Biomedical subjects

Lawrence Chan

Publications and source records attributed to Lawrence Chan.

8 recordsLinked to original sources

PubMed2003

NeuroD-betacellulin gene therapy induces islet neogenesis in the liver and reverses diabetes in mice.

To explore induced islet neogenesis in the liver as a strategy for the treatment of diabetes, we used helper-dependent adenovirus (HDAD) to deliver the pancreatic duodenal homeobox-1 gene (Ipf1; also known as Pdx-1) to streptozotocin (STZ)-treated diabetic mice. HDAD is relatively nontoxic as it is devoid of genes encoding viral protein. Mice treated with HDAD-Ipf1 developed fulminant hepatitis, however, because of the exocrine-differentiating activity of Ipf1. The diabetes of STZ mice was partially reversed by HDAD-mediated transfer of NeuroD (Neurod), a factor downstream of Ipf1, and completely reversed by a combination of Neurod and betacellulin (Btc), without producing hepatitis. Treated mice were healthy and normoglycemic for the duration of the experiment (>120 d). We detected in the liver insulin and other islet-specific transcripts, including proinsulin-processing enzymes, beta-cell-specific glucokinase and sulfonylurea receptor. Immunocytochemistry detected the presence of insulin, glucagon, pancreatic polypeptide and somatostatin-producing cells organized into islet clusters; immuno-electron microscopy showed typical insulin-containing granules. Our data suggest that Neurod-Btc gene therapy is a promising regimen to induce islet neogenesis for the treatment of insulin-dependent diabetes.

Adenoviridae↗

PubMed2003

Endothelial lipase is a major genetic determinant for high-density lipoprotein concentration, structure, and metabolism.

High-density lipoprotein (HDL) protects against atherosclerosis. Endothelial lipase (EL) has been postulated to be involved in lipoprotein, and possibly HDL, metabolism, yet the evidence has been scarce and conflicting. We have inactivated EL in mice by gene targeting. EL(-/-) mice have elevated plasma and HDL cholesterol, and increased apolipoproteins A-I and E. NMR analysis reveals an abundance of large HDL particles. There is down-regulation of the transcripts for phospholipid transfer protein, but up-regulation of those for hepatic lipase and lipoprotein lipase. Plasma lecithin:cholesterol acyltransferase is unchanged despite an increase in hepatic mRNA; lecithin:cholesterol acyltransferase activity toward endogenous EL(-/-) substrate is, however, reduced by 50%. HDL clearance is decreased in EL(-/-) mice; both the structure of HDL and the presence of EL are factors that determine the rate of clearance. To determine EL's role in humans, we find a significant association between a single-nucleotide polymorphism 584C/T in the EL (LIPG) gene and HDL cholesterol in a well characterized population of 372 individuals. We conclude that EL is a major determinant of HDL concentration, structure, and metabolism in mice, and a major determinant of HDL concentration in humans.

Animals↗

PubMed2002

Restoration of type VII collagen expression and function in dystrophic epidermolysis bullosa.

Dystrophic epidermolysis bullosa (DEB) is a family of inherited mechano-bullous disorders caused by mutations in the human type VII collagen gene (COL7A1). Individuals with DEB lack type VII collagen and anchoring fibrils, structures that attach epidermis and dermis. The current lack of treatment for DEB is an impetus to develop gene therapy strategies that efficiently transfer and stably express genes delivered to skin cells in vivo. In this study, we delivered and expressed full-length type VII collagen using a self-inactivating minimal lentivirus-based vector. Transduction of lentiviral vectors containing the COL7A1 transgene into recessive DEB (RDEB) keratinocytes and fibroblasts (in which type VII collagen was absent) resulted in persistent synthesis and secretion of type VII collagen. Unlike RDEB parent cells, the gene-corrected cells had normal morphology, proliferative potential, matrix attachment and motility. We used these gene-corrected cells to regenerate human skin on immune-deficient mice. Human skin regenerated by gene-corrected RDEB cells had restored expression of type VII collagen and formation of anchoring fibrils at the dermal-epidermal junction in vivo. These studies demonstrate that it is possible to restore type VII collagen gene expression in RDEB skin in vivo.

Cell Adhesion↗

PubMed2002

Increased beta -oxidation but no insulin resistance or glucose intolerance in mice lacking adiponectin.

Previous reports showed that recombinant fragments of adiponectin (adipo) displayed pharmacological effects when injected into rodents, but the relevance of these observations to the physiological function of adipo is unclear. We generated Adipo(-/-) mice by gene targeting. Adipo(-/-) mice are fertile with normal body and fat pad weights. Plasma glucose and insulin levels of Adipo(-/-) and Adipo(+/+) mice are similar under fasting conditions and during an intraperitoneal glucose tolerance test (GTT). Insulin tolerance test (ITT) also produces similar plasma glucose and insulin levels in the two groups of mice. Hyperinsulinemic-euglycemic clamp analysis showed that Adipo(-/-) and Adipo(+/+) mice have similar glucose infusion rates to maintain a similar serum glucose. High-fat diet feeding for 7 months led to similar weight gain and similar GTT and ITT responses. We next measured beta-oxidation and found it to be significantly increased in muscle and liver of Adipo(-/-) mice. In conclusion, our study indicates that absence of adipo causes increased beta-oxidation but does not cause glucose intolerance or insulin resistance in mice.

Adiponectin↗

PubMed2002

Cbfa1-independent decrease in osteoblast proliferation, osteopenia, and persistent embryonic eye vascularization in mice deficient in Lrp5, a Wnt coreceptor.

The low-density lipoprotein receptor-related protein (Lrp)-5 functions as a Wnt coreceptor. Here we show that mice with a targeted disruption of Lrp5 develop a low bone mass phenotype. In vivo and in vitro analyses indicate that this phenotype becomes evident postnatally, and demonstrate that it is secondary to decreased osteoblast proliferation and function in a Cbfa1-independent manner. Lrp5 is expressed in osteoblasts and is required for optimal Wnt signaling in osteoblasts. In addition, Lrp5-deficient mice display persistent embryonic eye vascularization due to a failure of macrophage-induced endothelial cell apoptosis. These results implicate Wnt proteins in the postnatal control of vascular regression and bone formation, two functions affected in many diseases. Moreover, these features recapitulate human osteoporosis-pseudoglioma syndrome, caused by LRP5 inactivation.

Animals↗

PubMed2002

PACS in private practice--effect on profits and productivity.

Picture archiving and communication systems (PACS) must be cost effective and productive to be successful. Referring physician and radiologist surveys, return on investment, and change in technical FTE productivity is evaluated. Referring physicians nearly unanimously prefer PACS over film, with productivity improvements claimed by 91%. Radiologists glean nearly 100% increased efficiency for computed tomography (CT), ultrasound, and Magnetic resonance imaging, and 50% for special procedures. Technologist productivity increased by 58% for MRI, 30% for CT, and 41% for ultrasound. Four-year experience with PACS reveals great success, with phase I return on investment after 3.5 years and more than $500,000 saved annually thereafter. There was instant conversion to 100% filmless interpretation and archive for all modalities on connection to PACS.

Attitude of Health Personnel↗

PubMed2002

Recent advances in liver-directed gene therapy for dyslipidemia.

As currently available preventive and therapeutic interventions for hypercholesterolemia are ineffective in a substantial proportion of patients, severe dyslipidemias associated with atherosclerotic vascular disease remain an important target for the development of novel gene therapies. The development of a safe and efficient gene transfer vector has been a major challenge in liver-directed gene therapy, but recently significant progress has been made in this area. Proof-of-principle experiments indicate that the transfer of lipid-modifying genes to the liver is an effective method to restore normal plasma lipids and protect against atherosclerosis. This article summarizes recent developments in liver-directed gene delivery and reviews data on the treatment of dyslipidemias and prevention of atherosclerosis in animals. The evidence presented suggests that some of the approaches taken in animals may be ready for clinical trials in the near future.

Gene Transfer Techniques↗

PubMed2002

Increased intracellular calcium transients by calmodulin antagonists differentially modulate tumor necrosis factor-alpha-induced E-selectin and ICAM-1 expression.

We investigated the role of intracellular calcium ([Ca(2+)](i)) in adhesion molecule expression in human umbilical vascular endothelial cells (HUVECs). Calmodulin (CaM) antagonists, W-7, trifluoperazine and chlorpromazine, triggered a rise in [Ca(2+)](i) in HUVECs. In the presence of extracellular Ca(2+), thapsigargin pretreatment completely prevented W-7-stimulated increase in [Ca(2+)](i), indicating that increase is attributable to the release of Ca(2+) from internal stores. The increased [Ca(2+)](i) acted as a second messenger to enhance tumor necrosis factor-alpha (TNF-alpha)-induced E-selectin and suppress intercellular cell adhesion molecule (ICAM-1) expression. Preincubation of HUVECs with the Ca(2+) chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraaceticacetomethyl ester blocked W-7-mediated effects on E-selectin and ICAM-1. The W-7 effects were paralleled by changes in the respective mRNAs, suggesting regulation at a pretranslational level. These findings indicate that CaM-regulated [Ca(2+)](i) in HUVECs may play an important role in controlling expression of endothelial adhesion molecules involved in atherogenesis.

Calcium↗