Biomedical subjects

D Y Hui

Publications and source records attributed to D Y Hui.

At least 19 recordsLinked to original sources

PubMed2001

HIV protease inhibitor induces fatty acid and sterol biosynthesis in liver and adipose tissues due to the accumulation of activated sterol regulatory element-binding proteins in the nucleus.

The mechanism by which human immunodeficiency virus (HIV) protease inhibitor therapy adversely induces lipodystrophy and hyperlipidemia has not been defined. This study explored the mechanism associated with the adverse effects of the prototype protease inhibitor ritonavir in mice. Ritonavir treatment increased plasma triglyceride and cholesterol levels through increased fatty acid and cholesterol biosynthesis in adipose and liver. Ritonavir treatment also resulted in hepatic steatosis and hepatomegaly. These abnormalities, which were especially pronounced after feeding a Western type high fat diet, were due to ritonavir-induced accumulation of the activated forms of sterol regulatory binding protein (SREBP)-1 and -2 in the nucleus of liver and adipose, resulting in elevated expression of lipid metabolism genes. Interestingly, protease inhibitor treatment did not alter SREBP mRNA levels in these tissues. Thus, the adverse lipid abnormalities associated with protease inhibitor therapy are caused by the constitutive induction of lipid biosynthesis in liver and adipose tissues due to the accumulation of activated SREBP in the nucleus.

Adipose Tissue↗

PubMed2001

Apolipoprotein E receptor binding versus heparan sulfate proteoglycan binding in its regulation of smooth muscle cell migration and proliferation.

This study showed that synthetic peptides containing either a single copy or tandem repeat of the receptor binding domain sequence of apolipoprotein (apo) E, or a peptide containing its C-terminal heparin binding domain, apoE-(211-243), were all effective inhibitors of platelet-derived growth factor (PDGF)-stimulated smooth muscle cell proliferation. In contrast, only the peptide containing a tandem repeating unit of the receptor binding domain sequence of apoE, apoE-(141-155)(2), was capable of inhibiting PDGF-directed smooth muscle cell migration. Peptide containing only a single unit of this sequence, apoE-(141-155), or the apoE-(211-243) peptide were ineffective in inhibiting PDGF-directed smooth muscle cell migration. Additional experiments showed that reductively methylated apoE, which is incapable of receptor binding yet retains its heparin binding capability, was equally effective as apoE in inhibiting PDGF-stimulated smooth muscle cell proliferation. However, reductively methylated apoE was unable to inhibit smooth muscle cell migration toward PDGF. Additionally, the receptor binding domain-specific apoE antibody 1D7 also mitigated the anti-migratory properties of apoE on smooth muscle cells. Finally, pretreatment of cells with heparinase failed to abolish apoE inhibition of smooth muscle cell migration. Taken together, these data documented that apoE inhibition of PDGF-stimulated smooth muscle cell proliferation is mediated by its binding to heparan sulfate proteoglycans, while its inhibition of cell migration is mediated through apoE binding to cell surface receptors.

Animals↗

PubMed2001

Apolipoprotein E: a cholesterol transport protein with lipid transport-independent cell signaling properties.

Apolipoprotein (apo) E is a 34-kDa glycoprotein associated with plasma lipoproteins. In contrast to other apolipoproteins, apoE is expressed ubiquitously in all tissues and appears to have a wide variety of functions in addition to lipid transport. Although the lipid transport properties of apoE are well characterized, the appreciation apoE functions other than lipid transport is still in an infancy stage. Nevertheless, there is increasing evidence that apoE regulates cell functions in a variety of tissues and organs. This review article summarizes briefly the current status of our understanding on the lipid transport-independent properties of this apolipoprotein.

Animals↗

PubMed2001

Compensatory phospholipid digestion is required for cholesterol absorption in pancreatic phospholipase A(2)-deficient mice.

BACKGROUND AND AIMS: Numerous studies have suggested phospholipid inhibition of dietary cholesterol absorption through the gastrointestinal tract. This study addressed the importance of luminal phospholipid hydrolysis in this process. METHODS: The effect of phospholipase inhibition on cholesterol transport from intestinal lumen to the lymphatics was evaluated in lymph fistula rats. Cholesterol and phospholipid absorption efficiency in intact animals was evaluated in control and phospholipase A(2) (PLA2) gene-targeted mice. RESULTS: The PLA2 inhibitor FPL 67047XX retarded cholesterol absorption in a lymph fistula rat model. Under basal chow-fed dietary conditions, cholesterol absorption efficiency from a single bolus meal, and plasma lipid levels, were similar among PLA2+/+, PLA2+/-, and PLA2-/- mice. Interestingly, the nonhydrolyzable phospholipid dioleoyl ether phosphatidylcholine suppressed cholesterol absorption by 10% to 18% in mice without regard to their PLA2 genotype. When 1-palmitoyl-2-[(14)C]oleoyl-phosphatidylcholine was used as the substrate, the radiolabeled phospholipid was found to be hydrolyzed and absorbed with equal efficiency in PLA2+/+, PLA2+/-, and PLA2-/- mice. CONCLUSIONS: These results suggested that although phospholipid digestion in the intestinal lumen is a prerequisite for efficient cholesterol absorption, additional enzyme(s) can compensate for pancreatic PLA2 in catalyzing phospholipid digestion and facilitating cholesterol absorption in PLA2 knockout mice.

Animals↗

PubMed2001

Targeted overexpression of IGF-I in smooth muscle cells of transgenic mice enhances neointimal formation through increased proliferation and cell migration after intraarterial injury.

The response of arterial smooth muscle cells to injury is governed by a complex series of events. Significant among them is the paracrine production of peptide growth factors. To determine the impact of local IGF-I gene expression on vascular injury, the left carotid arteries of SMP8-IGF-I mice (in which IGF-I is selectively overexpressed in smooth muscle cells by means of a smooth muscle alpha-actin promoter) and wild-type controls were injured mechanically with an epon resin probe. After 7 and 14 d, a progressive increase in medial area was seen in both SMP8-IGF-I and wild-type mice, but they were not significantly different from each other. However, by 14 d there was a more than 4-fold increase in neointimal area in transgenic vs. wild-type. The intima/media ratios were also strikingly increased at 14 d in the IGF-I-overexpressing animals. The mitotic index, determined in animals injected daily with bromodeoxyuridine for 3 d before death, was markedly elevated in both the media and neointima 7 d after injury in SMP8-IGF-I mice, but the effect had subsided by 14 d. Despite a higher rate of cell division, the relative increase in medial area was less in the SMP8-IGF-I mice than in wild-type mice at both 7 and 14 d, consistent with a stimulation of cell migration to the neointima. The experiments reported here provide compelling evidence that paracrine expression of IGF-I is a powerful stimulus for smooth muscle cell proliferation and migration in vivo.

Actins↗

PubMed2001

Lysosomal acid lipase-deficient mice: depletion of white and brown fat, severe hepatosplenomegaly, and shortened life span.

Lysosomal acid lipase (LAL) is essential for the hydrolysis of triglycerides (TG) and cholesteryl esters (CE) in lysosomes. A mouse model created by gene targeting produces no LAL mRNA, protein, or enzyme activity. The lal-/- mice appear normal at birth, survive into adulthood, and are fertile. Massive storage of TG and CE is observed in adult liver, adrenal glands, and small intestine. The age-dependent tissue and gross progression in this mouse model are detailed here. Although lal-/- mice can be bred to give homozygous litters, they die at ages of 7 to 8 months. The lal-/- mice develop enlargement of a single mesenteric lymph node that is full of stored lipids. At 6;-8 months of age, the lal-/- mice have completely absent inguinal, interscapular, and retroperitoneal white adipose tissue. In addition, brown adipose tissue is progressively lost. The plasma free fatty acid levels are significantly higher in lal-/- mice than age-matched lal+/+ mice, and plasma insulin levels were more elevated upon glucose challenge. Energy intake was also higher in lal-/- male mice, although age-matched body weights were not significantly altered from age-matched lal+/+ mice. Early in the disease course, hepatocytes are the main storage cell in the liver; by 3;-8 months, the lipid-stored Kupffer cells progressively fill the liver. The involvement of macrophages throughout the body of lal-/- mice provide evidence for a critical nonappreciated role of LAL in cellular cholesterol and fatty acid metabolism, adipocyte differentiation, and fat mobilization.

Adipocytes↗

PubMed2001

Differentiation-dependent expression and localization of the class B type I scavenger receptor in intestine.

The current study used the human Caco-2 cell line and mouse intestine to explore the topology of expression of the class B type I scavenger receptor (SR-BI) in intestinal cells. Results showed that intestinal cells expressed only the SR-BI isoform with little or no expression of the SR-BII variant. The expression of SR-BI in Caco-2 cells is differentiation dependent, with little or no expression in preconfluent undifferentiated cells. Analysis of Caco-2 cells cultured in Transwell porous membranes revealed the presence of SR-BI on both the apical and basolateral cell surface. Immunoblot analysis of mouse intestinal cell extracts demonstrated a gradation of SR-BI expression along the gastrocolic axis of the intestine, with the highest level of expression in the proximal intestine and decreasing to minimal expression levels in the distal intestine. Immunofluorescence studies with SR-BI-specific antibodies also confirmed this expression pattern. Importantly, the immunofluorescence studies also revealed that SR-BI immunoreactivity was most intense in the apical membrane of the brush border in the duodenum. The crypt cells did not show any reactivity with SR-BI antibodies. The localization of SR-BI in the jejunum was found to be different from that observed in the duodenum. SR-BI was present on both apical and basolateral surfaces of the jejunum villus. Localization of SR-BI in the ileum was also different, with little SR-BI detectable on either apical or basolateral membranes. Taken together, these results suggest that SR-BI has the potential to serve several functions in the intestine. The localization of SR-BI on the apical surface of the proximal intestine is consistent with the hypothesis of its possible role in dietary cholesterol absorption, whereas SR-BI present on the basolateral surface of the distal intestine suggests its possible involvement in intestinal lipoprotein uptake.

Animals↗

PubMed2000

Pulmonary surfactant proteins A and D are potent endogenous inhibitors of lipid peroxidation and oxidative cellular injury.

The lung is composed of a series of branching conducting airways that terminate in grape-like clusters of delicate gas-exchanging airspaces called pulmonary alveoli. Maintenance of alveolar patency at end expiration requires pulmonary surfactant, a mixture of phospholipids and proteins that coats the epithelial surface and reduces surface tension. The surfactant lining is exposed to the highest ambient oxygen tension of any internal interface and encounters a variety of oxidizing toxicants including ozone and trace metals contained within the 10 kl of air that is respired daily. The pathophysiological consequences of surfactant oxidation in humans and experimental animals include airspace collapse, reduced lung compliance, and impaired gas exchange. We now report that the hydrophilic surfactant proteins A (SP-A) and D (SP-D) directly protect surfactant phospholipids and macrophages from oxidative damage. Both proteins block accumulation of thiobarbituric acid-reactive substances and conjugated dienes during copper-induced oxidation of surfactant lipids or low density lipoprotein particles by a mechanism that does not involve metal chelation or oxidative modification of the proteins. Low density lipoprotein oxidation is instantaneously arrested upon SP-A or SP-D addition, suggesting direct interference with free radical formation or propagation. The antioxidant activity of SP-A maps to the carboxyl-terminal domain of the protein, which, like SP-D, contains a C-type lectin carbohydrate recognition domain. These results indicate that SP-A and SP-D, which are ubiquitous among air breathing organisms, could contribute to the protection of the lung from oxidative stresses due to atmospheric or supplemental oxygen, air pollutants, and lung inflammation.

Animals↗

PubMed2000

Importance of arginines 63 and 423 in modulating the bile salt-dependent and bile salt-independent hydrolytic activities of rat carboxyl ester lipase.

Previous studies using chemical modification approach have shown the importance of arginine residues in bile salt activation of carboxyl ester lipase (CEL) activity. However, the x-ray crystal structure of CEL failed to show the involvement of arginine residues in CEL-bile salt interaction. The current study used a site-specific mutagenesis approach to determine the role of arginine residues 63 and 423 in bile salt-dependent and bile salt-independent hydrolytic activities of rat CEL. Mutations of Arg(63) to Ala(63) (R63A) and Arg(423) to Gly(423) (R423G) resulted in enzymes with increased bile salt-independent hydrolytic activity against lysophosphatidylcholine, having 6.5- and 2-fold higher k(cat) values, respectively, in comparison to wild type CEL. In contrast, the R63A and R423A mutant enzymes displayed 5- and 11-fold decreases in k(cat), in comparison with wild type CEL, for bile salt-dependent cholesteryl ester hydrolysis. Although taurocholate induced similar changes in circular dichroism spectra for wild type, R63A, and R423G proteins, this bile salt was less efficient in protecting the mutant enzymes against thermal inactivation in comparison with control CEL. Lipid binding studies revealed less R63A and R423G mutant CEL were bound to 1,2-diolein monolayer at saturation compared with wild type CEL. These results, along with computer modeling of the CEL protein, indicated that Arg(63) and Arg(423) are not involved directly with monomeric bile salt binding. However, these residues participate in micellar bile salt modulation of CEL enzymatic activity through intramolecular hydrogen bonding with the C-terminal domain. These residues are also important, probably through similar intramolecular hydrogen bond formation, in stabilizing the enzyme in solution and at the lipid-water interface.

Animals↗

PubMed2000

Molecular structure and tissue-specific expression of the mouse pancreatic phospholipase A(2) gene.

Pancreatic phospholipase A(2) (PLA(2)) is involved with the hydrolysis of phospholipids into lysophospholipids and unesterified fatty acids. The enzyme has been postulated to play a key role in lipid absorption by intestinal absorptive cells as well as in the regulation of secretin release from intestinal endocrine cells. This manuscript reports the genomic organization and the primary sequence of the mouse PLA(2). The results showed that the mouse PLA(2) gene contains four exons interspersed by three introns, spans over 8kb in length, and is considerably larger than the human PLA(2) gene. The mouse PLA(2) protein contains 146 amino acid residues, including the signal peptide. The mouse protein is highly homologous to the rat, dog, and human enzyme, but is two residues shorter than the human protein. Mouse PLA(2) message is synthesized predominantly in the pancreas, but the lung also contains low levels of PLA(2) mRNA.

Amino Acid Sequence↗

PubMed2000

Variability of the intestinal uptake of lipids is genetically determined in mice.

The response of the plasma cholesterol concentration to changes in dietary lipids varies widely in humans and animals. There are variations in the in vivo absorption of cholesterol between different strains of mice. This study was undertaken in three strains of inbred mice to test the hypotheses that: (i) there are strain differences in the in vitro uptake of fatty acids and cholesterol and (ii) the adaptability of the intestine to respond to variations in dietary lipids is genetically determined. An in vitro intestinal ring technique was used to assess the uptake of medium- and long-chain fatty acids and cholesterol into jejunum and ileum of adult DBA/2, C57BL6, and C57L/J mice. The jejunal uptake of cholesterol was similar in C57L/J, DBA/2, or C57BL6 fed ad libitum a low-fat (5.7% fat, no cholesterol) chow diet. This is in contrast to a previous demonstration that in vivo cholesterol absorption was lower in C57L/J than in the other murine strains. The jejunal uptake of several long-chain fatty acids was greater in DBA/2 fed for 4 wk the high-fat (15.8% fat and 1.25% cholesterol) as compared with the low-fat diet. Furthermore, on the high-fat diet, the uptake of many long-chain fatty acids was higher in DBA/2 than in C57BL6 or C57L/J. The differences in cholesterol and fatty acid uptake were not explained by variations in food uptake, body weight gain, or the weight of the intestine. In summary: (i) there are strain differences in the in vitro intestinal uptake of fatty acids but not of cholesterol; (ii) a high-fat diet enhances the uptake of long-chain fatty acids in only one of the three strains examined in this study; and (iii) the pattern of strain- and diet-associated alterations in the in vivo absorption of cholesterol differs from the pattern of changes observed in vitro. We speculate that genetic differences in cholesterol and fatty acid uptake are explained by variations in the expression of protein-mediated components of lipid uptake.

Animals↗

PubMed2000

Apolipoprotein E inhibits neointimal hyperplasia after arterial injury in mice.

The potential cytostatic function of apolipoprotein (apo) E in vivo was explored by measuring neointimal hyperplasia in response to vascular injury in apoE-deficient and apoE-overexpressing transgenic mice. Results showed a significant increase in medial thickness, medial area, and neointimal formation after vascular injury in both apoE knockout and wild-type C57BL/6 mice. Immunochemical analysis with smooth muscle alpha-actin-specific antibodies revealed that the neointima contained proliferating smooth muscle cells. Neointimal area was 3.4-fold greater, and the intima/medial ratio as well as stenotic luminal area was more pronounced in apoE(-/-) mice than those observed in control mice (P < 0.05). The human apoE3 transgenic mice in FVB/N genetic background were then used to verify a direct effect of apoE in protection against neointimal hyperplasia in response to mechanically induced vascular injury. Results showed that neointimal area was reduced threefold to fourfold in mice overexpressing the human apoE3 transgene (P < 0.05). Importantly, suppression of neointimal formation in the apoE transgenic mice also abolished the luminal stenosis observed in their nontransgenic FVB/N counterparts. These results documented a direct role of apoE in modulating vascular response to injury, suggesting that increasing apoE level may be beneficial in protection against restenosis after vascular surgery.

Animals↗

PubMed2000

Adenovirus-mediated human pancreatic lipase gene transfer to rat bile: gene therapy of fat malabsorption.

This study explored the potential of using the gene therapy approach, based on adenovirus-mediated expression of pancreatic lipase in the hepatobiliary tract, to increase lipid digestion in the intestinal lumen and promote lipid absorption through the gastrointestinal tract. Recombinant adenovirus containing the human pancreatic lipase cDNA (AdPL) was shown to transduce and mediate pancreatic lipase biosynthesis in rat IEC-6 epithelial cells in vitro. Retrograde infusion of recombinant adenovirus (3 x 10(8) plaque-forming units) containing the bacterial LacZ gene (AdLacZ) into the bile duct of rats resulted in positive X-gal reaction products in the periportal liver cells 7 days after AdLacZ infusion. A high level of human pancreatic lipase was detected in bile after retrograde bile duct infusion of rats with AdPL but not in the bile of animals infused with AdLacZ. Triglyceride hydrolytic activity in the bile of AdPL-infused rats was equivalent to that present in pancreatic juice. In contrast, serum obtained from these animals did not contain any detectable pancreatic lipase activity. These results suggest that ectopic expression of pancreatic enzymes in the hepatobiliary tract may be an alternative therapeutic strategy for treating fat malabsorption due to pancreatic insufficiency.

Adenoviridae↗

PubMed2000

Apolipoprotein E inhibition of vascular smooth muscle cell proliferation but not the inhibition of migration is mediated through activation of inducible nitric oxide synthase.

Initial experiments revealed that low concentrations of apolipoprotein (apo) E (0.1 to 5 microg/mL) were effective in inhibiting platelet-derived growth factor (PDGF)-directed smooth muscle cell (SMC) migration by 60% to 80%. In contrast, higher concentrations of apoE, at 25 and 50 microg/mL, were necessary to achieve similar inhibition of PDGF-induced SMC proliferation. The potential role of nitric oxide (NO) in mediating the inhibitory effects of apoE was explored. Results showed that, although 0.1 to 5 microg/mL of apoE had no effect on NO production by SMCs, physiological concentrations of apoE (25 to 50 microg/mL) enhanced NO synthesis by 2-fold in a dose-dependent manner (P<0.001). Reverse transcription-polymerase chain reaction amplification of RNA obtained from control and apoE-treated SMCs demonstrated a direct role of apoE in activating inducible nitric oxide synthase (iNOS) gene expression. The apoE-induced nitric oxide production was significantly reduced by coincubation of the cells with aminoguanidine or N(G)-monomethyl-L-arginine (P<0.05) or with antisense iNOS oligodeoxynucleotides (P<0.01). Moreover, the inhibition of iNOS was shown to overcome apoE suppression of PDGF-induced vascular SMC proliferation. However, apoE suppression of PDGF-directed SMC migration was not affected by these treatments. Taken together, these results document that apoE exerts its inhibitory effects on cell proliferation via activation of iNOS. However, apoE inhibition of cell migration is mediated by a mechanism independent of iNOS activation.

Apolipoproteins E↗

PubMed1999

Pancreatic lipase/colipase-mediated triacylglycerol hydrolysis is required for cholesterol transport from lipid emulsions to intestinal cells.

This study tested the hypothesis that dietary cholesterol uptake by intestinal cells is dependent on the structure and composition of the lipid carriers in the extracellular milieu. In in vivo experiments with female C57BL/6 mice, cholesterol absorption from phospholipid/triacylglycerol emulsions was significantly reduced by administration of tetrahydrolipstatin, an inhibitor of pancreatic lipase. This inhibitor had no effect on the absorption of cholesterol from phospholipid vesicles. The importance of pancreatic-lipase-mediated triacylglycerol hydrolysis for cholesterol transport from emulsions to intestinal cells was confirmed by in vitro experiments with rat IEC-6 intestinal cells. Cellular uptake of cholesterol from emulsions with a phospholipid/triacylglycerol molar ratio of <0.3 could be stimulated by pancreatic lipase/colipase hydrolysis of the core neutral lipids. However, pancreatic lipase/colipase was ineffective in hydrolysing triacylglycerols in emulsions with a phospholipid/triacylglycerol molar ratio of >0.3. Phospholipase A2-mediated hydrolysis of the surface phospholipids was necessary prior to triacylglycerol hydrolysis in these phospholipid-rich emulsions and to the stimulation of cholesterol transport from these particles to IEC-6 cells. The data also revealed that minimal triacylglycerol hydrolysis was sufficient to significantly increase cholesterol transport from lipid emulsions to the intestinal cells. Thus the products of triacylglycerol hydrolysis, namely monoacylglycerol and non-esterified fatty acids, are key determinants in mediating cholesterol transport from lipid emulsions to intestinal cells. Taken together, these results support the hypothesis that remodelling of the surface and core components of lipid carriers is necessary prior to absorption of dietary cholesterol from the gastrointestinal tract.

Animals↗

PubMed1999

Carboxyl ester lipase activity in milk prevents fat-derived intestinal injury in neonatal mice.

Carboxyl ester lipase (bile salt-stimulated lipase) is a pancreatic enzyme capable of hydrolyzing esters of cholesterol and fat-soluble vitamins. It also efficiently digests triglycerides (TG) into free fatty acids and glycerol and is abundant in the milk of humans and several other species. We used the mouse as a model to test the hypothesis that milk-derived carboxyl ester lipase (CEL) digests milk TG and that without its activity milk lipids and their digestion intermediates can disrupt the intestinal epithelium of neonates. CEL protein and enzymatic activity were shown to be abundant in mouse milk. After 24-h administration of the CEL-specific inhibitor, WAY-121,751-5, the small intestines of treated and control neonates were analyzed histologically for signs of fat malabsorption and injury to their villus epithelium. In vehicle-fed controls, TG were digested and absorbed in the duodenum and jejunum, whereas, in inhibitor-fed littermates, large intracellular neutral lipid droplets accumulated in enterocytes of the ileum, resulting in damage to the villus epithelium. Similar results were observed in neonates nursed by CEL knockout females compared with heterozygous controls. The results suggest that lack of CEL activity causes incomplete digestion of milk fat and lipid accumulation by enterocytes in the ileum of neonatal mice.

Administration, Oral↗

PubMed1998

Apolipoprotein E inhibits platelet-derived growth factor-induced vascular smooth muscle cell migration and proliferation by suppressing signal transduction and preventing cell entry to G1 phase.

The anti-atherogenic effects of apolipoprotein (apo) E have been attributed to its ability to reduce plasma cholesterol level and to limit foam cell formation. The purpose of this study was to ascertain if apoE also may have cytostatic functions that could attenuate vascular occlusive diseases. Purified apoE inhibited smooth muscle cell migration directed to platelet-derived growth factor (PDGF) or oxidized LDL (oxLDL) (p < 0.0001). The purified apoE also suppressed PDGF- and oxLDL-induced smooth muscle cell proliferation (p < 0.001). These apoE inhibitory effects were not because of suppression of PDGF binding to its receptors on the smooth muscle cells, but was correlated with a significant reduction in agonist-stimulated mitogen-activated protein kinase activity (p < 0.01). ApoE also inhibited PDGF-induced cyclin D1 mRNA expression, suggesting that the apoE effect was mediated by growth arrest at the G0 to G1 phase. Taken together, these results suggest that apoE has cytostatic functions in the vessel wall and may protect against vascular diseases through inhibition of cell signaling events associated with growth factor-induced smooth muscle cell migration and proliferation.

Animals↗

PubMed1998

Synthesis and secretion of the pancreatic-type carboxyl ester lipase by human endothelial cells.

Human aortic extracts contain significant cholesteryl ester hydrolytic activity. The enzymic activity was shown to be activated by trihydroxylated bile salt, but not by dihydroxylated bile salt. Monospecific antibodies prepared against rat pancreatic carboxyl ester lipase (CEL, cholesterol esterase) immunoprecipitated cholesteryl ester hydrolytic activity from human aorta, demonstrating that the neutral CEL in aorta is highly similar to and probably identical with the pancreatic enzyme. Reverse transcriptase PCR amplification of mRNA from human aortic endothelial cells revealed de novo synthesis of the pancreatic-type CEL by these cells. Preincubating human aortic endothelial cells with oxidized or native low-density lipoprotein resulted in an 8- and 3-fold increase in CEL activity secreted into the culture medium respectively. A potential physiological role for the endothelial CEL was demonstrated by studies showing its ability to confer partial protection against the cytotoxic effects of lysophosphatidylcholine. The protective effect of CEL is related to its bile-salt-independent lysophospholipase activity. However, CEL hydrolysis of lysophosphatidylcholine can be inhibited by excess cholesterol. Taken together, these results indicate that pancreatic-type CEL is synthesized by cells lining the vessel wall. Moreover, vascular CEL may interact with cholesterol and oxidized lipoproteins to modulate the progression of atherosclerosis.

Animals↗