Effects of Polymyxin B on Superoxide Anion Release and Priming in Human Polymorphonuclear Leukocytes

Abstract

We studied the effect of a potent inhibitor of protein kinase C, polymyxin B (PMXB), on superoxide anion (O2-) release by human polymorphonuclear leukocytes (PMNL). PMXB was compared with another inhibitor of protein kinase C, 1-(5-isoquinoline-sulfonyl)-2-methyl piperazine (H-7). Both PMXB and H-7 inhibited phorbol myristate acetate (PMA)-stimulated O2- release. Formyl-methionyl-leucyl-phenylalanine (FMLP)-stimulated O2- release by cytochalasin B-treated PMNL was not inhibited significantly by either PMXB or H-7. 1-Oleoyl-2-acetyl-glycerol (OAG,25-100 microM) stimulated PMNL to release O2- with a long lag-time (8-10 min). Although H-7 inhibited OAG-stimulated O2- release, PMXB augmented the OAG-stimulated response by increasing rate and reducing lag time. The augmenting effect of PMXB was evident only when added after stimulation by OAG, with maximum effect observed at 3 min after addition of OAG. The augmenting effect was also seen with PMXB immobilized on agarose beads. PMXB did not affect the respiratory burst response to 1,2-dioctanoylglycerol. PMXB-augmented, OAG-stimulated O2- release was inhibited by the addition of H-7 before OAG. In contrast to the effect on O2- release, OAG-stimulated protein phosphorylation was inhibited similarly by either PMXB or H-7, when these agents were added 3 min after stimulation by OAG. These results suggested that initial activation of protein kinase C by OAG is essential for O2- release, but that PMXB acts in a manner independent from protein kinase C to augment OAG-stimulated O2- release. When priming by OAG for enhanced O2- release (as opposed to direct stimulation of O2- release) in FMLP-stimulated PMNL was examined, PMXB inhibited O2- release in OAG-primed PMNL, suggesting that protein kinase C is involved in priming of PMNL by OAG.

Comparison of the effects of Salmonella minnesota Re595 lipopolysaccharide, lipid A and monophosphoryl lipid A on nitric oxide, TNF-α, and IL-6 induction from RAW 264.7 macrophages

“…These ¢ndings suggested that polymyxin B might have a direct inhibitory e¡ect on NO pathway. When it was taken into account that polymyxin B has other actions on cells independently of LPS, such as the inhibition of protein kinase [42] and protein kinase C has a direct role in NO synthesis and nitric oxide production (because it was inhibited by protein kinase C inhibitor, Ro31-8220, in a dose-dependent manner) [43], this might be the case.…”

Interference of Antibacterial Agents with Phagocyte Functions: Immunomodulation or "Immuno-Fairy Tales"?

“…In general, peptide antibiotics do not significantly alter phagocyte functions at therapeutic concentrations. The drug most extensively studied in this respect is polymyxin B, one of the first recognized inhibitors of PKC; this latter property has made it a useful tool for the study of transductional pathways (7). The ability of polymyxin B to bind the lipid A portion of LPS is unfortunately associated with toxicity, which contraindicates its general use in septic shock (this drug is used in vitro to neutralize possible VOL.…”

Interference of Antibacterial Agents with Phagocyte Functions: Immunomodulation or “Immuno-Fairy Tales”?

“…In general, peptide antibiotics do not significantly alter phagocyte functions at therapeutic concentrations. The drug most extensively studied in this respect is polymyxin B, one of the first recognized inhibitors of PKC; this latter property has made it a useful tool for the study of transductional pathways (7). The ability of polymyxin B to bind the lipid A portion of LPS is unfortunately associated with toxicity, which contraindicates its general use in septic shock (this drug is used in vitro to neutralize possible LPS contamination).…”