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Biomedical subjects

B Clement

Publications and source records attributed to B Clement.

At least 73 records · Page 4Linked to original sources
PubMed1988

Polyadenylation of histone H3 and H4 mRNAs in dicotyledonous plants.

The histone H3 and H4 genes are shown to be expressed in both Arabidopsis plantlets and transitory multicellular suspension. The 5'- and 3'-ends of the H4 mRNAs have been localized on two H4 genes previously sequenced, H4A748 and H4A777. S1-nuclease mapping and reverse-transcriptase-primer-elongation experiments revealed the existence of two start points for transcription, located 31 and 37 nucleotides downstream from the TATA-box. The 3'-end of the mRNA corresponding to H4A748 was localized at 177 nt after the stop codon. The other gene, H4A777, most probably is not expressed. In addition to a long 3'-untranslated region, the H4 mRNA was shown to be polyadenylated in both plantlets and cell-suspension. This observation was extended to the H3 mRNAs of Arabidopsis and of two other dicots, tobacco and sunflower. Previous results on maize H3 and H4 mRNAs suggest that polyadenylation is a common feature for histone mRNAs in higher plants.

Base Sequence↗
PubMed1988

Clinical and angiographic correlates and prognostic significance of the coronary extent score.

The clinical and angiographic correlates and the prognostic significance of the "coronary extent score" in a consecutive series of 313 patients who were catheterized twice were studied. The extent score was defined as the number of 5 to 75% stenosed segments in a 15-segment coding system. The extent score was higher in subgroups of patients with new onset angina at the time of the first angiogram (4.3 +/- 2.4 vs 3.3 +/- 1.9, p less than 0.01), unstable angina at the time of the second angiogram (4.0 +/- 2.0 vs 3.3 +/- 1.9, p less than 0.05) or multifocal progression from the first to the second angiogram (4.0 +/- 2.1 vs 3.3 +/- 1.9, p less than 0.01), suggesting that it is an index of active coronary artery disease. The extent score did not correlate with the number of diseased vessels (r = 0.03), the ejection fraction (r = 0.03), the Friesinger score (r = 0.04) and the Gensini score (r = -0.07) (difference not significant for each). Cox's model was fit to the survival data recorded on a prospective basis after the second angiogram. Independent predictors of survival were ejection fraction (p less than 0.001), extent score (p = 0.001), number of diseased vessels (p = 0.01) and percent of left main luminal stenosis (p less than 0.05). The extent score was also an independent predictor of myocardial infarction and unstable angina. Thus, the extent score, an index of active progressive disease, is an independent predictor of mortality and cardiac events in patients with coronary artery disease.

Angina Pectoris↗
PubMed1988

Genotoxic activities of benzamidine and its N-hydroxylated metabolite benzamidoxime in Salmonella typhimurium and mammalian cells.

The genotoxic potentials of benzamidine and benzamidoxime were determined to study the toxicological relevance of the metabolic N-oxygenation (N-hydroxylation) of benzamidines to benzamidoximes. Benzamidoxime induced DNA single-strand breaks (in rat hepatocytes) and DNA amplification in SV40-transformed hamster cells. In the experiments performed, benzamidine itself was only marginally positive in the hepatocyte/DNA single-strand break assay. Since these cells possess an intact metabolization apparatus, the biological activities may be attributed to toxic and genotoxic metabolites formed by biotransformation. In the Salmonella typhimurium mutagenicity test (TA 98 and TA 100) benzamidoxime alone exhibited a low mutagenicity in the TA 98 strain in the presence of rabbit liver S-9 fractions. These results permit recognition of the metabolic N-hydroxylation of benzamidines to benzamidoximes as a process to toxication. Indirect evidence for the formation of a glucuronide of benzamidoxime has been obtained from in vitro experiments, but it could not be established that this process was a decisive factor in the genotoxicity of benzamidoxime.

Amidines↗
PubMed1988

Types I and IV procollagen gene expression in cultured rat hepatocytes.

The molecular mechanism involved in the expression of collagens by hepatocytes were investigated in both pure and co-culture with another rat liver epithelial cell type (RLEC). We measured the steady-state levels of mRNAs coding for pro alpha 1(I) and pro alpha 1(IV) chains by Northern analysis and by dot blotting, using specific recombinant cDNA probes. In freshly isolated hepatocytes, only small amounts of pro alpha 1(I) and pro alpha 1(IV) mRNAs were detected by dot-blot analysis. After 3 days in culture, the pro alpha 1(I) and pro alpha 1(IV) mRNA levels increased 2 to 5 times. The amount of pro alpha 1(IV) mRNAs was identical in hepatocyte cultured with RLECs while the pro alpha 1(I) mRNA level was 5 times that in pure hepatocyte culture. Hydrocortisone reduced pro alpha 1(I) mRNA in hepatocyte cultures, but had no effect on co-cultured cells. In both culture systems, this glucocorticoid did not act on the steady-state pro alpha 1(IV) mRNA level. Whatever the age and the type of culture (pure or mixed) RLECs exhibited the highest levels of pro alpha 1(I) and pro alpha 1(IV) mRNAs, which were reduced by hydrocortisone. These results show that procollagen gene expression by hepatocytes is not directly correlated with their functional state and that corticosteroids differently affect the expression of different collagen genes and collagen deposition.

Animals↗
PubMed1987

Hepatic microsomal N-demethylation of N-methylbenzamidine. N-dealkylation vs N-oxygenation of amidines.

The microsomal oxidative N-demethylation of N-methylbenzamidine, a model compound for active substances containing the basic amidine function, was investigated. N-Methylbenzamidine was converted into benzamidine and formaldehyde by aerobic incubation with non-induced microsomal fractions of rabbit liver homogenates and NADPH. The formation of benzamidine in the incubation mixtures under widely differing conditions was assayed using a newly-developed, high-performance, ion pair, reverse-phase partition chromatographic method. Optimal reaction conditions were determined. The benzamidine formation in the incubation mixture followed Michaelis-Menten kinetics and required the presence of molecular oxygen and NADPH. The effects of the inducer phenobarbital, methylcholanthrene, ethanol and N-methylbenzamidine itself on the activity were studied. Neither superoxide anion nor hydrogen peroxide was directly involved in the demethylation reaction. The direct involvement of cytochrome P-450 in this reaction is supported by the observation that the presence of inhibitors of cytochrome P-450, in particular of carbon monoxide, markedly decreased the rate of N-demethylation. This N-demethylation of N-methylbenzamidine proves the hypothesis that benzamidines with hydrogen atoms in the alpha-position to the amidine nitrogen atoms are N-dealkylated instead of N-oxygenated by the microsomal mixed function oxidase system.

Amidines↗
PubMed1987

Characteristics of the microsomal N-hydroxylation of benzamidine to benzamidoxime.

1. A simple and fast h.p.l.c. analysis of benzamidoxime formed by microsomal N-hydroxylation of benzamidine is presented which is well suited for the determination of the N-oxygenation activity of microsomal enzymes. 2. Optimal reaction conditions were determined. The apparent Km and Vmax values were, respectively, 1.61 mM and 0.38 nmol benzamidoxime/min per mg protein. 3. The effects of the inducers phenobarbital, 3-methylcholanthrene and benzamidine itself on hepatic benzamidine metabolizing activity in rabbits were determined. 4. Neither superoxide anion nor hydrogen peroxide is directly involved in the N-hydroxylation reaction. 5. The direct involvement of cytochrome P-450 in the N-hydroxylation of benzamidine is supported by the observation that inhibitors of cytochrome P-450, in particular carbon monoxide, markedly decreased the rate of N-oxygenation.

Amidines↗
PubMed1986

Constrained poststratification.

Adjustment for covariates (or poststratification) is frequently used in the analysis of randomized clinical trials. The purpose of such analysis is mainly to eliminate some residual bias resulting from any imbalance between treatment groups for some important covariates. Usually, covariate effect is modeled with the data at hand. In this paper, we present a new method of poststratification ("constrained poststratification") which consists of estimating the prognostic significance of covariates in a large historical data base, transferring the model's coefficients into the (smaller) randomized trial data set, and estimating treatment effects conditional on this a priori information. In a simulated experiment, constrained poststratification allowed not only reduction of the bias but also enhancement of the efficiency of the estimation of treatment effect.

Bayes Theorem↗
PubMed1985

Amidoximes of pentamidine: synthesis, trypanocidal and leishmanicidal activity.

For the study of the biotransformation of pentamidine and the evaluation of its trypanocidal and leishmanicidal properties the N-hydroxylated derivatives II and III were prepared. In II and III, one or both the terminal amidine moieties of pentamidine are replaced by an amidoxime. These amidoximes II and III were tested against various Trypanosoma species and Leishmania donovani in mice and golden hamsters, respectively. The studies demonstrate that the pentamidine derivatives II and III were active against various trypanosomes (T. brucei; T. vivax; T. congolense). However, besides having a pronounced activity against Trypanosoma rhodesiense compounds II and III exhibit a less action on other Trypanosomes than the standard drugs diminazene and in some cases the parent compound pentamidine. Derivatives II and III were also distinctly active against Leishmania donovani but their leishmanicidal effect was slightly less marked than that of pentamidine.

Animals↗
PubMed1985

Synthesis and phosphorylation of cytoskeleton components in foetal, regenerating and adult normal rat hepatocytes during culture.

Detergent insoluble material (DIM) was prepared by gentle treatment with detergent from foetal, regenerating and adult normal rat hepatocytes cultured for various times. It retained to some degree the morphology of the cells. After incubation of intact cells with 35S-methionine, most of the labelled DIM proteins were found to be components of the cytoskeleton. They included several cytokeratins, vimentin and actin. The synthesis rate varied with the age of animals and culture conditions. The high synthetic rate of vimentin in foetal and regenerating hepatocytes could be associated with cell proliferation. No correlation was found between cytokeratin synthesis and hepatocyte growth. Most of the cytoskeleton proteins could be phosphorylated in intact cells and in DIM from cultured hepatocytes. However the degree of phosphorylation of these proteins was not related to their synthetic rate. The decreased phosphorylation level in cultured adult rat hepatocytes could be related to the rapid loss of specific functions.

Animals↗
PubMed1985

Modulation of fetal and neonatal rat hepatocyte functional activity by glucocorticoids in co-culture.

Fetal and neonatal rat hepatocytes were cultured alone or in association with another liver epithelial cell type, in a medium with or without hydrocortisone. Secretion of albumin and alpha-fetoprotein decreased in pure hepatocyte culture, whereas in co-culture it remained stable for several days. Furthermore, addition of hydrocortisone to the co-culture medium induced a rapid increase in albumin production which was maintained at a high level. In contrast, alpha-fetoprotein production was inhibited. At the same time, an abundant extracellular material was secreted between and around hepatocyte colonies. The results demonstrate that the reciprocal relation between albumin and alpha-fetoprotein production which occurs during in vivo perinatal hepatocyte maturation is also observed in vitro. Both cell-cell contacts and glucocorticoids play a key role in this process. It appears that fetal and neonatal hepatocytes can maturate when maintained in a co-culture system.

Albumins↗
PubMed1985

A procedure for light and electron microscopic intracellular immunolocalization of collagen and fibronectin in rat liver.

Experimental conditions have been designed that permit both extracellular and intracellular immunolocalization of various collagen types and fibronectin in rat liver. The procedure involves paraformaldehyde fixation by perfusion of the organ, use of saponin as a membrane permeabilizing agent, and visualization of the matrix components by indirect immunoperoxidase. Intracellular demonstration of collagens was particularly sensitive to the composition of the fixative and the duration of fixation. Hepatocytes contained fibronectin and types I and IV collagen, whereas fat-storing and endothelial cells evidenced type III collagen in addition. All the components were specifically located in the endoplasmic reticulum and/or the Golgi apparatus.

Animals↗