Plant medicine in the treatment of radiation-induced normal tissue lesions-A review

Radiation-induced normal tissue lesions, once seen as a consequence of loss of proliferative integrity of clonogenic target cells, inevitable and untreatable are now viewed as a result of dynamic interactions between multiple cell lines within a particular tissue that can be intervened. Normal tissue damage is the most important limiting factor in radiotherapy and a major component in the medical management of radiation accidents. In general irradiation leads to an acute stress response followed by late consequential lesion. The response is initiated through kinases, transcription factors and altered production of inflammatory cytokines followed by a chronic inflammatory process, resembling that of wound healing, which involves vascular and parenchymal cell dysfunction and cell loss. At present there is not an approved method for the treatment of radiation-induced normal tissue lesions. A number of agents with diverse modes of action have been used in post irradiation modification of radiation-induced normal tissue reactions. Plants, as a result of their longstanding exposure to environmental stress factors including radiation, have developed protective mechanisms and substances that can potentially be exploited for the treatment of radiation lesions. Aloe vera, which is known for its wound healing effects and has been traditionally used for treating thermal burns and wounds, appears to be the oldest herbal agent used in the treatment of radiation lesions both in the form of fresh whole leaf or Aloe vera extract. The healing property of Aloe vera, which has been verified experimentally in recent years, has been attributed to mucilagenous mucopolysacccharides including acemannan and allantoin. Oil extracted from evening primrose (Oenothera spp.) has been proven to be beneficial in the treatment of a number of radiation-induced lesions. The beneficial effect of evening primrose oil is attributed to its gamma linolenic acid (GLA) content through cyclooxygenase pathway. Extracts of Withania somnifera, Plumbago rosea and Ocimum sanctum have also been reported to have protective effects against radiation damage. Recently, persistent oxidative stress has been suggested as a common pathway in the development of radiation-induced lesions that has been demonstrated in a number of tissues such as skin, kidney and spinal cord. The beneficial effects of maidenhair tree (Ginko biloba), turmeric (Curcuma longa) and green tea (Camellia sinensis) can be attributed to their strong antioxidant activity. This review article deals with plants medicines applicable in post-irradiation treatment of radiation lesions and discuss their modes of action.