Specific binding of non-steroidal anti-inflammatory drugs (NSAIDs) to phospholipase A2: structure of the complex formed between phospholipase A2 and diclofenac at 2.7 A resolution

β-keto amyrin isolated from Cryptostegia grandiflora R. br. inhibits inflammation caused by Daboia russellii viper venom: Direct binding of β-keto amyrin to phospholipase A2

The search for mechanism-based anti-inflammatory therapies is of fundamental importance to avoid undesired off-target effects. Phospholipase A2 (PLA2) activity is a potential molecular target for anti-inflammatory drugs because it fuels arachidonic acid needed to synthesize inflammation mediators, such as prostaglandins. Herein, we aim to investigate the molecular mechanism by which β-keto amyrin isolated from a methanolic extract of Cryptostegia grandiflora R. Br. Leaves can inhibit inflammation caused by Daboia russellii viper (DR) venom that mainly contains PLA2. We found that β-keto amyrin neutralizes DR venom-induced paw-edema in a mouse model. Molecular docking of PLA2 with β-keto amyrin complex resulted in a higher binding energy score of -8.86 kcal/mol and an inhibition constant of 611.7 nM. Diclofenac had a binding energy of -7.04 kcal/mol and an IC50 value of 620 nM, which predicts a poorer binding interaction than β-keto amyrin. The higher conformational stability of β-keto amyrin interaction compared to diclofenac is confirmed by molecular dynamics simulation. β-keto amyrin isolated from C. grandiflora inhibits the PLA2 activity contained in Daboia russellii viper venom. The anti-inflammatory property of β-keto amyrin is due to its direct binding into the active site of PLA2, thus inhibiting its enzyme activity.

A novel peptide able to reduce PLA2 activity and modulate inflammatory cytokine production

Phospholipases A2 (PLA2s) are associated with inflammatory response, performing a complex process involving, specially, cytokines. The excess of pro-inflammatory cytokines induces a chronic inflammatory response and can cause several disorders in the body. Therefore, the inhibition or regulation of cytokines' signaling pathways is a target for new treatment development strategies. Thus, this study aimed to select PLA2 inhibitor mimetic peptides through phage display technology with anti-inflammatory activity. Specific mimetic peptides were selected using BpPLA2-TXI, a PLA2 isolated from Bothrops pauloensis, as a target, and γCdcPL, a PLA2 inhibitor isolated from Crotalus durissus collilineatus, which was used as a competitor during the elution step. We selected the peptide C2PD, which seems to play a pivotal role in the modulation of IL-6, IL-1β, and IL-10 cytokines in inflammatory cells. The C2PD showed a significant reduction in PLA2 activity. Furthermore, the synthetic peptide was tested in PBMC and showed a significant down-modulation of IL-6 and IL-1β release, whereas IL-10 responses were up-regulated. Our findings suggest that this novel peptide may be a potential therapeutic candidate for the treatment of inflammatory diseases, mainly due to its anti-inflammatory properties and absence of cytotoxicity.

Structural Investigation of Diclofenac Binding to Ovine, Caprine, and Leporine Serum Albumins

Free drug concentration in the blood sera is crucial for its appropriate activity. Serum albumin, the universal blood carrier protein, is responsible for transporting drugs and releasing them into the bloodstream. Therefore, a drug's binding to SA is especially important for its bioavailability and it is a key problem in the drug design process. In this paper, we present crystal structures of three animal serum albumin complexes: ovine, caprine, and leporine, with diclofenac, a popular non-steroidal anti-inflammatory drug that is used in therapy of chronic and acute pain. Details of diclofenac binding mode by the presented serum albumins are compared with analogous complexes of human and equine serum albumins. The analysis of the occupied binding pockets in crystal structures of the investigated serum albumins from different mammals shows that they have two common and a number of unique diclofenac binding sites. The most intriguing is the fact that the albumins from the described species are able to bind different numbers of molecules of this popular anti-inflammatory drug, but none of the binding sites overlap with ones in the human serum albumin.

Evaluating the effect of diclofenac on hydrogen production by anaerobic fermentation of waste activated sludge

Hydrogen production from waste-activated sludge (WAS) anaerobic fermentation is considered to be an effective method of resource recovery. However, the presence of a large number of complex organic compounds in sludge will affect the biological hydrogen production process. As an extensively applied prevalent anti-inflammatory drug, diclofenac (DCF) is inevitably released into the environment. However, the effect of diclofenac on hydrogen production from WAS anaerobic fermentation has not been fully investigated. This work therefore aims to comprehensively investigate the removal efficiency of DCF in mesophilic anaerobic fermentation of WAS and its effect on hydrogen yield. Experiment results showed that 32.5%-38.3% of DCF was degraded in the fermentation process when DCF concentration was ranged from 6 to 100 mg/kg TSS (total suspended solids). DCF at environmental level inhibited hydrogen production, the maximal hydrogen yield decreased from 24.2 to 15.3 mL/g VSS (volatile suspended solids) with an increase of DCF addition from 6 to 100 mg/kg TSS. This is because the presence of DCF caused inhibitions to acetogenesis and acidogenesis, the processes responsible for hydrogen production, probably due to that the polar groups of DCF (i.e., carboxyl group) could readily bind to active sites of [FeFe]- Hydrogenase. Besides, the microbial analysis revealed that DCF increased the microbial diversity but had few influences on the microbial structure.

Role of respiratory uncoupling in drug-induced mitochondrial permeability transition

Mitochondrial injury contributes to severe drug-induced liver injury. Particularly, mitochondrial permeability transition (MPT) is thought to be relevant to cytolytic hepatitis. However, the mechanism of drug-induced MPT is unclear and prediction of MPT is not adequately evaluated in the preclinical stage. In a previous study, we found that troglitazone, a drug withdrawn due to liver injury, induced MPT via mild depolarization probably resulting from uncoupling. Herein, we investigated whether other drugs that induce MPT share similar properties as troglitazone, using isolated mitochondria from rat liver. Of the 22 test drugs examined, six drugs, including troglitazone, induced MPT and showed an uncoupling effect. Additionally, receiver operating characteristic analysis was conducted to predict the MPT potential from the respiratory control ratio, an indicator of uncoupling intensity. Results showed that 2.5 was the best threshold that exhibited high sensitivity (1.00) and high specificity (0.81), indicating that uncoupling was correlated with MPT potential. Activation of calcium-independent phospholipase A2 appeared to be involved in uncoupling-induced MPT. Furthermore, a strong relationship between MPT intensity and the uncoupling effect among similar compounds was confirmed. These results may help in predicting MPT potential using cultured cells and modifying the chemical structures of the drugs to reduce MPT risk.

Biochemical and functional characterization of a new recombinant phospholipase A2 inhibitor from Crotalus durissus collilineatus snake serum

Phospholipase A₂ plays an important role in many diseases. Thus, the production of bioactive molecules, which can modulate PLA₂ activity, became an important target for the pharmaceutical industry. Previously, we demonstrated the inhibitory and anti-angiogenic effect of γCdcPLI, the natural PLA₂inhibitor from Crotalus durissus collilineatus. The aim of the present study was to recombinantly express the γCdcPLI inhibitor and analyze its biochemical and functional characteristics. Based on the amino acid sequence from the natural protein, we designed a synthetic gene for production of a non-tagged recombinant recγCdcPLI using the pHis-Parallel2 vector. To enable disulfide bond formation, protein expression was performed using E. coli Rosetta-gamiB. The protein was purified by anion and affinity chromatography with a yield of 5 mg/L. RecγCdcPLI showed similar secondary structure in CD and FTIR, revealing predominately β-strands. Analogous to the natural protein, recγCdcPLI was able to form oligomers of ~5.5 nm. The inhibitor was efficiently binding to PLA₂ from honeybee (Kd = 1.48 μM) and was able to inhibit the PLA₂ activity. Furthermore, it decreased the vessel formation in HUVEC cells, suggesting an anti-angiogenic potential. Heterologous production of recγCdcPLI is highly efficient and thus enables enhanced drug design for treatment of diseases triggered by PLA₂ activity.

Scientific Rationale for a Bottom-Up Approach to Target the Host Response in Order to Try and Reduce the Numbers Presenting With Adult Respiratory Distress Syndrome Associated With COVID-19. Is There a Role for Statins and COX-2 Inhibitors in the Prevention and Early Treatment of the Disease?

The inflammatory response to and the subsequent development of Adult Respiratory Distress Syndrome (ARDS) is considered to underpin COVID-19 pathogenesis. With a developing world catastrophe, we need to examine our known therapeutic stocks, to assess suitability for prevention and/or treatment of this pro-inflammatory virus. Analyzing commonly available and inexpensive immunomodulatory and anti-inflammatory medications to assess their possible effectiveness in improving the host response to COVID-19, this paper recommends the following: (1) optimize current health-cease (reduce) smoking, ensure adequate hypertension and diabetes control, continue exercising; (2) start on an HMG CoA reductase inhibitor "statin" for its immunomodulatory and anti-inflammatory properties, which may reduce the mortality associated with ARDS; and (3) consider using Diclofenac (or other COX-2 inhibition medications) for its anti-inflammatory and virus toxicity properties. For purposes of effectiveness, this needs to be in the early course of the disease (post infection and/or symptom presentation) and given in a high dose. The downsides to these recommended interventions are considered manageable at this stage of the pandemic.

Increased PUFA levels in kidney epithelial cells in the course of diclofenac toxicity

This study evaluated polyunsaturated fatty acids (PUFAs) in human kidney epithelial cells exposed to diclofenac (DCL) toxicity. Kidney cells were treated with DCL to induce cytotoxicity and thymoquinone (TQ) was administered to decrease cytotoxic effects. Levels of arachidonic acid (AA, C20:4n-6), dihomo-gamma-linolenic acid (DGLA, C20:3n-6), eicosapentaenoic acid (EPA, C20:5n-3) and docosahexaenoic acid (DHA, C22:6n-3) were determined by liquid chromatography coupled with tandem mass spectrometry. Cytosolic phospholipase A₂ (cPLA₂), cyclooxygenase 1 (COX-1) and prostaglandin E₂ (PGE₂) were measured to evaluate changes in enzyme activity. Immunofluorescence staining and western blot analysis was performed to determine protein levels of COX- 1. Renal cell toxicity was accomplished by DCL and was alleviated by TQ treatment. Diclofenac significantly increased all measured PUFAs while pretreatment with TQ decreased PUFA levels in DCL treated cells. Cytosolic PLA₂ and total COX activity was significantly decreased in DCL treated cells. Immunofluorescence staining and western blot analysis confirmed significantly decreased COX-1 levels in DCL and DCL + TQ treated groups. The results of this study reveal that DCL treatment is associated with accumulation of PUFAs in kidney cells. We suggest that PUFA accumulation in DCL toxicity might be a consequence of both cPLA₂ and COX-1 inhibition. Thymoquinone administration, along with DCL treatment alleviated the buildup of PUFAs and DCL-induced cell death in kidney cells.

A Review of Chronic Musculoskeletal Pain: Central and Peripheral Effects of Diclofenac

Diclofenac is widely used to manage chronic inflammatory and degenerative joint diseases such as osteoarthritis (OA), rheumatoid arthritis (RA), ankylosing spondylitis, and extra-articular rheumatism. Its various mechanisms of action make it particularly effective in treating nociceptive pain, but it is also an alternative for treating spinal and chronic central pain. Osteoarthritis and rheumatoid arthritis are the most frequently encountered arthritic conditions in adults. The management of nociceptive pain requires a sequential hierarchical approach, with the initial NSAID treatment being characterized by the replacement of one drug with another, or complete discontinuation usually because of insufficient pain control. OA- and RA-related pain is complex and multifactorial, and due to physiological interactions between the signaling of the central and peripheral nervous systems. The mechanisms of action of diclofenac make it particularly effective in treating both nociceptive pain and chronic central pain. This review underlines the mechanisms of diclofenac involved in chronic and acute joint pain, the most relevant adverse events.

Protein-ligand binding site detection as an alternative route to molecular docking and drug repurposing

After the onset of the genomic era, the detection of ligand binding sites in proteins has emerged over the last few years as a powerful tool for protein function prediction. Several approaches, both sequence and structure based, have been developed, but the full potential of the corresponding tools has not been exploited yet. Here, we describe the development and classification of a large, almost exhaustive, collection of protein-ligand binding sites to be used, in conjunction with the Ligand Binding Site Recognition Application Web Application developed in our laboratory, as an alternative to virtual screening through molecular docking simulations to identify novel lead compounds for known targets. Ligand binding sites derived from the Protein Data Bank have been clustered according to ligand similarity, and given a known ligand, the binding mode of related ligands to the same target can be predicted. The collection of ligand binding sites contains more than 200,000 sites corresponding to more than 20,000 different ligands. Furthermore, the ligand binding sites of all Food and Drug Administration-approved drugs have been classified as well, allowing to investigate the possible binding of each of them (and related compounds) to a given target for drug repurposing and redesign initiatives. Sample usage cases are also described to demonstrate the effectiveness of this approach.

Structural Insight into Binding Mode of 9-Hydroxy Aristolochic Acid, Diclofenac and Indomethacin to PLA2

Phospholipase A₂ (PLA₂) catalyzes the hydrolysis of phospholipids into arachidonic acid and lysophospholipids. Arachidonic acid is modified by cyclooxygenases into active compounds called eicosanoids that act as signaling molecules in a number of physiological processes. Excessive production of eicosanoids leads to several pathological conditions such as inflammation. In order to block the inflammatory effect of these compounds, upstream enzymes such as PLA₂ are valid targets. In the present contribution, molecular dynamic analysis was performed to evaluate the binding of diclofenac, 9-hydroxy aristolochic acid (9-HAA) and indomethacin to PLA₂. Obtained results revealed that 9-HAA could form a more stable complex with PLA₂ when compared to diclofenac and indomethacin. Furthermore, analysis of intermolecular binding energy components indicated that hydrophobic interactions were dominant in binding process. On the basis of obtained data, inhibitors bearing fused rings with hydrogen acceptor/donor substituent(s) interacted with His48 and Asp49 residues of the active site. More affinity toward PLA₂ might be envisaged through negatively charged moieties via interaction with Trp31, Lys34 and Lys69.

Structural Insights into the Competitive Binding of Diclofenac and Naproxen by Equine Serum Albumin

The binding modes to equine serum albumin (ESA) of two nonsteroidal anti-inflammatory drugs (NSAIDs), diclofenac (Dic) and naproxen (Nps), were studied by X-ray crystallography and isothermal titration calorimetry. On the basis of the crystal structure of ESA/Dic determined to a resolution of 1.92 Å and the structure of the previously described ESA/Nps complex (2.42 Å), it was found that both NSAIDs bind within drug site 2 (DS2) of ESA and both occupy secondary binding sites in separate cavities of domain II (Nps) and domain III (Dic). The two structures of the ternary complex ESA/Dic/Nps, obtained by competitive cocrystallization (2.19 Å) and through a displacement experiment (2.35 Å), were determined to investigate possible competition of these widely used pharmaceutical drugs in binding to ESA. In these complexes Nps occupies the DS2 pocket common for both drugs, whereas the other distinct binding sites of Dic and Nps remain unaffected. These results suggest that combined application of both drugs may result in increased concentration of free diclofenac in plasma.

Connecting proteins with drug-like compounds: Open source drug discovery workflows with BindingDB and KNIME

Today's large, public databases of protein-small molecule interaction data are creating important new opportunities for data mining and integration. At the same time, new graphical user interface-based workflow tools offer facile alternatives to custom scripting for informatics and data analysis. Here, we illustrate how the large protein-ligand database BindingDB may be incorporated into KNIME workflows as a step toward the integration of pharmacological data with broader biomolecular analyses. Thus, we describe a collection of KNIME workflows that access BindingDB data via RESTful webservices and, for more intensive queries, via a local distillation of the full BindingDB dataset. We focus in particular on the KNIME implementation of knowledge-based tools to generate informed hypotheses regarding protein targets of bioactive compounds, based on notions of chemical similarity. A number of variants of this basic approach are tested for seven existing drugs with relatively ill-defined therapeutic targets, leading to replication of some previously confirmed results and discovery of new, high-quality hits. Implications for future development are discussed. Database URL: www.bindingdb.org.

Structures and binding studies of the complexes of phospholipase A2 with five inhibitors

Phospholipase A2 (PLA2) catalyzes the hydrolysis of phospholipids into arachidonic acid and lysophospholipids. Arachidonic acid is used as a substrate in the next step of the multistep pathway leading to the production of eicosanoids. The eicosanoids, in extremely low concentrations, are required in a number of physiological processes. However, the increase in their concentrations above the essential physiological requirements leads to various inflammatory conditions. In order to prevent the unwanted rise in the concentrations of eicosanoids, the actions of PLA2 and other enzymes of the pathway need to be blocked. We report here the structures of five complexes of group IIA PLA2 from Daboia russelli pulchella with tightly binding inhibitors, (i) p-coumaric acid, (ii) resveratrol, (iii) spermidine, (iv) corticosterone and (v) gramine derivative. The binding studies using fluorescence spectroscopy and surface plasmon resonance techniques for the interactions of PLA2 with the above five compounds showed high binding affinities with values of dissociation constants (KD) ranging from 3.7×10(-8) M to 2.1×10(-9) M. The structure determinations of the complexes of PLA2 with the above five compounds showed that all the compounds bound to PLA2 in the substrate binding cleft. The protein residues that contributed to the interactions with these compounds included Leu2, Leu3, Phe5, Gly6, Ile9, Ala18, Ile19, Trp22, Ser23, Cys29, Gly30, Cys45, His48, Asp49 and Phe106. The positions of side chains of several residues including Leu2, Leu3, Ile19, Trp31, Lys69, Ser70 and Arg72 got significantly shifted while the positions of active site residues, His48, Asp49, Tyr52 and Asp99 were unperturbed.

Molecular basis for nonspecificity of nonsteroidal anti-inflammatory drugs (NSAIDs)

Inhibition of the production of inflammatory mediators by the action of nonsteroidal anti-inflammatory drugs (NSAIDs) is highly accredited to their recognition of cyclooxygenase enzymes. Along with inflammation relief, however, NSAIDs also cause adverse effects. Although NSAIDs strongly inhibit enzymes of the prostaglandin synthesis pathways, several other proteins also serve as fairly potent targets for these drugs. Based on their recognition pattern, these receptors are categorised as enzymes modifying NSAIDs, noncatalytic proteins binding to NSAIDs and enzymes with catalytic functions that are inhibited by NSAIDs. The extensive binding of NSAIDs is responsible for their limited in vivo efficacy as well as the large spectrum of their effects. The biochemical nature of drugs binding to multiple protein targets and its implications on physiology are discussed.

Identification of distant drug off-targets by direct superposition of binding pocket surfaces

Correctly predicting off-targets for a given molecular structure, which would have the ability to bind a large range of ligands, is both particularly difficult and important if they share no significant sequence or fold similarity with the respective molecular target ("distant off-targets"). A novel approach for identification of off-targets by direct superposition of protein binding pocket surfaces is presented and applied to a set of well-studied and highly relevant drug targets, including representative kinases and nuclear hormone receptors. The entire Protein Data Bank is searched for similar binding pockets and convincing distant off-target candidates were identified that share no significant sequence or fold similarity with the respective target structure. These putative target off-target pairs are further supported by the existence of compounds that bind strongly to both with high topological similarity, and in some cases, literature examples of individual compounds that bind to both. Also, our results clearly show that it is possible for binding pockets to exhibit a striking surface similarity, while the respective off-target shares neither significant sequence nor significant fold similarity with the respective molecular target ("distant off-target").

Pyrazolo[3,4-d]pyrimidines as inhibitor of anti-coagulation and inflammation activities of phospholipase A 2 : insight from molecular docking studies

Phospholipase A2 (PLA2), isolated from Daboia russelli pulchella (Russell's viper), is enzymatically active as well as induces several pharmacological disorders including neurotoxicity, myotoxicity, cardiotoxicity, anti-coagulant, hemolytic, and platelet effects. Indomethacin reduces the effects of anti-coagulant and pro-inflammatory actions of PLA2. Pyrazolo[3,4-d]pyrimidines constitute a class of naturally occurring fused uracils that posses diverse biological activities. The in-silico docking studies of nine pyrazolo[3,4-d]pyrimidine molecules have been carried out with the X-ray crystal structure of Russell's viper PLA2 (PDB ID: 3H1X) to predict the binding affinity, molecular recognition, and to explicate the binding modes, using AUTODOCK and GLIDE (Standard precision and Extra precision) modules, respectively. Docking results through each method make obvious that pyrazolo[3,4-d]pyrimidine molecules with trimethylene linker can bind with both anti-coagulation and enzymatic regions of PLA2.

A novel pharmacophore model to identify leads for simultaneous inhibition of anti-coagulation and anti-inflammatory activities of snake venom phospholipase A(2)

In addition to catalytic action, snake venom phospholipase A(2) induces several pharmacological effects including neurotoxicity, cardiotoxicity as well as anti-coagulant and anti-platelet aggregation effects. Therefore, strategy to identify dual inhibitor for this enzyme will be of much importance in medical research. In this paper, structure-based pharmacophore mapping, molecular docking, protein-ligand interaction fingerprints, binding energy calculations, and binding affinity predictions were employed in a virtual screening strategy to identify new hits for dual inhibition of anti-coagulation and inflammation of phospholipase A(2) . A structure-based pharmacophore map was modeled which comprised of important interactions as observed in co-crystal of phospholipase A(2) and its dual inhibitor indomethacin. The generated model was used to retrieve molecules from ChemBridge, a free database of commercially available compounds. A total of 381 molecules mapped on the developed pharmacophore model from ChemBridge database. The hits retrieved were further screened by molecular docking, protein-ligand interaction fingerprints, binding energy calculations, and binding affinity predictions using Genetic Optimization for Ligand Docking and moe. Based on these results, 32 chemo-types molecules were predicted as potential lead scaffolds for developing novel, potent and structurally diverse dual inhibitor of phospholipase A(2.).

Enzymatic toxins from snake venom: structural characterization and mechanism of catalysis

Snake venoms are cocktails of enzymes and non-enzymatic proteins used for both the immobilization and digestion of prey. The most common snake venom enzymes include acetylcholinesterases, l-amino acid oxidases, serine proteinases, metalloproteinases and phospholipases A(2) . Higher catalytic efficiency, thermal stability and resistance to proteolysis make these enzymes attractive models for biochemists, enzymologists and structural biologists. Here, we review the structures of these enzymes and describe their structure-based mechanisms of catalysis and inhibition. Some of the enzymes exist as protein complexes in the venom. Thus we also discuss the functional role of non-enzymatic subunits and the pharmacological effects of such protein complexes. The structures of inhibitor-enzyme complexes provide ideal platforms for the design of potent inhibitors which are useful in the development of prototypes and lead compounds with potential therapeutic applications.

Performance of phased rotation, conformation and translation function: accurate protein model building with tripeptidic and tetrapeptidic fragments

The automatic building of protein structures with tripeptidic and tetrapeptidic fragments was investigated. The oligopeptidic conformers were positioned in the electron-density map by a phased rotation, conformation and translation function and refined by a real-space refinement. The number of successfully located fragments lay within the interval 75–95% depending on the resolution and phase quality. The overlaps of partially located fragments were analyzed. The correctly positioned fragments were connected into chains. Chains formed in this way were extended directly into the electron density and a sequence was assigned. In the initial stage of the model building the number of located fragments was between 60% and 95%, but this number could be increased by several cycles of reciprocal-space refinement and automatic model rebuilding. A nearly complete structure can be obtained on the condition that the resolution is reasonable. Computer graphics will only be needed for a final check and small corrections.

Diclofenac: an update on its mechanism of action and safety profile

BACKGROUND

Diclofenac is a proven, commonly prescribed nonsteroidal anti-inflammatory drug (NSAID) that has analgesic, anti-inflammatory, and antipyretic properties, and has been shown to be effective in treating a variety of acute and chronic pain and inflammatory conditions. As with all NSAIDs, diclofenac exerts its action via inhibition of prostaglandin synthesis by inhibiting cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2) with relative equipotency. However, extensive research shows the pharmacologic activity of diclofenac goes beyond COX inhibition, and includes multimodal and, in some instances, novel mechanisms of action (MOA).

DATA SOURCES

Literature retrieval was performed through PubMed/MEDLINE (through May 2009) using combinations of the terms diclofenac, NSAID, mechanism of action, COX-1, COX-2, and pharmacology. Reference citations resulting from publications identified in the literature search were reviewed when appropriate.

METHODS

This article reviews the established, putative, and emerging MOAs of diclofenac; compares the drug's pharmacologic and pharmacodynamic properties with other NSAIDs to delineate its potentially unique qualities; hypothesizes why it has been chosen for further recent formulation enhancement; and evaluates the potential effect of its MOA characteristics on safety.

DISCUSSION

Research suggests diclofenac can inhibit the thromboxane-prostanoid receptor, affect arachidonic acid release and uptake, inhibit lipoxygenase enzymes, and activate the nitric oxide-cGMP antinociceptive pathway. Other novel MOAs may include the inhibition of substrate P, inhibition of peroxisome proliferator activated receptor gamma (PPARgamma), blockage of acid-sensing ion channels, alteration of interleukin-6 production, and inhibition of N-methyl-D-aspartate (NMDA) receptor hyperalgesia. The review was not designed to compare MOAs of diclofenac with other NSAIDs. Additionally, as the highlighted putative and emerging MOAs do not have clinical data to demonstrate that these models are correct, further research is necessary to ascertain if the proposed pathways will translate into clinical benefits. The diversity in diclofenac's MOA may suggest the potential for a relatively more favorable profile compared with other NSAIDs.

Nonantibiotic properties of tetracyclines: structural basis for inhibition of secretory phospholipase A2

Secretory phospholipase A(2) is involved in inflammatory processes and was previously shown to be inhibited by lipophilic tetracyclines such as minocycline (minoTc) and doxycycline. Lipophilic tetracyclines might be a new lead compound for the design of specific inhibitors of secretory phospholipase A(2), which play a crucial role in inflammatory processes. Our X-ray crystal structure analysis at 1.65 A resolution of the minoTc complex of phospholipase A(2) (PLA(2)) of the Indian cobra (Naja naja naja) is the first example of nonantibiotic tetracycline interactions with a protein. MinoTc interferes with the conformation of the active-site Ca(2+)-binding loop, preventing Ca(2)(+) binding, and shields the active site from substrate entrance, resulting in inhibition of the enzyme. MinoTc binding to PLA(2) is dominated by hydrophobic interactions quite different from antibiotic recognition of tetracyclines by proteins or the ribosome. The affinity of minoTc for PLA(2) was determined by surface plasmon resonance, resulting in a dissociation constant K(d)=1.8 x 10(-)(4) M.