# Inhibition of IL‐6/STAT3 Signaling by N‐Trans‐Hibiscusamide and Its Derivative in a Mouse Model of Collagen‐Induced Arthritis

## TL;DR

This study shows that NHA and HAD reduce inflammation in a mouse model of rheumatoid arthritis by inhibiting the IL-6/STAT3 signaling pathway.

## Contribution

The study introduces NHA and HAD as novel inhibitors of IL-6/STAT3 signaling with potential therapeutic use in rheumatoid arthritis.

## Key findings

- NHA and HAD significantly reduced IL-6-induced luciferase activity and inhibited STAT3 phosphorylation and nuclear translocation.
- The compounds alleviated arthritis symptoms in mice and decreased serum levels of anti-type II collagen IgG and IL-17A.
- NHA and HAD inhibited the differentiation of CD4+ T cells into Th17 cells in vitro.

## Abstract

Rheumatoid arthritis is a chronic autoimmune disease characterized by persistent joint inflammation and progressive joint destruction, leading to pain, disability, and reduced quality of life. Interleukin‐6 is a key pro‐inflammatory cytokine that plays a central role in the pathogenesis of rheumatoid arthritis by activating downstream inflammatory signaling pathways. Dysregulation of the interleukin‐6‐mediated signaling cascade, particularly the signal transducer and activator of transcription 3 pathway, contributes to sustained inflammation and disease progression, highlighting this axis as an important therapeutic target. Rheumatoid arthritis (RA) is a chronic autoimmune disorder characterized by joint inflammation and destruction, with interleukin‐6 (IL‐6) playing a central role in its pathogenesis by driving inflammatory responses. Targeting the IL‐6/signal transducer and activator of transcription 3 (STAT3) pathway has emerged as a promising therapeutic approach for RA. This study investigates the inhibitory effects and underlying mechanisms of N‐trans‐hibiscusamide (NHA) and its derivative 4‐O‐(E)‐feruloyl‐N‐(E)‐hibiscusamide (HAD) on the IL‐6/STAT3 signaling axis. Using a phosphorylated STAT3 luciferase reporter assay, NHA and HAD significantly reduced IL‐6‐induced luciferase activity. They also downregulated IL‐6‐induced gene expression, inhibited STAT3 nuclear translocation and phosphorylation of signaling molecules, and suppressed IL‐6/interleukin‐6 receptor binding. In a collagen‐induced arthritis mouse model, both compounds alleviated arthritis symptoms, decreased serum levels of anti‐type II collagen immunoglobulin G and interleukin‐17A, and downregulated T helper 17‐specific genes in the spleen. Furthermore, in vitro experiments demonstrated that NHA and HAD inhibited the differentiation of naïve CD4‐positive T cells into T helper 17 cells. These findings suggest that NHA and HAD effectively modulate interleukin‐6–mediated inflammatory signaling and may serve as potential therapeutic candidates for the management of rheumatoid arthritis.

The IL‐6/STAT3 axis is crucial in rheumatoid arthritis (RA) via Th17 differentiation. The IL‐6/STAT3 signaling pathway is downregulated as a result of the inhibition of IL‐6 and IL‐6R binding by NHA and NAD. NHA and NAD decrease the Th17 differentiation, which lessens the severity of CIA.