Evaluation of serum MMP-9 as predictive biomarker for antisense therapy in Duchenne.

Duchenne Muscular Dystrophy (DMD) is a severe muscle disorder caused by lack of dystrophin. Predictive biomarkers able to anticipate response to the therapeutic treatments aiming at dystrophin re-expression are lacking. The objective of this study is to investigate Matrix Metalloproteinase-9 (MMP-9) as predictive biomarker for Duchenne. Two natural history cohorts were studied including 168 longitudinal samples belonging to 66 patients. We further studied 1536 samples obtained from 3 independent clinical trials with drisapersen, an antisense oligonucleotide targeting exon 51: an open label study including 12 patients; a phase 3 randomized, double blind, placebo controlled study involving 186 patients; an open label extension study performed after the phase 3. Analysis of natural history cohorts showed elevated MMP-9 levels in patients and a significant increase over time in longitudinal samples. MMP-9 decreased in parallel to clinical stabilization in the 12 patients involved in the open label study. The phase 3 study and subsequent extension study clarified that the decrease in MMP-9 levels was not predictive of treatment response. These data do not support the inclusion of serum MMP-9 as predictive biomarker for DMD patients.

FcgammaRI (CD64) contributes substantially to severity of arthritis, hypersensitivity responses, and protection from bacterial infection.

The high-affinity receptor for IgG, FcgammaRI, shares its capacity to bind IgG2a immune complexes (IgG2a-IC) with the low-affinity receptor FcgammaRIII and complement factors, hampering the definition of its biological role. Moreover, in vivo, FcgammaRI is occupied by monomeric IgG2a, reducing its accessibility to newly formed IgG2a-IC. By using a variety of FcgammaR(-/-) mice, we demonstrate that in the absence of FcgammaRI, the IgG2a-IC-induced cellular processes of phagocytosis, cytokine release, cellular cytotoxicity, and antigen presentation are impaired. FcgammaRI(-/-) mice showed impaired hypersensitivity responses, strongly reduced cartilage destruction in an arthritis model, and impaired protection from a bacterial infection. We conclude that FcgammaRI contributes substantially to a variety of IgG2a-IC-dependent immune functions and immunopathological responses.

Albumin restores lysophosphatidylcholine-induced inhibition of vasodilation in rat aorta.

BACKGROUND: Impairment of vasodilation by oxidized low-density lipoprotein has been attributed to lysophosphatidylcholine (LPC). Albumin avidly binds LPC. Therefore, hypoalbuminemia may directly impair vasodilation and thus contribute to increased risk of atherosclerosis in nephrotic syndrome. The addition of albumin reduces LPC in erythrocytes and endothelial cells. We hypothesized that the addition of albumin will salvage vasodilation in aortic rings previously exposed to LPC. LPC increases superoxide production and disturbs L-arginine availability. Therefore, we also decreased superoxide with a superoxide dismutase mimic, MnCl(2), and supplemented L-arginine in an attempt to restore vasodilation. METHODS: Rat aorta rings, which had been incubated with various concentrations of LPC and human serum albumin (HSA), were mounted in organ chambers. Relaxation was studied with acetylcholine (0.01 to 100 micromol/L) after precontraction with phenylephrine (CON, 0.3 micromol/L; LPC, 0.03 micromol/L). In some studies MnCl(2) or L-arginine was added to the organ chamber. RESULTS: LPC had time- and dose-dependent inhibitory effects on acetylcholine-mediated vasodilation, but no effect on nitroprusside-mediated vasodilation. Preincubation with albumin (50 or 6 g/L) could protect vasodilation against very high levels of LPC. After preincubation with LPC, the addition of albumin to the incubation salvaged vasodilation. Albumin was more effective after short LPC incubation. MnCl(2) had no specific effect on the LPC-mediated disturbance in vasodilation. L-arginine completely salvaged vasodilation at low concentrations of LPC. However, even high concentrations of L-arginine (1 mmol/L) could not improve vasodilation at LPC levels at which vasodilation was restored by albumin. CONCLUSIONS: LPC affects several pathways that inhibit vasodilation, all of which are salvaged by addition of albumin.

Opposite role of interferon-gamma and interleukin-4 on the regulation of blood pressure in mice.

There is growing evidence that T-lymphocyte dysfunction contributes to the development of hypertension. IL-4 and IFN-gamma are important regulators of T-lymphocyte function. Therefore, we investigated the effect of neutralizing antibodies against IL-4 (alpha-IL-4) and IFN-gamma (alpha-IFN-gamma) on the development of hypertension in NZBNZWF1 hybrid compared to normotensive NZW control mice. Antibody-producing cells were encapsulated and injected intraperitoneally in mice at 6,8 and 10 weeks of age. This treatment resulted in significant levels of antibody in the serum. At 12 weeks of age blood pressure was recorded under anesthesia. Mean arterial blood pressure (MAP) increased in NZBNZWF1 hybrids between the age of 6 and 12 weeks. This increase was inhibited by treatment with alpha-IL-4, but was not affected by alpha-IFN-gamma. Treatment with alpha-IL-4 did not influence MAP in normotensive NZW or C57B1/6J mice. However, in these mice, treatment with alpha-IFN-gamma increases MAP. This increase in MAP by alpha-IFN-gamma was prevented by simultaneous treatment with alpha-IL-4. The present study demonstrates the influence of endogenous IL-4 and IFN-gamma on blood pressure.

Mechanism of gram-positive shock: identification of peptidoglycan and lipoteichoic acid moieties essential in the induction of nitric oxide synthase, shock, and multiple organ failure.

The incidence of septic shock caused by gram-positive bacteria has risen markedly in the last few years. It is largely unclear how gram-positive bacteria (which do not contain endotoxin) cause shock and multiple organ failure. We have discovered recently that two cell wall fragments of the pathogenic gram-positive bacterium Staphylococcus aureus, lipoteichoic acid (LTA) and peptidoglycan (PepG), synergize to cause the induction of nitric oxide (NO) formation, shock, and organ injury in the rat. We report here that a specific fragment of PepG, N-acetylglucosamine-beta-[1--> 4]-N-acetylmuramyl-L-alanine-D-isoglutamine, is the moiety within the PepG polymer responsible for the synergism with LTA (or the cytokine interferon gamma) to induce NO formation in the murine macrophage cell line J774.2. However, this moiety is also present in the PepG of the nonpathogenic bacterium Bacillus subtilis. We have discovered subsequently that S. aureus LTA synergizes with PepG from either bacterium to cause enhanced NO formation, shock, and organ injury in the rat, whereas the LTA from B. subtilis does not synergize with PepG of either bacterium. Thus, we propose that the structure of LTA determines the ability of a particular bacterium to cause shock and multiple organ failure (pathogenicity), while PepG acts to amplify any response induced by LTA.

Reactive oxygen species regulate macrophage scavenger receptor type I, but not type II, in the human monocytic cell line THP-1.

The uptake of modified low density lipoprotein via the macrophage scavenger receptor (MSR) results in the formation of lipid-laden foam cells during atherosclerosis. Because increased oxidative stress has been implicated in the pathogenesis of atherosclerosis, the role of reactive oxygen species on the activity and expression of MSR was investigated. The uptake of acetylated low density lipoprotein and the levels of MSR-I mRNA were inhibited by treatment with the oxygen radical scavengers 2,2,6, 6-tetramethylpiperidine-N-oxyl, dimethylthiourea or sodium benzoate, or the iron chelator deferoxamine. Dimethylthiourea or benzoate also decreased the levels of MSR-I mRNA in the presence of the transcription inhibitor actinomycin D. These results indicate that hydroxyl radicals produced from superoxide anions and hydrogen peroxide in the presence of free iron, contribute to an increased MSR activity by stabilizing MSR-I mRNA. Several sources of reactive oxygen species are involved as inhibition of MSR activity and levels of MSR-I mRNA occurred in the presence of rotenone, a mitochondrial complex I inhibitor, or acetovanillone, a NADPH oxidase inhibitor. The (oxidative) stress responsive nuclear factor kappaB is not involved as inhibitors of its activation remained without significant inhibition. In contrast to MSR-I, the levels of MSR-II mRNA, which is formed by alternative splicing of the same gene transcript, were largely unaffected by the inhibitors of reactive oxygen species formation and activity. The present results suggest that oxidant stress contributes to an increased activity of MSR by stabilizing MSR-I mRNA.

Role of nitric oxide in the circulatory failure and organ injury in a rodent model of gram-positive shock.

1. The pathological features of Gram-positive shock can be mimicked by the co-administration of two cell wall components of Staphylococcus aureus, namely lipoteichoic acid (LTA) and peptidoglycan (PepG). This is associated with the expression of the inducible isoform of nitric oxide synthase (iNOS) in various organs. We have investigated the effects of dexamethasone (which prevents the expression of iNOS protein) or aminoguanidine (an inhibitor of iNOS activity) on haemodynamics, multiple organ dysfunction syndrome (MODS) as well as iNOS activity elicited by LTA + PepG in anaesthetized rats. 2. Co-administration of LTA (3 mg kg-1, i.v.) and PepG (10 mg kg-1, i.v.) resulted in a significant increase in the plasma levels of tumour necrosis factor-alpha (TNF alpha, maximum at 90 min) as well as a biphasic fall in mean arterial blood pressure (MAP) from 120 +/- 3 mmHg (time 0) to 77 +/- 5 mmHg (at 6 h, n = 8; P < 0.05). This hypotension was associated with a significant tachycardia (4-6 h, P < 0.05) and a reduction of the pressor response elicited by noradrenaline (NA, 1 microgram kg-1, i.v., at 1-6 h; n = 8, P < 0.05). Furthermore, LTA + PepG caused time-dependent increases in the serum levels of markers of hepatocellular injury, glutamate-pyruvate-transminase (GPT) and glutamate-oxalacetate-transaminase (GOT). In addition, urea and creatinine (indicators of renal dysfunction) were increased. There was also a fall in arterial oxygen tension (PaO2), indicating respiratory dysfunction, and metabolic acidosis as shown by the significant drop in pH, PaCO2 and HCO3-. These effects caused by LTA + PepG were associated with the induction of iNOS activity in aorta, liver, kidney and lungs as well as increases in serum levels of nitrite+nitrate (total nitrite). 3. Pretreatment of rats with dexamethasone (3 mg kg-1, i.p.) at 120 min before LTA + PepG administration significantly attenuated these adverse effects as well as the increases in the plasma levels of TNF alpha caused by LTA + PepG. The protective effects of dexamethasone were associated with a prevention of the increase in iNOS activity (in aorta, liver, lung, kidney), the expression of iNOS protein (in lungs), as well as in the increase in the plasma levels of total nitrite. 4. Treatment of rats with aminoguanidine (5 mg kg-1 + 10 mg kg-1 h-1) starting at 120 min after LTA + PepG attenuated most of the adverse effects and gave a significant inhibition of iNOS activity (in various organs) as well as an inhibition of the increase in total plasma nitrite. However, aminoguanidine did not improve renal function although this agent caused a substantial inhibition of NOS activity in the kidney. 5. Thus, an enhanced formation of NO by iNOS importantly contributes to the circulatory failure, hepatocellular injury, respiratory dysfunction and the metabolic acidosis, but not the renal failure, caused by LTA + PepG in the anaesthetized rat.

Analysis of the signal transduction in the induction of nitric oxide synthase by lipoteichoic acid in macrophages.

1. This study investigates the signal transduction mechanisms leading to the enhanced formation of nitric oxide (NO) due to the induction of NO synthase (iNOS) in murine J774.2 macrophages in culture activated with lipoteichoic acid (LTA), a cell wall component of the gram-positive bacterium Staphylococcus aureus. 2. LTA (10 microgram ml-1) caused within 24 h an enhanced accumulation of nitrite (an indicator of NO biosynthesis) in the supernatant of J774.2 macrophages which was prevented by the non-selective NOS inhibitor NG-monomethyl-L-arginine (L-NMMA; IC50: 35 microM) or by the iNOS-selective NOS inhibitor, aminoethyl-isothiourea (AE-ITU; IC50: 6 microM). The inhibition of nitrite formation afforded by these agents was prevented by excess L-arginine (3-30 mM), but not by D-arginine (3-30 mM). Furthermore, the degree of iNOS inhibition was similar when these NOS inhibitors were added to the macrophages 10 h after LTA. 3. Pretreatment of J774.2 macrophages with cyclohexamide or dexamethasone prevented the enhanced formation of nitrite caused by LTA. This inhibition did not occur when dexamethasone or cyclohexamide were added to the cells 10 h after LTA. The increase in nitrite formation stimulated by LTA (10 micrograms ml-1) was not affected by polymyxin B (0.05-0.5 microgram ml-1), an agent which binds and inactivates endotoxin. 4. A specific inhibitor of phosphatidylcholine-phospholipase C (PC-PLC), D609, prevented the increase in nitrite formation (IC50 = 20 micrograms ml-1) caused by LTA. The inhibition afforded by D609 was significantly smaller when this agent was added to the cells 10 h after LTA. 5. The structurally distinct tyrosine kinase inhibitors, erbstatin, genistein, and tyrphostin AG126 prevented the formation of nitrite caused by LTA. The inhibition afforded by these compounds was significantly attenuated when they were added to the cells 10 h after LTA. In contrast, daidzein or tyrphostin A-1, which are inactive analogues of genistein and tyrphostin (up to a concentration of 10 microM) did not affect the nitrite formation caused by LTA. 6. Inhibitors of the activation of the nuclear transcription factor NF-kappa B such as pyrrolidine dithiocarbamate (PDTC; an antioxidant and a metal chelator), butylated hydroxyanisole (BHA; an antioxidant), L-1-tosylamido-2-phenylethyl chloromethyl ketone (TPCK), calpain inhibitor I (both I kappa B-protease inhibitors), or rotenone (an antioxidant which inhibits electron transport) prevented the nitrite formation stimulated by LTA. The inhibition afforded by these agents was significantly smaller when they were added to the macrophages 10 h after LTA. 7. Incubation of J774.2 cells with LTA over 24 h resulted in the expression of iNOS protein (130 kDa) as identified by Western blot analysis. The expression of iNOS protein by LTA was significantly attenuated by cyclohexamide, D609, tyrphostin AG126, PDTC or by TPCK. 8. Thus, the signal transduction leading to the expression of iNOS protein and activity caused by LTA in murine J774.2 macrophages involves (i) the activation of PC-PLC, (ii) phosphorylation of tyrosine kinase, and (iii) the activation of the transcription factor NF-kappa B.

Role for intracellular platelet-activating factor in the circulatory failure in a model of gram-positive shock.

1. This study investigates the effects of two structurally different antagonists of platelet-activating factor (PAF), BN52021 and WEB2086, on the circulatory and renal failure elicited by lipoteichoic acid (LTA) from Staphylococcus aureus (an organism without endotoxin) in anaesthetized rats. 2. Administration of LTA (10 mg kg-1, i.v.) caused hypotension and vascular hyporeactivity to noradrenaline (1 microgram kg-1, i.v.) WEB2086 (5 mg kg-1, i.v., 20 min before and 150 min after LTA) inhibited the delayed fall in mean arterial blood pressure (at 300 min: 99 +/- 6 mmHg vs. 75 +/- 6 mmHg, P < 0.01) and prevented the decrease in pressor response to noradrenaline (at 300 min: 36 +/- 5 mmHg min vs. 17 +/- 5 mmHg min, P < 0.01). Surprisingly, BN52021 (20 mg kg-1, i.v., 20 min before and 150 min after LTA) neither prevented the hypotension (74 +/- 6 mmHg) nor the vascular hyporeactivity (21 +/- 5 mmHg min). However, BN52021 inhibited the hypotension to injections of PAF as well as the circulatory failure elicited by lipopolysaccharides (10 mg kg-1, i.v.). 3. LTA caused an increase in plasma concentration of creatinine from 39 +/- 5 microM (sham-operated) to 70 +/- 8 microM and urea from 4.7 +/- 0.1 to 13.1 +/- 1.6 mM. The renal failure elicited by LTA was significantly inhibited by WEB2086 (creatinine: 45 +/- 4 microM and urea: 5.7 +/- 0.7 mM), but not by BN52021. 4. The induction of nitric oxide synthase activity in lungs by LTA was attenuated by WEB2086 from 98 +/- 17 to 40 +/- 15 pmol L-citrulline 30 min-1 mg-1 protein (P < 0.01), but not by BN52021 (148 +/- 21 pmol L-citrulline 30 min-1 mg-1 protein). Similarly, WEB2086, but not BN52021, inhibited the increase in plasma nitrite concentration associated with the delayed circulatory failure caused by LTA. The release of tumour necrosis factor-alpha (TNF-alpha) after injection of LTA was not attenuated by WEB2086. 5. The induction of nitrite release by cultured macrophages activated with LTA (10 micrograms ml-1 for 24 h) was inhibited by 74 +/- 4% by WEB2086 (3 x 10(-4) M), but not by BN52021, indicating that only WEB2086 acts on intracellular PAF receptors. 6. Thus, the intracellular release of PAF contributes to the circulatory and renal failure and induction of nitric oxide synthase elicited by LTA in anaesthetized rats. The difference between the two structurally different PAF antagonists in our septic shock models using either LTA or lipopolysaccharide (LPS), shows the importance of models for Gram-positive sepsis in the elucidation of the pathophysiology of septic shock and for the evaluation of potential drugs.

The cell wall components peptidoglycan and lipoteichoic acid from Staphylococcus aureus act in synergy to cause shock and multiple organ failure.

Although the incidence of Gram-positive sepsis has risen strongly, it is unclear how Gram-positive organisms (without endotoxin) initiate septic shock. We investigated whether two cell wall components from Staphylococcus aureus, peptidoglycan (PepG) and lipoteichoic acid (LTA), can induce the inflammatory response and multiple organ dysfunction syndrome (MODS) associated with septic shock caused by Gram-positive organisms. In cultured macrophages, LTA (10 micrograms/ml), but not PepG (100 micrograms/ml), induces the release of nitric oxide measured as nitrite. PepG, however, caused a 4-fold increase in the production of nitrite elicited by LTA. Furthermore, PepG antibodies inhibited the release of nitrite elicited by killed S. aureus. Administration of both PepG (10 mg/kg; i.v.) and LTA (3 mg/kg; i.v.) in anesthetized rats resulted in the release of tumor necrosis factor alpha and interferon gamma and MODS, as indicated by a decrease in arterial oxygen pressure (lung) and an increase in plasma concentrations of bilirubin and alanine aminotransferase (liver), creatinine and urea (kidney), lipase (pancreas), and creatine kinase (heart or skeletal muscle). There was also the expression of inducible nitric oxide synthase in these organs, circulatory failure, and 50% mortality. These effects were not observed after administration of PepG or LTA alone. Even a high dose of LTA (10 mg/kg) causes only circulatory failure but no MODS. Thus, our results demonstrate that the two bacterial wall components, PepG and LTA, work together to cause systemic inflammation and multiple systems failure associated with Gram-positive organisms.

Delayed circulatory failure due to the induction of nitric oxide synthase by lipoteichoic acid from Staphylococcus aureus in anaesthetized rats.

1. This study investigates the effect of lipoteichoic acid (LTA) from the cell wall of Staphylococcus aureus, a micro-organism without endotoxin, on haemodynamics and induction of nitric oxide synthase (iNOS) in the anaesthetized rat. 2. Intravenous injection of LTA (10 mg kg-1) resulted in a decrease in blood pressure from 123 +/- 1 mmHg to 83 +/- 7 mmHg after 270 min (P < 0.001) and a reduction of the pressor response to noradrenaline (1 microgram kg-1) from 33 +/- 1 mmHg.min to 23 +/- 3 mmHg.min after 270 min (P < 0.05). 3. The delayed circulatory failure (hypotension and vascular hyporeactivity) caused by LTA was prevented by pretreatment of rats with dexamethasone (10 mg kg-1, 60 min prior to LTA) or the nitric oxide synthase inhibitor NG-monomethyl-L-arginine (L-NMMA, 10 mg kg-1 h-1, i.v. infusion starting 30 min prior to LTA). 4. In contrast, treatment of rats with polymyxin B (0.05 mg kg-1), an agent which binds endotoxin (lipopolysaccharides, LPS), did not affect the delayed circulatory failure caused by LTA. Polymyxin B, however, attenuated the hypotension and vascular hyporeactivity to noradrenaline afforded by endotoxaemia (2 mg kg-1 LPS, i.v.) for 270 min. 5. The delayed circulatory failure caused by LTA was associated with a time-dependent increase in (i) the expression of iNOS protein in the lung (Western blot analysis), and (ii) iNOS activity. This increase in iNOS protein and activity was prevented by pretreatment of LTA-rats with dexamethasone (10 mg kg-1). 6. Intravenous injection of LTA resulted in an increase in serum tumour necrosis factor (TNF)-alpha(maximum at 90 min after LTA), which was attenuated by pretreatment of rats with dexamethasone(10 mg kg-1, 60 min prior to LTA). The magnitude of the rise in TNF-alpha caused by LTA was similar to the one elicited by LPS (10mgkg-', i.v.).7. Thus, an enhanced formation of nitric oxide following the induction of iNOS contributes importantly to the delayed vascular failure (hypotension and vascular hyporeactivity) caused by LTA in the anaesthetized rat. We suggest that the endogenous release of TNF-alpha contributes to the induction ofiNOS caused by LTA in vivo.

Reversal of bradykinin-induced relaxation to contraction after interferon-gamma in bovine isolated mesenteric arteries.

Bovine isolated mesenteric arterial rings were preincubated for 20 h with interferon-gamma (100 U ml-1) and relaxation in response to bradykinin (10(-12) to 3 x 10(-8) M) was then measured isometrically in an organ bath. Interferon-gamma pretreatment for 20 h markedly attenuated the endothelium-dependent bradykinin relaxation in arteries precontracted with 9,11-dideoxy-11 alpha,9 alpha-epoxymethano prostaglandin F2 alpha (U46619), and the relaxation was reversed to contraction at the highest bradykinin concentrations (-72 +/- 5% for control vs. + 6 +/- 10% for interferon-gamma). Cycloheximide (20 micrograms ml-1) present during the 20-h preincubation completely prevented the interferon-gamma effect. Methyl-L-arginine (1 mM) treatment during the 20-h preincubation also inhibited the interferon-gamma effect on bradykinin relaxation (-47 +/- 18% for interferon-gamma and methyl-L-arginine), which suggests involvement of nitric oxide during the 20-h preincubation with interferon-gamma. In control arteries, des-Arg9-bradykinin, a bradykinin B1 receptor agonist, evoked contractions, which were augmented in rings preincubated for 20 h with interferon-gamma. The bradykinin B1 receptor antagonist, des-Arg9-Leu8-bradykinin (2 microM), present in the organ bath in combination with methyl-L-arginine (1 mM) only present during the 20-h preincubation with interferon-gamma completely restored the bradykinin relaxation (-79 +/- 12%). We suggest two mechanisms. Firstly, prolonged nitric oxide release induced by interferon-gamma during the 20-h preincubation may inhibit bradykinin stimulated endothelium-derived nitric oxide release and action. Secondly, interferon-gamma caused upregulation of the bradykinin B1 receptor-mediated contraction, which may contribute to the decrease in bradykinin-induced vasodilation and cause a reversal to contraction.

Induction of nitric oxide release by interferon-gamma inhibits vasodilation and cyclic GMP increase in bovine isolated mesenteric arteries.

The influence of interferon (IFN)-gamma on vasodilation was examined in bovine isolated mesenteric arteries. Arterial rings were incubated with IFN-gamma (100 U ml-1) for 20 hr and subsequently the response to vasodilators was determined isometrically in an organ bath. Treatment with IFN-gamma markedly inhibited endothelium-dependent relaxation to bradykinin and impaired vasodilation to nitroprusside, which was endothelium-independent. The decrease in relaxation was correlated with a decrease in bradykinin- and nitroprusside-induced cGMP production. Relaxation to the phosphodiesterase inhibitors 3-isobutyl-1-methylxanthine or zaprinast was not altered after IFN-gamma, which suggests that the IFN-gamma effect is specific for guanylate cyclase-activating agonists. Nitrite concentration in the incubation medium was increased after IFN-gamma, which indicates the induction of nitric oxide release during the incubation period. Inhibition of nitric oxide synthesis with NG-monomethyl-L-arginine during the 20-hr incubation with IFN-gamma completely prevented the decrease in relaxation and cGMP elevation to nitroprusside. We conclude that IFN-gamma induces a marked increase in release of arterial-derived nitric oxide resulting in a desensitization of guanylate cyclase, which contributes to a decrease in relaxation to bradykinin and nitroprusside. These results may implicate the existence of an important adaptive process in the regulation of vascular tone during pathological situations associated with the induction of nitric oxide synthesis.

Acetylcholine-induced relaxation in bovine isolated mesenteric arteries is suppressed by polymorphonuclear leukocytes.

1. The endothelium plays a critical role in maintaining vascular tone via generation of potent vasoconstrictor and dilator substances. We examined the effect of bovine purified polymorphonuclear leukocytes (PMN) on the endothelium-dependent relaxation to acetylcholine in isolated mesenteric arteries. 2. In the presence of PMN (2.5 x 10(6) cells ml-1) the maximal relaxation to acetylcholine was decreased from 76.1 +/- 2.4% to 44.9 +/- 7.4% of the precontraction (P < 0.001). This effect was inhibited by superoxide dismutase and NG-mono-methyl-L-arginine, but not by catalase or indomethacin. 3. PMN were not able to influence significantly the endothelium-independent relaxation to nitroprusside. 4. Removal of PMN after preincubation and prior to precontraction and relaxation did not influence the acetylcholine-induced relaxation, indicating that no irreversible vascular damage had occurred. 5. Superoxide anion production by unstimulated PMN was less than 10% compared to phorbol myristate acetate-activated PMN, measured by chemiluminescence and reduction of ferricytochrome c. 6. We conclude that small amounts of superoxide anions produced by unstimulated PMN contribute to a decrease in relaxation to acetylcholine by interfering with endothelium-derived nitric oxide.

Bovine polymorphonuclear leukocytes increase sensitivity to noradrenaline in isolated mesenteric arteries.

1. The effects of polymorphonuclear leukocytes (PMN) on vascular function to (-)-noradrenaline were examined in vitro. Purified bovine PMN were incubated in siliconized organ baths containing rings of bovine mesenteric arteries, after which a concentration-effect curve in response to (-)-noradrenaline was obtained. 2. PMN-derived products induced a long lasting concentration-dependent contraction of the blood vessels generating 24.4 +/- 6.8% of the maximal tension to (-)-noradrenaline at a cell concentration of 2.5 x 10(6) ml-1. The contractile response was also found in endothelium-denuded vascular rings. 3. PMN present in the organ bath caused an increase in the sensitivity of vascular rings to (-)-noradrenaline. At a cell number of 2.5 x 10(6) PMN ml-1 the pD2-value for (-)-noradrenaline was augmented 0.40 +/- 0.05 (P less than 0.001), while total contraction at the highest concentration (-)-noradrenaline was not affected. This increase in sensitivity was dependent on an intact endothelium. 4. The increase in sensitivity to (-)-noradrenaline by PMN was inhibited by superoxide dismutase, but not by catalase, dimethylthiourea, indomethacin or nordihydroguaiaretic acid. The non-stimulated bovine PMN produced oxygen radicals as measured by chemiluminescence. 5. Simultaneous incubation of PMN and (-)-noradrenaline with arterial rings induced an increase in the release of prostacyclin, measured by an elevated concentration of 6-keto-prostaglandin F1 alpha in the supernatant. 6. It is concluded that PMN can increase vascular tone directly or indirectly probably via the interaction of PMN-derived superoxide anions with endothelium-derived relaxing factor.