Bovine milk exosomes (BMEs) harbor regulatory proteins, lipids and microRNAs. Consumption of an exosome and RNA-depleted (ERD) diet elicited phenotypes compared to controls fed an exosome and RNA-sufficient (ERS) diet in mice. All other ingredients were identical in the diets. ERD and ERS diets were prepared by substituting ultrasonicated and non-ultrasonicated milk, respectively, for casein in the AIN-93G formulation.
Bovine milk was ultrasonicated and exosomes were isolated by ultracentrifugation (USE); controls were not ultrasonicated (NSE). Exosome count, size and morphology were assessed using a nanoparticle tracker and electron microscopy. RNAs, lipids and proteins were analyzed by RNA-sequencing and mass spectrometry. Intestinal transport, bioavailability and distribution were measured by using fluorophore-labeled USEs and NSEs in Caco-2 cells, FHs 74 Int cells and C57BL/6J mice (n = 3; age 6 – 8 weeks).
The exosome count was 76 ± 22% lower in USE compared to NSE (P < 0.05). Ultrasonication caused a degradation of up to 100% of microRNAs. USE and NSE contained 145 and 332 unique lipid signatures, respectively (P < 0.05). We detected total of 525 and 484 proteins in USE and NSE. The uptake of USEs decreased by 46 ± 30% and 40 ± 27% compared to NSEs in Caco-2 and FHs 74 Int cells, respectively (P < 0.05). The hepatic accumulation of USEs was 48% ± 28% lower than the accumulation of NSEs in mice (P < 0.05).
Ultrasonication of milk depletes bioavailable BMEs in studies of Caco-2 cells, FHs 74 Int cells and C57BL/6J mice and causes a near-complete degradation of microRNA cargos.