Correlation of Circulating Irisin and Adipokine Levels Across a Broad Spectrum of Body Mass Index Ranging From Undernourished to Obese and With Insulin Resistance and Risk Factors for the Metabolic Syndrome in Hispanic Children

Detailed Summary

Childhood obesity is one of the most serious global public health challenges of the 21st century (Daniels et al., 2009). Mexico has the highest prevalence of obesity, (Secretaría de Salud, 2009); 34.4% of children and 35% of adolescents are overweight or obese (ENSANUT 2012). Obesity has major health consequences for children and adolescents; On the other hand, undernutrition as well has important deleterious consequences on children's health. Anything that disrupts energy balance may cause individuals to be underweight, overweight or obese. Fat has been considered an endocrine organ for some time (Elizondo, 2011). Recently, skeletal muscle has been shown to function as a peripheral endocrine organ by releasing myokines, (Pedersen, 2012). Most recently, a new identified hormone secreted by muscle tissue in mouse, irisin, has been discovered. Irisin acts on white adipose cells in culture and in vivo to stimulate UCP1 expression and a broad program of brown-fat-like development. Irisin was induced with exercise in mice and humans which caused an increase in energy expenditure in mice with no changes in movement or food intake (Boström et al., 2012). Irisin was thus, promptly hypothesized as a hormone influencing body weight, obesity and type 2 diabetes mellitus, among other conditions (Sanchis-Gomar et al., 2012). Some studies have indicated that circulating levels of irisin in humans correlate positively with anthropometric parameters such as BMI, fat mass, fat free mass, and are higher in obese patients compared to lean ones (Stengel et al., 2013; Huh et al., 2012; Roca-Rivada et al., 2013; Crujeiras et al., 2014; Pardo, 2014). Studies have shown an association between irisin levels, insulin resistance and the metabolic syndrome (Park et al., 2013; de la Iglesia et al., 2014; Crujeiras et al., 2014; Pardo et al., 2014). However, some others have found a negative correlation with anthropometric parameters, finding lower irisin levels in obese patients (Moreno-Navarrete et al., 2013). Noteworthy, all these studies have been performed in adults. To date, there are only two studies evaluating irisin levels in children. One found that a 1-year long lifestyle intervention program was associated with an elevation in irisin levels in obese children, although no correlation was found between irisin levels and anthropometric markers (Blüher et al., 2014). The other study investigated normal weight Saudi children and found correlations between circulating irisin and glucose and HDLc, but a negative association with insulin resistance (Al-Daghri et al, 2014). Besides, associations between irisin levels and adiponectin, leptin and resistin in the set of obesity have been explored, the three of them are implicated in the physiopatology of obesity. As there are still conflicting data regarding the association of irisin with anthropometric parameters, obesity and the metabolic syndrome, as well as its 'association with other adiponectines, and most important, there is scarce data of these associations in children, the objective of this study will be to correlate the circulating irisin and adipokines levels across a broad spectrum of body mass index ranging from undernourished to obese as well as with insulin resistance and risk factors for the metabolic syndrome in Hispanic children. The sample size with statistical power for this study yielded a sample of 40 children. Frozen stored plasma (-80°C) will be taken from a previous study performed in children which has been published (Elizondo-Montemayor et al., 2014). The samples will be divided into five groups, 8 per group, according to the CDC and American Academy of Pediatrics body mass index percentile classification: 1.) underweight = \<3 percentile; 2.) normal weight = \>3 - \< 85 percentile; 3.) Overweight = \>85 - \< 95 percentile, and 4.) obese = \> 95 percentile. The fifth group will correspond to children with known metabolic syndrome according to the classification specified by Cooks et al (2008). Anthropometric measurements will include BMI, percentile BMI, waist circumference, % body fat, fat mass, fat free mass, and triceps skin fold. Biochemical measurements will include glucose, total cholesterol, low-density cholesterol (LDL), high-density cholesterol (HDL-c) and triglycerides. Clinical measurements will include blood pressure, physical activity records and dietary habits. All biochemical, anthropometric and clinical measurements were previously performed in a former published study (Elizondo-Montemayor et al., 2014). Irisin, adiponectin and leptin will be measured in plasma media using commercial ELISA kits.

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