Although a full understanding of the hepatic circulation is one of the keys to successfully perform liver surgery and to elucidate liver pathology, relatively little is known about the functional organization of the liver vasculature. Therefore, we materialized and visualized the human hepatic vasculature at different scales, and performed a morphological analysis by combining vascular corrosion casting with novel micro-computer tomography (CT) and image analysis techniques. A human liver vascular corrosion cast was obtained by simultaneous resin injection in the hepatic artery (HA) and portal vein (PV). A high resolution (110 lm) micro-CT scan of the total cast allowed gathering detailed macrovascular data. Subsequently, a mesocirculation sample (starting at generation 5; 88 9 68 9 80 mm³) and a microcirculation sample (terminal vessels including sinusoids; 2.0 9 1.5 9 1.7 mm³) were dissected and imaged at a 71-lm and 2.6-lm resolution, respectively. Segmentations and 3D reconstructions allowed quantifying the macro-and mesoscale branching topology, and geometrical features of HA, PV and hepatic venous trees up to 13 generations (radii ranging from 13.2 mm to 80 lm; lengths from 74.4 mm to 0.74 mm), as well as microvascular characteristics (mean sinusoidal radius of 6.63 lm). Combining corrosion casting and micro-CT imaging allows quantifying the branching topology and geometrical features of hepatic trees using a multiscale approach from the macro-down to the microcirculation. This may lead to novel insights into liver circulation, such as internal blood flow distributions and anatomical consequences of pathologies (e.g. cirrhosis).

Hypothermic machine perfusion (HMP) is experiencing a revival in organ preservation due to the limitations of static cold storage and the need for better preservation of expanded criteria donor organs. For livers, perfusion protocols are still poorly defined, and damage of sinusoidal endothelial cells and heterogeneous perfusion are concerns. In this study, an electrical model of the human liver blood circulation is developed to enlighten internal pressure and flow distributions during HMP. Detailed vascular data on two human livers, obtained by combining vascular corrosion casting, micro-CT-imaging and image processing, were used to set up the electrical model. Anatomical data could be measured up to 5--6 vessel generations in each tree and showed exponential trend lines, used to predict data for higher generations. Simulated flow and pressure were in accordance with literature data. The model was able to simulate effects of pressure-driven HMP on liver hemodynamics and reproduced observations such as flow competition between the hepatic artery and portal vein. Our simulations further indicate that, from a pure biomechanical (shear stress) standpoint, HMP with low pressures should not result in organ damage, and that fluid viscosity has no effect on the shear stress experienced by the liver microcirculation in pressure-driven HMP.

Angiogenesis contributes to the development of nonalcoholic steatohepatitis (NASH) and promotes inflammation, fibrosis, and progression to hepatocellular carcinoma (HCC). Angiopoietin‐2 (Ang‐2) is a key regulator of angiogenesis. We aimed to investigate the role of Ang‐2 and its potential as a therapeutic target in NASH using human samples, in vivo mouse models, and in vitro assays. Serum Ang‐2 levels were determined in 104 obese patients undergoing bariatric surgery and concomitant liver biopsy. The effect of the Ang‐2/Tie2 receptor inhibiting peptibody L1‐10 was evaluated in the methionine‐choline deficient (MCD) and streptozotocin‐western diet nonalcoholic fatty liver disease mouse models, and in vitro on endothelial cells and bone marrow–derived macrophages. The hepatic vasculature was visualized with µCT scans and scanning electron microscopy of vascular casts. Serum Ang‐2 levels were increased in patients with histological NASH compared with patients with simple steatosis and correlated with hepatic CD34 immunoreactivity as a marker of hepatic angiogenesis. Serum and hepatic Ang‐2 levels were similarly increased in mice with steatohepatitis. Both preventive and therapeutic L1‐10 treatment reduced hepatocyte ballooning and fibrosis in MCD diet‐fed mice and was associated with reduced hepatic angiogenesis and normalization of the vascular micro‐architecture. Liver‐isolated endothelial cells and monocytes from MCD‐fed L1‐10–treated mice showed reduced expression of leukocyte adhesion and inflammatory markers, respectively, compared with cells from untreated MCD diet‐fed mice. In the streptozotocin‐western diet model, therapeutic Ang‐2 inhibition was able to reverse NASH and attenuate HCC progression. In vitro, L1‐10 treatment mitigated increased cytokine production in lipopolysaccharide‐stimulated endothelial cells but not in macrophages. Conclusion: Our findings provide evidence for Ang‐2 inhibition as a therapeutic strategy to target pathological angiogenesis in NASH.

Perfusion characteristics of the human hepatic microcirculation based on 3D reconstructions and computational fluid dynamic analysis C. Debbaut et al.Paper BIO- permeabilities which were approximately equal. The mean 3D porosity was 14.3%. Conclusions.Our data indicate that the human hepatic microcirculation is characterized by a higher permeability along the central vein direction, and an about two times lower permeability along the radial and circumferential directions of a lobule. Since the permeability coefficients depend on the flow direction, (porous medium) liver microcirculation models should take into account sinusoidal anisotropy.Keywords. Human liver microcirculation, computational fluid dynamics, wall shear stress, permeability tensor, porosityPerfusion characteristics of the human hepatic microcirculation based on 3D reconstructions and computational fluid dynamic analysis C. Debbaut et al.Paper BIO-11-1408 4