Search PubMed⌕ Search

Biomedical subjects

J B Mitchell

Publications and source records attributed to J B Mitchell.

At least 307 records · Page 17Linked to original sources
PubMed1986

Enhancement of misonidazole cytotoxicity by iron.

The toxicity of misonidazole (MISO) to hypoxic Chinese hamster ovary (CHO) cells in serum-free medium is enhanced by Fe(III)-EDTA. Enhancement of MISO cytotoxicity by a factor of 1.6 was seen with 2 microM Fe(III)-EDTA, while 200 microM Fe(III)-EDTA results in sensitization by a factor of 2.0. Treatment of CHO cells with the iron chelator desferal resulted in protection against the hypoxic cytotoxicity in MISO (approximate protection factor of 2.5 with 100 microM desferal). Similar results were obtained with Chinese hamster V79 cells. Fe(III)-EDTA also enhanced binding of [2-14C] MISO to cellular macromolecules while desferal decreased binding of MISO to cellular macromolecules. These results suggest that iron plays an important role in the reductive metabolism of MISO and that modification of the intracellular metal ion status may be a useful approach to modulating the biological effect of nitro compounds.

Animals↗
PubMed1986

Selective cytotoxicity of 125I-labeled monoclonal antibody T101 in human malignant T cell lines.

The radiolabeled anti-T cell antibody T101 can be used for specific tumor localization, but unlabeled T101 produces limited cytotoxicity in patients. We thus studied the in vitro cytotoxic effects of T101 labeled with 125I, a radionuclide known for its short-range, high-linear-energy electrons. We showed that 125I-T101 could be readily prepared at high specific activity with high immunoreactivity. Human malignant T cell lines HUT 102, MOLT-4, and HUT 78 were found to differ in the number of T65 determinants (the antigen recognized by T101) and the sensitivity to external x-ray radiation, which were of significance for the cytotoxicity of 125I-T101 in vitro. The cytotoxic effects of 125I-T101 were also found to be dose dependent and increased with exposure time under frozen conditions. As controls, unlabeled T101 had no cytotoxic effect, while free Na 125I or the 125I-labeled irrelevant antibody 9.2.27 exerted minor cytotoxicity. In HUT 102 and MOLT-4, more than 3 logs' cell killing was achieved within four weeks. Because considerable cytotoxicity was demonstrated in vitro by 125I-T101 on T65-positive malignant cells, and because low-dose 111In-T101 can be used successfully for tumor localization, future trials using 125I-T101 at high specific radioactivity may improve therapeutic results in patients with T65-positive malignancies.

Antibodies, Monoclonal↗
PubMed1986

Selective modulation of glutathione levels in human normal versus tumor cells and subsequent differential response to chemotherapy drugs.

Cellular glutathione (GSH) levels were found to be 7-fold higher in a human lung adenocarcinoma cell line (A549) than in a normal human lung fibroblast line (CCL-210). Differential modulation of cellular GSH was explored in these cell lines by (a) stimulation of GSH synthesis by oxothiazolidine-4-carboxylate (OTZ) and (b) inhibition of GSH synthesis by buthionine sulfoximine (BSO). In the tumor cell line, OTZ treatment had no effect; however, GSH levels of 140-170% of control were achieved in the normal fibroblast line. With BSO, the normal cell line was depleted of GSH at a faster relative rate than with the tumor line. Within 7 h, 5% GSH remained in the CCL-210 line while approximately 40% GSH remained in the A549 line. Survival response of normal versus tumor cell lines to selected chemotherapy drugs was compared following modulation of GSH levels. OTZ pretreatment of the A549 line provided no protection to a 1-h exposure to melphalan, cisplatin, or bleomycin; however, OTZ pretreatment of CCL-210 elevated GSH and provided protection to melphalan, cisplatin, and bleomycin (protection ratios at 5% survival of 1.2, 1.4, and 1.4, respectively). Neocarzinostatin toxicity in the normal CCL-210 line pretreated with BSO was greatly reduced (protection ratio at 50% survival = 5.0). The same BSO treatment to A549 cells (40% GSH remaining) yielded a similar survival curve to control cells. These studies demonstrate that selective differential chemotherapy responses of normal versus tumor cells is possible by manipulating the GSH synthetic cycle. Should basic phenotypic differences with regard to reductive capacity exist in vivo, such manipulation in GSH levels might yield a therapeutic gain for carefully selected chemotherapy drugs.

Antineoplastic Agents↗
PubMed1986

Repair of ionizing radiation DNA base damage in ataxia-telangiectasia cells.

Micrococcus luteus endonuclease sensitive sites were measured by alkaline elution in normal human and ataxia-telangiectasia (AT) fibroblasts after ionizing radiation. Due to the sensitivity of this assay, repair of base damage after 3 to 6 kilorads has been measured after oxic or hypoxic radiation. With 5.5 kilorads of oxic radiation, more than 50% of the base damage was removed after 1.5 h of repair incubation in all cells, including exr+ and exr- AT cells, and approximately 75% was removed by 4 h. After 3 or 4.5 kilorads of hypoxic X-irradiation, repair was equivalent in normal and exr- AT cells. This study included three exr- AT strains which have been reported to be deficient in the removal of gamma-ray base damage at higher doses. Since these strains repaired ionizing radiation base damage normally at lower doses, which are more relevant to survival, it is concluded that the X-ray hypersensitivity of AT cells is probably not related to the repair of base damage.

Ataxia Telangiectasia↗
PubMed1986

Pavlovian conditioning of sexual arousal: parametric and background manipulations.

Recent studies have shown that a Pavlovian conditioned stimulus (CS) for unconsummated sexual arousal can increase the rate of copulation in the rat. This report includes five experiments examining the effects of parametric manipulations on the conditioned arousal response. Results show that between six and nine trials are necessary for reliable conditioning, but extinction is somewhat slower than acquisition. The function for the CS-US (unconditioned stimulus) interval is quadratic, with a minimum of several minutes required for effective conditioning. In the first three experiments, it appeared that background cues were conditioned as well as the designated CSs, and this was tested explicitly in the last two studies. In one, the effect of background cues was shown by training and testing in different situations; in the second, background cues were shown to be subject to latent inhibition. These results demonstrate the influence of Pavlovian learning in sexual behavior and help to provide the basis for an animal model of the acquisition of deviant sexual arousal in humans.

Animals↗
PubMed1985

Physician DRGs.

DRG-based reimbursement for inpatient services is an option currently being considered by federal policy makers, but little is known about how physician DRGs might work. We performed simulations of potential impacts, using Medicare claims from four states. Although physician-related inpatient costs associated with surgical DRGs were quite homogeneous, those associated with medical admissions varied dramatically. This suggests that DRG payment could be a lottery, with inequitable losses for some physicians and windfall gains for others. Potential gains and losses were also found to be systematically related to the specialty of the attending physician. General practitioners and ophthalmologists would gain financially on average, whereas medical specialists and some surgical specialists would incur net losses. These differences may be due to the triaging of more seriously ill patients within a given DRG to certain specialists.

Costs and Cost Analysis↗
PubMed1985

Glutathione depletion greatly reduces neocarzinostatin cytotoxicity in Chinese hamster V79 cells.

The role of the intracellular thiol glutathione in the reductive activation of neocarzinostatin was investigated in Chinese hamster V79 cells. The cells were pretreated with agents that either lower (buthionine sulfoximine or diethyl maleate) or elevate (oxothiazolidine carboxylate) intracellular glutathione levels. These cells were then exposed to 1-5 micrograms/ml neocarzinostatin for 1 h and assayed for survival. Depletion of glutathione to levels at or below the limit of detection resulted in a marked reduction in neocarzinostatin cytotoxicity, while increasing glutathione levels to 250% of control values had little or no effect on neocarzinostatin toxicity. High performance liquid chromatography analysis of cysteine in untreated and glutathione-depleted cells showed cysteine levels lower than 0.2 microM, indicating that cysteine does not play a major role in the reductive activation of neocarzinostatin in untreated or glutathione-depleted cells. When intracellular cysteine levels were artificially elevated by oxothiazolidine carboxylate treatment of glutathione-depleted cells, neocarzinostatin toxicity was about two-thirds that seen in cells with normal glutathione levels. In cell-free systems, others have shown that reducing agents such as 2-mercaptoethanol are necessary for the activation of neocarzinostatin to a species that will cleave DNA. In this study, we have identified glutathione as the major cellular reducing agent for the activation of neocarzinostatin in a mammalian cell line.

Animals↗
PubMed1985

Adaptive cellular response to hyperthermia: 31P-NMR studies.

Dynamic intracellular ATP and Pi levels were measured non-invasively for Chinese hamster V79 cells by 31P-NMR under conditions of thermotolerance and heat-shock protein induction. High densities of cells were embedded in agarose strands, placed within a standard NMR sample tube, and perfused with medium maintained either at 37 or 43 degrees C at pH 7.35. Cell survival and heat-shock protein synthesis were assessed either from parallel monolayer cultures or cells dislodged from the agarose strands post-treatment. Thermotolerance (heat resistance) and heat-shock protein synthesis was induced by a 1 h exposure to 43 degrees C followed by incubation for 5 h at 37 degrees C. After the 5 h incubation at 37 degrees C, marked thermal resistance was observed in regard to survival with concomitant synthesis of two major heat-shock proteins at 70 and 103 kDa. Studies were also conducted where tolerance and heat-shock protein synthesis were partially inhibited by depletion of cellular glutathione (GSH) prior to and during heat treatment. Dynamic measurement of intracellular ATP of cells heated with or without GSH depletion revealed no change in steady-state levels immediately after heating or during the 5 h post-heating incubation at 37 degrees C where thermotolerance and heat-shock proteins develop. These data are consistent with other reported data for mammalian cells and indicate that the steady-state ATP levels in mammalian cells remain unchanged during and after the acquisition of the thermotolerant state.

Adenosine Triphosphate↗
PubMed1985

The hidden mental health network. Treatment of mental illness by nonpsychiatrist physicians.

Building on a previous study, this report explores in more detail one aspect of the "de facto mental health services system," the treatment of mental disorders by nonpsychiatrist physicians in office-based practice. Data from the 1980 and 1981 National Ambulatory Medical Care surveys indicate that almost one half of all office visits to a physician resulting in a mental disorder diagnosis are to nonpsychiatrists, mostly in primary care. Nonpsychiatrists' mentally ill patients tend to be less seriously ill than patients of psychiatrists, and are more likely to come in with physical problems. They are also significantly more likely to be female, to be nonwhite, and to be elderly. Physicians treating these patients appear to be providing a different product than psychiatrists are, spending less time with patients, but using a wider range of diagnostic and therapeutic services during each office visit.

Adolescent↗
PubMed1985

Measurement of DNA polymerase beta in skin fibroblast cell lines from patients with ataxia telangiectasia.

DNA polymerase beta levels were measured in 4 cell lines of normal human skin fibroblasts and in 5 cell lines of skin fibroblasts from patients with ataxia telangiectasia, an autosomal recessive disease exhibiting marked X-ray sensitivity. The enzyme specific activities for the normal lines were similar and the mean value was 2-fold lower than the mean value for the ataxia lines. With both kinds of cells, the enzyme level did not change as the cultures progressed from logarithmic to stationary phase of growth. Thus, this putative DNA repair enzyme appears to be 'constitutive' in human skin fibroblast lines, and a modest elevation of beta-polymerase activity is associated with ataxia telangiectasia. These results are discussed in the context to current views about DNA-repair enzymes in X-ray-sensitive cultured mammalian cells.

Ataxia Telangiectasia↗
PubMed1985

A phase I study of intravenous iododeoxyuridine as a clinical radiosensitizer.

Twenty-four patients with locally advanced (19 patients) or metastatic (5 patients) tumors were treated in a Phase I study combining constant intravenous infusions of iododeoxyuridine (IUdR) and hyperfractionated radiation therapy. IUdR was given as a constant infusion for 12 hours/day for two separate 14-day infusion periods in most patients. The dose of IUdR was escalated from 250 to 1200 mg/m2/12-hour infusion in this study. The initial tumor volume was treated to 45 Gy/1.5 Gy BID/3 weeks followed by a cone-down boost to 20-25 Gy/1.25 Gy BID/2 weeks after a planned 2-week break. THe IUdR infusion preceded the initial and cone-down irradiation by 1 week. Local acute toxicity (within the radiation volume) was uncommon and few patients required an alteration of the planned treatment schedule. Two patients developed late local toxicity with one patient showing clinical signs of radiation hepatitis and another patient developing a large bowel obstruction that required surgical bypass. Dose-limiting systemic toxicity was confined to the bone marrow with moderate to severe thrombocytopenia developing on Day 10-14 of infusions at 1200 mg/m2/12 hours. Mild stomatitis and partial alopecia occurred in some patients at this dose level. No systemic skin toxicity was seen. Pharmacology studies revealed steady-state arterial plasma levels of IUdR of 1 to 8 X 10(-6) M over the dose range used. In vivo IUdR incorporation into tumors was studied in three patients with high-grade sarcomas using an anti-IUdR monoclonal antibody and immunohistochemistry and demonstrated incorporation in up to 50-70% of tumor cells. The preliminary treatment results, particularly in patients with unresectable sarcomas, are encouraging. In comparison to our previous experience with intravenous bromodeoxyuridine, this Phase I study of IUdR shows less systemic toxicity (especially to skin), higher (2-3X) steady-state arterial levels, and comparable in vivo tumor cell incorporation.

Biopsy↗
PubMed1985

When doctors listen: counseling patterns of nonpsychiatrist physicians.

Recent work has shown that nonpsychiatrist physicians are surprisingly active in the mental health arena. Using the two most recent National Ambulatory Medical Care Surveys (1980-1981), the authors analyzed the provision of counseling services by general medical physicians in more detail. Office visits involving counseling were a third again as long as the average office visit (20 minutes versus 15) and involved notably more diagnostic and therapeutic services. Although patients who received counseling services from nonpsychiatrist physicians were generally not mentally ill, about one in eight did have a psychiatric diagnosis and might have been better served in the mental health sector.

Adolescent↗
PubMed1985

Oxygen dependence of hematoporphyrin derivative-induced photoinactivation of Chinese hamster cells.

The oxygen dependence of hematoporphyrin derivative (HPD)-induced photoinactivation of Chinese hamster V79 cells was examined. Cells were treated with HPD (25 micrograms/ml) for 2 h and subsequently exposed to red light (greater than 590 nm) under either aerated or hypoxic (less than 10 ppm O2) conditions. Hypoxic cells were found to be extremely resistant to the lethal effects of HPD and light. The electron-affinic X-ray hypoxic cell sensitizer, SR-2508, did not sensitize hypoxic HPD-treated cells to light. The clinical implications of these findings are discussed, with consideration of the possibility that hypoxic areas in tumors may limit HPD phototherapy.

Animals↗
PubMed1985

Glutathione dependence of neocarzinostatin cytotoxicity and mutagenicity in Chinese hamster V-79 cells.

Neocarzinostatin (NCS) is mutagenic in bacteria, yeast, fungi, and mammalian cells. In cell-free systems, DNA strand breakage induced by NCS requires a reducing agent like 2-mercaptoethanol, unless very high (greater than 100 micrograms/ml) concentrations of NCS are used. In this study, we have investigated the role of the sulfhydryl compound glutathione (GSH), which is usually the most common intracellular thiol, in the bioactivation of NCS to a toxic and mutagenic species. Chinese hamster V79 cells were pretreated with one of two GSH depleting agents, buthionine sulfoximine or diethyl maleate. These agents deplete GSH via different mechanisms, but both will lower GSH levels within the cell to less than 5% of control (untreated) values. GSH-depleted cells and control cells were then exposed to NCS concentrations of 0.5-2.5 micrograms/ml for 1 h, assayed for survival, and plated for expression of hypoxanthine-guanine phosphoribosyltransferase-negative (HGPRT-) mutants. After an expression period of 7 days, during which the cultures were subcultured twice, HGPRT- mutants were selected by plating in hypoxanthine-free medium containing 5 micrograms of 6-thioguanine per ml, at a density of 2 X 10(5) cells per 100 mm dish. NCS alone decreased the surviving fraction to about 1% at 2.5 micrograms/ml and produced dose-related increases in HGPRT-mutants that reached greater than 10 times the spontaneous mutation frequency at 2.5 micrograms NCS per ml. In GSH-depleted cells, however, NCS was only mildly cytotoxic (60-80% surviving fraction) and did not produce dose-related increases in HGPRT- mutants over cells treated only with diethyl maleate or buthionine sulfoximine. Thus, GSH appears to be the main reducing agent for the bioactivation of NCS to a toxic and mutagenic species in Chinese hamster V79 cells.

Animals↗
PubMed1985

In vivo incorporation of bromodeoxyuridine into proliferating cells in the marrow and its effects on granulocyte-macrophage progenitor cells.

Bromodeoxyuridine (BUdR), a potential radiosensitizing drug, was given by intravenous infusion at 650-1000 mg/m2/day for up to 12 days. In vivo incorporation into human bone marrow was assayed by differential chromatid staining as well as by comparison of in vitro radiation survival curves of granulocyte-macrophage progenitor cells scored at both day 7 and day 14. Although a difference was found in the radiation survival of control (untreated) day-7 progenitor cells (Do = 1.39 Gy) and day-14 progenitor cells (Do = 0.89 Gy), a similar degree of in vitro radiosensitization was found for BUdR-treated bone marrow progenitor cells scored at day 7 and day 14. The culture technique provided a bioassay for the in vivo action of BUdR. BUdR treatment produced transient moderate myelosuppression that probably resulted from BUdR incorporation into normal marrow cells.

Bone Marrow↗
PubMed1985

Treatment of murine intraperitoneal ovarian ascitic tumor with hematoporphyrin derivative and laser light.

An ascitic murine tumor, ovarian embryonal carcinoma, was used as a model of human ovarian carcinoma restricted to the peritoneum. The tumor was treated with a combination of hematoporphyrin derivative (HPD) and i.p. 514-nm laser light. Mice were given injections of 2 X 10(5) tumor cells, and by 9 days, there were 2 to 4 g of ascitic tumor/mouse. On Day 9, mice (68) were treated as follows: (12) no treatment; (12) only HPD (50 mg/kg i.p.); (12) laser only (9.6 J for 16 min); and (32) HPD (50 mg/kg i.p.) and 2 h later, laser treatment. On Day 15, a second treatment with HPD and laser was given to 15 mice. All mice not receiving HPD-laser treatment died between Days 20 and 23. The response rate as determined by decrease in weight and abdominal size for HPD-laser-treated mice was 90%, but the response was short, and all but one animal died by Day 34. However, 6 of 15 of the twice-treated group are alive at 90 days and considered cured. Photoradiotherapy with HPD for i.p. ascitic tumors appears to have promise as a treatment modality.

Animals↗