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Biomedical subjects

E Ben-Hur

Publications and source records attributed to E Ben-Hur.

At least 109 records · Page 6Linked to original sources
PubMed1981

Effect of Panax ginseng saponins and Eleutherococcus senticosus on survival of cultured mammalian cells after ionizing radiation.

Panax ginseng saponin and Eleutherococcus senticosus extract were applied to cells in culture in order to assess the effect of these substances on resistance to gamma-irradiation. Eleutherococcus was slightly radio protective. However, ginseng saponin at a dose of 10 microgram/ml was significantly radioprotective (Do = 2.25 Gy) compared to control (Do = 1.80 Gy) when it was present prior to gamma-irradiation. It enhanced radiation response if it was also present for 4-6 hours after gamma-irradiation (Do = 1.10 Gy). Ginseng-treated cells made 30% less RNA and 14% more protein during a 1 hour pulse of labeled intermediates. The cells were morphologically altered. It is concluded that ginseng saponin can increase radiation resistance. The effect is indirect, due to alterations in cell physiology rather than DNA repair processes.

Animals↗
PubMed1980

pH dependence of the phototoxic and photomutagenic effects of chlorpromazine.

The pH dependence of the phototoxic effects of chloropromazine (CPZ) in Escherichia coli, Salmonella typhimurium and Chinese hamster cells were studied at pH 6--8. All three biological systems displayed higher photosensitization of the drug at lower pH-values. In S. typhimurium the combined action of drug and light also showed mutagenic activity which correlated with toxicity when exposed at pH 7 or 8. When solutions of protein or DNA and CPZ were exposed to near ultraviolet (UV) light, the drug became covalently attached to the macromolecules. This binding was pH dependent but did not correlate with the effects in vivo. It was found however that the permeability of the cells to the drug was enhanced at lower pH-values. It is suggested that the enhanced entrance of CPZ at lower pH-values into the cells facilitated the drug binding to DNA, RNA and proteins within the cells upon light exposure, and that this is the basis for the enhanced phototoxicity and mutagenicity of CPZ.

Animals↗
PubMed1980

Application of mutagenicity test for milk.

Mutagenic activity in milk and milk products was tested by the Salmonella mammalian-microsome mutagenicity test (Ames test). Salmonella mutants susceptible to base-pair substitution and frame-shift mutagens gave positive results with heat-sterilized milk, particularly after activation by the S-9 fraction of microsomes. Maximum increase of His+ revertants was more than twice the spontaneous increase. The chemical specification of the mutagenic activity was not yet defined, but it was present in the chloroform extract of milk.

Animals↗
PubMed1979

Enhancement of thermal killing by polyamines. IV. Effects of heat and spermine on protein synthesis and ornithine decarboxylase activity.

Protein synthesis is shown to be very heat-sensitive in Chinese hamster cells. It is shut off completely following 15-20 min at 42 degrees C whereas RNA and DNA syntheses are affected only after much longer exposure times. Cells recover from inhibition of protein synthesis upon transfer to 37 degrees C. The degree of recovery is inversely related to the duration of heat exposure and it fits cell survival quantitatively. Cells which become temporarily heat-resistant by prior heat-treatment, are able to recover translational capacity even after a very long exposure to heat (4 h at 42 degrees C). Spermine, which enhances heat-induced cell killing, does not increase the response to heat of protein, RNA and DNA synthesis. Ornithine decarboxylase (ODC, EC 4.1.1.17) activity is lost exponentially following a 20 min lag period during exposure at 42 degrees C. The half-life observed (12 min) is in agreement with the reported values of half-life of decay of ODC in other systems. It is concluded that the loss of activity is due to the shut-off of translation. The activity of ODC is recovered upon transfer to 37 degrees C. The presence of spermine during heating does not affect the loss of enzyme activity but delays its recovery by about 3 h upon transfer to 37 degrees C.

Acid Phosphatase↗
PubMed1978

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

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.

Animals↗
PubMed1978

Enhancement of thermal killing by polyamines. II. Uptake and metabolism of exogenous polyamines in hyperthermic Chinese hamster cells.

The uptake and metabolism of the polyamines spermine, spermidine, cadaverine and putrescine, previously shown to potentiate heat sensitivity, were studied in cultured Chinese hamster cells. Heat (42 degrees C) causes enhanced uptake of exogenously supplied polyamines into the acid-soluble fraction of the cells. Putrescine is taken up exceptionally fast at 37 degrees C, about 10 times faster than its homologue, cadaverine. This uptake is slower at 42 degrees C. The polyamines taken up were metabolized to some extent and the metabolites were similar at 37 degrees C and 42 degrees C except in the case of putrescine. These results suggest that potentiation of heat-sensitivity is probably mediated by the polyamines as such and not by their metabolites. Polyamines slightly protect the cells against the inhibitory effect of heat on RNA and protein synthesis. It is suggested that exogenous polyamines interact with nucleic acids inside the cell, and this interaction may underlie their synergism with heat. The exact nature of this interaction and the way it leads to enhanced thermal sensitivity are still obscure.

Animals↗
PubMed1978

Photosensitized inhibition of nitrate reductase induction by 4,5',8-trimethylpsoralen and near ultraviolet light.

4,5' ,8-trimethylpsoralen photosensitizes the inhibition of the induction of nitrate reductase in XD cells of tobacco, by near ultraviolet light. The photosensitization depends on the concentration of 4,5' ,8-trimethylpsoralen and the near ultraviolet light dose. Concomitant with the inhibition of nitrate reductase induction there is a severe inhibition of DNA and RNA synthesis. Oxygen uptake and protein synthesis are not affected. Translation of preexisting mRNA coding for nitrate reductase is insesitive to 4,5' ,8-trimethylpsoralen and near ultraviolet light. It is concluded that the DNA of these cells is the target for the photochemical reaction of 4,5' ,8-trimethylpsoralen. The template activity of the DNA is inhibited, and the expression of the genome thereby prevented. Translation of preexisting nRNA is not affected.

Coumarins↗