The structure and function of the glucagon-like peptide-1 receptor and its ligands

New Phenol Esters for Efficient pH-Controlled Amine Acylation of Peptides, Proteins, and Sepharose Beads in Aqueous Media

This paper describes the discovery, synthesis, and use of novel water-soluble acylation reagents for efficient and selective modification, cross-linking, and labeling of proteins and peptides, as well as for their use in the effective modification of sepharose beads under pH control in aqueous media. The reagents are based on a 2,4-dichloro-6-sulfonic acid phenol ester core combined with a variety of linker structures. The combination of these motifs leads to an ideal balance between hydrolytic stability and reactivity. At high pH, good to excellent conversions (up to 95%) and regioselectivity (up to 99:1 Nε/Nα amine ratio) in the acylation were realized, exemplified by the chemical modification of incretin peptides and insulin. At neutral pH, an unusually high preference toward the N-terminal phenylalanine in an insulin derivative was observed (>99:1 Nα/Nε), which is up until now unprecedented in the literature for more elaborate reagents. In addition, the unusually high hydrolytic stability of these reagents and their ability to efficiently react at low concentrations (28 μM or 0.1 mg/mL) are exemplified with a hydroxy linker-based reagent and are a unique feature of this work.

Dynamics of GLP-1R peptide agonist engagement are correlated with kinetics of G protein activation

The glucagon-like peptide-1 receptor (GLP-1R) has broad physiological roles and is a validated target for treatment of metabolic disorders. Despite recent advances in GLP-1R structure elucidation, detailed mechanistic understanding of how different peptides generate profound differences in G protein-mediated signalling is still lacking. Here we combine cryo-electron microscopy, molecular dynamics simulations, receptor mutagenesis and pharmacological assays, to interrogate the mechanism and consequences of GLP-1R binding to four peptide agonists; glucagon-like peptide-1, oxyntomodulin, exendin-4 and exendin-P5. These data reveal that distinctions in peptide N-terminal interactions and dynamics with the GLP-1R transmembrane domain are reciprocally associated with differences in the allosteric coupling to G proteins. In particular, transient interactions with residues at the base of the binding cavity correlate with enhanced kinetics for G protein activation, providing a rationale for differences in G protein-mediated signalling efficacy from distinct agonists.

The glucagon-like peptide-1 receptor (GLP-1R) can be targeted in the treatment of diabetes, obesity and other metabolic disorders. Here, the authors assess the molecular mechanisms of peptide agonists binding to GLP-1R and the responses elucidated by these ligands, including distinct kinetics of G protein activation.

An update on extra-oral bitter taste receptors

Bitter taste-sensing type 2 receptors (TAS2Rs or T2Rs), belonging to the subgroup of family A G-protein coupled receptors (GPCRs), are of crucial importance in the perception of bitterness. Although in the first instance, TAS2Rs were considered to be exclusively distributed in the apical microvilli of taste bud cells, numerous studies have detected these sensory receptor proteins in several extra-oral tissues, such as in pancreatic or ovarian tissues, as well as in their corresponding malignancies. Critical points of extra-oral TAS2Rs biology, such as their structure, roles, signaling transduction pathways, extensive mutational polymorphism, and molecular evolution, have been currently broadly studied. The TAS2R cascade, for instance, has been recently considered to be a pivotal modulator of a number of (patho)physiological processes, including adipogenesis or carcinogenesis. The latest advances in taste receptor biology further raise the possibility of utilizing TAS2Rs as a therapeutic target or as an informative index to predict treatment responses in various disorders. Thus, the focus of this review is to provide an update on the expression and molecular basis of TAS2Rs functions in distinct extra-oral tissues in health and disease. We shall also discuss the therapeutic potential of novel TAS2Rs targets, which are appealing due to their ligand selectivity, expression pattern, or pharmacological profiles.

Preproglucagon Products and Their Respective Roles Regulating Insulin Secretion

Historically, intracellular function and metabolic adaptation within the α-cell has been understudied, with most of the attention being placed on the insulin-producing β-cells due to their role in the pathophysiology of type 2 diabetes mellitus. However, there is a growing interest in understanding the function of other endocrine cell types within the islet and their paracrine role in regulating insulin secretion. For example, there is greater appreciation for α-cell products and their contributions to overall glucose homeostasis. Several recent studies have addressed a paracrine role for α-cell-derived glucagon-like peptide-1 (GLP-1) in regulating glucose homeostasis and responses to metabolic stress. Further, other studies have demonstrated the ability of glucagon to impact insulin secretion by acting through the GLP-1 receptor. These studies challenge the central dogma surrounding α-cell biology describing glucagon's primary role in glucose counterregulation to one where glucagon is critical in regulating both hyper- and hypoglycemic responses. Herein, this review will update the current understanding of the role of glucagon and α-cell-derived GLP-1, placing emphasis on their roles in regulating glucose homeostasis, insulin secretion, and β-cell mass.

Renoprotective Effects of Incretin-Based Therapy in Diabetes Mellitus

Glucagon-like peptide-1 (GLP-1) receptor agonists are recently discovered antidiabetic drugs with potent hypoglycemic effects. Among different mechanisms of activity, these compounds were shown to reduce blood glucose by suppression of glucagon secretion and stimulation of glucose-dependent insulin secretion. These antidiabetic agents have a minor risk of hypoglycemia and have been suggested as a second-line therapy to be added to metformin treatment to further optimize glycemic control in diabetes. More recently, scientific evidence suggests that GLP-1 receptor agonists may particularly afford protection from diabetic nephropathy through modulation of the molecular pathways involved in renal impairment and so improve renal function. This additional benefit adds further weight for these compounds to become promising drugs not only for glycemic control but also to prevent diabetic complications. In this review, we have updated evidence on the beneficial effects of GLP-1 receptor agonists on diabetic nephropathy and detailed the underlying pathophysiological mechanisms.

Small peptide-based GLP-1R ligands: an approach to reduce the kidney uptake of radiolabeled GLP-1R-targeting agents?

Aim

Elevated kidney uptake in insulinoma patients remains a major limitation of radiometallated exendin-derived ligands of the glucagon-like peptide 1 receptor (GLP-1R). Based on the previously published potent GLP-1R-activating undecapeptide 1, short-chained GLP-1R ligands were developed to investigate whether kidney uptake can be reduced by means of direct ¹⁸F-labeling (nuclide-based accelerated renal excretion) or the reduction of the overall ligand charge (ligand-based reduced kidney uptake).

Materials & methods

GLP-1R ligands were prepared according to optimized standard protocols via solid-phase peptide synthesis (SPPS) or, when not practicable, via fragment coupling in solution. Synthesis of (2‘-Et, 4‘-OMe)4, 4’-L-biphenylalanine ((2′-Et, 4′-OMe)BIP), required for the preparation of 1, was accomplished by Suzuki-Miyaura cross-coupling. In vitro experiments were performed using stably transfected GLP-1R⁺ HEK293-hGLP-1R cells.

Results

In contrast to the three reference ligands glucagon-like peptide 1 (GLP-1, IC₅₀ = 23.2 ± 12.2 nM), [Nle¹⁴, Tyr(3-I)⁴⁰]exendin-4 (IC₅₀ = 7.63 ± 2.78 nM) and [Nle¹⁴, Tyr⁴⁰]exendin-4 (IC₅₀ = 9.87 ± 1.82 nM), the investigated GLP-1R-targeting small peptides (9–15 amino acids), including lead peptide 1, exhibited only medium to low affinities (IC₅₀ > 189 nM). Only SiFA-tagged undecapeptide 5 (IC₅₀ = 189 ± 35 nM) revealed a higher affinity than 1 (IC₅₀ = 669 ± 242 nM).

Conclusion

The investigated small peptides, including lead peptide 1, could not compete with favorable in vitro characteristics of glucagon-like peptide 1 (GLP-1), [Nle¹⁴, Tyr(3-I)⁴⁰]exendin-4 and [Nle¹⁴, Tyr⁴⁰]exendin-4. The auspicious EC₅₀ values of 1 provided by the literature could not be transferred to competitive binding experiments. Therefore, the use of 1 as a basic scaffold for the design of further GLP-1R-targeting radioligands cannot be recommended. Further investigations might include the scaffold of 5, although substantial optimizations concerning affinity and lipophilicity would be required. In sum, GLP-1R-targeting radioligands with reduced kidney uptake could not be obtained in this work, which emphasizes the need for further ligands addressing this particular issue.

Supplementary Information

The online version contains supplementary material available at 10.1186/s41181-021-00136-x.

Targeted pH switched europium complexes monitoring receptor internalisation in living cells

We report the design and evaluation of pH responsive luminescent europium(iii) probes that allow conjugation to targeting vectors to monitor receptor internalisation in cells. The approach adopted here can be used to tag proteins selectively and to monitor uptake into more acidic organelles, thereby enhancing the performance of time-resolved internalisation assays that require pH monitoring in real time.

Therapeutic Potential of a Novel Glucagon-like Peptide-1 Receptor Agonist, NLY01, in Experimental Autoimmune Encephalomyelitis

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS), characterized by demyelination, gliosis, and neurodegeneration. While the currently available disease-modifying therapies effectively suppress the immune attack on the CNS, there are no therapies to date that directly mitigate neurodegeneration. Glucagon-like peptide-1 (GLP-1) is a small peptide hormone that maintains glucose homeostasis. A novel GLP-1 receptor (GLP-1R) agonist, NLY01, was recently shown to have neuroprotective effects in the animal models of Parkinson's disease and is now in a phase 2 clinical trial. In this study, we investigated the therapeutic potential of NLY01 in a mouse model of MS, experimental autoimmune encephalomyelitis (EAE). Our data show that NLY01 delays the onset and attenuates the severity of EAE in a prevention paradigm, when given before disease onset. NLY01 inhibits the activation of immune cells in the spleen and reduces their trafficking into the CNS. In addition, we show that NLY01 suppresses the production of chemokines that are involved in leukocyte recruitment to the site of inflammation. The anti-inflammatory effect of NLY01 at the early stage of EAE may block the expression of the genes associated with neurotoxic astrocytes in the optic nerves, thereby preventing retinal ganglion cell (RGC) loss in the progressive stage of EAE. In the therapeutic paradigm, NLY01 significantly decreases the clinical score and second attack in a model of relapsing-remitting EAE. GLP-1R agonists may have dual efficacy in MS by suppressing peripheral and CNS inflammation, thereby limiting neuronal loss.

Therapeutic Peptides Targeting PPI in Clinical Development: Overview, Mechanism of Action and Perspectives

Targeting protein-protein interactions (PPIs) has been recently recognized as an emerging therapeutic approach for several diseases. Up today, more than half a million PPI dysregulations have been found to be involved in pathological events. The dynamic nature of these processes and the involvement of large protein surfaces discouraged anyway the scientific community in considering them promising therapeutic targets. More recently peptide drugs received renewed attention since drug discovery has offered a broad range of structural diverse sequences, moving from traditionally endogenous peptides to sequences possessing improved pharmaceutical profiles. About 70 peptides are currently on the marked but several others are in clinical development. In this review we want to report the update on these novel APIs, focusing our attention on the molecules in clinical development, representing the direct consequence of the drug discovery process of the last 10 years. The comprehensive collection will be classified in function of the structural characteristics (native, analogous, heterologous) and on the basis of the therapeutic targets. The mechanism of interference on PPI will also be reported to offer useful information for novel peptide design.

The glucagon-like peptide 1 receptor agonist Exendin-4 induces tenogenesis in human mesenchymal stem cells

Tendon injuries are common and account for up to 50% of musculoskeletal injuries in the United States. The poor healing nature of the tendon is attributed to poor vascularization and cellular composition. In the absence of FDA-approved growth factors for tendon repair, engineering strategies using bioactive factors, donor cells, and delivery matrices to promote tendon repair and regeneration are being explored. Growth factor alternatives in the form of small molecules, donor cells, and progenitors offer several advantages and enhance the tendon healing response. Small drug molecules and peptides offer stability over growth factors that are known to suffer from relatively short biological half-lives. The primary focus of this study was to assess the ability of the exendin-4 (Ex-4) peptide, a glucagon-like peptide 1 (GLP-1) receptor agonist, to induce tenocyte differentiation in bone marrow-derived human mesenchymal stem cells (hMSCs). We treated hMSCs with varied doses of Ex-4 in culture media to evaluate proliferation and tendonogenic differentiation. A 20 nM Ex-4 concentration was optimal for promoting cell proliferation and tendonogenic differentiation. Tendonogenic differentiation of hMSCs was evaluated via gene expression profile, immunofluorescence, and biochemical analyses. Collectively, the levels of tendon-related transcription factors (Mkx and Scx) and extracellular matrix (Col-I, Dcn, Bgn, and Tnc) genes and proteins were elevated compared to media without Ex-4 and other controls including insulin and IGF-1 treatments. The tendonogenic factor Ex-4 in conjunction with hMSCs appear to enhance tendon regeneration.

Ligand-Receptor Interactions and Machine Learning in GCGR and GLP-1R Drug Discovery

The large amount of data that has been collected so far for G protein-coupled receptors requires machine learning (ML) approaches to fully exploit its potential. Our previous ML model based on gradient boosting used for prediction of drug affinity and selectivity for a receptor subtype was compared with explicit information on ligand-receptor interactions from induced-fit docking. Both methods have proved their usefulness in drug response predictions. Yet, their successful combination still requires allosteric/orthosteric assignment of ligands from datasets. Our ligand datasets included activities of two members of the secretin receptor family: GCGR and GLP-1R. Simultaneous activation of two or three receptors of this family by dual or triple agonists is not a typical kind of information included in compound databases. A precise allosteric/orthosteric ligand assignment requires a continuous update based on new structural and biological data. This data incompleteness remains the main obstacle for current ML methods applied to class B GPCR drug discovery. Even so, for these two class B receptors, our ligand-based ML model demonstrated high accuracy (5-fold cross-validation Q² > 0.63 and Q² > 0.67 for GLP-1R and GCGR, respectively). In addition, we performed a ligand annotation using recent cryogenic-electron microscopy (cryo-EM) and X-ray crystallographic data on small-molecule complexes of GCGR and GLP-1R. As a result, we assigned GLP-1R and GCGR actives deposited in ChEMBL to four small-molecule binding sites occupied by positive and negative allosteric modulators and a full agonist. Annotated compounds were added to our recently released repository of GPCR data.

GLP-1 peptide analogs for targeting pancreatic beta cells

Loss or dysfunction of the pancreatic beta cells or insulin receptors leads to diabetes mellitus (DM). This usually occurs over many years; therefore, the development of methods for the timely detection and clinical intervention are vital to prevent the development of this disease. Glucagon-like peptide-1 receptor (GLP-1R) is the receptor of GLP-1, an incretin hormone that causes insulin secretion in a glucose-dependent manner. GLP-1R is highly expressed on the surface of pancreatic beta cells, providing a potential target for bioimaging. In this review, we provide an overview of various strategies, such as the development of GLP-1R agonists (e.g., exendin-4), and GLP-1 sequence modifications for GLP-1R targeting for the diagnosis and treatment of pancreatic beta cell disorders. We also discuss the challenges of targeting pancreatic beta cells and strategies to address such challenges.

Glucagon-like peptide-1 (GLP-1) receptor agonists and their cardiovascular benefits-The role of the GLP-1 receptor

Cardiovascular outcome trials revealed cardiovascular benefits for type 2 diabetes mellitus patients when treated with long‐acting glucagon‐like peptide‐1 (GLP‐1) receptor agonists. In the last decade, major advances were made characterising the physiological effects of GLP‐1 and its action on numerous targets including brain, liver, kidney, heart and blood vessels. However, the effects of GLP‐1 and receptor agonists, and the GLP‐1 receptor on the cardiovascular system have not been fully elucidated. We compare results from cardiovascular outcome trials of GLP‐1 receptor agonists and review pleiotropic clinical and preclinical data concerning cardiovascular protection beyond glycaemic control. We address current knowledge on GLP‐1 and receptor agonist actions on the heart, vasculature, inflammatory cells and platelets, and discuss evidence for GLP‐1 receptor‐dependent versus independent effects secondary of GLP‐1 metabolites. We conclude that the favourable cardiovascular profile of GLP‐1 receptor agonists might expand their therapeutic use for treating cardiovascular disease even in non‐diabetic populations.

Insulin injections inhibits PTZ-induced mitochondrial dysfunction, oxidative stress and neurological deficits via the SIRT1/PGC-1α/SIRT3 pathway

With an associated 20% death risk, epilepsy mainly involves seizures of an unpredictable and recurrent nature. This study was designed to evaluate the neuroprotective effects and underlying mechanisms of insulin on mitochondrial disruption, oxidative stress, cell apoptosis and neurological deficits after epilepsy seizures. Mice were exposed to repetitive injections of pentylenetetrazol at a dose of 37 mg per kg. The influence of insulin was assessed by many biochemical assays, histopathological studies and neurobehavioral experiments. The administration of insulin was proven to increase the latency of seizures while also decreasing their intensity. It also caused a reversal of mitochondrial dysfunction and ameliorated oxidative stress. Additionally, insulin pretreatment upregulated Bcl-2, downregulated Bax, and then played a neuroprotective role against hippocampal neuron apoptosis. Furthermore, when insulin was administered, SIRT1/PGC-1α/SIRT3 signals were activated, possibly due to the fact that insulin's neuroprotective and anti-mitochondrial damage characteristics added to its observed antiepileptic functions. Finally, insulin treatment is thus extremely valuable for effecting improvements in neurological functions, as has been estimated in a series of functional tests. In conclude, the results of this study consequently demonstrate insulin to have significant potential for future application in epilepsy management.

Glucagon Like Peptide 1 Receptor Agonists for Targeted Delivery of Antisense Oligonucleotides to Pancreatic Beta Cell

The extra hepatic delivery of antisense oligonucleotides (ASOs) remains a challenge and hampers the widespread application of this powerful class of therapeutic agents. In that regard, pancreatic beta cells are a particularly attractive but challenging cell type because of their pivotal role in diabetes and the fact that they are refractory to uptake of unconjugated ASOs. To circumvent this, we have expanded our understanding of the structure activity relationship of ASOs conjugated to Glucagon Like Peptide 1 Receptor (GLP1R) agonist peptide ligands. We demonstrate the key role of the linker chemistry and its optimization to design maleimide based conjugates with improved in vivo efficacy. In addition, truncation studies and scoping of a diverse set of GLP1R agonists proved fruitful to identify additional targeting ligands efficacious in vivo including native hGLP1(7-36)NH2. Variation of the carrier peptide also shed some light on the dramatic impact of subtle sequence differences on the corresponding ASO conjugate performance in vivo, an area which clearly warrant further investigations. We have confirmed the remarkable potential of GLP1R agonist conjugation for the delivery of ASOs to pancreatic beta cell by effectively knocking down islet amyloid polypeptide (IAPP) mRNA, a potential proapoptotic target, in mice.

Effect of C-terminus Conjugation via Different Conjugation Chemistries on In Vivo Activity of Albumin-Conjugated Recombinant GLP-1

Glucagon-like peptide-1 (GLP-1) is a peptide hormone with tremendous therapeutic potential for treating type 2 diabetes mellitus. However, the short half-life of its native form is a significant drawback. We previously prolonged the plasma half-life of GLP-1 via site-specific conjugation of human serum albumin (HSA) at position 16 of recombinant GLP-1 using site-specific incorporation of p-azido-phenylalanine (AzF) and strain-promoted azide-alkyne cycloaddition (SPAAC). However, the resulting conjugate GLP1_8G16AzF-HSA showed only moderate in vivo glucose-lowering activity, probably due to perturbed interactions with GLP-1 receptor (GLP-1R) caused by the albumin-linker. To identify albumin-conjugated GLP-1 variants with enhanced in vivo glucose-lowering activity, we investigated the conjugation of HSA to a C-terminal region of GLP-1 to reduce steric hindrance by the albumin-linker using two different conjugation chemistries. GLP-1 variants GLP1_8G37AzF-HSA and GLP1_8G37C-HSA were prepared using SPAAC and Michael addition, respectively. GLP1_8G37C-HSA exhibited a higher glucose-lowering activity in vivo than GLP1_8G16AzF-HSA, while GLP1_8G37AzF-HSA did not. Another GLP-1 variant, GLP1_8A37C-HSA, had a glycine to alanine mutation at position 8 and albumin at its C-terminus and exhibited in vivo glucose-lowering activity comparable to that of GLP1_8G37C-HSA, despite a moderately shorter plasma half-life. These results showed that site-specific HSA conjugation to the C-terminus of GLP-1 via Michael addition could be used to generate GLP-1 variants with enhanced glucose-lowering activity and prolonged plasma half-life in vivo.

Stromal cell-derived factor-1/Exendin-4 cotherapy facilitates the proliferation, migration and osteogenic differentiation of human periodontal ligament stem cells in vitro and promotes periodontal bone regeneration in vivo

Objectives

Stromal cell‐derived factor‐1 (SDF‐1) actively directs endogenous cell homing. Exendin‐4 (EX‐4) promotes stem cell osteogenic differentiation. Studies revealed that EX‐4 strengthened SDF‐1‐mediated stem cell migration. However, the effects of SDF‐1 and EX‐4 on periodontal ligament stem cells (PDLSCs) and bone regeneration have not been investigated. In this study, we aimed to evaluate the effects of SDF‐1/EX‐4 cotherapy on PDLSCs in vitro and periodontal bone regeneration in vivo.

Methods

Cell‐counting kit‐8 (CCK8), transwell assay, qRT‐PCR and western blot were used to determine the effects and mechanism of SDF‐1/EX‐4 cotherapy on PDLSCs in vitro. A rat periodontal bone defect model was developed to evaluate the effects of topical application of SDF‐1 and systemic injection of EX‐4 on endogenous cell recruitment, osteoclastogenesis and bone regeneration in vivo.

Results

SDF‐1/EX‐4 cotherapy had additive effects on PDLSC proliferation, migration, alkaline phosphatase (ALP) activity, mineral deposition and osteogenesis‐related gene expression compared to SDF‐1 or EX‐4 in vitro. Pretreatment with ERK inhibitor U0126 blocked SDF‐1/EX‐4 cotherapy induced ERK signal activation and PDLSC proliferation. SDF‐1/EX‐4 cotherapy significantly promoted new bone formation, recruited more CXCR4⁺ cells and CD90⁺/CD34^‐ stromal cells to the defects, enhanced early‐stage osteoclastogenesis and osteogenesis‐related markers expression in regenerated bone compared to control, SDF‐1 or EX‐4 in vivo.

Conclusions

SDF‐1/EX‐4 cotherapy synergistically regulated PDLSC activities, promoted periodontal bone formation, thereby providing a new strategy for periodontal bone regeneration.

Growth Promotion and Increased ATP-Binding Cassette Transporters Expression by Liraglutide in Triple Negative Breast Cancer Cell Line MDA-MB-231

BACKGROUND

Glucagon-like petide-1 (GLP-1) agonists such as liraglutide are widely employed in type 2 diabetes due to their glucose reducing properties and small risk of hypoglycemia. Recently, it has been shown that GLP-1agonists can inhibit breast cancer cells growth. Nonetheless, concerns are remained about liraglutide tumor promoting effects as stated by population studies.

MATERIAL AND METHODS

We evaluated the effects liraglutide on proliferation of MDA-MB-231 cells by MTT assay and then ATP-binding cassette (ABC) transporters expressions assessed by Real time PCR. Statistical comparisons were made using one-way analysis of variance followed by a post hoc Dunnett test.

RESULTS

Here, we report that liraglutide can stimulate the growth of highly invasive triple negative cell line MDA-MB-231; which can be attributed to AMPK-dependent epithelial-mesenchymal transition (EMT) happening in MDA-MB-231 context. Toxicity effects were only observed with concentrations far above the serum liraglutide concentration. ATP-binding cassette (ABC) transporters expressions were upregulated, indicating the possible drug resistance and increased EMT.

CONCLUSION

In conclusion, these results suggest that liraglutide should be used with caution in patients who are suffering or have the personal history of triple negative breast cancer. However, more detailed studies are required to deepen understanding of liraglutide consequences in triple negative breast cancer. ▶Graphical Abstract.

Total synthesis and absolute structure of N55, a positive modulator of GLP-1 signaling

Glucagon-like peptide-1 (GLP-1) signaling is an established therapeutic target for type 2 diabetes mellitus (T2DM). We developed a 7-step synthesis of N55, a positive modulator of GLP-1 signaling isolated from fenugreek (Trigonella foenum-graecum) seeds, with 29% overall yield, and we determined the absolute structure of N55 to be N-((3R,4R,5S)-4,5-dimethyl-2-oxotetrahydrofur-3-yl)linoleic amide.

Cardiovascular effectiveness of human-based vs. exendin-based glucagon like peptide-1 receptor agonists: a retrospective study in patients with type 2 diabetes

AIMS

Glucagon like peptide-1 (GLP-1) receptor agonists (GLP-1RA) are effective to control type 2 diabetes (T2Ds) and can protect from adverse cardiovascular outcomes. GLP-1RA are based on the human GLP-1 or the exendin-4 sequence. We compared cardiovascular outcomes of patients with T2D who received human-based or exendin-based GLP-1RA in routine clinical practice.

METHODS AND RESULTS

We performed a retrospective study on the administrative database of T2D patients from the Veneto Region (North-East Italy). We identified patients who initiated a human-based or exendin-based GLP-1RA from 2011 to 2018. The primary outcome was occurrence of major adverse cardiovascular events (MACE). Secondary outcomes were individual MACE components, revascularization, hospitalization for heart failure, or for cardiovascular causes. From 330 193 patients with diabetes, 6620 were new users of GLP-1RA. After propensity score matching, we analysed 1098 patients in each group, who were on average 61 years old, 59.5% males, 13% with established cardiovascular disease, had an estimated diabetes duration of 8.4 years, and a baseline HbA1c of 7.9%. During a median follow-up of 18 months, patients treated with human-based GLP-1RA as compared to those treated with exendin-based GLP-1RA, showed lower rates of MACE [hazard ratio 0.61; 95% confidence interval (CI) 0.39-0.95], myocardial infarction (0.51; 95% CI 0.28-0.94), and hospitalization for cardiovascular causes (0.66; 95% CI 0.47-0.92).

CONCLUSION

We observed better cardiovascular outcomes among patients treated with human-based vs. exendin-based GLP-1RA under routine care. In the absence of comparative trials and in view of the limitations of retrospective studies, this finding provides a moderate level of evidence to guide clinical decision.

Glucagon and Glucagon-like Peptide-1 Receptors: Promising Therapeutic Targets for an Effective Management of Diabetes Mellitus

G-protein-coupled receptors (GPCRs) are membrane-bound proteins, which are responsible for the detection of extracellular stimuli and the origination of intracellular responses. Both glucagon and glucagon-like peptide-1 (GLP-1) receptors belong to G protein-coupled receptor (GPCR) superfamily. Along with insulin, glucagon and GLP-1 are critical hormones for maintaining normal serum glucose within the human body. Glucagon generally plays its role in the liver through cyclic adenosine monophosphate (cAMP), where it compensates for the action of insulin. GLP-1 is secreted by the L-cells of the small intestine to stimulate insulin secretion and inhibit glucagon action. Despite extensive research efforts and the multiple approaches adopted, the glycemic control in the case of type-2 diabetes mellitus remains a major challenge. Therefore, a deep understanding of the structure-function relationship of these receptors will have great implications for future therapies in order to maintain a normal glucose level for an extended period of time. The antagonists of glucagon receptors that can effectively block the hepatic glucose production, as a result of glucagon action, are highly desirable for the tuning of the hyperglycemic state in type 2 diabetes mellitus. In the same manner, GLP-1R agonists act as important treatment modalities, thanks to their multiple anti-diabetic actions to attain normal glucose levels. In this review article, the structural diversity of glucagon and GLP-1 receptors along with their signaling pathways, site-directed mutations and significance in drug discovery against type-2 diabetes are illustrated. Moreover, the promising non-peptide antagonists of glucagon receptor and agonists of GLP-1 receptor, for the management of diabetes are presented with elaboration on the structure-activity relationship (SAR).

Mechanisms of adhesion G protein-coupled receptor activation

Adhesion G protein-coupled receptors (AGPCRs) are a thirty-three-member subfamily of Class B GPCRs that control a wide array of physiological processes and are implicated in disease. AGPCRs uniquely contain large, self-proteolyzing extracellular regions that range from hundreds to thousands of residues in length. AGPCR autoproteolysis occurs within the extracellular GPCR autoproteolysis-inducing (GAIN) domain that is proximal to the N terminus of the G protein-coupling seven-transmembrane-spanning bundle. GAIN domain-mediated self-cleavage is constitutive and produces two-fragment holoreceptors that remain bound at the cell surface. It has been of recent interest to understand how AGPCRs are activated in relation to their two-fragment topologies. Dissociation of the AGPCR fragments stimulates G protein signaling through the action of the tethered-peptide agonist stalk that is occluded within the GAIN domain in the holoreceptor form. AGPCRs can also signal independently of fragment dissociation, and a few receptors possess GAIN domains incapable of self-proteolysis. This has resulted in complex theories as to how these receptors are activated in vivo, complicating pharmacological advances. Currently, there is no existing structure of an activated AGPCR to support any of the theories. Further confounding AGPCR research is that many of the receptors remain orphans and lack identified activating ligands. In this review, we provide a detailed layout of the current theorized modes of AGPCR activation with discussion of potential parallels to mechanisms used by other GPCR classes. We provide a classification means for the ligands that have been identified and discuss how these ligands may activate AGPCRs in physiological contexts.

A proopiomelanocortin-derived peptide sequence enhances plasma stability of peptide drugs

Bioactive peptide drugs hold promise for therapeutic application due to their high potency and selectivity but display short plasma half-life. Examination of selected naturally occurring peptide hormones derived from proteolytic cleavage of the proopiomelanocortin (POMC) precursor lead to the identification of significant plasma-stabilizing properties of a 12-amino acid serine-rich orphan sequence NSSSSGSSGAGQ in human γ3-melanocyte-stimulating hormone (MSH) that is homologous to previously discovered NS_n GGH (n = 4-24) sequences in owls. Notably, transfer of this sequence to des-acetyl-α-MSH and the therapeutically relevant peptide hormones neurotensin and glucagon-like peptide-1 likewise enhance their plasma stability without affecting receptor signaling. The stabilizing effect of the sequence module is independent of plasma components, suggesting a direct effect in cis. This natural sequence module may provide a possible strategy to enhance plasma stability, complementing existing methods of chemical modification.

Stomach 'tastes' the food and adjusts its emptying: A neurophysiological hypothesis (Review)

The presence of taste receptors and their secondary messengers in stomach raised the possibility that the stomach might play a role in food 'tasting' and consequently, it might initiate specific adaptations of its secretory and motor function. Furthermore, activated taste receptors release a variety of chemical mediators able to modulate the activity of the enteric nervous system (ENS), and also to influence both secretory and motor functions of the stomach. Based on the physiological fundamental structure of a reflex arch, the stimulation of the gastric taste receptors activates sensory neurons of the gastric wall, continues with motor neurons which initiate the contraction of the local smooth muscle fibers. Beyond this, compounds which act on different taste receptors initiate different responses, stimulatory or inhibitory. These interactions may be translated in the gastric ability to selectively evacuate different nutritive compounds into the duodenum. Consequently, sugars could be favored to the detriment of other compounds.

Integration of nano- and biotechnology for beta-cell and islet transplantation in type-1 diabetes treatment

Regenerative medicine using human or porcine β‐cells or islets has an excellent potential to become a clinically relevant method for the treatment of type‐1 diabetes. High‐resolution imaging of the function and faith of transplanted porcine pancreatic islets and human stem cell–derived beta cells in large animals and patients for testing advanced therapy medicinal products (ATMPs) is a currently unmet need for pre‐clinical/clinical trials. The iNanoBIT EU H2020 project is developing novel highly sensitive nanotechnology‐based imaging approaches allowing for monitoring of survival, engraftment, proliferation, function and whole‐body distribution of the cellular transplants in a porcine diabetes model with excellent translational potential to humans. We develop and validate the application of single‐photon emission computed tomography (SPECT) and optoacoustic imaging technologies in a transgenic insulin‐deficient pig model to observe transplanted porcine xeno‐islets and in vitro differentiated human beta cells. We are progressing in generating new transgenic reporter pigs and human‐induced pluripotent cell (iPSC) lines for optoacoustic imaging and testing them in transplantable bioartificial islet devices. Novel multifunctional nanoparticles have been generated and are being tested for nuclear imaging of islets and beta cells using a new, high‐resolution SPECT imaging device. Overall, the combined multidisciplinary expertise of the project partners allows progress towards creating much needed technological toolboxes for the xenotransplantation and ATMP field, and thus reinforces the European healthcare supply chain for regenerative medicinal products.

Recombinant Peptide Production Platform Coupled with Site-Specific Albumin Conjugation Enables a Convenient Production of Long-Acting Therapeutic Peptide

The number of therapeutic peptides for human treatment is growing rapidly. However, their development faces two major issues: the poor yield of large peptides from conventional solid-phase synthesis, and the intrinsically short serum half-life of peptides. To address these issues, we investigated a platform for the production of a recombinant therapeutic peptide with an extended serum half-life involving the site-specific conjugation of human serum albumin (HSA). HSA has an exceptionally long serum half-life and can be used to extend the serum half-lives of therapeutic proteins and peptides. We used glucagon-like-peptide 1 (GLP-1) as a model peptide in the present study. A “clickable” non-natural amino acid—p-azido-l-phenylalanine (AzF)—was incorporated into three specific sites (V16, Y19, and F28) of a GLP-1 variant, followed by conjugation with HSA through strain-promoted azide–alkyne cycloaddition. All three HSA-conjugated GLP-1 variants (GLP1_16HSA, GLP1_19HSA, and GLP1_28HSA) exhibited comparable serum half-lives in vivo. However, the three GLP1_HSA variants had different in vitro biological activities and in vivo glucose-lowering effects, demonstrating the importance of site-specific HSA conjugation. The platform described herein could be used to develop other therapeutic peptides with extended serum half-lives.

Fructo-oligosaccharides alleviate inflammation-associated apoptosis of GLP-1 secreting L cells via inhibition of iNOS and cleaved caspase-3 expression

Glucagon-like peptide 1 (GLP-1) released from enteroendocrine (L) cells regulates insulin secretion. Intestinal inflammation and impaired GLP-1 release have been found in type 2 diabetes mellitus (T2DM) patients. Fructo-oligosaccharides (FOS), a known prebiotic, improve GLP-1 release and glucose homeostasis in T2DM models. This study aimed to investigate the effect of tumor necrosis factor-α (TNF-α), a proinflammatory cytokine associated with intestinal inflammation in T2DM, on L cell apoptosis and the effect of FOS on inflammation-associated impairment of GLP-1 secretion. Herein, using cell death assays, immunofluorescence staining, real time PCR and Western blot analyses, we found that TNF-α induced L cell apoptosis via nuclear factor kappa B (NF-κB)- inducible nitric oxide synthase (iNOS)-cleaved caspase-3-dependent pathways. Interestingly, FOS did not suppress TNF-α-induced NF-κB nuclear translocation, but inhibited expression of iNOS and cleaved caspase-3. In addition, FOS alleviated apoptosis and rescued impaired GLP-1 release in TNF-α-treated L cells. Altogether, our data indicate that TNF-α induces L cell apoptosis via an NF-κB-iNOS-caspase-3-dependent pathway. FOS may be useful in suppressing inflammation-associated L cell apoptosis and maintaining GLP-1 level in T2DM patients.

Whole-Grain Consumption Does Not Affect Obesity Measures: An Updated Systematic Review and Meta-analysis of Randomized Clinical Trials

Since the release of a previous meta-analysis on the effect of whole-grain intake on obesity measures, several clinical trials have been published. Therefore, we aimed to update the previous meta-analysis on the effect of whole-grain intake on obesity measures by including recently published studies, as well as considering the main limitations in that analysis. We searched the online databases of PubMed, Scopus, Clarivate Web of Science, EmBase, and Google Scholar for relevant studies published up to February 2019, using relevant keywords. Randomized clinical trials investigating the effect of whole-grain products or diets high in whole-grain foods, compared with a control diet, on anthropometric measures [including body weight, BMI, waist circumference, and fat mass (FM)] were included. In total, 21 studies with a total sample of 1798 participants, aged ≥18 years, were considered. Based on 22 effect sizes from 19 studies on body weight, with a total sample of 1698 adults, we found no significant effect of whole-grain consumption on body weight. The same findings were obtained for BMIs, such that using 10 effect sizes from 10 clinical trials with a total sample of 769 individuals we did not find any significant effect. With regards to body fat percentage [weighted mean difference (WMD): 0.27; 95% CI: -0.05 to 0.58%; P = 0.09], FM (WMD: 0.45; 95% CI: -0.12 to 1.02 kg; P = 0.12), fat-free mass (WMD: 0.31; 95% CI: -0.67 to 0.06 kg; P = 0.10), and waist circumference (WMD: 0.06; 95% CI: -0.50 to 0.63 cm; P = 0.82), we failed to find any significant effect of whole-grain consumption. In conclusion, our findings did not support current recommendations of whole-grain intake in attempts to control obesity measures. Given the beneficial effects of whole-grain intake on other measures of human health, additional well-designed studies are required to further investigate the effect on obesity. The protocol has been registered with PROSPERO (registration number CRD42019125320).

Postprandial Lipemia Modulates Pancreatic Alpha-Cell Function in the Prediction of Type 2 Diabetes Development: The CORDIOPREV Study

Diabetes (T2DM) is a major global health issue, and developing new approaches to its prevention is of paramount importance. We hypothesized that abnormalities in lipid metabolism are involved in alpha-cell deregulation. We therefore studied the metabolic factors underlying alpha-cell dysfunction in T2DM progression after a dietary intervention (Mediterranean and low-fat). Additionally, we evaluated whether postprandial glucagon levels may be considered as a predictive factor of T2DM in cardiovascular patients. Non-T2DM participants from the CORDIOPREV study were categorized by tertiles of the area under the curve (AUC) for triacylglycerols and also by tertiles of AUC for glucagon. Our results showed that patients with higher triacylglycerols levels presented elevated postprandial glucagon (P = 0.009). Moreover, we observed higher risk of T2DM (hazard ratio: 2.65; 95% confidence interval: 1.56-4.53) in subjects with elevated glucagon. In conclusion, high postprandial lipemia may induce alpha-cell dysfunction in cardiovascular patients. Our results also showed that postprandial glucagon levels could be used to predict T2DM development.

Development and characterisation of a peptidergic N-and C-terminally stabilised mammalian NPY1R agonist which protects against diabetes induction

BACKGROUND

PYY (1-36) peptides from phylogenetically ancient fish, such as sea lamprey, have previously been shown to function as specific neuropeptide Y1 receptor (NPYR1) agonists. Although, sea lamprey PYY (1-36) is N-terminally stable, we reveal in this study that the peptide is subject to endopeptidase mediated C-terminal dipeptide degradation. In an attempt to prevent this, (d-Arg³⁵)-sea lamprey PYY (1-36) was developed.

METHODS

In vitro bioassays assessed enzymatic stability, insulinostatic activity as well as beta-cell anti-apoptotic actions of (d-Arg³⁵)-sea lamprey PYY (1-36). Follow-up studies examined the impact of twice daily administration of sea lamprey PYY (1-36) or (d-Arg³⁵)-sea lamprey PYY (1-36) in multiple low dose STZ-induced diabetic mice.

RESULTS

(d-Arg³⁵)-sea lamprey PYY (1-36) was fully resistant to plasma enzymatic degradation. The peptide possessed similar significant insulinostatic, as well as positive anti-apoptotic biological actions, as the parent peptide. Sea lamprey PYY (1-36) and (d-Arg³⁵)-sea lamprey PYY (1-36) delayed diabetes progression in STZ mice. Both treatment interventions induced a significant decrease in body weight, food and fluid intake as well as glucose and glucagon concentrations. In addition, glucose tolerance, plasma and pancreatic insulin were partially normalised. (d-Arg³⁵)-sea lamprey PYY (1-36) was significantly more effective than sea lamprey PYY (1-36) in terms of enhancing glucose-stimulate insulin release. Both treatments improved pancreatic islet morphology, linked to decreased apoptosis of beta-cells.

CONCLUSION

We present (d-Arg³⁵)-sea lamprey PYY (1-36) as the first-in-class N- and C-terminally stable PYY (1-36) peptide analogue.

GENERAL SIGNIFICANCE

Enzymatically stable, long-acting PYY (1-36) peptides highlight the therapeutic benefits of sustained activation of NPYR1's in diabetes.

Using Machine Learning to Classify Bioactivity for 3486 Per- and Polyfluoroalkyl Substances (PFASs) from the OECD List

A recent OECD report estimated that more than 4000 per- and polyfluorinated alkyl substances (PFASs) have been produced and used in a broad range of industrial and consumer applications. However, little is known about the potential hazards (e.g., bioactivity, bioaccumulation, and toxicity) of most PFASs. Here, we built machine-learning-based quantitative structure-activity relationship (QSAR) models to predict the bioactivity of those PFASs. By examining a number of available molecular data sets, we constructed the first PFAS-specific database that contains the bioactivity information on 1012 PFASs for 26 bioassays. On the basis of the collected PFAS data set, we trained 5 different machine learning models that cover a variety of conventional models (e.g., random forest and multitask neural network (MNN)) and advanced graph-based models (e.g., graph convolutional network). Those models were evaluated based on the validation data set. Both MNN and graph-based models demonstrated the best performance. The average of the best area-under-the-curve score for each bioassay is 0.916. For predictions on the OECD list, most of the biologically active PFASs have perfluoroalkyl chain lengths less than 12 and are categorized into fluorotelomer-related compounds and perfluoroalkyl acids and their precursors.

The role of linagliptin, a selective dipeptidyl peptidase-4 inhibitor, in the morphine rewarding effects in rats

Linagliptin is a selective dipeptidyl peptidase-4 (DPP-4) inhibitor which suppresses the rapid degradation of endogenous glucagon-like peptide-1 (GLP-1). In clinical practice, it is used as an antidiabetic drug, but recent studies have confirmed its role in the activity of the central nervous system (CNS). The reported study focused on the role of linagliptin (10 and 20 mg/kg, ip) in the morphine rewarding effect, analyzing how the agent had influenced the conditioned place preference (CPP) in rats via the expression, acquisition, extinction and reinstatement of the morphine rewarding effect. The obtained results clearly demonstrated linagliptin to inhibit the expression and acquisition, to accelerate the extinction and, eventually, to reduce the reinstatement of morphine-induced CPP. The undertaken experiments significantly extended our knowledge on the mechanisms behind the morphine rewarding effect.

Compactness of Protein Folds Alters Disulfide-Bond Reducibility by Three Orders of Magnitude: A Comprehensive Kinetic Case Study on the Reduction of Differently Sized Tryptophan Cage Model Proteins

A new approach to monitor disulfide-bond reduction in the vicinity of aromatic cluster(s) has been derived by using the near-UV range (λ=266-293 nm) of electronic circular dichroism (ECD) spectra. By combining the results from NMR and ECD spectroscopy, the 3D fold characteristics and associated reduction rate constants (k) of E19_SS, which is a highly thermostable, disulfide-bond reinforced 39-amino acid long exenatide mimetic, and its N-terminally truncated derivatives have been determined under different experimental conditions. Single disulfide bond reduction of the E19_SS model (with an 18-fold excess of tris(2-carboxyethyl)phosphine, pH 7, 37 °C) takes hours, which is 20-30 times longer than that expected, and thus, would not reach completion by applying commonly used reduction protocols. It is found that structural, steric, and electrostatic factors influence the reduction rate, resulting in orders of magnitude differences in reduction half-lives (900>t_1/2 >1 min) even for structurally similar, well-folded derivatives of a small model protein.

Molecular mechanisms by which GLP-1 RA and DPP-4i induce insulin sensitivity

Glucagon-like peptide-1 is a peptide of incretin family which is used in the management of diabetes as glucagon-like peptide-1 receptor agonist (GLP-1RA). Dipeptidyl peptidase-4 enzyme metabolizes glucagon-like peptide-1 and various dipeptidyl peptidase-4 enzyme inhibitors (DPP-4i) are also used in the management of diabetes. These antidiabetic agents provide anti-hyperglycemic effects via several molecular mechanisms including promoting insulin secretion, suppression of glucagon secretion and slowing the gastric emptying. There is some research suggesting that they can induce insulin sensitivity in peripheral tissues. In this study, we review the possible molecular mechanisms by which GLP-1RA and DPP-4i can improve insulin resistance and increase insulin sensitivity in insulin-dependent peripheral tissues.

A free-energy landscape for the glucagon-like peptide 1 receptor GLP1R

G-protein-coupled receptors (GPCRs) are among the most important receptors in human physiology and pathology. They serve as master regulators of numerous key processes and are involved in as well as cause debilitating diseases. Consequently, GPCRs are among the most attractive targets for drug design and pharmaceutical interventions (>30% of drugs on the market). The glucagon-like peptide 1 (GLP-1) hormone receptor GLP1R is closely involved in insulin secretion by pancreatic β-cells and constitutes a major druggable target for the development of anti-diabetes and obesity agents. GLP1R structure was recently solved, with ligands, allosteric modulators and as part of a complex with its cognate G protein. However, the translation of this structural data into structure/function understanding remains limited. The current study functionally characterizes GLP1R with special emphasis on ligand and cellular partner binding interactions and presents a free-energy landscape as well as a functional model of the activation cycle of GLP1R. Our results should facilitate a deeper understanding of the molecular mechanism underlying GLP1R activation, forming a basis for improved development of targeted therapeutics for diabetes and related disorders.

The investigation of protective effects of glucagon-like peptide-1 (GLP-1) analogue exenatide against glucose and fructose-induced neurotoxicity

Diabetes mellitus (DM) is one of the most common metabolic disorders characterized by hyperglycemia due to insufficiency of insulin and/or insulin resistance. Clinical studies have revealed a higher risk of neurodegenerative disorders such as Alzheimer's disease or Parkinson's disease in diabetic patients. Recently, glucagon-like peptide-1 (GLP-1) is an attractive potential treatment modality for various neurodegenerative diseases. In our study, we aimed to investigate whether exenatide, a GLP-1 analogue, has neuroprotective effects against glucose and fructose-induced toxicity in human SH-SY5Y neuroblastoma cell line. Neurotoxicity was induced by incubating SH-SY5Y cells with different doses (25-100 mM) of glucose and fructose for 24, 48 and 72 hours. Following determination of the significant toxic doses of glucose and fructose, the cells were treated with various doses of exenatide (10-250 nM) in the presence or absence of glucose and fructose. Neurotoxicity was evaluated by MTT assay and Hoechst 33258 staining. Caspase-3 activity and the levels of advanced glycation end products (AGEs) were determined in the cytosolic fractions of treated cells. Our results demonstrated that both glucose and fructose treatments decreased cell viability in neuronal cells dose and time-dependently. Glucose and fructose-treated groups showed increased numbers of apoptotic cells, caspase-3 activity and AGEs levels. Treatment of the cells with exenatide significantly prevented cell death. The most prominent effect was observed at 100 nM exenatide-treated cultures. Our results suggest that high doses of glucose and fructose may lead to neurotoxicity, and exenatide may have protective effects against neuronal damage through its anti-apoptotic feature.

Biomedical applications of radioiodinated peptides

The overexpression of peptide receptors in certain tumors as compared to endogeneous expression levels represents the molecular basis for the design of peptide-based tools for targeted nuclear imaging and therapy. Receptor targeting with radiolabelled peptides became a very important imaging and/or therapeutic approach in nuclear medicine and oncology. A great variety of peptides has been radiolabelled with clinical relevant radionuclides, such as radiometals and radiohalogens. However, to the best of our knowledge concise and updated reviews providing information about the biomedical application of radioiodinated peptides are still missing. This review outlines the synthetic efforts in the preparation of radioiodinated peptides highlighting the importance of radioiodine in nuclear medicine, giving an overview of the most relevant radioiodination strategies that have been employed and describes relevant examples of their use in the biomedical field.

A Mechanistic Model of Gut-Brain Axis Perturbation and High-Fat Diet Pathways to Gut Microbiome Homeostatic Disruption, Systemic Inflammation, and Type 2 Diabetes

Type 2 diabetes (T2D) is a highly prevalent metabolic disease, affecting nearly 10% of the American population. Although the etiopathogenesis of T2D remains poorly understood, advances in DNA sequencing technologies have allowed for sophisticated interrogation of the human microbiome, providing insight into the role of the gut microbiome in the development and progression of T2D. An emerging body of research reveals that gut-brain axis (GBA) perturbations and a high-fat diet (HFD), along with other modifiable and nonmodifiable risk factors, contribute to gut microbiome homeostatic imbalance. Homeostatic imbalance or disruption increases gut wall permeability and facilitates translocation of endotoxins (lipopolysaccharides) into the circulation with resultant systemic inflammation. Chronic, low-grade systemic inflammation ensues with pro-inflammatory pathways activated, contributing to obesity, insulin resistance (IR), pancreatic β-cell decline, and, thereby, T2D. While GBA perturbations and HFD are implicated in provoking these conditions, prior mechanistic models have tended to examine HFD and GBA pathways exclusively without considering their shared pathways to T2D. Addressing this gap, this article proposes a mechanistic model informed by animal and human studies to advance scientific understanding of (1) modifiable and nonmodifiable risk factors for gut microbiome homeostatic disruption, (2) HFD and GBA pathways contributing to homeostatic disruption, and (3) shared GBA and HFD pro-inflammatory pathways to obesity, IR, β-cell decline, and T2D. The proposed mechanistic model, based on the extant literature, proposes a framework for studying the complex relationships of the gut microbiome to T2D to advance study in this promising area of research.

Glucagon-Like Peptide-1 Receptor Agonists and Strategies To Improve Their Efficiency

Type 2 diabetes mellitus (T2DM) is increasing in global prevalence and is associated with serious health problems (e.g., cardiovascular disease). Various treatment options are available for T2DM, including the incretin hormone glucagon-like peptide-1 (GLP-1). GLP-1 is a therapeutic peptide secreted from the intestines following food intake, which stimulates the secretion of insulin from the pancreas. The native GLP-1 has a very short plasma half-life, owning to renal clearance and degradation by the enzyme dipeptidyl peptidase-4. To overcome this issue, various GLP-1 agonists with increased resistance to proteolytic degradation and reduced renal clearance have been developed, with several currently marketed. Strategies, such as controlled release delivery systems, methods to reduce renal clearance (e.g., PEGylation and conjugation to antibodies), and methods to improve proteolytic stability (e.g., stapling, cyclization, and glycosylation) provide means to further improve the ability of GLP-1 analogs. These will be discussed in this literature review.

Advances in reducing cardiovascular risk in the management of patients with type 2 diabetes mellitus

Treatment intended to lower cardiovascular (CV) risk in patients with diabetes has always been a primary goal of diabetes treatment. Due to the subdued effects of reducing hemoglobin A1c (HbA1c) on macrovascular complications, controlling other CV risk factors such as hypertension and hyperlipidemia instead of hyperglycemia has been the mainstay treatment to improve CV outcome in patients with type 2 diabetes mellitus (T2DM) until recent years. This review is intended to summarize and compare the results from the available cardiovascular outcome trials (CVOTs) for the two classes of glucose lowering drug: sodium-glucose co-transporter 2 inhibitor (SGLT2i) and glucagon-like peptide-1 receptor agonist (GLP-1 RA). The results including the EMPA-REG, CANVAS program and DECLARE-TIMI 58 trials for SGLT2i, and the ELIXA, LEADER, SUSTAIN-6, EXSCEL and HARMONY trials for GLP-1 RA were summarized. The potential mechanisms of these CV beneficial effects and the optimal CV risk reduction treatment in patients with T2DM based on patient risk stratification and evidence from these CVOTs in real-world setting were discussed.

Motilin: from gastric motility stimulation to hunger signalling

After the discovery of motilin in 1972, motilin and the motilin receptor were studied intensely for their role in the control of gastrointestinal motility and as targets for treating hypomotility disorders. The genetic revolution - with the use of knockout models - sparked novel insights into the role of multiple peptides but contributed to a decline in interest in motilin, as this peptide and its receptor exist only as pseudogenes in rodents. The past 5 years have seen a major surge in interest in motilin, as a series of studies have shown its relevance in the control of hunger and regulation of food intake in humans in both health and disease. Luminal stimuli, such as bitter tastants, have been identified as modulators of motilin release, with effects on hunger and food intake. The current state of knowledge and potential implications for therapy are summarized in this Review.

Pleiotropic Effects of GLP-1 and Analogs on Cell Signaling, Metabolism, and Function

The incretin hormone Glucagon-Like Peptide-1 (GLP-1) is best known for its "incretin effect" in restoring glucose homeostasis in diabetics, however, it is now apparent that it has a broader range of physiological effects in the body. Both in vitro and in vivo studies have demonstrated that GLP-1 mimetics alleviate endoplasmic reticulum stress, regulate autophagy, promote metabolic reprogramming, stimulate anti-inflammatory signaling, alter gene expression, and influence neuroprotective pathways. A substantial body of evidence has accumulated with respect to how GLP-1 and its analogs act to restore and maintain normal cellular functions. These findings have prompted several clinical trials which have reported GLP-1 analogs improve cardiac function, restore lung function and reduce mortality in patients with obstructive lung disease, influence blood pressure and lipid storage, and even prevent synaptic loss and neurodegeneration. Mechanistically, GLP-1 elicits its effects via acute elevation in cAMP levels, and subsequent protein kinase(s) activation, pathways well-defined in pancreatic β-cells which stimulate insulin secretion in conjunction with elevated Ca2+ and ATP. More recently, new studies have shed light on additional downstream pathways stimulated by chronic GLP-1 exposure, findings which have direct relevance to our understanding of the potential therapeutic effects of longer lasting analogs recently developed for clinical use. In this review, we provide a comprehensive description of the diverse roles for GLP-1 across multiple tissues, describe downstream pathways stimulated by acute and chronic exposure, and discuss novel pleiotropic applications of GLP-1 mimetics in the treatment of human disease.