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Biomedical subjects

M J Kelner

Publications and source records attributed to M J Kelner.

At least 55 records · Page 3Linked to original sources
PubMed1993

Patient control over dying: responses of health care professionals.

Decisions concerning how, when and where patients should die have traditionally been the exclusive domain of health care professionals. More recently, patients and their families are demanding increasing control over these decisions. This paper reports on the responses of 20 physicians and 20 nurses in a major teaching hospital regarding the desire of patients to exert more control over the circumstances of their dying. The findings, based on in-depth, semi-structured interviews, suggest that while health care professionals are generally in favour of the principle of patient control over dying, they have reservations about accommodating patients' wishes in actual clinical situations. Key factors that underly their ambivalence on this point are: (1) specific patient circumstances, such as age, severity of illness and mental competence; (2) moral and legal concerns; and (3) the type of intervention requested by patient. The results indicate that patient control over dying represents a challenge to the clinical judgement of health care professionals; that it runs counter to their perception of their role as healers and supporters; that it raises crucial concerns about their personal ethics and legal liability and that it poses a challenge to their professional autonomy and power. It is likely that health care practitioners will increasingly be pressured to concede their autonomy and enter into a partnership with patients in the decision-making process.

Adult↗
PubMed1992

HPLC determination of a new anticancer agent (acylfulvene) in serum.

High performance liquid chromatography (HPLC) combined with effective preseparation steps (liquid extraction, solid-phase extraction, preconcentration procedures) was used in pharmacokinetic studies of a novel anticancer agent (acylfulvene) in serum. HPLC conditions were optimized for the analysis of model clinical samples and real serum samples with different contents of acylfulvene. Extraction recoveries for both extraction procedures were evaluated and linearity was achieved for a wide concentration range. Detection limit for acylfulvene in serum was 0.075 microgram/ml, preconcentration minimum 5 times was recommended, especially after the solid-phase extraction step. The HPLC assay was applied for pharmacokinetic studies of acylfulvene in dogs and rats and pharmacokinetic parameters were determined.

Animals↗
PubMed1990

Preclinical evaluation of illudins as anticancer agents: basis for selective cytotoxicity.

Illudins are potent natural products derived from Omphalotus illudens and related fungi. The chemical structure of illudins differs from that of other conventional chemotherapeutic agents. While illudins are toxic to most tumor cells after prolonged exposure (greater than or equal to 48 hr), with shorter exposure times (less than or equal to 2 hr), they show selective toxicity for human myelocytic leukemia and epidermoid, lung, ovarian, and breast carcinoma cells of various species of origin. The apparent histologic specificity of illudin S toxicity is based on an energy-dependent transport mechanism present in sensitive cells, but absent in cells relatively resistant to illudin S. For human myeloid leukemia HL60 cells, the Michaelis constant was 4.2 microM and the maximum velocity was 12.2 pmol/minute per 10 million cells or 730 pmol/hour per 10 million cells. The energy-dependent transport mechanism was detected in other mammalian tumor cells.

Animals↗
PubMed1990

Alteration of endogenous glutathione peroxidase, manganese superoxide dismutase, and glutathione transferase activity in cells transfected with a copper-zinc superoxide dismutase expression vector. Explanation for variations in paraquat resistance.

Transfection of a human pSV2 (copper-zinc) superoxide dismutase expression vector into murine fibroblasts resulted in stable clones producing increased amounts of copper-zinc superoxide dismutase. A marked increase in endogenous glutathione peroxidase activity (up to 285%) and a smaller increase in glutathione transferase activity (up to 16%) also occurred. Manganese superoxide dismutase activity was decreased in all clones, whereas catalase and NADPH reductase activities were not affected. Alterations in glutathione peroxidase and manganese superoxide dismutase activities correlated with increases in copper-zinc superoxide dismutase activity. Whereas all clones were resistant to paraquat, a direct correlation between copper-zinc superoxide dismutase activity and resistance to paraquat did not exist. In agreement with previous reports clones expressing the highest copper-zinc superoxide dismutase activity did not display the highest resistance to paraquat. However, there was a direct correlation between the increase in glutathione peroxidase activity and paraquat resistance (p less than 0.002).

Animals↗
PubMed1990

Thioureas react with superoxide radicals to yield a sulfhydryl compound. Explanation for protective effect against paraquat.

Thiourea and superoxide dismutase were effective antidotes to paraquat toxicity in an HL60 cell culture system, whereas other hydroxyl scavengers were ineffective. The efficacy of thioureas was not due to blockage of intracellular paraquat uptake, inhibition of NADPH-P-450 reductase, or reaction with the paraquat radical. Thiourea also competitively inhibited the reduction of cytochrome c by the xanthine/xanthine oxidase superoxide-generating system, and the release of iron from ferritin by superoxide radicals. The reaction of superoxide with thiourea produced a sulfhydryl compound distinct from products formed by hydrogen peroxide or hydroxyl radicals. Spectrophotometric and chromatographic studies indicated the carbon-sulfide double bond was converted to a sulfhydryl group which reacted with Ellman's reagent. Additional confirmatory evidence for the sulfhydryl compound was obtained with carbon-13 NMR and mass spectroscopies. Thus, thioureas are direct scavengers of superoxide radicals as well as hydroxyl radicals and hydrogen peroxide. The rate constant for the reduction of thiourea by superoxide was estimated at 1.1 x 10(3) M-1 s-1. The implication of this finding on free radical studies, the mechanism of paraquat toxicity, and the metabolism of thioureas is discussed.

Acetonitriles↗
PubMed1990

Glutathione-dependent enzymes alone can produce paraquat resistance.

HL60 cells exposed to increasing paraquat concentrations were screened for clones without increased superoxide dismutase activities in an effort to examine cytotoxic events occurring after superoxide production. The resulting resistance to paraquat was not associated with alterations in paraquat uptake, catalase, or NADPH-P450 reductase activity, but to alterations in glutathione-dependent enzyme activities. While increases in glutathione-dependent enzymes upon exposure to paraquat have been reported, the increases were considered a secondary response to increases in superoxide dismutase activities. Our results demonstrate that glutathione-dependent enzymes alone provide protection against paraquat toxicity, and their increase upon exposure to paraquat can be independent of the response of superoxide dismutases. This supports a previous finding that cells resistant to Adriamycin, based on elevated glutathione peroxidase and transferase activities are also cross-resistant to paraquat. Unlike this previous report, the increase in glutathione peroxidase was not a persistent genetic event, as activities returned to normal upon removal of paraquat. An isolated increase in glutathione peroxidase without accompanying increases in superoxide dismutases was a rare event, as nearly all clones examined after exposure to paraquat had increased superoxide dismutase.

Drug Resistance↗
PubMed1989

Paraquat resistance associated with reduced NADPH reductase in an energy-dependent paraquat-accumulating cell line.

Despite intensive investigation into paraquat toxicity, neither the final cytotoxic mechanism nor a clinically useful antidote has been discovered. In vitro screening of potential antidotes that act by blocking paraquat uptake requires a cell line that accumulates paraquat by an energy-dependent mechanism. We screened various lymphoblastoid cell lines until we found a line accumulating paraquat by an energy-dependent mechanism. During study of this cell line, a marked resistance to paraquat developed in a clone. The resistance was associated with a reduction in NADPH reductase activity, confirming the original report (using microsomal preparations) that intracellular reduction of paraquat occurs primarily by this enzyme. One-half of the NADPH-P450 reductase activity, as well as one-half of the NADPH-dependent paraquat-inducible superoxide production, was decreased. This suggests that the decrease is secondary to a genetic alteration in one of the genes encoding for the enzyme. Other antioxidant enzymes and proteins were not affected. Despite the loss of only 50% of the activity, the relative resistance to paraquat exceeded previous reports involving marked increases in antioxidant enzymes. Most exogenous enhancers or inhibitors alter the activity of more than one enzyme, thereby making selective changes in any one enzyme difficult. Thus, this cell line will be useful for studying other toxins where the involvement of NADPH reductase is suspected, but not proven.

Cell Line↗
PubMed1989

Inactivation of intracellular copper-zinc superoxide dismutase by copper chelating agents without glutathione depletion and methemoglobin formation.

The copper chelator N,N'-diethyldithiocarbamate (DDC), is often used to inactivate intracellular copper-zinc superoxide dismutase in erythrocytes. However, in studies with red cells we found that the compound also reacted with oxyhemoglobin to produce oxygen radicals in addition to generating lipid peroxidation products, oxidized N,N'-diethyldithiocarbamate, methemoglobin, and sulfhemoglobin. Moreover, intracellular glutathione was depleted and vital cellular enzymes were susceptible to inactivation. We, and others, have confirmed these findings in nonerythrocytic cell lines. Thus, cells exposed to DDC are severely damaged before studies on the effects of added putative superoxide producing compounds can be performed with them. In this report, we have systematically investigated other copper chelators for their ability to inactivate intracellular copper-zinc superoxide dismutase without producing the deleterious effects mentioned above. Catechol, triethylenetetramine, and tetraethylenepentamine were found to be such agents when erythrocytes were dialyzed in the cold against dilute solutions of these chelators. In addition, with a myeloid leukemic cell line (HL-60), triethylenetetramine inhibited SOD without causing significant GSH oxidation. Examination of the affinity constants of chelators active against purified copper-zinc superoxide dismutase indicated that an affinity binding constant (log K1) between 12.6 and 13.8 was required for the chelator to successfully remove copper from the enzyme.

Cell Line↗
PubMed1988

Methylene blue competes with paraquat for reduction by flavo-enzymes resulting in decreased superoxide production in the presence of heme proteins.

Methylene blue competes 100 to 600 times more effectively than paraquat for reduction by three different flavo-containing enzymes; xanthine oxidase, NADH cytochrome c reductase, and NADPH cytochrome c reductase. Paraquat and methylene blue both interact with deflavo xanthine oxidase, indicating that neither electron acceptor reacted at the FAD site of the enzyme where molecular oxygen is reduced to superoxide. As the paraquat radical also directly reduced acetylated cytochrome c the hemeprotein could not be utilized for measuring superoxide production in the presence of the herbicide. In the presence of cytochrome c the methylene blue caused a sharp decrease in both paraquat-induced superoxide and hydroxyl radical production.

Cytochrome Reductases↗
PubMed1988

Potential of methylene blue to block oxygen radical generation in reperfusion injury.

Methylene blue interacts with xanthine oxidase at the iron-sulfide site in the electron pathway (Scheme I) that is known to serve as an electron-sink connecting the reductive and oxidative sites in both the oxidase and dehydrogenase forms. Thus, shunting of electrons to methylene blue at this site effectively diverts their flow away from the FAD site where molecular oxygen is converted to superoxide radicals. Since the electron affinity constants of xanthine oxidase for electron acceptors are FAD greater than iron/sulfide greater than molybdenum, methylene blue falls between the FAD and iron-sulfide site. Thus, methylene blue effectively inhibits superoxide and hydroxyl radical production while accelerating the conversion of xanthine to uric acid. As methylene blue is already approved for medicinal use in humans and is relatively nontoxic, the drug may have a role in reducing tissue injury associated with reperfusion. We are currently investigating this possibility in animal models.

Animals↗
PubMed1988

Definitive liquid-chromatographic demonstration that N-ethylglycine is the metabolite of lidocaine that interferes in the Kodak sarcosine oxidase-coupled method for creatinine.

Patients receiving lidocaine may show false increases of serum creatinine as assayed by the single-slide method on the Kodak Ektachem 700. Bissell et al. (Clin Chem 1987;33:951) suggested that this interference was due to oxidation of N-ethylglycine (NEG), a previously uncharacterized metabolite of lidocaine, by the sarcosine oxidase preparation used in the Ektachem creatinine slide. To investigate this possibility, we synthesized NEG, added it to drug-free human serum, and analyzed the NEG-supplemented sera for creatinine with the Ektachem 700. We found the following linear relationships between creatinine bias (y, mg/L) and NEG concentration (x, mg/L) for first (I), third (III), and fourth (IV) generation slides: I: y = 1.70x - 0.8 mg/L (n = 13, r = 1.0) III: y = 0.39x - 0.3 mg/L (n = 3, r = 1.0) IV: y = 0.79x - 1.8 mg/L (n = 13, r = 1.0) Using HPLC, we directly demonstrated the presence of NEG in sera of patients receiving lidocaine and quantified NEG concentrations in sera from four of these patients. The increasing artifactual bias in creatinine with increasing NEG concentration unequivocally confirmed that NEG is responsible for the lidocaine-associated interference in the Kodak Ektachem single-slide creatinine method.

Autoanalysis↗
PubMed1987

Preclinical evaluation of illudins as anticancer agents.

Illudins are low molecular weight natural products which were previously evaluated as anticancer drugs using rodent tumor models. In the present studies, we used in vitro cultures of human cancer cells to reevaluate their potential as anticancer agents. Using continuous exposure, Illudins S and M were cytotoxic to human leukemia cells at concentrations of 6-100 nM, but dihydroilludin M was 3 orders of magnitude less toxic, thus identifying a ketone site as a structural feature critical for cytotoxicity. Cytokinetic studies showed that illudin S caused a complete block at the G1-S phase interface of the cell cycle. Kinetics of inhibition of radiolabeled thymidine, uridine, and leucine incorporation suggested a primary effect on DNA synthesis. In colony and liquid culture assays, cell killing was time dependent but near maximal with a 2-h exposure. Myeloid and T-lymphocyte leukemia cells were most sensitive (50% inhibitory concentration, 6-11 nM), but B-cell leukemia/lymphoma, melanoma, and ovarian carcinoma cells were at least 10 times more resistant. Bone marrow granulocyte/macrophage progenitors showed intermediate sensitivity. Illudin S was equally effective against CEM T-lymphocyte leukemia cells expressing the multidrug resistance phenotype associated with Mr 180,000 glycoprotein and the parental cell line. CEM cells resistant to doxorubicin, epipodophyllotoxins, and 1-beta-D-arabinofuranosylcytosine showed only a 2-fold increased resistance to illudin S. Illudins are novel and potent cytotoxins which may be preferentially active against human myeloid and T-cell leukemias, including cells resistant to more conventional chemotherapeutic agents. The present studies illustrate the breadth of information which can be obtained on a new agent using present in vitro screening procedures and human cells.

Antineoplastic Agents↗
PubMed1987

Endocrine hormone abnormalities in Amanita poisoning.

Mushroom poisoning from the genus Amanita is being reported with increasing frequency in the United States. Endocrine hormone abnormalities were investigated in four patients who ingested mushrooms of the Amanita genus ("death cap", "destroying angel"). Marked abnormalities were found in the hormones controlling glucose, calcium, and thyroid homeostasis. Insulin and C-peptide concentrations were elevated at admission, indicating that the hypoglycemia associated with Amanita poisoning may not be solely secondary to hepatic failure. Serum calcitonin concentrations were elevated in conjunction with hypocalcemia. Parathyroid hormone concentrations (both the carboxyl- and amino-terminal assays) increased with time, but began returning to baseline as the hypocalcemia disappeared. The thyroxine concentrations were depressed in all four patients, and triiodothyronine (T3) concentrations were undetectable in three patients. Thyroid-stimulating hormone concentrations were never elevated, reflecting an unresponsive pituitary-hypothalamic axis to the development of hypothyroidism or a euthyroid-illness syndrome.

Adult↗
PubMed1987

Newer cardiac agents: antiarrhythmics and antianginal agents.

This article has briefly summarized the physiologic effects, pharmacokinetics, adverse effects, drug interactions, and methods of analysis for the newer cardiac agents. Methods of analysis for these newer agents are primarily chromatographic types, such as gas-liquid or high-pressure liquid chromatography. Conspicuously absent from methods of analysis for these agents are the newer immunologic methods such as RIA or enzyme-linked assays. This deficiency in methodology is due to several factors. Cross-reactivity between metabolites and parent compounds is often a problem with antibody-based assays, and several of these agents have metabolites that reach concentrations equivalent to that of the parent drug. Several of the newer antiarrhythmics are structurally related not only to each other but also to older agents such as lidocaine. Overcoming this cross-reactivity would be necessary before these assays could be used in patients being converted from intravenous lidocaine to the newer oral preparations. With the development of monoclonal antibody techniques, the need for close therapeutic monitoring of several of the drugs, and the increased emphasis on restraining costs in the clinical laboratory, the newer immunologic methods may soon be introduced in the United States.

Angina Pectoris↗
PubMed1986

Thiol stimulation of the cytochrome P-450-dependent reduction of 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) to 1,1-dichloro-2,2-bis(p-chlorophenyl)ethane (DDD).

The enzymatic reduction of 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) to 1,1-dichloro-2,2-bis(p-chlorophenyl)ethane (DDD) was studied with rat hepatic microsomal fractions. The reaction required NADPH and was inhibited by dioxygen and carbon monoxide, which shows that the reaction is catalyzed by cytochromes P-450. Moreover, when the reaction was studied in the presence of deuterium oxide, no deuterium was incorporated into the DDD, which suggests that a one-electron reduction of DDT to the 1,1-dichloro-2,2-bis(p-chlorophenyl)ethyl radical followed by hydrogen atom abstraction accounts for the formation of DDD. The microsomal reduction of DDT to DDD was stimulated markedly by several thiols, including glutathione. The stimulatory effect of thiols was concentration dependent and was not due to conservation of cytochrome P-450, because nonthiol antioxidants failed to stimulate the reaction. The mechanism of the stimulation is not understood, but thiols do not promote the formation of DDD by preventing the alkylation of microsomal lipids and, thereby, stimulating the formation of a reduced alkane. Finally, these results show that soluble, low-molecular weight compounds may enhance the activity of membrane-bound enzymes.

Animals↗