A highly efficient liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay for etomidate and etomidate acid in urine, liver and kidney.

Etomidate (ETO) is a highly-efficient drug that can induce anesthesia with increasing doses, thus subject to strict regulation. However, an accurate and efficient method for ETO intake detection is currently lacking. Therefore, this study developed a straightforward sample preparation method using LC-MS/MS to analyze ETO and its primary metabolite, etomidate acid (ETA), in urine, liver, and kidney samples. Snap frozen pig liver and kidney samples were ground into a fine powder. Then, all the biological samples, including human urine, pig liver and kidney tissues, were deproteinized using acetonitrile and filtered for analysis. The separation was achieved in 9.01 min with gradient elution. The calibration curves ranged from 0.5 to 50 ng/mL for ETO in urine and 0.5 to 50 ng/g in liver and kidney, while the curves ranged from 1 to 100 ng/mL for ETA in urine and 1 to 100 ng/g in liver and kidney. The correlation coefficients (R2) were greater than 0.9957. The Limit of detection (LOD) and limit of quantitation (LOQ) for ETO were 0.2 and 0.5 ng/mL in urine samples and 0.2 and 0.5 ng/g in liver and kidney samples, respectively. For ETA, the LOD and LOQ were 0.5 and 1 ng/mL in urine samples and 0.5 and 1 ng/g in liver and kidney samples. This method was assessed by validation parameters, including selectivity, intra- and inter-day precision and accuracy, recovery, matrix effect, dilution integrity and stability. It was successfully applied to a practical case, revealing ETO and ETA concentrations in urine of 1.01 and 5.58 µg/mL, in liver samples of 12.30 and 1.13 µg/g, and in kidney samples of 6.95 and 4.23 µg/g. This suggests that the method is suitable for routine forensic detection of illicit ETO abuse.

Molecular cloning and characterization of neutral ceramidase homologue from the red flour beetle, Tribolium castaneum.

Ceramidase plays an important role in regulating the metabolism of sphingolipids, such as ceramide, sphingosine (SPH), and sphingosine-1-phosphate (S1P), by controlling the hydrolysis of ceramide. Here we report the cloning and biochemical characterization of a neutral ceramidase from the red flour beetle Tribolium castaneum which is an important storage pest. The Tribolium castaneum neutral ceramidase (Tncer) is a protein of 696 amino acids. It shares a high degree of similarity in protein sequence to neutral ceramidases from various species. Tncer mRNA levels are higher in the adult stage than in pre-adult stages, and they are higher in the reproductive organs than in head, thorax, and midgut. The mature ovary has higher mRNA levels than the immature ovary. Tncer is localized to the plasma membrane. It uses various ceramides (D-erythro-C(6), C(12), C(16), C(18:1), and C(24:1)-ceramide) as substrates and has an abroad pH optimum for its in vitro activity. Tncer has an optimal temperature of 37 °C for its in vitro activity. Its activity is inhibited by Fe(2+). These results suggest that Tncer has distinct biochemical properties from neutral ceramidases from other species.