Enzyme deficiency in cholesteryl ester storage idisease

Loss of lysosomal acid lipase results in mitochondrial dysfunction and fiber switch in skeletal muscles of mice

OBJECTIVE

Lysosomal acid lipase (LAL) is the only enzyme known to hydrolyze cholesteryl esters (CE) and triacylglycerols in lysosomes at an acidic pH. Despite the importance of lysosomal hydrolysis in skeletal muscle (SM), research in this area is limited. We hypothesized that LAL may play an important role in SM development, function, and metabolism as a result of lipid and/or carbohydrate metabolism disruptions.

RESULTS

Mice with systemic LAL deficiency (Lal-/-) had markedly lower SM mass, cross-sectional area, and Feret diameter despite unchanged proteolysis or protein synthesis markers in all SM examined. In addition, Lal-/- SM showed increased total cholesterol and CE concentrations, especially during fasting and maturation. Regardless of increased glucose uptake, expression of the slow oxidative fiber marker MYH7 was markedly increased in Lal-/-SM, indicating a fiber switch from glycolytic, fast-twitch fibers to oxidative, slow-twitch fibers. Proteomic analysis of the oxidative and glycolytic parts of the SM confirmed the transition between fast- and slow-twitch fibers, consistent with the decreased Lal-/- muscle size due to the "fiber paradox". Decreased oxidative capacity and ATP concentration were associated with reduced mitochondrial function of Lal-/- SM, particularly affecting oxidative phosphorylation, despite unchanged structure and number of mitochondria. Impairment in muscle function was reflected by increased exhaustion in the treadmill peak effort test in vivo.

CONCLUSION

We conclude that whole-body loss of LAL is associated with a profound remodeling of the muscular phenotype, manifested by fiber type switch and a decline in muscle mass, most likely due to dysfunctional mitochondria and impaired energy metabolism, at least in mice.

Metabolic changes and propensity for inflammation, fibrosis, and cancer in livers of mice lacking lysosomal acid lipase

Lysosomal acid lipase (LAL) is the sole lysosomal enzyme responsible for the degradation of cholesteryl esters and triacylglycerols at acidic pH. Impaired LAL activity leads to LAL deficiency (LAL-D), a severe and fatal disease characterized by ectopic lysosomal lipid accumulation. Reduced LAL activity also contributes to the development and progression of non-alcoholic fatty liver disease (NAFLD). To advance our understanding of LAL-related liver pathologies, we performed comprehensive proteomic profiling of livers from mice with systemic genetic loss of LAL (Lal-/-) and from mice with hepatocyte-specific LAL-D (hepLal-/-). Lal-/- mice exhibited drastic proteome alterations, including dysregulation of multiple proteins related to metabolism, inflammation, liver fibrosis, and cancer. Global loss of LAL activity impaired both acidic and neutral lipase activities and resulted in hepatic lipid accumulation, indicating a complete metabolic shift in Lal-/- livers. Hepatic inflammation and immune cell infiltration were evident, with numerous upregulated inflammation-related gene ontology biological process terms. In contrast, both young and mature hepLal-/- mice displayed only minor changes in the liver proteome, suggesting that loss of LAL solely in hepatocytes does not phenocopy metabolic alterations observed in mice globally lacking LAL. These findings provide valuable insights into the mechanisms underlying liver dysfunction in LAL-D and may help in understanding why decreased LAL activity contributes to NAFLD. Our study highlights the importance of LAL in maintaining liver homeostasis and demonstrates the drastic consequences of its global deficiency on the liver proteome and liver function.

Molecular markers of brain cholesterol homeostasis are unchanged despite a smaller brain mass in a mouse model of cholesteryl ester storage disease

Lysosomal acid lipase (LAL), encoded by the gene LIPA, facilitates the intracellular processing of lipids by hydrolyzing cholesteryl esters and triacylglycerols present in newly internalized lipoproteins. Loss-of-function mutations in LIPA result in cholesteryl ester storage disease (CESD) or Wolman disease when mutations cause complete loss of LAL activity. Although the phenotype of a mouse CESD model has been extensively characterized, there has not been a focus on the brain at different stages of disease progression. In the current studies, whole-brain mass and the concentrations of cholesterol in both the esterified (EC) and unesterified (UC) fractions were measured in Lal-/- and matching Lal+/+ mice (FVB-N strain) at ages ranging from 14 up to 280 days after birth. Compared to Lal+/+ controls at 50, 68-76, 140-142, and 230-280 days of age, Lal-/- mice had brain weights that averaged approximately 6%, 7%, 18%, and 20% less, respectively. Brain EC levels were higher in the Lal-/- mice at every age, being elevated 27-fold at 230-280 days. Brain UC concentrations did not show a genotypic difference at any age. The elevated brain EC levels in the Lal-/- mice did not reflect EC in residual blood. An mRNA expression analysis for an array of genes involved in the synthesis, catabolism, storage, and transport of cholesterol in the brains of 141-day old mice did not detect any genotypic differences although the relative mRNA levels for several markers of inflammation were moderately elevated in the Lal-/- mice. The possible sites of EC accretion in the central nervous system are discussed.

Silencing of ATG6 and ATG8 promotes increased levels of triacylglycerol (TAG) in the fat body during prolonged starvation periods in the Chagas disease vector Rhodnius prolixus

Rhodnius prolixus is an obligatorily hematophagous insect known as an important vector of Chagas disease. Autophagy is a conserved cellular mechanism that acts in response to nutrient starvation, where components of the cytoplasm are sequestered by a double membrane organelle, named autophagosome, which is targeted to fuse with the lysosome for degradation. Lipophagy is the process of lipid degradation by selective autophagy, where autophagosomes sequester lipid droplets and degrade triacylglycerol (TAG) generating free fatty acids for β-oxidation. Here, two essential genes of the autophagic pathway, Atg6/Beclin1 (RpAtg6) and Atg8/LC3 (RpAtg8), were silenced and the storage of lipids during starvation in Rhodnius prolixus was monitored. We found that RNAi knockdown of both RpAtg6 and RpAtg8 resulted in higher levels of TAG in the fat body and the flight muscle, 24 days after the blood meal, as well as a larger average diameter of the lipid droplets in the fat body, as seen by Nile Red staining under the confocal fluorescence microscope. Silenced starved insects had lower survival rates when compared to control insects. Accordingly, when examined during the starvation period for monitored activity, silenced insects had lower spontaneous locomotor activity and lower forced flight rates. Furthermore, we found that some genes involved in lipid metabolism had their expression levels altered in silenced insects, such as the Brummer lipase (down regulated) and the adipokinetic hormone receptor (up regulated), suggesting that, as previously observed in mammalian models, the autophagy and neutral lipolysis machineries are interconnected at the transcriptional level. Altogether, our data indicate that autophagy in the fat body is important to allow insects to mobilize energy from lipid stores.

An optical nanoreporter of endolysosomal lipid accumulation reveals enduring effects of diet on hepatic macrophages in vivo

The abnormal accumulation of lipids within the endolysosomal lumen occurs in many conditions, including lysosomal storage disorders, atherosclerosis, nonalcoholic fatty liver disease (NAFLD), and drug-induced phospholipidosis. Current methods cannot monitor endolysosomal lipid content in vivo, hindering preclinical drug development and research into the mechanisms linking endolysosomal lipid accumulation to disease progression. We developed a single-walled carbon nanotube-based optical reporter that noninvasively measures endolysosomal lipid accumulation via bandgap modulation of its intrinsic near-infrared emission. The reporter detected lipid accumulation in Niemann-Pick disease, atherosclerosis, and NAFLD models in vivo. By applying the reporter to the study of NAFLD, we found that elevated lipid quantities in hepatic macrophages caused by a high-fat diet persist long after reverting to a normal diet. The reporter dynamically monitored endolysosomal lipid accumulation in vivo over time scales ranging from minutes to weeks, indicating its potential to accelerate preclinical research and drug development processes.

Lysosomal acid lipase deficiency - early diagnosis is the key

Lysosomal acid lipase deficiency (LAL-D) is an ultra-rare lysosomal storage disease that may present from infancy to late adulthood depending on residual enzyme activity. While the severe form manifests as a rapidly progressive disease with near universal mortality within the first 6 months of life, milder forms frequently go undiagnosed for prolonged periods and typically present with progressive fatty liver disease, enlarged spleen, atherogenic dyslipidemia and premature atherosclerosis. The adult variant of LAL-D is typically diagnosed late or even overlooked due to the unspecific nature of the presenting symptoms, which are similar to common changes observed in the context of the metabolic syndrome. This review is aimed at delineating clinically useful scenarios in which pediatric or adult medicine clinicians should be aware of LAL-D as a differential diagnosis for selected patients. This is particularly relevant as a potentially life-saving enzyme replacement therapy has become available and the diagnosis can easily be ruled out or confirmed using a dried blood spot test.

Hepatocyte-specific lysosomal acid lipase deficiency protects mice from diet-induced obesity but promotes hepatic inflammation

Lysosomal acid lipase (LAL) hydrolyzes cholesteryl esters (CE) and triglycerides (TG) to generate fatty acids (FA) and cholesterol. LAL deficiency (LAL-D) in both humans and mice leads to hepatomegaly, hypercholesterolemia, and shortened life span. Despite its essential role in lysosomal neutral lipid catabolism, the cell type-specific contribution of LAL to disease progression is still elusive. To investigate the role of LAL in the liver in more detail and to exclude the contribution of LAL in macrophages, we generated hepatocyte-specific LAL-deficient mice (Liv-Lipa^−/−) and fed them either chow or high fat/high cholesterol diets (HF/HCD). Comparable to systemic LAL-D, Liv-Lipa^−/− mice were resistant to diet-induced obesity independent of food intake, movement, and energy expenditure. Reduced body weight gain was mainly due to reduced white adipose tissue depots. Furthermore, Liv-Lipa^−/− mice exhibited improved glucose clearance during glucose and insulin tolerance tests compared to control mice. Analysis of hepatic lipid content revealed a massive reduction of TG, whereas CE concentrations were markedly increased, leading to CE crystal formation in the livers of Liv-Lipa^−/− mice. Elevated plasma transaminase activities, increased pro-inflammatory cytokines and chemokines as well as hepatic macrophage infiltration indicated liver inflammation. Our data provide evidence that hepatocyte-specific LAL deficiency is sufficient to alter whole-body lipid and energy homeostasis in mice. We conclude that hepatic LAL plays a pivotal role by preventing liver damage and maintaining lipid and energy homeostasis, especially during high lipid availability.

Impact of loss of SOAT2 function on disease progression in the lysosomal acid lipase-deficient mouse

Although only a small proportion of cholesterol in the body is esterified, in several diseases marked expansion of the esterified cholesterol (EC) pool occurs. These include Wolman disease (WD) and Cholesteryl Ester Storage Disease (CESD) which both result from mutations in LIPA, the gene that encodes lysosomal acid lipase (LAL). The respective contributions that our three cholesterol esterifying enzymes make to EC production, especially in disorders like CESD, are not well defined. The current studies represent a detailed exploration of our earlier findings in young male LAL-deficient mice also missing sterol O-acyltransferase 2 (SOAT2, also called ACAT2). Here we show that, even as they aged, male and female Lal-/-: Soat2- /- mice, compared to Lal-/-: Soat2+/+ littermates, had appreciably less hepatomegaly as well as a marked reduction in the level of sequestration of EC, in liver transaminase activities, and in hepatic mRNA expression levels for markers of inflammation. Loss of SOAT2 function also dramatically curtailed EC entrapment in the small intestine of the LAL-deficient mice. Together, these data imply that SOAT2 inhibition, if applied concurrently with enzyme replacement therapy for LAL deficiency, may blunt the re-esterification of newly released unesterified cholesterol thereby improving clinical outcomes.

Lysosomal acid lipase regulates fatty acid channeling in brown adipose tissue to maintain thermogenesis

Lysosomal acid lipase (LAL) is the only known enzyme, which hydrolyzes cholesteryl esters and triacylglycerols in lysosomes of multiple cells and tissues. Here, we explored the role of LAL in brown adipose tissue (BAT). LAL-deficient (Lal-/-) mice exhibit markedly reduced UCP1 expression in BAT, modified BAT morphology with accumulation of lysosomes, and mitochondrial dysfunction, consequently leading to regular hypothermic events in mice kept at room temperature. Cold exposure resulted in reduced lipid uptake into BAT, thereby aggravating dyslipidemia and causing life threatening hypothermia in Lal-/- mice. Linking LAL as a potential regulator of lipoprotein lipase activity, we found Angptl4 mRNA expression upregulated in BAT. Our data demonstrate that LAL is critical for shuttling fatty acids derived from circulating lipoproteins to BAT during cold exposure. We conclude that inhibited lysosomal lipid hydrolysis in BAT leads to impaired thermogenesis in Lal-/- mice.

A Carbon Nanotube Optical Reporter Maps Endolysosomal Lipid Flux

Lipid accumulation within the lumen of endolysosomal vesicles is observed in various pathologies including atherosclerosis, liver disease, neurological disorders, lysosomal storage disorders, and cancer. Current methods cannot measure lipid flux specifically within the lysosomal lumen of live cells. We developed an optical reporter, composed of a photoluminescent carbon nanotube of a single chirality, that responds to lipid accumulation via modulation of the nanotube's optical band gap. The engineered nanomaterial, composed of short, single-stranded DNA and a single nanotube chirality, localizes exclusively to the lumen of endolysosomal organelles without adversely affecting cell viability or proliferation or organelle morphology, integrity, or function. The emission wavelength of the reporter can be spatially resolved from within the endolysosomal lumen to generate quantitative maps of lipid content in live cells. Endolysosomal lipid accumulation in cell lines, an example of drug-induced phospholipidosis, was observed for multiple drugs in macrophages, and measurements of patient-derived Niemann-Pick type C fibroblasts identified lipid accumulation and phenotypic reversal of this lysosomal storage disease. Single-cell measurements using the reporter discerned subcellular differences in equilibrium lipid content, illuminating significant intracellular heterogeneity among endolysosomal organelles of differentiating bone-marrow-derived monocytes. Single-cell kinetics of lipoprotein-derived cholesterol accumulation within macrophages revealed rates that differed among cells by an order of magnitude. This carbon nanotube optical reporter of endolysosomal lipid content in live cells confers additional capabilities for drug development processes and the investigation of lipid-linked diseases.

Lysosomal acid lipase deficiency: a form of non-obese fatty liver disease (NOFLD)

INTRODUCTION

With the growing obesity epidemic, nonalcoholic fatty liver disease (NAFLD) is rapidly becoming one of the leading causes of liver disease worldwide. Although obesity is a main risk factor for the development of NAFLD, it can also develop in lean subjects and can be encountered in different clinical setting and in association with an array of genetic, metabolic, nutritional, infectious and drug-induced disorders. Areas covered: This article discusses causes of fatty liver in non-obese subjects focusing on Lysosomal acid lipase deficiency (LAL-D), a commonly overlooked disorder reviewing its prevalence, genetics, pathogenesis, clinical features, diagnosis and treatment. It will also review other causes of non-alcoholic fatty liver disease, which can be encountered in the absence of obesity and metabolic syndrome. Expert commentary: Although the prevalence of LAL-D has been estimated in the range of 1 in 40,000 and 1 in 300,000, this estimate is much more than the identified cases reported in the literature, which suggests that that the disease may be considerably under-diagnosed. There is a pressing need to educate clinicians about the disease, especially with the development of new promising therapeutic modalities.

Breaking fat: The regulation and mechanisms of lipophagy

Lipophagy is defined as the autophagic degradation of intracellular lipid droplets (LDs). While the field of lipophagy research is relatively young, an expansion of research in this area over the past several years has greatly advanced our understanding of lipophagy. Since its original characterization in fasted liver, the contribution of lipophagy is now recognized in various organisms, cell types, metabolic states and disease models. Moreover, recent studies provide exciting new insights into the underlying mechanisms of lipophagy induction as well as the consequences of lipophagy on cell metabolism and signaling. This review summarizes recent work focusing on LDs and lipophagy as well as highlighting challenges and future directions of research as our understanding of lipophagy continues to grow and evolve. This article is part of a Special Issue entitled: Recent Advances in Lipid Droplet Biology edited by Rosalind Coleman and Matthijs Hesselink.

Managing Cardiovascular Risk in Lysosomal Acid Lipase Deficiency

Lysosomal acid lipase deficiency (LAL-D) is a rare, life-threatening, autosomal recessive, lysosomal storage disease caused by mutations in the LIPA gene, which encodes for lysosomal acid lipase (LAL). This enzyme is necessary for the hydrolysis of cholesteryl ester and triglyceride in lysosomes. Deficient LAL activity causes accumulation of these lipids in lysosomes and a marked decrease in the cytoplasmic free cholesterol concentration, leading to dysfunctional cholesterol homeostasis. The accumulation of neutral lipid occurs predominantly in liver, spleen, and macrophages throughout the body, and the aberrant cholesterol homeostasis causes a marked dyslipidemia. LAL-D is characterized by accelerated atherosclerotic cardiovascular disease (ASCVD) and hepatic microvesicular or mixed steatosis, leading to inflammation, fibrosis, cirrhosis and liver failure. LAL-D presents as a clinical continuum with two phenotypes: the infantile-onset phenotype, formally referred to as Wolman disease, and the later-onset phenotype, formerly referred to as cholesteryl ester storage disease. Infants with LAL-D present within the first few weeks of life with vomiting, diarrhea, hepatosplenomegaly, failure to thrive and rapid progression to liver failure and death by 6-12 months of age. Children and young adults with LAL-D generally present with marked dyslipidemia, hepatic enzyme elevation, hepatomegaly and mixed steatosis by liver biopsy. The average age of the initial signs and symptoms of the later-onset phenotype is about 5 years old. The typical dyslipidemia is a significantly elevated low-density lipoprotein cholesterol (LDL-C) concentration and a low high-density lipoprotein cholesterol (HDL-C) concentration, placing these individuals at heightened risk for premature ASCVD. Diagnosis of the later-onset phenotype of LAL-D requires a heightened awareness of the disease because the dyslipidemia and hepatic transaminase elevation combination are common and overlap with other metabolic disorders. LAL-D should be considered in the differential diagnosis of healthy weight children and young adults with unexplained hepatic transaminase elevation accompanied by an elevated LDL-C level (>160 mg/dL) and low HDL-C level (<35 mg/dL) that is not caused by monogenic and polygenic lipid disorders or secondary factors. Treatment of LAL-D with sebelipase alfa (LAL replacement enzyme) should be considered as the standard of treatment in all individuals diagnosed with LAL-D. Other ASCVD risk factors that may be present (hypertension, tobacco use, diabetes mellitus, etc.) should be managed appropriately, consistent with secondary prevention goals.

Continuous transport of a small fraction of plasma membrane cholesterol to endoplasmic reticulum regulates total cellular cholesterol

Cells employ regulated transport mechanisms to ensure that their plasma membranes (PMs) are optimally supplied with cholesterol derived from uptake of low-density lipoproteins (LDL) and synthesis. To date, all inhibitors of cholesterol transport block steps in lysosomes, limiting our understanding of post-lysosomal transport steps. Here, we establish the cholesterol-binding domain 4 of anthrolysin O (ALOD4) as a reversible inhibitor of cholesterol transport from PM to endoplasmic reticulum (ER). Using ALOD4, we: (1) deplete ER cholesterol without altering PM or overall cellular cholesterol levels; (2) demonstrate that LDL-derived cholesterol travels from lysosomes first to PM to meet cholesterol needs, and subsequently from PM to regulatory domains of ER to suppress activation of SREBPs, halting cholesterol uptake and synthesis; and (3) determine that continuous PM-to-ER cholesterol transport allows ER to constantly monitor PM cholesterol levels, and respond rapidly to small declines in cellular cholesterol by activating SREBPs, increasing cholesterol uptake and synthesis.

Lysosomal acid lipase deficiency in all siblings of the same parents

We present 4 normal-weight sibling children with lysosomal acid lipase deficiency (LAL-D). LAL-D was considered in the differential diagnosis based on the absence of secondary causes and primary inherited traits for their marked hyperlipidemia, together with unexplained hepatic transaminase elevation. Residual lysosomal acid lipase activity confirmed the diagnosis. DNA sequencing of LIPA indicated that the siblings were compound heterozygotes (c.894G>A and c.428+1G>A). This case describes the unusual occurrence of all offspring from the same nonconsanguineous mother and father inheriting compound heterozygosity of a recessive trait and the identification of an apparently unique LIPA mutation (c.428+1G>A). It highlights the collaborative effort between a lipidologist and gastroenterologist in developing a differential diagnosis leading to the confirmatory diagnosis of this rare, life-threatening disease. With the availability of an effective enzyme replacement therapy (sebelipase alfa), LAL-D should be entertained in the differential diagnosis of children, adolescents, and young adults with idiopathic hyperlipidemia and unexplained hepatic transaminase elevation.

Lysosomal acid lipase deficiency: A hidden disease among cohorts of familial hypercholesterolemia?

BACKGROUND

Lysosomal acid lipase deficiency (LALD) is an autosomal recessive disorder and an unrecognized cause of dyslipidemia. Patients usually present with dyslipidemia and altered liver function and mutations in LIPA gene are the underlying cause of LALD.

OBJECTIVE

The aim of this study was to investigate LALD in individuals with severe dyslipidemia and/or liver steatosis.

METHODS

Coding, splice regions, and promoter region of LIPA were sequenced by Sanger sequencing in a cohort of mutation-negative familial hypercholesterolemia (FH) patients (n = 492) and in a population sample comprising individuals with several types of dyslipidemia and/or liver steatosis (n = 258).

RESULTS

This study led to the identification of LALD in 4 children referred to the Portuguese FH Study, all with a clinical diagnosis of FH. Mild liver dysfunction was present at the age of FH diagnosis; however, a diagnosis of LALD was not considered. No adults at the time of referral have been identified with LALD.

CONCLUSION

LALD is a life-threatening disorder, and early identification is crucial for the implementation of specific treatment to avoid premature mortality. FH cohorts should be investigated to identify possible LALD patients, who will need appropriate treatment. These results highlight the importance of correctly identifying the etiology of the dyslipidemia.

Novel treatment options for lysosomal acid lipase deficiency: critical appraisal of sebelipase alfa

Lysosomal acid lipase deficiency (LAL-D) is a rare disorder of cholesterol metabolism with an autosomal recessive mode of inheritance. The absence or deficiency of the LAL enzyme gives rise to pathological accumulation of cholesterol esters in various tissues. A severe LAL-D phenotype manifesting in infancy is associated with adrenal calcification and liver and gastrointestinal involvement with characteristic early mortality. LAL-D presenting in childhood and adulthood is associated with hepatomegaly, liver fibrosis, cirrhosis, and premature atherosclerosis. There are currently no curative pharmacological treatments for this life-threatening condition. Supportive management with lipid-modifying agents does not ameliorate disease progression. Hematopoietic stem cell transplantation as a curative measure in infantile disease has mixed success and is associated with inherent risks and complications. Sebelipase alfa (Kanuma) is a recombinant human LAL protein and the first enzyme replacement therapy for the treatment of LAL-D. Clinical trials have been undertaken in infants with rapidly progressive LAL-D and in children and adults with later-onset LAL-D. Initial data have shown significant survival benefits in the infant group and improvements in biochemical parameters in the latter. Sebelipase alfa has received marketing authorization in the United States and Europe as long-term therapy for all affected individuals. The availability of enzyme replacement therapy for this rare and progressive disorder warrants greater recognition and awareness by physicians.

Lysosomal acid lipase regulates VLDL synthesis and insulin sensitivity in mice

AIMS/HYPOTHESIS

Lysosomal acid lipase (LAL) hydrolyses cholesteryl esters and triacylglycerols (TG) within lysosomes to mobilise NEFA and cholesterol. Since LAL-deficient (Lal (-/-) ) mice suffer from progressive loss of adipose tissue and severe accumulation of lipids in hepatic lysosomes, we hypothesised that LAL deficiency triggers alternative energy pathway(s).

METHODS

We studied metabolic adaptations in Lal (-/-) mice.

RESULTS

Despite loss of adipose tissue, Lal (-/-) mice show enhanced glucose clearance during insulin and glucose tolerance tests and have increased uptake of [(3)H]2-deoxy-D-glucose into skeletal muscle compared with wild-type mice. In agreement, fasted Lal (-/-) mice exhibit reduced glucose and glycogen levels in skeletal muscle. We observed 84% decreased plasma leptin levels and significantly reduced hepatic ATP, glucose, glycogen and glutamine concentrations in fed Lal (-/-) mice. Markedly reduced hepatic acyl-CoA concentrations decrease the expression of peroxisome proliferator-activated receptor α (PPARα) target genes. However, treatment of Lal (-/-) mice with the PPARα agonist fenofibrate further decreased plasma TG (and hepatic glucose and glycogen) concentrations in Lal (-/-) mice. Depletion of hepatic nuclear factor 4α and forkhead box protein a2 in fasted Lal (-/-) mice might be responsible for reduced expression of microsomal TG transfer protein, defective VLDL synthesis and drastically reduced plasma TG levels.

CONCLUSIONS/INTERPRETATION

Our findings indicate that neither activation nor inactivation of PPARα per se but rather the availability of hepatic acyl-CoA concentrations regulates VLDL synthesis and subsequent metabolic adaptations in Lal (-/-) mice. We conclude that decreased plasma VLDL production enhances glucose uptake into skeletal muscle to compensate for the lack of energy supply.

PRD125, a potent and selective inhibitor of sterol O-acyltransferase 2 markedly reduces hepatic cholesteryl ester accumulation and improves liver function in lysosomal acid lipase-deficient mice

In most organs, the bulk of cholesterol is unesterified, although nearly all possess a varying capability of esterifying cholesterol through the action of either sterol O-acyltransferase (SOAT) 1 or, in the case of hepatocytes and enterocytes, SOAT2. Esterified cholesterol (EC) carried in plasma lipoproteins is hydrolyzed by lysosomal acid lipase (LAL) when they are cleared from the circulation. Loss-of-function mutations in LIPA, the gene that encodes LAL, result in Wolman disease or cholesteryl ester storage disease (CESD). Hepatomegaly and a massive increase in tissue EC levels are hallmark features of both disorders. While these conditions can be corrected with enzyme replacement therapy, the question arose as to whether pharmacological inhibition of SOAT2 might reduce tissue EC accretion in CESD. When weaned at 21 days, Lal(-/-) mice, of either gender, had a whole liver cholesterol content that was 12- to 13-fold more than that of matching Lal(+/+) littermates (23 versus 1.8 mg, respectively). In Lal(-/-) males given the selective SOAT2 inhibitor PRD125 1,11-O-o-methylbenzylidene-7-O-p-cyanobenzoyl-1,7,11-trideacetylpyripyropene A in their diet (∼10 mg/day per kg body weight) from 21 to 53 days, whole liver cholesterol content was 48.6 versus 153.7 mg in untreated 53-day-old Lal(-/-) mice. This difference reflected a 59% reduction in hepatic EC concentration (mg/g), combined with a 28% fall in liver mass. The treated mice also showed a 63% reduction in plasma alanine aminotransferase activity, in parallel with decisive falls in hepatic mRNA expression levels for multiple proteins that reflect macrophage presence and inflammation. These data implicate SOAT2 as a potential target in CESD management.

Lysosomal acid lipase: at the crossroads of normal and atherogenic cholesterol metabolism

Unregulated cellular uptake of apolipoprotein B-containing lipoproteins in the arterial intima leads to the formation of foam cells in atherosclerosis. Lysosomal acid lipase (LAL) plays a crucial role in both lipoprotein lipid catabolism and excess lipid accumulation as it is the primary enzyme that hydrolyzes cholesteryl esters derived from both low density lipoprotein (LDL) and modified forms of LDL. Evidence suggests that as atherosclerosis progresses, accumulation of excess free cholesterol in lysosomes leads to impairment of LAL activity, resulting in accumulation of cholesteryl esters in the lysosome as well as the cytosol in foam cells. Impaired metabolism and release of cholesterol from lysosomes can lead to downstream defects in ATP-binding cassette transporter A1 regulation, needed to offload excess cholesterol from plaque foam cells. This review focuses on the role LAL plays in normal cholesterol metabolism and how the associated changes in its enzymatic activity may ultimately contribute to atherosclerosis progression.

Sebelipase alfa over 52 weeks reduces serum transaminases, liver volume and improves serum lipids in patients with lysosomal acid lipase deficiency

BACKGROUND & AIMS

Lysosomal acid lipase deficiency is an autosomal recessive enzyme deficiency resulting in lysosomal accumulation of cholesteryl esters and triglycerides. LAL-CL04, an ongoing extension study, investigates the long-term effects of sebelipase alfa, a recombinant human lysosomal acid lipase.

METHODS

Sebelipase alfa (1mg/kg or 3mg/kg) was infused every-other-week to eligible subjects. Safety and tolerability assessments, including liver function, lipid profiles and liver volume assessment, were carried out at regular intervals.

RESULTS

216 infusions were administered to eight adult subjects through week 52 during LAL-CL04. At week 52, mean alanine aminotransferase and aspartate aminotransferase levels were normal with mean change from baseline of -58% and -40%. Mean changes for low-density lipoprotein, total cholesterol, triglyceride and high-density lipoprotein were -60%, -39%, -36%, and +29%, respectively. Mean liver volume by magnetic resonance imaging and hepatic proton density fat fraction decreased (12% and 55%, respectively). Adverse events were mainly mild and unrelated to sebelipase alfa. Infusion-related reactions were uncommon: three events of moderate severity were reported in two subjects; one patient's event was suggestive of a hypersensitivity-like reaction, but additional testing did not confirm this, and the subject has successfully re-started sebelipase alfa. Of samples tested to date, no anti-drug antibodies have been detected.

CONCLUSIONS

Long-term dosing with sebelipase alfa in lysosomal acid lipase-deficient patients is well tolerated and produces sustained reductions in transaminases, improvements in serum lipid profile and reduction in the hepatic fat fraction. A randomized, placebo-controlled phase 3 trial in children and adults is underway (ARISE: NCT01757184).

Hepatic entrapment of esterified cholesterol drives continual expansion of whole body sterol pool in lysosomal acid lipase-deficient mice

Cholesteryl ester storage disease (CESD) results from loss-of-function mutations in LIPA, the gene that encodes lysosomal acid lipase (LAL). Hepatomegaly and deposition of esterified cholesterol (EC) in multiple organs ensue. The present studies quantitated rates of synthesis, absorption, and disposition of cholesterol, and whole body cholesterol pool size in a mouse model of CESD. In 50-day-old lal(-/-) and matching lal(+/+) mice fed a low-cholesterol diet, whole animal cholesterol content equalled 210 and 50 mg, respectively, indicating that since birth the lal(-/-) mice sequestered cholesterol at an average rate of 3.2 mg·day(-1)·animal(-1). The proportion of the body sterol pool contained in the liver of the lal(-/-) mice was 64 vs. 6.3% in their lal(+/+) controls. EC concentrations in the liver, spleen, small intestine, and lungs of the lal(-/-) mice were elevated 100-, 35-, 15-, and 6-fold, respectively. In the lal(-/-) mice, whole liver cholesterol synthesis increased 10.2-fold, resulting in a 3.2-fold greater rate of whole animal sterol synthesis compared with their lal(+/+) controls. The rate of cholesterol synthesis in the lal(-/-) mice exceeded that in the lal(+/+) controls by 3.7 mg·day(-1)·animal(-1). Fractional cholesterol absorption and fecal bile acid excretion were unchanged in the lal(-/-) mice, but their rate of neutral sterol excretion was 59% higher than in their lal(+/+) controls. Thus, in this model, the continual expansion of the body sterol pool is driven by the synthesis of excess cholesterol, primarily in the liver. Despite the severity of their disease, the median life span of the lal(-/-) mice was 355 days.

Cholesteryl ester storage disease: review of the findings in 135 reported patients with an underdiagnosed disease

Cholesteryl ester storage disease (CESD) is caused by deficient lysosomal acid lipase (LAL) activity, predominantly resulting in cholesteryl ester (CE) accumulation, particularly in the liver, spleen, and macrophages throughout the body. The disease is characterized by microvesicular steatosis leading to liver failure, accelerated atherosclerosis and premature demise. Although CESD is rare, it is likely that many patients are unrecognized or misdiagnosed. Here, the findings in 135 CESD patients described in the literature are reviewed. Diagnoses were based on liver biopsies, LAL deficiency and/or LAL gene (LIPA) mutations. Hepatomegaly was present in 99.3% of patients; 74% also had splenomegaly. When reported, most patients had elevated serum total cholesterol, LDL-cholesterol, triglycerides, and transaminases (AST, ALT, or both), while HDL-cholesterol was decreased. All 112 liver biopsied patients had the characteristic pathology, which is progressive, and includes microvesicular steatosis, which leads to fibrosis, micronodular cirrhosis, and ultimately to liver failure. Pathognomonic birefringent CE crystals or their remnant clefts were observed in hepatic cells. Extrahepatic manifestations included portal hypertension, esophageal varices, and accelerated atherosclerosis. Liver failure in 17 reported patients resulted in liver transplantation and/or death. Genotyping identified 31 LIPA mutations in 55 patients; 61% of mutations were the common exon 8 splice-junction mutation (E8SJM(-1G>A)), for which 18 patients were homozygous. Genotype/phenotype correlations were limited; however, E8SJM(-1G>A) homozygotes typically had early-onset, slowly progressive disease. Supportive treatment included cholestyramine, statins, and, ultimately, liver transplantation. Recombinant LAL replacement was shown to be effective in animal models, and recently, a phase I/II clinical trial demonstrated its safety and indicated its potential metabolic efficacy.

The cytosolic adaptor AP-1A is essential for the trafficking and function of Niemann-Pick type C proteins

Niemann-Pick type C (NPC) disease is a fatal neurodegenerative disorder characterized by over-accumulation of low-density lipoprotein-derived cholesterol and glycosphingolipids in late endosomes/lysosomes (LE/L) throughout the body. Human mutations in either NPC1 or NPC2 genes have been directly associated with impaired cholesterol efflux from LE/L. Independent from its role in cholesterol homeostasis and its NPC2 partner, NPC1 was unexpectedly identified as a critical player controlling intracellular entry of filoviruses such as Ebola. In this study, a yeast three-hybrid system revealed that the NPC1 cytoplasmic tail directly interacts with the clathrin adaptor protein AP-1 via its acidic/di-leucine motif. Consequently, a nonfunctional AP-1A cytosolic complex resulted in a typical NPC-like phenotype mainly due to a direct impairment of NPC1 trafficking to LE/L and a partial secretion of NPC2. Furthermore, the mislocalization of NPC1 was not due to cholesterol accumulation in LE/L, as it was not rescued upon treatment with Mβ-cyclodextrin, which almost completely eliminated intracellular free cholesterol. Our cumulative data demonstrate that the cytosolic clathrin adaptor AP-1A is essential for the lysosomal targeting and function of NPC1 and NPC2.

Association of LIPA gene polymorphisms with obesity-related metabolic complications among severely obese patients

The lipase A, lysosomal acid, cholesterol esterase enzyme (LIPA) is involved in the hydrolysis of triglycerides (TGs) and cholesteryl esters (CEs) delivered to lysosomes. LIPA deficiency in human causes two distinct phenotypes characterized by intracellular storage of CE and derangements in the control of cholesterol production, namely the Wolman disease (WD) and the CE storage disease (CESD). To test the potential association of LIPA gene polymorphisms with obesity-related metabolic complications, promoter, exons, and intronic flanking regions of the LIPA gene were first sequenced in 25 individuals. From the 14 common polymorphisms identified, 12 tagging single-nucleotide polymorphisms (tSNPs) were genotyped in a cohort of 1,751 obese individuals. After adjustments for the effect of age, sex, diabetes, and medication, the C allele of SNP rs1051338 was associated with lower blood pressure (BP; systolic (SBP) P = 0.004; diastolic (DBP) P = 0.006). Three of the tested SNPs were associated with modifications of the plasma lipid profile. The G/G genotype of rs2071509 was associated with higher high-density lipoprotein cholesterol (HDL-C) levels (P = 0.009) and minor allele of rs1131706 was also associated with higher HDL-C (P = 0.004) and an association between rs3802656 and total cholesterol (total-C)/HDL-C ratio was identified (P = 0.04). These results thus suggest that LIPA polymorphisms contribute to the interindividual variability observed in obesity-related metabolic complications.

Niemann-Pick type C disease: molecular mechanisms and potential therapeutic approaches

Cholesterol is an important lipid of mammalian cells. Its unique physicochemical properties modulate membrane behavior and it serves as the precursor for steroid hormones, oxysterols and vitamin D. Cholesterol is effluxed from the late endosomes/lysosomes via the concerted action of at least two distinct proteins: Niemann-Pick C (NPC)1 and NPC2. Mutations in these two proteins manifest as NPC disease - a very rare, usually fatal, autosomal, recessive, neurovisceral, lysosomal storage disorder. In this review, we discuss the possible mechanisms of action for NPC1 and NPC2 in mediating cholesterol efflux, as well as the different therapeutic approaches being pursued for the treatment of this lipid storage disorder.

Lysosomal storage diseases as differential diagnosis of hepatosplenomegaly

In adults, elevated transaminases and hepatomegaly, often mild, with moderate to massive idiopathic splenomegaly might hint to a lysosomal storage disease (LSD). In most of these cases, hepatosplenomegaly does not eventually lead to cirrhosis, hepatocellular carcinoma or cholestasis. Nevertheless, the hepatic clinical findings might be the incentive for the patient to present at the physician's office. Many of the currently known >50 lysosomal storage diseases might manifest in liver: out of these, the most important ones in adults are: Gaucher disease, cholesterol ester storage disease (CESD) and the Niemann-Pick diseases. An increase of plasma chitotriosidase should alert the physician for the presence of an LSD. For Gaucher's disease, enzyme supplementation and substrate deprivation constitute effective therapeutic options. Fabry's disease, the most prevalent lysosomal storage disease, does usually not affect the liver, but causes painful episodes of hands' or feet pain (acroparesthesias), left ventricular hypertrophy, renal failure, early stroke and decreased life expectancy. The emerging advent of effective therapeutic options and the cumulative prevalence of lysosomal storage diseases urge the hepatologist to add these diagnostic pathways to the clinical repertoire.

Hepatosplenomegalic lipidosis: what unless Gaucher? Adult cholesteryl ester storage disease (CESD) with anemia, mesenteric lipodystrophy, increased plasma chitotriosidase activity and a homozygous lysosomal acid lipase -1 exon 8 splice junction mutation

A 36-year-old woman was admitted for hepatosplenomegaly and anemia. Bone marrow cytology showed "sea-blue histiocytes", vacuolated macrophages and plasma cells. As primary liver disease, malignancy or hematologic disorders were excluded, and plasma chitotriosidase activity was increased 27-fold over control, the presence of a lysosomal storage disease was suspected. Biochemical analysis of skin fibroblasts revealed normal glucocerebrosidase and sphingomyelinase activity, but lipid analysis showed a more than 15-fold accumulation of cholesterol esters within the cells. The activity of lysosomal acid lipase (LAL) in fibroblast homogenates was decreased to 12% of control subjects. Mutational analysis of the patient's blood showed the homozygous G-->A mutation at position -1 of the exon 8 splice donor site (E8SJM-allele) known for adult cholesteryl ester storage disease (CESD); the polymorphic background was that of the complex haplotype -6Thr, 2Gly, 894 G-->A. Based on clinical, laboratory, cytological and and biochemical findings, CESD can clearly be separated from other more frequent inherited lysosomal storage diseases, e.g. atypical forms of Gaucher disease.

Characterization of lysosomal acid lipase by site-directed mutagenesis and heterologous expression

Lysosomal acid lipase (LAL) is essential for the hydrolysis of cholesterol esters and triglycerides that are delivered to the lysosomes via the low density lipoprotein receptor system. The deficiency of LAL is associated with cholesteryl ester storage disease (CESD) and Wolman's disease (WD). We cloned the human LAL cDNA and expressed the active enzyme in the baculovirus system. Two molecular forms (M(r) approximately 41,000 and approximately 46,000) with different glycosylation were found intracellularly, and approximately 24% of the M(r) approximately 46,000 form was secreted into the medium. Tunicamycin treatment produced only an inactive M(r) approximately 41,000 form. This result implicates glycosylation occupancy in the proper folding for active-site function. Catalytic activity was greater toward cis- than trans-unsaturated fatty acid esters of 4-methylumbelliferone and toward esters with 7-carbon length acyl chains. LAL cleaved cholesterol esters and mono-, tri-, and diglycerides. Heparin had a biphasic effect on enzymatic activity with initial activation followed by inhibition. Inhibition of LAL activity by tetrahydrolipstatin and diethyl p-nitrophenyl phosphate suggested the presence of active serines in binding/catalytic domain(s) of the protein. Site-directed mutagenesis at two putative active centers, GXSXG, showed that Ser153 was important to catalytic activity, whereas Ser99 was not and neither was the catalytic nucleophile. Three reported mutations (L179P, L336P, and delta AG302 deletion) from CESD patients were created and expressed in the Sf9 cell system. None cleaved cholesterol esters, and L179P and L336P cleaved only triolein at approximately 4% of wild-type levels. These results suggest that mechanisms, in addition to LAL defects, may operate in the selective accumulation of cholesterol esters or triglycerides in CESD and WD patients.

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.

Acid cholesteryl ester hydrolase activity of mononuclear leukocytes in patients with non-insulin-dependent diabetes mellitus: studies before and after treatment of diabetes

The change of acid cholesteryl ester hydrolase activity in mononuclear leukocyte following treatment of diabetes mellitus was studied in 21 patients with non-insulin-dependent diabetes mellitus (NIDDM). Enzyme activity before treatment in the patients was significantly lower than that in 14 age-matched healthy subjects (1.20 +/- 0.15; mean +/- S.E. vs. 2.20 +/- 0.17 nmol/mg protein/h, P less than 0.01). Enzyme activity before treatment in the patients was significantly increased (P less than 0.05) after 4-8 weeks of treatment. However, enzyme activity of 1.43 +/- 0.14 nmol/mg protein/h observed after treatment in the patients was significantly lower (P less than 0.01) than that in the healthy subjects. There was a significant negative correlation between enzyme activity before treatment and the increase in enzyme activity following treatment (rs = -0.555, P less than 0.01, n = 21). These results indicate that low level of enzyme activity may be insufficiently improved by the treatment of diabetes, and the risk for the development of atherosclerosis as viewed from the enzyme activity may persist even after the treatment in NIDDM.

Effects of calcium antagonists on atherogenesis

Calcium antagonists are able to reduce the development of atherosclerotic lesions in many animal models of atherosclerosis. Although the precise mechanisms of their antiatherogenic effects are unknown studies have shown interference with several pathogenetic mechanisms of the atherosclerotic disease process, namely preservation of endothelial integrity, reduced smooth muscle cell migration and proliferation, increased low density lipoprotein uptake and degradation in smooth muscle cells and reduced synthesis of matrix components. Many of these effects are unrelated to their blocking effects on voltage-dependent slow calcium channels, and most effects have been observed with very high concentrations only. Furthermore, differing calcium antagonists seem to influence these mechanisms differently but available data are difficult to interpret because of differences in study design and models used. With the exception of data on calcium antagonists for secondary prevention after myocardial infarction and their influence on the rate of restenosis after percutaneous transluminal angioplasty, no data are available in man with respect to a possible influence on atherosclerosis. Results from on-going studies designed to address specifically this issue must be awaited to answer the question whether the experimental findings can be extended to human atherosclerosis.

[Lysosomal enzyme activity of monocytes/macrophages following incubation with postprandial hyperlipemic serum and its significance for the development of atherosclerosis]

Lipid accumulation in macrophages is a prominent feature of the atherosclerotic lesion. Decreased lysosomal function of these cells might play an important role in the pathogenesis of the atherosclerotic foam cell. In this investigation six normal volunteers were fed a meal with a high fat content (68.9% energy, P/S ratio 0.13). The hyperlipidemic postprandial serum was incubated with monocyte derived macrophages. The enzyme activity of cathepsin B, acid cholesterylester-hydrolase and N-acetyl-beta-hydrolase decreased significantly in these cells. Thus, inadequate response in enzyme activity of lysosomal enzymes in case of fat overload might contribute to the development of the atherosclerotic foam cell.

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.

Cholesteryl ester storage disease and Wolman disease: phenotypic variants of lysosomal acid cholesteryl ester hydrolase deficiency

The lysosomal enzyme responsible for cholesteryl ester hydrolysis, acid cholesteryl ester hydrolase, or acid lipase (E.C.3.1.1.13) plays an important role in cellular cholesterol metabolism. Loss of the activity of this enzyme in tissues of individuals with both Wolman disease and cholesteryl ester storage disease is believed to play a causal role in these conditions. The objectives of our studies were not only to directly compare and contrast the clinical features of Wolman disease and cholesteryl ester storage disease but also to determine the reasons(s) for the varied phenotype expression of acid cholesteryl ester hydrolase deficiency. Although both diseases manifest a type II hyperlipoproteinemic phenotype and hepatomegaly secondary to lipid accumulation, a more malignant clinical course with more significant hepatic and adrenal manifestations was observed in the patient with Wolman disease. However, the acid cholesteryl ester hydrolase activity in cultured fibroblasts in both diseases was virtually absent. In addition, fibroblasts from both Wolman disease and cholesteryl ester storage disease were able to utilize exogenously supplied enzyme, suggesting that neither disease was due to defective enzyme delivery by the mannose-6-phosphate receptor pathway. Coculture and cell fusion of fibroblasts from Wolman disease and cholesteryl ester storage disease subjects did not lead to correction of the enzyme deficiency, indicating that these disorders are allelic. However, the activities of the hepatic acid and neutral lipase in these two clinical variants were quite different. Hepatic acid lipase activity was only 4% normal in Wolman disease, but the activity was 23% normal in cholesteryl ester storage disease. The hepatic neutral lipase activity was normal in Wolman disease but increased more than twofold in cholesteryl ester storage disease. These combined results indicate that the clinical heterogeneity in acid cholesteryl ester hydrolase deficiency can be explained by a varied hepatic metabolic response to an allelic mutation.

Cholesterol ester storage disease in an adult presenting with sea-blue histiocytosis

An adult patient is described with hepatomegaly and sea-blue histiocytes in the bone marrow. A diagnosis of cholesterol ester storage disease was established following enzyme and lipid analyses on liver biopsy and cultured skin fibroblasts. Acid esterase activity was deficient (approx. 5% of controls) in liver and fibroblasts using [14C]-triolein or 4-methylumbelliferyl palmitate as substrates. Cholesterol ester levels were raised about 70-fold in liver, whereas triglyceride levels were only marginally raised. Marked accumulation of cholesterol esters was also demonstrated in cultured fibroblasts. Clinically, the patient responded favourably to phenobarbitone treatment. However, this was not reflected in liver acid esterase or lipid levels.