ArticlePDF AvailableLiterature Review

L-Cysteine metabolism and its nutritional implications

Authors:
  • institute of subtropical of agriculture, chinese academy of science

Abstract and Figures

L-Cysteine is a nutritionally semi-essential amino acid and is present mainly in the form of L-cystine in the extracellular space. With the help of a transport system, extracellular L-cystine crosses the plasma membrane and is reduced to L-cysteine within cells by thioredoxin and reduced glutathione (GSH). Intracellular L-cysteine plays an important role in cellular homeostasis not only as a precursor for protein synthesis, but also for the production of GSH, H2 S, and taurine. L-Cysteine-dependent synthesis of GSH has been investigated in many pathological conditions, while the pathway for L-cysteine metabolism to form H2 S has received little attention with regard to prevention and treatment of disease in humans. The main objective of this review is to highlight the metabolic pathways of L-cysteine catabolism to GSH, H2 S, and taurine, with special emphasis on therapeutic and nutritional use of L-cysteine to improve the health and well-being of animals and humans This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.
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Mol. Nutr. Food Res. 2015, 0,113 1
DOI 10.1002/mnfr.201500031
REVIEW
L-Cysteine metabolism and its nutritional implications
Jie Yin1,2, Wenkai Ren1,2 , Guan Yang3, Jielin Duan1,2, Xingguo Huang4, Rejun Fang4,
Chongyong Li1, Tiejun Li1∗∗, Yulong Yin1,5, Yongqing Hou6, Sung Woo Kim7
and Guoyao Wu1,6,8
1Scientific Observing and Experimental Station of Animal Nutrition and Feed Science in South-Central, Ministry of
Agriculture, Hunan Provincial Engineering Research Center of Healthy Livestock, Key Laboratory of
Agro-Ecological Processes in Subtropical Region, Institute of Subtropical Agriculture, Chinese Academy of
Sciences, Changsha, Hunan, China
2University of Chinese Academy of Sciences, Beijing, China
3Department of Animal Science, University of Florida, Gainesville, FL, USA
4Department of Animal Science, Hunan Agriculture University, Changsha, China
5School of Life Sciences, Hunan Normal University, Changsha, China
6Hubei Collaborative Innovation Center for Animal Nutrition and Feed Safety, Wuhan Polytechnic University,
Wuhan, China
7Department of Animal Science, North Carolina State University, Raleigh, NC, USA
8Department of Animal Science, Texas A&M University, College Station, TX, USA
Received: January 16, 2015
Revised: April 8, 2015
Accepted: April 23, 2015
L-Cysteine is a nutritionally semiessential amino acid and is present mainly in the form of
L-cystine in the extracellular space. With the help of a transport system, extracellular L-cystine
crosses the plasma membrane and is reduced to L-cysteine within cells by thioredoxin and
reduced glutathione (GSH). Intracellular L-cysteine plays an important role in cellular home-
ostasis as a precursor for protein synthesis, and for production of GSH, hydrogen sulfide (H2S),
and taurine. L-Cysteine-dependent synthesis of GSH has been investigated in many patholog-
ical conditions, while the pathway for L-cysteine metabolism to form H2S has received little
attention with regard to prevention and treatment of disease in humans. The main objective of
this review is to highlight the metabolic pathways of L-cysteine catabolism to GSH, H2S, and
taurine, with special emphasis on therapeutic and nutritional use of L-cysteine to improve the
health and well-being of animals and humans.
Keywords:
L-Cysteine / GSH / H2S / Nutritional potential / Taurine
1 Introduction
L-Cysteine is a nutritionally semiessential amino acid. Three
sources contribute to L-cysteine in the body: absorption from
diets, the transsulfuration pathway from L-methionine degra-
dation, and breakdown of endogenous proteins. In food and
tissue proteins and in the blood, L-cysteine exists mainly in
the form of L-cystine because L-cysteine is rapidly oxidized
to L-cystine in normoxic conditions. Inside cells, L-cysteine is
Correspondence: Yulong Yin
E-mail: yinyulong@isa.ac.cn
Abbreviations: 3MP, 3-mercaptopyruvate; -Glu-cys,-
glutamylcysteine; CBS, cystathionine -synthase; CDO,cysteine
dioxygenase; CSD, cysteinesulfinate decarboxylase; CSE,cys-
tathionine -lyase; GCL, glutamate cysteine ligase; GS,GSHsyn-
thase; GSH, glutathione; H2S, hydrogen sulfide; PLP, pyridoxal
5-phosphate; Tr x , thioredoxin
the prevailing form due to the highly reducing conditions [1].
Imbalance of extracellular L-cysteine/L-cystine is associated
with oxidative stress and other pathological disorders and
has been reviewed by other researchers [2–4]. Although L-
cysteine and L-cystine metabolism via multiple ways have not
been fully explored in all tissues, results of previous studies
indicate that the balance between extracellular and intracellu-
lar L-cysteine/L-cystine is largely regulated by transportation.
Currently, L-cysteine and L-cystine transport have been shown
to be associated with systems A, ASC, L, Xc,B
o,+,andX
AG
(Fig. 1) [1, 5, 6]. For more specific details of the contribution
of these transport systems, readers are referred to the reviews
by Conrad and Sato [1], Aoyama et al. [7], and Kilberg et al.
[8].
These authors contributed equally to this study.
∗∗Additional corresponding author: Tiejun Li
E-mail: tjli@isa.ac.cn
Colour online: See the article online to view Fig. 1 in colour.
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2J. Yin et al. Mol. Nutr. Food Res. 2015, 0,113
Figure 1. Extracellular and intracellular L-cysteine/L-cystine bal-
ance and L-cysteine/L-cystine transport systems. Glu, L-glutamate;
Cyss, L-cystine; Cys, L-cysteine; GSH, glutathione; Trx, thiore-
doxin.
Efflux of L-cysteine from cells and uptake of L-cystine by
cells improve the intracellular ratio of L-cystine to L-cysteine.
In contrast, uptake of L-cysteine by cells and its oxidation to
L-cystine, and the efflux of L-cystine by cells increase the ex-
tracellular ratio of L-cystine to L-cysteine (Fig. 1). Meanwhile,
in order to satisfy cellular requirements, L-cystine is widely
transported into cells. Intracellular conversion of L-cystine
into L-cysteine has been considered to be a key process to
mediate extracellular L-cysteine/L-cystine redox, as well as the
synthesis of protein and glutathione (GSH) [9]. However, spe-
cific redox systems or enzymes responsible for this reduction
have not been fully identified. Based on the current litera-
ture, at least two related systems are known to catalyze the re-
duction of L-cystine into L-cysteine: thioredoxin-1/thioredoxin
reductase 1 (Trx1/TR1) and glutaredoxin-1/GSH/GSH disul-
fide reductase (Grx1/GSH/GR) [10, 11]. Jones et al. [4] have
modeled reduced (Trx or GSH) or oxidized (reactive oxygen
specious, O2or CySS) redox-related reactions: PrSH +Cys-
tine PrSS-cysteine +L-cysteine (activity “on” or “off”) and
Pr-SS-cysteine +Trx/GSH PrSH +CySSG (the oppo-
site to the reaction above). Such network suggests that Trx
and GSH contribute to intracellular conversion of L-cystine
to L-cysteine and the intracellular reducing status, which has
been further confirmed by other lines of evidence. The redox
states of both Trx1 and GSH/oxidized GSH are more re-
ducing than intracellular L-cysteine/L-cystine redox (–160 to
–125 mV), with Trx1 being maintained in the range of –280
to –270 mV and GSH/oxidized GSH being fluctuated from
–250 mV in rapidly proliferating cells to –200 mV in differ-
entiated cells [3,12,13]. These data reveal the high capacity of
Trx and GSH for L-cystine reduction. The rate of intracellular
conversion of L-cystine to L-cysteine has been estimated to
be approximately 2 M/min in cells with 3 mM GSH and
30 ML-cystine, while the value may be catalytically reached
to about 7 M/min with the help of Grx or Trx [4, 14].
The metabolic pathways of intracellular L-cysteine include
protein synthesis, as well as the generation of GSH (-
glutamyl-cysteinyl-glycine), hydrogen sulfide (H2S), cysteine-
sulfinate, taurine, pyruvate, and inorganic sulfur (Fig. 2) [15].
Figure 2. Intracellular cysteine metabolism. Hcy, homocysteine;
Cysta, cystathionine; Cys, L-cysteine; L-Ser, serine; Cyss, L-cystine;
-Glu-cys, -glutamylcysteine; GSH, glutathione; CSA, cysteine-
sulfinate; CBS, cystathionine -synthase; CSE, cystathionine -
lyase; CDO, cysteine dioxygenase; CSD, cysteinesulfinate decar-
boxylase; 1, GSH/Trx systems; 2, GCL (glutamate cysteine ligase);
3, GS (GSH synthase); 4, aspartate (cysteinesulfinate) aminotrans-
ferase.
L-Cysteine can regulate nutrient metabolism, oxidative stress,
physiologic signaling pathways, and associated diseases via
the production of GSH, H2S, and taurine. This review high-
lights the metabolic pathways of L-cysteine catabolism to
GSH, H2S, and taurine, with special emphasis on therapeutic
and nutritional use of L-cysteine to improve the health and
well-being of animals and humans.
2L-Cysteine/GSH system
Apart from protein synthesis, L-cysteine mainly serves as
a precursor for GSH along with L-glutamate and glycine.
GSH is synthesized de novo in two successive enzymatic
ATP-dependent reactions. First, L-cysteine and L-glutamate
are coupled to form the dipeptide -glutamylcysteine (-Glu-
cys), with the reaction being catalyzed by glutamate cysteine
ligase (GCL). Then, GSH synthase (GS) converts -Glu-cys
and glycine to GSH [16, 17]. However, the main sources of
the GSH precursors have not been quantified. Thus, we
have evaluated the combined coefficients using an orthog-
onal array design in the liver of mice receiving dietary sup-
plementation with L-cysteine, glycine, and L-glutamate (Table
1A). The results showed that supplementation with L-cysteine
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Mol. Nutr. Food Res. 2015, 0,113 3
Ta b l e 1 . Liver GSH concentrations in mice receiving dietary supplementation with L-cysteine, L-glutamate, and glycine for 7 days
A
Groups Dietary supplementation GSH concentration
(mmol/L)a)
L-Cysteine L-Glutamate Glycine
1 0.0% 0.0% 0.0% 5.29 ±1.02
2 0.0% 0.5% 0.5% 3.58 ±1.46
3 0.0% 1.0% 1.0% 3.88 ±1.70
4 0.5% 0.0% 0.5% 5.90 ±0.65
5 0.5% 0.5% 1.0% 4.39 ±1.09
6 0.5% 1.0% 0.0% 6.39 ±0.50
7 1.0% 0.0% 1.0% 5.03 ±1.79
8 1.0% 0.5% 0.0% 4.86 ±1.36
9 1.0% 1.0% 0.5% 4.63 ±1.40
B
SSc) MSd) p-ValueDietary
supplementation
GSH concentration (mmol/L)
0.0%b) 0.5%b) 1.0%b)
L-Cysteine 4.48B5.61A4.81B22.37 6.57 0.002
L-Glutamate 5.47A4.19B4.93AB 23.48 6.90 0.002
Glycine 4.92 4.92 4.90 0.50 0.15 0.864
Values are means ±SD, n=10. Ninety male ICR mice (with an average body weight of 26 g) were randomly divided into one of nine groups
(n=10/group). Mice received dietary supplementation with L-cysteine, L-glutamate, or glycine or their combinations. The composition of
the basal diet was the same as previously reported [108]. At the end of the 7-day supplementation period, liver samples were harvested
and homogenized (1 g tissue in 9 mL saline) for GSH determination using an ELISA kit (Nanjing Jiancheng Bio. Institute, China).
a) Values are expressed as Mean ±SD.
b) Dietary dosage of amino acids.
c) Type II sum of squares.
d) Mean square; orthogonal analysis was subjected to general linear models. Multiple tests were performed using the Tukey’s multiple
comparisons test (IBM SPSS Statistic 20). Means in the same row with different superscripts are different (p<0.05).
and L-glutamate increases hepatic GSH synthesis (Table 1B).
Furthermore, we found that supplementation with an
appropriate dose of L-cysteine improves GSH synthesis, while
excessive dietary L-cysteine reduces liver GSH concentration
(Table 1B).
2.1 GCL
Chen et al. have reported that several factors can affect GSH
synthesis, including the amount of GCL, the availability of
L-cysteine, and the extent of feedback inhibition of GCL by
GSH [16]. Among these factors, GCL is a rate-controlling step
and plays a critical role in L-cysteine metabolism and GSH
synthesis. The eukaryotic GCL consists of a 73-kDa catalytic
subunit (GCLC) and a 31-kDa modifier subunit (GCLM), each
of which is encoded by separate genes and exhibits different
function in -Glu-cys synthesis [18]. GCLC contains binding
sites for L-glutamate, L-cysteine, and ATP and is responsible
for all the catalytic activity of GCL [19]. In contrast, GCLM has
a regulatory function affecting the affinity of the holoenzyme
for glutamate and GSH [20]. Of note, feedback inhibition by
GSH involves reduction of the enzyme and also competition
between GSH and glutamate for the glutamate-binding site
[19, 20]. Currently, two models of GCL activation are widely
cited in the GCL-related literature. The first model holds that
the GCL holoenzyme is predominantly sequestered in the
cytosol as an inactive heterodimer, which can be oxidized
to its activated state by formation of a disulfide bridge be-
tween GCLC and GCLM [18]. The activated GCL holoenzyme
substantially improves the efficiency of -Glu-cys synthesis.
Another model indicates that the active status of GCL de-
pends on a dynamic equilibrium between monomeric and
holoenzyme forms of the enzyme [18]. The shift of GCL to
the high activity pool involves a change in GCLC, such that
an N-terminal GCLC epitope associated with enzyme activity
is protected in extracts with high GCL activity. Likewise, in-
creased formation of high activity heterodimeric complexes
results in a shift to more efficient GSH production [18].
2.2 GS
In eukaryotes, GS is a homodimeric enzyme with two
identical subunits to catalyze the condensation of -Glu-cys
and glycine to form GSH [21]. Currently, GS has received
relatively little attention in GSH biosynthesis, because GCL
is considered to be the rate-limiting step and GS is not
subject to feedback regulation by excessive GSH. However,
we found that dietary supplementation with L-cysteine
showed a dosage-dependent inhibitory effect on GS activity
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4J. Yin et al. Mol. Nutr. Food Res. 2015, 0,113
Figure 3. The response of liver GS activity to dietary L-cysteine in
adult mice. The experimental detail is given in Table 1. Hepatic GS
activity was measured using an ELISA kit (Nanjing Jiancheng Bio.
Institute, China). Results were analyzed by one-way analysis of
variance. Comparison of means was performed using the Tukey’s
multiple test (INM SPSS Statistic 2.0). Values are expressed as
mean ±SD. Means in the same row with different superscripts
are different (p<0.05).
in the liver of mice (Fig. 3), while L-glutamate and glycine
failed to affect GS activity (unpublished data), indicating that
supplementation with an appropriate dose of L-cysteine
maintains a higher GS activity while excessive L-cysteine
inhibits GS activity. Physiological abundance and activity
of GS also play a key role in GSH synthesis and L-cysteine
homoeostasis. For example, decreased GS activity occurs
in response to the depletion of the GSH pool under many
pathological conditions, including surgical trauma [22]. GS
deficiency can lead to the accumulation of -Glu-cys in cells,
and this metabolite is further converted to 5-oxoproline.
5-Oxoproline is associated with severe metabolic acidosis,
hemolytic anemia, and damage to the central nervous system
[23, 24]. In support of this view, increased expression of
GS by all-trans retinoic acid (which has no effect on GCL
abundance) has been shown to enhance GSH synthesis in
myeloid-derived suppressor cells [25].
3L-Cysteine and H2S synthesis
H2S, nitric oxide, and carbon monoxide are the three gaseous
signaling molecules that have received considerable atten-
tion from biological scientists in recent years. These three
gasotransmitters perform a variety of homeostatic functions
[26]. Endogenous H2S is an anti-inflammatory, antioxidant,
and neuroprotective agent. Many diseases, including neuro-
logical diseases, cardiovascular diseases, inflammation, and
metabolic disorders, have been linked to metabolic disorders
of endogenous H2S [27–29]. The therapeutic administration
of H2S donors appears relevant in the treatment of various
diseases. L-Cysteine is the preferred substrate for H2Sgen-
eration and accounts for 70% of the gas produced under
normal conditions [30]. Meanwhile, a novel source of H2S
generation from D-cysteine has been observed in recent years,
and this metabolic pathway has been considered to be more
effective than L-cysteine in neuroprotection against oxidative
stress and ischemia-reperfusion injury [31].
3.1 H2S production from L-cysteine
L-Cysteine-mediated generation of endogenous H2Siscat-
alyzed by two pyridoxal 5-phosphate (PLP) dependent en-
zyme systems, including cystathionine -synthase (CBS)
and cystathionine -lyase (CSE) and PLP-independent mer-
captopyruvate sulfurtransferase (MST) along with L-cysteine
aminotransferase [32, 33]. CBS mainly catalyzes the -
replacement of the hydroxyl group of serine with homocys-
teine and then forms cystathionine with the release of H2O
[34]. L-Cysteine is structurally similar to serine with an OH
group replaced by an SH. Thus, CBS can also use L-cysteine
as a substrate to form cystathionine with the release of H2S
under pathological situations involving oxidative injury [34].
CBS has been demonstrated to be a major contributor for
the production of H2S. It is a highly regulated enzyme. S-
adenosylmethionine serves as its allosteric activator and plays
an important role in regulating its activity and concentration
[35]. Stipanuk et al. [32] reported that an increase in CBS activ-
ity by supplementation with S-adenosylmethionine markedly
promotes H2S production by about 50% in both liver and
kidney [32], while addition of amino-oxyacetate, a CBS in-
hibitor, blocks H2S production and deteriorates oxidative in-
jury [36]. Consequently, CBS knockout mice exhibit severe
accumulation of homocysteine, as well as an inhibition of the
-replacement reactions involving both serine and L-cysteine
[34].
However, Shibuya et al. [37] reported that brain ho-
mogenates of CBS knockout mice, even in the absence of
PLP, produced H2S at levels similar to those of wild-type
mice, suggesting the presence of another H2S-producing en-
zyme. Indeed, CSE has been reported to be the major al-
ternative reaction for H2S production. In addition to cat-
alyzing the catabolism of cystathionine to form L-cysteine,
CSE can directly facilitate the conversion of L-cysteine into
L-serine and H2Svia,elimination [34, 38]. Furthermore,
CSE participates in the disulfide elimination reaction to pro-
duce pyruvate, ammonia, and thiocysteine. Thiocysteine re-
acts with a thiol group in such substances as L-cysteine to
generate H2S [34]. Previous reports have estimated that CSE
contributes to about 70% of the total H2S generation under
the normal conditions [38]. Treatment with propargylglycine,
a CSE inhibitor, significantly suppresses sulfur anion pro-
duction and L-cysteine metabolism by about 50% in rat renal
cortical tubules [39]. The H2S-producing activity of CSE is
negatively regulated by cellular Ca2+concentration. CSE effi-
ciently produces H2S at steady-state low Ca2+concentrations,
but this reaction is suppressed at high Ca2+concentrations
in the presence of PLP [40]. Thus, physiological calcium lev-
els may control CSE-mediated H2S formation. Emerging ev-
idence has shown that a genetic deficiency of CSE results
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Mol. Nutr. Food Res. 2015, 0,113 5
in marked reductions in H2S concentrations in the serum,
heart, aorta, and other tissues in mice [41], leading to ex-
acerbated myocardial ischemia/reperfusion injury, impaired
cardiac mitochondrial function, and oxidative stress [42, 43].
Upregulation of the CSE/H2S pathway provides various ther-
apeutic avenues, including rescuing impaired arteriogenesis
in mouse hind limb ischemia [44], improving TNF-induced
insulin resistance associated with obesity and type 2 diabetes
[45], and modulating central neurotransmitter input [46].
In the MST-mediated pathway for H2S genera-
tion, L-cysteine firstly undergoes transamination with a-
ketoglutarate to form 3-mercaptopyruvate (3MP). CAT (a PLP-
dependent enzyme) is responsible for this reaction [47]. 3MP
is then covalently linked via a disulfide bond to the active-site
cysteine residue of MST to generate H2S [37, 48]. MST also
produces H2S form thiosulfate, and several reducing sub-
stances, such as Trx and dihydrolipoic acid, are likely to be
the major physiological persulfide acceptors and can facili-
tate H2S release from MST [49,50]. The MST/H2S pathway is
susceptible to oxidative stress, and treatment of H2O2inhibits
MST activity and interferes with the positive bioenergetic role
of the 3MP/MST/H2S pathway in vitro [51]. The MST/H2S
pathway may also be involved in the regulation of respiration
and protection in cells [52].
Although the contribution of MST versus the other two
H2S generators, CBS and CSE, has been difficult to evaluate
because of varied reaction conditions, we may make con-
clusions that the CBS-mediated H2S production mainly oc-
curs under pathological conditions involving oxidative stress,
while the CSE-catalyzed H2S formation largely contributes to
normal H2S metabolism. CBS and CSE are more likely to be
potential therapeutic targets than MST for H2Sproductionas
MST may not be responsible for the increased production of
H2S in various conditions [53].
3.2 H2S production from D-cysteine
More recently, Shibuya et al. [31, 33] found an additional
biosynthetic pathway for the production of H2SfromD-
cysteine involving MST and D-amino acid oxidase (DAO). D-
cysteine is derived from L-cysteine in food via racemization by
heat and alkaline treatment during food processing [54]. The
pathway for producing H2SfromD-cysteine is different from
that from L-cysteine. The differences include the optimal pH,
the dependency on PLP, and the stability against the freezing-
thawing procedure [33]. Unlike the L-cysteine/H2S pathway,
in which the responsible enzymes are expressed in many tis-
sues [32, 55, 56], D-cysteine-mediated H2S generation occurs
predominantly in the cerebellum and the kidney, as D-amino
acid oxidase is mainly expressed in astrocytes, glia, and sev-
eral types of neurons including the Golgi and Purkinje cells
[31, 57]. Furthermore, there are no enzymes associated with
D-cysteine metabolism, and D-cysteine has been widely hy-
pothesized to produce H2S directly via chemical degradation.
4 Hypotaurine and taurine
Several reports have indicated that an increase in L-cysteine
availability as a result of the consumption of a sulfur amino
acid rich diet can rapidly activates L-cysteine dioxygenase
(CDO) [58], which catalyzes the oxidation of the L-cysteine
thiol group to form cysteinesulfinate, which is also called cys-
teine sulfinic acid or 3-sulfinoalanine [34]. Cysteinesulfinate
is a major precursor of taurine, and this metabolic pathway
is involved in the decarboxylation and oxidation of cysteine-
sulfinate by cysteinesulfinate decarboxylase (CSD; Fig. 2).
4.1 CDO-mediated taurine formation
CDO is a highly regulated enzyme and widely expressed
in hepatocytes, adipocytes, exocrine cells, goblet cells, and
tubular epithelial [34]. Under conditions of a low intracellu-
lar concentration of L-cysteine, CDO activity is blocked via
ubiquitination by 26S proteasome [59], while elevated levels
of L-cysteine can rapidly increase hepatic or adipocyte CDO
activity by up to 45- or tenfold, respectively [34]. For example,
CDO activity increased with an increase in dietary protein
levels, and the higher enzyme activity was paralleled by a
greater rate of the production of taurine plus hypotaurine
plus sulfate from L-cysteine [60]. Thus, CDO may serve as a
major regulatory factor in intracellular L-cysteine levels and
taurine formation. Previous studies with cell culture systems
have shown that L-cysteine deprivation induces CDO ubiq-
uitination, while addition of lactacystin or proteasome in-
hibitor 1 (PS1, N-carboxybenzyl-IleGlu[OtBu]AlaLeu-CHO),
the 26S proteasome inhibitor, markedly blocks intracellular
CDO degradation in L-cysteine-deficient cells [34, 61]. Stud-
ies in vivo have further indicated the switch of CDO activity
in response to changes in intracellular L-cysteine levels. For
example, feeding a L-cysteine-rich diet (100 g casein +8.1 g
L-cysteine/kg) or a high protein diet (400 g casein) resulted in
a significant increase in hepatic CDO concentrations and a
decrease in ubiquitinated forms of the CDO pool. Addition-
ally, inhibition of 26S proteasome by PS1 stabilized hepatic
CDO in rats fed a low protein diet [59,62,63]. Metabolic anal-
ysis has indicated that the increased CDO activity promotes
L-cysteine metabolism toward hypotaurine and taurine pro-
duction in that hepatic hypotaurine level was about 37 nmol/g
in rats fed a low protein diet, but increased to 680 nmol/g at
3.5 h after the injection with PS1 [61]. Furthermore, primary
hepatocytes from mice lacking CDO showed increases in L-
cysteine concentrations and higher rates of metabolism of
L-cysteine to H2S and thiosulfate [64]. Thus, CDO sensitively
responds to a high intracellular concentration of L-cysteine
and plays an important role in the production of hypotaurine
and taurine.
Previous studies have extensively addressed the role of
CDO in L-cysteine metabolism and other neurological disor-
ders [64–66], but the regulatory mechanism for the effect of
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6J. Yin et al. Mol. Nutr. Food Res. 2015, 0,113
Ta b l e 2 . Summary of effects of dietary cysteine or its precursors in different pathological conditions
Risk factor Supplementary
conditions
Response Reference
HIV infection L-Cysteine and
L-glutamine or glycine
Taurine and GSH levels , insulin sensitivity[83, 109]
Aging L-Cysteine and glycine;
N-acetylcysteine
GSH levels , oxidative stress , proinflammatory state[110, 111]
Type-2 diabetes L-Cysteine or
N-acetylcysteine
GSH levels ; the insulin-dependent signaling cascades
of glucose metabolism; blood glucose, glycated
hemoglobin, NF-kappaB activation
[112–115]
Cardiovascular
disease
N-acetylcysteine Proinflammatory cytokines, antioxidative capacity,
energy metabolism
[116]
Inflammatory bowel
disease
L-Cysteine Proinflammatory cytokines, apoptosis[117]
Nonalcoholic
steatohepatitis
patients
L-Cysteine-rich whey
protein
GSH levels , hepatic macrovesicular steatosis[118]
Smoking N-acetylcysteine GSH levels [119]
Alzheimer’s disease N-acetylcysteine Cognitive functioning, AD neuropathology[120]
L-methionine
deficiency
L-Cysteine Plasma homocysteine concentration[121]
Gastric cancer S-propargyl-cysteine H2S production, tumor weights, and tumor volumes[122]
, increase; , decrease.
L-cysteine on CDO ubiquitination has not been fully explored.
Stipanuk’s group has investigated a substrate turnover de-
pendent formation of a thioether cross-link between the sul-
fur of residue Cys93 and the aromatic side chain of residue
Tyr157 in CDO [34]. Their results indicated that the imma-
ture CDO and inactive mutant forms of CDO fail to form
any cross-link and exhibit low enzymatic activity and that a
high catalytic efficiency can be achieved by the formation of
Cys-Tyr cofactors. More recently, Goldberg’s and Gao’s group
have reported structural and functional models for the active
site of CDO [66, 67]. Formation of a CDO-Cys-Tyr cross-link
requires a transition metal cofactor (ferrous iron [Fe2+]and
oxygen [O2]). It is speculated that the valence change of the
Fe center makes the Cys-bound complexes effectively catalyze
the oxidation of L-cysteine, as the ferric-superoxo species is an
active oxidant and exhibits high reactivity in such a reaction.
4.2 CSD-mediated taurine formation
The cysteinesulfinate produced by CDO can be further metab-
olized by CSD to hypotaurine, which is subsequently oxidized
to taurine. Transamination is another metabolic pathway for
cysteinesulfinate to form pyruvate and sulfite by aspartate
(cysteinesulfinate) aminotransferase. A previous report has
estimated that 66 and 34% cysteinesulfinate participates in
taurine and sulfite production, respectively [34]. The preferred
metabolic pathway of cysteinesulfinate is likely dependent on
the abundance of the enzymes and their affinities for their
substrates. Although there is little information about intra-
cellular concentrations of the enzymes, compelling evidence
has shown that high levels of CSD in liver and adipose tissue
contributes to a higher capacity for taurine synthesis [68,69].
Studies on kinetics of these enzymes have revealed that CSD
has a higher affinity for cysteinesulfinate as the Kmin taurine
synthesis for cysteinesulfinate is 0.04 – 0.17 mM, while the
value is 3 – 25 mM for aspartate aminotransferase [34].
However, the L-cysteine/taurine pathway can be limited at
high protein levels due to the decrease in CSD activity such
that sulfate production from cysteinesulfinate is favored [60].
5 Nutritional use of L-cysteine
The balance between L-cysteine and L-cystine plays a vital
role in controlling redox potential, synthesis of other active
substrates (i.e., GSH, H2S, and taurine), oxidative stress,
and inflammatory response [3, 4, 70]. Dietary intake of
sulfur amino acids affects cell signaling via modulating
intracellular concentrations of L-cysteine and L-cystine, as
well as L-cysteine/L-cystine redox state in the postprandial
period [71]. Thus, recent years have witnessed growing
interest in the use of L-cysteine for improving health in
animals and humans (Table 2).
5.1 Oxidative stress
We found that various kinds of stress can lead to oxida-
tive injury in animals [72–74]. Additionally, oxidative stress
is thought to be involved in the development of many
diseases or may exacerbate their symptoms [75]. GSH is
the most abundant cellular thiol antioxidant and plays a
C2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.mnf-journal.com
Mol. Nutr. Food Res. 2015, 0,113 7
protective role against toxicity arising from excessive amounts
of endogenous and exogenous electrophiles [16] via scaveng-
ing hydroxyl radical and superoxide directly, and serving as
a cofactor for the enzyme GSH peroxidase (GPx) in me-
tabolizing H2O2and lipid peroxides. Thus, current reports
mainly focused on the positive effects of L-cysteine in dif-
ferent pathological conditions via increasing GSH synthesis
and suppressing oxidative stress or inflammatory response,
while these reports failed to recognize other beneficial effects
of dietary L-cysteine in the production of H2S and taurine.
Increases in endogenous H2S generation by CBS and CSE
contribute to some pathological conditions [76]. Lu et al. [36]
also demonstrated that H2S has potential therapeutic value
for oxidative stress-induced brain damage via a mechanism
involving enhanced L-glutamate uptake. Oxidative stress can
impact the function of L-glutamate transporters [77] and result
in L-glutamate accumulation in the synaptic cleft, which fur-
ther leads to toxicity and neural injury via overactivation of re-
lated receptors. Thus, dysfunction of L-glutamate transporters
is commonly associated with neurodegenerative diseases and
some acute brain injuries [78]. In addition, L-glutamate is an
inhibitor of the Xcsystem, which transports one molecule
of L-cystine into cells and, therefore, releases one molecule of
glutamate into the extracellular space [1]. The excessive extra-
cellular glutamate plays a feedback inhibitory role in L-cystine
influx and, therefore, L-glutamate neurotoxicity is primarily
characterized by the depletion of cellular GSH [79]. In vitro
studies have reported that addition of NaHS (an H2S donor)
reverses H2O2-impaired L-glutamate transport and enhances
GSH production [36]. This pathway may be another important
factor contributing to the pathogenesis of brain and neural
diseases.
Taurine is an organic osmolyte involved in modulation of
intracellular free calcium concentration and has been con-
sidered as one of the most essential substances in the body
due to: (i) its broad distribution, cytoprotective effects, an-
tioxidative properties; (ii) its role in regulating intracellular
Ca2+concentration, movement of ions and neurotransmit-
ters, proinflammatory response; and (iii) its functional sig-
nificance in cell development, nutrition, and survival [80,81].
Recently, several reports have shown that taurine serves as
a protective agent against several environmental toxins and
drug-induced organ dysfunction and diabetes [82]. Thus, an
increase in the conversion of L-cysteine to taurine provides
a novel insight into L-cysteine nutrition and its therapeutic
potential. For example, dietary N-acetylcysteine (a stable and
water-soluble precursor of L-cysteine) significantly increased
the plasma levels of taurine and GSH in patients with the
human immunodeficiency virus (HIV) [83].
5.2 Gut function
Gut plays important roles in secretions, food digestion, nu-
trient absorption and metabolism, and cross-talk with the in-
testinal microbiota. Gut mucosal proteins and mucins, which
contribute to intestinal integrity, are rich in L-cysteine [84].
Compelling evidence from in vivo studies has shown that
L-cysteine plays key roles in maintaining intestinal struc-
ture and function [84, 85]. Bauchart-Thevret et al. [86] eval-
uated first-pass splanchnic metabolism of dietary L-cysteine
in weanling pigs and found that gastrointestinal tract utilizes
25% of the dietary L-cysteine intake and that synthesis of
mucosal epithelial proteins, such as GSH and mucins, is a
major nonoxidative metabolic fate for L-cysteine. Thus, we can
speculate that L-cysteine deficiency contributes significantly
to the intestinal mucosal atrophy and reduced secretion of
mucins [84]. Furthermore, Badaloo et al. [84] reported that
children with malnutrition exhibited gut mucosal atrophy
and depletion of mucins, produced less L-cysteine, and had
a greater requirement for dietary L-cysteine during early and
mid-nutritional rehabilitation. Thus, L-cysteine serves as an
essential substrate for maintaining gut function.
5.3 Lipid metabolism
Dietary supplementation with L-cysteine can improve lipid
metabolism. Elshorbagy et al. [87] reported that total L-
cysteine concentration in serum was positively correlated
with fat mass. Indeed, the correlation was stronger with to-
tal L-cysteine than with serum lipids such as triglycerides
[87]. Triglycerides are formed by combining glycerol with
three fatty acid molecules and play a critical role in lipid
metabolic network as energy sources and transporters of di-
etary fat. In humans and animals, high plasma concentrations
of triglycerides are associated with various diseases, including
atherosclerosis, heart disease, and stroke [88]. Lee et al. [89]
reported that L-cysteine effectively reduces triglyceride con-
centrations in serum and liver in a dose-dependent manner
in rats fed a normal diet [89]. The derivatives of L-cysteine also
regulate lipid metabolism. For example, S-methyl L-cysteine, a
hydrophilic L-cysteine-containing compound, exhibits hypo-
glycemic and antihyperlipidemic properties through reduc-
tion in fasting plasma levels of glucose, total cholesterol,
triglycerides, LDL cholesterol in fructose-induced diabetic
rats [90]. N-acetylcysteine also has been demonstrated to im-
prove lipid metabolism through affecting serum cholesterol,
triglycerides, VLDL, and HDL levels [91]. Although little is
known about the underlying mechanisms, some reports in-
dicate (i) supplementation with L-cysteine targets at gene ex-
pression of the sterol response element-binding protein, fatty
acid synthase, and stearoryl-coenzymeA desaturase-1 [92]; (ii)
reduced oxidation of L-cysteine to form taurine leads to a defi-
ciency of taurine [87,93] and abnormal lipid metabolism [94].
5.4 Growth
Previous reports have indicated that dietary supplementation
with L-cysteine affects animal growth performance, including
food intake, body weight gain, and feed efficiency. However,
the effect of L-cysteine on growth performance is not always
C2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.mnf-journal.com
8J. Yin et al. Mol. Nutr. Food Res. 2015, 0,113
Ta b l e 3 . Effects of dietary L-cysteine on growth performance in
rats
Health status Dosage Weight
gain
Food
intake
Reference
Healthy 1–2% diet ↓↓[89]
Healthy 1–4 mmol/kg - [95]
Aging 6.8 g/kg N [123]
Sucrose
stress
5.5–16 g/kg N N [115]
Diabetes 1 mg/kg N - [114]
L-methionine-
restricted
diet
0.5% N [124]
N, no effect; , increase; , decrease.
detected depending on experimental design (Table 3). Mc-
Gavigan et al. [95] reported that a low dosage of L-cysteine
(oral gavage: 4 mmol/kg) is more anorectic than L-arginine
and L-lysine [95], high dosages of which can inhibit feed in-
take [96]. Lee et al. [89] further investigated the anorectic effect
of L-cysteine and found that dietary supplementation with L-
cysteine effectively reduces final body weight, body weight
gain, food intake, and feed efficiency in rats [89]. We noted
that animals in these studies were either aging ones or in a
catabolic state, while an anorectic effect appeared in young
and healthy animals (Table 3). Collectively, these studies sug-
gest that the anorectic effect of L-cysteine depends on the
health status, nutritional level, and age of the animals. Un-
der normal conditions, supplementation with L-cysteine may
reduce feed intake and weight gain in young animals.
L-Cysteine confers a bitter taste, which can contribute to
its inhibitory effect on feed intake [89, 97]. This explanation
is not convincing, as a latest report showed that intraperi-
toneal administration of 2 mmol/kg also reduces feed intake
in rats [95]. McGavigan et al. [96] further investigated the
mechanism for L-cysteine to reduce feed intake and found
that L-cysteine activates promiscuous amino acid sensing re-
ceptors, such as T1R1/T1R3, CaSR, and GPRC6A [96]. How-
ever, these receptors may not mediate the effects of L-cysteine
on appetite, as other amino acids (i.e., L-serine, L-threonine,
and L-histidine) also induce a strong T1R1/T1R3-, CaSR-,
and GPRC6A-mediated response [98] but do not inhibit food
intake or growth performance of the animals [95]. More re-
cently, acyl ghrelin has been suggested to play a decisive role
in L-cysteine-mediated appetite stimulation, as a reduction
in the circulating level of acyl ghrelin occurred in both ro-
dents and humans receiving dietary supplementation with
L-cysteine [95]. Meanwhile, the anorectic effect of L-cysteine
is attenuated in transgenic mice overexpressing ghrelin [95].
5.5 Effects of supplemental L-methionine as a
L-cysteine precursor
L-methionine is the physiological precursor of endogenous
L-cysteine [99]. Thus, the metabolism and availability of
L-methionine can affect the nutritional efficacy of dietary L-
cysteine in animals [100, 101]. L-methionine can replace L-
cysteine in diets to maintain normal protein synthesis and
normal growth in animals, but not vice versa [102]. However,
L-cysteine can spare L-methionine in animals. Thus, supple-
menting L-cysteine to a L-methionine-restricted diet reverses
the adverse effects of L-methionine deficiency [103, 104]. Sev-
eral studies have concluded that when the diet contains both
L-methionine and L-cysteine, the mean requirements of L-
methionine and L-cysteine by infants are 38 and 91 mg
kg1day1L-cysteine, respectively [106]. The values for adult
men are 12.6 and 21 mg kg1day1for L-methionine and
L-cysteine, respectively [102].
The ability of dietary L-methionine to supply endogenous
L-cysteine has been studied in edematous severe acute malnu-
trition. In this case, L-methionine supplementation increases
L-cysteine production but has no effect on GSH synthesis
[105]. One explanation is that the conversion of L-methionine
to L-cysteine in the liver is insufficient for sustaining GSH
production. This necessitates dietary supplementation with
L-cysteine to partially fulfill the demand for this amino acid in
edematous severe acute malnutrition [105]. Effects of dietary
supplementation with L-cysteine or its precursors on animals
under different pathological conditions [106–124] are sum-
marized in Tables 2 and 3. Taken together, these findings
indicate that direct provision of L-cysteine in diets is required
under conditions of impaired L-methionine catabolism so as
to maintain whole-body protein synthesis and physiological
homeostasis.
6 Conclusion and perspectives
L-Cysteine is not only a building block of protein, but is also
a regulator of cell signaling pathways. Therefore, L-cysteine
is now classified as a functional amino acid in nutrition
[125]. There is a complex relationship between L-methionine
and L-cysteine in their metabolism and nutrition such that
dietary L-methionine is not always effective in supplying
endogenous L-cysteine [126]. Under certain conditions when
the absorption or catabolism of L-methionine is impaired, it
is necessary to include L-cysteine in diets so as to maintain
adequate protein synthesis in tissues and whole-body
physiological homeostasis [127, 128]. Dietary L-cysteine sup-
plementation can increase the synthesis of GSH, H2S, and
taurine in animals and humans [126–129]. However, the use
of L-cysteine supplementation as a nutritional intervention of
disease is limited. Emerging evidence shows a positive role
of L-cysteine-rich meals in several pathological conditions, in-
cluding oxidative stress, HIV infection, aging, type-2 diabetes,
and neurodegenerative diseases. In addition, dietary supple-
mentation with L-cysteine or its precursor N-acetyl-cysteine
can improve gut function, growth, and health [128–132].
Future research should focus on: (i) optimal requirements of
L-cysteine by animals and humans fed enteral or parenteral
diets, (ii) nutritional regulation of GSH, H2S, and taurine
C2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.mnf-journal.com
Mol. Nutr. Food Res. 2015, 0,113 9
synthesis in a cell- and tissue-specific manner, and (iii)
roles of these metabolites to treat and prevent metabolic
disorders. Additionally, caution must be exercised to avoid
high dosages of L-cysteine supplementation in animals and
humans, because L-cysteine exerts an N-methyl-D-aspartate
receptor-mediated excitatory effect in the nervous system. A
previous study indicated that a toxic dosage of intravenous ad-
ministration of L-cysteine for 28 days was 1 g/kg body weight
per day in adult male rats [107]. A toxic dosage of oral admin-
istration of L-cysteine remains to be determined for animals.
This study was supported by the National Natural Science
Foundation of China (nos. 31272463, 31372319, 31402084,
31330075, 31110103909), Hunan Provincial Natural Sci-
ence Foundation of China (no. 12JJ2014), the Hubei Provin-
cial Key Project for Scientific and Technical Innovation (no.
2014ABA022), the Hubei Hundred Talent Program, and Texas
A&M AgriLife Research (H-8200).
The authors have declared no conflict of interest.
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... Cysteine is a nutritionally semi-essential amino acid present mainly in the form of L-Cys in the extracellular space 15 . The balance between L-Cys and L-cystine plays a vital role in controlling redox potential, synthesis of other active substrates (GSH, H2S, and taurine), oxidative stress, and inflammatory response 16 . ...
... Increased ammonia in the body is toxic and may lead to brain malfunction and coma. Brain has a high capacity for active transport of neutral, dibasic, and dicarboxylic amino acids, e.g., elevation of phenylalanine or leucine, isoleucine and valine results in increased uptake of these amino acids into the brain, altering brain function leading to a variety of neurological problems such as impaired brain development and altered behavior and mental function 15 . Therefore, overconsumption of these selected prepared diets may results in neurological issues in the study area later in life. ...
... Therefore, overconsumption of these selected prepared diets may results in neurological issues in the study area later in life. However, the increased uptake of some amino acids such as tryptophan and tyrosine by the brain is particularly important because these amino acids act as precursors for a variety of hormones and/or neurotransmitters or modulators of nerve function (e.g., melatonin, serotonin, and dopamine) 15 . ...
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Background and aims: Amino acids composition of local and regional dietary proteins determines the protein quality. The study was aimed at evaluating amino acid profiles of some selected traditional diets commonly consumed in Jigawa (JG), Kano (KN) and Katsina (KT) States, Northwest Zone-Nigeria. Methods: The selected prepared diets (four per state) include; JG Tuwon masara using white maize served with Kuka soup (JG TMW SWKS), JG Tuwon masara using yellow maize served with Kuka soup (JG TMY SWKS), JG Danwake served with groundnut oil and pepper (JG Danwake SWGOP), JG Moimoi, KN Tuwon masara using white maize served with Kuka soup (KN TMW SWKS), KN Tuwon masara using yellow maize served with Kuka soup (KN TMY SWKS), KN rice and beans served with groundnut oil and pepper (KN Rice and Beans SWGOP), KN Danwake served with groundnut oil and pepper (KN Danwake SWGOP), KT Tuwon masara using white maize served with Kuka soup (KT TMW SWKS), KT Tuwon masara using yellow maize served with Kuka soup (KT TMY SWKS), KT Danwake served with groundnut oil and pepper (KT Danwake SWGOP) and KT Dambu. The preparations were dried and grounded into powdered form and analyzed using standard methods. Results: The amino acid profile of the diets consumed in the three states show higher content of total non-essential amino acids (NEAA) compared with essential amino acids (EAA). The amino acid score of the prepared diets though higher than the standard amino acid score by WHO/FAO/UNU (2007), may support the normal growth of all age groups except lysine. The limiting amino acid score was found to be either lysine or SAA (cysteine + methionine) in all the 3 states’ diets. Histidine was found to have the highest score in all the diets except in JG Moimoi and KN Danwake served with groundnut oil and pepper (SWGOP) respectively. The low levels of lysine and SAA in some of the diets may be due to low contents of these amino acids in the ingredients used. Conclusion: This study showed that, the amino acid score of the prepared diets though higher than the standard amino acid score established by WHO/FAO/UNU may support the normal growth of infants, children as well as adults except lysine. Keywords: traditional diets, amino acids, amino acid profile, amino acid score.
... A dietary supplement had been formulated by including discrete amounts of L-cystine, as the physiologic dietary source of cysteines 25 and taurine, as an enhancer of free cysteines. Supraphysiologic amounts of P5P were added to direct cysteines to H 2 S releasing reactions. ...
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Background: Hydrogen sulfide (H2S) is a pivotal gasotransmitter networking with nitric oxide (NO) and carbon monoxide (CO) to regulate basic homeostatic functions. It is released by the alternative pathways of transulfuration by the enzymes Cystathionine Beta Synthase (CBS) and Cystathionine Gamma Lyase (CSE), and by Cysteine AminoTransferase (CAT)/ 3-Mercaptopyruvate Sulfur Transferase (3MPST). A non-enzymatic, intravascular release is also in place. We retrospectively investigated the possibility to modulate the endogenous H2S release and signaling in humans by a dietary manipulation with supplemented micronutrients (L-cystine, Taurine and pyridoxal 5-phopsphate/P5P). Methods: Patients referring for antiaging purposes underwent a 10-day supplementation. Blood was collected at baseline and after treatment and the metabolome was investigated by mass spectrometry to monitor the changes in the metabolites reporting on H2S metabolism and related pathways. Results: Data were available from 6 middle aged subjects (2 women). Micronutrients increased 3-mercaptopyruvate (P = .03), reporting on the activity of CAT that provides the substrate for H2S release within mitochondria by 3MPST, decreased lanthionine (P = .024), reporting the release of H2S from CBS, and had no significant effect of H2S release from CSE. This is compatible with a homeostatic balancing. We also recorded a strong increase of reporters of H2S-induced pathways including 5-MethylTHF (P = .001) and SAME (P = .022), reporting on methylation capacity, and of BH4 (P = .021) and BH2 (P = .028) reporting on nitric oxide metabolism. These activations may be explained by the concomitant induction of non-enzymatic release of H2S. Conclusions: Although the current evidences are weak and will need to be confirmed, the effect of micronutrients was compatible with an increase of the H2S endogenous release and signaling within the control of homeostatic mechanisms, further endorsing the role of feeding in health and disease. These effects might result in a H2S boosting effect in case of defective activity of pathologic origin, which should be checked in duly designed clinical trials.
... Cystine is reduced to yield cysteine, which is the most important intermediate metabolite involved in GSH synthesis [30]. In certain cancers, cysteine depletion has been shown to induce ferroptosis and thus represents an attractive therapeutic approach [31]. ...
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Background Hepatocellular carcinoma (HCC) is among the most common forms of cancer and is associated with poor patient outcomes. The emergence of therapeutic resistance has hampered the efficacy of targeted treatments employed to treat HCC patients to date. In this study, we conducted a series of CRISPR/Cas9 screens to identify genes associated with synthetic lethality capable of improving HCC patient clinical responses. Methods CRISPR-based loss-of-function genetic screens were used to target 18,053 protein-coding genes in HCC cells to identify chemotherapy-related synthetic lethal genes in these cells. Synergistic effects were analyzed through in vitro and in vivo analyses, while related mechanisms were explored through RNA-seq and metabolomics analyses. Potential inhibitors of identified genetic targets were selected through high-throughput virtual screening. Results The inhibition of phosphoseryl-tRNA kinase (PSTK) was found to increase HCC cell sensitivity to chemotherapeutic treatment. PSTK was associated with the suppression of chemotherapy-induced ferroptosis in HCC cells, and the depletion of PSTK resulted in the inactivation of glutathione peroxidative 4 (GPX4) and the disruption of glutathione (GSH) metabolism owing to the inhibition of selenocysteine and cysteine synthesis, thus enhancing the induction of ferroptosis upon targeted chemotherapeutic treatment. Punicalin, an agent used to treat hepatitis B virus (HBV), was identified as a possible PSTK inhibitor that exhibited synergistic efficacy when applied together with Sorafenib to treat HCC in vitro and in vivo. Conclusions These results highlight a key role for PSTK as a mediator of resistance to targeted therapeutic treatment in HCC cells that functions by suppressing ferroptotic induction. PSTK inhibitors may thus represent ideal candidates for overcoming drug resistance in HCC.
... Cysteine is an essential glucogenic amino acid in the human body. [202][203][204] It is involved in detoxification, prevents radiation injury, skin whitening, reduces inflammation, dissolves cutin, and prevents aging. The cysteine concentration level in the human body is important; however, the current detection method requires sophisticated instruments and is complex and tedious. ...
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This work describes the synthesis of Ag decorated CoO nanocomposites (NCs) supported on chitosan (CS-Ag/CoO NCs) for simple, low cost and rapid colorimetric detection of L-cysteine, and for the photocatalytic reduction of hexavalent chromium (Cr(VI)) ion. The NCs was characterized thoroughly by using UV-vis spectrophotometer, fourier transform-infrared spectroscopy (FT-IR), high resolution transmission electron microscopy (HR-TEM), thermogravimetric analysis (TGA), X-ray diffraction spectroscopy (XRD), energy dispersive x-ray spectroscopy (EDAX), and X-ray photoelectron spectroscopy (XPS). The NCs displayed high specificity, sensitivity and selectivity towards the L-cysteine detection and quantification from aqueous samples. The limit of detection of the prepared probe was 4.67 nM. The particle size of CS-Ag/CoO NCs was found to be 8.52 ± 0.13 nm. The CS-Ag/CoO NCs interaction with L-cysteine, interestingly causes the aggregation of NCs with increase in particle size to 956 ± 0.23 nm. The colour change was observed from yellow to colour less. An excellent linear correlation exists between the absorbance vs logarithmic concentration of L-cysteine (10 nM- 1 mM). Here, 250 mg/L of NCs reduced 100 mg/L of Cr(VI) to Cr(III) within 180 min. The kinetic data suggested that the NCs exhibited greater photocatalytic reduction efficiency than CoO and Ag/CoO. The paper-based test strips were developed and applied for the rapid colorimetric assay for the onsite monitoring of L-cysteine from real samples. The study demonstrated a specific detection of L-cysteine irrespective of the source of samples using CS-Ag/CoO NCs. Hence, the prepared NCs can be used as a colorimetric probe and provides a practical application for photocatalytic reduction of Cr(VI).
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Melatonin has been reported to affect intestinal function by targeting microbiome, morphological structure, barrier integrity and nutrient absorptive system. While the effect of melatonin on intestinal development in newborn infants is obscure, thus, this study firstly attempted to investigate the hypothesis that melatonin treatment improves intestinal development in sucking piglets. 14 healthy newborn piglets received 10 ml melatonin solution (1 mg/ml) or drinking water (n = 7) for 21 days. The results showed that oral administration of melatonin increased liver relative weight (p < 0.05) but failed to affect growth performance in sucking piglets (p > 0.05). Immunostaining jejunal samples from melatonin group showed high expressions of nnos and claudin1, indicating that melatonin improved intestinal neural development and barrier integrity. Also, melatonin promoted intestinal absorptive function evidenced by the increased serum proline concentration in melatonin-treated piglets compared with the control (p < 0.05). Gut microbiota compositions were tested by 16S rDNA sequencing and the results showed that melatonin increased the relative abundance of Actinobacteria compared with the control (p < 0.05) at the phylum level. However, Selenomonadales was markedly reduced compared with the control at the order level (p < 0.05). Gut and faecal volatile fatty acids were tested to evaluate the microbiota metabolism, but no difference was noticed in volatile fatty acid concentrations (p > 0.05). Melatonin improved intestinal development by affecting neural development, barrier integrity, nutrient absorption and microbiota in sucking piglets.
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Sperm DNA injury is one of the common causes of male infertility. Folic acid deficiency would increase the methylation level of the important genes, including those involved in DNA double-strand break (DSB) repair pathway. In the early stages, we analysed the correlation between seminal plasma folic acid concentration and semen parameters in 157 infertility patients and 91 sperm donor volunteers, and found that there was a significant negative correlation between seminal folic acid concentration and sperm DNA Fragmentation Index (DFI; r = −0.495, p < 0.01). Then through reduced representation bisulphite sequencing, global DNA methylation of sperm of patients in the low folic acid group and the high folic acid group was analysed, it was found that the methylation level in Rad54 promoter region increased in the folic acid deficiency group compared with the normal folic acid group. Meanwhile, the results of animal model and spermatocyte line (GC-2) also found that folic acid deficiency can increase the methylation level in Rad54 promoter region, increased sperm DFI in mice, increased the expression of γ-H2AX, that is, DNA injury marker protein, and increased sensitivity of GC-2 to external damage and stimulation. The study indicates that the expression of Rad54 is downregulated by folic acid deficiency via DNA methylation. This may be one of the mechanisms of sperm DNA damage caused by folate deficiency.
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In the present study, a novel colorimetric dual sensor for ultra sensitive detection of S²⁻ ion or cysteine was designed by the encapsulation of Ag-ZnCo2O4 nanocomposite on chitosan (CS) matrix (CS-Ag-ZnCo2O4 NCs). The CS-Ag-ZnCo2O4 NCs was characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), fourier transform infrared spectroscopy (FTIR) and energy-dispersive X-ray spectroscopy (EDAX). TEM results shows that the nanomaterial was polydisperse in nature. The zeta potential and particle size of NCs were found to be -35.4 mV ± 3 mV and 12 ± 2 nm respectively. The synthesized NCs were highly sensitive, specific and sensitive towards the detection of S²⁻ ion or cysteine. The dual detection of S²⁻ ion or cysteine was confirmed by the disappearance of UV-visible absorption spectra of CS-Ag-ZnCo2O4 NCs at 404 nm. Here, the limit of detection (LOD) of S²⁻ ion or cysteine by the present probe was calculated to be 0.62 nM and 2.87 nM. In advent, the detection of S²⁻ ion or cysteine under varying environmental conditions were also performed. Thus, the CS-Ag-ZnCo2O4 NCs provides a convenient and reliable way for the detection of S²⁻ ion or cysteine.
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This study aimed to determine the requirements of standardized ileal digestible (SID) methionine (Met) + cysteine (Cys) of 15–30 kg barrows, maintaining or increasing the 1:1 ratio between SID Met and SID Cys. Seventy crossbred barrows averaging 15.2 ± 0.54 kg of live weight were allotted in a randomized block design 2 × 3 + 1 factorial scheme, with five replicates and two animals per pen. Treatments consisted of maintaining or increasing the 1:1 ratio between SID Met and SID Cys, three levels of SID Met + Cys (5.8, 6.4 and 7.0 g/kg) and a basal diet containing the lowest SID Met + Cys level (5.2 g/kg), formulated to provide a 1:1 ratio of SID Met (2.6 g/kg) and SID Cys (2.6 g/kg). Performance, blood parameters, longissimus dorsi muscle depth, backfat thickness and S–S linkages in the bristles were evaluated. The best average daily gain was estimated at 6.61 g/kg of SID Met + Cys, without maintaining the 1:1 ratio between sulphur amino acids (SAA). The daily intake of SID Met + Cys increased due to dietary SID Met + Cys levels, maintaining or increasing the same ratio between SAA. Plasma glucose increased and total cholesterol decreased according to SID Met + Cys levels, without maintaining the same ratio between the SAA. The requirement of SID Met + Cys for 15–30 kg barrows was 6.61 g/kg (7.88 g/day) for an optimum average daily gain, with no need to maintain the same ratio between the SAA.
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Resistance to apoptosis is a key mechanism underlying how cancer cells evade tumor therapy. Autophagy can prevent anticancer drug-induced apoptosis and promote tumor resistance. The purpose of this study was to improve the sensitivity and efficacy of chemotherapeutic drugs through the inhibition of autophagy. Hydrophobic doxorubicin–hydrazone–caproyl–maleimide (DOX-EMCH) and autophagy-inhibiting si-Beclin1 were simultaneously delivered via the amphiphilic peptide micelle system (Co-PMs) using poly(L-arginine)–poly(L-histidine)–DOX-EMCH as the copolymer building unit. The constructed micelle system promoted the escape of si-Beclin1 from endosomes and the release of DOX into the nucleus. The Co-PMs exhibited 2.7-fold higher cytotoxicity and proapoptotic ability in PC3 cells than DOX treatment alone, demonstrating that si-Beclin1 could inhibit the autophagic activity of prostate cancer (PCa) cells by targeting the type III PI3K pathway and enhance the sensitivity of the cells to the chemotherapeutic drug DOX. In addition, the peptide micelles successfully passively targeted DOX and si-Beclin1 to the tumor tissue. Compared with DOX or si-Beclin1 treatment alone, the Co-PMs showed a 3.4-fold greater tumor inhibitory potential in vivo, indicative of a significant antiproliferative effect. Our results suggested that the Co-PMs developed in this study have the potential to combine autophagy inhibition and chemotherapy in cancer treatment, especially for PCa.
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The present study has attempted to understand how oxidative stress contributes to the development of proinflammatory state in the brain during aging. Three groups of rats have been used in this study: young (4-6 months, Group I), aged (22-24 months, Group II) and aged with dietary antioxidant supplementation (Group III). The antioxidants were given daily from 18 months onwards in the form of a combination of N-acetyl cysteine (50 mg/100 g body weight), a-lipoic acid (3 mg/100 g body weight), and a-tocopherol (1.5 mg/100 g body weight) till the animals were used for the experiments between 22 and 24 months. Several measurements have been made to evaluate the ROS (reactive oxygen species) production rate, the levels of proinflammatory cytokines (IL-1b, IL-6 and TNF-a) and the activation status of NF-jb (p65 subunit) in brain of the three groups of rats under the study. Our results reveal that brain aging is accompanied with a significant increase in NADPH oxidase activity and mitochondrial ROS production, a distinct elevation of IL-1b, IL-6 and TNF-a levels along with increased nuclear translocation of NF-jb (p65 subunit) and all these phenomena are partially but significantly prevented by the long-term dietary antioxidant treatment. The results imply that chronic dietary antioxidants by preventing oxidative stress and proinflammatory state may produce beneficial effects against multiple age-related deficits of the brain.
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In various pathological conditions of tissue injury, oxidative stress is often associated with autophagy. However, H2O2-induced oxidative stress initiates autophagy and its molecular mechanism is still obscure. Here we report that intragastric and peritoneal administration of H2O2 caused different degrees of oxidative stress and changed intestinal permeability, morphology, and barrier function in piglets. Western blotting studies revealed that H2O2 increased the autophagosome-related protein LC3-I and LC3-II abundance and the ratio of LC3-II to LC3-I content after exposure to 10% H2O2 in the jejunum. Meanwhile, the data from beclin1 also indicated that H2O2 initiated autophagy in response to oxidative stress. In addition, H2O2 activates the NF-κB and Nrf2/Keap1 signals, which may be involved in H2O2-induced autophagy. In conclusion, administration of H2O2 caused intestinal oxidative stress and triggered an autophagic response, which might be associated with NF-κB and Nrf2/Keap1 signals.
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The aim of the present study was to determine whether increased consumption of methionine as dl-methionine (DLM) or its hydroxy analogue dl-2-hydroxy-4-methylthiobutanoic acid (HMTBA) could benefit milk synthesis and neonatal growth. For this purpose, eighteen cross-bred (Landrace × Yorkshire) primiparous sows were fed a control (CON), DLM or HMTBA diet (n 6 per diet) from 0 to 14 d post-partum. At postnatal day 14, piglets in the HMTBA group had higher body weight (P= 0·02) than those in the CON group, tended (P= 0·07) to be higher than those in the DLM group, and had higher (P< 0·05) mRNA abundance of jejunal fatty acid-binding protein 2, intestinal than those in the CON and DLM groups. Compared with the CON diet-fed sows, milk protein, non-fat solid, and lysine, histidine and ornithine concentrations decreased in the DLM diet-fed sows (P< 0·05), and milk fat, lactose, and cysteine and taurine concentrations increased in the HMTBA diet-fed sows (P< 0·05). Plasma homocysteine and urea N concentrations that averaged across time were increased (P< 0·05) in sows fed the DLM diet compared with those fed the CON diet. Metabolomic results based on 1H NMR spectroscopy revealed that consumption of the HMTBA and DLM diets increased (P< 0·05) both sow plasma methionine and valine levels; however, consumption of the DLM diet led to lower (P< 0·05) plasma levels of lysine, tyrosine, glucose and acetate and higher (P< 0·05) plasma levels of citrate, lactate, formate, glycerol, myo-inositol and N-acetyl glycoprotein in sows. Collectively, neonatal growth and milk synthesis were regulated by dietary methionine levels and sources, which resulted in marked alterations in amino acid, lipid and glycogen metabolism.
Book
Amino acid biochemistry and nutrition spans a broad range of fields including biochemistry, metabolism, physiology, immunology, reproduction, pathology, and cell biology. In the last half-century, there have been many conceptual and technical advancements, from analysis of amino acids by high-performance liquid chromatography and mass spectrometry to molecular cloning of transporters for amino acids and small peptides. Amino Acids: Biochemistry and Nutrition presents comprehensive coverage of these scientific developments, providing a useful reference for students and researchers in both biomedicine and agriculture. The text begins with the discoveries and basic concepts of amino acids, peptides, and proteins, and then moves to protein digestion and absorption of peptides and amino acids. Additional chapters cover cell-, tissue-, and species-specific synthesis and catabolism of amino acids and related nitrogenous substances, as well as the use of isotopes to study amino acid metabolism in cells and the body. The book also details protein synthesis and degradation, regulation of amino acid metabolism, physiological functions of amino acids, and inborn errors of amino acid metabolism. The final chapter discusses dietary requirements of amino acids by humans and other animals. While emphasizing basic principles and classical concepts of amino acid biochemistry and nutrition, the author includes recent progress in the field. This book also provides concise coverage of major historical developments of the scientific discipline, so that readers will appreciate the past, understand the current state of the knowledge, and explore the future of the field. Each chapter contains select references to provide comprehensive reviews and original experimental data on the topics discussed.
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Amino acids are known to elicit complex taste, but most human psychophysical studies on the taste of amino acids have focused on a single basic taste, such as umami (savory) taste, sweetness, or bitterness. In this study, we addressed the potential relationship between the structure and the taste properties of amino acids by measuring the human gustatory intensity and quality in response to aqueous solutions of proteogenic amino acids in comparison to D-enantiomers. Trained subjects tasted aqueous solution of each amino acid and evaluated the intensities of total taste and each basic taste using a category-ratio scale. Each basic taste of amino acids showed the dependency on its hydrophobicity, size, charge, functional groups on the side chain, and chirality of the alpha carbon. In addition, the overall taste of amino acid was found to be the combination of basic tastes according to the partial structure. For example, hydrophilic non-charged middle-sized amino acids elicited sweetness, and L-enantiomeric hydrophilic middle-sized structure was necessary for umami taste. For example, L-serine had mainly sweet and minor umami taste, and D-serine was sweet. We further applied Stevens' psychophysical function to relate the total-taste intensity and the concentration, and found that the slope values depended on the major quality of taste (e.g., bitter large, sour small).
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Background: Experimental evidence of essential amino acid requirement in neonates is scanty. Recently, the branched chain amino acid requirements in term neonates were successfully determined using the indicator amino acid oxidation method. Methionine, an essential amino acid, can be used for protein synthesis, but serves as a precursor for homocysteine and cysteine as well. Current recommended total sulphur amino acid requirement for infants 0-1 months is 57 mg/kg/d (methionine 28, cysteine 29 mg/kg/d), which is based upon the content of human milk. Commercially available formulas provide a methionine intake of 45-80 mg/kg/d.
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Once the cells are challenged by intra- and extracellular environmental stimuli such as nitric oxide, calcium and pathogenic organisms, the oxidative balance between reactive oxygen species (ROS) (such as O2·-, H2O2, OH·) production and antioxidant defense systems (such as glutathione reductase and catalase) is broken, resulting in accumulation of ROS within cells. ROS is linked with various cellular signaling pathways, including the nuclear factor erythroid 2-related factor 2/Keap1(Nrf2/Keap1), mitogen-activated protein kinases (MAPKs), the nuclear factor kappa B (NF-κB), protein kinase C (PKC), signal transducers and activators of transcription 3 (STAT3), and peroxisome proliferator-activated receptor-γ (PPARγ), which engaged in regulating pro-oxidant genes and antioxidant genes expression, and mediate cells oxidative injury and antioxidant defense system. This article therefore mainly focuses on: 1) the production of ROS; 2) Nrf2/Keap1, MAPKs, NF-κB, PKC, STAT3, and PPARγ activation mechanism by ROS.
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The catabolism of cysteine and cysteinesulfinate, the activities of key enzymes in cysteine catabolic pathways, and the effects of inhibitors of specific enzymes on cysteine catabolism were investigated in hepatocytes isolated from rats fed low (100 g casein/kg diet), moderate (300 g casein/kg diet) or high (600 g casein/kg diet) levels of dietary protein. Cysteine was catabolized predominantly by cysteinesulfinate-dependent pathways. Cysteine dioxygenase activity increased with increases In dietary casein level, and the higher enzyme activity was paralleled by a greater total catabolite production (taurine + hypotaurine + sulfate) from cysteine. However, taurine production did not closely follow cysteine dioxygenase activity. Taurine production doubled with an increase in dietary casein from 100 to 300 g/kg but did not increase with a further increase in dietary casein to 600 g/kg. Taurine production as a percentage of total catabolism decreased progressively with the increases in dietary casein and closely paralleled observed decreases in cysteinesulfinate decarboxylase activity. Thus, taurine production was limited at high protein levels by the decrease in cysteinesulfinate decarboxylase activity such that sulfate production from cysteinesulfinate was favored. D-Cysteinesulfinate inhibited cysteinesulfinate-dependent catabolism of cysteine, but inhibition of cysteinesulfinate decarboxylase was not specific.
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The integrity of the intestinal epithelium ensures its normal physiological function. Consequently, damage to the mucosal epithelium can impair the absorption of nutrients, thereby reducing the growth performance and compromising the health of animals. N-acetylcysteine (NAC) is pharmaceutically available either intravenously, orally, or by inhalation for reducing endothelial dysfunction, inflammation, fibrosis, invasion, cartilage erosion, acetaminophen detoxification, and transplant prolongation. NAC is rapidly metabolized by the small intestine to produce glutathione and can not be detected in animals without supplementation. The physiologic functions and therapeutic effects of NAC are largely associated with maintaining intracellular concentrations of reduced glutathione. Results from recent studies indicate that NAC reduces inflammation, alleviates oxidative stress, improves energy status, and ameliorates tissue damage in the intestine of lipopolysaccharide-challenged piglets. Moreover, dietary supplementation with NAC ameliorates acetic acid-induced colitis in a porcine model. The effects of NAC are associated with some intestinal cell signaling pathways, such as EGFR, TLR4, apoptosis and tight junction signaling. The current review focuses on the protective effects of NAC on intestinal health and the molecular mechanisms of its action.