CLINICAL STUDY Serum and urinary concentrations of calprotectin as markers of insulin resistance and type 2 diabetes Francisco J Ortega, Mo ´nica Sabater, Jose ´ M Moreno-Navarrete, Neus Pueyo, Patricia Botas 1 , Elias Delgado 1 , Wifredo Ricart, Gema Fru ¨ hbeck 2 and Jose ´ Manuel Ferna ´ndez-Real Department of Diabetes, Endocrinology and Nutrition (UDEN), Institut d’Investigacio ´ Biome ´dica de Girona (IdIBGi), CIBER de la Fisiopatologı ´a de la Obesidad y la Nutricio ´n (CIBERobn, CB06/03/0010) and Instituto de Salud Carlos III (ISCIII), Girona, Spain, 1 Hospital Central de Asturias, Oviedo, Spain and 2 Clı ´nica Universitaria de Navarra, CIBER de la Fisiopatologı ´a de la Obesidad y la Nutricio ´n (CIBERobn, CB06/03/0010) and Instituto de Salud Carlos III (ISCIII), Pamplona, Spain (Correspondence should be addressed to J M Ferna ´ndez-Real who is now at Section of Diabetes, Endocrinology and Nutrition, Hospital of Girona ‘Dr Josep Trueta’, Carretera de Franc ¸a s/n, 17007 Girona, Spain; Email: jmfernandezreal.girona.ics@gencat.cat) Abstract Objective: Increased circulating calprotectin has been reported in obese subjects but not in association with measures of insulin resistance and type 2 diabetes (T2D). The main aim of this study was to determine whether calprotectins in plasma and urine are associated with insulin resistance. Design: We performed both cross-sectional and longitudinal (diet-induced weight loss) studies. Methods: Circulating calprotectin concentrations (ELISA), other inflammatory markers, homeostasis model assessment of insulin resistance (HOMA-IR), and parameters of glucose and lipid metabolism were evaluated in 298 subjects (185 with normal (NGT) and 62 with impaired (IGT) glucose tolerance and 51 T2D subjects). Calprotectin was also evaluated in urine samples from 71 participants (50 NGT and 21 subjects with IGT). Insulin sensitivity (S I , Minimal Model) was determined in a subset of 156 subjects, and the effects of weight loss were investigated in an independent cohort of obese subjects (nZ19). Results: Circulating calprotectin was significantly increased in IGT–T2D (independently of BMI) and positively associated with HOMA-IR, obesity measures, inflammatory markers, and parameters of glucose and lipid metabolism. Similar findings were reported for calprotectin concentrations in urine. In the subset of subjects, the association of calprotectin with S I was independent of BMI and age. In fact, S I together with C-reactive protein contributed to 27.4% of calprotectin variance after controlling for age and blood neutrophils count. Otherwise, weight loss led to decreased circulating calprotectin in parallel to fasting glucose and HOMA-IR. Conclusion: These findings suggest that circulating and urinary concentrations of calprotectin are linked to chronic low-grade inflammation and insulin resistance beyond obesity. European Journal of Endocrinology 167 569–578 Introduction It is well known that chronic subclinical inflammation is intrinsic to the metabolic syndrome (the clustering of central obesity and alterations of glucose and lipid metabolism). Insulin resistance is central to the pathophysiology of these alterations, which runs together with the accumulation of fat and the presence of specific components (1, 2). The innate immune system is one of the first lines of defense against invading microorganisms. In recent years, it has become evident that abnormalities in the function of the innate immune system are intrinsically linked to metabolic pathways (3). Among factors implicated in modulation of the immune response, bactericidal/permeability-increasing protein, lipopoly- saccharide binding protein, complement factors, a-defensins, and lactoferrin are proteins of the innate immune system, which are also related to metabolic parameters in humans (4, 5, 6, 7). Calprotectin is a heterodimer composed by two calcium-binding cytoplasmic calgranulins (S100A8 and S100A9), mainly expressed in cells of the myeloid lineage (including monocytes and neutrophils), and endothelial cells in a tissue/cell-specific manner (8). The heterocomplex S100A8/A9 is secreted to the milieu in response to inflammation (8), participating in the transendothelial accumulation of monocytes at the site of inflammation (9). The molecular characterization of the S100-like domain, the translocation of phosphory- lated calprotectin chains to the membrane during neutrophil activation, and its calcium-dependent associ- ation to cytoskeleton structures suggest intracellular signal transduction functions (10, 11). Moreover, calprotectin interacts with heparin and heparan sulfate glycosaminoglycans, the receptor for advanced European Journal of Endocrinology (2012) 167 569–578 ISSN 0804-4643 q 2012 European Society of Endocrinology DOI: 10.1530/EJE-12-0374 Online version via www.eje-online.org Downloaded from Bioscientifica.com at 04/24/2020 08:06:19AM via free access