Effect of radix rehmanniae and its active compounds against autoimmune diseases through regulating oxidative stress-induced immunodysfunction

Abstract

Autoimmune diseases can be defined as clinical syndromes caused by the activation of T or B cells or both, in the absence of an ongoing infection or other discernible cause. Immunological tolerance (including regulatory T (Treg) and B (Breg) cells, etc.) impairs the immune system to mount responses against self-antigens. Conversely, the loss of immunological tolerance can lead to the development of autoimmunity. Thus, regulating Treg or Breg cells could be promising targets to reduce the infiltration of autoreactive T cells into the affected tissue and ameliorate autoimmunity. Reactive oxygen/nitrogen species (ROS/RNS) are important players contributing to the inflammatory and immune dysfunctions in autoimmune diseases. As a representative RNS, peroxynitrite exerts a crucial role in inducing inflammatory tissue damage in the pathogenesis of autoimmune diseases. However, whether peroxynitrite could modulate Treg/Breg cells and affect immunological tolerance remains unclear.

Multiple sclerosis (MS) is a canonical organ-specific autoimmune disease initiated by CD4 T helper cells (Th cells). In this study, I used the Experimental autoimmune encephalomyelitis (EAE) mice model, a widely adopted animal model of MS, to study the effect of peroxynitrite on regulating Treg cell. I found that peroxynitrite-mediated 3-nitrotyrosine on Tregs was coincidently increased with EAE progression, which was remarkably attenuated by peroxynitrite decomposition catalyst. Meanwhile, the inhibition of peroxynitrite increased Tregs, reducing Th1/Th17 infiltration into CNS in active EAE mice. After detecting the tyrosine nitration of Treg-specific protein, I found that the interleukin-2 receptor (IL-2R) was nitrated in the lymph nodes of active EAE mice. Thus, scavenging peroxynitrite could repair Treg cell function to attenuate CNS autoimmunity.

Radix Rehmanniae (RR) was a common natural herbal plant used in TCM clinical practice to treat autoimmune diseases. Our lab’s previous studies revealed that the extract of RR ameliorated neuroinflammation and inhibited demyelination in active EAE mice via scavenging peroxynitrite and suppressing macrophage-derived peroxynitrite production. In the present study, I screened the bioactivities of the chemical ingredients from RR, and RehD was identified as a representative compound in RR with a high capability of inhibiting 3-nitrotyrosine and BBB impermeable. Further, I found that RehD increased the release of IL-10 by Treg through reversing the nitration of IL-2R in active EAE mice and PBMCs of healthy donors and MS patients. Thus, RehD might be a promising drug candidate for inhibiting CD4+ T cell infiltration and demyelination and further ameliorating active EAE by blocking the nitration of IL-2R.

Moreover, Breg cells are also recognized for maintaining immune tolerance. The impaired Breg cell function with decreased IL‐10‐producing capacity has been found in autoimmune diseases, such as rheumatoid arthritis, lupus, and primary Sjogren's syndrome (pSS). Here, I found Acteoside, another active compound from RR with high ONOO- scavenging ability, promoted IL‐10 production from both human and murine B cells via critically regulating the TLR4/PI3K axis, thus restoring regulatory B cell function during autoimmune progression. This study might partially explain the mechanism of peroxynitrite-induced impairment of immunological tolerance and the therapeutic mechanism of RR, which might potentiate its clinical application to autoimmune disorders.