Recent studies have demonstrated that resveratrol (RSV) reduces the incidence of age-related macular degeneration, Alzheimer's disease (AD), and stroke, while melatonin (MEL) supplementation reduces the progression of the cognitive impairment in AD patients. The purpose of this investigation was to assess whether the co-administration of MEL and RSV exerts synergistic effects on their neuroprotective properties against β-amyloid (Aβ)-induced neuronal death.

The neuroprotective effects of co-treatment with MEL and RSV on Aβ1-42-induced cell death, was measured by MTT reduction assay. Aβ1-42 caused an increase in intracellular levels of reactive oxygen species (ROS), as assessed by H₂-DCF-DA dye, and a reduction of total glutathione (GSH) levels and mitochondrial membrane potential, as assessed using monochlorobimane and rhodamine 123 fluorescence, respectively. Western blotting was used to investigate the intracellular signaling mechanism involved in these synergic effects.

We treated a murine HT22 hippocampal cell line with MEL or RSV alone or with both simultaneously. MEL and RSV alone significantly attenuated ROS production, mitochondrial membrane-potential disruption and the neurotoxicity induced by Aβ1-42. They also restored the Aβ1-42-induced depletion of GSH, back to within its normal range and prevented the Aβ1-42-induced activation of glycogen synthase kinase 3β (GSK3β). However, co-treatment with MEL and RSV did not exert any significant synergistic effects on either the recovery of the Aβ1-42-induced depletion of GSH or on the inhibition of Aβ1-42-induced GSK3β activation. Aβ1-42 treatment increased AMP-activated protein kinase (AMPK) activity, which is associated with subsequent neuronal death. We demonstrated that MEL and RSV treatment inhibited the phosphorylation of AMPK.

Together, our results suggest that co-administration of MEL and RSV acts as an effective treatment for AD by attenuating Aβ1-42-induced oxidative stress and the AMPK-dependent pathway.