Ovine platelet factor 4: purification, amino acid sequence, radioimmunoassay and comparison with platelet factor 4 of other species

Intramammary treatment using allogeneic pure platelet-rich plasma in cows with subclinical mastitis caused by Gram-positive bacteria

The aims of the study were (1) to compare the cure risk of intramammary treatment of pure platelet rich plasma (P-PRP) or cefquinome sulfate (CS) in cows with subclinical mastitis (SCM) caused by Gram-positive bacteria, evaluated via somatic cell count (SCC) and the microbiological analysis of milk; (2) to compare the inflammatory/anti-inflammatory response of mammary gland to both treatments through the analyses of interleukins (IL), interferon gamma (IFN-γ), and tumour necrosis factor alpha (TNF-α) in milk. A non-inferiority randomized clinical trial was conducted. The null hypothesis was that cure risk in the experimental group (P-PRP) was inferior to the reference group (CS). A total of 103 cows were selected according to SCC and presence of Gram-positive bacteria, 49 cows were treated with CS and 54 cows were treated with P-PRP after determination of its cellular and molecular quality control. Cure was assessed by milk analyses at day 21 and 22 after treatment. Cows that remained with SCM were retreated at day 26, and cure assessed at day 47 and 48. Overall, bacteriological cure was observed in 16 cows (30%) of the P-PRP group, and 35 cows (71%) in CS group. Staphylococcus aureus cure risk was higher in CS group, but inconclusive for Streptococcus spp. The mean SCC increased in relation to time only in the P-PRP group. A direct relation between time and treatment for IL-1, IL-2, and IL-6 was observed, while no differences were observed for IL-4. Furthermore, IL-1 and IL-2 increased in cows treated twice in both groups. IL-8, IFN-γ, and TNF-α showed a significant interaction between time and treatment. IFN-γ concentration was lower in the P-PRP group compared to the CS on days 0 and 22. Leukocyte counts were lower in P-PRP when compared to whole blood. TGF-β1 and PF4 concentrations were higher in platelet lysates in comparison to P-PRGS and plasma. Moreover, PDGF-BB concentration was significantly higher in platelet lysates in comparison to plasma. Results obtained in this study demonstrate that SCM treated with PRP showed a lower rate of bacteriologic cure when compared to animals treated with CS.

The role of the CXC chemokines platelet factor-4 (CXCL4/PF-4) and its variant (CXCL4L1/PF-4var) in inflammation, angiogenesis and cancer

Chemokines are chemotactic cytokines which recruit leukocytes to inflammatory sites. They also affect tumor development and metastasis by acting as growth factor, by attracting pro- or anti-tumoral leukocytes or by influencing angiogenesis. Platelet factor-4 (CXCL4/PF-4) was the first chemokine shown to inhibit angiogenesis. CXCL4L1/PF-4var, recently isolated from thrombin-stimulated platelets, differing from authentic CXCL4/PF-4 in three carboxy-terminally located amino acids, was found to be more potent than CXCL4/PF-4 in inhibiting angiogenesis and tumor growth. Both glycosaminoglycans (GAG) and CXCR3 are implicated in the activities of the PF-4 variants. This report reviews the current knowledge on the role of CXCL4/PF-4 and CXCL4L1/PF-4var in physiological and pathological processes. In particular, the role of CXCL4/PF-4 in cancer, heparin-induced thrombocytopenia and atherosclerosis is described.

Antimicrobial fragments of the pro-region of cathelicidins and other immune peptides

In addition to the numerous cathelicidin peptides that are associated with the antimicrobial activity exhibited by a crude extract from ovine blood, a further three peptides with antimicrobial activity have been identified. These were part of the precursor cathelin domain of cathelicidins, a large fragment of platelet factor 4 and a small peptide similar to signal peptide of the T-cell glycoprotein CD4 precursor. Fragments of proteins that are involved in protecting the host from infection may have a secondary purpose as antimicrobial agents once they have carried out their primary purpose and are cleaved the main protein.

A baboon model for hematologic studies of cardiopulmonary bypass

Objective investigation of new inhibitors of blood protein or cellular systems that are activated during cardiopulmonary bypass (CPB) is impeded by the absence of a satisfactory animal model. Because most baboon hematologic proteins immunologically cross-react with those used for human assays, we developed a robust, reusable baboon model of CPB. Blood samples were obtained from adult baboons at six time intervals before, during, and after 60 minutes of partial CPB at 37 degrees C with peripheral cannulas. Both membrane (n = 7) and bubble oxygenators (n = 7) were investigated. We measured platelet and white blood cell counts; platelet response to adenosine diphosphate and release of beta-thromboglobulin; fibrinopeptide A, prothrombin fragment F1.2, thrombin-antithrombin complex, D-dimer, and plasmin-antiplasmin complex; activated complement (C3b/c and C4b/c); elastase-alpha1 proteinase inhibitor complex; and bleeding times. Adherent glycoprotein IIIa antigen in Triton X-100 washes of the perfusion circuit was also measured. Markers of baboon platelet, complement, and neutrophil activation and thrombosis significantly increased during CPB with bubble oxygenator systems but did not change appreciably in membrane oxygenator circuits. Markers of fibrinolysis, D-dimer, and plasmin-antiplasmin complex did not change with either oxygenator. The baboon model of CPB, when a bubble oxygenator is used, is a robust, reusable animal model for evaluating inhibitors of platelet, complement, and neutrophil activation and thrombosis during and after CPB.

Structure and bioactivity of recombinant human CTAP-III and NAP-2

Connective tissue-activating peptide III (CTAP-III) and neutrophil-activating peptide-2 (NAP-2) are both derived from a common precursor, platelet basic protein (PBP), which is stored in the alpha-granules of platelets and released upon their activation. CTAP-III is an 85-residue peptide which is converted to NAP-2 by enzymic removal of the 15 amino-terminal residues. Both peptides play a role in the early stages of wound healing and inflammation through different activities. We have cloned the cDNA for PBP and expressed constructs coding for the CTAP-III and NAP-2 polypeptides in Escherichia coli. We have purified and renatured these recombinant proteins. The integrity of the recombinant proteins has been ascertained by in vitro bioassays. CTAP-III causes 51% histamine release from the basophilic cell lin KU812 at 10(-7) M, whereas NAP-2 only causes 28% release at the same concentration. In assays on human neutrophils, NAP-2 had an EC50 of 2 x 10(-8) M in chemotaxis, an EC50 of 3 x 10(-8) M for shape change, and could displace IL-8 from neutrophils with a Kd of 7.5 x 10(-9) M. CTAP-III had no activity in these assays. The disulfide bonds have been identified by peptide mapping and sequence analysis, and are in the positions predicted by homology to interleukin-8 and platelet factor 4. Measurement of the molecular mass at physiologic concentrations by gel permeation chromatography has shown that CTAP-III forms predominantly tetramers and dimers, whereas NAP-2 is only dimetric. SDS/PAGE analysis of samples cross-linked with disuccinimidyl suberate support these topologies. We postulate a mechanism for tetramer formation based on the interaction of the amino-terminal extension in CTAP-III involving a helix-helix interaction that could stabilize the association of two CTAP-III dimers.

Differences in binding of platelet factor 4 to vascular endothelium in vivo and endothelial cells in vitro

The binding of fluorescein-labelled recombinant human platelet factor 4 (rhPF4) to the vasculature of the hamster cheek pouch in vivo was compared with that to cultured endothelial cells (EC) from human umbilical veins (HUVEC) and arteries (HUAEC) and from human aorta (HAEC). In vivo data: systemically injected rhPF4 rapidly disappeared from plasma in a biphasic pattern (t1/2 = 2 and 41 min). High intensity non-uniform binding of rhPF4 occurred at short specific sites along both arterioles and venules. The length of the intense sites was 76 +/- 46 microns and their frequency was 10 +/- 4 per cm2 cheek pouch. Heparin was injected at 4 and 9 min, but not 30 min, post-rhPF4 displaced most of the high intensity labelling indicating internalization with time. Neither pretreatment with more than 50-fold excess of unlabelled rhPF4 nor histamine- or LTB4-induced vascular macromolecular leakage changed the frequency of short intense sites. In vitro data: uniform time-dependent intense binding of rhPF4 occurred in a similar fashion in subconfluent HUVEC, HUAEC and HAEC. All cell types showed nuclear staining, demonstrating internalization. When heparin was given to EC prior to rhPF4, binding was delayed in time but not blocked. In conclusion, rhPF4 does not bind uniformly with high intensity along pre- and post-capillary vessels of the hamster cheek pouch in vivo as predicted by the rhPF4-labelling of subconfluent (migrating/proliferating) human EC in vitro. The short infrequent sites of intense rhPF4-labeling in vivo may represent regions of endothelial cell migration/proliferation similar to subconfluent EC in culture.

The complete primary structure of glycosylated porcine platelet factor 4

We have purified platelet factor 4 from porcine platelets and shown that it is glycosylated. The purified protein migrated as a broad band at approximately 14,000 Da, characteristic of glycoproteins. Electrospray mass spectroscopy of the intact protein gave a predominant mass of 11,111 Da, with a minor component of 10,804 Da. Sialidase digestion reduces both forms to a single mass of 10,497 Da. Upon Edman degradation, the amino terminus was found to be blocked by the presence of a pyroglutamate residue. We have determined the complete primary structure of platelet factor 4 by peptide mapping and Edman degradation, thereby completing information on the amino-terminal and carboxy-terminal regions which is missing in the previously published partial sequence. Sequencing of the intact and deglycosylated protein show that the glycosylation site is at Thr8. The amino acid composition accounts for a mass of 9623 Da, and the carbohydrate moeity was found to contribute 1490 Da. The biological activity of the porcine protein has been compared to recombinant human platelet factor 4 in an endothelial cell proliferation assay; both inhibit at a concentration giving half the maximal inhibition of 0.1 microM. Removal of the 19 amino-terminal residues carrying the carbohydrate moiety results in no change in the biological activity.

Rat platelets contain glycosylated and non-glycosylated forms of platelet factor 4. Identification and characterization by mass spectrometry

Platelet factor 4 is a heparin-binding protein released from the alpha granules of activated platelets. This study describes the purification and identification of two forms of rat platelet factor 4, the previously characterized non-glycosylated form of 7 kDa and an additional glycosylated form of molecular mass 9 kDa. The two proteins both neutralized the antithrombin-III-dependent inhibitory activity of heparin. Although their amino acid composition was found to be the same, in the N-terminal sequence of the 9-kDa protein, the second threonine residue could not be detected and a difference of 976Da was determined by mass spectrometry. After digestion with O-glycanase and sialidase, the two proteins showed the same molecular mass. Overall consideration of these data led to identification of the higher-molecular-mass protein as a glycosylated form of rat platelet factor 4 with O-glycosylation at the second N-terminal amino acid, while the structure of the oligosaccharide core was established by mass spectrometry and sugar differentiation with lectins. The two forms of platelet factor 4 are both present in platelets and secreted after platelet activation.

Platelet factor 4 binds to interleukin 8 receptors and activates neutrophils when its N terminus is modified with Glu-Leu-Arg

Amino acid deletion and mutagenesis experiments have indicated that the sequences Glu-Leu-Arg (ELR) preceding the first cysteine at the N terminus of interleukin 8 (IL-8) is required for receptor binding and neutrophil activation. Platelet factor 4 (PF4) is structurally related to IL-8 (35% sequence identity) but lacks the N-terminal ELR sequence and comparable effects on neutrophils. We introduced the ELR sequence at the N terminus of PF4 and found that the modified protein was a potent neutrophil activator and attractant. On the other hand, when the ELR sequence was introduced into the corresponding positions of two other proteins related to IL-8, gamma-interferon-inducible protein IP10 and monocyte chemoattractant protein 1, neither of them acquired neutrophil-activating properties, indicating that besides ELR additional structural determinants of IL-8 and PF4 are important for binding to IL-8 receptors. The conservation of these binding determinants suggests that PF4 may have evolved from a neutrophil activating protein.