Metabolic imaging in obesity: underlying mechanisms and consequences in the whole body

Abstract

Obesity is a phenotype resulting from a series of causative factors with a variable risk of complications. Etiologic diversity requires personalized prevention and treatment. Imaging procedures offer the potential to investigate the interplay between organs and pathways underlying energy intake and consumption in an integrated manner, and may open the perspective to classify and treat obesity according to causative mechanisms. This review illustrates the contribution provided by imaging studies to the understanding of human obesity, starting with the regulation of food intake and intestinal metabolism, followed by the role of adipose tissue in storing, releasing, and utilizing substrates, including the interconversion of white and brown fat, and concluding with the examination of imaging risk indicators related to complications, including type 2 diabetes, liver pathologies, cardiac and kidney diseases, and sleep disorders. The imaging modalities include (1) positron emission tomography to quantify organ-specific perfusion and substrate metabolism; (2) computed tomography to assess tissue density as an indicator of fat content and browning/ whitening; (3) ultrasounds to examine liver steatosis, stiffness, and inflammation; and (4) magnetic resonance techniques to assess blood oxygenation levels in the brain, liver stiffness, and metabolite contents (triglycerides, fatty acids, glucose, phosphocreatine, ATP, and acetylcarnitine) in a variety of organs.

Obesity-Associated Alterations in Glucose Metabolism Are Reversed by Chronic Bilateral Stimulation of the Abdominal Vagus Nerve

“…Such changes in HGU have been observed in obese subjects both before and after undergoing bariatric surgery (10). Abnormalities in HGU have been implicated in the pathogenesis of liver steatosis, hypertriglyceridemia and type 2 diabetes (21). Accordingly, vagally induced improvement in HGU may be of relevance in the context of obesity, despite the limited quantitative impact of HGU on whole-body glucose uptake (about 1% of whole-body glucose uptake).…”

“…Therefore, we believe that the investigation of the impact of vagal stimulation on glucose metabolism must be comprehensive. We have used a combination of methods, including quantitative PET imaging, which represents the gold standard, to investigate glucose metabolism at the systemic and organ levels (21). Potential confounding effects related to surgery were minimized by the development of 1) a laparoscopic surgical approach to insert dedicated electrodes on the dorsal and ventral vagal trunks and 2) a purpose-made dual-channel stimulator placed under the skin.…”

DBS for Obesity

“…In rodents, binging on sugar and the ingestion of fat diets increase the release of dopamine in the NAc [ 32 , 33 ]. In addition to the above-mentioned evidence, numerous neuroimaging studies using positron emission tomography or functional magnetic resonance imaging have been conducted in obese patients at baseline and during activation tasks (for a review see [ 34 , 35 ]). Overall, sensory stimuli related to palatable foods seem to activate cortical regions and the reward circuitry, including the ventral striatum [ 34 , 35 ].…”

Production of highly polarized [1‐13C]acetate by rapid decarboxylation of [2‐13C]pyruvate – application to hyperpolarized cardiac spectroscopy and imaging

“…Changes in fatty acid metabolism in various diseases have been studied using PET . In combination with [ 11 C]acetate as a validated tracer, cardiac oxidative metabolism has been assessed.…”