The effects of Magnolol on alpha-particle induced bystander effect

Abstract

In recent years, radiation-induced bystander effect (RIBE) has become a hot research topic in the field of radiobiology. The RIBE refers to the biological response found in cells (called bystander cells) which are not irradiated directly by ionizing radiation but are next to cells irradiated directly by ionizing radiation. The discovery of the bystander effect has posed new challenges to the existing knowledge on radiation damages. Hence the virtual potential radiation risks are greater then those presume whenever cells are exposed for radiations. The exact mechanism of the RIBE, however, is not yet well understood despite much effort has been dedicated to its study. Fortunately, there is considerable evidence showing that reactive oxygen species (ROS) probably play an important role in the bystander signal transmission. In view of this, the present project will focus on studying the effects of Magnolol, an antioxidant extracted from the bark of Magnolia officinalis which is used as a traditional Chinese medicine, on alpha-particle induced bystander effects. In particular, the effects of Magnolol on bystander effects in Chinese hamster ovary (CHO) cells were examined. Three different biological endpoints were assessed to study the bystander effects at the DNA level, the chromosome level as well as the cell level to form an integrative investigation. Chapter 1 gives the literature review. Chapter 2 describes our experiments in which CHO cells were cultured in custom made petri-dishes specifically designed for alpha-particle irradiation experiments. The bystander effects were studied through the medium transfer approach where the bystander cells would receive the medium for the irradiated cells. Cytokinesis-block micronucleus (CBMN) assay was performed to quantify the chromosome damages induced by alpha-particle irradiation. The results showed that the bystander effect indeed occurred in non-hit bystander cells within a short period of time after irradiation, and the alpha-particle induced micronuclei (MN) frequencies in bystander cells were suppressed with the presence of Magnolol but no suppression effect was found in the irradiated cells. Chapter 3 describes our experiments, in contrast to those described in the previous chapter, where the bystander effect was studied through a co-culture experiment, and clonogenic survival was used as the biological endpoint to demonstrate the bystander effect. Some bystander CHO cells were unable to form colony and thus showed a lower surviving fraction when compared to the control cells. Again, with the pretreatment of Magnolol, the bystander cells had a better clonogenic survival when compared to those bystander cells without the pretreatment of Magnolol. Chapter 4 describes our experiments where Chinese hamster ovary (CHO) cells were cultured in PADC-film-based dishes and were irradiated with low fluences of alpha particles passing through the PADC-films. The precise number of cells traversed or missed by alpha particles could be determined by studying the alpha-particle tracks developed on the PADC films upon subsequent chemical etching. TdT-mediated dUTP Nick-End Labeling (TUNEL) assay was employed to analyze the biological response of bystander cells in terms of DNA strand breaks. With the pretreatment of Magnolol, the DNA strand breaks in bystander cells were reduced, which showed that the alpha-particle induced bystander effects were suppressed with the presence of Magnolol. Chapter 5 gives the conclusions and discussion.

Date of Award	15 Jul 2009
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Kwan Ngok Peter YU (Supervisor)