Radioprotective effect of sodium selenite on bone repair in the tibia of ovariectomized rats

Reactive sulfur and selenium species in the regulation of bone homeostasis

Reactive oxygen species (ROS) are important modulators of physiological signaling and play important roles in bone tissue regulation. Both reactive sulfur species (RSS) and reactive selenium species (RSeS) are involved in ROS signaling, and recent work suggests RSS and RSeS involvement in the regulation of bone homeostasis. For example, RSS can promote osteogenic differentiation and decrease osteoclast activity and differentiation, and the antioxidant activity of RSeS play crucial roles in balancing bone remodeling. Here, we outline current research progress on the application of RSS and RSeS in bone disease and regeneration. Focusing on these investigations, we highlight different methods, tools, and sources of RSS and RSeS, and we also highlight future opportunities for delivery of RSS and RSeS in biological environments relating to bone.

Selenium as an adjuvant for modification of radiation response

Ionizing radiation plays a central role in several medical and industrial purposes. In spite of the beneficial effects of ionizing radiation, there are some concerns related to accidental exposure that could pose a threat to the lives of exposed people. This issue is also very critical for triage of injured people in a possible terror event or nuclear disaster. The most common side effects of ionizing radiation are experienced in cancer patients who had undergone radiotherapy. For complete eradication of tumors, there is a need for high doses of ionizing radiation. However, these high doses lead to severe toxicities in adjacent organs. Management of normal tissue toxicity may be achieved via modulation of radiation responses in both normal and malignant cells. It has been suggested that treatment of patients with some adjuvant agents may be useful for amelioration of radiation toxicity or sensitization of tumor cells. However, there are always some concerns for possible severe toxicities and protection of tumor cells, which in turn affect radiotherapy outcomes. Selenium is a trace element in the body that has shown potent antioxidant and radioprotective effects for many years. Selenium can potently stimulate antioxidant defense of cells, especially via upregulation of glutathione (GSH) level and glutathione peroxidase activity. Some studies in recent years have shown that selenium is able to mitigate radiation toxicity when administered after exposure. These studies suggest that selenium may be a useful radiomitigator for an accidental radiation event. Molecular and cellular studies have revealed that selenium protects different normal cells against radiation, while it may sensitize tumor cells. These differential effects of selenium have also been revealed in some clinical studies. In the present study, we aimed to review the radiomitigative and radioprotective effects of selenium on normal cells/tissues, as well as its radiosensitive effect on cancer cells.

Radioprotective Effect of Sodium Selenite on Mandible of Irradiated Rats

The purpose of this study was to test the radioprotective effect of selenium in the bone microarchitecture of irradiated rats mandibles. Forty rats were separated into 4 groups with 10 animals: control group (CG), irradiated group (IG), sodium selenite group (SSG) and sodium selenite irradiated group (SSIG). A single dose of 0.8 mg/kg sodium selenite was administered intraperitoneally in the SSG and SSIG groups. One hour later, animals of IG and SSIG groups were irradiated with 15 Gy of x-rays. Forty days after radiation a bilateral extraction of the mandibular first molars was performed. After the extraction procedure, five rats were killed after fifteen days and others five after thirty days. Micro- computed tomography was used to evaluate cortical and trabecular bone of each rat. The mean and standard deviation of each bone microarchitecture parameter were analyzed using the statistical test of two-way Analysis of Variance (ANOVA). At 15 days, the bone volume presented higher values in the CG and SSG groups (p=0.001). The same groups presented statistically significant higher values when bone volume fraction (p<0.001) and trabecular thickness (p<0.001) were analyzed. At 30 days, it was observed that in relation to the bone volume fraction, SSG group presented the highest value while SSIG group had the lowest value, with statistically significant difference (p=0.016). Sodium selenite demonstrated a median radioprotective effect in the bone microarchitecture of irradiated mandibles, which indicates the substance may be a potential radioprotective agent against chronic effects of high doses of ionizing radiation.

Therapeutic ionizing radiation induced bone loss: a review of in vivo and in vitro findings

Radiation therapy is one of the routine treatment modalities for cancer patients. Ionizing radiation (IR) can induce bone loss, and consequently increases the risk of fractures with delayed and nonunion of the bone in the cancer patients who receive radiotherapy. The orchestrated bone remodeling can be disrupted due to the affected behaviors of bone cells, including bone mesenchymal stem cells (BMSCs), osteoblasts and osteoclasts. BMSCs and osteoblasts are relatively radioresistant compared with osteoclasts and its progenitors. Owing to different radiosensitivities of bone cells, unbalanced bone remodeling caused by IR is closely associated with the dose absorbed. For doses less than 2 Gy, osteoclastogenesis and adipogenesis by BMSCs are enhanced, while there are limited effects on osteoblasts. High doses (>10 Gy) induce disrupted architecture of bone, which is usually related to decreased osteogenic potential. In this review, studies elucidating the biological effects of IR on bone cells (BMSCs, osteoblasts and osteoclasts) are summarized. Several potential preventions and therapies are also proposed.

Meloxicam as a Radiation-Protective Agent on Mandibles of Irradiated Rats

This study evaluated the action of ionizing radiation and the possible radioprotective effect of the non-steroidal anti-inflammatory drug meloxicam on the bone physiology of rat mandibles by assessing the alveolar socket healing and bone strength. Forty male Wistar rats were divided in 4 groups (n=10): control (CG), irradiated (IG), meloxicam (MG), meloxicam irradiated (MIG). A dose of 0.2 mg/kg meloxicam was administered to MG and MIG. After this, IG and MIG were irradiated with 15 Gy radiation dose in the mandible. Forty days after the above procedures, the mandibular first molars were extracted and the animals were killed after 15 or 30 days (n=5). Micro-computed tomography and bending test were used to evaluate alveolar socket healing and bone strength, respectively. At 15 days, bone volume, bone volume fraction and trabecular thickness were higher in the CG and MG than in the IG and MIG; and trabecular separation was higher in the IG compared with the others. At 30 days, there was a difference only in trabecular separation, which was higher in IG than in CG and MG, and MIG did not differ from the others. Bone strength was lower in IG compared with CG and MG, and MIG did not differ from the others. In conclusion, the ionizing radiation affected the bone physiology of rat mandibles, delaying the alveolar socket healing and reducing the bone strength. Moreover, the meloxicam had a positive effect on the trabecular separation in alveolar socket healing and on the bone strength.

Effect of Alendronate on Bone Microarchitecture in Irradiated Rats With Osteoporosis: Micro-CT and Histomorphometric Analysis

PURPOSE

The aim of the present study was to evaluate the effect of alendronate (ALN) on the bone microarchitecture of irradiated rats with estrogen deficiency, using microcomputed tomography (micro-CT) and histomorphometric analysis.

MATERIALS AND METHODS

Forty adult Wistar rats were subjected to ovariectomy and randomly divided into the following groups: control (CON), ALN, irradiated (IRR), and ALN/irradiated (ALN/IRR). Approximately 50 days after ovariectomy, the hind limbs of the rats in the IRR and ALN/IRR groups were irradiated with 15 Gy of x-radiation. The rats were euthanized 7 and 30 days after irradiation. The bone microarchitecture was analyzed using micro-CT and histomorphometry. The bone microarchitecture was evaluated using the Mann-Whitney U test, analysis of variance, and the post hoc Tukey test, with statistical significance set at 5%.

RESULTS

Irradiation had increased the thickness of the cortical bone at 7 days (P < .05) and also decreased the number of trabeculae per unit length and increased the average distance between the trabeculae (P < .05) at 30 days. ALN inhibited the deleterious effect of x-radiation, preventing the distance between the trabeculae from increasing and the number of trabeculae per unit length from decreasing (P < .05).

CONCLUSIONS

The present results have demonstrated that the initial effect of ALN could be positive, because it checked the deleterious action in the bone tissue submitted to x-radiation.

Radioprotective effect of sodium selenite on developing teeth

Radioprotective agents like selenium are used to reduce the damage caused by radiation in healthy tissues. The aim of this study was to evaluate the effect of sodium selenite on the development of the molars of offspring of rats irradiated during odontogenesis. Twenty pregnant rats were randomly divided into 4 groups: control, irradiated, selenium and selenium/irradiated. The selenium and selenium/irradiated groups received 0.3 mg/kg of sodium selenite at 18 days of pregnancy. The rats of the irradiated and selenium/irradiated groups received a single dose of 4 Gy of X rays on the abdominal region at the 19th day of pregnancy. The offspring was sacrificed at 3 and 4 days after birth for evaluation of the birefringence of the enamel organic matrix, and at 30 days for evaluation of the intercuspal dimensions of the molars. The selenium/irradiated group was similar to the irradiated group with respect to the thickness and irregularity of the enamel organic matrix region in the evaluated birefringence, as the intercuspal dimensions of the molars. In conclusion, sodium selenite had no radioprotective action on the development of the molars of offspring of rats irradiated during odontogenesis and had a toxic effect in the initial time.

The protective effects of trace elements against side effects induced by ionizing radiation

Trace elements play crucial role in the maintenance of genome stability in the cells. Many endogenous defense enzymes are containing trace elements such as superoxide dismutase and metalloproteins. These enzymes are contributing in the detoxification of reactive oxidative species (ROS) induced by ionizing radiation in the cells. Zinc, copper, manganese, and selenium are main trace elements that have protective roles against radiation-induced DNA damages. Trace elements in the free salt forms have protective effect against cell toxicity induced by oxidative stress, metal-complex are more active in the attenuation of ROS particularly through superoxide dismutase mimetic activity. Manganese-complexes in protection of normal cell against radiation without any protective effect on cancer cells are more interesting compounds in this topic. The aim of this paper to review the role of trace elements in protection cells against genotoxicity and side effects induced by ionizing radiation.