Changes in fatty acid compositions of total serum and lipoprotein particles, in growing rats given protein-deficient diets with either hydrogenated coconut or salmon oils as fat sources.

Abstract

The present study examines the effects of dietary saturated (hydrogenated coconut oil) and polyunsaturated (salmon oil) fats on the composition and metabolism of lipoproteins in growing rats fed on protein-deficient diets. Four groups of rats were fed on the following diets for 28 d: 200 g casein + 50 g coconut oil (COC)/kg, 20 g casein + 50 g coconut oil (COd)/kg, 200 g casein + 50 g salmon oil (SAC)/kg, 20 g casein + 50 g salmon oil (SAd)/kg. Both protein-deficient groups exhibited low concentrations of protein and triacylglycerol (in serum, very-low-density lipoprotein (VLDL), low-density lipoprotein-high-density lipoprotein, (LDL-HDL1) and HDL2-3), of cholesterol (in LDL-HDL1) and of phospholipids (in VLDL). Furthermore, serum and VLDL cholesterol concentrations were also reduced in the SAd group. Compared with rats given 200 g casein/kg diets, those fed on low-protein diets presented lower linoleic and arachidonic acid levels, in serum phospholipids and a dramatic decrease in the polyunsaturated: saturated fatty acid value. Relative amounts of linoleic and arachidonic acids in phospholipids of VLDL and HDL2-3 were also lowered in the COd group but not in the SAd group. However, proportions of 22:5n-6 and 22:6n-3 in VLDL and HDL2-3 phospholipid fractions were enhanced in the COd and SAd groups respectively. The most affected apolipoproteins (apo) were apo B100 and apo B48 in rats fed on protein-deficient diets, apo AI and apo E in the COd group, and apo AIV in the SAd group. Compared with rats fed hydrogenated coconut oil diets, those fed salmon oil diets had enhanced LDL-HDL1 and HDL2-3 but lower VLDL total apolipoproteins (mainly due to a fall in apo B100 and apo B48). Arachidonic and eicosapentaenoic acids, which are impaired by protein deficiency, are the precursors of prostaglandins, thromboxanes and leukotrienes which are implicated in a number of regulatory processes. Our results demonstrate that protein malnutrition is associated with impaired metabolism of arachidonic and eicosapentaenoic acids. Protein malnutrition and essential fatty acid (EFA) deficiency are characterized by many common clinical features and the link between the two may be an impaired production of eicosanoids, since arachidonic and eicosapentaenoic acids are the precursors of these important metabolic regulators. Because of the apparent involvement of EFA deficiency in the aetiology of protein malnutrition, it may be prudent to include adequate amounts of EFA in diets of infants suffering from kwashiorkor.