29th Annual Meeting of the American Society of Photobiology

Downtown Marriot

Chicago, Il.

The Potential Positive and Negative Effects of Melatonin and Hypericin

Abstract-
Environmental visible light and darkness drive the daily cycles of circadian rhythm and result in a complex series of neuroendocrine changes. Initially, a signal travels from the retina to the suprachiasmatic nucleus (SCN), triggering a release of either serotonin (in the light) or melatonin (in the dark). This chemical change (serotonin/melatonin) eventually leads to a cascade of hormonal changes in the pituitary, pineal, adrenal and thyroid glands. Circadian hormonal rhythm is drastically modified by air travel, living indoors during changing seasons, and working during normal sleeping hours. Disruption of this serotonin/melatonin cycle induces sleep disturbances and depression, and may contribute to the long-term risk of endocrine (breast, prostate) cancers. External control of the dark/light cycle and/or the administration of melatonin have led to effective treatments of sleep disorders, jet lag, and depression. Melatonin is also a potent agent which can inhibit the proliferation and invasiveness of steroid-dependent cancer cells and metastatic melanoma. Even in high dosages, melatonin is remarkably non-toxic. However, there is a potential for melatonin to enhance light sensitivity of the retina. The underlying etiology of depression, no matter what its source, is a decrease in excitatory neurotransmitters (norepinephrine, dopamine) and serotonin. Hypericin, the active ingredient in St. John's Wort, has been found to relieve moderate depression by selectively blocking the reuptake receptor for serotonin. Hypericin is also a potent antiviral agent and is being considered as an alternative dye for Photodynamic Therapy to treat non-responsive prostatic tumors. Hypericin is relatively non-toxic in the dark; however, in the presence of either UV or visible light it is potentially phototoxic to the lens and the retina and could conceivably lead to loss of vision. Hypericin has also been found to interfere with the metabolism and biological effects of important presciption drugs such as protease inhibitors (HIV medication) and birth control pills. . It is clear that these two over-the-counter remedies are effective treatments for some serious disorders. On the other hand, they must be used properly or they could lead to very serious side effects.

Keywords: melatonin, hypericin, St. John's Wort, eye damage