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 Daytime Exposure to Light from Blue-Enriched Light-Emitting Diodes on the Nighttime Melatonin Amplitude and Circadian Regulation of Rodent Metabolism and Physiology.

Regular cycles of exposure to light and dark control pineal melatonin production and temporally coordinate circadian rhythms of metabolism and physiology in mammals. Previously we demonstrated that the peak circadian amplitude of nocturnal blood melatonin levels of rats were more than 6-fold higher after exposure to cool white fluorescent (CWF) light through blue-tinted (compared with clear) rodent cages. Here, we evaluated the effects of light-phase exposure of rats to white light-emitting diodes (LED), which emit light rich in the blue-appearing portion of the visible spectrum (465-485 nm), compared with standard broadspectrum CWF light, on melatonin levels during the subsequent dark phase and on plasma measures of metabolism and physiology. Compared with those in male rats under a 12:12-h light:dark cycle in CWF light, peak plasma melatonin levels at the middark phase (time, 2400) in rats under daytime LED light were over 7-fold higher, whereas midlight phase levels (1200) were low in both groups. Food and water intakes, body growth rate, and total fatty acid content of major metabolic tissues were markedly lower, whereas protein content was higher, in the LED group compared with CWF group. Circadian rhythms of arterial plasma levels of total fatty acids, glucose, lactic acid, pO2, pCO2, insulin, leptin, and corticosterone were generally lower in LED-exposed rats. Therefore, daytime exposure of rats to LED light with high blue emissions has a marked positive effect on the circadian regulation of neuroendocrine, metabolic, and physiologic parameters associated with the promotion of animal health and wellbeing and thus may influence scientific outcomes.

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.

Melatonin Represses Metastasis in Her2-Postive Human Breast Cancer Cells by Suppressing RSK2 Expression.

The importance of the circadian/melatonin signal in suppressing the metastatic progression of breast and other cancers has been reported by numerous laboratories including our own. Currently, the mechanisms underlying the antimetastatic actions of melatonin have not been well established. In the present study, the antimetastatic actions of melatonin were evaluated and compared on the ERα-negative, Her2-positive SKBR-3 breast tumor cell line and ERα-positive MCF-7 cells overexpressing a constitutively active HER2.1 construct (MCF-7Her2.1 cells). Activation of Her2 is reported to induce the expression and/or phosphorylation-dependent activation of numerous kinases and transcription factors that drive drug resistance and metastasis in breast cancer. A key signaling node activated by the Her2/Mapk/Erk pathway is Rsk2, which has been shown to induce numerous signaling pathways associated with the development of epithelial-to-mesenchymal transition (EMT) and metastasis including: Creb, Stat3, cSrc, Fak, Pax, Fascin, and actin polymerization. The data demonstrate that melatonin (both endogenous and exogenous) significantly represses this invasive/metastatic phenotype through a mechanism that involves the suppression of EMT, either by promoting mesenchymal-to-epithelial transition, and/or by inhibiting key signaling pathways involved in later stages of metastasis. These data, combined with our earlier in vitro studies, support the concept that maintenance of elevated and extended duration of nocturnal melatonin levels plays a critical role in repressing the metastatic progression of breast cancer. IMPLICATIONS: Melatonin inhibition of Rsk2 represses the metastatic phenotype in breast cancer cells suppressing EMT or inhibiting other mechanisms that promote metastasis; disruption of the melatonin signal may promote metastatic progression in breast cancer. Mol Cancer Res; 14(11); 1159-69. ©2016 AACR.

Daytime Blue Light Enhances the Nighttime Circadian Melatonin Inhibition of Human Prostate Cancer Growth.

Light controls pineal melatonin production and temporally coordinates circadian rhythms of metabolism and physiology in normal and neoplastic tissues. We previously showed that peak circulating nocturnal melatonin levels were 7-fold higher after daytime spectral transmittance of white light through blue-tinted (compared with clear) rodent cages. Here, we tested the hypothesis that daytime blue-light amplification of nocturnal melatonin enhances the inhibition of metabolism, signaling activity, and growth of prostate cancer xenografts. Compared with male nude rats housed in clear cages under a 12:12-h light:dark cycle, rats in blue-tinted cages (with increased transmittance of 462-484 nm and decreased red light greater than 640 nm) evinced over 6-fold higher peak plasma melatonin levels at middark phase (time, 2400), whereas midlight-phase levels (1200) were low (less than 3 pg/mL) in both groups. Circadian rhythms of arterial plasma levels of linoleic acid, glucose, lactic acid, pO2, pCO2, insulin, leptin, and corticosterone were disrupted in rats in blue cages as compared with the corresponding entrained rhythms in clear-caged rats. After implantation with tissue-isolated PC3 human prostate cancer xenografts, tumor latency-to-onset of growth and growth rates were markedly delayed, and tumor cAMP levels, uptake-metabolism of linoleic acid, aerobic glycolysis (Warburg effect), and growth signaling activities were reduced in rats in blue compared with clear cages. These data show that the amplification of nighttime melatonin levels by exposing nude rats to blue light during the daytime significantly reduces human prostate cancer metabolic, signaling, and proliferative activities.