Increased fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene in the phorbol myristate acetate-stimulated plasma membrane of human neutrophils

Assessment of myeloperoxidase activity by the conversion of hydroethidine to 2-chloroethidium

Oxidants derived from myeloperoxidase (MPO) contribute to inflammatory diseases. In vivo MPO activity is commonly assessed by the accumulation of 3-chlorotyrosine (3-Cl-Tyr), although 3-Cl-Tyr is formed at low yield and is subject to metabolism. Here we show that MPO activity can be assessed using hydroethidine (HE), a probe commonly employed for the detection of superoxide. Using LC/MS/MS, (1)H NMR, and two-dimensional NOESY, we identified 2-chloroethidium (2-Cl-E(+)) as a specific product when HE was exposed to hypochlorous acid (HOCl), chloramines, MPO/H2O2/chloride, and activated human neutrophils. The rate constant for HOCl-mediated conversion of HE to 2-Cl-E(+) was estimated to be 1.5 × 10(5) M(-1)s(-1). To investigate the utility of 2-Cl-E(+) to assess MPO activity in vivo, HE was injected into wild-type and MPO-deficient (Mpo(-/-)) mice with established peritonitis or localized arterial inflammation, and tissue levels of 2-Cl-E(+) and 3-Cl-Tyr were then determined by LC/MS/MS. In wild-type mice, 2-Cl-E(+) and 3-Cl-Tyr were detected readily in the peritonitis model, whereas in the arterial inflammation model 2-Cl-E(+) was present at comparatively lower concentrations (17 versus 0.3 pmol/mg of protein), and 3-Cl-Tyr could not be detected. Similar to the situation with 3-Cl-Tyr, tissue levels of 2-Cl-E(+) were decreased substantially in Mpo(-/-) mice, indicative of the specificity of the assay. In the arterial inflammation model, 2-Cl-E(+) was absent from non-inflamed arteries and blood, suggesting that HE oxidation occurred locally in the inflamed artery. Our data suggest that the conversion of exogenous HE to 2-Cl-E(+) may be a useful selective and sensitive marker for MPO activity in addition to 3-Cl-Tyr.

Diabetes mellitus: polymorphonuclear leukocyte (PMN) filtration parameters and PMN membrane fluidity after chemotactic activation

The goal of this research was to determine leukocyte rheology at baseline and after chemotactic activation in type I and type II diabetics. In 19 normal subjects, 21 type I diabetics, and 16 type II diabetics at baseline and after in vitro chemotactic activation (prolonged for 5 and 15 minutes) with two stimulating agents (4-phorbol 12-myristate 13-acetate [PMA] and N-formyl-methionyl-leucyl-phenylalanine [fMLP]), we evaluated polymorphonuclear (PMN) filtration parameters (using a St. George filtrometer [Carri-Med, Dorking, UK] and considering the initial relative flow rate [IRFR] and the concentration of clogging particles [CP]) and PMN membrane fluidity (obtained by marking PMNs with the fluorescent probe 1-(4-[trimethylamino]phenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH). At baseline, there was a difference between normals and type I and II diabetics for PMN membrane fluidity only. After activation in normals and diabetics of both types, a significant variation was present in PMN filtration parameters (IRFR and CP) at both 5 and 15 minutes. In normals, no variation was present in PMN membrane fluidity after activation with PMA or fMLP. After PMN activation, only in type I diabetics was a significant decrease in PMN membrane fluidity present at both 5 and 15 minutes. After PMN activation with either PMA or fMLP in comparison to basal values, only the mean variation (delta%) of the IRFR was significantly different between normals, type I diabetics, and type II diabetics at both 5 and 15 minutes. From the data obtained, it is evident that after activation, the PMN filtration pattern shows a specific behavior in diabetics of both types, while PMN membrane fluidity changes only in type I diabetics. The latter finding may be the basis of a metabolic pattern present in PMNs of this type, revealed after in vitro activation.

Ubiquinol-10 protects human low density lipoprotein more efficiently against lipid peroxidation than does alpha-tocopherol

The temporal disappearance of natural antioxidants associated with human low density lipoprotein (LDL) in relation to the appearance of various classes of lipid hydroperoxides was investigated under three types of oxidizing conditions. Freshly isolated LDL from plasma of healthy subjects was free of detectable amounts of lipid hydroperoxides as measured by HPLC postcolumn chemiluminescence detection. Exposure of such LDL to a mild, constant flux of aqueous peroxyl radicals led to rapid and complete oxidation of ubiquinol-10, followed by slower partial depletion of lycopene, beta-carotene, and alpha-tocopherol. After an initial lag period of complete inhibition of detectable lipid peroxidation, formation of hydroperoxides of cholesterol esters, triglycerides, and phospholipids was observed. The onset of detectable lipid peroxidation corresponded closely with the completion of ubiquinol-10 consumption. However, small amounts of ascorbate, present as a contaminant in the LDL preparation, rather than ubiquinol-10 itself were responsible for the initial lag period. Thus, complete consumption of ubiquinol-10 was preceded by that of ascorbate, and exposure of ascorbate-free LDL to aqueous peroxyl radicals resulted in immediate formation of detectable amounts of lipid hydroperoxides. The rate of radical-mediated formation of lipid hydroperoxides in ascorbate-free LDL was low as long as ubiquinol-10 was present, but increased rapidly after its consumption, even though more than 80% and 95% of endogenous carotenoids and alpha-tocopherol, respectively, were still present. Qualitatively similar results were obtained when peroxyl radicals were generated within LDL or when the lipoprotein was exposed to oxidants produced by activated human polymorphonuclear leukocytes. LDL oxidation was reduced significantly by supplementing the lipoprotein preparation with physiological amounts of either ascorbate or ubiquinol-10. Our data show that ubiquinol-10 is much more efficient in inhibiting LDL oxidation than either lycopene, beta-carotene, or alpha-tocopherol.

Oxygen metabolites induced by phorbol myristate acetate increase lateral diffusion of wheat germ agglutinin-labeled glycoconjugates in human polymorphonuclear leukocytes

To assess the general effects of protein kinase C (PKC) activation on cell membrane receptor mobility in human neutrophilic polymorphonuclear leukocytes (PMNLs), the lateral diffusion of fluoresceinated succinylated wheat germ agglutinin (S-WGA-FITC)-labeled membrane glycoconjugates was measured using fluorescence recovery after photobleaching (FRAP). Activation of PKC was achieved by incubating the PMNLs with different concentrations (5-100 nM) of phorbol myristate acetate (PMA). The membrane effects of dimethyl sulfoxide (DMSO), another possible membrane perturbant, were also studied. We found that PMA treatment (greater than or equal to 10 nM) increased the glycoconjugate diffusion coefficient (D) 2-2.5-fold. The mobile fraction (R) remained constant, around 30%. With DMSO, no effect on the diffusion was seen. The increase in lateral mobility due to cell stimulation with PMA was totally inhibited by catalase (200 units/ml) but only partly with superoxide dismutase (2000 units/ml). Exogenous hydrogen peroxide (0.01-5 mM) had no effect on glycoconjugate mobility in unstimulated cells. We therefore propose that activation of PKC mediates augmented mobility of glycoconjugate receptors in PMNL, a reaction that seems to be critically dependent on formation of reactive oxygen metabolites. The results indicate that endogenous formation of reactive metabolites upon receptor stimulation may have a general effect on receptor mobility.

Changes of fluorescence anisotropy in plasma membrane of human polymorphonuclear leukocytes during the respiratory burst phenomenon

Steady state fluorescence anisotropy (rs) of TMA-DPH was measured to study the effect of respiratory burst activation with PMA, FMLP, and PAF on the physico-chemical structure of PMNs plasma membrane. Our results show a significant increase in rs during the respiratory burst activation. In the presence of NADPH-oxidase inhibitor DPI, only PAF induces changes in rs values. This suggests a non-specific effect of PAF on plasma membrane. Azide, which induces a supranormal release of H2O2, fails to increase the basal rs value after activation. Moreover, the catalase does not abolish the increase in rs induced upon activation. This rules out the possibility that changes of rs during the respiratory burst activation are attributed mainly to H2O2 release. We conclude that multiple processes accompanying the respiratory burst activation are responsible for the changes in the physico-chemical properties of PMNs plasma membrane.

Tumor promoter 12-0-tetradecanoyl-phorbol-13-acetate (TPA) can reduce the Ca-transporting ability of Ca-ionophores in T lymphocytes: the involvement of intracellular heavy metal ions

12-0-tetradecanoyl-phorbol-13-acetate (TPA) can significantly reduce the Ca-ionophore-induced rise in the intracellular calcium concentration (Cai) of T lymphocytes measured by quin2 or fura-2 fluorescence. This counteraction of TPA is maximal at a preincubation of 90 min at TPA concentrations higher than 20 nM. 45Ca uptake and efflux measurements directly indicate that TPA does not activate the calcium extrusion systems in thymocytes but impairs the Ca-transporting ability of Ca-ionophores. TPA causes no immobilization of the Ca-ionophores as it is demonstrated by the lack of significant changes in fluorescence and fluorescence polarisation of A23187 during TPA incubation. Similarly the energy transfer between the Tyr, Try groups of membrane proteins and A23187 shows no significant difference in control and TPA treated thymocytes. This indicates that A23187 is not in a membrane protein-bound form after TPA preincubation. The intracellular heavy metal chelator, N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) restores the ionophoretic ability of Ca-ionophores in TPA pretreated cells to the control level. Diacyl-glycerols also impair the Ca-transporting ability of Ca-ionophores. TPEN prevents this effect as well. These findings suggest that TPA and diacyl-glycerols may cause an increase in the availability of intracellular heavy metal ions. Our results may reflect a new, physiologically important mechanism of the action of diacyl-glycerols and phorbol esters.

Antioxidant properties of conjugated bilirubin and biliverdin: biologically relevant scavenging of hypochlorous acid

Conjugated bilirubin at low micromolar concentrations strongly inhibits the luminol-enhanced chemiluminescence response of stimulated human polymorphonuclear leukocytes. In contrast, it does not inhibit either reduction of ferricytochrome c or lucigenin-mediated chemiluminescence of stimulated cells. Also, conjugated bilirubin and its metabolic precursor, biliverdin, do not inhibit the enzyme myeloperoxidase (MPO) since (i) the MPO-dependent oxidation of guaiacol is not affected by biliverdin and (ii) the spectral changes observed when conjugated bilirubin is oxidized by a MPO-H2O2-Cl(-)-system are very similar to those obtained with reagent HOCl. As judged from these spectroscopic studies, each molecule of conjugated bilirubin can scavenge one molecule of HOCl giving rise to an oxidation product that itself is capable of scavenging further molecules of HOCl. Importantly, at physiological pH, both bile pigments can efficiently protect the elastase-inhibitory capacity of alpha 1-antiprotease against inactivation by reagent HOCl.

Antioxidant defenses and lipid peroxidation in human blood plasma

The temporal disappearance in human blood plasma of endogenous antioxidants in relation to the appearance of various classes of lipid hydroperoxides measured by HPLC postcolumn chemiluminescence detection has been investigated under two types of oxidizing conditions. Exposure of plasma to aqueous peroxyl radicals generated at a constant rate leads immediately to oxidation of endogenous ascorbate and sulfhydryl groups, followed by sequential depletion of bilirubin, urate, and alpha-tocopherol. Stimulating polymorphonuclear leukocytes in plasma initiates very rapid oxidation of ascorbate, followed by partial depletion of urate. Once ascorbate is consumed completely, micromolar concentrations of hydroperoxides of plasma phospholipids, triglycerides, and cholesterol esters appear simultaneously, even though sulfhydryl groups, bilirubin, urate, and alpha-tocopherol are still present at high concentrations. Nonesterified fatty acids, the only lipid class in plasma not transported in lipoproteins but bound to albumin, are preserved from peroxidative damage even after complete oxidation of ascorbate, most likely due to site-specific antioxidant protection by albumin-bound bilirubin and possibly by albumin itself. Thus, in plasma ascorbate and, in a site-specific manner, bilirubin appear to be much more effective in protecting lipids from peroxidative damage by aqueous oxidants than all the other endogenous antioxidants. Hydroperoxides of linoleic acid, phosphatidylcholine, and cholesterol added to plasma in the absence of added reducing substrates are degraded, in contrast to hydroperoxides of trilinolein and cholesterol linoleate. These findings indicate the presence of a selective peroxidase activity operative under physiological conditions. Our data suggest that in states of leukocyte activation and other types of acute or chronic oxidative stress such a simple regimen as controlled ascorbate supplementation could prove helpful in preventing formation of lipid hydroperoxides, some of which cannot be detoxified by endogenous plasma activities and thus might cause damage to critical targets.

Activation of the neutrophil respiratory burst by chemoattractants: regulation of the N-formyl peptide receptor in the plasma membrane

The N-formyl peptide receptor mediates a number of host defensive responses of human neutrophils that result in chemotaxis, secretion of hydrolytic enzymes, and superoxide generation. Inappropriate activation or defective regulation of these responses can result in pathogenic states responsible for inflammatory disease. The receptor is a 50 to 70-kD, integral plasma membrane glycoprotein with intracellular and surface localization. Its abundance in the membrane is regulated by membrane flow and recycling processes. Cytoskeletal interactions are believed to control its organization in the plane of the membrane and interaction with other proteins. The receptor's most important interaction is with guanyl nucleotide binding proteins that serve as signal transduction partners ultimately leading to activation of effector responses. Because the interaction of the receptor with G proteins is necessary for transduction, control of this interaction may be at the root of understanding the molecular control of responses in these cells. This review briefly summarizes some of the molecular properties, dynamics, and interactions of this receptor system in human neutrophils and discusses how these characteristics may pertain to the activation and control of superoxide generation.

Increased membrane heterogeneity in stimulated human granulocytes

TMA-DPH fluorescence decay in human PMN before and after stimulation with FMLP was studied using frequency domain fluorometry. Membrane heterogeneity was assessed by the width of the continuous distributions of lifetime values of Lorentzian shape used to describe the fluorescence decay. In non-stimulated granulocytes TMA-DPH fluorescence decay is characterized by two distributions of lifetime values centered at 6.5 and 1.0 ns and full width at half maximum of 0.3 and 1.2 ns, respectively. Within 15 min after stimulation, the center values of the two distribution components were 5.1 and 0.8 ns and the distribution width was 0.8 and 0.6 ns, respectively. These results indicate changes of membrane domain organization which can be ascribed to compositional changes and redistribution of membrane components.

Interleukin-3-specific modification of cell membrane "fluidity" of haemopoietic cells

The work reported here clearly demonstrates that a specific growth factor, interleukin-3 (IL-3), which acts on multipotent haemopoietic stem cells as well as on committed myeloid progenitor cells of different lineages (Schrader, 1988; Whetton and Dexter, 1986), specifically induces a modification of the physical state ("fluidity") of the cell membranes of two IL-3-responsive and apparently normal haemopoietic cell lines. Furthermore, in a derived IL-3 independent myeloid leukaemic cell line, no such physical response to IL-3 binding was observed. The rapidity of the "normal" response suggests further that it may be associated with, or even constitute per se a critical early effect elicited by IL-3 in sensitive cells, the necessity for which is abrogated in the malignant derivative.

Changes of membrane fluidity in chemotactic peptide-stimulated polymorphonuclear leukocytes

Although the phenomenon of stimulus-response coupling in polymorphonuclear leukocytes involves a series of membrane events the influence of stimulation on membrane fluidity is to clarify. In our experiments we have used 1-(4-trimethylaminophenyl) 6-phenyl-1,3,5-hexatriene and 1,6-diphenyl-1,3,5-hexatriene fluorescence polarization technique to evaluate membrane fluidity in living polymorphonuclear leukocytes after stimulation with N-formyl-methyonil-leucyl-phenylalanine peptide which has a well defined membrane receptor on the plasma membrane. We report that polymorphonuclear leukocytes stimulation increases 1-(4-trimethylaminophenyl)-6-phenyl-1,3,5-hexatriene polarization, only when colcemid, a microtubule disrupting drug, is added to polymorphonuclear leukocytes. This can be viewed as an indirect evidence that microtubules are involved in the control of polymorphonuclear leukocytes membrane fluidity. On the contrary no changes have been observed with 1,6-diphenyl-1,3,5-hexatriene. This study indicates the potential use of 1-(4-trimethylaminophenyl)-6-phenyl-1,3,5-hexatriene to evaluate the involvement of plasma membrane physical state during intact cell activity.

Phorbol myristate acetate (PMA) suppresses polarization and locomotion and alters F-actin content of Walker carcinosarcoma cells

This study demonstrates a novel feature of PMA, its ability to suppress chemokinetic polarization and locomotion of tumor cells. Walker carcinosarcoma cells exhibit two distinct types of polarization and locomotion, i.e. spontaneous polarization characterized by ruffles at the front and stimulated polarization and locomotion in response to the microtubule-disassembling agents colchicine, vinblastine and nocodazole, which are characterized by blebbing at the front. The tumor promotor phorbol myristate acetate (PMA), but not phorbol, was found to suppress both types of polarization and random locomotion at concentrations between 10(-8) and 10(-6)M. The effect of 10(-6)M PMA was virtually complete within 5 min. Inhibition of locomotion was due to both a reduction in the speed of migrating cells and the proportion of migrating cells. Changes in shape and chemokinesis of Walker carcinosarcoma cells were associated with alterations in the relative amount and the topographical distribution of F-actin as determined by NBD-phallacidin binding. Suppression by PMA was associated with loss of the polar topographical distribution of F-actin visualized by NBD-phallacidin binding. In the presence of PMA, the relative amount of F-actin was higher than in unstimulated controls and lower in cells exposed to microtubule-disassembling agents.

Selenium and drug metabolism--III. Relation of glutathione-peroxidase and other hepatic enzyme modulations to dietary supplements

Male mice were fed a torula yeast-based diet containing different amounts of added selenium for a period of 4 months. Liver glutathione peroxidase activity assayed with H2O2 showed a logarithmic dependence on dietary selenium with a saturation plateau above 2 ppm Se and an extrapolated zero of 0.02 ppm Se. In contrast, liver selenium content and GSH-Peroxidase activity showed a linear correlation. Glutathione peroxidase activity became undetectable at a liver Se content of about 90 ng Se/g liver wet wt. Thus, about 10% of liver selenium is not related to GSH-Px activity. Five dietary groups were supplemented, respectively, with 0, 0.05, 0.5, 5.0 and 10 ppm Se in the form of Na2SeO3. Some changes in drug metabolism enzymes were observed with the high Se diets. An increase occurred in Non-Se-GSH activity as well as in ethacrynic acid-assayed GSH transferase, these are interpreted as early signs of Se toxicity. The diet containing 0.01 ppm Se with no supplementary Se produced the multiple hepatic enzyme modulations which were previously reported. The animals raised on this very low Se diet had normal hepatic contents of glutathione, alpha-tocopherol, calcium, magnesium, iron, zinc, copper and manganese compared to controls supplemented with 0.5 ppm Se. However, significant changes in the microsomal fatty acid pattern were observed while the total phospholipid content as well as membrane fluidity showed no differences between the two dietary groups.

Phorbol myristate acetate stimulates ATP-dependent calcium transport by the plasma membrane of neutrophils

We studied the effect of phorbol myristate acetate (PMA) on the plasma membrane ATP-dependent calcium pump in neutrophils. Plasma membrane-enriched fractions ("podosomes") from PMA-stimulated guinea pig neutrophils exhibited a twofold stimulation of ATP-dependent calcium transport when compared with control podosomes. The stimulatory effect was rapid (beginning less than 2 min after exposure to PMA) and reached maximal values within 5 min. PMA increased the maximum velocity but not the affinity of the calcium pump for Ca++. Pump activation was not preceded by a rise in cytosolic free calcium concentration [Ca++]i, as assessed by the intracellularly trapped fluorescent calcium indicator Quin 2, but instead slightly lowered [Ca++]i and prevented the rise in [Ca++]i normally induced by the chemotactic peptide formyl-methionyl-leucyl-phenylalanine. These results suggest that the calcium pump in the plasma membrane of neutrophils may be stimulated by calcium-independent pathways, and that this activation could be one of the earliest events mediating some of the effects of phorbol esters.

Alpha-adrenergically mediated changes in membrane lipid fluidity and Ca2/ binding in isolated rat liver plasma membranes

Noradrenaline (0.1-5 microM, in the presence of 5 microM propranolol to block beta-receptors), ATP (100 microM) and angiotensin II (0.1 microM), which are thought to increase cytosolic Ca2+ concentration by mobilizing Ca2+ from internal stores, increased the lipid fluidity as measured by diphenylhexatriene fluorescence polarization in plasma membranes isolated from rat liver. The effect of noradrenaline was dose-dependent and blocked by the alpha-antagonists phenoxybenzamine (50 microM) and phentolamine (1 microM). The response to a maximal dose of noradrenaline (5 microM) and that to ATP (100 microM) were not cumulative, suggesting that both agents use a common mechanism to alter the membrane lipid fluidity. In contrast, the addition of noradrenaline (5 microM) along with the foreign amphiphile Na+-oleate (1-30 microM) resulted in an increase in membrane lipid fluidity which was equivalent to the sum of individual responses to the two agents. In the absence of Mg2+, reducing free Ca2+ concentration by adding EGTA increased membrane lipid fluidity and abolished the effect of noradrenaline, suggesting that Ca2+ is involved in the mechanism by which the hormone exerts its effect on plasma membranes. Noradrenaline (5 microM) and angiotensin II (0.1 microM) also promoted a small release of 45Ca2+ (16 pmol/mg membrane proteins) from prelabelled plasma membranes. The effect of noradrenaline was suppressed by the alpha-antagonist phentolamine (5 microM). It is proposed that noradrenaline, via alpha-adrenergic receptors and other Ca2+ -mobilizing hormones, increases membrane lipid fluidity by displacing a small pool of Ca2+ bound to phospholipids, removing thus the mechanical constraints brought about by this ion.