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B Giese

Publications and source records attributed to B Giese.

34 records · Page 2Linked to original sources
PubMed1997

Bipartite substrate discrimination by human nucleotide excision repair.

Mammalian nucleotide excision repair (NER) eliminates carcinogen-DNA adducts by double endonucleolytic cleavage and subsequent release of 24-32 nucleotide-long single-stranded fragments. Here we manipulated the deoxyribose-phosphate backbone of DNA to analyze the mechanism by which damaged strands are discriminated as substrates for dual incision. We found that human NER is completely inactive on DNA duplexes containing single C4'-modified backbone residues. However, the same C4' backbone variants, which by themselves do not perturb complementary hydrogen bonds, induced strong NER reactions when incorporated into short segments of mispaired bases. No oligonucleotide excision was detected when DNA contained abnormal base pairs without concomitant changes in deoxyribose-phosphate composition. Thus, neither C4' backbone lesions nor improper base pairing stimulated human NER, but the combination of these two substrate alterations constituted an extremely potent signal for double DNA incision. In summary, we used C4'-modified backbone residues as molecular tools to dissect DNA damage recognition by human NER into separate components and identified a bipartite discrimination mechanism that requires changes in DNA chemistry with concurrent disruption of Watson-Crick base pairing.

Base Composition↗
PubMed1997

DNA synthesis arrest at C4'-modified deoxyribose residues.

Many genotoxic agents form base lesions that inhibit DNA polymerases. To study the mechanism underlying termination of DNA synthesis on defective templates, we tested the capacity of a model enzyme (Klenow fragment of Escherichia coli DNA polymerase I) to catalyze primer elongation across a series of C4' deoxyribose derivatives. A site with inverted C4' configuration or two different C4' deoxyribose adducts were introduced into the backbone of synthetic templates without modifying the chemistry of the corresponding bases. Inverted deoxyribose moieties may arise in cellular DNA as a product of C4' radical attack. We found that DNA synthesis by the Klenow polymerase was arrested transiently at the C4' inversion and was essentially blocked at C4' deoxyribose adducts. Major termination sites were located one position downstream of a C4' selenophenyl adduct and immediately 3' to or opposite a C4' pivaloyl adduct. Primer extension studies in the presence of single deoxyribonucleotides showed intact base pairing fidelity opposite all three C4' variants regardless of whether the Klenow fragment or its proofreading-deficient mutant was tested. These results imply that the coding ability of template bases is maintained at altered C4' deoxyribose moieties. However, their capacity to impede DNA polymerase progression indicates that backbone distortion and steric hindrance are important determinants of DNA synthesis arrest on damaged templates. The strong inhibition by C4' adducts suggests a potential target for new chemotherapeutic strategies.

DNA Polymerase I↗
PubMed1996

Site-specific DNA substrates for human excision repair: comparison between deoxyribose and base adducts.

BACKGROUND: The genetic integrity of living organisms is maintained by a complex network of DNA repair pathways. Nucleotide excision repair (NER) is a versatile process that excises bulky base modifications from DNA. To study the substrate range of this system, we constructed bulky deoxyribose adducts that do not affect the chemistry of the corresponding bases. These novel adducts were incorporated into double-stranded DNA in a site-specific manner and the repair of the modified sites was investigated. RESULTS: Using restriction enzymes as a probe for DNA modification, we confirmed that the resulting substrates contained the bulky deoxyribose adducts at the expected position. DNA containing these unique adducts did not stimulate DNA repair synthesis when mixed with an NER-competent human cell extract. Inefficient repair of deoxyribose adducts was confirmed by monitoring the release of single-stranded oligonucleotides during the excision reaction that precedes DNA repair synthesis. As a control, the same human cell extract was able to process a base adduct of comparable size. CONCLUSIONS: Our results indicate that modification of DNA bases rather than disruption of the sugar-phosphate backbone is an important determinant for damage recognition by the human NER system. Specific positions in DNA may thus be modified without eliciting NER responses. This observation suggests new strategies for anticancer drug design to generate DNA modifications that are refractory to repair processes.

DNA Adducts↗
PubMed1996

Somatostatin reduces bile secretion and loss of bile constituents in patients with external biliary drainage.

The effect of 24-hours continuous somatostatin-14 infusion on the volume of the bile secretion and on the bile composition were studied in seven patients with malignant biliary obstruction who had transhepatic external biliary drainage. The bile acid composition was measured with high performance liquid chromatography (HPLC). Somatostatin infusion significantly reduced the daily bile loss from median 473 ml to 140 ml (41 per cent, p = 0.01) with a concomitant significant reduction in the daily molar loss of cholesterol, triglyceride, Na+, K+, Cl-, Ca+2 and Mg+2. The loss of chloride and sodium was reduced with median 50 mmol/day each (p = 0.01). The relative concentrations of the measured bile constituents did not change significantly, except for bile acids (p = 0.02): the concentration of glycochenodeoxycholic acid increased significantly (p = 0.04). The molar loss of taurocholic acid decreased significantly (p = 0.035), so the increased concentration of glycochenodeoxycholic acid resulted only in a marginally significant reduction in the total molar loss of bile aids (p = 0.051). Somatostatin is a potent inhibitor of bile secretion. The peptide may be used in severely bile depleted patients for reducing their serious electrolyte and acidity problems. Analysis of bile acid composition by HPLC is well suited for further investigations of the regulatory mechanisms of bile acid secretion.

Aged↗
PubMed1995

The chemistry of single-stranded 4'-DNA radicals: influence of the radical precursor on anaerobic and aerobic strand cleavage.

BACKGROUND: Deoxyribosylnucleotide radicals with a radical center at the 4'-position are important intermediates in radical-induced DNA strand cleavage. In the presence of O2, these DNA radicals yield cleavage products that are partly oxidized. In the past, the postulated peroxide intermediates could not be detected directly because they were unstable under the conditions of either radical generation, the work-up procedure, or the analytical techniques used. We set out to generate and analyze these crucial intermediates in radical-induced DNA strand cleavage under mild conditions. RESULTS: Photolysis experiments with modified single-stranded oligonucleotides generated 4'-DNA radicals that were trapped by O2. Using MALDI-MS, DNA peroxides could be detected directly. Depending upon the precursor, these peroxides are formed either before or after the cleavage of the single-stranded DNA radical. Reactions in the presence of 18O2 and/or H218O as well as subsequent transformations to the oxidized cleavage products confirmed the structure of the DNA peroxides. CONCLUSIONS: Our technique of selective DNA radical generation under mild conditions makes it possible to detect labile reaction products of single-stranded DNA radicals and to gain further insight into their cleavage reactions. In cases where a radical pair is formed, the shielding effect protects the DNA radical from external attack so that cleavage of the single strand competes successfully with trapping by O2. This shielding effect might be of general importance if the DNA radicals are generated by reagents that bind to the DNA.

Aerobiosis↗
PubMed1986

Bile acid metabolism in patients with Crohn's disease in terminal ileum.

Bile acid metabolism was studied by means of the fractional turnover rate or orally ingested 14C-labeled taurocholic acid and by gas chromatographic determination of fecal excretion of the bile acids cholic acid (CA), chenodeoxycholic acid (CDCA), deoxycholic acid (DCA), and lithocholic acid (LCA). Thirty patients with Crohn's disease (CD) of the small bowel, of whom 19 had been operated on with limited ileal resections, were studied and compared with 11 healthy volunteers. The unoperated group of CD patients did not show significant increase in bile acid excretion in the stools in contrast to the CD patients with ileal resection. The fecal excretion consisted mostly of primary bile acids, and a significant correlation between length of resection and bile acid excretion was found (rs = 0.81, p less than 0.01). The fractional turnover rate of CA + DCA was significantly increased in both unoperated (0.21 l/day) and operated (0.44 l/day) patients compared with normal controls (0.06 l/day). The bile acid pool of CA + DCA, however, was normal in patients with ileal resections, indicating a compensatory increase in bile acid synthesis. In unoperated patients the bile acid pool of CA + DCA was slightly decreased (3.1 mmol) compared with operated patients (6.2 mmol) and normal controls (4.8 mmol). The pool size was not significantly correlated to mean transit time of dietary residue, feces excretion, loss of weight, or amount of fat in feces. The mean transit time of dietary residue was decreased in both operated and unoperated CD patients.

Adult↗
PubMed1986

[Ultrasonic diagnosis in gynecology in small animals].

After a short introduction into the basics and the different methods of sonography a description of the ultrasonographic diagnosis of gynaecological diseases in small animals is given. The ultrasonographic method is indicated in all gynaecological diseases after the anamnesis, clinical and laboratory work up and before x-rays and invasive methods will be used. The sonographic characteristics for interpretation are described. Typical sonographic findings are demonstrated in 16 cases as in diseases of the cervix (inflammation, cyst), uterus (pregnancy, endometritis - pyometra), ovaries (cysts), and mamma (lactation, abscesses, tumors).

Animals↗
PubMed1985

A simplified method for estimating mean values of multiple specimens.

Determination of the correct average content of a constituent in multiple specimens requires measurements of concentration and volume of each specimen. We have evaluated a simplified method by which the mean content is estimated from one concentration determination and the total volume of the specimens. The greatest possible deviation from the correct mean value can be estimated, and is shown in diagrams. It is demonstrated that a simplified method can often be used with little loss of accuracy. The method is exemplified by measurements of lipid and biliary acids in faeces from healthy subjects and from patients with Crohn's disease.

Bile Acids and Salts↗
PubMed1985

A plastic bag freezing method for preparation of faeces for analysis.

In order to obtain a completely homogeneous mixture of a normal stool it is found necessary only to homogenize the stool samples for 2 min using a paint-can shaker. A method for handling faeces in chemical analyses is based on a freezing procedure in which the homogenized faeces are frozen in a plastic bag separated into different compartments. The frozen faeces can be cut off and weighed for analysis. Compared to the usual method, the plastic bag freezing method is faster and avoids unpleasant smell.

Feces↗
PubMed1985

Bile acid malabsorption in patients with an ileum reservoir with a long efferent leg to an anal anastomosis.

Biliary metabolism in 11 patients with ileum reservoirs with anal anastomosis and a long efferent leg was studied. Eleven healthy persons served as controls. A significantly higher excretion of bile acids was found in the patients, but they seemed to have a normal cholic acid pool size. The bile acids excreted were cholic acid and chenodeoxycholic acid, the so-called primary bile acids, for more than 90%, whereas the normal controls mainly excreted secondary bile acids (deoxycholic acid and lithocholic acid). Fat excretion was generally not increased in the group but was above normal in two patients. Vitamin B12 absorption was subnormal in two patients and was not correlated to bile acid excretion. Bile acid excretion was not correlated to the weight of feces. The bacterial flora was more feces-like than would have been expected from a normal terminal ileum but was correlated neither to the bile acid excretion nor to the quantity of feces. We conclude that the patients showed dysfunction of the terminal ileum with regard to biliary acid absorption comparable to that found in patients with partial ileal resections.

Adult↗
PubMed1985

The defecation pattern and diet in patients with an ileum reservoir and anal anastomosis with a long efferent leg.

The dietary habits and defecation patterns of 12 patients were examined 8-34 months after total colectomy with mucosal proctectomy and the construction of an ileal reservoir attached to an anal anastomosis. The reservoir was provided with a long efferent leg (12 cm) through the anal canal. The patients were divided into two groups in accordance with the frequency of defecation--one with fewer than six defecations per 24 h and another with more than six defecations per 24 h. The fecal output, however, was not significantly different in the two groups. The fecal content of sodium and potassium was the same as in feces from conventional ileostomies. The dietary intake was insufficient in energy content, vitamins, minerals, and trace elements. Dietary supplement was recommended.

Adult↗
PubMed1983

Effect of oat bran on lithogenic index of bile and bile acid metabolism.

Epidemiological studies lend support to the hypothesis that high-fibre diets might prevent and low-fibre diets might facilitate the formation of cholesterol gall stones. In the present study, the bile compositions after ingestion of oat bran 18 g/day and placebo 18 g/day for 2 X 2 weeks were compared in a randomized, double-blind cross-over study in 6 healthy volunteers. The lithogenic index of bile was not influenced, whereas the following changes (0.05 less than p less than 0.10) occurred: the cholic acid pool was enlarged, the relative proportion of chenodeoxycholate in bile was increased and that of deoxycholate reduced, while cholate remained unchanged. It is concluded that oat bran seems to influence the metabolism of bile acids.

Adult↗
PubMed1980

A software system for syntactic analysis of the EEG.

This paper describes an interlocking set of programs used for syntactic analysis of the electroencephalogram. This system constitutes a basic set of programs in the Vanderbilt EEG analysis system (VEAS). The concepts underlying the methods are explained and examples of the use of the system are given. The algorithms employed for spatial, temporal and global parsing of 'EEG sentences' are presented and examples of the use of various grammatical rules are described.

Computers↗
PubMedDate not supplied

Low-molecular-weight organoiodine and organobromine compounds released by polar macroalgae--the influence of abiotic factors.

The influence of temperature, light, salinity and nutrient availability on the release of volatile halogenated hydrocarbons was investigated in the Antarctic red macroalgal species Gymnogongrus antarcticus Skottsberg. Compared to standard culture condition, an increase in the release rates of iodocompounds was generally found for the exposure of the alga to altered environmental conditions. Macroalgae exhibited higher release rates after adaptation for two months to the changed factors, than after short-term exposure. Monitoring the release rates during a 24 h incubation period (8.25 h light, 15.75 h darkness) showed that changes between light and dark periods had no influence on the release of volatile halocarbons. Compounds like bromoform and 1-iodobutane exhibited constant release rates during the 24 h period. The formation mechanisms and biological role of volatile organohalogens are discussed. Although marine macroalgae are not considered to be the major source of biogenically-produced volatile organohalogens, they contribute significantly to the bromine and iodine cycles in the environment. Under possible environmental changes like global warming and uncontrolled entrophication of the oceans their significance may be increase.

Bromine↗