A practical fluorometric assay method to measure lysosomal acid lipase activity in dried blood spots for the screening of cholesteryl ester storage disease and Wolman disease

Lysosomal Acid Lipase Deficiency: Genetics, Screening, and Preclinical Study

Lysosomal acid lipase (LAL) is a lysosomal enzyme essential for the degradation of cholesteryl esters through the endocytic pathway. Deficiency of the LAL enzyme encoded by the LIPA gene leads to LAL deficiency (LAL-D) (OMIM 278000), one of the lysosomal storage disorders involving 50-60 genes. Among the two disease subtypes, the severe disease subtype of LAL-D is known as Wolman disease, with typical manifestations involving hepatomegaly, splenomegaly, vomiting, diarrhea, and hematopoietic abnormalities, such as anemia. In contrast, the mild disease subtype of this disorder is known as cholesteryl ester storage disease, with hypercholesterolemia, hypertriglyceridemia, and high-density lipoprotein disappearance. The prevalence of LAL-D is rare, but several treatment options, including enzyme replacement therapy, are available. Accordingly, a number of screening methodologies have been developed for this disorder. This review summarizes the current discussion on LAL-D, covering genetics, screening, and the tertiary structure of human LAL enzyme and preclinical study for the future development of a novel therapy.

Therapeutic efficacy of rscAAVrh74.miniCMV.LIPA gene therapy in a mouse model of lysosomal acid lipase deficiency

Lysosomal acid lipase deficiency (LAL-D) presents as one of two rare autosomal recessive diseases: Wolman disease (WD), a severe disorder presenting in infancy characterized by absent or very low LAL activity, and cholesteryl ester storage disease (CESD), a less severe, later onset disease form. Recent clinical studies have shown efficacy of enzyme replacement therapy for both forms of LAL-D; however, no gene therapy approach has yet been developed for clinical use. Here, we show that rscAAVrh74.miniCMV.LIPA gene therapy can significantly improve disease symptoms in the Lipa^−/− mouse model of LAL-D. Treatment dramatically lowered hepatosplenomegaly, liver and spleen triglyceride and cholesterol levels, and serum expression of markers of liver damage. Measures of liver inflammation and fibrosis were also reduced. Treatment of young adult mice was more effective than treatment of neonates, and enzyme activity was elevated in serum, consistent with possible bystander effects. These results demonstrate that adeno associated virus (AAV)-mediated LIPA gene-replacement therapy may be a viable option to treat patients with LAL-D, particularly patients with CESD.

Targeting LIPA independent of its lipase activity is a therapeutic strategy in solid tumors via induction of endoplasmic reticulum stress

Triple-negative breast cancer (TNBC) has a poor clinical outcome, due to a lack of actionable therapeutic targets. Herein we define lysosomal acid lipase A (LIPA) as a viable molecular target in TNBC and identify a stereospecific small molecule (ERX-41) that binds LIPA. ERX-41 induces endoplasmic reticulum (ER) stress resulting in cell death, and this effect is on target as evidenced by specific LIPA mutations providing resistance. Importantly, we demonstrate that ERX-41 activity is independent of LIPA lipase function but dependent on its ER localization. Mechanistically, ERX-41 binding of LIPA decreases expression of multiple ER-resident proteins involved in protein folding. This targeted vulnerability has a large therapeutic window, with no adverse effects either on normal mammary epithelial cells or in mice. Our study implicates a targeted strategy for solid tumors, including breast, brain, pancreatic and ovarian, whereby small, orally bioavailable molecules targeting LIPA block protein folding, induce ER stress and result in tumor cell death.

Cell-intrinsic Wnt4 ligand regulates mitochondrial oxidative phosphorylation in macrophages

Macrophages respond to their environment by adopting a predominantly inflammatory or anti-inflammatory profile, depending on the context. The polarization of the subsequent response is regulated by a combination of intrinsic and extrinsic signals and is associated with alterations in macrophage metabolism. Although macrophages are important producers of Wnt ligands, the role of Wnt signaling in regulating metabolic changes associated with macrophage polarization remains unclear. Wnt4 upregulation has been shown to be associated with tissue repair and suppression of age-associated inflammation, which led us to generate Wnt4-deficient bone marrow–derived macrophages to investigate its role in metabolism. We show that loss of Wnt4 led to modified mitochondrial structure, enhanced oxidative phosphorylation, and depleted intracellular lipid reserves, as the cells depended on fatty acid oxidation to fuel their mitochondria. Further we found that enhanced lipolysis was dependent on protein kinase C–mediated activation of lysosomal acid lipase in Wnt4-deficient bone marrow–derived macrophages. Although not irreversible, these metabolic changes promoted parasite survival during infection with Leishmania donovani. In conclusion, our results indicate that enhanced macrophage fatty acid oxidation impairs the control of intracellular pathogens, such as Leishmania. We further suggest that Wnt4 may represent a potential target in atherosclerosis, which is characterized by lipid storage in macrophages leading to them becoming foam cells.

Cholesteryl ester storage disease of clinical and genetic characterisation: A case report and review of literature

BACKGROUND

Cholesteryl ester storage disease (CESD) is a rare genetic disease. Its symptoms and severity are highly variable. CESD is a systemic disease that can lead to the accumulation of fat and inflammation in the liver, as well as gastrointestinal and cardiovascular disease. The majority of patients require liver transplantation due to decompensated cirrhosis. Enzyme replacement therapy has been approved based on a randomized trial. Our study aims to clinically and genetically evaluate two siblings with CESD who underwent liver transplantation, as well as their first-degree family members.

CASE SUMMARY

The siblings were compound heterozygous for the missense variant in LIPA exon 8, c.894G>A, (p.Gln298Gln) and a single base pair deletion, c.482del (p.Asn161Ilefs*19). Analyses of single nucleotide polymorphisms showed variants with an increased risk of fatty liver disease and fibrosis for both patients. Clinically, both patients show signs of recurrence of CESD in the liver after transplantation and additional gastrointestinal and cardiovascular signs of CESD. Three family members who were LIPA heterozygous had a lysosomal acid lipase activity below the reference value. One of these carriers, a seven-year-old boy, was found to have severe dyslipidemia and was subsequently treated with statins.

CONCLUSION

Our study underlines that CESD is a multi-organ disease, the progression of which may occur post-liver transplantation. Our findings underline the need for monitoring of complications and assessment of possible further treatment.

A fast, miniaturised in-vitro assay developed for quantification of lipase enzyme activity

The discovery of allosteric modulators is a multi-disciplinary approach, which is time- and cost-intensive. High-throughput screening combined with novel computational tools can reduce these factors. Thus, we developed an enzyme activity assay, which can be included in the drug discovery work-flow subsequent to the in-silico library screening. While the in-silico screening yields in the identification of potential allosteric modulators, the developed in-vitro assay allows for the characterisation of them. Candida rugosa lipase (CRL), a glyceride hydrolysing enzyme, has been selected for the pilot development. The assay conditions were adjusted to CRL’s properties including pH, temperature and substrate specificity for two different substrates. The optimised assay conditions were validated and were used to characterise Tropolone, which was identified as an allosteric modulator. In conclusion, the assay is a reliable, reproducible, and robust tool, which can be streamlined with in-silico screening and incorporated in an automated high-throughput screening workflow.

A kinetic assay of total lipase activity for detecting lysosomal acid lipase deficiency (LAL-D) and the molecular characterization of 18 LAL-D patients from Russia

Laboratory diagnostics of lysosomal acid lipase deficiency (LAL-D), a rare disorder associated with LIPA alterations, are based on the evaluation of LAL activity. In dry blood spots (DBS) submitted for LAL-D diagnostics (the screening cohort) over a two-year period or obtained from a cohort of retrospective LAL-D patients, we measured: (1) LAL activity using a two-reaction assay with 4-methylumbelliferone palmitate (4-MU-Palm) and Lalistat-2, a specific LAL inactivator; (2) total lipase (TL) activity by a 1-hour kinetic 4-MU-Palm cleavage reaction (no Lalistat-2). The TL activity was expressed as the area under the kinetic curve after 1 hour (TL-AUC1h) of the reaction and presented as the median (min-max). LAL activity was reduced in 30/537 individuals from the screening cohort, among which LIPA sequencing revealed six patients and one carrier. Overall, 16 (89%) individuals among six novel and 12 retrospective LAL-D patients carried at least one c.894G>A mutation (six were homozygous). The TL-AUC1h in nonLAL-D specimens with normal LAL activity (n = 90) was unambiguously higher (9471 [4015-23 585] RFU*h/punch) compared to LAL-D patients, including six new and nine retrospective patients (1810 [357-2608] RFU*h/punch). Importantly, in 13/15 examined nonLAL-D specimens with reduced LAL activity the TL-AUC1h was above a threshold of 2652 RFU*h/punch. Applying this threshold, the TL-AUC1h index discriminated all LAL-D patients (100% sensitivity) and 103/105 nonLAL-D specimens (98% specificity). Given that there is no need for Lalistat-2 and two parallel enzymatic reactions in conjunction with high sensitivity and specificity, the kinetic assay seems to be practical for LAL-D screening.

SYNOPSIS

Lysosomal acid lipase deficiency responsible for Wolman disease and cholesterol ester storage disease could be reliably detected using a kinetic assay of total lipase activity with a fluorogenic substrate.

Characterization of the mechanisms by which missense mutations in the lysosomal acid lipase gene disrupt enzymatic activity

Hydrolysis of cholesteryl esters and triglycerides in the lysosome is performed by lysosomal acid lipase (LAL). In this study we have investigated how 23 previously identified missense mutations in the LAL gene (LIPA) (OMIM# 613497) affect the structure of the protein and thereby disrupt LAL activity. Moreover, we have performed transfection studies to study intracellular transport of the 23 mutants. Our main finding was that most pathogenic mutations result in defective enzyme activity by affecting the normal folding of LAL. Whereas, most of the mutations leading to reduced stability of the cap domain did not alter intracellular transport, nearly all mutations that affect the stability of the core domain gave rise to a protein that was not efficiently transported from the endoplasmic reticulum (ER) to the Golgi apparatus. As a consequence, ER stress was generated that is assumed to result in ER-associated degradation of the mutant proteins. The two LAL mutants Q85K and S289C were selected to study whether secretion-defective mutants could be rescued from ER-associated degradation by the use of chemical chaperones. Of the five chemical chaperones tested, only the proteasomal inhibitor MG132 markedly increased the amount of mutant LAL secreted. However, essentially no increased enzymatic activity was observed in the media. These data indicate that the use of chemical chaperones to promote the exit of folding-defective LAL mutants from the ER, may not have a great therapeutic potential as long as these mutants appear to remain enzymatically inactive.

Prevalence of cholesteryl ester storage disease among hypercholesterolemic subjects and functional characterization of mutations in the lysosomal acid lipase gene

Lysosomal acid lipase hydrolyzes cholesteryl esters and triglycerides contained in low density lipoprotein. Patients who are homozygous or compound heterozygous for mutations in the lysosomal acid lipase gene (LIPA), and have some residual enzymatic activity, have cholesteryl ester storage disease. One of the clinical features of this disease is hypercholesterolemia. Thus, patients with hypercholesterolemia who do not carry a mutation as a cause of autosomal dominant hypercholesterolemia, may actually have cholesteryl ester storage disease. In this study we have performed DNA sequencing of LIPA in 3027 hypercholesterolemic patients who did not carry a mutation as a cause of autosomal dominant hypercholesterolemia. Functional analyses of possibly pathogenic mutations and of all mutations in LIPA listed in The Human Genome Mutation Database were performed to determine the pathogenicity of these mutations. For these studies, HeLa T-REx cells were transiently transfected with mutant LIPA plasmids and Western blot analysis of cell lysates was performed to determine if the mutants were synthesized in a normal fashion. The enzymatic activity of the mutants was determined in lysates of the transfected cells using 4-methylumbelliferone-palmitate as the substrate. A total of 41 mutations in LIPA were studied, of which 32 mutations were considered pathogenic by having an enzymatic activity <10% of normal. However, none of the 3027 hypercholesterolemic patients were homozygous or compound heterozygous for a pathogenic mutation. Thus, cholesteryl ester storage disease must be a very rare cause of hypercholesterolemia in Norway.

Wolman's disease and cholesteryl ester storage disorder: the phenotypic spectrum of lysosomal acid lipase deficiency

Lysosomal acid lipase deficiency is a rare, autosomal recessive condition caused by mutations in the gene encoding lysosomal acid lipase (LIPA) that result in reduced or absent activity of this essential enzyme. The severity of the resulting disease depends on the nature of the underlying mutation and magnitude of its effect on enzymatic function. Wolman's disease is a severe disorder that presents during infancy, resulting in failure to thrive, hepatomegaly, and hepatic failure, and an average life expectancy of less than 4 months. Cholesteryl ester storage disorder arises later in life and is less severe, although the two diseases share many common features, including dyslipidaemia and transaminitis. The prevalence of these diseases has been estimated at one in 40 000 to 300 000, but many cases are undiagnosed and unreported, and awareness among clinicians is low. Lysosomal acid lipase deficiency-which can be diagnosed using dry blood spot testing-is often misdiagnosed as non-alcoholic fatty liver disease (NAFLD), non-alcoholic steatohepatitis (NASH), hereditary dyslipidaemia, or cryptogenic cirrhosis. There are no formal guidelines for treatment of these patients, and treatment options are limited. In this Review we appraise the existing literature on Wolman's disease and cholesteryl ester storage disease, and discuss available treatments, including enzyme replacement therapy, oral lipid-lowering therapy, stem-cell transplantation, and liver transplantation.

The role of sebelipase alfa in the treatment of lysosomal acid lipase deficiency

Lysosomal acid lipase deficiency (LALD) is a lysosomal storage disorder (LSD) characterized either by infantile onset with fulminant clinical course and very poor prognosis or childhood/adult-onset disease with an attenuated phenotype. The disorder is often misdiagnosed or remains undiagnosed in children and adults due to a rather unspecific clinical presentation with dyslipidemia and steatohepatitis. Until recently, no good treatment options were available for LALD. Despite supportive and symptomatic therapies, death occurred before 1 year of age in patients with infantile-onset disease and patients with childhood/adult-onset LALD suffered from significant complications, such as liver cirrhosis, requiring liver transplantation and early-onset cardiovascular disease. With the recent approval of sebelipase alfa for clinical use in infantile- as well as childhood/adult-onset LALD, a new treatment era for this disorder has begun. Sebelipase alfa is a recombinant human lysosomal acid lipase (LAL), which is administered via the intravenous route. Clinical trials have shown significant improvement of disease parameters such as liver transaminases, hepatomegaly, and dyslipidemia in childhood/adult-onset LALD patients. Treatment of infants with the severe infantile-onset form of the disease has led to improved survival beyond the age of 1 year, and also showed improvement of hepatic and gastrointestinal symptoms, as well as growth. Overall, sebelipase alfa has a favorable safety profile and promises to be a good long-term treatment option for patients with LALD, with significant reduction of disease burden and increased life expectancy.

Perspectives in Pediatric Pathology, Chapter 21. Testicular Pathology in Heritable Metabolic Disease

Inborn errors of metabolism have wide and profound effects in many or all organs, and especially so in those with endocrine functions. The testes are greatly affected by systemic metabolic disorders, leading to specific histological findings that generally reveal the nature of the underlying disorder. Here we describe the main testicular changes seen in the setting of metabolic disease.

Best practice in the measurement and interpretation of lysosomal acid lipase in dried blood spots using the inhibitor Lalistat 2

Lysosomal acid lipase deficiency (LAL-D) is an inherited, autosomal recessive lysosomal storage disorder characterized by progressive damage in multiple organ systems. Diagnosis is especially important in infants, in whom the course of disease is rapidly lethal without treatment. The recent regulatory approval of recombinant human lysosomal acid lipase (LAL), sebelipase alfa, merits rapid diagnosis in clinical routine, particularly in infants. A method for measuring LAL activity in dried blood spot (DBS) samples using the highly specific LAL inhibitor Lalistat 2 is available. This method is shown to effectively discriminate between individuals with LAL-D and unaffected controls. With the increase in DBS LAL testing since the original publication of this method, a need to optimise assay performance has been identified. Here, we describe refinements to the DBS assay, including technical modifications, quality control measures and best-practice guidance for interpreting and reporting results. Particular attention is paid to alternatives to the use of mercuric chloride as the stop reagent and the choice of excitation wavelength for 4-methylumbelliferone palmitate under assay conditions at pH4.0. In addition, a simpler method of reporting results is proposed using cutoffs based on percentage mean normal enzyme activity.

Cholesteryl Ester Storage Disease: An underdiagnosed cause of cirrhosis in adults

Cholesteryl Ester Storage Disease (CESD), is a rare multisystem autosomal recessive disorder and belongs to the broad family of lysosomal storage disorders. It can present anytime from infancy and childhood to even adulthood. The clinical manifestations are generally severe in infants and with milder forms in adults. One of the prominent sites of involvement is liver. Due to low awareness of this condition among physicians including surgical pathologists, majority of the liver biopsies, especially from the adults are often misdiagnosed as non-alcoholic fatty liver disease/non-alcoholic steatohepatitis or cryptogenic cirrhosis. Given the recent availability of safe and effective enzyme replacement therapy that can alter the natural course of CESD, the pathologists signing out adult and pediatric liver biopsies should be aware of this entity, thus contributing to timely patient management. This review discusses the clinical features, pathogenesis, diagnostic approach, differential diagnosis and management of CESD in adults.

Targeting Wolman Disease and Cholesteryl Ester Storage Disease: Disease Pathogenesis and Therapeutic Development

Wolman disease (WD) and cholesteryl ester storage disease (CESD) are lysosomal storage diseases (LSDs) caused by a deficiency in lysosomal acid lipase (LAL) due to mutations in the LIPA gene. This enzyme is critical to the proper degradation of cholesterol in the lysosome. LAL function is completely lost in WD while some residual activity remains in CESD. Both are rare diseases with an incidence rate of less than 1/100,000 births for WD and approximate 2.5/100,000 births for CESD. Clinical manifestation of WD includes hepatosplenomegaly, calcified adrenal glands, severe malabsorption and a failure to thrive. As in CESD, histological analysis of WD tissues reveals the accumulation of triglycerides (TGs) and esterified cholesterol (EC) in cellular lysosomes. However, the clinical presentation of CESD is less severe and more variable than WD. This review is to provide an overview of the disease pathophysiology and the current state of therapeutic development for both of WD and CESD. The review will also discuss the application of patient derived iPSCs for further drug discovery.

Regulation of lysosomal ion homeostasis by channels and transporters

Lysosomes are the major organelles that carry out degradation functions. They integrate and digest materials compartmentalized by endocytosis, phagocytosis or autophagy. In addition to more than 60 hydrolases residing in the lysosomes, there are also ion channels and transporters that mediate the flux or transport of H⁺, Ca²⁺, Na⁺, K⁺, and Cl⁻ across the lysosomal membranes. Defects in ionic exchange can lead to abnormal lysosome morphology, defective vesicle trafficking, impaired autophagy, and diseases such as neurodegeneration and lysosomal storage disorders. The latter are characterized by incomplete lysosomal digestion and accumulation of toxic materials inside enlarged intracellular vacuoles. In addition to degradation, recent studies have revealed the roles of lysosomes in metabolic pathways through kinases such as mechanistic target of rapamycin (mTOR) and transcriptional regulation through calcium signaling molecules such as transcription factor EB (TFEB) and calcineurin. Owing to the development of new approaches including genetically encoded fluorescence probes and whole endolysosomal patch clamp recording techniques, studies on lysosomal ion channels have made remarkable progress in recent years. In this review, we will focus on the current knowledge of lysosome-resident ion channels and transporters, discuss their roles in maintaining lysosomal function, and evaluate how their dysfunction can result in disease.

Loss of Mitochondrial Function Impairs Lysosomes

Alterations in mitochondrial function, as observed in neurodegenerative diseases, lead to disrupted energy metabolism and production of damaging reactive oxygen species. Here, we demonstrate that mitochondrial dysfunction also disrupts the structure and function of lysosomes, the main degradation and recycling organelle. Specifically, inhibition of mitochondrial function, following deletion of the mitochondrial protein AIF, OPA1, or PINK1, as well as chemical inhibition of the electron transport chain, impaired lysosomal activity and caused the appearance of large lysosomal vacuoles. Importantly, our results show that lysosomal impairment is dependent on reactive oxygen species. Given that alterations in both mitochondrial function and lysosomal activity are key features of neurodegenerative diseases, this work provides important insights into the etiology of neurodegenerative diseases.

Cholesterol ester storage disease with a novel LIPA mutation (L264P) that presented massive hepatomegaly: A case report

Cholesterol ester storage disease (CESD) is an autosomal recessive disorder caused by deficient lysosomal acid lipase (LAL) activity, resulting in cholesteryl ester (CE) accumulation. CESD patients have liver disease associated with mixed dyslipidemia leading to liver failure. We here report the case of an 11-year-old male CESD patient with a novel mutation who had the chief complaint of massive hepatomegaly. The patient's liver reached to his pelvis, and his spleen was 2 cm below the costal margin. The patient had elevated serum liver enzymes and mixed dyslipidemia. The liver biopsy tissue showed characteristic CESD pathology, which included microvesicular steatosis, mild fibrosis and foamy macrophages. Electron microscopy showed a remnant cleft of CE crystals, and dried blood spot testing showed reduced LAL activity. We identified compound heterozygous mutations in the LIPA gene in this patient, namely, c.607G>C and c.791T>C. The former mutation was previously reported only in a Japanese patient, whereas the latter mutation is novel. The findings of this study suggest that LIPA gene mutations in Japanese CESD patients are different from those in Western patients. Although CESD is rare, it is likely that many patients are unrecognized or misdiagnosed, and thus the possibility of CESD should be considered in patients with hepatosplenomegaly and dyslipidemia.