Higher apoptotic state in Fabry disease peripheral blood mononuclear cells.: effect of globotriaosylceramide

Fabry disease is an X-linked lysosomal storage disorder (LSD) due to deficiency of the enzyme α-galactosidase A, resulting in intracellular deposition of globotriaosylceramide (Gb3). Accumulation of Gb3 is probably related to tissue and organ dysfunctions. Diverse pathological mechanisms are elicited in LSDs, giving together the phenotypic expression of each disease. The purpose of the present study is to investigate if apoptosis could play a role in Fabry disease pathogenesis and to understand the mechanisms involved in the proapoptotic state. We have demonstrated that Fabry disease peripheral blood mononuclear cells display a higher apoptotic state, which is reduced by enzyme replacement therapy (ERT), and is mediated, at least in part, by activation of the intrinsic pathway of caspases. We could rule out the implication of “unfolded protein response-ER stress” in this apoptotic process. To further confirm the suggestion that Gb3 is associated to apoptotic cell death, we treated normal cells with Gb3 at concentrations found in Fabry patients. Addition of Gb3 resulted in a dose-dependent induction of apoptosis involving the intrinsic pathway. In summary, PBMC from Fabry patients display a higher apoptotic state, which could be mainly related to elevated Gb3.     

Chaperone therapy update: Fabry disease,GM1-gangliosidosis and Gaucher disease

Chaperone therapy is a newly developed molecular therapeutic approach to lysosomal diseases, a group of human genetic diseases causing severe brain damage. Based on early molecular studies during the last decade of the 20th century and early years of the 21st century, mainly on Fabry disease and G_M1-gangliosidosis, we found some mutant enzyme proteins were unstable in the cell, and unable to express catalytic activities. Subsequently galactose and other active-site binding substrate analogs were found stabilized and enhance the mutant enzyme activity in culture cells. We concluded that the mutant misfolding enzyme protein and substrate analog competitive inhibitor (chemical chaperone) form a stable complex to be transported to the lysosome, to restore the catalytic activity of mutant enzyme after spontaneous dissociation under the acidic condition. This gene mutation-specific molecular interaction is a paradoxical phenomenon that an enzyme inhibitor in vitro serves as an enzyme stabilizer in situ. First we developed a commercially available compound 1-deoxygalactonojirimycin (DGJ) for Fabry disease, and confirmed the above molecular phenomenon. Currently DGJ has become a new candidate of oral medicine for Fabry disease, generalized vasculopathy involving the kidneys, heart and central nervous system in the middle age. This drug development has reached the phase 3 of human clinical study. Then we found two valienamine derivatives, N-octyl-4-epi-β-valienamine (NOEV) and N-octyl-β-valienamine (NOV), as promising therapeutic agents for human β-galactosidase deficiency disorders (G_M1-gangliosidosis and Morquio B disease) and β-glucosidase deficiency disorders (phenotypic variations of Gaucher disease), respectively. Originally NOEV and NOV had been discovered as competitive inhibitors, and then their paradoxical bioactivities as chaperones were confirmed in cultured fibroblasts from patients with these disorders. Subsequently G_M1-gangliosidosis model mice have been used for confirmation of clinical effectiveness, adverse effects and pharmacokinetic studies. Orally administered NOEV entered the brain through the blood–brain barrier, enhanced β-galactosidase activity, reduced substrate storage, and improved neurological deterioration clinically. Computational analysis revealed pH-dependent enzyme-chaperone interactions. Our recent study indicated chaperone activity of a new DGJ derivative, MTD118, for β-galactosidase complementary to NOEV. NOV also showed the chaperone effect toward several β-glucosidase gene mutants in Gaucher disease. Furthermore a commercial expectorant drug ambroxol was found to be a chaperone for β-glucosidase. A few Gaucher patients responded to this drug with remarkable improvement of oculomotor dysfunction and myoclonus. We hope chaperone therapy will become available for some patients with Fabry disease, G_M1-gangliosidosis, Gaucher disease, and other lysosomal storage diseases particularly with central nervous system involvement.