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EXPERI MENTAL AND THER APEUTIC M EDICINE
Abstract. Liver brosis is caused by liver injury induced by a
number of chronic liver diseases, including schistosome infec-
tion, hepatitis infection, metabolic disease, alcoholism and
cholestasis. The tissue damage occur ring after injury or inam-
mation of the liver is a reversible lesion; however, liver brosis
has become a worldwide problem and poses a threat to human
health. The development of an effective drug for the prevention
and treatment of liver brosis is ongoing and uses information
from different occurrences of liver brosis. In the present study,
carbon tetrachloride (CCl4)‑induced metabonomic changes
in serum and urine at 12 weeks were analyzed using gas
chromatography‑mass spectrometry (GC/MS) to investigate
potential biomarkers. Liver fibrosis was induced in rats by
subcutaneous injections of CCl4 twice a week for 12 consecu-
tive weeks. Histopathological changes were used to assess the
successful production of a CCl4‑induced liver brosis model.
Serum and urine samples from the two groups were collected
at 12 weeks. The metabolic profile changes were analyzed
by GC/MS alongside principal component analysis and
orthogonal projections to latent structures. Metabolic prole
studies indicated that the clustering of the two groups could be
separated and seven metabolites in serum and ve metabolites
in urine were identied. In serum, the metabolites identied
included isoleucine, L‑malic acid, α‑copper, carnitine, hippuric
acid, glutaric acid and glucose. In urine 2‑hydroxy butyric acid,
isoleucine, N‑acetyl‑β‑alanine, cytidine and corticoid were
identied. The present study demonstrated that the pathogen-
esis of liver brosis may be associated with the dysfunction of a
number of metabolic pathways, including glucose, amino acid,
P450, fatty acid, nucleic acid, water‑electrolyte and glutathione
biosynthesis. Assessing potential biomarkers may therefore
provide novel targets and theories for the innovation of novel
drugs to prevent and cure liver brosis.
Introduction
Liver brosis occurs as a wound‑healing process following
liver injury induced by chronic liver disease and is identied
by an exorbitant accumulation of extracellular matrix (ECM),
scar tissue or collagen (1). The deposition of ECM proteins
substitute for functional tissues and disrupt the normal
liver architecture, which in turn leads to pathophysiological
damage (2). The primary causes of liver brosis include chronic
high alcohol ingestion and infection with hepatitis B and C.
Less common causes include viral infection, hemochroma-
tosis, primary biliary cirrhosis, primary sclerosing cholangitis,
helminth infection, autoimmune diseases and nonalcoholic
steatohepatitis (3). Hepatic brosis is a vital stage that occurs
during the development of chronic liver disease. Cirrhosis and
hepatocellular carcinomas are of great concern worldwide
due to the high morbidity and mortality rates associated with
them (4). There are currently no effective therapies to treat liver
cirrhosis; however, it has been suggested that the damage may
be reversible if treated appropriately during the early, brotic
stage of cirrhosis (5). Therefore, identifying an effective treat-
ment for hepatic brosis is critical in order to decrease the
chances of patients with hepatic brosis developing chronic
liver disease.
Liver biopsy is the gold standard of diagnosis for different
stages of brosis and inammation. However, this technique
Detecting serum and urine metabolic prole changes
of CCl4‑liver brosis in rats at 12 weeks based on
gas chromatography‑mass spectrometry
JIARONG GAO1, XIU‑JUAN QIN1, HUI JIANG1, JIN‑FENG CHEN1, TING WANG2,
TING ZHANG2, SHUANG‑ZHI XU2 and JUN‑MEI SONG2
1Department of Pharmacy; 2College of Pharmacy, The First Afliated Hospital of
Anhui University of Chinese Medicine, Hefei, Anhui 230031, P.R. China
Received September 11, 2015; Accepted October 18, 2016
DOI: 10.3892/etm.2017.4668
Correspondence to: Professor Jiarong Gao, Department of
Pharmacy, The First Affiliated Hospital of Anhui University
of Chinese Medicine, 117 Meishan Road, Hefei, Anhui 230031,
P.R. China
E‑mail: zyfygjr2006@163.com
Abbreviations: CCl4, carbon tetrachloride; GC/MS, gas
chromatography‑mass spectrometry; PCA, principal component
analysis; OPLS, orthogonal projections to latent structures; DA,
discriminant analysis; ECM, extracellular matrix; H&E, hematoxylin
and eosin; BSTFA, bis‑(trimethylsilyl) trifluoroacetamide; SPSS,
Statistic Package for Social Science; TIC, total ion current; VIP,
variable importance projection; KEGG, Kyoto Encyclopedia
of Genes and Genomes; TCA, triglycerides; acetyl‑CoA,
acetyl‑coenzyme A; RAAS, renin‑angiotensin‑aldosterone system
Key words: hepatic fibrosis, carbon tetrachloride, serum, urine,
metabonomics, gas chromatography‑mass spectrometry
GAO et al: SERUM AND URINE METABOLIC PROFILE CHANGES OF CCL4‑LIVER FIBROSIS
2
may cause complications including bleeding, pain, bile peri-
tonitis, pneumothorax and mortality. Furthermore, there are
problems due to the procedure being invasive and sampling
errors occurring (6,7). Vessel imaging serves a crucial role in
the diagnosis of hepatic brosis. Additionally, vessel imaging
can help test for hepatic brosis in the early stages, making it
useful for investigating the development of hepatic brosis (8).
However, traditional imaging techniques widely used in clin-
ical practice, including magnetic resonance elastography and
conventional radiography, are ineffective at detecting mild to
moderate hepatic brosis, particularly in obese patients (9,10).
In recent years, technological developments have led to a
novel, non‑invasive method, protein fingerprinting of the
extracellular matrix remodeling (11), which is being developed
to diagnose hepatic brosis. The method includes biochem-
ical and hematological tests and the assessment of serum
biomarkers in connective tissue. However, it has no sensitive,
specic or reproducible application methods to detect the early
stages of brosis (11). Thus, it is important to investigate other
treatment options and identify effective techniques for the
early diagnosis of liver brosis. Liver brosis biomarkers and
characterization of metabolic changes indicate that the onset
of brosis occurs earlier than other diagnostic forms, including
noninvasive diagnostics such as imaging diagnosis (12). This
may provide an effective way to detect liver brosis early,
enabling the administration of effective treatment and a clearer
understanding of the molecular mechanisms.
Metabonomics is a comprehensive analytical technology
used to study biological systems and is dened as ‘the
quantitative measurement of the dynamic multi‑parametric
responses of a living system to pathophysiological stimuli
or genetic modication’ (13). Metabonomics screens for
metabolic biomarkers to detect related endogenous metabo-
lites, toxicological and pharmacological effects, describe
metabolic pathways, and explain the function of complex
biological systems to distinguish disease states (14). A number
of analytical platforms have been employed for metabonomic
analysis, including liquid chromatography coupled with mass
spectrometry, nuclear magnetic resonance, high‑performance
liquid chromatography/mass spectrometry and gas chroma-
tography‑mass spectrophotometry (GC/MS) (15). GC/MS is a
major analytical tool for metabonomic studies used to analyze
various types of samples including those from the serum, urine,
cerebrospinal uid and plasma. GC/MS produces results at a
high resolution, reproducibility, sensitivity and accuracy while
being simple and providing good separability (16). Multivariate
statistical methods, Including principal component analysis
(PCA) and orthogonal projections to latent structures (OPLS)
are generally used to assess metabonomic data collected by
GC/MS. PCA is an unsupervised mode recognition method
that changes a range of correlated variables into a number of
smaller uncorrelated variables called principal components.
OPLS‑discriminant analysis (OPLS‑DA) is a method of
discerning between two or more groups so that differences in
variables may be identied. These methods provide classica-
tion of observations and a vast amount of information regarding
the latent structures by regression during the modeling (17).
The present study investigated the main pharmacody-
namics index, assessed changes to serum and urine metabolite
group pathways that occur during liver brosis and identied
potential biomarkers for liver brosis using GC/MS. The study
aimed to examine the practicality of GC/MS in the study of
metabonomics and provide novel targets for innovative drugs
to treat liver brosis.
Materials and methods
Reagents. Analytical grade pyridine, chloral hydrate, olive oil
and L‑2‑chlorophenylalanine were purchased from Shanghai
Hengbai Biotech Co., Ltd., (Shanghai, China). Carbon tetra-
chloride (CCl4) was purchased from Xilong Chemical Co.,
Ltd., (Guangdong, China) and bis‑ (trimethylsilyl) triuoro-
acetamide (BSTFA) was purchased from Regis Technologies,
Inc. (Morton Grove, IL, USA).
Animal Experiments. A total of 10, male Sprague‑Dawley
rats weighing 180‑220 g and 7 weeks old were purchased
from Anhui Medical University (Anhui, China). All the rats
were allowed ad libitum access to food and water and housed
individually in a facility at 18‑22˚C, 40‑60% humidity and a
12 h light‑dark cycle. Surgery was performed under anesthesia
with sodium pentobarbital (2 ml/kg, intraperitoneal injec-
tion, IP) purchased from Shanghai chemical reagent Co., Ltd.
(Shanghai, China), and all efforts were made to minimize
suffering. The protocol was approved by the Committee on the
Ethics of Animal Experiments, Anhui University of Chinese
Medicine (approval no. 2012AH‑038‑01; Anhui, China).
CCl4 induction and treatment groups. Following 1 week of
acclimatization, rats were randomly separated into two groups:
Control group (n=5) and model group (n=5). The model group
was treated with CCl4 (0.1 ml/100 g 50% CCl4, diluted to 50%
in olive oil), injected subcutaneously into the back twice a
week for 12 weeks to induce liver brosis. Samples of over-
night (12 h) urine and serum were collected in metabolism
cages from all rats 12 weeks following initial CCl4 injection.
All urine and serum samples were stored at ‑80˚C.
Histopathology. At the end of the experimental period,
the animals were anesthetized with sodium pentobarbital
(2 ml/kg, IP). A lobe of liver tissue (~2.0x2.0x0.3 cm) from
each rat was removed during surgery and xed in 10% neutral
formalin at 25˚C (6‑12 h), which prior to staining with hema-
toxylin and eosin (H&E) and Masson stains for histological
examination as standard.
Sample preparation for GC/MS analysis. For samples of
serum and urine, 100 µl of each was used. The urine sample
was mixed with 10 µl urease suspension (160 mg/ml in
water) in 1.5 ml EP tubes and vortexed for 10 sec. This was
incubated at 37˚C for 1 h in order to decompose and remove
excess urea. Serum and urine samples were then each mixed
with 0.35 ml extraction liquid (3:1, Vmethanol:Vchloroform)
and 50 µl L‑2‑chlorophenylalanine (0.2 mg/ml stock in H2O)
as an internal standard, in 1.5 ml EP tubes prior to 10 sec
vortexing. The serum sample underwent centrifugation for
10 min at 23,500 x g at 4˚C. For samples of serum and urine,
0.35 ml supernatant was transferred into fresh 2 ml GC/MS
glass vials, dried in a vacuum concentrator without heating.
Methoxyamination reagent (Shanghai chemical reagent Co.,
EXPERI MENTAL AND THER APEUTIC M EDICINE 3
Lt d.; 80 ml of 20 mg /ml in pyridine) was added and the samples
underwent shaking for 2 h at 37˚C. A further 1 h of shaking at
70˚C was completed following the addition of 0.1 ml BSTFA
regent (1% TriMethyl Chloro Silane, Tri Methyl Chloro Silane,
v/v) to the sample aliquots. GC/MS analysis was completed
when samples had cooled to room temperature.
An Agilent 7890a gas chromatograph system (Agilent
Technologies, Santa Clara, CA, USA) coupled with a Pegasus
4D time‑of‑ight mass spectrometer (LECO Corporation®,
Saint Joseph, MI, USA) was used to perform GC/MS analysis.
This system utilizes a DB‑5MS capillary column coated with
5% diphenyl cross‑linked with 95% dimethylpolysiloxane
(30x250 µm inner diameter, 0.25 µm lm thickness; J&W
Scientic, Agilent Technologies). The carrier gas used was
helium, the gas ow rate through the column was 1 ml/min and
the front inlet purge ow was 3 ml/min. A 1 µl aliquot of the
analyte was injected in split‑less mode. The initial temperature
was kept at 80˚C for 12 sec, prior to being increased to 180˚C
at a rate of serum: 10˚C/min for serum (urine: 5˚C/min), then
to: 240˚C (urine: 220˚C) at a rate of: 5˚C/min (urine: 4˚C/min)
and nally to: 290˚C (urine: 285˚C) at a rate of 20˚C/min for
11 min (urine: 10 min). The transfer line, injection and ion
source temperatures were 270, 280, and 220˚C, respectively.
The energy was ‑70 eV in electron impact mode. Full‑scan
mode was used to acquire mass spectrometry data, with an
m/z range of 20‑600 at a rate of 100 spectra/sec following a
solvent delay of 492 sec.
Data analysis. Chroma TOF4.3X software (LECO corpora-
tion®) and LECO‑Fiehn Rtx5 database were used to examine
raw peaks (http://fiehnlab.ucdavis.edu/projects/FiehnLib/).
The data baselines ltered and calibrated the peak alignment,
deconvolution analysis, peak identication and integration of
the peak area. The peaks were normalized to the total sum of
the spectrum prior to multivariate analyses and the resulting
data were analyzed using PCA and OPLS with SIMCA‑P,
software version 11.5 (Umetrics, Umeå, Sweden) following
a unit variance procedure. The concentrations of potential
biomarkers were represented as their relative areas (divided by
the internal standard areas).
Statistical analysis. Quantitative data was presented as
mean ± standard deviation. Statistical analysis was completed
by one‑way analysis of variance with Student Newman‑Keuls
test using the Statistic Package for Social Science software,
version 17.0 (SPSS, Inc., Chicago, IL, USA). The histo-
logical grade of the liver was evaluated using Ridit analysis.
P<0.05 was considered to represent a statistically signicant
difference.
Result s
Histopathological changes to hepatic tissues. Fig. 1 presents
liver tissue samples from each group following H&E and
Masson staining. The control liver cell structure was clear
with a large and round nucleus and abundant in cytoplasm
with very little collagen deposition (Fig. 1A). The liver tissue
samples from the model group exhibited greater hyperplasia
of brous connective tissue, fatty degeneration, steatosis, cell
necrosis, inltration of inammatory cells and a larger number
of collagen bers compared with the control group (Fig. 1B).
Collagen bers were stained blue following Masson staining.
The portal area and interlobular septa had a small amount of
collagen bers deposited, which were shallow and small in the
control group (Fig. 1C). However, the model group exhibited
an increased amount of collagen ber hyperplasia, a diffusing
distribution of depth and a bulky and a false flocculus of
hepatic lobule a divided hepatic lobule into the pseudolobule
(Fig. 1D).
GC/MS spectra of the two groups. The typical GC/MS total ion
current (TIC) chromatograms of rat serum and urine 12 weeks
Figure 1. Histological examination of CCl4‑liver brosis in rats at 12 weeks (magnication, x200). Staining with H&E of the (A) control group and (B) model
group. Staining with Masson stain of the (C) control group and (D) model group. CCl4, carbon tetrachloride; H&E, hematoxylin and eosin stain.
GAO et al: SERUM AND URINE METABOLIC PROFILE CHANGES OF CCL4‑LIVER FIBROSIS
4
following injection for the model group is presented in Fig. 2.
The horizontal axis represents the time at which metabo-
lites occur while the vertical axis represents the metabolite
abundance. The peaks were considered to be representative
chemical ngerprints of endogenous metabolites and the time
above them represents their retention time (18). The area under
a peak represents the relative richness of the metabolites.
There were clear differences between the TIC proles of the
control and model groups. Spectra were pre‑treated further
and a pattern recognition analysis was performed to illuminate
changes in the metabolic proles.
PCA analysis. To understand the general trends and identify
differences and outliers among the groups in serum and urine
by GC/MS spectra, an unsupervised PCA was carried out to
analyze the multivariate data (19,20). In the score plot of PCA,
each data point represents the samples at week 12; the distance
between points in the score plot indicates the similarity between
samples. The results demonstrated that there were unsatisfactory
separations in the score plots between the two groups (Fig. 3).
OPLS‑analysis. To obtain a higher level of group separation
and enhance recognition of variables contribution to classi-
cation, OPLS analysis was completed (21). The experimental
results demonstrated that following OPLS analysis, the model
group had been separated from the control group in serum
and urine. This indicates that the model of liver brosis was
produced successfully and endogenous metabolites in serum
and urine of model rats were different compared with the
control group (Fig. 4).
Figure 2. Typical GC/MS TIC chromatograms of CCl4‑liver brosis in rat serum and urine samples obtained from the two groups (control and model group)
at 12 weeks. (A) Representative examples of serum results and (B) urine results. Samples obtained from different groups are illustrated at the top right corner
of the gure with the control and model groups indicated the orange and green respectively. GC/MS, gas chromatography‑mass spectrometry; TIC, total ion
current; CCl4, carbon tetrachloride.
EXPERI MENTAL AND THER APEUTIC M EDICINE 5
Identication of endogenous metabolites. To further investi-
gate the targeting biomarkers on the metabolite proles of liver
brosis, the rst principal component of variable importance
projection (VIP) was obtained by assessing the inuence of
every term in the matrix variable X on all the variable Y's,
where X and Y indicate the time and metabolite, respectively.
VIP is normalized so that Sum (VIP)2=K (number of terms
in the matrix X.) VIP values >1.0 were selected as changed
metabolites initially. The remaining variables were assessed by
Student's t‑test, which was reserved between two comparison
groups. To further identify the potential biomarkers, commer-
cial databases including the Kyoto Encyclopedia of Genes and
Genomes (KEGG, accessible at: http://www.genome.jp/kegg/)
and PubChem Compound (accessible at: https://pubchem.ncbi.
nlm.nih.gov/) were utilized to search for metabolites (22).
Based on the aforementioned analysis, seven metabolites in
serum (Table I) and ve metabolites in urine (Table II) were
listed as signicantly altered. For serum, the control group
exhibited increased levels of carnitine, glucose and fucose,
while isoleucine, L‑malic acid, α‑copper and hippuric acid
levels were increased in the model group. In the urine, levels of
N‑acetyl‑β‑alanine and cytidine were increased in the control
group compared with the model group while the model group
had increased levels of 2‑hydroxy butyric acid, isoleucine and
corticoid.
Biological pathway and function analysis. Metabolite
proling analyzes a group of metabolites related to a specic
metabolic pathway in biological states. To determine whether
the observed changes in the metabolites reflected coordi-
nate changes in defined metabolic pathways, CytoKEGG
version 3.0.1 (Cytoscape Consortium, San Diego, CA, USA)
was used for pathway construction. The pathways were
based on seven metabolites in serum, including isoleucine,
L‑malic acid, α‑copper, carnitine, hippuric acid, glutaric acid,
glucose and fucose. The substances were associated with
glucose, amino acid, P450, fatty acid or energy metabolism.
CytoKEGG was also used for pathway construction based
on the ve altered metabolites in urine, including 2‑hydroxy
butyric acid, isoleucine, n‑acetyl‑β‑alanine, cytidine and corti-
coid. The majority of these substances are related to amino
acid metabolism, energy metabolism, glutathione biosynthesis
and metabolism, nucleic acid metabolism or water‑electrolyte
metabolism (Fig. 5).
Discussion
Liver fibrosis is caused by a variety of factors, including
hepatic stellate cell activation and proliferation leading to the
synthesis and secretion of ECM. This leads to a large amount of
collagen ber deposition and eventually, the liver brosis (23).
Liver brosis is the pathological basis of liver disease, which
is a reversible lesion. However, the next step of liver disease,
liver cirrhosis is irreversible (24). Therefore, it is important to
develop methods to stop the progression of liver brosis.
CCl4 is one of the chemicals known to be a common
cause of acute chemical liver injury (25). As it causes a high
incidence of ECM secretion, this model is easy to reproduce
and is one of the common classical models of liver injury. The
present study demonstrated that the hepatic cell swelling and
marked necrosis observed in a number of collagen bers in
the model group may be induced by CCl4, proving that it is a
successful model of liver brosis.
Metabonomics is a novel analytical method that includes
analysis of endogenous metabolites in various biouids and
tissues and indicates potential associations between meta-
bolic prole changes and the physiological condition of the
biosystems (26,27). Regarding the analysis of serum and urine
samples at 12 weeks by GC/MS, the results indicated that CCl4
exposure caused signicant metabolic alterations in serum and
urine samples, which affected related metabolic pathways.
Carnitine is an unusual amino acid synthesized by lysine
and methionine in the liver. Carnitine has more important
functions than other amino acids as it is involved in the process
of protein synthesis and supplies energy through transporting
fat into the mitochondria. Therefore, it is an indispensable
factor in the process of fatty acid metabolism (28). A previous
study indicated that the content of carnitine in serum for the
model group was lower than in the control group (29). Thus,
Figure 3. Principal component analysis score plot of CCl4‑liver brosis in rat
(A) serum and (B) urine samples obtained from the two groups (control group
in red, model group in black) at 12 weeks. Samples with different groups are
indicated at the top right corner of the gure. CCl4, carbon tetrachloride.
GAO et al: SERUM AND URINE METABOLIC PROFILE CHANGES OF CCL4‑LIVER FIBROSIS
6
the change of carnitine content in the model group affects the
proceeding metabolism of fatty acids to a certain degree. The
disorder of fatty acid metabolism may damage the mitochondria
and lysosome, causing extracellular micro‑organ damage and
enhancing the toxicity of cytokines (30). This may lead to liver
degeneration, inammatory cell inltration and consequently,
brosis. Therefore, the present study indicates that there is an
association between liver brosis and fatty acid metabolism.
In the serum, the content of glucose and fucose decreased
in the model group compared with the control group. This
indicates that liver diseases, such as liver brosis, are associ-
ated with a disturbance of carbohydrate metabolism. In the
process of liver disease, the ability of insulin inactivation in
the liver is inhibited and due to this, insulin levels in serum
are markedly increased. This leads to the utilization of
glucose, therefor enhancing the level of fucose while glucose
levels decrease (31,32). This is consistent with the decrease of
saccharides observed in the model group of rats in the current
study. Saccharides, such as glucose, are the primary raw mate-
rial for energy usage in the liver; they are also essential factors
in the sugar metabolic pathways (33). In the present study, the
content of glucose and fucose was downregulated in the serum
of the model group, therefore, it is suggested that glucose and
fucose levels are associated with glycometabolism changes.
The change in glucose and fucose may also be related to the
inactivation of insulin in the process of hepatic brosis (34).
In both serum and urine, the isoleucine was increased in
the model group compared with the control group, indicating
that an amino acid metabolism disorder may exist in liver
brosis. A large number of experiments have demonstrated
that hepatopathy is strongly linked to inflammatory and
oxidative stress (35,36). Under oxidative stress, glycolysis and
gluconeogenesis are inhibited. Isoleucine is a branched‑chain
amino acid, which is involved in the synthesis of glucose
into triglycerides (TCA) in mammals by acetyl‑coenzyme A
(acetyl CoA) (37). If gluconeogenesis is restrained, it may lead
to an increase of isoleucine in hepatic cells (38). As the impor-
tant intermediate products of TCA, malic acid and α‑copper
glutaric acid are an energy supply for the body. Following CCl4
injections in rats, CCl4 decomposes into CCl3· and CCl3O3,
free radicals that induce oxidative stress by attacking the
liver cells (39). It has been demonstrated that the TCA cycle is
inhibited to reduce the generation of oxygen free radicals under
oxidative stress and may be associated with liver diseases (40).
Thus, an increase in the content of malic acid and α‑copper
glutaric acid may be caused by disturbance of the TCA cycle
in the model group.
Alanine is an essential amino acid, transformed to pyruvic
acid in hepatocytes and then pyruvic acid prior to entering the
mitochondrial TCA pathway (41). N‑acetyl‑β‑alanine is an
alanine derivative, which can be converted into acetyl‑CoA;
this enters the mitochondrial pathway and participates in
Figure 4. OPLS‑DA score plot of CCl4‑liver brosis in rats serum and urine samples obtained from the two groups (control group, model group) at 12 weeks.
Representative examples of (A) serum and (B) urine results. (Aa and Ba) These diagrams indicate that the model group had been separated from the control
group. (Ab and Bb) Metabolic substances are represented as dots, red indicates the potential biomarkers. CCl4, carbon tetrachloride; OPLS‑DA; Orthogonal
projections to latent structures‑discriminant analysis.
EXPERI MENTAL AND THER APEUTIC M EDICINE 7
the TCA cycle, which is involved in energy metabolism and
energy supply to the body (42). The variation of alanine and
N‑acetyl‑β‑alanine may be ascribed to the dysfunction of
TCA. Through the analysis of urine metabolite spectrum in
rats, it was demonstrated that the content of N‑acetyl‑β‑alanine
was reduced in the model rats, which may be associated with
disturbance of energy metabolism.
Compared with the control group, there was an increase of
hippuric acid in the model group. Hippuric acid is produced by
combining glycine with benzoic acid during cytochrome P450
catalysis (43). Consequently, changes in hippuric acid content in
the model group may occur following changes in cytochrome
P450, which is closely related to the formation of liver brosis.
The content of 2‑hydroxy butyric acid in the model group
is increased compared with in the control group. 2‑hydroxy
butyric acid is a type of organic acid derived from α‑butanone
acid and is involved in the synthesis and metabolism of gluta-
thione (44). Changes in glutathione synthesis consequently
result in the content of 2‑hydroxy butyric acid. It has been
demonstrated that glutathione can protect the liver from
oxidative stress damage, which is closely associated with liver
disease (45).
Cytosine is one of the pyrimidine bases in nucleic acids
and participates in complementary base pairing, which forms
cytidine, synthesizes cytidylic acid at a nucleoside triphos-
phate level and participates in nucleic acid synthesis and
metabolism (46). The liver is the area of nucleoside synthesis
within the body. Therefore, consistent with the results of the
present study, a number of reasons including injury, inamma-
tion and brosis lead to the loss of liver function and nucleic
acid synthesis insufciency. In urine, the content of cytidine in
the model group is lower than in the control group, which may
relate to a disturbance of nucleic acid metabolism.
The content of corticoid in the model group was increased
compared with the control group. Corticoid includes gluco-
corticoid and mineralocorticoid, while aldosterone is a
primary mineralocorticoid that is primarily regulated by
the renin‑angiotensin‑aldosterone system (RAAS), sodium
and potassium in the blood, which in turn is regulated by
water‑electrolyte metabolism (47). It has been indicated
that RAAS locally exists in the liver (48). When hepatic
brosis occurs, the level of inactivated aldosterone decreases
depending on how much the liver function subsides, thus
RAAS emerges at a high activity and is closely associated
Table I. Biomarkers and the changing trend of CCl4‑liver brosis in rat serum at 12 weeks.
Metabolite Var ID Possible Biomarker
No. (Primary) compounds RT, min VIP content in MG
1 143 isoleucine 9.86869 1.78195 Increasea
2 231 malic acid 12.2710 1.53429 Increaseb
3 274 α‑copper glutaric acid 13.4922 1.97915 Increasea
4 304 carnitine 14.3948 1.86529 Decreasea
5 368 glucose 17.5476 1.58140 Decreaseb
6 374 hippuric acid 17.7654 1.78514 Increasea
7 462 fucose 26.9799 1.48060 Decreaseb
519 peaks of the GC/MS spectra of the model and control groups were screened, corresponding to the number of the substance in serum when
the VarID was imported into the software, VIP values >1.0 were selected as changed metabolites. From this, 7 metabolites from serum were
demonstrated to be signicantly altered. aP<0.01, bP<0.05 vs. control group. CCl4, carbon tetrachloride; RT, retention time of the substance;
VIP, variable importance projection; MG, model group.
Table II. Biomarkers and the changing trend of CCl4‑liver brosis in rat urine at 12 weeks.
Metabolite Var ID Possible Biomarker
No. (Primary) compounds RT, min VIP content in MG
1 77 2‑hydroxy butyric acid 12.9871 2.48859 Increasea
2 114 isoleucine 15.0919 1.29507 Increasea
3 134 N‑acetyl‑β‑alanine 16.9516 2.53192 Decreasea
4 314 cytidine 24.8217 2.38341 Decreasea
5 491 corticoid 34.8550 2.96963 Increasea
519 peaks of the GC/MS spectra of the model and control groups were screened, corresponding to the number of the substance in serum when
the VarID was imported into the software, VIP values >1.0 were selected as changed metabolites. From this, 5 metabolites in the urine were
demonstrated to be signicantly altered. CCl4, carbon tetrachloride; RT, retention time of the substance; VIP, variable importance projection;
MG, model group. aP<0.05 vs. control group.
GAO et al: SERUM AND URINE METABOLIC PROFILE CHANGES OF CCL4‑LIVER FIBROSIS
8
with the formation of liver brosis. Therefore, the change of
corticoid content in the model group may be a reaction to the
change in water‑electrolyte metabolism.
In conclusion, the present study demonstrated that expo-
sure to CCl4 induced liver damage and signicantly altered a
number of metabolic pathways. Histological results indicated
that the model of liver brosis induced by CCl4 in rats was
successful. Pattern recognition with multivariate statistical
analysis indicated that the metabolic prole of CCl4‑induced
liver brosis was clearly separated from the control group.
Potential biomarkers were identified, seven metabolites in
serum and ve metabolites in urine, which may be associated
with the disturbance of energy, amino acid, carbohydrate,
cytochrome P450, glutathione synthesis, fatty acid, nucleic
acid and water‑electrolyte metabolisms. The current study
provided novel drug targets and demonstrated that meta-
bonomic methods based on GC/MS maybe a useful tool for
determining the pathogenesis of diseases.
Acknowledgements
The present study was financially supported by National
Natural Science Foundation of China (grant no. 81102874).
We are grateful to Ms. Jie Xu and Dr Junliang Deng (Biotree
Bio‑technology Co., Ltd., Shanghai, China) for providing help
with data analysis.
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