Acute exposure of toluene transiently potentiates p42/44 mitogen-activated protein kinase (MAPK) activity in cultured rat cortical astrocytes

Styrene alters potassium endolymphatic concentration in a model of cultured utricle explants

Despite well-documented neurotoxic and ototoxic properties, styrene remains commonly used in industry. Its effects on the cochlea have been extensively studied in animals, and epidemiological and animal evidence indicates an impact on balance. However, its influence on the peripheral vestibular receptor has yet to be investigated. Here, we assessed the vestibulotoxicity of styrene using an in vitro model, consisting of three-dimensional cultured newborn rat utricles filled with a high‑potassium (K⁺) endolymph-like fluid, called "cysts". K⁺ entry in the cyst ("influx") and its exit ("efflux") are controlled by secretory cells and hair cells, respectively. The vestibular epithelium's functionality is thus linked to K⁺ concentration, measured using a microelectrode. Known inhibitors of K⁺ efflux and influx validated the model. Cysts were subsequently exposed to styrene (0.25; 0.5; 0.75 and 1 mM) for 2 h or 72 h. The decrease in K⁺ concentration measured after both exposure durations was dose-dependent, and significant from 0.75 mM styrene. Vacuoles were visible in the cytoplasm of epithelial cells from 0.5 mM after 2 h and from 0.25 mM after 72 h. The results presented here are the first evidence that styrene may deregulate K⁺ homeostasis in the endolymphatic space, thereby altering the functionality of the vestibular receptor.

High temperature and hexane break pupal diapause in the flesh fly, Sarcophaga crassipalpis, by activating ERK/MAPK

Pupal diapause in the flesh fly, Sarcophaga crassipalpis, can be terminated by exposure to high temperatures or, artificially, with a topical application of organic solvents. To analyze the molecular mechanisms involved in diapause termination we explored the possibility that the mitogen-activated protein kinases (MAPK) are involved in this response. Levels of phospho-ERK increased within 10 min after hexane application. Extracellular signal-regulated kinase (ERK) was also activated when pupae were transferred from 20 to 25 degrees C, thus suggesting that ERK activation is a likely component of the signal transduction pathway used to initiate development in response to diapause-terminating signals. 20-Hydroxyecdysone and cyclic GMP terminate diapause in this fly, and the juvenile hormone analog methoprene shortens the diapause, but none of these agents activated ERK. ERK was readily activated in isolated abdomens treated with hexane, thus we conclude that ERK is directly activated by the hexane treatment. ERK activation was evident in the brain, epidermis, midgut and fat body, but not in the ventral nerve mass or ring gland, thus suggesting that ERK does not act directly on the ring gland to promote ecdysteroid synthesis but exerts its effect through stimulation of the brain.

Sub-chronic toxicity of low concentrations of industrial volatile organic pollutants in vitro

Organic solvents form an important class of pollutants in the ambient air and have been associated with neurotoxicity and immunotoxicity in humans. Here we investigated the biological effects of sub-chronic exposure to industrially important volatile organic solvents in vitro. Jurkat T cells were exposed to toluene, n-hexane and methyl ethyl ketone (MEK) individually for 5 days and solvent exposure levels were confirmed by headspace gas chromatography. A neuroblastoma cell line (SH-SY5Y) was exposed to toluene for the same period. Following exposure, cells were harvested and toxicity measured in terms of the following endpoints: membrane damage (LDH leakage), perturbations in intracellular free Ca(2+), changes in glutathione redox status and dual-phosphorylation of MAP kinases ERK1/2, JNK and p38. The results show that sub-chronic exposure to the volatile organic solvents causes membrane damage, increased intracellular free calcium and altered glutathione redox status in both cell lines. However, acute and sub-chronic solvent exposure did not result in MAP kinase phosphorylation. Toxicity of the solvents tested increased with hydrophobicity. The lowest-observed-adverse-effect-levels (LOAELs) measured in vitro were close to blood solvent concentrations reported for individuals exposed to the agents at levels at or below their individual threshold limit values (TLVs).

Histamine H(1) and H(3) receptors in the rat thalamus and their modulation after systemic kainic acid administration

In rat thalamus, histamine H(1) receptor and isoforms of H(3) receptor were expressed predominantly in the midline and intralaminar areas. Correspondingly, higher H(1) and H(3) receptor binding was also detected in these areas. All isoforms of H(3) receptor were expressed in several thalamic nuclei, but there were minor differences between their expression patterns. H(1) mRNA expression was high in the ventral thalamus, but the H(1) binding level was low in these areas. Since increased brain histamine appears to have an antiepileptic effect through the H(1) receptor activity, kainic acid (KA)-induced status epilepticus in rat was used to study modulation of H(1) and H(3) receptors in the thalamus following seizures. After systemic KA administration, transient decreases in mRNA expression of H(1) receptor and H(3) receptor isoforms with full-length third intracellular loops were seen in the midline areas and the H(1) receptor mRNA expression also decreased in the ventral thalamus. After 1 week, a robust increase in mRNA expression of H(3) receptor isoforms with a full-length third intracellular loop was found in the ventral posterior, posterior, and geniculate nuclei. The changes indicate a modulatory role of H(3) receptor in the sensory and motor relays, and might be involved in possible neuroprotective and compensatory mechanisms after KA administration. However, short-term increases in the H(3) receptor binding appeared earlier (72 h) than the increases of H(3) mRNA expression (1-4 w). The elevations in H(3) binding were evident in the intralaminar area, laterodorsal, lateral posterior, posterior and geniculate nuclei, and were likely to be related to the cortical and subcortical inputs to thalamus.

Toluene and p-xylene induced LLC-PK1 apoptosis

Occupational exposure to organic solvents was found to be associated with development and progression of tubulo-interstitial fibrosis and chronic renal failure. However, the cellular mechanism by which this occurs remains elusive. This study was conducted to evaluate the mode of cell death in proximal tubular cells exposed to organic solvents. LLC-PK1 cell line cytotoxicity due to exposure to 1 mM of either p-xylene or toluene was compared to untreated control by cell viability, LDH release, and DNA fragmentation. Cells were exposed to solvents for 96 hrs. Toluene and p-xylene reduced cell viability and increased DNA fragmentation. LDH release was unchanged. These data indicates that long-term exposure to organic solvents is associated with proximal tubule cell apoptosis, which may be the mechanism of progressive renal fibrosis and renal failure in patients with high solvent exposure.

Characterization of H2O2-induced acute apoptosis in cultured neural stem/progenitor cells

In the present study, we characterized hydrogen peroxide (H2O2)-induced cell apoptosis and related cell signaling pathways in cultured embryonic neural stem/progenitor cells (NS/PCs). Our data indicated that H2O2 induced acute cell apoptosis in NS/PC in concentration- and time-dependent manners and selectively, it transiently increased PI3K-Akt and Mek-Erk1/2 in a dose-dependent manner. Inhibition of PI3K-Akt with wortmannin, a PI3-K inhibitor, was found to significantly increase H2O2-induced acute apoptosis and dramatically decrease basal pGSK3beta levels. The level of pGSK3beta remained unchanged with H2O2 exposure. We conclude that the transient activation of PI3K-Akt signaling delays the H2O2-induced acute apoptosis in cultured NS/PCs in part through maintaining the basal pGSK3beta level and activating other downstream effectors.