Desong Kong

Curcumin attenuates angiogenesis in liver fibrosis and inhibits angiogenic properties of hepatic stellate cells

Hepatic fibrosis is concomitant with sinusoidal pathological angiogenesis, which has been highlighted as novel therapeutic targets for the treatment of chronic liver disease. Our prior studies have demonstrated that curcumin has potent antifibrotic activity, but the mechanisms remain to be elucidated. The current work demonstrated that curcumin ameliorated fibrotic injury and sinusoidal angiogenesis in rat liver with fibrosis caused by carbon tetrachloride. Curcumin reduced the expression of a number of angiogenic markers in fibrotic liver. Experiments in vitro showed that the viability and vascularization of rat liver sinusoidal endothelial cells and rat aortic ring angiogenesis were not impaired by curcumin. These results indicated that hepatic stellate cells (HSCs) that are characterized as liver‐specific pericytes could be potential target cells for curcumin. Further investigations showed that curcumin inhibited VEGF expression in HSCs associated with disrupting platelet‐derived growth factor‐β receptor (PDGF‐βR)/ERK and mTOR pathways. HSC motility and vascularization were also suppressed by curcumin associated with blocking PDGF‐βR/focal adhesion kinase/RhoA cascade. Gain‐ or loss‐of‐function analyses revealed that activation of peroxisome proliferator‐activated receptor‐γ (PPAR‐γ) was required for curcumin to inhibit angiogenic properties of HSCs. We concluded that curcumin attenuated sinusoidal angiogenesis in liver fibrosis possibly by targeting HSCs via a PPAR‐γ activation‐dependent mechanism. PPAR‐γ could be a target molecule for reducing pathological angiogenesis during liver fibrosis.

Tetramethylpyrazine induces G0/G1 cell cycle arrest and stimulates mitochondrial-mediated and caspase-dependent apoptosis through modulating ERK/p53 signaling in hepatic stellate cells in vitro

Activation of hepatic stellate cells (HSCs) is a pivotal event in the pathogenesis of liver fibrosis. Pharmacological induction of HSC apoptosis could be a promising strategy for fibrosis regression. Natural product tetramethylpyrazine (TMP) exhibits potent antifibrotic activities in vivo. However, the molecular mechanisms remain to be defined. The present study aimed at investigating the anti-proliferative and pro-apoptotic effects of TMP on HSCs and elucidating the underlying mechanisms. Our results demonstrated that TMP had no apparent cytotoxic effects on hepatocytes, but significantly inhibited HSC proliferation and induced cell cycle arrest at the G0/G1 checkpoint. These effects were associated with TMP regulation of cyclin D1, p21, p27 and p53. Furthermore, we found that TMP disrupted mitochondrial functions and led to activation of caspase cascades in HSCs. Mechanistic investigations revealed that TMP selectively blocked the extracellular signal-regulated kinase (ERK) signaling and activated p53, which was required for TMP induction of caspase-dependent mitochondrial apoptosis in HSCs. Autodock simulations predicted that TMP could directly bind to ERK2 with two hydrogen bonds and low energy score, indicating that ERK2 could be a direct target molecule for TMP within HSCs. Moreover, TMP altered expression of some marker proteins relevant to HSC activation. These data collectively revealed that TMP modulation of ERK/p53 signaling led to mitochondrial-mediated and caspase-dependent apoptosis in HSCs in vitro. These studies provided mechanistic insights into the antifibrotic properties of TMP that may be exploited as a potential option for hepatic fibrosis.

Peroxisome proliferator-activated receptor-γ as a therapeutic target for hepatic fibrosis: from bench to bedside.

Hepatic fibrosis is a dynamic chronic liver disease occurring as a consequence of wound-healing responses to various hepatic injuries. This disorder is one of primary predictors for liver-associated morbidity and mortality worldwide. To date, no pharmacological agent has been approved for hepatic fibrosis or could be recommended for routine use in clinical context. Cellular and molecular understanding of hepatic fibrosis has revealed that peroxisome proliferator-activated receptor-γ (PPARγ), the functioning receptor for antidiabetic thiazolidinediones, plays a pivotal role in the pathobiology of hepatic stellate cells (HSCs), whose activation is the central event in the pathogenesis of hepatic fibrosis. Activation of PPARγ inhibits HSC collagen production and modulates HSC adipogenic phenotype at transcriptional and epigenetic levels. These molecular insights indicate PPARγ as a promising drug target for antifibrotic chemotherapy. Intensive animal studies have demonstrated that stimulation of PPARγ regulatory system through gene therapy approaches and PPARγ ligands has therapeutic promise for hepatic fibrosis induced by a variety of etiologies. At the same time, thiazolidinedione agents have been investigated for their clinical benefits primarily in patients with nonalcoholic steatohepatitis, a common metabolic liver disorder with high potential to progress to fibrosis and liver-related death. Although some studies have shown initial promise, none has established long-term efficacy in well-controlled randomized clinical trials. This comprehensive review covers the 10-year discoveries of the molecular basis for PPARγ regulation of HSC pathophysiology and then focuses on the animal investigations and clinical trials of various therapeutic modalities targeting PPARγ for hepatic fibrosis.

Curcumin modulates cannabinoid receptors in liver fibrosis in vivo and inhibits extracellular matrix expression in hepatic stellate cells by suppressing cannabinoid receptor type-1 in vitro.

Activation of hepatic stellate cells (HSCs) is a pivotal event leading to extracellular matrix (ECM) overproduction during hepatic fibrogenesis. Compelling evidence indicates that cannabinoid receptors (CBRs) play an important role in chronic liver disease. Antagonism of hepatic CBR type 1 (CBR1) could be a novel therapeutic strategy for liver fibrosis. Our previous studies have demonstrated that curcumin has potent antifibrotic activity, but the mechanisms remain to be elucidated. The current work was to examine the curcumin effect on CBRs system and its relevance to inhibition of ECM expression in HSCs. Our in vivo data demonstrated that curcumin ameliorated fibrotic injury, and downregulated CBR1 but upregulated CBR2 at both mRNA and protein levels in rat fibrotic liver caused by carbon tetrachloride. The subsequent in vitro investigations showed that curcumin reduced the mRNA and protein abundance of CBR1 in cultured HSCs and decreased the expression of three critical ECM proteins. Further analyses revealed that CBR1 agonist abrogated the curcumin inhibition of ECM expression, but CBR1 antagonist mimicked and reinforced the curcumin effects. Autodock simulations predicted that curcumin could bind to CBR1 with two hydrogen bonds. Collectively, our current studies revealed that curcumin reduction of liver fibrosis was associated with modulation of CBRs system and that antagonism of CBR1 contributed to curcumin inhibition of ECM expression in HSCs.

Ligustrazine attenuates oxidative stress-induced activation of hepatic stellate cells by interrupting platelet-derived growth factor-β receptor-mediated ERK and p38 pathways.

Hepatic fibrosis represents a frequent event following chronic insult to trigger wound healing reactions with accumulation of extracellular matrix (ECM) in the liver. Activation of hepatic stellate cells (HSCs) is the pivotal event during liver fibrogenesis. Compelling evidence indicates that oxidative stress is concomitant with liver fibrosis irrespective of the underlying etiology. Natural antioxidant ligustrazine exhibits potent antifibrotic activities, but the mechanisms are poorly understood. Our studies were to investigate the ligustrazine effects on HSC activation stimulated by hydrogen peroxide (H(2)O(2)), an in vitro model mimicking the oxidative stress in liver fibrogenesis, and to elucidate the possible mechanisms. Our results demonstrated that H(2)O(2) at 5μM significantly stimulated HSC proliferation and expression of marker genes of HSC activation; whereas ligustrazine dose-dependently suppressed proliferation and induced apoptosis in H(2)O(2)-activated HSCs, and attenuated expression of fibrotic marker genes. Mechanistic investigations revealed that ligustrazine reduced platelet-derived growth factor-β receptor (PDGF-βR) expression and blocked the phosphorylation of extracellular regulated protein kinase (ERK) and p38 kinase, two downstream effectors of PDGF-βR. Further molecular evidence suggested that ligustrazine interruption of ERK and p38 pathways was dependent on the blockade of PDGF-βR and might be involved in ligustrazine reduction of fibrotic marker gene expression under H(2)O(2) stimulation. Furthermore, ligustrazine modulated some proteins critical for HSC activation and ECM homeostasis in H(2)O(2)-stimulated HSCs. These data collectively indicated that ligustrazine could attenuate HSC activation caused by oxidative stress, providing novel insights into ligustrazine as a therapeutic option for hepatic fibrosis.

Clearance of activated stellate cells for hepatic fibrosis regression: molecular basis and translational potential.

Hepatic fibrosis, characterized by abnormal accumulation of extracellular matrix (ECM), is a common pathological process of many chronic liver diseases. A growing number of studies have shown that the activation of hepatic stellate cells (HSCs) plays an important role in the pathogenesis of hepatic fibrosis. Inhibiting the activation of HSCs and accelerating the clearance of activated HSCs may be effective strategies for resolution of hepatic fibrosis. Therefore, understanding the underlying mechanisms of clearance of activated HSCs and the therapeutic implications is an active subject of research. Studies have shown that apoptosis, immune clearance, phenotype reversion and senescence are involved in clearance of activated HSCs. In this review, we will discuss the mechanisms of clearance of activated HSCs and their potential in resolution of hepatic fibrosis.

Paeonol inhibits hepatic fibrogenesis via disrupting nuclear factor-κB pathway in activated stellate cells: in vivo and in vitro studies.

Hepatic fibrosis represents a major cause of morbidity and mortality worldwide. The present study was to evaluate the antifibrogenesis effect of paeonol and involved mechanisms.

Tetramethylpyrazine reduces glucose and insulin-induced activation of hepatic stellate cells by inhibiting insulin receptor-mediated PI3K/AKT and ERK pathways

Hepatic stellate cell (HSC) activation is the central event during liver fibrogenesis. Metabolic syndrome characterized by hyperglycemia and hyperinsulinemia contributes to nonalcoholic steatohepatitis-associated liver fibrosis. This study was to investigate the effects of tetramethylpyrazine (TMP) on HSC activation induced by glucose and insulin (Glu/Ins) and the underlying mechanisms. Results showed that Glu/Ins significantly stimulated proliferation, invasion, adhesion, and extracellular matrix (ECM) production in HSCs. TMP inhibited HSC proliferation, invasion and adhesion, and reduced the expression of marker genes related to HSC activation in Glu/Ins-activated HSCs. Mechanistic evidence revealed that TMP reduced insulin receptor (InsR) expression and blocked the downstream phosphatidylinositol-3-kinase (PI3K)/AKT and extracellular signal-regulated kinase (ERK) cascades, which was required for TMP attenuation of HSC activation. Moreover, TMP modulated the genes relevant to ECM homeostasis favoring ECM degradation. It could be concluded that TMP inhibited Glu/Ins-stimulated HSC activation and ECM production by inhibiting InsR-mediated PI3K/AKT and ERK pathways.

Diallyl trisulfide protects against ethanol-induced oxidative stress and apoptosis via a hydrogen sulfide-mediated mechanism.

Garlic is one natural source of organic sulfur containing compounds and has shown promise in the treatment of chronic liver disease. Dietary garlic consumption is inversely correlated with the progression of alcoholic fatty liver (AFL), although the exact underlying mechanisms are not clear. Our previous studies also have shown that diallyl trisulfide (DATS), the primary organosulfur compound from Allium sativum L, displayed anti-lipid deposition and antioxidant properties in AFL. The aim of the present study was to clarify the underlying mechanisms. In the present study, we used the intragastric infusion model of alcohol administration and human normal liver cell line LO2 cultured with suitable ethanol to mimic the pathological condition of AFL. We showed that accumulation of intracellular reactive oxygen species (ROS) was lowered significantly by the administration of DATS, but antioxidant capacity was increased by DATS. Additionally, DATS inhibited hepatocyte apoptosis via down-regulating Bax expression and up-regulating Bcl-2 expression, and attenuated alcohol-induced caspase-dependent apoptosis. More importantly, using iodoacetamide (IAM) to block hydrogen sulfide (H2S) production from DATS, we noted that IAM abolished all the above effects of DATS in ethanol-treated LO2 cells. Lastly, we found DATS could increase the expressions of cystathionine gamma-lyase (CSE) and cystathionine beta-synthase (CBS), the major H2S-producing enzymes. These results demonstrate that DATS protect against alcohol-induced fatty liver via a H2S-mediated mechanism. Therefore, targeting H2S may play a therapeutic role for AFL.

Tetramethylpyrazine inhibits angiotensin II‐induced activation of hepatic stellate cells associated with interference of platelet‐derived growth factor β receptor pathways

Liver fibrosis represents a frequent event following chronic insult to trigger wound healing responses in the liver. Activation of hepatic stellate cells (HSCs) is a pivotal event during liver fibrogenesis. Compelling evidence indicates that the renin‐angiotensin system (RAS) takes part in the pathogenesis of liver fibrosis. Angiotensin II (Ang II), the primary effector peptide of the RAS, has been demonstrated to be a potent pro‐fibrogenic molecule for HSC activation. In this study we investigated the effects of tetramethylpyrazine (TMP) on HSC activation induced by Ang II in order to elucidate the underlying mechanisms. Our results demonstrated that Ang II significantly promoted cell growth, upregulated the expression of the fibrotic markers α‐smooth muscle actin (α‐SMA) and α1(I) procollagen, and enhanced the invasion capacity in HSCs. TMP inhibited proliferation and arrested the cell cycle at the G2/M checkpoint associated with altering several cell cycle regulatory proteins in Ang II‐treated HSCs. TMP also modulated Bcl‐2 family proteins and activated the caspase cascade leading to apoptosis in Ang II‐treated HSCs. Moreover, TMP reduced the expression of α‐SMA and α1(I) procollagen at mRNA and protein levels, and these effects were associated with interference of the platelet‐derived growth factor β receptor (PDGF‐βR) mediated PI3K/AKT/mTOR pathway in HSCs exposed to Ang II. Furthermore, Ang II‐enhanced HSC invasion capacity was diminished by TMP, which was associated with interference of PDGF‐βR/FAK signaling. These data collectively indicated that interference of PDGF‐βR‐mediated fibrotic pathways was involved in TMP inhibition of HSC activation caused by Ang II, providing novel mechanistic insights into TMP as a potential therapeutic remedy for hepatic fibrosis.