Antioxidative effects of melatonin in protection against cellular damage caused by ionizing radiation

Radioprotective effects of quercetin and ethanolic extract of propolis in gamma-irradiated mice

The aim of this study was to assess radioprotective effects of quercetin and the ethanolic extract of propolis (EEP) in CBA mice exposed to a single radiation dose 4 Gy (60Co). The mice were treated with 100 mg kg(-1) quercetin or EEP a day for three consecutive days either before (pre-treatment) or after gamma-irradiation (therapy). Leukocyte count was determined in blood drawn from the tail vein, and DNA damage in leukocytes was assessed using the alkaline comet assay. Genotoxic effects of the test compounds were also evaluated in non-irradiated mice. The levels of radioprotection provided by both test compounds were compared with those established in mice that were given chemical radioprotector S-(2-aminoethy1)isothiouronium bromide hydrobromide (AET). Mice that received pre-treatment were less sensitive to irradiation. Mice given the post-irradiation therapy showed a slight but not significant increase in total leukocyte count over irradiated negative control. Quercetin showed better protective properties than EEP in both pre-treatment and therapy, and activated a higher number of leukocytes in non-irradiated mice. The alkaline comet assay suggests that both natural compounds, especially when given as pre-treatment, protect against primary leukocyte DNA damage in mice. At tested concentrations, EEP and quercetin were not genotoxic to non-irradiated mice. AET, however, caused a slight but not significant increase in DNA damage. Although the results of this study show the radioprotective potential of the test compounds, further investigation is needed to clarify the underlying protection mechanisms.

Reducing oxidative/nitrosative stress: a newly-discovered genre for melatonin

The discovery of melatonin and its derivatives as antioxidants has stimulated a very large number of studies which have, virtually uniformly, documented the ability of these molecules to detoxify harmful reactants and reduce molecular damage. These observations have clear clinical implications given that numerous age-related diseases in humans have an important free radical component. Moreover, a major theory to explain the processes of aging invokes radicals and their derivatives as causative agents. These conditions, coupled with the loss of melatonin as organisms age, suggest that some diseases and some aspects of aging may be aggravated by the diminished melatonin levels in advanced age. Another corollary of this is that the administration of melatonin, which has an uncommonly low toxicity profile, could theoretically defer the progression of some diseases and possibly forestall signs of aging. Certainly, research in the next decade will help to define the role of melatonin in age-related diseases and in determining successful aging. While increasing life span will not necessarily be a goal of these investigative efforts, improving health and the quality of life in the aged should be an aim of this research.

Evaluation of the free radical scavenging activity and radioprotective efficacy of Grewia asiatica fruit

The radioprotective effect of Grewia asiatica fruit (GAE) which contains anthocyanin-type cyanidin 3-glucoside, vitamins C and A, minerals, carotenes and dietary fibre was studied. For the study Swiss albino mice were divided into five groups: (1) control (vehicle treated); (2) GAE treated (700 mg kg(-1) day(-1) for 15 days); (3) irradiated (5 Gy); (4) GAE+irradiated and (5) irradiated+GAE treated. The irradiation of animals resulted in a significant elevation of lipid peroxidation in terms of thiobarbituric acid reactive substances (TBARS) content and depletion in glutathione (GSH) and protein levels at all intervals studied, namely 1-30 days, in comparison to the control group. Treatment of mice with GAE before and after irradiation caused a significant depletion in TBARS content followed by a significant elevation in GSH and protein concentration in the intestine and testis of mice at all post-irradiation autopsy intervals in comparison to irradiated mice. Significant protection of DNA and RNA in testis was also noticed. GAE was found to have strong radical scavenging activity in 2,2-diphenyl-1-picrylhydrazyl (DPPH(*)) and O(2)(-) assays and also showed in vitro radioprotective activity in protein carbonyl assay in a dose-dependent manner. The above results prove the radioprotective efficacy of GAE.

Radioprotective effect of moderate wine consumption in patients with breast carcinoma

PURPOSE

Given the high cost and side effects of radioprotective agents such as amifostine, attention has been focused on potentially equally effective but less expensive and toxic natural substances. We evaluated the potential radioprotective effects of wine in preventing skin toxicity in patients with breast cancer.

METHODS AND MATERIALS

Before treatment, the medical history and habits of patients were assessed and the information recorded in their clinical folders. Patients were divided into three groups based on the dose/fractionation scheme used: control group, 60.4 Gy (standard technique); Modulated Accelerated Radiotherapy in Adjuvant treatment of breast cancer (MARA)-1 protocol group, 44 Gy (concomitant boost to tumoral bed); and MARA-2 protocol group, 60 Gy (concomitant boost to tumoral bed). The impact of the following variables on acute skin toxicity was evaluated by chart review: radiotherapy protocol, planning target volume (PTV), comorbidity (e.g., hypertension and diabetes), hemoglobin level before therapy, adjuvant hormone therapy, adjuvant chemotherapy, cigarette smoking, and drinking habits.

RESULTS

The study population consisted of 348 patients. More severe skin toxicity was significantly associated with the radiotherapy protocol (p < 0.001) and median PTV (p = 0.005). In addition, the incidence of acute toxicity of Grade 2 or greater was higher in patients without alcohol intake (38.4% vs. 22.3%, p = 0.021). The daily amount of alcohol intake also influenced the incidence of skin toxicity, with an incidence of 38.4% in patients with no wine intake, 31.8% in patients drinking half a glass per day, 13.6% in patients drinking one glass per day, and 35.0% in patients drinking two glasses per day. Multivariate analysis showed that wine intake, PTV, and radiotherapy protocol were all significantly correlated with acute toxicity.

CONCLUSIONS

Our results indicate that wine may have a radioprotective effect; however, prospective studies are needed to confirm this beneficial effect of wine and its components.

Melatonin prevents damage elicited by the organophosphorous pesticide diazinon on the mouse testis

Organophosphates like O,O-diethyl O-2-isopropyl-6-methyl pyrimidinyl-4-g-1-phosphorothioate (diazinon) are pesticides used worldwide, which can affect both animals and man even after a single exposure. Whereas their toxicity is due to acetylcholinesterase inhibition, their secondary toxic effects have been related to free oxygen radicals. This study evaluates the effects of a single dose of diazinon and melatonin-a powerful antioxidant-on plasmatic acetylcholinesterase activity and testis histopathology in adult mice 1 and 32 days post-treatment. Diazinon diminished the plasma acetylcholinesterase activity on day 1 post-treatment, although testosterone levels remained unaffected. Morphometrical analysis showed a decrease in seminiferous epithelium height (days 1 and 32), whereas an increase in testicular superoxide dismutase (SOD) activity was detected (day 32). Melatonin pretreatment prevented every alteration induced by diazinon, except the diminution of acetylcholinesterase plasmatic activity. Testicular damage might be due to elevated concentrations of free oxygen radicals released upon diazinon exposure, inducing alterations in the DNA and promoting local apoptosis; however, antioxidant pretreatment with melatonin prevents or diminishes this damage.

Comparison of the protective effects of melatonin and amifostine on radiation-induced epiphyseal injury

PURPOSE

We compared the effects of amifostine and melatonin in preventing radiation-induced epiphyseal growth plate injury in rats.

MATERIALS AND METHODS

Four-week-old (65-85 g), growing male Sprague-Dawley rats were randomly assigned to receive radiation alone, at 25 Gy in three fractions (group R), or this dose of fractionated radiation proceeded by prophylactic amifostine 200 mg/kg i.p. (group A), melatonin 15 mg/kg i.p. (group M), or amifostine + melatonin (group AM). The right rear extremity of each animal was irradiated while the contralateral leg was shielded from radiation, as a control. Bone growth based on the length of the tibia, femur, and overall limb was calculated 6 weeks after the treatment.

RESULTS

In groups R, A, M, and AM, the mean growth loss (GL) for the overall limb was 56.9 +/- 8.1%, 46.8 +/- 7.7%, 36.6 +/- 4.3%, and 38.5 +/- 5.1%, respectively. The limb length discrepancies (LLD) in groups R, A, M, and AM were 13.8 +/- 1.4%, 10.5 +/- 0.3%, 7.4 +/- 0.7%, and 8.8 +/- 1.1%, respectively. Differences in LLD were significant between each treatment group and group R (range: p = 0.0001-0.001). Differences in either of mean GL and LLD were not significant between groups M and AM; however both of these groups had significantly less GL and LLD than group A.

CONCLUSIONS

We observed a superior radioprotective function of melatonin over amifostine in preventing radiation-induced epiphyseal growth plate injury, without any increase in radioprotective effect by adding amifostine to melatonin.

Synthesis and antioxidant properties of novel benzimidazoles containing substituted indole or 1,1,4,4-tetramethyl-1,2,3,4-tetrahydro-naphthalene fragments

Some 6-fluoro-5-substituted-benzimidazole derivatives in which indole and 1,1,4,4-tetramethyl-1,2,3,4-tetrahydro-naphthalene groups were attached to the 2-position of the benzimidazole ring were synthesized and tested for antioxidant properties in vitro. Almost all the synthesized compounds at the 10(-3) M concentrations showed superoxide anion scavenging activity. Compounds 5, 3, 9, 4, 17 and 13 have strong inhibitory effects on superoxide anion formation (98%, 93%, 91%, 88%, 85% and 81%, respectively) at 10(-3) M concentration and these results are better than 30 IU of superoxide dismutase (SOD) (76%). Compound 11 is the most effective scavenger of 2,2-diphenyl-1-picrylhydrazyl (DPPH) stable free radical at 10(-3)M (61%) concentration.

Protective effects of melatonin and N-acetylserotonin on aflatoxin B1-induced lipid peroxidation in rats

Aflatoxin B1 (AFB1) is a potent hepatotoxic and hepatocarcinogenic mycotoxin. Reactive oxygen species are considered to participate in the main mechanism of aflatoxin toxicity. Melatonin (Mel) is a hormone which has antioxidative activities. N-acetylserotonin (NAc-5HT) is an immediate precursor of Mel. Melatonin is documented to be completely safe in humans and animals. The aim of our study was to examine the potential protective effects of Mel or NAc-5HT against lipid peroxidation (LPO), caused by AFB1 in male Wistar rats. Mel and NAc-5HT were intraperitoneally (i.p.) injected for 3 weeks in late afternoon (16:00-18:00) injections (20 mg kg(-1) BW/daily). AFB1 (50 microg kg(-1) BW/daily) was administered i.p. 6 h prior to indoleamine injections. Concentrations of malondialdehyde + 4-hydroxyalkenals (MDA + 4-HDA), as an index of LPO, were measured in liver, brain, lung, testis and kidney homogenates. The level of LPO in tissue homogenates was expressed as the amount of MDA + 4-HDA (nmol) per milligram of protein. AFB1 increased LPO in the liver, lung, brain and testis, but not the kidney. The increase of LPO caused by AFB1 injections was completely prevented by either Mel or NAc-5HT in all the tissues examined. Melatonin can be considered as a protective pharmacological agent in intoxication with AFB1 and the protective effect of NAc-5HT against aflatoxin-induced LPO broadens the knowledge about its antioxidative properties.

Effects of N-acetylcysteine amide (NACA), a thiol antioxidant on radiation-induced cytotoxicity in Chinese hamster ovary cells

Ionizing radiation is known to cause tissue damage in biological systems, mainly due to its ability to produce reactive oxygen species (ROS) in cells. Many thiol antioxidants have been used previously as radioprotectors, but their application has been limited by their toxicity. In this investigation, we have explored the possible radioprotective effects of a newly synthesized thiol antioxidant, N-acetylcysteine amide (NACA), in comparison with N-acetylcysteine (NAC), a commonly used antioxidant. Protective effects of NACA and NAC were assessed using Chinese hamster ovary (CHO) cells, irradiated with 6 gray (Gy) radiation. Oxidative stress parameters, including levels of reduced glutathione (GSH), cysteine, malondialdehyde (MDA), and activities of antioxidant enzymes like glutathione peroxidase, glutathione reductase, and catalase, were measured. Results indicate that NACA was capable of restoring GSH levels in irradiated cells in a dose dependent manner. In addition, NACA prevented radiation-induced loss in cell viability. NACA further restored levels of malondialdehyde, caspase-3 activity, and antioxidant enzyme activities to control levels. Although NAC affected cells in a similar manner to NACA, its effects were not as significant. Further, NAC was also found to be cytotoxic to cells at higher concentrations, whereas NACA was non-toxic at similar concentrations. These results suggest that NACA may be able to attenuate radiation-induced cytotoxicity, possibly by its ability to provide thiols to cells.

Oxidative stress impairs oocyte quality and melatonin protects oocytes from free radical damage and improves fertilization rate

We investigated the relationship between oxidative stress and poor oocyte quality and whether the antioxidant melatonin improves oocyte quality. Follicular fluid was sampled at oocyte retrieval during in vitro fertilization and embryo transfer (IVF-ET). Intrafollicular concentrations of 8-hydroxy-2'-deoxyguanosine (8-OHdG) in women with high rates of degenerate oocytes were significantly higher than those with low rates of degenerate oocytes. As there was a negative correlation between intrafollicular concentrations of 8-OHdG and melatonin, 18 patients undergoing IVF-ET were given melatonin (3 mg/day), vitamin E (600 mg/day) or both melatonin and vitamin E. Intrafollicular concentrations of 8-OHdG and hexanoyl-lysine adduct were significantly reduced by these antioxidant treatments. One hundred and fifteen patients who failed to become pregnant with a low fertilization rate (< or =50%) in the previous IVF-ET cycle were divided into two groups during the next IVF-ET procedure; 56 patients with melatonin treatment (3 mg/day) and 59 patients without melatonin treatment. The fertilization rate was improved by melatonin treatment compared to the previous IVF-ET cycle. However, the fertilization rate was not significantly changed without melatonin treatment. Oocytes recovered from preovulatory follicles in mice were incubated with H2O2 for 12 hr. The percentage of mature oocytes with a first polar body was significantly reduced by addition of H2O2 (300 microm). The inhibitory effect of H2O2 was significantly blocked by simultaneous addition of melatonin. In conclusion, oxidative stress causes toxic effects on oocyte maturation and melatonin protects oocytes from oxidative stress. Melatonin is likely to improve oocyte quality and fertilization rates.

Melatonin mitigates oxidative damage and apoptosis in mouse cerebellum induced by high-LET 56Fe particle irradiation

Cerebellum is a vital organ responsible for the motor coordination and recently it has been reported to be involved in cognitive function. Reactive oxygen species are implicated in neurodegeneration and cognitive disorders because of higher vulnerability of neuronal tissues. Therefore, the present study aimed at investigating the role of melatonin against high-LET (linear energy transfer) (56)Fe particle irradiation-induced oxidative damage and apoptosis in the mouse cerebellum. Radiation-induced oxidative damage was examined using a neuronal-specific terminal deoxynucleotidyl transferase-mediated nick end-labeling (TUNEL), quantitative histopathology, DNA damage (comet assay), carbonyl content and 4-HAE + MDA (4-hydroxyalkenal + malondialdehyde) status of the cerebellum. Radiation exposure augmented the number of TUNEL positive cell, DNA migration in the comet tail and carbonyl and 4-HAE + MDA level in the cerebellum. Melatonin pretreatment significantly inhibited the oxidative damage to biomolecules as well as cerebellar apoptosis. Melatonin-treated irradiated mice showed higher counts of intact Purkinje cells as compared to vehicle-treated irradiated mice. In addition, radiation induced augmentation of 8-hydroxy-2'-deoxyguanosine (8-OHdG) and a decline in the total antioxidant capacity in serum; these changes were also ameliorated by melatonin pretreatment. The present results provide evidence supporting the antioxidant and neuroprotective function of melatonin.

Cardiovascular diseases: protective effects of melatonin

This brief review considers some of the cardiac diseases and conditions where free radicals and related reactants are believed to be causative. The report also describes the beneficial actions of melatonin against oxidative cardiovascular disorders. Based on the data available, melatonin seems to have cardioprotective properties via its direct free radical scavenger and its indirect antioxidant activity. Melatonin efficiently interacts with various reactive oxygen and reactive nitrogen species (receptor independent actions) and it also upregulates antioxidant enzymes and downregulates pro-oxidant enzymes (receptor-dependent actions). Moreover, melatonin enters all cells and subcellular compartments and crosses morphophysiologic barriers. These findings have implications for the protective effects of melatonin against cardiac diseases induced by oxidative stress. Melatonin attenuates molecular and cellular damages resulting from cardiac ischemia/reperfusion in which destructive free radicals are involved. Anti-inflammatory and antioxidative properties of melatonin are also involved in the protection against a chronic vascular disease, atherosclerosis. The administration of melatonin, as a result of its antioxidant features, has been reported to reduce hypertension and cardiotoxicity induced by clinically used drugs. The results described herein help to clarify the beneficial effects of melatonin against these conditions and define the potential clinical applicability of melatonin in cardiovascular diseases.

Melatonin prevents inflammation and oxidative stress caused by abdominopelvic and total body irradiation of rat small intestine

We investigated the day-night differences in intestinal oxidative-injury and the inflammatory response following total body (TB) or abdominopelvic (AP) irradiation, and the influence of melatonin administration on tissue injury induced by radiation. Rats (male Wistar, weighing 220-280 g) in the irradiated groups were exposed to a dose of 8 Gy to the TB or AP region in the morning (resting period - 1 h after light onset) or evening (activity span - 13 h after light onset). Vehicle or melatonin was administered immediately before, immediately after and 24 h after irradiation (10, 2.0 and 10 mg/kg, ip, respectively) to the irradiated rats. AP (P < 0.05) and TB (P < 0.05) irradiation applied in the morning caused a significant increase in thiobarbituric acid reactive substance (TBARS) levels. Melatonin treatment in the morning (P < 0.05) or evening (P < 0.05) decreased TBARS levels after TB irradiation. After AP irradiation, melatonin treatment only in the morning caused a significant decrease in TBARS levels (P < 0.05). Although we have confirmed the development of inflammation after radiotherapy by histological findings, neither AP nor TB irradiation caused any marked changes in myeloperoxidase activity in the morning or evening. Our results indicate that oxidative damage is more prominent in rats receiving TB and AP irradiation in the morning and melatonin appears to have beneficial effects on oxidative damage irrespective of the time of administration. Increased neutrophil accumulation indicates that melatonin administration exerts a protective effect on AP irradiation-induced tissue oxidative injury, especially in the morning.

A radiobiological review on melatonin: a novel radioprotector

In spite of the fact that radiotherapy is a common and effective tool for cancer treatment; the radio sensitivity of normal tissues adjacent to the tumor which are unavoidably exposed to radiation limits therapeutic gain. For the sake of improvement in radiation therapy, radiobiology- the study of the action of ionizing radiation on living things- plays a crucial role through explaining observed phenomena, and suggesting improvements to existing therapies. Due to the damaging effects of ionizing radiation, radiobiologists have long been interested in identifying novel, nontoxic, effective, and convenient compounds to protect humans against radiation induced normal tissue injuries. In hundreds of investigations, melatonin (N-acetyl-5-methoxytryptamine), the chief secretory product of the pineal gland in the brain, has been documented to ameliorate the oxidative injuries due to ionizing radiation. This article reviews different features that make melatonin a potentially useful radioprotector. Moreover, based on radiobiological models we can hypothesize that melatonin may postpone the saturation of repair enzymes which leads to repairing more induced damage by repair system and more importantly allows the use of higher doses of radiation during radiotherapy to get a better therapeutic ratio. The implications of the accumulated observations suggest by virtue of melatonin's radioprotective and anticancer effects; it is time to use it as a radioprotector both for radiation workers and patients suffering from cancer either alone for cancer inhibition or in combination with traditional radiotherapy for getting a favorable efficacy/toxicity ratio during the treatment. Although compelling evidence suggests that melatonin may be effective for a variety of disorders, the optimum dose of melatonin for human radioprotection is yet to be determined. We propose that, in the future, melatonin improve the therapeutic ratio in radiation oncology.

Methylprednisolone and indomethacin inhibit oxidative stress mediated apoptosis in rat C6 glioblastoma cells

Glioblastoma patients receive anti-inflammatory agent for alleviation of vasogenic edema and pain prior to surgery, radiotherapy, and chemotherapy. Oxidative stress is an important mechanism of action of some chemotherapeutic agents in the treatment of glioblastoma. So, we examined the modulatory effects of methylprednisolone (MP, a steroidal anti-inflammatory agent) and indomethacin (IM, a non-steroidal anti-inflammatory agent) on apoptosis in rat C6 glioblastoma cells following oxidative stress with hydrogen peroxide (H(2)O(2)). Exposure of C6 cells to 1 mM H(2)O(2) for 24 h caused significant amounts of morphological and biochemical features of apoptosis. Expressions of Bax and Bcl-2 at mRNA and protein levels were altered resulting in an increase in Bax : Bcl-2 ratio in apoptotic cells, which also exhibited overexpression of 80 kDa calpain and an increase in calpain-cleaved 145 kDa alpha-spectrin breakdown product. Immunofluorescent and propidium iodide labeling detected caspase-3-p20 fragment in apoptotic cells, indicating activation of caspase-3 as well. Treatment of cells with 1 microM MP or 10 microM IM alone did not induce apoptosis. Pretreatment (1 h) with either 1 microM MP or 10 microM IM significantly inhibited H(2)O(2) mediated apoptosis in C6 cells. Thus, pretreatment of glioblastoma with an anti-inflammatory agent, either steroidal or non-steroidal, may compromise the action of a chemotherapeutic agent that mediates therapeutic action via oxidative stress.

Effect of curcumin and curcumin copper complex (1:1) on radiation-induced changes of anti-oxidant enzymes levels in the livers of Swiss albino mice

The effect of mononuclear copper (II) complex of curcumin in 1:1 stoichiometry (hereafter referred to as complex) administered 30 min before gamma-irradiation (4.5 Gy) on alterations in antioxidant and Thiobarbituric acid reactive substances (TBARS) levels in livers was studied in comparison to curcumin at a dose of 50 mg/kg. The different antioxidants like GSH, GST, catalase, SOD, TBARS and total thiols were estimated in the liver homogenates excised at different time intervals (1, 2 and 4 h) post irradiation using colorimetric methods. There was a radiation-induced decrease in the levels of all the studied enzymes at 1 h post irradiation, while an increase was observed at later time points. Both curcumin and complex treatment in sham-irradiated mice decreased the levels of GSH and total thiols, whereas there was an increase in the levels of catalase, GST and SOD compared to normal control. Under the influence of irradiation, both curcumin and complex treatment protected the decline in the levels of GSH, GST, SOD, catalase and total thiols, and inhibited radiation-induced lipid peroxidation. Further, the complex was found to be more effective in protecting the enzymes at 1 h post irradiation compared to curcumin treated group. This may be due to the higher rate constants of the complex compared to curcumin for their reactions with various free radicals.

Microcystin-induced 8-hydroxydeoxyguanosine in DNA and its reduction by melatonin, vitamin C, and vitamin E in mice

Microcystin LR (MC-LR), a liver-specific toxin synthesized by Microcystis aeruginosa, was investigated. MC-LR initiated reactive oxygen species formation followed by damaging DNA and some other cellular components. We investigated the ability of MC-LR to induce oxidative DNA damage by examining the formation of 8-hydroxydeoxyguanosine (8-OH-dG) using HPLC with electrochemical detection. Melatonin, vitamin C (ascorbate), and vitamin E (as Trolox), all of which are free radical scavengers, markedly inhibited the formation of 8-OH-dG in a concentration-dependent manner. The concentration that reduced DNA damage by 50% (IC(50)) was 0.55, 31.4, and 36.8 microM for melatonin, ascorbate, and Trolox, respectively. The results show that melatonin is 60- and 70-fold more effective than vitamin C or vitamin E, respectively, in reducing oxidative DNA damage. These findings are consistent with the conclusion that melatonin's highly protective effect against microcystin toxicity relates, at least in part, to its direct hydroxyl radical scavenging ability.

AFMK, a melatonin metabolite, attenuates X-ray-induced oxidative damage to DNA, proteins and lipids in mice

Antioxidant function of melatonin is well established. However, N(1)-acetyl-N(2)-formyl-5-methoxykynuramine (AFMK), a melatonin metabolite is a sparingly investigated biogenic amine, especially in relation to its in vivo antioxidant function. We have evaluated the oxidative damage to biomolecules (DNA, protein and lipid) induced by X-irradiation in C57BL mice and the prophylactic action of AFMK. The extent of DNA damage was analyzed by single-cell gel electrophoresis in cerebral cortex and serum 8-hydroxydeoxyguanosine (8-OHdG) levels by enzyme-linked immunosorbent assay. Oxidative modification of protein and lipid was measured in the terms of carbonyl content and 4-HAE + MDA (4-hydroxyalkenal + malondialdehyde) status of brain cortex. Radiation exposure dramatically augmented the level of 8-OHdG in serum as well as DNA migration in the comet tail. AFMK pretreatment significantly inhibited DNA damage. In addition, radiation-induced augmentation of protein carbonyl content and HAE + MDA was ameliorated by AFMK pretreatment. Whole-body exposure of mice to X-irradiation also reduced the level of brain sulfhydryl contents (protein-bound sulfhydryl, total sulfhydryl, and nonprotein sulfhydryl) which were significantly protected by AFMK. Radiation-induced decline in the total antioxidant capacity of plasma was significantly reversed in AFMK pretreated mice. Moreover, AFMK showed a very high level of in vitro hydroxyl radical scavenging potential which was measured by an electron spin resonance (ESR) study of the 2-hydroxy-5,5-dimethyl-1-pyrrolineN-oxide (DMPO-OH) adduct. IC(50) values resulting from ESR analysis was 338.08 nm. The present study indicate that AFMK is a potent antioxidant in both in vivo and in vitro systems.

Protective effects of melatonin and indole-3-propionic acid against lipid peroxidation, caused by potassium bromate in the rat kidney

Potassium bromate (KBrO(3)) is classified as a carcinogenic agent. KBrO(3) induces tumors and pro-oxidative effects in kidneys. Melatonin is a well known antioxidant and free radical scavenger. Indole-3-propionic acid (IPA), an indole substance, also reveals antioxidative properties. Recently, some antioxidative effects of propylthiouracil (PTU)-an antithyroid drug-have been found. The aim of the study was to compare protective effects of melatonin, IPA, and PTU against lipid peroxidation in the kidneys and blood serum and, additionally, in the livers and the lungs, collected from rats, pretreated with KBrO(3). Male Wistar rats were administered KBrO(3) (110 mg/kg b.w., i.p., on the 10th day of the experiment) and/or melatonin, or IPA (0.0645 mmol/kg b.w., i.p., twice daily, for 10 days), or PTU (0.025% solution in drinking water, for 10 days). The level of lipid peroxidation products-malondialdehyde + 4-hydroxyalkenals (MDA + 4-HDA)-was measured spectrophotometrically in thyroid homogenates. KBrO(3), when injected to rats, significantly increased lipid peroxidation in the kidney homogenates and blood serum, but not in the liver and the lung homogenates. Co-treatment with either melatonin or with IPA, but not with PTU, decreased KBrO(3)-induced oxidative damage to lipids in the rat kidneys and serum. In conclusion, melatonin and IPA, which prevent KBrO(3)-induced lipid peroxidation in rat kidneys, may be of great value as protective agents under conditions of exposure to KBrO(3).

Ameliorative effect of melatonin against gamma-irradiation-induced oxidative stress and tissue injury

While radiation hazards, due to free radical generation, present an enormous challenge for biological and medical safety, melatonin is a potent scavenger of a variety of free radicals. The aim of this study was to investigate the radioprotective effect of melatonin against oxidative stress and tissue injury induced by gamma radiation. Rats were subjected to two doses of 2 and 4Gy from cesium-137 source. Four days prior to irradiation, animals received melatonin daily (10mg/kg body weight i.p.). In the irradiated animals, the oxidative stress markers malondialdehyde (MDA) and protein carbonyl were significantly increased in the liver, while a marked decrease in hepatic contents of DNA, RNA, and glutathione (GSH) as well as activity of glutathione-S-transferase (GST) was demonstrated. In addition, catalase (CAT) activity was increased in the liver 5 days after irradiation. The levels of total lipids, cholesterol, triglyceride (TG), low-density lipoprotein (LDL), urea, and creatinine, as well as activities of aspartate aminotransferase (AST), alkaline phosphatase (ALP), and gamma-glutamyltransferase (GGT), were significantly increased in sera of the irradiated rats. This is coupled with decreased serum levels of high-density lipoprotein (HDL), total protein and albumin, and total globulins by irradiation. The administration of melatonin alone daily for 4 days caused significant decreases in MDA and protein carbonyl content and produced significant elevations of GSH content and GST activity in the liver. Moreover, significant decreases in total lipids, cholesterol, and TG without change in LDL or HDL levels in serum were demonstrated. Treatment with melatonin for 4 days before acute irradiation significantly abolished radiation-induced elevations in MDA and protein carbonyl levels in the liver and significantly maintained hepatic GSH content, GST, and CAT activities close to the control values. Preirradiation treatment with melatonin showed significantly higher hepatic DNA and RNA contents than irradiated rats. The levels of total lipids, cholesterol, TG, HDL, LDL, total proteins, albumin, total globulins, creatinine, and urea, as well as the activities of AST, ALT, and GGT in serum were significantly ameliorated when melatonin was injected before irradiation. In conclusion, the increase in oxidative stress markers and the concomitant change in antioxidant levels indicate the role of oxidative stress in radiation-induced tissue damage. Moreover, melatonin shows a radioprotective impact against ionizing-radiation-induced oxidative stress and organ injury.

The evaluation of the oxidant injury as a function of time following brain irradiation in a rat model

This study presents the evaluation of the oxidant injury as a function of time following brain irradiation in a rat model. Thirty-five Wistar rats were divided into seven groups. The rats in Group 1 through Group 6 underwent irradiation, whereas the rats in Group 7 underwent sham irradiation. The rats in Group 1 through Group 6 underwent euthanasia at 1 through 48 h following irradiation, whereas the rats in Group 7 underwent euthanasia immediately following sham irradiation. At the time of euthanasia, the brain tissue was dissected for evaluation of the malondialdehyde (MDA) level and the superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSHPX) activities. The mean MDA levels were increased and the mean SOD, CAT and GSHPX activities were decreased at all of the time points for evaluation for the rats that underwent irradiation as compared to the rats that underwent sham irradiation, substantial for Group 1 and gradually leveling out through Group 6. This study confirms that the oxidant injury is evaluated at its best through the first several hours following brain irradiation.

Comparison of 6-hydroxylmelatonin or melatonin in protecting neurons against ischemia/reperfusion-mediated injury

The protective effect of exogenous melatonin or 6-hydroxylmelatonin on neurons was examined in N2a cells following exposure to oxygen-glucose-serum deprivation insults. After N2a cells cultured in vitro were deprived of glucose, serum and oxygen for 90 min, the different concentrations of melatonin or 6-hydroxylmelatonin were added to the medium. Then, treated cells were cultured for different intervals. At the end of the treatment, the collected culture solution was used for the analysis of the activity of lactate dehydrogenase (LDH) and the cells were used for the examination of the following parameters: cell viability (MTT), DNA fragmentation, reactive oxygen species (ROS) production, mitochondrial transmembrane potential, cytochrome C and caspase 3 activity. The results show that melatonin and 6-hydroxylmelatonin both reduced oxygen-glucose-serum deprivation-mediated N2a cell apoptosis, but they could not completely inhibit the apoptosis of the cells and the inhibitory effect of melatonin was stronger than that of 6-hydroxylmelatonin. Both of them could inhibit LDH and cytochrome C release and caspase 3 activity. Although 6-hydroxylmelatonin could no longer maintain mitochondrial transmembrane potential 6 h after reperfusion, its inhibitory effect on cytochrome C release from mitochondria and the scavenging role of ROS were stronger than those of melatonin. Moreover, melatonin promoted ROS production at the 15th min of the reperfusion, and then it began to remove ROS from cells. Our study showed that melatonin and 6-hydroxylmelatonin can be used as supplements in the treatment of neurological disorders involving oxidative stress. Melatonin serves as more than a ROS scavenger and its other roles await further study.

Melatonin prevents X-ray irradiation induced oxidative damagein peripheral blood and spleen of the seasonally breeding rodent, Funambulus pennanti during reproductively active phase

PURPOSE

Biological effects of X-ray irradiation and protection by melatonin on the immune status of a tropical rodent, Funambulus pennanti, was examined by estimating oxidative damage of peripheral blood and spleen and protection by melatonin treatment.

MATERIAL AND METHODS

Seventy squirrels were divided into 4 sets of 25, 25, 10 and 10 having subdivisions into a total of eight groups. Squirrels of set 1 (groups A and B) received only normal saline, set 2 (groups C and D) received 25 microg/100 g body weight (bwt) melatonin and set 3 (groups E and F) received 25 microg/100 g bwt vitamin E for four weeks. Groups G and H of set 4 received high doses of melatonin (0.5 mg/100 g bwt) 30 min prior to and 30 min after X-ray irradiation, respectively, and were sacrificed 1 h after irradiation. Groups B and D were sacrificed after 4 h, 24 h, 48 h and 72 h of irradiation for total leukocyte count (TLC) in peripheral blood, percent apoptotic cells and lipid peroxidation (LPO) in spleen while group F was sacrificed after 4 h of irradiation to measure LPO.

RESULTS

Pre-melatonin treatment (25 microg/100 g bwt) restored TLC, percent apoptotic cells and LPO levels of X-ray exposed squirrels. High dose pre-melatonin treatment (0.5 mg/100 g bwt) restored the above conditions significantly while post treatment did not. Vitamin E reduced elevated LPO level in irradiated tissue, but the effect of melatonin was more potent.

CONCLUSION

Melatonin administration prior to X-ray irradiation prevented radiation-induced oxidative damage during the reproductively active phase of the seasonally breeding rodent suggesting a high protective role of melatonin following X-ray irradiation.

Protective effects of melatonin against low- and high-LET irradiation

To investigate the protective effects of melatonin against high-LET ionizing radiation, V79 Chinese hamster cells were irradiated with 100 keV/microm carbon beam. Parallel experiments were performed with 200 kV X-rays. To avoid the impact from extra solvents, melatonin was dissolved directly in culture medium. Cells were cultured in melatonin medium for 1 hr before irradiation. Cell inactivation was measured with conventional colony forming assay, medium containing 6-thioguanine was used for the selection of mutants at hprt locus, and the cell cycle was monitored by flow cytometry. Both carbon beam and X-rays induced cell inactivation, hprt gene mutation and cell cycle G2 block dose-dependently. But carbon beam showed stronger effects as indicated by all three endpoints and the relative biological effectiveness (RBE) was 3.5 for cell killing (at 10% survival level) and 2.9 for mutation induction (at 5 x 10(-5) mutants/cell level). Melatonin showed protective effects against ionizing radiation in a dose-dependent manner. In terms of cell killing, melatonin only increased the survival level of those samples exposed to 8Gy or larger of X-rays or 6 Gy or larger of carbon beam. In the induction of hprt mutation and G2 block, melatonin reduced such effects induced by carbon beam but not by X-rays. The results suggest that melatonin reduces the direct interaction of particles with cells rather than an indirect interaction. Further studies are required to disclose the underlying mechanisms.

Protective effects of melatonin on gamma-ray induced intestinal damage

PURPOSE

To examine the protective effects of melatonin on intestinal damage induced by gamma-rays.

MATERIALS AND METHODS

Six-week-old Slc:ICR male mice were used. Mice were given whole-body irradiation at various exposure doses (7-21 Gy) with (137)Cs gamma-rays (0.98 Gy/min). The mice were orally administered 1 ml of either 1% carboxymethyl cellulose sodium salt (CMC) or melatonin (1, 5, 10 or 20 mg/ml) freshly prepared as a uniform suspension in CMC before or after irradiation. The concentrations of plasma melatonin were determined by the radioimmunoassay (RIA) method. The mice were killed at 3.5 days after the exposure. The jejunum was removed, fixed in formalin and then stained with hematoxylin and eosin. The numbers of crypts per transverse circumference were counted using a microscope for 10 histological sections of each mouse.

RESULTS

The intestinal damage caused by gamma-ray irradiation was prevented by melatonin correlating to dosage. The D(0) (slope of the dose-survival curve) value significantly (p < 0.05) increased from 1.55 +/- 0.19 (mean +/- SD) Gy to 1.98 +/- 0.16 Gy by orally administering 20 mg melatonin 30 min before irradiation. The radioprotective effect of melatonin continued for 6 h after the administration.

CONCLUSIONS

Melatonin is judged to be a potential protector against intestinal damage associated with radiotherapy. Further experimental and clinical studies on this subject are needed to allow its use for radiotherapy.

Synthesis and Antioxidant Activity of New Tetrahydro-Naphthalene-Indole Derivatives as Retinoid and Melatonin Analogs

A number of retinoid-related compounds represent classes of antioxidative and proapoptotic agents with promising potential in the treatment of neoplastic diseases. Indeed, the synthetic retinoid amide fenretinide [N-(4-hydroxyphenyl)retinamide] induces apoptosis of cancer cells and acts as a chemotherapeutic drug in cancer therapy. In the present work, and as a continuation of our studies on retinoid-type compounds, the synthesis of melatonin retinamide derivatives was studied as a novel series of melatonin retinoids, using the condensation reaction sequence involving tetrahydrotetramethylnaphthalene carboxylic acid and appropriate melatonin-type moieties. Despite of the weak DPPH inhibition activity pattern of the synthesized compounds, some of them showed a strong inhibition on lipid peroxidation (IVa-b, Va, and VIIa-c, 88, 96, 90, 94, 93, and 86%, respectively at 10(-4) M concentration) when melatonin (85% at 10(-4) M concentration) was used as a reference compound.

Melatonin protects against lipopolysaccharide-induced intra-uterine fetal death and growth retardation in mice

Lipopolysaccharide (LPS) has been associated with adverse developmental outcomes, including intra-uterine fetal death (IUFD) and intra-uterine growth retardation (IUGR). However, the exact mechanism for LPS-induced IUFD and IURD remains unclear. LPS stimulates macrophages to generate reactive oxygen species (ROS). Therefore, we hypothesize that ROS may be involved in LPS-induced IUFD and IURD. Melatonin is a powerful endogenous antioxidant. In this study, we investigated the protective effects of melatonin on LPS-induced IUFD and IURD in ICR mice. All pregnant mice except controls received an intraperitoneal (75 microg/kg, i.p.) injection of LPS on gestational day (gd) 15-17. The experiment was carried out in two different modes. In mode A, the pregnant mice received two doses of melatonin within 24 hr, one (5 or 10 mg/kg) injected immediately after LPS and the other (5 or 10 mg/kg) injected at 3 hr after LPS. In mode B, the pregnant mice were pretreated with 10 mg/kg of melatonin 18 hr before LPS and then received two doses of melatonin in 24 hr, one (10 mg/kg) injected immediately after LPS and the other (10 mg/kg) injected 3 hr after LPS. The number of live fetuses, dead fetuses and resorption sites were counted on gd 18. Live fetuses in each litter were weighed. Crown-rump and tail lengths were examined and skeletal development was evaluated. Results showed that post-treatments with melatonin significantly attenuated LPS-induced IUFD in a dose-dependent manner. Surprisingly, pre- plus post-treatments with melatonin almost blocked LPS-induced IUFD. In addition, both post-treatments and pre- plus post-treatments with melatonin significantly alleviated LPS-induced decreases in crown-rump and tail lengths and reversed LPS-induced skeletal developmental retardation. However, melatonin had little effect on LPS-induced decrease in fetal weight. Furthermore, pre- plus post-treatments with melatonin significantly attenuated LPS-induced lipid peroxidation in maternal liver. These results indicate that melatonin protects against LPS-induced IURD and IUGR via counteracting LPS-induced oxidative stress.

Antioxidative protection by melatonin: multiplicity of mechanisms from radical detoxification to radical avoidance

Melatonin has been shown to protect against oxidative stress in various, highly divergent experimental systems. There are many reasons for its remarkable protective potential. Signaling effects comprise the upregulation of antioxidant enzymes, such as superoxide dismutases, peroxidases, and enzymes of glutathione supply, down-regulation of prooxidant enzymes, such as nitric oxide synthases and lipoxygenases, and presumably also the control of quinone reductase 2. Other mechanisms are based on direct interactions with several reactive oxygen and nitrogen species. Among these reactions, the capacity of easily undergoing single-electron transfer reactions is of particular importance. Electron donation by melatonin is not only an aspect of direct radical scavenging, but additionally represents the basis for formation of the protective metabolites AFMK (N1-ace-tyl-N2-formyl-5-methoxykynuramine) and AMK (N1-acetyl-5-methoxykynuramine). Recent investigations on mitochondrial metabolism indicate that melatonin as well as AMK are capable of supporting the electron flux through the respiratory chain, of preventing the breakdown of the mitochondrial membrane potential, and of decreasing electron leakage, thereby reducing the formation of superoxide anions. Radical avoidance is a new line of investigation, which exceeds mitochondrial actions and also comprises antiexcitatory effects and contributions to the maintenance of internal circadian phase relationships.

A proposed mechanism to explain the stimulatory effect of melatonin on antioxidative enzymes

Melatonin, the main secretory product of the pineal gland, is known to collaborate against oxidative stress within cells, but its mechanism of action in terms of stimulating antioxidant enzymes remains unclear. Herein, we propose that melatonin modulates antioxidant enzyme activities via its interaction with calmodulin, which in turn inhibits downstream processes that lead to the inactivation of nuclear RORalpha melatonin receptor. Eventually, this nuclear transcription factor downregulates NF-kappaB-induced antioxidant enzyme expression. Therefore, the increment in antioxidant enzyme activities induced by melatonin involves the inhibition of the RORalpha pathway. Thus, in addition to its direct free radical scavenging activities, melatonin has important actions in oxidative defense by stimulating enzymes which metabolize free radicals and radical products to innocuous metabolites.

Radical mediators and mitogen-activated protein kinase signaling in oxygen-dependent radiosensitivity of human tumor cell lines

Oxygen enhancement of tumor radiosensitivity is attributed to DNA damage by reactive oxygen species. The mechanism remains unclear but may involve mitochondria as major sources of oxygen and nitrogen radicals as well as central effectors of energy homeostasis and apoptosis. Here we used dihydrorhodamine and 2',7'-dichlorodihydrofluorescein to compare mitochondrial and total cell generation, respectively, of reactive oxygen or nitrogen species in cells irradiated at 5 Gy. Irradiation in the presence of oxygen selectively stimulated mitochondrial radical production in HeLa and MeWo cells, but in MCF7 cells radical production was more generalized. In all three cell lines oxygen impaired cell proliferation as measured by resazurin reduction 7 days after irradiation. Antioxidants N-acetylcysteine, ascorbic acid, and melatonin largely prevented dye oxidation during normoxic irradiation yet had no effect on oxygen-dependent irradiation injury. However, NO synthase inhibitor N(G)-monomethyl-L-arginine protected HeLa and MCF7 though not MeWo cells, consistent with their different levels of constitutive NO generation. SB203580 inhibition of p38 MAPK appreciably protected HeLa and marginally protected MCF7 cells against oxygen-dependent irradiation injury, while the less specific JNK/SAPK inhibitor SP600125 and ERK inhibitor U0126 had no effect. None of the inhibitors affected MeWo radiosensitivity. Therefore oxygen-enhanced radiosensitivity in these tumor cell lines does not depend on extensive production of oxygen radicals and is cell-type dependent. NO mediates oxygen-dependent injury in HeLa and MCF7 cells, by p38-dependent and MAPK-independent mechanisms, respectively. In MeWo cells this oxygen-enhanced radiosensitivity is independent of both NO and MAPK signaling.

Radioprotective effects of melatonin on radiation-induced cataract

One of the mechanisms proposed to explain lens opacification is the oxidation of crystallins, either by radiation or reactive oxygen species (ROS). It has been shown that melatonin has both an anti-peroxidative effect on several tissues and a scavenger effect on ROS. The purpose of this study was to determine the antioxidant role of melatonin (5 mg/kg/day) against radiation-induced cataract in the lens after total-cranium irradiation of rats with a single dose of 5 Gy. Sprague-Dawley rats were divided into four groups. Control group received neither melatonin nor irradiation. Irradiated rats (IR) and melatonin+irradiated rats (IR+Mel) groups were exposed to total cranium irradiation of 5 Gy in a single dose by using a cobalt-60 teletherapy unit. IR+Mel and melatonin (Mel) groups were administered 5 mg/kg melatonin daily by intraperitoneal injections during ten days. Chylack's cataract classification was used in this study. At the end of the 10th day, the rats were killed and their eyes were enucleated to measure the antioxidant enzymes i.e. the activity of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px), and lipid peroxidation level (malondialdehyde (MDA)). Irradiation significantly increased the MDA level, as an end product of lipid peroxidation, and also significantly decreased SOD and GSH-Px activity, emphasizing the generation of increased oxidative stress. Rats injected with melatonin only did not cause cataract formation. Melatonin supplementation with irradiation significantly increased the activity of SOD and GSH-Px enzymes and significantly decreased the MDA level. Total cranium irradiation of 5 Gy in a single dose enhanced cataract formation, and melatonin supplementation protected the lenses from radiation-induced cataract formation. Our results suggest that supplementing cancer patients with adjuvant therapy of melatonin may reduce patients suffering from toxic therapeutic regimens such as chemotherapy and/or radiotherapy and may provide an alleviation of the symptoms due to radiation-induced organ injuries.

Modulation of radiation-induced alteration in the antioxidant status of mice by naringin

The alteration in the antioxidant status and lipid peroxidation was investigated in Swiss albino mice treated with 2 mg/kg b.wt. naringin, a citrus flavoglycoside, before exposure to 0.5, 1, 2, 3, and 4 Gy gamma radiation. Lipid peroxidation, glutathione, glutathione peroxidase, catalase and superoxide dismutase were determined in the liver and small intestine of mice treated or not with naringin at 0.5, 1, 2, 4 and 8 h post-irradiation. Whole-body irradiation of mice caused a dose-dependent elevation in the lipid peroxidation while a dose-dependent depletion was observed for glutathione, glutathione peroxidase, superoxide dismutase and catalase in both liver as well as small intestine. Treatment of mice with 2 mg/kg b. wt. naringin inhibited the radiation-induced elevation in the lipid peroxidation as well as depletion of glutathione, glutathione peroxidase, superoxide dismutase and catalase in liver and small intestine. Radiation-induced lipid peroxidation increased with time, which was greatest at 2 h post-irradiation and declined thereafter in the liver and small intestine. Similarly, a maximum decline in the glutathione glutathione peroxidase, and superoxide dismutase was observed at 1 h, while catalase showed a maximum decline at 2 h post-irradiation. Our study demonstrates that naringin protects mouse liver and intestine against the radiation-induced damage by elevating the antioxidant status and reducing the lipid peroxidation.

Effects of dietary supplements on space radiation-induced oxidative stress in Sprague-Dawley rats

Of particular concern for the health of astronauts during space travel is radiation from protons and high-mass, high-atomic-number (Z), and high-energy particles (HZE particles). Space radiation is known to induce oxidative stress in astronauts after extended space flight. In the present study, the total antioxidant status was used as a biomarker to evaluate oxidative stress induced by gamma rays, protons and HZE-particle radiation. The results demonstrate that the plasma level of total antioxidants in Sprague-Dawley rats was significantly decreased (P < 0.01) in a dose-dependent manner within 4 h after exposure to gamma rays. Exposure to protons and HZE-particle radiation also significantly decreased the serum or plasma level of total antioxidants in the irradiated animals. Diet supplementation with L-selenomethionine alone or a combination of selected antioxidant agents was shown to partially or completely prevent the decrease in the serum or plasma levels of total antioxidants in animals exposed to gamma rays, protons or HZE particles. These findings suggest that exposure to space radiation may compromise the capacity of the host antioxidant defense and that this adverse biological effect can be prevented at least partially by dietary supplementation with L-selenomethionine and antioxidants.

Pro-oxidant activity of aluminum in the rat hippocampus: gene expression of antioxidant enzymes after melatonin administration

Aluminum (Al)-induced pro-oxidant activity and the protective role of exogenous melatonin, as well as the mRNA levels of some antioxidant enzymes, were determined in the hippocampi of rats following administration of Al and/or melatonin. Two groups of male rats were intraperitoneally injected with Al (as Al lactate) or melatonin only, at doses of 7 and 10 mg/kg/day, respectively, for 11 weeks. During this period, a third group of animals received Al (7 mg/kg/day) plus melatonin (10 mg/kg/day). At the end of the treatment, hippocampus was removed and processed to examine the following oxidative stress markers: glutathione transferase (GST), reduced glutathione (GSH), oxidized glutathione (GSSG), superoxide dismutase (SOD), glutathione reductase (GR), glutathione peroxidase (GPx), catalase (CAT), thiobarbituric acid reactive substances (TBARS), as well as protein content. Gene expression of Cu-ZnSOD, MnSOD, GPx, and CAT was evaluated by real-time RT-PCR. On the other hand, Al, Fe, Mn, Cu, and Zn concentrations in hippocampus were also determined. The results show that Al exposure promotes oxidative stress in the rat hippocampus, with an increase in Al concentrations. The biochemical changes observed in this tissue indicate that Al acts as pro-oxidant agent, while melatonin exerts antioxidant action by increasing the mRNA levels of the antioxidant enzymes evaluated. The protective effects of melatonin, together with its low toxicity and its capacity to increase mRNA levels of antioxidant enzymes, suggest that this hormone might be administered as a potential supplement in the treatment of neurological disorders in which oxidative stress is involved.

Comparison of potential protective effects of melatonin, indole-3-propionic acid, and propylthiouracil against lipid peroxidation caused by potassium bromate in the thyroid gland

Potassium bromate (KBrO3) is a prooxidant and carcinogen, inducing thyroid tumors. Melatonin and indole-3-propionic acid (IPA) are effective antioxidants. Some antioxidative effects of propylthiouracil (PTU)--a thyrostatic drug--have been found. The aim of the study was to compare protective effects of melatonin, IPA, and PTU against lipid peroxidation in the thyroids, collected from rats treated with KBrO3, and in homogenates of porcine thyroids, incubated in the presence of KBrO3. Wistar rats were administered KBrO3 (110 mg/kg b.w., i.p., on the 10th day of the experiment) and/or melatonin, or IPA (0.0645 mmol/kg b.w., i.p., twice daily, for 10 days), or PTU (0.025% solution in drinking water, for 10 days). Homogenates of porcine thyroids were incubated for 30 min in the presence of KBrO3 (5 mM) plus one of the antioxidants: melatonin (0.01, 0.1, 0.5, 1.0, 5.0, 7.5 mM), or IPA (0.01, 0.1, 0.5, 1.0, 5.0, 7.5, 10.0 mM), or PTU (0.01, 0.1, 0.5, 1.0, 5.0, 7.5, 10.0 mM). The level of lipid peroxidation products (MDA + 4-HDA) was measured spectrophotometrically in thyroid homogenates. In vivo pretreatment with either melatonin or with IPA or with PTU decreased lipid peroxidation caused by KBrO3--injections in rat thyroid gland. Under in vitro conditions, PTU (5.0, 7.5, and 10.0 mM), but neither melatonin nor IPA, reduced KBrO3-related lipid peroxidation in the homogenates of porcine thyroids. In conclusion, melatonin and IPA may be of great value as protective agents under conditions of exposure to KBrO3.

Melatonin protects against ionizing radiation-induced oxidative damage in corpus cavernosum and urinary bladder in rats

The objective of this study was to examine the potential radioprotective properties of pharmacological doses of melatonin on corpus cavernosum and bladder tissues of whole-body irradiated (IR) rats. A total of 32 male Sprague-Dawley rats were exposed to irradiation performed with a LINAC which produced 6 MV photons at a focus 100 cm distant from the skin. Under ketamine anesthesia, each rat received a single whole-body dose of 800 cGy. Immediately before and after IR, rats were treated with either saline or melatonin (20 and 10 mg/kg, i.p.) and decapitated at 12 hr after exposure to irradiation. Another group of rats was followed for 72 hr after IR, where melatonin injections were repeated once daily. Tissue levels of malondialdehyde (MDA), an index of lipid peroxidation, and glutathione (GSH), a key antioxidant, were estimated in corpus cavernosum and urinary bladder. Tissues were also examined microscopically. The results demonstrate that both 12 and 72 hr following IR, tissue levels of MDA were elevated (P < 0.001), while GSH levels were reduced (P < 0.01) in both tissues. On the other hand, melatonin reversed these changes significantly (P < 0.05-0.01), concomitant with the improvement in histological appearances. Our results show that whole-body irradiation causes oxidative damage in the tissues of the genitourinary system. As melatonin administration reversed oxidative organ injury, as assessed by biochemical and histopathological findings, it is suggested that supplementing cancer patients with adjuvant therapy of melatonin may have some benefit for successful radiotherapy.

Protection of antioxidants compound of Chinese drug on liver oxidative injury by local 60Co irradiation in rats with tumor

AIM: To observe the oxidative injury of livers induced by local irradiation and the protection of antioxidants compound of Chinese drug in rats with tumor.

METHODS: The Spraue-Dawley (SD) rats were divided into negative control group and trial groups. The tumor cells (Walker-256) were injected into the rat to get the solid tumor, which was then cut into small pieces to be embedded into the right rear buttocks under skin of rats. As the embedded tumor grew up successfully, the rats with solid tumor were randomly divided into 3 groups, i.e. tumor group, irradiative group and protective group. The protective group was given antioxidants compound by gavage and other groups were given the same dosage water. The irradiative group and the protective group were locally g-irradiated with the total doses of 47Gy, then all the rats were killed, the serum and livers were collected to measure the content of malondialdehyde (MDA), the activities of glutathione S-transferase (GST), total superoxide dismutase (T-SOD), manganese superoxide dismutase (Mn-SOD), the total antioxidant capacity (TAC), nitric oxide (NO), nitric oxide synthase (NOS) and the total proteins.

RESULTS: The activities of serum and liver GST (mkat/L and mkat/g) and the content of MDA (in liver protein, nmoL/g) in irradiative group were much higher than those in all the other groups (479±17 vs 427±59 and 421±36, 50.3±1.0 vs 46.8±2.3 and 47.5 ±1.0, 33.7±8.8 vs 21.4±7.2 and 21.7±6.8, P <0.05, P <0.01, P <0.01,respectively). The activities of T-SOD (in liver protein, mkat/g), Mn-SOD (in liver protein, mkat/g), GSH (in liver protein, mg/g) and TAC (in liver protein, mkat/g) in irradiative group were much lower than those in other groups (39.3±7.0 vs 48.8±2.8 and 47.7±4.3, 18.7 ±6.2 vs 28.8 ±2.5 and 28.2±7.7, 0.44±0.13 vs 0.57±0.06 and 0.61±0.22, 20.7± 5.3 vs 26.5 ±3.3 and 26.3±1.7, P <0.01, P <0.01, P <0.01, P <0.05, respectively).The content of NO (in liver protein, mmoL/g) in irradiative group increased significantly, the activity (in liver protein, mkat/g) of NOS also increased significantly than those in the control group (1.22 ±0.08 vs 0.98± 0.15, 4.92 ±0.94 vs 3.63± 0.77, P <0.01, P <0.05, respectively). The content of NO and the activity of NOS in protective group decreased markedly than those in irradiative group(0.77±0.22 vs 1.22 ±0.08, 3.62 ±0.49 vs 4.92±0.94, P <0.01, P <0.05, respectively).

CONCLUSION: Local irradiation can cause the oxidative injury on liver of the rats and the antioxidant compound shows good protective effect against this injury by increasing the activities of antioxidants and decreasing the content of NO, the activity and expression of NOS, which give us a new way to reduce the side effect during the radiotherapy.