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Ostrin, L. A. (2018). Ocular and systemic melatonin and the influence of light exposure. Clin Exp Optom, in press, in press.
Abstract: Melatonin is a neurohormone known to modulate a wide range of circadian functions, including sleep. The synthesis and release of melatonin from the pineal gland is heavily influenced by light stimulation of the retina, particularly through the intrinsically photosensitive retinal ganglion cells. Melatonin is also synthesised within the eye, although to a much lesser extent than in the pineal gland. Melatonin acts directly on ocular structures to mediate a variety of diurnal rhythms and physiological processes within the eye. The interactions between melatonin, the eye, and visual function have been the subject of a considerable body of recent research. This review is intended to provide a broad introduction for eye-care practitioners and researchers to the topic of melatonin and the eye. The first half of the review describes the anatomy and physiology of melatonin production: how visual inputs affect the pineal production of melatonin; how melatonin is involved in a variety of diurnal rhythms within the eye, including photoreceptor disc shedding, neuronal sensitivity, and intraocular pressure control; and melatonin production and physiological roles in retina, ciliary body, lens and cornea. The second half of the review describes clinical implications of light/melatonin interactions. These include light exposure and photoreceptor contributions in melatonin suppression, leading to consideration of how blue blockers, cataract, and light therapy might affect sleep and mood in patients. Additionally, the interactions between melatonin, sleep and refractive error development are discussed. A better understanding of environmental factors that affect melatonin and subsequent effects on physiological processes will allow clinicians to develop treatments and recommend modifiable behaviours to improve sleep, increase daytime alertness, and regulate ocular and systemic processes related to melatonin.
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Souman, J. L., Borra, T., de Goijer, I., Schlangen, L. J. M., Vlaskamp, B. N. S., & Lucassen, M. P. (2018). Spectral Tuning of White Light Allows for Strong Reduction in Melatonin Suppression without Changing Illumination Level or Color Temperature. J Biol Rhythms, 33(4), 420–431.
Abstract: Studies with monochromatic light stimuli have shown that the action spectrum for melatonin suppression exhibits its highest sensitivity at short wavelengths, around 460 to 480 nm. Other studies have demonstrated that filtering out the short wavelengths from white light reduces melatonin suppression. However, this filtering of short wavelengths was generally confounded with reduced light intensity and/or changes in color temperature. Moreover, it changed the appearance from white light to yellow/orange, rendering it unusable for many practical applications. Here, we show that selectively tuning a polychromatic white light spectrum, compensating for the reduction in spectral power between 450 and 500 nm by enhancing power at even shorter wavelengths, can produce greatly different effects on melatonin production, without changes in illuminance or color temperature. On different evenings, 15 participants were exposed to 3 h of white light with either low or high power between 450 and 500 nm, and the effects on salivary melatonin levels and alertness were compared with those during a dim light baseline. Exposure to the spectrum with low power between 450 and 500 nm, but high power at even shorter wavelengths, did not suppress melatonin compared with dim light, despite a large difference in illuminance (175 vs. <5 lux). In contrast, exposure to the spectrum with high power between 450 and 500 nm (also 175 lux) resulted in almost 50% melatonin suppression. For alertness, no significant differences between the 3 conditions were observed. These results open up new opportunities for lighting applications that allow for the use of electrical lighting without disturbance of melatonin production.
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El-Bakry, H. A., Ismail, I. A., & Soliman, S. S. (2018). Immunosenescence-like state is accelerated by constant light exposure and counteracted by melatonin or turmeric administration through DJ-1/Nrf2 and P53/Bax pathways. J Photochem Photobiol B, 186, 69–80.
Abstract: The awareness of the interrelationship between immunosenescence and constant light exposure can provide new insights into the consequences of excessive exposure to light at night due to light pollution or shift work. Here, we investigated whether constant light exposure (LL) acts as an inducer of immunosenescence. We also determined the role of melatonin or turmeric in reversing the putative effects of constant light and explored for the first time the underlying molecular mechanisms. Young (3-4-month-old) rats were exposed daily to LL alone or in combination with each of melatonin and turmeric for 12weeks. A group of aged rats (18-months old; n=6) was used as a reference for natural immunosenescence. Constant light exposure resulted in remarkable pathophysiological alterations resembling those noticed in normal aged rats, manifested as apparent decreases in antioxidant activities as well as Nrf2 and DJ-1 expressions, striking augmentation in oxidative stress, proinflammatory cytokines and expression of TNFalpha, Bax, and p53 genes, and deleterious changes of lymphoid organs, Co-administration of melatonin or turmeric was able to reverse all alterations induced by LL through upregulation of Nrf2/DJ-1 and downregulation of p53/Bax pathways. These data suggest that LL accelerates immunosenescence via oxidative stress and apoptotic pathways. They also demonstrate for the first time that turmeric is comparable to melatonin in boosting the immune function and counteracting the LL-associated immunosenescence. These effects suggest that turmeric supplementation can be used as an inexpensive intervention to prevent circadian disruption-related immunosenescence. However, to validate the effects of turmeric on humans further studies are warranted.
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Kim, Y. J., Kim, H. M., Kim, H. M., Jeong, B. R., Lee, H. - J., Kim, H. - J., et al. (2018). Ice plant growth and phytochemical concentrations are affected by light quality and intensity of monochromatic light-emitting diodes. Hortic. Environ. Biotechnol., 59(4), 529–536.
Abstract: The ice plant (Mesembryanthemum crystallinum L.), widely known to be an effective cure for diabetes mellitus, is also a functional crop. This study was conducted to examine the effects of light quality and intensity of monochromatic light-emitting diodes (LEDs) on ice plant growth and phytochemical concentrations in a closed-type plant production system. Ice plant seedlings were transplanted into a deep floating technique system with a recycling nutrient solution (EC 4.0 dS m−1, pH 6.5). Fluorescent lamps, as well as monochromatic red (660 nm) and blue (450 nm) LEDs, were used at 120 ± 5 or 150 ± 5 µmol m−2 s−1 PPFD with a photoperiod of 14 h/10 h (light/dark) for 4 weeks. Ice plants showed higher growth under the high light intensity treatment, especially under the red LEDs. Furthermore, the SPAD value and photosynthetic rate were higher under the red LEDs with 150 µmol m−2 s−1 PPFD. The ice plant phytochemical composition, such as antioxidant activity and myo-inositol and pinitol concentrations, were highest under the blue LEDs with 150 µmol m−2 s−1 PPFD. Total phenolic concentration was highest under the blue LEDs with 120 µmol m−2 s−1 PPFD. Despite a slightly different dependence on light intensity, phytochemical concentrations responded positively to the blue LED treatments, as compared to other treatments. In conclusion, this study suggests that red LEDs enhance ice plant biomass, while blue LEDs induce phytochemical
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Point, S. (2018). Blue Light Hazard: are exposure limit values protective enough for newborn infants? Radioprotection, in press, in press.
Abstract: Blue Light Hazard is an emerging concern for health of population. Nevertheless, acute exposure to blue rays from artificial light is well taken into account by normative requirements applicable to lamps engineering and risk for general population is low. There is also no evidence for a chronic effect of artificial lighting on retina for general population at radiance below exposure limit values. That said, children in the very first years of life constitute a specific population to consider. On one side, eye anatomy of very young infants is different from elder young people or adults. On the other side, infants can be in close contact with some luminous toys or night lights. This paper presents a first approach for taking into account the specific anatomy of newborn infants’ eyes in blue light hazard evaluation. Results show that differences of crystalline lens transparency, focal length and pupil diameter could induce a significantly higher retinal exposure than for adult.
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