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Biomedical subjects

B Singer

Publications and source records attributed to B Singer.

264 records · Page 15Linked to original sources
PubMedDate not supplied

Modelling the development of resistance of Plasmodium falciparum to anti-malarial drugs.

A hybrid transmission/genetics model for the development of resistance by Plasmodium falciparum to anti-malarial drugs is set forth. Field data on pyrimethamine resistance are used to calibrate and test the model. Simulated consequences of different drug dosage and population coverage strategies are presented to illustrate an ethical dilemma. A strategy of maximally effective treatment for all infected individuals in the short term can be deleterious--in terms of rapid development of drug resistance--for a community in the longer term.

Adolescent↗
PubMedDate not supplied

Fidelity in transcription assessed by DNA-dependent RNA polymerases.

The use of in vitro transcription of polynucleotides by prokaryotic and eukaryotic DNA-dependent RNA polymerases has proven of great usefulness in detecting mutagenic base modifications. Quite similar results are obtained with ribo- and deoxyribopolymers as templates, and with Mg2+ and Mn2+ at optimal concentrations. Recent studies have centered on polymers containing etheno C, as well as its hydrated form. These modifications are of particular interest, since they are the consequence of metabolised vinyl chloride, a proven human carcinogen.

Animals↗
PubMedDate not supplied

Synthesis of N2,3-ethenodeoxyguanosine, N2,3-ethenodeoxyguanosine 5'-phosphate, and N2,3-ethenodeoxyguanosine 5'-triphosphate. Stability of the glycosyl bond in the monomer and in poly(dG,epsilon dG-dC).

The synthesis of a new modified etheno-2'-deoxyguanosine is reported. N2,3-Ethenodeoxy-guanosine (epsilon dGuo) is a product in double-stranded DNA treated with the carcinogen vinyl chloride in vivo or its metabolite chloroacetaldehyde in vitro. The lability of its glycosyl bond has, however, interfered with its isolation from DNA. The synthesis, starting with O6-benzyl-2'-deoxyguanosine 5'-phosphate, reacted with bromoacetaldehyde, could only be accomplished in slightly alkaline media, which prevented significant loss of the sugar. The 5'-phosphate also decreased the lability of the glycosyl bond. The resulting compound, when deprotected, was converted to N2,3-ethenodeoxyguanosine 5'-triphosphate, as well as the corresponding nucleoside. Fluorescence, UV, and 1H NMR data were consistent with the assigned structures and almost identical with those of the previously synthesized much more stable ribo analogues [Kuśmierek et al. (1987) J. Org. Chem. 52, 2374-2378]. A systematic study of the pH-dependent glycosyl bond cleavage gave a t1/2, 37 degrees C, pH 6, of approximately 3.5 h for the nucleoside and 7-10 h for the nucleotides. Comparison, under the same conditions, of stability of the glycosyl bond in poly(dG,epsilon dG-dC) showed an increased stability of 2 orders of magnitude, t1/2 = approximately 600 h. The rate of sugar loss was, in all cases, greatly decreased at higher pH's, over the range of pH 5-9. These stability data indicate that when slightly alkaline conditions can be used, studies on incorporation of epsilon dGuo into polymers for in vitro mutagenesis studies are possible.

Acetaldehyde↗
PubMedDate not supplied

A new one-step method for the preparation of 3',5'-bisphosphates of acid-labile deoxynucleosides.

A method is described for preparing 3',5'-bisphosphates of labile deoxynucleosides. Under strictly anhydrous conditions, pyrophosphoryl tetrakistriazole apparently forms a ring structure bridging the 3'- and 5'-hydroxyl groups of deoxynucleosides, since upon the addition of water the ring opens and the 3',5'-bisphosphate is formed. Due to the presence of triethylamine no acid is generated at any time so that the entire procedure is in neutral solution. The bisphosphates of N2,3-ethenodeoxyguanosine, O2-ethyldeoxythymidine, and O4-methyldeoxythymidine, all of which are acid-labile, were prepared in good yield without degradation. Other modified bisphosphates prepared include O6-benzyldeoxyguanosine and 1,N6-ethenodeoxyadenosine, as well as those of unmodified deoxyguanosine and thymidine. Characterization was by 31P NMR and UV spectroscopy. Both 5'p(dT)p3' and 5'p(dG)p3' were substrates for RNA ligase, further proving the structure of the phosphorylated compounds.

Deoxyribonucleosides↗
PubMedDate not supplied

1,N2-ethenodeoxyguanosine: properties and formation in chloroacetaldehyde-treated polynucleotides and DNA.

1,N2-Etheno-2'-deoxyguanosine (1,N2-epsilon dGuo), not previously reported as a product of chloroacetaldehyde (CAA) reaction, has been synthesized and characterized. Reaction of deoxyguanosine with CAA in dimethylformamide in the presence of K2CO3 led to preparation of pure 1,N2-epsilon dGuo with 55% yield. pKa values are 2.2 and 9.2. The anionic form of the compound exhibits weak but defined fluorescence; the intensity is similar to that of N2,3-etheno-2'-deoxyguanosine (N2,3-epsilon dGuo) at neutrality. The stability of the glycosyl bond of 1,N2-epsilon dGuo (t1/2 = 2.3 h at 37 degrees C, pH 1) is 10-fold greater than of unmodified deoxyguanosine and at least one thousand-fold greater than of isomeric N2,3-epsilon dGuo. Reaction of CAA with model polynucleotides indicates that hydrogen bonding of guanine residues in the double-stranded structures is, as expected, an important factor in the formation of 1,N2-ethenoguanine. In contrast, the formation of isomeric N2,3-ethenoguanine is relatively independent of whether the DNA is single- or double-stranded. In salmon sperm DNA, reacted with CAA at neutrality, the formation of 1,N2-ethenoguanine could be demonstrated. However, we find the efficiency of formation of this adduct in double-stranded DNA to be lower than that of all other etheno derivatives.

Acetaldehyde↗
PubMedDate not supplied

[Long term administration of oral prednisone or prednisolone in treatment of myasthenia gravis. Report of five cases (author's transl)].

Five patients, four of them with severe or severe generalized myasthenia gravis, were treated by long term orally administrated prednisolone, with following results: one complete remission and two almost complete remissions (in three aged fernale patients), two substantial improvements (one in a male patient, one in a young adult female patient, both thymectomized). The least favourable result was observed in the male patient. Positive results of such treatment were similarly reported by several authors (with an average of 70% complete or almost complete remission, 20% substantial improvement, 7% moderate improvement). These results appear qualitatively superior to those obtained with ACTH, and may be long-lasting. Treatment with prednisolone may be applied to any form of myasthenia gravis, particularly those which do not react to anticholinesterasic agents in moderate dosages. At onset of treatment, patients should be under care of a reanimation unit. Dosage is initially high (60--100 mg daily, secondarily on alternate days), and should be reduced very slowly, once a definite improvement is achieved. The duration of this treatment depends upon the results obtained: it should not last under one year. Associated treatment with anticholinesterasic agents remains disputable, whereas associated thymectomy seems to provide best results.

Administration, Oral↗
PubMedDate not supplied

[Cases of abnormal movements].

Four patients with abnormal movements were treated with tiapridal. Very good results were obtained in a case of buccofacial dyskinesia associated with an extrapyramidal syndrome and dementia, and in another patient with middle-of-the-dose dyskinesias induced by L-dopa treatment for Parkinson's disease. No effect was observed, however in a case of beginning of the dose dyskinesias, and the extrapyramidal symptoms increased in severity. A dopadecarboxylase-inhibitor was associated with the L-dopa treatment in these three cases. In the fourth case, there was an increase in the spasms of the medial part of the face.

Aged↗
PubMedDate not supplied

[Normal and pathological aspects of the glenoid labrum in opaque arthro-scanner].

The morphology of the glenoid labrum was studied by CT arthrography in 88 patients. These were divided in 2 groups. In the first group, the patients underwent CT arthrography for a clinical instability of the shoulder. The second group was the reference group to study the morphology of the glenoid labrum, it included patients with rotator cuff tears or other pathology of the shoulder, without clinical instability. We described the normal labrum which presents important morphologic variations. Its study may be difficult because of the proximity of capsular structures of the shoulder, mainly the gleno-humeral ligaments. The normal variants and the pathologic aspects of the labrum were studied: the clefts, tears and degenerative phenomenous. The cleft aspect was studied comparatively in the instable population and in the reference population.

Arthrography↗