In-vitro evaluation of 5-lipoxygenase and cyclo-oxygenase inhibitors using bovine neutrophils and platelets and HPLC

Dihydroisocoumarins, Naphthalenes, and Further Polyketides from Aloe vera and A. plicatilis: Isolation, Identification and Their 5-LOX/COX-1 Inhibiting Potency

The present study aims at the isolation and identification of diverse phenolic polyketides from Aloe vera (L.) Burm.f. and Aloe plicatilis (L.) Miller and includes their 5-LOX/COX-1 inhibiting potency. After initial Sephadex-LH20 gel filtration and combined silica gel 60- and RP18-CC, three dihydroisocoumarins (nonaketides), four 5-methyl-8-C-glucosylchromones (heptaketides) from A. vera, and two hexaketide-naphthalenes from A. plicatilis have been isolated by means of HSCCC. The structures of all polyketides were elucidated by ESI-MS and 2D ¹H/¹³C-NMR (HMQC, HMBC) techniques. The analytical/preparative separation of 3R-feralolide, 3′-O-β-d-glucopyranosyl- and the new 6-O-β-d-glucopyranosyl-3R-feralolide into their respective positional isomers are described here for the first time, including the assignment of the 3R-configuration in all feralolides by comparative CD spectroscopy. The chromones 7-O-methyl-aloesin and 7-O-methyl-aloeresin A were isolated for the first time from A. vera, together with the previously described aloesin (syn. aloeresin B) and aloeresin D. Furthermore, the new 5,6,7,8-tetrahydro-1-O-β-d-glucopyranosyl- 3,6R-dihydroxy-8R-methylnaphtalene was isolated from A. plicatilis, together with the known plicataloside. Subsequently, biological-pharmacological screening was performed to identify Aloe polyketides with anti-inflammatory potential in vitro. In addition to the above constituents, the anthranoids (octaketides) aloe emodin, aloin, 6′-(E)-p-coumaroyl-aloin A and B, and 6′-(E)-p-coumaroyl-7-hydroxy-8-O-methyl-aloin A and B were tested. In the COX-1 examination, only feralolide (10 µM) inhibited the formation of MDA by 24%, whereas the other polyketides did not display any inhibition at all. In the 5-LOX-test, all aloin-type anthranoids (10 µM) inhibited the formation of LTB₄ by about 25–41%. Aloesin also displayed 10% inhibition at 10 µM in this in vitro setup, while the other chromones and naphthalenes did not display any activity. The present study, therefore, demonstrates the importance of low molecular phenolic polyketides for the known overall anti-inflammatory activity of Aloe vera preparations.

Evaluation of inhibitors of the arachidonic acid cascade with intact platelets using an on-line dilution and on-line solid phase extraction HPLC-MS method

An automatic on-line dilution/on-line solid phase extraction (SPE) system has been developed for the detection of metabolites of the arachidonic acid cascade in platelets. The method allows the direct injection of larger quantities of centrifugates from cell suspensions previously treated with an equal volume of an acetonitrile/methanol mixture for protein precipitation. The method was used to study the effect of inhibitors of platelet arachidonic acid cascade enzymes (cytosolic phospholipase A₂α, cyclooxygenase-1, thromboxane synthase, 12-lipoxygenase) and related targets (cyclooxygenase-2, microsomal prostaglandin E synthase-1, 5-lipoxygenase) in intact platelets after stimulation with calcium ionophore A23187. In addition to enzyme inhibition, the cell-damaging properties of the test compounds was determined by measuring the release of serotonin from the platelets into the incubation buffer.

Efficient synthesis and 5-LOX/COX-inhibitory activity of some 3-hydroxybenzo[b]thiophene-2-carboxylic acid derivatives

A series of 3-hydroxybenzo[b]thiophene-2-carboxylic acid derivatives has been prepared and subsequently evaluated with regards to the inhibition of 5-LOX/COX. Structure optimization furnished derivatives with promising in vitro activity as dual 5-LOX/COX inhibitors with submicromolar IC(50) values for inhibition of 5-LOX and COX-1, respectively.

Cyclooxygenase-2 inhibitors: a literature and patent review (2009 - 2010)

INTRODUCTION

COXs catalyze the complex conversion of arachidonic acid to prostaglandins and thromboxanes, which trigger as autacoids with autocrine and paracrine biological effects many physiological and pathophysiological responses. The structural similarities of the COX-1 and -2 enzymes make the search for selective inhibitors for COX-2 versus -1 a formidable challenge.

AREAS COVERED

The present review provides a survey of the development of novel COX-2 inhibitors covering literature and patents between 2009 and 2010. The presence of a central, typically 1,2-diaryl substituted, heterocycle or carbocycle as a characteristic structural motif in many selective COX-2 inhibitors represents the basis of their classification in this review. The classification in this review includes COX-2 inhibitors based on five- and six-membered heterocycles, benzoheterocycles (e.g., benzopyrans, benzopyranones, indoles and quinolines), quinones, chalcones, natural products and miscellaneous. When available, COX-2 inhibitors are presented with their related COX-2 inhibitory potency and selectivity.

EXPERT OPINION

The availability of detailed information on the crystal structure of the COX-2 enzyme with various substrates, cofactors and inhibitors, and the recently reported increased risk of cardiovascular events associated with selective COX-2 inhibitors will further stimulate development of COX-2 inhibitors with favorable COX-2 inhibition profiles without adverse effects to the cardiovascular system.

Diaryl-dithiolanes and -isothiazoles: COX-1/COX-2 and 5-LOX-inhibitory, *OH scavenging and anti-adhesive activities

Three series of non-steroidal anti-inflammatory drugs (NSAIDs) inhibiting the cyclooxygenase/5-lipoxygenase (COX/5-LOX) pathways as such as formation of hydroxyl radicals and adhesion were prepared: 4,5-diaryl isothiazoles, 4,5-diaryl 3H-1,2-dithiole-3-thiones and 4,5-diaryl 3H-1,2-dithiole-3-ones. The aim of the present study was to develop substances which can intervene into the inflammatory processes via different mechanisms of action as multiple target non-steroidal anti-inflammatory drugs (MTNSAIDs) with increased anti-inflammatory potential. The current lead 11a was evaluated in COX-1/2, 5-LOX and (*)OH scavenging in vitro assays and in a static adhesion assay where it proved to inhibit adhesion. Moreover, 11a treatment attenuated expression of macrophage adhesion molecule-1 (Mac-1) on extravasated polymorphonuclear leukocytes (PMNs) which indicates that the activation was reduced. The assays used are predictive for the in vivo efficacy of test compounds as shown for 11a in a peritonitis model of acute inflammation in mice. Thus, the novel 5-LOX/COX and (*)OH inhibitor 11a possesses anti-inflammatory activity that, in addition to COX/5-LOX inhibition, implicates effects on leukocyte-endothelial interactions.

Structure–activity relationship studies of 3-dodecanoylindole-2-carboxylic acid inhibitors of cytosolic phospholipase A2α-mediated arachidonic acid release in intact platelets: variation of the keto moiety

Recently we found that 1-methyldodecanoylindole-2-carboxylic acid (1) and 1-[2-(4-carboxyphenoxy)ethyl]-3-dodecanoylindole-2-carboxylic acid (4) were inhibitors of the cytosolic phospholipase A2alpha (cPLA2alpha)-mediated arachidonic acid release in calcium ionophore A23187-stimulated human platelets with IC50-values of 4.8 microM (1) and 0.86 microM (4). We have now replaced the 3-acyl residue of these compounds by alkylated sulfinyl-, sulfony-, sulfinamoyl-, sulfamoyl-, carbonylamino-, or carbonylaminomethyl-substituents. Structure-activity relationship studies revealed that the pronounced cellular activity of 4 strongly depends on the presence of the 3-acyl moiety. Surprisingly, when testing 4 and its derivatives in an assay with the isolated cPLA2, none of these compounds showed an inhibitory potency at 10 microM indicating that they do not inhibit cPLA2alpha in the cells by a direct interaction with the active site of the enzyme.

Investigations concerning the COX/5-LOX inhibiting and hydroxyl radical scavenging potencies of novel 4,5-diaryl isoselenazoles

The aim of this study was to investigate 4,5-diaryl isoselenazoles as multiple target non-steroidal anti-inflammatory drugs (MTNSAIDs) which can intervene into the inflammatory processes via different mechanisms of action creating a new class of compounds. Here we describe the synthesis of COX/LOX inhibitors which additionally reduce the level of reactive oxygen species, such as hydroxyl radicals which are well known for supporting inflammation processes in Parkinson's disease, Alzheimer's disease and rheumatoid arthritis.

Characterization of a Computerized Assay for Rapid and Easy Determination of Leukocyte Adhesion to Endothelial Cells

We report on a facile and rapid computerized in-vitro assay for the quantification of leukocyte adhesion to endothelial cells under static conditions using bovine polymorphonuclear neutrophils (PMN) or human leukaemic Mono Mac 6 cells (MM6) and bovine aorta endothelial cells (BAEC). Images of leukocytes adherent to BAEC monolayers grown in microtiter plates were obtained by a digital camera attached to a conventional microscope and transferred to the public domain NIH ImageJ program for analysis. Using individually adapted program routines adherent leukocytes are easily discriminated and reproducibly quantified. The results obtained with our assay correspond to previous findings and demonstrate the suitability of the described procedure, which can easily be adapted to further standards as proven by the use of two different leukocyte species. This assay lends itself to the screening of pharmacological substances with different mechanism of action that might act on either leukocytes or endothelial cells.

3-alkyl- and 3-aryl-(7-oxo-7H-furo[3, 2-g]chromen-5-yl)alkanoic acids as inhibitors of leukotriene B4 biosynthesis

The synthesis and biological properties of 3-alkyl-and 3-aryl-(7-oxo-7H-furo [3, 2-g]chromen-5-yl)alkanoic acids are described. The compounds were evaluated for their ability to inhibit soybean 15-lipoxygenase (15-LO) and the production of leukotriene B(4) (LTB(4)) in bovine polymorphonuclear leukocytes. The furocoumarins were further investigated for their lipophilicity and their capacity to photobleach N, N-dimethyl-p-nitrosoaniline (RNO) after irradiation with UVA light. The synthesised furocoumarins showed only a moderate ability to inhibit the 15-LO and the production of LT B(4). The 3-alkyl substituted furocoumarins had a higher capacity to photobleach RNO than then the 3-aryl substituted furocoumarinso. The inhibitory activity of the newcompounds was quite modest in comparison to other known inhibitors of 15-LO and LTB(4) production. Nevertheless, they may provide the basis for the development of more potent antiinflammatory potential photoreactive furocoumarins.

Convergent synthesis and preliminary biological evaluations of the stilbenolignan (+/-)-aiphanol and various congeners

Treatment of an equimolar mixture of stilbene 7 and cinnamyl alcohol 8 with silver carbonate in acetone-benzene afforded a ca. 2:1:2:1 mixture of the stilbenolignan (+/-)-aiphanol (1) and congeners 2-4 each of which show significant anti-angiogenic and COX-2 inhibitory properties.

Cyclooxygenase inhibitors--current status and future prospects

Prostaglandins are formed from arachidonic acid by the action of cyclooxygenase and subsequent downstream synthetases. Two closely related forms of the cyclooxygenase have been identified which are now known as COX-1 and COX-2. Both isoenzymes transform arachidonic acid to prostaglandins, but differ in their distribution and their physiological roles. Meanwhile, the responsible genes and their regulation have been clarified. COX-1, the pre-dominantly constitutive form of the enzyme, is expressed throughout the body and performs a number of homeostatic functions such as maintaining normal gastric mucosa and influencing renal blood flow and platelet aggregation. In contrast, the inducible form is expressed in response to inflammatory and other physiological stimuli and growth factors, and is involved in the production of the prostaglandins that mediate pain and support the inflammatory process. All the classic NSAIDs inhibit both COX-1 and COX-2 at standard anti-inflammatory doses. The beneficial anti-inflammatory and analgesic effects are based on the inhibition of COX-2, but the gastrointestinal toxicity and the mild bleeding diathesis are a result of the concurrent inhibition of COX-1. Agents that inhibit COX-2 while sparing COX-1 represent a new attractive therapeutic development and could represent a major advance in the treatment of rheumatoid arthritis and osteoarthritis. Apart from its involvement in inflammatory processes, COX-2 seems to play a role in angiogenesis, colon cancer and Alzheimer's disease, based on the fact that it is expressed during these diseases. The benefits of specific and selective COX-2 inhibitors are currently under discussion and offer a new perspective for a further use of COX-2 inhibitors.

Effect of flavonol derivatives on the carrageenin-induced paw edema in the rat and inhibition of cyclooxygenase-1 and 5-lipoxygenase in vitro

Alkoxyflavonols were synthesized by the Algar-Flynn-Oyamada (AFO) cyclization of chalcones. Hydroxyflavonols were prepared by dealkylation of methoxyflavonols by refluxing in hydroiodic acid. The alkoxyflavonols 3-hydroxy-2-(2,3,4-trimethoxyphenyl)-4H-chromen-4-one (6), 2-(4-ethoxyphenyl)-3-hydroxy-4H-chromen-4-one (7), 2-(4-butoxyphenyl)-3-hydroxy-4H-chromen-4-one (10), and 2-(3-n-butoxyphenyl)-3-hydroxy-4H-chromen-4-one (11) as well as the trihydroxy derivative 3-hydroxy-2-(3,4,5-trihydroxyphenyl)-4H-chromen-4-one (18) displayed high anti-inflammatory activity in carrageenin-induced rat paw edema. Additionally, the inhibition of enzymes of the arachidonic acid cascade by the derivatives was investigated in vitro. In contrast to the natural compound quercetin, the compounds were more potent inhibiting cyclooxygenase-1 than 5-lipoxygenase except for 3-hydroxy-7-methoxy-2-(4-methoxyphenyl)-4H-chromen-4-one (5). No correlation between the anti-inflammatory activity in the rat paw edema test and the inhibition of 5-lipoxygenase or cyclooxygenase-1 could be observed. In conclusion, the present results suggest that other effects than inhibition of these enzymes of the arachidonic acid cascade are important for the anti-inflammatory activity of the investigated alkoxyflavonols.

The pyrrole moiety as a template for COX-1/COX-2 inhibitors

Aroyl- and thiophene-substituted pyrrole derivatives have been synthesized as a new class of COX-1/COX-2 inhibitors. The inhibition of COX-1 was evaluated in a biological system using bovine PMNLs as the enzyme source, whereas LPS-stimulated human monocytes served as the enzyme source for inducible COX-2. The determination of the concentration of arachidonic acid metabolites was performed by HPLC for COX-1 and RIA for COX-2. Variation of the substitution pattern led to a series of active compounds which showed inhibition for COX-1 and COX-2. Structural requirements for the development of COX-1/COX-2 inhibitors are discussed.

Development and review of radioimmunoassay of 12-S-hydroxyheptadecatrienoic acid

For more than 25 years 12-S-hydroxyheptadecatrienoic acid (HHT) has been known to be a product of thromboxanesynthase (TX-Syn) when synthesized with thromboxane A2 (TXA2). Although there are some hints that HHT has anti-aggregatory effects, to date, it has neither been shown to have any specific pathological relevance nor is there much information about its physiological role. This review presents a summary of the physicochemical properties of HHT, its chemical synthesis, the impact of various biological systems on its enzymatic and non-enzymatic production and its physiological function and metabolization, as well as a survey of the most important methods for analyzing this unsaturated hydroxy-fatty acid. Due to the low antibody-raising potency expected in HHT, no immunological system for HHT quantification has been developed so far. In our report we present the development and validation of a sensitive and reliable, competitive radioimmunoassay (RIA) suitable for the quantitative determination of HHT. HHT was produced by an enhanced enzymatic method using platelet-rich plasma (PRP). With an effective and modified liquid-liquid and solid-phase extraction method we were able to produce highly purified HHT (97% purity by GC/MS) in sub-milligram ranges. These fractions were used for the synthesis of BSA-antigen-conjugates and for immunization of rabbits. The tritiated tracer was synthesized using prostaglandin H synthase for the production of prostaglandin H2 (PGH2) followed by an aqueous reaction with Fe(2+)-solution to rear-range PGH2 to HHT. The dynamic range of the assay was from 30-400 pg/tube, with a sensitivity of approximately 40 pg/tube. The evaluation of the assay was performed by a HPLC-RIA method as well as by correlation with a quantitative HPLC method and correlation with TXB2 concentrations in a blood coagulation study. The assay may be useful for the quantification of HHT in several tissues and body fluids under various physiological conditions and may also help to understand the possible physiological role of HHT in biological processes.

Synthesis and evaluation of a novel series of pyrrolizine derivatives as dual cyclooxygenase-1 and 5-lipoxygenase inhibitors

The aim of our study was to investigate structure activity relationship following the replacement of the 6-phenyl substituent at the 6,7-diaryl-2,3-dihydropyrrolizine template by various heteroaromatic residues. In this context we developed a new, efficient, and highly sensitive test method for the screening of dual cyclooxygenase-1 (COX-1) and 5-lipoxygenase (5-LOX) inhibitors. We used human platelets as a source of COX-1 and human PMNLs as a source of 5-LOX. Both cell types were isolated from the same volume of blood. PGE2 and LTB4 respectively were determined by highly selective and sensitive ELISA kits, using monoclonal antibodies. For a single determination at most 0.5 mL whole blood is needed.

Non-steroidal anti-inflammatory agents, Part 24. Pyrrolidino enaminones as models to mimic arachidonic acid

The pyrrolidino enaminones, with the carboxylic acid chain fixed at the nitrogen, inhibit cyclooxygenase more potently or selectively than 5-lipoxygenase. According to the structure-activity relationships discussed the potency depends significantly on the chain length of the carboxylic acid, the substitution pattern of the heterocyclic moiety and of the phenyl group. Compound 4c is the most efficient inhibitor of cyclooxygenase. For the binding profile the unfolded conformation of arachidonic acid and the energy-minimized conformations of flurbiprofen, diclofenac, ML 3000, and lead compound 4a were compared. In addition to known structural features, similar distances of the carboxylic acid function and the phenyl residue were found as hypothesized to explain the interaction with the active sites of the enzyme. The inhibition of cyclooxygenase was determined in a bovine thrombocyte intact cell assay and that of 5-lipoxygenase using intact bovine PMNLs.

Non-steroidal anti-inflammatory agents, Part 20. Method for testing non-steroidal anti-inflammatories: the modified hen's egg chorioallantoic membrane test (HET-CAM test) compared to other procedures

The delay of onset of irritation phenomena at the chorioallantoic membrane of incubated hen's eggs, a parameter for anti-inflammatory activity, was determined for the pharmaceutical substances diclofenac, flufenamic acid, ibuprofen, indomethacin, ketoprofen, piroxicam, phenylbutazone, salicylic acid, and sodium salicylate. Alongside questions relating to the dose-effect ratio, metabolisation, recovery, and diffusion of the substances to their site of action were investigated. The reproducibility of the procedure and its selectivity with regard to substances with a different mechanism of action is proven. The method allows classification of the substances according to their anti-inflammatory potency. However, correlation with the results of enzyme inhibition or in vivo results is only possible to a limited extent.

Effect of manoalide on human 5-lipoxygenase activity

The marine natural product manoalide (MLD) has been described to inactivate phospholipase A2 (PLA2) from several sources as well as to inhibit synthesis of eicosanoids in human polymorphonuclear leukocytes (HPMNL). MLD also reduces chemically-induced inflammation in vivo. In this investigation we have examined the effect of MLD on A23187-induced generation of leukotriene B4 (LTB4) and thromboxane B2 (TXB2) in HPMNL as well as 5-lipoxygenase (5-LO) activity from HPMNL sonicated preparations. In the intact cell system, MLD inhibited with similar potency biosynthesis of LTB4 and TXB2 (IC50 1.7 and 1.4 microM, respectively). In order to discern if inhibition of 5-LO is involved in the effect of MLD, we examined the action of this compound on 5-LO activity from 10,000 x g and 100,000 x g supernatants of sonicated HPMNL homogenates. The enzymatic activity was not affected at concentrations of MLD up to 50 microM. These data indicate that MLD is not a direct inhibitor of 5-LO activity from HPMNL and support the hypothesis that its anti-inflammatory action could be related with a reduction of eicosanoid biosynthesis via inhibition of PLA2.

2-Anthracenonyl acetic acids as 5-lipoxygenase inhibitors

The synthesis of 2-substituted anthracenonyl acetic acid (2-AA) derivatives is described. The key step is the Marschalk reaction of 1-hydroxy-8-methoxy-anthracenedione with glycolic acid. After protection of the resulting 2-anthracenonyl acetic acid derivative, the 2-monoalkylated derivatives are selectively obtained by direct alkylation. The methodology proves quite general and allows for the introduction of various substituents onto the 2-position of the carboxylic side chain. Reduction of the anthracenediones proceeds with concomitant protecting group removal and provides final 2-AA products in good yields. The results of initial biological studies demonstrate enhanced 5-lipoxygenase inhibition compared to anthralin.

Non-steroidal anti-inflammatory agents, Part 19. E-2-pyrrolizin-5-yl acrylic acids as potent dual or selective inhibitors of bovine cyclooxygenase and 5-lipoxygenase

The pyrrolizinyl substituted acrylic acid derivatives represent another class of dual and selective inhibitors of cyclooxygenase and 5-lipoxygenase. By modifying their substitution pattern at the phenyl moiety of C-6 the balance between the activity against cyclooxygenase and against 5-lipoxygenase can be shifted. Structure-activity relationships are discussed. Compound 6k is the most potent and well-balanced dual inhibitor of both enzymes, while the highest selectivity of lipoxygenase inhibition was found for 6j. The activity and selectivity of compounds with an additional sulfur moiety depend on the oxidation status of this atom, giving an indication of the discussed coupling between peroxidase and cyclooxygenase. The inhibition of cyclooxygenase was determined in a bovine thrombocyte intact cell assay and that of 5-lipoxygenase using intact bovine PMNLs.

Nonsteroidal antiinflammatory agents, XVIII: C-5 functionalized 6,7-diphenyl-2,3-dihydro-1H-pyrrolizines as inhibitors of bovine cyclooxygenase and 5-lipoxygenase

6-(4-Chlorophenyl)-7-phenyl-2,3-dihydro-1H-pyrrolizines with functional groups at position 5 of the heterocyclic moiety were synthesized and tested. To determine their antiinflammatory activity bovine blood was used as enzyme source for the cyclooxygenase and 5-lipoxygenase, respectively. The iminoxy acetic acid derivative and the iminotetrazole selectively inhibit the 5-lipoxygenase, all the other compounds show medium or low affinity to the active sites of cyclooxygenase and 5-lipoxygenase. In general all compounds inhibit 5-lipoxygenase more effectively than cyclooxygenase. Concerning the inhibition of 5-lipoxygenase the most active compounds found are equipotent to the corresponding propionic acid compounds, but they aren't well balanced dual inhibitors as shown for the carboxylic derivatives. A structure activity relationship and the enzyme selectivity are discussed.

Effects of oxygen radicals, hydrogen peroxide and water-soluble singlet oxygen carriers on 5- and 12-lipoxygenase

Inhibition of 5-lipoxygenase from bovine polymorphonuclear leukocytes and 12-lipoxygenase from bovine platelets by active oxygen species has been studied. Oxygen radicals and hydrogen peroxide markedly inhibited 12-lipoxygenase, whereas 5-lipoxygenase activity was only moderately influenced. Singlet oxygen liberated from water-soluble naphthalene endoperoxides was without effect.

Nonsteroidal antiinflammatory agents, XVII: Inhibition of bovine cyclooxygenase and 5-lipoxygenase by N-alkyldiphenyl-pyrrolyl acetic and propionic acid derivatives

A series of 19 N-alkyl-diarylpyrrolyl-acetic and-propionic acid derivatives was synthesized and tested. Using bovine blood as enzyme source the inhibition of cyclooxygenase and 5-lipoxygenase, respectively, was applied to determine the antiinflammatory activity. In general all compounds tested inhibit 5-lipoxygenase more effectively than cyclooxygenase. A structure-activity relationship is discussed.