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Biomedical subjects

M Oh

Publications and source records attributed to M Oh.

At least 19 recordsLinked to original sources
PubMed2005

Overtone-induced decarboxylation: a potential sink for atmospheric diacids.

Atmospheric photochemistry induced by solar excitation of vibrational overtone transitions has recently been demonstrated to be of importance in cleaving weak bonds (in HO(2)NO(2)) and inducing intramolecular rearrangement followed by reaction (in H(2)SO(4)). Here, we propose another potentially important process: the decarboxylation of organic acids. To demonstrate this possibility, we have calculated the decarboxylation pathways for malonic acid and its monohydrate. The barrier to the gas-phase decarboxylation was calculated to be in the range 26-28 kcal/mol at the B3LYP/6-311++G(3df,3pd) level of theory, in good agreement with previous results. The transition state is a six-membered ring structure which is accessed via concerted O-H and C-C stretches; excitation of v(OH) > or = 3 of either one of the OH stretching modes is sufficient to supply the energy needed for the decarboxylation. A low-energy isomer of the malonic acid-water complex forms an eight-membered, multiply hydrogen bonded structure, bound by 3-6 kcal/mol, somewhat less stable than the lowest energy, six-membered ring isomer. Decarboxylation of such complexes uses water as a catalyst; the water accepts an acidic proton from one malonic acid group and transfers a proton to the carbonyl of the other acid group. The barrier for this process is 20-22 kcal/mol, suggesting that complexes excited to v(OH) > or = 2 possess sufficient energy to react. Using estimated absorption cross sections for the OH overtone transitions, we suggest that the overtone-induced decarboxylation of malonic acid and its water complex is competitive with wet deposition of the acid and with gas-phase reaction with OH for removal of the acid.

Journal Article↗
PubMed1999

Sp1 mediates cell proliferation-dependent regulation of rat DNA topoisomerase IIalpha gene promoter.

DNA topoisomerase IIalpha (topo IIalpha) is an essential nuclear enzyme required for chromosome segregation during mitosis. Consistent with its critical role in cell division is the fact that the expression of the gene for topo IIalpha is strongly regulated by the proliferation state of cells. Using a transient expression system, we determined the contribution of putative cis-acting elements in its promoter region to its basal level and cell proliferation-dependent transcription. Experiments with 5' and/or 3' serial deletion and site-directed mutation revealed that (1) maximal promoter activity resides in the fragment extending to position -663 bp from the ATG initiation codon, (2) minimal promoter activity is harboured at -195 bp, (3) the defined minimal promoter contains only two putative elements, inverted CCAAT box 4 (ICB4) (-166 to -162 bp) and the most proximal GC-rich box in the promoter (GC2) (-149 to -143 bp), and (4) ICB4 is most important in the basal-level transcription of the gene for rat topo IIalpha. The luciferase activities of the mutated reporter plasmids in G(0)-arrested and exponentially growing cells showed that proliferation-specific regulation is controlled mainly by GC2. Electrophoretic mobility-shift assays indicated that Sp1 binds specifically to the GC2 site. The extent of DNA-protein complex formation increases after the stimulation of cells to proliferate. These results indicate that the increased binding activity of Sp1 to GC2 is important in the up-regulation of the gene for topo IIalpha in growing cells.

Animals↗
PubMed1999

Isolation and identification of Fur binding genes in Escherichia coli.

Fur (ferric uptake regulation) binding fragments were isolated by in vitro binding of purified Fur protein with Sau3AI-digested genomic DNA fragments. The Fur-bound DNA fragments were filtered on nitrocellulose paper, isolated, cloned, and sequenced. The protein binding was confirmed by gel retardation assay for five DNA fragments. The sequence data were used to identify the genes by comparison with the GenBank data. The proposed Fur binding regions lie on or near the putative promoter regions of marAB (multiple antibiotic resistance), pyrC (dihydroorotase), mreB (mecillinam resistance) and an unidentified gene (ecouw93) near argI and in the middle of the treBC (trehalose permease enzyme II) coding region. The proposed Fur binding sites of the known iron regulating operators including the genes of this work are AAT(pyrimidine) and A(purine)TT. The two conserved sequences are 10 bases apart and palindromic to each other, which might suggest the classical pattern of protein binding toward one side of the DNA in contrast to the concept of the Fur protein wrapping around the DNA.

Bacterial Proteins↗
PubMed1999

Effect of hydrogen peroxide on the metabolism of articular chondrocytes.

OBJECTIVE: To examine the effect of hydrogen peroxide on chondrocyte metabolism. MATERIALS AND METHODS: Bovine articular chondrocytes were used. Proteoglycan (PG) synthesis was measured with [35S] sulfate incorporation. For detection of apoptosis, the TdT-mediated dUTP-biotin nick end labeling (TUNEL) and annexin V assay were used. Extracellular-regulated protein kinase (ERK) activity was measured using a mitogen-activated protein kinase assay system. RESULTS: Addition of hydrogen peroxide resulted in the inhibition of PG synthesis, apoptosis, and enhanced ERK activity. CONCLUSION: Hydrogen peroxide plays an important role in regulating the metabolism of chondrocytes.

Animals↗
PubMed1999

Anti-proliferating effects of ginsenoside Rh2 on MCF-7 human breast cancer cells.

Ginsenoside Rh2 (G-Rh2) isolated from the root of Panax ginseng has been shown to have anti-cancer proliferation, differentiation and chemopreventive effects in certain cancer cell types. We investigated the mechanism of G-Rh2-induced growth inhibition in MCF-7 human breast carcinoma cells. G-Rh2 significantly inhibited the cell growth in a concentration-dependent manner, which effect was reversible, and induced a G1 arrest in cell cycle progression. G-Rh2 treatment down-regulated the protein level of cyclin D3 but upregulated the expression of cyclin-dependent kinase (Cdk) inhibitor p21WAF1/CIP1. The increased levels of p21 were associated with increased binding of p21 and Cdk2 concomitant with marked decrease in Cdk2 and cyclin E-dependent kinase activities with no changes in Cdk2 and cyclin E expression. G-Rh2 markedly reduced the phosphorylated retinoblastoma protein (pRb) and enchanced association of unphosphorylated pRb and the transcription factor E2F-1. These data suggest that G-Rh2 inhibited the growth of MCF-7 cells, by inducing protein expression of p21 and reducing the protein levels of cyclin D which resulted in the down-regulation of cyclin/Cdk complex kinase activity, decreasing phosphorylation of pRb, and inhibiting E2F release.

Antineoplastic Agents↗
PubMed1999

Frequency of the Fc gamma RIIIA-158F allele in African American patients with systemic lupus erythematosus.

OBJECTIVE: Defects in genes involved in immune complex clearance constitute one of the most common gene defects identified in patients with systemic lupus erythematosus (SLE). Defects in early complement components, complement receptors, and Fc receptors have all been implicated in the susceptibility to SLE. Recently, the role of functionally relevant Fc receptor polymorphisms in the etiology of SLE has been investigated. Specifically, a polymorphism of FC gamma RIII, termed Fc gamma RIIIA-158F, has been found to be associated with SLE in 2 largely Caucasian populations and appeared to constitute a risk factor for nephritis. We investigated the association of the Fc gamma RIIIA-158F and Fc gamma RIIIA-131R polymorphisms with SLE in an African American study population. METHODS: Nested polymerase chain reaction (PCR) and allele-specific PCR was used to genotype patients with SLE and controls. RESULTS: There was no difference in Fc gamma RIIIA-158F or Fc gamma RIIA-131R gene frequencies in the SLE populations compared to controls. There was no significant association between Fc gamma RIIIA-158F or Fc gamma RIIA-131R and any specific clinical or laboratory variable. CONCLUSION: In our African American study population, there did not appear to be any association of Fc gamma RIIA-158F or Fc gamma RIIA-131R with SLE.

Alleles↗
PubMed1998

Protein kinase C modulates the synthesis of nitric oxide by osteoblasts.

To determine the involvement of protein kinase C (PKC) in nitric oxide (NO) synthesis of osteoblast, a combination of proinflammatory cytokines (tumor necrosis factor-alpha, interferon-gamma, bacterial lipopolysaccharide) were added on rat osteoblast-like cells. Results show that these cytokines clearly enhanced the synthesis of NO. The activation of PKC with phorbol ester also resulted in the stimulation of NO synthesis in these cells. These cytokines activated PKC and increased the levels of intracellular Ca2+. In addition, the cytokine-induced synthesis of NO was blocked by PKC inhibitors. Findings suggest the involvement of PKC in the synthesis of NO by rat osteoblasts.

Animals↗
PubMed1998

Concurrent generation of nitric oxide and superoxide inhibits proteoglycan synthesis in bovine articular chondrocytes: involvement of peroxynitrite.

OBJECTIVE: Nitric oxide (NO), widely assumed to be a mediator of interleukin 1 (IL-1), inhibits proteoglycan synthesis in articular chondrocytes. IL-1 also produces superoxide anion. We hypothesized that the IL-1 inhibited proteoglycan synthesis is the result of peroxynitrite formed by the reaction of NO with superoxide. METHODS: Bovine articular chondrocytes were cultured in the presence of SIN-1, which leads to simultaneous generation of both NO and superoxide. Proteoglycan synthesis was measured based on the incorporation of [35S] sulfate, and the presence of peroxynitrite was confirmed using immunohistochemistry. RESULTS: SIN-1 inhibited proteoglycan synthesis and superoxide dismutase reversed SIN-1 inhibited proteoglycan synthesis, indicating the simultaneous generation of superoxide is essential to inhibit proteoglycan synthesis. IL-1 induced peroxynitrite in articular chondrocytes and addition of peroxynitrite inhibited proteoglycan synthesis. CONCLUSION: The concurrent generation of superoxide anion and NO is required for the action of IL-1 to inhibit proteoglycan synthesis. Peroxynitrite is a candidate for this underlying mechanism.

Animals↗
PubMed1997

Hyaluronic acid inhibits interleukin-1-induced superoxide anion in bovine chondrocytes.

OBJECTIVE: To examine the effect of hyaluronic acid (HA) on the induction of superoxide anion by IL-1 in chondrocytes. MATERIALS AND METHODS: Bovine articular chondrocytes were treated with different concentrations of IL-1. A chemiluminescent probe (L-012) was added to the medium and chemiluminescence detection was used to measure super oxide anion. RESULTS: IL-1 caused induction of superoxide anions in a dose-dependent manner. HA (10-100 micrograms/ml) countered superoxide induction caused by 20 ng/ml of IL-1. CONCLUSIONS: HA can afford protection against cartilage degradation, probably acting as a free-radical scavenger.

Animals↗
PubMed1997

Sequential versus simultaneous combination antiretroviral regimens for the treatment of human immunodeficiency virus type 1 infection in vitro.

Two-, three-, and four-drug antiretroviral combinations in either simultaneous or sequential regimens were evaluated for their ability to suppress human immunodeficiency virus (HIV) type 1 replication in vitro. Zidovudine, lamivudine, saquinavir, and nevirapine were used at IC(90)s, IC(99)s, or IC(> or = 99)s in a CD4-positive human lymphoblastoid cell line (H9 cells) acutely infected with HIV-1. In sequential regimens, drugs were added at weekly intervals. In simultaneous regimens, all drugs were added on day 0. Increasing the number of drugs in a combination regimen both increased the degree of viral inhibition and delayed the time of breakthrough viral replication. Simultaneous regimens provided more profound and earlier viral inhibition than did sequential regimens. However, sequential addition provided relatively more durable viral inhibition than did simultaneous regimens when drug concentrations were low. The relative effectiveness of different HIV-1 therapeutic strategies depends on both the numbers and concentrations of the drugs used.

Anti-HIV Agents↗
PubMed1996

Urea recycling: an aid to the excretion of potassium during antidiuresis.

Urea absorption in the inner medullary collecting duct provides a mechanism to elevate the concentration of urea in the papillary interstitial fluid and thereby permit the excretion of urea with as little water as possible. Urea reabsorption may have another important effect - to aid in the excretion of potassium (K). K excretion depends on two processes: first, factors such as aldosterone which cause the concentration of K in the luminal fluid of the cortical distal nephron to be high and, second, factors which augment the flow rate through those nephron segments. Since, the osmolality of the luminal fluid in the cortical collecting duct (CCD) and plasma are equal when antidiuretic hormone acts, the flow rate in the CCD is dependent on solute delivery. Urea is a major solute in the lumen of the CCD and thereby plays an important role in maintaining the CCD flow rate. Since urea and K are often found in the same foods, having urea help the excretion of K is potentially advantageous. If the excretion of urea was low, the flow rate in the terminal CCD would decline. In this circumstance, the luminal K concentration would have to rise in proportion to the fall in flow rate or there would be a diminished rate of excretion of K and, possibly, hyperkalemia.

Animals↗
PubMed1995

The Kasai procedure in the treatment of biliary atresia.

From 1978 to 1992, 62 patients were diagnosed as having extrahepatic biliary atresia (EHBA) at Childrens Hospital Los Angeles. The patients presented with either persistent jaundice, alcoholic stools, and/or hepatomegaly. Hepatobiliary IDA scans were performed in 47 of the patients; 46 had results typical of EHBA. Fifty-nine of the 62 patients underwent a Kasai portoenterostomy; three patients were more than 4 months of age at initial presentation and were referred directly for liver transplantation. The preoperative total bilirubin level for all patients averaged 8.6 mg/dL (range, 4.1 to 18.1). All patients underwent a standardized Kasai procedure using a 40-cm Roux-en-Y intestinal segment performed in the end-to-side fashion. Postoperative management included oral antibiotics and fat-soluble vitamins for at least 9 months. Long-term complications included cholangitis in 20 cases and portal hypertension in 25, which led to variceal hemorrhage in 12 cases. Growth rates were at or above the 50th percentile for age in 59% of the Kasai patients. Forty-one of the 59 Kasai patients survived (69.5%); six deaths occurred within 2 years after the Kasai procedure. Twelve patients were lost to follow-up within 2 years after surgery, and for calculation of mortality were presumed dead. Seventeen patients had follow-up for 5 or more years, 13 had follow-up for 2 to 5 years, and 29 had follow-up for less than 2 years. The average total bilirubin level for the patients with less than 2 years of follow-up was 7.9 mg/dL (0.3 to 20.8), and that for the patients with more than 2 years of follow-up was 1.6 mg/dL (0.3 to 18.1). Orthotopic liver transplantation was performed in 11 Kasai patients, in whom chronic liver failure eventually developed. Rejection occurred in one of these patients, which required retransplantation. Based on these results, the Kasai portoenterostomy procedure continues to offer palliation, if not long-term success, in a large percentage of patients with EHBA.

Anastomosis, Roux-en-Y↗
PubMed1994

The development and evaluation of new versions of the written examination for the American Heart Association Advanced Cardiac Life Support provider course.

STUDY OBJECTIVE: To create new versions of the written, multiple-choice examination used in the American Heart Association (AHA) Advanced Cardiac Life Support course, evaluate their reliability and difficulty, and then design revised versions with improved reliability and of standardized difficulty. DESIGN: Psychometric evaluation of new versions of the AHA Advanced Cardiac Life Support test and revisions. SETTING: AHA Advanced Cardiac Life Support courses. PARTICIPANTS: Candidates for completion of AHA Advanced Cardiac Life Support provider courses in five states. INTERVENTION: The course content was divided into 11 content areas that were weighted for importance and appropriateness for testing in a multiple-choice format. The weights were used to construct a blueprint for a 50-question, multiple-choice examination. Five versions of the examination were then constructed based on the content blueprint, drawing from new questions and expert revision of previously written questions. Reliability and difficulty were assessed using 915 administrations at five different sites nationwide. The initial test versions differed in their degree of difficulty, which was not explained by demographic factors. The results were used to revise three of the versions to improve reliability and equalize difficulty of the versions. MEASUREMENTS AND MAIN RESULTS: The final five versions have estimated reliability ranging from Cronbach's alpha of .62 to .86. Mean scores ranged from 87.4% to 89.1%. CONCLUSION: After field testing and revision, five examinations with acceptable reliability and roughly equal difficulty were constructed. The new examinations test the participants' knowledge of important aspects of resuscitation science and practice based on a blueprint of the course content.

American Heart Association↗
PubMed1981

Influence of arsenic exposure and smoking on lung cancer among smelter workers: a pilot study.

A pilot study of 300 smelter workers from the cohort reported by Lee and Fraumeni [1969] has been studied: 150 men from their heavy exposure group and 150 men from the rest of the cohort randomly selected. Usable smoking habits were obtained from 86% of the sample. Estimates of the total lifetime work exposure were made from available measurements. A very high risk of lung cancer (SMR 1429) was observed among the most heavily exposed workers. Excess risks, though still present, were much less in those with lower exposures. There was a lower proportion of nonsmokers among the heavily exposed arsenic workers than among the other workers. This suggests that there may be some interaction between smoking and arsenic exposure. Moreover, comparison of smoking habits reported by smelter workers suggested that, as a group, they smoked more heavily than average for the United States population. A small study of proxy smoking histories suggested that these were valid and unbiased. The work continues on an enlarged sample.

Arsenic↗