Prednisolone stimulates hepatic glutathione synthesis in mice.
Protection by prednisolone against acetaminophen hepatotoxicity
Speck RF; Schranz C; Lauterburg BH
Department of Clinical Pharmacology' University of Bern' Switzerland.
J Hepatol, 18(1):62-7 1993 Apr
Mediators of inflammation modulate the extent of hepatocellular
necrosis following the administration of hepatotoxins. Since
corticosteroids interfere with the generation of some of these
mediators they might thus protect against the hepatotoxicity
such as acetaminophen. To test this hypothesis mice were pretreated
with two doses of prednisolone (10 and 20 mg/kg i.p.' 17 and
respectively) prior to a hepatotoxic dose of 375 mg/kg acetaminophen
and the metabolism and toxicity of acetaminophen were assessed.
Twenty-four hours after acetaminophen the activity of ALT in
(737 vs. 6775 U/l) and the extent of hepatocellular necrosis
(4 vs. 45%
necrotic hepatocytes) were significantly lower in
prednisolone-pretreated mice. Prednisolone pretreatment resulted
decreased covalent binding of the toxic metabolite in vivo and
increased urinary excretion of glutathione-derived conJugates
acetaminophen' indicating an enhanced detoxification of the reactive
metabolite by glutathione. Nevertheless' hepatic glutathione
depleted by acetaminophen in the prednisolone group' indicating
increased capacity to resynthesize glutathione. This was confirmed
experiments with diethyl maleate which depletes hepatic glutathione
without causing cell inJury. Following the administration of
maleate to fed and fasted mice' hepatic glutathione was depleted
same extent after 45 min' but was significantly higher after
2.5 h in
prednisolone-pretreated mice. The present results indicate that
prednisolone increases the capacity to replete depleted hepatic
glutathione stores in mice.
Efficacy of oral versus intravenous N-acetylcysteine in acetaminophen
overdose: results of an open-label, clinical trial [see comments
Perry HE; Shannon MW
Division of Emergency Medicine, Children's Hospital, Boston,
J Pediatr, 132(1):149-52 1998 Jan
We compared the clinical course of pediatric patients (n = 25)
acetaminophen poisoning treated with an investigational intravenous
preparation of N-acetylcysteine (IV-NAC) with that of historical
control subjects (n = 29) treated with conventional oral NAC
therapy. Patients received IV-NAC for 52 hours; historical control
subjects received O-NAC (72 hours). There were no significant
intergroup differences between treatment groups in age (15.5
years), gender (88% vs 90% female) or distribution of risk categories
(probable risk, 12 vs 15; high risk; 13 vs 14). The peak prothrombin
time was significantly higher in the IV-NAC group (14.2 vs 13.6
seconds; p = 0.048). Mean treatment delay was significantly longer
the IV-NAC group (14.4 vs 10.4 hours; p = 0.001). Hepatoxicity
noted in two (8.0%) patients in the IV-NAC treatment group and
(6.9%) patients in the O-NAC group. All patients recovered. Our
indicate that 52 hours of intravenous NAC is as effective as
of oral NAC.
Selective protein arylation and acetaminophen-induced hepatotoxicity.
Cohen SD; Khairallah EA
Department of Pharmaceutical Sciences' University of Connecticut'
Storrs 06269' USA.
Drug Metab Rev, 29(1-2):59-77 1997 Feb-May
More than 20 years have passed since the early reports of acute
hepatotoxicity with APAP overdose. During that period investigative
research to discover the "mechanism" underlying the
toxicity has been
conducted in many species and strains of intact animals as well
as in a
variety of in vitro and culture systems. Such work has clarified
primary role of biotransformation and the protective role of
Understanding the former provides explanations for the toxic
interactions which may occur with alcohol or other xenobiotics'
understanding of the latter led to the development of antidotes
treatment of acute poisoning. acetaminophen (APAP)-induced
hepatotoxicity: roles for protein arylation. Initiating events
toxicity require biotransformation of APAP to NAPQI followed
arylation of several important proteins with subsequent alteration
protein structure and function. The immediate consequence of
alterations is detectable in several organelles and these may
multiple initiating events which are depicted as acting in concert
cause cell inJury (large arrowheads). Arylation of cytosolic
with subsequent translocation to the nucleus is depicted as a
signaling mechanism for determining outcome at the cell or organ
(within dotted boundary). For simplicity NAPQI`s potentials for
oxidizing protein sulfhydryls and direct binding to DNA have
omitted. Significant light has also been shed on the biochemical
cellular events which accompany APAP-induced hepatotoxicity.
such studies have not identified a unique mechanism of toxicity
universally accepted. The recent identification of several protein
targets which become arylated during toxicity--along with the
that arylation of some of those target proteins results in loss
protein function--demonstrates that covalent binding does' indeed'
biological consequences and is not merely an indicator of the
presence of reactive electrophiles. These observations further
that multiple independent insults to the cell may be involved
toxicity. it is now apparent that the concept of a multistage
that involves both initiation and progression events is appropriate
APAP toxicity' and it is unlikely that a unique initiating event
ever be identified. In light of recent findings it is more likely
a number of such cellular events occur very early after toxic
overdosage' and that they collectively set in motion and perpetuate
biochemical' cellular' and molecular processes which will determine
outcome. The importance of 58-ABP arylation with early' apparently
selective' translocation to the nucleus remains to be elucidated.
date there is nothing to suggest that this represents an initiating
event in toxicity. rather it is plausible that the translocation
play a role in signaling electrophile presence and in calling
cellular defense against electrophile insult. This is reflected
hypothetical model presented in Fig. 3. Critical experimental
of this model will advance our understanding of the cellular
molecular responses to toxic electrophile insult.
Zonation of acetaminophen metabolism and cytochrome P450 2E1-mediated
toxicity studied in isolated periportal and perivenous hepatocytes.
Anundi I; L ahteenm aki T; Rundgren M; Moldeus P; Lindros KO
Biomedical Research Center' ALKO Ltd.' Helsinki' Finland.
Biochem Pharmacol, 45(6):1251-9 1993 Mar 24
To study the mechanism of centrilobular damage developing in
centrilobular region after high doses of acetaminophen (APAP)'
metabolism and toxicity were compared in periportal and perivenous
hepatocytes isolated by digitonin/collagenase perfusion. Contrary
earlier reports' based on perfusions' no evidence for a periportal
dominance of APAP sulfation could be observed. Glucuronidation'
dominant pathway of conJugation at high (5 mM) APAP concentration'
faster in perivenous cells. During primary culture' prolonged
(> or = 24 hr) to 5 mM APAP damaged perivenous cells' with
P450 2E1 level than periportal cells. When cells were isolated
ethanol-pretreated rats' to induce P450 2E1 levels specifically
perivenous region' perivenous hepatocytes exhibited enhanced
vulnerability and extensive glutathione depletion. In contrast'
corresponding periportal cells retained good viability. Isoniazid'
inhibitor of cytochrome P450 2E1' protected cells against APAP
and prevented glutathione depletion. Induction of P450 2E1 also
a 3-fold increase in the covalent binding of reactive intermediates
from [14C APAP' and this increase was mainly confined to perivenous
cells. These results indicate that in rat liver there is only
perivenous zonation of APAP conJugation and suggest that zone-specific
APAP activation' mediated by the regional expression of
ethanol-inducible cytochrome P450 2E1' is responsible for the
characteristic centrilobular liver damage elicited by APAP.
In vivo murine studies on the biochemical mechanism of acetaminophen
Wells PG; Wilson B; Winn LM; Lubek BM
Faculty of Pharmacy' University of Toronto' ON' Canada.
Can J Physiol Pharmacol, 73(8):1123-9 1995 Aug
C57BL/6 and DBA/2 mice are' respectively' susceptible and resistant
both to the induction of aryl hydrocarbon hydroxylase (cytochrome
1A1' or CYP1A1) and to the cataractogenicity of acetaminophen'
may involve its bioactivation to a toxic reactive intermediate'
catalysed by P450 and (or) prostaglandin H synthase (PHS). Following
induction of P450 using beta-naphthoflavone' the cataractogenicity
acetaminophen (400 mg/kg ip) in C57BL/6 mice was reduced by
pretreatment with the P450 inhibitors SKF 525A and metyrapone'
glutathione precursor N-acetylcysteine' the antioxidant vitamin
the free radical spin trapping agent alpha-phenyl-N-t-butylnitrone
0.05). acetaminophen (200 mg/kg) cataractogenicity was enhanced
pretreatment with the glutathione depletor diethyl maleate (DEM)
the gamma-glutamylcysteine synthetase inhibitor buthionine sulfoximine
(BSO) (p < 0.05). No significant effect on acetaminophen
cataractogenicity was observed using the PHS cyclooxygenase inhibitors
aspirin or naproxen' or the glutathione reductase inhibitor
1'3-bis(2-chloroethyl)-1-nitrosourea (BCNU). Accordingly' acetaminophen
cataractogenicity in C57BL/6 mice does not appear to be dependent
bioactivation by PHS. In DBA/2 mice treated with beta-naphthoflavone'
high dose of acetaminophen (750 mg/kg ip) was not cataractogenic'
after pretreatment with DEM' BSO' or BCNU. The resistance of
to acetaminophen cataractogenesis' despite concomitant pretreatments
with an inducer of P450 and several agents that interfere with
glutathione-dependent detoxifying pathways' suggests differences
this strain involving cytoprotective pathways subsequent to
acetaminophen bioactivation and detoxification of the cataractogenic
reactive intermediate. These results indicate that acetaminophen
cataractogenicity in C57BL/6 mice results from P450-catalysed
bioactivation of acetaminophen to a reactive intermediate' possibly
benzoquinone imine and (or) a free radical' the toxicity of which
reduced by glutathione-dependent reactions.
Tylenol Extended Relief overdose.
Cetaruk EW; Dart RC; Hurlbut KM; Horowitz RS; Shih R
Rocky Mountain Poison Center' Denver' CO' USA.
Ann Emerg Med, 30(1):104-8 1997 Jul
In this report we describe the toxicokinetics of the Tylenol
Relief (TER) preparation of acetaminophen in human overdose.
collected 41 cases of TER overdose from five regional poison
Patients who met the following criteria were studied: a single
ingestion of TER alone; confirmed time of ingestion; at least
acetaminophen determinations; and normal concentrations of liver
function enzymes. With the exception of standard decontamination
measures' treatment with N-acetylcysteine (NAC) if any acetaminophen
level was above the treatment line of the Rumack-Matthew nomogram'
additional acetaminophen determinations' no interventions were
recommended. Our study group comprised 13 patients' 12 female
male' with single overdoses of 10.4 to 65 g TER. The acetaminophen
elimination half-life was 3.1 +/- .8 hours (mean +/- SD; range'
4.0 hours; n = 12). The elimination phase for patients 2' 3'
4' 6' 8'
9' 11' 13 was delayed until 8.0 +/- 2.8 hours (range' 5 to 14
after ingestion. Patients 3' 8' and 11--who had initial acetaminophen
levels below the "possible toxicity" line of the Rumack-Matthew
nomogram--later had acetaminophen levels above this line. No
demonstrated a late or second acetaminophen peak. We conclude
elimination half-life of TER acetaminophen is similar to that
in overdose of immediate-release acetaminophen overdose. In a
of patients' drug absorption continued beyond the 2 to 4 hours
previously reported in immediate-release acetaminophen overdose.
basis of our data' the use of a single 4-hour acetaminophen
determination may lead to failure to recognize patients with
potentially toxic TER ingestion. Until more toxicokinetic data
available' a reasonable approach would be to obtain at least
additional acetaminophen determination at least 4 to 6 hours
first' if the first is obtained 4 to 8 hours after ingestion.
treatment should be initiated if either level is above the nomogram
line but not if both levels fall below the nomogram line.
acetaminophen-induced hepatotoxicity. Analysis of total covalent
binding vs. specific binding to cysteine.
Matthews AM; Roberts DW; Hinson JA; Pumford NR
Division of Toxicology' University of Arkansas for Medical Sciences'
Little Rock 72205' USA.
Drug Metab Dispos, 24(11):1192-6 1996 Nov
acetaminophen-induced hepatotoxicity is believed to be mediated
covalent binding of the reactive metabolite N-acetyl-p-benzoquinone
imine to essential proteins in liver. It has been shown that
primary reaction of this metabolite with hepatic proteins is
formation of 3-(cysteine-S-yl)-acetaminophen adducts. The importance
covalent binding to other amino acids that may be formed by reaction
N-acetyl-p-benzoquinone imine with protein is unclear. Previously'
developed immunochemical assays for the acetaminophen cysteine
by immunizing animals with the conJugate
3-(N-acetylcystein-S-yl)acetaminophen-keyhole limpet hemocyanin'
wherein the carboxyl group of the N-acetyl-cysteine moiety was
to amino groups on the protein. A very sensitive and specific
immunochemical assay was developed for acetaminophen specifically
to cysteine groups on protein [3-(cystein-S-yl)acetaminophen
adducts . Analysis of protein adducts indicated that after toxic
acetaminophen covalently bound at high levels to cysteine residues
relatively small number of hepatic proteins. In the present work'
antiacetaminophen antiserum was prepared by immunizing mice with
4-acetamidobenzoic acid coupled to keyhole limpet hemocyanin.
Competitive ELISA data indicate that the resulting antiserum
excellent recognition of acetaminophen and related arylacetamide
derivatives. Using this new antiserum' Western blot analyses
proteins from acetaminophen-intoxicated mouse livers were performed
compared with similar assays using the
anti-3-(cystein-S-yl)acetaminophen antiserum. Visual and densitometric
analyses of the Western blots indicate that the two antisera
same primary acetaminophen protein adducts; however' minor differences
in the intensity of certain bands were observed. These differences
represent either differences in antibody accessibility to
3-(cystein-S-yl)acetaminophen adducts or differences in the proportion
of acetaminophen bound to cysteine vs. binding to other amino
Acute renal failure due to acetaminophen ingestion: a case report
review of the literature.
Blakely P; McDonald BR
Division of Nephrology and Hypertension' UCSD Medical Center'
J Am Soc Nephrol, 6(1):48-53 1995 Jul
acetaminophen is the most commonly reported drug overdose in
States. Acute renal failure occurs in less than 2% of all acetaminophen
poisonings and 10% of severely poisoned patients. At the therapeutic
dosages' acetaminophen can be toxic to the kidneys in patients
glutathione depleted (chronic alcohol ingestion' starvation'
fasting) or who take drugs that stimulate the P-450 microsomal
enzymes (anticonvulsants). Acute renal failure due to acetaminophen
manifests as acute tubular necrosis (ATN). ATN can occur alone
combination with hepatic necrosis. The azotemia of acetaminophen
toxicity is typically reversible' although it may worsen over
7 to 10
days before the recovery of renal function occurs. In severe
renal failure coincides with hepatic encephalopathy and dialysis
required. Recognition of acetaminophen nephropathy requires the
following: (1) a thorough drug history' including over-the-counter
medications such as Tylenol or Nyquil; (2) knowledge of the risk
factors that lessen its margin of safety at therapeutic ingestions'
i.e.' alcoholism; and (3) consideration of acetaminophen in the
differential diagnosis of patients who present with combined
dysfunction and ATN.
The killing of cultured hepatocytes by N-acetyl-p-benzoquinone
(NAPQI) as a model of the cytotoxicity of acetaminophen.
Harman AW; Kyle ME; Serroni A; Farber JL
Department of Pathology' Thomas Jefferson University' Philadelphia'
Biochem Pharmacol, 41(8):1111-7 1991 Apr 15
The killing of isolated hepatocytes by N-acetyl-p-benzoquinone
(NAPQI)' the maJor metabolite of the oxidation of the hepatotoxin
acetaminophen' has been studied previously as a model of liver
inJury by the parent compound. Such studies assume that the toxicity
acetaminophen is mediated by NAPQI and that treatment with exogenous
NAPQI reproduces the action of the endogenously produced product.
present study tested these assumptions by comparing under identical
conditions the toxicity of acetaminophen and NAPQI. The killing
hepatocytes by acetaminophen was mediated by oxidative inJury.
depended on a cellular Source of ferric iron; was potentiated
1'3-bis(2-chloroethyl)-1-nitrosourea (BCNU)' an inhibitor of
glutathione reductase; and was sensitive to antioxidants. By
the cytotoxicity of NAPQI was not prevented by chelation of ferric
iron; was unaffected by BCNU; and was insensitive to antioxidants.
Thus' the killing of cultured hepatocytes by NAPQI occurs by
mechanism different from that of acetaminophen. The killing by
was preceded by a collapse of the mitochondrial membrane potential
a depletion of ATP. Monensin potentiated the cell killing' and
extracellular acidosis prevented it. These manipulations are
characteristic of the toxicity of mitochondrial poisons' and
without effect on the depletion of ATP and the loss of mitochondrial
energization. Thus' mitochondrial de-energization by a mechanism
unrelated to oxidative stress is a likely basis of the cell killing
NAPQI. It is concluded that treatment of cultured hepatocytes
NAPQI does not model the cytotoxicity of acetaminophen in these