Different aspects of hormesis and radiation hormesis

Formerly Radiation Chemistry Department, Institute of Nuclear Medicine & Allied Sciences.

Brig. S. K. Mazumdar Road, Delhi-110 054, India

E-mail: saurin_upadhyay@yahoo.com

Manuscript received 6 August 2008, revised 10 September 2009, accepted 27 November 2009

Hormesis is adopted by seeds, plants, micro-organism, mice, guineapigs and human beings. It is induced by chemicals, pharmaceuticals, heavy metals and toxicological compounds of varied types. Physical inducing agents are temperature and different types of ionizing radiations.

Hormesis follows biphasic time-response and dose-response relationships which can be quantitated. The hormetic response is controlled by summation of information, effectors and sensors. It has been reported in erythropoetic tissue, lymphokine cascade in antibody formation and thymidine reuse in mammals etc.

Radiation hormesis is connected with radiation dose, LET, dose rate, size and mass of cells, types of radiation, probability of interaction of radiation with target, time lag between dose and response etc.

At its preliminary stage the concept of hormesis was dismissed but later a large number of authors have supported this concept.

Mechanistically radiation hormesis can be attributed to different causes namely : (i) cellular damage of DNA and its repair, (ii) mutagenesis and its repair, (iii) micronuclei formation and its repair, (iv) different types of chromosomal aberrations and their repair etc. These repairs are done by antioxidants, different types of enzymes and immune responses and cell cycle control etc.

Low dose hormesis has been reported under various conditions namely : (i) environmental and epistemological problems, (ii) background radiation dose estimation, (iii) dose estimation in nuclear installations, (iv) estimation of dose for atomic survivors, (v) accidental dose estimation in Chernobyl etc. In the above cases hormesis depends on internal factors like - lighting condition, intensity and duration of radiation, measurement time of exposure etc.

Societal aspects of hormesis e.g. application in biogerontology, radiation protection aspect, increase in life span for cancer - induced patients applying hormetic principles, environmental and toxicological aspects have been mentioned.

Future prospects or hormesis (both theoretical and practical) are given below :

Theoretical : (I) Low level effects, (ii) linear extrapolation from high level exposure, (iii) shape of dose-response curve and mechanism or radiation effects at low dose, (iv) molecular and cellular studies on mechanism of hormesis, (v) pharmacological hormesis mechanism, (vi) role of hormesis in environmental risk and hazard assessment methods and their evaluation, (vii) role of hormesis in the improvement of harmonization of cancer and non-cancer cases.

Practical : (i) Predictive assay of clinical and therapeutic measures using hormetic principles, (ii) toxicological, agricultural, behavioral, societal, biogerontological and economic aspects of hormesis.