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Biomedical subjects

T Page

Publications and source records attributed to T Page.

At least 55 records · Page 3Linked to original sources
PubMed1990

The metabolism of ribavirin in erythrocytes and nucleated cells.

1. The metabolism of the broad-spectrum antiviral drug ribavirin was examined in intact human erythrocytes, cultured skin fibroblasts and EBV-transformed lymphoblasts. At an extracellular ribavirin concentration of 35 microM all the cell types produced ribavirin mono-, di- and triphosphate, with the nucleotide concentration reaching half-maximum in 210, 245 and 267 min for fibroblasts, lymphoblasts and erythrocytes, respectively. The ratio of mono-, di- and triphosphates was ca 4:1:40 in fibroblasts, 3:1:8 in lymphoblasts and 1:5:17 in erythrocytes. 2. When ribavirin was removed from the medium, the half-life of ribavirin nucleotides was less than 2 hr in fibroblasts and lymphoblasts, but greater than 24 hr in erythrocytes. 3. In energy-starved erythrocytes, the catabolism of ribavirin nucleotides closely followed the catabolism of adenine nucleotides. 4. None of these cell types excreted appreciable amounts of the ribavirin catabolites triazole carboxamide, triazole carboxylate or triazole carboxylate ribonucleoside. 5. Cells deficient in adenosine kinase produced greater than 4% of the ribavirin nucleotides of normal controls. 6. The nucleated cells quickly hydrolyzed ribavirin 5'monophosphate to ribavirin, whereas this activity was negligible in erythrocytes.

Cell Nucleus↗
PubMed1990

Regional cooperative summer internship program for pharmacy students.

A regional summer internship program for pharmacy students that was coordinated by seven hospitals is described. Recruiting for the Mid-Missouri Summer Intern Program began during the winter of 1987-88. Students were recruited from pharmacy schools throughout the Midwest and were provided with housing and financial compensation while in the program. Each participating hospital agreed to hire at least one intern and appointed a preceptor or coordinating pharmacist, who met with the intern regularly. Students got most of their training and work experience at their home hospital; however, they also rotated to the other participating hospital pharmacy departments. Students had to keep a daily diary of their activities and to complete individual special projects. At the end of the summer, students and preceptors completed a written evaluation of the program. Students indicated that the program provided a valuable and unique educational experience. Preceptors thought that fourth-year and fifth-year students were best suited for the program. The hospital pharmacy directors agreed that the opportunity to evaluate a student's work ethic and professional capabilities before offering a position was a benefit. A regional summer internship program was successful in introducing pharmacy students to institutional pharmacy practice.

Curriculum↗
PubMed1989

Induction of erythroid differentiation in K562 cells by inhibitors of inosine monophosphate dehydrogenase.

The effects of three inhibitors of inosine monophosphate (IMP) dehydrogenase on a human erythroleukemic cell line, K562, were studied. Following incubation with these inhibitors, K562 cells underwent differentiation and accumulated hemoglobins. The induction of hemoglobin accumulation was dose dependent; maximum induction was observed at 100, 25, and 3 microM, respectively, for ribavirin, tiazofurin, and mycophenolic acid. The induction was associated with reduction of intracellular GTP content and was blocked by adding guanosine within 24 h after adding inducer. The effective dose for half-maximum induction by ribavirin was 3 times less than that for 50% inhibition of K562 proliferation; however, for tiazofurin and mycophenolic acid, it closely approximated the concentrations which suppressed cellular proliferation. Ribavirin was sequestered preferentially inside the K562 cells, and the induction by ribavirin had a greater than 30-fold increase in hemoglobin. Studies with isoelectric focusing, globin chain analyses, and immunochemical assays indicated that both A gamma and G gamma were detected and that the hemoglobin produced in the ribavirin-treated cells consisted of approximately 60% fetal hemoglobin and its acetylated equivalents. The adult-type alpha globin was found, while no beta globin chains were demonstrated. Thus, accumulation of fetal hemoglobin and production of alpha globin chain in ribavirin-treated cells are different from the pattern of hemoglobins induced by hemin.

Cell Compartmentation↗
PubMed1989

Evidence for the involvement of a gastrointestinal peptide in the regulation of glucose uptake in the mammary gland of the lactating rat.

1. A method of obtaining serial arterial and mammary-venous blood samples was used to identify possible factors involved in the regulation of glucose uptake in the gland of the lactating rat. 2. Administration of insulin alone increased the arteriovenous glucose difference across the mammary gland of starved rats, but the time course of the recovery could not account for the restoration of arteriovenous glucose difference observed during refeeding [Page & Kuhn (1986). Biochem. J. 239, 269-274]. 3. A crude extract of the gastrointestinal tract (stomach-ileum) from lactating rats enhanced the change in mammary glucose uptake observed with insulin, but only when large amounts (100 munits/rat) of insulin were used. To achieve a similar recovery of arteriovenous glucose difference using near-physiological amounts (5 munits/rat) of insulin it was necessary to sever the mammary nerves. 4. A peptide fraction (of less than 10 kDa) isolated from the gut extract enhanced the effect of insulin in a similar manner to the crude extract. 5. It is suggested that in addition to insulin at least another component, probably a gut peptide, is required for the restoration of mammary glucose uptake during refeeding. An inhibitory component may also contribute to the regulation of mammary glucose extraction in the lactating rat.

Amino Acids↗
PubMed1989

Purine nucleotide production in normal and HPRT- cells.

1. Both normal cells and cells deficient in hypoxanthine-guanine phosphoribosyltransferase (HPRT) are able to produce adenine and guanine nucleotides from aminoimidazole carboxamide (AICA) or its ribonucleoside (AICAR), but not from formaminoimidazole carboxamide ribonucleoside (FAICAR). 2. The level of purine nucleotide production from AICA in HPRT- cells is at least equal to the production of purine nucleotides from hypoxanthine in normal cells. 3. The concentration of AICA or AICAR at which nucleotide production was half-maximal was between 30 and 100 microM in various cell lines. 4. Adenosine kinase is required to convert AICAR to its nucleotide; adenine phosphoribosyltransferase is required to convert AICA to its nucleotide. Cells lacking either of these enzymes are unable to produce purine nucleotides from the respective precursor. 5. Purine production from AICAR in HPRT- cells is not greatly increased by the addition of formate, folate or leucovorin.

Aminoimidazole Carboxamide↗
PubMed1987

Metabolism of leucine in fibroblasts with defects in the leucine catabolic pathway.

1. The activity of the leucine catabolic pathway was measured by quantitation of the radiolabeled glutamic acid produced by intact cultured fibroblasts incubated with radiolabeled leucine. 2. Five normal cell lines produced an average of 179 +/- 47 pmol glutamic acid/mg cell protein/hr. 3. Six cell lines with defects in one of the enzymes of the pathway showed activities of 0-40 pmol glutamic acid/mg cell protein/hr. 4. Each of the cell lines with an enzyme defect produced a characteristic pattern of radiolabeled organic acids. In every case, the amounts of these organic acids produced was less than the amount of glutamic acid produced by normal cells. None of the cell lines accumulated CoA esters.

Amino Acid Metabolism, Inborn Errors↗
PubMed1987

Synergistic activity of purine metabolism inhibitors in cultured human tumor cells.

Cytotoxic effects of 3-deazaguanosine (3-DGUO) result from the inhibition of DNA synthesis and incorporation of the drug into DNA. Synergistic antiproliferative effects of a combination of 3-deazaguanosine and 2-beta-D-ribofuranosylthiazole-4-carboxamide, a potent inhibitor of inosine monophosphate dehydrogenase, was observed in human tumor cells. Inosine reversed the antiproliferative effects of the 3-deazaguanosine but not 2-beta-D-ribofuranosylthiazole-4-carboxamide. 3-Deazaguanosine monophosphate was shown to inhibit the activity of the de novo purine synthesis enzyme, 5'-phosphoribosyl-5-aminoimidazole-4-carboxamide transformylase. The data suggested a cytotoxic effect of 3-DGUO associated with the inhibition of de novo purine synthesis by drug nucleotides, an effect which may account for the synergistic action noted.

3-Deazauridine↗
PubMed1987

Syndrome of mild mental retardation, spastic gait, and skeletal malformations in a family with partial deficiency of hypoxanthine-guanine phosphoribosyltransferase.

A syndrome has been observed in a kindred with deficient activity of hypoxanthine-guanine phosphoribosyltransferase in which affected hemizygotes have had mild mental retardation, a spastic gait, pyramidal tract signs, shortness of stature, proximally placed thumbs and clinodactyly of the fifth fingers. Activity of the enzyme was virtually zero in lysates of erythrocytes or hair roots, but in intact fibroblasts, the level of activity was 7.5% of normal, placing this variant in a group distinct from any previously studied. Kinetic studies revealed a Michaelis constant for hypoxanthine that was also different from other enzymes studied. These observations indicate the presence in this kindred of a distinct variant of hypoxanthine-guanine phosphoribosyltransferase.

Adolescent↗
PubMed1986

Arteriovenous glucose differences across the mammary gland of the fed, starved, and re-fed lactating rat.

Arteriovenous glucose difference across the mammary gland of the lactating rat was used as an 'instantaneous' monitor of mammary glucose uptake. Plasma [glucose] and arteriovenous glucose difference varied according to whether Halothane, diethyl ether or sodium pentobarbitone anaesthesia was used. In pentobarbitone-treated rats a 60% glucose extraction in the fed state decreased to 5% after 18 h starvation, and recovered to 40% and 59% after 15 min and 60 min re-feeding respectively. The increase and decrease in plasma [fatty acids] and the depletion and restoration of hepatic glycogen mostly followed similar time courses. Re-feeding was accompanied by a brief surge of plasma [insulin]. Starved lactating rats showed a markedly greater capacity than age-matched virgin rats in the oral and intraperitoneal glucose tolerance tests. Mammary glucose uptake in the starved rat was significantly restored by oral or intraperitoneal glucose or by insulin, but not by acetoacetate or by heparin-induced elevation of plasma [fatty acids]. The role of insulin and of possible changes in mammary sensitivity to insulin in the return of mammary glucose uptake on re-feeding is discussed.

Anesthetics↗
PubMed1985

Studies on the mechanism of cytotoxicity of 3-deazaguanosine in human cancer cells.

The mechanism of toxicity of 3-deazaguanosine was studied in a number of human tumor cell lines by determination of the effects of various purine compounds on the growth of the cells in the presence of the drug and by studies of the effects of 3-deazaguanosine on the metabolism of radiolabeled precursors in these cells. The drug was found to be toxic to all of the cell lines tested. The toxicity was reversible with removal of the drug. None of the purine bases tested could restore normal growth after 48 h exposure to 3-deazaguanosine; the bases were more effective in preventing cytotoxicity when added simultaneously with the drug. Metabolic studies indicated decreased synthesis of DNA, variable inhibition of de novo purine synthesis, and complete inhibition of the enzyme guanosine monophosphate reductase by 3-deazaguanosine.

Adenine↗
PubMed1985

Separation of the intermediates of leucine catabolism by high-performance liquid chromatography.

A method has been developed for the separation of leucine, 2-ketoisocaproic acid, isovaleryl CoA, 3-methylcrotonyl CoA, 3-hydroxy-3-methylglutaryl CoA, 3-methylglutaconyl CoA, acetyl CoA, and acetoacetic acid by ion-exchange high-performance liquid chromatography. The analysis requires 180 min. Use of this method to assess the catabolism of radiolabeled leucine in normal cultured human skin fibroblasts shows that these cells do not accumulate CoA esters, but convert leucine mainly to 2-ketoisocaproic acid, glutamate, and hydroxyisovalerate. In the fibroblasts of a patient with maple syrup urine disease, only 2-ketoiscaproic acid is produced from leucine.

Biotransformation↗