Effects of rosmarinic acid on an experimental model of painful diabetic neuropathy in rats

Context: Diabetic neuropathic (DN) pain is one of the diabetes complications. Rosmarinic acid (RA), a natural phenol antioxidant, shows some biological activities, including anti-inflammatory, analgesic, and anti-diabetic effects. Objectives: We investigated the efficacy of RA administration (10 and 30 mg/kg) on streptozotocin (STZ)-induced neuropathy in rats. Material and methods: The animals received saline or RA (10 and 30 mg/kg, p.o.; once daily) for 8 weeks. DN was evaluated by the tail flick (TF) method, formalin test, and tactile allodynia. At the end, all rats were weighed and underwent plasma glucose measurement. Results: There was an increase in licking time during both formalin test phases in diabetic animals (138.5 +/- 10.7 and 448.7 +/- 2.6 s) that was decreased by RA10 mg/kg (103.5 +/- 7.5 and 284.4 +/- 19 s) and RA 30 mg/kg (81.8 +/- 11 and 192.7 +/- 14 s). RA 30 mg/kg caused anti-nociception during the early phase in treated controls (52.1 +/- 6 s) than untreated controls (99.4 +/- 5.9 s). The TF latency in diabetics (2.9 +/- 0.1 s) was increased in RA10 and 30 mg/kg treated diabetics (5.3 +/- 0.4 and 6 +/- 0.86 s). The paw withdrawal threshold (PWT) of the diabetics (3.6 +/- 0.7 g) was increased after RA 10 and 30 mg/kg (13.8 +/- 0.3 and 14 +/- 0.4 g) treatment. RA did not induce a significant change in body weight and plasma glucose of rats. Conclusion: RA showed efficacy in amelioration of some aspects of DN. Therefore, RA makes a good candidate for DN treatment in clinical studies.