The role of sinusoidal endothelial cells and TIMP1 in the regulation of fibrosis in a novel human liver 3D NASH model

BACKGROUND

The prevalence of NAFLD is rapidly increasing. NAFLD can progress to NASH, fibrosis, cirrhosis, and HCC, which will soon become the main causes of liver transplantation. To date, no effective drug for NASH has been approved by the Food and Drug Administration. This is partly due to the lack of reliable human in vitro models. Here, we present a novel human liver spheroid model that can be used to study the mechanisms underlying liver fibrosis formation and degradation.

METHODS AND RESULTS

Such spheroids, which contain hepatocytes, stellate cells, KC, and LSECs, spontaneously develop fibrosis that is exacerbated by treatment with free fatty acids. Conditioned medium from activated LSECs caused similar activation of fibrosis in spheroids containing primary human hepatocyte and NPCs, indicating the action of soluble mediators from the LSECs. Spheroids containing LSECs treated with free fatty acids produced tissue inhibitor of metalloproteinases inhibitor 1, a matrix metalloproteinases inhibitor important for fibrosis progression. Tissue inhibitor of metalloproteinases inhibitor 1 knockdown using siRNA led to a reduction in collagen and procollagen accumulation, which could be partially rescued using a potent matrix metalloproteinases inhibitor. Interestingly, tissue inhibitor of metalloproteinases inhibitor 1 was found to be expressed at higher levels, specifically in a subtype of endothelial cells in the pericentral region of human fibrotic livers, than in control livers.

CONCLUSION

Potential anti-NASH drugs and compounds were evaluated for their efficacy in reducing collagen accumulation, and we found differences in specificity between spheroids with and without LSECs. This new human NASH model may reveal novel mechanisms for the regulation of liver fibrosis and provide a more appropriate model for screening drugs against NASH.

Mechanisms of 5-HT receptor antagonists in the regulation of fibrosis in a 3D human liver spheroid model

Non-alcoholic steatohepatitis (NASH) is a major health problem leading to liver fibrosis and hepatocellular carcinoma, among other diseases, and for which there is still no approved drug treatment. Previous studies in animal models and in LX-2 cells have indicated a role for serotonin (5-HT) and 5-HT receptors in stellate cell activation and the development of NASH. In the current study, we investigated the extent to which these findings are applicable to a human NASH in vitro model consisting of human liver spheroids containing hepatocytes and non-parenchymal cells. Treatment of the spheroids with 5-HT or free fatty acids (FFA) induced fibrosis, whereas treatment of the spheroids with the 5-HT receptor antagonists ketanserin, pimavanserin, sarpogrelate, and SB269970 inhibited FFA-induced fibrosis via a reduction in stellate cell activation as determined by the expression of vimentin, TGF-β1 and COL1A1 production. siRNA-based silencing of 5-HT2A receptor expression reduced the anti-fibrotic properties of ketanserin, suggesting a role for 5-HT receptors in general and 5-HT2A receptors in particular in the FFA-mediated increase in fibrosis in the human liver spheroid model. The results suggest a contribution of the 5-HT receptors in the development of FFA-induced human liver fibrosis with implications for further efforts in drug development.

Mechanistic, Functional, and Clinical Aspects of Pro-inflammatory Cytokine Mediated Regulation of ADME Gene Expression in 3D Human Liver Spheroids

During systemic inflammation, pro-inflammatory cytokines alter metabolism and transport of drugs affecting the clinical outcome. We used an in vivo like human 3D liver spheroid model to study the effects and mechanisms of pro-inflammatory cytokines on the expression of 9 different genes encoding enzymes responsible for the metabolism of > 90% of clinically used drugs. Treatment of spheroids with pathophysiologically relevant concentrations of IL-1β, IL-6, or TNFα resulted in a pronounced decrease in mRNA expression of CYP3A4 and UGT2B10 within 5 hours. The reduction of CYP1A2, CYP2C9, CYP2C19, and CYP2D6 mRNA expression was less pronounced, whereas the pro-inflammatory cytokines caused increased CYP2E1, and UGT1A3 mRNA expression. The cytokines did not influence expression of key nuclear proteins, nor the activities of specific kinases involved in the regulation of genes encoding drug metabolizing enzymes. However, ruxolitinib, a JAK1/2 inhibitor, inhibited the IL-6 dependent increase in CYP2E1 and the decrease in CYP3A4 and UGT2B10 mRNA expression. We evaluated the effect of TNFα in hepatocytes in 2D plates and found a rapid decrease in drug-metabolizing enzyme mRNA both in the absence or presence of the cytokines. Taken together, these data suggest that pro-inflammatory cytokines regulate multiple gene- and cytokine-specific events seen in in vivo and in 3D but not in 2D liver models. We propose that the 3D spheroid system is suitable for the prediction of drug metabolism under conditions of inflammation and constitutes a versatile system for short- and long-term preclinical and mechanistic studies of cytokine-induced changes in drug metabolism.

The Role of CTGF in Liver Fibrosis Induced in 3D Human Liver Spheroids

Connective tissue growth factor (CTGF) is involved in the regulation of extracellular matrix (ECM) production. Elevated levels of CTGF can be found in plasma from patients with liver fibrosis and in experimental animal models of liver fibrosis, but the exact role of CTGF in, e.g., diet-induced human liver fibrosis is not entirely known. To address this question, we utilized a 3D human liver co-culture spheroid model composed of hepatocytes and non-parenchymal cells, in which fibrosis is induced by TGF-β1, CTGF or free fatty acids (FFA). Treatment of the spheroids with TGF-β1 or FFA increased COL1A1 deposition as well as the expression of TGF-β1 and CTGF. Recombinant CTGF, as well as angiotensin II, caused increased expression and/or production of CTGF, TGF-β1, COL1A1, LOX, and IL-6. In addition, silencing of CTGF reduced both TGF-β1- and FFA-induced COL1A1 deposition. Furthermore, we found that IL-6 induced CTGF, COL1A1 and TGF-β1 production, suggesting that IL-6 is a mediator in the pathway of CTGF-induced fibrosis. Taken together, our data indicate a specific role for CTGF and CTGF downstream signaling pathways for the development of liver inflammation and fibrosis in the human 3D liver spheroid model.

Clinically Relevant Cytochrome P450 3A4 Induction Mechanisms and Drug Screening in Three-Dimensional Spheroid Cultures of Primary Human Hepatocytes

Cytochrome P450 (CYP) 3A4 induction is an important cause of drug-drug interactions, making early identification of drug candidates with CYP3A4 induction liability in drug development a prerequisite. Here, we present three-dimensional (3D) spheroid cultures of primary human hepatocytes (PHHs) as a novel CYP3A4 induction screening model. Screening of 25 drugs (12 known CYP3A4 inducers in vivo and 13 negative controls) at physiologically relevant concentrations revealed a 100% sensitivity and 100% specificity of the system. Three of the in vivo CYP3A4 inducers displayed much higher CYP3A4 induction capacity in 3D spheroid cultures as compared with in two-dimensional (2D) monolayer cultures. Among those, we identified AZD1208, a proviral integration site for Moloney murine leukemia virus (PIM) kinase inhibitor terminated in phase I of development due to unexpected CYP3A4 autoinduction, as a CYP3A4 inducer only active in 3D spheroids but not in 2D monolayer cultures. Gene knockdown experiments revealed that AZD1208 requires pregnane X receptor (PXR) to induce CYP3A4. Rifampicin requires solely PXR to induce CYP3A4 and CYP2B6, while phenobarbital-mediated induction of these CYPs did not show absolute dependency on either PXR or constitutive androstane receptor (CAR), suggesting its ability to switch nuclear receptor activation. Mechanistic studies into AZD1208 uncovered an involvement of the mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) pathway in CYP3A4 induction that is sensitive to the culture format used, as revealed by its inhibition of ERK1/2 Tyrosine 204 phosphorylation and sensitivity to epidermal growth factor (EGF) pressure. In line, we also identified lapatinib, a dual epidermal growth factor receptor/human epidermal growth factor receptor 2 (EGFR/HER2) inhibitor, as another CYP3A4 inducer only active in 3D spheroid culture. Our findings offer insights into the pathways involved in CYP3A4 induction and suggest PHH spheroids for preclinical CYP3A4 induction screening.

Human Liver Spheroids as a Model to Study Aetiology and Treatment of Hepatic Fibrosis

Non-alcoholic fatty liver disease affects approximately one billion adults worldwide. Non-alcoholic steatohepatitis (NASH) is a progressive disease and underlies the advancement to liver fibrosis, cirrhosis, and hepatocellular carcinoma, for which there are no FDA-approved drug therapies. We developed a hetero-cellular spheroid system comprised of primary human hepatocytes (PHH) co-cultured with crude fractions of primary human liver non-parenchymal cells (NPC) from several matched or non-matched donors, to identify phenotypes with utility in investigating NASH pathogenesis and drug screening. Co-culture spheroids displayed stable expression of hepatocyte markers (albumin, CYP3A4) with the integration of stellate (vimentin, PDGFRβ), endothelial (vWF, PECAM1), and CD68-positive cells. Several co-culture spheroids developed a fibrotic phenotype either spontaneously, primarily observed in PNPLA3 mutant donors, or after challenge with free fatty acids (FFA), as determined by COL1A1 and αSMA expression. This phenotype, as well as TGFβ1 expression, was attenuated with an ALK5 inhibitor. Furthermore, CYP2E1, which has a strong pro-oxidant effect, was induced by NPCs and FFA. This system was used to evaluate the effects of anti-NASH drug candidates, which inhibited fibrillary deposition following 7 days of exposure. In conclusion, we suggest that this system is suitable for the evaluation of NASH pathogenesis and screening of anti-NASH drug candidates.

CYP3A5 is unlikely to mediate anticancer drug resistance in hepatocellular carcinoma

Recently, it was published that CYP3A5 contributes to chemotherapeutic drug resistance in a wide range of solid tumors, including hepatocellular carcinoma. However, CYP3A5 is highly polymorphic and 90% of Caucasians are homozygous for the loss-of-function allele CYP3A5*3. Here, we evaluate the relationship between CYP3A5 genotype and expression level of both CYP3A5 transcripts and protein in biopsies from 19 pairs of liver tumors and corresponding peritumoral tissue. We find that CYP3A5 transcript levels are reduced compared with peritumoral controls. Moreover, we do not detect CYP3A5 protein in homozygous CYP3A5*3 carriers and no relative increase of CYP3A5 in tumoral tissue of CYP3A5*1 carriers. We conclude that anticancer drug resistance is unlikely to be caused by increased CYP3A5 expression.

Massive rearrangements of cellular MicroRNA signatures are key drivers of hepatocyte dedifferentiation

Hepatocytes are dynamic cells that, upon injury, can alternate between nondividing differentiated and dedifferentiated proliferating states in vivo. However, in two-dimensional cultures, primary human hepatocytes (PHHs) rapidly dedifferentiate, resulting in loss of hepatic functions that significantly limits their usefulness as an in vitro model of liver biology, liver diseases, as well as drug metabolism and toxicity. Thus, understanding the underlying mechanisms and stalling of the dedifferentiation process would be highly beneficial to establish more-accurate and relevant long-term in vitro hepatocyte models. Here, we present comprehensive analyses of whole proteome and transcriptome dynamics during the initiation of dedifferentiation during the first 24 hours of culture. We report that early major rearrangements of the noncoding transcriptome, hallmarked by increased expression of small nucleolar RNAs, long noncoding RNAs, microRNAs (miRNAs), and ribosomal genes, precede most changes in coding genes during dedifferentiation of PHHs, and we speculated that these modulations could drive the hepatic dedifferentiation process. To functionally test this hypothesis, we globally inhibited the miRNA machinery using two established chemically distinct compounds, acriflavine and poly-l-lysine. These inhibition experiments resulted in a significantly impaired miRNA response and, most important, in a pronounced reduction in the down-regulation of hepatic genes with importance for liver function. Thus, we provide strong evidence for the importance of noncoding RNAs, in particular, miRNAs, in hepatic dedifferentiation, which can aid the development of more-efficient differentiation protocols for stem-cell-derived hepatocytes and broaden our understanding of the dynamic properties of hepatocytes with respect to liver regeneration.

CONCLUSION

miRNAs are important drivers of hepatic dedifferentiation, and our results provide valuable information regarding the mechanisms behind liver regeneration and possibilities to inhibit dedifferentiation in vitro. (Hepatology 2016;64:1743-1756).

Characterization of primary human hepatocyte spheroids as a model system for drug-induced liver injury, liver function and disease

Liver biology and function, drug-induced liver injury (DILI) and liver diseases are difficult to study using current in vitro models such as primary human hepatocyte (PHH) monolayer cultures, as their rapid de-differentiation restricts their usefulness substantially. Thus, we have developed and extensively characterized an easily scalable 3D PHH spheroid system in chemically-defined, serum-free conditions. Using whole proteome analyses, we found that PHH spheroids cultured this way were similar to the liver in vivo and even retained their inter-individual variability. Furthermore, PHH spheroids remained phenotypically stable and retained morphology, viability, and hepatocyte-specific functions for culture periods of at least 5 weeks. We show that under chronic exposure, the sensitivity of the hepatocytes drastically increased and toxicity of a set of hepatotoxins was detected at clinically relevant concentrations. An interesting example was the chronic toxicity of fialuridine for which hepatotoxicity was mimicked after repeated-dosing in the PHH spheroid model, not possible to detect using previous in vitro systems. Additionally, we provide proof-of-principle that PHH spheroids can reflect liver pathologies such as cholestasis, steatosis and viral hepatitis. Combined, our results demonstrate that the PHH spheroid system presented here constitutes a versatile and promising in vitro system to study liver function, liver diseases, drug targets and long-term DILI.

Expression and Function of mARC: Roles in Lipogenesis and Metabolic Activation of Ximelagatran

Recently two novel enzymes were identified in the outer mitochondrial membrane, mARC1 and mARC2. These molybdenum containing enzymes can reduce a variety of N-hydroxylated compounds, such as N-hydroxy-guanidines and sulfohydroxamic acids, as well as convert nitrite into nitric oxide (NO). However, their endogenous functions remain unknown. Here we demonstrate a specific developmental pattern of expression of these enzymes. mARC1, but not mARC2, was found to be expressed in fetal human liver, whereas both, in particular mARC2, are abundant in adult liver and also expressed in omental and subcutaneous fat. Caloric diet restriction of obese patients caused a decreased expression of mARC2 in liver, similar to that seen in the livers of starved rats. Knock down of mARC2 expression by siRNA in murine adipocytes had statistically significant effect on the level of diglycerides and on the fatty acid composition of some triglycerides, concomitantly a clear trend toward the reduced formation of most of triglyceride and phospholipid species was observed. The involvement of mARC2 in the metabolism of the hepatotoxic drug ximelagatran was evaluated in hepatocytes and adipocytes. Ximelagatran was shown to cause oxidative stress and knock down of mARC2 in adipocytes prevented ximelagatran induced inhibition of mitochondrial respiration. In conclusion, our data indicate that mARC1 and mARC2 have different developmental expression profiles, and that mARC2 is involved in lipogenesis, is regulated by nutritional status and responsible for activation of ximelagatran into a mitotoxic metabolite(s).