Fatty Acid Binding to the Allosteric Subunit of Cyclooxygenase-2 Relieves a Tonic Inhibition of the Catalytic Subunit

Synthesis, molecular dynamics simulation, and evaluation of biological activity of novel flurbiprofen and ibuprofen-like compounds

The frequent use of anti-inflammatory drugs and the side effects of existing drugs keep the need for new compounds constant. For this purpose, flurbiprofen and ibuprofen-like compounds, which are frequently used anti-inflammatory compounds in this study, were synthesized and their structures were elucidated. Like ibuprofen and flurbiprofen, the compounds contain a residue of phenylacetic acid. On the other hand, it contains a secondary amine residue. Thus, it is planned to reduce the acidity, which is the biggest side effect of NSAI drugs, even a little bit. The estimated ADME parameters of the compounds were evaluated. Apart from internal use, local use of anti-inflammatory compounds is also very important. For this reason, the skin permeability values of the compounds were also calculated. And it has been found to be compatible with reference drugs. The COX enzyme inhibitory effects of the obtained compounds were tested by in vitro experiments. Compound 2a showed significant activity against COX-1 enzyme with an IC50 = 0.123 + 0.005 μM. The interaction of the compound with the enzyme active site was clarified by molecular dynamics studies.

Bioisoteres for carboxylic acids: From ionized isosteres to novel unionized replacements

Carboxylic acids are key pharmacophoric elements in many molecules. They can be seen as a problem by some, due to perceived permeability challenges, potential for high plasma protein binding and the risk of forming reactive metabolites due to acyl-glucuronidation. By others they are viewed more favorably as they can decrease lipophilicity by adding an ionizable center which can be beneficial for solubility, and can add enthalpic interactions with the target protein. However, there are many instances where the replacement of a carboxylic acid with a bioisosteric group is required. This has led to the development of a number of ionizable groups which sufficiently mimic the carboxylic acid functionality whilst improving, for example, the metabolic profile of the molecule in question. An alternative strategy involves replacement of the carboxylate by neutral functional groups. This review initially details carefully selected examples whereby tetrazoles, acyl sulfonamides or isoxazolols have been beneficially utilized as carboxylic acid bioisosteres altering physicohemical properties, interactions with the target and metabolism and/or pharmacokinetics, before delving further into the binding mode of carboxylic acid derivatives with their target proteins. This analysis highlights new ways to consider the replacement of carboxylic acids by neutral bioisosteric groups which either rely on hydrogen bonds or cation-π interactions. It should serve as a useful guide for scientists working in drug discovery.

Defining the Conformational Ensembles Associated with Ligand Binding to Cyclooxygenase-2

Cyclooxygenases (COX) catalyze the committed step in the production of prostaglandins responsible for the maintenance of physiological homeostasis. While crystal structures of COX in complex with substrates and inhibitors have provided insight into the molecular interactions governing their binding, they have not uncovered specific details related to the protein conformational motions responsible for important aspects of the COX function. We created a cysteine-free COX-2 construct and introduced a free cysteine at position-122 to enable labeling with 3-bromo-1,1,1-trifluoroacetone (BTFA). Placement of the label adjacent to the cyclooxygenase channel entrance permitted the detection of alterations upon ligand binding. 19F-nuclear magnetic resonance spectroscopy (19F-NMR) was then used to probe the conformational ensembles arising from BTFA-labeled COX-2 constructs in the presence and absence of ligands known to allosterically activate or inhibit COX-2. 19F-NMR analyses performed in the presence of the time-dependent inhibitor flurbiprofen, as well as Arg-120, Tyr-355, and Glu-524 mutations, led to the classification of two ensembles as representing the relaxed and tightened states of the cyclooxygenase channel entrance. A third ensemble, generated in the presence of arachidonic acid and the Y355F mutant and modulated by the allosteric potentiators palmitic acid and oleic acid and the nonallosteric substrates 2-arachidonoyl glycerol ether and anandamide, was classified as being related to the allosteric regulation of COX activity. The ensemble-based insight into COX function demonstrated here complements the static information derived from crystal structure analyses, collectively providing a more detailed framework of the dynamics involved in the regulation of COX catalysis and inhibition.

Structural insights into the half-of-sites reactivity in homodimeric and homotetrameric metalloenzymes

Half-of-sites reactivity in many homodimeric and homotetrameric metalloenzymes has been known for half a century, yet its benefit remains poorly understood. A recently reported cryo-electron microscopy structure has given some clues on the less optimized reactivity of Escherichia coli ribonucleotide reductase with an asymmetric association of α2β2 subunits during catalysis. Moreover, nonequivalence of enzyme active sites has been reported in many other enzymes, possibly as a means of regulation. They are often induced by substrate binding or caused by a critical component introduced from a neighboring subunit in response to substrate loadings, such as in prostaglandin endoperoxide H synthase, cytidine triphosphate synthase, glyoxalase, tryptophan dioxygenase, and several decarboxylases or dehydrogenases. Overall, half-of-sites reactivity is likely not an act of wasting resources but rather a method devised in nature to accommodate catalytic or regulatory needs.

16R-HETE and 16S-HETE alter human cytochrome P450 1B1 enzyme activity probably through an allosteric mechanism

Cytochrome P450 1B1 (CYP1B1) has been widely associated with the development of cardiac pathologies due to its ability to produce cardiotoxic metabolites like midchain hydroxyeicosatetraenoic acids (HETEs) from arachidonic acid (AA) through an allylic oxidation reaction. 16-HETE is a subterminal HETE that is also produced by CYP-mediated AA metabolism. 19-HETE is another subterminal HETE that was found to inhibit CYP1B1 activity, lower midchain HETEs, and have cardioprotective effects. However, the effect of 16-HETE enantiomers on CYP1B1 has not yet been investigated. We hypothesized that 16(R/S)-HETE could alter the activity of CYP1B1 and other CYP enzymes. Therefore, this study was carried out to investigate the modulatory effect of 16-HETE enantiomers on CYP1B1 enzyme activity, and to examine the mechanisms by which they exert these modulatory effects. To investigate whether these effects are specific to CYP1B1, we also investigated 16-HETE modulatory effects on CYP1A2. Our results showed that 16-HETE enantiomers significantly increased CYP1B1 activity in RL-14 cells, recombinant human CYP1B1, and human liver microsomes, as seen by the significant increase in 7-ethoxyresorufin deethylation rate. On the contrary, 16-HETE enantiomers significantly inhibited CYP1A2 catalytic activity mediated by the recombinant human CYP1A2 and human liver microsomes. 16R-HETE showed stronger effects than 16S-HETE. The sigmoidal binding mode of the enzyme kinetics data demonstrated that CYP1B1 activation and CYP1A2 inhibition occurred through allosteric regulation. In conclusion, our study provides the first evidence that 16R-HETE and 16S-HETE increase CYP1B1 catalytic activity through an allosteric mechanism.

Insights into metabolic and pharmacological profiling of Aspergillus ficuum through bioinformatics and experimental techniques

BACKGROUND

Recently, numerous novel bioactive fungal metabolites have been identified that possess broad therapeutic activities including anti-inflammatory, antibiotic, antioxidant, and antitumor. The fungal mycochemicals as well as extracts have increased the interest of the scientific community in drug discovery research through a combination approach such as, molecular metabolic, pharmacological and computational techniques. Therefore, the natural fungus Aspergillus ficuum (A. ficuum) (FCBP-DNA-1266) was selected for metabolic and pharmacological profiling in this study.

RESULTS

The metabolic profile of A. ficuum was explored for the first time and revealed the presence of bioactive compounds such as choline sulfate, noruron, hydroxyvittatine, aurasperone D, cetrimonium, kurilensoside, heneicosane, nonadecane and eicosane. Similarly, a pharmacological screen of A. ficuum was performed for the first time in in vivo and in vitro models. Interestingly, both the ethyl acetate and n-hexane fractions of A. ficuum were found to be more active against Bacillus subtilis among five tested bacteria with their zone of inhibition (ZOI) values of 21.00 mm ±1.00 and 23.00 mm ±1.00, at a concentration of 150 μgmL^-1 respectively. Similarly, a significant decrease (P<0.001) and (P<0.01) in paw edema was observed in A. ficuum-treated animals at doses of 50 and 150 mgkg^-1, respectively, reflecting its potent anti-inflammatory effect. Furthermore, the docking results supported the antibacterial and anti-inflammatory effects of A. ficuum. In addition, the crude extract demonstrated no acute toxicity and the highest percent radical scavenging was recorded for both n-hexane and ethyl acetate extracts.

CONCLUSION

The metabolic profile of A. ficuum indicated the presence of biological relevant compounds. A. ficuum extract exhibited potent antibacterial and anti-inflammatory effects supported by docking results. Furthermore, A. ficuum extract demonstrated the highest percentage of radical scavenging activity along with no acute toxicity.

Metabolic and pharmacological profiling of Penicillium claviforme by a combination of experimental and bioinformatic approaches

BACKGROUND

Penicillium produces a wide range of structurally diverse metabolites with significant pharmacological impacts in medicine and agriculture. For the first time, a complete metabolome of Penicillium claviforme (P. claviforme) (FBP-DNA-1205) was studied alongside pharmacological research in this study.

METHODS

The metabolic profile of P. claviforme fermented on Potato Dextrose Broth (PDB) was investigated in this work. The complete metabolomics studies of fungus were performed using GC-MS and LC-MS-QTOF techniques. An in vitro model was utilised to study the cytotoxic and antioxidant activities, while an in vivo model was employed to investigate the antinociceptive and acute toxicity activities. Molecular Operating Environment (MOE) software was used for molecular docking analysis.

RESULTS

GC-MS study showed the presence of alkanes, fatty acids, esters, azo and alcoholic compounds. Maculosin, obtain, phalluside, quinoline, 4,4'-diaminostilbene, funaltrexamine, amobarbital, and fraxetin were among the secondary metabolites identified using the LC-MS-QTOF technique. The n-hexane fraction of P. claviforme displayed significant cytotoxic activity in vitro, with an LD50 value of 92.22 µgml^-1. The antinociceptive effects in vivo were dose-dependent significantly (p < .001). Interestingly, during the 72 h of investigation, no acute toxicity was demonstrated. In addition, a docking study of tentatively identified metabolites against the inflammatory enzyme (COX-2) supported the antinociceptive effect in an in silico model.

CONCLUSION

Metabolic profile of P. claviforme shows the presence of biologically relevant compounds in ethyl acetate extract. In addition, P. claviforme exhibits substantial antioxidant and cytotoxic activities in an in vitro model as well as antinociceptive activity in an in vivo model. The antinociceptive action is also supported by a molecular docking study. This research has opened up new possibilities in the disciplines of mycology, agriculture, and pharmaceutics. Key messagesThe first time explored complete metabolome through GC-MS and LC-MS-QTOF.Both in vivo & in vitro pharmacological investigation of P. claviforme.In silico molecular docking of LC-MS-QTOF metabolites.

Pyrazole-containing pharmaceuticals: target, pharmacological activity, and their SAR studies

Pyrazole is a five-membered heterocycle bearing two adjacent nitrogen atoms. Both pharmaceutical agents and natural products with pyrazole as a nucleus have exhibited a broad spectrum of biological activities. In the last few decades, more than 40 pyrazole-containing drugs have been approved by the FDA for the treatment of a broad range of clinical conditions including celecoxib (anti-inflammatory), CDPPB (antipsychotic), difenamizole (analgesic), etc. Owing to the unique physicochemical properties of the pyrazole core, pyrazole-containing drugs may exert better pharmacokinetics and pharmacological effects compared with drugs containing similar heterocyclic rings. The purpose of this paper is to provide an overview of all the existing drugs bearing a pyrazole nucleus that have been approved or in clinical trials, involving their pharmacological activities and SAR studies.

Inhibition of DDX3 and COX-2 by forskolin and evaluation of anti-proliferative, pro-apoptotic effects on cervical cancer cells: molecular modelling and in vitro approaches

Several studies have reported up-regulation of both cyclooxygenase-2 (COX-2) and DEAD-box RNA helicase3 (DDX3) and have validated their oncogenic role in many cancers. Inhibition of COX-2 and DDX3 offers a potential pharmacological strategy for prevention of cancer progression. The COX-2 isoform is expressed in response to pro-inflammatory stimuli in premalignant lesions, including cervical tissues. This study elucidates the potential role of plant derived compound Forskolin (FSK) in plummeting the expression of COX-2 and DDX3 in cervical cancer. To establish this, the cervical cancer cells were treated with the FSK compound which induced a dose dependent significant inhibition of COX-2 and DDX3 expression. The FSK treatment also significantly induced apoptosis in cancer cells by modulating the expression of apoptotic markers like caspase-3, cleaved caspase-3, caspase-9, cleaved caspase-9, full length-poly ADP ribose polymerase (PARP), cleaved-poly ADP ribose polymerase (C-PARP) and Bcl2 in dose dependent manner. Further FSK significantly modulated the cell survival pathway Phosphatidylinositol 3-kinase (PI3-K)/Akt signalling pathway upon 24 h of incubation in cervical cancer cells. The molecular docking studies revealed that the FSK engaged the active sites of both the targets by interacting with key residues.

Lipid nutrition: "In silico" studies and undeveloped experiments

This review examines lipids and lipid-binding sites on proteins in relation to cardiovascular disease. Lipid nutrition involves food energy from ingested fatty acids plus fatty acids formed from excess ingested carbohydrate and protein. Non-esterified fatty acids (NEFA) and lipoproteins have many detailed attributes not evident in their names. Recognizing attributes of lipid-protein interactions decreases unexpected outcomes. Details of double bond position and configuration interacting with protein binding sites have unexpected consequences in acyltransferase and cell replication events. Highly unsaturated fatty acids (HUFA) have n-3 and n-6 motifs with documented differences in intensity of destabilizing positive feedback loops amplifying pathophysiology. However, actions of NEFA have been neglected relative to cholesterol, which is co-produced from excess food. Native low-density lipoproteins (LDL) bind to a high-affinity cell surface receptor which poorly recognizes biologically modified LDLs. NEFA increase negative charge of LDL and decrease its processing by "normal" receptors while increasing processing by "scavenger" receptors. A positive feedback loop in the recruitment of monocytes and macrophages amplifies chronic inflammatory pathophysiology. Computer tools combine multiple components in lipid nutrition and predict balance of energy and n-3:n-6 HUFA. The tools help design and execute precise clinical nutrition monitoring that either supports or disproves expectations.

Flunixin Meglumine Reduces Milk Isoprostane Concentrations in Holstein Dairy Cattle Suffering from Acute Coliform Mastitis

Dysfunctional inflammation contributes significantly to the pathogenesis of coliform mastitis and the classical pro-inflammatory enzyme cyclooxygenase-2 (COX-2) is the target of medical intervention using the non-steroidal anti-inflammatory drug (NSAID) flunixin meglumine (FM). Inhibition of COX-2 by FM can decrease concentrations of pro-inflammatory fatty acid-based mediators called eicosanoids, providing antipyretic and analgesic effects in dairy cows suffering from coliform mastitis. However, approximately 50% of naturally occurring coliform mastitis with systemic involvement results in death of the animal, even with NSAID treatment. Inadequate antioxidant potential (AOP) to neutralize reactive oxygen species (ROS) produced during excessive inflammation allows for oxidative stress (OS), contributing to tissue damage during coliform mastitis. Biomarkers of lipid peroxidation by ROS, called isoprostanes (IsoP), were used in humans and cattle to quantify the extent of OS. Blood IsoP were shown to be elevated and correlate with oxidant status during acute coliform mastitis. However, the effect of FM treatment on oxidant status and markers of OS has not been established. Blood IsoP concentrations were used to quantify systemic OS, whereas milk was used to assess local OS in the mammary gland. Results indicate that FM treatment had no effect on blood markers of inflammation but reduced the oxidant status index (OSi) by increasing blood AOP from pre- to post-FM treatment. Milk AOP significantly increased from pre- to post-FM treatment, whereas ROS decreased, resulting in a decreased OSi from pre- to post-FM treatment. The only blood IsoP concentration that was significantly different was 5-iso-iPF2α-VI, with a decreased concentration from pre- to post-FM treatment. Conversely, milk 5-iso-iPF2α-VI, 8,12-iso-iPF2α-VI, and total IsoP concentrations were decreased following FM treatment. These results indicated that administration of FM did improve systemic and local oxidant status and reduced local markers of OS. However, differential effects were observed between those animals that survived the infection and those that died, indicating that pre-existing inflammation and oxidant status greatly affect efficacy of FM and may be the key to reducing severity and mortality associated with acute coliform infections. Supplementation to improve AOP and anti-inflammatory mediator production may significantly improve efficacy of FM treatment.

In Cellulo Generation of Fluorescent Probes for Live-Cell Imaging of Cylooxygenase-2

Live-cell imaging with fluorescent probes is an essential tool in chemical biology to visualize the dynamics of biological processes in real-time. Intracellular disease biomarker imaging remains a formidable challenge due to the intrinsic limitations of conventional fluorescent probes and the complex nature of cells. This work reports the in cellulo assembly of a fluorescent probe to image cyclooxygenase-2 (COX-2). We developed celecoxib-azide derivative 14, possessing favorable biophysical properties and excellent COX-2 selectivity profile. In cellulo strain-promoted fluorogenic click chemistry of COX-2-engaged compound 14 with non/weakly-fluorescent compounds 11 and 17 formed fluorescent probes 15 and 18 for the detection of COX-2 in living cells. Competitive binding studies, biophysical, and comprehensive computational analyses were used to describe protein-ligand interactions. The reported new chemical toolbox enables precise visualization and tracking of COX-2 in live cells with superior sensitivity in the visible range.

Structural and Chemical Biology of the Interaction of Cyclooxygenase with Substrates and Non-Steroidal Anti-Inflammatory Drugs

Cyclooxgenases are key enzymes of lipid signaling. They carry out the first step in the production of prostaglandins, important mediators of inflammation, pain, cardiovascular disease, and cancer, and they are the molecular targets for nonsteroidal anti-inflammatory drugs, which are among the oldest and most chemically diverse set of drugs known. Homodimeric proteins that behave as allosterically modulated, functional heterodimers, the cyclooxygenases exhibit complex kinetic behavior, requiring peroxide-dependent activation and undergoing suicide inactivation. Due to their important physiological and pathophysiological roles and keen interest on the part of the pharmaceutical industry, the cyclooxygenases have been the focus of a vast array of structural studies, leading to the publication of over 80 crystal structures of the enzymes in complex with substrates or inhibitors supported by a wealth of functional data generated by site-directed mutation experiments. In this review, we explore the chemical biology of the cyclooxygenases through the lens of this wealth of structural and functional information. We identify key structural features of the cyclooxygenases, break down their active site into regional binding pockets to facilitate comparisons between structures, and explore similarities and differences in the binding modes of the wide variety of ligands (both substrates and inhibitors) that have been characterized in complex with the enzymes. Throughout, we correlate structure with function whenever possible. Finally, we summarize what can and cannot be learned from the currently available structural data and discuss the critical intriguing questions that remain despite the wealth of information that has been amassed in this field.

DREAM-in-CDM Approach and Identification of a New Generation of Anti-inflammatory Drugs Targeting mPGES-1

Microsomal prostaglandin E2 synthase-1 (mPGES-1) is known as an ideal target for next generation of anti-inflammatory drugs without the side effects of currently available anti-inflammatory drugs. However, there has been no clinically promising mPGES-1 inhibitor identified through traditional drug discovery and development route. Here we report a new approach, called DREAM-in-CDM (Drug Repurposing Effort Applying Integrated Modeling-in vitro/vivo-Clinical Data Mining), to identify an FDA-approved drug suitable for use as an effective analgesic targeting mPGES-1. The DREAM-in-CDM approach consists of three steps: computational screening of FDA-approved drugs; in vitro and/or in vivo assays; and clinical data mining. By using the DREAM-in-CDM approach, lapatinib has been identified as a promising mPGES-1 inhibitor which may have significant anti-inflammatory effects to relieve various forms of pain and possibly treat various inflammation conditions involved in other inflammation-related diseases such as the lung inflammation caused by the newly identified COVID-19. We anticipate that the DREAM-in-CDM approach will be used to repurpose FDA-approved drugs for various new therapeutic indications associated with new targets.

Lipid mechanisms in hallmarks of cancer

Excess adiposity is a risk factor for several cancer types. This is likely due to complex mechanisms including alterations in the lipid milieu that plays a pivotal role in multiple aspects of carcinogenesis. Here we consider the direct role of lipids in regulating well-known hallmarks of cancer. Furthermore, we suggest that obesity-associated remodelling of membranes and organelles drives cancer cell proliferation and invasion. Identification of cancer-related lipid-mediated mechanisms amongst the broad metabolic disturbances due to excess adiposity is central to the identification of novel and more efficacious prevention and intervention strategies.

An Activity-Based Sensing Approach for the Detection of Cyclooxygenase-2 in Live Cells

Cyclooxygenase-2 (COX-2) overexpression is prominent in inflammatory diseases, neurodegenerative disorders, and cancer. Directly monitoring COX-2 activity within its native environment poses an exciting approach to account for and illuminate the effect of the local environments on protein activity. Herein, we report the development of CoxFluor, the first activity-based sensing approach for monitoring COX-2 within live cells with confocal microscopy and flow cytometry. CoxFluor strategically links a natural substrate with a dye precursor to engage both the cyclooxygenase and peroxidase activities of COX-2. This catalyzes the release of resorufin and the natural product, as supported by molecular dynamics and ensemble docking. CoxFluor enabled the detection of oxygen-dependent changes in COX-2 activity that are independent of protein expression within live macrophage cells.

Arg-513 and Leu-531 Are Key Residues Governing Time-Dependent Inhibition of Cyclooxygenase-2 by Aspirin and Celebrex

Aspirin and Celebrex are well-known time-dependent inhibitors of the cyclooxygenases (COX). Molecular dynamics simulations suggest that Arg-513 and Leu-531 contribute to the structural mechanisms of COX inhibition. We used mutagenesis and functional analyses to characterize how substitutions at these positions influence time-dependent inhibition by aspirin and Celebrex. We show that substitutions of Leu-531 with asparagine and phenylalanine significantly attenuate time-dependent inhibition of COX-2 by these drugs. The introduction of side chain bulk, rigidity, and charge would disrupt the formation of the initial noncovalent complex, in the case of aspirin, and the "high-affinity" binding state, in the case of Celebrex. Substitution of Arg-513 with histidine (the equivalent residue in COX-1) resulted in a 2-fold potentiation of aspirin inhibition, in support of the hypothesis that the presence of histidine in COX-1 lowers the activation barrier associated with the formation of the initial noncovalent enzyme-inhibitor complex. As a corollary, we previously hypothesized that the flexibility associated with Leu-531 contributes to the binding of arachidonic acid (AA) to acetylated COX-2 to generate 15R-hydroxyeicosatetraenoic acid (15R-HETE). We determined the X-ray crystal structure of AA bound to Co³⁺-protoporphyrin IX-reconstituted V349I murine COX-2 (muCOX-2). V349I muCOX-2 was utilized as a surrogate to trap AA in a conformation leading to 15R-HETE. AA binds in a C-shaped pose, facilitated by the rotation of the Leu-531 side chain. Ile-349 is positioned to sterically shield antarafacial oxygen addition at carbon-15 in a manner similar to that proposed for the acetylated Ser-530 side chain.

Computational Evaluation and Anti-inflammatory and Analgesic Activities of Nebrodenside A Isolated From Dodonaea viscosa

Nebrodenside A was isolated from the plant Dodonaea viscosa and its chemical structure was elucidated by spectroscopic methods. Molecular docking simulation predicted its strong ability to be tested as a potential anti-inflammatory compound. Carrageen-induced paw model and formalin test were utilized for the assessment of anti-inflammatory and analgesic potential. Nebrodenside A was found to be significantly active in reducing inflammation, when compared with diclofenac as a standard drug. Similarly, the compound also possesses substantial analgesic activity in the formalin-induced writhing test. Thus, nebrodenside A revealed a robust potential to be developed as a possible leading medicinal agent for better management of pain and inflammation.

Interactions of fatty acids, nonsteroidal anti-inflammatory drugs, and coxibs with the catalytic and allosteric subunits of cyclooxygenases-1 and -2

Prostaglandin endoperoxide H synthases-1 and -2, commonly called cyclooxygenases-1 and -2 (COX-1 and -2), catalyze the committed step in prostaglandin biosynthesis-the conversion of arachidonic acid to prostaglandin endoperoxide H₂ Both COX isoforms are sequence homodimers that function as conformational heterodimers having allosteric (Eallo) and catalytic (Ecat) subunits. At least in the case of COX-2, the enzyme becomes folded into a stable Eallo/Ecat pair. Some COX inhibitors (i.e. nonsteroidal anti-inflammatory drugs and coxibs) and common fatty acids (FAs) modulate Ecat activity by binding Eallo. However, the interactions and outcomes often differ between isoforms. For example, naproxen directly and completely inhibits COX-1 by binding Ecat but indirectly and incompletely inhibits COX-2 by binding Eallo. Additionally, COX-1 is allosterically inhibited up to 50% by common FAs like palmitic acid, whereas COX-2 is allosterically activated 2-fold by palmitic acid. FA binding to Eallo also affects responses to COX inhibitors. Thus, COXs are physiologically and pharmacologically regulated by the FA tone of the milieu in which each operates-COX-1 in the endoplasmic reticulum and COX-2 in the Golgi apparatus. Cross-talk between Eallo and Ecat involves a loop in Eallo immediately downstream of Arg-120. Mutational studies suggest that allosteric modulation requires a direct interaction between the carboxyl group of allosteric effectors and Arg-120 of Eallo; however, structural studies show some allosterically active FAs positioned in COX-2 in a conformation lacking an interaction with Arg-120. Thus, many details about the biological consequences of COX allosterism and how ligand binding to Eallo modulates Ecat remain to be resolved.

Higher baseline expression of the PTGS2 gene and greater decreases in total colonic fatty acid content predict greater decreases in colonic prostaglandin-E2 concentrations after dietary supplementation with ω-3 fatty acids

This study evaluated whether mRNA expression of major genes regulating formation of prostaglandin (PG)E2 in the colon and colonic fatty acid concentrations are associated with the reduction in colonic mucosal PGE2 after dietary supplementation with omega-3 (ω-3) fatty acids. Supplementation with ω-3 fatty acids was done for 12 weeks using personalized dosing that was expected to reduce colonic PGE2 by 50%. In stepwise linear regression models, the ω-3 fatty acid dose and baseline BMI explained 16.1% of the inter-individual variability in the fold change of colonic PGE2 post-supplementation. Increases in mRNA gene expression after supplementation were, however, modest and were not associated with changes in PGE2. When baseline expression of PTGS1, PTGS2 and HPGD genes was included in the linear regression model containing dose and BMI, only PTGS2, the gene coding for the inducible form cyclooxygenase, was a significant predictor. Higher relative expression of PTGS2 predicted greater decreases in colonic PGE2, accounting for an additional 13.6% of the inter-individual variance. In the final step of the regression model, greater decreases in total colonic fatty acid concentrations predicted greater decreases in colonic PGE2, contributing to an additional 18.7% of the variance. Overall, baseline BMI, baseline expression of PTGS2 and changes in colonic total fatty acids together accounted for 48% of the inter-individual variability in the change in colonic PGE2. This is consistent with biochemical data showing that fatty acids which are not substrates for cyclooxygenases can activate cyclooxygenase-2 allosterically. Further clinical trials are needed to elucidate the factors that regulate the fatty acid milieu of the human colon and how this interacts with key lipid metabolizing enzymes. Given the central role of PGE2 in colon carcinogenesis, these pathways may also impact on colon cancer prevention by other dietary and pharmacological approaches.

The Cardiovascular Pharmacology of Nonsteroidal Anti-Inflammatory Drugs

The principal molecular mechanisms underlying the cardiovascular (CV) and renal adverse effects of nonsteroidal anti-inflammatory drugs (NSAIDs), such as myocardial infarction and hypertension, are understood in more detail than most side effects of drugs. Less is known, however, about differences in the CV safety profile between chemically distinct NSAIDs and their relative predisposition to complications. In review article, we discuss how heterogeneity in the pharmacokinetics and pharmacodynamics of distinct NSAIDs may be expected to affect their CV risk profile. We consider evidence afforded by studies in model systems, mechanistic clinical trials, a meta-analysis of randomized controlled trials, and two recent large clinical trials, Standard Care vs. Celecoxib Outcome Trial (SCOT) and Prospective Randomized Evaluation of Celecoxib Integrated Safety versus Ibuprofen or Naproxen (PRECISION), designed specifically to compare the CV safety of the cyclooxygenase-2-selective NSAID, celecoxib, with traditional NSAIDs. We conclude that SCOT and PRECISION have apparently not compared equipotent doses and have other limitations that bias them toward underestimation of the relative risk of celecoxib.

Effects of fish oil supplementation on prostaglandins in normal and tumor colon tissue: modulation by the lipogenic phenotype of colon tumors

Dietary fish oils have potential for prevention of colon cancer, and yet the mechanisms of action in normal and tumor colon tissues are not well defined. Here we evaluated the impact of the colonic fatty acid milieu on the formation of prostaglandins and other eicosanoids. Distal tumors in rats were chemically induced to model inflammatory colonic carcinogenesis. After 21 weeks of feeding with either a fish oil diet containing an eicosapentaenoic acid/ω-6 fatty acid ratio of 0.4 or a Western fat diet, the relationships between colon fatty acids and prostaglandin E₂ (PGE₂) concentrations were evaluated. PGE₂ is a key proinflammatory mediator in the colon tightly linked with the initiation and progression of colon cancer. The fish oil vs. the Western fat diet resulted in reduced total fatty acid concentrations in serum but not in colon. In the colon, the effects of the fish oil on fatty acids differed in normal and tumor tissue. There were distinct lipodomic patterns consistent with a lipogenic phenotype in tumors. In tumor tissue, the eicosapentaenoic acid/arachidonic acid ratio, cyclooxygenase-2 expression and the mole percent of saturated fatty acids were significant predictors of inter-animal variability in colon PGE₂ after accounting for diet. In normal tissues from either control rats or carcinogen-treated rats, only diet was a significant predictor of colon PGE₂. These results show that the fatty acid milieu can modulate the efficacy of dietary fish oils for colon cancer prevention, and this could extend to other preventive agents that function by reducing inflammatory stress.