Dietary inflammation index association with serum levels of nitric oxide, prostacyclin, and thromboxane B2 among prinzmetal angina patients and healthy persons

BACKGROUND AND AIM

This study aimed to assess the association between dietary inflammation index with serum Nitric oxide, Prostacyclin, and Thromboxane B2 among Prinzmetal angina patients and healthy persons.

METHODS AND RESULTS

This case-control study was conducted among 120 Prinzmetal angina patients and 120 healthy persons referred to the Ardabil Imam Khomeini Hospital between 2021 and 2022. Blood samples were gained from all study participants for measurement of serum Nitric oxide, Prostacyclin, and Thromboxane B2. The serum Nitric oxide in patients who had higher DII was less than in patients with less dietary inflammation index (β = -0.75 p = 0.02). The serum Prostacyclin level in patients with greater dietary inflammation index was 0.68 ng/ml less than in patients with less dietary inflammation index (β = -0.68 p = 0.04). The level of serum Thromboxane B2 had a positive association with dietary inflammation index (β = 0.81 p = 0.04).

CONCLUSION

In Prinzmetal angina patients, more dietary inflammation index can increase the serum Thromboxane B2 and decrease the serum Nitric oxide and Prostacyclin. More clinical trial study is needed to confirm these results.

TXA2 mediates LPA1-stimulated uterine contraction in late pregnant mouse

Lysophosphatidic acid (LPA) is known to increase uterine contraction in the estrus cycle and early pregnancy, however, the effect of LPA in late pregnant uterus and its mechanisms are not clear. In the present study, we show the LPA receptor subtypes expressed and the mechanism of LPA-induced contractions in late pregnant mouse uterus. We determined the relative mRNA expression of LPA receptor genes by quantitative PCR and elicited log concentration-response curves to oleoyl-L-α-LPA by performing tension experiments in the presence and absence of nonselective and selective receptor antagonists and inhibitors of the TXA2 pathway. LPA1 was the most highly expressed receptor subtype in the late pregnant mouse uterus and LPA1/2/3 agonist (Oleoyl-L-α LPA) elicited increased contractions in this tissue that had lesser efficacy compared to oxytocin. LPA1/3 antagonist, Ki-16425, and a potent LPA1 antagonist (AM-095) significantly inhibited the LPA-induced contractions. Further, the nonselective COX inhibitor, indomethacin, and potent thromboxane A2 synthase inhibitor, furegrelate significantly impaired LPA-induced contractions. Moreover, selective thromboxane receptor (TP) antagonist, SQ-29548, and Rho kinase inhibitor, Y-27632 almost eliminated LPA-induced uterine contractions. LPA1 stimulation elicits contractions in the late pregnant mouse uterus using the contractile prostanoid, TXA2 and may be targeted to induce labor in uterine dysfunctions/ dystocia.

Exploring the mechanism of the antithrombotic effects of Pueraria lobata and Pueraria lobata var. thomsonii based on network pharmacology

ETHNOPHARMACOLOGICAL RELEVANCE

Pueraria lobata (Willd.) Ohwi and Pueraria lobata var. thomsonii (Benth.) Maesen are nutritious medicine food homology plants that are widely used in the food and health products industry and are excellent natural materials for the development of new health foods, with great potential for domestic and foreign markets. Clinically, P. lobata and P. thomsonii are used to treat coronary heart disease, atherosclerosis, cerebral infarction and other cardiovascular diseases, and antithrombotic actions may be their core effect in the treatment of thrombotic diseases. However, the underlying mechanisms of the antithrombotic properties of P. lobata and P. thomsonii have not been clarified.

METHODS

First, P. lobata and P. thomsonii were identified by high-performance liquid chromatography (HPLC). An arteriovenous bypass thrombosis rat model was established. Thrombus dry‒wet weight, platelet accumulation rate and the four coagulation indices, including activated partial thromboplastin time (APTT), prothrombin time (PT), thrombin time (TT) and fibrinogen (FIB), were detected in plasma to manifest the P. lobata and P. thomsonii antithrombotic function. Network pharmacology and molecular docking methods were used to obtain key targets and verify reliability. David 6.8 was used for GO and KEGG analyses to explore pathways and potential targets for P. lobata and P. thomsonii antithrombotic functions. Prostaglandin I2 (PGI2), thromboxane A2 (TXA2), cyclooxygenase 2 (COX-2), myeloperoxidase (MPO) and endothelial nitric oxide synthase (eNOS) were tested by enzyme-linked immunosorbent assay (ELISA).

RESULTS

The results indicated that P. lobata and P. thomsonii can reduce thrombus dry‒wet weight and platelet accumulation in rats and inhibit TT, APTT, FIB, and PT. A comprehensive network pharmacology approach successfully identified 9 active ingredients in P. lobata and P. thomsonii. The main active ingredients include polyphenols, amino acids and flavonoids. A total of 15 antithrombotic function targets were obtained, including 3 key targets (PTGS2, NOS3, MPO). Pathway analysis showed 10 significant related pathways and 29 biological processes. P. lobata and P. thomsonii inhibited platelet aggregation by upregulating PGI2 and downregulating TXA2, inhibited PTGS2 to reduce inflammation, and increased the level of eNOS to promote vasodilation. In addition, P. lobata and P. thomsonii alleviated oxidative stress by increasing SOD levels and significantly decreasing MDA contents.

CONCLUSION

The results of the study further clarify the antithrombotic mechanism of action of P. lobata and P. thomsonii, which provides a scientific basis for the development of new drugs for thrombogenic diseases and lays the foundation for the development of P. lobata and P. thomsonii herbal resources and P. lobata and P. thomsonii health products.

Utility of constraints reflecting system stability on analyses for biological models

Simulating complex biological models consisting of multiple ordinary differential equations can aid in the prediction of the pharmacological/biological responses; however, they are often hampered by the availability of reliable kinetic parameters. In the present study, we aimed to discover the properties of behaviors without determining an optimal combination of kinetic parameter values (parameter set). The key idea was to collect as many parameter sets as possible. Given that many systems are biologically stable and resilient (BSR), we focused on the dynamics around the steady state and formulated objective functions for BSR by partial linear approximation of the focused region. Using the objective functions and modified global cluster Newton method, we developed an algorithm for a thorough exploration of the allowable parameter space for biological systems (TEAPS). We first applied TEAPS to the NF-κB signaling model. This system shows a damped oscillation after stimulation and seems to fit the BSR constraint. By applying TEAPS, we found several directions in parameter space which stringently determines the BSR property. In such directions, the experimentally fitted parameter values were included in the range of the obtained parameter sets. The arachidonic acid metabolic pathway model was used as a model related to pharmacological responses. The pharmacological effects of nonsteroidal anti-inflammatory drugs were simulated using the parameter sets obtained by TEAPS. The structural properties of the system were partly extracted by analyzing the distribution of the obtained parameter sets. In addition, the simulations showed inter-drug differences in prostacyclin to thromboxane A2 ratio such that aspirin treatment tends to increase the ratio, while rofecoxib treatment tends to decrease it. These trends are comparable to the clinical observations. These results on real biological models suggest that the parameter sets satisfying the BSR condition can help in finding biologically plausible parameter sets and understanding the properties of biological systems.

We propose a new method to analyze the properties of biological dynamic models, which we named TEAPS (Thorough Exploration of Allowable Parameter Space). TEAPS can thoroughly determine combinations of parameter values for ordinary differential equations with which an initial state in a certain range converges to a particular fixed point. This stable and resilient behavior is a characteristic shared with many biological systems, including metabolic systems and intracellular signaling systems. Therefore, this thorough search outlined the possible parameter space as biological systems for target models, which helps to understand the system constraints when the target systems behave dynamically. The obtained parameter space can be used as an initial space for parameter tuning. For models that include a large number of parameters, the parameter space to be searched in the parameter tuning process is too large; therefore, narrowing down the space by TEAPS potentially contributes to the analysis of the dynamics of complicated biological models. Thus, our approach can partly overcome the current problem in parameter tuning and can advance the computational dynamic analyses of biological systems.

The F2-isoprostane 8-iso-PGF2α attenuates atherosclerotic lesion formation in Ldlr-deficient mice - Potential role of vascular thromboxane A2 receptors

The F2-isoprostane 8-iso-PGF_2α (also known as 15-F_2t-isoprostane, iPF_2α-III, 8-epi PGF_2α, 15(S)-8-iso-PGF_2α, or 8-Isoprostane), a thromboxane A₂ receptor (TP) agonist, stable biomarker of oxidative stress, and risk marker of cardiovascular disease, has been proposed to aggravate atherogenesis in genetic mouse models of atherosclerotic vascular disease. Moreover, the TP plays an eminent role in the pathophysiology of endothelial dysfunction, atherogenesis, and cardiovascular disease. Yet it is unknown, how the TP expressed by vascular cells affects atherogenesis or 8-iso-PGF_2α-related effects in mouse models of atherosclerosis. We studied Ldlr-deficient vascular endothelial-specific (EC) and vascular smooth muscle cell (VSMC)-specific TP knockout mice (TP^ECKO/Ldlr KO; TP^VSMCKO/Ldlr KO) and corresponding wild-type littermates (TP^WT/Ldlr KO). The mice were fed a Western-type diet for eight weeks and received either 8-iso-PGF_2α or vehicle infusions via osmotic pumps. Subsequently, arterial blood pressure, atherosclerotic lesion formation, and lipid profiles were analyzed. We found that VSMC-, but not EC-specific TP deletion, attenuated atherogenesis without affecting blood pressure or plasma lipid profiles of the mice. In contrast to a previous report, 8-iso-PGF_2α tended to reduce atherogenesis in TP^WT/Ldlr KO and TP^{EC KO}/Ldlr KO mice, again without significantly affecting blood pressure or lipid profiles of these mice. However, no further reduction in atherogenesis was observed in 8-iso-PGF_2α-treated TP^{VSMC KO}/Ldlr KO mice. Our work suggests that the TP expressed in VSMC but not the TP expressed in EC is involved in atherosclerotic lesion formation in Ldlr-deficient mice. Furthermore, we report an inhibitory effect of 8-iso-PGF_2α on atherogenesis in this experimental atherosclerosis model, which paradoxically appears to be related to the presence of the TP in VSMC.

Novel Peptide Motifs Containing Asp-Glu-Gly Target P2Y12 and Thromboxane A2 Receptors to Inhibit Platelet Aggregation and Thrombus Formation

Increasing evidence has shown that collagen peptides have multiple biological activities. Our previous study has separated and identified antiplatelet aggregation peptides Asp-Glu-Gly-Pro (DEGP) from Salmo salar skin. This study is to investigate the cellular target of DEGP on platelets and its underlying mechanism. DEGP inhibited platelet aggregation in a dose-dependent manner induced by 2MeS-ADP and U46619 and significantly attenuated tail thrombosis formation by 30% in mice at the dose of 50 mg/kg body weight. Mechanically, DEGP displayed apparent antagonism effects on TP and P₂Y₁₂ receptors by the drug affinity responsive target stability (DARTS) technique to regulate the phosphorylation of RhoA^S188, PLCβ3^S537, as well as VASP^S157. The molecular docking results revealed a stronger binding energy with the target protein of modified peptides DEGI and DDEGL. Practically, DEGI exhibited the highest inhibition activity against 2MeS-ADP- and U46619-induced platelet aggregation in vitro with IC₅₀ values of 0.88 ± 0.10 and 0.85 ± 0.10 mM, respectively, and comparable antithrombosis activity with aspirin at the dose of 25 mg/kg body weight in vivo. These results indicated the possibility that the peptide motifs containing Asp-Glu-Gly could potentially be developed as a novel therapeutic agent in the prevention and treatment of thrombotic diseases.

[Role of prostacyclin and thromboxane A2 in pulmonary hyper-permeability induced by mechanical ventilation in rabbits]

OBJECTIVE

To explore the role of prostacyclin (PGI2) and thromboxane A2 (TXA2) in lung hyper-permeability induced by mechanical ventilation (MV) in rabbits.

OBJECTIVE

Forty-eight healthy Japanese white rabbits were randomly allocated to vehicle treatment group (group V), tranylcypromine (a PGI2 synthase inhibitor) treatment group (group T), dazoxiben (a TXA2 synthase inhibitor) treatment group (group D), vehicle-treated MV group (group VM), tranylcyprominetreated MV group (group TM) and dazoxiben-treated MV group (group DM). The contents of PGI2 and TXA2 in the lung tissues and TNF-α level in BALF and lung tissues were measured by ELISA. The lung wet/dry weight (W/D) ratio, lung permeability index and pulmonary expressions of myosin light chain kinase (MLCK) protein and mRNA were detected to evaluate the pulmonary permeability. The severities of lung injury were assessed by lung histological scores.

OBJECTIVE

The measured parameters did not differ significantly among the rabbits receiving different treatments without MV. In rabbits in group VM, the contents of PGI2 and TXA2 in the lungs, TNF-α in BALF and lung tissues, PGI2/TXA2 ratio, lung W/D ratio, lung permeability index, pulmonary expressions of MLCK protein and mRNA and histological scores of the lungs all increased significantly (P < 0.05) as compared with those in group V, group T and group D. In rabbits undergoing MV, inhibition of PGI2 production by tranylcypromine significantly decreased the PGI2/TXA2 ratio (P < 0.05), further enhanced the production of TNF-α in the BALF and lung tissue (P < 0.05), and worsened lung hyper-permeability and lung injury (P < 0.05), while treatment with dazoxiben significantly reduced TXA2 production in the lung tissue (P < 0.05), increased the PGI2/TXA2 ratio (P < 0.05) and decreased TNF-α production in the BALF and lung tissue (P < 0.05), thus resulting in alleviated lung hyperpermeability and lung injury (P < 0.05).

OBJECTIVE

PGI2 plays a protective role against MV-induced lung hyper-permeability and lung injury by downregulating TNF-α/MLCK signaling pathway, while TXA2 can exacerbate MV-induced lung hyperpermeability in rabbits by up-regulating TNF-α/ MLCK signaling pathway.

Activation of metabolite receptor GPR91 promotes platelet aggregation and transcellular biosynthesis of leukotriene C4

BACKGROUND

Succinate is a Krebs cycle intermediate whose formation is enhanced under metabolic stress, and for which a selective sensor GPR91 has been identified on various cell types including platelets. Platelet-derived eicosanoids play pivotal roles in platelet activation/aggregation, which is key to thrombus formation and progression of atherothrombosis.

OBJECTIVES

This study aims to decipher the molecular mechanism(s) and potential involvement of eicosanoids in succinate enhanced platelet activation/aggregation.

METHODS

We used liquid chromatography-mass spectrometry (LC-MS)/MS-based lipid mediator profiling to identify eicosanoids regulated by succinate. We ran light transmittance aggregometry and flow cytometry to assess platelet aggregation, P-selectin expression, and platelet-polymorphonuclear leukocyte (PMN) adherence. Various pharmacological tools were used to assess the contributions of GPR91 signalling and eicosanoids in platelet aggregation.

RESULTS

Succinate and two types of synthetic non-metabolite GPR91 agonists-cis-epoxysuccinate (cES) and Cmpd131-potentiated platelet aggregation, which was partially blocked by a selective GPR91 antagonist XT1. GPR91 activation increased production of 12-hydroxy-eicosatetraenoic acid (12-HETE), thromboxane (TX) A2 , and 12-hydroxy-heptadecatrienoic acid (12-HHT) in human platelets, associated with phosphorylation of cytosolic phospholipase A2 (cPLA2 ), suggesting increased availability of free arachidonic acid. Blocking 12-HETE and TXA2 synthesis, or antagonism of the TXA2 receptor, significantly reduced platelet aggregation enhanced by GPR91 signalling. Moreover, platelet-PMN suspensions challenged with succinate exhibited enhanced transcellular biosynthesis of leukotriene C4 (LTC4 ), a powerful proinflammatory vascular spasmogen.

CONCLUSION

Succinate signals through GPR91 to promote biosynthesis of eicosanoids, which contribute to platelet aggregation/activation and potentially vascular inflammation. Hence, GPR91 may be a suitable target for pharmacological intervention in atherothrombotic conditions.

Nitric oxide specifically inhibits integrin-mediated platelet adhesion and spreading on collagen

BACKGROUND

Nitric oxide (NO) inhibits platelet adhesion to collagen, although the precise molecular mechanisms underlying this process are unclear.

OBJECTIVES

Collagen-mediated adhesion is a multifaceted event requiring multiple receptors and platelet-derived soluble agonists. We investigated the influence of NO on these processes.

RESULTS

S-nitrosoglutathione (GSNO) induced a concentration-dependent inhibition of platelet adhesion to immobilized collagen. Maximal adhesion to collagen required platelet-derived ADP and TxA(2). GSNO-mediated inhibition was lost in the presence of apyrase and indomethacin, suggesting that NO reduced the availability of, or signaling by, ADP and TxA(2). Exogenous ADP, but not the TxA(2) analogue U46619, reversed the inhibitory actions of GSNO on adhesion. Under adhesive conditions NO inhibited dense granule secretion but did not influence TxA(2) generation. These data indicated that NO may block signaling by TxA(2) required for dense granule secretion, thereby reducing the availability of ADP. Indeed, we found TxA(2)-mediated activation of PKC was required to drive dense granule secretion, a pathway that was inhibited by NO. Because our data demonstrated that NO only inhibited the activation-dependent component of adhesion, we investigated the effects of NO on individual collagen receptors. GSNO inhibited platelet adhesion and spreading on alpha(2)beta(1) specific peptide ligand GFOGER. In contrast, GSNO did not inhibit GPVI-mediated adhesion to collagen, or adhesion to the GPVI specific ligand, collagen related peptide (CRP).

CONCLUSIONS

NO targets activation-dependent adhesion mediated by alpha(2)beta(1), possibly by reducing bioavailability of platelet-derived ADP, but has no effect on activation-independent adhesion mediated by GPVI. Thus, NO regulates platelet spreading and stable adhesion to collagen.

3-D structure of serum paraoxonase 1 sheds light on its activity, stability, solubility and crystallizability

Serum paraoxonases (PONs) exhibit a wide range of physiologically important hydrolytic activities, including drug metabolism and detoxification of nerve gases. PON1 and PON3 reside on high-density lipoprotein (HDL) (the "good cholesterol"), and are involved in the alleviation of atherosclerosis. Members of the PON family have been identified not only in mammals and other vertebrates, but also in invertebrates. We earlier described the first crystal structure of a PON family member, a directly-evolved variant of PON1, at 2.2 A resolution. PON1 is a 6-bladed beta-propeller with a unique active-site lid which is also involved in binding to HDL. The 3-D structure, taken together with directed evolution studies, permitted analysis of mutations which enhanced the stability, solubility and crystallizability of this PON1 variant. The structure permits a detailed description of PON1's active site and suggests possible mechanisms for its catalytic activity on certain substrates.

Sildenafil inhibits the formation of superoxide and the expression of gp47phox NAD[P]H oxidase induced by the thromboxane A2 mimetic, U46619, in corpus cavernosal smooth muscle cells

OBJECTIVE

To assess the effect of sildenafil on superoxide formation and p47(phox) (the active subunit of NADPH oxidase) expression in cultured corpus cavernosal smooth muscle cells (CVSMCs).

MATERIALS AND METHODS

CVSMCs derived from rabbit penis were incubated with U46619 (thromboxane A2 analogue) with or without sildenafil for 1 or 16 h at 37 degrees C. Superoxide dismutase-inhibitable superoxide formation was assessed using the reduction of ferricytochrome c measured spectrophotometrically, and gp47(phox) assessed using Western blot analysis. The role of NAD[P]H oxidase and cGMP was further studied by using specific inhibitors of each.

RESULTS

Superoxide formation was significantly greater in cells incubated with U46619 after 1 and 16 h incubation than in controls, an effect blocked by NADP(H) oxidase inhibitors. These effects of U46619 were inhibited by sildenafil (1 and 10 nmol/L), which in turn were negated by the guanylyl cyclase inhibitor, ODQ; 10 nmol/L sildenafil inhibited p47phox expression induced by U46619.

CONCLUSIONS

Sildenafil is a potent inhibitor of superoxide formation in CVSMCs. This effect is mediated through the inhibition of PDE-5 which in turn augments the inhibitory action of the NO-cGMP axis on NAD[P]H oxidase expression and activity. This mechanism constitutes a new pharmacological action of sildenafil, consolidates the potential role of superoxide in ED, and indicates that thromboxane A(2) may be an important mediator of intrapenile oxidative stress.

Antioxidant, free radical scavenging and anti-inflammatory effects of aloesin derivatives in Aloe vera

Antioxidant components in Aloe vera were examined for lipid peroxidation using rat liver microsomal and mitochondrial enzymes. Among the aloesin derivatives examined, isorabaichromone showed a potent antioxidative activity. The DPPH radical and superoxide anion scavenging activities were determined. As one of the most potent components, isorabaichromone together with feruloylaloesin and p-coumaroylaloesin showed potent DPPH radical and superoxide anion scavenging activities. Electron spin resonance (ESR) using the spin trapping method suggested that the potent superoxide anion scavenging activity of isorabaichromone may have been due to its caffeoyl group. As A. vera has long been used to promote wound healing, the inhibitory effects of aloesin derivatives for cyclooxygenase (Cox)-2 and thromboxane (Tx) A 2 synthase were examined and the participation of p-coumaroyl and feruloyl ester groups in the aloesin skeleton was demonstrated. These findings may explain, at least in part, the wound healing effects of A.vera. Abbreviations. ADP:adenosine diphosphate ASA:ascorbic acid BHT:butylated hydroxytoluene BSA:bovine serum albumin DMPO:5,5-dimethyl-1-pyrroline N-oxide DPPH:1,1-diphenyl-2-picrylhydrazyl EDTA:edetic acid HEPES: N-(2-hydroxyethyl)-piperazine- N-2'-ethane-sulfonic acid NADH:reduced nicotinamide adenine dinucleotide NADPH:reduced nicotinamide adenine dinucleotide phosphate NBT:nitroblue tetrazolium Pg:prostaglandin SOD:superoxide dismutase TBA:thiobarbituric acid TCA:trichloroacetic acid XOD:xanthine oxidase

Release of tumor necrosis factor-alpha and prostanoids in whole blood cultures after in vivo exposure to low-dose aspirin

BACKGROUND

The preventive effect of low-dose aspirin in cardiovascular disease is generally attributed to its antiplatelet action caused by differential inhibition of platelet cyclooxygenase-1. However, there is evidence that aspirin also affects release of inflammatory cytokines, including tumor necrosis factor-alpha (TNF-alpha). It is not known whether this is caused by direct action on the cytokine pathway or indirectly through cyclooxygenase inhibition and altered prostanoid synthesis, or both.

METHODS

We assessed the capacity of lipopolysaccharide-activated leukocytes in whole blood cultures of eight healthy subjects following a single oral dose of 80 mg aspirin to release TNF-alpha, prostanoid E2 (PGE2) and prostanoid I2 (PGI2), and thromboxane A2 (TXA2). TNF-alpha and prostanoids were determined by enzyme-linked immunoassays.

RESULTS

In seven subjects, TNF-alpha release in blood cultures decreased 24h after intake of aspirin. The effect of aspirin on prostanoid release was assessed in three individuals: PGE2 increased in all subjects, PGI2 increased in two and remained unchanged in one, and TXA2 was reduced in two and unchanged in one individual The presence of DFU, a specific inhibitor of cyclooxygenase 2, did not affect the reduction of TNF-alpha release by aspirin, but abolished prostanoid production in all three individuals.

CONCLUSION

The capacity of activated leukocytes to release TNF-alpha is reduced by ingestion of low-dose aspirin, independent of changes in prostanoid biosynthesis.

Underexpression of neural cell adhesion molecule and neurotrophic factors in rat brain following thromboxane A(2)-induced intrauterine growth retardation

Intrauterine growth retardation (IUGR) often results in clinical neurodevelopmental disorders. To clarify the influence of uteroplacental insufficiency on central nervous system development, we have created a model of IUGR in rats using maternal administration of synthetic thromboxane A(2). We investigated expression patterns of neural cell adhesion molecule (NCAM) and reelin in this model by semiquantitative competitive polymerase chain reactions. On postnatal day 2, NCAM expression was decreased in rat cerebral cortex, and reelin expression was decreased in hippocampus from levels in controls without maternal thromboxane exposure. No significant differences in NCAM expression were seen in hippocampus, nor did reelin expression differ in cerebral cortex between control and IUGR groups. We also examined expression of two neurotrophic factors, brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3). In cerebral cortex the IUGR group showed less BDNF and NT-3 expression than controls. Delay of neuronal migration and histological changes observed in our IUGR rats may be related to altered expression of these molecules.

Abnormal cerebral neuronal migration in a rat model of intrauterine growth retardation induced by synthetic thromboxane A(2)

Many reports have associated intrauterine growth retardation (IUGR) with adverse neurological outcome, but the underlying pathology is imperfectly understood. We have developed a new rat model of IUGR using maternal administration of synthetic thromboxane A(2) (STA(2)). In the present study, the effect of this insult on neuronal migration in the rat cerebral cortex was examined. Bromodeoxyuridine (BrdU), a time-specific cell marker was administered intraperitoneally to the mothers on embryonic day (E) 19. At postnatal day (P) 3, P4, P5, and P6, pups were terminally anesthetized and brains were removed. BrdU-labeled cells were detected immunohistochemically and counted in cerebrum, which was divided into the cortical plate (CP), the intermediate zone, and the subventricular/ventricular zone (SVZ+VZ). Numbers of labeled cells in the three areas over time were compared between IUGR and control animals. Numbers of labeled cells in SVZ+VZ were significantly greater in IUGR than in controls at P3, 5, and 6 (P<0.05). In contrast, labeled cells in the CP were significantly less abundant in IUGR animals than in controls at P3, 4, and 6 (P<0.05). We concluded that neuronal migration was delayed in IUGR rats.

Two mechanisms for platelet-mediated killing of tumour cells: one cyclo-oxygenase dependent and the other nitric oxide dependent

We have tried to identify the cytotoxic effectors in platelet-mediated tumour cell killing, using two tumour cell lines K562 (a chronic myelogenic leukaemic cell line) and LU99A (a lung cancer cell line), which are both sensitive to platelet cytotoxicity. Cyclo-oxygenase inhibitors, acetylsalicylic acid (ASA) and indomethacin, effectively inhibited the platelet-mediated killing of K562 cells, but not that of LU99A cells. In contrast, inhibitors of the nitric oxide (NO) pathway. NG-nitro-1-arginine (L-NA), haemoglobin and methylene blue, reduced the cytotoxic activity of platelets against LU99A, but not against K562. Synthetic analogues of platelet cyclo-oxygenase products thromboxane A2/ prostaglandin H2(TXA2/PGH2) exerted cytotoxicity against K562 cells but not against LU99A cells. Electron microscopic study showed that TXA2/PGH2 analogues induced bleb formation and disruption of the plasma membrane of K562 cells. K562 cells enhanced the production of TXA2 by platelets, as inferred from the accumulation of thromboxane B2 (TXB2), a spontaneous hydrolysis product of TXA2. LU99A cells had no such effects. These results indicate that platelets kill these two tumour cell lines through different mechanisms. In K562, the cyclooxygenase products TXA2/PGH2 possibly play a significant role but in LU99A the NO pathway seems to be involved.

Exercise training alters aortic vascular reactivity in hypothyroid rats

Hypothyroidism induces a number of cardiovascular adaptations in rats, including decreases in blood flow to high-oxidative skeletal muscle and increases in total peripheral resistance. Conversely, exercise training results in elevations in blood flow to high-oxidative skeletal muscle and decreases in vascular resistance. The purpose of this study was to determine whether hypothyroidism induces changes in the vasomotor responses of arterial vessels and whether exercise training modifies these responses. Rats were divided into three groups, sedentary euthyroid (S-Eut), sedentary hypothyroid (S-Hypo), and exercise-trained hypothyroid (ET-Hypo). Responses to vasoactive compounds were examined in vitro using abdominal aortic rings. Maximal isometric contractile tension (g/mm2) evoked by KCl and norepinephrine (NE) were not different among groups. However, sensitivity to KCl [agonist concentration producing 50% of maximal vasoconstrictor response (EC50; in mM): S-Eut, 21.1 +/- 1.1; S-Hypo, 35.7 +/- 2.7; ET-Hypo, 43.8 +/- 2.0] and to NE [EC50 (in M): S-Eut, 4.0 x 10(-8) +/- 2.3 x 10(-8); S-Hypo, 8.3 x 10(-8) +/- 3.4 x 10(-8); ET-Hypo, 3.6 x 10(-7) +/- 1.1 x 10(-7)] was different among groups, and in the order S-Eut > S-Hypo > ET-Hypo. Maximal vasodilator responses induced by acetylcholine (10(-7) M NE preconstriction) were lower in rings from S-Hypo animals than those from S-Eut and ET-Hypo rats. Dilatory responses induced by sodium nitroprusside (SNP) with the same NE preconstriction were not different among groups. However, with a 10(-4) M NE preconstriction, maximal dilatory responses induced by SNP were lower in vessels from hypothyroid animals. Dilatory responses to forskolin (10(-4) M NE preconstriction) were not different among groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Modeling of human thromboxane A2 receptor and analysis of the receptor-ligand interaction

In order to elucidate the mode of the thromboxane A2 (TXA2) receptor-ligand interaction at the molecular level, a model for the human TXA2 receptor, a member of the G protein-coupled receptor family with seven transmembrane segments, was constructed on the basis of its amino acid sequence, which was determined recently (Hirata, M.; et al. Nature 1991, 349, 617-620). First, we made a model for the human beta 2-adrenergic receptor using its amino acid sequence and the known helix arrangement of bacteriorhodopsin. Then, a TXA2 receptor model was constructed based on the beta 2 receptor model and was used to analyze the receptor-ligand interaction. The ligand-binding pocket of the TXA2 receptor includes a serine residue from segment V, an arginine residue from segment VII, and a large hydrophobic pocket between these two residues. These results are consistent with the known properties of TXA2 and TXA2 antagonists having a hydrogen-bonding group such as hydroxyl, a carboxyl group, and a hydrophobic moiety. This model should be helpful for rational design of potent TXA2 antagonists.

The thromboxane A2 mimetic U46619 worsens canine myocardial hypoperfusion during exercise in the presence of a coronary artery stenosis

OBJECTIVE

The aim was to test the hypothesis that thromboxane A2 can cause vasoconstriction of coronary resistance vessels during exercise in hypoperfused regions of myocardium distal to an arterial stenosis.

METHODS

Eight adult mongrel dogs were studied. Chronically instrumented animals with a left circumflex coronary artery Doppler flow meter, hydraulic occluder, and indwelling catheter underwent treadmill exercise at heart rates of 190-200 beats.min-1. Myocardial blood flow was measured with microspheres during unimpeded arterial inflow and in the presence of a coronary stenosis which decreased distal pressure to 42-45 mm Hg. Measurements were repeated during infusion of the thromboxane A2 analogue, U46619.

RESULTS

When the occluder was partially inflated to produce a stenosis, blood flow in the region perfused by the stenotic artery was 58 (SEM 6)% of flow in the normally perfused region (p less than 0.01). U46619 (0.01 microgram.kg-1.min-1) caused a further 21 (7)% decrease in blood flow in the region perfused by the stenotic artery (p less than 0.05). The vasoconstriction produced by U46619 was uniform across the left ventricular wall from epicardium to endocardium. U46619 did not significantly decrease myocardial blood flow in the absence of a coronary stenosis.

CONCLUSIONS

Even during hypoperfusion produced by a flow limiting arterial stenosis, the coronary resistance vessels remain responsive to the vasoconstrictor effect of thromboxane A2. Liberation of thromboxane A2 during platelet activation at the site of a proximal coronary stenosis may worsen myocardial hypoperfusion by causing vasoconstriction of the distal resistance vessels.

Testosterone increases thromboxane A2 receptors in cultured rat aortic smooth muscle cells

Previous studies have demonstrated increased contractile responses to thromboxane A2 (TXA2) mimetics in aortas obtained from male rats compared with those obtained from females. This study was designed to determine the effects of testosterone and 17 beta-estradiol treatment on TXA2 receptors in cultured rat aortic smooth muscle cells (RASMCs). TXA2 receptor affinity and density were determined through equilibrium binding experiments using the TXA2/prostaglandin H2 mimetic [1S-(1 alpha,2 beta(5Z),3 alpha(1E,3R*),4 alpha)]-7-[3-(3- hydroxy-4-(4'-125iodophenoxy)-1-butenyl)-7-oxabicyclo[2.2.1]hep tan-2-yl]- 5-heptenoic acid (125I-BOP). Incubation with testosterone (100 nM) for 24 or 48 hours resulted in a significant (p less than 0.05) 31% and 48% increase in TXA2 receptor density without any change in affinity. 17 beta-Estradiol (100 nM) had no significant effect on either the density or affinity of TXA2 receptors. Coincubation with the testosterone receptor antagonist hydroxyflutamide (1 microM) blocked the testosterone-induced increase in TXA2 receptor density. The maximum increase in intracellular free calcium induced by I-BOP was significantly (p less than 0.05) greater in testosterone-treated RASMCs than controls. Similarly, increases in inositol trisphosphate induced by the TXA2/prostaglandin H2 mimetic U46619 were significantly (p less than 0.05) greater in testosterone-treated RASMCs compared with controls. The results demonstrate that testosterone increases vascular TXA2 receptor density and support the notion that sex steroid hormones modulate the expression of this receptor.

Differential effects of thromboxane A2 synthase inhibition, singly or combined with thromboxane A2/prostaglandin endoperoxide receptor antagonism, on occlusive thrombosis elicited by endothelial cell injury or by deep vascular damage in canine coronary arteries

In open-chest dogs, cyclic flow reductions (CFRs, 5.1-6.6/hr in controls; n = 24) caused by platelet deposition/dislodgment at sites of endothelial cell injury in critically stenosed left anterior descending coronary arteries (59% flow reduction) were attenuated to the same extent either by single thromboxane A2 (TXA2) synthase inhibition (0.31 mg/kg i.v. ridogrel; CFR, 0.16 +/- 0.16/hr; n = 6; p less than 0.05) or by a comparatively modest degree of TXA2/prostaglandin endoperoxide receptor antagonism on top of TXA2 synthase inhibition (5 mg/kg i.v. ridogrel; CFR, 0.22 +/- 0.1/hr; n = 10; p less than 0.05). By contrast, occlusive thrombosis on deep vascular damage elicited by intraluminal stimulation (150-microA anodal constant current) in nonpreconstricted canine coronary arteries (time to occlusion, 237.1 +/- 13.9 minutes; n = 7; incidence of occlusion within 300 minutes, six of seven experiments) was not affected by platelet cyclooxygenase inhibition (5 mg/kg i.v. acetylsalicylic acid; n = 7), single TXA2 synthase inhibition (1.25 mg/kg i.v. ridogrel; n = 7), or single TXA2/prostaglandin endoperoxide receptor antagonism (10 mg/kg + 10 mg/kg/hr i.v. sulotroban for 300 minutes; n = 5). However, such an occlusive thrombus formation was significantly reduced by combined TXA2 synthase/prostaglandin endoperoxide receptor inhibition (5 mg/kg i.v. ridogrel; time to occlusion greater than 300 minutes, n = 7; incidence of occlusion within 300 minutes, one of seven experiments; p less than 0.05). This study reveals 1) a differential efficacy of TXA2 synthase inhibition, singly or combined with TXA2/prostaglandin endoperoxide receptor antagonism, depending on the extent of the vessel wall lesion triggering thrombosis and the size of the thrombus required to obstruct the vascular lumen and 2) a significant synergism in preventing occlusive thrombosis of extensively damaged coronary arteries between strong TXA2 synthase inhibition and comparatively modest TXA2/prostaglandin endoperoxide receptor antagonism with ridogrel.

Bay U 3405 inhibits cerebral vasospasm induced by authentic thromboxane A2

Platelet activation results in the formation of various vasoactive mediators such as thromboxane A2 and serotonin. We investigated the effects of Bay U 3405 [(3R)-3- (4-fluorophenyl-sulfonamido)-1,2,3,4,-tetrahydro-9-carbazolepro panoic acid] on vasocontractions of isolated bovine cerebral arteries induced by U 46.619, a stable thromboxane/prostaglandin-endoperoxide analogue, and authentic thromboxane A2 released from thrombin-stimulated human platelets. Bay U 3405 (0.001-10 mumol/l) potently inhibited the contraction induced by U 46.619 and demonstrated a reduction of the thromboxane-mediated component of platelet-induced contractile response at higher concentrations (0.1-10 mumol).

The role of prostanoid TP- and DP-receptors in the bronchoconstrictor effect of inhaled PGD2 in anaesthetized guinea-pigs: effect of the DP-antagonist BW A868C

1. In anaesthetized, pump-ventilated guinea-pigs, bolus intravenous injection of prostaglandin D2 (PGD2 5-160 micrograms kg-1) caused a dose-dependent rise in both heart rate and systemic mean arterial blood pressure with only a small monophasic rise in pulmonary inflation pressure (PIP). 2. In contrast, inhaled PGD2 (0.1-1 mg ml-1, 30s) provoked a substantial concentration-dependent biphasic rise in PIP. The bronchoconstrictor action of inhaled PGD2 was accompanied by minimal cardiovascular effects. 3. The 3-benzyl substituted hydantoin BW A868C (0.1-1 mg kg-1 i.v.) a novel prostanoid DP-receptor antagonist, had no significant effect on the cardiovascular or bronchoconstrictor effects of intravenously administered or inhaled PGD2. 4. However, BW A868C (0.1-1 mg kg-1 i.v.) did inhibit the hypotensive actions of the DP-receptor agonist, BW 245C (1-3 micrograms kg-1 i.v.). 5. The prostanoid TP-receptor antagonist BM 13.177 (2.5 mg kg-1 i.v.) strongly inhibited the bronchoconstrictor effect of inhaled PGD2, abolishing the first phase of this response and reducing the peak increase in PIP provoked by PGD2 (0.1 or 1 mg ml-1 for 30 s), by 67 +/- 16% and 44 +/- 5% respectively. 6. A combination of BW A868C (0.1 or 1 mg kg-1 i.v.) with BM 13.177 (2.5 mg kg-1 i.v.) produced no greater inhibition of the bronchoconstrictor effect of inhaled PGD2 than that seen with BM 13.177 (2.5 mg kg-1 i.v.) alone. 7. Neither bilateral vagotomy, nor selective inhibition of arachidonate cyclo-oxygenase with indomethacin or 5-lipoxygenase with the novel acetohydroxamic acid BW A4C, significantly reduced the bronchoconstrictor effect of inhaled PGD2. 8. These findings indicate that the bronchoconstrictor effect of inhaled PGD2 in guinea-pigs in vivo is mediated primarily through direct TP-receptor activation and not through actions on DP-receptors.

Actions of a novel thromboxane A2-receptor antagonist, S-145, on isolated monkey and cat arteries

The effects of a novel thromboxane (Tx) A2-receptor antagonist, S-145, were investigated mainly in helical strips of monkey and cat arteries. S-145 (3 x 10(-10) to 3 x 10(-9) M) attenuated the contraction induced by U46619 (2 x 10(-10) to 10(-7) M), which produced concentration-dependent contraction in monkey cerebral, coronary, and mesenteric arteries, and cat cerebral arteries. The attenuation in the different monkey arteries did not differ much, and it tended to be greater in cat cerebral arteries than in monkey at concentrations of less than 10(-9) M S-145. S-145 also suppressed contractions in cat cerebral arteries induced by prostaglandin (PG) F2 alpha, PGE2, and PGD2. However, S-145 did not affect the contractile responses to PGF2 alpha in cat iris sphincter muscle and to PGE2 in guinea pig ileum. In cat mesenteric arteries, S-145 did not affect contractions induced by norepinephrine or K+, or relaxations induced by PGI2 or adenosine. The addition of S-145 (10(-9)-10(-8) M) produced a transient contraction in cat cerebral arteries, and when S-145 (3 x 10(-11) to 3 x 10(-7) M) was cumulatively added, the contraction was not produced. The measurement of antagonistic potency of S-145 was not complicated by its agonistic effect, since the former potency was always determined after confirming absence of the latter effect. These results suggest that S-145 is a potent TxA2-receptor antagonist with partial agonistic activity in vascular smooth muscle. PGF2 alpha, PGE2, and PGD2, however, at least in part, seemed to interact with the TxA2 receptor in vascular smooth muscle.

Eicosapentaenoic acid and docosahexaenoic acid are antagonists at the thromboxane A2/prostaglandin H2 receptor in human platelets

The present study investigated the mechanism by which eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) inhibit platelet activation induced by thromboxane A2. DHA was found to be more potent than EPA in blocking platelet aggregation induced by the stable thromboxane A2 mimetic, U46619. Furthermore, this inhibition by DHA or EPA was competitive. Binding studies using 3H-U46619 demonstrated that both EPA and DHA interact with the platelet thromboxane receptor. The potency of the inhibition of binding corresponded with that seen for the inhibition of aggregation. These results suggest that thromboxane receptor antagonism may be an important mechanism by which EPA and DHA modulate platelet reactivity in vivo.

Effects of respiratory alkalosis on thromboxane-induced pulmonary hypertension in piglets

Acute hypoxic pulmonary vasoconstriction is attenuated by respiratory alkalosis. It is unknown if alkalosis similarly reduces pulmonary vasoconstriction produced by thromboxane A2. Respiratory alkalosis does not always attenuate persistent pulmonary hypertension in newborns, some of whom have elevated serum thromboxane B2 levels. We hypothesized that alkalosis attenuates thromboxane-induced pulmonary vasoconstriction less than it does hypoxic pulmonary vasoconstriction in infants. Hemodynamic responses to respiratory alkalosis during pulmonary vasoconstriction produced in random order by breathing 12% inspired oxygen and by infusing 0.1 micrograms/kg/min of the thromboxane-mimetic U46,619 were compared in eight 2-wk-old piglets. Hypoxia increased mean pulmonary artery pressure from 12 +/- 3 to 29 +/- 2 mm Hg and pulmonary vascular resistance (PVR) from 11 +/- 4 to 25 +/- 8 mmHg/L/min; U46,619 increased pulmonary artery pressure from 16 +/- 5 to 37 +/- 6 mm Hg and PVR from 14 +/- 5 to 51 +/- 17 mm Hg/liter/min. U46,619 also decreased cardiac output accounting in part for the greater increase in PVR compared to hypoxia-induced vasoconstriction. Respiratory alkalosis decreased PVR to 14 +/- 6 mm Hg/liter/min during exposure to hypoxia and to 28 +/- 9 mm Hg/liter/min during infusion of U46,619. In six additional piglets with U46,619-induced pulmonary vasoconstriction, the effects of lung stretch and hypocapnic alkalosis were separated by doubling tidal volume and then adding inspired CO2 to return PaCO2 to prehyperventilation levels. Respiratory alkalosis decreased PVR from 52 +/- 36 to 35 +/- 21 mm Hg/liter/min. Despite the increased tidal volume, PVR increased to 53 +/- 35 Hg/liter/min when PaCO2 returned to 44 +/- 5 mm Hg.(ABSTRACT TRUNCATED AT 250 WORDS)

Platelet loss during experimental cardiopulmonary bypass and its prevention with prostacyclin

Prostacyclin (PGI2), a newly discovered short-acting prostaglandin that inhibits platelet aggregation, was evaluated as an agent for prevention of cardiopulmonary bypass-induced thrombocytopenia. Ten adult, splenectomized greyhounds were divided into three treatment groups prior to beginning 120 minutes of partial cardiopulmonary bypass. Group 1 animals received 300 units of heparin per kilogram of body weight, Group 2 animals received 300 units of heparin per kilogram plus PGI2, 1.5 micrograms per minute, and Group 3 animals received 300 units of heparin per kilogram plus PGI2 3.0 micrograms per minute. Bypass and PGI2 infusion were started simultaneously. Mean platelet counts of each group at 5 minutes were approximately 40% of prebypass levels. Additional platelet loss was seen in Groups 1 and 2 at 30, 60, and 120 minutes. However in Group 3, platelet counts at 30 and 60 minutes were essentially unchanged from prebypass levels. At 30, 60, and 120 minutes of cardiopulmonary bypass, the differences between Groups 1 and 3, and 2 and 3 are highly significant (p less than 0.01). We conclude that PGI2 is an effective agent for preserving platelet levels during experimental cardiopulmonary bypass. Furthermore, it is possible that platelet loss during cardiopulmonary bypass may be caused, in part, by an imbalance between PGI2 and thromboxane A2, which results in excessive platelet adhesion and aggregation.

Thromboxane molecules do not adopt the prostaglandin hairpin conformation

The hairpin conformational hypothesis has been proposed to rationalise much of the structure-activity and receptor-binding data which have accumulated for the prostaglandin (PG) hormones. The hairpin conformation, thought to be necessary for PG activity, requires that the alpha- and omega-chains of the molecule be extended and in parallel alignment, separated by a van der Waals contact distance for the full length of the chains, with the ends of the chains approximately 5.5 A apart. The similarity between the structures of the thromboxanes (TXs) and the PGs suggests that the profile of activity of TXs, like that of PGs, centres on subtle conformational variation of the hairpin geometry. Thromboxane B2 (TXB2) is a stable hydrolysis product of a highly reactive, short-lived intermediate, thromboxane A2 (TXA2), which is formed from the prostaglandin endoperoxide (PGH2) as indicated in Fig. 1. An examination of molecular models of TXA2 and TXB2 suggests that the structural differences between the ring moieties may have much less influence in altering the side-chain conformation of TXs than do substitutents on the relatively more flexible cyclopentane ring of a PG molecule. We report here the first diffraction analysis of a thromboxane structure and note that the molecular conformation is not hairpin shaped.

Peroxidase-dependent deactivation of prostacyclin synthetase

A study of the enzymes of the arachidonic acid cascade revealed a high sensitivity of prostacyclin synthetase and a complete resistance of thromboxane A2 synthetase to time-dependent destruction by an oxidant [Ox] released during the peroxidase-catalyzed reduction of hydroperoxy fatty acids. The destructive action of [Ox] derived from prostaglandin G1 (PGG1), 15-hydroperoxy-PGE1, 15-hydroperoxy-5,8,11,13-eicosatetraenoic acid, and 12-hydroperoxy-5,8,10,14-eicosatetraenoic acid upon prostacyclin synthetase was prevented by 2-aminomethyl-4-t-butyl-6-iodophenol. On the other hand, deactivation resulting from PGG2 metabolism was neither time-dependent nor sensitive to 2-aminomethyl-4-t-butyl-6-iodophenol. The possibility that the action of [Ox] may alter the arachidonic acid cascade in favor of thromboxane A2 is discussed in view of its possible implications in inflammatory and other pathological processes.