Caffeic acid protects human peripheral blood lymphocytes against gamma radiation-induced cellular damage

In the present study, we investigated in vitro radioprotective potential of caffeic acid (CA), a naturally occurring catecholic acid against gamma radiation-induced cellular changes. Different concentrations of CA (5.5, 11, 22, 44, 66, and 88 microM) were incubated with lymphocytes for 30 min prior to gamma-irradiation, and micronuclei (MN) scoring and comet assay were performed to fix the effective concentration of CA against gamma-irradiation. Among all concentrations, 66 microM of CA showed the optimum protection by effectively decreasing the MN frequencies and comet attributes. From the above-mentioned results, 66 microM of CA was selected as the effective concentration and was further used to investigate its radioprotective efficacy. For that purpose, a separate experiment was carried out on the lymphocytes in which lymphocytes were preincubated with CA (66 microM) and were exposed to different doses of radiation (1, 2, 3, and 4 Gy). Genetic damage (MN, dicentric aberration, and comet attributes) and biochemical changes were measured. Gamma-irradiated lymphocytes showed a dose-dependent increase in the genetic damage and thiobarbituric acid reactive substances, accompanied by the significant decrease in the antioxidant status, whereas CA pretreatment positively modulated all the radiation-induced changes through its antioxidant potential. The current study demonstrates that CA is effective in protecting lymphocytes against radiation-induced toxicity and encourages further in vivo study to evaluate radioprotective efficacy of CA.     

Apigenin ameliorates gamma radiation-induced cytogenetic alterations in cultured human blood lymphocytes

The aim of the present study was to assess the protective effect of apigenin, a dietary flavone, against cytogenetic alterations in human peripheral blood lymphocytes (HPBL) induced by Cobalt-60 radiation (3Gy). Results of MTT [3-(4, 5-dimethyl-2-thiaozolyl)-2,5-diphenyl-2H tetrazolium bromide] assay revealed that 37.2μM of apigenin was found to be non-toxic in HPBL. At this dose (37.2μM) of apigenin, the LD(50) radiation dose of HPBL increased from 2.9Gy to 3.4Gy, which resulted in a DMF of 1.17. Apigenin (37.2μM) treatment 1h before irradiation significantly (p<0.05) reduced DNA damage in irradiated HPBL as measured by comet assay (% tail DNA, tail length, tail moment, and olive tail moment). Moreover, apigenin treatment significantly decreased the frequencies of dicentric (DC), acentric fragments (AF), and acentric rings (AR) in irradiated HPBL. Apigenin pretreatment also reduced the radiation-induced CBMN (cytokinesis blocked micronuclei) anomalies such as micronuclei (MNi), nucleoplasmic bridges (NPB) and nuclear buds (NBUD) in HPBL. These results also showed that there was a significant correlation between NPB and DC frequencies and MNi and AF+AR. Treatment with apigenin alone had no significant effect on DNA damage and chromosomal aberrations in HPBL. Thus, the current studies indicate that apigenin protects HPBL from radiation-induced cytogenetic alterations.     

Effect of quercetin on nicotine-induced biochemical changes and DNA damage in rat peripheral blood lymphocytes

Abstract

We elucidated the protective effect of quercetin, a polyphenolic flavonoid, on lipid peroxidation, endogenous antioxidant status and DNA damage during nicotine-induced toxicity in cultured rat peripheral blood lymphocytes as compared to N-acetylcysteine (NAC), a well-known antioxidant. Lymphocytes were exposed to nicotine (3 mM) with and without quercetin and NAC (1 mM) in RPMI-1640 medium for 1 h. In preliminary experiments to fix the effective dose of quercetin, different doses of quercetin (25, 50, 75, 100 and 200 μM) were administered to lymphocytes with nicotine, and lipid peroxidation markers (thiobarbituric acid reactive substances and hydroperoxides) were analysed. A 75 μM dose of quercetin was found to be effective as evidenced by decreased lipid peroxidation. To evaluate the protective potential of quercetin against genotoxic effects of nicotine we used comet and micronucleus assays, which are valid parameters to assess genetic damage. In addition, biochemical changes including lipid peroxidation and antioxidant status were assessed. There were significant increases in the levels of lipid peroxidation, comet parameters and micronuclei frequencies, followed by decrease in the endogenous antioxidant status, in nicotine-treated lymphocytes, which were brought back to near normal by quercetin or NAC treatment. The protective effect of quercetin against nicotine toxicity was comparable to that of NAC. These findings suggest that quercetin can be as effective as NAC in protecting rat peripheral lymphocytes against nicotine-induced cellular and DNA damage.     

Effect of quercetin on nicotine-induced biochemical changes and DNA damage in rat peripheral blood lymphocytes

We elucidated the protective effect of quercetin, a polyphenolic flavonoid, on lipid peroxidation, endogenous antioxidant status and DNA damage during nicotine-induced toxicity in cultured rat peripheral blood lymphocytes as compared to N-acetylcysteine (NAC), a well-known antioxidant. Lymphocytes were exposed to nicotine (3 mM) with and without quercetin and NAC (1 mM) in RPMI-1640 medium for 1 h. In preliminary experiments to fix the effective dose of quercetin, different doses of quercetin (25, 50, 75, 100 and 200 microM) were administered to lymphocytes with nicotine, and lipid peroxidation markers (thiobarbituric acid reactive substances and hydroperoxides) were analysed. A 75 microM dose of quercetin was found to be effective as evidenced by decreased lipid peroxidation. To evaluate the protective potential of quercetin against genotoxic effects of nicotine we used comet and micronucleus assays, which are valid parameters to assess genetic damage. In addition, biochemical changes including lipid peroxidation and antioxidant status were assessed. There were significant increases in the levels of lipid peroxidation, comet parameters and micronuclei frequencies, followed by decrease in the endogenous antioxidant status, in nicotine-treated lymphocytes, which were brought back to near normal by quercetin or NAC treatment. The protective effect of quercetin against nicotine toxicity was comparable to that of NAC. These findings suggest that quercetin can be as effective as NAC in protecting rat peripheral lymphocytes against nicotine-induced cellular and DNA damage.     

Microcystin-LR induced DNA damage in human peripheral blood lymphocytes

Human exposure to microcystins, which are produced by freshwater cyanobacterial species, is of growing concern due to increasing appearance of cyanobacterial blooms as a consequence of global warming and increasing water eutrophication. Although microcystins are considered to be liver-specific, there is evidence that they may also affect other tissues. These substances have been shown to induce DNA damage in vitro and in vivo, but the mechanisms of their genotoxic activity remain unclear. In human peripheral blood lymphocytes (HPBLs) exposure to non-cytotoxic concentrations (0, 0.1, 1 and 10μg/ml) of microcystin-LR (MCLR) induced a dose- and time-dependent increase in DNA damage, as measured with the comet assay. Digestion of DNA from MCLR-treated HPBLs with purified formamidopyrimidine-DNA glycosylase (Fpg) displayed a greater number of DNA strand-breaks than non-digested DNA, confirming the evidence that MCLR induces oxidative DNA damage. With the cytokinesis-block micronucleus assay no statistically significant induction of micronuclei, nucleoplasmic bridges and nuclear buds was observed after a 24-h exposure to MCLR. At the molecular level, no changes in the expression of selected genes involved in the cellular response to DNA damage and oxidative stress were observed after a 4-h exposure to MCLR (1μg/ml). After 24h, DNA damage-responsive genes (p53, mdm2, gadd45a, cdkn1a), a gene involved in apoptosis (bax) and oxidative stress-responsive genes (cat, gpx1, sod1, gsr, gclc) were up-regulated. These results provide strong support that MCLR is an indirectly genotoxic agent, acting via induction of oxidative stress, and that lymphocytes are also the target of microcystin-induced toxicity.     

Melatonin protects human blood lymphocytes from radiation-induced chromosome damage

Cells in human peripheral blood were treated in vitro with increasing concentrations of melatonin (0.5 or 1.0 or 2.0 mM) for 20 min at 37 ± 1°C and then exposed to 150 cGy γ-radiation from a ¹³⁷Cs source. The lymphocytes which were pre-treated with melatonin exhibited a significant and concentration-dependent decrease in the frequency of radiation-induced chromosome damage as compared with the irradiated cells which did not receive the pre-treatment. The extent of the reduction in radiation-induced chromosome damage observed with 2.0 mM melatonin was similar to that found in lymphocytes pre-treated with 1.0 M dimethyl sulfoxide, a known free radical scavenger. Melatonin at 2.0 mM (a 500 X lower concentration) was as effective in decreasing the radiation-induced chromosome damage as dimethyl sulfoxide at 1.0 M. These observations may have implications for human protection against damage due to endogenously produced free radicals and also due to exposure to free radical producing physical and chemical mutagens and carcinogens.     

DNA damage and repair in human peripheral blood lymphocytes following treatment with microcystin-LR

The purpose of this study was to find a possible explanation of the inconsistency of data regarding the genotoxicity of microcystin-LR (MC-LR). We compared the results of the comet assay with the results of the analysis of chromosome aberrations and apoptosis. In order to investigate the influence of MC-LR on DNA damage in human lymphocytes, cells were treated with MC-LR at different concentrations (1, 10 and 25 microg/ml) for 6, 12, 18 and 24 h. Analyses of Olive Tail Moment (OTM) as an indicator of DNA damage showed that MC-LR treatment induced DNA damage in a time-dependent manner, reaching its maximum after 18 h. The lowest values of OTM were observed after 24 h. MC-LR had no effect on the frequency of chromosome aberrations in lymphocytes. Since some data available in the literature indicate that apoptosis may lead to overestimated or false positive results regarding the genotoxicity of mutagens in the comet assay, we measured the frequency of late apoptotic cells by use of the comet assay and the frequency of early apoptotic cells with the TUNEL method. The comet assay results revealed that the highest level of apoptosis was observed after 24 h and the lowest after 18 h. The comparison of the frequency of apoptotic cells determined by the comet assay with DNA damage (OTM) examined by the comet assay revealed a statistically significant, negative correlation. The TUNEL results showed that the frequency of apoptotic cells progressively increased in a dose- and time-dependent manner. The comparison of the frequency of apoptotic cells determined by TUNEL method with DNA damage (OTM) examined by the comet assay showed a significant positive correlation for lymphocytes treated with MC-LR for 6, 12 and 18 h. Therefore, our findings indicate that microcystin-LR-induced DNA damage observed in the comet assay may be related to the early stages of apoptosis due to cytotoxicity but not genotoxicity. In addition, we examined the DNA repair kinetics in lymphocytes following treatment with microcystin-LR and ionizing radiation. Our results indicate that MC-LR has an inhibiting effect on the repair of radiation-induced damage.     

Voltammetric determination of gamma radiation-induced DNA damage

Homopolydeoxyribonucleotides, poly[dGuo], poly[dAdo], poly[dThd], and poly[dCyd], and calf thymus single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA) aqueous solutions previously exposed to gamma radiation doses between 2 and 35 Gy, were studied by differential pulse voltammetry using a glassy carbon electrode. The interpretation of the voltammetric data was also supported by the electrophoretic migration profile obtained for the same ssDNA and dsDNA gamma-irradiated samples by nondenaturing agarose gel electrophoresis. The generation of 8-oxo-7,8-dihydroguanine, 2,8-dihydroxyadenine, 5-formyluracil, base-free sites, and single- and double-stranded breaks in the gamma-irradiated DNA samples was detected voltammetrically, with the amount depending on the irradiation time. It was found that the current peaks obtained for 8-oxoguanine increase linearly with the radiation dose applied to the nucleic acid sample, and values between 8 and 446 8-oxo-7,8-dihydroguanine (8-oxoGua) per 10(6) guanines per Gy were obtained according to the nucleic acid sample. The results showed that voltammetry can be used for monitoring and simultaneously characterizing different kinds of DNA damage caused by gamma radiation exposure.     

Assessment of radiation-induced DNA damage in human blood lymphocytes using the single-cell gel electrophoresis technique.

The ability of the alkaline single-cell gel (SCG) electrophoresis technique to detect single-strand breaks and alkali-labile DNA damage in human cells induced by low doses of radiation was evaluated. Peripheral blood lymphocytes were irradiated with gamma-rays from a 137Cs source at doses from 0.01 to 1 Gy and exposed to alkali (pH greater than 13) for 20, 40 or 60 min and then electrophoresed at 25 V and 300 mA for either 20 or 40 min. The extent of DNA damage that was expressed and detected as DNA migration depended directly on the dose of radiation, the duration of exposure to alkali and the length of electrophoresis. At all experimental conditions tested, it was possible to detect a significant increase in DNA damage induced by a radiation dose as low as 0.05 Gy. Based on an analysis of the ratio of the range to the standard deviation for each radiation dose and experimental condition, the distribution of damage among cells for all doses was neither excessively homogeneous nor heterogeneous. Furthermore, the distribution was independent of radiation treatment. The SCG technique is rapid and sensitive, and useful for investigations concerned with effects of low doses of radiation.     

Effect of gliclazide on DNA damage in human peripheral blood lymphocytes and insulinoma mouse cells

Type 2 diabetes mellitus is associated with increased oxidative stress. Free radicals produced during this stress may damage various cellular components. Gliclazide, a second-generation sulfonylurea, is an oral hypoglycemic drug that possesses antioxidant properties. Therefore, gliclazide may diminish the harmful consequences of oxidative stress in diabetic patients. The aim of our study was to evaluate the action of gliclazide on DNA damage and repair in normal human peripheral blood lymphocytes and insulinoma mouse cells (beta-TC-6). DNA damage and repair were induced by hydrogen peroxide, gamma and ultraviolet radiation and MNNG (N-methyl-N'-nitro-N-nitrosoguanidine) in the presence or absence of gliclazide and were analysed by the alkaline comet assay. DNA double-strand breaks were assayed by pulsed-field gel electrophoresis. Gliclazide protected DNA of both kinds of cells from DNA damage induced by chemicals and radiations. These results suggest that gliclazide may diminish the risk of free radical-related diseases associated with type 2 diabetes mellitus and possibly cancer.     

Protection against X-ray radiation-induced cellular damage of human peripheral blood lymphocytes by an aminothiazole derivative of dendrodoine

The present study was aimed to evaluate the radioprotective efficacy of dendrodoine analog (DA), an aminothiazole derivative against X-ray radiation-induced cellular damage in cultured human peripheral blood lymphocytes. Different concentrations of DA (2, 4, 6, 8, 10 μg/ml or 6.15, 12.29, 18.44, 24.59, 30.73 μM) were pre-incubated with lymphocytes for 30 min prior to irradiation [4 Gy] and the micronuclei (MN) scoring and comet assay were performed to fix the effective concentration of DA against 4 Gy irradiation-induced cellular damage. The results indicated that among all the concentrations, 6 μg/ml concentration of DA showed optimum protection by effectively decreasing the MN frequencies and comet attributes. Based on the above results, 6 μg/ml concentration of DA was fixed as the effective dose to further investigate its radioprotective efficacy. This was carried out by pre-incubating the lymphocytes with 6 μg/ml concentration of DA followed by exposure of the lymphocytes to different doses (1, 2, 3 and 4 Gy) of radiation and investigating the radiation-induced genetic damage (MN, comet assay, DNA fragmentation assay) and biochemical changes (changes in the level of enzymic and non-enzymic antioxidants, lipid peroxidation). The results indicated a dose-dependent increase in both genetic damage and thiobarbituric acid reactive substances (TBARS), accompanied by a significant decrease in the antioxidant status in the irradiated groups compared to DA treated groups which modulated the toxic effects through its antioxidant potential. Thus the current study shows DA to be an effective radioprotector against X-ray radiation induced in vitro cellular damage in lymphocytes.     

Unscheduled DNA synthesis in human peripheral blood lymphocytes undergoing combined exposure to gamma irradiation and methylmethane sulfonate

The value of the unscheduled DNA synthesis by exposure to combined action of damaging agents--gamma-irradiation and methyl methanesulfonate--does not exceed its value after separate actions of each particular agent in lymphocytes from healthy subjects as well as in those with Xeroderma pigmentosum in form II (XP2LE). This result is due to inhibiting effects of alkylating agents on DNA-polymerases.     

Protective effects of cimetidine on radiation-induced micronuclei and apoptosis in human peripheral blood lymphocytes

The radioprotective effects of cimetidine, which has been used clinically as an antagonist of H 2 receptor, on radiation-induced micronuclei and apoptosis in human peripheral blood lymphocytes (PBL) prepared from healthy donors were studied. Cells were treated with cimetidine before or after X-irradiation, and then cytokinesis-blocked micronucleus assay and flow cytometry for measurement of phosphatidylserine externalization were utilized to evaluate the radiation-induced cytogenetic damage and apoptosis. The protective effect of pre-irradiation treatment of cimetidine on radiation-induced micronuclei was dependent on the concentration. The maximum protection rates of cimetidine (1 mM) on frequencies of micronuclei were 38.8 and 30.2% for cells treated before and after X-irradiation (5 Gy), respectively. Protective effects of pre- and post-irradiation treatment with cimetidine on radiation-induced early apoptosis and decreased activity of caspase-3 were observed. A study of electron paramagnetic resonance-spin trapping with 5,5'-dimethyl-1- N -oxide revealed that the rate constant of cimetidine with radiation-induced OH radicals is about 4.5 ×10 9 l/mol/s. Cimetidine did not significantly increase the intracellular concentration of glutathione. These results suggest that cimetidine suppresses radiation-induced micronuclei and apoptosis via OH radical scavenging and an intracellular antioxidation mechanism. Cimetidine appears to be a useful candidate for the future development of post-irradiation radioprotectors.     

Quercetin protects radiation-induced DNA damage and apoptosis in kidney and bladder tissues of rats

Abstract

Ionizing radiation (IR) can induce cell damage and cell death through the reactive oxygen species generated by radiolytic hydrolysis. The present study was aimed to determine the possible protective effects of quercetin, a well-known antioxidant agent, against IR-induced bladder and kidney damage in rats. Sprague-Dawley rats were exposed to 8-Gy whole-abdominal IR and given either vehicle or quercetin (20 mg/kg, ip). Rats were decapitated at either 36 h or 10 days following IR, where quercetin or vehicle injections were repeated once daily, and kidney and bladder samples were obtained for the determination of myeloperoxidase and caspase-3 activities, an index of tissue neutrophil infiltration and apoptosis, respectively. Radiation-induced inflammation was evaluated through tissue cytokine, TNF-α levels. In order to examine oxidative DNA damage, tissue 8-hydroxydeoxyguanosine (8-OHdG) levels were measured. All tissues were also examined microscopically. In the saline-treated irradiation groups, myeloperoxidase and caspase-3 activities, 8-OHdG and TNF-α levels were found to be increased in both tissues (p < 0.05). In the quercetin-treated-IR groups, all these oxidant responses were prevented significantly (p < 0.05). The present data demonstrate that quercetin, through its free radical scavenging and antioxidant properties, attenuates irradiation-induced oxidative organ injury, suggesting that quercetin may have a potential benefit in radiotherapy by minimizing the adverse effects and will improve patient care.     

Dose curves for radiation-induced cytogenetic damage in human lymphocytes

Insufficient fitness of experimental data with convenient linear and linear-quadratic models of "dose-effect" dependence for the number of chromosome aberrations of different types were revealed. Proposed method of approximation of the experimental "dose-effect" dependence with piece-linear splines allows to obtain more accurate results in the most cases and therefore is more preferable than the linear and linear-quadratic models.     

DNA damage in peripheral blood lymphocytes in patients during combined chemotherapy for breast cancer

Combined chemotherapy is used for the treatment of a number of malignancies such as breast cancer. The target of these antineoplastic agents is nuclear DNA, although it is not restricted to malignant cells. The aim of the present study was to assess DNA damage in peripheral blood lymphocytes (PBLs) of breast cancer patients subjected to combined adjuvant chemotherapy (5-fluorouracil, epirubicin and cyclophosphamide, FEC), using a modified comet assay to detect DNA single-strand breaks (SSB) and double-strand breaks (DSB).

Forty-one female patients with advanced breast cancer before and after chemotherapy and 60 healthy females participated in the study. Alkaline and neutral comet assays were performed in PBLs according to a standard protocol, and DNA tail moment was measured by a computer-based image analysis system.

Breast cancer patients before treatment had higher increased background levels of SSB and DSB as compared to healthy women. During treatment, a significant increase in DNA damage was observed after the 2nd cycle, which persisted until the end of treatment. Eighty days after the end of treatment the percentage of PBLs with SSB and DSB remained elevated, but the magnitude of DNA damage (tail moment) returned to baseline levels. There was no correlation between PBL DNA damage and response to chemotherapy.

DNA-SSB and DSB in PBLs are present in cancer patients before treatment and increase significantly after combined chemotherapy. No correlation with response to adjuvant chemotherapy was found. Biomonitoring DNA damage in PBLs of cancer patients could help prevent secondary effects and the potential risks of developing secondary cancers.     

Glucose oxidase-produced H2O2 induces Ca2+-dependent DNA damage in human peripheral blood lymphocytes

DNA of lymphocytes from human peripheral blood was analyzed by using the single cell gel electrophoresis technique (comet assay). The cells were used either as received from the donors or after treatment with various concentrations of the H2O2-generating enzyme glucose oxidase, in order to achieve a continuous flow of H2O2. The formation of single strand breaks (SSB) was dose-related but the time course of the induction of SSB by relatively low concentrations of glucose oxidase was of a biphasic mode with a fast increase 2 to 5 min after the addition of glucose oxidase followed by a gradual decrease toward the original base level during the next 35 to 60 min. This response of the cells appears to be based on the activation of already existing defense system(s) because it was shown that H2O2 is continuously released during the reaction time and the inhibition of protein synthesis does not affect the observed pattern. Supplementation of the growth medium with various antioxidants resulted in substantial protection only when the agents were taken up by the cells. The presence of the intracellular calcium chelator BAPTA protected the cells from H2O2-induced DNA damage in a dose-dependent manner. Only at the higher rate of H2O2-generation considerable DNA damage was observed in the presence of BAPTA.These results suggest that H2O2, at low concentrations induces DNA damage through intracellular Ca2+ -mediated processes, which lead to DNA strand breaks possibly by endonuclease activation.     

DNA loop organization and DNA fragmentation during radiation-induced apoptosis in human lymphocytes

Apoptotic DNA fragmentation induced by gamma-rays has been compared with the DNA loop sizes in G0-human lymphocytes using pulsed field gel electrophoresis (PFGE). Genomic DNA was cleaved into the DNA loops at the topoisomerase II mediated attachment points using short treatment of cells with etoposide. The apoptotic fragmentation, with a distinct cut-off around 50 kb for a maximum length of fragments, appeared 5 h after irradiation when the most part of radiation-induced DNA double strand breaks (DSBs) have been repaired. The data indicate that apoptotic fragmentation of DNA in the G0-human lymphocytes begins when repair of radiation-induced DSBs has been completed. Similar apoptotic DNA fragmentation was also observed following the treatment of cells with etoposide. All genomic DNA was fragmented into 50-kb fragments during the final stages of apoptosis. Most of the DNA in resting lymphocytes is organized into Mb-size loops but loops of sizes down to 50 kb were also observed. A sharp border between the size distributions of DNA loops and apoptotic fragments was found. The data suggest that 50 kb apoptotic fragmentation is not based on excision of the DNA loops. No apoptotic fragments with the sizes more than 5.7 Mb were seen during the whole course of apoptosis. This observation indicates that despite intensive apoptotic fragmentation into the 50-kb fragments the chromosomes maintain integrity during radiation-induced apoptosis in human lymphocytes. We propose a model for radiation-induced apoptotic fragmentation in human lymphocytes that involves four stages: induction of DNA breaks and relaxation of DNA loops; DNA repair followed by reorganization of the DNA loops into the 50-kb units of condensed chromatin; co-operative fragmentation of the reorganized DNA loops into the distinct 50-kb fragments and resealing of the chromosome ends at the sites of this fragmentation; cleavage of the 50-kb fragments at the internucleosomal spacers.     

The repair of DNA damage induced in human lymphocytes by gamma rays and fast neurons

When Go human lymphocytes are exposed either to gamma-rays or to d(50)-Be neutrons and then immediately incubated in presence of cytosine arabinoside, the frequency of chromosomal aberrations which is normally observed after radiation exposure only is sharply increased. This enhancement of the aberrations, particularly the dicentrics, is, however, less marked when cytosine arabinoside is administered at longer intervals of time after irradiation. For gamma-rays, the treatment with cytosine arabinoside has no effect on the dicentrics yield when given 5 h after irradiation, indicating that the repair is completed within the 5 h after irradiation and that the lesions are not anymore available to produce exchange aberrations. For d(50)-Be neutrons, the time of repair takes approximately 5 h after a dose of 2.0 Gy, whereas it appears to be shorter (3 h) after a dose of 0.5 Gy.