Stimulation of MAP kinase pathways after maternal IL-1beta exposure induces fetal lung fluid absorption in guinea pigs

IL-1 promotes α-epithelial Sodium Channel (α-ENaC) expression in murine lung epithelial cells: involvement of NF-κB

Intra-amniotic exposure to proinflammatory cytokines such as interleukin-1 (IL-1) correlates with a decreased incidence of respiratory distress syndrome (RDS) in infants following premature birth. At birth, inadequate absorption of fluid from the fetal lung contributes to the onset RDS. Lung fluid clearance is coupled to Na⁺ transport via epithelial sodium channels (ENaC). In this study, we assessed the effects of IL-1 on the expression of ENaC, particularly the α-subunit which is critical for fetal lung fluid clearance at birth. Cultured mouse lung epithelial (MLE-12) cells were treated with either IL-1α or IL-1β to determine their effects on α-ENaC expression. Changes in IL-1-induced α-ENaC levels in the presence of IL-1 receptor antagonist (IL-1ra), cycloheximide, NF-κB inhibitor, and MAP kinase inhibitors were investigated. IL-1α and IL-1β independently induced a significant increase of α-ENaC mRNA and protein after 24 h compared to untreated cells. IL-1-dependent increases in α-ENaC protein were mitigated by IL-1ra and cycloheximide. IL-1 exposure induced NF-κB binding activity. Attenuation of IL-1-induced NF-κB activation by its inhibitor SN50 decreased α-ENaC protein abundance. Inhibition of ERK 1,2 MAPK significantly decreased both IL-1α and β-induced α-ENaC protein expression whereas inhibition of p38 MAPK only blocked IL-1β-induced α-ENaC protein levels. In contrast, IL-1-induced α-ENaC protein levels were unaffected by a c-Jun N-terminal kinase (JNK) inhibitor. Our results suggest that in MLE-12 cells, IL-1-induced elevation of α-ENaC is mediated via NF-κB activation and in part involves stimulation of the ERK 1,2 and p38 MAPK signaling pathways.

Involvement of p38MAPK on the antinociceptive action of myricitrin in mice

Previous studies from our group investigated the analgesic and anti-inflammatory properties of the flavonoid myricitrin. Here, we demonstrated the role of interleukin-1beta (IL-1beta), tumor necrosis factor-alpha (TNF-alpha) and mitogen-activated protein kinases (MAPKs) on the antinociceptive action of myricitrin. The nociceptive response was evaluated by monitoring biting behaviour following intratecal (i.t.) administration of IL-1beta and TNF-alpha in mice. Western blot analyses of total and phosphorylated MAPKs: p38(MAPK), extracellular-signal regulated kinase (ERK1/2) and c-Jun amino-terminal kinases (JNK1/2) from the spinal cord of mice injected with cytokines were measured. Myricitrin (0.03-30mg/kg) or vehicle (control) was administered 30 min beforehand by intraperitoneal (i.p.) injection. Myricitrin pre-treatment prevented cytokine-induced biting behaviour. The calculated ID(50) of myricitrin were 6.8 (4.6-9.0) and 2.6 (0.3-4.9) mg/kg and maximal inhibition of 83+/-9 and 100+/-0% for IL-1beta and TNF-alpha, respectively. Intrathecal injection of IL-1beta and TNF-alpha significantly increased p38(MAPK) phosphorylation and this was inhibited by myricitrin treatment. Cytokines administration did not alter ERK1/2 and JNK1/2 phosphorylation. Myricitrin prevented cytokine-induced biting behaviour and inhibited p38(MAPK) phosphorylation in response to cytokines stimulation. Taken together, it suggests that the mechanism for antinociceptive action of myricitrin in response to cytokines may involve a blockage on p38(MAPK) pathway. This finding could explain, at least in part, the antinociceptive action of this flavonoid in process like neuropathic and inflammatory chronic pain.