Eicosanoids最新文献

Osteoid osteoma is a benign osteoid-forming tumor of the bone characterized by pain which is relieved by nonsteroidal anti-inflammatory drugs. Very high levels of prostaglandins have been found in the lesion. In nine patients with osteoid osteoma, prostaglandin E2 (PGE2) and prostacyclin (PGI2) synthesis in explants from the nidus incubated in vitro yielded 947.3 +/- 482.6 (mean +/- SD) and 340.2 +/- 178.1 pg/mg of wet tissue respectively, values 32 and 49 times higher than in fragments of normal bone. In eight patients the excretion rate of the major urinary metabolite of PGI2, i.e. 2,3-dinor-6-keto-PGF1 alpha, was nearly double the control value (499 +/- 93 vs 257 +/- 117 pg/mg of creatinine; mean +/- SD). In six of them, from whom urine was collected 1 month after surgery, urinary 2,3-dinor-6-keto-PGF1 alpha decreased significantly (P less than 0.01) from 487 +/- 100 to 229 +/- 52 pg/mg creatinine. Urinary 6-keto-PGF1 alpha, largely a reflection of intrarenal PGI2 synthesis, was comparable to the control group (4.6 +/- 0.9 vs 4.5 +/- 1.0 ng/h, respectively) and remained unchanged after operation. These results suggest an enhanced PGI2 biosynthesis in vivo in patients with osteoid osteoma. This abnormality of arachidonate metabolism is consistent with enhanced biosynthetic capacity of the tumor in vitro, and is reversible upon its removal.

Intact decidual stromal cells and macrophages metabolized 3H-prostaglandins E2 and F2 alpha although the rate of metabolism of both prostaglandins was higher in the decidual macrophages than in decidual stromal cells. PGE2 was metabolised mainly to 13,14-dihydro-15-keto-PGE2 together with smaller quantities for PGB2 and 13,14-dihydro-15-keto-PGA2, whereas PGF2 alpha was metabolised to 13,14-dihydro-15-keto-PGF2 alpha, PGE2 and PGB2, and it seems that similar metabolic pathways were present in both cell types. The half-lives of both prostaglandins (8.8 +/- 3.4 h for PGE2 and 15.0 +/- 8.2 h for PGF2 alpha sigma in the presence of decidual stromal cells show that during incubations lasting more than a few hours significant metabolism of prostaglandins, especially PGE2, will occur, and that this must be allowed for in any assessment of total prostaglandin production by cultured decidual cells. One of the 6 tissue samples examined metabolised both prostaglandins very rapidly, such that the half-lives were less than 2 h. This may be the result of the presence of very high levels of metabolic enzymes, since the overall pattern of metabolites was similar to that from the other 5 samples.

Endotoxin stimulates macrophages to synthesize membrane-associated inflammatory mediators including eicosanoids and procoagulant activity (PCA). Alpha linolenic acid, a component of linseed oil, is metabolized to eicosapentaenoic acid, which may replace arachidonic acid in membrane phospholipids. Thus, ingestion of linseed oil may alter the generation of eicosanoids, PCA and other membrane-dependent responses. This study compared the in vitro endotoxin-induced synthesis of eicosanoids and expression of PCA by peritoneal macrophages obtained from rats fed a control diet and rats fed a diet enriched with linseed oil. The effect of endotoxin on in vivo plasma eicosanoid concentrations, leukogram, and microvascular permeability were determined. Endotoxin (5 ug/ml) stimulated synthesis of iTxB2, i6-keto PGF1 alpha and expression of PCA by macrophages in vitro. These in vitro responses of macrophages from linseed oil fed rats were significantly less than those of macrophages from control rats. In contrast, there were no significant differences in in vivo responses to endotoxin. The fatty acid composition of total lipids and phospholipids in liver and plasma from linseed oil fed rats and control rats were not different. These composite data suggest several possibilities: (1) linseed oil may have effects independent of alpha-linolenic acid on macrophage function, (2) linseed oil may alter the fatty acid composition of macrophage phospholipids prior to changing that of other tissues, and (3) the reduced in vitro responses of peritoneal macrophages may not reflect the systemic responses to endotoxin.

The determination of 11-dehydrothromboxane B2 (11-dehydro-TXB2) from unextracted human urine was studied by means of a specific radioimmunoassay based on the use of the 125I-labelled tyrosine methyl ester derivative of 11-dehydro-TXB2 as radioligand. The assay was evaluated in various incubation media by either dextran-coated charcoal (DCC) or polyethylene glycol (PEG) separation. Both the non-specific and the specific binding showed high variation in different assay media with DCC separation but with the use of PEG separation, however, the non-specific binding was constant. The verification tests carried out in both separation systems revealed a high variation of equilibrium with the individual samples. The albumin content of urine is proposed to be one important factor underlying poor reliability of direct radioimmunoassay. Both the immunoreactivity profiles observed after HPLC separation and the apparent 11-dehydro-TXB2-like immunoreactivity values determined by direct radioimmunoassay demonstrated that the unextracted urine contained a high ratio of interfering materials. It is concluded that efficient purification of human urine before determination is essential when this type of 125I-labelled radioligand is employed in radioimmunoassay.

Prostanoids, leukotrienes and platelet-activating factor were measured by radioimmunoassay in menstrual blood of seven women with primary dysmenorrhea and five healthy controls. The eicosanoids and PAF concentrations in dysmenorrheic patients were significantly higher than those found in healthy women (P less than 0.005 for PGF2 alpha, 11-dehydro-TXB2, 2,3-dinor-TXB2 and LTC4/D4; P less than 0.001 for PAE; P less than 0.05 for PGE2 and 2,3-dinor-6-keto-PGF1 alpha). Whereas no relationship could be found between the concentrations of PGF2 alpha, PGE2, 11-dehydro- and 2,3-dinor-TXB2 and severity of primary dysmenorrhea, a close correlation between LTC4/D4 and PAF and severity of the disease was observed, particularly in patients who responded poorly to therapy with prostaglandin synthetase inhibitors. We conclude that the hyperstimulation of myometrial activity is not caused by selective stimulation of one metabolic pathway of arachidonic acid, but rather by an overall stimulation of phospholipid metabolism. The assessment of prostanoids, leukotrienes and PAF in menstrual blood many be useful as a direct index of primary dysmenorrhea, and the development of their antagonists may have therapeutic implications in improved treatment of the disease.

The degradation of radiolabelled exogenous PGD2 and PGE2 was compared to that of endogenous labelled prostaglandins synthesized after stimulation with PMA in the perfused rat liver. With exogenous PGD2 and PGE2 the same degradation products were found in the perfused liver as in hepatocyte primary cultures. The major metabolite of PGD2 was dinor-PGD2 while tetranor-PGE1 was the main degradation product of PGE2. Some polar metabolites and tritiated water were also formed. The metabolites detected with endogenous prostaglandins were similar to those obtained with exogenous PGD2. Over 99% of the labelled prostaglandins were degraded in the recirculating perfusion within 40 min. In the open perfusion system, 95% of endogenous PGD2 was calculated to be degraded after a single passage through the liver, which suggests that hepatocytes play an important role in the removal of biologically active prostaglandins.

A pure lipoxygenase from dried green pea seeds (isoenzyme 1) oxygenates linoleic acid to 9(S/R)-hydroperoxy-10E,12Z-octadecadienoic acid (9-HPODE) and 13(S/R)-hydroperoxy-9Z,11E-octadecadienoic acid (13-HPODE). Furthermore (10E,12Z)-9-keto-10,12-octadecadienoic acid (9-KODE) and (9Z,11E)-13-keto-9,11-octadecadienoic acid (13-KODE) in a ratio of 1:1 were formed. Uv-spectroscopic measurements and HPLC data indicated a hydroperoxy fatty acid: keto fatty acid ratio of about 2:1. The product mixture formed from arachidonic acid was even more complex. 15-, 11-, 9- and 5-H(P)ETE1 and their corresponding keto derivatives have been detected. The chemical structures of the compounds have been identified by HPLC analysis, by uv- and ir-spectroscopy and gas chromatography/mass spectrometry of the native compounds and their hydrogenated derivatives. The data presented indicate that a pure lipoxygenase catalyzes the formation of both hydroperoxypolyenoic fatty acids and ketopolyenoic fatty acids from linoleic acid and arachidonic acid. The possible mechanism of the formation of the keto compounds is discussed.

We have recently shown that hepoxilins are formed by and act on human neutrophils leading to an increase in intracellular levels of calcium and activation of the release of arachidonic acid and diacylglycerol [6, 9]. Since neutrophil activation and accumulation is involved in the inflammatory process resulting in vascular permeability in the rat skin, we investigated the effects of hepoxilins on this process. Hepoxilins administered s.c. resulted in a concentration- and time-dependent leakage of dye to the extravascular compartment of skin from rats to which Evans Blue had been administered. These results were compared to experiments in which prostaglandin E2 was used. The threshold dose of hepoxilin that elicited an effect reached a level of significance over control within 5 min of administration at the 10 ng dose (139% +/- 7%, n = 6). Similar findings were obtained with prostaglandin E2, the level of significance was reached also at 5 min at the 10 ng dose (177% +/- 7% of control, n = 6). The maximum effect observed for both hepoxilin and prostaglandin E2 was 60 min although this did not differ significantly from 30 min except for the highest dose of PGE2 (100 ng). However, the extent of the effect observed for prostaglandin E2 was greater than that for hepoxilin after longer periods, i.e. at 60 min, the prostaglandin E2 effect being 238% +/- 10% of control, and hepoxilin A3 being 167% +/- 10% of control. These results demonstrate that hepoxilins may participate in inflammatory processes.

The actions of the in vivo metabolite of PGE1, 13,14-dihydro-PGE1 (PGE0), on platelet and neutrophil (PMN) function and vessel tone were studied in vitro. PGE0 inhibited aggregation, ATP release and thromboxane generation by human platelets (IC50 10-100 nmoles/l). The compound also inhibited superoxide anion generation and lysosomal enzyme release from human PMN. PGE0 was equipotent to PGE1 in both systems, while 15-keto-PGE1 was ineffective in platelets but produced some inhibition in PMN. These inhibitory effects of PGE0 and PGE1 were paralleled by concentration-dependent increases in cyclic AMP in platelets and PMN. Both compounds were also potent relaxants of several arterial preparations in the rabbit at comparable concentrations. In general, the vasorelaxing properties of PGE0 were somewhat lower and the contractile effects somewhat stronger in comparison to PGE1. These data demonstrate a significant and concentration-dependent inhibition of receptor-mediated activation of human platelets and PMN by PGE0. The molar potency of the compound is comparable to that of PGE1. Generation of PGE0 from infused PGE1 may contribute to the clinical efficacy of PGE1 in treatment of severe peripheral arterial occlusive disease.

12-Hydroxyeicosatetraenoic acid (HETE) is associated with a variety of inflammatory conditions. For studies on pathophysiological function of 12-HETE, metabolically more stable analogs of 12-HETE would be useful. We biologically synthesized 20,20,20-trifluoro-12-HETE (20-F3-12-HETE) by incubating enantioselectively synthesized 20,20,20-trifluoro-arachidonic acid with human platelets. The product was identified by UV absorption spectrophotometry and gas chromatography-mass spectrometry. When 1 microgram 20-F3-12-HETE was incubated with 5 X 10(6) human neutrophils for 45 min, only 5% of the analog was metabolized while 66% of 12-HETE was metabolized in the same incubation condition. With 2 X 10(7) neutrophils, 37% of the analog was metabolized at the same incubation condition while 87% of 12-HETE was metabolized. Thus, by blocking omega-oxidation of 12-HETE with fluorine atoms, the stability of 12-HETE was greatly increased. This result indicates that the omega-oxidation is a major pathway for 12-HETE metabolism. The analog demonstrated as much chemotactic activity on human neutrophils as 12-HETE, and binding affinity of the analog for 12-HETE receptor in human epidermal cell was equal to that of 12-HETE. An analog of 12-HETE, which has extended metabolic stability without alteration of neutrophil chemotactic activity and binding affinity, would be a useful tool for studies on pathophysiological role of 12-HETE in inflammatory conditions.