Dithizone (DTZ) is a recognized diabetogenic agent in vivo, and a supr
avital stain commonly used for identification of islets to be used for
transplantation. In the present studies, we compared DTZ staining of
freshly isolated and cultured canine, bovine, and porcine islets, and
the effect of DTZ on the function and viability of islets. Incubation
with DTZ resulted in staining of canine and porcine islets, but no dis
cernible staining with bovine islets. Insulin content of porcine, cani
ne, and bovine islet was 2.0 +/- 0.2, 2.2 +/- 0.3, and 1.9 +/- 0.2 mU/
EIN, indicating a lack of correspondence of DTZ staining and insulin c
ontent. Seven days of culture with canine islets resulted in greater t
han or equal to 50% reduction of DTZ stained cells. Exposure to DTZ at
50 mu g/mL resulted in a maximal number of stained cells in preparati
ons of purified islets (80-85%; counted after dispersion), a lower per
centage of cells stained faintly at 20 mu g/mL (50-55%), with no disce
rnible staining at 10 mu g/mL. Prolonged exposure of islets (4-48 h) t
o 20 mu g/mL DTZ led to reduced insulin secretion and islet cell death
. Incubation of canine or porcine islets with 100 mu g/mL of DTZ for 0
.5 h resulted in a dramatic loss of viability and diminished insulin s
ecretory function, which was not reversed with continued culture. The
concentration dependence of toxic effects paralleled the concentration
dependence of cellular staining. The minimally effective staining con
centration (20 mu g/mL) also resulted in a loss of viability. An addit
ional assessment of DTZ toxicity was made using the RIN-38 beta-cell l
ine, which shows no discernible staining with DTZ. Alh exposure to dit
hizone resulted in a dose-dependent loss of viable RIN-38 cells. We co
nclude first, that DTZ is cytotoxic to islet cells in vitro, at concen
trations used for islet staining. Although the toxicity of DTZ appears
to be related to its staining properties, high concentrations have to
xic effects that are unrelated to staining properties. We propose that
cellular accumulation of DTZ (staining), produces toxicity by concent
rating DTZ to toxic levels. Secondly, we conclude that DTZ does not st
ain islets of all species, despite the equivalent insulin content.