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Biomedical subjects

H Leonhardt

Publications and source records attributed to H Leonhardt.

At least 19 recordsLinked to original sources
PubMed1992

A targeting sequence directs DNA methyltransferase to sites of DNA replication in mammalian nuclei.

Tissue-specific patterns of methylated deoxycytidine residues in the mammalian genome are preserved by postreplicative methylation of newly synthesized DNA. DNA methyltransferase (MTase) is here shown to associate with replication foci during S phase but to display a diffuse nucleoplasmic distribution in non-S phase cells. Analysis of DNA MTase-beta-galactosidase fusion proteins has shown that association with replication foci is mediated by a novel targeting sequence located near the N-terminus of DNA MTase. This sequence has the properties expected of a targeting sequence in that it is not required for enzymatic activity, prevents proper targeting when deleted, and, when fused to beta-galactosidase, causes the fusion protein to associate with replication foci in a cell cycle-dependent manner.

3T3 Cells↗
PubMed1991

Expression in mammalian cells of a cloned gene encoding murine DNA methyltransferase.

Mammalian DNA cytosine-5-methyltransferase (MTase, EC 2.1.1.37) is an essential component for establishing and maintaining cell-type specific methylation patterns in the genome. The cDNA for the murine enzyme was previously cloned in segments. We have reconstructed the entire gene, encoding a protein of 1517 amino acids, from a set of overlapping cDNA clones. We report the assembly of two expression constructs in bacterial/mammalian shuttle vectors. Transcription in the first construct (pEMT) is driven by the cytomegalovirus enhancer/promoter and encodes a fusion protein with 15 additional aa at the N terminus, while the second construct (pJMT) is driven by the simian virus 40 early promoter/enhancer upstream from the natural ATG codon. Immunofluorescence microscopy and immunoblot analysis have shown that both constructs direct the synthesis of MTase in COS-1 cells. Enzyme activity in whole-cell lysates of transfected COS-1 cells transfected with pEMT and pJMT are on average tenfold and fivefold higher than in controls, respectively. The specific activities of the recombinant and endogenous mouse-cell enzyme are similar. These expression constructs will be of use in studies of DNA methylation in mammals.

Animals↗
PubMed1991

Parameters affecting plasmid stability in Bacillus subtilis.

For the analysis of parameters affecting plasmid stability in Bacillus subtilis, we used a pUB 110-derived shuttle plasmid containing direct and inverted nucleotide repeats (DRs and IRs). Deletions of up to 6 kb were found to occur between DRs of 7 to 16 bp. IRs as small as 43 or 58 bp were shown to stimulate the formation of these deletions in their neighbourhood. However, these structural features (DRs and IRs) per se were not responsible for plasmid instability. The unstable recombinant plasmids, but not their deletion-carrying (delta) derivatives, were found to impair the growth of the host and to accumulate high amounts of linear plasmid multimers [high mol. wt. (hmw) DNA]. We propose that the accumulation of hmw DNA may be the major reason for the selective pressure against recombinant plasmids, and the enrichment of delta-plasmids. Host mutations and other parameters increasing the stability of recombinant plasmids in B. subtilis are described.

Bacillus subtilis↗
PubMed1991

[Effect of meals on resorption of bismuth from an oral bismuth gallate/bismuth nitrate preparation].

In a cross-over study in ten healthy volunteers the effect of food on the absorption of bismuth following a single oral dose of 1200 mg (= 12 Bismofalk tablets) was evaluated by measuring its serum levels (0 to 24 h) and urinary excretion (for seven days). If this high dose was ingested one hour prior to the breakfast maximal serum concentrations (16.5 +/- 13.7 micrograms/l; mean +/- SD) were rapidly achieved (tmax = 0.7 +/- 0.5 h). These levels and the low urinary recovery of 0.32 +/- 0.25 mg (corresponding to 0.027% of the dose) indicated a minimal absorption. If the tablets were taken one hour after the breakfast absorption was slightly delayed (tmax = 1.9 +/- 2.4 h), however, the extent appeared to be unchanged. In spite of the high dosage as well as the large interindividual variability in the urinary recovery and the serum concentrations potential "toxic" serum levels of 100 micrograms/l were never reached. Thus, it can be concluded that the bismuth preparation used is suitable for topical action.

Administration, Oral↗
PubMed1991

Physical and biochemical characterization of recombination-dependent synthesis of linear plasmid multimers in Bacillus subtilis.

The synthesis and structure of linear multimeric plasmid molecules (hmw DNA) in Bacillus subtilis were investigated. The replication of covalently-closed-circular supercoiled (form I) DNA requires the rate-limiting plasmid-encoded replication initiation protein. Unlike form I, hmw DNA synthesis is partially resistant to inhibition of cellular transcription or translation and requires the host DnaB protein. In addition, hmw DNA synthesis involves host recombination and repair functions (RecE and Poll). Analysis of hmw DNA by electron microscopy displayed linear DNA molecules up to 100 kb in size, which were either single-stranded, double-stranded or double-stranded with single-stranded ends. Structural features of hmw DNA molecules were mapped by means of heteroduplex studies using defined strand-specific probes. The results suggest that a recombination intermediate, but not plasmid-encoded replication, is involved in the initiation of hmw DNA synthesis.

Bacillus subtilis↗
PubMed1990

Identification of a low-copy-number mutation within the pUB110 replicon and its effect on plasmid stability in Bacillus subtilis.

A mutation (cop1) within the minimal replicon of plasmid pUB110, reducing its copy number from 48 +/- 2 to 11 +/- 2 in a Bacillus subtilis host, was isolated. This mutation is a G----T transversion within the translation control region of the replication initiation gene (repU). The cop1 mutation, when present in the recombinant plasmid, increases both its structural and segregational stability.

Bacillus subtilis↗
PubMed1990

Feasibility and effectiveness of a defined-formula diet regimen in treating active Crohn's disease. European Cooperative Crohn's Disease Study III.

In a randomized multicenter trial the efficacy of treatment of active Crohn's disease by means of a liquid defined formula diet (DFD) was tested and compared with a combination of 6-methyl-prednisolone and sulfasalazine. A total of 95 patients participated in the study. By the end of 6 weeks, among 44 patients randomized to drug treatment, 32 showed improvement of the Crohn's disease activity index (CDAI) as compared with 21 of 51 patients receiving oral DFD (p less than 0.05). The proportion of withdrawals in the DFD group (29 of 51) was sevenfold higher than in the drug group (4 of 44). However, most patients (20 of 29) receiving DFD withdrew because of the unpalatability of the liquid diet. Analysis of patients in each group who finished the study showed equal effectiveness of DFD and the drug regimen. In these subsets of patients the CDAI decreased from 280.8 +/- 90.6 to 151.7 +/- 86.5 (DFD) and from 263.7 +/- 86.3 to 129.3 +/- 63.7 (drug), respectively. Improvement of inflammation factors was similar in both groups at the end of the study, although improvement was delayed in the DFD group. In conclusion, our data show a superiority of the drug combination over DFD in the treatment of Crohn's disease under the conditions of this trial. The results do suggest, however, that DFD offers a therapeutic alternative to prednisolone and sulfasalazine in a subgroup of patients, which has to be closer characterized in further studies.

Adult↗
PubMed1988

Functional analysis of the leading strand replication origin of plasmid pUB110 in Bacillus subtilis.

Supercoiled plasmid DNA is the substrate for initiation of pUB110 replication, and - by inference - for binding of its initiator protein (RepU) to the plasmid replication origin (oriU) in vivo. No hairpin structure is required for RepU-oriU recognition. RepH (the pC194 replication initiation protein) failed to initiate replication in trans at oriU. The nucleotides that determine the specificity of the replication initiation process are located within oriU but termination is unefficient. Therefore the segment that forms the full recognition signal for termination is probably located 3' of the oriU recognition sequence. Two overlapping domains, one for initiation and one required for termination, compose the leading strand replication origin of plasmid pUB110.

Bacillus subtilis↗
PubMed1988

Construction of a shuttle vector for inducible gene expression in Escherichia coli and Bacillus subtilis.

The construction of a shuttle vector for inducible gene expression allowing fast and easy cloning in Escherichia coli and subsequent transformation of Bacillus subtilis is presented. The expression is based on the regulation of the tac promoter by the Lac repressor which was assayed with the xylE gene from Pseudomonas putida as a marker gene. The lacIq gene, transcribed by the strong spo promoter, allowed full repression of the weak tac promoter.

Bacillus subtilis↗
PubMed1987

Compartments in the organum vasculosum laminae terminalis of the rat and their delineation against the outer cerebrospinal fluid-containing space.

Using intravenously injected horseradish peroxidase (HRP) as tracer, we demonstrate, that--in contrast to other neurohemal regions--the organum vasculosum laminae terminalis (OVLT) is composed of two functionally different divisions. Both parts of the OVLT are endowed with fenestrated capillaries which, however, obviously differ in their permeability for HRP. In one of these portions the neurohemal region remains unlabeled under the experimental conditions used, while the other portion, in analogy to the majority of neurohemal regions, is labeled by the tracer. The functionally different divisions of the OVLT are separated from one another by tanycytic processes and meningeal cells establishing a barrier between the two hemal compartments. The meningeal elements penetrate the organ in the form of an uninterrupted layer; they are continuous with the pia mater and produce large amounts of basal lamina-like material. Furthermore, they provide the delineation of the OVLT against the outer cerebrospinal fluid-containing compartment, a structural feature that is characteristic of both divisions of the OVLT and corresponds to the arrangement of meninges in all other portions of the brain where a blood vessel penetrates its surface.

Animals↗
PubMed1986

The absorption of piretanide from the gastro-intestinal tract is site-dependent.

The absorption of piretanide was investigated after placing the drug in the stomach, duodenum and ascending colon under visual control. The relative amounts absorbed and the rates of absorption were estimated from the area under the curve and the total mean time, respectively. Similar amounts of piretanide were absorbed and at almost the same rate after placement in the stomach and duodenum; the area under the curve for the stomach was 250 ng h/ml and for the duodenum 243 ng h/ml, the mean absorption times being 1.97 h and 1.51 h respectively. A marked difference was observed in the rate of from the ascending colon; the area amounted to 66 ng h/ml and the mean time to 3.99 h. Although area values for the colon were significantly different from those observed with the stomach and duodenum, it must be emphasised that the amount absorbed depends on the time the drug is in contact with the absorbing surface. There is discussion of whether the differences in absorption between the duodenum and colon can be explained by the physico-chemical properties of the drug alone, or whether the results reflect a saturable transport mechanism.

Adult↗
PubMed1985

Absorption of glibenclamide from different sites of the gastro-intestinal tract.

In a study of eight volunteers and six patients, glibenclamide was placed at different sites of the gastro-intestinal tract under visual control. The dose was instilled once into the stomach and once into the duodenum of the eight volunteers in a randomized crossover design. The six patients underwent diagnostic colonoscopy, and the dose was placed into the ascending colon if pathological findings were not present. The area under the concentration-time curve, completed by extrapolation, and the mean residence time of the drug in the body were calculated. These pharmacokinetic characteristics were examined using a Jonckheere test for ordered alternatives and a Wilcoxon signed rank pair test. The means of the areas under the curve were 477 +/- 131 ng . h ml-1 for the stomach, 475 +/- 142 ng . h ml-1 for the duodenum and 486 +/- 301 ng . h ml-1 for the colon. The mean residence time changed from 2.67 +/- 0.35 h for the stomach to 2.42 +/- 0.48 h for the duodenum and 3.55 +/- 0.68 h for the colon. These results indicate that although glibenclamide is absorbed from all three sites of the gastro-intestinal tract to the same extent, the rates of absorption are different. It is discussed whether these findings really confirm the pH-partition hypothesis in drug absorption. Since glibenclamide--a weak acid--has a pK-value of about 6.5, these data seem to confirm the pH-partition hypothesis of drug absorption.

Adolescent↗
PubMed1979

[Effect of uric acid lowering drugs in low dosage in patients with hyperuricemia and hypertriglyceridemia in a randomized group study].

The serum uric acid lowering effects of 100 mg Allopurinol (A), 20 mg Benzbromarone (B) and the combination of both were tested in a randomized block-trial in 12 male patients suffering from hyperuricemia and hyperlipoproteinemia type IIb/IV. Therapy periods lasted 4 weeks each. Allopurinol lowered the uric acid concentrations from 7,54 mg/100 ml to 5,95 mg/100 ml, Benzbromarone from 7,54 mg/100 ml to 6,11 mg/100 ml and the combination from 7,54 mg/100 ml to 4,90 mg/100 ml, all three significantly. The difference between the effect of the combination drug and Allopurinol and Benzbromarone respectively was also significant. An additive effect of both components is evident. Serum creatinin concentration remained constant. Uric acid and creatinin excretion could not be evaluated because of failure of patient compliance in the collecting of urine.

Adult↗
PubMed1979

Influence of the adrenal cortex on allograft rejections in rats.

I. The bibliography about corticosteroid influence on immune response is briefly reviewed. Generally, it is admitted that corticosteroids are immunosuppressive when administered in large amounts. Divergent opinions are recalled. II. The aims of the experiments are summarized: A) Investigate on the influence of corticoids (given in just substitutive amounts) on skin allograft rejection. B) Investigate on possible interactions between adrenal cortex and thymus with this test. III. It was observed, that A) Adrenalectomy resulted in a significant delay of allograft rejection. B) This could be suppressed partially by administering aldosterone, corticosterone, and desoxycorticosterone and completely by administering at least two of these hormones. C) Cortisol had shown a minor inhibitory influence. D) There was no obvious difference between adrenalectomized and thymectomized rats and those adrenalectomized only. IV. These observations are replaced in the context of bibliography and their significance is discussed.

Adrenal Cortex↗
PubMed1979

[Influence of the thymus hormone on radioleucosis in mice].

A partially purified thymic extract has determined the development of leucosis in 10 thymectomized irradiated CC57Bl mice out of 25. The pure hormone isolated from the same extract prevented the development of leucosis in intact irradiated Mice. This seems to indicate the presence of a second active substance in the extract (enhancing the development of the leucosis).

Animals↗