Collagen activates superoxide anion production by human polymorphonuclear neutrophils

A barrier against reactive oxygen species: chitosan/acellular dermal matrix scaffold enhances stem cell retention and improves cutaneous wound healing

Background

Stem cell therapies have gained great attention for providing novel solutions for treatment of various injuries and diseases due to stem cells’ self-renewal, ability to differentiate into various cell types, and favorite paracrine function. Nevertheless, the low retention of transplanted stem cell still limits their clinical applications such as in wound healing in view of an induced harsh microenvironment rich in reactive oxygen species (ROS) during inflammatory reactions.

Methods

Herein, a novel chitosan/acellular dermal matrix (CHS/ADM) stem cell delivery system is developed, which is of great ROS scavenging activity and significantly attenuates inflammatory response.

Result

Under ROS microenvironment, this stem cell delivery system acts as a barrier, effectively scavenging an amount of ROS and protecting mesenchymal stem cells (MSCs) from the oxidative stress. It notably regulates intracellular ROS level in MSCs and reduces ROS-induced cellular death. Most importantly, such MSCs delivery system significantly enhances in vivo transplanted stem cell retention, promotes the vessel growth, and accelerates wound healing.

Conclusions

This novel delivery system, which overcomes the limitations of conventional plain collagen-based delivery system in lacking of ROS-environmental responsive mechanisms, demonstrates a great potential use in stem cell therapies in wound healing.

Hyaluronan primes the oxidative burst in human neutrophils

Hyaluronan (HA) is a glycosaminoglycan that in its natural, high molecular mass (HMM) form, promotes tissue repair and homeostasis. With inflammation, HA metabolism and HMM HA fragmentation to low molecular mass (LMM) forms is greatly enhanced. Considerable evidence suggests that LMM HA may act as a damage-associated molecular pattern to initiate innate immune responses. However, the responsiveness of myeloid cells to LMM HA is controversial and largely unknown for neutrophils. Peripheral blood cells from healthy donors were incubated ex vivo with pharmaceutical grade HA of different molecular mass (HMM, LMM, and HA fragments <10 kDa). Key innate immune functions were assessed, namely production of cytokines and reactive oxygen species release (ROS), granule mobilization, and apoptosis. None of the tested sizes of HA altered cytokine production by PBMC and neutrophils. Also, HA had no effect on neutrophil granule mobilization and apoptosis. In contrast, HA primed neutrophils for rapid and robust release of ROS in response to a secondary stimulus (N-formyl-methionyl-leucyl phenylalanine). Priming occurred within 20 min of exposure to HA and was similar for all tested molecular mass. The observed effect was independent of granule mobilization and associated with the activation of intracellular signaling pathways involving Src family kinases, glycogen synthase kinase-3, and the proline-rich Akt substrate of 40 kDa. Our findings provide new evidence that HA, irrespective of molecular mass, is a specific priming agent of the neutrophil oxidative burst, which is a critical, early component of an innate immune response.

Extracellular superoxide dismutase in pulmonary fibrosis

Disruption of the oxidant/antioxidant balance in the lung is thought to be a key step in the development of many airway pathologies. Hence, antioxidant enzymes play key roles in controlling or preventing pulmonary diseases related to oxidative stress. The superoxide dismutases (SOD) are a family of enzymes that play a pivotal role protecting tissues from damage by oxidant stress by scavenging superoxide anion, which prevents the formation of other more potent oxidants such as peroxynitrite and hydroxyl radical. Extracellular SOD (EC-SOD) is found predominantly in the extracellular matrix of tissues and is ideally situated to prevent cell and tissue damage initiated by extracellularly produced ROS. EC-SOD has been shown to be protective in several models of interstitial lung disease, including pulmonary fibrosis. In addition, alterations in EC-SOD expression are also present in human idiopathic pulmonary fibrosis (IPF). This review discusses EC-SOD regulation in response to pulmonary fibrosis in animals and humans and reviews possible mechanisms by which EC-SOD may protect against fibrosis.

Fragments of extracellular matrix as mediators of inflammation

Classically, the extracellular matrix (ECM) was viewed as a supporting structure for stabilizing the location of cells in tissues and for preserving the architecture of tissues. This conception has changed dramatically over the past few decades with discoveries that ECM has profound influences on the structure, viability, and functions of cells. Much of the data supporting this new paradigm has been obtained from studies of normal and pathological structural cells such as fibroblasts, smooth muscle cells, and malignant cells, as, for example, breast cancer epithelial cells. However, there has also been recognition that effects of ECM on cells extend to inflammatory cells. In this context, attention has been drawn to fragments of ECM components. In this review, we present information supporting the concept that proteolytic fragments of ECM affect multiple functions and properties of inflammatory and immune cells. Our focus is particularly upon neutrophils, monocytes, and macrophages and fragments derived from collagens, elastin, and laminins. Hyaluronan fragments, although they are not products of proteolysis, are also discussed, as they are a notable example of ECM fragments that exhibit important effects on inflammatory cells. Further, we summarize some exciting recent developments in this field as a result of mouse models in which defined ECM fragments and their receptors are clearly implicated in inflammation in vivo. Thus, this review underscores the idea that proteolysis of ECM may well have implications that go beyond modifying the structural environment of cells and tissues.

Surface morphology and adsorbed proteins affect phagocyte responses to nano-porous alumina

This study evaluates human neutrophil responses to aluminum oxide membranes with different pore sizes (20 nm and 200 nm in diameter) uncoated and pre-coated with serum, collagen I, or fibrinogen. The effect of released neutrophil granule components on the survival of osteoblastic cells (MG63) bound to the alumina membranes has also been evaluated. Without protein coatings the 20 nm pore-size membranes prompt higher reactive oxygen species (ROS) production as assessed by luminol-amplified chemiluminescence than the 200 nm pore-size membranes. Such pore-size depending responses were also found on membranes pre-coated with fibrinogen, but not with collagen or serum were in fact a much lower ROS production was observed. In addition, uncoated and fibrinogen-coated membranes prompt stronger release of the granule enzymes, myeloperoxidase and elastase, than collagen or serum-coated alumina. Equally important, we found that surface-mediated phagocyte activation and the subsequent release of granule components had a significant affect on the adhesion, viability and proliferation of osteoblasts. This stresses the importance of studying not only cell/surface interactions but also cell/cell interactions in wound healing and tissue regeneration processes.

Enhanced bleomycin-induced pulmonary damage in mice lacking extracellular superoxide dismutase

Extracellular superoxide dismutase (EC-SOD) is highly expressed in the extracellular matrix of lung and vascular tissue. Localization of EC-SOD to the matrix of the lung may protect against oxidative tissue damage that leads to pulmonary fibrosis. This study directly examines the protective role of EC-SOD in a bleomycin model of pulmonary fibrosis and the effect of this enzyme on oxidative protein fragmentation. Mice null for ec-sod display a marked increase in lung inflammation at 14 d post-bleomycin treatment as compared to their wild-type counterparts. Hydroxyproline analysis determined that both wild-type and ec-sod null mice display a marked increase in interstitial fibrosis at 14 d post-treatment, and the severity of fibrosis is significantly increased in ec-sod null mice compared to wild-type mice. To determine if the lack of EC-SOD promotes bleomycin-induced oxidative protein modification, 2-pyrrolidone content (as a measure of oxidative protein fragmentation at proline residues) was assessed in lung tissue from treated mice. 2-Pyrrolidone levels in the lung hydrolysates from ec-sod null mice were increased at both 7 and 14 d post-bleomycin treatment as compared to wild-type mice, indicating EC-SOD can inhibit oxidative fragmentation of proteins in this specific model of oxidative stress.

Extracellular superoxide dismutase in biology and medicine

Accumulated evidence has shown that reactive oxygen species (ROS) are important mediators of cell signaling events such as inflammatory reactions (superoxide) and the maintenance of vascular tone (nitric oxide). However, overproduction of ROS such as superoxide has been associated with the pathogenesis of a variety of diseases including cardiovascular diseases, neurological disorders, and pulmonary diseases. Antioxidant enzymes are, in part, responsible for maintaining low levels of these oxygen metabolites in tissues and may play key roles in controlling or preventing these conditions. One key antioxidant enzyme implicated in the regulation of ROS-mediated tissue damage is extracellular superoxide dismutase (EC-SOD). EC-SOD is found in the extracellular matrix of tissues and is ideally situated to prevent cell and tissue damage initiated by extracellularly produced ROS. In addition, EC-SOD is likely to play an important role in mediating nitric oxide-induced signaling events, since the reaction of superoxide and nitric oxide can interfere with nitric oxide signaling. This review will discuss the regulation of EC-SOD and its role in a variety of oxidant-mediated diseases.

Depletion of pulmonary EC-SOD after exposure to hyperoxia

Extracellular superoxide dismutase (EC-SOD) is highly expressed in lung tissue. EC-SOD contains a heparin-binding domain that is sensitive to proteolysis. This heparin-binding domain is important in allowing EC-SOD to exist in relatively high concentrations in specific regions of the extracellular matrix and on cell surfaces. EC-SOD has been shown to protect the lung against hyperoxia in transgenic and knockout studies. This study tests the hypothesis that proteolytic clearance of EC-SOD from the lung during hyperoxia contributes to the oxidant-antioxidant imbalance that is associated with this injury. Exposure to 100% oxygen for 72 h resulted in a significant decrease in EC-SOD levels in the lungs and bronchoalveolar lavage fluid of mice. This correlated with a significant depletion of EC-SOD from the alveolar parenchyma as determined by immunofluorescence and immunohistochemistry. EC-SOD mRNA was unaffected by hyperoxia; however, there was an increase in the ratio of proteolyzed to uncut EC-SOD after hyperoxia, which suggests that hyperoxia depletes EC-SOD from the alveolar parenchyma by cutting the heparin-binding domain. This may enhance hyperoxic pulmonary injury by altering the oxidant-antioxidant balance in alveolar spaces.

Amelioration of joint disease in a rat model of collagen-induced arthritis by M40403, a superoxide dismutase mimetic

OBJECTIVE

To investigate the effects of M40403, a synthetic mimetic of superoxide dismutase (SOD), on collagen-induced arthritis (CIA) in rats.

METHODS

CIA was elicited in Lewis rats by intradermal injection of 100 microl of an emulsion of bovine type II collagen (CII) in Freund's incomplete adjuvant at the base of the tail. A second injection was given on day 21.

RESULTS

Immunization induced an erosive arthritis of the hind paws. Macroscopic evidence of CIA first appeared as periarticular erythema and edema in the hind paws by days 24-26 after the first injection, with a 100% incidence by days 27. Severity progressed over a 35-day period. Radiography revealed soft tissue swelling and focal resorption of bone, together with osteophyte formation in the tibiotarsal joint. Histopathologic features included erosion of the articular cartilage at the joint margins and subchondral bone resorption associated with bone-derived multinucleated cell-containing granulomatous lesions. Treatment with M40403 (2-10 mg/kg/day) starting at the onset of arthritis (day 25) ameliorated the clinical signs on days 26-35 and improved the histologic findings in the joint and paw. Immunohistochemical analysis for nitrotyrosine (a marker of peroxynitrite formation) and poly(ADP-ribose) polymerase (PARP; a nuclear enzyme activated by DNA single-strand damage) revealed positive staining in the inflamed joints of CII-treated rats, suggestive of the formation of peroxynitrite and DNA damage, both of which were markedly reduced by M40403 treatment. Radiographic evidence of protection from bone resorption, osteophyte formation, and soft tissue swelling was apparent in the tibiotarsal joints of M40403-treated rats. Arthritic rats treated with M40403 gained weight at the same rate and to the same extent as normal, nonarthritic rats.

CONCLUSION

This study shows that a low molecular weight mimetic of SOD, M40403, attenuates the degree of chronic inflammation, tissue damage, and bone damage associated with CIA in the rat, and supports the possible use of SOD mimetics as therapeutic agents for the management of chronic diseases such as rheumatoid arthritis.

Altered expression of extracellular superoxide dismutase in mouse lung after bleomycin treatment

The antioxidant enzyme extracellular superoxide dismutase (EC-SOD) is highly expressed in the extracellular matrix of lung tissue and is believed to protect the lung from oxidative damage that results in diseases such as pulmonary fibrosis. This study tests the hypothesis that proteolytic removal of the heparin-binding domain of EC-SOD results in clearance of the enzyme from the extracellular matrix of pulmonary tissues and leads to a loss of antioxidant protection. Using a polyclonal antibody to mouse EC-SOD, the immunodistribution of EC-SOD in normal and bleomycin-injured lungs was examined. EC-SOD labeling was strong in the matrix of vessels, airways, and alveolar surfaces and septa in control lungs. At 2 d post-treatment, a slight increase in EC-SOD staining was evident. In contrast, lungs examined 4 or 7 d post-treatment, showed an apparent loss of EC-SOD from the matrix and surface of alveolar septa. Notably, at 7 d post-treatment, the truncated form of EC-SOD was found in the bronchoalveolar lavage fluid of bleomycin-treated mice, suggesting that EC-SOD is being removed from the extracellular matrix through proteolysis. However, loss of EC-SOD through proteolysis did not correlate with a decrease in overall pulmonary EC-SOD activity. The negligible effect on EC-SOD activity may reflect the large influx of intensely staining inflammatory cells at day 7. These results indicate that injuries leading to pulmonary fibrosis have a significant effect on EC-SOD distribution due to proteolytic removal of the heparin-binding domain and may be important in enhancing pulmonary injuries by altering the oxidant/antioxidant balance in alveolar interstitial spaces.

In vitro glycoxidation alters the interactions between collagens and human polymorphonuclear leucocytes

Glycation and glycoxidation processes, which are increased in diabetes mellitus, are generally considered causative mechanisms of long-term complications. With reference to our previous studies, type-I and -IV collagens could induce differentially the adhesion and stimulation of polymorphonuclear leucocytes (PMNs). As PMNs play a role in sustained diabetic oxidative stress, the present study was designed to determine whether in vitro glycoxidation of these macromolecules could alter PMN adhesion, activation and migration. The adhesion of PMNs to in vitro-glycoxidized collagens was significantly increased when compared with control collagens: +37% (P<0.05) and +99% (P<0.01) for collagens I and IV, respectively. Glycoxidized type-I collagen increased the chemotactic properties of PMNs without significant stimulatory effect on respiratory burst, whereas pre-incubation of PMNs with glycoxidized type-I collagen induced a priming on subsequent stimulation by N-formyl-methionyl-leucyl-phenylalanine. Glycoxidation of type-IV collagen suppressed its inhibitory effect on further PMN stimulation or migration. Collectively, these results indicate that glycoxidation of two major extracellular-matrix collagens considerably alters their ability to modulate PMN migration and production of reactive oxygen species. This imbalance in PMN metabolism may be a major event in the increased oxidative status that characterizes diabetes mellitus.

Human blood monocytes interact with type I collagen through alpha x beta 2 integrin (CD11c-CD18, gp150-95)

Human blood monocytes are attracted into connective tissues during early steps of inflammation and wound healing, and locally interact with resident cells and extracellular matrix proteins. We studied the effects of type I collagen on monocyte adhesion and superoxide anion production, using human monocytes elutriated from peripheral blood and type I collagen obtained from rat tail tendon. Both acid-soluble and pepsin-digested type I collagens promoted the adhesion of monocytes, whereas only acid-soluble collagen with intact telopeptides induced the production of superoxide. Adhesion and activation of monocytes on acid-soluble type I collagen depended on the presence of divalent cations. mAbs directed against integrin subunits CD11c and CD18 specifically inhibited adhesion and activation of monocytes on type I collagen. Protein membrane extracts obtained from monocytes were submitted to affinity chromatography on collagen I-Sepharose 4B, and analyzed by Western blotting using specific anti-integrin subunit Abs. In the case of both acid-soluble and pepsin-digested collagens, two bands were revealed with mAbs against CD11c and CD18 integrin subunits. Our results demonstrate that monocytes interact with type I collagen through CD11c-CD18 (alpha x beta 2) integrins, which promote their adhesion and activation. For monocyte activation, specific domains of the type I collagen telopeptides are necessary. Interactions between monocytes and collagen are most likely involved in the cascade of events that characterize the initial phases of inflammation.

A peptide of the alpha 3(IV) chain of type IV collagen modulates stimulated neutrophil function via activation of cAMP-dependent protein kinase and Ser/Thr protein phosphatase

Previous reports from our laboratories showed that type IV collagen from anterior lens capsule (ALC) inhibited stimulated neutrophil function. This property was shown to reside in the region comprising residues 185-203 of the non-collagenous domain (NC1) of the alpha 3(IV) chain. We also reported that ALC-type IV collagen or the synthetic alpha 3(IV) 185-203 peptide, induced a rise in intracellular cAMP which persisted for up to 60 minutes. In the present work we extend our previous studies on signal transduction by alpha 3(IV) 185-203 and we provide new data showing the involvement of cAMP-dependent PKA and protein phosphatases. The data also show that the alpha 3(IV) peptide triggered a rise in intracellular calcium that was dependent on phospholipase C activation. Inhibitors of the Ca(2+)/calmodulin system suppressed both the alpha 3(IV) 185-203 peptide-induced cAMP increase and the inhibitory activity of the peptide on f-Met-Leu-Phe triggered O(2)(-) generation. When alpha 3(IV) 185-203 peptide-induced calcium mobilization was blocked by U-73122, an inhibitor of phospholipase C activation, or by BAPTA/AM, a chelator of intracellular calcium, the inhibitory effect of the peptide on PMA-triggered O(2)(-) production was also abolished. These findings provide evidence that signal transduction by the alpha 3(IV) peptide occurs via pathways which involve calcium. Indeed, the cAMP increase was shown to be mediated by adenosine and adenosine A2 receptors and required calcium elevation, since adenosine deaminase, theophilline, dimethylpropargylxanthine, trifluoperazine or autocamtide-2 related inhibitory peptide, suppressed the activity of the alpha 3(IV) peptide. The inhibitory effect of the peptide on f-Met-Leu-Phe-induced O(2)(-) generation was slightly affected by 1 microM KT5720 or H89, two inhibitors of cAMP-dependent PKA, but was completely suppressed by 10 nM calyculin A or 10 microM okadaic acid, two inhibitors of ser/thr phosphatases. These results suggest that Ser/Thr protein phosphatases and/or cAMP-dependent PKA are involved in signal transduction by the alpha 3(IV) 185-203 peptide and is consistent with the concept that adenosine receptor occupancy modulates neutrophil function.

The binding of type I collagen to lymphocyte function-associated antigen (LFA) 1 integrin triggers the respiratory burst of human polymorphonuclear neutrophils. Role of calcium signaling and tyrosine phosphorylation of LFA 1

Monoclonal antibodies to the alpha L beta 2 integrin inhibit the binding of type I collagen to PMN (polymorphonuclear neutrophil leukocytes) as well as the subsequent stimulation of superoxide production and enzyme secretion-elicited by this collagen. Pepsinized collagen still binds PMN but no longer stimulates them. The I domain of the alpha chain of the integrin is involved in the binding. Two sequences of the alpha 1(I) polypeptide chain of collagen participate in the process. Experiments of competitive inhibition by synthetic peptides showed that the sequence RGD (915-917) is used for binding to the cells and DGGRYY (1034-1039) serves to stimulate PMN. Experiments of radioactive labeling of the cells and affinity chromatography on Sepharose-collagen confirmed the presence in PMN extracts of two proteins, 95 and 185 kDa, respectively, corresponding to the molecular weights of the beta 2 and alpha L chains of the integrin and recognized by their specific monoclonal antibodies. The transduction pathways depending on the alpha L beta 2 integrin do not involve a G protein (ruled out by the use of cholera and pertussis toxins), whereas the cytoskeleton was found to participate in the process, as evidenced by inhibition by cytochalasin B. After collagen stimulation, cytoplasmic inositol trisphosphate and calcium ion increased sharply for less than 2 min. The use of the inhibitors staurosporine and calphostin C demonstrated that protein kinase C was involved. Evaluation of the activity of this enzyme showed that, upon stimulation of PMN with collagen I, it was translocated to plasma membrane. Acrylamide gel electrophoresis of the protein bands corresponding to the integrin alpha L beta 2, followed by immunoblotting using monoclonal antibodies to phosphotyrosine, permitted us to demonstrate that, prior to stimulation by type I collagen, there was no phosphorylation, whereas after stimulation, both alpha L and beta 2 chains were stained by anti-phosphotyrosine antibodies. The adhesion of PMN to pepsinized type I collagen triggered tyrosine phosphorylation of the beta 2 chain of the integrin, without stimulating O2-. production by these cells, whereas their stimulation by complete type I collagen induced the tyrosine phosphorylation of both alpha L and beta 2 subunits. The tyrosine phosphorylation of both integrin subunits during transduction of stimuli is a heretofore undescribed phenomenon that may correspond to a new system of transmembrane communication.

Nitric oxide reduces hydrogen peroxide production from human polymorphonuclear neutrophils

Nitric oxide has been reported to affect both adhesion and respiratory burst of neutrophils. This indicates a possible role of nitric oxide in regulation of acute inflammatory responses. Release of oxygen metabolites from neutrophils can be measured using luminol-enhanced chemiluminescence and this method can detect both extracellularly and intracellularly released oxygen metabolites. Neutrophils treated with nitroprusside and activated with FMLP, type I collagen or PMA decreased their extracellular release of oxygen metabolites, while their intracellular release was almost unaffected. The effect of nitroprusside was mediated by nitric oxide since treatment with cyanide had the opposite effect. N-ethylmalemide treatment decreased both extra- and intracellular release of oxygen metabolites. This indicates that nitric oxide affects membrane-bound NADPH-oxidase either indirectly or directly, and not a cytosol factor of the oxidase as earlier shown for N-ethylmaleimide. In conclusion, extracellular nitric oxide attenuates extracellularly released oxygen metabolites from activated neutrophils in an inflammatory response.

Priming of oxidative response in human neutrophils by anti-CD18 monoclonal antibodies

Type I collagen, the most abundant protein in the body, after acid extraction adheres to and can induce a respiratory burst from neutrophils. It has been proposed that the effects of collagen are mediated via the CD18 subfamily of integrins. In the present study, adhesion was measured by affinity chromatography in a column containing collagen-coated microcarriers, while oxygen metabolite production was measured with luminol-dependent chemiluminescence. Neutrophil adherence to collagen was attenuated by anti-CD18 monoclonal antibodies. The respiratory burst in response to collagen was not affected by the antibodies. Incubation of neutrophils with anti-CD18 antibodies prior to stimulation with FMLP increased both the extra- and intracellular respiratory burst. Treatment with antibodies prior to PMA stimulation increased only the extracellular respiratory burst. In conclusion, the respiratory burst from neutrophils is primed by pretreatment with anti-CD18 monoclonal antibodies. The collagen-stimulated respiratory burst is probably also primed, but the effect is hidden by the simultaneous attenuation of adhesion.

CD11b/CD18-dependent polymorphonuclear leucocyte interaction with matrix proteins in adhesion and migration

Adhesion of human polymorphonuclear leucocytes (PMN) stimulated with phorbol myristate acetate (PMA) to plastic dishes coated with the matrix proteins laminin (LM), fibronectin (FN), collagen type I (CI) or collagen type IV (CIV) was inhibited by the monoclonal antibody 60.3 (MoAb 60.3; anti-CD18). The highest inhibitory effect was seen on adhesion to CI. PMN adhesion to CI was also effectively inhibited by Mo1 (anti-CD11b) but this antibody had only a minor effect on attachment of PMN to the other matrix proteins. In other experiments MoAb 60.3 inhibited LTB4-induced migration of PMN through polycarbonate filters (3 microns pores) coated with LM, FN, CI or CIV, with the most pronounced effect on migration through those filters coated with CI. By contrast, the antibody Mo1 had no effect on migration through any of the protein-coated filters tested. The results in this study suggest that the CD18 epitope, recognized by 60.3, mediates both adhesion and migration of PMN while the epitope on CD11b recognized by the antibody Mo1 is restricted to adhesion. The results also indicate that CD11b/CD18 is the major receptor on human PMN for CI while interaction with LM, FN and CIV may in addition involve other mechanisms.

Adhesion and activation of human neutrophils on basement membrane molecules

In a previous study, we found that type I collagen activates human polymorphonuclear neutrophils by binding to a membrane integrin [3]. The activation depends on two sequences, both contained in the alpha 1 (I) CB6 peptide, one is RGD, starting at residue 915, and the second is DGGRYY, starting at residue 1034 of the alpha 1(I) chain. We checked the effect of several other types of collagens, principally type IV collagen from several origins. The basement membrane from bovine lens as well as type IV collagen prepared from it by tartaric acid extraction did not activate the human neutrophils. In contrast, when neutrophils had been previously in contact with type IV collagen their activation by type I or the alpha 1(I) CB6 peptide, or the bacterial peptide N-formyl-methionyl-leucyl-phenylalanine, was inhibited. This effect was abolished when type IV collagen had been previously treated by pepsin. On the other hand, the fractions of type IV collagen that resisted digestion by bacterial collagenase still exhibited this inhibiting effect. This effect probably explains the physiological property of neutrophils to cross vascular walls without being activated.

Oxidative damage to collagen

Extracellular matrix molecules, such as collagens, are good targets for oxygen free radicals. Collagen is the only protein susceptible to fragmentation by superoxide anion as demonstrated by the liberation of small 4-hydroxyproline-containing-peptides. It seems likely that hydroxyl radicals in the presence of oxygen cleave collagen into small peptides, and the cleavage seems to be specific to proline or 4-hydroxyproline residues. Hydroxyl radicals in the absence of oxygen or hypochlorous acid do not induce fragmentation of collagen molecules, but they trigger a polymerization of collagen through the formation of new cross-links such as dityrosine or disulfure bridges. Moreover, these cross-links can not explain the totality of high molecular weight components generated under these experimental conditions, and the nature of new cross-links induced by hydroxyl radicals or hypochlorous acid remains unclear.

Bovine lens capsule basement membrane collagen exerts a negative priming on polymorphonuclear neutrophils

After a 30 min contact between purified bovine lens capsule basement membrane type IV collagen and polymorphonuclear neutrophils, stimulation of these cells by N-formyl-methionyl-leucyl-phenylalanine, PMA or type I collagen releases a decreased amount of superoxide ions (negative priming). The inhibitory activity is located in the NCl domain. On the other hand, after pepsin digestion, the helical part of type IV collagen determines a positive priming of neutrophils.

The superoxide-generating oxidase of phagocytic cells. Physiological, molecular and pathological aspects

Professional phagocytes (neutrophils, eosinophils, monocytes and macrophages) possess an enzymatic complex, the NADPH oxidase, which is able to catalyze the one-electron reduction of molecular oxygen to superoxide, O2-. The NADPH oxidase is dormant in non-activated phagocytes. It is suddenly activated upon exposure of phagocytes to the appropriate stimuli and thereby contributes to the microbicidal activity of these cells. Oxidase activation in phagocytes involves the assembly, in the plasma membrane, of membrane-bound and cytosolic components of the oxidase complex, which were diassembled in the resting state. One of the membrane-bound components in resting phagocytes has been identified as a low-potential b-type cytochrome, a heterodimer composed of two subunits of 22-kDa and 91-kDa. The link between NADPH and cytochrome b is probably a flavoprotein whose subcellular localization in resting phagocytes remains to be determined. Genetic defects in the cytochrome b subunits and in the cytosolic factors have been shown to be the molecular basis of chronic granulomatous disease, a group of inherited disorders in the host defense, characterized by severe, recurrent bacterial and fungal infections in which phagocytic cells fail to generate O2- upon stimulation. The present review is focused on recent data concerning the signaling pathway which leads to oxidase activation, including specific receptors, the production of second messengers, the organization of the oxidase complex and the molecular defects responsible for granulomatous disease.

Inert wound dressing is not desirable

Four Yorkshire piglets were inflicted with a total of 92 split-thickness wounds 4.8 cm2 in area and 400 microns deep. The wounds were treated with eight dressing regimens under the same experimental design. The rate of reepithelialization of the wound was quantitated by a morphometric method. The magnitude of inflammatory reaction of the wound to the dressing was scored from histological slides. The results indicate a relationship between the rate of reepithelialization of split-thickness wounds and the inflammatory response of the wound to the dressing. Dressings, such as collagen sponge, polyethyleneglycol, Duoderm, and lanolin ointment, induce moderate to severe inflammatory changes when placed on the wounds. These wounds reepithelialize significantly faster than control, gauze-covered wounds. This contrasts with inert dressings, such as hydrated hydrogel membrane, Carbopol 934P, or Silvadene cream, which did not affect the rate of reepithelialization when compared with the healing of control wounds. Simultaneously, these dressings induced no or minimal inflammatory reaction in the wound tissue. Only when the inflammatory reaction to the wound dressing was excessive (methylcellulose) was the rate of reepithelialization of the wounds significantly inhibited in comparison with control wounds. We hypothesize that wound dressings, by inducing inflammatory reaction, enhance healing by activating cells, such as macrophages or fibroblasts, that produce growth factors and other mediators of the repair process.

Superoxide dismutase and catalase activities in the growth cartilage: relationship between oxidoreductase activity and chondrocyte maturation

Superoxide dismutase (SOD) and catalase are enzymes that protect cells from radical attack. Catalase disproportionates hydrogen peroxide, and SOD is an oxidoreductase that serves to dismutate the superoxide anion. The objective of this communication was to measure the activity of these disproportionating enzymes in the chick tibial growth cartilage and to relate enzyme activity to chondrocyte maturation and tissue calcification. Analytic techniques were optimized for the measurement of both enzymes; particular care was taken to ensure that the values obtained were due to SOD and catalase, not to the presence of other oxidases or contaminants. Catalase and SOD had similar profiles of activity in cartilage. For both enzymes, the highest levels of activity were observed in premineralized cartilage; as chondrocytes matured there was a progressive decrease in the activity of SOD and catalase. Comparison of chondrocyte SOD activity with nonmineralizing tissues indicated that the activity of cultured cartilage cells was low. We also measured the SOD activity of avascular chondrodystrophic cartilage and found it to be less than that of proliferating cartilage. When cartilage was electrofocused, three SOD isozymes were detected. The pI of the major isozyme corresponded to the copper-zinc isoform. We suggest that the observed changes in enzymatic activity are dependent on a number of cartilage-specific factors that include the vascular supply, the local production of oxygen radicals by chondrocytes, and the oxidative state of the tissue.

Collagen-stimulated superoxide production: evidence for coupled mobilization of calcium

Superoxide production by human neutrophils was stimulated by rat liver collagen. The stimulation was exponentially related to the collagen concentration, with maximal effect at 150 micrograms/ml. The collagen-induced effect was significantly enhanced by the presence of Ca2+ in the medium. Verapamil--a calcium channel blocker--caused a dose-dependent inhibition of superoxide production by collagen-stimulated neutrophils. Collagen-induced stimulation was associated with a transient rise in cytosolic free Ca2+ independent of the presence of Ca2+ in the medium. Depletion of intracellular calcium caused a significant decrease in superoxide activity; however, replenishment of Ca2+ in the medium significantly overcame the inhibition. These changes were associated with a direct binding of [14C]collagen with the neutrophils. Our data suggest that collagen-neutrophil interaction couples superoxide production with the process of Ca2+ mobilization and that this interaction may play a physiologic role in neutrophil stimulation.

Asbestos fibers induce release of collagenase by human polymorphonuclear leukocytes

The asbestos fibers chrysotile and crocidolite cause a dose-dependent release of specific granule collagenase by human polymorphonuclear leukocytes (PMNL). Release of azurophil granule elastase was induced by the asbestos fibers at higher concentrations, suggesting that asbestos fibers primarily cause the release of specific granule contents of human PMNL. Wollastonite, a fibrous silicate mineral, causes a weaker collagenase release and no elastase release. The collagenase was released in inactive, latent form. Carboxymethyl cellulose (CMC), an agent known to blunt chrysotile-induced hemolysis and production of reactive oxygen metabolites by human PMNL, specifically inhibits chrysotile-induced release of collagenase. Chrysotile asbestos was found to bind the PMNL serine proteinase cathepsin G. A role of collagenase release, production of reactive oxygen metabolites and cathepsin G binding by chrysotile for the perpetuation of the asbestos-induced alveolitis is suggested.

Activation of human neutrophils by type I collagen. Requirement of two different sequences

Contact between type I collagen purified from several species and human polymorphonuclear neutrophils (PMNs) triggers the production of O2.- by these cells. The activity of collagen is located in the alpha 1(I)-CB6 cyanogen bromide-cleaved (CB)-peptide, which is the C-terminal CB-peptide of the alpha 1(I) chain. Experiments based on the competitive inhibition of O2.- production by simultaneous incubation of PMNs with type I collagen and synthetic peptides identical to the conserved sequences of this collagen demonstrated that the binding of collagen to PMNs and the subsequent activation of these cells depend on the simultaneous presence of two sequences: Arg-Gly-Asp [residues 915, 916 and 917 of the complete alpha 1(I) chain, located in the helical part] Asp-Gly-Gly-Arg-Tyr-Tyr (residues 1034-1039, located in the C-terminal non-helical telopeptide).

Neutrophil bactericidal activity against Staphylococcus aureus adherent on biological surfaces. Surface-bound extracellular matrix proteins activate intracellular killing by oxygen-dependent and -independent mechanisms

The activation patterns of surface adherent neutrophils are modulated via interaction of extracellular matrix proteins with neutrophil integrins. To evaluate neutrophil bactericidal activity, Staphylococcus aureus adherent to biological surfaces were incubated with neutrophils and serum, and the survival of surface bacteria was determined. When compared to albumin-coated surfaces, the bactericidal activity of neutrophils adherent to purified human extracellular matrix was markedly enhanced (mean survival: 34.2% +/- 9.0% of albumin, P less than 0.0001) despite similar efficient ingestion of extracellular bacteria. Enhancement of killing was observed when surfaces were coated with purified constituents of extracellular matrix, i.e., fibronectin, fibrinogen, laminin, vitronectin, or type IV collagen. In addition to matrix proteins, the tetrapeptide RGDS (the sequence recognized by integrins) crosslinked to surface bound albumin was also active (survival: 74.5% +/- 5.5% of albumin, P less than 0.02), and fibronectin-increased killing was inhibited by soluble RGDS. Chemiluminescence measurements and experiments with CGD neutrophils revealed that both oxygen-dependent and -independent bactericidal mechanisms are involved. In conclusion, matrix proteins enhance intracellular bactericidal activity of adherent neutrophils, presumably by integrin recognition of RGDS-containing ligands. These results indicate a role for extracellular matrix proteins in the enhancement of the host defense against pyogenic infections.

Interaction of polymorphonuclear leukocytes with cartilage in vitro. Catabolic effects of serine proteases and oxygen radicals

The ability of purified PMN serine proteases as well as oxygen-derived free radicals (ODFR) generated by activated phagocytes to damage cartilage matrix has been thoroughly investigated in vitro. The question in the present study was the extent to which enzymatic and ODFR-mediated mechanisms can contribute to the degradation of bovine cartilage slices by zymosan-stimulated PMN. Tissue destruction as assessed by mechanical parameters of stability as well as by liberation of uronic acids from matrix proteoglycans was not inhibitable by the radical scavengers superoxide dismutase (SOD) and catalase (CAT), while serine protease inhibitors led to a significant reduction of matrix degradation. Thus an enzymatic mechanism may play a major part in PMN-induced cartilage damage. Besides this predominant role of especially serine proteases a direct, non-zymosan-dependent stimulatory effect of cartilage matrix on PMN to release elastase into the incubation medium was detected. Hence an as-yet unknown mechanism of PMN activation is indicated, while unspecific effects by bacterial contamination, complement factors, or endotoxin could be excluded as an explanation for the observed phenomenon.