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Biomedical subjects

E J Katz

Publications and source records attributed to E J Katz.

13 recordsLinked to original sources
PubMed1999

Cytotoxicity of organophosphate anticholinesterases.

Organophosphate (OP) anticholinesterases were found to modulate metabolic activities of human neuroblastoma cells and hepatocytes, which was detectable by the Cytosensor microphysiometer. The nerve gas ethyl-S-2-diisopropylaminoethyl methylphosphorothiolate (VX), at 10 microM, produced significant reduction in cell metabolism within 2 min, as measured by changes in the acidification rate of the medium. The reduction was dose- and time-dependent and irreversible after 4 h of exposure. Two alkaline degradation products of VX produced no cytotoxicity. Exposure for 24 h to 3 microM VX caused 36% and 94% irreversible loss of metabolism in hepatocytes and neuroblastoma cells, respectively. The insecticides parathion and chlorpyrifos stimulated hepatocyte metabolism but inhibited neuroblastoma cells. Their oxons were more active. Exposure of neuroblastoma cells for 4 h to VX, parathion, paraoxon, diisopropylfluorophosphate or chlorpyrifos gave an LC50 of 65, 775, 640, 340, or 672 microM, respectively, whereas 24 h gave an LC50 of 0.7, 3.7, 2.5, 29, and 31 microM, respectively. Preincubation of hepatocytes with phenobarbital enhanced their response to parathion and VX due to metabolic bioactivation. Atropine partially blocked the effects of VX and paraoxon on both cell types, which suggests the involvement of a muscarinic receptor as the target for cytotoxicity. There was no correlation between OP in vivo neurotoxicity and in vitro cytotoxicity. It is suggested that the former results from their cholinesterase inhibition, while the latter results from action on different targets and requires much higher concentrations.

Acetylcholinesterase↗
PubMed1997

Chlorpyrifos, parathion, and their oxons bind to and desensitize a nicotinic acetylcholine receptor: relevance to their toxicities.

The nicotinic acetylcholine receptor (nAChR) of the electric organ of the electric ray. Torpedo sp., the richest source of nAChR, with similar structure and pharmacology to the mammalian skeletal muscle nAChR, carries several binding sites for different ligands. Incubation of Torpedo membrane-bound nAChRs with the agonist carbamylcholine (Carb) stimulated the binding of [3H]thienyl-cyclohexylpiperidine ([3H]TCP), which binds to the receptor's noncompetitive antagonist binding site in its ionic channel, with high affinity (Kd of 196 nM). The agonist-stimulated binding of [3H]TCP (i.e., binding to activated nAChRs) was inhibited in a concentration-dependent manner by four organophosphate (OP) anticholinesterases, chlorpyrifos oxon (CPO), chlorpyrifos (CPS), parathion (PS), and paraoxon (PO) with IC50 (concentration that inhibits 50% of the effect) values of 5, 150, 200, and 300 microM, respectively. The binding of CPO was totally reversible. The OPs had no effect on equilibrium binding of [alpha-125I]bungarotoxin ([alpha-125I]BGT) to the receptor's acetylcholine (ACh)-binding site, but preincubation of the membranes with the OPs increased this site's affinity for Carb. In absence of agonist, 100 microM of the OPs increased the binding of [3H]TCP by two- to fivefold with the following order of decreasing potency: PS > CPO > CPS > PO. The data suggest that in addition to inhibition of acetylcholinesterase, these OPs bind to a site on the nAChR that is different from the sites that bind ACh or TCP and that this binding induces nAChR desensitization. The relevance of this direct action of OPs on nAChRs on their acute toxicities is discussed.

Animals↗
PubMed1990

Effect of topoisomerase modulators on cisplatin cytotoxicity in human ovarian carcinoma cells.

The in vitro interaction of modulators of topoisomerase I and II with cisplatin in human ovarian carcinoma cells might be synergistic. The interactions were evaluated by median effect analysis of survival data derived from continuous exposure to drug combinations for 10 days in colony-forming assays. The interaction between cisplatin and the topoisomerase I inhibitor camptothecin and the topoisomerase I activator beta-lapachone was additive, as was that between cisplatin and the topoisomerase II inhibitor novobiocin. Despite the clinical efficacy of the combination of etoposide (a topoisomerase II inhibitor) and cisplatin, the combination index at 50% cell kill indicated antagonism between these two drugs. Thus, biochemical synergism at the cellular level is not a prerequisite of improved therapeutic efficacy.

Antibiotics, Antineoplastic↗
PubMed1990

The effect of DNA polymerase inhibitors on the cytotoxicity of cisplatin in human ovarian carcinoma cells.

We examined the effect of specific inhibitors of DNA polymerases alpha and delta, and beta, on cisplatin (DDP) cytotoxicity in DDP-sensitive and -resistant human 2008 ovarian carcinoma cells. Under conditions of continuous exposure to drug combinations, neither aphidicolin glycinate (AG) nor dideoxythymidine enhanced the cytotoxicity of DDP in either cell line as determined by clonogenic survival assays. However, when clonogenic survival was determined following short-term drug exposure, AG exhibited strong synergism with DDP in the DDP-resistant, but not the DDP-sensitive cells, as indicated by median effect analysis of the data. DNA polymerase alpha mRNA levels were the same in both cell lines under basal conditions. DDP-sensitive cells, but not DDP-resistant cells, were able to increase their expression of DNA polymerase alpha in response to DDP exposure. Levels of mRNA for DNA polymerase beta and for the human DNA repair gene ERCC-1 were not elevated in resistant cells, either under basal conditions or 18 hr after a 1 hr exposure to IC20 concentrations of DDP. In another human ovarian carcinoma cell line, A2780, AG and DDP were synergistic in both DDP-sensitive and -resistant variants in short-term exposure. We conclude that DNA polymerases alpha and/or delta play a role in the DDP sensitivity of human ovarian carcinoma cells.

Antibiotics, Antineoplastic↗
PubMed1987

DNA nucleotide excision-repair synthesis is independent of perturbations of deoxynucleoside triphosphate pool size.

We have investigated the effects of fluctuations in deoxynucleoside triphosphate (dNTP) pool size on DNA repair and, conversely, the effect of DNA repair on dNTP pool size. In confluent normal human skin fibroblasts, dNTP pool size was quantitated by the formation of [3H]TTP from [3H]thymidine; DNA repair was examined by repair replication in cultures irradiated with UV light. As defined by HPLC analysis, the [3H]TTP pool was formed within 30 min of the addition of [3H]thymidine and remained relatively constant for the next 6 h. Addition of 2-10 mM hydroxyurea (HU) caused a gradual 2-4-fold increase in the [3H]TTP pool as HU inhibited DNA synthesis but not TTP production. No difference was seen between the [3H]TTP pool size in cells exposed to 20 J/m2 and unirradiated controls, although DNA-repair synthesis was readily quantitated in the former. This result was observed even though the repair replication protocol caused an 8-10-fold reduction in the size of the [3H]TTP pool relative to the initial studies. In the UV excision-repair studies the presence of hydroxyurea did not alter the specific activity of [3H] thymidine 5'-monophosphate incorporated into parental DNA due to repair replication. These results suggest that fluctuations in the deoxynucleoside triphosphate pools do not limit the extent of excision-repair synthesis in human cells and demonstrate that DNA nucleotide excision-repair synthesis does not significantly diminish the size of the [3H]TTP pool.

Cells, Cultured↗
PubMed1985

Water intoxication associated with nephrogenic diabetes insipidus secondary to lithium: case report.

In the psychiatric population, psychogenic polydipsia leading to water intoxication and nephrogenic diabetes insipidus secondary to lithium therapy are both well-recognized entities. A case is reported of the apparently unusual combination of these two conditions, where lithium probably not only has caused the nephrogenic diabetes insipidus, but might also have contributed to the state of psychogenic polydipsia.

Diabetes Insipidus↗
PubMed1983

Lack of effect of hydroxyurea on base excision repair in mammalian cells.

The effect of hydroxyurea on the initial steps of base excision repair has been examined in mammalian cells in 3 different proliferative states: i.e., quiescent cells, asynchronously growing cells undergoing multiple divisions prior to confluence; and synchronous cell populations undergoing the first cell cycle(s) after release from quiescence. Two parameters of the base excision repair pathway were examined: (1) The direct excision of 7-methylguanine from cellular DNA in the presence of increasing hydroxyurea concentrations was quantitated by high performance liquid chromatography; (2) the effects of hydroxyurea on the uracil DNA glycosylase were examined by quantitating the levels of this base excision repair enzyme in quiescent and proliferating cells. In quiescent cells, hydroxyurea at concentrations routinely used to quantitate DNA repair had no effect on the excision rates of 7-methylguanine examined over a span of 3 days; nor was there any effect on the specific activity of uracil DNA glycosylase in confluent cells. In asynchronously proliferating mammalian cells, identical hydroxyurea concentrations had no effect on the induction of the glycosylase. In synchronous growing cells HU had no effect on the temporal sequence of induction of uracil DNA glycosylase prior to DNA replication, nor on the extent of this induction. These results suggest that hydroxyurea at concentrations generally used to measure DNA repair has no effect on base excision repair.

Animals↗
PubMed1983

Effect of hyperthermia on the survival of normal human peripheral blood mononuclear cells.

Human peripheral blood mononuclear cells from normal healthy volunteers were exposed to elevated temperatures of 41-43 degrees for up to 6 hr. Thereafter, the cells were stimulated with phytohemagglutinin in vitro in order to measure indirectly the surviving fraction. DNA replication in heated cells in response to phytohemagglutinin was found to be a sensitive indicator of thermal injury. Exposure to even 40 degrees for 2 hr lowered thymidine incorporation at early time points after phytohemagglutinin stimulation, but the cells were able to recover from thermal injury after exposure for up to 4 hr at 42 degrees. At 43 degrees, exposure for even 1 to 2 hr caused irreversible damage. The changes in thymidine incorporation were not due to changes in endogenous nucleotide pools since parallel changes were observed in DNA polymerase activity. Thus, the heat sensitivity of normal human lymphocytes could be a limiting factor for use of hyperthermia as an adjunct to radiotherapy and chemotherapy of human cancer.

Cells, Cultured↗
PubMed1981

Lack of effect of hyperprolactinemia on glucose disposal and insulin secretion in patients with prolactinomas.

The role of prolactin as a diabetogenic hormone is still controversial. The present study examines intravenous glucose tolerance in six subjects with prolactin secretion pituitary adenomas. Testing was performed in each individual both in the untreated high prolactin state and again after prolactin was reduced by bromocriptine treatment for three months. Lowering serum prolactin failed to improve intravenous glucose tolerance or alter insulin release. It is concluded that prolactin has no significant effect on glucose disposal.

Adenoma↗
PubMed1981

Induction of the DNA repair enzymes uracil DNA glycosylase and 3-methyladenine DNA glycosylase in regenerating rat liver.

The capacity of eukaryotic cells to modulate the activities of DNA repair enzymes during cell proliferation was examined. Using regenerating rat liver as a model system, the specific activities of the DNA repair enzymes uracil DNA glycosylase and 3-methyladenine DNA glycosylase were determined at specific intervals after partial hepatectomy. The induction of DNA replication and the stimulation of DNA polymerase were also measured in order to relate changes in the potential for DNA repair to those observed for DNA replication. As measured in nuclear extracts, the specific activities of both the uracil DNA glycosylase and the 3-methyladenine DNA glycosylase were increased in regenerating rat liver reaching maximal levels 18--24 h after partial hepatectomy. The specific activity of each DNA repair enzyme returned to basal levels by 48 h after the hepatectomy. No increase in either enzyme activity was observed in sham operated controls. The products of the reactions were identified as 3-methyladenine or as uracil by high pressure liquid chromatography or by gel filtration on Sephadex G-10. The 2--3 fold increases in the specific activity observed for each nuclear DNA repair enzyme was comparable to the 2.7 fold increase observed for DNA polymerase activity. The stimulation of DNA repair enzymes in regenerating rat liver is a further suggestion that eukaryotic cells actively regulate excision repair pathways in the defined pattern of gene expression observed during the eukaryotic cell cycle.

Animals↗
PubMed1981

DNA replication of X-irradiated human lymphocytes.

Human peripheral blood lymphocytes are well-differentiated cells. Ordinarily, they do not divide and are considered to be in the G0 stage of the cell cycle. These cells can be stimulated to undergo DNA replication in culture by mitogens such as phytohemagglutinin. In the present study, we have examined cellular and biochemical events that occur after exposure of lymphocytes to X-irradiation. Irradiation with up to 100 rads, prior to stimulation with phytohemagglutinin, did not interfere with DNA replication. At later periods, DNA replication was inhibited proportionally to the amount of radiation. In comparison to DNA synthesis, the effect of X-irradiation on RNA and protein synthesis in phytohemagglutinin-stimulated lymphocytes was less marked. Furthermore, X-rays did not inhibit either the induction or the continual synthesis of DNA polymerase-alpha or -beta in response to phytohemagglutinin. Kinetic studies with different nucleotide substrates suggest that cellular pools of nucleotides are not significantly altered by X-irradiation. Thus, the inhibition of DNA synthesis in irradiated cells is likely to be due to damage to the cellular DNA template. The inhibition of DNA synthesis was accompanied by accumulation of cells in the G2 and M stages of the cell cycle, suggesting that inhibition of DNA replication by X-irradiation is a postmitotic event.

Cell Cycle↗
PubMed1977

Screening for deficits in DNA repair by the response of irradiated human lymphocytes to phytohemagglutinin.

An assay has been developed to measure the ability of human lymphocytes to repair damage to DNA. In this assay, purified human lymphocytes are exposed to graded doses of radiation and then stimulated with phytohemagglutinin to undergo DNA replication. The rate of incorporation of thymidine in irradiated lymphocytes during the second and subsequent rounds of DNA replication is taken to be indicative of the ability of the cells to repair damage to DNA. In lymphocytes from normal individuals, X-irradiation with doses of 100 to 800 rads was found to inhibit phytohemagglutinin-stimulated thymidine incorporation proportionally to the dose of radiation without curtailing the induction of DNA polymerase. The response to phytohemagglutinin of lymphocytes from a patient with xeroderma pigmentosum after exposure to graded doses of X-irradiation was found to be similar to that of the normal controls, whereas the response after ultraviolet irradiation was markedly impaired. In contrast, lymphocytes from patients with ataxia telangiectasia were hypersensitive to X-irradiation. The data on these clinical syndromes support the idea that this assay measures DNA repair and indicates the feasibility of using this method for screening individuals for genetic deficits in DNA repair.

Ataxia Telangiectasia↗