Effects of platelet-activating factor on human T and B cells--an overview

Associations of phase angle with platelet-activating factor metabolism and related dietary factors in healthy volunteers

Introduction

Phase angle (PA) is derived from bioelectrical impedance analysis (BIA). It reflects cell membrane function and decreases in disease. It is affected by inflammation, oxidative stress, and diet. Platelet-activating factor (PAF) is a potent inflammatory lipid mediator. Its levels, along with the activity of its metabolic enzymes, including CDP-choline:1-alkyl-2-acetyl-sn-glycerol-cholinephosphotransferase, acetyl-CoA:lyso-PAF-acetyltransferases, and PAF-AH/Lp-PLA2 are also related to dietary factors, such as the dietary antioxidant capacity (DAC). The aim of the study was to estimate whether the PAF metabolic circuit and related dietary factors are associated with PA in healthy volunteers.

Methods

In healthy subjects, PAF, its metabolic enzyme activity, and erythrocyte fatty acids were measured, while desaturases were estimated. Food-frequency questionnaires and recalls were used, and food groups, macronutrient intake, MedDietScore, and DAC were assessed. Lifestyle and biochemical variables were collected. DXA and BIA measurements were performed.

Results

Lp-PLA2 activity was positively associated with PA (rho = 0.651, p < 0.001, total population; rho = 0.780, p < 0.001, women), while PAF levels were negatively associated with PA only in men (partial rho = -0.627, p = 0.012) and inversely related to DAC. Estimated desaturase 6 was inversely associated with PA (rho = -0.404, p = 0.01, total sample). Moreover, the DAC correlated positively with PA (rho = 0.513, p = 0.03, women). All correlations were adjusted for age, body mass index, and sex (if applicable).

Conclusion

PA is associated with PAF levels and Lp-PLA2 activity in a gender-dependent fashion, indicating the involvement of PAF in cell membrane impairment. The relationship of PA with DAC suggests a protective effect of antioxidants on cellular health, considering that antioxidants may inhibit PAF generation.

Platelet-activating factor levels of serum and gingival crevicular fluid in nonsmoking patients with periodontitis and/or coronary heart disease

The purpose of the present study was to investigate systemic and local levels of platelet-activating factor (PAF), a potent proinflammatory mediator implicated in cardiovascular pathophysiology in adult nonsmoking patients with periodontitis with or without coronary heart disease (CHD). Eighty-seven volunteers, 25 periodontitis patients, 19 periodontitis with CHD patients, 19 CHD patients, and 24 healthy controls were included, and periodontal conditions were assessed. Gingival crevicular fluid (GCF) and venous blood were collected, and PAF levels were measured by enzyme-linked immunosorbent assay. PAF levels in serum (303.3 ± 204 pg/ml) and in GCF (26.3 ± 6 pg/μl) of the periodontitis group with CHD, the periodontitis group (serum, 302.4 ± 241 pg/ml and GCF, 26.3 ± 8 pg/μl) and the CHD group (serum, 284.7 ± 192 pg/ml and GCF, 20.8 ± 6 pg/μl) were significantly higher than the healthy control group (serum, 65.4 ± 35 pg/ml and GCF, 7.7 ± 3 pg/μl; p < 0.05). In summary, the present study could demonstrate that in patients with periodontitis, the inflammatory mediator PAF is released into serum at least in the same range as for patients with coronary heart disease. However, no additive effects were seen when both conditions were present.

Periodontal parameters and platelet-activating factor levels in serum and gingival crevicular fluid in a Chinese population

AIM

Platelet-activating factor (PAF) is a potent proinflammatory mediator and has been implicated in cardiovascular pathophysiology. The present clinical study assessed the relation between the severity of periodontal disease and PAF levels in gingival crevicular fluid (GCF) and serum.

METHODS

A total of 60 non-smoking subjects (21 periodontitis, 19 gingivitis patients and 20 healthy individuals) were included. Probing depth, attachment level, bleeding on probing, plaque index and sulphide levels were recorded at six sites of each tooth. GCF and blood samples were collected from all individuals, and PAF levels were investigated by enzyme-linked immunoabsorbent assay.

RESULTS

The periodontitis group showed significantly higher PAF levels in the serum (329.3+/-287.3 pg/ml) and GCF (21.8+/-7.0 pg/sample) compared with the gingivitis group (138.0+/-77.9 pg/ml, 13.8+/-3.6 pg/sample) and with healthy controls (68.9+/-42.8 pg/ml, 2.4+/-2.7 pg/sample). The differences between patients and controls were statistically significant (p<or=0.05). Positive correlations were observed between PAF levels in GCF and serum and for PAF levels and clinical parameters.

CONCLUSION

The present findings suggest a role of PAF in the pathogenesis of periodontitis. Based on the observed close correlation of GCF and serum PAF levels, future studies are warranted to test the hypothesis of a possible link between periodontitis and adverse systemic events mediated by PAF.

Host response of platelet-activating factor receptor-deficient mice during pulmonary tuberculosis

Platelet-activating factor (PAF) is a phospholipid with potent, diverse actions, which has been implicated as an important mediator in host defence against several intracellular pathogens. To determine the role of PAF in host defence in pulmonary tuberculosis, PAF receptor-deficient (PAFR-/-) and wild-type (PAFR+/+) mice were infected intranasally with a virulent strain of Mycobacterium tuberculosis. Mycobacterial outgrowth in lungs and liver did not differ significantly between PAFR-/- and PAFR+/+ mice at 2 or 6 weeks postinfection. After 28 weeks, 86% of PAFR-/- mice and 79% of PAFR+/+ mice had died (non-significant). In addition, both mouse strains were indistinguishable with respect to histopathology, the recruitment and activation of lymphocytes, and cytokine concentrations in the lung. These data suggest that PAF is not involved in the protective immune response to tuberculosis.

Levels of platelet-activating factor in gingival crevicular fluid and gingival tissue in specific periodontal diseases

BACKGROUND

Platelet-activating factor (PAF), a potent phospholipid mediator of inflammatory and immune reactions, is involved in a variety of biological responses seen in periodontal diseases. The aim of the present study was to examine the role of PAF in the pathogenesis of specific periodontal diseases.

METHODS

PAF levels were investigated in gingival crevicular fluid (GCF) and gingival tissue (GT) samples of 12 patients with generalized aggressive periodontitis (GAgP), 6 patients with localized aggressive periodontitis (LAgP), 10 patients with chronic periodontitis (CP), 6 with gingivitis (G), and 6 periodontally healthy subjects (H). Periodontal status was evaluated by measuring probing depth, gingival index, papillary bleeding index, and plaque index. PAF was extracted from GCF samples passing through amberlit resin columns, purified by high performance liquid chromatographic method, and then analyzed by radioimmunoassay.

RESULTS

GAgP, LAgP, and CP groups had significantly higher GCF PAF levels compared to the H group (P<0.005). Although statistically not significant, GCF PAF levels were also higher in the G group than those of the H group (P = 0.0784). GAgP, LAgP, and CP groups had similar GCF PAF levels (P>0.005). These groups had higher levels of GCF PAF than those of the G group, but the difference was significant only for the GAgP group (P<0.005). When the data were expressed as concentration, GAgP, LAgP, and CP groups were found to have higher concentrations of GCF PAF compared to the H group (P<0.005). GCF PAF concentration was similar in patient groups (P>0.005). All patient groups had significantly higher GT PAF levels compared to the H group (P<0.005). GAgP, LAgP, and CP groups had similar amounts of GCF and GT PAF (P>0.005). GAgP, LAgP, and CP groups had higher GT PAF levels than those of the G group, but the differences were only significant for LAgP and CP groups (P<0.005). No significant correlation was found between GCF and GT PAF levels and clinical parameters.

CONCLUSIONS

The results of the present study indicate that PAF is likely to be an important mediator in regulating inflammatory responses in the human periodontal tissues. To our knowledge, this is the first report investigating PAF levels in GCF and GT in specific periodontal diseases. We believe that this potent phospholipid mediator may need to be considered in the pathogenesis of periodontal diseases.

Activation via multiple signaling pathways induces down-regulation of platelet-activating factor receptors on human B lymphocytes

Platelet-activating factor receptor (PAFR) has been identified in B cell lines and primary human B cells, but the regulation of PAFR during B cell activation has not been completely elucidated. In the present study, we have investigated the effects of B cell activation on PAFR binding parameters, PAFR mRNA and PAF-triggered intracellular calcium mobilization. The human B lymphoid cell line LA350 was shown to exhibit high levels of PAFR (48,550 +/- 4,310 sites/cell) as determined by radio-ligand binding assay with PAFR antagonist [3H]WEB2086. Treatment with phorbol 12,13-dibutyrate caused a biphasic reduction of PAFR binding. The early phase was inhibited by the protein kinase C inhibitor bisindolylmaleimide I (BIM), whereas the late phase was not blocked by BIM, protein tyrosine kinase inhibitor genistein, or the mitogen-activated protein kinase/extracellular signal-related kinase inhibitor PD98059. However, staurosporine, a broad-spectrum protein kinase inhibitor, completely inhibited the late phase down-regulation. Ionomycin also decreased [3H]WEB2086 binding sites, whereas the combination of PDB and ionomycin induced a greater reduction than either agent alone. Cross-linking of B cell receptor by anti-IgM Ab also induced down-regulation of PAFR, which was abolished by genistein or PD98059, but not by BIM or staurosporine. The decrease in surface PAFR number was closely paralleled by the reduction in PAFR mRNA both in LA350 cells and human tonsillar B cells, and was associated with decreased response to PAF indicated by decreased intracellular calcium mobilization. These data show that multiple signaling pathways are involved in down-regulating PAFR expression during B cell activation and development.

Levels of leukotriene B4 and platelet activating factor in gingival crevicular fluid in renal transplant patients receiving cyclosporine A

BACKGROUND

Cyclosporine A (CsA) is a potent immunosuppressant effectively used to prevent organ transplant rejection and also to treat several systemic diseases. CsA-induced gingival overgrowth (CsA GO) is the most widely seen side effect of this drug; its pathogenesis is not completely understood. The aim of the present study was to identify the role of leukotriene B4 (LTB4) and platelet activating factor (PAF) in the pathogenesis of CsA GO.

METHODS

LTB4 and PAF levels were detected in gingival crevicular fluid (GCF) samples from renal transplant patients receiving CsA therapy and exhibiting CsA GO, from patients with gingivitis and from periodontally healthy subjects. Plaque index, papilla bleeding index, and hyperplastic index were recorded at each study site. GCF samples and clinical data were obtained from: 2 sites exhibiting CsA GO (CsA GO+) and 2 sites not exhibiting CsA GO (CsA GO-) in each CsA-treated patient; 2 diseased sites in each patient with gingivitis; and 2 healthy sites in each subject with clinically healthy periodontium. LTB4 was extracted from the samples by solid-phase method using C18 cartridge and purified by high-performance liquid chromatographic (HPLC) method and analyzed by radioimmunoassay (RIA). PAF was extracted from GCF samples passing through amberlit resin columns, purified by HPLC, and analyzed by RIA.

RESULTS

Total amounts of LTB4 and PAF in GCF were higher in CsA GO+ sites compared to the healthy sites from healthy controls. However, the amount of LTB4 and PAF elevation in CsA GO+ sites was not significantly higher than those in diseased sites. Clinical degrees of gingival inflammation were also similar between CsA GO+ and diseased sites. LTB4 and PAF total amounts in GCF were higher in CsA GO+ sites compared to CsA GO- sites in the same subjects, but this difference just failed to reach significance. Similar findings were obtained with concentration data.

CONCLUSIONS

The results of this study indicate that CsA therapy does not have a significant effect on GCF LTB4 and PAF levels and that gingival inflammation seems to be the main reason for their elevation. In CsA-treated patients, alterations in LTB4 and PAF levels might play a role in CsA GO through some asyet unknown mechanism. To our knowledge, this is the first report describing the levels of lipid mediators in GCF of CsA-treated patients. We assume that further studies will contribute to the understanding of the pathogenesis of CsA-induced gingival overgrowth.

PAF and haematopoiesis XII: macrophage colony-stimulating factor (M-CSF) decreases platelet-activating factor (PAF) acetylhydrolase production in macrophagic J774 cells

Platelet-activating factor (PAF) is a phospholipid mediator with major immunoregulatory activities. Macrophages produce PAF acetylhydrolase activity, which regulates blood PAF concentrations. Macrophage colony-stimulating factor (M-CSF) is involved in the differentiation and functions of cells from the monocytic/macrophagic lineage. We found that murine macrophagic J774 cells metabolized PAF with lyso PAF as the major metabolite product. As in mouse plasma, the metabolism of PAF by J774 cells was not inhibited by PMSF, p-BPB, DTNB and quinacrine, M-CSF (100-5000 U/ml) significantly decreased PAF acetylhydrolase activity of the J774 cell without exhibiting a significant effect on cell growth. Elevated concentrations of M-CSF are found in blood and tissues during inflammatory states. It could be suggested that a decreased PAF catabolism by tissue macrophages in response to M-CSF may induce local elevated PAF concentrations, thus amplifying the inflammatory response.

PAF and haematopoiesis. X. Macrophage colony-stimulating factor and granulocyte macrophage colony-stimulating factor enhance platelet-activating factor acetylhydrolase production by human blood-derived macrophages

Platelet-activating factor (PAF), a phospholipid autacoid with potent regulatory functions, is synthesized by stimulated monocytes. Macrophages are a source of the plasma acetylhydrolase activity (AHA) which regulates PAF concentrations. Granulocyte-macrophage colony-stimulating factor (GM-CSF) and macrophage colony-stimulating factor (M-CSF) are involved in the differentiation and functions of cells from the monocytic/macrophagic lineage. This work reports that M-CSF and GM-CSF stimulated AHA production by human blood monocyte-derived macrophages in a time- and dose-dependent manner. After 7 days of culture without serum, a 6- and 4-fold increase was found in cells treated with M-CSF (1000 U/ml) and GM-CSF (50 ng/ml), respectively. M-CSF (up to 1000 U/ml) and GM-CSF (up to 10 ng/ml) did not induce PAF production by human blood monocytes. While GM-CSF (10 ng/ml) and interleukin-1 (10 U/ml) stimulated M-CSF production from monocyte-derived macrophages, PAF did not. These results indicate that M-CSF and GM-CSF enhance AHA production by human blood-derived macrophages cultured in low serum concentrations. Clearly the effects of growth factors on AHA production in vivo deserve to be assessed.

PAF and haematopoiesis: III. Presence and metabolism of platelet-activating factor in human bone marrow

Platelet-activating factor (PAF) is a phospholipid compound with major immunoregulatory activities. The present study shows that human bone marrow contains 576 +/- 39 pg PAF/ml (n = 35). Bone marrow-derived PAF exhibits the same biophysical and biological properties that synthetic PAF. PAF concentrations in bone marrow are correlated with the granulocyte (r = 0.4, P = 0.02) but not with the lymphocyte (r = 0.24, P = 0.17) and the monocyte (r = 0.12, P = 0.48) counts. In bone marrow PAF is inactivated by a plasma PAF acetylhydrolase activity (48.0 +/- 2.3 nmol/min per ml, n = 34). Experiments with [3H]PAF indicate that human bone marrow cells actively metabolize this potent molecule by the deacetylation-transacylation pathway. Results of this investigation indicate the permanent presence of significant amounts of PAF in bone marrow suggesting its putative involvement in the processes of bone marrow cell proliferation and maturation.

PAF and haematopoiesis. IV. Modifications of spleen and thymus PAF contents after a single dose of the chemotherapeutic drug 5-fluorouracil in mice

The spleen and thymus of mice were examined for the presence of PAF after injection of 5-fluorouracil (5-FU) (200 mg/kg). A significant increase of the spleen (P = 0.005) and thymus (P < 0.05) PAF concentrations was noted 48 h after 5-FU infusion. PAF levels in thymus are similar to those of controls from days 4 to 14. By contrast, spleen PAF significantly decreased (0.005 < P < 0.03) from days 7 to 14. Conversely, the 5-FU administration did not modify the spleen and plasma acetylhydrolase activity, suggesting that the variations of PAF levels in thymus and spleen were mainly due to differences of local PAF production. Thus, the chemotherapeutic drug 5-FU modulates in vivo PAF production in haematopoietic organs of mice. Considering the effects of PAF in the processes of B- and T-cell proliferation and functions, these results could be of importance for the role of PAF during human cancer therapy and haematopoiesis in vivo.