Modulation of neutrophil functions by activated platelet release factors

A Hybrid Model for Predicting Bone Healing around Dental Implants

BACKGROUND

The effect of the short-term bone healing process is typically neglected in numerical models of bone remodeling for dental implants. In this study, a hybrid two-step algorithm was proposed to enable a more accurate prediction for the performance of dental implants.

METHODS

A mechano-regulation algorithm was firstly used to simulate the tissue differentiation around a dental implant during the short-term bone healing. Then, the result was used as the initial state of the bone remodeling model to simulate the long-term healing of the bones. The algorithm was implemented by a 3D finite element model.

RESULTS

The current hybrid model reproduced several features which were discovered in the experiments, such as stress shielding effect, high strength bone connective tissue bands, and marginal bone loss. A reasonable location of bone resorptions and the stability of the dental implant is predicted, compared with those predicted by the conventional bone remodeling model.

CONCLUSIONS

The hybrid model developed here predicted bone healing processes around dental implants more accurately. It can be used to study bone healing before implantation surgery and assist in the customization of dental implants.

An immunohistochemical study of human platelets using a rabbit antibody against H18-K24 of apolipoprotein CIII (HATKTAK)

H18-K24 of human apolipopotein CIII (Apo CIII) (HATKTAK) is an activator of the macromolecular activators of phagocytosis from platelets (MAPPs). Using a rabbit antibody against HATKTAK, we performed an immunohistochemical study of human platelets. Indirect ELISA showed that this antibody reacts with Apo CIII-derived peptides with a C-terminal of HATKTAK, but not with Apo CIII. Immunoelectron microscopy revealed that reaction of anti-HATKTAK antibody occurred in the pseudopods of activated platelets. In blood coagula produced from the peripheral blood and formalin-fixed after various incubation periods, reaction of this antibody with platelets appeared rapidly with a peak at 3 to 6 h of incubation, and then diminished gradually. Leukocytes in the blood coagula were stained strongly positive. In tissue sections, fresh thrombi and hemorrhages with slight fibrin formation revealed a positive response of platelets to anti-HATKTAK antibody, whereas older ones with leukocytic infiltration, fibrin formation and organization did not. In addition to platelets, endothelial cells and leukocytes were stained positive by anti-HATKTAK antibody. All of the positive reactions by anti-HATKTAK antibody disappeared or diminished by co-incubation with HATKTAK. In conclusion, the anti-HATKTAK antibody reveals platelets during the early phase of activation.

Platelet high-density lipoprotein activates transferrin-derived phagocytosis activators, MAPPs, following thrombin digestion

Macromolecular activators of phagocytosis from platelets (MAPPs), transferrin-derived phagocytosis activators released from platelets, activate leukocytic phagocytosis via Fcγ receptors. It has been found that MAPPs can be prepared using stored platelets or their lysate. Using this artificial MAPP production system, it has been found that they can be produced from precursors (tetrameric and dimeric transferrins) following reaction with a low-molecular-weight (LMW) activator of MAPPs, which is liberated from a high-molecular-weight activator of MAPP (HMW activator) by reaction with thrombin. In this study, the HMW activator in platelet lysate was characterized by assaying phagocytosis of washed neutrophils. In an ultracentrifugation study of the platelet lysate, HMW activator activity was observed in the fraction corresponding to the density of high-density lipoprotein (HDL). The activity was observed in the apolipoproteins obtained from the HDL fraction. Among the apolipoproteins tested only apolipoprotein CIII showed the activity to produce MAPP in vitro. Affinity chromatography of the apolipoproteins from the HDL fraction of the platelet lysate using an anti-apolipoprotein CIII column revealed that the substance that binds with the antibody showed MAPP-forming activity. In a gel filtration study of thrombin-treated apolipoprotein CIII, a peak of LMW activator activity was observed for fractions with a molecular size smaller than that of apolipoprotein CIII. Finally, MAPP-forming activity of HDL obtained from the plasma was examined. MAPP was formed only when delipidized HDL was used. In conclusion, it is suggested that platelet HDL is the HMW activator and that this activation is achieved via apolipoprotein CIII after thrombin reaction in platelets.

The basic science of peri-implant bone healing

Given the popularity of cementless orthopedic implants, it is imperative for orthopedic surgeons to have a basic understanding of the process of peri-implant bone healing. Contact and distance osteogenesis have been used to explain peri-implant bone healing. In contact osteogenesis, de novo bone forms on the implant surface, while in distance osteogenesis, the bone grows from the old bone surface toward the implant surface in an appositional manner. Contact osteogenesis may lead to bone bonding if the surface of the implant displays the appropriate surface topography. The early stage of peri-implant bone healing is very important and involves the body's initial response to a foreign material: protein adsorption, platelet activation, coagulation, and inflammation. This results in the formation of a stable fibrin clot that is a depot for growth factors and allows for osteoconduction. Osteoconduction is the migration and differentiation of osteogenic cells, such as pericytes, into osteoblasts. Osteoconduction allows for contact osteogenesis to occur at the implant surface. The late stage of healing involves the remodeling of this woven bone. In many respects, this process is similar to the bone healing occurring at a fracture site.

Close association between activated platelets and neutrophils in the active phase of ulcerative colitis in humans

BACKGROUND

Neutrophils are considered to play a causative role in inflammatory mucosal injury in ulcerative colitis (UC), and an association between platelets and neutrophils may contribute to the progression of the inflammatory processes. To test this hypothesis, we performed immunohistochemical and flow cytometric analyses on tissue and blood samples from patients with UC.

MATERIALS AND METHODS

Colonic mucosal tissues of patients with active (n = 27) or inactive (n = 16) UC and normal controls (n = 11) were subjected to immunohistochemical staining for markers of activated platelets (glycoprotein IIb/IIIa and P-selectin) and neutrophils (neutrophil elastase, myeloperoxidase, and CD66b). The amounts of stained cells were evaluated by computer-aided morphometry. Peripheral blood samples from patients (n = 8) and healthy volunteers (n = 8) were subjected to comparative flow cytometric analysis of activated platelets.

RESULTS

P-selectin-positive activated platelets were frequently aggregated in the inflamed mucosa, especially in ulcerative lesions, and were close to regions of dense neutrophil infiltration. An increase in the number of activated platelets in the colonic lesions was associated with an increase in infiltrating neutrophils and was related to the severity of the disease. The flow cytometric analysis indicated that circulating platelets of patients with UC were highly activated.

CONCLUSIONS

The present study demonstrated that a close association between activated platelets and neutrophils is a prominent pathological change in both the affected colonic mucosa and peripheral blood of patients with active-phase UC. This suggests that platelet-neutrophil association may play an important role in the progression of inflammatory processes in UC.

The emerging role of platelets in adaptive immunity

Platelets' foremost role in survival is hemostasis. However, a significant quantity of research has demonstrated that platelets are an integral part of inflammation and can also be potent effector cells of the innate immune response. CD154, a molecule of vital importance to adaptive immune responses, is expressed by activated platelets and has been implicated in platelet-mediated modulation of innate immunity and inflammatory disease states. Recent studies in mice extend the role of platelet CD154 to the adaptive immune response demonstrating that platelets can enhance antigen presentation, improve CD8 T cell responses, and play a critical function in normal T-dependent humoral immunity. The latter studies suggest that the current paradigm for the B cell germinal center response should be modified to include a role for platelets.

Effects of platelet release products on neutrophilic phagocytosis and complement receptors

INTRODUCTION

Platelets enhance leukocytic phagocytosis via the action of ATP and ADP in platelet release products (PRPr). The present study was designed to clarify the type of complements and complement receptors that are involved in phagocytosis activation by PRPr, ATP and ADP.

MATERIALS AND METHODS

Human peripheral blood was used as the source of neutrophils and platelets. The supernatant of the platelet suspension after simulation was used as PRPr. The effects of PRPr, ATP, ADP, and other substances on neutrophilic phagocytosis, rosette formation and expression of several antigens were investigated. For the markers of neutrophilic phagocytosis and rosette formation, IgM-sensitized sheep red blood cells (SRBC) were treated with diluted human serum (EAC) or purified complements (C1, C4, C2 and C3) (EAC3b) followed by C3 inactivation (EAC3bi). The expressions of CD11b, CD11c, CD18, and CD35 were evaluated using a flow cytometer.

RESULTS

Neutrophilic phagocytosis of EAC and EAC3bi was enhanced by PRPr, ATP, and ADP, whereas this phagocytosis activation was abolished by antibodies against CD11b and CD18. Neutrophil rosette formation with EAC3bi was increased by ATP and ADP. Flow cytometry revealed that the expressions of CD11b and CD35 on neutrophils were increased by PRPr, but not by ATP and ADP. The component in PRPr, responsible for the increase in expressions of these antigens, could not be identified.

CONCLUSION

PRPr increases the neutrophilic phagocytosis of complement-coated particles through the action of ATP and ADP by increasing the binding avidity with iC3b, but not the number of Mac-1 (CD11b/CD18).

Rho-GTPase-dependent platelet-neutrophil interaction affected by HMG-CoA reductase inhibition with altered adenosine nucleotide release and function

Platelet activation and aggregation is considered a crucial step in the initiation and aggravation of arterial thrombosis. ADP from activated platelets is recognized as major factor in thrombus formation and is a potent stimulator of oxygen-free radical release from neutrophils. The aim of the present investigation was to determine in vitro the direct effects of statins on ATP and ADP secretion by platelets and its impact on subsequent oxidative burst activity in neutrophils. Human neutrophils and platelets were isolated from peripheral blood. Levels of platelet-derived ATP and ADP were measured by high-performance liquid chromatography, oxygen-free radical release of neutrophils was measured fluorometrically, and chemotaxis experiments were performed. Rho-GTPases were studied by Western blot analysis. Thrombin-activated platelets primed neutrophils for enhanced oxygen-free radical release on triggering with formyl-Met-Leu-Phe, reduced by cerivastatin and simvastatin treatment of platelets. The two statins decreased the amount of adenosine-derivative release in these cells. Rho-GTPases, required for the thrombin signaling in platelets and neutrophils, were decreased after coincubation with statins. Data demonstrate that inhibition of Rho-GTPases by statins inhibit platelet ADP and ATP release and the consecutive augmentation of neutrophil oxygen-free radical release. Statins affect platelet-neutrophil interactions by altering Rho-GTPase-dependent adenosine nucleotide function.

A(3) adenosine receptors in human neutrophils and promyelocytic HL60 cells: a pharmacological and biochemical study

This work compares the pharmacological and biochemical properties of A(3) adenosine receptors in human polymorphonuclear neutrophil granulocytes (PMNs) and promyelocytic HL60 cells. The gene expression of A(3) receptors was examined by reverse transcription-polymerase chain reaction experiments, whereas the amount of A(3) subtype on the plasma membrane was quantified by using the high-affinity and selective A(3) antagonist [(3)H]5N-(4-methoxyphenyl-carbamoyl)amino-8-propyl-2-(2-furyl)pyrazolo-[4,3-e]1,2,4-triazolo[1,5-c]pyrimidine ([(3)H]MRE 3008F20). Saturation experiments reveal a single high-affinity binding site with K(D) values of 2.3 +/- 0.3, 2.6 +/- 0.4 nM, and B(max) values of 430 +/- 35, 345 +/- 31 fmol/mg of protein for PMNs and HL60 cells, respectively. Competition of radioligand binding by adenosine ligands displays a rank order of potency typical of the A(3) subtype. EC(50) values of N(6)-(3-iodo-benzyl)-2-chloro-adenosine-5'-N-methyluronamide (Cl-IB-MECA) for inhibition of cAMP levels via A(3) receptors are in good agreement with the binding data; furthermore, the response is potently inhibited by MRE 3008F20. In contrast, the high micromolar concentrations of Cl-IB-MECA and MRE 3008F20 in stimulating and blocking Ca(2+) mobilization, respectively, are not completely consistent with the involvement of an A(3) receptor. Furthermore, an important finding of this work is that the inhibition of PMNs oxidative burst is predominantly A(2A)-mediated, even though an effect of A(3) subtype could not be excluded. This conclusion is based on potent blockade of Cl-IB-MECA-mediated inhibition of oxidative burst by SCH 58261 and a minor but significant blockade by MRE 3008F20. In conclusion, HL60 cells express A(3) receptors similar to those in PMNs, thus providing a useful model for investigation of biochemical pathways leading to A(3) receptor activation.

Production of macromolecular activators of phagocytosis by lysed platelets

Macromolecular activators of phagocytosis from platelets (MAPP: 1-MAPP and s-MAPP) are released from activated fresh platelets and enhance leukocyte phagocytosis via the Fcgamma receptors. In this study, production of MAPP was investigated in lysate of freeze-thawed stored platelets (PL). Incubation of PL and thrombin with precursors of MAPP (pre-MAPP: pre-1-MAPP and pre-s-MAPP) produced 1-MAPP and s-MAPP, whereas products released from stored platelets by stimulation with thrombin or collagen did not produce MAPP after incubation with pre-MAPP. The action of thrombin in MAPP formation with PL and pre-MAPP was inhibited by antithrombin III and heparin, and sequential incubation studies indicated that the key site of action of thrombin was on a component of PL. Other serine proteases such as trypsin could be substituted for thrombin in this reaction, whereas the action of thrombin was specific when whole platelets were used instead of PL. Gel filtration of PL before and after treatment with thrombin suggested that a macromolecule in PL (PMA-I) is digested by thrombin and liberates a 700 to 800 Da substance (PMA-II) which converts pre-MAPP to MAPP.

Neutrophils in the molar tooth extraction wound in the rat: a transmission electron microscope (TEM) study

Neutrophils have been ascribed a number of functions from ultrastructural studies of healing wounds. All of the wounds so far examined have been relatively aseptic. This study investigates, by TEM, the structure of neutrophils in healing molar tooth sockets in rats. Prior to epithelial coverage, a dense infiltrate of neutrophils separated the viable wound tissues from the overlying debris and bacteria. The more deeply situated neutrophils contained many granules and only occasional phagosomes. More superficial neutrophils contained fewer granules and phagosomes with engulfed bacteria undergoing lysis. The most superficial neutrophils were degenerate, lacked granules and often contained viable bacteria. There were varying numbers of neutrophils containing granules in the blood clot, granulation tissue, wound epithelium and adjacent tissue. No extracellular neutrophil granules nor extracellular discharge of granules was found. These findings differ from those of previous ultrastructural studies of relatively aseptic healing wounds. Ultrastructurally, the only function of neutrophils in healing tooth extraction wounds appears to be phagocytosis of bacteria, which supports a role in the prevention of infection.

Modified chemotactic peptides: synthesis and activity of an azaTic-containing fMLP-OMe analogue

The synthesis and the biological activity of a pseudopeptide analogue of the chemotactic N-formyltripeptide fMLP-OMe, containing the azaTic (3,4-dihydro-2(1H)-phthalazinecarboxylic acid) residue replacing the native phenylalanine, is described. Whereas pseudopeptides containing linear alpha-azaamino acids are currently studied, data on the new group of analogues containing cyclic alpha-aza residues capable of limiting the rotameric distribution of the side chains (topological control) are just emerging in the literature. At our best knowledge, the here described [azaTic3]fMLP-OMe represents the first example of the introduction of this new type of alpha-aza residue into a natural bioactive peptide.

[3H]-SCH 58261 labelling of functional A2A adenosine receptors in human neutrophil membranes

1. The present study describes the direct labelling of A2A adenosine receptors in human neutrophil membranes with the potent and selective antagonist radioligand, [3H]-5-amino-7-(2-phenylethyl)-2-(2-furyl)-pyrazolo[4,3-e]-1,2,4 triazolo[l,5-c]pyrimidine, ([3H]-SCH 58261). In addition, both receptor affinity and potency of a number of adenosine receptor agonists and antagonists were determined in binding, adenylyl cyclase and superoxide anion production assays. 2. Saturation experiments revealed a single class of binding sites with Kd and Bmax values of 1.34 nM and 75 fmol mg(-1) protein, respectively. Adenosine receptor ligands competed for the binding of 1 nM [3H]-SCH 58261 to human neutrophil membranes, with a rank order of potency consistent with that typically found for interactions with the A2A adenosine receptors. In the adenylyl cyclase and in the superoxide anion production assays the same compounds exhibited a rank order of potency identical to that observed in binding experiments. 3. Thermodynamic data indicated that [3H]-SCH 58261 binding to human neutrophils is entropy and enthalpy-driven. This finding is in agreement with the thermodynamic behaviour of antagonists binding to rat striatal A2A adenosine receptors. 4. It was concluded that in human neutrophil membranes, [3H]-SCH 58261 directly labels binding sites with pharmacological properties similar to those of A2A adenosine receptors of other tissues. The receptors labelled by [3H]-SCH 58261 mediated the effects of adenosine and adenosine receptor agonists to stimulate cyclic AMP accumulation and inhibition of superoxide anion production in human neutrophils.

Two for-Met-Leu-Phe-OMe analogues trigger selective neutrophil responses. A differential effect on cytosolic free Ca2+

For-Thp-Leu-Ain-OMe and for-Met-delta(z)Leu-Phe-OMe are two conformationally restricted fMLP-OMe analogues able to discriminate between different biological responses of human neutrophils. In this paper, we demonstrate that the former peptide, which evokes only chemotaxis, does not alter human neutrophil Ca2+ levels. In contrast, for-Met-delta(z)Leu-Phe-OMe, which induces superoxide anion release and degranulation but not chemotaxis, significantly increases the cation concentration. The chelation of Ca2+ in both extracellular and intracellular media abolishes O2- production triggered by for-Met-delta(z)Leu-Phe-OMe, while the same procedure does not affect neutrophil chemotaxis towards for-Thp-Leu-Ain-OMe. We therefore suggest that chemotaxis, unlike superoxide anion release, is independent of Ca2+ enhancement in human neutrophils.

Synthesis, conformation, and biological activity of two fMLP-OMe analogues containing the new 2-[2'-(methylthio)ethyl]methionine residue

The new C alpha-tetrasubstituted alpha-amino acid residue 2-[2'-(methylthio)ethyl]methionine (Dmt) has been introduced into the reference chemotactic tripeptide HCO-Met-Leu-Phe-OMe (fMLP-OMe) in place of the leucine or methionine, respectively. The biological activity of the new analogues [Dmt2]fMLP-OMe (2) and [Dmt1]fMLP-OMe (3) has been determined; whereas 2 is active toward human neutrophils, stimulating directed migration, superoxide anion generation, and lysozyme release, 3 results practically inactive in all tested assays. A conformational analysis on 2 and 3 has been performed in solution by using ir absorption and 1H-nmr. The conformation of 2 was also examined in the crystal by x-ray diffraction methods. Both 2 and 3 adopt fully extended conformation in correspondence with the Dmt residue. Biological and conformational results are discussed and compared with related previously studied models.

Chemotactic peptide analogues. Centrally constrained chemotactic N-formyltripeptides: synthesis, conformation, and activity of two new analogues

The role exercised by the central residue of the chemotactic N-formyltripeptide HCO-Met-Leu-Phe-OMe (fMLP-OMe) in controlling both the backbone conformation and the biochemical activity is the subject of recent interest. Here, two new centrally constrained fMLP-OMe analogues, namely HCO-Met-azaPro-Phe-OMe (4) and HCO-Met-(gamma-lactam)-Phe-OMe (6) have been synthesized and their CDCI3 solution conformation and activity have been studied. The azapeptide 4 adopts beta-folded conformation with the azaPro residue at the i+2 position and an intramolecular H-bond involving the formylic oxygen and the Phe NH. The gamma-lactam tripeptide 6 prefers a semi-extended backbone conformation. When tested on human neutrophils both the new models were found practically devoid of biological activity. The role exerted by the NH groups as well as by the conformational preferences is discussed.

Modified chemotactic peptides: synthesis, conformation, and activity of HCO-Thp-Ac6c-Phe-OMe

HCO-Thp-Ac6c-Phe-OMe (3) has been synthesized as a new analogue of the prototypical chemotactic agent HCO-Met-Leu-Phe-OMe (fMLP-OMe). Compound 3 contains 4-aminotetra-hydrothiopyran-4-carboxylic acid (Thp) and 1-aminocyclohexane-1-carboxylic acid (Ac6c) as achiral, conformationally restricted mimics of Met and Leu, respectively. In the crystal, the formyltripeptide adopts an helical conformation at the Thp and Ac6c residues, of the type alpha R and alpha L, respectively, whereas the C-terminal phenylalanine is quasi-extended. A system of two consecutive gamma-turns, centered at the first two residues, better explains the nmr data as compared with an alternative beta-turn structure. The conformation of the new analogue 3 is compared with those of two related peptides containing Thp as N-terminal residue. The biological activity of 3 has been determined on human neutrophils and compared to that of the previously studied model [Ac6c2] fMLP-OMe. While the above analogue is highly active in the superoxide anion production, the new tripeptide 3 is practically unable to elicit any of the tested biological activities.

Effect of cyclic AMP level reduction on human neutrophil responses to formylated peptides

The increase in human neutrophil cyclic adenosine monophosphate (cAMP) levels evoked by formylated peptides is significantly reduced in the presence of MDL 12330A, SQ 22536, GDPssS and clonidine, which inhibit the adenylyl cyclase system by acting at different sites in this enzyme complex. A similar effect is exerted by adenosine deaminase and dipyridamole, which alter the extracellular adenosine concentration. Neutrophil preincubation with adenylyl cyclase inhibitors or dipyridamole reduces chemotaxis and superoxide anion production triggered by peptides; adenosine deaminase, on the contrary, has no effect on neutrophil responses. Our results seem to indicate that: (1) the peptide-induced increase in neutrophil cAMP is due mainly to an action on the adenylyl cyclase system; (2) an enhancement of this cyclic nucleotide, even slight and necessarily transient, is required for chemotaxis and O2 production induced in neutrophils by formylated peptides; and (3) cAMP does not represent the crucial second messenger for adenosine in the modulation of neutrophil responses.

The role of (Z)-2,3-didehydrophenylalanine and phenylalanine C-terminal residues in determining the chemotactic activity of formylpeptides

Several formylpeptides, analogs of the chemotactic agent HCO-Met-Leu-Phe-OMe, having the HCO-Xaa-Leu-delta ZPhe-OMe and HCO-Xaa-Leu-delta ZPhe-Phe-OMe structures (delta ZPhe = (Z)-2,3-didehydrophenylalanine), have been synthesized. The biological activity of these ligands has been determined on human neutrophils and compared to that of the corresponding HCO-Xaa-Leu-Phe-OMe derivatives not containing the unsaturated residue. The replacement of the C-terminal Phe with delta ZPhe causes, in all the examined tripeptides, the loss of any biological activity. On the other hand, the introduction into the delta ZPhe containing models of an additional C-terminal Phe residue leads to the formyltetrapeptides HCO-Xaa-Leu-delta ZPhe-Phe-OMe which show a biological activity very similar to that exhibited by the corresponding HCO-Xaa-Leu-Phe-OMe analogues.

Chemotactic peptide analogues. Synthesis and chemotactic activity of N-formyl-Met-Leu-Phe analogues containing (S)-phenylalaninol derivatives

The synthesis and the biological activity towards human neutrophils of some N-formyl-Met-Leu-Phe-OMe analogues containing (S)-phenylalaninol (Pheol) or its derivatives in place of the native phenylalanine are reported. While the analogue containing Pheol (4) was found to be devoid of significant biological activity, its esters 3 and 5, although inactive as chemoattractants, are able to strongly stimulate superoxide production and are active with a lower efficacy in the lysozyme release.

Effects of platelet depletion on PMA-induced acute lung injury in awake sheep

Little is known about the role of circulating platelets in PMA-induced lung injury in vivo. We investigated the effects of platelet depletion (PD) on the injury using seven unanesthetized sheep with lung lymph fistulas and eight other sheep for morphological study. PD diminished a decrease in the lymph to plasma concentration ratio (L/P) after 1 microgram/kg PMA treatment (n = 4) and caused more increases in lung lymph flow, L/P and lung lymph clearance after 5 micrograms/kg PMA treatment (n = 3) than in control sheep. The high dose was lethal to platelet-depleted sheep. However, PD had no effects on pulmonary hemodynamics. Morphologically, alveolar hemorrhages and exudate, and bleb formation of type I epithelial cells were more prominent in the platelet-depleted sheep than in the control sheep. We conclude that circulating platelets have protective effects against PMA-induced lung injury but have little involvement in PMA-induced pulmonary hypertension.

For-Met-Lys-Phe-For-Met-Lys-Phe-: a new cyclic analogue of the chemotactic formylpeptides

As a continuation of the studies on chemotactic N-formylpeptides, we report here the synthesis and activity of a new cyclic analogue of the prototypical ligand For-Met-Leu-Phe-OMe. The new compound For-Met-Lys-Phe-For-Met-Lys-Phe- (4) contains a 20-membered cyclic moiety made up of a dimeric -Lys-Phe- sequence in which For-Met is attached to each Lys alpha-NH2 and hence remains outside the ring. The conformation in the crystal of the cyclic precursor of 4, namely Boc-Lys-Phe-Boc-Lys-Phe- (2) and the activity of the structurally related linear analogue For-Met-Lys(Z)-Phe-OBzl (6), have also been examined. The new analogues 4 and 6 are active as chemoattractants, secretagogues, and superoxide anion generating agents, when tested on human neutrophils. The structure-activity relationship is discussed and related to that of a previously studied cyclic model.

Modified chemotactic peptides: synthesis, conformation, and biological activity of For-Thp-Leu-delta ZPhe-OMe

For-Thp-Leu-delta ZPhe-OMe (2), an analogue of the chemotactic tripeptide For-Met-Leu-Phe-OMe, containing 4-aminotetrahydrothiopyran-4-carboxylic acid (Thp) and (Z)-2,3-didehydrophenylalanine (delta ZPhe) as achiral, conformationally restricted mimics of Met and Phe, respectively, has been synthesized. In the crystal the new formyltripeptide adopts a type I beta-turn conformation stabilized by a weak H bond between the formylic oxygen and the delta ZPhe NH. 1H-nmr analysis based on NH solvent accessibility and nuclear Overhauser effect experiments suggests that the beta-turn is not preferred in CDCl3 solution where a gamma-turn, centered at the Thp residue, prevails. The biological activity of 2 has been determined on human neutrophils and compared to that of previously studied analogues. The tripeptide 2 is practically unable to elicit superoxide anion production and lysozyme release, while slight, but not statistically significant activity was induced in chemotaxis. The role of the orientation of the aromatic ring with respect to the backbone adjacent atoms is discussed.

Adhesion between neutrophils and platelets: a modulator of thrombotic and inflammatory events?

Recent studies have demonstrated that neutrophilic granulocytes and platelets have the capability to interact with each other. Either type of cell may release soluble factors, which either activate the other or increase its response to separate stimulating agents. Direct contact between the two types of cell generally increases the response, and it may be predicted that neutrophil-platelet adhesion will augment the potential for biochemical interaction in vivo. Adhesion may also promote immobilisation of neutrophils or platelets in thrombotic or inflamed tissue, while circulation aggregates could cause vascular blockage. Adhesion between neutrophils and platelets is dependent on P-selectin on activated platelets and sialyated carbohydrate moieties on the neutrophil, although other molecular mechanisms could stabilise the interaction. The adhesive interaction is strong enough to allow flowing neutrophils to adhere to immobilised platelets, and induce formation of aggregates in vivo. Thus, inhibition of neutrophil-platelet adhesion and modulation of their biochemical interactions could be a novel approach to treatment of thrombotic, ischaemic or inflammatory disorders.

Two new formylated peptides able to activate chemotaxis and respiratory burst selectively as tools for studying human neutrophil responses

Two new For-Met-Leu-Phe-OH (FMLP) methyl ester analogues, For-Thp-Leu-Ain-OMe [Thp1, Ain3] and For-Met-delta zLeu-Phe-OMe [delta zLeu2], able to activate selectively chemotaxis and superoxide anion (O2-) release, respectively modulate intracellular cyclic AMP (cAMP) levels in different ways. FMLP and [delta zLeu2] enhance human neutrophil cAMP levels per se, and this effect is potentiated by Ro 201724, a non-xanthinic phosphodiesterase (PDE) inhibitor, whereas it is counteracted by 3-isobutyl-1-methyl-xanthine (IBMX), a blocker of both phosphodiesterase and adenosine receptors. In contrast, [Thp1, Ain3] is ineffective. However, no formylated peptides influence cAMP phosphodiesterase activity. Neutrophil preincubation with Ro 201724 or IBMX drastically reduces chemotaxis and superoxide anion (O2-) production triggered by peptides. Our results suggest that: (1) peptide-induced cAMP increase is probably indirect, and due mainly to the action on adenosine-sensitive adenylate cyclase; (2) formylated peptide, endowed solely with chemotactic activity is unable to increase neutrophil cAMP concentration; (3) cAMP elevation may represent a feed-back mechanism to inhibit the physiological responses induced by formylated peptides.