Effects of melatonin and light on porphyrin synthesis in the bovine retina, pigment epithelium and choroid

Circadian clocks, clock networks, arylalkylamine N-acetyltransferase, and melatonin in the retina

Circadian clocks are self-sustaining genetically based molecular machines that impose approximately 24h rhythmicity on physiology and behavior that synchronize these functions with the solar day-night cycle. Circadian clocks in the vertebrate retina optimize retinal function by driving rhythms in gene expression, photoreceptor outer segment membrane turnover, and visual sensitivity. This review focuses on recent progress in understanding how clocks and light control arylalkylamine N-acetyltransferase (AANAT), which is thought to drive the daily rhythm in melatonin production in those retinas that synthesize the neurohormone; AANAT is also thought to detoxify arylalkylamines through N-acetylation. The review will cover evidence that cAMP is a major output of the circadian clock in photoreceptor cells; and recent advances indicating that clocks and clock networks occur in multiple cell types of the retina.

Melatonin protects against oxidative stress caused by delta-aminolevulinic acid: implications for cancer reduction

delta-Aminolevulinic acid (ALA) is a precursor of haem. The increased concentration of ALA is typically related to acute intermittent porphyria, hereditary tyrosinemia, and lead poisoning. delta-Aminolevulinic acid produced in excess accumulates in a number of organs, causes oxidative damage, and often leads to cancer. Melatonin (N-acetyl-5-methoxytryptamine) is a well-known antioxidant, free radical scavenger, and exhibits anticarcinogenic properties. It protects DNA, lipids, and proteins from oxidative damage. The protective effects of melatonin against ALA-induced oxidation of guanine bases, lipid peroxidation, and alterations in membrane fluidity in several organs have been documented. There is an inverse relationship between melatonin and ALA concentrations in both experimental and clinical conditions of porphyria. The marked efficacy of melatonin in protecting against ALA-related oxidative stress, its oncostatic properties, and low toxicity constitute reasons to consider the use of this indoleamine as a co-treatment in patients suffering from disturbances related to ALA accumulation.

Melatonin increases cyclic guanosine monophosphate: biochemical effects mediated by porphyrins, calcium and nitric oxide. Relationships to infant colic and the Sudden Infant Death Syndrome

It is hypothesized that melatonin, by its actions on porphyrin and nitric oxide biosynthesis, produces an increase in cyclic guanosine monophosphate.