Curcumin Attenuates Diabetic Neuropathic Pain by Downregulating TNF-alpha in a Rat Model

The mechanisms involved in diabetic neuropathic pain are complex and involve peripheral and central pathophysiological phenomena. Proinflammatory tumour necrosis factor alpha (TNF-alpha) and TNF-alpha receptor 1, which are markers of inflammation, contribute to neuropathic pain. The purpose of this experimental study was to evaluate the effect of curcumin on diabetic pain in rats. We tested 24 rats with diabetes induced by a single intraperitoneal injection of streptozotocin and 24 healthy control rats. Twelve rats in each group received 60 mg/kg oral curcumin daily for 28 days, and the other 12 received vehicle. On days 7, 14, 21, and 28, we tested mechanical allodynia with von Frey hairs and thermal hyperalgesia with radiant heat. Markers of inflammation in the spinal cord dorsal horn on day 28 were estimated with a commercial assay and Western blot analysis. Compared to control rats, diabetic rats exhibited increased mean plasma glucose concentration, decreased mean body weight, and significant pain hypersensitivity, as evidenced by decreased paw withdrawal threshold to von Frey hairs and decreased paw withdrawal latency to heat. Curcumin significantly attenuated the diabetes-induced allodynia and hyperalgesia and reduced the expression of both TNF-alpha and TNF-alpha receptor 1. Curcumin seems to relieve diabetic hyperalgesia, possibly through an inhibitory action on TNF-alpha and TNF-alpha receptor 1.