Protective effects of geraniol (a monoterpene) in a diabetic neuropathy rat model: attenuation of behavioral impairments and biochemical perturbations.

Involvement of oxidative stress, inflammatory response, and mitochondrial dysfunction in the development of diabetic neuropathy (DN) is well appreciated. The present study examines the potential of geraniol (GE), a well-known phytoconstituent commonly found in lemon, spices, rose oil, etc., to attenuate DN-associated oxidative/nitrosative stress by employing a streptozotocin (STZ) diabetic rat model. STZ-induced diabetic rats provided with oral supplements of GE (100 mg/kg bw/day, 8 weeks) exhibited significant improvement in tail-flick latency (sensory function) and the narrow beam test (motor function). Terminally, elevated levels of oxidative markers (reactive oxygen species, malondialdehyde, hydroperoxides) in cytosol of the sciatic nerve (SN) and in selected regions of the brain of diabetic rats were markedly reduced by GE supplements. Furthermore, GE significantly diminished the levels of protein carbonyls (a measure of protein oxidation) and nitrites in diabetic rats. In addition, in mitochondria, GE supplements restored the activities of enzymes, such as complexes I-III, succinate dehydrogenase, and citrate synthase, in brain regions of diabetic rats, with a concomitant reduction in the levels of oxidative markers. GE significantly lowered the enhanced cytosolic calcium levels and acetylcholinesterase activity in the SN and the brain regions of diabetic rats. Depleted dopamine levels evident in the SN and the cortex/striatum among diabetic rats were restored by GE. From our data, we hypothesize that GE may be a promising therapeutic candidate in the management of DN in humans. Further understanding of the molecular mechanisms of its neuromodulatory effects is essential in order to exploit its therapeutic efficacy.