Identification of an Epoxide Metabolite of Amitriptyline In Vitro and In Vivo.

Amitriptyline (ATL), a tricyclic antidepressant, has been reported to cause various adverse effects, particularly hepatotoxicity. The mechanisms of ATL-induced hepatotoxicity remain unknown. The study was performed to identify the olefin epoxidation metabolite of ATL and determine the possible toxicity mechanism. Two glutathione (GSH) conjugates (M1 and M2) and two N-acetylcysteine (NAC) conjugates (M3 and M4) were detected in rat liver microsomal incubations supplemented with GSH and NAC, respectively. Moreover, M1/M2 and M3/M4 were respectively found in ATL-treated rat primary hepatocytes and in bile and urine of rats given ATL. Recombinant P450 enzyme incubations demonstrated that CYP3A4 was the primary enzyme involved in the olefin epoxidation of ATL. Treatment of hepatocytes with ATL resulted in significant cell death. Inhibition of CYP3A attenuated the susceptibility to the observed cytotoxicity of ATL. The metabolic activation of ATL most likely participates in the cytotoxicity of ATL.

Metabolic Activation and Cytotoxicity of Labetalol Hydrochloride Mediated by Sulfotransferases.

Labetalol hydrochloride (LHCl), an α- and ß-adrenoreceptor blocker, is widely used for the treatment of hypertension as well as angina pectoris. Previous reports have demonstrated the adverse events during clinical application of LHCl, such as liver injury and acute renal failure. The present study aimed to investigate metabolic activation of LHCl to initiate the elucidation of the mechanisms of its liver toxicity. One glutathione (GSH) conjugate was detected in rat and human primary hepatocytes as well as bile of rats after exposure to LHCl. The GSH conjugate was chemically synthesized and characterized by Q-TOF and 1H NMR. Pretreatment of 2,6-dichloro-4-nitrophenol (DCNP), a broad-spectrum sulfotransferase (SULT) inhibitor, significantly attenuated the formation of the GSH conjugate in LHCl-treated hepatocytes and animals, indicating the participation of SULTs in metabolic activation of LHCl. Moreover, pretreatment with DCNP displayed significant protection against the observed cytotoxicity in rat primary hepatocytes, which suggests a correlation of the bioactivation of LHCl mediated by SULTs with LHCl-induced hepatotoxicity.

Toxicity and enantiospecific differences of two ß-blockers, propranolol and metoprolol, in the embryos and larvae of zebrafish (Danio rerio).

The risk presented by ß-blockers on aquatic organisms remains uncertain, particularly given the enantiospecific differences in toxicity of chiral ß-blockers. In this study, the toxicity of two ß-blockers, propranolol and metoprolol, was determined. The 96-h LC50 of propranolol in the zebrafish larvae was 2.48 mg/L, whereas 50 mg/L metoprolol did not result in death. Both ß-blockers decreased the heart rate and hatching rate and increased the mortality of the zebrafish embryos. Among these indicators, the heart rate was the most sensitive. However, the acute larval and embryo toxicity results displayed no enantioselectivity. Additionally, the transcriptional response of the genes encoding the ß-adrenergic receptors and those involved in other physiological processes, including the antioxidant response, detoxification, and apoptosis, in zebrafish larvae exposed to the ß-blockers was examined. Although the changes in gene transcription were fairly minor, significant enantioselectivity was observed for ß-blockers, suggesting that the transcriptional response was more sensitive for the evaluation of enantiospecific toxicity. Based on these results, the pharmaceutical drugs were not expected to pose a risk to fish; however, this conclusion should not be considered final. These results also demonstrated that the enantiospecific toxicity of chiral ß-blockers should be investigated when performing an ecological risk assessment.

[Soil respiration of Pinus koraiensis and P. sylvestriformis trees growing at elevated CO2 concentration].

The study with open-top chamber showed that at 500 micromol CO2 x mol(-1), the soil respiration rate under Pinus koraiensis and P. sylvestriformis decreased significantly, probably due to the slow diffusion of increased soil surface CO2 concentration. The soil surface CO2 concentration at 500 micromol CO2 x mol(-1) was significant higher than that in the control chamber and un-chambered field, with an increment of 40-150 micromol CO2 x mol(-1). The soil surface CO2 concentration of P. sylvestriformis in the control chamber was higher than that on unchambered field, but the difference was not significant, while a significant difference was observed in P. koraiensis. The total nitrogen and total organic carbon contents in P. sylvestriformis soil at 500 micromol CO2 x mol(-1) had no significant difference with those in the control chamber and on unchambered field, while their contents in P. koraiensis soil were significantly lower on unchambered field than those in the control chamber and at 500 micromol CO2 x mol(-1). Elevated CO2 and the microenvironment of open-top chamber had little effect on the soil temperature at 3 cm depth.