Requirement for the intestinal epithelial insulin-like growth factor-1 receptor in the intestinal responses to glucagon-like peptide-2 and dietary fat.

The intestinal hormone, glucagon-like peptide-2 (GLP-2), enhances the enterocyte chylomicron production. However, GLP-2 is known to require the intestinal-epithelial insulin-like growth factor-1 receptor (IE-IGF-1R) for its other actions to increase intestinal growth and barrier function. The role of the IE-IGF-1R in enterocyte lipid handling was thus tested in the GLP-2 signaling pathway, as well as in response to a Western diet (WD). IE-IGF-1R knockout (KO) and control mice were treated for 11 days with h(GLY2 )GLP-2 or fed a WD for 18 weeks followed by a duodenal fat tolerance test with C14 -labeled triolein. Human Caco-2BBE cells were treated with an IGF-1R antagonist or signaling inhibitors to determine triglyceride-associated protein expression. The IE-IGF-1R was required for GLP-2-induced increases in CD36 and FATP-4 in chow-fed mice, and for expression in vitro; FATP-4 also required PI3K/Akt. Although WD-fed IE-IGF-1R KO mice demonstrated normal CD36 expression, the protein was incorrectly localized 2h post-duodenal fat administration. IE-IGF-1R KO also prevented the WD-induced increase in MTP and decrease in APOC3, increased jejunal mucosal C14 -fat accumulation, and elevated plasma triglyceride and C14 -fat levels. Collectively, these studies elucidate new roles for the IE-IGF-1R in enterocyte lipid handling, under basal conditions and in response to GLP-2 and WD-feeding.

Dietary Cyanidin-3-Glucoside Attenuates High-Fat-Diet-Induced Body-Weight Gain and Impairment of Glucose Tolerance in Mice via Effects on the Hepatic Hormone FGF21.

BACKGROUND: Dietary polyphenols including anthocyanins target multiple organs. OBJECTIVE: We aimed to assess the involvement of glucagon-like peptide 1 (GLP-1), leptin, insulin and fibroblast growth factor 21 (FGF21) in mediating metabolic beneficial effects of purified anthocyanin cyanidin-3-glucoside (Cy3G). METHODS: Intestinal proglucagon gene (Gcg; encoding GLP-1) and liver Fgf21 expression were assessed in 6-wk-old male C57BL-6J mice fed a low-fat-diet (LFD; 10% of energy from fat), alone or with 1.6 mg Cy3G/L in drinking water for 3 wk [experiment (Exp.) 1; n = 5/group]. Similar mice were fed the LFD or a high-fat diet (HFD; 60% energy from fat) with or without Cy3G for 20 wk. Half of the mice administered Cy3G also received 4 broad-spectrum antibiotics (ABs) in drinking water between weeks 11 and 14, for a total of 6 groups (n = 8/group). Metabolic tolerance tests were conducted between weeks 2 and 16. Relevant hormone gene expression and plasma hormone concentrations were assessed mainly at the end of 20 wk (Exp. 2). RESULTS: In Exp. 1, Cy3G administration increased ileal but not colonic Gcg level by 2-fold (P < 0.05). In Exp. 2, Cy3G attenuated HFD-induced body-weight gain (20.3% at week 16), and improved glucose tolerance (26.5% at week 15) but not insulin tolerance. Although Cy3G had no effect on glucose tolerance in LFD mice, LFD/Cy3G/AB mice showed better glucose tolerance than LFD/Cy3G mice (23%). In contrast, HFD/Cy3G/AB mice showed worse glucose tolerance compared with HFD/Cy3G mice (15%). Beneficial effects of Cy3G in HFD mice were not associated with changes in plasma leptin, insulin or GLP-1 concentrations. However, Cy3G increased hepatic Fgf21 expression in mice in Exp. 1 by 4-fold and attenuated Fgf21 overexpression in HFD mice (Exp. 2, 22%), associated with increased expression of genes that encode FGFR1 and ß-klotho (>3-fold, P < 0.05). CONCLUSIONS: Dietary Cy3G may reduce body weight and exert metabolic homeostatic effects in mice via changes in hepatic FGF21.

In the Short-term, Milk Fat Globule Epidermal Growth Factor-8 Causes Site-specific Intestinal Growth in Resected Piglets.

OBJECTIVES: Short bowel syndrome (SBS) remains the leading cause of neonatal intestinal failure. Milk fat globule epidermal growth factor-8 (MFG-E8), present in human milk, has homology with epidermal growth factor (EGF), known to enhance adaptation in SBS. In this pilot study, the role of oral MFG-E8 treatment in SBS was explored in neonatal piglets. METHODS: Neonatal piglets underwent 75% intestinal resection, either distal (jejunal-colonic [JC] anastomosis) or mid-intestinal (jejunal-ileal [JI] anastomosis). Piglets were randomized to intragastric treatment with MFG-E8  (5 mg/kg per day) or saline and were maintained on parenteral nutrition and enteral nutrition for 7 days. Adaptation was assessed by intestinal length and weight, histopathology, fecal fat analysis and RT-qPCR analysis of mucosal transcripts, including growth factors. RESULTS: JI piglets demonstrated intestinal lengthening (P < 0.001), 2-fold greater in ileum than jejunum (P = 0.02), where lengthening was increased by MFG-E8 treatment (P = 0.02). JC piglets did not exhibit jejunal lengthening, regardless of treatment. Fat absorption was greater for JI piglets (P = 0.02), unaffected by treatment. In JI piglets, expression of Egf was increased in the ileum (P < 0.01) and MFG-E8 treatment increased Egfr (receptor) expression (P = 0.02). CONCLUSIONS: MF-EG8 demonstrated site-specific trophic effects, only with JI anatomy. This may limit the utility of this treatment for SBS, except for rare patients with retained ileum. The mechanisms of these site-specific effects, however, and the role of MFG-E8 in neonatal gut growth and in diseases, such as necrotizing enterocolitis that commonly target ileum, warrant further exploration.

Insulin-like growth factor-binding protein-4 inhibits epithelial growth and proliferation in the rodent intestine.

Insulin-like growth factor-binding protein-4 (IGFBP-4) is a binding protein that modulates the action of insulin-like growth factor-1 (IGF-1), a growth factor whose presence is required for the intestinotrophic effects of glucagon-like peptide-2 (GLP-2). GLP-2 is a gut hormone that uses both IGF-1 and epidermal growth factor (EGF) as intermediary factors to promote intestinal growth. Therefore, to elucidate the mechanism through which IGFBP-4 regulates IGF-1 activity in the intestine, proliferation assays were conducted using rat intestinal epithelial cells (IEC-6). IGF-1 and EGF synergistically enhanced proliferation, an effect that was dose-dependently decreased by IGFBP-4 ( P < 0.05-0.001) in an IGF-1 receptor (R)- and MEK1/2- but not a phosphatidylinositol 3-kinase-dependent manner ( P > 0.05 for IGFBP-4 effects with IGF-1R and MEK1/2 inhibitors). Intestinal organoids derived from IGFBP-4 knockout mice demonstrated significantly greater Ki-67 expression and an enhanced surface area increase in response to IGF-1 treatment, compared with organoids from control mice ( P < 0.05-0.01). GLP-2 is also known to increase the mucosal expression of IGFBP-4 mRNA. To investigate whether this occurs through the actions of its intermediaries, IGF-1 and EGF, inducible intestinal epithelial-IGF-1R knockout and control mice were treated for 10 days with and without the pan-ErbB inhibitor, CI-1033. However, no differences in mucosal IGFBP-4 mRNA expression were found for any of the treatment groups ( P > 0.05). Consistently, IEC-6 cells treated with IGF-1 and/or EGF displayed no alteration in IGFBP-4 mRNA or in cellular and secreted IGFBP-4 protein ( P > 0.05). Overall, this study establishes that endogenous IGFBP-4 plays an important role in inhibiting IGF-1-induced intestinal epithelial proliferation and that mucosal IGFBP-4 expression is independent of IGF-1 and EGF. NEW & NOTEWORTHY This study demonstrates, for the first time, the inhibitory role of locally expressed insulin-like growth factor-binding protein-4 (IGFBP-4) on the intestinal proliferative actions of IGF-1 and supports the notion of the synergistic roles of IGF-1 and EGF in promoting intestinal epithelial growth. In turn, intestinal IGFBP-4 expression was not found to be regulated by IGF-1 and/or EGF.

Synergy of glucagon-like peptide-2 and epidermal growth factor coadministration on intestinal adaptation in neonatal piglets with short bowel syndrome.

Glucagon-like peptide-2 (GLP-2) and epidermal growth factor (EGF) treatment enhance intestinal adaptation. To determine whether these growth factors exert synergistic effects on intestinal growth and function, GLP-2 and EGF-containing media (EGF-cm) were administered, alone and in combination, in neonatal piglet models of short bowel syndrome (SBS). Neonatal Landrace-Large White piglets were block randomized to 75% midintestinal [jejunoileal (JI) group] or distal intestinal [jejunocolic (JC) group] resection or sham control, with 7-day infusion of saline (control), intravenous human GLP-2 (11 nmol·kg-1·day-1) alone, enteral EGF-cm (80 µg·kg-1·day-1) alone, or GLP-2 and EGF-cm in combination. Adaptation was assessed by intestinal length, histopathology, Üssing chamber analysis, and real-time quantitative PCR of intestinal growth factors. Combined EGF-cm and GLP-2 treatment increased intestinal length in all three surgical models (P < 0.01). EGF-cm alone selectively increased bowel weight per length and jejunal villus height in the JI group only. The JC group demonstrated increased intestinal weight and villus height (P < 0.01) when given either GLP-2 alone or in combination with EGF-cm, with no effect of EGF-cm alone. Jejunal permeability of mannitol and polyethylene glycol decreased with combination therapy in both SBS groups (P < 0.05). No difference was observed in fat absorption or body weight gain. IGF-1 mRNA was differentially expressed in JI vs. JC piglets with treatment. Combined treatment with GLP-2 and EGF-cm induced intestinal lengthening and decreased permeability, in addition to the trophic effects of GLP-2 alone. Our findings demonstrate the benefits of novel combination GLP-2 and EGF treatment for neonatal SBS, especially in the JC model representing most human infants with SBS.NEW & NOTEWORTHY Glucagon-like peptide-2 (GLP-2) and epidermal growth factor (EGF) are intestinotrophic, with demonstrated benefit in both animal models and human studies of short bowel syndrome (SBS). The current research shows that over and above known trophic effects, the combination of GLP-2 and EGF synergistically lengthens the bowel in neonatal piglet models of SBS. Most notable benefit occurred with resection of the terminal ileum, the common clinical anatomy seen in neonatal SBS and associated with least de novo lengthening postsurgery.

Short-term sleep deprivation with nocturnal light exposure alters time-dependent glucagon-like peptide-1 and insulin secretion in male volunteers.

The intestinal L cell is the principal source of glucagon-like peptide-1 (GLP-1), a major determinant of insulin release. Because GLP-1 secretion is regulated in a circadian manner in rodents, we investigated whether the activity of the human L cell is also time sensitive. Rhythmic fluctuations in the mRNA levels of canonical clock genes were found in the human NCI-H716 L cell model, which also showed a time-dependent pattern in their response to well-established secretagogues. A diurnal variation in GLP-1 responses to identical meals (850 kcal), served 12 h apart in the normal dark (2300) and light (1100) periods, was also observed in male volunteers maintained under standard sleep and light conditions. These findings suggest the existence of a daily pattern of activity in the human L cell. Moreover, we separately tested the short-term effects of sleep deprivation and nocturnal light exposure on basal and postprandial GLP-1, insulin, and glucose levels in the same volunteers. Sleep deprivation with nocturnal light exposure disrupted the melatonin and cortisol profiles and increased insulin resistance. Moreover, it also induced profound derangements in GLP-1 and insulin responses such that postprandial GLP-1 and insulin levels were markedly elevated and the normal variation in GLP-1 responses was abrogated. These alterations were not observed in sleep-deprived participants maintained under dark conditions, indicating a direct effect of light on the mechanisms that regulate glucose homeostasis. Accordingly, the metabolic abnormalities known to occur in shift workers may be related to the effects of irregular light-dark cycles on these glucoregulatory pathways.

Role of vesicle-associated membrane protein 2 in exocytosis of glucagon-like peptide-1 from the murine intestinal L cell.

AIMS/HYPOTHESIS: Glucagon-like peptide-1 (GLP-1), secreted by the enteroendocrine L cell, is an incretin hormone that potently stimulates insulin secretion. Although signalling pathways promoting GLP-1 release are well characterised, the mechanisms by which GLP-1-containing granules fuse to the L cell membrane are unknown. As soluble NSF attachment proteins (SNAREs) are known to mediate granule-membrane fusion, the role of vesicle-associated membrane proteins (VAMPs) in GLP-1 exocytosis was examined. METHODS: SNARE expression was determined in murine GLUTag L cells by RT-PCR and immunoblot and in primary murine L cells by immunofluorescence. Co-immunoprecipitation was used to examine SNARE interactions, while tetanus toxin (TetX)-mediated cleavage of VAMP was used with a GLP-1 secretion assay and total internal reflection fluorescence microscopy to determine the role of VAMP2 in exocytosis. RESULTS: VAMP2 was expressed in murine L cells and localised to secretory granules in GLUTag cells. VAMP1/3 and the core membrane proteins syntaxin1a and synaptosomal-associated protein 25 kDa (SNAP25) were also detected. TetX cleaved VAMPs in GLUTag cells. However, only VAMP2 interacted with syntaxin1a, as did SNAP25 and Munc18-1. TetX treatment of GLUTag cells prevented glucose-dependent insulinotrophic peptide- and oleic-acid-stimulated GLP-1 secretion (p < 0.05-0.01), as well as K(+)-stimulated single-cell exocytosis (p < 0.05-0.001), while TetX-resistant VAMP2 expression rescued GLP-1 secretion (p < 0.01-0.001). CONCLUSIONS/INTERPRETATION: Together, these findings indicate an essential role for VAMP2 in GLP-1 exocytosis from the GLUTag L cell in response to a variety of established secretagogues. An improved understanding of the mechanisms governing the release of GLP-1 may lead to new therapeutic approaches to enhance the levels of this incretin hormone in patients with type 2 diabetes.

Exogenous glucagon-like peptide-2 improves outcomes of intestinal adaptation in a distal-intestinal resection neonatal piglet model of short bowel syndrome.

BACKGROUND: Endogenous glucagon-like peptide-2 (GLP-2) levels and intestinal adaptation are reduced in distal-intestinal resection animal models of short bowel syndrome (SBS) that lack remnant ileum. We hypothesized that exogenous GLP-2 would improve intestinal adaptation in a distal-intestinal resection neonatal piglet model of SBS. METHODS: In all, 35 piglets were randomized to 2 treatment and 3 surgical groups: control (sham), 75% mid-intestinal resection (JI), and 75% distal-intestinal resection (JC). Parenteral nutrition (PN) commenced on day 1 and was weaned as enteral nutrition (EN) advanced. IV GLP-2 (11 nmol/kg/d) or saline was initiated on day 2. Piglets were maintained for 14 d. Clinical, functional, morphological, and histological outcomes were obtained. RESULTS: JC-GLP-2 piglets had fewer days on PN (10.0 ± 0.6 vs. 13.8 ± 0.2), more days on EN (4.0 ± 0.6 vs. 0.2 ± 0.2), a higher percentage of EN at termination (92 ± 5 vs. 52 ± 10%), fewer days of diarrhea (8.0 ± 0.7 vs. 12.3 ± 0.4), increased intestinal length (19 ± 4 vs. -5 ± 3%), and deeper jejunal crypts (248 ± 21 vs. 172 ± 12 µm), compared with saline piglets. CONCLUSION: GLP-2 therapy improves clinical, morphological, and histological outcomes of intestinal adaptation in a distal-intestinal resection model of SBS. Since this anatomical subtype represents the majority of clinical cases of neonatal SBS, these results support a potential role for GLP-2 therapy in pediatric SBS.

Effects of prolonged exendin-4 administration on hypothalamic-pituitary-adrenal axis activity and water balance.

Exendin-4 (Ex-4) is a natural agonist of the glucagon-like peptide-1 (GLP-1) receptor, currently being used as a treatment for type 2 diabetes mellitus due to its insulinotropic properties. Previous studies have revealed that acute administration of both GLP-1 and, in particular, Ex-4 potently stimulates hypothalamic-pituitary-adrenal (HPA) axis activity. In this work, the effects of prolonged Ex-4 exposure on HPA function were explored. To this end, Sprague-Dawley rats were subjected to a daily regimen of two Ex-4 injections (5 µg/kg sc) for a minimum of 7 days. We found that subchronic Ex-4 administration produced a number of effects that resemble chronic stress situations, including hyperactivation of the HPA axis during the trough hours, disruption of glucocorticoid circadian secretion, hypertrophy of the adrenal gland, decreased adrenal gland sensitivity, impaired pituitary-adrenal stress responses, and reductions in both food intake and body weight. In addition, a threefold increase in diuresis was observed followed by a 1.5-fold increase in water intake; these latter effects were abolished by adrenalectomy. Together, these findings indicate that Ex-4 induces a profound dysregulation of HPA axis activity that may also affect renal function.

From diarrhea to obesity in prohormone convertase 1/3 deficiency: age-dependent clinical, pathologic, and enteroendocrine characteristics.

GOALS: The aim of this report is to delineate the clinical, pathologic, and enteroendocrine (EE) features of prohormone convertase 1/3 (PC1/3) deficiency in children. BACKGROUND: Prohormone convertases play a pivotal role in the activation of biologically inactive hormones. Congenital defects in the EE axis, such as PC1/3 deficiency, have been rarely reported and their pathophysiological mechanisms are largely unknown. STUDY: EE function and pathology was evaluated in 4 males (1, 2, 7, and 10 y old) from 2 families with PC1/3 deficiency at a university children's hospital. Clinical course, pathology analysis including immunohistochemistry for PC1/3, PC2, and glucagon-like peptide 1 (GLP-1) and electron microscopy, as well as EE function tests (GLP-1, GLP-2, oral glucose tolerance test) were performed. RESULTS: All (n=4) suffered from congenital severe diarrhea associated with malabsorption. The diarrhea improved during the first year of life and hyperphagia with excessive weight gain (BMI>97th percentile) became the predominant phenotype at an older age. Analysis of the enteroendocrine axis revealed high proinsulin levels (57 to 1116 pmol/L) in all patients, low serum GLP-2 levels, and impaired insulin and GLP-1 secretion after an oral glucose tolerance test at a young age, with improvement in 1 older child tested. Electron microscopy showed normal ultrastructure of enterocytes and EE cells. Immunohistochemistry revealed normal expression of chromogranin A, a marker of EE cells but markedly reduced immunostaining for PC1/3 and PC2 in all patients. CONCLUSIONS: PC1/3 deficiency is associated with an age dependent, variable clinical phenotype caused by severe abnormalities in intestinal and EE functions. Serum level of proinsulin can be used as an effective screening tool.

Glucagon-like peptide-2 increases dysplasia in rodent models of colon cancer.

The intestinal hormone, glucagon-like peptide-2 (GLP-2), enhances intestinal growth and reduces inflammation in rodent models. Hence, a degradation-resistant GLP-2 analog is under investigation for treatment of Crohn's disease. However, GLP-2 increases colonic dysplasia in murine azoxymethane (AOM)-induced colon cancer. Considering the increased colon cancer risk associated with chronic colitis, we have therefore examined the effects of long-acting hGly(2)GLP-2, as well as of endogenous GLP-2 using the antagonist hGLP-2(3-33) in two novel models of inflammation-associated colon cancer: rats fed the carcinogen 2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and a high-fat diet (HFD) for one or three cycles, and mice with chronic dextran sodium-sulfate (DSS)-induced colitis administered AOM. hGly(2)GLP-2 treatment of one-cycle PhIP/HFD rats increased the number of colonic aberrant crypt foci by 72 ± 11% (P < 0.01). Fifty-one weeks after three PhIP/HFD cycles, hGly(2)GLP-2-treated rats had a 22% incidence of colon cancer, compared with 0% in vehicle-treated rats. AOM-DSS mice treated with vehicle or hGly(2)GLP-2 had high-grade dysplasia/colon cancer incidences of 56 and 64%, respectively, compared with 46% in hGLP-2(3-33)-treated AOM-DSS animals (P < 0.05). Unexpectedly, hGLP-2(3-33) also reduced the colitis damage score by 32.0 ± 8.4% (P < 0.05). All high-grade dysplastic/cancerous tumors had nuclear localization of ß-catenin although ß-catenin mRNA transcript and protein levels did not differ between treatment groups. GLP-2 receptor mRNA expression also was not different. However, hGLP-2(3-33)-treated mice had markedly reduced numbers of doublecortin-and-calmodulin-kinase-like-1-positive stem cells, by 73.7 ± 8.6% (P < 0.05). In conclusion, the results of this study indicate a role for hGly(2)GLP-2 and endogenous GLP-2 as potential cancer promoters in rodents.

Loss of glucagon-like peptide-2-induced proliferation following intestinal epithelial insulin-like growth factor-1-receptor deletion.

BACKGROUND & AIMS: Glucagon-like peptide-2 (GLP-2) is an intestinal hormone that promotes growth of the gastrointestinal tract. Although insulin-like growth factor (IGF)-1 and the IGF-1 receptor (IGF-1R) are required for GLP-2-induced proliferation of crypt cells, little is known about localization of the IGF-1R which mediates the intestinotropic actions of GLP-2. METHODS: We examined intestinal growth and proliferative responses in mice with conditional deletion of IGF-1R from intestinal epithelial cells (IE-igf1rKO) after acute administration (30-90 min) of GLP-2, in response to 24-hour fasting and re-feeding (to induce GLP-2-dependent adaptation), and after chronic exposure (10 days) to GLP-2. RESULTS: IE-igf1rKO mice had normal small intestinal weight, morphometric parameters, proliferative indices, and distribution of differentiated epithelial cell lineages. Acute administration of GLP-2 increased nuclear translocation of ß-catenin in non-Paneth crypt cells and stimulated the crypt-cell proliferative marker c-Myc in control but not IE-igf1rKO mice. Small intestinal weight, crypt depth, villus height, and crypt-cell proliferation were decreased in control and IE-igf1rKO mice after 24-hour fasting. Although re-feeding control mice restored all of these parameters, re-fed IE-igf1rKO mice had reductions in adaptive regrowth of the villi and crypt-cell proliferation. Control mice that were given chronic GLP-2 had increases in small intestinal weight, mucosal cross-sectional area, crypt depth, villus height, and crypt-cell proliferation. However, the GLP-2-induced increase in crypt-cell proliferation was not observed in IE-igf1rKO mice, and growth of the crypt-villus axis was reduced. CONCLUSIONS: The proliferative responses of the intestinal epithelium to exogenous GLP-2 administration and conditions of GLP-2-dependent adaptive re-growth require the intestinal epithelial IGF-1R.

The Molecular Determinants of Glucagon-like Peptide Secretion by the Intestinal L cell.

The intestinal L cell secretes a diversity of biologically active hormones, most notably the glucagon-like peptides, GLP-1 and GLP-2. The highly successful introduction of GLP-1-based drugs into the clinic for the treatment of patients with type 2 diabetes and obesity, and of a GLP-2 analog for patients with short bowel syndrome, has led to the suggestion that stimulation of the endogenous secretion of these peptides may serve as a novel therapeutic approach in these conditions. Situated in the intestinal epithelium, the L cell demonstrates complex relationships with not only circulating, paracrine, and neural regulators, but also ingested nutrients and other factors in the lumen, most notably the microbiota. The integrated input from these numerous secretagogues results in a variety of temporal patterns in L cell secretion, ranging from minutes to 24 hours. This review combines the findings of traditional, physiological studies with those using newer molecular approaches to describe what is known and what remains to be elucidated after 5 decades of research on the intestinal L cell and its secreted peptides, GLP-1 and GLP-2.

Metabolic Homeostasis: It's All in the Timing.

Cross-talk between peripheral tissues is essential to ensure the coordination of nutrient intake with disposition during the feeding period, thereby preventing metabolic disease. This mini-review considers the interactions between the key peripheral tissues that constitute the metabolic clock, each of which is considered in a separate mini-review in this collation of articles published in Endocrinology in 2020 and 2021, by Martchenko et al (Circadian rhythms and the gastrointestinal tract: relationship to metabolism and gut hormones); Alvarez et al (The microbiome as a circadian coordinator of metabolism); Seshadri and Doucette (Circadian regulation of the pancreatic beta cell); McCommis et al (The importance of keeping time in the liver); Oosterman et al (The circadian clock, shift work, and tissue-specific insulin resistance); and Heyde et al (Contributions of white and brown adipose tissues to the circadian regulation of energy metabolism). The use of positive- and negative-feedback signals, both hormonal and metabolic, between these tissues ensures that peripheral metabolic pathways are synchronized with the timing of food intake, thus optimizing nutrient disposition and preventing metabolic disease. Collectively, these articles highlight the critical role played by the circadian clock in maintaining metabolic homeostasis.

Complementary and antagonistic effects of combined glucagon-like peptide-2 and glucagon-like peptide-1 receptor agonist administration on parameters relevant to short bowel syndrome.

BACKGROUND: Short bowel syndrome (SBS) is characterized by malabsorption requiring parenteral nutrition. The intestinotrophic glucagon-like peptide (GLP)-2 receptor agonist, h[Gly2]GLP2, is used to treat patients with SBS. Evidence suggests that GLP-1 receptor agonists such as exendin-4 (Ex4) may be beneficial in SBS given their ability to increase intestinal growth and delay gastric emptying (GE). METHODS: Intestinal growth, body weight (BW), food intake (FI), GE, gastrointestinal (GI) transit, intestinal permeability, and glucose tolerance were investigated in male and female C57/BL6 mice following vehicle, h[Gly2]GLP2, or Ex4 treatment, alone or in combination at "low," "medium," and "high" doses (0.1, 0.5, 1.0 and 0.01, 0.05, 0.1 µg/g, respectively). RESULTS: Only the h[Gly2]GLP2 low/Ex4 high-dose combination additively increased small intestinal (SI) weight compared with vehicle and both monoagonists (P < 0.01-0.001), via increased villus height (P < 0.01) and SI length (P < 0.05). This combination had no effects on BW; FI; and fat, liver, spleen, heart, and kidney weights but reduced GI transit (P < 0.001) versus low-dose h[Gly2]GLP2 monotreatment and abrogated the inhibitory effects of high-dose Ex4 on GE (P < 0.01) and of low-dose h[Gly2]GLP2 on intestinal permeability (P < 0.05). Ex4-induced improvements in glucose homeostasis were maintained upon combination with h[Gly2]GLP2 (P < 0.001). CONCLUSIONS: These findings suggest that combining specific doses of GLP-2- and GLP-1 receptor agonists additively improves SI growth and GI transit without detrimental effects on BW, FI, GE, and glucose homeostasis, and may be useful for the treatment of patients with SBS.

The intestine and the microbiota in maternal glucose homeostasis during pregnancy.

It is now well established that, beyond its role in nutrient processing and absorption, the intestine and its accompanying gut microbiome constitute a major site of immunological and endocrine regulation that mediates whole-body metabolism. Despite the growing field of host-microbe research, few studies explore what mechanisms govern this relationship in the context of pregnancy. During pregnancy, significant maternal metabolic adaptations are made to accommodate the additional energy demands of the developing fetus and to prevent adverse pregnancy outcomes. Recent data suggest that the maternal gut microbiota may play a role in these adaptations, but changes to maternal gut physiology and the underlying intestinal mechanisms remain unclear. In this review, we discuss selective aspects of intestinal physiology including the role of the incretin hormone, glucagon-like peptide 1 (GLP-1), and the role of the maternal gut microbiome in the maternal metabolic adaptations to pregnancy. Specifically, we discuss how bacterial components and metabolites could mediate the effects of the microbiota on host physiology, including nutrient absorption and GLP-1 secretion and action, and whether these mechanisms may change maternal insulin sensitivity and secretion during pregnancy. Finally, we discuss how these pathways could be altered in disease states during pregnancy including maternal obesity and diabetes.

Nobiletin ameliorates high fat-induced disruptions in rhythmic glucagon-like peptide-1 secretion.

The incretin hormone glucagon-like peptide-1 (GLP-1) is secreted by the intestinal L cell in response to nutrient intake. However, GLP-1 secretion also follows a circadian rhythm which is disrupted by the saturated fatty acid palmitate in vitro and high-fat diet (HFD) feeding in vivo. The flavonoid nobiletin is a clock enhancer which improves metabolic homeostasis. Therefore, the aim of this study was to elucidate whether and how nobiletin mitigates the negative effects of palmitate and HFD-feeding on rhythmic GLP-1 release. Pre-treatment of murine GLUTag L cells with palmitate dampened the GLP-1 secretory response at the normal peak of secretion, while nobiletin co-treatment restored GLP-1 secretion and upregulated the 'metabolic pathway' transcriptome. Mice fed a HFD also lost their GLP-1 secretory rhythm in association with markedly increased GLP-1 levels and upregulation of L cell transcriptional pathways related to 'sensing' and 'transducing' cellular stimuli at the normal peak of GLP-1 release. Nobiletin co-administration reduced GLP-1 levels to more physiological levels and upregulated L cell 'oxidative metabolism' transcriptional pathways. Furthermore, nobiletin improved colonic microbial 16S rRNA gene diversity and reduced the levels of Proteobacteria in HFD-fed mice. Collectively, this study establishes that nobiletin improves the normal rhythm in GLP-1 secretion following fat-induced disruption.

Disrupted and Elevated Circadian Secretion of Glucagon-Like Peptide-1 in a Murine Model of Type 2 Diabetes.

Metabolism and circadian rhythms are intimately linked, with circadian glucagon-like peptide-1 (GLP-1) secretion by the intestinal L-cell entraining rhythmic insulin release. GLP-1 secretion has been explored in the context of obesogenic diets, but never in a rodent model of type 2 diabetes (T2D). There is also considerable disagreement regarding GLP-1 levels in human T2D. Furthermore, recent evidence has demonstrated decreased expression of the ß-cell exocytotic protein secretagogin (SCGN) in T2D. To extend these findings to the L-cell, we administered oral glucose tolerance tests at 6 time points in 4-hour intervals to the high-fat diet/streptozotocin (HFD-STZ) mouse model of T2D. This revealed a 10-fold increase in peak GLP-1 secretion with a phase shift of the peak from the normal feeding period into the fasting-phase. This was accompanied by impairments in the rhythms of glucose, glucagon, mucosal clock genes (Arntl and Cry2), and Scgn. Immunostaining revealed that L-cell GLP-1 intensity was increased in the HFD-STZ model, as was the proportion of L-cells that expressed SCGN; however, this was not found in L-cells from humans with T2D, which exhibited decreased GLP-1 staining but maintained their SCGN expression. Gcg expression in isolated L-cells was increased along with pathways relating to GLP-1 secretion and electron transport chain activity in the HFD-STZ condition. Further investigation into the mechanisms responsible for this increase in GLP-1 secretion may give insights into therapies directed toward upregulating endogenous GLP-1 secretion.