The effect of free radical derived hydroxyeicosatetraenoic acids on hexose transport in the human polymorphonuclear leukocyte

The role of free radicals and antioxidants: how do we know that they are working?

This review briefly discusses how free radicals are formed and the possible participation of free radicals in disease. The review describes the basic radical reactions and the types of products that are formed from the free-radical reactions of cellular constituents. In many cases, in vivo free-radical oxidation can be detected by measuring products that were derived from radical reactions. Since aerobic organisms generate oxygen-containing free radicals during oxygen metabolism, they carry chemicals and enzymes that reduce the threat posed by these radicals. The more common sources of in vivo free radicals are described in the article as well as the methods used by cells to protect themselves from free-radical damage. Generation of free radicals in vivo also may be the result of exposure to certain chemical agents present in the environment. Many of these agents cause pathologic changes to the exposed tissues and organs by initiating free-radical reactions.

Bioactions of 5-hydroxyicosatetraenoate and its interaction with platelet-activating factor

In a variety of stimulated cells, platelet-activating factor (PAF) and numerous arachidonate derivatives are co-products that form as a consequence of receptor-mediated phospholipid mobilization. These lipid co-products produce a plethora of biological effects in a wide variety of cell systems. Furthermore, they often have a fascinating although less widely appreciated, interaction. 5-HETE, at submicromolar concentrations, exerts relatively few direct bioactions. It does, however, potently (16-160 nM) raise cytosolic free calcium [Ca2+]i and augment PAF-induced responses in human polymorphonuclear neutrophils (PMN) by as much as 100- to 1000-fold. 5-HETE acts on PMN by a structurally specific, stereospecific and pertussis toxin-inhibitable mechanism. In addition, PMN exposed to 5-HETE exhibit homologous but not heterologous desensitization. These findings suggest that 5-HETE, like PAF, may bind to its own specific plasmalemmal receptors to exert its unique set of bioactions. However, further investigation is required to demonstrate any putative 5-HETE receptors. Other potential mechanisms of 5-HETE-induced bioactions together with the possible effects of 5-HETE on PAF transduction mechanisms are also discussed.

The effect of 5-hydroxyeicosatetraenoic acid on the proliferation of granulocyte progenitors and embryonic fibroblasts of the chick

The clonal proliferation of chicken granulocytic progenitors was inhibited 5-20-fold by the eicosanoid, 5-HETE, at 1.0 microM. Inhibition occurred at the lowest concentration measured (0.12 microM). This compound at 0.6 to 1.0 microM also inhibited the clonal proliferation of chick embryo fibroblasts by as much as 10-fold.

Ex vivo effects of nonsteroidal antiinflammatory drugs on arachidonic acid metabolism in neutrophils from a reverse passive Arthus reaction

Rat neutrophils isolated from 4-h reverse passive Arthus reaction (RPAR) pleural exudates actively metabolize arachidonic acid via cyclooxygenase and lipoxygenase. Utilizing this system, the effect of oral doses of nonsteroidal antiinflammatory drugs on the ability of these cells to produce HHT, 5-HETE, and LTB from exogenously added arachidonic acid has been investigated. In vitro and ex vivo, indomethacin and timegadine inhibit cyclooxygenase activity in rat pleural neutrophils. In vitro, timegadine is a lipoxygenase as well as a cyclooxygenase inhibitor. This dual inhibition is confirmed by the observation that ex vivo timegadine inhibits the production of lipoxygenase as well as cyclooxygenase metabolites. While indomethacin, a cyclooxygenase inhibitor, primarily inhibits edema formation, the inhibition of both pathways of arachidonic acid metabolism by timegadine is reflected in the drug's ability to reduce cellular influx as well as edema formation in the RPAR pleural cavity inflammatory reaction.

Effect of 15-lipoxygenase-derived arachidonate metabolites on human neutrophil degranulation

Products of the 15-lipoxygenase pathway of arachidonate metabolism, prepared by techniques that effectively free them from contaminants, were examined for their ability to influence human neutrophil degranulation. 15(S)-Hydroxyicosatetraenoate [15(S)-HETE], 8(S),15(S)-dihydroxyicosatetraenoate, and 5(S),15(S)-dihydroxyicosatetraenoate did not directly stimulate this response, but 5(S),15(S)-dihydroxyicosatetraenoate (158-5000 nM) enhanced degranulation responses elicited by platelet-activating factor and its structural analogues. It had no such effect on the degranulation responses elicited by a tripeptide chemotactic factor, phorbol myristate acetate, leukotriene B4, or ionophore A23187. In many of these respects, the potentiating actions of 5,15-dihydroxyicosatetraenoate paralleled the actions of 5(S)-hydroxyicosatetraenoate. Indeed, these two metabolites had potentiating actions on platelet-activating factor that were non-additive and, under specific conditions, cross-desensitized each other. Based on the structural specificity demonstrated by these and other mono- and dihydroxyeicosatetraenoates in potentiating platelet-activating factor as well as their mutual cross-desensitizing actions, we suggest that 5-hydroxylated arachidonate metabolites act by a structurally specific receptor to potentiate human neutrophil responses to certain stimuli.

Stimulation of hexose transport by human polymorphonuclear leukocytes: a possible role for protein kinase C

The protein C kinase activators 1-O-oleoyl, 2-O-acetylglycerol, 12-O-tetradecanoyl phorbol-13-acetate, and mezerein, stimulated deoxyglucose uptake in human neutrophils. The responses were stimulus specific since no effect was noted with the diether analogues 1-O-hexadecyl-2-O-ethylglycerol, 1-O-palmitoyl-2-O-acetyl or 1-O-palmitoyl-3-O-acetyl diesters of propanediol, or with 1,2-diolein. Stimulation of deoxyglucose uptake had the characteristics of carrier facilitated hexose transport. Stimulated uptake of deoxy-glucose was inhibited by trifluoperazine (10-30 microM). Activation of protein kinase C therefore appears to trigger events involved in hexose transport.

Differential effects of anti-inflammatory drugs on lipoxygenase and cyclo-oxygenase activities of neutrophils from a reverse passive Arthus reaction

Rat neutrophils isolated from four-hour reverse passive Arthus reaction pleural exudates actively metabolize arachidonic acid. Production of 11-hydroxy- and 15-hydroxy-icosatetraenoic acid and 12-hydroxy-heptadecatrienoic acid is inhibited by indomethacin, benoxaprofen, BW 755C, piroxicam, ibuprofen, timegadine, and naproxen, suggesting that production of these arachidonic acid metabolites occurs at similar enzymic active sites. In addition, in the presence of the calcium inophore A23187 or the non-ionic detergent, BRIJ 56, rat neutrophils also produce the lipoxygenase products 5-hydroxy-icosatetraenoic acid and leukotriene B. The production of these metabolites is calcium dependent. Moreover, the calcium ionophore A23187 and BRIJ 56 synergistically act to augment the metabolism of exogenously added arachidonic acid via lipoxygenase. The formation of these metabolites is inhibited by BW 755C, benoxaprofen and timegadine but not by other non-steroidal anti-inflammatory drugs tested. In fact, at doses which inhibit cyclo-oxygenase activity, indomethacin, naproxen, and ibuprofen stimulate arachidonic acid metabolism via lipoxygenase.