Impairment of human polymorphonuclear leukocyte chemotaxis by 2,5-hexanedione

Monocyte-macrophage system and polymorphonuclear leukocytes in workers exposed to low levels of metallic mercury

Our previous research (Soleo L, Vacca A, Vimercati L et al. Occup Environ Med 1997;54:437-442) showed a reduction in tumor necrosis factor-alpha (TNF-alpha) serum levels in workers with prolonged exposure to low doses of inorganic mercury, suggesting an in vivo functional defect of the monocyte-macrophage system. On this basis, here we wondered whether workers exposed to lower doses of metallic mercury displayed possible changes in the monocyte-macrophage system. In this particular cohort of workers, we also sought for the effects of the exposure on the polymorphonuclear leukocytes (PMNL) chemotaxis. The monocyte-macrophage system and the natural killer (NK) cells were examined in 19 exposed workers and in 25 unexposed workers, as the control group (controls). Specifically, the circulating monocyte-macrophage cells and their CD13, CD15 and CD33 subsets, serum cytokines (IL-8, GM-CSF and TNF-alpha) and the NK cells were analyzed. In seven exposed and seven controls randomly chosen workers the PMNL chemotaxis was also assessed. The selected indicator of mercury exposure were the levels of mercury in the urine (U-Hg), that was significantly higher in exposed workers than the controls (9.7 +/- 5.5 microg/l and 2.4 +/- 1.2 microg/l, respectively). None of the exposed workers had shown signs of either acute or chronic inorganic mercury toxicity or any form of hypersensitivity. Several immunological variables tested, monocyte-macrophage cells and their subsets, NK cells and serum cytokines overlapped between the exposed and the control workers. When the workers were considered as a whole (exposed plus controls), no correlation was found between current U-Hg and all immunological parameters. However, when exposed workers were studied separately, an inverse correlation was disclosed between cumulative U-Hg and cells (as percentage) expressing the CD13 (r = -0.599; P = 0.007) and CD15 (r = -0.614; P = 0.005) molecules, and NK cells (r = -0.455; P = 0.05). Moreover, a significant impairment in the PMNL chemotaxis (t = 3.70; P = 0.003) was observed in the exposed workers. The results of our study suggest that the exposure to very low levels of metallic mercury led to subtle impairment of circulating monocyte and NK cells (as percentages) according to the increase in U-Hg levels, as well as of the PMNL chemotactic function in this particular group of workers, even though they remain clinically asymptomatic. Therefore, we suggest that impairment of these parameters provide a sensitive indicator of metallic mercury and other chemical contaminants present in the environment.

Plasma membrane polarity of polymorphonuclear leucocytes from children with primary ciliary dyskinesia

BACKGROUND

Polymorphonuclear leucocytes (PMN) from subjects with primary ciliary dyskinesia (PCD) can have abnormal locomotory systems. The locomotory activity of PMN is the result of biochemical events mediated by the plasma membrane. In this study we investigated plasma membrane polarity of PMN from children with PCD.

DESIGN

Membrane polarity was studied in 11 children with PCD and in healthy controls by measuring the steady-state fluorescence excitation and emission spectra of 2-dimethylamino[6-lauroyl]naphthalene (Laurdan), which is known to be incorporated at the hydrophobic-hydrophilic interface of the bilayer, displaying spectral sensitivity to the polarity of its surroundings. Laurdan shows a marked steady-state emission red shift in polar solvents, with respect to nonpolar solvents. Moreover, the effect of the microtubule disassembling agent colchicine on PMN membrane polarity was evaluated.

RESULT

Our results show a red shift of the fluorescence excitation and emission spectra of Laurdan in PMN from the PCD group with respect to the control group. These data indicate an increase in membrane polarity of PMN from the PCD group. Treatment of PMN with colchicine induced a red shift in the Laurdan excitation and emission spectra with the same trend observed in PMN from the PCD group.

CONCLUSION

PMN from children with PCD are characterized by an increased plasma membrane polarity. These changes could be the basis of the modifications in the locomotory activities of PMN. The observed alterations may be attributed to abnormalities in the cytoskeleton.

Chemotactic activity of human polymorphonuclear leukocytes and industrial xenobiotics: a brief review

This review deals with some of our contributions to the use of chemotaxis, as a tool in evaluating effects of industrial xenobiotics on PMN, either in vitro or ex vivo. In vitro experiments have shown that lead, arsenic, styrene and 2,5-hexanedione, a major neurotoxicant metabolite of n-hexane, reduce chemotaxis. The most important results of ex vivo experiments have confirmed those obtained in vitro with styrene and 2,5-hexanedione: a significant reduction of chemotaxis was indeed observed in PMN harvested from workers exposed to low levels of n-hexane or styrene who did not show any sign of biochemical or clinical alteration. After 3 weeks under non-exposed conditions, the chemotactic indexes were markedly increased in most of the workers which were exposed to styrene and in all the workers exposed to n-hexane, all of whom have shown a reduced chemotaxis at the first blood sampling. Moreover chemotaxis was found to be significantly reduced at relative low levels of lead: results of the in vitro and ex vivo experiments show a comparable ranking of midpoint inhibition concentrations. We are only at the dawn of the understanding of the relation between occupational xenobiotics and PMN chemotaxis. This research area is still promising for the future, since PMN chemotaxis seems to be adequate and it must therefore enter in well-defined study protocols for investigating the potential immunotoxicity of occupational chemicals to which humans are exposed at low levels.

The Use of the Vitality and Chemotaxis of Human Polymorphonuclear Leukocytes for the In Vitro Estimation of the Acute Toxicity of the First Ten Chemicals from the MEIC List

The acute cytotoxicity of the first ten MEIC chemicals has been estimated by others in various cell lines. In the present investigation, isolated human polymorphonuclear leukocytes (PMN) from ten healthy non-smoking laboratory personnel were used to assess in vitro toxicity of the same chemicals.

The cells were treated with different concentrations of the respective chemicals for three hours and their vitality and chemotaxis were tested. Vitality was measured by fluorescence microscopy after the addition of fluorescein diacetate and ethidium bromide. Living cells which took up and hydrolysed fluorescein diacetate, and dead cells, stained by ethidium bromide, were counted and the percentage of live cells was calculated.

Locomotion stimulated by the chemotactic peptide formyl-methionyl-leucyl-phenylalanine (F-MLP), was measured in blind-well Boyden chambers and a chemotactic index was calculated.

The results were mathematically transformed to produce a linear curve, and then fitted by the linear least squares procedure, from which LC50 and IC50 values were obtained by interpolation. All the chemicals decreased the vitality and inhibited the chemotaxis of the PMN. Obviously the chemotactic test was more sensitive than the vitality one. A correlation (r = 0.933) was found between vitality and chemotaxis inhibition. Spearman rank correlation analysis revealed significant correlations between our results and those from in vitro experiments conducted in other laboratories, as well as with data concerning mouse, rat and human lethal doses.

Effects of lead on polymorphonuclear leukocyte (PMN) functions in occupationally exposed workers

Previous in vitro experiments have shown that lead can inhibit PMN chemotaxis, phagocytosis and superoxide formation. Moreover, we have observed an inhibition of PMN chemotaxis in workers occupationally exposed to lead with a mean blood lead concentration of 3.06 mumol/l. The present study was carried out to evaluate locomotion and luminol assisted chemiluminescence (CL) of polymorphonuclear leukocytes (PMN) harvested from ten lead occupationally exposed workers with blood lead concentrations of 1.59 mumol/l (SD 0.27 mumol/l). Since lipids affect PMN activity and lipid composition is modified in erythrocytes of lead workers, PMN lipids were also studied. Ten healthy male subjects of the same age were taken as controls. Chemotaxis, i.e. locomotion stimulated through a specific membrane receptor, was impaired in the PMN of lead workers, but random migration, i.e. unstimulated cell locomotion, and respiratory burst were both unmodified. Cholesterol and phospholipids were not changed, but the percentage of arachidonic acid was significantly increased. The release of LTB4, generated by the oxidative metabolism of arachidonic acid, was increased. CL, which detects reactive oxygen species (ROS), was unmodified, but this lack of change could be the result of an increase in ROS, due to the augmentated percentage of arachidonic acid, and of a decrease in ROS, due to a direct inhibitory effect of lead on ROS generation. On the basis of the results from these ex vivo experiments, the conclusion that chemotaxis is the PMN function primarily affected by lead was confirmed. PMN are considered to be one of the first cellular targets for the action of lead; low exposure to lead modifies their activity and mainly modifies chemotaxis and LTB4 production.

Prevention of chemically induced changes in synaptosomal membrane order by ganglioside GM1 and alpha-tocopherol

Synaptosomal membrane order has been studied by analysis of light depolarization by fluorescent dyes intercalated within membranes following exposure to various environmental toxicants. Two probes were explored: 1,6-diphenyl-1,3,5-hexatriene (DPH), signaling predominantly from the lipid-rich membrane core, and 1-[4-(trimethylamino)phenyl]-6-phenyl-1,3,5-hexatriene (TMA-DPH), reporting from the more hydrophilic membrane surface. Chlordecone, a neurotoxic insecticide, decreased the anisotropy of either dye and this change could be prevented by prior treatment of synaptosomes with ganglioside GM1 but not alpha-tocopherol. Exposure to an iron-ascorbic acid oxidizing mixture enhanced synaptosomal membrane order and this effect was blocked by preincubation with alpha-tocopherol but not ganglioside GM1. While these interactions may have partially reflected additive anisotropy changes, the protective agents were also effective at concentrations where they did not in themselves modulate membrane order. Methyl mercuric chloride at concentrations up to 100 microM had no discernable effect upon membrane order. It is suggested that these changes in membrane order may underlie some of the previously reported variations in the content of ionic calcium and in the leakiness of synaptosomes.

Changes in membrane properties of erythrocytes and polymorphonuclear cells in psoriasis

Using fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene and its cationic derivative, 1-(4-trimethylaminophenyl)-6-phenyl-1,3,5-hexatriene, we evaluated membrane fluidity in living polymorphonuclear leukocytes and in erythrocytes of psoriatic patients. Our results have shown that erythrocyte membranes of psoriatic patients exhibit a decrease of fluidity. These changes were not associated with any relevant modifications of the cholesterol to phospholipid molar ratio. Moreover, we observed a decrease in polymorphonuclear leukocytes membrane fluidity associated with changes in chemotactic migration. Our results indicate changes of membrane fluidity involving membranes different from the epidermal cells and suggest the hypothesis of a defective membrane-cytoskeleton interaction in psoriasis.

Increased neutrophil leukocyte chemotaxis induced by release of a serum factor in toluene-diisocyanate (TDI) asthma

The activation of blood neutrophil leukocytes has been proven in subjects with IgE-mediated and non-IgE-mediated asthma. This event appears to be modulated by the release of humoral factors. We submitted 12 toluene-diisocyanate (TDI) asthmatic workers to TDI provocation. During the late asthmatic reaction there was release of a serum chemoattracting factor for normal neutrophil leukocytes and activation of asthmatic neutrophil leukocytes. This appears to be the first demonstration of neutrophil chemotactic activity liberated during the late TDI reaction in humans. The results are explained by an acute inflammatory process occurring during the late asthmatic reaction induced by TDI.

Human Granulocyte LTB4 Production and Respiratory Burst Impaired by Styrene

Human granulocytes (PMN) incubated in vitro with styrene at a concentration of 3.3 x 10-4 M have shown an impairment of leucotriene B4 (LTB4) production and of respiratory burst after stimulation with N-formyl-methyonil-leucyl-phenylalanine peptide (nFMLP), which has a specific membrane receptor. The level of impairment in LTB4 production was lower in cells pretreated for 15 minutes with styrene than in cells treated with styrene and nFMLP simultaneously. Styrene did not cause irreversible damage, because 15 minutes after styrene treatment PMN partially recovered their function. The determination of styrene and styrene oxide, the presumed active metabolite, in the supernatant of cell culture, showed that styrene rapidly enters the cell and only 15 minutes or more after styrene addition was styrene oxide found. On this basis, the action of styrene does not seem to be mediated by metabolites.

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.

Activation of the alternative complement pathway and generation of stimulating factors for granulocytes by glass fibers

Continuous-filament glass fibers coated with organic agents, candidate asbestos substitutes, were assessed for their ability to elicit from normal human serum complement-derived cleavage products which are able to stimulate the chemotaxis and the respiratory burst of polymorphonuclear leukocytes. Glass fibers generated chemoattracting and respiratory stimulating factors for polymorphonuclears from human serum. The effect was dose related for chemotaxis from the serum fiber concentration of 75 micrograms/ml to 1,250 micrograms/ml. The serum chemoattracting activity, as well the respiratory stimulation, were dramatically impaired when serum had been preliminarily absorbed with antiC5 antiserum. Since the impairment of chemotactic activity occurred also in the presence of EDTA, but not in the presence of EGTA, we assumed an activation of the alternative complement pathway. Glass fibers were studied in comparison to a UICC sample of Canadian chrysotile asbestos, which is able to activate in vitro the alternative complement pathway. Glass fibers exhibited less ability than asbestos fibers to generate complement cleavage products with chemotactic activity for polymorphonuclears; however, they produced an activity about equal to 80% of a chemotactic standard stimulus such as zymosan-activated plasma.

In vitro impairment of human granulocyte functions by lead

Chemotaxis and receptor independent phagocytosis of human polymorphonuclear leukocytes (PMNs) exposed to lead in vitro (concentrations between 1.2 microM and 115 microM) were studied. Chemotaxis was measured in Boyden chambers and phagocytosis was investigated using latex beads. Additional methods were also applied. Superoxide anion formation from PMNs activated with preopsonized zymosan was quantified as superoxide dismutase-inhibitable reduction of ferricytochrome c. Steady state fluorescence polarization was performed using trimethylammonium diphenylexatriene (TMA-DPH). Lead concentrations were highly correlated both with decreased chemotactic activity (r = 0.70 p less than 0.01) and with decreased phagocytosis (r = 0.68 p less than 0.01). Ferricytochrome c reduction was not significantly affected. An increase in fluorescence polarization was recorded at the highest concentration of lead used, i.e. 57.6 microM and 115 microM, both in unstimulated PMNs and in PMNs activated with N-formyl-methionyl-leucyl-phenylalanine chemotactic peptide (n-FMLP). Moreover, an increase in the fluorescence polarization was observed in PMNs pretreated with a microtubule disrupting drug, exposed to lead concentrations of 14.4 microM and 57.6 microM and then activated with n-FMLP; no increase was recorded at the lowest lead concentrations used, i.e. 1.2 microM and 3.6 microM. The possible interaction of lead with the membrane-cytoskeleton apparatus is discussed.

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.