2757-LB: Acute Postpartum Exercise Increases Acylcarnitine Content in Human Breast Milk Small Extracellular Vesicles

Introduction and Objective: Postpartum maternal exercise improves metabolic health of the offspring, yet the underlying mechanisms are not well defined. Breast milk metabolites, such as acylcarnitines (ACs) have been implicated as mediators of maternal-infant signaling. However, many metabolites are degraded in the gut. Breast milk is rich in small extracellular vesicles (BMsEVs) that can withstand digestion and deliver intact metabolic cargo to recipient cells. Methods: We tested whether 30-minutes of moderate-intensity postpartum exercise alters BMsEV AC content. Eleven healthy lactating women completed two days of standardized meals before study visits, including an exercise trial and time-matched sedentary control visit. Baseline breast milk samples were collected from the second pump of the day after 1hr of supervised rest. Participants remained sedentary or walked on an incline for 30 minutes at 70% VO2max. Breast milk was collected at 30-minutes (time-matched on sedentary visit) and 120-minutes post-exercise for isolation of sEVs by size-exclusion chromatography and ultracentrifugation. ACs (C0-C18:1) were measured in whole milk and BMsEVs by targeted LC-MS. Results: Concentrations of all quantifiable AC species (C0, C2, C3, iC4, C4, C12, C14, C16, C18, C18:1) in BMsEVs were significantly (P<0.05) elevated (ranging from Log2FC of 0.63 to 1.65) at 30 and 120 minutes post-exercise. No effect was observed in AC concentration in BMsEVs on the sedentary day. In contrast, whole milk long-chain ACs increased on both the exercise and sedentary visits, reflecting diurnal variation rather than an exercise effect. Conclusion: Increased BMsEV concentration suggests that postpartum exercise enriches breast milk with sEVs, providing an avenue for maternal-infant transfer of beneficial exercise-responsive metabolic cues. Disclosure S.S. Loona: None. V. Parmar: None. D. Gupta: None. K. Sevits: None. K. Klaus: None. L.M. Szymanski: None. A. Egan: None. M. Pataky: None. Funding NIH (DK141911)