Eicosanoids and septicaemia

H2S-donating sildenafil (ACS6) inhibits superoxide formation and gp91phox expression in arterial endothelial cells: role of protein kinases A and G

BACKGROUND AND PURPOSE

Superoxide (O(2)(*-)), derived from nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, is associated with acute respiratory distress syndrome (ARDS). NADPH oxidase activity and expression are blocked by nitric oxide (NO) and sildenafil. As another gas, hydrogen sulphide (H(2)S) is formed by blood vessels, the effect of sodium hydrosulphide (NaHS) and the H(2)S-donating derivative of sildenafil, ACS6, on O(2)(*-) formation and the expression of gp91(phox) (a catalytic subunit of NADPH oxidase) in porcine pulmonary arterial endothelial cells (PAECs) was investigated.

EXPERIMENTAL APPROACH

PAECs were incubated with 10 ng mL(-1) tumour necrosis factor-alpha (TNFalpha) (+/-NaHS or ACS6), both of which released H(2)S, for 2 h or 16 h. O(2)(*-) was measured. Expression of gp91(phox) was measured by western blotting and the role of cyclic AMP (cAMP) and/or cyclic GMP was assessed using protein kinase inhibitors.

KEY RESULTS

After either 2- or 16-h incubations, O(2)(*-) formation by PAECs was inhibited by NaHS or ACS6, with IC(50) values of about 10 nM and less than 1 nM, respectively. Both 100 nM NaHS and 1 nM ACS6 completely inhibited gp91(phox) expression induced by TNFalpha. The effects of NaHS were blocked by the inhibition of protein kinase A (PKA), but not PKG, and not by the inhibition of guanylyl cyclase. Effects of ACS6 were blocked by inhibition of both PKA and PKG. Both NaHS and ACS6 augmented cAMP formation.

CONCLUSION AND IMPLICATIONS

H(2)S inhibited O(2)(*-) formation and upregulation of NADPH oxidase in PAECs through the adenylyl cyclase-PKA pathway. ACS6 may be effective in treating ARDS through both elevation of cAMP and inhibition of phosphodiesterase type 5 activity.

Iloprost inhibits superoxide formation and gp91phox expression induced by the thromboxane A2 analogue U46619, 8-isoprostane F2alpha, prostaglandin F2alpha, cytokines and endotoxin in the pig pulmonary artery

Since the roles of thromboxane A2 (TXA2), prostacyclin (PGI2) and 8-isoprostane F2alpha in mediating vascular O2*- formation and its relation to adult respiratory distress syndrome (ARDS) is unknown, the effects of these eicosanoids on the expression of gp91phox (catalytic subunit of NADPH oxidase) and O2*- release from cultured pig pulmonary artery (PA) segments, PA vascular smooth muscle cells (PAVSMCs) and PA endothelial cells (PAECs) were investigated. PA segments, PAVSMCs and PAECs were incubated with the TXA2 analogue, U46619, (+/-LPS, tumour necrosing factor-alpha (TNF-alpha) or IL-1alpha), 8-isoprostane F2alpha and+/-iloprost (a stable PGI2 analogue) for 16 h. The formation of superoxide dismutase-inhibitable O2*- was then measured spectrophotometrically and gp91phox expression assessed using Western blotting. In parallel experiments, whole PA segments were treated with LPS, TNF-alpha and IL-alpha after which time TXA2, PGI2, PGF2alpha and 8-isoprostane F2alpha formation was measured using enzyme-linked immunoassays. U46619, PGF2alpha and 8-isoprostane F2alpha promoted the formation of O2*- in PA segments, PAVSMCs and PAECs, an effect inhibited by diphenyleneiodonium and apocynin (both NADPH oxidase inhibitors) and upregulated the expression of gp91phox in PAECs and PAVSMCs. These effects were augmented by LPS, TNF-alpha and IL-1alpha but inhibited by iloprost. Under identical incubation conditions, IL-1alpha, LPS and TNF-alpha all induced an increase in the formation of TXA2, PGF2alpha and 8-isoprostane F2alpha but reduced the concomitant formation of PGI2. These data demonstrate that LPS and cytokines influence the relative balance of TXA2, PGI2, PGF2alpha and 8-isoprostane F2alpha in pig PA, which in turn alter NADPH oxidase expression and O2*- formation. These novel findings have implications in devising effective strategies for treating ARDS.British Journal of Pharmacology (2004) 141, 488-496. doi:10.1038/sj.bjp.0705626

Role of the endothelium and nitric oxide synthases in modulating superoxide formation induced by endotoxin and cytokines in porcine pulmonary arteries

BACKGROUND

The interactive roles of cytokines, endotoxins, superoxide (O(2)(*-) ) and nitric oxide (NO) in the pathogenesis of adult respiratory distress syndrome (ARDS) have not been fully elucidated. The effects of tumour necrosis factor-alpha (TNF-alpha), interleukin 1alpha (IL-1alpha), and lipopolysaccharide (LPS) and the role of NO and the endothelium in mediating O(2)(*-) formation were therefore investigated in intact porcine pulmonary arteries in vitro.

METHODS

Intrapulmonary artery (PA) segments were obtained from White Landrace pigs (25-35 kg) and incubated with LPS, IL-1alpha, and TNF-alpha and O(2)(*-) release was measured by the superoxide dismutase (SOD) inhibitable reduction of ferricytochrome c. The source of O(2)(*-) formation was determined using a number of enzyme inhibitors. The role of NO was explored using NO synthase (NOS) inhibitors and the distribution of NOS isoforms and peroxynitrite (ONOO(-), an index of NO-O(2)(*-) interactions) assessed by immunocytochemistry.

RESULTS

LPS, IL-1alpha, and TNF-alpha promoted the formation of O(2)(*-) from PA compared with untreated controls in a time and dose dependent manner, an effect markedly enhanced by removal of the endothelium but completely inhibited by the NADPH oxidase inhibitor diphenylene iodonium chloride (DPI). L-NAME and the eNOS inhibitor N(5)-(1-iminoethyl)-ornithine (L-NIO) enhanced O(2)(*-) formation from PA (with endothelium) in response to IL-1alpha and TNF-alpha but had no effect on LPS mediated O(2)(*-) formation, whereas L-NAME and the iNOS inhibitor L-N(6)-(1-iminoethyl)-lysine-HCl (L-NIL) enhanced O(2)(*-) formation only in response to LPS.

CONCLUSIONS

LPS, IL-1alpha, and TNF-alpha promote O(2)(*-) formation through an upregulation of NADPH oxidase activity which is augmented by removal of the endothelium, as well as the inhibition of eNOS (in the case of cytokines) and iNOS (in the case of LPS). The concomitant expression of NOS isoforms (and NO formation) with that of NADPH oxidase may therefore constitute a protective system designed to remove O(2)(*-) through the formation of ONOO(-). If this is so, the integrity of the endothelium may be axiomatic in the progression and severity of ARDS.

Avian macrophage metabolism

This review considers the role of avian macrophages as a source of immune effector and immunoregulatory metabolites. Although considerable attention has been given to the importance of leukocytic cytokines, particularly the monokines such as interleukin-1 (IL-1), interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-alpha), and transforming growth factor-beta (TGF-beta), metabolites produced by macrophages appear to be of equal importance in determining the progression of immune responses. The three metabolite categories that have received the greatest attention are the reactive oxygen species (ROS), the reactive nitrogen intermediates (RNI), and the eicosanoids. Additionally, the xenobiotic metabolites produced via cytochrome P450 activity mediate some immune-environmental interactions. Each of these four metabolite categories is subject to different requirements for metabolite production, and each has distinct effector functions. An understanding of macrophage metabolite regulation could allow improvements in avian health management and production via the effective control of metabolite production. The present review considers prior and recent information on the production of the metabolites by avian macrophages. Additionally, the potential ramifications of metabolite production and regulation are discussed.

Local venous responses to endotoxin in humans

BACKGROUND

Septic shock is characterized by arterial and venous dilatation and decreased responsiveness to vasoconstrictors. We have developed a method to explore the effects and mechanisms of action of administration of endotoxin into a blood vessel in vivo.

METHODS AND RESULTS

Endotoxin was instilled into a dorsal hand vein for 1 hour and then removed. A dose-response curve to norepinephrine was constructed before and 1, 2, 3, and 4 hours after endotoxin. In a separate study, dose-response curves to norepinephrine were constructed in two separate veins on the same hand, only one of which received endotoxin. Sympathetic-mediated venoconstrictor responses were also studied. Cyclooxygenase inhibitors, nitric oxide synthase inhibitors, and hydrocortisone were used to explore the mechanisms of the effects seen. Endotoxin caused a rightward shift in the dose-response curve to norepinephrine. The effect was greatest at 1 hour (maximal constriction: before endotoxin, 87 +/- 4%; after endotoxin, 52 +/- 8%; occlusion n = 4; P < .05) and returned to normal by 4 hours. In addition, deep-breath venoconstrictor responses were abolished in the endotoxin-treated vein. Instillation of endotoxin daily for 3 days resulted in the development of tolerance (maximal constriction to norepinephrine after endotoxin; day 1, 39 +/- 6%; day 2, 67 +/- 7%; day 3, 85 +/- 7%). Cyclooxygenase and/or nitric oxide synthase inhibitors did not alter the response to endotoxin, whereas prior administration of hydrocortisone abolished the effects.

CONCLUSIONS

Instillation of endotoxin caused a glucocorticoid-inhibitable hyporesponsiveness to the constrictor effects of norepinephrine and abolished sympathetically induced and drug-induced venoconstriction. This acute response does not appear to be mediated by nitric oxide or prostanoids. Direct vascular tolerance to endotoxin occurs on repeated administration.

Nitric oxide synthase inhibition versus norepinephrine for the treatment of hyperdynamic sepsis in sheep

OBJECTIVES

To investigate the effects of Nomega-mono-methyl-L-arginine (L-NMMA), an inhibitor of nitric oxide synthesis, on hemodynamics, oxygen transport, and regional blood flow in an ovine model of hyperdynamic sepsis and to compare these effects with the responses to norepinephrine.

DESIGN

Prospective, nonrandomized, controlled experimental study with repeated measures.

SETTING

Investigational intensive care unit at a university medical center.

SUBJECTS

Twenty-five female, healthy, adult sheep of the Merino breed, divided into three groups: nine control sheep; eight sheep treated with L-NMMA; and eight sheep treated with norepinephrine.

INTERVENTIONS

All sheep were chronically instrumented. After a 5-day recovery period, a continuous infusion of live Pseudomonas aeruginosa (2.5 x 10(6) colony-forming units/min) was started and maintained for the remainder of the experiment. After 24 hrs of sepsis, eight sheep received L-NMMA (7 mg/kg/hr), eight sheep received norepinephrine, and nine sheep received the vehicle alone (0.9% saline). The norepinephrine dosage was continuously and individually adjusted to achieve the same increase in blood pressure as was observed in a matched sheep of the L-NMMA group.

MEASUREMENTS AND MAIN RESULTS

After 24 hrs of sepsis, all sheep developed a hyperdynamic circulatory state with increased cardiac indices and reduced arterial pressures, and systemic vascular resistances. L-NMMA reversed the hyperdynamic circulation, causing an increase in arterial pressure by peripheral vasoconstriction. Norepinephrine led to an increase in blood pressure by augmenting cardiac indices, leaving the systemic vascular resistance unaffected. The norepinephrine dose needed to keep the blood pressure high had to be continuously increased, reflecting the reduced vascular responsiveness to catecholamines during sepsis. Renal blood flow remained unaffected by all treatment forms. Norepinephrine and L-NMMA led to a dramatic increase in urine production. Blocking the nitric oxide synthase with L-NMMA did not interfere with the host's pulmonary ability to clear bacteria, nor did treatment with norepinephrine.

CONCLUSIONS

Blocking nitric oxide synthase had a marked vasoconstrictive effect. Both norepinephrine and L-NMMA increased arterial pressure without reducing renal blood flow, leading to an improved renal function.

Reduced prostacyclin and increased leukotriene B4 synthesis in porcine venous-arterial grafts

BACKGROUND

Migration and proliferation of vascular smooth muscle cells in the intima and superimposed atheroma are the main changes underlying late failure of saphenous vein bypass grafts. There is evidence that these events are partly modulated by complex interactions between inhibitors of vascular smooth muscle cell proliferation, such as prostacyclin (PGI2), and mitogens, such as leukotriene B4 (LTB4). Because the relative balance between these eicosanoids may play a role in vein graft failure, the synthesis of PGI2 and LTB4 was measured in porcine saphenous vein-carotid artery grafts 4 weeks after implantation and compared with ungrafted vein and common carotid artery from the same animal.

METHODS

Vessels were cut into 2-mm squares and preincubated in Dulbecco's minimum essential medium for 4 hours at 37 degrees C. Tissues were then further incubated with Dulbecco's minimum essential medium containing a range of concentrations of noradrenaline, arachidonate, and calcium ionophore A23187. Release of PGI2 and LTB4 into the supernatant was then assessed by radioimmunoassay.

RESULTS

In response to all stimulators, PGI2 release was markedly diminished in vein grafts compared with ungrafted saphenous veins and carotid arteries. The patterns of responses were similar in each vessel type. In contrast, LTB4 release was significantly enhanced in vein grafts compared to ungrafted saphenous veins and carotid arteries.

CONCLUSIONS

These data indicate that there is a down-regulation of cyclooxygenase or PGI2 synthase in porcine vein grafts, which may constitute a further phenotypic change that would augment the hyperplastic process. Local increases in LTB4 synthesis in the vein graft, which indicates an induction of lipoxygenase and LTB4 synthase enzymes (and possibly reflects release from leukocytes which have infiltrated the graft), may contribute to increased intimal proliferation by direct promitogenic effects on smooth muscle cells.

Peroxides in human leucocytes in acute septic shock: a preliminary study of acute phase changes and mortality

Peroxidation by peripheral blood leucocytes was measured in 15 patients in acute septic shock and 15 uninfected controls, using the probe dichloroflorescein. Mortality in septic subjects was 40%. In 14 of 15 patients from whom serial samples were analysed, periods of increased oxidative activity were detected. Increased peroxidation occurred early in the sequence of clinical changes, at the same time as increases in temperature, blood pressure and C-reactive protein. Peak peroxide production preceded increases in acute phase reactants and changes in leucocyte distribution. Mean peroxide production in leukocytes from patients who died was significantly higher (P < 0.001) than paired controls, and greater (P < 0.05) than peroxide production in patients who survived. The in vitro oxidative response to endotoxin was upregulated in infected patients. This supports the hypothesis that systemic mediators and leucocyte-derived reactive oxygen are involved in the vascular and organ damage associated with fatal septic shock.