Enzymatic formation of prostaglandin F2 alpha from prostaglandin H2 and D2. Purification and properties of prostaglandin F synthetase from bovine lung

Arachidonic acid-derived lipid mediators in multiple sclerosis pathogenesis: fueling or dampening disease progression?

BACKGROUND

Multiple sclerosis (MS) is a chronic autoimmune disease of the central nervous system (CNS), characterized by neuroinflammation, demyelination, and neurodegeneration. Considering the increasing prevalence among young adults worldwide and the disabling phenotype of the disease, a deeper understanding of the complexity of the disease pathogenesis is needed to ultimately improve diagnosis and personalize treatment opportunities. Recent findings suggest that bioactive lipid mediators (LM) derived from ω-3/-6 polyunsaturated fatty acids (PUFA), also termed eicosanoids, may contribute to MS pathogenesis. For example, disturbances in LM profiles and especially those derived from the ω-6 PUFA arachidonic acid (AA) have been reported in people with MS (PwMS), where they may contribute to the chronicity of neuroinflammatory processes. Moreover, we have previously shown that certain AA-derived LMs also associated with neurodegenerative processes in PwMS, suggesting that AA-derived LMs are involved in more pathological events than solely neuroinflammation. Yet, to date, a comprehensive overview of the contribution of these LMs to MS-associated pathological processes remains elusive.

MAIN BODY

This review summarizes and critically evaluates the current body of literature on the eicosanoid biosynthetic pathway and its contribution to key pathological hallmarks of MS during different disease stages. Various parts of the eicosanoid pathway are highlighted, namely, the prostanoid, leukotriene, and hydroxyeicosatetraenoic acids (HETEs) biochemical routes that include specific enzymes of the cyclooxygenases (COXs) and lipoxygenases (LOX) families. In addition, cellular sources of LMs and their potential target cells based on receptor expression profiles will be discussed in the context of MS. Finally, we propose novel therapeutic approaches based on eicosanoid pathway and/or receptor modulation to ultimately target chronic neuroinflammation, demyelination and neurodegeneration in MS.

SHORT CONCLUSION

The eicosanoid pathway is intrinsically linked to specific aspects of MS pathogenesis. Therefore, we propose that novel intervention strategies, with the aim of accurately modulating the eicosanoid pathway towards the biosynthesis of beneficial LMs, can potentially contribute to more patient- and MS subtype-specific treatment opportunities to combat MS.

Arachidonic Acid Derivatives and Neuroinflammation

Neuroinflammation is characterized by dysregulated inflammatory responses localized within the brain and spinal cord. Neuroinflammation plays a pivotal role in the onset of several neurodegenerative disorders and is considered a typical feature of these disorders. Microglia perform primary immune surveillance and macrophage-like activities within the central nervous system. Activated microglia are predominant players in the central nervous system response to damage related to stroke, trauma, and infection. Moreover, microglial activation per se leads to a proinflammatory response and oxidative stress. During the release of cytokines and chemokines, cyclooxygenases and phospholipase A2 are stimulated. Elevated levels of these compounds play a significant role in immune cell recruitment into the brain. Cyclic phospholipase A2 plays a fundamental role in the production of prostaglandins by releasing arachidonic acid. In turn, arachidonic acid is biotransformed through different routes into several mediators that are endowed with pivotal roles in the regulation of inflammatory processes. Some experimental models of neuroinflammation exhibit an increase in cyclic phospholipase A2, leukotrienes, and prostaglandins such as prostaglandin E2, prostaglandin D2, or prostacyclin. However, findings on the role of the prostacyclin receptors have revealed that their signalling suppresses Th2-mediated inflammatory responses. In addition, other in vitro evidence suggests that prostaglandin E2 may inhibit the production of some inflammatory cytokines, attenuating inflammatory events such as mast cell degranulation or inflammatory leukotriene production. Based on these conflicting experimental data, the role of arachidonic acid derivatives in neuroinflammation remains a challenging issue.

Deletion of the gene encoding prostamide/prostaglandin F synthase reveals an important role in regulating intraocular pressure

Prostamide/prostaglandin F synthase (PM/PGFS) is an enzyme with very narrow substrate specificity and is dedicated to the biosynthesis of prostamide F_2α and prostaglandin F_2α (PGF_2α.). The importance of this enzyme, relative to the aldo-keto reductase (AKR) series, in providing functional tissue prostamide F_2α levels was determined by creating a line of PM/PGFS gene deleted mice. Deletion of the gene encoding PM/PGFS (Fam213b / Prxl2b) was accomplished by a two exon disruption. Prostamide F_2α levels in wild type (WT) and PM/PGFS knock-out (KO) mice were determined by LC/MS/MS. Deletion of Fam213b (Prxl2b) had no observed effect on behavior, appetite, or fertility. In contrast, tonometrically measured intraocular pressure was significantly elevated by approximately 4 mmHg in PM/PGFS KO mice compared to littermate WT mice. Outflow facility was measured in enucleated mouse eyes using the iPerfusion system. No effect on pressure dependent outflow facility occurred, which is consistent with the effects of prostamide F_2α and PGF_2α increasing outflow through the unconventional pathway. The elevation of intraocular pressure caused by deletion of the gene encoding the PM/PGFS enzyme likely results from a diversion of the endoperoxide precursor pathway to provide increased levels of those prostanoids known to raise intraocular pressure, namely prostaglandin D₂ (PGD₂) and thromboxane A₂ (TxA₂). It follows that PM/PGFS may serve an important regulatory role in the eye by providing PGF_2α and prostamide F_2α to constrain the influence of those prostanoids that raise intraocular pressure.

Effect of Prostanoids on Human Platelet Function: An Overview

Prostanoids are bioactive lipid mediators and take part in many physiological and pathophysiological processes in practically every organ, tissue and cell, including the vascular, renal, gastrointestinal and reproductive systems. In this review, we focus on their influence on platelets, which are key elements in thrombosis and hemostasis. The function of platelets is influenced by mediators in the blood and the vascular wall. Activated platelets aggregate and release bioactive substances, thereby activating further neighbored platelets, which finally can lead to the formation of thrombi. Prostanoids regulate the function of blood platelets by both activating or inhibiting and so are involved in hemostasis. Each prostanoid has a unique activity profile and, thus, a specific profile of action. This article reviews the effects of the following prostanoids: prostaglandin-D₂ (PGD₂), prostaglandin-E₁, -E₂ and E₃ (PGE₁, PGE₂, PGE₃), prostaglandin F_2α (PGF_2α), prostacyclin (PGI₂) and thromboxane-A₂ (TXA₂) on platelet activation and aggregation via their respective receptors.

Potent and Selective Human Prostaglandin F (FP) Receptor Antagonist (BAY-6672) for the Treatment of Idiopathic Pulmonary Fibrosis (IPF)

Idiopathic pulmonary fibrosis (IPF) is a rare and devastating chronic lung disease of unknown etiology. Despite the approved treatment options nintedanib and pirfenidone, the medical need for a safe and well-tolerated antifibrotic treatment of IPF remains high. The human prostaglandin F receptor (hFP-R) is widely expressed in the lung tissue and constitutes an attractive target for the treatment of fibrotic lung diseases. Herein, we present our research toward novel quinoline-based hFP-R antagonists, including synthesis and detailed structure-activity relationship (SAR). Starting from a high-throughput screening (HTS) hit of our corporate compound library, multiple parameter improvements-including increase of the relative oral bioavailability F_rel from 3 to ≥100%-led to a highly potent and selective hFP-R antagonist with complete oral absorption from suspension. BAY-6672 (46) represents-to the best of our knowledge-the first reported FP-R antagonist to demonstrate in vivo efficacy in a preclinical animal model of lung fibrosis, thus paving the way for a new treatment option in IPF.

The enzymology of the human prostanoid pathway

Prostanoids are short-lived autocrine and paracrine signaling molecules involved in a wide range of biological functions. They have been shown to be intimately involved in many different disease states when their regulation becomes dysfunctional. In order to fully understand the progression of any disease state or the biological functions of the well state, a complete evaluation of the genomics, proteomics, and metabolomics of the system is necessary. This review is focused on the enzymology for the enzymes involved in the synthesis of the prostanoids (prostaglandins, prostacyclins and thromboxanes). In particular, the isolation and purification of the enzymes, their enzymatic parameters and catalytic mechanisms are presented.

Enhanced glucocorticoid exposure facilitates the expression of genes involved in prostaglandin and estrogen syntheses in bovine placentomes at induced parturition

The mechanism by which the fetal membrane detaches after parturition in cattle is poorly understood, but the upregulation of placentomal prostaglandin and estrogen synthesis are considered to be important. This study investigated whether enhanced glucocorticoid exposure affected the functional maturation of placentomes at induced parturition. Placentomes were collected immediately after spontaneous (beef; n = 5, dairy; n = 5) or induced parturition in beef and dairy cattle. Parturition was induced conventionally using prostaglandin F2α (beef; n = 7, dairy; n = 6) or dexamethasone (beef; n = 6) or with a combination of triamcinolone acetonide (a long-acting glucocorticoid) and a high dose of betamethasone (TABET treatment, beef; n = 6, dairy; n = 9). Gene expression levels and protein localization in placentomes were analyzed by RT-qPCR and immunohistochemistry, respectively. Compared with the conventional methods, TABET treatment resulted in upregulated PTGS2 expression in cotyledons. The expression levels of PTGS2 and PGES were positively correlated in both cotyledons and caruncles. TABET treatment also upregulated the expression of CYP17A1, but not of CYP19A1, in cotyledons. The results revealed, for the first time, that PLA2G4A was localized in microvascular endothelial cells in the cotyledonary villi and the maternal septum. PTGS2 and PGES were colocalized in mononucleated cells of the cotyledonary villi and caruncle epithelial cells adjacent to the chorionic plate. TABET treatment upregulated the expression of placentomal genes involved in PGE2 synthesis and the conversion of pregnenolone to androstenedione. Thus, enhanced glucocorticoid exposure might partially facilitate the functional maturation of placentomes at induced parturition in cattle.

The Role of Eicosanoids in Alzheimer's Disease

Alzheimer's disease (AD) is one of the most common neurodegenerative disorders known. Estimates from the Alzheimer's Association suggest that there are currently 5.8 million Americans living with the disease and that this will rise to 14 million by 2050. Research over the decades has revealed that AD pathology is complex and involves a number of cellular processes. In addition to the well-studied amyloid-β and tau pathology, oxidative damage to lipids and inflammation are also intimately involved. One aspect all these processes share is eicosanoid signaling. Eicosanoids are derived from polyunsaturated fatty acids by enzymatic or non-enzymatic means and serve as short-lived autocrine or paracrine agents. Some of these eicosanoids serve to exacerbate AD pathology while others serve to remediate AD pathology. A thorough understanding of eicosanoid signaling is paramount for understanding the underlying mechanisms and developing potential treatments for AD. In this review, eicosanoid metabolism is examined in terms of in vivo production, sites of production, receptor signaling, non-AD biological functions, and known participation in AD pathology.

Negative Cooperativity in the Interaction of Prostaglandin H Synthase-1 with the Competitive Inhibitor Naproxen Can Be Described as the Interaction of a Non-competitive Inhibitor with Heterogeneous Enzyme Preparation

The kinetic mechanism of the interaction of nonsteroidal anti-inflammatory drugs (NSAIDs) with their main pharmacological target, prostaglandin H synthase (PGHS), has not yet been established. We showed that inhibition of PGHS-1 from sheep vesicular glands by naproxen (a representative of NSAIDs) demonstrates a non-competitive character with respect to arachidonic acid and cannot be described within a framework of the commonly used kinetic schemes. However, it can be described by taking into account the negative cooperativity of naproxen binding to the cyclooxygenase active sites of the PGHS-1 homodimer (the first naproxen molecule forms a more stable complex (K₁ = 0.1 µM) with the enzyme than the second naproxen molecule (K₂ = 9.2 µM)). An apparent non-competitive interaction of PGHS-1 with naproxen is due to slow dissociation of the enzyme-inhibitor complexes. The same experimental data could also be described using commonly accepted kinetic schemes, assuming that naproxen interacts was a mixture of two enzyme species with the inhibition constants K_α = 0.05 µM and K_β = 18.3 µM. Theoretical analysis and numerical calculations show that the phenomenon of kinetic convergence of these two models has a general nature: when K₂ >> K₁, the kinetic patterns (for transient kinetics and equilibrium state) generated by the cooperative model could be described by a scheme assuming the presence of two enzyme forms with the inhibition constants K_α = K₁/2, K_β = 2·K₂. When K₂ << K₁, the cooperative model can be presented as a scheme with two inhibitor molecules simultaneously binding to the enzyme with the observed inhibition constant K (K = K₁·K₂). The assumption on the heterogeneity of the enzyme preparation in relation to its affinity to the inhibitor can be used instead of the assumption on the negative cooperativity of the enzyme-inhibitor interactions for convenient and easy practical description of such phenomena in enzymology, biotechnology, pharmacology, and other fields of science.

Plasma metabolic profile reveals PGF2α protecting against non-proliferative diabetic retinopathy in patients with type 2 diabetes

Diabetic retinopathy (DR) is the most frequent microvascular complications of diabetes and the leading cause of blindness in adults worldwide. Non-proliferative DR (NPDR) is the first stage of DR but currently has few recommended intervention. Eicosanoids play important roles in maintaining vessel homeostasis. However, the functions of eicosanoids in NPDR are still unknown. In this study, we investigated the eicosanoids profile difference in plasma between type 2 diabetes with NPDR or not. A total of 50 patients with type 2 diabetes were recruited and divided into non-DR (NDR) group and NPDR group based on fundus photographs. The eicosanoids profiles in plasma were determined by LC-MS/MS. Adhesion and transwell assay were used to detect the adhesion and migration effects of metabolites on primary bovine retinal pericyte cells (BRPC), respectively. Streptomycin (STZ)-induced diabetic mouse model was used to test the protective effects of selected metabolites according to retinal immunofluorescence staining and fluorescence confocal microscopy. Prostaglandin 2α (PGF2α) was decreased significantly in NPDR group compared to NDR group and negatively correlated with NPDR. In vitro, PGF2α was found to accelerate adhesion and migration by activating prostaglandin F receptor (FP receptor) and subsequent increasing RhoA activity in primary bovine retinal pericyte. Administration of PGF2α analogue diminished the damage on retinal capillary in an STZ-induced diabetic mouse model. Our results suggested that PGF2α may be a protective factor in the progression of NPDR in T2D patients. The protective mechanism of PGF2α was to increase pericyte mobility through FP receptor/RhoA pathway.

Endocannabinoids and their oxygenation by cyclo-oxygenases, lipoxygenases and other oxygenases

The naturally occurring mammalian endocannabinoids possess biological attributes that extend beyond interaction with cannabinoid receptors. These extended biological properties are the result of oxidative metabolism of the principal mammalian endocannabinoids arachidonoyl ethanolamide (anandamide; A-EA) and 2-arachidonoylglycerol (2-AG). Both endocannabinoids are oxidized by cyclo-oxygenase-2 (COX-2), but not by COX-1, to a series of prostaglandin derivatives (PGs) with quite different biological properties from those of the parent substrates. PG ethanolamides (prostamides, PG-EAs) and PG glyceryl esters (PG-Gs) are not only pharmacologically distinct from their parent endocannabinoids, they are distinct from the corresponding acidic PGs, and are differentiated from each other. Ethanolamides and glyceryl esters of the major prostanoids PGD2, PGE2, PGF2α, and PGI2 are formed by the various PG synthases, and thromboxane ethanolamides and glyceryl esters are not similarly produced. COX-2 is also of interest by virtue of its corollary central role in modulating endocannabinoid tone, providing a new therapeutic approach for treating pain and anxiety. Other major oxidative conversion pathways are provided for both A-EA and 2-AG by several lipoxygenases (LOXs), resulting in the formation of numerous hydroxyl metabolites. These do not necessarily represent inactivation pathways for endocannabinoids but may mimic or modulate the endocannabinoids or even display alternative pharmacology. Similarly, A-EA and 2-AG may be oxidized by P450 enzymes. Again a very diverse number of metabolites are formed, with either cannabinoid-like biological properties or an introduction of disparate pharmacology. The biological activity of epoxy and hydroxyl derivatives of the endocannabinoids remains to be fully elucidated. This review attempts to consolidate and compare the findings obtained to date in an increasingly important research area. This article is part of a Special Issue entitled "Oxygenated metabolism of PUFA: analysis and biological relevance".

Expression of genes related to prostaglandin synthesis or signaling in human subcutaneous and omental adipose tissue: depot differences and modulation by adipogenesis

OBJECTIVES

(1) To examine depot-specific PGE2 and PGF2α release and mRNA expression of enzymes or receptors involved in PG synthesis or signaling in human adipose tissues; (2) to identify changes in expression of these transcripts through preadipocyte differentiation; and (3) to examine associations between adipose tissue mRNA expression of these transcripts and adiposity measurements.

METHODS

Fat samples were obtained surgically in women. PGE2 and PGF2α release by preadipocytes and adipose tissue explants was measured. Expression levels of mRNA coding for enzymes or receptors involved in PG synthesis or signaling were measured by RT-PCR.

RESULTS

Cultured preadipocytes and explants from omental fat released more PGE2 and PGF2α than those from the subcutaneous depot and the corresponding transcripts showed consistent depot differences. Following preadipocyte differentiation, expression of PLA2G16 and PTGER3 mRNA was significantly increased whereas COX-1, COX-2, PTGIS, and PTGES mRNA abundance were decreased in both compartments (P ≤ 0.01 for all). Transcripts that were stimulated during adipogenesis were those that correlated best with adiposity measurements.

CONCLUSION

Cells from the omental fat compartment release more PGE2 and PGF2α than those from the subcutaneous depot. Obesity modulates expression of PG-synthesizing enzymes and PG receptors which likely occurs through adipogenesis-induced changes in expression of these transcripts.

Molecular evolution, characterization and expression profiling of uterine aldoketoreductase 1B5 gene in endometrium of goat (Capra hircus)

Aldoketoreductase 1B5 (AKR1B5), a member of the Aldoketoreductase family, is involved in the production of Prostaglandin F2α (PGF2α) as one of vital prostaglandin F synthase (PGFS). PGs (Prostaglandins) play a crucial role in female reproductive system. In the present study, we cloned and characterized the full-length open reading frame of AKR1B5 gene in Black Bengal (BB) goat. The complete coding sequence of AKR1B5 comprises an entire open reading frame of 951 bp, encoding 316 amino acid (AA) residues. BB AKR1B5 showed >82.9% identity with that of cattle, rabbit, human, and rat at nucleotide and amino acid levels, respectively. Further, a systematic study of AKR1B5 sequence evolution was also conducted using Phylogenetic Analysis by Maximum Likelihood (PAML), entropy plot, and Blossum 62 in a phylogenetic context. Analysis of nonsynonymous to synonymous nucleotide substitution rate ratios (Ka/Ks) revealed that negative selection may have been operating on this gene during evolution in goat, cattle, rabbit, human, and rat, which showed its conservation across species. Further, expression of AKR1B5 was determined by quantitative real-time PCR in goat endometrial tissues at different stages of the estrous cycle and early pregnancy. Our results indicated its high expression at luteolytic phase (stage III; day 16-21) during the estrous cycle. However, during early (day ∼30-40) pregnancy the expression was highest as compared to estrous cycle.

Expression of the prostaglandin F synthase AKR1B1 and the prostaglandin transporter SLCO2A1 in human fetal membranes in relation to spontaneous term and preterm labor

BACKGROUND

Human labor is a complex series of cellular and molecular events that occur at the materno-fetal and uterine levels. Many hypotheses have been proposed for the initiation of human labor, one hypothesis suggests that maturation of the fetus releases a signal in the amniotic fluid that will be transmitted to myometrium via the fetal membranes and initiate uterine contractions. There is strong evidence that prostaglandins (PGs) play a central role in initiation and progression of human labor.

OBJECTIVES

In this study we intended to investigate the expression of prostaglandin F synthase and the prostaglandin transporter in the human fetal membranes and to explore the relationship between cytokines and PGs in the mechanism of human labor.

METHODS

We used fetal membranes obtained before labor at term and after spontaneous labor at term or preterm to identify the changes in prostaglandin F synthase (AKR1B1) and human prostaglandin transporter (SLCO2A1) proteins in relation to parturition. Using fetal membranes explants we tested the effect of cytokines (interleukin-1 and tumor necrosis factor alpha) on PG production and the concomitant changes in cyclooxygenase-2 (PTGS2), AKR1B1 and SLCO2A1 expression.

RESULTS

Expression of PTGS2 and AKR1B1 was upregulated in the fetal membranes in association with term labor while SLCO2A1 was downregulated with advancing gestation and during term labor. Before labor, IL-1 increased the expression of PTGS2, however during labor TNF upregulated PTGS2 and AKR1B1 proteins.

CONCLUSIONS

The prostaglandin F synthase AKR1B1 is upregulated while prostaglandin transporter is downregulated during term labor. The amnion is more responsive than choriodecidua to stimulation with pro-inflammatory cytokines. The mechanisms of term and preterm labor are different.

Prostaglandin (PG) F2 alpha synthesis in human subcutaneous and omental adipose tissue: modulation by inflammatory cytokines and role of the human aldose reductase AKR1B1

INTRODUCTION

PGF2α may be involved in the regulation of adipose tissue function.

OBJECTIVES

1) To examine PGF2α release by primary preadipocytes, mature adipocytes and whole tissue explants from the subcutaneous and omental fat compartments; 2) To assess which PGF synthase is the most relevant in human adipose tissue.

METHODS

Fat samples were obtained by surgery in women. PGF2α release by preadipocytes, adipocytes and explants under stimulation by TNF-α, IL-1β or both was measured. Messenger RNA expression levels of AKR1B1 and AKR1C3 were measured by RT-PCR in whole adipose tissue and cytokine-treated preadipocytes. The effect of AKR1B1 inhibitor ponalrestat on PGF2α synthesis was investigated.

RESULTS

PGF2α release was significantly induced in response to cytokines compared to control in omental (p = 0.01) and to a lesser extent in subcutaneous preadipocytes (p = 0.02). Messenger RNA of COX-2 was significantly higher in omental compared to subcutaneous preadipocytes in response to combined TNF-α and IL-1β (p = 0.01). Inflammatory cytokines increased AKR1B1 mRNA expression and protein levels (p≤0.05), but failed to increase expression levels of AKR1C3 in cultured preadipocytes. Accordingly, ponalrestat blunted PGF2α synthesis by preadipocytes in basal and stimulated conditions (p≤0.05). Women with the highest PGF2α release by omental adipocytes had a higher BMI (p = 0.05), waist circumference (p≤0.05) and HOMAir index (p≤0.005) as well as higher mRNA expression of AKR1B1 in omental (p<0.10) and subcutaneous (p≤0.05) adipose tissue compared to women with low omental adipocytes PGF2α release. Positive correlations were observed between mRNA expression of AKR1B1 in both compartments and BMI, waist circumference as well as HOMAir index (p≤0.05 for all).

CONCLUSION

PGF2α release by omental mature adipocytes is increased in abdominally obese women. Moreover, COX-2 expression and PGF2α release is particularly responsive to inflammatory stimulation in omental preadipocytes. Yet, blockade of PGF synthase AKR1B1 inhibits most of the PGF2α release.

Insights into the prostanoid pathway in the ovary development of the penaeid shrimp Penaeus monodon

The prostanoid pathway converts polyunsaturated fatty acids (PUFAs) into bioactive lipid mediators, including prostaglandins, thromboxanes and prostacyclins, all of which play vital roles in the immune and reproductive systems in most animal phyla. In crustaceans, PUFAs and prostaglandins have been detected and often associated with female reproductive maturation. However, the presence of prostanoid biosynthesis genes remained in question in these species. In this study, we outlined the prostanoid pathway in the black tiger shrimp Penaeus monodon based on the amplification of nine prostanoid biosynthesis genes: cytosolic phospholipase A2, hematopoietic prostaglandin D synthase, glutathione-dependent prostaglandin D synthase, prostaglandin E synthase 1, prostaglandin E synthase 2, prostaglandin E synthase 3, prostaglandin F synthase, thromboxane A synthase and cyclooxygenase. TBLASTX analysis confirmed the identities of these genes with 51-99% sequence identities to their closest homologs. In addition, prostaglandin F2α (PGF2α), which is a product of the prostaglandin F synthase enzyme, was detected for the first time in P. monodon ovaries along with the previously identified PUFAs and prostaglandin E2 (PGE2) using RP-HPLC and mass-spectrometry. The prostaglandin synthase activity was also observed in shrimp ovary homogenates using in vitro activity assay. When prostaglandin biosynthesis was examined in different stages of shrimp ovaries, we found that the amounts of prostaglandin F synthase gene transcripts and PGF2α decreased as the ovaries matured. These findings not only indicate the presence of a functional prostanoid pathway in penaeid shrimp, but also suggest a possible role of the PGF2α biosynthesis in shrimp ovarian development.

Evaluation of the prostaglandin F synthase activity of human and bovine aldo-keto reductases: AKR1A1s complement AKR1B1s as potent PGF synthases

AKR1B1 of the polyol pathway was identified as a prostaglandin F2α synthase (PGFS). Using a genomic approach we have identified in the endometrium five bovine and three human AKRs with putative PGFS activity and generated the corresponding recombinant enzymes. The PGFS activity of the recombinant proteins was evaluated using a novel assay based on in situ generation of the precursor of PG biosynthesis PGH2. PGF2α was measured by ELISA and the relative potencies of the different enzymes were compared. We identified AKR1A1 and confirmed AKR1B1 as the most potent PGFS expressing characteristic inhibition patterns in presence of methylglyoxal, ponalrestat and glucose.

Catalytic mechanism of the primary human prostaglandin F2α synthase, aldo-keto reductase 1B1--prostaglandin D2 synthase activity in the absence of NADP(H)

Aldo-keto reductase 1B1 and 1B3 (AKR1B1 and AKR1B3) are the primary human and mouse prostaglandin F(2α) (PGF(2α)) synthases, respectively, which catalyze the NADPH-dependent reduction of PGH(2), a common intermediate of various prostanoids, to form PGF(2α). In this study, we found that AKR1B1 and AKR1B3, but not AKR1B7 and AKR1C3, also catalyzed the isomerization of PGH(2) to PGD(2) in the absence of NADPH or NADP(+). Both PGD(2) and PGF(2α) synthase activities of AKR1B1 and AKR1B3 completely disappeared in the presence of NADP(+) or after heat treatment of these enzymes at 100 °C for 5 min. The K(m), V(max), pK and optimum pH values of the PGD(2) synthase activities of AKR1B1 and AKR1B3 were 23 and 18 μM, 151 and 57 nmol·min(-1)·(mg protein)(-1), 7.9 and 7.6, and pH 8.5 for both AKRs, respectively, and those of PGF(2α) synthase activity were 29 and 33 μM, 169 and 240 nmol·min(-1)·(mg protein)(-1), 6.2 and 5.4, and pH 5.5 and pH 5.0, respectively, in the presence of 0.5 mm NADPH. Site-directed mutagenesis of the catalytic tetrad of AKR1B1, composed of Tyr, Lys, His and Asp, revealed that the triad of Asp43, Lys77 and His110, but not Tyr48, acts as a proton donor in most AKR activities, and is crucial for PGD(2) and PGF(2α) synthase activities. These results, together with molecular docking simulation of PGH(2) to the crystallographic structure of AKR1B1, indicate that His110 acts as a base in concert with Asp43 and Lys77 and as an acid to generate PGD(2) and PGF(2α) in the absence of NADPH or NADP(+) and in the presence of NADPH, respectively.

Preferential localization of prostamide/prostaglandin F synthase in myelin sheaths of the central nervous system

Prostaglandin (PG) F(₂α) is a product of cyclooxygenase (COX)-catalyzed metabolism of arachidonic acid and exerts biological functions in various tissues. Prostaglandin ethanolamide (prostamide) F(₂α) is a COX-2-catalyzed metabolite of arachidonoyl ethanolamide (anandamide) that induces pharmacological actions in ocular tissues. Although PGF(₂α) is one of the most abundant prostaglandins in the brain, function of PGF(₂α) in the central nervous system (CNS) has not been extensively investigated. Recently identified prostamide/PGF synthase catalyzes the reductions of prostamide H₂ to prostamide F(₂α) and PGH₂ to PGF(₂α), chiefly in the CNS. We examined tissue distribution of the enzyme in the CNS by immunohistochemistry, double immunofluorescence, and immuno-electron microscopy. We confirmed histological findings by immunofluorescence analyses of brain cell cultures. Prostamide/PGF synthase was expressed preferentially in the white matter bundles of the entire CNS of adult mice with less marked expression in neuronal cell bodies. The enzyme was colocalized with myelin basic protein (MBP) in myelin sheaths but not in axons. At the ultrastructural level, the enzyme was localized to myelin sheaths. Expression of the enzyme increased between P9 and P14 during the postnatal development, presumably in accordance with myelinogenesis. Cultured oligodendrocytes at 7 days in vitro expressed the enzyme in cytoplasmic processes where the enzyme was colocalized with MBP. Immunoreactivity for COX-2 was detected in white matter and cultured oligodendrocytes. Relatively selective localization of prostamide/PGF synthase suggests that myelin sheaths of the CNS may serve as the sites for producing prostamide F(₂α) and/or PGF(₂α), which may contribute to the formation and maintenance of central myelin.

Prostaglandin F(2alpha) suppresses early phase of adipogenesis, but is not associated with osteoblastogenesis in mouse mesenchymal stem cells

In this study, we investigated the roles of prostaglandin (PG) F(2alpha) in the differentiation of mouse ST2 mesenchymal stem cells (MSC) into adipocytes and osteoblasts. PGF(2alpha) was not produced in the undifferentiated ST2 MSC, but its highest level of production was detected at 3h after the initiation of adipogenesis and then quickly decreased. On the contrary, apparent PGF(2alpha) production was not detected during the osteoblastogenesis of ST2 MSC. The PGF(2alpha) production pattern during adipogenesis well resembled the expression profiles of aldo-keto reductase (AKR) 1B3, which acted as the PGF(2alpha) synthase, and cyclooxygenase-2 genes; but the pattern showed a slight delay compared with these profiles. The siRNA for AKR1B3, but not that for AKR1B8 or 1B10, decreased PGF(2alpha) production and enhanced the expression of adipogenic genes, but did not affect the mRNA levels of osteoblastogenic genes, during the adipogenesis of ST2 MSC. The FP receptor was expressed during adipogenesis of ST2 MSC, and its agonist or antagonist suppressed or enhanced, respectively, the lipid accumulation and the adipogenic gene expression; but this receptor was not associated with the osteoblastogenesis. These results indicate that AKR1B3-mediated PGF(2alpha) suppressed the early phase of adipogenesis through FP receptors, but did not affect osteoblastogenesis in ST2 MSC. Therefore, PGF(2alpha) suppressed the progression of early phase adipogenesis after determination of the cell fate that causes MSC to differentiate into adipocytes.

The prostaglandin transporter PGT transports PGH(2)

Prostaglandin H(2) not only serves as the common precursor of all other PGs, but also directly triggers signals (e.g. platelet aggregation), depending on its location and translocation. The prostaglandin carrier PGT mediates the transport of several prostanoids, such as PGE(2), and PGF(2alpha). Here we used PGT in the plasma membrane as a model system to test the hypothesis that PGT also transports PGH(2). Using wild-type and PGT-expressing MDCK cells, we show that PGH(2) uptake is mediated both by simple diffusion and by PGT. The PGH(2) influx permeability coefficient for diffusion is (5.66+/-0.63)x10(-6)cm/s. The kinetic parameters of PGH(2) transport by PGT are K(m)=376+/-34nM and V(max)=210.2+/-11.4 fmol/mg protein/s. PGH(2) transport by PGT can be inhibited by excess PGE(2) or by a PGT inhibitor. We conclude that PGT may play a role in transporting PGH(2) across cellular membranes.

Suppression of adipocyte differentiation by aldo-keto reductase 1B3 acting as prostaglandin F2alpha synthase

Prostaglandin (PG) F(2alpha) suppresses adipocyte differentiation by inhibiting the function of peroxisome proliferator-activated receptor gamma. However, PGF(2alpha) synthase (PGFS) in adipocytes remains to be identified. Here, we studied the expression of members of the aldo-keto reductase (AKR) 1B family acting as PGFS during adipogenesis of mouse 3T3-L1 cells. AKR1B3 mRNA was expressed in preadipocytes, and its level increased about 4-fold at day 1 after initiation of adipocyte differentiation, and then quickly decreased the following day to a level lower than that in the preadipocytes. In contrast, the mRNA levels of Akr1b8 and 1b10 were clearly lower than that level of Akr1b3 in preadipocytes and remained unchanged during adipogenesis. The transient increase in Akr1b3 during adipogenesis was also observed by Western blot analysis. The mRNA for the FP receptor, which is selective for PGF(2alpha), was also expressed in preadipocytes. Its level increased about 2-fold within 1 h after the initiation of adipocyte differentiation and was maintained at almost the same level throughout adipocyte differentiation. The small interfering RNA for Akr1b3, but not for Akr1b8 or 1b10, suppressed PGF(2alpha) production and enhanced the expression of adipogenic genes such as peroxisome proliferator-activated receptor gamma, fatty acid-binding protein 4 (aP2), and stearoyl-CoA desaturase. Moreover, an FP receptor agonist, Fluprostenol, suppressed the expression of those adipogenic genes in 3T3-L1 cells; whereas an FP receptor antagonist, AL-8810, efficiently inhibited the suppression of adipogenesis caused by the endogenous PGF(2alpha). These results indicate that AKR1B3 acts as the PGFS in adipocytes and that AKR1B3-produced PGF(2alpha) suppressed adipocyte differentiation by acting through FP receptors.

The aldo-keto reductase superfamily and its role in drug metabolism and detoxification

The aldo-keto reductase (AKR) superfamily comprises enzymes that catalyze redox transformations involved in biosynthesis, intermediary metabolism, and detoxification. Substrates of AKRs include glucose, steroids, glycosylation end-products, lipid peroxidation products, and environmental pollutants. These proteins adopt a (beta/alpha)(8) barrel structural motif interrupted by a number of extraneous loops and helixes that vary between proteins and bring structural identity to individual families. The human AKR family differs from the rodent families. Due to their broad substrate specificity, AKRs play an important role in the phase II detoxification of a large number of pharmaceuticals, drugs, and xenobiotics.

Cyclooxygenase and peroxidase inactivation of prostaglandin-H-synthase during catalysis

Prostaglandin-H-synthase (PGHS) is a bifunctional enzyme catalyzing cyclooxygenase and peroxidase reactions and undergoing irreversible inactivation during catalysis. A new method for kinetic studies of both PGHS activities in the course of cyclooxygenase as well as peroxidase reactions and also preincubation with hydroperoxides is suggested. It is shown that peroxidase activity is retained after complete cyclooxygenase inactivation and cyclooxygenase activity is retained after complete peroxidase inactivation. Two-stage cyclooxygenase inactivation occurs on preincubation of PGHS with hydrogen peroxide. Studies on inactivation under various conditions indicate that chemical mechanisms of cyclooxygenase and peroxidase inactivation are different. The data allow development of kinetic models.

Molecular characterization of a novel type of prostamide/prostaglandin F synthase, belonging to the thioredoxin-like superfamily

Prostaglandin F (PGF) ethanolamide (prostamide F) synthase, which catalyzed the reduction of prostamide H(2) to prostamide F(2alpha), was found in mouse and swine brain. The enzyme was purified from swine brain, and its amino acid sequence was defined. The mouse enzyme consisted of a 603-bp open reading frame coding for a 201-amino acid polypeptide with a molecular weight of 21,669. The amino acid sequence placed the enzyme in the thioredoxin-like superfamily with Cys(44) being the active site. The enzyme expressed in Escherichia coli as well as the native enzyme catalyzed not only the reduction of prostamide H(2) to prostamide F(2alpha) but also that of PGH(2) to PGF(2alpha). The V(max) and K(m) values for prostamide H(2) were about 0.25 micromol/min.mg of protein and 7.6 microm, respectively, and those for PGH(2) were about 0.69 micromol/min.mg of protein and 6.9 microm, respectively. Neither PGE(2) nor PGD(2) served as a substrate for this synthase. Based on these data, we named the enzyme prostamide/PGF synthase. Although the enzyme showed a broad specificity for reductants, reduced thioredoxin preferentially served as a reducing equivalent donor for this enzyme. Moreover, Northern and Western blot analyses in addition to the prostamide F synthase activity showed that the enzyme was mainly distributed in the brain and spinal cord, and the immunohistochemical study in the spinal cord showed that the enzyme was found mainly in the cytosol. These results suggest that prostamide/PGF synthase may play an important functional role in the central nervous system.

Novel cyclooxygenase-catalyzed bioactive prostaglandin F2alpha from physiology to new principles in inflammation

Prostaglandin F2alpha (PGF2alpha), a foremost stable vasoactive cyclooxygenase (COX)-catalyzed prostaglandin, regulates a number of key physiological functions such as luteolysis, ovarian function, luteal maintenance of pregnancy, and parturition as a constitutive part of ongoing reproductive processes of the body. It has recently been implicated in the regulation of intricate pathophysiological processes, such as acute and chronic inflammation, cardiovascular and rheumatic diseases. Since the discovery of a second isoform of COXs, it has been shown that PGF2alpha can be formed in vivo from arachidonic acid through both isoforms of COXs, namely cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2). Being synthesized in various parts of the body, it metabolizes instantly to a number of rather inactive metabolites mainly in the lungs, liver, kidney, and efficiently excretes into the urine. 15-Keto-dihydro-PGF2alpha, a major stable metabolite of PGF2alpha that reflects in vivo PGF2alpha biosynthesis, is found in larger quantities than its parent compound in the circulation and urine in basal physiological conditions, with short-lived pulses during luteolysis, induced termination of pregnancy and parturition, and is increased in tissues and various body fluids during acute, sub-chronic, and severe chronic inflammation. Further, the close relationship of PGF2alpha with a number of risk factors for atherosclerosis indicates its major role in inflammation pathology. This review addresses multiple aspects of PGF2alpha in addition to its emerging role in physiology to inflammation.

Decidual activation: abundance and localization of prostaglandin F2alpha receptor (FP) mRNA and protein and uterine activation proteins in human decidua at preterm birth and term birth

OBJECTIVE

To study how the decidua contributes to parturition, we examined prostaglandin F(2alpha) concentrations as well as prostaglandin 15-hydroxy dehydrogenase, prostaglandin F(2alpha) receptor, matrix metalloproteinases 2 and 9, oxytocin receptor, prostaglandin-H synthase-2, and the prostaglandin E(2) receptor expression in human decidua.

MATERIALS AND METHODS

Decidual samples were isolated from placentas collected from patients at preterm not in labor (PTNIL), preterm labor (PTL), term not in labor (TNIL), and term labor (TL). For immunohistochemistry, fresh membranes which included chorion, amnion and decidua from term patients were collected.

RESULTS

Prostaglandin F(2alpha) receptor mRNA was low in all preterm patients and then significantly increased towards term (p=0.049). Prostaglandin F(2alpha) receptor protein was identified in the amnion epithelium and mesoderm, chorion trophoblasts and decidua by immunohistochemistry, and levels were highest at TNIL (p=0.007) as measured by western blot. Prostaglandin F(2alpha) levels were higher at PTNIL than TNIL. Matrix metalloproteinases 2 and 9 protein and pro-enzyme activities were higher at TL than TNIL. There were no significant changes among the groups for any of the other factors measured.

CONCLUSIONS

These results suggest that the induction of Prostaglandin F(2alpha) receptor at term may facilitate the decidua contribution to parturition, and its regulation and role should be examined further.

Expression of enzymes of cyclooxygenase pathway and secretion of prostaglandin E2 and F2α by porcine myometrium during luteolysis and early pregnancy

Past studies of uterine prostaglandin (PGs) and pig reproduction have focused on endometrial rather than myometrial PGs. This study documents the synthesis and secretion of myometrial prostaglandins (PGs) in pigs and the involvement of oxytocin (OT) in these processes. Cyclooxygenase-2 (COX-2) expression was similar in myometrial explants from cyclic and pregnant pigs (days 14-16) and OT (10(-7) M) in vitro significantly increased COX-2 protein regardless of reproductive state. Basal expression of prostaglandin E2 synthase (PGES) was higher during pregnancy than during luteolysis. Conversely, prostaglandin F synthase (PGFS) was highest during luteolysis and lower in myometrium from gravid animals. OT had no influence on the expression of PGES and PGFS. In another tissue culture experiment, myometrial slices produced more PGE2 than PGF2alpha regardless of reproductive state of the female. OT stimulated PGE2 production in myometrium harvested during luteolysis and increased PGF2alpha production in all tissues examined. Progesterone (P4; 10(-5) M) blocked stimulatory effect of OT on myometrial PG release. Myometrial OTr mRNA was higher (P=0.03) during luteolysis than during pregnancy.

IN CONCLUSION

(1) oxytocin increases myometrial COX-2 expression, but does not influence the expression of terminal enzymes of PGs synthesis (PGES and PGFS); (2) porcine myometrium preferentially produces PGs during early pregnancy and secretes more PGE2 than PGF2alpha; (3) myometrial OT and OTr support secretion of PGs from myometrium during luteolysis.

Prostaglandin F2alpha formation from prostaglandin H2 by prostaglandin F synthase (PGFS): crystal structure of PGFS containing bimatoprost

Prostaglandin H(2) (PGH(2)) formed from arachidonic acid is an unstable intermediate and is efficiently converted into more stable arachidonate metabolites by the action of enzymes. Prostaglandin F synthase (PGFS) has dual catalytic activities: formation of PGF(2)(alpha) from PGH(2) by the PGH(2) 9,11-endoperoxide reductase activity and 9alpha,11beta-PGF(2) (PGF(2)(alphabeta)) from PGD(2) by the PGD(2) 11-ketoreductase activity in the presence of NADPH. Bimatoprost (BMP), which is a highly effective ocular hypotensive agent, is a PGF(2)(alpha) analogue that inhibits both the PGD(2) 11-ketoreductase and PGH(2) 9,11-endoperoxide reductase activities of PGFS. To examine the catalytic mechanism of PGH(2) 9,11-endoperoxide reductase, a crystal structure of PGFS[NADPH + BMP] has been determined at 2.0 A resolution. BMP binds near the PGD(2) binding site, but the alpha- and omega-chains of BMP are locate on the omega- and alpha-chains of PGD(2), respectively. Consequently, the bound BMP and PGD(2) direct their opposite faces of the cyclopentane moieties toward the nicotinamide ring of the bound NADP. The alpha- and omega-chains of BMP are involved in H-bonding with protein residues, while the cyclopentane moiety is surrounded by water molecules and is not directly attached to either the protein or the bound NADPH, indicating that the cyclopentane moiety is movable in the active site. From the complex structure, two model structures of PGFS containing PGF(2)(alpha) and PGH(2) were built. On the basis of the model structures and inhibition data, a putative catalytic mechanism of PGH(2) 9,11-endoperoxide reductase of PGFS is proposed. Formation of PGF(2)(alpha) from PGH(2) most likely involves a direct hydride transfer from the bound NADPH to the endoperoxide of PGH(2) without the participation of specific amino acid residues.

Molecular cloning and spatiotemporal expression of prostaglandin F synthase and microsomal prostaglandin E synthase-1 in porcine endometrium

Endometrial prostaglandins (PGs) and the PGE2/PGF2alpha ratio play an important role in regulating the estrous cycle and establishment of pregnancy. The enzymes downstream of cyclooxygenase-2 may determine the PGE2/PGF2alpha ratio in the porcine uterus. Thus, we have cloned porcine PGF synthase (PGFS) and microsomal PGE synthase-1 (mPGES-1) and characterized their expression in porcine endometrium during the estrous cycle and early pregnancy. PGFS and mPGES-1 amino acid sequences possessed a high degree (>67% and >77%, respectively) of identity with the other mammalian homologs. There was little modulation of mPGES-1 throughout the estrous cycle; however, PGFS expression was highly up-regulated in endometrium around the time of luteolysis. During early pregnancy, PGFS at the protein level showed a time-dependent increase (low on d 10-13, intermediate on d 14-23, and high on d 24-25). In pregnancy, expression of mPGES-1 was intermediate on d 10-11 and low on d 14-17 and then increased after d 22, reaching the maximum on d 24-25. Immunohistochemistry showed localization of PGFS and mPGES-1 proteins mainly in luminal and glandular epithelium. Concluding, the spatiotemporal expression of PGFS throughout the estrous cycle indicates an involvement of PGFS in regulating luteolysis in the pig. The comparison of endometrial PGFS and mPGES-1 expression on d 10-13 of the estrous cycle and pregnancy suggest a supportive role of these enzymes in determining the increase of uterine PGE2/PGF2alpha ratio during maternal recognition of pregnancy. Moreover, high expression of both PG synthases after initiation of implantation may indicate their significant role in placentation.

9α,11β-PGF2and its stereoisomer PGF2αare novel agonists of the chemoattractant receptor, CRTH2

CRTH2 is a recently described chemoattractant receptor for the prostaglandin, PGD(2), expressed by Th2 cells, eosinophils and basophils, and believed to play a role in allergic inflammation. Here we describe the potency of several PGD(2) metabolites at the receptor to induce cell migration and activation. We report for the first time that the PGD(2) metabolite, 9alpha,11beta-PGF(2), and its stereoisomer, PGF(2alpha), are CRTH2 agonists. 9alpha,11beta-PGF(2) is a major metabolite produced in vivo following allergen challenge, whilst PGF(2alpha) is generated independently of PGD synthetase, with implications for CRTH2 signalling in the presence or absence of PGD(2) production.

Localization of cyclooxygenases-1 and -2, and prostaglandin F synthase in human kidney and renal cell carcinoma

Prostaglandin (PG)F2alpha is one of the major prostanoids produced by the kidney, and its renal synthesis is regulated by sodium depletion, potassium depletion, and adrenal steroids. PGF synthase activity is detected in kidney of various mammals. Herein, we demonstrated immunochemically that PGF synthase was localized in proximal tubule of human kidney, together with cyclooxygenase (COX)-1, and that it was localized in human renal cell carcinoma, together with COX-2. These results suggest that PGF synthesized through COX-1 and PGF synthase plays an important physiological role in the kidney and that the expression of COX-2 in kidney is a useful maker for tumorigenesis of the renal call carcinoma in vivo.

Enzymatic formation of prostamide F2α from anandamide involves a newly identified intermediate metabolite, prostamide H2

Prostaglandin F2alpha 1-ethanolamide (prostamide F2alpha) is a potent ocular hypotensive agent in animals and represents a new class of fatty acid amide compounds. Accumulated evidence indicated that anandamide, an endogenous bioactive ligand for cannabinoid receptors, may serve as a common substrate to produce all prostamides, including prostamide F2alpha. After incubation of anandamide with cyclooxygenase 2 (COX-2), the reaction mixture was profiled by HPLC and an intermediate metabolite was discovered and characterized as a cyclic endoperoxide ethanolamide using HPLC-tandem mass spectrometry. Formation of prostamide F2alpha was also demonstrated when the intermediate metabolite was isolated and incubated with prostaglandin F synthase (PGF synthase). These results suggest that the biosynthesis of prostamide F2alpha proceeds in two consecutive steps: oxidation of anandamide to form an endoperoxide intermediate by COX-2, and reduction of the endoperoxide intermediate to form prostamide F2alpha by PGF synthase. This endoperoxide ethanolamide intermediate has been proposed as prostamide H2.

Phytoestrogen metabolites are much more active than phytoestrogens themselves in increasing prostaglandin F(2alpha) synthesis via prostaglanin F(2alpha) synthase-like 2 stimulation in bovine endometrium

Phytoestrogens have recently been suggested to be the cause of infertility by stimulating luteolytic prostaglandin (PG) F(2alpha) secretion from endometrium in cattle. The purpose of this study was to examine the enzymatic and molecular mechanisms involved in the preferential induction of PGF(2alpha) synthesis by phytoestrogens, and whether phytoestrogens influence endometrial cell viability. Cultured bovine endometrial epithelial and stromal cells were exposed to phytoestrogens (daidzein and genistein) and their metabolites (equol and p-ethyl phenol) for 24h. Prostaglandin F(2alpha) and PGE2 were stimulated by phytoestrogens in both stromal and epithelial cells, with a preference for PGF(2alpha) synthesis in epithelial cells (P<0.001). Although RT-PCR and Western Blot analyses did not reveal the influence of phytoestrogens on either gene expression or protein level of cyclooxygenase-2 (COX-2) and PGE2 synthase (PGES) in stromal and epithelial cells (P>0.05), the stimulative effects of equol and p-ethyl phenol on PGF(2alpha) synthase-like 2 (PGFSL2) gene expression and protein level were observed only in epithelial cells (P<0.05). The same compounds did not affect PGFSL2 gene expression and protein in stromal cells (P>0.05). Exposure to phytoestrogens and their metabolites decreased cell viability in both stromal and epithelial cells. Stromal cell viability decreased to 50% of the control and was more evident than that in epithelial cells (P<0.001). The overall results suggest that infertility in cattle, caused by phytoestrogen-dependent preferential stimulation of luteolytic PGF(2alpha) synthesis, is caused by increasing PGFSL2 in epithelial cells, and by decreasing stromal cell viability, which are the main source of luteotropic PGE2 production.

Structural and Mutational Analysis of Trypanosoma brucei Prostaglandin H2 Reductase Provides Insight into the Catalytic Mechanism of Aldo-ketoreductases

Trypanosoma brucei prostaglandin F2alpha synthase is an aldo-ketoreductase that catalyzes the reduction of prostaglandin H2 to PGF2alpha in addition to that of 9,10-phenanthrenequinone. We report the crystal structure of TbPGFS.NADP+.citrate at 2.1 angstroms resolution. TbPGFS adopts a parallel (alpha/beta)8-barrel fold lacking the protrudent loops and possesses a hydrophobic core active site that contains a catalytic tetrad of tyrosine, lysine, histidine, and aspartate, which is highly conserved among AKRs. Site-directed mutagenesis of the catalytic tetrad residues revealed that a dyad of Lys77 and His110, and a triad of Tyr52, Lys77, and His110 are essential for the reduction of PGH2 and 9,10-PQ, respectively. Structural and kinetic analysis revealed that His110, acts as the general acid catalyst for PGH2 reduction and that Lys77 facilitates His110 protonation through a water molecule, while exerting an electrostatic repulsion against His110 that maintains the spatial arrangement which allows the formation of a hydrogen bond between His110 and C11 that carbonyl of PGH2. We also show Tyr52 acts as the general acid catalyst for 9,10-PQ reduction, and thus we not only elucidate the catalytic mechanism of a PGH2 reductase but also provide an insight into the catalytic specificity of AKRs.

Crystal Structure and Possible Catalytic Mechanism of Microsomal Prostaglandin E Synthase Type 2 (mPGES-2)

Prostaglandin (PG) H(2) (PGH(2)), formed from arachidonic acid, is an unstable intermediate and is converted efficiently into more stable arachidonate metabolites (PGD(2), PGE(2), and PGF(2)) by the action of three groups of enzymes. Prostaglandin E synthase catalyzes an isomerization reaction, PGH(2) to PGE(2). Microsomal prostaglandin E synthase type-2 (mPGES-2) has been crystallized with an anti-inflammatory drug indomethacin (IMN), and the complex structure has been determined at 2.6A resolution. mPGES-2 forms a dimer and is attached to lipid membrane by anchoring the N-terminal section. Two hydrophobic pockets connected to form a V shape are located in the bottom of a large cavity. IMN binds deeply in the cavity by placing the OMe-indole and chlorophenyl moieties into the V-shaped pockets, respectively, and the carboxyl group interacts with S(gamma) of C110 by forming a H-bond. A characteristic H-bond chain formation (N-H...S(gamma)-H...S(gamma)...H-N) is seen through Y107-C113-C110-F112, which apparently decreases the pK(a) of S(gamma) of C110. The geometry suggests that the S(gamma) of C110 is most likely the catalytic site of mPGES-2. A search of the RCSB Protein Data Bank suggests that IMN can fit into the PGH(2) binding site in various proteins. On the basis of the crystal structure and mutation data, a PGH(2)-bound model structure was built. PGH(2) fits well into the IMN binding site by placing the alpha and omega-chains in the V-shaped pockets, and the endoperoxide moiety interacts with S(gamma) of C110. A possible catalytic mechanism is proposed on the basis of the crystal and model structures, and an alternative catalytic mechanism is described. The fold of mPGES-2 is quite similar to those of GSH-dependent hematopoietic prostaglandin D synthase, except for the two large loop sections.

Crystal structure of human prostaglandin F synthase (AKR1C3)

Prostaglandin H(2) (PGH(2)) formed from arachidonic acid is an unstable intermediate and is efficiently converted into more stable arachidonate metabolites (PGD(2), PGE(2), and PGF(2)) by the action of three groups of enzymes. Prostaglandin F synthase (PGFS) was first purified from bovine lung and catalyzes the formation of 9 alpha,11 beta-PGF(2) from PGD(2) and PGF(2)(alpha) from PGH(2) in the presence of NADPH. Human PGFS is 3 alpha-hydroxysteroid dehydrogenase (3 alpha-HSD) type II and has PGFS activity and 3 alpha-HSD activity. Human lung PGFS has been crystallized with the cofactor NADP(+) and the substrate PGD(2), and with the cofactor NADPH and the inhibitor rutin. These complex structures have been determined at 1.69 A resolution. PGFS has an (alpha/beta)(8) barrel structure. The cofactor and substrate or inhibitor bind in a cavity at the C-terminal end of the barrel. The cofactor binds deeply in the cavity and has extensive interactions with PGFS through hydrogen bonds, whereas the substrate (PGD(2)) is located above the bound cofactor and has little interaction with PGFS. Despite being largely structurally different from PGD(2), rutin is located at the same site of PGD(2), and its catechol and rhamnose moieties are involved in hydrogen bonds with PGFS. The catalytic site of PGFS contains the conserved Y55 and H117 residues. The carbonyl O(11) of PGD(2) and the hydroxyl O(13) of rutin are involved in hydrogen bonds with Y55 and H117. The cyclopentane ring of PGD(2) and the phenyl ring of rutin face the re-side of the nicotinamide ring of the cofactor. On the basis of the catalytic geometry, a direct hydride transfer from NADPH to PGD(2) would be a reasonable catalytic mechanism. The hydride transfer is facilitated by protonation of carbonyl O(11) of PGD(2) from either H117 (at low pH) or Y55 (at high pH). Since the substrate binding cavity of PGFS is relatively large in comparison with those of AKR1C1 and AKR1C2, PGFS (AKR1C3) could catalyze the reduction and/or oxidation reactions of various compounds over a relatively wide pH range.

Synthesis of prostaglandin F ethanolamide by prostaglandin F synthase and identification of Bimatoprost as a potent inhibitor of the enzyme: new enzyme assay method using LC/ESI/MS

Prostaglandin (PG) D(2) ethanolamide (prostamide D(2)) was reduced to 9alpha,11beta-PGF(2) ethanolamide (9alpha,11beta-prostamide F(2)) by PGF synthase, which also catalyzes the reduction of PGH(2) and PGD(2) to PGF(2alpha) and 9alpha,11beta-PGF(2), respectively. These enzyme activities were measured by a new method, the liquid chromatographic-electrospray ionization-mass spectrometry (LC/ESI/MS) technique, which could simultaneously detect the substrate and all products. PGF(2alpha), 9alpha,11beta-PGF(2), PGD(2), PGH(2), 9alpha,11beta-prostamide F(2), and prostamide D(2) were separated on a TSKgel ODS 80Ts column, ionized by electrospray, and detected in the negative mode. Selected ion monitoring (SIM) of m/z 353 ([M-H](-)), 353 ([M-H](-)), 351 ([M-H](-)), 333 ([M-H-H(2)O](-)), 456 ([M+59](-)), and m/z 358 ([M-37](-)) was used for quantifying PGF(2alpha), 9alpha,11beta-PGF(2), PGD(2), PGH(2), 9alpha,11beta-prostamide F(2), and prostamide D(2), respectively. The detection limit for PGF(2alpha) and 9alpha,11beta-PGF(2) was 0.01pmol; that for PGH(2) and PGD(2), 0.1pmol; and that for prostamide D(2) and 9alpha,11beta-prostamide F(2), 0.5 and 0.03pmol, respectively. The LC/ESI/MS technique for measuring PGF synthase activity showed higher sensitivity than other methods. Using this method, we found that Bimatoprost, the ethyl amide analog of 17-phenyl-trinor PGF(2alpha) and an anti-glaucoma agent, inhibited all three reductase activities of PGF synthase when used at a low concentration. These results suggest that Bimatoprost also behaves as a potent PGF synthase inhibitor in addition to having prostamide-like activity.

Prostaglandin synthases: recent developments and a novel hypothesis

Cells are continuously exposed to cues, which signal cell survival or death. Fine-tuning of these conflicting signals is essential for tissue development and homeostasis, and defective pathways are linked to many disease processes, especially cancer. It is well established that prostaglandins (PGs), as signalling molecules, are important regulators of cell proliferation, differentiation and apoptosis. PG production has been a focus of many researchers interested in the mechanisms of parturition. Previously, investigators have focussed on the committed step of PG biosynthesis, the conversion by prostaglandin H synthase (PGHS; also termed cyclo-oxygenase, COX) of arachidonic acid (AA) (substrate) to PGH2, the common precursor for biosynthesis of the various prostanoids. However, recently the genes encoding the terminal synthase enzymes involved in converting PGH2 to each of the bioactive PGs, including the major uterotonic PGs, PGE2 (PGE synthase) and PGF2alpha (PGF synthase), have been cloned and characterized. This review highlights how the regulation of the expression and balance of key enzymes can produce, from a single precursor, prostanoids with varied and often opposing effects.