Intersection of Brown Adipose Tissue and NAFLD: A Systematic Review.
T.P. Tran, Rohini Mehta, A. Birerdinc. A. Baranova
This is a collaborative project between
Molecular and Microbiology Department, College of Science,George Mason University, Fairfax, VA
Translational Reseach Institute, Inova Hospital, VA
Obesity currently is one of the leading problems overburdening our national public health system. Morbid obesity has been linked to a variety of severe, progressively degenerating conditions such as NASH, NAFLD, reproductive and cardiovascular disorders (Baranova et al. 2007). The increasing toll on individuals and public health resources alike has spurred the scientific community to investigate the intricate properties of fat formation and metabolism. Significant efforts have been made to understand the properties and functions of white adipose tissue (WAT) and its contribution to fat metabolism. Currently, another type of fat, namely brown fat (BAT) has drawn the attention of researchers. Some recent studies suggest that BAT may play and important role in adult body weight homeostasis, shedding some light on the protective function of BAT.
Brown adipose tissue (BAT) is thought to aid in the control of body temperature in hibernating animals and newborn infants. Animal studies indicate that BAT may be subtly but intricately involved in the regulation of overall body weight. Until recently, it was thought that BAT content in humans decreased with age and was lost in adults. However, recent studies have shown that not only is there active BAT cells in adult humans, but that the mechanisms of adaptive thermogenesis, thought to be a major function of BAT, may indeed be a factor to be considered when dealing with obesity (Lowell et al 2000).
A recent study using positron-emission tomography (PET) showed that glucose uptake after exposure to cold was increased by a factor of 15 in paracervical and supraclavicular adipose tissue of healthy adult subjects. Further analysis of this tissue indicated high levels of expression of uncoupling protein 1 (UCP1), leading the authors to conclude that adult humans may indeed have substantial amounts of metabolically active BAT tissue (Virtanen et al 2009).
A similar study involving 24 healthy men, 10 lean (BMI<25) and 14 obese (BMI>25), used integrated 18F-fluorodeoxyglucose positron-emission tomography and computed tomography under thermoneutral and mild cold (16 C) conditions and, found that obese men had significantly lower capabilities of adaptive thermogenesis than lean men. In addition the researchers found a significant positive correlation between adaptive thermogenesis and resting metabolic rate (van Marken Lichtenbelt et al 2009).
So far no research has been done on the detection of BAT in omental tissue from adult humans with varying degrees of obesity. Using the recently published data, we plan to perform a systematic review highlighting the intersection of BAT and NAFLD.
- Baranova A, Schlauch K, Elariny H, Jarrar M, Bennett C, Nugent C, Gowder SJ, Younoszai Z, Collantes R, Chandhoke V, Younossi ZM. Gene expression patterns in hepatic tissue and visceral adipose tissue of patients with non-alcoholic fatty liver disease. Obes Surg. 2007 Aug;17(8):1111-8. PubMed PMID: 17953248.
- Lowell BB, Spiegelman BM. Nature. Towards a molecular understanding of adaptive thermogenesis. 2000 Apr 6;404(6778):652-60. Review
- Virtanen KA, Lidell ME, Orava J, Heglind M, Westergren R, Niemi T, Taittonen M, Laine J, Savisto NJ, Enerbäck S, Nuutila P. Functional brown adipose tissue in healthy adults. N Engl J Med. 2009 Apr 9;360(15):1518-25.
- van Marken Lichtenbelt WD, Vanhommerig JW, Smulders NM, Drossaerts JM, Kemerink GJ, Bouvy ND, Schrauwen P, Teule GJ. Cold-activated brown adipose tissue in healthy men. N Engl J Med. 2009 Apr 9;360(15):1500-8. Erratum in: N Engl J Med. 2009 Apr 30;360(18):1917.