Bystander effect induced by counted high‐LET particles in confluent human fibroblasts: a mechanistic study

Abstract

The possible mechanism of a radiation-induced bystander response was investigated by using a high-LET heavy particle microbeam, which allows selected cells to be individually hit with precise numbered particles. Even when only a single cell within the confluent culture was hit by one particle of 40Ar (approximately 1260 keV/microm) or 20Ne (approximately 380 keV/microm), a 1.4-fold increase of micronuclei (MN) was detected demonstrating a bystander response. When the number of targeted cells increased, the number of MN biphasically increased; however, the efficiency of MN induction per targeted cell markedly decreased. When 49 cells in the culture were individually hit by 1 to 4 particles, the production of MN in the irradiated cultures were approximately 2-fold higher than control levels but independent of the number and LET of the particles. MN induction in the irradiated-culture was partly reduced by treatment with DMSO, a scavenger of reactive oxygen species (ROS), and was almost fully suppressed by the mixture of DMSO and PMA, an inhibitor of gap junctional intercellular communication (GJIC). Accordingly, both ROS and GJIC contribute to the above-mentioned bystander response and GJIC may play an essential role by mediating the release of soluble biochemical factors from targeted cells.

Bystander signaling between glioma cells and fibroblasts targeted with counted particles

“…Therefore, the bystander effect was independent of radiation dose delivered to the cell population. This result reinforces the finding that the microbeam-induced bystander effect in a confluent culture does not depend on the radiation dose and LET 18 and is also in agreement with other reports of the dose independence of the bystander effect induced by conditioned medium harvested from irradiated cells. 38 …”

“…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.…”

“…26 Our previous studies have shown that, when a single cell is targeted, a significant bystander response is induced in the populations of either human glioma T98G cells 27 or human primary fibroblast AG01522 cells. 18 It is not known, however, whether there are direct bystander interactions between normal and tumor cell populations, and if so, what signaling factors are involved. Here, we explored these questions by using 2 cell lines, namely, human glioma cells and fibroblasts, and individually targeting a fraction of cells through their nuclei within one population with a precise number of microbeam helium particles.…”

Heavy‐ion‐induced bystander killing of human lung cancer cells: Role of gap junctional intercellular communication

“…(4,7,(9)(10)(11)(12)(13) Gap junctions are membrane channels that connect the cytoplasm of cells and allow direct exchange of small molecules and ions between adjacent cells. GJIC is essential for the maintenance of tissue homeostasis and proliferation and the regulation of embryonic development and differentiation, and it plays a key role in induction of the bystander effect.…”

“…It has been proposed that the mediating mechanism involves secreted soluble factors, (4)(5)(6) an increase in oxidative stress, (7) plasma membrane-bound lipid rafts, (8) and gap junctional intracellular communication (GJIC). (4,7,(9)(10)(11)(12)(13) Gap junctions are membrane channels that connect the cytoplasm of cells and allow direct exchange of small molecules and ions between adjacent cells. GJIC is essential for the maintenance of tissue homeostasis and proliferation and the regulation of embryonic development and differentiation, and it plays a key role in induction of the bystander effect.…”