Elevated microsomal prostaglandin-E synthase-1 in Alzheimer's disease

Prostaglandin E2 synthases in neurologic homeostasis and disease

Prostaglandin E(2) synthases (PGES) currently comprise a group of three structurally and biologically distinct molecules. These enzymes are part of an important and complex paracrine signaling system involved in a wide range of biological processes. This review focuses on the normal physiological and pathological roles of these enzymes in the nervous system. Specific topics include the role of PGES(s) in fever and sickness behavior, inflammatory pain, and neural disease. Although the field is in its early stages, ongoing development of selective PGES inhibitors for possible use in people creates a significant need for more fully understanding the biological roles of these important enzymes.

Prostaglandin E2 reduces amyloid beta-induced phagocytosis in cultured rat microglia

Treatment with amyloid beta(1-42) (Abeta(1-42)) at 1microM for 60min increased phagocytosis of latex beads by cultured rat microglia. This increase was reduced dose-dependently by prostaglandin E(2) (PGE(2)), but PGD(2), PGF(2alpha), iloprost, or U-46619 had no effects. PGE(2) also reduced the phagocytosis of fluorescent-labeled Abeta(1-42). Abeta(1-42)-induced phagocytosis was reduced by butaprost but not by 17-phenyl trinor PGE(2), sulprostone, or PGE(1) alcohol. The reduction effect of PGE(2) on phagocytosis was reversed by AH6809, an E-prostanoid receptor 2 (EP2) antagonist, which inhibited cyclic adenosine monophosphate (AMP) accumulation induced by PGE(2). Butaprost, but not 17-phenyl trinor PGE(2), sulprostone, or PGE(1) alcohol increased intracellular cyclic AMP accumulation. In western blotting analysis, EP2-like immunoreactivity was detected in the crude membrane fraction of microglia. On the other hand, Abeta(1-42)-induced phagocytosis was not affected by SC-560, a cyclooxygenase-1 (COX-1) inhibitor, NS-398, a COX-2 inhibitor, or ibuprofen, a non-specific COX inhibitor. Abeta(1-42) or PGE(2) had little effect on the expression levels of COX-1 or COX-2. These results indicate that Abeta(1-42)-induced microglial phagocytosis is reduced by PGE(2) through EP2.

Resveratrol inhibits prostaglandin formation in IL-1beta-stimulated SK-N-SH neuronal cells

Resveratrol, a polyphenol present in grapes and red wine, has been studied due to its vast pharmacological activity. It has been demonstrated that resveratrol inhibits production of inflammatory mediators in different in vitro and in vivo models. Our group recently demonstrated that resveratrol reduced the production of prostaglandin (PG) E₂ and 8-isoprostane in rat activated microglia. In a microglial-neuronal coculture, resveratrol reduced neuronal death induced by activated microglia. However, less is known about its direct roles in neurons. In the present study, we investigated the effects of resveratrol on interleukin (IL)-1β stimulated SK-N-SH cells. Resveratrol (0.1-5 μM) did not reduce the expression of cyclooxygenase (COX)-2 and microsomal PGE₂ synthase-1 (mPGES-1), although it drastically reduced PGE₂ and PGD₂ content in IL-1β-stimulated SK-N-SH cells. This effect was due, in part, to a reduction in COX enzymatic activity, mainly COX-2, at lower doses of resveratrol. The production of 8-iso-PGF_2α, a marker of cellular free radical generation, was significantly reduced by resveratrol. The present work provides evidence that resveratrol reduces the formation of prostaglandins in neuroblastoma cells by reducing the enzymatic activity of inducible enzymes, such as COX-2, and not the transcription of the PG synthases, as demonstrated elsewhere.

Prostaglandin E(2) synthase inhibition as a therapeutic target

BACKGROUND

Most NSAIDs function by inhibiting biosynthesis of PGE(2) by inhibition of COX-1 and/or COX-2. Since COX-1 has a protective function in the gastro-intestinal tract (GIT), non-selective inhibition of both cycloxy genases leads to moderate to severe gastro-intestinal intolerance. Attempts to identify selective inhibitors of COX-2, led to the identification of celecoxib and rofecoxib. However, long-term use of these drugs has serious adverse effects of sudden myocardial infarction and thrombosis. Drug-mediated imbalance in the levels of prostaglandin I(2) (PGI(2)) and thromboxane A(2) (TXA(2)) with a bias towards TXA(2) may be the primary reason for these events. This resulted in the drugs being withdrawn from the market, leaving a need for an effective and safe anti-inflammatory drug.

METHODS

Recently, the focus of research has shifted to enzymes downstream of COX in the prosta glandin biosynthetic pathway such as prostaglandin E(2) synthases. Microsomal prostaglandin E(2) synthase-1 (mPGES-1) specifically isomerizes PGH(2) to PGE(2), under inflammatory conditions. In this review, we examine the biology of mPGES-1 and its role in disease. Progress in designing molecules that can selectively inhibit mPGES-1 is reviewed.

CONCLUSION

mPGES-1 has the potential to be a target for anti-inflammatory therapy, devoid of adverse GIT and cardiac effects and warrants further investigation.

Cytosolic prostaglandin E synthase: expression patterns in control and Alzheimer's disease brains

Anti-inflammatory drugs reduce the risk of Alzheimer's disease but fail to slow its progression. Studying the expression of prostaglandin E(2) synthases downstream of cyclooxygenase-2 is important. Here, the expression patterns of cytosolic prostaglandin E( 2) synthases, an immediate prostaglandin E(2) source was investigated. Sections taken from the middle frontal gyrus of brains of 10 patients with Alzheimer's and 5 age-matched controls were examined by immunostaining for the presence of the synthases. Immunofluorescence analysis of control brains showed that cytosolic prostaglandin E(2) synthases co-localize with microglia, neurons, and endothelium markers, but not with astrocytes or smooth muscle cells. Immunohistochemical staining for the synthases was positive in the pyramidal neurons of controls but barely detectable in the brain of Alzheimer's patients. These findings revealed that cytosolic prostaglandin E(2) synthases is found in microglia, neurons, and endothelium of control human middle frontal gyrus and that its levels decrease in pyramidal cells of Alzheimer's disease brains.