[The effect of berberine on ameliorating chronic inflammatory pain and depression]

Objective: To explore the effect of berberine on chronic inflammatory pain and the comorbid depression and the associated mechanisms. Methods: Forty healthy male ICR mice (2 months, 25-30 g) were used in the present study. The chronic inflammatory pain was induced by intraplantar injection of complete freund's adjuvant (CFA) to the hind paws. All animals were divided into 4 groups (n=10 for each group) according to random number table: the saline group (group A), the chronic pain group (group B), the saline+ berberine group (group C) and the chronic pain+ berberine group (group D). The baseline data of pain and depressive performance were measured on the day before any drug treatment.On d1, mice of B and D groups received intraplantar injections of 50 μl CFA emulsion (1∶1 diluted with saline); mice of A and C groups received intraplantar injections of the same volume of saline. During d15-d21, mice of C and D groups received intraperitoneal injections of berberine (50 mg/kg, daily for 7 days); mice of A and B groups received the equal volume of saline. The Hargreaves tests and the Von Frey tests were conducted before the injection of CFA and on d7, d14, d17 and d21 to measure the thermal and mechanical pain thresholds. The forced swimming tests and novelty-suppressed feeding tests were performed before the injection of CFA and on d21 to measure the depressive performance. After the behavioral tests, the levels of inflammatory cytokines interleukin-1β (IL-1β), interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α) at the lumbar (L4-L5) spinal cord were examined by enzyme-linked immunosorbent assay(ELISA). The mRNA level of chemokine C-C motif ligand 2 (CCL2) in the lumbar spinal cord was examined by quantitative real-time polymerase chain reaction(qRT-PCR). Results: Compared with group A, the thermal withdrawal latency of group B mice on d7, d14, d17, d21 was declined[(3.40±0.67)s vs (10.55±1.58)s, (7.49±1.04)s vs (11.47±1.92)s, (6.46±0.56)s vs (11.60±1.86)s, (6.04±0.54)s vs (10.33±1.59)s, all P<0.01], and the mechanical threshold was also decreased[(0.15±0.03)g vs (0.78±0.24)g, (0.23±0.12)g vs (0.60±0.16)g, (0.30±0.12)g vs (0.72±0.25)g, (0.40±0.00)g vs (0.72±0.19)g, all P<0.01], on d21 the immobility time was increased[(161.60±35.79)s vs (88.92±53.24)s , P<0.05]and the time of feeding latency was decreased[(227.40±57.5)s vs (77.25±26.45)s, P<0.01], suggesting that CFA could induce hyperalgesia and depression. After berberine treatment (daily for 7 days), compared with group B, the thermal withdrawal latency of group D mice was increased[(9.99±2.68)s vs (6.04±0.54)s, P<0.01], the mechanical threshold was elevated[(0.80±0.21)g vs (0.40±0.00)g, P<0.01], the immobility time was decreased[(92.97±44.31)s vs (161.60±35.79)s, P<0.05], and the feeding latency was declined[(105.00±50.00)s vs (227.40±57.5)s, P<0.01]. Compared with group A, the concentrations of spinal IL-1β, IL-6 and TNF-α in group B were increased[(29.90±4.87)pg/ml vs (21.00±5.46)pg/ml, (131.10±26.12)pg/ml vs (60.68±23.47)pg/ml, (21.54±4.93)pg/ml vs (11.39±3.66) pg/ml , all P<0.01], the mRNA level of CCL2 was upregulated[(2.21±0.60) vs (1.00±0.37), P<0.01]. After berberine treatment (daily for 7 days), compared with group B, the concentrations of IL-1β, IL-6 and TNF-α in group D were decreased[(19.44±4.83)pg/ml vs (29.90±4.87) pg/ml , (57.82±32.28)pg/ml vs (131.10±26.12)pg/ml , (9.29±2.46)pg/ml vs (21.54±4.93) pg/ml, all P<0.01], the mRNA level of CCL2 was downregulated[(1.33±0.40)vs (2.21±0.60), P<0.05]. Conclusion: Berberine can reverse chronic inflammatory pain induced by CFA and alleviated the comorbid depression. Its anti-nociceptive and anti-depressive effects may associate with downregulation of the spinal levels of the inflammatory cytokines and mRNA transcription of CCL2.