Anti-Inflammatory Effects of p-Coumaric Acid, a Natural Compound of Oldenlandia diffusa, on Arthritis Model Rats

Abstract

Objectives: In China, Oldenlandia diffusa (OD) is a natural herb that is widely used and has been proven to be effective in the treatment of rheumatoid arthritis (RA). This study aimed to preliminarily reveal the mechanism by which OD exerts its beneficial effect.

Methods: Ultra-performance liquid chromatography photodiode array was applied to identify the absorbable compounds in the plasma of collagen-induced arthritis (CIA) model rats. After 2 weeks, an OD decoction or the identified absorbable compound was administered to CIA rats. Morphology, X-ray images of the joints, pathological images, arthritis index, and cytokine (TNF-α and IL-6) levels were evaluated.

Results: p-Coumaric acid (p-CA) was identified as the absorbed compound in plasma. After administration of p-CA solution or the OD decoction, symptoms in the treated rats were alleviated as compared to the untreated model rats, and inflammatory cell infiltration was suppressed. The arthritis index and serum levels of TNF-α and IL-6 were decreased as compared to the control group.

Conclusions: OD may exert its anti-inflammatory effect on RA via its active ingredient, p-CA. This information sheds light on the mechanism by which OD exerts its anti-inflammatory effort in RA and forms the basis for further development of therapeutic agents for RA.

Figure 1

Chromatogram of each group (308 nm): (a) blank methanol; (b) 8 reference compounds; (c) test solution of OD. p-CA refers to p-coumaric acid.

Figure 2

Chromatogram of each group (308 nm): (a) plasma without added compounds; (b) 8 reference compounds; (c) the plasma of rats that had been given OD decoction by oral gavage. p-CA refers to p-coumaric acid.

Figure 3

Morphological changes of joints in each group, from the 1st day to the 42nd day. (a) Posterior limb of a rat in the normal group. (b) Posterior limb of a rat in the model group, on the 14th day. (c) Posterior limb of a rat in the model group, on the 28th day. (d) Posterior limb of a rat in the model group, on the 42nd day. (e) Posterior limb of a rat treated with p-CA, on the 28th day. (f) Posterior limb of a rat treated with p-CA, on the 42nd day. (g) Posterior limb of a rat treated with OD decoction, on the 28th day. (h) Posterior limb of a rat treated with OD decoction, on the 42nd day.

Figure 4

X-ray film of the joints in each group, from the 1st day to the 42nd day. (a) Posterior limb of a rat in the normal group. (b) Posterior limb of a rat in the model group, on the 14th day. (c) Posterior limb of a rat in the model group, on the 28th day. (d) Posterior limb of a rat in the model group, on the 42nd day. (e) Posterior limb of a rat treated with p-CA, on the 28th day. (f) Posterior limb of a rat treated with p-CA, on the 42nd day. (g) Posterior limb of a rat treated with OD decoction, on the 28th day. (h) Posterior limb of a rat treated with OD decoction, on the 42nd day.

Figure 5

Synovium pathomorphology as seen by hematoxylin-eosin-staining in each group, from the 1st day to the 42nd day. (a) Normal group. (b) Model group, 14th day. (c) Model group, 28th day. (d) Model group, 42nd day. (e) p-CA group, 28th day. (f) p-CA, 42nd day. (g) OD group, 28th day. (h) OD group, 42nd day.

Figure 6

Arthritis index (AI) in each group (means ± SD), from the 1st day to the 42nd day. From the 28th day to the 42nd day, the p-CA group and OD group showed statistically significant differences (^∗p < 0.05) as compared to the model group. On the 42nd day, the OD group showed a significant difference (^#p < 0.05) as compared with the p-CA group.

Figure 7

Serum levels of TNF-α and IL-6 in each group (means ± SD) on the 28th day and 42nd day. The p-CA group and OD group showed statistically significant differences (^∗p < 0.05) as compared with the model group. The OD group also showed a significant difference (^#p < 0.05) as compared with the p-CA group.