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Biomedical subjects

J M Collins

Publications and source records attributed to J M Collins.

At least 55 records · Page 3Linked to original sources
PubMed1995

Metabolism of taxol by human and rat liver in vitro: a screen for drug interactions and interspecies differences.

Human liver slices, human liver microsomes, and rat liver microsomes were used to investigate the metabolism of 3H-taxol. The effects of drugs frequently coadministered with taxol and the effects of several cytochrome P450 system probes were studied. In all, 16 compounds were screened. After incubation with liver slices or with microsomal protein, 3H-taxol was converted into several radioactive species resolved by HPLC. There were qualitative and quantitative species differences in the metabolism of taxol. The pattern of metabolism was similar for both human-derived preparations, with 6 alpha-hydroxytaxol being the major metabolite peak. In drug interaction studies performed with human liver microsomes, cimetidine 80 microM, and diphenhydramine 200 microM, had little or no effect on 6 alpha-hydroxytaxol formation. Quinidine, ketoconazole, dexamethasone and Cremophor EL inhibited 6 alpha-hydroxytaxol formation with IC50 values of 36 microM, 37 microM, 16 microM and 1 microliter/ml, respectively, but these concentrations exceed the usual clinical range. Cremophor EL also inhibited microsomal metabolism of taxol, but at 2 microliters/ml it had little or no effect on 6 alpha-hydroxytaxol production by human liver slices. These results suggest that: (1) taxol is metabolized by the cytochrome P450 system; (2) taxol metabolism is different in humans than in rats; (3) taxol metabolism in humans is unlikely to be altered by cimetidine, dexamethasone, or diphenhydramine, drugs regularly coadministered with taxol; (4) taxol metabolism can be indirectly affected by Cremophor EL, the formulation vehicle; (5) taxol metabolism may be altered by concentrations of ketoconazole achievable in humans only at very high doses; and (6) taxol metabolism and drug interaction studies of clinical relevance can be performed in vitro with human liver microsomes and human liver slices, but not with rat liver preparations.

Animals↗
PubMed1995

Effect of Percoll wash on sperm motion parameters and subsequent fertility in intrauterine insemination cycles.

PURPOSE: This study examined sperm motion parameters as measured by computerized automated semen analysis before and after a Percoll wash and determined if differences in any parameter were correlated with fertility subsequent to intrauterine insemination (IUI). RESULTS: Total motile sperm decreased following the washing procedure from 79.0 +/- 9.0 to 37.2 +/- 7.6 million sperm. Motility increased from a mean of 43.4% to 61.7% (P < 0.001). Other motility parameters also changed significantly (P < 0.001) as follows: curvilinear velocity (VCL), 43.4 to 61.7 microns/s; straight-line velocity (VSL), 21.3 to 26.7 microns/s; linearity 53.1 to 45.2%; lateral head displacement (ALH), 2.97 to 3.94 microns. Similar changes occurred following a swim-up preparation, although changes in mean motility, VCL, and ALH were significantly greater when compared to Percoll. The postwash changes were not accounted for merely by time lapse in preparation since reanalyzed untreated controls did not show the same changes in motion parameters. Prewash linearity in those specimens which resulted in pregnancies was greater than in those which did not (P = 0.28). No other significant differences in pre- or post-Percoll washed sperm motion parameters were found between pregnant vs nonfertile cycles. CONCLUSION: Following Percoll wash all CASA-generated motility parameters were significantly altered, but there was little association between these parameters and pregnancy achieved in IUI cycles.

Cell Separation↗
PubMed1995

Increased prostatic blood flow in response to microwave thermal treatment: preliminary findings in two patients with benign prostatic hyperplasia.

OBJECTIVES: To determine the effects on prostate blood flow of heat generated by microwave thermal treatment in patients with benign prostatic hyperplasia. METHODS: Prostate blood flow was evaluated by continuous transrectal color Doppler ultrasonography in 2 patients at baseline, after implantation of interstitial needles used for thermal mapping, and during microwave thermal treatment. Temperatures at 30 prostatic, periprostatic, urethral, and rectal sites were continuously monitored. In 1 patient, transrectal prostate compression was applied and the blood flow and temperature response to this maneuver noted. RESULTS: Microwave thermal treatment achieved maximum prostate temperatures of 59 degrees C at 5 mm radially from the urethra. Urethral and rectal temperatures remained low. Marked increases occurred in prostate blood flow in response to microwave thermal treatment. These increases were apparent throughout the prostate gland, with the greatest increase in perfusion occurring in the peripheral zone and the posterior half of the transitional zone. After 15 minutes of microwave treatment, peak systolic blood flow increased 99% and 70% in patients 1 and 2, respectively, while end-diastolic blood flow climbed 50% and 112%, respectively. Prostate compression resulted in a prompt quenching of blood flow and an increase in prostate temperature. CONCLUSIONS: Based on these preliminary findings in 2 patients, prostate blood flow increases markedly in response to microwave thermal treatment. This compensatory increase in blood flow is likely to be a significant treatment-limiting factor in achieving effective thermoablation.

Blood Flow Velocity↗
PubMed1995

An accurate technique for detailed prostatic interstitial temperature-mapping in patients receiving microwave thermal treatment.

A minimally invasive prostatic interstitial temperature-mapping technique is described that supplies accurate, detailed information on thermal doses delivered to precisely localized tissue sites. The technique employs a comparatively large numbers of thermosensors, highly accurate placement of those thermosensors at specified three-dimensional coordinates, fiberoptic technology that avoids significant interaction between the thermosensors and the applied microwave field, and continuous temperature readout. Biplane ultrasound imaging and fluoroscopy were used to ensure stereotactic accuracy of thermosensor placement. The technique was applied in 15 patients with benign prostatic hyperplasia (BPH) undergoing a 1-hour microwave thermal treatment session. The thermal mapping procedures and microwave treatment were generally well tolerated. The mean maximum temperature in the prostate and periprostatic tissue (57.9 +/- 1.9 degrees C) was significantly higher (P < 0.001) by more than 18 degrees C than that in either the urethra (39.6 +/- 0.9 degrees C) or the rectum (40.8 +/- 1.7 degrees C). In a representative patient, microwave treatment resulted in stable elevation of temperature 5 mm radially from the urethra that averaged 66.0 +/- 0.1 degrees C. At 10 mm from the urethra, the temperature averaged 50.5 +/- 0.1 degrees C. Urethral and rectal temperatures remained at innocuous levels. In conjunction with pathologic studies, this interstitial thermal mapping method should prove useful in defining the optimal thermal doses for microwave therapy. The method should also find uses in evaluating different microwave treatment systems, which can vary markedly in thermal performance, as well as other modalities that apply heat to prostatic tissue.

Aged↗
PubMed1994

Metabolism of taxol by human hepatic microsomes and liver slices: participation of cytochrome P450 3A4 and an unknown P450 enzyme.

Incubation of taxol with human hepatic microsomal fractions or freshly isolated human liver slices yields three metabolite high performance liquid chromatography peaks, metabolite A, metabolite B, and 6 alpha-hydroxytaxol. These metabolites are formed in patients given taxol, with 6 alpha-hydroxytaxol formation representing the principal biotransformation pathway. Metabolite B and 6 alpha-hydroxytaxol are shown to be products of different, highly regioselective cytochrome P-450 (P450) enzymes, while metabolite A results from stepwise metabolism by each of these enzymes. Correlation of metabolite B formation with P450 3A markers was good (r2 = 0.91-0.94), but the correlation of 6 alpha-hydroxytaxol formation with markers for several P450 enzymes was poor. Chemical inhibitors that selectively inhibited metabolite B formation (troleandomycin, cyclosporine), that selectively inhibited 6 alpha-hydroxytaxol formation (naringenin, quercetin), or that nonselectively inhibited both pathways (felodipine, ketoconazole) were found. Metabolite B formation was selectively reduced by anti-P450 3A4 antibodies. Expressed human P450 3A4 preparations were efficient catalysts of metabolite B formation; no expressed P450 preparation tested showed a capacity for catalyzing taxane 6 alpha-hydroxylation reactions. The combined results of several experimental approaches show that P450 3A4 is the major catalyst of metabolite B formation and that the identity of the P450 enzyme or enzymes responsible for 6 alpha-hydroxytaxol formation cannot be assigned with certainty.

Biotransformation↗
PubMed1994

Isolation, structural determination, and biological activity of 6 alpha-hydroxytaxol, the principal human metabolite of taxol.

The principal biotransformation product of taxol was found to be identical for human hepatic microsomes, human liver slices, and patient bile samples. We have isolated this metabolite from the bile of a patient given taxol, and we report its structure and its cytotoxicity relative to taxol. The NMR and SIMS data presented here indicate that, in humans, taxol is regiospecifically hydroxylated at the 6-position on the taxane ring and that this hydroxyl is stereospecifically placed trans to the hydroxyl at position 7, yielding 6 alpha-hydroxytaxol. This metabolite is apparently not formed in rats. Tests of the growth inhibition potential of 6 alpha-hydroxytaxol versus taxol in two human tumor cell lines showed that the metabolite was approximately 30-fold less cytotoxic than taxol. Thus the cytochrome P-450-mediated biotransformation of taxol to 6 alpha-hydroxytaxol can be classified as a detoxification reaction.

Bile↗
PubMed1994

Dirofilaria immitis: heartworm products contract rat trachea in vitro.

Subtle decreases in racing performance have been noted in asymptomatic greyhounds with heartworm burdens insufficient to obstruct pulmonary outflow, suggesting that alternative mechanisms may be involved in the pathogenesis of canine heartworm disease. Endothelium-dependent relaxation is depressed in the in vivo femoral artery of heartworm-infected dogs, in the in vitro pulmonary artery from heartworm-infected dogs, and in the in vitro rat aorta exposed to heartworms, heartworm-conditioned medium, and serum from heartworm-infected dogs. These findings suggest that circulating filarial factors may play a role in the pathogenesis of heartworm infection. We examined the effect of Dirofilaria immitis, the canine heartworm, on acetylcholine-induced contraction of rat tracheal rings. In epithelium-intact rings, both heartworms and heartworm-conditioned medium increased acetylcholine-induced contraction. Pretreatment of the parasites with aspirin prevented the filarial-induced increase in acetylcholine-induced contraction, suggesting that parasite cyclooxygenase products are responsible for the effect. In addition, heartworms caused contraction in both epithelium-intact and denuded rings and this effect was markedly decreased by pretreatment of the worms with aspirin. Filarial cyclooxygenase metabolites may cause airway hyperreactivity and parasite-derived factors could play a role in the subtle changes in exercise performance seen in asymptomatic greyhounds with low worm burdens. Comparable mechanisms may be operating in other filarial diseases, including those that affect humans in tropical countries.

Acetylcholine↗
PubMed1994

Alzheimer's disease and Down syndrome: leukocyte membrane fluidity alterations.

Down Syndrome (DS) patients over the age of 40 have brain lesions identical to those of patients with Alzheimer's Disease (AD). We have earlier shown that with some membrane probes, the plasma membranes of circulating leukocytes had increased fluidity in AD compared to the normally more rigid membranes in similarly aged subjects. We next questioned whether the occurrence of AD-like pathological lesions in older DS subjects would be associated with a similar increase in membrane fluidity. Fluidity was assessed by measurements of steady-state fluorescence anisotropy using TMA-DPH, which anchors at the plasma membrane surface, and a series of 9-anthroyloxy fatty acids substituted with the fluorescent moiety at different positions on the fatty acid, which permit measurement of fluidity at different depths of the plasma membrane. This was done simultaneously in neutrophils, lymphocytes, and monocytes utilizing flow cytometry. In older DS subjects (average age 52.6), plasma membrane fluidity was indeed increased, a finding similar to that with AD leukocytes. Membrane fluidity of leukocytes of young DS subjects (average age 23.6 years) was less than that seen in older subjects. Membrane changes may result from lipophilic substances released from the central nervous system, or may reflect intrinsic differences in membrane structure unique in DS.

Adolescent↗
PubMed1994

Toxicity, metabolism, DNA incorporation with lack of repair, and lactate production for 1-(2'-fluoro-2'-deoxy-beta-D-arabinofuranosyl)-5-iodouracil in U-937 and MOLT-4 cells.

Two cell lines, U-937 and MOLT-4, were used to investigate the toxicity, DNA incorporation, and effect on mitochondria of 1-(2'-fluoro-2'-deoxy-beta-D-arabinofuranosyl)-5-iodouracil (FIAU) and its putative metabolite 1-(2'-fluoro-2'-deoxy-beta-D-arabinofuranosyl)-uracil (FAU). After 72-hr incubation, the IC50 values for FIAU were 6.4 microM for U-937 cells and 26 microM for MOLT-4 cells. IC50 values for FAU were 10-fold higher in both cell lines. Incubation for 24 hr with 10 microM [2-14C]FIAU led to 2.1% and 0.93% replacement of thymidine in DNA of U-937 and MOLT-4 cells, respectively. The predominant radioactive species measurable in DNA was FIAU. A similar incubation with [2-14C]FAU resulted in 4-fold lower DNA incorporation of a single radioactive species that coeluted with 1-(2'-fluoro-2'-deoxy-beta-D-arabinofuranosyl)-5-methyluracil (FMAU). There was no evidence of a selective repair process after DNA incorporation of FIAU or FAU (FMAU). Increased intracellular concentrations of FIAU triphosphate and incorporation into DNA were associated with an increase in cellular toxicity. Continuous exposure to a clinically achievable concentration of FIAU, 0.44 microM, produced a constant DNA incorporation of 0.80% and 0.11% for U-937 and MOLT-4 cells, respectively. FIAU was not readily metabolized to FAU or iodouracil by human liver in vitro. Compared with 2',3'-dideoxycytidine as a positive control, after 12 days of continuous exposure of U-937 and MOLT-4 cells to FIAU there was no evidence of increased lactate production. These data negate several possible mechanisms (DNA chain termination, DNA polymerase inhibition, one form of selective mitochondrial poisoning, and FAU-mediated toxicity) and provide clues for possible mechanisms (FIAU triphosphate concentration and DNA incorporation). Further work is needed to develop a complete explanation for the delayed hepatic toxicity observed in the investigational clinical trials of FIAU.

Arabinofuranosyluracil↗
PubMed1993

Steady-state plasma concentrations and effects of taxol for a 250 mg/m2 dose in combination with granulocyte-colony stimulating factor in patients with ovarian cancer.

Taxol, a natural product initially isolated from the stem bark of the western yew Taxus brevifolia, is undergoing phase II and III evaluation due to its reported activity against a variety of tumors. Previous studies have described correlations between plasma concentrations and toxicity when taxol is given (a) at lower doses, (b) for shorter infusion times, and (c) without granulocyte-colony-stimulating factor. Because the 24-h infusion schedule is most commonly used in current clinical trials, we attempted to correlate steady-state plasma concentrations of taxol achieved with a 24-h continuous i.v. infusion with toxicities and responses. Plasma samples from 48 refractory ovarian cancer patients were obtained 1-2 h prior to the end of the first taxol infusion. Taxol concentrations were measured by high-performance liquid chromatography (HPLC). Interpatient variation of taxol plasma concentrations was small (mean +/- SD, 0.85 +/- 0.21 microM. Total taxol body clearance was 256 +/- 72 ml min-1 m-2 (mean +/- SD). Taxol plasma protein binding was 88.4% +/- 1.3% (mean +/- SD, n = 9). Grade 3-4 hematologic toxicity, mainly leukopenia, occurred in 92% of the patients. The leukopenia was transient and did not warrant a reduction in the dose of taxol. Grade 3-4 nonhematologic toxicity occurred in 8% of the patients. No severe hypersensitivity reaction or grade 3-4 neurotoxicity was observed. Correlations of plasma concentrations and toxicities were not feasible due to the high frequency of hematologic effects and the low frequency of nonhematologic toxicity. The low degree of interpatient variation in plasma concentrations hindered the development of correlations with response.

Blood Proteins↗
PubMed1993

The steady expiratory pressure-flow relation in a model pulmonary bifurcation.

Experiments were conducted over a range of Reynolds numbers from 50 to 8000 to study the pressure-flow relationship for a single bifurcation in a multi-generation model during steady expiratory flow. Using the energy equation, the measured static pressure drop was decomposed into separate components due to fluid acceleration and viscous energy dissipation. The frictional pressure drop was found to closely approximate that for an equivalent length of curved tube with the same curvature ratio as in the model bifurcation. The sensitivity of these results to changes in airway cross-sectional shape, non-planar configuration, and flow regime (laminar-turbulent) was investigated. In separate experiments using dye visualization and hot-wire anemometry, a transition to turbulent flow was observed at Reynolds numbers between 1000 and 1500. Transition had very little effect on the pressure-flow relation.

Acceleration↗
PubMed1992

Gas chromatographic-mass spectrometric method for routine monitoring of 5-fluorouracil in plasma of patients receiving low-level protracted infusions.

A gas chromatographic-mass spectrometric (GC-MS) method is described which quantitates 5-fluorouracil (5-FU) plasma levels ranging from 0.5 to 50 ng/ml. The analysis uses two internal standards, 1,3-[15N2]-5-fluorouracil and 5-chlorouracil. Extraction and derivatization of the pyrimidine bases were accomplished in a single step using acetonitrile. Compounds were analyzed as their 1,3-dipentafluorobenzyl derivatives by electron-impact MS, and the GC-MS analysis was automated with respect to sample injection and data reduction. Stability of the analysis was demonstrated by continuous unattended analysis of 5-FU in human plasma for periods of up to three days with no deterioration of the quantitative results. The method is applicable to quantitating 5-FU plasma levels in patients receiving protracted infusions of the drug for colorectal cancer or other malignancies.

Drug Monitoring↗
PubMed1992

Modulation of cell cycle kinetics in human cancer with total parenteral nutrition.

Prior DNA flow cytometric data from the laboratory of the Division of Surgical Oncology, Massey Cancer Center, demonstrated an increase in the hyperdiploid compartment of tumor cells taken from patients with squamous cell carcinoma of the head and neck after a course of total parenteral nutrition (TPN). To assess a putative increase in the percentage of tumor cells actively synthesizing DNA in this system, the authors administered bromodeoxyuridine (BrdU) intravenously to ten patients before and after the administration of TPN. Cell suspensions prepared from biopsy specimens of normal oral mucosa and tumor tissue were analyzed with flow cytometric study. Before TPN administration, the mean percentage of tumor cells incorporating BrdU was 2.47 +/- 1.11%. After TPN administration, the percentage of S-phase cells increased significantly (P less than 0.05) to a mean of 4.52 +/- 2.67%. Before TPN was given, normal mucosa demonstrated a mean of 7.97 +/- 2.69% of cells incorporating BrdU. After TPN was given, a mean of 8.47 +/- 2.51% was seen (not significant [NS]). A potential strategy for the use of TPN to enhance tumor cell susceptibility to S-phase-specific chemotherapy is strongly suggested by these data.

Adult↗
PubMed1992

Cell cycle and proliferation dynamics of adult rat oligodendrocytes.

Adult oligodendrocytes (OLGs) have been shown to be mitotically responsive when co-cultured with dorsal root ganglion. We have investigated the population dynamics of the OLG proliferative response, including the maximum percent of cells which will proliferate and the cell cycle duration time of the adult rat OLG. Adult OLGs were stimulated with pituitary extract and either continuously labeled or pulse labeled with bromodeoxyuridine (BrdU). The labeled cells were stained with a fluorescent anti-BrdU monoclonal antibody, and fluorescence measurements were made with a multiparameter flow cytometer. A maximum number of 53% of the adult OLGs entered the cell division cycle after 9 days. The cell division cycle duration time (Tc) was determined to be approximately 35.4 hr, and the durations of G1, S, and G2M found to be 12.1, 8.5, and 5.8 hr, respectively. A scenario was generated for adult OLG proliferation in which 2.2% of the initial population is stimulated to enter the cell division cycle in the first 24 hr. This initial population divides and continues in the cell division cycle. Another 2.2% of the initial population enters the cell division cycle during the second 24 hr period, divides, and continues in the cell division cycle. This entry of 2.2% of the cells into the proliferative phase continues until 53% of the initial population has left a quiescent state and entered the cell cycle.

Animals↗
PubMed1992

Aphidicolin-inducible common fragile-site expression: results from a population survey of twins.

Common chromosomal fragile sites appear to be ubiquitous in humans and other mammals, and, although the molecular basis and function of these sites remain an enigma, it has been speculated that they may be a cytogenetic expression of gene activity. A population survey of 28 twin pairs was conducted to assess the heritability of common fragile-site expression. Our data yielded a heritability estimate of .88 for total site expression, suggesting that these sites may result from some common process that is under relatively stringent genetic control. An analysis of the expression of individual autosomal sites revealed that expression on both homologues in the same cell occurred more frequently than expected.

Adolescent↗
PubMed1991

Comparisons of steady-state anisotropy of the plasma membrane of living cells with different probes.

We have used an extended Perrin equation which was in agreement with literature data for steady-state anisotropy (rSS) for a wide variety of artificial and isolated biological membranes labeled with various probes (Van der Meer et al. (1986) Biochim. Biophys. Acta 854, 38-44 to obtain the static component (r infinity) for the intact plasma membranes of living cells. We show that lipid structural order parameters can be obtained for DPH and TMA-DPH in the plasma membranes of intact cells. We have examined the relationship between 'fractional limiting hindered anisotropy', r infinity/r0, which is related to the lipid structural order parameter, of DPH, TMA-DPH, DPHpPC, and a series of depth-dependent probes (n-(9-anthroyloxy) fatty acids, with n = 2-16), using data from 19 cell types. There was a linear relationship between r infinity/r0 values of DPH and TMA-DPH, but the relationship between either of these probes was non-linear with respect to DPHpPC or the series of fatty acid probes. The relationship between r infinity/r0 values of DPHpPC and the series of fatty acid probes was linear, suggesting that they not only undergo similar motions in the membrane, but also experience similar types of restriction to motion, a type which is different from that experienced by DPH and TMA-DPH. We show that for the plasma membranes of living cells, 'second degree' order parameters can be estimated for DPH and TMA-DPH, and propose that the parameter r infinity/r0, or the 'fractional limiting hindered anisotropy', analogous to a 'first degree' order parameter, can be estimated for DPHpPC and the depth-dependent fatty acid probes to evaluate the density of membrane packing.

Cell Membrane↗
PubMed1991

Altered membrane anisotropy gradients of plasma membranes of living peripheral blood leukocytes in aging and Alzheimer's disease.

Several reports have suggested that membrane rigidity, a term that refers to the relative motion of membrane constituents, is decreased in Alzheimer's Disease. Accordingly, a series of fluorescent membrane probes was used to evaluate the rigidity from the surface to the center of the outer hemi-leaflet of the plasma membrane of living neutrophils, monocytes and lymphocytes. Anisotropy, a parameter which increases with increasing membrane rigidity, was calculated from flow cytometric measurements of vertically and horizontally polarized components of the fluorescence emission of the probes. These preliminary experiments suggest that whereas membrane rigidity in certain regions of the plasma membrane of peripheral blood leukocytes is increased as expected in elderly controls, it is decreased in Alzheimer's disease.

Aging↗