Inhibition by pesticides of prostaglandin formation in blood platelets

Incinerator fly ash provokes alteration of redox equilibrium and liberation of arachidonic acid in vitro

Numerous epidemiological studies have associated exposure to ambient particulate matter (PM) with pulmonary and cardiovascular health effects. Macrophages as a part of the primary pulmonary defence system play a crucial role by generating pro- and anti-inflammatory mediators. The aim of the present study was to examine the effect of incinerator fly ash (MAF02) as a model of environmental particulate matter on the formation of reactive oxygen species (ROS) and their ability to induce oxidative stress in RAW264.7 macrophages. Furthermore, the liberation of arachidonic acid (AA) was observed. The interaction of MAF02 with macrophages caused increased mobilisation of AA, accompanied by enhanced expression of cyclooxygenase-2 (COX-2). The MAF02-induced AA liberation was found to depend on an increased intracellular calcium concentration. In addition, MAF02-induced liberation of AA was selectively blocked by an ERK1/2 pathway-specific inhibitor, while inhibition of the p38 MAPK activity had no effect. Fly ash was also observed to induce an increase in cellular glutathione (GSH) content and antioxidative enzyme haem oxygenase-1 (HO-1). In correlation, experiments with dichlorofluorescein demonstrated increased formation of ROS upon treatment with fly ash. In summary, incinerator fly ash induces oxidative stress to a certain extent, resulting in the onset of important mechanisms related to inflammation.

Determination of the pK(a) of 12-S-hydroxyheptadecatrienoic acid by studies of its vial surface adsorption using high-performance liquid chromatography and liquid scintillation technique

When dissolving 12-S-hydroxyheptadecatrienoic acid (HHT) in aqueous buffer systems, a partition equilibrium is achieved between the liquid buffer phase and the solid vial phase. This adsorption equilibrium is dependent on the vial material, the ratio of solvent volume to moistened vial surface area (V/A), the pH of the aqueous solution the buffer additives and the contact time. Partition ratios (E) were established following determination of the recoveries (omega) of HHT in the liquid phases. The pK(a) of HHT could be calculated to be 4.4 +/- 0.2. The HHT concentration in the liquid phase rose considerably when increasing the pH value (17% at pH 1.9, up to 97% of applied HHT at pH 8.0) and increasing the V/A-ratio, as well as when using glass instead of polypropylene (PP) or adding acetonitrile as an organic solvent and HHT-affine substances like albumins or globulin. The HHT concentration was found to decrease during contact to PP surfaces as a result of HHT adsorption and diffusion into the hydrophobic vial material. This effect could be minimized by adding a larger percentage of acetonitrile (50-60%).

Development and review of radioimmunoassay of 12-S-hydroxyheptadecatrienoic acid

For more than 25 years 12-S-hydroxyheptadecatrienoic acid (HHT) has been known to be a product of thromboxanesynthase (TX-Syn) when synthesized with thromboxane A2 (TXA2). Although there are some hints that HHT has anti-aggregatory effects, to date, it has neither been shown to have any specific pathological relevance nor is there much information about its physiological role. This review presents a summary of the physicochemical properties of HHT, its chemical synthesis, the impact of various biological systems on its enzymatic and non-enzymatic production and its physiological function and metabolization, as well as a survey of the most important methods for analyzing this unsaturated hydroxy-fatty acid. Due to the low antibody-raising potency expected in HHT, no immunological system for HHT quantification has been developed so far. In our report we present the development and validation of a sensitive and reliable, competitive radioimmunoassay (RIA) suitable for the quantitative determination of HHT. HHT was produced by an enhanced enzymatic method using platelet-rich plasma (PRP). With an effective and modified liquid-liquid and solid-phase extraction method we were able to produce highly purified HHT (97% purity by GC/MS) in sub-milligram ranges. These fractions were used for the synthesis of BSA-antigen-conjugates and for immunization of rabbits. The tritiated tracer was synthesized using prostaglandin H synthase for the production of prostaglandin H2 (PGH2) followed by an aqueous reaction with Fe(2+)-solution to rear-range PGH2 to HHT. The dynamic range of the assay was from 30-400 pg/tube, with a sensitivity of approximately 40 pg/tube. The evaluation of the assay was performed by a HPLC-RIA method as well as by correlation with a quantitative HPLC method and correlation with TXB2 concentrations in a blood coagulation study. The assay may be useful for the quantification of HHT in several tissues and body fluids under various physiological conditions and may also help to understand the possible physiological role of HHT in biological processes.

A study of the effects of p,p'-DDE and other related chlorinated hydrocarbons on inhibition of platelet aggregation

A series of chlorinated hydrocarbons of interest in environmental toxicology were investigated concerning their effects on human platelet aggregation. Most potent in inhibiting platelet aggregation were p,p'-DDE and Arochlor 1242. Aggregation induced by arachidonic acid (1 mM) was more sensitive to inhibition by p,p'-DDE than was aggregation induced by ADP (10 microM). The former was completely inhibited by p,p'-DDE at a concentration of 1 x 10(-4) M, whereas there was only a 31% inhibition of the latter. Addition of Ca2+ (1 mM) blocked the inhibitory effect of p,p'-DDE on aggregation induced by both arachidonic acid and ADP. Calmodulin (1 microgram/ml) blocked the inhibitory effect of p,p'-DDE on aggregation induced by arachidonic acid but not that induced by ADP. The calmodulin inhibitory drugs trifluoperazine and calmidazolium had no effect at all or only a weak effect (-14%), respectively, on platelet aggregation. Increasing the concentrations of p,p'-DDE and Arochlor 1242 caused a delay in the onset of aggregation induced by the addition of arachidonic acid. The synthesis of thromboxane B2 and other prostaglandins in platelet membranes was dose-dependently reduced by p,p'-DDE. The structurally closely related isomers o,p'-DDE and p,p'-DDT did not significantly inhibit arachidonic acid-induced platelet aggregation or thromboxane B2 synthesis. It is concluded that p,p'-DDE and Arochlor 1242 inhibited platelet aggregation by inhibiting platelet cyclooxygenase activity.

1-naphthyl N-methyl carbamate effect on intra- and extracellular concentrations of arachidonic acid metabolites, and on the chemiluminescence generation by mouse peritoneal macrophages

1-Naphthyl N-methyl carbamate (carbaryl), potent carbamate insecticide with anticholinesterase activity, was tested for its ability to affect mouse peritoneal macrophages in particular arachidonic acid (AA) metabolism and oxidative burst. Carbaryl inhibited in a dose-related manner the reactive oxygen intermediate dependent chemiluminescence (CL) induced by opsonized zymosan (OZ), 12-O-tetradecanoyl phorbol-13-acetate (TPA) and calcium ionophore (A23187); this carbamate did not affect CL-mediated by AA. The intracellular and extracellular concentrations of prostaglandins (PGs) and 5-hydroxyeicosatetraenoic (5-HETE) generated in macrophages stimulated with OZ has been investigated for various periods. Carbaryl effect displayed two successive phases on AA metabolism stimulation. In a first phase (up to 2-15 min), carbaryl did not alter the rapid AA metabolite synthesis (total amount of intra- and extracellular metabolites) but it increased intracellular concentration of PGE2, PGA2, PGF2 alpha and decreased 5-HETE intracellular concentration. In a second phase (after 2-15 min), carbaryl inhibited AA metabolite synthesis. The release of cyclooxygenase (CO) and lipoxygenase (LO) metabolites decreased, in particular PGF2 alpha and PGD2 which in addition seemed to be submit to a cellular retention; the inhibition of other metabolite release appeared essentially related to the inhibition of their synthesis since the intracellular amount did not augment. The inhibition by carbaryl of the NADPH-oxidase dependent CL induced by OZ may be related to the alteration of the intra- and extracellular concentrations of AA metabolites.

Mechanism of inhibition of cyclo-oxygenase in human blood platelets by carbamate insecticides

Carbamates are a widely used class of insecticides and herbicides. They were tested for their ability to affect human blood platelet aggregation and arachidonic acid metabolism in platelets. (1) The herbicides of the carbamate type have no, or only little, influence up to a concentration of 100 microM; the carbamate insecticides, however, inhibit both aggregation and arachidonic acid metabolism in a dose- and time-dependent manner. (2) Carbaryl, the most effective compound, inhibits platelet aggregation and cyclo-oxygenase activity completely at 10 microM. The liberation of arachidonic acid from phospholipids and the lipoxygenase pathway are not affected, whereas the products of the cyclo-oxygenase pathway are drastically decreased. (3) By using [14C]carbaryl labelled in the carbamyl or in the ring moiety, it could be proved that the carbamyl residue binds covalently to platelet proteins. In contrast with acetylsalicylic acid, which acetylates only one protein, carbaryl carbamylates a multitude of platelet proteins. (4) One of the carbamylated proteins was found to be the platelet cyclo-oxygenase, indicating that carbaryl resembles in this respect acetylsalicylic acid, which is known to inhibit this enzyme specifically by acetylation.