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Morbid obesity is an increasing epidemic in the US and is the leading factor in the development of cardiovascular diseases such as coronary atherosclerosis, hypertension, dyslipidemia, and Type 2 diabetes (T2DM) [1,2,3]. Currently, gastrointestinal bypass surgery, specifically Roux-en-Y bypass (RGBP) surgery, is the most established and effective treatment for substantial and sustained weight loss in morbidly obese subjects [4,5,6]. However, the mechanism in which the tissue of the adipose organ changes is not well understood. Strategies have been developed to understand the role and changes of this endocrine organ before, during and after the RGBP surgery, particularly its spatial distribution, triglyceride composition , and mitochondrial density along with molecular and cellular approaches.
We will investigate AT using MRI and PET imaging on obese rats before and after RGBP surgery. A number of control obese rats will undergo a sham RGBP surgery. MRI-based characterization of AT will include analysis of: (a) spatial distribution (visceral and subcutaneous) using fat-water MRI, (b) triglyceride chain length, unsaturation degree and polyunsaturation degree composition , and (c) R2* relaxation time within AT to detect iron concentration increases associated with inflammation. Also we will perform PET/CT scans using 18F-FDG and TSPO contrast agents to respectively determine glucose uptake and mitochondrial density  within brown adipose tissue (BAT) that is distinct from white adipose tissue (WAT). We will compare our results with metabolic blood panels and molecular biology techniques to validate and understand AT changes before, during and after RGBP surgery.
Results & Significance
Many advances have been made to understand the underlying mechanism of prolonged weight loss after Roux-en-Y, but characterization of AT, specifically spatial distribution, triglyceride composition, inflammation status and mitochondrial density before and after surgery, has not been previously measured in a single imaging-based study. Investigating the role played by AT in combination with hormone and cellular signaling will provide a better understanding of weight loss mechanisms after gastrointestinal (GI) bypass intervention.
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Vanderbilt University Institute of Imaging Science (VUIIS)