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Title
In vivo effects of N-acetylcysteine on glutathione metabolism
and on
the biotransformation of carcinogenic and/or mutagenic compounds.
Author
De Flora S; Bennicelli C; Camoirano A; Serra D; Romano M; Rossi
GA;
Morelli A; De Flora A
Source
Carcinogenesis, 6(12):1735-45 1985 Dec
Abstract
N-acetylcysteine (NAC) was administered to rats in various combinations
with an enzyme inducer (Aroclor 1254) and with depletors of reduced
glutathione (GSH), i.e., diethyl maleate (DEM) and buthionine
sulfoximine (BSO). NAC increased intracellular glutathione levels
in
erythrocytes and in liver and lung cells, and replenished its
stores
following depletion. It did not affect the concentrations nor
the
spectral properties of cytochromes P-450 in hepatic and pulmonary
microsomes, whereas it stimulated, especially in Aroclor-pre-treated
animals, cytosolic enzyme activities involved in NADP reduction
(glucose 6-phosphate dehydrogenase and 6-phosphogluconate
dehydrogenase), in glutathione reduction (GSSG-reductase) and
in the
reductive detoxication of xenobiotics by-passing formation of
reactive
oxygen species (DT-diaphorase). In vivo treatment with the drug
enhanced detoxication by liver and lung S-12 fractions of direct-acting
mutagens (ICR 191, epichlorohydrin, 4-nitroquinolino-N-oxide
and
dichromate) and counteracted opposite effects triggered by
administration of GSH depletors. The metabolic activation of
procarcinogens (aflatoxin B1, 2-aminofluorene, cyclophosphamide,
benzo[a]pyrene, a tryptophan pyrolysate product and cigarette
smoke
condensate) was inhibited by NAC in uninduced rats, while it
was
further stimulated in Aroclor-pre-treated animals. Additional
assays,
performed also with other enzyme inducers (phenobarbital and
3-methylcholanthrene) suggested that the effect of NAC on the
metabolic
activation of procarcinogens depends on the balance between an
increased production of mutagenic metabolites (prevailing in
induced
animals) and their binding by intracellular thiols (prevailing
under
normal conditions). Thus, due to its dual role as a nucleophile
and as
a SH donor, NAC appears to exert protective effects by modulating
glutathione metabolism and the biotransformation of
mutagenic/carcinogenic compounds. This may have clinical relevance,
since NAC is administered to individuals, such as cigarette smokers,
who are more heavily exposed to GSH depletors and to carcinogenic
agents.
Title
GSH rescue by N-acetylcysteine.
Author
Ruffmann R; Wendel A
Address
Inpharzam SA' Cadempino' Schweiz.
Source
Klin Wochenschr, 69(18):857-62 1991 Nov 15
Abstract
Reduced glutathione (GSH) is the main intracellular low molecular
weight thiol. GSH acts as a nucleophilic scavenger and as an
enzyme-catalyzed antioxidant in the event of electrophilic/oxidative
tissue inJury. Therefore' GSH has a maJor role as a protector
of
biological structures and functions. GSH depletion has been recognized
as a hazardous condition during paracetamol intoxication. Conversely'
GSH rescue' meaning recovery of the protective potential of GSH
by
early administration of N-acetylcysteine (NAC)' has been found
to be
life-saving. Lack of GSH and electrophilic/oxidative inJury have
been
identified among the causes of the adult respiratory distress
syndrome
(ARDS)' idiopathic pulmonary fibrosis (IPF)' and the acquired
immunodeficiency syndrome (AIDS). Experimental and early clinical
data
(in ARDS) point to the role of NAC in the treatment of these
conditions. Recently' orally given NAC has been shown to enhance
the
levels of GSH in the liver' in plasma' and notably in the
bronchoalveolar lavage fluid. Rescue of GSH through NAC needs
to be
appreciated as an independent treatment modality for an array
of
different disease' all of which have one feature in common:
pathogenetically relevant loss of GSH.
Title
Nonxenobiotic manipulation and sulfur precursor specificity of
human
endothelial cell glutathione.
Author
Cotgreave IA; Constantin-Teodosiu D; Mold]eus P
Address
Department of Toxicology' Karolinska Institutet' Stockholm' Sweden.
Source
J Appl Physiol, 70(3):1220-7 1991 Mar
Abstract
Confluent human umbilical vein endothelial (HUVE) cells were
readily
(within 1 h) depleted of their glutathione (GSH) by diethylmaleate
(0.1-1.0 mM)' but dose-dependent cell detachment was noted. Buthionine
sulfoximine (BSO' 25 microM) depleted cell GSH with sigmoidal
kinetics'
showing an initial half-life of depletion of 4-6 h and greater
than 95%
depletion by 48 h without morphological changes to the cells.
However'
BSO-dependent depletion of cell GSH was only partially reversible
by
cell washing and reincubation with complete medium. Likewise'
incubation of the cells in sulfur-free medium depleted cell GSH
again
without morphological changes to the cells. However' unlike with
BSO'
these cells readily resynthesized GSH when resupplied with complete
medium' fresh plasma' or whole blood' with a characteristic overloading
of cell GSH (up to 200%) by 12 h. By use of the sulfur-free medium'
it
was shown that both cystine and cysteine are effective precursors
to
GSH synthesis in HUVE cells in culture and that cystine is the
most
likely precursor in vivo. During cystine-supported resynthesis
of GSH'
high levels of cysteine accumulated in the cells (up to 10% of
total
soluble free thiol). Physiologically relevant concentrations
of
extracellular GSH were not as effective as cystine or cysteine
in
stimulating GSH biosynthesis' whereas nonphysiologically high
(mM)
concentrations resulted in substantial elevation of GSH levels
above
those of control cells in a BSO-insensitive manner. These findings
provide a simple methodology for the manipulation of HUVE cell
GSH in
studies of endothelial-specific oxidant toxicity and the sulfur
dependence of the biochemistry and turnover of GSH in these human
cells.
Title
Effect of oral glutathione on hepatic glutathione levels in rats
and
mice.
Author
Viña J; Perez C; Furukawa T; Palacin M; Viña JR
Address
Department of Physiology, University of Valencia, Spain.
Source
Br J Nutr, 62(3):683-91 1989 Nov
Abstract
Administration of oral glutathione (GSH) increases hepatic GSH
levels
in fasted rats, in mice treated with GSH depletors such as diethyl
maleate and in mice treated with high doses of paracetamol. An
increase
in hepatic GSH levels after administration of oral GSH does not
occur
in animals treated with buthionine sulphoximine, an inhibitor
of GSH
synthesis. Administration of oral GSH leads to an increase in
the
concentration of L-cysteine, a precursor of GSH, in portal blood
plasma. Oral administration of L-methionine produced a significant
decrease of hepatic ATP in fasted rats, but not in fed rats.
Administration of N-acetylcysteine or GSH did not affect the
hepatic
ATP levels. The results show that the oral intake of GSH is a
safe and
efficient form of administration of its constituent amino acids
in
cases when GSH synthesis is required to replete hepatic GSH levels.
Title
Bioavailability of dietary glutathione: effect on plasma concentration.
Author
Hagen TM; Wierzbicka GT; Sillau AH; Bowman BB; Jones DP
Address
Department of Biochemistry' Emory University School of Medicine'
Atlanta' Georgia 30322.
Source
Am J Physiol, 259(4 Pt 1):G524-9 1990 Oct
Abstract
Plasma glutathione (GSH) concentration in rats increased from
approximately 15 to 30 microM after administration of GSH either
as a
liquid bolus (30 mumol) or mixed (2.5-50 mg/g) in AIN-76 semisynthetic
diet. GSH concentration was maximal at 90-120 min after GSH
administration and remained high for over 3 h. Administration
of the
amino acid precursors of GSH had little or no effect on plasma
GSH
values' indicating that GSH catabolism and resynthesis do not
account
for the increased GSH concentration seen. Inhibition of GSH synthesis
and degradation by L-buthionine-[S'R -sulfoximine and acivicin
showed
that the increased plasma GSH came mostly from absorption of
intact GSH
instead of from its metabolism. Plasma protein-bound GSH also
increased
after GSH administration' with a time course similar to that
observed
for free plasma GSH. Thus dietary GSH can be absorbed intact
and
results in a substantial increase in blood plasma GSH. This indicates
that oral supplementation may be useful to enhance tissue availability
Title
Low molecular weight thiol content in glutathione synthetase-deficient
human fibroblasts.
Author
Debieu D; Deschavanne PJ; Malaise EP
Address
Laboratoire de Radiobiologie Cellulaire, Unité INSERM
247, Institut
Gustave-Roussy, Villejuif, France.
Source
Clin Chim Acta, 170(2-3):161-8 1987 Dec
Abstract
The activity and the kinetic properties of glutathione synthetase
and
the concentrations of non-protein bound thiols of the gamma-glutamyl
cycle were measured in 11 human fibroblast cell strains. Six
of these
strains were derived from patients suffering from 5-oxoprolinuria,
a
recessive genetic disease characterized by a deficiency in glutathione
synthetase; the other cell strains were derived from healthy
heterozygous or homozygous relatives of the patients. The glutathione
synthetase activities of homozygous deficient strains were 1/3
of
control values while those of heterozygous strains were 2/3 of
control
values. The total thiol concentration was lower in only 3 of
the 6
deficient homozygotes and that of glutathione (GSH) was lower
in only 4
of the 6 deficient homozygotes. This lower GSH level was at least
partly offset by an accumulation of gamma-glutamylcysteine, a
precursor
of GSH, which is almost completely absent from control cells.
The total
quantities of thiols and GSH in plateau phase cells were about
50% and
30% respectively of the levels in growth phase cells. Approximately
80%
of the GSH was in the reduced form in both quiescent and growing
cells.
Title
Dietary modulation of the glutathione detoxification pathway
and the
potential for altered xenobiotic metabolism.
Author
Smith TK
Address
Department of Nutritional Sciences' University of Guelph' Ontario'
Canada.
Source
Adv Exp Med Biol, 289():165-9 1991
Abstract
This review summarizes the literature regarding nutritional regulation
of the pathways of glutathione synthesis and subsequent conJugation
of
xenobiotic compounds. The glutathione detoxification pathway
includes
the enzymes of the gamma-glutamyl cycle as well as sulfur conJugation
reactions. This promotes bodily excretion of xenobiotics as well
as
normal metabolites. Regulation of intracellular glutathione
concentrations is maintained largely through changes in the activity
of
gamma-glutamylcysteine synthetase. Availability of glutathione
for
detoxification purposes can be limited by the supply of intracellular
cysteine to serve as a precursor for glutathione synthesis through
the
gamma-glutamyl cycle. Dietary methionine' cysteine and cysteine
prodrugs have been examined for their potential to maximize glutathione
availability for detoxification purposes. Some xenobiotic challenges
have been reported to deplete hepatic glutathione reserves and
toxicity
correlates with the degree of depletion. Other foreign compounds'
however' have been observed to increase cellular glutathione
concentrations beyond normal levels despite regulation of the
synthetic
pathway. Such effects will be reviewed.
Title
Antioxidative and clinical effects of high-dose N-acetylcysteine
in
fibrosing alveolitis. Adjunctive therapy to maintenance
immunosuppression.
Author
Behr J; Maier K; Degenkolb B; Krombach F; Vogelmeier C
Address
Abteilung f ur Pneumologie, Klinikum Grosshadern,
Ludwig-Maximilians-Universit at M unchen, Germany.
Source
Am J Respir Crit Care Med, 156(6):1897-901 1997 Dec
Abstract
In fibrosing alveolitis (FA), activated phagocytes cause excessive
oxidative stress in the lower respiratory tract. Additionally,
levels
of glutathione, a major antioxidant of the human lung, are markedly
reduced. Since N-acetylcysteine (NAC) is a known precursor for
glutathione synthesis, we investigated the effect of NAC on redox
balance and lung function in FA. Eighteen patients with an established
diagnosis of FA were treated with 600 mg NAC three times daily
for 12
wk in addition to their latest immunosuppressive therapy. Before
and
after NAC therapy, pulmonary function tests (PFTs) and bronchoalveolar
lavage (BAL) were performed. BAL fluid was analyzed with regard
to cell
differential, glutathione status, and methionine sulfoxide content
of
BAL proteins (Met(O)), as an indicator of oxidative stress at
the
alveolar surface. There was an increase of total glutathione
(GSHt =
GSH +/- 2 x GSSG: 3.43 +/- 0.30 microM versus 4.20 +/- 0.66 microM,
p <
0.05) and of reduced glutathione (GSH: 2.58 +/- 0.24 microM versus
3.42
+/- 0.54 microM, p < 0.005) in native BAL fluid and in the
epithelial
lining fluid (GSHt: 267.3 +/- 26.0 microM versus 367.1 +/- 36.0
microM,
p < 0.005; GSH: 204.5 +/- 20.7 microM versus 302.9 +/- 32.2
microM, p <
0.005). The increase of GSH was accompanied by a decrease of
Met(O)
(6.83 +/- 0.71% versus 4.60 +/- 0.40%, p < 0.005). PFTs significantly
improved during NAC treatment. We conclude that high-dose NAC
significantly improved the antioxidant screen of the lungs by
elevating
GSH levels. Moreover, the decrease of Met(O) levels indicated
an
antioxidant effect at the alveolar surface. These biochemical
changes
were accompanied by an improvement of PFTs in patients under
maintenance immunosuppression. NAC supplementation should, therefore,
be considered as an adjunct therapy for FA.
Title
Intracellular glutathione in human peritoneal mesothelial cells
exposed
in vitro to dialysis fluid.
Author
Breborowicz A; Rodela H; Martis L; Oreopoulos DG
Address
Department of Pathophysiology' Medical School Poznan' Poland.
Source
Int J Artif Organs, 19(5):268-75 1996 May
Abstract
Effect of peritoneal dialysis fluids on glutathione (GSH/GSSG)
level in
human peritoneal mesothelial cells was tested in in vitro experiments.
To mimic in vivo conditions' cells were initially exposed to
dialysis
fluids (Dianeal 1.36%' Dianeal 2.27%' Dianeal 3.86%) that subsequently
were diluted with dialysate effluent at time intervals. GSH/GSSG
concentration in cells initially decreased but returned to normal
values thereafter. This decrease in the intracellular concentration
of
glutathione was less when pH of the tested dialysis fluid was
adJusted
to 7.3. In further experiments with mesothelial cells exposed
to
Earle`s salts solution supplemented with glucose and/or lactate'
we
have shown that in the presence of low pH' lactate is the main
factor
causing depletion of intracellular glutathione. When added to
the
dialysis solution at a concentration of 0.1 mM'
L-2-oxothiazolidine-4-carboxylate' a precursor of glutathione'
not only
prevents the initial decrease in glutathione concentration but
also
augments the final intracellular level of this thiol.
Title
Investigations into the loss of glutathione from lenses in organ
culture.
Author
Qin C; Tumminia SJ; Russell P; Rao PV; Zigler JS Jr
Address
Laboratory of Mechanisms of Ocular Disease' National Eye Institute'
National Institutes of Health' Bethesda' MD 20892' USA.
Source
Curr Eye Res, 15(7):719-25 1996 Jul
Abstract
PURPOSE. To investigate possible causes and implications of the
decrease in glutathione concentration in rat lenses during organ
culture. METHODS. Freshly excised lenses were incubated in modified
TC-199 medium. Ellman`s Reagent or the GSH-400 assay were used
to assay
glutathione levels in lenses cultured for different times and
under a
variety of altered culture conditions. RESULTS. In lenses from
young
rats the glutathione decrease was not ameliorated by reduction
of
oxygen tension in the incubator' nor by supplementation of the
culture
medium with various antioxidants or sulfhydryl compounds' nor
with the
amino acid precursors of glutathione. Addition of 2-mercaptoethanol
stimulated cysteine transport into the lens but had only a modest
effect in maintaining the level of glutathione. The decrease
in
glutathione concentration was less in cultured lenses from older
rats.
Lenses from rhesus monkeys exhibited no decrease in glutathione
levels
when maintained in organ culture for up to 48 h. CONCLUSIONS.
The basis
for the decreased glutathione in cultured young rat lenses is
still
uncertain. The data from the present study indicate a definite
relationship between glutathione loss and age for cultured rat
lenses'
with young lenses being much more susceptible. The resistance
of
cultured monkey lenses to loss of glutathione demonstrates species
differences in this property which may be relevant to previously
reported differences in susceptibility to oxidative damage.
Title
Maintenance of neuronal glutathione by glial cells.
Author
Sagara JI; Miura K; Bannai S
Address
Department of Biochemistry' University of Tsukuba Medical School'
Ibaraki' Japan.
Source
J Neurochem, 61(5):1672-6 1993 Nov
Abstract
glutathione levels in neurons and glial cells were investigated
in a
neuronal-glial coculture and in separate cultures. Brain cell
suspensions obtained from cerebral hemispheres of fetal rats
were
cultured' and after 5 days the glutathione content of this cell
population' consisting mainly of neurons and astroglial cells'
was 23.0
nmol/mg of cell protein' with a significantly high content in
glial
cells (28.0 nmol/mg of protein) in comparison with neurons (18.8
nmol/mg of protein). When the neurons and glial cells were separated
and recultured in fresh medium' neuronal glutathione rapidly
decreased'
whereas glial glutathione remained unchanged. cysteine is a
rate-limiting precursor for glutathione synthesis' and its level
was
also decreased in neurons' but not in glial cells. cysteine was
taken
up rapidly by both neurons and glial cells' but cystine was taken
up
only by glial cells. This accounts for the rapid decrease of
glutathione in the cultured neurons' because the culture medium
contains cystine' but not cysteine. It was also found that the
cultured
glial cells released cysteine into the medium. These results
suggest
that neurons maintain their glutathione level by taking up cysteine
provided by glial cells.
Title
Protein deficiency potentiates oxygen toxicity.
Author
Fanburg BL; Deneke SM
Address
Department of Medicine, New England Medical Center Hospitals,
Boston,
MA 02111.
Source
Exp Lung Res, 14 Suppl():911-9 1988
Abstract
Male rats (Charles River COBS-CD derived) fed protein-deficient
diets
showed enhanced toxicity with failure of elevation of lung glutathione
levels with exposure to greater than 98% O2. Replenishment of
S-containing amino acids in the protein-deficient diets allowed
elevation of lung glutathione and prevention of enhanced toxicity.
Studies with endothelial cell cultures exposed to hyperoxia showed
elevation of cellular glutathione coupled with enhanced uptake
of amino
acid precursors of glutathione. We postulate that hyperoxia causes
an
enhancement of uptake of S-containing amino acids necessary for
glutathione synthesis, overriding glutathione feedback of its
own
synthesis. Limitation of available S-containing amino acids prevents
elevation of glutathione synthesis and is detrimental to the
cell
exposed to hyperoxia.
Title
Effects of N-acetylcysteine stereoisomers on oxygen-induced lung
inJury
in rats.
Author
S arnstrand B; Tunek A; SJ odin K; Hallberg A
Address
Department of Pharmacology' Astra Draco AB' Lund' Sweden.
Source
Chem Biol Interact, 94(2):157-64 1995 Feb
Abstract
The effects of the stereoisomers of N-acetylcysteine (L-NAC and
D-NAC)
on oxygen-induced lung oedema have been studied in rats. The
NAC-isomers were given by an osmotic minipump in order to attain
continuous administration' either intravenously or intragastrically.
In
some experiments' plasma concentrations of NAC' cysteine and
glutathione (total concentrations' i.e.' concentrations obtained
after
reduction of the samples with dithiothreitol) were recorded.
Exposure
to oxygen induced an almost two-fold increase of the lung wet
weight.
When L-NAC or D-NAC were given intravenously' in dose of 1.1
mmol/day/kg body weight' the increase of lung wet weight was
prevented
by 40-50%. The plasma concentrations were approximately 40 microM
(L-NAC) and approximately 90 microM (D-NAC). Following intragastrical
administration of the same doses' plasma concentrations of L-NAC
and
D-NAC reached approximately 3 and approximately 60 microM'
respectively. Using this method of administration' only D-NAC
significantly diminished the increase of the lung wet weight.
The
difference in plasma concentrations of the NAC isomers' particularly
after intragastric administration' most likely reflects the fact
that
L-NAC is effectively hydrolysed in most tissues' while D-NAC
is
resistant to enzymatic hydrolysis' thus penetrating largely intact
into
the systemic circulation. The data presented shows that NAC'
regardless
of stereoconfiguration' will protect the lung against oxygen
toxicity'
provided sufficient systemic levels are obtained. Since D-NAC
is not a
precursor of L-cysteine' formation of glutathione cannot explain
the
protective effects of this isomer. L- and D-NAC may therefore
act via
direct antioxidant/radical scavenging mechanisms and not necessarily
as
precursors of glutathione in this model.
Title
The metabolism of N-acetylcysteine by human endothelial cells.
Author
Cotgreave I; Mold]eus P; Schuppe I
Address
Department of Toxicology' Karolinska Institutet' Stockholm' Sweden.
Source
Biochem Pharmacol, 42(1):13-6 1991 Jun 21
Abstract
When human umbilical endothelial cells were depleted of their
glutathione by incubation in a sulfur amino acid-free medium'
subsequent incubation of the cells with this deficient medium
supplemented with N-acetylcysteine resulted in a dose-dependent
stimulation of the synthesis of cellular glutathione. Similarly'
the
inclusion of N-acetylcysteine in the medium during the period
of
depletion of glutathione caused a dose-dependent retardation
of the
depletion kinetics. In contrast' the incubation of control cells
in
normal medium supplemented with N-acetylcysteine did not increase
cellular glutathione levels above controls. These observations
indicate
the presence of an N-deacetylase in/on the cells with specificity
for
N-acetylcysteine. Due to the large surface area of the endothelium
in
the vasculature it seems likely that endothelial cell N-deacetylation
plays a role in the metabolic disposition of N-acetylcysteine'
particularly when administered intravenously. N-Acetylcysteine
is'
however' a relatively poor precursor to glutathione biosynthesis
in
comparison to cystine. Thus' any cytoprotective' antioxidant
effect
exerted by N-acetylcysteine on the human endothelium is likely
to be
due to direct scavenging of reactive intermediates rather than
by
stimulated glutathione synthesis in the endothelial cells themselves.
Title
Maintenance of glutathione content is isolated hepatocyctes.
Author
Nina J; Hems R; Krebs HA
Source
Biochem J, 170(3):627-30 1978 Mar 15
Abstract
1. During the standard procedure for the preparation of rat
hepatocytes, about half of the cellular GSH (reduced glutathione)
is
lost. 2. This loss is prevented by the addition of 0.1 mM-EGTA
(but no
EDTA) to the perfusion medium. 3. On incubation with and without
EGTA,
isolated hepatocytes prepared in the presence of EGTA lose GSH.
This
loss is prevented by near-physiological concentrations of methionine
or
homocysteine, but not of cysteine. 4. cysteine, at concentrations
above
0.2 mM, causes a loss of GSH probably by non-enzymic formation
of a
mixed disulphide. 5. Serine together with methionine or homocystein
increases GSH above the value in cells from starved rats in vivo.
This
is taken to suggest that cystathionine may be a cysteine donor
in the
synthesis of gamma-glutamylcysteine, the precursor of GSH. |
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