Plasma metabolomics reveals biomarkers of the atherosclerosis
Transcript of Plasma metabolomics reveals biomarkers of the atherosclerosis
Research Article
Plasma metabolomics reveals biomarkers ofthe atherosclerosis
Atherosclerotic cardiovascular disease remains the leading cause of morbidity and
mortality in industrialized societies. The lack of metabolite biomarkers has impeded the
clinical diagnosis of atherosclerosis so far. In this study, stable atherosclerosis patients
(n 5 16) and age- and sex-matched non-atherosclerosis healthy subjects (n 5 28) were
recruited from the local community (Harbin, P. R. China). The plasma was collected from
each study subject and was subjected to metabolomics analysis by GC/MS. Pattern
recognition analyses (principal components analysis, orthogonal partial least-squares
discriminate analysis, and hierarchical clustering analysis) commonly demonstrated
plasma metabolome, which was significantly different from atherosclerotic and non-
atherosclerotic subjects. The development of atherosclerosis-induced metabolic pertur-
bations of fatty acids, such as palmitate, stearate, and 1-monolinoleoylglycerol, was
confirmed consistent with previous publication, showing that palmitate significantly
contributes to atherosclerosis development via targeting apoptosis and inflammation
pathways. Altogether, this study demonstrated that the development of atherosclerosis
directly perturbed fatty acid metabolism, especially that of palmitate, which was confirmed
as a phenotypic biomarker for clinical diagnosis of atherosclerosis.
Keywords: Atherosclerosis / Biomarkers / GC/MS / Plasma metabolomics /PalmitateDOI 10.1002/jssc.201000395
1 Introduction
Atherosclerotic cardiovascular disease remains the leading
cause of morbidity and mortality in industrialized societies
[1]. Atherosclerosis (also known as arteriosclerotic vascular
disease) is a condition characterized by thickening of the
arterial wall resulting from build-up of fatty materials such
as cholesterol. It is a syndrome affecting arterial blood
vessels, a chronic inflammatory response in the walls of
arteries, in large part due to the accumulation of macro-
phage white blood cells, promoted by low-density lipopro-
teins. The increased vascular wall thickness in
atherosclerosis is also due to the accumulation of the cells
and extracellular matrix between the endothelium and the
smooth muscle cell wall [2]. Epidemiological evidence
reveals a cause and relationship between chronic inflamma-
tion and atherosclerosis [3]. Microvascular barrier dysfunc-
tion is implicated in the initiation and progress of
inflammation in atherosclerosis [4], leading to chronic
infection and inflammation associated with the develop-
ment of atherosclerosis [5].
An important connection between inflammation and
disease may be attributed to the secretion of highly reactive
oxygen and nitrogen species by macrophages and neutro-
phils, including hypohalous acids, nitrous anhydride, and
nitrosoperoxycarbonate [4].
The lipid fraction of blood plasma has a profound effect
on the development of cardiovascular disease, an evidence
that the aqueous metabolites in vivo also have a role in
following the effects of myocardial infarction and monitor-
ing the development of atherosclerosis (reviewed by
Waterman et al. [6]).
Metabolites reveal the dynamic processes underlying
cellular homeostasis. Recent advances in analytical chem-
istry and molecular biology have set the stage for metabolite
profiling to help us understand complex molecular proces-
ses and physiology [7]. Metabolomics is the comparative
analysis of metabolite flux and how it relates to biological
phenotypes [7]. As an intermediate phenotype, metabolite
signatures capture a unique aspect of cellular dynamics that
is not typically interrogated, providing a distinct perspective
on cellular homeostasis [7].
Xi Chen1�
Lian Liu2�
Gustavo Palacios2
Jie Gao3
Ning Zhang4
Guang Li5
Juan Lu1
Ting Song1
Yingzhi Zhang1
Haitao Lv2
1Institute of Medicinal PlantDevelopment, Chinese Academyof Medical Sciences, PekingUnion Medical College, Beijing,P. R. China
2Department of Medicine, AlbertEinstein College of Medicine,New York, USA
3The First Hospital, HeilongjiangUniversity of Chinese Medicine,Harbin, P. R. China
4College of Jiamusi, HeilongjiangUniversity of Chinese Medicine,Jiamusi, P. R. China
5Department of Pharmacognosy,Heilongjiang University ofChinese Medicine, Harbin,P. R. China
Received June 4, 2010Revised July 11, 2010Accepted July 11, 2010
Abbreviations: FFA, free fatty acid; HCA, hierarchicalclustering analysis; OPLS-DA, orthogonal partial least-squares discriminate analysis; PCA, principal componentanalysis; SFA, saturated fatty acids �These authors contributed equally to this article.
Correspondence: Dr. Haitao Lv, Albert Einstein College ofMedicine, 1301 Morris Park Avenue, Price Center Room 368,and New York 10461, USAE-mail: [email protected]
& 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.jss-journal.com
J. Sep. Sci. 2010, 33, 2776–27832776
Atherosclerosis is a complicated and multifactorial
disease, induced not only by genotype, but also, even more
importantly, by environmental factors. The study on the
metabolic perturbation of endogenous compounds may
offer a deeper insight into the development of athero-
sclerosis [8]. As for this point, the metabolomics provides
the promise to improve our understanding of the complex
process of atherosclerosis development [9]. A body of data
demonstrated that metabolomics technology was applied to
study metabolites profiling modification and phenotype
development of atherosclerosis-based human and animal
models. The analytical techniques adopted from mass
spectrometry (LC/MS or GC/MS) to NMR, and main plas-
ma or urine were applied in these studies. Further, these
studies revealed the metabolic perturbations of phenylala-
nine, tryptophan, bile acids, amino acids, fatty acids, etc.involved in the development and progress of atherosclerosis
[10–12]. However, these studies mostly focused on clarifying
variations in the metabolites pool and the fingerprint of
urine and plasma, to phenotype metabolic syndrome during
the development of atherosclerosis. Low specific attention
was paid to the discovery of metabolite biomarkers used for
the clinical diagnosis of atherosclerosis.
The application of metabolomics in the discovery of
diagnostic disease-specific biomarkers has made some
progress [13–15]. The main purpose of this study was to
discover specific biomarkers for use in the clinical diagnosis
of atherosclerosis. We adopted a GC/MS-based approach of
analyzing the plasma metabolites from healthy subjects and
patients with stable atherosclerosis.
2 Materials and methods
2.1 Chemicals and reagents
Acetonitrile (HPLC grade) was purchased from Sigma
(USA); methoxyamine hydrochloride and triethylamine
(in heptanes) were purchased from Sigma. High-purity
water (LC-MS grade) was purchased from Fisher
Scientific (USA).
2.2 Study subjects and sampling
Stable atherosclerosis patients (n 5 16) and age- and sex-
matched non-atherosclerosis healthy subjects (n 5 28) were
recruited from the local community (Harbin, P. R. China).
Subjects provided written informed consent approved by the
Clinic Institutional Review of the Heilongjiang University of
Chinese Medicine Board and in accordance with the
Declaration of Helsinki. All study subjects were screened
with detailed medical history, physical examination, and
hematological and biochemical profile. A standard dinner
was given to each study subjects throughout seven days
before sampling blood. Five milliliters of arterialized venous
blood was obtained from a catheterized hand vein before
breakfast on the eighth day. Plasma was isolated and kept in
liquid nitrogen until GC/MS analysis.
2.3 Sample preparation
In this study, plasma samples were prepared by using a
simple protocol recorded in [16]. Briefly, the thawed plasma
samples were vortex-mixed with acetonitrile. The super-
natant was separated and dried out under a stream of N2
gas. Finally, the precipitation was derivatized by methox-
imation and trimethylsilylation for GC/MS analysis.
2.4 Plasma metabolic profiling
The GC/EI MS system consisted of an Agilent 6890/5973
GC/MS system, G1701DA workstation, NIST02 MS library,
and an SE54 capillary column (30 m� 0.25 mm� 0.25 mm)
(Agilent, USA). The injection port temperature was 2601C.
Injection into the GC-MS system was performed in the
pulsed splitless mode with a pulse pressure of 207 kPa and a
pulse time of 1.5 min. The GC oven was programmed with
an initial temperature of 1201C, which was held for 2 min
and then increased to 2701C at 51C/min and held at the final
temperature for 2 min. High-purity helium (99.999%) was
used for the carrier gas at a flow rate of 1 mL/min. The GC-
MS interface temperature was set at 2801C. The EI source
temperature was set at 2301C. The energy was 70 eV. The
split ratio was 1:20. The selected mass range was 30–650 Da
and the selected scan speed was 3.2 scans per second. The
pretreated plasma samples were profiled based on the above
GC/MS method. Identification of GC/MS detected peaks
was performed by comparing their mass spectra and
retention index in the NIST02 MS library. For overlapping
peaks, an AMDIS of deconvolution software was adopted to
identify all the peaks in the chromatogram before NIST02
MS library searching [17].
2.5 Data processing
By metabolic profiling analysis of Section 2.4, the raw data
of TIC metabolic profiling of the plasma samples from the
healthy subjects and the patients with stable atherosclerosis
will be achieved. The Agilent Mass Hunter Workstation
software (Demo Version) (Agilent) was used to generate a
3D data matrix constructed with the sample ID as
observations, the metabolites ID as the response variables,
and peak area of metabolites as abundance. Then, the 3D
data matrix was imported into Ezinfo software incorporated
in MakerLynxV4.1 SCN714 for pattern recognition analysis
(Waters Company, USA). By pattern recognition analysis of
raw data, the metabolic profiling modification will be
clarified. In this study, we adopted a pattern recognition
analysis that included principal components analysis (PCA),
orthogonal partial least-squares discriminate analysis
J. Sep. Sci. 2010, 33, 2776–2783 Gas Chromotagraphy 2777
& 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.jss-journal.com
(OPLS-DA) and hierarchical clustering analysis (HCA) [13,
18–21].
3 Results and discussion
Efforts to reduce cardiovascular events in ‘‘high-risk’’
individuals or recurrent events in patients with established
atherosclerotic cardiovascular disease emphasize broad-
based implementation of guideline-directed therapeutic
lifestyle changes and pharmacotherapy. Despite successful
implementation of these evidence-based strategies, many
individuals are not properly identified before their first event
or they continue to experience cardiovascular events despite
‘‘optimal’’ levels of biomarkers [9]. The key cause is the lack
of clinical metabolite biomarkers that could be used for the
clinical diagnosis of atherosclerosis. In this study, we mainly
focused on discovering a plasma biomarker for athero-
sclerosis, which can be validated to distinguish patients and
healthy subjects using a GC/MS-based metabolomics
analysis.
The typical MS TIC plots of the plasma samples are
shown in Fig. 1, which only indicated some macro-differ-
ence of the fingerprint regions between the healthy subjects
and the patients with stable atherosclerosis. The direct
observation of the metabolic profiling of TIC MS does not
characterize and clarify the subtle and essential metabolic
modifications of small molecular metabolites in plasma
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Figure 1. Typical MS TIC plots of plasma analysis from (A) healthy subject and (B) patient with atherosclerosis.
J. Sep. Sci. 2010, 33, 2776–27832778 X. Chen et al.
& 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.jss-journal.com
between the healthy subjects and the patients with stable
atherosclerosis.
These complex and subtle modifications could signifi-
cantly contribute to profound biochemical interpretation of
the pathophysiological events in biological body [13, 15].
This subtle and profound metabolome modification can
only be achieved by the pattern recognition analysis of raw
data of metabolic profiles. This is achieved by importing raw
data or pre-processed data into pattern recognition related
software.
In this study, a total of 240 metabolites were detected
and profiled by analysis of plasma samples of healthy
subjects and patients with stable atherosclerosis using the
Agilent Mass Hunter Workstation Software (Fig. 2), the
mass range of most of the metabolites is below 200 Da, and
almost concentrated, distributed within 30 min of running
time. Meanwhile, Agilent Mass Hunter Workstation Soft-
ware constructed the 3D data matrix with the sample IDs as
observations, the metabolites ID as the response variables,
and the peak area of metabolites as abundance. Then, the
Ezinfo software-based PCA was performed based on this 3D
data matrix. Obvious groups classification was characterized
by scores plot resulting from PCA, suggesting that the
plasma metabolites profiles of the patients with athero-
sclerosis were significantly different from those of the
healthy subjects. These are in accordance with the previous
studies [10–12], which confirm that the development of
atherosclerosis results in the obvious metabolic modifica-
tion of metabolites pool in human plasma due to modifi-
cations and perturbations of related metabolic pathways.
The scores plot resulting from OPLS-DA and the hier-
archical clustering plot furthermore confirmed this result
(Fig. 3B and C). The similarity value is only 0.10 in HCA
analysis; two separated clustering groups were validated,
created, and except few overlaid samples, suggesting that
highly significant difference of plasma metabolomes
between the healthy subjects and the patients with stable
atherosclerosis can be attributed to effect of atherosclerosis
on metabolites pool of human body [10–12].
By observing S-plot resulting from OPLS-DA, Fig. 4A,
three metabolites were found that contributed the most,
toward groups’ classification of plasma metabolome of
healthy subjects and patients with stable atherosclerosis,
which was characterized by the score plots resulting
from PCA and OPLS-DA. The chemical structure of
these three metabolites was identified by combining targe-
ted peak deconvolution of AMDIS software and NIST02
MS library searching as palmitate, stearate, and 1-mono-
linoleoylglycerol (Fig. 4B–D), which are all fatty acids. The
palmitate and stearate are long-chain saturated fatty acids
(SFAs). It has been shown earlier that the presence of the
long-chain SFAs in parenteral formulations may have
harmful effects on the vascular system [22].
Inflammation and insulin resistance associated with
visceral obesity are important risk factors for the develop-
ment of atherosclerosis, and the metabolic syndrome [23].
The dyslipidemia of insulin resistance, with high levels of
albumin-bound fatty acids, is a strong cardiovascular disease
risk [24]. However, overproduction of plasma fatty acid is
one of the main causes inducing inflammation and insulin
resistance [25–27]. The urokinase plasminogen activator
system with its receptor uPAR contributes to the migratory
potential of macrophages, a key event in atherosclerosis; the
free fatty acid (FFA) is proved to differentially stimulate the
uPAR expression in human monocytes/macrophages [28].
Especially, the long-chain SFA induce proinflammatory
cytokines in human macrophages via pathways involving denovo ceramide synthesis, contributing to the activation of
macrophages in atherosclerotic plaques [29].
Our results from this study revealed that the metabolic
disorder of fatty acids is the most obvious phenotype in the
development of atherosclerosis indicating that fatty acids
may be used as biomarkers for clinical diagnosis of ather-
osclerosis.
Palmitate is the most abundant fatty acid in vivo,
accounting for approximately 26% of the total plasma fatty
acids [30]. Palmitate can induce apoptosis via a p38 MAPK-
dependent pathway and a reduction in IB in hCAECs
independent of p38 MAPK activity [31]. Though apoptosis is
directly involved in the development and progression of
atherosclerotic lesions, the protein kinase C signalling is of
importance in atherosclerosis as well as apoptosis. Protein
kinase C iota is activated by saturated fatty acids and
mediates lipid-induced apoptosis of HCAEC [31]. This
suggests that palmitate induces apoptosis and inflammation
in hCAECs via distinctly different mechanisms and p38
MAPK may have exerted a key role in the FFA-induced
coronary endothelial injury and atherosclerosis [31]. Because
inflammatory cytokines are the potent activators of p38
MAPK, which plays a very important role in modulating
inflammation, most likely p38 MAPK is also involved in the
FFA-mediated inflammation in the vascular endothelium
[31]. In this study, our results showed that palmitate was
markedly increased by 8-fold in the plasma of patients with
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Figure 2. Coefficient plot of retention time, mass and abundanceof peak area, and distribution. This plot can phenotype thenumber of metabolites after deconvolution of peaks.
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& 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.jss-journal.com
stable atherosclerosis, when compared to the healthy
subjects (Fig. 5). This suggests that the development of
atherosclerosis can induce overproduction of palmitate. The
palmitate accelerates atherosclerosis development by indu-
cing apoptosis and inflammation via special p38 MAPK
pathways.
Stearate is also a type of saturated fatty acid (C18; 0), the
structure of which is very similar to palmitate (C16:0).
Stearate’s proinflammatory response was confirmed by the
phosphorylation of IkappaB-alpha and NF-kappaB in a dose-
dependent manner [25], and stearate has also been shown to
inhibit invasion and proliferation and induce apoptosis in
various human cell types [32, 33]. In this study, stearate was
significantly increased by 3-fold in plasma of patients with
stable atherosclerosis compared with healthy subjects,
suggesting that stearate also contributes to the development
of atherosclerosis via inducing apoptosis and inflammation
pathways. However, 1-monolinoleoylglycerol is a type of
unsaturated fatty acid (C18; 2) with two double bonds. The
expression levels were also significantly increased by 3-fold
in the plasma of patients with stable atherosclerosis
compared with the healthy subjects.
To date there is no data to support 1-mono-
linoleoylglycerol’s mechanisms of action on atherosclerosis
development. Therefore, it is questionable to select
1-monolinoleoylglycerol as biomarker to diagnose athero-
sclerosis in clinical practice. It requires further confirmation
and support from biochemical data to make such a
conclusion.
In summary, we confirm that fatty acids are the
most direct-targeted metabolites pool during the develop-
ment of atherosclerosis. Though the published data
[25, 32, 33] may support the potential effect relationship
between stearate and atherosclerosis development, the
proofs are obviously inferior to palmitate. The palmitate is
the ideal candidate of plasma biomarker for the clinical
healthy subjects
patients with atherosclerosis
A B
0.00.20.40.60.81.0
PSA
HSHSHSHSHSHSHSHSHSHSHSHSHSHSHSHSHSHSHSHSHSHSHSPSAPSAHSHSPSAPSAPSAHSPSAPSAPSAPSAPSAPSAPSAPSAPSAPSA
C
Figure 3. Scores plots from (A) PCA and (B)OPLS-DA and (C) hierarchical plot from HCA,the distance of similarity is only 0.1, suggest-ing dramatic inter-group differences of plas-ma metabolites. HS, Healthy subjects; PSA,patients with stable atherosclerosis.
J. Sep. Sci. 2010, 33, 2776–27832780 X. Chen et al.
& 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.jss-journal.com
diagnosis of atherosclerosis [22–31], and supported by the
data from our study. It also supports the concept that a
single biomarker is efficient to diagnose specific diseases
rather than a pool of metabolites, as previously
shown sarcosine was selected to diagnose prostate cancer
progression [13].
C
B
D
m/z
% a
bund
ance
% a
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ance
% a
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ance
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orre
latio
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1 - monolinoleoylglycerol
Palmitate
Stearate
A
Figure 4. Characterization of key metabolitescontributing to plasma metabolome separa-tion between healthy subjects and patientswith stable atherosclerosis. (A) S-plot result-ing from OPLS-DA; (B) derived structure andits product mass spectra of palmitate; (C)derived structure and its product massspectra of stearate; (D) derived structureand its product mass spectra of stearate1-monolinoleoylglycerol.
J. Sep. Sci. 2010, 33, 2776–2783 Gas Chromotagraphy 2781
& 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.jss-journal.com
4 Concluding remarks
In this study, the biomarkers discovery-based metabolomics
technology was applied to characterize plasma metabolic
profiling modification during the atherosclerosis develop-
ment by comparing with healthy subjects by GC/MS.
Subsequently, multiple tools of pattern recognition analyses
(PCA, OPLS-DA, and HCA) were introduced to characterize
plasma metabolome change between the healthy subjects
and the patients with atherosclerosis, which revealed that
key metabolites significantly contributed to the above
plasma metabolomes classification. Finally, three fatty acids:
palmitate, stearate, and 1-monolinoleoylglycerol were iden-
tified as probable potential biomarkers used for the clinical
diagnosis of atherosclerosis. Moreover, by carefully review-
ing the previously published data, and the results from our
study, palmitate was evidenced as a biomarker for the
clinical diagnosis of atherosclerosis.
This study was funded by the National Innovation PlatformProject of Key New Drug of China (Grant No. 2009ZX09502).
The authors have declared no conflict of interest.
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0
5
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Figure 5. Comparison of expression level of palmitate, stearate,and 1-monolinoleoylglycerol in plasma of healthy subjects(n 5 28) and patients with atherosclerosis (n 5 16).
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