|
Title
The antioxidant defense system of isolated guinea pig Leydig
cells.
Author
Kukucka MA; Misra HP
Address
Department of Biomedical Sciences, Virginia-Maryland Regional
College
of Veterinary Medicine, Virginia Polytechnic Institute &
State
University, Blacksburg 24061.
Source
Mol Cell Biochem, 126(1):1-7 1993 Sep 8
Abstract
Utilization of highly enriched preparations of steroidogenic
Leydig
cells have proven invaluable for studying the direct effects
of various
hormones and agents on Leydig cell function in vitro. However,
recent
work indicates that isolated Leydig cells are often subjected
to oxygen
(O2) toxicity when cultured at ambient (19%) oxygen concentrations.
Because intracellular antioxidants play an important role in
protecting
cells against oxygen toxicity, we have investigated the intracellular
antioxidant defense system of isolated Leydig cells. The cellular
levels of several antioxidants including catalase, glucose-6-phosphate
dehydrogenase (G-6-PDH), superoxide dismutase (SOD) of the Cu/Zn
& Mn
variety, glutathione peroxidase, glutathione reductase and total
glutathione were quantitated using enriched populations of Leydig
cells
isolated from adult male guinea pig testes. Compared to whole
testicular homogenates, Leydig cells contained significantly
(P < 0.01)
less G-6-PDH, total SOD, glutathione reductase and total glutathione,
but significantly (P < 0.001) more glutathione peroxidase.
Compared to
hepatic values previously reported in the guinea pig, Leydig
cells
contain nearly 400 times less catalase, about 14 times less glutathione
peroxidase and almost 11 times less glutathione reductase. Since
G-6-PDH and glutathione reductase are both necessary to regenerate
reduced glutathione (GSH) which couples with glutathione peroxidase
to
breakdown hydrogen peroxide (H2O2) under normal conditions, it
is
plausible that the oxygen toxicity observed in isolated Leydig
cells is
due to the intracellular accumulation of H2O2.(Abstract TRUNCATED
AT
250 WORDS)
Title
Inhibition of hepatic xenobiotic metabolism and of
glutathione-dependent enzyme activities by zinc
ethylene-bis-dithiocarbamate in the rabbit.
Author
Nebbia C; Dacasto M; Soffietti MG; Rasero R; Principato GB; Di
Simplicio P
Address
Department of Animal Pathology, University of Torino, Italy.
Source
Pharmacol Toxicol, 73(4):233-9 1993 Oct
Abstract
Effects of either a single (300 mg/kg) or a subchronic (0.3 and
0.6%
for 70 days) oral administration of a dithiocarbamate fungicide
(zinc
ethylene-bis-dithiocarbamate, zineb) on hepatic drug metabolism
and on
the activity of several glutathione-dependent enzymes were investigated
in male New Zealand White rabbits. While a pronounced reduction
in the
rate of oxidative biotransformations occurred after either single
or
repeated exposure, both cytochrome P450 and total haem content
were
lowered following acute challenge to zineb. None of the experimental
protocols affected microsomal carboxylesterase but induced a
marked
increase in glutathione content and none of the examined
glutathione-dependent enzymes was altered by the single administration
of zineb, whereas the subchronically exposed rabbits showed a
fall in
the activities of both total glutathione S-transferase and
selenium-independent glutathione peroxidase. In the 0.6% treated
animals, a decrease in class mu glutathione S-transferase and
glyoxalase I, and an increase in thiol-transferase activities
were also
recorded. It is concluded that (1) zineb is able to selectively
impair
oxidative drug metabolism with possible different mechanism(s)
according to the duration of the exposure, (2) only the subchronic
treatment affects glutathione-dependent enzymes, (3) the decrease
in
glutathione S-transferase activity would seem to be ascribed
to a
direct interaction with the fungicide.
Title
Inhibition of acetaminophen oxidation by cimetidine and the effects
on
glutathione and activated sulphate synthesis rates.
Author
Dalhoff K; Poulsen HE
Address
Department of Medicine A, Rigshospitalet, Copenhagen, Denmark.
Source
Pharmacol Toxicol, 73(4):215-8 1993 Oct
Abstract
The aim of the present study was to examine the effects of the
hepatotoxic drug, acetaminophen, on the synthesis rates of glutathione,
activated sulphate (PAPS, adenosine 3'-phosphate 5'-phosphosulphate)
and the acetaminophen metabolites, acetaminophen-glutathione
and
acetaminophen-sulphate after inhibition of cytochrome P-450 drug
oxidation by cimetidine in isolated rat hepatocytes. The synthesis
rates of glutathione and PAPS were determined simultaneously
by an
established method based on trapping of radioactivity (35S) in
the
prelabelled glutathione and PAPS pools. Preincubation of the
hepatocytes with 60 micrograms/ml cimetidine for 30 min. did
not affect
PAPS (1.71 versus 1.78 nmol/10(6) cells) nor glutathione concentration
(16.0 versus 16.4 nmol/10(6) cells). The subsequent incubation
with 5
mM acetaminophen resulted in decreased PAPS synthesis in the
cimetidine
treated cells [0.79 x 10(3) versus 0.92 x 10(3) nmol/(10(6) cells.hr)]
(P < 0.05). There was no difference in PAPS concentration
or
acetaminophen-sulphate synthesis [1.73 versus 1.79 nmol/10(6)
cells and
13.0 versus 12.9 nmol/(10(6) cells.hr), respectively]. Decreased
PAPS
synthesis may be related to decreased ATP supply or may be the
result
of a feed-back regulation due to diversion of sulphur from glutathione
synthesis to sulfoxidation. The glutathione synthesis was not
significantly affected by cimetidine treatment [57 x 10(3) versus
27 x
10(3) nmol/(10(6) cells.hr)]. As expected acetaminophen-glutathione
synthesis decreased by 38% [1.66 versus 2.68 nmol/(10(6) cells.hr)]
(P
< 0.01). Also the glutathione concentration was lower in cimetidine
treated cells [15.2 versus 15.9 nmol/10(6) cells] (P < 0.05).
We have
previously shown that glutathione synthesis was reduced if substrate
availability decreased (acetaminophen concentration lowered).(Abstract
TRUNCATED AT 250 WORDS)
Title
glutathione and glutathione linked enzymes in human small cell
lung
cancer cell lines.
Author
Sharma R; Singhal SS; Srivastava SK; Bajpai KK; Frenkel EP; Awasthi
S
Address
Department of Human Biological Chemistry and Genetics, University
of
Texas Medical Branch, Galveston 77555-1067.
Source
Cancer Lett, 75(2):111-9 1993 Dec 10
Abstract
glutathione levels and several glutathione-linked enzyme activities
have been variably correlated with cisplatin chemosensitivity
in
cultured neoplastic cells. In order to determine the relative
contribution of the glutathione-linked enzymes towards mediating
inherent cisplatin resistance in cancer cells, we have measured
the
chemosensitivity to cisplatin, glutathione levels and activities
of
glutathione S-transferase, glutathione peroxidase, glutathione
reductase and glucose-6-phosphate dehydrogenase in 8 cultured
human
small cell lung cancer (SCLC) cell lines with widely differing
cisplatin sensitivities. Of these parameters, only glutathione
S-transferase activity correlated with degree of cisplatin resistance
in a linear fashion.
Title
Modulation of hepatic glutathione system of enzymes in suckling
mouse
pups exposed translactationally to malathion.
Author
Chhabra SK; Hashim S; Rao AR
Address
Cancer Biology Laboratory, School of Life Sciences, Jawaharlal
Nehru
University, New Delhi, India.
Source
J Appl Toxicol, 13(6):411-6 1993 Nov-Dec
Abstract
The present study examines the transmammary modulation of the
glutathione system of enzymes in the F1 generation of mouse pups
postnatally exposed to malathion. Lactating Swiss albino mice
received
either 30 or 100 mg malathion kg-1 body wt. (98% pure) for 14
or 21
days postpartum. The acid-soluble sulphydryl content was significantly
increased (P < 0.001) in the liver of 14-day-old pups of dams
that had
received the higher malathion dose. A similar significant increase
was
seen in the 21-day-old male pups of dams that had received 30
mg (P <
0.05) or 100 mg (P < 0.01) malathion kg-1 body wt. Dams showed
an
enhanced hepatic glutathione S-transferase activity following
treatment
with 100 mg malathion kg-1 body wt. for 14 days (P < 0.02)
and 21 days
(P < 0.001). Pups of either age groups also showed enhanced
hepatic
glutathione S-transferase activity (P < 0.001). A significant
enhancement in glutathione reductase activity was observed with
malathion treatment in livers of dams and pups (P < 0.001).
However,
dams that had received 30 mg malathion kg-1 body wt. daily for
21 days
or 100 mg malathion kg-1 body wt. for either 14 or 21 days showed
significantly reduced hepatic glutathione peroxidase activity
(P <
0.01, P < 0.001). A significant decrease in glutathione peroxidase
activity was also observed in the liver of the 21-day-old male
(P <
0.01) and female (P < 0.02) pups of dams that were treated
with the
higher dose of malathion.
Title
Antioxidant defences in rat, pig, guinea pig, and human hearts:
comparison with xanthine oxidoreductase activity.
Author
Janssen M; van der Meer P; de Jong JW
Address
Cardiochemical Laboratory, Erasmus University Rotterdam, The
Netherlands.
Source
Cardiovasc Res, 27(11):2052-7 1993 Nov
Abstract
OBJECTIVE: Cardiac injury, related to ischaemia and reperfusion,
may be
caused by the action of oxygen free radicals. Xanthine oxidoreductase
activity may be an important free radical Source. During
cardiac
ischaemia, the native dehydrogenase form may be converted to
the
oxidase form, which uses molecular oxygen to form superoxide
radicals.
Superoxide dismutase converts the radicals to H2O2, which is
detoxified
by catalase and glutathione peroxidase. In view of the large
differences in xanthine oxidoreductase in various species, the
activity
of these antioxidant enzymes was investigated. METHODS: Normal
rodent
and porcine as well as explanted human hearts were perfused according
to Langendorff. After a 30 minute stabilisation period, hypoxanthine
was added to the perfusion buffer to estimate xanthine oxidoreductase.
Hearts or biopsies were freeze clamped after 90 minutes. Effluent
xanthine and urate were assayed with high performance liquid
chromatography; tissue reduced glutathione content and the activity
of
superoxide dismutase, catalase, glutathione peroxidase, and glutathione
reductase were determined spectrophotometrically. Apparent xanthine
oxidoreductase was calculated as xanthine +2 x urate production.
RESULTS: Xanthine oxidoreductase was (mU.g-1 protein, mean(SEM),
n =
5-7): rat, 470(40); guinea pig, 270(41); pig < 1.5; and human,
5.4(1.0). Superoxide dismutase activities were (U.g-1 protein):
rat,
13,370(1030); guinea pig, 10,100(1110); pig, 12,800(450); and
human,
7400(450). Catalase activity (k < or = 10.g-1 protein) was
low in all
species studied. glutathione peroxidase activity was 93(7) U.g-1
protein in rat heart, and 10 x lower in the other species. glutathione
reductase activity was (U.g-1 protein): rat, 15.0(1.6); guinea
pig,
10.4(1.3); pig, 16.0(1.5); and human, 26.6(2.0). Tissue reduced
glutathione concentrations were (mumol.g-1 protein): rat, 13.5(0.8);
guinea pig, 18.5(0.9); pig, 11.1(2.9); and human 17.2(1.7).
CONCLUSIONS: Considerable species differences in xanthine
oxidoreductase activity exist, contrasting with the smaller variations
in antioxidant enzyme activities. In the species examined catalase
activities were very low. Rat hearts are far better protected
against
H2O2 than the other three species. Xanthine oxidoreductase induced
free-radical damage probably plays a minor role in pig and human
hearts. Human myocardium seems less protected against superoxide
radicals.
Title
Ethacrynic acid and its glutathione conjugate as inhibitors of
glutathione S-transferases.
Author
Ploemen JH; van Ommen B; Bogaards JJ; van Bladeren PJ
Address
TNO Toxicology and Nutrition Institute, Department of Biological
Toxicology, Zeist, The Netherlands.
Source
Xenobiotica, 23(8):913-23 1993 Aug
Abstract
1. The diuretic drug ethacrynic acid (EA) is a potent reversible
inhibitor of rat and human glutathione S-transferases (GST),
with
I50-values (microM) of 4.6-6.0, 0.3-1.9 and 3.3-4.8 for alpha,
mu and
pi-class, respectively. 2. The reversible inhibition by the glutathione
conjugate of EA is even stronger for alpha and mu-class, with
I50-values (microM) of 0.8-2.8 and < 0.1-1.2, respectively,
while the
I50 for the pi-class is 11. 3. Inhibition of rat and human pi-class
GST
also occurs by covalent binding of ethacrynic acid. 14C-ethacrynic
acid, 0.8 nmol EA per nmol pi-class GST could be incorporated,
resulting in 65-93% inhibition of the catalytic activity. 4.
Owing to
the chemical nature of the covalent binding (Michael addition),
this
reaction should be reversible. Indeed, full restoration of the
catalytic activity of GST P1-1 inactivated by covalently-bound
EA was
reached in about 125 h by incubation with an excess of glutathione.
5.
EA has been used to inhibit GST in biological systems. The reversible
covalent binding may very well play a role in the observed inhibition
of GST by EA in vivo.
Title
glutathione-dependent bioactivation of xenobiotics.
Author
Dekant W; Vamvakas S
Address
Institut für Toxikologie und Pharmakologie, Universität
Würzburg,
Germany.
Source
Xenobiotica, 23(8):873-87 1993 Aug
Abstract
glutathione conjugation has been identified as an important
detoxication reaction. However, in recent years several
glutathione-dependent bioactivation reactions have been identified.
Current knowledge on the mechanisms and the possible biological
importance of these reactions are discussed. 1. Dichloromethane
is
metabolized by glutathione conjugation to formaldehyde via
S-(chloromethyl)glutathione. Both compounds are reactive intermediates
and may be responsible for the dichloromethane-induced tumorigenesis
in
sensitive species. 2. Vicinal dihaloalkanes are transformed by
glutathione S-transferase-catalyzed reactions to mutagenic and
nephrotoxic S-(2-haloethyl)glutathione S-conjugates. Electrophilic
episulphonium ions are the ultimate reactive intermediates formed.
3.
Several polychlorinated alkenes are bioactivated in a complex,
glutathione-dependent pathway. The first step is hepatic glutathione
S-conjugate formation followed by cleavage to the corresponding
cysteine S-conjugates, and, after translocation to the kidney,
metabolism by renal cysteine conjugate beta-lyase. Beta-Lyase-dependent
metabolism of halovinyl cysteine S-conjugates yields electrophilic
thioketenes, whose covalent binding to cellular macromolecules
is
responsible for the observed toxicity of the parent compounds.
4.
Finally, hepatic glutathione conjugate formation with hydroquinones
and
aminophenols yields conjugates that are directed to
gamma-glutamyltransferase-rich tissues, such as the kidney, where
they
undergo alkylation or redox cycling reactions, or both, that
cause
organ-selective damage. |
|
Return to Main Page
