Zackary R. Kenz (1), Grant. T Generaux (1), Diane M. Longo (1), Christina Battista (1), Paul B Watkins (2), Lisl Shoda (1), Brett A Howell (1), and Scott Q Siler (1)
(1) DILIsym Services, Inc., Research Triangle Park, NC; (2) UNC School of Medicine & UNC Eshelman School of Pharmacy, The University of North Carolina at Chapel Hill, Chapel Hill, NC
Introduction:
Non-alcoholic fatty liver disease (NAFLD) is of growing concern within developed countries, with recent estimates suggesting up to 30% of the US population may be affected [1]. NAFLD represents a spectrum of pathophysiology, ranging from hepatic steatosis, through non-alcoholic steatohepatitis (NASH) and hepatic fibrosis, and may result in cirrhosis and liver failure. Inflammation in NASH can be driven by the release of extracellular vesicles from steatotic hepatocytes, intensifying and modulating disease progression. Hepatic fibrosis in NASH is caused by excessive accumulation of extracellular matrix (ECM) proteins. Fibrosis progresses over time due to an increased number of activated hepatic stellate cells (HSCs) and subsequently increased production of hepatic ECM proteins. The relay race of steatosis, inflammation, and subsequent zonal ECM accumulation has not been captured in mathematical models of NASH fibrosis prior to this work.
Objectives:
Build a mechanistic model for NAFLD/NASH inflammation and fibrosis where patient variability can be overlaid. Utilize the model going forward to guide development of therapeutics aimed at treating NASH.
Methods:
Mathematical models of inflammation and fibrosis were developed as sub-models within the NAFLDsym quantitative systems pharmacology (QSP) model to represent dynamics of disease enhancement, collagen turnover, as well as zonal accumulation of collagen during the development of fibrosis in NASH. The model consists of a system of ordinary differential equations (ODEs) which describe the following processes in three discrete acinar zones of the liver: inflammatory cell responses and regulation due to steatosis; regulation of inflammatory response; activated hepatic stellate cell-driven collagen I and III synthesis; MMP/TIMP modulation of collagen degradation; and collagen crosslinking by lysyl oxidase.
Inflammatory macrophage and neutrophil populations as described in clinical data [2] were represented as a function of cellular activation due to extracellular vesicle release from lipid-laden hepatocytes [3] and cellular recruitment rates. Related changes in pro- and anti-inflammatory mediators as well as pro-fibrotic mediators consistent with disease progression were calibrated using clinical studies, for example [4,5]. Collagen I and III synthesis rates and amounts were estimated across the stages of fibrosis using a combination of clinical studies measuring turnover of 2H2O-labeled collagen [6] as well as collagen content from Elastica van Gieson-stained liver biopsy tissues in NASH patients [6,7]. The amount of collagen present across the stages of fibrosis was optimized by balancing the enzymatic activity of MMP/TIMP and lysyl oxidase. The spatio-temporal pattern of zonal collagen accumulation observed in histological scoring of fibrosis patients was captured by varying the Km of TGF-β driven activation of HSCs, with the Km increasing from the centrilobular (CL) to periportal (PP) to midlobular (ML) zones of the hepatic acinus.
Variability in the inflammation response, collagen synthesis rates, and hepatic collagen content across stages of fibrosis was accounted for by the creation of a simulated population (SimPops®) which incorporated variability in parameters related to stellate cell activation and collagen synthesis/degradation, as well as other mechanisms related to the pathophysiology of NAFLD/NASH.
Results:
NAFLDsym simulations accurately recapitulate a large range of inflammatory responses to steatotic hepatocytes as well as zonal accumulation of collagen during the progression of fibrosis. These simulation results are consistent with clinical study data [2-7] in key disease-related aspects of steatosis (e.g., liver fat), inflammation (e.g., pro- and anti-inflammatory and fibrotic mediators), and fibrosis (e.g., collagen synthesis and deposition).
Conclusions:
The integration of inflammation and fibrosis sub-models into the NAFLDsym QSP model accurately captures disease progression and zonal patterns of collagen accumulation in NASH-driven hepatic fibrosis and shows simulation results consistent with non-linear increases in hepatic collagen observed across fibrosis stages in NASH patients. This mechanistic mathematical model is serving as a useful tool to guide development of therapeutics aimed at treating NASH.
References:
[1] McPherson et al. (2015) J Hepatol 62:1148-55.
[2] Tajiri et al. (2009) Eur J Gast Hepatol 21:673-80.
[3] Povero et al. (2016) AASLD poster.
[4] Das et al. (2011) Ind J Clin Biochem 26:202-9.
[5] Yoshida et al. (2014) Int J Exp Path 98:221-33.
[6] Decaris et al. (2017) Hepatology 65:78-88.
[7] Masugi et al. (2017) Hepatol Commun 27:58-68.
Reference: PAGE 28 (2019) Abstr 9173 [www.page-meeting.org/?abstract=9173]
Poster: Drug/Disease Modelling - Other Topics