Quantitative brain morphometry identifies cerebellar, cortical, and subcortical gray and white matter atrophy in late-onset Tay-Sachs disease.

Cerebellar atrophy is a characteristic sign of late-onset Tay-Sachs disease (LOTS). Other structural neuroimaging abnormalities are inconsistently reported. Our study aimed to perform a detailed whole-brain analysis and quantitatively characterize morphometric changes in LOTS patients. Fourteen patients (8 M/6F) with LOTS from three centers were included in this retrospective study. For morphometric brain analyses, we used deformation-based morphometry, voxel-based morphometry, surface-based morphometry, and spatially unbiased cerebellar atlas template. The quantitative whole-brain morphometric analysis confirmed the finding of profound pontocerebellar atrophy with most affected cerebellar lobules V and VI in LOTS patients. Additionally, the atrophy of structures mainly involved in motor control, including bilateral ventral and lateral thalamic nuclei, primary motor and sensory cortex, supplementary motor area, and white matter regions containing corticospinal tract, was present. The atrophy of the right amygdala, hippocampus, and regions of occipital, parietal and temporal white matter was also observed in LOTS patients in contrast with controls (p < 0.05, FWE corrected). Patients with dysarthria and those initially presenting with ataxia had more severe cerebellar atrophy. Our results show predominant impairment of cerebellar regions responsible for speech and hand motor function in LOTS patients. Widespread morphological changes of motor cortical and subcortical regions and tracts in white matter indicate abnormalities in central motor circuits likely coresponsible for impaired speech and motor function.

Physiologically-Based Pharmacokinetic Model Development, Validation, and Application for Prediction of Eliglustat Drug-Drug Interactions.

Eliglustat is a glucosylceramide synthase inhibitor indicated as a long-term substrate reduction therapy for adults with type 1 Gaucher disease, a lysosomal rare disease. It is primarily metabolized by cytochrome P450 2D6 (CYP2D6), and variants in the gene encoding this enzyme are important determinants of eliglustat pharmacokinetics (PK) and drug-drug interactions (DDIs). The existing drug label addresses the DDIs to some extent but has omitted scenarios where both metabolizing CYPs (2D6 and 3A4) are mildly or moderately inhibited. The objectives of this study were (i) to develop and validate an eliglustat physiologically-based pharmacokinetic (PBPK) model with and without drug interactions, (ii) to simulate untested DDI scenarios, and (iii) to explore potential dosing flexibility using lower dose strength of eliglustat (commercially not available). PK data from healthy adults receiving eliglustat with or without interacting drugs were obtained from literature and used for the PBPK model development and validation. The model-predicted single-dose and steady-state maximum concentration (Cmax ) and area under the concentration-time curve (AUC) of eliglustat were within 50-150% of the observed values when eliglustat was administered alone or coadministered with ketoconazole or paroxetine. Then as model-based simulations, we illustrated eliglustat exposure as a victim of interaction when coadministered with fluvoxamine following the US Food and Drug Administration (FDA) dosing recommendations. Second, we showed that with lower eliglustat doses (21 mg, 42 mg once daily) the exposure in participants of intermediate and poor metabolizer phenotypes was within the outlined safety margin (Cmax <250 ng/mL) when eliglustat was administered with ketoconazole, where the current recommendation is a contraindication of coadministration (84 mg). The present study demonstrated that patients with CYP2D6 deficiency may benefit from lower doses of eliglustat.

Identification of a novel fusion Iduronidase with improved activity in the cardiovascular system.

Background: Lysosomal diseases are a group of over 70 rare genetic conditions in which a protein deficiency (most often an enzyme deficiency) leads to multi-system disease. Current therapies for lysosomal diseases are limited in their ability to treat certain tissues that are major contributors to morbidity and mortality, such as the central nervous system (CNS) and cardiac valves. For this study, the lysosomal disease mucopolysaccharidosis type I (MPS I) was selected as the disease model. In MPS I, mutations in the IDUA gene cause a deficiency of the α-L-iduronidase (IDUA) enzyme activity, leading to disease pathology in tissues throughout the body, including the CNS and cardiac valves. Current therapies have been unable to prevent neurodevelopmental deficits and cardiac valvular disease in patients with MPS I. This study aimed to evaluate the delivery of IDUA enzyme, via a novel gene therapy construct, to target tissues. Methods: MPS I mice were hydrodynamically injected through the tail vein with plasmids containing either a codon-optimized cDNA encoding the wild-type IDUA protein or one of four modified IDUAs under the control of the liver-specific human α1-antitrypsin (hAAT) promoter. Two modified IDUAs contained a ligand for the CB1 receptor, which is a highly expressed receptor in the CNS. Iduronidase activity levels were measured in the tissues and plasma using an enzyme activity assay. Results: The modified IDUAs did not appear to have improved activity levels in the brain compared with the unmodified IDUA. However, one modified IDUA exhibited higher activity levels than the unmodified IDUA in the heart (p = 0.0211). This modified iduronidase (LT-IDUA) contained a sequence for a six amino acid peptide termed LT. LT-IDUA was further characterized using a noncompartmental pharmacokinetic approach that directly analyzed enzyme activity levels after gene delivery. LT-IDUA had a 2-fold higher area under the curve (AUC) than the unmodified IDUA (p = 0.0034) when AUC was estimated using enzyme activity levels in the plasma. Conclusion: The addition of a six amino acid peptide improved iduronidase's activity levels in the heart and plasma. The short length of this LT peptide facilitates its use as fusion enzymes encoded as gene therapy or administered as enzyme replacement therapy. More broadly, the LT peptide may aid in developing therapies for numerous lysosomal diseases.

Chitotriosidase as a biomarker for gangliosidoses.

Elevated serum chitotriosidase (CHITO) is an indication of macrophage activation, and its capacity have been explored as a marker of inflammation in a number of disease states. For over a decade, CHITO plasma levels have been used by clinicians as a biomarker of inflammation in the lysosomal disease, Gaucher disease, including monitoring response to therapies in patients with Gaucher disease type I. Although it is becoming increasingly recognized that inflammation is a prominent component of many lysosomal diseases, the relation of CHITO levels to disease burden has not been well-characterized in the large majority of lysosomal diseases. Moreover, the role of CHITO in lysosomal diseases that affect the central nervous system (CNS) has not been systematically studied. In this study, one hundred and thirty-four specimens of CSF and serum were collected from 34 patients with lysosomal diseases affecting the CNS. This study included patients with GM1-gangliosidosis, GM2-gangliosidosis, mucopolysaccharidoses (MPS), multiple sulfatase deficiency and Gaucher disease. CHITO levels in the CSF were significantly higher in patients with more rapidly progressing severe neurological impairment: GM1-gangliosidosis vs MPS (p < 0.0001); GM2-gangliosidosis vs MPS (p < 0.0001). CHITO levels were higher in patients with the more severe phenotypes compared to milder phenotypes in GM1-gangliosidosis and GM2-gangliosidosis (serum CHITO in GM1-gangliosidosis infantile vs juvenile p = 0.025; CSF CHITO in Tay-Sachs infantile vs Tay-Sachs late-onset p < 0.0001). Moreover, higher CHITO levels in the CSF were significantly associated with lower cognitive test scores in patients with GM1-gangliosidosis, GM2-gangliosidosis, and MPS (p = 1.12*10-5, R2 = 0.72). Patients with infantile GM1-gangliosidosis showed increasing CSF CHITO over time, suggesting that CSF CHITO reflects disease progression and a possible surrogate endpoint for future clinical trials with infantile GM1-gangliosidosis. In summary, these results support the use of CSF CHITO to diagnose between different disease phenotypes and as a valuable tool for monitoring disease progression in patients. These results necessitate the inclusion of CHITO as an exploratory biomarker for clinical trials.

Examination of a blood-brain barrier targeting ß-galactosidase-monoclonal antibody fusion protein in a murine model of GM1-gangliosidosis.

GM1-gangliosidosis is a lysosomal disease resulting from a deficiency in the hydrolase ß-galactosidase (ß-gal) and subsequent accumulation of gangliosides, primarily in neuronal tissue, leading to progressive neurological deterioration and eventually early death. Lysosomal diseases with neurological involvement have limited non-invasive therapies due to the inability of lysosomal enzymes to cross the blood-brain barrier (BBB). A novel fusion enzyme, labeled mTfR-GLB1, was designed to act as a ferry across the BBB by fusing ß-gal to the mouse monoclonal antibody against the mouse transferrin receptor and tested in a murine model of GM1-gangliosidosis (ß-gal-/-). Twelve hours following a single intravenous dose of mTfR-GLB1 (5.0 mg/kg) into adult ß-gal-/- mice showed clearance of enzyme activity in the plasma and an increase in ß-gal enzyme activity in the liver and spleen. Long-term efficacy of mTfR-GLB1 was assessed by treating ß-gal-/- mice intravenously twice a week with a low (2.5 mg/kg) or high (5.0 mg/kg) dose of mTfR-GLB1 for 17 weeks. Long-term studies showed high dose mice gained weight normally compared to vehicle-treated ß-gal-/- mice, which are significantly heavier than heterozygous controls. Behavioral assessment at six months of age using the pole test showed ß-gal-/- mice treated with mTfR-GLB1 had improved motor function. Biochemical analysis showed an increase in ß-gal enzyme activity in the high dose group from negligible levels to 20% and 11% of heterozygous levels in the liver and spleen, respectively. Together, these data show that mTfR-GLB1 is a catalytically active ß-gal fusion enzyme in vivo that is readily taken up into tissues. Despite these indications of bioactivity, behavior tests other than the pole test, including the Barnes maze, inverted screen, and accelerating rotarod, showed limited or no improvement of treated mice compared to ß-gal-/- mice receiving vehicle only. Further, administration of mTfR-GLB1 was insufficient to create measurable increases in ß-gal enzyme activity in the brain or reduce ganglioside content (biochemically and morphologically).

Patients with Gaucher disease display systemic oxidative stress dependent on therapy status.

Gaucher disease is an autosomal recessive metabolic disorder caused by mutations in GBA1, which encodes for the lysosomal hydrolase enzyme, ß-glucocerebrosidase. The resulting misfolded protein can trigger endoplasmic reticulum stress and an unfolded protein response within the affected cells. The enzyme deficiency leads to accumulation of its substrates, glucosylceramide and glucosylsphingosine, within macrophage lysosomes and with prominent disease manifestations in macrophage rich tissues. Resultant lysosomal pathology and impaired autophagy leads to redox imbalance, mitochondrial dysfunction and intracellular oxidative stress. Here we have systematically examined a role for oxidative stress in individuals affected by Gaucher disease. We compared multiple oxidative stress biomarkers in plasma and red blood cell samples from patients who are currently untreated, with those who are stable on standard-of-care therapy, and with healthy controls. We found significant differences in key oxidative stress biomarkers in untreated patients compared to healthy control. In treated patients, results generally fell between the controls and the untreated patients. Interestingly, even asymptomatic and minimally symptomatic untreated patients had evidence of significant systemic oxidative stress. We conclude that underlying oxidative stress may contribute to Gaucher disease pathophysiology including long-term adverse outcomes such as Parkinsonism and malignancies. Therapies targeting oxidative stress may prove useful as adjuvant treatments for Gaucher disease and other lysosomal storage disorders.

Neurochemical abnormalities in patients with type 1 Gaucher disease on standard of care therapy.

Type 1 Gaucher disease (GD1), a glycosphingolipid storage disorder caused by deficient activity of lysosomal glucocerebrosidase, is classically considered non-neuronopathic. However, current evidence challenges this view. Multiple studies show that mutations in GBA1 gene and decreased glucocerebrosidase activity are associated with increased risk for Parkinson disease. We tested the hypothesis that subjects with GD1 will show neurochemical abnormalities consistent with cerebral involvement. We performed Magnetic Resonance Spectroscopy at 7 T to quantify neurochemical profiles in participants with GD1 (n = 12) who are on stable therapy. Age and gender matched healthy participants served as controls (n = 13). Neurochemical profiles were obtained from parietal white matter (PWM), posterior cingulate cortex (PCC), and putamen. Further, in the GD1 group, the neurochemical profiles were compared between individuals with and without a single L444P allele. We observed significantly lower levels of key neuronal markers, N-acetylaspartate, γ-aminobutyric acid, glutamate and glutamate-to-glutamine ratio in PCC of participants with GD1 compared to healthy controls (P < .015). Glutamate concentration was also lower in the putamen in GD1 (P = .01). Glucose + taurine concentration was significantly higher in PWM (P = .04). Interestingly, individuals without L444P had significantly lower aspartate and N-acetylaspartylglutamate in PCC (both P < .001), although this group was 7 years younger than those with an L444P allele. This study demonstrates neurochemical abnormalities in individuals with GD1, for which clinical and prognostic significance remains to be determined. Further studies in a larger cohort are required to confirm an association of neurochemical levels with mutation status and glucocerebrosidase structure and function. SYNOPSIS: Ultrahigh field magnetic resonance spectroscopy reveals abnormalities in neurochemical profiles in patients with GD1 compared to matched healthy controls.