Lipid and fatty acid composition of canine lipoproteins

Abstract

Lipid classes and their fatty acids were studied in the major lipoprotein fractions from canine, in comparison with human, plasma. In dogs, high-density-lipoprotein (HDL), the main carrier of plasma phospholipid (PL), cholesterol ester (CE) and free cholesterol, was the most abundant lipoprotein, followed by low and very-low density lipoproteins (LDL and VLDL). Notably, LDL and VLDL contributed similarly to the total dog plasma triacylglycerol (TG). The PL composition was similar in all three lipoproteins, dominated by phosphatidylcholine (PC). Even though the content and composition of lipids within and among lipoproteins differed markedly between dog and man, the total amount of circulating lipid was similar. All canine lipoproteins were relatively richer than those from humans in long-chain (C20-C22) n-6 and n-3 polyunsaturated fatty acids (PUFA) but had comparable proportions of total saturated and monoenoic fatty acids, with 18:2n-6 being the main PUFA in both mammals. The fatty acid profile of canine and human lipoproteins differed because they had distinct proportions of their major lipids. There were more n-3 and n-6 long-chain PUFA in canine than in human plasma, because dogs had more HDL, their HDL had more PC and CE, and both these lipids were richer in such PUFA.

Introduction

Vertebrates differ in their relative amounts of plasma lipoproteins. In the vast majority of mammals, including the dog, HDL is the predominant fraction (Chapman, 1986, Lehmann et al., 1993, Bauer, 1996). Those mammalian species where high density lipoproteins (HDL) account for 50% or more of the total particles of density less than 1.21 g/ml in plasma are considered ‘HDL mammals’ (Chapman, 1986). Physicochemical properties of canine lipoproteins and the enzymes involved in their metabolism are of interest because, in contrast to humans and other so termed ‘LDL mammals’, the dog is substantially resistant to the development of atherosclerosis and hypercholesterolemia (Watson and Barrie, 1993). Mahley and Weisgraber (1974) characterized dog lipoproteins including description of microscopic appearance, major apoprotein constituents and lipid classes. The fatty acid composition of the total plasma lipid was also reported in dogs in comparative studies with other mammals (Pekiner and Pennock, 1995). However, quantitative and qualitative information about the lipid constituents of dog lipoprotein fractions is still fragmentary. The aim of this work was to present a description of the lipid and fatty acid composition of the major lipoprotein classes in the dog. For that purpose, plasma lipoproteins were separated by applying the method developed by Vieira et al. (1996) for the rapid isolation of human LDL. The good separation between the three main lipoprotein fractions, and the short time of processing, made this method attractive and suitable for the study of lipoprotein lipids and their fatty acids. The present results compare, on the same methodological bases, the lipoprotein lipid constituents of dog and man. The latter is mostly used as a control, since the composition of human lipoproteins is widely known. Dog and man are shown to have a phosphatidylcholine-rich and a cholesterol ester-rich fasting plasma, respectively. Canine plasma is shown to be relatively richer in long-chain n-6 and n-3 PUFA than human plasma because of its distinctive lipoprotein profile, dominated by HDL.