Non‐classical pathways for n‐3 triglyceride‐rich particle clearance: in vivo and in vitro studies

Abstract

N-3-rich triglycerides (TG) ameliorate many diseases such as cardiovascular diseases. Thus, since the mechanism of n-3 TG-rich particles (TGRP) uptake is not well characterized, we questioned whether n-3 TGRP are removed via non-classical pathways. Chylomicron-sized, [3H]cholesteryl ether-labeled n-3 TGRP were injected to wild-type (WT) and CD36 knockout (CD36−/−) at non-saturating and saturating doses. Blood clearance and fractional catabolic rate (FCR) of n-3 TGRP were measured. Triton WR1339 and heparin were used to assess roles of lipoprotein lipase (LpL)-mediated TGRP removal. At saturating doses, blood clearance of n-3 TGRP was slower in CD36−/− mice relative to WT suggesting that CD36, in part, contributes to n-3 TGRP uptake. There were no major differences in the changes of FCR of n-3 TGRP after pre-injection of Triton or heparin between WT and CD36−/− mice. To further examine the non-classical pathways, n-3 TGRP uptakes in peritoneal-elicited macrophages from WT and CD36−/− mice were studied in the presence of apoE, lactoferrin, and chlorate to test the roles of apoE-mediated pathways and/or proteoglycans (PG). ApoE-mediated pathways compensated defective n-3 TGRP uptake in CD36−/− cells. Lactoferrin decreased n-3 TGRP uptake in the presence of apoE. N-3 TGRP uptake was reduced by chlorate, an inhibitor of PG sulfation, in both groups and the chlorate effects were independent of apoE. We conclude that while CD36 does contribute, it does not function as a primary contributor for the blood clearance of n-3 TGRP. The removal of n-3 TGRP relies more on non-classical pathways such as HSPG-mediated pathways and little or no hydrolysis by LpL for blood clearance and tissue uptake.