Metabolism of dihydroergotamine by a cytochrome P-450 similar to that involved in the metabolism of macrolide antibiotics

Abstract

1. Previous studies have shown that the macrolide antibiotics, such as oleandomycin and erythromycin, enhance their own transformation into a stable metabolite-cytochrome P-450 complex, thus impairing monooxygenase activity. This cytochrome P-450 induced by macrolides is similar to the major form induced in rats by pregnenolone-16 alpha-carbonitrile (PCN) (III A1 isozyme). 2. The cytochrome P-450 isozyme induced in rats by PCN or macrolide antibiotics bound dihydroergotamine (DHE) with high affinity and was also capable of metabolizing the drug. However, phenobarbital administration enhanced the metabolism of DHE to a greater extent than would be expected from the levels of the PB-PCNE isoenzyme, indicating that other cytochrome P-450 proteins may also be involved in DHE metabolism. 3. DHE metabolism was inhibited by macrolide antibiotics both ex vivo and in vitro. The metabolite-cytochrome P-450 complex formed by the antibiotics impairs the metabolism of DHE, so that when the complex is dissociated the metabolic activity is restored. These findings explain the observed clinical interactions between macrolides and other drugs, and such an approach may prove useful in their prediction.

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

“…Although in terms of sensitivity, enzymatic and radioimmunological techniques, such as, e.g., EIA [17,23] and RIA [9,[17][18][19][20][21][22] provide excellent sensitivity with limits of quantitation spanning the range from the lower ng/ml to lower pg/ml level, they very often are lacking specificity. As a consequence, more or less marked cross-reactions have to be taken into account but nevertheless "group" determinations may be accomplished.…”

“…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.…”

“…Hitherto available data from structurally-related compounds imply involvement of the cytochrome P450 system in the oxidative pathway when passing the liver [1,9]. This family of oxidizing enzymes composes of several isoforms with different substrate specificities [10] and is mainly responsible for the metabolism of a vast number of drugs [11,12].…”

“…For this reason, either radioimmunological methods (radioimmunoassay, RIA) [9,[17][18][19][20][21][22] and enzyme immunoassays (EIA) [17,23] have been preferentially used in the past. However, liquid chromatographic procedures, coupled to mass spectroscopic detection (MSD), provide some crucial advantages, in particular with concern to specificity.…”

“…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.…”