Vasodilation and inhibition of platelet aggregation by prostacyclins with modified omega-side chain

Decreased Iron Ion Concentrations in the Peripheral Blood Correlate with Coronary Atherosclerosis

(1) Background: Obesity and diabetes continue to reach epidemic levels in the population with major health impacts that include a significantly increased risk of coronary atherosclerosis. The imbalance of trace elements in the body caused by nutritional factors can lead to the progression of coronary atherosclerosis. (2) Methods: We measured the concentrations of sodium (Na), potassium (K), magnesium (Mg), calcium (Ca), Zinc (Zn), and iron (Fe) in peripheral blood samples from 4243 patients and performed baseline analysis and propensity matching of the patient datasets. The patients were grouped into acute myocardial infarction (AMI, 702 patients) and stable coronary heart disease (SCAD1, 253 patients) groups. Both of these groups were included in the AS that had a total of 1955 patients. The control group consisted of 2288 patients. The plasma concentrations of calcium, magnesium, and iron were measured using a colorimetric method. For comparison, 15 external quality assessment (EQA) samples were selected from the Clinical Laboratory Center of the Ministry of Health of China. SPSS software was used for statistical analysis. The average values and deviations of all of the indicators in each group were calculated, and a p-value threshold of <0.05 was used to indicate statistical significance. (3) Results: The iron ion concentrations of the acute myocardial infarction (AMI) group were significantly lower than the control group (p < 0.05, AUC = 0.724, AUC = 0.702), irrespective of tendency matching. Compared to the data from the stable coronary artery disease (SCAD) group, the concentration of iron ions in the acute myocardial infarction group was significantly lower (p < 0.05, AUC = 0.710, AUC = 0.682). Furthermore, the iron ion concentrations in the (AMI + SCAD) group were significantly lower (p < 0.05) than in the control group. (4) Conclusions: The data presented in this study strongly indicate that the concentration of iron ions in the peripheral blood is related to coronary atherosclerosis. Decreases in the levels of iron ions in the peripheral blood can be used as a predictive biomarker of coronary atherosclerosis.

Emerging Role of Phospholipase-Derived Cleavage Products in Regulating Eosinophil Activity: Focus on Lysophospholipids, Polyunsaturated Fatty Acids and Eicosanoids

Eosinophils are important effector cells involved in allergic inflammation. When stimulated, eosinophils release a variety of mediators initiating, propagating, and maintaining local inflammation. Both, the activity and concentration of secreted and cytosolic phospholipases (PLAs) are increased in allergic inflammation, promoting the cleavage of phospholipids and thus the production of reactive lipid mediators. Eosinophils express high levels of secreted phospholipase A2 compared to other leukocytes, indicating their direct involvement in the production of lipid mediators during allergic inflammation. On the other side, eosinophils have also been recognized as crucial mediators with regulatory and homeostatic roles in local immunity and repair. Thus, targeting the complex network of lipid mediators offer a unique opportunity to target the over-activation and 'pro-inflammatory' phenotype of eosinophils without compromising the survival and functions of tissue-resident and homeostatic eosinophils. Here we provide a comprehensive overview of the critical role of phospholipase-derived lipid mediators in modulating eosinophil activity in health and disease. We focus on lysophospholipids, polyunsaturated fatty acids, and eicosanoids with exciting new perspectives for future drug development.

Prostacyclin promotes oligodendrocyte precursor recruitment and remyelination after spinal cord demyelination

Adult oligodendrocyte precursor cells (OPCs) are located adjacent to demyelinated lesion and contribute to myelin repair. The crucial step in remyelination is the migration of OPCs to the demyelinated area; however, the mechanism of OPC migration remains to be fully elucidated. Here we show that prostacyclin (prostaglandin I2, PGI2) promotes OPC migration, thereby promoting remyelination and functional recovery in mice after demyelination induced by injecting lysophosphatidylcholine (LPC) into the spinal cord. Prostacyclin analogs enhanced OPC migration via a protein kinase A (PKA)-dependent mechanism, and prostacyclin synthase expression was increased in the spinal cord after LPC injection. Notably, pharmacological inhibition of prostacyclin receptor (IP receptor) impaired remyelination and motor recovery, whereas the administration of a prostacyclin analog promoted remyelination and motor recovery after LPC injection. Our results suggest that prostacyclin could be a key molecule for facilitating the migration of OPCs that are essential for repairing demyelinated areas, and it may be useful in treating disorders characterized by demyelination.

Conformation of receptor-associated PGI2: an investigation by molecular modeling

To elucidate the conformation of receptor-associated prostacyclin (PGI2), we first performed structure-activity correlation analysis of over 200 PGI2 analogues and derived from this analysis several crucial features pertaining to structural requirements for PGI2 activity [Ah-lim Tsai and Kenneth K. Wu, Eicosanoids, 2 (1989) 131-143]. These structural features proved to be useful guidelines for selecting 'model molecules' for further investigations by molecular mechanics. By properly selecting four analogues with either rigid or uniquely oriented alpha-side chain structure for geometric fitting, we succeeded in maximally minimizing the degree of freedom of the carboxylate terminus of PGI2. We were able to define the spatial relationship among the four critical functional groups, i.e., C1-COOH, C6a-O, C11-OH and C15-OH. More information is needed, however, to define the geometry of the omega-side chain, particularly for the moiety beyond C15. Nevertheless, results from structure-activity correlation analysis and molecular modeling provide useful information regarding the conformation of receptor-associated PGI2, which assumes an 'elongated' conformation instead of the traditional 'hairpin' structure.

The orally active thia-imino-prostacyclin Hoe 892: antiaggregatory and cardiovascular activities

The short chemical half-life limits the potential therapeutic value of Prostacyclin (PGI2). Replacement of the acid-labile enolether structure of PGI2 by a beta-thia-imino group resulted in the orally active and chemically stable analogue Hoe 892. Incubation of rabbit platelet rich plasma with PGI2 and Hoe 892 caused a dose dependent inhibition of collagen and arachidonic acid (AA) induced platelet aggregation with ID50 of 4.2 and 20.1 ng/ml for PGI2 respectively 43.3 and 170.2 ng/ml for Hoe 892. These effects could be potentiated by the phosphodiesterase inhibitor theophylline. Single oral administration of Hoe 892 in conscious rabbits inhibited platelet aggregation for more than 3 hrs with an ID50 of 0.2 mg/kg using collagen and 1.5 mg/kg using AA. These doses were without influence on systemic blood pressure (BP) in conscious rabbits. Intravenous injection of Hoe 892 induced a dose dependent decrease of systemic BP in anesthetized rats (ED25 of 2.2 micrograms/kg) and in the rats with acute renal hypertension. Hoe 892 stimulated renin release in anesthetized rats. The hemodynamic profile in anesthetized dogs (0.5 micrograms/kg/min i.v.) was characterized by a decrease of systemic BP, left ventricular pressure, pulmonary artery pressure, total peripheral resistance and in increase in heart rate, cardiac output and dp/dt max, thus demonstrating arteriolar vasodilation. In conscious dogs with two kidney, two wrapped hypertension oral treatment for 1 or 5 days resulted in a marked reduction of BP.

Reduced platelet aggregation by effects of pentoxifylline on vascular prostacyclin isomerase and platelet cyclic AMP

1. Inhibition of platelet aggregation in vitro by pentoxifylline is rather weak, requiring about 1 mM pentoxifylline. Ex vivo, however, 15 mg/kg p.o. pentoxifylline exerts an enhanced release of prostacyclin-(PGI2)-like antiaggregatory activity from rat aortas. 2. Rat aorta incubated in vitro with 1 microM pentoxifylline releases antiaggregatory activity in a similar manner. The conversion of prostaglandin H2 to PGI2-like activity which is catalyzed by vascular microsomes, also is drastically stimulated in vitro by addition of 1 microM pentoxifylline. 3. Despite its inhibitory effect on platelet cyclic AMP-phosphodiesterase pentoxifylline in vitro without PGI2 has no essential effect on cyclic AMP levels in human platelets. However, in presence of PGI2, release of which probably is increased by pentoxifylline cyclic AMP level as well as inhibition of aggregation are enhanced by pentoxifylline above the effects of PGI2 itself.

HL 725, an extremely potent inhibitor of platelet phosphodiesterase and induced platelet aggregation in vitro

The new pyrimido-isoquinoline compound HL 725 is an extremely potent inhibitor of the aggregation of human platelets induced in vitro by ADP, collagen, thrombin and epinephrine. The aggregation induced by 0,5 mM arachidonic acid is inhibited about 50% with 50 pM HL 725. Thus the potency of HL 725 is higher than that of prostacyclin, the most active natural inhibitor of aggregation. We hypothesize that HL 725 inhibits the enzymatic degradation of cyclic adenosine 3', 5'-monophosphate (cAMP) in the platelets. In accordance with this proposal is the strong inhibitory action on cAMP phosphodiesterase extracted from human platelets. About 250 pM HL 725 inhibited 50% of the activity of this enzyme at a substrate concentration of 0.5 microM. A marked elevation of cAMP levels in human platelets could be demonstrated after incubation in vitro with 100 nM HL 725.

Evening primrose oil, a dietary prostaglandin precursor, diminishes vascular reactivity to renin and angiotensin II in rats

Polyunsaturated fatty acids (PUFA) are biosynthetic precursors of prostaglandins (PG). Endogenous biosynthesis of PG in vessel wall and kidney contributes to the regulation of arterial blood pressure. By increasing the fraction of PUFA in the diet systemic blood pressure can be lowered while PUFA deficient diet leads to an increase in blood pressure. To evaluate the effect of an enhanced PG biosynthesis by dietary PG precursors on vascular reactivity and vascular formation of prostacyclin-like activity, the pressor response to intravenous renin and angiotensin II in rats pretreated p.o. for 3 months with evening primrose oil (EPO, 1 ml/day) was determined and the antiaggregatory activity released by aortas of treated rats studied. EPO is unique in that it contains beside linoleic acid (72%), gamma-linolenic acid itself (9%). In contrast to olive oil treated rats EPO pretreatment diminished vascular reactivity to the vasopressor stimuli of renin and angiotensin II and increased the formation of vascular prostacyclin-like activity (p less than 0.05). These studies imply the possibility of a selective modulation of PG production by dietary maneuvers.

Plasma renin activity and vasodepressor action of prostacyclins with modified omega-side chain in anesthetized rats

The effects of intravenous injection of prostacyclin (PGI2) and two of its analogues with modified omega-side chain on systemic blood pressure and on plasma renin activity were investigated in anesthetized rats. The PGI2 -methylester analogues with replacement of the n-pentyl moiety attached to C-15 by cyclohexyl or 3-thienyloxymethyl had exactly the same vasodepressor activities as PGI2. Despite these equipotent effects on blood pressure a marked difference between PGI2 and the analogues with respect to stimulation of plasma renin activity could be demonstrated. The cyclohexyl as well as the 3-thienyloxymethyl analogue induced a significantly stronger increase of plasma renin activity than PGI2. These findings strengthen the view of a direct involvement of prostacyclins in renin release mechanisms.