Drug-induced phospholipidosis

Synchrotron Photothermal Infrared Nanospectroscopy of Drug-Induced Phospholipidosis in Macrophages

Synchrotron resonance-enhanced infrared atomic force microscopy (RE-AFM-IR) is a near-field photothermal vibrational nanoprobe developed at Diamond Light Source (DLS), capable of measuring mid-infrared absorption spectra with spatial resolution around 100 nm. The present study reports a first application of synchrotron RE-AFM-IR to interrogate biological soft matter at the subcellular level, in this case, on a cellular model of drug-induced phospholipidosis (DIPL). J774A-1 macrophages were exposed to amiodarone (10 μM) or medium for 24 h and chemically fixed. AFM topography maps revealed amiodarone-treated cells with enlarged cytoplasm and very thin regions corresponding to collapsed vesicles. IR maps of the whole cell were analyzed by exploiting the RE-AFM-IR overall signal, i.e., the integrated RE-AFM-IR signal amplitude versus AFM-derived cell thickness, also on lateral resolution around 100 nm. Results show that vibrational band assignment was possible, and all characteristic peaks for lipids, proteins, and DNA/RNA were identified. Both peak ratio and unsupervised chemometric analysis of RE-AFM-IR nanospectra generated from the nuclear and perinuclear regions of untreated and amiodarone-treated cells showed that the perinuclear region (i.e., cytoplasm) of amiodarone-treated cells had significantly elevated band intensities in the regions corresponding to phosphate and carbonyl groups, indicating detection of phospholipid-rich inclusion bodies typical for cells with DIPL. The results of this study are of importance to demonstrate not only the applicability of Synchrotron RE-AFM-IR to soft biological matters with subcellular spatial resolution but also that the spectral information gathered from an individual submicron sample volume enables chemometric identification of treatment and biochemical differences between mammalian cells.

Investigating the role of endogenous opioid system in chloroquine-induced phospholipidosis in rat liver by morphological, biochemical and molecular modelling studies

Drug-induced phospholipidosis (DIPL) is characterized by phospholipid storage in the lysosomes of affected tissues. Many severe effects and toxicities have been linked to DIPL. The aim of this study was to determine whether the endogenous opioid system is involved in chloroquine-induced phospholipidosis. The effect of naltrexone as an antagonist of opioid receptors in chloroquine-induced phospholipidosis in rat liver was investigated by morphological, biochemical, and molecular modelling studies. Transmission electron microscopy (TEM) showed that morphological characteristic changes of rat liver, including the number of lamellar bodies, grade of vacuolization and cell steatosis, were markedly attenuated in rats treated with naltrexone alone or in combination with chloroquine, in comparison with chloroquine-treated rats. The results of liquid chromatography mass spectrometry (LC/MS) showed that the concentrations of phenylacetylglycine (PAG) and hippuric acid (HA) were significantly decreased and increased, respectively, in target groups. Besides, the concentration ratio of PAG/HA was significantly decreased. Spectrophotometry resulted in a notable decrease in alanine aminotransferase (ALT) and alkaline phosphatase (ALP) activities in target groups. The results from the molecular docking and molecular dynamic simulation studies demonstrated clear chloroquine interaction with the active site cavity of the µ opioid receptor. These data suggest that administration of naltrexone alone, or in combination with chloroquine, notably attenuates the side effects of chloroquine-induced phospholipidosis, as well as demonstrating an increased probability of the endogenous opioid system involvement in chloroquine-induced phospholipidosis in rat liver.

The Lysosomotropic Activity of Hydrophobic Weak Base Drugs is Mediated via Their Intercalation into the Lysosomal Membrane

Lipophilic weak base therapeutic agents, termed lysosomotropic drugs (LDs), undergo marked sequestration and concentration within lysosomes, hence altering lysosomal functions. This lysosomal drug entrapment has been described as luminal drug compartmentalization. Consistent with our recent finding that LDs inflict a pH-dependent membrane fluidization, we herein demonstrate that LDs undergo intercalation and concentration within lysosomal membranes. The latter was revealed experimentally and computationally by (a) confocal microscopy of fluorescent compounds and drugs within lysosomal membranes, and (b) molecular dynamics modeling of the pH-dependent membrane insertion and accumulation of an assortment of LDs, including anticancer drugs. Based on the multiple functions of the lysosome as a central nutrient sensory hub and a degradation center, we discuss the molecular mechanisms underlying the alteration of morphology and impairment of lysosomal functions as consequences of LDs’ intercalation into lysosomes. Our findings bear important implications for drug design, drug induced lysosomal damage, diseases and pertaining therapeutics.

A Systems Toxicology Approach for the Prediction of Kidney Toxicity and Its Mechanisms In Vitro

The failure to predict kidney toxicity of new chemical entities early in the development process before they reach humans remains a critical issue. Here, we used primary human kidney cells and applied a systems biology approach that combines multidimensional datasets and machine learning to identify biomarkers that not only predict nephrotoxic compounds but also provide hints toward their mechanism of toxicity. Gene expression and high-content imaging-derived phenotypical data from 46 diverse kidney toxicants were analyzed using Random Forest machine learning. Imaging features capturing changes in cell morphology and nucleus texture along with mRNA levels of HMOX1 and SQSTM1 were identified as the most powerful predictors of toxicity. These biomarkers were validated by their ability to accurately predict kidney toxicity of four out of six candidate therapeutics that exhibited toxicity only in late stage preclinical/clinical studies. Network analysis of similarities in toxic phenotypes was performed based on live-cell high-content image analysis at seven time points. Using compounds with known mechanism as reference, we could infer potential mechanisms of toxicity of candidate therapeutics. In summary, we report an approach to generate a multidimensional biomarker panel for mechanistic de-risking and prediction of kidney toxicity in in vitro for new therapeutic candidates and chemical entities.

Investigating the Suitability of High Content Image Analysis as a Tool to Assess the Reversibility of Foamy Alveolar Macrophage Phenotypes In Vitro

Many potential inhaled medicines fail during development due to the induction of a highly vacuolated or “foamy” alveolar macrophage phenotype response in pre-clinical studies. There is limited understanding if this response to an inhaled stimulus is adverse or adaptive, and additionally if it is a transient or irreversible process. The aim of this study was to evaluate whether high content image analysis could distinguish between different drug-induced foamy macrophage phenotypes and to determine the extent of the reversibility of the foamy phenotypes by assessing morphological changes over time. Alveolar-like macrophages derived from the human monocyte cell line U937 were exposed for 24 h to compounds known to induce a foamy macrophage phenotype (amiodarone, staurosporine) and control compounds that are not known to cause a foamy macrophage phenotype in vitro (fluticasone and salbutamol). Following drug stimulation, the cells were rested in drug-free media for the subsequent 24 or 48 h. Cell morphometric parameters (cellular and nuclear area, vacuoles numbers and size) and phospholipid content were determined using high content image analysis. The foamy macrophage recovery was dependent on the mechanism of action of the inducer compound. Amiodarone toxicity was associated with phospholipid accumulation and morphometric changes were reversed when the stimulus was removed from culture environment. Conversely cells were unable to recover from exposure to staurosporine which initiates the apoptosis pathway. This study shows that high content analysis can discriminate between different phenotypes of foamy macrophages and may contribute to better decision making in the process of new drug development.

Case Report: Retinal Toxicity Secondary to Ritonavir

SIGNIFICANCE

Because patients with HIV have increased life expectancies with the advent of new drug therapies, complications from iatrogenic syndromes such as drug toxicity can occur. Ritonavir-induced retinal toxicity is one such complication but has rarely been reported in the literature.

PURPOSE

This case report describes a patient with bilateral maculopathy and bone spicule-like pigmentary changes in the midperipheral retina due to ritonavir use. In addition, novel optical coherence tomography findings are described.

CASE REPORT

A 53-year-old man presented with gradual-onset blurry vision and difficulty seeing at night. He had been diagnosed as having HIV infection 19 years prior and had previously taken ritonavir for 7 years as part of highly active antiretroviral therapy. Best-corrected acuities were 20/30 in the right eye and 20/25 in the left eye. Clinical examination revealed a subtle annular pattern of retinal pigment epithelium mottling around the fovea and bone spicule-like pigment changes in the midperiphery of both retinas. Optical coherence tomography imaging revealed abnormal subfoveal hyperreflectivity of the ellipsoid zone with relative attenuation centrally, annular parafoveal ellipsoid zone loss, and punctate hyperreflectivity within the ellipsoid zone more eccentrically. Fundus autofluorescence in both eyes showed annular hyperautofluorescence in the parafoveal region, geographic hyperautofluorescence in the areas underlying the midperipheral pigmentary changes, and discrete patches of hyperautofluorescence along the far inferotemporal arcades in areas that appeared normal with biomicroscopy. A diagnosis of retinal toxicity secondary to ritonavir use was made based on the patient's history and clinical examination.

CONCLUSIONS

Ritonavir retinal toxicity seems to be an uncommon adverse event that can cause decreased visual function. This case report provides further evidence of the retinal toxicity and reviews the reported clinical and optical coherence tomography manifestations of the disease.

Computational Assessment of the Pharmacological Profiles of Degradation Products of Chitosan

Chitosan is a natural polymer revealing an increased potential to be used in different biomedical applications, including drug delivery systems, and tissue engineering. It implies the evaluation of the organism response to the biomaterial implantation. Low-molecular degradation products, the chito-oligomers, are resulting mainly from the influence of enzymes, which are found in the organism fluids. Within this study, we have performed the computational assessment of pharmacological profiles and toxicological effects on human health of small chito-oligomers with distinct molecular weights, deacetylation degrees, and acetylation patterns. Our approach is based on the fact that regulatory agencies and researchers in the drug development field rely on the use of modeling to predict biological effects and to guide decision making. To be considered as valid for regulatory purposes, every model that is used for predictions should be associated with a defined toxicological endpoint and has appropriate robustness and predictivity. Within this context, we have used FAF-Drugs4, SwissADME, and PreADMET tools to predict the oral bioavailability of chito-oligomers and SwissADME, PreADMET, and admetSAR2.0 tools to predict their pharmacokinetic profiles. The organs and genomic toxicities have been assessed using admetSAR2.0 and PreADMET tools but specific computational facilities have been also used for predicting different toxicological endpoints: Pred-Skin for skin sensitization, CarcinoPred-EL for carcinogenicity, Pred-hERG for cardiotoxicity, ENDOCRINE DISRUPTOME for endocrine disruption potential and Toxtree for carcinogenicity and mutagenicity. Our computational assessment showed that investigated chito-oligomers reflect promising pharmacological profiles and limited toxicological effects on humans, regardless of molecular weight, deacetylation degree, and acetylation pattern. According to our results, there is a possible inhibition of the organic anion transporting peptides OATP1B1 and/or OATP1B3, a weak potential of cardiotoxicity, a minor probability of affecting the androgen receptor, and phospholipidosis. Consequently, these results may be used to guide or to complement the existing in vitro and in vivo toxicity tests, to optimize biomaterials properties and to contribute to the selection of prototypes for nanocarriers.

Ganglioside GM2 catabolism is inhibited by storage compounds of mucopolysaccharidoses and by cationic amphiphilic drugs

The catabolism of ganglioside GM2 is dependent on the lysosomal enzyme β-hexosaminidase A and a supporting lipid transfer protein, the GM2 activator protein. A genetically based disturbance of GM2 catabolism, leads to several subtypes of the GM2 gangliosidosis: Tay-Sachs disease, Sandhoff disease, the AB-variant and the B1-variant, all of them having GM2 as major lysosomal storage compound. Further on it is known that the gangliosides GM2 and GM3 accumulate as secondary storage compounds in mucopolysaccharidoses, especially in Hunter disease, Hurler disease, Sanfilippo disease and Sly syndrome, with chondroitin sulfate as primary storage compound. The exact mechanism of ganglioside accumulation in mucopolysaccaridoses is still a matter of debate. Here, we show that chondroitin sulfate strongly inhibits the catabolism of membrane-bound GM2 by β-hexosaminidase A in presence of GM2 activator protein in vitro already at low micromolar concentrations. In contrast, hyaluronan, the major storage compound in mucopolysaccharidosis IX, a milder disease without secondary ganglioside accumulation, is a less effective inhibitor. On the other hand, hydrolysis of micellar-bound GM2 by β-hexosaminidase A without the assistance of GM2AP was not impeded by chondroitin sulfate implicating that the inhibition of GM2 hydrolysis by chondroitin sulfate is most likely based on an interaction with GM2AP, the GM2AP-GM2 complex or the GM2-carrying membranes. We also studied the influence of some cationic amphiphilic drugs (desipramine, chlorpromazine, imipramine and chloroquine), provoking drug induced phospholipidosis and found that all of them inhibited the hydrolysis of GM2 massively.

Emerging mechanisms of drug-induced phospholipidosis

Drug-induced phospholipidosis is a lysosomal storage disorder characterized by excessive accumulation of phospholipids. Its cellular mechanism is still not well understood, but it is known that cationic amphiphilic drugs can induce it. These drugs have a hydrophilic amine head group that can be protonated in the endolysosomal compartment. As cationic amphiphiles, they are trapped in lysosomes, where they interfere with negatively charged intralysosomal vesicles, the major platforms of cellular sphingolipid degradation. Metabolic principles observed in sphingolipid and phospholipid catabolism and inherited sphingolipidoses are of great importance for lysosomal function and physiological lipid turnover at large. Therefore, we also propose intralysosomal vesicles as major platforms for degradation of lipids and phospholipids reaching them by intracellular pathways like autophagy and endocytosis. Phospholipids are catabolized as components of vesicle surfaces by protonated, positively charged phospholipases, electrostatically attracted to the negatively charged vesicles. Model experiments suggest that progressively accumulating cationic amphiphilic drugs inserting into the vesicle membrane with their hydrophobic molecular moieties disturb and attenuate the main mechanism of lipid degradation as discussed here. By compensating the negative surface charge, cationic enzymes are released from the surface of vesicles and proteolytically degraded, triggering a progressive lipid storage and the formation of inactive lamellar bodies.

Exploiting ensemble learning to improve prediction of phospholipidosis inducing potential

Phospholipidosis is characterized by the presence of excessive accumulation of phospholipids in different tissue types (lungs, liver, eyes, kidneys etc.) caused by cationic amphiphilic drugs. Electron microscopy analysis has revealed the presence of lamellar inclusion bodies as the hallmark of phospholipidosis. Some phospholipidosis causing compounds can cause tissue specific inflammatory/retrogressive changes. Reliable and accurate in silico methods could facilitate early screening of phospholipidosis inducing compounds which can subsequently speed up the pharmaceutical drug discovery pipelines. In the present work, stacking ensembles are implemented for combining a number of different base learners to develop predictive models (a total of 256 trained machine learning models were tested) for phospholipidosis inducing compounds using a wide range of molecular descriptors (ChemMine, JOELib, Open babel and RDK descriptors) and structural alerts as input features. The best model consisting of stacked ensemble of machine learning algorithms with random forest as the second level learner outperformed other base and ensemble learners. JOELib descriptors along with structural alerts performed better than the other types of descriptor sets. The best ensemble model achieved an overall accuracy of 88.23%, sensitivity of 86.27%, specificity of 90.20%, mcc of 0.765, auc of 0.896 with 88.21 g-means. To assess the robustness and stability of the best ensemble model, it is further evaluated using stratified 10×10 fold cross validation and holdout testing sets (repeated 10 times) achieving 84.83% mean accuracy with 0.708 mean mcc and 88.46% mean accuracy with 0.771 mean mcc respectively. A comparison of different meta classifiers (Generalized linear regression, Gradient boosting machines, Random forest and Deep learning neural networks) in stacking ensemble revealed that random forest is the better choice for combining multiple classification models.

Insight into the Role of Extracellular Vesicles in Lysosomal Storage Disorders

Extracellular vesicles (EVs) have received increasing attention over the last two decades. Initially, they were considered as just a garbage disposal tool; however, it has progressively become clear that their protein, nucleic acid (namely miRNA and mRNA), and lipid contents have signaling functions. Besides, it has been established that cells release different types of vesicular structures for which characterization is still in its infancy. Many stress conditions, such as hypoxia, senescence, and oncogene activation have been associated with the release of higher levels of EVs. Further, evidence has shown that autophagic–lysosomal pathway abnormalities also affect EV release. In fact, in neurodegenerative diseases characterized by the accumulation of toxic proteins, although it has not become clear to what extent the intracellular storage of undigested materials itself has beneficial/adverse effects, these proteins have also been shown to be released extracellularly via EVs. Lysosomal storage disorders (LSDs) are characterized by accumulation of undigested substrates within the endosomal–lysosomal system, due either to genetic mutations in lysosomal proteins or to treatment with pharmacological agents. Here, we review studies investigating the role of lysosomal and autophagic dysfunction on the release of EVs, with a focus on studies exploring the release of EVs in LSD models of both genetic and pharmacological origin. A better knowledge of EV-releasing pathways activated in lysosomal stress conditions will provide information on the role of EVs in both alleviating intracellular storage of undigested materials and spreading the pathology to the neighboring tissue.

The Parkinson-associated human P5B-ATPase ATP13A2 modifies lipid homeostasis

Mutations in the ATP13A2 gene (PARK9, CLN12, OMIM 610513) were initially associated with a form of Parkinson's Disease (PD) known as Kufor Rakeb Syndrome (KRS). However, the genetic spectrum of ATP13A2-associated disorders was expanded in the last years, because it has been found to underlay variants of neuronal ceroid-lipofuscinoses (NCLs) and hereditary spastic paraplegia. As ATP13A2 seems to be a key component of the endo-lysosome pathway, the fact that these pathologies are commonly characterized by endo-lysosomal dysfunction is not surprising. Here we report that increasing the level of functional ATP13A2 in a stable SH-SY5Y cell line disrupts lipid homeostasis. ATP13A2 overexpression increases the fluorescence intensity of the fluorescent analog phosphatidylethanolamine (NBD-PE) and the formation of multilamellar bodies, resembling the so-called "drug-induced phospholipidosis". We also found that expression of ATP13A2 reduces the ceramide-fluorescence intensity and the content of bis(monoacylglyceryl)phosphate (BMP). BMP is required for lipid degradation and exosome biogenesis inside acidic compartments, so this result suggests that ATP13A2 may be modifying the lipid digestion capacity and/or the redistribution of lipids in these subcellular organelles. In addition, ATP13A2-overexpression decreased the total content of triglycerides (TGs), cholesterol and lipid droplets. As TGs are necessary for the synthesis of new membranes, this observation suggests that increasing the function of ATP13A2 switches the endo-lysosomal system towards vesicle secretion.

Metabolic disease and ABHD6 alter the circulating bis(monoacylglycerol)phosphate profile in mice and humans

Bis(monoacylglycerol)phosphate (BMP) is a phospholipid that is crucial for lipid degradation and sorting in acidic organelles. Genetic and drug-induced lysosomal storage disorders (LSDs) are associated with increased BMP concentrations in tissues and in the circulation. Data on BMP in disorders other than LSDs, however, are scarce, and key enzymes regulating BMP metabolism remain elusive. Here, we demonstrate that common metabolic disorders and the intracellular BMP hydrolase α/β-hydrolase domain-containing 6 (ABHD6) affect BMP metabolism in mice and humans. In mice, dietary lipid overload strongly affects BMP concentration and FA composition in the liver and plasma, similar to what has been observed in LSDs. Notably, distinct changes in the BMP FA profile enable a clear distinction between lipid overload and drug-induced LSDs. Global deletion of ABHD6 increases circulating BMP concentrations but does not cause LSDs. In humans, nonalcoholic fatty liver disease and liver cirrhosis affect the serum BMP FA composition and concentration. Furthermore, we identified a patient with a loss-of-function mutation in the ABHD6 gene, leading to an altered circulating BMP profile. In conclusion, our results suggest that common metabolic diseases and ABHD6 affect BMP metabolism in mice and humans.

Cytoplasmic Vacuolation and Tapetal Changes Induced by a Novel Analgesic Agent in Beagle Dogs

Drug-induced unique cytoplasmic vacuolation was found in the subchronic oral toxicity study of 4-dimethylamino-1-{3-(1-methyl-1H-imidazole-2-yl)propanoyl}piperidine (DMIP), a potential therapeutic agent for neuropathic pain, in beagle dogs. In the first study, DMIP was administered at a dose of 250, 500, or 1,000 mg/kg/day once daily for 14 days. Discoloration of tapetum lucidum accompanied by tapetal swelling was observed at ≥250 mg/kg/day. The tapetal swelling was correlated to the light microscopic observation of cytoplasmic vacuolation in tapetal cells, and similar vacuolation was observed in several other tissues, including the coronary artery and aortal arch, in a dose-dependent manner. Immunohistochemistry for lysosomal-associated membrane protein 2 indicated that the vacuoles were enlarged lysosomes. However, the nature of these vacuoles was different from that of phospholipidosis because no lamellar bodies were observed. In the second study, DMIP was administered at a dose of 10, 50, or 250 mg/kg/day once daily for 14 days followed by a 14-day recovery period. Tapetal changes and systemic vacuolation were not observed at ≤50 mg/kg/day, and vacuolation observed at 250 mg/kg/day was reversible. A few reports have described the enlargement of lysosomes not attributable to phospholipid accumulation. Our findings provide further information about the toxicological implications of drug-induced lysosomal swelling.

Lytic reactions of drugs with lipid membranes

Propranolol is shown to undergo lipidation reactions in three types of lipid membrane: (1) synthetic single-component glycerophospholipid liposomes; (2) liposomes formed from complex lipid mixtures extracted from E. coli or liver cells; and (3) in cellulo in Hep G2 cells. Fourteen different lipidated propranolol homologues were identified in extracts from Hep G2 cells cultured in a medium supplemented with propranolol. This isolation of lipidated drug molecules from liver cells demonstrates a new drug reactivity in living systems. Acyl transfer from lipids to the alcoholic group of propranolol was favoured over transfer to the secondary amine. Migration of acyl groups from the alcohol to the amine was diminished. Other drugs that were examined did not form detectable levels of lipidation products, but many of these drugs did affect the lysolipid levels in model membranes. The propensity for a compound to induce lysolipid formation in a model system was found to be a predictor for phospholipidosis activity in cellulo.

Genomics of lipid-laden human hepatocyte cultures enables drug target screening for the treatment of non-alcoholic fatty liver disease

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) is a major health burden in need for new medication. To identify potential drug targets a genomic study was performed in lipid-laden primary human hepatocyte (PHH) and human hepatoma cell cultures.

METHODS

PHH, HuH7 and HepG2 hepatoma cell cultures were treated with lipids and/or TNFα. Intracellular lipid load was quantified with the ORO assay. The Affymetrix HG-U133+ array system was employed to perform transcriptome analysis. The lipid droplet (LD) growth and fusion was determined by fluorescence microscopy. LD associated proteins were imaged by confocal immunofluorescence microscopy and confirmed by Western immunoblotting. Bioinformatics defined perturbed metabolic pathways.

RESULTS

Whole genome expression profiling identified 227, 1031 and 571 significant regulated genes. Likewise, the combined lipid and TNFα treatment of PHH, HuH7 and HepG2 cell cultures revealed 154, 1238 and 278 differentially expressed genes. Although genomic responses differed among in-vitro systems, commonalities were ascertained by filtering the data for LD associated gene regulations. Among others the LD-growth and fusion associated cell death inducing DFFA like effector C (CIDEC), perilipins (PLIN2, PLIN3), the synaptosome-associated-protein 23 and the vesicle associated membrane protein 3 were strongly up-regulated. Likewise, the PPAR targets pyruvate-dehydrogenase-kinase-4 and angiopoietin-like-4 were up-regulated as was hypoxia-inducible lipid droplet-associated (HILPDA), flotilin and FGF21. Their inhibition ameliorates triglyceride and cholesterol accumulation. TNFα treatment elicited strong induction of the chemokine CXCL8, the kinases MAP3K8, MAP4K4 and negative regulators of cytokine signaling, i.e. SOCS2&SOCS3. Live cell imaging of DsRED calreticulin plasmid transfected HuH7 cells permitted an assessment of LD growth and fusion and confocal immunofluorescence microscopy evidenced induced LD-associated PLIN2, CIDEC, HIF1α, HILPDA, JAK1, PDK4 and ROCK2 expression. Notwithstanding, CPT1A protein was repressed to protect mitochondria from lipid overload. Pharmacological inhibition of the GTPase-dynamin and the fatty acid transporter-2 reduced lipid uptake by 28.5 and 35%, respectively. Finally, a comparisons of in-vitro/NAFLD patient biopsy findings confirmed common gene regulations thus demonstrating clinical relevance.

CONCLUSION

The genomics of fat-laden hepatocytes revealed LD-associated gene regulations and perturbed metabolic pathways. Immunofluorescence microscopy confirmed expression of coded proteins to provide a rationale for therapeutic intervention strategies. Collectively, the in-vitro system permits testing of drug candidates.

An Expandable Mechanopharmaceutical Device (3): a Versatile Raman Spectral Cytometry Approach to Study the Drug Cargo Capacity of Individual Macrophages

PURPOSE

To improve cytometric phenotyping abilities and better understand cell populations with high interindividual variability, a novel Raman-based microanalysis was developed to characterize macrophages on the basis of chemical composition, specifically to measure and characterize intracellular drug distribution and phase separation in relation to endogenous cellular biomolecules.

METHODS

The microanalysis was developed for the commercially-available WiTec alpha300R confocal Raman microscope. Alveolar macrophages were isolated and incubated in the presence of pharmaceutical compounds nilotinib, chloroquine, or etravirine. A Raman data processing algorithm was specifically developed to acquire the Raman signals emitted from single-cells and calculate the signal contributions from each of the major molecular components present in cell samples.

RESULTS

Our methodology enabled analysis of the most abundant biochemicals present in typical eukaryotic cells and clearly identified "foamy" lipid-laden macrophages throughout cell populations, indicating feasibility for cellular lipid content analysis in the context of different diseases. Single-cell imaging revealed differences in intracellular distribution behavior for each drug; nilotinib underwent phase separation and self-aggregation while chloroquine and etravirine accumulated primarily via lipid partitioning.

CONCLUSIONS

This methodology establishes a versatile cytometric analysis of drug cargo loading in macrophages requiring small numbers of cells with foreseeable applications in toxicology, disease pathology, and drug discovery.

Review article: drug-induced liver injury in the context of nonalcoholic fatty liver disease - a physiopathological and clinical integrated view

BACKGROUND

Nonalcoholic fatty disease (NAFLD) is the most common liver disease, since it is strongly associated with obesity and metabolic syndrome pandemics. NAFLD may affect drug disposal and has common pathophysiological mechanisms with drug-induced liver injury (DILI); this may predispose to hepatoxicity induced by certain drugs that share these pathophysiological mechanisms. In addition, drugs may trigger fatty liver and inflammation per se by mimicking NAFLD pathophysiological mechanisms.

AIMS

To provide a comprehensive update on (a) potential mechanisms whereby certain drugs can be more hepatotoxic in NAFLD patients, (b) the steatogenic effects of drugs, and (c) the mechanism involved in drug-induced steatohepatitis (DISH).

METHODS

A language- and date-unrestricted Medline literature search was conducted to identify pertinent basic and clinical studies on the topic.

RESULTS

Drugs can induce macrovesicular steatosis by mimicking NAFLD pathogenic factors, including insulin resistance and imbalance between fat gain and loss. Other forms of hepatic fat accumulation exist, such as microvesicular steatosis and phospholipidosis, and are mostly associated with acute mitochondrial dysfunction and defective lipophagy, respectively. Drug-induced mitochondrial dysfunction is also commonly involved in DISH. Patients with pre-existing NAFLD may be at higher risk of DILI induced by certain drugs, and polypharmacy in obese individuals to treat their comorbidities may be a contributing factor.

CONCLUSIONS

The relationship between DILI and NAFLD may be reciprocal: drugs can cause NAFLD by acting as steatogenic factors, and pre-existing NAFLD could be a predisposing condition for certain drugs to cause DILI. Polypharmacy associated with obesity might potentiate the association between this condition and DILI.

A New Tool in the Quest for Biocompatible Phthalocyanines: Palladium Catalyzed Aminocarbonylation for Amide Substituted Phthalonitriles and Illustrative Phthalocyanines Thereof

The amide peptide bond type linkage is one of the most natural conjugations available, present in many biological synthons and pharmaceutical drugs. Hence, aiming the direct conjugation of potentially biologically active compounds to phthalocyanines, herein we disclose a new strategy for direct modulation of phthalonitriles, inspired by an attractive synthetic strategy for the preparation of carboxamides based on palladium-catalyzed aminocarbonylation of aryl halides in the presence of carbon monoxide (CO) which, to our knowledge, has never been used to prepare amide-substituted phthalonitriles, the natural precursors for the synthesis of phthalocyanines. Some examples of phthalocyanines prepared thereof are also reported, along with their full spectroscopic characterization and photophysical properties initial assessment.

Molecular mechanism of activation of the immunoregulatory amidase NAAA

Palmitoylethanolamide is a bioactive lipid that strongly alleviates pain and inflammation in animal models and in humans. Its signaling activity is terminated through degradation by N-acylethanolamine acid amidase (NAAA), a cysteine hydrolase expressed at high levels in immune cells. Pharmacological inhibitors of NAAA activity exert profound analgesic and antiinflammatory effects in rodent models, pointing to this protein as a potential target for therapeutic drug discovery. To facilitate these efforts and to better understand the molecular mechanism of action of NAAA, we determined crystal structures of this enzyme in various activation states and in complex with several ligands, including both a covalent and a reversible inhibitor. Self-proteolysis exposes the otherwise buried active site of NAAA to allow catalysis. Formation of a stable substrate- or inhibitor-binding site appears to be conformationally coupled to the interaction of a pair of hydrophobic helices in the enzyme with lipid membranes, resulting in the creation of a linear hydrophobic cavity near the active site that accommodates the ligand's acyl chain.

Derivatization of common antidepressant drugs increases inhibition of acid sphingomyelinase and reduces induction of phospholipidosis

In recent studies, major depressive disorder (MDD) was linked to an increase in acid sphingomyelinase (ASM) activity. Several drugs that are commonly used to treat MDD functionally inhibit the lysosomal enzyme ASM and are called functional inhibitors of ASM (FIASMAs). These drugs are classified as cationic amphiphilic drugs (CADs) that influence the catalytic activities of different lysosomal enzymes. This action results in the side effect of phospholipidosis (PLD), which describes a detrimental increase in the phospholipid content in lysosomes. FIASMAs differ only slightly in their physico-chemical properties, but their effects on ASM activity and induction of the lysosomal phospholipid content vary significantly. In this study, we systematically induced minor chemical modifications to the FIASMAs imipramine, desipramine and fluoxetine. We generated a library of 45 new CADs with slightly different log P (logarithmic partition coefficient) and pKa (logarithmic acid dissociation constant) values. The effects of the compounds on the ASM activity and lysosomal phospholipid content were assessed in cell culture assays. We identified four compounds with beneficial effects, i.e., increased ASM activity inhibition and reduced PLD induction compared with the original drugs. The compounds HT04, RH272B and RH272D outperformed the original imipramine, whereas RH281A performed better than desipramine. Thus, minor chemical variations of CADs impact lysosomal metabolism in a specific manner and can lead to antidepressant drugs with less deleterious side effects.

Imaging Mass Microscopy of Kidneys from Azithromycin-Treated Rats with Phospholipidosis

Drug-induced phospholipidosis is a lysosomal storage disorder characterized by the excess accumulation of tissue phospholipids. Although azithromycin can be used to induce phospholipidosis, no experimental studies evaluating the relationship between drug accumulation and phospholipid localization have been performed. In this study, azithromycin was orally administered to rats for 7 days, and the relationship between drug and phospholipid accumulation was performed using imaging mass microscopy. The administration of azithromycin induced tubular epithelial vacuolation in the inner stripe of the outer medulla of the kidney, consistent with the lamellar bodies that are typical manifestations of drug-induced phospholipidosis. Azithromycin and phospholipid tissue levels were extensively elevated in the kidneys of azithromycin-treated rats. Imaging mass microscopy revealed that both azithromycin and its metabolites were found in the kidneys of azithromycin-treated rats but not in control animals. The vacuolated areas of the kidneys were primarily found in the inner stripe of the outer medulla, consistent with the areas of high azithromycin concentration. Azithromycin was colocalized with several phospholipids-phosphatidylinositol (18:0/20:4), phosphatidylethanolamine (18:0/20:4 and 16:0/20:4), and possibly didocosahexaenoyl (C22:6)-bis(monoacylglycerol) phosphate, a putative biomarker of drug-induced phospholipidosis. In summary, we found correlations between regions of kidney damage and the accumulation of azithromycin, its metabolites, and phospholipids using imaging mass microscopy. Such analyses may help reveal the mechanism and identify putative biomarkers of drug-induced phospholipidosis.

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.

The Effect of Solithromycin, a Cationic Amphiphilic Drug, on the Proliferation and Differentiation of Human Meibomian Gland Epithelial Cells

PURPOSE

We previously discovered that azithromycin (AZM) acts directly on immortalized human meibomian gland epithelial cells (IHMGECs) to stimulate their lipid and lysosome accumulation and overall differentiation. We hypothesize that this phospholipidosis-like effect is due to AZM's cationic amphiphilic drug (CAD) nature. If our hypothesis is correct, then other CADs (e.g., solithromycin [SOL]) should be able to duplicate AZM's action on IHMGECs. Our purpose was to test this hypothesis.

MATERIALS AND METHODS

IHMGECs were cultured in the presence of vehicle or SOL (2, 10, or 20 µg/ml) for up to 7 days under proliferating or differentiating conditions. Positive (epidermal growth factor and bovine pituitary extract for proliferation; AZM for differentiation) and negative (vehicle) controls were included with the experiments. IHMGECs were evaluated for cell number, neutral lipid content, and lysosome accumulation.

RESULTS

Our results demonstrate that SOL induces a rapid and dose-dependent increase in the accumulation of neutral lipids and lysosomes in HMGECs. The lysosomal effects were most prominent with the 10 and 20 µg/ml doses, and occurred earlier (i.e., 1 day) with SOL than with the AZM (10 µg/ml) control. The effects of SOL and AZM on IHMGEC differentiation were essentially the same after 3 days of culture. SOL did not influence the proliferation of HMGECs during a 7-day time period.

CONCLUSIONS

Our results support our hypothesis that SOL, a CAD, is able to reproduce AZM's impact on lysosome and lipid accumulation, as well as the differentiation, of HMGECs. The effect of SOL on lysosome appearance was faster than that of AZM.

High-resolution sub-cellular imaging by correlative NanoSIMS and electron microscopy of amiodarone internalisation by lung macrophages as evidence for drug-induced phospholipidosis

Correlative NanoSIMS and EM imaging of amiodarone-treated macrophages shows the internalisation of the drug at a sub-cellular level and reveals its accumulation within the lysosomes, providing direct evidence for amiodarone-induced phospholipidosis. Chemical fixation using tannic acid effectively seals cellular membranes aiding intracellular retention of diffusible drugs.

Transcriptome analysis to assess the cholestatic hepatotoxicity induced by Polygoni Multiflori Radix: Up-regulation of key enzymes of cholesterol and bile acid biosynthesis

Polygoni Multiflori Radix (PMR) has been commonly used as a tonic in China for centuries. However, PMR-associated hepatotoxicity is becoming a safety issue. Cholestasis often occurs in PMR-induced hepatotoxicity in clinical medicine, but the exact mechanism is not completely understood. An RNA-Seq method was employed, in the present study, to explore the molecular mechanism of cholestatic liver injury induced by PMR, characterized by the hepatic transcriptional response in rats exposed to 1 and 20 g/kg PMR for 90 days. Pathological changes seen in rat livers exposed to PMR included increased bile ducts in portal areas and biliary epithelial cell hyperplasia, which were accompanied by the elevation of serum biochemistries. Dose-dependent increases in the expression of 14 transcripts encoding enzymes involved in the cholesterol biosynthetic pathway were identified. Furthermore, cholesterol 7-alpha hydroxylase (Cyp7a1), a rate-limiting enzyme in the synthesis of bile acids (BAs) from cholesterol, was found to be upregulated by PMR treatment. Protein analysis by western blot suggested that expression of 3-hydroxy-3-methylglutaryl CoA reductase (Hmgcr) and Cyp7a1 were increased in a dose-dependent manner. Collectively, the present study demonstrates that PMR upregulates key enzymes for biosynthesis of cholesterol and BA, which poses the risk of cholestatic liver injury.

SIGNIFICANCE

To the best of our knowledge, this is the first transcriptome analysis to highlight the main molecular changes occurring in rats chronic exposed to PMR. We have identified 39 specific differentially expressed genes (DEGs) that were present in various comparisons. A total of 14 of these altered gene transcripts were associated with cholesterol biosynthesis. Another factor of great importance in our opinion seemed to be the enhancement of bile acid (BA) biosynthesis, which were closely linked to cholesterol biosynthesis or metabolism. Our findings suggested that the disturbance on balance of BA formation and elimination might lead to a BA overload in hepatocytes, thereby resulting in liver injury.

Mitochondrial Dysfunction, Through Impaired Autophagy, Leads to Endoplasmic Reticulum Stress, Deregulated Lipid Metabolism, and Pancreatitis in Animal Models

BACKGROUND & AIMS

Little is known about the signaling pathways that initiate and promote acute pancreatitis (AP). The pathogenesis of AP has been associated with abnormal increases in cytosolic Ca2+, mitochondrial dysfunction, impaired autophagy, and endoplasmic reticulum (ER) stress. We analyzed the mechanisms of these dysfunctions and their relationships, and how these contribute to development of AP in mice and rats.

METHODS

Pancreatitis was induced in C57BL/6J mice (control) and mice deficient in peptidylprolyl isomerase D (cyclophilin D, encoded by Ppid) by administration of L-arginine (also in rats), caerulein, bile acid, or an AP-inducing diet. Parameters of pancreatitis, mitochondrial function, autophagy, ER stress, and lipid metabolism were measured in pancreatic tissue, acinar cells, and isolated mitochondria. Some mice with AP were given trehalose to enhance autophagic efficiency. Human pancreatitis tissues were analyzed by immunofluorescence.

RESULTS

Mitochondrial dysfunction in pancreas of mice with AP was induced by either mitochondrial Ca2+ overload or through a Ca2+ overload-independent pathway that involved reduced activity of ATP synthase (80% inhibition in pancreatic mitochondria isolated from rats or mice given L-arginine). Both pathways were mediated by cyclophilin D and led to mitochondrial depolarization and fragmentation. Mitochondrial dysfunction caused pancreatic ER stress, impaired autophagy, and deregulation of lipid metabolism. These pathologic responses were abrogated in cyclophilin D-knockout mice. Administration of trehalose largely prevented trypsinogen activation, necrosis, and other parameters of pancreatic injury in mice with L-arginine AP. Tissues from patients with pancreatitis had markers of mitochondrial damage and impaired autophagy, compared with normal pancreas.

CONCLUSIONS

In different animal models, we find a central role for mitochondrial dysfunction, and for impaired autophagy as its principal downstream effector, in development of AP. In particular, the pathway involving enhanced interaction of cyclophilin D with ATP synthase mediates L-arginine-induced pancreatitis, a model of severe AP the pathogenesis of which has remained unknown. Strategies to restore mitochondrial and/or autophagic function might be developed for treatment of AP.

Cytotoxicity of silver and copper nanoparticles on rainbow trout (Oncorhynchus mykiss) hepatocytes

Nanoparticles are commonly used in the industry and are present in consumer goods; therefore, evaluation of their potential toxicity is necessary. The aim of the present study was to assess the cytotoxic effects of the nanoparticles of silver (AgNPs) at the concentration of 1.5 mg L^-1 and copper (CuNPs) at 0.15 mg L^-1 on rainbow trout (Oncorhynchus mykiss) hepatocytes after 28 days of exposure. Histological analysis revealed dilated sinusoids, shrunken hepatocytes, nuclear necrosis, and increased number of Kupffer cells in the liver of fish exposed to nanoparticles. The lowest hepatocyte proliferation index was observed in fish treated with AgNPs. Ultrastructural studies revealed mitochondrial edema and cristolysis, dilated and loosened endoplasmic reticulum, cytoplasm vacuolation, accumulation of lipid droplets, glycogen depletion, and formation of myelin-like bodies. The results also revealed that the liver of fish exposed to copper nanoparticles showed higher regenerative potential indicated by higher proliferation index, more abundant glycogen, and more numerous Kupffer cells compared to the fish treated with silver nanoparticles.

A QSAR and molecular modelling study towards new lead finding: polypharmacological approach to Mycobacterium tuberculosis

Developing effective inhibitors against Mycobacterium tuberculosis (Mtb) is a challenging task, primarily due to the emergence of resistant strains. In this study, we have proposed and implemented an in silico guided polypharmacological approach, which is expected to be effective against resistant strains by simultaneously inhibiting several potential Mtb drug targets. A combination of pharmacophore and QSAR based virtual screening strategy taking three key targets such as InhA (enoyl-acyl-carrier-protein reductase), GlmU (N-acetyl-glucosamine-1-phosphate uridyltransferase) and DapB (dihydrodipicolinate reductase) have resulted in initial 784 hits from Asinex database of 435,000 compounds. These hits were further subjected to docking with 33 Mtb druggable targets. About 110 potential polypharmacological hits were taken by integrating the aforementioned screening protocols. Further screening was conducted by taking various parameters and properties such as cell permeability, drug-likeness, drug-induced phospholipidosisand structural alerts. A consensus analysis has yielded 59 potential hits that pass through all the filters and can be prioritized for effective drug-resistant tuberculosis. This study proposes about nine potential hits which are expected to be promising molecules, having not only drug-like properties, but also being effective against multiple Mtb targets.

A cell-based assay using HepaRG cells for predicting drug-induced phospholipidosis

The utility of HepaRG cells as an in vitro cell-based assay system for predicting drug-induced phospholipidosis (PLD) was investigated. In experiment 1, 10 PLD-positive compounds and 11 PLD-negative compounds were selected. HepaRG cells were treated with each compound for 48 hr. In experiment 2, loratadine and desloratadine, a major metabolite of loratadine, were used to assess metabolic activation for PLD. HepaRG cells were treated with loratadine and desloratadine in the presence or absence of 500 μM 1-aminobenzotriazole (ABT), a broad CYP inhibitor, for 48 hr. After treatment with compounds in experiments 1 and 2, the relative fluorescence intensity (RFI) was measured using LYSO-ID Red dye to assess the PLD induction. In experiment 1, our cell-based assay system using HepaRG cells exhibited 100% sensitivity and 100% specificity for predicting drug-induced PLD. In experiment 2, loratadine increased the RFI in the PLD assay. However, the increase in the RFI was not observed in co-treatment with loratadine and ABT. In addition, desloratadine increased the RFI in the presence and absence of ABT. These results suggested that metabolic activation of loratadine may contribute to PLD in HepaRG cells. We newly demonstrated that HepaRG cells have a high ability for predicting drug-induced PLD. In addition, we newly showed that HepaRG cells may predict drug-induced PLD mediated by metabolic activation of loratadine. Thus, a cell-based assay system using HepaRG cells is a useful model for predicting drug-induced PLD.

Electrophysiological features and multimodal imaging in ritonavir-related maculopathy

PURPOSE

The purpose of this study is to report a case of ritonavir-related retinal toxicity followed over a year. Electrophysiological features and multimodal imaging, including adaptive optics, are provided and discussed.

METHODS

Electrophysiological recordings and multimodal imaging were performed and repeated over 1 year.

RESULTS

Fundus examination revealed crystalline maculopathy in conjunction with pigment disruption. Spectral domain optical coherence tomography displayed thinning of the macula without cysts. Autofluorescence imaging revealed a mixed pattern of complete loss of the autofluorescence in the area of retinal pigment deposit and an increased transmission of the autofluorescence in the area of retinal thinning. Fluorescein angiography ruled out parafoveal telangiectasia. Indocyanine green angiography was not contributive. Increased spacing of the macular cone mosaic, crystal deposits and pigment migrations were seen with adaptive optics. Full-field electroretinogram was slightly reduced for both eyes, especially in the light-adapted responses, and mfERG confirmed bilateral maculopathy. Functional and structural abnormalities did not change with follow-up besides constant pigmentary changes monitored with adaptive optics.

CONCLUSION

Ritonavir-related retinal toxicity is a maculopathy with peculiar features including crystalline and pigment migration associated with central or temporofoveolar thinning and inconstant macular telangiectasia. Despite drug cessation, retinal remodelling continues to progress.

Recent controversies about MDR and XDR-TB: Global implementation of the WHO shorter MDR-TB regimen and bedaquiline for all with MDR-TB?

Tuberculosis (TB) is now the biggest infectious disease killer worldwide. Although the estimated incidence of TB has marginally declined over several years, it is out of control in some regions including in Africa. The advent of multidrug-resistant TB (MDR-TB) and extensively drug-resistant TB (XDR-TB) threatens to further destabilize control in several regions of the world. Drug-resistant TB constitutes a significant threat because it underpins almost 25% of global TB mortality, is associated with high morbidity, is a threat to healthcare workers and is unsustainably costly to treat. The advent of highly resistant TB with emerging bacillary resistance to newer drugs has raised further concern. Encouragingly, in addition to preventative strategies, several interventions have recently been introduced to curb the drug-resistant TB epidemic, including newer molecular diagnostic tools, new (bedaquiline and delamanid) and repurposed (linezolid and clofazimine) drugs and shorter and individualized treatment regimens. However, there are several controversies that surround the use of new drugs and regimens, including whether, how and to what extent they should be used, and who specifically should be treated so that outcomes are optimally improved without amplifying the burden of drug resistance, and other potential drawbacks, thus sustaining effectiveness of the new drugs. The equipoise surrounding these controversies is discussed and some recommendations are provided.

Comparing structural and transcriptional drug networks reveals signatures of drug activity and toxicity in transcriptional responses

We performed an integrated analysis of drug chemical structures and drug-induced transcriptional responses. We demonstrated that a network representing three-dimensional structural similarities among 5452 compounds can be used to automatically group together drugs with similar scaffolds, physicochemical parameters and mode-of-action. We compared the structural network to a network representing transcriptional similarities among a subset of 1309 drugs for which transcriptional response were available in the Connectivity Map data set. Analysis of structurally similar, but transcriptionally different drugs sharing the same MOA enabled us to detect and remove weak and noisy transcriptional responses, greatly enhancing the reliability of transcription-based approaches to drug discovery and drug repositioning. Cardiac glycosides exhibited the strongest transcriptional responses with a significant induction of pathways related to epigenetic regulation, which suggests an epigenetic mechanism of action for these drugs. Drug classes with the weakest transcriptional responses tended to induce expression of cytochrome P450 enzymes, hinting at drug-induced drug resistance. Analysis of transcriptionally similar, but structurally different drugs with unrelated MOA, led us to the identification of a 'toxic' transcriptional signature indicative of lysosomal stress (lysosomotropism) and lipid accumulation (phospholipidosis) partially masking the target-specific transcriptional effects of these drugs. We found that this transcriptional signature is shared by 258 compounds and it is associated to the activation of the transcription factor TFEB, a master regulator of lysosomal biogenesis and autophagy. Finally, we built a predictive Random Forest model of these 258 compounds based on 128 physicochemical parameters, which should help in the early identification of potentially toxic drug candidates.

Transcriptional responses to drug treatment can reveal mechanism of action and off-target effects thus enabling drug repositioning, but only if measured in the appropriate cells at clinically relevant concentrations. A team led by Diego di Bernardo and Diego Medina generated a network representing structural similarities among compounds to automatically group together drugs with similar scaffolds and MOA. By comparing the structural drug network with a transcriptional drug network based on similarities in transcriptional response, the team observed broad differences between the two. This observation led to the identification of a transcriptional signature related lysosomal stress and phospholipidosis, and a physicochemical model to identify such compounds. These results provide general guidelines to prevent erroneous conclusion when using transcriptional responses of small molecules for drug discovery and drug repositioning

Harmful at non-cytotoxic concentrations: SiO2-SPIONs affect surfactant metabolism and lamellar body biogenesis in A549 human alveolar epithelial cells

The pulmonary delivery of nanoparticles (NPs) is a promising approach in nanomedicine. For the efficient and safe use of inhalable NPs, understanding of NP interference with lung surfactant metabolism is needed. Lung surfactant is predominantly a phospholipid substance, synthesized in alveolar type II cells (ATII), where it is packed in special organelles, lamellar bodies (LBs). In vitro and in vivo studies have reported NPs impact on surfactant homeostasis, but this phenomenon has not yet been sufficiently examined. We showed that in ATII-like A549 human lung cancer cells, silica-coated superparamagnetic iron oxide NPs (SiO₂-SPIONs), which have a high potential in medicine, caused an increased cellular amount of acid organelles and phospholipids. In SiO₂-SPION treated cells, we observed elevated cellular quantity of multivesicular bodies (MVBs), organelles involved in LB biogenesis. In spite of the results indicating increased surfactant production, the cellular quantity of LBs was surprisingly diminished and the majority of the remaining LBs were filled with SiO₂-SPIONs. Additionally, LBs were detected inside abundant autophagic vacuoles (AVs) and obviously destined for degradation. We also observed time- and dose-dependent changes in mRNA expression for proteins involved in lipid metabolism. Our results demonstrate that non-cytotoxic concentrations of SiO₂-SPIONs interfere with surfactant metabolism and LB biogenesis, leading to disturbed ability to reduce hypophase surface tension. To ensure the safe use of NPs for pulmonary delivery, we propose that potential NP interference with LB biogenesis is obligatorily taken into account.

Development of 2-aminooxazoline 3-azaxanthene β-amyloid cleaving enzyme (BACE) inhibitors with improved selectivity against Cathepsin D

As part of an ongoing effort at Amgen to develop a disease-modifying therapy for Alzheimer's disease, we have previously used the aminooxazoline xanthene (AOX) scaffold to generate potent and orally efficacious BACE1 inhibitors. While AOX-BACE1 inhibitors demonstrated acceptable cardiovascular safety margins, a retinal pathological finding in rat toxicological studies demanded further investigation. It has been widely postulated that such retinal toxicity might be related to off-target inhibition of Cathepsin D (CatD), a closely related aspartyl protease. We report the development of AOX-BACE1 inhibitors with improved selectivity against CatD by following a structure- and property-based approach. Our efforts culminated in the discovery of a picolinamide-substituted 3-aza-AOX-BACE1 inhibitor absent of retinal effects in an early screening rat toxicology study.

TgPL2, a patatin-like phospholipase domain-containing protein, is involved in the maintenance of apicoplast lipids homeostasis in Toxoplasma

Patatin-like phospholipases are involved in numerous cellular functions, including lipid metabolism and membranes remodeling. The patatin-like catalytic domain, whose phospholipase activity relies on a serine-aspartate dyad and an anion binding box, is widely spread among prokaryotes and eukaryotes. We describe TgPL2, a novel patatin-like phospholipase domain-containing protein from the parasitic protist Toxoplasma gondii. TgPL2 is a large protein, in which the key motifs for enzymatic activity are conserved in the patatin-like domain. Using immunofluorescence assays and immunoelectron microscopy analysis, we have shown that TgPL2 localizes to the apicoplast, a non-photosynthetic plastid found in most apicomplexan parasites. This plastid hosts several important biosynthetic pathways, which makes it an attractive organelle for identifying new potential drug targets. We thus addressed TgPL2 function by generating a conditional knockdown mutant and demonstrated it has an essential contribution for maintaining the integrity of the plastid. In absence of TgPL2, the organelle is rapidly lost and remaining apicoplasts appear enlarged, with an abnormal accumulation of membranous structures, suggesting a defect in lipids homeostasis. More precisely, analyses of lipid content upon TgPL2 depletion suggest this protein is important for maintaining levels of apicoplast-generated fatty acids, and also regulating phosphatidylcholine and lysophosphatidylcholine levels in the parasite.

Alterations in endo-lysosomal function induce similar hepatic lipid profiles in rodent models of drug-induced phospholipidosis and Sandhoff disease

Drug-induced phospholipidosis (DIPL) is characterized by an increase in the phospholipid content of the cell and the accumulation of drugs and lipids inside the lysosomes of affected tissues, including in the liver. Although of uncertain pathological significance for patients, the condition remains a major impediment for the clinical development of new drugs. Human Sandhoff disease (SD) is caused by inherited defects of the β subunit of lysosomal β-hexosaminidases (Hex) A and B, leading to a large array of symptoms, including neurodegeneration and ultimately death by the age of 4 in its most common form. The substrates of Hex A and B, gangliosides GM2 and GA2, accumulate inside the lysosomes of the CNS and in peripheral organs. Given that both DIPL and SD are associated with lysosomes and lipid metabolism in general, we measured the hepatic lipid profiles in rodent models of these two conditions using untargeted LC/MS to examine potential commonalities. Both model systems shared a number of perturbed lipid pathways, notably those involving metabolism of cholesteryl esters, lysophosphatidylcholines, bis(monoacylglycero)phosphates, and ceramides. We report here profound alterations in lipid metabolism in the SD liver. In addition, DIPL induced a wide range of lipid changes not previously observed in the liver, highlighting similarities with those detected in the model of SD and raising concerns that these lipid changes may be associated with underlying pathology associated with lysosomal storage disorders.