Effect of NADPH oxidase inhibitor apocynin on the expression of hypoxia-induced factor-1α and endothelin-1 in rat carotid body exposed to chronic intermittent hypoxia

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The effects of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitor apocynin on the enhanced hypoxia induced factor-1α (HIF-1α) and endothelin-1 (ET-1) expression, elevated systolic blood pressure under chronic intermittent hypoxia (CIH) condition and its action mechanism were investigated. Thirty healthy 8-week old Sprague-Dawley (SD) male rats were randomly divided into three groups (n=10 each): sham group, CIH group, and apocynin-treated CIH group. Tail artery systolic blood pressure was measured by tail-cuff method. Real-time fluorescence quantitative polymerase chain reaction (PCR) was used to detect the mRNA expression of HIF-1α and ET-1 in the carotid body, and the HIF-1α protein expression was examined by using Western blotting. The levels of malondialdehyde (MDA) and superoxide dismutase (SOD) were determined by using colorimetric method. In addition, the plasma ET-1 and HIF-1α levels were measured by using enzyme-linked immunosorbent assay. It was found that CIH exposure was associated with increased MDA levels, and apocynin-treated CIH animals showed reduction in MDA levels. Apocynin treatment prevented CIH-induced hypertension as well as CIH-induced decrease in SOD. The increases of HIF-1α and ET-1 mRNA along with HIF-1α protein expression in the carotid body, and elevated circulating HIF-1α and ET-1 levels were observed in CIH-exposed animals. Treatment with apocynin significantly decreased the ET-1 mRNA, HIF-1α protein expression and circulating HIF-1α level in CIH-exposed animals, and there was no statistically significant difference in the HIF-1α mRNA expression between CIH group and apocynin-treated group. These results indicated that apocynin alleviated CIH-induced hypertension by inhibiting NADPH oxidase, further leading to the reduced vasoconstrictor ET-1 level and oxidative stress. HIF-1α/ET-1 system signal pathway may interact with CIH-induced NADPH oxidase-dependent oxidative stress. Inhibition of NADPH oxidase activity may hopefully serve as a useful strategy for prevention and treatment of obstructive sleep apnea hypopnea syndrome-induced hypertension.