Genotoxic properties of cyclopentenone prostaglandins and the onset of glutathione depletion.

Prostaglandins are endogenous mediators formed from arachidonic acid by cyclooxygenases and prostaglandin synthases during inflammatory processes. The five-membered ring can be dehydrated, and α,ß-unsaturated cyclopentenone PGs (cyPGs) are generated. Recent studies have been focused on their potential pharmacological use against inflammation and cancer. However, little is known so far about possible adverse health effects of cyPGs. We addressed the question whether selected cyPGs at a concentration range of 0.1-10 µM exhibit mutagenic and genotoxic properties in the hamster lung fibroblast V79 cell line and whether these effects are accompanied by a depletion of intracellular glutathione (GSH). The cyPGs 15-deoxy-Δ12,14-prostaglandin J2 (15dPGJ2) and prostaglandin A2 (PGA2) significantly induced DNA damage in V79 cells after 1 h of incubation. Furthermore, a more pronounced increase in formamidopyrimidine-DNA glycosylase (FPG) sensitive sites, indicative of oxidative DNA-damage, was observed. The findings on DNA-damaging properties were supported by our results that 15dPGJ(2) acts as an aneugenic agent which induces the amount of kinetochore positive micronuclei associated with an increase of apoptosis. The strong potency of cyPGs to rapidly bind GSH measured in a chemical assay and to significantly reduce the GSH level after only 1 h of incubation may contribute to the observed oxidative DNA strand breaks, whereas directly induced oxidative stress via reactive oxygen species could be excluded. However, after an extended incubation time of 24 h no genotoxicity could be measured, this may contribute to the lack of mutagenicity in the hypoxanthine phosphorybosyltransferase (HPRT) assay. In conclusion, potential in vitro genotoxicity of cyPG and a strong impact on GSH homeostasis have been demonstrated, which may be involved in carcinogenesis mediated by chronic inflammation.

New cytotoxic prostanoids from Taiwanese soft coral Clavularia viridis.

Chemical investigation of the AcOEt/MeOH extract of Clavularia viridis collected in Taiwan has afforded four new prostanoids, named claviridins A-D (1-4, resp.). The structures of compounds 1-4 were determined on the basis of 1D- and 2D-NMR techniques, including COSY, HMQC, HMBC, and NOESY experiments. Pharmacological studies revealed that compounds 1-4 exhibited potent cytotoxicity against human cancer cells.

Prostaglandins from a zoanthid: paclitaxel-like neurite-degenerating and microtubule-stabilizating activities.

Two prostaglandins, PGA2 and PGB2, were isolated from the Okinawan zoanthid, Palythoa kochii, during a search for paclitaxel-like neurite-degenerating compounds from natural sources using a cell-based assay method. In the presence of PGA2 at 30 microM, the neuronal processes induced in PC12 cells by the nerve growth factor (NGF) degenerated over 24 h, whereas PGB2 had no effect on the neuronal processes of PC12 cells. This activity of PGA2 was similar to that of the microtubule-stabilizing agents, paclitaxel (Taxol) and epothilone A, unlike the microtubule-depolymerizing agent, colchicine, which brought about quick neurite degeneration within 3 h. PGA2 stimulated tubulin polymerization, although less potently than paclitaxel. An examination of structure-activity relationships across several PGs suggests that the cyclopentenone ring structure and the orientation of its dipolar moment played an important role in the paclitaxel-like neurite-degenerating activity. These results suggest that the cyclopentenone-type PGs can interact with microtubules to inhibit their function like paclitaxel.

Prostaglandins as putative neurotoxins in Alzheimer's disease.

Chronic inflammatory reactions in the brain appear to be one of the primary etiological factors in the pathogenesis of Alzheimer's disease (AD). This is supported by the fact that the secretory products of inflammatory reactions, which include cytokines, complement proteins, adhesion molecules, and free radicals, are neurotoxic. We have recently reported that prostaglandins (PGs), which are also released during inflammatory reactions, cause rapid degenerative changes in differentiated murine neuroblastoma cells (NB) in culture. PGA1 is more effective than PGE1. Similar observations were made in a primary culture of fetal rat hippocampal cells. Epidemiological and clinical studies on AD also support the involvement of PGs in neuronal degeneration. Thus, we propose a hypothesis that PGs are one of the major extracellular signals that initiate neuronal degeneration, which is mediated by intracellular signals such as the beta-amyloid peptide (Abeta) and ubiquitin, since the levels of these proteins are increased by PG treatment. We further suggest that adenosine 3', 5'-cyclic monophosphate (cAMP) is one of the factors that regulate the levels of both Abeta and ubiquitin in NB cells. Increases in the level of Abeta in NB cells following an elevation of intracellular cAMP levels appear to be due to an increase in the rate of processing of the amyloid precursor protein (APP) rather than an increase in the expression of APP. The mechanisms underlying Abeta-induced neuronal degeneration have been under intense investigation, and several mechanisms of action have been proposed. We postulate that PG-induced elevation of Abeta may lead to an increased binding of Abeta to the 20S proteasome, resulting in a reduction of 20S proteasome-mediated degradation of ubiquitin-conjugated proteins. This is predicted to lead to an increase in an accumulation of abnormal proteins, which ultimately contribute to neuronal degeneration and death. Based on our hypothesis and on studies published by others, we propose that a combination of nonsteroidal anti-inflammatory drugs, which inhibit the synthesis of PGs, and antioxidant vitamins, which quench free radicals and both of which have been recently reported to be of some value in AD treatment when used-individually, may be much more effective in the prevention and treatment of AD than the individual agents alone.

Prostaglandins in the treatment of cancer.

Prostaglandins (PGs) with antiproliferative activity against tumor cells consist of the cyclopentenone PGs and the alkylidene cyclopentenone PGs. Such PGs are PGD2, PGJ2, delta 12-PGJ2, PGA1, delta 7-PGA1, and PGA2. Both PGJ2 and delta 12-PGJ2 are ultimate metabolites of PGD2 and have potent antiproliferative activity on tumor cells. delta 12-PGJ2 was identified in human urine, whereas delta 7-PGA1 has not been found in the human body. One important characteristic of both delta 7-PGA1 and delta 12-PGJ2 is that they have little cross resistance with cisplatin and adriamycin in vitro and in vivo. delta 7-PGA1 has 5-fold greater antitumor activity than delta 12-PGJ2. Methyl ester-delta 7PGA1 (methyl-delta 7-PGA1) is stable chemically and can be easily synthesized in large amounts. All four isomers of methyl-delta 7-PGA1 showed the same antiproliferative activities on ovarian carcinoma cells. In addition, methyl-delta 7-PGA1 integrated in lipid microspheres (lipo-methyl-delta 7-PGA1) is more soluble in water than methyl-delta 7-PGA1 alone. Hence, lipo-methyl-delta 7-PGA1 was selected for extensive preclinical studies. Intravenous administration of lipo-methyl-delta 7-PGA1 could inhibit the growth of both HeLa S3 and Lovo colon cancer cells transplanted subcutaneously in nude mice. Lipo-methyl-delta 7-PGA1 by intraperitoneal administration could prolong the survival of scid mice bearing 2008C/13* cells resistant to cisplatin. The combined administration of cisplatin and lipo-methyl-delta 7-PGA1 prolonged the survival of nude mice bearing HRA cells compared with each single agent alone.(ABSTRACT TRUNCATED AT 250 WORDS)

An in vitro system to screen for diarrheagenic chemicals.

We examined an in vitro system to screen for diarrheagenic chemicals using an established intestinal cell line (T84 human colonic carcinoma). The cells were grown on Millicell-PCF (polycarbonate membrane) wells. The cells were seeded at approximately 5 x 10(6) cells/30mm well and incubated for 9-11 days in a 5% CO2 incubator saturated with water at 37 degrees C. The culture medium was a 1:1 mixture of Ham's F12 and Dulbecco's MEM with 5% fetal bovine serum and 25 micrograms/ml gentamicin sulfate. The well containing cells was removed from the incubator and mounted in a modified Ussing chamber for measurement of short-circuit current (ISC). Chemical-induced increases in ISC are usually indicative of electrogenic epithelial Cl- secretion, which is associated with diarrheagenic effects in animals and humans. T84 cells grown on Millicell-PCF membrane responded with an increase in ISC after basolateral addition of the cholinergic (muscarinic) agonist carbachol, prostaglandin E2, 16,16-dimethylprostaglandin E2, and forskolin, while non-diarrheagenic prostaglandin D2 did not affect ISC. Based on our results, this in vitro system has the potential to be adapted as a rapid screen for detecting diarrheagenic chemicals.

Biologically significant physico-chemical properties of antioxidative prostaglandin derivatives.

A monomeric derivative and several oligomeric derivatives were synthesized from prostaglandin B2. Their lipid solubility was studied by measuring their octanol-water partition coefficients. With EPR spectroscopy, the oligomeric derivatives were shown to have g = 2 signal, indicating these compounds have intrinsic free radicals. Measuring the rate of adenochrome formation, it was shown that these derivatives could scavenge superoxide anions. Using a spin-trapping technique employing DMPO, we found that these oligomers could also scavenge hydroxyl radicals. The calcium chelating activity of these compounds were also studied. In an in vitro rat model, these compounds inhibited lipid peroxidation as measured by the production of thiobarbituric acid reacting substances. Other prostaglandin oligomeric derivatives synthesized from PGE1 were also studied, and their properties were compared with these new compounds. Results suggest that both the water solubility and the chelating activity for calcium ions may not be related to their protective effects in ischemic or traumatic injury.

Inhibitory effects of prostanoids on the proliferation of transformed human epidermal cells in culture.

The cytotoxic action of various prostanoids was examined on a transformed human epidermal cell line (HSC-1), and methyl(5S,6S,7Z)-5,6-diacetoxy-7-((2S)-4-chloro-2-hydroxy-2-((2 Z+ ++)-2-octenyl)-5-oxo-3-cyclopentenylidene)heptanoate (YM-11), which is a punaglandin compound, was found to be most active. YM-11 exerted a dose-dependent inhibition of HSC-1 cell growth over 0.03 microM (0.01 micrograms/ml), and at 0.3 microM (0.1 micrograms/ml) its growth was completely inhibited. The IC50 value of YM-11 on HSC-1 cell growth was calculated as 0.15 microM (0.05 micrograms/ml). Methyl(E)-7-(5-chloro-2-hydroxy-2-octyl-5-oxo-3-cyclopentenylidene )heptanoate (YM-3), which is also a punaglandin derivative, showed remarkable cytotoxicity on HSC-1 cells with an IC50 of 0.24 microM (0.08 micrograms/ml). Concerning other cytotoxic prostaglandins (PGs), the IC50 values of delta 7-PGA1, delta 12-PGJ2 and PGD2 were 1.5 microM (0.5 micrograms/ml), 2.1 microM (0.75 micrograms/ml) and 5.7 microM (2 micrograms/ml), respectively. On the basis of the present data and previous in vitro and in vivo evidence, punaglandin derivatives may be useful antineoplastic agents for skin cancer.

The cervical relaxant properties of prostaglandin E2 in non pregnant subjects.

PIP: To determine the cervical relaxant properties and side effects of intravaginal administration of prostaglandin E2 (PGE2) in nonpregnant patients, 5 subjects in midluteal phase were given 20 mg of PGE2 by intravaginal suppository. In 4 patients, no change was found in the diameter of the internal cervical os 12 hours after treatment; the other patient showed an increase of 1 mm. 4 of 5 experienced prolonged nausea, 3 experienced severe vomiting, 2 had diarrhea, all 5 suffered chills, 3 had tachycardia, 4 had fevers, 4 had abdominal cramping, and 1 suffered hypotension. These side effects were severe and their potential seriousness makes this drug inappropriate for use in nonpregnant patients via this route of administration.^ieng