Characterization of neutral and acid ester hydrolase in Wolman's disease

Lysosomal acid lipase deficiency in pediatric patients: a scoping review

OBJECTIVE

Lysosomal acid lipase deficiency (LAL-D) is an underdiagnosed autosomal recessive disease with onset between the first years of life and adulthood. Early diagnosis is crucial for effective therapy and long-term survival. The objective of this article is to recognize warning signs among the clinical and laboratory characteristics of LAL-D in pediatric patients through a scope review.

SOURCES

Electronic searches in the Embase, PubMed, Livivo, LILACS, Web of Science, Scopus, Google Scholar, Open Gray, and ProQuest Dissertations and Theses databases. The dataset included observational studies with clinical and laboratory characteristics of infants, children and adolescents diagnosed with lysosomal acid lipase deficiency by enzyme activity testing or analysis of mutations in the lysosomal acid lipase gene (LIPA). The reference selection process was performed in two stages. The references were selected by two authors, and the data were extracted in June 2020.

SUMMARY OF THE FINDINGS

The initial search returned 1593 studies, and the final selection included 108 studies from 30 countries encompassing 206 patients, including individuals with Wolman disease and cholesteryl ester storage disease (CESD). The most prevalent manifestations in both spectra of the disease were hepatomegaly, splenomegaly, anemia, dyslipidemia, and elevated transaminases.

CONCLUSIONS

Vomiting, diarrhea, jaundice, and splenomegaly may be correlated, and may serve as a starting point for investigating LAL-D. Familial lymphohistiocytosis should be part of the differential diagnosis with LAL-D, and all patients undergoing upper gastrointestinal endoscopy should be submitted to intestinal biopsy.

Rat carboxylesterase ES-4 enzyme functions as a major hepatic neutral cholesteryl ester hydrolase

Although esterification of free cholesterol to cholesteryl ester in the liver is known to be catalyzed by the enzyme acyl-coenzyme A:cholesterol acyltransferase, ACAT, the neutral cholesteryl ester hydrolase (nCEH) that catalyzes the reverse reaction has remained elusive. Because cholesterol undergoes continuous cycling between free and esterified forms, the steady-state concentrations in the liver of the two species and their metabolic availability for pathways, such as lipoprotein assembly and bile acid synthesis, depend upon nCEH activity. On the basis of the general characteristics of the family of rat carboxylesterases, we hypothesized that one member, ES-4, was a promising candidate as a hepatic nCEH. Using under- and overexpression approaches, we provide multiple lines of evidence that establish ES-4 as a bona fide endogenous nCEH that can account for the majority of cholesteryl ester hydrolysis in transformed rat hepatic cells and primary rat hepatocytes.

Molecular and enzymatic analyses of lysosomal acid lipase in cholesteryl ester storage disease

Human lysosomal acid lipase (hLAL) is essential for the hydrolysis of cholesteryl esters and triglycerides in the lysosome. Defective hLAL activity leads to two autosomal recessive traits, Wolman disease (WD) or cholesteryl ester storage disease (CESD). Phenotypically, WD has accumulation of both triglycerides and cholesteryl esters, while CESD has mainly elevated cholesteryl esters. We characterized mutations in the hLAL gene from two CESD siblings. By reverse transcriptase-PCR (RT-PCR) and cDNA cloning and sequencing, we identified homozygous deletion mutations of nucleotides 863 to 934, in the hLAL transcript. Normal levels of LAL mRNA were detected. The deletion in mRNA is due to a G to A transition in the last nucleotide of exon 8 of the hLAL gene, a splice junction mutation (E8SJM) that resulted in exon skipping, and a predicted in-frame deletion of the 24 amino acids. [35S]Met metabolic labeling studies in fibroblasts showed a low level of E8SJM LAL ( approximately 38%) that was highly unstable. Heterologous expression of E8SJM LAL in insect cells gave an LAL with low catalytic activity toward cholesteryl oleate and triolein. The effects of this mutation are complex with the production of decreased amounts of an unstable LAL that is catalytically defective. The results suggest that E8SJM leads to essentially a null allele and that the differences in WD and CESD phenotype involve other factors.

Purification, characterization and molecular cloning of human hepatic lysosomal acid lipase

Lysosomal acid lipase (LAL) is a hydrolase essential for the intracellular degradation of cholesteryl esters and triacylglycerols. This report describes a multi-step procedure for the purification of LAL from human liver. After solubilization with non-ionic detergent, acid hydrolase activity was purified 17000-fold to apparent homogeneity by sequential chromatography on Concanavalin A Sepharose, carboxymethyl-cellulose, phenyl Superose, Mono S cation exchange and Superose 12 gel-filtration columns. This procedure yielded two silver-staining protein bands of 56 kDa and 41 kDa on SDS/PAGE. Size-exclusion chromatography of the 41-kDa protein indicated that the enzyme was catalytically competent as a monomer of approximately 38 kDa. When assayed in the presence of cholesteryl oleate or trioleoylglycerol, purified acid lipase had Vmax values of 4390 nmol fatty acid.min-1.mg protein and 4756 nmol fatty acid.min-1.mg protein-1, and apparent Km values of 0.142 mM and 0.138 mM, respectively. The purified enzyme was most active at low pH (4.5-5.0) and required non-ionic detergent and ethylene glycol for optimal stability. Incubation of the 41-kDa acid lipase with endoglucosaminidase H reduced the molecular mass by 4-6 kDa, demonstrating Asn-linked glycosylation with high-mannose oligosaccharides. Deglycosylation did not affect enzymic activity, indicating that carbohydrates are not required for LAL activity. Based on partial peptide sequence, an oligonucleotide was synthesized and utilized to isolate LAL cDNA clones from a human liver cDNA library. A full-length LAL cDNA contained 2626 nucleotides and coded for a predicted protein of 372 amino acids, preceded by a 27 residue hydrophobic signal peptide. Hepatic LAL differed from fibroblast acid lipase at the N-terminus and revealed extensive similarities with human gastric lipase and rat lingual lipase, confirming a gene family of acid lipases. Northern hybridization using the complete LAL cDNA as a radiolabeled probe indicated striking differences in mRNA expression among human tissues. LAL mRNA was most abundant in brain, lung, kidney and mammary gland. Placenta and HeLa cells expressed intermediate amounts of LAL mRNA, while RNA extracted from liver and heart showed low levels of expression.

Hypocholesterolaemic effect of beta beta'-methyl-substituted hexadecanedioic acid (MEDICA 16) in the male hamster

Treatment of cholesterol-fed male hamsters kept on a diet of purina chow with beta beta'-methyl-substituted hexadecanedioic acid (MEDICA 16) resulted in a progressive hypocholesterolaemic effect, amounting to a 50% decrease in the cholesterol content of all plasma lipoproteins. The decrease in plasma cholesterol could be accounted for by activation of plasma-cholesterol efflux through the liver into the bile mediated by MEDICA 16-induced (a) increase of the number of liver LDL receptors, (b) activation of liver neutral cholesteryl ester hydrolase with a concomitant inhibition of liver acyl-CoA cholesterol acyltransferase, resulting in shifting of the liver cholesteryl ester/free-cholesterol cycle in the direction of free cholesterol, and (c) activation of cholesterol efflux from the liver into the bile. The increase in bile cholesterol output was accompanied by an increase in bile phospholipids but not in bile acids. In contrast with rats, MEDICA 16-treatment of male hamsters did not result in a hypotriacylglycerolaemic effect, inhibition of lipogenesis, nor in a substantial decrease in plasma apolipoprotein C-III content.

Effects of daltroban, a thromboxane (TX) A2 receptor antagonist, on lipid metabolism and atherosclerosis

In rat hepatocyte cultures daltroban reduced 14C-acetate incorporation stronger into cholesterol (CH) esters than into free CH. Further data suggest that the reduction of cellular sterols by daltroban is independent from its TXA2 receptor antagonistic activity and caused by reduced capacity of ACAT depending CH esterification. In rabbits fed CH-enriched diet treatment with daltroban led to an inhibition of platelet aggregation and to a significant reduction of progression of atherosclerosis. Both reduced CH esterification and TXA2 receptor antagonism may contribute to the diminution of progression of atherosclerosis by daltroban.

Neutral lipid storage disease: a possible functional defect in phospholipid- linked triacylglycerol metabolism

Neutral lipid storage disease (NLSD) (Chanarin-Dorfman Syndrome) is an autosomal recessive disorder of multisystem triacylglycerol (TAG) storage. Previous work has pointed to a defect in intracellular TAG metabolism. In the studies reported here, the lipid metabolism of three lines of NLSD fibroblasts were compared to normal skin fibroblasts. When pulsed with [3H]oleic acid, the earliest observed abnormality in NLSD cell lines was increased incorporation into phosphatidylethanolamine, followed by accumulation of radiolabel in TAG. Activities of several glycerolipid synthetic enzymes were comparable in NLSD and normal fibroblast lines, excluding oversynthesis of glycerolipid. The proportion of plasmalogen and neutral ether lipid synthesized was normal and alkylglycerols did not accumulate, excluding a defect in ether lipid metabolism. Activities of both acid lipase and Mn2(+)-sensitive lipase within the particulate fractions of NLSD and normal fibroblasts were comparable. These studies are most consistent with functional deficiency of a TAG lipase with activity against a pool of TAG that are normally utilized for phospholipid biosynthesis.

Intercellular transport of lysosomal acid lipase mediates lipoprotein cholesteryl ester metabolism in a human vascular endothelial cell-fibroblast coculture system

We present results from studies of human cell culture models to support the premise that the extracellular transport of lysosomal acid lipase has a function in lipoprotein cholesteryl ester metabolism in vascular tissue. Vascular endothelial cells secreted a higher fraction of cellular acid lipase than did smooth muscle cells and fibroblasts. Acid lipase and lysosomal beta-hexosaminidase were secreted at approximately the same rate from the apical and basolateral surface of an endothelial cell monolayer. Stimulation of secretion with NH4Cl did not affect the polarity. We tested for the ability of secreted endothelial lipase to interact with connective tissue cells and influence lipoprotein cholesterol metabolism in a coculture system in which endothelial cells on a micropore filter were suspended above a monolayer of acid lipase-deficient (Wolman disease) fibroblasts. After 5-7 d, acid lipase activity in the fibroblasts reached 10%-20% of the level in normal cells; cholesteryl esters that had accumulated from growth in serum were cleared. Addition of mannose 6-phosphate to the coculture medium blocked acid lipase uptake and cholesterol clearance, indicating that lipase released from endothelial cells was packaged into fibroblast lysosomes by a phosphomannosyl receptor-mediated pathway. Supplementation of the coculture medium with serum was not required for lipase uptake and cholesteryl ester hydrolysis by the fibroblasts, but was necessary for cholesterol clearance. Results from our coculture model suggest that acid lipase may be transported from intact endothelium to cells in the lumen or the wall of a blood vessel. We postulate that delivery of acid hydrolases and lipoproteins to a common endocytic compartment may occur and have an impact on cellular lipoprotein processing.

Cholesteryl ester storage disease: hepatopathology and effects of therapy with lovastatin

We describe three patients with cholesteryl ester storage disease. Diagnosis was confirmed by demonstrating a deficiency in lysosomal acid cholesteryl hydrolase activity in cultured skin fibroblasts from each of these patients. All had hepatomegaly, elevated serum aminotransferase activities and hyperlipoproteinemia. Histological examination of liver biopsy specimens before treatment revealed accumulation of fat within hepatocytes, bile duct epithelium and endothelial and Kupffer cells. Cholesterol crystals were recognized by their birefringence in frozen sections. A striking feature was the presence of markedly hypertrophied Kupffer cells and portal macrophages with foamy, tan-colored cytoplasm that stained readily with the periodic acid-Schiff reagent and aldehyde fuchsin. Periportal fibrosis was noted in all cases; incomplete cirrhosis was present in one case. Distinctive and hitherto undescribed lysosomal accumulations of triglyceride and cholesterol crystals were noted. The patients were treated with lovastatin, a cholesterol-lowering agent, for at least 12 mo. No significant changes were seen in serum lipoprotein concentrations or liver histopathology after therapy. Thus lovastatin did not have an obviously beneficial effect on abnormal lipid metabolism in these patients.

Relative fluorescence of normal and acid lipase-deficient cultured fibroblasts following administration of pyrene decanoic acid

Skin fibroblasts, derived from normal individuals or patients with Wolman's disease (an autosomal recessive disorder due to acid lysosomal lipase deficiency) were incubated with the fluorescent fatty acid, pyrene-decanoic acid (P10). Measurements of the fluorescence intensities of the total lipid extracts indicated that equal quantities of P10 were incorporated into both cell types. The fluorescence emitted by the intact cells was subsequently recorded in a fluorescence microscope equipped with a microdetector unit, which permitted determination of the fluorescence emitted by the intact cell or by specific regions thereof. The fluorescence intensities emitted by the lipidotic cells exceeded those of their normal counterparts 2- and 5-fold when comparing the entire cells or the perinuclear region, respectively. The cells were then subjected to subcellular fractionation and an analysis of the fractions revealed that up to 85-90% of the fluorescence of the lysosome-mitochondrial pellet was derived from free pyrenedecanoic acid; the latter contributed only 15-18% to the fluorescence of the homogenate or the cytosol. There was no difference in the fluorescence of the lipid extracts from the respective fractions of the lipidotic or normal cells. However, the fluorescence emitted by the intact lysosome-mitochondrial fraction of the lipidotic cells exceeded that of its normal counterpart 2.5-fold. These data suggest that the increased fluorescence intensity of the intact lipidotic cells resulted from a higher quantum yield of free P10 molecules solubilized in the hydrophobic environment of their neutral lipid-containing storage granules.

Extracellular origin of the lipid lysosomal storage in cultured fibroblasts from Wolman's disease

The experiments reported here allowed us to compare the metabolism of neutral lipids from extracellular origin (lipoproteins) and endogenous origin (triacylglycerol biosynthesis induced by feeding cells with high levels of free fatty acid) in normal and acid-lipase-deficient fibroblasts (Wolman's disease). When the cells were grown in hyperlipemic-rich medium, a major neutral lipid storage appeared in normal as well as in acid-lipase-deficient cells; this storage disappeared rapidly in normal cells during the 'chase', whereas in Wolman cells, the storage of cholesteryl esters and triacylglycerols remained unchanged, or only decreased very slowly. When the cells were fed with high levels of radiolabelled oleic acid, a major accumulation of radiolabelled triacylglycerols was observed. These cytoplasmic triacylglycerols were similarly degraded in normal and Wolman fibroblasts during the 'chase' period. From these results it was concluded that the neutral lipids stored in lysosomes of Wolman fibroblasts are only of extracellular origin (lipoproteins), whereas triacylglycerols biosynthesized by the cells do not participate in this accumulation. Therefore, both cellular compartments involved in triacylglycerol metabolism (lysosomes containing exogenous lipids and cytoplasmic granules of endogenously biosynthesized triacylglycerols) are strictly independent.

Cholesteryl ester hydrolysis in rat liver lysosomes: different response to female sex hormones

The regulation of the hydrolysis of cholesteryl oleate by female sex hormones was studied in the lysosomal fraction of rat liver. Cholesterol ester hydrolase activity was determined at pH 5.0 with an acetone-dissolved cholesteryl [1-14C]oleate substrate preparation. The administration of a single dose of progesterone decreased the enzyme activity during a 3- to 24-hr period following hormone injection. This effect was not correlated to changes in the lysosomal protein synthesis rate. The lysosomal hydrolysis of cholesteryl esters was also inhibited in a noncompetitive manner by the addition of progesterone at concentrations higher than 100 microM. The esterase failed to respond to the estradiol in vivo as well as in vitro. The findings of the present paper suggest that the lysosomal breakdown of cholesteryl esters in rat liver may be under selective hormonal regulation and that the inhibitory effect of progesterone on the enzyme activity might be, at least in part, responsible for the liver cholesterol ester accumulus produced by the administration of the hormone.

Evidence that cholesteryl ester hydrolase and triglyceride lipase are different enzymes in rat liver

Studies on intracellular cholesteryl ester hydrolase (CEH) and triglyceride lipase (TGL) from rat adipose tissue and adrenal cortex have suggested that a single protein is responsible for both activities. To determine whether one hepatic protein catalyzes both reactions, we studied several properties of CEH and TGL in rat liver. During liver perfusion with heparin, perfusate peaks of TGL and CEH did not consistently coincide, and TGL activity was considerably higher and less heat-stable than that of CEH. Significant TGL, but not CEH, activity was released during incubation of isolated hepatocytes. Although microsomes isolated from hepatocytes contained both activities, the specific activities of CEH and TGL in cytosol from hepatocytes were 95% and 3%, respectively, of those found in cytosol from whole liver. Preincubation of liver cytosol with 5 mM Mg2+ decreased CEH, but not TGL, activity. Intracellular CEH and TGL activities were completely separated by prep-disc gel electrophoresis. Finally, both cytosolic and microsomal TGL, but not CEH, activities were inhibited by antiserum against rat hepatic TGL. We conclude that extracellular TGL does not have CEH activity and intracellular CEH differs from TGL.

The effect of portacaval shunt on hepatic lipoprotein metabolism in familial hypercholesterolemia

The hyperlipidemia observed in familial hypercholesterolemia can be reduced by portacaval anastomosis. We report the effects of a portacaval shunt on hepatic morphology and biosynthetic pathways crucial to hepatic cholesterol homeostasis in homozygous receptor-negative familial hypercholesterolemia. Portacaval anastomosis was associated with a dramatic change in hepatocyte morphology, 28% reduction in plasma low-density lipoprotein concentration, and a decrease in hepatic total and free cholesterol content by 27 and 75%, respectively. Furthermore, the rate-limiting enzyme in cholesterol biosynthesis, 3-hydroxy-3-methylglutaryl coenzyme A reductase was decreased by 56%. Finally, the reduced binding of low-density lipoproteins to hepatic membranes preoperatively was increased following the portacaval shunt. These combined results indicate that the changes in circulating lipoprotein concentrations observed after portacaval shunt are due to alterations in the metabolic consequences of the defective recognition of low-density lipoproteins by the liver of familial hypercholesterolemic subjects.

Characterization of plasma lipids and lipoproteins in cholesteryl ester storage disease

Cholesteryl ester storage disease, caused by the loss of lysosomal acid ester hydrolase (EC 3.1.1.13), has been previously associated with hyperlipidemia and premature atherosclerosis. We identified a 23-month-old female with cholesteryl ester storage disease and characterized the plasma lipids and lipoproteins in the proband and her family. These studies illustrate several important points about this disease. First, a high index of suspicion is required to diagnose this disease since the major physical manifestation of the disorder, mild hepatomegaly, is subtle. Second, the Type II hyperlipoproteinemia in the proband is paralleled by a reduction in the concentration of high density lipoproteins. Third, analysis of the plasma lipids and lipoproteins in family members revealed both Type II and Type IV hyperlipoproteinemia with an inheritance pattern similar to that of familial combined hyperlipoproteinemia. Fourth, the parents and brother of this patient had 50% normal fibroblast acid ester hydrolase activity. These results raise the possibility that deficiency of the lysosomal acid ester hydrolase may be linked to familial combined hyperlipoproteinemia and that this enzyme deficiency may be more common than previously appreciated.

Enzyme studies on Epstein-Barr virus-transformed lymphoid cell lines from Wolman's disease. Lipases, cholesterol esterase and 4-methylumbelliferyl acyl ester hydrolases

(1) In lymphoid cell lines established by Epstein-Barr virus transformation of B-lymphocytes from normal subjects there exist two lipases hydrolysing triolein (the first one with acid optimum pH and the other one with alkaline optimum pH) and one cholesterol esterase (with acidic optimum pH). The acid triolein lipase (optimum pH 3.75-4.0) and the acid cholesterol esterase are activated by taurocholate (optimal concentration between 1 and 2.5 g/l) whereas alkaline triolein-lipase is inhibited by crude taurocholate. (2) Acid lipase deficiency is demonstrated in lymphoid cell lines from a Wolman's patient, using natural substrates, triolein and cholesteryl oleate (residual activity 5 and 8%, respectively). Thus, this similar deficiency demonstrates that, in lymphoid cell lines, triolein and cholesteryl esters are hydrolysed (under the conditions used here) by a single enzyme, i.e., lysosomal acid lipase muted in Wolman's disease. (3) pH profiles of synthetic substrate hydrolysis show marked differences between methylumbelliferyl oleate and methylumbelliferyl palmitate, and are greatly dependent on the assay conditions used. In the presence of optimal concentrations of taurocholate (1-2.5 g/l), nonspecific carboxylesterases are inhibited and acid lipase is activated: in this case, methylumbelliferyl oleate can be used to demonstrate the acid lipase deficiency in Wolman's lines (15-20% of residual activity). Methylumbelliferyl palmitate hydrolysis is less dependent on assay conditions and thus can be more accurately used for the diagnosis of Wolman's disease, with lower residual activity (10-15%) than using methylumbelliferyl oleate. Thus, Epstein-Barr virus-transformed lymphoid cell lines represent an accurate model system in culture for experimental studies of Wolman's disease.