Transgenic mice expressing human glucocerebrosidase variants: utility for the study of Gaucher disease.

Gaucher disease is an autosomal recessively inherited storage disorder caused by deficiency of the lysosomal hydrolase, acid ß-glucosidase. The disease manifestations seen in Gaucher patients are highly heterogeneous as is the responsiveness to therapy. The elucidation of the precise factors responsible for this heterogeneity has been challenging as the development of clinically relevant animal models of Gaucher disease has been problematic. Although numerous murine models for Gaucher disease have been described each has limitations in their specific utility. We describe here, transgenic murine models of Gaucher disease that will be particularly useful for the study of pharmacological chaperones. We have produced stable transgenic mouse strains that individually express wild type, N370S and L444P containing human acid ß-glucosidase and show that each of these transgenic lines rescues the lethal phenotype characteristic of acid ß-glucosidase null mice. Both the N370S and L444P transgenic models show early and progressive elevations of tissue sphingolipids with L444P mice developing progressive splenic Gaucher cell infiltration. We demonstrate the potential utility of these new transgenic models for the study of Gaucher disease pathogenesis. In addition, since these mice produce only human enzyme, they are particularly relevant for the study of pharmacological chaperones that are specifically targeted to human acid ß-glucosidase and the common mutations underlying Gaucher disease.

Longitudinal observations of serum heparin cofactor II-thrombin complex in treated Mucopolysaccharidosis I and II patients.

Monitoring of therapeutic response in mucopolysaccharidosis (MPS) patients is problematic as most biomarkers are specific for either disease complications or specific organ system involvement. Recent studies have indicated that serum heparin-cofactor II-thrombin complex (HCII-T) may serve as an important biomarker in the group of MPSs where dermatan sulphate is stored. This complex forms when blood coagulates in the presence of glycosaminoglycans (GAGs) where the ultimate amount of HCII-T that forms reflects the concentration of circulating GAGs. We have studied serum HCII-T levels in 9 MPS I and 11 MPS II treated patients and have compared values to studies of urinary GAGs. In severe MPS I patients treated with either transplantation or enzyme replacement therapy (ERT), serum HCII-T levels never reach the range of normal despite normalization of uGAGs in some patients. Some attenuated MPS I patients have normalization of HCII-T but require a protracted exposure time relative to the drop in urinary GAGs. Treated MPS II patients show a clear correlation of serum HCII-T levels with the presence of antibodies to Idursulfase, with antibody positive patients showing an early drop in HCII-T levels with eventual increases in levels often to levels above those seen at baseline. This is contrasted by a robust and persistent drop in uGAGs. Antibody negative MPS II patients show a drop in HCII-T levels on treatment but levels never normalize despite normalization of uGAGs. This study highlights the utility and biologic relevance of serum HCII-T levels in monitoring therapy in these disorders.

Heparin cofactor II-thrombin complex: a biomarker of MPS disease.

The mucopolysaccharidoses are a group of lysosomal storage disorders caused by defects in the degradation of glycosaminoglycans. Each disorder is characterized by progressive multi-system disease with considerable clinical heterogeneity. The clinical heterogeneity of these disorders is thought to be related to the degree of the metabolic block in glycosaminoglycan degradation which in turn is related to the underlying mutation at the respective locus. There are currently no objective means other than longitudinal clinical observation, or the detection of a recurrent genetic mutation to accurately predict the clinical course for an individual patient, particularly when diagnosed early. In addition, there are no specific disease biomarkers that reflect the total body burden of disease. The lack of specific biomarkers has made monitoring treatment responses and predicting disease course difficult in these disorders. The recent introduction of enzyme replacement therapy for MPS I, II, and VI highlights the need for objective measures of disease burden and disease responsiveness. We show that serum levels of heparin cofactor II-thrombin complex is a reliable biomarker of the mucopolysaccharidoses. Untreated patients have serum levels that range from 3- to 112-fold above control values. In a series of patients with varying severity of mucopolysaccharidosis I, the serum complex concentration was reflective of disease severity. In addition, serum heparin cofactor II-thrombin levels showed responsiveness to various treatment regimens. We propose that serum levels of heparin cofactor II-thrombin complex may provide an important assessment and monitoring tool for patients with mucopolysaccharidosis.