Circulating exosomes as delivery mechanism of free fatty acids (cFFA)

Background: Circulating free fatty acids (cFFA) are involved in different human diseases such as diabetes, atherosclerosis and metabolic syndrome, although the exact role of cFFA in each disease needs to be clarified. In this context, we studied how circulating exosomes function as cargo vesicles for the transportation of cFFA from blood to target tissues. Exosomes are small membrane vesicles (30-100 nm) formed by reverse budding in the cytoplasm and secreted by a large variety of cells. These nanovesicles participate in the intercellular communication by delivering a large variety of bioactive molecules among tissues. Methods: Serum from healthy donors was obtained before (PRE) and 20 min after (POST) a high caloric breakfast. Circulating exosomes (cExo) were purified by ultracentrifugation and characterized by Nanosight, SEM and detection of tetraspanins. Using Western blot we studied the levels of platelet glycoprotein 4 (CD36) in the isolated cExo. The content of lipids and the ability of cExo to uptake cFFA were measured using Red Nile dye and BODIPY® 500/510. Results: POST cExo showed higher levels of CD36 compare to PRE cExo. Using Nile Red we demonstrated that POST cExo have higher levels of lipids compare to PRE cExo, correlating with CD36 levels. CD36 has an important role in cFFA uptake by cells. Using BODIPY® 500/510 we demonstrate that cExo are capable of incorporating cFFA and that CD36 has an active role in this process. Furthermore, we also observed that cExo are able to deliver cFFA to human cardiac microvascular endothelial cells and cardiomyocytes. Summary/Conclusion: Taken together, our results shed light on the role of cFFA in metabolic pathologies. Our results indicate that circulating exosomes are able to actively incorporate free fatty acids by CD36 and deliver them to target tissues.