Abstract
Prior studies have suggested that FAs liberated in the small intestine from ingested 1,3-diacylglycerol (DAG) are inefficiently incorporated into triglyceride (TG) in enterocytes, with less chylomicron TG entering the circulation postprandially. We found less TG, but more monacylglyerol and DAG, with similar total acylglycerol in newly secreted chylomicrons after oral DAG or triacylglycerol (TAG). However, clearance of DAG-chylomicrons was more rapid than that of TAG-chylomicrons; this was associated with more efficient in vitro LPL-mediated lipolysis of DAG-derived chylomicrons. Intravenously infused DAG was also cleared faster than TAG in normal mice, via both LPL-mediated lipolysis and apolipoprotein E (apoE)-dependent hepatic uptake. Infusions of TAG, but not DAG, increased plasma TG levels. Greater delivery of DAG-derived FA to the liver during infusion of DAG led to greater TG secretion versus TAG; this allowed the maintenance of similar hepatic TG levels after DAG and TAG infusions. Of note, apoB secretion was similar after DAG versus TAG, indicating the assembly of larger very low density lipoproteins after DAG. In conclusion, reduced plasma TG levels, after oral or intravenous DAG, result from more efficient clearance of DAG by both LPL lipolysis and apoE-mediated hepatic endocytosis. DAG emulsions may by useful for intravenous nutrition in people with preexisting hypertriglyceridemia.
Highlights
Prior studies have suggested that FAs liberated in the small intestine from ingested 1,3-diacylglycerol (DAG) are inefficiently incorporated into triglyceride (TG) in enterocytes, with less chylomicron TG entering the circulation postprandially
The metabolic pathways for processing lipid emulsions injected intravenously are similar to those for chylomicrons and VLDL: apolipoproteins are acquired from circulating lipoproteins and are taken up by tissues, mainly the liver, after hydrolysis by LPL [10, 11]
To determine whether the increased FA delivery to the livers of mice infused with DAG induced b-oxidation, we examined the hepatic expression of mRNAs for acyl-coenzyme A oxidase (AOX), carnitine palmitoyltransferase-1 (CPT-1), and peroxisome proliferator-activated receptor a (PPARa)
Summary
Prior studies have suggested that FAs liberated in the small intestine from ingested 1,3-diacylglycerol (DAG) are inefficiently incorporated into triglyceride (TG) in enterocytes, with less chylomicron TG entering the circulation postprandially. Clearance of DAG-chylomicrons was more rapid than that of TAG-chylomicrons; this was associated with more efficient in vitro LPL-mediated lipolysis of DAG-derived chylomicrons. Infused DAG was cleared faster than TAG in normal mice, via both LPL-mediated lipolysis and apolipoprotein E (apoE)-dependent hepatic uptake. Reduced plasma TG levels, after oral or intravenous DAG, result from more efficient clearance of DAG by both LPL lipolysis and apoE-mediated hepatic endocytosis. Effects of triacylglycerol and diacylglycerol oils on blood clearance, tissue uptake, and hepatic apolipoprotein B secretion in mice. The metabolic pathways for processing lipid emulsions injected intravenously are similar to those for chylomicrons and VLDL: apolipoproteins are acquired from circulating lipoproteins and are taken up by tissues, mainly the liver, after hydrolysis by LPL [10, 11]. This article is available online at http://www.jlr.org
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