Oxymatrine attenuates chronic allograft rejection by modulating immune responses and inhibiting fibrosis

Background: Chronic rejection (CR) is a significant obstacle to long-term allograft survival. Oxymatrine (OMT) is a prominent bioactive compound widely utilized in traditional Chinese medicine for the management of inflammatory disorders and it has considerable potential as a therapeutic candidate for the treatment of CR.

Methods: Well-established major histocompatibility complex (MHC) class II mismatched B6 mice. C-H-2^bm12-to-C57BL/6 mouse transplantation was used as a CR model. Hematoxylin and eosin (H&E) staining, immunohistochemistry, and Masson's trichrome staining were used to assess pathological changes in the grafts, and the percentages of immune cells were determined by flow cytometry. The effects of OMT on the regulation of CD4⁺ T cell differentiation and cytokine secretion were verified in vitro.

Results: OMT effectively alleviated pathological graft damage, characterized by chronic changes in intimal lesions, vasculopathy, and fibrosis and significantly prolonged cardiac allograft survival. OMT exerted its immunomodulatory effects by inhibiting T helper 1 (Th1) and T helper 17 (Th17) cell differentiation while promoting Treg differentiation both in vivo and in vitro. Further studies revealed that OMT inhibited the phosphorylation of mammalian target of rapamycin (mTOR), which is a potential mechanism underlying its immunosuppressive effects. OMT also inhibited the activation of B cells and the production of donor-specific antibody (DSA). In addition, OMT effectively alleviated chronic changes in fibrosis in cardiac allografts, and these changes may be related to the inhibition of the transforming growth factor-β (TGF-β)-Smad 2/3 pathway.

Conclusions: OMT attenuated CR by modulating the immune response and inhibiting graft fibrosis. Further in-depth investigations of OMT may provide valuable insights into the development of novel therapeutic strategies for CR inhibition.