Defensin modulates tissue-type plasminogen activator and plasminogen binding to fibrin and endothelial cells

Plasma human neutrophil peptides as biomarkers of disease severity and mortality in patients with decompensated cirrhosis

BACKGROUND & AIMS

Human neutrophil peptides (HNP)-1, -2 and -3 are the most abundant proteins in neutrophil azurophilic granules and are rapidly released via neutrophil degranulation upon activation. The aims of our study were to assess the role of HNP1-3 as biomarkers of disease severity in patients with decompensated cirrhosis and their value in predicting short-term mortality.

METHODS

In this study, 451 patients with acutely decompensated cirrhosis (AD) were enrolled at the two medical centres. Overall, 281 patients were enrolled as the training cohort from October 2015 to April 2019, and 170 patients were enrolled as the validation cohort from June 2020 to February 2021. Plasma HNP1-3 levels were measured using enzyme-linked immunosorbent assay (ELISA).

RESULTS

Plasma HNP1-3 increased stepwise with disease severity (compensated cirrhosis: 0.3 (0.2-0.4); AD without acute-on-chronic liver failure (ACLF): 1.9 (1.3-4.8); ACLF-1: 2.3 (1.8-6.1); ACLF-2: 5.6 (2.9-12.3); ACLF-3: 10.3 (5.7-17.2) ng/ml). From the multivariate Cox regression analysis, HNP1-3 emerged as independent predictors of mortality at 30 and 90 days. Similar results were observed in the subgroup analysis. On ROC analysis, plasma HNP1-3 showed better predictive accuracy for 30- and 90-day mortality (area under the receiver operating characteristic (AUROC) of 0.850 and 0.885, respectively) than the neutrophil-to-lymphocyte ratio (NLR) and similar accuracy as end-stage liver disease (MELD: 0.881 and 0.874) and chronic liver failure-sequential organ failure (CLIF-SOFA: 0.887 and 0.878).

CONCLUSIONS

Plasma HNP1-3 levels were closely associated with disease severity and might be used to identify patients with AD at high risk of short-term mortality.

Association between tissue human neutrophil peptide 1-3 levels and cardiovascular phenotype: a prospective, longitudinal cohort study

Objective

Inflammation is associated with atherogenesis. Although a higher neutrophil count is associated with the plaque burden, the role of neutrophil activation is unclear. Human neutrophil peptides 1–3 (HNP1–3) are a risk factor for atherogenesis in bench models and are elevated in human atheromas. This study aimed to examine the association between skin HNP1–3 deposition and the severity of coronary artery disease (CAD), including long-term outcomes.

Methods

HNP1–3 levels were immunohistochemically quantified in skin biopsies, which were prospectively taken from 599 consecutive patients before clinically indicated coronary angiography. Established cardiovascular risk factors and blood markers for atheroinflammation were obtained. CAD severity and the incidence of repeat revascularization and mortality at 48 months of follow-up were assessed in relation to HNP1–3 levels.

Results

The risk of CAD was independently associated with age and HNP1–3 in the entire cohort (F = 0.71 and F = 7.4, respectively). Additionally, HNP1–3 levels were significantly associated with myocardial necrosis (R = 0.26). At the follow-up, high HNP1–3 levels negatively affected mortality (19.54%) and recurrent revascularization (8.05%).

Conclusion

HNP1–3 tissue deposition is positively associated with the severity of CAD, myonecrosis, and long-term sequelae. HNP1–3 levels may be suppressed using colchicine.

It takes two to thrombosis: Hemolysis and complement

Thromboembolic events represent the most common complication of hemolytic anemias characterized by complement-mediated hemolysis such as paroxysmal nocturnal hemoglobinuria and autoimmune hemolytic anemia. Similarly, atypical hemolytic uremic syndrome is characterized by hemolysis and thrombotic abnormalities. The main player in the development of thrombosis in hemolytic diseases is suggested to be the complement system. However, the release of extracellular hemoglobin and heme by hemolysis itself can also drive procoagulant responses. Both, complement activation and hemolysis promote the activation of neutrophils resulting in the formation of neutrophil extracellular traps and induce inflammation and vascular damage which all together might (synergistically) lead to hypercoagulability. In this review we aim to summarize the current knowledge on the role of complement activation and hemolysis in the onset of thrombosis in hemolytic diseases. This review will discuss the interplay between different biological systems and neutrophil activation contributing to the pathogenesis of thrombosis. Finally, we will combine this fundamental knowledge and address the pathophysiology of hemolysis in prototypical complement-driven diseases.

Insights Into Immunothrombosis: The Interplay Among Neutrophil Extracellular Trap, von Willebrand Factor, and ADAMTS13

Both neutrophil extracellular traps (NETs) and von Willebrand factor (VWF) are essential for thrombosis and inflammation. During these processes, a complex series of events, including endothelial activation, NET formation, VWF secretion, and blood cell adhesion, aggregation and activation, occurs in an ordered manner in the vasculature. The adhesive activity of VWF multimers is regulated by a specific metalloprotease ADAMTS13 (a disintegrin and metalloproteinase with thrombospondin type 1 motifs, member 13). Increasing evidence indicates that the interaction between NETs and VWF contributes to arterial and venous thrombosis as well as inflammation. Furthermore, contents released from activated neutrophils or NETs induce the reduction of ADAMTS13 activity, which may occur in both thrombotic microangiopathies (TMAs) and acute ischemic stroke (AIS). Recently, NET is considered as a driver of endothelial damage and immunothrombosis in COVID-19. In addition, the levels of VWF and ADAMTS13 can predict the mortality of COVID-19. In this review, we summarize the biological characteristics and interactions of NETs, VWF, and ADAMTS13, and discuss their roles in TMAs, AIS, and COVID-19. Targeting the NET-VWF axis may be a novel therapeutic strategy for inflammation-associated TMAs, AIS, and COVID-19.

Histone-induced thrombotic thrombocytopenic purpura in adamts13 -/- zebrafish depends on von Willebrand factor

Thrombotic thrombocytopenic purpura (TTP) is caused by severe deficiency of ADAMTS13 (A13), a plasma metalloprotease that cleaves endothelium-derived von Willebrand factor (VWF). However, severe A13 deficiency alone is often not sufficient to cause an acute TTP; additional factors may be required to trigger the disease. Using CRISPR/Cas9, we created and characterized several novel zebrafish lines carrying a null mutation in a13-/- , vwf, and both. We further used these zebrafish lines to test the hypothesis that inflammation that results in neutrophil activation and release of histone/DNA complexes may trigger TTP. As shown, a13-/- zebrafish exhibit increased levels of plasma VWF antigen, multimer size, and ability of thrombocytes to adhere to a fibrillar collagen-coated surface under flow. The a13-/- zebrafish also show an increased rate of occlusive thrombus formation in the caudal venules after FeCl3 injury. More interestingly, a13-/- zebrafish exhibit ~30% reduction in the number of total, immature, and mature thrombocytes with increased fragmentation of erythrocytes. Administration of a lysine-rich histone results in more severe and persistent thrombocytopenia and a significantly increased mortality rate in a13-/- zebrafish than in wildtype (wt) ones. However, both spontaneous and histone-induced TTP in a13-/- zebrafish are rescued by the deletion of vwf These results demonstrate a potentially mechanistic link between inflammation and the onset of TTP in light of severe A13 deficiency; the novel zebrafish models of TTP may help accelerate our understanding of pathogenic mechanisms and the discoveries of novel therapeutics for TTP and perhaps other arterial thrombotic disorders.

Human neutrophil peptide-1 inhibits thrombus formation under arterial flow via its terminal free cysteine thiols

Essentials Biological activity of human neutrophil peptide (HNP)-1 in hemostasis under physiological conditions is not fully understood. HNP-1 inhibits the adhesion/aggregation of murine platelets on a fibrillar collagen surface or an activated endothelial cell surface under flow. The anti-adhesion activity appears to depend on the terminal free thiols of HNP-1, which may inhibit VWF-VWF lateral associations. Our results suggest a protective role and potential novel therapeutic use of HNP-1 for arterial thrombosis. SUMMARY: Background Human neutrophil peptides (HNPs), also known as α-defensins, are released from degranulated neutrophils and play an important role in innate immunity. However, their biological roles in hemostasis under flow are not fully explored. Objective This study aims to determine the role of HNP-1 on platelet adhesion and aggregation on a collagen surface or ultra large von Willebrand factor (ULVWF) on endothelium under flow and elucidate the structural elements required for its activity. Methods Anticoagulated whole blood from wild-type or Adamts13-/- mice was incubated with a fluorescein-conjugated anti-human CD41 in the presence of increasing concentrations of a synthetic HNP-1 and perfused over a collagen surface or a tumor necrosis factor (TNF)-α activated murine endothelial cell surface under arterial flow. The rate of accumulation and the final surface coverage of fluoresceinated murine platelets or the rate of forming platelet-decorated ULVWF strings were determined using the BioFlux microfluidic system. Results HNP-1 inhibited the rate and final coverage of fluorescein-labeled murine platelets on a fibrillar collagen surface under flow (100 dyne/cm2 ) in a concentration-dependent manner and the anti-adhesive activity of HNP-1 depended on its terminal free cysteine thiols. HNP-1 (20 μM) also dramatically inhibited the formation of platelets-decorated ULVWF strings on TNF-α activated murine endothelial surface under arterial flow. Conclusions Our results demonstrate for the first time an antiplatelet adhesion or antithrombotic activity of HNP-1; this activity depends on its terminal free thiols, likely affecting VWF-VWF lateral associations. These findings may suggest a potential novel therapeutic strategy for arterial thrombosis.

Neutrophil α-defensins promote thrombosis in vivo by altering fibrin formation, structure, and stability

Inflammation and thrombosis are integrated, mutually reinforcing processes, but the interregulatory mechanisms are incompletely defined. Here, we examined the contribution of α-defensins (α-defs), antimicrobial proteins released from activated human neutrophils, on clot formation in vitro and in vivo. Activation of the intrinsic pathway of coagulation stimulates release of α-defs from neutrophils. α-Defs accelerate fibrin polymerization, increase fiber density and branching, incorporate into nascent fibrin clots, and impede fibrinolysis in vitro. Transgenic mice (Def++) expressing human α-Def-1 developed larger, occlusive, neutrophil-rich clots after partial inferior vena cava (IVC) ligation than those that formed in wild-type (WT) mice. IVC thrombi extracted from Def++ mice were composed of a fibrin meshwork that was denser and contained a higher proportion of tightly packed compressed polyhedral erythrocytes than those that developed in WT mice. Def++ mice were resistant to thromboprophylaxis with heparin. Inhibiting activation of the intrinsic pathway of coagulation, bone marrow transplantation from WT mice or provision of colchicine to Def++ mice to inhibit neutrophil degranulation decreased plasma levels of α-defs, caused a phenotypic reversion characterized by smaller thrombi comparable to those formed in WT mice, and restored responsiveness to heparin. These data identify α-defs as a potentially important and tractable link between innate immunity and thrombosis.

Relative Deficiency of Plasma A Disintegrin and Metalloprotease with Thrombospondin Type 1 Repeats 13 Activity and Elevation of Human Neutrophil Peptides in Patients with Traumatic Brain Injury

Traumatic microvascular injury (tMVI) is a universal endophenotype of traumatic brain injury (TBI) that is responsible for significant neurological morbidity and mortality. The mechanism underlying tMVI is not fully understood. The present study aims to determine plasma levels of von Willebrand factor (VWF), a disintegrin and metalloprotease with thrombospondin type 1 repeats (ADAMTS) 13 activity, and human neutrophil peptides (HNP) 1-3 and to correlate these biomarkers with functional outcomes after moderate-severe TBI. Thirty-one consecutive TBI patients (Glasgow Coma Scale [GCS] range, 3-12) were enrolled into the study between February 2010 and November 2014. Blood samples were collected on 0, 1, 2, 3, and 5 days after admission and analyzed for plasma levels of VWF antigen (VWFAg), collagen-binding activity (VWFAc), ADAMTS13 activity, and HNP1-3 proteins. Mean values of plasma VWFAg, VWFAc, and HNP1-3 were significantly increased in TBI patients compared to those in healthy controls (n = 30). Conversely, mean plasma values of ADAMTS13 activity in TBI patients were significantly decreased during the first 2 days after admission. This resulted in a dramatic reduction in the ratio of ADAMTS13 activity to VWFAg or ADAMTS13 to VWFAc in all 5 post-TBI days. Cluster analysis demonstrated that high median plasma levels of VWFAg and HNP1-3 were observed in the cluster with a high mortality rate. These results demonstrate that a relative deficiency of plasma ADAMTS13 activity, resulting from activation of neutrophils and endothelium, may contribute to the formation of microvascular thrombosis and mortality after moderate-severe TBI.

Multifaceted immune functions of human defensins and underlying mechanisms

Defensins have been long recognized as natural antimicrobial peptides, but they also possess diverse and versatile immune functions. Defensins can both induce inflammation and suppress inflammatory responses by acting on specific cells through distinct mechanisms. Defensins can also modulate the immune response by forming a complex with cellular molecules including proteins, nucleic acids, and carbohydrates. The mechanisms of defensin-mediated immune modulation appear to be cell-type and context specific. Because the levels of human defensins are often altered in response to infection or disease states, suggesting their clinical relevance, this review summarizes the complex immune functions of human defensins and their underlying mechanisms of action, which have implications for the development of new therapeutics.

Targeting and inactivation of bacterial toxins by human defensins

Defensins, as a prominent family of antimicrobial peptides (AMP), are major effectors of the innate immunity with a broad range of immune modulatory and antimicrobial activities. In particular, defensins are the only recognized fast-response molecules that can neutralize a broad range of bacterial toxins, many of which are among the deadliest compounds on the planet. For a decade, the mystery of how a small and structurally conserved group of peptides can neutralize a heterogeneous group of toxins with little to no sequential and structural similarity remained unresolved. Recently, it was found that defensins recognize and target structural plasticity/thermodynamic instability, fundamental physicochemical properties that unite many bacterial toxins and distinguish them from the majority of host proteins. Binding of human defensins promotes local unfolding of the affected toxins, destabilizes their secondary and tertiary structures, increases susceptibility to proteolysis, and leads to their precipitation. While the details of toxin destabilization by defensins remain obscure, here we briefly review properties and activities of bacterial toxins known to be affected by or resilient to defensins, and discuss how recognized features of defensins correlate with the observed inactivation.

α-Defensins and bacterial/permeability-increasing protein as new markers of childhood obesity

OBJECTIVES

The aim of this paper is to test whether α-defensins and bacterial/permeability-increasing protein were related to obesity and cardiovascular risk factors in prepubertal children.

METHODS

Plasma α-defensins and bacterial/permeability-increasing protein, body mass index (BMI), waist circumference, systolic blood pressure (SBP), carotid intima media thickness (cIMT), HOMA-IR and HMW-adiponectin were assessed.

RESULTS

In a cross-sectional study (N = 250), higher α-defensins concentrations were positively associated with BMI, waist, SBP, cIMT, HOMA-IR and negative correlated with HMW-adiponectin (all between r = 0.191 and r = 0.377, p ≤ 0.01 and p ≤ 0.0001). Conversely, plasma bacterial/permeability-increasing protein concentrations presented inversed associated with the same parameters (all between r = -0.124 and r = -0.329; p ≤ 0.05 and p ≤ 0.0001). In a longitudinal study (N = 91), α-defensins at age 7 were associated with BMI (β = 0.189, p = 0.002; model R²  = 0.847) and waist (β = 0.241, pthinsp;= 0.001; model R²  = 0.754) at age 10.

CONCLUSIONS

α-Defensins and bacterial/permeability-increasing protein may be the markers of childhood obesity. Increased concentrations of α-defensins may predict BMI and abdominal fat deposition in children.

Human neutrophil peptides and complement factor Bb in pathogenesis of acquired thrombotic thrombocytopenic purpura

Acquired thrombotic thrombocytopenic purpura is primarily caused by the deficiency of plasma ADAMTS13 activity resulting from autoantibodies against ADAMTS13. However, ADAMTS13 deficiency alone is often not sufficient to cause acute thrombotic thrombocytopenic purpura. Infections or systemic inflammation may precede acute bursts of the disease, but the underlying mechanisms are not fully understood. Herein, 52 patients with acquired autoimmune thrombotic thrombocytopenic purpura and 30 blood donor controls were recruited for the study. The plasma levels of human neutrophil peptides 1-3 and complement activation fragments (i.e. Bb, iC3b, C4d, and sC5b-9) were determined by enzyme-linked immunosorbent assays. Univariate analyses were performed to determine the correlation between each biomarker and clinical outcomes. We found that the plasma levels of human neutrophil peptides 1-3 and Bb in patients with acute thrombotic thrombocytopenic purpura were significantly higher than those in the control (P<0.0001). The plasma levels of HNP1-3 correlated with the levels of plasma complement fragment Bb (rho=0.48, P=0.0004) and serum lactate dehydrogenase (rho=0.28, P=0.04); in addition, the plasma levels of Bb correlated with iC3b (rho=0.55, P<0.0001), sC5b-9 (rho=0.63, P<0.0001), serum creatinine (rho=0.42, p=0.0011), and lactate dehydrogenase (rho=0.40, P=0.0034), respectively. Moreover, the plasma levels of iC3b and sC5b-9 were correlated (rho=0.72, P<0.0001), despite no statistically significant difference of the two markers between thrombotic thrombocytopenic purpura patients and the control. We conclude that innate immunity, i.e. neutrophil and complement activation via the alternative pathway, may play a role in the pathogenesis of acute autoimmune thrombotic thrombocytopenic purpura, and a therapy targeted at these pathways may be considered in a subset of these patients.

Human neutrophil peptides inhibit cleavage of von Willebrand factor by ADAMTS13: a potential link of inflammation to TTP

Infection or inflammation may precede and trigger formation of microvascular thrombosis in patients with acquired thrombotic thrombocytopenic purpura (TTP). However, the mechanism underlying this clinical observation is not fully understood. Here, we show that human neutrophil peptides (HNPs) released from activated and degranulated neutrophils inhibit proteolytic cleavage of von Willebrand factor (VWF) by ADAMTS13 in a concentration-dependent manner. Half-maximal inhibitory concentrations of native HNPs toward ADAMTS13-mediated proteolysis of peptidyl VWF73 and multimeric VWF are 3.5 μM and 45 μM, respectively. Inhibitory activity of HNPs depends on the RRY motif that is shared by the spacer domain of ADAMTS13. Native HNPs bind to VWF73 (KD = 0.72 μM), soluble VWF (KD = 0.58 μM), and ultra-large VWF on endothelial cells. Enzyme-linked immunosorbent assay (ELISA) demonstrates markedly increased plasma HNPs1-3 in most patients with acquired autoimmune TTP at presentation (median, ∼170 ng/mL; range, 58-3570; n = 19) compared with healthy controls (median, ∼23 ng/mL; range, 6-44; n = 18) (P < .0001). Liquid chromatography plus tandem mass spectrometry (LC-MS/MS) reveals statistically significant increases of HNP1, HNP2, and HNP3 in patient samples (all P values <.001). There is a good correlation between measurement of HNPs1-3 by ELISA and by LC-MS/MS (Spearman ρ = 0.7932, P < .0001). Together, these results demonstrate that HNPs1-3 may be potent inhibitors of ADAMTS13 activity, likely by binding to the central A2 domain of VWF and physically blocking ADAMTS13 binding. Our findings may provide a novel link between inflammation/infection and the onset of microvascular thrombosis in acquired TTP and potentially other immune thrombotic disorders.

α-Defensins Induce a Post-translational Modification of Low Density Lipoprotein (LDL) That Promotes Atherosclerosis at Normal Levels of Plasma Cholesterol

Approximately one-half of the patients who develop clinical atherosclerosis have normal or only modest elevations in plasma lipids, indicating that additional mechanisms contribute to pathogenesis. In view of increasing evidence that inflammation contributes to atherogenesis, we studied the effect of human neutrophil α-defensins on low density lipoprotein (LDL) trafficking, metabolism, vascular deposition, and atherogenesis using transgenic mice expressing human α-defensins in their polymorphonuclear leukocytes (Def(+/+)). Accelerated Def(+/+) mice developed α-defensin·LDL complexes that accelerate the clearance of LDL from the circulation accompanied by enhanced vascular deposition and retention of LDL, induction of endothelial cathepsins, increased endothelial permeability to LDL, and the development of lipid streaks in the aortic roots when fed a regular diet and at normal plasma levels of LDL. Transplantation of bone marrow from Def(+/+) to WT mice increased LDL clearance, increased vascular permeability, and increased vascular deposition of LDL, whereas transplantation of WT bone marrow to Def(+/+) mice prevented these outcomes. The same outcome was obtained by treating Def(+/+) mice with colchicine to inhibit the release of α-defensins. These studies identify a potential new link between inflammation and the development of atherosclerosis.

Endogenous plasminogen activators mediate progressive intracerebral hemorrhage after traumatic brain injury in mice

Persistent intracerebral hemorrhage (ICH) is a major cause of death and disability after traumatic brain injury (TBI) for which no medical treatment is available. Delayed bleeding is often ascribed to consumptive coagulopathy initiated by exposed brain tissue factor. We examined an alternative hypothesis, namely, that marked release of tissue-type plasminogen activator (tPA) followed by delayed synthesis and release of urokinase plasminogen activator (uPA) from injured brain leads to posttraumatic bleeding by causing premature clot lysis. Using a murine model of severe TBI, we found that ICH is reduced in tPA(-/-) and uPA(-/-) mice but increased in PAI-1(-/-) mice compared with wild-type (WT) mice. tPA(-/-), but not uPA(-/-), mice developed a systemic coagulopathy post-TBI. Tranexamic acid inhibited ICH expansion in uPA(-/-)mice but not in tPA(-/-) mice. Catalytically inactive tPA-S(481)A inhibited plasminogen activation by tPA and uPA, attenuated ICH, lowered plasma d-dimers, lessened thrombocytopenia, and improved neurologic outcome in WT, tPA(-/-), and uPA(-/-) mice. ICH expansion was also inhibited by tPA-S(481)A in WT mice anticoagulated with warfarin. These data demonstrate that protracted endogenous fibrinolysis induced by TBI is primarily responsible for persistent ICH and post-TBI coagulopathy in this model and offer a novel approach to interrupt bleeding.

Neutrophils Turn Plasma Proteins into Weapons against HIV-1

As a consequence of innate immune activation granulocytes and macrophages produce hypochlorite/hypochlorous acid (HOCl) via secretion of myeloperoxidase (MPO) to the outside of the cells, where HOCl immediately reacts with proteins. Most proteins that become altered by this system do not belong to the invading microorganism but to the host. While there is no doubt that the myeloperoxidase system is capable of directly inactivating HIV-1, we hypothesized that it may have an additional indirect mode of action. We show in this article that HOCl is able to chemically alter proteins and thus turn them into Idea-Ps (Idea-P = immune defence-altered protein), potent amyloid-like and SH-groups capturing antiviral weapons against HIV-1. HOCl-altered plasma proteins (Idea-PP) have the capacity to bind efficiently and with high affinity to the HIV-1 envelope protein gp120, and to its receptor CD4 as well as to the protein disulfide isomerase (PDI). Idea-PP was able to inhibit viral infection and replication in a cell culture system as shown by reduced number of infected cells and of syncytia, resulting in reduction of viral capsid protein p24 in the culture supernatant. The unmodified plasma protein fraction had no effect. HOCl-altered isolated proteins antithrombin III and human serum albumin, taken as representative examples of the whole pool of plasma proteins, were both able to exert the same activity of binding to gp120 and inhibition of viral proliferation. These data offer an opportunity to improve the understanding of the intricacies of host-pathogen interactions and allow the generation of the following hypothetical scheme: natural immune defense mechanisms generate by posttranslational modification of plasma proteins a potent virucidal weapon that immobilizes the virus as well as inhibits viral fusion and thus entry into the host cells. Furthermore simulation of this mechanism in vitro might provide an interesting new therapeutic approach against microorganisms.

Acute ST-segment elevation myocardial infarction is associated with decreased human antimicrobial peptide LL-37 and increased human neutrophil peptide-1 to 3 in plasma

AIM

Increasing evidence indicates that antimicrobial peptides, human neutrophil peptide-1, -2, and -3 (HNP1-3) and human antimicrobial peptide LL-37 are involved in the pathophysiology of atherosclerosis; however, little is known about their circulating protein levels in acute myocardial infarction (AMI). We therefore investigated whether their plasma levels are associated with stable coronary artery disease (CAD) and acute ST-segment elevation myocardial infarction (STEMI).

METHODS

Systemic or local (culprit artery) blood samples were obtained from 112 consecutive male subjects including no CAD (n = 31) controls, stable CAD (n = 44) and STEMI (n = 47). Plasma HNP1-3 and LL-37 levels were measured by the ready-to-use solid-phase enzyme-linked immunosorbent assay (ELISA) based on the sandwich principle.

RESULTS

Systemic HNP1-3 in STEMI was increased compared with no CAD (p = 0.000) and stable CAD (p = 0.008), and systemic HNP1-3 in stable CAD was higher than in no CAD (p = 0.004). Systemic LL-37 in STEMI was decreased compared with no CAD (p = 0.009) and stable CAD (p =0.001) and restored within 1 day following STEMI (p = 0.000). Local LL-37 levels in STEMI were higher than systemic levels (p = 0.013). The areas under the ROC curve of systemic HNP1-3 and LL-37 for STEMI were 0.717 (95% CI: 0.624, 0.811; p = 0.000) and 0.702 (95% CI: 0.609, 0.795; p = 0.000), respectively. In addition, ischemia time in the STEMI group correlated with systemic and local levels of HNP1-3 (rs = -0.360, p = 0.013; rs = 0.608, p = 0.000, respectively), and was also associated with systemic and local levels of hs-CRP (rs = 0.408, p = 0.004; rs = 0.425, p = 0.003, respectively), but not with those of LL-37 (all p > 0.05).

CONCLUSION

STEMI was associated with transiently decreased LL-37, but persistently increased HNP1-3 in the systemic circulation and the diagnostic accuracy for STEMI were moderate. Future studies should pay more attention to their prognostic values for myocardial infarction.

Antimicrobial peptides: general overview and clinical implications in human health and disease

Antimicrobial peptides (AMPs) are evolutionarily conserved molecules involved in the defense mechanisms of a wide range of organisms. Produced in bacteria, insects, plants and vertebrates, AMPs protect against a broad array of infectious agents. In mammals these peptides protect against bacteria, viruses, fungi, and certain parasites. Recently, novel biologic effects of AMPs have been documented such as endotoxin neutralization, chemotactic and immunomodulating activities, induction of angiogenesis and wound repair. Thus these ancestral molecules are crucial components of the innate immune system and attractive candidates for novel therapeutic approaches. This review focuses on cathelicin and defensins, the most documented human AMPs, and discusses their antimicrobial activity and pleiotropic immunomodulating effects on inflammatory and infectious diseases.

Neutrophil alpha-defensins cause lung injury by disrupting the capillary-epithelial barrier

RATIONALE

The involvement of neutrophil activation in the sentinel, potentially reversible, events in the pathogenesis of acute lung injury (ALI) is only partially understood. alpha-Defensins are the most abundant proteins secreted by activated human neutrophils, but their contribution to ALI in mouse models is hindered by their absence from murine neutrophils and the inability to study their effects in isolation in other species.

OBJECTIVES

To study the role of alpha-defensins in the pathogenesis of ALI in a clinically relevant setting using mice transgenic for polymorphonuclear leukocyte expression of alpha-defensins.

METHODS

Transgenic mice expressing polymorphonuclear leukocyte alpha-defensins were generated. ALI was induced by acid aspiration. Pulmonary vascular permeability was studied in vivo using labeled dextran and fibrin deposition. The role of the low-density lipoprotein-related receptor (LRP) in permeability was examined.

MEASUREMENTS AND MAIN RESULTS

Acid aspiration induced neutrophil migration and release of alpha-defensins into lung parenchyma and airways. ALI was more severe in alpha-defensin-expressing mice than in wild-type mice, as determined by inspection, influx of neutrophils into the interstitial space and airways, histological evidence of epithelial injury, interstitial edema, extravascular fibrin deposition, impaired oxygenation, and reduced survival. Within 4 hours of insult, alpha-defensin-expressing mice showed greater disruption of capillary-epithelial barrier function and ALI that was attenuated by systemic or intratracheal administration of specific inhibitors of the LRP.

CONCLUSIONS

alpha-Defensins mediate ALI through LRP-mediated loss of capillary-epithelial barrier function, suggesting a potential new approach to intervention.

Application of natural antimicrobials for food preservation

In this review, antimicrobials from a range of plant, animal, and microbial sources are reviewed along with their potential applications in food systems. Chemical and biochemical antimicrobial compounds derived from these natural sources and their activity against a range of pathogenic and spoilage microorganisms pertinent to food, together with their effects on food organoleptic properties, are outlined. Factors influencing the antimicrobial activity of such agents are discussed including extraction methods, molecular weight, and agent origin. These issues are considered in conjunction with the latest developments in the quantification of the minimum inhibitory (and noninhibitory) concentration of antimicrobials and/or their components. Natural antimicrobials can be used alone or in combination with other novel preservation technologies to facilitate the replacement of traditional approaches. Research priorities and future trends focusing on the impact of product formulation, intrinsic product parameters, and extrinsic storage parameters on the design of efficient food preservation systems are also presented.

Human neutrophil peptides: a novel potential mediator of inflammatory cardiovascular diseases

The traditional view of atherosclerosis has recently been expanded from a predominantly lipid retentive disease to a coupling of inflammatory mechanisms and dyslipidemia. Studies have suggested a novel role for polymorphonuclear neutrophil (PMN)-dominant inflammation in the development of atherosclerosis. Human neutrophil peptides (HNPs), also known as alpha-defensins, are secreted and released from PMN granules upon activation and are conventionally involved in microbial killing. Current evidence suggests an important immunomodulative role for these peptides. HNP levels are markedly increased in inflammatory diseases including sepsis and acute coronary syndromes. They have been found within the intima of human atherosclerotic arteries, and their deposition in the skin correlates with the severity of coronary artery diseases. HNPs form complexes with LDL in solution and increase LDL binding to the endothelial surface. HNPs have also been shown to contribute to endothelial dysfunction, lipid metabolism disorder, and the inhibition of fibrinolysis. Given the emerging relationship between PMN-dominant inflammation and atherosclerosis, HNPs may serve as a link between them and as a biological marker and potential therapeutic target in cardiovascular diseases including coronary artery diseases and acute coronary syndromes.

Human alpha-defensin-1 inhibits growth of human lung adenocarcinoma xenograft in nude mice

Human alpha-defensin-1 (HNP1), a small antimicrobial peptide, shows cytotoxicity to tumor cells in vitro and inhibitory activity for pathologic neovascularization in vivo. Here, we did a gene therapy with a plasmid that expresses a secretable form of HNP1 for assaying its antitumor activity. The expression and secretion of HNP1 were determined by reverse transcription-PCR and ELISA in vitro. We found that expression of HNP1 in A549 tumor cells caused significant growth inhibition. This effect is most likely cell autonomous, as a significant amount of recombinant HNP1 protein was found to be accumulated in the cytoplasm by immunohistochemical staining using an anti-HNP1 antibody and the supernatant containing secreted HNP1 failed to produce any noticeable antitumor activity. Flow cytometry and Hoechst 33258 staining showed that the number of apoptotic cells among the A549 cells expressing recombinant HNP1 proteins was significantly greater than that of the nontransfected control cultures, suggesting that this growth-inhibitory activity was due to an apoptotic mechanism triggered by the intracellular HNP1. The antitumor activity of intracellularly expressed HNP1 was also shown in vivo. Decreased microvessel density and increased lymphocyte infiltration were observed in tumor tissue from HNP1-treated mice through histologic analysis. These results indicate that intracellularly expressed HNP1 induces tumor cell apoptosis, which inhibits tumor growth. The antiangiogenesis effect of HNP1 may contribute to its inhibitory activity in vivo, and HNP1 might involve the host immune response to tumor. These findings provide a rationale for developing HNP1-based gene therapy for cancer.

Interleukin-22 deficiency accelerates the rejection of full major histocompatibility complex-disparate heart allografts

Interleukin-22 (IL-22) was recently described as an effector cytokine produced by TH17 CD4(+) T lymphocytes that, cooperatively with IL-17, mediates IL-23-driven inflammation. Because there was experimental evidence for the role of IL-17 in acute rejection of vascularized allografts, we undertook the present study to assess the function of IL-22 in the process. There was an early transient expression of IL-22 in C57BL/6 mouse cardiac allografts (2-4 days posttransplantation) transplanted to BALB/c recipients. The main source of IL-22 among infiltrating leukocytes was cells expressing the macrophage/monocyte markers Mac3 and CD11b. T cells and granulocytes present in the rejected graft did not express IL-22. Surprisingly, the absence of IL-22 accelerated the rejection of fully histoincompatible hearts. Histology of rejected organs revealed the presence of intensive intragraft thrombosis and disseminated hemorrhagic necrosis. Taken together, these results demonstrated that IL-22 was not an effector lymphokine in cardiac allograft rejection, but early intragraft expression of the cytokine protected it from rejection.

Neutrophil antimicrobial peptide alpha-defensin causes endothelial dysfunction in porcine coronary arteries

BACKGROUND

Defensins are cysteine-rich cationic polypeptides released from neutrophils that exhibit powerful antimicrobial activities. Because inflammation, including neutrophil infiltration and release of defensins, may play an important role in atherosclerosis and other vascular diseases, we determined whether alpha-defensin could cause endothelial dysfunction, a major initial event of atherosclerosis, in porcine coronary arteries.

METHODS

Porcine coronary arteries were sliced into 5-mm rings and treated with different concentrations of human recombinant alpha-defensin for 24 hours. Vasomotor reactivity was studied by using a myograph system. Levels of superoxide anion were detected by the lucigenin-enhanced chemiluminescence method. Endothelial nitric oxide synthase (eNOS) messenger RNA (mRNA) and protein levels were determined by real-time polymerase chain reaction and immunohistochemistry analysis, respectively.

RESULTS

Endothelium-dependent relaxation in response to bradykinin was significantly reduced by 40% for the rings treated with 1500 nM of alpha-defensin compared with controls (P< .05). Vessel contractility in response to the thromboxane A2 analogue U46619 and endothelium-independent relaxation in response to sodium nitroprusside were not affected with defensin treatment. In addition, the superoxide anion level at the endothelial layer of porcine coronary artery rings was significantly increased by 80% in the defensin-treated (1500 nM) vessels compared with controls (P< .05). Furthermore, the eNOS mRNA levels in endothelial cells isolated from the cultured rings treated with defensin (1500 nM) were significantly decreased by 27% compared with controls (P< .05). Immunoreactivity of eNOS in the defensin-treated vessel rings was also substantially reduced.

CONCLUSIONS

Defensin reduces the endothelium-dependent vasorelaxation. This effect is associated with increased superoxide radical production and decreased eNOS expression in porcine coronary arteries.

CLINICAL RELEVANCE

Inflammation is an important mechanism of atherosclerosis and other vascular diseases. The roles and interactions of biomediators released from inflammatory cells are not fully understood, however. This study provides new information about effects and potential molecular mechanisms of a major neutrophil releasing factor, alpha-defensin, on endothelial dysfunction of porcine coronary arteries. Thus, targeting alpha-defensin and its associated molecular mechanisms may become a new strategy to prevent vascular diseases.

Alpha defensins 1, 2, and 3: potential roles in dyslipidemia and vascular dysfunction in humans

OBJECTIVES

Alpha-defensins are natural antibiotics made by neutrophils that have been reported to modulate cholesterol metabolism and vascular function; however, their role in vivo remains largely unknown. We hypothesized that alpha-defensins 1 to 3 (DEFA1-3) are associated with serum lipids and vascular reactivity in humans.

METHODS AND RESULTS

One hundred thirteen apparently-healthy White men, participants in a prospective study of cardiovascular risk factors, were assessed for a lipid profile, insulin sensitivity (S(I), frequently-sampled intravenous glucose tolerance test), and non-stressed circulating DEFA1-3 (ELISA). In a subset of 52 subjects, vascular reactivity (high-resolution ultrasound of the brachial artery) was also assessed. Subjects in the highest quartile for plasma DEFA1-3 were found to be leaner and more insulin sensitive, and to have significantly reduced total and LDL-cholesterol, compared with subjects in the lowest quartile for circulating DEFA1-3 (P<0.0001 to P=0.002 for linear trend ANOVA). The associations with serum lipids persisted after adjustment for age, body mass index, insulin sensitivity, and smoking (which was associated with reduced plasma DEFA1-3 concentrations). Finally, endothelium-independent vasodilation increased with increasing circulating DEFA1-3 (P=0.003) and this association was not explained by age, body mass index, serum cholesterol, insulin sensitivity, or smoking.

CONCLUSIONS

Circulating DEFA1-3 are associated with serum cholesterol and vascular reactivity in humans. Alpha-defensins may have clinical implications in patients with either hypercholesterolemia or vascular dysfunction.

Multifunctional antimicrobial peptides: therapeutic targets in several human diseases

Antimicrobial peptides have emerged as promising agents against antibiotic-resistant pathogens. They represent essential components of the innate immunity and permit humans to resist infection by microbes. These gene-encoded peptides are found mainly in phagocytes and epithelial cells, showing a direct activity against a wide range of microorganisms. Their role has now broadened from that of simply endogenous antibiotics to multifunctional mediators, and their antimicrobial activity is probably not the only primary function. Although antimicrobial peptide deficiency, dysregulation, or overproduction is not known to be a direct cause of any single human disease, numerous studies have now provided compelling evidence for their involvement in the complex network of immune responses and inflammatory diseases, thereby influencing diverse processes including cytokine release, chemotaxis, angiogenesis, wound repair, and adaptive immune induction. The purpose of this review is to highlight recent literature, showing that antimicrobial peptides are associated with several human conditions including infectious and inflammatory diseases, and to discuss current clinical development of peptide-based therapeutics for future use.

alpha-Defensin: link between inflammation and atherosclerosis

BACKGROUND

Several markers of inflammation predict the risk of thrombotic cardiovascular events in patients with atherosclerosis. However, the mechanism by which vascular inflammation promotes atherothrombotic disease is incompletely understood. Human neutrophil peptides 1-3, also known as alpha-defensins, are found in human atherosclerotic arteries, inhibit LDL metabolism and fibrinolysis and promote Lp(a) binding. We asked, therefore, if alpha-defensins are risk factors for the presence and severity of atherosclerosis.

METHODS

alpha-Defensin was measured in skin biopsies taken from 53 male patients (age 58.7+/-11.3 years, mean+/-S.D.) immediately prior to coronary artery catheterization. Other established risk factors were measured concurrently. The correlation between alpha-defensin deposition in the skin and the severity of the coronary artery disease (CAD) was examined.

RESULTS

A statistically significant correlation was observed between the amount of alpha-defensin in skin and the severity of CAD (R=0.40, p=0.003). Multiple regression analysis showed that skin alpha-defensin is an independent predictor for CAD severity (F=4.68, p=0.035). Logistic regression analysis confirmed that skin alpha-defensin independently predicted the likelihood for CAD (p=0.016, odds estimate 5.97, 95% CL 1.4-24.2).

CONCLUSIONS

The deposition of alpha-defensin in the skin is a strong independent predictor of CAD in men. These results suggest a link between neutrophil activation and progression of atherosclerosis and provide a novel approach to assessment of risk factors for CAD.

α-Defensins from blood leukocytes of the monkey Papio hamadryas

Three antimicrobial peptides named PHD1-3 (Papio hamadryas defensin) have been isolated from hamadryas baboon blood leukocytes using preparative electrophoresis and reverse-phase HPLC. The primary structures of these peptides have been determined by automated Edman degradation and mass-spectrometry. The results suggest that the peptides belong to the alpha-defensin family. Structural homology analysis reveals that among alpha-defensins from other animal species, PHD3 is the most closely related to RMAD5 (rhesus macaque alpha-defensin) (90% homology) from rhesus macaque leukocytes and also highly similar to human alpha-defensin HD5 (60% homology), which is produced by intestinal Paneth cells. The homology of PHD3 with human neutrophil alpha-defensin HNP1 (human natural peptide) was 30%. The primary structures of PHD1 and PHD2 are most similar to RED1 (rhesus enteral defensin), one of six enteral alpha-defensins of rhesus monkeys. PHD1-3 have been shown to be active against the Gram-positive bacteria Listeria monocytogenes and Staphylococcus aureus, the Gram-negative bacterium Escherichia coli, and the fungus Candida albicans, similarly to the human HNP1 defensin.

Defensins in innate antiviral immunity

Defensins are small antimicrobial peptides that are produced by leukocytes and epithelial cells, and that have an important role in innate immunity. Recent advances in understanding the mechanisms of the antiviral action(s) of defensins indicate that they have a dual role in antiviral defence, acting directly on the virion and on the host cell. This Review focuses on the antiviral activities and mechanisms of action of mammalian defensins, and on the clinical relevance of these activities. Understanding the complex function of defensins in innate immunity against viral infection has implications for the prevention and treatment of viral disease.

Serum markers of vascular inflammation in dyslipemia

Atherosclerosis is widely recognized as an inflammatory disease because systemic and local inflammatory events mediate all phases of plaque development and progression. Basic and clinical studies have focused on identifying potentially useful markers of inflammation. In this article, we review the inflammatory pathogenesis of atherosclerosis, and highlight recent results of several of the more promising markers of inflammation for cardiovascular risk assessment. Of these markers, the most reliable and accessible for clinical use is currently high-sensitivity C-reactive protein (CRP). At present, most clinical guidelines do not recommend routine measurement of these inflammatory markers. However, these serum markers of vascular inflammation may be useful as an adjunct to lipid screening, especially for patients whose lipid values may not be severely elevated, but who are at intermediate risk according to scoring systems that take into account multiple established risk factors. In addition, since the pleiotropic effects of statins include the inhibition of inflammatory response, serum inflammatory markers could also be useful for monitoring this action. Nevertheless, several issues have to be evaluated before the measurements of inflammatory markers can be used for cardiovascular risk prediction in either clinical practice or in clinical trials evaluating anti-atherosclerotic drugs.

Inhibition of pathologic retinal neovascularization by alpha-defensins

Proliferative retinopathies, such as those complicating prematurity and diabetes, are major causes of blindness. A prominent feature of these retinopathies is excessive neovascularization, which is orchestrated by the hypoxia-induced vascular endothelial growth factor (VEGF) stimulating endothelial cells and the integrin-mediated adhesive interactions of endothelial cells with extracellular matrix components such as fibronectin (FN). Recently, we demonstrated that alpha-defensins interfere with alpha5beta1-FN interactions and dependent endothelial cell functions. Here, alpha-defensins were studied in hypoxia-induced proliferative retinopathy. In vitro, alpha-defensins specifically inhibited alpha5beta1-integrin-dependent migration of bovine retinal endothelial cells (BRECs) to FN, attenuated the VEGF-stimulated increase in endothelial permeability, and blocked BREC proliferation and capillary sprout formation in 3-dimensional fibrin-matrices. An up-regulation of beta1-integrin and FN was observed in the retinal vessels in the mouse model of hypoxia-induced retinal angiogenesis. Systemic and local administration of alpha-defensins reduced retinal neovascularization by 45% and 60%, respectively, and this effect was comparable to the inhibitory effect of alpha5beta1-blocking antibody. alpha-Defensins were detected in human diabetic retinas associated with normal retinal vessels but were absent from proliferative lesions. Together, these data show that alpha-defensins inhibit pathologic retinal neovascularization in vivo and may provide a clinically efficient strategy against proliferative retinopathies.

Defensins and cathelicidins: neutrophil peptides with roles in inflammation, hyperlipidemia and atherosclerosis

Atherosclerosis is a disease that begins in fetal life and represents a leading cause of morbidity and mortality associated with significant socioeconomic consequences. A central concept with regard to its pathogenesis is that of endothelial cell dysfunction, which is associated with the release of a large number of mediators secreted by leukocytes that are present in large numbers at the sites of atheroma formation. Neutrophil peptides defensins and cathelicidins are essential elements of the innate immunity and have been present in high concentrations in atherosclerotic plaques in humans. Recently, their role as potential mediators of vascular disease was investigated. Defensins are involved in the lipoprotein metabolism in the vessel wall, favoring LDL and lipoprotein (a) accumulation and modification in the endothelium and the extracellular matrix. They also interfere with the vascular smooth muscle cell function, exhibit prothrombotic activity, and play an inhibitory role in various phases of angiogenesis. Cathelicidins were recently found to enhance endothelial proliferation in cultures, induce functionally significant angiogenesis in animal models, and regulate endothelial cell apoptosis. Further study of these peptides could provide useful insight in the relationship between inflammation and atherosclerosis and is anticipated to have therapeutic and prognostic ramifications.

Regulation of neovascularization by human neutrophil peptides (α‐defensins): a link between inflammation and angiogenesis

Angiogenesis, the growth of new blood vessels, is a complex biological process that is orchestrated by several growth factors and components of the extracellular matrix, including fibronectin (FN) and its receptor the integrin alpha5beta1. Angiogenesis is a critical part of inflammation and wound repair, but the mechanism by which vascular proliferation and migration is regulated by inflammatory cells is not completely understood. We have previously shown that human neutrophil peptides (HNPs), also known as alpha-defensins, which are secreted in high concentrations when neutrophils are activated, bind specifically to FN in the extracellular matrix and inhibit plasminogen activation. Therefore, we asked whether HNPs act as a link between inflammation and angiogenesis. Alpha5beta1-mediated endothelial cell adhesion and migration to FN, both under control conditions and under stimulation by vascular endothelial growth factor (VEGF), were inhibited specifically and in a dose-dependent manner by HNPs, whereas endothelial cell adhesion and migration to other components of the extracellular matrix, such as vitronectin, collagen, or fibrinogen/fibrin were not. Consistent with this finding, HNPs bound to and promoted the binding of fibronectin to alpha5beta1 integrin in arginine-glycine-aspartic acid (RGD)-independent manner. HNPs also completely inhibited VEGF-induced proliferation and induced apoptosis of endothelial cells in a dose-dependent manner. Moreover, HNPs inhibited capillary tube formation in three-dimensional fibrin-matrices as well as neovascularization in vivo in the chicken chorioallantoic membrane assay. Taken together, these data indicate that HNPs can regulate angiogenesis by affecting endothelial cell adhesion and migration in an FN-dependent manner as well as endothelial cell proliferation. These findings provide new insight into the role of inflammatory cells in angiogenesis and might provide a platform for developing a novel class of anti-angiogenesis drugs.

The role of defensins in lung biology and therapy

Innate host defence, involving both cellular and humoral mediators, is a prominent function of the human airways. Cellular mediators of innate immunity include dendritic cells, natural killer cells, cytotoxic T cells, macrophages and neutrophils, while humoral mediators of innate immunity consist of components of the epithelial lining fluid (ELF) covering the airways. Microbicidal substances in the ELF can selectively disrupt bacterial cell walls and membranes, sequester microbial nutrients or act as decoys for microbial attachment. Antimicrobial components of airway secretions include lysozymes, lactoferrin, secretory leukoprotease inhibitor, defensins and cathelicidins. Defensins are the most widely studied family of antimicrobial peptides present in airway fluid. Humans produce at least 10 different defensin molecules, six alpha-defensins and four beta-defensins similar in structure and function. Direct evidence that defensins have central roles in host defense has only recently become available. Some defensins and defensin-like molecules could serve as templates for the development of pulmonary pharmaceuticals. As potential therapeutics, they possess several desirable properties, including the ability to kill a broad spectrum of micro-organisms while permitting little development of microbial resistance. Many peptides can also neutralize effects of lipopolysaccharide on macrophages and other host defense cells and decrease the release of proinflammatory cytokines thereby giving protection against septic shock. Protegrin-1 is a minidefensin isolated from pig leukocytes and has proved to be an attractive template for large-scale development of antibacterials. One such protegrin analog, iseganan is in phase III clinical trials for the treatment of oral mucositis secondary to systemic chemotherapy. Other prospective uses of iseganan include control of respiratory pathogens in patients with cystic fibrosis and reduction of oral bacteria to prevent ventilator-associated pneumonia. However, in order to advance the production and clinical testing of peptide-based therapeutics, technical hurdles of synthesizing large quantities of complexly folded peptides must be first overcome. Strategies to develop potent peptide-based microbicides are promising in the struggle against increasingly resistant pathogens.

Platelet factor 4 enhances the binding of oxidized low-density lipoprotein to vascular wall cells

Accumulation of low-density lipoprotein (LDL)-derived cholesterol by macrophages in vessel walls is a pathogenomic feature of atherosclerotic lesions. Platelets contribute to lipid uptake by macrophages through mechanisms that are only partially understood. We have previously shown that platelet factor 4 (PF4) inhibits the binding and degradation of LDL through its receptor, a process that could promote the formation of oxidized LDL (ox-LDL). We have now characterized the effect of PF4 on the binding of ox-LDL to vascular cells and macrophages and on the accumulation of cholesterol esters. PF4 bound to ox-LDL directly and also increased ox-LDL binding to vascular cells and macrophages. PF4 did not stimulate ox-LDL binding to cells that do not synthesize glycosaminoglycans or after enzymatic cleavage of cell surface heparan and chondroitin sulfates. The effect of PF4 on binding ox-LDL was dependent on specific lysine residues in its C terminus. Addition of PF4 also caused an approximately 10-fold increase in the amount of ox-LDL esterified by macrophages. Furthermore, PF4 and ox-LDL co-localize in atherosclerotic lesion, especially in macrophage-derived foam cells. These observations offer a potential mechanism by which platelet activation at sites of vascular injury may promote the accumulation of deleterious lipoproteins and offer a new focus for pharmacological intervention in the development of atherosclerosis.

Human alpha-defensin regulates smooth muscle cell contraction: a role for low-density lipoprotein receptor-related protein/alpha 2-macroglobulin receptor

We have previously identified alpha-defensin in association with medial smooth muscle cells (SMCs) in human coronary arteries. In the present paper we report that alpha-defensin, at concentrations below those found in pathological conditions, inhibits phenylephrine (PE)-induced contraction of rat aortic rings. Addition of 1 microM alpha-defensin increased the half-maximal effective concentration (EC(50)) of PE on denuded aortic rings from 32 to 630 nM. The effect of alpha-defensin was dose dependent and saturable, with a half-maximal effect at 1 microM. alpha-Defensin binds to human umbilical vein SMCs in a specific manner. The presence of 1 microM alpha-defensin inhibited the PE-mediated Ca(++) mobilization in SMCs by more than 80%. The inhibitory effect of alpha-defensin on contraction of aortic rings and Ca(++) mobilization was completely abolished by anti-low-density lipoprotein receptor-related protein/alpha(2-)macroglobulin receptor (LRP) antibodies as well as by the antagonist receptor-associated protein (RAP). alpha-Defensin binds directly to isolated LRP in a specific and dose-dependent manner; the binding was inhibited by RAP as well as by anti-LRP antibodies. alpha-Defensin is internalized by SMCs and interacts with 2 intracellular subtypes of protein kinase C (PKC) involved in muscle contraction, alpha and beta. RAP and anti-LRP antibodies inhibited the binding and internalization of alpha-defensin by SMCs and its interaction with intracellular PKCs. These observations suggest that binding of alpha-defensin to LRP expressed in SMCs leads to its internalization; internalized alpha-defensin binds to PKC and inhibits its enzymatic activity, leading to decreased Ca(++) mobilization and SMC contraction in response to PE.

Antimicrobial peptides are expressed and produced in healthy and inflamed human synovial membranes

The objective of this study was to determine the expression and production of antimicrobial peptides by healthy and inflamed human synovial membranes. Deposition of the antimicrobial peptides lysozyme, lactoferrin, secretory phospholipase A(2) (sPA(2)), matrilysin (MMP7), human neutrophil alpha-defensins 1-3 (HNP 1-3), human beta-defensin 1 (HBD-1), and human beta-defensin 2 (HBD-2) was determined by immunohistochemistry. Expression of mRNA for the antimicrobial peptides bactericidal permeability-increasing protein (BPI), heparin binding protein (CAP37), human cationic antimicrobial protein (LL37), human alpha-defensin 5 (HD5), human alpha-defensin 6 (HD6), HBD-1, HBD-2, and human beta-defensin 3 (HBD-3) was analysed by reverse transcription polymerase chain reaction (RT-PCR). RT-PCR revealed CAP37 and HBD-1 mRNA in samples of healthy synovial membrane. Additionally, HBD-3 and/or LL37 mRNA was detected in synovial membrane samples from patients with pyogenic arthritis (PA), osteoarthritis (OA) or rheumatoid arthritis (RA). BPI, HD5, HD6, and HBD-2 mRNAs were absent from all samples investigated. Immunohistochemistry identified lysozyme, lactoferrin, sPA(2), and MMP7 in type A synoviocytes of all samples. HBD-1 was only present in type B synoviocytes of some of the samples. Immunoreactive HBD-2 peptide was only visible in some inflamed samples. HNP1-3 was detected in both healthy and inflamed synovial membranes. The data suggest that human synovial membranes produce a broad spectrum of antimicrobial peptides. Under inflammatory conditions, the expression pattern changes, with induction of HBD-3 in PA (LL37 in RA; HBD-3 and LL37 in OA) as well as down-regulation of HBD-1. HBD-3 holds therapeutic potential in PA as it has a broad spectrum of antimicrobial activity and accelerates epithelial healing. However, caution is appropriate since defensins also promote fibrin formation and cell proliferation - key elements in joint infection. Clarification of the role of antimicrobial peptides in OA and RA will require further investigation.

[beta]-defensins in lung host defense

Host defenses at the mucosal surface of the airways evolved to present many layers of protection against inhaled microbes. Normally, the intrapulmonary airways are sterile. Airway secretions contain numerous factors with antimicrobial activity that contribute to innate defenses. Many protein and peptide components exert bacteriostatic or bacteriocidal effects against a wide variety of organisms and may act in synergistic or additive combinations. The beta-defensins are a relatively recently described family of peptide antimicrobials that are widely expressed at mucosal surfaces, including airway and submucosal gland epithelia. These small cationic peptides are products of individual genes that exhibit broad-spectrum activity against bacteria, fungi, and some enveloped viruses. Their expression in airway epithelia may be constitutive or inducible by bacterial products or pro-inflammatory cytokines. beta-defensins also act as chemokines for adaptive immune cells, including immature dendritic cells and T cells via the CCR6 receptor, and provide a link between innate and adaptive immunity. Alterations in the function of the beta-defensins may contribute to disease states. Here we review much of the biology of the beta-defensins, including gene discovery, genomic organization, molecular structure, regulation of expression, and function.

Bacteriocins: safe, natural antimicrobials for food preservation

Bacteriocins are antibacterial proteins produced by bacteria that kill or inhibit the growth of other bacteria. Many lactic acid bacteria (LAB) produce a high diversity of different bacteriocins. Though these bacteriocins are produced by LAB found in numerous fermented and non-fermented foods, nisin is currently the only bacteriocin widely used as a food preservative. Many bacteriocins have been characterized biochemically and genetically, and though there is a basic understanding of their structure-function, biosynthesis, and mode of action, many aspects of these compounds are still unknown. This article gives an overview of bacteriocin applications, and differentiates bacteriocins from antibiotics. A comparison of the synthesis. mode of action, resistance and safety of the two types of molecules is covered. Toxicity data exist for only a few bacteriocins, but research and their long-time intentional use strongly suggest that bacteriocins can be safely used.

Expression of natural peptide antibiotics in human articular cartilage and synovial membrane

In view of frequent present use of invasive procedures on limb joints, it is astonishing that articular joint inflammation is a rare event. We questioned whether antimicrobial peptides play a role in protecting human articular cartilage and synovial membrane against inflammatory agents. Our results implicate defensins in the protection of human articular joints against pathogens.

Expression of the peptide antibiotics human beta defensin-1 and human beta defensin-2 in normal human skin

Normal human skin is remarkably resistant to infection from the large numbers of microorganisms that routinely colonize its surface. In addition to the role of skin as a mechanical barrier, it has long been recognized that skin and other epithelia can produce a range of anti-microbial chemicals that play an important part in eliminating potential cutaneous pathogens. Anti-microbial peptides are an important evolutionarily conserved innate host defense mechanism in many organisms. Human beta defensin-1 and -2 are cysteine-rich, cationic, low molecular weight anti-microbial peptides that have recently been shown to be expressed in epithelial tissues. In this study, we describe the characterization of human beta defensin-1 and -2 mRNA and peptide expression in normal human skin. Using reverse transcription-polymerase chain reaction we demonstrate that human beta defensin-1 is consistently expressed in skin samples from various body sites. Human beta defensin-2 demonstrates expression that is more variable and is more readily detectable in facial skin and foreskin compared with skin from abdomen and breast. In situ hybridization localizes the human beta defensin-1 and -2 transcripts to keratinocytes within interfollicular skin. Using specific antibodies, we have shown that human beta defensin-1 and -2 peptides are localized to the Malpighian layer of the epidermis and/or stratum corneum and that there are interindividual and site-specific differences in intensity of immunostaining and the pattern of peptide localization. The localization of human beta defensins to the outer layer of the skin is consistent with the hypothesis that human beta defensins play an essential part in cutaneous innate immunity.

Animal antimicrobial peptides: an overview

Antibiotic peptides are a key component of the innate immune systems of most multicellular organisms. Despite broad divergences in sequence and taxonomy, most antibiotic peptides share a common mechanism of action, i.e., membrane permeabilization of the pathogen. This review provides a general introduction to the subject, with emphasis on aspects such as structural types, post-translational modifications, mode of action or mechanisms of resistance. Some of these questions are treated in depth in other reviews in this issue. The review also discusses the role of antimicrobial peptides in nature, including several pathological conditions, as well as recent accounts of their application at the preclinical level.

Identification of defensins in human lymphocyte nuclei

The cell nucleus plays an essential role in all aspects of cell function and regulation. Most of the nuclear proteins/peptides are synthesized in the cytoplasm and transported into the nucleus through the nuclear pore complexes. The nuclear proteins/peptides conjugate with each other and interact in transcriptional activation/inactivation. Several of the high molecular mass transcription factors (> 30 kDa) have been identified and characterized. However, the information on the low molecular mass proteins/peptides of the nucleus is limited. We have investigated these low molecular mass proteins/peptides from the nucleus of human peripheral blood lymphocytes using reversed-phase high-performance liquid chromatography (RP-HPLC). The HPLC fractions were further analysed by matrix assisted laser desorption/ionization time of flight (MALDI-TOF) mass spectrometry, electrospray ionization time of flight (ESI-TOF) mass spectrometry and electrospray ionization fourier transform ion cyclotron resonance (ESI-FTICR) mass spectrometry for mass determination. Using this combination of mass spectrometry techniques and microsequence analysis, we have shown that human lymphocyte nuclei contain defensins, a mixture of human neutrophil granule peptide 1, 2 and 3.