Incretin hormone receptors are required for normal beta cell development and function in female mice

The incretin hormones, glucose dependent insulinotropic polypeptide (GIP) and glucagon-like peptide 1 (GLP-1), potentiate insulin secretion and are responsible for the majority of insulin secretion that occurs after a meal. They may also, however, have a fundamental role in pancreatic beta cell development and function, independently of their role in potentiating insulin secretion after a meal. This has led to observations that a loss of GIP or GLP-1 action affects normal beta cell function, however each one of the incretin hormones may compensate when the action of the other is lost and therefore the overall impact of the incretin hormones on beta cell function is not known. We therefore utilized a mouse line deficient in both the GLP-1 and GIP receptor genes, the double incretin receptor knockout (DIRKO), to determine the consequences of a lifelong, complete lack of incretin hormone action on beta cell function, in vivo, in intact animals. We found that DIRKO mice displayed impaired glucose tolerance and insulin secretion in response to both oral glucose and mixed meal tolerance tests compared to wild-type mice. Assessment of beta cell function using the hyperglycemic clamp technique revealed an 80% decrease in first phase insulin response in DIRKO mice, but a normal second phase insulin secretion. A similar decline was seen when wild-type mice were given acute intravenous injection of glucose together with the GLP-1 receptor antagonist Ex9-39. Ex vivo assessments of the pancreas revealed significantly fewer islets in the pancreata of DIRKO mice despite no differences in total pancreatic mass. Insulin secretion from isolated islets of DIRKO mice was impaired to a similar extent to that seen during the hyperglycemic clamp. Insulin secretion in wild-type islets was impaired by acute treatment with Ex9-39 to a similar extent as the in vivo intravenous glucose tolerance tests. In conclusion, a loss of the action of both incretin hormones results in direct impairment of beta cell function both in vivo and in vitro in a process that appears to be independent of the intestinally secreted incretin hormones. We therefore conclude that the incretin hormones together significantly impact both beta-cell function and beta-cell development.     

Mapping interactions of gastric inhibitory polypeptide with GIPR N‐terminus using NMR and molecular dynamics simulations

Glucose‐dependent insulinotropic polypeptide (gastric inhibitory polypeptide, or GIP), a 42‐amino acid incretin hormone, modulates insulin secretion in a glucose‐concentration‐dependent manner. Its insulinotropic action is highly dependent on glucose concentration that surmounts the hypoglycemia side effects associated with current therapy. In order to develop a GIP‐based anti‐diabetic therapy, it is essential to establish the 3D structure of the peptide and study its interaction with the GIP receptor (GIPR) in detail. This will give an insight into the GIP‐mediated insulin release process. In this article, we report the solution structure of GIP(1–42, human)NH₂ deduced by NMR and the interaction of the peptide with the N‐terminus of GIPR using molecular modelling methods. The structure of GIP(1–42, human)NH₂ in H₂O has been investigated using 2D‐NMR (DQF‐COSY, TOCSY, NOESY, ¹H‐¹³C HSQC) experiments, and its conformation was built by constrained MD simulations with the NMR data as constraints. The peptide in H₂O exhibits an α‐helical structure between residues Ser8 and Asn39 with some discontinuity at residues Gln29 to Asp35; the helix is bent at Gln29. This bent gives the peptide an ‘L’ shape that becomes more pronounced upon binding to the receptor. The interaction of GIP with the N‐terminus of GIPR was modelled by allowing GIP to interact with the N‐terminus of GIPR under a series of decreasing constraints in a molecular dynamics simulation, culminating with energy minimization without application of any constraints on the system. The canonical ensemble obtained from the simulation was subjected to a detailed energy analysis to identify the peptide–protein interaction patterns at the individual residue level. These interaction energies shed some light on the binding of GIP with the GIPR N‐terminus in a quantitative manner. Copyright © 2010 European Peptide Society and John Wiley & Sons, Ltd.     

Gastric inhibitory polypeptide modulates adiposity and fat oxidation under diminished insulin action

Gut hormone gastric inhibitory polypeptide (GIP) stimulates insulin secretion from pancreatic β-cells upon ingestion of nutrients. Inhibition of GIP signaling prevents the onset of obesity and consequent insulin resistance induced by high-fat diet. In this study, we investigated the role of GIP in accumulation of triglycerides into adipocytes and in fat oxidation peripherally using insulin receptor substrate (IRS)-1-deficient mice and revealed that IRS-1^−/−GIPR^−/− mice exhibited both reduced adiposity and ameliorated insulin resistance. Furthermore, increased gene expression of CD36 and UCP2 in liver, and increased expression and enzyme activity of 3-hydroxyacyl-CoA dehydrogenase in skeletal muscle of IRS-1^−/−GIPR^−/− mice might contribute to the lower respiratory quotient and the higher fat oxidation in light phase. These results suggest that GIP plays a crucial role in switching from fat oxidation to fat accumulation under the diminished insulin action as a potential target for secondary prevention of insulin resistance.     

Characterization of the cellular and metabolic effects of a novel enzyme-resistant antagonist of glucose-dependent insulinotropic polypeptide

A novel N-terminally substituted Pro(3) analogue of glucose-dependent insulinotropic polypeptide (GIP) was synthesized and tested for plasma stability and biological activity both in vitro and in vivo. Native GIP was rapidly degraded by human plasma with only 39 +/- 6% remaining intact after 8 h, whereas (Pro(3))GIP was completely stable even after 24 h. In CHL cells expressing the human GIP receptor, (Pro(3))GIP antagonized the cyclic adenosine monophosphate (cAMP) stimulatory ability of 10(-7) M native GIP, with an IC(50) value of 2.6 microM. In the clonal pancreatic beta cell line BRIN-BD11, (Pro(3))GIP over the concentration range 10(-13) to 10(-8) M dose dependently inhibited GIP-stimulated (10(-7) M) insulin release (1.2- to 1.7-fold; P < 0.05 to P < 0.001). In obese diabetic (ob/ob) mice, intraperitoneal administration of (Pro(3))GIP (25 nmol/kg body wt) countered the ability of native GIP to stimulate plasma insulin (2.4-fold decrease; P < 0.001) and lower the glycemic excursion (1.5-fold decrease; P < 0.001) induced by a glucose load (18 mmol/kg body wt). Collectively these data demonstrate that (Pro(3))GIP is a novel and potent enzyme-resistant GIP receptor antagonist capable of blocking the ability of native GIP to increase cAMP, stimulate insulin secretion, and improve glucose homeostasis in a commonly employed animal model of type 2 diabetes.     

Xenin-25 Potentiates Glucose-dependent Insulinotropic Polypeptide Action via a Novel Cholinergic Relay Mechanism

The intestinal peptides GLP-1 and GIP potentiate glucose-mediated insulin release. Agents that increase GLP-1 action are effective therapies in type 2 diabetes mellitus (T2DM). However, GIP action is blunted in T2DM, and GIP-based therapies have not been developed. Thus, it is important to increase our understanding of the mechanisms of GIP action. We developed mice lacking GIP-producing K cells. Like humans with T2DM, “GIP/DT” animals exhibited a normal insulin secretory response to exogenous GLP-1 but a blunted response to GIP. Pharmacologic doses of xenin-25, another peptide produced by K cells, restored the GIP-mediated insulin secretory response and reduced hyperglycemia in GIP/DT mice. Xenin-25 alone had no effect. Studies with islets, insulin-producing cell lines, and perfused pancreata indicated xenin-25 does not enhance GIP-mediated insulin release by acting directly on the β-cell. The in vivo effects of xenin-25 to potentiate insulin release were inhibited by atropine sulfate and atropine methyl bromide but not by hexamethonium. Consistent with this, carbachol potentiated GIP-mediated insulin release from in situ perfused pancreata of GIP/DT mice. In vivo, xenin-25 did not activate c-fos expression in the hind brain or paraventricular nucleus of the hypothalamus indicating that central nervous system activation is not required. These data suggest that xenin-25 potentiates GIP-mediated insulin release by activating non-ganglionic cholinergic neurons that innervate the islets, presumably part of an enteric-neuronal-pancreatic pathway. Xenin-25, or molecules that increase acetylcholine receptor signaling in β-cells, may represent a novel approach to overcome GIP resistance and therefore treat humans with T2DM.     

Characterization and biological actions of N-terminal truncated forms of glucose-dependent insulinotropic polypeptide

The N-terminal domain of glucose-dependent insulinotropic polypeptide (GIP) plays an important role in regulating biological activity. This study examined biological properties of several N-terminal truncated forms of GIP and two novel forms with substitutions at Phe position-6 with Arg or Val. GIP(6-42), GIP(R6-42), GIP(V6-42), GIP(7-42) and GIP(9-42) stimulated cAMP production in BRIN-BD11 cells similar to native GIP, whereas responses to GIP(3-42), GIP(4-42), GIP(5-42) and GIP(8-42) were reduced (P < 0.01 to P < 0.001). GIP-induced cyclic AMP production was significantly inhibited by GIP(3-42), GIP(4-42), GIP(5-42), GIP(6-42), GIP(R6-42), GIP(7-42) and GIP(8-42) (P < 0.001). Compared with native GIP, in vitro insulinotropic activity of GIP(3-42), GIP(4-42), GIP(5-42), GIP(7-42) and GIP(8-42) was reduced (P < 0.05 to P < 0.001), with GIP(4-42), GIP(5-42), GIP(7-42) and GIP(8-42) also potently inhibiting GIP-stimulated insulin secretion (P < 0.001). In ob/ob mice, GIP(4-42) and GIP(8-42) increased (P < 0.05 to P < 0.01) plasma glucose concentrations compared to the glucose-lowering action of native GIP. When GIP(8-42) was co-administered with native GIP it countered the ability of the native peptide to lower plasma glucose and increase circulating insulin concentrations. These data confirm the importance of the N-terminal region of GIP in regulating bioactivity and reveal that sequential truncation of the peptide yields novel GIP receptor antagonists which may have functional significance.     

Actions of incretin metabolites on locomotor activity,cognitive function and in vivo hippocampal synaptic plasticity in high fat fed mice

The incretin hormones glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) improve markers of cognitive function in obesity–diabetes, however, both are rapidly degraded to their major metabolites, GLP-1(9-36)amide and GIP(3-42), respectively. Therefore, the present study investigated effects of GLP-1(9-36)amide and GIP(3-42) on locomotor activity, cognitive function and hippocampal synaptic plasticity in mice with diet-induced obesity and insulin resistance. High-fat fed Swiss TO mice treated with GLP-1(9-36)amide, GIP(3-42) or exendin(9-39)amide (twice-daily for 60 days) did not exhibit any changes in bodyweight, non-fasting plasma glucose and plasma insulin concentrations or glucose tolerance compared with high-fat saline controls. Similarly, locomotor and feeding activity, O₂ consumption, CO₂ production, respiratory exchange ratio and energy expenditure were not altered by chronic treatment with incretin metabolites. Administration of the truncated metabolites did not alter general behavior in an open field test or learning and memory ability as recorded during an object recognition test. High-fat mice exhibited a significant impairment in hippocampal long-term potentiation (LTP) which was not affected by treatment with incretin metabolites. These data indicate that incretin metabolites do not influence locomotor activity, cognitive function and hippocampal synaptic plasticity when administered at pharmacological doses to mice fed a high-fat diet.     

Characterisation and biological activity of Glu3 amino acid substituted GIP receptor antagonists

Glucose-dependent insulinotropic polypeptide (GIP) is an important gastrointestinal hormone, which regulates insulin release and glucose homeostasis, but is rapidly inactivated by enzymatic N-terminal truncation. Here we report the enzyme resistance and biological activity of several Glu(3)-substituted analogues of GIP namely; (Ala(3))GIP, (Lys(3))GIP, (Phe(3))GIP, (Trp(3))GIP and (Tyr(3))GIP. Only (Lys(3))GIP demonstrated moderately enhanced resistance to DPP-IV (p<0.05 to p<0.01) compared to native GIP. All analogues demonstrated a decreased potency in cAMP production (EC(50) 1.47 to 11.02 nM; p<0.01 to p<0.001) with (Lys(3))GIP and (Phe(3))GIP significantly inhibiting GIP-stimulated cAMP production (p<0.05). In BRIN-BD11 cells, (Lys(3))GIP, (Phe(3))GIP, (Trp(3))GIP and (Tyr(3))GIP did not stimulate insulin secretion with both (Lys(3))GIP and (Phe(3))GIP significantly inhibiting GIP-stimulated insulin secretion (p<0.05). Injection of each GIP analogue together with glucose in ob/ob mice significantly increased the glycaemic excursion compared to control (p<0.05 to p<0.001). This was associated with lack of significant insulin responses. (Ala(3))GIP, (Phe(3))GIP and (Tyr(3))GIP, when administered together with GIP, significantly reduced plasma insulin (p<0.05 to p<0.01) and impaired the glucose-lowering ability (p<0.05 to p<0.01) of the native peptide. The DPP-IV resistance and GIP antagonism observed were similar but less pronounced than (Pro(3))GIP. These data demonstrate that position 3 amino acid substitution of GIP with (Ala(3)), (Phe(3)), (Tyr(3)) or (Pro(3)) provides a new class of functional GIP receptor antagonists.     

Understanding interactions of gastric inhibitory polypeptide (GIP) with its G-protein coupled receptor through NMR and molecular modeling.

Gastric inhibitory polypeptide (GIP, or glucose-dependent insulinotropic polypeptide) is a 42-amino acid incretin hormone moderating glucose-induced insulin secretion. Antidiabetic therapy based on GIP holds great promise because of the fact that its insulinotropic action is highly dependent on the level of glucose, overcoming the sideeffects of hypoglycemia associated with the current therapy of Type 2 diabetes. The truncated peptide, GIP(1-30)NH2, has the same activity as the full length native peptide. We have studied the structure of GIP(1-30)NH2 and built a model of its G-protein coupled receptor (GPCR). The structure of GIP(1-30)NH2 in DMSO-d6 and H2O has been studied using 2D NMR (total correlation spectroscopy (TOCSY), nuclear overhauser effect spectroscopy (NOESY), double quantum filtered-COSY (DQF-COSY), 13C-heteronuclear single quantum correlation (HSQC) experiments, and its conformation built by MD simulations with the NMR data as constraints. The peptide in DMSO-d6 exhibits an alpha-helix between residues Ile12 and Lys30 with a discontinuity at residues Gln19 and Gln20. In H2O, the alpha-helix starts at Ile7, breaks off at Gln19, and then continues right through to Lys30. GIP(1-30)NH2 has all the structural features of peptides belonging to family B1 GPCRs, which are characterized by a coil at the N-terminal and a long C-terminal alpha-helix with or without a break. A model of the seven transmembrane (TM) helices of the GIP receptor (GIPR) has been built on the principles of comparative protein modeling, using the crystal structure of bovine rhodopsin as a template. The N-terminal domain of GIPR has been constructed from the NMR structure of the N-terminal of corticoptropin releasing factor receptor (CRFR), a family B1 GCPR. The intra and extra cellular loops and the C-terminal have been modeled from fragments retrieved from the PDB. On the basis of the experimental data available for some members of family B1 GPCRs, four pairs of constraints between GIP(1-30)NH2 and its receptor were used in the FTDOCK program, to build the complete model of the GIP(1-30)NH2:GIPR complex. The model can rationalize the various experimental observations including the potency of the truncated GIP peptide. This work is the first complete model at the atomic level of GIP(1-30)NH2 and of the complex with its GPCR.     

The effect of gastric inhibitory polypeptide on intestinal glucose absorption and intestinal motility in mice

Gastric inhibitory polypeptide (GIP) is released from the small intestine upon meal ingestion and increases insulin secretion from pancreatic β cells. Although the GIP receptor is known to be expressed in small intestine, the effects of GIP in small intestine are not fully understood. This study was designed to clarify the effect of GIP on intestinal glucose absorption and intestinal motility. Intestinal glucose absorption in vivo was measured by single-pass perfusion method. Incorporation of [¹⁴C]-glucose into everted jejunal rings in vitro was used to evaluate the effect of GIP on sodium-glucose co-transporter (SGLT). Motility of small intestine was measured by intestinal transit after oral administration of a non-absorbed marker. Intraperitoneal administration of GIP inhibited glucose absorption in wild-type mice in a concentration-dependent manner, showing maximum decrease at the dosage of 50 nmol/kg body weight. In glucagon-like-peptide-1 (GLP-1) receptor-deficient mice, GIP inhibited glucose absorption as in wild-type mice. In vitro examination of [¹⁴C]-glucose uptake revealed that 100 nM GIP did not change SGLT-dependent glucose uptake in wild-type mice. After intraperitoneal administration of GIP (50 nmol/kg body weight), small intestinal transit was inhibited to 40% in both wild-type and GLP-1 receptor-deficient mice. Furthermore, a somatostatin receptor antagonist, cyclosomatostatin, reduced the inhibitory effect of GIP on both intestinal transit and glucose absorption in wild-type mice. These results demonstrate that exogenous GIP inhibits intestinal glucose absorption by reducing intestinal motility through a somatostatin-mediated pathway rather than through a GLP-1-mediated pathway.     

Cyclic AMP production and insulin releasing activity of synthetic fragment peptides of glucose-dependent insulinotropic polypeptide

Synthetic fragment peptides of glucose-dependent insulinotropic polypeptide (GIP) were evaluated for their ability to elevate cellular cAMP production and stimulate insulin secretion. In GIP receptor transfected CHL cells, GIP(4–42) and GIP(17–30) dose-dependently inhibited GIP-stimulated cAMP production (40±8%; p<0.01 and 15±6%; p<0.05, respectively), while GIP(1–16) exerted very weak agonist effects on cAMP production. In the clonal pancreatic -cell line, BRIN-BD11, GIP(1–16) demonstrated weak insulin releasing activity compared with native GIP. In contrast, GIP(4–42) and GIP (17–30) weakly antagonized the insulin releasing activity of the native peptide (23±6%; p<0.05 and 11±3%, respectively). These data demonstrate the critical role of the N-terminus and the involvement of regions of the C-terminal domain in generating full biological potency of GIP.     

Two incretin hormones GLP-1 and GIP: comparison of their actions in insulin secretion and β cell preservation

Gastric inhibitory polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) are the two primary incretin hormones secreted from the intestine upon ingestion of glucose or nutrients to stimulate insulin secretion from pancreatic β cells. GIP and GLP-1 exert their effects by binding to their specific receptors, the GIP receptor (GIPR) and the GLP-1 receptor (GLP-1R), which belong to the G-protein coupled receptor family. Receptor binding activates and increases the level of intracellular cAMP in pancreatic β cells, thereby stimulating insulin secretion glucose-dependently. In addition to their insulinotropic effects, GIP and GLP-1 have been shown to preserve pancreatic β cell mass by inhibiting apoptosis of β cells and enhancing their proliferation. Due to such characteristics, incretin hormones have been gaining mush attention as attractive targets for treatment of type 2 diabetes, and indeed incretin-based therapeutics have been rapidly disseminated worldwide. However, despites of plethora of rigorous studies, molecular mechanisms underlying how GIPR and GLP-1R activation leads to enhancement of glucose-dependent insulin secretion are still largely unknown. Here, we summarize the similarities and differences of these two incretin hormones in secretion and metabolism, their insulinotropic actions and their effects on pancreatic β cell preservation. We then try to discuss potential of GLP-1 and GIP in treatment of type 2 diabetes.     

Human Gastric Inhibitory Polypeptide Receptor: Cloning of the Gene (GIPR) and cDNA

Gastric inhibitory polypeptide (GIP), which is released from the gastrointestinal tract, stimulates insulin secretion from pancreatic β cells and plays a crucial role in the regulation of insulin secretion during the postprandial phase. We have isolated the human gene (GIPR) and cDNA encoding the GIP receptor by a combination of the conventional screening and polymerase chain reaction procedures. Human GIP receptor cDNA encodes a protein of 466 amino acids that is 81.5 and 81.2% identical to the previously cloned hamster and rat GIP receptor, respectively. Hydropathic analysis shows the presence of a signal peptide and seven potential transmembrane domains, a feature characteristic of the VIP/glucagon/secretin receptor family of G protein-coupled receptors. The human GIPR gene is about 13.8 kb long, consists of 14 exons, and carries 17Alurepeats.     

A novel acylated form of (d-Ala)GIP with improved antidiabetic potential,lacking effect on body fat stores

Background

Rapid enzymatic degradation of the incretin hormone, glucose-dependent insulinotropic polypeptide (GIP), limits therapeutic use of the native peptide for diabetes. However, enzymatically stable analogues of GIP, such as (d-Ala²)GIP, have been generated, but are still susceptible to renal filtration.

Methods

The present study examines the in vitro and in vivo biological actions of a novel, acylated GIP analogue, (d-Ala²)GIP[Lys³⁷PAL].

Results

In BRIN-BD11 cells, (d-Ala²)GIP[Lys³⁷PAL] concentration-dependently stimulated (p < 0.05 to p < 0.001) insulin secretion at 5.6 and 16.7 mM glucose. Intraperitoneal administration of (d-Ala²)GIP[Lys³⁷PAL] to normal mice 8 h prior to a glucose load significantly reduced (p < 0.05) the overall glycaemic excursion compared to controls, and increased (p < 0.001) the insulinotropic response compared to (d-Ala²)GIP and saline treated high fat control mice. Once daily administration of (d-Ala²)GIP[Lys³⁷PAL] for 21 days in high fat fed mice did not affect energy intake, body weight or fat deposition. However, circulating blood glucose was significantly lower (p < 0.05) accompanied by increased (p < 0.05) insulin concentrations by day 21. In addition, (d-Ala²)GIP[Lys³⁷PAL] treatment significantly (p < 0.01) reduced the overall glycaemic excursion and increased pancreatic insulin content (p < 0.05) and the insulinotropic response (p < 0.01) to an exogenous glucose challenge on day 21. Chronic treatment with (d-Ala²)GIP[Lys³⁷PAL] did not result in resistance to the metabolic effects of a bolus injection of native GIP. Finally, insulin sensitivity was significantly improved (p < 0.001) in (d-Ala²)GIP[Lys³⁷PAL] treated mice compared to high fat controls.

Conclusions

These data confirm that (d-Ala²)GIP[Lys³⁷PAL] is a stable, long-acting potent GIP agonist.

General significance

(d-Ala²)GIP[Lys³⁷PAL] may be suitable for further evaluation and future clinical development.     

Naturally-occurring TGR5 agonists modulating glucagon-like peptide-1 biosynthesis and secretion

Selective GLP-1 secretagogues represent a novel potential therapy for type 2 diabetes mellitus. This study examined the GLP-1 secretory activity of the ethnomedicinal plant, Fagonia cretica, which is postulated to possess anti-diabetic activity. After extraction and fractionation extracts and purified compounds were tested for GLP-1 and GIP secretory activity in pGIP/neo STC-1 cells. Intracellular levels of incretin hormones and their gene expression were also determined. Crude F. cretica extracts stimulated both GLP-1 and GIP secretion, increased cellular hormone content, and upregulated gene expression of proglucagon, GIP and prohormone convertase. However, ethyl acetate partitioning significantly enriched GLP-1 secretory activity and this fraction underwent bioactivity-guided fractionation. Three isolated compounds were potent and selective GLP-1 secretagogues: quinovic acid (QA) and two QA derivatives, QA-3β-O-β-d-glycopyranoside and QA-3β-O-β-d-glucopyranosyl-(28 → 1)-β-d-glucopyranosyl ester. All QA compounds activated the TGR5 receptor and increased intracellular incretin levels and gene expression. QA derivatives were more potent GLP-1 secretagogues than QA. This is the first time that QA and its naturally-occurring derivatives have been shown to activate TGR5 and stimulate GLP-1 secretion. These data provide a plausible mechanism for the ethnomedicinal use of F. cretica and may assist in the ongoing development of selective GLP-1 agonists.     

Sub-chronic administration of stable GIP analog in mice decreases serum LPL activity and body weight

GIP receptor knockout mice were shown to be protected from the development of obesity on a high fat diet, suggesting a role of GIP in the development of obesity. In our study we aimed to test the hypothesis if excess of GIP could accelerate development of obesity and to identify GIP gene targets in adipose tissue. Therefore, mice were kept on a chow or a high fat diet and during the last 2 weeks D-Ala²-GIP or PBS injections were performed. Afterwards, serum LPL activity and several biochemical parameters (TG, FFA, cholesterol, glucose, insulin, resistin, IL-6, IL-1β, TNFα, GIP) were measured. Fat tissue was isolated and QPCR was performed for a set of genes involved in energy metabolism and inflammation. A DNA-microarray was used to identify GIP gene targets in adipose tissue of the chow diet group. We found that the D-Ala²-GIP injections caused a significant decrease in both body weight and LPL activity compared to controls. Serum biochemical parameters were not affected by D-Ala²-GIP, with an exception for resistin and insulin. The set of inflammatory genes were significantly decreased in adipose tissue in the D-Ala²-GIP injected animals on a chow diet. A DNA-microarray revealed that APO-genes and CYP-genes were affected by D-Ala²-GIP treatment in adipose tissue. These results suggest that the body weight-reducing effect of D-Ala²-GIP may be explained by lower LPL activity and insulin serum level. Moreover, the identified GIP candidate gene targets in adipose tissue link GIP action to lipid metabolism exerted by APO and CYP genes.     

Radioactive gold cluster immunoconjugates: Potential agents for cancer therapy

An 11 gold atom (undecagold) cluster was covalently attached to specific sites on Fab′, F(ab′)₂ and whole IgG molecules such that each carried 11–33 gold atoms without significant loss of native immunospecificity. Gold cluster labeled 17-1A monoclonal F(ab′)₂ antibody fragments showed 80% immunoreactivity compared to native antibody fragments in binding to human colon carcinoma cells in vitro. Radioactive gold in vivo biodistributions in nude mice with human tumors are also reported. By using clusters, potentially a larger destructive payload can be carried per antibody.     

Comparison of independent and combined chronic metabolic effects of GIP and CB1 receptor blockade in high-fat fed mice

GIP receptor antagonism with (Pro³)GIP protects against obesity, insulin resistance, glucose intolerance and associated disturbances in mice fed high-fat diet. Furthermore, cannabinoid CB₁ receptor antagonism with AM251 reduces appetite and body weight gain in mice. The present study has examined and compared the effects of chronic daily administrations of (Pro³)GIP (25 nmol/kg body weight), AM251 (6 mg/kg body weight) and a combination of both drugs in high-fat fed mice. Daily i.p. injection of (Pro³)GIP, AM251 or combined drug administration over 22 days significantly (P < 0.05 to <0.01) decreased body weight compared with saline-treated controls. This was associated with a significant (P < 0.05 to <0.01) reduction of food intake in mice treated with AM251. Plasma glucose levels and glucose tolerance were significantly (P < 0.05) lowered by 22 days (Pro³)GIP, AM251 or combined drug treatment. These changes were accompanied by a significant (P < 0.05) improvement of insulin sensitivity in all treatment groups. In contrast, AM251 lacked effects on glucose tolerance, metabolic response to feeding and insulin sensitivity in high-fat mice when administered acutely. These data indicate that chemical blockade of GIP- or CB₁-receptor signaling using (Pro³)GIP or AM251, respectively provides an effective means of countering obesity and related abnormalities induced by consumption of high-fat energy-rich diet. AM251 lacks acute effects on glucose homeostasis and there was no evidence of a synergistic effect of combined treatment with (Pro³)GIP.     

Exercise prior to fat ingestion lowers fasting and postprandial VLDL and decreases adipose tissue IL-6 and GIP receptor mRNA in hypertriacylglycerolemic men

Fasting and postprandial triacylglycerol (TAG) concentrations are risk factors for cardiovascular disease. This study evaluated whether interleukin-6 (IL-6) and incretin hormones [gastric inhibitory peptide (GIP) and glucagon-like peptide-1 (GLP-1) (active)] were associated with fasting and postprandial TAG in response to an oral lipid load, including very-low-density lipoprotein (VLDL) and chylomicron (CM) TAG, following one bout of exercise in nine men (age, 59±2 years; body mass index, 34±2 kg/m²; waist circumference, 113±3 cm) with high fasting TAG (2.9±0.2 mmol/L). Subjects completed two oral fat tolerance tests (OFTTs), randomized 1 week apart, that consisted of 1g fat/kg body weight emulsified lipids in the absence of carbohydrate and protein. Approximately 16 h prior to one OFTT, subjects completed 60 min of treadmill walking (estimated 55% VO₂ peak; heart rate, 122±4 beats/min). No exercise was performed on the day before the other OFTT. Fasted (0 h) and postprandial (1, 2, 3, 4, 5 and 6 h) blood samples were taken for analysis of TAG, IL-6 and incretins. Subcutaneous adipose tissue biopsies were taken at 0 and 6 h after OFTT ingestion for IL-6 and GIP receptor (GIPr) mRNA quantification. Exercise lowered fasting and postprandial TAG (P<.05) and VLDL TAG (P<.05), while postprandial CM TAG were similar in both OFTT trials (P>.05). Fasting and postprandial plasma IL-6, GIP and GLP-1 did not differ between rest and exercise OFTT trials (P>.05). Exercise reduced IL-6 and GIPr mRNA (P<.05) in adipose tissue. Our results suggest that the reduction in VLDL TAG following an acute bout of exercise is not associated with circulating IL-6 or incretin concentrations, despite reductions in the adipose tissue expression of IL-6 and GIPr.