Sulfur mustard-induced arachidonic acid release is mediated by phospholipase D in human keratinocytes

Sulfur mustard (2,2(')-dichloroethyl sulfide) is a chemical warfare agent that causes incapacitating skin blisters in humans 12-24h post-exposure following a variable asymptomatic phase. Recent reports demonstrate that inflammation plays a vital role in sulfur mustard toxicity. One of the key biochemical pathways involved in inflammation is the arachidonic acid cascade. In this report, we demonstrate that arachidonic acid is released in response to sulfur mustard and investigate the mechanisms of arachidonic acid release. Exposure to sulfur mustard caused a 5- to 8-fold increase in arachidonic acid release from human keratinocytes that had been radiolabeled with arachidonic acid. Maximal arachidonic acid release occurred between 12 and 24h. Several enzymatic pathways can lead to arachidonic acid release. Treatment with 2.0% (v/v) ethanol, an inhibitor of phospholipase D, decreased sulfur mustard-induced arachidonic acid release 40+/-7%. Additionally, 100 microM (+/-)-propranolol, an inhibitor of phosphatidic acid phosphohydrolase, blocked sulfur mustard-induced arachidonic acid release by 62+/-3%. These findings suggest that arachidonic acid release is mediated by phospholipase D and phosphatidic acid phosphohydrolase in human keratinocytes following sulfur mustard exposure. Due to the 12-24h delay in arachidonic acid release following sulfur mustard exposure, delayed therapeutic intervention may be possible. Indeed, we found that the addition of 100 microM (+/-)-propranolol up to 18 h after sulfur mustard exposure was still able to block arachidonic acid release by 30+/-3%.