Correlation of Irisin and Adipokine Levels With Body Mass Index and Risk Factors for Metabolic Syndrome in Hispanic Children
Condition: Overweight; Obesity; Thinness
MeSH terms: Overweight; Metabolic Syndrome; Thinness
Study type: Observational

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.
    

Detailed description: 
      Background 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,
      worldwide; 34.4% of children and 35% of adolescents are overweight or obese (ENSANUT 2012).
      Among other complications, overweight and obese children are predisposed to develop
      dyslipidemias, hypertension, the metabolic syndrome (MetS) and non-alcoholic fatty liver
      disease at a younger age, as well as to become obese as adults (Daniels et al., 2009;
      Elizondo-Montemayor et al., 2010). On the other hand, undernutrition in children conveys to
      very detrimental health effects such as stunting, puberty retardation, motor retardation
      (Roulet et al., 2005), osteoporosis and fractures (Saunders et al., 2011), immunologic
      deficit, and altered function of every organ and system, such as the heart, lungs, kidneys,
      gastrointestinal tract and the nervous system, among others (Lecours et al, 2001; Saunders et
      al., 2011).

      A balance between energy intake and energy expenditure is required to sustain a normal body
      weight. Anything that disrupts this balance may cause individuals to be underweight,
      overweight or obese. Diverse signals, central and peripheric participate in the regulation of
      energy balance. Fat has been considered an endocrine organ due to the many peptides and
      hormones that it secrets that act upon peripheral and central tissues, and their contribution
      to insulin resistance or sensitivity and body weight regulation among other functions
      (Elizondo, 2011). Recently, skeletal muscle has been shown to function as a peripheral
      endocrine organ by releasing myokines, peptide signals, which are implicated in the
      regulation of metabolic pathways (Pedersen and Febbraio, 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. In mouse, PGC1alfa expression in muscle stimulates
      increase in expression of FNDC5, a membrane protein that is cleaved and secreted as this
      novel hormone, irisin. Irisin is induced with exercise in mice and humans, and medley
      increased irisin levels in blood cause 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 as these
      parameters increase, this is, irisin levels 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 et al., 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
      in different circumstances or diseased states. 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 improvement in anthropometric and metabolic parameters and led to 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. Leptin plays a pivotal role in regulating energy homeostasis,
      food intake and many neuroendocrine functions, specially triggering puberty in children.
      Leptin is increased in obese patients, associated with a leptin-resistant state (Blüher and
      Mantzoros, 2009). Adiponectin is an insulin sensitizing hormone; obese patients have lower
      levels than normal-weight ones. Circulating adiponectin levels are low in central obesity
      (Dalamaga et al., 2012), and this low level has been associated with the metabolic syndrome
      across all ages (Siitonen et al., 2011). Resistin has been associated with insulin
      resistance, and recently as a proinflamatory adipocytokine (McTernan et al., 2006). Some
      studies have found a negative correlation between irisin and adiponectin levels (Park et al.,
      2013), while other have found no association either with leptin or adiponectin (Blüher et
      al., 2014) here are still conflicting data regarding the association of irisin with
      anthropometric parameters, obesity and the metabolic syndrome, as well as its 'association
      with other adipokines, 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.

      There is still conflicting data regarding the association of irisin with anthropometric
      parameters, obesity and the metabolic syndrome, as well as its 'association with other
      adipokines, and most important, there is scarce data of these associations in children.
      Therefore, 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.

      Study Population The population was previously described. (Elizondo-Montemayor et al., 2014)
      An open invitation was made to school-aged children from eight public schools representative
      of all geographical areas of Monterrey, the second largest city in México. Children that
      accepted the invitation were randomly selected and screened according to BMI percentiles. The
      sample size is 40 children. The population will be divided into five groups, 8 per group.
      Four of the groups will be divided according to the CDC body mass index percentiles: 1.)
      underweight = <3percentile; 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.

      Signed consent was obtained from both parents/care givers and children. Approvals by the
      Ethics and Research Committees of the School of Medicine Tecnológico de Monterrey and by the
      State Health Secretariat, as well as by the Education Authorities were obtained. Participants
      did not receive gratification during the study.

      Anthropometric and Clinical Evaluation Anthropometric measurements were performed in all
      participants at each school. Height was determined to the nearest 0.5 cm (portable Seca®
      stadiometer, North America) and weight to the nearest 0.1 kg while children wore light
      clothing, no socks or shoes (TANITA TBF 300® scale, Arlington, Illinois). Percentage of body
      fat (%BF) was measured by bioimpedance (same TANITA scale). WC was measured to the nearest
      0.1 cm at the level of the umbilicus with a flexible fiberglass tape while the subjects were
      standing, after gently exhaling, and with no clothing on the area. Tricipital skin fold (TSF)
      was measured using a Lange skinfold caliper. BMI was calculated by weight-kilograms divided
      by the square of height-meters. Fat mass and fat free mass were calculated according to the
      specific predetermined formulas. Measurements were performed at the same time each day by the
      same three trained registered dietitians (RD) in all children to control the inter-observer
      variability. Blood pressure was measured by the same physician, using an aneroid
      sphygmomanometer (Welch-Allyn®) following the American Heart Association (AHA) technique; two
      measurements were obtained while participants were calmed and seated.

      Laboratory Assessment Blood samples were taken after a 12-hour overnight fast and were kept
      at 2 to 8°C and centrifuged within the first 3 hours. Serum total cholesterol (TC), HDL-C,
      low-density lipoprotein cholesterol (LDL-C), triglycerides (TG), and glucose were measured by
      reflective photometry (Beer-Lambert's law) using an automated analyzer (Architect c8000;
      Abbott Laboratories, Abbott Park, IL), with an intra- and inter-assay coefficient variation
      below 4.7%. Plasma samples were then stored at -80°C. Irisin, adiponectin, insulin and leptin
      will be measured in plasma media using commercial ELISA kits. The assays will be conducted in
      96-well microplates according to the manufacturer's instructions (Irisin, adiponectin,
      insulin and leptin ELISA kit; Phoenix Pharmaceuticals, Inc., Burlingame, CA, USA). Absorbance
      from each sample will measured in duplicate using a spectrophotometric microplate reader at
      wavelength of 450 nm (BioTek Instruments, Winooski, VT, USA).

      Statistical Methods MINITAB version 16 (Minitab Inc., State College, PA, USA) will be used to
      analyze the differences between anthropometric and biochemical parameters and irisin levels;
      Microsoft Excel 2007 (Microsoft Corp., Redmond, WA, USA) will be used to incorporate the
      input of data. The results will be expressed as mean ± standard deviation (s.d.), as absolute
      number or as percentage (%) and their corresponding 95% confidence intervals (CI).
      Comparisons between groups for the dependent variables will be made using paired Student´s
      t-test for means and McNemar test for proportions. For independent variables, the normality
      will be revised both, graphically and by the Shapiro-Wilk test, and subsequently, the
      comparisons between groups will be determined using z-test. To assess the association between
      anthropometric, clinical and biochemical variables and irisin levels, a simple linear
      regression will be used. The mean comparisons between gender groups will be determined using
      t-test for independent samples. All tests will be interpreted based on two-tailed hypothesis.
      The significance level will be set at 0.05 in all cases.
    

Observational model: Cohort
Time perspective: Cross-Sectional
Sampling method: Probability Sample
Study population: 
        Obese, overweight, normal weight and underweight Hispanic, school-aged children from eight
        public schools representative of Monterrey, the second largest city in México.
      
Keywords: Irisin; Adiponectin; Leptin; Insulin resistance; Body Mass Index; Obesity; Metabolic Syndrome; Lipid Profile; Diabetes Mellitus