FK778 and Tacrolimus Prevent the Development of Obliterative Airway Disease After Heterotopic Rat Tracheal Transplantation

Role of transforming growth factor-β in airway remodelling in bronchiolitis obliterans

Airway remodelling is the main pathological mechanism of bronchiolitis obliterans (BO). Several studies have found that transforming growth factor-β (TGF-β) expression is increased in BO during airway remodelling, where it plays an important role in various biological processes by binding to its receptor complex to activate multiple signalling proteins and pathways. This review examines the role of TGF-β in airway remodelling in BO and its potential as a therapeutic target, highlighting the mechanisms of TGF-β activation and signalling, cellular targets of TGF-β actions, and research progress in TGF-β signalling and TGF-β-mediated processes.

Replacement of Rat Tracheas by Layered, Trachea-Like, Scaffold-Free Structures of Human Cells Using a Bio-3D Printing System

Current scaffold-based tissue engineering approaches are subject to several limitations, such as design inflexibility, poor cytocompatibility, toxicity, and post-transplant degradation. Thus, scaffold-free tissue-engineered structures can be a promising solution to overcome the issues associated with classical scaffold-based materials in clinical transplantation. The present study seeks to optimize the culture conditions and cell combinations used to generate scaffold-free structures using a Bio-3D printing system. Human cartilage cells, human fibroblasts, human umbilical vein endothelial cells, and human mesenchymal stem cells from bone marrow are aggregated into spheroids and placed into a Bio-3D printing system with dedicated needles positioned according to 3D configuration data, to develop scaffold-free trachea-like tubes. Culturing the Bio-3D-printed structures with proper flow of specific medium in a bioreactor facilitates the rearrangement and self-organization of cells, improving physical strength and tissue function. The Bio-3D-printed tissue forms small-diameter trachea-like tubes that are implanted into rats with the support of catheters. It is confirmed that the tubes are viable in vivo and that the tracheal epithelium and capillaries proliferate. This tissue-engineered, scaffold-free, tubular structure can represent a significant step toward clinical application of bioengineered organs.

Tacrolimus prevents laryngotracheal stenosis in an acute-injury rat model

OBJECTIVES/HYPOTHESIS

Acquired laryngotracheal stenosis is a challenging problem for otolaryngologists. Several studies suggest tacrolimus may inhibit post-transplant airway stenosis that occurs with coronary drug-eluting stents. The objective of the present study was to determine whether tacrolimus modulates wound healing of the airway mucosa and prevents laryngotracheal stenosis in an acute injury animal model.

STUDY DESIGN

Basic science.

METHODS

The laryngotracheal mucosa of rats was scraped with a nylon brush through the tracheostoma. Tacrolimus (0.2 mg/kg or 1.0 mg/kg) was systemically administered intramuscularly for 5 days. Nine days after scraping, the pathological changes and the degree of stenosis were assessed by hematoxylin and eosin staining or by immunohistochemical staining for nuclear factor of activated T cell and interleukin 2.

RESULTS

Lumen stenosis resulted from hyperplasia of the airway epithelium and a thickened submucosal layer with extensive fibrosis, angiogenesis, and collagen deposition. There was a significant preventive effect on airway stenosis at the tracheal and cricoid levels in the low-dose (0.2 mg/kg) tacrolimus-treated animals, compared to the untreated animals (P < .05). This effect was insignificant with treatment by high-dose tacrolimus (1.0 mg/kg). Immunohistochemistry showed that, after tacrolimus treatment, the expressions of nuclear factor of activated T cell and interleukin 2 were downregulated in submucosal fibroblasts, neovascular cells, and glandular cells.

CONCLUSIONS

This study suggests that low-dose systemic tacrolimus has a preventive effect on laryngotracheal stenosis by inhibiting the activation of immune cells in the injured airway mucosa via the calcineurin/nuclear factor of activated T cell/interleukin 2 pathway.

LEVEL OF EVIDENCE

NA.

Adverse effects of immunosuppressant drugs upon airway epithelial cell and mucociliary clearance: implications for lung transplant recipients

Optimal post-transplantation immunosuppression is critical to the survival of the graft and the patient after lung transplantation. Immunosuppressant agents target various aspects of the immune system to maximize graft tolerance while minimizing medication toxicities and side effects. The vast majority of patients receive maintenance immunosuppressive therapy consisting of a triple-drug regimen including a calcineurin inhibitor, a cell cycle inhibitor and a corticosteroid. Although these immunosuppressant drugs are frequently used after transplantation and to control inflammatory processes, limited data are available with regard to their effects on cells other than those from the immunological system. Notably, the airway epithelial cell is of interest because it may contribute to development of bronchiolitis obliterans through production of pro-inflammatory cytokines. This review focuses the current armamentarium of immunosuppressant drugs used after lung transplantation and their main side effects upon airway epithelial cells and mucociliary clearance.

Protective effect of immunosuppression on granulation tissue formation in metallic airway stents

OBJECTIVES/HYPOTHESIS

The use of self-expanding metallic airway stents has been extended in recent years in inoperable patients with malignant and benign airway diseases. The risk of granulation tissue formation in the stent is a major concern. The objective of the present study was to determine whether immunosuppression modulates granulation tissue formation in airway stents, as seen in coronary stents.

STUDY DESIGN

The study included 19 patients with benign airway obstructions and 11 recipients of lung transplants with anastomotic obstructions who were receiving immunosuppression therapy.

METHODS

The degree of in-stent granulation tissue formation was evaluated (score range, 0-3) every 3 months for 2 years.

RESULTS

Granulation tissue formation was significantly lower in the transplant recipients than in the nontransplant patients at 3 months (score 0.7 vs. 1.6, P = .031), 15 months (score 0 vs. 1.1, P = .026), and 18 months (score 0 vs. 1.8, P = .020). During the 2 years of follow-up, the transplant recipients underwent significantly fewer laser resections and brachytherapy treatments for in-stent granulation.

CONCLUSIONS

The immunosuppression given to lung transplant recipients may have an inhibitory effect on granulation tissue formation in metallic airway stents. Further studies are needed to evaluate the effect of systemic therapy or coated stents with drugs such as sirolimus.

Prevention and inhibition but not reversion of chronic allograft vasculopathy by FK778

BACKGROUND

This study aimed at investigating the efficacy of the novel immunosuppressant FK778 to prevent the development and progression of chronic allograft vasculopathy (CAV).

METHODS

Orthotopic aortic transplantations were performed in the PVG-to-ACI rat model and followed over the course of 120 days. Immunosuppression with FK778 (20 mg/kg) or sirolimus (2 mg/kg) was either started early or delayed when CAV was already present. Trough levels were monitored. Aortic luminal obliteration was quantified using computer morphometry and intragraft cytokine profiles were analyzed with Western Blotting. Donor-reactive antibodies were quantified by flow cytometry.

RESULTS

Untreated animals developed CAV with luminal obliteration of 25.2+/-13.6% and 41.4+/-23.3% after 80 and 120 days, respectively. Continuous immunosuppression with FK778 or sirolimus effectively prevented the development of vasculopathy. When the start of the immunosuppressive regimen was delayed until postoperative day 80, FK778 and sirolimus inhibited a progression of established CAV but did not reverse the luminal obliteration. Intragraft tumor growth factor-beta activity increased over the course of time in untreated recipients but was significantly suppressed after continuous immunosuppression with either agent. Expression of platelet-derived growth factor, intercellular adhesion molecule-1, and vascular adhesion molecule-1 also was moderately suppressed. A stable elevation of donor-reactive IgG-antibody levels was found over 120 days in the absence of treatment. With FK778 or sirolimus, antibody levels were effectively decreased. FK778 was very well tolerated and only sirolimus showed side effects with elevation of BUN, cholesterol, triglycerides, and ALT after 120 days.

CONCLUSIONS

FK778 prevents the development of CAV and inhibits a progression of established disease. It shows a similar efficacy but a safer drug profile when compared to sirolimus.

Experimental orthotopic tracheal transplantation: The Stanford technique

The rat heterotopic tracheal transplantation model is widely used as an experimental model to study the development of obliterative airway disease (OAD) and to assess immunosuppressive strategies for chronic rejection. Despite its widespread application, the heterotopic transplantation model does have a number of limitations like the lack of air flow and mucociliary clearance. The present article provides a detailed description of the surgical technique for orthotopic tracheal transplantations, which may share more similarities with lung transplants in humans. The technique is easy to learn, the procedure is well tolerated by the animals, and the grafts develop OAD lesions similar to those of human obliterative bronchiolitis.

The Effect of FK778 on the Progression of Chronic Allograft Nephropathy in a Rat Model

BACKGROUND

Chronic allograft nephropathy (CAN) still belongs to the leading causes of graft loss over the long term. The leflunomide derivative FK778 is a novel immunosuppressant with improved pharmacokinetic properties that effectively prolonged graft survival in several transplantation models. In the present study, we investigated the effects of FK778 at different phases after transplantation on the progression of CAN.

METHODS

Fisher 344 kidneys were orthotopically transplanted into Lewis recipients. Recipients were treated with FK778 (5 mg/kg/day) over different time periods (early: days 0-10 only, continuous: day 0 to week 24, or late: weeks 16-24 only posttransplantation). Proteinuria was measured every 4 weeks, whereas grafts were harvested at 24 weeks posttransplantation for morphological and immunohistochemical analysis as well as transforming growth factor-beta and platelet derived growth factor-B chain expression.

RESULTS

Continuous treatment with FK778 ameliorated the progression of CAN, whereas late treatment reduced proteinuria and resulted in a similar grade of CAN as compared to animals with continuous treatment. In contrast, FK778 given only during the early phase after transplantation had no effect on the progression of CAN as compared to controls.

CONCLUSION

In summary, FK778 is a potent immunosuppressive drug that can delay the progression of CAN, even when given at later stages after transplantation.

Is the Malononitrilamide FK778 Better for the Prevention of Acute or Chronic Rejection?

OBJECTIVE

The aim of this study was to assess the efficacy of FK778 to prevent acute and chronic allograft rejection compared with other immunosuppressive agents.

MATERIALS AND METHODS

Heterotopic Brown-Norway (BN)-to-Lewis rat cardiac transplantations and heterotopic BN-to-Lewis tracheal transplantations were performed to study acute heart rejection and the development of chronic obliterative airway disease (OAD), respectively. Recipients were treated with FK778, tacrolimus, MMF, or sirolimus for 10 days (acute rejection study) or 28 days (chronic OAD study) at varying doses.

RESULTS

In untreated recipients, cardiac allograft survival was 6.2 +/- 0.4 days. FK778 (20 mg/kg), tacrolimus (2 or 8 mg/kg), mycophenolate mofetil (MMF; 40 mg/kg), or sirolimus (0.5 or 2 mg/kg) significantly prolonged graft survival to 17.0 +/- 2.8, 18.5 +/- 2.7, 25.0 +/- 2.5, 20.7 +/- 3.8, 14.5 +/- 2.2, and 23.2 +/- 1.5 days, respectively (P < .05). Tracheal grafts in untreated recipients showed intense infiltration and complete luminal obliteration by day 28. FK778 (20 mg/kg), tacrolimus (1 or 4 mg/kg), MMF (10 or 40 mg/kg), or sirolimus (0.5 or 2 mg/kg) significantly inhibited tracheal luminal obliteration (19.5% +/- 16.4%, 44.2% +/- 33.6%, 12.3% +/- 3.3%, 61.7% +/- 18.6%, 18.3% +/- 11.3%, 55.0% +/- 30.9%, and 8.5% +/- 3.5% (P < .05). All 4 high-dose groups showed similar efficacy.

CONCLUSIONS

When used in therapeutic doses, tacrolimus and sirolimus were more effective than FK778 to prolong cardiac allograft survival. However, with its antiproliferative effects on smooth muscle cells, its good tolerability, and its blockade of cytomegalovirus replication, FK778 proved effective to prevent chronic OAD development. Thus, FK778 may acquire an important role in maintenance therapy for the prevention of long-term fibroproliferative complications.

Sirolimus and FK778: a comparison of two anti-proliferative immunosuppressants for prevention of experimental obliterative airway disease

This study examined the efficacies of sirolimus and the novel immunosuppressive agent FK778 to prevent obliterative airway disease (OAD). Tracheae from Brown-Norway donors were heterotopically transplanted in the greater omentum of Lewis rats. Recipients were treated for 28 days with sirolimus (0.5 or 2 mg/kg), FK778 (5 or 20 mg/kg), or combination regimens (0.5 + 5 mg/kg, 2 + 20 mg/kg). Tracheal segments were evaluated for degree of luminal obliteration, percentage of luminal epithelial cell coverage, and peritracheal infiltration. In vitro smooth muscle cell (SMC) proliferation and migration assays were performed to assess direct nonimmune-related effects of the drugs. Sirolimus 2 mg/kg and FK778 20 mg/kg effectively reduced graft infiltration and prevented airway obliteration, whereas FK778 5 mg/kg was insufficient. Sirolimus 0.5 mg/kg at least showed moderate inhibitory effects on luminal obliteration and graft infiltration. Combination regimens revealed no significant beneficial effects. Both sirolimus and FK778 barely showed preserved epithelial coverage. Within the range of relevant concentrations, FK778 showed more potent anti-proliferative and anti-migratory effects on SMC in vitro than sirolimus. Both agents proved effective to prevent OAD development without preserving relevant amounts of epithelium. The anti-proliferative potency on SMCs seems to be an especially important mechanism for FK778. De novo combination regimens revealed no beneficial interaction and thus remain doubtful.

FK778: New Cellular and Molecular Mechanisms of Action

PURPOSE

The new malononitrilamide FK778 is currently being evaluated as an immunosuppressant for organ transplantation. Its main mechanism is inhibition of a pivotal enzyme of pyrimidine biosynthesis. This report revealed new mechanisms of action on different cell types involved in acute and chronic allograft rejection.

METHODS

Purified Brown-Norway rat aortic endothelial cell (EC) cultures were pretreated with several concentrations of FK778. Endothelial adhesion molecule expression (ICAM-1/VCAM-1) stimulated with TNF-alpha was quantified by immunofluorescence. Purified Lewis rat lymphocytes (LC) incubated with FK778 were stimulated via TCR/CD28 signals, and CD25 expression was quantified using FACS analysis. Uridine addition was used in all assays to reverse the pyrimidine synthesis blockade. Lymphocyte-EC interaction was assessed by micromanipulator-assisted single-cell adhesion assays. Finally, smooth muscle cell (SMC) proliferation and migration was analyzed. Uridine addition was used in all assays to reverse the pyrimidine synthesis blockade.

RESULTS

TNF-alpha stimulation and TCR/CD28 co-stimulation significantly increased EC ICAM-1/VCAM-1-expression and LC CD25 surface expression, respectively. These effects were dose-dependently inhibited by FK778 and were not reversed by the addition of uridine. FK778 dose-dependently attenuated LC adhesion to allogeneic EC. The dose-dependent inhibition of SMC proliferation by FK778 was abolished by uridine addition, whereas the inhibitory effect on SMC migration was not affected by uridine supplementation.

CONCLUSIONS

FK778 directly reduced endothelial adhesion molecule up-regulation, inhibited lymphocyte activation, and attenuated lymphocyte-endothelium interactions, critical early steps in graft rejection. These effects were separate from the blockade of pyrimidine synthesis. The antiproliferative potency of FK778 on SMC may be an important mechanism to inhibit the fibroproliferative lesions of chronic organ rejection.