Relaxin Inhibits the Activation of Human Neutrophils: Involvement of the Nitric Oxide Pathway

Abstract

In animal models of inflammation, the pregnancy hormone relaxin was shown to reduce the recruitment of leukocytes, especially neutrophils, in inflamed tissues. The current study was designed to clarify whether relaxin could inhibit activation of isolated human neutrophils and, if so, whether the nitric oxide (NO) biosynthetic pathway was involved, as occurs in other relaxin targets. Human neutrophils were preincubated with 1, 10, and 100 nmol/liter porcine relaxin for 1 h before activation with N-formyl-Met-Leu-Phe (10 micromol/liter) or phorbol-12-myristate-13-acetate (0.1 micromol/liter). In selected experiments, the NO synthase inhibitor N(G)-monomethyl-L-arginine (L-NMMA, 100 micromol/liter) was added to the samples 30 min before relaxin. In other experiments, chemically inactivated relaxin (10 nmol/liter) was substituted for authentic relaxin. Untreated, nonactivated neutrophils were the controls. Relaxin reduced significantly and in a concentration-dependent fashion the expression of the surface activation marker CD11b, as well as the generation of superoxide anion, the rise of intracellular Ca(2+), the release of cytoplasmic granules, and the chemotactic migration. These effects of relaxin were blunted by N(G)-monomethyl-L-arginine and could not be reproduced by inactivated relaxin. Relaxin also increased neutrophil inducible NO synthase expression and NO generation. This study provides evidence that relaxin inhibits the activation of human neutrophils stimulated by different proinflammatory agents. This novel property of relaxin could be of relevance in toning down maternal neutrophil activation during pregnancy, thereby counteracting the occurrence of pregnancy-related disorders such as preeclampsia, which is regarded as an excess maternal inflammatory response to pregnancy.

Relaxin prevents the development of severe acute pancreatitis

“…The inhibition of either the nitric oxide pathway or glucocorticoid receptor stimulation significantly reduced the positive effects described previously for homogenous groups (10)(11)(12). Surprisingly for group 7 when we associated both inhibitors the severity that was developed although greater than for homogenous groups (6-7) was still less than that displayed by homogenous groups (3)(4) suggesting that there is another pathway involved in the treatment with relaxin.…”

“…It has been shown that relaxin up regulates nitric oxide synthase (NOS) II expression thus inducing nitric oxide mediated vasodilatation by a controlled activation of endogenous nitric oxide biosynthesis [11] . By regulating nitric oxide relaxin inhibits neutrophil extravasation, adhesion, recruitment and activation [12] ; decreases the expression of chemokines and adhesion molecules [13] ; inhibits histamine release by mast cells [14] ; depresses platelet aggregation [15] ; alters Ik-B phosphorylation and degradation diminishing NF-kB activation and binding to DNA and enhances the activation of the glucocorticoid receptor (GR) [16] . Therefore, via the nitric oxide pathway relaxin exerts vasorelaxant, anti-thrombotic and anti-infl ammatory properties.…”

“…We then integrated this information to rank the groups in order of "increased degree of severity" (Table 5) showing that the severe acute pancreatitis developed by homogenous groups (3-4) was signifi cantly ameliorated for homogenous groups (10)(11)(12).…”

Periodontitis Associates with a Type 1 IFN Signature in Peripheral Blood Neutrophils

“…Experiments were also performed to determine whether IFN-␣ could prime neutrophil NO production induced by fMLP, a known stimulator of NO (38). These results demonstrated that IFN-␣, at concentrations that primed Fc␥R-stimulated ROS generation, was unable to prime fMLP NO release (data not shown).…”

“…Subsequently, neutrophils were stimulated with 800 l of fMLP (1 mM, equivalent to 4 nM/1 ϫ 10 5 cells) or PBS for 2 h at 37°C. Following stimulation, cells were centrifuged (2 min, 100 ϫ g), the supernatants removed and assayed in triplicate for nitrite, the stable end product of NO metabolism, by the Greiss reaction as described previously (38). …”