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Biomedical subjects

A Samuni

Publications and source records attributed to A Samuni.

At least 73 records · Page 4Linked to original sources
PubMed1986

Cellular targets of adriamycin-induced damage in Escherichia coli.

The cellular targets of adriamycin (ADR) activity were studied in Escherichia coli by following colony forming ability and various cellular functions. The parameter exhibiting the best correlation with mortality was inhibition of RNA synthesis. Total DNA synthesis was inhibited to a lesser extent, but may reflect a concurrent inhibition of replication and stimulation of DNA repair activity. Protein synthesis, membrane function and rate of oxygen consumption were affected later. No extensive DNA fragmentation was observed. The inhibition of RNA synthesis was independent of the stringent response and of inhibition of DNA synthesis induced by nalidixic acid. ADR activated the SOS repair system, and the lesions induced by the drug could be repaired by recA dependent functions. These results indicate that the primary activity of ADR was directed against the DNA and interfered with the DNA template function.

Adenosine Triphosphate↗
PubMed1986

On the spin trapping and ESR detection of oxygen-derived radicals generated inside cells.

Recently several attempts to identify oxygen-derived radicals in whole cells by spin trapping and electron spin resonance have been reported by using 5,5-dimethyl-1-pyrroline-N-oxide as the spin trap. In the present study, the feasibility of this method is examined. Chinese hamster V79 cells and human erythrocytes served as the test systems, while OH radicals were generated by gamma radiolysis. Several spin traps were used to scavange the radicals and a distinction between exo- and endocellular ESR observable species was achieved using tri(oxalato) chromiate(III) as a line broadening agent. To distinguish between exo- and endocellular sites of radical formation, we studied the effects of high molecular weight scavengers (polyethylene glycols), which do not enter the cell. Various possible obstacles associated with trapping and detecting the radicals inside the cells were examined. The results indicate that the primary radicals react with the spin traps. However, these spin adducts decayed within the cells. Cellularly induced decay of 2-hydroxy-5,5-dimethyl-1-pyrrolidinyloxyl radical presented the major difficulty in detecting the endogenous radicals, and potential experimental approaches to overcome this difficulty are discussed.

Animals↗
PubMed1986

Enhancement of misonidazole cytotoxicity by iron.

The toxicity of misonidazole (MISO) to hypoxic Chinese hamster ovary (CHO) cells in serum-free medium is enhanced by Fe(III)-EDTA. Enhancement of MISO cytotoxicity by a factor of 1.6 was seen with 2 microM Fe(III)-EDTA, while 200 microM Fe(III)-EDTA results in sensitization by a factor of 2.0. Treatment of CHO cells with the iron chelator desferal resulted in protection against the hypoxic cytotoxicity in MISO (approximate protection factor of 2.5 with 100 microM desferal). Similar results were obtained with Chinese hamster V79 cells. Fe(III)-EDTA also enhanced binding of [2-14C] MISO to cellular macromolecules while desferal decreased binding of MISO to cellular macromolecules. These results suggest that iron plays an important role in the reductive metabolism of MISO and that modification of the intracellular metal ion status may be a useful approach to modulating the biological effect of nitro compounds.

Animals↗
PubMed1986

Physical and chemical modifications of adriamycin:iron complex by phospholipid bilayers.

Adriamycin (ADM) and the ADM:Fe(III) complex both interact with phosphatidylcholine bilayers in aqueous vesicle dispersions. The immediate interaction of either ADM or ADM:Fe(III) with phospholipid causes little change in their absorption or emission spectra, but considerably increases the steady-state fluorescence anisotropy of both species. This is followed by a conversion of the ADM:Fe(III) complex (but not of metal-free ADM) into a new compound in periods ranging from minutes to hours depending upon the Fe(III) concentration. This reaction does not require the presence of unsaturated acyl chains, net negatively charged phospholipid head groups, or the participation of molecular oxygen. This new compound has a characteristic absorption and fluorescence emission spectra which differ from those of the ADM:Fe(III) or of metal-free ADM. It can be isolated from the aqueous lipid dispersion by Folch extraction under acidic conditions. It is very lipophilic in comparison to ADM or the ADM:Fe(III) complex. It may be similar to the compound reported to form between cardiolipin and Adriamycin. Preliminary results indicate that it also forms spontaneously in intact biological membranes. Its highly lipophilic character may confine it to bilayers and membranes.

Doxorubicin↗
PubMed1985

The contribution of endogenous and exogenous effects to radiation-induced damage in the bacterial spore.

Radical scavengers such as polyethylene glycol 400 and 4000 and bovine albumin have been used to define the contribution of exogenous and endogenous effects to the gamma-radiation-induced damage in aqueous buffered suspensions of Bacillus pumilus spores. The results indicate that this damage in the bacterial spore is predominantly endogenous both in the presence of 1 atmosphere of oxygen, and in anoxia.

Animals↗
PubMed1984

Conformational adaptation of RTEM beta-lactamase to cefoxitin.

Cefoxitin, a poor substrate of the RTEM beta-lactamase (penicillin amido-beta-lactam hydrolase, EC 3.5.2.6), induces a reversible change in the conformation of the enzyme. The change is manifested in gradual loss of catalytic activity and increased susceptibility to proteolytic inactivation. It is prevented by antibodies, which stabilize the native conformation. By contrast, divalent cations, which have no effect on the native enzyme, delay recovery from the cefoxitin-induced state, presumably by reacting with sites made accessible in the partly unfolded enzyme. Prolonged exposure to excess of cefoxitin causes a similar delay. The kinetic evidence, namely, the initial burst of consumption of cefoxitin and the subsequent gradual recovery of activity with better substrates, appears to be consistent with acylation of the active site by cefoxitin followed by a slower deacylation step [Fisher et al. (1980) Biochemistry 19, 2895-2901]. However, additional evidence leads us to conclude that the kinetics observed reflect deformation of the active site, rather than its blockage, by cefoxitin. Of most significance is the transient change in specificity, i. e. a preferential interaction of the recovering enzyme with substrates which are closest in structure to cefoxitin.

Antibodies↗
PubMed1984

Controlled release of radioprotective agents from matrix tablets--effect of preparative conditions on release rates.

Release rates of radioprotective agents from insoluble matrix tablets were measured as a function of ethylcellulose/stearic acid ratio and active ingredient concentration in the matrix. The influence of the compacting pressure applied during tablet formation on the release of these aminothiol compounds was also examined. The kinetic data conformed with the Higuchi square root equation and first order release. As both plots were linearly acceptable, a statistical method for release mechanism identification using the kinetic experimental results obtained without any further transformation was used. This non-linear regression search procedure accompanied by the chi 2-square test has shown that that aminothiol release from the matrix tablets definitely follows the Higuchi square root equation. Increasing the ethylcellulose amount in the matrix consequently improves the degree of wettability and leads to a faster rate of solvent penetration. This tends to release the aminothiols more rapidly from the matrix tablets. Solvent penetration, which also follows a square root of time relationship, is probably the rate-limiting factor in the release process. The linear increase in release rates of the aminothiols observed with ethylcellulose concentration is explained by a parallel increase in the porosity of the matrix tablets. Increase in the drug concentration in the tablet increases the cysteine hydrochloride release rate and decreases the cysteamine hydrochloride release rate. A similar effect was also observed by applying increasing compacting pressure during matrix tablet formation. It was suggested that these two experimental factors differently affect the internal structure of the matrix during the preparation process.(ABSTRACT TRUNCATED AT 250 WORDS)

Cellulose↗
PubMed1984

Roles of copper and O(2) in the radiation-induced inactivation of T7 bacteriophage.

The effect of copper on the radiation damage induced in T7 bacteriophage has been investigated. The phages were gamma-irradiated and the effects of copper(II) ions in the presence of various additives and radical scavengers were examined in an attempt to better understand the effect of transition metal ions on the role of free radicals, particularly superoxide, in biological damage. The present work extends a study previously done on isolated enzyme to a whole biological entity. Copper(II) ions even at very low concentrations enhanced the lethal effect of radiation. This sensitization was observed in both the presence and the absence of oxygen. The effect of copper could be reverted by chelating agents such as EDTA or 1,10-phenanthroline. Hydrogen peroxide enhanced the sensitizing effect of copper, though little if any protection was provided by catalase or SOD. High molecular weight scavengers of free radicals in the presence of both copper(II) and hydrogen peroxide had no protective effect. (This is in contrast to metal-free systems where, although such scavengers are incapable of penetrating the phages, they protect them against inactivation.) These scavengers, without added H2O2, afforded only slight protection to the irradiated phages in the presence of Cu. Low molecular weight scavengers of free radicals reduced but did not eliminate the sensitizing effect of copper. The sensitizing effect of copper was also observed with other T-odd phages, but not with the T-even series. Copper(II) ions under similar experimental conditions did not sensitize T4 or T2 phages but rather had a protective effect. The results are interpreted in terms of a site-specific Fenton mechanism according to which the binding of the metal ion to the phages is a prerequisite for the occurrence of the biological damage. The results also indicate that most of the copper effect is endogenous. This is in accord with the failure of copper to sensitize the T-even phages, which differ by the rigidity and permeability of their outer coat structures.

Cesium Radioisotopes↗
PubMed1983

On the cytotoxicity of vitamin C and metal ions. A site-specific Fenton mechanism.

The toxicity of ascorbate towards phage lambda and the phages T2-T7 has been investigated. At room temperature the T-odd and lambda bacteriophages are highly susceptible to ascorbate-induced damage, whereas the T-even phages are practically resistant. The toxicity of ascorbate is dependent on the presence of copper (or iron) and oxygen, although oxygen is not required in the presence of H2O2. Hydrogen peroxide is essential for the ascorbate-induced phage inactivation and the damage is prevented by catalase. At the concentrations used, most of the copper ions are bound to the phage particles. Chelating agents such as EDTA or histidine fully protect the phages, whereas salicylate only reduces the rate of phage inactivation. OH scavengers such as sucrose, formate, mannitol, tert-butyl alcohol or poly(ethylene glycol) have no protective effect. Experiments with DNA labeled phages indicate that both phage adsorption and DNA injection are impaired as a result of the exposure to ascorbate and copper. The failure to express the viral genetic information as a result of single and double-strand breaks in the DNA, probably also contribute to the loss of the plaque-forming ability of the phages. The results are interpreted in terms of a 'site-specific' Fenton mechanism according to which the binding of the transition metal ions to the biological target is a prerequisite for the production of damage. The bound metal ion is reduced either by O(2), ascorbate or other reductants and is subsequently reoxidized by H2O2 yielding OH. radicals. This cyclic redox reaction of the metal generates OH. radicals which react with vital macromolecules with a high probability of causing 'multi-hit' damage. This 'site-specific' formation of OH. radicals, which takes place near the target molecules, accounts both for the high damaging efficiency and for the failure of OH. scavengers to protect against it.

Ascorbic Acid↗
PubMed1982

Tissue distribution of 2- and 4-[203Hg]-estradiol in mammary-tumor-bearing rats.

The newly synthesized 2-[203Hg]-estradiol-17 beta and 4-[203Hg]-estradiol-17 beta were injected into Fischer female rats bearing transplanted mammary adenocarcinomas and into Sprague-Dawley female rats bearing spontaneous mammary tumors. Four days after injection, tumor to blood ratios (and uterine to blood ratios) in the various groups were between 5 and 14, compared to a ratio of unity observed in normal mammary glands. When injected into male rats, the accumulation of 4-[203Hg]-estradiol in the prostate and in the epididimis was very low. With minute doses of 4-[203Hg]-estradiol injected into healthy male rats, the whole-body retention of the drug was found to decrease exponentially with time, and biphasic first order kinetics were observed. With pharmacological doses of the same drug, the clearance exhibited a biphasic pattern.

Adenocarcinoma↗
PubMed1981

Comparative studies of the aromatization of testosterone and epitestosterone by human placental aromatase.

The aromatization of epitestosterone (17 alpha-hydroxy-4-androsten-3-one) and testosterone by lyophilized human placental microsomes was studied. Upon incubation of epitestosterone, 12% was converted to 17 alpha-estradiol, 15% to 19-keto-epitestosterone (17 alpha-hydroxy-4-oxo-4-androsten-19-al), 10% to 19-hydroxyepitestosterone (17 alpha, 19-dihydroxy-4-androsten-3-one), and about 10% to several unidentified products. A similar incubation with testosterone resulted in 60% conversion to 17 beta-estradiol; 30% was unchanged. At increasing substrate concentrations (0.1-50 microM), the aromatization rate of epitestosterone increased gradually and did not reach a plateau, whereas aromatization rate of testosterone plateaued at about 3 microM. The presence of either testosterone or 17 beta-estradiol in concentrations 0.1-10 times the concentration of epitestosterone inhibited the aromatization of epitestosterone by about 70%, while the aromatization of testosterone was not inhibited by either epitestosterone or 17 alpha-estradiol. Lyophilization of fresh microsomes or storage of the lyophilized microsomes at -20 C greatly reduced the aromatizing activity upon epitestosterone but not upon testosterone. These results suggest that the aromatizing system for epitestosterone is different from that for testosterone.

Aging↗
PubMed1979

Quaternary structure of methemoglobin. Pulse radiolysis study of the binding of oxygen to the valence hybrid.

The pulse radiolysis of solutions of adult human methemogolbin was used in order to reduce a single heme iron within the protein tetramers. The valence hybrids thus formed were reacted with oxygen. Kinetics of the reactions were studied. The effects of pH and inositol hexaphosphate were examined. The kinetics of the ligation of oxygen to stripped valence hybrids showed a single phase behavior at the pH range 6.5 to 9. As the pH was lowered below 6.5, a second, slower phase became apparent. In the presence of inositol hexaphosphate, above pH 8, the kinetics of oxygen binding was of a single phase. As the pH was lowered, a transition to a second, slower phase was noticed. Below pH 7, the slower phase was the only detectable one. The analysis of the relative contribution of the faster phase to the total reaction as a function of the pH showed a typical transition curve characterized by a pK = 7.5 and a Hill parameter n = 2.9. On this basis, it is concluded that human adult stripped methemoglobin resides in an R quarternary structure, while the presence of IHP stabilizes the T structure at pH below 7.5. This transition between the quaternary structures of methemoglobin cannot be accounted for by the switch between the high spin and the low spin states of the ferric iron. This switch of spin state takes place at pH greater than 8.2.

Heme↗
PubMed1979

Dynamics of pH-induced spectral changes in bacteriorhodopsin.

The kinetics of the spectral shift induced in bacteriorhodopsin by low pH are investigated by using the rapid-mixing, stopped-flow technique. The generation of the acid form of the chromophore (A605) occurs in two distinct steps: a fast process (t1/2I = 21 +/- 4 ms) is followed by a much slower reaction (t1/2II = 6 +/- 2 s). The observations are interpreted in terms of neutralization of an acid group in the neighborhood of the retinyl chromophore, the double-staged kinetics being attributed to cooperative effects between chromophores. The method may serve as a tool for studying the kinetics of proton migration across the purple membrane.

Bacteriorhodopsins↗
PubMed1978

Quaternary states of methemoglobin and its valence-hybrid. A pulse radiolysis study.

Using the pulse radiolysis technique on solutions of stripped adult human methemoglobin, we found that the heme-iron within a single subunit in the tetramer was reduced to iron(II). The valence-hybrid thus formed was reacted with oxygen and with carbon monoxide. Kinetics of the reactions were studied. The effects of pH, inositol hexaphosphate, and temperature on these reactions were examined. The kinetics of the ligation of O2 and CO were used to characterize the affinity states of the valence-hybrid and its parent methemoglobin. Our results support the description of stripped methemoglobin A as residing in an R state. In the presence of inositol hexaphosphate methemoglobin is stabilized in a T state, but it switches into a high affinity state when the pH is raised a0ove 8.0. This structural transition was not found to coincide with the switch of spin state of the heme-iron that accompanies the ionization of water in aquomethemoglobin A.

Adult↗