Natural Compounds that Modulate Circadian Rhythms.

Circadian rhythms of innate 24 h cycles comprise well-conserved biological phenomena from cyanobacteria to mammalian. They are driven by light and regulated by clock genes that work as transcription factors and control the expression of many other genes and physiological functions in the cells. The expression of ~ 40% of protein-coding genes shows 24 h oscillation patterns in mice, implying their importance in normal body functions. Indeed, the physiological and behavioural rhythmicity generated through clock genes-mediated multiple mechanisms affects the quality of life at large. Disrupted circadian rhythmicity is associated with several kinds of diseases. For example, cancer cells show abnormal expression patterns for circadian rhythm genes that have been shown to regulate oncogenesis, drug responses, and disease prognosis. Furthermore, the modern globalisation of human lifestyle and business and social activities have disrupted innate circadian rhythm, resulting in a variety of diseases through disrupted humoral, immunological, and neuronal pathways. Safe and sustainable modulation of circadian rhythm has become a prevalent need that warrants basic and interventional research, as well as clinical investigations. Although traditional systems of medicine suggest some natural compounds with circadian rhythmmodulating potential, most of these have not been validated in laboratory or clinical studies. Reliable read-outs of the effects of test compounds on circadian rhythmicity have been limited by the availability of live cell assays. We have, herein, provided an overview of living cell-embedded real- time reporter gene assays designed for screening compounds that modulate circadian rhythm, and discussed the potential of some natural compounds for circadian rhythm modulation as validated by cell-based assay systems, and their role in disease therapeutics.