Alterations of Lecithin:Cholesterol Acyltransferase Activity and Cholesterol Metabolism in Obese Beagles During Weight Loss
Little research has focused on the relationship between lecithin:cholesterol acyltransferase (LCAT) activity and cholesterol metabolism in dogs even though it is the major lipid metabolic enzyme involved in reverse cholesterol transport. To study alterations in LCAT activity and lipid metabolism during weight loss in this species, four experimental weight-loss diets were fed to 12 obese female beagles for 8 wk in a partial crossover design (n = 6). High- (HGI) or low-glycemic index (LGI) starch (waxy corn or high amylose corn, respectively) and diacylglycerol (DAG) or triacylglycerol (TAG) oil were combined to compose diets with similar fatty acid (FA) profiles. Both starches were gelatinized prior to formulation. Experimental diets were fed as a water-based gruel after acclimating the dogs to a similar gruel type basal diet. Dogs were fed the amount of kcal required to maintain their obese body weights. Consumption records were kept daily and body weights were measured weekly. Fasted blood samples were obtained at baseline, wk4, and wk8 to measure plasma LCAT activity using a radiolabeled endogenous substrate technique. Total (TC), unesterified (UC), and esterified cholesterol (EC) concentrations were determined via enzymatic methods. Fatty acid composition of the plasma phospholipid (PL) and EC fractions were determined after total lipid extraction, fractionation via thin-layer chromatography, and capillary gas chromatography. All groups lost weight as a result of voluntary reduction of food intake of the gruel-based type of diet. Plasma UC concentrations increased in all groups from baseline to wk4 (p < 0.05). LCAT activities increased from baseline to wk4 in all groups and remained elevated at wk8 (p < 0.05). Plasma PL FA profiles reflected the diets fed with few diet or time effects. Plasma EC FA profiles reflected the previously observed specificity of canine LCAT for linoleic acid (LA) again with minimal diet or time effects. We conclude that an increase in LCAT activity and plasma UC concentration is observed in conjunction with weight loss in dogs. Diet effects on these two parameters were not observed, indicating that the changes in LCAT activity and UC concentration were indeed due to weight reduction because all diet groups experienced weight loss. Dietary oil type (TAG vs. DAG) did not affect the plasma EC or PL fatty acid composition. These findings are likely due to the similar fatty acid composition of the experimental oils and diets and indicates that positional isomers of oil do not affect resultant FA profiles under the conditions employed.