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At least 325 records · Page 18Linked to original sources
PubMed2006

DNA adduct measurements in zebra mussels, Dreissena polymorpha, Pallas. Potential use for genotoxicant biomonitoring of fresh water ecosystems.

The purpose of this study was to examine PAH accumulation and bulky DNA adduct formation in the digestive gland of zebra mussels exposed in their habitat or in controlled laboratory conditions to complex mixture of PAH. DNA adducts were measured using a 32P-postlabelling protocol with nuclease P1 enrichment adapted from Reddy and Randerath [Reddy, M.V., Randerath, K., 1986. Nuclease P1-mediated enhancement of sensitivity of 32P-postlabelling test for structurally diverse DNA adducts. Carcinogenesis 7, 1543-1551]. Specimens collected in the upper part of the Seine estuary were shown to accumulate higher levels of PAH (up to 1.6 microg g(-1) dry weight) in comparison to individuals from the reference site (0.053 microg g(-1) dry weight). The former exhibited elevated levels of DNA adducts (up to 4.0/10(8) nucleotides) and higher diversity of individual adducts with five distinct spots being specifically detected in individuals originating from the Seine estuary. Zebra mussels exposed for 5 days to 0.01% (v/v) of organic extract of sediment from the Seine estuary were shown to accumulate high amounts of PAH (up to 138 microg g(-1) dry weight) but exhibited relatively low levels of DNA adducts. Exposure to benzo[a]pyrene led to a dose-dependent accumulation of B[a]P (up to 7063 microg g(-1) dry weight) and a clear induction of DNA adduct formation in the digestive gland of mussels (up to 1.13/10(8) nucleotides). Comparisons with other bivalves exposed to the same model PAH, revealed similar levels of adducts and comparable adduct profiles with a main adduct spot and a second faint one. This study clearly demonstrated that zebra mussels are able to biotransform B[a]P and probably other PAH into reactive metabolites with DNA-binding activity. This work also demonstrated the applicability of the nuclease P1 enhanced 32P-postlabelling method for bulky adduct detection in the digestive gland of zebra mussels. DNA adduct measurement in zebra mussels could be a suitable biomarker to monitor PAH-exposure and evaluate genotoxicity in fresh water ecosystems.

Animals↗
PubMed2001

Characterization of sterically stabilized cisplatin liposomes by nuclear magnetic resonance.

Extensive scientific efforts are directed towards finding new and improved platinum anticancer agents. A promising approach is the encapsulation of cisplatin in sterically stabilized, long circulating, PEGylated 100 nm liposomes. This liposomal cisplatin (STEALTH cisplatin, formerly known as SPI-77) shows excellent stability in plasma and has a longer circulation time, greater efficacy and lower toxicity than much free cisplatin. However, so far, the physicochemical characterization of STEALTH cisplatin has been limited to size distribution, drug-to-lipid ratio and stability. Information on the physical state of the drug in the liposome aqueous phases and the drug's interaction with the liposome membrane has been lacking. This study was aimed at filling this gap. We report a multinuclear NMR study in which several techniques have been used to assess the physical nature of cisplatin in liposomal formulations and if and to what extent the drug affects the liposome phospholipids. Since NMR detects only the soluble cisplatin in the liposomes and not the insoluble drug, combining NMR and atomic absorption data enables one to determine how much of the encapsulated drug is soluble in the intraliposomal aqueous phase. Our results indicate that almost all of the cisplatin remains intact during the loading process, and that the entire liposomal drug is present in a soluble form in the internal aqueous phase of the liposomes.

Buffers↗
PubMed1990

Inhibition of thermolysin by phosphonamidate transition-state analogues: measurement of 31P-15N bond lengths and chemical shifts in two enzyme-inhibitor complexes by solid-state nuclear magnetic resonance.

31P and 15N chemical shifts and 31P-15N bond lengths have been measured with solid-state NMR techniques in two inhibitors of thermolysin, carbobenzoxy-Glyp-L-Leu-L-Ala (ZGpLA) and carbobenzoxy-L-Phep-L-Leu-L-Ala (ZFpLA), both as free lithium salts and when bound to the enzyme. Binding of both inhibitors to thermolysin results in large changes in the 31P chemical shifts. These changes are more dramatic for the tighter binding inhibitor ZFpLA, where a approximately 20 ppm downfield movement of the 31P isotropic chemical shift (sigma iso) is observed. This shift is due to changes in the shift tensor elements sigma 11 and sigma 22, while sigma 33 remains essentially constant. We observed a similar pattern for ZGpLA, but only a approximately 5 ppm change occurs in sigma iso. The changes in the 15N chemical shifts for both inhibitors are small upon binding, amounting to downfield shifts of 2 and 4 ppm for ZGpLA and ZFpLA, respectively. This indicates that there are no changes in the protonation state of the 15N in either the ZFpLA- or the ZGpLA-thermolysin complex. NMR distance measurements yield a P-N bond length rP-N = 1.68 +/- 0.03 A for the tight binding inhibitor ZFpLA both in its free lithium salt form and in its thermolysin-ZFpLA complex, a distance that is much shorter than the 1.90-A distance reported by X-ray crystallography studies [Holden et al. (1987) Biochemistry 26, 8542-8553].(ABSTRACT TRUNCATED AT 250 WORDS)

Binding Sites↗
PubMedDate not supplied

Non-invasive methods for studying brain energy metabolism: what they show and what it means.

This review summarises the ways in which magnetic resonance spectroscopy (MRS) and related methods can be used as windows on brain energy metabolism in vivo. (31)P-MRS can measure acute changes in non-oxidative ATP synthesis in transient states, and at steady state reflects the balance of ATP demand and mitochondrial function. (13)C-MRS labelling methods can measure a variety of carbon fluxes. The few (31)P- and (13)C-MRS studies of the response to functional activation suggest quite large increases in oxidative metabolism. Functional magnetic resonance imaging measures the hyperoxygenation that results from increase in cerebral blood flow in excess of glucose oxidation, attenuated somewhat by a smaller increase in oxygen consumption. Previous positron emission tomography studies disagree on the size of activation response. These are powerful but demanding techniques, valuable in understanding both normal physiology and pathophysiology. However, discrepancies remain to be reconciled, and this will require increasing sophistication of both techniques and analytical models.

Adenosine Triphosphate↗
PubMed1976

An accurate method for the determination of inorganic phosphate in serum.

Cali's approach to accuracy is reviewed, and it is concluded that the main factor limiting its extension to analytes other than elements is the lack of suitable definitive methods of analysis. The work published on calcium, andwork known to be under way on other elements, is based on the use of stable isotope dilution-mass spectrometry (I.D.M.S.) as the definitive technique. This paper outliones the theorectical considerations involved in extending I.D.M.S. to the determinatioons of molecules; in particular, exact equations for the calibration graph obtained by I.D.M.S. are developed, and special cases of practical significance are defined. It is concluded that in theory there is no reason why accurate resluts should not be realised. Ther determination of isotope rations is central to the tecnique of I.D.M.S. The means available for such measurments are discussed, and it is concluded that adequate precision cnan be achieved with standard equipment/ To illustrate the application for I.D.M.S. to molecules the steps involved in an assay for inorganic phosphate are defined, and the protocol this evolved is applied to specimens from the Wellcome Group Quality Control Programme. Although good correlation was found between I.D.M.S. results and the participants' mean results, there was a substantial bias. It is argued that this is a result of the difficulty of defining "inorganic phosphate" as a chemical entity. Some requirements for...

Evaluation Studies as Topic↗