Effects of plant and animal high protein diets on immune-inflammatory biomarkers: A 6-week intervention trial.

BACKGROUND & AIMS: Pro-inflammatory biomarkers are well-established contributors to insulin resistance and represent valid targets for diabetes management and prevention. Yet, little is known whether nutrition could play a role in modulating various aspects of immune-inflammatory responses. Our aim is to assess the effect of isocaloric animal and plant protein dietary interventions on selected biomarkers representing various immune-inflammatory pathways. METHODS: We enrolled 37 participants with type 2 diabetes (age 64 ± 6 years, body mass index 30.2 ± 3.6 kg/m2, glycated hemoglobin 7.0 ± 0.6%) who underwent an either high-animal protein (AP) or high-plant protein (PP) diet (30 E% protein, 40 E% carbohydrates, 30 E% fat) for 6-weeks. Clinical examinations were performed at beginning and end of the study. Levels of pro-inflammatory adipokines [chemerin, progranulin], cytokines [tumor necrosis factor α (TNF-α), interleukin 6 (IL-6), soluble urokinase-type plasminogen activator receptor (suPAR), transforming growth factor beta 1 (TGF-ß1)], and proteins [calprotectin, lactoferrin and growth differentiation factor 15 (GDF-15)] were determined in blood serum using enzyme-linked immunosorbent assay. RESULTS: Chemerin and progranulin concentrations decreased following AP and PP diets. TGF-ß1 increased in AP and decreased in PP, whereas calprotectin increased in PP and decreased in AP. No statistically significant differences in the concentrations of IL-6, TNF-α, suPAR, lactoferrin and GDF-15 could be seen in either of the protein diet arms. CONCLUSIONS: These results suggest that both AP and PP diets may effectively reduce the levels of the pro-inflammatory adipokines chemerin and progranulin. The effects on the additional immune-inflammatory biomarkers seem to be more complex. CLINICAL TRIAL REGISTRY NUMBER: NCT02402985 (ww.clinicaltrials.gov).

Rate of appearance of amino acids after a meal regulates insulin and glucagon secretion in patients with type 2 diabetes: a randomized clinical trial.

Background: Meal composition regulates the postprandial response of pancreatic and gastrointestinal hormones and plays an important role in patients with type 2 diabetes (T2D). Proteins have glucagon and insulinotropic effects, which may differ depending on amino acid composition, form of intake, and rate of digestibility and absorption. Objective: The aim of this study was to test effects of isolated pea protein-based (PP) compared with casein protein-based (CP) meals differing in amino acid compositions on endocrine responses to meal tolerance tests (MTTs) in patients with T2D. Design: Thirty-seven individuals with T2D [mean ± SD age: 64 ± 6 y; mean ± SD body mass index (kg/m2): 30.2 ± 3.6; mean ± SD glycated hemoglobin: 7.0% ± 0.6%] were randomly assigned to receive either high-animal-protein (∼80% of total protein) or high-plant-protein (∼72% of total protein) diets (30% of energy from protein, 40% of energy from carbohydrate, 30% of energy from fat) for 6 wk. MTTs were performed at study onset and after 6 wk. Participants received standardized high-protein (30% of energy) meals 2 times/d containing either CP-rich (∼85% wt:wt) or PP-rich (∼95% wt:wt) foods. Results: The CP and PP meals produced differences in insulin, C-peptide, glucagon, and glucose-dependent insulinotropic peptide (GIP) release. Total areas under the curve after CP were significantly lower than after the PP lunch by 40% for insulin and 23% for glucagon. Indexes of insulin sensitivity and secretion were significantly improved for the second CP MTT. This was accompanied by differential rates of appearance of amino acids. The ingestion of PP resulted in significant increases in amino acids after both meals, with a decline between meals. By contrast, CP intake resulted in increases in most amino acids after breakfast, which remained elevated but did not increase further after lunch. Conclusions: PP elicits greater postprandial increases in glucagon than does CP and consequently requires higher insulin to control glucose metabolism, which appears to be related to the rate of amino acid appearance. The metabolic impact of protein quality could be used as a strategy to lower insulin needs in patients with T2D. This trial was registered at www.clinicaltrials.gov as NCT02402985.

The novel adipokine WISP1 associates with insulin resistance and impairs insulin action in human myotubes and mouse hepatocytes.

AIMS/HYPOTHESIS: Wingless-type (Wnt) inducible signalling pathway protein-1 (WISP1) has been recently identified as a proinflammatory adipokine. We examined whether WISP1 expression and circulating levels are altered in type 2 diabetes and whether WISP1 affects insulin signalling in muscle cells and hepatocytes. METHODS: Serum and visceral adipose tissue (VAT) biopsies, for analysis of circulating WISP1 levels by ELISA and WISP1 mRNA expression by real-time quantitative RT-PCR, were collected from normal-weight men (control group, n = 33) and obese men with (n = 46) and without type 2 diabetes (n = 56) undergoing surgery. Following incubation of primary human skeletal muscle cells (hSkMCs) and murine AML12 hepatocytes with WISP1 and insulin, insulin signalling was analysed by western blotting. The effect of WISP1 on insulin-stimulated glycogen synthesis and gluconeogenesis was investigated in hSkMCs and murine hepatocytes, respectively. RESULTS: Circulating WISP1 levels were higher in obese men (independent of diabetes status) than in normal-weight men (mean [95% CI]: 70.8 [55.2, 86.4] ng/l vs 42.6 [28.5, 56.6] ng/l, respectively; p < 0.05). VAT WISP1 expression was 1.9-fold higher in obese men vs normal-weight men (p < 0.05). Circulating WISP1 levels were positively associated with blood glucose in the OGTT and circulating haem oxygenase-1 and negatively associated with adiponectin levels. In hSkMCs and AML12 hepatocytes, recombinant WISP1 impaired insulin action by inhibiting phosphorylation of insulin receptor, Akt and its substrates glycogen synthase kinase 3ß, FOXO1 and p70S6 kinase, and inhibiting insulin-stimulated glycogen synthesis and suppression of gluconeogenic genes. CONCLUSIONS/INTERPRETATION: Circulating WISP1 levels and WISP1 expression in VAT are increased in obesity independent of glycaemic status. Furthermore, WISP1 impaired insulin signalling in muscle and liver cells.

VEGF and GLUT1 are highly heritable, inversely correlated and affected by dietary fat intake: Consequences for cognitive function in humans.

OBJECTIVE: Reduction of brain glucose transporter GLUT1 results in severe neurological dysfunction. VEGF is required to restore and maintain brain glucose uptake across the blood brain barrier via GLUT1, which was shown to be acutely diminished in response to a high fat diet (HFD) in mice. The genetic and HFD-related regulation and association of VEGF and GLUT1 (SLC2A1) in humans was investigated in the NUtriGenomic Analysis in Twins (NUGAT) study. METHODS: 92 healthy and non-obese twins were standardized to a high-carbohydrate low-fat diet for 6 weeks before switched to a 6-week HFD under isocaloric conditions. Three clinical investigation days were conducted: after 6 weeks of low-fat diet and after 1 and 6 weeks of HFD. Serum VEGF and other cytokine levels were measured using ELISA. Gene expression in subcutaneous adipose tissue was assessed by quantitative Real-Time PCR. Genotyping was performed using microarray. The Auditory Verbal Learning Task was conducted to measure cognitive performance. RESULTS: In this human study, we showed that the environmental regulation of SLC2A1 expression and serum VEGF by HFD was inversely correlated and both factors showed strong heritability (>90%). In response to the HFD containing 45% fat, serum VEGF levels increased (P = 0.002) while SLC2A1 mRNA expression in adipose tissue decreased (P = 0.001). Higher BMI was additionally associated with lower SLC2A1 expression. AA-genotypes of the rs9472159 polymorphism, which explained ∼39% of the variation in circulating VEGF concentrations, showed significantly reduced serum VEGF levels (P = 6.4 × 10-11) but higher SLC2A1 expression (P = 0.009) in adipose tissue compared to CC/CA-genotypes after 6 weeks of HFD. Memory performance in AA-genotypes declined in response to the HFD compared to CC- and CA-genotypes. CONCLUSIONS: The results provide evidence to suggest the translatability of the dietary regulation of VEGF and GLUT1 from mouse models to humans. Our data demonstrate that HFD induces a genetically determined and correlated decrease of GLUT1 and increase of VEGF which may affect memory performance. CLINICAL TRIAL REGISTRATION NUMBER: NCT01631123.

Oral administration of nasturtium affects peptide YY secretion in male subjects.

SCOPE: Nasturtium plants contain the glucosinolate glucotropaeolin and its corresponding breakdown product benzyl isothiocyanate (BITC), the latter being intensively studied with regard to cancer chemoprevention and anti-inflammatory properties. In addition, recent research has shown that isothiocyanates are able to activate the release of several gut hormones in vitro and in rodent studies. Here, we tested the effects of a dietary nasturtium administration on circulating levels of gut hormones in humans. METHODS AND RESULTS: Metabolically healthy males (n = 15) received a single oral dose of 10 g freeze-dried nasturtium leaf material suspended in water or only water (control). Blood samples were taken every hour and serum concentrations of insulin, C-peptide, glucagon-like peptide 1 (GLP-1), glucose-dependent insulinotropic peptide (GIP), and peptide (PYY) were analyzed. Oral nasturtium intake resulted in an increased release of PYY over a time period of 6 h whereas circulating levels of other hormones were not changed. CONCLUSION: Given the finding that nasturtium consumption enhances secretion of PYY, a key hormone involved in energy regulation, special diets containing nasturtium, or supplementation with nasturtium or BITC might be considered in the treatment of obesity.

Modulation of circulating vasoactive peptides and extracellular matrix proteins are two novel mechanisms in the cardioprotective action of acarbose.

BACKGROUND: Acarbose, an alpha-glucosidase inhibitor, unexpectedly reduced the incidence of hypertension and cardiovascular endpoints in the STOP-NIDDM study. Based on the growing evidence of a link between vasoregulatory peptides and metabolic traits, we hypothesized that changes of the Glycemic Index by acarbose may modulate vasoregulatory peptide levels via regulation of postprandial metabolism. METHODS: Subjects with type 2 diabetes and with metabolic syndrome were treated with acarbose (12 weeks, 300mg/d) in a double-blind, placebo-controlled, cross-over intervention. Changes in fasting and postprandial levels of midregional pro-atrial natriuretic peptide (MR-proANP), C-terminal pro-endothelin-1 (CT-proET-1) and midregional pro-adrenomedullin (MR-proADM), WNT1 Inducible Signaling Pathway Protein 1 (WISP1) as well as fasting and postprandial glucose/insulin levels in the liquid meal test were assessed. RESULTS: Acarbose strongly decreased postprandial insulin concentrations in subjects with metabolic syndrome (P=0.004), and postprandial glucose excursions in both groups. Postprandial MR-proANP and CT-proET-1 levels increased after acarbose treatment (P<0.01 and P<0.05, respectively) in subjects with metabolic syndrome only. No effect of acarbose treatment on MR-prADM was observed in both groups. All three peptides were correlated with each over, but neither with insulin sensitivity in euglycemic clamps, nor with adiponectin levels. WISP1 decreased after acarbose treatment in subjects with metabolic syndrome. CONCLUSIONS: Plasma MR- proANP and CT-proET-1 concentrations, but not MR-prADM concentrations, were affected by treatment with acarbose over 12 weeks. Our findings provide new possible mechanisms of acarbose action in diabetes and metabolic syndrome.

Bioavailability and metabolism of benzyl glucosinolate in humans consuming Indian cress (Tropaeolum majus L.).

SCOPE: Benzyl isothiocyanate (BITC), which occurs in Brassicales, has demonstrated chemopreventive potency and cancer treatment properties in cell and animal studies. However, fate of BITC in human body is not comprehensively studied. Therefore, the present human intervention study investigates the metabolism of the glucosinolate (GSL) glucotropaeolin and its corresponding BITC metabolites. Analyzing BITC metabolites in plasma and urine should reveal insights about resorption, metabolism, and excretion. METHODS AND RESULTS: Fifteen healthy men were randomly recruited for a cross-over study and consumed 10 g freeze-dried Indian cress as a liquid preparation containing 1000 µmol glucotropaeolin. Blood and urine samples were taken at several time points and investigated by LC-ESI-MS/MS after sample preparation using SPE. Plasma contained high levels of BITC-glutathione (BITC-GSH), BITC-cysteinylglycine (BITC-CysGly), and BITC-N-acetyl-L-cysteine (BITC-NAC) 1-5 h after ingestion, with BITC-CysGly appearing as the main metabolite. Compared to human plasma, the main urinary metabolites were BITC-NAC and BITC-Cys, determined 4-6 h after ingestion. CONCLUSION: This study confirms that consumption of Indian cress increases the concentration of BITC metabolites in human plasma and urine. The outcome of this human intervention study supports clinical research dealing with GSL-containing innovative food products or pharmaceutical preparations.

Modulation of insulin degrading enzyme activity and liver cell proliferation.

Diabetes mellitus type 2 (T2DM), insulin therapy, and hyperinsulinemia are independent risk factors of liver cancer. Recently, the use of a novel inhibitor of insulin degrading enzyme (IDE) was proposed as a new therapeutic strategy in T2DM. However, IDE inhibition might stimulate liver cell proliferation via increased intracellular insulin concentration. The aim of this study was to characterize effects of inhibition of IDE activity in HepG2 hepatoma cells and to analyze liver specific expression of IDE in subjects with T2DM. HepG2 cells were treated with 10 nM insulin for 24 h with or without inhibition of IDE activity using IDE RNAi, and cell transcriptome and proliferation rate were analyzed. Human liver samples (n = 22) were used for the gene expression profiling by microarrays. In HepG2 cells, IDE knockdown changed expression of genes involved in cell cycle and apoptosis pathways. Proliferation rate was lower in IDE knockdown cells than in controls. Microarray analysis revealed the decrease of hepatic IDE expression in subjects with T2DM accompanied by the downregulation of the p53-dependent genes FAS and CCNG2, but not by the upregulation of proliferation markers MKI67, MCM2 and PCNA. Similar results were found in the liver microarray dataset from GEO Profiles database. In conclusion, IDE expression is decreased in liver of subjects with T2DM which is accompanied by the dysregulation of p53 pathway. Prolonged use of IDE inhibitors for T2DM treatment should be carefully tested in animal studies regarding its potential effect on hepatic tumorigenesis.

GIP increases adipose tissue expression and blood levels of MCP-1 in humans and links high energy diets to inflammation: a randomised trial.

AIMS/HYPOTHESIS: Obesity is associated with elevated monocyte chemoattractant protein-1 (MCP-1), a proinflammatory chemokine related to diabetes and cardiovascular disease. Since obesity is triggered by energy dense diets, we hypothesised that nutrient induced intestinal hormones such as glucose-dependent insulinotropic peptide (GIP) may directly stimulate the release of chemokines from adipose tissue and induce low-grade inflammation. METHODS: GIP effects on gene expression and secretion of inflammatory markers were studied by microarray analysis and PCR from human subcutaneous fat biopsies of slightly obese but healthy volunteers in the metabolic ward of German Institute of Human Nutrition, Department of Clinical Nutrition, Potsdam-Rehbrücke. To allocate the participants to the study arms they were numbered in order of their recruitment and then assigned to the groups by a random number generator. In a randomised, single-blind (participants) crossover design, the participants received GIP infusions in postprandial concentrations (2 pmol kg(-1) min(-1)) or saline (154 mmol/l NaCl) infusions for 240 min either alone, in combination with hyperinsulinaemic-euglycaemic (EU) or hyperinsulinaemic-hyperglycaemic (HC) clamps. Possible mechanisms of GIP effects were investigated in single and co-cultures of macrophage and adipocyte cell lines and in primary human monocytes, macrophages and adipocytes. RESULTS: A total of 17 participants were randomised to the following groups: EU with GIP infusion (n = 9); EU with NaCl infusion (n = 9); HC with GIP infusion (n = 8); HC with NaCl infusion (n = 8); sole GIP infusion (n = 11) and sole placebo infusion (n = 11). All 17 individuals were analysed. The study is completed. In human subcutaneous adipose tissue (hSCAT), infusions of GIP significantly increased inflammatory chemokine and cytokine gene networks in transcriptomic microarray analyses. Particularly MCP-1 (180 ± 26%), MCP-2 (246 ± 58%) and IL-6 (234 ± 40%) mRNA levels in adipose tissue as well as circulating plasma concentrations of MCP-1 (165 ± 12 vs 135 ± 13 pg/ml; GIP vs saline after 240 min; p < 0.05 for all variables) in humans increased independently of circulating insulin or glucose plasma concentrations. GIP stimulation increased Mcp-1 mRNA-expression in co-cultures of differentiated 3T3L1-adipocytes and RAW 264.7 macrophages but not in the isolated cell lines. Similarly, GIP increased MCP-1 transcripts in co-cultures of primary human macrophages with human adipocytes. GIP receptor (GIPR) transcripts were present in primary monocytes and the different cell lines and induced activation of extracellular related kinase (ERK) as well as increases in cAMP, indicating functional receptors. CONCLUSIONS/INTERPRETATION: Our findings suggest that the nutrient induced gut hormone GIP may initiate adipose tissue inflammation by triggering a crosstalk of adipocytes and macrophages involving MCP-1. TRIAL REGISTRATION: ClinicalTrials.gov NCT00774488. FUNDING: This work was supported by the German Research Foundation (DFG): grant No. Pf164/021002.

Regulation of nutrition-associated receptors in blood monocytes of normal weight and obese humans.

Obesity, type 2 diabetes and associated metabolic diseases are characterized by low-grade systemic inflammation which involves interplay of nutrition and monocyte/macrophage functions. We suggested that some factors such as nutrient components, neuropeptides involved in the control of gastrointestinal functions, and gastrointestinal hormones might influence immune cell functions and in this way contribute to the disease pathogenesis. The aim of this study was to investigate the mRNA expression of twelve nutrition-associated receptors in peripheral blood mononuclear cells (PBMC), isolated monocytes and monocyte-derived macrophages and their regulation under the switching from the high-carbohydrate low-fat diet to the low-carbohydrate high-fat (LC/HFD) isocaloric diet in healthy humans. The mRNA expression of receptors for short chain fatty acids (GPR41, GPR43), bile acids (TGR5), incretins (GIPR, GLP1R), cholecystokinin (CCKAR), neuropeptides VIP and PACAP (VIPR1, VIPR2), and neurotensin (NTSR1) was detected in PBMC and monocytes, while GPR41, GPR43, GIPR, TGR5, and VIPR1 were found in macrophages. Correlations of the receptor expression in monocytes with a range of metabolic and inflammatory markers were found. In non-obese subjects, the dietary switch to LC/HFD induced the increase of GPR43 and VIPR1 expression in monocytes. No significant differences of receptor expression between normal weight and moderately obese subjects were found. Our study characterized for the first time the expression pattern of nutrition-associated receptors in human blood monocytes and its dietary-induced changes linking metabolic responses to nutrition with immune functions in health and metabolic diseases.

WISP1 is a novel adipokine linked to inflammation in obesity.

WISP1 (Wnt1-inducible signaling pathway protein-1, also known as CCN4) is a member of the secreted extracellular matrix-associated proteins of the CCN family and a target gene of the Wingless-type (WNT) signaling pathway. Growing evidence links the WNT signaling pathway to the regulation of adipogenesis and low-grade inflammation in obesity. We aimed to validate WISP1 as a novel adipokine. Human adipocyte differentiation was associated with increased WISP1 expression and secretion. Stimulation of human macrophages with WISP1 led to a proinflammatory response. Circulating WISP1 and WISP1 subcutaneous adipose tissue expression were regulated by weight changes in humans and mice. WISP1 expression in visceral and subcutaneous fat tissue was associated with markers of insulin resistance and inflammation in glucose-tolerant subjects. In patients with nonalcoholic fatty liver disease, we found no correlation among disease activity score, liver fat content, and WISP1 expression. Insulin regulated WISP1 expression in adipocytes in vitro but had no acute effect on WISP1 gene expression in subcutaneous fat tissue in overweight subjects who had undergone hyperinsulinemic clamp experiments. The data suggest that WISP1 may play a role in linking obesity to inflammation and insulin resistance and could be a novel therapeutic target for obesity.

Dietary rapeseed/canola-oil supplementation reduces serum lipids and liver enzymes and alters postprandial inflammatory responses in adipose tissue compared to olive-oil supplementation in obese men.

SCOPE: Obesity is associated with hyperlipidemia, hepatic steatosis, and low-grade inflammation. Studies have shown that MUFA as well as PUFA have beneficial effects on blood lipids and the inflammatory state. METHODS AND RESULTS: This study investigates the effects of a daily supplementation of either 50 g of rapeseed/canola (RA) or olive (OL) oil over 4 wk on serum lipids, serum liver enzymes, and inflammatory gene expression in subcutaneous (s. c.) adipose tissue in obese men. Consuming RA resulted in increased serum n-3 fatty acids and a reduction in total cholesterol, LDL cholesterol, and serum aspartate aminotransferase compared to OL. In s. c. adipose tissue, gene expression of the pro-inflammatory cytokine IL6 was reduced in RA compared to OL. However, after 4 h after a test meal, containing the appropriate oil, white bread, and 400 mL of liquid diet drink (835 kcal in total), gene expression of IL6, IL1B, and EMR1 (egf-like module containing Mucin-like hormone receptor-like 1) was increased in RA and of monocyte chemoattractant protein-1 (CCL2) in both RA and OL. CONCLUSION: This demonstrates that consuming RA for 4 wk improves serum lipids, liver enzymes, and basal inflammation in s. c. adipose tissue, but it mediates an acute pro-inflammatory response in adipose tissue upon consuming a meal.

In vivo effect of glucose-dependent insulinotropic peptide (GIP) on the gene expression of calcitonin peptides in human subcutaneous adipose tissue.

BACKGROUND: Increased plasma levels of calcitonin gene-related peptide-I (CGRP-I) and procalcitonin (Pro-CT) (both also named calcitonin peptides (CT peptides)) are associated with obesity and systemic inflammation. Glucose-dependent insulinotropic polypeptide (GIP), a nutrient-dependent incretin hormone, was recently found to induce CGRP-I and CT expression in human adipocytes in vitro. However, a physiological relevance of a possible interaction between GIP and CT peptides has not yet been studied. METHODS: In this study, we analyzed the effect of GIP on the expression of CGRP-I and CT mRNA in human subcutaneous adipose tissue within a randomized, controlled trial. Seventeen male obese subjects were infused with GIP [2.0 pmol kg(-1) min(-1) for 240 min] or placebo, either in the fasting state, during euglycemic-hyperinsulinemic (EC) or hyperglycemic-hyperinsulinemic clamps (HC). RESULTS: The CGRP-I gene expression was detected in all investigated adipose tissue samples, whereas very low CT expression was found in only 8 out of 116 analyzed samples. No significant influence of either GIP or glucose and insulin infusions on the CGRP-I and CT expression was observed in any of the individual experiments (GIP infusion, EC and HC) or in the combined analysis of all experiments with and without GIP. Furthermore, CGRP-I expression was not correlated with plasma GIP level before or after 240 min of infusions or clamps. CONCLUSION: In contrast to in vitro data, an acute application of GIP has no effect on mRNA expression of CT peptides in subcutaneous adipose tissue of obese humans.

A polymorphism within the connective tissue growth factor (CTGF) gene has no effect on non-invasive markers of beta-cell area and risk of type 2 diabetes.

Chromosomal locus 6q23 is strongly linked to type 2 diabetes (T2DM) and related features including insulin secretion in various ethnic populations. Connective tissue growth factor (CTGF) gene is an interesting T2DM candidate gene in this chromosome region. CTGF is a key mediator of progressive pancreatic fibrosis up-regulated in type 2 diabetes. In contrast, CTGF inactivation in mice compromises islet cell proliferation during embryogenesis. The aim of our study was to investigate an impact of CTGF genetic variation on pancreatic beta-cell function and T2DM pathogenesis. We studied the effect of a common CTGF polymorphism rs9493150 on the risk of the T2DM development in three independent German cohorts. Specifically, the association between CTGF polymorphism and non-invasive markers of beta-cell area derived from oral glucose tolerance test was studied in subjects without diabetes. Neither in the Metabolic Syndrome Berlin Potsdam (MESYBEPO) study (n=1026) (OR=0.637, CI (0.387-1.050); p=0.077) nor in the European Prospective Investigation into Cancer and Nutrition-Potsdam (EPIC-Potsdam) (n=3049) cohort (RR=0.77 CI (0.49-1.20), p=0.249 for the recessive homozygote in general model), a significant association with increased diabetes risk was observed. The risk allele of rs9493150 had also no effect on markers of beta-cell area in the combined analysis of the MESYBEPO and Tübingen Family Study (n=1826). In conclusion, the polymorphism rs9493150 in the 5'-untranslated region of the CTGF gene has no association with T2DM risk and surrogate markers of beta-cell area.

Metabolomic linkage reveals functional interaction between glucose-dependent insulinotropic polypeptide and ghrelin in humans.

The gastric peptide ghrelin promotes energy storage, appetite, and food intake. Nutrient intake strongly suppresses circulating ghrelin via molecular mechanisms possibly involving insulin and gastrointestinal hormones. On the basis of the growing evidence that glucose-dependent insulinotropic polypeptide (GIP) is involved in the control of fuel metabolism, we hypothesized that GIP and/or insulin, directly or via changes in plasma metabolites, might affect circulating ghrelin. Fourteen obese subjects were infused with GIP (2.0 pmol·kg(-1)·min(-1)) or placebo in the fasting state during either euglycemic hyperinsulinemic (EC) or hyperglycemic hyperinsulinemic clamps (HC). Apart from analysis of plasma ghrelin and insulin levels, GC-TOF/MS analysis was applied to create a hormone-metabolite network for each experiment. The GIP and insulin effects on circulating ghrelin were analyzed within the framework of those networks. In the HC, ghrelin levels decreased in the absence (19.2% vs. baseline, P = 0.028) as well as in the presence of GIP (33.8%, P = 0.018). Ghrelin levels were significantly lower during HC with GIP than with placebo, despite insulin levels not differing significantly. In the GIP network combining data on GIP-infusion, EC+GIP and HC+GIP experiments, ghrelin was integrated into hormone-metabolite networks through a connection to a group of long-chain fatty acids. In contrast, ghrelin was excluded from the network of experiments without GIP. GIP decreased circulating ghrelin and might have affected the ghrelin system via modification of long-chain fatty acid pools. These observations were independent of insulin and offer potential mechanistic underpinnings for the involvement of GIP in systemic control of energy metabolism.

Polymorphisms within insulin-degrading enzyme (IDE) gene determine insulin metabolism and risk of type 2 diabetes.

Insulin-degrading enzyme (IDE) is the ubiquitously expressed major enzyme responsible for insulin degradation. Insulin-degrading enzyme gene is located on chromosome region 10q23-q25 and exhibits a well-replicated peak of linkage with type 2 diabetes (T2DM). Several genetic association studies examined IDE gene as a susceptibility gene for T2DM with controversial results. However, pathophysiological mechanisms involved have remained elusive. We verified associations of two IDE polymorphisms (rs1887922 and rs2149632) with T2DM risk in two independent German cohorts and evaluated in detail the association of common variants with insulin metabolism and glycemic traits. We confirmed previously published findings for diabetes-associated rs1887922 and rs2149632 in the European Prospective Investigation into Cancer and Nutrition-Potsdam cohort (n = 3049; RR 1.26, p = 0.003 and RR 1.33, p < 0.0001 for additive model). Haplotypes which carried one risk allele of rs2149632 or two risk alleles of both studied IDE SNPs also demonstrated a strong association with increased T2DM risk in this cohort (p = 0.001 and p < 0.0001, respectively). However, we found no significant T2DM association in the cross-sectional metabolic syndrome Berlin-Potsdam cohort (n = 1026). In nondiabetic subjects (NGT+IFG/IGT; n = 739), we found an association of rs2149632 with impaired glucose-derived insulin secretion and a trend to decreased insulin sensitivity for rs1887922. In the NGT subjects (n = 440), the association with decreased insulin secretion for rs2149632 remain significant, and the association with decreased hepatic insulin degradation for rs1887922 were observed additionally. This study validates and confirms the association of IDE polymorphisms with T2DM risk in the prospective German cohort and provides novel evidence of influences of IDE genetic variants on insulin metabolism.