Prostaglandin F2α produced by inducible cyclooxygenase may contribute to the resolution of inflammation

Cyclooxygenase-2 may play a role in resolution of carrageenan-induced pleurisy in rats by generating anti-inflammatory prostanoids. Here, we show exudate prostaglandin F_2α concentrations rise during resolution of this model. These were reduced by the selective cyclooxygenase-2 inhibitor NS-398, which exacerbated inflammation. Concomitant treatment with NS-398 and the synthetic FP receptor agonist fluprostenol reversed this exacerbation. This suggests prostaglandin F_2α produced by cyclooxygenase-2 contributes to resolution of this inflammatory reaction.     

Prostaglandin F2 alpha binding to bovine ocular and synthetic melanins in vitro

The binding of 3H-prostaglandin F2 alpha to bovine iris and synthetic melanin was studied in vitro using a ligand binding assay. Prostaglandin F2 alpha was reversibly bound to both types of melanin. The binding was saturable and the Scatchard analysis revealed the existence of at least two binding sites with the corresponding K(D) values of 3.71 nM and 1.99 microM for natural and 4.99 nM and 0.19 microM for synthetic melanin, respectively. The high affinity Bmax values were 3.4 nM/g for natural and 2.5 nM/g for synthetic melanin. The dissociation of prostaglandin F2 alpha from melanin after dilution of the complex was rapid and uniform.     

Prostaglandin F(2alpha) receptor-dependent regulation of prostaglandin transport

Prostaglandin (PG) F(2alpha) may act on its G protein-coupled receptor (FP) or be imported intracellularly via a transporter, which has high affinity for PGF(2alpha) and PGE(2), but not prostacyclin (PGI(2)). In cells overexpressing the epitope-tagged FP together with the human prostaglandin transporter (hPGT), stimulation of the FP with PGF(2alpha) (1 nM-1 microM), or the less potent FP agonist, the isoprostane 8,12-iso-iPF(2alpha)-III, inhibited prostaglandin uptake via the hPGT. This effect was abolished by pretreatment of the cells with cholera toxin, but not with pertussis toxin. Furthermore, two dominant negative constructs directed against Galpha(s) partially blocked FP-mediated regulation of hPGT function, also suggesting Galpha(s) involvement in this phenomenon. Surprisingly, neither an activator (dibutyryl cyclic AMP) nor an inhibitor (H89) of cyclic AMP-dependent protein kinase had any effect on FP-mediated inhibition of hPGT activity. Furthermore, although PGF(2alpha) increases intracellular cyclic AMP via Galpha(s) activation, it does not induce phosphorylation of the transporter, excluding a role of cyclic AMP-dependent protein kinase in hPGT regulation. Activation of the PGI(2) receptor, which is also coupled to Galpha(s), does not regulate hPGT activity, despite markedly augmenting adenylate cyclase activation. In conclusion, activation of the FP reduces intracellular import of prostaglandins for metabolic inactivation, increasing prostanoid availability for membrane receptor activation. This effect seems to be mediated via Galpha(s), independent of adenylate cyclase and cyclic AMP-dependent protein kinase activation.     

Glibenclamide relaxes vascular smooth muscle constriction produced by prostaglandin F2 alpha

The present study has demonstrated: (1) glibenclamide can reduce resting tension in canine cerebral arteries but has no effect on resting tension in the rat aorta; (2) glibenclamide can relax prostaglandin F2 alpha-induced contractions in the rat aorta, and in canine femoral, mesenteric, renal, coronary, basilar and middle cerebral arteries; (3) the relaxation produced by glibenclamide in rat aorta is comparable to that of glyceryl trinitrate and stronger than that of papaverine; (4) canine femoral arteries are less sensitive to glibenclamide than the other arteries; (5) in cerebral arteries glibenclamide was as effective as papaverine, but less effective than glyceryl trinitrate; (6) the actions of glibenclamide on cerebral arteries are not mediated by cGMP as they were not blocked by methylene blue, an inhibitor of guanylate cyclase; (7) the effects of glibenclamide are not endothelium-dependent. The mechanism by which glibenclamide produces relaxation is not clear; while the drug is known to block ATP-dependent potassium channels, in vascular smooth muscle this would cause contraction, not dilation. The action of glibenclamide may be at the level of the receptor or the signal transduction process.     

Reflex bradycardia and hypotension produced by prostaglandin F2alpha in the cat.

1 Intravenous administration of prostaglandin F2alpha results in a dose-dependent increase in pulmonary arterial pressure, decrease in systemic arterial pressure and a delayed bradycardia. Pulmonary vasoconstriction was observed at doses as low as 0.1 and 0.3 mug/kg. The systemic depressor and heart rate lowering effects were observed at 1 mug/kg doses and above. 2 A moderate bradycardia was still observed after atropine blockade but was abolished following bilateral vagotomy. Neither of these procedures affected the pulmonary vascular response. 3 Injections of submaximal doses of prostaglandin F2alpha (1--4 mug/kg) produced a greater and longer lasting bradycardia when injected into the left atrium than was observed following intravenous administration. In addition the latency of onset was much shorter following left atrial injection. These doses resulted in no change in heart rate and a minimal hypotension when injected into the brachiocephalic artery or into the aortic arch. 4 Small doses of prostaglandin F2alpha administered at the level of the origin of the coronary arteries produced marked decreases in heart rate and blood pressure whereas no change occurred following injection of the same amount into the ascending aorta at more distal sites. 5 These results suggest that prostaglandin F2alpha produces bradycardia and hypotension in the cat by activating 'receptors' located in the left heart or by acting on structures perfused by means of the coronary arteries.     

Prostaglandin F(2alpha) stimulation of cyclooxygenase-2 promoter activity by the FP(B) prostanoid receptor

We have recently shown that the FP(B) prostanoid receptor activates beta-catenin signaling through the activation of Rho in human embryo kidney (HEK)-293 cells stably expressing the FP(B) receptors. We now report that the FP(B) receptor can stimulate cyclooxygenase-2 promoter activity and may, therefore, regulate the expression of cyclooxygenase-2. This stimulation of cyclooxygenase-2 promoter activity is blocked by pretreatment with an inhibitor of Rho, but not with an inhibitor of protein kinase C (PKC). Potential up regulation of cyclooxygenase-2 expression by the FP(B) receptor would establish a positive feedback loop that would drive beta-catenin signaling and could be involved in cancer.     

Binding to PLA2 may contribute to the anti-inflammatory activity of catechol

Inhibiting PLA(2) activity should, in theory, be an effective approach to control the inflammation. Several naturally occurring polyphenolic compounds have been reported as inhibitors of PLA(2) . Among the naturally occurring polyphenols, catechol (1,2-dihydroxybenzene) possesses anti-inflammatory activity. Catechol can inhibit cyclooxygenase and lipo-oxygenase. By means of enzyme kinetic study, it was revealed that catechol can inhibit PLA(2) also. Crystal structure showed that catechol binds to PLA(2) at the opening of the active site cleft. This might stop the entry of substrate into the active site. Hence, catechol can be used as a lead compound for the development of novel anti-inflammatory drugs with PLA(2) as the target.     

Prostaglandin F2 alpha modifies the action of norepinephrine on alpha- and beta-adrenoceptors of isolated rat uterus

Cumulative dose-response curves were constructed for the effect of norepinephrine (NE) and isoproterenol (ISO) on the contractions of uterine strips from proestrous, estrous and metestrous rats. Both adrenergic agonists inhibited uterine spontaneous contractions in all three stages of the cycle. However strips isolated from estrous rats were more sensitive to the inhibitory action of NE or ISO than preparations obtained from proestrous or metestrous animals. It was also observed that PGF-like material released by uterine horns was significantly higher during estrus than during proestrus or metestrus, whereas PGE-like material was significantly higher in metestrus than in estrus or proestrus. The EC₅₀ of NE and ISO and the amount of PGF-like material generated by uterine horns correlated significantly during the three stages of the sex cycle. No correlation was found between the β-adrenergic inhibitory action of catecholamines and the PGE-like material released in the medium. A sub-threshold dose of PGF_2α (10^?10 M) shifted to the left the dose-response curves to NE of strips isolated from metestrous rats. When the tissue was pretreated with indomethacin and propranolol the dose-response curve to NE showed a clear shift to the left. On the other hand, the combination of indomethacin and propranolol shifted the NE dose-response curve to the right in the presence of sub-threshold doses of PGF_2α. Dose-response curves to methoxamine were constructed in the presence or absence of several PGs using uterine strips isolated from estrous rats. With indomethacin, a threshold dose of PGE₁ (10^?8 M) and PGE₂ (10^?8 M) shifted to the left the control curve of methoxamine, whereas PGF_2α (10^?8 M) shifted the curve to the right. The interaction between sex hormones, PGs and catecholamines acting on α- and β-adrenoceptors in the isolated rat uterus is discussed.     

Prostaglandin F2alpha reduces the algesic effect of bradykinin by antagonizing the pain enhancing action of endogenously released prostaglandin E.

1 The isolated perfused ear of the rabbit connected to the body only by its nerve, was used to investigate the influence of prostaglandin F2alpha on the algesic effect of bradykinin and acetylcholine. 2 Bradykinin and acetylcholine, following intra-arterial injection into the isolated perfused ear elicited a dose-related reflex fall in blood pressure due to stimulation of paravascular pain receptors (= algesic effect). 3 Infusion of prostaglandin F2alpha (0.1 to 1 ng/ml) into the rabbit ear reduced the algesic effect of bradykinin but not that of acetylcholine. 4 The onset of the reflex fall in blood pressure by bradykinin but not that by acetylcholine was delayed by infusion of prostaglandin F2alpha into the ear. 5 Infusion of prostaglandin E1 into the rabbit ear led to an enhancement of the algesic effect of bradykinin and acetylcholine. Enhancement of both effects was abolished by infusion of prostaglandin F2alpha. 6 During inhibition of the endogenous synthesis of prostaglandins (mainly E-type) by indomethacin, a low concentration of prostaglandin F2alpha no longer reduced the algesic effect of bradykinin. However, a high concentration of F2alpha continued to enhance the effect of bradykinin and acetylcholine. 7 Prostaglandin F2alpha influenced neither the brief reduction in venous outflow produced by bradykinin nor the brief increase in venous outflow caused by acetylcholine. 8 The results suggest that prostaglandin F2alpha does not directly reduce the effect of bradykinin but inhibits the enhancement of its algesic effect produced by prostaglandin E that is released endogenously by bradykinin. That the algesic effect of acetylcholine is not reduced by prostaglandin F2alpha is in keeping with its releasing very little endogenous prostaglandin E.     

Increased glutathione levels contribute to the beneficial effects of hydrogen sulfide and inducible nitric oxide inhibition in allergic lung inflammation

ObjectiveThe interaction between nitric oxide (NO) and hydrogen sulfide (H₂S) in the airways could have significant implications for the pathogenesis and therapeutic effects of both on lung diseases. In this study we investigated whether the beneficial effects of H₂S on asthma could be comparable to that inhibition of inducible NO synthase (iNOS).MethodsFemale BALB/C mice sensitized with ovalbumin (OVA) received either the H₂S donor sodium hydrosulfide (NaHS, 14 μmol/kg) or the iNOS inhibitor 1400 W (1 mg/kg), 30 min before each OVA challenge during six days. On the first, second and sixth days, the leucocyte infiltration in lung parenchyma and bronchoalveolar lavage was evaluated. The aconitase activity (a sensor of O₂ formation) and lipid peroxidation, as well as levels of reduced glutathione (GSH) and oxidized glutathione (GSSG) were determined in the lung tissues.ResultsOVA-challenge caused a significant and time-dependent increase in the eosinophil number in the airways, which was accompanied by a significant decrease of aconitase activity and GSH/GSSG ratio along with enhanced lipid peroxidation in the lungs. Treatment with NaHS or 1400 W significantly attenuated the airways eosinophilia that was paralleled by an increase in aconitase activity and decrease of lipid peroxidation. NaHS or 1400 W treatments also reversed the decreased GSH/GSSG ratio seen after OVA-challenge.ConclusionsThe present study shows for the first time that the increased GSH/GSSG ratio caused by either H₂S supplementation or iNOS-inhibition is a potential mechanism protecting airways against oxidative stress and inflammatory lung diseases.     

Prostaglandin hydroperoxidase-dependent oxidation of phenylbutazone: relationship to inhibition of prostaglandin cyclooxygenase

Prostaglandin H synthase (PHS) hydroperoxidase-mediated metabolism of phenylbutazone and the relationship of this metabolism to the inhibition of PHS cyclooxygenase by phenylbutazone was investigated. Phenylbutazone was metabolized to several intermediates and metabolites. A phenylbutazone carbon-centered radical (aN = 14.6 G) formed by PHS hydroperoxidase was trapped by 2-methyl-2-nitrosopropane and detected by ESR in incubations with ram seminal vesicle microsomes. 4-Hydroperoxy- and 4-hydroxyphenylbutazone were isolated from incubations of phenylbutazone with either ram seminal vesicle microsomes or horseradish peroxidase. Phenylbutazone (100 microM-2 mM) inhibited PHS cyclooxygenase in incubations of PHS apoenzyme reconstituted with hematin. Phenylbutazone (5-250 microM) did not inhibit PHS cyclooxygenase in incubations of PHS apoenzyme reconstituted with manganese protoporphyrin IX, which lacks hydroperoxidase activity. Thus, metabolism of phenylbutazone by PHS hydroperoxidase is required for it to inhibit PHS cyclooxygenase. 4-Hydroperoxy- and 4-hydroxyphenylbutazone were ineffective inhibitors of PHS cyclooxygenase. Other hydroperoxides that easily rearrange to peroxyl radicals were potent inhibitors of PHS cyclooxygenase, suggesting that the phenylbutazone peroxyl radical may be the inhibitor. 4-Hydroperoxyphenylbutazone was not reduced to 4-hydroxyphenylbutazone by PHS hydroperoxidase. We propose that 4-hydroxyphenylbutazone formation occurs by a nonenzymatic reaction of two phenylbutazone peroxyl radicals and their subsequent rearrangement to alkoxy radicals, which abstract hydrogen atoms. Our data indicate the importance of PHS hydroperoxidase in the inactivation of PHS cyclooxygenase by peroxides.     

Endothelium-mediated dilations contribute to the polarity of the arterial wall in vasomotion induced by alpha 2-adrenergic agonists

We tested whether or not an endothelium-mediated dilation is involved in the response of intact arteries to alpha-adrenergic stimulation, by separately applying agonists to the luminal or adventitial side of the arterial wall. Cumulative dose-response curves of the alpha 1-agonists l-phenylephrine or cirazoline applied luminally in rat tail arteries and in side branches of canine femoral arteries were identical to those obtained by adventitial application in the intact arteries, and were not modified by removal of the endothelium (eliminating acetylcholine-induced dilations). Constrictions induced by the alpha 2-agonists UK-14,304 or azepexole applied luminally were significantly lower than those induced by adventitial application, and were augmented significantly by removal of the endothelium. Half-maximally precontracted arteries were dilated by addition of alpha 2-agonists to the luminal perfusate; these dilations were abolished by removal of the endothelium. It is concluded that the functional polarity of the vascular wall of these arteries in response to alpha 2-agonists results from the release of a dilatory signal from the endothelial cells, counteracting the direct contractile activation of the adjacent smooth muscle cells by the agonists.     

Prostaglandin E2, prostaglandin I2 and the vascular changes of inflammation.

1. Plasma exudation and blood flow changes induced by intradermal injection of prostaglandins E2 (PGE2), I2 (PG12), D2 (PGD2) and F2 alpha (PGF2 alpha) were measured in rabbit dorsal skin by the use of [131I]-albumin and 133Xe. 2. Little plasma exudation was produced by any of the prostaglandins when injected alone. 3. Both PGE2 and PGI2 were potent at increasing blood flow, whereas PGF2 alpha and PGD2 produced an increase only at high doses. 4. All of the prostaglandins studied potentiated the plasma exudation induced by bradykinin. PGE2 and PGI2 had similar potent potentiating activity, whereas PGD2 and PGF2 alpha had activity at doses too high to be of biological significance. 5. Intradermal injections of arachidonate alone resulted in little plasma exudation but produced an increase in blood flow. Arachidonate potentiated bradykinin-induced plasma exudation. 6. Locally-injected indomethacin had no effect on basal blood flow and little effect on the exudation produced by bradykinin, but indomethacin did inhibit the vasodilatation and exudation potentiation produced by arachidonate. 7. PGE2 and PGI2 had similar potency in producing marked potentiation of plasma exudation induced by intradermal injection of zymosan. 8. In the reaction to zymosan, it is concluded that vasodilatation is the result of the release of arachidonate, which is subsequently coverted to either PGE2 or PGI2. These substances regulate the plasma exudation induced by independently-released vascular permeability-increasing mediators.     

Elevated serum tumor necrosis factor alpha and ferritin may contribute to the insulin resistance found in HCV positive Egyptian patients

OBJECTIVE: There is evidence of an increased incidence of insulin resistance and diabetes mellitus (DM) in patients with hepatitis C virus (HCV) infection. Several mechanisms have been proposed, including inadequate insulin secretion or interference with signaling within the insulin receptor. We assessed serum tumor necrosis factor alpha (TNFalpha) and ferritin levels as potential mediators of insulin resistance in HCV positive Egyptian patients. PATIENTS AND RESULTS: Patients (n = 27) with HCV infection, patients (n = 23) with hepatitis C and DM (HCV + DM), patients (n = 22) with DM, and sex- and age-matched controls (n = 18) were included in this study. The degree of insulin resistance (HOMA index) was significantly higher in the HCV, HCV + DM and DM groups compared to the controls. The mean +/- SD of the HOMA index was 4.53 +/- 2.84, 6.1 +/- 2.36, 3.69 +/- 2.2 and 1.32 +/- 0.49, in HCV, HCV + DM, DM and controls, respectively. Serum TNFalpha levels were significantly higher in the HCV, HCV + DM groups compared with the healthy controls and DM patients (p < 0.001). The median (range) values of TNFalpha in HCV, HCV + DM, DM patients and controls subjects were 25.5 (0.43-124.0), 19.8 (0.51-139), 0.85 (0-10.5) and 0.32 (0-5.8) pg/mL, respectively. There was a significant positive correlation between the HCV load and both HOMA index and TNF alpha level. HCV and HCV + DM patients also had significantly higher serum ferritin levels compared with healthy controls and patients with DM. The mean +/- SD of serum ferritin in HCV, HCV + DM, DM patients and controls subjects was 258.1 +/- 116.2, 285.8 +/- 124.3, 86.9 +/- 41.8 and 159.9 +/- 76.9 ng/mL, respectively. CONCLUSION: Patients with HCV infection had a significantly higher level of TNFalpha and ferritin which may explain their insulin resistance. HOMA index and serum TNFalpha levels correlated positively with the HCV load.