Chrono-Pharmacology in the Era of Precision Medicine: Mechanisms, Clinical Evidence, and Translational Perspectives

CHRONOBIOLOGY investigates biologic rhythms that are involved in the organization of living organisms. Biologic rhythms consist of variations of biologic phenomena that are periodic and foreseeable in time. They are genetically determined as indicated by their persistence during constant conditions such as continuous light or darkness. Temporal variations in cycles of light– dark, rest–activity, fasting–eating, and other environmental conditions, defined as synchronizers, give the organism temporal markers and thus impose their period on these biologic rhythms. These rhythms can therefore be characterized by different periods, leading to the division of circadian (a period of approximately 24 h), ultradian (a cycle that is shorter than 1 day), and infradian (a cycle that may last weeks, months, or seasons). These clocks influence how our bodies change throughout the day, affecting blood pressure, activity of the immune system, blood coagulation, and gastric and renal functions. Almost all hormones are regulated by circadian rhythms. For example, cortisol naturally decreases to its lowest concentrations at bedtime and reaches its highest concentrations during the early waking hours. This variation may be fit to a sinusoidal function by the cosinor method, a linear method of least squares (fig. 1). This function is characterized by parameters such as the midline-estimating statistic of rhythm (MESOR), i.e., the mean level that is equal to the 24-h average), amplitude (half of the peak-to-trough difference of the fitted cosinus function), and acrophase (the crest time of rhythm given in degrees, where 360° corresponds to a 24-h cycle, or in hours and minutes). Other methods, such as Fourier transformation, may be used to detect the periodicity of the rhythm. Biologic rhythms are influenced by socioecologic factors, such as jet lag and shiftwork, as well as by illness and drugs. Available clinical data have shown that signs and symptoms are not constant over time and often have cyclic patterns. More strokes and heart attacks occur in the morning compared with any other time of day, and people with osteoarthritis tend to feel less pain in the morning than at night. Studies also suggest that chemotherapy and treatments for asthma and arthritis may be more effective and less toxic if drugs are administered at carefully selected times. Taking into account the circadian rhythms for medical treatment by choosing the time of day for drug administration is called chronotherapy. Drug effects can be optimized and side effects can be reduced by basing drug administration on the circadian patterns of a disease. Chronopharmacology is the study of the influence of the moment of administration of a drug (hour, month, and year) on its response according to the temporal structure of the organism receiving it. Chronopharmacology also studies the drug-induced alterations of biologic rhythms. Two aspects of chronopharmacology must be distinguished: the time of administration of a drug may determine a different response from a qualitative or a quantitative point of view (chronopharmacodynamics) and/or a different effective drug concentration (chronopharmacokinetics). Pharmacokinetic parameters are influenced by different physiologic functions displaying circadian rhythm. Temporal changes of drug kinetics have been reported in animals and humans for more than a hundred drugs, including anesthetics. It has been shown, for example, that despite a constant infusion rate of heparin, the risk of bleeding and the activated partial thromboplastin are higher at night. Chronopharmacokinetic data may partly explain chronopharmacodynamic phenomena. Knowledge of the influence of the time of administration on the drug kinetics could therefore have implications for its prescription by modulating the distribution of the total daily dose over a 24-h period. The aim of this review is to provide an update on the chronobiologic and chronopharmacologic findings that could have an impact on the daily practice of anesthesiology and/or research in this area.

Circadian organization changes with age, but we do not know the extent to which age-related changes are the result of alterations in the central pacemakers, the peripheral oscillators, or the coupling mechanisms that hold the system together. By using transgenic rats with a luciferase (luc) reporter, we assessed the effects of aging on the rhythm of expression of the Period 1 (Per1) gene in the suprachiasmatic nucleus (SCN) and in peripheral tissues. Young (2 months) and aged (24-26 months) Per1-luc transgenic rats, entrained to light-dark cycles, were killed, and tissues were removed and cultured. Per1-luc expression was measured from 10 tissues. In the SCN, the central mammalian pacemaker, Per1-luc expression was robustly rhythmic for more than 7 weeks in culture. The only difference between SCN rhythmicity in young and old rats was a small but significant age-related shortening of the free-running period. Circadian rhythmicity in some peripheral tissues was unaffected by aging, whereas rhythmicity in other tissues was either phase advanced relative to the light cycle or absent. Those tissues that were arrhythmic could be induced to oscillate by application of forskolin, suggesting that they retained the capacity to oscillate but were not being appropriately driven in vivo. Overall, the results provide new insights into the effects of aging on the mammalian circadian system. Aging seems to affect rhythms in some but not in all tissues and may act primarily on interactions among circadian oscillators, perhaps attenuating the ability of the SCN to drive damped oscillators in the periphery.

Neurons of the suprachiasmatic nucleus (SCN), located in the ventromedial hypothalamus, comprise the central mammalian circadian pacemaker ([Reppert and Weaver 2002][1]). In dispersed culture, these neurons can generate autonomous circadian (ca. 24 h) oscillations in spontaneous firing rate ([Welsh

DOAJ is a unique and extensive index of diverse open access journals from around the world, driven by a growing community, committed to ensuring quality content is freely available online for everyone.

The mammalian circadian system comprises central and peripheral circadian clocks, the former localized within the suprachiasmatic nucleus (SCN) of the hypothalamus and the latter present in numerous peripheral tissues such as the muscle and liver. However, SCN-derived signals are thought to control peripheral tissue oscillations, and it has been difficult to understand this communication at a molecular level. Pando et al . show that dominance of the SCN clock is observed in a tissue implant system in which embryonic fibroblasts from one mouse (Mefs) are placed into the back of a genetically different host mouse. Mefs taken from a mouse that lacks the clock transcription factor Per1, a defect known not to affect oscillations in the SCN, displayed shorter oscillation periods in culture than did cells from wild-type mice. However, when transplanted into a wild-type mouse, the Per1-null Mefs adopted the normal oscillatory phenotype of the host SCN. When transplanted into a mouse with a longer oscillation period, the Mefs adopted those characteristics as well. The Mefs were only influenced by the host SCN if they expressed other functional clock components, suggesting that cues from the central pacemaker are interpreted by the implant's clock. This system may allow genetic and molecular dissection of what SCN signals initiate and maintain oscillations in implanted peripheral clocks and may also help address whether and how peripheral clocks are uncoupled from the central clock in response to certain environmental cues such as food intake. M. P. Pando, D. Morse, N. Cermakian, P. Sassone-Corsi, Phenotypic rescue of a peripheral clock genetic defect via SCN hierarchical dominance. Cell 110 , 107-117 (2002). [Online Journal]

Hepatic P450 monooxygenase activities, assessed by measurement of 7-alkoxycoumarin O-dealkylase (ACD) activities, show obvious daily fluctuations in male rats with high values during the dark period and low values during the light period. We have already confirmed that the ACD activities are controlled by the suprachiasmatic nucleus (SCN), which is well known as the oscillator of circadian rhythm. Recently, it is reported that circadian oscillators exist not only in the SCN but also in peripheral organs. To date, it is unclear which circadian oscillators predominantly drive the daily fluctuations of hepatic ACD activities. To address this question, we examined the effects of restricted feeding, which uncouples the circadian oscillators in the liver from the central pacemaker in the SCN, on the daily fluctuations in hepatic ACD activities in male rats. Here we show that restricted feeding inverts the oscillation phase of the daily fluctuations in hepatic ACD activities. Regarding the hepatic P450 content, there were no fluctuations between the light and dark periods under ad libitum and restricted feeding conditions. Therefore, it is considered that the daily fluctuations in hepatic ACD activities are predominantly driven by the circadian factors in peripheral organs rather than by the oscillator in the SCN directly.

In mammals, circadian oscillators exist not only in the suprachiasmatic nucleus, which harbors the central pacemaker, but also in most peripheral tissues. It is believed that the SCN clock entrains the phase of peripheral clocks via chemical cues, such as rhythmically secreted hormones. Here we show that temporal feeding restriction under light-dark or dark-dark conditions can change the phase of circadian gene expression in peripheral cell types by up to 12 h while leaving the phase of cyclic gene expression in the SCN unaffected. Hence, changes in metabolism can lead to an uncoupling of peripheral oscillators from the central pacemaker. Sudden large changes in feeding time, similar to abrupt changes in the photoperiod, reset the phase of rhythmic gene expression gradually and are thus likely to act through a clock-dependent mechanism. Food-induced phase resetting proceeds faster in liver than in kidney, heart, or pancreas, but after 1 wk of daytime feeding, the phases of circadian gene expression are similar in all examined peripheral tissues.

Circadian rhythms are regulated by clocks located in specific structures of the CNS, such as the suprachiasmatic nucleus (SCN) in mammals, and by peripheral oscillators present in various other tissues. The expression of essential clock genes oscillates both in the SCN and in peripheral pacemakers. Peripheral tissues in the fly and in the fish are directly photoreceptive. In particular, we have established the Z3 embryonic zebrafish cell line that recapitulates the dynamic light-dependent regulation of the vertebrate clock in vitro. In mammals the synchronization to daily light cycles involves neural connections from a subset of light-sensitive receptor-containing retinal ganglion cells. Humoral and/or hormonal signals originating from the SCN are thought to provide timing cues to peripheral clocks. However, alternative routes exist, as some peripheral clocks in mammals can be specifically entrained in a SCN-independent manner by restricted feeding regimes. Thus, not all peripheral tissues are equal in circadian rhythmicity. Testis, for example, displays no intrinsic circadian rhythmicity and the molecular mechanisms of clock gene activation in male germ cells appear to differ from other tissues. The study of the connecting routes that link the SCN to peripheral tissues is likely to reveal signalling pathways of fundamental physiological significance.

In mammals, the suprachiasmatic nucleus (SCN) is the central circadian pacemaker that governs rhythmic fluctuations in behavior and physiology in a 24-hr cycle and synchronizes them to the external environment by daily resetting in response to light. The bilateral SCN is comprised of a mere ~20,000 neurons serving as cellular oscillators, a fact that has, until now, hindered the systematic study of the SCN on a global proteome level. Here we developed a fully automated and integrated proteomics platform, termed AutoProteome system, for an in-depth analysis of the light-responsive proteome of the murine SCN. All requisite steps for a large-scale proteomic study, including preconcentration, buffer exchanging, reduction, alkylation, digestion and online two-dimensional liquid chromatography-tandem MS analysis, are performed automatically on a standard liquid chromatography-MS system. As low as 2 ng of model protein bovine serum albumin and up to 20 μg and 200 μg of SCN proteins can be readily processed and analyzed by this system. From the SCN tissue of a single mouse, we were able to confidently identify 2131 proteins, of which 387 were light-regulated based on a spectral counts quantification approach. Bioinformatics analysis of the light-inducible proteins reveals their diverse distribution in different canonical pathways and their heavy connection in 19 protein interaction networks. The AutoProteome system identified vasopressin-neurophysin 2-copeptin and casein kinase 1 delta, both of which had been previously implicated in clock timing processes, as light-inducible proteins in the SCN. Ras-specific guanine nucleotide-releasing factor 1, ubiquitin protein ligase E3A, and X-linked ubiquitin specific protease 9, none of which had previously been implicated in SCN clock timing processes, were also identified in this study as light-inducible proteins. The AutoProteome system opens a new avenue to systematically explore the proteome-wide events that occur in the SCN, either in response to light or other stimuli, or as a consequence of its intrinsic pacemaker capacity.

The mammalian circadian system comprises central and peripheral circadian clocks, the former localized within the suprachiasmatic nucleus (SCN) of the hypothalamus and the latter present in numerous peripheral tissues such as the muscle and liver. However, SCN-derived signals are thought to control peripheral tissue oscillations, and it has been difficult to understand this communication at a molecular level. Pando et al. show that dominance of the SCN clock is observed in a tissue implant system in which embryonic fibroblasts from one mouse (Mefs) are placed into the back of a genetically different host mouse. Mefs taken from a mouse that lacks the clock transcription factor Per1, a defect known not to affect oscillations in the SCN, displayed shorter oscillation periods in culture than did cells from wild-type mice. However, when transplanted into a wild-type mouse, the Per1-null Mefs adopted the normal oscillatory phenotype of the host SCN. When transplanted into a mouse with a longer oscillation period, the Mefs adopted those characteristics as well. The Mefs were only influenced by the host SCN if they expressed other functional clock components, suggesting that cues from the central pacemaker are interpreted by the implant's clock. This system may allow genetic and molecular dissection of what SCN signals initiate and maintain oscillations in implanted peripheral clocks and may also help address whether and how peripheral clocks are uncoupled from the central clock in response to certain environmental cues such as food intake.M. P. Pando, D. Morse, N. Cermakian, P. Sassone-Corsi, Phenotypic rescue of a peripheral clock genetic defect via SCN hierarchical dominance. Cell 110, 107-117 (2002). [Online Journal]

In mammals, the central circadian pacemaker in the suprachiasmatic nucleus (SCN) entrains to an environmental light-dark (LD) cycle and organizes the temporal order of circadian rhythms in physiology and behavior. Previously, some studies have demonstrated that scheduled exercise could entrain the free-running behavior rhythm in nocturnal rodents. However, it remains unknown whether entrainment by scheduled exercise alters the internal temporal order of the behavioral circadian rhythms or clock gene expression in the SCN, extra-SCN brain regions, and peripheral organs when mice are entrained to the scheduled exercise under constant darkness (DD). In the present study, we examined circadian rhythms in locomotor activity and clock gene Per1 expression by bioluminescence reporter (Per1-luc) in the SCN, arcuate nucleus (ARC), liver, and skeletal muscle of mice entrained to an LD cycle, mice free-running under DD, and mice entrained to daily exposure to a new cage with a running wheel (NCRW) under DD. All mice showed a steady-state entrainment of behavioral circadian rhythms to NCRW exposure under DD in parallel with shortening of the α when compared with that under DD. The temporal order of behavioral circadian rhythms and the Per1-luc rhythms in the SCN and peripheral tissues but not in the ARC were maintained in the mice entrained to the NCRW and LD cycles; in contrast, the temporal order was altered in the mice under DD. The present findings reveal that the SCN entrains to daily exercise, and daily exercise reorganizes the internal temporal order of behavioral circadian rhythms and clock gene expression in the SCN and peripheral tissues.

Patients with cirrhosis exhibit features of circadian disruption. Hyperammonaemia has been suggested to impair both homeostatic and circadian sleep regulation. Here, we tested if hyperammonaemia directly disrupts circadian rhythm generation in the central pacemaker, the suprachiasmatic nuclei (SCN) of the hypothalamus. Wheel-running activity was recorded from mice fed with a hyperammonaemic or normal diet for ~35 days in a 12:12 light-dark (LD) cycle followed by ~15 days in constant darkness (DD). The expression of the clock protein PERIOD2 (PER2) was recorded from SCN explants before, during and after ammonia exposure, ±glutamate receptor antagonists. In LD, hyperammonaemic mice advanced their daily activity onset time by ~1h (16.8 ± 0.3 vs. 18.1 ± 0.04 h, p=.009) and decreased their total activity, concentrating it during the first half of the night. In DD, hyperammonaemia reduced the amplitude of daily activity (551.5 ± 27.7 vs. 724.9 ± 59 counts, p=.007), with no changes in circadian period. Ammonia (≥0.01 mM) rapidly and significantly reduced PER2 amplitude, and slightly increased circadian period. The decrease in PER2 amplitude correlated with decreased synchrony among circadian cells in the SCN and increased extracellular glutamate, which was rescued by AMPA glutamate receptor antagonists. These data suggest that hyperammonaemia affects circadian regulation of rest-activity behaviour by increasing extracellular glutamate in the SCN.

Circadian rhythms are approximately 24-h oscillations in behavior and physiology, which are internally generated and function to anticipate the environmental changes associated with the solar day. A conserved transcriptional-translational autoregulatory loop generates molecular oscillations of 'clock genes' at the cellular level. In mammals, the circadian system is organized in a hierarchical manner, in which a master pacemaker in the suprachiasmatic nucleus (SCN) regulates downstream oscillators in peripheral tissues. Recent findings have revealed that the clock is cell-autonomous and self-sustained not only in a central pacemaker, the SCN, but also in peripheral tissues and in dissociated cultured cells. It is becoming evident that specific contribution of each clock component and interactions among the components vary in a tissue-specific manner. Here, we review the general mechanisms of the circadian clockwork, describe recent findings that elucidate tissue-specific expression patterns of the clock genes and address the importance of circadian regulation in peripheral tissues for an organism's overall well-being.

The circadian timing system controls glucose metabolism in a time-of-day dependent manner. In mammals, the circadian timing system consists of the main central clock in the bilateral suprachiasmatic nucleus (SCN) of the anterior hypothalamus and subordinate clocks in peripheral tissues. The oscillations produced by these different clocks with a period of approximately 24-h are generated by the transcriptional-translational feedback loops of a set of core clock genes. Glucose homeostasis is one of the daily rhythms controlled by this circadian timing system. The central pacemaker in the SCN controls glucose homeostasis through its neural projections to hypothalamic hubs that are in control of feeding behavior and energy metabolism. Using hormones such as adrenal glucocorticoids and melatonin and the autonomic nervous system, the SCN modulates critical processes such as glucose production and insulin sensitivity. Peripheral clocks in tissues, such as the liver, muscle, and adipose tissue serve to enhance and sustain these SCN signals. In the optimal situation all these clocks are synchronized and aligned with behavior and the environmental light/dark cycle. A negative impact on glucose metabolism becomes apparent when the internal timing system becomes disturbed, also known as circadian desynchrony or circadian misalignment. Circadian desynchrony may occur at several levels, as the mistiming of light exposure or sleep will especially affect the central clock, whereas mistiming of food intake or physical activity will especially involve the peripheral clocks. In this review, we will summarize the literature investigating the impact of circadian desynchrony on glucose metabolism and how it may result in the development of insulin resistance. In addition, we will discuss potential strategies aimed at reinstating circadian synchrony to improve insulin sensitivity and contribute to the prevention of type 2 diabetes.

Circadian oscillations in biological variables in mammals are controlled by a central pacemaker in the suprachiasmatic nuclei (SCN) of the hypothalamus which coordinates circadian oscillators in peripheral tissues. The molecular clockwork responsible for this rhythmicity consists of several clock genes and their corresponding proteins that compose interactive feedback loops. In the SCN, two of the genes, Per1 and Per2, show circadian rhythmicity in their expression and protein production. This SCN rhythmicity is modified by the length of daylight, i.e. the photoperiod. The aim of the present study was to find out whether profiles of PER1 and PER2 proteins in peripheral organs are also affected by the photoperiod. Rats were maintained under a long photoperiod with 16 h of light and 8 h of darkness per day (LD 16:8) and under a short, LD 8:16, photoperiod. The PER1 and PER2 daily profiles were measured in peripheral organs by Western blotting. The photoperiod affected significantly the PER1 profile in livers and the PER2 profile in lungs and hearts. In lungs, PER2 in the cytoplasmic, but not in the nuclear fraction, was affected significantly. The effect of the photoperiod on PER1 profiles in peripheral organs appears to differ from that in the SCN.