Assessing ectopic fat heterogeneity in human volunteers

Abstract

Accumulation of ectopic fat in liver and pancreas are seen as key indicators of the metabolic syndrome affecting over a third of the population in the western world. Deposition of these ectopic fat depots is linked to insulin resistance, a major risk factor in the development of type 2 diabetes.

Quantifying ectopic fat deposition, without the use of biopsy, has always been a challenge. Magnetic resonance (MR) techniques have emerged as the gold-standard for estimating overall fat deposition. However, little is known on the regional variation of fat deposition in liver and pancreas in human subjects. The aim of this project was to determine, using an in vivo Multi-Echo MR imaging technique, regional variations in ectopic fat deposition in liver and pancreas and assess the potential impact of environmental factors, including BMI, age, and gender.

The overall ranges in liver and pancreas fat ranged from 0.69- 32.27 % and 0.40 - 24.18% respectively. There was a strong correlation between liver fat, body weight, waist-to-hip ratio and waist circumferences. A significant correlation between pancreatic fat and waist-to-hip ratio, particularly in men, was also observed. The relationship between liver and pancreatic fat was surprisingly weak, suggesting different mechanism of accumulation.

Regional variations in liver and pancreatic fat were assessed by using surgical segmentations as anatomical markers, resulting in 8 anatomical segments for the liver and 3 for the pancreas.

Intra-abdominal adipose tissue and age had the largest effect on liver and pancreatic fat deposition.

Relative physical activity influenced the overall levels of liver ectopic fat content but did not significantly affect regional distribution in the pancreas. No gender differences in fat distribution in the liver were detected but a strong correlation with pancreas and men was detected.

Life-style interventions, such as weight loss programs, showed significant reduction in overall liver and pancreatic fat content. As for bariatric interventions, more significant reduction of overall ectopic fat in liver was seen with an increase in total and regional pancreas fat content.

In conclusion, I have shown, utilising an anatomical compartmentalisation of the liver and pancreas, that there are significant heterogeneity in fat deposition in the pancreas, and that different regions respond variably to lifestyle interventions. There is a more homogeneous fat deposition in the liver, which is more consistently modulated in response to lifestyle changes.