Proteomics of specific treatment-related alterations in Fabry disease: a strategy to identify biological abnormalities

Characterization of the plasma proteomic profile of Fabry disease: Potential sex- and clinical phenotype-specific biomarkers

Fabry disease (FD) is a X-linked rare lysosomal storage disorder caused by deficient α-galactosidase A (α-GalA) activity. Early diagnosis and the prediction of disease course are complicated by the clinical heterogeneity of FD, as well as by the frequently inconclusive biochemical and genetic test results that do not correlate with clinical course. We sought to identify potential biomarkers of FD to better understand the underlying pathophysiology and clinical phenotypes. We compared the plasma proteomes of 50 FD patients and 50 matched healthy controls using DDA and SWATH-MS. The >30 proteins that were differentially expressed between the 2 groups included proteins implicated in processes such as inflammation, heme and haemoglobin metabolism, oxidative stress, coagulation, complement cascade, glucose and lipid metabolism, and glycocalyx formation. Stratification by sex revealed that certain proteins were differentially expressed in a sex-dependent manner. Apolipoprotein A-IV was upregulated in FD patients with complications, especially those with chronic kidney disease, and apolipoprotein C-III and fetuin-A were identified as possible markers of FD with left ventricular hypertrophy. All these proteins had a greater capacity to identify the presence of complications in FD patients than lyso-GB3, with apolipoprotein A-IV standing out as being more sensitive and effective in differentiating the presence and absence of chronic kidney disease in FD patients than renal markers such as creatinine, glomerular filtration rate and microalbuminuria. Identification of these potential biomarkers can help further our understanding of the pathophysiological processes that underlie the heterogeneous clinical manifestations associated with FD.

Inflammatory and Cardiovascular Biomarkers to Monitor Fabry Disease Progression

Fabry disease is an invalidating multisystemic disorder affecting α-Galactosidase, a rate-limiting hydrolase dedicated to lipid catabolism. Non-metabolized substrates, such as Globotriaosylceramide and its derivatives trigger the direct or indirect activation of inflammatory events and endothelial dysfunction. In spite of the efficacy demonstrated by enzyme replacement therapy or pharmacological chaperones in delaying disease progression, few studies have analyzed whether these treatments can improve the pro-inflammatory state of FD patients. Therefore, the aim of this work was to assess cytokines and cardiovascular risk-related proteins detectable in plasma from FD patients, whether treated or not with ERT, to evaluate the reliability of these markers in monitoring disease stage and treatment effects. We identified inflammatory and endothelial dysfunction markers (ADAMTS-13, TNF-α, GDF-15, MIP-1β, VEGFA, MPO, and MIC-1) that cooperate in a common pathway and are increased in FD patients' plasma samples. As shown by the assessment of these proteins over time, they can help to evaluate the risk of higher severity in FD, as well as ERT effects. Even though the analyzed proteins cannot be considered as proper biomarkers due to their non-specificity to FD, taken together they can provide a signature of reference molecules with prognostic value for early diagnosis, and evaluation of disease progression and treatment efficacy, using blood samples.

Exploring Pro-Inflammatory Immunological Mediators: Unraveling the Mechanisms of Neuroinflammation in Lysosomal Storage Diseases

Lysosomal storage diseases are a group of rare and ultra-rare genetic disorders caused by defects in specific genes that result in the accumulation of toxic substances in the lysosome. This excess accumulation of such cellular materials stimulates the activation of immune and neurological cells, leading to neuroinflammation and neurodegeneration in the central and peripheral nervous systems. Examples of lysosomal storage diseases include Gaucher, Fabry, Tay–Sachs, Sandhoff, and Wolman diseases. These diseases are characterized by the accumulation of various substrates, such as glucosylceramide, globotriaosylceramide, ganglioside GM2, sphingomyelin, ceramide, and triglycerides, in the affected cells. The resulting pro-inflammatory environment leads to the generation of pro-inflammatory cytokines, chemokines, growth factors, and several components of complement cascades, which contribute to the progressive neurodegeneration seen in these diseases. In this study, we provide an overview of the genetic defects associated with lysosomal storage diseases and their impact on the induction of neuro-immune inflammation. By understanding the underlying mechanisms behind these diseases, we aim to provide new insights into potential biomarkers and therapeutic targets for monitoring and managing the severity of these diseases. In conclusion, lysosomal storage diseases present a complex challenge for patients and clinicians, but this study offers a comprehensive overview of the impact of these diseases on the central and peripheral nervous systems and provides a foundation for further research into potential treatments.

Proteomic Approaches and Potential Applications in Autosomal Dominant Polycystic Kidney Disease and Fabry Disease

Although rare, hereditary diseases, such as autosomal dominant polycystic kidney disease (ADPKD) and Fabry disease (FD) may significantly progress towards severe nephropathy. It is crucial to characterize it accurately, predict the course of the illness and estimate treatment effectiveness. A huge effort has been undertaken to find reliable biomarkers that might be useful for an early prevention of the disease progression and/or any invasive diagnostic procedures. The study of proteomics, or the small peptide composition of a sample, is a field of study under continuous development. Over the past years, several strategies have been created to study and define the proteome of samples from widely varying origins. However, urinary proteomics has become essential for discovering novel biomarkers in kidney disease. Here, the extracellular vesicles in human urine that contain cell-specific marker proteins from every segment of the nephron, offer a source of potentially valuable urinary biomarkers, and may play an essential role in kidney development and kidney disease. This review summarizes the relevant literature investigating the proteomic approaches and potential applications in the regular studies of ADPKD and FD.

Deep next-generation proteomics and network analysis reveal systemic and tissue-specific patterns in Fabry disease

Fabry disease (FD) is an X-linked lysosomal rare disease due to a deficiency of α-galactosidase A activity. The accumulation of glycosphingolipids mainly affects the kidney, heart, and central nervous system, considerably reducing life expectancy. Although the accumulation of undegraded substrate is considered the primary cause of FD, it is established that secondary dysfunctions at the cellular, tissue, and organ levels ultimately give rise to the clinical phenotype. To parse this biological complexity, a large-scale deep plasma targeted proteomic profiling has been performed. We analyzed the plasma protein profiles of FD deeply phenotyped patients (n = 55) compared to controls (n = 30) using next-generation plasma proteomics including 1463 proteins. Systems biology and machine learning approaches have been used. The analysis enabled the identification of proteomic profiles that unambiguously separated FD patients from controls (615 differentially expressed proteins, 476 upregulated, and 139 downregulated) and 365 proteins are newly reported. We observed functional remodeling of several processes, such as cytokine-mediated pathways, extracellular matrix, and vacuolar/lysosomal proteome. Using network strategies, we probed patient-specific tissue metabolic remodeling and described a robust predictive consensus protein signature including 17 proteins CD200, SPINT1, CD34, FGFR2, GRN, ERBB4, AXL, ADAM15, PTPRM, IL13RA1, NBL1, NOTCH1, VASN, ROR1, AMBP, CCN3, and HAVCR2. Our findings highlight the pro-inflammatory cytokines' involvement in FD pathogenesis along with extracellular matrix remodeling. The study shows a tissue-wide metabolic remodeling connection to plasma proteomics in FD. These results will facilitate further studies to understand the molecular mechanisms in FD to pave the way for better diagnostics and therapeutics.

Dysregulated DNA methylation in the pathogenesis of Fabry disease

Fabry disease is an X-linked lysosomal storage disorder caused by a deficiency of α-galactosidase A and subsequent accumulation of glycosphingolipids with terminal α-D-galactosyl residues. The molecular process through which this abnormal metabolism of glycosphingolipids causes multisystem dysfunction in Fabry disease is not fully understood. We sought to determine whether dysregulated DNA methylation plays a role in the development of this disease. In the present study, using isogenic cellular models derived from Fabry patient endothelial cells, we tested whether manipulation of α-galactosidase A activity and glycosphingolipid metabolism affects DNA methylation. Bisulfite pyrosequencing revealed that changes in α-galactosidase A activity were associated with significantly altered DNA methylation in the androgen receptor promoter, and this effect was highly CpG loci-specific. Methylation array studies showed that α-galactosidase A activity and glycosphingolipid levels were associated with differential methylation of numerous CpG sites throughout the genome. We identified 15 signaling pathways that may be susceptible to methylation alterations in Fabry disease. By incorporating RNA sequencing data, we identified 21 genes that have both differential mRNA expression and methylation. Upregulated expression of collagen type IV alpha 1 and alpha 2 genes correlated with decreased methylation of these two genes. Methionine levels were elevated in Fabry patient cells and Fabry mouse tissues, suggesting that a perturbed methionine cycle contributes to the observed dysregulated methylation patterns. In conclusion, this study provides evidence that α-galactosidase A deficiency and glycosphingolipid storage may affect DNA methylation homeostasis and highlights the importance of epigenetics in the pathogenesis of Fabry disease and, possibly, of other lysosomal storage disorders.

Metabolic Fingerprinting of Fabry Disease: Diagnostic and Prognostic Aspects

Fabry disease (FD) is an X-linked lysosomal disease due to a deficiency in the activity of the lysosomal-galactosidase A (GalA), a key enzyme in the glycosphingolipid degradation pathway. FD is a complex disease with a poor genotype–phenotype correlation. In the early stages, FD could involve the peripheral nervous system (acroparesthesias and dysautonomia) and the ski (angiokeratoma), but later kidney, heart or central nervous system impairment may significantly decrease life expectancy. The advent of omics technologies offers the possibility of a global, integrated and systemic approach well-suited for the exploration of this complex disease. In this narrative review, we will focus on the main metabolomic studies, which have underscored the importance of detecting biomarkers for a diagnostic and prognostic purpose in FD. These investigations are potentially useful to explain the wide clinical, biochemical and molecular heterogeneity found in FD patients. Moreover, the quantitative mass spectrometry methods developed to evaluate concentrations of these biomarkers in urine and plasma will be described. Finally, the complex metabolic biomarker profile depicted in FD patients will be reported, which varies according to gender, types of mutations, and therapeutic treatment.

Mass spectrometry-based proteomics in neurodegenerative lysosomal storage disorders

The major function of the lysosome is to degrade unwanted materials such as lipids, proteins, and nucleic acids; therefore, deficits of the lysosomal system can result in improper degradation and trafficking of these biomolecules. Diseases associated with lysosomal failure can be lethal and are termed lysosomal storage disorders (LSDs), which affect 1 in 5000 live births collectively. LSDs are inherited metabolic diseases caused by mutations in single lysosomal and non-lysosomal proteins and resulting in the subsequent accumulation of macromolecules within. Most LSD patients present with neurodegenerative clinical symptoms, as well as damage in other organs. The discovery of new biomarkers is necessary to understand and monitor these diseases and to track therapeutic progress. Over the past ten years, mass spectrometry (MS)-based proteomics has flourished in the biomarker studies in many diseases, including neurodegenerative, and more specifically, LSDs. In this review, biomarkers of disease pathophysiology and monitoring of LSDs revealed by MS-based proteomics are discussed, including examples from Niemann-Pick disease type C, Fabry disease, neuronal ceroid-lipofuscinoses, mucopolysaccharidosis, Krabbe disease, mucolipidosis, and Gaucher disease.

Parsing Fabry Disease Metabolic Plasticity Using Metabolomics

Background: Fabry disease (FD) is an X-linked lysosomal disease due to a deficiency in the activity of the lysosomal α-galactosidase A (GalA), a key enzyme in the glycosphingolipid degradation pathway. FD is a complex disease with a poor genotype–phenotype correlation. FD could involve kidney, heart or central nervous system impairment that significantly decreases life expectancy. The advent of omics technologies offers the possibility of a global, integrated and systemic approach well-suited for the exploration of this complex disease. Materials and Methods: Sixty-six plasmas of FD patients from the French Fabry cohort (FFABRY) and 60 control plasmas were analyzed using liquid chromatography and mass spectrometry-based targeted metabolomics (188 metabolites) along with the determination of LysoGb3 concentration and GalA enzymatic activity. Conventional univariate analyses as well as systems biology and machine learning methods were used. Results: The analysis allowed for the identification of discriminating metabolic profiles that unambiguously separate FD patients from control subjects. The analysis identified 86 metabolites that are differentially expressed, including 62 Glycerophospholipids, 8 Acylcarnitines, 6 Sphingomyelins, 5 Aminoacids and 5 Biogenic Amines. Thirteen consensus metabolites were identified through network-based analysis, including 1 biogenic amine, 2 lysophosphatidylcholines and 10 glycerophospholipids. A predictive model using these metabolites showed an AUC-ROC of 0.992 (CI: 0.965–1.000). Conclusion: These results highlight deep metabolic remodeling in FD and confirm the potential of omics-based approaches in lysosomal diseases to reveal clinical and biological associations to generate pathophysiological hypotheses.

Proteomics for the study of new biomarkers in Fabry disease: State of the art

Nephropathy represents a major complication of Fabry Disease and its accurate characterization is of paramount importance in predicting the disease progression and assessing the therapeutic responses. The diagnostic process still relies on performing renal biopsy, nevertheless many efforts have been made to discover early reliable biomarkers allowing us to avoid invasive procedures. In this field, proteomics offers a sensitive and fast method leading to an accurate detection of specific pathological proteins and the discovery of diagnostic and prognostic biomarkers that reflect disease progression and facilitate the evaluation of therapeutic responses. Here, we report a review of selected literature focusing on the investigation of several proteomic techniques highlighting their advantages, limitations and future perspectives in their application in the routine study of Fabry Nephropathy.

Fabry disease and COVID-19: international expert recommendations for management based on real-world experience

The rapid spread of coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 has raised questions about Fabry disease (FD) as an independent risk factor for severe COVID-19 symptoms. Available real-world data on 22 patients from an international group of healthcare providers reveals that most patients with FD experience mild-to-moderate COVID-19 symptoms with an additional complication of Fabry pain crises and transient worsening of kidney function in some cases; however, two patients over the age of 55 years with renal or cardiac disease experienced critical COVID-19 complications. These outcomes support the theory that pre-existent tissue injury and inflammation may predispose patients with more advanced FD to a more severe course of COVID-19, while less advanced FD patients do not appear to be more susceptible than the general population. Given these observed risk factors, it is best to reinforce all recommended safety precautions for individuals with advanced FD. Diagnosis of FD should not preclude providing full therapeutic and organ support as needed for patients with FD and severe or critical COVID-19, although a FD-specific safety profile review should always be conducted prior to initiating COVID-19-specific therapies. Continued specific FD therapy with enzyme replacement therapy, chaperone therapy, dialysis, renin-angiotensin blockers or participation to clinical trials during the pandemic is recommended as FD progression will only increase susceptibility to infection. In order to compile outcome data and inform best practices, an international registry for patients affected by Fabry and infected by COVID-19 should be established.

Biomarkers of Fabry Nephropathy: Review and Future Perspective

Progressive nephropathy is one of the main features of Fabry disease, which largely contributes to the overall morbidity and mortality burden of the disease. Due to the lack of specific biomarkers, the heterogeneity of the disease, and unspecific symptoms, diagnosis is often delayed. Clinical presentation in individual patients varies widely, even in patients from the same family carrying the same pathogenic GLA variant. Therefore, it is reasonable to anticipate that additional genomic, transcriptomic, proteomic, and metabolomics factors influence the manifestation and progression of the disease. The aim of this article is to provide an overview of nephropathy in Fabry patients and the biomarkers currently used in the diagnosis and follow-up. Current biomarkers are associated with late signs of kidney damage. Therefore, there is a need to identify biomarkers associated with early stages of kidney damage that would enable early diagnosis, which is crucial for effective treatment and prevention of severe irreversible complications. Recent advances in sequencing and -omics technologies have led to several studies investigating new biomarkers. We will provide an overview of the novel biomarkers, critically evaluate their clinical utility, and propose future perspectives, which we believe might be in their integration.

A Proteomics-Based Analysis Reveals Predictive Biological Patterns in Fabry Disease

Background: Fabry disease (FD) is an X-linked progressive lysosomal disease (LD) due to glycosphingolipid metabolism impairment. Currently, plasmatic globotriaosylsphingosine (LysoGb3) is used for disease diagnosis and monitoring. However, this biomarker is inconstantly increased in mild forms and in some female patients. Materials and Methods: We applied a targeted proteomic approach to explore disease-related biological patterns that might explain the disease pathophysiology. Forty proteins, involved mainly in inflammatory and angiogenesis processes, were assessed in 69 plasma samples retrieved from the French Fabry cohort (FFABRY) and from 83 healthy subjects. For predictive performance assessment, we also included other LD samples (Gaucher, Pompe and Niemann Pick C). Results: The study yielded four discriminant proteins that include three angiogenesis proteins (fibroblast growth factor 2 (FGF2), vascular endothelial growth factor A (VEGFA), vascular endothelial growth factor C (VEGFC)) and one cytokine interleukin 7 (IL-7). A clear elevation of FGF2 and IL-7 concentrations was observed in FD compared to other LD samples. No correlation was observed between these proteins and globotriaosylsphingosine (LysoGb3). A significant correlation exists between IL-7 and residual enzyme activity in a non-classical phenotype. This highlights the orthogonal biological information yielded by these proteins that might help in stratifying Fabry patients. Conclusion: This work highlights the potential of using proteomics approaches in exploring FD and enhancing FD diagnosis and therapeutic monitoring performances.

Circulating microRNAs in Fabry Disease

Fabry disease is an X-linked deficiency of the lysosomal hydrolase alpha-galactosidase A (alpha-Gal). This results in an accumulation of globotriaosylceramide (GL-3/Gb3) in a variety of cells with subsequent functional impairment. The continuous progress of FD often leads to decreased quality of life and premature death caused by multi-organic complications. The overall aim of our study was to determine the amount of circulating miRNAs in Fabry patients and to test whether ERT would alter the level of individual circulating miRNAs. We used miRNA sequencing by the HTG EdgeSeq System to identify the circulating miRNA pool from Fabry patients with and without enzyme replacement therapy (n = 6). In total, 296 miRNAs in serum of patients were identified. Among them 9 miRNAs were further evaluated in extra serum samples (n = 31) using real-time qPCR and 6 of them showed significant differential expression. The resulting miRNA pattern may help to better understand mechanisms involved in the beneficial effects of ERT and these new miRNA markers could help to estimate the efficacy of ERT or to identify Fabry patients with specific need for ERT.

Quantitative Microproteomics Based Characterization of the Central and Peripheral Nervous System of a Mouse Model of Krabbe Disease

Krabbe disease is a rare, childhood lysosomal storage disorder caused by a deficiency of galactosylceramide beta-galactosidase (GALC). The major effect of GALC deficiency is the accumulation of psychosine in the nervous system and widespread degeneration of oligodendrocytes and Schwann cells, causing rapid demyelination. The molecular mechanisms of Krabbe disease are not yet fully elucidated and a definite cure is still missing. Here we report the first in-depth characterization of the proteome of the Twitcher mouse, a spontaneous mouse model of Krabbe disease, to investigate the proteome changes in the Central and Peripheral Nervous System. We applied a TMT-based workflow to compare the proteomes of the corpus callosum, motor cortex and sciatic nerves of littermate homozygous Twitcher and wild-type mice. More than 400 protein groups exhibited differences in expression and included proteins involved in pathways that can be linked to Krabbe disease, such as inflammatory and defense response, lysosomal proteins accumulation, demyelination, reduced nervous system development and cell adhesion. These findings provide new insights on the molecular mechanisms of Krabbe disease, representing a starting point for future functional experiments to study the molecular pathogenesis of Krabbe disease. Data are available via ProteomeXchange with identifier PXD010594.

Pharmaceutical Advances and Proteomics Researches

Proteomics enables understanding the composition, structure, function and interactions of the entire protein complement of a cell, a tissue, or an organism under exactly defined conditions. Some factors such as stress or drug effects will change the protein pattern and cause the present or absence of a protein or gradual variation in abundances. The aim of this study is to explore relationship between proteomics application and drug discovery. "proteomics", "Application", and "pharmacology were the main keywords that were searched in PubMed (PubMed Central), Web of Science, and Google Scholar. The titles that were stablished by 2019, were studied and after study of the appreciated abstracts, the full texts of the 118 favor documents were extracted. Changes in the proteome provide a snapshot of the cell activities and physiological processes. Proteomics shows the observed protein changes to the causal effects and generate a complete three-dimensional map of the cell indicating their exact location. Proteomics is used in different biological fields and is applied in medicine, agriculture, food microbiology, industry, and pharmacy and drug discovery. Biomarker discovery, follow up of drug effect on the patients, and in vitro and in vivo proteomic investigation about the drug treated subjects implies close relationship between proteomics advances and application and drug discovery and development. This review overviews and summarizes the applications of proteomics especially in pharmacology and drug discovery.

Elevated Inflammatory Plasma Biomarkers in Patients With Fabry Disease: A Critical Link to Heart Failure With Preserved Ejection Fraction

Background Because systemic inflammation and endothelial dysfunction lead to heart failure with preserved ejection fraction, we characterized plasma levels of inflammatory and cardiac remodeling biomarkers in patients with Fabry disease ( FD ). Methods and Results Plasma biomarkers were studied in multicenter cohorts of patients with FD (n=68) and healthy controls (n=40). Plasma levels of the following markers of inflammation and cardiac remodeling were determined: tumor necrosis factor ( TNF ), TNF receptor 1 ( TNFR 1) and 2 ( TNFR 2), interleukin-6, matrix metalloprotease-2 ( MMP -2), MMP -8, MMP -9, galectin-1, galectin-3, B-type natriuretic peptide ( BNP ), midregional pro-atrial natriuretic peptide ( MR -pro ANP ), and globotriaosylsphingosine. Clinical profile, cardiac magnetic resonance imaging, and echocardiogram were reviewed and correlated with biomarkers. Patients with FD had elevated plasma levels of BNP , MR -pro ANP , MMP -2, MMP -9, TNF , TNFR 1, TNFR 2, interleukin-6, galectin-1, globotriaosylsphingosine, and analogues. Plasma TNFR 2, TNF , interleukin-6, MMP -2, and globotriaosylsphingosine were elevated in FD patients with left ventricular hypertrophy, whereas diastolic dysfunction correlated with higher BNP , MR -pro ANP , and MMP -2 levels. Patients with late gadolinium enhancement on cardiac magnetic resonance imaging had greater levels of BNP , MR -pro ANP , TNFR 1, TNFR 2, and MMP -2. Plasma BNP , MR -pro ANP , MMP -2, MMP -8, TNF , TNFR 1, TNFR 2, galectin-1, and galectin-3 were elevated in patients with renal dysfunction. Patients undergoing enzyme replacement therapy who have more severe disease had higher MMP -2, TNF , TNFR 1, TNFR 2, and globotriaosylsphingosine analogue levels. Conclusions Inflammatory and cardiac remodeling biomarkers are elevated in FD patients and correlate with disease progression. These features are consistent with a phenotype dominated by heart failure with preserved ejection fraction and suggest a key pathogenic role of systemic inflammation in FD .

Inhibition of Arachidonate 12/15-Lipoxygenase Improves α-Galactosidase Efficacy in iPSC-Derived Cardiomyocytes from Fabry Patients

(1) Background: A high incidence of intervening sequence (IVS)4+919 G>A mutation with later-onset cardiac phenotype have been reported in a majority of Taiwan Fabry cohorts. Some evidence indicated that conventional biomarkers failed to predict the long-term progression and therapeutic outcome; (2) Methods: In this study, we constructed an induced pluripotent stem cell (iPSC)-based platform from Fabry cardiomyopathy (FC) patients carrying IVS4+919 G>A mutation to screen for potential targets that may help the conventional treatment; (3) Results: The FC-patient-derived iPSC-differentiated cardiomyocytes (FC-iPSC-CMs) carried an expected IVS4+919 G>A genetic mutation and recapitulated several FC characteristics, including low α-galactosidase A enzyme activity and cellular hypertrophy. The proteomic analysis revealed that arachidonate 12/15-lipoxygenase (Alox12/15) was the most highly upregulated marker in FC-iPSC-CMs, and the metabolites of Alox12/15, 12(S)- and 15(S)-hydroxyeicosatetraenoic acid (HETE), were also elevated in the culture media. Late administration of Alox12/15 pharmacological inhibitor LOXBlock-1 combined with α-galactosidase, but not α-galactosidase alone, effectively reduced cardiomyocyte hypertrophy, the secretion of 12(S)- and 15(S)-HETE and the upregulation of fibrotic markers at the late phase of FC; (4) Conclusions: Our study demonstrates that cardiac Alox12/15 and circulating 12(S)-HETE/15(S)-HETE are involved in the pathogenesis of FC with IVS4+919 G>A mutation.

Pediatric endocrine and metabolic diseases and proteomics

The principles of Predictive, Preventive and Personalized Medicine (PPPM) dictate the need to recognize individual susceptibility to disease in a timely fashion and to offer targeted preventive interventions and treatments. Proteomics is a state-of-the art technology- driven science aiming at expanding our understanding of the pathophysiologic mechanisms that underlie disease, but also at identifying accurate predictive, diagnostic and therapeutic biomarkers, that will eventually promote the implementation of PPPM. In this review, we summarize the wide spectrum of the applications of Mass Spectrometry-based proteomics in the various fields of Pediatric Endocrinology, including Inborn Errors of Metabolism, type 1 diabetes, Adrenal Disease, Metabolic Syndrome and Thyroid disease, ranging from neonatal screening to early recognition of specific at-risk populations for disease manifestations or complications in adult life and to monitoring of disease progression and response to treatment.

SIGNIFICANCE

Proteomics is a state-of-the art technology- driven science aiming at expanding our understanding of the pathophysiologic mechanisms that underlie disease, but also at identifying accurate predictive, diagnostic and therapeutic biomarkers that will eventually lead to successful, targeted, patient-centric, individualized approach of each patient, as dictated by the principles of Predictive, Preventive and Personalized Medicine. In this review, we summarize the wide spectrum of the applications of Mass Spectrometry-based proteomics in the various fields of Pediatric Endocrinology, including Inborn Errors of Metabolism, type 1 diabetes, Adrenal Disease, Metabolic Syndrome and Thyroid disease, ranging from neonatal screening, accurate diagnosis, early recognition of specific at-risk populations for the prevention of disease manifestation or future complications.

Fabry disease: characterisation of the plasma proteome pre- and post-enzyme replacement therapy

Background

Fabry disease is characterised by the progressive accumulation of globotriaosylceramide (Gb3) and related glycosphingolipids in vascular endothelial cells. Enzyme replacement therapy (ERT) clears this accumulation. We analysed plasma proteome profiles before and after ERT to characterise its molecular pathology.

Methods

Two-dimensional electrophoresis and matrix-assisted laser desorption/ionisation-time of flight tandem mass spectrometry (MALDI-TOF MS) and tandem mass spectrometry (MS/MS) were done using plasma samples before and after ERT in eight patients with classical Fabry disease

Results

After short-term ERT (4–12 months), the levels of 15 plasma proteins involved in inflammation, oxidative and ischaemic injury, or complement activation were reduced significantly. Among them, β-actin (ACTB), inactivated complement C3b (iC3b), and C4B were elevated significantly in pre-ERT Fabry disease plasma compared with control plasma. After longer-term ERT (46–96 months), iC3b levels gradually decreased, whereas the levels of other proteins varied. The gradual reduction of iC3b was comparable to that of Gb3 levels. In addition, iC3b increased significantly in pre-ERT Fabry disease mouse plasma, and C3 deposits were notable in renal tissues of pre-enzyme replacement therapy patients.

Conclusion

These results indicated that C3-mediated complement activation might be altered in Fabry disease and ERT might promote its stabilisation.

Integrative Systems Biology Investigation of Fabry Disease

Fabry disease (FD) is a rare X-linked recessive genetic disorder caused by a deficient activity of the lysosomal enzyme alpha-galactosidase A (GLA) and is characterised by intra-lysosomal accumulation of globotriaosylceramide (Gb3). We performed a meta-analysis of peer-reviewed publications including high-throughput omics technologies including naïve patients and those undergoing enzyme replacement therapy (ERT). This study describes FD on a systems level using a systems biology approach, in which molecular data sourced from multi-omics studies is extracted from the literature and integrated as a whole in order to reveal the biochemical processes and molecular pathways potentially affected by the dysregulation of differentially expressed molecules. In this way new insights are provided that describe the pathophysiology of this rare disease. Using gene ontology and pathway term clustering, FD displays the involvement of major biological processes such as the acute inflammatory response, regulation of wound healing, extracellular matrix (ECM) remodelling, regulation of peptidase activity, and cellular response to reactive oxygen species (ROS). Differential expression of acute-phase response proteins in the groups of naïve (up-regulation of ORM1, ORM2, ITIH4, SERPINA3 and FGA) and ERT (down-regulation of FGA, ORM1 and ORM2) patients could be potential hallmarks for distinction of these two patient groups.

Fabry Disease: A Disorder of Childhood Onset

BACKGROUND

Fabry disease, an X-linked disorder of glycosphingolipids, markedly increases the risk of systemic vasculopathy, ischemic stroke, small-fiber peripheral neuropathy, cardiac dysfunction, and chronic kidney disease.

METHODS

We performed an extensive PubMed search on the topic of Fabry disease and drew from our cumulative 43 years of experience.

RESULTS

Most of these complications are nonspecific in nature and clinically indistinguishable from similar abnormalities that occur in the context of more common disorders in the general population. This disease is caused by variants of the GLA gene, and its incidence may have been underestimated. However, one must also guard against overdiagnosis of Fabry disease and unjustified enzyme replacement therapy, because some of the gene variants are benign. Specific therapy for Fabry disease has been developed in the last few years, but its clinical effect has been modest. Novel therapeutic agents are being developed. Standard "nonspecific" medical and surgical therapy is necessary and effective in slowing deterioration or compensating for organ failure in patients with Fabry disease.

CONCLUSIONS

Fabry disease is a treatable and modifiable genetic risk factor for a myriad of clinical organ complications. Fabry disease may be frequently overlooked but on occasion overdiagnosed.

Early markers of Fabry disease revealed by proteomics

Fabry disease (FD) is an X-linked lysosomal storage disorder caused by a deficiency of the lysosomal hydrolase α-galactosidase A (α-GalA) that leads to the intra-lysosomal accumulation of globotriaosylceramide (Gb3) in various organ systems. As a consequence, a multisystems disorder develops, culminating in stroke, progressive renal and cardiac dysfunction. Enzyme replacement therapy (ERT) offers a specific treatment for patients affected by FD, though the monitoring of treatment is hindered by a lack of surrogate markers of response. Remarkably, due to the high heterogeneity of the Fabry phenotype, both diagnostic testing and treatment decisions are more challenging in females than in males; thus, reliable biomarkers for Fabry disease are needed, particularly for female patients. Here, we use a proteomic approach for the identification of disease-associated markers that can be used for the early diagnosis of FD as well as for monitoring the effectiveness of ERT. Our data show that the urinary proteome of Fabry naïve patients is different from that of normal subjects. In addition, biological pathways mainly affected by FD are related to immune response, inflammation, and energetic metabolism. In particular, the up-regulation of uromodulin, prostaglandin H2 d-isomerase and prosaposin in the urine of FD patients was demonstrated; these proteins might be involved in kidney damage at the tubular level, inflammation and immune response. Furthermore, comparing the expression of these proteins in Fabry patients before and after ERT treatment, a decrease of their concentration was observed, thus demonstrating the correlation between the identified markers and the effectiveness of the pharmacological treatment.

Gender-specific plasma proteomic biomarkers in patients with Anderson-Fabry disease

AIMS

Anderson-Fabry disease (AFD) is an important X-linked metabolic disease resulting in progressive end-organ involvement, with cardiac disease being the dominant determinant of survival in a gender-dependent manner. Recent epidemiological screening for AFD suggests the prevalence is much higher than previously recognized, with estimates of 1:3000. Our aim was to discover novel plasma biomarker signatures in adult patients with AFD.

METHODS AND RESULTS

We used an unbiased proteomic screening approach to discover novel plasma biomarker signatures. In the discovery cohort of 46 subjects, 14 healthy controls and 32 patients with AFD, we used a mass spectrometry iTRAQ proteomic approach followed by multiple reaction monitoring (MRM) assays to identify biomarkers. Of the 38 protein groups discovered by iTRAQ, 18 already had existing MRM assays. Based on MRM, we identified an eight-protein biomarker panel (22 kDa protein, afamin, α1 antichymotrypsin, apolipoprotein E, β-Ala His dipeptidase, haemoglobin α-2, isoform 1 of sex hormone-binding globulin, and peroxiredoxin 2) that was very specific and sensitive for male AFD patients. In female AFD patients, we identified a nine-marker panel of proteins with only three proteins, apolipoprotein E, haemoglobin α-2, and peroxiredoxin 2, common to both genders, suggesting a gender-specific alteration in plasma biomarkers in patients with AFD. The biomarkers were validated in plasma samples from 48 subjects using MRM, and they performed inferiorly in patients with heart failure.

CONCLUSIONS

We have identified gender-specific plasma protein biomarker panels that are specific and sensitive for the AFD phenotype. The gender-specific panels offer important insight into potential differences in pathophysiology and prognosis between males and females with AFD.

The kidney in Fabry's disease

Fabry disease (FD) is an X-linked disease in which mutations of the GLA gene result in a deficiency of the enzyme α-galactosidase A and subsequent progressive, intralysosomal deposition of undegraded glycosphingolipid products, primarily globotriaosylceramide, in multiple organs. Progressive nephropathy is one of the main features of FD and is marked by an insidious development, with an overall rate of progression of chronic kidney disease (CKD) very similar to diabetic nephropathy. Untreated patients usually develop end stage renal disease in their 50s. The decline in renal function in FD is adversely affected by male gender, advanced CKD, hypertension and, in particular, severe proteinuria. Enzyme replacement therapy (ERT) has been shown to slow the progression of Fabry nephropathy. The current consensus is that ERT should be started in all men and women with signs of renal involvement.

Amiloride as an Alternate Adjuvant Antiproteinuric Agent in Fabry Disease: The Potential Roles of Plasmin and uPAR

Patients with Fabry disease present a higher risk of cardiovascular and kidney morbidity. We present a patient with a past history of biopsy-proven Fabry disease and stage 3 chronic kidney disease. Proteinuria partially dropped from 6.8 g/day to 2.1 g/day despite an aggressive regime which consisted of low-salt diet, agalsidase beta infusions, dual blockade of the renin-angiotensin system, and low-dose maintenance of steroids. As proteinuria is considered a risk marker of cardiovascular disease and of progression of kidney disease, we added amiloride 5 mg/day, a drug with proven effects in podocyte stabilization and proteinuria actions at the distal convoluted tubule. Proteinuria finally decreased to 0.8 g/day. This report highlights the relevance of intervening on proteinuria in a multitarget approach in order to reduce it as much as possible. Due to this pharmacological response, we suggest that although agalsidase beta specific treatment protects the endothelium, the podocyte, and the tubule in Fabry disease and secondary haemodynamic and immunologic pathways are treated with inhibition of the renin-angiotensin system and steroids, amiloride may act as a complementary tool in podocyte stabilization and in proteinuria effects at the distal tubule.

Vascular endothelial growth factor (VEGF-a) in Fabry disease: association with cutaneous and systemic manifestations with vascular involvement

INTRODUCTION

Fabry disease is an X-linked inherited metabolic disorder characterized by the deficiency of lysosomal α-galactosidase A enzyme. This leads to the accumulation, into lysosomes through the body, of glycosphingolipids, mainly Gb3. Skin involvement and progressive multi-organ failure are usually observed. Endothelium is the preferential target of the Gb3 storage that determines endothelial dysfunction and vasculopathy leading to the clinical manifestations of the disease. The serum levels of Vascular Endothelial Growth Factor-A (VEGF-A), a specific endothelial cell mitogen, were analyzed in Fabry patients to explore a possible association to the clinical manifestations with vascular involvement.

METHODS

Thirty-five patients with a biochemical and genetic diagnosis of Fabry disease, along with an age-gender-matched healthy control group, were enrolled. Serum samples were collected and analyzed by ELISA. The genetic mutations, the specific organ dysfunction, and the cardiovascular risk factors such as dyslipidaemia, diabetes, smoking habits and hypertension were evaluated in Fabry patients.

RESULTS

The mean serum level of VEGF-A in Fabry patients group was significantly higher than in the control group (P=0.006). A statistical significant association, between VEGF-A levels and the skin manifestation including angiokeratomas, sweating abnormalities and Fabry Facies was found. An association was also found between high VEGF-A and specific GLA mutations, the male gender, the renal and neurological manifestations, the presence of eye vessels tortuosity, smoking habit and hypertension.

CONCLUSIONS

We detected increased VEGF-A levels in patients with Fabry disease compared to the controls, and we hypothesized that this could be a response to the vascular damage characterising this lysosomal disorder. However, further studies are necessary to clarify the role of VEGF-A in Fabry.

Possible role of transforming growth factor-β1 and vascular endothelial growth factor in Fabry disease nephropathy

Fabry disease is a lysosomal storage disorder (LSD) caused by deficiency of α-galactosidase A (α-gal A), resulting in deposition of globotriaosylceramide (Gb3; also known as ceramide trihexoside) in the vascular endothelium of many organs. A gradual accumulation of Gb3 leads to cardiovascular, cerebrovascular and renal dysfunction. Endothelial cell dysfunction leads to renal complications, one of the main symptoms of Fabry disease. However, the pathological mechanisms by which endothelial dysfunction occurs in Fabry disease are poorly characterized. The purpose of this study was to investigate whether the expression of transforming growth factor-β1 (TGF-β1) and vascular endothelial growth factor (VEGF) is associated with the renal pathogenesis of Fabry disease. We found that the protein expression levels of renal thrombospondin-1 (TSP-1), TGF-β1 and VEGF were higher in the kidneys from Fabry mice compared to wild-type mice. The expression levels of VEGF receptor 2 (VEGFR2), fibroblast growth factor-2 (FGF-2) and phospho-p38 (P-p38) were also higher in the kidneys from Fabry mice compared with wild-type mice. Activities of cysteine aspartic acid protease (caspase)-6 and caspase-9 were higher in kidneys from Fabry than from the wild-type mice. These results suggest that overexpression of TGF-β1 and VEGF in the Fabry mouse kidney might contribute to Fabry disease nephropathy by inducing apoptosis. To test whether Gb3 accumulation can induce apoptosis, we incubated bovine aortic endothelial cells with Gb3 and found increased expression of TGF-β1, VEGFR2, VEGF, FGF-2 and P-p38. The combination of increased expression of TGF-β1 and VEGF caused by Gb3 accumulation may allow upregulation of FGF-2, VEGFR2 and P-p38 expression, and these changes may be associated with Fabry disease nephropathy by inducing apoptosis.

A distinct urinary biomarker pattern characteristic of female Fabry patients that mirrors response to enzyme replacement therapy

Female patients affected by Fabry disease, an X-linked lysosomal storage disorder, exhibit a wide spectrum of symptoms, which renders diagnosis, and treatment decisions challenging. No diagnostic test, other than sequencing of the alpha-galactosidase A gene, is available and no biomarker has been proven useful to screen for the disease, predict disease course and monitor response to enzyme replacement therapy. Here, we used urine proteomic analysis based on capillary electrophoresis coupled to mass spectrometry and identified a biomarker profile in adult female Fabry patients. Urine samples were taken from 35 treatment-naïve female Fabry patients and were compared to 89 age-matched healthy controls. We found a diagnostic biomarker pattern that exhibited 88.2% sensitivity and 97.8% specificity when tested in an independent validation cohort consisting of 17 treatment-naïve Fabry patients and 45 controls. The model remained highly specific when applied to additional control patients with a variety of other renal, metabolic and cardiovascular diseases. Several of the 64 identified diagnostic biomarkers showed correlations with measures of disease severity. Notably, most biomarkers responded to enzyme replacement therapy, and 8 of 11 treated patients scored negative for Fabry disease in the diagnostic model. In conclusion, we defined a urinary biomarker model that seems to be of diagnostic use for Fabry disease in female patients and may be used to monitor response to enzyme replacement therapy.

Quantitating glomerular endothelial fenestration: an unbiased stereological approach

BACKGROUND/AIMS

Glomerular endothelial cells are fenestrated, allowing for especially high transcellular hydraulic conductivity. Current knowledge about endothelial fenestration structural changes in disease conditions is limited, partly due to the absence of robust methodologies to quantitate these structures. Herein, we propose a novel method for estimating the percentage of endothelial fenestration.

METHODS

An unbiased stereological method based on contiguity of two phases and surface area density estimation using isotropic uniform random line probes was developed. A line grid for intercept counting and classifying endothelial coverage of fenestrated versus non-fenestrated areas was designed. The method was applied to renal biopsies from 15 patients with Fabry disease and 9 normal living kidney donor controls.

RESULTS

The percentage of glomerular capillary endothelial coverage which was fenestrated was lower in Fabry patients (43 ± 12%) versus controls (53 ± 9%; p = 0.047). The fraction of endothelial surface which was fenestrated was greater on the peripheral versus mesangial zones of the capillary walls in both Fabry patients (p = 0.00002) and controls (p = 0.0005).

CONCLUSION

The proposed method provides an unbiased tool to quantitate endothelial fenestration changes in glomeruli. The practical example introduced showed reduced glomerular endothelial fenestration in Fabry nephropathy.

Biomarkers in the diagnosis of lysosomal storage disorders: proteins, lipids, and inhibodies

A biomarker is an analyte indicating the presence of a biological process linked to the clinical manifestations and outcome of a particular disease. In the case of lysosomal storage disorders (LSDs), primary and secondary accumulating metabolites or proteins specifically secreted by storage cells are good candidates for biomarkers. Clinical applications of biomarkers are found in improved diagnosis, monitoring disease progression, and assessing therapeutic correction. These are illustrated by reviewing the discovery and use of biomarkers for Gaucher disease and Fabry disease. In addition, recently developed chemical tools allowing specific visualization of enzymatically active lysosomal glucocerebrosidase are described. Such probes, coined inhibodies, offer entirely new possibilities for more sophisticated molecular diagnosis, enzyme replacement therapy monitoring, and fundamental research.

Degradative proteomics and disease mechanisms

Protein degradation is a fundamental biological process, which is essential for the maintenance and regulation of normal cellular function. In humans and animals, proteins can be degraded by a number of mechanisms: the ubiquitin-proteasome system, autophagy and intracellular proteases. The advances in contemporary protein analysis means that proteomics is increasingly being used to explore these key pathways and as a means of monitoring protein degradation. The dysfunction of protein degradative pathways has been associated with the development of a number of important diseases including cancer, muscle wasting disorders and neurodegenerative diseases. This review will focus on the role of proteomics to study cellular degradative processes and how these strategies are being applied to understand the molecular basis of diseases arising from disturbances in protein degradation.

Simultaneous magnetically directed drug convection and MR imaging

Superparamagnetic iron oxide nanoparticles (IO NPs) are of interest for their usefulness in biomedical applications. In this work, we have synthesized iron oxide nanocomposites surface-modified with different biocompatible polymers. Bovine serum albumin (BSA) was physisorbed onto these IO NPs along with an excipient during freeze-drying. The mass transport of the protein attached to the iron oxide core-shell nanoparticles (IO cs-NPs) under a gradient magnetic field of an MRI instrument was observed in vitro and in an egg as a model system for a biological fluid. From the in vitro experiments in agarose gels, it was observed that the protein gets separated from the core during mass transport for some cs-IO, but co-migration was observed for PEG-modified IO cs-NPs. These experiments demonstrated proof-of-concept for the use of IO cs-NPs in magnetically directed drug convection.

Fabry disease

Fabry disease, an X-linked disorder of glycosphingolipids that is caused by the deficiency of alpha-galactosidase A, is associated with dysfunction of many cell types and includes a systemic vasculopathy. As a result, patients have a markedly increased risk of developing small-fiber peripheral neuropathy, stroke, myriad cardiac manifestations and chronic renal disease. Virtually all complications of Fabry disease are non-specific in nature and clinically indistinguishable from similar abnormalities that occur in the context of more common disorders in the general population. Although Fabry disease was originally thought to be very rare, recent studies have found a much higher incidence of mutations of the GLA gene, suggesting that this disorder is under-diagnosed. Although the etiology of Fabry disease has been known for many years, the mechanism by which the accumulating alpha-D-galactosyl moieties cause this multi-organ disorder has only recently been studied and is yet to be completely elucidated. Specific therapy for Fabry disease has been developed in the last few years but its role in the management of the disorder is still being investigated. Fortunately, standard 'non-specific' medical and surgical therapy is effective in slowing deterioration or compensating for organ failure in patients with Fabry disease. All these aspects are discussed in detail in the present review.

Biomarkers for lysosomal storage disorders: identification and application as exemplified by chitotriosidase in Gaucher disease

A biomarker is an analyte that indicates the presence of a biological process linked to the clinical manifestations and outcome of a particular disease. An ideal biomarker provides indirect but ongoing determinations of disease activity. In the case of lysosomal storage disorders (LSDs), metabolites or proteins specifically secreted by storage cells are good candidates for biomarkers. Potential clinical applications of biomarkers are found in improved diagnosis, monitoring of disease progression and assessment of therapeutic correction. These applications are illustrated by reviewing the use of plasma chitotriosidase in the clinical management of patients with Gaucher disease, the most common LSD. The ongoing debate on the value of biomarkers in patient management is addressed. Novel analytical methods have revolutionized the identification and measurement of biomarkers at the protein and metabolite level. Recent developments in biomarker discovery by proteomics are described and the future for biomarkers of LSDs is discussed.

CONCLUSION

Besides direct applications for biomarkers in patient management, biomarker searches are likely to render new insights into pathophysiological mechanisms and metabolic adaptations, and may provide new targets for therapeutic intervention.

Apoptotic abnormalities in differential gene expression in peripheral blood mononuclear cells from children with Fabry disease

AIM

This study was designed to examine the effect of enzyme replacement therapy (ERT) on differential gene expression in peripheral blood mononuclear cells (PBMCs) of children with Fabry disease who had not previously been exposed to ERT.

METHODS

Thirteen children with Fabry disease (age range, 6.5-17.0 years) were studied as part of a 6-month, open-label study of ERT with agalsidase alfa. Paired blood samples were taken at the start of the study and after 6 months of ERT. Further blood samples were also taken from 16 age-matched control subjects. PBMCs were isolated and, following RNA extraction, differential gene expression analysis was performed using the Human Genome U133 Plus 2.0 microarray.

RESULTS

Twenty-one genes were determined to be differentially expressed in PBMCs of ERT-naïve children with Fabry disease compared with healthy controls; neuronal apoptosis inhibitory protein ranked as the most significantly differentially expressed gene. Comparison of gene expression in children with Fabry disease prior to and after ERT showed that two genes were significantly differentially expressed (p < or = 0.05) following treatment; the expressed sequence tag (probe set ID, 243259_at) was downregulated, while expression of apoptosis-inducing factor was increased, possibly as an antioxidant counter-regulatory response.

CONCLUSION

This study identifies a number of genes that are differentially expressed in a small cohort of children with Fabry disease relative to healthy controls. These genes may relate to the underlying biological abnormalities in Fabry disease.

Enzyme reconstitution/replacement therapy for lysosomal storage diseases

PURPOSE OF REVIEW

Over the past 15 years, the lysosomal storage diseases have become paradigms for the specific treatment of monogenic disorders, particularly those affecting children. This review summarizes the phenotypes and recent literature regarding enzyme reconstitution (replacement) therapy and outcomes for such treatable lysosomal storage diseases: Gaucher disease, Fabry disease, Pompe disease and the mucopolysaccharidoses.

RECENT FINDINGS

Recent clinical trials have shown that enzyme reconstitution therapy effectively treats many of the manifestations of the lysosomal storage diseases. When initiated early in the disease course, enzyme reconstitution therapy can reverse some disease manifestations, but may not completely alleviate the disease progression. Enzyme reconstitution therapy is generally well tolerated. Many adverse events are antibody-related, but can be managed without requiring cessation of enzyme reconstitution therapy. Documented IgE reactions, i.e. anaphylactoid, are quite rare (fewer than 1%).

SUMMARY

Enzyme reconstitution therapy is a safe and effective treatment modality available for several of the lysosomal storage diseases. Owing to the short history of enzyme reconstitution therapy, the long-term outcomes of enzyme reconstitution therapy-treated individuals are unknown and require further investigation. Medical professionals must learn to identify patients likely to benefit from these life-changing therapies so as to prevent many of the devastating, irreversible complications of the lysosomal storage diseases.

Cellular and tissue localization of globotriaosylceramide in Fabry disease

The pathogenesis of Fabry disease is poorly understood. We used a variety of immunohistological techniques to localize globotriaosylceramide, the main glycolipid that accumulates in Fabry disease. Globotriaosylceramide immunoreactivity in a heterogenous pattern was present in all organs examined of a patient on long-term enzyme replacement therapy. In the brain, immmunopositivity was found only in the parahippocampal region. Globotriaosylceramide immunostaining was present in the cell membrane and cytoplasm of endothelial cells, even in the absence of lysosomal inclusions. In kidney tissue, globotriaosylceramide colocalized with lysosomal, endoplasmic reticulum, and nuclear markers. Pre- and postembedding immunogold electron microscopy of skin biopsies and untreated patient cultured skin fibroblasts confirmed the presence of globotriaosylceramide in the cell membrane, in various cytoplasmic structures, and in the nucleus. Control organ tissues and cultured fibroblasts from five unaffected subjects were uniformly negative for globotriaosylceramide by immunohistochemistry and immunogold electron microscopy. We conclude that a substantial amount of lysosomal and extralysosomal globotriaosylceramide immunoreactivity remains in cells and tissues even after years of enzyme replacement therapy in Fabry disease. These findings are crucial for the understanding of the disease mechanism and suggest the usefulness of immunostaining for globotriaosylceramide as a means to assess response to novel, specific therapies.

Novel therapeutic targets for the treatment of Fabry disease

Fabry disease is an X-linked lysosomal storage disorder resulting from deficient activity of alpha-galactosidase A. The traditional concept that is used to explain the complications of the disease involves progressive accumulation of globotriaosylceramide in endothelial and smooth muscle cells, resulting in vascular damage. Clinically, progressive renal insufficiency, cardiac involvement and brain pathology evolves. Two pharmaceutical companies have developed enzyme replacement therapy in Fabry disease. Although the first clinical trials showed great promise, it is clear that long-term effects are not as robust as was anticipated. Stabilisation of renal function and decreases in cardiac hypertrophy has been observed, but some patients may experience progressive complications. As there are recent indications that serum components contribute to the pathophysiology of Fabry disease, fundamental studies are needed to unravel the precise role and identity of these factors. Combination of these basic studies with clinical follow up may ultimately reveal when the 'point of no return' is reached. Advanced renal insufficiency seems to be a clinical indicator of lack of response, but other signs and symptoms are probably related to adverse outcome. It is anticipated that in the future controlled studies in early symptomatic or presymptomatic patients will be required. In addition, alternative strategies such as substrate reduction or chaperone therapy, either alone or in combination with enzyme replacement therapy, should be explored. Because Fabry disease is rare, collaborative efforts should be undertaken and openness of data should be strived for.

Genomic abnormalities of the murine model of Fabry disease after disease-related perturbation, a systems biology approach

Fabry disease is a disorder of alpha-D-galactosyl-containing glycolipids resulting from a deficiency of alpha-galactosidase A. Patients have a poorly understood vascular dysregulation. We hypothesized that disease-related perturbation by using enzyme replacement therapy in the murine model of Fabry disease would provide insight into abnormal biological processes in Fabry disease. Gene expression analyses of the heart, aorta, and liver of male alpha-galactosidase A knockout mice 28 weeks of age were compared with that of WT mice. Microarray analyses were performed before and after six weekly injections of alpha-galactosidase A. Alteration of Rpgrip1 ranked highest statistically in all three organs when knockout mice were compared with WT, and its splice variants responded in a unique way to alpha-galactosidase A. Enzyme replacement therapy tended to not only normalize gene expression, e.g., reduce the overexpression of securin, but also specifically modified gene expression in each tissue examined. Following multiple comparison analysis, gene expression correlation graphs were constructed, and a priori hypotheses were examined by using structural equation modeling. This systems biology approach demonstrated multiple and complex parallel cellular abnormalities in Fabry disease. These abnormalities form the basis for informed, in a Bayesian sense, sequential, hypothesis-driven research that can be subsequently tested experimentally.