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Biomedical subjects

D Lin

Publications and source records attributed to D Lin.

At least 163 records · Page 9Linked to original sources
PubMed1993

Automated interpretation of cardiac arrhythmias. Design and evaluation of a computerized model.

Historically, the development of computerized models that utilize the deductive methods used by clinicians for the interpretation of cardiac arrhythmias have been limited by the absence of a consistently reliable means of detecting atrial activation. In this study, a theoretical model was developed with a hierarchical organization of problem-solving strategies utilizing automated analysis of atrial activation from a commercially available esophageal pill electrode and ventricular activation from a simultaneously recorded surface electrocardiographic lead. The theoretical model was then tested in 21 patients with 1 or more of 28 distinct supraventricular and ventricular arrhythmias. Of the 641 individual cardiac cycles analyzed, 636 (99.2%) were correctly identified. The accuracy of a contextual, that is, more comprehensive, interpretation of consecutive cardiac cycles was 638/641 (99.5%). The following cardiac arrhythmias were identified: sinus rhythm, sinus bradycardia, atrial premature depolarizations, atrial flutter, and supraventricular tachycardias with normal and aberrant ventricular conduction, first-degree and second-degree heart block; junctional escape, junctional rhythm, idioventricular rhythm, ventricular premature depolarization, and ventricular tachycardia with and without retrograde activation; atrial bigeminy, atrial trigeminy, atrial couplets, ventricular bigeminy, ventricular trigeminy, and ventricular couplets. This study represents the first computerized model ever developed to incorporate the morphology and timing of atrial activation with the morphology and timing of ventricular activation for arrhythmia diagnosis. Such modeling appears to be capable of achieving accurate interpretation of spontaneous, complex clinical cardiac arrhythmias and atrioventricular relationships.

Arrhythmias, Cardiac↗
PubMed1993

Alterations in striatal neurotrophic activity induced by dopaminergic drugs.

The administration of dopaminergic drugs induces a variety of compensatory responses ostensibly designed to reinstate normal dopamine (DA) tone. We have hypothesized that drug-induced alterations in striatal-derived neurotrophic activity contributes to these compensatory processes. This phenomenon has been studied by examining the growth of mesencephalic cultures incubated with cell-free extracts of striatal tissue taken from patients or rats treated with various drugs. Our results reveal that reducing striatal DA tone by administering the DA antagonist haloperidol, the DA neurotoxin 6-hydroxydopamine, or as occurs naturally in Parkinson's disease, increases striatal trophic activity. Conversely, increasing striatal DA tone by administering the indirect DA agonists amphetamine or levodopa reduces trophic activity in the striatum. Kainic acid lesions of the striatum similarly reduce this trophic activity. The implications of these drug-induced alterations in trophic activity are discussed and reviewed.

Animals↗
PubMed1993

Congenital lipoid adrenal hyperplasia--genes for P450scc, side chain cleavage enzyme, are normal.

In the most severe form of congenital adrenal hyperplasia (CAH), termed lipoid CAH, both the adrenals and gonads fail to convert cholesterol to pregnenolone, so that no steroid hormones are made. Newborns have female external genitalia irrespective of karyotype, and suffer a severe salt-losing form of CAH. Previous studies have shown that adrenal or gonadal mitochondria from these patients also fail to convert cholesterol to pregnenolone in vitro, implicating a lesion in the single gene for P450scc, which is the sole enzyme converting cholesterol to pregnenolone. Two patients with XY karyotypes had female genitalia and unmeasurable steroids after stimulation with ACTH and hCG. ACTH stimulation tests of parents, obligate heterozygotes, showed normal stimulation of all precursor steroids. Southern blotting patterns of the P450scc gene were normal. Oligonucleotide-initiated enzymatic amplification (PCR) of all P450scc exons showed normal sequences on multiple amplifications and sequencing reactions, indicating normal P450scc genes. Northern blots of testicular RNA from a 6-month-old patient and from a control fetus showed normal P450scc mRNA, indicating a normal P450scc promoter. Reprobing of the blot with our cloned human cDNAs for adrenodoxin reductase and adrenodoxin showed that these electron transport cofactors used by P450scc were also normal. Similarly, probing with cDNAs for all three known factors involved in cholesterol transport to the mitochondria-sterol carrier protein 2, endozepine, and steroidogenesis activator peptide were also normal. These results suggest that the lesion in lipoid CAH is not in the P450scc system or in any known step upstream from P450scc.

Adrenal Hyperplasia, Congenital↗
PubMed1993

The human peripheral benzodiazepine receptor gene: cloning and characterization of alternative splicing in normal tissues and in a patient with congenital lipoid adrenal hyperplasia.

The mitochondrial benzodiazepine receptor (mBzR) appears to be a key factor in the flow of cholesterol into mitochondria to permit the initiation of steroid hormone synthesis. The mBzR consists of three components; the 18-kDa component on the outer mitochondrial membrane appears to contain the benzodiazepine binding site, and is hence often termed the peripheral benzodiazepine receptor (PBR). Using a cloned human PBR cDNA as probe, we have cloned the human PBR gene. The 13-kb gene is divided into four exons, with exon 1 encoding only a short 5' untranslated segment. The 5' flanking DNA lacks TATA and CAAT boxes but contains a cluster of SP-1 binding sites, typical of "house-keeping" genes. The encoded PBR mRNA is alternately spliced into two forms: "authentic" PBR mRNA retains all four exons, while a short form termed PBR-S lacks exon 2. While PBR-S contains a 102-codon open reading frame with a typical initiator sequence, the reading frame differs from that of PBR, so that the encoded protein is unrelated to PBR. RT-PCR and RNase protection experiments confirm that both PBR and PBR-S are expressed in all tissues examined and that expression PBR-S is about 10 times the level of PBR. Expression of PBR cDNA in pCMV5 vectors transfected into COS-1 cells resulted in increased binding of [3H]PK11195, but expression of PBR-S did not. It has been speculated that patients with congenital lipoid adrenal hyperplasia, who cannot make any steroids, might have a genetic lesion in mBzR. RT-PCR analysis of testicular RNA from such a patient, sequencing of the cDNA, and blotting analysis of genomic DNA all indicate that the gene and mRNA for the PBR component of mBzR are normal in this disease.

Adrenal Hyperplasia, Congenital↗
PubMed1993

Real-time arrhythmia identification from automated analysis of intraatrial and intraventricular electrograms.

Implantable cardioverter defibrillators have dramatically improved survival rates for patients at risk of sudden cardiac death, but the occurrence of inappropriate shocks remains an unresolved problem. Various means for better tachycardia detection, chiefly morphological analysis, have been proposed to address this problem. A new computerized scheme entitled Two-Channel Rate-Morphology (2CRM) was introduced. It is a real-time arrhythmia detection algorithm that combines timing and morphology information from intraatrial and intraventricular electrograms for arrhythmia diagnosis. The program 2CRM applies an initial cycle-by-cycle coding scheme followed by contextual diagnosis of underlying rhythm. The program was tested on 36 distinct passages of two-channel intracardiac signals from 30 patients. The distribution of the arrhythmias are as follows: 4 atrial fibrillation, 6 atrial flutter, 6 supraventricular tachycardia, 10 ventricular tachycardia, and 10 ventricular flutter-fibrillation. Of the analyzed 3,417 individual cardiac cycles 3,135 (91.7%) were correctly identified. Contextual diagnosis reversed 123 single-cycle errors to obtain a performance of 3,258 correct out of 3,417 (95.3%). Utilizing an uninterrupted continuous correct contextual diagnosis as indicator of successful arrhythmia detection, 2CRM obtained an accuracy of 34 out of 36 passages (94.4%).

Algorithms↗
PubMed1993

Effect of cocaine in early gestation on striatal dopamine and neurotrophic activity.

Prenatal exposure to the dopamine (DA) agonist cocaine, even if limited to early gestation, is associated with impaired developmental outcome in the human infant. We investigated the possible role of neurotrophic factors in this process by evaluating 4- to 6-d-old New Zealand White rabbit pups (n = 14) born to cocaine-exposed does (30 mg/kg/d s.c. from days 7 to 15 of a 32-d gestation) and control does (sterile H2O). Cocaine exposure reduced striatal dopamine by 46% (t = 2.31; p < 0.05) and striatal 3,4-dihydroxyphenyl acetic acid by 49% (t = 2.44; p < 0.05). The number of neuron-specific enolase immunoreactive neurons in mesencephalic cultures incubated with striatal extracts from pups exposed to cocaine was reduced by 61% relative to the effect of striatal extracts from control pups (t = 4.84; p < 0.01). The present results suggest that the reduction in striatal dopamine observed may result from a cocaine-induced decrease in striatal trophic activity.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1993

Regulation of proteins in the cholesterol side-chain cleavage system in JEG-3 and Y-1 cells.

The conversion of cholesterol to pregnenolone, the rate-limiting step in steroid hormone synthesis, occurs on mitochondrial cytochrome P450scc, which catalyzes this reaction by receiving electrons from NADPH via a flavoprotein [adrenodoxin reductase (AdRed)] and an iron sulfur protein [adrenodoxin (Adx)]. The behavior of the genes and mRNAs encoding these proteins has been studied in several systems, but little is known about the behavior of the human proteins. Using cloned cDNAs for human P450scc and AdRed, we constructed bacterial expression vectors to make milligram quantities of the corresponding proteins. These, plus purified human Adx similarly prepared by Dr. L. Vickery, were injected into rabbits to raise antiserum to each of the proteins. Each antiserum was highly specific and did not cross-react with other mitochondrial proteins detectable by Western blotting. Human JEG-3 choriocarcinoma cells and mouse Y-1 adrenocortical carcinoma cells were then incubated for 0-24 h with 1 mM 8-bromo-cAMP (8Br-cAMP) or 30 nM phorbol 12-myristate 13-acetate (PMA; phorbol ester) plus 1 microM A23187 (calcium ionophore) to activate the protein kinase-A and -C pathways, respectively. In JEG-3 cells, 8Br-cAMP increased and PMA/A23187 slightly decreased the abundance of P450scc and Adx, but neither treatment had a detectable effect on AdRed. The production of pregnenolone by these cells increased 3-fold in response to 8Br-cAMP and fell to one third in response to PMA/A23187. In Y-1 cells, 8Br-cAMP increased the abundance of all three proteins, while PMA/A23187 decreased the abundance of P450scc and Adx. The production of pregnenolone by these cells increased 9-fold in response to 8Br-cAMP and was unaffected by TPA/A23187. These studies show that the three proteins of the cholesterol side-chain cleavage system behave in response to 8Br-cAMP and PMA/A23187 as predicted from the study of their genes and mRNAs, indicating that the chronic regulation of steroidogenesis in these cell systems is regulated principally at the level of mRNA abundance.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1993

Steroid 17 alpha-hydroxylase and 17,20-lyase activities of P450c17: contributions of serine106 and P450 reductase.

Cytochrome P450c17 (EC 1.14.99.9) catalyzes both 17 alpha-hydroxylase and 17,20-lyase activities in mammalian steroidogenesis and also has some 16 alpha-hydroxylase activity. The ratio of 17 alpha-hydroxylase to 17,20-lyase activity differs in the adrenal and testis and is developmentally regulated at adrenarche, but the nature of the enzyme's active site and the differential regulation of its two principal activities are unknown. The spontaneous human P450c17 mutation Ser106-->Pro eliminates all enzymatic activity. We used site-directed mutagenesis to construct expression vectors for the conservative P450c17 mutations Ser106-->Thr and Ser106-->Ala. When expressed in transfected COS-1 cells, these mutants retain only 20-30% of the 17 alpha-hydroxylase and 17,20-lyase activities, but retain 60% of the 16 alpha-hydroxylase activity of the Ser106 wild type. Thus, the amino acid occupying position 106 greatly affects enzymatic activity. Ser is found at position 106 in P450c17 in all mammals and birds studied, but the corresponding residue (position 112) in fish (trout) is Thr. Both the trout Thr112 wild type and a Thr112-->Ser trout mutant had equivalent 16 alpha-hydroxylase, 17 alpha-hydroxylase, and 17,20-lyase activities, although these were only 5%, 5%, and 10%, respectively, of human Ser106. To catalyze its activities, P450c17 must receive electrons from NADPH via a flavoprotein termed P450 reductase. We examined the influence of the ratio of P450c17 to P450 reductase on enzymatic activity by cotransfecting COS-1 cells with varying amounts of vectors expressing each protein. The endogenous P450 reductase of COS-1 cells was sufficient to confer maximal 17 alpha-hydroxylase activity. P450 reductase produced from the transfected expression vector did not increase the conversion of [14C]progesterone to 17 alpha- or 16 alpha-hydroxyprogesterone, indicating that the endogenous immunodetectable P450 reductase of COS-1 cells was sufficient to confer maximal 17 alpha-hydroxylase activity. By contrast, the additional P450 reductase produced by the expression vector increased 17,20-lyase activity about 3-fold. Thus, the availability of reducing equivalents is a crucial factor in regulating 17,20-lyase activity. P450 reductase also increased the 17,20-lyase activity of the Thr106 and Ala106 mutants. These data suggest that the essential role of Ser106 is in the active site, rather than in interacting with P450 reductase, and that electron transfer may play an important role in regulating the 17,20-lyase activity of P450c17.

Aldehyde-Lyases↗
PubMed1993

Deletion of amino acids Asp487-Ser488-Phe489 in human cytochrome P450c17 causes severe 17 alpha-hydroxylase deficiency.

17 alpha-Hydroxylase deficiency blocks the biosynthesis of cortisol and sex steroids, resulting in mineralocorticoid excess, hypertension, sexual infantilism, and female phenotype in both genetic sexes. The disease is caused by mutations in the gene encoding cytochrome P450c17, which is the single enzyme that mediates both 17 alpha-hydroxylase and 17,20-lyase activities. We report a 14-yr-old patient from Thailand with a classical clinical presentation of this rare disorder. Analysis of her P450c17 gene by polymerase chain reaction amplification and sequencing showed a nine-base deletion, eliminating codons 487-489 (Asp-Ser-Phe) near the carboxy-terminus of P450c17. This deletion creates a BclI site in the mutant DNA, permitting accurate demonstration that the patient was homozygous for this lesion, whereas one parent and two siblings were heterozygous. By use of site-directed mutagenesis, we created a vector that could express this mutated form of P450c17 when transfected into non-steroidogenic COS-1 cells. Such transfected cells produced immunodetectable P450c17 protein, but had no 17 alpha-hydroxylase or 17,20-lyase activity, whereas cells similarly transfected with a vector expressing normal human P450c17 could 17 alpha-hydroxylate either pregnenolone or progesterone and convert 17 alpha-hydroxypregnenolone to dehydroepiandrosterone, showing the presence of both activities. This is the first report of the molecular genetic basis of 17 alpha-hydroxylase deficiency in a Southeast Asian patient.

17-Hydroxycorticosteroids↗
PubMed1993

Gas chromatography-mass spectrometry analysis of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine in urine and feces.

A method has been developed to measure levels of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) excreted in urine and feces. The method involves organic solvent extraction, derivatization to form electron-capturing bis-pentafluorobenzyl derivatives, and analysis by gas chromatography-negative ion chemical ionization mass spectrometry using a deuterium-labeled internal standard. The method can detect PhIP at levels of less than 1 ng/g in rat urine (5 ng/24 hr) and 5 ng/g (wet weight) in rat feces (50 ng/24 hr). Sprague-Dawley rats given a single 50 micrograms dose of PhIP by gavage excreted an average of 0.6% of the dose in the urine and 25% of the dose in the feces as unchanged PhIP, in the first 4 days after treatment. To make this method applicable for the analyses of biological fluids of PhIP-exposed human subjects, it is now being improved by using immunoaffinity chromatography.

Administration, Oral↗
PubMed1993

Urinary markers for measuring exposure to endogenous and exogenous alkylating agents and precursors.

Noninvasive methodologies for measuring carcinogen exposure in humans, based on the use of urinary markers, are being developed and validated for use in molecular epidemiological studies. A range of 3-alkyladenines can be determined in urine samples by an immunoaffinity purification-GC/MS approach [3-methyladenine, 3-ethyladenine, 3-(2-hydroxyethyl)adenine, and 3-benzyladenine]. Using this method, recent results in human subjects suggest that urinary 3-alkyladenines are potentially useful markers of alkylating agent exposure, particularly where the backgrounds of such adducts are much lower than 3-methyladenine. Urinary excretion of S-benzylmercapturic acid has been studied in experimental animals as a marker of exposure to benzylating agents such as N-nitroso-methylbenzylamine. 3-Nitrotyrosine (NTyr) is formed in vivo in tissue or blood proteins after exposure to nitrosating and/or nitrating agents such as tetranitromethane. After turnover of proteins, NTyr is released and excreted in urine as metabolites 3-nitro-4-hydroxy-phenylacetic acid and 3-nitro-4-hydroxyphenylacetic acid, which are determined by GC with a thermal energy analyzer. The sensitivity and specificity, combined with ease of use, of these noninvasive biomonitoring approaches means that they may be readily incorporated into molecular epidemiological studies in which exposure to nitrosating and alkylating agents may be important risk factors.

Acetylcysteine↗
PubMed1993

[Synchronous investigation of the effects of vesnarinone on action potential and muscle tension of isolated rabbit's ventricular papillary muscle].

This study adopted intracellular microelectrode technique to observe synchronously the effects of vesnarinone on intracellular potential and muscle tension of isolated rabbit's ventricular papillary muscle and analysed their variation. The results showed that vesnarinone increased the Tmax (P < 0.01) and Tdv/dt (P < 0.01) of isolated rabbit's ventricular papillary muscle and prolonged the action potential time (APT) without obvious effects on RP, APA and Vmax of papillary muscle. The relationship between them (r = 0.994, P < 0.05), suggesting that their changes be of the same mechanism and probably relate to the increase of inward calcium current.

Action Potentials↗
PubMed1993

A compliant biological vascular prosthesis.

One requirement of the mechanical parameters for an acceptable vascular prosthesis is compliance. The compliance of a vascular prosthesis is defined as the fractional change in luminal volume per unit change in applied pressure. A compliant prosthesis has been correlated to prosthesis patency and long-term efficacy in an animal study. However, there have been very few reports on how to manufacture a compliant prosthesis. It is the objective of this study to research the processing methods to manufacture a reasonably compliant vascular prosthesis. A new fixative, polyepoxy compound, was used to fix an artery. The arteries were fixed under different degrees of longitudinal retraction. By locking in the collagen micro-structure at an overly relaxed state and then crosslinking said collagen, the resulting biological prosthesis exhibited extreme compliance and pliability. A prosthesis matching its arterial origin in tensile modulus was achieved by crosslinking an artery at its 45% retraction longitudinally. This flexible prosthesis showed a volumetric compliance index of 18.4 +/- 0.9 % delta/100 mmHg and a longitudinal tensile modulus of 942 grams/cm2. Our current study indicated that a prosthesis fixed with polyepoxy compounds has shown more pliability than that with glutaraldehyde. Further animal study to correlate prostheses patency to different degrees of compliance is needed to confirm this proposed manufacturing approach.

Bioprosthesis↗
PubMed1993

Development and evaluation of a pliable biological valved conduit. Part I: Preparation, biochemical properties, and histological findings.

Different types of external valved conduits have been used for the repair of complex congenital cardiac anomalies that may have otherwise been inoperable. However, an ideal conduit has yet to be found due to complications such as stenosis, thrombosis, calcification of the valve and graft wall, and "peeling" of the neointima. To address those problems, a new extracardiac valved conduit made of bovine jugular vein was developed and evaluated in a preliminary animal study. Harvested bovine vein containing a naturally existing valve was initially incorporated with protamine on the inner surface and then was cross-linked in diglycidyl ether (DE). Fixation with DE allowed the vein and its leaflets to retain a tissue-like elasticity. To provide antithrombogenicity to the graft, heparin was introduced into the lumen to bind ionically to the pre-entrapped protamine. The biological valved conduit of approximately 14 mm diameter was implanted from the right ventricle to pulmonary artery as bypass graft in three dogs. After implantation, the native main pulmonary artery was ligated between the anastomotic sites of the bypass conduit. No anticoagulant or antiplatelet drugs were administered after surgery. One DE-fixed valved conduit was retrieved at 3 months, and the others were removed at 5 months. Only small thrombus areas were found on the white luminal surfaces. The valves and the conduits maintained softness and pliability, similar to before implantation. Additionally, the collagen content, shrink temperature, and tanning index of this newly developed biological valved conduit before and after fixation were measured in the study.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Development and evaluation of a pliable biological valved conduit. Part II: Functional and hemodynamic evaluation.

Many congenital cardiac malformations may require a valved conduit for the reconstruction of the right ventricular outflow tract. In spite of many endeavors made in the last 25 years, the clinical results of right ventricular outflow tract reconstruction with currently available valved conduits are still not satisfactory. Specific problems encountered clinically include suboptimal hemodynamic performance, conduit kinking or compression, and fibrous peeling from the luminal surface. To address these deficiencies, we undertook the development of a biological valved conduit: a bovine external jugular vein graft with a retained native valve cross-linked with a diglycidyl ether (DE). This study, using a canine model, was to evaluate the functional and hemodynamic performance of this newly developed valved conduit. Three 14 mm conduits, implanted as bypass grafts, right ventricle to pulmonary artery, were evaluated. The evaluation was conducted with a noninvasive color Doppler flow mapping system at pre-implantation, immediately post implantation, one- and three-months post implantation, and prior to retrieval (five-months post implantation). The two-dimensional tomographic inspection of the leaflet motion at various periods post implantation showed that the valvular leaflets in the DE treated conduit was quite pliable. No cardiac failure or valvular dysfunction was observed in any of the studied cases. The color Doppler flow mapping study demonstrated that the valve in the DE treated conduit was competent, with no conduit kinking or compression observed in any of the three cases. The spectral Doppler velocity study evidenced that the transvalvular pressure gradients of the DE treated conduit were minimal as compared to those of the currently available conduits. In conclusion, from the functional and hemodynamic performance points of view, this newly developed valved conduit is superior to those currently available.

Animals↗
PubMed1993

Evaluation of collagen modification and surface properties of a bovine artery via polyepoxy compound fixation.

Collagen of bovine internal thoracic artery (BITA) was treated with glutaraldehyde (GA) or polyepoxy compounds (PC). This study was to evaluate the surface properties as a result of tissue tanning reaction with PC. The fixation resulted in a significant reduction of available lysine, histidine, and other amino acid residues in PC fixed grafts as compared to fresh pre-fixed arteries. Among them, the lysine (Lys) content was reduced by about 80%, indicating that PC reactions mainly involve with Lys residues. Both PC and GA treatment led to crosslinking as evidenced by the increase in the denaturation temperature. The critical surface tension and the Fourier Transform Infrared Spectrum (FTIR) on a pre-implant and its 96 days explant were evaluated and found to be similar. The FTIR analysis of a pre-implant and the 96 day explant indicated that there was no lipid deposition.

Amino Acids↗