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Neuroprotective Effects of Melatonin Assessed

The neuroprotective effects of melatonin appear to be related to antioxidant and antiamyloidogenic features of the hormone, not to the involvement of melatonin receptors.

Researchers in the United States and Barcelona, Spain compared the free-radical scavenging potency of compounds with varying affinities for melatonin membrane receptors MLT 1a and 1b. They also assessed the Amyloid Beta (A^ß)-mediated neurotoxicity in human neuroblastoma cells and primary hippocampal neurons.

They found that melatonin membrane receptor agonists devoid of antioxidant activity were found to have no neuroprotection against A^ß toxicity. Cells were fully protected, however, in parallel control experiments which added either melatonin or the structurally unrelated free-radical scavenger phenyl-N-t-butyl nitrone (PBN) to A^ß-containing culture media.

It has been shown that exposure of neuronal cells to the A^ß protein--which is heavily implicated in pathogenesis of Alzheimer's Disease--results in extensive oxidative damage of bio-molecules that are profoundly harmful to neuronal homeostasis. It has further been demonstrated that melatonin protects neurons against A^ß-mediated neurotoxicity, including cell death and a spectrum of oxidative lesions.

The present study suggests that the hormone does not require binding to a melatonin receptor for its protective effects, the researchers say.
Journal of Pineal Research, 2002, vol. 32, no. 3;135-142(8). "The neuroprotective activities of melatonin against the Alzheimer [beta]-protein are not mediated by melatonin membrane receptors"

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