Tx Synthesis Research Articles

Fluoride-Free Synthesis of 2D Titanium Carbide (MXenes) Assisted by scCO2 -Based Ternary Solution.

2D MXene-Ti3 C2 Tx holds great promise in various electronic applications, especially for electromagnetic interference (EMI) shielding devices and supercapacitors. Ti3 C2 Tx synthesis typically involves the use of hazardous fluorine-containing chemicals that can result in the formation of inert fluoride functional groups on the surface of Ti3 C2 Tx , severely degrading its properties and posing a threat to the performance of electron transfer among electrical devices. Herein, a supercritical carbon dioxide-based ternary solution (scCO2 /DMSO/HCl) to produce fluoride-free Ti3 C2 Tx in mild conditions (via 0.5m HCl, 20MPa, 32 °C) is reported. The fluorine-free Ti3 C2 Tx films electrode presents an excellent gravimetric capacitance of 320 F g-1 at 2mV s-1 in 1m H2 SO4 . Besides, it is demonstrated that fluorine-free Ti3 C2 Tx films exhibit outstanding EMI shielding efficiency of 53.12dB at 2.5µm thickness. The findings offer a mild and practical approach to producing fluoride-free Ti3 C2 Tx and open opportunities for exploring MXenes' potential applications in various fields.

Life Cycle Assessment of Ti3 C2 Tx MXene Synthesis.

MXenes, two-dimensional transition metal carbides, nitrides, and carbonitrides, have been investigated for diverse applications since theirdiscovery, however, their life cycle analysis (LCA) has not been studied. Here, we perform a "cradle to gate" LCA to assess the cumulative energy demand (CED) and environmental impacts of lab-scale synthesis of Ti3 C2 Tx , the most researched MXene composition. We selected electromagnetic interface (EMI) shielding as it is one of MXenes' most promising applications and compared Ti3 C2 Tx synthesis LCA to aluminum and copper foils, two typical EMI shielding materials. Two laboratory-scale MXene synthesis systems-gram and kilogram batches-were examined. We investigated the CED and environmental implications of Ti3 C2 Tx based on its precursor production, selective etching, delamination processes, laboratory location, energy mix, and raw material type. Our results show that laboratory electricity usage for the synthesis processes accounts for > 70% of the environmental impacts. Manufacturing 1.0kg of industrials-scale aluminum and copper foil releases 23.0kg and 8.75kg of CO2 , respectively, while 1.0kg of lab-scale MXene synthesis released 428.10kg. Chemical usage is less impactful than electricity, which suggests recycled resources and renewable energy can make more sustainable MXene synthesis. Understanding MXene LCA will help with the industrial-scale manufacture of this 2D material . This article is protected by copyright. All rights reserved.

The administration of a loading dose of aspirin to patients presenting with acute myocardial infarction while receiving chronic aspirin treatment reduces thromboxane A2-dependent platelet reactivity

The optimal dose of aspirin for patients presenting with acute myocardial infarction (AMI) while receiving chronic aspirin therapy has not been clearly established. We evaluated whether continued treatment with 100 mg of aspirin or a loading dose (200–500 mg) influences thromboxane A2 (TX) suppression or platelet reactivity. Sixty-four consecutive patients with AMI and 98 healthy subjects (82 aspirin-free and 16 receiving 100 mg daily for a week) were evaluated. Treatment was at the discretion of the attending physician. Collagen (1 µg/ml)-induced TX synthesis, 14C-serotonin-release, platelet aggregation, and the PFA-100 assay were evaluated. The platelet TX synthesis of patients receiving a loading dose of aspirin was sixfold lower than that of patients receiving 100 mg of aspirin (p < 0.005). This was associated with marked reductions in 14C-serotonin-release and arachidonic-acid-induced aggregation and an increase in the PFA-100 closure time (p < 0.01). Categorization of patients according to their TX synthesis (<95% or ≥95% inhibition vs. healthy aspirin-free subjects) revealed that 8% of the patients treated with loading doses had a poor response (<95% inhibition) vs. 53% of those treated with 100 mg (p < 0.001). Patients with lower TX inhibition had higher serum NT-Pro-BNP (p < 0.005), a marker of poor left ventricular systolic function. Administration of a loading dose of aspirin to patients with AMI during existing chronic aspirin treatment induced greater reductions in platelet TX synthesis and TX-dependent platelet reactivity than the continued treatment alone.

Abstract 5299: Release of Sphingosine-1-Phosphate From Platelets Requires Thromboxane Synthesis and Thromboxane Receptor Activation

The sphingosine-derived lipid signaling molecule sphingosine-1-phosphate (S1P) is an important mediator of vascular homeostasis. S1P signaling has recently been shown to be a downstream signaling component of the receptors for thrombin, the protease-activated receptors (PARs). The present study investigates the requirement of thromboxane formation for the release of S1P induced by the prototypic thrombin receptor PAR1 from human platelets and the consequences for human monocyte and endothelial cell migration. S1P was detected by thin layer chromatography in [3H]sphingosine-labeled platelets and by mass spectrometry. Release of S1P was stimulated about 5 fold (0.3±0.1 vs. 1.6±0.5 nmol/1×106 platelets) by the selective PAR1-activating-peptide (PAR1-AP, 100 μ M). Acetylsalicylic acid (ASA) or the reversible cyclooxygenase inhibitors diclofenac and ibuprofen suppressed S1P release. Oral ASA (500 mg single dose) attenuated S1P release from platelets in healthy volunteers ex vivo which was paralleled by inhibition of TX formation. S1P release was increased by the thromboxane receptor (TXR) agonist U46619, and inhibited by the TXR antagonist ramatroban. In platelets from TXR-deficient mice, thrombin-induced release of S1P was attenuated and not affected by ASA. Supernatants from PAR1-AP-stimulated platelets increased human umbilical vein endothelial cell (HUVECs) migration and the chemotactic capacity of human peripheral blood monocytes (2- and 3-fold, respectively). These effects were inhibited when platelets were pretreated with ASA. S1P receptor-specific antagonists revealed that the chemotactic responses in HUVECs were mediated by the S1P receptor-1 (S1P1) and by S1P1 and S1P3 in monocytes. These data suggest that S1P release from platelets after thrombin receptor activation requires TX synthesis and TXR activation. This novel pathway likely contributes to the regulation of vascular homeostasis during platelet activation and inflammatory processes. Inhibition of S1P may be involved in the anti-inflammatory actions of ASA in vivo, for example by affecting recruitment of endothelial cells and monocytes to sites of vascular injury.

To the Heart of the Matter

When cyclooxygenase (COX)-2–selective inhibitors (coxibs) first entered the market about 5 years ago, the major concern with regard to cardiovascular side effects related to their potential to increase blood pressure and cause salt and water retention, in a manner similar to conventional (nonselective) nonsteroidal antiinflammatory drugs (NSAIDs). In the short time since, wariness about these side effects has grown into widespread alarm about putative prothrombotic actions and generation of excess major cardiovascular events with these agents. See p 1024 In September 2004, safety findings of the Adenomatous Polyp Prevention on Vioxx (APPROVe) study indicated an increase in risk for myocardial infarction and stroke among subjects randomized to rofecoxib compared with those randomized to placebo. This study had been designed to examine recurrent colonic polyps rather than cardiovascular disease end points and therefore could only be considered hypothesis generating. Subsequent data from a number of observational studies further implicated the drug’s association with arterial thromboembolic disease. As with APPROVe, no single study generated sufficiently robust attestation by itself, but they provided concordant signals, and the accumulating evidence eventually reached a critical mass. As the data on rofecoxib emerged, concerns about other COX-2–selective agents on the market also grew. This was based on the assumption of a “class effect” for an increase in risk of cardiovascular disease related to preferential inhibition of prostacyclin over thromboxane and thus a tendency toward prothrombosis. The results presented by McAdam and colleagues in this issue of Circulation 1 challenge our view with regard to this prostanoid hypothesis and raise new questions about the mechanisms underlying the potential cardiovascular side effects of coxibs and traditional NSAIDs. The authors hypothesized that the enhanced systemic biosynthesis of prostacyclin in smokers was dependent on COX-2 activity. They also sought to determine the functional importance of COX2–derived prostacyclin (PGI2) in limiting platelet activation in smokers in vivo. Contrary to the conventional wisdom of an expected increase in the biosynthesis of TxA2 (related to increased platelet activation via COX-1), the authors demonstrated the opposite finding—ie, that COX-2 contributed to, and a COX-2 inhibitor reduced, TxA2 biosynthesis in smokers.

Thromboxane mediates pulmonary hypertension and lung inflammation during hyperacute lung rejection

The role of thromboxane (Tx) in hyperacute rejection of pig lung by human blood was studied in an ex vivo model, wherein lungs from juvenile piglets were perfused with fresh heparinized human blood. In this model, hyperacute lung rejection was characterized by an abrupt rise in pulmonary vascular resistance (PVR; >1 cmH2O x ml(-1) x min) and prolific Tx elaboration (>15 ng/ml) within 5 min and loss of function within 10 min. Although papaverine significantly blunted the rise in PVR (<0.2 cmH2O x ml(-1) x min), Tx production was not inhibited (>20 ng/ml), and florid tracheal edema was usually evident within 20 min. In contrast, both inhibition of Tx synthesis (Tx < 3 ng/ml) with OKY-046 and blockade of the Tx receptor with SQ-30741 (Tx > 20 ng/ml) were not only associated with significantly lower peak PVRs (<0.2 cmH2O x ml(-1) x min) but also with attenuated increase in lung wet-to-dry ratio and airway edema. In concert, elaboration of histamine and tumor necrosis factor was blunted, and median survival increased >10-fold to 2 h (SQ-30741) and >4 h (OKY-046). Depletion of the pig lung macrophages with dichloromethyl bisphosphonate in liposomes, but not Pall filtration of the human blood or liposomes alone, significantly inhibited Tx elaboration (<0.2 vs. >8 ng/ml for Pall filtration or liposomes) and blunted PVR elevation (<0.3 cmH(2)O x ml(-1) x min) during initial perfusion. C3a and histamine elaboration were inhibited, and median survival was significantly prolonged (>4 h). These findings implicate Tx in the inflammation associated with hyperacute lung rejection and demonstrate that pulmonary intravascular macrophages are critical to its elaboration.

Directed vascular expression of the thromboxane A2 receptor results in intrauterine growth retardation.

Thromboxane (Tx) A2 is a platelet agonist, smooth muscle cell constrictor, and mitogen. Urinary Tx metabolite (Tx-M) excretion is increased in syndromes of platelet activation and early in both normal pregnancies and in pregnancy-induced hypertension. A further increment occurs in patients presenting with severe preeclampsia, in whom Tx-M correlates with other indices of disease severity. TxA2 exerts its effects through a membrane receptor (TP), of which two isoforms (alpha and beta; refs. 5,6) have been cloned. Overexpression of TP in the vasculature under the control of the pre-proendothelin-1 promoter results in a murine model of intrauterine growth retardation (IUGR), which is rescued by timed suppression of Tx synthesis with indomethacin. IUGR is commonly associated with maternal diabetes or cigarette smoking, both conditions associated with increased TxA2 biosynthesis.

Prostanoid stimulation of cytokine production in an amnion-derived cell line: evidence of a feed-forward mechanism with implications for term and preterm labor.

To test the hypothesis that amnion cytokine production might be regulated by prostanoids. Amnion-derived WISH cells were treated with a range of prostanoids and their effects on production of interleukin (IL)-6 and IL-8 were determined by enzyme-linked immunosorbent assay and Northern analysis. The effects of thromboxane inhibitors on cytokine production by term primary amnion explants also were examined. Prostaglandin (PG)A2, PGD2, PGF2 alpha, PGE2, PGJ2, and the PGI2 analogue carbaprostacyclin (1-1000 nmol/L) exhibited no significant effects on cytokine production. However, the thromboxane A2 (TXA2) agonist U46619 and carbocyclic (c)TXA2 both stimulated WISH cytokine production with similar potencies under basal or cytokine-stimulated conditions. Significant stimulation of IL-6 production was observed at concentrations > or = 8 nmol/L (P < .05 by analysis of variance), whereas IL-8 production was stimulated significantly but to a lesser extent. The effects of U46619 and cTXA2 were rapid; maximal stimulation of cytokine production occurred within 4 to 8 hours of treatment. U46619 augmented IL-1 beta-stimulated IL-6 and IL-8 mRNA expression within 2 hours of treatment. In amnion explants inhibitors of TX synthesis and action abrogated the stimulatory effects of IL-1 beta on cytokine production. These results are consistent with the presence of a feed-forward loop in amnion involving TXA2 and cytokines, which could play a significant role in the progression of the inflammatory response involved in the mechanism of infection-driven preterm labor.

Endotoxin modulates arachidonic acid-induced glycogenolysis in the perfused rat liver.

Effects of endotoxin on arachidonic acid (AA)-induced hepatic glycogenolysis were examined in perfused rat liver. In normal rat liver, infusion of AA increased oxygen consumption and glucose production concurrently. In rats injected with lipopolysaccharide (LPS) 6 h before, AA increased glucose production but suppressed oxygen consumption. The changes in LPS-injected rat were abolished by a thromboxane (Tx) A2 receptor antagonist. The release of Tx B2 by AA increased after LPS-injection. These results suggest that priming of hepatic macrophage by endotoxin in vivo enhances Tx synthesis, resulting in modulating hepatic glycogenolysis.

Protective effects of a thromboxane synthetase inhibitor and continuous arteriovenous hemofiltration in rat endotoxic shock

We determined the efficacy of continuous arteriovenous hemofiltration (CAVH) and a thromboxane synthetase inhibitor (TSI) on survival and their effect on TXA 2, PGI 2, TNFα, and IL-1β production in rat endotoxemia. Thirty-six endotoxemic rats were randomized to one of 4 groups: (A) no TSI, sham CAVH; (B) no TSI, CAVH; (C) TSI, sham CAVH; and (D) TSI, CAVH. Either CAVH (Group B) or pretreatment with TSI (Group C) resulted in increased survival time. CAVH did not prevent the rise in TX (Group B). TNFα levels at 2 h after LPS infusion were higher in Group D compared to Group B (26.1 ± 3.7 vs 13.2 ± 4.3 ng/mL, P < 0.05) respectively. IL-1β was detected earlier in Groups C,D when compared to Groups A,B ( P < 0.02). TNFα and IL-1β were not ultrafiltered. CAVH and the inhibition of TX synthesis independently improved survival in endotoxemia, however, their beneficial effects were not additive. While TSI may improve survival by blocking TXA 2 production, the salutary effects of CAVH appear to be from removal of an undetermined TXA 2 dependent mediator. TNFα and IL-1β concentrations do not appear to influence survival times in this model.

BENEFICIAL EFFECTS OF A THROMBOXANE SYNTHETASE INHIBITOR (UK 38,485) IN RAT ENDOTOXEMIA. 189

The objective of this study was to determine if UK 38,485, a thromboxane synthetase inhibitor (TSI), would prolong survival and attenuate acute lung injury (ALI) in rat endotoxemia. 24 mechanically ventilated rats received 10 mg/kg E. coli LPS. 12 rats received 5 mg/kg TSI, 1 hr prior to LPS infusion. Heart rate, BP, ABG and lactate levels were measured at 0, 30, 60, 90, 120 min. 2 hrs after LPS or at the time of death, alveolar macrophages were collected, washed and resuspended in media. A baseline and 24 hr incubated supernatant were collected for TX, nitric oxide (NO), and PGE2. Rats pretreated with TSI survived longer (117± 3 vs 92± 11 min, p<0.03) and at 30 min had less A-a gradient (247±30 vs 383±44 torr, p<0.01), and acidosis (pH 7.33±.02 vs 7.27±03, p<0.005). No differences in BP, HR, or lactate were observed between the 2 groups. The alveolar macrophages of rats receiving TSI produced more NO at baseline, (fig). Although TX production was inhibited in the plasma of TSI treated endotoxemic rats, the alveolar macrophages continued to produce TX in quantities similar to rats receiving LPS alone,(1000±22 vs 873±223 pg/ml). PGE2 was similar in both groups. Conclusions: TSI prolongs survival in acute endotoxemia by decreasing ALI. The lung protection by TSI appears secondary to an increased production of NO by alveolar macrophages rather than decreased pulmonary TX synthesis.

Antibody and complement reduce renal hemodynamic function in isolated perfused rat kidney.

To evaluate the effect of antibody and complement on renal hemodynamic changes, glomerular injury was induced in isolated perfused kidneys by an anti-thymocyte antibody (ATS) and rat serum (RS). Glomerular filtration rate (GFR), renal vascular resistance (RVR), and renal perfusate flow (RPF) were assessed over an 80-min period. The possible role of thromboxane (Tx) was tested by the application of the Tx synthesis inhibitor UK-38485 and the Tx receptor blocker daltroban. Perfusion of kidneys with ATS and RS significantly reduced GFR at 10 min (control, 501 +/- 111; ATS + RS, 138 +/- 86 ml.g kidney-1.min-1, significance of F = 0.000) after RS. Similarly, RPF (ml.g kidney-1.min-1) fell from 19.2 +/- 1.8 to 6.1 +/- 2.0 (significance of F = 0.000), whereas RVR (mmHg.ml-1.g.min) increased threefold from 5.2 +/- 0.4 to 17.9 +/- 5.0 at 10 min. These changes were ameliorated by the pretreatment of the rats with daltroban and UK-38485. Addition of erythrocytes to the perfusate increased RVR and GFR, whereas RPF decreased compared with cell-free perfused kidneys. ATS and RS in this preparation also decrease GFR and RPF. The hemodynamic alterations appeared without changes in filtration fraction. Compared with untreated, perfused control kidneys, glomerular Tx formation was significantly increased in ATS and RS perfused kidneys. These data demonstrate that antibody and RS induce impairment of renal hemodynamics, which are mediated by increased Tx formation.

Noradrenaline and dopamine infusions modulate arachidonic acid cyclooxygenase and 5-lipoxygenase pathways ex vivo in man

We have previously demonstrated that adrenaline infusion increases the thromboxane/leukotriene (TX/LT) ratio in whole blood in healthy volunteers. The aim of the present study was to see whether other catecholamines — noradrenaline and dopamine — are also capable of modulating arachidonic acid (AA) metabolism in man. Low doses of noradrenaline (0.025 μg/kg/min) and dopamine (3.0 μ/kg/min), which did not change hemodynamics, were infused for 60 min into healthy male volunteers. Both dopamine and noradrenaline decreased TX synthesis stimulated by spontaneous clotting, but no remarkable effect was seen when calcium ionophore A23187 was used as a stimulus. Dopamine but not noradrenaline increased prostaglandin E 2 (PGE 2) synthesis in A23187-stimulated whole blood. They both marginally decreased LTB 4 formation in A23187-stimulated whole blood. The findings indicate that not only adrenaline but also noradrenaline and dopamine modulate AA metabolism in man.

Role of renal thromboxane in salt-sensitive blood pressure rise in DOCA salt hypertension

Urinary excretion and release of prostaglandins (PG) from isolated glomeruli and renal papilla of deoxycorticosterone acetate (DOCA)-treated rats fed with a normal salt (0.6% NaCl) diet and a high salt (4%NaCl) diet were determined. Mean blood pressure was significantly higher in the high salt diet group than in the normal salt diet group (146.2 +/- 2.3 vs 118.6 +/- 1.9 mmHg, p < 0.01). Urinary excretion of thromboxane (Tx) B2, stable metabolite of Tx A2, and 6-keto PG-F1 alpha, a stable metabolite of prostacyclin, increased significantly in the high salt diet group compared to the values of the normal salt diet group increased significantly by 104%, 55%, and 74% compared to those of the normal salt diet group, respectively. Release of 6-keto-PG F1 alpha from renal papilla of the high salt diet group decreased significantly, but there were no intergroup differences in the release of PG E2 and Tx B2. Stepwise multiple linear regression analysis showed that the significant contributory factors underlying the mean blood pressure were urinary excretion of Na (F = 14.187, p < 0.01) and release of Tx B2 from isolated glomeruli (F = 4.135, p < 0.05). These findings suggest that the manifestation of Tx synthesis in renal glomeruli has a predominant role in the salt sensitive pressor response of DOCA salt hypertension in rats.

Selective eicosanoid formation during HL‐60 macrophage differentiation

Earlier studies on HL-60 cells induced to differentiate into macrophages by phorbol esters have shown a selective stimulation of thromboxane (Tx) formation from endoperoxide prostaglandin (PG) H2, indicating that Tx synthesis is regulated at the level of Tx synthase (TxS), one of the peripheral enzymes of the PGH-synthase pathway. We now report on the regulation of TxS during HL-60 macrophage differentiation using monoclonal anti-TxS serum and comparing turnover rates of TxS and its biological activity with those of other enzymes of arachidonic acid metabolism. Western-blot analysis, enzyme-linked immunosorbent assay, immunohistochemical staining and [35S]methionine-labeling experiments suggested a phorbol-ester-dependent early induction of synthesis of TxS. [35S]Methionine incorporation into TxS was stimulated within 4 h after initiation of differentiation and was associated with a major rise in the TxS catalytical activity. Pulse-chase experiments showed a half life for the TxS protein of 16.4 h in both control and phorbol-ester-treated cells. The biological half life of TxS was 10.5 h, as determined by PGH2 incorporation into TxB2 after cycloheximide treatment. In contrast, the biological half lives of PGH synthase, prostacyclin synthase and 5-lipoxygenase were significantly shorter and were 3, 2.5 and 2.5 h, respectively. These results reveal that Tx synthesis in macrophages is mediated by at least two distinct mechanisms; a protein-kinase-C-dependent induction of de novo synthesis of TxS and the selective resistance of the enzyme against the activity of protein kinase C.

Cardiopulmonary bypass and pulmonary thromboxane generation

Sporadic cases of inexplicable noncardiogenic pulmonary edema occur after operations requiring total cardiopulmonary bypass (CPB). Prostaglandins, such as thromboxane (Tx) A2, have been implicated in this form of pulmonary pathology in many clinical and experimental settings. Because Tx generation has been demonstrated in association with ischemia of solid organs, we postulated that total CPB, which decreases pulmonary tissue perfusion and oxygenation, would stimulate local Tx synthesis. Total CPB was examined in 7 sheep. The level of TxB2 (a stable metabolite of the active, unstable A2) was measured in the left and right atria before, during, and after 105 minutes of total CPB. Significant increases in TxB2 concentrations occurred in the left atrium compared with the right (p < 0.05) during CPB. Immediately after reperfusion, both the left atrial and right atrial TxB2 concentrations increased significantly over the baseline values (p < 0.05), but this increase and the atrial gradient were rapidly abolished with continued pulmonary perfusion. To determine the effect of extracorporeal circulation without significant (< 30%) alteration in pulmonary perfusion, we evaluated the effect of partial CPB in 5 sheep, increased TxB2 concentrations were noted at 15 and 30 minutes after the onset of partial CPB (left atrium increased significantly over baseline; p < 0.05), but this elevation spontaneously diminished to insignificance after 15 and 30 additional minutes of extracorporeal circulation. These data establish that total CPB stimulates Tx generation in the lung, and although the effect of partial CPB is transient, that of total CPB is progressive and abolished by reperfusion. Although the local pathophysiological effects of pulmonary Tx generation after CPB remain to be determined, this study may provide insight into a mechanism for sporadic, noncardiogenic pulmonary edema after CPB.

OKY-046 prevents increases in LTB4 and pulmonary edema in phorbol ester-induced lung injury in dogs.

Thromboxanes (Txs) were implicated as possible participants in the altered microvascular permeability of acute lung injury when the Tx synthase inhibitor, OKY-046, was reported to prevent pulmonary edema induced by phorbol myristate acetate (PMA). Recently, however, we found that OKY-046, at a dose just sufficient to block Tx synthesis in intact dogs, did not prevent PMA-induced pulmonary edema but rather merely reduced it modestly. The present study was designed to explore other mechanisms whereby OKY-046 might prevent PMA-induced pulmonary edema. The finding that 5-lipoxygenase (5-LO) metabolites of arachidonic acid were increased within the lung after PMA administration, coupled with the report that OKY-046 inhibited slow-reacting substance of anaphylaxis formation, permitted formulation of the hypothesis that OKY-046, at a dose in excess of that required to inhibit Tx synthesis, inhibits the formation of a product(s) of 5-LO and, thereby, prevents edema formation. In vehicle-pretreated pentobarbital-anesthetized male mongrel dogs (n = 4), PMA (20 micrograms/kg i.v.) increased pulmonary vascular resistance (PVR) from 4.4 +/- 0.3 to 26.3 +/- 8.8 mmHg.l-1 x min (P < 0.01) and extravascular lung water from 6.7 +/- 0.5 to 19.1 +/- 6.2 ml/kg body wt (P < 0.05). Concomitantly, both TxB2 and leukotriene B4 (LTB4) were significantly increased in the lung. Pretreatment with OKY-046 (100 mg/kg i.v., n = 8) prevented PMA-induced increases in TxB2, LTB4, and pulmonary edema formation but did not prevent the increase in PVR.(ABSTRACT TRUNCATED AT 250 WORDS)

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 throm☐ane(TX)B 2, 6-keto-prostaglandin(PG)F 1α, PGE 2 and sulphido-peptide leukotrienes (LTC 4, D 4, E 4) 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-PGF 1α > TXB 2 > PGE 2. 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 TXB 2 was excluded by 111In platelet labelling experiments. We assessed relative sensitivity to inhibition of cardiac TX synthesis relative to production of 6-keto-PGF 1α to inhibition by aspirin, ibuprofen, diclofenac and the specific throm☐ane synthase inhibitor OKY-046. Aspirin, ibuprofen and diclofenac decreased 6-keto-PGF 1α 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-PGF 1α/TXB 2 ratios, as obtained in these different conditions, vs coronary flow, showed no cor relation 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.

Contribution of platelet thromboxane production to enhanced urinary excretion and glomerular production of thromboxane and to the pathogenesis of albuminuria in the streptozotocin-diabetic rat

Previous studies have demonstrated that urinary thromboxane B 2 (TXB 2) excretion (U TXB2) and glomerular production of TXB 2 are enhanced in experimental diabetes and that selective inhibitors of TX synthesis prevent or delay the development of albuminuria. The present study was conducted to examine the contribution of platelet TXB 2 production to the enhancement of U TXB2 and glomerular TXB 2 production and to the pathogenesis of albuminuria in the partially insulin-treated moderately hyperglycemic (blood glucose, 200 to 400 mg/dL) streptozotocin-diabetic rat (SDR). Treatment of control rats or of SDR with diabetes of 5 months' duration with antiplatelet serum for 4 consecutive days reduced circulating platelet counts and serum TXB 2 generation, an index of platelet cyclooxygenase activity, by 80% or greater, but reduced U TXB2 excretion by only 30%. U TXB2 and glomerular production of TXB 2 of thrombocytopenic SDR remained markedly elevated compared with corresponding values from age-matched thrombocytopenic or platelet-replete, nondiabetic controls. Similarly, treatment of rats for 180 days with a dose of aspirin (ASA), which selectively inhibited platelet versus renal cyclooxygenase activity, reduced U TXB2 of both SDR and controls by 25% to 35%. The absolute reductions in U TXB2 induced by either ASA or thrombocytopenia in SDR were significantly greater than the absolute decrements in corresponding controls, suggesting that increased platelet TXB 2 production in SDR may contribute to the enhanced U TXB2. However, as in the thrombocytopenic SDR, U TXB2 and glomerular production of TXB 2 of SDR treated with ASA remained clearly above corresponding control values. Moreover, chronic ASA treatment failed to prevent the development of albuminuria in SDR. By contrast, 4′ (imidazol-1-yl) acetophenone, a selective inhibitor of TX synthesis given for 180 days at a dose that suppressed both platelet and glomerular TXB 2 production, prevented the development of albuminuria in SDR. The results indicate that platelets are not the major cellular source of increased U TXB2 or glomerular TXB 2 generation in SDR and that selective inhibition of platelet TXB 2 production does not prevent the development of albuminuria in this model. A pathogenetic role for local glomerular TX synthesis is suggested by the differential effects of ASA versus a TX synthetase inhibitor on glomerular TX production and on the development of albuminuria in SDR.

The role oxygen free radicals and prostaglandins in reperfusion injury to warm ischemic kidneys

The present study was designed to determine whether the administration of superoxide dismutase (SOD) can alleviate ischemic kidney damage and whether there is a relationship between oxygen free radicals and thromboxane (Tx). In 17 dogs, the right kidney was removed and the vascular pedicle of the left kidney was clamped for 75 min. Prior to reperfusion, the ischemic kidney was rinsed with 5 mg SOD and an additional 20 mg SOD was infused systemically. Blood samples were drawn from the renal vein before ischemia and after reperfusion to determine serum levels of thromboxane B2 (TxB2). All eight untreated dogs died within 1 week of renal failure, and the nine treated dogs demonstrated transient renal failure, with a significant difference (P less than 0.001) being found between the two groups. A significant difference (P less than 0.001) in TxB2 levels was found in the untreated dogs before and after ischemia and between the two groups following reperfusion. Animals that are treated with SOD after the ischemic event has occurred but before reperfusion exhibit a favorable clinical course in terms of survival and renal function. Tx synthesis in the kidney can be blocked by the administration of SOD.