T he circadian clock is a molecular mechanism underlying endogenous, self-sustained oscillations with a period of Ϸ24 h, manifested in diverse physiological and metabolic processes (1-3). The most striking feature of circadian clock is its flexible yet robust response to various environmental conditions. For example, circadian periodicity varies with light intensity (4-6) while remaining robust over a wide range of temperatures (''temperature compensation'') (1, 3, 7-9). This flexible-yetrobust characteristic is evolutionarily conserved in organisms ranging from photosynthetic bacteria to warm-blooded mammals (3, 10-12), and has interested researchers from a broad range of disciplines. However, despite many genetic and molecular studies (13-22), the detailed biochemical mechanism underlying this characteristic remains poorly elucidated (3).The simplest explanation for this flexible-yet-robust property is that the key period-determining reactions are insensitive to temperature but responsive to other environmental conditions. Indeed, Pittendrigh proposed the existence of a temperatureinsensitive component in the clock system in 1954 (7), and in 1968, he and his colleagues demonstrated that both the wave form and the period of circadian oscillations are invariant with temperature (23). However, the idea of a temperatureinsensitive biochemical reaction is counterintuitive, as elementary chemical processes are highly temperature-sensitive. One exception is the cyanobacterial clock, in which temperatureinsensitive enzymatic reactions are observed (24,25). However, the cyanobacterial clock is quite distinct from other clock systems, and this biochemical mechanism has not been demonstrated in other clocks.Recently, a chemical-biological approach was proposed to help elucidate the basic processes underlying circadian clocks (26), and high-throughput screening of a large chemical compound library was performed (27). In this report, to analyze systematically the fundamental processes involved in determining the period length of mammalian clocks, we tested 1,260 pharmacologically active compounds for their effect on period length in mouse and human clock cell lines, and found 10 compounds that most markedly lengthened the period of both clock cell lines affected both the central and peripheral circadian clocks. Most compounds inhibited CKI or CKI␦ activity, suggesting that CKI /␦-dependent phosphorylation is an important period-determining process in the mammalian circadian clock. Surprisingly, the degradation rate of endogenous PER2, which is regulated by CKI -dependent phosphorylation (28) and probably by CKI␦-dependent phosphorylation, was temperatureinsensitive in the living clock cells, and the temperatureinsensitivity was preserved even for the in vitro CKI /␦-dependent phosphorylation of a synthetic peptide derived from PER2. These results suggest that this period-determining process is flexible in response to chemical perturbation yet robust in the face of temperature perturbations. Based on these findings, we prop...

Detection of internal body time (BT) via a few-time-point assay has been a longstanding challenge in medicine, because BT information can be exploited to maximize potency and minimize toxicity during drug administration and thus will enable highly optimized medication. To address this challenge, we previously developed the concept, ''molecular-timetable method,'' which was originally inspired by Linné 's flower clock. In Linné 's flower clock, one can estimate the time of the day by watching the opening and closing pattern of various flowers. Similarly, in the molecular-timetable method, one can measure the BT of the day by profiling the up and down patterns of substances in the molecular timetable. To make this method clinically feasible, we now performed blood metabolome analysis and here report the successful quantification of hundreds of clock-controlled metabolites in mouse plasma. Based on circadian blood metabolomics, we can detect individual BT under various conditions, demonstrating its robustness against genetic background, sex, age, and feeding differences. The power of this method is also demonstrated by the sensitive and accurate detection of circadian rhythm disorder in jet-lagged mice. These results suggest the potential for metabolomics-based detection of BT (''metabolite-timetable method''), which will lead to the realization of chronotherapy and personalized medicine.chronotherapy ͉ circadian ͉ metabolome ͉ jet-lag ͉ LC-MS

A convenient way to estimate internal body time (BT) is essential for chronotherapy and time-restricted feeding, both of which use body-time information to maximize potency and minimize toxicity during drug administration and feeding, respectively. Previously, we proposed a molecular timetable based on circadian-oscillating substances in multiple mouse organs or blood to estimate internal body time from samples taken at only a few time points. Here we applied this molecular-timetable concept to estimate and evaluate internal body time in humans. We constructed a 1.5-d reference timetable of oscillating metabolites in human blood samples with 2-h sampling frequency while simultaneously controlling for the confounding effects of activity level, light, temperature, sleep, and food intake. By using this metabolite timetable as a reference, we accurately determined internal body time within 3 h from just two anti-phase blood samples. Our minimally invasive, moleculartimetable method with human blood enables highly optimized and personalized medicine.metabolomics | circadian rhythm | liquid chromatography mass spectrometry | diagnostic tool M any organisms possess a molecular time-keeping mechanism, a circadian clock, which has endogenous, self-sustained oscillations with a period of about 24 h. Circadian regulation of cell activity occurs in diverse biological processes such as electrical activity, gene/protein expression, and concentration of ions and substances (1, 2). In mammals, for example, several clock genes regulate circadian gene expression in central and peripheral clock tissues (3-9), as well as metabolites in the blood (10-15). Reflecting circadian regulation of such processes, the potency and toxicity of administered drugs depends on an individual's body time (BT) (16)(17)(18)(19)(20)(21)(22). Drug delivery according to body time improves the outcome of pharmacotherapy by maximizing potency and minimizing toxicity (23), and administrating drugs at an inappropriate body time can result in severe side effects (22). For example, rhythm disturbances were induced by administration of IFN-α during the early active phase in mice, although unaffected during the early rest phase (22); and the time of administration of two anticancer drugs, adriamycin (6:00 AM) and cisplatin (6:00 PM), made a lower toxicity effect than its antiphasic administration (24). However, several reports showed that internal body time varies by 5-6 h in healthy humans (25, 26) and as much as 10-12 h in shift workers without forced entrainments (27,28). Therefore, for efficient application of body-time drug delivery or "chronotherapy" (16-20) in a clinical setting, a simple and robust method for estimating an individual's internal body time is needed.Additionally, the timing of food intake may contribute to weight gain (29) and metabolic disease (30) because energy regulation and circadian rhythms are molecularly and physiologically intertwined (31-41). For example, mice fed a high-fat diet during a 12-h light phase gain significantly more ...

Detection of individual body time (BT) via a single-time-point assay has been a longstanding unfulfilled dream in medicine, because BT information can be exploited to maximize potency and minimize toxicity during drug administration and thus will enable highly optimized medication. To achieve this dream, we created a ''molecular timetable'' composed of >100 ''time-indicating genes,'' whose gene expression levels can represent internal BT. Here we describe a robust method called the ''molecular-timetable method'' for BT detection from a single-time-point expression profile. The power of this method is demonstrated by the sensitive and accurate detection of BT and the sensitive diagnosis of rhythm disorders. These results demonstrate the feasibility of BT detection based on single-time-point sampling, suggest the potential for expression-based diagnosis of rhythm disorders, and may translate functional genomics into chronotherapy and personalized medicine.DNA microarray ͉ gene expression ͉ chronotherapy D iverse physiological and metabolic processes exhibit circadian rhythms, which are endogenous self-sustained oscillations with a period of Ϸ24 hours. In mammals, several clock genes, including Clock, Bmal1͞Mop3, Per1, Per2, Cry1, Cry2, Cki, and RevErbA␣, including Dbp, E4bp4, Dec1͞Stra13, Dec2, Per3, Npas2, RevErbA␤, Ror␣, Ror␤, and Ror␥, regulate, at least in part, gene expression in central and͞or peripheral clocks (1). Reflecting the temporal changes in gene expression in central and peripheral clocks (2-5), the potency and͞or toxicity in drug administration depend on an individual's body time (BT) (6-10). It has been suggested that drug administration at the appropriate BT can improve the outcome of pharmacotherapy by maximizing potency and minimizing the toxicity of the drug (11), whereas drug administration at an inappropriate BT can induce severe side effects (12). Despite the effectiveness and importance of such BT-dependent therapy, termed ''chronotherapy'' (6-10), its clinical use has been obstructed by the lack of clinically applicable methods for BT detection. To address these difficulties, we attempted to create standard expression profiles, termed a ''molecular timetable,'' composed of Ͼ100 ''time-indicating genes'' and their expression levels during the course of a day, and then to apply this timetable to BT detection. Materials and MethodsAnimals. To select time-indicating genes and construct their standard expression profiles, we analyzed the previously obtained genome-wide expression profiles (5) from pooled livers of four Balb͞c mice (male) every 4 h over 2 d under 12-h light͞12-h dark (LD) or constant-dark (DD) conditions. We independently sampled livers from eight individual Balb͞c mice (male) at Zeitgeber time (ZT)12 (n ϭ 4), ZT6 (n ϭ 1), ZT18 (n ϭ 1), Circadian time (CT)6 (n ϭ 1), and CT18 (n ϭ 1) to verify the capability of the molecular-timetable method. ZT is used for a timescale under LD conditions, whereas CT is used for a timescale under DD conditions. ZT0 represents lights on, and ...