Prostaglandins in peptic ulcer disease. An overview of current status and future directions

Pharmacological separation between peripheral and central functions of cyclooxygenase-2 with CIAA, a novel cyclooxygenase-2 inhibitor

There are many reports concerning the physiological and pathological involvement of cyclooxygenase (COX)-2 in the central nervous system and peripheral tissue cells. Selective COX-2 inhibitors that mainly distribute peripherally have not been reported thus far. Therefore central and peripheral roles of COX-2 remain classified pharmacologically. In this study, in vivo pharmacological profiles of CIAA ([6-chloro-2-(4-chlorobenzoyl)-1H-indol-3-yl]acetic acid), a novel selective COX-2 inhibitor which distributes at higher concentrations in plasma than in brain, were compared with those of well-known selective COX-2 inhibitors, celecoxib and rofecoxib. Additionally, the possibility of pharmacological separation between peripheral and central actions of COX-2 with the inhibitors was investigated. CIAA selectively inhibited COX-2 activity compared with COX-1 in in vitro assays with rat whole blood. The compound exhibited lower brain penetration and higher plasma concentration (the brain/plasma concentration ratio was approximately 0.02) than celecoxib and rofecoxib after oral administration. Therefore, CIAA is mainly expected to act peripherally. Edema and prostaglandin E2 (PGE2) production in Carrageenan-injected rat paws, and pyrexia and PGE2 production in the brain in lipopolysaccharide (LPS)-injected rats were measured in in vivo experiments. CIAA exhibited lower ratios of anti-pyretic/anti-edematous activities and of inhibitory activities of PGE2 production in brain/paw than those of celecoxib and rofecoxib, and these ratios well-reflected brain/plasma concentration ratios. In conclusion, we discovered a novel selective COX-2 inhibitor, CIAA, which distributes at higher concentrations in plasma than in brain, which would make possible the pharmacological separation of the peripheral and central functions of COX-2.

QSAR and classification models of a novel series of COX-2 selective inhibitors: 1,5-diarylimidazoles based on support vector machines

The support vector machine, which is a novel algorithm from the machine learning community, was used to develop quantitation and classification models which can be used as a potential screening mechanism for a novel series of COX-2 selective inhibitors. Each compound was represented by calculated structural descriptors that encode constitutional, topological, geometrical, electrostatic, and quantum-chemical features. The heuristic method was then used to search the descriptor space and select the descriptors responsible for activity. Quantitative modelling results in a nonlinear, seven-descriptor model based on SVMs with root mean-square errors of 0.107 and 0.136 for training and prediction sets, respectively. The best classification results are found using SVMs: the accuracy for training and test sets is 91.2% and 88.2%, respectively. This paper proposes a new and effective method for drug design and screening.

QSAR analysis of cyclooxygenase inhibitor using particle swarm optimization and multiple linear regression

Quantitative structure-activity relationship (QSAR) models of inhibiting action of some diarylimidazole derivatives on cylcooxygenase (COX) enzyme were constructed using modified particle swarm optimization (PSO) method. As a comparison to this method, the genetic algorithm (GA) was also tested. It has been demonstrated that the modified PSO is a useful tool for variable selection comparable to GA and even superior to GA. QSAR models are constructed separately for COX-2 inhibitory activity and selectivity of COX-2 inhibition over COX-1. The spatial descriptors play a key role in the compounds' activity and selectivity to COX-2, especially Jurs descriptors. Polar interactions are the principal binding strength between compounds and COX-2 enzyme. In addition, the aqueous desolvation free energy (FH2O) value of substituent will affect the COX-2 inhibitory activity, while the charge distribution can affect the selectivity to COX-2.

Computer-aided design of non sulphonyl COX-2 inhibitors: an improved comparative molecular field analysis incorporating additional descriptors and comparative molecular similarity indices analysis of 1,3-diarylisoindole derivatives

A set of thirty five molecules of 1,3-diaryl-4,5,6,7-tetrahydro-2H-isoindoles endowed with selective COX-2 inhibitory activity was analyzed using comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA). Besides conventional steric and electrostatic fields, seven additional descriptors were incorporated to the CoMFA models. An improved CoMFA model (r(2)(cv)=0.536, r(2)(conv)=0.968, SEE=0.222, r(2)(pred)=0.6564) was obtained by taking into account the CMR as additional descriptor. This analysis provided useful information regarding the pharmacophoric requirements for COX-2 inhibitory activity. FlexX was used to find out the binding orientation of this new class of 1,3-diaryl isoindoles in the active site of COX-2. The contour maps produced by improved CoMFA model was superimposed onto the active site revealing a good correlation between the contour maps and the active site residue interactions.

Synthesis and structure-activity relationship of a new series of COX-2 selective inhibitors: 1,5-diarylimidazoles

The synthesis and the pharmacological activity of a series of 1,5-diarylimidazoles developed as potent and selective cyclooxygenase-2 (COX-2) inhibitors are described. The new compounds were evaluated both in vitro (COX-1 and COX-2 inhibition in human whole blood) and in vivo (carrageenan-induced paw edema, air-pouch, and hyperalgesia tests). Modification of all the positions of two regioisomeric imidazole cores led to the identification of 4-[4-chloro-5-(3-fluoro-4-methoxyphenyl)imidazol-1-yl]benzenesulfonamide (UR-8880, 51f) as the best candidate, which is now undergoing Phase I clinical trials.

Synthesis and SAR of a new series of COX-2-selective inhibitors: pyrazolo[1,5-a]pyrimidines

The synthesis and pharmacological activity of a series of bicyclic pyrazolo[1,5-a]pyrimidines as potent and selective cyclooxygenase-2 (COX-2) inhibitors are described. The new compounds were evaluated both in vitro (COX-1 and COX-2 inhibition in human whole blood) and in vivo (carrageenan-induced paw edema and air-pouch model). Modification of the pyrimidine substituents showed that 6,7-disubstitution provided the best activity and led to the identification of 3-(4-fluorophenyl)-6,7-dimethyl-2-(4-methylsulfonylphenyl)pyrazolo[1,5-a]pyrimidine (10f) as one of the most potent and selective COX-2 inhibitor in this series.

Topical application of a selective cyclooxygenase inhibitor suppresses UVB mediated cutaneous inflammation

Ultraviolet B (UVB) radiation causes much of the cutaneous damage after both acute and long-term exposure, and is also the most important etiologic agent in human skin cancer. UVB exposure initially induces an inflammatory response characterized by edema, dermal infiltration of leukocytes, sunburn cell formation, as well as the induction of cyclooxygenase-2 (COX-2) gene expression and subsequent increase in the production and release of prostaglandins. This process of inflammation induced by UVB exposure has been linked to tumor formation. Recently, a specific COX-2 inhibitor, Celecoxib, was developed, which inhibits COX-2-induced inflammation without inhibiting the cytoprotective function of cyclooxygenase-1 (COX-1). The present study compared the effects of topical treatment with Celecoxib (a specific COX-2 inhibitor) and Ibuprofen (a nonspecific COX inhibitor) on the acute UVB-induced cutaneous inflammatory response. We show that the specific inhibition of COX-2 effectively reduced many parameters of UVB-mediated inflammation, including edema, dermal neutrophil infiltration and activation, prostaglandin E2 (PGE2) levels and the formation of sunburn cells. By inhibiting this inflammatory response, topical Celecoxib treatment may ultimately be effective in preventing UVB-induced tumor development in the skin.

Selective cyclooxygenase-2 inhibitors: heteroaryl modified 1,2-diarylimidazoles are potent, orally active antiinflammatory agents

A series of heteroaryl modified 1,2-diarylimidazoles has been synthesized and found to be potent and highly selective (1000-9000-fold) inhibitors of the human COX-2. 3-Pyridyl derived COX-2 selective inhibitor (25) exhibited excellent activity in acute (carrageenan induced paw edema, ED(50) = 5.4 mg/kg) and chronic (adjuvant induced arthritis, ED(50) = 0.25 mg/kg) models of inflammation. The relatively long half-life of 25 in rat and dog prompted investigation of the pyridyl and other heteroaromatic systems containing potential metabolic functionalities. A number of substituted pyridyl and thiazole containing compounds (e.g., 44, 46, 54, 76, and 78) demonstrated excellent oral activity in every efficacy model evaluated. Several orally active diarylimidazoles exhibited desirable pharmacokinetics profiles and showed no GI toxicity in the rat up to 100 mg/kg in both acute and chronic models. The paper describes facile and practical syntheses of the targeted diarylimidazoles. The structure-activity relationships and antiinflammatory properties of a series of diarylimidazoles are discussed.

1,2-Diarylpyrroles as potent and selective inhibitors of cyclooxygenase-2

Series of 1,2-diarylpyrroles has been synthesized and found to contain very potent and selective inhibitors of the human cyclooxygenase-2 (COX-2) enzyme. The paper describes short and practical syntheses of the target molecules utilizing the Paal-Knorr reaction. Electrophilic substitution on 1 proceeds in a regioselective fashion, and the method was used to generate a number of tetrasubstituted pyrroles. Detailed SAR on the series has been studied by modifications of the aryl rings and the substituents in the pyrrole ring. Diarylpyrrole 1 is a very potent (COX-2, IC50 = 60 nm) and selective (COX-1/COX-2 = > 1700) inhibitor whereas the isomeric 2 is completely inactive against COX-2. Modifications of the substituents on the fluorophenyl ring in 1 yields very potent inhibitors of COX-2 (IC50 = 40-80 nm) with excellent selectivity (1200 to > 2500) vs COX-1. Analog 20 containing a sulfonamide group is an excellent inhibitor of COX-2 with an IC50 of 14 nm. Tetrasubstituted pyrroles containing groups such as COCF3, SO2CF3, or CH2OAr at position 3 in the pyrrole ring give excellent inhibitors (COX-2, IC50 = 30-120 nm). In vivo testing in the carrageenan-induced paw edema model in the rat establishes that the 1,2-diarylpyrroles are orally active antiinflammatory agents. Compound 3 is the most potent inhibitor of edema with an ED50 of 4.7 mpk.

1,2-Diarylimidazoles as potent, cyclooxygenase-2 selective, and orally active antiinflammatory agents

Series of 1,2-diarylimidazoles has been synthesized and found to contain highly potent and selective inhibitors of the human COX-2 enzyme. The paper describes a short synthesis of the target 1,2-diarylimidazoles starting with aryl nitriles. Different portions of the diarylimidazole (I) were modified to establish SAR. Systematic variations of the substituents in the aryl ring B have yielded very potent (IC50 = 10-100 nm) and selective (1000-12500) inhibitors of the COX-2 enzyme. The study on the influence of substituents in the imidazole ring established that a CF3 group at position 4 gives the optimum oral activity. A number of the diarylimidazoles showed excellent inhibition in the adjuvant induced arthritis model (e.g., ED50 = 0.02 mpk for 22 and 34). The diarylimidazoles are also potent inhibitors of carrageenan-induced edema (ED50 = 9-30 mpk) and hyperalgesia (ED50 = 11-40 mpk). Several orally active diarylimidazoles show no GI toxicity in the rat and mouse up to 200 mpk.

Modulation of noradrenaline release in rat isolated stomach by prostanoids, but not by histaminergic mechanisms

Several gastric functions are modulated by the sympathetic nervous system, but local mechanisms involved in the control of noradrenaline release are largely unknown. Overflow of endogenous noradrenaline was studied from isolated rat stomach incubated in Ussing chambers allowing the separate determination of mucosal and serosal overflow. Spontaneous noradrenaline overflow was similar at the mucosal and serosal side, but electrical field stimulation caused a frequency-dependent increase in noradrenaline overflow selectively at the serosal side. Evoked noradrenaline overflow was blocked by tetrodotoxin, not affected by indometacin and markedly enhanced (by about 250%) by yohimbine. In the presence of indometacin and yohimbine, sulprostone (an agonist at EP1/EP3 receptors) and misoprostol (an agonist at EP2/EP3 receptors) reduced the noradrenaline overflow evoked by stimulation at 3 Hz maximally by about 80% (EC50: 6 nmol/l and 11 nmol/l, respectively). The EP1 receptor selective antagonist AH 6809 (6-isopropoxy-9-oxoxanthene-2-carboxylic acid) did not antagonize the inhibition by sulprostone. Noradrenaline overflow evoked by stimulation at 1 Hz and 3 Hz was increased by scopolamine by about 50% and almost completely inhibited by oxotremorine. Neither, histamine nor the H3 receptor selective agonist (R)-alpha-methyl-histamine, nor the H1, H2 and H3 selective receptor antagonists mepyramine, cimetidine and thioperamide significantly affected noradrenaline overflow evoked by stimulation at 1 Hz or 3 Hz. In conclusion, impulse-induced noradrenaline release in the rat stomach is controlled by multiple presynaptic mechanisms involving alpha 2-adrenergic autoreceptors, EP3 prostanoid and muscarine heteroreceptors, whereas histaminergic mechanisms do not appear to be significant.

Selective inhibition of inducible cyclooxygenase 2 in vivo is antiinflammatory and nonulcerogenic

We have examined the role of cyclooxygenase 2 (COX-2) in a model of inflammation in vivo. Carrageenan administration to the subcutaneous rat air pouch induces a rapid inflammatory response characterized by high levels of prostaglandins (PGs) and leukotrienes in the fluid exudate. The time course of the induction of COX-2 mRNA and protein coincided with the production of PGs in the pouch tissue and cellular infiltrate. Carrageenan-induced COX-2 immunoreactivity was localized to macrophages obtained from the fluid exudate as well as to the inner surface layer of cells within the pouch lining. Dexamethasone inhibited both COX-2 expression and PG synthesis in the fluid exudate but failed to inhibit PG synthesis in the stomach. Furthermore, NS-398, a selective COX-2 inhibitor, and indomethacin, a nonselective COX-1/COX-2 inhibitor, blocked proinflammatory PG synthesis in the air pouch. In contrast, only indomethacin blocked gastric PG and, additionally, produced gastric lesions. These results suggest that inhibitors of COX-2 are potent antiinflammatory agents which do not produce the typical side effects (e.g., gastric ulcers) associated with the nonselective, COX-1-directed antiinflammatory drugs.

Antiulcer therapy

Perhaps older drugs to treat ulcers, such as antacids, are just as effective as the newer drugs, but veterinarians have all but abandoned these drugs in favor of H2-receptor antagonists, sucralfate, and omeprazole. For most patients, one of the H2-receptor antagonists or sucralfate is probably the initial drug of choice. For patients refractory to these drugs or for which once-a-day dosing is desirable, omeprazole has an advantage. The doses for these drugs are listed in Table 1. Patients presented with acute bleeding ulcers should be managed with emergency therapy. Fluid therapy and blood transfusions are the essential elements of the initial therapy. Surgical resection of the ulcers may be necessary, and most patients should be administered H2-receptor antagonists or sucralfate while they recuperate. Longer term therapy with antiulcer drugs will depend on the predisposing factors that initiated the ulcers. The practice of lavage of the stomach with iced saline or epinephrine to stop bleeding from gastric ulcers is not effective. A common cause of ulcers in small animals is the administration of NSAIDs. Ulcers caused by these agents should be managed like any other ulcers. Fortunately, if ulcers are diagnosed early, they usually heal once the NSAID is discontinued. Unfortunately, many NSAID-induced ulcers identified postmortem did not produce clinical signs, and the ulcers may not be apparent until severe bleeding occurs. In cases in which patients are at risk for developing ulcers from NSAIDs, there may be an advantage in administering the synthetic prostaglandin misoprostol. In many patients that are sensitive to the GI irritation of NSAIDs, switching from one NSAID to another may alleviate some of the signs. Buffered aspirin may be somewhat less irritating than plain uncoated aspirin but will not completely prevent ulcers. The administration of enteric-coated aspirin tablets to dogs is discouraged, because systemic absorption from these tablets is unpredictable.

Misoprostol versus antacid titration for preventing stress ulcers in postoperative surgical ICU patients

Bleeding from gastroduodenal lesions is a potentially life-threatening complication in patients subjected to overwhelming physiologic stress. Titration of gastric contents with antacid was the first prophylactic treatment regimen proved to decrease the incidence of bleeding and remains the standard by which other methods are compared. We designed a prospective double-blind, double-placebo study comparing the effectiveness of antacid titration with fixed doses of a synthetic prostaglandin E1 analog (misoprostol) for preventing stress gastritis and bleeding. To assess the success of each treatment regimen, we did endoscopic examinations before operation, 72 hours after operation, and after the patient had completed the study. A total of 281 patients entered the study (140 misoprostol, 141 antacid). The two groups were comparable with respect to preoperative parameters and type of operation. We found no statistically significant differences between the two treatment groups concerning upper gastrointestinal tract lesions or serious adverse effects. No clinically evident upper gastrointestinal hemorrhage occurred in either group. Mean gastric pH, measured at two-hour intervals during the initial 72 hours, was maintained at 4.0 or higher in both groups. We conclude that fixed-dose misoprostol is as effective as intensive antacid titration in preventing stress ulcers and bleeding in surgical ICU patients.

Flunoxaprofen, a new non-steroidal anti-inflammatory drug, does not interfere with prostaglandin synthesis in rat gastric mucosa

The anti-inflammatory activity and the eicosanoid generation in rat gastric mucosa after a single oral dose of S-(+)-2(4-fluorophenyl)-alpha-methyl-5-benzoxazolacetic acid (flunoxaprofen, 10 mg/kg) or indomethacin (5 mg/kg) were compared. The two compounds, at the dose used, show a similar degree of anti-inflammatory activity (50% inhibition of carrageenan-induced oedema in rat paw). Moreover flunoxaprofen does not modify the formation of 6-keto-PGF1 alpha by rat gastric mucosa in vitro while indomethacin causes 50% inhibition of gastric cyclooxygenase activity. This biochemical change induced by indomethacin is associated with gastric lesions. Chronic treatment of rats with flunoxaprofen (5 or 50 mg/kg p.o. for 15 days) shows an anti-inflammatory activity in the range of 60-70% inhibition in the rat paw oedema test without gastric mucosa damages and prostaglandin synthesis inhibition.

Rioprostil in the treatment of duodenal erosions

Thirty outpatients with erosions of the duodenal bulb unrelated to peptic ulcer were randomly allocated to an 8-week treatment regimen with either rioprostil, 200 micrograms b.d., or with sucralfate, 1 g t.i.d. At endoscopic control complete disappearance of duodenal erosions was found in 57.2% of rioprostil-treated patients and in 64.3% of patients treated with sucralfate. The difference was not statistically significant. The two drugs were shown to be significantly and equally effective in inducing relief of dyspeptic symptoms. No intestinal side effects were observed during treatment with rioprostil.

Sulfation in vitro of mucus glycoprotein by submandibular salivary gland: effects of prostaglandin and acetylsalicylic acid

Enzymatic sulfation of mucus glycoprotein by rat submandibular salivary gland and the effect of prostaglandin and acetylsalicylic acid on this process were investigated in vitro. The sulfotransferase enzyme which catalyzes the transfer of sulfate ester group from 3'-phosphoadenosine-5'-phosphosulfate to submandibular gland mucus glycoprotein has been located in the detergent extracts of Golgi-rich membrane fraction of the gland. Optimum enzyme activity was obtained at pH 6.8 with 0.5% Triton X-100, 25 mM NaF and 4 mM MgCl2, using the desulfated glycoprotein. The enzyme was also capable of sulfation of the intact mucus glycoprotein, but the acceptor capacity of such glycoprotein was 68% lower. The apparent Km of the submandibular gland sulfotransferase for salivary mucus glycoprotein was 11.1 microM. The 35S-labeled glycoprotein product of the enzyme reaction gave in CsCl density gradient a 35S-labeled peak which coincided with that of the glycoprotein. This glycoprotein upon reductive beta-elimination yielded several acidic 35S-labeled oligosaccharide alditols which accounted for 75% of the 35S-labeled glycoprotein label. Based on the analytical data, the two most abundant oligosaccharides were identified as sulfated tri- and pentasaccharides. The submandibular gland sulfotransferase activity was stimulated by 16,16-dimethyl prostaglandin E2 and inhibited by acetylsalicylic acid. The rate of enhancement of the glycoprotein sulfation was proportional to the concentration of prostaglandin up to 2.10(-5) M, at which point a 31% increase in sulfation was attained. The inhibition of the glycoprotein sulfation by acetylsalicylic acid was proportional to the drug concentration up to 2.5.10(-4) M at which concentration a 48% reduction in the sulfotransferase activity occurred. The apparent Ki value for sulfation of salivary mucus glycoprotein in presence of acetylsalicylic acid was 58.9 microM. The results suggest that prostaglandins may play a role in salivary mucin sulfation and that this process is sensitive to such nonsteroidal anti-inflammatory agents as acetylsalicylic acid.

Prostaglandin effect on the enzymatic sulfation of mucus glycoprotein in gastric mucosa

The effect of 16,16-dimethyl prostaglandin E2 (DMPGE2) on the sulfation of mucus glycoprotein in gastric mucosa was investigated. The enzymatic activity which catalyzes the transfer of the sulfate ester group from 3'-phosphoadenosine-5'-phosphosulfate to gastric mucus glycoprotein was located in the detergent extracts of Golgi-rich membrane fraction of antral and body mucosa of rat stomach. The sulfotransferase activity of this fraction from body mucosa, however, was 35% higher than that from the antrum. The enzyme exhibited optimum activity at pH 6.8 using 0.5% Triton X-100 and 30 mM NaF. The apparent Km of the enzyme for sulfation of mucus glycoprotein was 10.5 microM, and the sulfate ester was found incorporated into the carbohydrate chains of the glycoprotein. Introduction of DMPGE2 to the reaction mixtures led to an enhancement in the rate of mucus glycoprotein sulfation. The rate of enhancement was proportional to the concentration of DMPGE2 up to 1.0 x 10(-4) M and was of the competitive type, with an apparent Km value of 6.7 microM. Since sulfated mucins play an important role in gastric mucosal defense and the increase in their sulfation occurred at levels of prostaglandin present in gastric mucosa, the observed effect may be of significance to gastric mucosal defense in vivo.

Effect of enprostil on basal and meal-stimulated gastric acid and pepsin secretion, serum gastrin and gastric emptying in healthy persons

Ten healthy volunteers took part in a double-blind, randomized, cross-over study of the effect of single doses of enprostil (70 micrograms) and placebo on basal and meal-stimulated gastric acid, pepsin secretion and serum gastrin. Meal-stimulation was induced by modified sham feeding combined with repeated gastric instillation and withdrawal of meat soup. When studied between 1 and 2.5 hours after oral administration of the drug, enprostil decreased basal acid output by 92% (P less than 0.001) and stimulated acid output by 70% (P less than 0.001). Basal and stimulated volumes of gastric juice were decreased by 50% (P less than 0.02) and 35% (P less than 0.002), respectively. Enprostil decreased stimulated pepsin output by 34% (P less than 0.05), but had no effect on the concentration of pepsin. Neither basal nor stimulated serum gastrin concentrations were affected by enprostil. Percent recovery of the meal was measured by an unabsorbable marker, polyethylene glycol, instilled into the stomach mixed with the soup. Polyethylene glycol recovery decreased from 89% with placebo to 67% with enprostil (P less than 0.01), indicating an enhanced gastric emptying rate with enprostil.

Prostaglandin treatment for peptic ulcer

Prostaglandin analogues have been expected to outperform other antisecretory drugs as ulcer healing agents. This expectation arises from their ability to combine 'cytoprotection' with gastric secretory inhibition. Evidence of the existence of these two separate functions abounds in animals and in humans, but a clinical advantage has not evolved. Whereas most clinical trials show no difference between prostaglandin analogues and H2-receptor antagonists, some studies have shown the prostaglandins to be significantly less effective or no better than placebo. The role of cytoprotection in ulcer healing (as opposed to prevention) may be questioned and the present clinical role for these agents is unclear.

Effect of mifentidine on mepirizole-induced duodenal ulcer in the rat

The H2-receptor antagonists mifentidine, famotidine, cimetidine and ranitidine were examined for their ability to prevent the duodenal ulcer caused by mepirizole (250 mg/kg p.o.), a non-steroidal anti-inflammatory agent, in the conscious rat. All the compounds exerted a dose-related protective effect and on the basis of their ED50s, the following rank order of potency was found: mifentidine = famotidine greater than ranitidine greater than cimetidine. The antiulcer activity displayed by the H2-receptor antagonists evaluated in this model reflects their potency in inhibiting basal and stimulated gastric acid secretion in rat. The results of these studies indicate mifentidine as a potent anti-ulcer agent.