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Biophysical characterization and diagnosis of obesity from adipose tissue by fourier transform infrared spectroscopy and imaging

Küçük Baloğlu, Fatma
Obesity is a heterogeneous disorder originating from the enlargement of visceral (VAT) and subcutaneous (SCAT) adipose tissue mass in the body and this process usually results in disturbed glucose and lipid metabolism. The first part of this study aimed to characterize and compare VAT and SCAT with regard to biomolecular content and also investigate transdifferentiation between white and brown adipocytes. Regarding this aim, Fourier transform infrared (FTIR) microspectroscopy and uncoupling protein 1 (UCP1) immunohistological staining was used in VAT and SCAT of male Berlin fat mice inbred (BFMI) lines, which are spontaneously obese. The results indicated a remarkable increase in the lipid/protein ratio, accompanied with a decrease of UCP1 protein content which might be due to the transdifferentiation of brown to white adipocytes in obese groups. Additionally, the lower unsaturation/saturation lipid ratio, the longer hydrocarbon acyl chain length of lipids and the higher amount of triglycerides were obtained in both adipose tissues of mice lines compared to control line. The results also revealed that SCAT was more prone to obesity-induced structural changes than VAT. The excess deposition of triglycerides in adipose tissue is the main reason of obesity and this process causes the excess release of fatty acids to the circulatory system leading to insulin resistance. The second part of this study mainly aimed to propose triglyceride band located at 1770-1720 cm-1 spectral region as a sensitive obesity related biomarker. For this reason, the diagnostic potential of FTIR spectroscopy coupled with hierarchical cluster analysis (HCA) and principal component analysis (PCA) was used in SCAT and VAT samples obtained from control and four different obese male BFMI mice lines. Successful discrimination of the obese, obesity related insulin resistant and control groups were achieved with high sensitivity and specificity. The results revealed the power of FTIR spectroscopy coupled with chemometric approaches in internal diagnosis of abdominal obesity based on the spectral differences in the triglyceride region. Gender is an important factor in the evaluation of obesity, hence the purpose of the third part of the study is to investigate gender-based differences in obesity by comparing biomolecular content of SCAT and VAT in male and female mice lines. In accordance with this comparative approach, ATR-FTIR spectroscopy coupled with multivariate data analysis was applied to the spectra of some special regions to differentiate male and female samples. To determine gender-based differences in the effect of obesity on VAT and SCAT in obese mice lines, the biomolecular characteristics of these tissues were compared in male and female BFMI mice by FTIR microspectroscopy. UCP1 immunohistological staining was also performed to compare the appearance of brown and white adipocytes in different genders. The results indicated that obesity indicators were more significant in SCAT of female mice while they were more significant in VAT of male mice. Consequently, the effects of obesity on male’s health can be more harmful than females.