Biomedical subjects

Asad Mian

Publications and source records attributed to Asad Mian.

4 recordsLinked to original sources

PubMed2004

Toxicity and adaptive immune response to intracellular transgenes delivered by helper-dependent vs. first generation adenoviral vectors.

The host immune response to intracellular transgenes delivered by helper-dependent (HDV) vs. first generation (FGV) adenoviral vectors has been relatively unstudied. Previous studies showed short-term correction of bovine and murine argininosuccinate synthetase (ASS) deficiency after first generation adenoviral-mediated liver gene therapy. To determine whether the host adaptive immune response against the intracellular transgene human ASS (hASS) contributed to loss of gene expression in this setting, the same vector (FGV-CAG-hASS) was injected into Rag-/- (immunodeficient) mice. As in wild-type C57BL/6 (B6) mice, Rag-/- mice also showed significant loss of hASS expression and vector by week 4 post-injection, with concomitant elevation of liver enzymes and disruption of liver architecture. Therefore, direct toxicity due to vector rather than adaptive immune response against hASS primarily accounted for loss of expression with FGVs. In contrast to hASS, beta-galactosidase is strongly immunogenic and activates the host adaptive immune response. Loss of transgene expression was observed in B6 mice with either a FGV or a HDV expressing beta-galactosidase. However, the drop in gene expression observed with the HDV was primarily due to the adaptive immune response, since both beta-galactosidase expression and vector genome were sustained in immunodeficient mice treated with HDV. As expected, with weakly immunogenic hASS, vector genome and hASS expression were sustained with a HDV in spite of ubiquitous expression of the transgene. Therefore, viral gene expression is a primary determinant of intermediate and chronic toxicities at day 3 and week 4 post-injection. However, even in the absence of viral gene expression, strongly immunogenic intracellular transgenes can stimulate clearance of transduced hepatocytes.

Adaptation, Physiological↗

PubMed2004

Long-term correction of ornithine transcarbamylase deficiency by WPRE-mediated overexpression using a helper-dependent adenovirus.

The urea cycle disorders (UCDs) are important models for developing gene replacement therapy for liver diseases. Long-term correction of the most common UCD, ornithine transcarbamylase (OTC) deficiency, has yet to be achieved in clinical or preclinical settings. The single human clinical trial using early-generation adenovirus (Ad) failed to show any biochemical correction. In adult OTC-deficient mice, an E1/E2-deleted Ad vector expressing the mouse OTC gene, but not the human, was only transiently therapeutic. By using post-transcriptional overexpression in the context of the less immunogenic helper-dependent adenoviral vector, we achieved metabolic correction of adult OTC-deficient mice for >6 months. Demonstrating this result were normalized orotic aciduria, normal hepatic enzyme activity, and elevated OTC RNA and protein levels in the absence of chronic hepatotoxicity. Overexpressing the human protein may have overcome two potential mechanisms accounting for poor cross-species complementation: a kinetic block at the level of mitochondrial import or a dominant negative effect by the mutant polypeptide. These data represent an important approach for treating human inborn errors of hepatocyte metabolism like the UCDs that require high-level transduction and gene expression for clinical correction.

Adenoviridae↗

PubMed2003

Urea Cycle Disorders.

Urea cycle disorders comprise a group of inborn errors of metabolism that represent unique gene-nutrient interactions whose significant morbidity arises from acute and chronic neurotoxicity associated with often massive hyperammonemia. Current paradigms of treatment are focused on controlling the flux of nitrogen transfer through the hepatic urea cycle by a combination of dietary and pharmacologic approaches. Evolving paradigms include the development of cell and gene therapies. Current research is focused on understanding the pathophysiology of ammonia-mediated toxicity and prevention of neural injury.

Journal Article↗

PubMed2002

Urea-cycle disorders as a paradigm for inborn errors of hepatocyte metabolism.

Urea-cycle disorders (UCDs) are a group of inborn errors of hepatocyte metabolism that are caused by the loss of enzymes involved in the process of transferring nitrogen from ammonia to urea, via the urea cycle (UC). Recent genetic analyses of inherited disorders that present with hyperammonemia demonstrate the function of cellular transporters that regulate the availability of UC intermediates. The regulation of UC intermediates, such as arginine, could have far reaching implications on nitric-oxide synthesis and vascular tone. Hence, each UCD and UC-related disorder constitutes a unique gene-nutrient interaction that is crucial for postnatal homeostasis. Recent advances in the diagnosis and management of UCDs include the application of in vivo metabolic-flux measurements. Cumulative morbidity is still high despite dietary and pharmacological therapies and, hence, both cell and gene therapies are being pursued as possible long-term corrective treatments. Although gene-replacement therapy has suffered recent clinical setbacks, new vector developments offer hope for the treatment of cell-autonomous defects of hepatocyte metabolism.

Cell- and Tissue-Based Therapy↗