XAFS studies of Al/TiNx films on Si(100) at the Al K- and L3,2-edge.
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Journal Article↗
Biomedical subjects
L Chan
Publications and source records attributed to L Chan.
Human acyl-CoA:cholesterol acyltransferase-1 (ACAT-1) gene organization and evidence that the 4.3-kilobase ACAT-1 mRNA is produced from two different chromosomes.
Acyl-CoA:cholesterol acyltransferase (ACAT) plays important roles in cellular cholesterol homeostasis. Four human ACAT-1 mRNAs (7.0, 4.3, 3.6, and 2.8 kilobases (kb)) share the same short 5'-untranslated region (exon 1) and coding sequence (exons 2-15). The 4.3-kb mRNA contains an additional 5'-untranslated region (1289 nucleotides in length; exons Xa and Xb) immediately upstream from the exon 1 sequence. One ACAT-1 genomic DNA insert covers exons 1-16 and a promoter (the P1 promoter). A separate insert covers exon Xa (1277 base pairs) and a different promoter (the P7 promoter). Gene mapping shows that exons 1-16 and the P1 promoter sequences are located in chromosome 1, while exon Xa and the P7 promoter sequence are located in chromosome 7. RNase protection assays demonstrate three different protected fragments, corresponding to the 4.3-kb mRNA and the two other mRNAs transcribed from the two promoters. These results are consistent with the interpretation that the 4.3-kb mRNA is produced from two different chromosomes, by a novel RNA recombination mechanism involving trans-splicing of two discontinuous precursor RNAs.
5' Untranslated Regions↗
Ligand binding properties of the very low density lipoprotein receptor. Absence of the third complement-type repeat encoded by exon 4 is associated with reduced binding of Mr 40,000 receptor-associated protein.
The very low density lipoprotein receptor (VLDLR) binds, among other ligands, the Mr 40,000 receptor-associated protein (RAP) and a variety of serine proteinase-serpin complexes, including complexes of the proteinase urokinase-type plasminogen activator (uPA) with the serpins plasminogen activator inhibitor-1 (PAI-1) and protease nexin-1 (PN-1). We have analyzed the binding of RAP, uPA.PAI-1, and uPA.PN-1 to two naturally occurring VLDLR variants, VLDLR-I, containing all eight complement-type repeats, and VLDLR-III, lacking the third complement-type repeat, encoded by exon 4. VLDLR-III displayed approximately 4-fold lower binding of RAP than VLDLR-I and approximately 10-fold lower binding of the most C-terminal one of the three domains of RAP. In contrast, the binding of uPA.PAI-1 and uPA.PN-1 to the two VLDLR variants was indistinguishable. Surprisingly, uPA.PN-1, but not uPA.PAI-1, competed RAP binding to both VLDLR variants. These observations show that the third complement-type repeat plays a crucial role in maintaining the contact sites needed for optimal recognition of RAP, but does not affect the proteinase-serpin complex contact sites, and that two ligands can show full cross-competition without sharing the same contacts with the receptor. These results elucidate the mechanisms of molecular recognition of ligands by receptors of the low density lipoprotein receptor family.
Animals↗
Liver-specific inactivation of the abetalipoproteinemia gene completely abrogates very low density lipoprotein/low density lipoprotein production in a viable conditional knockout mouse.
Conventional knockout of the microsomal triglyceride transfer protein large subunit (lMTP) gene is embryonic lethal in the homozygous state in mice. We have produced a conditional lMTP knockout mouse by inserting loxP sequences flanking exons 5 and 6 by gene targeting. Homozygous floxed mice were born live with normal plasma lipids. Intravenous injection of an adenovirus harboring Cre recombinase (AdCre1) produced deletion of exons 5 and 6 and disappearance of lMTP mRNA and immunoreactive protein in a liver-specific manner. There was also disappearance of plasma apolipoprotein (apo) B-100 and marked reduction in apoB-48 levels. Wild-type mice showed no response, and heterozygous mice, an intermediate response, to AdCre1. Wild-type mice doubled their plasma cholesterol level following a high cholesterol diet. This hypercholesterolemia was abolished in AdCre1-treated lMTP-/- mice, the result of a complete absence of very low/intermediate/low density lipoproteins and a slight reduction in high density lipoprotein. Heterozygous mice showed an intermediate lipoprotein phenotype. The rate of accumulation of plasma triglyceride following Triton WR1339 treatment in lMTP-/- mice was <10% that in wild-type animals, indicating a failure of triglyceride-rich lipoprotein production. Pulse-chase experiments using hepatocytes isolated from wild-type and lMTP-/- mice revealed a failure of apoB secretion in lMTP-/- animals. Therefore, the liver-specific inactivation of the lMTP gene completely abrogates apoB-100 and very low/intermediate/low density lipoprotein production. These conditional knockout mice are a useful in vivo model for studying the role of MTP in apoB biosynthesis and the biogenesis of apoB-containing lipoproteins.
Abetalipoproteinemia↗
Reversal of hyperlipidaemia in apolipoprotein C1 transgenic mice by adenovirus-mediated gene delivery of the low-density-lipoprotein receptor, but not by the very-low-density-lipoprotein receptor.
We have shown previously that human apolipoprotein (apo)C1 transgenic mice exhibit hyperlipidaemia, due primarily to an impaired clearance of very-low-density lipoprotein (VLDL) particles from the circulation. In the absence of at least the low-density-lipoprotein receptor (LDLR), it was shown that APOC1 overexpression in transgenic mice inhibited the hepatic uptake of VLDL via the LDLR-related protein. In the present study, we have now examined the effect of apoC1 on the binding of lipoproteins to both the VLDL receptor (VLDLR) and the LDLR. The binding specificity of the VLDLR and LDLR for apoC1-enriched lipoprotein particles was examined in vivo through adenovirus-mediated gene transfer of the VLDLR and the LDLR [giving rise to adenovirus-containing (Ad)-VLDLR and Ad-LDLR respectively] in APOC1 transgenic mice, LDLR-deficient (LDLR-/-) mice and wild-type mice. Remarkably, Ad-VLDLR treatment did not reduce hyperlipidaemia in transgenic mice overexpressing human APOC1, irrespective of both the level of transgenic expression and the presence of the LDLR, whereas Ad-VLDLR treatment did reverse hyperlipidaemia in LDLR-/- and wild-type mice. On the other hand, Ad-LDLR treatment strongly decreased plasma lipid levels in these APOC1 transgenic mice. These results suggest that apoC1 inhibits the clearance of lipoprotein particles via the VLDLR, but not via the LDLR. This hypothesis is corroborated by in vitro binding studies. Chinese hamster ovary (CHO) cells expressing the VLDLR (CHO-VLDLR) or LDLR (CHO-LDLR) bound less APOC1 transgenic VLDL than wild-type VLDL. Intriguingly, however, enrichment with apoE enhanced dose-dependently the binding of wild-type VLDL to CHO-VLDLR cells (up to 5-fold), whereas apoE did not enhance the binding of APOC1 transgenic VLDL to these cells. In contrast, for binding to CHO-LDLR cells, both wild-type and APOC1 transgenic VLDL were stimulated upon enrichment with apoE. From these studies, we conclude that apoC1 specifically inhibits the apoE-mediated binding of triacylglycerol-rich lipoprotein particles to the VLDLR, whereas apoC1-enriched lipoproteins can still bind to the LDLR. The variability in specificity of these lipoprotein receptors for apoC1-containing lipoprotein particles provides further evidence for a regulatory role of apoC1 in the delivery of lipoprotein constituents to different tissues on which these receptors are located.
Adenoviridae↗
Sequence elements required for apolipoprotein B mRNA editing enhancement activity from chicken enterocytes.
Mammalian intestinal apolipoprotein B (apoB) mRNA edits codon 2153 from CAA in apoB100 mRNA to a stop codon (UAA) in apoB48 mRNA. By contrast, chicken intestinal apoB mRNA contains a CAA codon at the corresponding site, but is not edited. Chicken enterocyte S100 extracts fail to edit mammalian apoB RNA, but contain factor(s) which enhance the mammalian enterocytes editing activity. By converting the chicken apoB mooring sequences to the conserved mammalian sequences, the study confirmed that this 11-nucleotide stretch was necessary and sufficient for minimal RNA editing. Using rat and chicken apoB chimeric constructs, the study revealed that mammalian apoB sequences were required for editing enhancement. In concert with the 29-nucleotide conserved cassette, the 5' rat apoB element (nucleotides 6615-6629) increased editing at C-6666, and was necessary for editing enhancement of chicken enterocyte S100 extracts. Similarly, the 3' rat apoB element (nucleotides 6726-6752) was required for editing enhancement of chicken enterocyte S100 extracts, but to a lesser extent in efficiency, compared to the 5' region. In conclusion, this study identified the sequences required for editing enhancement activity from chicken enterocyte S100 extracts.
Animals↗
Close the South-North knowledge gap.
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Developing Countries↗
Normal perinatal rise in serum cholesterol is inhibited by hepatic delivery of adenoviral vector expressing apolipoprotein B mRNA editing enzyme (Apobec1) in rabbits.
BACKGROUND: Prenatal or neonatal hepatic gene delivery may result in more effective therapy for inborn errors of metabolism due to the immature immune system of the perinatal animal, and the ability to intervene prior to any significant cellular damage. Newborn New Zealand White rabbits have low serum levels of cholesterol at birth, with a significant and sustained rise of cholesterol while they are nursing. We used this physiologic hypercholesterolemia model to study the effect of adenovirus-mediated hepatic gene transfer of rat apolipoprotein B mRNA editing enzyme (Apobec1) on modulation of plasma cholesterol levels. METHODS AND RESULTS: Transcutaneous injection of recombinant adenovirus expressing Apobec1 (AvApobec1) into the liver of newborn rabbits in vivo resulted in efficient Apobec1 expression until Day 50, as detected by PCR-Southern blot analysis. By in vitro editing assay, liver extracts of AvApobec1-treated rabbits were found to have apoB mRNA editing activities of approximately 12, 15, and 15%, on Days 2, 10, and 20 after AvApobec1 administration, compared with 0% editing activity in AvLacZ control vector-injected animals. This physiological level of Apobec1 expression was associated with the production of apoB-48-containing lipoprotein particles from rabbit liver, with a concomitant 30% reduction in total plasma cholesterol compared to AvLacZ-treated or untreated control animals. CONCLUSION: Neonatal intrahepatic delivery of a first-generation adenoviral vector results in efficient gene transfer with little immune response, suggesting that repeated administration may be possible in the neonatal period.
APOBEC-1 Deaminase↗
Cesarean deliveries for medicaid patients: a comparison in public and private hospitals in Los Angeles county.
OBJECTIVE: The aims of the study were to describe the difference in cesarean delivery rates for Medicaid patients according to hospital type and adjusted for case mix and to determine cost implications for additional cesarean deliveries. STUDY DESIGN: This retrospective study used California discharge data for 92,800 patients delivered in 78 hospitals in Los Angeles County during 1991. Multivariable logistic regression was used to adjust for case mix and to calculate adjusted cesarean delivery rates according to hospital type. Cost estimates assumed $821 per day hospital reimbursement. RESULTS: The unadjusted cesarean delivery rate in private nonteaching hospitals (reference group) was 24.5%, compared with 13.2%, 17.4%, and 16.5% in public, health maintenance organization, and private teaching hospitals, respectively. Adjustment for case mix decreased the cesarean delivery rate in public (9.0%), health maintenance organization (12.0%), and private teaching hospitals (8.0%). Cesarean deliveries performed on patients in private nonteaching hospitals result in an additional $13.6 million in Medicaid health care expenses. CONCLUSIONS: There are increased health care costs related to increased cesarean deliveries performed on Medicaid patients in private nonteaching hospitals.
Cesarean Section↗
Do Medicare patients with disabilities receive preventive services? A population-based study.
OBJECTIVE: To compare health maintenance procedure rates of Medicare patients with different levels of disability. STUDY DESIGN: Observational study analyzing data from the 1995 Medicare Current Beneficiary Survey (MCBS, n = 15,590). Self-reported Pap smears, mammograms, and influenza and pneumococcal vaccinations were compared between groups with different levels of health-related difficulties in six activities of daily living (ADL). RESULTS: Compared to those without disabilities, the most severely disabled women (limitations in 5 or 6 ADL) reported fewer Pap smears (age < or =70, 23% vs 41%, p < .001) and mammograms (age > or = 50, 13% vs 44%, p < .001). In a controlled analysis, individuals with this high level of disability were 57% (95% confidence interval [CI], 33% to 72%) and 56% (95% CI, 43% to 76%) less likely to report receiving Pap smears and mammograms, respectively, compared with able-bodied women, regardless of their age, whether they were in an HMO, or whether they lived in a long-term care facility. Functional limitations were not a deterrent to receiving vaccinations. In general, patients in HMOs reported more procedures than those in fee-for-service, while those in long-term care facilities reported fewer procedures than those living in the community. CONCLUSIONS: Disability among Medicare patients is a significant, independent risk factor for not receiving mammograms and Pap smears. Efforts should be made to identify the most severely disabled because they are at particular risk.
Bacterial Vaccines↗
Mouse very low-density lipoprotein receptor (VLDLR): gene structure, tissue-specific expression and dietary and developmental regulation.
The very low density lipoprotein receptor (VLDLR) is a multifunctional apolipoprotein (apo) E receptor that shares a common structural feature as well as some ligand specificity to apo E with members of the low density lipoprotein receptor gene family. We have isolated and characterized the mouse VLDLR gene. The mouse VLDLR gene contains 19 exons spanning approximately 50 kb. The exon-intron organization of the gene is completely conserved between mouse and human. Since the 5'-flanking region of the mouse VLDLR gene contains two copies of a sterol regulatory element-1 like sequence (SRE-1), we next studied regulation of the VLDLR mRNA expression in heart, skeletal muscle and adipose tissue in C57BL/6, LDLR-/-, apo E-/- and LDLR-/-apo E-/- mice fed normal chow or atherogenic diet. The VLDLR mRNA expression was down-regulated 3-fold by feeding atherogenic diet in heart and skeletal muscle only in LDLR-/- mice. In contrast, VLDLR mRNA expression was up-regulated by atherogenic diet in adipose tissue in all animal models except double knockout mice. These results suggest that SRE-1 may be functional and VLDLR plays a role in cholesterol homeostasis in heart and skeletal muscle when LDLR is absent and that apo E is required for this modulation. Developmental regulation of the VLDLR mRNA expression was also tissue-specific. VLDLR mRNA expression in heart displayed significant up and down regulation during development. Maximal level was detected on post-natal day 3. However, the VLDLR mRNA levels in skeletal muscle remained relatively constant except a slight dip on post-natal day 7. In kidney and brain, VLDLR mRNA also peaked on post-natal day 3 but remained relatively constant thereafter. In liver, VLDLR mRNA expression was very low; it was barely detectable at day 19 of gestation and was decreased further thereafter. In adipose tissue, the VLDLR mRNA level showed an increase on post-natal day 13, went down again during weaning and then continued to increase afterwards. This developmental pattern as well as dietary regulation in adipose tissue supports the notion that VLDLR plays a role in lipid accumulation in this tissue. Although the primary role of VLDLR in heart, muscle and adipose tissue is likely in lipid metabolism, developmental pattern of this receptor in other tissues suggests that VLDLR has functions that are unrelated to lipid metabolism.
Adipose Tissue↗
Somatic gene therapy for dyslipidemias.
Somatic gene transfer is a valuable tool for the in vivo evaluation of lipoprotein metabolism. It has been used to dissect metabolic pathways, to establish structure-function relationships of various gene products, and to evaluate conventional lipid-lowering and novel therapeutic genes for the treatment of lipoprotein disorders. In this article we review some general aspects of somatic gene therapy and the different vehicles used for the delivery of therapeutic genes. We highlight some recent advances in adenoviral vector development that make this vector an attractive system for clinical trials.
Adenoviridae↗
Absence of a dose-response of cyclosporine levels to clinically used doses of diltiazem and verapamil.
We examined the effect of different doses of calcium channel blockers on plasma cyclosporine levels. As previously reported by multiple investigators, we observed that the administration of verapamil or diltiazem, but not nifedipine or isradipine, caused a significant increase in plasma cyclosporine levels achieved for a given dose of cyclosporine. In this article, we show that the effect of verapamil and diltiazem on cyclosporine levels appears to be independent of dosage within their usual prescription range.
Administration, Oral↗
Time course of response to pulse methylprednisolone therapy in renal transplant recipients with acute allograft rejection.
All rejection episodes that occurred from 1990 to 1995 treated by the University of Colorado renal transplant service were evaluated through a review of patient charts. Seventy-one episodes of rejection were treated initially with pulse steroids consisting of pulse methylprednisolone, 500 mg/d for 3 days, with sufficient follow-up to determine whether the patient would respond to this treatment. There was no difference between responders and nonresponders to methylprednisolone treatment with respect to serum creatinine level at time of diagnosis, age of allograft, nadir serum creatinine level, or presence of oliguria. The time course of change in serum creatinine levels (in milligrams per deciliter) in responders and nonresponders was similar until day 5, at which time significant differences could be seen (P < 0.01). In the 34 patients treated with OKT3 (muromonab-CD3), statistically significant differences between responders and nonresponders were only seen at day 14, but the small number of nonresponders (n = 4) makes this analysis inconclusive. Based on these data, it appears one cannot truly evaluate whether a patient will respond to three daily pulses of methylprednisolone until at least 3 days have passed since completion of therapy.
Acute Disease↗
Impact of medical student preceptorship on ED patient throughput time.
A prospective, consecutive study was performed to determine if medical student supervision in the emergency department (ED) changes patient throughput time (ie, the time from triage to discharge). The mean patient throughput time on days when medical students were present in the ED (group 1) was compared to the mean patient throughput time on days when medical students were absent from the ED (group 2). Throughput time was measured in minutes. The mean throughput times of the two groups were compared by the two tailed t test (P < .05). The study had a power of 90% (beta = .10) to detect a throughput time difference of 20 minutes. The two groups were also compared for mean daily acuity (as gauged by mean daily number of patient admissions) and mean daily patient census. The differences in mean daily throughput times (group 1, 145.2 min v group II, 150.6 min; P = .40), mean daily census (group 1, 28.1 patients v group 2, 28.1 patients; P = .75), and mean daily admissions (group 1, 10.4 patients v group 2, 10.7 patients; P = .74) were all insignificant. Precepting medical students in this ED did not significantly change patient throughput times.
Clinical Clerkship↗
Thrombolytic therapy and prophylactic anticoagulation in pregnant patients.
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Adult↗
Expeditious diagnosis of primary prosthetic valve failure.
Primary prosthetic valve failure is a catastrophic complication of prosthetic valves. Expeditious diagnosis of this complication is crucial because survival time is minutes to hours after valvular dysfunction. The only life-saving therapy for primary prosthetic valve failure is immediate surgical intervention for valve replacement. Because primary prosthetic valve failure rarely occurs, most physicians do not have experience with such patients and appropriate diagnosis and management may be delayed. A case is presented of a patient with primary prosthetic valve failure. This case illustrates how rapidly such a patient can deteriorate. This report discusses how recognition of key findings on history, physical examination, and plain chest radiography can lead to a rapid diagnosis.
Adult↗
Tension pneumoperitoneum caused by blunt trauma.
Tension pneumoperitoneum (TPP), the accumulation of free intraabdominal air under pressure, is a rare event. TPP usually occurs from bowel surgery or bowel perforations. Less commonly, TPP occurs in the presence of pneumothoraces or during positive pressure ventilation. Trauma has rarely been a reported cause of TPP. The cases of 2 patients with TPP after blunt trauma are reported. The pathophysiology and management of TPP are discussed.
Adult↗