UV-B induced changes in antioxidant enzymes and their isoforms in cucumber (Cucumis sativus L.) cotyledons

To assess the role of antioxidant defense system on exposure to ultra-violet-B (UV-B) radiation, the activities of antioxidant enzymes superoxide dismutase (SOD), ascorbic acid peroxidase (APX), glutathione reductase (GR) and guaiacol peroxidase (GPX), as well as the level of antioxidants ascorbic acid (AA) and alpha-tocopherol were monitored in cucumber (Cucumis sativus L. var long green) cotyledons. UV-B enhanced the activity of antioxidant enzymes as well as AA content, but decreased the level of alpha-tocopherol. Significant increase was observed in the activities of SOD and GPX. Analysis of isoforms of antioxidant enzymes by native-PAGE and activity staining revealed three isoforms of GPX in unexposed dark-grown cotyledons (control), and their intensity was enhanced by UV-B exposure. In addition, four new isoforms of GPX were observed in cotyledons after UV-B exposure. Although no new isoforms were observed for the other antioxidant enzymes, the activities of their existing isoforms were enhanced by UV-B.

Effects of sublethal UVA irradiation on activity levels of oxidative defense enzymes and protein oxidation in Escherichia coli

When bacterial cells are stressed by a change in the environment, they respond by changing the activity of enzymes at both the transcriptional and post-transcriptional levels. The UVA component (400-315 nm) of solar radiation reaching the Earth's surface is one of the most common stresses encountered by bacteria in their environment. Bacteria have evolved various antioxidant defense systems to increase survival when subjected to the deleterious effects of UVA irradiation. Recently, UVA-induced cytotoxicity and oxidative damage have been shown to be dependent on radiation intensity and dose distribution, not just total energy dose. We now report that when Escherichia coli is subjected to continuous sublethal, low-fluence UVA irradiation (7.4 W/m(2)) while growing to stationary phase, it responds by changing the activity levels of hydroperoxidases (HPI, HPII), glutathione reductase and manganese superoxide dismutase. This leads to an attenuation of the growth-delay response and an increase resistance to lethal UVA irradiation. When E. coli is given a UVA dose of 135 kJ/m(2) delivered at a fluence rate of 50 W/m(2), extensive protein oxidation occurs which may contribute to the inhibition of key cellular enzymes, leading to cellular dysfunction, DNA damage and eventually death. Changes in antioxidant enzymes induced by low-fluence UVA irradiation do not confer greater protection from protein oxidation after a challenge dose of UVA irradiation delivered at a fluence rate of 50 W/m(2).

Evidence for a novel mechanism of time-resolved flavin fluorescence depolarization in glutathione reductase

Time-resolved flavin fluorescence anisotropy studies on glutathione reductase (GR) have revealed a remarkable new phenomenon: wild-type GR displays a rapid process of fluorescence depolarization, that is absent in mutant enzymes lacking a nearby tyrosine residue that blocks the NADPH-binding cleft. Fluorescence lifetime data, however, have shown a more rigid active-site structure for wild-type GR than for the tyrosine mutants. These results suggest that the rapid depolarization in wild-type GR originates from an interaction with the flavin-shielding tyrosine, and not from restricted reorientational motion of the flavin. A novel mechanism of fluorescence depolarization is proposed that involves a transient charge-transfer complex between the tyrosine and the light-excited flavin, with a concomitant change in the direction of the emission dipole moment of the flavin. This interaction is likely to result from side-chain relaxation of the tyrosine in the minor fraction of enzyme molecules in which this residue is in an unsuitable position for immediate fluorescence quenching at the moment of excitation. Support for this mechanism is provided by binding studies with NADP+ and 2'P-5'ADP-ribose that can intercalate between the flavin and tyrosine and/or block the latter. Fluorescence depolarization analyses as a function of temperature and viscosity confirm the dynamic nature of the process. A comparison with fluorescence depolarization effects in a related flavoenzyme indicates that this mechanism of flavin fluorescence depolarization is more generally applicable.

Radioprotective mechanism of Podophyllum hexandrum during spermatogenesis

RP-1, a herbal preparation of Podophyllum hexandrum has already been reported to provide protection against whole body lethal gamma irradiation (10 Gy). It has also been reported to render radioprotection to germ cells during spermatogenesis. Present study was undertaken to unravel the cellular and molecular mechanism of action of RP-1 on testicular system in strain 'A' mice. Various antioxidant parameters such as thiol content, glutathione peroxidase (GPx), glutathione reductase (GR), glutathione-S-transferase (GST) enzyme activity, lipid peroxidation (LPO) and total protein levels were investigated. Thiol content was seen to increase significantly (p < 0.05) in both RP-1 alone and RP-1 pretreated irradiated groups over the irradiated groups at 8, 16 and 24 h. Irradiation (10 Gy) significantly decreased GPx, GST and GR activity in comparison to untreated control but RP-1 treatment before irradiation significantly (p < 0.05) countered radiation-induced decrease in the activity of these enzymes. Radiation-induced LPO was also found to be reduced at all time intervals by RP-1 treatment before irradiation. As compared to irradiated group the protein content in testicular tissue was increased in RP-1 pretreated irradiated group at 4 and 16 h significantly (p < 0.05). Comets revealed by single-cell gel electrophoresis were significantly longer (p < 0.001) in irradiated mice than in unirradiated control. RP-1 treatment before irradiation, however, rendered significant increase (p < 0.05) in comet length over the corresponding control and irradiated group initially at 4 h but at later time points, this was reduced significantly (p < 0.01) as compared to the irradiated group. RP-1 treatment alone rendered shorter comets at 8, 16 and 24 h than irradiated groups (p < 0.001). This study implies that RP-1 offers radioprotection at biochemical and cytogenetic level by protecting antioxidant enzymes, reducing LPO and increasing thiol content.

Similar stress responses are elicited by copper and ultraviolet radiation in the aquatic plant Lemna gibba: implication of reactive oxygen species as common signals

Metals and ultraviolet (UV) radiation are two environmental stressors that can cause damage to plants. These two types of stressors often impact simultaneously on plants and both are known to promote reactive oxygen species (ROS) production. However, little information is available on the potential parallel stress responses elicited by metals and UV radiation. Using the aquatic plant Lemna gibba, we found that copper and simulated solar radiation (SSR, a light source containing photosynthetically active radiation (PAR) and UV radiation) induced similar responses in the plants. Both copper and SSR caused ROS formation. The ROS levels were higher when copper was combined with SSR than when applied with PAR. Higher concentrations of copper plus PAR caused toxicity as monitored by diminished growth and chlorophyll content. This toxicity was more pronounced when copper was combined with SSR. Because the generation of ROS was also higher when copper was combined with SSR, we attributed this enhanced toxicity to elevated levels of ROS. In comparison to PAR-grown plants, SSR treated plants exhibited elevated levels of superoxide dismutase (SOD) and glutathione reductase (GR). These enzyme levels were further elevated under both PAR and SSR when copper was added at concentrations that generated ROS. Interestingly, copper treatment in the absence of SSR (i.e. copper plus PAR) induced synthesis of the same flavonoids as those observed in SSR without copper. Finally, addition of either dimethyl thiourea or GSH (two common ROS scavengers) lowered in vivo ROS production, alleviated toxicity and diminished induction of GR as well as accumulation of UV absorbing compounds. Thus, the potential of ROS being a common signal for acclimation to stress by both copper and UV can be considered.

Effects of infrared and low-power laser irradiation on cell viability, glutathione and glutathione-related enzyme activities in primary rat hepatocytes

BACKGROUND AND PURPOSE

Both infrared and low-power laser have been applied to improve circulation, wound repair, and pain control. Infrared and low-power laser therapies have the potential for stimulating enzyme activities which might contribute to increased glutathione (GSH) concentration and provide protection against oxidative damage. This study investigated cell viability, and GSH and its related enzyme activities in rat hepatocytes after irradiation.

METHODS

Hepatocytes were isolated from 8-week-old male Sprague-Dawley rats and the cultures were divided into infrared, laser, and control groups. The cells were treated with infrared and low-power laser at a distance of 35 cm for 20 minutes. The cell morphology, lactate dehydrogenase (LDH) leakage, lipid peroxidation, GSH concentration, GSH peroxidase, GSH reductase (GRd), and GSH S-transferase activities were measured after irradiation.

RESULTS

The morphology and LDH leakage of hepatocytes in the irradiation groups did not differ significantly from those of the control group. After infrared irradiation, a significant decrease in thiobarbituric acid-reactive substances and an increase in GSH concentration were found after 48 hours of incubation compared to the control group (p < 0.05). Furthermore, laser irradiation resulted in a significant increase in GRd activity after 48 hours of incubation compared to the control group (p < 0.05). A 48-hour incubation period produced greater GRd activity in all groups compared to a 24-hour period (p < 0.05).

CONCLUSIONS

Irradiation did not damage rat hepatocytes in this study. Infrared was shown to stimulate GSH production, while laser irradiation increased GRd activity.

Effects of continuous light exposure on antioxidant enzymes, porphyric enzymes and cellular damage in the Harderian gland of the Syrian hamster

The Syrian hamster Harderian gland (HG), an organ present in the male two secretory cell types (type-I and type-II cells), is physiologically exposed to high oxidative stress because of high concentrations of porphyrins and their precursor, 5-aminolevulinic acid. Because of its juxtaorbital location, the HG is accessible to light, and subject to phototoxic effects of these substances. After having previously demonstrated circadian rhythms in antioxidant enzymes, porphyric enzymes and oxidative damage of proteins and lipids, as well as influences of melatonin on these parameters, we have now studied the effects of continuous light (LL), which suppresses melatonin secretion by the pineal gland. Measurements were performed in two different circadian phases, in order to detect the presence or absence of day/night differences. In LL, no differences between circadian phases of subjective day and subjective night were demonstrable for 5-aminolevulinate synthase, 5-aminolevulinate dehydratase, porphobilinogen deaminase, or superoxide dismutase; temporal differences in glutathione reductase and catalase were markedly diminished, whereas all these parameters showed marked day/night differences in the rats exposed to a light/dark cycle of 14:10. In LL, oxidative damage to lipids was minimally effected, while protein damage was enhanced. LL also caused a reduction in the percentage of type-II cells. Therefore, cell differentiation in the HG does not seem to be controlled only by the androgen, but, unexpectedly, also by melatonin.

Effects of low chronic doses of ionizing radiation on antioxidant enzymes and G6PDH activities in Stipa capillata (Poaceae)

Stipa capillata (Poaceae) seeds were harvested from a control area (displaying a gamma dose rate of 0.23 micro Sv h(-1)) (C plants) and from two contaminated areas (5.4 and 25 micro Sv h(-1)) on the Semipalatinsk nuclear test site (SNTS) in Kazakhstan. The plants were grown for 124 d in a greenhouse under controlled conditions and exposed to three different treatments: (0) control; (E) external gamma irradiation delivered by a sealed 137Cs source with a dose rate of 66 micro Sv h(-1); (E+I) E treatment combined with internal beta irradiation due to contamination by 134Cs and 85Sr via root uptake from the soil. The root uptake led to a contamination of 100 Bq g(-1) for 85Sr and 5 Bq g(-1) for 134Cs (of plant dry weight) as measured at harvest. The activity of SOD, APX, GR, POD, CAT, G6PDH, and MDHAR enzymes was measured in leaves. Under (0) treatment, all enzymes showed similar activities, except POD, which had higher activity in plants originating from contaminated areas. Treatment (E) induced an enhancement of POD, CAT, GR, SOD, and G6PDH activities in plants originating from contaminated areas. Only control plants showed any stimulation of APX activity. Treatment (E+I) had no significant effect on APX, GR, CAT, and POD activities, but MDHAR activity was significantly reduced while SOD and G6PDH activities were significantly increased. The increase occurred in plants from all origins for SOD, with a greater magnitude as a function of their origin, and it occurred only in plants from the more contaminated populations for G6PDH. This suggests that exposure to a low dose rate of ionizing radiation for almost a half century in the original environment of Stipa has led to natural selection of the most adapted genotypes characterized by an efficient induction of anti-oxidant enzyme activities, especially SOD and G6PDH, involved in plant protection against reactive oxygen species.

Protective role of superoxide dismutases against ionizing radiation in yeast

The protective role of superoxide dismutases (SODs) against ionizing radiation, which generates reactive oxygen species (ROS) harmful to cellular function, was investigated in the wild-type and in mutant yeast strains lacking cytosolic CuZnSOD (sod1Delta), mitochondrial MnSOD (sod2Delta), or both SODs (sod1Deltasod2Delta). Upon exposure to ionizing radiation, there was a distinct difference between these strains in regard to viability and the level of protein carbonyl content, which is the indicative marker of oxidative damage to protein, intracellular H2O2 level, as well as lipid peroxidation. When the oxidation of 2',7'-dichlorofluorescin was used to examine the hydroperoxide production in yeast cells, the SOD mutants showed a higher degree of increase in fluorescence upon exposure to ionizing radiation as compared to wild-type cells. These results indicated that mutants deleted for SOD genes were more sensitive to ionizing radiation than isogenic wild-type cells. Induction and inactivation of other antioxidant enzymes, such as catalase, glucose 6-phosphate dehydrogenase, and glutathione reductase, were observed after their exposure to ionizing radiation both in wild-type and in mutant cells. However, wild-type cells maintained significantly higher activities of antioxidant enzymes than did mutant cells. These results suggest that both CuZnSOD and MnSOD may play a central role in protecting cells against ionizing radiation through the removal of ROS, as well as in the protection of antioxidant enzymes.

Studies of methyl 2-nitroimidazole-1-acetohydroxamate (KIN-804) 1: effect on free radical scavenging system in mice bearing Ehrlich ascites carcinoma

Methyl 2-nitroimidazole-1-acetohydroxamate (KIN-804) is a 2-nitroimidazole derivative containing a hydroxamate side chain designed to enhance the radiosensitization response of hypoxic cells. The possible sensitization of tumor tissue by KIN-804 can be evaluated through investigation of the levels of the free radical scavengers; namely, glutathione (GSH) and its complex enzyme system including glutathione reductase (GR) and glutathione peroxidase (GSH-Px), as well as glucose-6-phosphate dehydrogenase (G-6-PD). Female albino mice were inoculated with Ehrlich carcinoma in the thigh. Administration of KIN-804 (i.p. 80 mg/kg body weight) was carried out 20 min before localized irradiation of 10 Gy. The data revealed that KIN-804 administration, followed or not by gamma irradiation, resulted in a significant decrease in GSH content in tumor tissues associated with inhibition in GR and G-6-PD activities. Blood GSH-Px was enhanced in tumor inoculated mice and the administration of KIN-804 returned it to the normal value. These changes were more noticeable in tumor bearing mice exposed to both KIN-804 and irradiation.

Elevation of mouse liver glutathione level by low-dose gamma-ray irradiation and its effect on CCl4-induced liver damage

We examined the elevation of glutathione (GSH) levels in the liver of C57BL/6 female mice after low-dose r-ray irradiation and its inhibitory effect on CClI4-induced liver damage. The liver GSH level increased soon after irradiation with 50 cGy of gamma-rays, reached a maximum at around 12 post-treatment, and returned almost to the control level by 24 h. The activities of glutathione reductase, and glutathione peroxidase also showed the same pattern of change, while the activity of gamma-glutamylcysteine synthetase showed a gradual increase up to 24 h. The effect of pre-irradiation on CCl4-induced liver damage was also investigated. The activities of glutamic oxaloacetic transaminase and glutamic pyruvic transaminase in serum were markedly increased 12 h post-treatment with CCl4. Both increases were significantly suppressed by a single low-dose pre-irradiation. Malondialdehyde, a marker of lipidperoxidation, was also greatly elevated after CCl4 treatment, and its increase was suppressed by irradiation. These results suggest low-dose gamma-ray irradiation might be effective for the prevention of and/or therapy of various reactive oxygen species-related diseases including cancer.

Recovery of antioxidants and reduction in lipid hydroperoxides in murine epidermis and dermis after acute ultraviolet radiation exposure

In previous studies we have found that a single acute dose of ultraviolet radiation to murine skin causes a large degree of destruction of enzymic and non-enzymic antioxidants immediately after irradiation. In the present study, we wished to elucidate the recovery of antioxidants after a single dose of ultraviolet (UV) radiation. We measured antioxidants and lipid hydroperoxides (as a marker of membrane damage) in murine epidermis and the dermis at 0, 3, 12, 24, 72 and 120 h after exposure to UV radiation (25 J/cm2, UVA+UVB). Lipid hydroperoxides showed the highest values immediately after UV exposure and returned to control values within 24 h in both epidermis and dermis. The activities of catalase, glutathione peroxidase and glutathione reductase showed the lowest activities immediately after UV exposure; superoxide dismutase activities reached a minimum at 3 h postexposure. The pattern of recovery was different for each enzyme and for epidermis and dermis. The activities of superoxide dismutase and catalase decreased remarkably and recovered slowly. Superoxide dismutase in the dermis recovered full activity by 120 h and in the epidermis by 12 h. Catalase activity in both epidermis and dermis had returned to only 50% of control activity at 120 h, although the epidermis showed a temporary increase (to 93%) at 24 h. Glutathione peroxidase and glutathione reductase were slightly decreased immediately after irradiation, recovered to 100% at 3 h and then increased to 200-250% in both the epidermis and the dermis at various times; values had returned to 100% in epidermis by 120 h but remained elevated in dermis.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of glutathione reductase activity by a carbamoylating nitrosourea: effect on cellular radiosensitivity

Nitrosoureas inactivate cellular glutathione reductase. N,'N'1,3-bis(trans-4-hydroxycyclohexyl)-N'-nitrosoureas (BCyNU), a nitrosourea reported to selectively inhibit glutathione reductase (GR) activity, was examined to determine if it could be used as a means to inhibit cellular levels of this enzyme in radiobiology studies. Confirmation of drug-induced inhibition of GR activity was demonstrated using a cell-free model system employing purified GR. Cellular studies with Chinese hamster V79A03 showed that BCyNU decreased cellular glutathione content concomitant with an inhibition of specific GR activity. Under relatively nontoxic conditions, cellular exposure to BCyNU (25 microM, 0.25 h) either before or after radiation treatment, increased cellular radiosensitivity with the optimum time for drug addition being immediately following radiation. At a BCyNU dosage which produced less than or equal to 5% cell toxicity, a marked decrease in radioresistance was characterized as a reduction in both Dq (24 +/- 1.5%) and Do (8 +/- 0.5%) concomitant with a 25 +/- 2% decrease in cellular glutathione reductase (GR) activity. At cytotoxic drug dosages (25 microM, 1 h; cell survival 79 +/- 7%), a marked radiosensitization manifested by a 1.25 +/- .07-fold reduction in the Dq was observed concomitant with a 49 +/- 4% decrease in GR activity. Using cells enriched in different stages of the cell cycle, BCyNU caused cell-age dependent cytotoxicity with preferential killing of cells in the radioresistant late-S-phase, a likely explanation for its radiosensitizing capabilities at high drug dosages. Data obtained at nontoxic drug dosages suggest that GR-inactivation may be an important component of cellular response to free-radical induced damage.

Acute effects of near ultraviolet and visible light on the cutaneous antioxidant defense system

Reactive oxygen species are considered to play an important role in cutaneous pathology. Enzymic and non-enzymic antioxidants can prevent oxidative damage but may be overcome by strong pro-oxidative stimuli. The acute effect of a single exposure to near ultraviolet (UVA)/visible radiation (greater than 320 nm) on various skin antioxidants was examined in hairless mice immediately after irradiation. Impairment of cutaneous catalase and glutathione reductase activity was observed. Superoxide dismutase and glutathione peroxidase were not significantly influenced. Inhibition of catalase may render skin more susceptible to the damaging effects of hydrogen peroxide and its reaction products such as the hydroxyl radical. Partially diminished glutathione reductase activity is not accompanied by a change in reduced/oxidized glutathione level immediately after irradiation. There was a tendential (not statistically significant) decrease in cutaneous tocopherol, ubiquinol + ubiquinone 9 and ascorbic acid levels, either indicating direct photodestruction or consumption by reaction products of photooxidative stress. This partial impairment of the cutaneous antioxidant defense system by near ultraviolet/visible light, showing that the most susceptible component in skin is catalase, suggests possible pharmacological interventions.

[The function of enzymes for the antioxidative protection of the bone marrow cells in rats during irradiation, bone fracture and combined radiation injury]

The activity of superoxide dismutase, glutathione peroxidase, glutathione reductase and glutathione: dehydroascorbate oxidoreductase is lower in the bone marrow than in the liver. The changes in the cellular antioxidative enzymatic system during leg bones fracture and X-ray irradiation are more pronounced in the rat bone marrow, as compared to the liver. The data obtained are in keeping with selective bone-marrow radiosensitivity and with the effect of exogenous superoxide dismutase and glutathione as radioprotectors.

Effect of whole body gamma-radiation on glutathione reductase of rat tissues

Adult female Sprague Dawley rats approximate ten months old were exposed to whole body gamma radiation of sublethal (4 Gy) and lethal (10 Gy) doses of radiation. Serum glutathione reductase enzyme values of 4 Gy exposed rats did not show any change on first and fourth day but significantly decreased on eighth day, while enzyme values in 10 Gy exposed group remained unaltered throughout. Heart glutathione reductase activities of sublethal group did not show any change on first and eighth day but significantly decreased on fourth day. Rats exposed to lethal doses of radiation, enzyme activities remained unchanged throughout. Liver glutathione reductase enzyme values of 4 Gy exposed group showed significant decrease on first and fourth day but arrived at control values on eighth day while the same in 10 Gy exposed group showed significant decrease from first day till the eighth day. An appreciable diminution was observed in spleen glutathione reductase enzyme activities of sublethal and lethal exposed rats from first day till eighth day.

Changes of reduced glutathion, glutathion reductase, and glutathione peroxidase after radiation in guinea pigs

In this series of experiments the protective action of reduced glutathion due to ionizing radiation has been studied. In the experimental group 18 guinea pigs were exposed to successive radiations of 150 rad 3 or 4 days apart. Total dose given amounted to 750 rad which is the LD50 for guinea pigs. Blood samples were taken 30 min after each exposure. The control series were sham radiated but otherwise treated identically. The cells of the removed blood samples were separated by centrifugation and were subjected to the reduced glutathion stability test. GSSGR, GPer, and LDH enzyme activities were also measured of which the latter served as a marked enzyme. It was found that LDH did not show any alteration after radiation. The reduced glutathion stability test showed a consistent but minor reduction (P greater than 0.05), in the experimental group. GSSGR enzyme activity on the other hand was reduced significantly (from 176.48 +/- 11.32 to 41.34 +/- 1.17 IU/ml of packed erythrocytes, P less than 0.001) in the same group. GPer activity showed a consistent but minor elevation during the early phase of the experimental group. It was later increased significantly beginning after 600 rad total radiation on the fourth session (P less than 0.050).