Human platelet-derived growth factor stimulates prostaglandin synthesis by activation and by rapid de novo synthesis of cyclooxygenase

Systems Pharmacology-Based Research on the Mechanism of Tusizi-Sangjisheng Herb Pair in the Treatment of Threatened Abortion

Threatened abortion (TA) is a common complication with high incidence in the first trimester of pregnancy, which will end in miscarriage if not treated properly. The Chinese herbs Cuscutae Semen (Tusizi in Chinese) and Herba Taxilli (Sangjisheng in Chinese) first recorded in the ancient classic medical book Shennong Bencao Jing are effective and widely used as an herb pair for the treatment of TA, while the active ingredients and the functional mechanism of Tusizi-Sangjisheng herb pair treating TA are still unknown. In order to exploit the relationship between those two herbs and TA, systems pharmacology analysis was carried out in this study. A total of 75 ingredients of Tusizi-Sangjisheng were collected from Traditional Chinese Medicine System Pharmacology Database and Analysis Platform (TCMSP). 12 bioactive compounds were screened, and 153 directly related targets were predicted by systematic models. Besides, Gene Ontology (GO) enrichment analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis were used to systematically explore the potential mechanisms of Tusizi-Sangjisheng treating TA. Meanwhile, Compound-Target (C-T), Target-Disease (T-D), and Target-Pathway (T-P) networks were constructed to further quest the underlying functional mechanisms of Tusizi-Sangjisheng. As a result, 31 targets and 3 key pathways were found to be directly related to TA that includes mitogen-activated protein kinases (MAPKs), phosphatidylinositol-3-kinase/protein kinase B (PI3K-Akt), and transforming growth factor-β (TGF-β) signaling pathways. The results in this study may provide some valuable clues about the molecular mechanisms of the efficient Chinese herb pair Tusizi-Sangjisheng in the treatment of TA.

Sleep deficiency and chronic pain: potential underlying mechanisms and clinical implications

Pain can be both a cause and a consequence of sleep deficiency. This bidirectional relationship between sleep and pain has important implications for clinical management of patients, but also for chronic pain prevention and public health more broadly. The review that follows will provide an overview of the neurobiological evidence of mechanisms thought to be involved in the modulation of pain by sleep deficiency, including the opioid, monoaminergic, orexinergic, immune, melatonin, and endocannabinoid systems; the hypothalamus-pituitary-adrenal axis; and adenosine and nitric oxide signaling. In addition, it will provide a broad overview of pharmacological and non-pharmacological approaches for the management of chronic pain comorbid with sleep disturbances and for the management of postoperative pain, as well as discuss the effects of sleep-disturbing medications on pain amplification.

Reduced platelet aggregation in women after intercourse: a possible role for the cyclooxygenase pathway

We hypothesise that molecules in the cyclooxygenase pathway affect platelet activity when seminal fluid (SF) is present. We considered the influence of SF on platelet aggregation in women, and believe that the prostanoids in SF signalling are significant. Thirty-one female subjects were studied, 20 of whom were sexually active. Male partners were given either aspirin or indomethacin to inhibit cyclooxygenase. The 6-keto prostaglandin F1α (6-keto PGF1α) and prostaglandin E metabolite (PGE-M) in SF were measured by competitive assay. Platelets and prostanoids were evaluated in women, periodically, before and after intercourse. The platelets were tested with adenosine diphosphate (ADP) and arachidonic acid (AA). To block the interaction between the uterus and SF, some couples used condoms. We found that the 6-keto prostaglandin F1α in urine at 2 hours post-intercourse (1418.75 pg/mL, Std 688.39) was greater than pre-intercourse (772.68 pg/mL, Std 116.54). Post-intercourse, a transient decrease in platelet aggregation was observed in women whose partners did not use condoms. Averages for platelet aggregation were 20.16% with ADP, and more significantly, 37.79% with AA after 2 hours. In contrast, couples using condoms showed no changes, averaging 64.02% with ADP and 72.06% with AA. Women whose partners were taking aspirin or indomethacin also showed no changes. SF from men taking aspirin or indomethacin led to no reduction in platelet aggregometry in their partners. These results indicate that in cases of exposure to SF, the transient change in women's platelet activity could be related to the cyclooxygenase pathway.

Cyclooxygenase Activity in the Thoracoabdominal Aorta After 24 Hours of Intraaortic Balloon Counterpulsation: An Assessment of the Effects of Localized Mechanical Trauma

Using a canine model, the authors evaluated the effects of twenty-four hours of intraaortic balloon counterpulsation (IABCP) on the morphology of the thoracoabdominal aorta and its spontaneous and arachidonate stimulated pro duction of prostacyclin (PGI2). The treated group was counter-pulsed at a 1:1 ratio with a 40 cc balloon. The control group had the balloon inserted and left deflated across the thoracoabdominal aorta.

There were no differences between the IABCP or sham groups in prostanoid production either in the thoracic or abdominal aorta. Baseline PGI2 production in the control versus treated group of thoracic aortas was 1880 ± 1140 pg/cm2/ min vs 1992 ± 1125. The stimulated response in the control group, 9180 ± 1198, was statistically different from baseline (P < .001). The stimulated in crease in the IABCP group, 6269 ± 5240, relative to baseline was also signifi cant (P < .01). There were no significant differences, either between or within groups in the abdominal aortas. Poststimulation values (30 min) were signifi cantly below baseline in each group in each section of the aorta (P < .05). Light microscopy showed a statistically significant difference in endothelial preserva tion between the control and the balloon group, 66 ± 25% vs 19 ± 17% (P < 0.05) .

The authors conclude that IABCP results in severe endothelial destruction but that spontaneous and stimulated PGI2 production is unimpaired. It remains to be determined whether the aorta may sustain long-term damage due to the repair process after IABCP.

The multi-faceted roles of prostaglandin E2 in cancer-infiltrating mononuclear phagocyte biology

Extensive research in the last two decades implemented that the inflammatory cell infiltrate, especially in solid tumors, is a major determinant for patient prognosis. Mononuclear phagocytes, i.e. monocytes/macrophages, dendritic cells and myeloid-derived suppressor cells, constitute the majority of tumor-associated immune cells. Instead of inducing anti-tumor immunity, mononuclear phagocytes are functionally subverted by tumor microenvironmental factors to support each stage of oncogenesis. Although mechanisms how tumors program their inflammatory infiltrate to support tumor development are ill-defined, few master regulators are beginning to emerge. One of them is the inflammatory eicosanoid prostaglandin E(2) (PGE(2)), produced by tumor cells or the infiltrating immune cells. In this review we summarize the impact of PGE(2) on mononuclear phagocytes in inflammation and cancer and discuss potential implications for cancer therapy.

Effects of a non-selective COX inhibitor and selective COX-2 inhibitors on contractility of human and porcine ureters in vitro and in vivo

BACKGROUND AND PURPOSE

Anti-inflammatory drugs are used in the treatment of acute renal colic. The aim of this study was to investigate the effects of selective COX-2 inhibitors and the non-selective COX inhibitor diclofenac on contractility of human and porcine ureters in vitro and in vivo, respectively. COX-1 and COX-2 receptors were identified in human ureter and kidney.

EXPERIMENTAL APPROACH

Human ureter samples were used alongside an in vivo pig model with or without partial ureteral obstruction. COX-1 and COX-2 receptors were located in human ureters by immunohistochemistry.

KEY RESULTS

Diclofenac and valdecoxib significantly decreased the amplitude of electrically-stimulated contractions in human ureters in vitro, the maximal effect (Vmax) being 120 and 14%, respectively. Valdecoxib was more potent in proximal specimens of human ureter (EC50=7.3 x 10(-11) M) than in distal specimens (EC50=7.4 x 10(-10) M), and the Vmax was more marked in distal specimens (22.5%) than in proximal specimens (8.0%) in vitro. In the in vivo pig model, parecoxib, when compared to the effect of its solvent, significantly decreased the maximal amplitude of contractions (Amax) in non-obstructed ureters but not in obstructed ureters. Diclofenac had no effect on spontaneous contractions of porcine ureter in vivo. COX-1 and COX-2 receptors were found to be expressed in proximal and distal human ureter and in tubulus epithelia of the kidney.

CONCLUSIONS AND IMPLICATIONS

Selective COX-2 inhibitors decrease the contractility of non-obstructed, but not obstructed, ureters of the pig in vivo, but have a minimal effect on electrically-induced contractions of human ureters in vitro.

Regulation of cholesteryl ester hydrolases

Recent developments in understanding the biochemical and molecular nature of the CE hydrolases and their impact on cellular cholesterol trafficking have further defined the enzyme's mechanism of action with reasonable clarity. The availability of the cDNA probe for the human lysosomal acid lipase/CE hydrolase and the hormone-sensitive lipase now makes it possible to study CE hydrolase gene regulation and expression in human tissue; and it can now be stated with more assurance that the cytoplasmic CE hydrolase (NCEH) is most likely activated through phosphorylation by the cyclic AMP-dependent protein kinase. Evidence also shows that the NCEH is most likely identical to the hormone-sensitive lipase and that it plays an important role in cholesterol efflux properties of the cell. Recent advances in the discovery of the role of the eicosanoid/cytokine network in the regulation of CE hydrolysis, highlighted in Figure 10, further emphasize the interesting but complex nature of the cholesterol trafficking processes in cells, particularly under pathophysiological conditions such as cell injury, repair, and inflammation. It can be speculated that in several years, when the crystal structure of the CE hydrolase is known, the structure-function properties of this enzyme's catalytic domain, as it relates to the physical state of the CE substrates, should further clarify the precise role of this enzyme in intracellular cholesterol mobilization and trafficking under a variety of cellular conditions.

The Clinical Pharmacology of Cyclooxygenase-2–Selective and Dual Inhibitors

Over the past decade, there have been several nonsteroidal anti-inflammatory drugs (NSAIDS) introduced in veterinary medicine with an increased gastrointestinal safety profile consistent with a cyclooxygenase (COX)-1-sparing effect. More recently, an NSAID with additional 5-lipoxygenase (5-LOX) activity has also been approved for use. Although it is tempting to equate in vitro COX-2/COX-1 and 5-LOX inhibition to overall in vivo safety, the data do not support this approach. The true overall safety for any individual compound is based on its evaluation in laboratory margin-of-safety studies, reproductive safety studies, and blind multicenter field studies in client-owned animals. Therefore, when choosing a COX-2-selective or dual-inhibitor NSAID for clinical use, all in vivo data must be taken into account to understand comparative safety, and continued use must be based on the drug's performance in the individual being treated. Until head-to-head trials in multicenter blind studies are published, comments on comparative safety and effectiveness must be reserved.

Platelet-derived growth factor-induced arachidonic acid release for enhancement of prostaglandin E(2) synthesis in human gingival fibroblasts pretreated with interleukin-1beta

Platelet-derived growth factor (PDGF) is a biological mediator for connective tissue cells and plays a critical role in a wide variety of physiological and pathological processes. We here investigated the effect of PDGF on arachidonic acid release and prostaglandin E(2) (PGE(2)) synthesis in human gingival fibroblasts (HGF). PDGF induced arachidonic acid release in a time- and dose-dependent manner, and simultaneously induced a transient increase in intracellular Ca(2+) concentration ([Ca(2+)](i)), but less provoked PGE(2) release and cyclooxygenase-2 (COX-2) mRNA expression. When [Ca(2+)](i) was increased by Ca(2+)-mobilizing reagents, arachidonic acid release was increased. The PDGF-induced arachidonic acid release and increase in [Ca(2+)](i) were prevented by a tyrosine kinase inhibitor. On the other hand, in the HGF pre-stimulated with interleukin-1beta (IL-1beta), PDGF clearly increased PGE(2) release. The PDGF-induced PGE(2) release was inhibited by a tyrosine kinase inhibitor. In the HGF pretreated with IL-1beta, arachidonic acid strongly enhanced PGE(2) release and COX-2 mRNA expression. These results suggest that PDGF stimulates arachidonic acid release by the increase in [Ca(2+)](i) via tyrosine kinase activation, and which contributes to PGE(2) production via COX-2 expression in HGF primed with IL-1beta.

Cyclooxygenase Isozymes: The Biology of Prostaglandin Synthesis and Inhibition

Nonsteroidal anti-inflammatory drugs (NSAIDs) represent one of the most highly utilized classes of pharmaceutical agents in medicine. All NSAIDs act through inhibiting prostaglandin synthesis, a catalytic activity possessed by two distinct cyclooxygenase (COX) isozymes encoded by separate genes. The discovery of COX-2 launched a new era in NSAID pharmacology, resulting in the synthesis, marketing, and widespread use of COX-2 selective drugs. These pharmaceutical agents have quickly become established as important therapeutic medications with potentially fewer side effects than traditional NSAIDs. Additionally, characterization of the two COX isozymes is allowing the discrimination of the roles each play in physiological processes such as homeostatic maintenance of the gastrointestinal tract, renal function, blood clotting, embryonic implantation, parturition, pain, and fever. Of particular importance has been the investigation of COX-1 and -2 isozymic functions in cancer, dysregulation of inflammation, and Alzheimer's disease. More recently, additional heterogeneity in COX-related proteins has been described, with the finding of variants of COX-1 and COX-2 enzymes. These variants may function in tissue-specific physiological and pathophysiological processes and may represent important new targets for drug therapy.

Lipoteichoic acid-induced cyclooxygenase-2 expression requires activations of p44/42 and p38 mitogen-activated protein kinase signal pathways

This study investigated the role of p44/42 and p38 mitogen-activated protein kinase (MAPK) in cyclooxygenase-2 expression caused by lipoteichoic acid in human pulmonary epithelial cell line (A549). Lipoteichoic acid-induced increases in cyclooxygenase activity and cyclooxygenase-2 expression were attenuated by tyrosine kinase inhibitors (genistein and tyrphostin AG126), a MAPK/extracellular signal-regulated protein kinase (MEK) inhibitor [2'-amino-3'-methoxyflavone] (PD 98059) and a p38 MAPK inhibitor [4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)1H-imidazole] (SB 203580). Lipoteichoic acid-induced p44/42 MAPK activation was inhibited by protein kinase C (PKC) inhibitors [12-(2-cyanoethyl)6,7,12,13-tetrahydro-13-methyl-5-oxo-5H-indolo(2,3-a)pyrrolo(3,4-c)-carbazole] (Go 6976) and [3-[1-[3-(amidinothio)propyl-1H-indol-3-yl]-3-(1-methyl-1H-indol-3-yl)maleimide]] (Ro 31-8220), genistein and PD 98059. Lipoteichoic acid-induced increase in p38 MAPK activity was inhibited by Go 6976, Ro 31-8220, genistein and SB 203580. Lipoteichoic acid-mediated formation of nuclear factor-kappa B (NF-kappa B)-specific DNA-protein complex was inhibited by genistein, tyrphostin AG126, PD 98059 and SB 203580. These results suggest that the activations of both p44/42 and p38 MAPK by lipoteichoic acid result in stimulation of NF-kappa B-specific DNA-protein binding and subsequent cyclooxygenase-2 expression in A549 cells. Both events required activation of upstream tyrosine kinase and PKC.

Fatty acid oxidation and signaling in apoptosis

It is well established that fatty acid metabolites of cyclooxygenase, lipoxygenase (LOX), and cytochrome P450 are implicated in essential aspects of cellular signaling including the induction of programmed cell death. Here we review the roles of enzymatic and non-enzymatic products of polyunsaturated fatty acids in controlling cell growth and apoptosis. Also, the spontaneous oxidation of polyunsaturated fatty acids yields reactive aldehydes and other products of lipid peroxidation that are potentially toxic to cells and may also signal apoptosis. Significant conflicting data in terms of the role of LOX enzymes are highlighted, prompting a re-evaluation of the relationship between LOX and prostate cancer cell survival. We include new data showing that LNCaP, PC3, and Du145 cells express much lower levels of 5-LOX mRNA and protein compared with normal prostate epithelial cells (NHP2) and primary prostate carcinoma cells (TP1). Although the 5-LOX activating protein inhibitor MK886 killed these cells, another 5-LOX inhibitor AA861 hardly showed any effect. These observations suggest that 5-LOX is unlikely to be a prostate cancer cell survival factor, implying that the mechanisms by which LOX inhibitors induce apoptosis are more complex than expected. This review also suggests several mechanisms involving peroxisome proliferator activated receptor activation, BCL proteins, thiol regulation, and mitochondrial and kinase signaling by which cell death may be produced in response to changes in non-esterified and non-protein bound fatty acid levels. Overall, this review provides a context within which the effects of fatty acids and fatty acid oxidation products on signal transduction pathways, particularly those involved in apoptosis, can be considered in terms of their overall importance relative to the much better studied protein or peptide signaling factors.

Cyclooxygenase-2 deficiency results in a loss of the anti-proliferative response to transforming growth factor-beta in human fibrotic lung fibroblasts and promotes bleomycin-induced pulmonary fibrosis in mice

Prostaglandin E(2) (PGE(2)) inhibits fibroblast proliferation and collagen production. Its synthesis by fibroblasts is induced by profibrotic mediators including transforming growth factor (TGF)-beta(1). However, in patients with pulmonary fibrosis, PGE(2) levels are decreased. In this study we examined the effect of TGF-beta(1) on PGE(2) synthesis, proliferation, collagen production, and cyclooxygenase (COX) mRNA levels in fibroblasts derived from fibrotic and nonfibrotic human lung. In addition, we examined the effect of bleomycin-induced pulmonary fibrosis in COX-2-deficient mice. We demonstrate that basal and TGF-beta(1)-induced PGE(2) synthesis is limited in fibroblasts from fibrotic lung. Functionally, this correlates with a loss of the anti-proliferative response to TGF-beta(1). This failure to induce PGE(2) synthesis is because of an inability to up-regulate COX-2 mRNA levels in these fibroblasts. Furthermore, mice deficient in COX-2 exhibit an enhanced response to bleomycin. We conclude that a decreased capacity to up-regulate COX-2 expression and COX-2-derived PGE(2) synthesis in the presence of increasing levels of profibrotic mediators such as TGF-beta(1) may lead to unopposed fibroblast proliferation and collagen synthesis and contribute to the pathogenesis of pulmonary fibrosis.

Endocrine and paracrine regulation of birth at term and preterm

We have examined factors concerned with the maintenance of uterine quiescence during pregnancy and the onset of uterine activity at term in an animal model, the sheep, and in primate species. We suggest that in both species the fetus exerts a critical role in the processes leading to birth, and that activation of the fetal hypothalamic-pituitary-adrenal axis is a central mechanism by which the fetal influence on gestation length is exerted. Increased cortisol output from the fetal adrenal gland is a common characteristic across animal species. In primates, there is, in addition, increased output of estrogen precursor from the adrenal in late gestation. The end result, however, in primates and in sheep is similar: an increase in estrogen production from the placenta and intrauterine tissues. We have revised the pathway by which endocrine events associated with parturition in the sheep come about and suggest that fetal cortisol directly affects placental PGHS expression. In human pregnancy we suggest that cortisol increases PGHS expression, activity, and PG output in human fetal membranes in a similar manner. Simultaneously, cortisol contributes to decreases in PG metabolism and to a feed-forward loop involving elevation of CRH production from intrauterine tissues. In human pregnancy, there is no systemic withdrawal of progesterone in late gestation. We have argued that high circulating progesterone concentrations are required to effect regionalization of uterine activity, with predominantly relaxation in the lower uterine segment, allowing contractions in the fundal region to precipitate delivery. This new information, arising from basic and clinical studies, should further the development of new methods of diagnosing the patient at risk of preterm labor, and the use of scientifically based strategies specifically for the management of this condition, which will improve the health of the newborn.

Prostaglandin-E2 counteracts interleukin-1beta-stimulated upregulation of platelet-derived growth factor alpha-receptor on rat pulmonary myofibroblasts

The platelet-derived growth factor (PDGF) alpha-receptor (PDGF-Ralpha) is upregulated during lung fibrogenesis, and induction of PDGF-Ralpha on cultured lung myofibroblasts by interleukin (IL)-1beta results in an increased mitogenic response to PDGF. Because IL-1beta stimulates prostaglandin (PG) E2 production, we investigated whether IL-1beta could upregulate PDGF-Ralpha via a PGE2-dependent mechanism. IL-1beta increased the production of PGE2 by rat lung myofibroblasts and the cyclooxygenase (COX) inhibitor indomethacin blocked IL-1beta-induced PGE2 production. However, indomethacin did not inhibit IL-1beta-stimulated upregulation of [125I]PDGF-AA binding sites, indicating that PDGF-Ralpha induction does not require PGE2 synthesis. Instead, PGE2 downregulated PDGF-Ralpha protein and messenger RNA expression, and counteracted the IL-1beta-stimulated increase in [125I]PDGF-AA binding. Pretreatment of cells with indomethacin or the COX-2 specific inhibitor NS-398 attenuated the suppressive effect of exogenous PGE2 on PDGF-Ralpha, indicating that endogenous PGE2 released by IL-1beta treatment also contributed to downregulation of PDGF-Ralpha. PDGF-Rbeta expression was not altered by IL-1beta or PGE2. Pretreatment of myofibroblasts with IL-lbeta increased PDGF-stimulated mitogenesis, and this effect was blocked by coincubation with PGE2. In contrast, PGE2 enhanced epidermal growth factor- or basic fibroblast growth factor-2-stimulated cell proliferation approximately 50%. Because IL-1beta upregulates both PGE2 production and PDGF-Ralpha expression, these data suggest that PGE2 functions in a negative feedback loop to limit expression of PDGF-Ralpha and suppress PDGF-stimulated myofibroblast proliferation.

Interleukin-1beta-induced cyclooxygenase-2 expression requires activation of both c-Jun NH2-terminal kinase and p38 MAPK signal pathways in rat renal mesangial cells

The inflammatory cytokine interleukin-1beta (IL-1beta) induces cyclooxygenase-2 (Cox-2) expression with a concomitant release of prostaglandins from glomerular mesangial cells. We reported previously that IL-1beta rapidly activates the c-Jun NH2-terminal/stress-activated protein kinases (JNK/SAPK) and p38 mitogen-activated protein kinase (MAPK) and also induces Cox-2 expression and prostaglandin E2 (PGE2) production. The current study demonstrates that overexpression of the dominant negative form of JNK1 or p54 JNK2/SAPKbeta reduces Cox-2 expression and PGE2 production stimulated by IL-1beta. Similarly, overexpression of the kinase-dead form of p38 MAPK also inhibits IL-1beta-induced Cox-2 expression and PGE2 production. These results suggest that activation of both JNK/SAPK and p38 MAPK is required for Cox-2 expression after IL-1beta activation. Furthermore, our experiments confirm that IL-1beta activates MAP kinase kinase-4 (MKK4)/SEK1, MKK3, and MKK6 in renal mesangial cells. Overexpression of the dominant negative form of MKK4/SEK1 decreases IL-1beta- induced Cox-2 expression with inhibition of both JNK/SAPK and p38 MAPK phosphorylation. Overexpression of the kinase-dead form of MKK3 or MKK6 demonstrated that either of these two mutant kinases inhibited IL-1beta-induced p38 MAPK phosphorylation and Cox-2 expression but not JNK/SAPK phosphorylation and activation. This study suggests that the activation of both JNK/SAPK and p38 MAPK signaling cascades is required for IL-1beta-induced Cox-2 expression and PGE2 synthesis.

[New non-steroidal anti-rheumatic drugs: selective inhibitors of inducible cyclooxygenase]

MODE OF ACTION OF NON-STEROIDAL ANTI-INFLAMMATORY DRUGS: Non-steroidal anti-inflammatory drugs (NSAID) exert their major therapeutic and adverse effects by inhibition of prostanoid synthesis. Also the interactions with antihypertensive drugs and lithium are caused by this mechanism of action. Cyclooxygenation is a key enzymatic step in the synthesis of prostanoids. 1990 2 isoforms of the enzyme cyclooxygenase have been identified: Prostanoids synthesized by the constitutive cyclooxygenase (COX-1) are involved in physiological homeostasis. In contrast, the inducible cyclooxygenase (COX-2) produces large amounts of prostanoids, mainly contributing to the pathophysiological process of inflammation. COX-2 SELECTIVE NSAID: The discovery of the cyclooxgenase-isoenzymes ushered in a new generation of NSAID: A drug with selectivity for COX-2 would inhibit proinflammatory prostanoid synthesis while sparing physiologic prostanoid synthesis. Thus, a selective COX-2 inhibitor should be anti-inflammatory with less or no gastrointestinal or other NSAID-typical adverse effects. The experiences with currently used NSAID, which show an increasing incidence of side effects as COX-1 inhibition increases, and studies with the COX-2 selective NSAID salsalate and meloxicam, which have less adverse effects than nonselective COX inhibitors in equivalent antiphlogistic dosage, prove the concept of selective COX-2 inhibition to avoid the NSAID typical side effects. Newly developed drugs with a very high selectivity for COX-2 are now tested in clinical trials.

CONCLUSION

So far the results suggest, that selective and highly selective COX-2 inhibitors have significantly fewer gastrointestinal and renal adverse effects and do not inhibit platelet aggregation.

Induction of cyclooxygenase-2 by the activated MEKK1 --> SEK1/MKK4 --> p38 mitogen-activated protein kinase pathway

The mitogen-activated protein kinase (MAPK) cascade is believed to function as an important regulator of prostaglandin biosynthesis. Previously we reported that interleukin-1beta induces activation of JNK/SAPK and p38 MAPK with concomitant up-regulation of cyclooxygenase (Cox)-2 expression and prostaglandin E2 (PGE2) synthesis. Our experiments demonstrate that overexpression of DeltaMEKK1 (a constitutively active truncation mutant of MEKK1 containing the C-terminal 324 amino acids) increases Cox-2 expression and PGE2 production which is completely blocked by SC68376, a pharmacologic inhibitor of p38 MAPK. DeltaMEKK1 overexpression results in activation of both c-Jun N-terminal kinases/extracellular signal-regulated kinases (JNK/SAPK) and p38 MAPK. Furthermore, activation of MEKK1 increases SEK1/MKK4 but not MKK3 or MKK6 activity. These findings suggest that MEKK1 --> SEK1/MKK4 may function as an upstream kinase capable of activating both p38 MAPK and JNK/SAPK with subsequent induction of Cox-2 expression and PGE2 production. We also found that overexpression of the constitutively active form of SEK1 (SEK1-ED) increases both p38 MAPK and JNK/SAPK phosphorylation, and increases PGE2 production and Cox-2 expression. By comparison, overexpression of the dominant negative form of SEK1 (SEK1-AL) decreases the phosphorylation of both p38 MAPK and JNK/SAPK and reduces Cox-2 expression. Together, this data suggests a potential role for the MEKK1 --> SEK1/MKK4 --> p38 MAPK -->--> Cox-2 cascade linking members of the MAPK pathway with prostaglandin biosynthesis.

A classification of NSAIDs according to the relative inhibition of cyclooxygenase isoenzymes

Non-steroidal anti-inflammatory drugs (NSAIDs) are, as a group, the most frequently consumed drugs worldwide. They also cause the most, and often dangerous, side-effects reported to the US Food and Drug Administration, the majority of which are owing to damage of the gastrointestinal tract and kidneys. This explains the continuous interest of pharmacologists, clinical pharmacologists and pharmacoepidemiologists in this group of drugs. Based on an increasing body of data, J. Frölich proposes a simple alternative to the usual chemical classification of NSAIDs, allowing one to predict a drug's major effects according to its relative inhibition of the constitutive and inducible cyclooxygenase isoenzymes.

Platelet derived growth factor and subarachnoid haemorrhage: a study on cisternal cerebrospinal fluid

Platelet derived growth factor (PDGF) was identified as a powerful mitogenic growth factor which is released from activated platelets and has a marked activity as vasoconstrictor agent. In the present study we have measured cisternal cerebrospinal fluid (CSF) levels of PDGF in 72 patients operated on for intracranial aneurysm in order to verify whether it might be related to the clinical aspects of SAH with special regard to symptomatic vasospasm. CSF samples were obtained at surgery by cisternal puncture of the subarachnoid cistern the nearest to the aneurysm before aneurysm isolation and exclusion. The specimen were frozen in liquid nitrogen and stored at -80 degrees C until analysis. PDGF was measured using a commercially available reagent. Values are expressed as pg/ml of CSF. In 18 cases no radiological and clinical signs of SAH were detected and the mean cisternal CSF level of PDGF was 885.0 +/- 104.5 pg/ml; 20 patients were operated on between day 1 and 3 from the last SAH episode: mean cisternal CSF level of PDGF was 1917.5 +/- 459.4 pg/ml. In 34 patients treated with delayed surgery protocol, mean cisternal CSF level of PDGF was 995.3 +/- 73.8 pg/ml. Statistical analysis showed significant differences between groups (P: 0.011). In the subgroup of patients operated on within day 3 after SAH, 6 presented vasospasm and had mean cisternal CSF PDGF level which was significantly higher (P < 0.01) than in 14 patients without vasospasm. In the delayed "surgical" patients there was no significant difference in cisternal CSF levels of PDGF considering the occurrence of vasospasm. The results of the present study suggest that (a) after SAH there is a significant release of PDGF early after SAH and (b) higher levels of PDGF found in cisternal CSF of patients operated on within 72 hours after SAH may be predictive of symptomatic vasospasm.

Antimitotic actions of vasodilatory prostaglandins--clinical aspects

A variety of in-vitro antiatherosclerotic actions, among them those on vascular smooth muscle cells (mitotic activity, proliferation, extracellular matrix production), have been identified especially for PGE1 and PGI2, and proven in experimental animals. Ex-vivo data in humans are not yet available. We examined the effect of PGE1-, PGI2- and iloprost therapy of various duration (1-4 weeks) on smooth muscle cells (mitosis, proliferation, prostaglandin formation from exogenous and endogenous substrate) derived from vascular surgery samples. In-vivo PG-therapy decreases [3H]-thymidine incorporation as well as [35]S- and [14C]-proline uptake. These effects are dependent on the duration of treatment, PGE1 being trendwise more effective. Arachidonic acid conversion to PGI2 is significantly enhanced in activated smooth muscle cells of the plaque, both in the intima as well as in the media. Due to the activation of the gene for COX-2, the actual synthesis of PGI2 as well as the conversion rate to 6-oxo-PGF1 alpha are increased in activated smooth muscle cells, an effect being abolished by the PG's administered. It can thus be concluded that PG-therapy for advanced atherosclerosis seems to affect vascular smooth muscle cells beneficially, decreasing mitotic and proliferative activity as well as collagen and glycosaminoglycan synthesis. The somewhat less pronounced effect for PGI2 and iloprost could be explained by desensitization at the receptor level as preliminary findings suggest. This could become even more relevant if a long-term administrable stable (oral) analogue becomes available for routine therapy.

Down-regulation of cyclooxygenase-2 (COX-2) by interleukin-1 receptor antagonist in human monocytes

Cyclooxygenase (COX) is the key rate-limiting enzyme in the synthesis of prostanoids from arachidonic acid. Two isoforms of COX have been described in mammalian cells, referred to as cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2). COX-1 is a constitutively expressed enzyme; COX-2 is an inducible enzyme that appears to be expressed in inflamed tissue and following exposure to growth factors or cytokines, such as interleukin-1 (IL-1). The aim of the present study was to test if the antagonism on the binding of IL-1 to its cell-surface receptor by human recombinant IL-1 receptor antagonist (hrIL-1ra) may control the COX mRNA expression and prostaglandin E2 (PGE2) production by human monocyte cultures. Northern blot studies showed that hrIL-ra (500 ng/ml) had a strong inhibitory effect on inducible COX activity. The effect was evident after 6 hr incubation (2.7-fold decrease of mRNA COX-2 transcripts); and about a threefold decrease at 24hr incubation. A non-significant effect was observed with COX-1 transcripts. Induced PGE2 production by monocyte cultures treated with lipopolysaccharide (LPS) or interleukin-1 beta (IL-1 beta) was strongly inhibited in the presence of hrIL-1ra (500 ng/ml). In addition, a significant inhibition of COX-2 protein expression, as evaluated by Western blotting, was also observed. These data suggest that hrIL-1ra may be the key mediator in the down-regulation of the COX-2 inducible pathway.

Plasma stimulation of prostacyclin production by rat smooth muscle cells requires previous induction of phospholipase activity

Human normal platelet poor plasma (PPPn) stimulates prostacyclin (PGI2) production in a dose-dependent manner and after 15 to 60 min of incubation time when confluent rat smooth muscle cells (RSMC) were preincubated for 24 hours with fresh culture medium. This PGI2 production was independent of new protein synthesis, and was not observed in the cells maintained only in exhausted medium. The serum of fresh culture medium also induced a significant and transient increase of prostaglandin endoperoxide synthase (PGHS) activity as a function of preincubation time, which was dependent of protein synthesis. However, neither PGHS activity nor arachidonic acid availability limited the PPPn induced PGI2 synthesis in RSMC. Moreover, the previous addition of phorbol 13-myristate acetate also allowed the PPPn to induce PGI2 synthesis, that was significantly inhibited by a specific phospholipase A2 inhibitor. Furthermore, we found that PPPn induced a significant increase of intracellular calcium, and also stimulated PGI2 production at short incubation times due to its effect on phospholipases, and not by a direct supply of substrate. We conclude that a previous activation of phospholipase A2 was necessary to observe a significant and sustained PGI2 synthesis induced by PPPn in RSMC, and that the increase of intracellular calcium observed with PPPn might stimulate these previously activated phospholipases.

Effect of high potassium diets on the vascular and renal prostaglandin system in stroke-prone spontaneously hypertensive rats

High potassium (K) diets are known to have a protective effect on the endothelium and the kidney against hypertensive injury independent of blood pressure change. Vasodepressor prostaglandins (PGs) have been shown to be cytoprotective in various tissues. This study investigated the effect of high K diets on the vascular and renal eicosanoid system in stroke-prone spontaneously hypertensive rats (SHRsp). Eicosanoid production by the aorta and eicosanoid content in the renal cortex were examined in SHRsp rats fed high NaCl diets containing either 0.5% K (normal) or 2.1% K (high). Although the high K diet did not affect the blood pressure, SHRsp on the high K diet had less thickening of the aortic wall than SHRsp on the normal K diet (-15%, p < 0.001). The aortic strip of the high K SHRsp produced less vasodepressor PG than that of the normal K SHRsp when they were incubated in a medium (PGI2 -45%, p < 0.003; PGE2 -34%, p < 0.001). Furthermore, when the aorta was perfused in a chamber at hypertensive pressure, again the high K aorta showed reduced PGI2 production as compared with the normal K aorta (intravascular side -52%, p < 0.01). Eicosanoid content in the renal cortex was not significantly different between the normal K and the high K SHRsp (PGI2 79 vs 87 ng/g dry weight; PGE2 214 vs 233 ng/g dry weight). Thus, the high K diet reduced vascular eicosanoid production but did not alter eicosanoid content in the renal cortex. The reduced vascular eicosanoid production in the high K SHRsp may reflect the reduced necessity for cytoprotective vasodepressor PG against vascular injuries.

Induction of cyclooxygenase protein and stimulation of prostaglandin E2 release by epidermal growth factor in cultured guinea pig gastric mucous cells

The present study was undertaken to investigate whether epidermal growth factor (EGF) could stimulate prostaglandin E2 release, and if so, by what mechanism EGF would exert such an effect in gastric mucosal cells. In cultured guinea pig gastric mucous cells, EGF dose-dependently stimulated prostaglandin E2 release, with maximal stimulation observed at 10 ng/ml. EGF stimulated an increase in cyclooxygenase activity, which was reduced by protein synthesis inhibitor, actinomycin D, and cycloheximide. EGF also stimulated the enzyme protein synthesis estimated by Western blot analysis, whereas EGF did not stimulate phospholipase A2 activity. These results suggest that such an effect of EGF of de novo synthesis of cyclooxygenase protein and prostaglandin E2 release may be involved at least in part in the mechanism of EGF-induced local regulation of gastric mucosal integrity.

IL-3 and IL-5 enhance the production of LTB4 stimulated by calcium ionophore in rat basophilic leukemia cells

To determine the regulatory mechanism of Leukotriene (LT) B4 synthesis by cytokines, we investigated the regulation of LTB4 generation by short-term (30 min) priming and long-term (15 h) enzyme-inducing actions of the four cytokines interleukin (IL)-3, IL-5, tumor necrosis factor alpha (TNF-alpha), and transforming growth factor alpha (TGF-alpha) in rat basophilic leukemia-1 (RBL-1) cells. Pretreatment of cells with IL-3 or IL-5 for 30 min increased A23187- (5x10(-9)M) stimulated synthesis of LTB4 by three to four times over control levels. However, IL-3 or IL-5 lacked this effect when stimulated with exogenous arachidonic acid A at 10(-4)M. TNF-alpha and TGF-alpha had no priming effect on LTB4 synthesis following stimulation with either A23187 (5x10(-9)M) or AA(10(-4)M). Stimulation with the calcium ionophore (A23187)(10(-5)M) or AA(10(-4)M) following 15-h exposure to these cytokines had no effect. These results suggest that IL-3 and IL-5 increase the production of LTB4 by priming the activity of phospholipase A2(PLA2) without inducing enzymes in the arachidonate 5-lipoxygenase pathway. Such a priming effect may be important in regulating the development of allergic and other diseases involving the inflammatory reaction.

Different intracellular locations for prostaglandin endoperoxide H synthase-1 and -2

The subcellular locations of prostaglandin endoperoxide synthase-1 and -2 (PGHS-1 and -2) were determined by quantitative confocal fluorescence imaging microscopy in murine 3T3 cells and human and bovine endothelial cells using immunocytofluorescence with isozyme-specific antibodies. In all of the cell types examined, PGHS-1 immunoreactivity was found equally distributed in the endoplasmic reticulum (ER) and nuclear envelope (NE). PGHS-2 immunoreactivity was also present in the ER and NE. However, PGHS-2 staining was twice as concentrated in the NE as in the ER. A histofluorescence staining method was developed to localize cyclooxygenase/peroxidase activity. In quiescent 3T3 cells, which express only PGHS-1, histofluorescent staining was most concentrated in the perinuclear cytoplasmic region. In contrast, histochemical staining for PGHS-2 activity was about equally intense in the nucleus and in the cytoplasm, a pattern of activity staining distinct from that observed with PGHS-1. Our results indicate that there are significant differences in the subcellular locations of PGHS-1 and PGHS-2. It appears that PGHS-1 functions predominantly in the ER whereas PGHS-2 may function in the ER and the NE. We speculate that PGHS-1 and PGHS-2 acting in the ER and PGHS-2 functioning in the NE represent independent prostanoid biosynthetic systems.

Adenomatous polyposis coli, protein kinases, protein tyrosine phosphatase: the effect of sulindac

A putative explanation of the effect of sulindac on adenomatous colon and duodenal polyps from clinical observations and related in vitro experiments is presented. In cells with mutant APC genes, persistent high prostaglandin content of polyps leads to desensitization, downregulation of adenylate cyclase, uncoupling of cAMP synthesis from prostaglandin, and inactivation of protein kinase A (PKA). It is suggested that in normal cells, (APC) protein binds to catenins and microtubules to maintain structure and contribute to cell-cell communication, adherence, and the dephosphorylated state, a necessary condition for such functions. Cells with mutant APC product become isolated, deprived of communication and adhesion to other epithelial cells, overphosphorylated, and without corrective capability. The latter is largely due to downregulation of cAMP synthesis and protein kinase A activity secondary to high prostaglandin. Three main biochemical defects ensue: (1) the restrictive influence of PKA catalyzed phosphorylation of Raf-1 kinase and resultant effects on the MAP kinase cascade and transcription is lost, (2) the transcription of immediate early genes, including cyclooxygenase is stimulated, and (3) the stimulation of protein tyrosine phosphatase (PTPase) by PKA is in abeyance. These putative abnormalities are reversed by inhibition of cyclooxygenase-1 by sulindac. cAMP synthesis and PKA activity return to normal. PKA catalyzed phosphorylations block Raf-1 kinase at the confluence of the Ras and protein kinase C pathways. The MAP kinase cascade is inhibited as is transcription of immediate early genes. At the same time PKA stimulates PTPase, which dephosphorylates the cytoskeleton and restores cell-cell communication, adherence, and structure. The transformed phenotype is circumvented by adjustment of the phosphorylation state and mutant cells rejoin the epithelial community. The redox state of cytoplasm in mutant cells may be shifted toward reduction.

Signal transduction in atherosclerosis: second messengers and regulation of cellular cholesterol trafficking

The data summarized in this review demonstrate that the regulation of intracellular cholesterol trafficking is mediated not only by extracellular lipoprotein concentrations and transcriptional responses to alterations in intracellular free cholesterol content. Rather, the modulation of cholesterol trafficking is also regulated by the products synthesized following activation of signal transduction pathways originating at the cell surface. Furthermore, we have identified those cell-derived factors which utilize these signal transduction pathways to elicit alterations in cholesterol trafficking, and demonstrated the importance of the generation of second messengers, most notably eicosanoids, and cyclic AMP in promoting a modulatory influence on specific pro-atherogenic effects of mitogens.

Potentiation by cholesterol and vitamin D3 oxygenated derivatives of arachidonic acid release and prostaglandin E2 synthesis induced by the epidermal growth factor in NRK 49F cells: the role of protein kinase C

We have previously demonstrated that oxysterols and calcitriol potentiate arachidonic acid (AA) release and prostaglandin (PG) synthesis when NRK cells (fibroblastic clone 49F) are activated by foetal calf serum. As serum is essential for a full oxysterol effect, we hypothesized that these compounds could act on one or more of the events triggered by serum growth factor binding to their specific receptors and leading to PLA2 activation; we showed that the oxysterol effect on AA release is synergistic with, but not fully dependent on, protein kinase C (PKC) activity and Ca2+ ion fluxes, suggesting that oxysterols could effect early events in the cell signalling pathway. In the present paper, we investigated the effect of some oxysterols and calcitriol on epidermal growth factor (EGF)-induced AA release and PGE2 synthesis in NRK cells. The clear potentiation of EGF effect by most of the oxygenated sterols--chiefly when polyoxidized--cannot be explained by a modification of EGF high affinity binding site number which was only moderately increased after a 4 h incubation of cells with these compounds, and moreover was not related to the ability of a given oxysterol to increase PLA2 activity; whatever the compound, the dissociation constant (Kd) of either a high or low affinity binding site was unchanged (respectively, 3.5 x 10(-11) M and 4.4 x 10(-10) M). Genistein, a known inhibitor of EGF receptor tyrosine kinase, changed neither the EGF effect on AA release nor its potentiation by oxysterol, whereas it inhibited PGE2 synthesis in both situations. PKC activation by phorbol ester TPA increased the effect of EGF alone as well as the oxysterol potentiating effect, whereas PKC down-regulation strongly decreased both of these effects, showing that both are dependent on PKC activity. Nevertheless staurosporine, a PKC inhibitor, did not reproduce the effects of PKC down-regulation on EGF activation: stimulatory when AA release was induced by EGF alone, inhibitory when AA release is induced by TPA alone, this compound did not modify the oxysterol potentiating effect. In conclusion, the potentiating effect of oxysterols on AA release seems to be exerted downstream to the growth factor receptor (as demonstrated here with EGF) and probably at the PKC level, but not exclusively.

Human peritoneal mesothelial cell prostaglandin synthesis: induction of cyclooxygenase mRNA by peritoneal macrophage-derived cytokines

Increasing evidence suggests that the mesothelial cell contributes to the control of inflammation in both the normal and inflamed peritoneal cavity. The present study examines the regulation of prostaglandin production by human peritoneal mesothelial cells (HPMC) following stimulation with peritoneal macrophage-conditioned medium and the cytokines interleukin-1 beta (IL-1 beta) and tumor necrosis factor-alpha (TNF-alpha). IL-1 beta and TNF-alpha stimulated significant release of prostaglandin above background levels in a time and dose dependent manner. Stimulation of HPMC with IL-1 beta (500 pg/ml) or TNF-alpha (100 pg/ml) for 24 hours resulted in the release of 24.5 +/- 4.3 (N = 11) (z = 3.40, P < 0.001 vs. control) and 19.4 +/- 4.5 (N = 10; z = 3.29, P < 0.001 vs. control) pg 6-keto-PGF1 a/micrograms cellular protein, respectively. Pretreatment of HPMC with dexamethasone (10(-6) to 10(-9) M) inhibited both constitutive and cytokine stimulated prostaglandin synthesis in a dose dependent manner. Both PMø-CM and PMø-S.epiCM stimulated 6-keto-PGF1 alpha and PGE2 synthesis by HPMC in a time and dose dependent manner (PMø-S.epiCM >> PMø-CM). Co-incubation of HPMC with PMø-S.epiCM in the presence of anti-IL-1 beta and/or anti-TNF-alpha antibody, interleukin-1 receptor antagonist or soluble TNF receptor (TNF p75) significantly reduced the capacity of these supernatants to stimulate prostaglandin synthesis. Exposure of HPMC to cytokines or PMø-S.epiCM resulted in the time dependent increase in the levels of both Cox-1 and Cox-2 mRNA as assessed by RT/PCR analysis with the greatest increase being seen for Cox-2. These data demonstrate specific stimulation of eicosanoid metabolism in HPMC by peritoneal macrophage derived cytokines, indicating the possible importance of these mediators in the activation of intraperitoneal prostaglandin synthesis. HPMC prostaglandins might act as important pro/anti-inflammatory mediators contributing to a cytokine network in the peritoneal cavity during CAPD peritonitis.

Regulation of cyclooxygenase-2 expression in aortic smooth muscle cells

Activation of the gene for inducible cyclooxygenase (cyclooxygenase-2 [Cox-2], prostaglandin endoperoxide synthase) is an early response to injury in vascular smooth muscle cells. We used in vitro and in vivo models to demonstrate that activation of quiescent smooth muscle cells by mitogens leads to a rapid, short-term rise in mRNA for Cox-2, followed by synthesis of new Cox-2 enzyme protein and a marked increase in prostaglandin production that depends on new enzyme synthesis. Moreover, the Cox-2 mRNA response observed in smooth muscle cells differs in both time and degree, depending on the particular mitogenic stimulus. Serum, platelet-derived growth factor, epidermal growth factor, and thrombin are strong inducers of Cox-2 mRNA, whereas acidic and basic fibroblast growth factors and interleukin-1 alpha are weak inducers. In contrast to the transient activation of Cox-2 in vitro after introduction of a mitogenic stimulus, the Cox-2 response after in vivo vascular injury extends over many days and may represent protracted cellular activation. During induction of Cox-2 message and protein, expression of constitutive cyclooxygenase (Cox-1) remains unchanged, however. These data suggest a pathophysiological role for Cox-2 in the early modulation of vascular responses to injury.

Production of PGE2 by bovine cultured airway smooth muscle cells and its inhibition by cyclo-oxygenase inhibitors

1. Prostaglandin E2 (PGE2) is thought to be an important inhibitory modulator of inflammatory processes in the airway. It inhibits inflammatory cell function and cholinergic neurotransmission in vitro and roles have been postulated in vivo in refractoriness and in the mechanism of action of the diuretic agent, frusemide. 2. The production of PGE2 by bovine cultured airway smooth muscle cells has been studied under a range of conditions. The effects of cyclo-oxygenase inhibitors (flurbiprofen, indomethacin, acetyl salicylic acid) on serum-induced production of PGE2 were assessed over a range of concentrations (10(-7)-10(-4) M). 3. Serum-stimulated production of PGE2 in control wells ranged from 350 to 800 ng PGE2 ml-1 in cells from different animals. All three cyclo-oxygenase inhibitors inhibited PGE2 production with an order of potency, flurbiprofen > indomethacin > acetyl salicylic acid. Log IC50 values were -6.24 for flurbiprofen, -5.23 for indomethacin and -3.50 for acetyl salicylic acid. 4. PGE2 production was stimulated by arachidonic acid (10(-5) M) or addition of the proinflammatory mediator, bradykinin (10(-8)-10(-5) M). 5. Incubation of cells for 24 h with 5 bromo deoxyuridine (BRDU) (10(-4) M) to prevent DNA synthesis did not alter PGE2 production in response to serum, suggesting that it was not a function of proliferation per se. 6. Our study suggests that airway smooth muscle may be an important source of PGE2. Production of PGE2 may be a novel feedback mechanism whereby airway smooth muscle cells can negatively modulate airways inflammation. The differing potencies of the cyclo-oxygenase inhibitors may explain the contrasting effect of these drugs in recent studies in asthma.

The effect of sulindac on colon polyps: circumvention of a transformed phenotype--a hypothesis

Sulindac suppresses the growth of colon polyps in Gardner syndrome and familial adenomatous polyposis. The mechanism of action is not known. The problems are to ascertain the significance of high prostaglandin concentrations in transformed cells, colon polyps and cancers and to explain how sulindac restores normal growth patterns. A few clinical observations and an abundance of experimental data can be integrated to produce a reasonable model based on current biochemical and physiologic concepts. A fundamental defect in the formation of colon polyps is mutation of the APC (adenomatous polyposis coli) gene that leads to inadequate suppression of proliferation. There is high PGE2 content in colon polyps and cancers, presumably the result of stimulation by protein kinase C (PKC). In small quantities it stimulates cyclic AMP production but with persistent high concentrations it desensitizes and down-regulates specific PG receptors and inactivates adenylate cyclase, cAMP synthesis, and the cAMP-dependent mechanism for control of proliferation. The PKC pathway is thereby unopposed. It is hypothesized that restriction of PG synthesis by sulindac is accompanied by resensitization of PG receptors, and reactivation of the cAMP-dependent pathway for control of cell growth. It is further postulated that restoration of cAMP synthesis and protein kinase A activity converts a functionally inadequate mutant APC suppressor gene to one sufficient to inhibit colon polyp formation.

De novo synthesis of phospholipase A2 and prostacyclin production by proliferating rat smooth muscle cells

We investigated the role of phospholipase A2 (PLA2) in cell cycle-dependent alterations of endogenous prostacyclin (PGI2) synthesis in aortic smooth muscle cells in culture (VSMC) from Wistar Kyoto rats. Randomly cycling VSMC generated more PGI2 than the stationary cells. Cell cycle analysis showed that PGI2 production capacity was increased from the G0/G1 through the early DNA synthetic (S) phases. Enzyme analysis revealed that, although there were different mechanisms underlying this increase in the PGI2 production during the G0/G1, the peak at 4 hours coincided with a sharp increase in PLA2 activity. This increase in PLA2 activity was preceded by an increased expression of functional PLA2 messenger RNA, and protein synthesis inhibition prevented most of the increase in PGI2 production at 4 hours. These data indicate that endogenous PGI2 generation is mainly increased during the G0/G1 period and that this event is secondary to de novo synthesis of PLA2 and probably, at least in part, to cyclooxygenase induction. This mechanism provides a negative feedback regulating VSMC proliferation.

Attenuated prostaglandin formation in peroxisomal-deficient human skin fibroblasts

Peroxisomal-deficient skin fibroblasts from patients with Zellweger's syndrome or infantile Refsum's disease produced fewer prostaglandins than normal skin fibroblasts. Radioimmunoassay indicated a 45-55% decrease in prostaglandin E2 (PGE2) production when Zellweger's fibroblasts were incubated with arachidonic acid. This deficiency was not overcome by pretreatment of the Zellweger's fibroblasts with media containing arachidonic acid, and it was not due to channeling of arachidonic acid into other eicosanoid products. Modifications in the peroxide tone of the Zellweger's fibroblasts by addition of H2O2 or catalase failed to increase PGE2 production. Using Northern analysis, we were unable to detect an mRNA transcript for PGH synthase in unstimulated Zellweger fibroblasts but identified a 4.2-kb mRNA transcript after treatment with phorbol myristate acetate (PMA). Treatment for 6 h with 10 nM PMA raised PGE2 production in normal and Zellweger fibroblasts to equivalent levels. These increases were prevented by addition of H-7, staurosporine, cycloheximide, or actinomycin D. Our findings suggest that the reduced PGE2 production in peroxisomal deficient fibroblasts is due to a decrease in PGH synthase mRNA. The reduction in PGH synthase can be overcome by treatment of the cells with agents which enhance gene expression.