HPLC-MS/MS measurement of lidocaine in rat skin and plasma. Application to study the release from medicated plaster.

A simple, sensitive HPLC-MS/MS method was developed and validated for the determination of lidocaine in skin and plasma of rats. The methods were established and validated assessing lower limit of quantitation (LLOQ), linearity, intra and inter-day precision and accuracy, selectivity, recovery and matrix effect. Chromatography was done on a Gemini column embedded with C18 stationary phase (50 mm × 2.0 mm, 5 µm particle size), using a gradient with mobile phases consisting of 0.1% HCOOH in bidistilled water and 0.1% HCOOH in acetonitrile. The mass spectrometer worked with electrospray ionization in positive ion mode and selected reaction monitoring, using target ions m/z 235.10 for lidocaine and m/z 245.10 for lidocaine-d10, used as internal standard. RESULTS: The linearity of the method was in the ranges of lidocaine concentrations 10.0-200.0 ng/mL for skin homogenate (accuracy 94.1-105.5%; R2 ≥ 0.998) and 0.025-2 ng/mL for plasma (accuracy 96.2-104.8%; R2 ≥ 0.996). The intra- and inter-day precision and accuracy determined on three quality control samples (20, 75 and 170 ng/mL for skin and 0.075, 0.4 and 1.5 ng/mL for plasma) were ≤4.2% and 103.8-108.2% for skin and ≤12.4% and 95.5-101.4% for plasma. The LLOQ was 10 ng/mL in skin homogenate and 0.025 ng/mL in plasma. The applicability of the method was demonstrated by measuring lidocaine in skin and plasma after exposure to medicated patches containing 5% lidocaine.

Bile acids, nuclear receptors and cytochrome P450.

This review summarizes the importance of bile acids (BA) as important regulators of various homeostatic mechanisms with detailed focus on cytochrome P450 (CYP) enzymes. In the first part, synthesis, metabolism and circulation of BA is summarized and BA are reviewed as physiological ligands of nuclear receptors which regulate transcription of genes involved in their metabolism, transport and excretion. Notably, PXR, FXR and VDR are the most important nuclear receptors through which BA regulate transcription of CYP genes involved in the metabolism of both BA and xenobiotics. Therapeutic use of BA and their derivatives is also briefly reviewed. The physiological role of BA interaction with nuclear receptors is basically to decrease production of toxic non-polar BA and increase their metabolic turnover towards polar BA and thus decrease their toxicity. By this, the activity of some drug-metabolizing CYPs is also influenced what could have clinically relevant consequences in cholestatic diseases or during the treatment with BA or their derivatives.

The effect of (-)-linalool on the metabolic activity of liver CYP enzymes in rats.

(-)-Linalool is the major floral scent occurring mainly in families Lamiaceae, Lauraceae and Rutaceae and is the main active compound of lavender oil. The purpose of this study was to reveal the influence of subchronic systemic treatment with (-)-linalool on the metabolic activity of CYP2A, 2B, 2C6, 2C11 and 3A in rat liver microsomes (RLM). The second aim was to reveal possible inhibitory effect of (-)-linalool on CYP2C6 in vitro. Wistar albino male rats were treated with (-)-linalool intragastrically at the doses of 40, 120, and 360 mg/kg/day for 13 days. Treatment with (-)-linalool at the dose of 360 mg/kg increased the metabolic activity of CYP2A assessed with testosterone as a probe substrate. (-)-Linalool showed weak competitive inhibition of CYP2C6 in rat liver microsomes, with IC(50) of 84 microM with use of diclofenac as a probe substrate.

Can bioactive compounds of Crocus sativus L. influence the metabolic activity of selected CYP enzymes in the rat?

Safranal and crocin are biologically active compounds isolated from Crocus sativus L., commonly known as saffron. Clinical trials confirm that saffron has antidepressant effect, thus being a potential valuable alternative in the treatment of depression. The aim of the present study was to determine, whether systemic administration of safranal and crocin can influence the metabolic activity of CYP3A, CYP2C11, CYP2B, and CYP2A in rat liver microsomes (RLM). The experiments were carried out on male Wistar albino rats intragastrically administered with safranal (4, 20, and 100 mg/kg/day) or with intraperitoneal injections of crocin (4, 20, and 100 mg/kg/day). Our results demonstrate the ability of safranal and crocin to increase the total protein content and to change the metabolic activity of several CYP enzymes assessed as CYP specific hydroxylations of testosterone in RLM. Crocin significantly decreased the metabolic activity of all selected CYP enzymes, while safranal significantly increased the metabolic activity of CYP2B, CYP2C11 and CYP3A enzymes. Therefore, both substances could increase the risk of interactions with co-administered substances metabolized by cytochrome P450 enzymes.