Prostacyclin (PGI2) inhibits the formation of platelet thrombi in arterioles and venules of the hamster cheek pouch

Should aspirin be replaced with ADP blockers and anti-GPVI to manage thrombosis?

Platelets have a pivotal role in maintaining cardiovascular homeostasis. They are kept docile by endothelial-derived mediators. Aberration in haemostatic balance predisposes an individual to an elevated risk of a prothrombotic environment. Anti-platelet therapy has been a key component to reduce this risk. However, understanding how these medications affect the balance between the activation and inhibition of platelets is critical. There is no evidence that a key anti-platelet therapy - aspirin, may not be the most efficacious medicine of choice, as it can compromise both platelet inhibition and activation pathways. In this review, the rationale of aspirin as an anti-thrombotic drug has been critically discussed. This review looks at how recently published trials are raising key questions about the efficacy and safety of aspirin in countering cardiovascular diseases. There is an increasing portfolio of evidence that identifies that although aspirin is a very cheap and accessible drug, it may be used in a manner that is not always beneficial to a patient, and a more nuanced and targeted use of aspirin may increase its clinical benefit and maximize patient response. The questions about the use of aspirin raise the potential for changes in its clinical use for dual anti-platelet therapy. This highlights the need to ensure that treatment is targeted in the most effective manner and that other anti-platelet therapies may well be more efficacious and beneficial for CVD patients in their standard and personalized approaches.

Compassionate use of Pulmonary Vasodilators in Acute Severe Hypoxic Respiratory Failure due to COVID-19

BACKGROUND

There have been over 200 million cases and 4.4 million deaths from COVID-19 worldwide. Despite the lack of robust evidence one potential treatment for COVID-19 associated severe hypoxaemia is inhaled pulmonary vasodilator (IPVD) therapy, using either nitric oxide (iNO) or prostaglandins. We describe the implementation of, and outcomes from, a protocol using IPVDs in a cohort of patients with severe COVID-19 associated respiratory failure receiving maximal conventional support.

METHODS

Prospectively collected data from adult patients with SARS-CoV-2 admitted to the intensive care unit (ICU) at a large teaching hospital were analysed for the period 14th March 2020 - 11th February 2021. An IPVD was considered if the PaO2/FiO2 (PF) ratio was less than 13.3kPa despite maximal conventional therapy. Nitric oxide was commenced at 20ppm and titrated to response. If oxygenation improved Iloprost nebulisers were commenced and iNO weaned. The primary outcome was percentage changes in PF ratio and Alveolar-arterial (A-a) gradient.

RESULTS

Fifty-nine patients received IPVD therapy during the study period. The median PF ratio before IPVD therapy was commenced was 11.33kPa (9.93-12.91). Patients receiving an IPVD had a lower PF ratio (14.37 vs. 16.37kPa, p = 0.002) and higher APACHE-II score (17 vs. 13, p = 0.028) at ICU admission. At 72 hours after initiating an IPVD the median improvement in PF ratio was 33.9% (-4.3-84.1). At 72 hours changes in PF ratio (70.8 vs. -4.1%, p < 0.001) and reduction in A-a gradient (44.7 vs. 14.8%, p < 0.001) differed significantly between survivors (n = 33) and non-survivors (n = 26).

CONCLUSIONS

The response to IPVDs in patients with COVID-19 associated acute hypoxic respiratory failure differed significantly between survivors and non-survivors. Both iNO and prostaglandins may offer therapeutic options for patients with severe refractory hypoxaemia due to COVID-19. The use of inhaled prostaglandins, and iNO where feasible, should be studied in adequately powered prospective randomised trials.

Prostacyclin Analogues Inhibit Platelet Reactivity, Extracellular Vesicle Release and Thrombus Formation in Patients with Pulmonary Arterial Hypertension

(1) Background: Prostacyclin analogues (epoprostenol, treprostinil, and iloprost) induce vasodilation in pulmonary arterial hypertension (PAH) but also inhibit platelet function. (2) Objectives: We assessed platelet function in PAH patients treated with prostacyclin analogues and not receiving prostacyclin analogues. (3) Methods: Venous blood was collected from 42 patients treated with prostacyclin analogues (49.5 ± 15.9 years, 81% female) and 38 patients not receiving prostacyclin analogues (55.5 ± 15.6 years, 74% female). Platelet reactivity was analyzed by impedance aggregometry using arachidonic acid (AA; 0.5 mM), adenosine diphosphate (ADP; 6.5 µM), and thrombin receptor-activating peptide (TRAP; 32 µM) as agonists. In a subset of patients, concentrations of extracellular vesicles (EVs) from all platelets (CD61⁺), activated platelets (CD61⁺/CD62P⁺), leukocytes (CD45⁺), and endothelial cells (CD146⁺) were analyzed by flow cytometry. Platelet-rich thrombus formation was measured using a whole blood perfusion system. (4) Results: Compared to controls, PAH patients treated with prostacyclin analogues had lower platelet reactivity in response to AA and ADP (p = 0.01 for both), lower concentrations of platelet and leukocyte EVs (p ≤ 0.04), delayed thrombus formation (p ≤ 0.003), and decreased thrombus size (p = 0.008). Epoprostenol did not affect platelet reactivity but decreased the concentrations of platelet and leukocyte EVs (p ≤ 0.04). Treprostinil decreased platelet reactivity in response to AA and ADP (p ≤ 0.02) but had no effect on the concentrations of EVs. All prostacyclin analogues delayed thrombus formation and decreased thrombus size (p ≤ 0.04). (5) Conclusions: PAH patients treated with prostacyclin analogues had impaired platelet reactivity, EV release, and thrombus formation, compared to patients not receiving prostacyclin analogues.

Microvascular thrombosis: experimental and clinical implications

A significant amount of clinical and research interest in thrombosis is focused on large vessels (eg, stroke, myocardial infarction, deep venous thrombosis, etc.); however, thrombosis is often present in the microcirculation in a variety of significant human diseases, such as disseminated intravascular coagulation, thrombotic microangiopathy, sickle cell disease, and others. Further, microvascular thrombosis has recently been demonstrated in patients with COVID-19, and has been proposed to mediate the pathogenesis of organ injury in this disease. In many of these conditions, microvascular thrombosis is accompanied by inflammation, an association referred to as thromboinflammation. In this review, we discuss endogenous regulatory mechanisms that prevent thrombosis in the microcirculation, experimental approaches to induce microvascular thrombi, and clinical conditions associated with microvascular thrombosis. A greater understanding of the links between inflammation and thrombosis in the microcirculation is anticipated to provide optimal therapeutic targets for patients with diseases accompanied by microvascular thrombosis.

Innovative Three-Step Microwave-Promoted Synthesis of N-Propargyltetrahydroquinoline and 1,2,3-Triazole Derivatives as a Potential Factor Xa (FXa) Inhibitors: Drug Design, Synthesis, and Biological Evaluation

The coagulation cascade is the process of the conversion of soluble fibrinogen to insoluble fibrin that terminates in production of a clot. Factor Xa (FXa) is a serine protease involved in the blood coagulation cascade. Moreover, FXa plays a vital role in the enzymatic sequence which ends with the thrombus production. Thrombosis is a common causal pathology for three widespread cardiovascular syndromes: acute coronary syndrome (ACS), venous thromboembolism (VTE), and strokes. In this research a series of N-propargyltetrahydroquinoline and 1,2,3-triazole derivatives as a potential factor Xa (FXa) inhibitor were designed, synthesized, and evaluated for their FXa inhibitor activity, cytotoxicity activity and coagulation parameters. Rational design for the desired novel molecules was performed through protein-ligand complexes selection and ligand clustering. The microwave-assisted synthetic strategy of selected compounds was carried out by using Ullmann-Goldberg, N-propargylation, Mannich addition, Friedel-Crafts, and 1,3-dipolar cycloaddition type reactions under microwave irradiation. The microwave methodology proved to be an efficient way to obtain all novel compounds in high yields (73–93%). Furthermore, a thermochemical analysis, optimization and reactivity indexes such as electronic chemical potential (µ), chemical hardness (η), and electrophilicity (ω) were performed to understand the relationship between the structure and the energetic behavior of all the series. Then, in vitro analysis showed that compounds 27, 29–31, and 34 exhibited inhibitory activity against FXa and the corresponding half maximal inhibitory concentration (IC₅₀) values were calculated. Next, a cell viability assay in HEK293 and HepG2 cell lines, and coagulation parameters (anti FXa, Prothrombin time (PT), activated Partial Thromboplastin Time (aPTT)) of the most active novel molecules were performed to determine the corresponding cytotoxicity and possible action on clotting pathways. The obtained results suggest that compounds 27 and 29 inhibited FXa targeting through coagulation factors in the intrinsic and extrinsic pathways. However, compound 34 may target coagulation FXa mainly by the extrinsic and common pathway. Interestingly, the most active compounds in relation to the inhibition activity against FXa and coagulation parameters did not show toxicity at the performed coagulation assay concentrations. Finally, docking studies confirmed the preferential binding mode of N-propargyltetrahydroquinoline and 1,2,3-triazole derivatives inside the active site of FXa.

Hyperthermia-triggered UK release nanovectors for deep venous thrombosis therapy

Deep vein thrombosis (DVT) is a common and lethal complication of surgery.

Prostacyclin reverses platelet stress fibre formation causing platelet aggregate instability

Prostacyclin (PGI₂) modulates platelet activation to regulate haemostasis. Evidence has emerged to suggest that thrombi are dynamic structures with distinct areas of differing platelet activation. It was hypothesised that PGI₂ could reverse platelet spreading by actin cytoskeletal modulation, leading to reduced capability of platelet aggregates to withstand a high shear environment. Our data demonstrates that post-flow of PGI₂ over activated and spread platelets on fibrinogen, identified a significant reduction in platelet surface area under high shear. Exploration of the molecular mechanisms underpinning this effect revealed that PGI₂ reversed stress fibre formation in adherent platelets, reduced platelet spreading, whilst simultaneously promoting actin nodule formation. The effects of PGI₂ on stress fibres were mimicked by the adenylyl cyclase activator forskolin and prevented by inhibitors of protein kinase A (PKA). Stress fibre formation is a RhoA dependent process and we found that treatment of adherent platelets with PGI₂ caused inhibitory phosphorylation of RhoA, reduced RhoA GTP-loading and reversal of myosin light chain phosphorylation. Phospho-RhoA was localised in actin nodules with PKA type II and a number of other phosphorylated PKA substrates. This study demonstrates that PGI₂ can reverse key platelet functions after their initial activation and identifies a novel mechanism for controlling thrombosis.

Investigation of the long-term patency of a transmural heparinized polycaprolactone and poly(D,L-lactic/glycolic acid) scaffold

BACKGROUND

The transmural biodegradable polycaprolactone/poly(D,L-lactic/glycolic acid) (PCL/PLGA) scaffold is a promising modality for diffuse coronary atherosclerosis cases that are not suitable for bypass grafting. The purpose of this study was to evaluate the long-term performance of the PCL/PLGA scaffold in vivo in the setting of polymer and heparin degradation.

MATERIALS AND METHODS

After mechanical drilling through the ventricular wall was performed in the whole ventricular wall, two scaffolds were implanted into the ventricular wall. Animals were grouped into the single drilling group (SD group), the blank scaffold group (BS group), and the heparinized scaffold group (HS group) and were allowed to survived for 6 mo. Next, the patency and integrity of the scaffolds were evaluated by echocardiography and 3D-DOCTOR software. Endothelium coverage of the lumen was evaluated by scanning electron microscopy. Neovessels and collagen fiber within the scaffolds were identified by histologic staining. Metabolite production of prostacyclin (PGI2) and thromboxane A2 (TXA2) in the plasma was measured by an enzyme-linked immunosorbent assay. The expression levels of PGI2 synthase and cyclooxygenase 2 (COX-2) involved in PGI2 production and COX-1 involved in TXA2 production were measured by Western blot analysis.

RESULTS

The heparinized scaffolds were patent for up to 6 mo and the lumen was covered with confluent endothelial cells. Histologic staining revealed collagen fiber remodeling and reconstruction of the neovascular network immediately surrounding the lumen. The expression of PGI2 synthase and COX-2 in the HS group was significantly higher compared with the SD and BS groups (P < 0.01). The expression of COX-1 was similar in the three groups (P > 0.05). Consistent with synthetase expression, a PGI2 metabolite (6-keto-PGF1a) also showed a significant increase in the HS group relative to the SD and BS groups (P = 0.021 and P = 0.015, respectively). Concomitantly, as a PGI2 antagonist, the TXA2 metabolite (TXB2) did not exhibit a significant difference among the three groups (P = 0.17).

CONCLUSIONS

Despite polymer and heparin degradation, the scaffold could continuously maintain the structural integrity and lumen patency for up to 6 mo by reinforcement of host collagen fiber and the balance of PGI2/TXA2.

The P2Y12 antagonists, 2-methylthioadenosine 5'-monophosphate triethylammonium salt and cangrelor (ARC69931MX), can inhibit human platelet aggregation through a Gi-independent increase in cAMP levels

ADP plays an integral role in the process of hemostasis by signaling through two platelet G-protein-coupled receptors, P2Y1 and P2Y12. The recent use of antagonists against these two receptors has contributed a substantial body of data characterizing the ADP signaling pathways in human platelets. Specifically, the results have indicated that although P2Y1 receptors are involved in the initiation of platelet aggregation, P2Y12 receptor activation appears to account for the bulk of the ADP-mediated effects. Based on this consideration, emphasis has been placed on the development of a new class of P2Y12 antagonists (separate from clopidogrel and ticlopidine) as an approach to the treatment of thromboembolic disorders. The present work examined the molecular mechanisms by which two of these widely used adenosine-based P2Y12 antagonists (2-methylthioadenosine 5'-monophosphate triethylammonium salt (2MeSAMP) and ARC69931MX), inhibit human platelet activation. It was found that both of these compounds raise platelet cAMP to levels that substantially inhibit platelet aggregation. Furthermore, the results demonstrated that this elevation of cAMP did not require Gi signaling or functional P2Y12 receptors but was mediated through activation of a separate G protein-coupled pathway, presumably involving Gs. However, additional experiments revealed that neither 2MeSAMP nor ARC69931MX (cangrelor) increased cAMP through activation of A2a, IP, DP, or EP2 receptors, which are known to couple to Gs. Collectively, these findings indicate that 2MeSAMP and ARC69931MX interact with an unidentified platelet G protein-coupled receptor that stimulates cAMP-mediated inhibition of platelet function. This inhibition is in addition to that derived from antagonism of P2Y12 receptors.

Role of platelets in the development of atherosclerotic disease and possible interference with platelet inhibitor drugs

During the last two decades, significant advances have been made in the understanding of atherosclerotic disease. The pathogenesis of atherosclerosis appears to depend on a precise sequence of critical events based on the interaction of blood elements and lipids with the arterial wall. The major critical events and their sequence appears to be as follows: hemodynamic stress and endothelial injury; arterial wall-platelet interaction; smooth muscle cell proliferation; lipid entry and accumulation; significant arterial narrowing with fibrosis and development of thrombi; and complications in the form of calcification, ulceration, aneurysm, acute thrombotic occlusion and embolization. This sequence of critical events starts at a young age and in all geographic racial groups. Their evolution into advanced symptomatic lesions takes many years and varies in incidence and extent among different geographic and ethnic groups. It appears that in promoting and accelerating this process into the advanced stage of the disease, the presence at a young age of the so-called risk factors of atherosclerotic disease is most important. The recent advances in the understanding of the atherosclerotic process will be highlighted in this chapter with particular attention being focused on the role of platelets and thrombosis in the development of the disease and the possible role of platelet inhibitor drugs on the prevention of coronary atherosclerotic disease.

A critique of paradoxes in current advice on dietary lipids

Beliefs about credible hypotheses of dietary causes of disease still need well-defined mediators to test for logical proof or disproof. We know that food energy causes transient postprandial oxidative insults that may not be fully reversible. Also, eating vitamin-like 18-carbon polyunsaturated fatty acids (PUFA) in foods maintains the 20- and 22-carbon highly unsaturated fatty acids (HUFA) in tissues. Tissue HUFA form hormone-like mediators that each amplify transient postprandial insults into fatal inflammatory, thrombotic and arrhythmic events in cardiovascular disease, a major preventable cause of death. Similar diet-based amplified events may also occur in other inflammatory proliferative disorders including cancer, dementia, arthritis and asthma. Puzzling paradoxes come from fragmented views of this situation which convey incomplete knowledge in oversimplified messages. Tools now exist to demonstrate successful prevention of two fatal food imbalances with credible dietary preventive interventions, but organizers and financers to help gather the evidence remain unknown. The overall evidence accumulated about diet, disease and death may be nearing a paradigm shift in which prior observed facts remain while beliefs about their accepted interpretation change.

Melatonin reduces pancreatic prostaglandins production and protects against caerulein-induced pancreatitis in rats

Melatonin has been used to treat experimental pancreatitis, although not all the drug's therapeutic mechanisms of melatonin have been defined. Prostaglandins (PGs) are proinflammatory mediators that exert their effects mainly locally during inflammatory diseases. The present study was undertaken to examine whether treatment with melatonin influences local PG production. An acute pancreatitis model in male Sprague-Dawley rats (225-275 g) was established by continuously infusing caerulein (15 mg/kg/hr). Mean arterial pressure and pancreatic perfusion were monitored continuously. Melatonin was delivered via the intraperitoneal route at doses of either 2 or 10 mg/kg, 30 min after caerulein injection. Malondialdehyde and glutathione levels of the pancreas and liver and the trypsinogen activation peptide levels in the serum were measured at the end of the experiment (8 hr after infusion of caerulein). Intraperitoneal injection of melatonin (2 and 10 mg/kg) reduced the reduction in systemic arterial pressure and decreased pancreatic perfusion in the rat model of caerulein pancreatitis. Moreover, melatonin treatment changed local PG production toward control level. Higher dose of melatonin was somewhat more effective in preventing the caerulein-induced alterations than was the lower dose.

Beraprost sodium, a prostacyclin (PGI) analogue, ameliorates concanavalin A-induced liver injury in mice

BACKGROUND/AIMS

Prostacyclin (PGI(2)) is a potent mediator in the inflammatory and coagulation processes. The aim of this study was to test whether beraprost sodium, a PGI(2) analogue, could prevent experimental hepatic injury induced by concanavalin A (Con A), which is a model of fulminant hepatic failure.

METHODS

Beraprost (100 microg/kg) was administered intraperitoneally simultaneously with Con A (40 mg/kg) in C57B6J mice. Blood circulation in the liver was determined by laser-Doppler flowmetry. Plasma levels of alanine aminotransferase (ALT), tumor necrosis factor (TNF)-alpha, interferon (IFN)-gamma, and interleukin (IL)-6 were determined. Levels of TNF-alpha and IFN-gamma in culture supernatant of splenocytes were also determined.

RESULTS

Beraprost administration reduced the incidence of death following hepatic failure (76.5% vs. 29.4%, P<0.05). Plasma levels of ALT were significantly lower in the beraprost-treated group than in the control group, and in the former, there was concomitant suppression of the histological features of injury. Beraprost significantly increased hepatic blood flow volume in Con A-treated mice. Plasma levels of TNF-alpha and IFN-gamma were significantly reduced at 6 and 12 h after Con A injection, respectively, but the levels of IL-6 were increased at 6 h. In vitro, beraprost also suppressed Con A-induced TNF-alpha production in splenocytes, while it stimulated IFN-gamma production.

CONCLUSION

These findings imply that beraprost suppresses Con A-induced liver injury. These data also suggest that beraprost, which is clinically effective in treating pulmonary hypertension, may have therapeutic potential for preventing hepatic injury.

Role of prostacyclin on microcirculation in endotoxin-induced gastroprotection in rats: a microdialysis study

Numerous mechanisms relating to lipopolysaccharide- (LPS) induced gastroprotection have been proposed. The prostaglandin (PG) system is a promising candidate that has received considerable attention. However, the role of prostacyclin (PGI2) remains unclear. Adult, male Sprague-Dawley rats were divided into four groups: (1) control, n = 6; (2) LPS (LPS, 10 mg/kg, i.v.), n = 7; (3) LPS + indomethacin (Indo) (LPS, 10 mg/kg and indomethacin 5 mg/kg, i.v.), n = 7; and (4) Indo (indomethacin 5 mg/kg, i.v.), n = 7. Additionally, gastric microcirculation was investigated using in vivo microscopy. Tissue malondialdehyde (MDA) and glutathione levels were measured at the conclusion of the experiment. Specifically, microdialysis was used to measure the 6-keto-PGF1alpha, a stable metabolite of PGI2, while flow cytometry was used to measure the CD11b/CD18 expression of circulating neutrophils. Compared with LPS alone, LPS with Indo significantly impaired gastric microcirculation and systemic hemodynamics. LPS-induced gastroprotection was lost, as evidenced by the increased adherent leukocyte count, decreased flow velocity in the post-capillary venules, and increased tissue MDA production. Meanwhile, the luminal glucose and protein contents that comprised the gastric mucosa injury index were significantly increased. These effects of Indo are directly associated with the levels of PGI2 in gastric tissue, which increased with LPS alone and significantly decreased with a combination of LPS and Indo. This work demonstrates that PGI2 contributes to LPS-induced gastroprotection.

Efficacy of prostacyclin analogue (OP-2507) in viable hepatic grafts from pigs with non-beating hearts

We investigated whether the stable prostacyclin analogue (OP-2507; OP) would ameliorate warm ischemia-related injury of the liver graft under conditions of a nonbeating heart. Thirty-six mongrel pigs were arranged into 3 groups of 6 pairs. Group 1 pigs underwent orthotopic liver transplantation from heart-beating donors (HBD). In group 2, animals received liver grafts from nonheart-beating donors (NHBD), defined as 30 min of cardiac arrest. Group 3 pigs received grafts from NHBD, but the donor had been pretreated with OP by intraportal infusion (2 microg/kg x min for 30 min immediately before the induction of cardiac arrest). The grafts were preserved at 4 degrees C in Euro-Collins solution in which OP was dissolved at 200 microg/l. Five-day survival rates after transplantation improved significantly in OP-treated animals (3/6, for group 3), compared with 0/6 for group 2 (P < 0.05, generalized Wilcoxon test). Five of 6 animals survived more than 5 days in the HBD group (group 1). Although the serum transaminase activities and bile production did not differ in the early phase of recirculation among the groups, there was a significant improvement in the hepatic microcirculatory environment in the surviving groups (groups 1 and 3). Analysis of arterial prostanoid levels showed a substantial suppression of PGE2 release by OP treatment following reperfusion. Our data indicate that a stable prostacyclin analogue can be clinically useful for expanding the donor pool by improving the quality of the liver graft.

The influence of pulsatile preservation on renal transplantation in the 1990s

BACKGROUND

Unlike simple cold storage (CS), pulsatile machine preservation (MP) of kidneys for transplantation permits pharmacologic manipulation of the perfusate and aids in the pretransplant assessment of the kidney graft. These characteristics of MP may have importance in the era of increasing use of extended criteria donor kidneys. The overall aim of this article is to critically assess practices at our preservation unit with respect to graft function. Specific aims are to (1) compare the influence of MP versus CS on graft function, (2) determine which pretransplant variables have significance in pretransplant assessment, and (3) determine whether pharmacologic manipulation during MP is advantageous.

METHODS

There were 650 consecutive kidneys preserved in our laboratory between January 1, 1993 and March 1, 999, by either MP or CS. All MP kidneys were preserved by continuous hypothermic pulsatile perfusion using Belzer-MPS or Belzer II solution. Perfusion parameters and electrolytes were measured serially during pulsatile perfusion. All CS kidneys were stored in University of Wisconsin solution. All kidneys obtained from donors exhibiting extended criteria features underwent pretransplant frozen section biopsies. Transmission electron microscopy (EM) was performed on a subset of kidneys undergoing pharmacologic manipulation. Four agents were assessed prospectively for their ability to influence MP characteristics when added to perfusate: PGE1, trifluoperazine, verapamil, and papaverine.

RESULTS

MP was associated with improved immediate, 1-, and 2-year graft function and reduced length of initial hospital stay when compared with CS grafts. Changes in the machine perfusion variables flow and resistance, and the [Ca++] in perfusate, were significantly associated with delayed graft function (DGF) after the transplant. Biopsy information was not predictive of DGF. The addition of PGE1 to perfusate improved MP characteristics, reduced the release of [Ca++] into perfusate, and ameliorated mitochondrial ischemic injury in transmission EM images. Early graft function was improved in the presence of PGE1+MP, compared with function in the presence of other pharmacologic agents or CS alone.

CONCLUSIONS

MP is associated with improved early and long term renal function. Moreover, PGE1 augments MP in improving graft function. The combination of MP+PGE1 may be important in optimizing the ability to use extended donor criteria kidneys and, thereby, improve the overall efficiency of cadaveric renal transplantation.

Prostacyclin analogue (OP-2507) attenuates hepatic microcirculatory derangement, energy depletion, and lipid peroxidation in a rat model of reperfusion injury

BACKGROUND

Microcirculatory derangement, energy depletion, and lipid peroxidation are associated with the development of ischemia-reperfusion injury in the liver. This study investigated the effects of a prostacyclin analogue (OP-2507) on hepatic ischemia-reperfusion injury.

MATERIALS AND METHODS

Adult, male Sprague-Dawley rats were divided into four treatment groups: (1) sham-operated control (laparotomy only, no ischemia), N =6; (2) ischemia control (1 h ischemia, 2 h reperfusion), N = 6; (3) intravenous infusion with OP-2507 ([15-cis-14-propylcyclohexyl]-16, 17,18,19,20-pentanor-9-deoxy-9a,6-nitrilo-PGF, methyl ether; Ono Pharmaceutical Co, Ltd, Osaka, Japan) at a dose of 1 microg/kg/min plus ischemia (1 h ischemia, 2 h reperfusion), N = 6; and (4) intravenous infusion with OP-2507 at a dose of 0.1 microg/kg/min plus ischemia (1 h ischemia, 2 h reperfusion), N = 6. A laser-Doppler flowmeter and in vivo microscopy were used to investigate hepatic microcirculation. Tissue malondialdehyde (MDA) and adenosine triphosphate (ATP) levels were determined at the end of the experiment.

RESULTS

Compared with ischemia alone, OP-2507 significantly reduced the extent of microcirculatory and hemodynamic derangement following ischemia-reperfusion. The changes of mean systolic arterial pressure (MSAP) following ischemia-reperfusion showed biphasic alterations. OP-2507 at both doses significantly attenuated decreases in MSAP. OP-2507 lessened adherent leukocyte count and improved flow velocity in the sinusoids and postsinusoidal venules. OP-2507 at the dose of 1 microg/kg/min reduced MDA (1.04 +/- 0.27 micromol/g protein vs 2.64 +/- 0.59 micromol/g protein in the ischemia and reperfusion group) and increased ATP levels (2.03 +/- 0.17 micromol/g wet wt vs 0.73 +/- 0.21 micromol/g wet wt in the ischemia and reperfusion group), while OP-2507 at a smaller dose (0. 1 microg/kg/min) had lesser but significant effects on MDA and ATP alterations.

CONCLUSION

This study demonstrates that OP-2507 treatment of ischemia can ameliorate ischemia-reperfusion injury of the rat liver.

The effects of epoprostenol on drug disposition. I: A pilot study of the pharmacokinetics of digoxin with and without epoprostenol in patients with congestive heart failure

The influence of epoprostenol on the pharmacokinetics of drugs administered concurrently to patients with congestive heart failure (CHF) receiving epoprostenol was evaluated as a secondary objective of a Phase II pilot study. A total of 278 blood samples were collected from 30 patients with end-stage CHF receiving conventional therapy alone or conventional therapy plus epoprostenol. Estimates of oral clearance (Cl), volume of distribution, and absorption rate constant of digoxin were generated from plasma digoxin concentrations using nonlinear mixed effects modeling, and the effect of epoprostenol on Cl of digoxin was evaluated by univariate analysis. Additional factors that were evaluated by univariate analysis included age, obesity, time since study entry, cardiac output, concomitant use of angiotensin-converting enzyme (ACE) inhibitor, concomitant dobutamine, and estimated creatinine clearance. Backward elimination was used to arrive at a final model that included concomitant epoprostenol as a covariate. The final model revealed an approximate 15% decrease in Cl of digoxin in response to short-term administration of epoprostenol that was no longer apparent by the end of the 12-week treatment phase. Simulations revealed that this effect, although statistically significant, would not be clinically significant in most patients; however, the potential exists for short-term elevation of digoxin concentrations in response to concurrent administration of epoprostenol.

The effects of epoprostenol on drug disposition. II: A pilot study of the pharmacokinetics of furosemide with and without epoprostenol in patients with congestive heart failure

The effect of epoprostenol on the pharmacokinetics of furosemide was investigated in 23 patients with end-stage congestive heart failure (CHF) receiving conventional therapy alone or conventional therapy plus epoprostenol. Estimates of the apparent oral clearance, volume of distribution, and absorption rate constant for furosemide were generated from 198 serum furosemide concentrations using nonlinear mixed effects modeling (NONMEM). Univariate analyses were performed to assess the effects of patient factors on the apparent oral clearance of furosemide. The final multivariate model determined by backwards elimination included concomitant digoxin therapy. When concomitant epoprostenol therapy was included in the final model, there was a 13% decrease in the apparent oral clearance of furosemide in response to short-term administration of epoprostenol. However, the effect of concomitant epoprostenol therapy was not statistically significant and was no longer apparent by the end of the 12-week study. These data suggest that epoprostenol may have a slight short-term effect on the pharmacokinetics of furosemide; the interaction between epoprostenol and furosemide is not clinically significant, however.

Increased thromboxane A2 production at primary tumor site in metastasizing squamous cell carcinoma of the larynx

In order to evaluate the possible role of prostaglandins (PG) in invasion and metastasis of malignant cells in larynx carcinoma, arachidonic acid (AA) metabolite production by tumor tissue, peritumor tissue and node metastasis was investigated in comparison to that by healthy mucosa and unaffected lymph nodes. The study was performed by evaluating PGE2, 6ketoPGF1 alpha and thromboxane B2 (TXB2) production by radioimmunoassay in specimens from eight patients who underwent surgical treatment. The highest rate of AA metabolism was observed in peritumor tissue. PGE2 was the main metabolite produced in all tissues and its levels were significantly higher than those of 6ketoPGF1 alpha and TXB2 (p < 0.05). 6ketoPGF1 alpha production was higher (p < 0.01) than that of TXB2 and did not significantly change among the different tissues. TXB2 production was significantly increased (p < 0.05) by peritumor tissue as compared to healthy mucosa. The ratio between TXB2 and 6ketoPGF1 alpha production was found to be almost twofold higher in tumor tissue, peritumor tissue, metastatic and non-metastatic lymph nodes as compared to control tissue. The lowest AA metabolism was found in affected lymph nodes. These findings demonstrate a different AA metabolism at primary tumor sites in comparison to healthy mucosa suggesting a prometastatic role of TXB2 and supporting the hypothesis of the occurrence of an imbalance between TXB2 and 6ketoPGF1 alpha production in favouring metastatic spread.

Efficacy of PGI2 analog in preventing ischemia reperfusion damage of liver grafts from living donors

In living-related transplantation, warm ischemia/reperfusion damage (IRD) of liver grafts is inevitable during harvesting. In this study, we investigated the effects of prostacyclin (PGI2) on IRD of liver grafts in the rat liver transplant model. Donor rats underwent 30-min warm ischemia of part of the liver (right lateral and medial lobes). After 10 min of reflow, the ischemic partial livers were flushed with Ringer's lactate and immediately transplanted into untreated recipients. Donor animals were divided into two groups: group I received vehicle, and group II received PGI2 analog OP-41483 (OP, 500 ng/kg per min, i. v.) during the donor operation. One-week survival was studied and cellular adenine nucleotide levels of donor livers were assayed by high-performance liquid chromatography (HPLC). Donor treatment with PGI2 analog group II significantly improved 1-week survival (86%), in comparison with the controls group I (25%). The levels of total adenine nucleotides (TAN, micromol/g dry wt) of the grafts just before implantation were well maintained by PGI2 treatment (12.22), as compared with the controls (10.36). In summary, PGI2 treatment of the donor maintained high energy metabolism of the liver graft after IRD and improved the survival of recipients after transplantation. Our study suggested that PGI2 treatment of donors improves viability in liver grafts from living donors thus and increases graft availability for transplantation.

Reduced thrombus formation in vivo after administration of pentoxifylline (Trental)

The hamster cheek pouch model of experimental thrombosis in which thrombi are induced in the microvasculature by iontophoretical administration of adenosine diphosphate (ADP) was used to test the antithrombotic potential of pentoxifylline (Trental). Single intraperitoneal injections of 5, 10 and 20 mg/kg pentoxifylline reduced thrombus formation by 20 to 50% from 30 to 105 min following drug administration. The effect of a single application of 10 mg/kg was exceeded significantly (p less than 0.05) by the higher rate of inhibition after repeated injections of the same dose given three times daily. This suggests a residual antithrombotic effect from the preceding administrations.

The effects of PGI2 analog (OP-41483) on perfused porcine liver

The effects of a prostacyclin analog OP-41483 on energy metabolism were studied in an isolated porcine liver perfused with human blood for 8 h. OP-41483 was administered intravenously at a rate of 0.3 microgram/kg/min during the procurement and into the perfusate at a rate of 1.0 microgram/min during perfusion. Acetoacetate, beta-hydroxybutyrate, lactate, and pyruvate were measured before perfusion and at 1, 2, 3, 5, and 8 h after perfusion, from which values the ketone body ration (acetoacetate/beta-hydroxybutyrate, KBR), reflecting the redox state of liver mitochondria, was calculated. In the OP-41483 group, KBR increased rapidly from 0.34 to 0.95, 1.61, 1.51, 2.35, and 2.04, and lactate decreased rapidly from 9.81 to 6.30, 4.51, 3.22, 2.39, and 1.33 mmol/L at the respective hours after perfusion. There were significant differences after 3 h of perfusion as compared with the control group (p less than 0.05). These results suggest that administration of OP-41483 causes an increase in mitochondrial NAD+/NADH ratio (oxidized and reduced forms of free nicotinamide-adenine dinucleotides), leading to an enhancement of the metabolic capacity of the perfused liver.

Formation of prostacyclin-sensitive platelet aggregates in human whole blood in vitro. Part II. The occurrence of the phenomenon in males suffering from acute myocardial infarction

The de-aggregatory effect of prostacyclin (PGI2) and the rate of spontaneous platelet aggregation (SPA) were studied in vitro in whole blood of 24 males with acute myocardial infarction (MI) and 18 males, patient controls (PC). The de-aggregatory effect of PGI2 and the rate of SPA (measured as a percentage of changes in free platelet number in whole blood) were higher (p less than 0.01) in MI than PC. The de-aggregatory effect of PGI2 in whole blood was higher (p less than 0.05) on the first day of MI than on day 14 following MI. The highest de-aggregatory effect of PGI2 was found in whole blood of patients with MI complicated by ventricular fibrillation. In neither of the groups did the de-aggregatory effect of PGI2 correlate with patients' age, haematocrit, erythrocyte and leucocyte counts, triglycerides, HDL, LDL or total cholesterol levels. In the MI group, de-aggregatory effect of PGI2 was correlated with free platelet concentration (r = -0.59, p less than 0.05), elevation of glutamic oxalacetic transaminase (r = 0.53, p less than 0.05) and creatinine phosphokinase (r = 0.69, p less than 0.001). The de-aggregatory effect of PGI2 in blood of patients with evolving MI did not differ from that in PC. It is concluded that the increased rate of SPA and formation of PGI2-sensitive platelet aggregates in vitro in whole blood of MI patients are secondary to myocardial necrosis.

In vivo measurement of the disaggregatory action of prostacyclin. A methodological study

The disaggregating effect of PGI2 was measured in a modified in vivo model described by Hornstra. The arterial blood of mongrel dogs was directed through an extracorporeal filter by a roller pump, and the pressure proximal to the filter was measured. The filter became spontaneously occluded mostly by aggregates of platelets within a few minutes, and as a result the pressure before the filter increased continuously. PGI2, administered either before the filter or intravenously, produced dose-related reduction in filtration pressure. Results obtained in control experiments revealed that the rate of platelet aggregation was reproducible; neither the count of platelets in the circulating blood nor the in vitro sensitivity of platelets to ADP and PGI2 changes significantly in the course of an experiment. The technique described seems to be useful to determine the disaggregatory potency of prostacyclin and other substances.

Physiology and pharmacology of prostaglandins

Prostaglandins (PGs) are products of polyunsaturated acid metabolism, particularly arachidonic acid (AA) released from membrane phospholipids by the action of phospholipase A2 in response to a variety of physical, chemical, and neurohormonal factors. AA is rapidly metabolized to oxygenated products by two distinct enzymatic pathways: cyclooxygenase and lipoxygenase. The intermediate cyclooxygenase products are converted to primary PGs, while the lipoxygenase products are converted to leukotrienes. The generation of various cyclooxygenase products varies from tissue to tissue. Aspirin and related antiinflammatory drugs reduce tissue biosynthesis of all cyclooxygenase products; their therapeutic effects and side effects parallel the inhibition of cyclooxygenase. Exogenous PGs exhibit a broad spectrum of effects. PGs of the E series and PGI2 are generated by the endothelium and the vessel wall to maintain the microcirculation and to counteract the vasoconstrictive and proaggregatory actions of thromboxane A2 (TXA2). Exogenous PGs of the E and I series are potent vasodilators in various vascular beds, and result in decreased systemic blood pressure and reflex stimulation of heart rate. PGEs and PGI2 increase renal blood flow and provoke diuresis and natriuresis, partly by modulating the renin-angiotensin-aldosterone system. PGFs contract the bronchial and gut muscle, while PGEs and PGI2 have opposite effects. PGEs and PGFs, but not PGI2, cause a strong contraction of the uterine muscle, hence their undesirable uterotonic effects. PGEs relax bronchial muscle, whereas PGFs cause bronchoconstriction; their imbalance may contribute to the high bronchial tone in bronchial asthma. PGs of the E and I series and TXA2 are generated by the gastrointestinal mucosa and released into the lumen upon neural or hormonal stimulation; they probably participate in the maintenance of mucosal integrity and microcirculation. Exogenous PGs of the E and I series inhibit gastric acid secretion and stimulate alkaline secretion while increasing mucosal blood flow. All PGs, including those noninhibitory for acid secretion, are cytoprotective against various ulcerogens and necrotizing agents. The classic PGs constitute only a small fraction of biologically active products of AA metabolism, and recent studies on the lipoxygenase products emphasize their biological activity and involvement in a variety of pathological conditions.

Effect of calcium dobesilate and its interaction with aspirin on thrombus formation in vivo

The effect of calcium dobesilate (calcium dihydroxy-2,5 benzenesulphonate) on thrombus formation in vivo was evaluated. Experimental thrombi were induced in a venule of a hamster cheek pouch following iontophoresis of adenosine diphosphate (ADP). Calcium dobesilate administered intraperitoneally as a single injection inhibited thrombus formation in a time- and dose-dependent manner. Furthermore, the combination of calcium dobesilate and aspirin resulted in the potentiation of the inhibition of thrombus formation.

Prostaglandin endoperoxides and thromboxane A2 in thrombus formation in the hamster cheek pouch in vivo

Electrical stimulation in the presence of ADP of arterioles of the hamster cheek pouch caused endothelial damage and white thrombus formation. The thrombus formation was inhibited by cyclo-oxygenase inhibitors aspirin and sulphinpyrazone and its thioether derivative G 25671. Thromboxane synthetase inhibitors N-(7-carboxyheptyl) imidazole and butylimidazole failed to inhibit thrombus formation, although in the same doses both compounds inhibited serum levels of thromboxane. These results indicate that thromboxane is not important in thrombus formation in the hamster, but that prostaglandin endoperoxides are more significant. However, it is possible that the inhibition of white thrombus formation by aspirin, sulphinpyrazone and G 25671 may be mediated by a different mechanism altogether.

Manipulation of thrombus formation in the hamster cheek pouch with drugs that interact with PGI2 in vitro

A single platelet thrombus was formed in an arteriole of the hamster cheek pouch by electrical stimulation followed by topical application of ADP. The sizes of the thrombi were continuously recorded with a photocell placed on a TV monitor screen and quantified by areas on the record. Repeated application of small doses of ADP (5-15 nmole/10 microliters) resulted in very reproducible formation of the thrombi, and the size of the thrombi was reduced dose-dependently by topical application of PGI2. Three drugs were tested in this model. Cyclooxygenase inhibitor (indomethacin 10 mg/kg, i.p.) increased the formation of thrombi, while a smaller dose (3 mg/kg) did not have any significant effect. This could be explained by inhibition of the generation of endogenous PGI2, since aggregation of hamster platelets by ADP was not inhibited by indomethacin in vitro. EG-626 (phthalazinol, a phosphodiesterase inhibitor) (300 mg/kg, i.p.) decreased the size of thrombus. AI-122 (1.0 mg/kg, i.p.), which has been proven to enhance PGI2 biosynthesis from isolated rat aortae, also decreased the formation. Thus, drugs such as EG-626 or AI-122 are quite promising as anti-thrombotic drugs.

Effects of intravenous prostacyclin in variant angina

A lack in prostacyclin (PGI2) production due to atherosclerosis may play a role in the pathophysiology of some of the clinical manifestations of ischemic heart disease and in particular, of coronary vasospasm. We therefore evaluated the effects of i.v. PGI2 in nine patients with variant angina and six normal volunteers. In normal subjects, PGI2 (2.5, 5, 10 and 20 micrograms/kg/min) had significant antiplatelet effects, caused a dose-dependent decrease in both systolic and diastolic arterial pressure and a decrease in pulmonary resistance. Heart rate increased in a dose-dependent manner, but no consistent effects on myocardial contractility (evaluated by ultrasound) were observed. Side effects were negligible and readily reversible. Although producing obvious antiplatelet and vasodilatory effects, PGI2 did not affect the number, severity and duration of spontaneous ischemic episodes due to coronary vasospasm in five patients and ergonovine-induced spasm in three. However, the number of ischemic episodes was consistently reduced in one patient during four consecutive periods of PGI2 infusion alternated with placebo. a severe, prolonged ischemic episode with ST elevation and pain was consistently observed in this patient every time PGI2 was discontinued. In the appropriate environment, PGI2 can be administered safely to patients with ischemic heart disease. Occasionally, PGI2 may result in a complete disappearance of ischemic episodes due to coronary vasospasm, but usually it is ineffective. These conflicting results could be related to different etiologies of coronary spasm.

A radioimmunoassay for 6-ketoprostaglandin E1

A radioimmunoassay for 6-ketoprostaglandin E1 has been developed. 6-keto-prostaglandin E1 antibodies were produced in rabbits by repeated immunization with 6-ketoprostaglandin E1 coupled to bovine serum albumin. [125]-labeled hapten with high specific radioactivity was prepared by radioiodination of 6-ketoprostaglandin in E1-tyrosine methyl ester conjugate followed by purification with thin layer chromatography. The antibodies showed good specificity toward 6-ketoprostaglandin E1 and crossreacted only significantly with prostaglandin E1. The sensitivity of the assay was 10 pg per assay tube. Application of the radioimmunoassay was demonstrated by the detection of immunoreactive 6-ketoprostaglandin E1 from 6-ketoprostaglandin F1 alpha catalyzed by swine renal NADP+-linked 9-hydroxyprostaglandin dehydrogenase.

Biosynthesis of prostacyclin in rat cerebral microvessels and the choroid plexus

Microvessels, predominantly capillaries, were isolated from rat cerebrum by a modification of published procedures. The morphology and purity of the preparations were monitored by light and electron microscopy and by enrichment in alkaline phosphatase, gamma-glutamyl transpeptidase, and prostacyclin, synthetase. A reversed-phase high-pressure liquid chromatographic method was used in the purification of prostaglandins after extraction from aqueous incubation solutions. Prostacyclin synthesis in brain is localized in cerebral blood vessels and capillaries. The endogenous biosynthetic capacity of the isolated cerebral capillary fractions for prostacyclin, measured as its chemically stable breakdown product, 6-keto-prostaglandin F1 alpha, was 11 ng/mg protein/10 min. Choroid plexus and intact surface vessels synthesized 6-keto-prostaglandin F1 alpha at 37 and 35 ng/mg protein/10 min, respectively. The prostacyclin-synthesizing enzyme of the cerebral capillaries also converted the exogenously added prostaglandin endoperoxides to 6-keto-prostaglandin F1 alpha. Comparison of the synthesis of prostaglandins 6-keto-F1 alpha, E2, and F2 alpha showed that 6-keto-prostaglandin F1 alpha was the major prostaglandin formed in the microvessels, in the larger surface vessels, and in the choroid plexus. Prostaglandin D2 was not detected. Prostacyclin synthesis by the cerebral vasculature is similar to that in other blood vessels and cultured human endothelial cells. Possible physiological roles or prostacyclin in the cerebral microvasculature are discussed with special regard to the autoregulation of cerebral blood flow.

Prostaglandin I2 (prostacyclin)

Prostaglandin I2 (PGI2), or prostacyclin, is a recently discovered prostaglandin that affects many organ systems. It is both a potent inhibitor of platelet aggregation and a powerful vasodilator. The recent demonstration that it is the main prostaglandin synthesized by the blood vessel wall suggests that it may play an important role in limiting platelet-mediated thrombosis. However, despite considerable investigation, the exact physiological role of PGI2 has yet to be elucidated.