Differential expression of spinal γ-aminobutyric acid and opioid receptors modulates the analgesic effects of intrathecal curcumin on postoperative/inflammatory pain in rats

BACKGROUND: Curcumin is traditionally used as an herbal medicine. We explored the efficacy of intrathecal curcumin in relieving both postoperative and inflammatory pain and elucidated the mechanisms of action of curcumin interacting with γ-aminobutyric acid (GABA) and opioid receptors at the spinal level. METHODS: Experimental pain was induced in male Sprague-Dawley rats via paw incision or injection of intraplantar carrageenan. After examination of the effects of intrathecal curcumin on the pain, GABA and opioid receptor antagonists were intrathecally administered to explore the involvement of GABA or opioid receptors on the effect of curcumin. Additionally, the expression levels of the GABA and opioid receptors were assessed. RESULTS: Intrathecal curcumin reduced the withdrawal threshold of both incisional surgery- and carrageenan injection-induced nociception. Intrathecal GABA and opioid receptor antagonists reversed the curcumin-mediated antinociception. Incisional surgery decreased the levels of the GABA receptors mRNA, but little changed the levels of the opioid receptors mRNA. Carrageenan injection increased the levels of the opioid receptors mRNA, but not the GABA receptors mRNA levels. Intrathecal curcumin increased or decreased the levels of GABA receptors mRNA and opioid receptors mRNA in the spinal cords of incised or carrageenan-injected rats, respectively. CONCLUSIONS: Intrathecal curcumin was effective to postoperative and inflammatory pain and such antinociception of curcumin was antagonized by both GABA and opioid receptor antagonists. Also, intrathecal curcumin altered the levels of GABA and opioid receptors. Thus, spinal GABA and opioid receptors may, respectively, be directly or indirectly involved when curcumin alleviates postoperative and inflammatory pain.

Cytotoxic activity and subset populations of peripheral blood natural killer cells in patients with chronic pain

BACKGROUND: Chronic pain reportedly exerts complex effects on immune function. Natural killer (NK) cells are lymphocytes that play a critical role in cellular and innate immunity. This study examined changes in the subset populations and cytotoxic activity of peripheral blood NK cells in patients with chronic pain. METHODS: Thirty patients with chronic moderate-to-severe pain (group P) and age-matched pain-free subjects (group NoP) were enrolled. Peripheral whole blood was analyzed for the percentage and expression of NK cell surface markers (CD56 and CD16) by flow cytometry. Cytotoxic activity was assayed by evaluating CD69 expression on CD3−/CD56+NK cells. RESULTS: The percentage of NK cells among total lymphocytes was not significantly different between groups P and NoP (16.3 ± 9.3 vs. 20.2 ± 10.5%). Likewise, the percentages of two major NK cell subsets, CD56bright and CD56dim, were also not significantly different between the two groups. However, the percentage of CD56bright/CD16+ subset, was slightly but significantly increased in group P (1.0 ± 0.9%; P < 0.01) compared with group NoP (0.5 ± 0.6%). The cytotoxicity of NK cells was not different between the two groups, showing similar CD69 expression (P vs. NoP = 29.2 ± 15.2 vs. 32.0 ± 15.0%). These findings were not influenced by pain intensity, opioid use, or disease causing pain in group P. CONCLUSIONS: NK cell cytotoxic activity and major subset populations, with the exception of an increased percentage of the CD56bright/CD16+ subset, are not significantly altered in patients with chronic severe pain.