Structure-activity relationship studies of flavonoids as potent inhibitors of human platelet 12-hLO, reticulocyte 15-hLO-1, and prostate epithelial 15-hLO-2

Identification of Novel Human 15-Lipoxygenase-2 (h15-LOX-2) Inhibitors Using a Virtual Screening Approach

The human 15-lipoxygenase-2 (h15-LOX-2) catalyzes mainly the regio- and stereospecific oxygenation of arachidonate to its corresponding hydroperoxide (15(S)-HpETE). h15-LOX-2 is implicated in the biosynthesis of inflammatory lipid mediators and plays a role in the development of atherosclerotic plaques, but it is still underexploited as a drug target. Here, to search for novel h15-LOX-2 inhibitors, we used a virtual screening (VS) approach consisting of shape-based matching, two-dimensional (2D) structural "dissimilarity", docking, and visual inspection filters, which were applied to a "curated" ZINC database (∼8 × 106 compounds). The VS was experimentally validated, and six micromolar-range inhibitors were identified among 13 tested compounds (46.2%). The Ki values could be determined for two inhibitors, compounds 10 (Ki = 16.4 ± 8.1 μM) and 13 (Ki = 15.1 ± 7.6 μM), which showed a mixed-type mechanism of inhibition. Overall, the identified inhibitors fulfill drug-like criteria and are structurally novel compared with known h15-LOX-2 inhibitors.

Investigating the catalytic efficiency of C22-Fatty acids with LOX human isozymes and the platelet response of the C22-oxylipin products

Polyunsaturated fatty acids (PUFAs) have been extensively studied for their health benefits because they can be oxidized by lipoxygenases to form bioactive oxylipins. In this study, we investigated the impact of double bond placement on the kinetic properties and product profiles of human platelet 12-lipoxygenase (h12-LOX), human reticulocyte 15-lipoxygenase-1 (h15-LOX-1), and human endothelial 15-lipoxygenase-2 (h15-LOX-2) by using 22-carbon (C22) fatty acid substrates with differing double bond content. With respect to kcat/KM values, the loss of Δ4 and Δ19 led to an 18-fold loss of kinetic activity for h12-LOX, no change in kinetic capability for h15-LOX-1, but a 24-fold loss for h15-LOX-2 for both C22-FAs. With respect to the product profiles, h12-LOX produced mainly 14-oxylipins. For h15-LOX-1, the 14-oxylipin production increased with the loss of either Δ4 and Δ19, however, the 17-oxylipin became the major species upon loss of both Δ4 and Δ19. h15-LOX-2 produced mostly the 17-oxylipin products throughout the fatty acid series. This study also investigated the effects of various 17-oxylipins on platelet activation. The results revealed that both 17(S)-hydroxy-4Z,7Z,10Z,13Z,15E,19Z-DHA (17-HDHA) and 17-hydroxy-4Z,7Z,10Z,13Z,15E-DPAn6 (17-HDPAn6) demonstrated anti-aggregation properties with thrombin or collagen stimulation. 17-hydroxy-7Z,10Z,13Z,15E,19Z-DPAn3 (17-HDPAn3) exhibited agonistic properties, and 17-hydroxy-7Z,10Z,13Z,15E-DTA (17-HDTA) showed biphasic effects, inhibiting collagen-induced aggregation at lower concentrationsbut promoting aggregation at higher concentrations. Both 17-hydroxy-13Z,15E,19Z-DTrA (17-HDTrA), and 17-hydroxy-13Z,15E-DDiA (17-HDDiA) induced platelet aggregation. In summary, the number and placement of the double bonds affect platelet activation, with the general trend being that more double bonds generally inhibit aggregation, while less double bonds promote aggregation. These findings provide insights into the potential role of specific fatty acids and their metabolizing LOX isozymes with respect to cardiovascular health.

Inhibitory Investigations of Acyl-CoA Derivatives against Human Lipoxygenase Isozymes

Lipid metabolism is a complex process crucial for energy production resulting in high levels of acyl-coenzyme A (acyl-CoA) molecules in the cell. Acyl-CoAs have also been implicated in inflammation, which could be possibly linked to lipoxygenase (LOX) biochemistry by the observation that an acyl-CoA was bound to human platelet 12-lipoxygenase via cryo-EM. Given that LOX isozymes play a pivotal role in inflammation, a more thorough investigation of the inhibitory effects of acyl-CoAs on lipoxygenase isozymes was judged to be warranted. Subsequently, it was determined that C18 acyl-CoA derivatives were the most potent against h12-LOX, human reticulocyte 15-LOX-1 (h15-LOX-1), and human endothelial 15-LOX-2 (h15-LOX-2), while C16 acyl-CoAs were more potent against human 5-LOX. Specifically, oleoyl-CoA (18:1) was most potent against h12-LOX (IC50 = 32 μM) and h15-LOX-2 (IC50 = 0.62 μM), stearoyl-CoA against h15-LOX-1 (IC50 = 4.2 μM), and palmitoleoyl-CoA against h5-LOX (IC50 = 2.0 μM). The inhibition of h15-LOX-2 by oleoyl-CoA was further determined to be allosteric inhibition with a Ki of 82 +/- 70 nM, an α of 3.2 +/- 1, a β of 0.30 +/- 0.07, and a β/α = 0.09. Interestingly, linoleoyl-CoA (18:2) was a weak inhibitor against h5-LOX, h12-LOX, and h15-LOX-1 but a rapid substrate for h15-LOX-1, with comparable kinetic rates to free linoleic acid (kcat = 7.5 +/- 0.4 s-1, kcat/KM = 0.62 +/- 0.1 µM-1s-1). Additionally, it was determined that methylated fatty acids were not substrates but rather weak inhibitors. These findings imply a greater role for acyl-CoAs in the regulation of LOX activity in the cell, either through inhibition of novel oxylipin species or as a novel source of oxylipin-CoAs.

Arachidonate 15-lipoxygenase type B: Regulation, function, and its role in pathophysiology

As a lipoxygenase (LOX), arachidonate 15-lipoxygenase type B (ALOX15B) peroxidizes polyenoic fatty acids (PUFAs) including arachidonic acid (AA), eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and linoleic acid (LA) to their corresponding fatty acid hydroperoxides. Distinctive to ALOX15B, fatty acid oxygenation occurs with positional specificity, catalyzed by the non-heme iron containing active site, and in addition to free PUFAs, membrane-esterified fatty acids serve as substrates for ALOX15B. Like other LOX enzymes, ALOX15B is linked to the formation of specialized pro-resolving lipid mediators (SPMs), and altered expression is apparent in various inflammatory diseases such as asthma, psoriasis, and atherosclerosis. In primary human macrophages, ALOX15B expression is associated with cellular cholesterol homeostasis and is induced by hypoxia. Like in inflammation, the role of ALOX15B in cancer is inconclusive. In prostate and breast carcinomas, ALOX15B is attributed a tumor-suppressive role, whereas in colorectal cancer, ALOX15B expression is associated with a poorer prognosis. As the biological function of ALOX15B remains an open question, this review aims to provide a comprehensive overview of the current state of research related to ALOX15B.

Structural basis for altered positional specificity of 15-lipoxygenase-1 with 5S-HETE and 7S-HDHA and the implications for the biosynthesis of resolvin E4

Human 15-lipoxygenases (LOX) are critical enzymes in the inflammatory process, producing various pro-resolution molecules, such as lipoxins and resolvins, but the exact role each of the two 15-LOXs in these biosynthetic pathways remains elusive. Previously, it was observed that h15-LOX-1 reacted with 5S-HETE in a non-canonical manner, producing primarily the 5S,12S-diHETE product. To determine the active site constraints of h15-LOX-1 in achieving this reactivity, amino acids involved in the fatty acid binding were investigated. It was observed that R402L did not have a large effect on 5S-HETE catalysis, but F414 appeared to π-π stack with 5S-HETE, as seen with AA binding, indicating an aromatic interaction between a double bond of 5S-HETE and F414. Decreasing the size of F352 and I417 shifted oxygenation of 5S-HETE to C12, while increasing the size of these residues reversed the positional specificity of 5S-HETE to C15. Mutants at these locations demonstrated a similar effect with 7S-HDHA as the substrate, indicating that the depth of the active site regulates product specificity for both substrates. Together, these data indicate that of the three regions proposed to control positional specificity, π-π stacking and active site cavity depth are the primary determinants of positional specificity with 5S-HETE and h15-LOX-1. Finally, the altered reactivity of h15-LOX-1 was also observed with 5S-HEPE, producing 5S,12S-diHEPE instead of 5S,15S-diHEPE (aka resolvin E₄ (RvE₄). However, h15-LOX-2 efficiently produces 5S,15S-diHEPE from 5S-HEPE. This result is important with respect to the biosynthesis of the RvE₄ since it obscures which LOX isozyme is involved in its biosynthesis. Future work detailing the expression levels of the lipoxygenase isoforms in immune cells and selective inhibition during the inflammatory response will be required for a comprehensive understanding of RvE₄ biosynthesis.

Metabolomic profile and computational analysis for the identification of the potential anti-inflammatory mechanisms of action of the traditional medicinal plants Ocimum basilicum and Ocimum tenuiflorum

Ocimum basilicum and Ocimum tenuiflorum are two basil species widely used medicinally as an anti-inflammatory, antimicrobial and cardioprotective agent. This study focuses on the chemical characterization of the majoritarian compounds of both species and their anti-inflammatory potential. Up to 22 compounds such as various types of salvianolic acids, derivatives of rosmaniric acid and flavones were identified in both plants. The identified compounds were very similar between both plants and are consistent with previous finding in other studies in Portugal and Italy. Based on the identified molecules a consensus target prediction was carried out. Among the main predicted target proteins, we found a high representation of the carbonic anhydrase family (CA2, CA7 and CA12) and several key proteins from the arachidonic pathway (LOX5, PLA2, COX1 and COX2). Both pathways are well related to inflammation. The interaction between the compounds and these targets were explored through molecular docking and molecular dynamics simulation. Our results suggest that some molecules present in both plants can induce an anti-inflammatory response through a non-steroidal mechanism of action connected to the carbon dioxide metabolism.

Effect of the Chromone Core Substitution of Dirchromone on the Resultant Biological Activities

Dirchromone is a bioactive vinyl sulfoxide-bearing chromone first isolated from the shrub Dirca palustris. Altogether, 32 of its derivatives were prepared to assess the effect of substitution of its chromone core upon activities against cancer cell lines, Gram-positive bacteria, and fungi (such as Candida albicans). All compounds were synthesized following a synthetic strategy involving Pummerer and soft-enolization Baker-Venkataraman rearrangements. Substituent position changes induced little variability on the activities tested. There was no correlation between cytotoxic and antibacterial effects, suggesting different underlying mechanisms of action. In particular, hydroxy group and cyanide substituents diminished cytotoxicity, with the latter featuring enhanced antibacterial activity. Higher homologues of 6-alkoxydirchromones also exhibited progressively emerging antifungal activity. Other modifications had moderate effects on cytotoxicity with some derivatives leading to increased potency. This behavior highlights the robustness of the natural dirchromone pharmacophore toward decoration, thus paving the way for more elaborate future drug design.

Paralog- and ortholog-specificity of inhibitors of human and mouse lipoxygenase-isoforms

Lipoxygenases (ALOX-isoforms) are lipid peroxidizing enzymes, which have been implicated in cell differentiation and maturation but also in the biosynthesis of lipid mediators playing important roles in the pathogenesis of inflammatory, hyperproliferative and neurological diseases. In mammals these enzymes are widely distributed and the human genome involves six functional genes encoding for six distinct human ALOX paralogs. In mice, there is an orthologous enzyme for each human ALOX paralog but the catalytic properties of human and mouse ALOX orthologs show remarkable differences. ALOX inhibitors are frequently employed for deciphering the biological role of these enzymes in mouse models of human diseases but owing to the functional differences between mouse and human ALOX orthologs the uncritical use of such inhibitors is sometimes misleading. In this study we evaluated the paralog- and ortholog-specificity of 13 frequently employed ALOX-inhibitors against four recombinant human and mouse ALOX paralogs (ALOX15, ALOX15B, ALOX12, ALOX5) under different experimental conditions. Our results indicated that except for zileuton, which exhibits a remarkable paralog-specificity for mouse and human ALOX5, no other inhibitor was strictly paralog specific but some compounds exhibit an interesting ortholog-specificity. Because of the variable isoform specificities of the currently available ALOX inhibitors care must be taken when the biological effects of these compounds observed in complex in vitro and in vivo systems are interpreted.

Docking and mutagenesis studies lead to improved inhibitor development of ML355 for human platelet 12-lipoxygenase

Human platelet 12-(S)-Lipoxygenase (12-LOX) is a fatty acid metabolizing oxygenase that plays an important role in platelet activation and cardiometabolic disease. ML355 is a specific 12-LOX inhibitor that has been shown to decrease thrombosis without prolonging hemostasis and protect human pancreatic islets from inflammatory injury. It has an amenable drug-like scaffold with nM potency and encouraging ADME and PK profiles, but its binding mode to the active site of 12-LOX remains unclear. In the current work, we combined computational modeling and experimental mutagenesis to propose a model in which ML355 conforms to the "U" shape of the 12-LOX active site, with the phenyl linker region wrapping around L407. The benzothiazole of ML355 extends into the bottom of the active site cavity, pointing towards residues A417 and V418. However, reducing the active site depth alone did not affect ML355 potency. In order to lower the potency of ML355, the cavity needed to be reduced in both length and width. In addition, H596 appears to position ML355 in the active site through an interaction with the 2-methoxy phenol moiety of ML355. Combined, this binding model suggested that the benzothiazole of ML355 could be enlarged. Therefore, a naphthyl-benzothiazole derivative of ML355, Lox12Slug001, was synthesized and shown to have 7.2-fold greater potency than ML355. This greater potency is proposed to be due to additional van der Waals interactions and pi-pi stacking with F414 and F352. Lox12Slug001 was also shown to be highly selective against 12-LOX relative to the other LOX isozymes and more importantly, it showed activity in rescuing human islets exposed to inflammatory cytokines with comparable potency to ML355. Further studies are currently being pursued to derivatize ML355 in order to optimize the additional space in the active site, while maintaining acceptable drug-like properties.

Kinetic and structural investigations of novel inhibitors of human epithelial 15-lipoxygenase-2

Human epithelial 15-lipoxygenase-2 (h15-LOX-2, ALOX15B) is expressed in many tissues and has been implicated in atherosclerosis, cystic fibrosis and ferroptosis. However, there are few reported potent/selective inhibitors that are active ex vivo. In the current work, we report newly discovered molecules that are more potent and structurally distinct from our previous inhibitors, MLS000545091 and MLS000536924 (Jameson et al, PLoS One, 2014, 9, e104094), in that they contain a central imidazole ring, which is substituted at the 1-position with a phenyl moiety and with a benzylthio moiety at the 2-position. The initial three molecules were mixed-type, non-reductive inhibitors, with IC₅₀ values of 0.34 ± 0.05 μM for MLS000327069, 0.53 ± 0.04 μM for MLS000327186 and 0.87 ± 0.06 μM for MLS000327206 and greater than 50-fold selectivity versus h5-LOX, h12-LOX, h15-LOX-1, COX-1 and COX-2. A small set of focused analogs was synthesized to demonstrate the validity of the hits. In addition, a binding model was developed for the three imidazole inhibitors based on computational docking and a co-structure of h15-LOX-2 with MLS000536924. Hydrogen/deuterium exchange (HDX) results indicate a similar binding mode between MLS000536924 and MLS000327069, however, the latter restricts protein motion of helix-α2 more, consistent with its greater potency. Given these results, we designed, docked, and synthesized novel inhibitors of the imidazole scaffold and confirmed our binding mode hypothesis. Importantly, four of the five inhibitors mentioned above are active in an h15-LOX-2/HEK293 cell assay and thus they could be important tool compounds in gaining a better understanding of h15-LOX-2's role in human biology. As such, a suite of similar pharmacophores that target h15-LOX-2 both in vitro and ex vivo are presented in the hope of developing them as therapeutic agents.

Synthesis and molecular targets of N-13-hydroxy-octadienoyl-ethanolamine, a novel endogenous bioactive 15-lipoxygenase-derived metabolite of N-linoleoyl-ethanolamine found in the skin and saliva

N-Arachidonoyl-ethanolamine (AEA) is an endocannabinoid (eCB) and endogenous lipid mimicking many of the effects of Δ9-tetrahydrocannabinol, notably on brain functions, appetite, pain and inflammation. The eCBs and eCB-like compounds contain fatty acids, the main classes being the monoacylglycerols and the N-acyl-ethanolamines (NAEs). Thus, each long chain fatty acid likely exists under the form of a monoacylglycerol and NAE, as it is the case for arachidonic acid (AA) and linoleic acid (LA). Following their biosynthesis, AA and AEA can be further metabolized into additional eicosanoids, notably by the 15-lipoxygenase pathway. Thus, we postulated that NAEs possessing a 1Z,4Z-pentadiene motif, near their omega end, would be transformed into their 15-lipoxygenase metabolites. As a proof of concept, we investigated N-linoleoyl-ethanolamine (LAE). We successfully synthesized LEA and LEA-d4 as well as their 15-lipoxygenase-derived derivatives, namely 13-hydroxy-9Z,11E-octadecadienoyl-N-ethanolamine (13-HODE-EA) and 13-HODE-EA-d4, using Novozyme 435 immobilized on acrylic resin and soybean lipoxygenase respectively. We also show that both human 15-lipoxygenase-1 and -2 can biosynthesize 13-HODE-EA. Co-incubation of LEA and LA with either human 15-lipoxygenase led to the biosynthesis of 13-HODE-EA and 13-HODE in a ratio equal to or greater than 3:1, indicating that LEA is preferred to LA by these enzymes. Finally, we show that 13-HODE-EA is found in human saliva and skin and is a weak although selective TRPV1 agonist. The full biological importance of 13-HODE-EA remains to be explored.

In Vitro Biosynthetic Pathway Investigations of Neuroprotectin D1 (NPD1) and Protectin DX (PDX) by Human 12-Lipoxygenase, 15-Lipoxygenase-1, and 15-Lipoxygenase-2

In this paper, human platelet 12-lipoxygenase [h12-LOX (ALOX12)], human reticulocyte 15-lipoxygenase-1 [h15-LOX-1 (ALOX15)], and human epithelial 15-lipoxygenase-2 [h15-LOX-2 (ALOX15B)] were observed to react with docosahexaenoic acid (DHA) and produce 17S-hydroperoxy-4Z,7Z,10Z,13Z,15E,19Z-docosahexaenoic acid (17S-HpDHA). The kcat/KM values with DHA for h12-LOX, h15-LOX-1, and h15-LOX-2 were 12, 0.35, and 0.43 s-1 μM-1, respectively, which demonstrate h12-LOX as the most efficient of the three. These values are comparable to their counterpart kcat/KM values with arachidonic acid (AA), 14, 0.98, and 0.24 s-1 μM-1, respectively. Comparison of their product profiles with DHA demonstrates that the three LOX isozymes produce 11S-HpDHA, 14S-HpDHA, and 17S-HpDHA, to varying degrees, with 17S-HpDHA being the majority product only for the 15-LOX isozymes. The effective kcat/KM values (kcat/KM × percent product formation) for 17S-HpDHA of the three isozymes indicate that the in vitro value of h12-LOX was 2.8-fold greater than that of h15-LOX-1 and 1.3-fold greater than that of h15-LOX-2. 17S-HpDHA was an effective substrate for h12-LOX and h15-LOX-1, with four products being observed under reducing conditions: protectin DX (PDX), 16S,17S-epoxy-4Z,7Z,10Z,12E,14E,19Z-docosahexaenoic acid (16S,17S-epoxyDHA), the key intermediate in neuroprotection D1 biosynthesis [NPD1, also known as protectin D1 (PD1)], 11,17S-diHDHA, and 16,17S-diHDHA. However, h15-LOX-2 did not react with 17-HpDHA. With respect to their effective kcat/KM values, h12-LOX was markedly less effective than h15-LOX-1 in reacting with 17S-HpDHA, with a 55-fold lower effective kcat/KM in producing 16S,17S-epoxyDHA and a 27-fold lower effective kcat/KM in generating PDX. This is the first direct demonstration of h15-LOX-1 catalyzing this reaction and reveals an in vitro pathway for PDX and NPD1 intermediate biosynthesis. In addition, epoxide formation from 17S-HpDHA and h15-LOX-1 was negatively affected via allosteric regulation by 17S-HpDHA (Kd = 5.9 μM), 12S-hydroxy-5Z,8Z,10E,14Z-eicosatetraenoic acid (12S-HETE) (Kd = 2.5 μM), and 17S-hydroxy-13Z,15E,19Z-docosatrienoic acid (17S-HDTA) (Kd = 1.4 μM), suggesting a possible regulatory pathway in reducing epoxide formation. Finally, 17S-HpDHA and PDX inhibited platelet aggregation, with EC50 values of approximately 1 and 3 μM, respectively. The in vitro results presented here may help advise in vivo PDX and NPD1 intermediate (i.e., 16S,17S-epoxyDHA) biosynthetic investigations and support the benefits of DHA rich diets.

Iron Complexes of Flavonoids-Antioxidant Capacity and Beyond

Flavonoids are common plant natural products able to suppress ROS-related damage and alleviate oxidative stress. One of key mechanisms, involved in this phenomenon is chelation of transition metal ions. From a physiological perspective, iron is the most significant transition metal, because of its abundance in living organisms and ubiquitous involvement in redox processes. The chemical, pharmaceutical, and biological properties of flavonoids can be significantly affected by their interaction with transition metal ions, mainly iron. In this review, we explain the interaction of various flavonoid structures with Fe(II) and Fe(III) ions and critically discuss the influence of chelated ions on the flavonoid biochemical properties. In addition, specific biological effects of their iron metallocomplexes, such as the inhibition of iron-containing enzymes, have been included in this review.

Synthesis of a new zinc phthalocyanine–benzoquinone rigid dyad

A new zinc phthalocyanine–benzoquinone rigid dyad, QnZnPc–G[Formula: see text] was synthesized as a model compound to study photo-induced charge separation mimicking natural photosynthesis. Compared to its previously reported analog, this dyad has an additional fused benzene ring between the zinc phthalocyanine (ZnPc) (donor) and benzoquinone (acceptor) moieties. The rigid structure of QnZnPc–G[Formula: see text] ([Formula: see text] no rotamers) is designed to minimize the unusual electronic perturbation induced by the internal motions, which resulted in a significant increase in the lifetime of the charged separated state (from 40 ps to 252 ps). Physical and photochemical properties of this new dyad were examined and discussed in this paper.

Rapid identification model based on decision tree algorithm coupling with 1H NMR and feature analysis by UHPLC-QTOFMS spectrometry for sandalwood

Sandalwood is one of the most valuable woods in the world. However, today's counterfeits are widespread, it is difficult to distinguish authenticity. In this paper, similar genus (Dalbergia and Pterocarpus) and confused species (Gluta sp.) of sandalwood were quickly and efficiently identified. Rapid identification model based on ¹H NMR and decision tree (DT) algorithm was firstly developed for the identification of sandalwood, and the accuracy was improved by introducing the AdaBoost algorithm. The accuracy of the final model was above 95%. And the feature components between different species of sandalwood were further explored using UHPLC-QTOFMS and NMR spectrometry. The results showed that 183 compounds were identified, among which 99 were known components, 84 were unknown components. The ¹H NMR and ¹³C NMR signals of 505 samples were assigned, among them, 14 compounds were attributed, characteristic chemical shift intervals with great differences in the model were analysed. Furthermore, the fragmentation pattern of different compounds from sandalwood, in both positive and negative ion ESI modes, was summarized. The results showed a potential and rapid tool based on DT, NMR spectroscopy and UHPLC-QTOFMS, which had performed great potential for rapid identification and feature analysis of sandalwood.

Comprehensive quality evaluation of Lignum Caraganae and rapid discrimination of Caragana jubata and Caragana changduensis based on characteristic compound fingerprints by HPLC-UV and HPLC-MS/MS coupled with chemometrics analysis

INTRODUCTION

Caragana jubata Poir (CJ) and Caragana changduensis Liou f. (CC) are the two main original plants of Lignum Caraganae (LIC, a clinically effective Tibetan materia medica) and the red heartwoods of CJ and CC have been used for the treatment of polycythemia, hypertension and menstrual disorders.

OBJECTIVE

To establish a comprehensive method for rapid quality assessment of LIC based on revealing the characteristic components of LIC and to discriminate the plant sources and LIC from its adulterations.

METHODOLOGY

A multi-index and synthetically balanced orthogonal design L₉ (3⁴ ) experiment was performed to obtain an efficient ultrasonic extraction condition of LIC sample. High-performance liquid chromatography coupled with an ultraviolet detector (HPLC-UV) techniques were developed for fingerprinting and quantitative analysis of 14 major compounds in LIC, and the main components were identified by HPLC tandem mass spectrometry (HPLC-MS/MS). HPLC fingerprint and chemometrics analysis were employed to visualise the distinction and relationship of LIC obtained from CJ and CC and to determine their potential characteristic markers.

RESULTS

Fourteen compounds including a new compound were identified and quantified in LIC. The potential characteristic markers in LIC were identified based on qualitative and fingerprint analysis. The hierarchical cluster analysis (HCA) and principle component analysis (PCA) showed obvious discrimination between LIC obtained from CJ and CC. Five batches of LIC samples were authenticated, and its adulterations were successfully found.

CONCLUSION

A facile HPLC combined with fingerprint and chemometrics methods could rapidly evaluate the quality of LIC and discriminate LIC obtained from CJ and CC.

Nordihydroguaiaretic Acid: From Herbal Medicine to Clinical Development for Cancer and Chronic Diseases

Nordihydroguaiaretic acid (NDGA) is a phenolic lignan obtained from Larrea tridentata, the creosote bush found in Mexico and USA deserts, that has been used in traditional medicine for the treatment of numerous diseases such as cancer, renal, cardiovascular, immunological, and neurological disorders, and even aging. NDGA presents two catechol rings that confer a very potent antioxidant activity by scavenging oxygen free radicals and this may explain part of its therapeutic action. Additional effects include inhibition of lipoxygenases (LOXs) and activation of signaling pathways that impinge on the transcription factor Nuclear Factor Erythroid 2-related Factor (NRF2). On the other hand, the oxidation of the catechols to the corresponding quinones my elicit alterations in proteins and DNA that raise safety concerns. This review describes the current knowledge on NDGA, its targets and side effects, and its synthetic analogs as promising therapeutic agents, highlighting their mechanism of action and clinical projection towards therapy of neurodegenerative, liver, and kidney disease, as well as cancer.

Role of the 12-lipoxygenase pathway in diabetes pathogenesis and complications

12-lipoxygenase (12-LOX) is one of several enzyme isoforms responsible for the metabolism of arachidonic acid and other poly-unsaturated fatty acids to both pro- and anti-inflammatory lipid mediators. Mounting evidence has shown that 12-LOX plays a critical role in the modulation of inflammation at multiple checkpoints during diabetes development. Due to this, interventions to limit pro-inflammatory 12-LOX metabolites either by isoform-specific 12-LOX inhibition, or by providing specific fatty acid substrates via dietary intervention, has the potential to significantly and positively impact health outcomes of patients living with both type 1 and type 2 diabetes. To date, the development of truly specific and efficacious inhibitors has been hampered by homology of LOX family members; however, improvements in high throughput screening have improved the inhibitor landscape. Here, we describe the function and role of human 12-LOX, and mouse 12-LOX and 12/15-LOX, in the development of diabetes and diabetes-related complications, and describe promise in the development of strategies to limit pro-inflammatory metabolites, primarily via new small molecule 12-LOX inhibitors.

Computational Analysis of LOX1 Inhibition Identifies Descriptors Responsible for Binding Selectivity

Lipoxygenases are a family of cytosolic, peripheral membrane enzymes, which catalyze the hydroperoxidation of polyunsaturated fatty acids and are implicated in the pathogenesis of major human diseases. Over the years, a substantial number of scientific reports have introduced inhibitors active against one or another subtype of the enzyme, but the selectivity issue has proved to be a major challenge for drug design. In the present work, we assembled a dataset of 317 structurally diverse molecules hitherto reported as active against 15S-LOX1, 12S-LOX1, and 15S-LOX2 and identified, using supervised machine learning, a set of structural descriptors responsible for the binding selectivity toward the enzyme 15S-LOX1. We subsequently incorporated these descriptors in the training of QSAR models for LOX1 activity and selectivity. The best performing classifiers are two stacked models that include an ensemble of support vector machine, random forest, and k-nearest neighbor algorithms. These models not only can predict LOX1 activity/inactivity but also can discriminate with high accuracy between molecules that exhibit selective activity toward either one of the isozymes 15S-LOX1 and 12S-LOX1.

Successful Identification of Cardiac Troponin Calcium Sensitizers Using a Combination of Virtual Screening and ROC Analysis of Known Troponin C Binders

Calcium-dependent cardiac muscle contraction is regulated by the protein complex troponin. Calcium binds to the N-terminal domain of troponin C (cNTnC) which initiates the process of contraction. Heart failure is a consequence of a disruption of this process. With the prevalence of this condition, a strong need exists to find novel compounds to increase the calcium sensitivity of cNTnC. Desirable are small chemical molecules that bind to the interface between cTnC and the cTnI switch peptide and exhibit calcium sensitizing properties by possibly stabilizing cTnC in an open conformation. To identify novel drug candidates, we employed a structure-based drug discovery protocol that incorporated the use of a relaxed complex scheme (RCS). In preparation for the virtual screening, cNTnC conformations were identified based on their ability to correctly predict known cNTnC binders using a receiver operating characteristics analysis. Following a virtual screen of the National Cancer Institute's Developmental Therapeutic Program database, a small number of molecules were experimentally tested using stopped-flow kinetics and steady-state fluorescence titrations. We identified two novel compounds, 3-(4-methoxyphenyl)-6,7-chromanediol (NSC600285) and 3-(4-methylphenyl)-7,8-chromanediol (NSC611817), that show increased calcium sensitivity of cTnC in the presence of the regulatory domain of cTnI. The effects of NSC600285 and NSC611817 on the calcium dissociation rate was stronger than that of the known calcium sensitizer bepridil. Thus, we identified a 3-phenylchromane group as a possible key pharmacophore in the sensitization of cardiac muscle contraction. Building on this finding is of interest to researchers working on development of drugs for calcium sensitization.

Anti-inflammatory Activity of Natural Geranylated Flavonoids: Cyclooxygenase and Lipoxygenase Inhibitory Properties and Proteomic Analysis

Geranyl flavones have been studied as compounds that potentially can be developed as anti-inflammatory agents. A series of natural geranylated flavanones was isolated from Paulownia tomentosa fruits, and these compounds were studied for their anti-inflammatory activity and possible mechanism of action. Two new compounds were characterized [paulownione C (17) and tomentodiplacone O (20)], and all of the isolated derivatives were assayed for their ability to inhibit cyclooxygenases (COX-1 and COX-2) and 5-lipoxygenase (5-LOX). The compounds tested showed variable degrees of activity, with several of them showing activity comparable to or greater than the standards used in COX-1, COX-2, and 5-LOX assays. However, only the compound tomentodiplacone O (20) showed more selectivity against COX-2 versus COX-1 when compared with ibuprofen. The ability of the test compounds to interact with the above-mentioned enzymes was supported by docking studies, which revealed the possible incorporation of selected test substances into the active sites of these enzymes. Furthermore, one of the COX/LOX dual inhibitors, diplacone (14) (a major geranylated flavanone of P. tomentosa), was studied in vitro to obtain a proteomic overview of its effect on inflammation in LPS-treated THP-1 macrophages, supporting its previously observed anti-inflammatory activity and revealing the mechanism of its anti-inflammatory effect.

Bioactive Flavonoids and Catechols as Hif1 and Nrf2 Protein Stabilizers - Implications for Parkinson's Disease

Flavonoids are known to trigger the intrinsic genetic adaptive programs to hypoxic or oxidative stress via estrogen receptor engagement or upstream kinase activation. To reveal specific structural requirements for direct stabilization of the transcription factors responsible for triggering the antihypoxic and antioxidant programs, we studied flavones, isoflavones and catechols including dihydroxybenzoate, didox, levodopa, and nordihydroguaiaretic acid (NDGA), using novel luciferase-based reporters specific for the first step in HIF1 or Nrf2 protein stabilization. Distinct structural requirements for either transcription factor stabilization have been found: as expected, these requirements for activation of HIF ODD-luc reporter correlate with in silico binding to HIF prolyl hydroxylase. By contrast, stabilization of Nrf2 requires the presence of 3,4-dihydroxy- (catechol) groups. Thus, only some but not all flavonoids are direct activators of the hypoxic and antioxidant genetic programs. NDGA from the Creosote bush resembles the best flavonoids in their ability to directly stabilize HIF1 and Nrf2 and is superior with respect to LOX inhibition thus favoring this compound over others. Given much higher bioavailability and stability of NDGA than any flavonoid, NDGA has been tested in a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-animal model of Parkinson's Disease and demonstrated neuroprotective effects.

Biochemical and Cellular Characterization and Inhibitor Discovery of Pseudomonas aeruginosa 15-Lipoxygenase

Pseudomonas aeruginosa is an opportunistic pathogen that can cause nosocomial and chronic infections in immunocompromised patients. P. aeruginosa secretes a lipoxygenase, LoxA, but the biological role of this enzyme is currently unknown. LoxA is poorly similar in sequence to both soybean LOX-1 (s15-LOX-1) and human 15-LOX-1 (37 and 39%, respectively) yet has kinetics comparably fast versus those of s15-LOX-1 (at pH 6.5, Kcat = 181 ± 6 s(-1) and Kcat/KM = 16 ± 2 μM(-1) s(-1)). LoxA is capable of efficiently catalyzing the peroxidation of a broad range of free fatty acid (FA) substrates (e.g., AA and LA) with high positional specificity, indicating a 15-LOX. Its mechanism includes hydrogen atom abstraction [a kinetic isotope effect (KIE) of >30], yet LoxA is a poor catalyst against phosphoester FAs, suggesting that LoxA is not involved in membrane decomposition. LoxA also does not react with 5- or 15-HETEs, indicating poor involvement in lipoxin production. A LOX high-throughput screen of the LOPAC library yielded a variety of low-micromolar inhibitors; however, none selectively targeted LoxA over the human LOX isozymes. With respect to cellular activity, the level of LoxA expression is increased when P. aeruginosa undergoes the transition to a biofilm mode of growth, but LoxA is not required for biofilm growth on abiotic surfaces. However, LoxA does appear to be required for biofilm growth in association with the host airway epithelium, suggesting a role for LoxA in mediating bacterium-host interactions during colonization.

Use of Bromine and Bromo-Organic Compounds in Organic Synthesis

Bromination is one of the most important transformations in organic synthesis and can be carried out using bromine and many other bromo compounds. Use of molecular bromine in organic synthesis is well-known. However, due to the hazardous nature of bromine, enormous growth has been witnessed in the past several decades for the development of solid bromine carriers. This review outlines the use of bromine and different bromo-organic compounds in organic synthesis. The applications of bromine, a total of 107 bromo-organic compounds, 11 other brominating agents, and a few natural bromine sources were incorporated. The scope of these reagents for various organic transformations such as bromination, cohalogenation, oxidation, cyclization, ring-opening reactions, substitution, rearrangement, hydrolysis, catalysis, etc. has been described briefly to highlight important aspects of the bromo-organic compounds in organic synthesis.

A potent and selective inhibitor targeting human and murine 12/15-LOX

Human reticulocyte 12/15-lipoxygenase (h12/15-LOX) is a lipid-oxidizing enzyme that can directly oxidize lipid membranes in the absence of a phospholipase, leading to a direct attack on organelles, such as the mitochondria. This cytotoxic activity of h12/15-LOX is up-regulated in neurons and endothelial cells after a stroke and thought to contribute to both neuronal cell death and blood-brain barrier leakage. The discovery of inhibitors that selectively target recombinant h12/15-LOX in vitro, as well as possessing activity against the murine ortholog ex vivo, could potentially support a novel therapeutic strategy for the treatment of stroke. Herein, we report a new family of inhibitors discovered in a High Throughput Screen (HTS) that are selective and potent against recombinant h12/15-LOX and cellular mouse 12/15-LOX (m12/15-LOX). MLS000099089 (compound 99089), the parent molecule, exhibits an IC50 potency of 3.4±0.5 μM against h12/15-LOX in vitro and an ex vivo IC50 potency of approximately 10 μM in a mouse neuronal cell line, HT-22. Compound 99089 displays greater than 30-fold selectivity versus h5-LOX and COX-2, 15-fold versus h15-LOX-2 and 10-fold versus h12-LOX, when tested at 20 μM inhibitor concentration. Steady-state inhibition kinetics reveals that the mode of inhibition of 99089 against h12/15-LOX is that of a mixed inhibitor with a Kic of 1.0±0.08 μM and a Kiu of 6.0±3.3 μM. These data indicate that 99089 and related derivatives may serve as a starting point for the development of anti-stroke therapeutics due to their ability to selectively target h12/15-LOX in vitro and m12/15-LOX ex vivo.

An insight into the potentially old-wonder molecule-quercetin: the perspectives in foresee

Use of phyto-medicine and digitalization of phyto-compounds has been fallen enthralling field of science in recent years. Quercetin, a flavonoid with brilliant citron yellow pigment, is typically found in fruits and leafy vegetables in reasonable amount. Quercetin's potentials as an antioxidant, immune-modulator, antiinflammatory, anti-cancer, and others have been the subject of interest in this review. Although, profiling the insights in to the molecular characterization of quercetin with various targets provided the loop-holes in understanding the knowledge for the aforementioned mechanisms, still necessitates research globally to unearth it completely. Thus, the available science on the synthesis and significant role played by the old molecule - quercetin which does wonders even now have been vividly explained in the present review to benefit the scientific community.

Ameliorating role of rutin on oxidative stress induced by iron overload in hepatic tissue of rats

Iron is an essential element that participates in several metabolic activities of cells; however, excess iron is a major cause of iron-induced oxidative stress and several human diseases. Natural flavonoids, as rutin, are well-known antioxidants and could be efficient protective agents. Therefore, the present study was undertaken to evaluate the protective influence of rutin supplementation to improve rat antioxidant systems against IOL-induced hepatic oxidative stress. Sixty male albino rats were randomly divided to three equal groups. The first group, the control, the second group, iron overload group, the third group was used as iron overload+rutin group. Rats received six doses of ferric hydroxide polymaltose (100 mg kg(-1) b.wt.) as one dose every two days, by intraperitoneal injections (IP) and administrated rutin (50 mg kg(-1) b.wt.) as one daily oral dose until the sacrificed day. Blood samples for serum separation and liver tissue specimens were collected three times, after three, four and five weeks from the onset of the experiment. Serum iron profiles total iron, Total Iron Binding Capacity (TIBC), Unsaturated Iron Binding Capacity (UIBC), transferrin (Tf) and Transferrin Saturation% (TS%)}, ferritin, albumin, total Protein, total cholesterol, triacylglycerols levels and aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activities were determined. Moreover, total iron in the liver, L-malondialdehyde (L-MDA), glutathione (GSH), Nitric Oxide (NO) and Total Nucleic Acid (TNA) levels and glutathione peroxidase (GPx), catalase (CAT) and superoxide dismutase (SOD) activities were also determined. The obtained results revealed that, iron overload (IOL) resulted in significant increase in serum iron, TIBC, Tf, TS% and ferritin levels and AST and ALT activities and also increased liver iron, L-MDA and NO levels. Meanwhile, it decreased serum UIBC, total cholesterol, triacylglycerols, albumin, total protein and liver GSH, TNA levels and Gpx, CAT and SOD activities when compared with the control group. Rutin administration to iron-overloaded rats resulted in significant decrease in serum total iron, TIBC, Tf, TS%, ferritin levels and AST and ALT activities and liver total iron, L-MDA and NO levels with significant increases in serum UIBC, albumin, total protein and total cholesterol levels and in liver GSH, CAT and SOD activities compared with the IOL group. This study provides in vivo evidence that rutin administration can improve the antioxidant defense systems against IOL-induced hepatic oxidative stress in rats. This protective effect in liver of iron-loaded rats may be due to both antioxidant and metal chelation activities.

Minireview: 12-Lipoxygenase and Islet β-Cell Dysfunction in Diabetes

The insulin producing islet β-cells have increasingly gained attention for their role in the pathogeneses of virtually all forms of diabetes. Dysfunction, de-differentiation, and/or death of β-cells are pivotal features in the transition from normoglycemia to hyperglycemia in both animal models of metabolic disease and humans. In both type 1 and type 2 diabetes, inflammation appears to be a central cause of β-cell derangements, and molecular pathways that modulate inflammation or the inflammatory response are felt to be prime targets of future diabetes therapy. The lipoxygenases (LOs) represent a class of enzymes that oxygenate cellular polyunsaturated fatty acids to produce inflammatory lipid intermediates that directly and indirectly affect cellular function and survival. The enzyme 12-LO is expressed in all metabolically active tissues, including pancreatic islets, and has received increasing attention for its role in promoting cellular inflammation in the setting of diabetes. Genetic deletion models of 12-LO in mice reveal striking protection from metabolic disease and its complications and an emerging body of literature has implicated its role in human disease. This review focuses on the evidence supporting the proinflammatory role of 12-LO as it relates to islet β-cells, and the potential for 12-LO inhibition as a future avenue for the prevention and treatment of metabolic disease.

Enzymatic Studies of Isoflavonoids as Selective and Potent Inhibitors of Human Leukocyte 5-Lipo-Oxygenase

Continuing our search to find more potent and selective 5-LOX inhibitors, we present now the enzymatic evaluation of seventeen isoflavones (IR) and nine isoflavans (HIR), and their in vitro and in cellulo potency against human leukocyte 5-LOX. Of the 26 compounds tested, 10 isoflavones and 9 isoflavans possessed micromolar potency, but only three were selective against 5-LOX (IR-2, HIR-303, and HIR-309), with IC50 values at least 10 times lower than those of 12-LOX, 15-LOX-1, and 15-LOX-2. Of these three, IR-2 (6,7-dihydroxy-4-methoxy-isoflavone, known as texasin) was the most selective 5-LOX inhibitor, with over 80-fold potency difference compared with other isozymes; Steered Molecular Dynamics (SMD) studies supported these findings. The presence of the catechol group on ring A (6,7-dihydroxy versus 7,8-dihydroxy) correlated with their biological activity, but the reduction of ring C, converting the isoflavones to isoflavans, and the substituent positions on ring B did not affect their potency against 5-LOX. Two of the most potent/selective inhibitors (HIR-303 and HIR-309) were reductive inhibitors and were potent against 5-LOX in human whole blood, indicating that isoflavans can be potent and selective inhibitors against human leukocyte 5-LOX in vitro and in cellulo.

A high throughput screen identifies potent and selective inhibitors to human epithelial 15-lipoxygenase-2

Lipoxygenase (LOX) enzymes catalyze the hydroperoxidation of arachidonic acid and other polyunsaturated fatty acids to hydroxyeicosatetraenoic acids with varying positional specificity to yield important biological signaling molecules. Human epithelial 15­lipoxygenase­2 (15-LOX-2) is a highly specific LOX isozyme that is expressed in epithelial tissue and whose activity has been correlated with suppression of tumor growth in prostate and other epithelial derived cancers. Despite the potential utility of an inhibitor to probe the specific role of 15-LOX-2 in tumor progression, no such potent/specific 15­LOX­2 inhibitors have been reported to date. This study employs high throughput screening to identify two novel, specific 15­LOX­2 inhibitors. MLS000545091 is a mixed-type inhibitor of 15-LOX-2 with a K_i of 0.9+/−0.4 µM and has a 20-fold selectivity over 5-LOX, 12-LOX, 15-LOX-1, COX-1, and COX-2. MLS000536924 is a competitive inhibitor with a K_i of 2.5+/−0.5 µM and also possesses 20-fold selectivity toward 15-LOX-2 over the other oxygenases, listed above. Finally, neither compound possesses reductive activity towards the active-site ferrous ion.

Inhibitory and mechanistic investigations of oxo-lipids with human lipoxygenase isozymes

Oxo-lipids, a large family of oxidized human lipoxygenase (hLOX) products, are of increasing interest to researchers due to their involvement in different inflammatory responses in the cell. Oxo-lipids are unique because they contain electrophilic sites that can potentially form covalent bonds through a Michael addition mechanism with nucleophilic residues in protein active sites and thus increase inhibitor potency. Due to the resemblance of oxo-lipids to LOX substrates, the inhibitor potency of 4 different oxo-lipids; 5-oxo-6,8,11,14-(E,Z,Z,Z)-eicosatetraenoic acid (5-oxo-ETE), 15-oxo-5,8,11,13-(Z,Z,Z,E)-eicosatetraenoic acid (15-oxo-ETE), 12-oxo-5,8,10,14-(Z,Z,E,Z)-eicosatetraenoic acid (12-oxo-ETE), and 13-oxo-9,11-(Z,E)-octadecadienoic acid (13-oxo-ODE) were determined against a library of LOX isozymes; leukocyte 5-lipoxygenase (h5-LOX), human reticulocyte 15-lipoxygenase-1 (h15-LOX-1), human platelet 12-lipoxygenase (h12-LOX), human epithelial 15-lipoxygenase-2 (h15-LOX-2), soybean 15-lipoxygenase-1 (s15-LOX-1), and rabbit reticulocyte 15-LOX (r15-LOX). 15-Oxo-ETE exhibited the highest potency against h12-LOX, with an IC₅₀=1 ± 0.1 μM and was highly selective. Steady state inhibition kinetic experiments determined 15-oxo-ETE to be a mixed inhibitor against h12-LOX, with a Kic value of 0.087 ± 0.008 μM and a Kiu value of 2.10 ± 0.8 μM. Time-dependent studies demonstrated irreversible inhibition with 12-oxo-ETE and h15-LOX-1, however, the concentration of 12-oxo-ETE required (Ki=36.8 ± 13.2 μM) and the time frame (k₂=0.0019 ± 0.00032 s(-1)) were not biologically relevant. These data are the first observations that oxo-lipids can inhibit LOX isozymes and may be another mechanism in which LOX products regulate LOX activity.

Potent and selective inhibitors of human reticulocyte 12/15-lipoxygenase as anti-stroke therapies

A key challenge facing drug discovery today is variability of the drug target between species, such as with 12/15-lipoxygenase (12/15-LOX), which contributes to ischemic brain injury, but its human and rodent isozymes have different inhibitor specificities. In the current work, we have utilized a quantitative high-throughput (qHTS) screen to identify compound 1 (ML351), a novel chemotype for 12/15-LOX inhibition that has nanomolar potency (IC₅₀ = 200 nM) against human 12/15-LOX and is protective against oxidative glutamate toxicity in mouse neuronal HT22 cells. In addition, it exhibited greater than 250-fold selectivity versus related LOX isozymes, was a mixed inhibitor, and did not reduce the active-site ferric ion. Lastly, 1 significantly reduced infarct size following permanent focal ischemia in a mouse model of ischemic stroke. As such, this represents the first report of a selective inhibitor of human 12/15-LOX with demonstrated in vivo activity in proof-of-concept mouse models of stroke.

Synthesis and structure-activity relationship studies of 4-((2-hydroxy-3-methoxybenzyl)amino)benzenesulfonamide derivatives as potent and selective inhibitors of 12-lipoxygenase

Human lipoxygenases (LOXs) are a family of iron-containing enzymes which catalyze the oxidation of polyunsaturated fatty acids to provide the corresponding bioactive hydroxyeicosatetraenoic acid (HETE) metabolites. These eicosanoid signaling molecules are involved in a number of physiologic responses such as platelet aggregation, inflammation, and cell proliferation. Our group has taken a particular interest in platelet-type 12-(S)-LOX (12-LOX) because of its demonstrated role in skin diseases, diabetes, platelet hemostasis, thrombosis, and cancer. Herein, we report the identification and medicinal chemistry optimization of a 4-((2-hydroxy-3-methoxybenzyl)amino)benzenesulfonamide-based scaffold. Top compounds, exemplified by 35 and 36, display nM potency against 12-LOX, excellent selectivity over related lipoxygenases and cyclooxygenases, and possess favorable ADME properties. In addition, both compounds inhibit PAR-4 induced aggregation and calcium mobilization in human platelets and reduce 12-HETE in β-cells.

Synthesis, docking study and relaxant effect of 2-alkyl and 2-naphthylchromones on rat aorta and guinea-pig trachea through phosphodiesterase inhibition

Chromone (4), which form the base structure of various flavonoids isolated as natural products, is capable of relaxing smooth muscle. This is relevant to the treatment of high blood pressure, asthma and chronic obstructive pulmonary disease. The former disorder involves the contraction of vascular smooth muscle (VSM), and the latter two bronchoconstriction of airway smooth muscle (ASM). One of the principal mechanisms by which flavonoids relax muscle tissue is the inhibition of phosphodiesterases (PDEs), present in both VSM and ASM. Therefore, a study was designed to analyze the structure-activity relationship of chromone derivatives in vaso- and bronchorelaxation through the inhibition of PDE. Docking studies showed that these chromones bind at the catalytic site of PDEs. Consequently, we synthesized analogs of chromones substituted at position C-2 with alkyl and naphthyl groups. These compounds were synthesized from 2-hydroxyacetophenone and acyl chlorides in the presence of DBU and pyridine, modifying the methodology reported for the synthesis of 3-acylchromones by changing the reaction temperature from 80 to 30°C and using methylene chloride as solvent, yielding the corresponding phenolic esters 10a-10h. These compounds were cyclized with an equivalent of DBU, pyridine as solvent, and heated at reflux temperature, yielding the chromones 11a-11h. Evaluation of the vasorelaxant effect of 4, 11a-11h on rat aorta demonstrated that potency decreases with branched alkyl groups. Whereas the EC50 of compound 11d (substituted by an n-hexyl group) was 8.64±0.39 μM, that of 11f (substituted by an isobutyl group) was 14.58±0.64 μM. Contrarily, the effectiveness of the compound is directly proportional to the length of the alkyl chain, as evidenced by the increase in maximal effect of compound 11c versus 11d (66% versus 100%) and 11e versus 11f (60% versus 96%). With an aromatic group like naphthyl as the C-2 substituent, the effectiveness was only 43%. All compounds tested on guinea pig trachea showed less than 55% effectiveness. Compounds 4, 11a-11h were evaluated as PDE inhibitors in vitro, with 11d showing the greatest effect (73%), corroborating the importance of a long alkyl chain, which inhibits the decomposition of cGMP. Docking studies showed that the compound 11d was selective for the inhibition of PDE-5.

Discovery of a novel dual fungal CYP51/human 5-lipoxygenase inhibitor: implications for anti-fungal therapy

We report the discovery of a novel dual inhibitor targeting fungal sterol 14α-demethylase (CYP51 or Erg11) and human 5-lipoxygenase (5-LOX) with improved potency against 5-LOX due to its reduction of the iron center by its phenylenediamine core. A series of potent 5-LOX inhibitors containing a phenylenediamine core, were synthesized that exhibit nanomolar potency and >30-fold selectivity against the LOX paralogs, platelet-type 12-human lipoxygenase, reticulocyte 15-human lipoxygenase type-1, and epithelial 15-human lipoxygenase type-2, and >100-fold selectivity against ovine cyclooxygenase-1 and human cyclooxygnease-2. The phenylenediamine core was then translated into the structure of ketoconazole, a highly effective anti-fungal medication for seborrheic dermatitis, to generate a novel compound, ketaminazole. Ketaminazole was found to be a potent dual inhibitor against human 5-LOX (IC₅₀ = 700 nM) and CYP51 (IC₅₀ = 43 nM) in vitro. It was tested in whole blood and found to down-regulate LTB4 synthesis, displaying 45% inhibition at 10 µM. In addition, ketaminazole selectively inhibited yeast CYP51 relative to human CYP51 by 17-fold, which is greater selectivity than that of ketoconazole and could confer a therapeutic advantage. This novel dual anti-fungal/anti-inflammatory inhibitor could potentially have therapeutic uses against fungal infections that have an anti-inflammatory component.

Pseudoperoxidase investigations of hydroperoxides and inhibitors with human lipoxygenases

Understanding the mode of action for lipoxygenase (LOX) inhibitors is critical to determining their efficacy in the cell. The pseudoperoxidase assay is an important tool for establishing if a LOX inhibitor is reductive in nature, however, there have been difficulties identifying the proper conditions for each of the many human LOX isozymes. In the current paper, both the 234 nM decomposition (UV) and iron-xylenol orange (XO) assays are shown to be effective methods of detecting pseudoperoxidase activity for 5-LOX, 12-LOX, 15-LOX-1 and 15-LOX-2, but only if 13-(S)-HPODE is used as the hydroperoxide substrate. The AA products, 12-(S)-HPETE and 15-(S)-HPETE, are not consistent hydroperoxide substrates since they undergo a competing transformation to the di-HETE products. Utilizing the above conditions, the selective 12-LOX and 15-LOX-1 inhibitors, probes for diabetes, stroke and asthma, are characterized for their inhibitory nature. Interestingly, ascorbic acid also supports the pseudoperoxidase assay, suggesting that it may have a role in maintaining the inactive ferrous form of LOX in the cell. In addition, it is observed that nordihydroguaiaretic acid (NDGA), a known reductive LOX inhibitor, appears to generate radical species during the pseudoperoxidase assay, which are potent inhibitors against the human LOX isozymes, producing a negative pseudoperoxidase result. Therefore, inhibitors that do not support the pseudoperoxidase assay with the human LOX isozymes, should also be investigated for rapid inactivation, to clarify the negative pseudoperoxidase result.

Bioactivity-guided fractionation of the lipoxygenase and cyclooxygenase inhibiting constituents from Chisocheton polyandrus Merr

Lipoxygenase (LOX)-inhibiting compounds from the leaves of Chisocheton polyandrus Merr. were isolated in this study using a bioactivity-guided fractionation technique. Two dammarane triterpenoids, dammara-20,24-dien-3-one (1) (IC(50)=0.69±0.07 μM) and 24-hydroxydammara-20,25-dien-3-one (2) (IC(50)=1.11±0.38 μM), were isolated and identified based on the soybean LOX assay. Dammara-20,24-dien-3-one (1) exhibited dual inhibition of both human 5-LOX (IC(50)=24.27±2.92 μM) and cyclooxygenase-2 (COX-2) (IC(50)=3.17±0.90 μM), whereas 24-hydroxydammara-20,25-dien-3-one (2) did not exhibit any significant inhibitory effects. This report is the first to detail the inhibition of LOX and COX by both C. polyandrus and its isolated compounds.

A fluorimetric assay for human reticulocyte 15-lipoxygenase-1 activity

A rapid and sensitive fluorescence-based assay for the determination of human 15-lipoxygenase-1 (15-LOX-1) activity is described in this article. The assay utilizes the ability of 15-LOX-1-generated lipid hydroperoxides to oxidize nonfluorescent dihydrorhodamine 123, producing the highly fluorescent dye rhodamine 123. Formation of rhodamine 123 can be monitored through fluorescence spectroscopy using Ex/Em of 500 nm/536 nm. The IC(50) values of three well-known 15-LOX-1 inhibitors, nordihydroguaiaretic acid, quercetin, and fisetin, were evaluated in 96- and 384-well formats, and they conform to previously reported data. We believe this assay can be broadly used for the discovery of novel lipoxygenase inhibitors.