Differences in MPS I and MPS II Disease Manifestations.

Mucopolysaccharidosis (MPS) type I and II are two closely related lysosomal storage diseases associated with disrupted glycosaminoglycan catabolism. In MPS II, the first step of degradation of heparan sulfate (HS) and dermatan sulfate (DS) is blocked by a deficiency in the lysosomal enzyme iduronate 2-sulfatase (IDS), while, in MPS I, blockage of the second step is caused by a deficiency in iduronidase (IDUA). The subsequent accumulation of HS and DS causes lysosomal hypertrophy and an increase in the number of lysosomes in cells, and impacts cellular functions, like cell adhesion, endocytosis, intracellular trafficking of different molecules, intracellular ionic balance, and inflammation. Characteristic phenotypical manifestations of both MPS I and II include skeletal disease, reflected in short stature, inguinal and umbilical hernias, hydrocephalus, hearing loss, coarse facial features, protruded abdomen with hepatosplenomegaly, and neurological involvement with varying functional concerns. However, a few manifestations are disease-specific, including corneal clouding in MPS I, epidermal manifestations in MPS II, and differences in the severity and nature of behavioral concerns. These phenotypic differences appear to be related to different ratios between DS and HS, and their sulfation levels. MPS I is characterized by higher DS/HS levels and lower sulfation levels, while HS levels dominate over DS levels in MPS II and sulfation levels are higher. The high presence of DS in the cornea and its involvement in the arrangement of collagen fibrils potentially causes corneal clouding to be prevalent in MPS I, but not in MPS II. The differences in neurological involvement may be due to the increased HS levels in MPS II, because of the involvement of HS in neuronal development. Current treatment options for patients with MPS II are often restricted to enzyme replacement therapy (ERT). While ERT has beneficial effects on respiratory and cardiopulmonary function and extends the lifespan of the patients, it does not significantly affect CNS manifestations, probably because the enzyme cannot pass the blood-brain barrier at sufficient levels. Many experimental therapies, therefore, aim at delivery of IDS to the CNS in an attempt to prevent neurocognitive decline in the patients.

Safety and tolerability of inebilizumab (MEDI-551), an anti-CD19 monoclonal antibody, in patients with relapsing forms of multiple sclerosis: Results from a phase 1 randomised, placebo-controlled, escalating intravenous and subcutaneous dose study.

BACKGROUND: B cells may be involved in the pathophysiology of multiple sclerosis (MS). Inebilizumab (formerly MEDI-551) binds to and depletes CD19+ B cells. OBJECTIVES: To assess safety, tolerability, pharmacokinetics, pharmacodynamics and immunogenicity of inebilizumab in adults with relapsing MS. METHODS: This phase 1 trial randomised 28 patients 3:1 (21, inebilizumab; 7, placebo) to inebilizumab (2 intravenous (IV) doses, days 1 and 15: 30, 100 or 600 mg; or single subcutaneous (SC) dose on day 1: 60 or 300 mg) or matching placebo, with follow-up until at least week 24 or return of CD19+ B-cell count to ⩾80 cells/µL. RESULTS: Complete B-cell depletion was observed across all doses. Infusion/injection (grade 1/2) reactions occurred in 6/15 patients receiving inebilizumab IV, 2/5 placebo IV and 1/6 inebilizumab SC. Serious adverse events occurred in three patients receiving inebilizumab: pyrexia, mixed-drug intoxication (unrelated to inebilizumab; resulted in death) and urinary tract infection. Mean number of cumulative new gadolinium-enhancing lesions over 24 weeks was 0.1 with inebilizumab versus 1.3 with placebo; mean numbers of new/newly enlarging T2 lesions were 0.4 and 2.4, respectively. CONCLUSION: Inebilizumab had an acceptable safety profile in relapsing MS patients and showed a trend in reductions in new/newly enlarging and gadolinium-enhancing lesions.

Mucopolysaccharidosis Type I: Current Treatments, Limitations, and Prospects for Improvement.

Mucopolysaccharidosis type I (MPS I) is a lysosomal disease, caused by a deficiency of the enzyme alpha-L-iduronidase (IDUA). IDUA catalyzes the degradation of the glycosaminoglycans dermatan and heparan sulfate (DS and HS, respectively). Lack of the enzyme leads to pathologic accumulation of undegraded HS and DS with subsequent disease manifestations in multiple organs. The disease can be divided into severe (Hurler syndrome) and attenuated (Hurler-Scheie, Scheie) forms. Currently approved treatments consist of enzyme replacement therapy (ERT) and/or hematopoietic stem cell transplantation (HSCT). Patients with attenuated disease are often treated with ERT alone, while the recommended therapy for patients with Hurler syndrome consists of HSCT. While these treatments significantly improve disease manifestations and prolong life, a considerable burden of disease remains. Notably, treatment can partially prevent, but not significantly improve, clinical manifestations, necessitating early diagnosis of disease and commencement of treatment. This review discusses these standard therapies and their impact on common disease manifestations in patients with MPS I. Where relevant, results of animal models of MPS I will be included. Finally, we highlight alternative and emerging treatments for the most common disease manifestations.

Mucopolysaccharidosis Type I: A Review of the Natural History and Molecular Pathology.

Mucopolysaccharidosis type I (MPS I) is a rare autosomal recessive inherited disease, caused by deficiency of the enzyme α-L-iduronidase, resulting in accumulation of the glycosaminoglycans (GAGs) dermatan and heparan sulfate in organs and tissues. If untreated, patients with the severe phenotype die within the first decade of life. Early diagnosis is crucial to prevent the development of fatal disease manifestations, prominently cardiac and respiratory disease, as well as cognitive impairment. However, the initial symptoms are nonspecific and impede early diagnosis. This review discusses common phenotypic manifestations in the order in which they develop. Similarities and differences in the three animal models for MPS I are highlighted. Earliest symptoms, which present during the first 6 months of life, include hernias, coarse facial features, recurrent rhinitis and/or upper airway obstructions in the absence of infection, and thoracolumbar kyphosis. During the next 6 months, loss of hearing, corneal clouding, and further musculoskeletal dysplasias develop. Finally, late manifestations including lower airway obstructions and cognitive decline emerge. Cardiac symptoms are common in MPS I and can develop in infancy. The underlying pathogenesis is in the intra- and extracellular accumulation of partially degraded GAGs and infiltration of cells with enlarged lysosomes causing tissue expansion and bone deformities. These interfere with the proper arrangement of collagen fibrils, disrupt nerve fibers, and cause devastating secondary pathophysiological cascades including inflammation, oxidative stress, and other disruptions to intracellular and extracellular homeostasis. A greater understanding of the natural history of MPS I will allow early diagnosis and timely management of the disease facilitating better treatment outcomes.

Effects of aging and hypoxia-inducible factor-1 activity on angiogenic cell mobilization and recovery of perfusion after limb ischemia.

Ischemia is a stimulus for production of angiogenic cytokines that activate local vascular cells and mobilize angiogenic cells to the circulation. These responses are impaired in elderly patients with peripheral arterial disease. Hypoxia-inducible factor (HIF)-1 mediates adaptive responses to ischemia, including production of angiogenic cytokines. In this study, we demonstrate that aging and HIF-1 loss-of-function impair the expression of multiple angiogenic cytokines, mobilization of angiogenic cells, maintenance of tissue viability, and recovery of limb perfusion following femoral artery ligation. We show that HIF-1 directly activates transcription of the gene encoding stem cell factor and that mice lacking the cognate receptor C-KIT have impaired recovery from ischemia. Administration of AdCA5, an adenovirus encoding a constitutively active form of HIF-1alpha, improved the recovery of perfusion in older mice to levels similar to those in young mice. Injection of AdCA5 into nonischemic limb was sufficient to increase the number of circulating angiogenic cells. These results indicate that HIF-1 activity is necessary and sufficient for the mobilization of angiogenic cells and that HIF-1alpha gene therapy can counteract the pathological effects of aging in a mouse model of limb ischemia.

PTEN inhibitors cause a negative inotropic and chronotropic effect in mice.

Inactivation of phosphatase and tensin homologue deleted on chromosome ten (PTEN) decreases cardiac contractility under basal conditions and induces cardioprotection against ischemia-reperfusion injury. However, the pharmacological effect of PTEN inhibitors on cardiac contractility has not been studied before. In the present study, we investigated the hypothesis that PTEN inhibition decreases cardiac contractility in mice. We first exposed isolated mouse hearts to the PTEN inhibitor bpV(phen) (40µM), the phosphoinositide-3 kinase inhibitor wortmannin (1µM), and the PTEN-resistant PIP3 analog 3-phosphorothioate-PtdIns(3,4,5)P3 (3-PT-PTP, 0.5µM) for 10min. Left ventricular pressure was measured by a Mikro-tip pressure catheter. We then inhibited PTEN in mice by intra-peritoneal injection of VO-OHpic (10µg/kg) 30min before ischemia and then exposed them to 30min of ischemia and 120min of reperfusion. At the end of the experiments, hearts were isolated for measurement of myocardial infarct size by 1.5% triphenyltetrazolium chloride. Left ventricular systolic pressure and heart rate were significantly decreased by bpV(phen). Consistent with the result, the maximal rate of left ventricular pressure increase or decrease was significantly decreased by bpV(phen). 3-PT-PIP3 mimicked the effect of bpV(phen), and the opposite effect on cardiac contractility was seen with wortmannin. Moreover, inhibition of PTEN in vivo by VO-OHpic decreased left ventricular systolic pressure and heart rate before ischemia, but resulted in an increase in cardiac functional recovery and a decrease in myocardial infarct size after ischemia-reperfusion. In conclusion, PTEN inhibition causes a negative inotropic and chronotropic effect while inducing cardioprotection against ischemia-reperfusion injury.

Mitochondrial autophagy is an HIF-1-dependent adaptive metabolic response to hypoxia.

Autophagy is a process by which cytoplasmic organelles can be catabolized either to remove defective structures or as a means of providing macromolecules for energy generation under conditions of nutrient starvation. In this study we demonstrate that mitochondrial autophagy is induced by hypoxia, that this process requires the hypoxia-dependent factor-1-dependent expression of BNIP3 and the constitutive expression of Beclin-1 and Atg5, and that in cells subjected to prolonged hypoxia, mitochondrial autophagy is an adaptive metabolic response which is necessary to prevent increased levels of reactive oxygen species and cell death.

Spermidine/spermine N(1)-acetyltransferase-1 binds to hypoxia-inducible factor-1alpha (HIF-1alpha) and RACK1 and promotes ubiquitination and degradation of HIF-1alpha.

Hypoxia-inducible factor-1 (HIF-1) is a master regulator of oxygen homeostasis that controls the expression of genes encoding proteins that play key roles in angiogenesis, erythropoiesis, and glucose/energy metabolism. The stability of the HIF-1alpha subunit is regulated by ubiquitination and proteasomal degradation. In aerobic cells, O(2)-dependent prolyl hydroxylation of HIF-1alpha is required for binding of the von Hippel-Lindau tumor suppressor protein VHL, which then recruits the Elongin C ubiquitin-ligase complex. SSAT2 (spermidine/spermine N-acetyltransferase-2) binds to HIF-1alpha and promotes its ubiquitination/degradation by stabilizing the interaction of VHL and Elongin C. Treatment of cells with heat shock protein HSP90 inhibitors induces the degradation of HIF-1alpha even under hypoxic conditions. HSP90 competes with RACK1 for binding to HIF-1alpha, and HSP90 inhibition leads to increased binding of RACK1, which recruits the Elongin C ubiquitin-ligase complex to HIF-1alpha in an O(2)-independent manner. In this work, we demonstrate that SSAT1, which shares 46% amino acid identity with SSAT2, also binds to HIF-1alpha and promotes its ubiquitination/degradation. However, in contrast to SSAT2, SSAT1 acts by stabilizing the interaction of HIF-1alpha with RACK1. Thus, the paralogs SSAT1 and SSAT2 play complementary roles in promoting O(2)-independent and O(2)-dependent degradation of HIF-1alpha.

Spermidine/spermine-N1-acetyltransferase 2 is an essential component of the ubiquitin ligase complex that regulates hypoxia-inducible factor 1alpha.

Hypoxia-inducible factor 1 (HIF-1) is a heterodimeric transcription factor that functions as a master regulator of oxygen homeostasis. The HIF-1alpha subunit is subjected to O(2)-dependent prolyl hydroxylation leading to ubiquitination by the von Hippel-Lindau protein (VHL)-Elongin C ubiquitin-ligase complex and degradation by the 26 S proteasome. In this study, we demonstrate that spermidine/spermine-N(1)-acetyltransferase (SSAT) 2 plays an essential role in this process. SSAT2 binds to HIF-1alpha, VHL, and Elongin C and promotes ubiquitination of hydroxylated HIF-1alpha by stabilizing the interaction of VHL and Elongin C. Multivalent interactions by SSAT2 provide a mechanism to ensure efficient complex formation, which is necessary for the extremely rapid ubiquitination and degradation of HIF-1alpha that is observed in oxygenated cells.