Cells were exposed to a fixed concentration of PCN (50 μM) for 24 h. Supernatants were harvested for measuring IL-8 by ELISA. *p < 0.05, **p < 0.01 compared with the PCN group. PMA: phorbol 12-myristate 13-acetate. Effect of antioxidant on PCN-induced IL-8 release To further authenticate whether oxidative stress was involved in PCN-induced IL-8 production and protective Screening Library role of NAC in cells exposed to PCN, different concentrations

of NAC (5, 10, or 20 mmol/L) were added into fresh medium of PMA-differentiated U937 cells 60 min before PCN administration. After 24 hours of further incubation, supernatants were collected and IL-8 concentrations were measured. The results showed that NAC significantly decrease the secretion of IL-8, indicating a pivotal role for oxidative stress in PCN-induced IL-8 expression in PMA-differentiated U937 cells (Figure 5). Figure 5 Antioxidant can inhibit PCN-induced IL-8 release. Different concentrations of N-acetyl cysteine (NAC) (5, 10 or 20 mM) were added into fresh medium of PMA-differentiated U937 cells for 60 min before PCN was added. After 24 h, supernatants were collected and IL-8 concentrations were detected by ELISA. *p <0.05,

**p < 0.01 compared with the PCN groups. PMA: phorbol learn more 12-myristate 13-acetate. Effects of MAPK and NF-κB inhibitors on PCN-induced IL-8 mRNA To determine whether activation of MAPK and NF-κB mediates the PCN-dependent increase in IL-8 mRNA, we

tested the effects of several MAPK and NF-κB inhibitors: SB203580 (a p38 inhibitor, 30 μM or 50 μM) and PD98059 (an ERK1/2 inhibitor, 30 μM or 50 μM) or PDTC (an NF-κB inhibitor, 200 μM). For these experiments, cells were pretreated for 60 min with SB203580, PD98059, or PDTC and then stimulated for 2 h with 50 μM PCN. The respective inhibitor was present throughout the experiments. RNA was then isolated and levels of mRNA were determined as described in materials and methods. The results showed that Adenosine all blockers used can Epigenetics Compound Library reduce the expression of IL-8 mRNA (Figure 6). Figure 6 MAPKs and NF-κB inhibitors can attenuate PCN-induced IL-8 mRNA. PMA-differentiated U937 cells were pretreated for 60 min with SB203580 (30 μM or 50 μM), PD98059 (30 μM or 50 μM) or PDTC (200 μM) and then stimulated for 2 h with 50 μM PCN. Inhibitors were present throughout. RNA was then isolated, and levels of mRNA were determined. Expression of IL-8 mRNA was quantified by densitometry and standardized by β-actin. *p < 0.05, **p < 0.01 compared with PCN. MAPK: mitogen-activated protein kinase; PMA: phorbol 12-myristate 13-acetate. PCN increases phosphorylation of p38 and ERK1/2 MAPKs To gain direct insights into PCN effect on MAPK activation, we then used PCN (50 μM) to stimulate U937 cells with or without pretreatment with MAPK inhibitors (SB 20358 or PD98059, both at 30 μM) for 1 h.