Anti-atherosclerotic activity of triacsin C, an acyl-CoA synthetase inhibitor

ACSL1 is a key regulator of inflammatory and macrophage foaming induced by short-term palmitate exposure or acute high-fat feeding

Foamy and inflammatory macrophages play pathogenic roles in metabolic disorders. However, the mechanisms that promote foamy and inflammatory macrophage phenotypes under acute-high-fat feeding (AHFF) remain elusive. Herein, we investigated the role of acyl-CoA synthetase-1 (ACSL1) in favoring the foamy/inflammatory phenotype of monocytes/macrophages upon short-term exposure to palmitate or AHFF. Palmitate exposure induced a foamy/inflammatory phenotype in macrophages which was associated with increased ACSL1 expression. Inhibition/knockdown of ACSL1 in macrophages suppressed the foamy/inflammatory phenotype through the inhibition of the CD36-FABP4-p38-PPARδ signaling axis. ACSL1 inhibition/knockdown suppressed macrophage foaming/inflammation after palmitate stimulation by downregulating the FABP4 expression. Similar results were obtained using primary human monocytes. As expected, oral administration of ACSL1 inhibitor triacsin-C in mice before AHFF normalized the inflammatory/foamy phenotype of the circulatory monocytes by suppressing FABP4 expression. Our results reveal that targeting ACSL1 leads to the attenuation of the CD36-FABP4-p38-PPARδ signaling axis, providing a therapeutic strategy to prevent the AHFF-induced macrophage foaming and inflammation.

Elucidation of the Cellular Interactome of African Swine Fever Virus Fusion Proteins and Identification of Potential Therapeutic Targets

African swine fever virus (ASFV) encodes more than 150 proteins, most of them of unknown function. We used a high-throughput proteomic analysis to elucidate the interactome of four ASFV proteins, which potentially mediate a critical step of the infection cycle, the fusion and endosomal exit of the virions. Using affinity purification and mass spectrometry, we were able to identify potential interacting partners for those ASFV proteins P34, E199L, MGF360-15R and E248R. Representative molecular pathways for these proteins were intracellular and Golgi vesicle transport, endoplasmic reticulum organization, lipid biosynthesis, and cholesterol metabolism. Rab geranyl geranylation emerged as a significant hit, and also Rab proteins, which are crucial regulators of the endocytic pathway and interactors of both p34 and E199L. Rab proteins co-ordinate a tight regulation of the endocytic pathway that is necessary for ASFV infection. Moreover, several interactors were proteins involved in the molecular exchange at ER membrane contacts. These ASFV fusion proteins shared interacting partners, suggesting potential common functions. Membrane trafficking and lipid metabolism were important categories, as we found significant interactions with several enzymes of the lipid metabolism. These targets were confirmed using specific inhibitors with antiviral effect in cell lines and macrophages.

Synthesis and Photophysical Properties of a New Push–Pull Pyrene Dye with Green-to-Far-red Emission and its Application to Human Cellular and Skin Tissue Imaging

Herein, we discuss a new pyrene-based push–pull dye (PC) and our investigation of its photophysical properties and applicability to biological applications. The newly synthesized dye exhibits highly polarity-sensitive fluorescence over...

Biosynthesis of triacsin featuring an N-hydroxytriazene pharmacophore

Triacsins are an intriguing class of specialized metabolites possessing a conserved N-hydroxytriazene moiety not found in any other known natural products. Triacsins are notable as potent acyl-CoA synthetase inhibitors in lipid metabolism, yet their biosynthesis has remained elusive. Through extensive mutagenesis and biochemical studies, we here report all enzymes required to construct and install the N-hydroxytriazene pharmacophore of triacsins. Two distinct ATP-dependent enzymes were revealed to catalyze the two consecutive N-N bond formation reactions, including a glycine-utilizing, hydrazine-forming enzyme (Tri28) and a nitrite-utilizing, N-nitrosating enzyme (Tri17). This study paves the way for future mechanistic interrogation and biocatalytic application of enzymes for N-N bond formation.

Lipid droplet: A functionally active organelle in monocyte to macrophage differentiation and its inflammatory properties

Lipid droplets (LDs) perform several important functions like inflammatory responses, membrane trafficking, acts as secondary messengers, etc. rather than simply working as an energy reservoir. LDs have been implicated as a controlling factor in the progression of atherosclerosis followed by foam cell formation that derives from macrophages during the differentiation process. However, the role of LDs in monocyte differentiation or its further immunological function is still an area that mandates in-depth investigation. We report that LD dynamics is important for differentiation of monocytes and is absolutely required for sustained and prolonged functional activity of differentiated macrophages. In THP-1 cell line model system, we elucidated that increase in total LD content in monocyte by external lipid supplements, can induce monocyte differentiation independent of classical stimuli, PMA. Differential expression of PLIN2 and ATGL during the event, together with abrogation of de novo lipogenesis further confirmed the fact. Besides, an increase in LD content by free fatty acid supplement was able to exert a synergistic effect with PMA on differentiation and phagocytic activity compared to when they are used alone. Additionally, we have shown Rab5a to play a vital role in LDs biosynthesis/maturation in monocytes and thereby directly affecting differentiation of monocytes into macrophages via AKT pathway. Thus our study reveals the multi-faceted function of LDs during the process of monocyte to macrophage differentiation and thereby helping to maintain the functional activity.

Qualitative and Quantitative Analysis of Ukrainian Iris Species: A Fresh Look on Their Antioxidant Content and Biological Activities

The major groups of antioxidant compounds (isoflavonoids, xanthones, hydroxycinnamic acids) in the rhizome methanol extracts of four Ukrainian Iris sp. (Iris pallida, Iris hungarica, Iris sibirica, and Iris variegata) were qualitatively and quantitatively analyzed using HPLC-DAD and UPLC-MS/MS. Gallic acid, caffeic acid, mangiferin, tectoridin, irigenin, iristectorigenin B, irisolidone, 5,6-dihydroxy-7,8,3',5'-tetramethoxyisoflavone, irisolidone-7-O-β-d-glucopyranoside, germanaism B, and nigricin were recognized by comparing their UV/MS spectra, chromatographic retention time (tR) with those of standard reference compounds. I. hungarica and I. variegata showed the highest total amount of phenolic compounds. Germanaism B was the most abundant component in the rhizomes of I. variegata (7.089 ± 0.032 mg/g) and I. hungarica (6.285 ± 0.030 mg/g). The compound analyses showed good calibration curve linearity (r² > 0.999) and low detection and quantifications limit. These results validated the method for its use in the simultaneous quantitative evaluation of phenolic compounds in the studied Iris sp. I. hungarica and I. variegata rhizomes exhibited antioxidant activity, as demonstrated by the HPLC-ABTS system and NRF2 expression assay and anti-inflammatory activity on respiratory burst in human neutrophils. Moreover, the extracts showed anti-allergic and cytotoxic effects against cancer cells. Anti-coronavirus 229E and lipid formation activities were also evaluated. In summary, potent antioxidant marker compounds were identified in the examined Iris sp.

Inhibitors of VPS34 and lipid metabolism suppress SARS-CoV-2 replication

Therapeutics targeting replication of SARS coronavirus 2 (SARS-CoV-2) are urgently needed. Coronaviruses rely on host membranes for entry, establishment of replication centers and egress. Compounds targeting cellular membrane biology and lipid biosynthetic pathways have previously shown promise as antivirals and are actively being pursued as treatments for other conditions. Here, we tested small molecule inhibitors that target membrane dynamics or lipid metabolism. Included were inhibitors of the PI3 kinase VPS34, which functions in autophagy, endocytosis and other processes; Orlistat, an inhibitor of lipases and fatty acid synthetase, is approved by the FDA as a treatment for obesity; and Triacsin C which inhibits long chain fatty acyl-CoA synthetases. VPS34 inhibitors, Orlistat and Triacsin C inhibited virus growth in Vero E6 cells and in the human airway epithelial cell line Calu-3, acting at a post-entry step in the virus replication cycle. Of these the VPS34 inhibitors exhibit the most potent activity.

Monitoring Lipid Droplet Dynamics in Living Cells by Using Fluorescent Probes

We have developed three types of lipid droplet (LD)-specific fluorescent probes for live-cell imaging, Lipi-Blue, Lipi-Green, and Lipi-Red, which exhibit fluorescence upon being incorporated into LDs both of living and of fixed cells. These Lipi-probes are LD-specific probes that contain a pyrene or perylene group as a fluorescent scaffold and can be used to observe dynamics of LD in live cells and also interrelations with other organelles by simultaneous staining with multiple organelle-specific probes. Additionally, Lipi-Blue and Lipi-Green allow monitoring LDs in live cells even for 48 h after the staining. Here we show that newly formed LDs and previously existed LDs can be separately monitored in a single cell by using these probes and that intercellular transfer of whole LDs is observed in KB cells, but not in HepG2 cells under the same culturing condition. These findings indicate that newly developed LD-specific probes are useful to analyze the dynamics of LDs in live cells.

Triacsin C reduces lipid droplet formation and induces mitochondrial biogenesis in primary rat hepatocytes

Intracellular long-chain acyl-CoA synthetases (ACSL) activate fatty acids to produce acyl-CoA, which undergoes β-oxidation and participates in the synthesis of esterified lipids such as triacylglycerol (TAG). Imbalances in these metabolic routes are closely associated with the pathogenesis of non-alcoholic fatty liver disease (NAFLD). Triacsin C is one of the few compounds that inhibit TAG accumulation into lipid droplets (LD) by suppressing ACSL activity. Here we report that treatment of primary rat hepatocytes with triacsin C at concentrations lower than the IC₅₀ (4.1 μM) for LD formation: (i) diminished LD number in a concentration-dependent manner; (ii) increased mitochondrial amount; (iii) markedly improved mitochondrial metabolism by enhancing the β-oxidation efficiency, electron transport chain capacity, and degree of coupling - treatment of isolated rat liver mitochondria with the same triacsin C concentrations did not affect the last two parameters; (iv) decreased the GSH/GSSG ratio and elevated the protein carbonyl level, which suggested an increased reactive oxygen species production, as observed in isolated mitochondria. The hepatocyte mitochondrial improvements were not related to either the transcriptional levels of PGC-1α or the content of mTOR and phosphorylated AMPK. Triacsin C at 10 μM induced hepatocyte death by necrosis and/or apoptosis through mechanisms associated with mitochondrial permeability transition pore opening, as demonstrated by experiments using isolated mitochondria. Therefore, triacsin C at sub-IC₅₀ concentrations modulates the lipid imbalance by shifting hepatocytes to a more oxidative state and enhancing the fatty acid consumption, which can in turn accelerate lipid oxidation and reverse NAFLD in long-term therapies.

Inhibition of RPE65 Retinol Isomerase Activity by Inhibitors of Lipid Metabolism

RPE65 is the isomerase catalyzing conversion of all-trans-retinyl ester (atRE) into 11-cis-retinol in the retinal visual cycle. Crystal structures of RPE65 and site-directed mutagenesis reveal aspects of its catalytic mechanism, especially retinyl moiety isomerization, but other aspects remain to be determined. To investigate potential interactions between RPE65 and lipid metabolism enzymes, HEK293-F cells were transfected with expression vectors for visual cycle proteins and co-transfected with either fatty acyl:CoA ligases (ACSLs) 1, 3, or 6 or the SLC27A family fatty acyl-CoA synthase FATP2/SLCA27A2 to test their effect on isomerase activity. These experiments showed that RPE65 activity was reduced by co-expression of ACSLs or FATP2. Surprisingly, however, in attempting to relieve the ACSL-mediated inhibition, we discovered that triacsin C, an inhibitor of ACSLs, also potently inhibited RPE65 isomerase activity in cellulo. We found triacsin C to be a competitive inhibitor of RPE65 (IC50 = 500 nm). We confirmed that triacsin C competes directly with atRE by incubating membranes prepared from chicken RPE65-transfected cells with liposomes containing 0-1 μM atRE. Other inhibitors of ACSLs had modest inhibitory effects compared with triascin C. In conclusion, we have identified an inhibitor of ACSLs as a potent inhibitor of RPE65 that competes with the atRE substrate of RPE65 for binding. Triacsin C, with an alkenyl chain resembling but not identical to either acyl or retinyl chains, may compete with binding of the acyl moiety of atRE via the alkenyl moiety. Its inhibitory effect, however, may reside in its nitrosohydrazone/triazene moiety.

Inhibition of long chain fatty acyl-CoA synthetase (ACSL) and ischemia reperfusion injury

Various triacsin C analogs, containing different alkenyl chains and carboxylic acid bioisoteres including 4-aminobenzoic acid, isothiazolidine dioxide, hydroxylamine, hydroxytriazene, and oxadiazolidine dione, were synthesized and their inhibitions of long chain fatty acyl-CoA synthetase (ACSL) were examined. Two methods, a cell-based assay of ACSL activity and an in situ [(14)C]-palmitate incorporation into extractable lipids were used to study the inhibition. Using an in vivo leukocyte recruitment inhibition protocol, the translocation of one or more cell adhesion molecules from the cytoplasm to the plasma membrane on either the endothelium or leukocyte or both was inhibited by inhibitors 1, 9, and triacsin C. The results suggest that inhibition of ACSL may attenuate the vascular inflammatory component associated with ischemia reperfusion injury and lead to a decrease of infarct expansion.

Amelioration of Cryptosporidium parvum infection in vitro and in vivo by targeting parasite fatty acyl-coenzyme A synthetases

BACKGROUND

Cryptosporidium is emerging as 1 of the 4 leading diarrheal pathogens in children in developing countries. Its infections in patients with AIDS can be fatal, whereas fully effective treatments are unavailable. The major goal of this study is to explore parasite fatty acyl-coenzyme A synthetase (ACS) as a novel drug target.

METHODS

A colorimetric assay was developed to evaluate biochemical features and inhibitory kinetics of Cryptosporidium parvum ACSs using recombinant proteins. Anticryptosporidial efficacies of the ACS inhibitor triacsin C were evaluated both in vitro and in vivo.

RESULTS

Cryptosporidium ACSs displayed substrate preference toward long-chain fatty acids. The activity of parasite ACSs could be specifically inhibited by triacsin C with the inhibition constant Ki in the nanomolar range. Triacsin C was highly effective against C. parvum growth in vitro (median inhibitory concentration, 136 nmol/L). Most importantly, triacsin C effectively reduced parasite oocyst production up to 88.1% with no apparent toxicity when administered to Cryptosporidium-infected interleukin 12 knockout mice at 8-15 mg/kg/d for 1 week.

CONCLUSIONS

The findings of this study not only validated Cryptosporidium ACS (and related acyl-[acyl-carrier-protein]-ligases) as pharmacological targets but also indicate that triacsin C and analogues can be explored as potential new therapeutics against the virtually untreatable cryptosporidial infection in immunocompromised patients.

Eicosapentaenoic acid suppresses palmitate-induced cytokine production by modulating long-chain acyl-CoA synthetase 1 expression in human THP-1 macrophages

BACKGROUND

Chronic inflammation caused by macrophages may be associated with progression of arteriosclerosis or obesity, both risk factors for cardiovascular events. In the Japan EPA Lipid Intervention Study (JELIS), eicosapentaenoic acid (EPA), an n-3 polyunsaturated fatty acid, was found to reduce the incidence of cardiovascular events.

METHODS

The effect of EPA on the expression of inflammatory factors induced by palmitate, a saturated fatty acid, was investigated using human THP-1 macrophages.

RESULTS

Palmitate induced expression of inflammatory cytokines and activated NF-κB, similar to lipopolysaccharide (LPS). EPA strongly suppressed palmitate-induced up-regulation of inflammatory factors while slightly suppressing LPS-induced factors. Both palmitate and LPS up-regulated expression of long-chain acyl-CoA synthetase (ACSL) 1, while EPA preferentially suppressed palmitate-induced ACSL1 expression. Although an acyl-CoA synthetase inhibitor and ACSL1 siRNA both suppressed palmitate-induced tumor necrosis factor (TNF)-α expression, the former had no effect on LPS-induced TNF-α expression. Palmitate may therefore stimulate cytokine production through a different mechanism than LPS mediated through Toll-like receptor 4, at least partly, and ACSL1 may play an important role in this mechanism. Finally, palmitate induced expression of sterol regulatory element-binding protein-1a and ACSL1, while EPA suppressed the expression of these genes.

CONCLUSION

The suppressive effects of EPA on palmitate-induced cytokine production may be mediated by the suppression of ACSL1 expression, at least partly. This anti-inflammatory effect of EPA may contribute to suppression of chronic inflammation caused by macrophages in atherosclerotic plaques.

Diabetes promotes an inflammatory macrophage phenotype and atherosclerosis through acyl-CoA synthetase 1

The mechanisms that promote an inflammatory environment and accelerated atherosclerosis in diabetes are poorly understood. We show that macrophages isolated from two different mouse models of type 1 diabetes exhibit an inflammatory phenotype. This inflammatory phenotype associates with increased expression of long-chain acyl-CoA synthetase 1 (ACSL1), an enzyme that catalyzes the thioesterification of fatty acids. Monocytes from humans and mice with type 1 diabetes also exhibit increased ACSL1. Furthermore, myeloid-selective deletion of ACSL1 protects monocytes and macrophages from the inflammatory effects of diabetes. Strikingly, myeloid-selective deletion of ACSL1 also prevents accelerated atherosclerosis in diabetic mice without affecting lesions in nondiabetic mice. Our observations indicate that ACSL1 plays a critical role by promoting the inflammatory phenotype of macrophages associated with type 1 diabetes; they also raise the possibilities that diabetic atherosclerosis has an etiology that is, at least in part, distinct from the etiology of nondiabetic vascular disease and that this difference is because of increased monocyte and macrophage ACSL1 expression.

ACSL3 and GSK-3β are essential for lipid upregulation induced by endoplasmic reticulum stress in liver cells

The endoplasmic reticulum (ER) is essential for lipid biosynthesis, and stress signals in this organelle are thought to alter lipid metabolism. Elucidating the mechanisms that underlie the dysregulation of lipid metabolism in hepatocytes may lead to novel therapeutic approaches for the treatment of lipid accumulation. We first tested the effects of several inhibitors on lipid dysregulation induced by tunicamycin, an ER stress inducer. Triacsin C, an inhibitor of long-chain acyl-CoA synthetase (ACSL) 1, 3, and 4, was the most potent among these inhibitors. We then analyzed the expression of the ACSL family during ER stress. The expression of ACSL3 was induced by ER stress in HuH-7 cells and in mice livers. ACSL3 shRNA, but not ACSL1 shRNA, inhibited the induction of lipid accumulation. GSK-3β inhibitors attenuated ACSL3 expression and the lipid accumulation induced by ER stress in HuH-7 cells. shRNA that target GSK-3β also inhibited the upregulation of ACSL3 and lipid accumulation in HuH-7 and HepG2 cells. The hepatitis B virus mutant large surface protein, which is known to induce ER stress, increased the lipid content of cells. Similarly, Triacsin C, and GSK-3β inhibitors abrogated the lipid dysregulation caused by the hepatitis B virus mutant large surface protein. Altogether, ACSL3 and GSK-3β represent novel therapeutic targets for lipid dysregulation by ER stress.

Dissecting the role of critical residues and substrate preference of a Fatty Acyl-CoA Synthetase (FadD13) of Mycobacterium tuberculosis

Newly emerging multi-drug resistant strains of Mycobacterium tuberculosis (M.tb) severely limit the treatment options for tuberculosis (TB); hence, new antitubercular drugs are urgently needed. The mymA operon is essential for the virulence and intracellular survival of M.tb and thus represents an attractive target for the development of new antitubercular drugs. This study is focused on the structure-function relationship of Fatty Acyl-CoA Synthetase (FadD13, Rv3089) belonging to the mymA operon. Eight site-directed mutants of FadD13 were designed, constructed and analyzed for the structural-functional integrity of the enzyme. The study revealed that mutation of Lys⁴⁸⁷ resulted in ∼95% loss of the activity thus demonstrating its crucial requirement for the enzymatic activity. Comparison of the kinetic parameters showed the residues Lys¹⁷² and Ala³⁰² to be involved in the binding of ATP and Ser⁴⁰⁴ in the binding of CoenzymeA. The influence of mutations of the residues Val²⁰⁹ and Trp³⁷⁷ emphasized their importance in maintaining the structural integrity of FadD13. Besides, we show a synergistic influence of fatty acid and ATP binding on the conformation and rigidity of FadD13. FadD13 represents the first Fatty Acyl-CoA Synthetase to display biphasic kinetics for fatty acids. FadD13 exhibits a distinct preference for C₂₆/C₂₄ fatty acids, which in the light of earlier reported observations further substantiates the role of the mymA operon in remodeling the cell envelope of intracellular M.tb under acidic conditions. A three-dimensional model of FadD13 was generated; the docking of ATP to the active site verified its interaction with Lys¹⁷², Ala³⁰² and Lys⁴⁸⁷ and corresponded well with the results of the mutational studies. Our study provides a significant understanding of the FadD13 protein including the identification of residues important for its activity as well as in the maintenance of structural integrity. We believe that the findings of this study will provide valuable inputs in the development of inhibitors against the mymA operon, an important target for the development of antitubercular drugs.