Motilin: a panoply of communications between the gut, brain, and pancreas

Common Pathophysiological Mechanisms and Treatment of Diabetic Gastroparesis

Diabetic gastroparesis (DGP) is a common complication of diabetes mellitus, marked by gastrointestinal motility disorder, a delayed gastric emptying present in the absence of mechanical obstruction. Clinical manifestations include postprandial fullness and epigastric discomfort, bloating, nausea, and vomiting. DGP may significantly affect the quality of life and productivity of patients. Research on the relationship between gastrointestinal dynamics and DGP has received much attention because of the increasing prevalence of DGP. Gastrointestinal motility disorders are closely related to a variety of factors including the absence and destruction of interstitial cells of Cajal, abnormalities in the neuro-endocrine system and hormone levels. Therefore, this study will review recent literature on the mechanisms of DGP and gastrointestinal motility disorders as well as the development of prokinetic treatment of gastrointestinal motility disorders in order to give future research directions and identify treatment strategies for DGP.

Dietary Fibre for the Prevention of Post-Pancreatitis Diabetes Mellitus: A Review of the Literature and Future Research Directions

Post-pancreatitis diabetes mellitus-the most common sequela of pancreatitis-leads to poorer glycaemic control compared with type 2 diabetes. Because post-pancreatitis diabetes mellitus is an exemplar of secondary diabetes (with a clear underlying cause), much post-pancreatitis diabetes mellitus is preventable or treatable early. Earlier literature established the important role of dietary fibre in reducing plasma glucose in individuals with type 2 diabetes. The present review benchmarks available evidence on the role of habitual dietary fibre intake in pancreatitis and post-pancreatitis diabetes mellitus. It also paves the way for future research on the use of dietary fibre in the post-pancreatitis setting.

The ghrelin receptor GHSR has two efficient agonists in the lobe-finned fish Latimeria chalumnae

The peptide hormone ghrelin (an agonist) and LEAP2 (an antagonist) play important functions in energy metabolism via their receptor GHSR, an A-class G protein-coupled receptor. Ghrelin, LEAP2, and GHSR are widely present from fishes to mammals. However, our recent study suggested that fish GHSRs have different binding properties to ghrelin: a GHSR from the lobe-finned fish Latimeria chalumnae (coelacanth) is efficiently activated by ghrelin, but GHSRs from the ray-finned fish Danio rerio (zebrafish) and Larimichthys crocea (large yellow croaker) have lost binding to ghrelin. Do fish GHSRs use another peptide as their agonist? In the present study we tested to two fish motilins from D. rerio and L. chalumnae because motilin is distantly related to ghrelin. In ligand binding and activation assays, the fish GHSRs from D. rerio and L. crocea displayed no detectable or very low binding to all tested motilins; however, the fish GHSR from L. chalumnae bound to its motilin with high affinity and was efficiently activated by it. Therefore, it seemed that motilin is not a ligand for GHSR in the ray-finned fish D. rerio and L. crocea, but is an efficient agonist for GHSR in the lobe-finned fish L. chalumnae, one of the closest fish relatives of tetrapods. The results of present study suggested that GHSR might have two efficient agonists, ghrelin and motilin, in ancient fishes; however, this feature might be only preserved in some extant fishes with ancient evolutionary origins.

Intra-pancreatic fat deposition across the pancreatitis spectrum and the influence of gut hormones

BACKGROUND AND AIMS

Acute pancreatitis (AP) and chronic pancreatitis (CP) often represent parts of the spectrum of disease. While growing evidence indicates that intra-pancreatic fat deposition (IPFD) plays an important role in the pathogenesis of pancreatitis, no study of living individuals has investigated IPFD in both AP and CP. Further, the associations between IPFD and gut hormones remain to be elucidated. The aims were to investigate the associations of IPFD with AP, CP, and health; and to study whether gut hormones affect these associations.

METHODS

Magnetic resonance imaging on the same 3.0 Tesla scanner was used to determine IPFD in 201 study participants. These participants were arranged into the health, AP, and CP groups. Gut hormones (ghrelin, glucagon-like peptide-1, gastric inhibitory peptide, peptide YY, and oxyntomodulin) were measured in blood, both after an 8-hour overnight fasting and after ingestion of a standardised mixed meal. A series of linear regression analyses was run, accounting for age, sex, ethnicity, body mass index, glycated haemoglobin, and triglycerides.

RESULTS

Both the AP group and CP group had significantly higher IPFD in comparison with the health group, consistently across all models (p for trend 0.027 in the most adjusted model). Ghrelin in the fasted state had a significant positive association with IPFD in the AP group (but not the CP or health group), consistently across all models (p = 0.019 in the most adjusted model). None of the studied gut hormones in the postprandial state was significantly associated with IPFD.

CONCLUSION

Fat deposition in the pancreas is similarly high in individuals with AP and those with CP. The gut-brain axis, and more specifically overexpression of ghrelin, may contribute to increased IPFD in individuals with AP.

Relationship between Habitual Intake of Vitamins and New-Onset Prediabetes/Diabetes after Acute Pancreatitis

Vitamins have many established roles in human health. However, the role of habitual dietary intake of vitamins in glucose homeostasis in individuals after acute pancreatitis (AP) is yet to be elucidated. The aim was to investigate the associations between habitual intake of fat- and water-soluble vitamins/vitamers and markers of glucose metabolism (fasting plasma glucose (FPG), homeostasis model assessment insulin resistance (HOMA-IR) index, and homeostasis model assessment β-cell function (HOMA-β)) in individuals after AP. A total of 106 participants after AP were included in this cross-sectional study and were grouped based on glycaemic status: new-onset prediabetes/diabetes after AP (NODAP), pre-existing prediabetes/type 2 diabetes (T2DM), and normoglycaemia after AP (NAP). Habitual intake of seven fat-soluble vitamins/vitamers and seven water-soluble vitamins were determined by the EPIC-Norfolk food frequency questionnaire. Multiple linear regression analyses were conducted using five statistical models built to adjust for covariates (age, sex, daily energy intake, visceral/subcutaneous fat volume ratio, smoking status, daily alcohol intake, aetiology of AP, number of AP episodes, cholecystectomy, and use of antidiabetic medications). In the NODAP group, three fat-soluble vitamins/vitamers (α-carotene, β-carotene, and total carotene) were significantly associated with HOMA-β. One water-soluble vitamin (vitamin B3) was also significantly associated with HOMA-β in the NODAP group. None of the studied vitamins were significantly associated with FPG or HOMA-IR in the NODAP group. Prospective longitudinal studies and randomised controlled trials are now warranted to investigate if the observed associations between vitamin/vitamer intake and NODAP are causal and to unveil the specific mechanisms underlying their involvement with NODAP.

Roles of Endothelial Motilin Receptor and Its Signal Transduction Pathway in Motilin-Induced Left Gastric Artery Relaxation in Dogs

Background: Motilin increases left gastric artery (LGA) blood flow in dogs via the endothelial motilin receptor (MLNR). This article investigates the signaling pathways of endothelial MLNR.

Methods: Motilin-induced relaxation of LGA rings was assessed using wire myography. Nitric oxide (NO), and cyclic guanosine monophosphate (cGMP) levels were measured using an NO assay kit and cGMP ELISA kit, respectively.

Results: Motilin concentration-dependently (EC₅₀=9.1±1.2×10⁻⁸M) relaxed LGA rings precontracted with U46619 (thromboxane A₂ receptor agonist). GM-109 (MLNR antagonist) significantly inhibited motilin-induced LGA relaxation and the production of NO and cGMP. N-ethylmaleimide (NEM; G-protein antagonist), U73122 [phospholipase C (PLC) inhibitor], and 2-aminoethyl diphenylborinate [2-APB; inositol trisphosphate (IP₃) blocker] partially or completely blocked vasorelaxation. In contrast, chelerythrine [protein kinase C (PKC) inhibitor] and H89 [protein kinase A (PKA) inhibitor] had no such effect. Low-calcium or calcium-free Krebs solutions also reduced vasorelaxation. N-nitro-L-arginine methyl ester [L-NAME; nitric oxide synthase (NOS) inhibitor] and ODQ [soluble guanylyl cyclase (sGC) inhibitor] completely abolished vasodilation and synthesis of NO and cGMP. Indomethacin (cyclooxygenase inhibitor), 18α-glycyrrhetinic acid [18α-GA; myoendothelial gap junction (MEGJ) inhibitor], and K⁺ channel inhibition through high K⁺ concentrations or tetraethylammonium (TEA-Cl; K_Ca channel blocker) partially decreased vasorelaxation, whereas glibenclamide (K_ATP channel blocker) had no such effect.

Conclusion: The current study suggests that motilin-induced LGA relaxation is dependent on endothelial MLNR through the G protein-PLC-IP₃ pathway and Ca²⁺ influx. The NOS-NO-sGC-cGMP pathway, prostacyclin, MEGJ, and K⁺ channels (especially K_Ca) are involved in endothelial-dependent relaxation of vascular smooth muscle (VSM) cells.

Differential expression of motilin receptors on the endothelium of dog gastrointestinal arteries and motilin-induced motilin receptor dependent relaxation of corresponding arteries

BACKGROUND

Motilin's role in the regulation of vascular tone and hemodynamic besides gastrointestinal motility is concerned. This study aimed to investigate the expression of motilin receptors in gastrointestinal arteries and motilin-induced relaxation.

MATERIAL AND METHODS

The expression of motilin receptors in the left gastric artery (LGA), superior mesenteric artery (SMA), and inferior mesenteric artery (IMA) of adult dogs (1.5-5 years old) were analyzed by immunochemistry, RT-PCR, and western blotting. Motilin's effects on the gastrointestinal arteries were evaluated in a multi-wire myograph system.

RESULTS

Immunohistochemical staining showed that motilin receptor was expressed on the membranes of endothelial cells with the fluorescence intensity LGA > SMA > IMA (P < 0.01). The motilin receptor's mRNA and protein expression levels shared the same distribution patterns as it in fluorescence intensity (P < 0.01). In isolated LGA preparations precontracted with U46619 (a thromboxaneA2 analog), motilin induced a concentration-dependent relaxation, and the EC₅₀ was 8.8 × 10^-8 ± 0.9 × 10^-8 M. Motilin-induced relaxation on the three arteries also shared the same pattern as it in fluorescence intensity (P < 0.01) and inhibited by denuded-endothelium and GM-109 (a motilin receptor antagonist) but not by atropine (a muscarinic receptor antagonist).

CONCLUSIONS

Motilin receptors are expressed differentially on the membranes of endothelial cells in dog gastrointestinal arteries with a significantly high expression in the LGA. Motilin-induced relaxation is endothelium- and motilin receptor-dependent. The motilin receptor expressed on the endothelial cell membrane of the LGA is the molecular basis for motilin regulating gastric blood flow under physiological conditions in dogs.

Post-pancreatitis diabetes mellitus: investigational drugs in preclinical and clinical development and therapeutic implications

Introduction: Post-pancreatitis diabetes mellitus is one of the most common types of secondary diabetes. The pharmaceutical armamentarium in the field of diabetology can be broadened if the design of novel drugs is informed by pathogenetic insights from studies on post-pancreatitis diabetes mellitus.Areas covered: The article provides an overview of preclinical and clinical studies of compounds selectively antagonizing the gastric inhibitory peptide receptor, simultaneously stimulating both the glucagon-like peptide-1 and glucagon receptors, and activating ketogenesis.Expert opinion: The current pharmacotherapy for post-pancreatitis diabetes mellitus is relatively ineffective. This type of diabetes represents a unique platform for rigorous, efficient, and practical search for glucose-lowering therapeutic candidates. Various methods of gastric inhibitory peptide receptor (expressed in the pancreas) antagonism have undergone extensive preclinical testing in diabetes, with promising compounds being trialed in man. Molecular mimicry with oxyntomodulin ─ an extra-pancreatic hormone homologous with pancreatic hormone glucagon and involved in the regulation of exocrine pancreatic function ─ could be harnessed. The emerging findings of a salutary effect of ketosis mimetics in people with prediabetes set the stage for a novel approach to preventing diabetes.

Xiangbinfang granules enhance gastric antrum motility via intramuscular interstitial cells of Cajal in mice

BACKGROUND

Interdigestive migrating motor complexes (MMC) produce periodic contractions in the gastrointestinal tract, but the exact mechanism of action still remains unclear. Intramuscular interstitial cells of Cajal (ICC-IM) participate in gastrointestinal hormone and neuromodulation, but the correlation between ICC-IM and MMC is also unclear. We found that xiangbinfang granules (XBF) mediated the phase III contraction of MMC. Here, the effects of XBF on gastric antrum motility in W/W^v mice and the effects of ICC-IM on gastric antrum MMC are reported.

AIM

To observe the effects of ICC-IM on gastric antrum motility and to establish the mechanism of XBF in promoting gastric antrum motility.

METHODS

The density of c-kit-positive ICC myenteric plexus (ICC-MP) and ICC-IM in the antral muscularis of W/W^v and wild-type (WT) mice was examined by confocal microscopy. The effects of XBF on gastric antrum slow waves in W/W^v and WT mice were recorded by intracellular amplification recording. Micro-strain-gauge force transducers were implanted into the gastric antrum to monitor the MMC and the effect of XBF on gastric antrum motility in conscious W/W^v and WT mice.

RESULTS

In the gastric antrum of W/W^v mice, c-kit immunoreactivity was significantly reduced, and no ICC-IM network was observed. Spontaneous rhythmic slow waves also appeared in the antrum of W/W^v mice, but the amplitude of the antrum slow wave decreased significantly in W/W^v mice (22.62 ± 2.23 mV vs 2.92 ± 0.52 mV, P < 0.0001). MMCs were found in 7 of the 8 WT mice but no complete MMC cycle was found in W/W^v mice. The contractile frequency and amplitude index of the gastric antrum were significantly increased in conscious WT compared to W/W^v mice (frequency, 3.53 ± 0.18 cpm vs 1.28 ± 0.12 cpm; amplitude index, 23014.26 ± 1798.65 mV·20 min vs 3782.16 ± 407.13 mV·20 min; P < 0.0001). XBF depolarized smooth muscle cells of the gastric antrum in WT and W/W^v mice in a dose-dependent manner. Similarly, the gastric antrum motility in WT mice was significantly increased after treatment with XBF 5 mg (P < 0.05). Atropine (0.1 mg/kg) blocked the enhancement of XBF in WT and W/W^v mice completely, while tetrodotoxin (0.05 mg/kg) partially inhibited the enhancement by XBF.

CONCLUSION

ICC-IM participates in the regulation of gastric antrum MMC in mice. XBF induces MMC III-like contractions that enhance gastric antrum motility via ICC-IM in mice.

Effect of Artemisia rupestris L. Extract on Gastrointestinal Hormones and Brain-Gut Peptides in Functional Dyspepsia Rats

Artemisia rupestris L. is the perennial herb of rupestris belonging to Artemisia (Compositae), which is wildly distributed in Xinjiang (China), middle Asia, and Europe. It is known to have anti-inflammatory, hepatoprotective, immune function regulation, and gastrointestinal function regulation effects. AR is used to treat digestive diseases, but the effects of AR on antifunctional dyspepsia (FD) activity have not yet been reported. In this study, we aimed to investigate the therapeutic effects of Artemisia rupestris L. extract (ARE) on gastrointestinal hormones and brain-gut peptide in functional dyspepsia (FD) rats. Sixty Sprague-Dawley rats were randomly divided into 6 groups. An FD rat model was established by irregular tail clamp stimulation for 14 days except the blank group. After FD rat models, the blank group and model group were given menstruum, and the medicated rats were given corresponding medicine for 14 days. The general observations, bodyweight, and food intake were observed, and the content of serum gastrin (GAS), plasma motilin (MTL), plasma vasoactive intestinal peptide (VIP), and plasma somatostatin (SS) by the enzyme-linked immunosorbent assay was observed. The content of plasma VIP and plasma SS in the ARE group was significantly lower than in the model group, and the content of serum GAS and plasma MTL was increased in the ARE group; the GAS expression of antrum and hypothalamus was increased in the ARE group, and SS expression of antrum and hypothalamus was decreased in the ARE group by immunohistochemical detection; the results of semiquantitative reverse transcription polymerase chain reaction (RT-PCR) indicate that ARE inhibits the mRNA expression of VIP. Our results suggest that ARE can recover gastrointestinal hormone levels and regulation of the peripheral and central nervous system and alter gut peptide levels, which confirm the therapeutic effect of ARE on functional dyspepsia.

Iron metabolism and the exocrine pancreas

Although the pathophysiological mechanisms and consequences of gross derangements in iron metabolism are well known, little is known about the pathophysiological mechanisms underlying mild-to-moderate alterations in iron metabolism and their consequences. Growing evidence indicates that the exocrine pancreas has a bidirectional relationship with iron metabolism. Studies have shown alterations in circulating markers of iron metabolism, iron absorption, and intra-pancreatic iron deposition in pancreatitis. At the same time, exocrine pancreatic dysfunction has been shown in iron overload disorders. These observations reveal a compelling connection between the exocrine pancreas and iron metabolism, which are further elucidated by observations of therapeutic benefits of iron chelating agents and pancreatic enzyme replacement therapy. While the pancreas is not a major reservoir of iron in the body, better understanding of its relationship with iron metabolism may yield unexpected insights.