E. Ben‐Hur

Bio: E. Ben‐Hur is an academic researcher from Israel Atomic Energy Commission. The author has contributed to research in topics: Thymidine & Bromodeoxyuridine. The author has an hindex of 5, co-authored 5 publications receiving 135 citations.

Photochemical reactions of chlorpromazine; chemical and biochemical implications.

Abstract: — The photoexcited chlorpromazine reacts with methanol to yield promazine and 2-methoxypromazine by two different reaction pathways: hydrogen atom abstraction and nucleophilic attack. respectively. When the photoexcitation of chlorpromazine is performed in the presence of protein or nucleic acids, chlorpromazine binds to the biopolymer. This binding is drastically pH-dependent and correlates to the phototoxic effect exhibited in chlorpromazine—photosensitization of E. coli. No photodynamic damage of E. coli attributed to CPZ-sensitization of molecular oxygen could be detected.

Enhancement of thermal killing by polyamines. I. Survival of Chinese hamster cells.

Abstract: Exposure of Chinese hamster cells to polyamines at an elevated temperature (42 degrees C) results in synergistic cell killing. The effectiveness of polyamines in potentiating thermal killing decreases in the following order: spermine greater than spermidine greater than cadaverine greater than putrescine. The magnitude of the synergism increases with exposure time. The survival curves, when plotted as a function of polyamine concentration, display a shoulder during 1 h exposure at 42 degrees C, followed by exponential cell killing. Longer exposure times eliminate the shoulder and result in steeper slopes of the survival curves. The effect is maximal when exposure to polyamines and heat is simultaneous. Separation in time between the two treatments causes a rapid disappearance of the synergism. The order of application is of only minor importance in this regard. The results suggest that the intracellular level of spermine may be a major factor in determining heat sensitivity of Chinese hamster cells.

Dna damage and repair: induction and removal of thymine dimers in ultraviolet light irradiated intact water plants

Abstract: — The production of UV-induced thymine dimers and their fate upon post-irradiation incubation in the dark was studied in DNA of the intact water plants Wolffia microscopica and Spirodela polyrhiza. The results demonstrate production of thymine dimers, and the ability of the plant cells to remove the dimers from their DNA. The rate of removal is rapid during the first few h of post-irradiation incubation in the dark. It continues at a slower rate for the next 24–48 h, at which time it is essentially complete. The disappearance of thymine dimers in light or in the dark is analogous to the well-known processes in other biological systems, namely, photoreactivation and dark excision.

PHOTOCHEMISTRY OF THE BISBENZIMIDAZOLE DYE 33258 HOECHST WITH BROMODEOXYURIDINE AND ITS BIOLOGICAL EFFECTS ON BrdUrd‐SUBSTITUTED ESCHERICHIA COLI

Abstract: — Exposure of BrdUrd-substituted E. coli cells to 360 nm light in the presence of the bisbenzimi-dazole dye 33258 Hoechst increases their sensitivity dramatically. Mutant cells deficient in excision repair of DNA damage (uur B) are more sensitive than wild type cells, indicating that the cells are able to repair this type of damage. However, they perform only a limited amount of liquid holding recovery (LHR). Exposure of the dye with BrdUrd to near UV light in solution results in the appearance of two BrdUrd derived photoproducts. One appears to be deoxyuridine, and the other — an adduct of BrdUrd-dye. The adduct is acid labile and as a result only uracil is observed in acid-hydrolyzates of DNA after exposure of BrdUrd-substituted cells to 360 nm light in the presence of 33258 Hoechst. The production of uracil is linearly dependent on light exposure. Cells in which 85% of thymidine was replaced by BrdUrd are unable to remove more than 5–10% of uracil from their DNA during postirradiation incubation. However, when only 4% of thymidine is replaced, about 50% of the uracil is removed during 30min incubation after exposure. The results are consistent with our previous work, indicating that BrdUrd interferes with repair via excision-resynthesis. A working hypothesis is suggested to explain this interference.

Photochemical interaction of furocoumarins with bromodeoxyuridine and polydeoxy‐nucleotides containing bromodeoxyuridine: its biological implications

Abstract: — The photoreaction of 5-bromodeoxyuridine (BUdR) exposed to 360 nm light in the presence of the furocoumarins, 4,5′,8-trimethylpsoralen (TMP) and 8-methoxypsoralen (&MOP), was studied and compared to those of thymidine. BUdR reacted with furocoumarins, producing cyclobutane-containing adducts, as does thymidine. Furocoumarins reacted also with BUdR-containing polymer, poly(dA-BUdR) in the double stranded form, at a rate similar to that of thymidine-containing polymer, poly(dA-dT). Polyamines, which slow the photoreactions of TMP with DNA, had no effect on its binding to the two former polynucleotides. It is suggested that because of the similar photoreactions of BUdR and thymidine with furocoumarins, this combination could be used to elucidate the mechanism by which BUdR sensitizes biological systems. In Escherichia coli some sensitization by BUdR of TMP plus 360 nm light killing was observed. It is therefore concluded that at least part of the sensitization of bacteria by BUdR to UV and ionizing radiation is caused by interference with the repair processes. Since no such sensitization was observed in a uvr B mutant, BUdR apparently impairs the efficiency of the excision resynthesis pathway of repair.

Photochemistry and photobiology of psoralens.

Abstract: — The photochemistry and photobiology of psoralens have been rcvicwed on the basis of selected literature. In addition to the well establishcd photoaddition of psoralens to DNA. photoreac-tions involving RNA. tRNA and proteins warrant further studies. Although thymine seems to be one of the predominant bases for the psoralen photocycloaddition in DNA. photoreactions of other bases such as adenine and the mechanisms other than cycloaddition should also be investigated in order to fully assess the specificity of psoralen photoreactions and their application BS a probe for biopolymer structure and as a tool for photobiological studies of microorganisms. The relativc photobiological importance of monoaddition vs crosslinking of psoralens to nucleic acids also remains to be fully elucidated.

Photodegradation of pharmaceuticals in the aquatic environment: A review

Abstract: A review with 310 references. Photochemical degradation is likely to be an important loss mechanism for many pharmaceutical pollutants in surface waters. This review summarizes the current knowledge of the photochemical behavior of pharmaceuticals and highlights the use of the fundamental photochemistry and phototoxicity literature to help understand and predict the aquatic fate of pharmaceuticals. Naproxen and diclofenac are shown to exemplify the idea that photochemical behavior obtained from fundamental photochemistry studies can be related to environmental conditions. There are, however, numerous compounds that have been found in environmental matrices for which no photochemistry data relatable to environmental conditions are available. It will be necessary to combine the results available in the large body of fundamental photochemistry and phototoxicity literature with laboratory and field experiments designed to determine direct and indirect photolysis rates and to identify photoproducts. This course will lead to a thorough understanding of the role of photodegradation on the fate and impact of pharmaceutical pollutants.

UV-B-Inducible and Temperature-Sensitive Photoreactivation of Cyclobutane Pyrimidine Dimers in Arabidopsis thaliana.

Abstract: Removal of cyclobutane pyrimidine dimers (CBPDs) in vivo from the DNA of UV-irradiated eight-leaf seedlings of Arabidopsis thaliana was rapid in the presence of visible light (half-life about 1 hour); removal of CBPDs in the dark, presumably via excision repair, was an order of magnitude slower. Extracts of plants contained significant photolyase in vitro, as assayed by restoration of transforming activity to UV-irradiated Escherichia coli plasmids; activity was maximal from four-leaf to 12-leaf stages. UV-B treatment of seedlings for 6 hours increased photolyase specific activity in extracts twofold. Arabidopsis photolyase was markedly temperature-sensitive, both in vitro (half-life at 30°C about 12 minutes) and in vivo (half-life at 30°C, 30 to 45 minutes). The wavelength dependency of the photoreactivation cross-section showed a broad peak at 375 to 400 nm, and is thus similar to that for maize pollen; it overlaps bacterial and yeast photolyase action spectra.

The Phthalocyanines: A New Class of Mammalian Cells Photosensitizers with a Potential for Cancer Phototherapy

Abstract: SummaryPhthalocyanines, porphyrin-like compounds with maximum absorption in the red, which were previously reported to localize selectively in tumours, have been shown to be efficient photosensitizers of mammalian cells in culture, thus making them possible candidates to replace haematoporphyrin derivatives in cancer phototherapy.