and therapy

Kidney allograft fibrosis results from a reactive process mediated by humoral and cellular events and the activation of transforming growth factor beta1. It is a process that involves both parenchymal and graft infiltrating cells and can lead to organ failure if injury persists or if the response to injury is excessive. In this review, we will address the role of preventive and therapeutic strategies that target kidney allograft fibrogenesis. We conclude that in addition to preventive strategies, therapies based on bone morphogenetic protein 7, hepatocyte growth factor, connective tissue growth factor, and pirfenidone have shown promising results in preclinical studies. Clinical trials are needed to examine the effect of these therapies on long-term outcomes.

Alterations in lung arginine metabolism in lambs with pulmonary hypertension associated with increased pulmonary blood flow

Previous studies demonstrate impaired nitric oxide (NO) signaling in children and animal models with congenital heart defects and increased pulmonary blood flow. However, the molecular mechanisms underlying these alterations remain incompletely understood. The purpose of this study was to determine if early changes in arginine metabolic pathways could play a role in the reduced NO signaling demonstrated in our lamb model of congenital heart disease with increased pulmonary blood flow (Shunt lambs). The activities of the arginine recycling enzymes, argininosuccinate synthetase (ASS) and argininosuccinate lyase (ASL) were both decreased in lung tissues of Shunt lambs while arginase activity was increased. Associated with these alterations, lung L-arginine levels were decreased. These changes correlated with an increase in NO synthase-derived reactive oxygen species (ROS) generation. This study provides further insights into the molecular mechanisms leading to decreased NO signaling in Shunt lambs and suggests that altered arginine metabolism may play a role in the development of the endothelial dysfunction associated with pulmonary hypertension secondary to increased pulmonary blood flow.

Arginase: an emerging key player in the mammalian immune system

The enzyme arginase metabolizes L-arginine to L-ornithine and urea. Besides its fundamental role in the hepatic urea cycle, arginase is also expressed the immune system of mice and man. While significant interspecies differences exist regarding expression, subcellular localization and regulation of immune cell arginase, associated pathways of immunopathology are comparable between species. Arginase is induced in murine myeloid cells mainly by Th2 cytokines and inflammatory agents and participates in a variety of inflammatory diseases by down-regulation of nitric oxide synthesis, induction of fibrosis and tissue regeneration. In humans, arginase I is constitutively expressed in polymorphonuclear neutrophils and is liberated during inflammation. Myeloid cell arginase-mediated L-arginine depletion profoundly suppresses T cell immune responses and this has emerged as a fundamental mechanism of inflammation-associated immunosuppression. Pharmacological interference with L-arginine metabolism is a novel promising strategy in the treatment of cancer, autoimmunity or unwanted immune deviation.

Pirfenidone inhibits T-cell activation, proliferation, cytokine and chemokine production, and host alloresponses

BACKGROUND

We previously showed that pirfenidone, an anti-fibrotic agent, reduces lung allograft injury or rejection. In this study, we tested the hypothesis that pirfenidone has immune modulating activities and evaluated its effects on the function of T-cell subsets, which play important roles in allograft rejection.

METHOD

We first evaluated whether pirfenidone alters T-cell proliferation and cytokine release in response to T-cell receptor (TCR) activation, and whether pirfenidone alters regulatory T cells (CD4CD25) suppressive effects using an in vitro assay. Additionally, pirfenidone effects on alloantigen-induced T-cell proliferation in vivo were assessed by adoptive transfer of carboxyfluorescein diacetate succinimidyl ester-labeled T cells across a parent->F1 major histocompatibility complex mismatch, as well as using a murine heterotopic cardiac allograft model (BALB/c->C57BL/6).

RESULTS

Pirfenidone was found to inhibit the responder frequency of TCR-stimulated CD4 cell total proliferation in vitro and in vivo, whereas both CD4 and CD8 proliferation index were reduced by pirfenidone. Additionally, pirfenidone inhibited TCR-induced production of multiple pro-inflammatory cytokines and chemokines. Interestingly, there was no change on transforming growth factor-beta production by purified T cells, and pirfenidone had no effect on the suppressive properties of naturally occurring regulatory T cells. Pirfenidone alone showed a small but significant (P<0.05) effect on the in vivo allogeneic response, whereas the combination of pirfenidone and low dose rapamycin had more remarkable effect in reducing the alloantigen response with prolonged graft survival.

CONCLUSION

Pirfenidone may be an important new agent in transplantation, with particular relevance to combating chronic rejection by inhibiting both fibroproliferative and alloimmune responses.

Role of IL-4 and Th2 responses in allograft rejection and tolerance

PURPOSE OF REVIEW

Due to the dominance of Th1 cytokines in rejection and the ability of Th2 cytokines, particularly IL-4, to inhibit Th1 responses, it has long been held that Th2 cytokines can improve transplant outcomes. Although there is some support for this, there is mounting evidence that IL-4 and Th2 cytokines can promote graft dysfunction. These disparate effects are reviewed.

RECENT FINDINGS

The role of Th2 cytokines in graft dysfunction is not necessarily due to promotion of humoral immunity, but is due to their ability to drive T-cell and non-T-cell responses including alternative activation of macrophages. Alternatively, activated macrophages compete with classically activated macrophages for arginine and they are mutually exclusive, analogous to mutual competition between Th1 and Th2 cells. Recent findings also point to two subsets of regulatory T cells (Tregs), each dependent on either Th1 or Th2 cytokines. In addition to its effects on bone marrow-derived cells, IL-4 affects parenchymal cells by signalling through the type II receptor, which consists of the IL-4R alpha chain (IL-4Ralpha) and the IL-13Ralpha1, which also binds IL-13.

SUMMARY

The effects of Th2 cytokines in transplantation depend on their cellular targets, the timing and form of administration and on Th2 cytokine-dependent Tregs.

Current and future anti-fibrotic therapies for chronic liver disease

Chronic injury results in a wound healing response that eventually leads to fibrosis. The response is generalized, with features common among multiple organ systems. In the liver, various different types of injury lead to fibrogenesis, implying a common pathogenesis. Although several specific therapies for patients who have different liver diseases have been successfully developed, including antiviral therapies for those who have hepatitis B and hepatitis C virus infection, specific and effective antifibrotic therapy remains elusive. Over the past 2 decades, great advances in the understanding of fibrosis have been made and multiple mechanisms underlying hepatic fibrogenesis uncovered. Elucidation of these mechanisms has been of fundamental importance in highlighting novel potential therapies. Preclinical studies have indicated several putative therapies that might abrogate fibrogenesis. This article emphasizes mechanisms underlying fibrogenesis and reviews available and future therapeutics.

Cationic amino acid transporter-2 regulates immunity by modulating arginase activity

Cationic amino acid transporters (CAT) are important regulators of NOS2 and ARG1 activity because they regulate L-arginine availability. However, their role in the development of Th1/Th2 effector functions following infection has not been investigated. Here we dissect the function of CAT2 by studying two infectious disease models characterized by the development of polarized Th1 or Th2-type responses. We show that CAT2(-/-) mice are significantly more susceptible to the Th1-inducing pathogen Toxoplasma gondii. Although T. gondii infected CAT2(-/-) mice developed stronger IFN-gamma responses, nitric oxide (NO) production was significantly impaired, which contributed to their enhanced susceptibility. In contrast, CAT2(-/-) mice infected with the Th2-inducing pathogen Schistosoma mansoni displayed no change in susceptibility to infection, although they succumbed to schistosomiasis at an accelerated rate. Granuloma formation and fibrosis, pathological features regulated by Th2 cytokines, were also exacerbated even though their Th2 response was reduced. Finally, while IL-13 blockade was highly efficacious in wild-type mice, the development of fibrosis in CAT2(-/-) mice was largely IL-13-independent. Instead, the exacerbated pathology was associated with increased arginase activity in fibroblasts and alternatively activated macrophages, both in vitro and in vivo. Thus, by controlling NOS2 and arginase activity, CAT2 functions as a potent regulator of immunity.

Pirfenidone: a novel potential therapeutic agent in the management of chronic allograft rejection

Chronic allograft dysfunction is a leading cause of allograft failure, morbidity, and mortality after solid organ transplantation. The pathogenesis of chronic allograft failure has a final common pathway leading to organ fibrosis. Pirfenidone is an effective and novel antifibrotic agent with anti-inflammatory properties. Clinical use of the agent has been tested in a number of nontransplant recipients and has a favorable safety profile based on available clinical data. Building on these observations and findings, and considering the role of fibrosis in chronic allograft rejection, pirfenidone was initially investigated as adjunct therapy in a rat heterotopic tracheal transplantation model. This led to several studies confirming that pirfenidone may well be worth considering for further investigation. This paper reviews the possibility of using pirfenidone in clinical transplantation management.

Nonviral gene delivery with indoleamine 2,3-dioxygenase targeting pulmonary endothelium protects against ischemia-reperfusion injury

Pulmonary endothelial dysfunction induced by inflammation and inflammation-associated reactive oxygen species is a central component in the pathophysiology of lung transplant ischemia-reperfusion (IR) injury. Indoleamine-2,3-dioxygenase (IDO) is a unique cytosolic enzyme possessing both immune modulating and antioxidant properties. This study investigated whether enhanced pulmonary endothelial IDO activity by a targeted nonviral gene transfer approach ameliorates lung IR injury. Orthotopic syngeneic lung transplants were performed in Lewis rats. A human IDO (hIDO)-expressing plasmid driven by an endothelial cell-specific endothelin-1 promoter was generated and intravenously delivered to donor lung using cationic polymer polyethylenimine. This nonviral gene transfer approach augmented hIDO expression specifically in endothelial cells within lung grafts. Importantly, enhanced IDO activity induced by the hIDO transgene prevented endothelial cell apoptosis, reduced vascular permeability and leukocyte extravasation, and consequently improved graft function and histologic appearance. Furthermore, our in vitro studies showed that increased IDO activity in endothelial cells protected its mitochondrial function and ultrastructure from oxidative stress through stabilization of intracellular redox status. The approach used in these experiments has properties that could eliminate the inherent side effects associated with viral vectors and/or antibody-directed targeted therapy, and thus may represent a potential therapeutic strategy against lung IR injury in patients.

Allograft inflammatory factor-1 and its immune regulation

The allograft inflammatory factor-1 (AIF-1) is a 17 kDa interferon-gamma (IFN-gamma) inducible Ca(2+)-binding EF-hand protein that is encoded within the HLA class III genomic region. Three proteins including ionized Ca(2+)-binding adaptor 1, microglia response factor-1, and daintain are identical with AIF-1. The expression of AIF-1 was mostly limited to the monocyte/macrophage lineage, and augmented by cytokines such as IFN-gamma. It was assumed that AIF-1 was a novel molecule involved in inflammatory responses, allograft rejection, as well as the activation and function of macrophages. However, it has been reported that AIF-1 is also expressed in macrophages and microglial cells in autoimmune diseases such as experimental autoimmune encephalomyelitis, neuritis and uveitis models, suggesting that AIF-1 may play a pivotal role in autoimmunity. In the present manuscript, the genomic and functional characteristics of AIF-1 family proteins as well as their immune regulatory effects are reviewed.

Sleeping Beauty-based gene therapy with indoleamine 2,3-dioxygenase inhibits lung allograft fibrosis

Sleeping Beauty (SB) transposon is a natural nonviral gene transfer system that can mediate long-term transgene expression. Its potential utility in treating organ transplantation-associated long-term complications has not yet been explored. In the present study we generated an improved SB transposon encoding the human gene indoleamine-2,3-dioxygenase (hIDO), an enzyme that possesses both T cell-suppressive and antioxidant properties and selectively delivered the SB transposon in combination with a hyperactive transposase plasmid to donor lung using the cationic polymer polyethylenimine (PEI) as transfection reagent. This nonviral gene therapeutic approach led to persistent and uniform transgene expression in the rat lung tissue without noticeable toxicity and inflammation. Importantly, IDO activity produced by hIDO transgene showed a remarkable therapeutic response, as evident by near normal pulmonary function (peak airway pressure and oxygenation), histological appearance, and reduced collagen content in lung allografts. In addition, we established a hIDO-overexpressing type II cell line using the SB-based gene transfer system and found that hIDO-overexpressing lung cells effectively inhibited transforming growth factor-beta-stimulated fibroblast proliferation in vitro. In summary, the SB-based gene therapy with hIDO represents a new strategy for treating lung transplantation-associated chronic complications, e.g., obliterative bronchiolitis.