Glucagon-like peptide-1 suppresses neuroinflammation and improves neural structure.

Glucagon-like peptide-1 (GLP-1) is a hormone mainly secreted from enteroendocrine L cells. GLP-1 and its receptor are also expressed in the brain. GLP-1 signaling has pivotal roles in regulating neuroinflammation and memory function, but it is unclear how GLP-1 improves memory function by regulating neuroinflammation. Here, we demonstrated that GLP-1 enhances neural structure by inhibiting lipopolysaccharide (LPS)-induced inflammation in microglia with the effects of GLP-1 itself on neurons. Inflammatory secretions of BV-2 microglia by LPS aggravated mitochondrial function and cell survival, as well as neural structure in Neuro-2a neurons. In inflammatory condition, GLP-1 suppressed the secretion of tumor necrosis factor-alpha (TNF-α)-associated cytokines and chemokines in BV-2 microglia and ultimately enhanced neurite complexity (neurite length, number of neurites from soma, and secondary branches) in Neuro-2a neurons. We confirmed that GLP-1 improves neurite complexity, dendritic spine morphogenesis, and spine development in TNF-α-treated primary cortical neurons based on altered expression levels of the factors related to neurite growth and spine morphology. Given that our data that GLP-1 itself enhances neurite complexity and spine morphology in neurons, we suggest that GLP-1 has a therapeutic potential in central nervous system diseases.

Glucagon-like peptide 1 signaling inhibits allergen-induced lung IL-33 release and reduces group 2 innate lymphoid cell cytokine production in vivo.

BACKGROUND: IL-33 is one of the most consistently associated gene candidates for asthma identified by using a genome-wide association study. Studies in mice and in human cells have confirmed the importance of IL-33 in inducing type 2 cytokine production from both group 2 innate lymphoid cells (ILC2s) and TH2 cells. However, there are no pharmacologic agents known to inhibit IL-33 release from airway cells. OBJECTIVE: We sought to determine the effect of glucagon-like peptide 1 receptor (GLP-1R) signaling on aeroallergen-induced airway IL-33 production and release and on innate type 2 airway inflammation. METHODS: BALB/c mice were challenged intranasally with Alternaria extract for 4 consecutive days. GLP-1R agonist or vehicle was administered starting either 2 days before the first Alternaria extract challenge or 1 day after the first Alternaria extract challenge. RESULTS: GLP-1R agonist treatment starting 2 days before the first Alternaria extract challenge decreased IL-33 release in the bronchoalveolar lavage fluid and dual oxidase 1 (Duox1) mRNA expression 1 hour after the first Alternaria extract challenge and IL-33 expression in lung epithelial cells 24 hours after the last Alternaria extract challenge. Furthermore, GLP-1R agonist significantly decreased the number of ILC2s expressing IL-5 and IL-13, lung protein expression of type 2 cytokines and chemokines, the number of perivascular eosinophils, mucus production, and airway responsiveness compared with vehicle treatment. GLP-1R agonist treatment starting 1 day after the first Alternaria extract challenge also significantly decreased eosinophilia and type 2 cytokine and chemokine expression in the airway after 4 days of Alternaria extract challenge. CONCLUSION: These results reveal that GLP-1R signaling might be a therapy to reduce IL-33 release and inhibit the ILC2 response to protease-containing aeroallergens, such as Alternaria.

GI inflammation Increases Sodium-Glucose Cotransporter Sglt1.

A correlation between gastrointestinal (GI) inflammation and gut hormones has reported that inflammatory stimuli including bacterial endotoxins, lipopolysaccharides (LPS), TNFα, IL-1ß, and IL-6 induces high levels of incretin hormone leading to glucose dysregulation. Although incretin hormones are immediately secreted in response to environmental stimuli, such as nutrients, cytokines, and LPS, but studies of glucose-induced incretin secretion in an inflamed state are limited. We hypothesized that GI inflammatory conditions induce over-stimulated incretin secretion via an increase of glucose-sensing receptors. To confirm our hypothesis, we observed the alteration of glucose-induced incretin secretion and glucose-sensing receptors in a GI inflammatory mouse model, and we treated a conditioned media (Mϕ 30%) containing inflammatory cytokines in intestinal epithelium cells and enteroendocrine L-like NCI-H716 cells. In GI-inflamed mice, we observed that over-stimulated incretin secretion and insulin release in response to glucose and sodium glucose cotransporter (Sglt1) was increased. Incubation with Mϕ 30% increases Sglt1 and induces glucose-induced GLP-1 secretion with increasing intracellular calcium influx. Phloridzin, an sglt1 inhibitor, inhibits glucose-induced GLP-1 secretion, ERK activation, and calcium influx. These findings suggest that the abnormalities of incretin secretion leading to metabolic disturbances in GI inflammatory disease by an increase of Sglt1.

A surface plasmon resonance assay for characterisation and epitope mapping of anti-GLP-1 antibodies.

The incretin hormone glucagon-like peptide-1 (GLP-1) has been subject to substantial pharmaceutical research regarding the treatment of type 2 diabetes mellitus. However, quantification of GLP-1 levels remains complicated due to the low circulation concentration and concurrent existence of numerous metabolites, homologous peptides, and potentially introduced GLP-1 receptor agonists. Surface plasmon resonance (SPR) facilitates real-time monitoring allowing a more detailed characterisation of the interaction compared with conventional enzyme-linked immunosorbent assays (ELISA). In this paper, we describe the development of the first SPR assays for characterisation of anti-GLP-1 antibodies for ELISA purposes. Binding responses were obtained on covalently immobilised anti-GLP-1 antibodies at 12°C, 25°C, and 40°C and fitted to a biomolecular (1:1) interaction model showing association rates of 1.01 × 103 to 4.54 × 103  M-1  s-1 and dissociation rates of 3.56 × 10-5 to 1.56 × 10-3  s-1 leading to affinities of 35.2 to 344 nM, depending on the temperature. Determination of thermodynamic properties revealed an enthalpy driven interaction (ΔH < ΔS < 0) with higher affinities at lower temperatures due to the formation and stabilisation of hydrogen bonds within the binding site primarily composed of polar amino acids (ΔCp  < 0). Pair-wise epitope mapping was performed on captured anti-GLP-1 antibodies followed by subsequent interaction with GLP-1 (7-36) and other anti-GLP-1 antibodies. A global evaluation of every binding response led to an epitope map elucidating the potential of various anti-GLP-1 antibody pairs for sandwich ELISA and hence pinpointing the optimal antibody combinations. The SPR assays proved capable of providing vital information for ELISA development endorsing it as a useful optimisation tool.

Cut to the chase: a review of CD26/dipeptidyl peptidase-4's (DPP4) entanglement in the immune system.

CD26/DPP4 (dipeptidyl peptidase 4/DP4/DPPIV) is a surface T cell activation antigen and has been shown to have DPP4 enzymatic activity, cleaving-off amino-terminal dipeptides with either L-proline or L-alanine at the penultimate position. It plays a major role in glucose metabolism by N-terminal truncation and inactivation of the incretins glucagon-like peptide-1 (GLP) and gastric inhibitory protein (GIP). In 2006, DPP4 inhibitors have been introduced to clinics and have been demonstrated to efficiently enhance the endogenous insulin secretion via prolongation of the half-life of GLP-1 and GIP in patients. However, a large number of studies demonstrate clearly that CD26/DPP4 also plays an integral role in the immune system, particularly in T cell activation. Therefore, inhibition of DPP4 might represent a double-edged sword. Apart from the metabolic benefit, the associated immunological effects of long term DPP4 inhibition on regulatory processes such as T cell homeostasis, maturation and activation are not understood fully at this stage. The current data point to an important role for CD26/DPP4 in maintaining lymphocyte composition and function, T cell activation and co-stimulation, memory T cell generation and thymic emigration patterns during immune-senescence. In rodents, critical immune changes occur at baseline levels as well as after in-vitro and in-vivo challenge. In patients receiving DPP4 inhibitors, evidence of immunological side effects also became apparent. The scope of this review is to recapitulate the role of CD26/DPP4 in the immune system regarding its pharmacological inhibition and T cell-dependent immune regulation.

Multiplexed Quantification of Proglucagon-Derived Peptides by Immunoaffinity Enrichment and Tandem Mass Spectrometry after a Meal Tolerance Test.

BACKGROUND: Proglucagon-derived peptides (PGDPs), which include glucagon-like peptide (GLP)-1, glucagon, and oxyntomodulin, are key regulators of glucose homeostasis and satiety. These peptide hormones are typically measured with immuno-based assays (e.g., ELISA, RIA), which often suffer from issues of selectivity. METHODS: We developed a multiplexed assay for measuring PGDPs including GLP-1 (7-36) amide, GLP-1 (9-36) amide, glucagon, and oxyntomodulin by mass spectrometry and used this assay to examine the effect of a meal tolerance test on circulating concentrations of these hormones. Participants fasted overnight and were either given a meal (n = 8) or continued to fast (n = 4), with multiple blood collections over the course of 3 h. Plasma samples were analyzed by microflow immunoaffinity (IA)-LC-MS/MS with an isotope dilution strategy. RESULTS: Assay performance characteristics were examined and established during analytical validation for all peptides. Intra- and interassay imprecision were found to be 2.2%-10.7% and 6.8%-22.5%, respectively. Spike recovery was >76%, and dilution linearity was established up to a 16-fold dilution. Immediately after the meal tolerance test, GLP-1 and oxyntomodulin concentrations increased and had an almost identical temporal relationship, and glucagon concentrations increased with a slight delay. CONCLUSIONS: IA-LC-MS/MS was used for the simultaneous and selective measurement of PGDPs. This work includes the first indication of the physiological concentrations and modulation of oxyntomodulin after a meal.

Multifunctional Antibody Agonists Targeting Glucagon-like Peptide-1, Glucagon, and Glucose-Dependent Insulinotropic Polypeptide Receptors.

Glucagon-like peptide-1 (GLP-1) receptor (GLP-1R), glucagon (GCG) receptor (GCGR), and glucose-dependent insulinotropic polypeptide (GIP, also known as gastric inhibitory polypeptide) receptor (GIPR), are three metabolically related peptide hormone receptors. A novel approach to the generation of multifunctional antibody agonists that activate these receptors has been developed. Native or engineered peptide agonists for GLP-1R, GCGR, and GIPR were fused to the N-terminus of the heavy chain or light chain of an antibody, either alone or in pairwise combinations. The fusion proteins have similar in vitro biological activities on the cognate receptors as the corresponding peptides, but circa 100-fold longer plasma half-lives. The GLP-1R mono agonist and GLP-1R/GCGR dual agonist antibodies both exhibit potent effects on glucose control and body weight reduction in mice, with the dual agonist antibody showing enhanced activity in the latter.

Specificity and sensitivity of commercially available assays for glucagon-like peptide-1 (GLP-1): implications for GLP-1 measurements in clinical studies.

AIMS: To evaluate the performances of commercially available glucagon-like peptide-1 (GLP-1) assays and the implications for clinical studies. METHODS: Known concentrations (5-300 pmol/l) of synthetic GLP-1 isoforms (GLP-1 1-36NH2, 7-36NH2, 9-36NH2, 1-37, 7-37 and 9-37) were added to the matrix (assay buffer) supplied with 10 different kits and to human plasma, and recoveries were determined. Assays yielding meaningful results were analysed for precision and sensitivity by repeated analysis and ability to discriminate low concentrations. Endogenous GLP-1 levels in clinical samples were assessed using three commercial kits. RESULTS: The USCN LIFE assay detected none of the GLP-1 isoforms. The active GLP-1 enzyme-linked immunosorbent assays (ELISAs) from Millipore and DRG appeared identical and were specific for intact GLP-1 in buffer and plasma. The Meso Scale Discovery (MSD) total GLP-1 kit detected all six GLP-1 isoforms, although recovery of non-active forms was incomplete, especially in plasma. Millipore total GLP-1 ELISA kit detected all isoforms in buffer, but mainly amidated forms in plasma. The Alpco, Phoenix and Bio-Rad kits detected only amidated GLP-1, but the Alpco kit had a limited measurement range (30 pmol/l), the Phoenix kit had incomplete recovery in plasma and the Bio-Rad kit was insensitive (detection limit in plasma 40 pmol/l). The pattern of postprandial GLP-1 responses in clinical samples was similar between the kits tested, but the absolute concentrations measured varied. CONCLUSIONS: The specificity and sensitivity of commercially available kits for the analysis of GLP-1 levels vary considerably. This should be taken into account when selecting which assay to use and when comparing data from different studies.

GLP-1R agonist therapy and vaccine response: Neglected implications.

Glucagon-like peptide-1 receptor agonists (GLP-1RAs), such as semaglutide (Ozempic®), have emerged as effective treatments for diabetes and weight management. However, recent evidence indicates that GLP-1R signalling influences various tissues, including the immune system. Notably, GLP-1 has a short half-life (< 5 minutes) and exists in the picomolar range, while GLP-1RAs like semaglutide have extended half-lives of several days and are administered at supraphysiological doses. This review explores the potential impact of these medications on vaccine efficacy. We examine evidence suggesting that GLP-1RAs may attenuate vaccine responses through direct effects on immune cells and modulation of other tissues. Additionally, we discuss how GLP-1R signalling may create a tolerogenic environment, potentially reducing vaccine immunogenicity. Given the widespread use of GLP-1RAs, it is crucial to understand their impact on immune responses and the translational implications for vaccination outcomes.

Glucagon-like peptide-1 (GLP-1), immediately prior to reperfusion, decreases neutrophil activation and reduces myocardial infarct size in rodents.

Glucagon-like peptide-1 (GLP-1) is an incretin that has glucoregulatory effects as well as protective effects in a variety of tissues, including the heart. We hypothesized that GLP-1 may have a direct effect on neutrophils (PMNs) after myocardial ischemia, to ameliorate reperfusion injury. Deeply anesthetized Sprague-Dawley rats underwent 30 min of left coronary artery occlusion followed by 120 min of reperfusion. Immediately prior to reperfusion, rats were treated with either GLP-1 (human rGLP-1, 30 pM/kg/min) or PBS as placebo. GLP-1 significantly decreased myocardial infarct size [73.2±11.7% INF/AAR in PBS (n=4) vs. 15.7 ±5.52% INF/AAR in GLP-1-treated animals (n=5), p<0.05], PMN activation in blood in vivo (fMLP-stimulated CD11b surface expression: PBS 2.78±1.14 vs. GLP-1 1.7±0.21, TFI, p<0.05), and accumulation in myocardium (PBS: 6.52±0.31 vs. GLP-1: 4.78±0.90, n=4-6 animals/group, p<0.05). In addition, we found that GLP-1 mitigated PMN CD11b surface expression in whole rat blood in vitro, an effect that was abolished by GLP-1 receptor blockade (PBS 6.52±0.31 vs. GLP-1 4.78±0.90, TFI, p<0.05). These findings suggest that one mechanism by which GLP-1 decreases reperfusion injury may be the attenuation of PMN-mediated reperfusion injury.

Continuous stimulation of dual-function peptide PGLP-1-VP inhibits the morbidity and mortality of NOD mice through anti-inflammation and immunoregulation.

Multiple animal and human studies have shown that administration of GLP-1RA can enhance ß-cell recovery, reduce insulin dosage, reduce HbA1c content in the blood, reduce the risk of hypoglycemia and reduce inflammation. In the NOD mouse model, peptide VP treatment can prevent and treat type 1 diabetes through immunomodulation. Therefore, we designed a new dual-functional PGLP-1-VP, which is expected to combine the anti-inflammatory effect of PGLP-1 and the immunomodulatory effect of VP peptide. In streptozotocin-induced hyperglycemic mice model, we demonstrated that PGLP-1-VP can act as a GLP-1R agonist to improve hyperglycemia and increase insulin sensitivity. In the NOD mouse model, PGLP-1-VP treatment reduced morbidity, mortality, and pancreatic inflammation, and showed superior effect to PGLP-1 or VP treatment alone, confirming that PGLP-1-VP may act as a dual-function peptide. PGLP-1-VP provided immunomodulatory effect through increasing Th2 cell percentage and balancing the ratio of Th2/Th1 in spleen and PLN, similar to P277 and VP. Additionally, PGLP-1-VP and PGLP-1 act the anti-inflammation by increasing Treg cells and TGF-ß1 content like DPP-IV inhibitor. Taken together, our data shows that the dual-functional PGLP-1-VP reduces morbidity and mortality in the NOD model, suggesting a potential role in preventing and treating type 1 diabetes.

Dipeptidyl peptidase 4 inhibitors: Applications in innate immunity?

Dipeptidyl peptidase (DPP)-4 inhibitors are a class of orally available, small molecule inhibitors that prolong the insulinotropic activity of the incretin hormone glucagon-like peptide-1 (GLP-1) and are highly effective for the treatment of Type-2 diabetes. DPP4 can also cleave several immunoregulatory peptides including chemokines. Emerging evidence continues to implicate DPP4 inhibitors as immunomodulators, with recent findings suggesting DPP4 inhibitors modify specific aspects of innate immunity. This review summarises recent insights into how DPP4 inhibitors could be implicated in endothelial, neutrophil and monocyte/macrophage mediated immunity. Additionally, this review highlights additional avenues of research with DPP4 inhibitors in the context of the COVID-19 pandemic.

Expression of glucagon-like peptide-1 in the taste buds of rat circumvallate papillae.

Glucagon-like peptide-1 (GLP-1), a 30-amino-acid peptide hormone, is a typical peptide of the brain-gut axis and can affect the metabolism of various tissues and organs. GLP-1 is secreted by intestinal L cells in response to nutrient ingestion. Some studies have shown that taste signaling elements were co-expressed in enteroendocrine cells of the small intestine, and in particular by L-cells. The present study was performed to explore the protein and mRNA expression of GLP-1 in the taste buds of rat circumvallate papillae and to try to determine the significance of its secretion. GLP-1 immunoreactivity was observed in spindle-shaped taste bud cells, with positive cells displaying a characteristic distribution of reaction product that was confined to the cytosol. Reverse transcription polymerase chain reaction (RT-PCR) assay showed that GLP-1 mRNA was expressed in circumvallate papillae. The expression of GLP-1 suggests that it may play an important role in the taste stimulation of nutrients and gut hormone secretion.

Akkermansia muciniphila can reduce the damage of gluco/lipotoxicity, oxidative stress and inflammation, and normalize intestine microbiota in streptozotocin-induced diabetic rats.

This study aimed to investigate how Akkermansia muciniphila can implicate type 2 diabetes mellitus and the mechanisms underlying the effects A. muciniphila on type 2 diabetes mellitus. Normal and streptozotocin-induced diabetic Sprague-Dawley rats were orally administered with A. muciniphila and solvent. After 4 weeks of treatment, diabetic rats orally administered with live or pasteurized A. muciniphila exhibited significant increase in the blood concentration of high-density lipoprotein, and decrease in the hepatic glycogen, serum plasminogen activator inhibitor-1, tumor necrosis factor-α, lipopolysaccharide, malondialdehyde and total glucagon-like peptide-1. Moreover, diabetic rats orally administered with A. muciniphila showed significantly increased species alpha diversity and gene function in gut microbes. These results indicated that A. muciniphila can improve liver function, reduce gluco/lipotoxicity, alleviate oxidative stress, suppress inflammation and normalize intestine microbiota of the host animal, thereby ameliorating type 2 diabetes mellitus. Akkermansia muciniphila might be considered as one of the ideal new probiotics used in the management of type 2 diabetes mellitus in future.

Lymphocytic infiltration and immune activation in metallothionein promoter-exendin-4 (MT-Exendin) transgenic mice.

Glucagon-like peptide 1 (GLP-1) exhibits considerable potential for the treatment of type 2 diabetes because of its effects on stimulation of insulin secretion and the inhibition of gastric emptying, appetite, and glucagon secretion. However, native GLP-1 undergoes rapid enzymatic inactivation, prompting development of long-acting degradation-resistant GLP-1 receptor agonists such as exendin-4 (Ex-4). To study the consequences of sustained exposure to Ex-4, we generated metallothionein promoter-exendin-4 (MT-Exendin) mice that continuously express a proexendin-4 transgene in multiple murine tissues. We now report that MT-Exendin mice develop extensive tissue lymphocytic infiltration with increased numbers of CD4(+) and CD8a(+) cells in the liver and/or kidney and increased numbers of B220(+) cells present in the pancreas and liver. MT-Exendin mice generate antibodies directed against Ex-4, exendin NH(2)-terminal peptide (ENTP), and proexendin-4 as well as antibodies that cross-react with native GLP-1. Furthermore, lymphocytes isolated from MT-Exendin mice proliferate in response to proexendin-4 but not after exposure to Ex-4 or ENTP. These findings demonstrate that expression of a proexendin-4 transgene may be associated with activation of humoral and cellular immune responses in mice.

Beta-glucans and cancer: The influence of inflammation and gut peptide.

Dietary ß-glucans are soluble fibers with potentially health-promoting effects. Gut peptides are important signals in the regulation of energy and glucose homeostasis. This article reviews the effects of different enriched ß-glucan food consumption on immune responses, inflammation, gut hormone and cancer. Gut hormones are influenced by enriched ß-glucan food consumption and levels of such peptide as YY, ghrelin, glucagon-like peptide 1 and 2 in humans influence serum glucose concentration as well as innate and adaptive immunity. Cancer cell development is also regulated by obesity and glucose dishomeostasy that are influenced by ß-glucan food consumption that in turn regulated gut hormones.

Dulaglutide for the treatment of type 2 diabetes.

INTRODUCTION: Glucagon-like peptide-1 receptor agonists (GLP-1 RAs) are injectable agents used for the treatment of hyperglycemia in type 2 diabetes. The interest for this pharmacological class is rising with the development of once weekly compounds and the demonstration of a potential reduction in cardiorenal outcomes. Areas covered: The paper describes the main pharmacokinetic/pharmacodynamic characteristics of dulaglutide, a new once-weekly GLP-1 RA. Dulaglutide was extensively investigated in the phase-3 AWARD program, which demonstrated its safety and efficacy when compared to placebo or active glucose-lowering agents in patients treated with diet alone, metformin or sulfonylurea monotherapy, oral dual therapies and basal insulin. In both Caucasian and Japanese patients, comparative trials showed better glucose control with dulaglutide, with a minimal risk of hypoglycemia and weight loss, but at the expense of an increased dropout rate due to side effects, mostly transient gastrointestinal disturbances. Dulaglutide proved its non-inferiority versus liraglutide and the safety and tolerance profile is similar to that of other GLP-1 RAs. Expert opinion: The once-weekly formulation and the combined positive effects on both glucose control and weight improves patient satisfaction despite nausea. Dulaglutide must prove its capacity to reduce cardiovascular and diabetic complications in the ongoing prospective REWIND trial.

A dual-monoclonal, sandwich immunoassay specific for glucagon like peptide-19-36/7 (GLP-19-36/7).

OBJECTIVE: Glucagon-like peptide-1 (GLP-1) is a peptide hormone secreted by intestinal L-cells which stimulates glucose-dependent insulin secretion. GLP-1 is initially secreted as the active peptide GLP-17-36/7, but rapidly undergoes cleavage by dipeptidyl peptidase 4 (DPP4) to yield the inactive form, GLP-19-36/7. Despite a reduced affinity for the GLP-1 receptor, GLP-19-36/7 may have cardioprotective properties. There is currently no described immunoassay capable of specifically measuring GLP-19-36/7. DESIGN AND METHODS: We generated a monoclonal antibody specific for the N-terminal neoepitope of GLP-19-36/7. After affinity maturation, we paired this capture antibody with an anti-total GLP-1 monoclonal detection antibody to create a sandwich ELISA specific for GLP-19-36/7. RESULTS: The sandwich ELISA was highly specific for GLP-19-36/7 and did not recognize GLP-17-36 or GLP-17-37. The ELISA exhibited a broad dynamic range and a lower limit of detection (LLOD) of 3.17ng/L. In healthy volunteers, concentrations of GLP-19-36/7 increased dramatically in the postprandial state compared to the fasted state and were markedly elevated at both 30 and 120-minute postprandial time points. CONCLUSIONS: The optimization of an N-terminal-specific monoclonal antibody for GLP-19-36/7 enabled the development of a sensitive and specific sandwich ELISA assay capable of measuring physiological concentrations of GLP-19-36/7. This ELISA may have the potential to help expand our knowledge of GLP-1 biology.

Distribution of K and L cells in the feline intestinal tract.

Glucose-dependent insulinotropic peptide (GIP), glucagon-like peptide (GLP)-1 and GLP-2 are hormones secreted from specialized K cells (GIP) and L cells (GLP-1, GLP-2) in the intestinal mucosa. These hormones play major roles in health and disease by modulating insulin secretion, satiety, and multiple intestinal functions. The aim of this study was to describe the distribution of K cells and L cells in the intestines of healthy cats. Samples of duodenum, mid-jejunum, ileum, cecum, and colon were collected from 5 cats that were euthanized for reasons unrelated to this study and had no gross or histologic evidence of gastrointestinal disease. Samples stained with rabbit-anti-porcine GIP, mouse-anti-(all mammals) GLP-1, or rabbit-anti-(all mammals) GLP-2 antibodies were used to determine the number of cells in 15 randomly selected 400× microscopic fields. In contrast to other mammals (eg, dogs) in which K cells are not present in the ileum and aborally, GIP-expressing cells are abundant throughout the intestines in cats (>6/high-power field in the ileum). Cells expressing GLP-1 or GLP-2 were most abundant in the ileum (>9/high-power field) as in other mammals, but, although GLP-1-expressing cells were abundant throughout the intestines, GLP-2-expressing cells were rarely found in the duodenum. In conclusion, the distribution of GIP-secreting K cells in cats is different from the distribution of K cells that is described in other mammals. The difference in distribution of GLP-2- and GLP-1-expressing cells suggests that more than 1 distinct population of L cells is present in cats.

A dipeptidyl peptidase-4 inhibitor, sitagliptin, exerts anti-inflammatory effects in type 2 diabetic patients.

AIMS/HYPOTHESIS: Glucagon-like peptide-1 (GLP-1) exerts beneficial effects on the cardiovascular system. Here, we examined the effect of sitagliptin, a dipeptidyl peptidase-4 (DPP-4) inhibitor, on systemic inflammation and pro-inflammatory (M1)/anti-inflammatory (M2)-like phenotypes of peripheral blood monocytes in diabetic patients. METHODS: Forty-eight type 2 diabetic patients were divided into the following two groups: sitagliptin-treatment (50mg daily for 3months) (n=24) and untreated control (n=24) groups. Measurements were undertaken to assess changes in glucose-lipid metabolism, serum levels of inflammatory cytokines such as serum amyloid A-LDL (SAA-LDL), C-reactive protein (CRP), interleukin-6 (IL-6), IL-10 and tumor necrosis factor-α (TNF-α). Furthermore, the effects of sitagliptin treatment on M1/M2-like phenotypes in peripheral blood monocytes were examined. RESULTS: Treatment with sitagliptin significantly decreased fasting plasma glucose, hemoglobin A1c (HbA1c), serum levels of inflammatory markers, such as SAA-LDL, CRP, and TNF-α. In contrast, sitagliptin increased serum IL-10, an anti-inflammatory cytokine, as well as plasma GLP-1. In addition, sitagliptin increased monocyte IL-10 expression and decreased monocyte TNF-α expression. Multivariate regression analysis revealed that the sitagliptin treatment was the only factor independently associated with an increase in monocyte IL-10 (ß=0.499; R(2)=0.293, P<0.05). However, other factors including the improvement of glucose metabolism were not associated with the increase. CONCLUSIONS/INTERPRETATION: This study is the first to show that a DPP-4 inhibitor, sitagliptin, reduces inflammatory cytokines and improves the unfavorable M1/M2-like phenotypes of peripheral blood monocytes in Japanese type 2 diabetic patients.