Current treatment options and novel nanotechnology-driven enzyme replacement strategies for lysosomal storage disorders

Lysosomal storage disorders (LSDs) are a vast group of more than 50 clinically identified metabolic diseases. They are singly rare, but they affect collectively 1 on 5,000 live births. They result in most of the cases from an enzymatic defect within lysosomes, which causes the subsequent augmentation of unwanted substrates. This accumulation process leads to plenty of clinical signs, determined by the specific substrate and accumulation area. The majority of LSDs present a broad organ and tissue engagement. Brain, connective tissues, viscera and bones are usually afflicted. Among them, brain disease is markedly frequent (two-thirds of LSDs). The most clinically employed approach to treat LSDs is enzyme replacement therapy (ERT), which is practiced by administering systemically the missed or defective enzyme. It represents a healthful strategy for 11 LSDs at the moment, but it solves the pathology only in the case of Gaucher disease. This approach, in fact, is not efficacious in the case of LSDs that have an effect on the central nervous system (CNS) due to the existence of the blood-brain barrier (BBB). Additionally, ERT suffers from several other weak points, such as low penetration of the exogenously administered enzyme to poorly vascularized areas, the development of immunogenicity and infusion-associated reactions (IARs), and, last but not least, the very high cost and lifelong needed. To ameliorate these weaknesses lot of efforts have been recently spent around the development of innovative nanotechnology-driven ERT strategies. They may boost the power of ERT and minimize adverse reactions by loading enzymes into biodegradable nanomaterials. Enzyme encapsulation into biocompatible liposomes, micelles, and polymeric nanoparticles, for example, can protect enzymatic activity, eliminating immunologic reactions and premature enzyme degradation. It can also permit a controlled release of the payload, ameliorating pharmacokinetics and pharmacodynamics of the drug. Additionally, the potential to functionalize the surface of the nanocarrier with targeting agents (antibodies or peptides), could promote the passage through biological barriers. In this review we examined the clinically applied ERTs, highlighting limitations that do not allow to completely cure the specific LSD. Later, we critically consider the nanotechnology-based ERT strategies that have beenin-vitroand/orin-vivotested to improve ERT efficacy.

Toward newborn screening of metachromatic leukodystrophy: results from analysis of over 27,000 newborn dried blood spots

PURPOSE

Metachromatic leukodystrophy (MLD) is a lysosomal storage disorder caused by the deficiency of arylsulfatase A (ARSA), which results in the accumulation of sulfatides. Newborn screening for MLD may be considered in the future as innovative treatments are advancing. We carried out a research study to assess the feasibility of screening MLD using dried blood spots (DBS) from de-identified newborns.

METHODS

To minimize the false-positive rate, a two-tier screening algorithm was designed. The primary test was to quantify C16:0-sulfatide in DBS by ultraperformance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The screening cutoff was established based on the results from 15 MLD newborns to achieve 100% sensitivity. The secondary test was to measure the ARSA activity in DBS from newborns with abnormal C16:0-sulfatide levels. Only newborns that displayed both abnormal C16:0-sulfatide abundance and ARSA activity were considered screen positives.

RESULTS

A total of 27,335 newborns were screened using this two-tier algorithm, and 2 high-risk cases were identified. ARSA gene sequencing identified these two high-risk subjects to be a MLD-affected patient and a heterozygote.

CONCLUSION

Our study demonstrates that newborn screening for MLD is highly feasible in a real-world scenario with near 100% assay specificity.

Saposin C is a frequent target of paraproteins in Gaucher disease-associated MGUS/multiple myeloma

Patients with Gaucher disease (GD) have an increased risk of monoclonal gammopathies for which antigenic targets might play a role in their pathogenesis. Here we report the identification of saposin C (sapC) as high-titre (1:1 000 000) target structure of 7/16 GD-associated paraproteins. Anti-sapC immunoglobulin (Ig) showed identity with the paraprotein Ig type and subclass in each patient that showed anti-sapC immunoreactivity. Absorption and depletion studies completely removed the paraprotein from the sera of GD patients. No immunoreactivity against sapC was detected in healthy donors and in other plasma cell dyscrasias, demonstrating that anti-sapC reactivity is highly restricted to GD. Several uncharacterized forms of post-translational modified sapC were detected but their role in the pathogenesis is not clear. We confirm the frequent presence of low-titre (1:250) anti-lysolipid reactivities in the sera of GD patients but we could show that this immunoreactivity is not mediated by the paraprotein and is not restricted to GD patients.

Diagnosis of lysosomal storage disorders: current techniques and future directions

Lysosomal storage disorders represent a group of over 45 distinct genetic diseases. The broad spectrum of clinical presentation of this group of disorders has led to the development of diagnostic protocols to facilitate their rapid and accurate diagnosis. However, with the development of new therapies, testing for many of these disorders now extends beyond diagnosis of affected individuals. The efficacy of many current and proposed therapies will rely heavily upon early detection and treatment prior to the onset of irreversible pathology. Newborn screening holds the promise of early detection. However, presymptomatic diagnosis raises a number of issues relating to patient management and treatment. Methods for prognoses and monitoring therapy in asymptomatic individuals will be required.

Saposin C protects glucocerebrosidase against α-synuclein inhibition

Mutations in GBA1, the gene for glucocerebrosidase (GCase), are genetic risk factors for Parkinson disease (PD). α-Synuclein (α-Syn), a protein implicated in PD, interacts with GCase and efficiently inhibits enzyme activity. GCase deficiency causes the lysosomal storage disorder Gaucher disease (GD). We show that saposin C (Sap C), a protein vital for GCase activity in vivo, protects GCase against α-syn inhibition. Using nuclear magnetic resonance spectroscopy, site-specific fluorescence, and Förster energy transfer probes, Sap C was observed to displace α-syn from GCase in solution and on lipid vesicles. Our results suggest that Sap C might play a crucial role in GD-related PD.

The identification of new biomarkers for identifying and monitoring kidney disease and their translation into a rapid mass spectrometry-based test: evidence of presymptomatic kidney disease in pediatric Fabry and type-I diabetic patients

Using label-free quantative proteomics, we have identified 2 potential protein biomarkers that indicate presymptomatic kidney disease in the urine of pediatric patients with type-I diabetes and Fabry disease (n = 20). Prosaposin and GM2 activator protein (GM2AP) were observed to be elevated in the urine of these patient groups compared to age- and sex-matched controls. These findings were validated by development of a rapid MRM-based tandem mass spectrometry test. Prosaposin was observed to be both significantly elevated in the urine of patients with Fabry disease compared to controls (p = 0.02) and reduced after 12 months enzyme replacement therapy (ERT, p = 0.01). Similarly, GM2AP concentrations were observed to be significantly higher compared to controls in the diabetic group (p = 0.049) and the pretreatment Fabry group (p = 0.003). In addition, this observed to be reduced significantly in the Fabry group following 12 months of ERT (p = 0.01). The process of detection of the biomarkers, development into a test and implications for monitoring patients and treatment are discussed.

Diagnostic strategy for mucolipidosis II/III

Overlapping clinical phenotypes are a diagnostic challenge to the clinician, especially in the cases of mucolipidosis (ML) and mucopolysaccharide disorders (MPS), due to overlapping phenotypes. Present study was carried out in 147 children suspected to have ML or MPS and 100 controls. They were screened for ML II/III by colorimetric method using substrate pNCS. Six children were found screen positive for ML II/III and further confirmatory study showed significantly raised activity in plasma confirming high specificity of the ML screening test. Forty-two (28.5%) children out of remaining 141 children that were screen negative, were found to have various MPS disorders, while rest 99 had normal enzyme activity in plasma and leucocytes. Present study demonstrates prompt and specific chemical method that can be used as a tool for estimating ML II/III, with high specificity.

Saposin B is a human coenzyme q10-binding/transfer protein

Coenzyme Q10 (CoQ10) is essential for ATP production in the mitochondria, and is an important antioxidant in every biomembrane and lipoprotein. Due to its hydrophobicity, a binding and transfer protein for CoQ10 is plausible, but none have yet been isolated and characterized. Here we purified a CoQ10-binding protein from human urine and identified it to be saposin B, a housekeeping protein necessary for sphingolipid hydrolysis in lysosomes. We confirmed that cellular saposin B binds CoQ10 in human sperm and the hepatoma cell line HepG2 by using saposin B monoclonal antibody. The molar ratios of CoQ10 to saposin B were estimated to be 0.22 in urine, 0.003 in HepG2, and 0.12 in sperm. We then confirmed that aqueous saposin B extracts CoQ10 from hexane to form a saposin B-CoQ10 complex. Lipid binding affinity to saposin B decreased in the following order: CoQ10>CoQ9>CoQ7>>α-tocopherol>>cholesterol (no binding). The CoQ10-binding affinity to saposin B increased with pH, with maximal binding seen at pH 7.4. On the other hand, the CoQ10-donating activity of the saposin B-CoQ10 complex to erythrocyte ghost membranes increased with decreasing pH. These results suggest that saposin B binds and transports CoQ10 in human cells.

Gaucher disease and parkinsonism, a molecular link theory

Mutant GBA was found recently to be the most prevalent risk factor for familial parkinsonism. The two diseases do not share common symptoms and there is no direct pathway to explain the mechanism by which GBA mutations can confer the risk. Increased burden on the degradative pathway caused by defective glucocerebrosidase, or toxic side effects of glycosylated lipids accumulation were proposed to explain brain damage. Both hypotheses are not sufficient to explain the linkage. In order to develop a more inclusive theory we introduced into the model the prion theory and the second hit. Other possibilities are also brought into consideration.

Glial fibrillary acidic protein is elevated in the lysosomal storage disease classical late-infantile neuronal ceroid lipofuscinosis, but is not a component of the storage material

Classical late-infantile neuronal ceroid lipofuscinosis (LINCL) is a fatal neurodegenerative disease of children caused by mutations in TPP1, the gene encoding the lysosomal protease tripeptidyl peptidase 1. LINCL is characterized by lysosomal accumulation of storage material of which only a single protein component, subunit c of mitochondrial ATP synthase, has been well established to date. Identification of other protein constituents of the storage material could provide useful insights into the pathophysiology of disease and the natural substrates for TPP1. We have therefore initiated a proteomic analysis of storage material in brain from a LINCL mouse model. One protein, GFAP (glial fibrillary acidic protein), was found to be elevated in the LINCL mice compared with normal controls in both isolated storage bodies and a lysosome-enriched subcellular fraction that contains storage material. To determine whether GFAP accumulates within the lysosome in LINCL, we examined its intracellular distribution using subcellular fractionation and morphological methods. These experiments demonstrate that GFAP is not a component of the storage material in LINCL, suggesting that reports of GFAP storage in other NCLs may need to be re-examined. A number of other proteins were elevated in the storage material and/or lysosome-enriched fraction from the LINCL mice, but it remains unclear whether these proteins are true constituents of the storage material or, like GFAP, whether they associate with this material upon purification.

Validation of disaccharide compositions derived from dermatan sulfate and heparan sulfate in mucopolysaccharidoses and mucolipidoses II and III by tandem mass spectrometry

Glycosaminoglycans (GAGs) are accumulated in various organs in both mucopolysaccharidoses (MPS) and mucolipidoses II and III (ML II and III). MPS and ML II and III patients can not properly degrade dermatan sulfate (DS) and/or heparan sulfate (HS). HS storage occurs in the brain leading to neurological signs while DS storage involves mainly visceral and skeletal manifestations. Excessive DS and HS released into circulation and thus blood levels of both are elevated, therefore, DS and HS in blood could be critical biomarkers for MPS and ML. Such measurement can provide a potential early screening, assessment of the clinical course and efficacy of therapies. We here assay DS and HS levels in MPS and ML patients using liquid chromatography tandem mass spectrometry (LC/MS/MS). Plasma samples were digested by heparitinase and chondroitinase B to obtain disaccharides of DS and HS, followed by LC/MS/MS analysis. One hundred-twenty samples from patients and 112 control samples were analyzed. We found that all MPS I, II, III and VI patients had a significant elevation of all DS+HS compositions analyzed in plasma, compared with the controls (P<0.0001). Specificity and sensitivity was 100% if the cut off value is 800 ng/ml between control and these types of MPS group. All MPS I, II and III patients also had a significant elevation of plasma HS, compared with the controls (P<0.0001). All MPS VI patients had a significant elevation of plasma DS, compared with the controls (P<0.0001). These findings suggest measurement of DS and/or HS levels by LC/MS/MS is applicable to the screening for MPS I, II, III and VI patients.

Non-invasive high-risk screening for Fabry disease hemizygotes and heterozygotes

The most appropriate time for screening for Fabry disease (FD) is school age. For this reason, we developed non-invasive methods for measuring urinary alpha-galactosidase A (alpha-gal A) protein, using enzyme-linked immunosorbent assay (ELISA), and for globotriaosylceramide (GL-3), using tandem mass spectrometry (MS/MS). We measured these two biomarkers in the urine of previously diagnosed FD hemizygotes and heterozygotes, and in controls. All the classic FD hemizygotes were clearly distinguished from controls by either method alone, and combining the two assays produced 96% sensitivity for detecting heterozygotes. To assess the utility of these methods for screening school children and adults at high risk of FD, a pilot study was conducted. To distinguish FD from 432 controls, cut-off values for alpha-gal A protein and GL-3 were set at the 5th and 95th centile values of the controls, respectively. Among the high-risk patients, the measurements exceeded the cut-off values for both biomarkers in male and female subjects and were strong indicators for Fabry hemizygotes and heterozygotes. However, we recommend that if the results of the first measurements exceed the cut-off values for only one of these biomarkers, another urine sample should be requested for re-assay to confirm the result.

Newborn screening for lysosomal storage disorders

Lysosomal storage disorders (LSD) are chronic progressive diseases that have a devastating impact on the patient and family. Most patients are clinically normal at birth but develop symptoms early in childhood. Despite no curative treatment, a number of therapeutic options are available to improve quality of life. To achieve this, there is a pressing need for newborn screening to identify affected individuals early, before the onset of severe irreversible pathology. We have developed a multiplexed immune-quantification assay of 11 different lysosomal proteins for the identification of individuals with an LSD and evaluated this assay in a retrospective study using blood-spots from; newborns subsequently diagnosed with an LSD (n=19, six different LSD), individuals sampled after diagnosis of an LSD (n=92, 11 different LSD), newborn controls (n=433), and adult controls (n=200). All patients with mucopolysaccharidosis type I (MPS I), MPS II, MPS IIIA, MPS VI, metachromatic leukodystrophy, Niemann-Pick disease type A/B, and multiple sulfatase deficiency could be identified by reduced enzyme levels compared to controls. All mucolipidosis type II/III patients were identified by the elevation of several lysosomal enzymes, above the control range. Most Fabry, Pompe, and Gaucher disease patients were identified from either single protein differences or profiles of multiple protein markers. Newborn screening for multiple LSD is achievable using multiplexed immune-quantification of a panel of lysosomal proteins. With further validation, this method could be readily incorporated into existing screening laboratories and will have a substantial impact on patient management and counseling of families.

Immunochemistry of lysosomal storage disorders

BACKGROUND

Lysosomal storage disorders are a group of genetic diseases, each with a broad spectrum of clinical presentation that ranges from attenuated to severe. The immunochemical analysis of patient samples is aimed at several key aspects of patient management, including early detection of the disorder, prediction of clinical severity, determining the most appropriate therapeutic regimen, and monitoring of patients on therapy.

METHODS

In this study, we review the current and emerging technology available to achieve these assessments.

RESULTS

Immune assays have direct practical application for the early detection, diagnosis and prognosis of lysosomal storage disorder patients. Multiplexing of these assays may provide a platform to allow newborn screening for multiple lysosomal storage disorders.

CONCLUSIONS

We have reviewed the immunochemical techniques available for the analysis of lysosomal storage disorder patient samples and advise that these may be used in conjunction with other technologies for effective patient management.

Detection of mucopolysaccharidosis type II by measurement of iduronate-2-sulfatase in dried blood spots and plasma samples

BACKGROUND

Mucopolysaccharidosis type II (MPS II) is a lysosomal storage disorder related to a deficiency in the enzyme iduronate-2-sulfatase (IDS). Clinical trials of enzyme replacement therapy are in progress, but effective treatment will require screening assays to enable early detection and diagnosis of MPS II. Our study evaluated the diagnostic accuracy of IDS protein and enzyme activity measurements in dried blood spots and plasma.

METHODS

We collected dried-blood-spot and plasma samples from unaffected control individuals and from MPS II patients. We measured IDS protein concentration with a 2-step time-delayed dissociation-enhanced lanthanide fluorescence immunoassay. To measure enzyme activity, we immobilized anti-IDS antibody on microtiter plates to capture the enzyme and measured its activity with the fluorogenic substrate 4-methylumbelliferyl sulfate.

RESULTS

Dried-blood-spot samples from MPS II patients showed an almost total absence of IDS activity (0-0.075 micromol x h(-1) x L(-1)) compared with control blood spots (0.5-4.7 micromol x h(-1) x L(-1)) and control plasma (0.17-8.1 micromol x h(-1) x L(-1)). A dried-blood-spot sample from only 1 of 12 MPS II patients had detectable concentrations of IDS protein (24.8 microg/L), but no IDS protein was detected in plasma from MPS II patients. Ranges for IDS protein in control samples were 25.8-153 microg/L for blood spots and 22.8-349.4 microg/L for plasma.

CONCLUSION

Measurement of the IDS protein concentration and enzyme activity (as measured by a simple fluorogenic assay with an immune capture technique) enables identification of the majority of MPS II patient samples from both dried blood spots and plasma samples.

[The biochemical diagnosis of Gaucher disease]

Gaucher disease is a disease of overload lyosomale which we often met since a score of years. Since 1980 we had to answer several requests for diagnosis of this metabolic disease. Requests emanating primarily from paediatric services. Twelve cases were confirmed within sight of measurement of the intra-leucocytic activity of the beta-glucocerebrosidase, enzyme intervening in the catabolism of the sphingolipides. We report here our experiment in the biochemical diagnosis of Gaucher disease by showing mainly the variability and the extreme heterogeneity of the activity of the beta-glucosidasic during practised measurements. In addition, we expose the problems of diagnosis etiologic which certain patients raise in front of the discordances between the measured enzymatic activity and clinical signs of the disease of left-handed person. In addition, we develop the biological parameters useful to proportion for the monitoring of the treatment which is finally available in our country.

Laronidase Treatment of Mucopolysaccharidosis I

The lysosomal storage disorder (LSD) mucopolysaccharidosis type I (MPS I, McKusick 25280, Hurler syndrome, Hurler-Scheie syndrome, Scheie syndrome) is caused by a deficiency in the lysosomal enzyme, alpha-L-iduronidase (EC 3.2.1.76). MPS I patients can present within a diverse clinical spectrum, ranging from classical Hurler syndrome to attenuated Scheie syndrome. Laronidase (Aldurazyme) enzyme replacement therapy has been developed as a treatment strategy for MPS I patients and has been approved for clinical practice. Here we review the pre-clinical studies and clinical trials that have been used to demonstrate that intravenous laronidase therapy is well tolerated and effective for treating MPS I patients who do not have neuronal pathology. Current challenges for a viable treatment strategy for all MPS I patients include development of an early screening protocol that identifies patients before the onset of irreversible pathology, methods to predict disease severity, appropriate treatment for neuropathology, and an effective patient monitoring regimen.

Determination of oligosaccharides and glycolipids in amniotic fluid by electrospray ionisation tandem mass spectrometry: in utero indicators of lysosomal storage diseases

Prenatal diagnosis is available for many lysosomal storage disorders (LSD) using chorionic villus samples or amniocytes. Such diagnoses can be problematical if sample transport and culture are required prior to analysis. The purpose of this study was to identify useful biochemical markers for the diagnosis of lysosomal storage disorders from amniotic fluid. Amniotic fluid samples from control (n=49) and LSD affected (n=36) pregnancies were analysed for the protein markers LAMP-1 and saposin C by ELISA, and for oligosaccharide and lipid metabolite markers by electrospray ionisation-tandem mass spectrometry. Lysosomal storage disorder samples include; aspartylglucosaminuria, galactosialidosis, Gaucher disease, GM1 gangliosidosis, mucopolysaccharidosis types I, II, IIIC, IVA, VI, and VII, mucolipidosis type II, multiple sulfatase deficiency, and sialidosis type II. Each disorder produced a unique signature metabolic profile of protein, oligosaccharide, and glycolipid markers. Some metabolite elevations directly related to the disorder whilst others appeared unrelated to the primary defect. Many lysosomal storage disorders were clearly distinguishable from control populations by the second trimester and in one case in the first trimester. Samples from GM1 gangliosidosis and mucopolysaccharidosis type VII displayed a correlation between gestational age and amount of stored metabolite. These preliminary results provide proof of principal for the use of biomarkers contained in amniotic fluid as clinical tests for some of the more frequent lysosomal storage disorders causal for hydrops fetalis.

Immunoquantification of α-Galactosidase: Evaluation for the Diagnosis of Fabry Disease

Background: Fabry disease is an X-linked inborn error of glycosphingolipid catabolism resulting from a deficiency of the lysosomal exoglycohydrolase, α-galactosidase. Enzyme replacement therapy is currently available for Fabry disease, but early diagnosis before the onset of irreversible pathology will be mandatory for successful treatment. Presymptomatic detection would be possible through the use of a newborn-screening program. We report on the use of sensitive assays for the measurement of α-galactosidase protein and activity and for the protein saposin C, which are diagnostic markers for Fabry disease.

Methods: Two sensitive immunoassays for the measurement of α-galactosidase activity and protein were used to determine the concentrations of α-galactosidase in dried filter-paper blood spots and plasma samples from control patients and patients with a lysosomal storage disorder (LSD).

Results: Fabry hemizygous individuals were clearly identified from control populations by decreases in both α-galactosidase activity and protein. Fabry heterozygotes generally fell between the hemizygotes and controls. Including the measurement of saposin C enabled differentiation between Fabry heterozygotes and controls. In blood spots, all Fabry individuals could be distinguished from control blood spots as well as from 16 other LSD patients.

Conclusions: The determination of α-galactosidase activity or protein in dried filter-paper blood spots could be used for the diagnosis of Fabry patients. With further validation, these assays could be used for the identification of Fabry patients in newborn-screening programs and may also be suitable for screening high-risk populations.

Newborn screening for lysosomal storage disorders: clinical evaluation of a two-tier strategy

OBJECTIVE

To evaluate the use of protein markers using immune-quantification assays and of metabolite markers using tandem mass spectrometry for the identification, at birth, of individuals who have a lysosomal storage disorder.

METHODS

A retrospective analysis was conducted of Guthrie cards that were collected from newborns in Denmark during the period 1982-1997. Patients whose lysosomal storage disorder (LSD; 47 representing 12 disorders) was diagnosed in Denmark during the period 1982-1997 were selected, and their Guthrie cards were retrieved from storage. Control cards (227) were retrieved from the same period. Additional control cards (273) were collected from the South Australian Screening Centre (Australia).

RESULTS

From 2 protein and 94 metabolite markers, 15 were selected and evaluated for their use in the identification of LSDs. Glycosphingolipid and oligosaccharide markers showed 100% sensitivity and specificity for the identification of Fabry disease, alpha-mannosidosis, mucopolysaccharidosis (MPS) IVA, MPS IIIA, Tay-Sachs disease, and I-cell disease. Lower sensitivities were observed for Gaucher disease and sialidosis. No useful markers were identified for Krabbe disease, MPS II, Pompe disease, and Sandhoff disease. The protein markers LAMP-1 and saposin C were not able to differentiate individuals who had an LSD from the control population.

CONCLUSIONS

Newborn screening for selected LSDs is possible with current technology. However, additional development is required to provide a broad coverage of disorders in a single, viable program.

Lysosomal storage disorders: diagnostic dilemmas and prospects for therapy

PURPOSE

The main purpose of this review is to address some concerns regarding the accurate and timely diagnosis of lysosomal storage disorders (LSD).

METHODS

Using their experience in diagnosing LSD in more than 2500 individuals, the authors highlight several diagnostic difficulties and solutions and review the latest methods for early diagnosis and treatment.

RESULTS

While "classic" patients can be accurately diagnosed using relatively simple methods in an experienced laboratory, atypical patients require more detailed studies. With a few exceptions, almost all LSD can be diagnosed in leukocytes or plasma. Methods for screening all newborns without a family history of a LSD have been proposed, but such screening may require a large amount of effort for little gain.

CONCLUSIONS

With effective therapy becoming available for some LSD, early diagnosis is critically important. If the goal is to prevent serious complications related to the nervous and skeletal systems, earlier diagnosis is potentially advantageous. Accurate prognosis and assessing the need for aggressive therapy in newly diagnosed patients are problems that need further study.

Correlation among genotype, phenotype, and biochemical markers in Gaucher disease: implications for the prediction of disease severity

Gaucher disease is a lysosomal storage disorder characterized by a deficiency of the enzyme acid beta-glucosidase. The clinical manifestations of Gaucher disease are highly variable, and although certain genotypes are often associated with mild or severe symptoms, a defined correlation between genotype and phenotype does not exist. Identification of biochemical markers characteristic of pathology may be of use in predicting the progression of the disease state. In this study the relationship among genotype, glycolipid substrates, lysosomal proteins, and the clinical manifestations of Gaucher disease has been evaluated. Plasma glycolipids were analyzed using electrospray ionization-tandem mass spectrometry. Lysosomal-associated membrane protein-1 (LAMP-1) and saposin C were determined by immunoquantification. Patients with Gaucher disease were shown to have an increased 16:0-glucosylceramide/16:0-lactosylceramide ratio and elevated concentrations of LAMP-1 and saposin C in plasma. A general relationship was found to exist among the 16:0-glucosylceramide/16:0-lactosylceramide ratio, LAMP-1 and saposin C levels, and patient phenotype, providing a refinement of the genotype-phenotype correlation. These findings have major implications for the diagnosis, prediction of disease severity, and monitoring of therapy in patients with Gaucher disease.

J3-crystallin of the jellyfish lens: similarity to saposins

J3-crystallin, one of the three major eye-lens proteins of the cubomedusan jellyfish (Tripedalia cystophora), shows similarity to vertebrate saposins, which are multifunctional proteins that bridge lysosomal hydrolases to lipids and activate enzyme activity. Sequence alignment of deduced J3-crystallin indicates two saposin-like motifs arranged in tandem, each containing six cysteines characteristic of this protein family. The J3-crystallin cDNA encodes a putative precursor analogous to vertebrate prosaposins. The J3-crystallin gene has seven exons, with exons 2-4 encoding the protein. Exon 3 encodes a circularly permutated saposin motif, called a swaposin, found in plant aspartic proteases. J3-crystallin RNA was found in the cubomedusan lens, statocyst, in bands radiating from the pigmented region of the ocellus, in the tentacle tip by in situ hybridization, and in the embryo and larva by reverse transcription-PCR. Our data suggest a crystallin role for the multifunctional saposin protein family in the jellyfish lens. This finding extends the gene sharing evolutionary strategy for lens crystallins to the cnidarians and indicates that the putative primordial saposin/swaposin J3-crystallin reflects both the chaperone and enzyme connections of the vertebrate crystallins.

Metabolic liver disease

The discovery of novel metabolic pathways and the genetic basis for diseases of the liver continues to yield new insights into the pathogenesis of inherited metabolic diseases of the liver, whereas the application of new technologies to their treatment continues to advance therapeutic options. This review of selected articles covers a wide range of subjects, from the identification of novel proteins and transport pathways to disease diagnosis and treatment of acute liver failure. Four selected topics, Wilson disease, hemochromatosis and iron overload disorders, alpha-1 antitrypsin disease, and exciting new therapeutic options for lysosomal storage diseases are the focus of this review.

Cellular pathology and pathogenic aspects of neuronal ceroid lipofuscinoses

Lysosomal accumulation of autofluorescent, ceroid lipopigment material in various tissues and organs is a common feature of the neuronal ceroid lipofuscinoses (NCLs). However, recent clinicopathologic and genetic studies have evidenced that NCLs encompass a group of highly heterogeneous disorders. In five of the eight NCL variants distinguished at present, genes associated with the disease process have been isolated and characterized (CLN1, CLN2, CLN3, CLN5, CLN8). Only products of two of these genes, CLN 1 and CLN2, have structural and functional properties of lysosomal enzymes. Nevertheless, according to the nature of the material accumulated in the lysosomes, NCLs in humans as well as natural animal models of these disorders can be divided into two major groups: those characterized by the prominent storage of saposins A and D, and those showing the predominance of subunit c of mitochondrial ATP synthase accumulation. Thus, taking into account the chemical character of the major component of the storage material, NCLs can be classified currently as proteinoses. Of importance, although lysosomal storage material accumulates in NCL subjects in various organs, only brain tissue shows severe dysfunction and cell death, another common feature of the NCL disease process. However, the relation between the genetic defects associated with the NCL forms, the accumulation of storage material, and tissue damage is still unknown. This chapter introduces the reader to the complex pathogenesis of NCLs and summarizes our current knowledge of the potential consequences of the genetic defects of NCL-associated proteins on the biology of the cell.

Are there useful biochemical markers of disease activity in lysosomal storage diseases?

The primary biochemical consequence of a defect in a gene encoding a functional component of the lysosomal system is disruption of the catabolism or processing of macromolecules in the lumen of the lysosome. Transport of the resulting digestion products through the lysosomal membrane may also be affected. This leads to the accumulation of specific metabolites within the lysosomes of affected cells. The nature of these storage products depends upon the functional protein affected and the cell type. The accumulation of storage products is progressive and leads to hypertrophy of the lysosomal system, the hallmark of lysosomal storage diseases (LSDs). Subsequent cell necrosis or, possibly, exocytosis results in the appearance in body fluids of the storage products and components of the lysosomes at much higher concentrations than seen in normal unaffected individuals. Measurement of these increased levels of metabolites and proteins provides disease-specific and generic biochemical markers for LSDs. Secondary changes in metabolism and cellular function may also produce characteristic changes in the levels of metabolites or proteins, which can also be used as markers of the disease process. Although the rate of appearance of these biochemical markers in an individual will depend upon the underlying mutation in the gene and on other genetic and environmental factors, it provides a good indicator of the progression of the disease. As the novel forms of treatment being developed may reverse the hypertrophy of the lysosomal system, biochemical markers could also be used to monitor the reversal of pathology and the efficacy of treatment.