We recently showed that activation of G protein-coupled receptor 119 (GPR119) (also termed glucose dependent insulinotropic receptor) improves glucose homeostasis via direct cAMP-mediated enhancement ...of glucose-dependent insulin release in pancreatic β-cells. Here we show that GPR119 also stimulates incretin hormone release and thus may regulate glucose homeostasis by this additional mechanism. GPR119 mRNA was found to be expressed at significant levels in intestinal subregions that produce glucose-dependent insulinotropic peptide and glucagon-like peptide (GLP)-1. Furthermore, in situ hybridization studies indicated that most GLP-1-producing cells coexpress GPR119 mRNA. In GLUTag cells, a well-established model of intestinal L-cell function, the potent GPR119 agonist AR231453 stimulated cAMP accumulation and GLP-1 release. When administered in mice, AR231453 increased active GLP-1 levels within 2 min after oral glucose delivery and substantially enhanced total glucose-dependent insulinotropic peptide levels. Blockade of GLP-1 receptor signaling with exendin(9–39) reduced the ability of AR231453 to improve glucose tolerance in mice. Conversely, combined administration of AR231453 and the DPP-4 inhibitor sitagliptin to wild-type mice significantly amplified both plasma GLP-1 levels and oral glucose tolerance, relative to either agent alone. In mice lacking GPR119, no such enhancement was seen. Thus, GPR119 regulates glucose tolerance by acting on intestinal endocrine cells as well as pancreatic β-cells. These data also suggest that combined stimulation of incretin hormone release and protection against incretin hormone degradation may be an effective antidiabetic strategy.
The study objective was to evaluate the interaction between corticotrophin releasing factor (
CRF
) receptor signaling and prophylactic antibiotic administration on intestinal physiology in newly ...weaned and transported pigs. Pigs (n = 56; 5.70 ± 1.05 kg) were weaned (20.49 ± 0.64 d), a blood sample was taken, and then pigs were given an intraperitoneal injection of saline (
SAL
; n = 28 pigs) or a CRF receptor antagonist (
CRFA
; n = 28 pigs; 30 μg/kg body weight; Astressin B), and then were transported in a livestock trailer for 12 h and 49 min. A second and third intraperitoneal injection was given at 4 h 42 min and 11 h 36 min into the transport process, respectively. Following transport, 4 SAL and 4 CRFA pigs were blood sampled and euthanized. The remaining 48 pigs were individually housed and given dietary antibiotics
AB
; n = 12 SAL and 12 CRFA pigs; chlortetracycline (441 ppm) + tiamulin (38.6 ppm) or no dietary antibiotics (
NAB
; n = 12 SAL and 12 CRFA pigs) for 14 d post-transport. Blood was collected at 12 h and on d 3, 7, and 14, and then pigs were euthanized on d 7 (n = 24) and d 14 (n = 24) post-weaning and transport. Circulating cortisol was reduced (
p
= 0.05) in CRFA pigs when compared to SAL pigs post-weaning and transport. On d 7, jejunal villus height and crypt depth was greater overall (
p
< 0.05) in AB-fed pigs versus NAB-fed pigs. On d 14, ileal crypt depth was reduced (
p
= 0.02) in CRFA pigs when compared to SAL pigs. Jejunal CRF mRNA abundance tended to be reduced (
p
= 0.09) on d 7 in CRFA pigs versus SAL pigs. On d 14, jejunal tumor necrosis factor-alpha was reduced (
p
= 0.01) in AB-fed pigs versus NAB-fed pigs. On d 7, change in glucose short-circuit current tended to be increased (
p
= 0.07) in CRFA pigs fed the AB diet when compared to CRFA pigs fed the NAB diet. In conclusion, CRFA pigs and pigs fed AB had some similar biological intestinal function measures post-weaning and transport.
Nicotinic acid (niacin) induces beneficial changes in serum lipoproteins and has been associated with beneficial cardiovascular effects. Niacin reduces low-density lipoprotein, increases high-density ...lipoprotein, and decreases triglycerides. It is well established that activation of the seven-transmembrane G(i)-coupled receptor GPR109A on Langerhans cells results in release of prostaglandin D₂, which mediates the well-known flushing side effect of niacin. Niacin activation of GPR109A on adipocytes also mediates the transient reduction of plasma free fatty acid (FFA) levels characteristic of niacin, which has been long hypothesized to be the mechanism underlying the changes in the serum lipid profile. We tested this "FFA hypothesis" and the hypothesis that niacin lipid efficacy is mediated via GPR109A by dosing mice lacking GPR109A with niacin and testing two novel, full GPR109A agonists, MK-1903 and SCH900271, in three human clinical trials. In mice, the absence of GPR109A had no effect on niacin's lipid efficacy despite complete abrogation of the anti-lipolytic effect. Both MK-1903 and SCH900271 lowered FFAs acutely in humans; however, neither had the expected effects on serum lipids. Chronic FFA suppression was not sustainable via GPR109A agonism with niacin, MK-1903, or SCH900271. We conclude that the GPR109A receptor does not mediate niacin's lipid efficacy, challenging the long-standing FFA hypothesis.
Regulation of cellular metabolism by the citric acid cycle occurs in the mitochondria. However, the citric acid cycle intermediate succinate was shown recently to be a ligand for the ...G‐protein‐coupled receptor GPR91. Here, we describe a role for succinate and its receptor in the stimulation of hematopoietic progenitor cell (HPC) growth. GPR91 mRNA and protein expression were detected in human bone marrow CD34+ progenitor cells, as well as in erythroid and megakaryocyte cultures and the erythroleukemic cell line TF‐1. Treatment of these cell cultures with succinate resulted in increased proliferation rates. The proliferation response of TF‐1 cells was pertussis toxin (PTX)‐sensitive, suggesting a role for Gi signaling. Proliferation was also blocked when TF‐1 cells were transfected with small interfering RNA specific for GPR91. Succinate stimulated activation of the Erk MAPK pathway and inositol phosphate accumulation in a PTX‐sensitive manner. Pretreatment of TF‐1 cells with the Erk1/2 kinase (MEK) inhibitor PD98059 blocked the proliferation response. Succinate treatment additionally protected TF‐1 cells from cell death induced by serum deprivation. Finally, in vivo administration of succinate was found to elevate the levels of hemoglobin, platelets, and neutrophils in a mouse model of chemotherapy‐induced myelosuppression. These results suggest that succinate‐GPR91 signaling is capable of promoting HPC development.
Nicotinic acid, used for atherosclerosis treatment, has an adverse effect of skin flushing. The flushing mechanism, thought to be caused by the release of prostaglandin D2 (PGD2), is not well ...understood. We aimed to identify which cells mediate the flushing effect. Nicotinic acid receptor (GPR109A) gene expression was assessed in various tissues and cell lines. Cells expressing GPR109A mRNA were further assayed for PGD2 release in response to nicotinic acid. Of all samples, only skin was able to release PGD2 upon stimulation with nicotinic acid. The responsive cells were localized to the epidermis, and immunocytochemical studies revealed the presence of GPR109A on epidermal Langerhans cells. CD34+ cells isolated from human blood and differentiated into Langerhans cells (hLC-L) also showed GPR109A expression. IFNγ treatment increased both mRNA and plasma membrane expression of GPR109A. IFNγ-stimulated hLC-Ls released PGD2 in response to nicotinic acid in a dose-dependant manner (effector concentration for half-maximum response=1.2mm±0.7). Acifran, a structurally distinct GPR109A ligand, also increased PGD2 release, whereas isonicotinic acid, a nicotinic acid analog with low affinity for GPR109A, had no effect. These results suggest that nicotinic acid mediates its flushing side effect by interacting with GPR109A on skin Langerhans cells, resulting in release of PGD2.
Pancreatic β-cell dysfunction is a hallmark event in the pathogenesis of type 2 diabetes. Injectable peptide agonists of the glucagon-like peptide 1 (GLP-1) receptor have shown significant promise as ...antidiabetic agents by virtue of their ability to amplify glucose-dependent insulin release and preserve pancreatic β-cell mass. These effects are mediated via stimulation of cAMP through β-cell GLP-1 receptors. We report that the Gαs-coupled receptor GPR119 is largely restricted to insulin-producing β-cells of pancreatic islets. Additionally, we show here that GPR119 functions as a glucose-dependent insulinotropic receptor. Unlike receptors for GLP-1 and other peptides that mediate enhanced glucose-dependent insulin release, GPR119 was suitable for the development of potent, orally active, small-molecule agonists. The GPR119-specific agonist AR231453 significantly increased cAMP accumulation and insulin release in both HIT-T15 cells and rodent islets. In both cases, loss of GPR119 rendered AR231453 inactive. AR231453 also enhanced glucose-dependent insulin release in vivo and improved oral glucose tolerance in wild-type mice but not in GPR119-deficient mice. Diabetic KK/Ay mice were also highly responsive to AR231453. Orally active GPR119 agonists may offer significant promise as novel antihyperglycemic agents acting in a glucose-dependent fashion.
G protein-coupled receptor 119 (GPR119) is largely restricted to pancreatic insulin-producing β-cells and intestinal glucagon-like peptide-1-producing L-cells. Synthetic agonists of this receptor ...elicit glucose-dependent release of these endocrine factors, thereby enhancing glycemic control. Oleoylethanolamide also activates GPR119, but it remains unclear whether endogenous production of this lipid modulates GPR119 activity under normal or dysglycemic conditions. We show here that a relatively diverse set of lipid amides activate GPR119. Among these, the endovallinoid N-oleoyldopamine (OLDA) stimulated cAMP accumulation in GPR119-transfected cells as effectively as oleoylethanolamide and the previously described synthetic agonist AR231453. None of these lipid amides increased cAMP in control-transfected cells or in cells transfected with a number of other G protein-coupled receptors. OLDA stimulated both cAMP accumulation and insulin release in HIT-T15 cells, which express GPR119 endogenously, and in GPR119-transfected RIN-5F cells. Oral administration of OLDA to C57bl/6 mice elicited significant improvement in glucose tolerance, whereas GPR119-deficient mice were essentially unresponsive. OLDA also acutely elevated plasma gastric inhibitory peptide levels, a known hallmark of GPR119 activation. OLDA represents a possible paracrine modulator of GPR119 in pancreatic islets, where markers of dopamine synthesis correlated well with GPR119 expression. However, no such correlation was seen in the colon. Collectively, these studies indicate that multiple, distinct classes of lipid amides, acting via GPR119, may be important modulators of glucose homeostasis.
Structurally novel endogenous activators of GPR119 are identified, suggesting that diverse lipid amides may contribute to receptor activation in vivo.
The complete sequencing of the human genome has afforded researchers the opportunity to identify novel G-protein-coupled receptors (GPCRs) that are expressed in human tissues. The successful ...identification of hundreds of GPCRs represents the single greatest opportunity for novel drug development today. However, the lack of identified ligands for these GPCRs has limited their utility for traditional drug discovery approaches that focus on ligand-based assay methods to discover and pharmacologically characterize drug candidates. Here, we review the use of constitutively activated GPCRs in the discovery pathway, both as a means to overcome the limitations of traditional drug discovery at novel GPCRs and as a tool to investigate the functionality of these receptors.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Rationale
Synergistic or supra-additive interactions between the anorectics (dex)fenfluramine and phentermine have been reported previously in the rat and in the clinic. Studies with 5-HT
2C
...antagonists and 5-HT
2C
knockouts have demonstrated dexfenfluramine hypophagia in the rodent to be mediated by actions at the 5-HT
2C
receptor. Given the recent FDA approval of the selective 5-HT
2C
agonist lorcaserin (BELVIQ®) for weight management, we investigated the interaction between phentermine and 5-HT
2C
agonists on food intake.
Objectives
This study aims to confirm dexfenfluramine-phentermine (dex-phen) synergy in a rat food intake assay, to extend these findings to other 5-HT
2C
agonists, and to determine whether pharmacokinetic interactions could explain synergistic findings with particular drug combinations.
Methods
Isobolographic analyses were performed in which phentermine was paired with either dexfenfluramine, the 5-HT
2C
agonist AR630, or the 5-HT
2C
agonist lorcaserin, and inhibition of food intake measured in the rat. Subsequent studies assessed these same phentermine-drug pair combinations spanning both the full effect range and a range of fixed ratio drug combinations. Satellite groups received single doses of each drug either alone or in combination with phentermine, and free brain concentrations were measured.
Results
Dex-phen synergy was confirmed in the rat and extended to the 5-HT
2C
agonist AR630. In contrast, although some synergistic interactions between lorcaserin and phentermine were observed, these combinations were largely additive. Synergistic interactions between phentermine and dexfenfluramine or AR630 were accompanied by combination-induced increases in brain levels of phentermine.
Conclusions
Dex-phen synergy in the rat is caused by a pharmacokinetic interaction, resulting in increased central concentrations of phentermine.
Nicotinic acid remains the most effective therapeutic agent for the treatment and prevention of atherosclerosis resulting from low high density lipoprotein cholesterol. The therapeutic actions of ...nicotinic acid are mediated by GPR109A, a Gi protein-coupled receptor, expressed primarily on adipocytes, Langerhans cells, and macrophage. Unfortunately, a severe, cutaneous flushing side effect limits its use and patient compliance. The mechanism of high density lipoprotein elevation is not clearly established but assumed to be influenced by an inhibition of lipolysis in the adipose. The flushing side effect appears to be mediated by the release of prostaglandin D2 from Langerhans cells in the skin. We hypothesized that the signal transduction pathways mediating the anti-lipolytic and prostaglandin D2/flushing pathways are distinct and that agonists may be identified that are capable of selectively eliciting the therapeutic, anti-lipolytic pathway while avoiding the activation of the parallel flush-inducing pathway. We have identified a number of GPR109A pyrazole agonists that are capable of fully inhibiting lipolysis in vitro and in vivo and not only fail to elicit a flushing response but can antagonize the ability of nicotinic acid to elicit a flush response in vivo. In contrast to flushing agonists, exposure of cells expressing GPR109A to the non-flushing agonists fails to induce internalization of the receptor or to activate ERK 1/2 mitogen-activated protein kinase phosphorylation.
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