Rational Development of a Potent 15-Lipoxygenase-1 Inhibitor with in Vitro and ex Vivo Anti-inflammatory Properties

Pharmacological potential of Jussiaea repens L. against CuSO4 and bacterial lipopolysaccharide O55:B5 induced inflammation using in-vivo zebrafish models

ETHNOPHARMACOLOGICAL RELEVANCE

The Northeastern state of India is known for its remarkable biodiversity and untapped medicinal resources. Jussiaea repens L., commonly known as water primrose, is a plant found in this region that has been traditionally used by indigenous communities for various purposes. It has been employed to treat skin ulcerations, bone fractures, rheumatism, stomach pain, and intestinal worms. Despite its long-standing ethnopharmacological usage, there is limited scientific research on the bioactivity of Jussiaea repens L. However, preliminary studies have shown its potential antioxidant properties and cytotoxicity against cancer cells. Further exploration of its medicinal properties, particularly its potential as an anti-inflammatory agent, is warranted.

AIM OF THE STUDY

This study aimed to investigate the anti-inflammatory properties of Jussiaea repens L., a plant species found in the biodiverse Northeastern region of India. The plant has been traditionally used by indigenous communities for various ailments. By utilizing zebrafish as an animal model and evaluating its effects in different inflammation models, the study aimed to uncover the plant's potential as an anti-inflammatory agent. The research contributes to the scientific understanding of this traditional remedy and its potential therapeutic applications.

METHODS

Jussiaea repens L. extract was obtained from the stem and leaves using methanol as the solvent. Zebrafish embryos were used for in vivo assays. The anti-inflammatory study included two models: CuSO4-induced inflammation and tail wounding followed by bacterial lipopolysaccharide-induced inflammation. The activities of catalase (CAT) and superoxide dismutase (SOD) were measured in CuSO4-induced inflammation. Leukocyte migration at the injury site was observed in the tail wounding model. The extract's inhibition of the 15-LOX enzyme was assessed. All procedures followed established protocols and ethical guidelines.

RESULTS AND CONCLUSION

Jussiaea repens L. extract exhibited anti-inflammatory activity in two in vivo zebrafish models: CuSO4-induced inflammation and tail wounding combined with bacterial lipopolysaccharide-induced inflammation. The extract reduced mortality rates and showed antioxidant effects by increasing catalase (CAT) and superoxide dismutase (SOD) activities in the CuSO4 model. In the tail wounding model, the extract reduced leukocyte migration in a concentration-dependent manner. Additionally, the extract demonstrated dose-dependent inhibition of the 15-LOX enzyme in the in vitro assay. These results suggest that Jussiaea repens L. extract possesses anti-inflammatory properties and inhibits the 15-LOX enzyme.

Dual COX-2/15-LOX inhibitors: A new avenue in the prevention of cancer

Dual cyclooxygenase 2/15-lipoxygenase inhibitors constitute a valuable alternative to classical non-steroidal anti-inflammatory drugs (NSAIDs) and selective COX-2 (cyclooxygenase-2) inhibitors for the treatment of inflammatory diseases, as well as preventing the cancer. Indeed, these latter present diverse side effects, which are reduced or absent in dual-acting agents. In this review, COX-2 and 15-LOX (15-lipoxygenase) pathways are first described in order to highlight the therapeutic interest of designing such compounds. Various structural families of dual inhibitors are illustrated. This study discloses various structural families of dual 15-LOX/COX-2 inhibitors, thus pave the way to design potentially-active anticancer agents with balanced dual inhibition of these enzymes.

Different Structures-Similar Effect: Do Substituted 5-(4-Methoxyphenyl)-1H-indoles and 5-(4-Methoxyphenyl)-1H-imidazoles Represent a Common Pharmacophore for Substrate Selective Inhibition of Linoleate Oxygenase Activity of ALOX15?

Mammalian 15-lipoxygenases (ALOX15) are lipid peroxidizing enzymes that exhibit variable functionality in different cancer and inflammation models. The pathophysiological role of linoleic acid- and arachidonic acid-derived ALOX15 metabolites rendered this enzyme a target for pharmacological research. Several indole and imidazole derivatives inhibit the catalytic activity of rabbit ALOX15 in a substrate-specific manner, but the molecular basis for this allosteric inhibition remains unclear. Here, we attempt to define a common pharmacophore, which is critical for this allosteric inhibition. We found that substituted imidazoles induce weaker inhibitory effects when compared with the indole derivatives. In silico docking studies and molecular dynamics simulations using a dimeric allosteric enzyme model, in which the inhibitor occupies the substrate-binding pocket of one monomer, whereas the substrate fatty acid is bound at the catalytic center of another monomer within the ALOX15 dimer, indicated that chemical modification of the core pharmacophore alters the enzyme-inhibitor interactions, inducing a reduced inhibitory potency. In our dimeric ALOX15 model, the structural differences induced by inhibitor binding are translated to the hydrophobic dimerization cluster and affect the structures of enzyme-substrate complexes. These data are of particular importance since substrate-specific inhibition may contribute to elucidation of the putative roles of ALOX15 metabolites derived from different polyunsaturated fatty acids in mammalian pathophysiology.

Synthesis of new multitarget-directed ligands containing thienopyrimidine nucleus for inhibition of 15-lipoxygenase, cyclooxygenases, and pro-inflammatory cytokines

A new series of thieno[2,3-d]pyrimidine derivatives 4, 5, 6a-o, and 11 was designed and synthesized starting from cyclohexanone under Gewald condition with the aim to develop multitarget-directed ligands (MTDLs) having anti-inflammatory properties against both 15-LOX and COX-2 enzymes. Moreover, the potential of the compounds against the proinflammatory mediators NO, ROS, TNF-α, and IL-6 were tested in LPS-activated RAW 264.7 macrophages. Compound 6o showed the greatest 15-LOX inhibitory effect (IC₅₀ = 1.17 μM) which was superior to that of the reference nordihydroguaiaretic acid (NDGA, IC₅₀ = 1.28 μM); meanwhile, compounds 6h, 6g, 11, and 4 exhibited potent activities (IC₅₀ = 1.29-1.77 μM). The ester 4 (SI = 137.37) and the phenyl-substituted acetohydrazide 11 (SI = 132.26) showed the highest COX-2 selectivity, which was about 28 times more selective than the reference drug diclofenac (SI = 4.73), however, it was lower than that of celecoxib (SI = 219.25). Interestingly, compound 6o, which showed the highest 15-LOX inhibitory activity and 5 times higher COX-2 selectivity than diclofenac, showed a greater poteny in reducing NO (IC₅₀ = 7.77 μM) than both celecoxib (IC₅₀ = 22.89 μM) and diclofenac (IC₅₀ = 25.34), but comparable activity in inhibiting TNF-α (IC₅₀ = 11.27) to diclofenac (IC₅₀ = 10.45 μM). Similarly, compounds 11 and 6h were more potent in reducing TNF-α and IL6 levels than diclofenac, meanwhile, compound 4 reduced ROS, NO, IL6, and TNF-α levels with comparable potency to the reference drugs celecoxib and diclofenac. Furthermore, docking studies for our compounds within 15-LOX and COX-2 active sites revealed good agreement with the biological evaluations. The proposed compounds could be promising multi-targeted anti-inflammatory candidates to treat resistant inflammatory conditions.

Synthesis, Biological Evaluation, and Molecular Dynamics of Carbothioamides Derivatives as Carbonic Anhydrase II and 15-Lipoxygenase Inhibitors

A series of hydrazine-1-carbothioamides derivatives (3a-3j) were synthesized and analyzed for inhibitory potential towards bovine carbonic anhydrase II (b-CA II) and 15-lipoxygenase (15-LOX). Interestingly, four derivatives, 3b, 3d, 3g, and 3j, were found to be selective inhibitors of CA II, while other derivatives exhibited CA II and 15-LOX inhibition. In silico studies of the most potent inhibitors of both b-CA II and 15-LOX were carried out to find the possible binding mode of compounds in their active site. Furthermore, MD simulation results confirmed that these ligands are stably bound to the two targets, while the binding energy further confirmed the inhibitory effects of the 3h compound. As these compounds may have a role in particular diseases, the reported compounds are of great relevance for future applications in the field of medicinal chemistry.

4-Chlorophenyl-N-furfuryl-1,2,4-triazole Methylacetamides as Significant 15-Lipoxygenase Inhibitors: an Efficient Approach for Finding Lead Anti-inflammatory Compounds

Lipoxygenases (LOXs) are a class of enzymes that catalyze the production of pro-inflammatory mediators, such as leukotrienes and lipoxins, via an arachidonic acid cascade as soon as they are released from the membrane phospholipids after tissue injury. In continuation of our efforts in search for new LOX inhibitors, a series of chlorophenyl-furfuryl-based 1,2,4-triazole derivatives were prepared and evaluated for their 15-LOX inhibitory activities. A simple precursor, 4-chlorobenzoic acid (a), was consecutively transformed into benzoate (1), hydrazide (2), semicarbazide (3), and N-furfuryl 5-(4-chlorobenzyl)-4H-1,2,4-triazole (4), which when further merged with electrophiles (6a-o) resulted in end products (7a-o). The structural elucidations of the newly synthesized compounds (7a-o) were carried out by Fourier transform infrared, 1H-, 13C NMR spectroscopy, EI-MS, and HR-EI-MS spectrometry. The inhibitive capability of compounds (7a-o) on soybean 15-LOX was performed in vitro using the chemiluminescence method. The compounds 7k, 7o, 7m, 7b, and 7i demonstrated potent activities (IC50 17.43 ± 0.38, 19.35 ± 0.71, 23.59 ± 0.68, 26.35 ± 0.62, and 27.53 ± 0.82 μM, respectively). These compounds revealed 79.5 to 98.8% cellular viability as measured by the MTT assay at 0.25 mM concentration. The structure-activity relationship (SAR) studies showed that the positions and the nature of substituents bonded to the phenyl ring are important in the determination of 15-LOX inhibitory activities. ADME, in silico, and density functional theory studies supported the evidence as yet another class of triazoles with potential lead properties in search for anti-LOX compounds with a safe gastrointestinal safety profile for various inflammatory diseases. Further work is in progress on the synthesis of more derivatives in search for anti-inflammatory agents.

Microwave-Assisted Synthesis of 2-Methyl-1H-indole-3-carboxylate Derivatives via Pd-Catalyzed Heterocyclization

Indole moiety is well-known as a superlative framework in many natural products and synthetic pharmaceuticals. Herein, we report an efficient procedure to synthesize a series of functionalized 2-methyl-1H-indole-3-carboxylate derivatives from commercially available anilines properly functionalized by different electron-withdrawing and -donating groups through a palladium-catalyzed intramolecular oxidative coupling. The conversion of a variety of enamines into the relevant indole was optimized by exposing the neat mixture of reactants to microwave irradiation, obtaining the desired products in excellent yields and high regioselectivity. The synthesized compounds were confirmed by 1H and 13C spectroscopic means as well as by high-resolution mass spectrometry.

The indole nucleus as a selective COX-2 inhibitor and anti-inflammatory agent (2011–2022)

Anti-inflammatory bioactivity of diversely substituted indole derivatives, mainly N-1 and C-3 substituted indoles.

Discovery of natural 15-LOX small molecule inhibitors from Chinese herbal medicine using virtual Screening, biological evaluation and molecular dynamics studies

Chinese herbal medicines (CHM) are frequently used to treat different types of inflammatory diseases and 15-Lipoxygenase (15-LOX) is a critical target enzyme for treating various inflammatory diseases. In this study, natural 15-LOX inhibitors were identified in CHM using an approach of virtual screening combined with the biological assays. First, an in-house Chinese medicine database containing 360 compounds was screened using a virtual screening approach based on pharmacophore and molecular docking to uncover several novel potential 15-LOX inhibitors. Secondly, the inhibitory effect of virtual screening hits against the 15-LOX enzyme was validated in an in vitro enzyme inhibition assay. Then, a tumor necrosis factor-α (TNF-α) release assay was carried out to explore the anti-inflammatory response of the active compounds. Furthermore, molecular dynamics (MD) simulation and binding free energy calculation were applied to analyze the process of inhibitors binding and also compared the mode of binding of the inhibitors by using the Molecular Mechanics-Generalized Born Surface Area (MM/GBSA) method. Finally, licochalcone B and eriodictyol were confirmed as inhibitors of the 15-LOX enzyme with IC₅₀ values of 9.67 and 18.99 μM, respectively. In vitro cell-based assay showed that licochalcone B and eriodictyol inhibited the release of TNF-α factor in RAW264.7 cells stimulated by lipopolysaccharides (LPS) in a dose-dependent manner. Molecular dynamics and binding free energy analysis showed that the two 15-LOX-ligand systems immediately attained equilibrium with almost 1 Å fluctuation, the calculated binding free energies were found around -18.89 and -12.96 kcal/mol for licochalcone B and eriodictyol, respectively. Thr412, Arg415, Val420, Thr429, Ile602 and Trp606 were the main amino acid residues for the inhibition of 15-LOX enzyme activity. The current study confirms that licochalcone B and eriodictyol are 15-LOX inhibitors and can suppress the release of the TNF-α factor in RAW264.7 cells stimulated by LPS, thus providing a basis for the follow-up research and development for 15-LOX inhibitors.

Investigating the effects of two novel 4-MMPB analogs as potent lipoxygenase inhibitors for prostate cancer treatment

Background

Lipoxygenases are one of the critical signaling mediators which can be targeted for human prostate cancer (PC) therapy. In this study, 4-methyl-2-(4-methylpiperazinyl)pyrimido[4,5-b]benzothiazine (4-MMPB) and its two analogs, 4-propyl-2-(4-methylpiperazinyl)pyrimido[4,5-b]benzothiazine (4-PMPB) and 4-ethyl-2-(4-methylpiperazinyl)pyrimido[4,5-b]benzothiazine (4-EMPB), were proposed to have anti-tumor properties in prostate cancer.

Methods

After synthesizing the compounds, cytotoxic effects of 4-MMPB and its two analogs against PC-3 cancerous and HDF normal cells were investigated by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay and then mechanism of cell death was assessed by flow cytometry. Finally, the anti-tumor effects of the mentioned compounds were investigated in an immunocompromised C57BL/6 mouse model.

Results

4-PMPB and 4-EMPB had similar anti-cancer effects on PC-3 cells as compared with 4-MMPB, while they were not effective on normal cells. Moreover, apoptosis and ferroptosis were the main mechanisms of induced cell death in these cancerous cells. Furthermore, in vivo results indicated that both analogs had similar anti-cancer effects as 4-MMPB, leading to delayed tumor growth without any noticeable side effects in weight loss and histological investigations.

Conclusion

Thus, our results suggest that specific targeting of lipoxygenases via 4-MMPB analogs can be considered as a treatment of choice for PC therapy, although it requires further investigations.

Enantioselective synthesis of indole derivatives by Rh/Pd relay catalysis and their anti-inflammatory evaluation

An efficient Rh/Pd relay catalyzed intermolecular and cascade intramolecular hydroamination for the synthesis of exclusive trans 1-indolyl dihydronaphthalenols (up to 88% yield, 99% ee) is described under mild conditions. Moreover, the in silico and in vitro screening showed that the novel 1-indolyl dihydronaphthalenol products are potent lead compounds for treating inflammation disease.

Catalytic enantioselective addition of organometallics to unprotected carboxylic acids

Conjugate addition of organometallics to carbonyl based Michael acceptors is a widely used method that allows the building of new carbon-carbon (C-C) bonds and the introduction of chirality in a single step. However, conjugate additions to the simplest Michael acceptors, namely unprotected, unsaturated carboxylic acids, are considered to be prohibited by the fact that acid-base reactions overpower any other type of reactivity, including nucleophilic addition. Here we describe a transient protecting group strategy that allows efficient catalytic asymmetric additions of organomagnesium reagents to unprotected α,β-unsaturated carboxylic acids. This unorthodox pathway is achieved by preventing the formation of unreactive carboxylate salts by means of a reactive intermediate, allowing modifications of the carbon chain to proceed unhindered, while the stereochemistry is controlled with a chiral copper catalyst. A wide variety of β-chiral carboxylic acids, obtained with excellent enantioselectivities and yields, can be further transformed into valuable molecules through for instance catalytic decarboxylative cross-coupling reactions.

Replacement of an Indole Scaffold Targeting Human 15-Lipoxygenase-1 Using Combinatorial Chemistry

Human 15-lipoxygenase-1 (15-LOX-1) belongs to the class of lipoxygenases, which catalyze oxygenation of polyunsaturated fatty acids, such as arachidonic and linoleic acid. Recent studies have shown that 15-LOX-1 plays an important role in physiological processes linked to several diseases such as airway inflammation disease, coronary artery disease, and several types of cancer such as rectal, colon, breast and prostate cancer. In this study, we aimed to extend the structural diversity of 15-LOX-1 inhibitors, starting from the recently identified indolyl core. In order to find new scaffolds, we employed a combinatorial approach using various aromatic aldehydes and an aliphatic hydrazide tail. This scaffold-hopping study resulted in the identification of the 3-pyridylring as a suitable replacement of the indolyl core with an inhibitory activity in the micromolar range (IC 50=16±6 μm) and a rapid and efficient structure-activity relationship investigation.

Novel 15-Lipoxygenase-1 Inhibitor Protects Macrophages from Lipopolysaccharide-Induced Cytotoxicity

Various mechanisms for regulated cell death include the formation of oxidative mediators such as lipid peroxides and nitric oxide (NO). In this respect, 15-lipoxygenase-1 (15-LOX-1) is a key enzyme that catalyzes the formation of lipid peroxides. The actions of these peroxides are interconnected with nuclear factor-κB signaling and NO production. Inhibition of 15-LOX-1 holds promise to interfere with regulated cell death in inflammatory conditions. In this study, a novel potent 15-LOX-1 inhibitor, 9c (i472), was developed and structure–activity relationships were explored. In vitro, this inhibitor protected cells from lipopolysaccharide-induced cell death, inhibiting NO formation and lipid peroxidation. Thus, we provide a novel 15-LOX-1 inhibitor that inhibits cellular NO production and lipid peroxidation, which set the stage for further exploration of these mechanisms.

Identification of potential antivirulence agents by substitution-oriented screening for inhibitors of Streptococcus pyogenes sortase A

Antimicrobial resistance resulting in ineffective treatment of infectious diseases is an increasing global problem, particularly in infections with pathogenic bacteria. In some bacteria, such as Streptococcus pyogenes, the pathogenicity is strongly linked to the attachment of virulence factors. Their attachment to the cellular membrane is a transpeptidation reaction, catalyzed by sortase enzymes. As such, sortases pose an interesting target for the development of new antivirulence strategies that could yield novel antimicrobial drugs. Using the substitution-oriented fragment screening (SOS) approach, we discovered a potent and specific inhibitor (C10) of sortase A from S. pyogenes. The inhibitor C10 showed high specificity towards S. pyogenes sortase A, with an IC₅₀ value of 10 μM and a K_d of 60 μM. We envision that this inhibitor could be employed as a starting point for further exploration of sortase's potential as therapeutic target for antimicrobial drug development.

Comparison of eight 15-lipoxygenase (LO) inhibitors on the biosynthesis of 15-LO metabolites by human neutrophils and eosinophils

Neutrophils and eosinophils are important sources of bioactive lipids from the 5- and the 15-lipoxygenase (LO) pathways. Herein, we compared the effectiveness of humans eosinophils and eosinophil-depleted neutrophils to synthesize 15-LO metabolites using a cocktail of different 15-LO substrates as well as their sensitivities to eight documented 15-lipoxygenase inhibitors. The treatment of neutrophils and eosinophils with linoleic acid, dihomo-γ-linolenic acid, arachidonic acid, eicosapentaenoic acid, docosahexaenoic acid and arachidonyl-ethanolamide, led to the synthesis of 13-HODE, 15-HETrE, 15-HETE, 15-HEPE, 14-HDHA/17-HDHA, and 15-hydroxy-AEA. Neutrophils and eosinophils also metabolized the endocannabinoid 2-arachidonoyl-glycerol into 15-HETE-glycerol, although this required 2-arachidonoyl-glycerol hydrolysis inhibition. Neutrophils and eosinophils differed in regard to dihomo-γ-linolenic acid and linoleic acid utilization with 15-HETrE/13-HODE ratios of 0.014 ± 0.0008 and 0.474 ± 0.114 for neutrophils and eosinophils respectively. 15-LO metabolite synthesis by neutrophils and eosinophils also differed in regard to their relative production of 17-HDHA and 14-HDHA.The synthesis of 15-LO metabolites by neutrophils was concentration-dependent and rapid, reaching a plateau after one minute. While investigating the biosynthetic routes involved, we found that eosinophil-depleted neutrophils express the 15-lipoxygenase-2 but not the 15-LO-1, in contrast to eosinophils which express the 15-LO-1 but not the 15-LO-2. Moreover, 15-LO metabolite synthesis by neutrophils was not inhibited by the 15-LO-1 inhibitors BLX769, BLX3887, and ML351. However, 15-LO product synthesis was partially inhibited by 100 μM NDGA. Altogether, our data indicate that the best 15-LO-1 inhibitors in eosinophils are BLX3887, BLX769, NDGA and ML351 and that the synthesis of 15-LO metabolites by neutrophils does not involve the 15-LO-1 nor the phosphorylation of 5-LO on Ser-663 but is rather the consequence of 15-LO-2 or another unidentified 15-LO.

Recent development of lipoxygenase inhibitors as anti-inflammatory agents

Inflammation is favorable in most cases, because it is a kind of body defensive response to external stimuli; sometimes, inflammation is also harmful, such as attacks on the body's own tissues. It could be that inflammation is a unified process of injury and resistance to injury. Inflammation brings extreme pain to patients, showing symptoms of rubor, swelling, fever, pain and dysfunction. As the specific mechanism is not clear yet, the current anti-inflammatory agents are given priority for relieving suffering of patients. Thus it is emergent to find new anti-inflammatory agents with rapid effect. Lipoxygenase (LOX) is a kind of rate-limiting enzyme in the process of arachidonic acid metabolism into leukotriene (LT) which mediates the occurrence of inflammation. The inhibition of LOX can reduce LT, thereby producing an anti-inflammatory effect. In this review, the LOX inhibitors reported in recent years are summarized, and, in particular, their activities, structure-activity relationships and molecular docking studies are emphasized, which will provide new ideas to design novel LOX inhibitors.

Photoactivation provides a mechanistic explanation for pan-assay interference behaviour of 2-aminopyrroles in lipoxygenase inhibition

Human 15-lipoxygenase-1 (h-15-LOX-1) is a promising drug target in inflammation and cancer. In this study substitution-oriented screening (SOS) has been used to identify compounds with a 2-aminopyrrole scaffold as inhibitors for h-15-LOX-1. The observed structure activity relationships (SAR) proved to be relatively flat. IC₅₀'s for the most potent inhibitor of the series did not surpass 6.3 μM and the enzyme kinetics demonstrated uncompetitive inhibition. Based on this, we hypothesized that the investigated 2-aminopyrroles are pan assay interference compounds (PAINS) with photoactivation via a radical mechanism. Our results demonstrated clear photoactivation of h-15-LOX-1 inhibition under UV and visible light. In addition, the investigated 2-aminopyrroles decreased viability of cultured human hepatocarcinoma cells HCC-1.2 in a dose-dependent manner with LD₅₀ ranging from 0.55 ± 0.15 μM (21B10) to 2.75 ± 0.91 μM (22). Taken together, this indicates that photoactivation can play an important role in the biological activity of compounds with a 2-amino-pyrrole scaffold as investigated here.

A 6-alkylsalicylate histone acetyltransferase inhibitor inhibits histone acetylation and pro-inflammatory gene expression in murine precision-cut lung slices

Lysine acetylations are post-translational modifications of cellular proteins, that are crucial in the regulation of many cellular processes. Lysine acetylations on histone proteins are part of the epigenetic code regulating gene expression and are installed by histone acetyltransferases. Observations that inflammatory lung diseases, such as asthma and chronic obstructive pulmonary disease, are characterized by increased histone acetyltransferase activity indicate that development of small molecule inhibitors for these enzymes might be a valuable approach towards new therapies for these diseases. The 6-alkylsalicylate MG149 is a candidate to explore this hypothesis because it has been demonstrated to inhibit the MYST type histone acetyltransferases. In this study, we determined the Ki value for inhibition of the MYST type histone acetyltransferase KAT8 by MG149 to be 39 ± 7.7 μM. Upon investigating whether the inhibition of histone acetyltransferases by MG149 correlates with inhibition of histone acetylation in murine precision-cut lung slices, inhibition of acetylation was observed using an LC-MS/MS based assay on histone H4 res 4-17, which contains the target lysine of KAT8. Following up on this, upon treatment with MG149, reduced pro-inflammatory gene expression was observed in lipopolysaccharide and interferon gamma stimulated murine precision-cut lung slices. Based on this, we propose that 6-alkylsalicylates such as MG149 have potential for development towards applications in the treatment of inflammatory lung diseases.

Lipoxygenase Activity Accelerates Programmed Spore Germination in Aspergillus fumigatus

The opportunistic human pathogen Aspergillus fumigatus initiates invasive growth through a programmed germination process that progresses from dormant spore to swollen spore (SS) to germling (GL) and ultimately invasive hyphal growth. We find a lipoxygenase with considerable homology to human Alox5 and Alox15, LoxB, that impacts the transitions of programmed spore germination. Overexpression of loxB (OE::loxB) increases germination with rapid advance to the GL stage. However, deletion of loxB (ΔloxB) or its signal peptide only delays progression to the SS stage in the presence of arachidonic acid (AA); no delay is observed in minimal media. This delay is remediated by the addition of the oxygenated AA oxylipin 5-hydroxyeicosatetraenoic acid (5-HETE) that is a product of human Alox5. We propose that A. fumigatus acquisition of LoxB (found in few fungi) enhances germination rates in polyunsaturated fatty acid-rich environments.

HDAC1-3 inhibitor MS-275 enhances IL10 expression in RAW264.7 macrophages and reduces cigarette smoke-induced airway inflammation in mice

Chronic obstructive pulmonary disease (COPD) constitutes a major health burden. Studying underlying molecular mechanisms could lead to new therapeutic targets. Macrophages are orchestrators of COPD, by releasing pro-inflammatory cytokines. This process relies on transcription factors such as NF-κB, among others. NF-κB is regulated by lysine acetylation; a post-translational modification installed by histone acetyltransferases and removed by histone deacetylases (HDACs). We hypothesized that small molecule HDAC inhibitors (HDACi) targeting class I HDACs members that can regulate NF-κB could attenuate inflammatory responses in COPD via modulation of the NF-κB signaling output. MS-275 is an isoform-selective inhibitor of HDAC1-3. In precision-cut lung slices and RAW264.7 macrophages, MS-275 upregulated the expression of both pro- and anti-inflammatory genes, implying mixed effects. Interestingly, anti-inflammatory IL10 expression was upregulated in these model systems. In the macrophages, this was associated with increased NF-κB activity, acetylation, nuclear translocation, and binding to the IL10 promoter. Importantly, in an in vivo model of cigarette smoke-exposed C57Bl/6 mice, MS-275 robustly attenuated inflammatory expression of KC and neutrophil influx in the lungs. This study highlights for the first time the potential of isoform-selective HDACi for the treatment of inflammatory lung diseases like COPD.

Lipid peroxidation in cell death

Disruption of redox homeostasis is a key phenotype of many pathological conditions. Though multiple oxidizing compounds such as hydrogen peroxide are widely recognized as mediators and inducers of oxidative stress, increasingly, attention is focused on the role of lipid hydroperoxides as critical mediators of death and disease. As the main component of cellular membranes, lipids have an indispensible role in maintaining the structural integrity of cells. Excessive oxidation of lipids alters the physical properties of cellular membranes and can cause covalent modification of proteins and nucleic acids. This review discusses the synthesis, toxicity, degradation, and detection of lipid peroxides in biological systems. Additionally, the role of lipid peroxidation is highlighted in cell death and disease, and strategies to control the accumulation of lipid peroxides are discussed.

COST Action CM1201 "Biomimetic Radical Chemistry": free radical chemistry successfully meets many disciplines

The COST Action CM1201 "Biomimetic Radical Chemistry" has been active since December 2012 for 4 years, developing research topics organized into four working groups: WG1 - Radical Enzymes, WG2 - Models of DNA damage and consequences, WG3 - Membrane stress, signalling and defenses, and WG4 - Bio-inspired synthetic strategies. International collaborations have been established among the participating 80 research groups with brilliant interdisciplinary achievements. Free radical research with a biomimetic approach has been realized in the COST Action and are summarized in this overview by the four WG leaders.

Activity-Based Probes for 15-Lipoxygenase-1

Human 15-lipoxygenase-1 (15-LOX-1) plays an important role in several inflammatory lung diseases, such as asthma, COPD, and chronic bronchitis, as well as various CNS diseases, such as Alzheimer's disease, Parkinson's disease, and stroke. Activity-based probes of 15-LOX-1 are required to explore the role of this enzyme further and to enable drug discovery. In this study, we developed a 15-LOX-1 activity-based probe for the efficient activity-based labeling of recombinant 15-LOX-1. 15-LOX-1-dependent labeling in cell lysates and tissue samples was also possible. To mimic the natural substrate of the enzyme, we designed activity-based probes that covalently bind to the active enzyme and include a terminal alkene as a chemical reporter for the bioorthogonal linkage of a detectable functionality through an oxidative Heck reaction. The activity-based labeling of 15-LOX-1 should enable the investigation and identification of this enzyme in complex biological samples, thus opening up completely new opportunities for drug discovery.

Key Residues for Catalytic Function and Metal Coordination in a Carotenoid Cleavage Dioxygenase

Carotenoid cleavage dioxygenases (CCDs) are non-heme iron-containing enzymes found in all domains of life that generate biologically important apocarotenoids. Prior studies have revealed a critical role for a conserved 4-His motif in forming the CCD iron center. By contrast, the roles of other active site residues in catalytic function, including maintenance of the stringent regio- and stereo-selective cleavage activity, typically exhibited by these enzymes have not been thoroughly investigated. Here, we examined the functional and structural importance of active site residues in an apocarotenoid-cleaving oxygenase (ACO) from Synechocystis Most active site substitutions variably lowered maximal catalytic activity without markedly affecting the Km value for the all-trans-8'-apocarotenol substrate. Native C15-C15' cleavage activity was retained in all ACO variants examined suggesting that multiple active site residues contribute to the enzyme's regioselectivity. Crystallographic analysis of a nearly inactive W149A-substituted ACO revealed marked disruption of the active site structure, including loss of iron coordination by His-238 apparently from an altered conformation of the conserved second sphere Glu-150 residue. Gln- and Asp-150-substituted versions of ACO further confirmed the structural/functional requirement for a Glu side chain at this position, which is homologous to Glu-148 in RPE65, a site in which substitution to Asp has been associated with loss of enzymatic function in Leber congenital amaurosis. The novel links shown here between ACO active site structure and catalytic activity could be broadly applicable to other CCD members and provide insights into the molecular pathogenesis of vision loss associated with an RPE65 point mutation.

Human 15-LOX-1 active site mutations alter inhibitor binding and decrease potency

Human 15-lipoxygenase-1 (h15-LOX-1 or h12/15-LOX) reacts with polyunsaturated fatty acids and produces bioactive lipid derivatives that are implicated in many important human diseases. One such disease is stroke, which is the fifth leading cause of death and the first leading cause of disability in America. The discovery of h15-LOX-1 inhibitors could potentially lead to novel therapeutics in the treatment of stroke, however, little is known about the inhibitor/active site interaction. This study utilizes site-directed mutagenesis, guided in part by molecular modeling, to gain a better structural understanding of inhibitor interactions within the active site. We have generated eight mutants (R402L, R404L, F414I, F414W, E356Q, Q547L, L407A, I417A) of h15-LOX-1 to determine whether these active site residues interact with two h15-LOX-1 inhibitors, ML351 and an ML094 derivative, compound 18. IC₅₀ values and steady-state inhibition kinetics were determined for the eight mutants, with four of the mutants affecting inhibitor potency relative to wild type h15-LOX-1 (F414I, F414W, E356Q and L407A). The data indicate that ML351 and compound 18, bind in a similar manner in the active site to an aromatic pocket close to F414 but have subtle differences in their specific binding modes. This information establishes the binding mode for ML094 and ML351 and will be leveraged to develop next-generation inhibitors.

Friedel-Crafts dealkylation reaction mediated by a stereoselective proton transfer in the fragmentation of protonated cyclic indolyl α-amino esters

RATIONALE

Chiral cyclic indolyl α-amino esters are valuable substructures of peptides and peptidomimetics. Systematically exploring the fragmentation behavior of the protonated cyclic indolyl α-amino esters by a combination of high-resolution high-energy collisional dissociation mass spectrometry, hydrogen-deuterium exchange experiments and density functional theory (DFT) calculations is useful for further understanding their intrinsic properties and the fragmentation mechanisms of peptidomimetics constructed with them.

METHODS

All high-resolution high-energy collisional dissociation tandem mass spectrometry experiments were carried out using electrospray ionization hybrid Quadrupole-Orbitrap mass spectrometry in positive ion mode. Only the labile hydrogens were exchanged with deuterium in hydrogen-deuterium exchange experiments. Theoretical calculations were carried out by the DFT method at the B3LYP level with the 6-311G(d,p) basis set in the Gaussian 03 package of programs.

RESULTS

In the fragmentation of protonated cyclic indolyl α-amino esters, when the two labile hydrogens on the N(8) position are successively transferred to the C(3) and C(4) positions, a Friedel-Crafts dealkylation reaction takes place spontaneously, with concomitant formation of an ion-neutral complex of [cyclic N-sulfonyl ketimino esters/protonated indoles]. Direct separation of this complex formed the protonated indoles, while a stereoselective proton transfer between the two components in the complex gave rise to protonated cyclic N-sulfonyl ketimino esters, which coincided with the hydrogen-deuterium experiments.

CONCLUSIONS

Using H/D exchange experiments combined with theoretical calculations, a Friedel-Crafts dealkylation reaction mediated by a stereoselective proton transfer in the [cyclic N-sulfonyl ketimino esters/protonated indoles] complex was proposed for the fragmentation of protonated cyclic indolyl α-amino esters in high-energy collisional dissociation tandem mass spectrometry for the first time. Copyright © 2016 John Wiley & Sons, Ltd.

Design of a novel thiophene inhibitor of 15-lipoxygenase-1 with both anti-inflammatory and neuroprotective properties

The enzyme 15-lipoxygenase-1 (15-LOX-1) plays a dual role in diseases with an inflammatory component. On one hand 15-LOX-1 plays a role in pro-inflammatory gene expression and on the other hand it has been shown to be involved in central nervous system (CNS) disorders by its ability to mediate oxidative stress and damage of mitochondrial membranes under hypoxic conditions. In order to further explore applications in the CNS, novel 15-LOX-1 inhibitors with favorable physicochemical properties need to be developed. Here, we present Substitution Oriented Screening (SOS) in combination with Multi Component Chemistry (MCR) as an effective strategy to identify a diversely substituted small heterocyclic inhibitors for 15-LOX-1, denoted ThioLox, with physicochemical properties superior to previously identified inhibitors. Ex vivo biological evaluation in precision-cut lung slices (PCLS) showed inhibition of pro-inflammatory gene expression and in vitro studies on neuronal HT-22 cells showed a strong protection against glutamate toxicity for this 15-LOX-1 inhibitor. This provides a novel approach to identify novel small with favorable physicochemical properties for exploring 15-LOX-1 as a drug target in inflammatory diseases and neurodegeneration.

HDAC 3-selective inhibitor RGFP966 demonstrates anti-inflammatory properties in RAW 264.7 macrophages and mouse precision-cut lung slices by attenuating NF-κB p65 transcriptional activity

The increasing number of patients suffering from chronic obstructive pulmonary disease (COPD) represents a major and increasing health problem. Therefore, novel therapeutic approaches are needed. Class I HDACs 1, 2 and 3 play key roles in the regulation of inflammatory gene expression with a particular pro-inflammatory role for HDAC 3. HDAC 3 has been reported to be an important player in inflammation by deacetylating NF-κB p65, which has been implicated in the pathology of COPD. Here, we applied the pharmacological HDAC 3-selective inhibitor RGFP966, which attenuated pro-inflammatory gene expression in models for inflammatory lung diseases. Consistent with this, a robust decrease of the transcriptional activity of NF-κB p65 was observed. HDAC 3 inhibition affected neither the acetylation status of NF-κB p65 nor histone H3 or histone H4. This indicates that HDAC 3 inhibition does not inhibit NF-κB p65 transcriptional activity by affecting its deacetylation but rather by inhibiting enzymatic activity of HDAC 3. Taken together, our findings indicate that pharmacological HDAC 3-selective inhibition by inhibitors such as RGFP966 may provide a novel and effective approach toward development of therapeutics for inflammatory lung diseases.

The histone acetyltransferase p300 inhibitor C646 reduces pro-inflammatory gene expression and inhibits histone deacetylases

Lysine acetylations are reversible posttranslational modifications of histone and non-histone proteins that play important regulatory roles in signal transduction cascades and gene expression. Lysine acetylations are regulated by histone acetyltransferases as writers and histone deacetylases as erasers. Because of their role in signal transduction cascades, these enzymes are important players in inflammation. Therefore, histone acetyltransferase inhibitors could reduce inflammatory responses. Among the few histone acetyltransferase inhibitors described, C646 is one of the most potent (Ki of 0.4μM for histone acetyltransferase p300). C646 was described to affect the NF-κB pathway; an important pathway in inflammatory responses, which is regulated by acetylation. This pathway has been implicated in asthma and COPD. Therefore, we hypothesized that via regulation of the NF-κB signaling pathway, C646 can inhibit pro-inflammatory gene expression, and have potential for the treatment of inflammatory lung diseases. In line with this, we demonstrate here that C646 reduces pro-inflammatory gene expression in RAW264.7 murine macrophages and murine precision-cut lung slices. To unravel its effects on cellular substrates we applied mass spectrometry and found, counterintuitively, a slight increase in acetylation of histone H3. Based on this finding, and structural features of C646, we presumed inhibitory activity of C646 on histone deacetylases, and indeed found inhibition of histone deacetylases from 7μM and higher concentrations. This indicates that C646 has potential for further development towards applications in the treatment of inflammation, however, its newly discovered lack of selectivity at higher concentrations needs to be taken into account.