Fraction of unsaturated fatty acids in visceral adipose tissue (VAT) is lower in subjects with high total VAT volume – a combined ¹H MRS and volumetric MRI study in male subjects

Abstract

Visceral adipose tissue (VAT) is thought to play an important role in the pathogenesis of obesity and insulin resistance. However, little is known about the composition of VAT with regard to the amount of mono- (MUFAs) and polyunsaturated fatty acids (PUFAs) in triglycerides. Volume-selective MRS was performed in addition to MRI for the quantification of VAT. Analysis comprised proton signals from the vinyl-H group (H-C=C-H), including protons from MUFA+PUFA, and diallylic-H, i.e. methylene-interrupted PUFAs. The methyl (-CH(3) ) resonance, which is the only peak with a defined number of protons/triglyceride (n=9), served as reference. Twenty male subjects participated in this prospective study and underwent MRS of VAT on a 3-T whole-body unit. Spectra were recorded by a single-voxel stimulated echo acquisition mode (STEAM) technique (TE/TM/TR=20/10/4000 ms; volume of interest between 20 × 25 × 20 and 30 × 30 × 20 mm(3); 48-80 acquisitions depending on the size of the volume of interest; bandwidth, 1200 Hz). Post-processing was performed by a Java-based magnetic resonance user interface (jMRUI; AMARES). The volume of VAT was quantified in a separate session on a 1.5-T imager a few days prior to the MRS session by T(1) -weighted imaging. The relative amount of VAT was calculated as a percentage of body weight (%VAT). Ratios of vinyl-H to -CH(3) and diallylic-H to -CH(3) were calculated. All spectra recorded from VAT were of high quality, enabling reliable quantification of the mentioned resonances. %VAT and vinyl-H/CH(3) varied over a broad range (2.8-8.3% and 0.45-0.64, respectively). A strong negative correlation between %VAT and vinyl-H/CH(3) was found (r= -0.92), whereas diallylic-H/CH(3) alone was clearly less well correlated with %VAT (r= -0.21). The composition of VAT shows strong interindividual variations. The greater the total amount of VAT, the less unsaturated the fatty acids. This is a preliminary result in mainly obese male subjects, and it remains to be determined whether this correlation holds for other cohorts of different age, gender and body mass index. Furthermore, changes in VAT composition during weight loss or different forms of diet have yet to be examined.

Effects of Different Dietary Fatty Acids on Human Energy Balance, Body Weight, Fat Mass, and Abdominal Fat

“…The analysis of adipose tissue biopsies in cross-sectional studies found that the size of subcutaneous and visceral adipocytes was negatively associated with dietary PUFA intake, while adipocyte cell number negatively correlated with MUFA and positively correlated with SFA intake [99]. The fatty acid content of visceral fat was also higher in SFA and lower in unsaturated fatty acids compared to subcutaneous fat [97,100], suggesting that the visceral fat depot is a major storage site of SFA. Collectively, epidemiological data appear to support a potential protective role for unsaturated fat against body fat mass accumulation, especially in the abdominal region.…”

Magnetic Resonance Imaging of Adipose Tissue in Metabolic Dysfunction

“…3, 4) and thus can contribute to a risk assessment for the development of obesity-related complications [10,63,64]. In that regard, Machann et al found that the fraction of unsaturated fatty acids in VAT was lower in subjects with high total VAT volume [18]. Thomas et al found the "thin-onthe-outside fat-on-the-inside" subphenotype, with a higher ratio of intraabdominal over subcutaneous abdominal adipose tissue, to have an increased metabolic risk.…”

Assessment methods of body composition

“…Selektivna magnetna rezonanca u kombinaciji sa magnetnom rezonancom celog tela može da razdvaja i kvantifikuje volumene grupa adipocita pronađenih u skeletnom mišićnom kompartmanu, kao i količinu triglicerida u i izvan skeletnih mišićnih vlakana [49]. Kvanititativna magnetna rezonanca je dragocen metod za kvantifikovanje malih promena u masnoj masi [50].…”