Altered interaction and distribution of glycosaminoglycans and growth factors in mucopolysaccharidosis type I bone disease.

The mucopolysaccharidoses (MPSs) comprise a group of lysosomal storage disorders characterized by deficient degradation and subsequent accumulation of glycosaminoglycans (GAGs). Progressive bone and joint disease are a major cause of morbidity, and current therapeutic strategies have limited effect on these symptoms. By elucidating pathophysiological mechanisms underlying bone disease, new therapeutic targets may be identified. Longitudinal growth is regulated by interaction between GAGs and growth factors. Because GAGs accumulate in the MPSs, we hypothesized that altered interaction between growth factors and GAGs contribute to the pathogenesis of MPS bone disease. In this study, binding between GAGs from MPS I chondrocytes and fibroblast growth factor 2 (FGF2) was not significantly different from binding of FGF2 to GAGs from control chondrocytes. FGF2 signaling, however, was increased in MPS I chondrocytes after incubation with FGF2, as compared to control chondrocytes. Using bone cultures, we demonstrated decreased growth of WT mouse bones after incubation with FGF2, but no effect on MPS I bone growth. However, MPS I bones showed decreased growth in the presence of GAGs from MPS I chondrocytes. Finally, we demonstrate altered GAG distribution in MPS I chondrocytes, and altered GAG, FGF2 and Indian hedgehog distribution in growth plates from MPS I mice. In summary, our results suggest that altered interaction and distribution of growth factors and accumulated GAGs may contribute to the pathogenesis of MPS bone disease. In the future, targeting growth factor regulation or the interaction between in growth factors and GAGs might be a promising therapeutic strategy for MPS bone disease.

A Multiplex Assay for the Diagnosis of Mucopolysaccharidoses and Mucolipidoses.

INTRODUCTION: Diagnosis of the mucopolysaccharidoses (MPSs) generally relies on an initial analysis of total glycosaminoglycan (GAG) excretion in urine. Often the dimethylmethylene blue dye-binding (DMB) assay is used, although false-negative results have been reported. We report a multiplexed diagnostic test with a high sensitivity for all MPSs and with the potential to identify patients with I-cell disease (ML II) and mucolipidosis III (ML III). METHODS: Urine samples of 100 treatment naive MPS patients were collected and analyzed by the conventional DMB assay and a multiplex assay based on enzymatic digestion of heparan sulfate (HS), dermatan sulfate (DS) and keratan sulfate (KS) followed by quantification by LC-MS/MS. Specificity was calculated by analyzing urine samples from a cohort of 39 patients suspected for an inborn error of metabolism, including MPSs. RESULTS: The MPS cohort consisted of 18 MPS I, 16 MPS II, 34 MPS III, 10 MPS IVA, 3 MPS IVB, 17 MPS VI and 2 MPS VII patients. All 100 patients were identified by the LC-MS/MS assay with typical patterns of elevation of HS, DS and KS, respectively (sensitivity 100%). DMB analysis of the urine was found to be in the normal range in 10 of the 100 patients (sensitivity 90%). Three out of the 39 patients were identified as false-positive, resulting in a specificity of the LS-MS/MS assay of 92%. For the DMB this was 97%. All three patients with MLII/MLIII had elevated GAGs in the LC-MS/MS assay while the DMB test was normal in 2 of them. CONCLUSION: The multiplex LC-MS/MS assay provides a robust and very sensitive assay for the diagnosis of the complete spectrum of MPSs and has the potential to identify MPS related disorders such as MLII/MLIII. Its performance is superior to that of the conventional DMB assay.

Adverse Effects of Genistein in a Mucopolysaccharidosis Type I Mouse Model.

Mucopolysaccharidosis type I (MPS I) is a lysosomal storage disorder characterized by diminished degradation of the glycosaminoglycans heparan sulfate (HS) and dermatan sulfate (DS). Patients present with a variety of symptoms, including severe skeletal disease. Current therapeutic strategies have only limited effects on bone disease. The isoflavone genistein has been studied as a potential therapy for the mucopolysaccharidoses because of its putative ability to inhibit GAG synthesis and subsequent accumulation. Cell, animal, and clinical studies, however, showed variable outcomes. To determine the effects of genistein on MPS I-related bone disease, wild-type (WT) and MPS I mice were fed a genistein-supplemented diet (corresponding to a dose of approximately 160 mg/kg/day) for 8 weeks. HS and DS levels in bone and plasma remained unchanged after genistein supplementation, while liver HS levels were decreased in genistein-fed MPS I mice as compared to untreated MPS I mice. Unexpectedly, genistein-fed mice exhibited significantly decreased body length and femur length. In addition, 60% of genistein-fed MPS I mice developed a scrotal hernia and/or scrotal hydrocele, manifestations, which were absent in WT or untreated MPS I mice. In contrast to studies in MPS III mice, our study in MPS I mice demonstraes no beneficial but even potential adverse effects of genistein supplementation. Our results urge for a cautious approach on the use of genistein, at least in patients with MPS I.

Biomarker responses correlate with antibody status in mucopolysaccharidosis type I patients on long-term enzyme replacement therapy.

BACKGROUND: Antibody formation can interfere with effects of enzyme replacement therapy (ERT) in lysosomal storage diseases. Biomarkers are used as surrogate marker for disease burden in MPS I, but large systematic studies evaluating the response of biomarkers to ERT are lacking. We, for the first time, investigated the response of a large panel of biomarkers to long term ERT in MPS I patients and correlate these responses with antibody formation and antibody mediated cellular uptake inhibition. METHODS: A total of 428 blood and urine samples were collected during long-term ERT in 24 MPS I patients and an extensive set of biomarkers was analyzed, including heparan sulfate (HS) and dermatan sulfate (DS) derived disaccharides; total urinary GAGs (DMBu); urinary DS:CS ratio and serum heparin co-factor II thrombin levels (HCII-T). IgG antibody titers and the effect of antibodies on cellular uptake of the enzyme were determined for 23 patients. RESULTS: Median follow-up was 2.3 years. In blood, HS reached normal levels more frequently than DS (50% vs 12.5%, p=0.001), though normalization could take several years. DMBu normalized more rapidly than disaccharide levels in urine (p=0.02). Nineteen patients (83%) developed high antibody titers. Significant antibody-mediated inhibition of enzyme uptake was observed in 8 patients (35%), and this correlated strongly with a poorer biomarker response for HS and DS in blood and urine as well as for DMBu, DS:CS-ratio and HCII-T (all p<0.006). CONCLUSIONS: This study shows that, despite a response of all studied biomarkers to initiation of ERT, some biomarkers were less responsive than others, suggesting residual disease activity. In addition, the correlation of cellular uptake inhibitory antibodies with a decreased biomarker response demonstrates a functional role of these antibodies which may have important clinical consequences.

Genistein increases glycosaminoglycan levels in mucopolysaccharidosis type I cell models.

Mucopolysaccharidosis type I (MPS I) is a lysosomal storage disorder characterized by diminished degradation of the glycosaminoglycans (GAGs) heparan sulfate and dermatan sulfate, which results in the accumulation of these GAGs and subsequent cellular dysfunction. Patients present with a variety of symptoms, including severe skeletal disease. Genistein has been shown previously to inhibit GAG synthesis in MPS fibroblasts, presumably through inhibition of tyrosine kinase activity of the epidermal growth factor receptor (EGFR). To determine the potentials of genistein for the treatment of skeletal disease, MPS I fibroblasts were induced into chondrocytes and osteoblasts and treated with genistein. Surprisingly, whereas tyrosine phosphorylation levels (as a measure for tyrosine kinase inhibition) were decreased in all treated cell lines, there was a 1.3 and 1.6 fold increase in GAG levels in MPS I chondrocytes and fibroblast, respectively (p < 0.05). Sulfate incorporation in treated MPS I fibroblasts was 2.6 fold increased (p < 0.05), indicating increased GAG synthesis despite tyrosine kinase inhibition. This suggests that GAG synthesis is not exclusively regulated through the tyrosine kinase activity of the EGFR. We hypothesize that the differences in outcomes between studies on the effect of genistein in MPS are caused by the different effects of genistein on different growth factor signaling pathways, which regulate GAG synthesis. More studies are needed to elucidate the precise signaling pathways which are affected by genistein and alter GAG metabolism in order to evaluate the therapeutic potential of genistein for MPS patients.

A role for the human peroxisomal half-transporter ABCD3 in the oxidation of dicarboxylic acids.

Peroxisomes play a major role in human cellular lipid metabolism, including fatty acid ß-oxidation. Free fatty acids (FFAs) can enter peroxisomes through passive diffusion or by means of ATP binding cassette (ABC) transporters, including HsABCD1 (ALDP, adrenoleukodystrophy protein), HsABCD2 (ALDRP) and HsABCD3 (PMP70). The physiological functions of the different peroxisomal half-ABCD transporters have not been fully determined yet, but there are clear indications that both HsABCD1 and HsABCD2 are required for the breakdown of fatty acids in peroxisomes. Here we report that the phenotype of the pxa1/pxa2Δ yeast mutant, i.e. impaired oxidation of oleic acid, cannot only be partially rescued by HsABCD1, HsABCD2, but also by HsABCD3, which indicates that each peroxisomal half-transporter can function as homodimer. Fatty acid oxidation measurements using various fatty acids revealed that although the substrate specificities of HsABCD1, HsABCD2 and HsABCD3 are overlapping, they have distinctive preferences. Indeed, most hydrophobic C24:0 and C26:0 fatty acids are preferentially transported by HsABCD1, C22:0 and C22:6 by HsABCD2 and most hydrophilic substrates like long-chain unsaturated-, long branched-chain- and long-chain dicarboxylic fatty acids by HsABCD3. All these fatty acids are most likely transported as CoA esters. We postulate a role for human ABCD3 in the oxidation of dicarboxylic acids and a role in buffering fatty acids that are overflowing from the mitochondrial ß-oxidation system.

An algorithm to predict phenotypic severity in mucopolysaccharidosis type I in the first month of life.

INTRODUCTION: Mucopolysaccharidosis type I (MPS I) is a progressive multisystem lysosomal storage disease caused by deficiency of the enzyme α-L-iduronidase (IDUA). Patients present with a continuous spectrum of disease severity, and the most severely affected patients (Hurler phenotype; MPS I-H) develop progressive cognitive impairment. The treatment of choice for MPS I-H patients is haematopoietic stem cell transplantation, while patients with the more attenuated phenotypes benefit from enzyme replacement therapy. METHODS: Thirty patients were included in this study. Genotypes were collected from all patients and all patients were phenotypically categorized at an age of > 18 months based on the clinical course of the disease. In 18 patients, IDUA activity in fibroblast cultures was measured using an optimized IDUA assay. Clinical characteristics from the first month of life were collected from 23 patients. RESULTS: Homozygosity or compound heterozygosity for specific mutations which are associated with MPS I-H, discriminated a subset of patients with MPS I-H from patients with more attenuated phenotypes (specificity 100%, sensitivity 82%). Next, we found that enzymatic analysis of IDUA activity in fibroblasts allowed identification of patients affected by MPS I-H. Therefore, residual IDUA activity in fibroblasts was introduced as second step in the algorithm. Patients with an IDUA activity of < 0.32 nmol x mg(-1) × hr(-1) invariably were MPS I-H patients, while an IDUA activity of > 0.66 nmol × mg(-1) × hr(-1) was only observed in more attenuated patients. Patients with an intermediate IDUA activity could be further classified by the presence of differentiating clinical characteristics, resulting in a model with 100% sensitivity and specificity for this cohort of patients. CONCLUSION: Using genetic, biochemical and clinical characteristics, all potentially available in the newborn period, an algorithm was developed to predict the MPS I phenotype, allowing timely initiation of the optimal treatment strategy after introduction of NBS.

Plasma and urinary levels of dermatan sulfate and heparan sulfate derived disaccharides after long-term enzyme replacement therapy (ERT) in MPS I: correlation with the timing of ERT and with total urinary excretion of glycosaminoglycans.

INTRODUCTION: Mucopolysaccharidosis type I (MPS I) results in a defective breakdown of the glycosaminoglycans (GAGs) heparan sulfate and dermatan sulfate, which leads to a progressive disease. Enzyme replacement therapy (ERT) results in clearance of these GAGs from a range of tissues and can significantly ameliorate several symptoms. The biochemical efficacy of ERT is generally assessed by the determination of the total urinary excretion of GAGs. However, this has limitations. We studied the concentrations of heparan sulfate and dermatan sulfate derived disaccharides (HS and DS, respectively) in the plasma and urine of seven patients and compared these levels with total urinary GAGs (uGAGs) levels. METHODS: Plasma and urine samples were collected at different time points relative to the weekly ERT for three non-consecutive weeks in seven MPS I patients who had been treated with ERT for at least 2.5 years. Heparan and dermatan sulfate in plasma and urine were enzymatically digested into disaccharides, and HS and DS levels were determined by HPLC-MS/MS analysis. uGAGs were measured by the DMB test. RESULTS: The levels of HS and DS were markedly decreased compared with the levels before the initiation of ERT. However, the concentrations of DS in plasma and of both HS and DS in urine remained significantly elevated in all studied patients, while in six patients the level of total uGAGs had normalized. The concentrations of plasma and urinary HS during the weekly ERT followed a U-shaped curve. However, the effect size is small. The concentrations of plasma and urinary DS and uGAGs appeared to be in a steady state. CONCLUSIONS: HS and DS are sensitive biomarkers for monitoring the biochemical treatment efficacy of ERT and remain elevated despite long-term treatment. This finding may be related to the labeled dose or antibody status of the patient. The timing of the sample collection is not relevant, at least at the current dose of 100 IU/kg/weekly.

Heparan sulfate and dermatan sulfate derived disaccharides are sensitive markers for newborn screening for mucopolysaccharidoses types I, II and III.

INTRODUCTION: Mucopolysaccharidoses (MPSs) are a group of lysosomal storage disorders (LSDs) caused by a defect in the degradation of glycosaminoglycans (GAGs). The accumulation of GAGs in MPS patients results in extensive, severe and progressive disease. Disease modifying therapy is available for three of the MPSs and is being developed for the other types. Early initiation of treatment, before the onset of irreversible tissue damage, clearly provides a favorable disease outcome. However, early diagnosis is difficult due to the rarity of these disorders in combination with the wide variety of clinical symptoms. Newborn screening (NBS) is probably the optimal approach, and several screening techniques for different MPSs have been studied. Here we describe a relatively simple and sensitive method to measure levels of dermatan and heparan sulfate derived disaccharides in dried blood spots (DBS) with HPLC-MS/MS, and show that this reliably separates MPS I, II and MPS III newborns from controls and heterozygotes. METHODS: Newborn DBS of 11 MPS I, 1 MPS II, and 6 MPS III patients, with phenotypes ranging from severe to relatively attenuated, were collected and levels of dermatan and heparan sulfate derived disaccharides in these DBS were compared with levels in DBS of newborn MPS I and MPS III heterozygotes and controls. RESULTS: The levels of dermatan and heparan sulfate derived disaccharides were clearly elevated in all newborn DBS of MPS I, II and III patients when compared to controls. In contrast, DBS of MPS I and III heterozygotes showed similar disaccharide levels when compared to control DBS. CONCLUSIONS: Our study demonstrates that measurement of heparan and dermatan sulfate derived disaccharides in DBS may be suitable for NBS for MPS I, II and MPS III. We hypothesize that this same approach will also detect MPS VI, and VII patients, as heparan sulfate and/or dermatan sulfate is also the primary storage products in these disorders.

Genistein in Sanfilippo disease: a randomized controlled crossover trial.

OBJECTIVE: Sanfilippo disease (mucopolysaccharidosis type III [MPS III]) is a rare neurodegenerative metabolic disease caused by a deficiency of 1 of the 4 enzymes involved in the degradation of heparan sulfate (HS), a glycosaminoglycan (GAG). Genistein has been proposed as potential therapy but its efficacy remains uncertain. We aimed to determine the efficacy of genistein in MPS III. METHODS: Thirty patients were enrolled. Effects of genistein were determined in a randomized, crossover, placebo-controlled intervention with a genistein-rich soy isoflavone extract (10mg/kg/day of genistein) followed by an open-label extension study for patients who were on genistein during the last part of the crossover. RESULTS: Genistein resulted in a significant decrease in urinary excretion of total GAGs (p = 0.02, slope -0.68 mg GAGs/mmol creatinine/mo) and in plasma concentrations of HS (p = 0.01, slope -15.85 ng HS/ml/mo). No effects on total behavior scores or on hair morphology were observed. Parents or caregivers could not predict correctly during which period of the crossover a patient was on genistein. INTERPRETATION: Genistein at 10mg/kg/day effectively reduces urinary excretion of GAGs and plasma HS concentration in patients with MPS III. However, the absolute reduction in GAGs and in HS is small and values after 12 months of treatment remain within the range as observed in untreated patients. No clinical efficacy was detected. Substantially higher doses of genistein might be more effective as suggested by recent studies in animal models.