Effect of interleukin-8 (IL-8) knockdown on NADPH oxidase (Nox) 1 (a, b) or Nox4 (c, d) expression in lipopolysaccharide (LPS) -stimulated human umbilical vein endothelial cells (HUVECs). (a, b) Effect of IL-8 knockdown on Nox1 messenger (m) RNA expression in HUVECs 8 hr (a) or 12 hr (b) after LPS stimulation. The relative mRNA expression of Nox1 was determined by real-time polymerase chain reaction (PCR). The expression level is shown relative to that in LPS-stimulated HUVECs treated with control small interfering (si) RNA. The data represent mean values ± SD (n = 4, **P < 0·01, Student's t-test). (c, d) Effect of IL-8 knockdown on Nox4 mRNA expression in HUVECs 8 hr (c) or 12 hr (d) after LPS stimulation. The relative mRNA expression of Nox4 was determined by real-time PCR. The expression level is shown relative to that in LPS-stimulated HUVECs treated with control siRNA. The data represent mean values ± SD (n = 4).