l-Ornithine affects peripheral clock gene expression in mice

Temporal patterns of increased growth hormone secretion in mice after oral administration of L-ornithine: possible involvement of ghrelin receptors

l-Ornithine is known to stimulate growth hormone (GH) release in mammals. Here, we demonstrated that increases in plasma GH levels after oral administration of l-ornithine were first observed 150 min after administration, and the elevated levels were sustained for more than 90 min in mice. The increase was significantly delayed compared with the reported timing of plasma and tissue levels of l-ornithine after administration. The l-ornithine-induced increase in GH release was completely blocked by [D-Lys³]-GHRP-6, a ghrelin receptor antagonist, but not by cyclosomatostatin or JV-1-38, antagonists of somatostatin and GH-releasing hormone, respectively. These results suggest the involvement of ghrelin receptor-mediated pathways in l-ornithine-induced increases in GH release.

Is There a Utility of Chrono-Specific Diets in Improving Cardiometabolic Health?

Modern lifestyle is generally associated with the consumption of three main meals per day, one of which is typically in the evening or at night. It is also well established that consumption of meals in the later part of the day, notably in the evenings, is associated with circadian desynchrony, which in turn increases the risk of non-communicable diseases, particularly cardiometabolic diseases. While it is not feasible to avoid food consumption during the evenings altogether, there is an opportunity to provide chrono-specific, diet-based solutions to mitigate some of these risks. To date, there has been substantial progress in the understanding of chrononutrition, with evidence derived mainly from in vitro and in vivo animal studies. Some of these approaches include the manipulation of the quality and quantity of certain nutrients to be consumed at specific times of the day, as well as incorporating certain dietary components (macronutrients, micronutrients, or non-nutrient bioactives, including polyphenols) with the ability to modulate circadian rhythmicity. However, robust human studies are generally lacking. In this review, the study has consolidated and critically appraised the current evidence base, with an aim to translate these findings to improve cardiometabolic health and provides recommendations to move this field forward.

Oak extracts modulate circadian rhythms of clock gene expression in vitro and wheel-running activity in mice

Introduction

In mammals, the central circadian clock is located in the suprachiasmatic nucleus (SCN) of the hypothalamus, which coordinates the circadian rhythm and controls locomotor activity rhythms. In addition to SCN cells, the peripheral tissues and embryonic fibroblasts also have clock genes, such as Per1/2 and Bmal1, which generate the transcriptional-translational feedback loop to produce an approximately 24-h cycle. Aging adversely affects the circadian clock system and locomotor functions. Oak extract has been reported to improve age-related physiological changes. However, no study has examined the effect of oak extract on the circadian clock system.

Methods

We examined the effects of oak extract and its metabolites (urolithin A [ULT] and ellagic acid [EA]) on clock gene expression rhythms in mouse embryonic fibroblasts (MEFs) and SCN. Furthermore, locomotor activity rhythm was assessed in young and aged mice.

Results

Chronic treatment with EA and ULT delayed the phase of PER2::LUC rhythms in SCN explants, and ULT prolonged the period of PER2::LUC rhythms in MEFs in a dose-dependent manner and increased the amplitude of PER2::LUC rhythms in MEFs, though only at low concentrations. Acute treatment with ULT affected the phase of PER2::LUC rhythms in MEFs depending on the concentration and timing of the treatment. In addition, oak extract prolonged the activity time of behavioral rhythms in old mice and tended to increase daily wheel-running revolutions in both young and old mice.

Conclusions

These results suggest that oak extract is a novel modulator of the circadian clock in vitro and in vivo.

Supplementary Information

The online version contains supplementary material available at 10.1007/s41105-021-00365-2.

Melatonin ameliorates anxiety-like behaviors induced by sleep deprivation in mice: Role of oxidative stress, neuroinflammation, autophagy and apoptosis

Increasing evidence suggests there is a relationship between anxiety disorders and sleep deprivation (SD). However, underlying molecular mechanism remains elusive and currently there is no effective therapy to negate the effects of SD. We established a mouse model of acute SD with or without melatonin supplementation. We found that melatonin supplementation suppressed an increase of corticosterone level caused by SD. Behavioral data indicated that 72 h SD exposure induced anxiety-like behaviors, as evidenced by the reduced central area travels in OFT. Immunohistochemical staining and western blot analysis revealed that SD promoted neuronal loss by inducing pro-apoptotic protein Bax and cleaved-caspase-3 and autophagic proteins (LC3II, ATG5 and Beclin1) and reducing the levels of the anti-apoptotic protein Bcl-2. In contrast, the aforementioned SD-inductions were reversed by supplementation using 20 mg/kg and 40 mg/kg melatonin in SD mice. Meanwhile, we observed that melatonin reduced activated gliosis via attenuation of Iba1, and inhibited increase of anti-inflammatory cytokines (IL-4 and IL-10) and the decrease of pro-inflammatory cytokines (IL-6 and TNF-α). Furthermore, melatonin supplementation inverted the SD-induced the decline of antioxidant enzyme activities (T-AOC and CAT etc) and the increase of p-P65 and p-IκB proteins in the hippocampus. On the whole, our findings revealed that melatonin attenuated SD-induced anxiety-like behavior via ameliorating oxidative stress, activation of NF-κB pathway, neuroinflammation, apoptosis and excessive autophagy.

Artificial light at night interacts with predatory threat to alter reef fish metabolite profiles

Light cycles and predatory threat define activity patterns (e.g. feeding/sleeping, activity/rest) in most diurnal fish species. Artificial light at night (ALAN) may disrupt natural cycles and biochemical processes, a mismatch which can eventually reduce condition and fitness. We evaluate the separate and joint effects of ALAN and predator threat on metabolism within brain, liver and muscle tissue of a common, wild caught damselfish, blue green chromis (Chromis viridis). The effects of ALAN varied according to tissue type and predator exposure. In all tissues we observed changes in metabolic pathways associated with increased activity under continuous light (despite provision of shelter), specifically those associated with energy metabolism, cell signalling, responses to oxidative stress and markers of cellular damage. In both the brain and liver tissues, predator threat served to moderate the influence of ALAN on metabolic change, likely due to increased sheltering behaviour. However, no interaction of predator threat with ALAN was observed in metabolism of the muscle tissue. Our results highlight complex sub-acute effects of ALAN exposure on tissue specific and whole organism energy metabolism. Collectively these effects indicate that ALAN has significant scope to reduce fitness of coastal fishes and potentially threaten ecosystem services, but that these changes are highly complex and may be altered by biotic drivers of activity.

Cacao polyphenols regulate the circadian clock gene expression and through glucagon-like peptide-1 secretion

Energy metabolism and circadian rhythms are closely related together, i.e., the timing of nutrient intake affects metabolism under the regulation of circadian rhythms. Previously, we have reported that cacao liquor procyanidin (CLPr) promotes energy metabolism, resulting in preventing obesity and hyperglycemia. However, it is not unclear whether CLPr regulates clock gene expression. In this study, we investigated whether the administration timing of CLPr affected clock gene expression and found that CLPr regulated the circadian clock gene expression through the glucagon-like peptide-1 (GLP-1) signaling pathway. CLPr administration at Zeitgeber time 3 increased the expression level of Per family and Dbp in the liver. At the same administration timing, CLPr increased GLP-1 and insulin concentration in the plasma and phosphorylation of AMPK in the liver. It was noteworthy that an antagonist for GLP-1 receptor Exendin (9-39) canceled CLPr-increased expression of Per family and Dbp and phosphorylation of AMPK in the liver, in addition to insulin secretion. These results strongly suggest that CLPr-induced GLP-1 regulates the changes in clock gene expression in the liver through increased insulin. Thus, CLPr is a possible functional food material for prevention and/or amelioration of metabolic disorders through preventing circadian disruption through GLP-1 and AMPK pathways.

Circadian expression of Glycoprotein 2 (Gp2) gene is controlled by a molecular clock in mouse Peyer's patches

The expression levels of many cell-surface proteins vary with the time of day. Glycoprotein 2 (Gp2), specifically expressed on the apical surface of M cells in Peyer's patches, functions as a transcytotic receptor for mucosal antigens. We report that cAMP response element-binding protein (CREB) regulates the transcription of the Gp2 gene, thereby generating the circadian change in its expression in mouse Peyer's patches. The transcytotic receptor activity of Gp2 was increased during the dark phase when the Gp2 protein abundance increased. Rhythmic expression of clock gene mRNA was observed in mouse Peyer's patches, and expression levels of Gp2 mRNA also exhibited circadian oscillation, with peak levels during the early dark phase. The promoter region of the mouse Gp2 gene contains several cAMP response elements (CREs). Chromatin immunoprecipitation assays revealed that CREB bound to the CREs in the Gp2 gene in Peyer's patches. Forskolin, which promotes CREB phosphorylation, increased the transcription of the Gp2 gene in Peyer's patches. As phosphorylation of CREB protein was increased when Gp2 gene transcription was activated, CREB may regulate the rhythmic expression of Gp2 mRNA in Peyer's patches. These findings suggest that intestinal immunity is controlled by the circadian clock system.

Phase resetting of circadian peripheral clocks using human and rodent diets in mouse models of type 2 diabetes and chronic kidney disease

The expression rhythms of clock genes, such as Per1, Per2, Bmal1, and Rev-erb α, in mouse peripheral clocks, are entrained by a scheduled feeding paradigm. In terms of food composition, a carbohydrate-containing diet is reported to cause strong entrainment through insulin secretion. However, it is unknown whether human diets entrain peripheral circadian clocks. In this study, we used freeze-dried diets for type 2 diabetes (DB) and chronic kidney disease (CKD), as well as low-carbohydrate diets. After 24 h of fasting, PER2::LUC knock-in mice were given access to food for 2 days during inactive periods, and bioluminescence rhythm was then measured using an in vivo imaging system. AIN-93M, the control mouse diet with a protein:fat:carbohydrate (PFC) ratio of 14.7:9.5:75.8, caused a significant phase advance (7.3 h) in the liver clock compared with that in 24 h fasted mice, whereas human diets caused significant but smaller phase advances (4.7-6.2 h). Compared with healthy and high fat/sucrose-induced DB mice, adenine-induced CKD mice showed attenuation of a phase-advance with a normal diet. There were no significant differences in phase-advance values between human diets (normal, DB, and CKD). In addition, a normal-carbohydrate diet (PFC ratio of 20.3:23.3:56.4) and a low-carbohydrate diet (PFC ratio of 36.4:42.9:20.7) caused similar phase advances in peripheral clocks. The present results strongly suggest that scheduled feeding with human diets can cause phase advances in the peripheral clocks of not only healthy, but also DB and CKD mice. This discovery provides support to the food-induced entrainment of peripheral clocks in human clinical trials.

Entrainment of the mouse circadian clock: Effects of stress, exercise, and nutrition

The circadian clock system in mammals plays a fundamental role in maintaining homeostasis. Entrainment is an important characteristic of the internal clock, by which appropriate timing is maintained according to external daily stimuli, such as light, stress, exercise, and/or food. Disorganized entrainment or a misaligned clock time, such as jet lag, increases health disturbances. The central clock in the suprachiasmatic nuclei, located in the hypothalamus, receives information about arousal stimuli, such as physical stress or exercise, and changes the clock time by modifying neural activity or the expression of circadian clock genes. Although feeding stimuli cannot entrain the central clock in a normal light-dark cycle, the central clock can partially detect the metabolic status. Local clocks in the peripheral tissues, including liver and kidney, have a strong direct response to the external stimuli of stress, exercise, and/or food that is independent of the central clock. The mechanism underlying entrainment by stress/exercise is mediated by glucocorticoids, sympathetic nerves, oxidative stress, hypoxia, pH, cytokines, and temperature. Food/nutrition-induced entrainment is mediated by fasting-induced hormonal or metabolic changes and re-feeding-induced insulin or oxyntomodulin secretion. Chrono-nutrition is a clinical application based on chronobiology research. Future studies are required to elucidate the effects of eating and nutrient composition on the human circadian clock. Here, we focus on the central and peripheral clocks mostly in rodents' studies and review the findings of recent investigations of the effects of stress, exercise, and food on the entrainment system.

Glucagon and/or IGF-1 Production Regulates Resetting of the Liver Circadian Clock in Response to a Protein or Amino Acid-only Diet

The circadian system controls the behavior and multiple physiological functions. In mammals, the suprachiasmatic nucleus (SCN) acts as the master pacemaker and regulates the circadian clocks of peripheral tissues. The SCN receives information regarding the light-dark cycle and is thus synchronized to the external 24-hour environment. In contrast, peripheral clocks, such as the liver clock, receive information from the SCN and other factors; in particular, food intake which leads to insulin secretion induces strong entrainment of the liver clock. On the other hand, the liver clock of insulin-depleted mice treated with streptozotocin (STZ) has been shown to be entrained by scheduled feeding, suggesting that insulin is not necessary for entrainment of the liver clock by feeding. In this study, we aimed to elucidate additional mechanism on entraining liver clock by feeding a protein-only diet and/or amino-acid administration which does not increase insulin levels. We demonstrated that protein-only diet and cysteine administration elicit entrainment of the liver clock via glucagon secretion and/or insulin-like growth factors (IGF-1) production. Our findings suggest that glucagon and/or IGF-1 production are additional key factors in food-induced entrainment.

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Dietary protein or cysteine increase serum glucagon and hepatic IGF-1 levels, and entrain liver circadian rhythm.

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Increasing IGF-1 levels is an additional entrainment factor of liver circadian rhythm.

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Hepatic IGF-1 production is found to be a key factor in the entrainment of liver circadian rhythm in STZ-treated mice.

Disruption of the circadian rhythm leads to multiple disorders; thus the maintenance of circadian oscillation is necessary for maintaining normalized physiological functions. Postprandial insulin secretion is known as an entraining factor of peripheral circadian rhythm; however, this pathway is not appropriate for diabetes patients in whom insulin signaling is disrupted. Here we report that both dietary protein and cysteine alone entrain liver circadian rhythm by increasing glucagon and/or IGF-1 levels independently of insulin. Findings indicate an additional entrainment factor that can be applied to chronotherapy by controlling food content or by supplementation in peoples with diabetes, circadian rhythm disorders.

Modulation of circadian clocks by nutrients and food factors

Daily activity rhythms that are dominated by internal clocks are called circadian rhythms. A central clock is located in the suprachiasmatic nucleus of the hypothalamus, and peripheral clocks are located in most mammalian peripheral cells. The central clock is entrained by light/dark cycles, whereas peripheral clocks are entrained by feeding cycles. The effects of nutrients on the central and peripheral clocks have been investigated during the past decade and much interaction between them has come to light. For example, a high-fat diet prolongs the period of circadian behavior, a ketogenic diet advances the onset of locomotor activity rhythms, and a high-salt diet advances the phase of peripheral molecular clocks. Moreover, some food factors such as caffeine, nobiletin, and resveratrol, alter molecular and/or behavioral circadian rhythms. Here, we review nutrients and food factors that modulate mammalian circadian clocks from the cellular to the behavioral level.