The Toxicologist - Society of Toxicology

ODD in both WT (maximum 177% of control) and MT-null cells (maximum
276% of control) but ODD levels were markedly lower in WT cells, in a fashion
similar to that for Cd treatment. Thus, MT protects against Cd-induced and oxidant-induced
ODD possibly by multiple mechanisms, including sequestration of
the metal ion and of oxidant radicals. MT-null cells may adapt to Cd by turning on
the oxidant response system.
266 SEXUAL DIMORPHISM OF CADMIUM-INDUCED
TOXICITY IN RATS: INVOLVEMENT OF
PROGESTERONE.
H. Shimada1 , T. Hashiguchi1 , A. Yasutake2 , M. P. Waalkes3 and Y. Imamura4 .
1Kumamoto University, Kumamoto, Japan, 2National Institute for Minamata
Disease, Kumamoto, Japan, 3NIEHS, Research Triangle Park, NC and 4Nihon Pharmaceutical University, Saitama, Japan.
The toxic effect of cadmium (Cd) varies with sex in experimental animals. Our recent
studies have demonstrated that the pretreatment with female sex hormone
progesterone markedly enhances the susceptibility to Cd toxicity in Fischer 344
(F344) rats, suggesting a role for progesterone in the sexual dimorphism of Cd toxicity.
In the present study, we further attempted to elucidate the mechanism for sex
difference of Cd-induced toxicity in F344 rats. A single administration of Cd (5.0
mg/kg, sc) was lethal in 0/10 (0 %) female compared to 4/10 (40 %) male rats.
Using lower dose of Cd (3.0 mg/kg), circulating alanine aminotransferase (ALT) activity,
indicative of hepatotoxicity, was much higher in the Cd treated females than
in the males. However, no difference in the hepatic Cd accumulation, metallothionein
(MT) or glutathione (GSH) levels were observed between male and female
rats. When Cd (5.0 mg/kg) was administered to young rats at 5 weeks of age, sexrelated
difference was hardly recognized for the Cd-induced lethality. Furthermore,
although ovariectomy decreased the Cd-induced lethal toxicity, the decreased effect
was restored by the pretreatment with progesterone (40 mg/kg, sc, 7 consecutive
days) to ovariectomized rats. These results provide further evidence that progesterone
is involved in the sexual dimorphism of Cd toxicity in rats.
267 CADMIUM ACCUMULATES WITHIN PANCREATIC
ISLETS RESULTING IN IMPAIRED GLUCOSE
STIMULATED INSULIN SECRETION IN AN ANIMAL
MODEL OF SUBCHRONIC EXPOSURE.
J. Edwards, R. Fitzgerald and A. Olsen. Department of Pharmacology, Midwestern
University, Downers Grove, IL.
There is increasing interest to understand how environmental contaminants can
contribute to the onset of diabetes. Recent epidemiological studies show that exposure
to the metal cadmium (Cd), is associated with diabetes and reduced serum insulin.
The goal of this study was to examine the effects of Cd on insulin secretion
using a well established animal model of sub chronic Cd exposure. Male Sprague
Dawley rats were injected (s.c.) daily with either saline (control) or Cd (0.6 mg
Cd/kg/day, 5 days per week). After weeks 9 and 12 of treatment tissue samples were
analyzed for Cd content, serum insulin levels, and pancreatic islets were isolated.
Previous experimental studies report Cd accumulation in the whole pancreas (islets
+ acinar cells) to be about 20% of that found in the renal cortex. In contrast, the
current study shows that islet cells alone contain levels of Cd similar to that found
in the renal cortex. Specifically, the islets contained 69% of the total amount of Cd
in renal cortex at week 9 and 81% at week 12. This accumulation of Cd within the
islets had deleterious effects on insulin release. The mean fasting serum insulin
value was 33% lower in the Cd treatment group at week 9. In another experiment,
islets were isolated and incubated in various glucose solutions. The amount of insulin
release from islets isolated from control animals was approximately one fold
higher when incubated in high (3.0mg/ml) glucose solutions as compared to low
(0.5mg/ml) glucose, indicating the islets were normal and healthy. Conversely,
islets isolated from Cd treated animals resulted in a 16% to 26% decrease in insulin
release when islets were incubated in high glucose solutions as compared to low.
This study indicates that Cd accumulates to a greater degree in pancreatic islets
than previously thought. Furthermore, this Cd accumulation may result in islet
dysfunction as evidenced by lower fasting serum insulin levels and blunted physiological
responses such as glucose stimulated insulin release.
268 CADMIUM ALTERS MICRORNA EXPRESSION IN
HUMAN A549 ALVEOLAR EPITHELIAL CELLS.
M. J. Fay, P. Rodriguez, L. A. Alt and W. C. Prozialeck. Pharmacology,
Midwestern University, Downers Grove, IL.
Acute respiratory exposure to Cd results in pulmonary edema and hemorrhaging,
which is later followed by inflammation, scarring and fibrosis. Long-term respiratory
exposure has been associated with development of chronic obstructive pul-
monary disease, and possibly, some forms of lung cancer. While the general toxic effects
of Cd in the lung have been well-characterized, the specific molecular mechanisms
underlying these effects have yet to be fully elucidated. MicroRNAs are small
noncoding RNAs that decrease gene expression at the post-transcriptional level.
Alterations in the microRNA expression profile have been implicated in both cellular/tissue
toxicity and cancer development. In this study we investigated the effects
of Cd exposure on microRNA expression in the human alveolar epithelial A549 cell
line. This cell line, which exhibits many characteristics of type-II pneumocytes, has
been extensively used as an in vitro model for Cd-induced pulmonary injury. Subconfluent
(70-80%) cells were exposed to CdCl2 (10 microM) for 24 hrs in serumfree
medium. Cytotoxicity was evaluated using trypan blue and hemacytometer cell
counting, and WST-1 assays. MicroRNA array analysis showed that acute exposure
to a relatively non-cytotoxic concentration of Cd caused a statistically significant (ttest,
P< 0.05) alteration in the expression of 7 human MicroRNAs (miR-1308,
miR-3127, miR-23b, miR-23a, miR-92b, miR-222, and miR-1915). Northern
blot analysis for miR-1308 confirmed the array results and indicated increased expression
of miR-1308 with Cd-treatment. These finding suggest that alterations in
the microRNA expression profile may play a role in the pathophysiology of Cd-induced
lung injury.
Supported in part by Midwestern University, NIH Grant RO1 ES006478 to
W.C.P., and NIH Grant R15 CA122003 to M.J.F.
269 SUPPRESSION OF IRON TRANSPORT SYSTEM IN
DUODENUM BY CADMIUM.
M. Satoh, H. Banno and Y. Fujiwara. Laboratory of Pharmaceutical Health
Sciences, School of Pharmacy, Aichi Gakuin University, Nagoya, Japan.
It is known that cadmium (Cd) causes iron deficiency anemia, but the mechanism
is not clear. In this study, to elucidate the mechanism of Cd-induced iron deficiency
anemia, we examined the effect of Cd on the expression of iron transport-related
genes in the duodenum of mice. Eight-week-old female C57BL/6J mice were given
a single oral administration of Cd at a dose of 50 mg/kg and were sacrificed at 3 and
24 h after the Cd administration. The mRNA levels of duodenal cytochrome b
(Dcytb), divalent metal transporter 1 (DMT1), ferroportin 1 (FPN1) and hephaestin
(HEP), which are iron transport-related genes, in the duodenum were determined
using real-time RT-PCR analysis. Serum iron concentration was measured
using Fe C-test wako kit (Wako Pure Chemicals, Osaka, Japan). The mRNA
levels of Dcytb, DMT1, FPN1 and HEP in the duodenum were remarkably decreased
at 3 h after the Cd administration. On the other hand, serum iron concentration
was significantly reduced to 24 h after the Cd administration. The present
study clearly found that Cd inhibits the expression of iron transport-related genes
in the duodenum of mice. These results suggest that Cd may inhibit iron absorption
through suppression of iron transport system in the duodenum.
270 COMBINED EFFECT OF ABDOMINAL SURGERY AND
CHRONIC CADMIUM ADMINISTRATION ON
HEPATIC RIBONUCLEASE ACTIVITY,
METALLOTHIONEIN, AND ALPHA-2-
MACROGLOBULIN CONCENTRATION.
E. Brambila, M. R. Vieyra-Lobato, B. A. Leon-Chavez and P. Aguilar-Alonso.
Clinical Chemistry, University of Puebla, Puebla, Puebla, Mexico.
Ribonucleases (RNases) are a group of enzymes that hydrolyze different classes of
RNA and its activity regulates indirectly intracellular protein synthesis. Earlier we
described that hepatic acid RNase activity is decreased after an experimental surgery,
which can be an important event to favor acute phase protein synthesis, including
metallothionein (MT). In addition, several studies in vitro have shown that
cadmium (Cd) inhibit RNase activity by an interaction of Cd with amino acids
near the active site. In this work we studied the combined effect of inflammation
and chronic cadmium administration in rats on hepatic RNase activity, MT and
alpha-2-macroglobulin synthesis. Rats (groups of 5) were administered i.p. with
0.25 and 0.5 mg of Cd/Kg by 15, 30, 60 and 90 days, and then each rat received
and abdominal 3 cm incision. Controls were administered with sterile water or 0.5
mg of Cd/Kg, but no surgical treatment. Hepatic RNase activity, Cd, MT and
alpha-2-macroglobulin were measured. Results obtained shown a time-concentration
liver accumulation of Cd, same pattern was observed with MT liver concentration,
however, liver RNase activity decreased significantly in relation with the accumulated
Cd. These results suggest that combination of inflammation and chronic
exposure of Cd inhibit RNase activity to increase protein synthesis, which is confirmed
with the observed increase of alpha-2-macroglobulin in our animal model.
SOT 2011 ANNUAL MEETING 57