A model for studying LCAT reaction: In vitro cholesterol esterification in pig ovarian follicular fluid

Phosphatidylcholine acyltransferase (lecithin:cholesterol acyltransferase or LCAT; EC 2.3.1.43) activity was found to be present in pig ovarian follicular fluid (POFF), in addition to pig serum (PS). The cholesterol esterification rate in both POFF and PS is linear with incubation time up to 2 hr. The mean absolute rate of POFF-cholesterol esterification was 8.1±0.4 nmoles per ml per hr approximately one-fourth of that in PS. However, the fractional rate (percent of labeled cholesterol esterified per hr) of POFF-cholesterol esterification was similar to that observed in PS. There was little variation of absolute rate of cholesterol esterification in the fluid obtained from different sizes of follicles. Fatty acid or triacylglycerol did not participate in the reaction of cholesterol esterification in POFF. No appreciable change in enzymatic activity was found from storing POFF at 4 C for periods of time up to 24 hr or at −70 C up to 2 months, but activity was lost thereafter. On the other hand, PS showed a much longer period of stability (5 days at 4 C and 9 months at −70 C). A discrepancy between the fatty acid composition of cholesteryl esters formed by the LCAT reaction and the fatty acid composition at the C-2 position of phosphatidylcholine led us to propose a two-step mechanism for the LCAT reaction. It is concluded that the LCAT of POFF, as well as that of plasma, is specific for individual fatty acids rather than for the fatty acid composition of phosphatidylcholine. The fatty acid concentration of lysophosphatidylcholine decreased during prolonged incubation times (6 to 21 hr) suggesting that the increased lysophosphatidylcholine formed as a product of the LCAT reaction may be reused as substrate for the LCAT reaction or for hydrolysis by lysophosphatidylcholine hydrolase. Presented at the AOCS Meeting, New York, May 1977.     

Effect of polyestradiol on lecithin:cholesterol acyltransferase in male and female rats

The effects of two doses of polyestradiol phosphate on lecithin:cholesterol acyltransferase activity and on liver and plasma cholesterol levels have been studied on female and male rats. Both treatments increased the hepatic content of esterified cholesterol, but the LCAT activity expressed as a percentage of cholesterol esterification was unaltered. The progress of esterification was not affected by the administration of the hormone. The LCAT activity in terms of the initial rate of esterification was decreased by the high dose of estradiol. This decrease was associated with a reduction of free plasma cholesterol level, as there is a significant positive correlation between these two parameters. The findings suggest that the increased esterified cholesterol in liver of estradiol-treated rats is not mediated by an alteration in the LCAT activity.     

Effect of cupric ions on serum and liver cholesterol metabolism

Cupric ions were administered subcutaneously to male Sprague-Dawley rats at a single dose of 200 μmol/kg. At 24 hr after administration, a remarkable increase of total and free cholesterol was seen in the rat serum. Also, when lecithin-cholesterol acyltransferase (LCAT) (E.C. 2.3.1.43) activity was expressed as the percentage of the total serum that free cholesterol esterified, the acyltransferase activity in rats treated with cupric ions showed a slight decrease while the triglyceride content in rat serum and liver decreased by 54% and 61%, respectively. However, the content of hepatic cholesterol in rats treated with cupric ions did not show such a marked change. On the other hand, acid cholesteryl ester hydrolase activity (Acid CEH) (E.C. 3.1.1.14) in liver lysosomes of rats treated with cupric ions showed a marked decrease with increasing cupric ion concentration both in vivo and in vitro. Furthermore, cupric ions caused a marked release of the lysosomal enzymes cathepsin D and β-glucuronidase into the cytosolic fraction. The changes in acid cholesteryl ester hydrolase activity induced by cupric ions appear to be a direct effect of cupric ions on the enzyme. These results suggest that excessive cupric ion concentrations could cause various disorders in lipid metabolism.     

Moderate Dietary Intake of Myristic and Alpha-Linolenic Acids Increases Lecithin-Cholesterol Acyltransferase Activity in Humans

Cholesterol removal from tissues into HDL depends on the activity of lecithin-cholesterol acyltransferase (LCAT; E.C. 2.3.1.43) that is associated with lower cardiovascular diseases risk. HDL cholesterol concentration and LCAT activity can be modulated by dietary fatty acids. Original data with substrate models have shown a positive effect of myristic acid (MA) on the esterification rate of cholesterol. The purpose of this study was to examine the effect of moderate intakes of MA associated with recommended intake of alpha-linolenic acid (ALA) on LCAT activity in humans. Two experimental diets were tested for 3 months each. Diet 1-MA 1.2% of total energy (TE) and ALA 0.9% TE, diet 2-MA 1.8% and ALA 0.9% TE; a control diet (MA 1.2% and ALA 0.4% TE) was given 3 months before diet 1 and diet 2. The endogenous activity of LCAT was determined at completion of each diet. Compared with the control diet (13.2 ± 3.1 μmol CE/(L.h)), LCAT activity increased significantly (P < 0.001) with diet 1 (24.2 ± 3.6 μmol CE/(L.h)) and diet 2 (33.3 ± 7.4 μmol CE/(L.h)); the increase observed with diet 2 was significantly (P < 0.001) greater than that due to diet 1. These results suggest that ALA (from rapeseed oil, mainly in sn-2 position) and MA (from dairy fat, mainly in sn-2 position) favor LCAT activity, by respective increases of 83 and 38%. When they are supplied together, a complementary effect was observed (average increase of 152%). Moreover, these observations were associated with a decrease of the ratio of total to HDL-cholesterol. In conclusion, our results suggest that moderate supply of MA (1.8% TE) associated with the recommended intake of ALA (0.9% TE) contributes to improve LCAT activity.     

Net lipid transfer between lipoproteins in fish-eye disease plasma supplemented with normal high density lipoproteins

Native fish-eye disease plasma, which is deficient of both high density lipoproteins (HDL) and lecithin-cholesterol acyltransferase activity (α-LCAT), processing the free cholesterol of these lipoproteins, has been supplemented with normal isolated HDL₂ or HDL₃ and incubated in vitro at 37 C. After incubation for 0,7.5 and 24 hr the very low density (VLDL) and low density (LDL) lipoproteins as well as HDL were isolated, and their contents of triglycerides, phospholipids and free, esterified and total cholesterol were quantified. The resulting net mass transfer of the different lipids revealed a functioning transfer of cholesteryl esters and all other analyzed lipids between the lipoproteins, although no de novo esterification of the HDL cholesterol by LCAT in this plasma occurred. In accordance with previous findings there was a functioning esterification process of the free cholesterol of the combined VLDL and LDL of fish-eye disease plasma. The present results make it reasonable to conclude that the lack of HDL cholesterol esterification in this disease is not a result of a deficiency of cholesteryl ester transfer or lipid transfer activities.     

Cholesteryl ester metabolism in tissue culture cells: II. Source of accumulated esterified cholesterol in Fu5AH rat hepatoma cells

Previous investigations had demonstrated that Fu5AH rat hepatoma cells accumulated large quantities of esterified cholesterol when grown in hyperlipemic rabbit serum. The present investigation has determined the sources of the cellular esterified cholesterol when the cells were grown in hyperlipemic serum. Cellular esterification of endogenous and exogenous free cholesterol contributed 10% and 30%, respectively. The remaining 60% of the accumulated cellular esterified cholesterol was derived from exogenous (serum) cholesteryl esters. Evidence for the hydrolysis of a portion of the incorporated esterified cholesterol is presented. A stimulation of free cholesterol incorporation and cellular esterification is elicited by hyperlipemic serum and serum lipoproteins when compared to normolipemic serum present at equivalent exogenous cholesterol concentrations. The effect of hyperlipemic serum is reduced by Tween-80 and Triton WR-1339. Comparative data on esterified cholesterol accumulation, free cholesterol incorporation, and cellular cholesterol esterification in Fu5-5 rat hepatoma cells, L-cells, and rabbit aortic medial cells are presented. This work was done during the tenure as Established Investigator of the American Heart Association.     

Exchange of free cholesterol between plasma and erythrocytes from hyperthyroid and hypothyroid ratsin Vitro

In our previous studies, we found that circulating thyroid hormone levels alter cholesterol partition between plasma and erythrocytes by changing the phospholipid content of erythrocytes (Ruggiero, F.M.,et al. (1984)Horm. Metabol. Res. 16, 37–40; Ruggiero, F.M.,et al. (1987)Lipids 22, 148–151). As an extension of this work, we now followed the exchange of free cholesterol between plasma and erythrocytes in control, hyperthyroid and hypothyroid rats under various experimental conditionsin vitro. In control rats, erythrocytes incubated with plasma at 37°C for 4 hr lose 10% of cholesterol which was esterified by lecithin: cholesterol acyltransferase (LCAT) present in the plasma. In hyperthyroid rats, erythrocytes incubated with plasma lose 30% of cholesterol within the same time. By contrast, in the case of hypothyroid rats incubation for 4 hr was necessary to transfer 24% of free cholesterol from plasma to erythrocytes. Inhibition of cholesterol esterification did not affect the loss of erythrocyte cholesterol in control and in hyperthyroid rats. Ca²⁺ increased the LCAT activity in the plasma of these rats. The findings shed light on the role of thyroid hormones in regulating cholesterol levels in plama through active cholesterol transfer between plasma and erythrocytes.     

Age-related changes in the metabolism of cholesterol in rat liver microsomes

The effects of aging on the hepatic metabolism of cholesterol were studied in 1-, 6- and 24-month-old male Sprague-Dawley rats. Microsomal 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase activity, which regulates cholesterol biosynthesis, decreased from 835±144 (SEM) pmol/min/mg protein in the youngest group to 219±34 and 205±53 pmol/min/mg protein (p<0.001) in the 6- and 24-month-old groups, respectively. Cholesterol 7α-hydroxylase activity, which governs bile acid synthesis, was gradually reduced from 70±14 pmol/min/mg protein in the 1-month-old group to 32±7 and 16±3 pmol/min/mg protein (p<0.05) in the 6- and 24-month-old groups, respectively. Acyl coenzyme A:cholesterol acyltransferase activity, which catalyzes the esterification of cholesterol, averaged 431±47 and 452 ±48 pmol/min/mg protein in the 1- and 6-month-old groups, respectively, and was increased to 585±55 pmol/min/mg protein (p<0.05) in the 24-month-old group. The level of total cholesterol showed an age-related increase from 1.56±0.16 mg/g liver in the 1-month-old group to 1.70±0.15 and 2.20±0.19 mg/g liver (p<0.05) in the 6- and 24-month-old groups, respectively. The increase was mainly caused by an accumulation of esterified cholesterol. We conclude that a marked decrease in HMG-CoA reductase occurs between 1 and 6 months of age; thereafter the enzyme activity stays unchanged. The activity of cholesterol 7α-hydroxylase decreases progressively and drastically with age, whereas the capacity for esterifying cholesterol increases slightly. We speculate that the reduced conversion of cholesterol to bile acids may be one explanation of the age-related increase of plasma cholesterol seen in rats.     

Effects of pregnenolone-16α-carbonitrile on the metabolism of cholesterol in rat liver microsomes

The effects of pregnenolone-16α-carbonitrile (PCN) on hepatic metabolism of cholesterol were studied in rat liver microsomes in order to clarify the underlying mechanisms of the PCN-induced biliary hypersecretion of cholesterol. Male Sprague-Dawley rats were fed a diet supplemented with 0.05% of PCN for one week. The microsomal activity of 3-hydroxy-3-methylglutaryl coenzyme A reductase, regulating cholesterol biosynthesis, decreased from 577 ± 46 (SEM) to 367 ± 38 pmol/min/mg protein compared to the controls. Cholesterol 7 α-hydroxylase activity, governing bile acid synthesis, was 9.0 ± 1.1 pmol/min/mg protein in the treated group and 34.8 ± 7.4 pmol/min/mg protein in the controls, a reduction of 74% (P<0.01). The acyl CoA:cholesterol acyltransferase (ACAT) activity, catalyzing the esterification of cholesterol, remained unchanged, as did the levels of total and free cholesterol in liver homogenates and microsomes. The results of this study provide evidence that the increase in biliary cholesterol secretion during PCN treatment is not caused by a change in ACAT activity, but can be explained by a decreased catabolism of cholesterol to bile acids.     

Free and esterified cholesterol in developing feline white matter

The content of free and esterified cholesterol was examined in the cervical spinal cord lateral funiculus and in the corpus callosum of the cat during postnatal development. The concentration of free cholesterol increased with development from 8 to 56 μg/mg in the lateral funiculus and from 4 to 37 μg/mg in the corpus callosum. The total content per specimen increased 130 and 70 times, respectively. The major part of the postnatal increase in the free cholesterol occurred late postnatally. The concentration of esterified cholesterol decreased with development from 0.96 to 0.07% and from 9.50 to 0.30% of total sterol in the lateral funiculus and corpus callosum, respectively. In both regions, the total content per specimen increased with maturation. Throughout development, the content of cholesteryl ester was higher in the corpus callosum than in the lateral funiculus. A transient increase in esterified cholesterol concentration was seen during the first postnatal days in the lateral funiculus and 3 weeks postnatally in the corpus callosum. The results suggest that most of the postnatal increase of free cholesterol in the white matter is related to a continued growth of established myelin sheaths and not to de novo myelination. The transient increase in concentration of esterified cholesterol in the early postnatal lateral funiculus coincides in time with a spontaneous myelin sheath disintegration. This supports the view that the ester peak may be primarily related to myelin breakdown rather than to myelin production. The significance of the high ester concentration in the neonatal corpus callosum and the ester peak seen during initial myelination remains obscure and calls for further developmental morphological studies.     

Inhibition of LCAT in plasma from man and experimental animals by chlorpromazine

Chlorpromazine (CPZ), a major tranquilizer, was found to be a potent inhibitor of lecithin:cholesterol acyltransferase (LCAT, EC 2.3.1.43) in the plasma of normal man, rat, rabbit and dog in vitro. The inhibitory effect of CPZ reached 35–50% at 0.5 mM depending on species; dog plasma LCAT appeared to be somewhat more sensitive than that of the other species. In rats fed CPZ or lidocaine for 14 days (0.05% in the diet), there was no statistically significant change in total plasma cholesterol levels or the size of the plasma-free (unesterified) cholesterol pool. However, 5 hr after an intracardial injection of [¹⁴C] cholesterol, the percentage of plasma [¹⁴C] cholesterol that was esterified was significantly lower (ca. 6%, p<0.05) in the CPZ-treated group, suggesting that CPZ may also inhibit LCAT to some extent in vivo. The percentage of plasma [¹⁴C] cholesterol esterified in the lidocainetreated group was similar to control values and did not reflect its ability to inhibit LCAT in vitro.     

Impaired cholesterol esterification in the plasma in patients with breast cancer

An important factor which determines the movement of cholesterol in and out of the cells is the free cholesterol (FC)/esterified cholesterol (EC) ratio in the plasma. Although this ratio has been shown to be increased in several types of malignancies in humans as well as experimental animals, it is not known whether such an abnormality is found in breast cancer patients. Furthermore, the reasons for such an increase in cancer patients are unknown. We studied the plasma lipid composition and the activity of lecithin-cholesterol acyltransferase (LCAT), the enzyme responsible for the formation of most of EC in human plasma, in 12 women with breast cancer and 9 agematched control women. The plasma EC concentration was found to be significantly decreased in cancer patients, whereas the FC concentration was unchanged, leading to increased FC/EC ratios (P<0.05). The concentration of phosphatidylcholine, the acyl donor in the LCAT reaction, was decreased significantly, whereas all other phospholipids were unaffected. The cholesterol-esterifying activity of LCAT was significantly lower in cancer patients, whether assayed with endogenous substrates (P<0.05), or with an exogenous substrate (P<0.01). However, another function of the enzyme, namely the lysolecithin acyltransferase activity, was increased (P<0.02), indicating that the enzyme concentration in plasma may not be decreased. These results show that the increase in the FC/EC ratio in cancer patients is due to an impaired esterification of cholesterol by plasma LCAT, probably due to an alteration in the composition of substrate lipoproteins, or the presence of an inhibitory factor.     

Effects of ketoconazole on cholesterol synthesis and precursor concentrations in the rat liver

Ketoconazole, an antimycotic agent, given to rats for a week as 0.05% food addition had no effect on the hepatic concentrations of free and esterified cholesterol or on the activity of acyl coenzyme A: cholesterol-acyltransferase (ACAT). However, the levels of free methylated cholesterol precursors, especially lanosterols, less markedly Δ^8,24 and Δ⁸-dimethyl sterols and monomethyl sterols, were increased after only one day's treatment, while those of esterified methyl sterols were increased inconsistently, and those of free and esterified Δ⁸-lathosterol, lathosterol and desmosterol were not affected at all. Cholestyramine treatment had no significant effect on ACAT in spite of a decrease in the hepatic content of esterified cholesterol and caused a marked increase in the free cholesterol precursor levels, especially in those of lathosterols. Cholestyramine given to ketoconazole-treated rats increased the hepatic levels of Δ⁸ and Δ⁷-lathosterols but not desmosterol or methylated cholesterol precursors. Ketoconazole increased and cholestyramine markedly decreased plantssterols, sitosterol and campesterol in the liver. In serum, the contents of both lanosterols and lathosterol were increased but that of cholesterol tended to be decreased by ketoconazole (−19%). The results indicate that ketoconazole impairs demethylation processes at C-14 and to some extent at C-4 in the rat liver, resulting in lowered serum cholesterol level.     

Conjugated linoleic acid supplementation in humans: effects on fatty acid and glycerol kinetics

Recent studies with mouse adipocytes have shown that dietary conjugated linoleic acid (CLA) may reduce body fat by increasing lipolysis. The present study examined the effect of CLA supplementation on fatty acid and glycerol kinetics in six healthy, adult women who were participating in a controlled metabolic ward study. These women were fed six CLA capsules per day (3.9 g/d) for 64 d following a baseline period of 30 d. The subjects were confined to a metabolic suite for the entire 94-d study, where diet and activity were controlled and held constant. The rate of appearance (Ra) of glycerol, which indicates lipolytic rates, was similar at baseline and after 4 wk of CLA supplementation at rest (1.87±0.21 and 2.00±0.39 μmol/kg/min, respectively) and during exercise (7.12±0.74 and 6.40±0.99 μmol/kg/min, respectively). Likewise, the Ra of free fatty acids (FFA) was not significantly different after 4 wk of dietary CLA at rest (2.72±0.06 and 2.74±0.12 μmol/kg/min, respectively) or during exercise (6.99±0.40 and 5.88±0.29 μmol/kg/min, respectively). CLA supplementation also had no effect on the percentage of FFA released from lipolysis that were re-esterified. The apparent rate of FFA re-esterification was 65.2±4.2% at rest and 32.1±3.44% during exercise. Four weeks of CLA supplementation had no significant effect on fatty acid or glycerol metabolism in healthy, weight-stable, adult women.     

The interaction of human plasma low density lipoproteins with glycosamino-glycans: Influence of the chemical composition

Human plasma of 5 normolipemic individuals was incubated for 24 hr at 37 C in the presence or in the absence of lecithin: cholesterol acyltransferase (LCAT)-inhibitors. Plasma steored at 4 C served as a control. The low density lipoprotein (LDL) fractions of the samples were isolated and investigated with respected to changes in chemical composition and complexing activity with glycosamino glycans (GAG). Incubation of plasma in the presence of LCAT inhibitors caused a significant increase of LDL triglycerides at the expense of cholesteryl esters. Incubation with active LCAT not only changed the core but also the surface constituents (decrease in phospholipids and in free cholesterol). The amount of GAG bound per mg of LDL was not uniformly changed in samples incubated after LCAT inhibition. LDL isolated from plasma incubated in the presence of LCAT, on the other hand, showed a significant reduction in GAG binding. The ratio of free cholesterol: GAG in the complex was most significantly reduced in LCAT-modified LDL. There was in addition a highly significant correlation between the LDL:GAG ratio in the complex and the free cholesterol and phospholipid content of the LDL samples. It is concluded that alterations in surface lipid constitutents of LDL strongly after their interaction with sulfated polysaccharides, an effect which may be relevant also in vivo for the interaction of LDL with cell surfaces and intercellular matrices.     

Quantification of lowered cholesterol oxidation in guinea pigs with latent vitamin C deficiency

Fifty-two male guinea pigs fed on a scorbutigenic diet were divided into a control group (10 mg ascorbicacid per animal per day) and a group with latent vitamin C deficiency (2 weeks on the scorbutigenic diet only, followed by a maintaining dose of 0.5 mg ascorbic acid per animal per day). After 13 weeks, 26-¹⁴C-cholesterol was administered intraperitoneally to all the animals, in which the¹⁴C excretion in the expired CO₂ and the urine and cholesterol specific activity in the blood serum and liver were then studied at intervals of 24 hr and 1, 3, 5, 7, 9 and 11 weeks. The ascorbic acid concentration in the liver and spleen of the control animals was five times higher than in vitain C-deficient animals. The total cholesterol concentration in serum and liver was significantly higher in the vitamin C-deficient guinea pigs. A two-pool analysis of the disappearance curves of serum cholesterol specific activity showed that the size of the cholesterol pool A (blood and tissues with rapid cholesterol exchange) was greater in the vitamin C-deficient animals. The rate of the transformation of cholesterol to bile acids was estimated as the ratio of¹⁴CO₂ expired to liver cholesterol specific activity. Latent vitamin C deficiency caused significant slowing down of this process (controls: 11.8±0.6; vitamin C deficiency: 8.3±0.4 mg/24 r/500 g w/w). A significant correlation between the liver ascorbic acid concentration and the rate of cholesterol transformation to bile acids was found. The results demonstrate that ascorbic acid is necessary for a normal course of cholesterol catabolism. In latent vitamin C deficiency, the rate of cholesterol catabolism slows down and cholesterol consequently accumulates in the blood and liver of vitamin C-deficient guinea pigs.     

Preferential redistribution of lipoprotein-unassociated apoA-IV to an HDL subpopulation with a high degree of LCAT modification

The relationship between LCAT mediated HDL modification and the redistribution of lipoprotein-unassociated apoA-IV to HDL was investigatedin vitro. Immunoaffinity-isolated rat lipoprotein-unassociated apoA-IV was added to apoB-, apoE-, apoA-IV depleted, [³H]cholesterol labelled rat plasma and incubated at 37°C. The addition of lipoprotein-unassociated apoA-IV resulted in a modest (10%) but significant reduction in the rate of cholesterol esterification. Incubations conducted in the presence of active LCAT led to a time-dependent increase in the amount of the³H label retained by an anti-apoA-IV immunoaffinity column. Lipoproteins retained by the anti-apoA-IV immunoaffinity column had experienced a greater conversion of [³H]cholesterol to [³H]cholesteryl esters (48% esterification at 30 min) than the unretained lipoproteins (19% esterification at 30 min). These data suggest that during the course of LACT-induced cholesterol esterification, lipoprotein-unassociated apoA-IV transfers to a subpopulation of HDL which has been modified by LCAT to a greater extent than the remaining HDL. Further analysis of the data demonstrates that 48% cholesterol esterification is sufficient to allow apoA-IV to be accommodated on the surface of an HDL particle.     

Different metabolism of saturated and unsaturated long chain plasma free fatty acids by intestinal mucosa of rats

During fat absorption, unsaturated long chain fatty acids are esterified at a higher rate than saturated fatty acids of similar chain length. This phenomenon has been attributed to differences in the binding affinity of fatty acids to a cytosolic fatty acid-binding protein. As intestinal mucosa utilizes plasma free fatty acids as well, we investigated whether long chainplasma free fatty acids of different degree of saturation are metabolized also at different rates.³H-Palmitic and¹⁴C-linoleic acid complexed to rat serum were injected rapidly into a tail vein of fasting rats. One, 2 and 4 min later there was no difference between³H and¹⁴C-radioactivity in intestinal mucosa, suggesting equal initial uptake of the two labeled fatty acids from plasma. Despite their equal uptake, the incorporation of the isotopes into ester lipids was significantly different, however: at 2 min, 53.1±3.9% of³H and 73.8±4.6% of¹⁴C were recovered in ester lipids. Phospholipids and triglycerides accounted for most of the mucosal³H and¹⁴C. At 4 min, a similar distribution of isotopes in intestinal mucosal metabolites was found. These data show that despite equal initial uptake by intestinal mucosa unsaturated long chain fatty acids taken up from plasma are esterified to a higher and oxidized to a lower extent than saturated plasma free fatty acids. Unsaturated plasma free fatty acids, therefore, may provide a more important source of fatty acids for endogenous intestinal lipoprotein lipids than saturated plasma free fatty acids. It is speculated that the fatty acid binding protein might be operative not only in the intracellular transport and metabolism of luminal fatty acids but of plasma free fatty acids as well.     

Plasma LCAT Activity and Lipid Subfraction Composition in Obese Beagles Undergoing Weight Loss

The relationship between lecithin:cholesterol acyltransferase (LCAT) activity and weight loss in dogs was investigated. Four experimental weight-loss diets were fed to 12 obese female beagles for 56 days in a partial crossover design (n = 6). High- (HGI) or low- (LGI) glycemic index starch and diacylglycerol or triacylglycerol oils were combined to compose experimental diets with similar fatty acid profiles. Food intake and body weights were measured daily and weekly, respectively. Fasted blood samples were drawn at day 0, day 28, and day 56 to measure plasma LCAT activity and total (TC), unesterified (UC), and esterified (EC) cholesterol concentrations, and for fatty acid analysis of the phospholipid (PL) and EC fractions. The LGI groups lost more weight than the HGI groups due to starch digestibility differences. An HGI starch effect on TC and UC concentrations was observed but was unrelated to weight loss. LCAT activities increased over time but were not different after controlling for percentage weight loss. However, a positive linear correlation was found between LCAT and UC concentrations in all groups. Plasma PL fatty acid profiles reflected the diets fed, but increases in 16 and 18 carbon saturated and monounsaturated fatty acids in all groups appeared to be an effect of fatty acid mobilization from storage sites. Both plasma PL and EC fatty acid profiles were similar with both acylglycerol types and EC fatty acids reflected linoleic acid specificity with minimal diet or time effects.     

Decreased lecithin: Cholesterol acyltransferase activity in the plasma of hypercholesterolemic pigs

Lecithincholesterol acyltransferase (LCAT) activity levels were determined, as function of plasma total cholesterol (TC) in 13 normocholesterolemic (TC<85 mg/dL) and in 28 hypercholesterolemic (TC>98 mg/dL) pigs. The normocholesterolemic group consisted of pigs that carried apo-B allelic genes other thanLpb ⁵ and orLpb ⁸. The hypercholesterolemic group consisted ofLpb ^5/x andLpb ^5/8 heterozygous andLpb ^5/5 homozygous animals. The data reported in this study show that the LCAT activity in the plasma of hypercholesterolemic (HC) pigs (79±43 units) was significantly lower (p<0.0005) compared to the normocholesterolemic controls (175±45 units). Furthermore, LCAT activity was positively correlated with TC in the normocholesterolemic group (r=+0.54; p<0.05), whereas it was negatively correlated with TC in the hypercholesterolemic group (r=−0.73; p<0.001). Additional data obtained from incubation experiments suggest that the lower LCAT activity in hypercholesterolemic pigs may be due, at least in part, to inhibition of LCAT activity by components found in the lipoprotein-deficient fractions of the plasma of hypercholesterolemic pigs.