Fibrogenesis in chronic allograft rejection: underlying mechanisms and pharmacological control

Chronic Rejection After Intestinal Transplant: Where Are We in Order to Avert It?

Chronic rejection affects the long-term survival of all solid organ transplants and, among intestinal allografts, occurs in up to 10% of the recipients. The insidious clinical evolution of the chronic allograft enteropathy, the absence of noninvasive biomarkers, and the late endoscopic findings delay its diagnosis. No pharmacological approach has been proven effective, and allograft removal nowadays still represents the only available therapy. The inclusion of the liver in the visceral allograft appears to be the only intervention affecting the development of chronic rejection, as revealed by large-center studies and registry reports. A significant body of evidence emerged from the experimental setting and provided essential knowledge on the complex mechanisms behind the development of chronic allograft enteropathy. More recently, donor-specific antibodies have been suggested as an early, key element in the natural history of chronic allograft enteropathy and several novel approaches, tackling the antibody-mediated graft injury, have gained acceptance in clinical settings and are believed to impact on chronic rejection. The inclusion of a liver allograft is advocated when re-transplanting a sensitized recipient, due to its protective effect against humoral immunity. Multicenter trials are required to understand and tackle chronic rejection, and find the therapeutic answer to this clinical dilemma.

Mechanisms of action of mycophenolate mofetil

Mycophenolate mofetil (MMF, CellCept®) is a prodrug of mycophenolic acid (MPA), an inhibitor of inosine-5′‘monophosphate dehydrogenase. MPA depletes guanosine nucleotides preferentially in T and B lymphocytes and inhibits their proliferation, thereby suppressing cell-mediated immune responses and antibody formation. MPA also inhibits the glycosylation and expression of adhesion molecules, and the recruitment of lymphocytes and monocytes into sites of inflammation. MPA depletes tetrahydrobiopterin and decreases the production of nitric oxide by inducible NO synthase without affecting the activity of constitutive NO synthases. Activated macrophages produce NO and superoxide, which combine to generate tissue-damaging peroxynitrite. By these two mechanisms MMF exerts anti-inflammatory activity. Unlike calcineurin inhibitors, MMF is not nephrotoxic and does not induce the production of TGF β, which is fibrogenic. MMF does not increase blood pressure, cholesterol levels or triglyceride levels in recipients. MMF reduces acute and chronic rejection in allograft recipients and is efficacious in some nephropathies. Evidence is accumulating that MMF may have clinical utility in some autoimmune disorders.

Short-term TNF-alpha inhibition reduces short-term and long-term inflammatory changes post-ischemia/reperfusion in rat intestinal transplantation

BACKGROUND

Tumor necrosis factor (TNF)-α inhibition was shown to reduce ischemia/reperfusion injury (IRI) after intestinal transplantation (ITX). We studied the effects of different TNFα inhibitors on acute IRI and long-term inflammatory responses in experimental ITX.

METHODS

Orthotopic ITX was performed in an isogenic ischemia/reperfusion model in Lewis rats. The TNFα inhibition groups received infliximab post-reperfusion; etanercept pre-reperfusion and at postoperative days (POD) 1, 3, 5, and 7; or pentoxifylline pre-reperfusion and at POD 1 to 5. Tissue samples were taken from proximal and distal graft sections and mesenteric lymph nodes at 20 min, 12 hr, 7 day, and 6 months post-reperfusion for histopathology, immunohistology, terminal deoxyribosyl transferase-mediated dUTP nick-end labeling (TUNEL) assay, and real-time RT-PCR. Lung sections were stained for the myeloperoxidase assay.

RESULTS

TNFα inhibitors decreased inflammatory changes after IRI in all treatment groups. Infliximab significantly improved 7-day survival and reduced the histological and immunohistochemical signs of IRI, the numbers of graft-infiltrating T cells and ED1 monocytes and macrophages, and pulmonary neutrophil infiltration, and also enhanced the accumulation of cytoprotective markers. Graft injury was more prominent in the distal graft than in the proximal graft in all groups, regardless of TNFα inhibition.

CONCLUSION

Infliximab significantly reduced both acute IRI and, as with other TNFα inhibitors, long-term inflammatory responses after rat ITX. TNFα inhibition may help diminish chronic inflammatory long-term effects and avoid chronic allograft enteropathy.

The renal benefit of mycophenolate mofetil after liver transplantation

BACKGROUND

The risk and benefit of adding mycophenolate mofetil (MMF) to a standard immunosuppressive regimen at the time of liver transplantation (LT) is not well described.

METHODS

We performed a retrospective case-control analysis comparing one-yr outcomes of all LT recipients at our institution treated with post-operative tacrolimus (TAC), MMF, and steroids vs. TAC and steroids.

RESULTS

A total of 101 LT recipients (50:51 case:control) were analyzed. Despite more renal dysfunction at LT, the MMF + TAC group had similar serum creatinine (Cr) and glomerular filtration rate (GFR) as the TAC group one-yr post-LT. In this time period, Cr decreased (1.57-1.22 mg/dL, p = 0.04) and GFR increased (57.5-65.1 mL/min per 1.73 m(2), p = 0.05) in the MMF + TAC group, while Cr increased (1.11-1.35, p < 0.01) and GFR declined (73.5-60.1, p < 0.001) in the TAC group. These findings occurred without a difference in absolute rejection episodes, hospitalizations, infections, deaths, or time to above events (p > 0.05). Subgroup analysis of patients stratified by pre-transplant renal dysfunction (Cr ≥ 1.2 mg/dL) supported the previous. MMF was reasonably well tolerated with a low rate of discontinuation.

CONCLUSIONS

The use of adjunctive MMF immediately after LT may protect against calcineurin inhibitor nephrotoxicity, potentially without the need for dose reduction or increased risk of adverse events.

Features of chronic allograft rejection on rat small intestine transplantation

The aim of this study was to develop a model of chronic rejection of the entire small intestine transplantation and to analyze the features of chronic rejection. Allogenic small bowel transplantation was performed in a rat combination of Lewis to F344. Intestines were procured at the 60th and the 90th day after operation. We compared the semiquantitative score of histological parameters. The immunological components involved in the chronic rejection process were evaluated by immunohistochemical staining and the cytokine levels in grafts. The significant characteristics of the allograft on histology were changes of villous architecture, interstitial fibrosis, leukocyte infiltration, and obliterative arteriopathy. Allografts on the 60th day post-transplantation had more score in inflammatory events, while the grafts on the 90th day after operation had more values in ischemia/fibrotic events. The number of infiltrating CD4, CD8 and macrophage cells in allografts progressively decreased over time. The level of intragraft cytokines such as IL-6, TNF-alpha and IL-10 in the 90th day after transplantation also decreased compared with that in the 60th day. These data suggested that in the early stage (POD 60), there were more active and intense inflammatory events; later (POD 90) allografts manifested less inflammation and more arterial obliteration and fibrosis.

Mechanisms of action of mycophenolate mofetil in preventing acute and chronic allograft rejection

Mycophenolate mofetil (MMF), a prodrug of mycophenolic acid (MPA), an inhibitor of inosine-5'-monophosphate dehydrogenase, has several immunosuppressant actions. MPA depletes guanosine and deoxyguanosine nucleotides preferentially in T and B lymphocytes, inhibiting proliferation and suppressing cell-mediated immune responses and antibody formation, major factors in acute and chronic rejection. MPA also can induce T-lymphocyte apoptosis. MPA suppresses dendritic cell maturation and can induce human monocyte-macrophage cell line differentiation, decreasing the expression of interleukin (IL)-1 and enhancing expression of the IL-1 receptor antagonist. In addition, MPA inhibits adhesion molecule glycosylation and expression and lymphocyte and monocyte recruitment. Activated macrophages produce nitric oxide (NO) and superoxide, which combine to generate tissue-damaging peroxynitrite. MPA depletes tetrahydrobiopterin and decreases NO production by inducible NO synthase without affecting constitutive NO synthase activity. By these mechanisms, MMF exerts anti-inflammatory activity, which could attenuate both acute and chronic rejection. Unlike calcineurin inhibitors, MMF is nonnephrotoxic and does not induce transforming growth factor-beta production, which is fibrogenic. MMF inhibits arterial smooth muscle cell proliferation, a contributor to graft proliferative arteriopathy, and does not increase blood pressure, cholesterol, or triglyceride levels. By decreasing high-density lipoprotein oxidation and macrophage recruitment, MMF also may delay onset/progression of graft atherosclerosis. Thus, MMF may prevent chronic rejection by several mechanisms. MMF activity is synergistic with that of other agents such as valganciclovir for treating cytomegalovirus infection. MMF also has synergistic activity with angiotensin-converting enzyme inhibitors or angiotensin II receptor antagonists in the treatment of some nephropathies in experimental animals. This combination may prevent progression toward end-stage renal disease in humans with chronic allograft, lupus, and diabetic nephropathies.

Mechanisms of action of mycophenolate mofetil

Mycophenolate mofetil (MMF, CellCept) is a prodrug of mycophenolic acid (MPA), an inhibitor of inosine-5'-monophosphate dehydrogenase. MPA depletes guanosine nucleotides preferentially in T and B lymphocytes and inhibits their proliferation, thereby suppressing cell-mediated immune responses and antibody formation. MPA also inhibits the glycosylation and expression of adhesion molecules, and the recruitment of lymphocytes and monocytes into sites of inflammation. MPA depletes tetrahydrobiopterin and decreases the production of nitric oxide by inducible NO synthase without affecting the activity of constitutive NO synthases. Activated macrophages produce NO and superoxide, which combine to generate tissue-damaging peroxynitrite. By these two mechanisms MMF exerts anti-inflammatory activity. Unlike calcineurin inhibitors, MMF is not nephrotoxic and does not induce the production of TGFbeta, which is fibrogenic. MMF does not increase blood pressure, cholesterol levels or triglyceride levels in recipients. MMF reduces acute and chronic rejection in allograft recipients and is efficacious in some nephropathies. Evidence is accumulating that MMF may have clinical utility in some autoimmune disorders.

Steroid avoidance in renal transplantation using basiliximab induction, cyclosporine-based immunosuppression and protocol biopsies

BACKGROUND

Reducing chronic steroid exposure is important to minimize steroid-related morbidity, particularly for susceptible renal transplant recipients. Steroid-free and steroid-sparing protocols have shown benefits, but safety has not been established for all populations. We investigated the safety of steroid avoidance (SA) in a population including African-Americans, using modern immunosuppression with protocol biopsy monitoring.

METHODS

A randomized-controlled SA trial (early discontinuation, days 2-7) was conducted in a population (n = 77) including African-Americans and cadaveric kidney recipients. Patients received basiliximab, cyclosporine (CsA), and mycophenolate mofetil (MMF). In controls, steroids were tapered to 5 mg prednisone/d by day 30. Protocol biopsies were performed (1, 6, 12 and 24 months) to evaluate subclinical acute rejection (SCAR) and chronic allograft nephropathy (CAN).

RESULTS

The SA did not result in significantly higher incidences of graft loss, AR, SCAR, CAN, or renal fibrosis. SA patients experienced similar renal function, comparable serum lipid levels, and a trend toward fewer cases of new-onset diabetes. Clinical outcomes of African-American and non-African-American patients did not significantly differ.

CONCLUSIONS

The SA is safe in the context of basiliximab induction and CsA-based immunosuppression. This protocol could minimize steroid-related side effects in susceptible groups, including African-Americans, without increasing the risk of AR or graft failure.