Myeloperoxidase-catalyzed inactivation of alpha 1-protease inhibitor by human neutrophils

N-acetylcysteine pretreatment of cardiac surgery patients influences plasma neutrophil elastase and neutrophil influx in bronchoalveolar lavage fluid

OBJECTIVE

Study of leukocyte activation and release of toxic mediators during extracorporeal circulation (ECC). ECC can be used to study the potential protective effect of a pharmacon against neutrophil-mediated lung injury. Clinical studies have indicated that N-acetylcysteine (NAC) may improve systemic oxygenation and reduce the need for ventilatory support when given to patients with acute lung injury.

DESIGN

Cardiac surgery patients were pretreated with high-dose NAC in order to assess the potential role of NAC to interfere with neutrophil-mediated inflammation and lung injury.

PATIENTS

18 patients who underwent ECC: group 1 (n = 8) no premedication (only placebo); group 2 (n = 10) NAC (72 mg/kg i.v. as a bolus, later 72 mg/kg over 12 h).

MEASUREMENTS AND RESULTS

In group 2, the partial pressure of oxygen in arterial blood/fractional inspired oxygen 4 h after surgery was significantly higher than in group 1 (213 +/- 31 vs 123 +/- 22; p = 0.044). NAC pretreatment prevented an increase in plasma neutrophil elastase activity (18.9 +/- 6.9 vs 49.9 +/- 5.6 ng/ml in group 1 at the end of ECC; p = 0.027). Release of myeloperoxidase (MPO) was not affected (group 1:1105 +/- 225 ng/ml vs group 2:1127 +/- 81 at the end of ECC; p = 0.63). At the end of ECC, total antigenic human neutrophil elastase (group 1:671 +/- 72 ng/ml vs group 2:579 +/- 134; p = 0.37) and complex formation between elastase and alpha 1-proteinase inhibitor were no different in the two groups. There were no significant difference in cellular composition and mediators in the lavage fluid, although values for total number of neutrophils, elastase, MPO and interleukin-8 were lower in group 2.

CONCLUSION

Pretreatment with NAC may prevent lung injury by diminishing elastase activity. Since the release of mediators, especially MPO, is not affected, this diminished activity of elastase may be achieved by enhanced inactivation by antiproteases after initial treatment.

Bronchoalveolar oxyradical inflammatory elements herald bronchopulmonary dysplasia

OBJECTIVES

To quantify oxyradical inflammatory markers in serial endotracheal tube aspirates obtained from premature neonates at risk for developing bronchopulmonary dysplasia, and to correlate these parameters with clinical manifestations of the disease.

DESIGN

Prospective cohort study.

SETTING

Tertiary neonatal intensive care unit.

PATIENTS

Twenty-eight intubated, premature infants, with 15 infants displaying simple respiratory distress syndrome and 13 infants eventually developing bronchopulmonary dysplasia.

INTERVENTIONS

Endotracheal tube aspirates were collected and clinical severity scores were calculated longitudinally from an inception cohort during the first week of life. Diagnosis of bronchopulmonary dysplasia by standard criteria was recorded at 30 days of life. Various biochemical analyses related to pulmonary oxyradical stress were determined on endotracheal tube aspirates and were normalized according to the magnitude of serum/aspirate urea ratios. The demographic, illness severity, and biochemical characteristics of infants with simple respiratory distress syndrome and those characteristics of infants developing bronchopulmonary dysplasia were evaluated by masked comparison.

MEASUREMENTS AND MAIN RESULTS

Populations of respiratory distress syndrome and bronchopulmonary dysplasia infants could be differentiated during the first week of life by means of the following parameters: gestational age; birth weight; Score of Neonatal Acute Physiology; Neonatal Therapeutic Intervention Scoring System; epithelial lining fluid leukocytes; elastase; myeloperoxidase; xanthine oxidase and catalase enzyme activities; and total sulfhydryls.

CONCLUSIONS

Infants with simple respiratory distress syndrome could be segregated from those infants who developed bronchopulmonary dysplasia by the magnitude of the epithelial lining fluid oxyradical inflammation markers. While infants developing bronchopulmonary dysplasia typically exhibited increased concentrations of these markers during the first week of life, those infants with simple respiratory distress syndrome displayed low, uniform, or decreasing values of these markers over this interval. Infants developing bronchopulmonary dysplasia demonstrate an early pulmonary inflammatory response, and one key aspect of this response involves various oxyradical-generating systems.

The characterization of antioxidants

The role of antioxidants in nutrition is an area of increasing interest. Antioxidants are used (1) to prolong the shelf life and maintain the nutritional quality of lipid-containing foods, and (2) to modulate the consequences of oxidative damage in the human body. This review discusses what an antioxidant is and how the properties of antioxidants may be characterized.

Influences of tobacco smoke and vitamin E depletion on the distal lung of weanling rats

Tobacco smoke is associated with pulmonary emphysema via elastase-antielastase and oxidant-antioxidant imbalance. This study addressed the tobacco smoke-induced changes in the lungs of weanling rats with vitamin E depletion. Three-week-old Wistar rats fed on vitamin E-depleted or normal diet were intermittently exposed to tobacco smoke by Hamburg II machines for 4 weeks. Tobacco smoke significantly suppressed body weight increases, particularly in the vitamin E-depleted group. In the normal diet group, tobacco smoke induced emphysematous changes with significant increases in the mean linear intercept (Lm) and the destructive index (DI), which was supported by an increase in elastase-like activity and a decrease in elastase inhibitory capacity (EIC) in bronchoalveolar lavage (BAL) fluid. Vitamin E depletion alone altered neither Lm nor DI. In tobacco-exposed animals in addition to vitamin E depletion, elastase-like activity, EIC in BAL fluid and DI were comparable to that in tobacco-exposed animals on a normal diet. However, Lm was markedly decreased with thickened epithelium and shrunk alveolar space. These results suggest that vitamin E depletion, when linked to tobacco exposure, might induce impaired lung development in the weanling rats, which is different from the emphysematous changes.

Monitoring of immunotherapy with cytokines or monoclonal antibodies

Recombinant cytokines and monoclonal antibodies (mAbs) are increasingly used in the treatment of a number of human diseases. Monitoring of the clinical efficacy of these agents requires specific clinical and laboratory measurements. A number of these novel therapies share common side effects, ranging from fever, headache and general malaise to hypotension, the development of edema leading to the vascular leak syndrome, the occurrence of thromboembolic processes and, in severe cases, organ dysfunction. As an example of the pathogenesis of these side effects, recent data are presented which were obtained in patients receiving immunotherapy with high doses of the cytokine interleukin-2 as an anti-cancer treatment.

Oxidation of methionyl residues in proteins: tools, targets, and reversal

Methionine (Met) is one of the most readily oxidized amino acid constituents of proteins. It is attacked by H2O2, hydroxyl radicals, hypochlorite, chloramines, and peroxynitrite, all these oxidants being produced in biological systems. The oxidation product, Met sulfoxide, can be reduced back to Met by Met sulfoxide reductase. Numerous proteins lose functional activity by Met oxidation. However, functional activation of proteins by Met oxidation has also been observed. Functional changes by Met oxidation in a given protein appear to have pathophysiological significance in some cases. Considering the reversibility of Met oxidation and the functional changes associated with the oxidation, it seems possible that Met oxidation/reduction in proteins may be one means to control homeostasis in biological systems.

Sputum peroxidase activity correlates with the severity of lung disease in cystic fibrosis

Patients with cystic fibrosis (CF) of the same age differ significantly in their degree of pulmonary disease. Based on preliminary observations, we postulated that the activity of myeloperoxidase would be significantly increased in patients with greater structural lung damage than in those with less lung damage. Acid extracts of weighed sputum samples were assayed for lactoferrin concentrations by ELISA. Activities of peroxidase, cathespsin G, and elastase (with and without proteinase 3) were determined by kinetic analysis using chromogenic substrates. The patients were divided into quartiles based on their Brasfield chest-radiograph score. Patients in the first quartile (least amount of structural lung abnormality) were compared to those in the fourth quartile. The concentration of lactoferrin, a specific (secondary) granule protein of neutrophils, did not differ between the two patient groups. However, the activities of the neutrophil primary granule proteins, peroxidase, elastase, and elastase plus proteinase 3, were significantly elevated in the group with the most structural lung abnormality. Sputum albumin concentration was used to estimate leakages of plasma proteins into the airways. Peroxidase activity, but not the activity of cathepsin G, of elastase, or of elastase plus proteinase 3, correlated significantly with albumin/g sputum in both quartile groups. To confirm the association of sputum peroxidase activity with differences in lung structure and to test its correlation with lung function, spirometry was performed in a second group of patients during the week prior to the time of sputum sampling. In this second group, increased sputum peroxidase activity was associated with worse Brasfield scores and with decreased percent-predicted forced expiratory volume in 1 sec.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetaldehyde inhibits the anti-elastase activity of alpha 1-antitrypsin

There are genetic and exogenous factors responsible for alpha 1-antitrypsin (alpha 1-AT) deficiency which may lead to cirrhosis of the liver and emphysema. The present study was initiated on a biochemical level in order to determine whether acetaldehyde, the major product of ethanol metabolism, is capable of influencing the physiological effect of alpha 1-AT upon elastase, an enzyme which is capable of inducing emphysema. The effects of acetaldehyde and ethanol upon elastase and alpha 1-AT were tested. Acetaldehyde at 0.3-M and 1.2-M concentrations inhibited the anti-elastase activity of alpha 1-AT. Acetaldehyde at 0.03-M and 0.07-M concentrations did not affect elastase activity and had a slight effect at 0.12-M levels. Equivalent amounts of ethanol were without influence upon elastase activity or alpha 1-AT function. These data provide biochemical support for the possibility that heterozygous males with lower than normal alpha 1-AT levels may be at much higher risk to develop liver disease, emphysema, and alpha 1-AT deficiency as a consequence of chronic exposure to ethanol and concomitant circulating acetaldehyde levels.

Inhibition of crevicular fluid neutrophil elastase by alpha 1-antitrypsin in periodontal health and disease

Gingival crevicular fluid (GCF) was collected from two healthy, two gingivitis and two periodontitis sites of two groups of individuals presenting for treatment of chronic adult periodontitis (group 1, 25 subjects; group 2, seven subjects) and from distal approximal sites of two incisors and one molar of 10 subjects with periodontal health. GCF eluates of periodontitis group 1 and controls, prepared by a technique that lysed polymorphonuclear leucocytes (PMN) in the samples, were assayed for functional neutrophil elastase (NE) and immunoreactive alpha 1-antitrypsin (alpha 1-AT) and alpha 1-antitrypsin-neutrophil elastase complex (alpha 1-AT-NE). Periodontitis group 2 GCF eluates, generated by a method that did not disrupt PMNs, were assayed for functional NE in the presence and absence of a specific NE inhibitor. A greater amount of NE (ng/5-s sample) was found in eluates of GCF from diseased sites irrespective of whether or not the eluates contained products of lysed PMNs. However, the GCF eluates prepared without disrupting PMNs contained only about one-tenth as much NE as eluates of corresponding sites that included constituents of lysed PMNs. The amount of alpha-AT in GCF was insufficient to inactivate most of the NE available for release into the gingival sulcus at either healthy or diseased sites. In addition, much of the alpha 1-AT in GCF was not complexed with NE under conditions of excess NE. More than 90% of the NE in GCF from each site category was inactivated by the NE specific inhibitor. It is concluded, because of the large quantity of NE available in PMNs compared to the amount of NE inhibitors in GCF, that at least locally transient free NE occurs, which contributes to tissue destruction in chronic adult periodontitis.

Ultrastructural and ultracytochemical alteration of rat neutrophils induced by G-CSF

Recombinant human granulocyte colony-stimulating factor (G-CSF) was administered intravenously to rats, and its effects on the neutrophils from bone marrow and peripheral blood were examined by electron microscopy. Immature cells such as the promyelocytes in the bone marrow of the rats 12 hours after G-CSF administration revealed more irregular nuclei than those in untreated rats. Forty-eight hours after G-CSF administration, these changes became more marked. In the peripheral blood, the number of cytoplasmic granules was increased 12 hours after administration of G-CSF. The nuclei of mature neutrophils at 48 hours showed hypersegmentation with slight chromatin aggregation. The peroxidase reaction observed by electron microscopy revealed an increase in the number of positive granules in the immature neutrophils 48 hours after G-CSF administration, and some of the granules tended to be large. Different from untreated granulocytes, a positive peroxidase reaction was observed in the perinuclear space and rough endoplasmic reticulum of mature cells in the peripheral blood 48 hours after G-CSF administration. These granules also tended to be large. The present electron microscopic investigations demonstrated alterations of the neutrophils in G-CSF-administered rats, and these cells retained ultracytochemical evidence of prematurity even at their mature stage.

X-ray crystal structure of canine myeloperoxidase at 3 A resolution

The three-dimensional structure of the enzyme myeloperoxidase has been determined by X-ray crystallography to 3 A resolution. Two heavy atom derivatives were used to phase an initial multiple isomorphous replacement map that was subsequently improved by solvent flattening and non-crystallographic symmetry averaging. Crystallographic refinement gave a final model with an R-factor of 0.257. The root-mean-square deviations from ideality for bond lengths and angles were 0.011 A and 3.8 degrees. Two, apparently identical, halves of the molecule are related by local dyad and covalently linked by a single disulfide bridge. Each half-molecule consists of two polypeptide chains of 108 and 466 amino acid residues, a heme prosthetic group, a bound calcium ion and at least three sites of asparagine-linked glycosylation. There are six additional intra-chain disulfide bonds, five in the large polypeptide and one in the small. A central core region that includes the heme binding site is composed of five alpha-helices. Regions of the larger polypeptide surrounding this core are organized into locally folded domains in which the secondary structure is predominantly alpha-helical with very little organized beta-sheet. A proximal ligand to the heme iron atom has been identified as histidine 336, which is in turn hydrogen-bonded to asparagine 421. On the distal side of the heme, histidine 95 and arginine 239 are likely to participate directly in the catalytic mechanism, in a manner analogous to the distal histidine and arginine of the non-homologous enzyme cytochrome c peroxidase. The site of the covalent linkage to the heme has been tentatively identified as glutamate 242, although the chemical nature of the link remains uncertain. The calcium binding site has been located in a loop comprising residues 168 to 174 together with aspartate 96. Myeloperoxidase is a member of a family of homologous mammalian peroxidases that includes thyroid peroxidase, eosinophil peroxidase and lactoperoxidase. The heme environment, defined by our model for myeloperoxidase, appears to be highly conserved in these four mammalian peroxidases. Furthermore, the conservation of all 12 cysteine residues involved in the six intra-chain disulfide bonds and the calcium binding loop suggests that the three-dimensional structures of members of this gene family are likely to be quite similar.

Free radical scavenging and inhibition of lipid peroxidation by beta-blockers and by agents that interfere with calcium metabolism. A physiologically-significant process?

It has been proposed that beta-blockers and agents affecting Ca2+ metabolism might exert cardioprotective actions because of their ability to act as antioxidants in vivo. The feasibility of this proposal was tested by examining the reaction of a series of such compounds with various oxygen-derived species. None of the compounds tested was sufficiently reactive with superoxide radical, hydrogen peroxide or hypochlorous acid for scavenging of these species to be feasible in vivo at the drug concentrations present in patients given the usual therapeutic doses. All the drugs tested were powerful scavengers of hydroxyl radical except for flunarizine, which stimulated iron ion-dependent hydroxyl radical generation from hydrogen peroxide. However, none of the drugs significantly inhibited production of hydroxyl radicals in this system. Propranolol, verapamil and flunarizine had significant inhibitory effects on the peroxidation of rat liver microsomes in the presence of iron ions and ascorbic acid. All three compounds exerted weaker inhibitory effects on peroxidation of arachidonic acid caused by a mixture of myoglobin and H2O2: pindolol stimulated peroxidation in this system. It is concluded that the ability of beta-blockers and "Ca(2+)-blockers" to inhibit lipid peroxidation varies with the lipid substrate used and the mechanism by which peroxidation is induced. We conclude that suggestions that beta-blockers and "Ca(2+)-blockers" exert antioxidant effects in vivo are not well founded, although there is a possibility that verapamil and propranolol might have some inhibitory effects against peroxidation if they accumulate in membranes to a sufficiently-high concentration in vivo. We could not confirm the reported ability of propranolol to inhibit the enzyme xanthine oxidase.

The antioxidant action of ergothioneine

Ergothioneine is a product of plant origin that accumulates in animal tissues. Its suggested ability to act as an antioxidant has been evaluated. Ergothioneine is a powerful scavenger of hydroxyl radicals (.OH) and an inhibitor of iron or copper ion-dependent generation of .OH from hydrogen peroxide (H2O2). It is also an inhibitor of copper ion-dependent oxidation of oxyhaemoglobin, and of arachidonic acid peroxidation promoted by mixtures of myoglobin (or haemoglobin) and H2O2. Ergothioneine is a powerful scavenger of hypochlorous acid, being able to protect alpha 1-antiproteinase against inactivation by this molecule. By contrast, it does not react rapidly with superoxide (O2-) or hydrogen peroxide (H2O2) and it does not inhibit microsomal lipid peroxidation in the presence of iron ions. Overall, our results show that ergothioneine at the concentrations present in vivo could act as an antioxidant.

Inhibition of polymorphonuclear leukocyte-mediated endothelial cell detachment by antileukoprotease: a comparison with other proteinase inhibitors

The role of elastase and proteinase inhibitors in polymorphonuclear leukocyte(PMN)-mediated injury to human umbilical cord venous endothelial cells (HUVEC) was investigated. Both purified human neutrophil elastase and PMN that were stimulated with serum-treated zymosan (STZ) induced detachment, but not lysis of HUVEC. PMN-, but not purified elastase-mediated detachment was enhanced by the presence of methionine, which indicates a role for reactive oxygen metabolites in PMN-mediated HUVEC detachment. Detachment of HUVEC could be inhibited by secretory leukocyte proteinase inhibitor or antileukoprotease (ALP), alpha 1-proteinase inhibitor (alpha 1-PI) and N-methoxy-succinyl-ala-ala-pro-val-chloromethyl ketone (CMK). At concentrations at which elastase-mediated detachment was maximally inhibited, ALP and CMK, but not alpha 1-PI, were also able to inhibit maximally PMN-mediated detachment. An explanation for this difference could be that the larger size of alpha 1-PI reduces the access of alpha 1-PI to the interface between the PMN and the HUVEC.

The influence of superoxide on the production of hypochlorous acid by human neutrophils

Human neutrophils stimulated with opsonized zymosan promoted hypochlorous acid (HOCl)-dependent loss of monochlorodimedon. Formation of HOCl was completely inhibited by catalase, and it was also inhibited up to 70% by SOD. There was no inhibition by desferal, DTPA, mannitol or dimethylsulphoxide, which excluded the involvement of .OH. Our results indicate that generation of O2- by neutrophils enables these cells to enhance their production of HOCl. Furthermore, inhibition of neutrophil processes by SOD and catalase does not necessarily implicate .OH. We propose that O2- may potentiate oxidant damage at inflammatory sites by boosting the myeloperoxidase-dependent production of HOCl.

Evaluation of the ability of the angiotensin-converting enzyme inhibitor captopril to scavenge reactive oxygen species

Captopril, an inhibitor of angiotensin-converting enzyme, has been suggested to have additional cardioprotective action because of its ability to act as an antioxidant. The rates of reaction of captopril with several biologically-relevant reactive oxygen species were determined. Captopril reacts slowly, if at all, with superoxide (rate constant less than 10(3) M-1 s-1) or hydrogen peroxide (rate constant less than M-1 s-1). It does not inhibit peroxidation of lipids stimulated by iron ions and ascorbate or by the myoglobin/H2O2 system. Indeed, mixtures of ferric ion and captopril can stimulate lipid peroxidation. Captopril reacts rapidly with hydroxyl radical (rate constant greater than 10(9) M-1 s-1) but might be unlikely to compete with most biological molecules for OH because of the low concentration of captopril that can be achieved in vivo during therapeutic use. Captopril did not significantly inhibit iron ion-dependent generation of hydroxyl radicals from hydrogen peroxide. By contrast, captopril is a powerful scavenger of hypochlorous acid: it was able to protect alpha 1-antiproteinase (alpha 1 AP) against inactivation by this species and to prevent formation of chloramines from taurine. We suggest that the antioxidant action of captopril in vivo is likely to be limited, and may be restricted to protection against damage by hypochlorous acid derived from the action of neutrophil myeloperoxidase.

Erythrocytes protect alpha-1-proteinase inhibitor from oxidative inactivation induced by chemicals, the myeloperoxidase-H2O2-halide system and stimulated polymorphonuclear leukocytes

The oxidative inactivation of the alpha-1-proteinase inhibitor (alpha 1PI) is one of the mechanisms responsible for creating the elastase/antielastase imbalance during inflammation in the lower respiratory tract. Chronic supremacy of elastase may cause degradation of elastin fibers leading to the pulmonary emphysema. In this study we have investigated the effect of erythrocytes (RBC, concentrations 0.125 to 1.5%) on the oxidative inactivation of alpha 1PI by the phorbol myristate acetate-stimulated polymorphonuclear leukocytes (PMNL) and PMNL myeloperoxidase-H2O2-halide system. During exposure of alpha 1PI to both systems in the presence of RBC the significant protection (p less than 0.001) of alpha 1PI was found for all RBC concentrations, e.g. at RBC concentration of 1% the elastase inhibitory capacity (EIC) of alpha 1PI increased from 0 to 60 +/- 6 and 88 +/- 9% of the control value (untreated alpha 1PI), n = 5, respectively. The preincubation of RBC with chloramine-T (1 mM), inhibition of RBC catalase or depletion of RBC reduced glutathione alone did not diminish the capacity of RBC to protect alpha 1PI. However, these treatments together completely deprived RBC of their protective properties. Moreover, we have compared the decrease in the EIC of human blood and its plasma after incubation with H2O2 (0.1 mM to 0.1 M) or chloramine-T (1 microM to 1 mM). For the incubation with H2O2 no decrease in blood EIC was found whereas in plasma the loss of EIC was already visible at a H2O2 concentration of 0.1 mM. Also for the incubation with chloramine-T the EIC of blood was more resistant to oxidant damage than EIC of plasma. It is suggested that RBC contaminations present in the phagocyte inflammatory infiltration in the lower airways may protect alpha 1PI from oxidative inactivation and thus indirectly diminish proteolytic lung injury related to inflammation.

Plasminogen activator is involved in the hCG-induced neutrophil extravasation and vasopermeability increase in the rat testis

The role of proteolytic enzymes in the hCG-induced increase in testicular vasopermeability and neutrophil extravasation was studied using protease inhibitors. An intra-testicular injection of hCG together with incubation medium conditioned by polymorphonuclear leucocytes (PMNs) caused a significant increase in vasopermeability and a coincident extravasation of PMN's from the postcapillary venules in the rat testis. When p-aminobenzamidine, a serine protease inhibitor which inhibits urokinase-type plasminogen activator, was administered together with hCG in the incubation medium, both the permeability increase and PMN extravasation were prevented. Aprotinin, another serine protease inhibitor, and Eglin C, a specific neutrophil elastase and cathepsin G inhibitor were, however, without effect. None of these inhibitors caused any non-specific vascular effects in the testis at the concentrations used. These results support the concept that the hCG-induced increase in vasopermeability in the rat testis is related to extravasation of PMNs and suggest that urokinase-type plasminogen activator is involved in migration of these cells through the postcapillary venular walls.

Superoxide enhances hypochlorous acid production by stimulated human neutrophils

Stimulated neutrophils undergo a respiratory burst discharging large quantities of superoxide and hydrogen peroxide. They also release myeloperoxidase, which catalyses the conversion of hydrogen peroxide and Cl- to hypochlorous acid. Human neutrophils stimulated with opsonized zymosan promoted the loss of monochlorodimedon. This loss was entirely due to hypochlorous acid, since it did not occur in Cl(-)-free buffer, was inhibited by azide and cyanide, and was enhanced by adding exogenous myeloperoxidase. It was not inhibited by desferal, diethylenetriaminepentaacetic acid, mannitol or dimethylsulfoxide, which excluded involvement of the hydroxyl radical. Approx. 30% of the detectable superoxide generated was converted to hypochlorous acid. As expected, formation of hypochlorous acid was completely inhibited by catalase, but it was also inhibited by up to 70% by superoxide dismutase. Superoxide dismutase also inhibited the production of hypochlorous acid by neutrophils stimulated with phorbol myristate acetate. Our results indicate that generation of superoxide by neutrophils enables these cells to enhance their production of hypochlorous acid. Furthermore, inhibition of neutrophil processes by superoxide dismutase and catalase does not necessarily implicate the hydroxyl radical. It is proposed that superoxide may potentiate oxidant damage at inflammatory sites by optimizing the myeloperoxidase-dependent production of hypochlorous acid.

Inactivation of alpha 1-proteinase inhibitor by Cu(II) and hydrogen peroxide

When alpha 1-proteinase inhibitor was treated with 1-5 microM CuSO4 in the presence of H2O2 (250-1000 microM), its elastase inhibitory capacity was markedly decreased. Several other metal ions tested had either very little or no effect. The Cu(II)-catalyzed decreased in the inhibition of elastase activity can also be demonstrated in dialyzed plasma. These results are consistent with the hypothesis that in several pathological conditions in which extracellular copper levels are elevated, Cu(II)-catalyzed peroxidation of alpha 1-proteinase inhibitor may occur at sites of inflammation where H2O2 is secreted as a major product by activated phagocytes.

Naphthalenes as inhibitors of myeloperoxidase: direct and indirect mechanisms of inhibition

Control of myeloperoxidase (MPO) may be an important consideration in disorders where excessive PMN elastase activity is a significant factor. There are, however, two mechanisms for the apparent regulation of MPO: 1) inhibit the enzyme directly, and ii) prevent the ensuing HOC1 induced oxidation by using a surrogate reducing agent. Appropriate methodology has been devised to distinguish true MPO inhibitors. With the exception of NaN3, many MPO inhibitors fall into the latter category and do not actually regulate the enzyme. Several potent organic inhibitors have been discovered, which, because of their structural selectivity, appear to associate specifically with a binding site on the enzyme, rather than attaching indiscriminately to a hydrophobic domain. By controlling the enzyme, these compounds protect alpha-1-PI from MPO induced damage, and could serve better than antioxidants to define the role of MPO in elastase induced injury.

How to characterize a biological antioxidant

An antioxidant is a substance that, when present at low concentrations compared to those of an oxidizable substrate, significantly delays or prevents oxidation of that substrate. Many substances have been suggested to act as antioxidants in vivo, but few have been proved to do so. The present review addresses the criteria necessary to evaluate a proposed antioxidant activity. Simple methods for assessing the possibility of physiologically-feasible scavenging of important biological oxidants (superoxide, hydrogen peroxide, hydroxyl radical, hypochlorous acid, haem-associated ferryl species, radicals derived from activated phagocytes, and peroxyl radicals, both lipid-soluble and water-soluble) are presented, and the appropriate control experiments are described. Methods that may be used to gain evidence that a compound actually does function as an antioxidant in vivo are discussed. A review of the pro-oxidant and anti-oxidant properties of ascorbic acid that have been reported in the literature leads to the conclusion that this compound acts as an antioxidant in vivo under most circumstances.

Nicotine inhibits alpha-1-proteinase inhibitor inactivation by oxidants derived from human polymorphonuclear leukocytes

Cigarette smoke can inactivate the alpha-1-proteinase inhibitor (alpha 1PI) by oxidative mechanisms and thus predisposes to the development of pulmonary emphysema. There are differences between the whole smoke and gas phase acting as alpha 1PI inactivators in vitro which suggests that the whole smoke is less oxidizing than the gas phase. Also studies on alpha 1PI oxidative inactivation in the lung of cigarette smokers gave controversial results. The reductive properties of cigarette tar which contains most of smoke nicotine may be some explanation of it. Therefore in this study we have investigated the effect of nicotine (0.4 mumol/l to 4 mmol/l) on the oxidative inactivation of human alpha 1PI by phorbol myristate acetate-activated polymorphonuclear leukocytes (PMNL), chloramine-T (15 mumol/l), hydrogen peroxide (15 mmol/l) and the superoxide radical (O2-.) generating system-xanthine (0.2 mmol/l)-xanthine oxidase (80 U/l). Nicotine at concentrations of greater than 40 mumol/l protected alpha 1PI from stimulated PMNL. The preincubation of PMNL with these concentrations of nicotine did not diminish their ability to inactivate alpha 1PI after stimulation. Nicotine (above 0.4 mumol/l) also protected alpha 1PI from chloramine-T but not from H2O2. The inhibition of O2-.-mediated alpha 1PI inactivation by nicotine was low and was observed only at a concentration of 4 mmol/l. This nicotine concentration did not affect xanthine oxidase activity. It is suggested that cigarettes with low nicotine contents can cause greater oxidative lung injury than their high nicotine counterparts and be a greater risk factor for the development of lung emphysema.

Scavenging of hypochlorous acid and of myoglobin-derived oxidants by the cardioprotective agent mercaptopropionylglycine

Mercaptopropionylglycine (MPG) has a marked cardioprotective action in several model systems of ischaemia-reoxygenation injury. Suggested mechanisms of action include scavenging of hydroxyl radical and of hypochlorous acid and reacting with an oxidant formed by reaction of myoglobin with H2O2, thereby slowing lipid peroxidation stimulated by myoglobin-H2O2 mixtures. This oxidant seems not to be singlet O2 or hydroxyl radical. Studies in vitro show that scavenging of hypochlorous acid is a feasible mechanism of cardioprotective action for MPG in vivo in ischaemia/reperfusion systems to which neutrophil-mediated injury contributes. However, the poor ability of MPG to inhibit lipid peroxidation stimulated by myoglobin/H2O2 mixtures and its ability to increase iron ion release from myoglobin in the presence of a large excess of H2O2 suggests that MPG is unlikely to protect the myocardium by interfering with oxidants produced by the myoglobin-H2O2 system.

Chemotactic activity of histones for human polymorphonuclear leukocytes

The chemotactic activity of histones for human polymorphonuclear leukocytes (PMNL) was investigated using the under-agarose method. Total histone and histone fractions H1, H2a, H2b, H3, H4 were prepared from calf thymus and dissolved in phosphate buffered saline (PBS) pH 7.4. At concentrations of 1 and 0.1 mg/ml all histone preparations were chemotactic for PMNL. The PMNL migration (expressed as a chemotactic index) to total histone (1 mg/ml) was 1.5 +/- 0.2 (n = 8) and to histone fractions it ranged from 1.2 to 1.4. The injection of total histone (50 micrograms) to the mouse pleural cavity induced cell influx. The mean PMNL number found in this cavity (0.33 +/- 0.15 X 10(6] was 3.6-fold higher in this group as compared to PBS-treated animals. Human PMNL during 60 min incubation with total histone (10 micrograms/ml) or with total histone and cytochalasin B (CB, 4.8 micrograms/ml) released 12.9 +/- 2.5 (n = 9) and 40.6 +/- 4.9 (n = 4) % of the total myeloperoxidase cell activity. Total histone (1 to 10 micrograms/ml) did not stimulate hydrogen peroxide generation independently of the presence of CB and had no influence on its production induced by phorbol myristate acetate. Our results suggest that histones released from cell debris in the place of inflammation could secondarily modulate to some extent its course by enhancing PMNL influx and their activation. These findings may be important for the course of inflammatory response in lungs especially in the light of their susceptibility to proteolytic injury.

Apparent inactivation of alpha 1-antiproteinase by sulphur-containing radicals derived from penicillamine

alpha 1-Antiproteinase is the major inhibitor of proteolytic enzymes, such as elastase, in human plasma. Its elastase-inhibitory capacity can be inactivated by exposure to hydroxyl radicals (.OH) generated either by pulse radiolysis or by an Fe3+-EDTA/H2O2/ascorbic acid system. Inactivation of alpha 1-antiproteinase by radiolytically-generated .OH under anoxic conditions was decreased by adding a range of anti-inflammatory drugs to the reaction mixtures, including the thiol compound penicillamine. However, under conditions favouring formation of oxysulphur radicals, protection by thiols such as penicillamine was much decreased. It is proposed that sulphur-containing radicals resulting from attack of biologically-produced oxidants upon penicillamine in the presence of O2 can themselves inactivate alpha 1-antiproteinase, and that such radicals might contribute to the side-effects produced by penicillamine or gold thiol therapy in rheumatoid arthritis.

Adult respiratory distress syndrome

The Adult Respiratory Distress Syndrome (ARDS) is a fulminant form of respiratory failure affecting many seriously ill patients. The early manifestations of ARDS are caused by increased permeability of the alveolo-capillary barrier leading to pulmonary edema, stiff lungs, and a large right-to-left intrapulmonary shunt. Polymorphonuclear leukocytes (PMNS) are involved in the pathogenesis of most ARDS, and multiple PMN mechanisms can effect pulmonary injury; interactions between PMN adherence, proteolytic enzyme release, and oxygen radical production are emphasized. ARDS therapy remains largely supportive and has had little impact on mortality. The complications of infection and multiorgan failure play important roles in determining ARDS outcome.

Murexide bleaching: a new direct assay method for characterizing reactive oxygen species

The murexide (5,5'-nitrilodibarbituric acid, monoammonium salt) is an efficient scavenger for superoxide and hydroxyl radicals. When exposed to oxygen radicals, murexide is converted to a colorless alloxan derivative and its absorbance at 520 nm decreases in proportion to the radicals produced. It is used to detect these reactive oxygen species in biochemical systems such as acetaldehyde oxidation by xanthine oxidase and the respiratory burst of polymorphonuclear leukocytes induced by phorbol 12-myristate, 13-acetate. The method was sensitive enough to allow direct monitoring of the production of superoxides from 10(6) phorbol 12-myristate, 13-acetate polymorphonuclear leukocyte-stimulated cells. Moreover, murexide bleaching is inhibited in the presence of radical scavengers, allowing a comparison of their scavenging activities.

Novel therapy for Alzheimer's disease

Recent results support the hypothesis that microglia and/or macrophages of the brain, by producing oxidants, could play a role in the local inactivation of the Kunitz protease inhibitor (KPI) domain of beta-amyloid precursor protein (APP), thereby facilitating deposition of abnormal amyloid filaments in patients with Alzheimer's disease (AD). Protease inhibitors and/or free radical scavengers might serve as therapy for the amyloidosis of AD.

Interaction of hCG with testicular interstitial fluid produces a leucotactic factor

An intratesticular injection of hCG (5 ng) mixed with testicular interstitial fluid (IF) increases vascular permeability in the rat testis. The present results show that the permeability increase induced by this treatment is accompanied by a massive accumulation of polymorphonuclear leucocytes (PMNs) in both the testicular postcapillary venules and the interstitium. Depletion of neutrophils in the circulation by treatment with anti-neutrophil serum significantly inhibited the permeability increase induced by this treatment. An intratesticular injection of PMNs (10(7) cells) or hCG alone had no effect on permeability, but a combination of the two caused a significant increase in permeability. The PMNs were found to secrete a component in vitro which, when injected intratesticularly together with hCG, caused a increase and a simultaneous massive accumulation of PMNs in the postcapillary venules and interstitium. This permeability increase was prevented by the serine protease inhibitor p-aminobenzamidine, suggesting an involvement of the plasminogen activator system in the response. The results suggest that hCG interacts with an IF component to produce leucotactic factors that increase permeability indirectly by attracting PMNs to the tissue, and that the IF component may originate in the PMNs.

Effects of chlorinated amines on endothelial and epithelial barriers in vitro and ex vivo

Chlorinated amines are long-lived oxidants released from inflammatory cells. They have been observed to alter the function of important inflammatory molecules. Whether they can contribute directly to the inflammatory alteration of cellular barriers is not known. Monolayers of cultured porcine pulmonary artery endothelial cells, monolayers of cultured dog kidney tubular epithelial cells (MDCK), and the vascular surface of an isolated perfused rabbit lung were exposed to taurine chloramine. Taurine chloramine increased albumin flux across the endothelium, decreased the electrical resistance across the epithelium, and increased the hydraulic conductivity of the rabbit lung vasculature. These alterations in barrier function appeared to occur in the absence of cytolysis of the cells making up the barriers. These results suggest that chlorinated amines, long-lived oxidants released from inflammatory cells, may contribute directly to alteration of cellular barriers.

Free radicals inactivate human neutrophil elastase and its inhibitors with comparable efficiency

Free radicals produced in a Fenton reaction (H202/Cu), modelling some xenobiotic and cell-mediated inflammatory affronts, efficiently inactivated the elastase-inhibitor eglin, but equally, human neutrophil elastase itself. Elastase activity was not regenerated from proteinase/inhibitor complexes during radical attack. Three different elastase inhibitors, eglin, secretory leukocyte proteinase inhibitor and alpha-1-proteinase inhibitor were all similarly sensitive to inactivation. Unlike certain oxidants which can selectively inactivate alpha-1-proteinase inhibitor, free radicals may influence comparably the availability of both proteinase inhibitors and their targets.

Interactions between cancer cells and the microvasculature: a rate-regulator for metastasis

Hematogenous metastasis is a major consideration in the staging, treatment and prognosis of patients with cancer. Key events affecting hematogeneous metastasis occur in the microvasculature. This is a brief, selective review of some interactions involving cancer cells and the microvasculature in pathologic sequence, specifically: (1) intravasation of cancer cells; (2) the arrest of circulating cancer cells in the microvasculature; (3) cancer cell trauma associated with arrest; (4) microvascular trauma; (5) the inflammatory; and (6) the hemostatic coagulative responses associated with arrest, and finally (7) angiogenesis, leading to tumor vascularization. The evidence shows that through a series of complex interactions with cancer cells, the microvasculature acts as a rate-regulator for the metastatic process, in addition to providing routes for cancer cell dissemination and arrest sites for cancer cell emboli.

Determination of carbonyl groups in oxidatively modified proteins by reduction with tritiated sodium borohydride

Oxidatively modified proteins have been implicated in a variety of physiologic and pathologic processes. Oxidative modification typically causes inactivation of enzymes and also the introduction of carbonyl groups into amino acid side chains of the protein. We describe a method to quantify oxidatively modified proteins through reduction of these carbonyl groups with tritiated borohydride. The technique was applied to purified, oxidatively modified glutamine synthetase and to bronchoalveolar lavage fluid from dogs and from humans. Since the protein content of lung lavage fluid is low, a very sensitive method was required to measure the oxidized residues. Reduction of the carbonyl group generated during oxidation of proteins with tritiated borohydride provided excellent sensitivity. Incorporation of tritium was directly proportional to the amount of protein with a range from 10 to 1000 micrograms. Should moieties other than amino acids be labeled, they are easily removed by rapid benchtop hydrolysis of the protein followed by chromatography on Dowex 50.

Inhibition of neutrophil elastase by alpha-1-proteinase inhibitor oxidized by activated neutrophils

The present study was aimed at testing whether neutrophil-oxidized alpha 1-proteinase inhibitor (alpha 1PI) is a slow-binding inhibitor of neutrophil elastase like N-chlorosuccinimide-oxidized alpha 1PI or whether it does not inhibit this enzyme at all as currently thought. alpha 1PI was reacted with phorbol-myristate-acetate-activated neutrophils and isolated from the oxidation medium by fast protein liquid chromatography on an anion exchange column. When sufficient time was allowed for oxidized alpha 1PI to react with neutrophil elastase (2 h), enzyme-inhibitor complex formation could be demonstrated by three means: (1) inhibition of elastase activity, (2) detection of the complex using an enzyme-linked immunosorbent assay specific for the native alpha 1PI-elastase complex, and (3) SDS-polyacrylamide gel electrophoresis, which evidenced a complex with a molecular weight of 80,000. Porcine pancreatic elastase was not inhibited. Neutrophil-oxidized alpha 1PI behaved as an irreversible inhibitor of neutrophil elastase, as revealed by the kinetic analysis of the inhibition reaction. The rate constant for the inhibition of neutrophil elastase by neutrophil-oxidized alpha 1PI (0.76 +/- 0.22 x 10(4) M-1 s-1) was close to that for the inhibition of the enzyme by N-chlorosuccinimide-oxidized alpha 1PI (0.96 +/- 0.24 x 10(4) M-1 s-1), but it was more than three orders of magnitude lower than that for the reaction of native alpha 1PI with neutrophil elastase. Both native and oxidized alpha 1PI were temporary elastase inhibitors: the enzyme slowly and spontaneously escaped the complex with formation of an inactive alpha 1PI derivative with a molecular weight of 49,000.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential absorption of vitamin D3 and 1,25-dihydroxyvitamin D3 by intestinal jejunal cells of the rat

An intestinal perfusion technique is reported for the study of the differential absorption of vitamin D3 and its active metabolite, 1,25-dihydroxyvitamin D3, through intact jejunal segments of rats. Samples of introduced and collected perfusates, intestinal homogenates, and portal blood were assayed for [14C]vitamin D3 or [3H]1 alpha,25-dihydroxyvitamin D3 content at specified time intervals in control rats and in rats injected ip with cycloheximide (3 mg/kg body weight). Vitamin D3 uptake from the perfusates in cycloheximide-treated groups did not differ from controls. However, an approximately 2-fold increase of vitamin D3 retention in the perfused intestinal segments was observed after cycloheximide treatment. A 0.25-fold decrease was observed in the uptake of 1,25-dihydroxyvitamin D3 from the perfusates after cycloheximide treatment, and an approximately 2.5-fold increase in its intestinal retention was noted. An increase in the active metabolite concentration was observed in the portal venous system 75 min after initiation of perfusion, with no detectable amounts being recorded prior to the first hour. The results suggest that intracellular binding proteins may be involved in the transport of labeled vitamin D3 and labeled 1,25-dihydroxyvitamin D3 through rat enterocytes. Furthermore, vitamin D3 may have been more readily channeled through an esterification process than 1,25-dihydroxyvitamin D3 prior to their appearance in the portal venous system.

The antioxidant action of N-acetylcysteine: its reaction with hydrogen peroxide, hydroxyl radical, superoxide, and hypochlorous acid

N-acetylcysteine has been widely used as an antioxidant in vivo and in vitro. Its reaction with four oxidant species has therefore been examined. N-acetylcysteine is a powerful scavenger of hypochlorous acid (H--OCl); low concentrations are able to protect alpha 1-antiproteinase against inactivation by HOCl. N-acetylcysteine also reacts with hydroxyl radical with a rate constant of 1.36 X 10(10) M-1s-1, as determined by pulse radiolysis. It also reacts slowly with H2O2, but no reaction of N-acetylcysteine with superoxide (O2-) could be detected within the limits of our assay procedures.

Enhancement of proteinase-mediated degradation of proteins modified by chlorination

1. Pretreatment of some proteins (albumin, immunoglobulin G, elastin and fibrinogen) with hypochlorite or with the MPO-H2O2-Cl- system increased their susceptibility to proteolysis by trypsin, chymotrypsin or elastase. 2. The optimal activities of these three proteinases were attained at a different extent of albumin chlorination. 3. Elastase was found to develop a specially efficient activity towards chlorinated albumin or chlorinated elastin being by itself resistant to chlorinating species.