Hyperthermia, radiation carcinogenesis and the protective potential of vitamin A and N-acetylcysteine

Radiation-Induced Oral Mucositis

Radiation-induced oral mucositis (RIOM) is a major dose-limiting toxicity in head and neck cancer patients. It is a normal tissue injury caused by radiation/radiotherapy (RT), which has marked adverse effects on patient quality of life and cancer therapy continuity. It is a challenge for radiation oncologists since it leads to cancer therapy interruption, poor local tumor control, and changes in dose fractionation. RIOM occurs in 100% of altered fractionation radiotherapy head and neck cancer patients. In the United Sates, its economic cost was estimated to reach 17,000.00 USD per patient with head and neck cancers. This review will discuss RIOM definition, epidemiology, impact and side effects, pathogenesis, scoring scales, diagnosis, differential diagnosis, prevention, and treatment.

Radioprotective agents for radiation therapy: future trends

Only two radioprotective compounds, amifostine and palifermin, currently have the US FDA approval for use in radiation therapy. However, several agents have been reported that show therapeutic promise. Many of these agents are free radical scavengers/antioxidants. Superoxide dismutase and superoxide dismutase mimetics, nitroxides and dietary antioxidants are all being investigated. Recently, alternative strategies of drug development have been evolving, which focus on targeting the series of cellular insult recognition/repair responses initiated following radiation. These agents, which include cytokines/growth factors, angiotensin-converting enzyme inhibitors and apoptotic modulators, show promise of having significant impact on the mitigation of radiation injury. Herein, we review current literature on the development of radioprotectors with emphasis on compounds with proven or potential usefulness in radiation therapy.

Alpha lipoic acid attenuates radiation-induced thyroid injury in rats

Exposure of the thyroid to radiation during radiotherapy of the head and neck is often unavoidable. The present study aimed to investigate the protective effect of α-lipoic acid (ALA) on radiation-induced thyroid injury in rats. Rats were randomly assigned to four groups: healthy controls (CTL), irradiated (RT), received ALA before irradiation (ALA + RT), and received ALA only (ALA, 100 mg/kg, i.p.). ALA was treated at 24 h and 30 minutes prior to irradiation. The neck area including the thyroid gland was evenly irradiated with 2 Gy per minute (total dose of 18 Gy) using a photon 6-MV linear accelerator. Greater numbers of abnormal and unusually small follicles in the irradiated thyroid tissues were observed compared to the controls and the ALA group on days 4 and 7 after irradiation. However, all pathologies were decreased by ALA pretreatment. The quantity of small follicles in the irradiated rats was greater on day 7 than day 4 after irradiation. However, in the ALA-treated irradiated rats, the numbers of small and medium follicles were significantly decreased to a similar degree as in the control and ALA-only groups. The PAS-positive density of the colloid in RT group was decreased significantly compared with all other groups and reversed by ALA pretreatment. The high activity index in the irradiated rats was lowered by ALA treatment. TGF-ß1 immunoreactivity was enhanced in irradiated rats and was more severe on the day 7 after radiation exposure than on day 4. Expression of TGF-ß1 was reduced in the thyroid that had undergone ALA pretreatment. Levels of serum pro-inflammatory cytokines (TNF-α, IL-1ß and IL-6) did not differ significantly between the all groups. This study provides that pretreatment with ALA decreased the severity of radiation-induced thyroid injury by reducing inflammation and fibrotic infiltration and lowering the activity index. Thus, ALA could be used to ameliorate radiation-induced thyroid injury.

Preventive or potential therapeutic value of nutraceuticals against ionizing radiation-induced oxidative stress in exposed subjects and frequent fliers

Humans are constantly exposed to ionizing radiation deriving from outer space sources or activities related to medical care. Absorption of ionizing radiation doses over a prolonged period of time can result in oxidative damage and cellular dysfunction inducing several diseases, especially in ageing subjects. In this report, we analyze the effects of ionizing radiation, particularly at low doses, in relation to a variety of human pathologies, including cancer, and cardiovascular and retinal diseases. We discuss scientific data in support of protection strategies by safe antioxidant formulations that can provide preventive or potential therapeutic value in response to long-term diseases that may develop following exposure.

Effects of N-acetyl-L-cysteine on fish hepatoma cells treated with mercury chloride and ionizing radiation

Organisms are exposed to natural radiations from cosmic or terrestrial origins. Furthermore the combined action of radiation with various chemicals is an inevitable feature of modern life. Radiation is known to cause cell death, mainly due to its ability to produce reactive oxygen species in cells. N-acetyl-L-cysteine (NAC) is a well-known sulfhydryl-containing antioxidant whose role in radioprotection has been reported. Synergistic effects of radiation and mercury chloride on human cells was previously reported by the authors. Based on the previous report, this study was designed to assess the synergistic effects of radiation and mercury chloride on fish hepatoma cells, as well as to investigate the protective effects of NAC on the cells. The cytotoxicity of radiation was enhanced in the presence of mercury chloride. NAC in lower concentrations prevented cells from death after irradiation with lower doses (<300 Gy) while it did not prevent cells from radiation-induced death after irradiation with higher doses (300, 500 Gy). The intracellular glutathione (GSH) levels significantly decreased after irradiation while the combined treatment of NAC and radiation alleviated the decrease in the GSH levels. The investigations give a clue for the action mechanism of synergistic or protective effects of NAC on the cells. Due to their high resistance to ionizing radiation, the PLHC-1 cells can be effectively used as a screening tool for assessing the combined effects of radiation with toxic chemicals.

Antioxidant N-acetylcysteine attenuates the acute liver injury caused by X-ray in mice

The aim of this study was to evaluate the protective effects of different doses and administration modes of N-acetylcysteine (NAC) against X-ray -induced liver damage in mice. Kun-Ming mice were divided into four groups, each composed of six animals: two control groups and two NAC-treated groups. An acute study was carried out to determine alterations in lipid peroxidation (determined by measuring malondiadehyde (MDA) level), glutathione (GSH) content and superoxide dismutase (SOD) activity (assayed by colorimetric method), and DNA damage (characterized by DNA-single strand break using with comet assay) as well as cell apoptosis (measured by flow cytometry) at 12 h after irradiation. The results showed that there were dose-related decreases in MDA level, DNA damage and cell apoptosis, and dose-dependent increases in GSH content and SOD activity in all NAC-treated groups compared to control groups, indicating that pre-treatment or post-treatment with NAC significantly attenuates the acute liver damage caused by X-ray. In addition, significant positive correlations were observed between MDA level and DNA damage or cell apoptosis, implying that lipid peroxidation plays a major role in X-ray-induced liver injury. The data suggest that NAC exerts its radioprotective effect by counteracting accumulated reactive oxygen species in the liver through its properties as a direct antioxidant and a GSH precursor, when administered before or after X-ray irradiation.

Rationale for using multiple antioxidants in protecting humans against low doses of ionizing radiation

Health risks of low doses of ionizing radiation (10 cGy or less) may not be accurately estimated in humans by epidemiological study or mathematical modelling because of several inherent confounding factors including environmental, dietary and biological variables that cannot be accounted for in any radio-epidemiological study. In addition, the expression of radiation-induced damage in humans not only depends upon total dose, dose rate, linear energy transfer (LET), and fractionation and protraction of total doses, but also on repair mechanisms, bystander effects, and exposure to chemical carcinogens, tumour promoters and other toxins. It also depends upon the levels of anti-carcinogenic and anti-tumour promoting agents. Low doses of ionizing radiation should not be considered insignificant with regard to increasing the incidence of somatic mutations (neoplastic and non-neoplastic diseases) and heritable mutations in humans owing to its interaction with other toxins that can enhance damage produced by irradiation. It is very prudent to continue to support the well-established radiobiological concept that no radiation dose can be considered completely safe, and that all efforts must be made to reduce both the radiation dose and biological damage, no matter how small that damage might be, without sacrificing the benefits of radiation. Based on the results of many scientific experiments, formulations containing multiple antioxidants for biological protection against radiation damage in humans can be developed, and this strategy together with the existing physical concept of radiation protection, should further reduce potential risks of low doses of ionizing radiation in humans.

Hsp70 protects mitotic cells against heat-induced centrosome damage and division abnormalities

The effect of heat shock on centrosomes has been mainly studied in interphase cells. Centrosomes play a key role in proper segregation of DNA during mitosis. However, the direct effect and consequences of heat shock on mitotic cells and a possible cellular defense system against proteotoxic stress during mitosis have not been described in detail. Here, we show that mild heat shock, applied during mitosis, causes loss of dynamitin/p50 antibody staining from centrosomes and kinetochores. In addition, it induces division errors in most cells and in the remaining cells progression through mitosis is delayed. Expression of heat shock protein (Hsp)70 protects against most heat-induced division abnormalities. On heat shock, Hsp70 is rapidly recruited to mitotic centrosomes and normal progression through mitosis is observed immediately after release of Hsp70 from centrosomes. In addition, Hsp70 expression coincides with restoration of dynamitin/p50 antibody staining at centrosomes but not at kinetochores. Our data show that during mitosis, centrosomes are particularly affected resulting in abnormal mitosis. Hsp70 is sufficient to protect against most division abnormalities, demonstrating the involvement of Hsp70 in a repair mechanism of heat-damaged mitotic centrosomes.

Influence of different radioprotective compounds on radiotolerance and cell cycle distribution of human progenitor cells of granulocytopoiesis in vitro

Ficoll-separated mononuclear cells (MNC) of cryopreserved human bone marrow were incubated with isotoxic doses of diltiazem, N-acetylcysteine (NAC), glycopolysaccharide extract of spirulina platensis (SPE), tempol, thiopental, WR2721 and WR1065. After irradiation with a single dose of 0.73 Gy, survival of granulocyte/macrophage colony-forming cells (GM-CFC) was determined at d 10-14, using an agar culture system. Diltiazem, NAC, tempol and WR1065 significantly improved radiotolerance with protection factors (PF) between 1.21 and 1.36 (n = 5, P < 0.05) at 0.73 Gy (PF-0.73 Gy). The survival curves of diltiazem (D0 = 0.88 Gy, n = 1.00), NAC (D0 = 0.92 Gy, n = 1.10), tempol (D0 = 0.99 Gy, n = 1.10), WR1065 (D0 = 0.89 Gy, n = 1.16) and control (D0 = 0.78 Gy, n = 1.00) over 0.36-2.91 Gy showed a significant radioprotective effect for D0 only for tempol (P = 0.018) and for the extrapolation number 'n' only in the case of NAC (P = 0.023). Cell cycle analysis of the CD34+ cell subpopulation (control-0 h: G1 = 82.7%, S = 13.7%, G2/M = 3.6%) revealed that all compounds with a significant PF-0.73 Gy also caused a significant increase in CD34+ cells in S phase up to 48 h. Within the first 24 h, only NAC (26.7 +/- 4.1%), tempol (14.3 +/- 1.0%) and possibly WR1065 (15.5 +/- 1.6%) had higher fractions of CD34+ S-phase cells compared with controls. This observation and the improvement of GM-CFC cloning efficiency indicated that only NAC was able to recruit progenitor cells in the cell cycle, whereas tempol and WR1065 possibly inhibited cell cycle progression by S and G2/M arrest. Of the radioprotectors tested, NAC, tempol and WR1065 may be suitable to support, alone or combined with cytokine therapy, accelerated haematopoietic recovery after irradiation.

Radio frequency radiation of millimeter wave length: potential occupational safety issues relating to surface heating

Currently, technology is being developed that makes use of the millimeter wave (MMW) range (30-300 GHz) of the radio frequency region of the electromagnetic spectrum. As more and more systems come on line and are used in everyday applications, the possibility of inadvertent exposure of personnel to MMWs increases. To date, there has been no published discussion regarding the health effects of MMWs; this review attempts to fill that void. Because of the shallow depth of penetration, the energy and, therefore, heat associated with MMWs will be deposited within the first 1-2 mm of human skin. MMWs have been used in states of the former Soviet Union to provide therapeutic benefit in a number of diverse disease states, including skin disorders, gastric ulcers, heart disease and cancer. Conversely, the possibility exists that hazards might be associated with accidental overexposure to MMWs. This review attempts to critically analyze the likelihood of such acute effects as burn and eye damage, as well as potential long-term effects, including cancer.

Modeling radioprotective mechanisms in the dose effect relation at low doses and low dose rates of ionizing radiation

A new model (Random Coincidence Model--Radiation Adapted (RCM-RA)) is proposed which explains a possible pseudo threshold for stochastic radiation effects. It describes the formation of cancer in the case of multistep fixation of lesions in the critical regions of tumor associated genes such as proto-oncogenes or tumor-suppressor genes. The RCM-RA contains two different possibilities of DNA damage to complementary nucleotides. The damage may be caused either by radiation or by natural processes such as cellular radicals or thermal damage or by chemical cytotoxins. The model is based on the premise that radiation initially is bionegative, damaging organisms at their different levels of organization. The radiation, however, also induces various cellular radioprotective mechanisms which decrease the damage by natural processes. Considering both effects together, the theory explains apparent thresholds in the dose-response relation for radiation carcinogenesis without contradiction to the classical assumption that radiation is predominantly bionegative at doses typically found in occupational exposures.