A fish-eye disease-like familial condition with massive corneal clouding and dyslipoproteinemia. Report of clinical, histologic, electron microscopic, and biochemical features

Fish-eye disease (FED) is a rare familial condition characterized by progressive bilateral corneal clouding and dyslipoproteinemia previously described in one family and an unrelated woman of Swedish descent. Biochemical studies have clearly demonstrated the existence of this entity as a unique dyslipoproteinemia. We present a non-Swedish family of Mediterranean ancestry afflicted with bilateral corneal clouding and lipoprotein analysis consistent with FED-like state. This family's biochemical profile, corneal button histology, and electron microscopy of one member are reviewed. Other dyslipoproteinemias causing corneal changes are considered. Corneal tissue and familial biochemical analyses differed significantly from previous descriptions. On the basis of these findings, explanation of pathologic deposition and disease mechanism is proposed.

High density lipoproteins: physiopathology and clinical relevance

On September 13-14 1991 a Symposium on High Density Lipoproteins: Physiopathology and Clinical Relevance was held in Bellagio (Italy). This Symposium was aimed at discussing various aspects of HDL from epidemiology to the most recent advances in the understanding of HDL metabolism and factors (diets, drugs) affecting their levels.

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)

Postheparin plasma lipoprotein and hepatic lipase are determinants of hypo- and hyperalphalipoproteinemia

To study the role of the two postheparin plasma lipolytic enzymes, lipoprotein lipase (LPL) and hepatic lipase (HL) in high density lipoprotein (HDL) metabolism at a population level, we determined serum lipoproteins, apoproteins A-I, A-II, B, and E, and postheparin plasma LPL and HL activities in 65 subjects with a mean HDL-cholesterol of 34 mg/dl and in 62 subjects with a mean HDL-cholesterol of 87 mg/dl. These two groups represented the highest and lowest 1.4 percentile of a random sample consisting 4,970 subjects. The variation in HDL level was due to a 4.1-fold difference in the HDL2 cholesterol (P less than 0.001) whereas the HDL3 cholesterol level was increased only by 32% (P less than 0.001) in the group with high HDL-cholesterol. Serum apoA-levels were 128 +/- 2.2 mg/dl and 210 +/- 2.8 mg/dl (mean +/- SEM) in hypo- and hyper-HDL cholesterolemia, respectively. Serum apoA-II concentration was elevated by 28% (P less than 0.001) in hyperalphalipoproteinemia. The apoA-I/A-II ratio was elevated only in women with high HDL-cholesterol but not in men, suggesting that elevation of apoA-I is involved in hyperalphalipoproteinemia in females, whereas both apoA proteins are elevated in men with high HDL cholesterol. Serum concentration of apoE and its phenotype distribution were similar in the two groups. The HL activity was reduced in the high HDL-cholesterol group (21.2 +/- 1.5 vs. 38.5 +/- 1.8 mumol/h/ml, P less than 0.001), whereas the LPL activity was elevated in the group with high HDL-cholesterol compared to subjects with low HDL-cholesterol (27.8 +/- 1.3 vs. 19.9 +/- 0.8 mumol/h/ml, P less than 0.001). The HL and LPL activities correlated in opposing ways with the HDL2 cholesterol (r = 0.57, P less than 0.001 and r = 0.51, P less than 0.001, respectively), and this appeared to be independent of the relative ponderosity by multiple correlation analysis. The results demonstrate major influence of both HL and LPL on serum HDL cholesterol concentration at a population level.

[Acceptance of cholesterol by high density lipoproteins in people with dys-alpha-lipoproteinemia and the possible role of apoprotein E in this process]

Both subfraction "2" of high density lipoproteins (HDL2) from patients with hypo-alpha-lipoproteinemia and subfraction HDL3 from persons with normal content of cholesterol were shown to accept the erythrocyte membranes cholesterol in vitro. Under these conditions HDL3 subfraction was transformed into HDL2-like particles, where content of unesterified cholesterol and its esters was increased simultaneously with enlargement of the particles size. The HDL subfraction, isolated from persons with high content of cholesterol, did not accept cholesterol under the experimental conditions. Apoprotein E, containing in the HDL subfractions, was not responsible for the particles cholesterol-accepting properties. Apoprotein E itself was capable of cholesterol elimination from erythrocytes as well as of cholesterol esters from HDL3 and HDL2-like particles with formation of a specific complex.

Lipoprotein abnormalities associated with lipopolysaccharide-induced lecithin: cholesterol acyltransferase and lipase deficiency

Density gradient ultracentrifugation was used to isolate and characterize the plasma lipoproteins from African green monkeys before and 24 and 48 h after subcutaneous injection of 300 micrograms/kg lipopolysaccharide (LPS) to induce an acute phase response. Compared with 0 h values, reductions occurred in plasma cholesterol (39%), high density lipoprotein (HDL) cholesterol (54%), lecithin:cholesterol acyltransferase (LCAT) activity (55%), and post-heparin plasma lipase activity (68%) 48 h after LPS injection while plasma triglyceride concentrations increased 700%. Cholesterol distribution among lipoproteins shifted from 7 to 41% in very low density lipoproteins (VLDL), 65 to 38% in low density lipoproteins (LDL), and 28 to 21% in HDL after LPS injection. At 48 h after LPS injection, all lipoprotein classes were relatively enriched in phospholipid and triglyceride and depleted of cholesteryl ester. The plasma concentration of all chemical constituents in VLDL was increased 3-9-fold within 48 h after LPS injection. By negative stain electron microscopy, HDL were discoidal in shape while VLDL and LDL appeared to have excess surface material present. Even though total HDL protein concentration in plasma was unaffected, the plasma mass of the smallest HDL subfractions (HDL3b,c) doubled while the mass of intermediate-sized subfractions (HDL3a) was dramatically decreased within 24 h after treatment. HDL became enriched in apoE, acquired apoSAA, and became depleted of apoA-I, A-II, and Cs by 48 h after LPS injection while apoB-100 remained the major apoprotein of VLDL and LDL. We conclude that administration of LPS to monkeys prevents normal intravascular metabolism of lipoproteins and results in the accumulation of relatively nascent forms of lipoproteins in plasma. These immature lipoproteins resemble those isolated from the recirculating perfusion of African green monkey livers, which are relatively deficient of LCAT activity and those isolated from the plasma of patients with familial LCAT deficiency.

Increased urinary mevalonic acid excretion in patients with abetalipoproteinemia and homozygous hypobetalipoproteinemia

Previous reports in which cholesterol homeostasis has been examined in patients with phenotypic abetalipoproteinemia have shown an increase in whole body cholesterol synthesis when measured by sterol balance techniques but normal rates of cholesterol synthesis when measured by isotopic cholesterol turnover. Recent studies have indicated that increases in cholesterol biosynthesis are paralleled by increases in the plasma concentrations of mevalonic acid and by higher rates of excretion of mevalonic acid in the urine. In the present report we have measured the 24-h urinary excretion of mevalonic acid in 7 patients with phenotypic abetalipoproteinemia and compared this to control subjects. Urinary excretion of mevalonic acid was significantly higher in the patients with abetalipoproteinemia (57.2 +/- 10.2 nmol/kg body weight per day, mean +/- SEM) as compared to control subjects (23.1 +/- 1.5 nmol/kg per day). The magnitude of the increase in urinary mevalonic acid excretion seen in patients with abetalipoproteinemia (148%) is greater than the increase in whole body cholesterol biosynthesis assessed by sterol balance techniques (57% increase). Our results serve to further validate the usefulness of urinary mevalonate as an indicator of relative rates of cholesterol biosynthesis in humans and suggest that this measurement provides a valuable means to potentially screen for disorders associated with an oversynthesis of cholesterol.

Lipid deposition at the limbus

Lipid deposition at the limbus is a feature of familial and non-familial dyslipoproteinemias and can also occur without apparent accompanying systemic abnormality. Hyperlipoproteinemia, most notably type II hyperlipoproteinemia, is frequently associated with bilateral corneal arcus, with less common association in types III, IV and V. Diffuse bilateral opacification of the cornea with accentuation towards the limbus is a feature of HDL deficiency syndromes and LCAT deficiency. Whereas the lipid accumulation of hyperlipoproteinemia may be representative of excessive insudation of lipoprotein from plasma into the cornea that of hypolipoproteinemia is more likely to be a consequence of defective lipid clearance. The situation is yet further complicated by the modifying influences of secondary factors, both local and systemic.

Low-density lipoprotein (LDL) distribution shown by 99mtechnetium-LDL imaging in patients with myeloproliferative diseases

STUDY OBJECTIVE

To image and identify by noninvasive methods the sites of low-density lipoprotein (LDL) catabolism in patients with myeloproliferative disease in whom chronic hypocholesterolemia was previously reported.

STUDY DESIGN

The 99mTechnetium-LDL (Tc-LDL) distribution in patients with myeloproliferative diseases was compared with that in normal subjects. The Tc-LDL distribution was also compared with the distribution and organ uptake of a macrophage-seeking radiotracer. 99mTc-sulfur colloid (Tc-SC).

SETTING

Major metropolitan referral center and institutional practice.

PATIENTS

Three normal subjects, two patients with polycythemia vera, two with post polycythemia myeloid metaplasia, and one with agnogenic myeloid metaplasia. The patients were being managed with hydroxyurea or phlebotomy.

INTERVENTION

Ten mCi of Tc-LDL (homologous) was injected intravenously.

MEASUREMENTS AND MAIN RESULTS

Gamma camera images of Tc-LDL biodistribution and organ uptake were obtained 4 hours after injection of the tracer. In normal subjects, the Tc-LDL was predominantly taken up by the liver, with relative nonvisualization of spleen and central or peripheral marrow. Patients with myeloproliferative disease showed marked splenic uptake of Tc-LDL. Peripheral bone marrow uptake extended to the lower tibia in two patients with post-polycythemia myeloid metaplasia. Splenic and bone marrow uptake paralleled that of Tc-SC. Hypercellularity of central and peripheral marrow at the sites of Tc-LDL uptake was confirmed by biopsy specimens. The Tc-LDL uptake, however, was not correlated with collagen fibrosis.

CONCLUSIONS

These results indicate that spleen and bone marrow are sites of LDL catabolism in patients with myeloproliferative disease and suggest the role of macrophages in the hypocholesterolemia and accelerated LDL catabolism of myeloproliferative disease.

Lactosaminated Fab fragments specific for low density lipoproteins/hepatocyte targeting and hypolipoproteinemic activity

We have previously reported that Fab fragments of IgGs modified by lactosamination (lac-Fab) can direct macromolecules, including low density lipoproteins (LDL), to the liver. In the present paper we demonstrate that lac-Fab that is specific for LDL is an effective and selective hypolipoprotein agent. A plasma pool of about 60 mg/dl of apoprotein B (apo B) was induced in rats by bolus injection of human LDL (hLDL), which increased the cholesterol value to about 150 mg/dl. Three hours after injection of the highest dose of lac-Fab, the total cholesterol decreased to 80 mg/dl, compared to 120 mg/dl in control animals. Studies conducted with 131I-tyramine-cellobiose-labeled LDL indicated that the liver was the only organ in which lac-Fab increased LDL uptake and degradation. The effect of lac-Fab was dose-dependent. With amounts of lac-Fab between 13 to 42 mg/kg body weight, the amount of hLDL cleared through the lac-Fab mechanism ranged from 30% to 70% of the initial pool. Analysis of the plasma lipoprotein subfractions revealed that high density lipoprotein levels were not affected. Histologic examination of liver sections after sequential injection of fluorescently labeled hLDL and lac-Fab indicated specific uptake in the hepatocytes when compared to control sections obtained from animals injected with Dil-LDL alone. The uptake of fluorescent LDL induced by lac-Fab was completely prevented by a co-injection of an excess of asialofetuin. We conclude that lac-Fab that is specific for LDL is a selective hypolipoproteinemic agent and a specific carrier to the hepatocytes.

In vivo metabolism of proapolipoprotein A-I in Tangier disease

Tangier disease is a rare familial disorder characterized by extremely low levels of apolipoprotein A-I (apoA-I) and high density lipoproteins (HDL). In normal subjects, proapoA-I is secreted into plasma and converted to mature apoA-I by the cleavage of the amino-terminal six amino acids with the major isoprotein in plasma being mature apoA-I. In contrast, in Tangier disease there is a marked relative increase of proapoA-I as compared with mature apoA-I. ProapoA-I and mature apoA-I were isolated from normal and Tangier disease subjects, radio-labeled, and autologous apoA-I isoproteins injected into normal and Tangier subjects. The in vivo catabolism and conversion of proapoA-I and mature apoA-I in normal and Tangier disease subjects were quantitated. A comparison of the rate of catabolism of apoA-I isoproteins from plasma revealed a significantly faster rate of catabolism of both isoproteins of apoA-I in Tangier subjects when compared with normal subjects. The fractional conversion rate of proapoA-I to mature apoA-I was 3.9 d-1 in normal subjects and 3.6 d-1 in Tangier subjects. The results indicate that (a) apoA-I enters plasma as the pro isoprotein in both normal and Tangier subjects, (b) Tangier disease subjects have a normal fractional rate of conversion of proapoA-I to mature apoA-I, (c) proapoA-I is catabolized at the same rate as mature apoA-I in Tangier subjects, and (d) Tangier subjects catabolize both pro and mature apoA-I at a much greater rate than do normal subjects. Therefore, the relative increase in proapoA-I in Tangier disease is due to a marked decrease in mature apoA-I resulting from rapid catabolism of both pro- and mature apoA-I and not to defective conversion of proapoA-I to mature apoA-I.

Impaired intermediate-density lipoprotein triglyceride hydrolysis in familial lecithin:cholesterol acyltransferase (LCAT) deficiency

A new lecithin:cholesterol acyltransferase (LCAT)-deficient family was found in Japan. In the proband, both LCAT activity and LCAT mass were deficient. The patient's parents, child, and sister, diagnosed as heterozygotes, had half-normal LCAT activity and LCAT mass. In the patient, an increase of intermediate-density lipoprotein (IDL, 1.006 less than d less than 1.019) fraction was observed. In postheparin plasma, both lipoprotein lipase and hepatic triglyceride lipase activities were low. Hydrolysis of [14C] triolein by human hepatic triglyceride lipase in patient IDL was decreased compared to that in IDL from normal postprandial serum. Preincubation of these IDL with normal plasma in the absence of 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB) increased the rate of hydrolysis, in the presence of DTNB, this increment was not observed. These results suggest that one cause of IDL increase in the LCAT-deficient patient might be the difficulty of hydrolysis of these lipoprotein particles by hepatic triglyceride lipase.

Interaction of high density lipoprotein with adipocytes in a new patient with Tangier disease

A 56-year-old man, the offspring of a consanguineous first cousin marriage, presented with clinical, morphological, and biochemical features of familial deficiency of high-density lipoproteins (Tangier disease). Of 8 first- and second-degree relatives examined, 4 had either plasma apo A-I or HDL cholesterol concentrations 2 standard deviations below normal population mean on at least 1 occasion. The patient and a majority of his relatives also had high plasma apo B concentrations relative to their levels of cholesterol. Adipose tissue biopsy was undertaken to study HDL interaction with the patients' cells. Specific uptake of HDL3 was demonstrated in adipocytes of this patient, but was decreased relative to a control of similar fat cell size. However, no marked difference in fat cell cholesterol content was observed between the Tangier patient and the control. Thus it appears unlikely that adipocytes play a role in the etiology of Tangier disease.

Lipid composition and lipolytic activities in milk from a patient with homozygous familial hypobetalipoproteinemia

We have investigated the composition of breast milk from a patient with abetalipoproteinemia. Activity level and specific activity of lipoprotein lipase in milk samples obtained at 0.5 and 3 mo postpartum were higher than those found in normal milk; activity of bile salt-activated lipase was found to be higher in the milk at 6 mo postpartum than in normal milk but average specific activity of this enzyme in milk samples was not increased. Except for higher protein content of patient's milk, there was no apparent abnormality in the protein pattern as determined by SDS-polyacrylamide gel electrophoresis. Lipid analysis indicated a shift in the molecular weight distribution of triglycerides, which favored lower molecular weight forms and reflected an increase in medium-chain and a major decrease in long-chain essential fatty acids (omega 6 and omega 3) in milk triglycerides.

Increased catabolism of VLDL-apolipoprotein B and synthesis of bile acids in a case of hypobetalipoproteinemia

A 29-year-old man is described who has reduced concentrations of low density lipoprotein (LDL)-cholesterol seemingly due to an unusual variant of hypobetalipoproteinemia. The patient developed retinitis pigmentosa at age 14. When studied at age 28, his total cholesterol was 104 mg/dL, triglycerides 58 mg/dL, LDL-cholesterol 44 mg/dL, and HDL-cholesterol 51 mg/dL. Lipid and lipoprotein levels of his parents and sister were normal. His excretion of bile acids (13.9 mg/kg/d) was markedly elevated at about three times normal, although absorption rates of cholesterol and bile acids appeared to be in the normal range. His high excretion of bile acids equates to a threefold increase in bile acid synthesis. Isotope kinetic studies of his lipoproteins produced unexpected findings. Total production of VLDL-apolipoprotein B (apo B) was estimated to be 20.8 mg/kg/d, which was in the normal range. Synthesis of VLDL-triglycerides was also normal at 12.0 mg/kg/h. However, 75% of VLDL-apo B was removed directly from the circulation, which was much higher than values for direct removal of VLDL-apo B in control subjects. His production rate of LDL-protein (5.2 mg/kg/d) consequently was below normal, although his fractional catabolic rate for LDL (0.40 pools/d) was not distinctly elevated. These data suggest that the patient's hypobetalipoproteinemia was due to increased direct removal of VLDL remnants and not to reduced synthesis of VLDL-apo B; this abnormality may have been the result of enhanced activity of LDL receptors, which in turn was secondary to increased synthesis of bile acids.

The degradation of platelet-activating factor in the plasma of a patient with familial high density lipoprotein deficiency (Tangier disease)

Platelet Activating Factor (PAF) (1-O-alkyl-2-acetyl sn-glycerol 3-phosphocholine) has been characterized by its ability to aggregate platelets at low concentrations and its profound hypotensive effects. There is evidence that the rate of catabolism of this compound in the plasma regulates its concentration. In humans, we and others have shown that a PAF acetylhydrolase is associated with low density lipoprotein (LDL). The LDL particle in the plasma of patients with Tangier disease is quite different from normal as its lipid core appears to be enriched with triacylglycerol. Thus, we have studied the potential of this abnormal lipoprotein to degrade PAF. The assay for PAF acetylhydrolase was based on the release of 3H from PAF that was labelled in the acetate moiety of the sn-2 position. Tangier disease plasma had approximately 3.3-fold higher PAF acetylhydrolase activity (208 +/- 9 nmol/min/mL) than controls (63 +/- 18 nmol/min/mL). This increase was brought about by an increase in the Vmax (400 +/- 40, Tangier disease; 54 +/- 5, controls) and Km for PAF (120 +/- 20 mumol/L, Tangier disease; 28 +/- 4 mumol/L, controls). The activity appears to be a specific acetylhydrolase rather than a phospholipase A2 as preincubation of the substrate with 0 to 100 mumol/L phosphatidylcholine did not affect the amount of [3H] acetate released. The role of PAF, and its degradation by LDL-bound PAF acetylhydrolase in the phenotypic expression of this patient with Tangier disease, is not known. However, this is the first patient so far described who has an increased ability to degrade PAF in the plasma.

Familial lecithin:cholesterol acyltransferase deficiency. Biochemistry of the cornea

Opacification of the cornea from lipid accumulation is an early and characteristic feature of familial lecithin:cholesterol acyltransferase (LCAT) deficiency. Visual impairment in a female age 48 years led to keratoplasty and the first detailed analysis of cornea in this disorder. Multilaminar figures were present, and total lipid extracts were enriched with phospholipid and cholesterol; cholesteryl esters were reduced, and accounted for about 12% of the cholesterol. Linoleate C18:2 was the predominant residue in the cholesteryl ester fatty acid fraction, with a C18:1/18:2 ratio of 1:6.5. This ratio differs from that in normal cornea, and from that in plasma and in other tissue deposits in LCAT deficiency. Various disorders of the HDL/LCAT system in plasma can lead to corneal lipid accumulation and opacification. These disorders may share general defects of lipid clearance from the cornea, but this study of LCAT cornea indicates that the character of the accumulating lipid is significantly influenced by active local metabolism, irrespective of the defect in the HDL/LCAT system also present.