The potentiation of adrenaline-induced in vitro platelet aggregation by ADP, collagen and serotonin and its inhibition by naftopidil and doxazosin in normal human subjects

The antiplatelet effect of mirtazapine is mediated by co-blocking 5-HT2A and α2-adrenergic receptors on platelets: An in vitro human plasma-based study

Mirtazapine (MTZ) is a noradrenergic and specific serotonergic antidepressant that has been associated with an increased risk of bleeding. However, there is insufficient evidence confirming this association. We hypothesised that 5-HT2A and α2 receptor-mediated inhibitory effects of MTZ on platelets suppress platelet aggregation and increase the risk of bleeding. In this study, we examined the antiplatelet effect of MTZ on human platelets to test our hypothesis. Blood samples for platelet aggregation tests were obtained from 14 healthy volunteers. The antiplatelet effect of MTZ was evaluated using light transmission aggregometry. MTZ significantly suppressed platelet aggregation mediated both by the synergistic interaction of serotonin (5-HT) and adrenaline and the synergistic interaction of ADP and 5-HT or adrenaline. In conclusion, MTZ exerts its antiplatelet effects by co-blocking the 5-HT2A and α2-adrenergic receptors on platelets and also suppresses platelet aggregation induced by ADP and 5-HT or adrenaline. Therefore, when MTZ is used, especially for patients with a high risk of bleeding, the significance of its use must be considered carefully. In addition, the platelet aggregation pattern by adrenaline + 5-HT, ADP + adrenaline, and ADP + 5-HT was similar between humans and mice; however, this study did not directly compare the effects of MTZ on human and murine platelets. Therefore, under the conditions for inducing platelet aggregation using adrenaline + 5-HT, ADP + adrenaline, and ADP + 5-HT, mouse platelets can be used in the evaluation of the efficacy of antiplatelet drugs in humans.

Effects of High Concentrations of Naftopidil on Dorsal Root-Evoked Excitatory Synaptic Transmissions in Substantia Gelatinosa Neurons In Vitro

Purpose

Naftopidil ((±)-1-[4-(2-methoxyphenyl) piperazinyl]-3-(1-naphthyloxy) propan-2-ol) is prescribed in several Asian countries for lower urinary tract symptoms suggestive of benign prostatic hyperplasia. Previous animal experiments showed that intrathecal injection of naftopidil abolished rhythmic bladder contraction in vivo. Naftopidil facilitated spontaneous inhibitory postsynaptic currents in substantia gelatinosa (SG) neurons in spinal cord slices. These results suggest that naftopidil may suppress the micturition reflex at the spinal cord level. However, the effect of naftopidil on evoked excitatory postsynaptic currents (EPSCs) in SG neurons remains to be elucidated.

Methods

Male Sprague-Dawley rats at 6 to 8 weeks old were used. Whole-cell patch-clamp recordings were made using SG neurons in spinal cord slices isolated from adult rats. Evoked EPSCs were analyzed in Aδ or C fibers. Naftopidil or prazosin, an α1-adrenoceptor blocker, was perfused at 100 μM or 10 μM, respectively.

Results

Bath-applied 100 μM naftopidil significantly decreased the peak amplitudes of Aδ and C fiber-evoked EPSCs to 72.0%±7.1% (n=15) and 70.0%±5.5% (n=20), respectively, in a reversible and reproducible manner. Bath application of 10μM prazosin did not inhibit Aδ or C fiber-evoked EPSCs.

Conclusions

The present study suggests that a high concentration of naftopidil reduces the amplitude of evoked EPSCs via a mechanism that apparently does not involve α1-adrenoceptors. Inhibition of evoked EPSCs may also contribute to suppression of the micturition reflex, together with nociceptive stimulation.

Science behind the cardio-metabolic benefits of omega-3 polyunsaturated fatty acids: biochemical effects vs. clinical outcomes

Lower incidence of cardiovascular disease (CVD) in the Greenland Inuit, Northern Canada and Japan has been attributed to their consumption of seafood rich in long chain omega-3 polyunsaturated fatty acids (LCn-3PUFA). While a large majority of pre-clinical and intervention trials have demonstrated heart health benefits of LCn-3PUFA, some studies have shown no effects or even negative effects. LCn-3PUFA have been shown to favourably modulate blood lipid levels, particularly a reduction in circulating levels of triglycerides. High density lipoprotein-cholesterol (HDL-C) levels are elevated following dietary supplementation with LCn-3PUFA. Although LCn-3PUFA have been shown to increase low-density lipoprotein-cholesterol (LDL-C) levels, the increase is primarily in the large-buoyant particles that are less atherogenic than small-dense LDL particles. The anti-inflammatory effects of LCn-3PUFA have been clearly outlined with inhibition of NFkB mediated cytokine production being the main mechanism. In addition, reduction in adhesion molecules (intercellular adhesion molecule, ICAM and vascular cell adhesion molecule 1, VCAM-1) and leukotriene production have also been demonstrated following LCn-3PUFA supplementation. Anti-aggregatory effects of LCn-3PUFA have been a subject of controversy, however, recent studies showing sex-specific effects on platelet aggregation have helped resolve the effects on hyperactive platelets. Improvements in endothelium function, blood flow and blood pressure after LCn-3PUFA supplementation add to the mechanistic explanation on their cardio-protective effects. Modulation of adipose tissue secretions including pro-inflammatory mediators and adipokines by LCn-3PUFA has re-ignited interest in their cardiovascular health benefits. The aim of this narrative review is to filter out the reasons for possible disparity between cohort, mechanistic, pre-clinical and clinical studies. The focus of the article is to provide possible explanation for the observed controversies surrounding heart health benefits of LCn-3PUFA.

In vitro Research of the Concentration Dependence of Effect of Adrenaline on Platelets Aggregation

PURPOSE

Paper intended to present experimental evidences that adrenaline has a direct effect of inducing platelets aggregation in the concentration range 1-8µM.

MATERIAL/METHODS

Platelet rich plasma from patients of Colentina Clinical Hospital, following an informed consent. The platelet rich plasma (PRP) was prepared by centrifuging the anticoagulated sample at 200 G for 10 minutes. Aggregation was evaluated by optical aggregometry, classical method of Born, using Helena PACKS-4 Aggregometer.

RESULTS

The curves transmission light-time followed the structure: a lag-time, a first phase aggregation, more or less linear, defined by a "Slope 1", a second wave of aggregation defined by "slope 2" and a "saturation" phase. Slope 1 increases with the concentration of adrenaline. The second slopes of the aggregation curves, maximum aggregation and areas under curves depended linear on adrenaline concentration.

CONCLUSIONS

Adrenaline, in concentrations in the 1-8µM, induce aggregation of human platelets from platelet rich plasma. Linear regression models for slope and area were practically identical suggesting a rather unique than biphasic mechanism of action of adrenaline during the time course of aggregation.

Naftopidil, a selective alpha-1 adrenoceptor antagonist, inhibits growth of human prostate cancer cells by G1 cell cycle arrest

Alpha-1 adrenoceptor antagonists are generally prescribed for benign prostate hyperplasia with lower urinary tract symptoms. Naftopidil, a selective alpha-1 adrenoceptor antagonist, is frequently used in Japan because it has fewer side effects. Here we demonstrate for the first time that naftopidil has growth inhibitory effect in androgen-sensitive and -insensitive human prostate cancer cell lines. The concentrations causing 50% inhibition (IC50) of cancer cell growth were 22.2 +/- 4.0 microM in androgen-sensitive LNCaP cells and 33.2 +/- 1.1 microM in androgen-insensitive PC-3 cells. FACS analysis revealed that cell growth inhibition by naftopidil was due to the arrest of the G1 cell cycle. Expressions of p27(kip1) and p21(cip1) were significantly increased in LNCaP cells treated with naftopidil. In PC-3 cells, naftopidil induced p21(cip1) but not p27(kip1). In vivo, oral administration of naftopidil to nude mice inhibited the growth of PC-3 tumors as compared to vehicle-treated controls. These results suggest that naftopidil may be useful in the chemoprevention of prostate cancer and the intervention of hormone refractory prostate cancer.

Cytoplasmic free calcium mobilization in platelets, expression of P-selectin, phosphatidylserine, and microparticle formation, measured by whole blood flow cytometry, in hypertensive patients. Effect of doxazosin GITS

The effects of doxazosin on expression of CD62 (P-selectin) and phosphatidylserine on platelet membrane and platelet calcium flux were studied in 50 uncomplicated essential hypertensive patients (World Health Organization stages 1-2) and 80 normotensive control subjects, matched for age, sex, and cardiovascular risk factors. Hypertensive patients showed greater in vivo platelet activation at baseline than control patients (percentage of CD62-positive platelets, 4.1+/-2.2% versus 2.4+/-1.5%, p<0.001; percentage of phosphatidylserine-positive platelets, 0.8+/-0.5% versus 0.5+/-0.3%, p<0.001). Increased platelet activation was associated with significant changes in the mobilization of free intraplatelet calcium, evaluated by a whole blood flow cytometric kinetic method. With this method, an arbitrary Ca(2+) mobilization index was defined as the ratio of cytoplasmic free calcium before activation with thrombin to the slope of the calcium removal rate following the action of the agonist. This index was significantly higher in untreated hypertensive patients than in normotensive controls (0.12+/-0.06 versus 0.05+/-0.08, p<0.001). Treatment of hypertensive patients with doxazosin gastrointestinal therapeutic system (4 mg/day as a single dose) for 2 months normalized both platelet activation and Ca(2+) mobilization. Changes in the expression of CD62 and phosphatidylserine in the platelet membrane after treatment with doxazosin gastrointestinal therapeutic system may be related to normalization of the kinetics of cytoplasmic free Ca(2+). Normalization of platelet activation may represent an additional beneficial effect to the known antihypertensive action of doxazosin gastrointestinal therapeutic system.

Flow cytometric analysis of platelet activation in hypertensive patients. Effect of doxazosin

The percentage of spontaneously activated platelets and the platelet response to several agonists were studied in 26 hypertensive patients. The percentage of platelets expressing glycoprotein (GP) IIb/IIIa in its active conformation (GPIIb/IIIa*), P-selectin and phosphatidylserine (PS) was measured by flow cytometry at baseline and 1 and 2 months after treatment with doxazosin (4 mg/day). The response to ADP and Ca2+ ionophore was also evaluated. The results were compared with those of a control group of 71 normotensive volunteers. Spontaneous platelet activation was higher in patients than in controls (P-selectin-positive results in 4.4+/-2.0% patients vs. 2.7+/-1.7 controls, p<0.05; phosphatidylserine-positive results in 0.7+/-0.4% vs. 0.5+/-0.3%, respectively, p<0.05), and higher in response to ionophore action (phosphatidylserine-positive results 51.8+/-11.1% vs. 43.4+/-11.7%, p<0.01). Platelet activation in patients decreased after 2 months of doxazosin administration compared to baseline (P-selectin-positive results 2.7+/-1.4% vs. 4.4+/-2.0%, p<0.05; phosphatidylserine-positive results 0.3+/-0.2% vs. 0.7+/-0.4%, p<0.05). No significant differences were noted in GPIIb/IIIa*. The clinical significance of normalization of platelet activity by doxazosin remains to be established.

Platelet aggregation may not be a prerequisite for collagen-stimulated platelet generation of nitric oxide

By determining the sum of the supernatant concentrations of nitrite and nitrate the stimulated generation of nitric oxide (NO) by human washed platelets induced by a range of fibrillar collagen concentrations (0.0156-25 microg ml(-1)) was investigated. Platelet serotonin (5-hydroxytryptamine, 5-HT) efflux and platelet aggregation were also measured. Under resting conditions (0 microg ml(-1) collagen) platelet NO release was equivalent to 1.06+/-0.17 nmol per 10(8) platelets. Maximal NO release, equivalent to 2.1+/-0. 37 nmol per 10(8) platelets, was observed with only 0.0625 microg ml(-1) collagen (P<0.02, stimulated vs. resting release), higher collagen concentrations producing no further increases in platelet NO output. By contrast, maximal platelet aggregation and 5-HT efflux did not occur until collagen concentrations of 2.5 microg ml(-1) and 10-25 microg ml-1), respectively, had been achieved. L-NAME (1 mmol l(-1)) and L-NMMA (1 mmol l(-1)) inhibited stimulated platelet NO generation by 78+/-6% and 72%, respectively. Contrasting with fibrillar collagen, fibrillar beta-amyloid protein had no effect on platelet NO generation, or on 5-HT efflux or aggregation. These data perhaps indicate that NO generation by human platelets is stimulated by concentrations of fibrillar collagen insufficient to elicit an aggregatory response. Such a mechanism could operate in vivo to inhibit platelet aggregation which might otherwise be induced by low concentrations of circulating agonists.