An enzymatic mechanism for the antithrombotic and antihemostatic actions of aspirin

A retrospective study on IVF/ICSI outcomes in patients with persisted positive of anticardiolipin antibody: Effects of low-dose aspirin plus low molecular weight heparin adjuvant treatment

Antiphospholipid (aPL) antibodies are more frequently detected among infertile women, but the association between aPL and in vitro fertilization (IVF)/intracytoplasmic sperm injection (ICSI) outcomes and whether need to get routine treatment are still controversial. The present study aims to find out whether infertile population with persistent aPL positive need treatment and which therapy is more effective. This retrospective study included 181 persistent aPL positive women, including 149 cases receiving anticoagulant treatment, either low-dose aspirin, low molecular weight heparin (LMWH) or aspirin plus LMWH adjuvant treatment (treated group), and 32 cases not receiving any treatment (untreated group). The treated group were further divided by combination therapy group (using both aspirin and LMWH，52 cases) and monotherapy group (only using aspirin，76 cases). The live birth rate and other clinical outcomes, including pregnancy rate, implantation rate, ongoing pregnancy rate and miscarriage rate were compared. The results show anticoagulant therapy can significantly improve live birth rate (59.06 % VS 34.48 %, P = 0.019), implantation rate (59.64 % VS 46.15 %, P＜0.001), ongoing pregnancy rate (59.73 % VS 34.38 %, P = 0.016), as well as reduce miscarriage rate (8.25 % VS 31.25 %, P＜0.001). Combination treatment of aspirin and LMWH exerts a higher live birth rate than monotherapy (75.00 % VS 53.95 %, P = 0.026). Infertile women with aPL positive might be classified as high-risk and low-risk aPL profiles. Those high-risk aPL positive infertile populations should be identified during IVF/ICSI and given corresponding thromboprophylaxis, and aspirin plus LMWH adjuvant treatment might be recommended.

Long-term pituitary downregulation before frozen embryo transfer improves clinical outcomes in women positive for serum autoantibodies

OBJECTIVE

Autoantibodies are associated with worse outcomes in vitro fertilization (IVF)/intracytoplasmic sperm injection (ICSI), including increasing miscarriage rate, lowering pregnancy rate, and lowering delivery rate. However, little is known about improving IVF/ICSI outcomes for autoantibody-positive women, especially in frozen-thawed embryo transfer (FET) cycles. This study aimed to investigate whether pituitary suppression before FET improves the clinical pregnancy rate (CPR) and live birth rate (LBR) for IVF/ICSI women positive for serum autoantibodies.

STUDY DESIGN

A total of 181 infertile women positive for serum autoantibodies were recruited, including 65 women receiving GnRHa and hormone replacement therapy protocols (G-HRT group) and 116 women using modified natural cycles (MNC)/mild stimulated cycles (MSC) as FET protocols (MNC/MSC group). The outcomes were compared between two groups, including CPR, implantation rate (IR), miscarriage rate (MR), ongoing pregnancy rate (OPR), LBR, and gestational age (GA). The primary outcome of the study was CPR.

RESULTS

CPR, OPR, and LBR per embryo transferred in the G-HRT groups were significantly higher than those in the MNC/MSC group. No statistically significant differences were observed in the IR and MR. The CPR, IR, MR, OPR, and LBR was 72.23%, 64.00%, 12.77%, 63.07%, and 63.07% in the G-HRT group, respectively, while that was 56.90%, 53.07%, 10.60%, 50.00%, and 50.00% in the MNC/MSC group, respectively. After adjusting for partial potential confounding factors using multiple logistic regression, the type of endometrial preparation is the factor independently associated with enhanced CPR (OR = 0.48, 95%CI: 0.24-0.96, P = 0.039).

CONCLUSIONS

The current study showed that prior long-term GnRHa suppression could benefit patients with high serum autoantibody levels during IVF/ICSI FET cycles.

Association of serum autoantibodies with pregnancy outcome of patients undergoing first IVF/ICSI treatment: A prospective cohort study

The relevance of antiphospholipid (aPL), antinuclear (ANA) or antithyroid (ATA) antibodies in women undergoing in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI) are controversial. The present study aims to investigate which autoantibodies are associated with the pregnancy outcome of patients undergoing first IVF/ICSI treatment. A total of 3763 IVF/ICSI patients were recruited from January to December 2015. Forty-five patients positive for aPL presenting adverse outcomes in their first cycle received low-dose aspirin treatment before the second transfer. Logistic regression analyses were performed to assess any association between autoantibodies and IVF/ICSI outcomes. The aCL-IgG was significantly associated with live birth rate (OR 0.58, 95% CI 0.36-0.96, p<0.05) and miscarriage rate (OR 2.04, 95% CI 1.23-3.40, p<0.01). The aCL-IgM was associated with miscarriage rate (OR 2.14, 95% CI 1.29-3.54, p<0.01). The aβ₂GPI-IgG was associated with implantation rate and clinical pregnancy rate (OR 0.61, 95% CI 0.24-0.96, p<0.05; OR 0.40, 95% CI 0.13-0.87, p<0.05, respectively). After the low-dose aspirin treatment, the live birth rate (37.0% vs. 19.1%, p<0.05) increased significantly in patients with positive for aPL. In contrary, the aβ₂GPI-IgM, ANA, anti-thyroglobulin (aTG) and anti-thyroperoxidase (aTPO) antibodies had no association with IVF/ICSI outcome. It is suggested that the presence of aCL-IgG, aCL-IgM and aβ₂GPI-IgG might exert a detrimental effect on IVF/ICSI outcomes. Low-dose aspirin treatment could be useful for patients positive for these antibodies. Therefore, it is suggested that these antibodies should be assessed prior to IVF/ICSI treatment.

Prostaglandins temporally regulate cytoplasmic actin bundle formation during Drosophila oogenesis

Tight regulation of actin remodeling is essential for development, and misregulation results in disease. Cytoskeletal dynamics are regulated by prostaglandins (PGs)—lipid signals. PGs temporally regulate actin remodeling during Drosophila oogenesis, at least in part, by modulating the activity of the actin elongation factor Enabled.

Prostaglandins (PGs)—lipid signals produced downstream of cyclooxygenase (COX) enzymes—regulate actin dynamics in cell culture and platelets, but their roles during development are largely unknown. Here we define a new role for Pxt, the Drosophila COX-like enzyme, in regulating the actin cytoskeleton—temporal restriction of actin remodeling during oogenesis. PGs are required for actin filament bundle formation during stage 10B (S10B). In addition, loss of Pxt results in extensive early actin remodeling, including actin filaments and aggregates, within the posterior nurse cells of S9 follicles; wild-type follicles exhibit similar structures at a low frequency. Hu li tai shao (Hts-RC) and Villin (Quail), an actin bundler, localize to all early actin structures, whereas Enabled (Ena), an actin elongation factor, preferentially localizes to those in pxt mutants. Reduced Ena levels strongly suppress early actin remodeling in pxt mutants. Furthermore, loss of Pxt results in reduced Ena localization to the sites of bundle formation during S10B. Together these data lead to a model in which PGs temporally regulate actin remodeling during Drosophila oogenesis by controlling Ena localization/activity, such that in S9, PG signaling inhibits, whereas at S10B, it promotes Ena-dependent actin remodeling.

Role of basic science in the development of new medicines: examples from the eicosanoid field

The role of basic science in the development of health care has received more and more attention. In my own area of research involving the so-called eicosanoids, there are many examples of how studies of structure and function of small molecules, as well as proteins and genes, have led to new therapeutic agents for treatment of a variety of diseases. In most of the cases, the discoveries have resulted in the recognition of novel therapeutic targets amenable to modulation by small molecules. However, there are also examples in which the molecular mechanisms of actions of drugs, discovered by phenotypic screening, have been elucidated. The majority of the examples in this article consist of approved drugs; however, in some cases, ongoing developments of potential therapeutics are cited.

The combined effects of ginkgo biloba extracts and aspirin on viability of sk-N-mc, neuroblastoma cell line in hypoxia and reperfusion condition

OBJECTIVE

The purpose of this study is to investigate the combined effects of ginkgo biloba extract, ginkgolide A and B and aspirin on SK-N-MC, human neuroblastoma cell viability and mRNA expression of growth associated protein43 (GAP43), Microtubule-associated protein 2 (MAP2), B-cell lymphoma2 (Bcl2) and protein53 (p53) gene in hypoxia and reperfusion condition.

METHODS

SK-N-MC cells were cultured with Dulbecco's Modified Eagle's Medium (DMEM) media in 37℃, 5% CO(2) incubator. The cells were cultured for 8 hours in non-glucose media and hypoxic condition and for 12 hours in normal media and O(2) concentration. Cell survival rate was measured with Cell Counting Kit-8 (CCK-8) reagent assay. Reverse transcriptase polymerase chain reaction (RT-PCR) was used to estimate mRNA levels of GAP43, MAP2, Bcl2, and p53 genes.

RESULTS

The ginkgolide A and B increased viable cell number decreased in hypoxic and reperfused condition. The co-treatment of ginkgolide B with aspirin also increased the number of viable cells, however, there was no additive effect. Although there was no increase of mRNA expression of GAP43, MAP2, and Bcl2 in SK-N-MC cells with individual treatment of ginkgolide A, B or aspirin in hypoxic and reperfused condition, the co-treatment of ginkgolide A or B with aspirin significantly increased GAP43 and Bcl2 mRNA levels. In MAP2, only the co-treatment of ginkgolide A and aspirin showed increasing effect. The mRNA expression of p53 had no change in all treating conditions.

CONCLUSION

This study suggests that the combined treatments of Ginkgo biloba extracts and aspirin increase the regeneration of neuroblastoma cells injured by hypoxia and reperfusion.

Low-dose aspirin reduces uteroplacental vascular impedance in early and mid gestation in IVF and ICSI patients: a randomized, placebo-controlled double-blind study

OBJECTIVE

To determine whether low-dose aspirin improves uteroplacental hemodynamics in unselected in-vitro fertilization/intracytoplasmic sperm injection (IVF/ICSI) subjects when medication is started concomitantly with controlled ovarian hyperstimulation.

METHODS

Thirty-seven pregnant women who had undergone IVF/ICSI and had been randomized to receive 100 mg aspirin (n = 17) or placebo (n = 20) daily, started concomitantly with controlled ovarian hyperstimulation, were included in this study. Doppler ultrasound examination was performed at 6, 10, 13 and 18 weeks' gestation. Uterine artery (UtA) pulsatility index (PI) was calculated and bilateral UtA notching was noted. Subplacental arcuate artery PI was obtained at 6 and 10 weeks' gestation. Umbilical artery (UA) PI and mean velocity were calculated at 10, 13 and 18 weeks' gestation. In the aspirin group there was one early pregnancy miscarriage, and one patient discontinued the study medication owing to early pregnancy bleeding. A total of 15 women in the aspirin group and 20 women in the placebo group underwent the complete ultrasound protocol.

RESULTS

At 6 weeks' gestation, arcuate artery PI and at 18 weeks' gestation, UtA PI were lower (P < 0.05) in the aspirin group than in the placebo group. At 18 weeks' gestation, bilateral UtA notching tended to be more common in the placebo group (40%) than in the aspirin group (13%) (P = 0.06). UA PI and mean velocity did not differ significantly between the groups.

CONCLUSION

Low-dose aspirin reduces uteroplacental vascular impedance in early and mid pregnancy in unselected IVF/ICSI subjects when medication is started concomitantly with controlled ovarian hyperstimulation.

Aspirin in women undergoing in vitro fertilization treatment: a systematic review and meta-analysis

OBJECTIVE

Many trials have evaluated the effects of aspirin in women undergoing IVF or intracytoplasmic sperm injection (ICSI) treatment. These trials have generally shown inconclusive or inconsistent findings. We conducted a systematic review of trials of aspirin during IVF or ICSI treatment to generate more precise estimates of effects and attempt to explore the reasons for the inconsistencies.

DESIGN

A systematic review and meta-analysis.

SETTING

Assisted conception units in different countries.

PATIENT(S)

Seven trials including 1,241 women undergoing controlled ovarian hyperstimulation (COH), IVF, or ICSI and day 3 embryo transfer.

INTERVENTION(S)

Low-dose aspirin supplementation versus placebo or no supplementation.

MAIN OUTCOME MEASURE(S)

Clinical pregnancy and live birth.

RESULT(S)

Searches were conducted in MEDLINE, EMBASE, Cochrane Library, ISI Proceedings, and SCISEARCH, and all randomized controlled trials that evaluated the effectiveness of aspirin compared to placebo or no treatment in women undergoing IVF-ICSI treatment were included. Study selection, quality appraisal, and data extractions were performed independently and in duplicate. Seven relevant trials were identified. Meta-analysis of these studies did not show a significant benefit of aspirin therapy in improving clinical pregnancy rate (relative risk [RR] 1.11, 95% confidence interval [CI] 0.95, 1.31) or live birth rate (RR 0.94, 95% CI 0.64, 1.39). There was no significant difference in miscarriage rate (RR 1.06, 95% CI 0.53, 2.11) or ectopic pregnancy rate (RR 2.24, 95% CI 0.70, 7.24). An improvement was noted in uterine artery pulsatility index (weighted mean difference: -0.78, 95% CI -0.87, -0.69) in women taking low-dose aspirin. The evidence regarding other outcomes was either not significant or contradictory.

CONCLUSION(S)

Currently available evidence does not support the use of aspirin in IVF or ICSI treatment. However, the noted trend of improvement in clinical pregnancy, and the lack of power even when the studies were pooled highlight the need for a definitive trial.

Low-dose aspirin for in vitro fertilization: a systematic review and meta-analysis

Despite recent advances in ovarian stimulation regimens and laboratory techniques, the pregnancy rate of assisted reproduction remains relatively low. New methods that would potentially improve implantation rates are needed. One proposed strategy involves enhancement of blood flow at the implantation site with the use of low-dose aspirin. We conducted a systematic review and meta-analysis to investigate the effect of low-dose aspirin on likelihood of pregnancy in women undergoing in vitro fertilization (IVF)/intracytoplasmic sperm injection (ICSI). An electronic search of the literature was conducted targeting reports published over the last 26 years. Only randomized controlled trials (RCTs) comparing aspirin with placebo or no treatment in IVF/ICSI women were included in the meta-analysis. A number of relevant outcomes including pregnancy and live birth (LB) rates were investigated. Pooled relative risk (RR) and 95% confidence interval (CI) were calculated using a random-effects model. Inter-study heterogeneity among the trials was assessed using the Cochran's Q test. Ten RCTs were identified from the literature search, six of which met the criteria for inclusion in the meta-analysis. Clinical pregnancy (CP) rate per embryo transfer (ET) was not found to be significantly different between patients who received low-dose aspirin and those who received placebo or no treatment (RR 1.09, 95% CI 0.92-1.29). None of the other outcomes, including CP per cycle, spontaneous abortion or ectopic pregnancy per CP and LB rate per cycle or ET was found to differ significantly between the compared groups. On the basis of up-to-date evidence, low-dose aspirin has no substantial positive effect on likelihood of pregnancy and, therefore, it should not be routinely recommended for women undergoing IVF/ICSI.

Low-dose aspirin does not improve ovarian responsiveness or pregnancy rate in IVF and ICSI patients: a randomized, placebo-controlled double-blind study

BACKGROUND

Poor ovarian and endometrial responses to gonadotrophin stimulation in assisted reproduction techniques lead to decreased pregnancy rates. The aim of the present study was to test the hypothesis that low-dose aspirin started prior to controlled ovarian stimulation improves ovarian responsiveness, pregnancy rate (PR) and pregnancy outcome.

METHODS

A total of 374 women who were to undergo IVF/ICSI were randomized to receive 100 mg of aspirin (n=186) or placebo (n=188) daily. Treatment was started on the first day of controlled ovarian stimulation. It was continued until menstruation or a negative pregnancy test. Pregnant women continued the medication until delivery. The main outcome measures were the number of oocytes, number and quality of embryos, the clinical PR and pregnancy outcome.

RESULTS

The mean (+/-SD) number of oocytes (12.0+/-7.0 versus 12.7+/-7.2), the total mean number of embryos (5.82+/-4.35 versus 5.99+/-4.66), the mean number of top quality embryos (0.99+/-1.39 versus 1.18+/-1.51) and the number of embryos transferred (1.64+/-0.64 versus 1.63+/-0.71) did not differ in the aspirin and placebo groups. Between the aspirin and placebo group, there was no statistically significant difference in clinical PR per embryo transfer (25.3%, n=44 out of 174 versus 27.4%, n=48 out of 175) or clinical PR per cycle initiated (23.7% versus 25.5%). Birth rate per embryo transfer did not differ significantly between the aspirin (18.4%) and placebo (21.1%) groups. The incidence of poor responders [12 (6.5%) versus 13 (6.9%)] was similar in both groups.

CONCLUSIONS

The present results indicate that low-dose aspirin treatment does not have any beneficial effect on ovarian responsiveness, PR and pregnancy outcome in unselected women undergoing IVF/ICSI.

Addition of eicosapentaenoic acid to gamma-linolenic acid-supplemented diets prevents serum arachidonic acid accumulation in humans

Previous studies reveal that supplementation of human diets with gamma-linolenic acid (GLA) reduces the generation of lipid mediators of inflammation and attenuates clinical symptoms of chronic inflammatory disorders such as rheumatoid arthritis. However, we have shown that supplementation with this same fatty acid also causes a marked increase in serum arachidonate (AA) levels, a potentially harmful side effect. The objective of this study was to design a supplementation strategy that maintained the capacity of GLA to reduce lipid mediators without causing elevations in serum AA levels. Initial in vitro studies utilizing HEP-G2 liver cells revealed that addition of eicosapentaenoic acid (EPA) blocked Delta-5-desaturase activity, the terminal enzymatic step in AA synthesis. To test the in vivo effects of a GLA and EPA combination in humans, adult volunteers consuming controlled diets supplemented these diets with 3.0 g/d of GLA and EPA. This supplementation strategy significantly increased serum levels of EPA, but did not increase AA levels. EPA and the elongation product of GLA, dihomo-gamma-linolenic acid (DGLA) levels in neutrophil glycerolipids increased significantly during the 3-wk supplementation period. Neutrophils isolated from volunteers fed diets supplemented with GLA and EPA released similar quantities of AA, but synthesized significantly lower quantities of leukotrienes compared with their neutrophils before supplementation. This study revealed that a GLA and EPA supplement combination may be utilized to reduce the synthesis of proinflammatory AA metabolites, and importantly, not induce potentially harmful increases in serum AA levels.

A chelate theory for the mechanism of action of aspirin-like drugs

Two hundred years after the discovery of the pharmaceutical usefulness of aspirin, it and aspirin-like drugs, a family with an ever-increasing number of members, are an indispensable part of modern life. However, the question as to how these drugs work in the body has remained unsettled. It is postulated here that this group of drugs may exert their therapeutic (and adverse) effects by chelating various physiologically important metallic cations in the body. The chelate theory is supported by the vast majority, if not all, of the observations on these drugs made in the past.

Early Treatment Diabetic Retinopathy Study design and baseline patient characteristics. ETDRS report number 7

The Early Treatment Diabetic Retinopathy Study (ETDRS), a multicenter collaborative clinical trial supported by the National Eye Institute, was designed to assess whether argon laser photocoagulation or aspirin treatment can reduce the risk of visual loss or slow the progression of diabetic retinopathy in patients with mild-to-severe nonproliferative or early proliferative diabetic retinopathy. The 3711 patients enrolled in the ETDRS were assigned randomly to either aspirin (650 mg per day) or placebo. One eye of each patient was assigned randomly to early argon laser photocoagulation and the other to deferral of photocoagulation. Both eyes were to be examined at least every 4 months and photocoagulation was to be initiated in eyes assigned to deferral as soon as high-risk proliferative retinopathy was detected. Examination of a large number of baseline ocular and patient characteristics indicated that there were no important differences between randomized treatment groups at baseline.

Biochemical and functional abnormalities in hypercholesterolemic rabbit platelets

This study was designed to elucidate changes in rabbit platelet lipids induced by a cholesterol rich diet and to explore the possible correlation of these lipid changes with platelet abnormalities. Pronounced biochemical alterations were observed when serum cholesterol levels of 700-1000 mg% were reached. Hypercholesterolemic (HC) platelets contained 37% more neutral lipids and 16% less phospholipids than the controls. Lysolecithin, cholesterol esters and phosphatidylinositol (PI) levels were increased in HC platelets, and the levels of phosphatidylcholine (PC) were decreased. The cholesterol/phospholipid molar ratio of lipidemic platelets increased from 0.55 +/- 0.011 to 0.89 +/- 0.016 (P less than 0.01) in eight weeks. HC platelets had 90% more arachidonic acid (AA) in the PI than normal platelets. No significant changes in AA of PC were observed. Platelet function was monitored by the uptake and release of [14C]serotonin in platelet rich plasma (PRP), using varying concentrations of collagen as an aggregating agent. The uptake of [14C]serotonin in HC and normal platelets ranged from 78-94%. The percent of [14C]serotonin released from normal and HC platelets was proportional to the concentration of collagen. However, lipidemic platelets were hyperreactive to low concentrations of collagen. Incorporation of 50 microM acetylsalicylic acid into the aggregating medium suppressed the release of [14C]serotonin in normal PRP by more than 90%, but had only a partial effect on lipidemic PRP.

Purification and characterization of sheep platelet cyclo-oxygenase. Acetylation by aspirin prevents haemin binding to the enzyme

Arachidonate cyclo-oxygenase (prostaglandin synthetase; prostaglandin endoperoxide synthetase; EC 1.14.99.1) was purified from sheep platelets. The purification procedure involved hydrophobic column chromatography using either Ibuprofen-Sepharose, phenyl-Sepharose or arachidic acid-Sepharose as the first step followed by metal-chelate Sepharose and haemin-Sepharose affinity chromatography. The purified enzyme (Mr approximately 65,000) was homogeneous as observed by SDS/polyacrylamide-gel electrophoresis and silver staining. The enzyme was a glycoprotein with mannose as the neutral sugar. Haemin or haemoglobin was essential for activity. The purified enzyme could bind haemin exhibiting a characteristic absorption maximum at 410 nm. The enzyme after metal-chelate column chromatography could undergo acetylation by [acetyl-3H]aspirin. The labelled acetylated enzyme could not bind to haemin-Sepharose, presumably due to acetylation of a serine residue involved in the binding to haemin. The acetylated enzyme also failed to show its characteristic absorption maximum at 410 nm when allowed to bind haemin.

Prostaglandins and human platelet aggregation. Implications for the anti-aggregating activity of thromboxane-synthase inhibitors

Selective pharmacological blockade of thromboxane-synthase in human platelets by dazoxiben resulted in the reorientation of cyclic-endoperoxides towards PGE2, PGD2 and PGF2 alpha. At concentrations which can be reached when thromboxane-synthase is inhibited, PGE2 (100-500 nM) exerted a marked, concentration-dependent pro-aggregatory effect. This required the formation of endogenous or the addition of exogenous endoperoxides and was prevented by PGD2 or 13-aza-prostanoic acid, a selective antagonist of PGH2/TxA2 receptors. The anti-aggregating effect of PGD2 was evident at concentrations lower than those obtained in dazoxiben-treated platelets. It is proposed that in the absence of TxA2 generation, a combination of endoperoxides and PGE2 may result in normal aggregation. The latter may be inhibited by PGD2. No interference of PGF2 alpha on platelet function could be shown.

Involvement of bivalent cations and arachidonic acid in neutrophil aggregation

Chemotactic factors and arachidonic acid aggregate neutrophils; indomethacin and 5,8,11,14-eicosatetraynoic acid, two blockers of cellular arachidonate metabolism, inhibit these responses. Additionally, A23187, an ionophore which specifically transports bivalent cations into cells, also aggregates the neutrophils, and this response, as well as the response to chemotactic factors, requires the presence of extracellular calcium and magnesium. In this report these relationships were further studied. It was found that human neutrophil aggregation stimulated by arachidonic acid required calcium and magnesium. Furthermore, cells preincubated with arachidonate for 4 min before exposure to the bivalent cations did not aggregate before or after this exposure and, following this exposure, were refractory to subsequent stimulation by more arachidonate, a chemotactic tripeptide (formylmethionylleucylphenylalanine), or A23187, i.e., these cells had become nonselectively desensitized to the aggregating agents. Finally, indomethacin and 5,8,11,14-eicoasatetraynoic acid inhibited the aggregation response stimulated by A23187 and their potency in doing so paralleled their potency in inhibiting the responses induced by arachidonate or the chemotactic tripeptide. Thus, the neutrophil aggregation responses induced by arachidonate, chemotactic factor, and A23187 were similarly influenced by preincubating the cells with arachidonate, had similar requirements for calcium and magnesium, and were similarly inhibited by blockers of arachidonate metabolism. It appears that bivalent cations and arachidonic acid play essential and, perhaps, interacting roles in the aggregation response to diverse stimuli.

Prostaglandins, platelets, and atherosclerosis

Metabolism of arachidonic acid (AA) in blood platelets and in vascular endothelium does not lead to prostaglandins, but thromboxane A2 and prostacyclin are generated. These labile metabolites of AA antagonize each other: thromboxane A2 is a vasoconstrictor and proaggregatory agent, whereas prostacyclin dilates arteries, prevents platelets from aggregation, and dissipates the preformed platelet clumps. Prostacyclin is a powerful stimulator of adenylate cyclase in platelets and therefore its antiplatelet action is potentiated by phosphodiesterase inhibitors such as theophylline or dipyridamole. Cyclo-oxygenase of AA is inhibited by aspirin, thromboxane synthetase by analogues of prostaglandin endoperoxides, and prostacyclin synthetase by linear lipid peroxides. A hypothesis is put forward that atherosclerosis develops because of pathological, nonenzymic lipid peroxides. A hypothesis is put forward that atherosclerosis develops because of pathological, nonenzymic lipid peroxydation in the body and the subsequent molecular damage to prostacyclin synthetase in the rheologically determined areas of arterial walls. Endothelium deprived of prostacyclin is the basis for microthrombi formation, and follows a sequence of events described by Rokitansky and later by Ross. Prostacyclin is also a circulating hormone which is generated by the lungs. Thereby a damage of this "endocrine gland" by respiratory disorders, air pollution, or tobacco smoking are likely to contribute to pathogenesis of atherosclerosis, myocardial infarction, and arterial thromboembolism. Pharmacological treatment and prevention of these diseases should logically include antioxydants, prostacyclin and its analogues, thromboxane synthetase inhibitors and perhaps cyclooxygenase inhibitors (aspirin ?). Prostacyclin was already infused intravenously to men and its powerful antiaggregatory and deaggregatory actions were demonstrated. These properties of prostacyclin along with its vasodilator and positive inotropic actions destine this hormone to be a new type of antithrombotic drug in acute myocardial infarction.

Inhibition of prostaglandin biosynthesis by eicosapentaenoic acid

Eicosapentaenoic acid [20 : 5 (n-3)] is not oxidized by the purified cyclooxygenase from sheep vesicular glands in the conditions of low peroxide tone in which arachidonate [20 : 4 (n-6)] is rapidly oxygenated. When the level of peroxide in incubation mixtures is allowed to rise, there is a dramatic change in reactivity of the cyclooxygenase to react with 20 : 5 (n-3) at one-halt the rate and one-third the extent observed with 20 : 4 (n-6). Overall, the low peroxide levels expected in vivo would most probably cause the (n-3) type of fatty acid to be a general inhibitor of prostaglandin formation, through both reversible and irreversible actions at the enzyme site.

The protective effects of dietary fish oil on focal cerebral infarction

The protective effect of the (n-3) fatty acids in menhaden fish oil on acute cerebral ischemia was investigated in cats. Cerebral ischemia was produced by ligation of the left middle cerebral artery of cats fed either a basal diet of feline cat chow or the basal diet supplemented with 8% of the calories as menhaden oil for 18-24 days. Fatty acids esters of 20:5 (n-3) were increased and the 18:2 (n-6) decreased in the heart and liver of cats fed supplemental fish oil, but the brain lipid showed no effect of the diet. We found that the neurological deficit and the volume of brain infarction in the group treated with fish oil was less than that of the control group. The present findings suggest that moderate dietary supplements of fish oil may be beneficial in the prophylactic treatment of ischemic cerebral vascular disease.

Role of arachidonic acid derivatives in neutrophil aggregation: a hypothesis

Chemotactic substances stimulate neutrophils in suspension to aggregate. Arachidonic acid (but not several structurally related fatty acids) induces a similar neutrophil response. We now report that two blockers of arachidonic acid metabolism, indomethacin and 5,8,11,14-eicosatetraynoic acid, inhibit this arachidonic acid-mediated response. Moreover, both blockers also inhibit aggregation stimulated by a synthetic chemotactic tripeptide, formyl-methionyl-leucyl-phenylalanine, and their potency in doing so parallels their potency in inhibiting the response to arachidonic acid. These results suggest that metabolites of arachidonic acid may stimulate certain neutrophil functions and be involved in cellular responses to at least some chemotactic substances.

Proposed metabolic dysfunctions in diabetic microthromboses and microangiopathy

This report describes, at least in part, the role of prostaglandin and cyclic nucleotide metabolism in the etiology of the vascular disease associated with diabetes mellitus. Alterations in this metabolism seem associated with induction of platelet aggregation leads to microthromboses leads to microangiopathy sequences that are subtle but inexorable over a long period of time. Prostaglandins are generally elevated in blood from patients having frank signs of diabetic retinopathy when compared with nondiabetic subjects. Prostaglandin concentration remained elevated in diabetic retinopathy patients receiving indomethacin. We formed, therefore, the working hypothesis--yet to be fully tested either in patients or animal models with and without indomethacin treatment--that the increased prostacyclin (synthesized by endothelial microsomes) and cyclic-AMP production, both of which favor prevention of platelet aggregation, accompany the increased concentration of one or more of the prostaglandin E and F compounds. Concurrently, there may be an accompanying reduction of thromboxane A2 (synthesized by platelet microsomes) and cyclic-GMP (both of which favor platelet aggregation) production in the diabetic patients. The elevated prostaglandin in the diabetic patients not receiving indomethacin could possibly be directed toward slowing but not preventing the progression of the complex disease process in diabetes.

Drug effects on platelet adherence to collagen and damaged vessel walls

The interaction of platelets with damaged vessel walls leads to the formation of platelet-fibrin thrombi and may also contribute to the development of atherosclerotic lesions because platelets adherent to exposed collagen release a mitogen that stimulates smooth muscle cell proliferation. The first step in thrombus formation, platelet adherence to an injured vessel wall, can be studied quantitatively by the use of platelets labeled with 51chromium. In these investigations, rabbit aortas were damaged by passage of a balloon catheter and segments of the aortas were everted on probes that were rotated in platelet suspensions. Collagen-coated glass cylinders were also used. Adherence was measured in a medium containing approximately physiologic concentrations of calcium, magnesium, protein and red blood cells. Conditions of testing influence the effect of non-steroidal anti-inflammatory drugs, sulfinpyrazone, and dipyridamole on platelet adherence. Aspirin and sulfinpyrazone were not inhibitory when tested in a medium with a 40% hematocrit; this indicates that products formed by platelets from arachidonate probably do not play a major part in the adherence of the first layer of platelets to the surface, although they may be involved in thrombus formation. Indomethacin, dipyridamole, prostaglandin E1, methylprednisolone and penicillin G and related antibiotics did inhibit platelet adherence although the concentrations required were higher than would likely be achieved in vivo upon administration to human patients. None of the non-steroidal anti-inflammatory drugs inhibited the release of granule contents from adherent platelets. Pretreatment of the damaged vessel wall with aspirin increased platelet adherence, presumably because it prevented the formation of PGI2 by the vessel wall. Platelet adherence to undamaged or damaged vessel walls was enhanced by prior exposure of the wall to thrombin. Platelet reactions with aggregating agents and platelet survival can be modified by changes in dietary lipids but there is very little evidence concerning the effects of lipids on platelet adherence. If some forms of dietary fat damage the endothelium, platelet interaction with the damaged area and release of the mitogen for smooth muscle cells would contribute to the development of atherosclerotic lesions.

Inhibition of arachidonic acid induced mortality in rabbits with several non-steroidal anti-inflammatory agents

The intravenous administration of arachidonic acid to rabbits is an effective in vivo model for evaluating potential anti-thrombotic drugs. Most of the non-steroidal anti-inflammatory agents (NSAIFA) inhibit this arachidonic acid induced mortality (except sodium salicylate and acetaminophen). However, there is a lack of correlation between the relative potencies from various assays (rabbit anti-thrombotic, anti-inflammatory, alalgesic, ulcerogenic and inhibition of prostaglandin synthetase evaluations). These studies imply other actions with NSAIFA than an effect solely on the prostaglandin biosynthetic pathway.

Impairment by heparin of primary haemostasis and platelet [14C]5-hydroxytryptamine release

Heparin was administered to 34 normal subjects by intravenous injection (100 mu/kg) and the template bleeding time was significantly increased both 10 min and 120 min following injection. Before heparin the bleeding time was 5-3 +/- 1.0 min (mean +/- 1 SD); 10 min after injection it was 9.8 +/- 5.6 min (P less than 0.001); and 120 min after injection it was 7.2 +/- 3.9 min (P less than 0.001). Increases in the bleeding time were unrelated to changes in platelet count, and independent of heparin's effect on plasma coagulation. In blood drawn 10 min and 120 min following heparin injection, there was significantly less [14C]5-HT released from platelet-rich plasma (PRP) in response to collagen, 0.41 mM epinephrine and 8 micron ADP, although in vitro addition of heparin (0.1 mu/ml, 0.5 mu/ml and 2.5 mu/ml) to baseline PRP of three subjects did not depress [14C]5-HT release. Our experiments suggest that intravenous administration of a therapeutic dose of heparin can cause a significant reversible inpairment of platelet haemostatic properties, possibly by an indirect mechanism.

The effect of 2,3-diphosphoglycerate on oxygen consumption burst in thrombin-stimulated platelets

2,3-Diphosphoglycerate (2,3-DPG) modifies platelet function; it diminishes aggregation and the release reaction. The hypothesis that this occurs through a modification of the intracellular level of cyclic AMP or through an alteration in the synthesis of prostaglandins has been proposed. Since the release reaction occurs simultaneously with a burst in the consumption of oxygen, the authors have studied the effect of 2,3-DPG on oxygen consumption after the addition of thrombin with or without the addition of substances which modify platelet metabolism (aspirin, theophylline, glucagon, etc.). It was observed that 2,3-DPG diminishes oxygen consumption induced by thrombin. This mechanism alters the platelet membrane function.

On the formation and effects of thromboxane A2 in human platelets

Incubation of arachidonic acid and prostaglandin G2 with a suspension of human platelets led to formation of an unstable (t1/2, 41+/-7 s) compound, thromboxane A2. Thromboxane A2 induced irreversible aggregation of washed platelets and of platelets in platelet-rich plasma and caused release of serotonin and ADP from platelets in platelet-rich plasma.

Metabolism of 8,11,14-eicosatrienoic acid in human platelets

The following labeled compounds were isolated and identified after incubation of 8,11,14-eicosatrien [1-14C] oic acid with human platelets: 12-L-hydroxy-8,10,14-eicosatrienoic acid, 8,11,12-trihydroxy-9,14-eicosadienoic acid, 8,9,12-trihydroxy-10,14-eicosadienoic acid, 12-L-hydroxy-8,10-heptadecadienoic acid, prostaglandin E1, prostaglandin D1, and 8-(1-hydroxy-3-oxopropyl)-9,12-dihydroxy-10-heptadecenoic acid (thromboxane B1).