Effects of some isoprostanes on the human umbilical artery in vitro.
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1. Cumulative concentration-effect curves for the selective prostanoid TP receptor agonist U46619 and six isoprostanes were constructed in the human isolated umbilical artery. 2. All compounds except 8-iso-PGF3 alpha produced concentration-dependent contractions. The contractile response to the isoprostanes increased with each cumulative addition up to a point, after which subsequent addition reduced the contraction below the previous level. This 'downturn' in the concentration-effect curve did not occur with U46619. 3. The potencies of the compounds tested were as follows (pEC50 +/- s.e.mean): U46619, 6.7 +/- 0.2; 8-iso-PGE2, 6.5 +/- 0.1; 8-iso-PGF2 alpha, 5.8 +/- 0.2; 8-iso-PGE1, 5.4 +/- 0.1; 8-iso-PGF1 alpha, 5.0 +/- 0.1; 8-iso-PGF2 beta > 4.8; 8-iso-PGF3 alpha >> 4.8 (n = 4-17). Neither 8-iso-PGF2 beta nor 8-iso-PGF3 alpha at 44 microM had a significant effect on cumulative concentration-effect curves to U46619. 4. The selective TP receptor antagonist GR32191 (0.1 microM) caused rightward shifts in the concentration-effect curves to all the active compounds. pA2 values for GR32191 against U46619, 8-iso-PGE2, 8-iso-PGF2 alpha, 8-iso-PGE1 were 7.6 +/- 0.2, 9 +/- 1, 8.2 +/- 0.3 and 7.7 +/- 0.3, respectively (n = 4). 5. Neither N omega-nitro-L-arginine methyl ester (100 microM) nor the selective DP receptor antagonist BW A868C (50 nM) affected the complex concentration-effect curve to 8-iso-PGE2 (n = 3). 6. Stable contractions to U46619 (1-3 microM) were unaffected by anandamide at concentrations up to 60 microM. (+info)
Isoprostanes, novel eicosanoids that produce nociception and sensitize rat sensory neurons.
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Isoprostanes are a novel class of eicosanoids primarily formed by peroxidation of arachidonic acid. Because of their potential as inflammatory and/or hyperalgesic agents whose formation is largely independent of cyclooxygenases, we examined whether 8-iso prostaglandin E(2) (8-iso PGE(2)) or 8-iso prostaglandin F(2alpha) (8-iso PGF(2alpha)) reduces mechanical and thermal withdrawal threshold in rats, and whether they sensitize rat sensory neurons. Injection of 1 microg of 8-iso PGE(2) (in 2.5 microl) into the hindpaw of rats significantly reduced mechanical and thermal withdrawal thresholds, whereas 1 microg of 8-iso PGF(2alpha) elicited a transient decrease in only the mechanical withdrawal threshold. Both isoprostanes enhanced the firing of C-nociceptors in a concentration-dependent manner when injected into peripheral receptive fields. Exposing sensory neurons grown in culture to 1 microM 8-iso PGE(2) or 8-iso PGF(2alpha) augmented the number of action potentials elicited by a ramp of depolarizing current. In contrast, 8-iso PGE(2) but not 8-iso PGF(2alpha) enhanced the release of substance P- and calcitonin gene-related peptide-like immunoreactivity from isolated sensory neurons. Ten micromolar 8-iso PGE(2) stimulated peptide release directly, whereas treatment with 1 microM 8-iso PGE(2) augmented the release evoked by either bradykinin or capsaicin. Pretreating neuronal cultures with the nonsteroidal anti-inflammatory drug ketorolac did not alter the sensitizing action of 8-iso PGE(2) on peptide release, suggesting that this action of the isoprostane was not secondary to the production of prostaglandins via the cyclooxygenase pathway. These data support the notion that isoprostanes are an important class of inflammatory mediators that augment nociception. (+info)
Characterization of prostanoid receptors mediating actions of the isoprostanes, 8-iso-PGE(2) and 8-iso-PGF(2alpha), in some isolated smooth muscle preparations.
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We investigated the contracting actions of the isoprostanes (isoPs), 8-iso-prostaglandin (PG) F(2alpha) and 8-iso-PGE(2), in comparison to the effects of the thromboxane (TX) A(2)-mimetic U 46619 and the traditional prostaglandin PGE(2) in the isolated rat aorta, isolated rat gastric fundus and the isolated guinea-pig ileum. U 46619 and 8-iso-PGF(2alpha) caused contractions in the rat aorta and rat gastric fundus in a concentration-dependent manner, whereas these agonists showed no effects in the guinea-pig ileum. However, 8-iso-PGE(2) and PGE(2) caused contractions in all isolated organs used. The prostanoid TP-receptor antagonist SQ 29,548 (10 nM) significantly antagonized vasoconstrictions induced by the agonists used in the rat aorta. SQ 29,548 at a final concentration of 3 microM, but not at lower concentrations, significantly inhibited contractions induced by U 46619, 8-iso-PGF(2alpha) and 8-iso-PGE(2) in the rat fundus. Responses to PGE(2) were unchanged. The prostanoid EP(1)-receptor antagonist SC 51089 (3 microM) significantly inhibited contractions induced by 8-iso-PGE(2) and PGE(2) in the rat fundus and in the guinea-pig ileum. SC 51089 had no effect on responses to any of the agonists tested. Our results show that 8-iso-PGE(2), in contrast to 8-iso-PGF(2alpha), can also cause contractions by activation of the EP(1)-receptors in the rat gastric fundus and the guinea-pig ileum. The findings of the present study do not support the existence of a unique isoP-receptor in the tissues used. (+info)
Excitatory and inhibitory actions of isoprostanes in human and canine airway smooth muscle.
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Isoprostanes are generated nonenzymatically during free radical-mediated lipid peroxidation, and are used clinically and experimentally as markers of oxidative stress. However, their biological effects are poorly understood. We examined the effects of seven different 8-isoprostanes in human and canine airway smooth muscles. In large order airways (carina) of the human, several isoprostanes evoked powerful contractions, with 8-iso-prostaglandin (PG) E(2), 8-iso-PGF(1 alpha), and 8-iso-PGF(2 alpha) being the most efficacious (and with logEC(50) values of 7.0, 5.9, and 6.2 microM, respectively). These contractions were sensitive to the prostanoid TP receptor antagonist ICI 192,605 (0.1-1 microM), but not the EP prostanoid receptor antagonist AH-6809 (50 microM), or the leukotriene receptor antagonists monteleukast or ICI 198,615 (both 1 microM). Qualitatively similar results were obtained in small order human airways (<2 mm o.d.), except that the isoprostanes were generally slightly less potent. None of the isoprostanes had any marked excitatory effect in canine airways. In carbachol-preconstricted tissues (pretreated with ICI 192,605 to block any potential contraction), several isoprostanes completely relaxed canine airways: 8-iso-PGE(1), 8-iso-PGE(2), and 8-iso-PGF(3 alpha) were the most potent, with logIC(50) values of 6.9, 6.9, and 5.7, respectively. Only 8-iso-PGF(3 alpha) relaxed human airways (logIC(50) = 4.9). Our results show that several 8-isoprostanes are highly biologically active in human and canine airways, evoking both excitatory and/or inhibitory effects, and that these effects are compound, species, and tissue dependent. (+info)
Effects of isoprostanes and prostanoids on porcine small intestine.
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The isoprostanes are prostaglandin (PG)-like compounds formed in vivo by free-radical-catalyzed peroxidation of polyunsaturated fatty acids and are synthesized independent of cyclooxygenase. It has been debated whether the biological effects of the isoprostanes are exerted on prostanoid receptors [thromboxane A2 (TP) receptors and prostanoid E (EP) receptors] or on a "unique" isoprostane receptor. We sought to define the receptors involved in the actions of isoprostanes on the porcine small intestine. Stripped intestinal sheets were mounted in Ussing chambers, and bioelectrical parameters were recorded. Serosal application of 8-iso-PGE2 (pEC(50) = 5.71), PGE2 (pEC(50) = 6.45 and pEC(50) = 5.04), and PGF2alpha (pEC(50) = 5.07) elicited concentration-dependent increases in the short-circuit current (I(SC)). No responses were seen with 8-iso-PGF2alpha. The TP receptor agonist U46619 induced transient increase in I(SC), and the tissue responded to a further challenge to PGE2. Pretreatment with U46619 did not alter responses to a subsequent addition of either PGE2 or 8-iso-PGE2. The TP receptor antagonist SQ29,548 significantly reduced responses to the TP agonist, U46619, but did not antagonize responses to 8-iso-PGE2. Homologous and heterologous desensitization between 8-iso-PGE2, PGE2, and PGF2alpha suggested the involvement of prostanoid EP and prostanoid F (FP) receptors in the response elicited to 8-iso-PGE2. The effects of 8-iso-PGE2 were not inhibited by tetrodotoxin. Pretreatment of the tissues with bumetanide significantly reduced the increase in I(SC). The results indicate that 8-iso-PGE2 induces a Cl- secretion, and the effects involve prostanoid EP and FP receptors but not TP receptors in the porcine small intestine. (+info)
Prostaglandin F(2alpha) metabolite and F(2)-isoprostane excretion rates in migraine.
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The pathophysiology theory of migraine postulates a local, neurogenic inflammation and the possible involvement of oxidative stress. We analysed the levels of 15-oxo-dihydro-prostaglandin F(2alpha) (a metabolite of prostaglandin F(2alpha)) and 8-iso-prostaglandin F(2alpha) (a major isoprostane), which are biomarkers for inflammation and oxidative stress respectively, in urine from 21 patients with migraine, with and without aura. Urine samples from migraine patients were collected during a migraine attack, and control samples were collected from the same subjects on a migraine-free morning. The mean basal levels of 15-oxo-dihydro-prostaglandin F(2alpha) and 8-iso-prostaglandin F(2alpha) in the morning control urine samples were 0.54+/-0.11 and 0.31+/-0.13 nmol/mmol of creatinine respectively. The mean levels of 15-oxo-dihydro-prostaglandin F(2alpha) and 8-iso-prostaglandin F(2alpha) in the urine samples collected during the migraine attack in the 21 patients were 0.53+/-0.13 and 0.32+/-0.11 nmol/mmol of creatinine respectively. Thus there were no differences in the 15-oxo-dihydro-prostaglandin F(2alpha) and 8-iso-prostaglandin F(2alpha) excretion rates during the migraine attack compared with on the migraine-free day. However, the basal 8-iso-prostaglandin F(2alpha) excretion levels on the migraine-free day were significantly lower in pre-menopausal women (0.24+/-0.08 nmol/mmol of creatinine, n=11) compared with post-menopausal women (0.39+/-0.14 nmol/mmol of creatinine; n=7; P=0.009). In conclusion, in this study we found no support for the involvement of inflammation and oxidative stress in migraine pathophysiology. Our results indicate, however, a lower level of oxidative stress in pre-menopausal compared with post-menopausal women. (+info)
Epoxyisoprostane and epoxycyclopentenone phospholipids regulate monocyte chemotactic protein-1 and interleukin-8 synthesis. Formation of these oxidized phospholipids in response to interleukin-1beta.
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Monocyte recruitment to the vessel wall, mediated by monocyte chemotactic protein-1 (MCP-1) and interleukin-8 (IL-8), plays an important role in atherogenesis. We have shown previously that minimally oxidized low density lipoprotein, oxidized 1-palmitoyl-2-arachidonyl-sn-glycero-3-phosphorylcholine (Ox-PAPC), activates endothelial cells to produce MCP-1 and IL-8. By using liquid chromatography/mass spectrometry methods coupled with bioassay, we report a family of epoxyisoprostane (PEIPC) and epoxycyclopentenone (PECPC) phospholipids that are the components of Ox-PAPC responsible for the majority of this activity. Ox-PAPC contains five chromatographically distinguishable active PEIPC components (m/z 825.5) and four PECPC components (m/z 810.5). All nine components induced endothelial cell synthesis of IL-8 and MCP-1 in a dose-dependent fashion between 0.1 and 5 microm concentrations. The five PEIPC components had identical functional groups and all underwent dehydration to produce m/z 810.5. We present evidence that these phospholipids are regioisomers with epoxide groups at the 5,6-, 8,9-, 11,12-, or 14,15-positions of the sn-2 fatty acid and their epoxide groups is important for biological activity. We have shown previously that peroxisome proliferator-activated receptor alpha is involved in MCP-1 synthesis in response to Ox-PAPC. We now show that PEIPC and PECPC isomers are potent activators of peroxisome proliferator-activated receptor alpha. PEIPC and PECPC isomers are strongly recognized by specific circulating murine natural autoantibodies (EO6) and accumulate in cells treated with IL-1beta. These studies demonstrate that PEIPC and PECPC isomers are potent activators of endothelial cells increasing synthesis of IL-8 and MCP-1. Their accumulation in cells exposed to cytokines and in atherosclerotic lesions suggests that these lipids may play a role in a number of chronic disease processes. (+info)
Repetitive mild brain trauma accelerates Abeta deposition, lipid peroxidation, and cognitive impairment in a transgenic mouse model of Alzheimer amyloidosis.
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Traumatic brain injury (TBI) increases susceptibility to Alzheimer's disease (AD), but it is not known how TBI contributes to the onset or progression of this common late life dementia. To address this question, we studied neuropathological and behavioral consequences of single versus repetitive mild TBI (mTBI) in transgenic (Tg) mice (Tg2576) that express mutant human Abeta precursor protein, and we demonstrate elevated brain Abeta levels and increased Abeta deposition. Nine-month-old Tg2576 and wild-type mice were subjected to single (n = 15) or repetitive (n = 39) mTBI or sham treatment (n = 37). At 2 d and 9 and 16 weeks after treatment, we assessed brain Abeta deposits and levels in addition to brain and urine isoprostanes generated by lipid peroxidation in these mice. A subset of mice also was studied behaviorally at 16 weeks after injury. Repetitive but not single mTBI increased Abeta deposition as well as levels of Abeta and isoprostanes only in Tg mice, and repetitive mTBI alone induced cognitive impairments but no motor deficits in these mice. This is the first experimental evidence linking TBI to mechanisms of AD by showing that repetitive TBI accelerates brain Abeta accumulation and oxidative stress, which we suggest could work synergistically to promote the onset or drive the progression of AD. Additional insights into the role of TBI in mechanisms of AD pathobiology could lead to strategies for reducing the risk of AD associated with previous episodes of brain trauma and for preventing progressive brain amyloidosis in AD patients. (+info)