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.