Human cardiovascular disease model predicts xanthine oxidase inhibitor cardiovascular risk.

Some health concerns are often not identified until late into clinical development of drugs, which can place participants and patients at significant risk. For example, the United States Food and Drug Administration (FDA) labeled the xanthine oxidase inhibitor febuxostat with a"boxed" warning regarding an increased risk of cardiovascular death, and this safety risk was only identified during Phase 3b clinical trials after its approval. Thus, better preclinical assessment of drug efficacy and safety are needed to accurately evaluate candidate drug risk earlier in discovery and development. This study explored whether an in vitro vascular model incorporating human vascular cells and hemodynamics could be used to differentiate the potential cardiovascular risk associated with molecules that have similar on-target mechanisms of action. We compared the transcriptomic responses induced by febuxostat and other xanthine oxidase inhibitors to a database of 111 different compounds profiled in the human vascular model. Of the 111 compounds in the database, 107 are clinical-stage and 33 are FDA-labelled for increased cardiovascular risk. Febuxostat induces pathway-level regulation that has high similarity to the set of drugs FDA-labelled for increased cardiovascular risk. These results were replicated with a febuxostat analog, but not another structurally distinct xanthine oxidase inhibitor that does not confer cardiovascular risk. Together, these data suggest that the FDA warning for febuxostat stems from the chemical structure of the medication itself, rather than the target, xanthine oxidase. Importantly, these data indicate that cardiovascular risk can be evaluated in this in vitro human vascular model, which may facilitate understanding the drug candidate safety profile earlier in discovery and development.

Ketohexokinase inhibition improves NASH by reducing fructose-induced steatosis and fibrogenesis.

BACKGROUND & AIMS: Increasing evidence highlights dietary fructose as a major driver of non-alcoholic fatty liver disease (NAFLD) pathogenesis, the majority of which is cleared on first pass through the hepatic circulation by enzymatic phosphorylation to fructose-1-phosphate via the ketohexokinase (KHK) enzyme. Without a current approved therapy, disease management emphasises lifestyle interventions, but few patients adhere to such strategies. New targeted therapies are urgently required. METHODS: We have used a unique combination of human liver specimens, a murine dietary model of NAFLD and human multicellular co-culture systems to understand the hepatocellular consequences of fructose administration. We have also performed a detailed nuclear magnetic resonance-based metabolic tracing of the fate of isotopically labelled fructose upon administration to the human liver. RESULTS: Expression of KHK isoforms is found in multiple human hepatic cell types, although hepatocyte expression predominates. KHK knockout mice show a reduction in serum transaminase, reduced steatosis and altered fibrogenic response on an Amylin diet. Human co-cultures exposed to fructose exhibit steatosis and activation of lipogenic and fibrogenic gene expression, which were reduced by pharmacological inhibition of KHK activity. Analysis of human livers exposed to 13C-labelled fructose confirmed that steatosis, and associated effects, resulted from the accumulation of lipogenic precursors (such as glycerol) and enhanced glycolytic activity. All of these were dose-dependently reduced by administration of a KHK inhibitor. CONCLUSIONS: We have provided preclinical evidence using human livers to support the use of KHK inhibition to improve steatosis, fibrosis, and inflammation in the context of NAFLD. LAY SUMMARY: We have used a mouse model, human cells, and liver tissue to test how exposure to fructose can cause the liver to store excess fat and become damaged and scarred. We have then inhibited a key enzyme within the liver that is responsible for fructose metabolism. Our findings show that inhibition of fructose metabolism reduces liver injury and fibrosis in mouse and human livers and thus this may represent a potential route for treating patients with fatty liver disease in the future.

Gene Expression Predicts Histological Severity and Reveals Distinct Molecular Profiles of Nonalcoholic Fatty Liver Disease.

The heterogeneity of biological processes driving the severity of nonalcoholic fatty liver disease (NAFLD) as reflected in the transcriptome and the relationship between the pathways involved are not well established. Well-defined associations between gene expression profiles and disease progression would benefit efforts to develop novel therapies and to understand disease heterogeneity. We analyzed hepatic gene expression in controls and a cohort with the full histological spectrum of NAFLD. Protein-protein interaction and gene set variation analysis revealed distinct sets of coordinately regulated genes and pathways whose expression progressively change over the course of the disease. The progressive nature of these changes enabled us to develop a framework for calculating a disease progression score for individual genes. We show that, in aggregate, these scores correlate strongly with histological measures of disease progression and can thus themselves serve as a proxy for severity. Furthermore, we demonstrate that the expression levels of a small number of genes (~20) can be used to infer disease severity. Finally, we show that patient subgroups can be distinguished by the relative distribution of gene-level scores in specific gene sets. While future work is required to identify the specific disease characteristics that correspond to patient clusters identified on this basis, this work provides a general framework for the use of high-content molecular profiling to identify NAFLD patient subgroups.

Translating scientific discovery: the need for preclinical models of nonalcoholic steatohepatitis.

Non-alcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver disease in the Western world, affecting about 1/3 of the US general population and remaining as a significant cause of morbidity and mortality. The hallmark of the disease is the excessive accumulation of fat within the liver cells (hepatocytes), which eventually paves the way to cellular stress, injury and apoptosis. NAFLD is strongly associated with components of the metabolic syndrome and is fast emerging as a leading cause of liver transplant in the USA. Based on clinico-pathologic classification, NAFLD may present as isolated lipid collection (steatosis) within the hepatocytes (referred to as non-alcoholic fatty liver; NAFL); or as the more aggressive phenotype (known as non-alcoholic steatohepatitis; NASH). There are currently no regulatory agency- approved medication for NAFLD, despite the enormous work and resources that have gone into the study of this condition. Therefore, there remains a huge unmet need in developing and utilizing pre-clinical models that will recapitulate the disease condition in humans. In line with progress being made in developing appropriate disease models, this review highlights the cutting-edge preclinical in vitro and animal models that try to recapitulate the human disease pathophysiology and/or clinical manifestations.

Non-alcoholic fatty liver disease (NAFLD) models in drug discovery.

INTRODUCTION: The progressive disease spectrum of non-alcoholic fatty liver disease (NAFLD), which includes non-alcoholic steatohepatitis (NASH), is a rapidly emerging public health crisis with no approved therapy. The diversity of various therapies under development highlights the lack of consensus around the most effective target, underscoring the need for better translatable preclinical models to study the complex progressive disease and effective therapies. Areas covered: This article reviews published literature of various mouse models of NASH used in preclinical studies, as well as complex organotypic in vitro and ex vivo liver models being developed. It discusses translational challenges associated with both kinds of models, and describes some of the studies that validate their application in NAFLD. Expert opinion: Animal models offer advantages of understanding drug distribution and effects in a whole body context, but are limited by important species differences. Human organotypic in vitro and ex vivo models with physiological relevance and translatability need to be used in a tiered manner with simpler screens. Leveraging newer technologies, like metabolomics, proteomics, and transcriptomics, and the future development of validated disease biomarkers will allow us to fully utilize the value of these models to understand disease and evaluate novel drugs in isolation or combination.

Development of an in vitro human liver system for interrogating nonalcoholic steatohepatitis.

A barrier to drug development for nonalcoholic steatohepatitis (NASH) is the absence of translational preclinical human-relevant systems. An in vitro liver model was engineered to incorporate hepatic sinusoidal flow, transport, and lipotoxic stress risk factors (glucose, insulin, free fatty acids) with cocultured primary human hepatocytes, hepatic stellate cells (HSCs), and macrophages. Transcriptomic, lipidomic, and functional endpoints were evaluated and compared with clinical data from NASH patient biopsies. The lipotoxic milieu promoted hepatocyte lipid accumulation (4-fold increase, P < 0.01) and a lipidomics signature similar to NASH biopsies. Hepatocyte glucose output increased with decreased insulin sensitivity. These changes were accompanied by increased inflammatory analyte secretion (e.g., IL-6, IL-8, alanine aminotransferase). Fibrogenic activation markers increased with lipotoxic conditions, including secreted TGF-ß (>5-fold increase, P < 0.05), extracellular matrix gene expression, and HSC activation. Significant pathway correlation existed between this in vitro model and human biopsies. Consistent with clinical trial data, 0.5 µM obeticholic acid in this model promoted a healthy lipidomic signature, reduced inflammatory and fibrotic secreted factors, but also increased ApoB secretion, suggesting a potential adverse effect on lipoprotein metabolism. Lipotoxic stress activates similar biological signatures observed in NASH patients in this system, which may be relevant for interrogating novel therapeutic approaches to treat NASH.

Human haemodynamic frequency harmonics regulate the inflammatory phenotype of vascular endothelial cells.

Haemodynamic variations are inherent to blood vessel geometries (such as bifurcations) and correlate with regional development of inflammation and atherosclerosis. However, the complex frequency spectrum characteristics from these haemodynamics have never been exploited to test whether frequency variations are critical determinants of endothelial inflammatory phenotype. Here we utilize an experimental Fourier transform analysis to systematically manipulate individual frequency harmonics from human carotid shear stress waveforms applied in vitro to human endothelial cells. The frequency spectrum, specifically the 0 th and 1st harmonics, is a significant regulator of inflammation, including NF-κB activity and downstream inflammatory phenotype. Further, a harmonic-based regression-model predicts eccentric NF-κB activity observed in the human internal carotid artery. Finally, short interfering RNA-knockdown of the mechanosensor PECAM-1 reverses frequency-dependent regulation of NF-κB activity. Thus, PECAM-1 may have a critical role in the endothelium's exquisite sensitivity to complex shear stress frequency harmonics and provide a mechanism for the focal development of vascular inflammation.

Endothelial Kruppel-like factor 4 protects against atherothrombosis in mice.

The endothelium regulates vascular homeostasis, and endothelial dysfunction is a proximate event in the pathogenesis of atherothrombosis. Stimulation of the endothelium with proinflammatory cytokines or exposure to hemodynamic-induced disturbed flow leads to a proadhesive and prothrombotic phenotype that promotes atherothrombosis. In contrast, exposure to arterial laminar flow induces a gene program that confers a largely antiadhesive, antithrombotic effect. The molecular basis for this differential effect on endothelial function remains poorly understood. While recent insights implicate Kruppel-like factors (KLFs) as important regulators of vascular homeostasis, the in vivo role of these factors in endothelial biology remains unproven. Here, we show that endothelial KLF4 is an essential determinant of atherogenesis and thrombosis. Using in vivo EC-specific KLF4 overexpression and knockdown murine models, we found that KLF4 induced an antiadhesive, antithrombotic state. Mechanistically, we demonstrated that KLF4 differentially regulated pertinent endothelial targets via competition for the coactivator p300. These observations provide cogent evidence implicating endothelial KLFs as essential in vivo regulators of vascular function in the adult animal.

Atheroprone hemodynamics regulate fibronectin deposition to create positive feedback that sustains endothelial inflammation.

RATIONALE: The extracellular matrix protein fibronectin (FN) is focally deposited in regions of atherosclerosis, where it contributes to inflammatory signaling. OBJECTIVE: To elucidate the mechanism by which FN deposition is regulated by local shear stress patterns, its dependence on platelet-endothelial cell adhesion molecule (PECAM)-1 mechanotransduction and the role this pathway plays in sustaining an atheroprone/proinflammatory phenotype. METHODS AND RESULTS: Human endothelial cells were exposed in vitro to atheroprone or atheroprotective shear stress patterns derived from human carotid arteries. Onset of atheroprotective flow induced a transient increase in FN deposition, whereas atheroprone flow caused a steady increase in FN expression and integrin activation over time, leading to a significant and sustained increase in FN deposition relative to atheroprotective conditions. Comparing FN staining in ApoE(-/-) and ApoE(-/-)PECAM(-/-) mice showed that PECAM-1 was essential for FN accumulation in atheroprone regions of the aortic arch. In vitro, small interfering RNA against PECAM-1 blocked the induction of FN and the activation of nuclear factor (NF)-kappaB by atheroprone flow, which was rescued by the addition of exogenous FN. Additionally, blocking NF-kappaB activation attenuated the flow-induced FN expression. Small interfering RNA against FN significantly reduced NF-kappaB activity, which was rescued by the addition of exogenous FN. CONCLUSIONS: These results indicate that FN gene expression and assembly into matrix fibrils is induced by atheroprone fluid shear stress. This effect is mediated at least in part by the transcription factor NF-kappaB. Additionally, because FN promotes activation of NF-kappaB, atheroprone shear stress creates a positive feedback to maintain inflammation.

Human IL-8 regulates smooth muscle cell VCAM-1 expression in response to endothelial cells exposed to atheroprone flow.

OBJECTIVE: Interleukin-8 (IL-8) is a soluble human-specific chemokine implicated in the development of the chronic inflammatory disease atherosclerosis. Recently, we showed that atheroprone hemodynamics induced IL-8 secretion from endothelial cells (ECs) concurrent with increased EC/smooth muscle cell (SMC) VCAM-1 expression in a human hemodynamic coculture model. Despite an IL-8 association with inflammation, we show here that blocking IL-8 activity during atheroprone flow resulted in increased levels of EC/SMC VCAM-1 expression. We tested the hypothesis that IL-8 limits SMC VCAM-1 expression in response to inflammatory stimuli, either atheroprone flow or cytokine interleukin-1beta (IL-1beta) addition. METHODS AND RESULTS: Atheroprone flow increased monocyte adhesion in both EC/SMCs, concurrent with the induction of VCAM-1 protein. VCAM-1 antisera attenuated this response. IL-1beta upregulated VCAM-1 in SMCs by 3-fold, a response inhibited by the addition of IL-8 at 24 hours. Neither IL-1beta nor IL-8 induced proliferation or migration. Neutralization of the IL-8 receptor, CXCR2, further induced VCAM-1 in the presence of IL-1beta, and phospho-p38 was required for NF-kappaB activation and VCAM-1 expression. Additionally, IL-8 reduced p38 activation and NF-kappaB activity induced by IL-1beta alone. CONCLUSIONS: Together, these findings provide evidence for a novel role whereby IL-8 limits the inflammatory response in ECs/SMCs via VCAM-1 modulation.

Endothelial cell PECAM-1 promotes atherosclerotic lesions in areas of disturbed flow in ApoE-deficient mice.

OBJECTIVE: Platelet endothelial cell adhesion molecule-1 (PECAM-1, CD31) has recently been shown to form an essential element of a mechanosensory complex that mediates endothelial responses to fluid shear stress. The aim of this study was to determine the in vivo role of PECAM-1 in atherosclerosis. METHODS AND RESULTS: We crossed C57BL/6 Pecam1(-/-) mice with apolipoprotein E-deficient (Apoe(-/-)) mice. On a Western diet, Pecam1(-/-)Apoe(-/-) mice showed reduced atherosclerotic lesion size compared to Apoe(-/-) mice. Striking differences were observed in the lesser curvature of the aortic arch, an area of disturbed flow, but not in the descending thoracic or abdominal aorta. Vascular cell adhesion molecule-1 (VCAM-1) expression, macrophage infiltration, and endothelial nuclear NF-kappaB were all reduced in Pecam1(-/-)Apoe(-/-) mice. Bone marrow transplantation suggested that endothelial PECAM-1 is the main determinant of atherosclerosis in the aortic arch, but that hematopoietic PECAM-1 promotes lesions in the abdominal aorta. In vitro data show that siRNA-based knockdown of PECAM-1 attenuates endothelial NF-kappaB activity and VCAM-1 expression under conditions of atheroprone flow. CONCLUSIONS: These results indicate that endothelial PECAM-1 contributes to atherosclerotic lesion formation in regions of disturbed flow by regulating NF-kappaB-mediated gene expression.

GRP78 upregulation by atheroprone shear stress via p38-, alpha2beta1-dependent mechanism in endothelial cells.

OBJECTIVE: The initiation of atherosclerosis is in part dependent on the hemodynamic shear stress environment promoting a proinflammatory phenotype of the endothelium. Previous studies demonstrated increased expression of ER stress protein and unfolded protein response (UPR) regulator, GRP78, within all vascular cells in atherosclerotic lesions and its regulation in the endothelium by several atherosclerotic stressors; however, regulation of GRP78 by shear stress directly has not been established. METHOD AND RESULTS: Using an in vitro model to simulate human arterial shear stress waveforms, atheroprone or atheroprotective flow was applied to human endothelial cells. GRP78 was found to be significantly upregulated (3-fold) in a sustained manner under atheroprone, but not atheroprotective flow up to 24 hours. This response was dependent on both sustained activation of p38, as well integrin alpha2beta1. Increased GRP78 correlated with the activation of the ER stress sensing element (ERSE1) promoter by atheroprone flow as a marker of the UPR. Shear stress regulated GRP78 through increased protein stability when compared to other flow regulated proteins, such as connexin-43 and vascular cell adhesion molecule (VCAM)-1. Increased endothelial expression of GRP78 was also observed in atheroprone versus atheroprotective regions of C57BL6 mice. CONCLUSIONS: This study supports a role of the hemodynamic environment in preferentially inducing GRP78 and the UPR in atheroprone regions, before lesion development, and suggests a potential atheroprotective (ie, prosurvival), compensatory effect in response to ER stress within atherosclerotic lesions.