Modulation of neuropathic pain in experimental diabetes mellitus

The main objective of the current article is to investigate the diabetic polyneuropathy which represents a major preoccupation within the context of high incidence of diabetes mellitus (DM) and its complications. Moreover, neuropathy may develop despite intensive hyperglycaemic control. The effect of Zn and black grape seed polyphenols (BGSP) in streptozotocin diabetic rats was studied. Zn and BGSP were administered by gavage, daily, for 16 weeks to Wistar rats that have been rendered diabetic by a single i.v. injection of streptozotocin (55 mg/kg body weight). Dysalgesia was investigated under the conditions of nociceptive stimulation through the following tests: the thermoalgesic mechanism through the tail-flick test, the hot plate test and the plantar test, and the mechanoalgesic mechanism through the algesimetric test. Thermal hyperalgesia detected in the diabetic group is significantly reduced (p < 0.001) through the administration of polyphenols, or even better, of Zn. Diabetes-associated mechanical hyperalgesia decreased significantly (p < 0.001) probably through the inhibition of the NMDA receptors. Administration of Zn or BGSP to the diabetic group improves glycosylated haemoglobin (HbA1c) values but does not bring them to normal. The present data suggest a favourable effect of Zn and BGSP in inhibiting diabetic complications by several mechanisms.