Cofactor requirements of the enzyme synthesizing prostagland in bovine seminal vesicles

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

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

Towards aspirin-inspired self-immolating molecules which target the cyclooxygenases

Cyclooxygenases (COXs) are enzymes that play a vital role in the inflammatory cascade through the generation of prostaglandins. Their over-expression has been implicated in numerous diseases. In particular, over-expression of COX-2 has been shown to be a predictive biomarker for progression of pre-malignant lesions towards invasive cancer in various tissues. This makes the early detection of COX-2 expressing lesions of high clinical relevance. Herein we describe the development of the first self-immolating trigger which targets COXs. We incorporated our trigger design into 2 activatable fluorogenic probes and demonstrated COX-specific activation in vitro. Experimental data revealed probe activation was likely caused by solvent-exposed amino acids on the surface of the COXs. Overall, the probes reported here mark the first step towards developing self-immolating imaging/therapeutic agents targeted to specific COXs.

Development of a radiochemical cyclooxygenase-1 and -2 in vitro assay for identification of natural products as inhibitors of prostaglandin biosynthesis

A radiochemical enzyme assay for studying cyclooxygenase (COX)-catalyzed prostaglandin biosynthesis in vitro was optimized with respect to both COX-1 and COX-2 activity. The assay can be used to assess the relative selectivity of plant-derived inhibitors on COX-1 and COX-2 Assay conditions were optimized for both enzymes with respect to concentration of cofactors (l-epinephrine, reduced glutathione, and hematin), activation time (enzyme and cofactors), reaction time, and pH. Moreover, the kinetic parameters, Km and Kcat, of both enzymes were estimated. Five COX inhibitors were used to validate the assay, indomethacin, aspirin, naproxen, ibuprofen, and the arylsulfonamide NS-398, all with different COX selectivity and time dependency. Time-dependent inhibition was determined by comparing the inhibition, with and without preincubation of enzyme and inhibitor. Two flavonoids, (+)-catechin and quercitrin, were examined with respect to inhibition of COX-catalyzed prostaglandin biosynthesis. (+)-Catechin showed equal inhibitory effects on the two enzymes. Quercitrin was found to be inactive toward both COX-1- and COX-2-catalyzed prostaglandin biosynthesis. The optimization procedure resulted in a considerable reduction of the amount of enzyme required for adequate prostglandin biosynthesis and a reliable method suited to evaluate natural products on inhibition of COX-2-catalyzed prostaglandin biosynthesis, as well as on COX-1.

Heterogeneity in prostacyclin and thromboxane synthesis in ovine pulmonary vascular tree: effect of age and oxygen tension

Intrapulmonary arteries and veins of 8 near-term fetal lambs (141-145 days gestation) and 8 ewes were isolated into segments of > 3mm, 1-3 mm, and < mm in diameter. Vessels were incubated in Krebs' buffer at 37 degrees C at PO2 approximately 100 torr (normoxia) and PO2 < 50 torr (hypoxia) to study local vascular production of prostanoids. Prostacyclin and thromboxane (Tx) A2 produced were measured by radioimmunoassay and expressed in ng/mg dry wt, means +/- SEM. During normoxia, fetal arteries > 3 mm synthesized more prostacyclin than adult arteries of the same size (1.71 +/- 0.3 vs 0.45 +/- 0.04). However, fetal arteries < 1 mm synthesized less prostacyclin than adult arteries < 1 mm (0.47 +/- 0.1 vs 1.75 +/- 0.16). Prostacyclin production by veins > 3 mm was similar in the fetus and adult (0.49 +/- 0.06 vs 0.67 +/- 0.08), but in veins < 1 mm was greater in adult than in fetal vessels (1.73 +/- 0.17 0.54 +/- 0.06). Hypoxia-attenuated prostacyclin production by fetal arteries and veins of all sizes, but only in 1 to 3-mm-size adult arteries. In general, production of TxA2 by segments of fetal and adult vessels was less than 50% of that of prostacyclin. Protein and DNA concentrations in similar sized fetal and adult vessels were similar. The data show that there is heterogeneity in the production of prostacyclin and TxA2 along the ovine pulmonary vascular tree. Prostanoid synthesis of fetal vessels is markedly influenced by hypoxia, with a greater suppression of prostacyclin synthesis. Similar protein and DNA concentrations in fetal and adult vessels suggest that differences in prostanoid production by vessel segments may be due to differences in enzyme activity rather than cell number or tissue mass.

Peroxidative oxidation of leuco-dichlorofluorescein by prostaglandin H synthase in prostaglandin biosynthesis from polyunsaturated fatty acids

Prostaglandin H synthase can oxidize arachidonic acid with leuco-dichlorofluorescein as reducing cosubstrate. Addition of 0.5 mM phenol increases the oxidation of leuco-dichlorofluorescein to dichlorofluorescein 5-fold, probably by acting as a cyclic intermediate in the oxidation. Tetramethyl-p-phenylenediamine is also oxidized as cosubstrate. Its oxidation is not influenced by phenol. A stoichiometry of close to one mole of tetramethyl-p-phenylenediamine or leuco-dichlorofluorescein consumed per mole of arachidonic acid was found in the initial phase of the reaction. In the presence of phenol + leuco-dichlorofluorescein, the oxidation rate of arachidonic acid is about 40% lower than with phenol alone as cosubstrate. Since dichlorofluorescein has a molar extinction coefficient of 91 . 10(3) at 502 nm, the oxidation of less than 1 microM leuco-dichlorofluorescein can be detected spectrophotometrically. The rate of extinction change with leuco-dichlorofluorescein (at 502 nm) is about 4-fold more rapid than with tetramethyl-p-phenylenediamine (at 611 nm). With this spectrophotometric assay we have confirmed that arachidonic acid, linolenic acid, adrenic acid, gamma-linolenic acid, eicosapentaenoic acid, are substrates for prostaglandin H synthase with decreasing reaction rates in the mentioned order. The same order of reaction rates were found when oxygen consumption was measured. The assay also shows that docosahexaenoic acid is substrate for the enzyme. The reaction rate of the enzyme evidently is decreased both by a n-3 double bond and by deviation from a 20 carbon chain length of the fatty acid substrate.

Effect of glutathione manipulation on prostaglandin synthesis in renal medullary homogenates

1. The effect of glutathione (GSH) manipulation on arachidonic acid (AA) metabolism in renal medullary (RM) homogenates was investigated. 2. Diethyl maleate (DEM) depleted GSH initially by 50% (P less than 0.05) and produced a general suppression (P less than 0.05) of all PGs with the exception of TXB2. GSH was further depleted during homogenization and a 30-min incubation period (P less than 0.01). 3. Adding glutathione monoethyl ester (GSH-MEE) (0, 0.8, 1.6 or 3.2 mmol/ml) to RM homogenates increased GSH (P less than 0.01) and decreased RM homogenates' PGs-synthesizing capability (P less than 0.05), with the exception of PGE2 and TXB2 at the highest concentration. 4. The results indicate that homogenization has a significant impact (P less than 0.05) on GSH concentration of the media and alterations in GSH concentration affect the profile and quantity of AA metabolites in renal medullary homogenates.

Platelet activating factor receptor blockade ameliorates murine systemic lupus erythematosus

Untreated 16-week-old MRL/MpJ-lpr/lpr (lpr) mice, when compared to congenic MRL/MpJ-+/+ (+/+) mice, are characterized by a systemic lupus erythematosus syndrome, including severe glomerulonephritis, proteinuria and reduction of renal function. We hypothesized that platelet activating factor (PAF), a potent chemotactic and proinflammatory phospholipid mediator synthesized and released by circulating cells, glomerular mesangial and renal medullary interstitial cells, may play a role in the development of renal injury in lupus mice. We assessed renal PAF synthesis in lpr as well as +/+ mice and the effect of treatment with a PAF receptor blocking agent. Treatment with the PAF receptor antagonist L659,989 for four weeks, starting at 12 weeks of age, significantly reduced acute glomerular infiltration and proliferation, and prevented chronic glomerular histological changes; proteinuria and serum creatinine levels were also significantly reduced in treated mice. Renal PAF production was increased in lpr when compared to +/+ mice, and treatment with L659,989 restored renal PAF synthesis to the control levels. Our results support the hypothesis that PAF can be one of the mediators of glomerular injury characteristic of murine lupus nephritis, and indicate the possible therapeutic utility of PAF receptor antagonists in immunologic renal diseases.

Lymphatic pumping in response to changes in transmural pressure is modulated by erythrolysate/hemoglobin

Red blood cells and lysate products (erythrolysate) are observed consistently in lymph draining acute and chronic inflammatory reactions and from tissues subjected to trauma or surgical procedures. Using hemoglobin as a marker for erythrolysate, we have measured hemoglobin in lymph up to the 10(-6) M range in a number of pathophysiological states. Data demonstrate that erythrolysate alters the pumping characteristics of lymphatic vessels. To test the effects of erythrolysate on lymphatic pumping, bovine lymphatics were suspended in an organ bath preparation with the vessels cannulated at both inflow and outflow ends. By raising the heights of the Krebs reservoir and the outflow catheters appropriately, a transmural pressure that stimulated pumping activity could be applied to the vessels. With a fixed transmural pressure of 6 cm H2O applied to the ducts, sheep erythrolysate depressed pumping activity between 40% and 100%, with dilutions containing between 10(-8) and 10(-5) M hemoglobin. Although the active principle in the red blood cells has not been characterized, evidence from precipitation purification experiments suggests that hemoglobin is an important component. Once suppressed, pumping could be restored in many but not all vessels (often to control levels) by elevating the distending pressure above 6 cm H2O. The relation between transmural pressure and fluid pumping is expressed as a bell-shaped curve, with pumping increasing up to a peak pressure (usually 8 cm H2O) and declining at pressures above this level. By comparing pressure/flow curves, we were able to ascertain that hemoglobin shifted the lymphatic function curve to the right and, on average, reduced the maximum pumping capability of the vessels. We speculate that the presence of erythrolysate/hemoglobin in lymph may modulate the ability of lymphatic vessels to drain liquid and protein from the tissue spaces.

Concentration-activity profile of the modulation of cyclooxygenase product formation by reduced glutathione in microsomal fractions from the goat lung

Age-related changes in pulmonary formation of arachidonic acid (AA) metabolites are thought to play an important role in regulating cardiopulmonary function. This study addresses the potential role of reduced glutathione (GSH) in modulating cyclooxygenase product formation in the developing lung. Prostaglandin H2 (PGH2) metabolism was studied in microsomal fractions isolated from the lungs of unventilated fetal, neonatal and adult goats. GSH-dependent PGH2 to PGE2 isomerase activity in microsomal fractions from the perinatal (fetal and neonatal) goat lung was not saturable with respect to GSH and can respond to changes in GSH concentration over the range of 0.01 to 30 mM, which encompasses the full range the intracellular GSH levels reported in the literature. However, in fractions from the adult, a lower rate of PGE2 formation is observed at higher GSH concentrations. In addition, the tissue levels of GSH exhibited developmental stage-related differences with fetal being higher than neonatal or adult. The present observations may have physiologic relevance, in that decreases in pulmonary GSH levels after birth may contribute to decreases in plasma PGE2 levels by decreasing pulmonary PGE2 synthesis, thereby contributing to closure of the ductus arteriosus; conversely, increased GSH levels associated with hyperoxia may contribute to persistence of ductal patency. Formation of 6-keto-PGF1 alpha and of TXB2 (the stable metabolites of prostacyclin and TXA2) was decreased when PGE2 formation was increased by GSH activation of PGE2 isomerase in fractions isolated from all three developmental stages. A similar pattern of product formation was observed when AA was employed as substrate. These data suggest the possibility that changes in GSH concentration may modulate eicosanoid formation in cells that contain GSH-dependent PGE2 isomerase, as well as either or both prostacyclin or thromboxane synthase(s).

Glutathione disulfide production during arachidonic acid oxygenation in human platelets

Washed human platelets stimulated with 50 microM sodium arachidonate rapidly accumulated glutathione disulfide to a peak concentration of 0.620 nmole per 10(9) cells, 200% of control (unstimulated) levels. Total glutathione remained unchanged. The rise in glutathione disulfide was transitory, returning to control values within 30 seconds in aggregating platelets. Similar findings were observed in washed platelets aggregated with 5 U/ml thrombin. Platelet aggregation was not necessary for the generation of glutathione disulfide. However, cyclooxygenase activity was necessary for the generation of glutathione disulfide. Aspirin treated platelets aggregated with thrombin demonstrated no thromboxane B2 production and no glutathione disulfide generation. Dose response studies with both agonists demonstrated a direct relationship between the amount of thromboxane B2 produced and the amount of glutathione disulfide generated by stimulated platelets. During the conversion of arachidonic acid to thromboxane B2, unesterified arachidonic acid is oxygenated to prostaglandin G2 which is subsequently reduced to prostaglandin H2. Both reactions are catalyzed by the enzyme prostaglandin H synthase. Our data support the hypothesis that glutathione is an important supplier of reducing equivalents to prostaglandin H synthase during the production of prostaglandin H2 in human platelets.

Initiation of lipid peroxidation in biological systems

The direct oxidation of PUFA by triplet oxygen is spin forbidden. The data reviewed indicate that lipid peroxidation is initiated by nonenzymatic and enzymatic reactions. One of the first steps in the initiation of lipid peroxidation in animal tissues is by the generation of a superoxide radical (see Figure 16), or its protonated molecule, the perhydroxyl radical. The latter could directly initiate PUFA peroxidation. Hydrogen peroxide which is produced by superoxide dismutation or by direct enzymatic production (amine oxidase, glucose oxidase, etc.) has a very crucial role in the initiation of lipid peroxidation. Hydrogen peroxide reduction by reduced transition metal generates hydroxyl radicals which oxidize every biological molecule. Hydrogen peroxide also activates myoglobin, hemoglobin, and other heme proteins to a compound containing iron at a higher oxidation state, Fe(IV) or Fe(V), which initiates lipid peroxidation even on membranes. Complexed iron could also be activated by O2- or by H2O2 to ferryl iron compound, which is supposed to initiate PUFA peroxidation. The presence of hydrogen peroxide, especially hydroperoxides, activates enzymes such as cyclooxygenase and lipoxygenase. These enzymes produce hydroperoxides and other physiological active compounds known as eicosanoids. Lipid peroxidation could also be initiated by other free radicals. The control of superoxide and perhydroxyl radical is done by SOD (a) (see Figure 16). Hydrogen peroxide is controlled in tissues by glutathione-peroxidase, which also affects the level of hydroperoxides (b). Hydrogen peroxide is decomposed also by catalase (b). Caeruloplasmin in extracellular fluids prevents the formation of free reduced iron ions which could decompose hydrogen peroxide to hydroxyl radical (c). Hydroxyl radical attacks on target lipid molecules could be prevented by hydroxyl radical scavengers, such as mannitol, glucose, and formate (d). Reduced compounds and antioxidants (ascorbic acid, alpha-tocopherol, polyphenols, etc.) (e) prevent initiation of lipid peroxidation by activated heme proteins, ferryl ion, and cyclo- and lipoxygenase. In addition, cyclooxygenase is inhibited by aspirin and nonsteroid drugs, such as indomethacin (f). The classical soybean lipoxygenase inhibitors are antioxidants, such as nordihydroguaiaretic acid (NDGA) and others, and the substrate analog 5,8,11,14 eicosatetraynoic acid (ETYA), which also inhibit cyclooxygenase (g). In food, lipoxygenase is inhibited by blanching. Initiation of lipid peroxidation was derived also by free radicals, such as NO2. or CCl3OO. This process could be controlled by antioxidants (e).(ABSTRACT TRUNCATED AT 400 WORDS)

Stimulation of cyclooxygenase by activated human neutrophils is enhanced by uric acid

Activated human neutrophils supernatant enhances prostanoids production by bull seminal cyclooxygenase (455% of control). Superoxide anion and hydrogen peroxide are not involved in this stimulation, in these experimental conditions. Myeloperoxidase (by its hemic nature) and HPETEs (by their -OOH function) could trigger cyclooxygenase. In the presence of uric acid (10(-3) M), a potent hydroxyl radical scavenger, the cyclooxygenase stimulation by supernatant is increased until 709% of the control.

The combined effects of 2,3-DPG and Na-arachidonate on platelet aggregation and on TXA2 formation

We have investigated the effects of 2,3-DPG on platelet aggregation in the presence of suboptimal concentrations of Na-Arachidonate by using the two cuvette transfer experiments of Hamberg, Svensson and Samuelsson (3). The results show that 2,3-DPG enhanced or induced platelet aggregation in the presence of suboptimal concentrations of Na-Arachidonate. Imidazole, a TXA2 synthetase inhibitor, and Lasix, when added inhibited 2,3-DPG effects on platelet aggregation, suggesting that 2,3-DPG may act either on cyclooxygenase or on TXA2 synthetase of prostaglandin synthesis. A specific RIA assay showed that 2,3-DPG when added to suboptimal concentrations of Na-Arachidonate enhanced the formation of TXB2, a stable metabolite of TXA2. We have concluded that during intravascular hemolysis 2,3-DPG release may be a key component in preventing and/or inducing thrombosis.

Comparative pharmacology of cyclooxygenase inhibitors on platelet function

Previous studies from our laboratory have demonstrated a critical role for ferrous heme in prostaglandin synthesis. Based upon these studies, we proposed a model for heme-arachidonic acid interaction and demonstrated that compounds which interfere with this interaction inhibit arachidonic oxidation by ferrous heme. In this study, we have examined the effect of four different inhibitors for their effect on platelet arachidonic acid metabolism and function. The compounds studied were an iron chelator, 2,2'-dipyridyl, the cyclooxygenase inhibitors, Ibuprofen and aspirin, and a polyenoic acid, docosahexaenoic acid. All four compounds at approximately 100 microM concentration blocked the second wave of platelet aggregation in response to epinephrine or adenosine diphosphate. They were equally potent in inhibiting 14C-arachidonic conversion by platelets to thromboxane. However, inhibition of platelet thromboxane production and function by dipyridyl and DHA was reversible. Removal of these compounds from the medium restored platelets ability to respond to agonists and generate products through the cyclooxygenase pathway. The inhibitory effect of Ibuprofen and aspirin on cyclooxygenase activity could not be reversed by washing the platelets. However, Ibuprofen treated platelets aggregated when stirred with arachidonate in a normal way. No such response could be elicited from aspirin treated platelets. All compounds (except DHA) interfered with heme-arachidonic acid interaction in a cell-free system and prevented arachidonic acid oxidation. Results of our studies suggest a common mechanism of action for these different classes of compounds. In spite of the common mechanism, each class of drug seems to have a relatively different effect upon platelet cyclooxygenase and function.

Endogenous stimulant of prostaglandin endoperoxide synthase activity in human amniotic fluid

In this study we describe the discovery and characterization of a substance in human amniotic fluid that stimulates prostaglandin biosynthesis by a microsome-enriched preparation of bovine seminal vesicles. The stimulatory activity is not retained substantially upon anisotropic ultrafiltration through a filter with a molecular weight exclusion limit of 500. Stimulation of prostaglandin biosynthesis by this substance is time- and concentration-dependent; maximal stimulation of approx. 200% being observed within 20 min of commencing incubation with 1 ml-equivalent of stimulant fraction. Stimulatory activity is demonstrable both in the presence of reduced glutathione (1.3 mM) and L-tryptophan (20 mM), either separately or combined, and in the presence of exogenous arachidonic acid (5-120 microM). In the absence of added cofactors, the stimulatory substance increases the rates of biosynthesis of prostaglandin E2 and prostaglandin F2 alpha to equal extents. The amount of stimulatory substance added to incubations is correlated positively with increased oxygen consumption during incubations. The stimulatory substance is stable to heating at 100 degrees C for 10 min but is inactivated substantially (to less than 20% of original activity) by treatment with pronase. It is concluded that human amniotic fluid contains a substance of relatively low molecular weight, which is proteinaceous in character, that stimulates prostaglandin endoperoxide synthase activity.

Synthesis of prostaglandins and leukotrienes. Effects of ethanol

Prostaglandins, thromboxane, and leukotrienes are metabolites of arachidonic acid that have a variety of physiological effects at low concentrations. Effects include smooth muscle contraction, platelet aggregation, platelet disaggregation, bronchoconstriction, increased capillary permeability, cardiac dysfunction, and polymorphonuclear leukocyte accumulation. Although their formation does not appear to be essential for life, these eicosanoid activities are wide ranging and have important roles in normal physiology as well as pathophysiology. At the center of eicosanoid biosynthesis lies the plasma cell membrane which serves as the arachidonic acid reservoir. It has been widely appreciated that ethanol exerts effects on the lipid bilayer, and it is not surprising that a growing body of evidence supports the concept that important interactions between ethanol and eicosanoid biosynthesis can occur. Furthermore, at various steps leading to ultimate prostaglandin, thromboxane and leukotriene production, reactive intermediates such as radicals are involved whose lifetime in the biological milieu can be profoundly modulated by ethanol.

Structure of the active site of prostaglandin synthase from studies of depsides: an alternate view

Evaluation of the structure of the lichen depside, 4-0-methylcryptochlorophaeic acid, the most potent inhibitor of prostaglandin synthesis known, and its potential interaction with heme supports a model of the active site of prostaglandin synthase initially suggested by studies of arachidonic acid-heme interaction.

Role of intrinsic arachidonate metabolites in the vascular action of erythrocyte breakdown products

In helically-cut strips of dog basilar and mesenteric arteries, the isometric tension developed by application of ghost-free hemolysate from dog erythrocytes was recorded. The hemolysate contracted basilar arteries in a concentration-dependent fashion, the response being attenuated by treatment with either aspirin or polyphloretin phosphate, a prostaglandin antagonist. Mesenteric arteries were contracted only slightly by high concentrations of hemolysate. When the mesenteric arteries had partially been contracted with prostaglandin F2 alpha or norepinephrine, the hemolysate induced relaxations, which were abolished by aspirin in approximately half the preparations used. Studies on rat stomach strips exposed to superfusate of dog cerebral arteries showed a release of prostaglandin-like substance by the hemolysate application. It may be concluded that the hemolysate contracts basilar arteries and relaxes mesenteric arteries, mainly through prostaglandins synthesized in and released from the vascular wall. Such a mechanism may be involved in the pathogenesis of cerebral vasospasm following a subarachnoid hemorrhage.

Stimulation of prostaglandin biosynthesis by urine of the human fetus may serve as a trigger for parturition

Urine of the human fetus stimulated prostaglandin biosynthesis in vitro by increasing the conversion of arachidonic acid into prostaglandins. The stimulatory activity in urine from fetuses delivered at term after labor of spontaneous onset was greater than that in urine from fetuses delivered by cesarean section at term before the onset of labor. Such stimulation of prostaglandin biosynthesis by the fetal membranes, by way of a substance released into the urine and thence into amniotic fluid, could serve as a signal for the initiation of parturition.

Nabumetone (BRL 14777, 4-[6-methoxy-2-naphthyl]-butan-2-one): a new anti-inflammatory agent

Nabumetone is a compound of novel structure which displays acute anti-inflammatory activity in the carrageenan-induced oedema model in rats and the ultraviolet-induced erythema model in guinea-pigs. Its activity in these tests is greater than that of aspirin but less than that of naproxen and indomethacin. In the cotton pellet-induced granuloma model in the rat, the compound is active and produces no signs of toxicity at doses much greater than the lowest effective dose, unlike aspirin, naproxen or indomethacin. Nabumetone is also active in the adjuvant-induced arthritis test in rats. In contrast to aspirin, indomethacin and naproxen, the compound is well tolerated by the stomach of fasted rats at doses in excess of those with anti-inflammatory activity. These findings could be linked to the relatively poor ability of nabumetone to inhibit the synthesis of prostaglandins in vitro and to its non-acidic structure. The compound has greater mild analgesic activity than paracetamol, is equi-active with phenylbutazone, but less active than aspirin, naproxen and indomethacin. Nabumetone also has antipyretic activity in the rabbit. No interactions with the hypothalamic-pituitary-adrenal axis have been found.

Depside as potent inhibitor of prostaglandin biosynthesis: a new active site model for fatty acid cyclooxygenase

Forty depsides and depsidones, the esters of phenolcarboxylic acids, were examined for their inhibitory effect against prostaglandin biosynthesis with rabbit renal microsomes. 4-0-Methylcryptochlorophaeic acid was the most active inhibitor so far tested and its IC50 value was 0.34 muM. Kinetic investigation has shown that this depside acts competitively with respect to arachidonic acid as most of the non - steroidal antiinflammatory drugs. X-Ray analysis has revealed that 4-0-methylcryptochlorophaeic acid maintains its rigid conformation by forming a strong hydrogen bond between the hydroxyl and methoxyl groups. Comparison of CPK models between 4-0-methylcryptochlorophaeic acid and non-steroidal antiinflammatory drugs revealed that the carboxyl group and the two rings of these drugs are almost superimposable to those of the depside. This finding led us to propose a new active site model based on the three dimentional structure of the depside.

Anti-inflammatory properties of copper implants in the rat paw edema: a preliminary study

Metallic copper has been shown to possess anti-inflammatory activity in the carrageenan foot paw edema of the rat, when applied in the form of an implant. The implant was installed two months before the edema was induced. It is postulated that the anti-inflammatory activity is due to dissolved copper from the implant.

In vitro effects of synthetic antioxidants and vitamin E on arachidonic acid metabolism and thromboxane formation in human platelets and on platelet aggregation

The "in vitro" effects of alpha-tocopherol, butylhydroxytoluene (BHT) and butylhydroxyanisole (BHA) were studied on aggregation of human platelets induced by collagen and arachidonic acid (AA), on the metabolic conversion of 14C AA through the cyclooxygenase and lipoxygenase pathways and on the formation of thromboxane B2 (TXB2) in washed platelets after stimulation with collagen. Vitamin E completely inhibited AA induced platelet aggregation only at high concentration (mM) and after 10 minutes of preincubation, with limited effects on AA metabolism in platelets and no effect on TXB2 formation from endogenous substrate. BHA completely inhibited platelet aggregation in the 10(-6) M range, gave 50% inhibition of AA metabolism in the 10(-5) M range and almost complete inhibition of thromboxane formation in the 10(-4) M range. BHT was about 100 times less active on platelet aggregation and AA metabolism. The lipoxygenase and cyclooxygenase pathways were differentially affected at low concentrations of BHA and only at concentrations greater than 5 X 10(-5) M were both pathways depressed.

Epinephrine and other activators of prostaglandin endoperoxide synthetase can reduce Fe3+-heme to Fe2+-heme

In view of recent evidence that activation of prostaglandin endoperoxide synthetase by lipid peroxides may relate to the ability of such peroxides to reduce heme, we tested other activators of this enzyme. Epinephrine, norepinephrine, ascorbic acid and tryptophan were all found to reduce Fe3+-heme to Fe2+-heme, though tryptophan was considerably weaker than the others. We suggest that reduction of heme by these compounds might account for their ability to reduce the lag phase on addition of substrate to the enzyme. Epinephrine was assessed for its effects on the lag phase in activation of soybean lipoxygenase and was found to cause a similar reduction of the lag phase of this related enzyme. These findings support the concept that reduction of Fe3+-heme to Fe2+-heme is critical to activation of both the prostaglandin endoperoxide synthetase and soybean lipoxygenase enzymes, and that mechanisms involved in regulation of the valence of iron are important for regulating enzyme activity.

A hypothesis for a role for unsaturated fatty acids in electron transport and its potential application to understanding the mitochondrial respiratory chain

Unsaturated fatty acids are required for mitochondrial oxidative phosphorylation and electron transport, though their role has not been determined. We have considered the possibility that unsaturated fatty acids might facilitate electron transfer from non-heme iron to heme iron. Unsaturated fatty acids markedly enhanced the reduction of ferric cytochrome c by ferrous iron. Neither stearic acid nor methyl arachidonic acid were effective suggesting that both a double bond and the carboxylic acid group were essential. Thus unsaturated fatty acids can directly facilitate electron transfer from non-heme iron to heme iron. We hypothesize that unsaturated fatty acids may play a similar critical role in mitochondrial oxidative phosphorylation and other biological processes where rapid electron transfer occurs.

Piroxicam, a structurally novel anti-inflammatory compound. Mode of prostaglandin synthesis inhibition

Piroxicam is a potent inhibitor of prostaglandin biosynthesis. Experiments utilizing cell culture and microsomes derived from various sources have demonstrated that piroxicam is a selective inhibitor of the cyclooxygenase step of arachidonic acid metabolism. Little blocking activity is observed at the phospholipase, thromboxane or prostacyclin synthetase, and arachidonic acid lipoxygenase steps.

The release of prostaglandin E2 from the skin of the plaice, Pleuronectes platessa L

1 A fungal extract which produces a cutaneous hypersensitivity reaction in the plaice, Pleuronectes platessa L., was incubated in vitro with the skin of this teleost fish. Samples of incubation media were assayed for smooth muscle stimulating activity. 2 Prostaglandin E2 was identified by bioassay, thin-layer chromatography, ultraviolet absorption spectroscopy and gas chromatography--mass spectrometry. Release from challenged skin was maximum after 60 min incubation. 3 Analysis of the fatty acid composition of plaice skin showed that although arachidonic acid was present (3% of total fatty acids), the precursor of prostaglandin E3, eicosapentaenoic acid contributed 9% of total. 4 Indomethacin (50 mg/kg i.p) did not inhibit the erythema induced by the fungal extract, whilst a dose of 1 mg/kg maximally inhibited prostaglandin release from skin on incubation in vitro. 5 It is concluded that prostaglandins do not have an exclusive role in the mediation of the hypersensitivity reaction.

Peroxidatic oxidation of benzo[a]pyrene and prostaglandin biosynthesis

The arachidonic acid dependent oxidation of benzo[a]pyrene to a mixture of 3,6-, 1,6-, and 6,12-quinones has been studied by using enzyme preparations from sheep seminal vesicles. Maximal oxidation is observed at 100 microM benzo[a]pyrene and 150 microM arachidonic acid. The arachidonic acid dependent oxidation is peroxidatic and utilizes prostaglandin G2 (PGG2), generated in situ from arachidonate, as the hydroperoxide substrate. 15-Hydroperoxy-5,8,11,13-eicosatetraenoic acid is equivalent to PGG2 as a hydroperoxide substrate, but hydrogen peroxide, cumene hydroperoxide, and tert-butyl hydroperoxide are much poorer substrates. Arachidonic acid dependent benzo[a]pyrene oxidation by microsomal and solubilized enzyme preparations is markedly.