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Biomedical subjects

B S Mitchell

Publications and source records attributed to B S Mitchell.

At least 127 records · Page 7Linked to original sources
PubMed1983

Alterations in erythrocyte adenine nucleotide pools resulting from 2'-deoxycoformycin therapy.

2'-Deoxycoformycin, a tight-binding adenosine deaminase inhibitor, was administered to 11 adult patients with refractory lymphoproliferative diseases. Total doses ranged from 1.0 to 13.5 mg/kg. Inhibition of lymphoblast adenosine deaminase was obtained in all cases and tumor cytoreduction was noted in eight of ten cases, but no clinically meaningful remissions were obtained. Major toxicities occurred in five patients and included pulmonary edema, renal failure, central nervous system toxicity, hypotension, and death. Toxicity prevented retreatment in several cases in which marked cytoreduction occurred. Deoxyadenosine triphosphate accumulated to a variable extent in the red blood cells of all patients, and a reciprocal decrease in erythrocyte adenosine triphosphate was noted in all cases but one. All patients who suffered major organ toxicity had red blood cell deoxyadenosine triphosphate/adenosine triphosphate ratios greater than 1.3. These data suggest that the degree of replacement of adenosine triphosphate by deoxyadenosine triphosphate in erythrocytes reflects the biochemical milieu which may result in systemic toxicity following treatment with 2'-deoxycoformycin.

Adenine Nucleotides↗
PubMed1983

S-adenosylhomocysteine catabolism and basis for acquired resistance during treatment of T-cell acute lymphoblastic leukemia with 2'-deoxycoformycin alone and in combination with 9-beta-D-arabinofuranosyladenine.

A patient with refractory T-cell acute lymphoblastic leukemia was treated with eight courses of the adenosine deaminase inhibitor, 2'-deoxycoformycin (dCF), over a 5-month period. After developing resistance to dCF, he responded to treatment with the combination of dCF and 9-beta-D-arabinofuranosyladenine (ara-A). We monitored the levels in plasma and urine of adenosine, 2'-deoxyadenosine, and ara-A as well as the accumulation of their nucleotide derivatives in erythrocytes and circulating lymphoblasts. We also monitored the activities of adenosine deaminase and S-adenosylhomocysteine (AdoHcy) hydrolase and the concentrations of AdoHcy and S-adenosylmethionine in lymphoblasts. Production of 2'-deoxyadenosine was related to both the duration of dCF infusion and the magnitude of cytolysis that occurred during treatment: much more 2'-deoxyadenosine was produced by dCF infusion when disease was active than by the same infusion given during remission. Resistance to dCF was associated with a decrease of greater than 90% in the amount of deoxyadenosine 5'-triphosphate accumulated by circulating lymphoblasts. Infusion of dCF resulted in increases of up to 20-fold in the concentration of AdoHcy in circulating lymphoblasts, causing a decrease in the S-adenosylmethionine:AdoHcy ratio (the "methylation index") from a pretreatment value of greater than 40:1 to less than 4:1. This ratio decreased to 2.5:1 during combined treatment with dCF and ara-A, which caused nearly complete inactivation of lymphoblast AdoHcy hydrolase. Decline in the methylation index was accompanied by inhibition of the methylation of newly synthesized lymphoblast RNA. Impaired ability to catabolize AdoHcy may have contributed to the cytolytic responses to dCF and ara-A, as well as to hepatic and central nervous system toxicity associated with their combined use.

Acute Disease↗
PubMed1983

Deoxyribonucleoside triphosphate accumulation by leukemic cells.

The toxicity of the deoxyribonucleosides, 2'-deoxyadenosine, 2'-deoxyguanosine, and thymidine, for human T lymphoblasts is mediated by the accumulation of the corresponding deoxyribonucleoside triphosphate (dATP, dGTP, or dTTP, respectively). We have examined whether leukemic cells of non-T-cell origin are capable of accumulating deoxyribonucleotides in culture and whether this capability correlates with the activities of purine metabolizing enzymes in these cells. We have found that non-T, non-B acute lymphoblastic leukemia cells with low ecto-5'-nucleotidase and high adenosine deaminase activities increase their dATP pools by greater than tenfold when exposed to deoxyadenosine and an inhibitor of adenosine deaminase in culture. Cells from 2 of 9 patients with chronic lymphocytic leukemia and 4 of 11 patients with acute nonlymphoblastic leukemia achieved similar elevations in dATP, but there was no relationship between dATP accumulation and adenosine deaminase, purine nucleoside phosphorylase, or ecto-5'-nucleotidase activities. Treatment of four individuals with acute lymphoblastic leukemia with the adenosine deaminase inhibitor, 2'-deoxycoformycin, resulted in elevations in plasma deoxyadenosine concentrations and in increments in lymphoblast dATP levels that were similar to those measured in lymphoblasts cultured with deoxyadenosine and deoxycoformycin prior to treatment. In vitro incubations of leukemic cells with deoxyribonucleosides may provide a rational basis for the use of these compounds as chemotherapeutic agents.

Adenosine Deaminase↗
PubMed1981

Inhibition of purine nucleoside phosphorylase by 8-aminoguanosine: selective toxicity for T lymphoblasts.

The guanosine analog 8-aminoguanosine is an effective inhibitor of the purine degradative enzyme purine nucleoside phosphorylase, both in vitro and in intact lymphoid cells. In a human lymphoblast tissue culture system, 8-aminoguanosine, in combination with low concentrations of 2'-deoxyguanosine, causes toxicity toward T cells but not B cells. The selective T cell toxicity correlates with increased accumulation of deoxyguanosine triphosphate in the treated T lymphoblasts.

B-Lymphocytes↗
PubMed1981

Localisation of immunoglobulin (IgG) in granulated metrial gland cells of deciduomata of the pseudopregnant rat.

Using an immunoperoxidase technique, after fixation in saturated alcoholic mercuric chloride, it was possible to detect cytoplasmic immunoglobulin (IgG) in granulated metrial gland cells from deciduomata of pseudopregnancy in the rat. The extent of the reaction for IgG was variable but did not appear to be related to the day of pseudopregnancy or to the extent of the decidual reaction. Examination of single cell suspension enabled quantification of IgG-containing cells, but no significant differences were detected in the numbers of positive cells at the days of pseudopregnancy which were examined. Surface IgG was detected on a small proportion of the cells, and they were distinguished from the Fcgamma receptor-bearing cells in the metrial gland of deciduomata of pseudopregnancy.

Animals↗
PubMed1980

Localisation of immunoglobulin (IgG) within the rat metrial gland.

An immunohistological method was used to assess the IgG content of the rat metrial gland at different stages of pregnancy. The result apparently varied according to the type of fixative used. Saturated alcoholic mercuric chloride was found to produce the most consistent demonstration, with the IgG located in cells which also contained diastase-fast, PAS-positive granules. Using single cell suspensions prepared from metrial glands, significantly more cells were shown to contain cytoplasmic IgG at day 13, compared to day 14 of pregnancy. However, there were no other significant differences at other stages of pregnancy examined. Surface IgG was detected on a small proportion of the cells and the findings are discussed in relation to the hypothesis of a lymphocytic origin for the granulated metrial gland cells.

Animals↗
PubMed1980

Multiple myeloma: current concepts in diagnosis and management.

The basic pathologic process in multiple myeloma is the neoplastic proliferation of a single clone of plasma cells. Although the events which trigger autonomous cell growth are not well understood, the secretion of an M component, a serum or urinary immunoglobulin molecule or a light chain fragment by the vast majority of myeloma cells has provided a biologic marker which has greatly facilitated the study of this disease Some of the more recent clinical concepts which have evolved from studies on the plasma cell and the immunoglobulin molecule are discussed.

Alkylating Agents↗
PubMed1980

ATP depletion as a consequence of adenosine deaminase inhibition in man.

Hereditary deficiency of the enzyme adenosie deaminase (adenosine aminohydrolase, EC 3.5.4.4) results in an immunodeficiency syndrome characterized by a marked reduction in circulating lymphocytes. We have administered 2'-deoxycoformycin, a potent inhibitor of adenosine deaminase, to a patient with a lymphoproliferative malignancy. The clinical consequences of pharmacologic inhibition of adenosine deaminase activity included an abrupt decrease in the lymphocyte count, abnormalities of renal and hepatic function, and hemolytic anemia. The plasma concentrations of adenosine and deoxyadenosine rose to peak values of 13 microM and 5 microM, respectively, and erythrocyte dATP levels increased to 110 pmol/10(6) cells over 9 days. There was a corresponding decrease in erythrocyte ATP levels from 128 to < 6 pmol/10(6) cells. A similar profound reductin in ATP occurred in the erythrocytes of a second patient. The rapid and unexpected depletion of ATP associated with dATP accumulation may account, at least in part, for the toxicity associated with 2'-deoxycoformycin administration. The inverse relationship of ATP and dATP raises major questions about the control of energy metabolism in erythrocytes.

Adenosine↗
PubMed1980

Purinogenic immunodeficiency diseases: clinical features and molecular mechanisms.

Deficiencies of two enzymes that catalyze sequential reactions in the purine catabolic pathway have been causally associated with immunodeficiency states. Adenosine deaminase (ADA) deficiency results in severe combined immunodeficiency disease, while purine nucleoside phosphorylase (PNP) deficiency results in an isolated T-cell defect. Recent work in this area has provided major new insights into the molecular pathology of these syndromes. Deoxyadenosine and deoxyguanosine, substrates that accumulate in ADA and deoxyguanosine, substrates that accumulate in ADA and PNP deficiency, respectively, appear to be selectively phosphorylated by lymphoid cells to the corresponding deoxynucleoside triphosphate, resulting in inhibition of DNA synthesis in these cells. Both deoxynucleosides are far more toxic to cultured T lymphoblasts than to B lymphoblasts. Adenosine and deoxyadenosine may have additional lymphotoxic effects mediated by inhibition of essential methylation reactions. These observations help to explain the immunologic manifestations of ADA and PNP deficiency. Perhaps more important, they lay the foundation for the use of deoxynucleosides or enzyme inhibitors, or both, as selective immunosuppressive and chemotherapeutic agents.

5'-Nucleotidase↗
PubMed1980

Inhibition of adenosine deaminase activity results in cytotoxicity to T lymphoblasts in vivo.

We have treated a patient with refractory T-cell acute lymphoblastic leukemia with 2'-deoxycoformycin, a potent inhibitor of the enzyme adenosine deaminase. Inhibition of adenosine deaminase activity resulted in (1) an abrupt rise in plasma deoxyadenosine, but not adenosine, concentrations; (2) accumulation of deoxyadenosine triphosphate by lymphoblasts; (3) inhibition of the enzyme S-adenoylhomocysteine hydrolase; and (4) rapid lysis of the leukemic cells. The patient died suddenly 3 days after therapy was discontinued, and postmortem examination revealed a complete absence of leukemic cells in all organs. Pharmacologic inhibition of adenosine deaminase activity can result in the lysis of T lymphoblasts in vivo, and this effect appears to be mediated by deoxyadenosine.

Adenosine↗
PubMed1979

The use of proteolytic enzymes to improve immunoglobulin staining by the PAP technique.

Proteolytic enzymes, protease and trypsin have recently been introduced to reduce the inconsistency hitherto encountered in the unlabelled antibody--enzyme method using PAP. This study investigated factors determining the optimum conditions for use of such enzymes in order to establish which one is most suitable. Trypsin was the most effective enzyme; however, its activity decreased over 3 h, a feature paralleled immunocytochemically. Method and duration of fixation appears to influence the required time of exposure to trypsin in order that consistent immunostaining may be produced. Treatment of sections with trypsin prior to the use of the unlabelled antibody--enzyme method using PAP renders the technique reliable, provided the enzyme is used in a carefully controlled manner.

Humans↗
PubMed1979

Biochemical basis for differential deoxyadenosine toxicity to T and B lymphoblasts: role for 5'-nucleotidase.

Deoxyadenosine metabolism was investigated in cultured human cells to elucidate the biochemical basis for the sensitivity of T lymphoblasts and the resistance of B lymphoblasts to deoxyadenosine toxicity. T lymphoblasts have a 20-to 45-fold greater capacity to synthesize deoxyadenosine nucleotides than B lymphoblasts at deoxyadenosine concentrations of 50--300 micron. During the synthesis of dATP, T lymphoblasts accumulate large quantities of dADP, whereas B lymphoblasts do not accumulate dADP. Enzymes affecting deoxyadenosine nucleotide synthesis were assayed in these cells. No substantial differences were evident in activities of deoxyadenosine kinase (ATP: deoxyadenosine 5'-phosphotransferase, EC 2.7.1.76) or deoxyadenylate kinase [ATP:(d)AMP phosphotransferase, EC 2.7.4.11]. The activity of 5'-nucleotidase (5'-ribonucleotide phosphohydrolase, EC 3.1.3.5) was increased 44-fold for AMP and 7-fold for dAMP in B lymphoblasts. A model for the regulation of deoxyadenosine nucleotide synthesis by 5'-nucleotidase activity is proposed on the basis of the observations.

Adenosine Deaminase↗
PubMed1979

Purinogenic immunodeficiency diseases. Differential effects of deoxyadenosine and deoxyguanosine on DNA synthesis in human T lymphoblasts.

Deoxyadenosine and deoxyguanosine are toxic to human lymphoid cells in culture and have been implicated in the pathogenesis of the immunodeficiency states associated with adenosine deaminase and purine nucleoside phosphorylase deficiency, respectively. We have studied the relative incorporation of several labeled nucleosides into DNA and into nucleotide pools to further elucidate the mechanism of deoxyribonucleoside toxicity. In the presence of an inhibitor of adenosine deaminase [erythro-9-(2-hydroxy-3-nonyl)adenine [EHNA], 5 muM], deoxyadenosine (1-50 muM) progressively decreased the incorporation of thymidine, uridine, and deoxyuridine into DNA, but did not affect uridine incorporation into RNA. This decrease in DNA synthesis was associated with increasing dATP and decreasing dCTP pools. Likewise, incubation of cells with deoxyguanosine caused an elevation of dGTP, depletion of dCTP, and inhibition of DNA synthesis. To test the hypothesis that dATP and dGTP accumulation inhibit DNA synthesis by inhibiting the enzyme ribonucleotide reductase, simultaneous rates of incorporation of [(3)H]uridine and [(14)C]thymidine into DNA were measured in the presence of deoxyadenosine plus EHNA or deoxyguanosine, and in the presence of hydroxyurea, a known inhibitor of ribonucleotide reductase. Hydroxyurea (100 muM) and deoxyguanosine (10 muM) decreased the incorporation of [(3)H]uridine but not of [(14)C]thymidine into DNA; both compounds also substantially increased [(3)H]cytidine incorporation into the ribonucleotide pool while reducing incorporation into the deoxyribonucleotide pool. In contrast, deoxyadenosine plus EHNA did not show this differential inhibition of [(3)H]uridine incorporation into DNA, and the alteration in [(3)H]cytidine incorporation into nucleotide pools was less impressive. These data show an association between accumulation of dATP or dGTP and a primary inhibition of DNA synthesis, and they provide support for ribonucleotide reductase inhibition as the mechanism responsible for deoxyguanosine toxicity. Deoxyadenosine toxicity, however, appears to result from another, or perhaps a combination of, molecular event(s).

Adenine↗
PubMed1978

Purinogenic immunodeficiency diseases: selective toxicity of deoxyribonucleosides for T cells.

Deoxyadenosine at low concentrations and in the presence of an inhibitor of adenosine deaminase (adenosine aminohydrolase, EC 3.5.4.4) is markedly toxic to lymphoblast cell lines of T cell origin but does not impair growth of B cell lines. Deoxyguanosine is also more toxic for T lymphoblasts. In the presence of deoxyadenosine or deoxyguanosine, elevation of the corresponding deoxyribonucleoside triphosphate (dATP or dGTP) occurs in T cell, but not in B cell, lines. The addition of deoxycytidine or dipyridamole results in lower dATP and dGTP levels and prevents deoxyribonucleoside toxicity. These findings provide a molecular basis for the immunodeficiency observed in individuals with several inborn errors of purine metabolism.

B-Lymphocytes↗