• Welcome to Crohn's Forum, a support group for people with all forms of IBD. While this community is not a substitute for doctor's advice and we cannot treat or diagnose, we find being able to communicate with others who have IBD is invaluable as we navigate our struggles and celebrate our successes. We invite you to join us.

Anti-fibrotics in Treatment of Crohn's Disease – Lessons Learnt from other Diseases

Anti-fibrotics in Treatment of Crohn's Disease – Lessons Learnt from other Diseases

Review Article: Anti-fibrotic Agents for the Treatment of Crohn's Disease – Lessons Learnt from other Diseases

Alimentary Pharmacology & Therapeutics. 2009;31(2):189-201. © 2009 Blackwell Publishing

Abstract and Introduction
Abstract
Background The current therapies for Crohn's disease (CD) are mainly focused on blockade of inflammation. Fibrosis remains one of the major complications of CD often leading to surgery, affecting patients' quality-of-life.
Aim To summarize the published data regarding the potential anti-fibrotic role of drugs commonly used in CD and the most effective anti-fibrotic drugs used in other diseases evaluating their potential use to treat intestinal fibrosis in CD.
Methods A literature search was performed in the PubMed, Medline, Cochrane and EMBASE databases, considering in vitro, animal and human studies on fibrosis in inflammatory bowel disease and other similar chronic pathologies.
Results Treatment of fibrosis in CD is limited to surgery or endoscopic dilatation, although some of the drugs currently used may have anti-fibrotic activity. In other diseases, anti-fibrotic agents are already used or are in preclinical or clinical trials. ACE inhibitors, Angiotensin Receptor Blockers, and HMG-CoA inhibitors merit further investigation in CD because of their role in preventing fibrosis in cardiovascular and renal diseases.
Conclusions Anti-fibrotic drugs are under evaluation or already used in clinical practice in other chronic inflammatory diseases. In CD, there is a great need for investigation into agents that may prevent, reduce or reverse intestinal fibrosis.


Introduction
Although numerous findings in the field of immunopathology have identified dozens of possible target molecules for the treatment of the inflammatory bowel diseases (IBD),[1] in this article, we concentrate on a less understood, but clinically highly relevant aspect: intestinal fibrosis in Crohn's disease (CD), one of the two major forms of IBD. Chronic inflammation plays a crucial role in fibrotic changes, by disrupting the natural balance of pro- and anti-fibrotic mechanisms. Transmural inflammation because of dysregulated wound healing mechanisms leads to fibrotic stenosis in one-third of patients with CD.[2, 3] In the absence of a reliable marker, ongoing fibrosis and consequent stricture development is often not diagnosed until the process is already irreversible. Being the most common indication for surgical intervention, this very frequent complication of CD can significantly influence the patients' quality-of-life.

The pathogenesis of fibrosis in CD remains poorly understood. Some studies have shown that transforming growth factor (TGF) β1, acting together with SMAD proteins and insulin growth factor (IGF) 1, plays a crucial role in promoting gene transcription for collagenous proteins, especially type III collagen and fibronectin. In addition, fibroblast contraction is facilitated by the hyperexpression of TGFβ1.[4] Investigation into a possible linkage between fibrostenotic CD and gene mutations has demonstrated that any mutation of the NOD2/CARD15 gene concerning R702W, G908R and 3020InsC sequences is frequently associated with this particular phenotype. Fibrosis is also more frequent in patients presenting the V249 CX3CR1 allele polymorphism.[5]

Chronic inflammation can affect almost every human tissue, causing fibrotic changes that significantly impair organ function, with associated therapeutic challenges. Fibrogenesis in every tissue, including the gut, is a complex process characterized by increased production of components of the extracellular matrix (ECM) by activated myofibroblasts. These may be the differentiation of stem cells, perycites, fibrocytes or stellate cells that are activated by cytokines, chemokines and growth factors (Figure 1).[6] The possible inhibitory mechanisms have been examined in several pathologies affecting different organs, such as systemic sclerosis, liver cirrhosis, nephrosclerosis in diabetic and IgA nephropathy, rheumatoid arthritis, and chronic pancreatitis.[7–10] In spite of all the progress that has been made in advancing our understanding of the pathophysiology of these conditions, clinical treatment remains a major challenge. The traditional medical interventions have focused on symptom control and the slowing down of disease progression. Although some of the currently available therapeutics display antifibrotic effects, they are unable to taper pro-fibrotic changes.


Methods
A literature review was performed by searching for the terms 'fibrosis', 'anti-fibrotic' and 'fibrogenesis', combined with the terms 'corticosteroid', 'anti-TNFα', 'azathioprine', 'cyclophosphamide', 'methotrexate', 'systemic sclerosis', 'liver cirrhosis', 'pulmonary fibrosis', 'nephrosclerosis', 'rheumatoid arthritis', 'retroperitoneal fibrosis' and 'cardiac remodelling', in the PubMed, Medline, Cochrane and EMBASE databases. All relevant articles in English published by May 2009 were reviewed. Data were analysed from several in vitro, animal and human studies of fibrosis, pro- and anti-fibrotic therapeutic approaches in IBD and several other pathologies affecting different organs. Reviewed anti-fibrotic agents and their effects on fibrosis are summarized in Table 1.

Results
The Anti-fibrotic Effect of Therapeutics Currently Used for the Treatment of CD
The agents that are currently used for the treatment of CD are not intended to act on intestinal fibrosis, but to reduce inflammation and relieve the patients' symptoms. Nonetheless, some of these agents display additional anti-fibrotic effects.

Corticosteroids are important for controlling inflammation and are used for the treatment of many different pathologies. The anti-fibrotic effect of corticosteroids is a very well-known phenomenon, causing deficiency in general wound healing. This effect results from a decrease in collagen synthesis[3] and for this reason, positive effects have been observed with corticosteroids in other fibrotic diseases, such as retroperitoneal fibrosis,[6, 7] systemic sclerosis[8] and idiopathic pulmonary fibrosis.[9, 10] However, there are several drawbacks associated with steroid use: first of all, long-term systemic use of steroids is not recommended because of several significant side effects and secondly, there is some doubt as to whether this anti-fibrotic action occurs in intestinal smooth muscle cells. Indeed, these cells appear refractory to corticosteroids in vitro, as the administration of dexamethasone increased expression of the procollagen gene.[11] In spite of these data, promising results have been obtained with local endoscopic injections of cortisone in patients undergoing endoscopic dilation for fibrotic strictures due to CD,[12] although a recent study has been giving negative results.[13] Further evidence with controlled studies is necessary to confirm these observations.

Azathioprine, the most common immunosuppressive agent used for the treatment of patients with CD, along with other immunosuppressant agents, such as cyclophosphamide and methotrexate, has been used for the treatment of several chronic inflammatory diseases. This drug was effective for the treatment of mild cases of retroperitoneal fibrosis or in severe disease for maintenance therapy after intravenous cyclophosphamide treatment[14] and may have some additional effects when administered with corticosteroids in fibrotic pulmonary disease.[10, 15–17] The successful use of azathioprine in preventing post-operative recurrence of CD, even in the absence of studies designed to evaluate its effect on intestinal fibrosis, supports the hypothesis that thiopurines can prevent or at least slow the fibrotic process in patients with CD.[18]

The role of TNF-α in intestinal fibrogenesis and the effect of anti-TNF-α agents on fibrotic strictures were not clear for a long time. TNF-α is potentially an anti-fibrogenetic factor, with inhibition therefore theoretically favouring fibrosis. In addition, the mucosal healing effects of anti-TNFα agents suggest that, besides healing, they may induce fibrotic changes in the layers of the intestinal wall.[19, 20] Indeed, early reports seemed to confirm this theory, as obstructive complications were observed in some patients administered infliximab.[21–23] For a long period, its use in cases of known intestinal stenosis was discouraged, even by the manufacturer, although later, multivariable analysis of the data from the observational TREAT registry and the ACCENT I multi-centre trial demonstrated that disease duration, disease severity, ileal disease and new corticosteroid use are the only factors associated with stricture formation.[24] The first positive results with anti-TNF-α therapy were reported in cases of inflammatory or mixed stenosis, but as the diagnostic strategies for characterizing the nature of intestinal strictures were still being evaluated, these reports did not change clinical practice.[25, 26]
 
The role of TNF-α in intestinal fibrogenesis and the effect of anti-TNF-α agents on fibrotic strictures were not clear for a long time. TNF-α is potentially an anti-fibrogenetic factor, with inhibition therefore theoretically favouring fibrosis. In addition, the mucosal healing effects of anti-TNFα agents suggest that, besides healing, they may induce fibrotic changes in the layers of the intestinal wall.[19, 20] Indeed, early reports seemed to confirm this theory, as obstructive complications were observed in some patients administered infliximab.[21–23] For a long period, its use in cases of known intestinal stenosis was discouraged, even by the manufacturer, although later, multivariable analysis of the data from the observational TREAT registry and the ACCENT I multi-centre trial demonstrated that disease duration, disease severity, ileal disease and new corticosteroid use are the only factors associated with stricture formation.[24] The first positive results with anti-TNF-α therapy were reported in cases of inflammatory or mixed stenosis, but as the diagnostic strategies for characterizing the nature of intestinal strictures were still being evaluated, these reports did not change clinical practice.[25, 26]

More recently, new imaging techniques such as magnetic resonance imaging (MRI) combined with use of oral and intravenous contrast media or contrast-enhanced computer tomography have helped to distinguish inflammatory and fibrotic strictures; however, the cost and availability of these examinations remain an important limiting factor in the clinical setting.[27] Bench research has also demonstrated that, besides reducing inflammation, anti-TNF-α agents have anti-fibrotic effects. In in vitro studies involving isolated CD myofibroblasts, infliximab modulated the migratory potential of these cells, as well as collagen and tissue inhibitor of metalloproteases (TIMP)-1 production.[28] In addition, serum levels of basic fibroblast growth factor and vascular endothelial growth factor (VEGF), both involved in intestinal fibrosis, were decreased in patients treated with infliximab.[29] A case series involving three patients with stricturing CD showed that intralesional injection of infliximab in patients with colonic strictures because of the disease resulted in a dilation of the stricture itself.[30] Another retrospective study on a small number of patients (n = 18) has shown efficacy of infliximab in stricturing symptomatic CD.[31] These results suggest that anti-TNF-α treatment might be effective in the early stages, when fibrogenesis is still reversible.[32–34]

In animal models of liver fibrosis induced by CCl4, or a methionine- and choline-deficient diet, infliximab was hepatoprotective, reducing both necro-inflammation and fibrogenesis.[35] Early clinical studies in idiopathic and collagen vascular disease-associated pulmonary fibrosis suggested that blockade of TNF-α may stabilize the progression of fibrosis; however, no conclusions could be drawn because of the small number of patients and lack of control group.[36, 37] An open-label pilot study evaluated the effect of short-term infliximab treatment in 16 patients with systemic sclerosis. After 22 weeks of treatment with infliximab, secretion of type I collagen from lesional fibroblast cultures was significantly reduced compared with baseline; however, no changes in the expression of TGF-β1 were reported. In addition, a trend of improvement in skin score was noted, although the high number of adverse events and anti-infliximab antibody formation (in one-third of the subjects) suggested that an additional immunosuppressive therapy should be considered in subsequent trials.[38]

No data are yet available on adalimumab and certolizumab, even though it is reasonable to surmise that they could demonstrate the same efficacy as infliximab in the treatment or prevention of fibrosis. No data are available for natalizumab at the moment and no studies investigating the effects of 5 aminosalycilic acid (5-ASA) on fibrosis have been published thus far. Only one study has shown induction of fibrotic colonopathy in animals treated by resins such as Eudragit, which is normally used as coat for mesalazine (mesalamine) compounds.[39] As no cases of mesalazine-induced intestinal fibrosis have been reported, we can conclude that mesalazine has no significant effects, profibrotic or antifibrotic, in patients with CD.

Possible Future Candidates for the Treatment of Fibrosis in Patients with CD
The main goal in the treatment of any chronic inflammatory disease is to prevent the development of fibrosis in the first place. Reversal of fibrosis is also an important aim to achieve, but this may present more of a challenge. Understanding the stage at which fibrosis starts in patients with CD, as well as how to follow-up fibrosis in the intestine of these patients, is a big challenge for clinicians. Most of the drugs acting on chronic inflammation, such as TGFβ blockers, statins, inhibitors of angiotensin converting enzyme or molecules acting on angiogenesis, may also prevent fibrosis. Several drugs have been used in fibrotic disease, expecially in the treatment of early stage fibrosis, including colchicine, tamoxifene, mycophenolate mofetil or avotermin.

Focus on: TGF-β Pathways and Possible Targets. In the last few years, TGF-β and its extra- and intracellular pathways have become the most studied subject in the field of fibrosis because of promising results observed in early in vitro studies.[39–42] TGFβ is a profibrogenic cytokine involved in fibrosis in many body systems, including intestinal fibrosis in patients with CD. The TGFβ1 isoform is actively implicated in promoting extracellular matrix (ECM) synthesis and contraction of fibroblasts.[5] The pathway TGFβ/SMADs plays a crucial role in promoting fibrosis in patients with CD.[43] In this pathway, TGFβ receptor I kinase phophorylates Smad2 and Smad3, which then bind to the common mediator Smad4 and translocate to the nucleus to regulate gene transcription (as shown in Figure 2). This mechanism is regulated by two other inhibitory Smad proteins (Smad6 and Smad7) that compete for the TGFβ receptor I kinase and inhibit phosphorylation of Smad.[44, 45] Both TGFβ and its receptors are overexpressed in intestinal cells of patients with CD.[42] It has been observed that myofibroblasts isolated from the strictured bowel overexpress collagen type III and fibronectin.[46] The production of ECM components and of collagen type I is increased in response to the action of TGFβ.[47, 48] This cytokine can facilitate fibrogenesis by stimulating production of TIMP-1 or inhibiting expression of matrix metalloproteinases (MMPs).[49] Finally, TGFβ1 enhances myofibroblast contractile activity, predisposing to scar contraction and stricture development.[50] Overall, these data indicate that the TGFβ/SMAD pathway might be a possible target for new anti-fibrotic drugs for the treatment of patients with CD.

The first line of possible blockade is the neutralization of soluble TGF-β. The first clinical trial was performed with metelimumab (CAT-192), a monoclonal antibody that binds to the TGF-β1 isoform. This multi-centre study compared intravenously administered metelimumab to placebo in 45 patients with systemic sclerosis. However, no improvement in disease activity was observed in the group administered the active compound and a greater frequency of adverse events was reported in these patients.[51] An antibody that binds to the TGF-β2 isoform has been tested in an animal model of glaucoma surgery in which subconjunctival injection of the antibody significantly reduced post-surgical collagen deposition.[52] Finally, the pan-specific anti-TGFβ antibody GC1008 is currently being investigated for the treatment of idiopathic pulmonary fibrosis, focal segmental glomerulosclerosis, renal carcinoma and melanoma malignum.[53–55]

As TGF-β is not only involved in profibrotic mechanisms but is also one of the most important factors in cell-to-cell communication and cell transformation, the total blockade of this growth factor will likely be problematic in humans. Thus, the aim of more recent studies has been to identify more selective, but nonetheless effective inhibitors. Membrane integrin αvβ6 catalyses the activation of latent TGF-β on epithelial cells.[56] It has been investigated in two animal models of pulmonary fibrosis, and has demonstrated efficacy for the treatment of both radiation and bleomycin-induced experimental fibrosis.[57, 58]

Intracellular signalling by TGF-β could trigger profibrotic changes though two possible pathways: the canonical and unique TGF-β SMAD pathway and the so called non-SMAD pathways, which are shared with different cytokines and growth factors.[59] The first possible target of the SMAD signalling axis is activine-like receptor kinase 5 (ALK5), a transmembrane serine–threonine kinase that induces phosphorylation of cytoplasmatic SMAD2 and SMAD3 in response to activation of the TβR1 TGF-β receptor. In the first studies reported in experimental models, ALK5 inhibitors abrogated activation of fibroblasts,[60] but in clinical trials, undesirable effects have been reported because of high cross-reactivity with other kinase inhibitors.[61]

Hepatic growth factor (HGF) proved to be a natural inhibitor of SMAD2/SMAD3 nuclear translocation in fibroblasts.[62] HGF was successfully used in various animal models of chronic kidney disease and liver fibrosis; however, any use of HGF in humans needs to take into serious consideration the potential for increased risk of hepatocellular carcinoma.[62–65]
 
More recently, new imaging techniques such as magnetic resonance imaging (MRI) combined with use of oral and intravenous contrast media or contrast-enhanced computer tomography have helped to distinguish inflammatory and fibrotic strictures; however, the cost and availability of these examinations remain an important limiting factor in the clinical setting.[27] Bench research has also demonstrated that, besides reducing inflammation, anti-TNF-α agents have anti-fibrotic effects. In in vitro studies involving isolated CD myofibroblasts, infliximab modulated the migratory potential of these cells, as well as collagen and tissue inhibitor of metalloproteases (TIMP)-1 production.[28] In addition, serum levels of basic fibroblast growth factor and vascular endothelial growth factor (VEGF), both involved in intestinal fibrosis, were decreased in patients treated with infliximab.[29] A case series involving three patients with stricturing CD showed that intralesional injection of infliximab in patients with colonic strictures because of the disease resulted in a dilation of the stricture itself.[30] Another retrospective study on a small number of patients (n = 18) has shown efficacy of infliximab in stricturing symptomatic CD.[31] These results suggest that anti-TNF-α treatment might be effective in the early stages, when fibrogenesis is still reversible.[32–34]

In animal models of liver fibrosis induced by CCl4, or a methionine- and choline-deficient diet, infliximab was hepatoprotective, reducing both necro-inflammation and fibrogenesis.[35] Early clinical studies in idiopathic and collagen vascular disease-associated pulmonary fibrosis suggested that blockade of TNF-α may stabilize the progression of fibrosis; however, no conclusions could be drawn because of the small number of patients and lack of control group.[36, 37] An open-label pilot study evaluated the effect of short-term infliximab treatment in 16 patients with systemic sclerosis. After 22 weeks of treatment with infliximab, secretion of type I collagen from lesional fibroblast cultures was significantly reduced compared with baseline; however, no changes in the expression of TGF-β1 were reported. In addition, a trend of improvement in skin score was noted, although the high number of adverse events and anti-infliximab antibody formation (in one-third of the subjects) suggested that an additional immunosuppressive therapy should be considered in subsequent trials.[38]

No data are yet available on adalimumab and certolizumab, even though it is reasonable to surmise that they could demonstrate the same efficacy as infliximab in the treatment or prevention of fibrosis. No data are available for natalizumab at the moment and no studies investigating the effects of 5 aminosalycilic acid (5-ASA) on fibrosis have been published thus far. Only one study has shown induction of fibrotic colonopathy in animals treated by resins such as Eudragit, which is normally used as coat for mesalazine (mesalamine) compounds.[39] As no cases of mesalazine-induced intestinal fibrosis have been reported, we can conclude that mesalazine has no significant effects, profibrotic or antifibrotic, in patients with CD.

Possible Future Candidates for the Treatment of Fibrosis in Patients with CD
The main goal in the treatment of any chronic inflammatory disease is to prevent the development of fibrosis in the first place. Reversal of fibrosis is also an important aim to achieve, but this may present more of a challenge. Understanding the stage at which fibrosis starts in patients with CD, as well as how to follow-up fibrosis in the intestine of these patients, is a big challenge for clinicians. Most of the drugs acting on chronic inflammation, such as TGFβ blockers, statins, inhibitors of angiotensin converting enzyme or molecules acting on angiogenesis, may also prevent fibrosis. Several drugs have been used in fibrotic disease, expecially in the treatment of early stage fibrosis, including colchicine, tamoxifene, mycophenolate mofetil or avotermin.

Focus on: TGF-β Pathways and Possible Targets. In the last few years, TGF-β and its extra- and intracellular pathways have become the most studied subject in the field of fibrosis because of promising results observed in early in vitro studies.[39–42] TGFβ is a profibrogenic cytokine involved in fibrosis in many body systems, including intestinal fibrosis in patients with CD. The TGFβ1 isoform is actively implicated in promoting extracellular matrix (ECM) synthesis and contraction of fibroblasts.[5] The pathway TGFβ/SMADs plays a crucial role in promoting fibrosis in patients with CD.[43] In this pathway, TGFβ receptor I kinase phophorylates Smad2 and Smad3, which then bind to the common mediator Smad4 and translocate to the nucleus to regulate gene transcription (as shown in Figure 2). This mechanism is regulated by two other inhibitory Smad proteins (Smad6 and Smad7) that compete for the TGFβ receptor I kinase and inhibit phosphorylation of Smad.[44, 45] Both TGFβ and its receptors are overexpressed in intestinal cells of patients with CD.[42] It has been observed that myofibroblasts isolated from the strictured bowel overexpress collagen type III and fibronectin.[46] The production of ECM components and of collagen type I is increased in response to the action of TGFβ.[47, 48] This cytokine can facilitate fibrogenesis by stimulating production of TIMP-1 or inhibiting expression of matrix metalloproteinases (MMPs).[49] Finally, TGFβ1 enhances myofibroblast contractile activity, predisposing to scar contraction and stricture development.[50] Overall, these data indicate that the TGFβ/SMAD pathway might be a possible target for new anti-fibrotic drugs for the treatment of patients with CD.

The first line of possible blockade is the neutralization of soluble TGF-β. The first clinical trial was performed with metelimumab (CAT-192), a monoclonal antibody that binds to the TGF-β1 isoform. This multi-centre study compared intravenously administered metelimumab to placebo in 45 patients with systemic sclerosis. However, no improvement in disease activity was observed in the group administered the active compound and a greater frequency of adverse events was reported in these patients.[51] An antibody that binds to the TGF-β2 isoform has been tested in an animal model of glaucoma surgery in which subconjunctival injection of the antibody significantly reduced post-surgical collagen deposition.[52] Finally, the pan-specific anti-TGFβ antibody GC1008 is currently being investigated for the treatment of idiopathic pulmonary fibrosis, focal segmental glomerulosclerosis, renal carcinoma and melanoma malignum.[53–55]

As TGF-β is not only involved in profibrotic mechanisms but is also one of the most important factors in cell-to-cell communication and cell transformation, the total blockade of this growth factor will likely be problematic in humans. Thus, the aim of more recent studies has been to identify more selective, but nonetheless effective inhibitors. Membrane integrin αvβ6 catalyses the activation of latent TGF-β on epithelial cells.[56] It has been investigated in two animal models of pulmonary fibrosis, and has demonstrated efficacy for the treatment of both radiation and bleomycin-induced experimental fibrosis.[57, 58]

Intracellular signalling by TGF-β could trigger profibrotic changes though two possible pathways: the canonical and unique TGF-β SMAD pathway and the so called non-SMAD pathways, which are shared with different cytokines and growth factors.[59] The first possible target of the SMAD signalling axis is activine-like receptor kinase 5 (ALK5), a transmembrane serine–threonine kinase that induces phosphorylation of cytoplasmatic SMAD2 and SMAD3 in response to activation of the TβR1 TGF-β receptor. In the first studies reported in experimental models, ALK5 inhibitors abrogated activation of fibroblasts,[60] but in clinical trials, undesirable effects have been reported because of high cross-reactivity with other kinase inhibitors.[61]

Hepatic growth factor (HGF) proved to be a natural inhibitor of SMAD2/SMAD3 nuclear translocation in fibroblasts.[62] HGF was successfully used in various animal models of chronic kidney disease and liver fibrosis; however, any use of HGF in humans needs to take into serious consideration the potential for increased risk of hepatocellular carcinoma.[62–65]

Two other natural inhibitors are currently undergoing preclinical investigation: the proteins BMP-7 and decorin, both of which appear to inhibit the effects of TGFβ including fibrogenesis. Both agonists and antagonists of BMP-7 have been investigated; although administration of recombinant BMP-7 significantly enhanced liver regeneration[66] and ameliorated interstitial fibrosis in different chronic kidney disease models,[67–69] no effects on bleomycin-induced skin and liver fibrosis were observed.[70] In cultured human heart fibroblasts that were isolated after mechanical circulatory support (MCS), decorin levels were significantly higher than prior to MCS, which was associated with decreased collagen synthesis and an increase in p-SMAD2 levels downstream of the TGF-β pathway.[71]
 
The non-SMAD pathway is composed of various tyrosine kinases, among which one of the most well known is c-Abelson (c-Abl), part of the Bcr-Abl oncogene. Experimental blockade of this pathway and subsequent human studies have progressed faster, as tyrosine-kinase inhibitors of c-Abl are already used for the treatment of chronic myelogenous leukaemia (CML). Of these agents, imatinib (Gleevec) has completely changed the treatment of CML since its introduction a few years ago. In addition, this agent inhibits the tyrosine kinase of platelet-derived growth factor, a cytokine that stimulates fibroblast transformation and proliferation.[72] Clinical trials are currently underway to evaluate the anti-fibrotic effects of imatinib in pulmonary fibrosis, systemic sclerosis, liver cirrhosis and chronic kidney disease.[67, 72–78] Moreover, two other tyrosine kinase inhibitors, dasatinib (Sprycel) and nilotinib (Tasigna), have recently been approved for the treatment of CML. In addition to inhibiting abl-kinases and the PDGF receptor, nilotinib inhibits src- kinases,[79] and both nilotinib and dasatinib inhibit abl-kinases more potently than imatinib.[80]

One case report has been published describing the use of imatinib in a patient with CD. The patient had chronic active disease and was treated with oral corticosteroids and mesalazine, then with infliximab. After a subsequent diagnosis of BCR-ABL (Philadelphia chromosome) positive CML, the patient was started on hydroxyurea and then imatinib therapy. For reasons of haematological co-morbidity, infliximab was discontinued, yet the patient continued to report general well being and suspended both prednisone and mesalazine on his own initiative. Surprisingly, the formerly active disease remained asymptomatic with imatinib monotherapy for 3 years; however, no information was provided about the possible structural nature of the disease.[81]

Turnover of the Extracellular Matrix. A common finding in fibrotic diseases is an imbalance between the synthesis and degradation of ECM proteins. As MMPs degradate the ECM, they were expected to have beneficial effects on nephrosclerosis, but the effects observed in preclinical studies indicate that the situation is much more complex.[82] Downregulation of TIMP should also ameliorate fibrosis, but deletion of TIMP in mice did not increase renal fibrosis.[83] The importance of degradation of the ECM was also recognized in liver fibrosis and the possible therapeutic use of MMPs or TIMP inhibitors are under evaluation;[84] however, other factors such as cross-linking of the ECM and the resulting degradation of inhibitory transglutaminases might also bear consideration.[85]

HMG-CoA Reductase Inhibitors. Anti-inflammatory and anti-fibrotic effects of the widely used cholesterol level-lowering HMG-CoA reductase inhibitors (statins) have been examined in several in vitro studies.[86–91] The first interest in this potential new therapeutic use of statins came from the field of nephrology, with numerous works reporting the ability of these drugs to reduce proteinuria and alleviate pathological changes in chronic nephropathy.[86] Administration of provastatin to an animal model of chronic ciclosporin induced nephropathy; indeed not only did it reduce the local level of the inflammatory markers ostepontin and C-reactive protein (CRP), and decreased the expression of pro-fibrotic TGF-β, but it also downregulated both monocyte chemoattractant protein-1 and macrophage infiltration in the renal tissue.[87] Provastatin also supressed proliferation of mesangial cells, expression of TGF-β and the production of the ECM components fibronectin and type IV collagen in vitro in cultured activated renal mesenchymal cells.[87–89] In the deoxycorticosterone-acetate-salt hypertension rat model of renal disease, fluvastatin decreased mortality, glomerular proliferation, macrophage infiltration and glomeruloscerosis.[90] In spite of these results, existing data still do not support the prescription of statins unless there is associated cardiovascular co-morbidity or dyslipidaemia. Multi-centre clinical trials are currently underway to evaluate the effect of statins on proteinuria in diabetic and non-diabetic patients with renal disease, as it is a marker of the progression of renal damage that leads to fibrosis. Positive results might be a basis to investigate statins as anti-fibrotic progression agents.[86, 92, 93]

Although fewer studies have investigated the effects of statins in pulmonary fibrosis, the data obtained are very similar. Administration of simvastatin to human lung fibroblasts isolated from patients with idiopathic pulmonary fibrosis significantly downregulated expression of the connective tissue growth factor (CTGF) gene, which together with TGF-β, plays an important role in profibrotic mechanisms.[91]

Atorvastatin is the only statin that has been studied in patients with CD. However, despite the fact that the currently published studies only involved a small number of patients, nonetheless they indicate that that atorvastatin may decrease plasma levels of CXCL10, a ligand for CXCR3 receptor, thus blocking recruitment of T-cells and the perpetuation of inflammation that may cause fibrosis over the long-term. Two small studies have shown the anti-inflammatory effects of atorvastatin in patients with CD, where it reduces plasma levels of several inflammatory markers, such as claprotectin, CRP, TNF and other chemokines.[92–95] Larger randomized controlled trials are needed to confirm these preliminary results, as well as to investigate effects on fibrogenesis as a primary outcome.
 
Further support for the use of atorvastatin may come from studies of other diseases, especially cardiac remodelling, although the data from trials in humans were not unequivocal. In the UNIVERSE multi-centre trial, atorvastatin did not ameliorate left ventricular remodelling in heart failure patients compared with placebo. On the other hand, in a randomized trial of atorvastatin for reduction of myocardial damage during elective angioplasty, there was a significant reduction in myocardial injury in patients pretreated with statins.[96, 97] A phase III trial is currently underway that is examining the effect of rosuvastatin on left ventricular remodelling in patients with dilated cardiomyopathy.[98]

Promising results have been obtained with pravastatin in radiation-induced intestinal fibrosis, as it decreases the level of CTGF through the Rho/ROCK pathway, and modulates the secretory phenotype of mesenchymal cells, thus reducing the production of fibronectin and type one collagen both in human explants and smooth muscle cells isolated from radiation enteropathy.[99] Administration of pravastatin has also improved radiation enteropathy in rats.[99] Finally, Burke et al. demonstrated that the anti-fibrotic effect of simvastatin is based on the inhibition of SMAD-3 phosphorylation, thus decreasing TGF-β1-mediated activation of intestinal fibroblasts.[100]

Angiotensin-blocking Agents. Angiotensin II (AT-II), part of the renin-angiotensin System (RAS), appears to play a key role in promoting fibrosis in several organs, by interaction with TGF-β1.[101] In cardiac and renal fibrosis, production of TGF-β1 may be enhanced by AT-II. Recently, a significant relationship was observed between inheritance of high TGF-β1 and angiotensin-producing genotypes, and the development of progressive hepatic fibrosis. Angiotensin also influences ECM accumulation by increasing expression of plasminogen activator inhibitor-1 (PAI-1), which increases the levels of MMPs.[101]

Hypertension and fibrosis are often connected, as in hypertensive nephropathy, or portal hypertension in hepatic fibrosis. Moreover, in the latter case, a more direct role has been demonstrated, as hepatic stellate cells were found to bear AT1 receptors, while AT-II stimulated synthesis of collagen and expression of TGF-β.[102, 103] Thus, in these pathologies, the renin-angiotensin system may be a good target for anti-fibrotic agents.

The importance of hypertension has also been demonstrated in a retrospective analysis of the anti-fibrotic effects of various angiotensin-convertase enzyme inhibitors (ACEI) and angiotensin receptor blockers (ARB) on liver fibrosis in hepatitis C virus (HCV) positive patients. Three groups of patients were examined, one of normotensive subjects, one that received ACEI or ARB and one that received other anti-hypertensive drugs. In the normotensive group, activation of the renin-angiotensin system by hypertension had a negative effect on the progression of liver fibrosis; however, progression of liver fibrosis was significantly decreased in the group receiving ACEI or ARB compared with the other two groups. Even though this was a retrospective study, with associated limitations in the evaluation of the data including not being able to differentiate between the various angiotensin-blocking agents, an association can clearly be seen.[103] Other ACEI, such as losartan, candesartan and irbesartan, have already been investigated in trials involving a small number of patients and there has been variation in the findings reported; the results of recently completed larger trials are therefore eagerly awaited.[101, 104]

This group of drugs is already used as the 'gold standard' in the treatment in chronic renal diseases. In addition to the anti-hypertensive effects, countless studies have proven that they have preventive effects on the progression of tissue damage.[105] Moreover, especially in renal and cardiac diseases, local renin-angiotensin activation has clearly been shown to play a significant role.[105–108]

Angiogenesis, Lymphangiogenesis and Fibrosis. A recently published work described elevated levels of expression of VEGF-C and lymphangiogenesis in diabetic nephropathy.[109] Increased levels of another vascular endothelial growth factor, VEGF-A, in patients with IBD and its blockade were therapeutically effective in preclinical animal models.[110] These data suggest that a VEGF blocking agent may affect inflammation and fibrosis. BIBF 1120 is an indolinone derivative that blocks the VEGF receptor, PDGFR and FGFR kinase activity and has entered phase III clinical trials for the treatment of idiopathic pulmonary fibrosis.[111]

Lessons from Idiopathic Retroperitoneal Fibrosis. Colchicine is an anti-inflammatory drug with a lot of pharmacological effects. It is currently used in the treatment of acute gout and to prevent attacks of familial Mediterranean fever, as well as to prevent amyloidosis, a complication of that disease.[112] Its effects have been studied in several fibrotic disease, such as idiopathic retroperitoneal fibrosis, pulmonary fibrosis, scleroderma, myocarditis and chronic liver diseases, despite scarce evidence of its efficacy.[113–120] Rationale for the use of this drug comes from data that show that it may suppress basal and TGF-β induced expression of type I collagen mRNA in direct proportion to its concentration in scleroderma,[121] and may have down-regulatory effects on the expression of TGF-β on a Peyronie's-like condition in an animal model.[122] Recently, colchicine has been demonstrated to reduce fibrotic renal damage because of ciclosporin in rats, by acting on TGF-β and levels of serum malonyldialdehyde.[123] Further studies are needed to test colchicine in fibrotic diseases including CD.

Together with colchicine, other anti-inflammatory and potential anti-fibrotic agents have been tested in idiopathic retroperitoneal fibrosis, which might be considered a model of intestinal fibrosis. Although the data in the literature are limited, tamoxifene and mycophenolate mofetil effectively reduced retroperitoneal fibrosis in steroid-refractory patients, or maintained a steroid-free remission.[124] These data are limited and therefore there is a strong need for further studies.

Avotermin. While TGF-β1 promotes fibrosis, TGFβ 3 has anti-fibrotic effects as demonstrated in studies of skin scar formation. Three double-blind placebo controlled trials with avotermin, a recombinant active human TGFβ 3, administered by intradermal injection in skin scars, resulted in a significant reduction of scar formation in approximately 60% of patients compared with 33% of the placebo group. Results were confirmed after a follow-up of 6 weeks. Only minimal and transient erythema and oedema in some of the avotermin group were observed, thus avotermin can be considered relatively safe.[125] Further studies on other fibrotic diseases are needed.
 
Conclusion
Fibrosis in patients with CD is one of the less understood complications of the disease, in terms of pathogenesis, early diagnosis and treatment. Indeed, research on IBD will be focusing on this particular aspect of the disease in the near future, to change the natural history of the disease and reduce hospitalization and surgery. The possible target molecules for future therapies aimed at treating or preventing intestinal fibrosis discussed above is far from comprehensive. Recent changes in the treatment approach to chronic fibrotic diseases have led to new research strategies and resulted in the discovery of several new target molecules. As revealed by our literature research, TGF-β apparently plays the major role in the fibrogenesis and may therefore become the main target. Many of the potential new drugs are in the preclinical phase of evaluation, while several of them are already being evaluated in clinical trials for the treatment of chronic inflammatory diseases complicated by fibrosis.

We can conclude that prevention and treatment of fibrosis in CD is a key point for further research in the field of IBD. TGF-β induced mechanisms of fibrosis are the main targets for the development of new strategies for the treatment of patients with CD. Drugs with anti-fibrotic activity, especially those currently used to prevent fibrosis on other diseases, such as ACEi or statins, may open a new way in the treatment of CD. Difficulty in determining the presence and grade of fibrosis, as well as monitoring potential evolution of fibrosis, remains the main limitation to studies of anti-fibrotic agents.
 
Figure 2.
TGF-β binds TGF-β receptors I and II and induces phosporylation of Smad2 and 3, with consequent Smad4 activation that induces intranuclear gene activation and collagen production. Smad7 acts as a negative regulator on smad-2 and 3 phospohorylation

F2.jpg
 
This is interesting stuff, but if your collagen production is damaged because of a flouroquinelone such as cipro, won't these therapies exacerbate recovery from adverse effects resulting from damage to the collagen producing fibers in tendons, muscles, and the skin?

It makes me wonder whether CD should be treated with FQ's. It also makes sense why corticosteroids and FQ's are not recommended for the elderly. Should they also not be recommended for CD patients?
 
Top