Conversion Of Prostaglandin H2 Research Articles

Enzymatic Deglycosylation of Opuntia ficus indica improves its Estrogen Receptor-Subtype Selective Transcriptional and Anti-Inflammatory Activities

Flavonoids are polyphenols widely present as aglycone or sugar-attached glycosides in agricultural products and possess various beneficial activities. Glycosylation affects the physicochemical properties of flavonoid aglycones, leading to changes in their biological activities. Opuntia ficus indica (OFI) fruits are reported to have anti-diabetic, anti-inflammatory, and phytoestrogenic activities. In this study, the role of glycosylation in OFI grown in Jeju, Korea has been investigated, focusing on narcissin, which is the major flavonoid glycoside. Efficient and mild hydrolysis of the glycosides in extracts of Jeju OFI fruits (OFIE) was investigated using hydrolysis enzymes. The enzyme-treated OFIE displayed estrogen receptor β−selective transcriptional activity and inhibition of the nuclear factor-κB signaling pathway in cell line models. Additionally, it inhibited the enzyme that catalyzes the conversion of prostaglandin H2 to inflammatory prostaglandin D2. Our data suggests that enzymatic deglycosylation of OFIE may increase healthpromoting benefits such as the estrogen replacement effect with anti-inflammatory activity.

First Report of Transheterozygosity in a Patient with An Inherited Platelet Bleeding Disorder Due to Mutations in the Thromboxane A2 Receptor (TBXA2R) and cyclooxygenase1 (PTGS1),

Abstract 3260Platelet aggregation by thromboxane (TBXA2) stimulation of its G protein-coupled receptor TXA2R is initiated after conversion of arachidonic acid (AA) into prostaglandin H2 (PGH2) by cyclooxygenase1 (PTGS1) and subsequently by conversion of PGH2 into TXA2 by thromboxane synthase (TBXAS1). Hirata et al (JCI, 1994) reported the first TBXA2R mutation that resulted in reduced platelet responses to U46619 and low AA concentrations in subjects with a heterozygous R60L mutation. This functional defect in combination with mild clinical bleeding problems was only described for the one patient that was homozygous for this mutation. A second TBXA2 patient with an obvious bleeding diathesis carried a heterozygous D304N mutation but it was reported that this variant by itself could not explain the bleeding phenotype as other family members heterozygous for D304N presented with abnormal aggregation responses but no bleeding problems (Mumford, Blood, 2010). Functional SNPs in PTGS1 were described in pharmacogenetic studies including the L237M variant with 50% reduced COX1 metabolic activity but its effect on platelet function was not studied (Lee CR, Pharmacogenet Genomics, 2007).We here describe a 6-year old patient with ecchymosis, easy bruising and important post-traumatic bleeding complications after adenotonsillectomy and circumcision. The boy presents with normal coagulation parameters, normal platelet count and MPV, structurally normal platelets, normal ATP secretion by collagen, and the PFA100 closure time was normal for Col/Epi and mildly prolonged for Col/ADP. Platelet aggregation studies further showed an absent response to 1 mM AA as determined on different occasions, a reduced but not absent response to U46619 and a normal activation with ADP, ristocetin and Horm collagen. His parents and sister presented with increased sensitivity for ecchymoses but none had severe clinical bleeding problems and their platelets showed normal aggregation responses except for the father and sister with a reduced though not absent response to AA. Thromboxane B2 formation was determined and found to be normal in basal (plasma) and maximal stimulated (serum) conditions. In contrast, TXB2 levels were decreased after activation with U46619 for the patient but also for the father and sister compared to the control or mother. Activation with AA also resulted in reduced TXB2 levels for the patient and mildly reduced levels for all other family member compared to controls. This strongly suggests the presence of an autosomal recessive disorder. The TBXAS1, PTGS1 and TBXA2R genes were sequenced for the patient and we identified two heterozygous mutations in separate genes being R60H in TXBA2R and the functional L237M variant in PTGS1. Interestingly, his mother carried the L237M variant while R60H was present in father and sister with similar functional platelet defects as earlier described for the other heterogenous TBXA2R mutations but no clinical bleeding symptoms. To our knowledge, this is the first case of transheterozygosity for mutations explaining an autosomal recessive bleeding disorder. We hypothesize that this pattern of inheritance might be more common than expected and therefore this possibility should be taken into account when analyzing patients in the future using exome or genome wide sequencing platforms. Disclosures:No relevant conflicts of interest to declare.

Mutation of a Critical Arginine in Microsomal Prostaglandin E Synthase-1 Shifts the Isomerase Activity to a Reductase Activity That Converts Prostaglandin H2 into Prostaglandin F2α*

Microsomal prostaglandin E synthase type 1 (mPGES-1) converts prostaglandin endoperoxides, generated from arachidonic acid by cyclooxygenases, into prostaglandin E2. This enzyme belongs to the membrane-associated proteins in eicosanoid and glutathione metabolism (MAPEG) family of integral membrane proteins, and because of its link to inflammatory conditions and preferential coupling to cyclooxygenase 2, it has received considerable attention as a drug target. Based on the high resolution crystal structure of human leukotriene C4 synthase, a model of mPGES-1 has been constructed in which the tripeptide co-substrate glutathione is bound in a horseshoe-shaped conformation with its thiol group positioned in close proximity to Arg-126. Mutation of Arg-126 into an Ala or Gln strongly reduces the enzyme's prostaglandin E synthase activity (85–95%), whereas mutation of a neighboring Arg-122 does not have any significant effect. Interestingly, R126A and R126Q mPGES-1 exhibit a novel, glutathione-dependent, reductase activity, which allows conversion of prostaglandin H2 into prostaglandin F2α. Our data show that Arg-126 is a catalytic residue in mPGES-1 and suggest that MAPEG enzymes share significant structural components of their active sites.