Association of insulin resistance and GLP-2 secretion in obesity: a pilot study

Associação entre resistência insulínica e secreção de GLP-2 em obesos: um estudo piloto

Abstracts

OBJECTIVE: The objective of this pilot study was to determine whether glugagon-like peptide 2 (GLP-2) secretion relates to insulin sensitivity (IS) in obese subjects. SUBJECTS AND METHODS: Twenty four obese subjects [body mass index (BMI) 40.0 ± 3.0 kg/m² (mean ± standard deviation)] were included, nine of which were male, age 43 ± 8 years. Twelve subjects had type 2 diabetes, all treated with oral anti-diabetic agents only. The subjects were submitted to standard meal tolerance test (MTT) for dosage of the curves: glucose, insulin, and GLP-2. Insulin sensitivity was measured by HOMA-IR, and OGIS was derived from the MTT. Spearman linear correlations and partial correlations were obtained. RESULTS: There was an inverse relationship between the GLP-2 secretion and IS: HOMA-IR correlated with GLP-2 AUC (R = 0.504; p = 0.012), and OGIS correlated with GLP-2 incremental AUC (R = -0.54; p = 0.054). The correlation persisted after controlling for BMI. CONCLUSION: We found an association of GLP-2 secretion and insulin resistance (IR). The understanding of the underlying mechanisms may provide future directions in the pharmacological manipulation of incretins, and in the treatment of obesity and related metabolic disorders.

GLP-2; insulin resistance; HOMA-IR; OGIS; obese patients

OBJETIVO: O objetivo deste estudo piloto foi determinar a relação entre a secreção de glugagon like peptide 2 (GLP-2) e a sensibilidade insulínica (SI) em indivíduos obesos. SUJEITOS E MÉTODOS: Vinte e quatro indivíduos obesos [IMC 40.0 ± 3.0 kg/m² (média ± desvio-padrão)] foram incluídos no estudo, sendo 9 homens, com idade de 43 ± 8 anos. Do total, 12 indivíduos tinham diabetes tipo 2, todos tratados somente com antidiabéticos orais. Os sujeitos foram submetidos ao teste de refeição padrão (MTT) para dosagens das curvas: glicose, insulina e GLP-2. A sensibilidade insulínica foi mensurada pelos HOMA-IR e OGIS, obtidos pelos valores do MTT. As correlações lineares e correlações parciais foram obtidas. RESULTADOS: Observou-se uma relação inversa entre a secreção de GLP-2 e SI: HOMA-IR correlacionou-se com GLP-2 AUC (R = 0,504; p = 0,012) e OGIS correlacionou-se com GLP-2 incremental AUC (R = -0,54; p = 0,054). A correlação persistiu controlando o IMC. CONCLUSÃO: Encontramos uma associação entre a secreção de GLP-2 e a resistência insulínica. A compreensão desses mecanismos poderá direcionar o futuro farmacológico da manipulação de incretinas no tratamento da obesidade e das desordens metabólicas.

GLP-2; resistência insulínica; HOMA-IR; OGIS; obesos

ORIGINAL ARTICLE

Association of insulin resistance and GLP-2 secretion in obesity: a pilot study

Associação entre resistência insulínica e secreção de GLP-2 em obesos: um estudo piloto

Bruno Geloneze; Marcelo Miranda de Oliveira Lima; José Carlos Pareja; Maria Rita Lazzarini Barreto; Daniéla Oliveira Magro

Laboratório de Investigação em Metabolismo e Diabetes (LIMED) do Gastrocentro, Faculdade de Ciências Médicas, Universidade Estadual de Campinas (Unicamp), Campinas, SP, Brazil

^{Correspondence to}

ABSTRACT

OBJECTIVE: The objective of this pilot study was to determine whether glugagon-like peptide 2 (GLP-2) secretion relates to insulin sensitivity (IS) in obese subjects.

SUBJECTS AND METHODS: Twenty four obese subjects [body mass index (BMI) 40.0 ± 3.0 kg/m² (mean ± standard deviation)] were included, nine of which were male, age 43 ± 8 years. Twelve subjects had type 2 diabetes, all treated with oral anti-diabetic agents only. The subjects were submitted to standard meal tolerance test (MTT) for dosage of the curves: glucose, insulin, and GLP-2. Insulin sensitivity was measured by HOMA-IR, and OGIS was derived from the MTT. Spearman linear correlations and partial correlations were obtained.

RESULTS: There was an inverse relationship between the GLP-2 secretion and IS: HOMA-IR correlated with GLP-2 AUC (R = 0.504; p = 0.012), and OGIS correlated with GLP-2 incremental AUC (R = -0.54; p = 0.054). The correlation persisted after controlling for BMI.

CONCLUSION: We found an association of GLP-2 secretion and insulin resistance (IR). The understanding of the underlying mechanisms may provide future directions in the pharmacological manipulation of incretins, and in the treatment of obesity and related metabolic disorders.

Keywords: GLP-2; insulin resistance; HOMA-IR; OGIS; obese patients

RESUMO

OBJETIVO: O objetivo deste estudo piloto foi determinar a relação entre a secreção de glugagon like peptide 2 (GLP-2) e a sensibilidade insulínica (SI) em indivíduos obesos.

SUJEITOS E MÉTODOS: Vinte e quatro indivíduos obesos [IMC 40.0 ± 3.0 kg/m² (média ± desvio-padrão)] foram incluídos no estudo, sendo 9 homens, com idade de 43 ± 8 anos. Do total, 12 indivíduos tinham diabetes tipo 2, todos tratados somente com antidiabéticos orais. Os sujeitos foram submetidos ao teste de refeição padrão (MTT) para dosagens das curvas: glicose, insulina e GLP-2. A sensibilidade insulínica foi mensurada pelos HOMA-IR e OGIS, obtidos pelos valores do MTT. As correlações lineares e correlações parciais foram obtidas.

RESULTADOS: Observou-se uma relação inversa entre a secreção de GLP-2 e SI: HOMA-IR correlacionou-se com GLP-2 AUC (R = 0,504; p = 0,012) e OGIS correlacionou-se com GLP-2 incremental AUC (R = -0,54; p = 0,054). A correlação persistiu controlando o IMC.

CONCLUSÃO: Encontramos uma associação entre a secreção de GLP-2 e a resistência insulínica. A compreensão desses mecanismos poderá direcionar o futuro farmacológico da manipulação de incretinas no tratamento da obesidade e das desordens metabólicas.

Descritores: GLP-2; resistência insulínica; HOMA-IR; OGIS; obesos

INTRODUCTION

Glucagon-like peptide-2 (GLP-2) is a hormone co-secreted with glucagon-like peptide-1 from enteroendocrine cells in the small and large bowels, also expressed in the pancreas and the brain (1,2). GLP-2 secretion is regulated by food nutrients, mainly fat and carbohydrates, and targets receptors in the gastrointestinal tract, from the stomach to the colon. The major known action of GLP-2 is mucosal growth, especially in the proximal bowel, increasing villous height and crypt cell proliferation, and inhibiting apoptosis in both the crypt and villous compartments (3).

The potent intestinotrophic action of GLP-2 results in increased nutrient absorption, which justifies interest in potential therapeutic applications in conditions of malabsorption and intestinal injury/atrophy, with promising initial results (4,5). On the other hand, little is known about the role of this hormone in conditions related to increased uptake of energy and macronutrients, specially fatty acids, such as obesity and insulin resistance (IR).

Our hypothesis is that insulin sensitivity is influenced by increased absorption of nutrients mediated by GLP-2. The objective of this pilot study was to determine whether GLP-2 secretion relates to insulin sensitivity (IS) in obese subjects.

SUBJECTS AND METHODS

The study was approved by the Institutional Ethics Review Board at University of Campinas (Unicamp – number: 801/2008). All participants provided written informed consent before participation. Twenty four obese subjects [body mass index (BMI) 40.0 ± 3.0 kg/m² (mean ± standard deviation)] were included, nine of which were male, aged 43 ± 8 years. Twelve subjects had type 2 diabetes, all treated with metformin and/or sulfonylureas only.

After an overnight fast (12 h), subjects were submitted to standard meal tolerance test (MTT), based in a mixed meal containing 515 kcal (41.8% fat, 40.7% carbohydrates, and 17.5% protein). For diabetic subjects, oral antidiabetic drugs were discontinued one day before the test. Blood samples were drawn for glucose, insulin, and GLP-2 at -15, 0, 30, 45, 60, 90, 120, 150, and 180 minutes. Glucose was determined by the glucose oxidase method. For GLP-2 analysis, blood samples were collected in tubes with EDTA3 plus Sigma diprotin. Serum samples were stored in a freezer at -80°C for posterior analysis of insulin (ELISA, Bayer Corp.) and GLP-2 (ELISA, Millipore Corp.).

Statistical methods

The area under the curve (AUC) of GLP-2, glucose and insulin were calculated by the trapezoidal method. The incremental AUC was calculated as total AUC minus the area under the basal value.

Insulin sensitivity (IS) was estimated by two me–thods: (1) the Homeostatic Model Assessment (HOMA-IR) from the formula [glucose (mmol/L) X Insulin (µU/mL)/22.5], for which higher values represent lower IS; and (2) the Oral Glucose Insulin Sensitivity (OGIS) obtained from MTT, which represents the postprandial glucose clearance adjusted for body surface area⁵, and for which higher values represent higher IS.

SSPS 16.0 was used for statistical analyses with Spearman linear correlations and partial correlations. Statistical significance was assumed if p < 0.05.

RESULTS

The metabolic characteristics of the subjects are presented in table 1.

Insulin sensitivity (IS) and GLP-2 AUCs were statistically similar between diabetic and non-diabetic subjects (data not shown).

We observed an inverse relationship between the GLP-2 secretion and IS: HOMA-IR correlated with GLP-2 AUC (R = 0.504; p = 0.012) (Figure 1), and OGIS correlated with GLP-2 incremental AUC (R = -0.54; p = 0.054) (Figure 2). The correlation persisted after controlling for BMI.

DISCUSSION

We report, for the first time, an association between GLP-2 secretion and IR in obese subjects.

The strength of our finding is the use of two complementary indexes of IS: one based in a fasting basal method (HOMA-IR), which measures mainly hepatic IS (6); and one that is a postprandial, dynamic method (OGIS) that measures whole-body IS (hepatic and peripheral) (5).

There are some hypotheses to explain this finding. The first hypothesis is that GLP-2 induced an increased absorption of nutrients, especially fatty acids, which could contribute to IR. GLP-2 has an intestinotrophic effect in the proximal and distal bowels (7), and has acute effects in intestinal fat absorption and lipoprotein production, which result in increased postprandial circulating triglycerides and free fatty acids in rodents (8) and humans (9). Fatty acids are a key factor for IR in skeletal muscles and liver by a number of mechanisms: preferential oxidation over glucose; impaired insulin signaling and glucose transport; inflammation and oxidative stress secondary either to fat metabolites (ceramides, diacylglycerol, acyl-CoA) or binding to fatty acid receptors (G-coupled protein or peroxisome proliferator-activated receptors) (10).

The intestinal microbiota could have a contribution to this hypothesis. Food fermentation both increases energy harvesting in animal and human obesity (11) and produces short-chain fatty acids linked to increased expression of pro-enteroglucagon in rodents (12) and to proximal and distal bowel hypertrophy (13).

There are some counterpoints to the discussion above. First, we cannot exclude the hypothesis that increased GLP-2 secretion could be a manifestation of intestinal IR (14). Second, Cani and cols. (15) demonstrated that GLP-2 has a protective effect on metabolic endotoxemia in mice, demonstrated by lower plasma lipopolysaccharide (LPS) and cytokines and decreased lipid content and inflammation in the liver. Such effect was, at least in part, related to lower intestinal permeability, preventing LPS translocation.

A second hypothesis is that glucagon could be the link between GLP-2 and IR. GLP-2 directly stimulates glucagon secretion and counteracts the glucagonostatic action of GLP-1 in healthy subjects (9), and in type 1 and type 2 diabetic subjects (3,16). Glucagon is counter-regulatory to insulin action, increasing glucose output and inhibiting glucose uptake in the liver, and has been linked to IR in obese subjects with normal or impaired glucose tolerance (17,18).

Some limitations of the study are that we have not assayed fatty acids and glucagon, and have not evaluated intestinal absorption and histology.

The relationship of GLP-2 and IR should be considered in future studies of pharmacological use of GLP-2 and its analogues, especially for potential adverse metabolic events.

We found an association of GLP-2 secretion and IR. The understanding of the underlying mechanisms may provide future directions in the pharmacological manipulation of incretins, and in the treatment of obesity and related metabolic disorders.

Acknowledgements: grants for this study were provided by Fundação de Apoio à Pesquisa do Estado de São Paulo (Fapesp), São Paulo, Brazil (Protocol – 2009/50430-6).

Received on Oct/29/2012

Accepted on Aug/1/2013

Disclosure: no potential conflict of interest relevant to this article was reported.

Statement of authorship:

Bruno Geloneze: design, data analysis and interpretation, contribution to discussion.

Marcelo Miranda de Oliveira Lima: contribution to discussion.

José Carlos Pareja: contribution to discussion.

Maria Rita Lazzarini Barreto: data collection.

Daniéla Oliveira Magro: design, data analysis and interpretation, contribution to discussion, revision/edition of manuscript.

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Publication Dates

• Publication in this collection
  11 Dec 2013
• Date of issue
  Nov 2013

History

• Received
  29 Oct 2012
• Accepted
  01 Aug 2013