Biomedical subjects

J C White

Publications and source records attributed to J C White.

At least 73 records · Page 4Linked to original sources

PubMed1990

Partitioning of teniposide into membranes and the role of lipid composition.

We have examined the partitioning behavior of the anticancer agent teniposide (VM-26) into multilamellar vesicles composed of various phospholipid species. Partitioning was found to be sensitive to the composition of the liposomal membrane since changes in the head group or acyl chain constituents could dramatically alter the affinity of the drug for the bilayer. [3H]VM-26 partitioned most readily into 1,2-monounsaturated species of phosphatidylcholine (PC) with a molar partition coefficient (Kp) of 4290 for dioleoyl-PC at 37 degrees C. Inclusion of additional phospholipids having a different head group reduced partitioning in the order cardiolipin greater than phosphatidylglycerol greater than phosphatidylserine greater than phosphatidylethanolamine. The Kp for dioleoyl-PC with 33 mol% cardiolipin was reduced to 1370. Partitioning into completely saturated species of PC was much less than that for unsaturated species and was inversely proportional to the hydrocarbon chain length at temperatures either above or below the chain melting temperature. The Kp for fluid phase dimyristoyl-PC was 2300. Partitioning into dimyristoyl-PC or dioleoyl-PC at 37 degrees C (fluid) or dipalmitoyl-PC at 25 degrees C (gel) was reduced by the addition of 5-30 mol% cholesterol in proportion to its bilayer concentration. Etoposide (VP-16) at concentrations up to 10 mol% did not compete with [3H]VM-26 for association with dioleoyl-PC. Addition of calf serum or serum albumin could significantly reduce the association of [3H]VM-26 with the liposomes.

Etoposide↗

PubMed1990

Studies on the energy metabolism of opossum (Didelphis virginiana) erythrocytes: V. Utilization of hypoxanthine for the synthesis of adenine and guanine nucleotides in vitro.

High pressure liquid radiochromatography was used to test the ability of opossum erythrocytes to incorporate tracer amounts of [G-3H] hypoxanthine (Hy) into [3H] labelled triphosphates of adenine and guanine. In the presence of supraphysiologic (30 mM) phosphate which is optimal for PRPP synthesis, both ATP and GTP are extensively labelled. When physiologic (1 mM) medium phosphate is used, red cells incubated under an atmosphere of nitrogen accumulate [3H] ATP in a linear fashion suggesting ongoing PRPP synthesis in red cells whose hemoglobin is deoxygenated. In contrast, a lesser increase of labelled ATP is observed in cells incubated under oxygen, suggesting that conditions for purine nucleotide formation from ambient Hy are more favorable in the venous circulation.

Adenine↗

PubMed1990

The effect of ara-C-induced inhibition of DNA synthesis on its cellular pharmacology.

The cytotoxicity of ara-C is believed to result from incorporation of ara-CTP into DNA and inhibition of DNA synthesis. Since complete inhibition of DNA synthesis would prevent further incorporation of ara-CTP, ara-C may have a self-limiting effect on its own cytotoxicity, particularly at the high concentrations typical of high-dose ara-C clinical protocols. In this study, the incorporation of [3H]-dThd and [3H]-ara-C into DNA were compared. Within 1 h of exposure of L5178Y cells to ara-C, the rate of [3H]-dThd incorporation into the acid-insoluble fraction was reduced by 98%. Despite this nearly complete block in [3H]-dThd incorporation, DNA synthesis was not completely inhibited since [3H]-ara-C continued to be incorporated for up to 6 h, although a plateau in ara-CDNA synthesis was observed between 2 and 3 h exposure when ara-CTP levels were maximal. The effect of ara-C on [3H]-dThd incorporation into DNA was due in part to an indirect effect of ara-C on the metabolism of intracellular [3H]-dThd to [3H]-dTTP. Within 30 min exposure to 10 microM ara-C, the rate of cellular [3H]-dTTP synthesis was slowed to only 15% of the control rate. This was not due to inhibition of [3H]-dThd transport, since the intracellular and extracellular concentrations of the nucleoside were equal. The effect of ara-C on [3H]-dTTP synthesis resulted from significant changes in deoxynucleoside 5'-triphosphate (dNTP) pools. dTTP, dATP, and dGTP levels were increased, whereas the dCTP concentration was decreased. When dThd kinase from L5178Y cells was assayed with increased dTTP levels induced by ara-C vs the dTTP level in control cells, its activity was reduced by 72%. Thus, the [3H]-dThd incorporation experiment overestimated the extent of inhibition of DNA synthesis by ara-C due to increased feedback inhibition of dThd kinase and increased competition for DNA polymerase between the elevated unlabeled dTTP pool and the decreased levels of [3H]-dTTP. In vitro assay of DNA polymerase in the presence of the ara-CTP concentration achieved after 0.5 or 3 h exposure to 10 microM ara-C (60 microM and 200 microM, respectively), plus the mixture of dNTPs found intracellularly at these times, resulted in 57% and 80% inhibition of the polymerase, respectively. This inhibition may account for the plateau in the accumulation of ara-CDNA that was observed at 3 h and suggests that ara-C incorporation may be self-limiting at high cellular concentrations of ara-CTP.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1990

Enhanced retention of cytosine arabinoside and its metabolites and synergistic cytotoxicity by sequential treatment with dipyridamole in L5178Y leukemia.

Sequential treatment of murine leukemia L5178Y with cytosine arabinoside (ara-C) followed by dipyridamole (DP) resulted in synergistic cytotoxicity. Viability of cells exposed to 1 microM ara-C for 4 h was 88% of control values, but if DP was included in the cloning medium, cell viability was reduced to only 30%. When cells exposed to 1 microM ara-C were resuspended in ara-C-free medium containing 10 microM DP, intracellular ara-C and its metabolites were retained for a significantly longer period than when cells were resuspended in drug-free medium. At 4 h after resuspension in ara-C-free medium, total intracellular [3H] was 1.9 pmol/10(6) cells in control cells but amounted to 6.2 pmol/10(6) cells in DP-treated cells. Unchanged ara-C was 5.5-fold higher in the DP-treated cells. Presumably because of its effect on the concentration of intracellular ara-C, DP increased the half-life for ara-CTP from 97 to 250 min. Ara-CDP-choline declined with a half-life of 76 min on the transfer of cells to control medium, but levels of this metabolite remained constant or increased slightly in cells transferred to medium containing DP. After 4 h in ara-C-free medium with DP, [3H]-ara-C incorporated into the acid-insoluble fraction was 140% of the level attained when cells were transferred to control medium. The increased levels of ara-C metabolites presumably represent the basis for the enhancement of ara-C cytotoxicity by sequential DP treatment.

Animals↗

PubMed1990

Effects of the lipophilic anticancer drug teniposide (VM-26) on membrane transport.

The epipodophyllotoxin glucopyranosides have previously been shown to interact with membrane lipids and to alter the activity of several lipid-embedded membrane proteins. To determine if these agents are acting as general membrane perturbants, we have further examined their effects on membrane processes in Ehrlich ascites tumor cells. [3H]VM-26 and [3H]VP-16 were taken up rapidly and concentrated within the cells in proportion to their lipophilicity. Neither agent was found to have any significant effect on the influx of L-[3H]leucine or alpha-[3H]aminoisobutyric acid. Likewise, these drugs had no significant effects on the hexose transporter. The nucleoside transporter, which is structurally and functionally similar to the hexose transporter, was dramatically affected, however. VM-26 was a non-competitive inhibitor of equilibrium-exchange influx of cytosine arabinoside in Ehrlich cells with a Ki of 15 microM. Equilibrium-exchange influx increased with temperature in control cells (Q10 = 2) but not in VM-26-treated cells; thus, VM-26 was a more potent inhibitor at higher temperatures. VM-26 also significantly reduced zero-trans influx in Ehrlich, P388, L5178Y, and ML-1 cells, and these effects were immediate in onset. VM-26 inhibited high-affinity binding of the nucleoside transport inhibitor nitrobenzylmercaptopurine riboside (NBMPR), but VM-26 enhanced non-specific NBMPR binding to Ehrlich cells. The apparent specificity of the epipodophyllotoxins for the nucleoside transporter is discussed.

Amino Acids↗

PubMed1990

Studies on the energy metabolism of opossum (Didelphis virginiana) erythrocytes--VI. De novo purine nucleotide biosynthesis is limited to the final steps of the pathway in vitro.

1. High pressure liquid radiochromatography was used to show the incorporation of [14C] formate with Z-compounds into ATP and GTP in opossum erythrocytes. 2. The use of Z-riboside with [14C] formate resulted in more extensive labeling of ATP than the Z-base/[14C] formate combination as substrates for nucleotide biosynthesis. 3. Substantial accumulation of ZMP and ZTP, but no ZDP was detected in the chromatograms. 4. ATP was unstable in red cells metabolizing in the presence of Z-compounds under an atmosphere of air as gas phase in these experiments.

Adenosine Triphosphate↗

PubMed1990

Design of an antithrombotic-antihypertensive agent (Wy 27569). Synthesis and evaluation of a series of 2-heteroaryl-substituted dihydropyridines.

An approach to the design of potential combined antithrombotic-antihypertensive agents is described. A series of 1,4-dihydropyridines bearing a 1H-imidazol-1-yl or pyrid-3-yl substituted side chain in the 2-position were synthesized and tested for antihypertensive activity in spontaneously hypertensive rats and for inhibition of TXA2 synthetase in rabbit platelets, in vitro. 1,4-Dihydro-2-(1H-imidazol-1-ylmethyl)-6-methyl- 4-(3-nitrophenyl)pyridine-3,5-dicarboxylic acid 3-ethyl 5-methyl diester (1) was shown to be similar in potency to nitrendipine as an antihypertensive agent. Compound 1 inhibited TXA2 synthetase in rabbit and human platelets in vitro and reduced plasma TXB2 levels in rats at antihypertensive dose levels. The reductions in thromboxane production observed in vivo and in vitro were accompanied by enhanced levels of 6-KPGF1 alpha, reflecting diversion of the arachidonic acid cascade toward prostacyclin synthesis.

6-Ketoprostaglandin F1 alpha↗

PubMed1990

Granulocyte plasma membrane damage by leukotoxic supernatant from Pasteurella haemolytica A1 and protection by immune serum.

Bovine respiratory disease caused by Pasteurella haemolytica may be partially mediated by a leukotoxin secreted by the microorganism. We examined the effect of leukotoxic Pasteurella supernatants on leakage of the cytosol enzyme lactate dehydrogenase and the lysosomal enzyme arylsulfatase from bovine granulocytes. Lactate dehydrogenase release (94%) was much higher than arylsulfatase release (38%) over 30 minutes of incubation. The Pasteurella supernatants inhibited superoxide production by stimulated granulocytes at concentrations which also caused substantial cell death as measured by failure to exclude trypan blue. Both toxic effects were prevented by serum from aerosol-immunized calves, and protection appeared to be antibody-specific by comparison with fetal bovine serum or with serum absorbed against intact P. haemolytica. These findings suggest that the leukotoxin may selectively disrupt the granulocyte plasma membrane, and that antibody directed against a surface component of the microorganism is also capable of protecting against the leukotoxin effect.

Animals↗

PubMed1989

Determination of 3H-labelled cytosine arabinoside and eight metabolites in cell extracts by high-performance liquid chromatography and scintillation spectrometry.

We have developed a method for the separation and quantitation of radiolabeled cytosine arabinoside and its eight metabolites in cell extracts by anion-exchange gradient high-performance liquid chromatography. Baseline separation of cytosine arabinoside and uracil arabinoside and their respective 5'-mono-, di- and triphosphates, as well as cytosine arabinoside diphosphocholine was obtained with the shortest interval between peaks being 3 min. This degree of separation was found to be essential for quantitation of 3H-labeled metabolites by scintillation counting of 1-min fractions. Application of this procedure to the quantitation of [3H] cytosine arabinoside and its metabolites from HL60 human leukemia cells is demonstrated.

Arabinofuranosyluracil↗

PubMed1989

Consumer participation: a personal journey.

One consumer shares a personal journey that enabled her to participate in the Canadian Mental Health Association. Committees, boards and other groups can encourage consumer participation by accepting and supporting these individuals. Consumers bring a personal, passionate knowledge of the problems and potential solutions. Partnership among consumers, professionals, family members, and community leaders increases effectiveness. Consumers who choose to identify themselves and participate face financial and emotional costs. Their anger with the system is a motive to create change. People who are taking risks need practical and emotional support. Other group members can help provide safety that makes consumer participation possible.

Canada↗

PubMed1989

Neutrophil oxidative metabolism after exposure to bacterial phospholipase C.

The effects of phospholipase C (PLC) from Clostridium perfringens and Bacillus cereus on bovine neutrophil oxidative metabolism were studied by measuring superoxide production and oxygen consumption in response to PLC alone or in combination with other stimuli. PLC from both species elicited superoxide production and enhanced the response to stimulation by NaF when the two stimuli were given simultaneously. However, oxygen consumption in response to latex beads was markedly inhibited by pretreatment of cells with B. cereus PLC. The results suggest that some bacterial PLC exoenzymes may initially activate neutrophils but leave the cells relatively unresponsive to subsequent stimuli.

Animals↗

PubMed1989

Effects of the anticancer agent VM-26 on hexose uptake in Ehrlich cells.

The chemotherapeutic agent VM-26 is a membrane-interactive drug which we have previously demonstrated to be a potent inhibitor of nucleoside transport. Since the carriers mediating nucleoside and hexose transport are structurally and functionally similar, we have further characterized the membrane related properties of this agent by examining its effect on the transport and phosphorylation of hexoses in Ehrlich ascites cells. Under conditions in which only the transport component of hexose uptake was measured, VM-26 had no effect on the influx of 2-deoxyglucose, 3-0-methylglucose, or D-glucose. Glucose-sensitive cytochalasin B binding was only weakly inhibited by the drug. However, VM-26 was an apparent non-competitive inhibitor of the net uptake of 2-deoxyglucose (transport and phosphorylation). Measurement of hexokinase activity in cell extracts failed to demonstrate any significant effect of VM-26 on enzyme activity. In summary, although VM-26 is a potent inhibitor of the transport of nucleosides, it has no apparent effect on the transmembrane flux of hexoses indicating a differential effect on nucleoside and hexose transporters. The ability of the drug to decrease the net accumulation of hexoses in the absence of any detectable effect on hexokinase activity warrants further investigation.

3-O-Methylglucose↗

PubMed1988

A comparison of EMG procedures in the carpal tunnel syndrome with clinical-EMG correlations.

One hundred and twenty-two patients were selected on the basis of symptoms of finger numbness and tingling thought to suggest carpal tunnel syndrome. The severity of the symptoms was graded and the patients were studied with seven established EMG procedures, motor inching to the abductor pollicis brevis and second lumbrical muscles, and sensory inching. Symptom severity was compared with the degree of nerve conduction abnormality and results from symptomatic hands with those abnormal results from patient's asymptomatic hands. Motor inching to the abductor pollicis brevis muscle was the most sensitive study and, when combined with sensory inching, gave a sensitivity of 97-100% (depending on symptom severity). Motor inching to the second lumbrical muscle alone detected the lesion site in several severely involved nerves. Guidelines are suggested with which one can estimate the likelihood that a patient's finger sensory symptoms are on the basis of carpal tunnel syndrome.

Adolescent↗

PubMed1988

Childhood malignant tumours in Papua New Guinea.

Data from the Papua New Guinea Tumour Registry and the Central Pathology Department were reviewed in order to document the incidence and pattern of malignancies in children in Papua New Guinea. Altogether, 680 cases of histologically defined childhood malignancies were recorded during the 14.5 years from 1971 to 1985. The frequencies of the various tumours were compared with past data and with published data from other countries. The incidence of malignancies in Papua New Guinean children appeared to be low, 36.5/1,000,000/year, with a male:female ratio of 1.6:1. Lymphoma was the most commonly occurring tumour and Burkitt's tumour accounted for 53% in this group. The relative frequency of leukaemia compared with lymphoma appeared to have increased since a previous report. A relatively high incidence of retinoblastoma (6.9%) and of other embryonal tumours (4.8%) was recorded, whilst the recorded incidences of tumours of the central nervous system (3.8%) and neuroblastoma (3.7%) were low. Ewing's sarcoma accounted for almost half of the bone tumours, whilst Kaposi's sarcoma was a relatively frequent soft tissue tumour. Differences and similarities between the Papua New Guinea data and those from other countries are discussed.

Adolescent↗

PubMed1988

Acute pseudogout following parathyroidectomy.

Four patients developed acute arthritis following parathyroidectomy over a 3 year period in two general surgical practices. The diagnosis of pseudogout was made by clinical presentation, radiologic findings and demonstration of synovial fluid crystals exhibiting weakly positive birefringence. Rapid resolution of clinical arthritis followed joint aspiration and administration of anti-inflammatory agents in all four patients. Patients with hypercalcemia have a high incidence of calcium pyrophosphate dihydrate crystal deposition into joints. Rapid drops in serum calcium levels can cause shedding of these crystals into synovial fluid which may precipitate acute attacks of pseudogout. Because the relative hypocalcemia following parathyroidectomy provides a good stimulus for crystal shedding, it follows that hypercalcemic patients undergoing parathyroidectomy should experience a high incidence of acute pseudogout. Although this entity has been described before, its occurrence is not widely recognized in clinical practice. It is proposed that these four cases observed over a 3 year period indicate that pseudogout following parathyroidectomy occurs more commonly than previously recognized.

Calcium Pyrophosphate↗

PubMed1987

Raman spectroscopy of interferon-induced 2',5'-linked oligoadenylates.

Raman spectra of model compounds and of 2',5'-oligoadenylates in D2O were utilized to assign the Raman bands of 2',5'-oligoadenylates. The Raman spectra of A2'pA2'pA, pA2'pA2'pA, and pppA2'pA2'pA contained features that were similar to those of adenosine, adenosine 5'-monophosphate (AMP), and adenosine 5'-triphosphate, respectively. When AMP and pA2'pA2'pA were titrated from pH 2 to 9, the normalized Raman intensity of their ionized (980 cm-1) and protonated (1080 cm-1) phosphate bands revealed similar pKa's for the 5'-monophosphates. The Raman spectrum of pA2'pA2'pA was altered slightly by elevations in temperature, but not in a manner supporting the postulate that 2-5A possesses intermolecular base stacking. Major differences in the Raman spectrum of 2',5'- and 3',5'-oligoadenylates were observed in the 600-1200-cm-1 portion of the spectrum that arises predominately from ribose and phosphate vibrational modes. Phosphodiester backbone modes in A3'pA3'pA and pA3'pA3'pA produced a broad band at 802 cm-1 with a shoulder at 820 cm-1, whereas all 2',5'-oligoadenylates contained a major phosphodiester band at 823 cm-1 with a shoulder at 802 cm-1. The backbone mode of pppA2'pA2'pA contained the sharpest band at 823 cm-1, suggesting that the phosphodiester backbone may be more restrained in the biologically active, 5'-triphosphorylated molecule. The Raman band assignments for 2',5'-oligoadenylates provide a foundation for using Raman spectroscopy to explore the mechanism of binding of 2',5'-oligoadenylates to proteins.

Adenine Nucleotides↗

PubMed1987

Role of uridine triphosphate in the phosphorylation of 1-beta-D-arabinofuranosylcytosine by Ehrlich ascites tumor cells.

Pyrimidine nucleotide pools were investigated as determinants of the rate of phosphorylation of 1-beta-D-arabinofuranosylcytosine (ara-C) by Ehrlich ascites cells and cell extracts. Cells were preincubated for 2 h with 10 microM pyrazofurin, 10 mM glucosamine, 50 microM 3-deazauridine, or 1 mM uridine in order to alter the concentrations of pyrimidine nucleotides. Samples of the cell suspensions were taken for assay of adenosine 5'-triphosphate (ATP), uridine 5'-triphosphate (UTP), cytidine 5'-triphosphate, guanosine 5'-triphosphate, deoxycytidine 5'-triphosphate (dCTP), and deoxythymidine 5'-triphosphate; then 1 microM [3H]ara-C was added and its rate of intracellular uptake was measured for 30 min. 3-Deazauridine lowered dCTP and stimulated ara-C uptake; however, pyrazofurin and glucosamine were potent inhibitors of ara-C uptake although they also decreased dCTP levels. Uridine stimulated ara-C uptake despite an increase in dCTP. A crude cytoplasmic extract was prepared by a procedure which permitted results of ara-C kinase assays to be expressed as pmol per min per 10(6) cells as in the cellular uptake studies. When assayed in the presence of mixtures of ribo- and deoxyribonucleoside triphosphates at concentrations close to their cellular levels, ara-C kinase activity closely approximated the cellular uptake rate for the five incubation conditions. Deletion of cytidine 5'-, guanosine 5'-, or deoxythymidine 5'-triphosphate from the assay mixture had little effect, while deletion of dCTP increased kinase activity 9-fold. Elimination of ATP also did not alter kinase activity in the presence of the remaining five ribo- and deoxyribonucleoside triphosphates; however, deletion of UTP reduced activity to 22% of the rate with the control mixture. When ara-C kinase was assayed with only 3 mM ATP, dCTP was a very potent inhibitor (50% inhibition concentration = 0.4 microM). Inhibition was complete at 10 microM dCTP, a concentration below the intracellular dCTP level in control cells (25 microM). With 0.9 mM UTP, enzyme activity was 2-fold greater in the absence of dCTP and the dCTP was 15-fold less potent as an inhibitor (50% inhibition concentration = 6 microM). We conclude that the actual phosphate donor for the phosphorylation of 1 microM ara-C in Ehrlich cells is UTP and not ATP. These observations suggest that successful combination protocols aimed at stimulating ara-C uptake by means of a decrease in dCTP levels must simultaneously preserve or increase UTP pools.

Animals↗

PubMed1987

Photostability studies of phycobiliprotein fluorescent labels.

Photostability studies of four fluorescent phycobiliproteins were conducted to identify stable chromophores for biological labeling applications. Phycobiliprotein photodestruction was linear with the applied laser power and depended on the total number of photons absorbed per molecule. Photodestruction quantum yields phi of 1.1 X 10(-5) for R-phycoerythrin, 6.6 X 10(-6) for B-phycoerythrin, 4.5 X 10(-6) for allophycocyanin, and 2.5 X 10(-6) for C-phycocyanin were measured. C-Phycocyanin is a factor of 10.8 more photostable than fluorescein. The photostability of R-phycoerythrin was improved by a factor of 1.7 by adding n-propyl gallate. The addition of superoxide dismutase, catalase, sodium dithionite, ascorbate, dithiothreitol, EDTA, or deoxygenation with argon bubbling had no effect on the photostability of R-phycoerythrin.

Catalase↗