Recombinant human brain natriuretic peptide attenuates trauma-/haemorrhagic shock-induced acute lung injury through inhibiting oxidative stress and the NF-κB-dependent inflammatory/MMP-9 pathway

Abstract

Acute lung injury (ALI) is one of the most serious complications in traumatic patients and is an important part of multiple organ dysfunction syndrome (MODS). Recombinant human brain natriuretic peptide (rhBNP) is a peptide with a wide range of biological activity. In this study, we investigated local changes in oxidative stress and the NF-κB-dependent matrix metalloproteinase-9 (MMP-9) pathway in rats with trauma/haemorrhagic shock (TH/S)-induced ALI and evaluated the effects of pretreatment with rhBNP. Forty-eight rats were randomly divided into four groups: sham operation group, model group, low-dosage rhBNP group and high-dosage rhBNP group (n = 12 for each group). Oxidative stress and MPO activity were measured by ELISA kits. MMP-9 activity was detected by zymography analysis. NF-κB activity was determined using Western blot assay. With rhBNP pretreatment, TH/S-induced protein leakage, increased MPO activity, lipid peroxidation and metalloproteinase (MMP)-9 activity were inhibited. Activation of antioxidative enzymes was reversed. The phosphorylation of NF-κB and the degradation of its inhibitor IκB were suppressed. The results suggested that the protection mechanism of rhBNP is possibly mediated through upregulation of anti-oxidative enzymes and inhibition of NF-κB activation. More studies are needed to further evaluate whether rhBNP is a suitable candidate as an effective inhaling drug to reduce the incidence of TH/S-induced ALI.

Keywords: NF-κB; acute lung injury; antioxidative enzymes; brain natriuretic peptide; trauma/haemorrhagic shock.

Figure 1

Effects of rhBNP on TH/S‐induced histological changes in lung. The lungs from the sham operation group (a), the model group (b), the L‐rhBNP group (c) and the H‐rhBNP group (d) with rhBNP pretreatment 30 min before surgery were subjected to HE staining. Representative images of HE‐stained lung sections from each group are shown (magnification: 100 × ). b‐ Marked interstitial oedema and inflammatory cell infiltration were found. c, d‐ Such pathological changes were attenuated by rhBNP pretreatment.

Figure 2

Effects of rhBNP on pulmonary histological scores, TH/S‐induced protein accumulation and leucocytes infiltration in BALF. (a) Pulmonary histological scores. (b) leucocytes count in BALF. (c) Pulmonary permeabilities determined by protein contents quantification in cell‐free BALF. Values are expressed as mean ± SD (n = 12 in each group). *Represents a significant difference between the indicated and the operation group; ^#between the indicated and model groups, P < 0.05.

Figure 3

Effects of rhBNP on TH/S‐induced MMP‐9 activation in lung tissue. The activity of MMP‐9 in BALF was analysed by zymography assay. The fold of MMP‐9 activation between the treated and sham operation groups was calculated. Values are expressed as mean ± SD (n = 12 in each group). *Represents a significant difference between the indicated and the operation group; ^#between the indicated and model groups, P < 0.05.

Figure 4

Effects of rhBNP on TH/S‐induced NF‐κB p65 phosphorylation and IκB degradation in lung tissue. Lung tissues harvested from post‐treated rats were analysed by Western blotting. The fold of NF‐κB p65 phosphorylation and IκB degradation between the treated and sham operation groups was calculated. Values are expressed as mean ± SD (n = 12 in each group). *Represents a significant difference between the indicated and the operation group; ^#between the indicated and model groups, P < 0.05.