Exploitation of hypoxia for radiation therapy: a lesson from phenothiazines

Radioprotection and radiosensitization by curcumin

This chapter gives an overview of the radioprotective and radiosensitizing effect of curcumin. Ionizing radiations interact with biological molecules inducing radiolytic products like e(aq), *OH, *H, -OH, +H, O2, and peroxides. These free radicals damage important biomolecules and subsequently inflict deleterious effects in the organism. Whole-body exposure to ionizing radiations results in central nervous system, gastrointestinal tract, and bone marrow syndromes, whereas chronic irradiation causes cancer, birth anomalies, erythema, and dysfunctions to almost all organ of the body depending on the total dose and site of irradiation. Curcumin (diferuloyl methane), a yellow pigment present in the rhizomes of turmeric, has been used in Southeast Asia to give yellow color and flavor to curries. Turmeric has been used to treat various ailments in the Ayurvedic system of medicine in India. Recently, it has been evaluated for its radioprotective and radiosensitizing activities. Curcumin has been found to exert a dual mode of action after irradiation depending on its dose. It has been reported to protect various study systems against the deleterious effects induced by ionizing radiation and to enhance the effect of radiation. Therefore, curcumin can be very useful during radiotherapy of cancer. Administration of curcumin in patients will be able to kill the tumor cells effectively by enhancing the effect of radiation and, at the same time, protect normal cells against the harmful effects of radiation. The available information on curcumin suggests that the radioprotective effect might be mainly due to its ability to reduce oxidative stress and inhibit transcription of genes related to oxidative stress and inflammatory responses, whereas the radiosensitive activity might be due the upregulation of genes responsible for cell death.

Eugenol as an in vivo radioprotective agent

In the present work, an attempt has been made to evaluate the possible in vivo radioprotection by eugenol. Swiss albino mice were administered different doses of eugenol (75,150 and 300 mg/kg) before exposure to 1.5 Gy of gamma radiation. The micronucleus test was carried out to determine the genetic damage in bone marrow. Our results demonstrated significant reduction in the frequencies of micronucleated polychromatic erythrocytes (MnPCEs) with all three eugenol doses. Eugenol (150 mg/kg) was also tested against different doses of radiation (0.5, 1, 1.5, and 2 Gy) and was found to afford significant radioprotection. Reduction in the incidence of MnPCEs could be noticed up to 72 h postirradiation (1.5 Gy). Moreover, the level of peroxidative damage and the specific activities of lactate dehydrogenase (LDH) and methylglyoxalase I (Gly I) were observed in the liver of mice treated with eugenol for seven days in comparison to untreated mice. The results revealed that eugenol exerted significant protection against oxidative stress. This possibility was further supported by the enhanced response of Gly I and the lowered activity of LDH. The present findings suggested that eugenol has a radioprotective potential.

Modulation of radioresponse of glyoxalase system by curcumin

Human beings have been exposed to radiation for many years. It is quite possible that antioxidant phytochemicals consumed in their diet might be providing a variable degree of radioprotection. However, their radiomodifying ability is not well understood. In the present work, curcumin (diferuloyl methane), a phytochemical present in the rhizome of Curcuma longa Linn. has been examined for its radioprotective property using the glyoxalase system which is vital for various biological functions. Curcumin (5, 25 and 50 mg/kg body weight) in olive oil was given orally to Swiss albino male mice (7-8 weeks old) daily for 2 weeks and irradiated with different doses of gamma-radiation (0-6 Gy) at 0.027 Gy per second dose rate on last day of the treatment. The specific activities of glyoxalase I and II were determined in the liver and spleen. The treatment of curcumin prior to irradiation restored the specific activity of glyoxalase system to almost the control level which was suggestive of the radioprotective ability of curcumin. Free radical scavenging and electron/hydrogen donation are probable attributes for the protective effect of curcumin.