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F P Chow

Publications and source records attributed to F P Chow.

16 recordsLinked to original sources
PubMed1993

Phosphorylation of recombinant tau by cAMP-dependent protein kinase. Identification of phosphorylation sites and effect on microtubule assembly.

Tau protein is an integral component of paired helical filaments, a pathological feature of Alzheimer's disease. tau extracted from these filaments displays decreased electrophoretic mobility due to aberrant phosphorylation. Here we show that recombinant human tau can be phosphorylated by cAMP-dependent protein kinase resulting in decreased electrophoretic mobility. Phosphorylation of tau by cAMP-dependent protein kinase caused a 92% decrease in the maximum rate of tau-induced microtubule assembly. The sites of phosphorylation were identified by digesting phosphorylated tau with proteases, separating the peptides by reversed-phase HPLC, and analyzing the isolated peptides by liquid-secondary ion mass spectrometry and solid-phase N-terminal sequencing. Five phosphorylation sites were identified, two of which were located within microtubule binding domains. One site was previously shown to be the sole phosphorylation site for CaM kinase II; phosphorylation at this site by CaM kinase II was sufficient to cause decreased electrophoretic mobility (Steiner, B., Mandelkow, E. M., Biernat, J., Gustke, N., Meyer, H. E., Schmidt, B., Mieskes, G., Soling, H. D., Drechsel, D., Kirschner, M. W., Goedert, M., and Mandelkow, E. (1990) EMBO J. 9, 3539-3544). Thus two different second messenger-dependent protein kinases can phosphorylate tau at the same site and induce a shift in tau mobility like that seen in Alzheimer's disease.

Adenosine Triphosphate↗
PubMed1993

Regulation of megakaryocyte colony forming cell numbers and ploidy by dideoxynucleosides in immunodeficient mice.

We have recently demonstrated that azidothymidine (AZT) elevates the levels of circulating platelets in mice made immune deficient by infection with LP-BM5 murine leukemia virus (MAIDS mice). In an attempt to elucidate the mechanisms of the AZT platelet elevating effect, we examined the number of splenic and bone marrow megakaryocyte colony-forming cells (CFU-mk) and the ploidy of megakaryocytes derived from CFU-mk using fluorescence cytophotometric methods. Two other dideoxynucleosides (ddN) 2'3'-dideoxyinosine (ddl) and 2'3'-dideoxycytidine (ddC) were assessed to determine the specificity of the effect of AZT. MAIDS mice were given ddN in drinking water for 15 days. AZT was the only ddN that significantly increased circulating platelet levels in MAIDS mice. AZT significantly increased splenic CFU-mk in MAIDS mice, but bone marrow CFU-mk were not affected. ddl and ddC failed to change either platelet levels or the numbers of splenic or bone marrow CFU-mk. The ploidy of megakaryocytes derived from splenic and bone marrow CFU-mk were examined by first identifying CFU-mk by staining for acetylcholinesterase, followed by nuclear staining with propidium iodide. The fluorescence of individual cells was then measured using a Perceptics image analysis system. Modal ploidy of CFU-mk megakaryocytes derived from spleen cells of AZT-treated immunodeficient mice was shifted upwards from 16N to 32N. Similarly, AZT treatment changed the modal ploidy number of colony megakaryocytes derived from bone marrows of immunodeficient mice from 16N to 32N. The ploidy distribution was also significantly shifted. ddl and ddC failed to significantly alter either modal ploidy number or distribution of megakaryocytes derived from splenic or bone marrow CFU-mk. These findings suggest that AZT may affect physiological processes that lead to platelet formation.

Animals↗
PubMed1993

Failure of stem cell factor to ameliorate AZT-induced anemia in immunodeficient mice.

Recent attempts to reduce 3' azido-3' deoxythymidine (AZT)-induced anemia in AIDS patients have focused both on AZT dose reduction and on the use of recombinant cytokines. The newly cloned cytokine stem cell factor (SCF) is a potent regulator of hematopoietic progenitor cell proliferation. Therefore, we attempted to ameliorate AZT-induced anemia using stem cell factor (SCF) in the LP-BM5 murine leukemia virus-induced model of AIDS (MAIDS). SCF was administered with oral AZT for up to 1 month, and effects on erythropoiesis examined. SCF alone increased both splenic BFU-E and CFU-E. AZT alone also increased the number of splenic BFU-E and CFU-E. SCF, administered to AZT-treated MAIDS mice, did not further enhance these increases. SCF increased bone marrow cellularity in AZT-treated MAIDS mice. However, the total number of bone marrow BFU-E was unaffected. In contrast, AZT, SCF, and the combination significantly decreased bone marrow CFU-E. SCF alone increased the absolute numbers of peripheral blood reticulocytes in MAIDS mice, but did not increase reticulocyte numbers in AZT-treated mice. SCF did not significantly increase hematocrits in either control or AZT-treated mice. Further studies are needed to maximize the differentiating capacity of the enlarged erythroid progenitor cell pool induced by SCF.

Anemia↗
PubMed1993

Effects of in vivo administration of stem cell factor on thrombopoiesis in normal and immunodeficient mice.

Thrombocytopenia is an important clinical problem for many acquired immunodeficiency syndrome (AIDS) patients. Recently, the utility of recombinant cytokines in alleviating the hematopoietic complications of AIDS and AIDS therapy has been evaluated. The newly cloned cytokine stem cell factor (SCF) has been demonstrated to be a potent regulator of hematopoietic progenitor cell proliferation. Therefore, we evaluated the ability of SCF to alleviate thrombocytopenia caused by infection with LP-BM5 murine leukemia virus (mLV) in a murine model of AIDS (MAIDS). In addition, we evaluated the effects of SCF on previously demonstrated azidothymidine (AZT)-induced elevations of platelet counts. SCF was administered to normal or LP-BMS-infected C57BL/6 mice in combination with oral AZT for up to 1 month and effects on platelet, megakaryocyte (MK), and megakaryocyte colony-forming cell (CFU-MK) numbers were evaluated. SCF alone significantly increased the number of circulating platelets in thrombocytopenic MAIDS mice by 53%. SCF also significantly elevated platelet levels by 29% in normal mice. AZT elevated platelet counts 100% in normal and 50% in MAIDS mice. AZT and SCF increased platelet counts in an additive manner. SCF alone was a potent inducer of splenic CFU-MK in both MAIDS and normal mice, increasing splenic CFU-MK 13- to 15-fold at day 15 as compared with untreated controls. By day 30, however, the numbers of splenic CFU-MK had returned to control levels. In infected mice, AZT alone increased the number of splenic CFU-MK. SCF administered to AZT-treated MAIDS mice did not further enhance these increases. In contrast, in normal mice, AZT decreased splenic CFU-MK numbers. In AZT-treated mice, SCF enhanced the numbers of splenic CFU-MK 90-fold at day 8. In MAIDS mice, the number of bone marrow CFU-MK was significantly increased by SCF treatment at all time points. SCF significantly affected the total number of femoral CFU-MK in AZT-treated mice only at day 15. In normal mice, SCF or SCF and AZT in combination increased the total number of bone marrow CFU-MK five-fold at day 8, but failed to induce changes in the total number of femoral CFU-MK after that. These results indicate that SCF elevates platelet levels in both thrombocytopenic MAIDS and normal mice and profoundly affects CFU-MK proliferation. Combinations of SCF and AZT may be further explored to enhance the therapeutic effectiveness of these two drugs in alleviating thrombocytopenia.

Animals↗
PubMed1993

Sustained elevation of platelet counts by long-term azidothymidine treatment of immunosuppressed mice.

Azidothymidine (AZT) has been demonstrated to increase platelet counts in patients suffering from acquired immunodeficiency syndrome (AIDS). However, the ability of long-term AZT treatment to sustain increases in platelet counts is controversial. We have recently demonstrated that AZT elevates the levels of circulating platelets in both normal C57BL/6 mice and mice made immunodeficient by infection with LP-BM5 murine leukemia virus (MAIDS mice). We therefore studied the effect of long-term AZT administration on platelet formation in both normal and MAIDS mice. Peripheral blood indices, levels of femoral and splenic megakaryocyte colony forming units (CFU-MK), and plasma levels of cytokines important in platelet formation-interleukin-6 (IL-6) and granulocyte-macrophage colony-stimulating factor (GM-CSF)--were examined. Platelet counts remained elevated throughout a 120-day AZT treatment period. Splenic CFU-MK were not significantly changed in MAIDS mice, except at day 15 when they were elevated. Splenic CFU-MK were significantly decreased in normal mice at days 8 and 120, and increased at day 30. Bone marrow CFU-MK were increased by AZT treatment at all time points tested in both normal and MAIDS mice. Plasma levels of GM-CSF were unchanged by AZT treatment in both normal and MAIDS mice. Plasma levels of IL-6 were unchanged in AZT-treated normal mice but decreased in AZT-treated MAIDS mice. These results indicate that long-term AZT treatment maintains elevated levels of platelets in both normal and MAIDS mice and affects CFU-MK colony formation. Our studies add to a growing body of work suggesting that AZT can ameliorate thrombocytopenia associated with HIV disease.

Animals↗
PubMed1992

Time-dependent changes induced by azidothymidine in erythroid progenitor colonies in immunodeficient mice.

The effect of azidothymidine (AZT) on erythropoiesis in C57BL/6 mice made immunodeficient by infection with LP-BM5 murine leukemia virus (MuLV) was examined. Earlier work from our laboratory indicated that long-term treatment of LP-BM5 MuLV-infected mice with AZT induced peripheral anemia but increased the number of splenic and bone marrow erythroid burst-forming units (BFUe). In contrast, other workers have demonstrated that short-term intensive AZT treatment decreases bone marrow BFUe of normal mice. The purpose of the present study was to determine the effects of short-term oral AZT treatment in immune deficient animals. LP-BM5 MuLV-infected and normal mice were given 0, 1, and 2.5 mg/ml of AZT in their drinking water. Mice were killed after 2, 4, 8, 15, and 30 days of AZT treatment. The hematocrits of all AZT-treated mice decreased in a dose- and time-dependent fashion. AZT treatment decreased the absolute numbers of circulating reticulocytes in both normal and infected mice after 4 days of treatment. In contrast, the percentage of bone marrow early erythroblasts was increased in both normal and infected animals after 4 days of treatment. AZT at both doses decreased the number of BFUe per femur in both infected and normal mice after 2, 4, and 8 days. However, after 15 days the number of bone marrow BFUe increased. In spleen, the numbers of BFUe were increased only with high-dose AZT in both normal and infected mice at all time points, although the increases were more dramatic in infected mice. Our results indicate that the effect of AZT on bone marrow BFUe is time dependent, with inhibition being observed only at early time points. These results further demonstrate the complex effects of AZT on erythropoiesis in vivo.

Administration, Oral↗
PubMed1991

Sensitivity of erythroid progenitor colonies to erythropoietin in azidothymidine treated immunodeficient mice.

The anaemia induced by 3'-azido-3'dideoxythymidine (AZT) is poorly understood. We have used a murine model of AIDS, infection of female C57BL/6 mice with LP-BM5 murine leukaemia (MuLV) virus, to determine if AZT-induced anaemia is due, in part, to decreased responsiveness of erythropoietic precursors (BFU-e) to erythropoietin (EPO). Mice in the early stage of LP-BM5 MuLV disease were given AZT in their drinking water at 1.0 and 2.5 mg/ml. AZT produced anaemia in both groups, in a dose-dependent fashion. Despite the anaemia, the number of splenic and bone marrow BFU-e in AZT treated mice increased up to five-fold over levels observed in infected untreated animals after 15 d of treatment. Colony formation by splenic and bone marrow BFUe was stimulated at lower concentrations of EPO in mice receiving AZT for 15 d than for infected, untreated mice. By day 30, sensitivity of both splenic and bone marrow BFU-e of treated animals returned to that observed from cells of infected untreated animals. The mean plasma levels of EPO observed in AZT treated mice were appropriate for the degree of anaemia observed when compared with phenylhydrazine (PHZ) treated mice. The numbers of BFU-e and the percentage of bone marrow erythroblasts observed were comparable in AZT and PHZ treated mice with similar degrees of anaemia. However, reticulocytosis was inappropriate for the degree of anaemia observed in AZT treated infected mice. AZT-induced peripheral anaemia in the face of increased numbers of BFU-e and increased levels of plasma EPO suggest a lesion in terminal differentiation.

Anemia↗
PubMed1991

In vivo evaluation of the anemia induced by azidothymidine (AZT) in a murine model of AIDS.

Azidothymidine (AZT) induces severe anemia in patients with acquired immune deficiency syndrome (AIDS). To evaluate the mechanism of anemia in immune-suppressed animals, a murine model of AIDS (MAIDS), caused by infection with LP-BM5 murine leukemia virus (LP-BM5 MuLV) was used at early and late stages of the disease. AZT-induced anemia was dose- and time-dependent. An increased percentage of erythroblasts in bone marrow was observed, with an increased ratio of early to late erythroblasts in both disease stages. Increases in splenic erythroid burst-forming units (BFUe) were observed in early-stage AZT-treated mice. Mean plasma erythropoietin (EPO) levels were increased by AZT in both groups in a dose-dependent manner and were inversely proportional to hematocrit values. These data suggest that the anemia induced by AZT stimulated a response by immature erythroid elements, but that the maturation or survival of early erythroblasts may be impaired.

Acquired Immunodeficiency Syndrome↗
PubMed1990

3'-Azido-3'-deoxythymidine ameliorates the thrombocytopenia observed in a murine model of AIDS.

3'-Azido-3'-deoxythymidine (AZT) is used in the management of acquired immunodeficiency syndrome (AIDS) and AIDS-related complex (ARC). The myelotoxic actions of AZT are well known but its effect on platelets is not clear. We studied the effect of AZT at 1 and 2.5 mg/ml in drinking water on platelets in a murine model of AIDS. Three stages of the disease were examined, as determined by the serum IgM levels and other physical features. As early as 15 days after the initiation of drug treatment, AZT was found to significantly increase platelet production. To ascertain that this activity was authentic, a further study was carried out using uninfected mice. Mice were given AZT at both doses for 15 and 30 days. All mice on AZT had significantly increased numbers of platelets. These increases were dose and time dependent. AZT is therefore a potent inducer of thrombocytosis and may be a potential candidate in the treatment of thrombocytopenia in AIDS.

Acquired Immunodeficiency Syndrome↗
PubMed1988

[The binding characteristics of antibody with antigen in enzyme immunosensor].

The enzyme immunosensor developed by Aizawa et al for assaying antigens is regarded as a rapid and accurate method for immunoassay. The key point involved in this technique is the binding force of an antigen with a membrane-bound antibody. In this report, a simplified method was adopted to determine the amount of membrane-bound antibody and the binding constant between antigen and membrane-bound antibody. The plot of C* vs C*/A0* facilitates the determination of binding constant K' and the amount of membrane-bound antibody, B0. From the equations expressing competitive binding reactions of labeled and nonlabeled antigen-antibody reactions, the value of K was determined from the value of K' and relative concentrations of antigen and antigen-antibody complex. The determination of K' and K was exemplified by obtaining the data of anti-IgG and anti-hCG antibodies (immobilized on triacetyl cellulose membrane) with their antigens.

Antibodies↗
PubMed1981

Portal vein prostacyclin activity in experimental portal hypertension in rats.

1. Portal hypertension was produced experimentally in rats by partial ligation of the portal vein. 2. One week later portal veins of these animals were shown to release significantly greater amounts of prostacyclin than control animals. 3. It is postulated that if this response occurs in man, local vasodilatation and inhibition of platelet aggregation may be exacerbatory factors in the severity of haemorrhage from oesophageal varices that complicate portal hypertension.

Animals↗
PubMed1980

Prostacyclin-like activity in the female rat thoracic aorta and the inferior vena cava after ethinyloestradiol and norethisterone.

1. Female rats were injected with ethinyloestradiol, norethisterone or both compounds for 30 days. Prostacyclin-like activity was measured in the thoracic aorta and inferior vena cava. 2. In the thoracic aorta of rats injected with ethinyloestradiol and ethinyloestradiol/norethisterone, prostacyclin-like activity was significantly increased. Norethisterone alone had no effect. 3. In the inferior vena cava of rats injected with ethinyloestradiol, norethisterone or both compounds, prostacyclin-like activity was not significantly altered. The amount of prostacyclin generated by the inferior vena cava was much lower than that by the aorta. 4. Experimentally induced changes in the vessel wall after the administration of contraceptive steroids must be due to factors other than diminished prostacyclin production.

Animals↗
PubMedDate not supplied

Inhibitors of platelet aggregation in the fetoplacental unit and myometrium with particular reference to the ADP-degrading property of placenta.

Extracts of fresh tissue from the feto-placental unit and myometrium were tested for their ability to inhibit ADP-induced platelet aggregation and to degrade ADP. Placental extracts caused rapid reversal of aggregation and degraded ADP, both effects being mimicked by HPAP. However, whereas the latter was inhibited by L-phenylalanine but not by heating to 65 degrees C for 5 minutes, the reverse was true for crude placental extracts. Umbilical cord vessels and myometrium totally inhibited platelet aggregation in a similar way to pure PGI2. Both tissues also exhibited ADP-ase activity but were much less potent in this respect than placenta. In the system used, little or no anti-aggregatory activity was detected in extracts of non-vascular cord tissue, fetal membranes or amniotic fluid, although the two latter tissues had a weak ADP-degrading effect. Thus, it appears that in contrast to myometrium and umbilical cord vessels, the major inhibitor of platelet aggregation in placenta is an ADP-ase and not PGI2. While part of the inhibitory effect of placenta may be due to HPAP, other ADP-degrading enzymes also seem to contribute to the overall anti-aggregatory property of this organ.

Alkaline Phosphatase↗