Norisoboldine ameliorates collagen-induced arthritis through regulating the balance between Th17 and regulatory T cells in gut-associated lymphoid tissues.

Norisoboldine (NOR), the main active ingredient of the dry root of Lindera aggregata, was previously proven to have substantial therapeutic effects on collagen-induced arthritis (CIA) in mice by oral administration. However, it exhibited a very poor bioavailability in normal rats. The pharmacokinetic-pharmacodynamics disconnection attracts us to explore its anti-arthritic mechanism in more detail. In this study, NOR, administered orally, markedly attenuated the pathological changes in CIA rats, which was accompanied by the down-regulation of pro-inflammatory cytokines and the up-regulation of anti-inflammatory cytokine IL-10. Pharmacokinetic studies demonstrated that the plasma concentration of NOR was moderately elevated in CIA rats compared with normal rats, but it was still far lower than the minimal effective concentration required for inhibiting the proliferation and activation of T lymphocytes in vitro. Interestingly, NOR was shown to regulate the balance between Th17 and regulatory T (Treg) cells in the intestinal lymph nodes more strikingly than in other tissues. It could increase the expression of Foxp3 mRNA in both gut and joints, and markedly up-regulate the number of integrin α4β7 (a marker of gut source)-positive Foxp3(+) cells in the joints of CIA rats. These results suggest that the gut might be the primary action site of NOR, and NOR exerts anti-arthritis effect through regulating the balance between Th17 and Treg cells in intestinal lymph nodes and yielding a trafficking of lymphocytes (especially Treg cells) from the gut to joint. The findings of the present study also provide a plausible explanation for the anti-arthritic effects of poorly absorbed compounds like NOR.