Evaluation and validation of multiple cell lines and primary mouse macrophages to predict phospholipidosis potential

Uncovering the toxicity mechanisms of a series of carboxylic acids in liver cells through computational and experimental approaches

Hepatotoxicity poses a significant concern in drug design due to the potential liver damage that can be caused by new drugs. Among common manifestations of hepatotoxic damage is lipid accumulation in hepatic tissue, resulting in liver steatosis or phospholipidosis. Carboxylic derivatives are prone to interfere with fatty acid metabolism and cause lipid accumulation in hepatocytes. This study investigates the toxic behaviour of 24 structurally related carboxylic acids in hepatocytes, specifically their ability to cause accumulation of fatty acids and phospholipids. Using high-content screening (HCS) assays, we identified two distinct lipid accumulation patterns. Subsequently, we developed structure-activity relationship (SAR) and quantitative structure-activity relationship (QSAR) models to determine relevant molecular substructures and descriptors contributing to these adverse effects. Additionally, we calculated physicochemical properties associated with lipid accumulation in hepatocytes and examined their correlation with our chemical structure characteristics. To assess the applicability of our findings to a wide range of chemical compounds, we employed two external datasets to evaluate the distribution of our QSAR descriptors. Our study highlights the significance of subtle molecular structural variations in triggering hepatotoxicity, such as the presence of nitrogen or the specific arrangement of substitutions within the carbon chain. By employing our comprehensive approach, we pinpointed specific molecules and elucidated their mechanisms of toxicity, thus offering valuable insights to guide future toxicology investigations.

Use of 3D Human Liver Organoids to Predict Drug-Induced Phospholipidosis

Drug-induced phospholipidosis (PL) is a storage disorder caused by the formation of phospholipid-drug complexes in lysosomes. Because of the diversity of PL between species, human cell-based assays have been used to predict drug-induced PL in humans. We established three-dimensional (3D) human liver organoids as described previously and investigated their liver characteristics through multiple analyses. Drug-induced PL was initiated in these organoids and in monolayer HepG2 cultures, and cellular changes were systemically examined. Organoids that underwent differentiation showed characteristics of hepatocytes rather than HepG2 cells. The organoids also survived under PL-inducing drug conditions for 48 h and maintained a more stable albumin secretion level than the HepG2 cells. More cytoplasmic vacuoles were observed in organoids and HepG2 cells treated with more potent PL-induced drugs, but to a greater extent in organoids than in HepG2 cells. Lysosome-associated membrane protein 2, a marker of lysosome membranes, showed a stronger immunohistochemical signal in the organoids. PL-distinctive lamellar bodies were observed only in amiodarone-treated organoids by transmission electron microscopy. Human liver organoids are thus more sensitive to drug-induced PL and less affected by cytotoxicity than HepG2 cells. Since PL is a chronic condition, these results indicate that organoids better reflect metabolite-mediated hepatotoxicity in vivo and could be a valuable system for evaluating the phospholipidogenic effects of different compounds during drug development.

An optical nanoreporter of endolysosomal lipid accumulation reveals enduring effects of diet on hepatic macrophages in vivo

The abnormal accumulation of lipids within the endolysosomal lumen occurs in many conditions, including lysosomal storage disorders, atherosclerosis, nonalcoholic fatty liver disease (NAFLD), and drug-induced phospholipidosis. Current methods cannot monitor endolysosomal lipid content in vivo, hindering preclinical drug development and research into the mechanisms linking endolysosomal lipid accumulation to disease progression. We developed a single-walled carbon nanotube-based optical reporter that noninvasively measures endolysosomal lipid accumulation via bandgap modulation of its intrinsic near-infrared emission. The reporter detected lipid accumulation in Niemann-Pick disease, atherosclerosis, and NAFLD models in vivo. By applying the reporter to the study of NAFLD, we found that elevated lipid quantities in hepatic macrophages caused by a high-fat diet persist long after reverting to a normal diet. The reporter dynamically monitored endolysosomal lipid accumulation in vivo over time scales ranging from minutes to weeks, indicating its potential to accelerate preclinical research and drug development processes.

Role of Toll-like receptor 4/oxidant-coupled activation in regulating the biosynthesis of omega-3 polyunsaturated fatty acid derivative resolvin D1 in primary murine peritoneal macrophage

We have previously shown that reactive oxygen species (ROS) as prooxidants can activate Toll-like receptor 4 (TLR4) with the potential to initiate, propagate and maintain "sterile" inflammation of innate immunity, which plays a mediatory role in a host of human disease states. We now present new evidence that ROS can also activate TLR4 to counter the inflammatory phenotype by increasing the production of resolvin D1 (RvD1), which is a specialized anti-inflammatory and pro-resolving lipid mediator. We used primary murine peritoneal macrophages (pM) derived from both TLR4-WT and TLR4-KO mice as a cellular model. We used potassium peroxychromate (PPC) as a direct in vitro source of exogenous ROS. PPC treatment increased intracellular ROS levels, which decreased intracellular total antioxidant capacity, thus suggesting an enhanced cellular oxidative stress. PPC and LPS-EK (a TLR4-specific agonist) increased pro-inflammatory TNFα production with noeffect on IL-10, an anti-inflammatory cytokine. Treatment with the prooxidant increased the expression of 12 lipoxygenase (12-LOX) and 5-lipoxygenase (5-LOX) only in pM derived from TLR4 WT but not in pM from TLR4-KO mice. 5-LOX and 12-LOX are the key enzymes in the RvD1 biosynthetic pathway. In addition, PPC increased the expression of RvD1 receptor, a member of G-protein-coupled receptor only in pM from TLR4-WT mice. Our data support the involvement of TLR4-mediated oxidant-induced pro-inflammatory phenotypes that are in opposition to the production of anti-inflammatory/pro-resolution phenotypes in macrophages. Now, we show that through TLR4 activation, exogenous oxidants can play a role both in producing proinflammatory phenotypes at the same time that it enhances resolution of inflammation to maintain a state of cellular homeostasis and prevent tissue damage/disease.

Detection of nanocarrier potentiation on drug induced phospholipidosis in cultured cells and primary hepatocyte spheroids by high content imaging and analysis

Considerable effort has been made to develop nanocarriers for controlled drug delivery over the last decade, while it remains unclear how the strength of adverse drug effect will be altered when a drug is loaded on the nanocarrier. Drug-induced phospholipidosis (DIP) is characterized with excessive accumulation of phospholipids in cells and is common for cationic amphiphilic drugs (CAD). Previously, we have reported that PEGylated graphene oxide (PEG-GO) loaded with several CAD can potentiate DIP. In current study, we extended our study on newly identified phospholipidosis (PLD) inducers that had been identified from the Library of Pharmacologically Active Compounds (LOPAC), to investigate if PEO-GO loaded with these CAD can alter DIP. Twenty-two CAD were respectively loaded on PEG-GO and incubated with RAW264.7, a macrophage cell line. The results showed that when a CAD was loaded on PEG-GO, its strength of PLD induction can be enhanced, unchanged or attenuated. PEG-GO loaded with Ifenprodil exhibited the highest PEG-GO potentiation effect compared to Ifenprodil treatment alone in RAW264.7 cells, and this effect was confirmed in human hepatocellular carcinoma HepG2, another cell line model for PLD induction. Primary hepatocyte culture and spheroids mimicking in vivo conditions were used to further validate nanocarrier potentiation on DIP by Ifenprodil. Stronger phospholipid accumulation was found in PEG-GO/Ifenprodil treated hepatocytes or spheroids than Ifenprodil treatment alone. Therefore, evidences were provided by us that nanocarriers may increase the adverse drug effects and guidance by regulatory agencies need to be drafted for the safe use of nanotechnology in drug delivery.

Inflammatory response of TLR4 deficient spleen macrophages (CRL 2471) to Brucella abortus S19 and an isogenic ΔmglA deletion mutant

Brucellosis is a worldwide distributed zoonosis caused by members of the genus Brucella. One of them, Brucella abortus, is the etiological agent of bovine brucellosis. With the attenuated strain B. abortus S19 a vaccine is available. However, both, virulence (safety) and the ability to induce a protective B and T cell response (efficacy) have to be tested in suitable assays before successful use in the field. For this purpose, several macrophage cell lines of various origins have been used while splenic macrophages are the preferred host cells in vivo. We here characterized the in vitro response of the murine splenic macrophage cell line CRL 2471(I-13.35) to B. abortus. This cell line still depends on the presence of colony-stimulating factor 1 (CSF1) and is derived from LPS resistant (TLR4 deficient) C3H/HeJ mice. For infection the vaccine strain B. abortus S19A as well as the formerly described isogenic deletion mutant B. abortus S19A ΔmglA 3.14 were used. While numbers of viable bacteria did not differ significantly between the vaccine strain and the deletion mutant at 6h post infection, a higher bacterial load was measured in case of the mutant at 24h and 48h after infection. This was also true, when IFNγ was used for macrophage activation. A comprehensive gene expression profile of macrophages was analysed 6 and 24h after infection by means of an RT-PCR based gene expression array. The mutant strain B. abortus S19A ΔmglA 3.14 elicited a stronger cellular response of the splenic macrophages as compared to the parental vaccine strain. This was most prominent for the pro-inflammatory cytokines IL-1α, IL-1β, TNF-α and IL6 as well as for the chemokine ligands CXCL1, CXCL2, CXCL10, CCL2, CCL5, CCL7, CCL17 and the co-stimulatory molecules CD40 and ICAM1. While these differences were also present in IFNγ-stimulated macrophages, an addition of IFNγ after infection not only resulted in a dramatic increase of the translation of the afore mentioned genes but also resulted in the translation of IFNß1, IL12ß, MIP1α and β (CCL3, CCL4), NOS2 (and SOD2) and FAS.

CONCLUSION

The TLR4 deficient murine splenic macrophage cell line CRL 2471 was used for the first time for the characterization of macrophage-Brucella interaction to investigate the pre-immune phase of brucellosis in vitro. Typical pro-inflammatory cytokines and certain surface receptors were differentially induced by B. abortus S19 A and an isogenic ΔmglA deletion mutant in vitro. This model may be useful for further studies to characterize the inflammatory response of splenic macrophages to intracellular gram-negative bacteria avoiding cell responses to soluble LPS.

Morphological and Functional Characterization and Assessment of iPSC-Derived Hepatocytes for In Vitro Toxicity Testing

Drug-induced liver injury (DILI) remains a great challenge and a major concern during late-stage drug development. Induced pluripotent stem cells (iPSC) represent an exciting alternative in vitro model system to explore the role of genetic diversity in DILI, especially when derived from patients who have experienced drug-induced hepatotoxicity. The development and validation of the iPSC-derived hepatocytes as an in vitro cell-based model of DILI is an essential first step in creating more predictive tools for understanding patient-specific hepatotoxic responses to drug treatment. In this study, we performed extensive morphological and functional analyses on iPSC-derived hepatocytes from a commercial source. iPSC-derived hepatocytes exhibit many of the key morphological and functional features of primary hepatocytes, including membrane polarity and production of glycogen, lipids, and key hepatic proteins, such as albumin, asialoglycoprotein receptor and α1-antitrypsin. They maintain functional activity for many drug-metabolizing enzyme pathways and possess active efflux capacity of marker substrates into bile canalicular compartments. Whole genome-wide array analysis of multiple batches of iPSC-derived cells showed that their transcriptional profiles are more similar to those from neonatal and adult hepatocytes than those from fetal liver. Results from experiments using prototype DILI compounds, such as acetaminophen and trovafloxacin, indicate that these cells are able to reproduce key characteristic metabolic and adaptive responses attributed to the drug-induced hepatotoxic effects in vivo. Overall, this novel system represents a promising new tool for understanding the underlying mechanisms of idiosyncratic DILI and for screening new compounds for DILI-related liabilities.

High-content screening technology for studying drug-induced hepatotoxicity in cell models

High-content screening is the application of automated microscopy and image analysis to both cell biology and drug discovery. Over the last decade, this technique has emerged as a useful technology that allows the simultaneous measurement of different parameters at a single-cell level. Hepatotoxicity is a compelling reason for drug nonapprovals and withdrawals. It is recognized that the safety of a compound cannot be based on a single in vitro assay, and existing methods are not predictive of drug-induced toxicity. However, different HCS assays have been recently demonstrated as being powerful for identifying different mechanisms implicated in drug-induced toxicity with high sensitivity and specificity. These assays integrate the data obtained from different cell function indicators and can be easily incorporated into basic screening processes for the safety evaluation and selection of drug candidates; thus, they contribute greatly to lessen the likelihood of drug failure. Exploring the use of cellular imaging technology in drug-induced liver injury by reviewing the different tests proposed provides evidence that this technology has a strong impact on drug discovery.

Identification of hepatic phospholipidosis inducers in sandwich-cultured rat hepatocytes, a physiologically relevant model, reveals altered basolateral uptake and biliary excretion of anionic probe substrates

Drug-induced phospholipidosis (PLD) is characterized by phospholipid accumulation within the lysosomes of affected tissues, resulting in lysosomal enlargement and laminar body inclusions. Numerous adverse effects and toxicities have been linked to PLD-inducing drugs, but it remains unknown whether drug-induced PLD represents a distinct toxicity or cellular adaptation. In silico and immortalized cellular models have been used to evaluate the PLD potential of new drugs, but these systems have some limitations. The aims of this study were to determine whether primary sandwich-cultured hepatocytes (SCH) can serve as a sensitive and selective model to evaluate hepatic drug-induced PLD, and to evaluate the impact of PLD on the uptake and biliary excretion of probe substrates, taurocholate (TC) and rosuvastatin (RSV). Rat SCH were cultured for 48 h with prototypic hepatic PLD-inducing drugs, amiodarone (AMD), chloroquine (CHQ), desipramine (DES), and azithromycin (AZI), as well as the renal PLD inducer gentamicin (GTM). LysoTracker Red localization and transmission electron microscopy indicated enlarged lysosomal compartments and laminar body inclusions in SCH treated with AMD, CHQ, DES, and AZI, but not GTM, relative to control. PLD resulted in a 51-92% decrease in the in vitro biliary clearance of both TC and RSV; the biliary excretion index significantly decreased for TC from 88 to 35-73%. These data suggested that PLD significantly reduced both organic anion transporting polypeptide-mediated uptake, and bile salt export pump-mediated biliary transport processes. The current study demonstrates that the rat SCH system is a promising model to study hepatic PLD in vitro. Altered hepatic transport of anionic substrates secondary to drug-induced PLD is a novel finding.

Identification of drugs inducing phospholipidosis by novel in vitro data

Drug-induced phospholipidosis (PLD) is a lysosomal storage disorder characterized by the accumulation of phospholipids within the lysosome. This adverse drug effect can occur in various tissues and is suspected to impact cellular viability. Therefore, it is important to test chemical compounds for their potential to induce PLD during the drug design process. PLD has been reported to be a side effect of many commonly used drugs, especially those with cationic amphiphilic properties. To predict drug-induced PLD in silico, we established a high-throughput cell-culture-based method to quantitatively determine the induction of PLD by chemical compounds. Using this assay, we tested 297 drug-like compounds at two different concentrations (2.5 μM and 5.0 μM). We were able to identify 28 previously unknown PLD-inducing agents. Furthermore, our experimental results enabled the development of a binary classification model to predict PLD-inducing agents based on their molecular properties. This random forest prediction system yields a bootstrapped validated accuracy of 86 %. PLD-inducing agents overlap with those that target similar biological processes; a high degree of concordance with PLD-inducing agents was identified for cationic amphiphilic compounds, small molecules that inhibit acid sphingomyelinase, compounds that cross the blood-brain barrier, and compounds that violate Lipinski's rule of five. Furthermore, we were able to show that PLD-inducing compounds applied in combination additively induce PLD.