The effect of physical activity on serum IL-6 and vaspin levels in late elementary school children.

PURPOSE: This study investigates the effects of physical activity on serum IL-6 and vaspin in late elementary school children.
METHODS: Those who (n = 220) completed the 7-day physical activity monitoring underwent a second round of measurements including body fat, serum glucose and insulin, and serum IL-6 and vaspin. One way ANOVAs followed by LSD post hoc tests were used to test for significant differences in dependent variables across incremental physical activity levels at p=0.05. Multivariate stepwise linear regression analyses were used to determine significant predictors for serum IL-6 and vaspin levels at p=0.05.
RESULTS: The results showed significant inverse linear trends for body fat parameters across incremental physical activity levels (from low to high); the lower the body fat, the higher the physical activity levels. On the other hand, there were no significant linear trends for insulin resistance markers or dietary intake across incremental physical activity levels. Multiple stepwise linear regression analyses were used to determine significant predictors for individual variations in serum IL-6 and vaspin in the study population. We found that body mass index (p=0.002) and low- and moderate-intensity physical activities (p=0.002 and p=0.0045, respectively) were significant determinants of serum IL-6. In addition, low- and moderate-intensity physical activities (p=0.01 & p=0.022, respectively) were significant determinants of serum vaspin levels in this study population.
CONCLUSION: In summary, the findings of the current study suggest that promotion of physical activity along with a healthy diet should be key components of lifestyle interventions to improve serum cytokine profiles associated with insulin resistance syndrome in late elementary school children.

INTRODUCTION

The increasing trend in childhood obesity can be attributed to energy imbalance, meaning relatively low energy utilization compared to the caloric intake [1]. In the long term, this imbalance results in not only surplus subcutaneous fat, but also in ectopic fat accumulation of neutral lipids in both the skeletal muscles and in hepatic tissue.

Body fat itself is a very important tissue that serves an energy repository with endocrine functions [2]. It also controls functions related to body metabolism, such as insulin sensitivity, fatty acid synthesis, glycometabolism, and appetite, in peripheral tissues including skeletal muscles and the liver [3]. On the other hand, excessive body fat, especially ectopic fat, increases the expression of insulin resistant cytokines (C-reactive protein, tumor necrosis factor-ɑ, interleukin-6, retinol binding protein-4, leptin), reducing the expression of insulin sensitive cytokines (adiponectin, visfatin, vaspin) and having a compensatory effect on insulin resistance. Primarily, it causes an inflammatory reaction due to the imbalance of cytokine expression [4,5]. Secondly, it results in defunctionalization of the buffer action of adipose tissue, inducing insulin function degradation in the liver and in skeletal muscles. Ultimately, excessive body fat is known to play a key role in the development of insulin resistance and type 2 diabetes [6].

Studies have been actively conducted on the hormones and cytokines that induce insulin resistance and those secreted from body fat. Among them, the concentration of interleukin-6 (IL-6) secreted from subcutaneous adipocytes is three times higher than that from visceral adipocytes. The secreted IL-6 stimulates neutral lipid synthesis in each tissue through the circulatory system to cause hypertriglyceridemia [7]. Also, the serum IL-6 concentration is not only significantly higher in insulin resistant and obese patients compared to normal people, but is also known to be an independent predictive factor for the risk of type 2 diabetes [8,9]. Especially from the perspective of causing insulin resistance, the IL-6 excessively secreted in the obese state originates from the fat within the abdominal cavity and directly circulates to the liver, where it stimulates the secretion of triglyceride. It was also reported to create insulin inducing sugar damage in the hepatocyte, and to damage the insulin signal transmission from the adipocyte [10].

Meanwhile, vaspin, which was recently discovered, is a member of the serine protease inhibitor family of cytokines that increases insulin sensitivity. The fact that extreme obesity or blood insulin level is apparent in the visceral adipose tissue of maximum age obese rat Otsuka Long-Evans Tokushima fatty (OLETF) was first reported recently by Hida et al. [11]. Serum vaspin concentration is stated to increase as a compensatory mechanism according to an increase in BMI or an increase in insulin resistance. According to the above study related to serum vaspin, vaspin expression and blood level are higher in overweight men and women compared to normal weight or obese individuals. As age increases while diabetes continues to progress, vaspin expression and blood level decrease. Therefore, decreased vaspin expression and blood level in diabetic and aging individuals can be recovered by diabetes treatment drugs such as insulin and thiazolidinedione (TZD) and through exercise. A notable point is that the increase in vaspin expression through exercise was the same level of increase in response to the administration of TZD. It is also known that the administration of recombinant human vaspin (rhVaspin) decreases the leptin, resistin, and TNF- a levels in rats that consumed high-fat, hyperglycemic diets and also significantly increases GLUT4 and adiponectin [12,13]. Additionally, it was reported that for non-active individuals, the vaspin concentration in the blood is increased by exercise training.

Thus, due to excessive intake energy, the increase in body fat subsequently increases the expression of insulin resistant cytokines in the peripheral organs, resulting in insulin resistance in peripheral organs such as the liver and skeletal muscles. Adipocyte, similar to vaspin in having a compensatory function on insulin resistance, secretes insulin sensitive cytokines to contribute to the maintenance of homoeostasis. Youn et al. [12] reported that the serum vaspin level of the normal weight group and the diabetic patients increased significantly after aerobic exercises such as regular running, cycling, and swimming for 4 weeks. Although there is no clear explanation available for increased serum vaspin secondary to physical activity, both serum vaspin and physical activity improve the insulin resistance syndrome, which is a common pathological denominator of diabetes, hyperlipidemia, and cardiovascular disease.

Physical activity not only burns adipose tissue, but is also an essential factor effecting insulin resistance and sensitivity. However, existing domestic studies on physical composition, insulin resistance and cytokines in the blood mostly involved obese patients including female university students and obese middle-aged women and therefore, lack quantified objective data on the role of physical activity on the insulin resistance and sensitivity of late school aged children. Therefore, the main purpose of this study was to identify the increase of body fat during adolescence in late school aged children, and to verify the role of physical activity on the level of cytokines in the blood.

METHODS

Study subject

For this study, a total of 220 students, 91 male students and 129 female students in the fifth and sixth grades of elementary school in S-city, Gyeonggi-do were recruited to perform all variable measurements including body mass index, insulin resistance index, serum interleukin-6 and vaspin content. The amount of physical activity and dietary intake were measured and statistical analysis was performed. Before the study, the content, purpose and related procedures were fully described to the subjects and their guardians. The participants voluntarily signed consent forms to participate in the study.

Measurement and analysis items

Measurement of all dependent variables was performed after 12 hours of gastric emptying. Height and weight measurements were performed by the researchers after receiving training according to the guidelines for standardization. The subjects were measured in comfortable clothes.

Body mass index

Wearing thin clothes, the weight was measured by using automatic measurement equipment (DS-102, JEnix Co., Korea). The percent body fat (%BF) was measured with the X-Scan Body Composition Analyzer (Jawon Medical Co., Korea), an automatic body composition analysis device utilizing bioelectric resistance. Body mass index (BMI) was calculated using the［weight(kg)/height(m)2］formula, The waist measurement was obtained in the erect posture using a tape measure that circled the navel in parallel. The measurements were performed twice and the average was calculated to be used as the analysis data.

Insulin resistance index

To measure the serum-sugar level, after 12 hours of fasting, approximately 8ml of venous blood was collected from the brachial vein of the subject. A Green Vac-Tube in a gel-type activator was used to immediately perform centrifugation (3000rpm, 15 minutes) to separate the serum, which was stored in a -80℃ cryogenic refrigerator. The stored serum was analyzed for fasting blood glucose (FBG) by using the Vitro Chemistry DT60Ⅱ kit (Johnson & Johnson, NY, USA). Insulin was determined using the Human Insulin ELISA kit (ALPCO Diagnostics) (the CVs for intra- and interassays = 4.3% and 6.8%, respectively). For the Homeostasis model assessment of insulin resistance (HOMA-IR), [fasting insulin (μU/mL) × fasting glucose (mM)/22.5] was calculated, as described by Matthews et al. [14].

Serum interleukin-6 and vaspin

The serum obtained as described above and stored in the cryogenic refrigerator (-80℃) was used to analyze the concentration of serum interleukin-6 (Human IL-6 ELISA kit, DSL, Texas, USA) and vaspin (Human Vaspin ELISA kit, AdipoGen, Seoul, Korea).

Daily average physical activity and dietary intake

As the index of cardio pulmonary fitness, maximum oxygen intake was measured. For the maximum oxygen intake test, after over 4 hours of gastric emptying, an exercise tolerance test was performed with the Bruce protocol (1974), using a treadmill (Medtrack ST 65, Quinton, USA) and gas analyzer (True-one, Quinton, USA). The standard for reaching maximum capacity was first, 1.15 or higher respiratory exchange ratio, second, 17 or higher RPE, third, constant VO2 value despite increased exercise intensity, and fourth, the subject stopping voluntarily. The subjects wore motion accelerometers (Life Coder EX, 2006, Suzuken, Japan) on the right side of the waist (center of the navel and the side line) to record 7 days of exercise and overall physical activity as well as normal life. Before starting the study, the individual’s age, gender, height, weight, initial measurement date and time were inputted. Sleeping and shower times were excluded. The life coder used in this study was the uniaxial accelerometer, which can store 200 days of data such as amount of physical activity, exercise intensity, maintenance and calorie consumption corresponding to 4 second intervals using the METS concept. In this study, 1 day of average maintenance and exercise intensity were analyzed and are presented in . For the dietary intake, blank forms were distributed to the subjects to record the name and amount of food consumed for breakfast, snack, lunch, snack, dinner, and snack. The dietary intake was recorded for 3 days (Tuesday, Thursday, and Saturday) in 1 week and the average value was used. All types and amounts of food recorded were converted into weight (Korea Food Industry Association. Household measures of commonly used food items, 1998) and analyzed with the nutrition evaluation program developed by the Nutrition Information Center in the Korean Nutrition Society, CAN-Pro 2.0 (Computer Aided Nutritional Analysis Program), then converted to nutrient intake amount. The individual intakes of carbohydrate (%), fat (%), protein (%) and daily average calorie intake (kcal/day) were calculated.