Issue 40

I. Doulamis et alii, Frattura ed Integrità Strutturale, 40 (2017) 85-94; DOI: 10.3221/IGF-ESIS.40.08 86 I NTRODUCTION besity's adverse effects on health include increased risk for diabetes (type-2), heart disease and certain types of cancer [1] leading to poor quality of life and ultimately to reduced life expectancy [2]. The continuous rise in its prevalence worldwide has highlighted obesity as one of the major epidemics of our time [3]. With regards to the risk for bone fracture, obesity has been traditionally believed to have a protective role [4,5]. Moreover a significant number of studies reported a positive relation between Body Mass Index (BMI) and bone density [6]. How- ever, the aforementioned classic view on the effect of obesity has been put into question from findings that link obesity to the loss of bone mass and osteopenia [7, 8] and studies highlighting lean body mass as a stronger determinant of bone density in men than BMI [9, 10]. Currently adipose tissue (i.e. body fat) is considered to be hormonally active with a pivotal role with regards to energy homeostasis and metabolism and not just an organ for storing excess energy [11]. More specifically, adipose tissue has been found to produce and secrete numerous substances including the hormone adiponectin. Adiponectin is exclusively secreted by adipose tissue and appears to be linked to increased insulin sensitivity and to have anti-atherogenic and anti- inflammatory properties [12]. The levels of plasma adiponectin are strongly associated with BMI and appear to be higher in obese subjects compared to lean subjects [13, 14]. Animal models have been widely used for the investigation of the effect of obesity, nutrition and exercise. According to these models obesity is induced by subjecting the animals (mainly rats or mice) to a high-fat diet (HFD) [15]. According to literature one of possible ways to prevent bone mass loss is exercise [16, 17]. Besides of its overall positive effect on health, exercise is considered to positively influence bone microstructure [18] and improved strength [19, 20]. In this context the aim of this study is to assess the effect of HFD - induced obesity on bone biomechanics and biochemical measurements and investigate whether exercise can reverse its potentially negative effects. M ATERIALS AND METHODS Selection and description of animals total of 26 male c57bl/6 mice, aged 10-11 weeks, were used. The mice were housed in groups of three in the Animal Housing Facility of the Laboratory of Experimental Surgery and Surgical Research “N.S. Christeas”, National and Kapodistrian University of Athens, in a controlled environment. All conditions followed National and European legislation and standards, including cages (Tecniplast S.p.a., Italy) and the environment with 55% relative humidity, central ventilation (15 air changes/h), temperature of 20°C ± 2°C and artificial 12-h light-dark cycle. Access to food and water was ad libitum. The experimental protocol was approved by the Ethics Committee of the local Veterinary Directorate. Following acclimatization, the rodents were randomized and allocated into three groups: Control group (Group A, n=6), which received a standard chow diet for 37 weeks; High Fat Diet (HFD) group (group B, n=10), which received a high fat diet (standard chow diet enriched with 45% fat) for 37 weeks; High Fat Diet and Exercise (HFDE) group (group C, n=10), which received the same diet as group B for 37 weeks and ran on a treadmill three times a week for the last nine weeks of the experimental protocol. Treadmill exercise The duration of the exercise of group C was nine weeks in total. A specially designed treadmill was used (Columbus Instruments, USA, Model: Exer-3/6). An escalation of the vigorousness of exercise was followed. More specifically, the first two weeks were characterized as the adjustment period. Meanwhile, the mice began to run at speed of 5 m/min and gradually (additional 5 m/min per time) reached the speed of 30 m/min at the end of the second week. This was their final running speed until the end of the study. Each exercise session lasted precisely 30 minutes. Biochemical measurements Blood samples were collected at baseline, at 12 weeks, at 28 weeks and at the end of the study (37 weeks) prior to eutha- nasia following a 12-h fast of the animals. Animals were anesthetized with ether and a quantity of approximately 500 μl of blood was collected from the ocular canthus of each mouse. Blood was collected in Vacutainer tubes (BD Diagnostics, NJ, USA). Serum was separated by centrifugation at 3000 rpm for 10 minutes and was stored at -20°C until analysis. O A