Exposing 24-hour cycles in bile acids of male humans

Abstract

Bile acids are trans-genomic molecules arising from the concerted metabolism of the human host and the intestinal microbiota and are important for digestion, energy homeostasis and metabolic regulation. While diurnal variation has been demonstrated in the enterohepatic circulation and the gut microbiota, existing human data are poorly resolved, and the influence of the host circadian system has not been determined. Using entrained laboratory protocols, we demonstrate robust daily rhythms in the circulating bile acid pool in healthy male participants. We identify temporal relationships between bile acids and plasma lipids and show that these relationships are lost following sleep deprivation. We also highlight that bile acid rhythmicity is predominantly lost when environmental timing cues are held constant. Here we show that the environment is a stronger determinant of these temporal dynamics than the intrinsic circadian system of the host. This has significance for the intimate relationship between circadian timing and metabolism.

Fig. 1. Circulating bile acids follow a daily cycle.

A Study design for the entrained human study (24 h sleep/wake) followed by 24 h of wakefulness. B Daily patterns in the abundance of circulating plasma bile acids. Cosine cycles were observed in Z scored mean time courses of tauro-, glyco-, and unconjugated forms of the primary bile acids, cholic acid (CA) and chenodeoxycholic acid (CDCA), and the secondary bile acids, deoxycholic acid (DCA) and lithocholic acid (LCA), following a cosine pattern across the 36-hour period during the sleep/wake phase. Values are the mean Z scores (shaded area indicates standard deviation) from all DLMO-corrected individual time courses, calculated for each bile acid (DLMO, 21:46 ± 0:29 h:min, mean ± SEM). C Cross-correlation analysis indicating phase differences between all bile acid species. Values and red background intensity indicate the magnitude of phase difference in decimal hours. Substantial phase differences can be observed between conjugated and unconjugated bile acids. Source data are provided as a Source Data file.

Fig. 2. Cross-correlation analysis of circulating rhythmic bile acid species (n = 16) with plasma metabolites and lipids in participants following the entrained protocol.

Colors indicate metabolite class, and symbol size indicates correlation strength. The distance of the edge indicates the phase difference between peak bile acid concentration and peak metabolite concentration.

Fig. 3. Sleep deprivation does not alter bile acid dynamics, but it disrupts the relationship between plasma bile acids and the circulating metabolome.

A Phase differences in individual bile acids under entrained and sleep deprivation conditions. B Phase differences in the cross-correlations between bile acid pairs under entrained and sleep deprivation conditions. All pairs shown including rhythmic and non-rhythmic bile acids. Red dashed line indicates no difference in phase. C Phase differences in the relationships between bile acids and metabolites under both conditions. All pairs shown including rhythmic and non-rhythmic bile acids with metabolites and lipids. Blue lines and symbol color indicates no difference, and red lines and symbols indicate a 12-hour shift in the relationship between conditions. D Histogram indicating the frequency of bile acid-metabolite changes by circular hours between the two study conditions. A peak can be observed in 0–2 hours phase shift between the two conditions (i.e., no change) and 7–8 hours phase shift. CA cholic acid, CDCA chenodeoxycholic acid, DCA deoxycholic acid, GCA glycocholic acid, GCDCA glycochenodeoxycholic acid, GDCA glycodeoxycholic acid, GHCA glycohyocholic acid, GUDCA glycoursodeoxycholic acid, HCA hyocholic acid, LCA lithocholic acid, TCA taurocholic acid, TCDCA taurochenodeoxycholic acid, TDCA taurodeoxycholic acid, TLCA taurolithocholic acid, UDCA ursodeoxycholic acid. Source data are provided as a Source Data file.

Fig. 4. Circulating bile acid rhythmicity is lost in the constant routine protocol that removes the influence of exogenous factors.

Primary and secondary bile acids in their conjugated (glycine- and taurine-) and unconjugated forms are displayed for all individuals from the entrained wake/sleep, entrained with 24-hour wakefulness (sleep deprivation), and constant routine protocols. Values are the mean Z scores (shaded area indicates standard error of the mean) from all DLMO-corrected individual time courses, calculated for each bile acid. Source data are provided as a Source Data file.