Biomedical subjects

Patrick C Choy

Publications and source records attributed to Patrick C Choy.

12 recordsLinked to original sources

PubMed2006

Cloning and characterization of a cDNA encoding human cardiolipin synthase (hCLS1).

Cardiolipin (CL) is a phospholipid localized to the mitochondria, and its biosynthesis is essential for mitochondrial structure and function. We report here the identification and characterization of a cDNA encoding the first mammalian cardiolipin synthase (CLS1) in humans and mice. This cDNA exhibits sequence homology with members of a CLS gene family that share similar domain structure and chemical properties. Expression of the human CLS (hCLS1) cDNA in reticulocyte lysates or insect cells led to a marked increase in CLS activity. The enzyme is specific for CL synthesis, because no significant increase in phosphatidylglycerol phosphate synthase activity was observed. In addition, CL pool size was increased in hCLS1-overexpressing cells compared with controls. Furthermore, the hCLS1 gene was highly expressed in tissues such as heart, skeletal muscle, and liver, which have been shown to have high CLS activities. These results demonstrate that hCLS1 encodes an enzyme that synthesizes CL.

Amino Acid Sequence↗

PubMed2005

Cloning and characterization of murine 1-acyl-sn-glycerol 3-phosphate acyltransferases and their regulation by PPARalpha in murine heart.

AGPAT (1-acyl-sn-glycerol 3-phosphate acyltransferase) exists in at least five isoforms in humans, termed as AGPAT1, AGPAT2, AGPAT3, AGPAT4 and AGPAT5. Although they catalyse the same biochemical reaction, their relative function, tissue expression and regulation are poorly understood. Linkage studies in humans have revealed that AGPAT2 contributes to glycerolipid synthesis and plays an important role in regulating lipid metabolism. We report the molecular cloning, tissue distribution, and enzyme characterization of mAGPATs (murine AGPATs) and regulation of cardiac mAGPATs by PPARalpha (peroxisome-proliferator-activated receptor alpha). mAGPATs demonstrated differential tissue expression profiles: mAGPAT1 and mAGPAT3 were ubiquitously expressed in most tissues, whereas mAGPAT2, mAGPAT4 and mAGPAT5 were expressed in a tissue-specific manner. mAGPAT2 expressed in in vitro transcription and translation reactions and in transfected COS-1 cells exhibited specificity for 1-acyl-sn-glycerol 3-phosphate. When amino acid sequences of five mAGPATs were compared, three highly conserved motifs were identified, including one novel motif/pattern KX2LX6GX12R. Cardiac mAGPAT activities were 25% lower (P<0.05) in PPARalpha null mice compared with wild-type. In addition, cardiac mAGPAT activities were 50% lower (P<0.05) in PPARalpha null mice fed clofibrate compared with clofibrate fed wild-type animals. This modulation of AGPAT activity was accompanied by significant enhancement/reduction of the mRNA levels of mAGPAT3/mAGPAT2 respectively. Finally, mRNA expression of cardiac mAGPAT3 appeared to be regulated by PPARalpha activation. We conclude that cardiac mAGPAT activity may be regulated by both the composition of mAGPAT isoforms and the levels of each isoform.

1-Acylglycerol-3-Phosphate O-Acyltransferase↗

PubMed2005

Hyperhomocysteinemia induces hepatic cholesterol biosynthesis and lipid accumulation via activation of transcription factors.

Hyperhomocysteinemia is an independent risk factor for cardiovascular disorders. Elevated plasma homocysteine (Hcy) concentration is associated with other cardiovascular risk factors. We previously reported that Hcy stimulated cholesterol biosynthesis in HepG2 cells. In the present study, we investigated the underlying mechanisms of Hcy-induced hepatic cholesterol biosynthesis in an animal model. Hyperhomocysteinemia was induced in Sprague-Dawley rats by feeding a high-methionine diet for 4 wk. The mRNA expression and the enzyme activity of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase were significantly increased in livers of hyperhomocysteinemic rats. There were marked hepatic lipid accumulation and an elevation of plasma cholesterol concentration in hyperhomocysteinemic rats. Three transcription factors, namely, sterol regulatory element-binding protein-2 (SREBP-2), cAMP response element-binding protein (CREB), and nuclear factor Y (NF-Y) were activated in livers of hyperhomocysteinemic rats. Upon Hcy treatment of hepatocytes, there was a significant increase in HMG-CoA reductase mRNA expression in these cells. The activation of SREBP-2, CREB, and NF-Y preceded the increase in HMG-CoA reductase expression in Hcy-treated cells. Pretreatment of hepatocytes with inhibitors for transcription factors not only blocked the activation of SREBP-2, CREB, and NF-Y but also attenuated Hcy-induced HMG-CoA reductase mRNA expression. These results suggested that hyperhomocysteinemia-induced activation of SREBP-2, CREB, and NF-Y was responsible for increased cholesterol biosynthesis by transcriptionally regulating HMG-CoA reductase expression in the liver leading to hepatic lipid accumulation and subsequently hypercholesterolemia. In conclusion, the stimulatory effect of Hcy on hepatic cholesterol biosynthesis may represent an important mechanism for hepatic lipid accumulation and cardiovascular disorder associated with hyperhomocysteinemia.

Acyl Coenzyme A↗

PubMed2005

Ganoderma lucidum inhibits inducible nitric oxide synthase expression in macrophages.

Nitric oxide (NO) is a principal mediator in many physiological and pathological processes. Overproduction of NO via the inducible nitric oxide synthase (iNOS) has cytotoxic effect through the formation of peroxynitrite with superoxide anion. The iNOS is mainly expressed in macrophages and is able to produce large amount of NO. The expression of iNOS is mainly regulated at the transcriptional level. The iNOS-mediated NO production plays a role in the development of atherosclerosis. Ganoderma lucidum (G. lucidum, Linzhi or Reishi) is a traditional herbal medicine which is commonly used as health supplement. Several studies have demonstrated its effectiveness against cancer, immunological disorders and cardiovascular diseases. The objective of the present study was to investigate the effect of G. lucidum on iNOS-mediated NO production in macrophages. Human monocytic cell (THP-1) derived macrophages were incubated with lipopolysaccharide (LPS) for 24 h. Such treatment significantly stimulated NO production (253% versus the control). Such a stimulatory effect was resulted from increased iNOS mRNA expression (270% versus the control) and iNOS activity (169.5% versus the control) in macrophages. The superoxide anion level was also elevated (150% versus the control) in LPS-treated macrophages. Treatment of macrophages with G. lucidum extract (100 microg/ml) completely abolished LPS-induced iNOS mRNA expression and NO production. Such an inhibitory effect of G. lucidum was mediated via its antioxidant action against LPS-induced superoxide anion generation in macrophages. These results suggest that G. lucidum may exert a therapeutic effect against atherosclerosis via ameliorating iNOS-mediated NO overproduction in macrophages.

Antioxidants↗

PubMed2005

Emerging issues in traditional Chinese medicine.

Traditional Chinese medicine (TCM) has many beneficial effects and has been practiced for several thousand years. It is known to treat the cause of a disease rather than to alleviate its symptoms. Based on a belief that TCM is natural, safe, and of lower cost, consumers worldwide are spending more out-of-pocket money on this form of therapy. This increased spending, and reports of adverse reactions, has drawn the attention of many regulatory agencies. Scientists have called for more evidence-based and scientific research on the risks and benefits of TCM. In Canada, the Natural Health Product Regulations came into effect January 2004. TCM herbal product manufacturers will need to provide products of reputable quality to the market. Many will apply modern technology and good science to support their products. The issues facing producers, scientists, and consumers alike are quality control and assessment, standardization of bioactive components, mechanisms of actions, and integration of the evolved modern Chinese medicine into the healthcare system. Solid science, better regulation of the final product, and better education of consumers are necessary to extract the best of TCM to complement existing conventional medicine to deliver the best healthcare.

Animals↗

PubMed2004

17-Beta estradiol enhances prostaglandin E2 production in human U937-derived macrophages.

Prostaglandins (PGs) are potent eicosanoid lipid mediators that have been implicated in numerous homeostatic functions and inflammation. Estrogens have been shown to regulate the expression of genes in lipid metabolism in many cellular systems. In this study, the activation of macrophages and the modulation of PG release by estrogens were examined. The effects of 17-alpha and 17-beta estradiols, phytoestrogen Genistein and several selective estrogen receptor modulators on the release of PGE2 were investigated in human U937-derived macrophages. 17-Beta estradiol caused an enhancement of PGE2 production in a time- and dose-dependent manner. Treatment of macrophages with 17-beta estradiol elicited an increased arachidonic acid (AA) release and an up-regulation of both cyclooxygenesis-1 and cyclooxygenesis-2 enzymes at both the transcript and protein levels. In addition, immunostaining of nuclear estrogen receptor alpha and the observation of ICI182 780 blockade of PGE2 production indicated that 17-beta estradiol-induced PGE2 release was mainly through nuclear estrogen receptor alpha.

Arachidonic Acid↗

PubMed2004

Lipids and atherosclerosis.

Atherosclerosis is the leading cause of death in North America and within the next two decades will be the leading cause worldwide. Atherosclerosis is characterized by vascular obstruction from the deposits of plaque, resulting in reduced blood flow. Plaque rupture and the consequent thrombosis may lead to sudden blockage of the arteries and cause heart attack. High serum lipid levels, especially the elevated level of low-density lipoprotein (LDL), have been shown to be strongly related to the development of atherosclerosis. It is generally accepted that atherosclerotic lesions are initiated via an enhancement of LDL uptake by monocytes and macrophages. In the liver, uptake of plasma LDL is mediated via specific LDL receptors, but a scavenger receptor system is employed by macrophages. Plasma LDL must be modified prior to uptake by macrophages. Analysis of the lipid content in the oxidatively modified LDL from hyper lipidemic patients revealed that the level of lysophosphatidylcholine was greatly elevated, and the high level of the lysolipid was shown to impair the endothelium-dependent relaxation of the blood vessels. In a separate study, we showed that a high level of homocysteine caused the increase in cholesterol production and apolipoprotein B-100 secretion in hepatic cells. Statins have been used effectively to control the production of cholesterol in the liver, and recently, ezetimibe has been shown to supplement the efficacy of statins by inhibiting cholesterol absorption. The factor of elevated levels of triglyceride-rich lipoproteins in association with depressed high-density lipoproteins, usually in the context of insulin resistance, is an important contributor to atherosclerosis and can be effectively treated with fibric acid derivatives. In hyperhomocysteinemia, folic acid supplements may have a role in the control of cholesterol by reducing the plasma homocysteine level.

Arteriosclerosis↗

PubMed2004

Complex expression pattern of the Barth syndrome gene product tafazzin in human cell lines and murine tissues.

Tafazzins, a group of proteins that are defective in patients with Barth syndrome, are produced by alternate splicing of the gene G4.5 or TAZ. RT-PCR and transcription-coupled in vitro translation analysis were undertaken to determine the expression of alternatively spliced TAZ mRNA in mouse tissues and human cell lines. Only two tafazzin transcripts, both lacking exon 5, were expressed in murine tissues, whereas four tafazzin transcripts, all lacking exon 5, were observed in human umbilical vein vascular endothelial cells and U937 human monoblasts indicating a species-specific difference in the expression of TAZ mRNAs in mouse and humans. Only TAZ lacking exon 5 was expressed in murine heart. Differentiation of U937 human monoblasts into macrophages did not alter expression of the tafazzin transcripts indicating that TAZ expression is independent of monocyte differentiation. Cloning and in vitro expression of both murine and human tafazzin cDNA revealed two prominent protein bands that corresponded to the expected sizes of alternative translation. A novel fifth motif, identified as critical for the glycerolphosphate acyltransferase family, was observed in human tafazzin. The presence of a mutation in this region in Barth syndrome patients indicates that this motif is essential for tafazzin function.

Acyltransferases↗

PubMed2003

Stimulation of cardiac cardiolipin biosynthesis by PPARalpha activation.

The role of peroxisome proliferator-activated receptor alpha (PPARalpha)-stimulated phospholipase A2 (PLA2) in cardiac mitochondrial cardiolipin (CL) biosynthesis was examined in both in vivo and in vitro models. Treatment of rat heart H9c2 cells with clofibrate increased the expression and activity of 14 kDa PLA2 but did not affect the pool size of CL. Clofibrate treatment stimulated de novo CL biosynthesis via an increase in phosphatidylglycerolphosphate (PGP) synthase activity, accounting for the unaltered CL content. Cardiac PLA2, PGP synthase, and CDP-1,2-diacyl-sn-glycerol synthase (CDS-2) activities and CDS-2 mRNA levels were elevated in mice fed clofibrate for 14 days compared with controls. In PPARalpha-null mice, clofibrate feeding did not alter cardiac PLA2, PGP synthase activities, or CDS-2 activity and mRNA level, confirming that these enzymes are regulated by PPARalpha activation. In contrast to mouse heart, clofibrate treatment did not affect the activity or mRNA levels of CDS-2 in H9c2 cells, indicating that CDS-2 is regulated differently in rat heart H9c2 cells in vitro and in mouse heart in vivo. These results clearly indicate that cardiac CL de novo biosynthesis is stimulated by PPARalpha activation in responsive rodent models and that CDS-2 is an example of an enzyme that exhibits alternative regulation in vivo and in cultured cell lines. This study is the first to demonstrate that CL de novo biosynthesis is regulated by PPARalpha activation.

Animals↗

PubMed2003

Change in lipid profile and impairment of endothelium-dependent relaxation of blood vessels in rats after bile duct ligation.

Hyperlipidemia, a condition normally observed in cholestatic liver disease, is also a risk factor for the development of atherosclerosis. The relationship between the elevation of lipoproteins in cholestatic liver diseases and atherosclerosis formation has not been elucidated. In this study, we propose that the impairment of endothelium-dependent relaxation (EDR) of blood vessels in cholestatic liver diseases may lead to the development of atherosclerosis. Using bile duct ligation (BDL) in rats as a model, we examined the liver function, serum lipid profile, EDR and morphologic change of the aorta from both sham operated and BDL rats. Significant increases in liver and spleen weights, serum alanine transaminase (ALT) and aspartate transaminase (AST) activities and the bilirubin level were observed in BDL rats. Upon bile duct ligation, the total and low-density lipoprotein cholesterol levels were increased but the high-density lipoprotein cholesterol and triglyceride levels were reduced. Less contractility and lowered response to acetylcholine-induced relaxation were found in aorta segments. In addition, the acetylcholine-induced relaxation was blocked by both L-NAME and 15 mM KCl. Our results suggest that both nitric oxide and endothelium-derived hyperpolarizing factor are important elements for the impairment of the EDR in BDL rats. In addition, a mild atrophy of the media of the aorta was detected in BDL rats. We conclude that the alterations of lipid profile and the mild atrophy of the media may lead to the impairment of EDR in the aorta in BDL rats, and these factors may potentiate the development of atherosclerosis.

Acetylcholine↗

PubMed2003

Cyclooxygenase expression is elevated in retinoic acid-differentiated U937 cells.

Cyclooxygenase (COX) is the rate-limiting enzyme for the biosynthesis of prostaglandins in monocytes/macrophages. The COX-1 is constitutively expressed in most tissues and may be involved in cellular homeostasis, whereas the COX-2 is an inducible enzyme that may play an important role in inflammation and mitogenesis. When U937 monocytic cells were incubated with retinoic acid (RA) for 48 h, cell differentiation took place with concomitant increases in prostaglandin E2 (PGE2) production and COX activity. In this study, the mechanism of RA (all-trans- or 9-cis-RA)-induced enhancement of PGE2 biosynthesis in U937 cells was examined. Treatment of cells with all-trans- or 9-cis-RA up to 48 h caused an increase in PGE2 production in a time- and dose-dependent manner. Both RA isomers caused the enhancement of PGE2 production and the up-regulation of COX-1 expression at the protein and mRNA levels. The increase in COX-1 mRNA was found to precede the increase in COX-1 protein expression. Interestingly, the COX-2 protein and COX-2 mRNA were not detected in U937 cells, and their levels remained undetectable during the entire course of RA treatment. We conclude that treatment of U937 cells by RA for 48 h caused the initiation of cell differentiation, which was found to be concomitant with a significant increase in PGE2 production mediated via the up-regulation of COX-1 mRNA and protein expression.

Antineoplastic Agents↗

PubMed2003

Regulation of cytosolic phospholipase A2, cyclooxygenase-1 and -2 expression by PMA, TNFalpha, LPS and M-CSF in human monocytes and macrophages.

Cytosolic phospholipases A2 (cPLA2) and cyclooxygenases-1 and -2 (COX-1 and -2) play a pivotal role in the metabolism of arachidonic acid (AA) and in eicosanoid production. The coordinate regulation and expression of these enzymes is not well defined. In this study, the effect of phorbol 12-myristate 13-acetate (PMA), tumor necrosis factor alpha (TNFalpha), lipopolysaccharide (LPS) and macrophage-colony stimulating factor (M-CSF) on AA release and prostaglandin E2 (PGE2) production and the expression of cPLA2 and COX-1 and -2 were investigated in U937 human pre-monocytic cells and fully differentiated macrophages. Treatment of U937 cells with PMA or macrophages with LPS increased AA release and PGE2 production. Incubation of U937 cells or macrophages for 8 h with all stimuli elevated cPLA2 expression. In contrast, cPLA2 expression was reduced upon further incubation of U937 cells or macrophages for 24 h with all stimuli indicating a bi-phasic expression pattern of this enzyme. PMA induced COX-1 expression in U937 cells whereas LPS induced COX-2 expression in macrophages. Although TNFalpha and M-CSF induced a significant amount of AA release in both cell models, they failed to induce a comparable production of PGE2 since they were unable to induce the coordinate expression of the downstream key enzymes, COX-1 or COX-2. The results suggest that the enhancement of AA release in both U937 cells and macrophages may be caused by both increased cPLA2 activity and elevated cPLA2 protein expression. In addition, PMA stimulates PGE2 production via up-regulation of COX-1, and likely COX-2, expression in U937 cells whereas LPS stimulates PGE2 production via induction of COX-2 expression in macrophages.

Arachidonic Acid↗