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D J Warren

Publications and source records attributed to D J Warren.

At least 19 recordsLinked to original sources
PubMed2001

Effect of the glutathione/glutathione disulfide redox couple on thiopurine methyltransferase.

The susceptibility of recombinant human thiopurine methyltransferase (hTPMT) to thiol-disulfide exchange was investigated. The enzyme was incubated in buffers of the redox couple GSH and GSSG. The values of the chosen concentrations and concentration ratios of the redox couple equaled those expected to occur in vivo. Activity measurements of the enzyme over time in these buffers at 30 degrees C indicated that thiol-disulfide exchange may be a part of the posttranslational modulation of hTPMT activity. Activity varied between 5% and 100%, with the lowest activities in buffers of low [GSH]/[GSSG] concentration ratios and of low total concentration of the redox couple. A thiol-disulfide exchange mechanism involving a mixed disulfide was proposed. Titration of the protein thiol groups with Ellmann's reagent (5,5'-dithiobis[2-nitrobenzoic acid]) revealed that at least two protein thiols were readily accessible for conjugation with the reagent, while others were conjugated more slowly. The previous model of hTPMT constructed by our group was in accordance with the experimental results. Inspection of the model indicated that one of the protein thiols subject to slow thiol-disulfide exchange may be situated at the binding site of the co-substrate of the enzyme and thus be responsible for the glutathione/glutathione disulfide modulation of the activity of hTPMT.

Buffers↗
PubMed2001

High-resolution spatio-temporal mapping of visual pathways using multi-electrode arrays.

The parallel processing of visual information was studied with penetrating microelectrode arrays. We studied the high-resolution visuotopic organization of cat primary visual cortex, and the encoding of simple visual stimuli by ensembles of ganglion cells in the isolated turtle retina. The high-resolution visuotopic organization of visual cortex is non-conformal. Regions of visual cortex separated by 400 mu may have receptive field centers that are separated by as much as 3 degrees, or they may superimpose. Ganglion cells are 'generalists', and are poor specifiers of the color of full field visual stimuli. Groups of 'luminosity' type ganglion cells can assist in the specification of stimulus color, but even individual 'chromatic' ganglion cells are not capable of quality color specification. These basic studies have relevance to the development of visual neuroprostheses based upon electrical stimulation of the retina and cortex.

Animals↗
PubMed2001

High-resolution two-dimensional spatial mapping of cat striate cortex using a 100-microelectrode array.

Much of our understanding of the visuotopic organization of striate cortex results from single-electrode penetrations and serial recording of receptive field properties. However, the quality of these maps is limited by imprecision in quantifying electrode position, combining data from multiple laminae, and eye drift during the measurement of the receptive field properties. We have addressed these concerns by using an array of 100 closely spaced microelectrodes to investigate the two-dimensional visuotopic organization of layer IV in cat striate cortex. This array allowed simultaneous measurement of the receptive field properties of multiple single units on a regularly spaced grid. We found the relationship between cortical and visual space to be locally non-conformal: the receptive field locations associated with a closely spaced line of electrodes appeared randomly scattered in visual space. To quantify the scatter, we fitted a linear transformation of electrode sites onto the associated receptive field locations. We found that the distribution of the difference between the predicted receptive field location and the measured location had standard deviations of 0.59 degrees and 0.45 degrees in the horizontal and the vertical axes, respectively. Although individual receptive field positions differed from the predicted locations in a non-conformal sense, the trend across multiple receptive fields followed the maps described elsewhere. We found, on average, that the 13 mm2 of cortex sampled by the array mapped onto a 5.8-degrees) region of visual space. From the scaling of this map and a combination of the statistics of the receptive field size (2.7+/-1.5 degrees) and scatter, we have explored the impact of electrode spacing on the completeness and redundancy in coverage of visual space sampled by an array. The simulation indicated an array with 1.2-mm spacing would completely sample the region of visual space addressed by the array. These results have implications for neuroprosthetic applications. Assuming phosphene organization resembles the visuotopic organization, remapping of visual space may be necessary to accommodate the scatter in phosphene locations.

Animals↗
PubMed2001

Development of a rapid and sensitive immunofluorometric assay for glutathione S-transferase A.

BACKGROUND: The short half-life of the alpha-class glutathione S-transferases (GSTAs) in plasma combined with their even distribution throughout the liver lobule suggests that they may be useful complements to the more traditionally used liver markers. However, the currently available assays for measuring GSTAs in biological fluids have a poor dynamic range and are cumbersome, requiring multiple steps and prolonged incubation times. METHODS: Hybridomas that secrete monoclonal antibodies to human GSTAs were produced and used to develop a rapid one-step immunometric assay for the determination of GSTA in serum. The assay uses a time-resolved immunofluorometric assay (TR-IFMA) format and requires 35 min of incubation. The reference interval was determined using 208 serum samples from healthy blood donors. We also compared our TR-IFMA with a commercially available enzyme immunoassay (EIA) for GSTAS: RESULTS: The assay had a detection limit of 0.07 microg/L with a measuring range up to 625 microg/L. Within-run imprecision (CV) was 1.8-2.6% over the concentrations of GSTA tested (2.5-311 microg/L), with a between-run CV of <5%. In healthy blood donors, the median values and reference intervals were 2.0 microg/L and 0.6-7.2 microg/L for females and 2.6 microg/L and 0.7-9.8 microg/L for males, respectively. GSTA concentrations determined with the TR-IFMA correlated well with those obtained using a commercially available EIA. CONCLUSIONS: This report describes a new assay for monitoring the concentrations of GSTAs in human serum. The method may be useful in further evaluating the potential of monitoring serum GSTAs in the routine clinical setting.

Animals↗
PubMed2001

Cerebral arteriovenous malformations: comparison of novel magnetic resonance angiographic techniques and conventional catheter angiography.

OBJECTIVE: To investigate the potential of novel magnetic resonance (MR) angiographic techniques for the assessment of cerebral arteriovenous malformations. METHODS: Forty patients who were about to undergo stereotactic radiosurgery were prospectively recruited. Three-dimensional, sliding-slab interleaved ky (SLINKY), time-of-flight acquisition was performed, as was a dynamic MR digital subtraction angiography (DSA) procedure in which single thick slices (6-10 cm) were obtained using a radiofrequency spoiled Fourier-acquired steady-state sequence (1 image/s). Sixty images were acquired, in two or three projections, during passage of a 6- to 10-ml bolus of gadolinium chelate. Subtraction and postprocessing were performed, and images were viewed in an inverted cine mode. SLINKY time-of-flight acquisition was repeated after the administration of gadolinium. Routine stereotactic conventional catheter angiography was performed after MR imaging. All images were assessed (in a blinded randomized manner) for Spetzler-Martin grading and determination of associated vascular pathological features. RESULTS: Forty-one arteriovenous malformations were assessed in 40 patients. Contrast-enhanced (CE) SLINKY MR angiography was the most consistent MR imaging technique, yielding a 95% correlation with the Spetzler-Martin classification defined by conventional catheter angiography; MR DSA exhibited 90% agreement, and SLINKY MR angiography exhibited 81% agreement. CE SLINKY MR angiography provided improved nidus delineation, compared with non-CE SLINKY MR angiography. Dynamic information from MR DSA significantly improved the observation of early-draining veins and associated aneurysms. CONCLUSION: CE SLINKY MR angiographic assessment of cerebral arteriovenous malformations offers significant advantages, compared with the use of non-CE SLINKY MR angiography, including improved nidus demonstration. MR DSA shows promise as a noninvasive method for dynamic angiography but is presently restricted by limitations in both temporal and spatial resolution.

Adult↗
PubMed2000

A comparison of the effects of nine folate analogs on early and late murine hematopoietic progenitor cells in vitro.

PURPOSE: Since the clinical introduction of the antifolates aminopterin (AMT) and methotrexate (MTX) many promising analogs have been developed. A common feature of these compounds is their ability to induce bone marrow suppression. However, few studies have been undertaken on the effect of the folic acid analogs on the cells comprising the hematopoietic system. METHODS: In this paper we describe the effects of the novel thymidylate synthase (TS) inhibitors raltitrexed (Tomudex, ZD1694), AG337 (nolatrexed, Thymitaq), and the two closely related analogs 5,8-dideazaisofolic acid (IAHQ2a) and 2-desamino-2-methyl 5,8-dideazaisofolic acid (IAHQ2c), the glycinamide-ribonucleosyl (GAR) transformylase inhibitor lometrexol (DDATHF), and the dihydrofolate reductase (DHFR) inhibitors MTX, AMT, trimetrexate (TMTX), and edatrexate (EDX) on purified populations of early and late murine hematopoietic progenitor cells. RESULTS/CONCLUSION: All the antifolates inhibited bone marrow proliferation in suspension cultures and all drugs except DDATHF inhibited colony formation by more mature progenitor cells (CFU-C) in clonogenic assays. The lipophilic agents TMTX and AG337 were most toxic, totally abolishing CFU-C colony formation at high concentrations. When IAHQ2c, raltitrexed, DDATHF, and MTX were investigated further for effects on the immature high proliferative potential colony-forming cells (HPP-CFCs) in semisolid and limiting dilution cultures, none of these agents were found to be toxic to the HPP-CFC, but induced a reversible developmental arrest in the progenitor cell population.

Aminopterin↗
PubMed1999

A neural interface for a cortical vision prosthesis.

The development of a cortically based vision prosthesis has been hampered by a lack of basic experiments on phosphene psychophysics. This basic research has been hampered by the lack of a means to safely stimulate large numbers of cortical neurons. Recently, a number of laboratories have developed arrays of silicon microelectrodes that could enable such basic studies on phosphene psychophysics. This paper describes one such array, the Utah electrode array, and summarizes neurosurgical, physiological and histological experiments that suggest that such an array could be implanted safely in visual cortex. We also summarize a series of chronic behavioral experiments that show that modest levels of electrical currents passed into cortex via this array can evoke sensory percepts. Pending the successful outcome of biocompatibility studies using such arrays, high count arrays of penetrating microelectrodes similar to this design could provide a useful tool for studies of the psychophysics of phosphene perception in human volunteers. Such studies could provide a proof-of-concept for cortically based artificial vision.

Animals↗
PubMed1999

Determination of mitotane (o,p-DDD) and its metabolites o,p-DDA and o,p-DDE in plasma by high-performance liquid chromatography.

The adrenolytic agent mitotane (o,p'-DDD or 1,1-(o,p'-dichlorodiphenyl)-2,2-dichoroethane) is believed to be metabolically activated, resulting in the generation of reactive intermediates or the formation of o,p'-DDA. A new high-performance liquid chromatographic (HPLC) method for measurement of mitotane and two of its metabolites, o,p'-DDA (1,1-(o,p'-dichlorodiphenyl) acetic acid) and o,p'-DDE (1,1-(o,p'-dichlorodiphenyl)-2,2 dichloroethene), in plasma has been developed. Sample preparation involves precipitation of plasma proteins with acetone before chromatographic separation under isocratic conditions on a silica-based diphenyl column. Mitotane and metabolites are quantified by ultraviolet detection at 218 nm. Recoveries for the three compounds range between 99% and 110%, with between-day and within-day coefficients of variation <6% within the therapeutic range. Limits of detection are 0.5 microM and the assay is linear up to at least 800 microM for o,p'-DDA and 100 microM for mitotane and o,p'-DDE. The method has been evaluated using samples from three patients on mitotane therapy, revealing o,p'-DDA levels in plasma 3 to 10 times higher than the levels of the parent compound.

Adrenal Cortex Neoplasms↗
PubMed1996

Determination of extracellular methotrexate tissue levels by microdialysis in a rat model.

We used a microdialysis technique to determine tissue methotrexate (MTX) levels during steady state in a rodent model. Two different approaches were employed to measure the actual extracellular MTX concentrations in muscle, liver, and kidney tissues of anesthetized Wistar rats. With the reduced-perfusion-rate technique, the flow in the microdialysis perfusate was gradually decreased toward zero to permit calculation of zero-flow intercepts. Using the net change technique, microdialysis probes were perfused with different MTX concentrations to allow an assessment of equilibrium drug levels. For these two methods to be used, drug concentrations in the matrix to be analyzed must remain unchanged during the experimental procedure. In the animal model, steady state was attained after 1.5 h and maintained throughout the rest of the experiments by the administration of MTX as continuous infusions through a venous catheter. In vitro and in vivo, both the reduced-perfusion-rate and net change techniques gave reproducible data that permitted the estimation of extracellular drug concentrations in the dialyzed tissue compartments.The data suggest that the level of unbound MTX in the circulation is fairly similar to the extracellular concentrations in the muscle and liver. In the kidney, MTX levels were measured to be 3-8 times higher than those of unbound, circulating MTX, and a considerable discrepancy between the two methods used for estimations was apparent. These results demonstrate that both the net change and reduced-flow microdialysis techniques can produce reproducible and precise data. The results may constitute a basis for determining recoveries and, thus, true extracellular drug levels during in vivo microdialysis of MTX. This may be of importance in delineation of the relationship between tissue MTX levels and outcome in a variety of normally inaccessible compartments during cancer pharmacotherapy.

Animals↗
PubMed1996

Differential effects of the antifolates methotrexate, aminopterin and trimetrexate on murine haemopoietic progenitor cells.

We investigated the effects of the antifolates methotrexate (MTX), aminopterin (AMT) and trimetrexate (TMTX) on murine haemopoietic progenitor cells. Colony formation by late progenitors (CFU-C) was inhibited by the antifolates and the addition of leucovorin (LV) to the cultures on day 0 or day 5 wholly or partially reversed the effects of MTX or AMT. The effect of TMTX was only effectively rescued by hypoxanthine plus thymidine (HT). In the high proliferative potential colony forming cell (HPP-CFU-C) assay the antifolates induced formation of smaller colonies, but not a reduction in absolute colony numbers. This effect was reversed by LV and indicated that the antifolates (except high TMTX concentrations) were not toxic to the HPP-CFU-C but reversibly inhibited proliferation of more mature progenitor cells. The direct effects of the drugs on HPP-CFU-C were investigated in limiting dilution assays performed with fractionated bone marrow cells. Untreated cultures contained almost only large colonies, where the addition of antifolates induced a reversible shift towards smaller colonies. The present study indicates that MTX, AMT and low TMTX concentrations are not toxic to HPP-CFU-C but that the drugs induce a developmental arrest in more mature progenitor cell populations.

Aminopterin↗
PubMed1995

Quantitation of 6-thioguanine residues in peripheral blood leukocyte DNA obtained from patients receiving 6-mercaptopurine-based maintenance therapy.

The antimetabolite 6-mercaptopurine is widely utilized in maintenance therapy for childhood acute lymphoblastic leukemia. Following p.o. administration, this prodrug undergoes extensive biotransformation, resulting in the generation of a plethora of metabolites including 2'-deoxy-6-thioguanosine triphosphate. Incorporation of 6-thioguanine (6-TG) bases into DNA is generally considered to be central to thiopurine-mediated cytotoxicity. We have developed a novel precolumn derivatization HPLC technique for quantifying 6-TG base accumulation into leukocyte DNA obtained from acute lymphoblastic leukemia patients receiving 6-mercaptopurine maintenance therapy. The method is based on enzymatic degradation of DNA to 2'-deoxyribonucleosides and the derivatization of released 2'-deoxy-6-thioguanosine with a thiol-reactive reagent containing a 7-amino-4-methylcoumarin-3-acetic acid fluorophore. The 2'-deoxy-6-thioguanosine-7-amino-4-methylcoumarin-3-acetic acid adduct is resolved by reversed-phase HPLC and quantified fluorometrically. Assay response is linear from 15 pmol to 60 fmol 6-TG bases/microgram DNA with a limit of quantitation corresponding to the incorporation of 1 6-TG residue per 50,000 bases. In a small cohort of acute lymphoblastic leukemia patients receiving p.o. 6-mercaptopurine-based maintenance therapy, significant interindividual variation in the accumulation of 6-TG bases into leukocyte DNA was revealed. The determined levels of drug base incorporation ranged from 95 to 710 fmol 6-TG bases/microgram DNA (6-TG base:nucleotide ratio 1:32,000 to 1:4,000). The assay may provide a novel methodology for pharmacological monitoring of thiopurine therapy either in the routine clinical setting or during studies of alternative routes of drug delivery.

Cell Line↗
PubMed1995

Pharmacokinetics of different doses of methotrexate at steady state by in situ microdialysis in a rat model.

We used a microdialysis technique to monitor extracellular methotrexate (MTX) levels during the steady state in a rodent model. Microdialysis probes were implanted in the muscle, liver, and kidney of anesthetized male Wistar rats. MTX (18.75-500 mg/kg) was given as a continuous infusion through a venous catheter, and blood samples were obtained through a second venous catheter. Heparinized plasma, ultrafiltered plasma, microdialysis effluent from tissues, and tissue samples (obtained at the end of experiments) were analyzed for MTX content by high-performance liquid chromatography (HPLC). Steady state was demonstrated in the blood and tissues from 2 h until the end of the experiments (6 h). Extracellular drug levels in muscle and liver displayed a linear correlation with doses, whereas kidney levels reached a plateau at an MTX dose of 150 mg/kg per 6 h. Microdialysis-fluid endpoint levels for muscle, liver, and kidney were positively correlated to the endpoint total tissue levels (r2 = 0.80, 0.85, and 0.68, respectively). In the kidneys, the maximal relative tissue MTX accumulation was measured at a total dose of 75 mg/kg per 6 h. At higher doses, the relative drug sequestration declined to less than half of the values observed at this dose. This study demonstrates that the microdialysis technique can provide reproducible data on MTX tissue exposure in an animal model and that it offers a means of serial and reproducible monitoring of extracellular-tissue MTX levels at steady state and over a wide dose range. Pending additional studies, microdialysis may be a helpful technique for elucidating the kinetics of drug delivery to both targeted and toxicity-prone tissues during chemotherapy.

Animals↗
PubMed1995

Establishment and characterization of a novel hepatoblastoma-derived cell line.

Hepatoblastoma is the most common pediatric liver cancer, and complete resection is required for long-term survival. There are few reported hepatoblastoma cell lines available for study. In order to develop in vitro and animal models, the authors isolated an additional cell line (HB1) from a human hepatoblastoma and here report its characteristics in culture. Cells were analyzed for growth rate, clonigenicity, and tumorigenicity, using electron microscopy. Immunocytochemistry and Northern analysis for the expression of specific surface markers and genes of interest were also performed. HB1 cells required fetal calf serum but grew well in culture (population doubling time of 2 days) and had an undifferentiated appearance under electron microscopy. Epidermal growth factor (EGF) and hydrocortisone stimulated growth with or without serum, but not autocrine growth stimulation via the epidermal growth factor receptor was detected. Proteins produced by HB1 cells under normal culture conditions included alpha-fetoprotein, cytokeratins 8 and 18, and lactate dehydrogenase (with an isozyme subunit composition similar to that of liver). HB1 cells showed chronic, high expression of c-myc and Ha-ras oncogenes but no N-myc and apparently normal RB gene expression. This cell line shows characteristics in culture consistent with malignant, hepatic epithelial cells and is apparently EGF dependent. It may provide a model system for the future development of alternative therapies.

Blotting, Northern↗
PubMed1995

A high-pressure liquid chromatographic method for measuring mitotane [1,1-(o,p'-Dichlorodiphenyl)-2,2-dichloroethane] and its metabolite 1,1-(o,p'-Dichlorodiphenyl)-2,2-dichloroethene in plasma.

The adrenolytic agent mitotane [o,p'-DDD or 1,1-(o,p'-dichlorodiphenyl)-2, 2-dichloroethane] has been employed in the nonsurgical treatment of patients with adrenal carcinoma for several decades. Its use is hampered by serious side effects, which may be limited by analytically guided dose modifications in the individual patient. Mitotane analyses have previously been undertaken by gas chromatography with electron capture detection. A sensitive high-pressure liquid chromatographic method for measuring mitotane in plasma is described. After protein precipitation with 1.5 vol of acetone, mitotane and its metabolite 1,1-(o,p'-dichlorodiphenyl)-2,2-dichloroethene (o,p'-DDE) are resolved by isocratic elution from a C18 reversed-phase support and quantified by ultraviolet detection at 230 nm. Recoveries of mitotane and o,p'-DDE after deproteinization were quantitative. Within-run and between-day coefficients of variation were < 4% over the entire therapeutic range. The limit of detection was 0.25 mumol/L and the standard curve was linear in the 1-100 mumol/L range. The method has been evaluated using samples obtained from an adolescent girl who had metastatic adrenocortical carcinoma. Data from this single patient may suggest that systemic absorption of mitotane is adequate, and toxicity possibly decreased, when mitotane is administered by the rectal route.

Absorption↗
PubMed1995

Effect of methotrexate on murine bone marrow cells in vitro: evidence of a reversible antiproliferative action.

Methotrexate (MTX) acts by inducing cellular depletion of reduced folates, which ultimately leads to an inhibition of DNA synthesis. Like many anticancer drugs, this antimetabolite has little selectivity for tumor cells, and its effectiveness is limited by toxicity to normal tissues, particularly gastrointestinal epithelium and bone marrow. Previous studies have shown that MTX inhibits colony formation of the hematopoietic progenitor cells (CFU-C) in vitro. Whether this effect is due to a cytotoxic or a cytostatic mechanism has not been resolved. The present study was undertaken to eludicate the mechanism by which MTX inhibits CFU-C formation. Bone marrow cells in agarose cultures supplemented with recombinant murine granulocyte-macrophage colony-stimulating factor (rmGM-CSF) were incubated for 7 days in the presence or absence of MTX. Exposure to 33 nM to 1 microM MTX reduced colony formation by more than 80% when compared to control cultures. When bone marrow suspension cultures supplemented with rmGM-CSF were incubated for 5 days in the presence or absence of MTX, exposure to 10 nM to 1 microM MTX resulted in a 60 to 80% reduction in cell numbers when compared to untreated cultures. Residual CFU-C numbers were determined in the same cultures by replating into agarose. Exposure to 10 nM MTX was found to enhance CFU-C recovery three-fold as compared to controls and cultures exposed to higher MTX concentrations. Addition of 10 microM of the reduced folate leucovorin (LV; 5-formyl-tetrahydrofolate) prevented CFU-C accumulation in the presence of 10 nM MTX. The kinetics of LV rescue of CFU-C, pre-exposed to 100 nM MTX, were investigated in clonogenic assays. The addition of 1 microM LV to semisolid bone marrow cultures preincubated with 100 nM MTX for up to 8 days completely abolished the inhibition of colony formation seen with 100 nM MTX alone. When the dose range of MTX was expanded from 33 nM to 3.3 microM, we found that administration of 10 microM LV on day 5 rescued the hematopoietic progenitors from MTX inhibition in all groups. These observations suggest that MTX is not cytotoxic to hematopoietic progenitors over its entire dose range but that it can induce a reversible block in the proliferation and differentiation of cells in the progenitor compartment.

Animals↗
PubMed1994

Quantitation of cell-associated doxorubicin by high-performance liquid chromatography after enzymatic desequestration.

A method for measuring cellular concentrations of the anthracycline doxorubicin was developed. The assay involves cell lysis and protein degradation by detergent and proteinase K treatment followed by DNA hydrolysis using DNase I. Prior to high-performance liquid chromatography, samples are deproteinized by the addition of ZnSO4 and methanol. The assay is linear with respect to both the cellular drug content and the number of cells assayed over the ranges tested, and drug recovery is close to 100%. The method has a limit of detection of 50 fmol injected doxorubicin. Within run and between-day coefficients of variation have consistently been found to be in the 5% and 10% range, respectively, in different cell lines exposed to doxorubicin in vitro. The method has been evaluated in analyses of doxorubicin levels in mononuclear blood cells of patients. The assay offers several advantages over commonly used organic extraction techniques and may improve cellular drug monitoring during anthracycline therapy in patients.

Breast Neoplasms↗
PubMed1994

Evaluation of methotrexate tissue exposure by in situ microdialysis in a rat model.

The feasibility of using a microdialysis technique to obtain pharmacokinetic data on tissue exposure to methotrexate (MTX) was investigated. Microdialysis probes were implanted in the jugular vein, femoral muscle, and liver of anesthetized male Wistar rats. MTX (100 mg/kg) was given as a bolus injection through an indwelling venous catheter, and blood samples were obtained through a second venous access and by microdialysis for a total of 6 h. Heparinized plasma, ultrafiltered plasma, and microdialysis effluent from tissue and venous probes were analyzed by high-performance liquid chromatography. Centrifugal ultrafiltration of rat plasma spiked in vitro with MTX (1-100 microM) revealed a mean binding to plasma proteins of 21%. In vitro microdialysis of this spiked plasma resulted in 23% relative recovery of the unbound fraction. In rats receiving MTX, plasma protein binding was 23% and the relative drug recovery as assessed with venous microdialysis probes was 18%. Plotting of unbound (i.e., ultrafiltrate) MTX concentrations in the blood against venous microdialysis perfusate values in the blood gave a good linear correlation with a coefficient of correlation (r2) of 0.98. There was also a linear correlation between the total MTX concentrations in venous blood and the drug levels in microdialysis samples from muscle and liver (r2 = 0.93 and 0.74, respectively). Area under the curve estimations were consistent with an MTX exposure of 30% and 46% for the muscle and liver as compared with the circulation. The present study demonstrates that the microdialysis technique can provide reproducible data on tissue exposure to MTX in an animal model and indicates that the methodology is adaptable to clinical settings.

Animals↗