Lyso-PAF acetyltransferase activity in neutrophils of patients during acute asthma and after recovery

Abstract

L Ly ys so o--P PA AF F a ac ce et ty yl lt tr ra an ns sf fe er ra as se e a ac ct ti iv vi it ty y i in n n ne eu ut tr ro op ph hi il ls s o of f p pa at ti ie en nt ts s d du ur ri in ng g a ac cu ut te e a as st th hm ma a a an nd d a af ft te er r r re ec co ov ve er ry y ABSTRACT: The production of platelet-activating factor (PAF) by inflammatory cells is regulated by lyso-PAF acetyltransferase, and the activity of this enzyme is increased in neutrophils of stable asthmatic patients. The aim of this investigation was to determine whether acetyltransferase activity is further upregulated in asthmatic patients experiencing acute symptoms. A radioenzymatic assay was used to measure the enzymatic affinity constant (Km) and maximal enzymatic activity (Vmax) for acetyltransferase from unstimulated and Ca 2+ ionophore (A23187)-stimulated neutrophils from 16 patients with acute asthma, and the measurement was repeated at the time of discharge (n=9) and after recovery from the acute episode (n=13).During acute asthma, Km (median 93.8 (interquartile range 64.1-109.7) µM) was lower than that measured in nonasthmatic subjects in a previous study using identical methods (155.1 (122.2-179.9) µM; p=0.0001), and in 10 out of 13 acute patients Km for unstimulated neutrophils increased following recovery. In A23187-stimulated neutrophils, Km during acute asthma (84.3 (73.6-100.2) µM) and at discharge (83.9 (83.1-94.8) µM) were similar, but Km after recovery was increased (115.0 (95.6-119.5) µM; p=0.02). The change in Km following stimulation with A23187 was also significantly less during acute asthma than previously measured in nonasthmatic subjects (p=0.003). Although Vmax during acute asthma (12.9 (interquartile range 10.5-22.5) nmol·min -1 ·mg -1 protein) did not differ significantly from that at discharge (14.4 (12.3-20.4) nmol·min -1 ·mg -1 ) or after recovery (17.3 (12.3-18.4) nmol·min -1 ·mg -1 ), both median Km and Vmax tended to be lowest during acute asthma and increase at discharge and after recovery.An increase in lyso-PAF acetyltransferase activity alone may not account for increased systemic PAF concentrations during acute asthma. However, the reduction in the enzymatic affinity constant and its smaller change following in vitro stimulation suggest that alterations in the affinity of acetyltransferase for acetylcoenzyme A (CoA) and in the regulation of enzyme activity may be occurring during acute asthma.

Platelet activating factor (PAF) and activity of its biosynthetic and catabolic enzymes in blood and leukocytes of male patients with newly diagnosed heart failure

“…biosynthetic enzyme lyso-PAF AT was lower in comparison to other studies examining neutrophils of asthmatic [23] and normal [24] volunteers as well as in untreated eosinophils of healthy subjects [25], although such comparisons are risky to make as experimental conditions may be different. As far as the activity of PAF-CPT is concerned our results are not directly comparable to those of another study, in which PAF-CPT activity was not expressed per mg of protein [26].…”

Vasoactive Intestinal Peptide Knockout (VIP KO) mouse model of sulfite-sensitive asthma: up-regulation of novel lung carbonyl reductase

“…Neutrophils from patients with acute asthma have increased levels of acetyltransferase activity which regulate production of platelet activating factor in inflammatory cells. Downregualtion of pyruvate dehydrogenase in VIP KO ice would therefore be a counter-regulatory mechanism [14]. …”