Protein tyrosine kinase involvement in the production of superoxide anion by neutrophils exposed to Aroclor 1242, a mixture of polychlorinated biphenyls

Toxins-useful biochemical tools for leukocyte research

Leukocytes are a heterogeneous group of cells that display differences in anatomic localization, cell surface phenotype, and function. The different subtypes include e.g., granulocytes, monocytes, dendritic cells, T cells, B cells and NK cells. These different cell types represent the cellular component of innate and adaptive immunity. Using certain toxins such as pertussis toxin, cholera toxin or clostridium difficile toxin, the regulatory functions of Gα_i, Gαs and small GTPases of the Rho family in leukocytes have been reported. A summary of these reports is discussed in this review.

Mechanism and characteristics of stimuli-dependent ROS generation in undifferentiated HL-60 cells

It has been widely believed that undifferentiated human promyelocytic leukemia cells (HL-60) have no ability to generate reactive oxygen species (ROS) responding to stimuli. We report here that undifferentiated HL-60 cells possess NADPH oxidase and that generation of superoxide can be measured using a highly sensitive chemiluminescence dye, L-012. Five subunits of NADPH oxidase, namely, gp91(phox), p22(phox), p67(phox), p47(phox), and Rac 2, were detected in undifferentiated HL-60 cells by immunoblotting analysis. The contents of these NADPH oxidase components in the cells were increased with the differentiation induced by phorbol myristate acetate (PMA), except for p22(phox). Messenger RNAs of these subunits were also detected by the RT-PCR method, and their expressions increased except that of p22(phox) with the differentiation induced by PMA. Kinetic analysis using L-012 revealed that HL-60 cells generated substantial amounts of ROS by various stimulants, including formylmethionyl-leucyl-phenylalanine, PMA, myristic acid, and a Ca2+ ionophore, A23187. Both diphenyleneiodonium (an inhibitor of FAD-dependent oxidase) and apocynin (a specific inhibitor of NADPH oxidase) suppressed this stimuli-dependent ROS generation. Genistein, staurosporine, uric acid, and sodium azide inhibited the ROS generation in undifferentiated HL-60 cells in a similar way to that in undifferentiated neutrophils. These results suggested that the mechanism of ROS generation in undifferentiated HL-60 cells is the same as that in primed neutrophils.

A commercial mixture of the brominated flame retardant pentabrominated diphenyl ether (DE-71) induces respiratory burst in human neutrophil granulocytes in vitro

Polybrominated diphenyl ethers (PBDEs) are widely used brominated flame retardants (BFRs), which have become ubiquitous in the environment. This study investigates the effects of the pentabrominated diphenyl ether mixture, DE-71, on human neutrophil granulocytes in vitro. DE-71 enhanced production of reactive oxygen species (ROS) in a concentration-dependent manner measured as lucigenin-amplified chemiluminescence. Octabrominated diphenyl ether (OBDE), decabrominated diphenyl ether (DBDE), and the non-brominated diphenyl ether did not induce ROS formation at the concentrations tested. DPI (4 microM), an inhibitor of the NADPH oxidase completely inhibited DE-71 induced ROS formation, highlighting a role for NADPH oxidase activation. The protein kinase C inhibitor BIM (0.25 microM) and the selective chelator of intracellular calcium, BAPTA-AM (5 microM), also inhibited NADPH oxidase activation, indicating a calcium-dependent activation of PKC. ROS formation was also inhibited by the tyrosine kinase inhibitor tyrphostin (1 microM), the phospholipase C inhibitor ET-18-OCH3 (5 microM), and the phosphatidylinositol-3 kinase inhibitor LY294002 (25 microM). Alterations in intracellular calcium were measured using fura-2/AM, and a significant increase was measured after exposure to DE-71 both with and without extracellular calcium. The tetra brominated compound BDE-47 also enhanced ROS formation in a concentration dependent manner. The combination of DE-71 with the bacteria-derived N-formyl peptide fMLP and PCB153 induced an additive effect in the lucigenin assay. We suggest that tyrosine kinase mediated activation of PI3K could result in enhanced activation of calcium-dependent PKC by enhanced PLC activity, followed by intracellular calcium release leading to ROS formation in neutrophil granulocytes.

Effects of methoxychlor, dieldrin and lindane on sea urchin fertilization and early development

We have studied the effects of methoxychlor (MXC), dieldrin, and lindane on fertilization and early development of sea urchin egg. These organochlorine pesticides have often been found in polluted ground and water near agricultural sites, and have therefore been detected from time to time in the food chain and in drinking water. They have been reported to alter various reproduction functions in various animals including marine populations. We observed that the rate of fertilization decreased when the sperm was incubated with dieldrin or lindane. Treatment of eggs with each pesticide did not prevent fertilization, but increased the rate in polyspermy, delayed or blocked the first mitotic divisions, and altered early embryonic development. Moreover, all pesticides could alter several intracellular biochemical pathways that control first mitotic divisions and early development, including intracellular calcium homeostasis, MPF (mitosis promoting factor) activity and formation of the bipolar mitotic spindle. We found that lindane was the most potent of the three pesticides to alter all biochemical events. All these effects were observed at relatively high concentrations. However, bio-accumulation in sediments and aquatic organisms have been reported. Sea urchin eggs may then be in contact with very high concentrations of these pesticides in areas where these pesticides are not handled or stocked properly, and then develop into abnormal embryos.

Evaluation of the probes 2',7'-dichlorofluorescin diacetate, luminol, and lucigenin as indicators of reactive species formation

This study attempts to provide a critical assessment of three different common approaches to identifying teactive species formed in biological systems: the 2',7'-dichlorofluorescin diacetate (DCFH-DA) assay, and the luminol- and lucigenin-amplified chemiluminescence assays. There have been several contradictory reports about the specificity of these methods. Our results show that DCFH is oxidized to the fluorescent compound 2',7'-dichlorofluorescin (DCF) in human neutrophils exposed to the following compounds: Aroclor (A)1242, hydrogen peroxide (H(2)O(2)), nitric oxide (NO), and FeSO(4). Use of a cell-free DCFH system showed increased formation of DCF by peroxynitrite (ONOO(-)), horseradish peroxidase (HRP) alone, and HRP in combination with H(2)O(2), FeSO(4) alone, and a mixture of FeSO(4) and H(2)O(2). The hydroxyl radical (z.rad;OH) scavenger formate and the iron ion chelator deferoxamine reduced the DCF formation induced by FeSO(4) in combination with H(2)O(2). DCFH was insensitive to NO and H(2)O(2) in the cell-free system. In the presence of neutrophils, the A1242-induced luminol chemiluminescence was decreased by the superoxide dismutase inhibitor diethyldithiocarbamic acid (DDC) and the myeloperoxidase inhibitor salicylhydroxamic acid (SHA). Exposure of the neutrophils to NO, FeSO(4), or H(2)O(2) alone did not have any effect. A1242-induced lucigenin chemiluminescence in the neutrophils was increased slightly by DDC, but was not affected by SHA, NO, FeSO(4), or H(2)O(2). In conclusion, we suggest that the DCF assay is only suitable for measurements of ONOO(-), H(2)O(2) in combination with cellular peroxidases, and z.rad;OH. Luminol is sensitive towards HOCl, while lucigenin is oxidized by O(2)z.rad;(-).

Dieldrin induces human neutrophil superoxide production via protein kinases C and tyrosine kinases

We have recently found that dieldrin is a potent human neutrophil agonist in vitro and induces neutrophilic inflammation in vivo. Among the responses observed in vitro, dieldrin was found to induce superoxide (O2-) production by a yet unknown mechanism. In the present study, dieldrin- and phorbol 12-myristate 13-acetate (PMA)-induced O2- responses were compared. For this purpose, cells were preincubated with a panel of signal transduction inhibitors including genistein, H-7, HA-1077, pertussis toxin, staurosporine, calphostin C, SB203580, PD098059, and wortmannin. Dieldrin-induced O2- response was significantly reduced with treatment with genistein, H-7, HA-1077, staurosporine, and calphostin C, whereas PMA-induced response was significantly reduced by treatment with H-7, HA-1077, and staurosporine. This indicates that dieldrin mediates its effect via protein kinases C (PKCs) and tyrosine kinases. Involvement of tyrosine kinases in dieldrin-induced human neutrophils was further demonstrated by an increase in tyrosine phosphorylated protein level expression. Finally, we found that treatment with the mitochondrial stabilizer bongkrekic acid and with the inhibitor of vesicular transport brefeldin A did not reverse dieldrin-induced O2- response.

Toxaphene, but not beryllium, induces human neutrophil chemotaxis and apoptosis via reactive oxygen species (ROS): involvement of caspases and ROS in the degradation of cytoskeletal proteins

Chemicals of environmental concern are known to alter the immune system. Recent data indicate that some contaminants possess proinflammatory properties by activating neutrophils, an area of research that is still poorly investigated. We have previously documented that toxaphene activates human neutrophils to produce reactive oxygen species (ROS) and accelerates apoptosis by a yet unknown mechanism. In this study, we found that toxaphene induces another neutrophil function, chemotaxis. Furthermore, we found that toxaphene induces both chemotaxis and apoptosis via a ROS-dependent mechanism, since these responses were blocked by the addition of catalase to the culture. In addition, toxaphene was found to induce the degradation of the cytoskeletal proteins gelsolin, paxillin, and vimentin during apoptosis, and this was reversed by the addition of z-VAD-FMK (caspase inhibitor) or catalase, demonstrating the importance of caspases and ROS in this process. In contrast to toxaphene, we found that beryllium does not induce superoxide production, and, this correlates with its inability to induce chemotaxis and apoptosis. We conclude that toxaphene induces chemotaxis and apoptosis via ROS and that caspases and ROS are involved in the degradation of cytoskeletal proteins.

Participation of Ca2+/calmodulin during activation of rat neutrophils by polychlorinated biphenyls

The effects of Ca2+ and Ca2+/calmodulin on the polychlorinated biphenyl (PCB)-induced activation of phospholipase A2 (PLA2) in rat neutrophils were examined. The commercial PCB mixture Aroclor 1242 induced activation of PLA2 and promoted an increase in the intracellular free calcium concentration ([Ca2+]i). Bromoenol lactone (BEL), an inhibitor of the Ca2+-independent PLA2 isoform (iPLA2) activated by PCBs, did not abrogate the increase in [Ca2+]i, suggesting that this change in Ca2+ concentration is not downstream from the activation of iPLA2. TMB-8 [8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate], a blocker of the release of intracellular Ca2+, decreased Aroclor 1242-induced stimulation of PLA2 with a maximal inhibition of 17% at 50 microM. These two results suggest little direct dependence between the PCB-induced activation of iPLA2 and increase in [Ca2+]i. Calmidazolium and W7 [N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide], two chemically distinct calmodulin inhibitors, inhibited Aroclor 1242-induced PLA2 activity, whereas trifluoperazine (TFP), another inhibitor of calmodulin, had no effect at noncytotoxic concentrations. Thus, activation of PLA2 is dependent, in part, on calmodulin. Furthermore, both TFP and Aroclor 1242 inhibited neutrophil degranulation stimulated by the bacterial peptide formyl-methionyl-leucyl-phenylalanine. These results raise the possibility that some of the effects of PCBs on neutrophil function can be explained by effects on Ca2+/calmodulin-dependent processes.

Role of protein phosphorylation in activation of phospholipase A2 by the polychlorinated biphenyl mixture Aroclor 1242

Polychlorinated biphenyls (PCBs) activate neutrophils to induce degranulation and undergo superoxide production through a mechanism that involves stimulation of phospholipase A(2) (PLA(2)). Since the biochemical processes leading to the PCB-induced activation of this enzyme are unknown, the objective of this study was to determine whether protein phosphorylation has a role in this mechanism. Isolated rat neutrophils were labeled with [(3)H]-arachidonic acid ([(3)H]-AA), and activation of PLA(2) was determined from release of radioactivity into the medium. Exposure to the PCB mixture Aroclor 1242 induced release of [(3)H]-AA, and pretreatment with bromoenol lactone (BEL), an inhibitor of calcium-independent PLA(2), diminished release by 80%. Genistein, an inhibitor of tyrosine kinases, caused a small but significant decrease in Aroclor 1242-stimulated release of [(3)H]-AA. Daidzein, a genistein analog with no activity to inhibit tyrosine kinases, had no effect on [(3)H]-AA release. An inhibitor of p38 mitogen-activated protein kinase (MAPK), SB203580, did not affect Aroclor 1242-induced PLA(2) activity at concentrations selective for p38 MAPK; however, PD 98059, which inhibits MAPK kinase (MEK), decreased [(3)H]-AA release to about the same extent as genistein. Treatment of neutrophils with Aroclor 1242 induced phosphorylation of p44 MAPK, and this phosphorylation was unaffected by BEL but was inhibited by PD 98059. Staurosporine, a nonselective inhibitor of protein kinase C (PKC), inhibited PCB-induced release of [(3)H]-AA. Ro 32-0432, a selective inhibitor of PKC(alpha) and PKC(beta1), produced the greatest degree of inhibition (40%) among the tested protein kinase inhibitors. These results suggest that tyrosine kinases, PKC, and the MEK/MAPK pathway are involved in a fraction of Aroclor 1242-induced activation of PLA(2).

Functional responses of human neutrophils to sodium sulfite (Na2SO3) in vitro

An influx of neutrophils into the airways is a common feature observed during pulmonary inflammation induced by air pollutants, including sulfur dioxide and sulfates. In the present study focusing on the in vitro interactions of sodium sulfite (Na2SO3) with human neutrophils, we confirm results indicating that this sulfite induces superoxide production (O2-) by itself. We demonstrated that this response can occur more rapidly than previously reported (within 5 min), and that Na2SO3 can act as a priming agent, in a concentration-dependent fashion, to the bacterial tripeptide N-formyl-methionine-leucine-phenylalanine (fMLP) by increasing O2-production. In addition, our results show that Na2SO3 induces gene expression in human neutrophils in a concentration-dependent manner as assessed by incorporation of 5-[3H] uridine into total RNA. However, it does not induce cell shape changes. We also demonstrated that Na2SO3 does not modulate neutrophil apoptosis nor reverse the well-known delaying effect of granulocyte-macrophage colony-stimulating factor (GM-CSF) on apoptosis. We conclude that Na2SO3 acts rapidly on neutrophil physiology, within a few minutes with respect to superoxide production, and a few hours (4 h) with respect to gene expression without altering a biological process such as the rate of apoptosis evaluated after a long period of incubation (20 h). We further conclude that Na2SO3-induced production of O2does not drive neutrophils to undergo apoptosis, a mechanism known to occur in other conditions. Therefore, the potential toxicity of Na2SO3 during pulmonary inflammation or lung-associated diseases may be related to its ability to induce superoxide production without altering neutrophil apoptosis rate.