Hypertonicity Contributes To Seawater Aspiration-induced Lung Injury: Role Of Hypoxia-Inducible Factor1α

Drowning is a major but often neglected public health problem.Acute lunginjury is the most serious hurt to the human body when people aspirate waterduring near-drowning.Compared to freshwater aspiration,the acute lung injuryinduced by seawater aspiration is more severe and more easy to become actuerespiratory distress syndrome.Currently,there is not a particular theory about themechanism of seawater aspiration-induced lung injury.Hypoxia is a commoneffect factor during all kinds of acute lung injury,whereas hypertonicty is anexclusive effect factor which exists in seawater aspiration-induced lung injury.To investigate the role of hypoxia-inducible factor1α (HIF-1α) in seawateraspiration-induced lung injury, rats were divided into six groups and instilledinto the lungs with seawater, hypertonic sorbitol solution, isotonic seawater,isotonic sorbitol solution, distilled water, and nothing, respectively. At indicatedtime, the PaO2, PaCO2inflammatory cytokines (TNF-α, IL-1β, and IL-6)contents, bronchoalveolar lavage fluid white cell amount, pulmonary vascular leakage, Wet-to-dry weight ratio, HIF-1α protein and mRNA levels in eachgroup were detected. The results showed that degree of hypoxia, inflammation,pulmonary vascular leakage, and lung edema in lung tissues of rats which wereinstilled with hypertonic fluids were more severe, and also with the increase ofHIF-1α protein and mRNA expression, compared with those of the rats instilledwith isotonic and hypotonic fluids. Additionally, NR8383macrophages weretreated with seawater, hypertonic sorbitol solution, hypertonic albumin solutionand distilled water, respectively. We found that hypertonicity, but not isotonicityor hypotonicity, increased both HIF-1α protein and mRNA in a time-anddose-dependent manner. After the cells were treated with both seawater (25%)and hypoxia (3%O2), the results suggested that hypertonicity and hypoxiasynergistically increased HIF-1α protein in NR8383macrophages. Furthermore,we used inhibitors of ATM (KU55933), PI3K (LY294002), and p38(SB203580)to demonstrate the signal pathways involved in the hypertonic induction ofHIF-1α. We found that hypertonicity increased HIF-1α by promoting its mRNAexpression through both ATM and PI3K activation and suppressing HIF-1αprotein degradation via p38activation in NR8383macrophages. We also usedHIF-1α siRNA and permeability assay to find that during hyperosmotic stress,HIF-1α promoted the production of the inflammatory cytokines in NR8383macrophages and HIF-1α promoted monolayer permeability through increasingVEGF protein level in RLMVEC.In conclusions, hypertonicity induced by seawater aspiration aggravated lunginjury through increasing HIF-1α which promoted inflammation and edema inlung tissues of rats.