BOLD-MRI evaluation of subcutaneous and visceral adipose tissue oxygenation status: effect of dietary salt intake

Abstract

To investigate the feasibility of blood oxygen level dependent magnetic resonance imaging (BOLD-MRI) in evaluating human subcutaneous and visceral adipose tissue (AT) oxygenation status, as well as their responses to dietary salt loading/depletion, we enrolled 16 healthy subjects [mean body mass index (BMI): 24.8 ± 2.7 kg/m(2)] to conduct a dietary intervention study, beginning with a 3-day run-in period for usual diet, followed by a 7-day high-salt diet (≥ 15 g NaCl/day) and a 7-day low-salt diet (≤ 5 g NaCl/day). Abdominal BOLD-MRI scan was performed to evaluate oxygenation in waist subcutaneous and perirenal (visceral) AT. Two subjects with lower BMI were excluded because of the difficulty to identify subcutaneous AT. High salt diet led to a consistent increase in R2* signal (a parameter for increased hypoxia) both in subcutaneous and visceral AT (all P < 0.0001), which was completely regressed to baseline levels by low salt diet. In addition, subcutaneous AT R2* values at any time points, were all higher than that of visceral AT (all P < 0.0001). Pearson correlation analysis revealed that the visceral AT R2* levels were negatively associated obesity indicators (waist circumference, waist-to-hip ratio and BMI). On the contrary, although a trend towards negative associations between the subcutaneous AT R2* and obesity indicators was observed, none of the associations reached statistical significances. Thus, our data demonstrate the possibility of simultaneous detection of human subcutaneous and visceral AT oxygenation status using BOLD-MRI. In addition, there is a more close relationship visceral AT oxygenation status and the development of obesity.

Keywords: BOLD-MRI; hypoxia; oxygenation; salt intake; subcutaneous adipose tissue; visceral adipose tissue.

Figure 1

Dietary intervention protocol.

Figure 2

Blood oxygen level-dependent magnetic resonance imaging (BOLD-MRI) of subcutaneous and visceral AT during dietary intervention. A: A typical abdominal coronal MRI image for the measurement of AT oxygenation. B: The waist subcutaneous and perirenal (visceral) AT from Figure A is highlighted by green and red color for ROI (region of interest) selection, respectively. C: Statistical comparison of BOLD-MRI signals during the intervention (n = 14, one-way repeated-measures ANOVA). D to F: Representative changes of BOLD-MRI images of one participant during dietary intervention on baseline (day 3), high salt (day 10) and low salt (day 17), respectively.

Figure 3

Linear correlation analyses of subcutaneous AT R2* values and visceral AT R2* values during dietary intervention.

Figure 4

Linear correlation analyses of subcutaneous and visceral AT R2* values at baseline and obesity indicators [waist circumference, waist-to-hip ratio and body mass index (BMI)].