Biochemical and histopathological studies on patients with mucopolysaccharidoses, two of whom had been treated by fibroblast transplantation

IgG Fusion Proteins for Brain Delivery of Biologics via Blood-Brain Barrier Receptor-Mediated Transport

The treatment of neurological disorders with large-molecule biotherapeutics requires that the therapeutic drug be transported across the blood–brain barrier (BBB). However, recombinant biotherapeutics, such as neurotrophins, enzymes, decoy receptors, and monoclonal antibodies (MAb), do not cross the BBB. These biotherapeutics can be re-engineered as brain-penetrating bifunctional IgG fusion proteins. These recombinant proteins comprise two domains, the transport domain and the therapeutic domain, respectively. The transport domain is an MAb that acts as a molecular Trojan horse by targeting a BBB-specific endogenous receptor that induces receptor-mediated transcytosis into the brain, such as the human insulin receptor (HIR) or the transferrin receptor (TfR). The therapeutic domain of the IgG fusion protein exerts its pharmacological effect in the brain once across the BBB. A generation of bifunctional IgG fusion proteins has been engineered using genetically engineered MAbs directed to either the BBB HIR or TfR as the transport domain. These IgG fusion proteins were validated in animal models of lysosomal storage disorders; acute brain conditions, such as stroke; or chronic neurodegeneration, such as Parkinson’s disease and Alzheimer’s disease. Human phase I–III clinical trials were also completed for Hurler MPSI and Hunter MPSII using brain-penetrating IgG-iduronidase and -iduronate-2-sulfatase fusion protein, respectively.

Blood-brain barrier delivery for lysosomal storage disorders with IgG-lysosomal enzyme fusion proteins

The majority of lysosomal storage diseases affect the brain. Treatment of the brain with intravenous enzyme replacement therapy is not successful, because the recombinant lysosomal enzymes do not cross the blood-brain barrier (BBB). Biologic drugs, including lysosomal enzymes, can be re-engineered for BBB delivery as IgG-enzyme fusion proteins. The IgG domain of the fusion protein is a monoclonal antibody directed against an endogenous receptor-mediated transporter at the BBB, such as the insulin receptor or the transferrin receptor. This receptor transports the IgG across the BBB, in parallel with the endogenous receptor ligand, and the IgG acts as a molecular Trojan horse to ferry into brain the lysosomal enzyme genetically fused to the IgG. The IgG-enzyme fusion protein is bi-functional and retains both high affinity binding for the BBB receptor, and high lysosomal enzyme activity. IgG-lysosomal enzymes are presently in clinical trials for treatment of the brain in Mucopolysaccharidosis.

In utero adenine base editing corrects multi-organ pathology in a lethal lysosomal storage disease

In utero base editing has the potential to correct disease-causing mutations before the onset of pathology. Mucopolysaccharidosis type I (MPS-IH, Hurler syndrome) is a lysosomal storage disease (LSD) affecting multiple organs, often leading to early postnatal cardiopulmonary demise. We assessed in utero adeno-associated virus serotype 9 (AAV9) delivery of an adenine base editor (ABE) targeting the Idua G→A (W392X) mutation in the MPS-IH mouse, corresponding to the common IDUA G→A (W402X) mutation in MPS-IH patients. Here we show efficient long-term W392X correction in hepatocytes and cardiomyocytes and low-level editing in the brain. In utero editing was associated with improved survival and amelioration of metabolic, musculoskeletal, and cardiac disease. This proof-of-concept study demonstrates the possibility of efficiently performing therapeutic base editing in multiple organs before birth via a clinically relevant delivery mechanism, highlighting the potential of this approach for MPS-IH and other genetic diseases.

Glycosaminoglycan levels in dried blood spots of patients with mucopolysaccharidoses and mucolipidoses

Mucopolysaccharidoses (MPSs) and mucolipidoses (ML) are groups of lysosomal storage disorders in which lysosomal hydrolases are deficient leading to accumulation of undegraded glycosaminoglycans (GAGs), throughout the body, subsequently resulting in progressive damage to multiple tissues and organs. Assays using tandem mass spectrometry (MS/MS) have been established to measure GAGs in serum or plasma from MPS and ML patients, but few studies were performed to determine whether these assays are sufficiently robust to measure GAG levels in dried blood spots (DBS) of patients with MPS and ML.

MATERIAL AND METHODS

In this study, we evaluated GAG levels in DBS samples from 124 MPS and ML patients (MPS I=16; MPS II=21; MPS III=40; MPS IV=32; MPS VI=10; MPS VII=1; ML=4), and compared them with 115 age-matched controls. Disaccharides were produced from polymer GAGs by digestion with chondroitinase B, heparitinase, and keratanase II. Subsequently, dermatan sulfate (DS), heparan sulfate (HS-0S, HS-NS), and keratan sulfate (mono-sulfated KS, di-sulfated KS, and ratio of di-sulfated KS in total KS) were measured by MS/MS.

RESULTS

Untreated patients with MPS I, II, VI, and ML had higher levels of DS compared to control samples. Untreated patients with MPS I, II, III, VI, and ML had higher levels of HS-0S; and untreated patients with MPS II, III and VI and ML had higher levels of HS-NS. Levels of KS were age dependent, so although levels of both mono-sulfated KS and di-sulfated KS were generally higher in patients, particularly for MPS II and MPS IV, age group numbers were not sufficient to determine significance of such changes. However, the ratio of di-sulfated KS in total KS was significantly higher in all MPS patients younger than 5years old, compared to age-matched controls. MPS I and VI patients treated with HSCT had normal levels of DS, and MPS I, VI, and VII treated with ERT or HSCT had normal levels of HS-0S and HS-NS, indicating that both treatments are effective in decreasing blood GAG levels.

CONCLUSION

Measurement of GAG levels in DBS is useful for diagnosis and potentially for monitoring the therapeutic efficacy in MPS.

Molecular Genetics and Metabolism Report Long-term follow-up of post hematopoietic stem cell transplantation for Hurler syndrome: clinical, biochemical, and pathological improvements

Mucopolysaccharidosis type I (MPS I; Hurler Syndrome) is a lysosomal storage disease caused by a deficiency of the enzyme α-L-iduronidase which affects multiple organs such as central nervous system (CNS), skeletal system, and physical appearance. Hematopoietic stem cell transplantation (HSCT) is recommended as a primary therapeutic option at an early stage of MPS I with a severe form to ameliorate CNS involvement; however, no description of pathological improvement in skeletal dysplasia has been investigated to date. We here report a 15-year-old male case with MPS I post-HSCT. This patient received successful HSCT at the age of 2 years and 1 month, followed for over 10 years. His activity of daily living including cognitive performance has been kept normal and the present height and weight are 162 cm and 55 kg. Bone deformity has been still developed, resulting in hemiepiphysiodesis of bilateral medial proximal tibia at 12 years of age and successive arthrodesis of thoraco-lumbar spine at 13 years of age; however, skeletal histopathology from surgical remnants showed substantial improvement in bone lesion with markedly reduced occurrence and cell size of vacuolated cells. After a series of surgical procedures, he became ambulant and independent in daily activity. The levels of GAGs in blood were substantially reduced. In conclusion, this long-term post-HSCT observation should shed light on a new aspect of therapeutic effect associated with skeletal pathology and GAG levels as a biomarker, indicating that HSCT is a primary choice at an early stage for not only CNS but skeletal system in combination of appropriate surgical procedures.

Establishment of glycosaminoglycan assays for mucopolysaccharidoses

Mucopolysaccharidoses (MPS) are a group of lysosomal storage disorders caused by deficiency of the lysosomal enzymes essential for catabolism of glycosaminoglycans (GAGs). Accumulation of undegraded GAGs results in dysfunction of multiple organs, resulting in distinct clinical manifestations. A range of methods have been developed to measure specific GAGs in various human samples to investigate diagnosis, prognosis, pathogenesis, GAG interaction with other molecules, and monitoring therapeutic efficacy. We established ELISA, liquid chromatography tandem mass spectrometry (LC-MS/MS), and an automated high-throughput mass spectrometry (HT-MS/MS) system (RapidFire) to identify epitopes (ELISA) or disaccharides (MS/MS) derived from different GAGs (dermatan sulfate, heparan sulfate, keratan sulfate, and/or chondroitin sulfate). These methods have a high sensitivity and specificity in GAG analysis, applicable to the analysis of blood, urine, tissues, and cells. ELISA is feasible, sensitive, and reproducible with the standard equipment. HT-MS/MS yields higher throughput than conventional LC-MS/MS-based methods while the HT-MS/MS system does not have a chromatographic step and cannot distinguish GAGs with identical molecular weights, leading to a limitation of measurements for some specific GAGs. Here we review the advantages and disadvantages of these methods for measuring GAG levels in biological specimens. We also describe an unexpected secondary elevation of keratan sulfate in patients with MPS that is an indirect consequence of disruption of catabolism of other GAGs.

Newborn screening and diagnosis of mucopolysaccharidoses: application of tandem mass spectrometry

Mucopolysaccharidoses (MPS) are a group of lysosomal storage disorders caused by the deficiency of lysosomal enzymes. The enzymes are required to break down glycosaminoglycans (GAGs) that help build bone, cartilage, tendons, corneas, skin and connective tissue. In patients with MPS, a missing enzyme leads to the accumulation of GAGs in the cells, blood, connective tissues, and multiple organs. The consequence is permanent, with progressive cellular damage affecting patients' appearance, physical abilities, organ and system function, and skeletal and mental development. The measurement of each specific GAG in a variety of specimens is required to establish the correlation between GAGs and physiological status of patients and/or prognosis and pathogenesis of the disease and to separate the patients with MPS from the healthy controls. We have developed a highly accurate, sensitive, and cost-effective liquid chromatography tandem mass spectrometry (LC-MS/MS) method for measurements of disaccharides derived from four specific GAGs [chondroitin sulfate (CS), dermatan sulfate (DS), heparan sulfate (HS), and keratan sulfate (KS)]. Disaccharides were produced by specific enzyme digestion of each GAG, and subsequently, quantified by negative ion mode of multiple reaction monitoring. Subclasses of GAGs with the same molecular weights can be separated by liquid chromatography. We have also developed another GAG assay by high-throughput mass spectrometry (HT-MS/MS). The HT-MS/MS consists of an integrated solid phase extraction robot that binds and de-salts samples from assay plates and directly injects them into a MS/MS detector, reducing sample processing time to within ten seconds. HT-MS/MS consequently yields much faster throughput than conventional LC-MS/MS-based methods; however, the HT-MS/MS system does not use a chromatographic step, and therefore, cannot separate GAGs that have the same molecular weights. Both techniques can be applied to the analysis of dried blood spots, blood, and urine specimens. In this review, we describe the assay methods for GAGs and the application to newborn screening and diagnosis of MPS.

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.

Genetic engineering of a lysosomal enzyme fusion protein for targeted delivery across the human blood-brain barrier

Mucopolysaccharidosis Type I, Hurler's Syndrome, is a lysosomal storage disorder that affects the brain. The missing enzyme, alpha-L-iduronidase (IDUA), does not cross the blood-brain barrier (BBB). To enable BBB transport of the enzyme, human IDUA was fused to the carboxyl terminus of the heavy chain of a chimeric monoclonal antibody (MAb) to the human insulin receptor (HIR). The HIRMAb crosses the BBB on the endogenous insulin receptor, and acts as a molecular Trojan horse to ferry into brain the IDUA. Transfection of COS cells resulted in high levels of IDUA enzyme activity both in the medium and in the intracellular space. The size of the fusion heavy chain, as measured with Western blotting and antibodies to either human IDUA or human IgG, was increased about 80 kDa, relative to the size of the heavy chain of the parent HIRMAb. The IDUA enzyme specific activity of the affinity purified HIRMAb-IDUA fusion protein was 363 +/- 37 U/microg protein, which is comparable to specific activity of recombinant IDUA. The accumulation of glycosoaminoglycans in Hurler fibroblasts was decreased 70% by treatment with the HIRMAb-IDUA fusion protein. Confocal microscopy showed targeting of the fusion protein to the lysosome. The HIRMAb-IDUA fusion protein bound with high affinity to the HIR, and was rapidly transported into the brain of the adult Rhesus monkey following intravenous administration. The HIRMAb-IDUA fusion protein is a new treatment for Hurler's syndrome, which has been specifically engineered to cross the human BBB.

Saposins A, B, C, and D in Plasma of Patients with Lysosomal Storage Disorders

Background: Early diagnosis of lysosomal storage disorders (LSDs), before the onset of irreversible pathology, will be critical for maximum efficacy of many current and proposed therapies. To search for potential markers of LSDs, we measured saposins A, B, C, and D in patients with these disorders.

Methods: Four time-delayed fluorescence immunoquantification assays were used to measure each of the saposins in plasma from 111 unaffected individuals and 334 LSD-affected individuals, representing 28 different disorders.

Results: Saposin A was increased above the 95th centile of the control population in 59% of LSD patients; saposins B, C, and D were increased in 25%, 61%, and 57%, respectively. Saposins were increased in patients from several LSD groups that in previous studies did not show an increase of lysosome-associated membrane protein-1 (LAMP-1).

Conclusion: Saposins may be useful markers for LSDs when used in conjunction with LAMP-1.

Stereological and morphometric analysis of dermal fibroblasts before and after bone marrow transplantation in a case of mucopolysaccharidosis I Scheie phenotype

Bone marrow transplantation (BMT) has been used therapeutically in several types of mucopolysaccharidoses (MPS) and other inherited metabolic disorders. Fibroblasts are severely affected in MPS due to the intralysosomal accumulation of glycosaminoglycans. We report a stereological and morphometric study at light and electron microscopy levels of dermal fibroblasts before and 21 months after BMT in a young girl with MPS I Scheie phenotype (MPS I-S). Dermal fibroblasts showed remarkable morphological changes although their density, expressed as number of fibroblasts per unit volume of dermis (number density), was not modified in the post-BMT samples as compared to pre-BMT ones. Stereological and morphometric parameters referring to cell characteristics of post-BMT fibroblasts (nuclear and cell surface densities, and both nucleus/cell and cell/nucleus volume densities) showed significant differences when compared with pre-BMT fibroblasts, and non-significant differences regarding control cells. On the other hand, quantitative parameters of the lysosomal compartment from post-BMT fibroblasts showed intermediate values between pre-BMT and control fibroblasts. These results, at cellular level, are in agreement with previous biochemical and clinical results, and clearly showed a progressive course to a non-pathological state. All parameters estimated may be considered useful tools in evaluating the success of BMT. These parameters provide quantitative data which can be statistically compared, showing the changes due to the reduction of storage material after BMT. Cell/nucleus volume density is especially interesting since not only is it easy to estimate, even by automatic procedures, but it could also constitute a numerical expression of skin anatomopathological analyses performed post-BMT.

Ocular changes in the mucopolysaccharidoses after bone marrow transplantation. A preliminary report

Metabolic correction and physiologic response were evaluated after bone marrow transplantation in mucopolysaccharidosis. Eleven patients were prospectively evaluated to determine the effect of bone marrow transplantation on the progressive ocular manifestations of these disorders. Follow-up of 0.6 to 2.8 years after successful donor stem cell engraftment showed that some patients had slow clearing of the corneal clouding, reduction of intracytoplasmic inclusions in the conjunctiva, resolution of optic nerve edema, and stabilized or improved retinal function as determined by electroretinography. These preliminary results suggest that early bone marrow transplantation may alter some of the progressive ophthalmic characteristics of the mucopolysaccharidoses. Long-term follow-up is necessary to determine if these early alterations in the ocular features are predictive of a prolonged functional improvement in the visual status.

Skeletal muscle involvement in mucopolysaccharidosis type IIA: severe type of Hunter syndrome

A patient with mucopolysaccharidosis type IIA (MPS IIA) and progressive gait disturbance is described. The histopathology of biopsied muscle was studied; Dorling's method revealed muscle fibers and interstitial cells containing metachromatic granules which suggested the storage of sulfated acidic glycosaminoglycans. Electron microscopy demonstrated that the membrane-bound vacuoles were present in muscle fibers, subsarcolemmal area, vascular endothelial cells, satellite cells, and endomysial fibroblasts. Besides clinical features, this ultrastructural pathology in MPS IIA muscles of MPS IIA was more severe than MPS IIB muscles. The accumulation of glycosaminoglycans in muscle tissue may be an additional factor contributing to gradual motor impairment of patients with MPS IIA.

Neuropathological and clinical correlations in Hurler disease

We report studies on two patients (1 and 2) with Hurler disease. They both had all of the non-neurological features of Hurler disease to a similar and extreme degree and similar signs of brain damage on computed tomography. However, intellectual function was unusually well-preserved in patient 1, but seriously and typically impaired in patient 2. The reason for this discrepancy has been investigated by reference to the neuropathological findings, the results of alpha-L-iduronidase assays using different substrates and comparisons to other cases (patients 3 and 4). We suggest that patient 1 is an unusual variant of the disease who may have had a very low residual alpha-L-iduronidase activity in neuronal cells only, and that this could not be demonstrated by either enzyme assays on whole brain using the 4-methylumbelliferyliduronide substrate (Crow et al., 1983) or in studies on fibroblast lysates using a radioactive disaccharide substrate.

Histopathological studies of the temporal bones in Hurler's disease [mucopolysaccharidosis (MPS) IH]

The structural basis of the combined conductive and sensorineural deafness has been described in two patients with Hurler's disease. All parts of the ear contained numerous large vacuolated Hurler cells, the vacuoles being distended lysosomes from which accumulated glycosaminoglycans had been dissolved during fixation of the tissue. The external and middle ears also showed chronic inflammation. There was resorption of the bone in the mastoid process by masses of Hurler cells and abnormal new bone with prominent cement lines. The blood vessels were surrounded by a 'blue mantle' of osteoid tissue similar to that which is usually associated with otosclerosis. The stapes appeared deformed and was covered by thickened mucosa and granulation tissue. The bone structure of the ossicles resembled that of the mastoid process. The organ of Corti was degenerate and the Reissner's and tectorial membranes were adherent to one another and covered by haemorrhagic material near the vascular striae. The blood vessels in the striae were congested and the scalae media and tympani contained some blood. The neurons in the basal coil of the spiral ganglion were replaced by Hurler cells. The vestibulo-cochlear nerves were disrupted by numerous Hurler cells. These pathological findings adequately explain the combined conductive and sensorineural deafness in these cases. They are also discussed in relation to some other clinical and pathological aspects of these two specific patients.