Individual variation in the production of a `bystander signal' following irradiation of primary cultures of normal human urothelium

Abstract

The existence of a bystander effect following both alpha and gamma irradiation of many cell lines is not now in dispute. The significance of this effect for cancer risk assessment and radiotherapy treatment planning requires demonstration of its relevance in vivo. The problem in demonstrating the existence of the effect in vivo is that other systemic effects may mask or confound the effect being investigated and it is practically impossible to attribute an effect in a particular cell to a signal produced in another irradiated cell. To approach this problem, we have developed an assay where fragments of human tissue can be irradiated ex vivo and the media harvested and added to unirradiated, allogenic explants or to a clonogenic cell line which has a well characterized and stable response to the bystander signal. The variation in production of the signal from patient to patient can thus be assessed using molecular and cellular endpoints. A study using tissue from over 100 patients and from mouse strains with well characterized responses to low level radiation exposure shows that there is variation in the effect of the signal produced by irradiated tissue from different patients. Gender, smoking status and the existence of a bladder malignancy influence the expression of the signal by normal urothelium. The effects of exposure to medium containing the signal are transmitted to distant progeny of the exposed cell population. The results may be important not only for understanding radiation risk mechanisms for protection but also for radiotherapy treatment planning where they may open new avenues for development of drugs for combined therapy.

A proliferation-dependent bystander effect in primary porcine and human urothelial explants in response to targeted irradiation

“…It has been demonstrated that gap-junction-mediated communication in human bladder explant outgrowth depends on a smoking status of the tissue donors (Lyng et al, 1996). Also, other studies have reported a relationship between the level of bystander signal produced and gender and malignancy status (Mothersill et al, 2001). Further studies in defined populations using the model described here would clearly be useful to clarify the variations in response we have observed.…”

Radiation-induced genomic instability and bystander effects: inter-related nontargeted effects of exposure to ionizing radiation

“…The promitogenic response was attributed to increases in the concentrations of a cytokine (TGF-b1) in cell supernatants; a concentration that also induced intracellular ROS in unirradiated cells and, unlike the gap-junction-mediated mechanism in skin fibroblasts (Azzam et al, 2001), led to decreased cellular levels of CDKN1A/p21 and also p53 (Iyer and Lehnert, 2000). Potentially related to the mechanisms mediating cytogenetic damage not requiring gap-junctional communication is the finding that the medium in which certain cells have been irradiated contains an activity, probably a protein, that produces cytotoxic effects in nonirradiated cells Lyng et al, 2000Lyng et al, , 2002Mothersill et al, 2000bMothersill et al, , 2001Seymour and Mothersill, 2000). The first detectable effect of the medium containing the cytotoxic activity on recipient cells is a rapid (1-2 min) calcium pulse followed 30 min-2 h later by changes in mitochondrial membrane permeability and the induction of ROS (Lyng et al, 2000(Lyng et al, , 2002; a role for mitochondrial metabolism is suggested by the lack of signal production by cells that lacked functional glucose-6-phosphate dehydrogenase (Mothersill et al, 2000b).…”

Bystander signaling between glioma cells and fibroblasts targeted with counted particles

“…For confluent cell monolayers and 3-dimensional cell clusters, gap junctional intercellular communication (GJIC) has been found to play a critical role in radiation-induced bystander effects. [14][15][16][17][18] In other cases, soluble extracellular factors, including reactive oxygen species (ROS) and cytokines, [19][20][21] which are released from irradiated cells and even human tissue, 22 contribute to the bystander responses. We and others have found that radiation-induced nitric oxide (NO) has multiple bystander effects on non-irradiated cells.…”