Bernhard A. Peskar

Low dose aspirin and inhibition of thromboxane B2 production in healthy subjects.

Abstract We studied the time- and dose-dependence of the inhibitory effect of oral aspirin on platelet production of thromboxane (TX) B2 in response to endogenously formed thrombin, by allowing the whole blood to clot at 37°C for 30 min and measuring TXB2 concentrations by radioimmunoassay in the separated serum. The concentrations of generated TXB2 averaged 222.4 ± 81.3 (SD) ng/ml of serum in 45 healthy subjects, and were highly reproducible in the same subject upon repeated sampling. A single 100-mg aspirin dose reduced serum TXB2 by 98% during the 1st hour. Single doses of 100–400 mg aspirin resulted in 94–98% inhibition after 24 and 48 h, and 90–92% after 72h. Thereafter, serum TXB2 returned to control levels with a time course consistent with platelet turnover. More than 90% inhibition could be maintained, over one month, by giving a 200-mg aspirin dose every 72h. Thus, aspirin can achieve a ceiling effect on TXB2 production in healthy subjects at a considerably lower dosage than currently employed regimens for antithrombotic therapy.

Anti-inflammatory effects of aspirin and sodium salicylate.

Aspirin (acetylsalicylic acid) is one of the most widely used drugs worldwide. It acetylates cyclooxygenases thereby irreversibly blocking the conversion of arachidonic acid to prostanoids. Biotransformation of aspirin yields salicylate, a compound that possesses similar anti-inflammatory potency as aspirin but lacks aspirins inhibitory effect on the activity of isolated cyclooxygenase. This article is aimed at providing an overview about the often conflicting results concerning the mechanisms of action of aspirin and sodium salicylate. At present, there is no common agreement about the extent to which salicylate contributes to aspirins anti-inflammatory properties, as well as there is still no final conclusion reached about the mechanisms of action of sodium salicylate. Several possible sites of action of salicylate have been suggested: It has been shown that in intact cells-but not in purified enzyme preparations-, sodium salicylate inhibits prostanoid biosynthesis. This effect seems to be prevented in the presence of high concentrations of arachidonic acid, which has been shown to interfere with inhibition by salicylate of cyclooxygenase-2-mediated prostanoid formation in vitro. Other possible sites of action that are not directly related to cyclooxygenase inhibition have been suggested based on observations made in vitro using high concentrations of aspirin and sodium salicylate. These effects target intracellular signaling mechanisms such as kinases, including the mitogen activated protein-kinases (MAPK) cascade. With the exception of reported salicylate-induced activation of p38 MAPK, observed effects are usually inhibitory. This may be one reason for the observation that, downstream to kinases, inhibitory effects of salicylates have been observed on several nuclear transcription factors, such as nuclear transcription factor kappa B (NF-kB) or activator protein 1 (AP-1). Several reports have also shown interference by salicylates with the expression of cyclooxygenase-2, which, depending on experimental models, can be observed as inhibitory but also stimulatory effects. Antioxidant properties of salicylates, adenosine release induced by sodium salicylate and aspirin-triggered lipoxin formation are additional mechanisms that may contribute to anti-inflammatory properties of aspirin and/or sodium salicylate. An additional focus of this review is the discussion of interactions between aspirin, sodium salicylate and other non-steroidal anti-inflammatory drugs (NSAIDs), which are of particular relevance in the gastro-intestinal and cardiovascular systems.

Ethanol stimulates formation of leukotriene C4 in rat gastric mucosa

Ethanol-induced gastric mucosal damage is characterized by microcirculatory changes such as stasis and plasma leakage. Sluggish blood flow and stasis have also been observed after administration of exogenous leukotriene (LT) C4. The effect of ethanol on the release of LTC4 from rat gastric mucosa was therefore investigated. It was found that intragastric instillation of ethanol increases gastric mucosal release of LTC4 in a dose- and time-dependent manner parallel to the production of gastric lesions. The lipoxygenase inhibitor nordihydroguaiaretic acid (NDGA) and the anti-ulcer drug carbenoxolone (CX) inhibited mucosal release of LTC4 and simultaneously protected against gastric damage caused by ethanol. It is concluded that increased formation of LTC4 and/or other 5-lipoxygenase-derived products of arachidonate metabolism may be involved in ethanol-induced gastric damage. Furthermore, inhibition of the 5-lipoxygenase pathway may be an important mechanism of action of gastric protective drugs.

Afferent nerve-mediated protection against deep mucosal damage in the rat stomach☆

Intragastric capsaicin protects against ethanol-induced gross mucosal lesion formation by stimulation of afferent nerve endings in the rat stomach. The aims of the present study were to examine histologically the protective effect of capsaicin and to test whether this effect is related to changes in mucosal eicosanoid formation and mucosal blood flow. Intragastric capsaicin (160 microM) significantly reduced gross mucosal lesion formation induced by 25% ethanol. Light microscopy revealed that the depth of erosions was attenuated likewise. However, capsaicin did not prevent ethanol from causing superficial damage to the mucosa as observed by light and scanning electron microscopy. The protective action of capsaicin against ethanol remained unchanged by a dose of indomethacin that reduced the ex vivo formation of prostaglandin E2 and 6-oxo-prostaglandin F1 alpha in the gastric mucosa by about 90%. Capsaicin alone did not affect the ex vivo formation of these prostaglandins and of leukotriene C4. Intragastric capsaicin (160 microM) enhanced gastric mucosal blood flow by 89% as measured by the hydrogen gas clearance technique. This effect was also observed when capsaicin was administered together with 25% ethanol. These data indicate that afferent nerve stimulation by intragastric capsaicin protects against deep mucosal damage in response to ethanol, an effect that seems related to an increase in mucosal blood flow but not to eicosanoid formation.

Evidence for a Direct Stimulatory Effect of Prostacyclin on Renin Release in Man

THE OBJECTIVES OF THIS INVESTIGATION WERE: (a) to characterize the time and dose dependence of the effects of prostacyclin (PGI(2)) on renin release in healthy men; (b) to define whether PGI(2)-induced renin release is secondary to hemodynamic changes; (c) to determine the plasma and urine concentrations of 6-keto-PGF(1alpha) (the stable breakdown product of PGI(2)) associated with renin release induced by exogenous or pharmacologically enhanced endogenous PGI(2). Intravenous PGI(2) or 6-keto-PGF(1alpha) infusions at nominal rates of 2.5, 5.0, 10.0, and 20.0 ng/kg per min were performed in each of six normal human subjects; in three of them, PGI(2) infusion was repeated after beta-adrenergic blockade and cyclooxygenase inhibition. PGI(2), but not 6-keto-PGF(1alpha), caused a time- and dose-dependent increase of plasma renin activity, which reached statistical significance at 5.0 ng/kg per min and was still significantly elevated 30 min after discontinuing the infusion. Although combined propranolol and indomethacin treatment significantly enhanced the hypotensive effects of infused PGI(2), it did not modify the dose-related pattern of PGI(2)-induced renin release. Plasma 6-keto-PGF(1alpha) levels rose from undetectable levels (<7.5 pg/ml) in a stepwise fashion during increasingly higher infusion rates of PGI(2) or 6-keto-PGF(1alpha). The threshold concentration of plasma 6-keto-PGF(1alpha) associated with a statistically significant stimulation of renin release was approximately 200 pg/ml. Upon discontinuing PGI(2) or 6-keto-PGF(1alpha) infusion, the disappearance of 6-keto-PGF(1alpha) from blood showed an identical biphasic behavior, the initial phase having an apparent t((1/2)) of 3.2 min. The intravenous infusion of furosemide, which is known to stimulate renin release via a cyclooxygenase-dependent mechanism, caused a three-to fourfold increase of urinary 6-keto-PGF(1alpha) excretion rate, concomitant with the elevation of plasma renin activity levels, in six healthy women. 6-Keto-PGF(1alpha) remained undetectable in peripheral venous plasma throughout the study. WE CONCLUDE THAT IN HUMAN SUBJECTS: (a) PGI(2)-induced renin release occurs with a dose and time dependence similar to its reported platelet effects; (b) PGI(2)-induced renin release is not mediated by adrenergic stimuli or cyclooxygenase-dependent mechanisms secondary to hemodynamic changes; (c) furosemide-induced renin release is associated with increased renal PGI(2) formation; and (d) PGI(2) appears to act as a local modulator rather than a circulating hormone in controlling juxtaglomerular function.

Aspirin-like drugs may block pain independently of prostaglandin synthesis inhibition

Using flurbiprofen, a chiral anti-inflammatory and analgesic 2-arylpropionic acid derivative, the enantiomers of which are not converted to each other (less than 5%) in rats or man, we obtained evidence that prostaglandin synthesis inhibition is primarily mediating the anti-inflammatory activity but prostaglandin synthesis independent mechanisms contribute to the analgesic effects. Thus, the S-form inhibited prostaglandin synthesis, inflammation and nociception in rats. The R-form had much less effect on prostaglandin synthesis and did not affect inflammation. It did, however, block nociception in rats almost as potently as the S-form. S-flurbiprofen, in contrast to the R-form, was clearly ulcerogenic in the gastrointestinal mucosa. These results indicate additional molecular mechanisms of analgesia and suggest the use of R-arylpropionic acids as analgesics.

Inhibition by anti-inflammatory drugs of prostaglandin production in cultured macrophages

Summary1.A sensitive, simple, reproducible, and economical assay for structure-activity investigations of non-steroidal anti-inflammatory drugs (NSAID) is lacking. This has promted us to investigate the advantages and limitations of defining for that purpose the potency of NSAIDs as inhibitors of tumour promoter-induced prostaglandin (PG) release from mouse peritoneal macrophages in culture.2.These cells release mainly PGE2 and PGI2 (measured as its stable hydrolysis product 6-keto-PGF1α) upon stimulation with the tumour promoter 12-O-tetradecanoylphorbol-13-acetate (TPA).3.The PG release was dose-dependently inhibited by a variety of NSAIDs. Their inhibitory potency was dependent on the culture conditions employed. The widely used acidic NSAIDs were more potent when assayed under serum free culture conditions at low pH.4.Dose response curves for acidic NSAID tested under serum free conditions allowed for the definition of IC50 values being reproducible within their 95% confidence limits.5.The IC50 values obtained for different standard acidic NSAIDs varied within 4 orders of magnitude. They corresponded favourably to their clinical potency and their potency in a variety of standard tests for antiinflammatory drugs.6.IC50 values of five congeners of indomethacin differed up to 2 orders of magnitude in agreement with in vivo observations indicating the applicability of this assay for structure-activity investigations.

Release of calcitonin gene-related peptide induced by capsaicin in the vascularly perfused rat stomach

It has been suggested that capsaicin-induced gastric mucosal protection results from the local release of vasodilator peptides such as calcitonin gene-related peptide (CGRP) from afferent nerve endings within the stomach, since CGRP is able to reduce gastric lesion formation. This concept is supported by the present finding that capsaicin (10(-5) M), administered to the vascularly perfused stomach of the rat, produces a more than 30-fold rise of the CGRP content of the venous effluent. High-pressure liquid chromatography revealed only one peak of immunoreactivity coeluting with synthetic CGRP.

Muscular side effects of statins.

Lipid lowering has been shown to be effective in preventing primary and recurrent cardiovascular events and to save life. Statins almost exclusively used for this purpose meanwhile became one of the most widely prescribed families of drugs world-wide. Myopathies – mainly not well characterized – are the major group of side effects. We here review different types of clinical appearances, localizations, symptoms and the biochemical background. The data indicate that severe muscular side effects are rare. Patients and their doctors, however, easily overlook mild ones. Myopathic symptoms without any known biochemical correlate are not rare. No general guideline exists about exact diagnosis and differential diagnosis. Strict adherence to the measures of life-style change and performance of regular exercise can even further enhance significantly these side effects. Much more research should be directed onto the pathophysiological (genetic?) background to finally evaluate possible therapeutic consequences rather than simply to withdraw or change the respective statin.

Δ12-Prostaglandin J2, a Plasma Metabolite of Prostaglandin D2, Causes Eosinophil Mobilization from the Bone Marrow and Primes Eosinophils for Chemotaxis

PGD2, a major mast cell mediator, is a potent eosinophil chemoattractant and is thought to be involved in eosinophil recruitment to sites of allergic inflammation. In plasma, PGD2 is rapidly transformed into its major metabolite Δ12-PGJ2, the effect of which on eosinophil migration has not yet been characterized. In this study we found that Δ12-PGJ2 was a highly effective chemoattractant and inducer of respiratory burst in human eosinophils, with the same efficacy as PGD2, PGJ2, or 15-deoxy-Δ12,14-PGJ2. Moreover, pretreatment of eosinophils with Δ12-PGJ2 markedly enhanced the chemotactic response to eotaxin, and in this respect Δ12-PGJ2 was more effective than PGD2. Δ12-PGJ2-induced facilitation of eosinophil migration toward eotaxin was not altered by specific inhibitors of intracellular signaling pathways relevant to the chemotactic response, phosphatidylinositol 3-kinase (LY-294002), mitogen-activated protein kinase/extracellular signal-regulated kinase kinase (U-0126), or p38 mitogen-activated protein kinase (SB-202190). Desensitization studies using calcium flux suggested that Δ12-PGJ2 signaled through the same receptor, CRTH2, as PGD2. Finally, Δ12-PGJ2 was able to mobilize mature eosinophils from the bone marrow of the guinea pig isolated perfused hind limb. Given that Δ12-PGJ2 is present in the systemic circulation at relevant levels, a role for this PGD2 metabolite in eosinophil release from the bone marrow and in driving eosinophil recruitment to sites of inflammation appears conceivable.