Vascular endothelial growth factor synthesis in the acute phase of experimental and clinical lung injury

Vascular endothelial growth factor (VEGF) is a potent angiogenic and endothelial survival factor, which is abundantly expressed in the normal lung. Conceivably, VEGF may be released by numerous cell types found around the airspaces, including alveolar type 2 cells, alveolar macrophages, and polymorphonuclear neutrophils. Using a bacteria-induced lung injury model in rats, VEGF expression in lung was investigated. Both VEGF protein and VEGF messenger ribonucleic acid (mRNA), 4 and 24 h after bacterial challenge (Pseudomonas aeruginosa), were decreased compared with sham rats. VEGF protein was also investigated in bronchoalveolar lavage (BAL) from patients studied within 7 days of acute respiratory distress syndrome (ARDS) onset and in patients without ARDS. VEGF protein levels in BAL were decreased in patients with ARDS versus those without (14.3 +/- 11.1 pg x mL(-1) versus 76.8 +/- 51.1 pg x mL(-1), p = 0.03). In aggregate, these findings show that the initial phase of acute lung injury is associated with a decrease in vascular endothelial growth factor in the lung. This downregulation may represent a protective mechanism aimed at limiting endothelial permeability, and may participate in the decrease in capillary number that is observed during early acute respiratory distress syndrome.

Expression and regulation of vascular endothelial growth factor in human pulmonary epithelial cells

Vascular endothelial growth factor (VEGF) is a potent endothelial cell growth and permeability factor highly expressed in rodent alveolar epithelium after injury and repair. To investigate VEGF synthesis in human lung epithelial cells, we examined VEGF expression by cultured cells under basal conditions and after cytokine treatment or oxidative stress. Basal VEGF expression was detected in transformed human epithelial cell lines (A549 and 1HAEo-) and in primary human bronchial epithelial cells with RT-PCR, Western blot, and immunocytochemistry. Among the cytokines tested, only transforming growth factor-beta1 increased the levels of excreted VEGF(165) as measured by ELISA. Under hypoxia (0% O(2) for 24 h), the VEGF(165) level increased fivefold, and this effect was O(2) concentration dependent. VEGF concentrations in the medium of all the cell types studied reached values similar to those found in bronchoalveolar lavage fluids from normal patients. Endothelial cells (human umbilical vein endothelial cells) exposed to conditioned medium from primary bronchial epithelial cell cultures showed an increased growth rate, which was inhibited in the presence of a specific neutralizing antibody to VEGF. These results suggest that lung epithelial cells participate in the endothelial repair and angiogenesis that follow lung injury through the synthesis of VEGF.