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Anti-fibrotic effect of thymoquinone on hepatic stellate cells.


Hepatic stellate cells (HSCs) are the major cell type involved in the production of extracellular matrix in liver. After liver injury, HSCs undergo transdifferentiation process from quiescent state to activated state, which plays an important role in liver fibrosis. Previous studies have shown that thymoquinone (TQ) might have protective effect against liver fibrosis in animal models; however, the underlying mechanism of action is not fully understood. The aim of this study is to examine whether TQ has any direct effect on HSCs. Our results showed that pretreatment of mice with TQ, has protective effect against C[Cl.sub.4]-induced liver injury compared to control group (untreated), which is consistent with previous studies. Moreover, our in vivo study showed that COL1A1 and a-SMA mRNA levels were significantly down-regulated by TQ treatment. Similarly, in vitro study confirmed that TQ downregulated COL1A1.COL3A1 and a-SMA mRNA levels in activated rat HSCs and LX2 cells, an immortalized human hepatic stellate cell line. Pretreatment with TQ also inhibited the LPS-induced proinflammatory response in LX2 cells as demonstrated by reduced mRNA expression of IL-6 and MCP-1. Mechanistically, inactivation of NF-[kappa]B pathway is likely to play a role in the TQ-mediated inhibition of proinflammatory response in HSCs. Finally, we have shown that TQ inhibited the culture-triggered transdifferentiation of freshly isolated rat HSCs as shown by significant downregulation of mRNA expression of several fibrosis-related genes. In conclusion, our study suggests that TQ has a direct effect on HSCs, which may contribute to its overall antifibrotic effect.



Hepatic stellate cells



Liver fibrosis

Carbon tetrachloride


Liver fibrosis is one of the leading causes of morbidity and mortality worldwide (Moreira 2007). Liver fibrosis results from an excessive accumulation of extracellular matrix proteins that represents the liver's response to injury. Liver fibrosis is not an independent disease, rather an outcome of many chronic liver diseases such as HCV infection, alcohol abuse, and nonalcoholic steatohepatitis (NASH) (Bataller and Brenner 2005; Friedman 2003). Untreated liver fibrosis results in progression to cirrhosis, liver failure, and portal hypertension (Bataller and Brenner 2005). Importantly, strong evidence now exists to support the concept that liver fibrosis is a reversible condition (Benyon and Iredale 2000; Dufour et al. 1997; Friedman and Bansal 2006). Therefore, the chances of reversibility at fibrosis stage are much higher than if the condition progresses to cirrhosis (Friedman 2003).

Currently, there is no standard treatment for liver fibrosis. Removal of the causative agent is still considered the most effective therapy (Bataller and Brenner 2001; Cheng and Mahato 2007; Davis et al. 2003). In the past decade, significant progress has been made in the comprehending of the underlying mechanism of liver fibrosis. It has been well established that hepatic stellate cells (HSCs) play a central role in liver fibrosis (Bataller and Brenner 2001). Following liver injury, HSCs undergo "activation" or transdifferentiation process from quiescent vitamin-A storing cells to myofibroblast-like cells. This process leads to notable changes in phenotypic features of HSCs including: increased expression of a SMA (protein that is involved in cell motility and contractility), loss of retinoid-storing capacity, enhanced cell migration and adhesion, increased proliferation, production of chemotactic proteins, enrichment of rough endoplasmic reticulum and acquisition of fibrogenic capacity (Atzori et al. 2009; Moreira 2007).

Thymoquinone (TQ) is the main active constituent of Nigella sativa plant oil, also known as black seed or black cumin (Sayed 1980). TQ is commonly used as food additive and has been known for centuries for its ability to prevent and cure many diseases (Al-Ghamdi 2003). Several studies have shown that TQ has many pharmacological effects, including antioxidation and hepatoprotective effects against hepatotoxins (Mansour 2000; Nagi et al. 1999; Ragheb et al. 2009; Woo et al. 2012). For instance, pretreatment of mice with TQ led to significant decreases in C[Cl.sub.4]-induced liver injury as shown by histology examination and serum enzyme (ALT, AST and LDH) tests (Anderson and Smith 2003). A recent study by Oguz et al. shows that TQ inhibits common bile duct ligation (CBDL)-induced liver damage in rats including the fibrotic changes in the liver (Oguz et al. 2012). So far, the hepatoprotective and antifibrotic effects of TQ is largely attributed to its antioxidative activity that leads to decreased hepatocyte damage and thus decreased transactivation of HSCs. However, the detailed mechanism remains incompletely understood. Particularly, a role of TQ in directly inhibiting the fibrogenic activity of HSCs has not been studied.

In this study, we showed that TQ can protect liver damage induced by C[Cl.sub.4], which is consistent with the published work. We have also shown that TQ can directly act on HSCs via inhibiting their transactivation and the expression of fibrosis-related genes. Our study unveils a new mechanism that may contribute to the overall antifibrotic effect of TQ.

Materials and methods


Female CD-1 mice weighing ~25g were purchased from The Jackson Laboratory (Bar Harbor, ME). Male Sprague-Dawley rats (200-250 g) from Charles River Laboratories (Wilmington, MA) were used for HSC isolation.


Lipopolysaccharides (LPS), silymarin (SM), and TQ were purchased from Sigma-Aldrich (St. Louis, MO). The purity (GC) of TQ is [greater than or equal to] 98.5% as per the manufacturer's specification. Carbon tetrachloride (C[Cl.sub.4]) was purchased from Merck (Whitehouse Station, NJ).

Cell line

LX2, an immortalized human hepatic stellate cell line, was kindly provided by Dr. Scott L. Friedman (Mount Sinai School of Medicine, New York, NY) and cultured in Dulbecco's modified Eagle's medium (DMEM) with 10% fetal bovine serum (FBS) and antibiotics.

Rat HSCs isolation

Retired male Sprague-Dawley rats, weighing 200-250 g, were used to isolate HSCs. HSCs were isolated via in situ proteinase/collagenase perfusion followed by density gradient centrifugation as described (Li et al. 2011). The purity of isolated cells was >90%. Isolated HSCs were cultured in 6-well plates in DMEM with 10% FBS and antibiotics for 7 days to allow the process of activation.

Assessment of TQ protective effect in mice

Four groups were used (n = 4) in this study including group A that received no treatment, group B that was treated with oral TQ (25 mg/kg dissolved in sesame oil), group C that received i.p. injection of C[Cl.sub.4] (dissolved in sesame oil), and group D that received both TQ and C[Cl.sub.4] treatment. Mice in groups B and D were treated with TQ daily for 7 days while mice in groups C and D received a single dose of C[Cl.sub.4] on day 6. All mice were sacrificed 2 days after C[Cl.sub.4] injection. Samples from liver tissues were directly stored in -80 [degrees]C freezer for gene expression study or fixed in 4% paraformaldehyde for histology study.

Mouse liver tissue processing

The liver was sectioned and fixed in 4% paraformaldehyde for histological analysis. Each formaldehyde-fixed sample was embedded in paraffin, cut into 5 [micro]m-thick sections and stained with hematoxylin-eosin (H-E) and Masson's trichrome according to standard procedures.

Cytotoxicity assay

LX2 cells were seeded in 96-well plates and incubated in DMEM containing 10% FBS overnight. Cells were then treated with various concentrations of TQor SM (in DMSO) for 24 h. Cell viability was measured by MTT assay (Roche Diagnostics, Indianapolis, IN) as described (Huang et al. 2012).

RNA isolation and qRT-PCR

Total RNA was extracted with TRIzol reagent (Invitrogen). The total RNA was measured by NanoDrop 2000 (Thermo Scientific). Extracted RNA concentration was adjusted to be 1 [micro]g per reverse transcription reaction using Superscript III reverse transcriptase (Invitrogen). The primers for COL1 Al, COL3A1, a-SMA, MCP-1, IL-6 and GAPDH were obtained from MWG Biotech. After synthesis of first strand cDNA, real-time PCR was performed using SYBR Green-based assays with the ABI Prism 7300 (Applied Biosystems, Foster City, CA) (Li et al. 2008a).

Assessment of TQ inhibitory effect on LPS-induced proinflammatory response in LX2 cells

LX2 cells were seeded in a 6-well plate in DMEM containing 10% FBS overnight. Cells were pretreated with TQ for 24 h, challenged with LPS (100 ng/ml) for 4 h, and then were harvested with TRIzol reagent. MCP-1 and IL-6 mRNA expression levels were measured as described above.

Assessment of TQ inhibitory effect on culture-triggered transdifferentiation, and fully activated primary rat HSCs and LX2 cells

Rat HSCs were isolated as described above. Cells were divided into 7 groups: untreated cells that were harvested on day 1, vehicle-treated cells that were treated with DMSO (0.1%) and harvested on day 7, TQ-treated cells that were treated with TQ (4 [micro]M) once every 2 days and harvested on day 7, and cells cultured for 7 days followed by treatment with TQ (1 and 4 [micro]M) for 24 h, and cells cultured for 7 days followed by treatment with silymarin (10 and 40 [micro]M) for 24 h. The mRNA expression levels of COL1 Al and [alpha]-SMA genes were assessed by qRT-PCR as described above. Similarly, LX2 cells were treated with different concentrations of TQand SM for 24 h, and the mRNA expression levels of COL1 Al and [alpha]-SMA genes were assessed by qRT-PCR.

Western blot

Cells were harvested after being washed and lysed in lysis buffer (0.2% Triton X-100) for 5 min on ice. Cell lysates were collected and centrifuged 12,000 rpm for 10 min at 4[degrees]C. Equal amounts of proteins were heated to 95 [degrees]C for 5 min in loading buffer and then separated on 10% SDS-polyacrylamide gel. The proteins were transferred to polyvinylidene difluoride membranes (Thermo Scientific) that were blocked for 1 h and then probed overnight at 4 [degrees]C with an antibody specific to p-NF-[kappa]B p65 (Santa Cruz Biotechnology, Santa Cruz, CA). Blots were then incubated with horseradish peroxidase (FIRP)-conjugated secondary antibody. HRP was detected using chemiluminescence detection reagent (Denville Scientific Inc.).

Statistical analysis

Values for all measurements are expressed as mean [+ or -] SEM. Each experiment was performed in triplicate. Comparisons between two groups were made with unpaired Student's t test. Differences were considered statistically significant if the p value was less than 0.05.


TQ protects against C[Cl.sub.4]-induced liver damage

We first investigated TQ protective effect in mice that were pretreated with TQ (25 mg/kg) for 5 days followed by C[Cl.sub.4] injection. TQ-pretreated group showed significant resistance to C[Cl.sub.4]-induced injury compared to the group that received only C[Cl.sub.4] (without TQ pretreatment) (Fig. 1C and D). Mice treated with TQ alone showed a liver histology similar to that of untreated group (Fig. 1A and B).

TQ downregulates the mRNA expression of COL1A1 and [alpha]-SMA in mouse liver

Following the demonstration of the hepatoprotective effect of TQ we then investigated the effect of TQ on the mRNA expression of COL1 Al and a-SMA in the liver of C[Cl.sub.4]-treated mice. COL1 Al is the major collagen in fibrotic liver (Friedman et al. 1985) and its mRNA expression level was significantly upregulated in the liver of C[Cl.sub.4]treated mice (Fig. 2). TQ pretreatment significantly inhibited the C[Cl.sub.4]-induced upregulation of COL1A1 mRNA expression in mouse liver. TQ similarly inhibited the C[Cl.sub.4]-induced upregulation of aSMA, a known marker for HSC activation (Mabuchi et al. 2004) (Fig. 2). These data suggest that TQ exhibits antifibrotic activity.

In vitro cytotoxicity of TQ

The hepatoprotective effect of TQ is likely to play a role in its antifibrotic activity due to the decreased damage of hepatocytes and thus decreased HSC activation. We hypothesized that TQ also inhibits the fibrogenic activity via a direct effect on HSCs. To test this hypothesis, we first examined the effect of TQ on the proliferation of HSCs in vitro as induction of HSC apoptosis is currently being explored as a therapeutic approach for the prevention and/or treatment of liver fibrosis (Hagens et al. 2008). Fig. 3A shows the result of a MMT assay with LX2 cells. LX2 is an immortalized human hepatic stellate cell line and these cells are fully activated (Xu et al. 2005). Our results indicated that TQ inhibited the proliferation of LX2 cells in a dose-dependent manner. Silymarin showed minimal effect on the proliferation of HSCs at the concentrations used (Fig. 3B).

TQ downregulates the expression of several fibrosis-related genes in LX2 cells and culture-activated primary rat HSCs

Following the demonstration of the growth inhibitory effect of TQ on LX2 cells, we went on to further examine the effect of TQ on the mRNA expression of several fibrosis-related genes including COL1 Al, COL3A1, and a-SMA in both LX2 and culture-activated primary rat HSCs. TQ was applied to cells at the concentrations that were shown to have minimal effect on cell growth (Fig. 3). As shown in Fig. 4A, TQ inhibited the mRNA expression of all of the three genes in LX2 cells in a concentration dependent manner. Moreover, TQ significantly downregulated COL1 Al and a-SMA mRNA expression in culture-activated primary rat HSCs as shown in Fig. 4B. Similar effects were shown for silymarin at concentrations that were nontoxic to the cells (Fig. 4A and B).

TQ suppresses the LPS-induced proinflammatory response in LX2 cells

It is known that HSCs can produce certain types of chemokines and cytokines in response to various types of stimuli such as LPS, which could have both paracrine and autocrine effects (Gressner and Weiskirchen 2006). To examine if TQ can inhibit the proinflammatory response of HSCs toward LPS, LX2 cells were pretreated with TQ followed by challenge with LPS and the mRNA expression of monocyte chemoattractant protein-1 (MCP-1) and interlukin-6 (1L-6) was examined. As shown in Fig. 5, LPS induced significant upregulation in the mRNA expression of both MCP-1 and IL-6 genes. Both responses were significantly inhibited when LX2 cells were pretreated with TQ(Fig. 5).

TQ inhibits NF-[kappa]B activation induced by LPS

It is known that MCP-1 and IL-6 are two target genes of NF-[kappa]B signaling (Libermann and Baltimore 1990; Ueda et al. 1994). Thus, we investigated the effect of TQ on NF-[kappa]B signaling to elucidate a potential role of NF-[kappa]B inhibition in TQ-mediated inhibition of LPS-induced MCP-1/IL-6 response. Western blot analysis showed that TQ significantly suppressed NF-[kappa]B activation induced by LPS as evidenced by decreased levels of phosphorylated NF-[kappa]B p65 protein (p-NF-[kappa]B p65) (Fig. 6). In addition, TQ pretreatment inhibited the serum-induced phosphorylation of NF-[kappa]B p65 (Fig. 6).

TQ_inhibits culture-triggered transdifferentiation of primary rat HSCs

The above studies have demonstrated the antifibrotic and antiproinflammatory activity of TQ on LX2, a fully transactivated human HSC cell line and fully activated primary rat HSCs. To examine the effect of TQ on transactivation, freshly isolated rat HSCs were cultured for 7 days in the presence or absence of TQ and the mRNA expression levels of COL1 Al, COL3A1 and a-SMA genes were determined via qRT-PCR. As shown in Fig. 7, there were significant increases in the mRNA expression levels of all three genes examined after 7 days in culture, suggesting culture-induced transactivation of rat HSCs. In contrast, TQ treatment significantly inhibited the culture-induced upregulation of the expression of all three genes, suggesting that TQ effectively inhibited the culture-triggered transactivation of primary HSCs.


TQ is a natural product with various biological activities including hepatoprotective effects against hepatotoxins. A recent study has also demonstrated anti-fibrotic effect for TQ in a rat model of CBDL-induced liver injury (Oguz et al. 2012). However, the detailed mechanism for the antifibrotic activity of TQ remains largely unknown. It is generally regarded that the hepatoprotective activity of TQ plays an important role as decreased hepatocyte damage shall lead to reduced activation of HSCs and the associated fibrogenic events. The results from the present study clearly demonstrated a direct inhibitory effect of TQ on HSCs, unveiling a new mechanism for the antifibrotic effect of TQ.

Activation of HSCs represents the key initial step in the pathogenesis of liver fibrosis. Our data showed that TQ treatment significantly inhibited the culture-induced transactivation of primary rat HSCs as demonstrated by drastic inhibition of culture-triggered upregulation of several fibrosis-related genes including COL1A1, COL3A1, and a-SMA. In addition to blocking the transactivation of quiescent HSCs, TQ significantly inhibited the fibrogenic activity in fully activated cells: TQ-treated LX2 cells showed significantly reduced mRNA expression levels of COL1A1 and COL3A1 compared to vehicle-treated cells. A recent study by Bai et al. showed that TQ treatment reduced the LPS-induced upregulation of COL1 Al and a-SMA in T-HSC/C1-6 cells, an immortalized rat hepatic stellate cell line (Bai et al. 2013). We have further shown that TQ could inhibit the LPS-induced proinflammatory response as demonstrated by significant inhibition of LPS-induced upregulation in the mRNA expression levels of MCP-1 and IL-6. It is well known the cytokines and chemokines produced by activated HSCs can work on both HSCs and neighboring cells in autocrine and paracrine fashions, which serve to amplify the proinflammatory and fibrogenic events (Bataller and Brenner 2005). Thus, TQ can intervene at various steps of the complicated fibrogenic processes.

In addition to direct inhibition of fibrogenic activity in HSCs, TQ shows growth inhibitory effect on HSCs. It has been known that liver fibrosis is a reversible process, particularly at early stage, and elimination of activated HSCs via apoptosis plays an important role in the resolution of fibrotic changes (Wright et al. 2001). This has led to the development of a number of therapeutic strategies that are targeted at induction of apoptosis of activated HSCs in fibrotic liver (Li et al. 2008b). It remains to be determined whether the inhibitory effect of TQ on the proliferation of HSCs will contribute to the overall antifibrotic activity of TQ in vivo, which will be further addressed in the future.

The mechanism for the anti-fibrotic activity of TQ is not completely understood; however, its antioxidant activity likely plays an important role. It has been known that the LPS/TLR4 signaling is critically involved in transactivation of HSCs during liver injury (Bai et al. 2013). It has also been known that LPS initially promotes the production of reactive oxygen species (ROS), which elicits a wide spectrum of responses by activating transcription factor NF-[kappa]B through MAPKs and PI3K/Akt pathways (Bai et al. 2013; Shi et al. 2013). Activation of NF-[kappa]B leads to the expression of not only various proinflammatory and profibrogenic factors but also antiapoptotic proteins such as XIAP and cellular FLIP (c-FLIPL) that might enhance the survival and proliferation of activated HSCs. Our data showed that activation of NF-[kappa]B by LPS in LX2 cells was significantly inhibited by TQ. The study by Bai et al. showed that LPS treatment led to activation of PI3K signaling, which was significantly attenuated by TQ. These data are in consistent with the antioxidant activity of TQ. This is further supported by the observation that silymarin, a well-established antioxidant (Bindoli et al. 1977; Trappoliere et al. 2009), similarly inhibited the fibrogenic activity in both human and rat FISCs. More studies are needed to better understand the mechanism by which TQ exerts its antifibrotic and antiproliferation activity in HSCs.

In summary, we have shown in this study that TQ has direct antifibrotic and antiproliferation effect on HSCs. Considering its excellent safety profile and the various favorable biological properties, TQ may represent a new type of antifibrotic therapy that warrants more studies in the future.

Abbreviations: HSCs, hepatic stellate cells; TQ, thymoquinone; NASH, nonalcoholic steatohepatitis; ALT, alanine aminotransferase; AST, aspartate amino-transferase; LDH, lactate dehydrogenase; CBDL, common bile duct ligation; LPS, lipopolysaccharide; CCU, carbon tetrachloride; DMEM, Dulbecco's modified Eagle's medium; FBS, fetal bovine serum; H-E, hematoxylin and eosin; DMSO, dimethyl sulfoxide; HRP, horseradish peroxidase; MCP-1, monocyte chemotactic protein-1; IL-6, interleukin 6; NF-[kappa]B, nuclear factor kappa-B; ROS, reactive oxygen species; c-FLIPL, cellular FLICE-inhibitory protein; SM, silymarin.


Article history:

Received 6 May 2013

Received in revised form 7 August 2013

Accepted 19 September 2013


We thank Dr. S.L. Friedman, Mount Sinai School of Medicine, NY, for his generous gift of LX2 cells.


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Mohammed Ghazwani (a), Yifei Zhang (a), Xiang Gao (a), Jie Fan (b), Jiang Li (a), *, Song Li (a), *

(a) Center for Pharmacogenetics, Department of Pharmaceutical Sciences, School of Pharmacy, University of Pittsburgh, Pittsburgh, PA 15261, USA

(b) Department of Surgery, School of Medicine, University of Pittsburgh, Pittsburgh, PA 15261, USA

* Corresponding authors. Tel.: +1 412 383 7976; fax: +1 412 648 1664.

E-mail addresses: (J. Li), (S. Li).
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Author:Ghazwani, Mohammed; Zhang, Yifei; Gao, Xiang; Fan, Jie; Li, Jiang; Li, Song
Publication:Phytomedicine: International Journal of Phytotherapy & Phytopharmacology
Article Type:Report
Geographic Code:1USA
Date:Feb 15, 2014
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