The early history of GIP 1969-2000: From enterogastrone to major metabolic hormone

This paper describes the early history of Gastric Inhibitory Polypeptide, better referred to simply as GIP, from its isolation by purification from a crude preparation of CCK-PZ (cholecystokinin/pancreozymin) to its recognition as a key play in the pathogenesis of obesity and other metabolic disorders far removed from the enterogastrone properties by which it was originally identified. Augmentation of glucose mediated insulin release, the incretin effect, was discovered soon after GIP was first isolated and only much later was its important role in the pathogenesis of obesity, through mechanism other than its insulin secretion, appreciated. Immunoassay - the method by which the concentration of GIP was measured in plasma until quite recently - was found to be flawed and to depend upon which specific epitope of the hormone an assay detected. This was especially true if it was an amino-acid sequence specific to porcine rather than human GIP. A further confounder was the discovery that much of the GIP measured by immunoassay was its biological antagonist produced by cleavage of its two N-terminal amino-acids in the circulation by the same dipeptidyl-peptidase as de-activates GLP-1. Potential use of synthetic agonistic and antagonistic GIP analogues in therapeutics was barely alluded to before year 2000.

Rationale, design, methods and baseline characteristics of the Asklepios Study

The Asklepios Study is a longitudinal population study focusing on the interplay between ageing, cardiovascular haemodynamics and inflammation in (preclinical) cardiovascular disease. The 2524 participants (1301 women) are a representative cohort of 35-55-year-old individuals, free from overt cardiovascular disease at study initiation, randomly sampled from the twinned Belgian communities of Erpe-Mere and Nieuwerkerken. Baseline examinations (all single-observer, single-device, single-site, single 2-year consecutive timeframe) include: questionnaires, conventional risk factors and biochemistry. Additional phenotypes under study include: (a) vascular structure and function: carotid and femoral atherosclerosis (intima-media thickness, plaque), arterial distension and pressure curves (brachial, carotid, femoral; wall-tracking and applanation tonometry); (b) cardiac structure and function. A novel aspect of the study is 'integrated' non-invasive biomechanical assessment of cardiac, arterial and ventriculovascular function through a combination of modeling, fundamental hydraulical measurements and system identification techniques. Integrated phenotypes result from combining at least two sets of curves (flow/pressure/distension). The value of this 'integrated' haemodynamic phenotype in the detection, prediction and prevention of clinical cardiovascular pathology (atherosclerosis progression, atherothrombosis, development of heart failure) will be tested. A second novel aspect is the systematic determination of peripheral blood leukocyte telomere length as a marker for biological ageing. During follow-up, baseline examinations will be repeated and the incidence of cardiovascular events will be monitored. Sex-specific baseline risk factor and biochemical data are provided in the current analyses. The primary aim is to build a combined dataset that will act as a tool to answer a cluster of questions about ageing, haemodynamics and the emergence of cardiovascular disease, especially the incidence of atherothrombotic events and the development of adverse haemodynamic profiles (arterial stiffening, heart failure). The study will reassess current risk factors and provide a long-term base for the detection of novel (epi)genetic and non-genetic risk factors and for more performant risk stratification modalities. Within these broader goals, a constant will be to strive towards more fundamental mechanistic-haemodynamic insights into cardiovascular disease processes.

Potential effect of chronic Helicobacter pylori infection on glucose metabolism of Mongolian gerbils

AIM: To assess the effect of Helicobacter pylori (H. pylori) infection on metabolic parameters in Mongolian gerbils.

METHODS: A total of 40 male, 5- to 8-wk-old, specific-pathogen-free Mongolian gerbils (30-50 g) were randomly allocated into two groups: a control group (n = 20) and an H. pylori group (n = 20). After a two-week acclimation period, the control group was administered Brucella broth and the H. pylori group was challenged intra-gastrically five times every other day with approximately 10⁹/CFU H. pylori ATCC43504 (CagA+, VacA+). Each group was then divided into two subgroups, which were sacrificed at either 6 or 12 mo. The control and H. pylori subgroups each contained 10 Mongolian gerbils. Body weight, abdominal circumference, and body length were measured, and body mass index (BMI) and Lee’s index were calculated. Biochemical assays were used to detect serum indexes, including glucose, glycated hemoglobin (GHb), glycated hemoglobin A1c (HbA1c), triacylglycerol, and total cholesterol, using an automatic biochemistry analyzer. Inflammatory cytokines, including interleukin (IL)-1β, IL-2, IL-4, IL-10, IL-12, tumor necrosis factor-α (TNF-α) and interferon (IFN)-γ, were assayed using ELISA. The expression of insulin and insulin-like growth factor 1 (IGF-1) was detected by immunohistochemistry, and islet apoptosis was measured using the terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay.

RESULTS: At each time point, body weight, abdominal circumference, BMI, and Lee’s index were increased after H. pylori infection. However, these differences were not significant. H. pylori infection significantly increased the GHb (5.45 ± 0.53 vs 4.98 ± 0.22, P < 0.05) and HbA1c (4.91 ± 0.61 vs 4.61 ± 0.15, P < 0.05) levels at 12 mo. We observed no significant differences in serum biochemical indexes, including fasting blood glucose, triacylglycerol and total cholesterol, at 6 or 12 mo after infection. H. pylori infection significantly increased the expression of IGF-1 (P < 0.05). Insulin levels from the pancreas and the apoptotic rate of islet β-cells remained unchanged. Also, we observed no significant differences among cytokines levels, including IL-1β, IL-2, IL-4, IL-10, IL-12, TNF-α and IFN-γ. IL-4 was the only exception, which increased at 6 (44.36 ± 25.17 vs 17.38 ± 3.47, P < 0.05) and 12 mo (33.41 ± 10.00 vs 18.91 ± 5.31, P < 0.05) after H. pylori infection.

CONCLUSION: Long-term H. pylori infection is significantly associated with high levels of HbA1c in Mongolian gerbils, indicating a potential role of H. pylori infection in glucose dysregulation.

Loss of CD24 in Mice Leads to Metabolic Dysfunctions and a Reduction in White Adipocyte Tissue

CD24 is a glycophosphatidylinositol (GPI)-linked cell surface receptor that is involved in regulating the survival or differentiation of several different cell types. CD24 has been used to identify pre-adipocytes that are able to reconstitute white adipose tissue (WAT) in vivo. Moreover, we recently found that the dynamic upregulation of CD24 in vitro during early phases of adipogenesis is necessary for mature adipocyte development. To determine the role of CD24 in adipocyte development in vivo, we evaluated the development of the inguinal and interscapular subcutaneous WAT and the epididymal visceral WAT in mice with a homozygous deletion of CD24 (CD24KO). We observed a significant decrease in WAT mass of 40% to 74% in WAT mass from both visceral and subcutaneous depots in male mice, with no significant effect in female mice, compared to wild-type (WT) sex- and age-matched controls. We also found that CD24KO mice had increased fasting glucose and free fatty acids, decreased fasting insulin, and plasma leptin. No major differences were observed in the sensitivity to insulin or glucose, or in circulating triglycerides, total cholesterol, HDL-cholesterol, or LDL-cholesterol levels between WT and CD24KO mice. Challenging the CD24KO mice with either high sucrose (35%) or high fat (45%) diets that promote increased adiposity, increased WAT mass and fasting insulin, adiponectin and leptin levels, as well as reduced the sensitivity to insulin and glucose, to the levels of WT mice on the same diets. The CD24-mediated reduction in fat pad size was due to a reduction in adipocyte cell size in all depots with no significant reduction pre-adipocyte or adipocyte cell number. Thus, we have clearly demonstrated that the global absence of CD24 affects adipocyte cell size in vivo in a sex- and diet-dependent manner, as well as causing metabolic disturbances in glucose homeostasis and free fatty acid levels.

Synthesis, characterization, and preclinical evaluation of new thiazolidin-4-ones substituted with p-chlorophenoxy acetic acid and clofibric acid against insulin resistance and metabolic disorder

We synthesized twenty thiazolidin-4-one derivatives, which were then characterized by standard chromatographic and spectroscopic methods. From the in vitro glucose uptake assay, two compounds behaved as insulin sensitizers, where they enhanced glucose uptake in isolated rat diaphragm. In high-carbohydrate diet-induced insulin resistant mice, these two thiazolidin-4-ones attenuated hyperglycemia, hyperinsulinemia, hypertriglyceridemia, hypercholesterolemia, and glucose intolerance. They raised the plasma leptin but did not reverse the diabetes-induced hypoadiponectinemia. Additionally, compound 3a reduced adiposity. The test compounds were also able to reverse the disturbed liver antioxidant milieu. To conclude, these two novel thiazolidin-4-ones modulated multiple mechanisms involved in metabolic disorders, reversing insulin resistance and thus preventing the development of type-2 diabetes.

Chronic inflammation exacerbates glucose metabolism disorders in C57BL/6J mice fed with high-fat diet

Inflammatory stress is closely related to metabolic disease and insulin resistance. The precise cellular mechanism linking obesity and diabetes is largely unknown, but about 14-20% of obese individuals develop diabetes. In this study, we investigated whether chronic inflammation exacerbated glucose metabolism disorder by impairing β cell function in high-fat diet (HFD)-fed C57BL/6J mice. We used s.c. casein injection to induce chronic inflammation in HFD-fed C57BL/6J mice; 14 weeks on a HFD resulted in weight gain, hyperlipidemia, and low insulin sensitivity in these mice which nevertheless had normal blood glucose and serum inflammatory cytokines levels. Casein injection in the background of HFD elevated serum tumor necrosis factor α (TNFα) and serum amyloid A levels and increased TNFα and MCP1 expression in the adipose tissue, liver, and muscle of HFD-fed mice. Chronic inflammation induced by casein injection further decreased insulin sensitivity and insulin signaling, resulting in insulin deficiency and hyperglycemia in these mice. Islet mass and insulin content were markedly increased in HFD mice. However, in contrast with HFD-fed alone, chronic inflammation in HFD-fed mice decreased both islet mass and insulin content, reduced the genetic expression of insulin synthesis and secretion, and increased β cell apoptosis. We conclude that chronic inflammation exacerbated glucose metabolism disorders by impairing β cell function in HFD-fed C57BL/6J mice, suggesting that this mechanism may operate in obese individuals with chronic inflammation, making them prone to hyperglycemia.

Circulating endothelial progenitor cells in women with gestational alterations of glucose tolerance

Endothelial progenitor cells (EPCs) play a role in angiogenesis during pregnancy. The aim of this study was to evaluate circulating EPCs in pregnant women with gestational alterations of glucose tolerance. Glucose tolerance, insulin sensitivity and β-cell function were derived from oral glucose tolerance tests in 23 women with normal glucose tolerance (NGT), 18 with gestational impaired glucose tolerance (GIGT) and 24 with gestational diabetes mellitus (GDM). Circulating cells expressing CD34 in combination with CD133, kinase insert domain receptor (KDR) or both were quantified by flow cytometry. Women with GIGT and GDM had lower CD34(+)KDR(+) and CD34(+)CD133( +)KDR(+) cells at 27±3.2 weeks' gestation compared with NGT (ANOVA p<0.02 for both). CD34(+)KDR(+) and CD34(+)CD133(+)KDR(+) cells were inversely correlated with the area-under-the-glucose-curve (p<0.005, for both) and positively to insulin secretion-sensitivity index (p<0.05, for both). Alterations of glucose tolerance during pregnancy are associated with a decrease in EPCs. Hyperglycaemia might exert a direct effect on depletion of EPCs.

Ketone bodies as a therapeutic for Alzheimer's disease

An early feature of Alzheimer's disease (AD) is region-specific declines in brain glucose metabolism. Unlike other tissues in the body, the brain does not efficiently metabolize fats; hence the adult human brain relies almost exclusively on glucose as an energy substrate. Therefore, inhibition of glucose metabolism can have profound effects on brain function. The hypometabolism seen in AD has recently attracted attention as a possible target for intervention in the disease process. One promising approach is to supplement the normal glucose supply of the brain with ketone bodies (KB), which include acetoacetate, beta-hydroxybutyrate, and acetone. KB are normally produced from fat stores when glucose supplies are limited, such as during prolonged fasting. KB have been induced both by direct infusion and by the administration of a high-fat, low-carbohydrate, low-protein, ketogenic diets. Both approaches have demonstrated efficacy in animal models of neurodegenerative disorders and in human clinical trials, including AD trials. Much of the benefit of KB can be attributed to their ability to increase mitochondrial efficiency and supplement the brain's normal reliance on glucose. Research into the therapeutic potential of KB and ketosis represents a promising new area of AD research.

Effect of glucometabolic disorders on the formation of coronary collaterals in occlusive coronary artery disease

OBJECTIVE

The primary aim of this study was to assess the effect of glucometabolic disorders on coronary collateral vessels in patients with occlusive coronary artery disease.

METHODS AND RESULTS

Hundred and ninety-five consecutive patients with at least single-vessel occlusion were enrolled in this study prospectively. The standard oral glucose tolerance test was performed according to the criteria of the World Health Organization. Collateral circulation was graded according to the Rentrop classification. The mean Rentrop scores in normal glucose tolerance (NGT), impaired glucose tolerance (IGT), and diabetes were 1.40 +/- 1.02, 1.05 +/- 0.84, 1.00 +/- 0.98, respectively (P = 0.043). The percentage of patients without collateral circulation (Rentrop-0) was greatest in the diabetic group (44.4%), while the percentage was 21.8% in the IGT group and 22.0% in the NGT group. Ninety-five patients with at least one totally occluded coronary artery were analysed as a subgroup. In the totally occluded artery subgroup postprandial glycaemia was the only parameter that was associated with the Rentrop score in the univariate analysis (r = -0.34, P = 0.002)

CONCLUSIONS

In conclusion, our study results, which are in agreement with previous results, indicate that not only diabetic glucose tolerance but also impaired glucose tolerance has an adverse impact on the development of coronary collaterals.

Adiponectin resistance exacerbates insulin resistance in insulin receptor transgenic/knockout mice

OBJECTIVE

Adiponectin increases insulin sensitivity and contributes to insulin's indirect effects on hepatic glucose production.

RESEARCH DESIGN AND METHODS

To examine adiponectin's contribution to insulin action, we analyzed adiponectin levels and activation of AMP-activated protein kinase (AMPK) in insulin receptor transgenic/knockout mice (L1), a genetic model of resistance to insulin's indirect effects on hepatic glucose production.

RESULTS

In euglycemic, insulin-resistant L1 mice, we detected hyperadiponectinemia with normal levels of adiponectin receptor-1 and -2. Moreover, adiponectin administration is unable to lower glucose levels or induce activation of AMPK, consistent with a state of adiponectin resistance. In a subset of hyperglycemic L1 mice, we observed decreased mRNA expression of AdipoR2 in liver and muscle, as well as decreased peroxisome proliferator-activated receptor (PPAR)alpha target gene expression in liver, raising the possibility that deterioration of adiponectin/AdipoR2 signaling via PPARalpha activation contributes to the progression from compensated insulin resistance to diabetes. In contrast, we failed to detect changes in other markers of the systemic or local inflammatory response.

CONCLUSIONS

These data provide evidence for a mechanism of adiponectin resistance and corroborate the notion that adiponectin potentiates hepatic insulin sensitivity.

Glucokinase Thermolability and Hepatic Regulatory Protein Binding Are Essential Factors for Predicting the Blood Glucose Phenotype of Missense Mutations

To better understand how glucokinase (GK) missense mutations associated with human glycemic diseases perturb glucose homeostasis, we generated and characterized mice with either an activating (A456V) or inactivating (K414E) mutation in the gk gene. Animals with these mutations exhibited alterations in their blood glucose concentration that were inversely related to the relative activity index of GK. Moreover, the threshold for glucose-stimulated insulin secretion from islets with either the activating or inactivating mutation were left- or right-shifted, respectively. However, we were surprised to find that mice with the activating mutation had markedly reduced amounts of hepatic GK activity. Further studies of bacterially expressed mutant enzymes revealed that GK(A456V) is as stable as the wild type enzyme, whereas GK(K414E) is thermolabile. However, the ability of GK regulatory protein to inhibit GK(A456V) was found to be less than that of the wild type enzyme, a finding consistent with impaired hepatic nuclear localization. Taken together, this study indicates that it is necessary to have knowledge of both thermolability and the interactions of mutant GK enzymes with GK regulatory protein when attempting to predict in vivo glycemic phenotypes based on the measurement of enzyme kinetics.