Electrochemical simulation of biotransformation reactions of citrinin and dihydroergocristine compared to UV irradiation and Fenton-like reaction.

Mycotoxins occur widely in foodstuffs and cause a variety of mold-related health risks to humans and animals. Elucidation of the metabolic fate of mycotoxins and the growing number of newly discovered mycotoxins have enhanced the demand for fast and reliable simulation methods. The viability of electrochemistry coupled with mass spectrometry (EC/ESI-MS), Fenton-like oxidation, and UV irradiation for the simulation of oxidative phase I metabolism of the mycotoxins citrinin (CIT) and dihydroergocristine (DHEC) was investigated. The specific reaction products are compared with metabolites produced by human and rat liver microsomes in vitro. Depending on the applied potential between 0 and 2000 mV vs. Pd/H2 by using a flow-through cell, CIT and DHEC are oxidized to various products. Besides dehydrogenation and dealkylation reactions, several hydroxylated DHEC and CIT species are produced by EC and Fenton-like reaction, separated and analyzed by LC-MS/MS and ESI-HRMS. Compared to reaction products from performed microsomal incubations, several mono- and dihydroxylated DHEC species were found to be similar to the reaction products of EC, Fenton-like reaction, and UV-induced oxidation. Consequentially, nonmicrosomal efficient and economic simulation techniques can be useful in early-stage metabolic studies, even if one-to-one simulation is not always feasible.

Identification and human pharmacokinetics of dihydroergotoxine metabolites in man: preliminary results.

Dihydroergotoxine is a mixture of semi-synthetic ergot alkaloids mainly used for age-related cognitive impairment. In this study, dihydroergotoxine (30 microM) was added to incubates of rat and bovine liver microsomes, and the resulting major metabolites were identified as hydroxy-dihydroergocornine, hydroxy-dihydroergocryptine and hydroxy-dihydroergocristine on the basis of molecular mass measurements, determined with a time-of-flight mass spectrometer. The relevance of these to humans was then investigated by simultaneously monitoring dihydroergotoxine and its hydroxy-metabolites in human plasma by LC-MS/MS after oral dosing of dihydroergotoxine mesylate (27 mg) to a healthy volunteer (male, age 45, height 1.93 m, weight 103 kg). In this preliminary approach, the peaks (C(max)) of dihydroergocornine, dihydroergocryptine and dihydroergocristine were about 0.04 microg/l. The peaks (C(max)) of their hydroxy-metabolites were 0.98, 0.53 and 0.30 microg/l, respectively. In conclusion, in this preliminary approach it was found that hydroxy-dihydroergocornine, hydroxy-dihydroergocryptine and hydroxy-dihydroergocristine were one order of magnitude higher in concentration than their parents in human plasma.

Pharmacokinetics of dihydroergocristine and its major metabolite 8'-hydroxy-dihydroergocristine in human plasma.

Dihydroergocristine (DHEC) is a semi-synthetic drug mainly used for age-related cognitive impairment. In this study, its major metabolite 8'-hydroxy-dihydroergocristine (8'-OH-DHEC) was produced in incubates of a bovine liver preparation using dihydroergocristine mesylate (DHECM) as substrate. Purification was achieved by flash silica gel column and reverse phase liquid chromatographies, and identification was based on accurate molecular mass measurements, mass fragmentation spectra and NMR ((1)H/(13)C) chemical shifts. By using the substance produced in vitro, a fast, sensitive, specific and robust LC/MS/MS method for the simultaneous determination of DHEC and its major metabolite in human plasma was developed and validated. Bromocriptine was used as internal standard and limits of quantification for DHEC and 8'-OH-DHEC were 10 pg/ml and 20 pg/ml, respectively. Pharmacokinetic parameters were investigated on 12 male healthy volunteers to whom a single dose of 18 mg DHECM was administered in tablets (Iskevert). The peak of DHEC was 0.28 +/- 0.22 microg/l, the t(max) 0.46 +/- 0.26 h, the AUC(last) 0.39 +/- 0.41 microg/l.h and the terminal elimination half-life 3.50 +/- 2.27 h. The peak of 8'-OH-DHEC was 5.63 +/- 3.34 microg/l, the t(max) 1.04 +/- 0.66 h, the AUC(last) 13.36 +/- 5.82 microg/l.h and the terminal elimination half-life 3.90 +/- 1.07 h. Dosing of 18 mg DHECM was well tolerated, causing no adverse events.

Spinal gabapentin and antinociception: mechanisms of action.

Spinal gabapentin has been known to show the antinociceptive effect. Although several assumptions have been suggested, mechanisms of action of gabapentin have not been clearly established. The present study was undertaken to examine the action mechanisms of gabapentin at the spinal level. Male SD rats were prepared for intrathecal catheterization. The effect of gabapentin was assessed in the formalin test. After pretreatment with many classes of drugs, changes of effect of gabapentin were examined. General behaviors were also observed. Intrathecal gabapentin produced a suppression of the phase 2 flinching, but not phase 1 in the formalin test. The antinociceptive action of intrathecal gabapentin was reversed by intrathecal NMDA, AMPA, D-serine, CGS 15943, atropine, and naloxone. No antagonism was seen following administration of bicuculline, saclofen, prazosin, yohimbine, mecamylamine, L-leucine, dihydroergocristine, or thapsigargin. Taken together, intrathecal gabapentin attenuated only the facilitated state. At the spinal level, NMDA receptor, AMPA receptor, nonstrychnine site of NMDA receptor, adenosine receptor, muscarinic receptor, and opioid receptor may be involved in the antinociception of gabapentin, but GABA receptor, L-amino acid transporter, adrenergic receptor, nicotinic receptor, serotonin receptor, or calcium may not be involved.

Spinal Gabapentin and Antinociception: Mechanisms of Action

Spinal gabapentin has been known to show the antinociceptive effect. Although several assumptions have been suggested, mechanisms of action of gabapentin have not been clearly established. The present study was undertaken to examine the action mechanisms of gabapentin at the spinal level. Male SD rats were prepared for intrathecal catheterization. The effect of gabapentin was assessed in the formalin test. After pretreatment with many classes of drugs, changes of effect of gabapentin were examined. General behaviors were also observed. Intrathecal gabapentin produced a suppression of the phase 2 flinching, but not phase 1 in the formalin test. The antinociceptive action of intrathecal gabapentin was reversed by intrathecal NMDA, AMPA, D-serine, CGS 15943, atropine, and naloxone. No antagonism was seen following administration of bicuculline, saclofen, prazosin, yohimbine, mecamylamine, L-leucine, dihydroergocristine, or thapsigargin. Taken together, intrathecal gabapentin attenuated only the facilitated state. At the spinal level, NMDA receptor, AMPA receptor, nonstrychnine site of NMDA receptor, adenosine receptor, muscarinic receptor, and opioid receptor may be involved in the antinociception of gabapentin, but GABA receptor, L-amino acid transporter, adrenergic receptor, nicotinic receptor, serotonin receptor, or calcium may not be involved.