Puerarin alleviates neuropathic pain by inhibiting neuroinflammation in spinal cord

Abstract

Neuropathic pain responds poorly to drug treatments, and partial relief is achieved in only about half of the patients. Puerarin, the main constituent of Puerariae Lobatae Radix, has been used extensively in China to treat hypertension and tumor. The current study examined the effects of puerarin on neuropathic pain using two most commonly used animal models: chronic constriction injury (CCI) and diabetic neuropathy. We found that consecutive intrathecal administration of puerarin (4-100 nM) for 7 days inhibited the mechanical and thermal nociceptive response induced by CCI and diabetes without interfering with the normal pain response. Meanwhile, in both models puerarin inhibited the activation of microglia and astroglia in the spinal dorsal horn. Puerarin also reduced the upregulated levels of nuclear factor-κB (NF-κB) and other proinflammatory cytokines, such as IL-6, IL-1β, and TNF-α, in the spinal cord. In summary, puerarin alleviated CCI- and diabetes-induced neuropathic pain, and its effectiveness might be due to the inhibition of neuroinflammation in the spinal cord. The anti-inflammation effect of puerarin might be related to the suppression of spinal NF-κB activation and/or cytokines upregulation. We conclude that puerarin has a significant effect on alleviating neuropathic pain and thus may serve as a therapeutic approach for neuropathic pain.

Figure 1

The effects of puerarin on mechanical stimulus test in normal rats. Normal rats received intrathecal 100 nmol puerarin or vehicle. The mechanical withdrawal thresholds (g) of the right hind paws were measured 60 min after drug administration. Data were presented as mean ± SEM. Each group consisted of 5 rats. At 100 nM, puerarin did not affect mechanical withdrawal threshold.

Figure 2

The effects of puerarin on CCI- and diabetes-induced mechanical allodynia. (a), (c) The temporal profile of mechanical withdrawal threshold on CCI- (a) and diabetes- (c) induced mechanical allodynia; (b), (d) the maximal possible efficiency of puerarin on the 11th day after CCI surgery (b) and the 27th day after streptozotocin injection; CCI: chronic constriction injury. Data are presented as mean ± SEM. ***P < 0.001, model group versus control group; ^# P < 0.05, ^## P < 0.01, ^### P < 0.001, puerarin treatment group versus model group (one-way ANOVA with post hoc LSD t-test). Each group consisted of 6–10 rats.

Figure 3

The effects of puerarin on CCI-induced microglia and astroglia activation in ipsilateral spinal dorsal horn of rats. (a) and (b) Representative images of ipsilateral spinal dorsal microglia (a) and astroglia (b) activation in control rats, CCI rats, CCI rats receiving vehicle, 20 and 100 nM puerarin on the 11th day after CCI surgery. Scale bar: 100 μm. (c) Quantification of microglia activation in the spinal cord on the 11th day after CCI surgery. CCI: chronic constriction injury. Data are presented as mean ± SEM. ***P < 0.001, CCI model versus control; ^### P < 0.001, puerarin versus CCI model (one-way ANOVA with post hoc LSD t-test). Each group consisted of 6–10 rats.

Figure 4

The effects of puerarin on diabetes-induced microglia and astroglia activation in ipsilateral spinal dorsal horn of rats. (a) and (b) Representative images of ipsilateral spinal dorsal microglia (a) and astroglia (b) activation in control rats, diabetic rats receiving vehicle, 20 and 100 nM puerarin on the 27th day after streptozotocin injection. Scale bar: 100 μm. (c) Quantification of microglia and astroglia activation in the spinal cord on the 27th day after streptozotocin injection. Data are presented as mean ± SEM. ***P < 0.001, diabetic rats versus control; ^### P < 0.001, puerarin versus diabetes model (one-way ANOVA with post hoc LSD t-test). Each group consisted of 6–10 rats.

Figure 5

The effects of puerarin on CCI- and diabetes-induced proinflammatory cytokines overexpression (a) and NF-κB overactivation ((b), (c), (d)) on the 11th day after CCI surgery, and on the 27th day after streptozotocin injection in rat spinal cord. Data are presented as mean ± SEM. CCI: chronic constriction injury; Cyt: cytoplasmic; Nuc: nuclear. ***P < 0.001, CCI and diabetes models versus control; ^# P < 0.05, ^## P < 0.01, ^### P < 0.001, puerarin versus CCI and diabetes models (one-way ANOVA with post hoc LSD t-test). Each group consisted of 6–10 rats.

Figure 6

Hypothetical mechanisms of antineuroinflammation activity of puerarin.