Bernard Veyret

Aryl hydrocarbon receptor control of a disease tolerance defence pathway

Disease tolerance is the ability of the host to reduce the effect of infection on host fitness. Analysis of disease tolerance pathways could provide new approaches for treating infections and other inflammatory diseases. Typically, an initial exposure to bacterial lipopolysaccharide (LPS) induces a state of refractoriness to further LPS challenge (endotoxin tolerance). We found that a first exposure of mice to LPS activated the ligand-operated transcription factor aryl hydrocarbon receptor (AhR) and the hepatic enzyme tryptophan 2,3-dioxygenase, which provided an activating ligand to the former, to downregulate early inflammatory gene expression. However, on LPS rechallenge, AhR engaged in long-term regulation of systemic inflammation only in the presence of indoleamine 2,3-dioxygenase 1 (IDO1). AhR-complex-associated Src kinase activity promoted IDO1 phosphorylation and signalling ability. The resulting endotoxin-tolerant state was found to protect mice against immunopathology in Gram-negative and Gram-positive infections, pointing to a role for AhR in contributing to host fitness.

l-Arginine Availability Modulates Local Nitric Oxide Production and Parasite Killing in Experimental Trypanosomiasis

ABSTRACT Nitric oxide (NO) is an important effector molecule of the immune system in eliminating numerous pathogens. Peritoneal macrophages fromTrypanosoma brucei brucei-infected mice express type II NO synthase (NOS-II), produce NO, and kill parasites in the presence ofl-arginine in vitro. Nevertheless, parasites proliferate in the vicinity of these macrophages in vivo. The present study shows thatl-arginine availability modulates NO production. Trypanosomes use l-arginine for polyamine synthesis, required for DNA and trypanothione synthesis. Moreover, arginase activity is up-regulated in macrophages from infected mice from the first days of infection. Arginase competes with NOS-II for their common substrate, l-arginine. In vitro, arginase inhibitors decreased urea production, increased macrophage nitrite production, and restored trypanosome killing. In vivo, a dramatic decrease inl-arginine concentration was observed in plasma from infected mice. In situ restoration of NO production and trypanosome killing were observed when excess l-arginine, but notd-arginine or l-arginine plusNω-nitro-l-arginine (a NOS inhibitor), was injected into the peritoneum of infected mice. These data indicate the role of l-arginine depletion, induced by arginase and parasites, in modulating the l-arginine–NO pathway under pathophysiological conditions.

Nitric oxide-mediated cytostatic activity on Trypanosoma brucei gambiense and Trypanosoma brucei brucei

Macrophages collected from BCG-infected mice or exposed in vitro to interferon-gamma plus lipopolysaccharide developed a cytostatic activity on Trypanosoma brucei gambiense and Trypanosoma brucei brucei. This trypanostatic activity of activated macrophages was inhibited by addition of N-monomethyl-L-arginine, an inhibitor of the L-arginine-nitric oxide (NO) metabolic pathway, indicating a role for NO as the effector molecule. Contrary to trypanosomes treated with N2gas, trypanosomes treated with NO gas did not proliferate in vitro on normal macrophages. Compared to mice infected with control parasites, mice infected with NO-treated parasites had decreased parasitemias in the first days postinfection and had a prolonged survival. Addition of excess iron reversed the trypanostatic effect of both activated macrophages and NO gas. These data show that activated macrophages exert an antimicrobial effect on T.b. gambiense and T.b. brucei through the L-arginine-NO metabolic pathway. In trypanosomes, NO could trigger iron loss from critical targets involved in parasite division. The participation of this effector mechanism among the other immune elements involved in the control of African trypanosomes (antibodies, complement, phagocytic events) remains to be defined.

Stimulation of Ca2+ influx in rat pituitary cells under exposure to a 50 Hz magnetic field

The effect of exposure of single rat pituitary cells to 50 Hz sine wave magnetic fields of various strengths on the intracellular free Ca2+ concentration ([Ca2+]i), was studied by using dual-emission microfluorimetry, using indo-1 as probe. A 30 min exposure of the cells to vertical 50 microT peak magnetic field triggered a long-lasting increase in [Ca2+]i from a basal value of about 185 +/- 4 nM to 326 +/- 41 nM (S.E.; n = 150). The vertical and horizontal components of the static magnetic field were 57 and 15 microT, respectively. The 50 Hz ambient magnetic field was always below 0.1 microT rms. The effect was observed both at 25 +/- 2 degrees C and at 37 +/- 2 degrees C. Responsive cells, for which [Ca2+]i rose to values above 309 nM, were identified as lactotrophs and represented 29% of the total pituitaries. [Ca2+]i increase, for the most part, was due to Ca2+ influx through voltage-dependent dihydropiridine-sensitive calcium channels inhibited by PN 200-110. However, neither Ca2+ channel blockers nor removal of Ca2+ from the external medium during exposure completely prevented the field-induced [Ca2+]i increase. Additional experiments using an MTT colorimetric assay showed that alteration of Ca2+ homeostasis of lactotrophs was associated with impairment of some mitochondrial processes.

In vitro and in vivo genotoxicity of radiofrequency fields

There has been growing concern about the possibility of adverse health effects resulting from exposure to radiofrequency radiations (RFR), such as those emitted by wireless communication devices. Since the introduction of mobile phones many studies have been conducted regarding alleged health effects but there is still some uncertainty and no definitive conclusions have been reached so far. Although thermal effects are well understood they are not of great concern as they are unlikely to result from the typical low-level RFR exposures. Concern rests essentially with the possibility that RFR-exposure may induce non-thermal and/or long-term health effects such as an increased cancer risk. Consequently, possible genetic effects have often been studied but with mixed results. In this paper we review the data on alleged RFR-induced genetic effects from in vitro and in vivo investigations as well as from human cytogenetic biomonitoring surveys. Attention is also paid to combined exposures of RFR with chemical or physical agents. Again, however, no entirely consistent picture emerges. Many of the positive studies may well be due to thermal exposures, but a few studies suggest that biological effects can be seen at low levels of exposure. Overall, however, the evidence for low-level genotoxic effects is very weak.

Kinetics of the reaction of HO2 with CH3C(O)O2 in the temperature range 253–368 K

The kinetics of the reaction between the HO2 and CH3C(O)O2 radicals has been studied in the gas phase at atmospheric pressure between 253 and 368 K. Flash photolysis was used to produce the radicals which were detected by their absorption in the UV. The two reactive channels for this reaction are CH3C(O)O2+HO2→CH3C(O)OOH+O2 (1a) and→CH3C(O)OH+O3 (1b). The overall rate constant measurement gave a value of k1 = (4.3±1.2)×10−13 exp[(1040±100)/T] cm3 molecule−1 s−1; the branching ratio k1b/(k1a+k1b) was found to be independent of temperature and equal to 0.33±0.07.

Effects of radiofrequency electromagnetic fields on the human nervous system

The effects of exposure to radiofrequency electromagnetic fields (EMF), specifically related to the use of mobile telephones, on the nervous system in humans have been the subject of a large number of experimental studies in recent years. There is some evidence of an effect of exposure to a Global System for Mobile Telecommunication (GSM)-type signal on the spontaneous electroencephalogram (EEG). This is not corroborated, however, by the results from studies on evoked potentials. Although there is some evidence emerging that there may be an effect of exposure to a GSM-type signal on sleep EEG, results are still variable. In summary, exposure to a GSM-type signal may result in minor effects on brain activity, but such changes have never been found to relate to any adverse health effects. No consistent significant effects on cognitive performance in adults have been observed. If anything, any effect is small and exposure seems to improve performance. Effects in children did not differ from those in healthy adults. Studies on auditory and vestibular function are more unequivocal: neither hearing nor the sense of balance is influenced by short-term exposure to mobile phone signals. Subjective symptoms over a wide range, including headaches and migraine, fatigue, and skin itches, have been attributed to various radiofrequency sources both at home and at work. However, in provocation studies a causal relation between EMF exposure and symptoms has never been demonstrated. There are clear indications, however, that psychological factors such as the conscious expectation of effect may play an important role in this condition.

Interaction of Cationic Colloids at the Surface of J774 Cells: A Kinetic Analysis

We have characterized the binding of multilamellar colloids to J774 cells. Cationic colloids were shown to bind much more efficiently than neutral ones. Particle uptake by cells was followed by flow cytometry and fluorescence microscopy. Analysis of the kinetics of uptake of cationic particles indicated that binding on the cell surface occurred with two characteristic times. Analysis of the dissociation properties allowed discriminating between several alternative models for adsorption and led us to propose a mechanism that involved two independent classes of binding sites on the cell surface. One class of sites appeared to be governed by a classic mass action law describing a binding equilibrium. The other sites were populated irreversibly by particles made of 10% cationic lipids. This was observed in the absence of endocytosis, under conditions where both the equilibrium and the irreversible binding occurred at the cell surface. We determined the rate constants for the different steps. We found that the reversible association occurred with a characteristic time of the order of tens of seconds, whereas the irreversible binding took a hundred times longer. The presence of serum proteins in the incubation medium did not drastically affect the final uptake of the particles. In contrast, the capture of the particles by cells significantly dropped when the fraction of positively charged lipids contained in the colloids was decreased from 10% to 5%. Finally, the results will be discussed within a comprehensive model where cationic particles find labile binding sites in the volume of the pericellular network (glycocalyx and extracellular matrix) and less-accessible irreversible binding sites at the cell membrane itself.

Flash photolysis kinetic study of reactions of the BrO radical with BrO and HO2

Abstract The reaction between BrO and HO 2 radicals: BrO + HO 2 → HOBr + O 2 (1a) → HBr + O 3 (1b) was investigated using flash photolysis with UV absorption detection of the radicals, at 298 K and 760 Torr total pressure. BrO and HO 2 radicals were formed in the flash photolysis of Br 2 /O 3 /Cl 2 /CH 3 OH/O 2 /He mixtures. The self-reaction of BrO radicals was also studied: BrO + BrO → 2Br + O 2 (2a) → Br 2 + O 2 (2b). Kinetic simulations of decays of BrO radicals yielded k 1 = (3.4 ± 1.0) X 10 −11 cm 3 molecule −1 s −1 and k 2 = (3.1 ± 0.4) X 10 −12 cm 3 molecule −1 s −1 .

The rate constant for the HO2+HO2 reaction at elevated temperatures

Abstract The HO 2 +HO 2 reaction has been studied at atmospheric pressure between 298 and 777 K, using a new high-temperature flash photolysis/UV kinetic spectroscopy apparatus. An upward curvature of the Arrhenius plot is observed at temperatures above 600 K, supporting a recent suggestion that - in addition to the well-established low-temperature association complex mechanism - a direct abstraction reaction with a positive activation energy operates at combustion temperatures. Arrhenius parameters for this direct reaction are estimated.