Vasoactive eicosanoids in the rat heart: Clues to a contributory role of cardiac throm☐ane to post-ischaemic hyperaemia

To assess the potential role of vasoactive cardiac eicosanoids in the modulation of coronary flow, we measure thromboxane(TX)B2, 6-keto-prostaglandin(PG)F1 alpha, PGE2 and sulphido-peptide leukotrienes (LTC4, D4, E4) in the coronary effluent of isolated perfused rat heart in both baseline and post-ischaemic conditions. Leukotrienes were undetectable. The order of production rate for the other eicosanoids was 6-keto-PGF1 alpha > TXB2 > PGE2. Production of such substances was increased about seven-fold over control after 5 min. global ischaemia; experiments with hypoxia showed that this was due to an actual increase in synthesis and not to a washout effect. A platelet source for TXB2 was excluded by 111In platelet labelling experiments. We assessed relative sensitivity to inhibition of cardiac TX synthesis relative to production of 6-keto-PGF1 alpha to inhibition by aspirin, ibuprofen, diclofenac and the specific thromboxane synthase inhibitor OKY-046. Aspirin, ibuprofen and diclofenac decreased 6-keto-PGF1 alpha production at a concentration always greater than required for a similar extent of TX inhibition. On the other hand a selective inhibition (> 90%) of TX was observed in the presence of OKY-046. Regression analysis of various 6-keto-PGF1 alpha/TXB2 ratios, as obtained in these different conditions, vs coronary flow, showed no correlation in baseline conditions, but a significant positive correlation (r = 0.59, P < 0.01) for post-ischaemic values. These data suggest a role for cardiac eicosanoids, including a non-platelet, cardiac-derived TX, in modulating the hyperaemic response in the isolated rat heart.     

Interactions between epidermal growth factor-mediated autocrine regulation and linoleic acid-stimulated growth of a human prostate cancer cell line.

Human prostate cancer (PC) cell lines possess epidermal growth factor (EGF) receptors and secrete EGF-related polypeptides. We used an EGF receptor-blocking antibody (anti-EGF.R) to demonstrate a functional autocrine loop, as well as the interaction between this and the effects of linoleic acid (LA), an omega-6 fatty acid, on PC cell growth. The anti-EGF.R competed effectively with [125I]EGF for receptors on DU145 PC cells, and on a high-passage DU145 variant (DU145M); when added to the culture medium, it suppressed both DU145 and DU145M cell growth in a dose-dependent manner. LA, a precursor for eicosanoid synthesis, had little effect on DU145 cell growth rate but stimulated DU145M growth in a concentration-related manner over a range of 0.25-2.0 micrograms/ml. anti-EGF.R (10(-9) M) caused suppression of LA-stimulated growth of DU145M cells in serum-free medium, which was prevented by the addition of 2 nM EGF. We conclude that an EGF.R-mediated autocrine loop is involved in PC cell growth regulation and that at least one site of action may be the synthesis of eicosanoids from their LA precursor.     

Efficacy of recombinant granulocyte colony-stimulating factor (rhG-CSF) in experimental colitis

Inflammatory bowel disease is associated with mucosal neutrophil recruitment and activatation, mediated in part by arachidonic acid metabolites. G-CSF attenuates the immune response to sepsis and ameliorates glycogen storage disease Ib-related colitis. These actions may be effected through the shedding of neutrophil adhesion molecules, or inhibition of proinflammatory mediator synthesis. Immune complex colitis was used to evaluate the effect of rhG-CSF on colonic mucosal inflammation, neutrophil recruitment and the generation of eicosanoids. Immune complex colitis was induced in White New Zealand rabbits. Animals were pretreated with rhG-CSF either 24 h before induction, or at induction, with dosages of 50 and 200 μg/kg. rhG-CSF caused a time- and dose-dependent neutrophilia in all animals. Pretreatment with rhG-CSF resulted in increased tissue myeloperoxidase levels, despite a histologically similar mucosal polymorphonuclear cell infiltrate between treated and control colitis groups. Leukotriene B₄ (LTB₄) and thromboxane B₂ (TXB₂) dialysis fluid levels were lower in treated animals, in particular in the groups receiving two doses (LTB₄: both P < 0.01; TXB₂: both P < 0.01. Prostaglandin E₂ (PGE₂) levels in dialysis fluid of the rhG-CSF-treated animals showed no difference from controls. In this model of experimental colitis, high-dose therapy with G-CSF resulted in a marked decrease of proinflammatory mediators, but mucosal generation of the protective PGE₂ was preserved. These results suggest that prolonged high-dose therapy with G-CSF may have anti-inflammatory effects in colitis.     

12-Lipoxygenases and 12(S)-HETE: role in cancer metastasis

Arachidonic acid metabolites have been implicated in multiple steps of carcinogenesis. Their role in tumor cell metastasis, the ultimate challenge for the treatment of cancer patients, are however not well-documented. Arachidonic acid is primarily metabolized through three pathways, i.e., cyclooxygenase, lipoxygenase, and P450-dependent monooxygenase. In this review we focus our attention on one specific lipoxygenase, i.e., 12-lipoxygenase, and its potential role in modulating the metastatic process. In mammalian cells there exist three types of 12-lipoxygenases which differ in tissue distribution, preferential substrates, and profile of their metabolites. Most of these 12-lipoxygenases have been cloned and sequenced, and the molecular and biochemical determinants responsible for catalysis of specific substrates characterized. Solid tumor cells express 12-lipoxygenase mRNA, possess 12-lipoxygenase protein, and biosynthesize 12(S)-HETE [12(S)-hydroxyeicosatetraenoic acid], as revealed by numerous experimental approaches. The ability of tumor cells to generate 12(S)-HETE is positively correlated to their metastatic potential. A large collection of experimental data suggest that 12(S)-HETE is a crucial intracellular signaling molecule that activates protein kinase C and mediates the biological functions of many growth factors and cytokines such as bFGF, PDGF, EGF, and AMF. 12(S)-HETE plays a pivotal role in multiple steps of the metastatic cascade encompassing tumor cell-vasculature interactions, tumor cell motility, proteolysis, invasion, and angiogenesis. The fact that 12-lipoxygenase is expressed in a wide diversity of tumor cell lines and 12(S)-HETE is a key modulatory molecule in metastasis provides the rationale for targeting these molecules in anti-cancer and anti-metastasis therapeutic protocols.     

Effect of leukotriene C4D4 antagonist on colonic damage induced by intracolonic administration of trinitrobenzene sulfonic acid in rats

We examined the effects of eicosanoid antagonists on colonic damage induced by trinitrobenzene sulfonic acid (TNB) in a rat inflammatory bowel model. TNB (30 mg) dissolved in 0.25 ml of 50% ethanol, was given intrarectally. The appropriate doses of ONO-1078 (a leukotriene C₄D₄ antagonist), ONO-4057 (a leukotriene B₄ antagonist), and OKY-046 (a thromboxane A₂ synthetase inhibitor) were given to obtain the same blood level, either 4 h before (pre-treatment model) or 24 h after (the post-treatment model) the administration of TNB (n=8 in all groups). Drugs were given once daily for 6 days through a gastric feeding tube. Autopsy was performed on the 7th day. Colonie damage was assessed in terms of colonie damage scores, and myeloperoxidase (MPO) activity and eicosanoid concentrations in colonie tissues were measured. Compared with the group given TNB alone, the colonie damage score was reduced to 10% in the pre-treatment model with ONO-1078, but the score was not reduced in other groups, MPO activity was not changed in any group. The concentration of leukotriene C₄ was reduced with ONO-1078 treatment, in both pre- and post-treatment models. These results demonstrated that a leukotriene C₄D₄ antagonist reduced colonie inflammation; however, its anti-inflammatory effect was limited in this colitis model.     

Oral prostaglandin (PGE2) therapy for chronic viral hepatitis B and C

The cytoprotective effects of prostaglandins have been utilized in the prevention of hepatitis B virus reactivation after liver transplantation. This pilot study evaluated the effects of oral prostaglandin E₂ (PGE₂) in chronic viral hepatitis B and C. Twenty patients with chronic hepatitis B and 20 patients with chronic hepatitis C received 4mgday^–1 PGE₂ for 6 months. The lymphocyte antiviral enzyme 2',5'-oligoadenylate synthetase (2',5'-OAS) and peripheral blood monocyte procoagulant activity (PCA) were measured before, during and after the treatment. Three of 20 hepatitis B and five of 20 hepatitis C patients withdrew from the study. Eight of 17 hepatitis B patients responded: in seven of these eight patients, serum alanine aminotransferase (ALT) levels normalized; loss of viral replication was sustained in all eight patients; and seroconversion from hepatitis Be antigen (HBeAg) to hepatitis Be antibody (HBeAb) positivity occurred in seven patients over the 48-week duration of this study. In 14 of the 15 hepatitis C patients, hepatitis C virus (HCV) RNA remained detectable and the serum ALT levels remained elevated. 2',5'-OAS levels and PCA values did not correlate with other markers of response to PGE₂ therapy in either chronic hepatitis B or C. In summary, PGE₂ was associated with sustained loss of viral replication in 47% of chronic hepatitis B patients; no beneficial effects were apparent in chronic hepatitis C.     

Spinal cord injury and protection

Subsequent to traumatic injury of the spinal cord, a series of pathophysiological events occurs in the injured tissue that leads to tissue destruction and paraplegia. These include hemorrhagic necrosis, ischemia, edema, inflammation, neuronophagia, loss of Ca2+ from the extracellular space, and loss of K+ from the intracellular space. In addition, there is trauma-initiated lipid peroxidation and hydrolysis in cellular membranes. Both lipid peroxidation and hydrolysis can damage cells directly; hydrolysis also results in the formation of the biologically active prostaglandins and leukotrienes (eicosanoids). The time course of membrane lipid alterations seen in studies of antioxidant interventions suggests that posttraumatic ischemia, edema, inflammation, and ionic fluxes are the result of extensive membrane peroxidative reactions and lipolysis that produce vasoactive and chemotactic eicosanoids. A diverse group of compounds has been shown to be effective in ameliorating spinal cord injury in experimental animals. These include the synthetic glucocorticoid methylprednisolone sodium succinate (MPSS); the antioxidants vitamin E, selenium, and dimethyl sulfoxide (DMSO); the opiate antagonist naloxone; and thyrotropin-releasing hormone (TRH). With the exception of TRH, all of these agents have demonstrable antioxidant and/or anti-lipid-hydrolysis properties. Thus the effectiveness of these substances may lie in their ability to quench membrane peroxidative reactions or to inhibit the release of fatty acids from membrane phospholipids, or both. Whatever the mode of action, early administration appears to be a requirement for maximum effectiveness.     

Metabolomics revealed decreased level of omega‐3 PUFA‐derived protective eicosanoids in pregnant women with pre‐eclampsia

Pre‐eclampsia (PE) is considered a leading cause of mortality and morbidity in pregnant women worldwide. Eicosanoids derived from polyunsaturated fatty acids (PUFAs) might play an important role in the occurrence and development of PE. Omega‐3 PUFAs are nutrients that are popular supplements for pregnant women and can reduce blood pressure. However, the levels of eicosanoids derived from omega‐3 PUFAs in women with PE is not clear. The purpose of this study was to investigate the eicosanoid metabolic signature of PE. We performed a case–control study using data for pregnant women (n = 10) with PE and normotensive pregnant women (n = 10). We investigated the difference in eicosanoid profile between the groups by LC‐MS/MS‐based metabolomics. The plasma levels of arachidonic acid metabolites and some of the lipoxygenase metabolites of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) showed an increasing trend, and those of the cytochrome P450 metabolites of EPA and DHA were decreased in women with PE. Levels of leukotriene B4, 14,15‐dihydroxy‐eicosatetraenoate, 16‐hydroxydocosahexaenoic acid and 8,9‐epoxy eicosatetraenoic acid were significantly correlated with PE occurrence. These eicosanoids might take part in the progression of PE in pregnant women.     

Umbilical cord prostaglandins in term and preterm parturition

Objective: Prostaglandins (PGs) are considered the universal mediators of parturition. Amniotic fluid PGE₂ and PGF_2α concentrations increase before the onset of spontaneous labor at term, as well as during labor. This study was conducted to determine if the concentrations of umbilical cord PGE₂ and PGF₂α change with advancing gestational age, spontaneous labor at term, and preterm labor (with and without funisitis).

Methods: Umbilical cord (UC) tissue samples were obtained from women (N?=?158) with singleton pregnancies in the following groups: (1) term deliveries without labor (TNL; n?=?20); (2) term deliveries with labor (TIL; n?=?20); (3) spontaneous preterm deliveries (sPTD) with (n?=?20) and without acute funisitis (n?=?20); and (4) preeclampsia without labor (n?=?78). The concentrations of PGs were determined in different locations of the UC. PGE₂ and PGF_2α were measured by specific immunoassays. Non-parametric statistics were used for analysis.

Results: (1) In spontaneous preterm deliveries, the median UC PGE₂ concentration was higher in cases with funisitis than in those without funisitis (233.7?pg/µg versus 87.4?pg/µg of total protein, p?=?0.001); (2) the median UC PGE₂ concentration in sPTD with funisitis was also higher than that obtained from samples who had undergone labor at term (233.7?pg/µg versus 116.1?pg/µg of total protein, p?=?0.03); (3) the UC PGE₂ and PGF_2α concentration increased as a function of advancing gestational age before 36 weeks (PGE₂: ρ?=?0.59, p?<?0.001; PGF_2α: ρ?=?0.39, p?=?0.01), but not after 36 weeks (PGE₂: ρ?=??0.1, p?=?0.5; PGF_2α: ρ?=??0.2, p?=?0.2); (4) the median UC concentrations of PGE₂ and PGF_2α at term was similar in samples obtained from women with and without labor (PGE₂: TNL 133.7?pg/µg versus TIL 116.1?pg/µg of total protein, p?=?0.9; PGF_2α: TNL 8.4?pg/µg versus TIL 8.1?pg/µg of total protein, p?=?0.7); and (5) there was no correlation between UC PG concentration and gestational age at term pregnancy (PGE₂: ρ?=?0.01, p?=?0.9; PGF_2α: ρ?=?0.07, p?=?0.7).

Conclusions: (1) PGE₂ concentrations in the UC are higher in the presence of acute funisitis than in the absence of this lesion; (2) spontaneous labor at term was not associated with a change in the UC concentration of PGE₂ and PGF_2α; and (3) the UC concentrations of PGE₂ and PGF_2α increased as a function of gestational age. We propose that UC PGs act as inflammatory mediators generated in the context of fetal systemic inflammation.