Cell death and survival are critical events for neurodegeneration, mitochondria being increasingly seen as important determinants of both.
Mitochondrial dysfunction is considered a major causative factor in
Alzheimer's disease (AD),
Parkinson's disease (PD) and
Huntington's disease (HD). Increased
free radical generation, enhanced mitochondrial inducible
nitric oxide (
NO) synthase activity and NO production, and disrupted electron transport system and mitochondrial permeability transition, have all been involved in impaired mitochondrial function.
Melatonin, the major secretory product of the pineal gland, is an
antioxidant and an effective protector of mitochondrial bioenergetic function. Both in vitro and in vivo,
melatonin was effective to prevent oxidative stress/nitrosative stress-induced
mitochondrial dysfunction seen in experimental models of AD, PD and HD. These effects are seen at doses 2-3 orders of magnitude higher than those required to affect sleep and circadian rhythms, both conspicuous targets of
melatonin action.
Melatonin is selectively taken up by mitochondria, a function not shared by other
antioxidants. A limited number of clinical studies indicate that
melatonin can improve sleep and circadian rhythm disruption in PD and AD patients. More recently, attention has been focused on the development of potent
melatonin analogs with prolonged effects which were employed in clinical trials in sleep-disturbed or depressed patients in doses considerably higher than those employed for
melatonin. In view that the relative potencies of the analogs are higher than that of the natural compound, clinical trials employing
melatonin in the range of 50-100mg/day are needed to assess its therapeutic validity in
neurodegenerative disorders.