Lecithin:Cholesterol Acyltransferase Activity and its Fatty ACYL Specificity in Cats Fed Diets of Varying Fatty Acid Composition
Beyond the fact that cats express low delta-6 desaturase activities, lipid metabolism in this species remains to be fully explored under varying dietary or other experimental conditions including other important metabolic enzymes such as lecithin:cholesterol acyltransferase (LCAT), which is involved in reverse cholesterol transport. To characterize LCAT activity and demonstrate its fatty acyl specificity in cats fed varying types of dietary fat, intact young females were fed diets enriched with high-oleic sunflower (n = 9), menhaden fish (n = 10), or safflower (n = 10) oil (8g oil/100g kibble) for 4 wk. Fasted blood samples were drawn at d0, d14, and d28 for determination of plasma total (TC), unesterified (UC), and esterified cholesterol (EC) concentrations, LCAT activity, and fatty acid (FA) composition of the EC fraction. UC decreased at d28 compared to d0 and d14, while EC increased at d28 compared to d0 and d14 (all p < 0.05). LCAT and TC showed no time or diet effects. Plasma EC FA profiles reflected the specificity of LCAT for linoleic acid (LA) and numerous diet and time effects were observed. Even though similar amounts of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) were supplied by the fish oil diet and significant amounts of EPA were detected in the plasma EC fraction, no DHA was identified in this fraction, indicating very little or no affinity of feline LCAT for DHA. The fish oil diet supplied docosapentaenoic acid (DPA) as well, but this FA was also absent in the plasma EC fraction, suggesting little or no affinity of feline LCAT for DPA. We conclude that feline LCAT has no measurable affinity for DHA, but that feline LCAT demonstrated specificity for LA regardless of diet fed. Finally, it was noteworthy that some changes in feline plasma EC FA composition were statistically significant after only 14 days of feeding the experimental diets. This observation indicates rapid modification of feline FA metabolism by dietary fatty acid composition. By d28, further significant differences due to time were seen, indicating that while initial differences can be seen in as little as 14 days, a longer study period may be necessary to establish a metabolic steady state. Whether 28 days is enough time to achieve this effect cannot be determined by the present study. However, our studies in dogs and other species indicate that 28 days is suitable to achieve steady state effects of plasma fatty acids. Nonetheless, we did demonstrate that 28 days feeding is a long enough study period to observe alterations in feline FA metabolism. Finally, because no diet or time effects were seen on LCAT activity, the values for all cats at all time points were averaged to obtain a basal LCAT activity for adolescent cats of 92.4 ± 4.5 nmol of UC esterified/ml of plasma/hr (mean ± SEM). This is lower than an earlier reported value for LCAT activity in adolescent cats, and is likely due to differences in methodology. The present work utilized an endogenous substrate method while the earlier study employed an artificial proteoliposome substrate technique.