Pentoxifylline Prevents Loss of PP2A Phosphatase Activity and Recruitment of Histone Acetyltransferases to Proinflammatory Genes in Acute Pancreatitis

Mitogen-activated protein kinases (MAPKs) are considered major signal transducers early during the development of acute pancreatitis. Pentoxifylline is a phosphodiesterase inhibitor with marked anti-inflammatory properties through blockade of extracellular signal regulated kinase (ERK) phosphorylation and tumor necrosis factor alpha production. Our aim was to elucidate the mechanism of action of pentoxifylline as an anti-inflammatory agent in acute pancreatitis. Necrotizing pancreatitis induced by taurocholate in rats and taurocholate-treated AR42J acinar cells were studied. Phosphorylation of ERK and ERK kinase (MEK1/2), as well as PP2A, PP2B, and PP2C serine/threonine phosphatase activities, up-regulation of proinflammatory genes (by reverse transcription-polymerase chain reaction and chromatin immunoprecipitation), and recruitment of transcription factors and histone acetyltransferases/deacetylases to promoters of proinflammatory genes (egr-1, atf-3, inos, icam, il-6, and tnf-alpha) were determined in the pancreas during pancreatitis. Pentoxifylline did not reduce MEK1/2 phosphorylation but prevented the marked loss of serine/threonine phosphatase PP2A activity induced by taurocholate in vivo without affecting PP2B and PP2C activities. The rapid loss in PP2A activity induced by taurocholate in acinar cells was due to a decrease in cAMP levels that was prevented by pentoxifylline. Pentoxifylline also reduced the induction of early (egr-1, atf-3) responsive genes and abrogated the up-regulation of late (inos, icam, il-6, tnf-alpha) responsive genes and recruitment of transcription factors (nuclear factor kappaB and C/EBPbeta) and histone acetyltransferases to their gene promoters during pancreatitis. In conclusion, the beneficial effects of pentoxifylline--and presumably of other phosphodiesterase inhibitors--in this disease seem to be mediated by abrogating the loss of cAMP levels and PP2A activity as well as chromatin-modifying complexes very early during acute pancreatitis.