Joshua Pacheco

Inhibiting glycosphingolipid synthesis ameliorates hepatic steatosis in obese mice

Steatosis in the liver is a common feature of obesity and type 2 diabetes and the precursor to the development of nonalcoholic steatohepatitis (NASH), cirrhosis, and liver failure. It has been shown previously that inhibiting glycosphingolipid (GSL) synthesis increases insulin sensitivity and lowers glucose levels in diabetic rodent models. Here we demonstrate that inhibiting GSL synthesis in ob/ob mice not only improved glucose homeostasis but also markedly reduced the development of hepatic steatosis. The ob/ob mice were treated for 7 weeks with a specific inhibitor of glucosylceramide synthase, the initial enzyme involved in the synthesis of GSLs. Besides lowering glucose and hemoglobin A1c (HbA1c) levels, drug treatment also significantly reduced the liver/body weight ratio, decreased the accumulation of triglycerides, and improved several markers of liver pathology. Drug treatment reduced liver glucosylceramide (GL1) levels in the ob/ob mouse. Treatment also reduced the expression of several genes associated with hepatic steatosis, including those involved in lipogenesis, gluconeogenesis, and inflammation. In addition, inhibiting GSL synthesis in diet‐induced obese mice both prevented the development of steatosis and partially reversed preexisting steatosis. Conclusion: These data indicate that inhibiting GSL synthesis ameliorates the liver pathology associated with obesity and diabetes, and may represent a novel strategy for treating fatty liver disease and NASH. (HEPATOLOGY 2009.)

Substrate Reduction Augments the Efficacy of Enzyme Therapy in a Mouse Model of Fabry Disease

Fabry disease is an X-linked glycosphingolipid storage disorder caused by a deficiency in the activity of the lysosomal hydrolase α-galactosidase A (α-gal). This deficiency results in accumulation of the glycosphingolipid globotriaosylceramide (GL-3) in lysosomes. Endothelial cell storage of GL-3 frequently leads to kidney dysfunction, cardiac and cerebrovascular disease. The current treatment for Fabry disease is through infusions of recombinant α-gal (enzyme-replacement therapy; ERT). Although ERT can markedly reduce the lysosomal burden of GL-3 in endothelial cells, variability is seen in the clearance from several other cell types. This suggests that alternative and adjuvant therapies may be desirable. Use of glucosylceramide synthase inhibitors to abate the biosynthesis of glycosphingolipids (substrate reduction therapy, SRT) has been shown to be effective at reducing substrate levels in the related glycosphingolipidosis, Gaucher disease. Here, we show that such an inhibitor (eliglustat tartrate, Genz-112638) was effective at lowering GL-3 accumulation in a mouse model of Fabry disease. Relative efficacy of SRT and ERT at reducing GL-3 levels in Fabry mouse tissues differed with SRT being more effective in the kidney, and ERT more efficacious in the heart and liver. Combination therapy with ERT and SRT provided the most complete clearance of GL-3 from all the tissues. Furthermore, treatment normalized urine volume and uromodulin levels and significantly delayed the loss of a nociceptive response. The differential efficacies of SRT and ERT in the different tissues indicate that the combination approach is both additive and complementary suggesting the possibility of an improved therapeutic paradigm in the management of Fabry disease.

Iminosugar-based inhibitors of glucosylceramide synthase prolong survival but paradoxically increase brain glucosylceramide levels in Niemann–Pick C mice

Niemann Pick type C (NPC) disease is a progressive neurodegenerative disease caused by mutations in NPC1 or NPC2, the gene products of which are involved in cholesterol transport in late endosomes. NPC is characterized by an accumulation of cholesterol, sphingomyelin and glycosphingolipids in the visceral organs, primarily the liver and spleen. In the brain, there is a redistribution of unesterified cholesterol and a concomitant accumulation of glycosphingolipids. It has been suggested that reducing the aberrant lysosomal storage of glycosphingolipids in the brain by a substrate reduction therapy (SRT) approach may prove beneficial. Inhibiting glucosylceramide synthase (GCS) using the iminosugar-based inhibitor miglustat (NB-DNJ) has been reported to increase the survival of NPC mice. Here, we tested the effects of Genz-529468, a more potent iminosugar-based inhibitor of GCS, in the NPC mouse. Oral administration of Genz-529468 or NB-DNJ to NPC mice improved their motor function, reduced CNS inflammation, and increased their longevity. However, Genz-529468 offered a wider therapeutic window and better therapeutic index than NB-DNJ. Analysis of the glycolipids in the CNS of the iminosugar-treated NPC mouse revealed that the glucosylceramide (GL1) but not the ganglioside levels were highly elevated. This increase in GL1 was likely caused by the off-target inhibition of the murine non-lysosomal glucosylceramidase, Gba2. Hence, the basis for the observed effects of these inhibitors in NPC mice might be related to their inhibition of Gba2 or another unintended target rather than a result of substrate reduction.

Intracerebroventricular delivery of glucocerebrosidase reduces substrates and increases lifespan in a mouse model of neuronopathic Gaucher disease

Gaucher disease is caused by a deficit in the enzyme glucocerebrosidase. As a consequence, degradation of the glycolipids glucosylceramide (GluCer) and glucosylsphingosine (GluSph) is impaired, and their subsequent buildup can lead to significant pathology and early death. Type 1 Gaucher patients can be treated successfully with intravenous replacement enzyme, but this enzyme does not reach the CNS and thus does not ameliorate the neurological involvement in types 2 and 3 Gaucher disease. As one potential approach to treating these latter patients, we have evaluated intracerebroventricular (ICV) administration of recombinant human glucocerebrosidase (rhGC) in a mouse model of neuronopathic Gaucher disease. ICV administration resulted in enzyme distribution throughout the brain and alleviated neuropathology in multiple brain regions of this mouse model. Treatment also resulted in dose-dependent decreases in GluCer and GluSph and significantly extended survival. To evaluate the potential of continuous enzyme delivery, a group of animals was treated ICV with an adeno-associated viral vector encoding hGC and resulted in a further extension of survival. These data suggest that ICV administration of rhGC may represent a potential therapeutic approach for type 2/3 Gaucher patients. Preclinical evaluation in larger animals will be needed to ascertain the translatability of this approach to the clinic.

Lyso-sphingomyelin is elevated in dried blood spots of Niemann–Pick B patients

Niemann-Pick disease type B (NPD-B) is caused by a partial deficiency of acid sphingomyelinase activity and results in the accumulation of lysosomal sphingomyelin (SPM) predominantly in macrophages. Notably, SPM is not significantly elevated in the plasma, whole blood, or urine of NPD-B patients. Here, we show that the de-acylated form of sphingomyelin, lyso-SPM, is elevated approximately 5-fold in dried blood spots (DBS) from NPD-B patients and has no overlap with normal controls, making it a potentially useful biomarker.

Nonclinical safety assessment of recombinant human acid sphingomyelinase (rhASM) for the treatment of acid sphingomyelinase deficiency:the utility of animal models of disease in the toxicological evaluation of potential therapeutics.

Recombinant human acid sphingomyelinase (rhASM) is being developed as an enzyme replacement therapy for patients with acid sphingomyelinase deficiency (Niemann-Pick disease types A and B), which causes sphingomyelin to accumulate in lysosomes. In the acid sphingomyelinase knock-out (ASMKO) mouse, intravenously administered rhASM reduced tissue sphingomyelin levels in a dose-dependent manner. When rhASM was administered to normal rats, mice, and dogs, no toxicity was observed up to a dose of 30mg/kg. However, high doses of rhASM≥10mg/kg administered to ASMKO mice resulted in unexpected toxicity characterized by cardiovascular shock, hepatic inflammation, adrenal hemorrhage, elevations in ceramide and cytokines (especially IL-6, G-CSF, and keratinocyte chemoattractant [KC]), and death. The toxicity could be completely prevented by the administration of several low doses (3mg/kg) of rhASM prior to single or repeated high doses (≥20mg/kg). These results suggest that the observed toxicity involves the rapid breakdown of large amounts of sphingomyelin into ceramide and/or other toxic downstream metabolites, which are known signaling molecules with cardiovascular and pro-inflammatory effects. Our results suggest that the nonclinical safety assessment of novel therapeutics should include the use of specific animal models of disease whenever feasible.

The chemosensitizing activity of inhibitors of glucosylceramide synthase is mediated primarily through modulation of P-gp function.

Glucosylceramide synthase (GCS) is a key enzyme engaged in the biosynthesis of glycosphingolipids and in regulating ceramide metabolism. Studies exploring alterations in GCS activity suggest that the glycolase may have a role in chemosensitizing tumor cells to various cancer drugs. The chemosensitizing effect of inhibitors of GCS (e.g. PDMP and selected analogues) has been observed with a variety of tumor cells leading to the proposal that the sensitizing activity of GCS inhibitors is primarily through increases in intracellular ceramide leading to induction of apoptosis. The current study examined the chemosensitizing activity of the novel GCS inhibitor, Genz-123346 in cell culture. Exposure of cells to Genz-123346 and to other GCS inhibitors at non-toxic concentrations can enhance the killing of tumor cells by cytotoxic anti-cancer agents. This activity was unrelated to lowering intracellular glycosphingolipid levels. Genz-123346 and a few other GCS inhibitors are substrates for multi-drug resistance efflux pumps such as P-gp (ABCB1, gP-170). In cell lines selected to over-express P-gp or which endogenously express P-gp, chemosensitization by Genz-123346 was primarily due to the effects on P-gp function. RNA interference studies using siRNA or shRNA confirmed that lowering GCS expression in tumor cells did not affect their responsiveness to commonly used cytotoxic drugs.

Glycosphingolipids are modulators of disease pathogenesis in amyotrophic lateral sclerosis

Significance Glycosphingolipids are a heterogeneous group of membrane lipids formed through the covalent linkage of a glycan moiety to ceramide. Genetic evidence suggests that aberrant glycosphingolipid metabolism plays an important role in several neuromuscular diseases. Here, we investigated whether alterations in glycosphingolipids contribute to neurodegeneration in amyotrophic lateral sclerosis (ALS). We show that ALS patients and model mice display disease-related changes in spinal cord glycosphingolipids levels and in the enzymes that regulate their metabolism. Importantly, we demonstrate that inhibition of glycosphingolipid synthesis in ALS model mice exacerbated disease progression, whereas administration of GM3, a subtype of glycosphingolipids, slowed it, thus implicating glycosphingolipids as potentially important participants in ALS pathogenesis and potential targets for future drug development. Recent genetic evidence suggests that aberrant glycosphingolipid metabolism plays an important role in several neuromuscular diseases including hereditary spastic paraplegia, hereditary sensory neuropathy type 1, and non-5q spinal muscular atrophy. Here, we investigated whether altered glycosphingolipid metabolism is a modulator of disease course in amyotrophic lateral sclerosis (ALS). Levels of ceramide, glucosylceramide, galactocerebroside, lactosylceramide, globotriaosylceramide, and the gangliosides GM3 and GM1 were significantly elevated in spinal cords of ALS patients. Moreover, enzyme activities (glucocerebrosidase-1, glucocerebrosidase-2, hexosaminidase, galactosylceramidase, α-galactosidase, and β-galactosidase) mediating glycosphingolipid hydrolysis were also elevated up to threefold. Increased ceramide, glucosylceramide, GM3, and hexosaminidase activity were also found in SOD1G93A mice, a familial model of ALS. Inhibition of glucosylceramide synthesis accelerated disease course in SOD1G93A mice, whereas infusion of exogenous GM3 significantly slowed the onset of paralysis and increased survival. Our results suggest that glycosphingolipids are likely important participants in pathogenesis of ALS and merit further analysis as potential drug targets.

Glucosylsphingosine promotes α-synuclein pathology in mutant GBA-associated Parkinson's disease

Glucocerebrosidase 1 (GBA) mutations responsible for Gaucher disease (GD) are the most common genetic risk factor for Parkinsons disease (PD). Although the genetic link between GD and PD is well established, the underlying molecular mechanism(s) are not well understood. We propose that glucosylsphingosine, a sphingolipid accumulating in GD, mediates PD pathology in GBA-associated PD. We show that, whereas GD-related sphingolipids (glucosylceramide, glucosylsphingosine, sphingosine, sphingosine-1-phosphate) promote α-synuclein aggregation in vitro, glucosylsphingosine triggers the formation of oligomeric α-synuclein species capable of templating in human cells and neurons. Using newly generated GD/PD mouse lines of either sex [Gba mutant (N370S, L444P, KO) crossed to α-synuclein transgenics], we show that Gba mutations predispose to PD through a loss-of-function mechanism. We further demonstrate that glucosylsphingosine specifically accumulates in young GD/PD mouse brain. With age, brains exhibit glucosylceramide accumulations colocalized with α-synuclein pathology. These findings indicate that glucosylsphingosine promotes pathological aggregation of α-synuclein, increasing PD risk in GD patients and carriers. SIGNIFICANCE STATEMENT Parkinsons disease (PD) is a prevalent neurodegenerative disorder in the aging population. Glucocerebrosidase 1 mutations, which cause Gaucher disease, are the most common genetic risk factor for PD, underscoring the importance of delineating the mechanisms underlying mutant GBA-associated PD. We show that lipids accumulating in Gaucher disease, especially glucosylsphingosine, play a key role in PD pathology in the brain. These data indicate that ASAH1 (acid ceramidase 1) and GBA2 (glucocerebrosidase 2) enzymes that mediate glucosylsphingosine production and metabolism are attractive therapeutic targets for treating mutant GBA-associated PD.

Adeno‐associated virus‐mediated expression of acid sphingomyelinase decreases atherosclerotic lesion formation in apolipoprotein E−/− mice

The secretory form of acid sphingomyelinase (ASM) is postulated to play a key role in the retention and aggregation of lipoproteins in the subendothelial space of the arterial wall by converting sphingomyelin in lipoproteins into ceramide. The present study aimed to determine whether the level of circulating ASM activity affects lesion development in mouse model of atherosclerosis.