Method for quantitative analysis of PGA2 from plasma using deuterated carrier and gas--liquid chromatography--mass spectrometry

Clinical potential of serum prostaglandin A2 as a novel diagnostic biomarker for hepatocellular cancer

BACKGROUND

Hepatocellular cancer (HCC) is one of the most harmful tumors to human health. Currently, there is still a lack of highly sensitive and specific HCC biomarkers in clinical practice. In this study, we aimed to explore the diagnostic performance of prostaglandin A2 (PGA2) for the early detection of HCC.

METHODS

Untargeted metabolomic analyses on normal control (NC) and HCC participants in the discovery cohort were performed, and PGA2 was identified to be dysregulated in HCC. A liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for detecting serum PGA2 was established and applied to validate the dysregulation of PGA2 in another independent validation cohort. Receiver operating characteristic (ROC), decision curve analysis (DCA) and some other statistical analyses were performed to evaluate the diagnostic performance of PGA2 for HCC.

RESULTS

At first, PGA2 was found to be dysregulated in HCC in untargeted metabolomic analyses. Then a precise quantitative LC-MS/MS method for PGA2 has been established and has passed rigorous method validation. Targeted PGA2 analyses confirmed that serum PGA2 was decreased in HCC compared to normal-risk NC and high-risk cirrhosis group. Subsequently, PGA2 was identified as a novel biomarker for the diagnosis of HCC, with an area under the ROC curve (AUC) of 0.911 for differentiating HCC from the combined NC + cirrhosis groups. In addition, PGA2 exhibited high performance for differentiating small-size (AUC = 0.924), early-stage (AUC = 0.917) and AFP (-) HCC (AUC = 0.909) from the control groups. The combination of PGA2 and AFP might be useful in the surveillance of risk population for HCC and early diagnosis of HCC.

CONCLUSION

This study establishes that PGA2 might be a novel diagnostic biomarker for HCC.

Molecular, chemical, and structural characterization of prostaglandin A2 as a novel agonist for Nur77

Nur77 is a transcription factor belonging to the NR4A subfamily of nuclear hormone receptors. Upon induction, Nur77 modulates the expression of its target genes and controls a variety of biological and pathophysiological processes. Prior research that revealed a structurally atypical ligand-binding domain (LBD) and failed to locate an endogenous ligand had led to a classification of Nur77 as an orphan receptor. However, several more recent studies indicate that small synthetic molecules and unsaturated fatty acids can bind to Nur77. Discovery of additional endogenous ligands will facilitate our understanding of the receptor's functions and regulatory mechanisms. Our data have identified prostaglandin A2 (PGA2), a cyclopentenone prostaglandin (PG), as such a ligand. Cyclopentenone PGs exert their biological effects primarily by forming protein adducts via the characteristic electrophilic β-carbon(s) located in their cyclopentenone rings. Our data show that PGA2 induces Nur77 transcriptional activity by forming a covalent adduct between its endocyclic β-carbon, C9, and Cys566 in the receptor's LBD. The importance of this endocyclic β-carbon was substantiated by the failure of PGs without such electrophilic properties to react with Nur77. Calculated chemical properties and data from reactive molecular dynamic simulations, intrinsic reaction co-ordinate modeling, and covalent molecular docking also corroborate the selectivity of PGA2's C9 β-carbon towards Nur77's Cys. In summary, our molecular, chemical, and structural characterization of the PGA2-Nur77 interaction provides the first evidence that PGA2 is an endogenous Nur77 agonist.

Cyclopentenone prostaglandins: new insights on biological activities and cellular targets

The cyclopentenone prostaglandins PGA2, PGA1, and PGJ2 are formed by dehydration within the cyclopentane ring of PGE2, PGE1, and PGD2. PGJ2 is metabolized further to yield Delta(12)-PGJ(2) and 15-deoxy-Delta(12,14)-PGJ(2) (15d-PGJ(2)). Various compounds within the cyclopentenone prostaglandin family possess potent anti-inflammatory, anti-neoplastic, and anti-viral activity. Most actions of the cyclopentenone prostaglandins do not appear to be mediated by binding to G-protein coupled prostanoid receptors. Rather, the bioactivity of these compounds results from their interaction with other cellular target proteins. 15-deoxy-Delta(12,14)-PGJ(2) is a high affinity ligand for the nuclear receptor PPARgamma and modulates gene transcription by binding to this receptor. Other activities of the cyclopentenone prostaglandins are mediated by the reactive alpha,beta-unsaturated carbonyl group located in the cyclopentenone ring. The transcription factor NF-kappaB and its activating kinase are key targets for the anti-inflammatory activity of 15d-PGJ2, which inhibits NF-kappaB-mediated transcriptional activation by PPARgamma-dependent and independent molecular mechanisms. Other cyclopentenone prostaglandins, such as Delta(7)-PGA1 and Delta(12)-PGJ2, have strong anti-tumor activity. These compounds induce cell cycle arrest or apoptosis of tumor cells depending on the cell type and treatment conditions. We review here recent progress in understanding the mechanisms of action of the cyclopentenone prostaglandins and their possible use as therapeutic agents.

Glutathione-prostaglandin A1 conjugate as substrate in the purification of prostaglandin 9-ketoreductase from rabbit kidney

Using GSH-PGA1 as substrate for determination of enzyme activity a pI 4.8 form of rabbit kidney prostaglandin 9-keto-reductase has been purified 95 times to a specific activity of 1755 nmol/min per mg protein. The purification procedures involve ion-exchange chromatography, gel-filtration and affinity chromatography. The latter procedure comprises Blue Sepharose affinity chromatography, and GSH-PGA1-Sepharose affinity chromatography. The purified enzyme preparation also showed a weak NADP+-dependent 15-hydroxyprostaglandin dehydrogenase activity, 20 nmol/min per mg protein with PGE1 as substrate. Km (PGE1) for the dehydrogenase is 142.6 +/- 45.1 microM (S.E., n = 7).

Metabolism of N-acetyl PGE2 carboxamide in the rat

After intratracheal administration to rats, the bronchodilator N-acetyl PGE2 carboxamide was converted rapidly to PGE2 and 13,14-dihydro-15-keto-PGE2, the major plasma metabolite. Oxidation of the N-acetyl carboxamide by prostaglandin dehydrogenase and hydrolysis of the imide bond were demonstrated in vitro.

Selective ion monitoring in clinical chemistry

The principles of selective ion monitoring are described. Choice of instrumentations, derivatives, and internal standards is discussed. The most important factors influencing sensitivity, specificity, and precision are summarized. Applications of selective ion monitoring for quantitative assay of steroids, fat soluble vitamins, triglycerides, prostaglandins, biogenic amines, amino acids, carbohydrates, and several other organic compounds of clinical interest are critically reviewed. It is concluded that isotope dilution selective ion monitoring is one of the most sensitive and accurate techniques presently available for quantitation of a large number of endogenous compounds of clinical interest. In view of the high accuracy, the technique is useful not only for the clinical chemists dealing with determination of specific compounds which are difficult to analyze by other methods, but also for those dealing with quality control of routine analyses of simple organic compounds.

New derivatives of prostaglandin A1 and specific detection of prostaglandin A's and 190hydroxylated prostaglandin A's in human semen

The derivatization of prostaglandins of the A series with 1:1 mixtures of bis-(trimethylsilyl)trifluoroacetamide and nitrogen-containing non-aromatic heterocyclics such as piperidine, pyrrolidine, morpholine and hexamethylenimine (1--4 h at 60--70 degrees C) gives new types of derivatives, designated as 11-heterocycle, 9-enol PGA (TMS)3. These derivatives show very simplified and characteristic mass spectral patterns strikingly dominated by a common [M-173]+ fragment ion and easily detectable by selected ion monitoring. This feature allows the concurrent analytical detection of both prostaglandin A's and 19-hydroxy prostaglandin A's in biological samples. In this case 2 ml samples of human semen were extracted by direct ultrafiltration on a Pellicon membrane with a nominal molecular weight limit of 1000. The prostaglandins in the approximately or equal to 1.6 ml of ultrafiltrate thus obtained were recovered in ethyl acetate, derivatized as indicated above and detected by monitoring of the corresponding [M-173]+ ions.

A selected bibliography of biomedical and environmental applications of stable isotopes. I--Deuterium 1971-1976

A compilation of selected references to the use of deuterium in biochemical, pharmacological, clinical and environmental applications for the period 1971-1976 is presented. As a further aid, author and subject indices have been compiled.

Plasma prostaglandin E concentrations from birth through childhood

The prostaglandins are synthesized in a variety of tissues and participate in an extensive number of physiologic processes. As prostaglandin concentrations have not been reported in infants and children, we measured PGE levels from birth through childhood. PGE levels in cord blood were significantly higher than those in adults. By 48 to 72 hours of age, however, they had fallen to levels that were significantly lower than those in adults. Although PGE concentrations increased with age, they remained significantly lower than did adult levels. These low levels may be related to some of the functional pecularities of the immature kidney.