In vitroidentification of the cytochrome P450 isoform responsible for the metabolism of a-dihydroergocryptine

Abstract

1. The in vitro metabolism of alpha-dihydroergocryptine (DHEC, Almirid), an ergot-derived dopamine agonist for the treatment of Parkinson's disease, has been studied in cultured cell lines following incubation with DHEC. Human hepatocytes as well as two sets of metabolically competent cell lines expressing one single human cytochrome P450 (1A1, 1A2, 1B1, 2A6, 2C8, 2C9, 2C18, 2C19, 2D6, 2E1, 3A4) were used. 2. Mono- and dihydroxy metabolites of DHEC could only be detected in the culture media of the cell line expressing human cytochrome CYP3A4. The same metabolites were found in the media of cultured human hepatocytes derived from three different donors. After 24-h incubation with 1 microM DHEC, approximately 60% mono- and approximately 20% dihydroxy metabolites were detected, i.e. approximately 80% of DHEC was metabolized. Further, DHEC demonstrated an inhibitory effect on CYP3A4-mediated testosterone metabolism and additionally could induce CYP3A4 and CYP2E1 mRNA when added at 10 microM to cultured human hepatocytes. 3. The data suggest that DHEC metabolism in humans is primarily mediated by the CYP3A4 isoform. The results are in accordance with findings derived from other ergot alkaloids.

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

“…A third even more hydrophilic metabolite was formed in a substrate-dependent rate (M3/DHEN; M6/DHEP), being formed fastest in the DHEN incubate ( Figure 2). As these reactions might be biocatalysed by the same cytochrome P450 isoform (3A4 [17][18][19]), k m differences could possibly explain these results. As oxygenations and hydrolysis were largely favored in the in vitro conditions used, the characterization of metabolites based on the elemental composition focused on the empirical formula containing either the same number or fewer C atoms than the parent compounds (Table 1).…”

Determination of dihydroergocryptine in human plasma and urine samples using on-line sample extraction?column-switching reversed-phase liquid chromatography?mass spectrometry

“…[30]. Previous investigations in our laboratory [15] took advantage from SPE "on-line"-coupled to HPLC, a procedure described for the first time in 1981 [33], using so-called biocompatible cartridge systems, such as BioTrap TM pre-column materials. For this reason, there was no question to exploit the potential of this powerful and time-saving technique during the course of the present investigations.…”

“…The fact that ergot alkaloids possess different amine functions requires the use of buffered mobile phase systems and performed by either isocratic elution [6,8,14,[24][25][26][28][29][30] or in the gradient mode [1,[7][8][9]13,15,16,25] on C 18 and C 8 columns. In some applications acetonitrile-10 mM ammonium carbonate mixtures [1,9,13,24,25,28] were used but except Ref.…”

“…It has been shown in the past that bromocriptine and other derivatives of the ergot alkaloid family undergo biotransformation by action of cytochrome oxidase P450 3A4 (CYP3A4) [1,13,14]. Recently a paper reporting on in-vitro identification of the cytochrome P450 isoforms responsible for the metabolism of dihydroergocryptine was published [15]. Although both DHEC and bromocriptine are inhibitors of CYP3A4 themselves [15,16] bioavailability of DHEC was nevertheless markedly increased by co-administration of erythromycin, a macrolide antibiotic, which acts as a strong CYP3A4 inhibitor [17].…”

“…However, liquid chromatographic procedures, coupled to mass spectroscopic detection (MSD), provide some crucial advantages, in particular with concern to specificity. Indeed, high performance liquid chromatographic methods [1,[6][7][8][9]13,[15][16][17][24][25][26][27][28][29][30] prevail in analytical investigations of ergot alkaloids targeted either to get more precise insight into the metabolic pattern or to obtain thorough information of their concentrations in a biological environment, such as, e.g., serum or plasma, urine, tissue, etc. Among them three methods apply the selective "on-line" LC-MS hyphenation [13,15,17] allowing direct and unequivocal structural assignment of the compounds of interest even in those cases where co-elution of two or more species occurs provided ionization energy is not quantitatively consumed by the interfering ones.…”