S-Aspirin Protects Aspirin-Induced Gastric Injury Figure 1. Effect of Asp at 200 mg/kg and ACS14 (430mg/kg) on the morphology of gastric mucosa in rats. ACS14 or Asp was administered to rats 3 h by intragastric administration. Representative photographs (A) and group data (B) showing that Asp, but not ACS14, induced significant gastric mucosal injury. Data are presented as means 6 SE. n = 6. * P,0.05 compared with control; # P,0.05 compared with Asp. doi:10.1371/journal.pone.0046301.g001 H2S donor) at 0.73 mg/kg (produced H2S approximately equiv- alent to that caused by ACS14 at 5 mg/kg) also decreased the gastric mucosal injury induced by Asp to a similar extent caused by ACS14 at 5 mg/kg. These data imply that ACS14 may protect gastric mucosa against Asp-induced mucosal injury via releasing H2S. ACS14 and NaHS Increased H2S Concentrations in Plasma and Gastric Tissue Rats treated with Asp didn’t affect the H2S concentrations in plasma. Treatment with ACS14 (5 and 10 mg/kg) and NaHS (0.73 mg/kg) significantly increased the H2S concentrations in plasma (Fig. 3A). Interestingly, Asp treatment significantly decreased the local H2S concentration in gastric tissue. This effect was reversed by ACS14 pretreatment at 10 mg/kg. (Fig. 3B). Effect of ACS14 and NaHS on Gastric Blood Flow Since H2S may dilate blood vessel, we therefore examined the effect of ACS14 on gastric blood flow. As shown in Fig. 3C, Asp significantly decreased gastric blood flow. This effect was reversed by ACS14 at 10 mg/kg. ACS14 at 1 mg/kg, 5 mg/kg and NaHS at 0.73 mg/kg failed to significantly change the gastric blood flow. Effects of ACS14 on COX-2 Expression and PGE2 Content in Gastric Tissue Cyclooxygenase 2 (COX-2) is an inducible enzyme that participates in inflammation by producing prostanoids including PGE2. COX-2 expression was significantly increased in the gastric tissue after treatment with Asp (Fig. 4A). Pretreatment with ACS14 at 5–10 mg/kg and NaHS at 0.73 mg/kg reversed the up- regulated expression of COX-2, suggesting that the protective effects may be mediated by suppression of COX-2 expression. However, the PGE2 level was markedly reduced in rats treated PLOS ONE | www.plosone.org 3 September 2012 | Volume 7 | Issue 9 | e46301