Abstract Body: Background: Postprandial triglyceride (TAG) levels are an independent predictor of cardiovascular risk in humans. Chylomicrons (CMs) are the primary carrier of dietary TAG and they travel to the circulation via intestinal lymph. The protein components of CM’s can impact their metabolism in the circulation, however, the composition of CM’s is difficult to study because these particles are rapidly metabolized upon entry to the circulation.

Objectives: 1) Determine the protein and lipid composition of mesenteric lymph during fasting and after a lipid bolus, and 2) identify proteins in lymph that may impact the metabolism of newly secreted chylomicrons prior to entry into the circulation.

Methods and Results: A conscious lymph fistula procedure was used to collect mesenteric lymph from mice before and after infusion of a mixed lipid bolus into the duodenum. Wild type mice were compared to Dennd5b^-/- mice (n=5-8 mice/group), a model of impaired chylomicron secretion. This study revealed that, compared to wild type mice, Dennd5b^-/- mice exhibit significantly reduced TAG content in the lymph (-94%, p<0.001). Electron micrographs revealed that the lymph of wild type mice had both greater number and larger sized lipid particles compared to Dennd5b^-/- mice. In addition, lipidomics analysis of fasting and postprandial lymph showed significant increases in triglycerides and free fatty acids in wildtype, but not Dennd5b^-/- mice. Shotgun proteomics revealed significant changes in the lymph proteome of wild type mice after lipid bolus (14 proteins increased and 18 decreased; p<0.01). Key protein changes were confirmed by western blotting. One notable finding was an increase in lymph Saa1 after the lipid bolus (+200%, p<0.001). Size-exclusion chromatography was used to determine the distribution of Saa1 across lipoprotein fractions in lymph and demonstrated that Saa1 was associated primarily with fractions that contain chylomicrons and to a lesser extent with HDL-containing fractions.

Conclusions: We identified several proteins in intestinal lymph that respond to dietary lipid ingestion. In wildtype mice, lipid feeding increases lymphatic Saa1, which appears to be predominantly associated with chylomicrons. This response was not observed in Dennd5b^-/- mice, suggesting that it is dependent on successful CM secretion from intestinal epithelium. Current studies are aimed at understanding how CM-associated Saa1 may influence CM metabolism in the lymph or circulation.