Effects of cadmium acetate and sodium selenite on mucociliary functions and adenosine triphosphate content in mouse trachea organ cultures

Studies on Mechanisms of the Toxic Effects of Cadmium in Mouse Tracheal Organ Culture

Exposure of tracheal organ cultures to 10μM cadmium acetate resulted in a reduction of ciliary activity by 89% and a profound swelling of the epithelial cells within 4 hours. Substances with specific effects on ion transport systems did not interact with these cadmium induced effects. The swelling took place without any significant alterations of the intracellular electrolyte content (Na+, K+). Trifluoperazine (0.1mM), a calmodulin-specific drug, resulted in a reduction of ciliary activity similar to that induced by 10μM cadmium acetate, and induced a prominent swelling in part of the epithelial cell layer. A possible mechanism for the toxicity of cadmium could thus be binding of Cd2+ to the Ca2+ sites on calmodulin, causing dysfunctions of its normal regulatory role in both ciliary activity and volume control.

Selenium Diminishes Docetaxel-Induced Cell Death, Oxidative Stress, and Inflammation in the Laryngotracheal Epithelium of the Mouse

Docetaxel (DOCX) kills tumor cells through the formation of microtubules, calcium ion influx, apoptosis, and inflammation. However, DOCX has adverse effect on normal tissues through the production of reactive oxygen species (ROS), despite the adverse effect was inhibited by antioxidants. We investigated the protective role of selenium against DOCX-induced apoptosis and mitochondrial oxidative injury in laryngotracheal epithelial (LARYN) cells of mice. Thirty-two mice were divided into four groups (n = 8). The first group was used as a control. The second and third groups were treated with sodium selenite (Na-Sel) and DOCX, respectively. The fourth group was the combined group of Na-Sel and DOCX. At the end of the experiment, LARYN mucosa and cells were obtained from the mice. In the LARYN cells, the cell viability level was low in DOCX group, although glutathione peroxidase activity and cell viability level were increased by the treatment of Na-Sel. Increased lipid peroxidation, intracellular ROS, mitochondrial membrane depolarization, cell death levels, TNF-α, IL-1β, IL-6, caspase -3, and -9 activities in the DOCX group of LARYN cells were diminished by the treatment of Na-Sel. In conclusion, DOCX increased mitochondrial ROS, cell death, and inflammation in the LARYN cells, although the increase was reduced in the cells by Na-Sel treatment. DOCX-induced adverse oxidant, inflammatory, and apoptotic effects in the tissue might be reduced by the Na-Sel treatment.

Mucociliary transport as a link between chronic rhinosinusitis and trace element dysbalance

Chronis rhinosinusitis is considered as a widespread public health issue with a prevalence of 10%. The disease significantly reduces quality of life and increases the risk of cardiovascular diseases as well as certain forms of cancer. Alteration of mucociliary clearance frequently observed in the patients and plays a significant role in disease pathogenesis. Certain studies have demonstrated that patients with chronic rhinosinusitis are characterized by significant reduction of essential trace elements and toxic metal overload. However, the particular mechanisms of the role of trace element dysbalance in chronic rhinosinusitis are unclear. We hypothesize that exposure to toxic trace elements (arsenic, nickel, cadmium) damages ciliary mucosal epithelium thus affecting mucociliary transport. In turn, altered mucociliary transport results in reduced removal of the inhaled metal-containing particles from nasal mucosa leading to their absorption and further aggravation of toxicity. Essential trace elements (zinc, selenium) play a significant role in regulation of mucociliary transport and immunity, thus their deficiency (either dietary or due to antagonism with toxic metals) may be associated with impaired functions and increased toxic metal toxicity. Therefore, a vicious circle involving metal accumulation and toxicity, essential element deficiency, impairment of mucociliary transport and metal particle removal, resulting in further accumulation of metals and aggravation of toxic effects is formed. The present hypothesis is supported by the findings on the impact of trace elements especially zinc and arsenic on mucociliary clearance, the role of mucociliary transport in heavy metal particles elimination from the airways, trace element dysbalance in chronic rhinosinusitis, as well as toxic and essential metal antagonism. The data from hypothesis testing and its verification may be used for development of therapeutic approach for management of chronic rhinosinusitis. Particularly, the use of essential elements (zinc, selenium) may reduce toxic metal toxicity thus destroying the vicious circle of heavy metal exposure, toxicity, alteration of mucociliary clearance, and aggravation of chronic rhinosinusitis. Essential element supplementation may be considered as a tool for management of chronic refractory rhinosinusitis. In addition, analysis of essential and toxic trace element status may provide an additional diagnostic approach to risk assessment of chronic rhinosinusitis in highly polluted environments.

Antagonism of cadmium cytotoxicity by differentiation inducers

Studies on the antagonism of toxicity can provide information about toxic mechanisms and suggest chemotherapeutic strategies. A rapid cell growth assay that measures the effects of test agents on the accumulation of cell protein (Shopsis and Eng, Toxicol. Lett. 1985;26:1) has been applied to studies of the antagonism of the cytotoxicity of cadmium. Exposure of Balb/c mouse 3T3 cells to 15 mumol/L Cd2+ for 24 h or 7 mumol/L Cd2+ for 48 h caused a 50% decrease in total cell protein. Zn2+ and selenite ion, antagonists of Cd toxicity in vivo, antagonized Cd2+ cytotoxicity when added in micromolar concentrations at the initiation of exposure to Cd2+. A diverse group of chemicals that can induce differentiation in vitro in cultured erythroleukemia and other cells were also found to antagonize the cytotoxic effects of Cd2+ to 3T3 cells. Dimethyl sulfoxide (DMSO), hexamethylene bisacetamide, N,N-dimethyl formamide, N-methyl formamide, dimethyl acetamide, hypoxanthine, hemin, ouabain, and sodium butyrate, when added to cultures simultaneously with Cd2+, each antagonized Cd2+ toxicity. These agents were used at concentrations equal to or lower than the concentrations at which they induce cellular differentiation. Other cytotoxicity assays and morphological studies confirmed these observations. DMSO added as much as 6 h after the initiation of a 24-h exposure to Cd2+ still protected cells; conversely, pretreatment of cultures with butyrate or DMSO for 24 h followed by their removal did not confer protection against subsequent Cd2+ challenge. Ethanol and methanol (noninducers of differentiation) did not antagonize Cd2+ cytotoxicity, and differentiation-inducing agents did not protect the cells from Zn(2+)- or Hg(2+)-induced cytotoxicity. DMSO treatment does not induce an increase in the concentrations of metallothionein or glutathione in these cells.

Ion transport and cadmium-induced inhibition of ciliary activity and induction of swelling of epithelial cells in mouse trachea organ culture

Swelling of epithelial cells and reduction of ciliary activity in mouse trachea organ culture occurred after incubation for 4 h with a rather low concentration of cadmium acetate (10 microM). Specific inhibitors of ion transport (Na+, K+, Cl-) such as furosemide, amiloride and ouabain did not mimic, abolish or increase the toxic effects induced by cadmium acetate. Exposure to cadmium acetate had no significant effect on electrolyte uptake (22Na+ and 86Rb+). These results suggest that the swelling of epithelial cells induced by cadmium acetate is not due to an osmotic swelling from an accumulation of electrolytes. Ba2+, known to have several biological properties in common with Ca2+, and to influence basolateral K+ flux, counteracted the toxic effects of cadmium acetate, whereas a more rapid and extensive swelling occurred with cadmium acetate in a medium without Ca2+. No effect on the uptake of 109Cd2+ was found with barium chloride, whereas in a medium without Ca2+ the Cd2+ uptake increased by 47%. Trifluoperazine (100 microM), a drug which in vitro binds tightly to calmodulin, imitated the toxic effects of 10 microM cadmium acetate. The combination of 10 microM cadmium acetate and 100 microM trifluoperazine resulted in an additive toxic effect. A possible mechanism for the cadmium acetate-induced swelling and inhibition of ciliary activity could, thus, be a disturbance of the regulatory activity of calmodulin.