Advanced glycation end products stimulate an enhanced neutrophil respiratory burst mediated through the activation of cytosolic phospholipase A2 and generation of arachidonic Acid.
BACKGROUND
Advanced glycation end products (AGEs) enhance NADPH oxidase, and hence respiratory burst activity, of stimulated neutrophils. They are thus potentially vasculopathic, especially in diabetes, uremia, and aging, in which AGEs classically accumulate. We investigated the underlying mechanisms.


RESULTS
Neutrophils prelabeled with [3H]arachidonic acid display increased [3H]arachidonate release on exposure to AGE-albumin over exposure to albumin alone (by 151+/-16%, P<0.01). Arachidonic acid (AA) itself seems to mediate the AGE-augmented neutrophil respiratory burst (ascertained by chemiluminescence). Inhibitors of the cyclooxygenase pathway (indomethacin) and lipoxygenase pathway (MK-886) do not impair this AGE effect, excluding a contribution from AA metabolites. Cytosolic phospholipase A2 (cPLA2) controls AA generation. Its inhibition by methyl arachidonyl fluorophosphonate abrogates the AGE-enhanced activated neutrophil respiratory burst, and it is demonstrably stimulated in AGE-exposed neutrophils, as evidenced by isoform gel-shift and an increasingly membrane-translocated state in Western blots of neutrophil subfractions. Inhibition of other PLA2 isoforms, secretory PLA2 and calcium-independent PLA2, by manoalide and haloenol-lactone suicide substrate, respectively, does not affect this effect of AGEs relative to inhibitor-treated controls. The thiol antioxidant NAC reduces activation of cPLA2 (assessed by isoform gel-shift and membrane translocation), production of AA in AGE-albumin-exposed neutrophils (H3 release reduced to 104+/-17%, P=0.94 compared with albumin-exposed neutrophils), and the AGE-augmented neutrophil respiratory burst.


CONCLUSIONS
AGE augmentation of the activated neutrophil respiratory burst requires AA generation, through which neutrophil NADPH oxidase may be upregulated, enhancing reactive oxygen species output. AA is generated by cPLA2, which may be stimulated through an AGE-activated redox-sensitive pathway.
Wong
Richard K M
RK
Division of Medicine and Therapeutics, University of Leicester, Leicester Royal Infirmary, Leicester, UK.
Pettit
Andrew I
AI
Quinn
Paulene A
PA
Jennings
Sonja C
SC
Davies
Joan E
JE
Ng
Leong L
LL
D000111:Acetylcysteine / Q000494:pharmacology; D000328:Adult; D016718:Arachidonic Acid / Q000096:biosynthesis* / Q000502:physiology; D001095:Arachidonic Acids / Q000494:pharmacology; D002478:Cells, Cultured / Q000187:drug effects / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D017127:Glycation End Products, Advanced / Q000494:pharmacology*; D054513:Group IV Phospholipases A2; D006801:Humans; D007213:Indomethacin / Q000494:pharmacology; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology; D009504:Neutrophils / Q000187:drug effects / Q000502:physiology*; D063065:Organophosphonates / Q000494:pharmacology; D010084:Oxidation-Reduction; D010741:Phospholipases A / Q000037:antagonists & inhibitors / Q000502:physiology*; D054467:Phospholipases A2; D011796:Quinacrine / Q000494:pharmacology; D017382:Reactive Oxygen Species / Q000378:metabolism; D016897:Respiratory Burst / Q000187:drug effects / Q000502:physiology*; D014652:Vascular Diseases / Q000209:etiology / Q000503:physiopathology
D001095:Arachidonic Acids; D004791:Enzyme Inhibitors; D017127:Glycation End Products, Advanced; D063065:Organophosphonates; D017382:Reactive Oxygen Species; C104810:methyl arachidonylfluorophosphonate; D016718:Arachidonic Acid; D009240:N-Formylmethionine Leucyl-Phenylalanine; D010741:Phospholipases A; D054513:Group IV Phospholipases A2; D054467:Phospholipases A2; D011796:Quinacrine; D000111:Acetylcysteine; D007213:Indomethacin