Plasma lecithin: cholesterol acyltransferase activity in liver disease

A thorny matter: Spur cell anemia

Spur cell anemia (SCA) is an acquired form of non-autoimmune hemolytic anemia that occurs in advanced liver disease. It is characterized by the presence of acanthocytes or spur cells, spiculated erythrocytes whose shortened life span causes anemia that is unresponsive to transfusion. SCA has been regarded as a rare condition with an ominous prognosis for which the only known cure is liver transplantation, but recent prospective studies have demonstrated the existence of a milder form of SCA in which there are smaller numbers of acanthocytes, but which is nevertheless associated with hemolysis and poor outcomes. This form of SCA appears to be considerably more common than the severe classical variant. The conventional understanding of the pathogenesis of SCA is that abnormalities of lipid metabolism are the primary event driving the formation of spur cells. However, the studies that underpin this theory are based on small numbers of patients with heterogeneous clinical features and inconsistent use of nomenclature for dysmorphic red blood cells. In this review, we discuss the evolution of the current understanding of SCA and therapeutic strategies that have been employed based on this understanding. Our goal is to raise awareness of this understudied condition that has significant implications for patient outcomes. Furthermore, we highlight the need for rigorous, contemporary research into the underlying cause or causes of SCA in order to develop an effective therapy for this disorder.

A mutant of deleted variant of hepatocyte growth factor (dHGF) with alanine substitution in the N-terminal basic region has higher activity in vivo

In a previous study, we generated a mutant of dHGF (deleted variant of hepatocyte growth factor), termed #2, with higher specific activity than dHGF in assays of mitogenic activity on rat hepatocytes and America opossum kidney epithelial cells (OK). In the present study, we examine in vivo hepatotropic and renotropic activities of #2 and its distribution to target tissues, liver and kidney. Administration of #2 to normal rats significantly increased serum levels of total protein, albumin, free-cholesterol, and HDL-cholesterol and liver weight in a dose-dependent manner. Analysis of these parameters suggests that #2 is more potent than dHGF as a hepatotropic factor in vivo. In addition, #2 reduced mortality of mercuric chloride-administered mice and the effect was stronger than that of dHGF. When injected to mice, a larger amount of #2 than dHGF was rapidly distributed to the liver. Sixty minutes after injection, the concentrations of #2 in plasma, liver, and kidney were higher than those of dHGF. These distribution properties and the higher mitogenic activity in vitro may explain why #2 exerts more potent in vivo biological activity than dHGF.

Amelioration of disordered hepatic protein synthesis by the deleted form of hepatocyte growth factor in models of liver failure in rats

Because the liver plays an important role in protein synthesis and cholesterol metabolism and reductions in these functions are observed in almost all hepatic disorders, the effects of the deleted form of hepatocyte growth factor (dHGF) on disordered hepatic protein synthesis were studied in various liver-injured rat models using Wistar male rats. In the 70% hepatectomized rats, plasma clotting time was prolonged and the serum level of total protein and the liver protein content were decreased. The treatment of the animals with dHGF (100-500 micrograms kg-1, i.v., twice daily) ameliorated these parameters at 48 or 72 h. The administration of carbon tetrachloride or D-galactosamine to hepatectomized rats induced a marked prolongation of plasma clotting time and hypoproteinaemia. In the animals treated with dHGF (500 micrograms kg-1, i.v., twice daily) these parameters were rapidly reversed compared with those of control groups. In a hepatocellular necrosis model induced by dimethylnitrosamine, the plasma clotting time was extremely prolonged, and liver protein content, serum total protein, albumin, HDL-cholesterol (as an index of lipoprotein) and plasma lecithin-cholesterol acyltransferase activity severely reduced. In this severely injured model, dHGF (5-500 micrograms kg-1, i.v., twice daily for 28 days) dose-dependently prevented the loss of liver protein content and improved the disordered plasma coagulability and serum protein levels. These results suggest that dHGF is useful for ameliorating the disorders in hepatic functions such as protein synthesis.

Lipoprotein pattern and plasma lecithin cholesterol acyl transferase activity in children with Alagille syndrome

Alagille syndrome is frequently associated with hyperlipidemia and xanthoma. The aim of the study was to assess the lipid profile (plasma lipoproteins, apolipoproteins (apo)) and lecithin cholesterol acyl transferase (LCAT) activity, with and without treatment with cholestyramine in Alagille syndrome. Five children (mean age = 6 +/- 4 years) with Alagille syndrome were studied at two different times while receiving no treatment, and while receiving cholestyramine. They were compared with 12 normal controls, who were not different from patients for age and sex. In Alagille syndrome, total serum cholesterol, triglycerides and phospholipids were elevated compared with the controls (P < 0.008). VLDL-cholesterol, LDL-cholesterol, HDL-triglycerides, LDL-triglycerides and VLDL-phospholipids were higher, whereas HDL-cholesterol was lower than controls (P < 0.03). Apo B, CIII, E and lipoprotein particles Lp AI were higher (P < 0.001), whereas Lp AI:AII was lower than controls (P < 0.03). Lipoprotein-X was present in the 5 children with Alagille syndrome and explained in part the elevation of plasma cholesterol, phospholipids, and apo CIII. LCAT activity was decreased (P < 0.01) and might cause some abnormalities of HDL with lower cholesterol, higher triglycerides, apo E and apo CIII contents than controls, and abnormalities of VLDL and LDL with higher cholesterol, triglycerides, phospholipids and apo B contents than controls. Some of the risk factors of atherosclerosis were found in Alagille syndrome, namely high levels of plasma cholesterol, LDL cholesterol, apo B, apo B/apo AI. Treatment with cholestyramine resulted in a few modifications to the lipid profile, while lipoprotein-X and the decrease of LCAT activity persisted.

Lecithin-cholesterol acyltransferase and lipid transfer protein activities in liver disease

The activities of lecithin-cholesterol acyltransferase (LCAT) and lipid transfer protein (LTP) were assayed using sensitive radioassay methods in controls (n = 113) and in patients with various liver diseases (n = 72). Plasma LCAT activity decreased with progression of hepatocellular damage. Plasma LTP activity in controls was 216 +/- 68 nmol/mL/h, and there were no significant differences between controls and patients with chronic hepatitis ([CH], 193 +/- 70), compensated liver cirrhosis (LC) with or without hepatocellular carcinoma ([HCC], 197 +/- 48 and 193 +/- 62, respectively), or decompensated liver cirrhosis ([dLC], 182 +/- 65). In acute viral hepatitis, LTP activity decreased significantly; however, the degree of reduction was not as dramatic as that for LCAT. There was no correlation between LCAT and LTP activity both in controls and patients with various liver diseases. LCAT activity was positively correlated with serum albumin (r = .52, P < 0.1) and cholinesterase (r = .37, P < .01) levels, and inversely correlated with serum bilirubin level (r = -.38, P < 0.1); there was no correlation between plasma LTP activity and these parameters of liver function. That plasma LTP activity did not change with hepatocellular damage may indicate that the liver in humans may not be the primary site of LTP production.

The effect of an eucaloric high carbohydrate diet on circulating levels of glucose, fructose and non-esterified fatty acids in patients with cirrhosis

Twelve cirrhotic patients and six controls were fed an eucaloric high carbohydrate (CHO) diet for 3 days. Fasting serum triglyceride (TG), non-esterified fatty acids (NEFA), glucose, insulin and glycerol were estimated daily. On the 3rd day of the study we measured NEFA, glucose, insulin, and fructose every 45 min from 07:45 h until 19:45 h, and then every 4 h until 07:45 h the next day. The patients were divided into two groups of six on the basis of plasma lecithin-cholesterol acyltransferase (LCAT) activity: group A cirrhotics (with good liver function--LCAT activity: 40.6-65.7 nmol.ml-1.h-1; mean 48.5), and group B (poor liver function--LCAT: 23.7-32.3; mean 27.4). On the high CHO diet there was an increase in the fasting serum TG with a peak after 2 or 3 days. The increase in serum TG in controls was greater (p less than 0.01) than in either group of cirrhotics. In the controls and in group A most of the extra TG was carried in VLDL; in group B only 39% of the TG increment was found in VLDL. Fasting NEFA fell with 3 days of CHO feeding in the control group (p less than 0.01); they were unchanged in group A, and rose in group B to a significantly higher level than in controls (p less than 0.01). During day 3 when a high CHO diet was fed plasma NEFA levels fell in cirrhotics, and for most of the day the mean NEFA concentration in group B patients was significantly (p less than 0.05) lower than in normals. On day 3 glucose and fructose levels rose after each meal--much more in cirrhotics than in controls (and more in group B than in group A), and for most of the day they were significantly higher in group B patients as compared to the controls (glucose p less than 0.01, fructose p less than 0.001). Our results supported the hypothesis that plasma NEFA would be lower following high CHO meals in cirrhotics than in controls. This suggests that a high NEFA utilisation, which occurs in fasting cirrhotics, is not present throughout the day. Following a CHO meal, we suggest that tissues derive energy directly from the dietary sugars which are present in high concentration during the period of absorption and that this reduces the post prandial requirement for NEFA.

Evidence that C4b-binding protein (proline-rich protein) is synthesized by hepatocytes

C4b-binding protein (C4bp), a glycoprotein involved in regulating the classical pathway of the complement system, binds the activated form of C4b and accelerates the decay rate of the C4b, C2a complex. Recently, sequence analysis of the cDNA for proline-rich protein (PRP) demonstrated that PRP is identical with C4bp. We measured the concentration of C4bp in serum by single radial immunodiffusion in patients with various liver diseases. Concentration of C4bp was significantly lower in hepatic cirrhosis (P = 0.001) and higher in fatty liver (P = 0.0002) than the control values, after adjusting for age, sex, and concentration of total cholesterol, triglyceride, and C-reactive protein. Significant positive correlations were observed between the concentration of C4bp in serum and total protein, albumin, cholinesterase level, and lecithin-cholesterol acyltransferase activity. Immunohistochemical analysis of human liver with specific antiserum to human C4bp demonstrated reaction endproducts in the hepatocytes around the central veins. These observations provide evidence that C4bp is synthesized by hepatocytes.

Dyslipoproteinaemia of liver disease

Hepatic diseases differ from most other causes of secondary dyslipidaemia in that the circulating lipoproteins are not only present in abnormal amounts but they frequently also have abnormal composition, electrophoretic mobility and appearance. Pre-beta and alpha bands can be absent on electrophoresis in all types of liver disease although material in the VLDL and HDL ranges can be isolated in the ultracentrifuge. Cholestatic liver disease has been the most extensively studied and the hyperlipidaemia can be extreme with marked elevations of free cholesterol and phospholipids. This results largely from the presence of LP-X, an abnormal LDL, with a vesicular structure that appears in rouleaux formation under the electron microscope. It is virtually specific for cholestasis and familial LCAT deficiency. The LDL, however, is heterogeneous and may also contain a large triglyceride-rich particle (LP-Y) as well as more normal-looking particles, which are none the less depleted in cholesteryl esters and rich in triglycerides. Indeed, when patients with cholestasis are hypertriglyceridaemic the excess triglyceride is to be found predominantly in these two LDL fractions rather than in VLDL. HDL in cholestasis may contain disc-like particles, similar to those newly secreted by the liver and intestine, as well as more normal-looking spherical particles. In extrahepatic obstruction concentrations of HDL and its major apolipoproteins, apoAI and apoAII, are frequently reduced, although a subfraction rich in apoE is often found. In all but the latest stages of chronic intrahepatic cholestasis due to primary biliary cirrhosis, however, HDL, especially HDL2, concentrations are increased, probably due to the presence of a circulating inhibitor of HL. Many of these lipoprotein changes found in cholestasis resemble those of familial LCAT deficiency, although the hyperlipidaemia is not usually so severe in the latter condition. Indeed, in patients with cholestasis but well-preserved LCAT activity many of the characteristic lipoprotein changes, such as LP-X, LP-Y and discoidal HDL, may not be seen. In acute hepatocellular disease, such as alcoholic or viral hepatitis, it is not unusual for the patient to go through a cholestatic phase and many of the same lipoprotein changes may be seen. In cirrhosis without cholestasis the patients are not usually significantly hyperlipidaemic and in advanced cases cholesterol and apoB levels may be reduced. Although LCAT activity and the proportion of plasma cholesterol esterified may also be markedly reduced, LP-X is not usually seen, possibly because the flux of free cholesterol and phospholipid (lecithin), the LCAT substrates, is relatively low. Discoidal HDLs are often present.(ABSTRACT TRUNCATED AT 400 WORDS)

Plasma lipid and lipoprotein response to carbohydrate feeding in cirrhotic patients

Serum lipids and lipoproteins, and glucose and insulin, were measured after an overnight fast, and during 3 days of a eucaloric diet rich in carbohydrate, in 15 patients with cirrhosis and seven normal subjects. Following the high-carbohydrate diet triglyceride rose in all groups but the increase in cirrhotics was lower than in normals. In normals and in cirrhotics with good liver function most of the triglyceride increment was carried in VLDL; in cirrhotics with poor liver function only 31% of the increment was found in VLDL, and 56% in triglyceride-rich LDL. In an earlier study on fat feeding, our cirrhotic patients with poor liver function had an impaired chylomicron and VLDL response; they also carried most of the triglyceride increment in triglyceride-rich LDL. The markedly impaired response of triglyceride-rich lipoproteins to both carbohydrate and fat feeding suggests that sick cirrhotics may have a problem with storage of dietary energy and that this contributes to loss of their adipose tissue.

Changes in serum lipids related to the presence of experimental colon cancer

People at risk from coronary heart disease and large bowel cancer are drawn from the same urbanised, industrialised Western populations. Whilst changes in blood lipids are well recognised in heart disease, little is known of their role in large bowel cancer. This study investigates serial alterations in blood lipids in the 1,2-dimethylhydrazine (DMH) rat model of colon cancer. Eighty Wistar rats received a 5 weekly regimen of DMH. At week 10, and at 5 weekly intervals until week 40, random groups of 10 rats were killed and blood taken for total and free cholesterol, phospholipids, triglycerides and liver enzymes. All colonic neoplasms were histologically classified either as adenomas or carcinomas with groups being allocated into tumour-free (n = 16) or tumour-bearing (n = 54), the latter group being further sub-divided into animals with adenoma alone (n = 8) and those with carcinoma (n = 46). Results were considered both sequentially and according to tumour status. Sequential results showed that with increase in colonic neoplasms with time there were accompanying increases in free and % free cholesterol and in phospholipids (P less than 0.001). There were no changes in total cholesterol, triglycerides or liver enzymes. Results according to tumour status showed that whilst there was no difference in total cholesterol or triglycerides between tumour-free and tumour-bearing rats, there was a significant increase in free (P less than 0.01) and % free cholesterol (P less than 0.001) and a decrease in phospholipids in the tumour-bearing animals (P less than 0.001). There was no difference in any serum lipid between tumour-free and adenoma-bearing rats. In animals with carcinoma, while there was no difference in total cholesterol or triglycerides, there was an increase in free (P less than 0.005) and % free cholesterol (P less than 0.001) and a decrease in phospholipids (P less than 0.001) compared to tumour-free rats. The data show for the first time a clear relationship between blood lipids and the presence or absence of large bowel cancer.

Lecithin: cholesterol acyltransferase in liver disease

Lecithin: cholesterol acyltransferase (LCAT) activity in patients with liver disease has been found to be either normal or lower than normal, but no information on LCAT mass in these patients is available. In this study, LCAT mass concentration together with LCAT activity and cholesterol esterification rate were measured in the plasma of 19 patients with cholestatic liver disease and 21 patients with non-cholestatic liver disease. The LCAT mass in plasma correlated positively with serum albumin (r = 0.69, p less than 0.001) and pre-albumin (r = 0.77, p less than 0.001) and negatively with serum bilirubin (r = -0.42, p less than 0.01) and bile salts (r = -0.43, p less than 0.01), thus reflecting the severity of liver disease and liver protein synthesizing capacity. In plasma, LCAT mass concentration also correlated well with LCAT activity (r = 0.88, p less than 0.001) and cholesterol esterification rate (r = 0.73, p less than 0.001), thereby indicating that the decrease of LCAT activity and cholesterol esterification rate in liver disease is primarily a function of decreased LCAT mass.

Predicting severity of liver disease: twelve laboratory tests evaluated by multiple regression

To determine the predictive value of laboratory procedures for severity of liver disease, twelve laboratory tests were evaluated in seventy-two patients with various liver disease and in nine non-liver disease hospitalized cases. A numerical score based on the number and extent of abnormal findings was developed for grading clinical and histological severity. Multiple linear regression, utilizing a forward stepwise selection procedure, was used to find the best combination of laboratory tests for prediction of disease severity. The best predictive model for both clinical and histological severity was found for lecithin cholesterol acyltransferase (LCAT), total plasma cholesterol, alkaline phosphatase and bile acids. Of the routine tests prothrombin time and albumin/globulin were useful if the four-test combination listed above was not used. There was a significant correlation (p less than 0.001) between the clinical and the histological score, confirming validity of clinical scoring. In conclusion, this study shows LCAT to rank as first in predicting severity of liver disease. Cholesterol metabolism appears to be affected by liver disease even more than prothrombin time, albumin and globulins. LCAT and bile acids have a place in routine testing of severity of liver disease.

Lipoprotein abnormalities in patients with early primary biliary cirrhosis

In twelve females with early forms of primary biliary cirrhosis (PBC) serum lipoproteins, the intravenous fat tolerance test ( IVFTT ) and the lecithin: cholesterol acyl transferase (LCAT) rate were determined and compared to healthy controls. The cholestatic LDL (LP-X) test was negative in all cases. PBC patients had lower very low density lipoprotein TG concentrations than controls and had levels of (high-density lipoprotein) HDL-TG, -cholesterol and -phospholipids that were about 50% higher than in controls. In PBC the HDL2-cholesterol concentration was double but the HDL3-cholesterol concentration was 60% of control values (P less than 0.001 for both). The LCAT rate and the IVFTT value did not differ between the groups. A typical finding on agarose gel electrophoresis was the appearance of a slow-moving alpha-band. Several interpretations of these results are possible. In PBC the hepatic lipase activity may be impaired leading to a shift of the HDL2/HDL3 relation. The transport of HDL2 to the liver lipase site may also be affected and HDL3 production reduced due to malabsorption in the intestine.

Pattern of lecithin-cholesterol-acyl-transferase (L-CAT) activity in the course of liver cirrhosis

Considering liver cirrhosis a limit model, and therefore a condition suitable for the analysis of changes of lipid metabolism in liver disorders generally, the authors examined the L-CAT pattern, total and free cholesterol, HDL-cholesterol and APO-A in sixty-five subjects; fifty-three were suffering from liver cirrhosis, and were subdivided into those who were diabetic in addition, and those who were not, as well as according to the severity and duration of the liver disease; the remaining twelve were healthy controls. Analysis of the findings showed L-CAT to diminish significantly as the metabolic changes due to liver injury worsen. Contrary to the other parameters studied, L-CAT was the only one for which significant changes were found on analysis of variance comparing non-diabetic cirrhotics of varying severity. Further comparison suggested the idea that the reduction of L-CAT activity was correlated to the rate of progression of the disease rather than to the temporary condition of compensation or decompensation, so much so as to suggest itself as a valid parameter for the prognosis of liver cirrhosis.

An optimized method for measuring lecithin : cholesterol acyltransferase activity, independent of the concentration and quality of the physiological substrate

The aim of the study was to achieve the measurement of lecithin : cholesterol acyltransferase (EC 2.3.1.43) activity independent of and uninfluenced by equilibration of lipids between different lipoproteins, their molar ratios or by possible differences in their substrate quality. A mixture of sodium phosphotungstic acid/MgCl2 was added to serum samples to achieve total precipitation of all plasma lipoproteins. The filtrate containing the total plasma lecithin : cholesterol acyltransferase activity, apolipoprotein A-I and major plasma proteins was used for the assay. Liposomes comprised of phosphatidylcholine, cholesterol and dicetylphosphate served as substrate. The decrease in free cholesterol was determined enzymatically after incubation for 60 min at 37 degrees C. The assay followed zero-order kinetics and was linear for more than 60 min. The following Km values for various substrates were obtained: liposomes, 0.43 mM; HDL, 0.63 mM; LDL, 0.0; VLDL, 0.0; abnormal lipoprotein, found in cholestasis, (LP-X), 0.0. Comparison with generally used lecithin : cholesterol acyltransferase assay methods revealed similar activities for healthy controls, but in different forms of dyslipoproteinemia higher values were obtained with our method and, in special cases, the activity could be enhanced by addition of apolipoprotein A-I.

A lipoprotein independent assay for human serum lecithin-cholesterol acyltransferase

A method has been developed for estimation of human serum lecithin-cholesterol acyltransferase free of interference by endogenous lipoproteins. Precipitation of serum low and very low density lipoproteins by sodium phosphotungstate and magnesium chloride results in complete recovery of lecithin-cholesterol acyltransferase activity in the supernatant. One microliter of the supernatant can be accurately assayed with a highly efficient substrate containing phosphatidylcholine-cholesterol vesicles and apo-high density lipoproteins (HDL), with no interference from endogenous HDL or residual precipitation reagents. Serum levels of the enzyme were found to be reduced in patients with parenchymal liver disease, renal disease, gastrointestinal tumors and anemias.

Lipoprotein-X

Lipoprotein-X is an abnormal lipoprotein that appears in the sera of patients with obstructive jaundice, and thus is a sensitive indicator of cholestasis. In patients with familial plasma lecithin, Cholesterol acyltransferase (LCAT) deficiency, there is an inverse relationship between plasma Lp-X levels and LCAT activity. Ultracentrifugation procedures utilized for isolation of Lp-X have shown that it is associated with the low density lipoprotein fraction. Lp-X can be visualized by electrophoresis on either Agar or Agarose. The purity of Lp-X preparations has been documented by immunochemical procedures. The availability of highly purified antisera to Lp-X has served as a basis of one of the assay procedures for this lipoprotein. It's chemical composition has been established. Phospholipids and unesterified cholesterol constitute the bulk of the Lp-X molecule. Electron microscopic studies have demonstrated that Lp-X is a spherical particle which has strong aggregating properties. Membrane bound enzymes have been shown to aggregate with Lp-X. The fact that bile lipoprotein can be converted to Lp-X by the addition of albumin and that Lp-X can be converted to bile lipoprotein by the addition of bile salts offers a possible explanation for the origins of Lp-X. Phospholipases of plasma might play a role in the catabolism of Lp-X. The value and limitations of Lp-X determinations will also be addressed in this review.

Determination of lecithin:cholesterol acyltransfer in mouse plasma and the influence of mercaptoethanol and sulphydryl blocking agents on its activity

1. The cholesterol esterifying activity in mouse plasma has been identified as lecithin:cholesterol acyltransferase (LCAT) on the basis of stoichiometric data, predominant transfer of polyunsaturated fatty acids, wide pH optimum and inhibition of esterification by phospholipase A2 and sulphydryl blocking agents. The esterifying activity differed from that present in plasma of man, rat and other species since it was partially inhibited by mercaptoethanol and other thiols. 2. Stoichiometric correlations between unesterified cholesterol, lecithin and lysolecithin were not exact, suggesting possible involvement of other enzymes in the overall esterification process during in vitro incubation of mouse plasma. 3. The initial rate of cholesterol esterification was determined by in vitro incubation of mouse plasma, whose cholesterol had been labelled by prior in vivo injection of 3H-mevalonic acid. The mean rate was 281 +/- 74 nmol/ml/hr (mean +/- S.D., n = 12) and correlated with unesterified cholesterol concentration (r = 0.73, P less than 0.01).

[Diagnostic significance of heat-induced inhibition of erythrocyte sedimentation (author's transl)]

Heat-induced inhibition of erythrocyte sedimentation (HIES) was examined in 158 cases. HIES is significantly lower in patients with a liver cell damage isolated or due to metastases of a neoplastic process in comparison to that in patients suffering from inflammation or malign tumor not involving the liver. Generally, HIES depends upon the concentration of lysophosphatidyl choline (lysolecithin) which is set free in plasma by lecithin-cholesterol-acyltransferase (LCAT) during incubation. In patients with lever cell damage, LCAT is diminished. HIES is being influenced by several factors: Lysophosphatidyl choline is bound to albumin, and this prevents its reaction on the erythrocyte surface. Lysophospholipase reduces the concentration of lysophosphatidyl choline in the plasma by splitting off its fatty acid in the alpha-position. Specific serum proteins, the so-called agglomerines, which are responsible for the acceleration of erythrocyte sedimentation, are counteracting the HIES. The concentration of albumin and agglomerines in plasma and the activity of lysophospholipase are subject to physiologically and pathologically caused deviations. Thereby, HIES is being influenced individually at varying degrees. This makes it difficult to estimate the LCAT activity which represents the principal cause of HIES. As a consequence, HIES seems not to be suitable for clinical diagnostics.

Serum total lipids, lipoprotein cholesterol, and apolipoprotein A in acute viral hepatitis and chronic liver disease

Serum total lipids, lipoprotein cholesterol, apolipoprotein A (Apo A), and liver function tests have been investigated in patients with acute viral hepatitis and chronic liver disease. Hypertriglyceridaemia, absence of alpha and pre beta bands on the lipoprotein electrophoresis pattern, low level of Apo A, and presence of abnormal lipoproteins (beta-VLDL and beta2-LP) were observed in the early phase of acute hepatitis. A positive correlation was found between Apo A and high-density lipoprotein cholesterol, and a negative one between Apo A and triglyceride, bile acids, total bilirubin, and serum alanine aminotransferase. Lipoprotein abnormalities found in the early phase of acute hepatitis are probably due to low lecithin-cholesterol acyltransferase activity. The reappearance of alpha lipoprotein and the increase of Apo A are sensitive indices of improvement of liver function. In chronic liver disease low levels of cholesterol and Apo A indicate the severity of liver cell injury.

Plasma lipids and lipoproteins in liver disease

There are many changes in the plasma, lipids, and lipoproteins in patients with liver disease. They have proved difficult to study but our understanding of these changes has increased greatly during recent years. In obstructive jaundice hyperlipidaemia is a fairly constant finding and this appears to be due to the regurgitation of phospholipid from the obstructed biliary tree. The plasma lipids tend to fall with parenchymal liver disease. The composition of the lipoproteins depends on the activity of the plasma enzyme lecithin: cholesterol acyl transferase. When LCAT activity is high the individual lipoprotein fractions are normal. When it is reduced all of the lipoprotein fractions are affected but the pattern found with obstruction is quite different from that found with parenchymal disease. The changes in plasma lipoproteins appear to be associated with change in the lipid composition of cellular membranes and this may have important functional implications.

Plasma cholesterol esterification and plasma lipoproteins in bile-duct-ligated dogs

To study the lipoprotein changes in cholestasis while the capacity for plasma cholesterol esterification was normal, the common bile duct was ligated in dogs and plasma investigated 8 h and 48 h later. The plasma concentration of cholesteryl esters was slightly increased, concomitant with a tendency toward an increase in the activity of lecithin:cholesterol acyltransferase (LCAT). The content of cholesteryl esters in the main lipoprotein classes was normal. Marked alteration in the low density lipoproteins (LDL) and the high density lipoproteins (HDL) took place and were essentially similar 8 h and 48 h after bile duct ligation. In LDL, (density 1.006--1.019 g/ml) and LDL2 (density 1.019--1.063 g/ml) an increase in the content of polar lipids was observed, and in LDL2 heterogeneity in particle size was demonstrated by gelfiltration on 2% agarose and by electron microsopcy. Large myelin structures, flattened disc-shaped particles, and particles with the appearance of normal LDL2 were present. HDL isolated after operation was characterized by a decreased protein/lipid ratio and an increased content of phospholipids. By gelfiltration on Sephadex G-200 and by electron microscopy changes in particle size were observed, with the presence of disc-shaped particles with a tendency in form rouleaux. These results demonstrate that marked lipoprotein changes occur as early as 8 h after bile duct-ligation in dogs and indicate that a deficient LCAT mechanism is present in cholestasis even with normal or high plasma LCAT activity.

Secondary hypertriglyceridaemia in patients with parenchymal liver disease

Hypertriglyceridaemia occurring in patients with liver disease has been studied by measuring hepatic triglyceride lipase (H-TGL) and plasma lipoprotein lipase (LPL) by selective precipitation of H-TGL with specific antibodies. Lipid analysis, determination of lecithin-cholesterol-acyltransferase (LCAT) activity, and liver function tests were performed in parallel in fifty patients with acute hepatitis, twenty patients with chronic active or persistent hepatitis and fifty with cirrhosis of the liver. Total post-heparin lipolytic activity (PHLA) decreased with the severity of liver dysfunction. This decrease was due to low H-TGL and only to some degree to low LPL activity. With improvement over several weeks of hospitalization, hypertriglyceridaemia disappeared with a concomitant increase of H-TGL and LPL. It is concluded that impaired triglyceride metabolism in liver disease is at least partly caused by diminished plasma hepatic TGL activity.

[Determination of lecithin-cholesterol acyltransferase. Studies on the precipitation of beta-lipoproteins by dextran sulphate (author's transl)]

Uncertainties in assays of lecithin-cholesterol acyltransferase (LCAT) are generally related to the degree of isotopic equilibrium obtained by rapid exchange of unesterified cholesterol between the different lipoproteins. A new method is presented based on the precipitation of serum beta-lipoprotein with sulfated polysaccharides prior to the LCAT determination. In the absence of Beta-lipoproteins, more than 7 per cent of serum free cholesterol is esterified in the first hour and the reaction rate is linear for about 2 h. LCAT activities with normal serum expressed as cholesterol esterified per microliter mol/1/h are lower than the values reported by others. The reason for this discrepancy is that free cholesterol specific activity in total serum does not reflect the true specific activity of LCAT cholesterol substrate.

Lipoprotein-X: a substrate for lecithin: cholesterol acyltransferase

The action of lecithin:cholesterol acyltransferase (LCAT) was studied on an abnormal lipoprotein (LP-X) rich in phosphatidylcholine and cholesterol from the plasma of patients with obstructive liver disease. 60 mg LP-X isolated free of other lipoproteins and subsequently labelled with 3H-cholesterol were incubated with 1 mg highly purified enzyme in the presence of albumin. After 45 h at 37 degrees C, the incubation mixture was subjected to zonal ultracentrifugation. 3H-cholesterol and 3H-cholesteryl esters were quantified in each fraction of the zonal gradient. More than 95% of the lipoproteins in this mixture banded in the density range of LP-X with no change in size distribution, but did contain 593 nmoles of newly formed cholesteryl esters. Agarose electrophoresis revealed an alpha-migrating band in addition to the original beta-band. Also on agar, the typically cathode migrating LP-X was changed to anode moving material. These studies indicate that LP-X can serve as a substrate for LCAT.

The influence of LP-X and other lipoproteins associated with hepatic dysfunction on the activity of lecithin:cholesterol acyltransferase

A study was made of the in vitro effects of the abnormal serum lipoproteins associated with liver disease on the activity of the enzyme lecithin:cholesterol acyltransferase. At lipoprotein concentrations equivalent to those found in hepatic disease sera, the results indicate that: (1) LP-X levels greater than 2.5 mg/ml produced total inhibition of enzyme activity. (2) LP-X levels remained constant even up to 36 h incubation, despite active cholesterol esterification in the presence of LP-X concentrations less than 2.5 mg/ml. In addition, the specific activity of radiolabelled LP-X, and its electrophoretic properties remained unchanged after incubation showing that the molecule remained intact. (3) Low density lipoproteins other than LP-X stimulated the enzymes activity, but this effect was overcome by LP-X. (4) Additional concentrations of high density lipoproteins also produced enhancement of enzyme activity, but at higher levels inhibition was seen. LP-X prevented the enhancement of lecithin:cholesterol acyltransferase activity. (5) Small samples of pure LP-X, obtained with the minimum of physical manipulation, showed a complete absence of cholesterol ester and triacylglycerol from the molecule. The implications of these results are discussed, particularly in relation to other reports which have presented evidence that LP-X is a substrate for lecithin:cholesterol acyltransferase.

[Incorporation of 4-14C-labeled cholesterol into the cholesterol ester fractions of plasma lipoproteins in patients with cirrhosis of the liver (author's transl)]

In vivo incorporation studies with 4-14C-cholesterol were performed in five patients with cirrhosis of the liver. All patients showed low concentrations of total cholesterol, esterified cholesterol, and a low activity of the lecithin: cholesterol acyltransferase activity (LCAT). The pattern of incorporation corresponded to the results known from hypercholesterolemic, normocholesterolemic and hypertriglyceridemic patients. Low cholesterol ester concentrations and low LCAT activity do not modify the pattern of incorporation into the lipoprotein ester fractions.

Activity of lecithin: cholesterol acyltransferase in different parts of the circulatory system in man

In 24 patients without liver disease lipids and LCAT activity were determined in the inferior vena cava, the hepatic vein, the pulmonary vein and in the left ventricle. The total cholesterol, free cholesterol and cholesterol ester concentrations are identical and differences in the LCAT activity cannot be demonstrated.

Lipoprotein and lecithin: cholesterol acyltransferase changes in galactosamine-induced rat liver injury

Abnormal lipoproteins and drcreased lecithin: cholesterol acyltransferase activity are found in rat plasma following intraperitoneal injection of D-galactosamine. The changes observed, including absence of alpha-lipoprotein and the presence of lipoproteins rich in phospholipid and unesterified cholesterol but deficient in cholesteryl esters, are remarkably similar to changes found in human pathologic states of lecithin: cholesterol acyltransferase deficiency. When examined by electron microscopy, all of the major lipoprotein classes isolated by ultracentrifugation showed morphological abnormalities including the formation of rouleaus consisting of disk-shaped particles.

Plasma lipoproteins in rats with experimental biliary obstruction. I. A chemical study

Acute biliary obstruction in the rat is associated with striking alterations of the plasma level and the physico-chemical properties of plasma lipoproteins. 1. The level of very low density lipproteins (VLDL) in plasma increases from 2 to 3 fold. The chemical composition of VLDL is characterized by a high content of phospholipids and cholesterol and by a diminution of the relative content of triacylglycerols and protein. On cellulose acetate electrophoresis, VLDL show a beta-mobility. 2. The plasma concentration of low density lipoproteins (1.019--1.063 g/ml, LDL2) increases several fold above the control level. Phospholipids and unesterified cholesterol are the major components of this fraction which contains only a minute amount of cholesteryl ester (4%) and triacylglycerols (10%). LDL2 contain a component which migrates to the cathode in 1% agar gel electrophoresis. Separation of LDL2 by gel filtration on 2% agarose column results in the identification of three subfractions. Subfraction I contains a large proportion of cholesterol and triacylgylcerols, subfraction II is rich in unesterified cholesterol and phospholipids whereas subfraction III has a chemical composition fairly similar to that of the control LDL2. 3. The level of high density lipoproteins (HDL) also increases after bile duct ligation. The chemical composition of HDL2 (1.063-1.125 g/ml) is characterized by a high content of unesterified cholesterol and phospholipids and by a remarkable reduction in the content of cholesteryl esters and protein.

The relationship of red cell membrane lipid content to red cell morphology and survival in patients with liver disease

The relationship of red blood cell (RBC) membrane lipid content to RBC morphology and survival was studied in patients with liver diseases. An increase in RBC cholesterol and phospholipid was detected in most patients with hepatocellular disease or cholestatic jaundice but the alteration in RBC lipid content did not correlate with RBC survival. The main abnormality of RBC morphology observed was the presence of macrocytes and target cells. In a small proportion of patients (approximately 3%) with severe hepatocellular disease, significant numbers of severely deformed ("spur") cells were seen. In these patients haemolysis was moderately severe and the RBC lipid profile showed increased membrane cholesterol without a concomitant increase in phospholipids. It is concluded that only in patients with "spur" cell anaemia do the morphological alterations lead to premature removal of cells from the circulation. The cause of the shortened RBC survival in jaundiced patients without "spur" cells remains to be determined.