Humulus japonicus extract ameliorates collagen‑induced arthritis in mice through regulation of overall articular inflammation.

Humulus japonicus (HJ) is a widely used herbal medicine in Asia with anti‑oxidative, anti‑microbial, and anti‑inflammatory effects. We investigated the potential therapeutic effects of HJ in rheumatoid arthritis (RA) using a mouse model of collagen‑induced arthritis (CIA) and a lipopolysaccharide‑stimulated murine macrophage cell line (RAW 264.7). The CIA mice were administered 300 mg/kg HJ orally starting 3 days prior to second immunization. The clinical and histopathological findings were assessed in the paw of CIA mice. The levels of autoantibodies and inflammatory markers were determined in the plasma and cell culture supernatant, respectively. The expression at mRNA and protein levels was analyzed by reverse transcription quantitative‑PCR and western blot analysis, respectively. HJ significantly decreased the gross arthritic scores and paw swelling in CIA mice. Furthermore, synovial inflammation, cartilage destruction, and bone erosion were markedly reduced by HJ. It also decreased the expression of inflammatory enzymes in both the paw of mice and RAW 264.7 cells. Moreover, the expression of genes related to all macrophages and pro‑inflammatory M1 macrophage were significantly decreased, whereas the expression of anti‑inflammatory M2 macrophage marker was markedly increased in the paw of HJ‑treated CIA mice. In addition, HJ suppressed the levels of plasma anti‑type II collagen antibody following the decreased expression of T helper type 1 (Th1) and Th2 cell‑associated surface markers and cytokines in the paw. HJ also significantly inhibited the expression of IL‑6 both in vitro and in vivo, followed by reduced STAT3 phosphorylation and expression in the paw of CIA mice. Finally, the expression of osteoclast‑related genes was decreased in the paw of HJ‑treated CIA mice. These findings suggest that HJ can play a role in suppressing the development of CIA by overall regulation of articular inflammation. This study should provide new insights into the use of HJ as a therapeutically effective natural product against RA.