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J C Matthews

Publications and source records attributed to J C Matthews.

At least 37 records · Page 2Linked to original sources
PubMed1998

Sources of error in tissue and tumor measurements of 5-[18F]fluorouracil.

UNLABELLED: Central to the assessment of variability of pharmacokinetic parameters is knowledge of bias and variability of the measurement technique, preventing observed differences from being ascribed inappropriate significance. This article presents an evaluation of sources of error in the measurement of normal tissue and tumor pharmacokinetics using 18F-labeled 5-fluorouracil (FU) and PET. METHODS: A standard approach to data acquisition, processing and analysis was developed using a PET scanner, filtered backprojection reconstruction and region of interest analysis. Fourteen tracer 5-[18F]FU patient studies and a phantom study were completed, with 4 of the patient studies repeated 1 wk later. These data allowed evaluation of the overall reproducibility of the technique and the components of measurement variability due to tissue sampling. The effect of reconstruction technique and sampling region size on quantification was assessed using phantom data. RESULTS: All measured radioactivity versus time curves were tissue specific. Week-to-week variability in the area under this curve (representing combined physiological and measurement difference) was -3% to +15% for liver and -9% to -16% for spleen and kidney. Metastasis variability was greatest at -20%. Visual and computer realignment of the second paired study produced similar results. Interobserver effects were small compared to differences between studies. CONCLUSION: These results confirm the feasibility of using PET as a pharmacokinetic tool for 5-[18F]FU studies. Although overall experimental error (i.e., random variation in data acquisition, processing and analysis) was low, constraints in data interpretation emerged.

Adult↗
PubMed1997

An expression system for mammalian amino acid transporters using a stably maintained episomal vector.

Despite its versatility and effectiveness in numerous studies, the vaccinia/HeLa cell expression model may not be optimal for the study of all transport proteins. To evaluate an alternative expression model for amino acid transport Systems ASC and X-AG, the mRNA content and transport activity encoded by human hippocampal ASCT1 cDNA and rat hippocampal EAAC1 cDNA, respectively, were measured in pDR2-cDNA-transfected human embryonic kidney 293 cells made competent by stable transfection with the Epstein-Barr neutral antigen-1 (EBNA-1) cDNA (293c18 cells) to evaluate the EBNA-1/293c18 expression system. The results show that (i) the EBNA-1/293c18 expression system results in a larger increase over background of Systems ASCT1 (6.4x) and EAAC1 (39x) transport activity than does the vaccinia/HeLa expression system (2.6x and 22x, respectively); (ii) transfection and hygromycin B selection for the pDR2 vector do not affect the endogenous transport velocities of Systems ASC, X-AG, or A; and (iii) the endogenous transport velocities of Systems ASC and X-AG in 293c18 cells were not affected by the expression of exogenous EAAC1 or ASCT1. We conclude that the EBNA-1/293c18 cell expression model represents a useful transient expression regimen to characterize mammalian amino acid transport proteins, especially for transporters that may exhibit relatively low activity in transient expression systems lacking a selection mechanism.

Amino Acid Transport System X-AG↗
PubMed1997

Studies on the metabolism of the novel antitumor agent [N-methyl-11C]N-[2-(dimethylamino)ethyl]acridine-4-carboxamide in rats and humans prior to phase I clinical trials.

This study reports on the biodistribution and metabolism of the 11C-labeled novel antitumor agent N-[2-(dimethylamino)ethyl]acridine-4-carboxamide (DACA) (also known as NSC 601316) in rats (plasma and tissues) and humans (plasma). Information on plasma metabolites was uniquely obtained in humans prior to Phase I clinical trial following i.v. injection of [11C]DACA at tracer dose. DACA was labeled in the N-methyl position using no-carrier-added [11C]iodomethane. Rapid high-performance liquid chromatography methods were developed for metabolite analysis of [11C]DACA. The metabolism of [11C]DACA was investigated in patients by plasma sampling. The biodistribution and metabolism of [11C]DACA was investigated in rats by plasma sampling, sacrifice experiments with tissue analyses, and imaging using positron emission tomography scanning. Analysis of human plasma demonstrated rapid and extensive metabolism of [11C]DACA. The levels of [11C]DACA changed from 77 +/- 8% (SD) at 5 min to 25 +/- 5% at 45 min postinjection. Seven radioactive metabolites were observed in human plasma, and one was identified as [11C]DACA-N-oxide. Rapid clearance of 11C radioactivity from rat blood, plasma, and major organs was observed. The half-life of 11C radioactivity clearance in rat blood between 15 and 90 min was calculated to be 3.2 h; the levels of [11C]DACA in rat plasma decreased from 69 +/- 3% (SD) at 2 min to 29 +/- 1.5% at 25 min. The number of radioactive metabolites in rat plasma was the same as in human plasma except that the proportions differed. Again, one metabolite was identified as the [11C]DACA-N-oxide. Analysis of rat tissues showed rapid and extensive metabolism in tissues, particularly liver and kidney; however, [11C]DACA (i.e., the parent compound) was the major radioactive component in the lung, heart, and brain over 40 min. Positron emission tomography scanning using [11C]DACA in the rat showed little retention of 11C radioactivity in major organs with rapid excretion via gut and kidney. The rat data were consistent with animal (mouse and rat) preclinical data obtained with preexisting techniques with longer-lived isotopes. Labeling of potential anticancer drugs with positron-emitting radionuclides and performing in vivo preclinical evaluation at tracer doses in animals and humans prior to Phase I clinical trials provides unique information that could speed up the assessment of the drug and could potentially assist drug development programs. In this example, there was no unexpected interspecies difference in metabolism of DACA that would have alerted us to make a change in the planned Phase I study.

Acridines↗
PubMed1997

Demonstration of system y+L activity on the basal plasma membrane surface of rat placenta and developmentally regulated expression of 4F2HC mRNA.

Na(+)-independent cationic amino acid transport in the rat placenta occurs by leucine-sensitive and leucine-insensitive pathways. The ontogeny of these transport mechanisms within the rat placenta has been described recently. To assign the leucine-inhibitable portion of uptake definitively the uptake of [3H]arginine was studied in the presence of both BCH (to inhibit system Bo,+) and varied concentrations of leucine. Uptake of arginine into basal-enriched membrane vesicles derived from rat placenta was, in the presence of sodium, inhibited by micromolar concentrations of leucine, consistent with assignment of this activity to system y+L. In contrast, the majority of arginine uptake into apical-enriched membrane vesicles was leucine insensitive. Messenger RNA derived from rat placenta at days 14, 16, 18 and 20 of gestation was hybridized with full-length rat cDNA probes against NBAT and 4F2HC (thought to encode proteins associated with system bo,+ and y+L activities, respectively). No NBAT mRNA was detected, whereas 4F2HC mRNA was present at all gestational stages, increasing 12-fold over the last third of gestation. It is concluded that system y+L is present in the basal plasma membrane of the rat placenta syncytium and is subject to developmental regulation by a mechanism that alters the steady content of 4F2HC mRNA.

Amino Acid Transport Systems, Basic↗
PubMed1996

Demonstration and characterization of a transport system capable of lysine and leucine absorption that is encoded for in porcine jejunal epithelium by expression of mRNA in Xenopus laevis oocytes.

Defolliculated Xenopus laevis oocytes were injected with size-fractionated poly(A)+ RNA (RNA) isolated from the jejunal epithelium of growing pigs (average BW 33.8 kg) to identify proteins capable of Na+ -independent amino acid transport. The ability of oocytes to absorb L-lysine (lysine) or L-leucine (leucine) from Na+- free media was quantified in oocytes after injection of RNA fractions or water. Specific RNA fractions were identified that induced saturable uptake of lysine (Kt = 52 microM) and leucine (Kt = 97 microM), whereas endogenous oocyte uptake was not saturable. Induced uptake of .05 mM lysine by oocytes was inhibited (P < .05) 68.1% by 5 mM leucine and 38.9% by .2 mM L-cystine (cystine). Induced uptake of .05 mM leucine was inhibited (P < .05) 83.1% by 5 mM lysine and 23.2% by .2 mM cystine. Although not significant (P > .05), 5 mM L-glutamate (glutamate) quantitatively stimulated the induced uptake of .05 mM lysine by 18.8% and the induced uptake of .05 mM leucine by 60%. To identify mRNA species responsible for this bo,+ transporter-like activity, oocytes were co-injected with the RNA fractions and degenerate DNA oligomers complementary (antisense) to the cloned human kidney bo,+ amino acid transporter, or (as a negative control) with a DNA oligomer complementary to the rabbit intestinal Na+/glucose cotransporter, or with water. Only those oocytes injected with two specific RNA fractions and the antisense DNA oligomer complementary to the bo,+ transporter displayed reduced (P < .05) uptake of lysine (45.7, 55.4%) and leucine (44.1, 65.9%). These results indicate that messenger RNA encoding for a protein capable of stimulating the competitive absorption of lysine and leucine is expressed by the jejunal epithelia of growing pigs.

Animals↗
PubMed1996

Demonstration and characterization of dipeptide transport system activity in sheep omasal epithelium by expression of mRNA in Xenopus laevis oocytes.

Research from this laboratory has recently demonstrated that the omasal epithelium of sheep is capable of absorbing dipeptides. In order to express proteins potentially responsible for the mediated absorption of small peptides, size-fractionated poly(A)+RNA (RNA) isolated from omasal epithelial tissue of sheep (average BW 67.5 kg) were injected into defolliculated Xenopus laevis oocytes. The ability of oocytes injected with RNA or water to absorb [14C]glycyl-L-sarcosine (Gly-Sar) from media (usually pH 5.5) was compared. After 4 d (P < .02) of culture, specific RNA fractions induced an increased (P < .02) rate of Gly-Sar absorption, as compared with water-injected oocytes. The dependency of Gly-Sar uptake on the presence of a pH gradient was evaluated at pH 5.0, 5.5, 6.0, 6.5, and 7.5. Inducible uptake increased (P < .001) in the presence of increasing proton concentrations, whereas endogenous uptake of Gly-Sar decreased (P < .001). At pH 5.5, induced Gly-Sar uptake was saturable (Kt = .4 mM), but endogenous uptake was not. The specificity of Gly-Sar absorption was studied by the co-incubation of .1 mM Gly-Sar with 5 mM levels of competing substrates (pH 5.5). Induced uptake was inhibited (P < .05) 44% by carnosine, 94% by methionylglycine, and 91% by glycylleucine, but not by glycine. Incubation of RNA with DNA oligomers that were complementary to the rabbit intestinal transporter completely inhibited (P < .05) induced Gly-Sar uptake. These results indicate that sheep omasal epithelial cells express messenger RNA that encode for proteins that are capable of H(+)-dependent dipeptide transport activity.

Animals↗
PubMed1995

Comparison of glutamine-enhanced glutamate release from slices and primary cultures of rat brain.

Increased extracellular glutamate has been associated with a wide range of effects including production of neurotoxicity. Glutamine has previously been shown to cause increased release of glutamate from a variety of preparations. Extracellular central nervous system (CNS) glutamine levels are known to increase with neurotoxin exposures, hepatic failure, renal failure, head trauma or stroke. However, the action of glutamine to enhance the release of glutamate under nondepolarizing conditions has not been well studied. Since glutamine-mediated increases in extracellular glutamate are potentially of significance in cellular damage as a result of CNS insult, further examination of this phenomenon is important. Striatal and hippocampal slices or virtually neuron-free primary striatal glial cultures were employed in studies to further elucidate the mechanism(s) of glutamine-enhanced glutamate release. Elevated extracellular glutamine caused increased glutamate release in all three preparations. In hippocampal and striatal slices elevated glutamine caused an enhancement of N-methyl-D-aspartate (NMDA) receptor-mediated [3H]catecholamine release equivalent to that produced by high concentrations (up to 100 microM) of exogenous glutamate. In both striatal slices and primary cultures kynurenate increased glutamate release in the presence of 500 microM glutamine, while kainate either had no effect or decreased glutamate levels in the presence of glutamine. Since several presynaptic modulators of release did not affect the glutamate release produced by glutamine in slices, vesicular release of glutamate from nerve terminals was probably not involved in the effects of the exogenous glutamine. The similarities between striatal slices and primary striatal cultures indicate that enzymatic conversion of glutamine to glutamate within glia may be an important factor in the glutamine-mediated elevation of extracellular glutamate levels.

Analysis of Variance↗
PubMed1995

Resolution of the nirD locus for heme d1 synthesis of cytochrome cd1 (respiratory nitrite reductase) from Pseudomonas stutzeri.

The genetic organization of the nirD locus of Pseudomonas stutzeri ZoBell, necessary for a catalytically active cytochrome cd1 (EC 1.9.3.2), was determined. The locus comprises the unidirectionally transcribed open reading frames nirFDLGH, downstream of nirMC of the nir gene cluster, and immediately upstream of the norCB operon encoding nitric oxide (NO) reductase (EC 1.7.99.7). Notable sequence relatedness was found between NirF and cytochrome cd1 (NirS), within NirDLGH, and between NirM and NirC, suggesting several gene duplication events in this region. The derived NirF protein (391 amino acids, M(r) 43,137) has 23.8% identity (51.1% overall similarity) with NirS, but lacks the N-terminal heme-c-binding domain of NirS. Insertional mutagenesis of the five open reading frames resulted in the loss of respiratory nitrite reductase activity in vivo and in vitro. Mutant strains, when induced with nitrate for denitrification, synthesized a periplasmic cytochrome cd1 lacking heme d1. The defect was caused by the inability of the cell to synthesize heme d1. The nirD locus is proposed to encode a multimeric and multifunctional enzyme complex involved in the synthesis of heme d1. Mutations in nirFDLGH lowered substantially the expression level of norCB. Nir- mutants, unable to generate NO in vivo, provide indirect evidence for an NO sensor and an inducer role of NO for its cognate reductase.

Amino Acid Sequence↗
PubMed1995

Siroamide: a prosthetic group isolated from sulfite reductases in the genus Desulfovibrio.

While isolating siroheme from enzymes or whole cells of Desulfovibrio species, it was discovered that the main product after metal removal and esterification was not the octamethyl ester derivative of sirohydrochlorin, but a monoamide, heptamethyl ester derivative. The structure of this derivative was established by mass spectrometry and NMR. Nuclear Overhauser enhancement measurements in combination with chemical shift analogy arguments indicate that the 2(1)-acetate has been stereospecifically amidated. Other cellular sources of siroheme were investigated, but only the octamethyl ester derivative was found, with no traces of the amide derivative. The results suggest that, in Desulfovibrio, the physiologically active prosthetic group may be an amidated form of siroheme.

Desulfovibrio↗
PubMed1995

Absorption of L-carnosine, L-methionine, and L-methionylglycine by isolated sheep ruminal and omasal epithelial tissue.

The absorption of carnosine, methionine, and methionylglycine (using 35S-methionine and 35S-methionylglycine as representative markers) across ruminal and omasal epithelia collected from four (carnosine) and seven sheep (methionine and methionylglycine) were studied using parabiotic chambers that were repeatedly sampled over a 240-min incubation. The quantity of all substrates transferred was linearly (P < .01) dependent on initial substrate concentration and time. More (P < .01) carnosine, methionine, and methionylglycine was transferred across omasal than across ruminal epithelia. Carnosine was absorbed across both tissues without hydrolysis. Methionylglycine was transferred intact across both tissues. A greater (P < .01) quantity was hydrolyzed by omasal than by ruminal epithelia, after 240 min of incubation. Greater (P < .06) quantities of methionine and methionylglycine accumulated in ruminal tissue after 240 min. Total absorption of methionine and methionylglycine did not differ within tissues, but total absorption of both substrates was greater (P < .01) by omasal tissues. There was little evidence for saturable absorption. These results indicate that omasal epithelial tissue possesses a greater ability to absorb both free and peptide-bound amino acids than does ruminal epithelial tissues.

Animals↗
PubMed1994

Calcium and the effects of ultrasound on frog skin.

Therapeutic ultrasound is used to enhance the repair of soft tissue, muscle, etc., and because many of the cellular reactions involved in these processes are dependent on the intracellular availability of free calcium ions, it becomes important to study the effects of ultrasound in the presence and the absence of calcium ions. Using frog skin as a biological model, the effect of therapeutic ultrasound (300 mW/cm2 1 MHz CW) was investigated. Sonication for two minutes caused a significantly larger increase in total ionic conductance (Gt) in the presence of calcium ions (140% vs. 27%). However, the time constant for Gt to return to steady state was significantly longer in calcium-free solutions (122 vs. 18 min.). This study demonstrates that the biological effects of ultrasound are influenced by calcium ions. Furthermore, the recovery time constants confirm recent findings regarding the function of calcium ions in the formation of tight junctions. The role of free radicals produced by cavitation and calcium potentiated lipid and protein peroxidation is discussed.

Animals↗
PubMed1993

Recent developments in gastrointestinal absorption and tissue utilization of peptides: a review.

Considerable evidence has been accumulated regarding the absorption of dipeptides and tripeptides, yet, even with the growing body of knowledge, the nutritional and metabolic significance of peptide absorption is not fully understood, especially in ruminants. Muscle, mammary gland, liver, kidney, intestinal mucosa, and other tissues either have been shown to have, or are suspected to have, the ability to utilize peptides as a source of AA to meet cellular demands. Investigations suggest that ruminal microbes have the ability to produce substantial amounts of small peptides as a consequence of their hydrolysis of dietary proteins. The extent to which intact peptides may be absorbed into the blood is controversial. Some of the inconsistency in reported observations may be because of limitations of analytical procedures, species differences, or both. Peptide absorption appears to be an important physiological process in ruminants and may constitute the primary source of absorbed AA. The recent observation that the stomach region of the gastrointestinal tract may be an important site of peptide absorption is highly significant. Emerging evidence for the contribution that peptide absorption makes to AA provisioning of ruminants may change some of the currently held views about protein utilization in these unique animals.

Absorption↗
PubMed1992

Peptide absorption: a review of current concepts and future perspectives.

Absorption of di- and tripeptides from the gastrointestinal tract is accepted as being an important biological phenomenon. The extent to which peptides are absorbed and the nutritional and metabolic significance of peptide absorption remain unclear. Evidence is strong for the existence of multiple peptide transport systems, including one type that is electrogenic in nature and that requires a protonmotive force and cotransports two H+ for every peptide transported. The rate of absorption of peptides can be responsive to level of dietary intake and level of dietary protein. Peptide absorption seems to be an important physiological process in ruminants, and this process may account for a large portion of absorbed amino acids. An important new observation is that the nonmesenteric portion of the portal-drained viscera of the ruminant is a major site of peptide absorption. These new observations may result in a reshaping of the currently accepted theory concerning protein utilization by ruminants.

Adaptation, Physiological↗
PubMed1991

Stimulation of 22Na+ efflux from rat forebrain membrane vesicles by L-glutamic acid, L-aspartic acid and kainic acid.

A glass fiber filter assay method is described for measuring 22Na+ efflux stimulated by L-glutamic acid, L-aspartic acid and kainic acid from osmotically sensitive membrane vesicles prepared from rat brain. L-Glutamic acid and L-aspartic acid showed the greatest efficacy for the stimulation of 22Na+ efflux with EC50 values of 3 microM. Kainic acid produced 28% of the maximal efflux seen with L-glutamic acid or L-aspartic acid with an EC50 value of 1.5 microM. Quisqualic acid never showed statistically significant increases in 22Na+ efflux over control experiments. N-Methyl-D-aspartic acid showed no detectable efflux activity in this preparation. DL-2-Amino-4-phosphonobutyric acid (APB) inhibited up to 40% of the 50 microM L-glutamic acid-stimulated or 50 microM L-aspartic acid-stimulated 22Na+ efflux with an IC50 value of 1.5 nM. Calcium was required for the inhibitory action of APB, but not for the stimulatory actions of L-glutamic, L-aspartic, or kainic acids. L-Glutamic, L-aspartic, and kainic acids at concentrations above 100 microM were found to inhibit rather than to stimulate 22Na+ efflux. Veratridine (1 microM) had no influence on the 22Na+ efflux component which was produced by L-glutamic or kainic acids. We are unable to firmly establish the mechanism for the stimulated 22Na+ efflux.

Animals↗
PubMed1991

Nutrition, neurotoxicants and age-related neurodegeneration.

The National Institute on Aging supports a program of investigation of "biomarkers" of aging (biological parameters that change in magnitude with age), some of which may be among the, as yet unknown, causes of Alzheimer's disease. Exposure to neurotoxicants can also produce symptoms similar to Alzheimer's disease and has been proposed as a causative factor. We have examined the role of dietary factors and age on Alzheimer's disease-like neurohistological and behavioral symptoms as well as on the neurochemical effects of treatment with a prototypical neurotoxicant, trimethyltin (TMT). We found that aging greatly increased the susceptibility of hippocampal neurons to TMT-induced neurodegeneration. Limiting the dietary intake of calories, which has been reported to slow the aging process, also reduced the neurotoxic effects of a given dose of TMT. Our current research focuses on the use of neurotoxins to model neurodegenerative conditions of aging in animals. We propose that by identifying an age-amplified biomarker or biomarkers somewhere along the chain from neurotoxic stimulus to neuronal necrosis we may also discover an up- or down-regulated gene, via it's gene product, that contributes to the etiology of human dementias. Our preliminary data suggest that up-regulated synthesis of post-synaptic glutamate receptors of the kainic acid-preferring subtype may be such a biomarker.

Aging↗
PubMed1990

Influence of pupil size on measurements made with the Lens Opacity Meter 701.

The Lens Opacity Meter 701 (Interzeag, Switzerland) is a recently developed instrument for assessing cataract. It measures the degree of scatter of a red light beam by the lens. Fifty patients prior to cataract surgery had measurements made before and after dilatation of the pupil. Inconsistent results were found at pupil diameters of less than 4 mm. It is postulated that this was due to absorption of scattered light by the iris.

Cataract↗
PubMed1990

Effect of milk sample delivery methods and arrival conditions on bacterial contamination rates.

A cross sectional study was performed of factors believed to contribute to the contamination of bovine milk sample cultures submitted to the Ithaca Regional Laboratory of the Quality Milk Promotion Services/New York State Mastitis Control. Of 871 samples entered in the study, 137 (15.7%) were contaminated. There were interactions between the sample source (veterinarian vs dairyman), delivery method, and time between sample collection and arrival at the laboratory. If only those samples collected and hand delivered by the dairyman within 1 day of collection were compared to a like subset of samples collected and hand delivered by veterinarians, no statistically significant differences in milk sample contamination rate (MSCR) were found. Samples were delivered to the laboratory by hand, US Postal Service, United Parcel Service, via the New York State College of Veterinary Medicine Diagnostic Laboratory, or Northeast Dairy Herd Improvement Association Courier. The MSCR was only 7.6% for hand delivered samples, while 26% of Postal Service samples were contaminated. These rates differed significantly from other delivery methods (P less than 0.0001). The USPS samples arrived a longer time after sampling than did samples sent by other routes, and time had a significant effect on MSCR (0 to 1 day, 8.9%; greater than 1 day, 25.9%; P less than 0.01). Samples packaged with ice packs sent by routes other than the Postal Service had a lower MSCR than those not packaged with ice packs, but ice packs did not reduce the MSCR for samples sent by the Postal Service.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗