Reduction in cadmium-induced toxicity and c-Jun N-terminal kinase activation by glutathione in cultured mouse embryonic cells.

INTRODUCTION: Cadmium (Cd(2+)) induces limb defects and other malformations in experimental animals. However, the mechanisms of the developmental toxicity of this metal are not fully understood. The ubiquitous intracellular tripeptide glutathione (GSH) protects nonembryonic cells from Cd(2+)-induced cell death and is essential for normal embryonic development. We predicted that pretreatment with GSH would prevent cytotoxicity in cultured mouse embryonic limb bud cells exposed to Cd(2+). Additionally, it was expected that GSH pretreatment would prevent the Cd(2+)-induced activation of the signaling molecule c-Jun N-terminal kinase (JNK), which becomes phosphorylated upon exposure to Cd(2+). METHODS: Primary micromass cultures of limb bud cells obtained from organogenesis-stage mouse embryos were treated with either Cd(2+) or GSH alone, or both Cd(2+) and GSH. Treatment with GSH commenced 4 hr prior to Cd(2+) treatment. RESULTS: Cell proliferation was inhibited by approximately 50% after exposure to 4 µM Cd(2+) for 5 days. Cd(2+) treatment also resulted in a dose-dependent increase in the intracellular GSH content as measured after 5 days of exposure. Pretreatment with 4 mM GSH for 4 hr prevented the Cd(2+)-induced inhibition of cell proliferation and differentiation and also inhibited a threefold activation of JNK induced by 4 µM Cd(2+) after 24 and 48 hr of exposure. CONCLUSION: Exogenous GSH protects cultured embryonic limb bud cells from Cd(2+)-induced inhibition of cell proliferation and differentiation, which is associated with the activation of JNK.

Nicotine dose-concentration relationship and pregnancy outcomes in rat: biologic plausibility and implications for future research.

Cigarette smoke (CS) exposure during pregnancy can lead to profound adverse effects on fetal development. Although CS contains several thousand chemicals, nicotine has been widely used as its surrogate as well as in its own right as a neuroteratogen. The justification for the route and dose of nicotine administration is largely based on inferential data suggesting that nicotine 6 mg/kg/day infused continuously via osmotic mini pumps (OMP) would mimic maternal CS exposure. We provide evidence that 6 mg/kg/day nicotine dose as commonly administered to pregnant rats leads to plasma nicotine concentrations that are 3-10-fold higher than those observed in moderate to heavy smokers and pregnant mothers, respectively. Furthermore, the cumulative daily nicotine dose exceeds by several hundred fold the amount consumed by human heavy smokers. Our study does not support the widely accepted notion that regardless of the nicotine dose, a linear nicotine dose-concentration relationship exists in a steady-state OMP model. We also show that total nicotine clearance increases with advancing pregnancy but no significant change is observed between the 2nd and 3rd trimester. Furthermore, nicotine infusion even at this extremely high dose has little effect on a number of maternal and fetal biologic variables and pregnancy outcome suggesting that CS constituents other than nicotine mediate the fetal growth restriction in infants born to smoking mothers. Our current study has major implications for translational research in developmental toxicology and pharmacotherapy using nicotine replacement treatment as an aid to cessation of cigarette smoking in pregnant mothers.

Hypoxemia and low Crs in vagally denervated lambs result from reduced lung volume and not pulmonary edema.

Vagal denervation performed in the intrathoracic region in newborn lambs leads to hypoxemia and decreased respiratory system compliance (Crs), which could result from atelectasis and/or pulmonary edema. The objective of the present study was to quantify the relative roles of alveolar derecruitment and pulmonary edema as underlying cause(s) of respiratory failure. Vagal denervation was performed in the intrathoracic region and below the recurrent laryngeal nerves in six newborn lambs within 24 h of birth, whereas six were sham operated. Pre- and postinflation Crs was measured to investigate the presence of alveolar derecruitment. Pulmonary edema was assessed with lung wet-dry-to-wet and lung tissue wet-to-dry ratios, total protein, and FITC-BSA recovery in lung tissue and bronchoalveolar lavage. Compared with that in the sham-operated animals, Crs was significantly lower in vagally denervated animals. However, postinflation, pulmonary system compliance obtained by quasi-static lung inflation and deflation to 30 cmH2O showed no significant difference between the sham-operated and denervated lambs. The lung wet-dry-to-wet and lung tissue wet-to-dry ratios, total protein, and FITC-BSA recovery in lung tissue and bronchoalveolar lavage were similar in denervated and sham-operated groups. We provide evidence that reduced lung volume and not pulmonary edema is associated with intrathoracic vagal denervation and is the likely underlying mechanism for hypoxemia and low Crs.