Synthesis of norisoboldine derivatives and bioactivity assay for inducing the generation of regulatory T cells

Discovery of Norisoboldine Analogue III11 as a Novel and Potent Aryl Hydrocarbon Receptor Agonist for the Treatment of Ulcerative Colitis

The aryl hydrocarbon receptor (AhR) is a transcript factor, belonging to the basic helix-loop-helix-Per-ARNT-SIM family, is closely associated with health and diseases. Targeting AhR is an emerging therapeutic strategy for various diseases. Norisoboldine (NOR), which is the main alkaloid of Linderae Radix, has been known to activate AhR. Unfortunately, the oral bioavailability (F) of NOR is only 2.49%. To improve the chemical efficacy and bioavailability, we designed and synthesized NOR analogues. Using various in vitro assays, 2-methoxy-5,6,6a,7-tetrahydro-4H-dibenzo[de,g]quinoline-9-ol (III₁₁) was discovered as a potent AhR agonist. Compound III₁₁ enhanced the expression of AhR downstream target genes, triggered AhR nuclear translocation, and promoted differentiation of regulatory T cells. More importantly, III₁₁ exhibited good bioavailability (F = 87.40%) and remarkable therapeutic effects in a mouse model of ulcerative colitis at a dosage of 10 mg/kg. These findings may serve as a reference for the design of novel AhR agonists against immune and inflammatory diseases.

Norisoboldine induces the development of Treg cells by promoting fatty acid oxidation-mediated H3K27 acetylation of Foxp3

Norisoboldine (NOR), an alkaloid isolated from Radix Lindera, was previously reported to promote the differentiation of regulatory T cells (Treg cells), an important subtype of lymphocytes capable of controlling autoimmune diseases. The present study was performed to explore the mechanism of NOR in the view of cellular metabolism. A global metabolomic analysis indicated that NOR preferentially altered the fatty acid oxidation (FAO) pathway and elevated the content of related metabolites during Treg cell differentiation. The detection of oxygen consumption rate (OCR) and mRNA expression of FAO-related enzymes demonstrated that NOR promoted FAO in the early stage of Treg cell differentiation. Consistently, pharmacological or genetic inhibition of FAO markedly diminished the induction of NOR on Treg cell differentiation. Furthermore, NOR was shown to elevate the level of acetyl-CoA derived from FAO and acetylation of lysine 27 on histone 3 (H3K27) at the Foxp3 promoter and CNS2 regions. A knockdown of CPT1, the rate-limiting enzyme of FAO, weakened the promotion of NOR on the development, acetyl-CoA level, and acetylation of H3K27 of Treg cells in vitro and in the mice with collagen-induced arthritis, and attenuated the anti-arthritic effect of NOR. These findings demonstrate that NOR induces the development of Treg cells through promoting FAO, therefore, facilitating gene transcription of Foxp3 via acetyl-CoA-mediated H3K27 acetylation modification, and FAO might serve as a novel target to induce Treg cell development.