**5. Acknowledgements**

The grant provided by DRDO vide project No RD-P1-2000/INM-289 and by DST for ILTP project A 9.5) for these studies is gratefully acknowledged. The efforts of research fellows (D. Singh, M. Dwivedi, A. Arya and S. Singh); trainees (Ashutosh, Divya, Sugandh); and technical assistants (C. Prakash and A. Sharma) in performing some of experimental studies, are also acknowledged.

### **6. References**

Arya, A.K., Garg, A.P. & Bala M. (2006). Upregulation of Cox1 and Shy1 genes following exposure to low dose ionizing radiation in *accharomyces cerevisiae. Indian Journal of Radiation Research.* Vol. 3, No. 4 (Nov). pp 273. ISSN 0973-0168.

Exposure to low dose radiation could be of significance in clinical evaluation of risk assessment, radiotherapy and radiation protection. Although a number of mechanisms such as enhanced DNA repair, alterations in stress proteins, immuno-modulation, and antioxidant defense system have been proposed to contribute to beneficial effects of low dose exposure, the understanding about the mechanisms inadequate. This is primarily because the reports are scattered, and among the available reports there is variability of dose response, the model systems as well as the experimental design followed in different laboratories. Our studies with a uniform experimental design on two different model systems viz. *Saccharomyces cerevisiae* and human PBMCs, has clearly demonstrated that irradiation with lower doses of ionizing radiation has a beneficial effect on the organism. Moreover, the effect of lower dose of radiation can not be predicted simply by extrapolating the effect of higher doses. The term 'Radiation induced radioresistance' or 'RIR' was suggested in our studies to refer a phenomenon where a single small dose radiation exposure could lead to better tolerance to the subsequently given lethal doses of radiation, and the effect was transient. Although, the RIR caused by low dose irradiation appears to be a complex interplay of many genes, this study shows that the genes of *MRX/MRN* complex, *HSP* family and also mitochondrial gene have a confirmed role in phenomenon leading to RIR. *KAR2* is an integral component of unfolded protein response (UPR) pathway. Up regulation of *KAR2* negatively regulated UPR pathway (Kimata et al., 2003), and, therefore may have caused accumulation of unfolded cytosolic proteins. If this is true then, after low dose irradiation, up regulation of *KAR2* helped the accumulation of proteins that might have unfolded due to radiation stress. The accumulation of unfolded proteins may have been responsible for increased levels of *SSA1* /*SSA2* /*SSA4* similar to that observed in *S. cerevisiae* cells after heat shock (Stone & Craig 1990). Also, it was observed the mitochondrial genes for maintaining the functional integrity of mitochondria; as well as to counter the reactive oxygen species that may have been produced because of oxidative stress produced after irradiation, were up-regulated. Further, the absence of mutation in representative sequences, decrease in revertants as well as tryptophan prototrophs, decrease in the micronuclei frequency together with enhanced levels of error-free DNA repair*,* strongly suggested that priming with low doses imparted transient radio-resistance to the cells

culminating in the survival benefits via error-free mechanisms.

The grant provided by DRDO vide project No RD-P1-2000/INM-289 and by DST for ILTP project A 9.5) for these studies is gratefully acknowledged. The efforts of research fellows (D. Singh, M. Dwivedi, A. Arya and S. Singh); trainees (Ashutosh, Divya, Sugandh); and technical assistants (C. Prakash and A. Sharma) in performing some of experimental studies,

Arya, A.K., Garg, A.P. & Bala M. (2006). Upregulation of Cox1 and Shy1 genes following

*Radiation Research.* Vol. 3, No. 4 (Nov). pp 273. ISSN 0973-0168.

exposure to low dose ionizing radiation in *accharomyces cerevisiae. Indian Journal of* 

**5. Acknowledgements** 

are also acknowledged.

**6. References** 

**4. Summary and conclusion** 


Radiation Induced Radioresistance – Role of DNA Repair and Mitochondria 169

Nambi, K.S.V. & Soman, S.D. (1990). Further observations on environmental radiation and cancer in India. *Health Phys*. Vol. 59, No. 3 (September), pp. 339-344. Olivieri, G., Bodycot, J. & Wolff, S. (1984). Adaptive response of human lymphocytes to low

Pandey, B.N., Sarma H.D., Shukla, D. & Misra, K. P. (2006). Low dose radiation induced

Sanderson, B.J. & Morley, A.A.(1986). Exposure of human lymphocytes to ionizing radiation

Sahara, T., Goda, T. And Ohgiya, S. (2002). Comprehensive expression analysis of time

Sasaki, M.S., Ejima, Y., Tachibana, A., Yamada, T., Ishizaki, K., Shimizu, T. & Nomura, T.

Seo, H.R., Chung, H.Y., Lee, Y.J., Bae, S., Lee, S.J. & Lee, Y.S. (2006). p27Cip/Kip Is Involved

Shadley, J.D. & Wiencke J.K. (1989). Induction of the adaptive response by X-rays is

Shadley, J.D. & Wolff, S. (1987). Very low doses of X-rays can cause human lymphocytes to

Sharma, A.K. & Bala, M., (2002). Beneficial effect of low level 60Co--radiation on yeast

Smolka M. B., Albuquerque C. P., Chen S. H., Zhou H. (2007)"Proteome-wide identification

Stone D.E. & Craig, E.A. (1990) Self regulation of 70-kilodalton heat shock proteins in *Saccharomyces cerevisiae*, *Mol. Cell. Biol*. Vol. 10,No. 4 (April), pp. 1622-1632. Stiff T., Reis C., Alderton G.K., Woodbine L., O'Driscoll M., Jeggo P.A. (2005) Nbs1 is required for ATR-dependent phosphorylation events. EMBO J. 24, pp. 199-208. UNSCEAR (1994) United Nations Scientific Committee on the effects of Atomic Radiation

UNSCEAR, (2000). Report to the General Assembly, with Scientific Annexes. Volume II:

Waltes R., Kalb R., Gatei M., Kijas A.W., Stumm M., Sobeck A., Wieland B., Varon R.,

*Int. J. Low Radiation.* Vol. 2, No. ½ , pp. 111-118.

277, No.51 (December), pp. 50015-50021.

*J. Radiat. Res*. Vol. 47, No. 1 (March), pp 83.90.

Annexes. Annex B. New York: United Nations.

E.00.IX.4. United Nations, New York.

504, No. 1-2 (July), pp. 101-118.

594-597.

95-96.

616.

(January), pp 77-82.

Vol. 104, pp. 10364-10369.

(December), pp 347-351.

concentration of radioactive thymidine. *Science* Vol. 223, No. 4636 (February), pp.

modification of ROS and apoptosis in thymocytes of whole body irradiated mice,

reduces mutagenesis by subsequent ionizing radiation. *Mutat. Res*. Vol. 164, No. 6

dependent genetic responses in yeast cells to low temperatures. *J Biol Chem*, Vol.

(2002). DNA damage response pathway in radio-adaptive response, *Mutat. Res*,Vol.

in Hsp25 or Inducible Hsp70 Mediated Adaptive Response by Low Dose Radiation.

dependent on radiation intensity. *Int. J. Radiat. Biol*. Vol. 56, No. 1 (July) pp 107-118.

become less susceptible to ionizing radiation*. Mutagenesis*. Vol.2, No.2 (March), pp.

*Saccharomyces cerevisiae*. Vijnana Parishad Anusand. Patrika. Vol. 45, No. 1

of in vivo targets of DNAdamage checkpoint kinases." Proc. Natl. Acad. Sci. U.S.A.

report on "Adaptive response to radiation in cells and organisms, Sources and effects of ionizing radiation: Report to the General Assembly, with Scientific

Effects. Annex I: Epidemiological Evaluation of Radiation-Induced Cancer No.

Lerenthal Y., Lavin M.F., Schindler D., Doerk T. (2009) Human RAD50 deficiency in a Nijmegen breakage syndrome-like disorder. *Am. J. Hum. Genet*. Vol 84, pp. 605-


Carson, C.T., Schwartz, R.A., Stracker, T.H., Lilley, C.E., Lee, D.V. & Weitzman, M.D. (2003).

Chaubey R.C., Bhilwade, H.N.Sonawane, V. R. & Rajagopalan R. (2006). Effect of low dose

Collis, S.J., Schwaninger, J.M., Ntambi, A.J., Keller T.W., Nelson, W.G., Dillehay, L.E. &

Dasu, A. & Denekamp, J. (2002). Inducible repair and inducible radiosenstivity : a complex

Dwivedi, M., Singh, S., Sharma, A.K., Mathew, L. and Bala, M., (2001). Cytogenetis

Dwivedi, M., Sehgal, N. & Bala M. (2008). The effects of low dose 60Co-gamma-radiation on

in *Saccharomyces cerevisiae.Int. J. of Low Radiation,* Vol. 5, No. 4, pp 290-309. Fenech, M. (1993). The cytokinesis-block micronucleus technique: a detailed description of

Franco, N., Lamartine, J., Frouin, V., Le Minter, P., Petat, C., Leplat, J.J., Libert, F., Gridol, X.

Frappart, P.O., Tong, W.M., Demuth, I., Radovanovic I., Herceg, Z., Aguzzi, A., Digweed M.

Hohl M, Kwon Y, Galván S.M., Xue X, Tous C, Aguilera A, Sung P, Petrini J.H.J. (2011) The

Jager, De. M., Van N. J., Vangent, D.C., Dekker, C., Kanaar, R. & Wyman, C. (2001). Human

Kimata, Y., Kimata, Y.I., Shimizu, Y., Abe, H., Farcasanu, I.C. & Takeuchi, M. et al. (2003).

Luckey, T.D. (2008). Atomic bomb health benefits. *Dose Response,* Vol. 6, No. 4 (August), pp.

cerebellar defects. *Nature Medicine,* Vol. 11, No. 5 (May), pp. 538-544. Gupta D, Arora R, Garg A P, Bala M, Goel H C. 2004. Modication of radiation-damage to

*Structural & Molecular Biology* Volume: 18, pp. 1124-1131

*EMBO J*, Vol. 22, No. 24 (December), pp. 6610- 6620.

doses. *Nuclear Energy,* Vol. 38, pp. 157-164.

*Mutat. Res*, Vol. 285, No. 1 (January), pp. 35-44.

*Mol Cell Biochem* Vol. 266: pp. 65-77.

Rad50/Mre11 is a flexible complex that

49624-49632.

2001.

2569.

369-382.

(June), pp. 623-635

The Mre11 complex is required for ATM activation and the G2/M checkpoint.

and low-dose rates of gamma radiation on DNA damage in peripheral blood leukocytes using comet assay *Int. J. of Low Radiation,* Vol. 2, No. ½, pp. 71-83. Cohen, B.L. (1999). Validity of the linear threshold theory of radiation carcinogenesis at low

Deweese, T.L. (2004). Evasion of early cellular response mechanisms following low level radiation induced DNA damage. *J. Biol. Chem*, 279, No. 48 (November), pp.

but predictable relationship? *Radiation Research*. Vol. 153, No. 3 (March) pp. 279-288.

alterations associated with radio-adaptive response in proliferating and stationary phase cells of *Saccharomyces cerevisiae.* Proceedings of Biotechnocon-2001, first conference of Biotechnology Society of India. at V.P. Chest Institute, Delhi, Oct,

radioresistence, mutagenesis, gene conversion, cell cycle and transcriptome profile

the method and its application to genotoxicity studies in human populations.

& Martin, M.T. (2005). Low dose exposure to gamma rays induces specific gene regulations in normal human keratinocytes. *Radiation Research,* Vol. 163, No. 6

& Wang, Z.Q. (2005). An essential function for NBS1 in the prevention of ataxia and

mitochondrial system in vivo by Podophyllum hexandrum: mechanistic aspects.

Rad50 coiled-coil domain is indispensable for Mre11 complex functions. *Nature* 

Genetic evidence for a role of Bip/Kar2 that regulates Ire1 in response to accumulation of unfolded proteins, *Mol. Biol. Cell*. Vol. 14, No. 6 (June), pp. 2559-


**9** 

*Brazil* 

**Sterilization by Gamma Irradiation** 

*Federal University of Pernambuco-Department of Nuclear Energy* 

Sterilization is defined as any process that effectively kills or eliminates almost all microorganisms like fungi, bacteria, viruses, spore forms. There are many different sterilization methods depending on the purpose of the sterilization and the material that will be sterilized. The choice of the sterilization method alters depending on materials and devices for giving no harm. These sterilization methods are mainly: dry heat sterilization, pressured vapor sterilization, ethylene oxide (EtO) sterilization, formaldehyde sterilization, gas plasma (H2O2 ) sterilization, peracetic acid sterilization, e-beam sterilization and gamma

Gamma radiation sterilization and e-beam sterilization are mainly used for the sterilization of pharmaceuticals. Gamma radiation delivers a certain dose that can take time for a period of time from minutes to hours depending on the thickness and the volume of the product. Ebeam irradiation can give the same dose in a few seconds but it can only give it to small products. Depending on their different mechanism of actions, these sterilization methods affect the pharmaceutical formulations in different ways. Thus, the sterilization method

To be effective, gamma or e-beam sterilization requires time, contact and temperature. The effectiveness of any method of sterilization is also dependent upon four other factors like the type of microorganism present. Some microorganisms are very difficult to kill. Others die easily the number of microorganisms present. It is much easier to kill one organism than many the amount and type of organic material that protects the microorganisms. Blood or tissue remaining on poorly cleaned instruments acts as a shield to microorganisms during the sterilization process, the number of cracks and crevices on an instrument that might harbor microorganisms. Microorganisms collect in, and are protected by, scratches, cracks

Finally, here is no single sterilization process for all the pharmaceuticals and medical devices. It is hard to assess a perfect sterilization method because every method has some advantages and disadvantages. For this reason, sterilization process should be selected according to the chemical and physical properties of the product. It is fairly clear that different sterilization processes are used in hospital and in industry applications. While EtO or autoclave sterilization is used in hospitals, gamma radiation or e-beam sterilization is used in industry depending on the necessity of a developed institution. Superiority of radiation sterilization to EtO and other sterilization methods are known by all over the

chosen must be compatible with the item to be sterilized to avoid damage.

and crevices such as the serrated jaws of tissue forceps.

**1. Introduction** 

sterilization.

Kátia Aparecida da Silva Aquino

Zimmermann, F.K., Kern, R. & Rosenberger, H. (1975). A yeast strain for simultaneous detection of induced mitotic crossing over, mitotic gene conversion and reverse mutation. *Mutat. Res*. Vol. 28, No. 3 (June), pp. 381-388.
