INTERACTION OF IONIZING RADIATION AND ULTRAVIOLET-LIGHT IN DIPLOID YEAST STRAINS OF DIFFERENT SENSITIVITY*

Abstract— The interaction of ionizing radiation and UV-light regarding colony forming ability in 3 diploid yeast strains of Saccharomyces cerevisiae was investigated. A wild type and two radiation sensitive mutants were used. No difference in the response of the three strains could be detected when the UV dose was given first, but when ionizing radiation was applied shortly before UV, there were essential differences depending on the kind of mutation. The involvement of repair mechanisms in the interaction is discussed.     

Increased levels of 8-hydroxy-2'-deoxyguanosine in Drosophila larval DNA after irradiation with 364-nm laser light but not with X-rays

Exposure to UVA light causes damage to cellular components such as DNA and membrane lipids. We showed previously that UVA irradiation can induce mutations in Drosophila larvae and that the major lesions responsible for mutations were not thymidine dimers when wavelengths tested became longer. The use of a longer wavelength with UVA laser apparatus (364 nm) has made it possible to test the effects of this powerful light in biological organisms. In the present study, we irradiated third instar larvae of the urate-null Drosophila mutant strain y v ma-l, which is sensitive to oxidative stress, and compared the effects of 364 nm light irradiation with the effects of X-rays. To assay viability, some of the larvae were kept at 25 degrees C until they eclosed in order to obtain a measure of viability. The remaining larvae were used to measure the amount of 8-hydroxydeoxyguanosine (8-OHdG), an indicator of oxidative DNA damage. The amount of 8-OHdG increased and viability decreased in response to increased UV dose in both the y v ma-l and wild-type strains. With irradiation of 600 kJ m(-2), 8-OHdG/10(6)dG was 7.2 +/- 3.2 and 6.2 +/- 2.0 in y v ma-l and wild-type strains, respectively, whereas the respective levels were 2.2 +/- 0.6 and 2.3 +/- 0.8 without irradiation. Our results indicated that irradiation with a 364-nm laser light caused significant oxidative damage in Drosophila larval DNA; however, induction of the damage was not prohibited by urate. To the best of our knowledge, this is the first report of a study in whole animals that shows increased levels of 8-OHdG in response to 364-nm UVA. X-ray ionizing radiation is also thought to generate reactive oxygen species in irradiated cells. We found that the amount of 8-OHdG in DNA following X-ray radiation remained unchanged in both strains, though survival rates were affected. X-ray-generated oxidative damage in Drosophila cells was followed by cell death but not DNA base oxidation, and the damage was suppressed by urate. The overall results suggest significant differences in the major in vivo oxidative damage caused by 364-nm light and X-rays.     

HOST-CELL REACTIVATION OF NON-LETHAL ULTRAVIOLET-EFFECTS

Abstract— Delay of intracellular growth of u.v.-irradiated bacteriophage T1 and Λ was compared in host-cell reactivating [HCR(+)] and non-host-cell reactivating [HCR(—)] bacterial strains. At a given phage survival level, intracellular growth delay occurs to the same extent in HCR (+) and HCR (-) strains; at a given absolute u.v.-dose, this delay is considerably more expressed in HCR (-) than in HCR (+) strains. Therefore, it does not reflect the time required for the HCR repair of otherwise lethal U.V. lesions. The results rather suggest that U.V. causes, besides lethal lesions, stable photoproducts in the DNA, which are a priori non-lethal, and which are recognized and efficiently eliminated by the HCR repair system. The HCR enzymes likewise act on (non-lethal) u.v.-photoproducts causing prophage induction in lysogenic cells. Consequently, one obtains the maximum induction effect in a lysogenic HCR (-) strain at a much lower u.v.-dose than in the corresponding lysogenic HCR (+) strain. In contrast, u.v.-damage causing loss of the host cell's capacity to support growth of unirradiated phage is not affected by HCR.     

STUDIES OF THE ROLE OF THE COAT PROTEIN IN THE U.V. PHOTOINACTIVATION OF U(1) AND U(2) STRAINS OF TMV*

Abstract— Two properties of the u.v. inactivation process in the u.v. sensitive U(2) strain have been investigated: (1) The increased binding of protein to RNA induced by irradiation of the virus at 254 nm; (2) The action spectrum for u.v. inactivation of U(2) between 250 nm and 285 nm. The extent of the u.v. induced binding of protein to RNA is similar to that previously found in the resistant U(1) strain, thereby eliminating the possibility that the capacity for this binding phenomenon bears any correlation to the difference in u.v. sensitivities of these two viruses at 254 nm. The results indicate that the radiation induced interaction of protein and RNA in U(1) and U(2) are probably similar. The action spectrum for U(2) resembles the absorption spectrum of the RNA between 250 nm and 285 nm implicating the RNA as the primary absorber leading to inactivation of the virus in this region of the spectrum. Quantum yields calculated for U(2) virus and free TMV-RNA irradiated at 254 nm reveal that the irradiated free RNA may be as much as 1–4 times more sensitive to inactivation at this wavelength than RNA in the intact virus. It is concluded that the coat protein of U(2) probably offers some protection to the enclosed RNA against u.v. damage at 254 nm, therefore, the difference in u.v. sensitivity between U(1) and U(2) TMV at this wavelength is a consequence of a difference in the degree of protection offered by the respective coat proteins to the enclosed RNA.     

RECOVERY OF HAEMOPHILUS INFLUENZAE FROM ULTRAVIOLET AND X-RAY DAMAGE

Abstract— Results of experiments on reactivation of ultraviolet (u.v.)-irradiated Haemophilus influenzae and cellular reactivation of u.v.-damaged transforming deoxyribonucleic acid (DNA) and bacteriophage are reported. Liquid-holding recovery (LHR) is small for the u.v.-sensitive mutant BC100 which, relative to the wild type, also has greatly reduced host-cell reactivation (HCR) of u.v.-inactivated phage, and competent cultures show reduced competent cell reactivation (CCR) of u.v.-inactivated transforming DNA. BC100 cells can be transformed with DNA isolated from the wild type strain Rd to a u.v. resistance similar to that of Rd, and irradiation of the DNA reduces the transformation frequency for this marker (uvr). The u.v.-resistant mutant BC200 displays very little LHR under the usual conditions where reactivation occurs after plating. The colony-forming ability (cfa) of irradiated BC200 is greater than that of Rd, but HCR and CCR are the same on this mutant as on the wild type. The major difference between Rd and BC200 is the enhanced u.v. survival of cfa of the latter. It was determined that this difference reflects cell lysis of irradiated Rd and lack of lysis in BC200 cultures. That lysis is closely correlated with damage to the bacterial chromosome is suggested by the finding that the lytic response of Rd (as determined turbidimetrically) can be negated by the liquid-holding procedure, but lysis of BC100 (which lacks comparable DNA-repair ability) can be only partially inhibited by this procedure. LHR occurs when post-plating dark recovery is incomplete, is temperature-sensitive, and occurs unimpeded when post-u.v. protein synthesis is inhibited by chloramphenicol. It is suggested that enzymatically catalyzed reactivation of DNA occurs or is initiated during liquid-holding of u.v.-irradiated H. influenzae Rd and that the necessary enzyme(s) exists prior to appearance of u.v. lesions in the DNA. Results are reported for X-ray inactivation of transforming DNA as assayed on BC100, Rd and BC200 and of the cfa of the three strains.     

EFFECTS OF DOSE FRACTIONATION ON ULTRAVIOLET SURVIVAL OF ESCHERICHIA COLI

Abstract— Exposure of E. coli B/r and B at low average dose rates of u.v. radiation (2537 Å), produced either by fractionated doses or by continuous irradiation at a very low dose rate (80 ergs/mm²/hr), results in much increased survival compared to single exposure at high dose rate. This increase is attributed to repair taking place during the irradiation period. The effect is small in the repair-deficient strains E. coli B_8-1_, and C syn- , and is absent in phage T1 and T4, which cannot undergo repair in the extracellular state. However, the prolonged time available for repair in these experiments accounts for only a very minor part of the increase in survival. The principal factor apparently is that the number of lesions present at any time remains relatively low. Presumably complete repair, not only the excision step, can occur in buffer during the irradiation period. This interpretation is supported by experiments in which cells were exposed to combinations of highly fractionated irradiation and single-dose irradiation. We therefore propose that mutual interference in repair, possibly by overlapping of repair regions in complementary DNA strands, reduces considerably the repair efficiency if many lesions are present. This hypothesis explains the 'shouldered' survival curves of B/r and possibly other E. coli strains as due to decreasing repair efficiency with increasing u.v. dose     

THE ROLE OF HOST-CELL REPAIR IN LIQUID-HOLDING RECOVERY OF U.V.-IRRADIATED ESCHERICHIA COLI

Abstract— The experiments reported give evidence that liquid-holding recovery (LHR) of u.v. irradiated E. coli cells involves basically the same type of dark repair which causes reactivation of phage and which results in much increased survival of the cells themselves [host-cell reactivation (HCR)]. LHR is very small in the two HCR(-) strains B syn^- and B_s-1, but occurs to larger but different extents in the three HCR(+) strains B, B/r, and B/r (Λ). LHR is inhibited if the liquid contains caffeine or acriflavine, both of which are known to inhibit HCR. The results indicate that most of the LHR effect, if not all, occurs during the liquid holding, rather than under growth conditions after liquid holding. It is assumed that the holding itself allows a prolonged time for, and therefore an enhancement of, HCR. It is thus implicit that LHR can be observed only where otherwise HCR of repairable u.v. damage would be incomplete, and that different extents of LHR, as observed in the three HCR(+) strains, reflect different extents of incompleteness of HCR. It is concluded that the repairable u.v. hits which are not fully repaired by HCR are predominantly those concerned with the extra u.v. sensitivity of the strains B and B/r (Λ), relative to B/r.     

THE EFFECTS OF ULTRAVIOLET AND VISIBLE RADIATION ON MOUSE ASCITES TUMOUR CELLS

Abstract— Effects of ultraviolet and visible radiation on the viability of Landschutz ascites tumour cells have been tested by growing control and treated tumour samples in adult mice. The tumour cells were irradiated as a dilute suspension in isotonic buffered salt solution, and were equilibrated at 0°C with oxygen or with nitrogen before irradiation.
Tumour cell proliferation was measured by a variety of techniques. The preferred assay-method was the growth of solid tumours in the axillae and groins of mice after sub-cutaneous inoculation of varying dilutions of treated or control ascites tumour cells. The immune response of the mice to the injected cells was reduced by whole body irradiation with a 300r dose of x-rays two days before inoculation. Results were calculated from parallel line assays using the reciprocal of the delay in appearance of the solid tumours up to 30 days post-innoculation. This reciprocal (1/T) was linearly related to the logarithm of the number of cells inoculated.
Photoreactivation has been demonstrated for this system, in which both U.V. and visible radiations were absorbed by the same cells. Light delivered alone in oxygen or in nitrogen was without effect on cell-viability, but it increased cell-survival after u.v.-irradiation in nitrogen and decreased survival after u.v.-irradiation in oxygen. Ultraviolet radiation alone was not significantly more lethal in oxygen than in nitrogen. A further observation in this work was an interaction between irradiated and control tumour cells injected into the same animal.
It is suggested that the radiation used may affect the antigenic character of the tumour cells as well as their reproductive capadity.     

ULTRAVIOLET-INDUCED APOCHLOROSIS AND PHOTOREACTIVATION IN TWO STRAINS OF EUGLENA GRACILIS*

Abstract— Very low doses of ultraviolet irradiation result in a complete loss of the ability to synthesize chlorophyll in two closely related strains of Euglena gracilis (var. hacillaris and strain Z). Both strains are equally sensitive in this response under non-photoreactivating conditions. The ability to synthesize chlorophyll is completely photoreactivated by visible light in E. grncilis var. bacillaris , even after lethal doses of u.v.: the Z strain. however, while photoreactivable following low doses of u.v., remains bleached after doses adequate to kill only 10–20 per cent of the cells.     

DISTRIBUTIONS OF FREE RADICALS AMONG AMINO ACIDS FROM LYOPHILIZED ULTRAVIOLET-IRRADIATED PROTEINS

Abstract— The effects of u.v.-irradiation at 254 nm upon lyophilized ribonuclease, lysozyme, insulin, and chymotrypsinogen have been investigated by electron spin resonance (ESR). enzymatic assay, and labeling of free radical sites with tritiated hydrogen sulfide (HST). The ESR signal of the irradiated protein diminishes on exposure to HST, and tritium becomes covalently bound to carbon. The distribution of tritium among the amino acids of each protein. studied as an indicator of the carbon free radical distribution, differs markedly from those observed previously to result from exposure to gamma radiation, electrical discharge. or hydrogen atoms. However, the earlier observation that the tritium distribution is influenced by protein conformation holds true as well for u.v.-irradiation. Moreover, the distributions of tritium among the amino acids of u.v.-irradiated proteins indicate a broad scattering of free radicals. Tyrosine and phenylalanine, residues that absorb light energy in the region of the wavelength employed, are not particularly important as radical carriers. Thus, for ribonuclease, these residues incorporated 3.8 and 1.5 per cent of the total tritium, but they absorb 51 and 12 per cent of the light, respectively. These results, together with the observed low recoveries of methionine, an amino acid that does not absorb at 254 nm, add weight to the concept that a migration of energy ensues after the initial absorption of light energy and that photolytic damage may thus be due to destruction of amino acids other than those initially absorbing the u.v.-radiation.     

VUV Fourier-transform absorption study of the Lyman and Werner bands in D2

An extensive survey of the D(2) absorption spectrum has been performed with the high-resolution VUV Fourier-transform spectrometer employing synchrotron radiation. The frequency range of 90,000-119,000 cm(-1) covers the full depth of the potential wells of the B (1)Σ(u)(+), B' (1)Σ(u)(+), and C (1)Π(u) electronic states up to the D(1s) + D(2l) dissociation limit. Improved level energies of rovibrational levels have been determined up to respectively v = 51, v = 13, and v = 20. Highest resolution is achieved by probing absorption in a molecular gas jet with slit geometry, as well as in a liquid helium cooled static gas cell, resulting in line widths of ≈0.35 cm(-1). Extended calibration methods are employed to extract line positions of D(2) lines at absolute accuracies of 0.03 cm(-1). The D (1)Π(u) and B' (1)Σ(u)(+) electronic states correlate with the D(1s) + D(3l]) dissociation limit, but support a few vibrational levels below the second dissociation limit, respectively, v = 0-3 and v = 0-1, and are also included in the presented study. The complete set of resulting level energies is the most comprehensive and accurate data set for D(2). The observations are compared with previous studies, both experimental and theoretical.     

CYTOTOXIC AND MUTAGENIC EFFECTS OF THE PHOTODYNAMIC ACTION OF CHLOROALUMINUM PHTHALOCYANINE AND VISIBLE LIGHT IN L5178Y CELLS

Abstract The cytotoxic and mutagenic effects of chloroaluminum phthalocyanine (CAPC) plus red light have been measured in strains of L5178Y mouse lymphoma cells which differ in their DNA repair capacities. Strain LY-R, deficient in the excision repair of UV-induced dimers, was found to be relatively more sensitive to the cytotoxic effects of CAPC plus light, whereas strain LY-S, deficienl in the repair of DNA double-strand breaks, was more sensitive than strain LY-R to the mutagenic effects of the treatment. Mutation frequencies were measured in LY-S and LY-R sub-strains which were heterozygous or hemizygous at the thymidine kinase (tk) locus. The mutation frequency at the tk locus induced in the heterozygous strain LY-SI by CAPC plus light was lower than that induced by an equitoxic dose of ionizing radiation but similar to that induced by an equitoxic dose of UVC radiation: The mutation frequency at the F., dose of CAPC plus light was approximately 1100 per 10⁶ surviving cells. The induced frequency in strain LY-S1 was much higher than in either tk+l-heterozygous or ik+10 hemizygous strains of LY-R. The rate and extent of incorporation of CAPC by the LY-R strains was somewhat greater than for strain LY-S1 at early times after CAPC addition, but by the time the cells were irradiated (18 h after CAPC addition) the difference was not great enough to account for the difference in cytotoxicity. It is possible that the cytotoxic and mutagenic lesions differ and that either the quantities of the respective lesions induced or the efficiencies of repair of the respective lesions differ inversely in the two strains. light have been measured in strains of L5178Y mouse lymphoma cells which differ in their DNA repair capacities. Strain LY-R, deficient in the excision repair of UV-induced dimers, was found to be relatively more sensitive to the cytotoxic effects of CAPC plus light, whereas strain LY-S, deficienl in the repair of DNA double-strand breaks, was more sensitive than strain LY-R to the mutagenic effects of the treatment. Mutation frequencies were measured in LY-S and LY-R sub-strains which were heterozygous or hemizygous at the thymidine kinase (tk) locus. The mutation frequency at the tk locus induced in the heterozygous strain LY-SI by CAPC plus light was lower than that induced by an equitoxic dose of ionizing radiation but similar to that induced by an equitoxic dose of UVC radiation: The mutation frequency at the F., dose of CAPC plus light was approximately 1100 per 10⁶ surviving cells. The induced frequency in strain LY-S1 was much higher than in either tk+l-heterozygous or ik+10 hemizygous strains of LY-R. The rate and extent of incorporation of CAPC by the LY-R strains was somewhat greater than for strain LY-S1 at early times after CAPC addition, but by the time the cells were irradiated (18 h after CAPC addition) the difference was not great enough to account for the difference in cytotoxicity. It is possible that the cytotoxic and mutagenic lesions differ and that either the quantities of the respective lesions induced or the efficiencies of repair of the respective lesions differ inversely in the two strains.     

THE DOSE-RESPONSE RELATION FOR THE PHOTO-REACTIVATION OF ULTRAVIOLET INACTIVATED STATIONARY PHASE TETRAHYMENA PYRIFORMIS

Abstract— Some kinetics of photoreactivation of the lethal effect of u.v. light on Tetrahymena pyriformis have been determined. The dose-response relation appears to be first order (single-hit). First-order photoreactivation kinetics have been found in some other systems and are difficult to reconcile with current knowledge about other aspects of photoreactivation.     

THE INFLUENCE OF NUTRITION ON THE DNA CONTENT OF ESCHERICHZA COLI AND ITS RESPONSE TO ULTRAVIOLET LIGHT

Abstract— The influence of nutrition on the sensitivity of Escherichia coli 15 T- to ultraviolet light (u.v.) and the synthesis of DNA has been studied. Growth in media containing glucose or NH,⁺ has been found to endow cells with a greater resistance to lethal u.v. damage than those grown in media containing succinate or amino acids, respectively. In addition, the sensitivity of the lactose ( lac ) locus of the DNA to mutagenic damage has been found to be altered by changes in the carbon supply but not by changes in the nitrogen source, while the sensitivity of loci controlling amino acid synthesis was altered by changes in the nitrogen source but not in the carbon source. Cells fed with glucose or NH₄⁺ have been found to possess more DNA than cells fed with succinate or amino acids, respectively. The data indicate that the type of carbon and nitrogen supplied to the cells will determine whether or not set regions of the DNA will undergo more than one round of replication. The presence in the cell of identical genetic loci either in duplicate or in multiples, directed by the particular types of carbon and nitrogen supplied, is suggested to be, in part, the reason why an alteration in nutrition is able to influence the sensitivity of bacterial cells to radiation.     

THE VARIATION OF RADIATION SENSITIVITY OF BACTERIA FED TETRAHYMENA PYRIFORMIS DURING THE GROWTH CYCLE AND FACTORS RELATED TO ITS ORIGIN

Abstract— Tetrahymena pyriformis shows a cyclic variation of sensitivity (for lethality) to u.v. light while the response to X-rays is almost constant throughout the growth (division to division) cycle. It is demonstrated in this paper, and elsewhere, that survival of caffeine treated animals is higher after higher doses than after the lower doses of radiation; such a response indicates that the increased radiation dose induces a resistant state not existing at lower doses. Response of synchronized animals to postirradiation treatment with caffeine is interpreted as indicating that recovery from the lethal effect of radiation has two components as previously postulated: (1) a caffeine sensitive recovery system (termed the ' N ' system) and, (2) an activated recovery capacity (termed the ' T' system) which is less sensitive to caffeine.
The maximum activated ( T ) system repair capacity only equals the repair capacity of the ( N ) non-activated system for X-ray induced lesions and, since the N system does not seem to show a cyclic variation of effectiveness for X-ray induced lesions, the X-ray survival remains constant throughout the growth cycle.
The repair capacity of the activated ( T ) repair system is, throughout most of the cycle and especially during the S period, much greater than that of the N system for u.v. induced lesions. Thus the u.v. response vanes in a manner largely dependent upon the capacity of the activated system and the fraction of the population showing the activated response; in G 2, a time when the activated repair system is rather ineffective, the non-activated ( N ) system appears to become unusually efficient in the repair of u.v. induced lesions.     

Observation and calculation of the Cs2 2 3Delta(1g) and b 3Pi(0u) states

The Cs(2) 2 (3)Delta(1g) and b (3)Pi(0u) states have been observed by infrared-infrared double resonance spectroscopy for the first time. 221 2 (3)Delta(1g)<--A (1)Sigma(u) (+)<--X (1)Sigma(g) (+) double resonance lines have been assigned to transitions into the 2 (3)Delta(1g) v=6-13 vibrational levels. Resolved fluorescence into the b (3)Pi(0u) v(')=0-48 levels has been recorded. Molecular constants and potential energy curves are determined by the global fit of the entire set of the experimental data. Theoretical potential energy curves of the 2 (3)Delta(g) and b (3)Pi(u) states have been determined in the framework of the pseudopotential method and are compared with the experimental results.     

ON SOME POSSIBILITIES OF PROTECTING CELLS FROM DAMAGING EFFECTS OF ULTRAVIOLET IRRADIATION

Abstract. The possibility of increasing the cell resistance to short-wave u. v. rays has been investigated with some chemicals. Ciliated epithelium cells of gills of pearly mussel Unio crassus Phillipsson have been shown to become more resistant after treatment with 0^.25–0.50 per cent solutions of calcium chloride during 24 hr or by 0.001– 0.001 per cent solutions of 2-benzyl-benzimidazole during 3–7 days or by 0.0001 per cent solution of 5–6-di-methyl-benzimidazole during 7 days. When irradiated with u. v. light (λ=2537 Å) these cells survive for a longer time than irradiated control cells.     

PHOTOBIOLOGY OF RNA BACTERIOPHAGES—I. ULTRAVIOLET INACTIVATION AND PHOTOREACTIVATION STUDIES*

Abstract— Biologically active f2-RNA, Obtained from bacteriophage f2, was inactivated by ultraviolet (u.v) light (2537 Å) with a quantum yield of 3.3 ± 0.3 times 10^-3 when assayed in the dark with protoplasts of an F- strain of E. coli k12. Assay under “black light” gave a quantum yield of 2.7 ± 0.5 times 10^-3 which was just enough lower to suggest that 17 per cent photorecovery of the u.v. lesions has taken place. Intact phage f2 was inactivated by u.v. radiation with a quantum yield of 0.7 ± 0.12 times 10^-3, Thus the whole phage is much less sensitive than the free RNA. No evidence of photorecovery was found in u.v.-irradiated RNA phage 7S assayed in its host Pseudomonas aeruginosa.     

CONCERNING THE PRODUCTION OF FREE RADICALS IN PROTEINS BY ULTRAVIOLET LIGHT

Abstract— Using electron paramagnetic resonance techniques, the response to u.v. light of several solid proteins and model compounds has been studied in vacuum and at low temperature. Emphasis has been placed on determining the response as a function of the wavelength (Λ 250 nm) and intensity of the incident radiation. Correlation of the parameters of radical production with sample luminescence, molecular amino-acid sequence and tertiary structure, light intensity and total irradiation time has allowed some insight into the mechanisms of free radical formation.
It is shown that the details of amino acid composition, sequence and the tertiary structure of a protein are important in determining both the rate of, and the mechanism for, radical production (two basic mechanisms are described), and in determining the conditions under which sulfur-type radicals can be produced. The results are related to enzyme inactivation and to the u.v. stability of proteins generally.     

Adjuvant antiproliferative and cytotoxic effect of aloin in irradiated HeLaS3 cells

Naturally occurring phytoanthracycline, aloin, was used to radiosensitize HeLaS3 human cervix carcinoma cells. The results indicated that the cytotoxic adjuvant effect of aloin was synergistic with gammaionizing radiation at all drug concentrations and comparable to the cytotoxicity of 5–10 Gy ionizing radiation alone. Radiosensitization of HeLaS3 cells was achieved by 60 μM aloin, which reduced the IC₅₀ dose of ionizing radiation from 3.4 to 2 Gy. Ionizing radiation and aloin alone or in combination are shown to cause perturbation of the HeLaS3 cell-cycle and increase the percentage of cells in the DNA synthesis (S) phase of the cell cycle. While either of the agents applied alone causes programmed cell death by apoptosis, the simultaneous cell damage by both agents through the altered redox balance compromised cell capacity to conduct this program and led to synergic cytotoxic cell death by necrosis. The text was submitted by the authors in English.