Radiation-Induced Toxicity and Radiation Response Modifiers in Zebrafish - Zebrafish: Methods for Assessing Drug Safety and Toxicity - page 291

enables a view of the gastrointestinal lumen filled with fluorescent PED6 and un-
quenched by the activity of phospholipase A2 present in the mucosal lining of the
gastrointestinal tract (Fig. 21.1c). IR (15Gy) severely impairs fluorescence intensity and
blunts lumen formation consistent with significant damage to the GI tract of higher
vertebrates exposed to 10-15Gy IR (Bhanja et al., 2009). The histological appearance of
the gastrointestinal mucosa 5 days after radiation exposure reveals widespread damage
caused by a sublethal IR dose (12Gy). Specifically, the mucosal epithelium of the
hindgut proximal to the cloaca is shaped irregularly with redistribution of nuclei away
from the basal lamina and decreased goblet cell numbers (Daroczi et al., 2009).
21.7 RADIATION-ASSOCIATED NEPHROTOXICITY
Impairment of renal function has been recognized as a result of radiation therapy in
the clinical setting. In zebrafish embryos, radiation exposure induced extensive edema
formation raising the question whether kidney damage leads to water retention.
However, edema may also be the result of damage to organs other than the kidneys
including the heart and vessels. To assess kidney function, a technique based on renal
clearance of fluorescently labeled dextran originally described by Hentschel
et al. (2005) was employed. The labeled dextran is injected at 72 hpf into the cardiac
venous sinus and the relative fluorescent intensity of the cardiac area measured within
24 h. Compared with nonirradiated controls, exposure to 20 Gy markedly reduces
clearance of this agent from the heart in the absence of gross morphological
alterations of the intracardiac lumen (Fig. 21.1d). This result is consistent with retention
of the labeled contrast agent due to reduced renal excretion and points to compro-
mised renal function associated with radiation exposure. Time lapse microscopy of
cardiac contractility (Incardona et al., 2004) represents a useful tool to distinguish
whether edema formation in zebrafish embryos is secondary to reduced cardiac
function. In the case of irradiated embryos, this analysis revealed only marginal
effects of 20 Gy ionizing radiation on heart rate and blood flow of sham-irradiated and
irradiated fish (unpublished results). Collectively, these results demonstrate the utility
of using organ function assays to evaluate radiation toxicity even when the cell or
tissue type responsible for the observed toxicity is unknown (Daroczi et al., 2006).
21.8 OTOTOXICITY IN IRRADIATED ZEBRAFISH
Neurotoxicity represents a dose-limiting toxicity associated with radiation therapy of
the central nervous system. While short-term assays to ascertain nerve cell damage
have yet to be adapted to the radiation setting, an assay for ototoxicity has been used to
monitor radiation-induced effects on these specialized nerve cells. This is done by
using the vital dye DASPEI (Molecular Probes) that exclusively stains mechanore-
ceptive hair cells (neuromasts) that are comparable to inner ear nerve hair cells in
higher vertebrates. When embryos are exposed to 80 Gy IR at 5 dpf, staining of
neuromasts is markedly reduced at 6 dpf whereas lower doses (20-60 Gy) do not exert
measurable effect on neuromast development (Daroczi et al., 2006).