jeanflop/post_ocr_correction2 huggingface dataset:
TDP and CDP. Treatment of cells with the natural nucleoside precursor thymidine results in the same effect by increasing dTTP biosynthesis via a salvage pathway. We therefore investigated the effect of HU and thymidine, both of which producing ultimately a decrease in dCTP synthesis as explained above. Figure 2A shows the effect of increasing concentrations of HU alone on the establishment of G418 resistant colonies as well as the cytotoxic effect on 3T3 cells. The data clearly show that at non-cytotoxic concentrations, HU significantly decreases the replication of the virus. This is in agreement with recent reports which demonstrated that HU impairs reverse transcription of viral RNA via dNTP pool depletion [7-9]. Figure 2B shows the dose response of ddC in the absence and in the presence of 50 µM HU. When adjusted for the effect of HU alone, the IC50 values of ddC decrease by a factor of 10 in the presence of 50 µM HU. Combination treatment with 40 µM ddC and 50 µM HU resulted in about 95% inhibition of virus replication. As stated above, thymidine, which is readily converted into dTTP in cells, selectively inhibits the reduction of pyrimidine diphosphate occasioning a marked decrease in dCTP biosynthesis. As already observed in HU experiments, the treatment of cells with non-cytotoxic concentrations of thymidine gave rise to a significant decrease in G418 resistant colonies (Fig. 3A) although the IC50 value was close to 100 µM. Figure 3B shows that the presence of 50 µM thymidine leads to marked enhancement of ddC efficiency which is obvious given the decrease in the IC50 value of one order of magnitude. This effect is markedly increased in the presence of 100 µM thymidine which reduced the IC50 value by a factor close to 50. Figures 3C and 3D illustrate respectively the effect of treatment with a combination of ddC and thymidine on 3T3 cloning efficiency (toxic effect) and on the establishment of G418 resistant colonies (antiviral effect). These figures clearly show that the association of non-cytotoxic concentrations of thymidine and ddC strongly decreases G418 colony formation. The combination of 100 µM ddC
biosynthesis. As already observed in HU experiments, the treatment of cells with non-cytotoxic concentrations of thymidine gave rise to a significant decrease in G418 resistant colonies (Fig. 3A) although the IC50 value was close to 100 µM. Figure 3B shows that the presence of 50 µM thymidine leads to marked enhancement of ddC efficiency which is obvious given the decrease in the IC50 value of one order of magnitude. This effect is markedly increased in the presence of 100 µM thymidine which reduced the IC50 value by a factor close to 50. Figures 3C and 3D illustrate respectively the effect of treatment with a combination of ddC and thymidine on 3T3 cloning efficiency (toxic effect) and on the establishment of G418 resistant colonies (antiviral effect). These figures clearly show that the association of non-cytotoxic concentrations of thymidine and ddC strongly decreases G418 colony formation. The combination of 100 µM ddC and 100 µM thymidine, which are non-toxic concentrations and thus relevant in terms of pharmacology, results in the quite complete disappearance of G418 resistant clones. It should be pointed out that thymidine has a more highly selective synergistic effect on ddC than HU. This may stem from the fact that, besides its inhibitory action on CDP reduction, dTTP enhances the deoxycytidine kinase-mediated phosphorylation reaction leading to increased phosphorylation of ddC to ddCMP and a subsequent increase in ddCTP biosynthesis. Previous reports dealing with similar experiments performed in HIV-1 infected ATH8 cells have provided disappointing results [22]. This is probably because human T lymphocytes ATH8 offer highly favorable metabolic conditions for ddC activity which cannot be significantly improved with combination treatments. Conclusion In agreement with recent reports, our results confirm first of all that alteration of dNTP levels could represent a possible strategy to selectively inhibit retrovirus replication. Along this line, we clearly showed that the dNTP modulators hydroxyurea and thymidine strongly decrease the viral replication at non-cytotoxic concentrations. Both compounds have been used in cancer therapy and display toxic side effects less pronounced than other anticancer agents. Accordingly, when administered at dosages not greater than 40 mg/kg/day, toxic effects including
besides its inhibitory action on CDP reduction, dTTP enhances the deoxycytidine kinase-mediated phosphorylation reaction leading to increased phosphorylation of ddC to ddCMP and a subsequent increase in ddCTP biosynthesis. Previous reports dealing with similar experiments performed in HIV-1 infected ATH8 cells have provided disappointing results [22]. This is probably because human T lymphocytes ATH8 offer highly favorable metabolic conditions for ddC activity which cannot be significantly improved with combination treatments. Conclusion In agreement with recent reports, our results confirm first of all that alteration of dNTP levels could represent a possible strategy to selectively inhibit retrovirus replication. Along this line, we clearly showed that the dNTP modulators hydroxyurea and thymidine strongly decrease the viral replication at non-cytotoxic concentrations. Both compounds have been used in cancer therapy and display toxic side effects less pronounced than other anticancer agents. Accordingly, when administered at dosages not greater than 40 mg/kg/day, toxic effects including marrow depression produced by hydroxyurea are readily reversible whereas it has been reported that injection of massive doses of thymidine as high as 3g/kg every 3 h into nude mice did not result in apparent toxicity (see [23] for general review). The second main data obtained is that the depletion of dCTP level following the action of hydroxyurea and thymidine results in a strong increase of the antiviral property of ddC. This effect comes from the fact that the antiviral effectiveness of ddC is strictly linked to the metabolic status of intracellular nucleotides. The two main critical parameters are the extent of dNTP biosynthesis and the phosphorylation of the drugs by selective kinase enzymes along the salvage pathways. The most unfavourable setting is characterized by high dNTP biosynthesis and low phosphorylation of the drugs. Both parameters strongly depend on the phenotype of the cells and the cell cycle. Given the variety of target cells potentially infectible by retroviruses such as HIV, such unfavourable circumstances are highly likely to occur and could account for the relative ineffectiveness of nucleoside analogs in the clinic. Antiviral action could be therefore enhanced by appropriately manipulating the metabolism of endogenous nucleotides. This underscores the possible
of dCTP level following the action of hydroxyurea and thymidine results in a strong increase of the antiviral property of ddC. This effect comes from the fact that the antiviral effectiveness of ddC is strictly linked to the metabolic status of intracellular nucleotides. The two main critical parameters are the extent of dNTP biosynthesis and the phosphorylation of the drugs by selective kinase enzymes along the salvage pathways. The most unfavourable setting is characterized by high dNTP biosynthesis and low phosphorylation of the drugs. Both parameters strongly depend on the phenotype of the cells and the cell cycle. Given the variety of target cells potentially infectible by retroviruses such as HIV, such unfavourable circumstances are highly likely to occur and could account for the relative ineffectiveness of nucleoside analogs in the clinic. Antiviral action could be therefore enhanced by appropriately manipulating the metabolism of endogenous nucleotides. This underscores the possible elaboration of rational chemotherapeutic protocols for the treatment of viral diseases including AIDS in which low doses of suitable dNTP modulators could be administered in combination with nucleoside analogs such as ddC or AZT. Cela souligne la nécessité de l'établissement de protocoles rationnels de polychimiothérapie dans le traitement du SIDA. ▲ REFERENCES 1. Varmus H. E., Padgett T., Heasley S., Simon G., Bishop J. M. 1977. Cellular functions are required for the synthesis and intégration of avian sarcoma virus-specific DNA. Cell 11: 307-19. 2. Fritsch E. F., Temin H. M. 1977. Inhibition of viral DNA synthesis in stationary chicken embryo fibroblasts infected with avian retroviruses. J. Virol. 24: 461-9. 3. Harel J., Rassort E., Jolicoeur P. 1981. Cell cycle dependence of synthesis of unintegrated viral DNA in mouse cells newly infected with murine leukemia virus. Virology 110: 202-7. 4. Stevenson M., Stanwick T. L., Dempsey M. P., Lamonica C. A. 1990. HIV-1 replication is controlled at the level of T cell activation and proviral intégration. EMBO J. 9: 1551-60. 5. Zack J. A., Haislip A. M., Krogstad P., Chen I. S. Y. 1992. Incompletely reverse-transcribed human immunodeficiency virus type 1 genomes in quiescent cells can function as intermediates in the
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patients à thalassémie. Par d'autres signes elle se rapproche d'une anémie hémolytique à corps de Heinz. Chez les sujets hétérozygotes l'étude électrophorétique ne révèle aucune anomalie ; en revanche, chez les malades on note à la fois la présence de l'hémoglobine anormale et celle de l'hémoglobine H, toutes deux en très faibles quantités. L'hémoglobine Taybe est un exemple particulièrement éloquent d'une telle anomalie. Ce variant a été identifié chez une jeune femme arabe israélienne souffrant depuis sa naissance d'une anémie hémolytique sévère, hautement régénérative, ayant nécessité une splénectomie à l'âge de 16 ans. Les méthodes de la chimie des protéines ont révélé la délétion d'un résidu de thréonine en position a38 ou 39, confirmée par le séquençage du gène al de globine. L'anomalie structurale est donc localisée dans l'hélice C, région à la fois proche de l'interface al(31 et de l'interface al(32. La patiente ainsi que deux autres membres de sa fratrie, également anémiques, sont homozygotes pour l'hémoglobine Taybe. L'étude de la famille a montré que les parents hétérozygotes étaient totalement asymptomatiques. Pour de telles hémoglobines il existe donc un seuil en dessous duquel elles restent muettes et au-dessus duquel leur présence se traduit cliniquement et biologiquement par des anomalies sévères. Mots clés : Hb Taybe, a-globine, anémie hémolytique. ABSTRACT Several a-chain hemoglobin variants have been described as responsible, in homozygous or compound heterozygous patients, for a chronic hemolytic disease that overlaps thalassemia and Heinz bodies hemolytic anémie phenotypes. These variants are present in trace amounts together with some Hb H in the lysate of the patients. In the asymptomatic heterozygous carriers, they are usually not detected by electrophoretic methods. Hb Taybe is an example of such an unstable and thalassemic a-hemoglobin variant. This hemoglobin was observed in a young Israeli Arab woman having suffered since birth from a severe and highly regenerative hemolytic anémie for which she was splenectomized at âge sixteen. The structural abnormality was characterized by protein chemistry as the deletion of a threonine residue at position a38 or 39 and assigned to the al gène by sélective DNA sequencing. This structural modification is localized in hélix
sévères. Mots clés : Hb Taybe, a-globine, anémie hémolytique. ABSTRACT Several a-chain hemoglobin variants have been described as responsible, in homozygous or compound heterozygous patients, for a chronic hemolytic disease that overlaps thalassemia and Heinz bodies hemolytic anémie phenotypes. These variants are present in trace amounts together with some Hb H in the lysate of the patients. In the asymptomatic heterozygous carriers, they are usually not detected by electrophoretic methods. Hb Taybe is an example of such an unstable and thalassemic a-hemoglobin variant. This hemoglobin was observed in a young Israeli Arab woman having suffered since birth from a severe and highly regenerative hemolytic anémie for which she was splenectomized at âge sixteen. The structural abnormality was characterized by protein chemistry as the deletion of a threonine residue at position a38 or 39 and assigned to the al gène by sélective DNA sequencing. This structural modification is localized in hélix C, which is a highly conserved 310 hélix participating in the a 1(32 contact and close to the a 1/31 interface. The propositus and deux siblings, who were also anémie, were found to be homozygous for the molecular defect, although the abnormal Hb was not detected in the latters. Consanguinity in this family demonstrated the threshold effect in the clinical manifestations of such a-gene disorders since hétérozygotes were clinically and biologically normal. Key words : Hb Taybe, a-globin, hemolytic anémie. Voir Version abrégée (p. 443) Abnormal hemoglobins and thalassemias have been considered historically as two separate genetic entities. In the first case, a structurally abnormal globin subunit is produced, while in the second case the biosynthesis of one of the globin subunits is decreased or abolished. In récent years several abnormal hemoglobins have been recognized as responsible for a phenotype that overlaps both thalassemias and hemolytic anémies due to unstable hemoglobins [1-3]. This is especially well documented for a-chain variants that are expressed within the red blood cell at such a low level that they could not be detected by standard techniques [4, 5]. The clinical features, in the hétérozygotes, are those of thalassemia intermedia: a severe dysérythropoïétique anémie is