Systemic correction of the muscle disorder glycogen storage disease type II after hepatic targeting of a modified adenovirus vector encoding human acid-alpha-glucosidase

Intercellular transfer of the virally derived precursor form of acid alpha-glucosidase corrects the enzyme deficiency in inherited cardioskeletal myopathy Pompe disease

Pompe disease is a lethal cardioskeletal myopathy in infants and results from genetic deficiency of the lysosomal enzyme acid alpha-glucosidase (GAA). Genetic replacement of the cDNA for human GAA (hGAA) is one potential therapeutic approach. Three months after a single intramuscular injection of 10(8) plaque-forming units (PFU) of E1-deleted adenovirus encoding human GAA (Ad-hGAA), the activity in whole muscle lysates of immunodeficient mice is increased to 20 times the native level. Direct transduction of a target muscle, however, may not correct all deficient cells. Therefore, the amount of enzyme that can be transferred to deficient cells from virally transduced cells was studied. Fibroblasts from an affected patient were transduced with AdhGAA, washed, and plated on transwell culture dishes to serve as donors of recombinant enzyme. Deficient fibroblasts were plated as acceptor cells, and were separated from the donor monolayer by a 22-microm pore size filter. Enzymatic and Western analyses demonstrate secretion of the 110-kDa precursor form of hGAA from the donor cells into the culture medium. This recombinant, 110-kDa species reaches the acceptor cells, where it can be taken up by mannose 6-phosphate receptor-mediated endocytosis. It then trafficks to lysosomes, where Western analysis shows proteolytic processing to the 76- and 70-kDa lysosomal forms of the enzyme. Patient fibroblasts receiving recombinant hGAA by this transfer mechanism reach levels of enzyme activity that are comparable to normal human fibroblasts. Skeletal muscle cell cultures from an affected patient were also transduced with Ad-hGAA. Recombinant hGAA is identified in a lysosomal location in these muscle cells by immunocytochemistry, and enzyme activity is transferred to deficient skeletal muscle cells grown in coculture. Transfer of the precursor protein between muscle cells again occurs via mannose 6-phosphate receptors, as evidenced by competitive inhibition with 5 mM mannose 6-phosphate. In vivo studies in GAA-knockout mice demonstrate that hepatic transduction with adenovirus encoding either murine or human GAA can provide a depot of recombinant enzyme that is available to heart and skeletal muscle through this mechanism. Taken together, these data show that the mannose 6-phosphate receptor pathway provides a useful strategy for cell-to-cell distribution of virally derived recombinant GAA.

Liquid chromatographic assay for a glucose tetrasaccharide, a putative biomarker for the diagnosis of Pompe disease

A HPLC method associated with butyl-p-aminobenzoate derivatization has been developed for the analysis of a tetraglucose oligomer, Glcalpha1-6Glcalpha1-4Glcalpha1-4Glc, designated Glc(4), in biological fluids. This tetraglucose, normally excreted in the urine, has previously been shown to be elevated in a number of pathological conditions including Pompe disease (glycogen storage disease type II), which is caused by a deficiency of the lysosomal enzyme acid alpha-glucosidase. Concentrations of Glc(4) in both urine and plasma were established for the age ranges of <1, 1-5, 6-10, 11-20, and >20 years, both in normal individuals and in a cohort of 21 patients with enzymatically confirmed Pompe disease. The Glc(4) concentration decreased with age in both groups, but all the patients had elevated Glc(4) levels compared with age-matched controls. Electrospray tandem mass spectrometry was employed to establish the homogeneity of the HPLC peak for Glc(4) and to investigate the identity of other unusual oligosaccharides excreted in patient urine. Our results demonstrate that this method is suitable for application in clinical laboratories to help establish the diagnosis of Pompe disease.

Gene therapy in lysosomal diseases

Lysosomal storage diseases are monogenic metabolic disorders resulting from a deficiency in intralysosomal enzymes involved in macromolecule catabolism. Various groups have been delineated according to the affected pathway and the accumulated substrate: mucopolysaccharidoses, lipidoses, glycoproteinoses and glycogenosis type II. Their clinical severity and the absence of efficient therapy for the majority of these disorders justify the development of gene transfer methods. Most of the genes encoding the normal lysosomal enzymes have been cloned and recently numerous animal models have been obtained for nearly all these diseases. Due to the clinical heterogeneity of lysosomal diseases, showing multivisceral involvement or affecting predominantly the reticuloendothelial system, muscle or central nervous system, various gene therapy strategies have to be developed. Vectors, ways of access, results and limits will be reviewed. Interesting results have already been obtained in the gene transfer for lysosomal diseases, but improvements are needed before a future application to humans.

Gene therapy and molecular approaches to the treatment of hereditary muscular disorders

Gene therapy for inherited muscle disease is an active area of research and development. Initial emphasis has been on gene replacement but alternative approaches are increasingly being considered in order to overcome difficulties, such as the immune rejection of transduced cells, the need for appropriate and tissue-specific control of expression, and the requirement for systemic spread in some conditions. However, the most significant obstacles to the clinical success of gene therapy are still the lack of efficiency and accuracy of gene medicine delivery.

Determination of Acid α-Glucosidase Protein: Evaluation as a Screening Marker for Pompe Disease and Other Lysosomal Storage Disorders

Background: In recent years, there have been significant advances in the development of enzyme replacement and other therapies for lysosomal storage disorders (LSDs). Early diagnosis, before the onset of irreversible pathology, has been demonstrated to be critical for maximum efficacy of current and proposed therapies. In the absence of a family history, the presymptomatic detection of these disorders ideally can be achieved through a newborn screening program. One approach to the development of such a program is the identification of suitable screening markers. In this study, the acid α-glucosidase protein was evaluated as a marker protein for Pompe disease and potentially for other LSDs.

Methods: Two sensitive immunoquantification assays for the measurement of total (precursor and mature) and mature forms of acid α-glucosidase protein were used to determine the concentrations in plasma and dried blood spots from control and LSD-affected individuals.

Results: In the majority of LSDs, no significant increases above control values were observed. However, individuals with Pompe disease showed a marked decrease in acid α-glucosidase protein in both plasma and whole blood compared with unaffected controls. For plasma samples, this assay gave a sensitivity of 95% with a specificity of 100%. For blood spot samples, the sensitivity was 82% with a specificity of 100%.

Conclusions: This study demonstrates that it is possible to screen for Pompe disease by screening the concentration of total acid α-glucosidase in plasma or dried blood spots.

Towards a molecular therapy for glycogen storage disease type II (Pompe disease)

Glycogen storage disease type II (GSD-II), also known as Pompe disease, is a fatal genetic muscle disorder caused by a deficiency of acid alpha-glucosidase, a glycogen-degrading lysosomal enzyme. Currently, there is no treatment for this fatal disorder. However, several lines of research suggest the possibility of future treatment. Enzyme replacement strategies hold the greatest hope for patients currently affected by GSD-II, but future strategies could include in vivo or ex vivo gene therapy approaches and/or mesenchymal stem cell or bone-marrow transplantation approaches. Each of the approaches might eventually be combined to further improve the overall clinical efficacy of any one treatment regimen. The lessons learned from GSD-II research will also benefit a great number of individuals affected by other genetic disorders.