Effects of human cathelicidin antimicrobial peptide LL‐37 on lipopolysaccharide‐induced nitric oxide release from rat aorta in vitro

Abstract

Background: Lipopolysaccharides (LPS), released by Gram‐negative bacteria, cause vascular expression of inducible nitric oxide synthase (iNOS) leading to nitric oxide (NO) production and septic shock. Human cathelicidin antimicrobial peptide (LL‐37) can bind and neutralize LPS. We wanted to study whether LL‐37 affects LPS or interleukin‐1β (IL‐1β)‐induced production, release and function of NO in intact rat aorta rings and cultured rat aorta smooth muscle cells.Methods: Isolated segments of thoracic aorta and cultured cells were incubated in the presence of LPS, LL‐37, LPS + IL‐37, IL‐1β, IL‐1β + IL‐37 or in medium alone. Smooth muscle contraction in response to phenylephrine and accumulation of the sdegradation products of NO, nitrate and nitrite, were measured on aorta segments. Levels of iNOS were assessed by Western blot and cytotoxic effects were detected by measurement of DNA fragmentation in cultured cells. Number of viable cells were determined after Trypan blue treatment.Results: Both LPS and IL‐1β reduced contractility in response to phenylephrine and increased NO production as well as iNOS expression. LL‐37 inhibited the LPS depression of vascular contractility induced only by LPS. LL‐37 reduced both the LPS‐ and IL‐1β‐induced NO production and iNOS expression. LL‐37 at high concentrations induced DNA fragmentation and decreased the number of living cells.Conclusion: IL‐37 reduces NO production induced by LPS and IL‐1β. The reduction does not seem to result only from neutralization of LPS but also from a cytotoxic effect, possibly via induction of apoptosis.

The Human Cationic Peptide LL-37 Induces Activation of the Extracellular Signal-Regulated Kinase and p38 Kinase Pathways in Primary Human Monocytes

“…The properties of LL-37 have been demonstrated to be altered in the presence of serum (32). In fact, in the absence of serum, moderate concentrations (30 -100 g/ml) of LL-37 and related peptides were cytotoxic toward both prokaryotic and eukaryotic cells (24,33,34). However, in the presence of serum, cytotoxicity toward both cell types was substantially reduced (33,35).…”

Cathelicidin-Deficient (Cnlp−/−) Mice Show Increased Susceptibility toPseudomonas aeruginosaKeratitis

“…Rather, the data suggest that the major contributory role of cathelicidin in this model is as an antimicrobial peptide. It should be noted that in addition to a direct ability to kill bacteria, cathelicidin (LL-37) has also been shown to neutralize endotoxin and block activation of toll-like receptors, [71][72][73][74][75] ; thus, all these factors probably contribute to the overall antimicrobial effect of the peptide. It remains to be determined whether the in vitro effects of LL-37 we have seen 19 are meaningful in terms of corneal epithelial wound healing in vivo.…”

Antimicrobial and Chemoattractant Activity, Lipopolysaccharide Neutralization, Cytotoxicity, and Inhibition by Serum of Analogs of Human Cathelicidin LL-37

“…LL-37 has also been shown to induce apoptosis in vascular smooth muscle cells (2). The cytotoxic effects of LL-37 liberated into the circulation are inhibited by its binding to plasma proteins, e.g., apolipoprotein A-I, but unfortunately, the antimicrobial effects are also inhibited by this binding (8,24,28).…”