Platelets arrive at the scene of fibrosis……studies

Localized inhibition of platelets and platelet derived growth factor by a matrix targeted glycan mimetic significantly attenuates liver fibrosis

New therapeutic strategies are needed for the growing unmet clinical needs in liver disease and fibrosis. Platelet activation and PDGF activity are recognized as important therapeutic targets; however, no therapeutic approach has yet addressed these two upstream drivers of liver fibrosis. We therefore designed a matrix-targeting glycan therapeutic, SBR-294, to inhibit collagen-mediated platelet activation while also inhibiting PDGF activity. Herein we describe the synthesis and characterization of SBR-294 and demonstrate its potential therapeutic benefits in vitro and in vivo. In vitro SBR-294 was found to bind collagen (EC₅₀ = 23 nM), thereby inhibiting platelet-collagen engagement (IC₅₀ = 60 nM). Additionally, SBR-294 was found to bind all PDGF homodimeric isoforms and to inhibit PDGF-BB mediated hepatic stellate cell activation and proliferation. Translating these mechanisms in vivo, SBR-294 reduced fibrosis by up to 54% in the CCl4 mouse model (p = 0.0004), as measured by Sirius red histological analysis. Additional fibrosis measurements were also supportive of the therapeutic benefit in this model. These results support the therapeutic benefit of platelet and PDGF antagonism and warrant further investigation of SBR-294 as a potential treatment for liver fibrosis.

Exploring the Link Between Platelet Numbers and Vascular Homeostasis Across Early and Late Stages of Fibrosis in Hepatitis C

BACKGROUND

Thrombocytopenia is a hallmark of advanced liver disease. Platelets, growth factors (GFs), and vascular integrity are closely linked factors in disease pathogenesis, and their relationship, particularly in early disease stages, is not entirely understood. The aim was to compare circulating platelets, growth factors, and vascular injury markers (VIMs) in hepatitis C-infected (HCV) patients with early fibrosis and cirrhosis.

METHODS

Retrospective evaluation of serum GFs and VIMs by ELISA were evaluated from twenty-six HCV patients. Analytes from an earlier time-point were correlated with MELD at a later time-point.

RESULTS

Platelets and GFs decreased, and VIMs increased with fibrosis. Platelets correlated positively with PDGF-AA, PDGF-BB, TGFB1, EGF, and P-selectin, and negatively with ICAM-3 and VCAM-1. P-selectin showed no correlations with VIMs but positively correlated with PDGF-AA, PDGF-BB, TGFB1, and EGF. Soluble VCAM-1 and ICAM-3 were linked to increasing fibrosis, liver enzymes, and synthetic dysfunction. Higher VCAM-1 and ICAM-3 and lower P-selectin at an earlier time-point were linked to higher MELD score at a later time-point.

CONCLUSION

In chronic HCV, progressive decline in platelets and growth factors with fibrosis and their associations suggest that platelets are an important source of circulating GFs and influence GF decline with fibrosis. Enhanced markers of vascular injury in patients with early fibrosis suggest an earlier onset of endothelial dysfunction preceding cirrhosis. Associations of VIMs with platelets suggest a critical link between platelets and vascular homeostasis. Circulating markers of vascular injury may not only have prognostic importance but emphasize the role of vascular dysfunction in liver disease pathogenesis (NCT00001971).

Platelets: No longer bystanders in liver disease

Growing lines of evidence recognize that platelets play a central role in liver homeostasis and pathobiology. Platelets have important roles at every stage during the continuum of liver injury and healing. These cells contribute to the initiation of liver inflammation by promoting leukocyte recruitment through sinusoidal endothelium. They can activate effector cells, thus amplifying liver damage, and by modifying the hepatic cellular and cytokine milieu drive both hepatoprotective and hepatotoxic processes.

CONCLUSION

In this review we summarize how platelets drive such pleiotropic actions and attempt to reconcile the paradox of platelets being both deleterious and beneficial to liver function; with increasingly novel methods of manipulating platelet function at our disposal, we highlight avenues for future therapeutic intervention in liver disease. (Hepatology 2016;64:1774-1784).

Hypersplenism: History and current status

Hypersplenism is a common disorder characterized by an enlarged spleen which causes rapid and premature destruction of blood cells. This review summarizes the history of hypersplenism, discuss its classification and pathogenesis, and examines its diagnosis and treatment options. We performed a comprehensive literature search using PubMed, Web of Knowledge and the China National Knowledge Infrastructure (CNKI) database, reviewed hypersplenism-related articles and summarized the major findings. According to its etiological causes, hypersplenism is characterized by splenomegaly and peripheral cytopenias. It can be classified into three categories: i) primary hypersplenism; ii) secondary hypersplenism; and iii) occult hypersplenism. A number of mechanisms causing hypersplenism have been identified, and mainly involve retention in the spleen, phagocytosis, and autoimmunity. Treatment options for hypersplenism include etiological treatment, non-surgical treatment, total splenectomy and liver transplantation. In any case, treatment should be individualized for each patient.

Blood platelets and inflammation: their relationship with liver and digestive diseases

An expansion of knowledge from basic and clinical research has highlighted the critical role of platelets in inflammation and tissue repair in addition to their established contribution to hemostasis. Activated platelets are a rich source of mediators participating to inflammation and tissue regeneration. Platelet-derived microparticles recapitulate essential platelet functions and their contribution to the pathogenesis of inflammatory diseases has been emphasized. Recent findings suggest that platelets are both friends and foes for the liver. Platelets are essential to liver regeneration, platelet-derived serotonin being critical. However platelets can also exacerbate liver damage, as in immune-mediated injury. The dual role of platelets has recently been exemplified in animal models of liver fibrosis. Platelets release profibrogenic mediators, such as CXC Chemokine Ligand 4, that is instrumental in the progression of liver fibrosis. On the other hand, thrombocytopenia aggravates liver fibrosis, an outcome linked to the downregulation of hepatic stellate cell collagen production by platelet derived hepatocyte growth factor. CD154, a key molecule in inflammation, is expressed by platelets and is a pathogenic mediator in inflammatory bowel disease. Here, we summarize some of the mechanisms linking platelets with inflammation and comment few recent articles indicating why platelets may prove to be important pathogenic mediators in liver and gastrointestinal diseases.