Background: This study compares the accumulation of pre-formed chylomicron-remnants, chylomicrons and low-density lipoproteins (LDL) in rabbit thoracic aorta. To determine whether lipoproteins are delivered via the vasa vasorum, the aortic uptake of lipoproteins was compared to that of the common carotid artery. The uptake of chylomicron remnants and LDL were compared in lesioned and non-lesioned aortic tissue from Watanabe heritable hyperlipidaemic (WHHL) rabbits.
Methods: Chylomicrons, chylomicron-remnants and LDL were radio-labelled with tyramine-cellobiose and injected into rabbits. Arterial uptake was determined after 2 h as the percentage of injected lipoproteins associated with arterial tissue and also expressed as a fraction of mean arterial exposure.
Results: Aortic accumulation of radio-labelled chylomicron-remnants was substantially greater than for chylomicrons, and both were significantly greater than LDL. The data suggests that chylomicrons must first be hydrolysed to smaller particles before uptake. In normal rabbits, there was no difference in uptake of the lipoproteins between the aorta and carotid vessels, suggesting that the vasa vasorum is not significantly involved in lipoprotein delivery. However, in WHHL rabbits there was significantly greater aortic uptake of chylomicrons and LDL compared to the carotid vessel and, in cholesterol-fed rabbits, significantly greater aortic uptake of chylomicrons, suggesting that in hypercholesterolaemia the lipoprotein retention properties of some arterial beds change. In arterial fatty lesions from WHHL and cholesterol-fed rabbits there was an exclusive increase in chylomicron remnant uptake, whereas LDL uptake was similar to non-lesioned tissue.
Conclusions: Chylomicron remnants and not their precursors might be primary atherogenic lipoprotein because they penetrate arterial tissue efficiently and are selectively retained in sites of lesion formation.