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Regulation of protein turnover by glutamine in
heat-shocked skeletal myotubes
Zhou X, Thompson JR
Department of Animal Science, The University of British
Columbia, Vancouver, Canada.
Biochim Biophys Acta 1997 Jun 27;1357(2):234-42
Skeletal muscle accounts for approximately one-half of the
protein pool in the whole body. Regulation of protein turnover
in skeletal muscle is critical to protein homeostasis in the
whole body. Glutamine has been suggested to exert an anabolic
effect on protein turnover in skeletal muscle. In the present
work, we characterized the effect of glutamine on the rates of
protein synthesis and degradation in cultured rat skeletal
myotubes under both normal and heat-stress conditions. We
found that glutamine has a stimulatory effect on the rate of
protein synthesis in stressed myotubes (21%, P < 0.05) but
not in normal-cultured myotubes. Glutamine shows a
differential effect on the rate of degradation of short-lived
and long-lived proteins. In both normal-cultured and stressed
myotubes, the half-life of short-lived proteins was not
altered while the half-life of long-lived proteins increased
with increasing concentrations of glutamine in a
concentration-dependent manner. In normal-cultured myotubes,
when glutamine concentration increased from 0 to 15 mM, the
half-life of long-lived proteins increased 35% (P < 0.001)
while in stressed myotubes, it increased 27% (P < 0.001).
We also found that glutamine can significantly (P < 0.001)
increase the levels of heat-shock protein 70 (HSP70) in
stressed myotubes, indicating that HSP70 may participate in
the mechanism underlying the effect of glutamine on protein
turnover. We conclude that in cultured skeletal myotubes the
stimulatory effect of glutamine on the rate of protein
synthesis is condition-dependent, and that the inhibitory
effect of glutamine on the rate of protein degradation occurs
only on long-lived proteins.
Effect of glutamine on leucine metabolism in
humans
Hankard RG, Haymond MW, Darmaun D
Nemours Children's Clinic, Jacksonville, Florida 32247,
USA.
Am J Physiol 1996 Oct;271(4 Pt 1):E748-54
The aim of this study was to determine whether the putative
protein anabolic effect of glutamine:
1) is mediated by increased protein synthesis or decreased
protein breakdown and
2) is specific to glutamine.
Seven healthy adults were administered 5-h intravenous
infusions of L-(1-14C)leucine in the postabsorptive state
while receiving in a randomized order an enteral infusion of
saline on one day or L-glutamine (800 micromol . kg-1 . h-1,
equivalent to 0.11 g N/kg) on the other day. Seven additional
subjects were studied using the same protocol except they
received isonitrogenous infusion of glycine. The rates of
leucine appearance (R(a Leu)), an index of protein
degradation, leucine oxidation (Ox(Leu)), and nonoxidative
leucine disposal (NOLD), an index of protein synthesis, were
measured using the 14C specific activity of plasma
alpha-ketoisocaproate and the excretion rate of 14CO2 in
breath. During glutamine infusion, plasma glutamine
concentration doubled (673 plus or minus 66 vs. 1,184 plus or
minus 37 microM, P < 0.05), whereas R(a Leu) did not change
(122 plus or minus 9 vs. 122 plus or minus 7 micromol . kg-1 .
h-1), Ox(Leu) decreased (19 plus or minus 2 vs. 11 plus or
minus 1 micromol kg-1 . h-1, P < 0.01), and NOLD increased
(103 plus or minus 8 vs. 111 plus or minus 6 micromol . kg-1 .
h-1, P < 0.01). During glycine infusion, plasma glycine
increased 14-fold (268 plus or minus 62 vs. 3,806 plus or
minus 546 microM, P < 0.01), but, in contrast to glutamine,
R(a Leu) (124 plus or minus 6 vs. 110 plus or minus 4 micromol
. kg- 1 . h-1, P = 0.02), Ox(Leu) (17 plus or minus 1 vs. 14
plus or minus 1 micromol . kg-1 . h- 1, P = 0.03), and NOLD
(106 plus or minus 5 vs. 96 plus or minus 3 micromol . kg-1 .
h-1, P < 0.65) all decreased. We conclude that glutamine
enteral infusion may exert its protein anabolic effect by
increasing protein synthesis, whereas an isonitrogenous amount
of glycine merely decreases protein turnover with only a small
anabolic effect resulting from a greater decrease in
proteolysis than protein synthesis.
Glutamine metabolism and transport in skeletal
muscle and heart and their clinical relevance
Rennie MJ, Ahmed A, Khogali SE, Low SY, Hundal HS, Taylor
PM
Department of Anatomy and Physiology, University of Dundee,
Scotland, United Kingdom.
J Nutr 1996 Apr;126(4 Suppl):1142S-9S
The glutamine and glutamate transporters in skeletal muscle
and heart appear to play a role in control of the steady-state
concentration of amino acids in the intracellular space and,
in the case of skeletal muscle at least, in the rate of loss
of glutamine to the plasma and to other organs and tissues.
This article reviews what is currently known about transporter
characteristics and mechanisms in skeletal muscle and heart,
the alterations in transport activity in pathophysiological
conditions and the implications for anabolic processes and
cardiac function of altering the availability of glutamine.
The possibilities that glutamine pool size is part of an
osmotic signaling mechanism to regulate whole body protein
metabolism is discussed and evidence is shown from work on
cultured muscle cells. The possible uses of glutamine in
maintaining cardiac function perioperatively and in promoting
glycogen metabolism are discussed.
Inhibition of lipolysis and muscle protein
degradation by EPA in cancer cachexia
Tisdale MJ
Pharmaceutical Sciences Institute, Aston University,
Birmingham, United Kingdom.
Nutrition 1996 Jan;12(1 Suppl):S31-3
Depletion of muscle and adipose tissue in cancer cachexia
appears to arise not only from decreased food intake but also
from the production of catabolic factors by certain tumours.
Experiments with the cachexia-inducing MAC16 tumour in mice
showed that when part of the carbohydrate calories were
replaced by fish oil, host body weight loss was inhibited. The
effect occurred without an alteration of either the total
calorie consumption or nitrogen intake. Instead, one of the
polyunsaturated fatty acids (PUFA) in fish oil,
eicosapentaenoic acid (EPA), was found directly to inhibit
tumour- induced lipolysis. The effect was structurally
specific, as two related PUFA, docosahexaenoic acid (DHA) and
gamma-linolenic acid (GLA), were without effect. The
antilipolytic effect of EPA arose from an inhibition of the
elevation of cyclic AMP in adipocytes in response to the lipid
mobilizing factor. The increased protein degradation in the
skeletal muscle of cachectic animals was also inhibited by
EPA. This effect was due to the inhibition of the rise in
muscle prostaglandin E2 in response to a tumour-produced
proteolytic factor by EPA. Thus, reversal of cachexia by EPA
in this mouse model results from its capacity to interfere
with tumour-produced catabolic factors. Similar factors have
been detected in human cancer cachexia.
Glutamine: From basic science to clinical
applications
Ziegler TR, Szeszycki EE, Estivariz CF, Puckett AB, Leader
LM
Department of Medicine, Emory University School of Medicine,
Atlanta, Georgia, USA.
Nutrition 1996 Nov-Dec;12(11-12 Suppl):S68-70
Glutamine (Gln) has been one of the most intensively
studied nutrients in the field of nutrition support in recent
years. Interest in provision of Gln derives from animal
studies in models of catabolic stress, primarily in rats.
Enteral or parenteral Gln supplementation improved organ
function and/or survival in most of these investigations.
These studies have also supported the concept that Gln is a
critical nutrient for the gut mucosa and immune cells. Recent
molecular and protein chemistry studies are beginning to
define the basic mechanism involved in Gln action in the gut,
liver and other cells and organs. Double-blind prospective
clinical investigations to date suggest that Gln-enriched
parenteral or enteral feedings are generally safe and
effective in catabolic patients. Intravenous Gln (either as
the L-amino acid or as Gln-dipeptides) has been shown to
increase plasma Gln levels, exert protein anabolic effects,
improve gut structure and/or function and reduce important
indices of morbidity, including infection rates and length of
hospital stay in selected patients subgroups. Additional
blinded studies of Gln administration in catabolic patients
and increasing clinical experience with Gln-enriched nutrient
products will determine whether routine Gln supplementation
should be given in nutrition support, and to whom. Taken
together, the data obtained over the past decade or so of
intensive research on Gln nutrition demonstrate that this
amino acid is an important dietary nutrient and is probably
conditionally essential in humans in certain catabolic
conditions.
Glutamine: Effects on the immune system, protein
metabolism and intestinal function
Roth E, Spittler A, Oehler R
Chirurgisches Forschungslaboratorium, Universitatsklinik fur
Chirurgie, Allgemeines Krankenhaus, Wien.
Wien Klin Wochenschr 1996;108(21):669-76
Glutamine is the most abundant free amino acid of the human
body. In catabolic stress situations such as after operations,
trauma and during sepsis the enhanced transport of glutamine
to splanchnic organs and to blood cells results in an
intracellular depletion of glutamine in skeletal muscle.
Glutamine is an important metabolic substrate for cells
cultivated under in vitro conditions and is a precursor for
purines, pyrimidines and phospholipids. Increasing evidence
suggests that glutamine is a crucial substrate for
immunocompetent cells. Glutamine depletion in the cultivation
medium decreases the mitogen-inducible proliferation of
lymphocytes, possibly by arresting the cells in the G0-G1
phase of the cell cycle. Glutamine depletion in lymphocytes
prevents the formation of signals necessary for late
activation. In monocytes glutamine deprivation downregulates
surface antigens responsible for antigen preservation and
phagocytosis. Glutamine is a precursor for the synthesis of
glutathionine and stimulates the formation of heat-shock
proteins. Moreover, there are suggestions that glutamine plays
a crucial role in osmotic regulation of cell volume and causes
phosphorylation of proteins, both of which may stimulate
intracellular protein synthesis. Experimental studies revealed
that glutamine deficiency causes a necrotising enterocolitis
and increases the mortality of animals subjected to bacterial
stress. First clinical studies have demonstrated a decrease in
the incidence of infections and a shortening of the hospital
stay in patients after bone marrow transplantation by
supplementation with glutamine. In critically ill patients
parenteral glutamine reduced nitrogen loss and caused a
reduction of the mortality rate. In surgical patients
glutamine evoked an improvement of several immunological
parameters. Moreover, glutamine exerted a trophic effect on
the intestinal mucosa, decreased the intestinal permeability
and thus may prevent the translocation of bacteria. In
conclusion, glutamine is an important metabolic substrate of
rapidly proliferating cells, influences the cellular hydration
state and has multiple effects on the immune system, on
intestinal function and on protein metabolism. In several
disease states glutamine may consequently, become an in
dispensable nutrient, which should be provided exogenously
during artificial nutrition.
The emerging role of glutamine as an indicator of
exercise stress and overtraining
Rowbottom DG, Keast D, Morton AR
Department of Microbiology, University of Western Australia,
Perth.
Sports Med 1996 Feb;21(2):80-97
Glutamine is an amino acid essential for many important
homeostatic functions and for the optimal functioning of a
number of tissues in the body, particularly the immune system
and the gut. However, during various catabolic states, such as
infection, surgery, trauma and acidosis, glutamine homeostasis
is placed under stress, and glutamine reserves, particularly
in the skeletal muscle, are depleted. With regard to glutamine
metabolism, exercise stress may be viewed in a similar light
to other catabolic stresses. Plasma glutamine responses to
both prolonged and high intensity exercise are characterised
by increased levels during exercise followed by significant
decreases during the post-exercise recovery period, with
several hours of recovery required for restoration of
pre-exercise levels, depending on the intensity and duration
of exercise. If recovery between exercise bouts is inadequate,
the acute effects of exercise on plasma glutamine level may be
cumulative, since overload training has been shown to result
in low plasma glutamine levels requiring prolonged recovery.
Athletes suffering from the overtraining syndrome (OTS) appear
to maintain low plasma glutamine levels for months or years.
All these observations have important implications for organ
functions in these athletes, particularly with regard to the
gut and the cells of the immune system, which may be adversely
affected. In conclusion, if methodological issues are
carefully considered, plasma glutamine level may be useful as
an indicator of an overtrained state.
[The role of glutamine in nutrition in clinical
practice]
Campos FG, Waitzberg DL, Logulo AF, Mucerino DR, Habr-Gama
A
Departamento de Gastroenterologia, Faculdade de Medicina,
Universidade de Sao Paulo
Arq Gastroenterol 1996 Apr-Jun;33(2):86-92
Nutritional therapy using nutrients with pharmacological
properties has been intensively discussed in the recent
literature. Among these nutrients, glutamine has gained
special attention. Glutamine is the most abundant amino acid
in the blood stream of the mammals and, besides it has been
considered a non-essential amino acid, glutamine is a
non-dispensable nutrient in catabolic states. In this
situation, there are alterations in its inter-organic flux,
leading to lower plasmatic concentrations. Glutamine is the
main fuel to enterocytes and it has an important role in the
maintenance of intestinal structure and functions. Moreover,
supplementation with glutamine has proved to be beneficial to
the immunological system functions, improves nitrogen balance
and nutritional parameters in the post-operative period and
lessens protein loss in severe catabolic states. For these
reasons, glutamine enriched-diets must be considered in the
nutritional support of many diseases; new controlled,
prospective and randomized studies will help to define what
group of patients can really benefit from glutamine
supplementation. (47 Refs.)
[The metabolic role of glutamine]
Balzola FA, Boggio-Bertinet D
Dipartimento Sperimentale di Gastroenterologia, Ospedale
Molinette, Torino.
Minerva Gastroenterol Dietol 1996
Mar;42(1):17-26
Glutamine is a non essential amino acid. Nevertheless it
has to be considered a "conditionally essential" amino acid
for several metabolic reactions in which it is involved.
Glutamine is the most abundant amino acid in human plasma and
muscle. Because glutamine is highly unsteady, it was never
used for enteral and parenteral nutrition in the past. It
appears to be a unique amino acid for rapidly proliferating
cells serving as a preferred fuel compared to glucose. It
seems to be essential for cellular replication such as a
"nitrogen carrier" between the tissues. A deficiency state of
glutamine causes morphology and functional changing and
negative nitrogen metabolism. The need for glutamine is
particularly high when metabolism is increased as in the
critically ill (surgical stress, sepsis, inflammatory states,
fasten, burns) especially in the tissues with a rapid cell
turn-over. In these conditions the body requirements of
glutamine appear to exceed the individual's muscle deposits
(muscle is the most important place of synthesis and storage),
causing an increased synthesis with a high energy waste and
loss of muscle mass. Glutamine is essential for bowel mucosa
trophism and its deficiency in all the catabolic states allows
bacterial translocation. In these cases feeding is not
sufficient to restore basal conditions. At present enteral or
parenteral glutamine supplementations are of high interest for
the feeding of critically ill patients. (96 Refs.)
Glutamine and arginine metabolism in tumor-bearing
rats receiving total parenteral nutrition
Yoshida S, Ishibashi N, Noake T, Shirouzu Y, Oka T, Shirouzu
K
First Department of Surgery, School of Medicine, Kurume
University, Fukuoka, Japan.
Metabolism 1997 Apr;46(4):370-3
Arginine supplementation increases glutamine levels in
muscle and plasma. Since glutamine production is increased in
catabolic states, these observations prompted us to
investigate whether the flux of arginine to glutamine was
increased in tumor-bearing (TB) rats, and we measured the
synthesis rate of glutamine from arginine in control versus TB
rats receiving standard total parenteral nutrition (TPN)
solution. Male Donryu rats (N = 36; body weight, 200 to 225 g)
were divided into two groups, control and TB rats. Yoshida
sarcoma cells (1 x 106) were inoculated into the back of the
rats (n = 18) subcutaneously on day 0. The rats were given
free access to water and rat chow. On day 5, all animals,
including non-TB rats (n = 18), were catheterized at the
jugular vein and TPN was begun. On day 10, TPN solution
containing either U-14C-glutamine (2.0 microCi/h) or
U-14C-arginine (2.0 microCi/h) was infused as a 6-hour
constant infusion. At the end of the isotope infusion, plasma
was collected to determine the glutamine production rate in
rats receiving U-14C-glutamine, and the ratio of specific
activity of glutamine to specific activity of arginine was
measured in rats receiving U- 14C-arginine. Only 2 g tumor
caused a decrease in glutamine levels and an increase in
glutamine and arginine production. The low flux rate of
arginine to glutamine was observed in control rats (Arg to
Gln, 41.0 plus or minus 11.9 micromol/kg/h). On the other
hand, TB caused a significant increase in Arg to Gln compared
with the control (213.3 plus or minus 66.1 micromol/kg/h, P
< .01 v control). An increase in the flux rate of Arg to
Gln was associated with an enhancement in the ratio of
specific activity of ornithine to specific activity of
arginine in TB rats (control 51.5% plus or minus 10.9% v 77.4%
plus or minus 8.9%, P < .05). We conclude that (1)
glutamine and arginine metabolism is altered with very small
tumors, (2) although the flux of Arg to Gln was increased in
TB and rats, the small increase in Arg to Gln cannot explain
the observed large increase in Gln production.
Ornithine alpha-ketoglutarate metabolism after
enteral administration in burn patients: Bolus compared with
continuous infusion
Le Bricon T, Coudray-Lucas C, Lioret N, Lim SK, Plassart F,
Schlegel L, De Bandt JP, Saizy R, Giboudeau J, Cynober L
Service de Biochimie A, Hopital St-Antoine, Paris,
France.
Am J Clin Nutr 1997 Feb;65(2):512-8
Ornithine alpha-ketoglutarate (OKG) has been successfully
used as an enteral supplement in the treatment of catabolic
states, including burn injury. However, specific questions
remain unanswered concerning burn patients, including OKG
metabolism and metabolite production, appropriate mode of
administration, and dose. We thus performed a kinetic study
and followed plasma ornithine and OKG metabolite
concentrations on day 7 postburn in 42 (35 men, 7 women)
consecutive burn patients aged 33 plus or minus 2 y with a
mean (plus or minus SEM) total burn surface area (TBSA) of 31
plus or minus 1%. Patients were randomly assigned to receive
OKG as a single bolus (10 g; n = 13) or in the form of a
continuous gastric infusion (10, 20, or 30 g/d over 21 h; n =
13) or an isonitrogenous control (n = 16). Plasma
pharmacokinetics of ornithine followed a one-compartment model
with first-order input (r = 0.993, P < 0.005). OKG was
extensively metabolized in these patients (absorption constant
= 0.028 min-1, elimination half-life = 89 min), with the
production of glutamine, arginine, and proline; proline was
quantitatively the main metabolite (in OKG bolus, area under
the curve (AUC)(0-7h): proline, 41.4 plus or minus 5.6 nmol .
min/L; glutamine, 20.4 plus or minus 5.7 mmol . min/L; and
arginine, 7.3 plus or minus 1.9 mmol . min/L). Proline
production was dose-dependent and quantitatively similar
between modes of OKG administration. Glutamine and arginine
production were not dose-dependent and were higher in the
bolus group than in the infusion group. Overall, the bolus
mode of OKG administration appeared to be associated with
higher metabolite production compared with continuous infusion
in burn patients, especially for glutamine and arginine.
Dietary modulation of amino acid transport in rat
and human liver
Espat NJ, Watkins KT, Lind DS, Weis JK, Copeland EM, Souba
WW
Department of Surgery, University of Florida, Gainesville
32601, USA.
J Surg Res 1996 Jun;63(1):263-8
Specialized diets enriched in the amino acids glutamine and
arginine have been shown to benefit surgical patients. In the
liver, glutamine supports glutathione biosynthesis, arginine
regulates nitric oxide synthesis, and both of these amino
acids serve as precursors for ureagenesis, gluconeogenesis,
and acute phase protein synthesis. The effects of a diet
enriched with glutamine and arginine on hepatic plasma
membrane transport activity have not been studied in humans.
We hypothesized that feeding supradietary amounts of these
nutrients would enhance the activities of the specific
carriers which mediate their transmembrane transport in the
liver. We fed surgical patients (n = 8) and rats (n = 6) one
of three diets: a) a regular diet, b) an enteral liquid diet
containing arginine and glutamine, or c) an enteral diet
supplemented with pharmacologic amounts of glutamine and
arginine. Diets were isocaloric and were administered for 3
days. Hepatic plasma membrane vesicles were prepared from rat
liver and from human wedge biopsies obtained at laparotomy.
The transport of glutamine and arginine by rat and human
vesicles was assayed. Vesicle integrity and functionality were
verified by osmolarity plots, enzyme marker enrichments, and
time courses. Provision of both a standard enteral liquid diet
and one enriched with glutamine and arginine increased the
activities of Systems N (glutamine) and y' (arginine) in rat
and human liver compared to a control diet. The diet
supplemented with glutamine and arginine was the most
effective in increasing transport activity. We conclude that
the liver responds to diets enriched with specific amino acids
by increasing membrane transport activity. This adaptive
response provides essential precursors for hepatocytes which
may enhance hepatic synthetic functions during catabolic
states. This study provides insights into the mechanisms by
which enteral nutrition regulates nutrient transport at the
cellular level and may provide a biochemical rationale for the
use of formulas which are enriched with conditionally
essential nutrients.
The increased synthesis of inducible nitric oxide
inhibits IL-1ra synthesis by human articular chondrocytes:
Possible role in osteoarthritic cartilage degradation
Pelletier JP, Mineau F, Ranger P, Tardif G, Martel-Pelletier
J
Louis-Charles Simard Research Center, Notre-Dame Hospital,
Department of Medicine, University of Montreal, Quebec,
Canada.
Osteoarthritis Cartilage 1996 Mar;4(1):77-84
The degradation of osteoarthritic (OA) cartilage is likely
related to the synthesis and the release of catabolic factors
by chondrocytes. Nitric oxide (NO) has recently been suggested
as playing a role in cartilage degradation. Since NO
production is largely dependent on stimulation by IL-1, its
effects on factors regulating the IL-1 biological activity,
such as IL-1ra, are of the utmost importance. This study
examined and compared the level of NO production by normal and
OA cartilage and chondrocytes, as well as studied the effect
of IL-1-induced NO production on the synthesis and
steady-state mRNA of interleukin-l receptor antagonist
(IL-1ra). The NO baseline production by normal cartilage
explants was undetectable but inducible by rhIL-1beta. OA
cartilage spontaneously produced NO. About a two-fold increase
in NO production was found in OA rhIL-1beta-stimulated
(0.5-100 units/ml) cartilage as compared with the similarly
stimulated normal cartilage. On chondrocytes
rhIL-1beta-stimulation (0.5-100 units/ml) produced a
dose-dependent enhancement of both NO production and IL-1ra
synthesis. Treatment with 200 microM
N(g)-monomethyl-L-arginine (L-NMA), a well known NO synthase
inhibitor, induced over 70% inhibition of the NO production
and a marked increased IL-1ra synthesis (average of 84%) and
expression (mRNA level). Inhibition of prostaglandin synthesis
by indomethacin had no effect on both the NO production or the
IL-1ra level. In the present study, we demonstrated the
capacity of OA cartilage to produce a larger amount of NO than
the normal controls, both in spontaneous and IL-1-stimulated
conditions. These data support the notion that, in vivo, OA
chondrocytes are stimulated by factors, possibly IL-1, which
in turn may induce the expression of NO synthase, thus the
synthesis of NO itself. Importantly, our results showed that
the elevation of NO production may be an important factor in
the pathophysiology of OA since it can reduce IL-1ra synthesis
by chondrocytes. As such, an increased level of IL-1,
associated with a decreased IL-1ra level, may be responsible
for the stimulation of OA chondrocytes by this cytokine,
leading to an enhancement of cartilage matrix degradation.
The role of nitric oxide in proteoglycan turnover
by bovine articular cartilage organ cultures
Stefanovic-Racic M, Morales TI, Taskiran D, McIntyre LA,
Evans CH
Ferguson Laboratory, Department of Orthopedic Surgery,
University of Pittsburgh School of Medicine, PA 15261,
USA.
J Immunol 1996 Feb 1;156(3):1213-20
Monolayer cultures of articular chondrocytes synthesize
large amounts of nitric oxide (NO) following exposure to IL-1.
The latter has antianabolic and procatabolic activities on
these cells, but little is known about the role, if any, of NO
in the integrated metabolic pathways of the chondrocyte. In
the present study, the role of endogenously produced NO in
both the synthesis and degradation of proteoglycans was
investigated for the first time. Bovine articular cartilage
slices exposed to 20 U/ml human rIL-1beta (hrIL-1beta)
synthesized large amounts of NO for 1 to 2 days, after which
production fell to a steady state level similar20% of the peak
value for the remainder of the 14- day incubation. The NO
synthase inhibitor, N-monomethyl L-arginine (L-NMA, 1 mM),
blocked NO production and enhanced the acute catabolic effects
of hrIL- 1beta in cartilage derived from both calves and adult
animals. However, in late cultures, release of proteoglycans
was reduced in the presence of L-NMA. The proteolytic activity
in conditioned medium of these cultures (measured as
caseinolytic activity) was enhanced by L-NMA; however, this
inhibitor did not affect the rates of synthesis of
proteoglycans. Although NO is widely assumed to be a mediator
of cartilage catabolism, our data suggest that it may instead
have an acute protective effect. Whether this effect is
maintained chronically is less clear.
Alanylglutamine-enriched total parenteral nutrition
improves protein metabolism more than branched chain amino
acid-enriched total parenteral nutrition in protracted
peritonitis
Naka S, Saito H, Hashiguchi Y, Lin MT, Furukawa S, Inaba T,
Fukushima R, Wada N, Muto T
Department of Surgery, The University of Tokyo, Japan.
J Trauma 1997 Feb;42(2):183-90
Branched chain amino acids (BCAAs) and glutamine are both
recommended in catabolic states. The object of this study was
to compare the efficacies of alanylglutamine
(Ala-Gln)-enriched and BCAA-enriched total parenteral
nutrition (TPN) on the protein kinetics in peritonitis. Rats
were divided into Ala-Gln and BCAA groups after
intraperitoneal implantation of an osmotic pump, delivering a
continuous infusion of Escherichia coli. Glutamine composed
30.0% (w/v) of the total amino acids in the Ala-Gln group, and
BCAA composed 30.5% (w/v) of the total amino acids in the BCAA
group. The two solutions were isocaloric and isonitrogenous.
Whole body protein turnover and organ fractional protein
synthetic rates (FSR) were measured on days 3 and 5. Serum
amino acid levels and mucosal morphology were determined.
Ala-Gln group had higher rates of whole body protein turnover,
and hepatic FSR on both days. Serum glutamine levels
correlated with hepatic and muscle FSR. Ala-Gln TPN group had
greater mucosal thickness, numbers of mitoses per crypt, and
FSR in distal intestine. Ala-Gln-enriched TPN may be a useful
nutritional treatment modality in sepsis.
The effect of branched-chain amino acid-enriched
parenteral nutrition on gut permeability
McCauley R, Heel KA, Barker PR, Hall J
University Department of Surgery, Royal Perth Hospital,
Australia.
Nutrition 1996 Mar;12(3):176-9
In situations of catabolic stress, the gut becomes atrophic
and has a diminished barrier function as evidenced by an
increased permeability to a variety of molecules. It is known
that the parenteral administration of branched-chain amino
acids (BCAA) reduce gut atrophy. The aim of this study was to
examine the effect of BCAA-enriched solutions of parenteral
nutrients on gut permeability. A secondary aim was to observe
the association between gut permeability and variables that
have been used to assess jejunal atrophy. Central venous lines
were inserted into 30 rats before randomization to receive
nutritional support with: (1) a conventional parenteral
solution (CPN), (2) A 2.0% BCAA-enriched solution (BCAA), or
(3) rat food ad lib (Rat Food). The rats were assessed after 7
d for nutritional status, gut morphology, and gut permeability
ratio (ratio of the permeability to 14C raffinose and 3H
mannitol). We found that rats in the Rat Food Group lost the
least amount of weight, had the least amount of jejunal
atrophy, and had better preservation of harrier function as
determined by gut permeability. When compared with the CPN
Group, the BCAA Group had better preservation of jejunal
morphology and protein content (p < 0.05), but a similar
gut permeability. A cross-correlation matrix demonstrated a
significant negative correlation between permeability to
mannitol and mucosal weight, mucosal protein content and
mucosal DNA content. Branched-chain amino acid-enriched
parenteral nutrition reduced gut atrophy but not the gut
permeability associated with parenteral nutrition. In the
parenterally nourished rat model, atrophy of the jejunum is
associated with increased permeability to small molecules.
Elevated hepatic gamma-glutamylcysteine synthetase
activity and abnormal sulfate levels in liver and muscle
tissue may explain abnormal cysteine and glutathione levels in
SIV-infected rhesus macaques I
Gross A, Hack V, Stahl-Hennig C, Droge W
Department of Immunochemistry, Deutsches
Krebsforschungszentrum, Heidelberg, Germany.
AIDS Res Hum Retroviruses 1996 Nov
20;12(17):1639-41
To establish whether the low cysteine and glutathione
levels in HIV-infected patients and SIV-infected rhesus
macaques may be consequences of an abnormal cysteine
catabolism, we analyzed sulfate and glutathione levels in
macaques. Muscle tissue (m. vastus lateralis and m.
gastrocnemius) of SIV- infected macaques (n = 25) had higher
sulfate and lower glutathione and glutamate levels than that
of uninfected controls (n = 9). Hepatic tissue, in contrast,
showed decreased sulfate and glutathione disulfide (GSSG)
levels, and increased gamma-glutamylcysteine synthetase
(gamma-GCS) activity. These findings suggest drainage of the
cysteine pool by increased cysteine catabolism in skeletal
muscle tissue, and by increased hepatic glutathione
biosynthesis. Cachectic macaques also showed increased urea
levels and decreased glutamine/urea ratios in the liver, which
are obviously related to the abnormal urea excretion and
negative nitrogen balance commonly observed in cachexia. As
urea production and net glutamine synthesis in the liver are
strongly influenced by proton-generating processes, the
abnormal hepatic urea production may be the direct consequence
of the cysteine deficiency and the decreased catabolic
conversion of cysteine into sulfate and protons in the
liver.
Development of an intravenous glutamine supply
through dipeptide technology
Langer K
Department of Research and Development, Pharmacia &
Upjohn, Erlangen, Germany.
Nutrition 1996 Nov-Dec;12(11-12 Suppl):S76-7
Glutamine is considered as semi-essential amino acid during
catabolic stress. Due to its chemical instability in aqueous
solutions during heat sterilization and long term storage, it
could not be added to infusion solutions so far. In contrast,
the dipeptide glycl-L-glutamine exhibits all properties needed
for use as glutamine derivative in parenteral nutrition. It is
freely soluble in water and does not decompose during heat
sterilization. The peptide undergoes rapid enzymatic
hydrolysis after infusion. This results in perfect
utilization. Glycyl-L-glutamine is already produced in large
amounts by chemical synthesis techniques. Both chemical and
optical purity of the dipeptide can be controlled by modem
chromatographic methods. Glamin, a newly developed complete
amino acid solution, contains 20 g of glutamine per liter in
form of glycyl-L-glutamine. Since no additional free glycine
is added, no imbalances are created by the amino-terminal
amino acid of the peptide structure.
Alanyl-glutamine prevents muscle atrophy and
glutamine synthetase induction by glucocorticoids
Hickson RC, Wegrzyn LE, Osborne DF, Karl IE
School of Kinesiology, University of Illinois at Chicago
60608-1516, USA.
Am J Physiol 1996 Nov;271(5 Pt 2):R1165-72
The aims of this work were to establish whether glutamine
infusion via alanyl-glutamine dipeptide provides effective
therapy against muscle atrophy from glucocorticoids and
whether the glucocorticoid induction of glutamine synthetase
(GS) is downregulated by dipeptide supplementation. Rats were
given hydrocortisone 21-acetate or the dosing vehicle and were
infused with alanyl-alanine (AA) or alanyl-glutamine (AG) at
the same concentrations and rates (1.15 micromol . min-1 . 100
g body wt-1, 0.75 ml/h) for 7 days. Compared with AA infusion
in hormone-treated animals, AG infusion prevented total body
and fast-twitch muscle mass losses by over 70%. Glucocorticoid
treatment did not reduce muscle glutamine levels. Higher serum
glutamine was found in the AG-infused (1.72 plus or minus 0.28
micromol/ml) compared with the AA-infused group (1.32 plus or
minus 0.06 micromol/ml), but muscle glutamine concentrations
were not elevated by AG infusion. Following glucocorticoid
injections, GS enzyme activity was increased by two- to
threefold in plantaris, fast-twitch white (superficial
quadriceps), and fast-twitch red (deep quadriceps)
muscle/fiber types of the AA group. Similarly, GS mRNA was
elevated by 3.3- to 4.1-fold in these same muscles of
hormone-treated, AA-infused rats. AG infusion diminished
glucocorticoid effects on GS enzyme activity to 52-65% and on
GS mRNA to 31-37% of the values with AA infusion. These
results provide firsthand evidence of atrophy prevention from
a catabolic state using glutamine in dipeptide form. Despite
higher serum and muscle alanine levels with AA infusion than
with AG infusion, alanine alone is not a sufficient stimulus
to counteract muscle atrophy. The AG-induced muscle sparing is
accompanied by diminished expression of a
glucocorticoid-inducible gene in skeletal muscle. However,
glutamine regulation of GS appears complex and may involve
more regulators than muscle glutamine concentration alone.
Tissue-specific regulation of glutamine synthetase
gene expression in acute pancreatitis is confirmed by using
interleukin-1 receptor knockout mice
Abcouwer SF; Norman J; Fink G; Carter G; Lustig RJ; Souba
WW
Department of Surgery, Massachusetts General Hospital,
Harvard Medical School, Boston 02114, USA.
Surgery (USA), 1996, 120/2 (255-264); discussion
263-4
Background. Acute pancreatitis causes a pronounced
depletion of plasma and muscle glutamine pools. In several
other catabolic disease states expression of the enzyme
glutamine synthetase (GS) is induced in lung and muscle to
support glutamine secretion by these organs. The hormonal
mediators of GS induction have not been conclusively
identified. We used mice deficient for the expression of the
type 1 interleukin-1 receptor (IL-1R1 knockout mice) to
investigate the expression of GS during acute edematous
pancreatitis.
Methods. Acute edematous pancreatitis ways induced in adult
male wild-type and IL-1R1 knockout mice by means of the
intraperitoneal administration of cerulein, and their
conditions were monitored. Five organs, including lung, liver,
gastrocnemius muscle, spleen, and pancreas, were assayed for
relative GS messenger RNA (mRNA) content by Northern
blotting.
Results. The ultimate severity of pancreatitis was reduced
by IL-1R1 deficiency. GS mRNA levels increased during
progression of pancreatitis in lung, spleen, and muscle tissue
from each group. No consistent increase in GS mRNA level was
observed in liver. IL-1R1 deficiency did not affect GS mRNA
expression in lung tissue but consistently retarded GS
induction in the spleens of knockout animals. IL-1R deficiency
altered the kinetics of GS induction in muscle.
Conclusions. Cerulein-induced experimental pancreatitis
causes an induction in GS mRNA levels in a tissue-specific
fashion. IL-1R1 deficiency reduced the ultimate severity of
the condition and altered the induction of GS mRNA in the
spleen and muscle.
Glutamine content of protein and peptide-based
enteral products
Kuhn K.S.; Stehle P.; Furst P.
Biological Chemistry/Nutrition Inst., University of
Hohenheim, Garbenstrasse 30, 70593 Stuttgart Germany
Journal of Parenteral and Enteral Nutrition (USA), 1996, 20/4
(292-295)
Background: Glutamine is a conditionally essential amino
acid for patients with severe catabolic illness, intestinal
dysfunction, or immunodeficiency syndromes. Glutamine is a
natural component in many enteral preparations, yet lacking
methodology hampers its quantitative determination in dietary
products.
Objective: The present study was assigned to assess
glutamine contents in selected enteral products by using a
newly developed method enabling the assessment of
protein/peptide bound glutamine.
Methods: Fourteen commercially available enteral diets (10
protein based and 4 peptide based) were investigated. After
removal of interfering fat and carbohydrates, the nitrogen
content of the purified preparations was determined by
chemiluminescence and protein/peptide bound glutamine was
assessed using a three-step procedure; by using a novel
prehydrolysis derivatization technique with
bis(1,1-trifluoroacetoxy)iodobe nzene, glutamine is converted
to acid stable diaminobutyric acid. The derivatives are
hydrolyzed with a new microwave technology, and subsequently
the amino acid composition is determined by reversed
phase-high-performance liquid chromatography after
dansyl-chloride derivatization.
Results: The content in the protein-based preparations
varied between 5.2 and 8.1 g/16 g nitrogen. In the peptide-
based products, considerably lower glutamine contents were
measured (1.3 to 5.6 g/16 g nitrogen).
Conclusion: In the present study, we report for the first
time glutamine contents in ready to use enteral products. The
dally amount might be satisfactory for healthy individuals but
probably not sufficient for the adequate support of the
stressed patient. Reliable assessment of glutamine in enteral
formulae is a prerequisite to perform clinical studies
investigating glutamine requirements in the catabolic
state.
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