Background: Occupational asthma is characterized by airway inflammation and hyperresponsiveness associated with increased vascular permeability. AMP-activated protein kinase (AMPK) has been suggested to be a novel signaling molecule modulating inflammatory responses.
Objective: We sought to evaluate the involvement of AMPK in pathogenesis of occupational asthma and more specifically investigate the effect and molecular mechanisms of AMPK activation in regulating vascular permeability.
Methods: The mechanisms of action and therapeutic potential of an AMPK activator, 5-aminoimidazole-4-carboxamide-1-β-D-ribofuranoside (AICAR) were tested in a murine model of toluene diisocyanate (TDI)-induced asthma.
Results: AICAR attenuated airway inflammation and hyperresponsiveness increased by TDI inhalation. Moreover, TDI-induced increases in levels of hypoxia-inducible factor (HIF)-1α, HIF-2α, vascular endothelial growth factor A (VEGFA), and plasma exudation were substantially decreased by treatment with AICAR. Our results also showed that VEGFA expression was remarkably reduced by inhibition of HIF-1α and HIF-2α with 2-methoxyestradiol (2ME2) and that an inhibitor of VEGFA activity, CBO-P11 as well as 2ME2 significantly suppressed vascular permeability, airway infiltration of inflammatory cells, and airway hyperresponsiveness induced by TDI. In addition, AICAR reduced reactive oxygen species (ROS) generation and levels of malondialdehyde and T-helper type 2 cytokines (IL-4, IL-5, and IL-13), while this agent enhanced expression of an anti-inflammatory cytokine, IL-10.
Conclusions: These results suggest that AMPK activation ameliorates airway inflammatory responses by reducing vascular permeability via HIF/VEGFA pathway as well as by inhibiting ROS production and thus may be a possible therapeutic strategy for TDI-induced asthma and other airway inflammatory diseases.