Chenjuan Yao

Inorganic arsenic primarily originates from geological processes and human activities. Exposure to high concentrations of inorganic arsenic can cause diverse health problems, with lung injury being one of the main hazards. The present study sought to elucidate the cytotoxicity and underlying mechanisms of inorganic arsenic in BEAS-2B cells. The results showed that exposure of BEAS-2B cells to arsenic trioxide (As₂O₃) for 24 h resulted in a dose-dependent decline in viability. As₂O₃ triggered reactive oxygen species (ROS) production in BEAS-2B cells, and ROS contributed to increased p-IRE1α and p-eIF2α abundance relative to β-actin, along with GRP78 protein expression. The autophagy-associated and apoptotic responses induced by As₂O₃ in BEAS-2B cells were likewise associated with ROS. Further analysis revealed that increased p-IRE1α abundance relative to β-actin is involved in As₂O₃-triggered autophagy-associated responses and apoptosis in BEAS-2B cells. The antioxidant N-acetylcysteine (NAC) markedly attenuated As₂O₃-induced apoptosis and autophagy-associated responses and reduced p-IRE1α abundance relative to β-actin. Collectively, these findings indicate that the ROS/IRE1α pathway contributes to As₂O₃-triggered autophagy-associated responses and apoptosis in BEAS-2B cells.

Aquaporin 5 (AQP5) plays an important role in the salivary gland function. The mRNA and protein for AQP5 are expressed in the acini from embryonic days E13-16 and E17-18, respectively and for entire postnatal days. Ligation-reopening of main excretory duct induces changes in the AQP5 level which would give an insight for mechanism of regeneration/self-duplication of acinar cells. The AQP5 level in the submandibular gland (SMG) decreases by chorda tympani denervation (CTD) via activation autophagosome, suggesting that its level in the SMG under normal condition is maintained by parasympathetic nerve. Isoproterenol (IPR), a β-adrenergic agonist, raised the levels of membrane AQP5 protein and its mRNA in the parotid gland (PG), suggesting coupling of the AQP5 dynamic and amylase secretion-restoration cycle. In the PG, lipopolysaccharide (LPS) is shown to activate mitogen-activated protein kinase (MAPK) and nuclear factor-kappa B (NF-κB) signalings and potentially downregulate AQP5 expression via cross coupling of activator protein-1 (AP-1) and NF-κB. In most species, Ser-156 and Thr-259 of AQP5 are experimentally phosphorylated, which is enhanced by cAMP analogues and forskolin. cAMP-dependent phosphorylation of AQP5 does not seem to be markedly involved in regulation of its intracellular trafficking but seems to play a role in its constitutive expression and lateral diffusion in the cell membrane. Additionally, Ser-156 phosphorylation may be important for cancer development.

In the membrane fraction of mouse parotid gland (PG), the protein level of aquaporin 5 (AQP5), a member of the water channel family, was increased by injection (ip) of isoproterenol (IPR), a β-adrenergic agonist, at 1 h, and stayed at high levels until 6 h; this change occurred simultaneously as amylase secretion. The AQP5 level then decreased and returned toward the original level at 12–48 h. After IPR injection, the AQP5 mRNA gradually increased and reached a maximum at 24 h. The facts suggest a rapid appearance of AQP5 at plasma membrane by IPR and subsequent degradation/metabolism by activation of proteolytic systems. Pretreatment of animals with two calpain inhibitors, N-Ac-Leu-Leu-methininal (ALLM) and calpeptin, as well as a protein synthesis inhibitor, cycloheximide (CHX), significantly suppressed the IPR-induced AQP5 degradation in the PG membrane fraction; such suppression was not observed by two proteasome inhibitors, MG132 and lactacystin, or the lysosome denaturant chloroquine, although most of these inhibitors increased AQP5 protein levels in unstimulated mice. The AQP5 protein was also degraded by μ-calpain in vitro. Furthermore, we demonstrated that μ-calpain was colocalized with AQP5 in the acinar cells by immunohistochemistry, and its activity in the PG was increased at 6 h after IPR injection. These results suggest that the calpain system was responsible for IPR-induced AQP5 degradation in the parotid gland and that such a system was coupled to the secretory-restoration cycle of amylase in the PG.

To investigate the mechanism of the different levels of serum bisphenol A (BPA) between rat and mouse after oral administration. A total of 18 specific pathogen free (SPF) male rats and 18 mice were treated with 300 mg/kg BPA by oral administration, blood samples were taken from rats and mice after BPA administration at 0.5, 1.0, 12.0 h time points (n = 6 at each point). Serum BPA levels were quantified using fluorescence-high performance liquid chromatography (FL-HPLC) analysis. The rats and mice (n = 6, respectively) were perfused with 100 ml of 0.1 mmol/L BPA by intestinal absorption in situ, then the BPA levels of perfusion fluid at 0.5, 1.0, 2.0 h time points and serum at 2.0 h after BPA perfusion were determined by FL-HPLC analysis. The levels of UDP-glucuronosyltransferase 2B1 (UGT2B1) mRNA expression in the liver of rats and mice were analyzed by semi-quantitative RT-PCR and UGT2B1 enzymatic activity was determined by FL-HPLC method. The rats and mice (n = 6, respectively) were treated with 300 mg/kg BPA by oral administration after fasting 24 h, the feces were collected during 24 h and the levels of BPA in feces were determined by FL-HPLC analysis. At 0.5, 1.0, 12.0 h after oral administration at 300 mg/kg BPA, the levels of serum BPA in mice ((66.57 ± 14.95), (51.16 ± 16.06), (22.73 ± 5.00) µg/ml, respectively) were significantly higher than in rats ((15.63 ± 5.65), (18.34 ± 5.02), (7.65 ± 2.58) µg/ml, respectively) (F values were 50.660, 17.957, 8.420, respectively, P < 0.05), the rates of absorption in mice small intestine during 0 h-, 0.5 h-, 1.0 - 2.0 h ((10.20 ± 4.20), (1.49 ± 0.67), (1.31 ± 0.55) µg × cm(-2) × min(-1), respectively) were higher than that in rats ((1.87 ± 0.69), (0.47 ± 0.13), (0.36 ± 0.08) µg × cm(-2) × min(-1), respectively) (F values were 14.954, 8.877, 11.536, respectively, P < 0.05), the serum BPA levels in mice ((22.64 ± 4.35) µg/ml) were significantly higher than in rats ((4.13 ± 0.83) µg/ml) after 2 h perfusion with 0.1 mmol/L BPA (F = 74.643, P = 0.000), the levels of UGT2B1 mRNA expression and enzymatic activity in the rats liver were obviously higher than in the mice liver. After oral administration at 300 mg/kg BPA, the feces BPA levels of rats ((1.50 ± 0.32) mg/g) were significantly higher than that of the mice ((0.57 ± 0.35) mg/g) (F = 21.215, P = 0.001) during 24 h. The serum BPA level of mouse is significantly higher than the rat after oral administration at 300 mg/kg BPA, which may be caused by BPA high absorption rate of mouse small intestine and strong ability of BPA glucuronidation and excretion of the rat.

To investigate the relationship of time-concentration of bisphenol A (BPA) in male Sprague-Dawley (SD) rats after single oral BPA administration. A total of 66 specific pathogen free (SPF) SD male rats were divided into 10 experimental groups and control group (n = 6). The experimental group rats were treated with BPA of 300 mg/kg by oral gavage and blood samples were taken from one group at 0.5, 1, 2, 4, 6, 12, 24, 36, 60, 84 h time point after oral administration, respectively. The serum BPA concentration was determined by fluorescence-high performance liquid chromatography (FL-HPLC) analysis. After oral administration of 300 mg/kg, the total serum BPA concentration of 17.13 microg/ml was the highest in rats at 1 h, then decreased, but it increased to 15.18 microg/ml again at 24 h, then gradually decreased to 0.51 microg/ml at 84 h. The level of serum free BPA was lower than that of total serum BPA after oral administration, the serum free BPA was 0.57 microg/ml at 0.5 h after oral administration. The serum free BPA level decreased to 0.06 microg/ml at 1 h, 0.03 microg/ml at 4 h, 0.01 microg/ml at 36 h after oral administration. The free BPA was only 4.15% (0.57/13.73) in total BPA in serum at 0.5 h after oral administration of 300 mg/kg BPA. These results suggested that conjugated BPA was the main metabolite of BPA in rat serum after single oral administration. Enterohepatic circulation of BPA glucuronide in rats may results in two peak levels of total BPA in serum.