Plasma and urinary platelet activating factor concentrations and leukotriene releasing activity of leukocytes in steroid sensitive nephrotic syndrome of childhood

Urothelial cell platelet-activating factor production mediated by calcium-independent phospholipase A2γ

OBJECTIVES

To determine the effect of phospholipase A(2) (PLA(2)) inhibitors on urothelial cell platelet-activating factor (PAF) production in response to tryptase stimulation.

METHODS

Urothelial cells isolated from normal human ureters were immortalized with the human papillomavirus type 16E6E7 cell line (TEU-2 cells). PLA(2) activity in TEU-2 cells was measured using (16:0, [(3)H]18:1) plasmenylcholine and phosphatidylcholine substrates in the presence and absence of calcium. [(3)H]PAF production was measured in TEU-2 cells prelabeled with [(3)H] acetic acid. PAF-acetylhydrolase activity was measured by determining the amount of [(3)H] acetate hydrolyzed from [(3)H]PAF incubated with TEU-2 cellular protein. Adherence of human polymorphonuclear leukocyte (PMN) to TEU-2 cells was assessed by measuring myeloperoxidase activity in adherent PMNs after incubation with TEU-2 cells.

RESULTS

Most PLA(2) activity measured in TEU-2 cells was determined to be membrane-associated, calcium-independent PLA(2) and selective for plasmenylcholine substrate. Stimulation of TEU-2 cells with tryptase results in increased production of PAF and increased PMN adherence that were inhibited completely by pretreatment with the membrane-associated, calcium-independent PLA(2)γ-selective inhibitor (R)-bromoenol lactone. Pretreatment with the cytosolic PLA(2) inhibitor methyl arachidonyl fluorophosphonate resulted in potentiation of tryptase-stimulated PAF production and PMN adherence to TEU-2 cells that is a result of PAF-acetylhydrolase inhibition.

CONCLUSIONS

Tryptase stimulation of TEU-2 cells results in activation of membrane-associated, calcium-independent PLA(2)γ, leading to an increase in PAF production and increased PMN adherence. Inhibition of TEU-2 cell PAF-acetylhydrolase activity with methyl arachidonyl fluorophosphonate potentiated tryptase-stimulated PAF production and PMN adherence.

Intraleucocyte platelet-activating factor levels in desmopressin-treated patients with haemophilia A and von Willebrand disease

Despite the intensive clinical use of 1-deamino-8-D-arginine vasopressin (desmopressin; DDAVP) for 20 years, its mechanism of action is still not completely explained. It has been proposed that DDAVP stimulates release of a 'second messenger' which in turn stimulates release of von Willebrand factor (vWF) from endothelial cells. Platelet-activating factor (PAF) and interleukin (IL)-6 were individually proposed to be mediators for haemostatic action. The aim of this study was to investigate cellular-based PAF levels in patients with haemophilia A (HA) and von Willebrand disease (vWD) before and after DDAVP treatment and also to look for any probable relationship between the haemostatic response of DDAVP and cellular PAF activities. In total, 20 patients (11 HA and nine vWD) were enrolled in the study. DDAVP was given subcutaneously as a single dose (0.3 microg kg(-1)). Ten patients responded to DDAVP and were defined as the 'able group' (four mild HA, six type 1 vWD). The remaining 10 patients did not respond to DDAVP and were defined as the 'unable group' (seven severe HA, three type 3 vWD). Released (extracellular) and intracellular (intraleucocyte) PAF levels under the stimulation of specific agents (A23187 and Zymosan) were measured by high-performance liquid chromatography and radioimmunoassay. Extracellular and intracellular PAF activities were not detected without stimulation in healthy children whereas significantly higher PAF levels were found in the patients (extracellular: 37.5 +/- 34.4 ng per 10(7) cells; intracellular: 24.8 +/- 23.5 ng per 10(7) cells; P=0.0001). Intracellular PAF levels obtained from in vitro unstimulated cells were significantly higher in DDAVP-responsive (able) patients in comparison to DDAVP-unresponsive (unable) patients (52.1 +/- 18.5 vs. 28.9 +/- 8.0 ng per 10(7)cells). After in vitro stimulation by A23187, intracellular PAF activities were significantly higher in patients than in controls (209.3 +/- 26.1 vs. 172 +/- 18.1 ng per 10(7) cells). Intracellular PAF levels obtained from in vitro stimulated cells by A23187 were also significantly higher in the 'able' patients in comparison to the 'unable' patients (277 +/- 43.5 vs. 225 +/- 30 ng per 10(7)cells). In conclusion, cellular PAF activities are significantly higher in patients with HA and vWD. We also suggest that PAF, especially intracellular PAF mediates intracellular signalling and may be one of the important mediators for the haemostatic response of DDAVP.

Platelet-activating factor acetylhydrolase gene mutation in Japanese nephrotic children

BACKGROUND

Platelet-activating factor (PAF) may be involved in the pathogenesis of steroid-responsive nephrotic syndrome (SRNS). PAF is degraded to inactive products by PAF acetylhydrolase. We have investigated whether PAF acetylhydrolase gene mutation is involved in SRNS in Japanese children.

METHODS

We identified a point mutation in the PAF acetylhydrolase gene (G994T) using the polymerase chain reaction in 101 Japanese children with SRNS and 100 healthy Japanese.

RESULTS

There was no difference in the genotype and allele frequencies between patients with SRNS and normal controls. The mean number of relapses during the first year after onset was significantly higher in the 26 patients who were heterozygous for the mutant allele (GT) than in 75 wild-type homozygotes (GG) (2.61 +/- 1.98 vs. 1.33 +/- 1.35; P = 0.0019).

CONCLUSIONS

We conclude that analysis of the PAF acetylhydrolase gene mutation at position 994 in Japanese children with SRNS allows the identification of patients who are more likely to have a disease relapse.