Beneficial effects of substrate reduction therapy in a mouse model of GM1 gangliosidosis

Multi-system disorders of glycosphingolipid and ganglioside metabolism

Glycosphingolipids (GSLs) and gangliosides are a group of bioactive glycolipids that include cerebrosides, globosides, and gangliosides. These lipids play major roles in signal transduction, cell adhesion, modulating growth factor/hormone receptor, antigen recognition, and protein trafficking. Specific genetic defects in lysosomal hydrolases disrupt normal GSL and ganglioside metabolism leading to their excess accumulation in cellular compartments, particularly in the lysosome, i.e., lysosomal storage diseases (LSDs). The storage diseases of GSLs and gangliosides affect all organ systems, but the central nervous system (CNS) is primarily involved in many. Current treatments can attenuate the visceral disease, but the management of CNS involvement remains an unmet medical need. Early interventions that alter the CNS disease have shown promise in delaying neurologic involvement in several CNS LSDs. Consequently, effective treatment for such devastating inherited diseases requires an understanding of the early developmental and pathological mechanisms of GSL and ganglioside flux (synthesis and degradation) that underlie the CNS diseases. These are the focus of this review.

Treating lysosomal storage diseases with pharmacological chaperones: from concept to clinics

Lysosomal storage diseases (LSDs) are a group of genetic disorders due to defects in any aspect of lysosomal biology. During the past two decades, different approaches have been introduced for the treatment of these conditions. Among them, enzyme replacement therapy (ERT) represented a major advance and is used successfully in the treatment of some of these disorders. However, ERT has limitations such as insufficient biodistribution of recombinant enzymes and high costs. An emerging strategy for the treatment of LSDs is pharmacological chaperone therapy (PCT), based on the use of chaperone molecules that assist the folding of mutated enzymes and improve their stability and lysosomal trafficking. After proof-of-concept studies, PCT is now being translated into clinical applications for Fabry, Gaucher and Pompe disease. This approach, however, can only be applied to patients carrying chaperone-responsive mutations. The recent demonstration of a synergistic effect of chaperones and ERT expands the applications of PCT and prompts a re-evaluation of their therapeutic use and potential. This review discusses the strengths and drawbacks of the potential therapies available for LSDs and proposes that future research should be directed towards the development of treatment protocols based on the combination of different therapies to improve the clinical outcome of LSD patients.

Substrate-reduction therapy with miglustat for glycosphingolipid storage disorders affecting the brain

A number of lysosomal storage disorders (LSDs) are characterized by glycosphingolipid (GSL) storage in the brain. Although enzyme-replacement therapy is an effective treatment for the visceral manifestations of some of these disorders, this approach has not, to date, been useful in CNS disease. Substrate reduction therapy (SRT) is an alternative approach to treatment in which the aim is to reduce the rate of synthesis of GSL to a level where the residual enzyme activity in the affected cell can prevent lysosomal storage. Miglustat, an iminosugar, is an inhibitor of the first step of GSL synthesis and has been used successfully for SRT in Gaucher disease. Miglustat is a small molecule and can enter the brain. It has been shown to delay symptom onset and prolong life in a number of animal models of GSL LSDs. This review describes the current progress in the clinical development of SRT with miglustat for these disorders.

Niemann-Pick disease type C1 is a sphingosine storage disease that causes deregulation of lysosomal calcium

Niemann-Pick type C1 (NPC1) disease is a neurodegenerative lysosomal storage disorder caused by mutations in the acidic compartment (which we define as the late endosome and the lysosome) protein, NPC1. The function of NPC1 is unknown, but when it is dysfunctional, sphingosine, glycosphingolipids, sphingomyelin and cholesterol accumulate. We have found that NPC1-mutant cells have a large reduction in the acidic compartment calcium store compared to wild-type cells. Chelating luminal endocytic calcium in normal cells with high-affinity Rhod-dextran induced an NPC disease cellular phenotype. In a drug-induced NPC disease cellular model, sphingosine storage in the acidic compartment led to calcium depletion in these organelles, which then resulted in cholesterol, sphingomyelin and glycosphingolipid storage in these compartments. Sphingosine storage is therefore an initiating factor in NPC1 disease pathogenesis that causes altered calcium homeostasis, leading to the secondary storage of sphingolipids and cholesterol. This unique calcium phenotype represents a new target for therapeutic intervention, as elevation of cytosolic calcium with curcumin normalized NPC1 disease cellular phenotypes and prolonged survival of the NPC1 mouse.

Glycosphingolipid depletion in PC12 cells using iminosugars protects neuronal membranes from anti-ganglioside antibody mediated injury

Autoimmune neuropathies are frequently associated with pathogenic anti-ganglioside antibodies targeting ganglioside-rich neuronal and glial membranes. The extent of injury is determined by the concentration of membrane ganglioside and thus reduction might be expected to attenuate disease. In this study, we suppressed ganglioside biosynthesis in PC12 cells with the glucosylceramide synthase inhibitor, N-butyldeoxynojirimycin and observed reduced plasma membrane antibody binding and a major neuroprotective effect in complement-mediated lysis assays. These data demonstrate that iminosugar inhibitors, currently used to treat type 1 Gaucher disease, are also of potential value for depleting antigen and thereby suppressing tissue injury in anti-ganglioside antibody-associated neuropathy.

Treating lysosomal storage disorders: current practice and future prospects

There are over 40 human disease states that are caused by defects in various aspects of lysosomal function. Over the past two decades there has been dramatic progress in the development and evaluation of therapies for lysosomal storage disorders, several of which are now in routine clinical use or in clinical trials. The greatest current challenge is in developing effective therapies for treating the CNS manifestations of these complex disorders. In this article, we will review the current therapies/approaches being considered for treating lysosomal storage diseases and give a perspective on the scientific, medical, social and ethical issues they raise.