Delineating Zinc Influx Mechanisms during Platelet Activation

Zinc (Zn2+) is released by platelets during a hemostatic response to injury. Extracellular zinc ([Zn2+]o) initiates platelet activation following influx into the platelet cytosol. However, the mechanisms that permit Zn2+ influx are unknown. Fluctuations in intracellular zinc ([Zn2+]i) were measured in fluozin-3-loaded platelets using fluorometry and flow cytometry. Platelet activation was assessed using light transmission aggregometry. The detection of phosphoproteins was performed by Western blotting. [Zn2+]o influx and subsequent platelet activation were abrogated by blocking the sodium/calcium exchanged, TRP channels, and ZIP7. Cation store depletion regulated Zn2+ influx. [Zn2+]o stimulation resulted in the phosphorylation of PKC substates, MLC, and β3 integrin. Platelet activation via GPVI or Zn2+ resulted in ZIP7 phosphorylation in a casein kinase 2-dependent manner and initiated elevations of [Zn2+]i that were sensitive to the inhibition of Orai1, ZIP7, or IP3R-mediated pathways. These data indicate that platelets detect and respond to changes in [Zn2+]o via influx into the cytosol through TRP channels and the NCX exchanger. Platelet activation results in the externalization of ZIP7, which further regulates Zn2+ influx. Increases in [Zn2+]i contribute to the activation of cation-dependent enzymes. Sensitivity of Zn2+ influx to thapsigargin indicates a store-operated pathway that we term store-operated Zn2+ entry (SOZE). These mechanisms may affect platelet behavior during thrombosis and hemostasis.

Zinc regulates reactive oxygen species generation in platelets

Vascular complications resulting from atherosclerosis development are a major cause of death. Reactive oxygen species (ROS) are produced by platelets during activation, and have been demonstrated to positively regulate platelet activatory responses. Zn2+ is also an important hemostatic cofactor in platelets, acting both as a platelet agonist and second messenger. Whilst the effect of Zn2+-dependent signaling mechanisms on ROS production in nucleated cells has been demonstrated, comparable roles in platelets have yet to be investigated. In this study we investigated the relationship between fluctuations in cytosolic Zn2 [Zn2+]i and platelet ROS production. Agonist-evoked ROS production, GSH levels and GPx activity are abrogated in platelets treated with the Zn2+-chelator, TPEN. Conversely, increasing platelet [Zn2+]i using Zn2+ ionophores potentiated ROS generation and decreased GSH levels and GPx activity. Zn2+-dependent ROS production was sensitive to pretreatment with DPI or mitoTEMPO, NADPH oxidase and mitochondria inhibitors respectively. Increasing [Zn2+]i resulted in increases of Erk1/2 and JNK phosphorylation. Our data are consistent with a functional association between [Zn2+]i and ROS production in platelets that could influence thrombus formation in a clinical context.

Agonist-Evoked Increases in Intra-Platelet Zinc Couple to Functional Responses

Background  Zinc (Zn ²⁺ ) is an essential trace element that regulates intracellular processes in multiple cell types. While the role of Zn ²⁺ as a platelet agonist is known, its secondary messenger activity in platelets has not been demonstrated.

Objectives  This article determines whether cytosolic Zn ²⁺ concentrations ([Zn ²⁺ ] _i ) change in platelets in response to agonist stimulation, in a manner consistent with a secondary messenger, and correlates the effects of [Zn ²⁺ ] _i changes on activation markers.

Methods  Changes in [Zn ²⁺ ] _i were quantified in Fluozin-3 (Fz-3)-loaded washed, human platelets using fluorometry. Increases in [Zn ²⁺ ] _i were modelled using Zn ²⁺ -specific chelators and ionophores. The influence of [Zn ²⁺ ] _i on platelet function was assessed using platelet aggregometry, flow cytometry and Western blotting.

Results  Increases of intra-platelet Fluozin-3 (Fz-3) fluorescence occurred in response to stimulation by cross-linked collagen-related peptide (CRP-XL) or U46619, consistent with a rise of [Zn ²⁺ ] _i . Fluoresence increases were blocked by Zn ²⁺ chelators and modulators of the platelet redox state, and were distinct from agonist-evoked [Ca ²⁺ ] _i signals. Stimulation of platelets with the Zn ²⁺ ionophores clioquinol (Cq) or pyrithione (Py) caused sustained increases of [Zn ²⁺ ] _i , resulting in myosin light chain phosphorylation, and cytoskeletal re-arrangements which were sensitive to cytochalasin-D treatment. Cq stimulation resulted in integrin α _IIb β ₃ activation and release of dense, but not α, granules. Furthermore, Zn ²⁺ -ionophores induced externalization of phosphatidylserine.

Conclusion  These data suggest that agonist-evoked fluctuations in intra-platelet Zn ²⁺ couple to functional responses, in a manner that is consistent with a role as a secondary messenger. Increased intra-platelet Zn ²⁺ regulates signalling processes, including shape change, α _IIb β ₃ up-regulation and dense granule release, in a redox-sensitive manner.

Stapled peptides as a new technology to investigate protein-protein interactions in human platelets

We describe the first application of stapled peptides in human platelets. Bim BH3 stapled peptides are used to overcome the limitations of traditional methods and uncover a new role for Bim in platelet activation.

Platelets are blood cells with numerous crucial pathophysiological roles in hemostasis, cardiovascular thrombotic events and cancer metastasis. Platelet activation requires the engagement of intracellular signalling pathways that involve protein–protein interactions (PPIs). A better understanding of these pathways is therefore crucial for the development of selective anti-platelet drugs. New strategies for studying PPIs in human platelets are required to overcome limitations associated with conventional platelet research methods. For example, small molecule inhibitors can lack selectivity and are often difficult to design and synthesise. Additionally, development of transgenic animal models is costly and time-consuming and conventional recombinant techniques are ineffective due to the lack of a nucleus in platelets. Herein, we describe the generation of a library of novel, functionalised stapled peptides and their first application in the investigation of platelet PPIs. Moreover, the use of platelet-permeable stapled Bim BH3 peptides confirms the part of Bim in phosphatidyl-serine (PS) exposure and reveals a role for the Bim protein in platelet activatory processes. Our work demonstrates that functionalised stapled peptides are a complementary alternative to conventional platelet research methods, and could make a significant contribution to the understanding of platelet signalling pathways and hence to the development of anti-platelet drugs.

Design, synthesis, characterization, quantum-chemical calculations and anti-inflammatory activity of novel series of thiophene derivatives

Interaction of 1-(4-morpholinophenyl)ethanone 1 with either malononitrile or ethyl cyanoacetate 2 afforded Knoevenagel-Cope product 3. In subsequent treatment of 3 with sulfur, the 2-aminothiophene derivatives (4a, 4b) are formed under basic conditions. The solvent-free reaction of thiophene derivative 4a with ethyl cyanoacetate afforded thieno[2,3-d][1,3]oxazine derivative 6. The base catalyzed condensation of 2-aminothiophene derivative (4a) with ethyl cyanoacetate afforded N-(thieno-2-yl) cyanoacetamide derivative 7. The latter was used to synthesize different heterocyclic derivatives comprising, pyridine and coumarin rings. Also, several substituted thieno[2,3-d]pyrimidines have been prepared from reaction of 2-aminothiophene-3-carbonitrile 4b with some electrophilic reagents. The structure of the newly compounds were confirmed on the basis of elemental analysis and spectral data. The molecular modeling of the synthesized compounds has been drawn and their molecular parameters were calculated. Also, valuable information is obtained from calculation of the molecular parameters including electronegativity, net dipole moment of the compounds, total energy, electronic energy, binding energy, HOMO and LUMO energy. Evaluation of anti-inflammatory activity of the tested compounds was performed in albino rats by producing carrageenan induced paw oedema and measuring the zone of inflammation at different time intervals i.e. 1, 2, 3 and 4h after carrageenan injection. Results indicated that most of the tested compounds showed moderate to good activity comparable to indomethacin. Also, compound 16 with additional morpholine ring beside the thiophene ring inhibits carrageenan induced paw oedema more than the standard indomethacin drug at all the time scales studied. Thus, compound 16 is considered as a promising compound for further modification to obtain clinically useful anti-inflammatory agent.

An eco-friendly N-sulfonylation of amines using stable and reusable Zn-Al-hydrotalcite solid base catalyst under ultrasound irradiation

Synthetic nanosized Zn-Al-hydrotalcite (Zn-Al-HT) with 20 nm crystallite size and 61 m(2)/g BET-surface area is found to be a mild and efficient catalyst for N-sulfonylation of amines in quantitative yields under ultrasound irradiation. Exclusive synthesis of sulfonamides, using Zn-Al-HT, under ultrasound irradiation, was realized by compatible basic sites of catalyst used. The products were isolated after simple work-up in high yields and purity.

Confirmatory studies on the antioxidant and antidiabetic effect of quercetin in rats

Quercetin (QE), one of natural flavanoid group, was widely distributed as a secondary metabolite in plant kingdom. It has been believed that oxidative stress plays a role in the pathogenesis of diabetes mellitus (DM). The aim of the present study was the evaluation of possible effects of QE on blood glucose and antioxidant enzymes in experimental streptozotocin (STZ)-induced diabetes in rats. STZ was injected intraperitoneally with single dose of 50 mg/kg for diabetes induction. QE (15 mg/kg bw day, intraperitoneal (i.p.) injection) was injected for 3 days prior to STZ administration; these injections were continued to the end of the study (for 25 days). Glucose tolerance test and random plasma glucose were done for all animals. Cellular antioxidant enzymes such as glutathione peroxidase (GSHPx), superoxide dismutase (SOD) and catalase (CAT) activities were measured in pancreatic homogenates. Quercetin had no effect on plasma glucose level of normal animals but its pre- treatment was able to prevent diabetes induced by single intraperitoneal injection of streptozocintreated rats. Antioxidant enzyme activity significantly decreased in STZ induced diabetic group. QE treatment significantly increased the antioxidant enzyme activities. It could be concluded that quercetin, a flavonoid with antioxidant properties, exerting its beneficial antidiabetic effects.

Assessment of lead toxicity in traffic controllers of Alexandria, Egypt, road intersections

Blood lead level (BPbL) was determined in forty-five traffic controllers working on Alexandria road intersections. Central nervous system dysfunction in the subjects studied was investigated by means of performance tests. Biochemical indicators related to lead exposure such as delta-aminolevulinic acid dehydratase and hemoglobin in their blood were also determined. Results indicated that most of the subjects studied have a comparably high BPbL. They also showed significantly poorer performance scores than that obtained in a previous study with a group of textile workers of the same age and educational levels. The mean of the BPbL in the traffic controllers was found to be 68.28 +/- 13.22 micrograms/dl. This is a very high level compared to an acceptable level of 30.00 micrograms/dl. All neurobehavioral symptoms demonstrated in the traffic controllers could be attributed to a high level of lead exposure.

Distribution and metabolism of O-ethyl O-4-nitrophenyl phenylphosphonothioate after a single oral dose in one-week old chicks

The toxicokinetics and metabolism of a single 1 mg (2.7 muCi/kg) oral dose of uniformly phenyl-labeled [14C]EPN (O-ethyl O-4-nitrophenyl [14C]phenylphosphonothioate) have been studied in 1-week old chicks. One control and three treated chicks were killed at each of the following time intervals: 0.5, 2, 4, 8, and 12 days. Radioactivity was rapidly absorbed from the gastrointestinal tract and distributed in all tissues. 14C in tissues reached a peak of 16.9% of the dose after 0.5 day and decreased to 0.6% at 4 days. The tissues of the gastrointestinal tract had the highest concentration of radioactivity, followed by bile and liver. Among nervous tissues, concentration of the 14C was highest in the peripheral nerves. The spinal cord had the next highest concentration, while the brain had the least. After 4 days 91.3% of the 14C had been eliminated in the combined urinary-fecal excreta. By the end of the 12-day experiment this percentage reached 93.1%. No 14C was detected in the expired CO2. Following the oral administration of [14C]EPN, a monophasic body level curve was observed. The half-life for the elimination of 14C from chick body was 16 h, corresponding to a rate constant of 0.04 h -1. Most of the excreted 14C materials were identified as O-ethyl phenylphosphonic acid, phenylphosphonic acid, and O-ethyl phenylphosphonothioic acid.

Two acute human poisoning cases resulting from exposure to diazinon transformation products in Egypt

Two spraymen working in public health occupations in Alexandria, Egypt, experienced acute toxicity resulting from exposure to diazinon. Symptomatology was similar to that previously reported for exposure to parathion or other organophosphorus insecticides. Plasma and red blood cell cholinesterase activity values were determined in blood samples obtained from both individuals at various times after the incident. Cholinesterase activity showed a marked reduction up to 18 days after exposure. Blood cholinesterase activity recovered to approximately 90% of the normal level of activity 28 days after the poisoning incident in one individual. This activity recovered to about the same level in the other individual, but after only 20 days from the poisoning date. Experimental results suggested that this acute toxicity resulted from unsuitable storage conditions of the emulsifiable concentrate formulation of diazinon. The diazinon that was applied was stored in "tin" containers made of tin-plated sheet steel. The emulsifiable concentrate (60%) was not in compliance with the World Health Organization's standard specifications regarding the emulsion stability tests because of the presence of crystals in the emulsifiable concentrate. A sample of this crystalline material was analyzed. Gas chromatographic analysis combined with mass spectrometric techniques failed to identify intact diazinon in samples of that material. The sample represented virtually complete conversion of diazinion into transformation products. Sulfotepp and monothiono-TEPP were two of the identified products in the sample, both of which are much more toxic than diazinon.

Biochemical interaction of six OP delayed neurotoxicants with several neurotargets

Five organophosphorous insecticides: Leptophos, EPN, Cyanofenphos, trichloronate and salithion proved to cause irreversible ataxia not only to chicken but also to mice and sheep. TOCP was included as a reference. Cyanofenphos blocked the catecholamine B-receptor binding activity with 3H-norepinephrine at a level similar to that of the specific inhibitor propranolol in the mouse heart preparation. In the lamb heart preparation, the B-receptor was more sensitive to Leptophos, salithion and TOCP than to propranolol. The six compounds and their oxons were screened for their in-vitro inhibition to monamine oxidase (MAO), acetyl cholinesterase (AChE) and neurotoxic esterase (NTE) in the brain of either mouse, lamb or chicken. It is believed that their AChE inhibition stands for their acute toxicity, while NTE inhibition is responsible for their paralytic ataxia.

Subcellular distribution of neurotoxic esterase activity in lamb and mouse brain

Brain tissue samples of mice (7.6 g from 25 mouse brains and lamb (25 g) were homogenized and subcellular fractions prepared in order to assay the distribution of neurotoxic esterase (NTE) activity. The specific inhibitor, N,N-diisopropylphosphorodiamidic fluoride (mipafox) was synthesized and purified. Maximum specific activity of NTE was reached in the microsomal fraction (110,000 g) while the enzyme activity in the soluble fraction (110,000 g) was extremely low. This subcellular distribution of NTE activity in mammal brains is an original contribution. Brain microsomal fraction is suggested to be a more reliable source for the highest activity of NTE. The specific activity of NTE of lamb brain was much higher than that of mouse brain. This might help interpretation of the characteristic species variation in susceptibility to NTE inhibitors which are known to be potent delayed neurotoxic agents.

Purification and Properties of Ribonuclease From Buffalo Milk Whey

A procedure was developed for isolation and identification of ribonuclease from buffalo milk whey. Ribonuclease was precipitated with (NH₄)₂SO₄ between 65 and 90% saturation. The precipitate was dissolved, dialyzed, and fractionated on DEAE-cellulose. Two ribonuclease-rich fractions were collected, i.e. ribonuclease A and B. Ribonuclease A had an optimum pH of 7 .0, and ribonuclease B had an optimum pH of 8.6. Both had an optimum temperature at 38 C. The ribonucleases in the purified state were unstable to heat and their activity decreased as the time of exposure increased. Both enzyme fractions were sensitive to inhibitors. NaCl and NaN₃ were stimulatory for ribonuclease A, while ribonuclease B was stimulated only by NaCl.