Anti-rheumatoid arthritis potential of Rhododendron molle G. Don leaf extract in adjuvant induced arthritis rats

The aim of this study was to test the anti-rheumatic arthritis effects of Rhododendron molle G. Don leaf extract in arthritis rats and inflammatory RAW 264.7 cells. Preliminary analysis and comparison of potential medicinal components of three polar extracts by HPLC and UHPLC-Q-TOF-MS.

SD rats were subcutaneously injected with complete Freund's adjuvant (CFA) to induce inflammation on the right hind paw. RAW 264.7 cells were induced by lipopolysaccharide (LPS) to established cell inflammatory model. The volume of rat hind paw was measured with a volume meter to detect swelling, and the weight of rats was measured with an electronic balance. The severity of arthritis in rats was evaluated by arthritis score. The pathological sections of rat hind paw joints were observed by hematoxylin-eosin staining, and the contents of IL-6 and IL-1β in serum were detected. qRT-PCR was used to detect the expression of IL-1β, IL-6, TNF-α and COX-2 genes in RAW 264.7 cells. The release of nitric oxide was measured by Griess reaction. The expression levels of IL-6 and IL-1β were detected by Western-Blot.

and discussion: The chloroform extract from R. molle leaves (CERL), Ethyl acetate extract from R. molle leaves (EERL), n-butanol extract from R. molle leaves (BERL) could significantly inhibit hind paws swelling and reduce arthritis index in arthritis rats. And it showed dose dependence. Compared with tripterygium glycosides (TG) tablets, an effective drug of RA treatment, CERL have better anti-RA effect after administration. In addition, the three kinds of the polar extracts of Rhododendron molle leaves (PERL) had lower toxicity, with the LD₅₀ 279.87, 239.65, 500.08 (mg/kg) respectively, while TG group's LD₅₀ was 96.00 (mg/kg). In vitro experiments showed that the three PERLs can significantly inhibit the level of pro-inflammatory factors and inflammatory mediator, such as TNF-α, IL-1β, IL-6, COX-2 and NO, which were consistent with their anti-RA ability. Among the three kinds of PERLs, CERL showed the best inhibitory activity.

The R. molle leaf is a potential medicinal part for the treatment of RA. This study explored the anti-RA and anti-inflammatory activities of CERL, EERL, BERL, which laid a foundation for further promoting the clinical application of R. molle.