The anti-inflammatory effects of prostaglandins

Long regarded as proinflammatory molecules, prostaglandins (PGs) also have anti-inflammatory effects. Both prostaglandin D2 (PGD2) and its dehydration end product 15-deoxy-Delta-prostaglandin J2 (15d-PGJ2) seem to play important roles in regulating inflammation, via both receptor-dependent (DP1 and DP2 receptors) and receptor-independent mechanisms. Intracellular effects of PGD2 and 15d-PGJ2 that may suppress inflammation include inhibition of nuclear factor-kappaB (NF-kappaB) by multiple mechanisms (IkappaB kinase inhibition and blockade of NF-kappaB nuclear binding) and activation of peroxisome proliferator-activated receptor-gamma (PPAR-gamma). Prostaglandin F2alpha (PGF2alpha) may also have important anti-inflammatory effects, although current data are limited. In animal models, expression of both PGD and PGF synthases declines during acute inflammation, only to rise again during the resolution phase, suggesting their possible role in resolving inflammation. Prostaglandin E2 (PGE2), the classic model of a proinflammatory lipid mediator, also has anti-inflammatory effects that are both potent and context dependent. Thus, accumulating data suggest that PGs not only participate in initiation, but may also actively contribute to the resolution of inflammation. Indeed, classic inhibitors of PG synthesis such as nonselective and cyclooxygenase-2 (COX-2) selective inhibitors (nonsteroidal anti-inflammatory drugs) may actually prolong inflammation when administered during the resolution phase. These effects may regulate not only tissue inflammation but also vascular disease, possibly shedding light on the controversy surrounding nonsteroidal anti-inflammatory drug use and its relation to myocardial infarction. In this review, we summarize the current understanding of PGs as dichotomous molecules in the inflammatory process.