Influence of Daytime LED Light Exposure on Circadian Regulatory Dynamics of Metabolism and Physiology in Mice.

Light is a potent biologic force that profoundly influences circadian, neuroendocrine, and neurobehavioral regulation in animals. Previously we examined the effects of light-phase exposure of rats to white light-emitting diodes (LED), which emit more light in the blue-appearing portion of the visible spectrum (465 to 485 nm) than do broad-spectrum cool white fluorescent (CWF) light, on the nighttime melatonin amplitude and circadian regulation of metabolism and physiology. In the current studies, we tested the hypothesis that exposure to blue-enriched LED light at day (bLAD), compared with CWF, promotes the circadian regulation of neuroendocrine, metabolic, and physiologic parameters that are associated with optimizing homeostatic regulation of health and wellbeing in 3 mouse strains commonly used in biomedical research (C3H [melatonin-producing], C57BL/6, and BALB/c [melatonin-non-producing]). Compared with male and female mice housed for 12 wk under 12:12-h light:dark (LD) cycles in CWF light, C3H mice in bLAD evinced 6-fold higher peak plasma melatonin levels at the middark phase; in addition, high melatonin levels were prolonged 2 to 3 h into the light phase. C57BL/6 and BALB/c strains did not produce nighttime pineal melatonin. Body growth rates; dietary and water intakes; circadian rhythms of arterial blood corticosterone, insulin, leptin, glucose, and lactic acid; pO2 and pCO2; fatty acids; and metabolic indicators (cAMP, DNA, tissue DNA 3H-thymidine incorporation, fat content) in major organ systems were significantly lower and activation of major metabolic signaling pathways (mTOR, GSK3ß, and SIRT1) in skeletal muscle and liver were higher only in C3H mice in bLAD compared with CWF. These data show that exposure of C3H mice to bLAD compared with CWF has a marked positive effect on the circadian regulation of neuroendocrine, metabolic, and physiologic parameters associated with the promotion of animal health and wellbeing that may influence scientific outcomes. The absence of enhancement in amelatonic strains suggests hyperproduction of nighttime melatonin may be a key component of the physiology.

Effect of Daytime Blue-enriched LED Light on the Nighttime Circadian Melatonin Inhibition of Hepatoma 7288CTC Warburg Effect and Progression.

Liver cancer is the second leading cause of cancer death worldwide. Metabolic pathways within the liver and liver cancers are highly regulated by the central circadian clock in the suprachiasmatic nuclei (SCN). Daily light and dark cycles regulate the SCN-driven pineal production of the circadian anticancer hormone melatonin and temporally coordinate circadian rhythms of metabolism and physiology in mammals. In previous studies, we demonstrated that melatonin suppresses linoleic acid metabolism and the Warburg effect (aerobic glycolysis)in human breast cancer xenografts and that blue-enriched light (465-485 nm) from light-emitting diode lighting at daytime (bLAD) amplifies nighttime circadian melatonin levels in rats by 7-fold over cool white fluorescent (CWF) lighting. Here we tested the hypothesis that daytime exposure of tissue-isolated Morris hepatoma 7288CTC-bearing male rats to bLAD amplifies the nighttime melatonin signal to enhance the inhibition of tumor growth. Compared with rats housed under a 12:12-h light:dark cycle in CWF light, rats in bLAD light evinced a 7-fold higher peak plasma melatonin level at the mid-dark phase; in addition, high melatonin levels were prolonged until 4 h into the light phase. After implantation of tissue-isolated hepatoma 7288CTC xenografts, tumor growth rates were markedly delayed, and tumor cAMP levels, LA metabolism, the Warburg effect, and growth signaling activities were decreased in rats in bLAD compared with CWF daytime lighting. These data show that the increased nighttime circadian melatonin levels due to bLAD exposure decreases hepatoma metabolic, signaling, and proliferative activities beyond what occurs after normal melatonin signaling under CWF light.

Effect of Isoflurane Anesthesia on Circadian Metabolism and Physiology in Rats.

Isoflurane anesthesia alters the blood levels of several neuroendocrine hormones associated with normal metabolism and physiology and increases stress, but the effect of brief CO2 anesthesia on these parameters is unknown. In this study, we examined the effects of isoflurane (4%) compared with brief CO2 (70% CO2, 30% air) anesthesia on circadian rhythms of plasma measures of physiology and metabolism. Adult male Sprague-Dawley rats (Crl:SD; n = 6 per group) were maintained on a 12:12-h light:dark (300 lx; lights on, 0600) photoperiod. After 1 wk of acclimation, a series of 6 low-volume blood draws were collected by cardiocentesis under anesthesia using isoflurane (10 min or less) compared with CO2 (1 min or less) at a single circadian time point every 4 d (0400, 0800, 1200, 1600, 2000, or 2400) over 3 wk to assess arterial blood glucose, lactic acid, and potassium and plasma melatonin, leptin, insulin, total fatty acids, and corticosterone concentrations. Results revealed that plasma levels (mean ± SEM) of melatonin were low (11 ± 1 pg/mL) during the light phase in both groups but were significantly lower during the dark phase in the isoflurane group (48 ± 6 pg/mL) compared with the CO2 group (162 ± 18 pg/mL). In addition, prominent circadian rhythms of arterial plasma levels of corticosterone, glucose, total fatty acids, lactic acid, and potassium were altered in the isoflurane group compared with the CO2 group. These findings demonstrate that the normal circadian rhythms of endocrine physiology and metabolism observed during brief CO2 anesthesia in rats are markedly disrupted by isoflurane anesthesia.

Effects of Colored Enrichment Devices on Circadian Metabolism and Physiology in Male Sprague-Dawley Rats.

Environmental enrichment (EE) gives laboratory animals opportunities to engage in species-specific behaviors. However, the effects of EE devices on normal physiology and scientific outcomes must be evaluated. We hypothesized that the spectral transmittance (color) of light to which rats are exposed when inside colored enrichment devices (CED) affects the circadian rhythms of various plasma markers. Pair-housed male Crl:SD rats were maintained in ventilated racks under a 12:12-h light:dark environment (265.0 lx; lights on, 0600); room lighting intensity and schedule remained constant throughout the study. Treatment groups of 6 subjects were exposed for 25 d to a colored enrichment tunnel: amber, red, clear, or opaque. We measured the proportion of time rats spent inside their CED. Blood was collected at 0400, 0800, 1200, 1600, 2000, and 2400 and analyzed for plasma melatonin, total fatty acids, and corticosterone. Rats spent more time in amber, red, and opaque CED than in clear tunnels. All tubes were used significantly less after blood draws had started, except for the clear tunnel, which showed no change in use from before blood sampling began. Normal peak nighttime melatonin concentrations showed significant disruption in the opaque CED group. Food and water intakes and body weight change in rats with red-tinted CED and total fatty acid concentrations in the opaque CED group differed from those in other groups. These results demonstrate that the color of CED altered normal circadian rhythms of plasma measures of metabolism and physiology in rats and therefore might influence the outcomes of scientific investigations.

The influence of red light exposure at night on circadian metabolism and physiology in Sprague-Dawley rats.

Early studies on rodents showed that short-term exposure to high-intensity light (> 70 lx) above 600 nm (red-appearing) influences circadian neuroendocrine and metabolic physiology. Here we addressed the hypothesis that long-term, low-intensity red light exposure at night (rLEN) from a 'safelight' emitting no light below approximately 620 nm disrupts the nocturnal circadian melatonin signal as well as circadian rhythms in circulating metabolites, related regulatory hormones, and physi- ologic parameters. Male Sprague-Dawley rats (n = 12 per group) were maintained on control 12:12-h light:dark (300 lx; lights on, 0600) or experimental 12:12 rLEN (8.1 lx) lighting regimens. After 1 wk, rats underwent 6 low-volume blood draws via cardiocentesis (0400, 0800, 1200, 1600, 2000, and 2400) over a 4-wk period to assess arterial plasma melatonin, total fatty acid, glucose, lactic acid, pO2, pCO2, insulin, leptin and corticosterone concentrations. Results revealed plasma melatonin levels (mean ± 1 SD) were high in the dark phase (197.5 ± 4.6 pg/mL) and low in the light phase (2.6 ± 1.2 pg/mL) of control condi- tions and significantly lower than controls under experimental conditions throughout the 24-h period (P < 0.001). Prominent circadian rhythms of plasma levels of total fatty acid, glucose, lactic acid, pO2, pCO2, insulin, leptin, and corticosterone were significantly (P < 0.05) disrupted under experimental conditions as compared with the corresponding entrained rhythms under control conditions. Therefore, chronic use of low-intensity rLEN from a common safelight disrupts the circadian organization of neuroendocrine, metabolic, and physiologic parameters indicative of animal health and wellbeing.

Effect of spectral transmittance through red-tinted rodent cages on circadian metabolism and physiology in nude rats.

Light entrains normal circadian rhythms of physiology and metabolism in all mammals. Previous studies from our laboratory demonstrated that spectral transmittance (color) of light passing through cages affects these responses in rats. Here, we addressed the hypothesis that red tint alters the circadian nocturnal melatonin signal and circadian oscillation of other metabolic and physiologic functions. Female nude rats (Hsd:RH-Foxn1(rnu); n = 12 per group) were maintained on a 12:12-h light (300 lx; 123.0 µW/cm(2); lights on 0600):dark regimen in standard polycarbonate translucent clear or red-tinted cages. After 1 wk, rats underwent 6 low-volume blood draws via cardiocentesis over a 4-wk period. Plasma melatonin levels were low during the light phase (1.0 ± 0.2 pg/mL) in rats in both types of cages but were significantly lower in red-tinted (105.0 ± 2.4 pg/mL) compared with clear (154.8 ± 3.8 pg/mL) cages during the dark. Normal circadian rhythm of plasma total fatty acid was identical between groups. Although phase relationships of circadian rhythms in glucose, lactic acid, pO2, and pCO2 were identical between groups, the levels of these analytes were lower in rats in red-tinted compared with clear cages. Circadian rhythms of plasma corticosterone, insulin, and leptin were altered in terms of phasing, amplitude, and duration in rats in red-tinted compared with clear cages. These findings indicate that spectral transmittance through red-colored cages significantly affects circadian regulation of neuroendocrine, metabolic, and physiologic parameters, potentially influencing both laboratory animal health and wellbeing and scientific outcomes.

Effects of spectral transmittance through standard laboratory cages on circadian metabolism and physiology in nude rats.

Light is potent in circadian, neuroendocrine, and neurobehavioral regulation, thereby having profound influence on the health and wellbeing of all mammals, including laboratory animals. We hypothesized that the spectral quality of light transmitted through colored compared with clear standard rodent cages alters circadian production of melatonin and temporal coordination of normal metabolic and physiologic activities. Female nude rats (Hsd:RH-Foxn1(rnu); n = 6 per group) were maintained on a 12:12-h light:dark regimen (300 lx; lights on, 0600) in standard translucent clear, amber, or blue rodent cages; intensity and duration of lighting were identical for all groups. Rats were assessed for arterial blood levels of pO(2) and pCO(2), melatonin, total fatty acid, glucose, lactic acid, insulin, leptin, and corticosterone concentrations at 6 circadian time points. Normal circadian rhythms of arterial blood pO(2) and pCO(2) were different in rats housed in cages that were blue compared with amber or clear. Plasma melatonin levels (mean ± 1 SD) were low (1.0 ± 0.2 pg/mL) during the light phase in all groups but higher at nighttime in rats in blue cages (928.2 ± 39.5 pg/mL) compared with amber (256.8 ± 6.6 pg/mL) and clear (154.8 ± 9.3 pg/mL) cages. Plasma daily rhythms of total fatty acid, glucose, lactic acid, leptin, insulin, and corticosterone were disrupted in rats housed in blue or amber compared with clear cages. Temporal coordination of circadian rhythms of physiology and metabolism can be altered markedly by changes in the spectral quality of light transmitted through colored standard rodent cages.

Eliminating animal facility light-at-night contamination and its effect on circadian regulation of rodent physiology, tumor growth, and metabolism: a challenge in the relocation of a cancer research laboratory.

Appropriate laboratory animal facility lighting and lighting protocols are essential for maintaining the health and wellbeing of laboratory animals and ensuring the credible outcome of scientific investigations. Our recent experience in relocating to a new laboratory facility illustrates the importance of these considerations. Previous studies in our laboratory demonstrated that animal room contamination with light-at-night (LAN) of as little as 0.2 lx at rodent eye level during an otherwise normal dark-phase disrupted host circadian rhythms and stimulated the metabolism and proliferation of human cancer xenografts in rats. Here we examined how simple improvements in facility design at our new location completely eliminated dark-phase LAN contamination and restored normal circadian rhythms in nontumor-bearing rats and normal tumor metabolism and growth in host rats bearing tissue-isolated MCF7(SR(-)) human breast tumor xenografts or 7288CTC rodent hepatomas. Reducing LAN contamination in the animal quarters from 24.5 ± 2.5 lx to nondetectable levels (complete darkness) restored normal circadian regulation of rodent arterial blood melatonin, glucose, total fatty and linoleic acid concentrations, tumor uptake of O(2), glucose, total fatty acid and CO(2) production and tumor levels of cAMP, triglycerides, free fatty acids, phospholipids, and cholesterol esters, as well as extracellular-signal-regulated kinase, mitogen-activated protein kinase, serine-threonine protein kinase, glycogen synthase kinase 3ß, γ-histone 2AX, and proliferating cell nuclear antigen.