| Dietary
precursors and brain neurotransmitter formation.
Fernstrom JD.
Annu Rev Med (United States) 1981, 32 p413-25
The rates of synthesis of serotonin, acetylcholine,
and, under certain circumstances, dopamine and norepinephrine
by brain neurons depend considerably on the availability
to brain of the respective dietary precursors. This
precursor dependence seems to be related to the fact
that the enzyme catalyzing the rate-limiting step
in the synthetic pathway for each transmitter is unsaturated
with substrate at normal brain concentrations. Moreover,
brain levels of the individual precursors rise following
oral or parenteral administration of the pure compound
or the ingestion of certain foods. Precursor-induced
increases in brain transmitter formation seem to influence
a variety of brain functions and behaviors, which
suggests that transmitter release has been enhanced.
It now appears that these precursors may become useful
as therapeutic agents for the treatment of selected
disease states, wherein the disease is related to
reduced release of transmitter. Examples of Parkinson's
disease (tyrosine), myasthenia gravis (choline or
phosphatidylcholine), depression (tyrosine), and possibly
abnormal appetite (tryptophan). Perhaps the future
will bring the identification of still other neurotransmitters,
whose rates of synthesis depend on precursor availability.
Two potential candidates for which some information
is already available are glycine (a spinal cord transmitter)
and the prostaglandins (some of which may function
as neuromodulators or transmitters) (48, 49). Each
time a new precursor- product relationship is described,
an opportunity becomes available for determining whether
the precursor might be useful in treating disease
states related to reduced transmitter release by neurons.
The opportunities are worth exploring, since the use
of a natural dietary constituent, even in purified
form, is likely to produce fewer unwanted side-effects
than are seen following administration of synthetic
drugs.
Protection against chronic
cadmium toxicity by glycine.
Shaikh ZA, Tang W. Department of Biomedical Sciences,
University of Rhode Island, Kingston 02881, USA. zshaikh@uriacc.uri.edu
Toxicology 1999 Feb 15;132(2-3):139-46
A Japanese drug containing glycine, glycyrrhizin, and
cysteine (Stronger Neo-Minophagen C) has been reported
to protect against chronic cadmium (Cd) toxicity.
The present study was conducted to evaluate which
of the three constituents of this drug was the main
antagonist for Cd toxicity and whether the mechanism
of protection involved antioxidant action. Adult female
Sprague-Dawley rats were injected sc with 5 micromol
CdCl2/kg per day, five times per week, for 15 weeks.
Four groups of Cd-injected animals received co-treatments
with either 10 mg glycyrrhizin/kg, 100 mg glycine/kg,
5 mg cysteine/kg, or with a mixture of all three compounds,
five times per week, starting from week 7. An additional
Cd-injected group was co-treated with vitamin E (100
mg/kg, five times per week, starting from week 7)
as a positive control. Only those animals that received
vitamin E, Minophagen mixture, or glycine were protected
against Cd-induced hepatotoxicity as well as nephrotoxicity.
All three co-treatments suppressed Cd-induced hepatic
and renal lipid peroxidation. We conclude that the
reported beneficial effects of Stronger Neo-Minophagen
C are due to glycine, which appears to protect against
chronic Cd toxicity by reducing oxidative stress.
Dietary glycine inhibits activation
of nuclear factor kappa B and prevents liver injury
in hemorrhagic shock in the rat.
Mauriz JL, Matilla B, Culebras JM, Gonzalez P, Gonzalez-Gallego
J. Department of Physiology, University of Leon, Leon,
Spain.
Free Radic Biol Med 2001 Nov 15;31(10):1236-44
We investigated the effects of a glycine-containing
diet (5%) on liver injury caused by hemorrhagic shock
and resuscitation in rats. Anesthetized rats were
bled to a mean arterial blood pressure of 35-40 mm
Hg for 1 h and then resuscitated with 60% of shed
blood and lactated Ringer's solution. Feeding the
rats glycine significantly reduced mortality, the
elevation of plasma transaminase levels and hepatic
necrosis. The increase in plasma TNFalpha and nitric
oxide (NO) was also blunted by glycine feeding. Hemorrhagic
shock resulted in oxidative stress (significant elevations
in TBARS and in the oxidized/reduced glutathione ratio)
and was accompanied by a reduced activity of the antioxidant
enzymes Mn- and Cu,Zn-superoxide dismutase, glutathione
peroxidase and catalase, overexpression of inducible
NO synthase (iNOS), and activation of nuclear factor
kappa B (NF-kappaB). Glycine ameliorated oxidative
stress and the impairment in antioxidant enzyme activities,
inhibited NF-kappaB activation, and prevented expression
of iNOS. Dietary glycine blocks activation of different
mediators involved in the pathophysiology of liver
injury after shock.
Pre-column derivatization
high-performance liquid chromatographic method for
determination of cysteine, cysteinyl-glycine, homocysteine
and glutathione in plasma and cell extracts.
Katrusiak AE, Paterson PG, Kamencic H, Shoker A, Lyon
AW. Department of Pathology, College of Medicine,
University of Saskatchewan, Saskatoon, Canada.
J Chromatogr B Biomed Sci Appl 2001 Jul 15;758(2):207-12
A sensitive high-performance liquid chromatographic
method for quantification of sulphydryl and disulfide
amino acids in human plasma using ultra violet spectrophotometric
detection was developed. Precolumn derivatization
with 5,5'-dithio-bis-nitrobenzoic acid (DTNB) and
an optional pre-derivatization reaction with dithiothreitol
allowed both quantitative reduction of disulfides
for measurement of total amino acid levels and the
measurement of the reduced forms. A dynamic range
of 500 nmol/l-750 micromol/l allowed the major analytes
of interest to be quantified in plasma without sample
dilution. The assay is a sensitive and precise method
for the determination of sulphydryl and disulfide
amino acids in plasma and cell extracts.
Glycine supply to human enterocytes
mediated by high-affinity basolateral GLYT1.
Christie GR, Ford D, Howard A, Clark MA, Hirst BH.
Department of Physiological Sciences, University of
Newcastle upon Tyne, Medical School, Newcastle upon
Tyne, England.
Gastroenterology 2001 Feb;120(2):439-48
BACKGROUND & AIMS: Intestinal glycine transport
is involved in nutrient absorption and enterocyte
homeostasis, particularly for glutathione synthesis.
The primary aim of this study was to characterize
the mechanism of postabsorptive (basolateral) glycine
acquisition by the enterocyte. METHODS: Assimilation
of [(14)C]glycine was studied in human enterocytic
Caco-2 cells, and expression of the glycine transporter
GLYT1 was examined in Caco-2 cells and human intestine
by reverse-transcription polymerase chain reaction,
immunoblotting, and immunohistochemistry. The regulation
of glycine transport in Caco-2 cells by phorbol-ester-induced
protein kinase C activation was investigated. RESULTS:
Basolateral glycine uptake into Caco-2 cells is predominantly
Na(+) and Cl(-) dependent and is 4-fold greater than
apical uptake. The dominant Na(+)- and Cl(-)-dependent
mechanism was characterized by a restricted inhibition
profile, selectively sensitive to sarcosine, with
an apparent Michaelis constant of 40-80 micromol/L,
indicating system GLY. Consistent with these functional
data, molecular techniques detected expression of
GLYT1 messenger RNA and protein in the human intestine
and Caco-2 cells. Protein kinase C activation reduced
maximum velocity for GLYT1-mediated glycine uptake
without effect on the Michaelis constant. The reduction
in functional activity was independent of a measured
protein kinase C-induced decrease in GLYT1 messenger
RNA levels. CONCLUSIONS: Enterocytes express GLYT1
along the length of the crypt-villus axis, where it
mediates high-affinity basolateral glycine uptake.
Influence of glycine on the
damage induced in isolated perfused rat liver by five
hepatotoxic agents.
Deters M, Siegers CP, Strubelt O. Institut fur Toxikologie
der Medizinischen Universitat zu Lubeck, Germany.
Toxicology 1998 Jun 26;128(1):63-72
Livers of fasted rats were perfused over 120 min in
a recirculating hemoglobin-free system. Hepatotoxic
injury induced by the addition of 1-butanol (130.2
mmol/l), CdCl2 (0.1 mmol/l), CuCl2 (0.03 mmol/l),
Na3VO4 (2 mmol/l) or t-butylhydroperoxide (t-BuOOH,
0.5 mmol/l) to the perfusate was shown by strong increases
in lactate dehydrogenase (LDH) and glutamate-pyruvate
transaminase (GPT) release, decreased oxygen consumption
between 50 and 60%, and a nearly complete suppression
of bile flow. Hepatic adenosine triphosphate (ATP)
and reduced glutathione (GSH) concentrations were
reduced by between 30 and 80%, and 20 and 80% respectively.
Only Na3VO4 and t-BuOOH evoked increased releases
of glutamate dehydrogenase (GLDH) in the perfusate.
Malondialdehyde (MDA) concentrations were enhanced
by all toxicants in the perfusate and by all except
1-butanol in the liver. The MDA increase, however,
was much higher after Na3VO4 and t-BuOOH than after
the other toxicants. When glycine (12 mmol/l) was
added 30 min before the toxicants to the perfusate
it prevented the enzyme releases induced by all hepatotoxic
agents by about 80%. Furthermore, glycine prevented
the Na3VO4 induced increase of MDA in liver and perfusate,
the hepatic ATP and GSH level reductions induced by
1-butanol and attenuated the reduction of oxygen consumption
induced by CuCl2 and t-BuOOH. Glycine, however, did
not reverse the reductions of oxygen consumption induced
by CdCl2 and Na3VO4, the suppressions of bile flow
and, with the exception of 1-butanol, the decreases
of hepatic ATP levels induced by all agents.
Glycine facilitates gamma-glutamylcysteinylethyl
ester-mediated increase in liver glutathione level.
Nishida K, Ohta Y, Ishiguro I. Department of Biochemistry,
School of Medicine, Fujita Health University, Aichi,
Japan. knishida@fujita-hu.ac.jp
Eur J Pharmacol 1997 Aug 27;333(2-3):289-92
gamma-Glutamylcysteinylethyl ester (gamma-GCE) increases
reduced glutathione (GSH) levels in GSH-depleted rat
hepatocytes. Because glycine, a constituent of GSH,
exists at 0.3 to 0.4 mM in rat plasma, we examined
the influence of glycine added to the medium on the
action of gamma-GCE to increase GSH levels in the
rat hepatocytes. Glycine (0.2-0.8 mM) dose-dependently
enhanced gamma-GCE-mediated increase in intracellular
GSH levels with an increase in intracellular gamma-GCE
levels. These results indicate that exogenous glycine
facilitates gamma-GCE-mediated increase in intracellular
GSH levels in rat hepatocytes possibly by enhancing
the uptake of gamma-GCE into the cells.
Glycine attenuates Fanconi
syndrome induced by maleate or ifosfamide in rats.
Nissim I, Weinberg JM. Division of Biochemical Development
and Molecular Diseases, Children's Hospital of Philadelphia,
University of Pennsylvania School of Medicine, USA.
Kidney Int 1996 Mar;49(3):684-95
It has become widely recognized that glycine (Gly)
depletion predisposes isolated proximal tubules (PT)
to necrotic cell damage induced by diverse insults
and that Gly replacement in vitro is highly cytoprotective.
However, the effectiveness of supplementation with
Gly in vivo, where blood and tissue Gly normally are
maintained at high levels, is incompletely defined.
Our aim was to assess whether: (a) supplementation
of Gly in drinking water of rats would attenuate the
proximal tubule damage and the Fanconi syndrome (FS)
induced by maleate (Mal), a classical proximal tubule
toxin, or ifosfamide (IFO), an antineoplastic drug;
and (b) to explore the mechanisms responsible for
such effects, since Gly supplementation might be especially
beneficial in treating the FS, where the kidney tends
to waste amino acids. Rats received daily injection
of Mal (2 mmol/kg) for two days without or with oral
supplementation of 2% Gly. IFO, 50 mg/kg, was injected
daily for five days without or with oral Gly. Control
rats were injected with saline, without or with oral
Gly. The results demonstrated that both Mal and IFO
induced a FS characterized by wasting of amino and
organic acids, glucose, and electrolytes, along with
elevated plasma creatinine (Crn) and BUN, and decreased
Crn clearance rate. Light microscopy revealed a necrotic
lesion in the proximal tubules of the Mal group, but
no necrosis after IFO. Gly strongly ameliorated the
severity of renal necrosis and/or dysfunction induced
by Mal or IFO, with significant decreases in total
and fractional excretion of Na+, K+, PO4(3-) and glucose,
decreased plasma BUN and Crn, and increased Crn clearance.
Analysis of freeze-clamped cortical tissue showed
substantial depletion of [Gly], [ATP] and [GSH] along
with increased GSSG in Mal or IFO groups and correction
of [Gly] and [ATP] with Gly supplementation, but no
improvement with Gly of reduced gluthatione [GSH]
or the ratio of reduced to oxidized gluthatione (GSH/GSSG).
31P-NMR analysis of the renal cortex indicated a decrease
in Pi and various membrane phospholipids in Mal and
IFO rats and prevention of this damage with Gly. These
observations demonstrate that oral supplementation
of Gly can provide protection against Mal or IFO-induced
renal tubular cell dysfunction and structural damage.
The lack of effect on glutathione oxidation and depletion
suggests an action distal to toxin uptake and intracellular
interactions, which is similar to the characteristics
of Gly cytoprotection against diverse insults in vitro.
The results also suggest modification by Gly of the
primary toxicity of the agents and effects on phospholipid
synthesis that could contribute to repair.
Protective properties of amino
acids in liver preservation: effects of glycine and
a combination of amino acids on anaerobic metabolism
and energetics.
Churchill TA, Green CJ, Fuller BJ. University Department
of Surgery, Royal Free Hospital & School of Medicine,
London, UK.
J Hepatol 1995 Dec;23(6):720-6
BACKGROUND/AIMS/METHODS: In this study, we investigated
the hepatoprotective effects of three storage solutions
containing glycine (180 mM), glycylglycine (180 mM),
and a mixture of 20 amino acids (combined concentration
of 180 mM) on energy metabolism and levels of glucose
and lactate (as an index of glycolytic flux) in rat
livers. All effects were compared to those of livers
flushed/stored with a modified University of Wisconsin
solution. RESULTS: Glycine-treatment showed no improvement
in liver energetics (ATP, ADP, AMP) and lactate accumulation;
this solution had the lowest buffering capacity of
the four tested (approximately 30% of the University
of Wisconsin solution). The glycylglycine solution
had the highest buffering capacity of the four solutions
tested (including University of Wisconsin solution).
Complete titration of the glycine-, combined amino
acids-, and University of Wisconsin solutions (from
8.0 to pH = 6.0) resulted in a minor decrease in glycylglycine
buffer pH; pH dropped by 0.2 pH units. In glycylglycine-treated
livers, energetics showed an improvement over the
first 1 h cold storage; ATP and 'energy charge' values
remained high and ADP levels (and consequently total
adenylate contents) were 0.7-2.4 micro mol/g greater
than livers stored in University of Wisconsin solution.
A 2-fold increase in lactate accumulation suggested
that the improvement in liver energetics for the glycylglycine
buffer was due to maintained flux through glycolysis
brought about by enhanced buffering capacity. The
solution containing a combination of amino acids exhibited
maximum maintenance of liver energetics via increased
glycolytic flux, despite its slightly inferior buffering
capacity (85% of University of Wisconsin solution).
ATP levels were maintained over the first 2 h storage
and ADP levels (and consequently, total adenylate
contents) were 1.2-2.1 micro mol/g greater than University
of Wisconsin solution-treated livers during the entire
24 h storage period. Energy charge values for livers
treated with the combination of amino acids were also
significantly higher than with glycine-, glycylglycine-
and University of Wisconsin solution-treatment; even
at 24 h, energy charge was 0.36 (comparable to only
4 h storage in University of Wisconsin solution).
CONCLUSIONS: Our data suggest that a combination of
amino acids may be required for maximum protection
of the liver, and furthermore there may be several
independent mechanisms, including buffering capacity,
responsible for cytoprotection of the liver during
cold storage.
Protection by glycine of
proximal tubules from injury due to inhibitors of
mitochondrial ATP production.
Weinberg JM, Davis JA, Abarzua M, Kiani T, Kunkel
R. Department of Internal Medicine, Veterans Administration
Medical Center, Ann Arbor, Michigan.
Am J Physiol 1990 Jun;258(6 Pt 1):C1127-40
We have determined whether glycine or glutathione can
protect rabbit proximal tubules damaged by chemical
inhibitors of oxidative phosphorylation: antimycin
A, rotenone, cyanide, oligomycin, or carbonyl cyanide
m-chlorophenylhdrazone (CCCP). All the agents severely
depleted cell ATP levels within 15 min and caused
lethal cell injury, as quantified by lactate dehydrogenase
(LDH) release. Glycine and glutathione largely prevented
this injury without altering the primary effects of
the inhibitors on tubule respiration or the depletion
of ATP. Buthionine sulfoximine and 1,3-bis(2-chloroethyl)-1-nitrosourea
decreased cell glutathione but did not prevent the
protective effects of either glycine or glutathione
in tubules treated with rotenone. Protection was sustained
during both a 15-min exposure and a 45-min postwash
period irrespective of whether the wash removed the
agent or mitochondrial function recovered. Cysteine
uniquely induced a dramatic recovery of mitochondrial
function in tubules washed after treatment with CCCP.
These data 1) demonstrate that the cytoprotective
effects of glycine previously seen during hypoxia
extend to other tubule lesions characterized by severe
ATP depletion, 2) emphasize the actions of glycine
to preserve cell structural integrity in spite of
sustained severe impairment of ATP-generating processes
in proximal tubules, and 3) indicate that it is glycine
rather than intracellular or extracellular glutathione
which mediates protection.
Relationship between cell
adenosine triphosphate and glutathione content and
protection by glycine against hypoxic proximal tubule
cell injury.
Weinberg JM, Davis JA, Abarzua M, Kiani T. Department
of Internal Medicine, Veterans Administration Medical
Center Ann Arbor, MI.
J Lab Clin Med 1989 May;113(5):612-22
We designed studies to characterize metabolic aspects
of the protective effects of glycine and glutathione
against hypoxic proximal tubule cell injury b clarifying
the relationship between protection and preservation
of tubule cell adenosine triphosphate (ATP) and glutathione
levels. The tubule preparation was glutatione depleted
as isolated although some recovery occurred during
incubation at 37 degrees C, and this recovery was
enhanced by treatment with glutatione precursors.
Increasing the duration of hypoxia from 30 minutes
to 60 minutes produced increasingly extensive lethal
tubule cell injury that was almost completely prevented,
even at the 60-minute duration, by inclusion of either
2 mmol/L glutathione or 2 mmol/L glycine in the tubule
incubation medium. Cell ATP levels decreased to the
same extent and at the same rate in protected and
unprotected hypoxic tubules. Glycine- and glutathione-protected
tubules maintained higher cell glutathione levels
than unprotected tubules at all durations of hypoxia
studied. However, completely eliminating this increment
of glutathione with either the gamma-glutamylcysteine
synthetase inhibitor, buthionine sulfoximine, or the
glutathione reductase inhibitor, 1,3-bis(2-chloroethyl)-1-nitrosourea,
did not prevent protection. The data indicate that
the striking protection against hypoxic injury to
the isolated tubules provided by treatment with glycine
or glutathione is independent of preservation of tubule
cell ATP and glutathione levels, to the extent that
difference of these levels can be discriminated in
intact cells with present methods.
Cytoprotective effects of
glycine and glutathione against hypoxic injury to
renal tubules.
Weinberg JM, Davis JA, Abarzua M, Rajan T. Department
of Internal Medicine, Veterans Administration Medical
Center, Ann Arbor, Michigan.
J Clin Invest 1987 Nov;80(5):1446-54
Roles for both the tripeptide, GSH, and individual
amino acids in modifying the cellular response to
oxygen deprivation-induced injury have been suggested
by prior work in kidney and other tissues, but the
precise interrelationships have not been clearly defined.
We have studied the effects of GSH, its component
amino acids, and related compounds on the behavior
of isolated renal proximal tubules in a well characterized
model of hypoxic injury in vitro. GSH, the combination
of cysteine, glutamate, and glycine and glycine alone,
when present in the medium during 30 min hypoxia,
a duration sufficient to produce extensive irreversible
injury in untreated tubules, were protective. Significant
effects were detected at 0.25 mM concentrations of
the reagents, and protection was nearly complete at
concentrations of 1 mM and above. Glutamate and cysteine
alone were not protective. The exogenous GSH added
to the tubule suspensions was rapidly degraded to
its component amino acids. Treatment of tubules with
GSH or cysteine, but not glycine, increased intracellular
GSH levels. Oxidized GSH was protective. Serine, N-(2-mercaptopropionyl)-glycine,
and a panel of agents known to modify injury produced
by reactive oxygen metabolites were without benefit.
These observations identify a novel and potent action
of glycine to modify the course of hypoxic renal tubular
cell injury. This effect is independent of changes
in cellular GSH metabolism and appears to be unrelated
to alterations of cell thiols or reactive oxygen metabolites.
Further elucidation of its mechanism may provide insight
into both the basic pathophysiology of oxygen deprivation-induced
cell injury and a practical way to ameliorate it.
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