Biomedical subjects

D S Hwang

Publications and source records attributed to D S Hwang.

At least 37 records · Page 2Linked to original sources

PubMed1997

Histamine 2 receptor blocker-ranitidine and sinus node dysfunction.

BACKGROUND: Histamine 2 (H2) receptors were observed to be present in the sinus node. H2 receptor blockers could attenuate the histamine-induced increase in sinus rate and could thereby worsen sinus node dysfunction. However, the data pertaining to electrophysiological effects of H2 receptor blocker ranitidine on sinus node function are not available as yet, although bradycardia has been occasionally reported along with ranitidine. The present study evaluates the electrophysiological effects of ranitidine on sinus node function, and also determines the safety of administering ranitidine to patients suffering from sinus node dysfunction. METHODS: Thirty-nine patients with clinical diagnosis of sinus node dysfunction were selected for this study. Electrophysiological effects of intravenous injection of 150 mg ranitidine on sinus node function was evaluated. Tests were performed for 21 patients in the basal state (Group 1) and for 18 patients (Group 2) after autonomic blockade (propranolol 0.2 mg/kg, and atropine 0.04 mg/kg). The sinus cycle length (SCL), sinus node recovery time (SNRT), corrected sinus node recovery time (CSNRT), sinoatrial conduction time (SACT), atrio-His (AH) and His-ventricle (HV) intervals and blood pressure (BP) before and after ranitidine were analyzed. RESULTS: In Group 1, changes in SCL, SNRT, CSNRT, SACT, AH, HV and BP were not found to be significant. However, in Group 2, wherein the patients received ranitidine after autonomic blockade, it was observed that ranitidine significantly prolonged SCL (905.0 +/- 31.0 to 1000.0 +/- 40.0 msec, p = 0.001), decreased systolic BP (134.7 +/- 4.7 to 124.8 +/- 4.8 mmHg, p < 0.001), and diastolic BP (71.9 +/- 2.0 to 67.9 +/- 1.9 mmHg, p = 0.001), while the changes in SNRT, CSNRT, SACT, AH and HV were not significant. CONCLUSIONS: A clinical dose of 150 mg ranitidine must be administered by a slow intravenous infusion for at least 5 minutes in case of patients suffering from sinus node dysfunction. Continuous monitoring of BP and heart rate are necessary, especially in cases of autonomic denervation.

Adult↗

PubMed1996

Purification and characterization of mitochondrial ribonuclease P from Aspergillus nidulans.

Mitochondrial ribonuclease (RNase) P from Aspergillus nidulans was purified to near homogeneity using whole-cell extract as the starting material. A 4400-fold purification with a yield of 5.2% was achieved by ammonium sulfate fractionation, heat treatment, and five types of column chromatography, including tRNA-affinity column chromatography. This enzyme, which has a molecular mass of 232 kDa determined by glycerol gradient sedimentation analysis, appears to be composed of seven polypeptides and an RNA moiety. These seven polypeptides consistently copurified with the RNase P activity through two ion-exchange chromatography columns and in a glycerol gradient. As judged by nuclease sensitivity, the enzyme requires an RNA component for its activity. The 3'-end-labeled RNAs that copurified with the enzyme displayed identical sequences but had variable lengths for the 5' end, indicating that they originated from a common RNA molecule, the putative RNA component of RNase P. The purified enzyme cleaved mitochondrial precursor tRNAHis, resulting in an 8-bp acceptor stem. This implies that the purified RNase P is a mitochondrial enzyme and that an additional guanylate residue (at position -1) of tRNAHis in A. nidulans mitochondria is generated by a mode that is analogous to the generation of their counterparts in prokaryotes and chloroplasts.

Aspergillus nidulans↗

PubMed1996

Transcriptional activation of the dnaA gene encoding the initiator for oriC replication by IciA protein, an inhibitor of in vitro oriC replication in Escherichia coli.

Transcription of the Escherichia coli dnaA gene, encoding DnaA protein required for initiation of chromosomal DNA replication at oriC in E. coli, starts from two promoters, 1P and 2P. Gel-shift and DNase I-protection assays revealed that IciA protein, an inhibitor of initiation of in vitro E. coli chromosomal DNA replication at oriC, bound to two sites in the dnaA promoter region. One site is located upstream of promoter 1P, and the second is located downstream of promoter 2P. Whereas IciA protein did not affect transcription from the promoter 2P, transcription from the promoter 1P was specifically enhanced by IciA protein in vivo and in vitro. DnaA protein bound to the DnaA box between the two promoters 1P and 2P, acts as an transcriptional repressor. Under this condition, IciA protein counteracted the repressive effect of DnaA protein on the promoter 1P. These findings suggest that IciA protein may regulate the initiation of chromosomal DNA replication at oriC by controlling expression of the dnaA gene, as well as by inhibiting the initiation of chromosomal DNA replication at oriC.

Bacterial Proteins↗

PubMed1996

Evidence of genetic heterogeneity of hypertrophic cardiomyopathy in eight Chinese patients.

BACKGROUND: The genetic basis causing hypertrophic cardiomyopathy (HCM) was found due to missense mutations in cardiac beta-myosin heavy chain (beta-MHC), cardiac troponin T and alpha-tropomyosin genes in certain affected families. However, most mutations and majority of the affected families were reported to be related to beta-MHC gene. Till now, 20 different missense mutations of beta-MHC gene identified in more than 40 independent families were distributed in exons 8, 9, 13, 14, 15, 16, 19, 20, 21 and 23. Therefore, we chose these 10 exons for screening. METHODS: Eight probands with HCM and 1 normal control were included for screening. 32P-labeled PCR products of these 10 exons of beta-MHC gene were amplified from genomic DNA obtained from peripheral lymphocytes. PCR-DNA single strand conformation polymorphism (PCR-SSCP) analysis was performed using electrophoresis with polyacrylamide gels with and without 10% glycerol. Large amount copies of these 10 exons were also made from genomic DNA with PCR. Detection of sequencing variation of these exons was determined by the direct sequencing method with dideoxy chain termination method and 35S. RESULTS: No abnormal extra bands were noted on PCR-SSCP analysis. Sequencing analysis showed no missense mutation in these probands. CONCLUSIONS: Genetic heterogeneity of HCM is evident in Chinese patients with HCM.

Aged↗

PubMed1995

Stereospecific blocking effects of naloxone against hemodynamic compromise and ventricular dysfunction due to myocardial ischemia and reperfusion.

Endogenous opioid peptides subserve regulatory roles in cardiovascular function and are released upon myocardial ischemia contributing to the development of ischemic arrhythmias and cardiogenic shock, which are reversed by the opioid antagonist naloxone. Since the hallmark of myocardial infarction is the impairment of hemodynamics and ventricular function, we evaluated further if blockade of opioids reverses the ischemia induced hemodynamic compromise, and if the effects are mediated by opioid receptors. Thirty-two mongrel dogs were anesthetized and artificially ventilated. Median thoracotomy was performed, the heart exposed, and the left anterior descending coronary artery isolated for subsequent occlusion and reperfusion. All cardiac parameters were recorded on an Electronics for Medicine recorder through the intracardiac catheters advanced from femoral vessels. Results indicate that naloxone significantly reversed the ischemic and reperfusion induced reduction in aortic, left ventricular and pulmonary arterial pressures, and left ventricular dp/dt. The inactive (+) stereoisomer of naloxone was without effect. These data demonstrate that opioids may have a role in the pathophysiology of myocardial infarction, mediated by opioid receptors, and provide new insight and strategies for the understanding and treatment of ischemic heart disease.

Animals↗

PubMed1993

Replicatively active complexes of DnaA protein and the Escherichia coli chromosomal origin observed in the electron microscope.

DnaA protein and the Escherichia coli chromosomal origin (oriC) form an initial complex at an early stage in the initiation of DNA replication. We have used electron microscopy to determine which structure among the several formed in the reconstitution of this multicomponent system is the replicatively active complex. One distinctive structure could be correlated with activity and localized to oriC, whilst several others could not. Formation of an open complex in the next stage of initiation was accompanied by the presence of a structure similar in size and shape to that of the functional initial complex. Whereas the initial complex was observed with either ATP or the ADP-forms of DnaA protein, only the ATP-form was effective in producing the open complex. Mutagenesis of several DNA sequence elements in oriC, known to be important for replication, was employed to determine the effects of these alterations on formation of the initial complex. As judged by electron microscopy and by functional assays, the region containing the four 9-mer dnaA boxes proved to be essential for the formation of the initial complex, while the three contiguous AT-rich 13-mers, known sites for opening of oriC, were not.

Adenosine Diphosphate↗

PubMed1993

Hydrolysis of the IciA protein, an inhibitor of DNA replication initiation, by protease Do in Escherichia coli.

The 33 kDa IciA protein, an inhibitor of replication initiation of the Escherichia coli chromosome, was found to be specifically cleaved to 27 kDa fragment by protease Do, the htrA gene product. The 27 kDa polypeptide could no longer interact with the oriC region, and therefore the cleavage-site is likely to reside within the N-terminal DNA-binding domain of the IciA protein. In addition, protease Do was found to localize primarily to the cytoplasm although it also could bind to membranes through an ionic interaction. These results suggest that intracellular breakdown of the IciA protein by protease Do may provide a potential mechanism involving the regulation of initiation of DNA replication in Escherichia coli.

Animals↗

PubMed1993

A novel binding protein of the origin of the Escherichia coli chromosome.

The replication origin of Escherichia coli (oriC) was probed for specific binding proteins, using the gel shift assay. A 33-kDa protein that binds specifically to the right border of oriC, next to the rightmost of the binding sites of the initiator protein, DnaA, was identified and purified. The stoichiometry of protein to DNA is about 6 to 1. Around 5000 monomers of the protein, named Rob (right oriC binding), are present per cell. The rob gene has been located near 99.8 min on the E. coli map, cloned, and overexpressed. The total protein sequence reveals strong homologies to several regulatory proteins with which it shares the helix-turn-helix motif.

Amino Acid Sequence↗

PubMed1993

Pharmacokinetics of fluvastatin and specific drug interactions.

Fluvastatin sodium (Lescol) is the first synthetic 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA)-reductase inhibitor to be studied extensively in humans. Absorption of fluvastatin is complete and unaffected by the presence of food. Systemic exposure is limited because of extensive sequestration by the liver and/or first-pass metabolism, a plasma half-life of approximately 30 min, no circulating active metabolites, and no accumulation of drug during chronic dosing. Approximately 95% of a single dose of fluvastatin is excreted via the biliary route with less than 2% as the parent compound. Studies investigating the effect of food on fluvastatin pharmacokinetics have demonstrated marked reductions in the rate of bioavailability (Cmax) of 40% to 60%. A comparison of drug administration with the evening meal or at bedtime revealed no significant differences in either the extent of bioavailability (area under the curve; AUC) or pharmacodynamic effect [reduction in low-density lipoprotein cholesterol (LDL-C)]. Relative to the general population, plasma fluvastatin concentrations do not vary as a function of either age or gender. Administration of a single 40-mg dose to a patient population with hepatic insufficiency resulted in a 2.5-fold increase in both AUC and Cmax. Drug interaction studies with fluvastatin and cholestyramine (CME) demonstrated a lower rate and extent of fluvastatin bioavailability; no impact on efficacy was demonstrated when CME was given 4 h before fluvastatin dosing in clinical trials. Interaction studies with niacin and propranolol demonstrated no effects on fluvastatin plasma levels, and fluvastatin administered to a patient population chronically receiving digoxin had no effect on the AUC of digoxin compared with controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1993

Bioavailability of temazepam: comparison of four 7.5-MG capsules with a single 30-MG capsule.

OBJECTIVE: To compare the bioavailability of four temazepam 7.5-mg capsules (Restoril, Sandoz Pharmaceuticals) with that of a single temazepam 30-mg capsule. DESIGN: Single-dose, open-label, two-period, crossover (replicated Latin square). SETTING: Domiciled environment for clinical testing. PARTICIPANTS: Twenty-six healthy male volunteers aged 18-40 years; 25 completed the study. INTERVENTIONS: Subjects randomly received either four temazepam 7.5-mg capsules or one temazepam 30-mg capsule. Blood samples were drawn at various time points after each period (0-48 h), and analyzed for plasma concentration of temazepam. The washout period between doses was five days. MAIN OUTCOME MEASUREMENTS: Five parameters of both dosage forms were compared: (1) area under curve (AUC), (2) peak concentration (Cmax), (3) time to peak concentration (Tmax), (4) apparent rate constant for absorption, and (5) lag time for appearance of drug in plasma. Statistical procedures included ANOVA, power analysis, and confidence limits. RESULTS: The mean AUC for the four 7.5-mg capsules and one 30-mg capsule differed by less than 2 percent and the mean Cmax differed by less than 14 percent for the two dosage strengths; neither of these differences reached statistical significance (p > 0.05). The 7.5-mg capsules reached peak plasma concentrations significantly faster than the 30-mg dosage form (mean Tmax 1.18 and 1.73 h, respectively; p = 0.01). CONCLUSIONS: The two formulations of temazepam were bioequivalent with respect to the extent of bioavailability. Regarding the rate of absorption, however, the 7.5-mg capsules reached peak plasma concentrations significantly faster than the 30-mg dosage form.

Adolescent↗

PubMed1992

Opening of the replication origin of Escherichia coli by DnaA protein with protein HU or IHF.

Opening of the three tandem repeats of a 13-mer in the replication origin (oriC) of Escherichia coli is a prime event in the replication in vitro of minichromosomes (Bramhill, D., and Kornberg, A. (1988) Cell 54, 915-918). DnaA, the initiator protein, requires protein HU or IHF, along with a millimolar level of ATP and negative superhelical density in the plasmid to open this region. The extent of opening, as judged by cleavage by a single-strand-specific endonuclease (i.e. P1 nuclease), correlated closely with replication of the oriC plasmid. In an initial complex, preceding opening of the 13-mers, the footprint of DnaA protein bound by ATP covered its four 9-mer recognition sequences. The footprint of the nucleotide-free form of the protein, by contrast, was more extensive and thus, less specific.

Bacterial Proteins↗

PubMed1992

Opposed actions of regulatory proteins, DnaA and IciA, in opening the replication origin of Escherichia coli.

The opening of the three tandem 13-mers (iterons) in the replication origin (oriC) of Escherichia coli by DnaA protein, assisted by protein HU or IHF (Hwang, D. S., and Kornberg, A. (1992) J. Biol. Chem. 267, 23083-23086), represents an essential early stage in the initiation of chromosomal replication (Bramhill, D., and Kornberg, A. (1988) Cell 54, 915-918). We now show by mutational alterations of the 13-mer region that oriC function, both in vitro and in vivo, requires AT-richness in the left 13-mer and sequence specificity in the middle and right 13-mers. Interactions of DnaA protein with the middle and right 13-mers are crucial for the opening of the region. Binding of the protein to the top strand of the 13-mers appeared to maintain single-strandedness in the bottom strand. IciA protein, the inhibitor of initiation, binds the three 13-mers and blocks the opening of the region. The degrees of inhibition by IciA protein of 13-mer opening and of oriC plasmid replication observed with mutant forms of the 13-mers could be correlated with the binding affinity of IciA protein. Whereas the binding of IciA protein to the 13-mers did not affect the binding of DnaA protein to its four 9-mers boxes, interaction of DnaA protein with the 13-mers was blocked. The selective interactions of DnaA and IciA proteins with the 13-mer region appear to be components of the on/off switch that controls initiation of E. coli chromosomal replication.

Bacterial Proteins↗

PubMed1992

Characteristics and prognostic implications of myosin missense mutations in familial hypertrophic cardiomyopathy.

BACKGROUND: Familial hypertrophic cardiomyopathy is characterized by a variable degree of myocardial hypertrophy and a wide range of symptoms. Different mutations in the beta cardiac myosin heavy-chain gene have been identified in three affected families. However, neither the proportion of cases attributable to myosin mutations nor the effects of different mutations on clinical outcome are known. METHODS: Using a ribonuclease protection assay, we screened the beta cardiac myosin heavy-chain genes of probands from 25 unrelated families with familial hypertrophic cardiomyopathy; this assay is a sensitive method for detecting the presence and location of mutations. We further defined the mutations by analyzing their nucleotide sequences. The clinical features of the disease were compared in families with various myosin mutations. RESULTS: Seven mutations in the beta cardiac myosin heavy-chain gene were identified in 12 of the 25 families. All were missense mutations (i.e., causing the substitution of a single amino acid) clustered in the head and head-rod junction regions of the molecule. Six mutations resulted in a change in the charge of the amino acid. Patients with mutations that changed the charge of the altered amino acid (such as that from arginine to glutamine at nucleotide 403 or from arginine to cysteine at nucleotide 453) had a significantly shorter life expectancy (mean age at death, 33 years), whereas patients with the one mutation that did not produce a change in charge (Val606Met) had nearly normal survival. However, patients with different mutations did not differ appreciably in their clinical manifestations of familial hypertrophic cardiomyopathy. CONCLUSIONS: Different missense mutations in the beta cardiac myosin heavy-chain gene can be identified in approximately 50 percent of families with hypertrophic cardiomyopathy. In those families, a definite genetic diagnosis can be made in all members. Since the location of a mutation or its DNA-sequence alteration (or both) appears to influence survival, we suggest that the precise definition of the disease-causing mutation can provide important prognostic information about affected members.

Amino Acid Sequence↗

PubMed1992

IciA protein, a specific inhibitor of initiation of Escherichia coli chromosomal replication.

Specific binding of IciA protein to the 13-mers in the origin of a minichromosome (oriC) inhibits initiation of replication in vitro by blocking the opening of this region effected by the initiator DnaA protein (Hwang, D.S., and Kornberg, A. (1990) Cell 63, 325-331). Isolation of the iciA gene (Thöny, B., Hwang, D.S., Fradkin, L., and Kornberg, A. (1991) Proc. Natl. Acad. Sci. U.S.A. 88, 4066-4070) has made possible the construction of an IciA-overproducing strain, which in turn has simplified the isolation of a large quantity of the protein, indistinguishable from that of the wild-type strain. Based on sedimentation and gel filtration, the IciA protein is an elongated dimer of a 33.4-kDa subunit. The specific binding of IciA protein to the 13-mers was stable for 2 h at 30 degrees C. The amounts of IciA protein, detected by immunoassays, increased 4-fold compared with levels (about 100 dimers) in log-phase cells whereas levels of DnaA protein decreased upon entry of cells into the stationary phase.

Bacterial Proteins↗

PubMed1992

Sporadic hypertrophic cardiomyopathy due to de novo myosin mutations.

Hypertrophic cardiomyopathy occurs as an autosomal dominant familial disorder or as a sporadic disease without familial involvement. While missense mutations in the beta cardiac myosin heavy chain (MHC) gene account for approximately half of all cases of familial hypertrophic cardiomyopathy, the molecular causes of sporadic hypertrophic cardiomyopathy are unknown. To determine whether beta cardiac MHC mutations are also associated with sporadic disease, we screened this gene in seven individuals with sporadic hypertrophic cardiomyopathy. Mutations in the beta cardiac MHC genes were identified in two probands with sporadic disease. In that their parents were neither clinically nor genetically affected, we conclude that mutations in each proband arose de novo. Transmission of the mutation and disease to an offspring occurred in one pedigree, predicting that these are germline mutations. The demonstration of hypertrophic cardiomyopathy arising within a pedigree coincident with the appearance of a de novo mutation provides compelling genetic evidence that beta cardiac MHC mutations cause this disease. We suggest that de novo mutations account for some instances of sporadic hypertrophic cardiomyopathy and that these mutations can be transmitted to children. The clinical benefits of defining mutations responsible for familial hypertrophic cardiomyopathy should also be available to some patients with sporadic disease.

Adult↗

PubMed1992

Pericardiocentesis: a 20 patients study.

Emergency pericardiocentesis, guided by a two-dimensional echocardiography, was performed on twenty patients with symptomatic pericardial effusion of various types and causes. There were fourteen men and six women. The underlying causes were: primary lung cancer (6 cases), metastatic cardiac tumors (3 cases), tuberculosis (4 cases), complicated interventional procedures with cardiac chamber or vessel perforations (2 cases), dissecting aortic aneurysm (1 case), systemic lupus erythematous (1 case), idiopathic pericarditis (1 case), bacterial pericarditis (1 case), and myxedema heart disease (1 case). Seventeen cases were performed through the left xipho-sternal approach and 3 cases through the apical approach. None of the patients died as a result of these procedures. A two-dimensional echocardiogram is useful in diagnosing cardiac tamponade as well as in guiding pericardiocentesis, and obtaines highly positive results (20/20). The positive rate of pericardial fluid cytology for malignant cells was 89% (8/9), however, pericardial fluid cultures or direct smear for tuberculosis were negative (0/4). In cancer patients, the mean survival time following pericardiocentesis was 4.2 months (range, 1-7.8 months). We concluded that neoplastic involvement of the pericardium is the most frequent cause of symptomatic pericardial effusion. Pericardiocentesis assisted by a two-dimensional echocardiogram is safe and easy. In addition, pericarditis caused by TB is still significant and must be considered in every case in our nation.

Adult↗

PubMed1991

Preclinical diagnosis of familial hypertrophic cardiomyopathy by genetic analysis of blood lymphocytes.

BACKGROUND: The clinical diagnosis of familial hypertrophic cardiomyopathy is usually made on the basis of the physical examination, electrocardiogram, and echocardiogram. Making an accurate diagnosis can be particularly difficult in children, who may not have cardiac hypertrophy until adulthood. Recently, we demonstrated that mutations in the cardiac myosin heavy-chain genes cause familial hypertrophic cardiomyopathy in some families. We report a diagnostic test for familial hypertrophic cardiomyopathy that relies on the detection of mutations in the beta myosin heavy-chain gene in circulating lymphocytes that we used to evaluate three generations of a family, including the children. METHODS AND RESULTS: Using the polymerase chain reaction, we found that normal and mutant beta cardiac myosin heavy-chain genes are transcribed in circulating lymphocytes. This allowed us to examine beta cardiac myosin heavy-chain messenger RNA from blood lymphocytes, even though ordinary expression of the gene is virtually restricted to the heart. Base sequences amplified from this messenger RNA were analyzed with a ribonuclease protection assay to identify small deletions, abnormal splicing, or missense mutations. Using this technique we identified a novel missense mutation in a patient with familial hypertrophic cardiomyopathy. We evaluated 15 of the patient's adult relatives and found perfect agreement with the clinical diagnosis (8 affected and 7 not affected). Clinical analysis of 14 of the children (age, 1 to 20 years) of these affected family members revealed 1 child with echocardiographic findings diagnostic of familial hypertrophic cardiomyopathy. However, genetic analyses showed that six other children had also inherited the missense mutation and might later manifest the disease. CONCLUSIONS: Transcripts of beta cardiac myosin heavy-chain gene can be detected in blood lymphocytes and used to screen for mutations that cause familial hypertrophic cardiomyopathy. This approach makes practical the identification of mutations responsible for this disorder and may be applicable to other diseases in which direct analysis is difficult because the mutated gene is expressed only in certain tissues. Preclinical or prenatal screening in an affected family will make it possible to study the disease longitudinally and to develop preventive interventions.

Adolescent↗

PubMed1991

iciA, an Escherichia coli gene encoding a specific inhibitor of chromosomal initiation of replication in vitro.

The gene encoding the protein that binds the three 13-mers in the origin (oriC) of Escherichia coli to block initiation of replication in vitro has been cloned, sequenced, and overexpressed. The gene possesses an open reading frame for 297 amino acids (mass of 33,471 Da). The protein has a motif for DNA-binding (helix-turn-helix) and has homology to a diverse set of prokaryotic regulatory proteins, known as the LysR family. The protein, previously referred to as the 33-kDa protein, has been named IciA (for inhibitor of chromosome initiation). The iciA gene is at 62.8 min on the chromosomal map. Cells with enhanced levels of the protein grow at a normal rate but generally exhibit a pronounced lag upon transfer to a fresh medium.

Amino Acid Sequence↗