Chlamydia trachomatis growth inhibition and restoration of LDL-receptor level in HepG2 cells treated with mevastatin.

Abstract

Perihepatitis is rare but consistently occurring extragenital manifestation of untreated Chlamydia trachomatis infection. Despite of possible liver involvement in generalized C. trachomatis infection, the ability of the pathogen to propagate in the hepatic cells and its impact on liver functions is not thoroughly investigated. The effect of mevastatin, an inhibitor of 3-hydroxy-3-methylglutaryl CoA reductase, on C. trachomatis growth in human hepatoma cell line HepG2 has been studied. Bacterial growth was assessed by immunostaining with FITC-labeled monoclonal antibody against chlamydial lipopolysaccharide and by RT-PCR for two chlamydial genetic markers (16S rRNA and euo).
Chlamydial inclusion bodies were seen in approximately 50% of hepatocytes at 48 hours in the post infection period. Lysates obtained from infected hepatocytes were positive in the infective progeny test at 48 and especially in 72 hours after infection initiation. It has been shown that chlamydial infection in hepatocytes also leads to the decline of LDL-receptor mRNA which reflects infection multiplicity rate. Additions of mevastatin (1, 20 and 40 microM) 1 hour before inoculation restored and upregulated LDL-receptor mRNA level in a dose-dependent manner. Mevastatin treatment had no effect on internalization of chlamydial particles. However it reduced drastically the number of chlamydial 16S rRNA and euo transcripts as well as overall infection rate in HepG-2 cells. Complete eradication of infection has been seen by immunofluorescent staining at 40 microM mevastatin concentration, when expression level of chlamydial 16S rRNA and euo was undetectable. Lower concentration of mevastatin (20 microM) promoted euo expression level and the appearance of atypically small chlamydial inclusions, while there was a noticeable reduction in the number of infected cells and 16S rRNA transcripts.
C. trachomatis can efficiently propagate in hepatocytes affecting transcription rate of some liver-specific genes. Ongoing cholesterol synthesis is essential for chlamydial growth in hepatocytes. Inhibitors of cholesterol biosynthesis can supplement conventional strategy in the management of C. trachomatis infection.

Full text

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RESEARCHOpen Access
Chlamydia trachomatis growth inhibition and
restoration of LDL-receptor level in HepG2 cells
treated with mevastatin
Yuriy K Bashmakov1*†, Nailya A Zigangirova1,2†, Yulia P Pashko2, Lidia N Kapotina2, Ivan M Petyaev1
Abstract
Background: Perihepatitis is rare but consistently occurring extragenital manifestation of untreated Chlamydia
trachomatis infection. Despite of possible liver involvement in generalized C. trachomatis infection, the ability of the
pathogen to propagate in the hepatic cells and its impact on liver functions is not thoroughly investigated. The
effect of mevastatin, an inhibitor of 3-hydroxy-3-methylglutaryl CoA reductase, on C. trachomatis growth in human
hepatoma cell line HepG2 has been studied. Bacterial growth was assessed by immunostaining with FITC-labeled
monoclonal antibody against chlamydial lipopolysaccharide and by RT-PCR for two chlamydial genetic markers
(16S rRNA and euo).
Results: Chlamydial inclusion bodies were seen in approximately 50% of hepatocytes at 48 hours in the post
infection period. Lysates obtained from infected hepatocytes were positive in the infective progeny test at 48 and
especially in 72 hours after infection initiation. It has been shown that chlamydial infection in hepatocytes also
leads to the decline of LDL-receptor mRNA which reflects infection multiplicity rate. Additions of mevastatin (1, 20
and 40 μM) 1 hour before inoculation restored and upregulated LDL-receptor mRNA level in a dose-dependent
manner. Mevastatin treatment had no effect on internalization of chlamydial particles. However it reduced
drastically the number of chlamydial 16S rRNA and euo transcripts as well as overall infection rate in HepG-2 cells.
Complete eradication of infection has been seen by immunofluorescent staining at 40 μM mevastatin
concentration, when expression level of chlamydial 16S rRNA and euo was undetectable. Lower concentration of
mevastatin (20 μM) promoted euo expression level and the appearance of atypically small chlamydial inclusions,
while there was a noticeable reduction in the number of infected cells and 16S rRNA transcripts.
Conclusions: C. trachomatis can efficiently propagate in hepatocytes affecting transcription rate of some liver-
specific genes. Ongoing cholesterol synthesis is essential for chlamydial growth in hepatocytes. Inhibitors of
cholesterol biosynthesis can supplement conventional strategy in the management of C. trachomatis infection.
Background
Chlamydia trachomatis is a prevalent bacterial pathogen
causing most of the cases of urogenital infections and
preventable blindness in the world. Epididymitis and
urethritis in men, cervical as well as the urethral inflam-
mation in woman may lead to acute pelvic inflammatory
disease and variety of other extragenital manifestations
in both sexes. Among most frequent extragenital mani-
festations of C. trachomatis are sexually acquired
reactive arthritis (SARA), conjunctivitis and perihepatitis
[1]. In most of the cases of ophthalmological manifesta-
tions C. trachomatis can be detected and/or isolated in
the eye swabs [2]. It is believed that immunological and
hormonal phenotype as well as some genotype charac-
teristics, particularly expression of human leucocyte
antigen B27, predetermine the severity of extragenital
manifestations caused by C. trachomatis [3]. Delayed
cell-mediated immunological response is also known to
play an important role in the systemic generalization of
chlamydial disease [4].
However there is a growing body of evidence that C.
trachomatis can be present and isolated from
* Correspondence: YBash47926@aol.com
† Contributed equally
1Cambridge Theranostics Ltd, Babraham Research Campus, Babraham,
Cambridge, CB2 4AT, UK
Bashmakov et al. Comparative Hepatology 2010, 9:3
http://www.comparative-hepatology.com/content/9/1/3
© 2010 Bashmakov et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative
Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and
reproduction in any medium, provided the original work is properly cited.

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extragenital tissues and organs. Bacterial antigens, DNA
and/or RNA can be detected in whole blood [5,6] since
C. trachomatis can efficiently propagate in mononuclear
cells [7] as well as in astrocytes [8], muscle cells [9] and
myocardiocytes [10]. Virulent forms of C. trachomatis
can be isolated from synovial exudate [11], ascitic fluid
[12,13], liver biopsy material [14], and respiratory secre-
tion fluids [15]. Similar pattern of extragenital manifes-
tations has been reported in animal experiments.
Lesions containing virulent C. trachomatis have been
reported in lungs, liver and spleen of BALB/c mice in
the post-infection period [16]. With the exception of a
single report [14] there are no confirmed cases of C.
trachomatis isolation from the human liver or any
well articulated insights on the potential role of chla-
mydial infection in hepatobilliary pathology. However,
recently shown ability of C. trachomatis to propagate
in hepatocytes [17,18] leads to many questions about
possible involvement of liver in systemic chlamydial
disease.
In the present paper we have investigated the infect-
ability of C. trachomatis toward immortalized human
hepatoma cells (HepG2 cell line) and some metabolic
consequences of chlamydia propagation in the hepatic
cell line. In particular, of mRNA regulation of major
lipogenic genes in the host cells and effect of mevasta-
tin, an inhibitor of 3-hydroxy-3-methyglutaryl CoA
reductase (HMG-CoA reductase), in cases of chlamydial
infection in HepG2 cells are reported below.
Methods
Reagents
All reagents were purchased from Sigma-Aldrich unless
specifically mentioned otherwise. HepG2 and Hep2 cells
were obtained from “European Collection of Cell Cul-
tures” (Salisbury, UK).
Cell culture and organisms
HepG2 cells were cultured in 5% CO2in DMEM sup-
plemented with 10% Fetal Bovine Serum (FBS) and 2
mM glutamine. Cells were grown in 6, 24, and 96 well
plates until confluence rate of 80% was reached. Addi-
tion of mevastatin at concentrations ranging from 1 μM
to 40 μM was done 1 hour before inoculation of C. tra-
chomatis. Strain L2/Bu434 of C. trachomatis was kindly
provided by Dr. P. Saikku (University of Oulu, Finland).
Chlamydial strains were initially propagated in Hep2
cells and purified by Renografin gradient centrifugation
as described [19]. Chlamydial titers were determined by
infecting Hep2 cells with 10-fold dilutions of thawed
stock suspension. Purified elementary bodies (EB) with
known titer were suspended in sucrose-phosphate-gluta-
mic acid buffer [19] and used as inoculums for HepG2
cells.
HepG2 plates were infected with C. trachomatis at
multiplicities of infection (MOI) of 1 or 2 in DMEM
with 0.4% glucose without FBS and cycloheximide and
centrifuged for 0.5 hour at 1500 g. The cells were har-
vested for RNA analysis in 24 hours (expression of chla-
mydial genes) and in 48 hours (expression of eukaryotic
genes and immunofluorescence analysis) after infection
after the inoculation of C. trachomatis. Acell viability
assay was conducted routinely for each group of the
experiment using 2% trypan blue exclusion test. The cell
monolayers with viability > 85% were used for RNA
extraction and/or immunostaining. There was a signifi-
cant decrease in number of viable hepatocytes during
the late stage of chlamydial infection in HepG2 cells (72
hours).
Immunofluoresence staining
Infected HepG2 monolayers grown 48 hours on cover-
slips in 24 well plates, which were fixed with methanol.
Permeabilized cells were stained by direct immunofluor-
escence using FITC - conjugated monoclonal antibody
against chlamydial lipopolysaccharide (NearMedic Plus,
RF). Inclusion-containing cells were visualized using
Nikon Eclipse 50 i microscope fluorescence microscope
at X1350 magnification.
Internalization assay
Internalization assay has been performed as described
[20]. Briefly, to visualize attachment of C. trachomatis to
HepG2 cells, elementary bodies (EB) of C. trachomatis
were added at MOI 50 to the 24 well plates with cover-
slips containing hepatocytes monolayers. The EB were
allowed to attach in presence or absence of 40 μM
mevastatin for 60 min at 4°C after which the inoculum
was removed, cell were washed 3 times with ice-cold
PBS. To visualize attached particles, the cell monolayers
were fixed in 4% paraformaldehyde for 15 min on ice.
This regimen of fixation is believed to maintain the
integrity of the plasma membrane in the host cells [20].
After fixation the cells were washed with PBS and incu-
bated for 30 min with monoclonal chlamydial LPS-spe-
cific antibody labeled with FITC (1 μg/ml, NearMedic
Plus, RF) for visualization of attached particles. Interna-
lization has been studied in separate set of experiments.
To allow attachment, HepG2 cells were incubated with
EB of C. trachomatis in presence or absence of 40 μM
mevastatin for 1 hour at 4°C after which the inoculum
was removed and the cells were washed 3 times with
ice-cold PBS. The cells were transferred to 37°C for 1
hour to permit internalization. After fixation with 4%
paraformaldehyde (15 min, room temperature) the cells
were incubated for 30 min with the polyclonal antibody
raised against EB of C. trachomatis (Gamaleya Institute
of Microbiology and Epidemiology, Moscow, RF). This
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step was performed in order to block attachment sites of
non-internalized EB. After fixation with methanol (15
min, room temperature), which allows penetration of
antibody inside of the cells [20], cell monolayers were
incubated for 30 min with 1 μg/ml of monoclonal
FITC-conjugated antibody against C. trachomatis major
outer membrane protein (MOMP) (NearMedic Plus,
RF). The cells were washed thoroughly with PBS and
analyzed by immunofluorescent microscope.
Assessment of infective progeny
In order to assess the infective progeny accumulation in
HepG2 cells after 48 hour cultivation period, HepG2
cells were harvested, frozen and thawed, as described
elsewhere. Serial dilutions of lysates were inoculated onto
Hep-2 cells and centrifuged for 0.5 hour at 1500 g. The
infected cells were visualized with C. trachomatis LPS-
specific antibody in 48 hours of the post-infection period.
RNA extraction and reverse transcription
RNA was isolated from HepG2 monolayers grown on 6-
well plates using TRIZol (Invitrogen). Total mRNA pre-
treated with DNase I (DNA-free™, Ambion) and quanti-
fied on the spectrophotometer NanoDrop ND-100
(ThermoFisher Scientific, Wilmington, USA) was con-
verted into cDNA using random hexamer primers and a
SuperScript III First-Strand Synthesis Kit (Invitrogen,
Karlsruhe, Germany).
Quantitative real-time PCR
The mRNA levels for two different developmental
genes of C. trachomatis were analyzed in HepG2
cells by quantitative RT-PCR using thermocycler
ANK 32 (Syntol, RF). The 16S rRNA and gene encod-
ing DNA-binding protein Euo were studied as constitu-
tive markers of the early stage of chlamydial
developmental cycle. Primers for C. trachomatis 16S
rRNA (sense - 5’-GGCGTATTTGGGCATCCGAGT
AACG-3’, antisense - 5’-TCAAATCCAGCGGGTATTA
ACCGCCT-3’) and C. trachomatis Euo (sense - 5’-TC
CCCGACGCTCTCCTTTCA-3’, antisense - 5’-CTCG
TCAGGCTATCTATGTTGCT-3’) were verified and
used under thermal cycling conditions - 95°C for 10
min and 50 cycles of 95°C for 15 seconds, 60°C for 1
min and 72°C for 20 seconds. Serial dilutions of C. tra-
chomatis RNA, extracted from chlamydia-infected Hep-
2 cells, were used as a standard for quantification of
chlamydial gene expression. The results of PCR analysis
for chlamydia-specific genes were normalized to mRNA
values of human beta actin (b-actin, primers: sense - 5’-
GCACCCAGCACAATGAAGAT-3’, antisense - 5’-GC
CGATCCACACGGAGTAC-3’). Among other human-
specific genes studied were major lipogenic enzymes: 3-
hydroxy-3-methyglutaryl CoA reductase (HMG CoA
reductase, primers: sense-5’-CAAGGAGCATGCAAA-
GATAATCC-3’ antisense -5’-GCCATTACGGTCC
CACACA-3’); 3-hydroxy-3-methyglutaryl CoA synthase
(HMG CoA Syn, primers: sense - 5’-GACTTGTGC
ATTCAAACATAGCAA-3’, antisense - 5’-GCTGTAGC
AGGGAGTCTTGGTACT-3’); squalene synthase (SS,
primers: sense - 5’-ATGACCATCAGTGTGGAAAAG
AAG-3’, antisense - 5’-CCGCAGTCTGGTTGGTAA-3’);
and fatty acid synthase (FAS, primers: sense-5’-TC
GTGGGCTACAGCATGGT-3’, antisense - 5’-GCC
CTCTGAAGTCGAAGAAGAA-3’).
The mRNA levels for lipogenic enzymes as well
as mRNAs for LDL-receptor (LDL-R, primers: sense -
5’-GGCTGCGTTAATGTGACACTCT-3’, antisense -
5’-CTCTAGCCATGTTGCAGACTTTGT-3’)
LDL-receptor related protein (LRP, primers: - 5’-CCT
ACTGGACGCTGA CTTTGC-3’ antisense - 5’-GGC
CCCCCATGTAGAGTGT-3’) in the host cells were nor-
malized to human b-actin expression level. The mRNA
expression levels in the host cells were referenced to the
CT values in uninfected HepG2 cells grown at the same
conditions. That reference value was taken as 1.00. Each
cDNA sample was tested by PCR at least three times.
All experiments were repeated at least twice. Represen-
tative sets of results are shown below.
and
Results
C. trachomatis growth in HepG2 cells
Immunofluorescent images of HepG2 infected cells
reveal that C. trachomatis can efficiently grow in
immortalized hepatocytes cells line. Positive immuno-
fluorescence was first apparent within 24 hours of post-
infection period and did not differ in intensity at MOIs
of 1 and 2. Inclusion bodies were seen in about 50% of
cells at 48 hours in the post-infection period at MOI of
1. Up to 70% of the infected cells were seen at multipli-
city rate of 2. Most of the immunostaining was localized
throughout whole cytoplasm. However some cells had
perinuclear pattern of immunofluorescence with no
intranuclear inclusions seen. At 48 and especially 72
hours of the post-infection period, immunostaining was
stronger with numerous inclusion bodies. Some of them
were released from the ruptured cells. To determine if
C. trachomatis can be cultured from HepG2 mono-
layers, we harvested 24 and 48 hour cultures of hepato-
cytes. Replication was not observed when 24 hour
lysates of hepatocytes were inoculated to Hep2 cells.
However the lysates obtained in 48 and especially 72
hour were positive in the infective progeny test.
LDL-receptor mRNA and multiplicity of infection
As can be seen from Table 1, 48 hour propagation of C.
trachomatis in HepG2 cells did not affect mRNA for a
major housekeeping gene - 36B4, nor mRNAs for
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lipogenic enzymes. However, there is dose-dependent
decline in LDL-receptor mRNA, reflecting multiplicity
infection level. LDL-receptor related protein mRNA
remained unchanged.
Mevastatin reverses LDL-receptor mRNA decline
Inhibitors of HMG-CoA reductase are the most power-
ful activators of LDL receptor, whose activity on the
LDL-receptor is mediated by SREBP pathway [21]. The
addition of mevastatin to HepG2 cells infected with C.
trachomatis at MOI of 1 did not affect cell viability nor
mRNA levels of 36B4 (Table 2). However, LDL-receptor
mRNA level was dose-dependently upregulated with the
increasing concentrations of mevastatin, reaching 2 fold
induction at 40 μM level. This effect was even more
pronounced at 72 hours of the post-infection period
though cell viability was declining (results not shown).
Thereisalsodose-dependent upregulationof
cholesterologenic enzymes (HMG-CoA reductase,
HMG-CoA synthase, SS) which is well known effect of
statins in the cultures cells [22]. Notably, LDL-receptor
related protein mRNA was not impacted under all con-
ditions studied.
Mevastatin inhibits chlamydial growth in HepG2 cells
Figure 1 shows representative immunofluorescent
images of HepG2 cells infected with C. trachomatis in
presence of increasing concentrations of mevastatin. As
can be seen, the effect of mevastatin was marginal at the
concentration of 1 μM, though some decline in the
number of infected cells has been noticed. However, 20
μM mevastatin reduced both the number of inclusion
bodies in the infected cells, promoting a perinuclear pat-
tern of staining. Mevastatin-treated cells (20 μM)
appeared to contain smaller inclusion bodies similar to
those that occur during persistent chlamydial infection
[23]. The highest concentration of mevastatin tested (40
μM) abolished the number of infected cells almost com-
pletely. Analysis of bacterial transcripts showed a similar
tendency. As can be seen from Figure 2, 16S rRNA and
euo mRNA were undetectable at highest concentration
of mevastatin used, whereas at 20 μM and 1 μM mevas-
tatin reduced the expression level for 16S rRNA by 8
and 3 fold respectively. There is significant induction of
euo mRNA at 20 μM mevastatin concentration.
Inhibition of chlamydial growth in cultured cells in
presence of mevastatin may take place due to abnormal
internalization of chlamydial particles, since the entry of
chlamydial particles into mammalian cells requires
interaction of pathogens with lipid rafts of plasma mem-
brane [24]. Therefore, we next investigated the internali-
zation rate of chlamydial particles into HepG2 cells in
presence of 40 μM mevastatin. As can be seen from Fig-
ure 3, HepG2 cells treated with 40 μM mevastatin have
similar number of chlamydial particles attached to the
plasma membrane when compared to untreated control
cells. Mevastatin treatment did not affect the number of
internalized particles as well (results not shown).
Discussion
Although there is a small but growing body of evidence
that C. trachomatis can be disseminated widely through-
out the human body, the physiological consequences
and overall medical relevance of extragenital propaga-
tion of C. trachomatis remains poorly understood. First
of all, our results confirm initial observations [25] show-
ing the ability of C. trachomatis to propagate in HepG2
hepatoma cell line. More importantly, we have demon-
strated that propagation of C. trachomatis in hepato-
cytes follows full infectious cycle leading to the
formation of infectious progeny in 48 and 72 hours of
post-infection period. Propagation of the pathogen
Table 1 Folds and mRNA changes in HepG2 cells infected
with C. trachomatis at different infectivity rates.
Parameter Non-infected cells Infected cells
MOI 1
18.26
1.31
1.06
1.21
0.76
0.87
0.88
MOI2
18.01
0.98
0.87
0.89
0.56
0.99
0.89
36B4ct
HMG-CoA Red
HMG-CoA Synth
SS
LDL-R
LRP
FAS
18.37
1
1
1
1
1
1
HepG2 cells were set up, grown and infected with C. trachomatis in presence
or absence of mevastatin as described in Methods. RNA was extracted in 48
hours after inoculation of the bacteria. RNA levels for the genes of interest
were normalized to 36B4 expression level, whose CT values are represented in
the upper row of the Table. All RNA values in the infected cells are referenced
to non-infected control
Table 2 Folds and mRNA changes in C. trachomatis-
infected HepG2 cells after addition of mevastatin.
Parameter Non-infected cellsInfected cells – Addition of
mevastatin
0 μM1 μM
17.04 16.94
1.061.17
0.791.46
0.871.27
0.691.38
1.090.85
0.950.92
20 μM
16.98
1.7
1.53
1.54
1.63
0.91
0.89
40 μM
17.01
1.81
1.89
1.73
2.08
0.99
0.96
36B4ct
HMG-CoA Red
HMG-CoA Synth
SS
LDL-R
LRP
FAS
16.94
1
1
1
1
1
1
HepG2 cells were set up, grown and infected with C. trachomatis in presence
or absence of mevastatin as described in Methods. RNA was extracted in 48
hours after inoculation of the bacteria. RNA levels for the genes of interest
were normalized to 36B4 expression level, whose CT values are represented in
the upper row of the Table. All RNA values in the infected cells are referenced
to non-infected control.
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Figure 1 Immunofluorescent images of HepG2 cells infected with C. trachomatis in presence of mevastatin. HepG2 cells were set up,
grown and infected with C. trachomatis in presence or absence of mevastatin as described in Methods. Immunofluorescence analysis was
performed 48 hours after inoculation of the pathogen. A - non-infected cells; B – infected cells with no mevastatin; C – infected cells in
presence of 1 μM mevastatin: D – infected cells in presence of 20 μM mevastatin; E – infected cells in presence of 40 μM mevastatin. Scale bar
= 10 μm.
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distinctively affects some specific functions of the liver
cells. In particular, C.trachomatis ameliorates transcrip-
tion of LDL-receptor in hepatocytes, which may have
various consequences for lipid homeostasis.
Chlamydial organisms are strict intracellular parasites,
whose requirements in the metabolites are covered by
the host cells. Enhanced uptake of the substrates and
metabolites by the infected host cells is a well known
“signature” strategy of chlamydial infection mandatory
for successful accomplishment of its infectious cycle
[25]. However, in the case of the chlamydial growth in
HepG2 cells we have seen significant decline in LDL-
receptor mRNA, which may potentially result in the
reduction of lipid uptake. The biological significance of
this finding remains unclear. However it is possible to
assume, that decline in the LDL-receptor mRNA might
represent a mechanism of metabolic adaption of the
host cell to chlamydial infection targeted on limitation
of lipid supply and chlamydial growth in the cells.
Unfortunately we were not able to document corre-
sponding changes in LDL-receptor protein level due to
decline in number of viable HepG2 cells that occurs at
72 hour time point of post-infection period. Models of
persistent chlamydial infection might be required for
evaluating hepatic LDL-receptor turnover in the infected
liver cells.
Figure 2 Expression of chlamydial 16S RNA and euo in infected hepatocytes grown at different concentration of mevastatin. HepG2
cells were set up, grown and infected with C. trachomatis in presence or absence of mevastatin as described in Methods. RNA was extracted in
24 hours after inoculation of the bacteria. Expression of chlamydial genes was normalized to copy number of eukaryotic b-actin.
Figure 3 Attachment of chlamydial particles to plasma membrane of hepatocytes in presence or absence of mevastatin. HepG2 cells
were set up, grown and incubated with chlamydial particles (EB) in presence or absence of mevastatin as described in Methods. Attached
particles were visualized with FITC-labeled antibody against chlamydial LPS. A – attachment of chlamydial particles in absence of 40 μM
mevastatin: B – attachment of chlamydial particles in presence of 40 μM mevastatin. Scale bar = 10 μm.
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Secondly, we have clearly shown that mevastatin, an
inhibitor of cholesterol biosynthesis, restores LDL-recep-
tor mRNA and has a significant anti-chlamydial activity
reducing chlamydial growth in infected hepatocytes.
Genome of C. trachomatis does not contain genes
responsible for lipid biosynthesis. Chlamydial species are
known to acquire cholesterol, fatty acids and triglycer-
ides from the host cells [26]. Therefore, it was reason-
able to believe that targeting the cholesterol biosynthetic
pathway in the host cells might affect chlamydial infec-
tion rate. This prediction was confirmed by RT PCR
analysis. It is well acknowledged, that C. trachomatis
16S rRNA gene expression is an informative criterion of
chlamydial developmental cycle expressed in both early
and late stages of C. trachomatis infection [27]. Detec-
tion of 16S rRNA transcript as a marker of viable and
metabolically active Chlamydia allows to evaluate the
effectiveness of different antibacterial agents [28]. Maxi-
mum inhibition of 16S rRNA as well as drastic reduc-
tion in the number of infected immunofluorescence-
positive cell has been seen at 40 μM mevastatin level.
Less pronounced decline in 16S rRNA transcript level
has been observed at 20 μM mevastatin concentration.
Even though addition of 20 μM mevastatin did not
result in complete inhibition of chlamydial growth in
HepG2 cells, there was formation of smaller chlamydial
inclusions. Those are often observed in antibiotic- and/
or cytokine-treated cells when concentration of the
agent is not enough to induce complete eradication of
the pathogen [23]. “Aberrant” chlamydial cells are
known to have some metabolic activity but fail to
induce new rounds of chlamydial infection [23,28].
Therefore inhibition of chlamydial growth in mevasta-
tin-treated HepG2 cells takes place in clearly dose-
dependent manner. Step-wise decline in 16S rRNA level
was accompanied by reduction in the number of
infected cells (1 and 20 μM mevastatin), as well as the
appearance of “aberrant” chlamydial forms (20 μM
mevastatin) until complete eradication of chlamydial
growth takes place (40 μM mevastatin). Euo mRNA
level has been changing in a similar manner, except
inconsistent increase seen at 20 μM concentration of
mevastatin. However, it is known that euo mRNA can
be highly induced when the developmental cycle of C.
trachomatis in cultured cells is compromised by addi-
tion of cytokines and other substances affecting chlamy-
dial growth [28]. It has been proposed, that increased
expression of euo may inhibit transcription of the genes
specific for “late phase” of chlamydial developmental
cycle [28,29]. Thus, enhanced transcription rate of euo
may represent self-sufficient mechanism predetermining
anti-chlamydial activity of mevastatin.
It is also important to conclude, that according to our
results mevastatin has no effect on initial interaction of
chlamydial particles with host cell, allowing the entry of
the pathogen into hepatocytes. Therefore we assume that
later stages of chlamydial developmental cycle are affected
by mevastatin treatment. The effect of different metabolites
and inhibitors of mevalonate pathway needs to be tested in
hepatocytes infected with C. trachomatis in presence of
mevastatin. It is possible, that anti-chlamydial activity of
mevastatin takes place due to reduced geranylgeranylation
of host cell proteins as it happens in case of lovastatin-trea-
ted hepatocytes infected with hepatitis C virus [30].
Conclusions
We have demonstrated that ongoing cholesterol synth-
esis is essential for chlamydial growth in hepatocytes.
Although the precise mechanism of anti-chlamydial
activity of mevastatin remains to be elucidated, targeting
the cholesterol biosynthetic pathway may represent an
effective strategy in management of chlamydial infection.
Acknowledgements
Ms Agni Roce is appreciated for invaluable help during experimental work
and manuscript preparation.
Author details
1Cambridge Theranostics Ltd, Babraham Research Campus, Babraham,
Cambridge, CB2 4AT, UK.2Department of Medical Microbiology, Institute of
Epidemiology and Microbiology RAMS, 18 Gamaleya Str, Moscow 123098,
Russia.
Authors’ contributions
YKB and NAZ contributed equally into design, acquisition of data, analysis
and interpretation of the results. YPP and LNK performed immunostaining
and RNA protocols. IMP contributed into primary concept, drafting the
manuscript, and final approval for publishing the results. All authors read
and approved the final manuscript.
Competing interests
The authors declare that they have no competing interests.
Received: 1 July 2009
Accepted: 28 January 2010 Published: 28 January 2010
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doi:10.1186/1476-5926-9-3
Cite this article as: Bashmakov et al.: Chlamydia trachomatis growth
inhibition and restoration of LDL-receptor level in HepG2 cells treated
with mevastatin. Comparative Hepatology 2010 9:3.
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