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Effect of nifedipine' verapamil' diltiazem and trifluoperazine on
Acetaminophen toxicity in mice.
Dimova S; Koleva M; Rangelova D; Stoythchev T
Department of Drug Toxicology' Bulgarian Academy of Sciences' Sofia'
Arch Toxicol, 70(2):112-8 1995
The hepatotoxicity of Acetaminophen overdose depends on the metabolic
activation to a toxic reactive metabolite by the hepatic mixed function
oxidases. There is evidence that an increase in cytosolic Ca2+ is
involved in Acetaminophen hepatotoxicity. The effects of the
Ca2+-antagonists nifedipine (NF)' verapamil (V)' diltiazem (DL) and of
the calmodulin antagonist trifluoperazine (TFP) on the activity of some
drug-metabolizing enzyme systems' lipid peroxidation and acute
Acetaminophen toxicity were studied in male albino mice. No changes in
the drug-metabolizing enzyme activities studied and in the cytochrome
P-450 and b5 contents were observed 1 h after oral administration of V
(20 mg/kg). DL (70 mg/kg) and TFP (3 mg/kg). NF (50 mg/kg) increased
cytochrome P-450 content' NADPH-cytochrome c reductase and
ethylmorphine-N-demethylase activities. DL and TFP significantly
decreased lipid peroxidation. NF' V' DL and TFP administered 1 h before
Acetaminophen (700 mg/kg orally) increased the mean survival time of
animals. A large increase of serum aspartate aminotransferase(AST)' and
liver weight and depletion of liver reduced glutathione (GSH) occurred
in animals receiving toxic Acetaminophen dose. NF' V and DL prevented
and TFP decreased the Acetaminophen-induced hepatic damage measured
both by plasma AST and by liver weight. NF' V' DL and TFP changed
neither the hepatic GSH level nor the GSH depletion provoked by the
toxic dose of Acetaminophen. This suggests that V' DL and TFP do not
influence the amount of the Acetaminophen toxic metabolite formed in
the liver. The possible mechanism of the protective effect of NF' V' DL
and TFP on the Acetaminophen-induced toxicity is discussed.

Phase II enzymes and bioactivation.
Hinson JA; Forkert PG
Department of Pharmacology and Toxicology' Division of Toxicology'
University of Arkansas for Medical Sciences' Little Rock' AR 72205'
Can J Physiol Pharmacol, 73(10):1407-13 1995 Oct
A colloquium entitled Phase II enzymes and bioactivation was held
during the 10th International Symposium on Microsomes and Drug
Oxidations in Toronto' Ont.' on July 20' 1994. This colloquium was a
tribute in recognition of the contributions by Dr. James R. Gillette in
advancing our understanding of drug metabolism and chemical toxicity. A
maJor focus of the colloquium was formation of conJugates such as those
with glutathione (GSH) that may not lead to detoxification but to
bioactivation. The GSH conJugates may be further metabolized to
reactive species that cause toxicity. The nephrotoxicity of
hydroquinone and bromobenzene is mediated via quinone - glutathione
conJugates' and is manifested in cellular changes' including induction
of the gadd-153 and hsp-70 mRNA. The formation of GSH conJugates is
also involved in the bioactivation of the vicinal dihalopropane
1'2-dibromo-3-chloropropane; cytotoxic lesions are observed in the
kidney and testes The evidence indicates that conJugation is mediated
by the GSH S-transferases. The symposium also covered aspects of the
importance of conJugation in the pharmacokinetics of certain drugs.
ConJugation reactions including sulfation are markedly influenced by
the manner in which the liver processes the drug. Characteristics such
as erythrocyte binding' as in the case of acetaminophen' become
limiting factors in the conJugation reactions. ConJugation reactions
can lead to a different outcome' such as acquired drug resistance.
ConJugation of metallothioneins with the alkylating mustard drugs
melphalan and chlorambucil can lead to the formation of protein
adducts. ConJugation of reactive intermediates with these small
molecular weight proteins may be considered as a phase II reaction and
a mechanism of detoxification. A different pathway for the metabolism
of xenobiotics is catalyzed by the carboxylesterases' a family of
enzymes that is involved in hydrolysis of chemical compounds' generally
leading to detoxification. Three rat esterases have been purified'
cloned' and characterized. Two forms' hydrolase A and hydrolase B' are
present in liver microsomes in a number of species' including the
human. These are also detected in extrahepatic tissues. A third
esterase' hydrolase S' is found in rat liver microsomes and rat serum'
and may be a serum carboxylesterase secreted from the liver. A better
knowledge of esterases will advance our understanding of
pharmacokinetics and mechanisms of the effects of chemicals such as
phenacetin and acetaminophen' two drugs that Dr. Gillette has worked
with extensively. The data presented herein reflect the new and
innovative approaches that have been adopted to investigate various
aspects of chemical toxicity and drug metabolism. These data also
indicate that significant insights are likely to come from integrated
approaches utilizing established toxicological techniques together with
those from other disciplines' including molecular biology and
analytical chemistry.

Cytotoxicity of Acetaminophen in human cytochrome P4502E1-transfected
HepG2 cells.
Dai Y; Cederbaum AI
Department of Biochemistry' Mount Sinai School of Medicine' City
University of New York' USA.
J Pharmacol Exp Ther, 273(3):1497-505 1995 Jun
Acetaminophen (APAP) when administered in excess can cause severe
hepatic necrosis in vivo. To study the mechanism of APAP toxicity and
the role of cytochrome P450' a previously established human hepatoma
HepG2 subline' MVh2E1-9' that constitutively expresses human CYP2E1 was
used as a model. At high concentrations (above 5 mM) and when
intracellular reduced glutathione (GSH) was depleted' APAP caused
severe cytotoxicity in MVh2E1-9' but not in MV-5 cells which lack
CYP2E1. The APAP cytotoxicity was dependent on the concentration of
APAP and time of exposure' and could be blocked by 4-methylpyrazole'
ethanol' diallyl sulfide' N-acetylcysteine and
N-t-butyl-alpha-phenylnitrone' but not by propylgallate' an inhibitor
of lipid peroxidation. Significantly more 14C-labeled APAP protein
adduct was detected in MVh2E1-9 cells than MV-5 cells' especially after
depletion of GSH. The formation of the APAP adducts could be inhibited
by the same agents which prevent APAP cytotoxicity. At a lower
concentration (1-2 mM)' APAP inhibited proliferation in both MVh2E1-9
and the control MV-5 cells to similar extents. This antiproliferative
action of APAP did not require depletion of GSH as did the cytotoxic
action of APAP. These data suggest that APAP has a dual toxic effect on
MVh2E1-9 cells: a P450-independent antiproliferative effect and the
CYP2E1-dependent cytotoxic effect. These results demonstrate the
ability of human CYP2E1 to activate APAP to reactive metabolites which
form covalent protein adducts and cause toxicity to a hepatoma cell

Sex- and age-dependent Acetaminophen hepato- and nephrotoxicity in
Sprague-Dawley rats: role of tissue accumulation' nonprotein sulfhydryl
depletion' and covalent binding.
Tarloff JB; Khairallah EA; Cohen SD; Goldstein RS
Department of Pharmacology and Toxicology' Philadelphia College of
Pharmacy and Science' Pennsylvania 19104-4495' USA.
Fundam Appl Toxicol, 30(1):13-22 1996 Mar
Acetaminophen (APAP) produces sex-dependent nephrotoxicity and
hepatotoxicity in young adult Sprague-Dawley (SD) rats and
age-dependent toxicity in male rats. There is no information regarding
the susceptibility of aging female SD rats to APAP toxicity. Therefore'
the present studies were designed to determine if sex-dependent
differences in APAP toxicity persist in aging rats and to elucidate
factors contributing to sex- and age-dependent APAP hepatotoxicity and
nephrotoxicity. Young adult (3 months old) and aging (18 months old)
male and female rats were killed from 2 through 24 hr after receiving
APAP (0-1250 mg/kg' ip) containing [ring-14C APAP. Trunk blood was
collected for determination of blood urea nitrogen (BUN) concentration'
serum alanine aminotransferase (ALT) activity' and plasma APAP
concentration; urine was collected for determination of glucose and
protein excretion; and liver and kidneys were removed for determination
of tissue glutathione (GSH) concentration' APAP concentration' and
covalent binding. APAP at 1250 mg/kg induced nephrotoxicity (as
indicated by elevations in BUN concentration) in 3-month-old females
but not males' whereas APAP induced hepatotoxicity (as indicated by
elevations in serum ALT activity) in 3-month-old males but not females.
Sex differences in APAP toxicity were no longer apparent in
18-month-old rats. APAP at 750 mg/kg ip produced liver and kidney
damage in 18-month-old but not 3-month-old male and female rats. No
consistent sex- or age-dependent differences in serum' hepatic' and
renal APAP concentrations were observed that would account for
differences in APAP toxicity. No sex- or age-dependent differences in
tissue GSH depletion or covalent binding of radiolabel from APAP in
livers or kidneys were observed following APAP administration.
Utilizing an affinity-purified polyclonal antibody raised against APAP'
arylated proteins with electrophoretic mobility similar to those
observed in mice were prominent in rat livers following APAP
administration to 3- and 18-month-old rats of both sexes. In contrast'
no arylated proteins were detected in any rat kidneys following APAP
administration. Absence of immunochemically detectable proteins in rat
kidney following APAP administration is in direct contrast to
observations in mice and supports the hypothesis that mechanisms of
APAP hepatotoxicity and nephrotoxicity in rats and mice are distinctly
different. In conclusion' sex differences in APAP toxicity are observed
only in young adult (3-month-old) rats and sex differences are
organ-specific with males more susceptible to hepatotoxicity and
females more susceptible to nephrotoxicity. Aging rats are more
susceptible to APAP-induced damage to both the liver and the kidney
than are 3-month-old rats but sex differences are no longer apparent in
18-month-old rats. The mechanisms contributing to sex- and
age-dependent differences in APAP toxicity cannot be attributed to
differences in tissue APAP concentrations' GSH depletion' or covalent

In vivo effects of Acetaminophen on rat RBC and role of vitamin E.
Suhail M; Ahmad I
Department of Biochemistry' Faculty of Science' University of
Allahabad' India.
Indian J Exp Biol, 33(4):269-71 1995 Apr
Non-therapeutic toxic dose (250 mg/kg) of Acetaminophen (paracetamol)'
in vivo to albino rats significantly decreased red cell reduced
glutathione (GSH) content and activity of (Na+' K+)-ATPase enzyme'
whereas osmotic fragility (O.F.) was increased. However' no change was
observed in the activity of glutathione reductase (GR) after
Acetaminophen treatment' while Acetaminophen plus vitamin E treated
rats showed significant increase in GR activity. Supplementation of
vitamin E to the drug treated rats effectively brought the GSH content'
(Na+' K+)-ATPase activity and O.F. back to almost normal. The results
suggest that Acetaminophen toxic dose treatment induces metabolic and
membranal alterations making red cells prone to hemolysis' while
vitamin E which is an antioxidant shows its ameliorating role to these

Gender-related differences in susceptibility to Acetaminophen-induced
protein arylation and nephrotoxicity in the CD-1 mouse.
Hoivik DJ; Manautou JE; Tveit A; Hart SG; Khairallah EA; Cohen SD
Department of Pharmaceutical Sciences' University of Connecticut'
Storrs 06269-2092.
Toxicol Appl Pharmacol, 130(2):257-71 1995 Feb
Acetaminophen (APAP) is a commonly used analgesic and antipyretic agent
which' in high doses' causes liver and kidney necrosis in man and
animals. Damage in both target organs is greatly dependent upon
biotransformation. However' in the CD1 mouse only males exhibit
cytochrome P450-dependent nephrotoxicity and selective protein covalent
binding. The lack of renal toxicity in female mice may reflect the
androgen dependence of renal CYP2E1. To study this' female mice were
pretreated with testosterone propionate and then challenged 6 days
later with APAP. Groups of control males and females were similarly
challenged with APAP for comparison. All groups exhibited
hepatotoxicity after APAP with similar glutathione (GSH) depletion'
covalent binding' centrilobular necrosis' and elevation of plasma
sorbitol dehydrogenase activity. By contrast' APAP-induced
nephrotoxicity occurred only in males and in the females pretreated
with testosterone. No nephrotoxicity was evident in APAP-challenged
control females. The selective pattern of hepatic and renal protein
arylation previously reported for male mice was similarly observed in
testosterone-pretreated female mice. Western blot analysis of
microsomes showed that testosterone increased renal CYP2E1 levels
without altering hepatic CYP2E1. Testosterone pretreatment' in vivo'
also resulted in increased activation of APAP in vitro in kidney
microsomes with no effect on the in vitro activation of APAP in liver
microsomes. These data suggest that APAP-mediated GSH depletion'
covalent binding' and toxicity in the kidneys of
testosterone-pretreated females results from increased APAP activation
by the testosterone-induced renal CYP2E1. This further suggests that
renal' rather than hepatic' biotransformation of APAP to a toxic
electrophile is central to APAP-induced nephrotoxicity in the mouse.

Anti-hepatitis B virus activity of N-acetyl-L-cysteine (NAC): new
aspects of a well-established drug.
Weiss L; Hildt E; Hofschneider PH
Max-Planck-Institut f ur Biochemie' Martinsried' Germany.
Antiviral Res, 32(1):43-53 1996 Aug
N-acetyl-L-cysteine (NAC) is commonly administered as an antidote
against Acetaminophen intoxication and is the preferred agent in the
treatment of pulmonary diseases. It is furthermore commonly considered
that it restrains human immunodeficiency virus (HIV) replication by
scavenging reactive oxygen intermediates (ROI) and thus suppressing
activation of nuclear factor kappa B (NF kappa B). We show here that
NAC is in addition able to inhibit hepatitis B virus (HBV) replication'
but by a mechanism independent of the intracellular level of reactive
oxygen intermediates. Treatment of HBV-producing cell lines with NAC
resulted in an at least 50-fold reduction of viral DNA in the tissue
culture supernatant within 48 h. This decrease of viral DNA and thus of
virions in the tissue culture supernatant is caused by a disturbance of
the virus assembly' rather than by a reduction of viral transcripts.
Our data strongly suggest a potential use of this well-established'
non-toxic drug for the treatment of HBV infection. Since NAC' in
contrast to interferon' exerts its anti-HBV activity at a
posttranscriptional level' a combination of NAC with the established
interferon therapy could also be considered.

Molybdate depletes hepatic 3-phosphoadenosine 5-phosphosulfate and
impairs the sulfation of Acetaminophen in rats.
Oguro T; Gregus Z; Madhu C; Liu L; Klaassen CD
Department of Pharmacology' Toxicology and Therapeutics' University of
Kansas Medical Center' Kansas City.
J Pharmacol Exp Ther, 270(3):1145-51 1994 Sep
Molybdate (15 mmol/kg p.o.) decreased serum sulfate concentrations of
rats 70% within 6 hr after administration. Parallel to this depletion'
there was a dramatic decrease in hepatic sulfate and 3-phosphoadenosine
5-phosphosulfate (PAPS) concentrations (about 40 and 65%'
respectively). However' renal PAPS concentrations did not change
significantly. Molybdate reduced serum' hepatic and renal sulfate as
well as hepatic PAPS concentration in a dose-dependent manner up to the
dose of 10 mmol/kg. However' renal PAPS did not change. The results
indicate that molybdate reduced not only sulfate concentrations in
serum and tissue' but also PAPS concentrations in liver. The effect of
molybdate on the pharmacokinetics of Acetaminophen (AA' 150 mg/kg i.v.)
was also investigated in order to determine whether molybdate-induced
depletion of PAPS might be a useful tool for examining the importance
of sulfation in the detoxication and toxication of xenobiotics.
AA-sulfate concentration in blood decreased 40 and 80% after
administration of molybdate at doses of 2.5 and 15 mmol/kg'
respectively. Molybdate also decreased the excretion of AA-sulfate into
bile and urine by about 60 and 80%' respectively. However' molybdate
did not alter the excretion of AA-glucuronide and
AA-glutathione/cysteine. The excretion of the parent AA increased
2-fold after molybdate administration (15 mmol/kg). In conclusion'
molybdate effectively lowers inorganic sulfate in serum and tissues'
and PAPS in the liver. Reduction of hepatic PAPS markedly decreases the
sulfation of AA' suggesting that molybdate treatment could be used to
study the importance of sulfation in pharmacology and toxicology.

Cysteamine in combination with N-acetylcysteine prevents
Acetaminophen-induced hepatotoxicity.
Peterson TC; Brown IR
Department of Medicine' Dalhousie University' Halifax' N.S.' Canada.
Can J Physiol Pharmacol, 70(1):20-8 1992 Jan
N-Acetylcysteine (NAC) is protective against Acetaminophen-induced
hepatotoxicity primarily by providing precursor for the glutathione
synthetase pathway' while cysteamine has been demonstrated to alter the
cytochrome P-450 dependent formation of toxic Acetaminophen metabolite.
Mice administered Acetaminophen (500 mg/kg) had elevations of serum
alanine aminotransferase (ALT) to 273.0 +/- 37.5 and 555.8 +/- 193.4
U/mL at 12 and 24 h' respectively' after inJection. Administration of
cysteamine (100 mg/kg) or NAC (500 mg/kg) significantly reduced serum
ALT activity (p less than 0.001). Reducing the dose of NAC or
cysteamine by 50% greatly reduced their hepatoprotective effect while
the co-administration of the reduced doses of NAC (250 mg/kg) and
cysteamine (50 mg/kg) following Acetaminophen overdose prevented
elevation of serum ALT activity (39.2 +/- 1.17 and 32.5 +/- 5.63 U/mL
at 12 and 24 h post-inJection' p less than 0.001) and preserved normal
mouse hepatic histology. Neither NAC (500 mg/kg)' cysteamine (100
mg/kg)' or the lower doses in combination of both agents were found to
alter the half-life or peak levels of Acetaminophen. Liver microsomal
aryl hydrocarbon hydroxylase activity measured 24 h after drug
administration was not significantly different between treatment groups
and controls receiving only saline. These results indicate a possible
role for the concomitant use of NAC and cysteamine in the prevention of
hepatic necrosis following toxic doses of Acetaminophen. Neither
decrease in plasma Acetaminophen levels nor depression of cytochrome
P-450 enzyme activity appears to be the mechanism of protection when
these doses of NAC' cysteamine' or both drugs together are administered
with a toxic dose of Acetaminophen in mice.

Clofibrate pretreatment diminishes Acetaminophen`s selective covalent
binding and hepatotoxicity.
Manautou JE; Hoivik DJ; Tveit A; Hart SG; Khairallah EA; Cohen SD
Department of Pharmaceutical Sciences' University of Connecticut'
Storrs 06269-2092.
Toxicol Appl Pharmacol, 129(2):252-63 1994 Dec
Peroxisome proliferators have been shown to diminish Acetaminophen
(APAP) hepatotoxicity (Biochem. Pharmacol. 43' 1395' 1992). To
investigate the mechanistic basis for this protection CD-1 male mice
were given corn oil or 500 mg clofibrate (CFB)/kg' ip' daily for 10
days. They were then fasted overnight and either killed without
challenge or at 4 or 12 hr after challenge with 800 mg APAP/kg (in 50%
propylene glycol). At 12 hr' hepatotoxicity was evidenced by elevated
plasma sorbitol dehydrogenase and histopathology in corn oil but not in
CFB-pretreated mice. At 4 hr after APAP treatment' hepatic glutathione
(GSH) depletion and selective arylation of the maJor APAP target
proteins were both greatly diminished by CFB pretreatment. Western blot
analysis with the anti-58 antibody of liver cytosol from unchallenged
mice showed no apparent changes in the levels of the 58-kDa maJor APAP
target protein with CFB treatment. These findings suggest that
protection could be the result of diminished net availability of
generated electrophile. In vitro' measurements indicated that the
specific activity in microsomes for APAP oxidation by cytochrome P450
was not changed by CFB treatment; whereas GSH S-transferase activity in
cytosol was decreased by 25%. Pretreatment with CFB also produced a
significant elevation in hepatic GSH. These studies indicate that
protection by CFB might result from increased availability of hepatic
GSH which could trap APAP electrophile nonenzymatically' thereby
decreasing covalent binding and preventing toxicity.


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