A Kinetic Approach for Assessing the Uptake of Ag from Pristine and Sulfidized Ag Nanomaterials to Plants.

Nanomaterials (NMs) are thermodynamically unstable by nature, and exposure of soil organisms to NMs in the terrestrial environment cannot be assumed constant. Thus, steady-state conditions may not apply to NMs, and bioaccumulation modeling for uptake should follow a dynamic approach. The one-compartment model allows the uptake and elimination of a chemical to be determined, while also permitting changes in exposure and growth to be taken into account. The aim of the present study was to investigate the accumulation of Ag from different Ag NM types (20 nm Ag0 NMs, 50 nm Ag0 NMs, and 25 nm Ag2 S NMs) in the crop plant wheat (Triticum aestivum). Seeds were emerged in contaminated soils (3 or 10 mg Ag/kg dry soil, nominal) and plants grown for up to 42 d postemergence. Plant roots and shoots were collected after 1, 7, 14, 21, and 42 d postemergence; and total Ag was measured. Soil porewater Ag concentrations were also measured at each sampling time. Using the plant growth rates in the different treatments and the changing porewater concentrations as parameters, the one-compartment model was used to estimate the uptake and elimination of Ag from the plant tissues. The best fit of the model to the data included growth rate and porewater concentration decline, while showing elimination of Ag to be close to zero. Uptake was highest for Ag0 NMs, and size did not influence their uptake rates. Accumulation of Ag from Ag2 S NMs was lower, as reflected by the lower porewater concentrations. Environ Toxicol Chem 2021;40:1861-1872. © 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Extending standard testing period in honeybees to predict lifespan impacts of pesticides and heavy metals using dynamic energy budget modelling.

Concern over reported honeybee (Apis mellifera spp.) losses has highlighted chemical exposure as a risk. Current laboratory oral toxicity tests in A. mellifera spp. use short-term, maximum 96 hour, exposures which may not necessarily account for chronic and cumulative toxicity. Here, we use extended 240 hour (10 day) exposures to examine seven agrochemicals and trace environmental pollutant toxicities for adult honeybees. Data were used to parameterise a dynamic energy budget model (DEBtox) to further examine potential survival effects up to 30 day and 90 day summer and winter worker lifespans. Honeybees were most sensitive to insecticides (clothianidin > dimethoate ≫ tau-fluvalinate), then trace metals/metalloids (cadmium, arsenic), followed by the fungicide propiconazole and herbicide 2,4-dichlorophenoxyacetic acid (2,4-D). LC50s calculated from DEBtox parameters indicated a 27 fold change comparing exposure from 48 to 720 hours (summer worker lifespan) for cadmium, as the most time-dependent chemical as driven by slow toxicokinetics. Clothianidin and dimethoate exhibited more rapid toxicokinetics with 48 to 720 hour LC50s changes of <4 fold. As effects from long-term exposure may exceed those measured in short-term tests, future regulatory tests should extend to 96 hours as standard, with extension to 240 hour exposures further improving realism.

Mechanism of apoptosis in HL-60 cells induced by n-3 and n-6 polyunsaturated fatty acids.

The biochemical properties and specificity of n-3 and n-6 polyunsaturated fatty acids (PUFAs) are not well known. Because PUFAs induce apoptosis of different cells, we studied the effect of various PUFAs, such as arachidonic acid (AA), eicosapentaenoic acid (EPA), and docosapentaenoic acid (DPA), on the fate of cultured human promyelocytic leukemia cells (HL-60) to elucidate the mechanism of apoptosis and the difference in action between n-3 and n-6 PUFAs. Fairly low concentrations of PUFAs inhibited the growth of HL-60 cells and induced their apoptosis by a mechanism that is sensitive to DMSO, an antioxidant, and z-Val-Ala-Asp(OMe)-fluoromethylketone (z-VAD-fmk), a pan-caspase inhibitor. PUFAs stimulated the generation of reactive oxygen species (ROS) and activated various types of caspase-like proteases, such as caspase-3, -6, -8, and -9, but not caspase-1. In addition, PUFAs triggered the reaction leading to the cleavage of Bid, a death agonist member of the Bcl-2 family, and also released cytochrome c from mitochondria into the cytosol. PUFAs also decreased the mitochondrial membrane potential of intact HL-60 cells. All of these actions of n-3 PUFAs were stronger than those of AA, an n-6 PUFA, although the mechanism is not known. PUFAs stimulate swelling and membrane depolarization of isolated mitochondria in a cyclosporin A-sensitive manner. The results indicated that PUFA-induced apoptosis of HL-60 cells may be caused, in part, by direct action on the cells and by activation of the caspase cascade through cytochrome c release coupled with mitochondrial membrane depolarization.

Effect of n-3 and n-6 polyunsaturated fatty acids and their ethylesters on stimuli-dependent superoxide generation in neutrophils.

Polymorphonuclear leukocytes from healthy volunteers (HPMN) generated superoxide (O2*-) following treatment with various stimuli, such as phorbol myristate acetate (PMA), opsonized zymozan (OZ) and arachidonic acid (AA). Other types of n-3 polyunsaturated fatty acids (PUFAS), such as docosahexaenoic acid (DHA), docosapentaenoic acid (DPA), and eicosapentaenoic acid (EPA), also stimulated O2*- generation. The free form of DHA enhanced the generation of O2*- induced by PMA but inhibited that induced by OZ. In contrast, the ethylester of DHA (DHA-E) inhibited O2*- generation induced by PMA but stimulated that induced by OZ. Similar effects were also observed with ethylesters of EPA (EPA-E), DPA (DPA-E) and AA (AA-E). High concentrations of DHA-E reduced the PMA-induced formation of superoxide without affecting the cellular activity of protein kinase C (PKC). Similar phenomena were also observed with oral neutrophils from healthy volunteers (OPMN). These results indicate that PUFAS and their esters affect 02*- generation in human PMN via different pathways, thereby modulating inflammatory reactions.

Caspase activation and cytochrome c release during HL-60 cell apoptosis induced by a nitric oxide donor.

Nitric oxide (NO) from (Z)-1-[N-(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1- ium-1,2-diolate (NOC-18) induces apoptosis in human leukemia HL-60 cells. This effect was prevented by the pan-caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone (Z-VAD-FMK), thereby implicating caspase activity in the process. NOC-18 treatment resulted in the activation of several caspases including caspase-3, -6, -8, and -9(-like) activities and the degradation of several caspase substrates such as nuclear lamins and SP120 (hnRNP-U/SAF-A). Moreover, release of cytochrome c from mitochondria was also observed during NOC-18-induced apoptosis. This change was substantially prevented by Z-VAD-FMK, thereby suggesting that the released cytochrome c might function not only as an initiator but also as an amplifier of the caspase cascade. Bid, a death agonist member of the Bcl-2 family, was processed by caspases following exposure of cells to NOC-18, supporting the above notion. Thus, NO-mediated apoptosis in HL-60 cells involves a caspase/cytochrome c-dependent mechanism.

Selective inhibition of formyl-methionyl-leucyl-phenylalanine (fMLF)-dependent superoxide generation in neutrophils by pravastatin, an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase.

It has been shown previously that inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, such as compactin, lovastatin, and pravastatin, block cholesterol synthesis, suppress lymphocyte functions, and beneficially affect atherogenesis. Recently, it was reported that compactin and lovastatin inhibit the respiratory burst of DMSO-differentiated HL-60 cells, an effect reversed by mevalonic acid. The mode of action of these inhibitors in this role is not understood fully. Thus, we studied the mechanism of inhibition of neutrophil superoxide (O2*-) generation by pravastatin and found that pravastatin at 0.5 mM inhibited the receptor-mediated tyrosine kinase (TK)-dependent pathway of O2*- generation and also luminol chemiluminescence but not the protein kinase C (PKC)-dependent or the TK- and PKC-independent pathways of O2*- generation in neutrophils. Pravastatin also inhibited the tumor necrosis factor-alpha- and formyl-methionyl-leucyl-phenylalanine-induced phosphorylation of a tyrosine of a 115-kDa protein. These effects were not reversed by mevalonate. From these results it is concluded that pravastatin inhibited receptor-mediated O2*-generation by decreasing tyrosine phosphorylation but not by inhibiting the formation of an intermediate in the biosynthesis of cholesterol.

Effects of milk and colostrum on superoxide generation of oral polymorphonuclear neutrophils and the changes that occur during storage at low temperature.

Human oral polymorphonuclear neutrophils (OPMN) generate reactive oxygen species even in the absence of stimulants. Because OPMN from newborn babies are exposed to colostrum and mature milk, the biological properties of these cells including the generation of reactive oxygen species might possibly be affected by the constituents of colostrum and milk. The present work reports the effects of colostrum and mature milk, including the effects of storage at low temperature, on superoxide generation by OPMN. Fresh colostrum and mature milk did not affect either endogenous or formyl-methionyl-leucyl-phenylalanine-induced generation of superoxide by OPMN. However, superoxide generation stimulated by phorbol myristate acetate or arachidonic acid was inhibited by colostrum and mature milk presumably due to binding of the ligands to milk proteins. During the storage of milk at 4 degrees C, free forms of unsaturated long-chain fatty acids increased, and there was concomitant increase in the ability of milk to generate superoxide radicals in OPMN. Kinetic analysis suggested that colostrum and mature milk regulate superoxide generation by OPMN, thereby modulating the bactericidal activity of these cells in the oral cavity.

Geranylgeranylacetone induces apoptosis in HL-60 cells.

Geranylgeranylacetone (GGA) induces apoptosis in human leukemia HL-60 cells in a dose- and time-dependent manner. This effect was completely prevented by the pan-caspase inhibitor z-Val-Ala-Asp(OMe) fluoromethylketone, thereby implicating the caspase cascade in the process. Prior to DNA fragmentation, GGA treatment markedly activated caspase-3(-like) proteases, which might be responsible for the observed apoptosis. In addition, GGA treatment interfered with the processing and membrane localization of Rap1 and Ras, and these changes may be a result of apoptosis. Moreover, nitric oxide donors significantly accentuated the GGA-induced apoptosis, suggesting that the apoptotic pathway induced by GGA might be regulated by a redox-sensitive mechanism. Taken together, these data suggest that the isoprenoid, GGA, is an effective inducer of apoptotic cell death in HL-60 cells.

Resistance to nitric oxide-mediated apoptosis in HL-60 variant cells is associated with increased activities of Cu,Zn-superoxide dismutase and catalase.

Nitric oxide (NO) released from (Z)-1-[N-(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1- ium-1,2-diolate (DETA/NO or NOC-18) induces apoptosis in human leukemia HL-60 cells. In this study, we isolated a HL-60 variant cell line, HL-NR6, that is resistant to DETA/NO toxicity as assessed by DNA fragmentation, morphology, and colony forming ability. The variant cells also showed resistance to reactive oxygen species (ROS) such as superoxide and hydrogen peroxide as well as NO donors, but not to anti-tumor drugs. We found that HL-NR6 cells when compared with HL-60 cells possessed twice the activities of Cu,Zn-superoxide dismutase (Cu,Zn-SOD) and catalase, but no change in Mn-SOD nor in glutathione peroxidase. Immunoblotting confirmed the high levels of both enzymes in the variant cell. We also observed that ROS generation following DETA/NO exposure was substantially higher in HL-60 cells than in HL-NR6 cells, using the 2',7'-dichlorofluorescein fluorometric method. Moreover, the SOD mimetic Mn(III) tetrakis(1-methyl-4-pyridyl) porphyrin and exogenous catalase effectively attenuated DETA/NO-elicited DNA fragmentation in HL-60 cells. Taken together, these data suggested that the NO resistance in HL-NR6 cells is associated with the increased Cu,Zn-SOD/catalase and that NO-mediated apoptosis in HL-60 cells is correlated with the generation of ROS and derived molecules like peroxynitrite.

Role of nuclear lamins in nuclear segmentation of human neutrophils.

Nuclear breakdown leading to the formation of apoptotic bodies has been postulated to involve degradation of nuclear structural proteins, such as lamins A/C and B. Although nuclear segmentation occurs during the maturation of polymorphonuclear leukocytes (neutrophils), its mechanism is not known. We found that human neutrophils have lamin B but lack lamins A/C while mononuclear cells possess all three types of lamin as assessed by immunoblotting. Differentiation of human promyelocytic HL-60 cells into neutrophil-like cells was also accompanied by the down-regulation of lamins A/C but not of lamin B. Moreover, when compared with normal cells, neutrophils with the Pelger-Huët anomaly of nuclear hyposegmentation exhibited significantly lower activity of caspase-6, a lamin A/C-cleaving enzyme. Differentiated HL-60 cells showed higher activity of caspase-6 than that of untreated cells. These observations allow us to speculate that remodeling of nuclear lamins might underlie the mechanism for nuclear segmentation of neutrophils.

Superoxide dismutase-like activity of metal substituted lactoferrin derivatives.

Lactoferrin (LF) is an iron-binding glycoprotein present in various secretions including milk and the specific granules of neutrophils. The main biological properties of this protein are thought to concern the regulation of iron absorption, antimicrobial activity and modulation of neutrophil activity. Copper bound LF (Cu-LF) inhibited the stimulation-dependent reduction of cytochrome c (Cyt. c) in guinea pig peritoneal neutrophils (GPMN) but were without effect on NADPH oxidase activity of the respiratory burst. However, Cu-LF stimulated the stimulation-dependent production of hydrogen peroxide as seen with superoxide dismutase (SOD). Similar but weaker inhibition of Cyt. c reduction than that shown by Cu-LF was observed with manganese-LF (Mn-LF) but not with ferrous-LF (Fe-LF) or apo-LF (Apo-LF). The inhibitory activity was concentration-dependent and the ID50s of Cu-LF and of Mn-LF were 0.1 and 5 microM, respectively. Reactive oxygen species (ROS) detected by luminol chemiluminescence (LCL) of stimulated-GPMN were partially inhibited by Cu-LF. Changes in LCL of stimulated GPMN induced by Cu-LF were similar to those of superoxide dismutase (SOD). Thus, it is concluded that low concentrations of Cu-LF had SOD-like activity and high concentrations of Cu-LF inhibited the stimulation-dependent generation of ROS.

Molecular mechanisms of apoptosis in HL-60 cells induced by a nitric oxide-releasing compound.

Nitric oxide (NO) generated from 1-hydroxy-2-oxo-3, 3-bis(2-aminoethyl)-1-triazene (NOC 18), an NO-releasing compound, induced monocytic differentiation of human promyelocytic leukemia HL-60 cells as assessed by expression of nonspecific esterases and morphologic maturation. Simultaneously, DNA fragmentation and morphological alterations typical of apoptosis were also induced. To investigate the mechanisms of apoptosis during differentiation of HL-60 cells induced by NO, the endogenous levels of Bcl-2 and Bax were assessed by immunoblotting. Treatment of cells with NOC 18 slightly reduced the level of Bcl-2 followed by Bax. These changes might be involved in the induction of apoptosis. The involvement of the activation of the interleukin-1 beta converting enzyme (ICE) family of proteases (caspases), such as ICE and CPP32, in the pathways was also investigated. CPP32, but not ICE, was strongly activated in response to NOC 18 stimulation, thereby implicating CPP32-like activity in the induction of apoptosis. Moreover, the possible involvement of tyrosine phosphorylation in apoptosis was investigated. Pretreatment of cells with herbimycin A, an inhibitor of tyrosine kinases, suppressed DNA fragmentation and CPP32-like activity, whereas pretreatment with vanadate, an inhibitor of tyrosine phosphatases, enhanced both parameters, suggesting that tyrosine phosphorylation might be involved in the pathways of apoptosis in HL-60 cells induced by NO.

Effects of eicosanoids on parameters in isolated rat hepatocytes and isolated rat hepatocyte couplets: protective effects of eicosanoid receptor antagonists.

A number of eicosanoids caused plasma membrane blebbing in hepatocytes and this could be inhibited in a dose-dependent fashion by the receptor antagonists AH6809 and ICI 192605. The pattern of effectiveness of eicosanoids interfering with canalicular vacuole accumulation in hepatocyte couplets differed from that causing blebbing; the two most effective eicosanoids here were PGD2 and PGF2 alpha.

Oxygen-dependent reversible inhibition of mitochondrial respiration by nitric oxide.

Effects of nitric oxide (NO) and NO generating agents, on the electron transport system of mitochondria were examined in a study of the mechanism and physiological importance of NO in energy metabolism. In the presence of various substrates, uncoupled respiration was inhibited by NO in manner which was both dose- and oxygen tension-dependent. Simultaneously measuring changes in cytochrome absorption spectra and respiration showed that the site of action of NO is cytochrome oxidase. Similar inhibition was also brought about by 1-hydroxy-2-oxo-3,3-bis(2-aminoethyl)-1-triazene (NOC 18), an NO donor. Electron paramagnetic resonance (EPR) analysis revealed that inhibition of uncoupled respiration occurred only during the presence of NO in the reaction mixture. The inhibitory effect of NO was increased significantly by lowering the concentration of mitochondrial protein. No appreciable inhibition of respiration was observed in the presence of 3-morpholinosydnonimine (SIN-1), a peroxynitrite anion (ONOO-) generating reagent, but inhibition did occur in the presence of superoxide dismutase (SOD). These results indicate that NO reversibly interacts with mitochondria at complex IV thereby inhibiting respiration particularly under physiologically low oxygen tension and that de novo generated ONOO may have no significant effect under the present experimental conditions.

Oxygen-dependent-regulation of Ehrlich ascites tumor cell respiration by nitric oxide.

Effects of nitric oxide (NO) on oxygen uptake of Ehrlich ascites tumor cells (EATC) were examined in a study of the biological actions of NO on respiration and energy metabolism at the cellular level. Endogenous respiration of EATC was inhibited reversibly by NO in a dose dependent manner. Oxyhemoglobin, an NO trapping agent, restored the respiration promptly. The inhibitory action of NO also depended on oxygen-concentration, and the duration of suppression was prolonged remarkably at low oxygen tension. Similar inhibition was also observed in the presence of glucose. In this case, both lactate production and glucose consumption were promoted by NOC 18, an NO generating agent, and the activation was enhanced by lowering the oxygen-concentration. Furthermore, the membrane potential of EATC was depolarized transiently by adding NO, and the degree of depolarization was decreased in the presence of glucose. These results suggest that at physiologically low oxygen tension in ascites fluid, NO acts not only as a cytotoxic respiratory inhibitor but also as a regulatory factor in the energy metabolism of EATC.

Inhibition of neutrophil-superoxide generation by alpha-tocopherol and coenzyme Q.

Effects of various derivatives of alpha-tocopherol (VE) and coenzyme Q (CoQ) on superoxide (O2.-) generation of neutrophils and protein kinase C (PKC) activity were examined. VE and CoQ8 inhibited O2.- generation of neutrophils stimulated by a protein kinase C mediated process monitored by cytochrome c reduction and spin trapping methods. The inhibitory action was observed not only with alpha-tocopherol, but also with beta-, gamma-, delta-tocopherols and with tocol which is a chemical similar to VE but lacking methyl groups on the chromanol ring structure and which is not a radical scavenger. By contrast, no inhibition was observed with 2-carboxy-2, 5, 7, 8-tetramethyl-6-chromanol (CTMC, trolox) or 2, 2, 5, 7, 8,-pentamethyl-6-chromanol (PMC) which are water soluble VE derivatives having radical scavenging activity. Compounds having a similar isoprenoid chain, such as CoQ, also have inhibitory activity on PKC-dependent O2.- generation of neutrophils. The inhibitory activity of CoQ derivatives is dependent on the length of the unsaturated isoprenoid chain. CoQ derivatives having 16, 24 and 32 carbon isoprenoid chains corresponding to CoQ4, 6, and 8 inhibited O2.- generation but 4 and 40 carbon isoprenoid chains corresponding to CoQ2 and 10 had no inhibitory activity on O2.- generation. Alpha-tocopherol and CoQ inhibited PKC activity but the ID50 for O2.- generation and PKC activity was different for each compound. However, no direct relationship between VE content and O2.- generation of neutrophils was observed. These results suggest that isoprenoids of VE and CoQ participate in the inhibition of the NADPH oxidase activation system through modulation of the neutrophil membrane probably by the inhibition of PKC.

Inhibition of neutrophil superoxide generation by hypericin, an antiretroviral agent.

We previously reported that phorbol 12-myristate 13-acetate (PMA)-induced superoxide (O2.-) generation of neutrophils was inhibited by hypericin, a photosensitizing pigment found in St. Johnswort (herb Hypericin triquetrifolium Turra), via a mechanism involving protein kinase C (PKC). To obtain further insights into the mechanism of inhibition, the effects of hypericin on stimulation-dependent O2.- generation and related enzymes of neutrophils were investigated. Hypericin inhibited O2.- generation of neutrophils induced by PKC-dependent and -independent stimuli in a light- and concentration-dependent manner. Oxygen was required for the light-dependent inhibition by hypericin. NADPH oxidase activity in a cell-free system and TNF-alpha-induced tyrosyl phosphorylation of neutrophil proteins were also inhibited by hypericin in a concentration- and light-dependent manner. However, tyrosine kinase of p60src, an enzyme not bound to a membrane, was not inhibited either in the light or in the dark. Oxygen uptake of neutrophils by photosensitization with hypericin resulted in the formation of singlet oxygen (1O2), O2.-, and hydroxyl radical (.OH) and enhanced lipid peroxidation. The formation of 1O2 was inhibited by azide, a quencher of 1O2, but not by desferrioxamine (DSF), a ferric ion chelator. By contrast, both generation of .OH and lipid peroxidation were inhibited by DSF but not by azide. Furthermore, PMA-induced O2.- generation inhibited by hypericin partially recovered in the presence of azide but not DSF. These results suggested that the light-dependent inhibition of O2.- generation by hypericin might be due to inhibition of tyrosine kinase, PKC, and NADPH oxidase via an oxygen-dependent mechanism, possibly through both Type I and II photosensitization mechanisms.

Effect of the antiretroviral agent hypericin on rat liver mitochondria.

The photosensitizing effect of hypericin (HY), an antiretroviral agent, on the functions of isolated rat liver mitochondria has been investigated. The respiratory control ratio (RCR), ADP/O and membrane potential of mitochondria were decreased by HY in a light-dependent manner. Uncoupled respiration of mitochondria in the presence of succinate was also inhibited by HY in a light-dependent manner. The ID50 of hypericin for these inhibitions was approximately 0.5 microM. These inhibitory effects of HY were not observed when photosensitization was conducted under anaerobic conditions and were not affected by desferrioxamine (DSF) or superoxide dismutase (SOD). Upon photosensitization of HY, mitochondria consumed oxygen in the absence of respiratory substrate with concomitant formation of thiobarbituric acid reactive substance (TBARS). The amount of oxygen consumed was 100-times greater than that of TBARS formed. The oxygen uptake was partially inhibited by NaN3, and formation of TBARS was inhibited by DSF. Upon photosensitization of HY in the presence of mitochondrial membranes, the electron spin resonance (ESR) signal of 2,2-dimethyl-5-hydroxy-1-pyrrolidinyloxyl (DMPO/.OH) was increased by a mechanism which was suppressed by DSF. An ESR signal for singlet oxygen bound to 2,5-dimethylfuran, 2,2,6,6-tetramethyl-4-piperidone (TEMP) was also detected under light in the presence of mitochondria. This signal of the TEMP-N-oxyl radical (TEMPO) was decreased by azide, which physically quenches singlet oxygen, but was increased by DSF. These results indicate that HY might inhibit mitochondrial functions by a type II photodynamic mechanism but that lipid peroxidation of biological membranes through an active oxygen-mediated photodynamic mechanism is not involved.

Inhibition of stimulus-specific neutrophil superoxide generation by alpha-tocopherol.

Alpha-tocopherol but not 2-carboxy-2,5,7,8-tetramethyl-6-chromanol (trolox or CTMC) and 2,2,5,7,8 pentamethyl-6-hydroxy chromane (PMC), derivatives of alpha-tocopherol, inhibited the superoxide (O2-.) generation of rat peritoneal neutrophils (RPMN) induced by phorbol 12-myrisate 13-acetate (PMA). ID50 for neutrophils obtained from the peritoneal cavity of rat and guinea pig was about 1microM. This concentration, however, was much lower than that for the inhibition of PMA-activated phospholipid-dependent protein kinase (PKC) (ID50 = 30 microM). The alpha-tocopherol sensitive O2-. generation was also observed in neutrophils induced by dioctanoylglycerol (diC8) and calcium ionophore A23187 but not by formylmethionyl-leucyl-phenylalanine (FMLP), opsonized zymosan (OZ) and sodium dodecyl sulfate (SDS). The pattern of inhibition by alpha-tocopherol was quite similar to that of staurosporine, a specific inhibitor of PKC. The alpha-tocopherol content of RPMN was 12 ng/10(6) cells and a linear increase to 200 ng/10(6) cells by addition of alpha-tocopherol to the cell suspension corresponded with an increased inhibition of O2-. generation. These results indicate that both the chemical structure and the content of alpha-tocopherol might be important factors in O2-. generation by neutrophils.

Photoactivated inhibition of superoxide generation and protein kinase C activity in neutrophils by blepharismin, a protozoan photodynamically active pigment.

Blepharismin is an endogenous photosensitizing pigment found in the protozoan Blepharisma. This pigment inhibited the generation of superoxide anion (O2-.) in neutrophils not only via a diacylglycerol-induced protein kinase C (PKC)-dependent reaction but also by an arachidonate-induced PKC-independent reaction. The inhibition was light and concentration dependent for both reactions. Light-activated inhibition was strong at wavelengths between 520 and 570 nm but not above 610 nm. PKC activity in neutrophils and from rat brain was inhibited by blepharismin in a light- and concentration-dependent manner. Moreover, arachidonate-activated NADPH oxidase activity in a cell-free system was also inhibited by the pigment in a light- and concentration-dependent manner. These results suggest that blepharismin inhibits NADPH oxidase activation through the non-specific inhibition of various membrane-bound enzymes and that this inhibition may also be correlated with that of PKC.