Consequences of mitochondrial injury induced by pharmaceutical fatty acid oxidation inhibitors is characterized in human and rat liver slices

Interactions of Nanoparticles with Macrophages and Feasibility of Drug Delivery for Asthma

Understanding the interaction between nanoparticles and immune cells is essential for the evaluation of nanotoxicity and development of nanomedicines. However, to date, there is little data on the membrane microstructure and biochemical changes in nanoparticle-loaded immune cells. In this study, we observed the microstructure of nanoparticle-loaded macrophages and changes in lipid droplets using holotomography analysis. Quantitatively analyzing the refractive index distribution of nanoparticle-loaded macrophages, we identified the interactions between nanoparticles and macrophages. The results showed that, when nanoparticles were phagocytized by macrophages, the number of lipid droplets and cell volume increased. The volume and mass of the lipid droplets slightly increased, owing to the absorption of nanoparticles. Meanwhile, the number of lipid droplets increased more conspicuously than the other factors. Furthermore, alveolar macrophages are involved in the development and progression of asthma. Studies have shown that macrophages play an essential role in the maintenance of asthma-related inflammation and tissue damage, suggesting that macrophage cells may be applied to asthma target delivery strategies. Therefore, we investigated the target delivery efficiency of gold nanoparticle-loaded macrophages at the biodistribution level, using an ovalbumin-induced asthma mouse model. Normal and severe asthma models were selected to determine the difference in the level of inflammation in the lung. Consequently, macrophages had increased mobility in models of severe asthma, compared to those of normal asthma disease. In this regard, the detection of observable differences in nanoparticle-loaded macrophages may be of primary interest, as an essential endpoint analysis for investigating nanomedical applications and immunotheragnostic strategies.

Preclinical models of idiosyncratic drug-induced liver injury (iDILI): Moving towards prediction

Idiosyncratic drug-induced liver injury (iDILI) encompasses the unexpected harms that prescription and non-prescription drugs, herbal and dietary supplements can cause to the liver. iDILI remains a major public health problem and a major cause of drug attrition. Given the lack of biomarkers for iDILI prediction, diagnosis and prognosis, searching new models to predict and study mechanisms of iDILI is necessary. One of the major limitations of iDILI preclinical assessment has been the lack of correlation between the markers of hepatotoxicity in animal toxicological studies and clinically significant iDILI. Thus, major advances in the understanding of iDILI susceptibility and pathogenesis have come from the study of well-phenotyped iDILI patients. However, there are many gaps for explaining all the complexity of iDILI susceptibility and mechanisms. Therefore, there is a need to optimize preclinical human in vitro models to reduce the risk of iDILI during drug development. Here, the current experimental models and the future directions in iDILI modelling are thoroughly discussed, focusing on the human cellular models available to study the pathophysiological mechanisms of the disease and the most used in vivo animal iDILI models. We also comment about in silico approaches and the increasing relevance of patient-derived cellular models.

Bioengineered Liver Models for Investigating Disease Pathogenesis and Regenerative Medicine

Owing to species-specific differences in liver pathways, in vitro human liver models are utilized for elucidating mechanisms underlying disease pathogenesis, drug development, and regenerative medicine. To mitigate limitations with de-differentiated cultures, bioengineers have developed advanced techniques/platforms, including micropatterned cocultures, spheroids/organoids, bioprinting, and microfluidic devices, for perfusing cell cultures and liver slices. Such techniques improve mature functions and culture lifetime of primary and stem-cell human liver cells. Furthermore, bioengineered liver models display several features of liver diseases including infections with pathogens (e.g., malaria, hepatitis C/B viruses, Zika, dengue, yellow fever), alcoholic/nonalcoholic fatty liver disease, and cancer. Here, we discuss features of bioengineered human liver models, their uses for modeling aforementioned diseases, and how such models are being augmented/adapted for fabricating implantable human liver tissues for clinical therapy. Ultimately, continued advances in bioengineered human liver models have the potential to aid the development of novel, safe, and efficacious therapies for liver disease.

Mitochondria-A target for attenuation of astrocyte pathology

Astrocyte pathology is a feature of neuromyelitis optica spectrum disorder (NMOSD) pathology. Recently mitochondrial dysfunction and metabolic changes were suggested to play a role in NMOSD. To elucidate the role of mitochondrial dysfunction, astrocyte pathology was induced in C57BL/6 J female mice by intracerebral injection of aquaporin-4-immunoglobulin G from an NMOSD patient, together with complement. Etomoxir has been shown to cause mitochondrial dysfunction. Etomoxir was delivered to the central nervous system and resulted in decreased astrocyte pathology. The ameliorating effect was associated with increases in different acylcarnitines and amino acids. This suggests that mitochondria may be a therapeutic target in NMOSD.

In vitro cytotoxicity study of superparamagnetic iron oxide and silica nanoparticles on pneumocyte organelles

Inhalation is the main route of nanoparticles (NP) exposure during manufacturing. Although many mechanisms of toxicity have been described, the interaction of NP with relevant pneumocytes organelles is not widely understood. Considering that the physicochemical properties of NP influence their toxicological responses, the objective of this study was to evaluate whether exposure to different NP, crystalline Fe₃O₄ NP and amorphous SiO₂ NP could alter pneumocytes organelles in alveolar epithelial cells. To achieve this goal, cell viability, ultrastructural changes, lysosomal damage, mitochondrial membrane potential (MMP), lipid droplets (LD) formation and cytokines production were evaluated by MTT, electron microscopy, lysotracker red staining, JC-1, Oil Red staining and Milliplex® assay respectively. Both NP were observed within lamellar bodies (LB), lysosomes, and cytoplasm causing morphological changes. Exposure to SiO₂ NP at 6 h induced lysosomal activation, but not Fe₃O₄ NP. MMP decreased and LD increased at the highest concentrations after both NP exposure. Pro-inflammatory cytokines were released only after SiO₂ NP exposure at 48 h. These results indicate that SiO₂ NP have a greater impact than Fe₃O₄ NP on organelles responsible for energy, secretion, degradation and metabolism in pneumocytes leading to the development of respiratory disorders or the exacerbation of preexisting conditions. Therefore, the established biocompatibility for amorphous NP has to be reconsidered.

Mitochondrial dysfunction and apoptosis underlie the hepatotoxicity of perhexiline

Perhexiline is an anti-anginal drug developed in the late 1960s. Despite its therapeutic success, it caused severe hepatoxicity in selective patients, which resulted in its withdrawal from the market. In the current study we explored the molecular mechanisms underlying the cytotoxicity of perhexiline. In primary human hepatocytes, HepaRG cells, and HepG2 cells, perhexiline induced cell death in a concentration- and time-dependent manner. Perhexiline treatment also caused a significant increase in caspase 3/7 activity at 2 h and 4 h. Pretreatment with specific caspase inhibitors suggested that both intrinsic and extrinsic apoptotic pathways contributed to perhexiline-induced cytotoxicity, which was confirmed by increased expression of TNF-α, cleavage of caspase 3 and 9 upon perhexiline treatment. Moreover, perhexiline caused mitochondrial dysfunction, demonstrated by the classic glucose-galactose assay at 4 h and 24 h. Results from JC-1 staining suggested perhexiline caused loss of mitochondrial potential. Blocking mitochondrial permeability transition pore using inhibitor bongkrekic acid attenuated the cytotoxicity of perhexiline. Western blotting analysis also showed decreased expression level of pro-survival proteins Bcl-2 and Mcl-1, and increased expression of pro-apoptotic protein Bad. Direct measurement of the activity of individual components of the mitochondrial respiratory complex demonstrated that perhexiline strongly inhibited Complex IV and Complex V and moderately inhibited Complex II and Complex II + III. Overall, our data demonstrated that both mitochondrial dysfunction and apoptosis underlies perhexiline-induced hepatotoxicity.

Analysis of metabolic flux in felid spermatozoa using metabolomics and 13C-based fluxomics†

Spermatozoa from three feline species-the domestic cat (Felis catus), the cheetah (Acinonyx jubatus), and the clouded leopard (Neofelis nebulosa)-were analyzed using metabolomic profiling and 13C-based fluxomics to address questions raised regarding their energy metabolism. Metabolic profiles and utilization of 13C-labeled energy substrates were detected and quantified using gas chromatography-mass spectrometry (GC-MS). Spermatozoa were collected by electroejaculation and incubated in media supplemented with 1.0 mM [U13C]-glucose, [U13C]-fructose, or [U13C]-pyruvate. Evaluation of intracellular metabolites following GC-MS analysis revealed the uptake and utilization of labeled glucose and fructose in sperm, as indicated by the presence of heavy ions in glycolytic products lactate and pyruvate. Despite evidence of substrate utilization, neither glucose nor fructose had an effect on the sperm motility index of ejaculated spermatozoa from any of the three felid species, and limited entry of pyruvate derived from these hexose substrates into mitochondria and the tricarboxylic acid cycle was detected. However, pathway utilization was species-specific for the limited number of individuals (four to seven males per species) assessed in these studies. An inhibitor of fatty acid beta-oxidation (FAO), etomoxir, altered metabolic profiles of all three felid species but decreased motility only in the cheetah. While fluxomic analysis provided direct evidence that glucose and fructose undergo catabolic metabolism, other endogenous substrates such as endogenous lipids may provide energy to fuel motility.

Non-alcoholic fatty liver disease is a potential risk factor for liver injury caused by immune checkpoint inhibitor

BACKGROUND AND AIM

Because of their survival benefits, immune checkpoint inhibitors (ICIs) are widely administered to patients with various advanced-stage malignancies. During ICI treatment, drug-induced liver injury (DILI) occasionally occurs. In particular, hepatic immune-related adverse events (irAEs) are rare but serious and fatal. In patients with hepatic irAEs, immediate steroid treatment is generally recommended; however, the risk factors for ICI-associated DILI remain unknown. In the present study, we identified a risk factor for ICI-associated DILI.

METHODS

We retrospectively analyzed 135 patients treated with anti-programmed cell death-1 (PD-1) antibodies, such as nivolumab and pembrolizumab, at Asahikawa Medical University Hospital. We investigated grade ≥ 2 hepatotoxic AEs during anti-PD-1 therapy, and PD-1 inhibitor-associated DILI was then diagnosed according to the Digestive Disease Week Japan (DDW-J) 2004 scale. The risk factors for PD-1 inhibitor-associated DILI were identified by Cox hazard analysis.

RESULTS

Thirty-six patients developed grade ≥ 2 hepatic AEs during anti-PD-1 therapy. Among them, eight patients were diagnosed with PD-1 inhibitor-associated DILI based on the DDW-J 2004 scale. Cox hazard analysis revealed that non-alcoholic fatty liver disease (NAFLD) was a risk factor for PD-1 inhibitor-associated DILI. In addition, we revealed that the outcomes of patients with the DDW-J 2004 score = 3 were improved without steroid treatment.

CONCLUSIONS

NAFLD is a potential risk factor for PD-1 inhibitor-associated DILI based on the DDW-J 2004 scale. The DDW-J 2004 scale might be useful for determining whether steroid treatment is required in patients with PD-1 inhibitor-associated DILI.

A novel homozygous missense SLC25A20 mutation in three CACT-deficient patients: clinical and autopsy data

Carnitine-acylcarnitine translocase (CACT) deficiency is a fatty acid ß-oxidation disorder of the carnitine shuttle in mitochondria, with a high mortality rate in childhood. We evaluated three patients, including two siblings, with neonatal-onset CACT deficiency and revealed identical homozygous missense mutations of p.Arg275Gln within the SLC25A20 gene. One patient died from hypoglycemia and arrhythmia at 26 months; his pathological autopsy revealed increased and enlarged mitochondria in the heart but not in the liver.

Stem-cell based organ-on-a-chip models for diabetes research

Diabetes mellitus (DM) ranks among the severest global health concerns of the 21st century. It encompasses a group of chronic disorders characterized by a dysregulated glucose metabolism, which arises as a consequence of progressive autoimmune destruction of pancreatic beta-cells (type 1 DM), or as a result of beta-cell dysfunction combined with systemic insulin resistance (type 2 DM). Human cohort studies have provided evidence of genetic and environmental contributions to DM; yet, these studies are mostly restricted to investigating statistical correlations between DM and certain risk factors. Mechanistic studies, on the other hand, aimed at re-creating the clinical picture of human DM in animal models. A translation to human biology is, however, often inadequate owing to significant differences between animal and human physiology, including the species-specific glucose regulation. Thus, there is an urgent need for the development of advanced human in vitro models with the potential to identify novel treatment options for DM. This review provides an overview of the technological advances in research on DM-relevant stem cells and their integration into microphysiological environments as provided by the organ-on-a-chip technology.

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.

The Peroxisome-Mitochondria Connection: How and Why?

Over the past decades, peroxisomes have emerged as key regulators in overall cellular lipid and reactive oxygen species metabolism. In mammals, these organelles have also been recognized as important hubs in redox-, lipid-, inflammatory-, and innate immune-signaling networks. To exert these activities, peroxisomes must interact both functionally and physically with other cell organelles. This review provides a comprehensive look of what is currently known about the interconnectivity between peroxisomes and mitochondria within mammalian cells. We first outline how peroxisomal and mitochondrial abundance are controlled by common sets of cis- and trans-acting factors. Next, we discuss how peroxisomes and mitochondria may communicate with each other at the molecular level. In addition, we reflect on how these organelles cooperate in various metabolic and signaling pathways. Finally, we address why peroxisomes and mitochondria have to maintain a healthy relationship and why defects in one organelle may cause dysfunction in the other. Gaining a better insight into these issues is pivotal to understanding how these organelles function in their environment, both in health and disease.

Liver Effects of Clinical Drugs Differentiated in Human Liver Slices

Drugs with clinical adverse effects are compared in an ex vivo 3-dimensional multi-cellular human liver slice model. Functional markers of oxidative stress and mitochondrial function, glutathione GSH and ATP levels, were affected by acetaminophen (APAP, 1 mM), diclofenac (DCF, 1 mM) and etomoxir (ETM, 100 μM). Drugs targeting mitochondria more than GSH were dantrolene (DTL, 10 μM) and cyclosporin A (CSA, 10 μM), while GSH was affected more than ATP by methimazole (MMI, 500 μM), terbinafine (TBF, 100 μM), and carbamazepine (CBZ 100 μM). Oxidative stress genes were affected by TBF (18%), CBZ, APAP, and ETM (12%–11%), and mitochondrial genes were altered by CBZ, APAP, MMI, and ETM (8%–6%). Apoptosis genes were affected by DCF (14%), while apoptosis plus necrosis were altered by APAP and ETM (15%). Activation of oxidative stress, mitochondrial energy, heat shock, ER stress, apoptosis, necrosis, DNA damage, immune and inflammation genes ranked CSA (75%), ETM (66%), DCF, TBF, MMI (61%–60%), APAP, CBZ (57%–56%), and DTL (48%). Gene changes in fatty acid metabolism, cholestasis, immune and inflammation were affected by DTL (51%), CBZ and ETM (44%–43%), APAP and DCF (40%–38%), MMI, TBF and CSA (37%–35%). This model advances multiple dosing in a human ex vivo model, plus functional markers and gene profile markers of drug induced human liver side-effects.

Viability, function and morphological integrity of precision-cut liver slices during prolonged incubation: Effects of culture medium

Precision-cut liver slices (PCLS) are an ex vivo model for metabolism and toxicity studies. However, data on the maintenance of the morphological integrity of the various cell types in the slices during prolonged incubation are lacking. Therefore, our aims were to characterize morphological and functional changes in rat PCLS during five days of incubation in a rich medium, RegeneMed®, and a standard medium, Williams' Medium E. Although cells of all types in the slices remain viable, profound changes in morphology were observed, which were more prominent in RegeneMed®. Slices underwent notable fibrosis, bile duct proliferation and fat deposition. Slice thickness increased, resulting in necrotic areas, while slice diameter decreased, possibly indicating cell migration. An increased proliferation of parenchymal and non-parenchymal cells (NPCs) was observed. Glycogen, albumin and Cyp3a1 were maintained albeit to a different level in two media. In conclusion, both hepatocytes and NPCs remain viable and functional, enabling five-day toxicity studies. Tissue remodeling and formation of a new capsule-like cell lining around the slices are evident after 3–4 days. The differences in effects between media emphasize the importance of media selection and of the recognition of morphological changes in PCLS, when interpreting results from toxicological or pharmacological studies.

Impaired mitochondrial fat oxidation induces adaptive remodeling of muscle metabolism

The correlations between intramyocellular lipid (IMCL), decreased fatty acid oxidation (FAO), and insulin resistance have led to the hypothesis that impaired FAO causes accumulation of lipotoxic intermediates that inhibit muscle insulin signaling. Using a skeletal muscle-specific carnitine palmitoyltransferase-1 KO model, we show that prolonged and severe mitochondrial FAO inhibition results in increased carbohydrate utilization, along with reduced physical activity; increased circulating nonesterified fatty acids; and increased IMCLs, diacylglycerols, and ceramides. Perhaps more importantly, inhibition of mitochondrial FAO also initiates a local, adaptive response in muscle that invokes mitochondrial biogenesis, compensatory peroxisomal fat oxidation, and amino acid catabolism. Loss of its major fuel source (lipid) induces an energy deprivation response in muscle coordinated by signaling through AMP-activated protein kinase (AMPK) and peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1α) to maintain energy supply for locomotion and survival. At the whole-body level, these adaptations result in resistance to obesity.

The application of engineered liver tissues for novel drug discovery

INTRODUCTION

Drug-induced liver injury remains a major cause of drug attrition. Furthermore, novel drugs are being developed for treating liver diseases. However, differences between animals and humans in liver pathways necessitate the use of human-relevant liver models to complement live animal testing during preclinical drug development. Microfabrication tools and synthetic biomaterials now allow for the creation of tissue subunits that display more physiologically relevant and long-term liver functions than possible with declining monolayers.

AREAS COVERED

The authors discuss acellular enzyme platforms, two-dimensional micropatterned co-cultures, three-dimensional spheroidal cultures, microfluidic perfusion, liver slices and humanized rodent models. They also present the use of cell lines, primary liver cells and induced pluripotent stem cell-derived human hepatocyte-like cells in the creation of cell-based models and discuss in silico approaches that allow integration and modeling of the datasets from these models. Finally, the authors describe the application of liver models for the discovery of novel therapeutics for liver diseases.

EXPERT OPINION

Engineered liver models with varying levels of in vivo-like complexities provide investigators with the opportunity to develop assays with sufficient complexity and required throughput. Control over cell-cell interactions and co-culture with stromal cells in both two dimension and three dimension are critical for enabling stable liver models. The validation of liver models with diverse sets of compounds for different applications, coupled with an analysis of cost:benefit ratio, is important for model adoption for routine screening. Ultimately, engineered liver models could significantly reduce drug development costs and enable the development of more efficacious and safer therapeutics for liver diseases.

Apoptotic efficacy of etomoxir in human acute myeloid leukemia cells. Cooperation with arsenic trioxide and glycolytic inhibitors, and regulation by oxidative stress and protein kinase activities

Fatty acid synthesis and oxidation are frequently exacerbated in leukemia cells, and may therefore represent a target for therapeutic intervention. In this work we analyzed the apoptotic and chemo-sensitizing action of the fatty acid oxidation inhibitor etomoxir in human acute myeloid leukemia cells. Etomoxir caused negligible lethality at concentrations up to 100 µM, but efficaciously cooperated to cause apoptosis with the anti-leukemic agent arsenic trioxide (ATO, Trisenox), and with lower efficacy with other anti-tumour drugs (etoposide, cisplatin), in HL60 cells. Etomoxir-ATO cooperation was also observed in NB4 human acute promyelocytic cells, but not in normal (non-tumour) mitogen-stimulated human peripheral blood lymphocytes. Biochemical determinations in HL60 cells indicated that etomoxir (25–200 µM) dose-dependently inhibited mitochondrial respiration while slightly stimulating glycolysis, and only caused marginal alterations in total ATP content and adenine nucleotide pool distribution. In addition, etomoxir caused oxidative stress (increase in intracellular reactive oxygen species accumulation, decrease in reduced glutathione content), as well as pro-apoptotic LKB-1/AMPK pathway activation, all of which may in part explain the chemo-sensitizing capacity of the drug. Etomoxir also cooperated with glycolytic inhibitors (2-deoxy-D-glucose, lonidamine) to induce apoptosis in HL60 cells, but not in NB4 cells. The combined etomoxir plus 2-deoxy-D-glucose treatment did not increase oxidative stress, caused moderate decrease in net ATP content, increased the AMP/ATP ratio with concomitant drop in energy charge, and caused defensive Akt and ERK kinase activation. Apoptosis generation by etomoxir plus 2-deoxy-D-glucose was further increased by co-incubation with ATO, which is apparently explained by the capacity of ATO to attenuate Akt and ERK activation. In summary, co-treatment with etomoxir may represent an interesting strategy to increase the apoptotic efficacy of ATO and (with some limitations) 2-deoxy-D-glucose which, although clinically important anti-tumour agents, exhibit low efficacy in monotherapy.

Evaluation of drug-induced injury and human response in precision-cut tissue slices

1.Drug induced organ injury is multifaceted, encompassing a spectrum of cell types and numerous networks reflecting cell-cell and cell-matrix interactions. Characterization of drug induced side effects and human response can be addressed in organ slice models. 2.The application of human tissue to various organ slice models including liver, intestine, kidney, liver-blood co-cultures and thyroid enhances our ability to focus on the clinical relevance of side effects identified in animal studies for human, and to evaluate potential biomarkers of the side effects. Dose-response relationships can help discern drug concentrations which alter organ function or affect morphology, to identify drug concentrationswhich could pose a risk for humans. 3.Insight into pathways of organ injury, by incorporating gene and protein expression profiling, with functional measurements and morphology, aid to define species differences and sensitivity. 4.Human organ slice studies are valuable for bridging the extrapolation of animal derived data and for identifying mechanisms relevant for humans, thereby expanding the scope of translational research for drug safety assessment.

75-kd sirtuin 1 blocks tumor necrosis factor α-mediated apoptosis in human osteoarthritic chondrocytes

OBJECTIVE

Sirtuin 1 (SirT1) has been implicated in the regulation of human cartilage homeostasis and chondrocyte survival. Exposing human osteoarthritic (OA) chondrocytes to tumor necrosis factor α (TNFα) generates a stable and enzymatically inactive 75-kd form of SirT1 (75SirT1) via cathepsin B-mediated cleavage. Because 75SirT1 is resistant to further degradation, we hypothesized that it has a distinct role in OA, and the present study was undertaken to identify this role.

METHODS

The presence of cathepsin B and 75SirT in OA and normal human chondrocytes was analyzed. Confocal imaging of SirT1 was used to monitor its subcellular trafficking following TNFα stimulation. Coimmunofluorescence staining for cathepsin B, mitochondrial cytochrome oxidase subunit IV, and lysosome-associated membrane protein 1 together with SirT1 was performed. Human chondrocytes were tested for apoptosis by fluorescence-activated cell sorter analysis and immunoblotting for caspases 3 and 8. Human chondrocyte mitochondrial extracts were obtained and analyzed for 75SirT1-cytochrome c association.

RESULTS

Confocal imaging and immunoblot analyses following TNFα challenge of human chondrocytes demonstrated that 75SirT1 was exported to the cytoplasm and colocalized with the mitochondrial membrane. Consistent with this, immunoprecipitation and immunoblot analyses revealed that 75SirT1 is enriched in mitochondrial extracts and associates with cytochrome c following TNFα stimulation. Preventing nuclear export of 75SirT1 or reducing levels of full-length SirT1 and 75SirT1 augmented chondrocyte apoptosis in the presence of TNFα. Levels of cathepsin B and 75SirT1 were elevated in OA versus normal chondrocytes. Additional analyses showed that human chondrocytes exposed to OA-derived synovial fluid generated the 75SirT1 fragment.

CONCLUSION

These data suggest that 75SirT1 promotes chondrocyte survival following exposure to proinflammatory cytokines.

Lipid-induced mitochondrial stress and insulin action in muscle

The interplay between mitochondrial energetics, lipid balance, and muscle insulin sensitivity has remained a topic of intense interest and debate for decades. One popular view suggests that increased oxidative capacity benefits metabolic wellness, based on the premise that it is healthier to burn fat than glucose. Attempts to test this hypothesis using genetically modified mouse models have produced contradictory results and instead link muscle insulin resistance to excessive fat oxidation, acylcarnitine production, and increased mitochondrial H(2)O(2)-emitting potential. Here, we consider emerging evidence that insulin action in muscle is driven principally by mitochondrial load and redox signaling rather than oxidative capacity.

Enhancing liver mitochondrial fatty acid oxidation capacity in obese mice improves insulin sensitivity independently of hepatic steatosis

BACKGROUND & AIMS

Despite major public health concern, therapy for non-alcoholic fatty liver, the liver manifestation of the metabolic syndrome often associated with insulin resistance (IR), remains elusive. Strategies aiming to decrease liver lipogenesis effectively corrected hepatic steatosis and IR in obese animals. However, they also indirectly increased mitochondrial long-chain fatty acid oxidation (mFAO) by decreasing malonyl-CoA, a lipogenic intermediate, which is the allosteric inhibitor of carnitine palmitoyltransferase 1 (CPT1A), the key enzyme of mFAO. We thus addressed whether enhancing hepatic mFAO capacity, through a direct modulation of liver CPT1A/malonyl-CoA partnership, can reverse an already established hepatic steatosis and IR in obese mice.

METHODS

Adenovirus-mediated liver expression of a malonyl-CoA-insensitive CPT1A (CPT1mt) in high-fat/high-sucrose (HF/HS) diet-induced or genetically (ob/ob) obese mice was followed by metabolic and physiological investigations.

RESULTS

In association with increased hepatic mFAO capacity, liver CPT1mt expression improved glucose tolerance and insulin response to a glucose load in HF/HS and ob/ob mice, showing increased insulin sensitivity, and corrected IR in ob/ob mice. Surprisingly, hepatic steatosis was not affected in CPT1mt-expressing obese mice, indicating a clear dissociation between hepatic steatosis and IR. Moreover, liver CPT1mt expression rescued HF/HS-induced impaired hepatic insulin signaling at the level of IRS-1, IRS-2, Akt, and GSK-3β, most likely through the observed decrease in the HF/HS-induced accumulation of lipotoxic lipids, oxidative stress, and JNK activation.

CONCLUSIONS

Enhancing hepatic mFAO capacity is sufficient to reverse a state of IR and glucose intolerance in obese mice independently of hepatic steatosis.

Inhibition of fatty acid oxidation enhances oxidative protein folding and protects hepatocytes from endoplasmic reticulum stress

The unfolded protein response regulates lipid metabolism, but the functional benefit of this regulation to ER function is not clear. This work shows that inhibition of fatty acid oxidation raises cellular oxidation potential, facilitates ER oxidative folding, and protects hepatocytes from ER stress.

The unfolded protein response (UPR) signals protein misfolding in the endoplasmic reticulum (ER) to effect gene expression changes and restore ER homeostasis. Although many UPR-regulated genes encode ER protein processing factors, others, such as those encoding lipid catabolism enzymes, seem unrelated to ER function. It is not known whether UPR-mediated inhibition of fatty acid oxidation influences ER function or, if so, by what mechanism. Here we demonstrate that pharmacological or genetic inhibition of fatty acid oxidation renders liver cells partially resistant to ER stress–induced UPR activation both in vitro and in vivo. Reduced stress sensitivity appeared to be a consequence of increased cellular redox potential as judged by an elevated ratio of oxidized to reduced glutathione and enhanced oxidative folding in the ER. Accordingly, the ER folding benefit of inhibiting fatty acid (FA) oxidation could be phenocopied by manipulating glutathione recycling during ER stress. Conversely, preventing cellular hyperoxidation with N-acetyl cysteine partially negated the stress resistance provided by blocking FA oxidation. Our results suggest that ER stress can be ameliorated through alteration of the oxidizing environment within the ER lumen, and they provide a potential logic for the transient regulation of metabolic pathways by the UPR during stress.

Evaluation of mitochondrial toxicity in Marmota himalayana treated with metacavir, a novel 2',3'-dideoxyguanosine prodrug for treatment of hepatitis B Virus

Metacavir (PNA) is a novel synthetic nucleoside analogue for the treatment of hepatitis B virus (HBV). Our recent studies showed that PNA, a prodrug of 2',3'-dideoxyguanosine (ddG), exhibited lower mitochondrial toxicity in long-term cultures of HepG2 cells. In the current study, we examined the long-term effects of PNA on mitochondrial toxicity in Marmota himalayana (Himalayan marmot). Himalayan marmots were treated daily with oral PNA (50 or 100 mg/kg), ziduvidine (AZT) (100 mg/kg), or water (control) for 90 days. PNA treatment did not alter the body weight or plasma lactate acid level. In livers from the animals treated with PNA at 100 mg/kg/day, histopathology showed mild steatosis or small focal liver cell necrosis. Electron microscopy also showed minor proliferation and partial mitochondrial swelling with crista reduction. Measurement of respiratory chain complex enzyme activity and mitochondrial DNA (mtDNA) content revealed no significant differences in skeletal muscle, liver, and kidney tissues between animals treated with PNA and controls. In contrast, in Himalayan marmots treated with AZT we observed delayed toxicity, including lactic acidosis, severe hepatic steatosis, obvious mitochondrial damage, and significant decreases in respiratory chain complex enzyme activity and mtDNA content. This is similar to the delayed toxicity syndrome observed previously in animals and humans. In summary, PNA treatment did not alter mitochondrial enzyme activity or mtDNA content. This suggests that PNA could pose a very low risk for adverse mitochondrion-related effects. However, long-term hepatotoxic effects of PNA were observed, and this indicates a need for continued monitoring of PNA-associated hepatotoxicity in clinical trials.

Novel plasma phospholipid biomarkers of autism: mitochondrial dysfunction as a putative causative mechanism

Autism is a neurological disorder that manifests as noticeable behavioral and developmental abnormalities predominantly in males between the ages of 2 and 10. Although the genetics, biochemistry and neuropathology of this disease have been extensively studied, underlying causal factors to this disease have remained elusive. Using a longitudinal trial design in which three plasma samples were collected from 15 autistic and 12 non-autistic age-matched controls over the course of 1 year, universal and unambiguous alterations in lipid metabolism were observed. Biomarkers of fatty acid elongation and desaturation (poly-unsaturated long chain fatty acids (PUFA) and/or saturated very long chain fatty acids (VLCFA)-containing ethanolamine phospholipids) were statistically elevated in all autistic subjects. In all 8 of the affected/non-affected sibling pairs, the affected sibling had higher levels of these biomarkers than the unaffected sibling. Exposure of neurons, astrocytes and hepatocytes in vitro to elevated extracellular glutamate levels resulted in lipid biomarker changes indistinguishable from those observed in autistic subjects. Glutamate stress also resulted in in vitro decreased levels of reduced glutathione (GSH), methionine and cysteine, in a similar way to the decreases we observed in autism plasma. Impaired mitochondrial fatty acid oxidation, elevated plasma VLCFAs, and glutamate toxicity as putative causal factors in the biochemistry, neuropathology, and gender bias in autism are discussed.

Lipid droplets: their role in nanoparticle-induced oxidative stress

Lipid droplets are cytoplasmic organelles found in almost all cells under physiological or pathological conditions. Certain nanoparticles can induce lipid droplet formation under oxidative stress conditions. Small metallic nanoparticles such as cadmium telluride (CdTe) nanoparticles, particularly those with incompletely protected surfaces, induce oxidative stress and may inflict damages to several intracellular organelles. The objective of this study was to assess formation of lipid droplets in cells treated with CdTe nanoparticles and relate their status to cell function (mitochondrial activity and cell viability). Multicolor labeling of cellular organelles (lipid droplets and lysosomes) showed that lipid droplets formed in pheochromocytoma (PC12) cells following nanoparticle or oleic acid treatment. Some lipid droplets were found closely apposed to lysosomes suggesting possible communication between these organelles during severe oxidative stress. Combination of microscopy of living cells with cell viability assays showed that oleic acid-induced lipid droplets not only serve as intracellular lipid storage sites but also play a protective role in starving stressed cells. Results from these studies suggest that oleic acid-induced LD in PC12 cells are dynamic and adaptive organelles, which provide energy to starving cells and facilitate their rescue under starvation and exposure to metallic nanoparticles.

Structural insight into function and regulation of carnitine palmitoyltransferase

The control of fatty acid translocation across the mitochondrial membrane is mediated by the carnitine palmitoyltransferase (CPT) system. Modulation of its functionality has simultaneous effects on fatty acid and glucose metabolism. This encourages use of the CPT system as drug target for reduction of gluconeogenesis and restoration of lipid homeostasis, which are beneficial in the treatment of type 2 diabetes mellitus and obesity. Recently, crystal structures of CPT-2 were determined in uninhibited forms and in complexes with inhibitory substrate-analogs with anti-diabetic properties in animal models and in clinical studies. The CPT-2 crystal structures have advanced understanding of CPT structure-function relationships and will facilitate discovery of novel inhibitors by structure-based drug design. However, a number of unresolved questions regarding the biochemistry and pharmacology of CPT enzymes remain and are addressed in this review.

Modulation of the hepatic malonyl-CoA-carnitine palmitoyltransferase 1A partnership creates a metabolic switch allowing oxidation of de novo fatty acids

Liver mitochondrial beta-oxidation of LCFAs (long-chain fatty acids) is tightly regulated through inhibition of CPT1A (carnitine palmitoyltransferase 1A) by malonyl-CoA, an intermediate of lipogenesis stimulated by glucose and insulin. Moreover, CPT1A sensitivity to malonyl-CoA inhibition varies markedly depending on the physiopathological state of the animal. In the present study, we asked whether an increase in CPT1A activity solely or in association with a decreased malonyl-CoA sensitivity could, even in the presence of high glucose and insulin concentrations, maintain a sustained LCFA beta-oxidation and/or protect from triacylglycerol (triglyceride) accumulation in hepatocytes. We have shown that adenovirus-mediated expression of rat CPT1wt (wild-type CPT1A) and malonyl-CoA-insensitive CPT1mt (CPT1AM593S mutant) in cultured fed rat hepatocytes counteracted the inhibition of oleate beta-oxidation induced by 20 mM glucose/10 nM insulin. Interestingly, the glucose/insulin-induced cellular triacylglycerol accumulation was prevented, both in the presence and absence of exogenous oleate. This resulted from the generation of a metabolic switch allowing beta-oxidation of de novo synthesized LCFAs, which occurred without alteration in glucose oxidation and glycogen synthesis. Moreover, CPT1mt expression was more effective than CPT1wt overexpression to counteract glucose/insulin effects, demonstrating that control of CPT1A activity by malonyl-CoA is an essential driving force for hepatic LCFA metabolic fate. In conclusion, the present study highlights that CPT1A is a prime target to increase hepatic LCFA beta-oxidation and that acting directly on the degree of its malonyl-CoA sensitivity may be a relevant strategy to prevent and/or correct hepatic steatosis.

Characterization of hepatic mitochondrial injury induced by fatty acid oxidation inhibitors

Impairment of liver mitochondrial beta-oxidation is an important mechanism of drug-induced liver injury. Four inhibitors of fatty acid oxidation were compared in short-term rat in vivo studies in which the rats were administered one or four doses. The hepatocellular vacuolation represented ultra-structural mitochondrial changes. Urine nuclear magnetic resonance (NMR) spectroscopy revealed that both FOX988 and SDZ51-641 induced a persistent dicarboxylic aciduria, suggesting an inhibition of mitochondrial beta-oxidation and incomplete fatty acid metabolism. Etomoxir caused minimal mitochondrial ultrastructural changes and induced only transient dicarboxylic aciduria. CPI975 served as a negative control, in that there were no significant perturbations to the mitochondrial ultrastructural morphology or in the urine NMR composition; however, compound exposure was confirmed by the up-regulation of liver gene expression compared to vehicle control. The liver gene expression changes that were altered by the compounds were indicative of mitochondria, general and oxidative stress, and peroxisomal enzymes involved in beta-oxidation, suggestive of a compensatory response to the inhibition in the mitochondria. In addition, both FOX988 and SDZ51-641 up-regulated ribosomal genes associated with apoptosis, as well as p53 pathways linked with apoptosis. In summary, metabonomics and liver gene expression provided mechanistic information on mitochondrial dysfunction and impaired fatty acid oxidation to further define the clinical pathology and histopathology findings of hepatotoxicity.

Gene expression profiling in livers of mice after acute inhibition of beta-oxidation

Inborn errors of mitochondrial beta-oxidation cause ectopic fat accumulation, particularly in the liver. Fatty liver is associated with insulin resistance and predisposes to hepatic fibrosis. The factors underlying the pathophysiological consequences of hepatic fat accumulation have remained poorly defined. Gene expression profiling in a model of acute fatty liver disease induced by blocking long-chain fatty acid beta-oxidation was performed to study the early effects of steatosis on the transcriptome. Tetradecylglycidic acid (TDGA) was used to irreversibly inhibit carnitine palmitoyltransferase 1, a key enzyme in the control of mitochondrial beta-oxidation. TDGA treatment induced massive microvesicular hepatic steatosis within a 12-h time frame in male C57BL6/J mice. Increased hepatic long-chain acyl-CoA content, particularly of C16:0, C16:1 and C18:1, was associated with profound effects on the transcriptome as revealed by unbiased gene expression profiling and quantitative real-time PCR. The results indicate drastic changes in the expression of genes encoding proteins involved in lipid, carbohydrate, and amino acid metabolism. Pathway analysis identified transcription factors and coregulators such as hepatocyte nuclear factor 4 (HNF4), peroxisome proliferator-activated receptor-alpha (PPAR-alpha), and PPAR gamma coactivator 1alpha (PGC-1alpha ) as key players in these metabolic adaptations. Apoptotic and profibrotic responses were also affected. Surprisingly, a strong reduction in the expression of genes involved in hepatic bile salt metabolism and transport was observed. Therefore, this transcriptome analysis opens new avenues for research.

The role of mitochondria in pharmacotoxicology: a reevaluation of an old, newly emerging topic

In addition to their well-known critical role in energy metabolism, mitochondria are now recognized as the location where various catabolic and anabolic processes, calcium fluxes, various oxygen-nitrogen reactive species, and other signal transduction pathways interact to maintain cell homeostasis and to mediate cellular responses to different stimuli. It is important to consider how pharmacological agents affect mitochondrial biochemistry, not only because of toxicological concerns but also because of potential therapeutic applications. Several potential targets could be envisaged at the mitochondrial level that may underlie the toxic effects of some drugs. Recently, antiviral nucleoside analogs have displayed mitochondrial toxicity through the inhibition of DNA polymerase-γ (pol-γ). Other drugs that target different components of mitochondrial channels can disrupt ion homeostasis or interfere with the mitochondrial permeability transition pore. Many known inhibitors of the mitochondrial electron transfer chain act by interfering with one or more of the respiratory chain complexes. Nonsteroidal anti-inflammatory drugs (NSAIDs), for example, may behave as oxidative phosphorylation uncouplers. The mitochondrial toxicity of other drugs seems to depend on free radical production, although the mechanisms have not yet been clarified. Meanwhile, drugs targeting mitochondria have been used to treat mitochondrial dysfunctions. Importantly, drugs that target the mitochondria of cancer cells have been developed recently; such drugs can trigger apoptosis or necrosis of the cancer cells. Thus the aim of this review is to highlight the role of mitochondria in pharmacotoxicology, and to describe whenever possible the main molecular mechanisms underlying unwanted and/or therapeutic effects.

A prospective study of acute drug-induced liver injury in patients suffering from non-alcoholic fatty liver disease

AIM

Liver damage due to facultative hepatotoxins is scarcely foreseeable. We evaluated the prevalence of acute drug-induced liver injury (DILI) in a specific setting, assessing eventual interactions with pre-existing hepatic illnesses.

METHODS

The research was carried out in an Italian tertiary care hospital, by analyzing 248 patients with non-advanced liver disease, divided into two well-matched groups: 174 patients (median age 53, 94 females) with hepatitis C virus-related chronic hepatitis; and 74 (median age 55, 39 females) with non-alcoholic fatty liver disease (NAFLD).

RESULTS

Six patients (2.4% of the whole population) belonging to the NAFLD group (chi(2)-test, P = 0.004) suffered from acute hepatoxicity related to the following drugs, that is antihypertensive, acting on platelet aggregation, antimicrobial, non-steroidal anti-inflammatory and proton pump inhibitor. The NAFLD presence was an independent risk factor in determining drug-related acute hepatitis, with an odds ratio of 3.95 (95% confidence intervals: 11.48-1.35). Central obesity was relevant in every patient with acute toxicity. Alcohol consumption and drug association did not influence the acute drug-induced liver damage.

CONCLUSION

NAFLD conveys a nearly fourfold increase of DILI risk in obese middle-aged patients. NAFLD, characterized by mitochondrial dysfunction, could predispose to drug-induced hepatotoxicity that probably shares the same pathophysiological mechanism.