The Role of N-Acetylcysteine Amide (NACA) As Prophylactic Treatment for Acute Graft-Versus-Host Disease

Aim

The current study aimed to investigate the role of N-acetylcysteine amide (NACA) as prophylactic treatment for acute graft-versus-host disease (GvHD) and to explore the underlying mechanism of action.

Background

GvHD remains one of the major complications after allogeneic hematopoietic cell transplantation (allo-HCT). In addition, GvHD is a significant cause of morbidity, mortality and deteriorated life quality in transplanted patients. At the present, several strategies have been suggested as a prophylactic treatment against GvHD. Due to the good anti-proliferative effects on the donor T cells, calcineurin inhibitors (cyclosporine or tacrolimus) in combination with methotrexate (MTX) or mycophenolate mofetil (MMF) are recommended by several transplantation centers. Recently, several studies have reported good results of post-transplant cyclophosphamide treatment because of its ability to induce apoptosis of donor allo-activated T cells and to promote transplant tolerance. However, inevitable off-target effect and dose-related toxicity frequently occur regardless of the treatment selected. Evidence showed that oxidative stress is elevated in the recipients of allo-HCT and is linked to the pathogenesis of GvHD.

Methods

Using a classic murine GvHD model with complete MHC-mismatched allo-HCT (C57Bl/6 to Balb/c), the effect of NACA on the occurrence and severity of acute GvHD was evaluated. In order to reveal the underling mechanism of action, clinical manifestations, survival, cytokine profiles, ROS accumulation, T cell allo-responses, and target tissue damage in NACA-treated GvHD mice were scrutinized and compared with the same parameters observed in N-acetylcysteine (NAC)-treated GvHD mice.

Results

We found that NACA treatment significantly prolonged the survival and decreased GvHD severity score, in mice underwent allo-HCT. Moreover, NACA downregulated the pro-inflammatory cytokines, such as IFNγ, TNFα, IL-1β and IL-6, but upregulated the anti-inflammatory IL-4 in the mouse serum. Data also showed that NACA administration significantly reduced ROS accumulation in the spleen on day +7 and day +14 after transplantation. In addition, a modest dividing defect in donor T cells was observed upon NACA administration regardless of the experienced antigen classes, and the remarkably lower percentage of Ki67 expression in donor T cells substantiated their inhibited proliferation. In the meanwhile, NACA restrained Th1 and Th17 differentiation of donor T cells but enhanced the regulatory polarization. Furthermore, the migration capability of donor T cells was suppressed by NACA as well, resulting in a less severe intervention of the GvHD target organs. Importantly, NACA did not alter the engraftment as was observed in the bone marrow and spleen chimera but facilitated the neutrophil engraftment. Opposite to NACA, the effect of NAC on GvHD was not significant.

Conclusion

• The present investigation showed that NACA, rather than NAC, has a prophylactic effect in acute GvHD mouse model.

• The protective effect is mediated by antioxidation, anti-inflammation and downregulation of T-cell allo-responses without altering the engraftment and its process.

• NACA treatment has significantly improved survival, lower the severity score and shortened the recovery time. However, it was not able to fully eliminate the occurrence of acute GvHD.

• It is important to consider the combination of NACA with other clinical-used drugs in order to achieve complete disease remission and minimize treatment-related toxicity.

• The encouraging present results in combination with the clinical reported results of the use of NACA may open the door for a new prophylactic treatment of GvHD.

No relevant conflicts of interest to declare.