NO-aspirin: mechanism of action and gastrointestinal safety

Potentially active aspirin derivative to release nitric oxide: In-vitro, in-vivo and in-silico approaches

The series of newer salicylate derivatives incorporating nitroxy functionality were synthesized and evaluated for their potential effect in gastrointestinal (GI) related toxicity produced by aspirin. The synthesized compounds (5a-j) were subjected to %NO (nitric oxide) release study, in-vitro anti-inflammatory potential, % inhibition of carrageenan-induced paw edema and the obtained results were validated by in-silico studies including molecular docking, MD simulations and in-silico ADME (absorption, distribution, metabolism, and elimination) calculations. Compounds 5a (20.86 %) and 5g (18.20 %) displayed the highest percentage of NO release in all the tested compounds. Similarly, 5a and 5h were found to have (77.11 % and 79.53 %) &(78.56 % and 66.10 %) inhibition in carrageenan induced paw edema in animal mode which were relatively higher than ibuprofen (standard used). The obtained results were validated by molecular docking and MD simulations studies. The molecular docking study of 5a and 5h revealed that docking scores were also obtained in very close proximity of -8.35, -9.67 and -8.48 for ibuprofen, 5g and 5h respectively. In MD simulations studies, the calculated lower RMSD (root mean square deviation) values 2.8 Å and 5.6 Å for 5g and 5h, respectively indicated the stability of ligand-protein complexes. Similarly lower RSMF (root mean square fluctuation) values indicated the molecules remained in the active pocket throughout the entire MD simulations run. Further, in-silico ADME calculations were determined and all compounds obey the Lipinski's rule of five and it was predicted that these molecules would be orally active without any serious toxic effect.

Druggable Prostanoid Pathway

Prostanoids (prostaglandins, prostacyclin and thromboxane) belong to the oxylipin family of biologically active lipids generated from arachidonic acid (AA). Protanoids control numerous physiological and pathological processes. Cyclooxygenase (COX) is a rate-limiting enzyme involved in the conversion of AA into prostanoids. There are two COX isozymes: the constitutive COX-1 and the inducible COX-2. COX-1 and COX-2 have similar structures, catalytic activities, and subcellular localizations but differ in patterns of expression and biological functions. Non-selective COX-1/2 or traditional, non-steroidal anti-inflammatory drugs (tNSAIDs) target both COX isoforms and are widely used to relieve pain, fever and inflammation. However, the use of NSAIDs is associated with various side effects, particularly in the gastrointestinal tract. NSAIDs selective for COX-2 inhibition (coxibs) were purposefully designed to spare gastrointestinal toxicity, but predisposed patients to increased cardiovascular risks. These health complications from NSAIDs prompted interest in the downstream effectors of the COX enzymes as novel drug targets. This chapter describes various safety issues with tNSAIDs and coxibs, and discusses the current development of novel classes of drugs targeting the prostanoid pathway, including nitrogen oxide- and hydrogen sulfide-releasing NSAIDs, inhibitors of prostanoid synthases, dual inhibitors, and prostanoid receptor agonists and antagonists.

Conformational study of the electronic interactions and nitric oxide release potential of new S‑nitrosothiols esters derivatives of ibuprofen, naproxen and phenyl acids substituted (SNO-ESTERS): Synthesis, infrared spectroscopy analysis and theoretical calculations

The conformational study on the new S‑nitrosothiols esters (SNO-ESTERS): para-substituted (X = H, OMe, Cl and NO₂) S‑nitrosothiol derivatives 2‑methyl‑2‑(sulfanyl)propyl phenylacetates (R1), 2‑(4‑isobutylphenyl)propanoate (ibuprofen, R2), and 2‑(4‑isobutylphenyl)propanoate of 2‑methyl‑2‑(nitrososulfanyl)propyl (naproxen, R3) was performed using infrared spectroscopy (IR) in solvents with increasing polarity (CCl₄, CH₃Cl, and CH₃CN), and theoretical calculations, to determine the preferential conformer and the potential of these compounds to release nitric oxide (NO). S‑Nitrosothiols were synthesized by esterification reactions, using chlorides of the corresponding carboxylic acids, with good yields (~60%). IR results showed that these compounds presented only one conformation, and the experimental data were supported by the theoretical results obtained by density functional theory (DFT) calculations using the 6311+G (2df, 2p) basis set. The calculations revealed that all S‑nitrosothiols presented one preferential anticlinal (ac) geometric conformation, which agrees with the data obtained experimentally in CCl₄. These conformers are stabilized by intramolecular hydrogen bonds. Examination of the geometry with regard to the RSNO group revealed that these compounds are preferentially in the trans (anti) conformation. The calculation of the orbital interactions using the Natural Bond Orbital (NBO) method showed that the n_O(NO) → σ_(SN)^∗ hyper-conjugative interaction increases the SN bond length. The strong n_S → π_(NO)^∗ interaction and electronic delocalization induces a partial π character to the SN bond. The weak σ_SN bond indicates strong delocalization of the electron pair in O (NO) by the n_O(NO) → σ_(SN)^∗ interaction, thereby increasing the capacity of NO release from SNO-ESTERS.

Gasotransmitters and the immune system: Mode of action and novel therapeutic targets

Gasotransmitters are a group of gaseous molecules, with pleiotropic biological functions. These molecules include nitric oxide (NO), hydrogen sulfide (H₂S), and carbon monoxide (CO). Abnormal production and metabolism of these molecules have been observed in several pathological conditions. The understanding of the role of gasotransmitters in the immune system has grown significantly in the past years, and independent studies have shed light on the effect of exogenous and endogenous gasotransmitters on immune responses. Moreover, encouraging results come from the efficacy of NO-, CO- and H₂S -donors in preclinical animal models of autoimmune, acute and chronic inflammatory diseases. To date, data on the influence of gasotransmitters in immunity and immunopathology are often scattered and partial, and the scarcity of clinical trials using NO-, CO- and H₂S -donors, reveals that more effort is warranted. This review focuses on the role of gasotransmitters in the immune system and covers the evidences on the possible use of gasotransmitters for the treatment of inflammatory conditions.

Investigational drugs targeting the prostaglandin E2 signaling pathway for the treatment of inflammatory pain

Non-steroidal anti-inflammatory drugs (NSAID) are the most commonly used drugs for the treatment of pain, inflammation and fever. Although they are effective for a huge number of users, their analgesic properties are not sufficient for several patients and the occurrence of side effects still constitutes a big challenge during long term therapy. Areas covered: This review gives an overview about the first and second generations of NSAIDs (COX1/2 non-selective, COX-2 selective), and their main side effects which gave still an urgent need for safer drugs and for the establishment of novel treatment strategies (improved safety, tolerability, patient convenience). The current developments of a possible third generation NSAID class comprise changes in the formulation of already approved drugs, combination therapies, dual cyclooxygenase-lipoxygenase inhibitors, NO- and H₂S-releasing NSAIDs, prostaglandin synthase inhibitors and EP receptor modulators, respectively. Literature search has been done with PubMed NCBI. Expert opinion: Currently, there is no newly developed drug that is superior to the already approved selective and non-selective NSAIDs. Several novel approaches show promising analgesic efficacy but side effects are still an important problem. Solutions might be constituted by combination therapies allowing administration of lower drug doses or by individualized therapies targeting molecules apart from COX, respectively.

NOSH-aspirin (NBS-1120), a novel nitric oxide- and hydrogen sulfide-releasing hybrid has enhanced chemo-preventive properties compared to aspirin, is gastrointestinal safe with all the classic therapeutic indications

Aspirin is chemopreventive; however, side effects preclude its long-term use. NOSH-aspirin (NBS-1120), a novel hybrid that releases nitric oxide and hydrogen sulfide, was designed to be a safer alternative. Here we compare the gastrointestinal safety, anti-inflammatory, analgesic, anti-pyretic, anti-platelet, and chemopreventive properties of aspirin and NBS-1120 administered orally to rats at equimolar doses. Gastrointestinal safety: 6h post-administration, the number and size of hemorrhagic lesions in stomachs were counted; tissue samples were frozen for PGE2, SOD, and MDA determination. Anti-inflammatory: 1h after drug administration, the volume of carrageenan-induced rat paw edemas was measured for 5h. Anti-pyretic: fever was induced by LPS (ip) an hour before administration of the test drugs, core body temperature was measured hourly for 5h. Analgesic: time-dependent analgesic effects were evaluated by carrageenan-induced hyperalgesia. Antiplatelet: anti-aggregatory effects were studied on collagen-induced platelet aggregation of human platelet-rich plasma. Chemoprevention: nude mice were gavaged daily for 25 days with vehicle, aspirin or NBS-1120. After one week, each mouse was inoculated subcutaneously in the right flank with HT-29 human colon cancer cells. Both agents reduced PGE2 levels in stomach tissue; however, NBS-1120 did not cause any stomach ulcers, whereas aspirin caused significant bleeding. Lipid peroxidation induced by aspirin was higher than that exerted by NBS-1120. SOD activity was significantly inhibited by aspirin but increased by NBS-1120. Both agents showed similar anti-inflammatory, analgesic, anti-pyretic, and anti-platelet activities. Aspirin increased plasma TNFα more than NBS-1120-treated animals. NBS-1120 was better than aspirin as a chemopreventive agent; it dose-dependently inhibited tumor growth and tumor mass.

Positional isomers of aspirin are equally potent in inhibiting colon cancer cell growth: differences in mode of cyclooxygenase inhibition

We compared the differential effects of positional isomers of acetylsalicylic acid (o-ASA, m-ASA, and p-ASA) on cyclooxygenase (COX) inhibition, gastric prostaglandin E2 (PGE2), malondialdehyde, tumor necrosis factor-alpha (TNF-α) levels, superoxide dismutase (SOD) activity, human adenocarcinoma colon cancer cell growth inhibition, cell proliferation, apoptosis, and cell-cycle progression. We also evaluated the gastric toxicity exerted by ASA isomers. All ASA isomers inhibit COX enzymes, but only the o-ASA exerted an irreversible inhibitory profile. We did not observe a significant difference between ASA isomers in their ability to decrease the in vivo synthesis of PGE2 and SOD activity. Furthermore, all isomers increased the levels of gastric and TNF-α when administered orally at equimolar doses. We observed a dose-dependent cell growth inhibitory effect; the order of potency was p-ASA > m-ASA ≈ o-ASA. There was a dose-dependent decrease in cell proliferation and an increase in apoptosis, with a concomitant Go/G1 arrest. The ulcerogenic profile of the three ASA isomers showed a significant difference between o-ASA (aspirin) and its two positional isomers when administered orally at equimolar doses (1 mmol/kg); the ulcer index (UI) for o-ASA indicated extensive mucosal injury (UI = 38), whereas m-ASA and p-ASA produced a significantly decreased toxic response (UI = 12 and 8, respectively) under the same experimental conditions. These results suggest that the three positional isomers of ASA exert practically the same biologic profile in vitro and in vivo but showed different safety profiles. The mechanism of gastric ulcer formation exerted by aspirin and its two isomers warrants a more detailed and thorough investigation.

Aspirin and immune system

The time-tested gradual exploration of aspirin's diverse pharmacological properties has made it the most reliable therapeutic agent worldwide. In addition to its well-argued anti-inflammatory effects, many new and exciting data have emerged regarding the role of aspirin in cells of the immune system and certain immunopathological states. For instance, aspirin induces tolerogenic activity in dendritic cells and determines the fate of naive T cells to regulatory phenotypes, which suggests its immunoregulatory potential in relevance to immune tolerance. It also displays some intriguing traits to modulate the innate and adaptive immune responses. In this article, the immunomodulatory relation of aspirin to different immune cells, such as neutrophils, macrophages, dendritic cells (DCs), natural killer (NK) cells, and the T and B lymphocytes has been highlighted. Moreover, the clinical prospects of aspirin in terms of autoimmunity, allograft rejection and immune tolerance have also been outlined.

Synthesis and biological activity of acetyl-protected hydroxybenzyl diethyl phosphates (EHBP) as potential chemotherapeutic agents

Several acetyl-protected hydroxybenzyl diethyl phosphates (EHBPs) that are capable of forming quinone methide intermediates were synthesized and their cell growth inhibitory properties were evaluated in four different human cancer cell lines. Compounds 1, 1a, and 1b, corresponding to (4-acetyloxybenzyl diethylphosphate), (3-methyl-4-acetyloxybenzyl diethylphosphate), and (3-chloro-4-acetyloxybenzyl diethylphosphate), were significantly more potent than compounds 2 and 3, (2-acetyloxybenzyl diethylphosphate) and (3-acetyloxybenzyl diethylphosphate), respectively. Using HT-29 human colon cancer cells, compounds 1 and 3 increased apoptosis, inhibited proliferation, and caused a G(2)/M block in the cell cycle. Our data suggest that these compounds merit further investigation as potential anti-cancer agents.

Carbenoxolone gastroprotective mechanism: participation of nitric oxide/(c) GMP/K(ATP) pathway in ethanol-induced gastric injury in the rat

Carbenoxolone, a semi-synthetic triterpenoid, exhibits gastroprotective activity related to the participation of nitric oxide (NO); however, the complete NO/(c) GMP/K(ATP) channels pathway for carbenoxolone is unknown. Therefore the aim of this study was to examine the NO/(c) GMP/K(ATP) channels pathway as the gastroprotective mechanism of carbenoxolone in the ethanol-induced gastric injury model in the rat. Oral administration of carbenoxolone (30 mg/kg, p.o.) exhibited gastroprotective effect against ethanol-induced gastric injury in rats. Pretreatment with N(G) -nitro-l-arginine methyl ester (L-NAME, 70 mg/kg, i.p.); 1H-[1,2,4]oxadiazolo[4,3-a]quinoxaline-1-one (ODQ, guanylate cyclase inhibitor, 10 mg/kg, i.p.); or glibenclamide (K(ATP) channels inhibitor, 1 mg/kg, i.p.) reversed the gastroprotective effect of carbenoxolone for ethanol-induced gastric injury. Furthermore, gastric prostaglandins and NO levels increased after carbenoxolone administration in ethanol-induced gastric injury in rats. In conclusion, our results suggest that the increase of NO levels in gastric tissue after pretreatment with carbenoxolone activates the NO/(c)GMP/K(ATP) channels pathway, the principal gastroprotective mechanism of carbenoxolone.

Comparison between 3-Nitrooxyphenyl acetylsalicylate (NO-ASA) and O2-(acetylsalicyloxymethyl)-1-(pyrrolidin-1-yl)diazen-1-ium-1,2-diolate (NONO-ASA) as safe anti-inflammatory, analgesic, antipyretic, antioxidant prodrugs

Chronic inflammation is an underlying etiological factor in carcinogenesis; nonsteroidal anti-inflammatory drugs (NSAIDs) and their chemically modified NO-releasing prodrugs (NO-NSAIDs) are promising chemopreventive agents. The aim of this study was to conduct a head-to-head comparison between two NO-ASAs possessing different NO donor groups, an organic nitrate [3-nitrooxyphenyl acetylsalicylate (NO-ASA; NCX-4016)] and an N-diazeniumdiolate [NONO-ASA, O(2)- (acetylsalicyloxymethyl)-1-(pyrrolidin-1-yl)diazen-1-ium-1,2-diolate (NONO-ASA; CVM-01)], as antiulcerogenic, analgesic, anti-inflammatory, and antipyretic agents. All drugs were administered orally at equimolar doses. For antiulcerogenic study, 6 h after administration, the number and size of hemorrhagic lesions in stomachs from euthanized animals were counted. Tissue samples were frozen for prostaglandin E(2) (PGE(2)), superoxide dismutase (SOD), and malondialdehyde determination. For anti-inflammatory study, 1 h after drug administration, the volume of carrageenan-induced rat paw edemas was measured for 6 h. For antipyretic study, 1 h after dosing, fever was induced by intraperitoneal LPS, and body core temperatures measured for 5 h. For analgesic study, time-dependent analgesic effect of prodrugs was evaluated by carrageenan-induced hyperalgesia. Drugs were administered 30 min after carrageenan. NO-ASA and NONO-ASA were equipotent as analgesic and anti-inflammatory agents but were better than aspirin. Despite a drastic reduction of PGE(2) in stomach tissue, both prodrugs were devoid of gastric side effects. Lipid peroxidation induced by aspirin was higher than that observed by prodrugs. SOD activity induced by both prodrugs was similar, but approximately 2-fold higher than that induced by aspirin. CVM-01 is as effective as NCX-4016 in anti-inflammatory, analgesic, and antipyretic assays in vivo, and it showed an equivalent safety profile in the stomach. These results underscore the use of N-diazeniumdiolate moieties in drug design.

New antiplatelet agents

PURPOSE OF REVIEW

Cardiovascular events are still a major concern despite dual antiplatelet treatment with aspirin and clopidogrel. Moreover, recent developments that improved platelet inhibition were associated with increased bleeding complications, suggesting that personal dose adjustment might be needed. This review is dedicated to new developments in antiplatelet agents other than ADP P2Y12 receptor blockers, which are discussed in a separate article of this issue.

RECENT FINDINGS

The thrombin receptor protease activable receptor-1 antagonist SCH530348 and the thromboxane receptor antagonist terutroban are two promising agents that are now undergoing phase III clinical trials. Cilostazol, a phosphodiesterase III inhibitor, is currently tested in phase IV trials for several new indications. Despite previous disappointing results with oral GPIIbIIIa antagonists, new compounds with unique features are under development. In addition, targeting intracellular signaling pathways is a new area of research, with several attractive targets.

SUMMARY

Recent development of new antiplatelet agents, including inhibitors of thrombin receptor, thromboxane receptor, phosphodiesterase, glycoprotein VI, GPIIbIIIa and signaling pathways, may lead to a more effective and yet safe antiplatelet therapy with an improved clinical outcome.

A novel hybrid aspirin-NO-releasing compound inhibits TNFalpha release from LPS-activated human monocytes and macrophages

Background

The cytoprotective nature of nitric oxide (NO) led to development of NO-aspirins in the hope of overcoming the gastric side-effects of aspirin. However, the NO moiety gives these hybrids potential for actions further to their aspirin-mediated anti-platelet and anti-inflammatory effects. Having previously shown that novel NO-aspirin hybrids containing a furoxan NO-releasing group have potent anti-platelet effects, here we investigate their anti-inflammatory properties. Here we examine their effects upon TNFα release from lipopolysaccharide (LPS)-stimulated human monocytes and monocyte-derived macrophages and investigate a potential mechanism of action through effects on LPS-stimulated nuclear factor-kappa B (NF-κB) activation.

Methods

Peripheral venous blood was drawn from the antecubital fossa of human volunteers. Mononuclear cells were isolated and cultured. The resultant differentiated macrophages were treated with pharmacologically relevant concentrations of either a furoxan-aspirin (B8, B7; 10 μM), their respective furazan NO-free counterparts (B16, B15; 10 μM), aspirin (10 μM), existing nitroaspirin (NCX4016; 10 μM), an NO donor (DEA/NO; 10 μM) or dexamethasone (1 μM), in the presence and absence of LPS (10 ng/ml; 4 h). Parallel experiments were conducted on undifferentiated fresh monocytes. Supernatants were assessed by specific ELISA for TNFα release and by lactate dehydrogenase (LDH) assay for cell necrosis. To assess NF-κB activation, the effects of the compounds on the loss of cytoplasmic inhibitor of NF-κB, IκBα (assessed by western blotting) and nuclear localisation (assessed by immunofluorescence) of the p65 subunit of NF-κB were determined.

Results

B8 significantly reduced TNFα release from LPS-treated macrophages to 36 ± 10% of the LPS control. B8 and B16 significantly inhibited monocyte TNFα release to 28 ± 5, and 49 ± 9% of control, respectively. The B8 effect was equivalent in magnitude to that of dexamethasone, but was not shared by 10 μM DEA/NO, B7, the furazans, aspirin or NCX4016. LDH assessment revealed none of the treatments caused significant cell lysis. LPS stimulated loss of cytoplasmic IκBα and nuclear translocation of the p65 NF-κB subunit was inhibited by the active NO-furoxans.

Conclusion

Here we show that furoxan-aspirin, B8, significantly reduces TNFα release from both monocytes and macrophages and suggest that inhibition of NF-κB activation is a likely mechanism for the effect. This anti-inflammatory action highlights a further therapeutic potential of drugs of this class.

NSAIDs, coxibs, CINOD and H2S-releasing NSAIDs: what lies beyond the horizon

Nonsteroidal anti-inflammatory drugs are widely prescribed for treatment of pain and inflammation, despite their association with gastrointestinal complications, including bleeding and perforation. Inhibition of cyclo-oxygenases, is the main mechanism of action of aspirin and nonsteroidal anti-inflammatory drugs. Non-selective nonsteroidal anti-inflammatory drugs inhibit cyclo-oxygenase-1 and cyclo-oxygenase-2. Inhibition of cyclo-oxygenase-1 derived prostanoids in the stomach represent the underlying mechanism involved in development of gastric and duodenal ulcers in patients taking nonsteroidal anti-inflammatory drugs. Selective cyclo-oxygenases-2 inhibitor (coxibs) spare cyclo-oxygenase-1 show enhanced safety profile in the gastrointestinal tract, but increase the risk of heart attack and stroke. Spurred by these findings, two coxibs, rofecoxib and valdecoxib, were withdrawn from the market. In addition to prostanoids, two gaseous mediators, nitric oxide (NO) and hydrogen sulfide (H(2)S) exert protective effects in gastric mucosa. The inhibitory effects of NO on nonsteroidal anti-inflammatory drugs-induced leukocyte adherence have been exploited in the development of NO-releasing nonsteroidal anti-inflammatory drugs, also indicated as cyclo-oxygenase-inhibiting NO-donating drugs. Despite its non-selective profile versus cyclo-oxygenase isoenzymes, naprocyclo-oxygenase-inhibiting NO-donating drugs, the prototype of this class of anti-inflammatory agents, reduces systemic blood pressure and might have enhanced cardiovascular safety than coxibs, while causing less gastrointestinal damage than its parent drug, the naproxen. H(2)S-releasing nonsteroidal anti-inflammatory drugs derivatives have been recently developed, based on the observed ability of this gaseous mediator to cause vasodilation and to prevent leukocyte adherence. In pre-clinical settings, H(2)S-releasing nonsteroidal anti-inflammatory drugs produce less gastric damage as compared to the parent drugs. Cyclo-oxygenases-inhibiting NO-donating drugs and H(2)S-releasing nonsteroidal anti-inflammatory drugs represent examples of new anti-inflammatory drugs created through the exploitation of the beneficial effects of endogenous gaseous mediators in the gastrointestinal and cardiovascular systems.

Recent developments in nitric oxide donor drugs

During the 1980s, the free radical, nitric oxide (NO), was discovered to be a crucial signalling molecule, with wide-ranging functions in the cardiovascular, nervous and immune systems. Aside from providing a credible explanation for the actions of organic nitrates and sodium nitroprusside that have long been used in the treatment of angina and hypertensive crises respectively, the discovery generated great hopes for new NO-based treatments for a wide variety of ailments. Decades later, however, we are still awaiting novel licensed agents in this arena, despite an enormous research effort to this end. This review explores some of the most promising recent advances in NO donor drug development and addresses the challenges associated with NO as a therapeutic agent.

Therapeutic effects of nitric oxide-aspirin hybrid drugs

This review examines the therapeutic potential and mechanisms of action of drugs known as nitric oxide (NO)-aspirins. Drugs of this class have an NO-releasing moiety joined by ester linkage to the aspirin molecule. NO-aspirins have the capability to release NO in addition to retaining the cyclooxygenase-inhibitory action of aspirin. The protective nature of NO led to the development of NO-aspirins in the hope that they might avoid the gastric side effects associated with aspirin. However, it has become apparent that the drug-derived NO instills potential for a wide range of added beneficial effects over the parent compound. In this review, the authors focus on the analgesic, anti-inflammatory, cardiovascular and chemopreventative actions of compounds of this emerging drug class.

Mining the Wnt pathway for cancer therapeutics

Aberrant activation of the Wnt pathway is implicated in driving the formation of various human cancers, particularly those of the digestive tract. Inhibition of aberrant Wnt pathway activity in cancer cell lines efficiently blocks their growth, highlighting the great potential of therapeutics designed to achieve this in cancer patients. Here we provide an overview of the promise and pitfalls of current drug development strategies striving to inhibit the Wnt pathway and present new opportunities for therapeutic intervention.

A novel electron paramagnetic resonance-based assay for prostaglandin H synthase-1 activity

Background

Prostaglandin H₂ synthase (PGHS) is the enzyme that catalyses the two-stage conversion of arachidonic acid to prostaglandin H₂ (PGH₂) prior to formation of prostanoids that are important in inflammation. PGHS isozymes (-1 and -2) are the target for nonsteroidal anti-inflammatory drugs (NSAIDs).

Given the rekindled interest in specific anti-inflammatory PGHS inhibitors with reduced unwanted side effects, it is of paramount importance that there are reliable and efficient techniques to test new inhibitors. Here, we describe a novel in vitro electron paramagnetic resonance (EPR)-based assay for measuring the activity of PGHS-1.

Methods

We validated a novel in vitro PGHS-1 activity assay based on the oxidation of spin-trap agent, 1-hydroxy-3-carboxy-pyrrolidine (CPH) to 3-carboxy-proxy (CP) under the action of the peroxidase element of PGHS-1. This quantifiable spin-adduct, CP, yields a characteristic 3-line electron paramagnetic (EPR) spectrum.

Results

The assay is simple, reproducible and facilitates rapid screening of inhibitors of PGHS-1. Aspirin (100 μM, 1 mM) caused significant inhibition of spin-adduct formation (72 ± 11 and 100 ± 16% inhibition of control respectively; P < 0.05). Indomethacin (100 μM) also abolished the signal (114 ± 10% inhibition of control; P < 0.01). SA and the PGHS-2-selective inhibitor, NS398, failed to significantly inhibit spin-adduct generation (P > 0.05).

Conclusion

We have demonstrated and validated a simple, reproducible, quick and specific assay for detecting PGHS-1 activity and inhibition. The EPR-based assay described represents a novel approach to measuring PGHS activity and provides a viable and competitive alternative to existing assays.

Mechanism of action of novel NO-releasing furoxan derivatives of aspirin in human platelets

Incorporation of a nitric oxide (NO)-releasing moiety in aspirin can overcome its gastric side effects. We investigated the NO-release patterns and antiplatelet effects of novel furoxan derivatives of aspirin (B8 and B7) in comparison to existing antiplatelet agents. Cyclooxygenase (COX) activity was investigated in purified enzyme using an electron paramagnetic resonance-based technique. Concentration-response curves for antiplatelet agents +/- the soluble guanylate cyclase inhibitor, ODQ (50 microM) were generated in platelet-rich plasma (PRP) and washed platelets (WP) activated with collagen using turbidometric aggregometry. NO was detected using an isolated NO electrode. The furoxan derivatives of aspirin (B8, B7) and their NO-free furazan equivalents (B16, B15; all 100 microM) significantly inhibited COX activity (P < 0.01; n = 6) in vitro and caused aspirin-independent, cGMP-dependent inhibition of collagen-induced platelet aggregation in WP. B8 was more potent than B7 (PRP IC(50) = 0.62 +/- 0.1 microM for B8; 400 +/- 89 microM for B7; P < 0.0001. WP IC(50)s = 0.6 +/- 0.1 and 62 +/- 10 microM, respectively). The NO-free furazan counterparts were less potent antiplatelet agents (WP IC(50)s = 54 +/- 3 microM and 62 +/- 10 microM, respectively; P < 0.0001, B8 vs B16). Of the hybrids investigated, only B8 retained antiplatelet activity in PRP.NO release from furoxan-aspirin hybrids was undetectable in buffer alone, but was accelerated in the presence of either plasma or plasma components, albumin (4%), glutathione (GSH; 3 microM) and ascorbate (50 microM), the effects of which were additive for B7 but not B8. NO generation from furoxans was greatly enhanced by platelet extract, an effect that could largely be explained by the synergistic effect of intracellular concentrations of GSH (3 mM) and ascorbate (1 mM). We conclude that the decomposition of furoxan-aspirin hybrids to generate biologically active NO is catalysed by endogenous agents which may instil a potential for primarily intracellular delivery of NO. The blunting of the aspirin effects of furoxan hybrids is likely to be due to loss of the acetyl moiety in plasma; the observed antiplatelet effects are thereby primarily mediated via NO release. Compounds of this class might represent a novel means of inhibiting platelet aggregation by a combination of NO generation and COX inhibition.

Wnt/beta-catenin-pathway as a molecular target for future anti-cancer therapeutics

Conventional chemotherapeutic drugs used for the treatment of cancer patients in advanced stages have yielded only limited benefit, regarding survival time not to mention cure of the patients. To improve the clinical outcome of cancer, agents aimed at novel molecular targets are required. Colorectal and many other cancers are caused by hyperactivity of the Wnt/beta-catenin signaling pathway that results in constitutive beta-catenin mediated transactivation of T cell factor (Tcf)-dependent genes. Accordingly, disruption of this signaling pathway holds promise for the development of new anti-cancer drugs. Our study describes recent therapeutic strategies to interfere with tumor growth by blocking the unrestricted activation of the Wnt/beta-catenin pathway. The antagonists, which may become lead compounds of new anticancer therapeutics include established drugs in new application areas, recombinant biomolecules, virus mediated selective cell killing, and small molecules, disrupting protein-protein interactions.

Review article: prevention of non-steroidal anti-inflammatory drug gastrointestinal complications--review and recommendations based on risk assessment

The incidence of non-steroidal anti-inflammatory drug-related ulcer complications remains high despite the availability of potent anti-ulcer drugs and selective cyclo-oxygenase-2 inhibitors. Non-steroidal anti-inflammatory drug-related ulcer complications can be minimized by prospective assessment of patients' baseline risk, rational choice and use of non-steroidal anti-inflammatory drugs, and selective use of co-therapy strategies with gastroprotectives. Current recommendations regarding strategies using anti-ulcer drugs and cyclo-oxygenase-2 inhibitors for prevention of clinical non-steroidal anti-inflammatory drug upper gastrointestinal events are largely derived from studies using surrogates such as endoscopic ulcers, erosions, and symptoms in low- to average-risk patients. Conclusions based on surrogate and potentially manipulatable end-points are increasingly suspect with regard to applicability to clinical situations. This article reviews the risks associated with non-steroidal anti-inflammatory drugs including aspirin and includes the effect of the patients' baseline risk, and the confounding effects of Helicobacter pylori infection. In addition, uncertainties regarding the clinical efficacy of anti-ulcer drugs and cyclo-oxygenase-2 inhibitors against non-steroidal anti-inflammatory drug-related ulcer complications are put into perspective. We propose management strategies based on the risk category: low risk (absence of risk factors) (least ulcerogenic non-steroidal anti-inflammatory drug at lowest effective dose), moderate risk (one to two risk factors) (as above, plus an antisecretory agent or misoprostol or a cyclo-oxygenase-2 inhibitor), high risk (multiple risk factors or patients using concomitant low-dose aspirin, steroids, or anticoagulants) (cyclo-oxygenase-2 inhibitor alone with steroids, plus misoprostol with warfarin, or plus a proton pump inhibitors or misoprostol with aspirin), and very high risk (history of ulcer complications) (avoid all non-steroidal anti-inflammatory drugs, if possible or a cyclo-oxygenase-2 plus a proton pump inhibitors and/or misoprostol). The presence of H. pylori infection increases the risk of upper gastrointestinal complications in non-steroidal anti-inflammatory drug users by two- to fourfold suggesting that all patients requiring regular non-steroidal anti-inflammatory drug therapy be tested for H. pylori.

Chemiluminescence and LC–MS/MS analyses for the study of nitric oxide release and distribution following oral administration of nitroaspirin (NCX 4016) in healthy volunteers

The metabolic fate of nitric oxide (NO) released from nitroaspirin, benzoic acid, 2-(acetyloxy)-3-[(nitrooxy)methyl]phenyl ester (NCX 4016), the lead compound of a new class of NO-releasing non-steroidal anti-inflammatory drugs (NO-NSAIDs) has been studied in eight healthy male Caucasian subjects following p.o. administration of 1600 mg (single dose), by monitoring at different times in plasma the bioactive storage forms of NO, S-nitrosothiols (RSNO) and its oxidation products (NOx). Plasma levels of NOx and RSNO and urinary levels of NOx were determined by an ozone-based chemiluminescent assay using a sensitive Nitric Oxide Analyzer (LOQ: 10 pmol NO injected). In parallel plasma samples were analyzed by a newly developed LC-MS/MS method for analysis of NCX 4015, the metabolite bearing the nitrate ester function. Using MS/MS with multiple reaction monitoring (MRM) in negative ion mode for NCX 4015 and the internal standard (NCX 4015- 13C-D2) it was possible to detect with sufficient accuracy and precision the metabolite in plasma with a quantification limit of 78.1 ng ml(-1). Concentration versus time profile of plasma NCX 4015 gave a Cmax value of 161.94 +/- 47.4 ng ml(-1) and a tmax 4.5 +/- 1 h. The results indicate that both NOx and RSNO (these last for the first time determined in vivo in man following oral administration of a NO-donor drug) are effective plasma markers of NO release in vivo, the latter being an earlier indicator of NO distribution (tmax 2.0 +/- 0.6 h versus 5.4 +/- 1.2 h).

Gastrointestinal safety of NO-aspirin (NCX-4016) in healthy human volunteers: a proof of concept endoscopic study

BACKGROUND AND AIMS

NCX-4016 is a nitric oxide-releasing derivative of aspirin with antiplatelet activity. The aim of this study was to investigate the effect of NCX-4016 on gastrointestinal mucosa and platelet functions in healthy human volunteers.

METHODS

This was a parallel-group, double-blind, placebo-controlled study. Forty healthy subjects were randomly allocated to receive 7 days of treatment with NCX-4016 (400 and 800 mg twice daily), equimolar doses of aspirin (200 and 420 mg twice daily), or placebo. Upper endoscopies were performed before and at the end of the treatment period, and gastroduodenal lesions were graded using a predefined scoring system. Basal and posttreatment platelet aggregation in response to arachidonic acid (AA) and serum thromboxane (TX) B(2) and AA-stimulated platelet TXB(2) production were investigated.

RESULTS

Mucosal endoscopic injury score on day 7 was 0.63 +/- 0.16 in the placebo group and 11.0 +/- 3.0 and 16.1 +/- 1.6 in healthy volunteers treated with 200 and 420 mg aspirin twice daily (P < 0.0001 vs. placebo). NCX-4016 was virtually devoid of gastric and duodenal toxicity, resulting in a total gastric and duodenal endoscopic score of 1.38 +/- 0.3 and 1.25 +/- 0.5 (P < 0.0001 vs. aspirin, not significant vs. placebo). NCX-4016 inhibited AA-induced platelet aggregation as well as serum TXB(2) and platelet TXB(2) generation induced by AA to the same extent as aspirin (not significant vs. aspirin).

CONCLUSIONS

In this study, we have proven the concept that addition of an NO-donating moiety to aspirin results in a new chemical entity that maintains cyclooxygenase-1 and platelet inhibitory activity while nearly avoiding gastrointestinal damage.