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

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.