Luteolin and scoparone produce synergistic anti-rheumatoid arthritis effects in experimental models

Rheumatoid arthritis (RA) is a chronic inflammatory autoimmune disease characterized by chronic synovitis and progressive erosion of cartilage and bone1. Current RA therapies have limitations2. We have previously shown that an herbal formula comprising Rosae Multiflorae Fructus (RMF) and Lonicerae Japonicae Flos (LJF) possesses anti-RA effects in rats3-5. We have further found that luteolin (Lu, occurs in LJF) and scoparone (Sco, occurs in RMF) are the main anti-RA compounds of this herbal formula. This study aimed to investigate whether the combination of Lu and Sco (Lu-plus-Sco) has anti-RA effects, and to investigate the acute and sub-chronic toxicities of this combination.

The collagen-induced arthritis (CIA) DBA-1J mouse model was used to examine the in vivo anti-RA effects of Lu-plus-Sco. LPS-stumulated RAW264.7 cells and IL-6/soluble IL-6 receptor (IL-6/sIL-6R)-stimulated RA-FLS were used to evaluate the in vitro effects of Lu-plus-Sco. Synergism of the drug combination was evaluated using the coefficient of drug interaction (CDI) value. Acute and sub-chronic oral dosing toxicity assessments were employed to establish the toxicity profiles of Lu-plus-Sco.

In cell assays, Lu and Sco exerted synergistic effects in inhibiting NO production in LPS-stimulated RAW264.7 cells and suppressing the hyperproliferation of IL-6/sIL-6R-stimulated RA-FLS. In animal assays, we found that intragastric administration of Lu-plus-Sco attenuated paw swelling and bone erosion, suppressed synovial hyperplasia, down-regulated serum levels of pro-inflammatory cytokines (TNF-α, IL-1β, IL-6 and IL-17), and improved body weight gain of CIA mice. Acute oral dosing toxicity assessments showed that LD50 of Lu-plus-Sco on female and male mice were 1,022.6 mg/kg and 1,298.5 mg/kg (Lu:Sco=1:6), respectively. Sub-chronic toxicity study showed that intragastric gavage with Lu-plus-Sco for 14 days caused liver injury in female mice, while caused kidney injury and reproductive injury in male mice.

In summary, we for the first time demonstrated that Lu in combination with Sco exhibits synergetic anti-RA effects in cell models, and Lu-plus-Sco ameliorates CIA in mice. We also demonstrated that a 14-day intragastric administration of Lu-plus-Sco causes toxicities in mice. This study provides pharmacological and toxicological data for developing Lu-plus-Sco into a novel anti-RA agent.