Plasma LCAT Activity Research Articles

Deficient Cholesterol Esterification in Plasma of apoc2 Knockout Zebrafish and Familial Chylomicronemia Patients.

Hypertriglyceridemia is an independent risk factor for cardiovascular disease. Apolipoprotein C-II (APOC2) is an obligatory cofactor for lipoprotein lipase (LPL), the major enzyme catalyzing plasma triglyceride hydrolysis. We have created an apoc2 knockout zebrafish model, which mimics the familial chylomicronemia syndrome (FCS) in human patients with a defect in the APOC2 or LPL gene. In this study, we measured plasma levels of free cholesterol (FC) and cholesterol esters (CE) and found that apoc2 mutant zebrafish have a significantly higher FC to CE ratio (FC/CE), when compared to the wild type. Feeding apoc2 mutant zebrafish a low-fat diet reduced triglyceride levels but not the FC/CE ratio. In situ hybridization and qPCR results demonstrated that the hepatic expression of lecithin-cholesterol acyltransferase (lcat), the enzyme responsible for esterifying plasma FC to CE, and of apolipoprotein A-I, a major protein component of HDL, were dramatically decreased in apoc2 mutants. Furthermore, the FC/CE ratio was significantly increased in the whole plasma and in a chylomicron-depleted fraction of human FCS patients. The FCS plasma LCAT activity was significantly lower than that of healthy controls. In summary, this study, using a zebrafish model and human patient samples, reports for the first time the defect in plasma cholesterol esterification associated with LPL deficiency.

Role of plasma and liver cholesterol- and lipoprotein-metabolism determinants in LpX formation in the mouse

Cholestasis is characterized by hypercholesterolemia and the appearance of an abnormal lipoprotein, lipoprotein X (LpX), in plasma. The mechanisms responsible for this cholestatic plasma lipid phenotype are not fully understood. We used ATP-binding cassette A1 (ABCA1)(−/−) and scavenger receptor class B type I (SR-BI)(−/−) mice to test the hypothesis that hepatic sinusoidal cholesterol transporters contribute to LpX formation and hypercholesterolemia during cholestasis. Bile-duct ligation (BDL) of both ABCA1(−/−) and SR-BI(−/−) mice, as well as their respective controls, induced a dramatic increase in plasma cholesterol and phospholipid concentrations. Plasma fractionation revealed the presence of LpX in plasma of cholestatic mice, irrespective of their genetic background. We observed that the presence of HDL before cholestasis, a decrease in the activity of LCAT, and an increase in VLDL synthesis were not required for hypercholesterolemia and lipoprotein modifications induced by obstructive cholestasis in mice. In addition, murine cholestasis resulted in increased hepatic cholesterol synthesis that may contribute to the higher plasma free cholesterol levels found during the early hours after BDL. Together these findings indicate that hypercholesterolemia and LpX formation associated with obstructive cholestasis are correlated with an increase in hepatic cholesterol synthesis and are independent of plasma HDL levels, LCAT activity, VLDL synthesis, and ABCA1 and SR-BI expression.

Diminished macrophage cholesterol removal rate by the altered HDL metabolism in the Nagase analbuminemic rat

Dyslipoproteinemia of the Nagase analbuminemic rat (NAR) is characterized by elevated concentrations of VLDL and LDL attributed to increased rates of liver lipoprotein synthesis. Increased lysophosphatidylcholine (LPC) in NAR HDL has been attributed to high plasma LCAT activity. We show here that, as compared with Sprague-Dawley rats (SDR), NAR plasma triacylglycerol (TAG), total cholesterol (TC), HDL TAG, protein, total phospholipids (PL), LPC, and PS are increased. These alterations rendered the NAR HDL particle more susceptible to the activity of the enzyme hepatic lipoprotein lipase (HL), which otherwise was unaltered in our study. Fractional catabolic rates in blood of the autologous 125I-apoHDL (median and lower quartile values), were, respectively, 0.231 and 1.645 (n = 10) in NAR as compared with 0.140 and 0.109 (n = 10) in SDR (P = 0.012), corresponding to synthesis rates of HDL protein of 89.8 +/- 33.7 mg/d in NAR and 17.4 +/- 6.5 mg/d in SDR (P = 0.0122). Furthermore, Swiss mouse macrophage free-cholesterol (FC) efflux rates, measured as the percent [14C]-cholesterol efflux/6 h, were 8.2 +/- 2.3 (n = 9) in NAR HDL and 11.2 +/- 3.2 (n = 10) in SDR HDL (P = 0.03). Therefore, in NAR the modification of the HDL composition slows down the cell FC efflux rate, and together with the increased rate of plasma HDL metabolism influences the reverse cholesterol transport system.

HDLs in apoA-I transgenic Abca1 knockout mice are remodeled normally in plasma but are hypercatabolized by the kidney

Patients homozygous for Tangier disease have a near absence of plasma HDL as a result of mutations in ABCA1 and hypercatabolize normal HDL particles. To determine the relationship between ABCA1 expression and HDL catabolism, we investigated intravascular remodeling, plasma clearance, and organ-specific uptake of HDL in mice expressing the human apolipoprotein A-I (apoA-I) transgene in the Abca1 knockout background. Small HDL particles (7.5 nm), radiolabeled with (125)I-tyramine cellobiose, were injected into recipient mice to quantify plasma turnover and the organ uptake of tracer. Small HDL tracer was remodeled to 8.2 nm diameter particles within 5 min in human apolipoprotein A-I transgenic (hA-I(Tg)) mice (control) and knockout mice. Decay of tracer from plasma was 1.6-fold more rapid in knockout mice (P < 0.05) and kidney uptake was twice that of controls, with no difference in liver uptake. We also observed 2-fold greater hepatic expression of ABCA1 protein in hA-I(Tg) mice compared with nontransgenic mice, suggesting that overexpression of human apoA-I stabilized hepatic ABCA1 protein in vivo. We conclude that ABCA1 is not required for in vivo remodeling of small HDLs to larger HDL subfractions and that the hypercatabolism of normal HDL particles in knockout mice is attributable to a selective catabolism of HDL apoA-I by the kidney.

Changes in serum lipoprotein lipids and their fatty acid compositions and lipid peroxidation in growing rats fed soybean protein versus casein with or without cholesterol*1

We compared the effects of diets based on soybean protein and casein supplemented or not supplemented with 0.1% cholesterol on plasma lipoprotein lipid amounts and their fatty acid compositions, lecithin:cholesterol acyl-transferase activity, and lipid peroxidation. The composition and concentration of lipid and apolipoprotein in different lipoprotein classes, plasma LCAT activity, and lipid peroxidation were determined in rats fed 20% highly purified soybean protein or casein with or without 0.1% cholesterol for 2 mo. Soybean protein and casein diets with or without cholesterol had similar plasma total cholesterol concentrations. Soybean protein consumption diminished very low-density lipoprotein particle number, as measured by diminished contents of very low-density lipoprotein triacylglycerol, phospholipid, and apolipoprotein-B100. Lecithin:cholesterol acyl-transferase activity was not significantly modified by either protein. The soybean protein diet decreased the linoleate desaturation index (20:4[ω-6]/18:2[ω-6]) in liver and high-density lipoprotein fraction 2–3-phospholipids but enhanced red blood cell resistance against free radical attack. Addition of cholesterol to both protein diets decreased concentrations of high-density lipoprotein fraction 2–3 cholesterol. Lecithin:cholesterol acyl-transferase activity tended to be greater after cholesterol feeding, likely due to the enhanced high-density lipoprotein fraction 2–3 apolipoprotein-AI, a cofactor activator for lecithin:cholesterol acyl-transferase. Regardless of dietary protein source, cholesterol supplementation decreased the linoleate desaturation index in liver and plasma lipoprotein lipids and red blood cell resistance to free radical attack. Our results suggest that the dietary protein origin affects lipid peroxidation and polyunsaturated fatty acid biosynthesis and distribution among liver and different lipoprotein lipid classes, but plays only a minor role in the regulation of plasma and lipoprotein cholesterol concentrations. Providing dietary cholesterol (0.1%) with casein or soybean protein attenuates the effects of these proteins, with the exception of plasma cholesterol.

Changes in serum lipoprotein lipids and their fatty acid compositions and lipid peroxidation in growing rats fed soybean protein versus casein with or without cholesterol

Objective We compared the effects of diets based on soybean protein and casein supplemented or not supplemented with 0.1% cholesterol on plasma lipoprotein lipid amounts and their fatty acid compositions, lecithin:cholesterol acyl-transferase activity, and lipid peroxidation. Methods The composition and concentration of lipid and apolipoprotein in different lipoprotein classes, plasma LCAT activity, and lipid peroxidation were determined in rats fed 20% highly purified soybean protein or casein with or without 0.1% cholesterol for 2 mo. Results Soybean protein and casein diets with or without cholesterol had similar plasma total cholesterol concentrations. Soybean protein consumption diminished very low-density lipoprotein particle number, as measured by diminished contents of very low-density lipoprotein triacylglycerol, phospholipid, and apolipoprotein-B100. Lecithin:cholesterol acyl-transferase activity was not significantly modified by either protein. The soybean protein diet decreased the linoleate desaturation index (20:4[ω-6]/18:2[ω-6]) in liver and high-density lipoprotein fraction 2–3-phospholipids but enhanced red blood cell resistance against free radical attack. Addition of cholesterol to both protein diets decreased concentrations of high-density lipoprotein fraction 2–3 cholesterol. Lecithin:cholesterol acyl-transferase activity tended to be greater after cholesterol feeding, likely due to the enhanced high-density lipoprotein fraction 2–3 apolipoprotein-AI, a cofactor activator for lecithin:cholesterol acyl-transferase. Regardless of dietary protein source, cholesterol supplementation decreased the linoleate desaturation index in liver and plasma lipoprotein lipids and red blood cell resistance to free radical attack. Conclusions Our results suggest that the dietary protein origin affects lipid peroxidation and polyunsaturated fatty acid biosynthesis and distribution among liver and different lipoprotein lipid classes, but plays only a minor role in the regulation of plasma and lipoprotein cholesterol concentrations. Providing dietary cholesterol (0.1%) with casein or soybean protein attenuates the effects of these proteins, with the exception of plasma cholesterol.

Effect of deficiency of vitamins C and/or E on lipoprotein metabolism in osteogenic disorder Shionogi rat, a strain unable to synthesize ascorbic acid.

The effects of vitamin C and/or E deficiency on lipoprotein metabolism were investigated in the inherently scorbutic Osteogenic Disorder Shionogi (ODS) rat. In the vitamin C-deficient (C-def) group, marked increases in plasma VLDL and LDL cholesterol were observed (by comparison with the vitamins C- and E-sufficient control group). In rats kept deficient in both vitamin C and vitamin E (C,E-def), LDL cholesterol was significantly higher than in the C-def group even though the levels of VLDL and HDL cholesterol were similar between the two groups. TBARS values for the LDL fraction in the C-def group were of the same magnitude as in the E-def group, and these values were significantly higher than those obtained for the control group. In the C,E-def group, the values were even higher than in the E-def and C-def groups. The nondenatured PAGE of the LDL fraction indicated the appearance of HDLc in the C-def and C,E-def groups. The SDS-PAGE of the LDL fraction showed increased apo B-48 in the C-def and C,E-def groups and increased apo E in the C,E-def group. Decreased plasma LCAT activity in the E-def, C-def, and C,E-def groups indicated an alteration in HDL metabolism as a result of oxidation. These results suggest that lipid peroxidation and some distinct features of lipoprotein metabolism resulting from vitamin C deficiency become more significant when vitamin E is also deficient along with vitamin C deficiency.

Correction of hypoalphalipoproteinemia in LDL receptor-deficient rabbits by lecithin:cholesterol acyltransferase

Familial hypercholesterolemia (FH), a disease caused by a variety of mutations in the low density lipoprotein receptor (LDLr) gene, leads not only to elevated LDL-cholesterol (C) concentrations but to reduced high density lipoprotein (HDL)-C and apolipoprotein (apo) A-I concentrations as well. The reductions in HDL-C and apoA-I are the consequence of the combined metabolic defects of increased apoA-I catabolism and decreased apoA-I synthesis. The present studies were designed to test the hypothesis that overexpression of human lecithin:cholesterol acyltransferase (hLCAT), a pivotal enzyme involved in HDL metabolism, in LDLr defective rabbits would increase HDL-C and apoA-I concentrations. Two groups of hLCAT transgenic rabbits were established: 1) hLCAT+/LDLr heterozygotes (LDLr+/–) and 2) hLCAT+/LDLr homozygotes (LDLr–/–). Data for hLCAT+ rabbits were compared to those of nontransgenic (hLCAT–) rabbits of the same LDLr status. In LDLr+/– rabbits, HDL-C and apoA-I concentrations (mg/dl), respectively, were significantly greater in hLCAT+ (62 ± 8, 59 ± 4) relative to hLCAT–rabbits (21 ± 1, 26 ± 2). This was, likewise, the case when hLCAT+/LDLr–/– (27 ± 2, 19 ± 6) and hLCAT–/LDLr–/– (5 ± 1, 6 ± 2) rabbits were compared. Kinetic experiments demonstrated that the fractional catabolic rate (FCR, d–1) of apoA-I was substantially delayed in hLCAT+ (0.376 ± 0.025) versus hLCAT– (0.588) LDLr+/– rabbits, as well as in hLCAT+ (0.666 ± 0.033) versus hLCAT– (1.194 ± 0.138) LDLr–/– rabbits. ApoA-I production rate (PR, mg·kg·d–1) was greater in both hLCAT+/LDLr+/– (10 ± 2 vs. 6) and hLCAT+/LDLr–/– (9 ± 1 vs. 4 ± 1) rabbits. Significant correlations (P < 0.02) were observed between plasma LCAT activity and HDL-C (r = 0.857), apoA-I FCR (r = –0.774), and apoA-I PR (r = 0.771), while HDL-C correlated with both apoA-I FCR (–0.812) and PR (0.751).▪ In summary, these data indicate that hLCAT overexpression in LDLr defective rabbits increases HDL-C and apoA-I concentrations by both decreasing apoA-I catabolism and increasing apoA-I synthesis, thus correcting the metabolic defects responsible for the hypoalphalipoproteinemia observed in LDLr deficiency.—Brousseau, M. E., J. Wang, S. J. Demosky, Jr., B. L. Vaisman, G. D. Talley, S. Santamarina-Fojo, H. B. Brewer, Jr., and J. M. Hoeg. Correction of hypoalphalipoproteinemia in LDL receptor-deficient rabbits by lecithin:cholesterol acyltransferase.

Increased activity of lecithin: Cholesterol acyltransferase during short-term oral estrogen progestin replacement therapy in a group of postmenopausal women

The aim of the study was to assess the short-term effect of estrogen-progestin therapy on the plasma level of lecithin: cholesterol acyltransferase ([LCAT] EC 2.3.1.43), a key enzyme in the cholesterol reverse-transport process. The trial included 21 women with at least 6 months of menopause, which was confirmed by anamnesis, physical evaluation, and follicle-stimulating hormone (FSH) determination. Women receiving pharmacological treatment or who had any kind of endocrine disorder were excluded. In addition, we evaluated and confirmed normal Papanicolaou and mammography tests in all 21 women included in the trial. They received conjugated equine estrogen 0.625 mg daily, plus cyclic medroxyprogesterone acetate (5 mg daily) for 12 days each month. Plasma levels of LCAT, cholesterol, low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), triglycerides, apoB, and apoAl were evaluated before and after 1 and 3 months of therapy. Pretherapy and posttherapy results were analyzed statistically by Wilcoxon's rank-sum test for paired samples. No significant changes were observed either for body mass index or for blood pressure. A significant increase in plasma LCAT activity was found at the first and third month posttherapy ( P < .005). In addition, after 3 months of therapy, HDL-C significantly increased ( P < .005), in contrast to the significant decrease detected in total cholesterol ( P < .025), LDL-C ( P < .005), cholesterol to HDL-C and LDL-C HDL-C ratios ( P < .005). Triglyceride levels did not show significant modification. In conclusion, our results indicate that short-term estrogen-progestin therapy produces a significant increase in plasma LCAT activity, as well as beneficial changes in the lipid profile, in postmenopausal women.

High density lipoprotein particle size restriction in apolipoprotein A-I(Milano) transgenic mice

Human carriers of apolipoprotein A-I(Milano) (Arg173 --> Cys substitution in apolipoprotein A-I) are characterized by an HDL deficiency in which small, dense HDL accumulate in plasma. Because affected individuals are heterozygous for this mutation, the full impact of apolipoprotein A-I(Milano) (apoA-I(Milano)) on HDL-cholesterol metabolism is unknown. In this study, apoA-I(Milano) transgenic mice were used to evaluate the extent of apoA-I(Milano) dimerization and HDL particle size restriction in the absence of wild-type apoA-I. Murine apoA-I knockout mice were utilized to express apoA-I(Milano) and human apoA-II in the presence of wild-type, human apoA-I (apoA-IMilano/A-Iwt/A-II) and in its absence (apoA-IMilano/A-II). Plasma HDL-cholesterol concentrations were similar (30 mg/dl) in both lines of apoA-I(Milano) transgenic mice. In the apoA-IMilano/A-Iwt/A-II phenotype, 14% of the apoA-I(Milano) formed homodimers and 33% formed heterodimers with apoA-II. ApoA-I(Milano) homodimers increased by 71% in the apoA-IMilano/A-II transgenics and was associated with an abundance of small, 7.6-nm HDL3-sized particles compared to the 9.5, 8.3, and 7.6-nm-sized particles in apoA-IMilano/A-Iwt/A-II mice. The unesterified cholesterol/cholesteryl ester mole ratio of HDL was elevated by 45% in apoA-IMilano/A-Iwt/A-II mice and by 90% in apoA-IMilano/A-II transgenics compared to wild-type (human apoA-I/A-II). Both apoA-I(Milano) transgenics possessed normal levels of plasma LCAT activity, but endogenous cholesterol esterification rates were reduced by 50% compared to controls. Thus, HDL particle size restriction was not the result of impaired LCAT activation; rather, dimerization of apoA-I(Milano) limited the esterification of cholesterol on endogenous HDL. In the absence of wild-type apoA-I, the more extensive dimerization of apoA-I(Milano) severely limited cholesteryl ester accumulation on plasma HDL accounting for the abundance of small, 7.6-nm HDL3 particles in apoA-IMilano/A-II mice.

12 Plasma LCAT and CEPT activity during lipid lowering therapy

12 Plasma LCAT and CEPT activity during lipid lowering therapy

Endotoxin and TNF lead to reduced plasma LCAT activity and decreased hepatic LCAT mRNA levels in Syrian hamsters.

Endotoxin (LPS) administration, which mimics infection, stimulates the production of many cytokines, including TNF, that are thought to mediate the alterations in lipid metabolism that occur during infection. The aims of this study were to determine the effect of LPS or TNF administration on plasma LCAT activity and hepatic LCAT mRNA levels in Syrian hamsters. Plasma LCAT activity was decreased 8 h after LPS administration, reached a maximum level of inhibition at 16 h which persisted for at least 24 h, at which time the activity was 53% of control values. The decrease in plasma LCAT activity was first seen at an LPS dose of 0.01 microgram/100 g body weight and reached a maximum at 50-100 micrograms/100 g body weight. The ratio of free to esterified cholesterol in the plasma increased in the LPS-treated animals. Moreover, LPS administration decreased LCAT mRNA levels in the liver. The decrease in hepatic LCAT mRNA levels preceded the decrease in plasma LCAT activity. Additionally, TNF treatment (16.7 micrograms/100 g body weight) decreased plasma LCAT activity by 35% and LCAT mRNA levels in the liver by 60% 16 h after administration. Lastly, in cultured rat H35 hepatocytes, TNF decreased LCAT mRNA levels in the liver by 60% 16 h after administration. Lastly, in cultured rat H35 hepatocytes, TNF decreased LCAT mRNA levels by 50% with a 1/2 maximal dose of approximately 1 ng/ml. Thus, plasma LCAT activity and hepatic mRNA levels are decreased by LPS or TNF treatment. LCAT is a member of a group of proteins that affect lipid and lipoprotein metabolism whose levels are altered during the host's acute phase response.

High density lipoproteins with differing apolipoproteins: relationships to postprandial lipemia, cholesteryl ester transfer protein, and activities of lipoprotein lipase, hepatic lipase, and lecithin: cholesterol acyltransferase.

To gain insight into metabolic determinants of high density lipoproteins (HDL) containing apolipoproteins A-I and A-II (LpA-I/A-II) and those containing A-I, but devoid of A-II (LpA-I), the plasma concentration of LpA-I and LpA-I/A-II within the HDL2 and HDL3 density spectrum was measured in 14 normolipidemic male subjects on a standardized diet. Apolipoprotein plasma concentrations of HDL subspecies were compared with the magnitude of postprandial lipemia, activities of lipoprotein lipase and hepatic lipase in postheparin plasma, plasma lecithin:cholesterol acyltransferase (LCAT) activity, and cholesteryl ester transfer protein (CETP) mass. Plasma levels of LpA-I/A-II were 2.5 times higher than levels of LpA-I (123 +/- 20 vs. 48.3 +/- 22.1 mg protein/dl) and the partition of LpA-I and LpA-I/A-II between HDL2 and HDL3 differed in that the proportion of LpA-I associated with HDL2 was greater than that of LpA-I/A-II (23 +/- 19 vs. 6 +/- 6%, P < 0.002). With increasing levels of HDL2, the proportion of LpA-I in HDL2 increased (P < 0.002). Furthermore, levels of LpA-I and LpA-I/A-II were strongly correlated within the HDL2 but not within the HDL3 density region. Plasma levels of LpA-I, but not LpA-I/A-II, were inversely correlated with the magnitude of postprandial lipemia. However, activities of lipoprotein lipase and hepatic lipase tended to show stronger associations with the partition of LpA-I/A-II between HDL2 and HDL3 than with that of LpA-I. Within the HDL3, but not the HDL2 density spectrum, LpA-I/A-II exhibited a positive association with plasma LCAT activity, while LpA-I displayed an inverse association with plasma CETP mass. These results are consistent with differences in substrate properties of LpA-I and LpA-I/A-II for lipoprotein modifying enzymes and imply different, but overlapping metabolic pathways of LpA-I and LpA-I/A-II.

Plasma lipoproteins and apolipoproteins in insulin-dependent and young non-insulin-dependent Arab women

Plasma lipids, lipoproteins and apolipoproteins (apo) were analysed in 30 young Arab IDDM and 50 young insulin-requiring NIDDM women. The mean age of IDDM and NIDDM groups was 20.2 and 34.5 years, and mean duration of diabetes was 5.7 and 4.6 years, respectively. Two groups of 40 and 60 healthy women (matched for age and BMI) provided corresponding control groups. In comparison with control subjects, diabetics showed marked increases in the following parameters: total cholesterol (TC), low density lipoprotein (LDL) cholesterol, total triglycerides (TG), very low density lipoprotein (VLDL) triglycerides, phospholipids, apoB, LDL apoB, glucose and glycosylated hemoglobin (HbA1c) as well as the ratios of total cholesterol/high density lipoprotein (HDL) cholesterol, LDL-cholesterol/HDL-cholesterol, LDL cholesterol/high density lipoprotein (HDL) cholesterol, LDL-cholesterol/HDL-cholesterol, LDL cholesterol/high density lipoprotein 2 (HDL2) cholesterol and apoB/apoAI. Plasma LCAT activity, concentrations of HDL3 apoAI and apoAII in plasma and lipoprotein fractions were normal in both the diabetic groups. Levels of C-peptide, HDL, HDL2 and HDL3 cholesterol, plasma apoAI, HDL apoAI and HDL2 apoAI were markedly decreased in the diabetic groups as compared to their corresponding controls. There was no significant correlation between fasting glucose or HbA1c and any of the above parameters. Despite insulin therapy in both the diabetic groups studied, abnormalities in lipids, apoB and apoAI still persisted. Our data suggest a possible higher risk of atherosclerosis in these patients.

Influence of serum amyloid A on cholesterol esterification in human plasma

Lecithin-cholesterol acyltransferase (EC 2.3.1.43, LCAT) is the enzyme responsible for the formation of the bulk of cholesteryl ester in human plasma. The LCAT-reaction takes place mainly on high-density lipoproteins and requires an apolipoprotein as activator. Besides apolipoprotein (apo) A-I several other potent activator apolipoproteins (AIV, E and CI) were identified, furthermore apo A-II was shown to be a modulator of the enzyme's reaction in the presence of apo A-I. Serum amyloid A, an apolipoprotein mainly associated with high-density lipoprotein, massively accumulates in plasma upon acute phase reactions. We therefore studied the possible influence of this acute phase reactant on cholesterol esterification in human plasma. There was a significant decrease of esterified cholesterol in plasma during acute phase reaction. We found a highly significant correlation between the unesterified part of plasma cholesterol and serum amyloid A levels (r = 0.694, P = 0.0001). Also, plasma LCAT activity was negatively correlated with serum amyloid A levels. Lipoproteins containing apo A-I and A-II (LpA-I: A-II) and lipoproteins containing apo A-I but no A-II (LpA-I) decreased significantly with the appearance in plasma of serum amyloid A. To study the influence of serum amyloid A on the LCAT reaction, artificial substrates were prepared either by a detergent dialysis procedure or by addition of apolipoprotein to a sonicated aqueous dispersion of lipid. In addition two different molar ratios of apolipoprotein/phospholipid (PC) (1:50 and 1:310) were chosen at a constant molar ratio of total cholesterol/PC of 1:20. The various substrates were incubated with purified LCAT enzyme. DMPC - or egg yolk phosphatidylcholine - cholesterol-[4-14C]cholesterol-serum amyloid A complexes per se did not stimulate LCAT activity significantly. However, apo serum amyloid A incorporated together with apo A-I by a detergent dialysis procedure lead at low concentrations of serum amyloid A to a marked increase in cholesteryl ester formation as compared to apo A-I alone but inhibited the cholesteryl ester formation at high concentrations. Thus, the low levels of esterified cholesterol in acute phase plasma are to some extent due to decreased plasma enzyme activity and in part may be due to interference of apo serum amyloid A with the natural substrate complexes of plasma HDL.

ラット血漿LCAT活性に及ぼすElastase様酵素の影響

ラット血漿LCAT活性に及ぼすElastase様酵素の影響

Plasma lipoproteins and lecithin:cholesterol acyltransferase distribution in patients on dialysis

AbstractPlasma lipoproteins and lecithin:cholesterol acyltransferase distribution in patients on dialysis. Plasma lipoproteins and LCAT activity were studied using a single spin density gradient separation and an exogenous substrate enzyme assay in 41 patients on chronic hemodialysis and in 11 normal subjects. The plasma HDL cholesterol was markedly decreased (33 vs. 63 mg/dl, P < 0.001) while total and LDL-cholesterol were unchanged in the patients. Plasma LCAT activity was significantly lower in the patient group (42 vs. 59 nmoles/4 hr/ml, P < 0.001), but the distribution of activity (studied in 13 dialysis patients and 12 control subjects) was not different between the two groups: 90% being associated with HDL and VHDL lipoprotein fractions. To examine the possible genetic influence on the development of hypertriglyceridemia in the patient group, we examined the ratio of apolipoproteins E3/E2 and CII/CIII in ten of the patients and another group of 13 control subjects. The frequency of heterozygotes for E3 deficiency was not different between the patient (one of ten) and the control (two of 13) groups. While the patient group had lower CII/CIII ratio, the figures did not reach statistical significance. The low LCAT activity in the face of higher plasma triglycerides and low HDL may contribute to impaired lipolysis previously documented in uremic patients. A follow-up study performed 1 year after the initial study confirmed the decreased HDL (51 vs. 71 mg/dl, P < 0.01) and LCAT activity (50 vs. 59 nmoles/hr/ml, P < 0.02) in an exogenous substrate system (N = 20). LCAT measured using the endogenous substrate was not significantly different from the control group (49 vs. 55 nmoles/hr/ml). Changes in LCAT activity induced by a single dialysis were not significant in either assay system.Lipoprotéines plasmatiques et distribution de la lécithine:cholestérol acyltransférase chez des malades en dialyse. Les lipoprotéines plasmatiques et l'activité LCAT ont été étudiées en utilisant une séparation par centrifugation unique sur gradient de densité et un dosage enzymatique avec un substrat exogène chez 41 malades en hémodialyse chronique et chez 11 sujets normaux. Le cholestérol plasmatique HDL était diminué de façon marquée (33 contre 63 mg/dl, P < 0,001) tandis que les cholestérols total et LDL étaient inchangés chez les malades. L'activité LCAT plasmatique était significativement plus faible dans le groupe des malades (42 contre 59 nmoles/4 hr/ml, P < 0,001), mais la distribution de l'activité (étudiée chez 13 hémodialysés et 12 sujets contrôles) n'était pas différente entre les deux groupes: 90% étaient associés avec les fractions HDL et VHDL des lipoprotéines. Afin d'examiner une possible influence génétique sur le développement d'une hypertrigly-céridémie dans le groupe des malades, nous avons examiné le rapport des apolipoprotéines E3/E2 et CII/CIII chez dix des malades et chez un autre groupe de 13 sujets contrôles. La fréquence des hétérozygotes pour un déficit en E3 n'était pas différente entre les groupes des malades (un des dit) ou des contrôles (deux des 13). Bien que le groupe des malades ait eu un rapport CII/CIII plus faible, les valeurs n'ont pas atteint la signification statistique. La faible activité LCAT en présence de triglycérides plasmatiques plus élevés et de HDL bas pourrait contribuer à l'anomalie de lipolyse préalablement documentée chez les malades urémiques. Une étude évolutive faite un an après l'étude initiale a confirmé la diminution des HDL (51 contre 71 mg/dl, P < 0,01) et de l'activité LCAT (50 contre 59 nmoles/hr/ml, P < 0,02) dans un système utilisant un substrat exogène (N = 20). La LCAT mesurée en utilisant le substrat endogène n'était pas significativement différente du groupe contrôle (49 contre 55 nmoles/hr/ml). Les modifications d'activité LCAT induites par une dialyse unique n'étaient pas significatives dans aucun des systèmes de dosage.

家族性LCAT欠損症(本邦第3家系)の家系調査における血漿アポ蛋白とLCATの分析

LCAT mass and its activity were measured in Japanese cases with familial LCAT deficiency. They were the menbers of the third family found in Japan.Haptoglobin types were 2-2 in all cases. Among plasma apoproteins, A-I, A-II, B, D levels were decreased in a homozygote. In heterozygotes, plasma apoprotein levels were almost normal. Plasma cholesterol-cholesterol ester ratio was 60-70% of normal range even in heterozygotes. Plasma LCAT activity was below 10% of normal range in a homozygote and 60% in heterozygotes, these were similar to other cases previously reported. Plasma LCAT mass was 35% in a homozygote and almost normal in heterozygotes. In other reports, LCAT mass was undetectable in homozygotes and 50% in heterozygotes. In this Japanese family, homozygote has no LCAT activity but has 35% of normal LCAT mass. Heterozygotes have half-normal activity and normal mass. This suggests that deficiency of LCAT activity in this family is caused by presence of LCAT like protein which has no activity.

Changes of high density lipoprotein subfraction concentration and composition by intralipid in vivo and by lipolysis of intralipid in vitro.

Serum lipoproteins were measured during a single infusion of intralipid and during parenteral nutrition with intralipid and glucose. Postheparin plasma lipolytic enzymes and plasma LCAT activity were assayed before and after the parenteral nutrition. Both single and repeated infusions of intralipid were followed by a significant rise of HDL2 concentration (p less than 0.01), whereas the HDL3 decreased. The composition of HDL subclasses altered. The HDL2 triglyceride and phospholipids increased, while the HDL3 esterified cholesterol and protein decreased. In vitro incubation of serum with intralipid alone caused no changes in the zonal profile of HDL subclasses, but hydrolysis of intralipid by lipoprotein lipase was followed by conversion of HDL3 into lighter particles floating in the density range of HDL2. The present results provide additional evidence for a precursor-product relationship between the HDL2 and HDL3. During 4 days of parenteral nutrition with intralipid, the basal (morning) values of serum total and VLDL triglyceride did not change. The LDL phospholipids increased progressively (from 67 to 98 mg/dl, p less than 0.05). The total HDL cholesterol decreased and this change was due to the fall of HDL3 cholesterol esters (from 19 to 12 mg/dl, p less than 0.05). Also the basal values of apo A-I and A-II in HDL3 decreased. The basal level of the HDL2 remained constant. Postheparin plasma LPL activity increased by 52% (p less than 0.01) but hepatic lipase activity fell by 49% (p less than 0.05). These changes may account for the maintenance of plasma HDL2, whereas the progressive fall of the basal HDL3 is probably due to the lack of intestinal apoprotein synthesis during absent intestinal absorption.

Plasma LCAT activities in renal allograft recipients.

Plasma LCAT activities were measured in 51 renal allograft recipients as well in 18 patients before and after successful renal transplantation. The mean plasma LCAT activity of the 51 patients did not differ significantly from that of 27 normal subjects. When the patients were separated into two groups according to whether they had normal or impaired renal function, there was no significant difference in their mean LCAT activities. Plasma LCAT activities correlated significantly with total cholesterol and total triglyceride concentrations. The sequential study demonstrates that the low plasma LCAT activities in uraemic patients rose towards normal after successful transplantation. At the same time, total cholesterol and HDL-cholesterol concentrations also increased. The increase in LCAT activity after renal transplantation is due to increased concentrations of the enzyme and probably reflects increased turnover of triglyceride-rich lipoproteins.