Effect Of Singlet Oxygen Research Articles

Membrane ionic current photomodification by rose bengal and menadione: role of singlet oxygen.

Photosensitized modification of ionic leak current and potassium current was studied in frog cardiac atrial cells using whole cell patch clamp techniques. Rose bengal (RB) and menadione (MQ) were used as photosensitizers. Separate photophysical studies of the photosensitizers in deuterium oxide solution demonstrated that MQ did not produce singlet oxygen as evidenced by the lack of luminescence at 1270 nm, whereas RB was an efficient singlet oxygen generator. Both photosensitizers sensitized block of potassium current in atrial cells, and both sensitized an increase of ionic leak current. However, when photosensitizer concentrations and illumination intensities were adjusted to match the rate of block of potassium current by the two photosensitizers, there were dramatic differences in leak current increase, both quantitatively and qualitatively. Menadione sensitized a much slower increase in leak current than did RB. Further, the leak current sensitized by MQ had a more positive reversal potential than that sensitized by RB, suggesting a less potassium-selective leak current pathway. The results suggest that, while the effects of singlet oxygen and non-singlet oxygen modification of cell membranes may be similar, there may also be significant differences in the resulting membrane permeabilities. The results also demonstrate that MQ and RB may be useful agents to study the role of singlet oxygen versus non-singlet oxygen modification of biological systems.

MEMBRANE IONIC CURRENT PHOTOMODIFICATION BY ROSE BENGAL and MENADIONE: ROLE OF SINGLET OXYGEN

Abstract –Photosensitized modification of ionic leak current and potassium current was studied in frog cardiac atrial cells using whole cell patch clamp techniques. Rose bengal (RB) and menadione (MQ) were used as photosensitizers. Separate photophysical studies of the photosensitizers in deuterium oxide solution demonstrated that MQ did not produce singlet oxygen as evidenced by the lack of luminescence at 1270 nm, whereas RB was an efficient singlet oxygen generator. Both photosensitizers sensitized block of potassium current in atrial cells, and both sensitized an increase of ionic leak current. However, when photosensitizer concentrations and illumination intensities were adjusted to match the rate of block of potassium current by the two photosensitizers, there were dramatic differences in leak current increase, both quantitatively and qualitatively. Menadione sensitized a much slower increase in leak current than did RB. Further, the leak current sensitized by MQ had a more positive reversal potential than that sensitized by RB, suggesting a less potassium‐selective leak current pathway. The results suggest that, while the effects of singlet oxygen and non‐singlet oxygen modification of cell membranes may be similar, there may also be significant differences in the resulting membrane permeabilities. The results also demonstrate that MQ and RB may be useful agents to study the role of singlet oxygen versus non‐singlet oxygen modification of biological systems.

Chemiluminescence from oxidation of formamidine amitraz. The generation of cytotoxic oxygen species and electronically excited compounds

This study was undertaken to determine the nature of the emitters occurring in chemiluminescence (CL) during the oxidation reaction of amitraz in the presence of CuSO 4. The spectral distribution of CL and fluorescence as well as quantum yield of CL were measured. The effect of singlet oxygen ( 1O 2) quenchers, catalase, superoxide dismutase, hydroxyl radical (HO .) and superoxide radical (O 2 −) inhibitors was also studied. Generation of 1O 2 ( 1 Δ g) and HO-radical during oxidation of amitraz was also confirmed by electron spin resonance detection using the spin-trapping method. Chemiluminescence intensity and light sum were found to be linearly proportional to amitraz concentration ranging from 50 μM to 2 mM. The limit of the amitraz concentration for detection was 50 μM/ml (14.65 μg/ml).

Singlet oxygen induced DNA damage and mutagenicity in a single-stranded SV40-based shuttle vector.

The effects of singlet oxygen (1O2), generated by the thermal decomposition of water soluble NDPO2 (endoperoxide of the disodium 3,3'-(1,4-naphthylidene) dipropionate), on a single-stranded shuttle vector were analysed. 1O2 induces a much higher level of breaks in the phosphodiester backbone of single-stranded than double-stranded DNA. This may be due to a higher accessibility of guanine residue, primarily damaged by 1O2. The damaged vector was transfected into monkey COS7 cells where single-stranded DNA was converted to the double-stranded replicative form DNA. After 3 days, extrachromosomal DNA was extracted and the plasmids rescued in E. coli to study mutagenesis. There is a significant increase in mutation frequency of damaged single-stranded DNA in comparison to untreated DNA. It is concluded that 1O2 induces breaks in the backbone of single-stranded DNA and that the 1O2-damaged molecules are mutated after passage through mammalian cells.

Effects of singlet oxygen on the biological activity of DNA and its involvement in single strand-break formation.

The formation of singlet molecular oxygen (1O2) has been shown to occur during photoexcitation of a variety of biological and also clinically applied compounds, such as porphyrins, psoralens and tetracyclines (see, for example references 1–3), but also occurs during enzymatic reactions including cyclooxygenase4 and chloroperoxidase.5 Regarding the biological consequences of 1O2 formation, DNA is of particular interest. 1O2 is known to react with guanine 6,7; however, results on biologically active DNA were conflicting, in particular regarding 1O2-dependent strand-break formation under neutral conditions, i.e. without alkaline treatment. 8-11 Here we emphasize two aspects of 1O2-mediated damage. First, the effect of 1O2 on the transforming activity of pBR322 and M1 3 DNA in E. coli is presented. Second, two different sources of 1O2 are employed for investigation of strand-break formation; these are microwave discharge and the thermodissociable endoperoxide of disodium 3,3′-(1,4-naphthylidene)dipropionate (NDPO2).

Lipid peroxidation in erythrocyte membranes: cholesterol product analysis in photosensitized and xanthine oxidase-catalyzed reactions.

The effects of singlet oxygen- and oxygen radical-induced lipid peroxidation on cell membrane integrity were compared, using the human erythrocyte ghost as a model system. Resealed ghosts underwent lipid peroxidation and lysis (release of trapped glucose-6-P) when irradiated in the presence of uroporphyrin (UP) or when incubated with xanthine (X), xanthine oxidase (XO) and iron. The UP-sensitized process was inhibited by azide but not by phenolic antioxidants, consistent with singlet oxygen (nonradical) involvement. This was confirmed by showing that the predominant photoproduct of membrane cholesterol was the 5 alpha-hydroperoxide. Total hydroperoxide (LOOH) content in UP-photooxidized ghosts increased linearly during the prelytic lag and throughout the period of rapid lysis. Unlike the photoreaction, X/XO/iron-dependent peroxidation and lysis was inhibited by catalase, superoxide dismutase and phenolic antioxidants, indicating O2-/H2O2 intermediacy and a free radical mechanism. Correspondingly, only radical reaction products of cholesterol were formed, notably the 7 alpha-, 7 beta-hydroperoxide pair. Membrane lysis had a distinct lag as in photooxidation; however, the LOOH profile was more complex, with an initial lag followed by a sharp increase and then slow decline. X/XO/iron-induced lysis commenced when LOOH levels were 2-3 times higher than in photosensitized lysis, suggesting that the pathways of membrane lesion formation are different in the two systems.(ABSTRACT TRUNCATED AT 250 WORDS)

Identity of succinate dehydrogenase in chemotrophically and phototrophically grown Rhodospirillum rubrum

The specific succinate dehydrogenase (EC 1.3.99.1 succinate: phenazine methosulfate oxidoreductase) activity of membranes of aerobically grown Rhodospirillum rubrum was found to be 4–7-fold greater than that of membranes from phototrophically grown cells. The enzymes obtained from cells grown under both conditions were compared in crossed immunoelectrophoresis and were shown to have the same electrophoretic mobility and immunological identity. As succinate dehydrogenase activity is associated with chromatophore membrane in phototrophically grown R. rubrum, this study demonstrates the presence of a chromatophore-specific component in aerobic cells. The succinate dehydrogenase activity of Triton extracts of membranes from phototrophic cells was subject to photoinactivation. The succinate dehydrogenase extracted from the membranes from aerobic cells was photoinactivated only if a bacteriochlorophyll a extract was added to the enzyme preparation. As this photopigment-dependent photoinactivation was inhibited by NaN3 or by a N2 atmosphere, it is attributed to the effects of singlet oxygen sensitized by bacteriochlorophyll a.