Bariatric Surgery Is Accompanied by Changes in Extracellular Vesicle-Associated and Plasma Fatty Acid Binding Protein 4

Background: Bariatric surgery markedly reduces fat mass with beneficial effects on cardiometabolic health but the mechanisms involved are not fully understood. Extracellular vesicles (EVs) are secreted by a variety of cells, including adipocytes, and may mediate some of these benefits. However, the effects of bariatric surgery on circulating EVs are unclear. Methods: Concentration of plasma EVs isolated by ultracentrifugation at baseline, 1 and 6 months post-bariatric surgery (n = 20) was established using Nanoparticle Tracking Analysis. EV origin (CD9: exosome; CD41: platelet; CD235a: erythrocyte; CD11b: leukocyte; CD144: endothelial), cytokine (interferon γ, interleukin-6, TNF-α) and adipocyte marker (adiponectin, FABP4, PPARγ) expression was measured by time-resolved fluorescence immunoassay. Results: EV concentration and cell-of-origin markers (CD41, CD235a, CD11b, CD144) did not alter in response to surgery, neither did EV-expressed interferon γ, IL-6, TNF-α, adiponectin, PPARγ or CD9. EV-derived fatty acid binding protein 4 (FABP4) increased at 1 month (+ 49%) before returning to baseline by 6 months (− 51%, p < 0.05), corresponding to similar changes in circulating plasma FABP4 (+ 22 and − 24% at 1 and 6 months, respectively; p < 0.001). Patients who underwent biliopancreatic diversion had lower FABP4-expressing EVs at 6 months compared to those who underwent sleeve gastrectomy/gastric banding (p < 0.05), despite similar percentage weight reduction (− 19 vs − 20%, respectively). CD9 expression correlated with EV-expressed FABP4, adiponectin, TNF-α and interferon γ (r = 0.5, r = 0.59, r = 0.53, r = 0.41, respectively, p < 0.005), suggesting transport by an EV population of exosomal rather than microvesicular origin. Conclusions: Bariatric surgery leads to a transient change in circulating EV- and plasma-derived FABP4, reflecting alterations in adipose tissue homeostasis.