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Bitter taste receptors (taste 2 receptors, TAS2Rs) serve as warning sensors in the lingual system against the ingestion of potentially poisonous food. Here, we investigated the functional role of TAS2Rs in the human gut and focused on their potential to trigger an additional host defense pathway in the intestine. Human jejunal crypts, especially those from individuals with obesity, responded to bitter agonists by inducing the release of antimicrobial peptides ([alpha]-defensin 5 and regenerating islet-derived protein 3 [alpha] [REG3A]) but also regulated the expression of other innate immune factors (mucins, chemokines) that affected E. coli growth. We found that the effect of aloin on E. coli growth and on the release of the mucus glycoprotein CLCA1, identified via proteomics, was affected by TAS2R43 deletion polymorphisms and thus confirmed a role for TAS2R43. RNA-Seq revealed that denatonium benzoate induced an NRF2-mediated nutrient stress response and an unfolded protein response that increased the expression of the mitokine GDF15 but also ADM2 and LDLR, genes that are involved in anorectic signaling and lipid homeostasis. In conclusion, TAS2Rs in the intestine constitute a promising target for treating diseases that involve disturbances in the innate immune system and body weight control. TAS2R polymorphisms may be valuable genetic markers to predict therapeutic responses., Introduction Bitter is an aversive taste perceived on the tongue that acts as the first defense mechanism to protect our body against the ingestion of potentially poisonous compounds (1). Bitter [...]

The direct infusion of bitter solutions in the gastrointestinal tract can reduce the secretion of orexigenic hormones and influence appetite and food intake. We aimed to explore whether oral ingestion of the bitter tastant hydroxychloroquine sulfate can exert similar effects. Ten lean adult women were included in this double-blind, randomized, two-visit, crossover study. After an overnight fast, each volunteer received film-coated tablets containing 400 mg of hydroxychloroquine sulfate (Plaquenil®) or placebo. Plasma-ghrelin, -motilin, -insulin and blood-glucose concentrations were determined every 10 min before and 30 min after feeding; appetite was scored every 10 min. Hunger scores were investigated with a special interest 50–60 min after the ingestion of hydroxychloroquine sulfate, right before a rewarding chocolate milkshake was offered to drink ad libitum. Compared with the placebo, hydroxychloroquine sulfate tended to reduce hunger at the time of interest (p = 0.10). No effect was found upon subsequent milkshake intake. Motilin plasma concentrations were unaltered, but acyl-ghrelin plasma concentrations decreased after the ingestion of hydroxychloroquine sulfate (t = 40–50; p < 0.05). These data suggest that the oral intake of hydroxychloroquine sulfate tablets reduces subjective hunger via a ghrelin-dependent mechanism but does not affect motilin release, hedonic food intake or insulin levels in healthy women. [ABSTRACT FROM AUTHOR]

Background: Secondary bile acids entrain peripheral circadian clocks and inhibit colonic motility via the bile acid receptor GPBAR1. We aimed to investigate whether chronodisruption affected the rhythm in serum bile acid levels and whether this was associated with alterations in clock gene and Gpbar1 mRNA expression in the colonic smooth muscle layer. We hypothesized that this in turn may affect the rhythm in the inhibitory effect of secondary bile acids on colonic contractility. Methods: Mice were exposed to 4 weeks of chronic jetlag induction. The expression of Gpbar1 and clock genes was measured in colonic smooth muscle tissue using RT‐qPCR over 24 h (4 h time interval). The effect of secondary bile acids on electrical field‐induced neural contractions was measured isometrically in colonic smooth muscle strips. Key Results: Chronic jetlag abolished the rhythmicity in serum bile acid levels. This was associated with a phase‐shift in diurnal clock gene mRNA fluctuations in smooth muscle tissue. Chronic jetlag induced a rhythm in Gpbar1 expression in the colonic smooth muscle layer. In parallel, a rhythm was induced in the inhibitory effect of taurodeoxycholic acid (TDCA), but not deoxycholic acid, on neural colonic contractions that peaked together with Gpbar1 expression. Conclusions & Inferences: Chronodisruption abolished the rhythm in bile acid levels which might contribute to a shift in smooth muscle clock gene expression. Our findings suggest that chronodisruption caused a transcriptional reprogramming in the colonic smooth layer thereby inducing a rhythm in the expression of Gpbar1 and in the inhibitory effect of TDCA on colonic contractility. [ABSTRACT FROM AUTHOR]

Research was conducted to examine the hypothesis that the changes in intestinal contractility that accompanies inflammation of the gut are agonist specific. A comparison of the response of inflamed strips to substance P(SP), motilin, ACh and K+ as a function of time was performed. Results reveals that TNBS-induced colitis in the rabbit alters the contractile response of circular colonic smooth muscle tissue. However, the extent of the change and its time course depends on the stimulus.

Aim: Chronodisruption desynchronizes peripheral clocks and leads to metabolic diseases. Feeding cues are important synchronizers of peripheral clocks and influence rhythmic oscillations in intestinal microbiota and their metabolites. We investigated whether chronic jetlag, mimicking frequent time zone travelling, affected the diurnal fluctuations in faecal short‐chain fatty acid (SCFA) levels, that feed back to the gut clock to regulate rhythmicity in gut function. Methods: Rhythms in faecal SCFAs levels and in the expression of clock genes and epithelial markers were measured in the colonic mucosa of control and jetlagged mice. The entraining effect of SCFAs on the rhythm in clock gene mRNA expression was studied in primary colonic crypts. The role of the circadian clock in epithelial marker expression was studied in Arntl−/− mice. Results: Chronic jetlag increased body weight gain and abolished the day/night food intake pattern which resulted in a phase‐delay in the rhythm of faecal SCFAs that paralleled the shift in the expression of mucosal clock genes. This effect was mimicked by stimulation of primary colonic crypts from control mice with SCFAs. Jetlag abolished the rhythm in Tnfα, proglucagon and ghrelin expression but not in the expression of tight junction markers. Only a dampening in plasma glucagon‐like peptide‐1 but not in ghrelin levels was observed. Rhythms in ghrelin but not proglucagon mRNA expression were abolished in Arntl−/− mice. Conclusion: The altered food intake pattern during chronodisruption corresponds with the changes in rhythmicity of SCFA levels that entrain clock genes to affect rhythms in mRNA expression of gut epithelial markers. [ABSTRACT FROM AUTHOR]

Background: In our 24-hour society, an increasing number of people are required to be awake and active at night. As a result, the circadian rhythm of feeding is seriously compromised. To mimic this, we subjected mice to restricted feeding (RF), a paradigm in which food availability is limited to short and unusual times of day. RF induces a food-anticipatory increase in the levels of the hunger hormone ghrelin. We aimed to investigate whether ghrelin triggers the changes in body weight and gastric emptying that occur during RF. Moreover, the effect of genetic deletion of the core clock gene Bmal1 on these physiological adaptations was studied. Methods: Wild-type, ghrelin receptor knockout and Bmal1 knockout mice were fed ad libitum or put on RF with a normal or high-fat diet (HFD). Plasma ghrelin levels were measured by radioimmunoassay. Gastric contractility was studied in vitro in muscle strips and in vivo (13C breath test). Cytokine mRNA expression was quantified and infiltration of immune cells was assessed histologically. Results: The food-anticipatory increase in plasma ghrelin levels induced by RF with normal chow was abolished in HFD-fed mice. During RF, body weight restoration was facilitated by ghrelin and Bmal1. RF altered cytokine mRNA expression levels and triggered contractility changes resulting in an accelerated gastric emptying, independent from ghrelin signaling. During RF with a HFD, Bmal1 enhanced neutrophil recruitment to the stomach, increased gastric IL-1α expression and promoted gastric contractility changes. Conclusions: This is the first study demonstrating that ghrelin and Bmal1 regulate the extent of body weight restoration during RF, whereas Bmal1 controls the type of inflammatory infiltrate and contractility changes in the stomach. Disrupting the circadian rhythm of feeding induces a variety of diet-dependent metabolic, immune and gastrointestinal alterations, which may explain the higher prevalence of obesity and immune-related gastrointestinal disorders among shift workers. [ABSTRACT FROM AUTHOR]

The article presents the discussion on time-restricted feeding in mice prevents the disruption of the peripheral circadian clocks and its metabolic impact during chronic jetlag concerning the origin of the definition of chronodisruption.

Abstract: Ghrelin is an orexigenic peptide present in the stomach with gastroprokinetic properties. Previous in vivo studies have shown that the ghrelin receptor antagonist, D-Lys3-GHRP-6, reduced food intake and delayed gastric emptying in rodents but these effects are at variance with the normal phenotype of the ghrelin knockout mice. To verify the specificity of the effects observed with D-Lys3-GHRP-6 this study aimed to investigate the pharmacology of D-Lys3-GHRP-6 in vitro. Rat fundic strips were suspended in a tissue bath and the contraction of strips to 10−5 M of ghrelin, GHRP-6 or D-Lys3-GHRP-6 was measured isometrically in the absence and presence of blockers. Neither ghrelin, nor GHRP-6, induced significant contractions in the absence of electrical field stimulation thereby excluding the presence of ghrelin receptors on smooth muscle cells. In contrast D-Lys3-GHRP-6, induced a pronounced biphasic contraction of 13.9±1.8% and 40.5±3.2% relative to the response to 60 mM KCl. The contraction was blocked by the 5-HT1,2 receptor antagonist methysergide and was markedly reduced by the 5-HT2B receptor antagonist, yohimbine, which also profoundly affected 5-HT induced contractions in fundic strips. The existence of 5-HT2B receptors in the fundus was confirmed by use of the 5-HT2B receptor agonist, BW 723C86. In contrast to ghrelin and GHRP-6, the ghrelin receptor antagonist, D-Lys3-GHRP-6, induced pronounced smooth muscle contractions in the rat fundus by interacting with 5-HT2B receptors. This may question the role of endogenous ghrelin in the effects observed with D-Lys3-GHRP-6 on food intake and gastric emptying in vivo. [Copyright &y& Elsevier]

1 Inflammation may affect subpopulations of neurons of the myenteric plexus. 2 In the present study the effect of trinitrobenzene sulphonic acid (TNBS) induced colitis on nitrergic, purinergic and adrenergic inhibitory neurotransmission was studied as well as the consequences of the related changes on the response of 5-HT agonists using these neurotransmitters to mediate their effect. 3 Strips from normal and colitis rabbits (135 mg kg¹ TNBS) were subjected to electrical field stimulation (EFS, 0.3 ms, 6V, 0.5—32 Hz, 10 s train). The response was measured isometrically in the absence or presence of L-NAME, suramin, guanethidine, the 5-HT agonists (5-HT[1 5A/7]: 5-carboxamidotryptamine (5-CT), 5-HT[sub2]; α-methyl-5-HT, 5-HT[sub3]: 2-methyl-5-HT, 5-HT[sub4]: 5-methoxy-tryptamine (5-MeOT)) or a combination. 4 In normal strips L-NAME (1 -32 Hz), suramin (0,5-2, 8 Hz) and guanethidine (4, 16, 32 Hz) increased the response to EFS. This effect was abolished in inflamed strips and was accompanied by a decrease in nNOS expression. 5 In normal strips all 5-HT agonists induced pronounced (5-CT, α-methyl-5-HT) or small (2-methyl-5-HT, 5-MeOT) inhibitory neural responses. In inflamed strips this was reversed to cholinergic excitatory responses. 6 The effect of inflammation on the 5-HT[sub4] response was mimicked by preincubation of normal strips with L-NAME or suramin. Accordingly, in inflamed strips L-NAME or suramin did not affect the excitatory effects of 5-MeOT. 7 TNBS-colitis abolishes nitrergic, purinergie and adrenergic neurotransmission. This reverses serotonergic inhibition into excitation. [ABSTRACT FROM AUTHOR]

We used time-restricted feeding (TRF) to investigate whether microbial metabolites and the hunger hormone ghrelin can become the dominant entraining factor during chronic jetlag to prevent disruption of the master and peripheral clocks, in order to promote health. Therefore, hypothalamic clock gene and Agrp/Npy mRNA expression were measured in mice that were either chronically jetlagged and fed ad libitum, jetlagged and fed a TRF diet, or not jetlagged and fed a TRF diet. Fecal short-chain fatty acid (SCFA) concentrations, plasma ghrelin and corticosterone levels, and colonic clock gene mRNA expression were measured. Preventing the disruption of the food intake pattern during chronic jetlag using TRF restored the rhythmicity in hypothalamic clock gene mRNA expression of Reverbα but not of Arntl. TRF countered the changes in plasma ghrelin levels and in hypothalamic Npy mRNA expression induced by chronic jetlag, thereby reestablishing the food intake pattern. Increase in body mass induced by chronic jetlag was prevented. Alterations in diurnal fluctuations in fecal SCFAs during chronic jetlag were prevented thereby re-entraining the rhythmic expression of peripheral clock genes. In conclusion, TRF during chronodisruption re-entrains the rhythms in clock gene expression and signals from the gut that regulate food intake to normalize body homeostasis. [ABSTRACT FROM AUTHOR]

Aim: The microbiota shows diurnal oscillations that are synchronized by the host's circadian clock and feeding rhythms. Short‐chain fatty acids (SCFAs) produced by the microbiota are possible synchronizers of peripheral circadian clocks. We aimed to investigate whether faecal SCFAs show a diurnal rhythm that regulates the rhythm of SCFA receptor expression (FFAR2/3, OLFR78, HCAR2) and SCFA‐induced colonic contractility. The role of the circadian clock was studied in mice lacking the core clock gene Bmal1. Methods: Mice were sacrificed at 4‐hour intervals. Faecal SCFA concentrations and SCFA receptor expression were determined. The effect of increasing concentrations of a SCFA mix on electrical field‐induced neural responses in colon strips was measured isometrically. Results: Diurnal fluctuations in faecal SCFA concentrations (peak 4 hours after lights on) were observed that were in phase with the rhythm of Ffar2/3 expression in the colonic muscle layer. Olfr78 expression was not diurnal and Hcar2 was not detectable. The inhibitory effect of a SCFA mix on neural contractions in colonic smooth muscle strips showed a diurnal rhythm and oscillated in phase with faecal SCFA concentrations and Ffar2/3 expression. In contrast, neither excitatory neural responses nor acetylcholine‐induced smooth muscle contractions showed a diurnal rhythm. In Bmal1−/− mice, no fluctuations in faecal SCFA levels, Ffar3 expression and neural responses to SCFAs were observed. Conclusion: Diurnal microbial SCFA levels regulate the rhythm of Ffar3 expression in the colonic myenteric plexus, which causes rhythmicity in SCFA‐induced colonic motility. Deletion of Bmal1 abolishes rhythmicity of SCFA levels and their downstream effects. [ABSTRACT FROM AUTHOR]

Bitter taste receptors (TAS2Rs) are present in extra-oral tissues, including gut endocrine cells. This study explored the presence and mechanism of action of TAS2R agonists on gut smooth muscle in vitro and investigated functional effects of intra-gastric administration of TAS2R agonists on gastric motility and satiation. TAS2Rs and taste signalling elements were expressed in smooth muscle tissue along the mouse gut and in human gastric smooth muscle cells (hGSMC). Bitter tastants induced concentration and region-dependent contractility changes in mouse intestinal muscle strips. Contractions induced by denatonium benzoate (DB) in gastric fundus were mediated via increases in intracellular Ca2+ release and extracellular Ca2+-influx, partially masked by a hyperpolarizing K+-efflux. Intra-gastric administration of DB in mice induced a TAS2R-dependent delay in gastric emptying. In hGSMC, bitter compounds evoked Ca2+-rises and increased ERK-phosphorylation. Healthy volunteers showed an impaired fundic relaxation in response to nutrient infusion and a decreased nutrient volume tolerance and increased satiation during an oral nutrient challenge test after intra-gastric DB administration. These findings suggest a potential role for intestinal TAS2Rs as therapeutic targets to alter gastrointestinal motility and hence to interfere with hunger signalling. [ABSTRACT FROM AUTHOR]

Background & Aims: Circadian disturbances result in adverse health effects, including gastrointestinal symptoms. We investigated which physiological pathways in jejunal mucosa were disrupted during chronic jetlag and prevented during time-restricted feeding (TRF). Enteroids from Bmal1 +/+ and Bmal1 -/- mice were used to replicate the processes that were affected by chronic jetlag and rescued by TRF., Methods: C57BL/6J male mice were subjected to chronic jetlag or night-TRF for 4 weeks. An around-the-clock bulk-RNA sequencing study was performed on the jejunal mucosa. Bmal1 +/+ and Bmal1 -/- mouse enteroids were generated to study the jejunal epithelial clock dependency of rhythmic jejunal processes., Results: Chronic jetlag disrupted the rhythmicity of jejunal clock genes and the jejunal transcriptome which was partially rescued by TRF. Genes whose rhythm was altered by chronic jetlag but prevented by TRF were primarily associated with nutrient transport, lipid metabolism, ketogenesis and cellular organization. In vivo, chronic jetlag caused a phase shift in the rhythmic accumulation of neutral lipids and induced a diurnal rhythm in the number of crypt epithelial cells, both of which were prevented by TRF. In vitro, enteroids replicated the in vivo rhythmic accumulation of neutral lipids in a clock-dependent manner, while the rhythm of S phase proliferation was ultradian in both genotypes of enteroids., Conclusions: This pioneering transcriptomic study demonstrates that TRF acts as a robust entrainer during chronic jetlag, realigning disturbances in the circadian clock and the transcriptome involved in metabolic functions in the jejunal mucosa. Enteroids can replicate the rhythmic accumulation of neutral lipids dependent on the jejunal epithelial clock, enabling these functions to be studied in vitro., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Chemosensory signaling in organs such as the mouth and gut contributes to the mechanisms that control metabolism. We investigated the chemosensory pathways that regulate secretion of the hunger hormone ghrelin in response to neurotransmitters, bitter and sweet tastants at the cellular level in the human gut mucosa, and the disturbances in this regulatory pathway induced by obesity. Obesity impaired ghrelin protein production and adrenalin-induced ghrelin secretion in fundic cells, which was counterbalanced by somatostatin. Bitter agonists selective for taste receptor type 2 (TAS2Rs), TAS2R5 and TAS2R10 stimulated ghrelin secretion in fundic cells. The stimulatory effect of the broadly tuned bitter agonist, denatonium benzoate, was selectively blunted by obesity in the small intestine but not in the fundus. Luminal glucose concentrations inhibited ghrelin secretion via sodium-dependent glucose cotransporter and taste receptor type 1 member 3. Obesity altered the sensitivity of the ghrelin cell to glucose in the small intestine but not in the fundus. Sweet taste receptor activation inhibited bitter taste signaling of the ghrelin cell. In conclusion, obesity impairs the sympathetic drive that controls ghrelin release in the fundus and affects the sensitivity of the ghrelin cell to bitter and sweet stimuli in the small intestine but not in the fundus. Region-selective targeting of gut taste receptors in obesity is indicated.-Wang, Q., Liszt, K. I., Deloose, E., Canovai, E., Thijs, T., Farré, R., Ceulemans, L. J., Lannoo, M., Tack, J., Depoortere, I. Obesity alters adrenergic and chemosensory signaling pathways that regulate ghrelin secretion in the human gut.

Tachyphylaxis may have contributed to the failure of the motilide ABT-229 [N-ethyl, N-methyl 4'' deoxy erythromycin (EM)-B enolether] in clinical trials. We compared the desensitizing potency of structurally related motilides [EM-A, EM-A enolether (ME4), N-ethyl, N-methyl EM-A (ME36), EM-B enolether (ME67), N-ethyl, N-methyl EM-A enolether (EM523), ABT-229 and 4'' deoxy EM-A enolether (KOS1326)] in a Chinese hamster ovary (CHO)-K1 cell line expressing the human motilin receptor (MTLR) and in rabbit duodenal segments. CHO-MTLR cells were preincubated with motilides prior to stimulation with motilin. The negative logarithm of the preincubation concentration reducing the maximal motilin-induced Ca(2+) flux to 50% was calculated (pDC(50)). Internalization was visualized in CHO-K1 cells containing an enhanced green fluorescent protein (EGFP)-tagged MTLR and quantified in binding experiments. The contractile response of repeated stimulations was measured in duodenal segments. In CHO-MTLR cells, the pDC(50) was ABT-229 (8.78) > motilin (7.77) > EM-A (4.78), different from their order of potency to induce Ca(2+) release (pEC(50)): motilin (9.39) > ABT-229 (8.46) > EM-A (7.11). In cells with the EGFP-tagged MTLR, ABT-229 decreased membrane fluorescence by 25 +/- 2% compared with 16 +/- 2% for motilin and 8 +/- 2% for EM-A. Binding studies confirmed that EM-A did not induce MTLR internalization (residual binding 96 +/- 4% compared with motilin, 31 +/- 3% and ABT-229, 21 +/- 1%). Comparison of the pDC(50) and pEC(50) values of the other motilides ME4 (5.90; 8.08), ME67 (6.03; 8.12), ME36 (3.32; 6.62), EM-523 (6.02; 8.22), and KOS1326 (7.32; 8.14) suggested that the strong desensitizing properties of ABT-229 are mostly related to the removal of the 4''-OH of the cladinose sugar. The decline of the contractile response in duodenal segments correlated with the pDC(50). The ability to desensitize and internalize the MTLR is not only determined by potency. This may be an important criterion for the development of a clinically useful compound.

The structural relationship between the motilin and the growth hormone secretagogue receptor (GHS-R), and between their respective ligands, motilin and ghrelin, prompted us to investigate whether ghrelin and the GHS-R agonist growth hormone-releasing peptide-6 (GHRP-6), could interact with the motilin receptor. The interaction was evaluated in the rabbit gastric antrum with binding studies on membrane preparations and with contraction studies on muscle strips in the presence of selective antagonists under conditions of electrical field stimulation (EFS) or not. Binding studies indicated that the affinity (pK(d)) for the motilin receptor was in the order of ghrelin (4.23 +/- 0.07) < GHRP-6 (5.54 +/- 0.08) < motilin (9.13 +/- 0.03). The interaction of ghrelin with the motilin receptor requires the octanoyl group. Motilin induced smooth muscle contractile responses but ghrelin and GHRP-6 were ineffective. EFS elicited on- and off-responses that were increased by motilin already at 10(-9) M, but not by 10(-5) M ghrelin. In contrast, GHRP-6 also enhanced the on- and off-responses. The motilin antagonist Phe-cyclo[Lys-Tyr(3-tBu)-betaAla-] trifluoroacetate (GM-109) blocked the effect of GHRP-6 on the off-responses but not on the on-responses. Under nonadrenergic noncholinergic conditions, the effects of motilin and GHRP-6 on the on-responses were abolished; those on the off-responses were preserved. All responses were blocked by neurokinin (NK)(1) and NK(2) antagonists. In conclusion, ghrelin is unable to induce contractions via the motilin receptor. However, GHRP-6 enhances neural contractile responses, partially via interaction with the motilin receptor on noncholinergic nerves with tachykinins as mediator, and partially via another receptor that may be a GHS-R subtype on cholinergic nerves that corelease tachykinins.