What's next for chronobiology and drug discovery

A "4D" systemic view on meridian essence: Substantial, functional, chronological and cultural attributes

The term Jingluo, translated as meridian or channel, is a core component of traditional Chinese medicine (TCM) and has played a fundamental role in guiding the clinical practice of acupuncture for thousands of years. However, the essence of the meridian remains elusive and is a source of both confusion and debate for researchers. In this study, a "4D" systemic view on the essence of the meridian, namely substantial, functional, chronological, and cultural dimensions, was proposed based on a review of the ancient medical classics, recent research developments, and results from clinical practice. Previous studies have primarily focused on the substantial dimension of the meridian system, with scant interpretation about its functional domain. Neither systemic data nor evaluations have been adequately documented. Additionally, a limited but increasing number of studies have focused on the chronological and cultural dimensions. More investigations that embody the holistic concept of TCM and integrate the systemic modes and advanced techniques with dominant diseases of TCM need to be performed to obtain a more comprehensive understanding of the essence of meridians. The goal of this study is to yield useful information in understanding the essence of meridians and provide a reference and perspective for further research.

Nobiletin: Targeting the Circadian Network to Promote Bioenergetics and Healthy Aging

The circadian clock is the biological mastermind governing orderly execution of bodily processes throughout the day. In recent years, an emerging topic of broad interest is clock-modulatory agents, including small molecules both of synthetic and natural origins, and their potential applications in disease models. Nobiletin is a naturally occurring flavonoid with the greatest abundance found in citrus peels. Extensive research has shown that Nobiletin is endowed with a wide range of biological activities, yet its mechanism of action remains unclear. We recently found through unbiased chemical screening that Nobiletin impinges on the clock machinery to activate temporal control of downstream processes within the cell and throughout the body. Using animal models of diseases and aging, we and others illustrate potent beneficial effects of Nobiletin on cellular energetics in both periphery and brain to promote healthy aging. Given its excellent safety profile, Nobiletin may represent a promising candidate molecule for development of nutraceutical and chronotherapeutic agents against chronic and age-related neurodegenerative diseases.

Small-molecule modulators of the circadian clock: Pharmacological potentials in circadian-related diseases

Disruption of circadian oscillations has a wide-ranging impact on health, with the potential to induce the development of clock-related diseases. Small-molecule modulators of the circadian clock (SMMCC) target core or noncore clock proteins, modulating physiological effects as a consequence of agonist, inverse agonist, or antagonist interference. These pharmacological modulators are usually identified using chemical screening of large libraries of active compounds. However, target-based screens, chemical optimization, and circadian crystallography have recently assisted in the identification of these compounds. In this review, we focus on established and novel SMMCCs targeting both core and noncore clock proteins, identifying their circadian targets, detailed circadian effects, and specific physiological effects. In addition, we discuss their therapeutic potential for the treatment of diverse clock-related disorders (such as metabolic-associated disorders, autoimmune diseases, mood disorders, and cancer) and as chronotherapeutics. Future perspectives are also considered, such as clinical trials, and potential safety hazards, including those in the absence of clinical trials.

Coordinate Regulation of Cholesterol and Bile Acid Metabolism by the Clock Modifier Nobiletin in Metabolically Challenged Old Mice

Cholesterol and bile acid (BA) homeostasis plays a central role in systemic metabolism. Accumulating evidence suggests a key regulatory function of the circadian clock, our biological timer, in lipid metabolism, particularly cholesterol and bile acid flux. Previously, we showed that Nobiletin (NOB), a natural compound targeting the ROR (Retinoic acid receptor-related orphan receptor) nuclear receptors in the circadian oscillator, strongly protects lipid homeostasis, including normal serum cholesterol levels in high-fat (HF) fed mice at both young and old ages. In this study, we further examined the role of NOB in cholesterol metabolism in HF-fed aged mice, and found that NOB lowered the serum LDL/VLDL cholesterol levels and consequently the LDL/HDL ratio. BA levels in the serum were markedly reduced in the HF.NOB group, and examination of additional hepatic markers further indicate a protective role of NOB in the liver. At the molecular level, whereas HF feeding downregulated hepatic expression of several ROR target genes involved in bile acid synthesis, NOB treatment (HF.NOB) was able to rescue it. In accordance, fecal BA excretion was enhanced by NOB, and microbial 16S sequencing revealed alteration of several taxa known to be involved in secondary BA production in the gut. Together, these results demonstrate concerted effects of the clock-modulating compound NOB in cholesterol and BA metabolism, suggesting pharmacological manipulation of the clock as a novel therapeutic strategy against metabolic disorders and age-related decline.

Emerging relevance of circadian rhythms in headaches and neuropathic pain

Circadian rhythms of physiology are the keys to health and fitness, as dysregulation, by genetic mutations or environmental factors, increases disease risk and aggravates progression. Molecular and physiological studies have shed important light on an intrinsic clock that drives circadian rhythms and serves essential roles in metabolic homoeostasis, organ physiology and brain functions. One exciting new area in circadian research is pain, including headache and neuropathic pain for which new mechanistic insights have recently emerged. For example, cluster headache is an intermittent pain disorder with an exceedingly precise circadian timing, and preliminary evidence is emerging linking several circadian components (eg, Clock and Nr1d1) with the disease. In this review, we first discuss the broad metabolic and physiological relevance of the circadian timing system. We then provide a detailed review of the circadian relevance in pain disease and physiology, including cluster headache, migraine, hypnic headache and neuropathic pain. Finally, we describe potential therapeutic implications, including existing pain medicines and novel clock-modulating compounds. The physiological basis for the circadian rhythms in pain is an exciting new area of research with profound basic and translational impact.