Protective effect of melatonin against fractionated irradiation-induced epiphyseal injury in a weanling rat model

Melatonin has a protective effect against lipid peroxidation in the bone tissue of diabetic rats subjected to acute swimming exercise

Aim The present study aimed to examine the effects of melatonin supplementation on lipid peroxidation in the bone tissue of diabetic rats subjected to acute swimming exercise. Methods The study was conducted on 80 Sprague-Dawley type adult male rats which were equally allocated to eight groups: group 1, general control; group 2, melatonin-supplemented control; group 3, melatonin-supplemented diabetic control; group 4, swimming control; group 5, melatonin-supplemented swimming; group 6, melatonin-supplemented diabetic swimming; group 7, diabetic swimming; group 8, diabetic control. In order to induce diabetes, the animals were subcutaneously injected with 40 mg/kg streptozotocin (STZ). The animals were supplemented with 3 mg/kg/day melatonin intraperitoneally (IP) for 4 weeks. At the end of the study, the animals were decapitated to collect bone tissue samples which were examined to find out the malondialdehyde (MDA) (nmol/g/protein) and glutathione (GSH) (mg/dL/g protein) levels. Results The highest MDA values in the bone tissue were found in groups 7 and 8. MDA levels in the bone tissue in groups 3 and 6 were lower than the levels in groups 7 and 8, but higher than those in all other groups. Groups 3, 5 and 6 had the highest bone tissue GSH values. On the other hand, the lowest GSH level was established in groups 7 and 8. Conclusion The results of the present study indicated that the cell damage caused by acute swimming exercise and diabetes in the bone tissue could be prevented by melatonin supplementation.

Melatonin can Ameliorate Radiation-Induced Oxidative Stress and Inflammation-Related Deterioration of Bone Quality in Rat Femur

The aim of the present study was to evaluate the radioprotective effects of melatonin on the biomechanical properties of bone in comparison to amifostine (WR-2721). Forty Sprague Dawley rats were divided equally into 5 groups namely; control (C), irradiation (R; single dose of 50 Gy), irradiation + WR-2721 (R + WR-2721; irradiation + 200 mg/kg WR-2721) radiation + melatonin 25 mg/kg (R + M25; irradiation + 25 mg/kg melatonin), and radiation + melatonin 50 mg/kg (R + M50; irradiation + 50 mg/kg melatonin). In order to measure extrinsic (organ-level mechanical properties of bone; the ultimate strength, deformation, stiffness, energy absorption capacity) and intrinsic (tissue-level mechanical properties of bone; ultimate stress, ultimate strain, elastic modulus, toughness) features of the bone, a three-point bending (TPB) test was performed for biomechanical evaluation. In addition, a bone mineral density (BMD) test was carried out. The BMD and extrinsic properties of the diaphyseal femur were found to be significantly higher in the R + M25 group than in group R (p < 0.05). A significant increase was observed in R + M50 (p < 0.05) in comparison to group R in the cross-sectional area of the femoral shaft and elastic modulus parameter. The protective effect of melatonin was similar to that of WR-2721. Thus, biomechanical quality of irradiated bone can be ameliorated by free radical scavenger melatonin.

Neuroprotective effect of acute melatonin treatment on hippocampal neurons against irradiation by inhibition of caspase-3

Neuronal cell apoptosis is associated with various factors that induce neurological damage, including radiation exposure. When administered prior to exposure to radiation, a protective agent may prevent cellular and molecular injury. The present study aimed to investigate whether melatonin exerts a neuroprotective effect by inhibiting the caspase cell death pathway. Male Sprague-Dawley rats were administered melatonin (100 mg/kg body weight) 30 min prior to radiation exposure in red light during the evening. In order to elucidate whether melatonin has a neuroprotective role, immunohistochemistry, terminal deoxynucleotidyl transferase dUTP nick-end labeling, Nissl staining, reverse transcription-quantitative polymerase chain reaction, reactive oxygen species analysis and western blotting were performed. At 24 h post-melatonin treatment, caspase-3 mRNA and protein expression levels were significantly decreased. These results demonstrated that melatonin may protect hippocampal neurons via the inhibition of caspase-3 when exposed to irradiation. Therefore, caspase-3 inhibition serves a neuroprotective and antioxidant role in the interventional treatment of melatonin. The results of the present study suggested that melatonin may have a potential therapeutic effect against irradiation; however, further studies are required in order to elucidate the underlying antioxidant mechanisms.

Radiation protection following nuclear power accidents: a survey of putative mechanisms involved in the radioprotective actions of taurine during and after radiation exposure

There are several animal experiments showing that high doses of ionizing radiation lead to strongly enhanced leakage of taurine from damaged cells into the extracellular fluid, followed by enhanced urinary excretion. This radiation-induced taurine depletion can itself have various harmful effects (as will also be the case when taurine depletion is due to other causes, such as alcohol abuse or cancer therapy with cytotoxic drugs), but taurine supplementation has been shown to have radioprotective effects apparently going beyond what might be expected just as a consequence of correcting the harmful consequences of taurine deficiency per se. The mechanisms accounting for the radioprotective effects of taurine are, however, very incompletely understood. In this article an attempt is made to survey various mechanisms that potentially might be involved as parts of the explanation for the overall beneficial effect of high levels of taurine that has been found in experiments with animals or isolated cells exposed to high doses of ionizing radiation. It is proposed that taurine may have radioprotective effects by a combination of several mechanisms: (1) during the exposure to ionizing radiation by functioning as an antioxidant, but perhaps more because it counteracts the prooxidant catalytic effect of iron rather than functioning as an important scavenger of harmful molecules itself, (2) after the ionizing radiation exposure by helping to reduce the intensity of the post-traumatic inflammatory response, and thus reducing the extent of tissue damage that develops because of severe inflammation rather than as a direct effect of the ionizing radiation per se, (3) by functioning as a growth factor helping to enhance the growth rate of leukocytes and leukocyte progenitor cells and perhaps also of other rapidly proliferating cell types, such as enterocyte progenitor cells, which may be important for immunological recovery and perhaps also for rapid repair of various damaged tissues, especially in the intestines, and (4) by functioning as an antifibrogenic agent. A detailed discussion is given of possible mechanisms involved both in the antioxidant effects of taurine, in its anti-inflammatory effects and in its role as a growth factor for leukocytes and nerve cells, which might be closely related to its role as an osmolyte important for cellular volume regulation because of the close connection between cell volume regulation and the regulation of protein synthesis as well as cellular protein degradation. While taurine supplementation alone would be expected to exert a therapeutic effect far better than negligible in patients that have been exposed to high doses of ionizing radiation, it may on theoretical grounds be expected that much better results may be obtained by using taurine as part of a multifactorial treatment strategy, where it may interact synergistically with several other nutrients, hormones or other drugs for optimizing antioxidant protection and minimizing harmful posttraumatic inflammatory reactions, while using other nutrients to optimize DNA and tissue repair processes, and using a combination of good diet, immunostimulatory hormones and perhaps other nontoxic immunostimulants (such as beta-glucans) for optimizing the recovery of antiviral and antibacterial immune functions. Similar multifactorial treatment strategies may presumably be helpful in several other disease situations (including severe infectious diseases and severe asthma) as well as for treatment of acute intoxications or acute injuries (both mechanical ones and severe burns) where severely enhanced oxidative and/or nitrative stress and/or too much secretion of vasodilatory neuropeptides from C-fibres are important parts of the pathogenetic mechanisms that may lead to the death of the patient. Some case histories (with discussion of some of those mechanisms that may have been responsible for the observed therapeutic outcome) are given for illustration of the likely validity of these concepts and their relevance both for treatment of severe infections and non-infectious inflammatory diseases such as asthma and rheumatoid arthritis.

Physeal bystander effects in rhabdomyosarcoma radiotherapy: experiments in a new xenograft model

Radiotherapy used in the treatment of pediatric musculoskeletal sarcomas may result in crippling defects of skeletal growth. Several radioprotective strategies have shown potential for preserving function of the irradiated epiphysis but have not been evaluated in a tumor-bearing animal model. We developed two bioluminescent human rhabdomyosarcoma cell lines that were used to establish xenograft tumors in skeletally immature mice. Bioluminescence imaging and radiography allowed serial evaluation of tumor growth and tibial elongation following localized radiotherapy. High-dose (10 Gy) radiotherapy significantly reduced tumor growth velocity and prolonged the median survival of tumor-bearing mice but also resulted in a significant 3.3% shortening of the irradiated limb. Exposure to a lower, 2 Gy dose resulted in 4.1% decrease in limb length but did not extend survival. This new model provides a clinically relevant means to test the efficacy and safety of novel radioprotectant and radiorecovery strategies for use in this context.

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.

Therapeutic treatments potentially mediated by melatonin receptors: potential clinical uses in the prevention of osteoporosis, cancer and as an adjuvant therapy

Melatonin's therapeutic potential is grossly underestimated because its functional roles are diverse and its mechanism(s) of action are complex and varied. Melatonin produces cellular effects via a variety of mechanisms in a receptor independent and dependent manner. In addition, melatonin is a chronobiotic agent secreted from the pineal gland during the hours of darkness. This diurnal release of melatonin impacts the sensitivity of melatonin receptors throughout a 24-hr period. This changing sensitivity probably contributes to the narrow therapeutic window for use of melatonin in treating sleep disorders, that is, at the light-to-dark (dusk) or dark-to-light (dawn) transition states. In addition to the cyclic changes in melatonin receptors, many genes cycle over the 24-hr period, independent or dependent upon the light/dark cycle. Interestingly, many of these genes support a role for melatonin in modulating metabolic and cardiovascular physiology as well as bone metabolism and immune function and detoxification of chemical agents and cancer reduction. Melatonin also enhances the actions of a variety of drugs or hormones; however, the role of melatonin receptors in modulating these processes is not known. The goal of this review is to summarize the evidence related to the utility of melatonin as a therapeutic agent by focusing on its other potential uses besides sleep disorders. In particular, its use in cancer prevention, osteoporosis and, as an adjuvant to other therapies are discussed. Also, the role that melatonin and, particularly, its receptors play in these processes are highlighted.

Effects of melatonin on suppression of renal scarring in experimental model of pyelonephritis

OBJECTIVES

To determine the effects of melatonin combined with antibiotic administration on the suppression of renal scarring in an experimental pyelonephritis model.

METHODS

The control group underwent a sham operation without infection. In the other groups, treatment began 72 hours after direct bacterial inoculation. In the no-treatment group, rats received daily intraperitoneal injections of saline. In the antibiotic-only group, the rats were treated only with ceftriaxone intramuscularly at a dose of 50 mg/kg once daily for 5 days. In the melatonin-only group, only 20 mg/kg of melatonin once daily was given by intraperitoneal injection for 5 days. In the antibiotic plus melatonin group, melatonin and ceftriaxone were administered at the same dosages and duration as for the single-modality treatment groups. After 6 weeks, the kidneys were removed for malondialdehyde measurements and histopathologic examination (inflammatory response and cicatrization).

RESULTS

Melatonin only (134.25 +/- 13.42) and antibiotic plus melatonin treatment (122.62 +/- 8.91) caused a marked reduction in the mean malondialdehyde values compared with no treatment (214.12 +/- 17.77) and antibiotic-only treatment (161.37 +/- 16.03), with no significant difference compared with that of the control group (120.75 +/- 9.83). Histopathologically, in the no-treatment group, the severity of scarring correlated directly with the severity of inflammation (r = 0.93). No significant differences were found in the renal scarring scores in rats receiving no treatment and those treated only with antibiotic or melatonin. In the antibiotic plus melatonin treatment group, the cicatrization score was not statistically different from that of the control group.

CONCLUSIONS

When combined with antibiotics, melatonin causes a significant inhibition of malondialdehyde production and neutrophil infiltration caused by acute pyelonephritis in an experimental rat model, and these are responsible for the protective effect of melatonin against renal damage, preventing renal scarring formation.

The effects of external beam irradiation on the growth of flat bones in children: modeling a dose-volume effect

PURPOSE

To model the effects of external beam irradiation on the developing flat bones of pediatric patients undergoing radiation therapy (RT) for tumors involving the musculoskeletal system.

METHODS AND MATERIALS

Patients with image-guided RT plans including areas adjacent to facial or pelvic flat bones underwent retrospective contouring of nontumor involved flat bones ipsilateral and contralateral to the treatment side. Radiation dose-volume information and bone volume data (initial and the most recent follow-up) were analyzed in 15 paired flat bones from 10 patients (ages 1.0-17.0 years). The models to predict bone growth after completion of RT (v(post)) were based on initial bone volume (v(pre)), the patient's age, time to follow-up (t), and the dose-volume parameter (v(Int35+)).

RESULTS

We developed a dose effects model as follows: Log (v(post) / v(pre)) = beta(time)t + beta(age group)t + beta(dose)t v(Int35). The dose-volume parameter v(Int35) predicted significantly for alterations in growth in younger patients, but not for older patients. The predictability of the fitted model for relative change in bone growth improved in the younger age group with the addition of the dose-volume term v(Int35) (correlation coefficient of r = 0.5510 to r = 0.6760 with the addition v(Int35)).

CONCLUSIONS

Our model accurately predicted flat bone growth and is notable for the inclusion of radiation dose-volume information, which is now available in the image-guided RT era. Further refinement of this model in a prospective patient population is underway.

Melatonin as a radioprotective agent: a review

Melatonin (N-acetyl-5-methoxytryptamine), the chief secretory product of the pineal gland in the brain, is well known for its functional versatility. In hundreds of investigations, melatonin has been documented as a direct free radical scavenger and an indirect antioxidant, as well as an important immunomodulatory agent. The radical scavenging ability of melatonin is believed to work via electron donation to detoxify a variety of reactive oxygen and nitrogen species, including the highly toxic hydroxyl radical. It has long been recognized that the damaging effects of ionizing radiation are brought about by both direct and indirect mechanisms. The direct action produces disruption of sensitive molecules in the cells, whereas the indirect effects ( approximately 70%) result from its interaction with water molecules, which results in the production of highly reactive free radicals such as *OH, *H, and e(aq)- and their subsequent action on subcellular structures. The hydroxyl radical scavenging ability of melatonin was used as a rationale to determine its radioprotective efficiency. Indeed, the results from many in vitro and in vivo investigations have confirmed that melatonin protects mammalian cells from the toxic effects of ionizing radiation. Furthermore, several clinical reports indicate that melatonin administration, either alone or in combination with traditional radiotherapy, results in a favorable efficacy:toxicity ratio during the treatment of human cancers. This article reviews the literature from laboratory investigations that document the ability of melatonin to scavenge a variety of free radicals (including the hydroxyl radical induced by ionizing radiation) and summarizes the evidence that should be used to design larger translational research-based clinical trials using melatonin as a radioprotector and also in cancer radiotherapy. The potential use of melatonin for protecting individuals from radiation terrorism is also considered.