ABSTRACT
Evidence suggests that activated protein C (APC) attenuates acute lung injury (ALI) through antithrombotic and anti-inflammatory mechanisms. The aim of this study was to determine the effects of APC on ALI in adult rats exposed to hyperoxic environment. Rats were divided into control, hyperoxia, hyperoxia + APC, and APC. Hyperoxia and hyperoxia + APC were exposed to 1, 3, and 5 days of hyperoxia. Hyperoxia + APC and APC were injected with APC (5 mg/kg, i.p.) every 12 h. Control and hyperoxia received isotonic sodium chloride solution injection. Measurement of wet to dry ratio and albumin leak demonstrated significant improvement in hyperoxia + APC when compared with hyperoxia. Apoptosis, as measured by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling assay, was significantly reduced in hyperoxia + APC when compared with hyperoxia. Histological evaluation of lung sections showed significant reduction in inflammation, edema, and in the number of marginating neutrophils in hyperoxia + APC as compared with hyperoxia. Transcriptional expression of lung inflammatory mediators demonstrated a time-dependent surge in the levels TNF-alpha, IL-1beta, and IL-6 in response to hyperoxia that was attenuated with APC administration in the presence of hyperoxia. In this rat model, APC attenuates lung injury and the expression of inflammatory mediators in ALI secondary to hyperoxia.
Subject(s)
Acute Lung Injury/drug therapy , Apoptosis/drug effects , Hyperoxia/pathology , Protein C/therapeutic use , Acute Lung Injury/mortality , Acute Lung Injury/pathology , Animals , Enzyme Activation , Hyperoxia/metabolism , Hyperoxia/mortality , In Situ Nick-End Labeling , Inflammation/drug therapy , Inflammation Mediators/metabolism , Male , Protein C/metabolism , RatsABSTRACT
BACKGROUND: The aim of the study is to examine the effect of limited and prolonged hyperoxia on neonatal rat lung. This is done by examining the morphologic changes of apoptosis, the expression of ceramide, an important mediator of apoptosis, the expression of inflammatory mediators represented by IL-1beta and the expression of 2 proto-oncogenes that appear to modulate apoptosis (Bax and Bcl-2). METHODS: Newborn rats were placed in chambers containing room air or oxygen above 90% for 7 days. The rats were sacrificed at 3, 7 or 14 days and their lungs removed. Sections were fixed, subjected to TUNEL, Hoechst, and E-Cadherin Staining. Sections were also incubated with anti-Bcl-2 and anti-Bax antisera. Bcl-2 and Bax were quantitated by immunohistochemistry. Lipids were extracted, and ceramide measured through a modified diacylglycerol kinase assay. RT-PCR was utilized to assess IL-1beta expression. RESULTS: TUNEL staining showed significant apoptosis in the hyperoxia-exposed lungs at 3 days only. Co-staining of the apoptotic cells with Hoechst, and E-Cadherin indicated that apoptotic cells were mainly epithelial cells. The expression of Bax and ceramide was significantly higher in the hyperoxia-exposed lungs at 3 and 14 days of age, but not at 7 days. Bcl-2 was significantly elevated in the hyperoxia-exposed lungs at 3 and 14 days. IL-1beta expression was significantly increased at 14 days. CONCLUSION: Exposure of neonatal rat lung to hyperoxia results in early apoptosis documented by TUNEL assay. The early rise in Bax and ceramide appears to overcome the anti-apoptotic activity of Bcl-2. Further exposure did not result in late apoptotic changes. This suggests that apoptotic response to hyperoxia is time sensitive. Prolonged hyperoxia results in acute lung injury and the shifting balance of ceramide, Bax and Bcl-2 may be related to the evolution of the inflammatory process.
