The Toxicologist - Society of Toxicology

2088 RETINOIC ACID AND TESTOSTERONE LEVELS IN
TESTIS AFTER MOLINATE: IN VITRO AND IN VITRO
STUDIES.
F. G. Zuno, B. S. Winder, D. Holstege and M. G. Miller. Environmental
Toxicology, University of California, Davis, CA.
Molinate (MOL) is a herbicide and testicular toxicant that is metabolically activated
via sulfoxidation. Inhibition of esterase activity is seen after molinate administration
and it has been proposed that inhibition of hydrolysis of cholesterol esters
with decreased availability of cholesterol for testosterone biosynthesis accounts for
the testicular effects. An alternate hypothesis is that inhibition of retinyl ester hydrolysis
decreases retinoic acid levels in the testis. MOL is also a known inhibitor of
aldehyde dehydrogenase (ALDH) and could inhibit ALDH-catalyzed metabolism
of retinaldehyde to retinoic acid. To investigate these possibilities, studies were carried
out both in vitro and vivo. In rat Leydig cell cultures, IC50s for inhibition of
nonspecific esterase (NSE) activity by MOL and molinate sulfoxide (MSO) were
5.42 μM and 1.9 nM, respectively. These values were more than two orders of magnitude
below that required to inhibit testosterone production (750 uM for MOL
and 60 μM for MSO) suggesting that the two effects may be unrelated. In testis S9
fractions, neither MOL (800 uM) nor MSO (800 uM) were potent inhibitors of
the conversion of retinaldehyde to retinoic acid. To directly measure the effect of
MOL on testis levels of testosterone and retinoids in the whole animal, male
Sprague-Dawley rats were administered MOL (200 mg/kg in corn oil, ip). Retinoid
measurements were made at 6, 12, 48 and 168 h time points after MOL administration.
Testis levels of retinol and retinaldehyde were not significantly affected by
MOL. However, retinoic acid levels were decreased in a statistically significant manner
at the 12 and 48 h time points. In contrast to modest effects on retinoic acid
levels, MOL markedly decreased testis levels of testosterone. Overall, the data suggest
that NSE inhibition is not directly related to the decrease in testis testosterone
levels seen after MOL. Moreover, MOL decreases testis levels of retinoic acid but
the magnitude of this effect is much less than the effect of MOL on testosterone.
2089 CHARACTERIZATION OF CHLORPYRIFOS TOXICITY
ON THE PANCREATIC BETA CELL LINE RINM5F.
Z. Yan and D. R. Cool. Pharmacology/Toxicology, Wright State University, Dayton,
OH. Sponsor: C. Sulentic.
Chlorpyrifos (CPF) is a well-known organophosphate (OP) insecticide that inhibits
acetylcholinesterase (AChE). Organophosphates have been shown to induce hyperglycemia
in both humans and animals that cannot be explained by AChE inhibition
alone. Pancreatic β-cells are responsible for secreting insulin and playing a fundamental
role in glucose homeostasis. However, no studies have investigated the
direct effect of CPF on pancreatic β-cell viability. The aim of this research was to
investigate CPF toxicity on the insulin secreting β-cell line RINm5f (RIN). We determined
that cytotoxic concentrations of CPF between 50 μM and 200 μM induced
a dose-dependent increase in RIN cell apoptosis using ELISA apoptotic assay
and caspase 3/7 activation assay (p