Effects of caffeine on the human circadian clock in vivo and in vitro

Abstract

Caffeine’s wakefulness-promoting and sleep-disrupting effects are well established, yet whether caffeine affects human circadian timing is unknown. Here we show that evening caffeine consumption delays the human circadian melatonin rhythm in vivo, and chronic application of caffeine lengthens the circadian period of molecular oscillations in vitro primarily via an adenosine receptor/cyclic AMP-dependent mechanism. In a double-blind, placebo controlled, ~49-day long within-subject study, we found the equivalent amount of caffeine as that in a double espresso 3 hours before habitual bedtime induced a phase delay of the circadian melatonin rhythm in humans by ~40 minutes. This magnitude of delay was nearly half of the magnitude of the phase-delaying response induced by exposure to 3-hours of evening bright-light (~3000 lux; ~7 Watts/m2) that began at habitual bedtime. Furthermore, using human osteosarcoma U2OS cells expressing clock gene luciferase reporters, we found a dose-dependent lengthening of circadian period by caffeine. By pharmacological dissection and siRNA knockdown we established that perturbation of adenosine receptor signaling, but not ryanodine receptor or phosphodiesterase activity, is sufficient to account for caffeine’s effects on cellular timekeeping. We also used a cyclic AMP biosensor to show that caffeine increased cyclic AMP levels, indicating that caffeine can influence a core component of the cellular circadian clock. Taken together, our findings demonstrate that caffeine influences human circadian timing and gives new insight into how the world’s most widely consumed psychoactive drug impacts upon human physiology.

In-depth Characterization of Firefly Luciferase as a Reporter of Circadian Gene Expression in Mammalian Cells

“…Human U2OS cells were obtained from ATCC (Teddington, UK) and stably transfected with pGL4.20 constructs (Promega) to express Fluc either constitutively (SV40:Luc) or under the control of the Per2 or Bmal1 promoter, as described previously (Burke et al, 2015). PER2::LUC fibroblasts were isolated from adult mouse lung tissue and immortalized as described previously (Causton et al, 2015).…”

Endocrine regulation of circadian physiology

“…Occupations requiring shift work or irregular working hours, chronic stress, mistimed light exposure, e.g. through artificial lighting or the use of light-emitting electronic devices (Chang et al 2015), and the frequent intake of arousal stimulating beverages such as coffee at night (Burke et al 2015) are all established disruptors of the circadian system. Altered circadian hormonal regulation compromises one's health such as by promoting the development of metabolic disorders.…”

Circadian-Based Therapies for Circadian Rhythm Sleep-Wake Disorders

“…However, another study recently demonstrated that caffeine is capable of causing phase delays in the timing of the circadian pacemaker raising the possibility that caffeine could be used as a true chronobiotic. Burke et al [27] administered 2.9 mg/kg of caffeine 3 hours before habitual bedtime in a double-blind, placebo controlled fashion in 5 healthy individuals and found that caffeine caused a phase delay that was approximately 40 minutes longer than the dim-light placebo control. In comparison, the response to a 3 hour exposure of ~3,000 lux beginning at habitual bedtime was about 85 minutes longer than the dim-light placebo.…”