Human cyclooxygenase-1 activity and its responses to COX inhibitors are allosterically regulated by nonsubstrate fatty acids

Experimental investigation and molecular simulations of quinone related compounds as COX/LOX inhibitors

Quinone-containing compounds have risen as promising anti-inflammatory targets; however, very little research has been directed to investigate their potentials. Accordingly, the current study aimed to design and synthesize group of quinones bearing different substituents to investigate the effect of these functionalities on the anti-inflammatory activities of this important scaffold. The choice of these substituents was carefully done, varying from a directly attached heterocyclic ring to different aromatic moieties linked through a nitrogen spacer. Both in vitro and in vivo anti-inflammatory activities of the synthesized compounds were assessed relative to the positive standards: celecoxib and indomethacin. The in vitro enzymatic and transcription inhibitory actions of all the synthesized compounds were tested against cyclooxygenase-2 (COX-2), cyclooxygenase-1 (COX-1), and 5-lipoxygenase (LOX) and the in vivo gene expression of Interleukin-1, interleukin 10, and Tumor Necrosis Factor-α (TNF-α) were determined. The IC50 against COX-1 and COX-2 enzymes obtained by the immunoassay test revealed promising activities of sixteen compounds with selectivity indices higher than 100-fold COX-2 selectivity. Out of those, four compounds revealed selectivity indices comparable to celecoxib as a reference drug. Furthermore, all the tested compounds inhibited LOX with an IC50 in the range of 1.59-3.11 µM superior to that of the reference drug used; zileuton (IC50 = 3.50 µM). Consequently, these results highlight the promising LOX inhibitory activity of the tested compounds. The obtained in vivo paw edema results showed high inhibitory percentage for the compounds 9a, 9b, and 11a with the significant lower TNF-α relative mRNA expression for compounds 5a, 5d, 9a, 9b, 12d, and 12e. Finally, in silico docking of the most active compounds (5b, 5d, 9a, 9b) against COX2 enzymes presented an acceptable justification of the obtained in vitro inhibitory activities. As a conclusion, Compounds 5b, 5d, 9a, 9b, and 11b showed promising results and thus deserves further investigation.

Bioassay-guided detection, identification and assessment of antibacterial and anti-inflammatory compounds from olive tree flower extracts by high-performance thin-layer chromatography linked to spectroscopy

Olive trees are one of the most widely cultivated fruit trees in the world. The chemical compositions and biological activities of olive tree fruit and leaves have been extensively researched for their nutritional and health-promoting properties. In contrast, limited data have been reported on olive flowers. The present study aimed to analyse bioactive compounds in olive flower extracts and the effect of fermentation-assisted extraction on phenolic content and antioxidant activity. High-performance thin-layer chromatography (HPTLC) hyphenated with the bioassay-guided detection and spectroscopic identification of bioactive compounds was used for the analysis. Enzymatic and bacterial in situ bioassays were used to detect COX-1 enzyme inhibition and antibacterial activity. Multiple zones of antibacterial activity and one zone of COX-1 inhibition were detected in both, non-fermented and fermented, extracts. A newly developed HPTLC-based experimental protocol was used to measure the high-maximal inhibitory concentrations (IC50) for the assessment of the relative potency of the extracts in inhibiting COX-1 enzyme and antibacterial activity. Strong antibacterial activities detected in zones 4 and 7 were significantly higher in comparison to ampicillin, as confirmed by low IC50 values (IC50 = 57-58 µg in zone 4 and IC50 = 157-167 µg in zone 7) compared to the ampicillin IC50 value (IC50 = 495 µg). The COX-1 inhibition by the extract (IC50 = 76-98 µg) was also strong compared to that of salicylic acid (IC50 = 557 µg). By comparing the locations of the bands to coeluted standards, compounds from detected bioactive bands were tentatively identified. The eluates from bioactive HPTLC zones were further analysed by FTIR NMR, and LC-MS spectroscopy. Multiple zones of antibacterial activity were associated with the presence of triterpenoid acids, while COX-1 inhibition was related to the presence of long-chain fatty acids.

Structure-guided approach on the role of substitution on amide-linked bipyrazoles and its effect on their anti-inflammatory activity

A structure-guided modelling approach using COX-2 as a template was used to investigate the effect of replacing the chloro atom located at the chlorophenyl ring of amide-linked bipyrazole moieties, aiming at attaining better anti-inflammatory effect with a good safety profile. Bromo, fluoro, nitro, and methyl groups were revealed to be ideal candidates. Consequently, new bipyrazole derivatives were synthesised. The in vitro inhibitory COX-1/COX-2 activity of the synthesised compounds exhibited promising selectivity. The fluoro and methyl derivatives were the most active candidates. The in vivo formalin-induced paw edoema model confirmed the anti-inflammatory activity of the synthesised compounds. All the tested derivatives had a good ulcerogenic safety profile except for the methyl substituted compound. In silico molecular dynamics simulations of the fluoro and methyl poses complexed with COX-2 for 50 ns indicated stable binding to COX-2. Generally, our approach delivers a fruitful matrix for the development of further amide-linked bipyrazole anti-inflammatory candidates.

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.

Characterization of cyclooxygenase-2 acetylation and prostanoid inhibition by aspirin in cellular systems

The most recognized mechanism of aspirin (acetylsalicylic acid, ASA) action, at therapeutic dosing, is the inhibition of prostanoid biosynthesis through the acetylation of cyclooxygenase (COX)-isozymes (COX-1 at serine-529 and COX-2 at serine-516). Whether aspirin, also when given at the low-doses recommended for cardiovascular prevention, reduces the risk of colorectal cancer by affecting COX-2 activity in colorectal adenomatous lesions is still debated. We aimed to develop a direct biomarker of aspirin action on COX-2 by assessing the extent of acetylation of COX-2 at serine-516 using the AQUA strategy, enabling absolute protein quantitation by liquid chromatography-mass spectrometry. We compared the extent of acetylation and the inhibition of prostanoid biosynthesis by ASA using human recombinant COX-2 (hu-COX-2), the human colon cancer cell line HCA-7, isolated human monocytes stimulated with LPS (lipopolysaccharide) or human intestinal epithelial cells stimulated with interleukin (IL)-1β. Hu-COX-2 exposed in vitro to an excess of ASA was acetylated by approximately 40-50% associated with the inhibition of COX-2 activity by 80-90%. In the three cell-types expressing COX-2, the extent of COX-2 acetylation and reduction of prostaglandin (PG) E₂ biosynthesis by ASA was concentration-dependent with comparable EC₅₀ values (in the low μM range). The maximal % acetylation of COX-2 averaged 80%, at ASA 1000 μM, and was associated with a virtually complete reduction of PGE₂ biosynthesis (97%). In conclusion, we have developed a proteomic assay to evaluate the extent of acetylation of COX-2 at serine-516 by aspirin; its use in clinical studies will allow clarifying the mechanism of action of aspirin as anticancer agent.

The endocannabinoid hydrolase FAAH is an allosteric enzyme

Fatty acid amide hydrolase (FAAH) is a membrane-bound homodimeric enzyme that in vivo controls content and biological activity of N-arachidonoylethanolamine (AEA) and other relevant bioactive lipids termed endocannabinoids. Parallel orientation of FAAH monomers likely allows both subunits to simultaneously recruit and cleave substrates. Here, we show full inhibition of human and rat FAAH by means of enzyme inhibitors used at a homodimer:inhibitor stoichiometric ratio of 1:1, implying that occupation of only one of the two active sites of FAAH is enough to fully block catalysis. Single W445Y substitution in rat FAAH displayed the same activity as the wild-type, but failed to show full inhibition at the homodimer:inhibitor 1:1 ratio. Instead, F432A mutant exhibited reduced specific activity but was fully inhibited at the homodimer:inhibitor 1:1 ratio. Kinetic analysis of AEA hydrolysis by rat FAAH and its F432A mutant demonstrated a Hill coefficient of ~1.6, that instead was ~1.0 in the W445Y mutant. Of note, also human FAAH catalysed an allosteric hydrolysis of AEA, showing a Hill coefficient of ~1.9. Taken together, this study demonstrates an unprecedented allosterism of FAAH, and represents a case of communication between two enzyme subunits seemingly controlled by a single amino acid (W445) at the dimer interface. In the light of extensive attempts and subsequent failures over the last decade to develop effective drugs for human therapy, these findings pave the way to the rationale design of new molecules that, by acting as positive or negative heterotropic effectors of FAAH, may control more efficiently its activity.

The Biosynthesis of Enzymatically Oxidized Lipids

Enzymatically oxidized lipids are a specific group of biomolecules that function as key signaling mediators and hormones, regulating various cellular and physiological processes from metabolism and cell death to inflammation and the immune response. They are broadly categorized as either polyunsaturated fatty acid (PUFA) containing (free acid oxygenated PUFA "oxylipins", endocannabinoids, oxidized phospholipids) or cholesterol derivatives (oxysterols, steroid hormones, and bile acids). Their biosynthesis is accomplished by families of enzymes that include lipoxygenases (LOX), cyclooxygenases (COX), cytochrome P450s (CYP), and aldo-keto reductases (AKR). In contrast, non-enzymatically oxidized lipids are produced by uncontrolled oxidation and are broadly considered to be harmful. Here, we provide an overview of the biochemistry and enzymology of LOXs, COXs, CYPs, and AKRs in humans. Next, we present biosynthetic pathways for oxylipins, oxidized phospholipids, oxysterols, bile acids and steroid hormones. Last, we address gaps in knowledge and suggest directions for future work.

A New Look at the Structures of Old Sepsis Actors by Exploratory Data Analysis Tools

Sepsis is a life-threatening condition that accounts for numerous deaths worldwide, usually complications of common community infections (i.e., pneumonia, etc), or infections acquired during the hospital stay. Sepsis and septic shock, its most severe evolution, involve the whole organism, recruiting and producing a lot of molecules, mostly proteins. Proteins are dynamic entities, and a large number of techniques and studies have been devoted to elucidating the relationship between the conformations adopted by proteins and what is their function. Although molecular dynamics has a key role in understanding these relationships, the number of protein structures available in the databases is so high that it is currently possible to build data sets obtained from experimentally determined structures. Techniques for dimensionality reduction and clustering can be applied in exploratory data analysis in order to obtain information on the function of these molecules, and this may be very useful in immunology to better understand the structure-activity relationship of the numerous proteins involved in host defense, moreover in septic patients. The large number of degrees of freedom that characterize the biomolecules requires special techniques which are able to analyze this kind of data sets (with a small number of entries respect to the number of degrees of freedom). In this work we analyzed the ability of two different types of algorithms to provide information on the structures present in three data sets built using the experimental structures of allosteric proteins involved in sepsis. The results obtained by means of a principal component analysis algorithm and those obtained by a random projection algorithm are largely comparable, proving the effectiveness of random projection methods in structural bioinformatics. The usefulness of random projection in exploratory data analysis is discussed, including validation of the obtained clusters. We have chosen these proteins because of their involvement in sepsis and septic shock, aimed to highlight the potentiality of bioinformatics to point out new diagnostic and prognostic tools for the patients.

Design, synthesis and molecular docking of benzophenone conjugated with oxadiazole sulphur bridge pyrazole pharmacophores as anti inflammatory and analgesic agents

The prostaglandins (PG) a group of physiologically active lipid compounds having diverse hormone like effects are important mediators of the body's response to pain and inflammation, and are formed from essential fatty acids found in cell membranes. This reaction is catalyzed by cyclooxygenase, a membrane associated enzyme occurring in two isoforms, COX-1 and COX-2. Nonsteroidal anti-inflammatory drugs (NSAIDs) act by inhibiting the activity of COX. In view of this, a series of novel benzophenones conjugated with oxadiazole sulphur bridge pyrazole moiety 8a-l were designed, synthesized, characterized and subsequently evaluated for anti-inflammatory and analgesic property. The investigation of novel analogues 8a-l for potential anti-inflammatory activity showed high levels of COX-1 and COX-2 inhibitory activity. Among the series, compound 8i with electron withdrawing fluoro group at the para position of the benzoyl ring of benzophenone was characterized by highest IC₅₀ values for both COX-1 and COX-2 inhibition, which is comparable to the standard drug. Further, molecular docking studies have been performed for the potent compound.

Increases in Colonic Bacterial Diversity after ω-3 Fatty Acid Supplementation Predict Decreased Colonic Prostaglandin E2 Concentrations in Healthy Adults

BACKGROUND

The intestinal microbiome is an important determinant of inflammatory balance in the colon that may affect response to dietary agents.

OBJECTIVE

This is a secondary analysis of a clinical trial, the Fish Oil Study, to determine whether interindividual differences in colonic bacteria are associated with variability in the reduction of colonic prostaglandin E2 (PGE2) concentrations after personalized supplementation with ω-3 (n-3) fatty acids.

METHODS

Forty-seven healthy adults (17 men, 30 women, ages 26-75 y) provided biopsy samples of colonic mucosa and luminal stool brushings before and after personalized ω-3 fatty acid supplementation that was based on blood fatty acid responses. Samples were analyzed using 16S ribosomal RNA sequencing. The data analyses focused on changes in bacterial community diversity. Linear regression was used to evaluate factors that predict a reduction in colonic PGE2.

RESULTS

At baseline, increased bacterial diversity, as measured by the Shannon and Inverse Simpson indexes in both biopsy and luminal brushing samples, was positively correlated with dietary fiber intakes and negatively correlated with fat intakes. Dietary supplementation with ω-3 fatty acids increased the Yue and Clayton community dis-similarity index between the microbiome in luminal brushings and colon biopsy samples post-supplementation (P = 0.015). In addition, there was a small group of individuals with relatively high Prevotella abundance who were resistant to the anti-inflammatory effects of ω-3 fatty acid supplementation. In linear regression analyses, increases in diversity of the bacteria in the luminal brushing samples, but not in the biopsy samples, were significant predictors of lower colonic PGE2 concentrations post-supplementation in models that included baseline PGE2, baseline body mass index, and changes in colonic eicosapentaenoic acid-to-arachidonic acid ratios. The changes in bacterial diversity contributed to 6-8% of the interindividual variance in change in colonic PGE2 (P = 0.001).

CONCLUSIONS

Dietary supplementation with ω-3 fatty acids had little effect on intestinal bacteria in healthy humans; however, an increase in diversity in the luminal brushings significantly predicted reductions in colonic PGE2. This trial was registered at www.clinicaltrials.gov as NCT01860352.

A seven-step plan for becoming a moderately rich and famous biochemist

Omega-6 polyunsaturated fatty acids were identified as essential nutrients in 1930. Their essentiality is largely due to their function as prostaglandin (PG) precursors. I spent most of my career in biochemistry determining how PG biosynthesis is regulated. PGs are lipid mediators formed in response to certain circulating hormones and cytokines. PGs act near their sites of synthesis to signal neighboring cells to coordinate their responses (e.g. when platelets interact with blood vessels). The committed step in PG synthesis is the conversion of a 20-carbon omega-6 fatty acid called arachidonic acid to prostaglandin endoperoxide H₂ (PGH₂). Depending on the tissue and the hormone or cytokine stimulus, this reaction is catalyzed by either cyclooxygenase-1 or cyclooxygenase-2 (COX-1 or COX-2). Once formed, PGH₂ is converted, again depending on the context, to one of several downstream PG subtypes that act via specific G protein-coupled receptors. Nonsteroidal anti-inflammatory drugs (e.g. aspirin, ibuprofen, and naproxen) block PG synthesis by inhibiting COX-1 and COX-2. COX-2 is also inhibited by COX-2-selective inhibitors. Inhibition of COX-1 by low-dose aspirin prevents thrombosis. COX-2 inhibition reduces inflammation and pain. Investigating the mysteries of COXs anchored my scientific career. I attribute my successes to the great good fortune of having been surrounded by people who helped me make the most of my talents. I have written this reflection in a light-hearted fashion as a self-help essay, while highlighting the people and factors that most impacted me during my upbringing and then during my maturation and evolution as a biochemist.

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.

Variability in analgesic response to non-steroidal anti-inflammatory drugs

Nonsteroidal anti-inflammatory drugs (NSAIDs) are among the most commonly used agents for the treatment of acute and chronic pain. However, it has long been recognized that there is substantial inter-individual variability in the analgesic response to NSAIDs, reflecting the complex interplay between mechanisms of pain, differences between distinct NSAIDs, and patient-specific factors such as genetic variation. This review summarizes the current knowledge regarding how these factors contribute to variability in the analgesic response to NSAIDs.

Effect of Polyphenols From Campomanesia adamantium on Platelet Aggregation and Inhibition of Cyclooxygenases: Molecular Docking and in Vitro Analysis

Campomanesia adamantium is a medicinal plant of the Brazilian Cerrado. Different parts of its fruits are used in popular medicine to treat gastrointestinal disorders, rheumatism, urinary tract infections and inflammations. Despite its widespread use by the local population, the mechanisms involving platelet aggregation and the inhibition of cyclooxygenase by C. adamantium are unknown. This study evaluated the chemical composition, antioxidant activities and potential benefits of the C. adamantium peel extract (CAPE) and its components in the platelet aggregation induced by arachidonic acid in platelet-rich plasma. Aspects of the pharmacological mechanism were investigated as follows: platelet viability, calcium mobilization, levels of the cyclic nucleotides cAMP and cGMP, thromboxane B₂ levels, and the inhibitory effects on COX-1 and COX-2 were studied in vitro and using molecular docking in the catalytic domain of these proteins. The major CAPE constituents standing out from the chemical analysis are the flavonoids, namely those of the flavones and chalcones class. The results showed that CAPE, quercetin and myricetin significantly decreased arachidonic acid-induced platelet aggregation; the assays showed that CAPE and quercetin decreased the mobilization of calcium and thromboxane B₂ levels in platelets and increased cAMP and cGMP levels. Moreover, CAPE inhibited the activity of COX-1 and COX-2, highlighting that quercetin could potentially prevent the access of arachidonic acid more to the catalytic site of COX-1 than COX-2. These results highlight CAPE’s potential as a promising therapeutic candidate for the prevention and treatment of diseases associated with platelet aggregation.

Negative Cooperativity in the Interaction of Prostaglandin H Synthase-1 with the Competitive Inhibitor Naproxen Can Be Described as the Interaction of a Non-competitive Inhibitor with Heterogeneous Enzyme Preparation

The kinetic mechanism of the interaction of nonsteroidal anti-inflammatory drugs (NSAIDs) with their main pharmacological target, prostaglandin H synthase (PGHS), has not yet been established. We showed that inhibition of PGHS-1 from sheep vesicular glands by naproxen (a representative of NSAIDs) demonstrates a non-competitive character with respect to arachidonic acid and cannot be described within a framework of the commonly used kinetic schemes. However, it can be described by taking into account the negative cooperativity of naproxen binding to the cyclooxygenase active sites of the PGHS-1 homodimer (the first naproxen molecule forms a more stable complex (K₁ = 0.1 µM) with the enzyme than the second naproxen molecule (K₂ = 9.2 µM)). An apparent non-competitive interaction of PGHS-1 with naproxen is due to slow dissociation of the enzyme-inhibitor complexes. The same experimental data could also be described using commonly accepted kinetic schemes, assuming that naproxen interacts was a mixture of two enzyme species with the inhibition constants K_α = 0.05 µM and K_β = 18.3 µM. Theoretical analysis and numerical calculations show that the phenomenon of kinetic convergence of these two models has a general nature: when K₂ >> K₁, the kinetic patterns (for transient kinetics and equilibrium state) generated by the cooperative model could be described by a scheme assuming the presence of two enzyme forms with the inhibition constants K_α = K₁/2, K_β = 2·K₂. When K₂ << K₁, the cooperative model can be presented as a scheme with two inhibitor molecules simultaneously binding to the enzyme with the observed inhibition constant K (K = K₁·K₂). The assumption on the heterogeneity of the enzyme preparation in relation to its affinity to the inhibitor can be used instead of the assumption on the negative cooperativity of the enzyme-inhibitor interactions for convenient and easy practical description of such phenomena in enzymology, biotechnology, pharmacology, and other fields of science.

Reduced Variability to Aspirin Antiplatelet Effect by the Coadministration of Statins in High-Risk Patients for Cardiovascular Disease

We studied the influence of cardiovascular (CV) risk factors, previous CV events, and cotreatments with preventive medicines, on residual platelet thromboxane (TX)B₂ production in 182 patients chronically treated with enteric coated (EC)-aspirin (100 mg/day). The response to aspirin was also verified by assessing arachidonic acid-induced platelet aggregation and urinary 11-dehydro-TXB₂ levels. Residual serum TXB₂ levels exceeded the upper limit value for an adequate aspirin response in 14% of individuals. This phenomenon was detected at 12 hours after dosing with aspirin. The coadministration of statins (mostly atorvastatin) was an independent predictor of residual serum TXB₂ levels, and the percentage of patients with enhanced values was significantly lower in statin users vs. nonusers. We provide evidence in vitro that atorvastatin reduced residual TXB₂ generation by increasing the extent of acetylation of platelet COX-1 by aspirin. In conclusion, the coadministration of statins may counter the mechanisms associated with reduced bioavailability of aspirin detected in some individuals with CV disease.

Part-of-the-sites binding and reactivity in the homooligomeric enzymes - facts and artifacts

For a number of enzymes composed of several subunits with the same amino acid sequence, it was documented, or suggested, that binding of a ligand, or catalysis, is carried out by a single subunit. This phenomenon may be the result of a pre-existent asymmetry of subunits or a limiting case of the negative cooperativity, and is sometimes called "half-of-the-sites binding (or reactivity)" for dimers and could be called "part-of-the-sites binding (or reactivity)" for higher oligomers. In this article, we discuss molecular mechanisms that may result in "part-of-the-sites binding (and reactivity)", offer possible explanations why it may have a beneficial role in enzyme function, and point to experimental problems in documenting this behaviour. We describe some cases, for which such a mechanism was first reported and later disproved. We also give several examples of enzymes, for which this mechanism seems to be well documented, and profitable. A majority of enzymes identified in this study as half-of-the-sites binding (or reactive) use it in the flip-flop version, in which "half-of-the-sites" refers to a particular moment in time. In general, the various variants of the mechanism seems to be employed often by oligomeric enzymes for allosteric regulation to enhance the efficiency of enzymatic reactions in many key metabolic pathways.

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.

The anti-inflammatory compound palmitoylethanolamide inhibits prostaglandin and hydroxyeicosatetraenoic acid production by a macrophage cell line

The anti‐inflammatory agent palmitoylethanolamide (PEA) reduces cyclooxygenase (COX) activity in vivo in a model of inflammatory pain. It is not known whether the compound reduces prostaglandin production in RAW264.7 cells, whether such an action is affected by compounds preventing the breakdown of endogenous PEA, whether other oxylipins are affected, or whether PEA produces direct effects upon the COX‐2 enzyme. RAW264.7 cells were treated with lipopolysaccharide and interferon‐γ to induce COX‐2. At the level of mRNA, COX‐2 was induced >1000‐fold following 24 h of the treatment. Coincubation with PEA (10 μmol/L) did not affect the levels of COX‐2, but reduced the levels of prostaglandins D₂ and E₂ as well as 11‐ and 15‐hydroxyeicosatetraenoic acid, which can also be synthesised by a COX‐2 pathway in macrophages. These effects were retained when hydrolysis of PEA to palmitic acid was blocked. Linoleic acid‐derived oxylipin levels were not affected by PEA. No direct effects of PEA upon the oxygenation of either arachidonic acid or 2‐arachidonoylglycerol by COX‐2 were found. It is concluded that in lipopolysaccharide and interferon‐γ‐stimulated RAW264.7 cells, PEA reduces the production of COX‐2‐derived oxylipins in a manner that is retained when its metabolism to palmitic acid is inhibited.

Antitumor Activity of Cytotoxic Cyclooxygenase-2 Inhibitors

Targeted delivery of chemotherapeutic agents to tumors has been explored as a means to increase the selectivity and potency of cytotoxicity. Most efforts in this area have exploited the molecular recognition of proteins highly expressed on the surface of cancer cells followed by internalization. A related approach that has received less attention is the targeting of intracellular proteins by ligands conjugated to anticancer drugs. An attractive target for this approach is the enzyme cyclooxygenase-2 (COX-2), which is highly expressed in a range of malignant tumors. Herein, we describe the synthesis and evaluation of a series of chemotherapeutic agents targeted to COX-2 by conjugation to indomethacin. Detailed characterization of compound 12, a conjugate of indomethacin with podophyllotoxin, revealed highly potent and selective COX-2 inhibition in vitro and in intact cells. Kinetics and X-ray crystallographic studies demonstrated that compound 12 is a slow, tight-binding inhibitor that likely binds to COX-2's allosteric site with its indomethacin moiety in a conformation similar to that of indomethacin. Compound 12 exhibited cytotoxicity in cell culture similar to that of podophyllotoxin with no evidence of COX-2-dependent selectivity. However, in vivo, compound 12 accumulated selectively in and more effectively inhibited the growth of a COX-2-expressing xenograft compared to a xenograft that did not express COX-2. Compound 12, which we have named chemocoxib A, provides proof-of-concept for the in vivo targeting of chemotherapeutic agents to COX-2 but suggests that COX-2-dependent selectivity may not be evident in cell culture-based assays.

Metabolism and phospholipid assembly of polyunsaturated fatty acids in human bone marrow mesenchymal stromal cells

High arachidonic acid (20:4n-6) and low n-3 PUFA levels impair the capacity of cultured human bone marrow mesenchymal stromal cells (hBMSCs) to modulate immune functions. The capacity of the hBMSCs to modify PUFA structures was found to be limited. Therefore, different PUFA supplements given to the cells resulted in very different glycerophospholipid (GPL) species profiles and substrate availability for phospholipases, which have preferences for polar head group and acyl chains when liberating PUFA precursors for production of lipid mediators. When supplemented with 20:4n-6, the cells increased prostaglandin E2 secretion. However, they elongated 20:4n-6 to the less active precursor, 22:4n-6, and also incorporated it into triacylglycerols, which may have limited the proinflammatory signaling. The n-3 PUFA precursor, 18:3n-3, had little potency to reduce the GPL 20:4n-6 content, while the eicosapentaenoic (20:5n-3) and docosahexaenoic (22:6n-3) acid supplements efficiently displaced the 20:4n-6 acyls, and created diverse GPL species substrate pools allowing attenuation of inflammatory signaling. The results emphasize the importance of choosing appropriate PUFA supplements for in vitro hBMSC expansion and suggests that for optimal function they require an exogenous fatty acid source providing 20:5n-3 and 22:6n-3 sufficiently, but 20:4n-6 moderately, which calls for specifically designed optimal PUFA supplements for the cultures.

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

Prostaglandin endoperoxide H synthase-2 (PGHS-2), also called cyclooxygenase-2 (COX-2), converts arachidonic acid to PGH₂ PGHS-2 is a conformational heterodimer composed of allosteric (E_allo) and catalytic (E_cat) subunits. Fatty acids (FAs) bind to Arg-120 of E_allo increasing to different degrees, depending on the FA, the V_max of its E_cat partner. We report here that movement of helical residues 120-122 and loop residues 123-129 of E_allo underlies the allosteric effects of FAs and allosteric COX-2 inhibitors, including naproxen and flurbiprofen. An S121P substitution in both PGHS-2 monomers yields a variant (S121P/S121P PGHS-2) that has 1.7-1.8 times the V_max of native PGHS-2 and is relatively insensitive to activation by FAs or inhibition by allosteric inhibitors. The S121P substitution in E_allo is primarily responsible for these effects. In X-ray crystal structures, the Cα atoms of helical residues 119-122 of S121P/S121P PGHS-2 are displaced from their normal positions. Additionally, the S121P/S121P PGHS-2 variants in which Pro-127 and Ser-541 are replaced by cysteines spontaneously forms Cys-127 to Cys-541 cross-links between monomers. This is unlike the corresponding native PGHS-2 variant and suggests that S121P substitutions also unhinge the loop involving residues 123-129. We conclude the following: (a) the region involving residues 120-129 of unoccupied E_allo tonically inhibits E_cat; (b) binding of an activating FA (e.g. arachidonic, palmitic, or oleic acid) to E_allo or an S121P substitution in E_allo repositions this region to increase E_cat activity; and (c) allosteric COX inhibitors act by preventing FA binding to E_allo and additionally by relocating E_allo residues to inhibit E_cat.

Colonic Saturated Fatty Acid Concentrations and Expression of COX-1, but not Diet, Predict Prostaglandin E2 in Normal Human Colon Tissue

Prostaglandin E2 (PGE2) in the colon is a pro-inflammatory mediator that is associated with increased risk of colon cancer. In this study, expression of genes in the PGE2 pathway were quantified in colon biopsies from a trial of a Mediterranean versus a Healthy Eating diet in 113 individuals at high risk for colon cancer. Colon biopsies were obtained before and after 6 months of intervention. Quantitative, real-time PCR was used to measure mRNA expression of prostaglandin H synthases (PTGS1 and 2), prostaglandin E synthases (PTGES1 and 3), prostaglandin dehydrogenase (HPGD), and PGE2 receptors (PTGER2, PTGER4). The most highly expressed genes were HPGD and PTGS1. In multivariate linear regression models of baseline data, both colon saturated fatty acid concentrations and PTGS1 expression were significant, positive predictors of colon PGE2 concentrations after controlling for nonsteroidal anti-inflammatory drug use, gender, age, and smoking status. The effects of dietary intervention on gene expression were minimal with small increases in expression noted for PTGES3 in both arms and in PTGER4 in the Mediterranean arm. These results indicate that short-term dietary change had little effect on enzymes in the prostaglandin pathway in the colon and other factors, such as differences in fatty acid metabolism, might be more influential.

Enhanced expression of human prostaglandin H synthase-2 in the yeast Pichia pastoris and removal of the C-terminal tag with bovine carboxypeptidase A

Vertebrate prostaglandin H synthases (PGHSs) are membrane-bound disulphide-containing hemoglycoproteins. Therefore, eukaryotic expression systems are required for the production of recombinant PGHSs. Recently we announced the expression of human PGHS-2 (hPGHS-2) in the yeast Pichia pastoris. Here we report improved production of hPGHS-2 in P. pastoris and a convenient method for the purification and de-tagging of the protein. An affinity tag comprised of a proline, a glycine and eight histidines was introduced into the C-terminal end of hPGHS-2. The tagged hPGHS-2 was expressed intracellularly in P. pastoris under the control of a constitutive or methanol-inducible promoter. Compared to constitutive expression, methanol-induced expression yielded approximately four times more protein. The analysis of high and low gene copy number recombinants revealed a positive correlation between the gene copy number and the expression level of hPGHS-2. The recombinant hPGHS-2 was purified using immobilised metal ion affinity chromatography. A novel elution method, treatment of the affinity resin with bovine carboxypeptidase A, was employed. The yield of pure de-tagged hPGHS-2 from 1l of yeast culture was approximately 3mg. The protein purification process with simultaneous removal of the C-terminal polyhistidine tag could be easily applied for the affinity purification of other proteins.

Interactions of 2-O-arachidonylglycerol ether and ibuprofen with the allosteric and catalytic subunits of human COX-2

Prostaglandin (PG) endoperoxide H synthase (PGHS)-2, also known as cyclooxygenase (COX)-2, can convert arachidonic acid (AA) to PGH2 in the committed step of PG synthesis. PGHS-2 functions as a conformational heterodimer composed of an allosteric (Eallo) and a catalytic (Ecat) monomer. Here we investigated the interplay between human (hu)PGHS-2 and an alternative COX substrate, the endocannabinoid, 2-arachidonoylglycerol (2-AG), as well as a stable analog, 2-O-arachidonylglycerol ether (2-AG ether). We also compared the inhibition of huPGHS-2-mediated oxygenation of AA, 2-AG, and 2-AG ether by the well-known COX inhibitor, ibuprofen. When tested with huPGHS-2, 2-AG and 2-AG ether exhibit very similar kinetic parameters, responses to stimulation by FAs that are not COX substrates, and modes of inhibition by ibuprofen. The 2-AG ether binds Ecat more tightly than Eallo and, thus, can be used as a stable Ecat-specific substrate to examine certain Eallo-dependent responses. Ibuprofen binding to Eallo of huPGHS-2 completely blocks 2-AG or 2-AG ether oxygenation; however, inhibition by ibuprofen of huPGHS-2-mediated oxygenation of AA engages a combination of both allosteric and competitive mechanisms.

The lack of aspirin resistance in patients with coronary artery disease

Background

Aspirin resistance established by different laboratory methods is still a debated problem. Using COX1 specific methods no aspirin resistance was detected among healthy volunteers. Here we tested the effect of chronic aspirin treatment on platelets from patients with stable coronary artery disease. The expression of COX2 mRNA in platelets and its influences on the effect of aspirin was also investigated.

Methods

One hundred and forty four patients were enrolled in the study. The direct measurement of COX1 acetylation was carried out by monoclonal antibodies specific to acetylated and non-acetylated COX1 (acCOX1 and nacCOX1) using Western blotting technique. Arachidonic acid (AA) induced TXB₂ production by platelets was measured by competitive immunoassay. AA induced platelet aggregation, ATP secretion and VerifyNow Aspirin Assay were also performed. COX2 and COX1 mRNA expression in platelets were measured in 56 patients by RT-qPCR.

Results

In 138 patients only acCOX1 was detected, in the remaining six patients nacCOX1 disappeared after a compliance period. AA induced TXB₂ production by platelets was very low in all patients including the 6 patients after compliance. AA induced platelet aggregation, secretion and with a few exceptions the VerifyNow Assay also demonstrated the effect of aspirin. Smoking, diabetes mellitus and inflammatory conditions did not influence the results. The very low amount of COX2 mRNA detected in 39 % of the investigated platelets did not influence the effect of aspirin.

Conclusions

No aspirin resistance was detected among patients with stable coronary artery disease. COX2 expression in platelets did not influence the effect of aspirin.

Conservative Secondary Shell Substitution In Cyclooxygenase-2 Reduces Inhibition by Indomethacin Amides and Esters via Altered Enzyme Dynamics

The cyclooxygenase enzymes (COX-1 and COX-2) are the therapeutic targets of nonsteroidal anti-inflammatory drugs (NSAIDs). Neutralization of the carboxylic acid moiety of the NSAID indomethacin to an ester or amide functionality confers COX-2 selectivity, but the molecular basis for this selectivity has not been completely revealed through mutagenesis studies and/or X-ray crystallographic attempts. We expressed and assayed a number of divergent secondary shell COX-2 active site mutants and found that a COX-2 to COX-1 change at position 472 (Leu in COX-2, Met in COX-1) reduced the potency of enzyme inhibition by a series of COX-2-selective indomethacin amides and esters. In contrast, the potencies of indomethacin, arylacetic acid, propionic acid, and COX-2-selective diarylheterocycle inhibitors were either unaffected or only mildly affected by this mutation. Molecular dynamics simulations revealed identical equilibrium enzyme structures around residue 472; however, calculations indicated that the L472M mutation impacted local low-frequency dynamical COX constriction site motions by stabilizing the active site entrance and slowing constriction site dynamics. Kinetic analysis of inhibitor binding is consistent with the computational findings.

Different Fatty Acids Compete with Arachidonic Acid for Binding to the Allosteric or Catalytic Subunits of Cyclooxygenases to Regulate Prostanoid Synthesis

Prostaglandin endoperoxide H synthases (PGHSs), also called cyclooxygenases (COXs), convert arachidonic acid (AA) to PGH2. PGHS-1 and PGHS-2 are conformational heterodimers, each composed of an (Eallo) and a catalytic (Ecat) monomer. Previous studies suggested that the binding to Eallo of saturated or monounsaturated fatty acids (FAs) that are not COX substrates differentially regulate PGHS-1 versus PGHS-2. Here, we substantiate and expand this concept to include polyunsaturated FAs known to modulate COX activities. Non-substrate FAs like palmitic acid bind Eallo of PGHSs stimulating human (hu) PGHS-2 but inhibiting huPGHS-1. We find the maximal effects of non-substrate FAs on both huPGHSs occurring at the same physiologically relevant FA/AA ratio of ∼20. This inverse allosteric regulation likely underlies the ability of PGHS-2 to operate at low AA concentrations, when PGHS-1 is effectively latent. Unlike FAs tested previously, we observe that C-22 FAs, including ω-3 fish oil FAs, have higher affinities for Ecat than Eallo subunits of PGHSs. Curiously, C-20 ω-3 eicosapentaenoate preferentially binds Ecat of huPGHS-1 but Eallo of huPGHS-2. PGE2 production decreases 50% when fish oil consumption produces tissue EPA/AA ratios of ≥0.2. However, 50% inhibition of huPGHS-1 itself is only seen with ω-3 FA/AA ratios of ≥5.0. This suggests that fish oil-enriched diets disfavor AA oxygenation by altering the composition of the FA pool in which PGHS-1 functions. The distinctive binding specificities of PGHS subunits permit different combinations of non-esterified FAs, which can be manipulated dietarily, to regulate AA binding to Eallo and/or Ecat thereby controlling COX activities.

Competition and allostery govern substrate selectivity of cyclooxygenase-2

Cyclooxygenase-2 (COX-2) oxygenates arachidonic acid (AA) and its ester analog, 2-arachidonoylglycerol (2-AG), to prostaglandins (PGs) and prostaglandin glyceryl esters (PG-Gs), respectively. Although the efficiency of oxygenation of these substrates by COX-2 in vitro is similar, cellular biosynthesis of PGs far exceeds that of PG-Gs. Evidence that the COX enzymes are functional heterodimers suggests that competitive interaction of AA and 2-AG at the allosteric site of COX-2 might result in differential regulation of the oxygenation of the two substrates when both are present. Modulation of AA levels in RAW264.7 macrophages uncovered an inverse correlation between cellular AA levels and PG-G biosynthesis. In vitro kinetic analysis using purified protein demonstrated that the inhibition of 2-AG oxygenation by high concentrations of AA far exceeded the inhibition of AA oxygenation by high concentrations of 2-AG. An unbiased systems-based mechanistic model of the kinetic data revealed that binding of AA or 2-AG at the allosteric site of COX-2 results in a decreased catalytic efficiency of the enzyme toward 2-AG, whereas 2-AG binding at the allosteric site increases COX-2's efficiency toward AA. The results suggest that substrates interact with COX-2 via multiple potential complexes involving binding to both the catalytic and allosteric sites. Competition between AA and 2-AG for these sites, combined with differential allosteric modulation, gives rise to a complex interplay between the substrates, leading to preferential oxygenation of AA.

Effects of a Mediterranean Diet Intervention on Anti- and Pro-Inflammatory Eicosanoids, Epithelial Proliferation, and Nuclear Morphology in Biopsies of Normal Colon Tissue

This randomized trial evaluated the effects of intervention with either a Healthy Eating or a Mediterranean diet on colon biomarkers in 120 healthy individuals at increased colon cancer risk. The hypothesis was that eicosanoids and markers of proliferation would be favorably affected by the Mediterranean diet. Colon epithelial biopsy tissues and blood samples were obtained at baseline and after 6 mo of intervention. Colonic eicosanoid concentrations were evaluated by HPLC-MS-MS, and measures of epithelial proliferation and nuclear morphology were evaluated by image analysis of biopsy sections. There was little change in proinflammatory eicosanoids and in plasma cytokine concentrations with either dietary intervention. There was, however, a 50% increase in colonic prostaglandin E3 (PGE3), which is formed from eicosapentanoic acid, in the Mediterranean arm. Unlike PGE2, PGE3, was not significantly affected by regular use of non-steroidal anti-inflammatory drugs at baseline, and normal weight subjects had significantly higher colon PGE3 than overweight or obese subjects. Increased proliferation in the colon at baseline, by Ki67 labeling, was associated with morphological features that defined smaller nuclei in the epithelial cells, lower colon leukotriene concentrations and higher plasma cytokine concentrations. Dietary intervention had little effect on measures of epithelial proliferation or of nuclear morphology. The increase in PGE3 with a Mediterranean diet indicates that in normal colon, diet might affect protective pathways to a greater extent than proinflammatory and proliferative pathways. Hence, biomarkers from cancer models might not be relevant in a true prevention setting.

13-Methylarachidonic acid is a positive allosteric modulator of endocannabinoid oxygenation by cyclooxygenase

Cyclooxygenase-2 (COX-2) oxygenates arachidonic acid (AA) and the endocannabinoids 2-arachidonoylglycerol (2-AG) and arachidonylethanolamide to prostaglandins, prostaglandin glyceryl esters, and prostaglandin ethanolamides, respectively. A structural homodimer, COX-2 acts as a conformational heterodimer with a catalytic and an allosteric monomer. Prior studies have demonstrated substrate-selective negative allosteric regulation of 2-AG oxygenation. Here we describe AM-8138 (13(S)-methylarachidonic acid), a substrate-selective allosteric potentiator that augments 2-AG oxygenation by up to 3.5-fold with no effect on AA oxygenation. In the crystal structure of an AM-8138·COX-2 complex, AM-8138 adopts a conformation similar to the unproductive conformation of AA in the substrate binding site. Kinetic analysis suggests that binding of AM-8138 to the allosteric monomer of COX-2 increases 2-AG oxygenation by increasing kcat and preventing inhibitory binding of 2-AG. AM-8138 restored the activity of COX-2 mutants that exhibited very poor 2-AG oxygenating activity and increased the activity of COX-1 toward 2-AG. Competition of AM-8138 for the allosteric site prevented the inhibition of COX-2-dependent 2-AG oxygenation by substrate-selective inhibitors and blocked the inhibition of AA or 2-AG oxygenation by nonselective time-dependent inhibitors. AM-8138 selectively enhanced 2-AG oxygenation in intact RAW264.7 macrophage-like cells. Thus, AM-8138 is an important new tool compound for the exploration of allosteric modulation of COX enzymes and their role in endocannabinoid metabolism.

Synthesis and evaluation of new benzimidazole-based COX inhibitors: a naproxen-like interaction detected by STD-NMR

Non-steroidal anti-inflammatory drugs exert their pharmacological activity through inhibition of cyclooxygenase 1 and 2 (COX-1 and COX-2).

A cyclooxygenase-2-dependent prostaglandin E2 biosynthetic system in the Golgi apparatus

Cyclooxygenases (COXs) catalyze the committed step in prostaglandin (PG) biosynthesis. COX-1 is constitutively expressed and stable, whereas COX-2 is inducible and short lived. COX-2 is degraded via endoplasmic reticulum (ER)-associated degradation (ERAD) following post-translational glycosylation of Asn-594. COX-1 and COX-2 are found in abundance on the luminal surfaces of the ER and inner membrane of the nuclear envelope. Using confocal immunocytofluorescence, we detected both COX-2 and microsomal PGE synthase-1 (mPGES-1) but not COX-1 in the Golgi apparatus. Inhibition of trafficking between the ER and Golgi retarded COX-2 ERAD. COX-2 has a C-terminal STEL sequence, which is an inefficient ER retention signal. Substituting this sequence with KDEL, a robust ER retention signal, concentrated COX-2 in the ER where it was stable and slowly glycosylated on Asn-594. Native COX-2 and a recombinant COX-2 having a Golgi targeting signal but not native COX-1 exhibited efficient catalytic coupling to mPGES-1. We conclude that N-glycosylation of Asn-594 of COX-2 occurs in the ER, leading to anterograde movement of COX-2 to the Golgi where the Asn-594-linked glycan is trimmed prior to retrograde COX-2 transport to the ER for ERAD. Having an inefficient ER retention signal leads to sluggish Golgi to ER transit of COX-2. This permits significant Golgi residence time during which COX-2 can function catalytically. Cytosolic phospholipase A2α, which mobilizes arachidonic acid for PG synthesis, preferentially translocates to the Golgi in response to physiologic Ca(2+) mobilization. We propose that cytosolic phospholipase A2α, COX-2, and mPGES-1 in the Golgi comprise a dedicated system for COX-2-dependent PGE2 biosynthesis.

Bacterial and algal orthologs of prostaglandin H₂synthase: novel insights into the evolution of an integral membrane protein

Prostaglandin H₂synthase (PGHS; EC 1.14.99.1), a bi-functional heme enzyme that contains cyclooxygenase and peroxidase activities, plays a central role in the inflammatory response, pain, and blood clotting in higher eukaryotes. In this review, we discuss the progenitors of the mammalian enzyme by using modern bioinformatics and homology modeling to draw comparisons between this well-studied system and its orthologs from algae and bacterial sources. A clade of bacterial and algal orthologs is described that have salient structural features distinct from eukaryotic counterparts, including the lack of a dimerization and EGF-like domains, the absence of gene duplicates, and minimal membrane-binding domains. The functional implications of shared and variant features are discussed.

Biomarkers for personalizing omega-3 fatty acid dosing

Prostaglandin E2 (PGE2) has been linked to a higher risk of colorectal cancer. PGE2 in colon tissue can be reduced by increasing dietary eicosapentaenoic acid (EPA). The dose-dependent relationships between dietary EPA, serum EPA:arachidonate (AA) ratio, urinary PGE2 metabolites, and colonic eicosanoids were evaluated to develop biomarkers for prediction of colonic PGE2. Male rats were fed diets containing EPA:ω6 fatty acid ratios of 0, 0.1, 0.2, 0.4, or 0.6 for 5 weeks. Increasing the dietary EPA:ω6 fatty acid ratio increased EPA:AA ratios in serum and in the proximal, transverse, and distal colon (P < 0.001). The urinary PGE2 metabolite was reduced (P = 0.006). EPA-rich diets reduced colonic tissue PGE2 concentrations by 58% to 66% and increased PGE3 by 19- to 28-fold. Other AA-derived eicosanoids were reduced by 35% to 83%. The changes were not linear, with the largest changes in eicosanoids observed with the lower doses. A mathematical model predicts colonic tissue eicosanoids from the EPA:AA ratio in serum and the EPA dose. Every 10% increase in serum EPA:AA was associated with a 2% decrease in the (geometric) mean of PGE2 in the distal colon. These mathematical relationships can now be applied to individualized EPA dosing in clinical trials.

N-glycosylation site occupancy in human prostaglandin H synthases expressed in Pichia pastoris

Prostaglandin H synthases (PGHSs) are N-glycosylated membrane proteins that catalyse the committed step in prostaglandin synthesis. Unlike PGHS-2, the production of recombinant PGHS-1 in non-mammalian expression systems is complicated. The majority of the heterologous enzyme is inactive due to misfolding. Correct N-glycosylation is proposed to be obligatory for proper folding of mammalian PGHSs. In this study, human PGHS-1 and -2 (hPGHS-1 and -2) were expressed in the yeast Pichia pastoris. Recombinant hPGHS-2 was catalytically active, whereas hPGHS-1 was inactive. Accumulation of non-glycosylated hPGHSs was not observed in the crude lysate of the yeast cells. The N-glycosylation patterns of the purified recombinant proteins were characterised using nano-LC/MS/MS. The isoforms exhibited similar N-glycosylation site occupancy. The results indicate that there are more complex grounds for the inactivity of the recombinant hPGHS-1 produced in yeast.

Reappraisal of the clinical pharmacology of low-dose aspirin by comparing novel direct and traditional indirect biomarkers of drug action

BACKGROUND

Even though the acetylation of platelet cyclooxygenase (COX)-1 at serine-529 is the direct mechanism of action of low-dose aspirin, its antiplatelet effect has been characterized using indirect indexes of COX-1 activity.

OBJECTIVES

We performed a clinical study with enteric-coated low-dose aspirin (EC-aspirin), in healthy subjects, to evaluate the effects on the extent and duration of platelet COX-1 acetylation, using a novel proteomic strategy for absolute protein quantification (termed AQUA), as compared with traditional pharmacokinetic and pharmacodynamic parameters.

SUBJECTS AND METHODS

In a phase I, single-arm, open-label study of EC aspirin (100 mg day(-1) ) administered to 24 healthy subjects, we compared, over a 24 h-period on day 1 and 7, % platelet acetylated COX-1 (AceCOX-1) with traditional pharmacokinetic and pharmacodynamics [i.e. serum thromboxane (TX) B2 , platelet function by monitoring CEPI(collagen/epinephrine) closure time (CT) using whole-blood PFA-100 and urinary excretion of 11-dehydro-TXB2 ] parameters.

RESULTS

Acetylation of platelet COX-1 was measurable before detection of aspirin levels in the systemic circulation and increased in a cumulative fashion upon repeated dosing. After the last dose of EC-aspirin, %AceCOX-1, serum TXB2 and CEPI-CT values were maximally and persistently modified throughout 24 h; they averaged 76 ± 2%, 99.0 ± 0.4% and 271 ± 5 s, respectively. EC-aspirin caused 75% reduction in urinary 11-dehydro-TXB2 excretion. After chronic dosing with aspirin, the pharmacokinetics of acetylsalicylic acid was completely dissociated from pharmacodynamics.

CONCLUSIONS

The demonstrated feasibility of quantifying the extent and duration of platelet COX-1 acetylation will allow characterizing the genetic, pharmacokinetic and pharmacodynamic determinants of the inter-individual variability in the antiplatelet response to low-dose aspirin as well as identifying extra-platelet sites of drug action.

Dietary polyunsaturated fatty acids and inflammation: the role of phospholipid biosynthesis

The composition of fatty acids in the diets of both human and domestic animal species can regulate inflammation through the biosynthesis of potent lipid mediators. The substrates for lipid mediator biosynthesis are derived primarily from membrane phospholipids and reflect dietary fatty acid intake. Inflammation can be exacerbated with intake of certain dietary fatty acids, such as some ω-6 polyunsaturated fatty acids (PUFA), and subsequent incorporation into membrane phospholipids. Inflammation, however, can be resolved with ingestion of other fatty acids, such as ω-3 PUFA. The influence of dietary PUFA on phospholipid composition is influenced by factors that control phospholipid biosynthesis within cellular membranes, such as preferential incorporation of some fatty acids, competition between newly ingested PUFA and fatty acids released from stores such as adipose, and the impacts of carbohydrate metabolism and physiological state. The objective of this review is to explain these factors as potential obstacles to manipulating PUFA composition of tissue phospholipids by specific dietary fatty acids. A better understanding of the factors that influence how dietary fatty acids can be incorporated into phospholipids may lead to nutritional intervention strategies that optimize health.

Pre-existent asymmetry in the human cyclooxygenase-2 sequence homodimer

Prostaglandin endoperoxide H synthase-2 (PGHS-2), also known as cyclooxygenase-2 (COX-2), is a sequence homodimer. However, the enzyme exhibits half-site heme and inhibitor binding and functions as a conformational heterodimer having a catalytic subunit (Ecat) with heme bound and an allosteric subunit (Eallo) lacking heme. Some recombinant heterodimers composed of a COX-deficient mutant subunit and a native subunit (i.e. Mutant/Native PGHS-2) have COX activities similar to native PGHS-2. This suggests that the presence of heme plus substrate leads to the subunits becoming lodged in a semi-stable Eallo-mutant/Ecat-Native∼heme form during catalysis. We examined this concept using human PGHS-2 dimers composed of combinations of Y385F, R120Q, R120A, and S530A mutant or native subunits. With some heterodimers (e.g. Y385F/Native PGHS-2), heme binds with significantly higher affinity to the native subunit. This correlates with near native COX activity for the heterodimer. With other heterodimers (e.g. S530A/Native PGHS-2), heme binds with similar affinities to both subunits, and the COX activity approximates that expected for an enzyme in which each monomer contributes equally to the net COX activity. With or without heme, aspirin acetylates one-half of the subunits of the native PGHS-2 dimer, the Ecat subunits. Subunits having an S530A mutation are refractory to acetylation. Curiously, aspirin acetylates only one-quarter of the monomers of S530A/Native PGHS-2 with or without heme. This implies that there are comparable amounts of two noninterchangeable species of apoenzymes, Eallo-S530A/Ecat-Native and Eallo-Native/Ecat-S530A. These results suggest that native PGHS-2 assumes a reasonably stable, asymmetric Eallo/Ecat form during its folding and processing.

Historical lessons in translational medicine: cyclooxygenase inhibition and P2Y12 antagonism

The development of drugs that inhibit platelets has been driven by a combination of clinical insights, fundamental science, and sheer luck. The process has evolved as the days of stumbling on therapeutic gems, such as aspirin, have long passed and have been replaced by an arduous process in which a drug is designed to target a specific protein implicated in a well-characterized pathophysiological process, or so we would like to believe. The development of antiplatelet therapy illustrates the importance of understanding the mechanisms of disease and the pharmacology of the compounds we develop, coupled with careful clinical experimentation and observation and, yes, still, a fair bit of luck.

Eicosanoids in metabolic syndrome

Chronic persistent inflammation plays a significant role in disease pathology of cancer, cardiovascular disease, and metabolic syndrome (MetS). MetS is a constellation of diseases that include obesity, diabetes, hypertension, dyslipidemia, hypertriglyceridemia, and hypercholesterolemia. Nonalcoholic fatty liver disease (NAFLD) is associated with many of the MetS diseases. These metabolic derangements trigger a persistent inflammatory cascade, which includes production of lipid autacoids (eicosanoids) that recruit immune cells to the site of injury and subsequent expression of cytokines and chemokines that amplify the inflammatory response. In acute inflammation, the transcellular synthesis of antiinflammatory eicosanoids resolve inflammation, while persistent activation of the autacoid-cytokine-chemokine cascade in metabolic disease leads to chronic inflammation and accompanying tissue pathology. Many drugs targeting the eicosanoid pathways have been shown to be effective in the treatment of MetS, suggesting a common linkage between inflammation, MetS and drug metabolism. The cross-talk between inflammation and MetS seems apparent because of the growing evidence linking immune cell activation and metabolic disorders such as insulin resistance, dyslipidemia, and hypertriglyceridemia. Thus modulation of lipid metabolism through either dietary adjustment or selective drugs may become a new paradigm in the treatment of metabolic disorders. This review focuses on the mechanisms linking eicosanoid metabolism to persistent inflammation and altered lipid and carbohydrate metabolism in MetS.