Plasma levels of the lyso-derivative of platelet-activating factor in acute severe systemic illness

The metabolism of platelet-activating factor in severe and cerebral malaria

In order to examine the effects of platelet-activating factor (PAF) in complicated Plasmodium falciparum infections, plasma concentrations of lyso-PAF, stable metabolite and principal precursor of PAF, were measured in 25 Vietnamese adults with severe malaria. The concentration of PAF in the cerebrospinal fluid (CSF) was determined in a sub-group of 23 comatose patients and, together with that of lyso-PAF, in the plasma of 20 patients on recovery of consciousness. The concentration of lyso-PAF in the plasma was depressed on admission to hospital (median [range]; 21 [8-143] vs. 293 [215-410] ng/ml in 10 controls; P < 0.001). There was, however, no change in plasma activity of acetylhydrolase which converts PAF to lyso-PAF (P > 0.01 vs. controls) while simultaneous reduction in the concentration of lipoproteins associated with lyso-PAF were less than those of lyso-PAF per se in the plasma. The plasma concentration of lyso-PAF on admission was associated with parasitaemia and the concentration of serum triglycerides (rs = -0.42, P = 0.04 in each case), the latter being consistent with hepatic effects of PAF reported in previous studies. CSF concentrations of PAF on admission were low (2.3 [0.5-7.7] vs. 0.9 [0-2.5] ng/ml after recovery, P < 0.01) compared with values reported previously in bacterial meningitis. Plasma concentrations of lyso-PAF after recovery lay between admission and control values. While increased availability of PAF may reflect parasite burden and may modulate liver-mediated metabolic disturbances such as hypoglycaemia and lactic acidosis, the role of PAF in cerebral malaria is uncertain.

Neutrophil platelet-activating factor production and acetyltransferase activity in clinical acute myocardial infarction

1. Neutrophil function was studied in 10 males presenting with acute myocardial infarction (MI) within 6 h of onset and in 10 normal males. Neutrophil production of platelet-activating factor (PAF), determined by bioassay, that of leukotriene B4 by HPLC, and the activity of an enzyme involved in the synthesis of PAF, acetyltransferase (AT), were measured before and after stimulation with opsonized zymosan and calcium ionophore, A23187. 2. The neutrophil count was significantly raised at presentation in those with MI (8.2 +/- 0.8 vs 2.8 +/- 0.3 (s.e.m.) x 10(9) cells/L, P < 0.001; t-test, 18 d.f.). Production of PAF per neutrophil in response to both stimulants was greater than normal in those with MI (zymosan: 21 +/- 4 vs 12 +/- 1 ng/10(7) cells, P < 0.05; ionophore: 174 +/- 18 vs 113 +/- 11 ng/10(7) cells, P < 0.02) despite normal leukotriene B4 production and depressed AT activity. By 7 days, the neutrophil count had significantly fallen but it remained greater than normal as did PAF production. 3. Acute MI is associated with increased potential for production of PAF by neutrophils which may be important in the pathogenesis of MI.

Platelet-activating factor and lipid metabolism in acute malaria

Platelet-activating factor (PAF) contributes to a range of pathophysiological responses in severe illness. To examine PAF metabolism in acute malaria, venous blood was drawn from 10 untreated adults with falciparum malaria, from 8 with untreated vivax malaria, and from 10 controls. Plasma lyso-PAF, produced from PAF through the enzyme acetylhydrolase (AH), was bioassayed, after acetylation to PAF, by platelet [14C]-serotonin release. AH activity was measured by hydrolysis of [3H]-acetyl-PAF. Amounts of plasma lyso-PAF were lower in falciparum (median [range] 24 [9-221] ng/ml) and vivax (35 [7-236] ng/ml) infected patients than in controls (399 [212-504] ng/ml; P < 0.01), and correlated significantly with serum total and HDL-cholesterol (P < 0.001). Plasma AH activities were similar in the control, falciparum and vivax malaria groups. These data suggest that in malaria plasma lyso-PAF values fall together with other blood lipids, but independently of changes in AH activity. This may reflect a generalised decrease in lipid and phospholipid synthesis. However, the reduction of plasma lyso-PAF concentrations in our patients was much greater than that of serum lipoproteins. This is consistent with conversion of lyso-PAF to PAF or with increased PAF-receptor interactions. These two possibilities would have pathophysiological implications.

Influence of a platelet-activating factor antagonist on severe pancreatitis in two experimental models

This study investigates the role of platelet-activating factor (PAF) in experimental pancreatitis. The concentration of PAF quantified in ascites of bile-induced pancreatitis by radioimmunoassay (RIA) ranged from 3.67 +/- 0.39 pmol/mL 2 h to 0.954 +/- 0.39 pmol/mL 10 h after injection of taurocholate. Administration of a potent PAF antagonist, WEB-2170, prior to injection of taurocholate prolonged mean survival time in rats receiving i.v. camostate and albumin (46.4 h, n = 15, vs controls 38.3 h, n = 13). However, the survival rate after 72 h was not improved. The histologically estimated severity of pancreatitis and pancreatic enzymes in blood, tissue, or ascites was not affected. WEB-2170 had no effect on survival when injected simultaneously with taurocholate into the pancreatic duct or given i.v. after induction of pancreatitis (1, 0.1, or 0.01 mg/kg WEB-2170 vs controls). Subcutaneous injection of 10 mg/kg WEB-2170 also did not improve survival in pancreatitis induced by choline-deficient, ethionine-supplemented diet in mice. It is concluded that administration of a PAF antagonist after the onset of severe experimental pancreatitis does not influence its outcome, although activation of PAF may play a role in the pathogenesis of pancreatitis.