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Biomedical subjects

W Adam

Publications and source records attributed to W Adam.

At least 73 records · Page 4Linked to original sources
PubMed1996

Formation of singlet oxygen in the thermal decomposition of 3-hydroxymethyl-3,4,4-trimethyl-1,2-dioxetane, a chemical source of triplet-excited ketones.

Triplet-excited carbonyl species can be generated by photoexcitation of carbonyl compounds or alternatively by thermal decomposition of 1,2-dioxetanes. Such electronically excited species are involved in the oxidative modification of biologically important molecules such as DNA. This study demonstrates that thermal decomposition of 3-hydroxymethyl-3,4,4-trimethyl-1,2-dioxetane (HTMD), which is a chemical source of triplet-excited ketones, is accompanied by infrared photoemission at 1270 nm characteristic for singlet oxygen monomol emission. The intensity of infrared photoemission at 1270 nm was solvent-dependent, in agreement with the reported lifetime of singlet oxygen in the employed solvents. Calibration of monomol emission with the endoperoxide of 1,4-dimethylnaphthalene (DMNO2) showed that HTMD (30 mM) produced 25 microMs of singlet oxygen. Thus, the yield of singlet oxygen production in the thermal decomposition of HTMD in carbon tetrachloride is about 0.1%.

Heating↗
PubMed1995

Genotoxicity induced by furocoumarin hydroperoxides in mammalian cells upon UVA irradiation.

The mutagenicity and micronucleus induction by the furocoumarin hydroperoxides 1a and 2a and, for comparison, their corresponding alcohols 1b and 2b were investigated in L5178Y tk+/- mouse lymphoma cells and AS52 Chinese hamster ovary cells. The furocoumarin hydroperoxide 1a enhanced the micronucleus frequency in L5178Y tk+/- mouse lymphoma cells significantly, while its alcohol 1b exhibited a rather moderate effect. In contrast, both the furocoumarin hydroperoxide 2a and its alcohol 2b induced high frequencies of micronuclei. Only the furocoumarin hydroperoxide 1a, but not its alcohol 1b, was mutagenic in both L5178Y tk+/- and AS52 cells. On the other hand, the furocoumarin hydroperoxide 2a and its alcohol 2b were mutagenic. For all furocoumarin derivatives 1a,b and 2a,b no mutagenicity and genotoxicity was observed in the absence of UVA light. The multifunctional furocoumarin hydroperoxides may serve as potential photochemotherapeutic agents.

Animals↗
PubMed1995

From free radicals to electronically excited species.

Biologically/medically important compounds, when metabolized, can generate free radicals from which electrically excited products--often in the triplet state--are generated. Peroxidases are particularly apt to catalyze such processes, which usually entail oxidations by electron transfer. In the latter case, the chemiluminescence may derive from peroxyl and alkoxyl radicals or excited states derived from dioxetanes. Besides peroxidases, prostaglandin-H synthase and lipoxygenase may catalyze the formation of excited carbonyls. The pronounced similarity in the chemical behavior and reactivity of radicals and excited species derives in part from the biradical nature of the latter. Usually in analyzing the biological effects of xenobiotics, only radicals and/or reactive ground state products have been considered. However, in such processes the generation of excited species is possible, which should be tested for by direct and/or sensitized emission or by photochemical transformation.

Animals↗
PubMed1995

Assessment of genotoxicity and mutagenicity of 1,2-dioxetanes in human cells using a plasmid shuttle vector.

1,2-Dioxetanes are efficient sources of triplet excited carbonyl compounds on thermal decomposition. They cause photochemical and photobiological transformations in the dark. In order to study the genotoxicity and mutagenicity of 1,2-dioxetanes, the replicating shuttle vector pZ189 was damaged with 3,3,4-trimethyl-1,2-dioxetane (TrMD) or 3-hydroxymethyl-3,4,4-trimethyl-1,2-dioxetane (HTMD) in vitro and subsequently transfected into normal human lymphoblasts. We found a dose-dependent increase of genotoxicity (decrease of plasmid survival) and increase of mutation frequency with both dioxetanes. However, TrMD was less mutagenic than HTMD at similar genotoxicity. Sequence analysis of the supF gene revealed more point mutations with TrMD and 100% with HTMD were G:C to T:A and G:C to C:G transversions. These are the typical mutations following 7,8-dihydro-8-oxoguanine (8-oxo-G) formation, the main DNA lesion induced by TrMD and HTMD. Only with TrMD we found 5.4% G:C to A:T transitions, probably reflecting the more pronounced ability of TrMD to form some pyrimidine dimers. Our results indicate that 8-oxo-G is also the most relevant modification in in vivo mutagenesis.

Base Sequence↗
PubMed1995

Formation of 7,8-dihydro-8-oxoguanine in the 1,2-dioxetane-induced oxidation of calf thymus DNA: evidence for photosensitized DNA damage by thermally generated triplet ketones in the dark.

Isolated calf thymus DNA was treated with the 1,2-dioxetanes 3-acetoxymethyl-3,4,4-tri-methyl-1,2-dioxetane, 2,3-dimethylbenzofuran dioxetane, 3-hydroxymethyl-3,4,4-trimethyl-1,2-dioxetane (HTMD), 3,3,4,4-tetramethyl-1,2-dioxetane and 3,4,4-trimethyl-1,2-dioxetane (TrMD), which on thermal decomposition generate triplet-excited carbonyl products. To monitor quantitatively the formation of the mutagenic oxidation product 7,8-dihydro-8-oxoguanine (8-oxoGua), a sensitive and selective HPLC electrochemical assay was used after acidic hydrolysis (HF/pyridine) of the dioxetane-treated DNA. High yields of 8-oxoGua (up to ca 4% of the available guanine) were obtained for HTMD and TrMD. Both were investigated in detail with respect to effects of concentration, time and temperature. The oxidative reactivity of 1,2-dioxetanes was compared with several type I (benzophenone and riboflavin) and type II (methylene blue and rose bengal) photooxidants and disodium 1,4-etheno-2,3-benzodioxin-1,4-dipropionate as a chemical source of singlet oxygen. The persistence of 8-oxoGua towards oxidation by HTMD was examined in the reaction with 7,8-dihydro-8-oxo-2'-deoxyguanosine (8-oxodGuo) and with oxidized DNA. It was shown that, indeed, 8-oxoGua is consumed in the oxidized DNA on prolonged exposure to an excess of HTMD. The reaction of 8-oxodGuo with HTMD afforded the two 4R* and 4S* diastereomers of 9-(2-deoxy-beta-D-erythropentofuranosyl)-4, 8-dihydro-4-hydroxy-8-oxoguanine as main oxidation products. Trapping experiments with tert-butanol confirmed that hydroxyl radicals are not involved, whereas the use of the triplet quenchers sodium 9,10-dibromo-anthracene-2-sulfonate and 2,3-diazabicyclo[2.2.1]hept-2-ene established that triplet-excited states are mainly responsible for the observed DNA oxidation through type I action (electron transfer chemistry). The role of singlet oxygen was tested by means of deuterium isotope effects in D2O versus H2O, but no definitive conclusion could be reached in regard to the involvement of 1O2 in these oxidations.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Vasopressin V1 and V2 receptors in diabetes mellitus.

Diabetes mellitus causes hypertonicity, increased plasma arginine vasopressin (AVP), polydipsia, and polyuria. Downregulation of AVP V2 receptors may contribute to the polyuria through diminished V2 receptor-mediated free water retention. After 2 wk of streptozotocin-induced diabetes mellitus, the diabetic rats had raised plasma glucose, AVP, and osmolality levels (P < 0.001) compared with nondiabetic controls (Sham). Insulin treatment (4 U long-acting insulin sc, daily) partially lowered these values (P < 0.01). There was a reduction in the number of renal and hepatic V1 receptors in the diabetic and diabetic+insulin animals compared with the sham animals (P < 0.05). The receptor affinity remained unchanged. In parallel, there was a reduction in maximum AVP-activated total inositol phosphate production in the liver and kidney of the diabetic and diabetic+insulin animals compared with the sham animals (P < 0.05). The density and affinity of renal V2 receptors and AVP-stimulated adenosine 3',5'-cyclic monophosphate production in the diabetic and diabetic+insulin animals were unchanged compared with the sham. These results demonstrate differential regulation of AVP receptors and suggest that downregulation of renal V2 receptors does not contribute to the polyuria of diabetes. In contrast, downregulation of V1 receptors might contribute to diminished V1 receptor-mediated biological responses to AVP seen in diabetes mellitus.

Animals↗
PubMed1994

Daily variations of functional parameters and density distribution in human blood platelets.

Blood platelets play a critical role in the onset of myocardial infarction, which has been shown to have a circadian rhythmicity with a peak incidence in the morning. In an attempt to correlate platelet parameters with the outcome of cardiovascular diseases, we studied the daily (24-h) variation of the following platelet parameters: distribution pattern of functional heterogeneous platelet subpopulations; serotonin uptake; ketanserin binding; aggregation upon thrombin, serotonin, and ADP stimulation; and platelet count. Furthermore, we analyzed the tryptophan and serotonin concentrations in the blood samples. The percentage of less dense platelets, which represent the subpopulation with the highest preactivation, showed a rhythmicity period of 24 h and an acrophase at 21:18 h. The time course of intermediate and high density platelets was inverse to that of low density platelets. The serotonin uptake exhibited also a rhythmicity with a 24-h period. The acrophase was at 13:50 h. The aggregation curves were inverse to the ketanserin binding curves. The serotonin concentration exhibited a 12-h rhythmicity. The results obtained suggest that (a) changes in platelet activity are reflected by several parameters of platelet function that underlie daily variations; (b) the aggregation curves show a peak in the morning, with an additional peak in the afternoon; and (c) changes in the distribution pattern occur independently from variations in platelet functions like aggregation and serotonin binding.

Adenosine Triphosphate↗
PubMed1993

Endonuclease-sensitive DNA modifications induced by acetone and acetophenone as photosensitizers.

Repair endonucleases, viz. endonuclease III, formamidopyrimidine-DNA glycosylase (FPG protein), endonuclease IV, exonuclease III and UV endonuclease, were used to analyse the modifications induced in bacteriophage PM2 DNA by 333 nm laser irradiation in the presence of acetone or acetophenone. In addition to pyrimidine dimers sensitive to UV endonuclease, 5,6-dihydropyrimidines (sensitive to endonuclease III) and base modifications sensitive to FPG protein were generated. The level of the last in the case of acetone was 50% and in the case of acetophenone 9% of the level of pyrimidine dimers. HPLC analysis of the bases excised by FPG protein revealed that least some of them were 8-hydroxyguanine (7,8-dihydro-8-oxoguanine). In the damage induced by direct excitation of DNA at 254 nm, which was analysed for comparison, the number of FPG protein-sensitive base modifications was only 0.6% of that of the pyrimidine dimers. Mechanistic studies demonstrated that the formation of FPG protein-sensitive modifications did not involve singlet oxygen, as the damage was not increased in D2O as solvent. Hydroxyl radicals, superoxide and H2O2 were also not involved, since the relative number of single strand breaks and of sites of base loss (AP sites) was much lower than in the case of DNA damage induced by hydroxyl radicals and since the presence of SOD or catalase had no effect on the extent of the damage. However, the mechanism did involve an intermediate that was much more efficiently quenched by azide ions than the triplet excited carbonyl compounds and which was possibly a purine radical. Together, the data indicate that excited triplet carbonyl compounds react with DNA not only by triplet-triplet energy transfer yielding pyrimidine dimers, but also by electron transfer yielding preferentially base modifications sensitive to FPG protein, which include 8-hydroxyguanine.

Acetone↗
PubMed1993

Genotoxicity studies of benzofuran dioxetanes and epoxides with isolated DNA, bacteria and mammalian cells.

1,2-Dioxetanes, very reactive and high energy molecules, are involved as labile intermediates in dioxygenase-activated aerobic metabolism and in physiological processes. Various toxicological tests reveal that dioxetanes are indeed genotoxic. In supercoiled DNA of bacteriophage PM2 they induce endonuclease-sensitive sites, most of them are FPG protein-sensitive base modifications (8-hydroxyguanine, formamidopyrimidines). Pyrimidine dimers and sites of base loss (AP sites) which were probed by UV endonuclease and exonuclease III are minor lesions in this system. While the alkyl-substituted dioxetanes do not show any significant mutagenic activity in different Salmonella typhimurium strains, heteroarene dioxetranes such any significant mutagenic activity in different Salmonella typhimurium strains, heteroarene dioxetanes such as benzofuran and furocoumarin dioxetanes are strongly mutagenic in S. typhimurium strain TA100. DNA adducts formed with an intermediary alkylating agent appear to be responsible for the mutagenic activity of benzofuran dioxetane. We assume that the benzofuran epoxides, generated in situ from benzofuran dioxetanes by deoxygenation are the ultimate mutagens of the latter, since benzofuran epoxides are highly mutagenic in the S. typhimurium strain TA100 and they form DNA adducts, as detected by the 32P-postlabelling technique. Our results imply that the type of DNA damage promoted by dioxetanes is dependent on the structural feature of dioxetanes. Furthermore, the direct photochemical DNA damage by energy transfer, i.e., pyrimidine dimers, plays a minor role in the genotoxicity of dioxetanes. Instead, photooxidation dominates in isolated DNA, while radical damage and alkylation prevail in the cellular system.

Alkylating Agents↗
PubMed1993

DNA damage induced by furocoumarin hydroperoxides plus UV (360 nm).

When irradiated at 360 nm, furocoumarins with a hydroperoxide group in a side chain efficiently give rise to a type of DNA damage that can best be explained by a photo-induced generation of hydroxyl radicals from the excited photosensitizers. The observed DNA damage profiles, i.e. the ratios of single-strand breaks, sites of base loss (AP sites) and base modifications sensitive to formamidopyrimidine--DNA glycosylase (FPG protein) and endonuclease III, are similar to the DNA damage profile produced by hydroxyl radicals generated by ionizing radiation or by xanthine and xanthine oxidase in the presence of Fe(III)--EDTA. No such damage is observed with the corresponding furocoumarin alcohols or in the absence of near-UV radiation. The damage caused by the photo-excited hydroperoxides is not influenced by superoxide dismutase (SOD) or catalase or by D2O as solvent. The presence of t-butanol, however, reduces both the formation of single-strand breaks and of base modifications sensitive to FPG protein. The cytotoxicity caused by one of the hydroperoxides in L5178Y mouse lymphoma cells is found to be dependent on the near-UV irradiation and to be much higher than that of the corresponding alcohol. Therefore the new type of photo-induced damage occurs inside cells. Intercalating photosensitizers with an attached hydroperoxide group might represent a novel and versatile class of DNA damaging agents, e.g. for phototherapy.

Animals↗
PubMed1992

Photochemical DNA modifications induced by 1,2-dioxetanes.

1,2-Dioxetanes are efficient sources of triplet excited carbonyl compounds, into which they decompose on thermal or photochemical activation. In the presence of DNA, the decomposition of dioxetanes gives rise to DNA modifications, which have been studied by means of specific repair endonucleases. Cyclobutane pyrimidine dimers, which are generated by triplet-triplet energy transfer, were detected by a UV endonuclease; they made up between 2% and 30% of the total modifications recognized by a crude repair endonuclease preparation from Micrococcus luteus. For various 1,2-dioxetanes, the yield of pyrimidine dimers was proportional to their triplet excitation flux. DNA strand breaks, sites of base loss (AP sites; recognized by exonuclease III and endonuclease IV) and dihydropyrimidines (recognized by endonuclease III) were found to represent only a small fraction of the modifications. The majority of the modifications detected were recognized by formamidopyrimidine-DNA glycosylase (FPG protein) and represent 8-hydroxyguanine (7,8-dihydro-8-oxoguanine) residues or other yet not defined base modifications which are recognized by this enzyme. The modifications were generated in similar relative yields by thermal and photo-induced decomposition of the 1,2-dioxetanes and therefore emanate under both conditions from the excited carbonyl compounds. The formation of the FPG protein-sensitive modifications was efficiently quenched by azide anions; the Stern-Volmer quenching of these modifications was 150-fold more effective than that of the pyrimidine dimers. The relative amounts of the two types of modifications were strongly dependent on the structure of the 1,2-dioxetanes and on the concentration of molecular oxygen. Singlet oxygen appears to be involved only to some extent in the generation of the FPG protein-sensitive base modifications as their yield was only moderately (approximately 2-fold) increased in D2O as solvent. A mechanism is suggested in which oxidized guanine is predominantly formed by a single-electron-transfer reaction of the triplet excited carbonyl product derived from the 1,2-dioxetane, followed by unknown secondary oxidations, which involve molecular oxygen and/or undecomposed 1,2-dioxetane.

DNA↗
PubMed1992

Progressive soft tissue uptake of Tc-99m MDP reflecting metastatic microcalcification.

A 49-year-old woman had longstanding renal impairment. Markedly increased uptake of Tc-99m MDP in the heart, lungs, and kidneys was an incidental finding on bone scintigraphy performed to exclude metastatic bone disease. These findings persisted on repeat bone imaging 1 year later. In addition, gastric and skeletal muscle uptake was subsequently seen. Soft tissue microcalcification was confirmed by computed tomography and renal biopsy. A consideration of the differential diagnosis is presented.

Bone Neoplasms↗
PubMed1991

[Experiences with 800 mg ibuprofen retard in ambulatory patients with activated osteoarthrosis and extra-articular rheumatic manifestations].

The efficacy and tolerance of ibuprofen retard at a dose of 2 x 800 mg daily was investigated in an open multicenter study over a period of 3 weeks on 7931 out-patients with activated degenerative joint disease and/or extraarticular rheumatic symptoms. The overall assessment of the treatment, made by the patients and physicians at the end of the observational study, was positive in 94.7% and 95.7% of the cases, respectively. The therapy was assessed as inadequate in only 5.2% and 4.3% of the cases, respectively. The patient's compliance was assessed by the physicians as being high at 92.6%. Adverse events during the treatment were observed in 7.8% of the patients; these concerned mainly intestinal complaints. Gastrointestinal bleeding was observed in five cases. One patient died from a heart attack during the observational study; this was not related to the drug therapy. The frequency of side effects was within the range of the findings from earlier studies with conventional drug formulations. It can be concluded from the results obtained that ibuprofen 800 retard is well-suited for and demonstrates a good tolerance in the treatment of acute, chronic-persisting, and chronic-intermittent painful conditions of degenerative joint disease and extraarticular rheumatic symptoms.

Adult↗