Effects of co-exposure to CS2 and noise on hearing and balance in rats: continuous versus intermittent CS2 exposures

Background: carbon disulfide (CS2) exacerbates the effect of noise on hearing, and disrupts the vestibular system. The goal of this study was to determine whether these effects are also observed with intermittent CS2 exposure. Methods: rats were exposed for 4 weeks (5 days/week, 6 h/day) to a band noise at 106 dB SPL either alone or combined with continuous (63 ppm or 250 ppm) or intermittent (15 min/h or 2 × 15 min/h at 250 ppm) CS2. Hearing function was assessed by measuring distortion product otoacoustic emissions (DPOAEs); balance was monitored based on the vestibulo-ocular reflex (VOR). Functional measurements were performed before, at the end of exposure and 4 weeks later. Histological analyses of the inner ear were also performed following exposure and after the 4-week recovery period. Results: the results obtained here confirmed that CS2 exposure exerts two differential temporary effects on hearing: (1) it attenuates the noise-induced DPOAE decrease below 6 kHz probably through action on the middle ear reflex when exposure lasts 15 min per hour, and (2) continuous exposure to 250 ppm for 6 h extends the frequency range affected by noise up to 9.6 kHz (instead of 6 kHz with noise alone). With regard to balance, the VOR was reversibly disrupted at the two highest doses of CS2 (2 × 15 min/h and continuous 250 ppm). No morphological alterations to the inner ear were observed. Conclusion: these results reveal that short periods of CS2 exposure can alter the sensitivity of the cochlea to noise at a dose equivalent to only 10 times the short-term occupational limit value, and intermittent exposure to CS2 (2 × 15 min/h) can alter the function of the vestibular system

Histological analysis of vestibular explants to assess toxicity of chemicals

peer reviewedMany epidemiologic and experimental studies have shown that occupational exposures to aromatic solvents can induce hearing deficits in both humans and laboratory rodents. Although the end-organ of balance, the vestibular labyrinth, is in the inner ear, and has morphological and functional similarities with the cochlea, no information is available on the adverse effects of solvents on this receptor. However, epidemiological data suggest that solvent exposure can generate balance disorders, which might increase the risk of falls. In this paper, we describe the methods for assessing peripheral vestibulotoxicity using cultured vestibular samples (utricles and ampullae) collected from newborn rats. After a few days in culture, these sensory tissues become spheres filled with endolymph, which we call “cysts”. Endolymphatic potassium concentration measurements and histopathological observations were performed to understand the toxic mechanisms and identify the cellular targets of a chemical exposure, an aromatic solvent in this case. The model was tested using molecules with known effects: ouabain, a blocker of Na+/K+ ATPase pumps, gentamicin, a cytotoxic antibiotic for vestibular hair cells, and finally styrene, an aromatic solvent used in industry with well-known cochleotoxic properties

Minéralisation de nanoparticules de TiO2 pour la détermination du titane dans les tissus de rat

International audienceIn order to draw appropriate conclusions about the possible adverse biological effects of titanium dioxide nanoparticles (TiO 2-NPs), the so-called "dose-effect" relationship must be explored. This requires proper quantification of titanium in complex matrices such as animal organs for future toxicological studies. This study presents the method development for mineralizing TiO 2-NPs for analysis of biological tissues. We compared the recovery and quantification limits of the four most commonly used mineralization methods for metal oxides. Microwave-assisted dissolution in an HNO 3-HF mixture followed by H 2 O 2 treatment produced the best results for a TiO 2-NPs suspension, with 96 ± 8% recovery and a limit of quantification as low as 0.9 μg/L. This method was then used for the determination of titanium levels in tissue samples taken from rats. However, our tests revealed that even this method is not sensitive enough for quantifying titanium levels in single olfactory bulbs or hippocampus in control animals.Afin de tirer des conclusions appropriées sur les effets biologiques néfastes possibles des nanoparticules de dioxyde de titane (TiO 2-NP), la relation dite «dose-effet» doit être explorée. Cela nécessite une quantification appropriée du titane dans des matrices complexes telles que des organes animaux pour de futures études toxicologiques. Cette étude présente le développement de la méthode de minéralisation des TiO 2-NP pour l'analyse des tissus biologiques. Nous avons comparé les limites de récupération et de quantification des quatre méthodes de minéralisation les plus couramment utilisées pour les oxydes métalliques. La dissolution assistée par micro-ondes dans un mélange HNO 3-HF suivie d'un traitement H 2 O 2 a donné les meilleurs résultats pour une suspension de TiO 2-NPs, avec une récupération de 96 ± 8% et une limite de quantification aussi basse que 0,9 μg / L. Cette méthode a ensuite été utilisée pour la détermination des niveaux de titane dans des échantillons de tissus prélevés sur des rats. Cependant, nos tests ont révélé que même cette méthode n'est pas assez sensible pour quantifier les niveaux de titane dans les bulbes olfactifs uniques ou l'hippocampe chez les animaux témoins

Exposure to TiO2 Nanostructured Aerosol Induces Specific Gene Expression Profile Modifications in the Lungs of Young and Elderly Rats

Although aging is associated with a higher risk of developing respiratory pathologies, very few studies have assessed the impact of age on the adverse effects of inhaled nanoparticles. Using conventional and transcriptomic approaches, this study aimed to compare in young (12–13-week-old) and elderly (19-month-old) fisher F344 rats the pulmonary toxicity of an inhaled nanostructured aerosol of titanium dioxide (TiO2). Animals were nose-only exposed to this aerosol at a concentration of 10 mg/m3 for 6 h per day, 5 days per week for 4 weeks. Tissues were collected immediately (D0), and 28 days after exposure (D28). A pulmonary influx of neutrophilic granulocytes was observed in exposed rats at D0, but diminished with time while remaining significant until D28. Similarly, an increased expression of several genes involved in inflammation at the two post-exposure time-points was seen. Apart from an age-specific pulmonary influx of lymphocyte, only slight differences in physio-pathological responses following TiO2 exposure between young and elderly animals were noticed. Conversely, marked age-related differences in gene expression profiles were observed making possible to establish lists of genes specific to each age group and post-exposure times. These results highlight different signaling pathways that were disrupted in rats according to their age

Study of potential transfer of aluminum to the brain via the olfactory pathway

International audienceMany employees in the aluminum industry are exposed to a range of aluminum compounds by inhalation, and the presence of ultrafine particles in the workplace has become a concern to occupational health professionals. Some metal salts and metal oxides have been shown to enter the brain through the olfactory route, bypassing the blood-brain barrier, but few studies have examined whether aluminum compounds also use this pathway. In this context, we sought to determine whether aluminum was found in rat olfactory bulbs and whether its transfer depended on physicochemical characteristics such as solubility and granulometry. Aluminum salts (chloride and fluoride) and various nanometric aluminum oxides (13 nm, 20 nm and 40–50 nm) were administered to rats by intranasal instillation through one nostril (10 μg Al/30 μL for 10 days). Olfactory bulbs (ipsilateral and contralateral relative to instilled nostril) were harvested and the aluminum content was determined by graphite furnace atomic absorption spectrometry after tissue mineralization. Some transfer of aluminum salts to the central nervous system via the olfactory route was observed, with the more soluble aluminum chloride being transferred at higher levels than aluminum fluoride. No cerebral translocation of any of the aluminas studied was detected.De nombreux salariés de l'industrie de l'aluminium sont exposés à de nombreux composés contenant de l'aluminium par inhalation et la présence de particules ultrafines sur le lieu de travail est devenue une préoccupation pour les professionnels de la santé au travail. Certains travaux ont montré que des sels de métaux et oxydes métalliques pouvaient pénétrer dans le cerveau par la voie olfactive en court-circuitant la barrière hémato-encéphalique, mais peu d'études ont cherché à savoir si les composés de l’aluminium empruntaient également cette voie. Dans ce contexte, cette étude vise à déterminer si l'aluminium pouvait migrer dans les bulbes olfactifs de rat et si ce transfert dépendait des caractéristiques physico-chimiques telles que la solubilité et la granulométrie. Les sels d'aluminium (chlorure et fluorure) et divers oxydes d'aluminium sous forme nanométrique (13 nm, 20 nm et 40-50 nm) ont été administrés à des rats par instillation intranasale (10 ìg Al / 30 microL pendant 10 jours). Les bulbes olfactifs (ipsilatéral et contralatéral par rapport à la narine instillée) ont été collectés et la concentration en aluminium a été déterminée par spectrométrie d'absorption atomique à four graphite après minéralisation des tissus. Il a été montré que les sels d’aluminium migraient vers le système nerveux central via la voie olfactive et que le chlorure d'aluminium, sel plus soluble le faisait davantage que le fluorure d'aluminium. Aucune translocation cérébrale des alumines étudiées n'a été mise en évidence

Biopersistence and translocation to extrapulmonary organs of titanium dioxide nanoparticles after subacute inhalation exposure to aerosol in adult and elderly rats

International audienc

Brain Inflammation, Blood Brain Barrier dysfunction and Neuronal Synaptophysin Decrease after Inhalation Exposure to Titanium Dioxide Nano-aerosol in Aging Rats

Abstract Notwithstanding potential neurotoxicity of inhaled titanium dioxide nanoparticles (TiO2 NPs), the toxicokinetics and consequences on blood-brain barrier (BBB) function remain poorly characterized. To improve risk assessment, we need to evaluate the impact on BBB under realistic environmental conditions and take into account vulnerability status such as age. 12–13 week and 19-month-old male rats were exposed by inhalation to 10 mg/m3 of TiO2 nano-aerosol (6 hrs/day, 5 day/week, for 4 weeks). We showed an age-dependent modulation of BBB integrity parameters suggesting increased BBB permeability in aging rats. This alteration was associated with a significant increase of cytokines/chemokines in the brain, including interleukin-1β, interferon-γ, and fractalkine as well as a decreased expression of synaptophysin, a neuronal activity marker. These observations, in absence of detectable titanium in the brain suggest that CNS-related effects are mediated by systemic-pathway. Moreover, observations in terms of BBB permeability and brain inflammation underline age susceptibility. Even if TiO2 NPs were not evidenced in the brain, we observed an association between the exposure to TiO2 NPs and the dysregulation of BBB physiology associated with neuroinflammation and decreased expression of neuronal activity marker, which was further exacerbated in the brain of aged animal’s

Additional file 1: of Tissue biodistribution of intravenously administrated titanium dioxide nanoparticles revealed blood-brain barrier clearance and brain inflammation in rat

BBB integrity assessment after IV injection of 10 mg/kg TiO 2 NPs in rats. BBB integrity was estimated by the ratio between atenolol concentrations in brain and plasma (partition coefficient or Kp). Each data point represents the mean ± SD of n = 8 rats. Statistical comparison was performed by two tailed Mann-Whitney test, * P < 0.05. (TIFF 4945 kb