Photodynamic treatment with fractionated light decreases production of reactive oxygen species and cytotoxicity in vitro via regeneration of glutathione

Photodynamic therapy removes unwanted or harmful cells by overproduction of reactive oxygen species (ROS). Fractionated light delivery in photodynamic therapy may enhance the photodynamic effect in tumor areas with insufficient blood supply by enabling the reoxygenation of the treated area. This study addresses the outcome of fractionated irradiation in an in vitro photodynamic treatment (PDT) system, where deoxygenation can be neglected. Our results show that fractionated irradiation with light/dark intervals of 45/60 s decreases ROS production and cytotoxicity of PDT. This effect can be reversed by addition of 1,3-bis-(2-chlorethyl)-1-nitrosurea (BCNU), an inhibitor of the glutathione reductase. We suggest that the dark intervals during irradiation allow the glutathione reductase to regenerate reduced glutathione (GSH), thereby rendering cells less susceptible to ROS produced by PDT compared with continuous irradiation. Our results could be of particular clinical importance for photodynamic therapy applied to well-oxygenated tumors.     

Isotope ratio monitoring gas chromatography/Mass spectrometry of D/H by high temperature conversion isotope ratio mass spectrometry

Of all the elements, hydrogen has the largest naturally occurring variations in the ratio of its stable isotopes (D/H). It is for this reason that there has been a strong desire to add hydrogen to the list of elements amenable to isotope ratio monitoring gas chromatography/mass spectrometry (irm-GC/MS). In irm-GC/MS the sample is entrained in helium as the carrier gas, which is also ionized and separated in the isotope ratio mass spectrometer (IRMS). Because of the low abundance of deuterium in nature, precise and accurate on-line monitoring of D/H ratios with an IRMS requires that low energy helium ions be kept out of the m/z 3 collector, which requires the use of an energy filter. A clean mass 3 (HD(+.)) signal which is independent of a large helium load in the electron impact ion source is essential in order to reach the sensitivity required for D/H analysis of capillary GC peaks. A new IRMS system, the DELTA(plus)XL(trade mark), has been designed for high precision, high accuracy measurements of transient signals of hydrogen gas. It incorporates a retardation lens integrated into the m/z 3 Faraday cup collector. Following GC separation, the hydrogen bound in organic compounds must be quantitatively converted into H(2) gas prior to analysis in the IRMS. Quantitative conversion is achieved by high temperature conversion (TC) at temperatures >1400 degrees C. Measurements of D/H ratios of individual organic compounds in complicated natural mixtures can now be made to a precision of 2 per thousand (delta notation) or, better, with typical sample amounts of approximately 200 ng per compound. Initial applications have focused on compounds of interest to petroleum research (biomarkers and natural gas components), food and flavor control (vanillin and ethanol), and metabolic studies (fatty acids and steroids). Copyright 1999 John Wiley & Sons, Ltd.     

Glucose is required to maintain high ATP-levels for the energy-utilizing steps during PDT-induced apoptosis

Photodynamic therapy (PDT) may trigger apoptosis or necrosis in cancer cells. Several steps in the induction and execution of apoptosis require high amounts of adenosine-5'-triphosphate (ATP). Because the mitochondrial membrane potential (delta psi) decreases early in apoptosis, we raised the question about the mechanisms of maintaining a sufficiently high ATP level. We therefore monitored delta psi and the intracellular ATP level of apoptotic human epidermoid carcinoma cells (A431) after photodynamic treatment with aluminum (III) phthalocyanine tetrasulfonate. A maximum of caspase-3-like activity and nuclear fragmentation was found at fluences of about 4 J cm(-2). Under these conditions apoptotic cells reduced delta psi rapidly, while the ATP level remained high for 4-6 h after treatment for cells supplied with glucose. To analyze the contribution of glycolysis to the energy supply during apoptosis, experiments were carried out with cells deprived of glucose. These cells showed a rapid drop of ATP content and neither caspase activation nor nuclear fragmentation could be detected. We conclude that the use of glucose as a source of ATP is obligatory for the execution of PDT-induced apoptosis.     

How does cold constrain life cycles of terrestrial plants and animals?

Short summer seasons with low thermal energy input characterise polar ecosystems. Climatic variables and physical isolation of terrestrial habitats act as selective filters which must be passed to allow colonisation, establishment and survival in these extreme environments. Life history studies of the terrestrial biota of such ecosystems give little evidence of adaptive responses to low temperatures having evolved in situ, even though behavioural, ecophysiological and biochemical features allowing tolerance of the likely extremes are well-developed. Observed life history strategies are often consistent with the general predictions of adversity (A) or stress (S) selection. However, biota successful in these extreme environments may be better-grouped by the lack of particular life history features, rather than common possession.