Further, this inhibitory effect was dose dependent (Fig 7B) (P = .16 for dapsone 0.3 mg/mL and P < .01 for dapsone 1 and 10 mg/mL), but 0.1 mg/mL DEX decreased this by ^40% (P < .05). LPS 10 mg/mL increased IL-8 mRNA level more than fivefold of control (P< .001). Dapsone at 1 mg/mL and 10 mg/mL significantly inhibited LPS-induced IL-8 mRNA overexpression (P < .05 for each). DEX at 0.1 mg/mL also inhibited this (P < .01).
Effect of Dapsone on LPS-Induced Phosphorylation of MAPKs
MAPK signaling are important pathways in the synthesis of IL-8. We evaluated the effect of dapsone on LPS-induced phosphorylation of ERK1/2, p38, and JNK in NHBE cells. LPS at 10 mg/mL significantly phosphorylated ERK1/2 at 1, 4, and 24 h (P < .05 for each) but not p38 and JNK (Fig 5). Dapsone 1 mg/mL inhibited LPS-induced ERK1/2 phosphorylation at 1 h (P < . 05), although this effect disappeared after 4 h. We then assessed the effect of PD98059, a selective cell-permeable MEK inhibitor Viagra Australia. As shown in Figure 6, LPS dose dependently increased ERK1/2 phosphorylation and IL-8 secretion, and 20 mM 2′-amino-3′-methoxyflavone (PD98059) abolished 10 mg/mL LPS-induced ERK1/2 phosphorylation. However, this concentration of PD98059 did not inhibit IL-8 secretion.
Temporal effect of dapsone on LPS-induced mitogen-activated protein kinase activation over 24 h. Growth factors were withdrawn from the culture medium 24 h before LPS or dapsone exposure. Threonine and tyrosine phosphorylation of ERK1/2, p38, and JNK was measured by Western blotting. The band intensity was calculated with National Institutes of Health Image J software. LPS 10 mg/mL increased the ratio of p-ERK1/2/ERK1/2, but not p-p38/p38. P-JNK was not detected. Dapsone 1 mg/mL inhibited LPS-induced ERK1/2 phosphorylation at 1 h, but not at 4 and 24 h. Data are presented as mean ± SE from more than three independent experiments. *P < .05 compared with control subjects (LPS — and dapsone — at each time). #P < .05 compared with LPS alone. ERK = extracellular-regulated protein kinase; JNK = c-Jun NH2-terminal protein kinase; p = phospho; SAPK = stress-activated protein kinase. See Figure 2 legend for expansion of other abbreviation.