pH-dependent regulation of leukocyte 5-lipoxygenase activity in inflammatory exudates by albumin.
OBJECTIVE
In order to study the regulation of cellular 5-lipoxygenase activity under inflammatory conditions, the effects of inflammatory exudates on rat leukocyte 5 lipoxygenase activity were investigated.


METHODS
Peritoneal leukocytes and inflammatory exudates were collected from glycogen treated rats.


METHODS
Glycogen (1 g/kg body weight, in a final volume of 3 ml PBS) was injected intraperitoneally into male Wistar rats. After 4 h, the inflammatory exudate was collected.


METHODS
Rat peritoneal leukocytes were isolated and the cellular 5-lipoxygenase activity was determined by HPLC after cell stimulation with calcium ionophore A23187.


RESULTS
Inflammatory exudates from glycogen treated animals strongly inhibited cellular 5-lipoxygenase activity of ionophore challenged leukocytes. Albumin was identified as the inhibitor in exudates. Inhibition of cellular 5-lipoxygenase activity by albumin was pH-dependent and was strongly increased by the alkaline pH (7.9-8.0) of the exudate. The albumin effect increased in the range of pH 7.4-8.2 where albumin undergoes a conformational change called neutral to base (N-B) transition. S-Carboxymethyl-albumin had a similar activity to that of albumin, which indicated that the free SH-group at Cys-34 of albumin is not necessary for the effect. The albumin dimer showed a significantly higher inhibition than albumin and it suppressed cellular 5-lipoxygenase activity by 98%. Peptic and tryptic fragments of albumin which comprise domains I, II and II, III, respectively, were less active or inactive. Thus, an intact albumin molecule or the dimer are required for efficient inhibition of cellular 5-lipoxygenase activity.


CONCLUSIONS
Our data suggest that during inflammation, albumin extravasation and changes in pH-value are involved in the regulation of the inflammatory reaction by suppression of leukotriene release.
Benz
M
M
Institute of Pharmaceutical Chemistry, University of Frankfurt, Germany.
Werz
O
O
Jacob
R
R
Steinhilber
D
D
D000818:Animals; D001094:Arachidonate 5-Lipoxygenase / Q000378:metabolism*; D001202:Ascitic Fluid / Q000201:enzymology*; D002417:Cattle; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006003:Glycogen; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007962:Leukocytes / Q000201:enzymology*; D016859:Lipoxygenase Inhibitors; D008297:Male; D010446:Peptide Fragments / Q000494:pharmacology; D010533:Peritoneal Lavage; D010538:Peritonitis / Q000139:chemically induced / Q000201:enzymology*; D051381:Rats; D017208:Rats, Wistar; D012709:Serum Albumin / Q000494:pharmacology*; D012710:Serum Albumin, Bovine / Q000494:pharmacology
D004791:Enzyme Inhibitors; D016859:Lipoxygenase Inhibitors; D010446:Peptide Fragments; D012709:Serum Albumin; D012710:Serum Albumin, Bovine; D006003:Glycogen; D001094:Arachidonate 5-Lipoxygenase