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Title
Species differences in biliary excretion of methylmercury--role
of
non-protein sulfhydryls in bile.
Author
Urano T; Naganuma A; Imura N
Address
Department of Public Health, School of Pharmaceutical Sciences,
Kitasato University, Tokyo, Japan.
Source
Res Commun Chem Pathol Pharmacol, 62(2):339-51 1988 Nov
Abstract
Species differences in biliary excretion of methylmercury and
non-protein sulfhydryls (NPSHs) were studied using male rats,
mice,
rabbits, guinea pigs and hamsters. EDTA was added to all mixtures
used
throughout the experimental procedures to prevent oxidation of
NPSHs.
The rates of mercury excretion into the bile of guinea pigs and
rabbits
after the administration of methylmercury were significantly
lower than
those in rats, mice and hamsters. Total NPSH concentrations in
the bile
of guinea pigs and rabbits analyzed by HPLC were also relatively
low
compared with those in the other species. These results suggested
that
NPSH excretion plays an important role in species differences
of
methylmercury excretion into bile. The chemical form of the
methylmercury in the bile was analyzed by gel filtration with
Sephadex
G-15, and most of methylmercury in bile of all species used in
the
experiment was bound to low molecular weight substances. The
main form
of methylmercury in the bile was methylmercury-glutathione (MM-GSH)
in
mice and hamsters and methylmercury-cysteinylglycine (MM-CysGly)
in
guinea pigs. Methylmercury in the bile of mice, hamsters and
guinea
pigs was associated with the main component of NPSHs in bile
of the
respective species. In the rat bile, however, GSH accounted for
a
majority (80%) of NPSHs, but methylmercury was separated in two
peaks
on gel filtration, i.e. MM-CysGly (70%) and MM-GSH (30%). This
may be
explained by the higher affinity of CysGly to methylmercury than
that
of GSH. Our data indicate that species differences in the chemical
forms of biliary methylmercury reflect the species differences
in NPSH
components in the bile.
Title
Effect of inhibition of gamma-glutamyltranspeptidase on biliary
and
urinary excretion of glutathione-derived thiols and methylmercury.
Author
Gregus Z; Stein AF; Klaassen CD
Source
J Pharmacol Exp Ther, 242(1):27-32 1987 Jul
Abstract
Acivicin (AT-125; 6.25-200 mumol/kg i.v.) inhibited hepatic,
biliary
and renal gamma-glutamyltranspeptidase (GGT) activity up to 88,
99 and
97%, respectively, in 4-week-old rats. This inhibition of GGT
by
acivicin resulted in a 10- to 12-fold increase in the biliary
excretion
of reduced (GSH) and oxidized glutathione. Because the biliary
excretion of cysteinylglycine (Cys-Gly), Cys-Gly disulfide, cysteine
(Cys) and cystine concomitantly decreased (63-99%), the biliary
excretion rate of total glutathione-derived thiols and disulfides
did
not change. In contrast, acivicin treatment dramatically elevated
the
urinary excretion rate of glutathione-derived thiols in a
dose-dependent fashion, resulting in a 390-fold increase at the
highest
dosage. This mainly originated from enhancement of urinary excretion
of
GSH (up to 7200-fold), although the excretion of Cys and Cys-Gly
into
urine was also increased. Acivicin treatment did not affect hepatic
and
renal levels of GSH but, at high dosages, reduced the concentration
of
Cys in these organs. GSH and oxidized glutathione concentrations
in
serum were increased, whereas cystine was diminished in
acivicin-treated rats. Inhibition of GGT by acivicin (100 mumol/kg
i.v.) failed to influence the biliary excretion of methylmercury
but
increased urinary excretion 34-fold. Even though the urinary
thiol
excretion was much higher than the biliary thiol excretion in
the
acivicin-treated rats, methylmercury was preferentially excreted
into
bile rather than urine, indicating the importance of the liver
as an
excretory organ for methylmercury.(ABSTRACT TRUNCATED AT 250
WORDS)
Title
Effect of lipoic acid on biliary excretion of glutathione and
metals.
Author
Gregus Z; Stein AF; Varga F; Klaassen CD
Address
Department of Pharmacology, University Medical School of Pécs,
Hungary.
Source
Toxicol Appl Pharmacol, 114(1):88-96 1992 May
Abstract
Several metals are excreted in bile as glutathione complexes,
and their
biliary excretion is facilitated by increased hepatobiliary transport
of glutathione. The present study analyzed the effect of lipoic
acid
(LA; thioctic acid; 37.5-300 mumol/kg, iv), an endogenous disulfide
which can be reduced in vivo to a dithiol, on the hepatobiliary
disposition of glutathione-related thiols and the biliary excretion
of
metals (10 mumol/kg, iv) in rats. Administration of LA enhanced
the
biliary excretion of reduced glutathione in a dose-dependent
fashion.
Despite increasing glutathione output, LA (150 mumol/kg, iv)
did not
increase, but rather decreased, the biliary excretion of methylmercury,
cadmium, zinc, and copper, which are transported into bile in
a
glutathione-dependent manner, as indicated by a marked reduction
in
their biliary excretion after diethyl maleate-induced glutathione
depletion. In contrast, biliary excretion of inorganic mercury,
which
is minimally affected by glutathione depletion, was dramatically
enhanced (12- to 37-fold) by LA administration. Following injection
of
LA, the concentrations of endogenous disulfides in arterial blood
plasma (e.g., cystine, glutathione disulfide, cysteine-glutathione,
protein-cysteine, and protein-glutathione mixed disulfides) were
considerably diminished, while the levels of endogenous thiols
(e.g.,
glutathione and cysteine) were increased. This finding indicates
that
LA, probably after enzymatic conversion to dihydrolipoic acid,
can
reduce endogenous disulfides to thiols. It appears that LA induces
the
transport of glutathione into bile by the temporary formation
of
dihydrolipoic acid-glutathione mixed disulfide, which after being
translocated into bile is cleaved to LA and reduced glutathione.
Because the glutathione molecule thus transported into bile cannot
complex metals at the thiol group, this might be the mechanism
for the
observed failure of the LA-induced increase in biliary excretion
of
glutathione to enhance the hepatobiliary transport of metals
that are
transported into bile as glutathione complexes (i.e., methylmercury,
cadmium, zinc, and copper). The observations also raise the possibility
that endogenous dihydrolipoic acid, by forming a stable complex
with
mercuric ion, may play the role of a carrier molecule in the
hepatobiliary transport of inorganic mercury.
Title
Mechanism of urinary excretion of methylmercury in mice.
Author
Yasutake A; Hirayama K; Inoue M
Address
Biochemistry Section, National Institute for Minamata Disease,
Kumamoto, Japan.
Source
Arch Toxicol, 63(6):479-83 1989
Abstract
To elucidate the mechanisms by which methyl-mercury (MeHg) is
eliminated from organisms, male C57BL/6N mice were orally administered
with MeHg chloride (5 mg/kg) and the chemical forms of its metabolites
in plasma, urine and kidney were determined by column chromatographic
analysis. Orally administered MeHg rapidly entered the circulation,
accumulated in the kidney and other tissues, and was slowly excreted
in
the urine. Ultrafiltration and gel filtration analysis revealed
that
most of plasma MeHg was accounted for by its albumin conjugate.
Cell
fractionation analysis revealed that about 80% of renal MeHg
was
recovered from the 15,000 g supernatant fraction of the kidney
homogenate. If the kidney was homogenized in the presence of
serine-borate complex, a potent inhibitor of
gamma-glutamyltranspeptidase (gamma-GTP), about 50% of the MeHg
in the
supernatant fraction was recovered as its glutathione S-conjugate
while
the rest was bound to cytosolic protein(s). The major part of
urinary
MeHg was accounted for by its cysteine conjugate. However, urinary
excretion of its glutathione conjugate increased significantly
if
animals were pretreated with acivicin, an affinity labeling reagent
for
gamma-GTP. These and other results suggested that MeHg bound
to albumin
accumulated in the kidney predominantly via some non-filtrating
peritubular mechanism, and localized in renal cytosolic compartment
as
its glutathione- and protein-bound forms. The glutathione S-conjugate
of MeHg in the tubule cells might be transferred to the lumenal
space,
hydrolyzed to the cysteine S-conjugate, and then excreted in
urine.
These sequential events might constitute an important eliminatory
pathway for a hazardous mercurial metabolite in mice.
Title
Further study of effects of chelating agents on excretion of
inorganic
mercury in rats.
Author
Shimada H; Fukudome S; Kiyozumi M; Funakoshi T; Adachi T; Yasutake
A;
Kojima S
Address
Department of Hygienic Chemistry, Faculty of Pharmaceutical Sciences,
Kumamoto University, Japan.
Source
Toxicology, 77(1-2):157-69 1993 Jan 29
Abstract
The effects of three chelating agents, N-benzyl-D-glucamine
dithiocarbamate (BGD), 2,3-dimercaptopropanol (BAL) and D-penicillamine
(D-PEN), on the excretion of mercury in rats exposed to mercuric
chloride (HgCl2), the chemical forms of mercury compounds excreted
in
the bile and urine and the intestinal reabsorption of mercury
compounds
in the bile were studied. Rats were injected intraperitoneally
with
203HgCl2 (300 micrograms Hg and 74 kBq of 203Hg/kg) and 24 h
later,
they were injected intraperitoneally with a chelating agent (a
quarter
of an LD50). The injection of the chelating agents significantly
enhanced the biliary and urinary excretions of mercury. The enhancing
effect of BGD on the excretions of mercury was almost the same
as that
of BAL and much larger than that of D-PEN. The major chemical
form of
mercury in the bile and urine of rats injected with BGD after
HgCl2
treatment was Hg-BGD compounds. The chemical form of mercury
in the
bile and urine of rats injected with BAL after HgCl2 treatment
was
mainly Hg-GSH compound. The mercury after HgCl2 and D-PEN treatment
was
excreted mainly via the urine in the form of Hg-D-PEN compound.
The
intestinal reabsorption of mercury from the bile of rats injected
with
BGD or D-PEN was only 0.18% or 0.38% of the dose, respectively.
The
intestinal reabsorption of mercury from the bile of rats injected
with
BAL was 27.38% of the dose. It was suggested that the Hg-GSH
compound
excreted in the bile after HgCl2 and BAL treatment is partly
degraded
to Hg-cysteine (Cys) by the intestinal membranous enzymes and
that the
ligand of Hg-Cys is replaced by BAL in the bile, resulting in
the
effective reabsorption of Hg-BAL compound from the intestine.
Title
Influence of dietary protein levels on the fate of methylmercury
and
glutathione metabolism in mice.
Author
Adachi T; Yasutake A; Hirayama K
Address
Department of Basic Medical Sciences, National Institute for
Minamata
Disease, Kumamoto, Japan.
Source
Toxicology, 72(1):17-26 1992
Abstract
We investigated the influence of dietary protein levels on the
fate of
methylmercury (MeHg), the tissue glutathione (GSH) levels and
the
efflux rates of GSH in C57BL/6N male mice. One group of mice
was fed a
7.5% protein diet (low protein diet, LPD) and the other was fed
a 24.8%
protein diet (normal protein diet, NPD). The cumulative amount
of Hg in
urine in LPD-fed mice was approximately 3.7-times lower than
in NPD
group during the 7 days after oral administration of MeHg (20
mumol/kg), although the fecal Hg levels were identical in the
two
groups. Hg concentration in kidney, liver and blood decreased
time-dependently for 7 days after the administration in both
groups of
mice, whereas the brain levels continued to increase during this
period. Tissue Hg levels in the LPD group were significantly
higher
than in the NPD group except for the liver. Although the hepatic
GSH
level in LPD-fed mice was significantly lower than in NPD-fed
mice, the
levels in the kidney, brain, blood and plasma were not different
between the two groups. The efflux rate (mumol/g body weight
per day)
of hepatic GSH in LPD-fed mice was significantly lower than in
the NPD
group, whereas the efflux rates of renal GSH were identical in
both
groups. When MeHg (20 mumol/kg)-pretreated mice were injected
with
acivicin, a specific inhibitor of gamma-glutamyltranspeptidase,
the
urinary Hg levels increased by 60- and 36-fold in groups fed
LPD and
NPD, respectively. As a result, the difference in urinary Hg
levels
between the two groups disappeared with acivicin treatment. This
result
indicated that LPD feeding might decrease urinary Hg excretion
by
increasing the retention of MeHg metabolite(s) in renal cells.
Thus,
our present study suggested that the dietary protein status,
which
could modulate the metabolism of thiol compounds, played an important
role in determining the fate of MeHg.
Title
The mechanism of biliary excretion of methyl mercury: studies
with
methylthiols.
Author
Refsvik T
Source
Acta Pharmacol Toxicol (Copenh), 53(2):153-8 1983 Aug
Abstract
The S-methylated derivatives of N-acetylpenicillamine, thiola
and
cysteine as well as methyl iodide decreased biliary excretion
of methyl
mercury markedly. Excretion of sulfhydryl in bile was not influenced
by
S-methyl-cysteine, S-methylthiola, S-methyl-N-acetylpenicillamine
or a
low dose of methyliodide (0.5 mmol/kg body weight). This seems
to
indicate that coupling of methyl mercury to glutathione in the
liver
before biliary excretion is a glutathione S-transferase dependent
reaction. It also indicates that the methylthiols tested, or
metabolites of these compounds are likely to be inhibitors of
S-transferase. The effect of S-methylcysteine and low doses of
methyl
iodide probably reflects glutathione S-transferase inhibition
as both
compounds are metabolized to the S-transferase inhibitor
S-methylglutathione in the liver. A higher dose of methyl iodide
(1
mmol/kg body weight) seems to deplete the liver of reduced glutathione
through S-methylation as illustrated by decreased biliary excretion
of
sulfhydryl. S-methylthiola and S-methyl-N-acetylpenicillamine
are
metabolized in the liver to unknown components which are excreted
in
bile. Whether S-methylthiola and S-methyl-N-acetylpenicillamine
are
inhibitors of S-transferase themselves or cause inhibition through
metabolites cannot be stated from the present investigation.
Title
Redox activities of mercury-thiol complexes: implications for
mercury-induced porphyria and toxicity.
Author
Miller DM; Woods JS
Address
Department of Environmental Health, School of Public Health and
Community Medicine, University of Washington, Seattle 98195.
Source
Chem Biol Interact, 88(1):23-35 1993 Jul
Abstract
mercury exposure causes oxidative damage to the kidney, resulting
in
numerous biochemical changes, including the excretion of excess
porphyrins in the urine (porphyrinuria). Hg(II)-induced porphyrinuria
may occur, in part, by the previously reported oxidation of reduced
porphyrins (porphyrinogens) by a GSH/Hg(II) complex and H2O2.
To
further elucidate the mechanism(s) of porphyrinogen oxidation
by GSH,
Hg(II), and H2O2, we compared the ability of several thiol compounds
and peroxides to substitute for GSH or H2O2, respectively, in
the
oxidation of uroporphyrinogen (urogen). Every thiol compound
tested
resulted in enhanced urogen oxidation in the presence of Hg(II)
and
H2O2, albeit at different rates. Additionally, t-butyl or cumene
hydroperoxide substituted for H2O2 in promoting urogen oxidation,
although neither peroxide was as effective in this regard.
mercury-thiol complexes synthesized from Hg(I) and GSSG also
promoted
urogen oxidation in the presence of H2O2. Additionally, in the
absence
of urogen, both GSH/Hg(II) or GSSG/Hg(I) catalyzed the decomposition
of
H2O2. Finally, incubation of GSH/Hg(II) or GSSG/Hg(I) with H2O2
resulted in HPLC-detectable products distinct from GSH, GSSG,
or
GS2Hg(II). These findings suggest that mercury-thiol complexes
possess
redox activity in biological systems, which promotes the oxidation
of
porphyrinogens and possibly other biomolecules.
Title
Species variations in biliary excretion of glutathione-related
thiols
and methylmercury.
Author
Stein AF; Gregus Z; Klaassen CD
Address
Department of Pharmacology, Toxicology and Therapeutics, University
of
Kansas Medical Center, Kansas City 66103.
Source
Toxicol Appl Pharmacol, 93(3):351-9 1988 May
Abstract
The biliary excretion of methylmercury is thought to be related
to the
biliary excretion of nonprotein thiols in rats. Species differences
in
biliary excretion of glutathione (GSH) and related thiols are
unknown;
therefore, the relationship between the biliary excretion of
GSH-related thiols and methylmercury in five species was studied.
The
biliary excretion rate of GSH-related thiols and disulfides was
369,
192, 94, 50, and 19 nmol/min/kg for mice, rats, hamsters, guinea
pigs,
and rabbits, respectively. The main thiol in mouse, hamster,
and rat
bile was GSH, whereas guinea pig and rabbit bile contained mainly
cysteinylglycine (Cys-Gly). The larger percentage of Cys-Gly
in guinea
pig and rabbit bile was correlated with their greater hepatic
gamma-glutamyltranspeptidase (GGT) activity than that observed
in the
other species. The biliary excretion rate (nmol/min/kg) of
methylmercury was approximately 0.8 in mice, rats, and hamsters
compared to significantly lower rates in guinea pigs and rabbits
(0.15
and 0.03, respectively). It is concluded that the species-specific
composition of GSH-related thiols and disulfides in bile is related
to
species variations in hepatic GGT activity, and that the species
variation in biliary excretion of GSH-related thiols does not
entirely
account for the species variation in methylmercury excretion,
indicating other factors are also apparently involved in determining
the rate of biliary excretion of methylmercury.
Title
Excretion of methyl mercury in rat bile: the effect of diethylmaleate,
cyclohexene oxide and acrylamide.
Author
Refsvik T
Source
Acta Pharmacol Toxicol (Copenh), 42(2):135-41 1978 Feb
Abstract
Diethylmaleate, cyclohexene oxide and acrylamide administered
intraperitoneally to rats, have been shown markedly to inhibit
biliary
excretion of methyl mercury. Simultaneously the sulphhydryl and
sulphide content of the bile decreases. These results probably
reflect
the conjugation of acrylamide, diethylmaleate and cyclohexene
oxide to
glutathione in the liver, thereby blocking the biliary excretion
of
methyl mercury. A high concentration of liver glutathione seems
to be a
prerequisite for the normal translocation of methyl mercury from
liver
to bile. These results indicate that methyl mercury is transported
from
liver to bile as a glutathione complex.
Title
Enzyme activity and sulfhydryl status in rat renal cortex following
mercuric chloride and dithiothreitol administration.
Author
Klonne DR; Johnson DR
Address
Department of Environmental Health, Kettering Laboratory, University
of
Cincinnati College of Medicine, OH 45267.
Source
Toxicol Lett, 42(2):199-205 1988 Aug
Abstract
Previous experiments indicated that the partial reversal of mercuric
chloride-induced renal dysfunction in rats by subsequent dithiothreitol
(DTT) administration was not related to increased mercury excretion,
decreased renal mercury concentration, a change in renal cortical
subcellular mercury distribution, or the formation of a Hg-DTT
complex.
The present studies investigated whether DTT, a sulfhydryl reducing
agent, protected renal cortical sulfhydryl status in general,
or the
activity of various renal enzymes (Mg- and Na,K-ATPases, alkaline
phosphatase, and glutathione peroxidase) in particular. Additionally,
the occurrence of conjugated dienes was used to assess the degree
of
lipid peroxidation. HgCl2 produced significant decreases in renal
cortical protein-bound sulfhydryl concentration, alkaline phosphatase
activity, and ATPase activity within 2.5 h of administration,
with no
effect observed on glutathione peroxidase activity or the levels
of
conjugated dienes in rat renal cortex. Administration of DTT
60 min
after mercury neither provided protection from inhibition nor
promoted
restoration of the affected enzymes or sulfhydryl status. It
is
concluded that the partial protection of renal function offered
by DTT
in the early stages of mercury toxicity does not result from
maintaining the integrity of renal cortical sulfhydryl status
or the
activity of the enzymes investigated. Furthermore, the early
stages of
mercury toxicity did not appear to be related to lipid peroxidation.
Title
The influence of some thiols on biliary excretion of methyl mercury.
Author
Refsvik T
Source
Acta Pharmacol Toxicol (Copenh), 52(1):22-9 1983 Jan
Abstract
N-Acetylpenicillamine and thiola increased biliary excretion
of methyl
mercury and sulfhydryl right after administration. Cysteine increased
excretion of methyl mercury in bile after a temporary decrease
following administration. During the interval of decreased mercury
excretion biliary excretion of cysteine passed through a maximum.
This
indicates the existence of a common factor of the excretory systems
for
cysteine and methyl mercury and illustrates that cysteine cannot
carry
methyl mercury from liver to bile. Relatively large proportions
of
unchanged thiola and N-acetylpenicillamine were excreted in bile.
Bile
collected after administration of one of these compounds, in
addition
to thiola or N-acetylpenicillamine, contained other methyl mercury
carrying components not present in control bile. From the experiments
undertaken it cannot be stated whether these components play
any role
in the increased excretion of methyl mercury in bile caused by
thiola
and N-acetylpenicillamine. The mechanisms of increased biliary
excretion of methyl mercury following administration of
N-acetylpenicillamine, thiola and cysteine are discussed.
Title
Slow biliary elimination of methyl mercury in the marine elasmobranchs,
Raja erinacea and Squalus acanthias.
Author
Ballatori N; Boyer JL
Source
Toxicol Appl Pharmacol, 85(3):407-15 1986 Sep 30
Abstract
The present study examined the ability of two marine elasmobranchs
(Raja erinacea, little skate, and Squalus acanthias, spiny dogfish
shark) to excrete methyl mercury into bile, a major excretory
route in
mammals. 203Hg-labeled methyl mercury chloride was administered
via the
caudal vein, and bile collected through exteriorized cannulas
in the
free swimming fish. Skates and dogfish sharks excreted only a
small
fraction of the 203Hg into bile over a 3-day period: in the skate,
the
3-day cumulative excretion (as a % of dose) was 0.44 +/- 0.10
(n = 4,
+/- SD), 0.71 +/- 0.23 (n = 6), and 1.00 +/- 0.34(n = 4) for
doses of
1, 5, and 20 mumol/kg, respectively, while the shark excreted
only 0.15
+/- 0.15% (n = 8) at a dose of 5 mumol/kg. As in mammals, the
availability of hepatic and biliary glutathione was a determinant
of
the biliary excretion of methyl mercury in these species: the
administration of sulfobromophthalein, a compound known to inhibit
both
glutathione and methyl mercury excretion in rats, or of
L-buthionine-S,R-sulfoximine, an inhibitor of glutathione biosynthesis,
decreased the biliary excretion of both glutathione and mercury
in the
skate. The slow hepatic excretory process for methyl mercury
in the
skate and shark was attributed to an inordinately slow rate of
bile
formation: from 1 to 4 ml/kg X day. An inefficient biliary excretory
process in fish may account in part for the long biological half-times
for methyl mercury in marine species.
Title
Genetic variation in the susceptibility to mercury and other
metal
compounds in Drosophila melanogaster.
Author
Magnusson J; Ramel C
Source
Teratog Carcinog Mutagen, 6(4):289-305 1986
Abstract
The tolerance of Drosophila melanogaster to heavy metal compounds
was
investigated with special emphasis on methylmercury. A pronounced
variation in tolerance to CH3HgOH, HgCl2, (C2H5)3PbCl, (CH3)3SnCl,
and
CdCl2 was recorded between 12 wild-type strains. After ranking
the
tolerance of the strains with respect to the five compounds rank
correlations for experiments within and between compounds were
calculated. The results showed a high degree of correlation within
compounds but no unequivocal indication of a correlation between
compounds, indicating that different mechanisms of genetic control
for
tolerance were operating for the five compounds. Rank correlations
for
experiments with 12 different mercury, lead, tin, and cadmium
compounds
and the same 12 wild-type strains only indicated one significant
correlated response, between tripropyltin and tributyltin. A
selection
experiment for tolerance to methylmercury was performed with
a
foundation population, synthesized from four wild-type strains,
showing
a high initial tolerance. One control and two levels of treatment
doses
were used. A distinct selection response was obtained and a high
tolerance was reached particularly for the high-dose selection
line
after 12 generations, when the experiment ended. Genetic analysis
of
the tolerance indicated a dominant and polygenic inheritance.
Investigation of the uptake and excretion of CH3Hg203OH showed
that the
level of tolerance to methylmercury was correlated with the uptake
of
the mercury but apparently not with the rate of excretion. Cystein
increased the susceptibility to methylmercury. Inorganic mercury
and
trimethyl lead exhibited a synergistic toxic effect, evidently
as the
result of an in vitro transmethylation of mercury. A high somatic
susceptibility to methylmercury also applied to the induction
of
nondisjunction and sex-linked recessive lethals. |
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