Toward optimizing lighting as a countermeasure to sleep and circadian disruption in space flight

Skeletal muscle gene expression dysregulation in long-term spaceflights and aging is clock-dependent

The circadian clock regulates cellular and molecular processes in mammals across all tissues including skeletal muscle, one of the largest organs in the human body. Dysregulated circadian rhythms are characteristic of aging and crewed spaceflight, associated with, for example, musculoskeletal atrophy. Molecular insights into spaceflight-related alterations of circadian regulation in skeletal muscle are still missing. Here, we investigated potential functional consequences of clock disruptions on skeletal muscle using published omics datasets obtained from spaceflights and other clock-altering, external (fasting and exercise), or internal (aging) conditions on Earth. Our analysis identified alterations of the clock network and skeletal muscle-associated pathways, as a result of spaceflight duration in mice, which resembles aging-related gene expression changes observed in humans on Earth (e.g., ATF4 downregulation, associated with muscle atrophy). Furthermore, according to our results, external factors such as exercise or fasting lead to molecular changes in the core-clock network, which may compensate for the circadian disruption observed during spaceflights. Thus, maintaining circadian functioning is crucial to ameliorate unphysiological alterations and musculoskeletal atrophy reported among astronauts.

The Effect of Correlated Colour Temperature on Physiological, Emotional and Subjective Satisfaction in the Hygiene Area of a Space Station

The hygiene area is one of the most important facilities in a space station. If its environmental lighting is appropriately designed, it can significantly reduce the psychological pressure on astronauts. This study investigates the effect of correlated colour temperature (CCT) on heart rate, galvanic skin response, emotion and satisfaction in the hygiene area of a space station. Forty subjects participated in experiments in a hygiene area simulator with a controlled lighting environment. The lighting conditions included 2700 K, 3300 K, 3600 K, 5000 K and 6300 K; physiological responses (heart rate, galvanic skin response), as well as emotion and satisfaction, were recorded. The results showed that CCT significantly influenced the participants’ physiological and subjective responses in the space station hygiene area. 6300 K led to the best emotion and satisfaction levels, the highest galvanic skin response and the lowest heart rate. The opposite was true for 2700 K.

Keeping the right time in space: importance of circadian clock and sleep for physiology and performance of astronauts

The circadian clock and sleep are essential for human physiology and behavior; deregulation of circadian rhythms impairs health and performance. Circadian clocks and sleep evolved to adapt to Earth's environment, which is characterized by a 24-hour light-dark cycle. Changes in gravity load, lighting and work schedules during spaceflight missions can impact circadian clocks and disrupt sleep, in turn jeopardizing the mood, cognition and performance of orbiting astronauts. In this review, we summarize our understanding of both the influence of the space environment on the circadian timing system and sleep and the impact of these changes on astronaut physiology and performance.

Using space-based investigations to inform cancer research on Earth

Experiments conducted in the microgravity environment of space are not typically at the forefront of the mind of a cancer biologist. However, space provides physical conditions that are not achievable on Earth, as well as conditions that can be exploited to study mechanisms and pathways that control cell growth and function. Over the past four decades, studies have shown how exposure to microgravity alters biological processes that may be relevant to cancer. In this Review, we explore the influence of microgravity on cell biology, focusing on tumour cells grown in space together with work carried out using models in ground-based investigations.

Effect of cyclodextrins on the complexation and nasal permeation of melatonin

The inclusion complexation of melatonin (MT) with modified cyclodextrins (CDs) was studied with an objective of improving the solubility and nasal absorption of MT. The formation of inclusion complex of MT with Hydroxypropyl beta CD (HPbeta CD) and randomly methylated beta CD (RMbeta CD) was characterized in solution and solid states by phase solubility and differential scanning calorimetry analyses. The phase solubility data indicate a linear increase in the solubility of MT with CDs demonstrating Higuchi's A(L)-type phase solubility profiles. The effect of CDs on the permeation of MT across EpiAirway(TM)-100 cultures was studied using a modified nonstatic diffusion setup. CDs were employed at different concentrations with 1% w/v micronized MT suspension in hydroxypropyl methyl cellulose (HPMC) vehicle. At low CD concentrations (1% w/v), the permeation of MT from HPMC formulation was significantly increased (125%,p < .001). However, the permeation was significantly reduced when CDs were used at relatively high concentrations (5 to 10% w/v concentration for HPbetaCD and 10% w/v concentration for RMbetaCD,p < .001). All the tissues were viable with good tissue integrity at the end of permeation experiments, as measured by methylthiazoletetrazolium assay and transepithelial electrical resistance measurements. In conclusion, formation of inclusion complex of MT with HPbetaCD and RMbetaCD was demonstrated in solution and solid state. Both HPbetaCD and RM betaCD at 1% w/v concentration were found to improve the nasal permeability of MT from HPMC gel formulations.

Sleep under extreme environments: Effects of heat and cold exposure, altitude, hyperbaric pressure and microgravity in space

Human sleep is sensitive to the individual's environment. The present review examines current knowledge of human sleep patterns under different environments: heat exposure, cold exposure, altitude, high pressure and microgravity in space. Heat exposure has two effects. In people living in temperate conditions, moderate heat loads (hot bath, sauna) prior to sleep provoke a delayed reaction across time (diachronic reaction) whereby slow-wave sleep (SWS) augments in the following night (neurogenic adaptive pathway). Melanoids and Caucasians living in the Sahel dry tropical climate experience diachronic increases in SWS throughout seasonal acclimatization. Such increases are greater during the hot season, being further enhanced after daytime exercise. On the contrary, when subjects are acutely exposed to heat, diachronic decreases in total sleep time and SWS occur, being often accompanied by synchronic (concomitant) diminution in REM sleep. Stress hormones increase. Nocturnal cold exposure provokes a synchronic decrease in REM sleep along with an activation of stress hormones (synchronic somatic reaction). SWS remains undisturbed as it still occurs at the beginning of the night before nocturnal body cooling. Altitude and high pressure are deleterious to sleep, especially in non-acclimatized individuals. In their controlled environment, astronauts can sleep well in microgravity. Exercise-induced sleep changes help to understand environmental effects on sleep: well-tolerated environmental strains may improve sleep through a neurogenic adaptive pathway; when this "central" adaptive pathway is overloaded or bypassed, diachronic and synchronic sleep disruptions occur.

Photoreception for Circadian, Neuroendocrine, and Neurobehavioral Regulation

In the art and science of lighting, four traditional objectives have been to provide light that: 1) is optimum for visual performance; 2) is visually comfortable; 3) permits aesthetic appreciation of the space; and 4) conserves energy. Over the past 25 years, it has been demonstrated that there are nonvisual, systemic effects of light in healthy humans. Furthermore, light has been used to successfully treat patients with selected affective and sleep disorders as well as healthy individuals who have circadian disruption due to shift work, transcontinental jet travel, or space flight. Recently, there has been an upheaval in the understanding of photoreceptive input to the circadian system of humans and other mammals. Analytical action spectra in rodents, primates, and humans have identified 446-484 nm (predominantly the blue part of the spectrum) as the most potent wavelength region for neuroendocrine, circadian, and neurobehavioral responses. Those studies suggested that a novel photosensory system, distinct from the visual rods and cones, is primarily responsible for this regulation. Studies have now shown that this new photosensory system is based on a small population of widely dispersed retinal ganglion cells that are intrinsically responsive to light, and project to the suprachiasmatic nuclei and other nonvisual centers in the brain. These light-sensitive retinal ganglion cells contain melanopsin, a vitamin A photopigment that mediates the cellular phototransduction cascade. Although light detection for circadian and neuroendocrine phototransduction seems to be mediated principally by a novel photosensory system in the eye, the classic rod and cone photoreceptors appear to play a role as well. These findings are important in understanding how humans adapt to lighting conditions in modern society and will provide the basis for major changes in future architectural lighting strategies.

Circadian effectiveness of two polychromatic lights in suppressing human nocturnal melatonin

Forty subjects participated in a study to test the accuracy of a recent model of human circadian phototransduction for predicting the relative effectiveness of two polychromatic light sources at suppressing nocturnal melatonin. Brief exposures to four different light levels (30, 100, 300 and 1000 photopic lux at the cornea) and two different "white" lamp spectra (4100 and 8000 K) were used. Results suggest that the model can properly order the relative magnitudes of the two circadian stimuli, but that nocturnal melatonin suppression follows a rate-limited response to light that cannot be predicted from the magnitude of the suppressing light stimulus alone. Some practical implications of these results are discussed.