Peroxiredoxin 2 oxidation reveals hydrogen peroxide generation within erythrocytes during high-dose vitamin C administration

Intravenous infusion of high dose (>10 g) vitamin C (IVC) is a common alternative cancer therapy. IVC results in millimolar levels of circulating ascorbate, which is proposed to generate cytotoxic quantities of H₂O₂ in the presence of transition metal ions. In this study we report on the in vitro and in vivo effects of millimolar ascorbate on erythrocytes. Addition of ascorbate to whole blood increased erythrocyte intracellular ascorbate approximately 35-fold. Within 10 min of ascorbate addition, we detected increased oxidation of erythrocyte peroxiredoxin 2 (Prx2), a major thiol antioxidant protein and a sensitive marker of H₂O₂ production. Up to 50% of Prx2 was present in the oxidised form after 60 min. The presence of extracellular catalase, removal of plasma or the addition of a metal chelator did not prevent ascorbate-induced Prx2 oxidation, suggesting that the H₂O₂ responsible for Prx2 oxidation was generated within the erythrocyte. Ascorbate is known to increase the rate of haemoglobin autoxidation and H₂O₂ production. Through spectral monitoring of oxidised haemoglobin we estimated a generation rate of 15 μM H₂O₂/min inside erythrocytes. We also investigated changes in erythrocyte ascorbate concentration and Prx2 oxidation following IVC infusion in a cohort of patients with cancer. Plasma ascorbate levels ranged from 7.8 to 35 mM immediately post infusion, while erythrocyte ascorbate levels reached 1.5–3.4 mM 4 h after beginning infusion. Transient oxidation of erythrocyte Prx2 was observed. We conclude that erythrocytes accumulate ascorbate during IVC infusion, providing a significant reservoir of ascorbate, and this ascorbate increases H₂O₂ generation within the cells. The consequence of increased erythrocyte Prx2 oxidation warrants further investigation.

Ascorbate modulates the hypoxic pathway by increasing intracellular activity of the HIF hydroxylases in renal cell carcinoma cells

Purpose: Protein levels and activity of the hypoxia-inducible transcription factors HIF-1 and HIF-2 are controlled by hydroxylation of the regulatory alpha chains. Proline hydroxylases (PHDs) target the protein for degradation via the von-Hippel-Lindau (VHL)-ubiquitin-ligase complex, and asparagine hydroxylation by Factor Inhibiting HIF (FIH) leads to transcriptional inactivation. In cell-free systems, these enzymes require ascorbate as a cofactor, and this is also inferred to be an intracellular requirement for effective hydroxylation. However, how intracellular concentrations of ascorbate affect hydroxylase activity is unknown. In this study, we investigated the modulation of the regulatory hydroxylases in cancer cells by intracellular ascorbate.

Materials and methods: To facilitate this investigation, we used clear cell renal carcinoma cell lines that were VHL-proficient (Caki-1), with a normal hypoxic response, or VHL-defective (Caki-2 and 786-0), with uncontrolled accumulation of HIF-α chains. We monitored the effect of intracellular ascorbate on the hypoxia-induced accumulation of HIF-1α, HIF-2α and the expression of downstream HIF targets BNIP3, cyclin D1 and GLUT1. Changes in hydroxylation of the HIF-1α protein in response to ascorbate were also investigated in 786-0 cells gene-modified to express full-length HIF-1α (786-HIF1).

Results: In VHL-proficient cells, hypoxia induced accumulation of HIF-1α and BNIP3 which was dampened in mild hypoxia by elevated intracellular ascorbate. Increased HIF-2α accumulation occurred only under severe hypoxia and this was not modified by ascorbate availability. In VHL-defective cells, ascorbate supplementation induced additional accumulation of HIF under hypoxic conditions and HIF pathway proteins were unchanged by oxygen supply. In 786-HIF1 cells, levels of hydroxylated HIF-1α were elevated in response to increasing intracellular ascorbate levels.

Conclusion: Our data provide evidence that the hypoxic pathway can be modulated by increasing HIF hydroxylase activity via intracellular ascorbate availability. In VHL-defective cells, accumulation of HIF-alpha proteins is independent of hydroxylation and is unaffected by intracellular ascorbate levels.

Ascorbate availability affects tumor implantation-take rate and increases tumor rejection in Gulo-/- mice

In solid tumors, HIF1 upregulates the expression of hundreds of genes involved in cell survival, tumor growth, and adaptation to the hypoxic microenvironment. HIF1 stabilization and activity are suppressed by prolyl and asparagine hydroxylases, which require oxygen as a substrate and ascorbate as a cofactor. This has led us to hypothesize that intracellular ascorbate availability could modify the hypoxic HIF1 response and influence tumor growth. In this study, we investigated the effect of variable intracellular ascorbate levels on HIF1 induction in cancer cells in vitro, and on tumor-take rate and growth in the Gulo^-/- mouse. These mice depend on dietary ascorbate, and were supplemented with 3,300 mg/L, 330 mg/L, or 33 mg/L ascorbate in their drinking water, resulting in saturating, medium, or low plasma and tissue ascorbate levels, respectively. In Lewis lung carcinoma cells (LL/2) in culture, optimal ascorbate supplementation reduced HIF1 accumulation under physiological but not pathological hypoxia. LL/2, B16-F10 melanoma, or CMT-93 colorectal cancer cells were implanted subcutaneously into Gulo^-/- mice at a range of cell inocula. Establishment of B16-F10 tumors in mice supplemented with 3,300 mg/L ascorbate required an increased number of cancer cells to initiate tumor growth compared with the number of cells required in mice on suboptimal ascorbate intake. Elevated ascorbate intake was also associated with decreased tumor ascorbate levels and a reduction in HIF1α expression and transcriptional activity. Following initial growth, all CMT-93 tumors regressed spontaneously, but mice supplemented with 33 mg/L ascorbate had lower plasma ascorbate levels and grew larger tumors than optimally supplemented mice. The data from this study indicate that improved ascorbate intake is consistent with increased intracellular ascorbate levels, reduced HIF1 activity and reduced tumor initiation and growth, and this may be advantageous in the management of cancer.

Human skeletal muscle ascorbate is highly responsive to changes in vitamin C intake and plasma concentrations

BACKGROUND

Vitamin C (ascorbate) is likely to be essential for skeletal muscle structure and function via its role as an enzyme cofactor for collagen and carnitine biosynthesis. Vitamin C may also protect these metabolically active cells from oxidative stress.

OBJECTIVE

We investigated the bioavailability of vitamin C to human skeletal muscle in relation to dietary intake and plasma concentrations and compared this relation with ascorbate uptake by leukocytes.

DESIGN

Thirty-six nonsmoking men were randomly assigned to receive 6 wk of 0.5 or 2 kiwifruit/d, an outstanding dietary source of vitamin C. Fasting blood samples were drawn weekly, and 24-h urine and leukocyte samples were collected before intervention, after intervention, and after washout. Needle biopsies of skeletal muscle (vastus lateralis) were carried out before and after intervention.

RESULTS

Baseline vastus lateralis ascorbate concentrations were ~16 nmol/g tissue. After intervention with 0.5 or 2 kiwifruit/d, these concentrations increased ~3.5-fold to 53 and 61 nmol/g, respectively. There was no significant difference between the responses of the 2 groups. Mononuclear cell and neutrophil ascorbate concentrations increased only ~1.5- and ~2-fold, respectively. Muscle ascorbate concentrations were highly correlated (P < 0.001) with dietary intake (R = 0.61) and plasma concentrations (R = 0.75) in the range from 5 to 80 μmol/L.

CONCLUSIONS

Human skeletal muscle is highly responsive to vitamin C intake and plasma concentrations and exhibits a greater relative uptake of ascorbate than leukocytes. Thus, muscle appears to comprise a relatively labile pool of ascorbate and is likely to be prone to ascorbate depletion with inadequate dietary intake. This trial was registered at the Australian New Zealand Clinical Trials Registry (www.anzctr.org.au) as ACTRN12611000162910.

Regulation of apoptosis by vitamin C. Specific protection of the apoptotic machinery against exposure to chlorinated oxidants

We have investigated the ability of intracellular vitamin C to protect human umbilical vein endothelial cells from exposure to hypochlorous acid (HOCl) and a range of derived chloramines. Ascorbate provided minimal protection against the cytotoxicity induced by these oxidants, as measured by propidium iodide uptake. In contrast, there was a marked effect on apoptosis, monitored by caspase-3 activation and phosphatidylserine exposure. Extended incubation of the cells with glycine chloramine or histamine chloramine completely blocked apoptosis initiated in the cells by serum withdrawal. This effect was significantly abrogated by ascorbate. Inhibition of apoptosis required the oxidant to be present for an extended period after serum withdrawal and occurred prior to caspase-3 activation. General protection of thiols by ascorbate was not responsible for the protection of apoptosis, because intracellular oxidation by HOCl or chloramines was not prevented in supplemented cells. The results suggest a new role for vitamin C in the regulation of apoptosis. We propose that, by protection of an oxidant-sensitive step in the initiation phase, ascorbate allows apoptosis to proceed in endothelial cells under sustained oxidative stress.

Hypochlorous acid stimulation of the mitogen-activated protein kinase pathway enhances cell survival

We investigated the activation of three subfamilies of mitogen-activated protein kinases (MAP kinase), the extracellular regulated kinase (ERK1/2), p38, and c-Jun N-terminal kinase (JNK), by the myeloperoxidase-derived oxidant HOCl, in human umbilical vein endothelial cells (HUVEC) and human skin fibroblasts. Treatment of fibroblasts with 10-30 microM HOCl induced a dose-dependent increase in the tyrosine phosphorylation of several proteins. ERK1/2 was activated by exposure to sublethal concentrations of reagent HOCl or by HOCl generated by myeloperoxidase as shown by immune complex kinase assays. Maximum activation was seen at 20 microM and peak activation occurred within 10 min. Western blot analysis demonstrated activation of p38 with 30 microM HOCl, occurring at 15-30 min. No activation of JNK was detected in the concentration range investigated. These results show that HOCl is able to activate MAP kinases. Effective doses were considerably lower than with H2O2 and the lack of JNK activation contrasts with the activation frequently seen with H2O2. Exposure to HOCl caused a loss of viability in HUVEC that was markedly enhanced when ERK1/2 activation was inhibited by U0126. This suggests that the activation of ERK promotes cell survival in response to the oxidative challenge.

Fatty acid chlorohydrins and bromohydrins are cytotoxic to human endothelial cells

Reaction of unsaturated lipids with the hypohalous acids (hypochlorous acid and hypobromous acid) results in the addition of the halide (X) across double bonds to form halohydrins (-CH2CH(OH)CH(X)CH2-). These modified lipids could be potentially destabilising to cell membranes due to their increased polarity. We have investigated the effect of pre-formed halohydrins on human umbilical vein endothelial cells (HUVEC) by incubating cultured cells with oleic acid micelles containing chlorohydrins or bromohydrins. Cell detachment and necrotic death were observed with increasing doses of halohydrins, whereas the cells were unaffected by equivalent doses of oleic acid. Bromohydrins caused more lysis than did chlorohydrins at equivalent doses. Complete lysis was seen with 200 microM fatty acid/chlorohydrin micelles and with 50 microM fatty acid/bromohydrin micelles. Chlorohydrin uptake was much less than the oleic acid control whereas bromohydrins were incorporated into the endothelial cells similarly to oleic acid. This difference or the bulkier nature of the bromohydrins could account for their increased toxicity. This study has demonstrated the potential toxicity of the halohydrins, and implications for their formation in inflammation are discussed.

Glutathione oxidation by hypochlorous acid in endothelial cells produces glutathione sulfonamide as a major product but not glutathione disulfide

Treatment of cells with hypochlorous acid (HOCl) at sublethal doses causes a concentration-dependent loss in reduced glutathione (GSH) levels. We have investigated the products of the reaction of HOCl with GSH in human umbilical vein endothelial cells. Despite a complete loss of GSH, there were only very small increases in intracellular and extracellular glutathione disulfide and glutathione sulfonic acid after exposure to HOCl. (35)S labeling of the GSH pool showed only a minimal increase in protein-bound GSH, suggesting that S-thiolation was not a major contributor to HOCl-mediated loss of GSH in endothelial cells. Rather, the products of the reaction were mostly exported from cells and included a peak that co-eluted with the cyclic sulfonamide that is a product of the reaction of GSH with reagent HOCl. Evidence of this species in endothelial cell supernatants after HOCl treatment was also obtained using electrospray mass spectrometry. In conclusion, exposure to HOCl causes the irreversible loss of cellular GSH with the formation of novel products that are rapidly exported from the cell, and resynthesis of GSH will be required to restore levels. The loss of GSH would alter the redox state of the cell and compromise its defenses against further oxidative stress.

Living with a killer: the effects of hypochlorous acid on mammalian cells

The production of hypochlorous acid (HOCl) by the myeloperoxidase-H2O2-Cl- system of phagocytes plays a vital role in the ability of these cells to kill a wide range of pathogens. However, the generation of a potent oxidant is not without risk to the host, and there is evidence that HOCl contributes to the tissue injury associated with inflammation. In this review, we discuss the biological reactivity of HOCl, and detail what is known of how it interacts with mammalian cells. The outcome of exposure is dependent on the dose of oxidant, with higher doses causing necrosis, and apoptosis or growth arrest occurring with lower amounts. Glutathione (GSH) and protein thiols are easily oxidized, and are preferred targets with low, sublethal amounts of HOCl. Thiol enzymes vary in their sensitivity to HOCl, with glyceraldehyde-3-phosphate dehydrogenase being most susceptible. Indeed, loss of activity occurred before GSH oxidation. The products of these reactions and the ability of cells to regenerate oxidized thiols are discussed. Recent reports have indicated that HOCl can activate cell signaling pathways, and these studies may provide important information on the role of this oxidant in inflammation.

Myeloperoxidase

This review covers recent advances in the biology of myeloperoxidase. Mechanisms of posttranslational processing and how these fail in some of the common deficiency mutants are discussed. We also review the enzymology that points to myeloperoxidase having a number of physiologic substrates in addition to chloride and the evidence that it produces hypochlorous acid in the neutrophil phagosome in sufficient quantities to be bactericidal. Evidence is accumulating that myeloperoxidase-derived oxidants modify biologic macromolecules and cell-regulatory pathways and that they play a role in atherosclerosis. Investigation of disease incidence in relation to a polymorphism in the promoter region of the gene has produced interesting associations. These links with inflammatory diseases can now be pursued further using specific biomarkers of myeloperoxidase activity.

Hypochlorous acid causes caspase activation and apoptosis or growth arrest in human endothelial cells

We have investigated the effect of hypochlorous acid (HOCl) on cultured human umbilical-vein endothelial cells and shown that, whereas higher concentrations cause rapid necrosis, smaller amounts of this oxidant induce apoptosis or growth arrest. Exposure to 20-40 nmol of HOCl per 1.2x10(5) cells initiated apoptosis that was determined morphologically, by the identification of apoptotic nuclei with Hoechst 33342, and by detection of phosphatidylserine on the outer membrane. Degraded DNA was detected by flow cytometry. HOCl induced caspase activity; specific inhibition of caspases was shown to prevent apoptosis. No caspase activation could be detected with 50 nmol of HOCl per 1.2x10(5) cells, a dose that caused more extensive necrosis. Lower doses of HOCl, which did not cause cell death, resulted in a transient growth arrest that was apparent with as little as 5 nmol of HOCl per 1.2x10(5) cells. These results show that HOCl can modify cellular responses that are dependent on signal transduction pathways in a manner similar to that of other oxidants.

Loss of GSH and thiol enzymes in endothelial cells exposed to sublethal concentrations of hypochlorous acid

We investigated the effect of sublethal concentrations of hypochlorous acid (HOCl) on intracellular thiol groups. Exposure of human umbilical vein endothelial cells to HOCl caused a decrease in cell viability, with concentrations of </=25 microM HOCl being sublethal. At these concentrations, we saw a loss of glutathione and total protein thiol groups. Of the thiol enzymes we investigated, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) was particularly susceptible to inactivation, creatine kinase was moderately susceptible, and lactate dehydrogenase was unaffected by HOCl at the concentrations used. Similar results were obtained with HOCl generated over 30 min by myeloperoxidase. GAPDH activity could be regenerated on reincubation of cells in Hanks' balanced salt solution or reduction with dithiothreitol. In contrast, glutathione loss was not reversible, and further decreased with time. Cellular ATP levels decreased with sublethal HOCl concentrations and this appeared to be unrelated to the inactivation of GAPDH. Our results demonstrate that intracellular thiol groups differ in their reactivity with HOCl and suggest that HOCl may be able to regulate specific cellular functions.

Presenting treatment protocols with Web technology

This paper describes a Web-based version of a protocol information system (ProtoVIEW) with which a wide range of diagnostic or therapeutic protocols can be retrieved and viewed. The Web-based version contains all functionalities of the non web-based version plus several new functionalities. The web version contains an X-ray viewer and a great deal of interactivity such as validation of electronic patient data forms. The most important additional function is the context sensitive protocol support which may lead to improved protocol adherence. Finally, the web-based version can be accessed from any working place since patient data and protocols are stored centrally.

Building a flexible protocol information system with ready for use' web-technology

This paper describes how web technology, currently available, can be used to build a fast and easy flexible protocol information system. The interface design and functionalities of the system were based on experiences with a previous version of a protocol information system (ProtoVIEW). A wide range of diagnostic or therapeutic protocols could be retrieved and viewed with ProtoVIEW. The Web-based version contains all functionalities of the non web-based version plus several new functionalities. The web version contains an X-ray viewer and a great deal of interactivity such as validation of electronic patient data forms. The most important additional function is the context sensitive protocol support that may lead to improved protocol adherence. Finally, the web-based version can be accessed from any working place since patient data and protocols are stored centrally.

Comparison of human red cell lysis by hypochlorous and hypobromous acids: insights into the mechanism of lysis

Human red blood cells are lysed by the neutrophil-derived oxidant hypochlorous acid (HOCl), although the mechanism of lysis is unknown. Hypobromous acid (HOBr), a similarly reactive oxidant, lysed red cells approx. 10-fold faster than HOCl. Therefore we compared the effects of these oxidants on thiols, membrane lipids and proteins to determine which reactions are associated with lysis. There was no difference in the loss of reduced glutathione or membrane thiols with either oxidant, but HOBr reacted more readily with membrane lipids and proteins. Bromohydrin derivatives of phospholipids and cholesterol were seen at approx. one-tenth the level of oxidant than chlorohydrins were. However, these products were detected only with high concentrations of HOCl or HOBr, which caused instant haemolysis. Membrane protein modification occurred at much lower doses of oxidant and was more closely correlated with lysis. SDS/PAGE analysis showed that band 3, the anion transport protein, was lost at the lowest dose of HOBr and at the higher concentrations of HOCl. Labelling the red cells with eosin 5-maleimide, a fluorescent label for band 3, suggested possible clustering of this protein in oxidant-exposed cells. There was also irreversible cross-linking of all the major membrane proteins; this reaction occurred more readily with HOBr. The results indicate that membrane protein modification is the reaction responsible for HOCl-mediated lysis. These effects, and particularly cross-link formation, might result in clustering of band 3 and other membrane and cytoskeletal proteins to form haemolytic pores.

Modification of red cell membrane lipids by hypochlorous acid and haemolysis by preformed lipid chlorohydrins

Hypochlorous acid (HOCl), a strong oxidant generated by the myeloperoxidase system of neutrophils and monocytes, has been implicated in inflammatory tissue damage by these cells. Reaction of HOCl with the double bonds of unsaturated lipids produces alpha, beta-chlorohydrin isomers. We have exposed red cell membranes to HOCl and used thin layer chromatography (TLC) of the extracted lipids and enzyme-linked immunosorbent assay (ELISA), using an antichlorohydrin monoclonal antibody, to show that fatty acyl chlorohydrins are formed. The ELISA was approximately 25 fold more sensitive than TLC, and chlorohydrins were detected when membranes from 10(6) cells were treated with > or = 0.16 nmoles HOCl. Lipid chlorohydrins are more polar and bulky than their parent lipids and as such could affect membrane stability and function. To determine the effect of incorporation of lipid chlorohydrins into cell membranes, preformed fatty acid and cholesterol chlorohydrins were incubated with red cells. Lysis was measured as release of haemoglobin and incorporation of lipids was determined by 14C scintillation counting. Addition of HOCl-treated oleic acid to red cells resulted in rapid lysis of a fraction of the cells in a concentration dependent manner. HOCl-treated cholesterol also caused a small amount of cell lysis that was predominantly due to chlorohydrin 3, one of the three major cholesterol chlorohydrin products. Chlorohydrin 3, which has a decreased planarity and polarity, was also primarily responsible for altering the critical micelle concentration of HOCl-treated cholesterol-containing liposomes.

Introduction of a computerised protocol in clinical practice: is there anything to gain?

OBJECTIVES

To assess the potential benefit of a protocol for the diagnostic work-up and management of patients with obstructive jaundice, by comparing its recommendations with the policies actually followed in patients and to compare local expertise with diagnostic and therapeutic procedures with that described in published reports.

DESIGN

A retrospective analysis of patients' records.

SETTING

University hospital, The Netherlands.

SUBJECTS

49 consecutive patients who presented to the departments of internal medicine and surgery between June 1990 and June 1992 with serum alkaline phosphatase activities > 125 mumol/L, and serum bilirubin concentrations > 17 mumol/L.

MAIN OUTCOME MEASURES

The proportions of diagnostic and therapeutic decisions that deviated from the recommendations, and the success rates of diagnostic and therapeutic procedures.

RESULTS

In patients with bile duct stones the treatment strategies did not deviate from those recommended in the protocol. In patients with cancer 38 (30%) of the 128 diagnostic decisions and 4 (11%) of the 37 therapeutic decisions deviated from the protocol. Success rates of all diagnostic investigations were comparable with those reported, and success rates of endoscopic biliary drainage tended to be lower than those reported.

CONCLUSIONS

The introduction of a protocol for the diagnostic work-up of patients with obstructive jaundice may reduce unnecessary investigations and diagnostic omissions by half. Because local expertise of some of the procedures seems to be significantly less than reported elsewhere it may be necessary to modify the protocol to better fit local circumstances.

Hypochlorous acid disrupts the adhesive properties of subendothelial matrix

We have investigated whether the cell adhesion-promoting properties of the subendothelial matrix are affected by exposure to neutrophil-derived oxidants. Native subendothelial matrix was exposed to increasing doses of H2O2 in the presence of myeloperoxidase and Cl- or to reagent hypochlorous acid (HOCl). Increasing doses of either oxidant system resulted in progressive loss in the adhesive properties of the matrix, and phase contrast microscopy showed that the cells failed to attach to and spread on the oxidant-treated surface. When cells were replated on the treated matrix in the presence of 20% serum, they did attach, but showed abnormal spreading and morphology in longer-term culture. In a modified ELISA system, binding of antibodies specific to fibronectin, thrombospondin and laminin was also disrupted by prior exposure of the matrix to HOCl. Of these components, the cell-binding region of fibronectin was most affected by HOCl, thrombospondin and laminin were less sensitive, and the collagen-binding region of fibronectin was the most resistant. SDS-PAGE of 35S-labelled subendothelial matrix proteins indicated that there was no major irreversible crosslink formation or fragmentation after exposure to HOCl or the myeloperoxidase system, although formation of disulfides is quite likely.

Evaluating the MACRO solution. Multimedia Application for Clinical Research in Oncology

This paper describes the evaluation approach of the MACRO project. This approach is based on earlier work in the European 3rd Framework Programme (AIM). We describe how user requirements and expectations play a role in the design of the various assessment studies in MACRO.

Impact of a protocol processing system (ProtoVIEW) on clinical behaviour of residents and treatment

A protocol processing system (ProtoVIEW), containing therapeutic trauma protocols, was used in the Accident and Emergency (A and E) department for a period of 7 months to investigate the impact of automated protocols on firstly, medical decision making of physicians and secondly, on quality of treatments eventually received by the patients. A randomized controlled trial showed that mandatory use of the system led to a more uniform working strategy while fracture treatment only seemed to improve in a subgroup of patient for whom residents established a correct diagnosis.

Effects of a supportive protocol processing system (ProtoVIEW) on clinical behaviour of residents in the accident and emergency department

A randomized two period crossover trial was performed at the Accident and Emergency (A & E) department of the University Hospital in Nijmegen (The Netherlands). We assessed what the impact was of (mandatory) consultation of a protocol for the management of isolated traumas on treatment decisions of residents. All eight surgical residents who regularly worked in the A & E department participated in the trial. All patients who entered the A & E department between October 13, 1992 and June 9, 1993, of age 16 years or older with an isolated fracture without concomitant lesions were admitted to the study. During the experimental periods, the management protocol was available on computer (using ProtoVIEW) and during the control periods on paper. Main measurements were treatment adjustments made by residents (after consulting different information sources), and their opinion about ProtoVIEW as an information source assessed by means of a questionnaire. When protocol consultation was mandatory, residents changed their treatments almost four times more often towards the protocol than during the control periods (P = 0.01 Chi-square test). Most residents found ProtoVIEW easy to use, liked it as a useful training source while half of them said they would use the system in daily clinical practice. We conclude that mandatory protocol consultation using ProtoVIEW influenced protocol adherence positively.

Protocol processing system (ProtoVIEW) to support residents at the emergency ward

This paper describes the design, implementation and evaluation of a prototype protocol processing system (ProtoVIEW). ProtoVIEW provides protocol information for diagnostic and therapeutic purposes. The developed system described here is used as a research instrument to investigate the impact of automated protocols on the medical decision making of physicians. A first evaluation indicates that residents like to use the system and that usage of the system leads to a more uniform working strategy.

Development, implementation and a first evaluation of a protocol processing system (ProtoVIEW)

In this contribution the protocol information system ProtoVIEW is presented. The system provides the necessary information to physicians about diagnostic procedures and therapies. It is implemented as a stand alone system. The design criteria are discussed and the results of a first evaluation presented. It appears that interns can easily find the required information with the help of the system. The time that they need for accessing the relevant information is relatively short (about 1 min). The users expressed the opinion that the system is easy to use and does support them in the management of their patients. On the basis of this evaluation and evaluations reported elsewhere it is concluded (a) that stand-alone protocol systems can support daily patient management in a positive way and (b) that the design criteria for a protocol information system as presented in this paper are useful for prospective protocol information system developers.

Oxidation of intracellular glutathione after exposure of human red blood cells to hypochlorous acid

Exposure of human red blood cells to low doses of hypochlorous acid (HOCl) resulted in the loss of intracellular GSH. Oxidation occurred less than 2 min after the addition of HOCl, and required approx. 2.5 mol of HOCl per mol of GSH lost. Loss of GSH preceded oxidation of membrane thiols, the formation of chloramines and haemoglobin oxidation. The susceptibility of intracellular GSH to oxidation by HOCl was two-thirds that of GSH in cell lysates. These results indicate that HOCl can penetrate the red cell membrane, which provides little barrier protection for cytoplasmic components, and that GSH oxidation by HOCl may be a highly selective process. Virtually all of the GSH lost was converted into GSSG. If glucose was added to the medium, most of the GSH oxidized by low doses of HOCl was rapidly regenerated. At higher doses, recovery was less efficient. However, when HOCl was added as a slow infusion rather than in a single bolus, there was increased recovery at higher doses. This indicates that in metabolically active cells regeneration is rapid and GSH may protect cell components from damage by HOCl. HOCl-induced lysis was only slightly delayed by adding glucose to the medium, indicating that lytic injury is not ameliorated by GSH.

Consultation behaviour of residents supported with a protocol processing system (ProtoVIEW) at the emergency ward

We evaluated the consultation behaviour of residents using a protocol processing system in routine clinical practice. A total of 125 consecutive patients, of age 16 years or older with an isolated fracture without concomitant lesions, were treated with computer support between 13 October 1992 and 9 June 1993. All eight surgical residents who worked at the emergency ward of the University Hospital in Nijmegen, The Netherlands participated. The mean consultancy time, method of information retrieval, number of correct protocols found, number of windows retrieved and attitude towards ProtoVIEW as a useful information source were estimated. Main results are: a mean consultancy time of 1.5 min per case, residents browsed through the protocol information more often than using keyword search. The correct protocols were found in 98% of the cases while on average a minimum number of text-browse windows was retrieved. Residents were positive about the way protocols were presented and about the information supplied by ProtoVIEW. From this study we may conclude that ProtoVIEW consultation is hardly time consuming, and easy to use. Since keyword search was hardly used, expanding the number of synonyms may stimulate searching by keyword more often.

Membrane changes associated with lysis of red blood cells by hypochlorous acid

This study was carried out to investigate HOCl-induced lysis of human erythrocytes. Using reagent HOCl with isolated red cells, we showed that the rate of lysis was dependent on the dose of HOCl per red cell rather than on the concentration of oxidant. The process was inhibited by scavengers such as methionine and taurine, but only if they were present at the time of addition of HOCl. Lysis was preceded by a decrease in cell density, a change in the deformability of the membrane as evidenced by ektacytometry, and an increase in K(+)-leak. Electron microscopy showed extensive disruption of the membrane. Increasing doses of HOCl caused progressive loss of membrane thiols, but complete thiol oxidation by N-ethylmaleimide did not result in an equivalent rate of lysis. Restoration of oxidised thiols by incubation with glucose did not significantly alter the pattern of lysis. Taken together, these results suggest that thiol oxidation was not responsible for HOCl-mediated lysis. There was evidence of increasing crosslinking of membrane proteins on electrophoresis, only some of which was due to the formation of disulfides. TLC of the membrane lipids indicated that there may be formation of chlorohydrins by reaction of HOCl with the fatty acid double bonds. This reaction results in the formation of a more polar species which, if formed, would be extremely disrupting to the lipid bilayer. The results indicate that HOCl-mediated damage to the membrane proteins or to the lipid bilayer comprises an initial damaging event that sets the cells on a path toward eventual lysis.

Bacterial killing by neutrophils in hypertonic environments

The effects of hypertonic sodium chloride and urea solutions on the phagocytosis and killing of Escherichia coli by neutrophils were examined. Neutrophil function was progressively inhibited by increasing osmolarity, with sodium chloride more inhibitory than urea. However, neutrophils killed at 25% of normal rates in 500 mosmol/L NaCl, and in 300 mosmol/L NaCl with 800 mosmol/L urea. These concentrations would rarely be exceeded in the human urinary tract. Inhibition of neutrophil superoxide production and degranulation was similar to that observed with phagocytosis and killing. Neutrophils also phagocytosed and killed E. coli in isotonic and hypertonic urine, but no improvement in function attributable to the uptake of urinary osmoprotectants was evident. It is concluded that physiologic levels of sodium chloride and urea will slow, but not prevent, neutrophil activity at a hypertonic site of infection.

Proteinase-antiproteinase balance in tracheal aspirates from neonates

We wanted to identify the inhibitors of neutrophil elastase, quantify their activities in the upper airways of neonates, and relate these to the presence of active elastase and the likelihood of elastolytic injury occurring due to inhibitory capacity being overwhelmed. Activities of neutrophil elastase and its inhibitors were measured in tracheal aspirates from 17 infants, 10 of whom subsequently developed bronchopulmonary dysplasia. All aspirates contained immunologically detectable alpha 1-proteinase inhibitor (alpha 1-PI), but their inhibitory capacity against neutrophil elastase ranged from being undetectable to being in excess of the amount of alpha 1-PI detected immunologically. When the alpha 1-PI was removed from each of the aspirates, using a specific antibody, from 0-50% of the original activity remained, indicating the presence of another elastase inhibitor. Its properties were consistent with it being the low molecular mass, secretory leucoproteinase inhibitor (SLPI), also known as bronchial antileucoproteinase. The alpha 1-PI was from 0-100% active. Most of the inactive inhibitor was shown by western blotting to be complexed with elastase, with a small amount of cleaved material. There was no evidence of major oxidative inactivation. Free elastase was detected in only three of the aspirates; these had little or no detectable elastase inhibitory capacity, and most of their alpha 1-PI was complexed. Elastase load, comprising the sum of free and complexed elastase, correlated closely with myeloperoxidase activity, a recognized marker of inflammatory activity. Active SLPI levels showed a positive correlation with gestational age (r = 0.66). We conclude that most neutrophil elastase in the upper airways of ventilated infants is complexed.(ABSTRACT TRUNCATED AT 250 WORDS)

A single assay for measuring the rates of phagocytosis and bacterial killing by neutrophils

We have developed a method that enables the rates of phagocytosis and killing of bacteria by neutrophils to be measured in a single assay. Neutrophils were incubated with bacteria, and at specific intervals were separated from uningested bacteria by low speed centrifugation. Rates of phagocytosis and killing were calculated from the decrease in number of extracellular bacteria and change in the number of intracellular bacteria. Both phagocytosis and killing were shown to follow first-order kinetics, and rate constants were calculated without having to separate the assay into two phases. In contrast to two-step methods, our method measures killing from the moment the neutrophils start ingesting the bacteria, and also eliminates the need to halt neutrophil activity temporarily and restart the assay after the extracellular bacteria have been removed. We obtained reproducible results for the phagocytosis and killing of Staphylococcus aureus (t1/2 = 9 min and 6 min respectively) and Escherichia coli (t1/2 = 10 min and 2 min respectively). We also were able to detect a 56% impairment in the rate of killing of S. aureus by neutrophils from an individual with a low level of myeloperoxidase.

Computer supported patient management

Both a prototype medical record system and a protocol information system are presented. Both systems are used for research purposes. The philosophy behind the medical record system is that the system should provide both freedom of vocabulary and freedom of level of detail. The freedom of vocabulary is guaranteed by allowing free text entry. Freedom of level of detail is obtained by structuring the medical record in a hierarchical way and to allow the physician to enter data at the level of detail that suits him best. The protocol information system supports the physician in managing the patient. It guides the user through the protocol and allows him to obtain background information about the protocol. Both flowcharts and images are included. After each session a summary of the steps taken can be printed. A first evaluation indicates that physicians like to use the system and learn from it.

Different effects of hypochlorous acid on human neutrophil metalloproteinases: activation of collagenase and inactivation of collagenase and gelatinase

Human neutrophils stimulated with phorbol 12-myristate 13-acetate (PMA) produce the reactive oxidant hypochlorous acid (HOCl) and release the matrix metalloproteinases collagenase and gelatinase from secretory granules. We have investigated the stoichiometry of activation and inactivation of the two metalloproteinases with HOCl. HOCl activated purified neutrophil procollagenase at ratios between 10 and 40 mol of HOCl/mol enzyme, but caused inactivation at higher ratios. Maximum activation was about the same as that achieved by p-aminophenyl-mercuric acetate. However, less than a third of the total collagenase released from PMA-stimulated neutrophils was activated by coreleased HOCl and most of the activity was destroyed after 1 h of stimulation. These results indicate that the HOCl/enzyme ratio must fall within a narrow range for activation to occur. In contrast to collagenase, purified progelatinase underwent negligible activation (2.5 +/- 1.2%) at HOCl/enzyme molar ratios less than 30 and was destroyed at higher ratios. Likewise no active gelatinase could be detected in supernatant from PMA-stimulated cells and almost all of the proenzyme was destroyed by HOCl after 60 min stimulation. Our results illustrate that only collagenase can be activated by HOCl in vitro and that gelatinase is much more sensitive to inactivation. Since a precise HOCl/enzyme ratio is required for collagenase activation it is doubtful whether effective enzyme regulation by HOCl could occur in vivo where various HOCl scavengers are present.

Oxidative damage to fibronectin. II. The effect of H2O2 and the hydroxyl radical

The effect of H2O2 and the hydroxyl radical (.OH) on fibronectin was investigated. .OH was generated in three ways: (i) by radiolysis with 60Co under N2O, or by the Fenton system using either (ii) equimolar Fe(2+)-EDTA and H2O2 or (iii) H2O2 and catalytic amounts of Fe(2+)-EDTA recycled with ascorbate. Each system had a different effect. H2O2 alone caused no changes, even at an 800-fold molar excess. Radiolytic .OH caused a rapid loss of tryptophan fluorescence, an increase in bityrosine fluorescence, and extensive crosslinking. The Fenton system using Fe-EDTA, H2O2, and ascorbate caused a loss in tryptophan fluorescence, a smaller increase in bityrosine than was seen with radiolytic .OH, and a threefold increase in carbonyl groups. On sodium dodecyl sulfate-polyacrylamide gel electrophoresis fragmentation of fibronectin was seen. In contrast, when .OH was generated with equimolar Fe-EDTA and H2O2, the only change was a small increase in bityrosine fluorescence at the highest dose of oxidant. None of the systems used affected cysteine. All the changes except the loss of tryptophan by radiolytic .OH were completely inhibited with mannitol. The differences seen with radiolytic .OH and the Fe-EDTA, H2O2, ascorbate system were not solely due to O2 in the latter system since similar results were obtained under N2. The differences between radiolytic .OH and the Fenton systems could be partly due to the components of the latter systems reacting with .OH and thus competing with fibronectin. Our results demonstrate that the extent and type of fibronectin damage by .OH is dependent on the mode of radical generation.

Oxidative damage to fibronectin. I. The effects of the neutrophil myeloperoxidase system and HOCl

Exposure of purified human plasma fibronectin to the myeloperoxidase-H2O2-Cl- system of neutrophils or to reagent HOCl resulted in extensive changes to its primary and tertiary structures. When 1.14 microM fibronectin was exposed to 50-400 microM HOCl or 50-400 microM H2O2 plus myeloperoxidase and Cl-, there was progressive loss of tryptophan fluorescence and cysteines, and an increase in bityrosine fluorescence and carbonyl content. Analysis by SDS-PAGE indicated extensive crosslinking of the fibronectin, the crosslinks being stable under reducing conditions. The coincident increase of bityrosine fluorescence suggests that crosslinking may be largely due to intermolecular bityrosines rather than disulfides. All changes observed with the myeloperoxidase system were inhibited by azide or methionine, and were dependent upon the presence of chloride, indicating that they are mediated by HOCl. The reaction between HOCl and fibronectin resulted in the formation of long-lived chloramines. Exposure to increasing amounts of oxidant resulted in an increase in the susceptibility of fibronectin to proteolytic attack by purified neutrophil elastase. Analysis by SDS-PAGE showed a different fragmentation pattern for oxidant-treated fibronectin compared with the native protein. This suggests that regions of the molecule which were previously resistant to proteolysis were denatured to create susceptible sites for elastase. This demonstration that fibronectin is extensively modified by the myeloperoxidase system has implications for the mechanism of tissue injury by neutrophils in inflammation, since a loss of functional fibronectin would result in cell detachment and a distortion of normal tissue organization.

Human neutrophil collagenase cleaves alpha 1-antitrypsin

Inactivation of the plasma serine-proteinase inhibitor alpha 1-antitrypsin (alpha 1-AT) by neutrophil metalloproteinases has been reported [Vissers, George, Bathurst, Brennan & Winterbourn (1987) Fed. Proc. Fed. Am. Soc. Exp. Biol. 46, 1390a; (1988) J. Clin. Invest. 82, 706-711; Desrochers & Weiss (1988) J. Clin. Invest. 81, 1646-1650]. To identify the enzyme responsible, supernatant from neutrophils stimulated with phorbol 12-myristate 13-acetate was subjected to preparative SDS/PAGE, both with and without activation of latent metalloproteinases with HgCl2. The lanes were subsequently sliced into pieces, the slices incubated with equimolar amounts of type I collagen and alpha 1-AT in the presence of HgCl2, and the reaction products separated by SDS/PAGE. With the latent supernatant, the characteristic collagen-cleavage products and cleaved alpha 1-AT were present in the same slices, corresponding to an Mr of 80,000-85,000. On treatment with HgCl2 both degradative activities underwent the same molecular-mass shift to a position corresponding to Mr 60,000-65,000. Western blots of neutrophil supernatants, using a polyclonal antibody to purified collagenase, showed Mr values of 83,000 for the latent enzyme and 63,000 for the HgCl2-activated enzyme. Neutrophil collagenase was purified to homogeneity and shown also to exist in a second latent form with Mr 70,000. When activated to the Mr-63,000 form by HgCl2 and incubated with equimolar amounts of collagen and alpha 1-AT, collagenase cleaved alpha 1-AT at almost twice the rate at which collagen was cleaved. alpha 1-AT cleavage was inhibited by 1,10-phenanthroline and by high concentrations of collagen. That the purified collagenase did not contain a contaminant proteinase such as stromelysin was indicated by inability of the preparation to cleave casein. Taken together these results lead us to conclude that neutrophil collagenase is capable of degrading alpha 1-AT. Neutrophil gelatinase also cleaved alpha 1-AT, but cleavage was slow when compared with its activity against gelatin.

Inhibition of hypochlorous acid-mediated reactions by desferrioxamine. Implications for the mechanism of cellular injury by neutrophils

Inhibition of free radical mechanisms by desferrioxamine, an iron chelator, is often thought to be a good indicator of iron-catalyzed hydroxyl radical (OH.) production. The specificity of desferrioxamine is critical for such identification. This study was undertaken to determine whether desferrioxamine could prevent the in vitro cytotoxic reactions of hypochlorous acid (HOCl), a major neutrophil-derived oxidant. Red blood cells were used as a target for HOCl, and cell lysis and haemoglobin oxidation were measured. Desferrioxamine, and its iron-chelated form, ferrioxamine, were shown to prevent both effects of HOCl. However, desferrioxamine was 6 to 8 times more efficient than either ferrioxamine or taurine, another amine which prevents HOCl-mediated cell lysis, in preventing both lysis and Hb oxidation. After reaction with HOCl, ferrioxamine and taurine retained almost all the oxidizing equivalents as long-lived chloramine. However, with desferrioxamine less than half the oxidizing equivalents were recovered as chloramines indicating that sites other than the terminal amine reacted with HOCl. The chloramines formed were able to oxidize molecules in solution, but being hydrophilic they were confined to the extracellular medium and cell lysis did not occur. The results indicate that scavenging of HOCl could be a factor in the inhibition by desferrioxamine of neutrophil-mediated cell lysis in vitro.

Comparative ability of human monocytes and neutrophils to degrade glomerular basement membrane in vitro

We have compared the ability of human peripheral blood monocytes and neutrophils to degrade glomerular basement membrane (GBM) in vitro. When isolated cells were incubated with GBM containing anti-GBM immune complexes, both neutrophils and monocytes adhered and spread on the surface of the GBM, underwent a respiratory burst and released lysosomal enzymes into the medium. With neutrophils, this resulted in rapid degradation of the GBM, measured both as solubilization of collagenous and noncollagenous protein. In contrast, monocytes degraded GBM very slowly, with a slight increase in the rate of hydroxyproline solubilization after approximately 24 hours incubation. Degradation of GBM by neutrophils was predominantly due to the action of serine proteinases, whereas inhibition of monocyte-mediated hydroxyproline release required both phenylmethylsulfonyl fluoride and o-phenanthroline, suggesting some synergy between serine and metalloproteinases. The results indicate that neutrophils are more able to degrade GBM components than are monocytes, and suggest that they may be capable of greater damage to the GBM in vivo, mostly due to their higher proteolytic capacity.

Human platelets mediate iron release from transferrin by adenine nucleotide-dependent and -independent mechanisms

We assessed the ability of platelet sonicates and mediators secreted by unstimulated and thrombin-stimulated platelets to facilitate the release of iron from transferrin. Platelet sonicates and platelet conditioned media potentiated the release of iron from transferrin. The rate of release of iron was dependent on the pH of the reaction and amount of platelet sample added. Conditioned media from thrombin-stimulated platelets was more effective in mediating the release of iron from transferrin than was conditioned media from unstimulated cells. The rate of iron released from transferrin following addition of ATP and ADP in amounts equivalent to that present in platelet conditioned media was significantly less than the rate of iron released following the addition of conditioned media from platelets. Depletion of ATP and ADP in platelet conditioned media by incubation with apyrase only partially inhibited their ability to enhance the rate of iron release from transferrin. These observations indicate that platelets enhance the release of iron from transferrin by adenine nucleotide-dependent and -independent mechanisms. These observations are consistent with the hypothesis that platelets promote oxidant-induced tissue injury at sights of inflammation secondary to their ability to enhance the local release of iron from transferrin.

Glomerular basement membrane-containing immune complexes stimulate tumor necrosis factor and interleukin-1 production by human monocytes

The ability of human peripheral blood monocytes to produce tumor necrosis factor (TNF) and interleukin-1 (IL-1) in an in vitro model of immune complex-mediated glomerulonephritis was investigated. When isolated monocytes were incubated with human glomerular basement membrane (GBM) containing anti-GBM immune complexes, both TNF and IL-1 were produced and secreted into the medium. The time course of secretion differed, with IL-1 production being maximal after approximately 8 hours, whereas TNF levels continued to rise for 30 hours. The activities of the monocyte-derived TNF and IL-1 were inhibitable by specific antibodies. No effect was seen when monocytes were incubated separately with either GBM alone or anti-GBM IgG. The levels of TNF and IL-1 released were comparable with those induced by high concentrations of LPS, indicating that production was close to the maximal levels reported for these cells. High levels of TNF and IL-1 also were produced in response to soluble immune complexes. The results show that monocytes can produce significant levels of TNF and IL-1 in response to both surface-bound and soluble immune complexes and provide support for the participation of these monokines in glomerulonephritis.

Cleavage and inactivation of alpha 1-antitrypsin by metalloproteinases released from neutrophils

Human neutrophils, when stimulated with phorbol myristate acetate or fMet-Leu-Phe in the presence or absence of cytochalasin B, released metalloproteinases that catalytically inactivated the plasma serine proteinase inhibitor, alpha 1-antitrypsin. Inactivation, measured as loss of elastase inhibitory capacity, was accompanied by cleavage of a Mr 4,000 peptide from the COOH-terminus. Cleavage of alpha 1-antitrypsin by cell supernatants was inhibited by EDTA, o-phenanthroline, and DTT, but not by inhibitors of serine or thiol proteinases. Gelatinase and collagenase were separated from the medium of stimulated neutrophils. Both preparations cleaved and inactivated alpha 1-antitrypsin, with cleavage occurring close to the reactive center, at the Phe-Leu bond between positions P7 and P6. Cleavage by purified gelatinase was very slow and could account for only a minor fraction of the activity of neutrophil supernatants. The collagenase preparation was more active. However, the unusual cleavage site, and the ability of fMet-Leu-Phe-stimulated neutrophils to cleave alpha 1-antitrypsin without releasing collagenase, suggests that collagenase is not responsible for cleavage by the cells, which, by implication, is due to an as yet uncharacterized metalloenzyme. Our results demonstrate that by releasing metalloproteinases, neutrophils could proteolytically inactivate alpha 1-antitrypsin at sites of inflammation. This provides an alternative to the previously documented mechanism of inactivation by neutrophil-derived oxidants.

Rapid purification of human peripheral blood monocytes by centrifugation through Ficoll-Hypaque and Sepracell-MN

We have developed a rapid and simple method for isolating human peripheral blood monocytes in suspension. The procedure combines two separation media and involves isolation of the mononuclear cells by centrifugation through Ficoll-Hypaque followed by purification of the monocytes using Sepracell-MN, a colloidal silica-based medium. The final cell population contained approximately 90% monocytes with good functional ability. The contaminating cells were lymphocytes. Viability was always greater than or equal to 99% with 90% recovery of the monocytes from the mononuclear cells.

Gelatinase contributes to the degradation of glomerular basement membrane collagen by human neutrophils

Neutrophils contain a number of proteinases active at neutral pH which are able to degrade extracellular matrices. We have determined the contribution of the major neutral proteinases to human neutrophil-mediated degradation of glomerular basement membrane type IV collagen in an in vitro model of immune complex-induced injury. Studies with proteinase inhibitors showed that with intact neutrophils stimulated by immune complexes trapped within the basement membrane, approximately 70% of the degradation was due to serine proteinases and 30% to metalloproteinases. Identical results were obtained with cell-free medium containing neutrophil granule contents. Elastase accounted for almost all the digestion by serine proteinases with a minimal contribution by cathepsin G. All the metalloproteinase activity was due to gelatinase rather than collagenase, and purified gelatinase was also shown to degrade basement membrane collagen. Hence, gelatinase has activity against type IV collagen and may be able to degrade collagens not cleaved by specific collagenases.

Activation of human neutrophil gelatinase by endogenous serine proteinases

The role of serine proteinases and oxidants in the activation of gelatinase released from human neutrophils was investigated. Gelatinase was measured by its ability to degrade both gelatin and native glomerular basement-membrane type IV collagen. When fMet-Leu-Phe or phorbol 12-myristate 13-acetate was used to stimulate the neutrophils, no gelatinase activity was measured in the absence of a mercurial activator, indicating that the enzyme was released entirely in latent form. However, when fMet-Leu-Phe-stimulated cells were treated with cytochalasin B, 50-70% of the maximal gelatinase activity was released. Activation was blocked by the serine-proteinase inhibitor phenylmethanesulphonyl fluoride and a specific inhibitor of neutrophil elastase, but was not affected by an inhibitor of cathepsin G. Addition of catalase or azide to prevent oxidative reactions did not affect activation of gelatinase under any conditions of stimulation, indicating that oxidants were not involved in activation. Our results imply that oxidative activation of gelatinase does not occur readily. However, neutrophil serine proteinases, particularly elastase, provide an alternative and apparently more efficient mechanism of activation.

Inhibition of neutrophil degranulation and superoxide production by sulfasalazine. Comparison with 5-aminosalicylic acid, sulfapyridine and olsalazine

Sulfasalazine is a potent inhibitor of superoxide production and granule enzyme release by stimulated neutrophils, and modulation of these responses may contribute to its anti-inflammatory properties. It is a composite drug consisting of 5-aminosalicylic acid and sulfapyridine joined through an azo linkage. To investigate which functional groups on the molecule are active against neutrophil responses, 5-aminosalicylic acid, sulfapyridine and olsalazine were added to cells stimulated with fMet-Leu-Phe or immune complexes. The inhibitory effects of sulfasalazine on superoxide production, degranulation and neutrophil-mediated collagen degradation were closely mimicked by olsalazine, with the other two compounds having little effect on either function. Thus the azo link appears to be the important structural feature of sulfasalazine that affects neutrophil responses. This suggests that sulfasalazine could be anti-inflammatory in its own right rather than just acting as a source of 5-aminosalicylic acid. Our findings are also a favourable indication for olsalazine (Dipentum), which is currently under trial as an anti-inflammatory agent.

Inhibition by nonsteroidal anti-inflammatory drugs of superoxide production and granule enzyme release by polymorphonuclear leukocytes stimulated with immune complexes or formyl-methionyl-leucyl-phenylalanine

The effects of nonsteroidal anti-inflammatory agents on superoxide production and granule enzyme release by human polymorphonuclear leukocytes stimulated with either formyl-methionyl-leucyl-phenylalanine (fMet-Leu-Phe] or immune complexes were investigated. Cytochrome c reduction and the release of lysozyme, beta-glucuronidase, myeloperoxidase and gelatinase were measured. Auranofin, phenylbutazone, sulfasalazine and the phospholipase A2 inhibitor, 4-bromophenacyl bromide, strongly inhibited these responses in fMet-Leu-Phe stimulated cells, at concentrations below 50 microM. Indomethacin, piroxicam, mefenamic acid, primaquine and quinacrine at 50-250 microM were inhibitory. Up to 1 mM ibuprofen and chloroquine inhibited superoxide production but had little effect on degranulation. With cells stimulated by IgG aggregates (immune complexes), up to 1 mM ibuprofen, mefenamic acid and piroxicam did not inhibit either response. Indomethacin, phenylbutazone, sulfasalazine and primaquine inhibited, but considerably higher concentrations were required than with fMet-Leu-Phe. Quinacrine inhibited superoxide production equally well with both stimuli but inhibited enzyme release only with fMet-Leu-Phe. Only auranofin, 4-bromophenacyl bromide, and the weakly effective chloroquine exerted approximately the same effect with both stimuli. D-Penicillamine did not affect enzyme release with either stimulus and interfered in the superoxide assay. Gelatinase release induced by fMet-Leu-Phe was affected to the same extent, or slightly more, than release of the other granule enzymes. With immune complexes, there was only modest inhibition of gelatinase release by any of the drugs at 250-1000 microM. Our results reinforce previous observations that many anti-inflammatory drugs affect neutrophil functions, but their effects vary with stimulus. The relative insensitivity of immune complex-induced responses to most of the drugs must be taken into account when considering their mode of action.

Inhibition of neutrophil-mediated degradation of isolated basement membrane collagen by nonsteroidal antiinflammatory drugs that inhibit degranulation

The ability of nonsteroidal antiinflammatory drugs to inhibit neutrophil-mediated degradation of type IV collagen in an in vitro tissue injury model using glomerular basement membrane (GBM) containing immune complexes was investigated. Auranofin (2.5-10 microM), phenylbutazone (50-250 microM), sulfasalazine (250-1,000 microM), and 4-bromophenacyl bromide (5-20 microM) each inhibited up to 70% of the collagen degradation, in parallel with almost complete inhibition of the release of azurophil and specific granule enzymes. These drugs had much less an effect on gelatinase release. Indomethacin and the antimalarials, which inhibited the neutrophil oxidative burst but not degranulation, had little effect on GBM collagen degradation. Our results do not necessarily imply that inhibition of neutrophil-mediated degradation of connective tissue is relevant to the action of nonsteroidal antiinflammatory drugs in vivo; however, using the GBM model system, we have shown that when a drug inhibits granule enzyme release, there is an associated decrease in collagen degradation, whereas inhibition of the oxidative burst has relatively little effect.

Myeloperoxidase-dependent oxidative inactivation of neutrophil neutral proteinases and microbicidal enzymes

The susceptibility of a number of human neutrophil granule enzymes to oxidative inactivation was investigated. Addition of H2O2 to the cell-free medium from stimulated neutrophils resulted in inactivation of all enzymes tested. This was inhibited by azide and methionine, indicating that inactivation was due to myeloperoxidase-derived oxidants. Lysozyme was more than 50% inactivated by one addition of 100 nmol of H2O2/ml, whereas myeloperoxidase, beta-glucuronidase, gelatinase and collagenase were almost completely inactivated by three additions. Cathepsin G was slightly less susceptible, whereas elastase was extremely resistant to oxidative attack. Myeloperoxidase-dependent enzyme inactivation may be a means whereby the neutrophil can terminate the activity of its granule enzymes and control the release of degradative enzymes into the tissues.

The effect of oxidants on neutrophil-mediated degradation of glomerular basement membrane collagen

The contribution of activated oxygen species to neutrophil-mediated degradation of basement membrane collagen was investigated. In preliminary experiments, pre-exposure of either albumin or glomerular basement membrane to neutrophil myeloperoxidase with H2O2 and chloride increased their susceptibility to proteolysis 2-3-fold. In the basement membrane model, neutrophils are stimulated by trapped immune complexes to adhere, produce oxidants and degranulate. Degradation, measured as the amount of hydroxyproline solubilised, was due to neutral proteinases, particularly elastase, and depended on cell number and the amount of proteinase released. Experiments with oxidant scavengers and inhibitors and with neutrophils from donors with chronic granulomatous disease or myeloperoxidase deficiency showed that oxidants did not affect degradation of the basement membrane when this was measured on a per cell basis. However, oxidative inactivation of the released granule enzymes occurred. Activities of elastase, beta-glucuronidase and lysozyme were 1.5-2-times higher in the presence of catalase, but were unaffected by superoxide dismutase or hydroxyl radical scavengers. Inactivation did not occur with chronic granulomatous disease or myeloperoxidase deficient neutrophils. When related to the activity of released elastase, or to other degranulation markers, collagen degradation was decreased in the presence of catalase, or with chronic granulomatous disease or myeloperoxidase deficient cells. This implies that the basement membrane was made more digestible by myeloperoxidase-derived oxidants, as occurred in the cell-free experiments. Taken together, the results indicate that neutrophil oxidants have two opposing effects. They increase the susceptibility of the collagen to proteolysis and inactivate the proteinases responsible.

Neutrophils adherent to a nonphagocytosable surface (glomerular basement membrane) produce oxidants only at the site of attachment

Adherence of neutrophils to glomerular basement membrane containing immunoglobulin G aggregates was accompanied by a marked increase in oxygen uptake (eightfold). Very little of the O2 consumed was recovered as superoxide, measured by cytochrome c reduction, or as H2O2, measured with horseradish peroxidase and scopoletin. When neutrophils were incubated with the basement membrane preparation in the presence of cerium chloride to detect H2O2, electron micrographs showed cerium perhydroxide deposits in the contact area between the cells and the basement membrane, but not on the remainder of the cell surface. The results imply that superoxide is produced only where the plasma membrane is in contact with the basement membrane matrix, and that it mostly breaks down to H2O2 or undergoes other reactions at this site. The longer lifetime of H2O2 compared with that of superoxide allows some of the H2O2 produced to be detected in the medium. The results also suggest that the area of contact between the neutrophil and surfaces such as basement membrane is inaccessible to proteins in the medium, eg, cytochrome c. Circulating scavengers such as superoxide dismutase or catalase, or proteolytic inhibitors, may therefore be unable to control events occurring at this site.

A genetically engineered mutant of alpha 1-antitrypsin protects connective tissue from neutrophil damage and may be useful in lung disease

The effectiveness of a genetically engineered mutant of human alpha 1-antitrypsin (358 Met----Val) as an inhibitor of connective tissue breakdown was tested in a model of inflammation. The degradation of basement membrane collagen by stimulated neutrophils was efficiently inhibited by a tenfold lower concentration (0.2 mg/ml) of the mutant inhibitor than of the normal alpha 1-antitrypsin (2.4 mg/ml). Effective inhibition by normal alpha 1-antitrypsin occurred at much lower concentrations when azide or catalase was added, or when normal neutrophils were replaced by those from a donor with chronic granulomatous disease. These results confirm that neutrophils augment tissue proteolysis by the oxidative inactivation of the methionine at the reactive centre of alpha 1-antitrypsin. The replacement of this methionine by valine gives an effective inhibitor that is not inactivated by neutrophil oxidants. The availability of this genetically engineered mutant suggests the possibility of prophylaxis of lung dysplasias, notably emphysema, and of the shock syndromes associated with massive neutrophil activation.