Ramadhan fasting for people living with chronic illness: A narrative literature review.

Muslims constitute approximately 20% of the world's population. In South Africa, Muslims constitute just under 2% of the total population. Fasting is one of the mandatory activities of adherents of the Islamic faith, where all healthy adult Muslims abstain from food, drink, and sexual activities between dawn and dusk during the month of Ramadhan. Medical doctors are frequently required to provide advice to their Muslim patients about the safety or other health impacts of this type of fasting. This narrative review provides an overview of research conducted on Muslim populations during the fasting period, with special reference to non-communicable diseases (NCDs) that are prevalent in the Muslim community. In the absence of evidence-based clinical guidelines, this article summarises the latest published research on this topic, providing a resource for clinicians and researchers. This paper provides an evidence summary to clinicians when engaging with their patients who may be engaging in Ramadhan fasting, while also identifying gaps in the body of evidence that could inform future research.

Divergent roles for the gut intraepithelial lymphocyte GLP-1R in control of metabolism, microbiota, and T cell-induced inflammation.

Gut intraepithelial lymphocytes (IELs) are thought to calibrate glucagon-like peptide 1 (GLP-1) bioavailability, thereby regulating systemic glucose and lipid metabolism. Here, we show that the gut IEL GLP-1 receptor (GLP-1R) is not required for enteroendocrine L cell GLP-1 secretion and glucose homeostasis nor for the metabolic benefits of GLP-1R agonists (GLP-1RAs). Instead, the gut IEL GLP-1R is essential for the full effects of GLP-1RAs on gut microbiota. Moreover, independent of glucose control or weight loss, the anti-inflammatory actions of GLP-1RAs require the gut IEL GLP-1R to selectively restrain local and systemic T cell-induced, but not lipopolysaccharide-induced, inflammation. Such effects are mediated by the suppression of gut IEL effector functions linked to the dampening of proximal T cell receptor signaling in a protein-kinase-A-dependent manner. These data reposition key roles of the L cell-gut IEL GLP-1R axis, revealing mechanisms linking GLP-1R activation in gut IELs to modulation of microbiota composition and control of intestinal and systemic inflammation.

Re-imagining health professions education in the coronavirus disease 2019 era: Perspectives from South Africa.

BACKGROUND: The coronavirus disease 2019 (COVID-19) pandemic hit South Africa in March 2020, severely disrupting health services and health education. This fundamentally impacted the training of future health professionals and catalysed a significant response from across the health education sector. In 2020, the South African Association of Health Educationalists requested members to submit reflections on different aspects of their COVID-19 related educational responses.Responding to the pandemic: Seven vignettes focused specifically on clinical training in the context of primary care and family medicine. This short report highlights the key insights that emerged from these vignettes, considering what has been learnt in terms of health professions education and what we need to take forward. These insights include building on what was already in place, the student role, technology in the clinical learning context, taking workshops online, vulnerability and presence and the way going forward. DISCUSSION AND CONCLUSION: The contributions emphasised the value of existing relationships between the health services and training institutions, collaboration and transparent communication between stakeholders when navigating a crisis, responsiveness to the changed platform and dynamic environment and aligning teaching with healthcare needs. It is more important than ever to set explicit goals, have clarity of purpose when designing learning opportunities and to provide support to students. Some of these learning points may be appropriate for similar contexts in Africa. How we inculcate what we have learned into the post-pandemic period will bear testimony to the extent to which this crisis has enabled us to re-imagine health professions education.

TCF7 is not essential for glucose homeostasis in mice.

OBJECTIVE: Glucose-dependent insulinotropic polypeptide (GIP) and Glucagon-like peptide-1 (GLP-1) are incretin hormones that exert overlapping yet distinct actions on islet ß-cells. We recently observed that GIP, but not GLP-1, upregulated islet expression of Transcription Factor 7 (TCF7), a gene expressed in immune cells and associated with the risk of developing type 1 diabetes. TCF7 has also been associated with glucose homeostasis control in the liver. Herein we studied the relative metabolic importance of TCF7 expression in hepatocytes vs. islet ß-cells in mice. METHODS: Tcf7 expression was selectively inactivated in adult mouse hepatocytes using adenoviral Cre expression and targeted in ß-cells using two different lines of insulin promoter-Cre mice. Glucose homeostasis, plasma insulin and triglyceride responses, islet histology, hepatic and islet gene expression, and body weight gain were evaluated in mice fed regular chow or high fat diets. Tcf7 expression within pancreatic islets and immune cells was evaluated using published single cell RNA-seq (scRNA-seq) data, and in islet RNA from immunodeficient Rag2-/-Il2rg-/- mice. RESULTS: Reduction of hepatocyte Tcf7 expression did not impair glucose homeostasis, lipid tolerance or hepatic gene expression profiles linked to control of metabolic or immune pathways. Similarly, oral and intraperitoneal glucose tolerance, plasma insulin responses, islet histology, body weight gain, and insulin tolerance were not different in mice with targeted recombination of Tcf7 in insulin-positive ß-cells. Surprisingly, islet Tcf7 mRNA transcripts were not reduced in total islet RNA containing endocrine and associated non-endocrine cell types from Tcf7ßcell-/- mice, despite Cre-mediated recombination of islet genomic DNA. Furthermore, glucose tolerance was normal in whole body Tcf7-/- mice. Analysis of scRNA-seq datasets localized pancreatic Tcf7 expression to islet progenitors during development, and immune cells, but not within differentiated islet ß-cells or endocrine lineages within mature islets. Moreover, the expression of Tcf7 was extremely low in islet RNA from Rag2-/-Il2rg-/- mice and, consistent with expression within immune cells, Tcf7 was highly correlated with levels of Cd3g mRNA transcripts in RNA from wild type mouse islets. CONCLUSIONS: These findings demonstrate that Tcf7 expression is not a critical determinant of glucose homeostasis in mice. Moreover, the detection of Tcf7 expression within islet mRNA is attributable to the expression of Tcf7 RNA in islet-associated murine immune cells, and not in islet ß-cells.

Loss of Glp2r signaling activates hepatic stellate cells and exacerbates diet-induced steatohepatitis in mice.

A glucagon-like peptide-2 (GLP-2) analog is used in individuals with intestinal failure who are at risk for liver disease, yet the hepatic actions of GLP-2 are not understood. Treatment of high-fat diet-fed (HFD-fed) mice with GLP-2 did not modify the development of hepatosteatosis or hepatic inflammation. In contrast, Glp2r-/- mice exhibited increased hepatic lipid accumulation, deterioration in glucose tolerance, and upregulation of biomarkers of hepatic inflammation. Both mouse and human liver expressed the canonical GLP-2 receptor (GLP-2R), and hepatic Glp2r expression was upregulated in mice with hepatosteatosis. Cell fractionation localized the Glp2r to hepatic stellate cells (HSCs), and markers of HSC activation and fibrosis were increased in livers of Glp2r-/- mice. Moreover, GLP-2 directly modulated gene expression in isolated HSCs ex vivo. Taken together, these findings define an essential role for the GLP-2R in hepatic adaptation to nutrient excess and unveil a gut hormone-HSC axis, linking GLP-2R signaling to control of HSC activation.

Intestine-selective reduction of Gcg expression reveals the importance of the distal gut for GLP-1 secretion.

OBJECTIVE: Glucagon-like peptide-1 is a nutrient-sensitive hormone secreted from enteroendocrine L cells within the small and large bowel. Although GLP-1 levels rise rapidly in response to food ingestion, the greatest density of L cells is localized to the distal small bowel and colon. Here, we assessed the importance of the distal gut in the acute L cell response to diverse secretagogues. METHODS: Circulating levels of glucose and plasma GLP-1 were measured in response to the administration of L cell secretagogues in wild-type mice and in mice with (1) genetic reduction of Gcg expression throughout the small bowel and large bowel (GcgGut-/-) and (2) selective reduction of Gcg expression in the distal gut (GcgDistalGut-/-). RESULTS: The acute GLP-1 response to olive oil or arginine administration was markedly diminished in GcgGut-/- but preserved in GcgDistalGut-/- mice. In contrast, the increase in plasma GLP-1 levels following the administration of the GPR119 agonist AR231453, or the melanocortin-4 receptor (MC4R) agonist LY2112688, was markedly diminished in the GcgDistalGut-/- mice. The GLP-1 response to LPS was also markedly attenuated in the GcgGut-/- mice and remained submaximal in the GcgDistalGut-/- mice. Doses of metformin sufficient to lower glucose and increase GLP-1 levels in the GcgGut+/+ mice retained their glucoregulatory activity, yet they failed to increase GLP-1 levels in the GcgGut-/- mice. Surprisingly, the actions of metformin to increase plasma GLP-1 levels were substantially attenuated in the GcgDistalGut-/- mice. CONCLUSION: These findings further establish the importance of the proximal gut for the acute response to nutrient-related GLP-1 secretagogues. In contrast, we identify essential contributions of the distal gut to (i) the rapid induction of circulating GLP-1 levels in response to pharmacological selective agonism of G-protein-coupled receptors, (ii) the increased GLP-1 levels following the activation of Toll-Like Receptors with LPS, and iii) the acute GLP-1 response to metformin. Collectively, these results reveal that distal gut Gcg + endocrine cells are rapid responders to structurally and functionally diverse GLP-1 secretagogues.

The gut hormone receptor GIPR links energy availability to the control of hematopoiesis.

OBJECTIVE: Glucose-dependent insulinotropic polypeptide (GIP) conveys information from ingested nutrients to peripheral tissues, signaling energy availability. The GIP Receptor (GIPR) is also expressed in the bone marrow, notably in cells of the myeloid lineage. However, the importance of gain and loss of GIPR signaling for diverse hematopoietic responses remains unclear. METHODS: We assessed the expression of the Gipr in bone marrow (BM) lineages and examined functional roles for the GIPR in control of hematopoiesis. Bone marrow responses were studied in (i) mice fed regular or energy-rich diets, (ii) mice treated with hematopoietic stressors including acute 5-fluorouracil (5-FU), pamsaccharide (LPS), and Pam3CysSerLys4 (Pam3CSK4), with or without pharmacological administration of a GIPR agonist, and (iii) mice with global (Gipr-/-) or selective deletion of the GIPR (GiprTie2-/-) with and without bone marrow transplantation (BMT). RESULTS: Gipr is expressed within T cells, myeloid cells, and myeloid precursors; however, these cell populations were not different in peripheral blood, spleen, or BM of Gipr-/- and GiprTie2-/- mice. Nevertheless, gain and loss of function studies revealed that GIPR signaling controls the expression of BM Toll-like receptor (TLR) and Notch-related genes regulating hematopoiesis. Loss of the BM GIPR attenuates the extent of adipose tissue inflammation and dysregulates the hematopoietic response to BMT. GIPR agonism modified BM gene expression profiles following 5-FU and Pam3CSK4 whereas loss of the Gipr altered the hematopoietic responses to energy excess, two TLR ligands, and 5-FU. However, the magnitude of the cellular changes in hematopoiesis in response to gain or loss of GIPR signaling was relatively modest. CONCLUSION: These studies identify a functional gut hormone-BM axis positioned for the transduction of signals linking nutrient availability to the control of TLR and Notch genes regulating hematopoiesis. Nevertheless, stimulation or loss of GIPR signaling has minimal impact on basal hematopoiesis or the physiological response to hematopoietic stress.

Localization of Glucagon-Like Peptide-2 Receptor Expression in the Mouse.

Glucagon-like peptide-2 (GLP-2), secreted from enteroendocrine cells, attenuates gut motility, enhances barrier function, and augments nutrient absorption, actions mediated by a single GLP-2 receptor (GLP-2R). Despite extensive analyses, the precise distribution and cellular localization of GLP-2R expression remains controversial, confounded by the lack of suitable GLP-2R antisera. Here, we reassessed murine Glp2r expression using regular and real-time quantitative PCR (qPCR), in situ hybridization (ISH), and a Glp2rLacZ reporter mouse. Glp2r mRNA expression was detected from the stomach to the rectum and most abundant in the jejunum. Glp2r transcripts were also detected in cerebral cortex, mesenteric lymph nodes, gallbladder, urinary bladder, and mesenteric fat. Surprisingly, Glp2r mRNA was found in testis by qPCR at levels similar to jejunum. However, the testis Glp2r transcripts, detected by different primer pairs and qPCR, lacked 5' mRNA coding sequences, and only a minute proportion of them corresponded to full-length Glp2r mRNA. Within the gut, Glp2r-driven LacZ expression was localized to enteric neurons and lamina propria stromal cells, findings confirmed by ISH analysis of the endogenous Glp2r mRNA. Unexpectedly, vascular Glp2rLacZ expression was localized to mesenteric veins and not arteries. Moreover, mesenteric fat Glp2rLacZ expression was detected within blood vessels and not adipocytes. Reporter LacZ expression was not detected in all tissues expressing an endogenous Glp2r transcript, such as gallbladder, urinary bladder, and mesenteric lymph nodes. Collectively, these findings extend our understanding of the cellular domains of Glp2r expression and highlight limitations inherent in application of commonly used technologies to infer analysis of gene expression.

Circulating Levels of Soluble Dipeptidyl Peptidase-4 Are Dissociated from Inflammation and Induced by Enzymatic DPP4 Inhibition.

Dipeptidyl peptidase-4 (DPP-4) controls glucose homeostasis through enzymatic termination of incretin action. We report that plasma DPP-4 activity correlates with body weight and fat mass, but not glucose control, in mice. Genetic disruption of adipocyte Dpp4 expression reduced plasma DPP-4 activity in older mice but did not perturb incretin levels or glucose homeostasis. Knockdown of hepatocyte Dpp4 completely abrogated the obesity-associated increase in plasma DPP-4 activity, reduced liver cytokine expression, and partially attenuated inflammation in adipose tissue without changes in incretin levels or glucose homeostasis. In contrast, circulating levels of soluble DPP4 (sDPP4) were dissociated from inflammation in mice with endothelial-selective or global genetic inactivation of Dpp4. Remarkably, inhibition of DPP-4 enzymatic activity upregulated circulating levels of sDPP4 originating from endothelial or hematopoietic cells without inducing systemic or localized inflammation. Collectively, these findings reveal unexpected complexity in regulation of soluble versus enzymatic DPP-4 and control of inflammation and glucose homeostasis.

GLP-2 receptor signaling controls circulating bile acid levels but not glucose homeostasis in Gcgr-/- mice and is dispensable for the metabolic benefits ensuing after vertical sleeve gastrectomy.

OBJECTIVE: Therapeutic interventions that improve glucose homeostasis such as attenuation of glucagon receptor (Gcgr) signaling and bariatric surgery share common metabolic features conserved in mice and humans. These include increased circulating levels of bile acids (BA) and the proglucagon-derived peptides (PGDPs), GLP-1 and GLP-2. Whether BA acting through TGR5 (Gpbar1) increases PGDP levels in these scenarios has not been examined. Furthermore, although the importance of GLP-1 action has been interrogated in Gcgr-/- mice and after bariatric surgery, whether GLP-2 contributes to the metabolic benefits of these interventions is not known. METHODS: To assess whether BA acting through Gpbar1 mediates improved glucose homeostasis in Gcgr-/- mice we generated and characterized Gcgr-/-:Gpbar1-/- mice. The contribution of GLP-2 receptor (GLP-2R) signaling to intestinal and metabolic adaptation arising following loss of the Gcgr was studied in Gcgr-/-:Glp2r-/- mice. The role of the GLP-2R in the metabolic improvements evident after bariatric surgery was studied in high fat-fed Glp2r-/- mice subjected to vertical sleeve gastrectomy (VSG). RESULTS: Circulating levels of BA were markedly elevated yet similar in Gcgr-/-:Gpbar1+/+ vs. Gcgr-/-:Gpbar1-/- mice. Loss of GLP-2R lowered levels of BA in Gcgr-/- mice. Gcgr-/-:Glp2r-/- mice also exhibited shifts in the proportion of circulating BA species. Loss of Gpbar1 did not impact body weight, intestinal mass, or glucose homeostasis in Gcgr-/- mice. In contrast, small bowel growth was attenuated in Gcgr-/-:Glp2r-/- mice. The improvement in glucose tolerance, elevated circulating levels of GLP-1, and glucose-stimulated insulin levels were not different in Gcgr-/-:Glp2r+/+ vs. Gcgr-/-:Glp2r-/- mice. Similarly, loss of the GLP-2R did not attenuate the extent of weight loss and improvement in glucose control after VSG. CONCLUSIONS: These findings reveal that GLP-2R controls BA levels and relative proportions of BA species in Gcgr-/- mice. Nevertheless, the GLP-2R is not essential for i) control of body weight or glucose homeostasis in Gcgr-/- mice or ii) metabolic improvements arising after VSG in high fat-fed mice. Furthermore, despite elevations of circulating levels of BA, Gpbar1 does not mediate elevated levels of PGDPs or major metabolic phenotypes in Gcgr-/- mice. Collectively these findings refine our understanding of the relationship between Gpbar1, elevated levels of BA, PGDPs, and the GLP-2R in amelioration of metabolic derangements arising following loss of Gcgr signaling or after vertical sleeve gastrectomy.

Enteroendocrine-derived glucagon-like peptide-2 controls intestinal amino acid transport.

OBJECTIVE: Glucagon-like peptide-2 (GLP-2) is co-secreted with GLP-1 from gut endocrine cells, and both peptides act as growth factors to expand the surface area of the mucosal epithelium. Notably, GLP-2 also enhances glucose and lipid transport in enterocytes; however, its actions on control of amino acid (AA) transport remain unclear. Here we examined the mechanisms linking gain and loss of GLP-2 receptor (GLP-2R) signaling to control of intestinal amino acid absorption in mice. METHODS: Absorption, transport, and clearance of essential AAs, specifically lysine, were measured in vivo by Liquid Chromatography triple quadrupole Mass Spectrometry (LC-MS/MS) and ex vivo with Ussing chambers using intestinal preparations from Glp2r+/+ and Glp2r-/- mice. Immunoblotting determined jejunal levels of protein components of signaling pathways (PI3K-AKT, and mTORC1-pS6-p4E-BP1) following administration of GLP-2, protein gavage, and rapamycin to fasted Glp2r+/+ and Glp2r-/- mice. Expression of AA transporters from full thickness jejunum and 4F2hc from brush border membrane vesicles (BBMVs) was measured by real-time PCR and immunoblotting, respectively. RESULTS: Acute administration of GLP-2 increased basal AA absorption in vivo and augmented basal lysine transport ex vivo. GLP-2-stimulated lysine transport was attenuated by co-incubation with wortmannin, rapamycin, or tetrodotoxin ex vivo. Phosphorylation of mTORC1 effector proteins S6 and 4E-BP1 was significantly increased in wild-type mice in response to GLP-2 alone, or when co-administered with protein gavage, and abolished following oral gavage of rapamycin. In contrast, activation of GLP-1R signaling did not enhance S6 phosphorylation. Disruption of GLP-2 action in Glp2r-/- mice reduced lysine transport ex vivo and attenuated the phosphorylation of S6 and 4E-BP1 in response to oral protein. Moreover, the expression of cationic AA transporter slc7a9 in response to refeeding, and the abundance of 4F2hc in BBMVs following protein gavage, was significantly attenuated in Glp2r-/- mice. CONCLUSIONS: These findings reveal an important role for GLP-2R signaling in the physiological and pharmacological control of enteral amino acid sensing and assimilation, defining an enteroendocrine cell-enterocyte axis for optimal energy absorption.

Glucagon-like peptide-2 promotes gallbladder refilling via a TGR5-independent, GLP-2R-dependent pathway.

OBJECTIVE: Glucagon-like peptides (GLPs) are secreted from enteroendocrine cells in response to nutrients and bile acids and control metabolism via actions on structurally-related yet distinct G protein coupled receptors. GLP-1 regulates gut motility, appetite, islet function, and glucose homeostasis, whereas GLP-2 enhances intestinal nutrient absorption. GLP-1R agonists are used to treat diabetes and obesity, and a GLP-2R agonist is approved to treat short bowel syndrome. Unexpectedly, reports of gallbladder disease have been associated with the use of both GLP-1R and GLP-2R agonists and after bariatric surgery, although the mechanisms remain unknown. METHODS: We investigated whether GLP-1 or GLP-2 acutely controls gallbladder (GB) volume and whether GLP-2 regulates GB muscle activity in mice. The expression of Tgr5, Glp2r, and Glp1r was assessed in mouse GB, and the effects of GLP-2 on hepatic bile acid (BA) flow, intestinal and liver BA uptake, and GB gene expression were determined. GLP-2 regulation of GB volume was assessed in wildtype, Glp2r-/- and Tgr5-/- mice. The effect of GLP-2 on GB smooth muscle (GBSM) calcium transients was characterized ex vivo. RESULTS: Acute administration of the GLP-1R agonist exendin-4 lowered glucose but had no effect on GB volume in mice. In contrast, GLP-2 rapidly enhanced GB filling in a dose-dependent manner, actions maintained in the presence of cholecystokinin, and mediated through the canonical GLP-2R. GLP-2 also rapidly induced immediate early gene expression in GB, consistent with detection of the endogenous Glp2r in GB RNA. The ability of GLP-2 to increase GB volume was not abrogated by systemic administration of hexamethonium, propranolol, a vasoactive peptide receptor antagonist or N-Nitroarginine methyl ester, and was maintained in Tgr5-/- mice. In contrast, lithocholic acid, a Tgr5 agonist, increased GB filling in Glp2r-/- but not in Tgr5-/- mice. GLP-2 had no effect on ileal uptake or hepatic clearance of taurocholic acid or on hepatic bile flow, yet reduced the frequency of spontaneous calcium transients in murine GBSM ex vivo, in a tetrodotoxin-sensitive manner. CONCLUSIONS: Our data extend endocrine concepts of regulation of GB filling beyond FXR-FGF15/19 and the direct effects of BA via Tgr5, to encompass a novel BA-Tgr5-L cell GLP-2 axis providing nutrient-mediated feedback from BA to terminate meal-related GB contraction. These findings have implications for conditions characterized by elevated circulating levels of GLP-2 such as after bariatric surgery and the development and use of agents that promote Tgr5 activation, L cell secretion, or GLP-2R agonism for the treatment of metabolic disease.

Cellular Sites and Mechanisms Linking Reduction of Dipeptidyl Peptidase-4 Activity to Control of Incretin Hormone Action and Glucose Homeostasis.

Pharmacological inhibition of the dipeptidyl peptidase-4 (DPP4) enzyme potentiates incretin action and is widely used to treat type 2 diabetes. Nevertheless, the precise cells and tissues critical for incretin degradation and glucose homeostasis remain unknown. Here, we use mouse genetics and pharmacologic DPP4 inhibition to identify DPP4+ cell types essential for incretin action. Although enterocyte DPP4 accounted for substantial intestinal DPP4 activity, ablation of enterocyte DPP4 in Dpp4Gut-/- mice did not produce alterations in plasma DPP4 activity, incretin hormone levels, and glucose tolerance. In contrast, endothelial cell (EC)-derived DPP4 contributed substantially to levels of soluble plasma DPP4 activity, incretin degradation, and glucose control. Surprisingly, DPP4+ cells of bone marrow origin mediated the selective degradation of fasting GIP, but not GLP-1. Collectively, these findings identify distinct roles for DPP4 in the EC versus the bone marrow compartment for selective incretin degradation and DPP4i-mediated glucoregulation.