Combining angiotensin receptor blockade and enzyme replacement therapy for vascular disease in mucopolysaccharidosis type I

Vascular involvement in the genetic disorder mucopolysaccharidosis type I (MPS I) has features of atherosclerotic disease near branch points of arterial vasculature, such as intimal thickening with disruption of the internal elastic lamina, and proliferation of macrophages and myofibroblasts. Inflammatory pathways are implicated in the pathogenesis of vascular disease in MPS I animal models, evidenced by cytokines like CD18 and TGF-β within arterial plaques. The angiotensin II-mediated inflammatory pathway is well studied in human atherosclerotic coronary artery disease. Recent work indicates treatment with the angiotensin receptor blocker losartan may improve vascular MPS I disease in mouse models. Here, we combined losartan with the standard therapy for MPS I, enzyme replacement therapy (ERT), to measure effects on cytokines in serum and aortic vasculature. Each treatment group (losartan, ERT, and their combination) equally normalized levels of cytokines that were largely differential between normal and mutant mice. Some cytokines, notably CD30 ligand, Eotaxin-2, LIX, IL-13, IL-15, GM-CSF, MCP-5, MIG, and CCL3 showed elevations in mice treated with ERT above normal or mutant levels; these elevations were reduced or absent in mice that received losartan or combination therapy. The observations suggest that losartan may impact inflammatory cascades due to MPS I and may also blunt inflammation in combination with ERT.

Brain transplantation of genetically corrected Sanfilippo type B neural stem cells induces partial cross-correction of the disease

Sanfilippo syndrome type B (mucopolysaccharidosis type IIIB) is a recessive genetic disorder that severely affects the brain due to a deficiency in the enzyme α-N-acetylglucosaminidase (NAGLU), leading to intra-lysosomal accumulation of partially degraded heparan sulfate. There are no effective treatments for this disorder. In this project, we carried out an ex vivo correction of neural stem cells derived from Naglu ^-/- mice (iNSCs) induced pluripotent stem cells (iPSC) using a modified enzyme in which human NAGLU is fused to an insulin-like growth factor II receptor binding peptide in order to improve enzyme uptake. After brain transplantation of corrected iNSCs into Naglu ^-/- mice and long-term evaluation of their impact, we successfully detected NAGLU-IGFII activity in all transplanted animals. We found decreased lysosomal accumulation and reduced astrocytosis and microglial activation throughout transplanted brains. We also identified a novel neuropathological phenotype in untreated Naglu ^-/- brains with decreased levels of the neuronal marker Map2 and accumulation of synaptophysin-positive aggregates. Upon transplantation, we restored levels of Map2 expression and significantly reduced formation of synaptophysin-positive aggregates. Our findings suggest that genetically engineered iNSCs can be used to effectively deliver the missing enzyme to the brain and treat Sanfilippo type B-associated neuropathology.

Genetically Corrected iPSC-Derived Neural Stem Cell Grafts Deliver Enzyme Replacement to Affect CNS Disease in Sanfilippo B Mice

Sanfilippo syndrome type B (mucopolysaccharidosis type IIIB [MPS IIIB]) is a lysosomal storage disorder primarily affecting the brain that is caused by a deficiency in the enzyme α-N-acetylglucosaminidase (NAGLU), leading to intralysosomal accumulation of heparan sulfate. There are currently no treatments for this disorder. Here we report that, ex vivo, lentiviral correction of Naglu-/- neural stem cells derived from Naglu-/- mice (iNSCs) corrected their lysosomal pathology and allowed them to secrete a functional NAGLU enzyme that could be taken up by deficient cells. Following long-term transplantation of these corrected iNSCs into Naglu-/- mice, we detected NAGLU activity in the majority of engrafted animals. Successfully transplanted Naglu-/- mice showed a significant decrease in storage material, a reduction in astrocyte activation, and complete prevention of microglial activation within the area of engrafted cells and neighboring regions, with beneficial effects extending partway along the rostrocaudal axis of the brain. Our results demonstrate long-term engraftment of iNSCs in the brain that are capable of cross-correcting pathology in Naglu-/- mice. Our findings suggest that genetically engineered iNSCs could potentially be used to deliver enzymes and treat MPS IIIB.

A Humoral Immune Response Alters the Distribution of Enzyme Replacement Therapy in Murine Mucopolysaccharidosis Type I

Antibodies against recombinant proteins can significantly reduce their effectiveness in unanticipated ways. We evaluated the humoral response of mice with the lysosomal storage disease mucopolysaccharidosis type I treated with weekly intravenous recombinant human alpha-l-iduronidase (rhIDU). Unlike patients, the majority of whom develop antibodies to recombinant human alpha-l-iduronidase, only approximately half of the treated mice developed antibodies against recombinant human alpha-l-iduronidase and levels were low. Serum from antibody-positive mice inhibited uptake of recombinant human alpha-l-iduronidase into human fibroblasts by partial inhibition compared to control serum. Tissue and cellular distributions of rhIDU were altered in antibody-positive mice compared to either antibody-negative or naive mice, with significantly less recombinant human alpha-l-iduronidase activity in the heart and kidney in antibody-positive mice. In the liver, recombinant human alpha-l-iduronidase was preferentially found in sinusoidal cells rather than in hepatocytes in antibody-positive mice. Antibodies against recombinant human alpha-l-iduronidase enhanced uptake of recombinant human alpha-l-iduronidase into macrophages obtained from MPS I mice. Collectively, these results imply that a humoral immune response against a therapeutic protein can shift its distribution preferentially into macrophage-lineage cells, causing decreased availability of the protein to the cells that are its therapeutic targets.

Immune response to intrathecal enzyme replacement therapy in mucopolysaccharidosis I patients

BACKGROUND

Intrathecal (IT) enzyme replacement therapy with recombinant human α-L-iduronidase (rhIDU) has been studied to treat glycosaminoglycan storage in the central nervous system of mucopolysaccharidosis (MPS) I dogs and is currently being studied in MPS I patients.

METHODS

We studied the immune response to IT rhIDU in MPS I subjects with spinal cord compression who had been previously treated with intravenous rhIDU. We measured the concentrations of specific antibodies and cytokines in serum and cerebrospinal fluid (CSF) collected before monthly IT rhIDU infusions and compared the serologic findings with clinical adverse event (AE) reports to establish temporal correlations with clinical symptoms.

RESULTS

Five MPS I subjects participating in IT rhIDU trials were studied. One subject with symptomatic spinal cord compression had evidence of an inflammatory response with CSF leukocytosis, elevated interleukin-5, and elevated immunoglobulin G. This subject also complained of lower back pain and buttock paresthesias temporally correlated with serologic abnormalities. Clinical symptoms were managed with oral medication, and serologic abnormalities were resolved, although this subject withdrew from the trial to have spinal decompressive surgery.

CONCLUSION

IT rhIDU was generally well tolerated in the subjects studied, although one subject had moderate to severe clinical symptoms and serologic abnormalities consistent with an immune response.

Features of brain MRI in dogs with treated and untreated mucopolysaccharidosis type I

The mucopolysaccharidosis type I (MPS I) dog model has been important in the development of therapies for human patients. We treated dogs with enzyme replacement therapy (ERT) by various approaches. Dogs assessed included untreated MPS I dogs, heterozygous carrier dogs, and MPS I dogs treated with intravenous ERT as adults (beginning at age 13 to 16 mo), intrathecal and intravenous ERT as adults (beginning at age 13 to 16 mo), or intrathecal ERT as juveniles (beginning at age 4 mo). We then characterized the neuroimaging findings of 32 of these dogs (age, 12 to 30 mo). Whole and midsagittal volumes of the corpus callosum, measured from brain MRI, were significantly smaller in affected dogs compared with unaffected heterozygotes. Corpus callosum volumes in dogs that were treated with intrathecal ERT from 4 mo until 21 mo of age were indistinguishable from those of age-matched carrier controls. Dogs with MPS I showed cerebral ventricular enlargement and cortical atrophy as early as 12 mo of age. Ventricular enlargement was greater in untreated MPS I dogs than in age-matched dogs treated with intrathecal ERT as juveniles or adults. However, treated dogs still showed some ventricular enlargement or cortical atrophy (or both). Understanding the progression of neuroimaging findings in dogs with MPS I and their response to brain-directed therapy may improve preclinical studies for new human-directed therapies. In particular, corpus callosum volumes may be useful quantitative neuroimaging markers for MPS-related brain disease and its response to therapy.

Biochemical characterization of fluorescent-labeled recombinant human alpha-L-iduronidase in vitro

In vivo tracking of the delivery of therapeutic proteins is a useful tool for preclinical studies. However, many labels are too large to use without disrupting the normal uptake, function, or other properties of the protein. Low-molecular-weight fluorescent labels allow in vivo and ex vivo tracking of the distribution of therapeutic proteins, and should not alter the protein's characteristics. We tested the in vitro properties of fluorescent-labeled recombinant human alpha-l-iduronidase (rhIDU, the enzyme deficient in Hurler syndrome) and compared labeled to unlabeled proteins. Labeled rhIDU retained full enzymatic activity and showed similar kinetics to nonlabeled rhIDU. Uptake of labeled rhIDU into human Hurler fibroblasts, measured by activity assay, was equivalent to unlabeled rhIDU enzyme and showed an uptake constant of 0.72 nM. Labeled rhIDU was also able to enter cells via the mannose 6-phospate receptor pathway and reduce glycosaminoglycan storage in Hurler fibroblasts. Subcellular localization was verified within lysosomes by confocal microscopy. These findings suggest that fluorescent labeling does not significantly interfere with enzymatic activity, stability, or uptake, and validates this method as a way to track exogenously administered enzyme.

Early versus late treatment of spinal cord compression with long-term intrathecal enzyme replacement therapy in canine mucopolysaccharidosis type I

Enzyme replacement therapy (ERT) with intravenous recombinant human alpha-l-iduronidase (IV rhIDU) is a treatment for patients with mucopolysaccharidosis I (MPS I). Spinal cord compression develops in MPS I patients due in part to dural and leptomeningeal thickening from accumulated glycosaminoglycans (GAG). We tested long-term and every 3-month intrathecal (IT) and weekly IV rhIDU in MPS I dogs age 12-15months (Adult) and MPS I pups age 2-23days (Early) to determine whether spinal cord compression could be reversed, stabilized, or prevented. Five treatment groups of MPS I dogs were evaluated (n=4 per group): IT+IV Adult, IV Adult, IT + IV Early, 0.58mg/kg IV Early and 1.57mg/kg IV Early. IT + IV rhIDU (Adult and Early) led to very high iduronidase levels in cervical, thoracic, and lumber spinal meninges (3600-29,000% of normal), while IV rhIDU alone (Adult and Early) led to levels that were 8.2-176% of normal. GAG storage was significantly reduced from untreated levels in spinal meninges of IT + IV Early (p<.001), IT+IV Adult (p=.001), 0.58mg/kg IV Early (p=.002) and 1.57mg/kg IV Early (p<.001) treatment groups. Treatment of dogs shortly after birth with IT+IV rhIDU (IT + IV Early) led to normal to near-normal GAG levels in the meninges and histologic absence of storage vacuoles. Lysosomal storage was reduced in spinal anterior horn cells in 1.57mg/kg IV Early and IT + IV Early animals. All dogs in IT + IV Adult and IV Adult groups had compression of their spinal cord at 12-15months of age determined by magnetic resonance imaging and was due to protrusion of spinal disks into the canal. Cord compression developed in 3 of 4 dogs in the 0.58mg/kg IV Early group; 2 of 3 dogs in the IT + IV Early group; and 0 of 4 dogs in the 1.57mg/kg IV Early group by 12-18months of age. IT + IV rhIDU was more effective than IV rhIDU alone for treatment of meningeal storage, and it prevented meningeal GAG accumulation when begun early. High-dose IV rhIDU from birth (1.57mg/kg weekly) appeared to prevent cord compression due to protrusion of spinal disks.

An acceptor splice site mutation in HOXD13 results in variable hand, but consistent foot malformations

HOXD13 is the most 5' of the HOXD cluster of homeobox genes in chromosome band 2q31.1. Heterozygous expansions of a polyalanine tract in HOXD13 are typically associated with synpolydactyly characterized by insertional digit duplication associated with syndactyly. We screened for mutations of HOXD13 in patients with a variety of limb malformations and identified a novel heterozygous mutation (758-2delA) in a three-generation family without the typical synpolydactyly phenotype in the hands, but with bilateral partial duplication of the 2nd metatarsals within the first web space of the feet. This mutation locates in the acceptor splice site of exon 2 and is predicted to cause failure of normal splicing of HOXD13. The foot abnormality in this family is similar to that described in two families by Goodman et al. [1998: Am. J. Hum. Genet. 63: 992-1000] in which different deletions of HOXD13 were reported. These findings together lend support to a distinct phenotype resulting from haploinsufficiency of HOXD13.

Genomic screening of fibroblast growth-factor receptor 2 reveals a wide spectrum of mutations in patients with syndromic craniosynostosis

It has been known for several years that heterozygous mutations of three members of the fibroblast growth-factor-receptor family of signal-transduction molecules-namely, FGFR1, FGFR2, and FGFR3-contribute significantly to disorders of bone patterning and growth. FGFR3 mutations, which predominantly cause short-limbed bone dysplasia, occur in all three major regions (i.e., extracellular, transmembrane, and intracellular) of the protein. By contrast, most mutations described in FGFR2 localize to just two exons (IIIa and IIIc), encoding the IgIII domain in the extracellular region, resulting in syndromic craniosynostosis including Apert, Crouzon, or Pfeiffer syndromes. Interpretation of this apparent clustering of mutations in FGFR2 has been hampered by the absence of any complete FGFR2-mutation screen. We have now undertaken such a screen in 259 patients with craniosynostosis in whom mutations in other genes (e.g., FGFR1, FGFR3, and TWIST) had been excluded; part of this screen was a cohort-based study, enabling unbiased estimates of the mutation distribution to be obtained. Although the majority (61/62 in the cohort sample) of FGFR2 mutations localized to the IIIa and IIIc exons, we identified mutations in seven additional exons-including six distinct mutations of the tyrosine kinase region and a single mutation of the IgII domain. The majority of patients with atypical mutations had diagnoses of Pfeiffer syndrome or Crouzon syndrome. Overall, FGFR2 mutations were present in 9.8% of patients with craniosynostosis who were included in a prospectively ascertained sample, but no mutations were found in association with isolated fusion of the metopic or sagittal sutures. We conclude that the spectrum of FGFR2 mutations causing craniosynostosis is wider than previously recognized but that, nevertheless, the IgIIIa/IIIc region represents a genuine mutation hotspot.

The major immunogenic epitopes of Epstein-Barr virus (EBV) nuclear antigen 1 are encoded by sequence domains which vary among nasopharyngeal carcinoma biopsies and EBV-associated cell lines

Epstein-Barr virus (EBV) nuclear antigen 1 (EBNA-1) is a protein expressed consistently in EBV-infected cells and EBV-associated malignant tissues. A panel of monoclonal antibodies (MAbs) was generated against the C terminus of EBNA-1 and evaluated for the detection of EBNA-1 in different cell lines. The epitopes recognized were mapped. Since sequence variations of EBNA-1 have been reported in nasopharyngeal carcinoma (NPC) tissues and in infected healthy individuals, the ability of these MAbs to recognize a recombinant protein derived from an NPC biopsy was also analysed. MAb 4H11 appeared to react with EBNA-1 sequences from different sources, whereas MAbs 5C11, 5F12 and 8F6 failed to recognize a recombinant EBNA-1 protein cloned from an NPC patient. Using different recombinant EBNA-1 fragments in an immunoblot format, this study demonstrates that the domain bounded by amino acids 408 and 498 is very immunogenic in mice in that epitopes in this region are recognized by various MAbs. Amino acid sequences of EBNA-1 were also deduced from nucleotide sequences amplified from three Burkitt's lymphoma cell lines, two spontaneous lymphoblastoid cell lines, two NPC biopsies and one NPC hybrid cell line, NPC-KT, and compared to the sequence from B95-8. The amino acid sequence of EBNA-1 in Akata is almost identical to that in an NPC biopsy, except for amino acid 585. The results of this study indicate that the immunogenic epitopes of EBNA-1 are highly variable.

Epidemiology of vertebral fractures in women

Vertebral fracture prevalence was assessed in an age-stratified random sample of Rochester, Minnesota women aged 50 years and over. Vertebral fractures, including wedge and concavity as well as compression fractures, were common and increased with age. The estimated incidence of new vertebral fractures also rose with age, reaching 29.6 per 1,000 person-years in women aged greater than or equal to 85 years. The prevalence of one or more vertebral fractures also increased with declining bone mass, reaching 42% in women with spinal bone mineral density less than 0.6 g/cm2 by dual photon absorptiometry. Bone mass and age contributed independently to the risk of vertebral fracture, but "age" may reflect other manifestations of osteoporosis.

Lifetime fracture risk: an approach to hip fracture risk assessment based on bone mineral density and age

Hip fractures occur late in life following a substantial reduction in skeletal mass. If risk for such fractures could be predicted early, efforts to prevent excessive bone loss would be more successful and could be directed at the individuals most likely to be affected. With this objective in mind, we devised an approach to estimating the lifetime risk of a proximal femur fracture based on age and on current femoral bone mineral density, using population-based data from ongoing studies of osteoporosis and fractures among Rochester, Minnesota, women. Our calculations indicate that, at any given age, the lifetime risk of a proximal femur fracture rises as current bone density diminishes. At any given level of femoral bone density, lifetime risk rises with younger age and increasing life expectancy. While these trends seem robust, estimates of risk vary substantially with the assumptions that underlie the model. Consequently, these assumptions must be validated before our findings can be applied clinically to predict risk for individual patients.

Errors in longitudinal measurements of bone mineral: effect of source strength in single and dual photon absorptiometry

The effect of changing strength during the useful life of a radiation source was evaluated in studies performed on four dual photon (DPA) and two single photon (SPA) bone absorptiometry instruments. Two DPA units and one SPA unit did not show any systematic dependence of measured bone mineral content or bone mineral areal density (BMD) on source activity when evaluated over an entire source life. One DPA and one SPA instrument, however, showed significant time trends associated with source activity. The fourth DPA instrument had a significant linear decrease in BMD over a source life in the automatic mode but performed better in the manual mode.

Risk of osteoporotic fractures in women with breast cancer: a population-based cohort study

A population-based study was undertaken to assess the risk of osteoporotic fractures in an inception cohort of breast cancer patients and an age-matched cohort of women from the community. Prior to the index date, 9.4% of cases and 12.3% of controls (p = 0.30) had one or more osteoporotic fractures. After the index date, these proportions were 16.2 and 20.0% (p = 0.28), but follow-up was shorter for cases due to reduced survival. When duration of follow-up was accounted for in a person-years analysis, the relative risk of any fracture was 1.0 and for any osteoporotic fracture was 0.9 (95% C.I. 0.7-1.2). After adjusting for other factors in a proportional hazards model, the relative risk of any osteoporotic fracture in breast cancer cases compared to controls was 0.9. Despite contentions that breast cancer patients have more often been exposed to estrogenic factors, we found little to suggest that such women are substantially protected from osteoporotic fractures.