Decreased insulin clearance (IC) is an early marker of disturbances in glucose metabolism as it is observed in first-degree relatives of type 2 diabetics [1] and in obese insulin resistant subjects [2, 3]. When IC is primarily experimentaly reduced [4] insulin resistance slowly develops suggesting that the change in IC might not be only adapative but also maladaptative. In indirect support of this idea a number of genes related to IC have been repeatedly associated both to the risk of developing diabetes and glucose impairment [5]. Whether altered IC contributes to, or is a consequence of, the insulin resistant state, or wether there are patient groups with different aetiologies of the disease is unknown (i.e. reflecting the view that type 2 diabetes is not one disease but a cluster of different diseases with lack of insulin action as the common factor). Insulin degrading enzyme (IDE) and protein dissulfide isomerase (PDI) are the two key hepatic enzymes responsible forthe removal of ~50-70% of the released insulin by the pancreas. IDE in the liver is also modulated by nitric oxide, which is known to be a key player in insulin sensitivity states in response to nutrient ingestion [6]. The studies proposed herein are focused on the hypothesis that inherited or acquired reduction in IC in response to high-fat or high-carbohydrate feeding determine chronic hyperinsulinemia which is followed by a compensatory insulin resistance in normoglycaemic and pre-diabetic subjects leading to progressive insulin resistance in a vicious circle. Furthermore, we hypothesize that the interaction of the IDE or PDI or NOS genes variants with dietary regimens leads to chronic IC deterioration. The present proposal will clarify the contribution of IC to whole-body insulin action with both observational clinical studies exploring the relationship between IC, insulin action and insulin secretion and mechanistic studies using animal models and clinical studies to determine the role of genes, nutritional manipulations and liver NO on IC function. The acute changes in IC after nutrient ingestion will be also evaluated in terms of their relationship with insulin secretion and insulin sensitivity, in terms of their mechanisms and the consequences of their manipulations. The clinical studies will focus on defining the role of IC in glucose homeostasis exploiting the European RISC (Relationship between Insulin sensitivity and Cardiovascular Disease) cohort (1005 subjects) and the PREVADIAB (Prevalence of Diabetes in Portugal) cohort (1200 subjects). In the RISC cohort we will explore the physiologic relationship between IC, both fasting and post OGTT, and insulin secretion and insulin sensitivity and will generate a definition for normal, low and high IC. RISC database will be exploited also to generate an accurate estimate of IC using two insulin and C-peptide values in the OGTT. In both cohorts we will evaluate whether IC is associated with disease progression and we aim to identify genetic or environmental risk factors underlying IC impairments. Candidate genes are those coding for the enzymes involved in IC regulation: IDE, PDI and NOS2A; and candidate environmental variables are age, obesity, exercise, diet and fatty liver. The animal studies will be used as a model of genetic and environment interaction (nutrigenomic approach) on hepatic IC and insulin actions. In the first set of experiments we aim to assess the glucometabolic consequences for IC of genetic knockdowns of the key component enzymes (IDE and PDI) in the liver. The second set of experiments aims to elucidate the regulatory function of hepatic NO levels on hepatic insulin clearance. In the third set of experiments we will study the interaction between nutrition (high fructose and high fat diets) and genes on hepatic IC and development of whole body insulin resistance. In these experiments IDE and PDI enzymes will be selectively silenced in the liver by gene knockout. Plasma glucose, insulin, C-peptide, lipid profile, free fatty acids, adinopectin and nitrate levels will be measured before and during an OGTT. Hepatic IC, insulin sensitivity and β-cell function will be assessed. In summary, alterations in IC are consistently associated with hyperglycemia and insulin resistance, but whether altered IC contributes to or is a consequence of the insulin resistant state remains unclear. Our studies aim at addressing this issue through observational and prospective clinical studies as well as through experimental models designed to understand IC regulation by environmental and gene-expression factors.

• Project/scholarship ID

  124357

• Reference

  PTDC/DTP-EPI/0207/2012

• FundRef URI

  http://www.fct.pt/apoios/projectos/consulta/vglobal_projecto.phtml.en?idProjecto=124357&idElemConcurso=5825

• Funder

  FCT - Fundação para a Ciência e a Tecnologia, I.P.

• Funder's country

  Portugal

• Funding program

  3599-PPCDT

• Funding amount

  199,288.00 €

• Start date

  2013-06-01

• End date

  2016-05-31