Antiangiogenic therapies in portal hypertension: a breakthrough in hepatology

Antiangiogenic therapy for portal hypertension in liver cirrhosis: Current progress and perspectives

Developing medicines for hemodynamic disorders that are characteristic of cirrhosis of the liver is a relevant problem in modern hepatology. The increase in hepatic vascular resistance to portal blood flow and subsequent hyperdynamic circulation underlie portal hypertension (PH) and promote its progression, despite the formation of portosystemic collaterals. Angiogenesis and vascular bed restructurization play an important role in PH pathogenesis as well. In this regard, strategic directions in the therapy for PH in cirrhosis include selectively decreasing hepatic vascular resistance while preserving or increasing portal blood flow, and correcting hyperdynamic circulation and pathological angiogenesis. The aim of this review is to describe the mechanisms of angiogenesis in PH and the methods of antiangiogenic therapy. The PubMed database, the Google Scholar retrieval system, and the reference lists from related articles were used to search for relevant publications. Articles corresponding to the aim of the review were selected for 2000-2017 using the keywords: “liver cirrhosis”, “portal hypertension”, “pathogenesis”, “angiogenesis”, and “antiangiogenic therapy”. Antiangiogenic therapy for PH was the inclusion criterion. In this review, we have described angiogenesis inhibitors and their mechanism of action in relation to PH. Although most of them were studied only in animal experiments, this selective therapy for abnormally growing newly formed vessels is pathogenetically reasonable to treat PH and associated complications.

Tyrosine kinase inhibitors: friends or foe in treatment of hepatic fibrosis?

Aberrant activity of tyrosine kinases has been proved to be associated with multiple diseases including fibrotic diseases. Tyrosine kinases inhibitors (TKIs) might be a novel approach to transform the anti-fibrotic treatment. However, both beneficial and adverse effects are observed by researchers when using these TKIs in either preclinical animal models or patients with hepatic fibrosis. Since hepatotoxicity of TKIs is the leading cause for drug withdrawals thus limits its application in anti-fibrosis, not only efficacy but also safety of TKIs should be paid great concerns. It has been observed in a few studies that TKIs could induce relatively high rate of hepatic biochemical markers elevations and even result in liver failure. Fortunately, several strategies have been adopt to handle with the hepatotoxicity. Accumulating evidences suggest that hepatic stellate cells (HSC) play a pivotal role in hepatic fibrogenesis, so it might be a good option to develop selective TKIs specifically targeting HSCs. The present review will briefly summarize the anti-fibrotic mechanism of TKIs, adverse effects of TKIs as well as the novel developed selective delivery of TKIs.

New Insight into the Anti-liver Fibrosis Effect of Multitargeted Tyrosine Kinase Inhibitors: From Molecular Target to Clinical Trials

Tyrosine kinases (TKs) is a family of tyrosine protein kinases with important functions in the regulation of a broad variety of physiological cell processes. Overactivity of TK disturbs cellular homeostasis and has been linked to the development of certain diseases, including various fibrotic diseases. In regard to liver fibrosis, several TKs, such as vascular endothelial growth factor receptor, platelet-derived growth factor receptor, fibroblast growth factor receptor, and epidermal growth factor receptor kinases, have been identified as central mediators in collagen production and potential targets for anti-liver fibrosis therapies. Given the essential role of TKs during liver fibrogenesis, multitargeted inhibitors of aberrant TK activity, including sorafenib, erlotinib, imatinib, sunitinib, nilotinib, brivanib and vatalanib, have been shown to have potential for treating liver fibrosis. Beneficial effects are observed by researchers of this field using these multitargeted TK inhibitors in preclinical animal models and in patients with liver fibrosis. The present review will briefly summarize the anti-liver fibrosis effects of multitargeted TK inhibitors and molecular mechanisms.

Angiogenesis in liver regeneration and fibrosis: "a double-edged sword"

Angiogenesis, defined as the formation of new microvasculature from preexisting blood vessels and mature endothelial cells, plays a major role in wound healing and scar formation, and it is associated with inflammatory responses. Angiogenesis can occur in physiological conditions, such as during liver regeneration, and in pathological situations, such as during the progression of fibrosis to cirrhosis and also during tumor angiogenesis. Cellular cross-talk among liver sinusoidal endothelial cells (LSECs), hepatic stellate cells and hepatocytes is believed to play an important role in the angiogenesis process during both liver regeneration and development of cirrhosis. In addition to mature endothelial cells, bone marrow (BM)-derived circulating endothelial progenitor cells (EPCs) have been recently identified for their contribution to post-natal vasculogenesis/angiogenesis. In vivo, EPCs are mobilized into the peripheral blood in response to tissue ischemia or traumatic injury, migrate to the sites of injured endothelium and differentiate into mature endothelial cells. In our recent studies, we have explored the role of EPC-mediated angiogenesis in liver regeneration and/or cirrhosis. Results have demonstrated significantly increased endogenous levels of circulating EPCs in cirrhotic patients in comparison to the controls. Also, EPCs from cirrhotic patients have been observed to stimulate substantial angiogenesis by resident LSECs in vitro via paracrine factors such as vascular endothelial growth factor and platelet-derived growth factor. This review gives an overview of the angiogenesis process in liver regeneration and disease and discusses a new mechanism for intrahepatic angiogenesis mediated by BM-derived EPCs.

Relationship between vascular endothelial growth factors and liver diseases

Vascular endothelial growth factors play an important role in the processes of cell differentiation and maturation. As a kind of multi-functional factor, they are closely related to the occurrence and progression of liver diseases. They can not only promote postoperative liver regeneration but also repress the propagation of chronic hepatitis B and liver cirrhosis. In addition, they have a role in cancer diagnosis and treatment and graft rejection in liver transplantation. In this paper, we will give a brief introduction of vascular growth factors and their role in liver regeneration, cirrhosis, liver cancer and liver transplantation.

The mechanism through which octreotide inhibits hepatic stellate cell activity

Hepatic stellate cells (HSCs) are important in the development of liver fibrosis and in the pathogenesis of portal hypertension. Octreotide, an analogue of somatostatin, has been demonstrated to effectively treat fibrosis and portal hypertension; however, its relative mechanism in HSCs remains unknown. LX‑2, the immortalized HSC line, was used to study the mechanism whereby octreotide functions at different concentrations. Real‑time polymerase chain reaction (PCR) and western blot analysis were used to analyze the expression of fibrosis markers and transcription factors following treatment with octreotide. Soluble secreted endothelin‑1 (ET‑1), collagen I and vascular endothelial growth factor (VEGF) were assessed in the supernatants of cultured cells by enzyme-linked immunosorbent assay (ELISA). In the present study, it was shown that octreotide was able to inhibit the proliferative ability of the LX‑2 cells and decrease the expression of transforming growth factor β (TGF‑β), α‑smooth muscle actin (α‑SMA) and smad‑4a. The transcription factors, including c‑Jun and sp‑1, were downregulated in a dose‑dependent manner following treatment with octreotide. The levels of ET‑1 and collagen I in the supernatant decreased significantly in contrast with the normal levels, whereas the levels of VEGF in the LX‑2 cells and the supernatant increased at a high octreotide concentration (10‑5 nM). Octreotide may exert its effects on ET‑1 or other targeting genes in HSCs through the downregulation of c‑Jun and specificity protein 1 (sp‑1), and the increased levels of VEGF may be the reason for the side effects observed at high concentrations of octreotide.

The chinese herbal decoction danggui buxue tang inhibits angiogenesis in a rat model of liver fibrosis

In this study, we investigated the anti-angiogenic effect of the Chinese herbal decoction Danggui Buxue Tang (DBT; Radix Astragali and Radix Angelicae sinensis in 5 : 1 ratio) in a rat model of liver fibrosis, in order to elucidate its mechanisms of action against liver fibrosis. Liver fibrosis was induced with CCl(4) and high-fat food for 6 weeks, and the rats were treated with oral doses of DBT (6 g raw herbs/kg/d) and N-Acetyl-L-cysteine (NAC; 0.1 g/kg/d). The results showed that both DBT and NAC attenuated liver fibrosis and neo-angiogenesis. Furthermore, DBT and NAC improved SOD activity but decreased MDA content and 8-OH-dG in fibrotic livers, with DBT being more effective than NAC. DBT decreased the expression of VEGF, Ang1 and TGF-β1 and their signaling mediators, whereas NAC had no effect on VEGF and VEGFR2 expression. Both DBT and NAC reduced HIF-1α gene and protein expression in fibrotic livers, with DBT being more effective. These data clearly demonstrate that the anti-fibrotic properties of DBT are related to its ability to inhibit angiogenesis and its anti-angiogenic mechanisms are associated with improving oxidative stress, regulating the expression and signaling of angiogenic factors, and especially modulating HIF-1α in fibrotic livers.

Reversible decrease of portal venous flow in cirrhotic patients: a positive side effect of sorafenib

Portal hypertension, the most important complication with cirrhosis of the liver, is a serious disease. Sorafenib, a tyrosine kinase inhibitor is validated in advanced hepatocellular carcinoma. Because angiogenesis is a pathological hallmark of portal hypertension, the goal of our study was to determine the effect of sorafenib on portal venous flow and portosystemic collateral circulation in patients receiving sorafenib therapy for advanced hepatocellular carcinoma. Porto-collateral circulations were evaluated using a magnetic resonance technique prior sorafenib therapy, and at day 30. All patients under sorafenib therapy had a decrease in portal venous flow of at least 36%. In contrast, no specific change was observed in the azygos vein or the abdominal aorta. No portal venous flow modification was observed in the control group. Sorafenib is the first anti-angiogenic therapy to demonstrate a beneficial and reversible decrease of portal venous flow among cirrhotic patients.