Progesterone biotransformation by human P4503A4 in yeast

Use of human microsomes and deuterated substrates: an alternative approach for the identification of novel metabolites of ketamine by mass spectrometry

In vitro biosynthesis using pooled human liver microsomes was applied to help identify in vivo metabolites of ketamine by liquid chromatography (LC)-tandem mass spectrometry. Microsomal synthesis produced dehydronorketamine, seven structural isomers of hydroxynorketamine, and at least five structural isomers of hydroxyketamine. To aid identification, stable isotopes of the metabolites were also produced from tetra-deuterated isotopes of ketamine or norketamine as substrates. Five metabolites (three hydroxynorketamine and two hydroxyketamine isomers) gave chromatographically resolved components with product ion spectra indicating the presence of a phenolic group, with phenolic metabolites being further substantiated by selective liquid-liquid extraction after adjustments to the pH. Two glucuronide conjugates of hydroxynorketamine were also identified. Analysis by LC-coupled ion cyclotron resonance mass spectrometry gave unique masses in accordance with the predicted elemental composition. The metabolites, including the phenols, were subsequently confirmed to be present in urine of subjects after oral ketamine administration, as facilitated by the addition of deuterated metabolites generated from the in vitro biosynthesis. To our knowledge, phenolic metabolites of ketamine, including an intact glucuronide conjugate, are here reported for the first time. The use of biologically synthesized deuterated material as an internal chromatographic and mass spectrometric marker is a viable approach to aid in the identification of metabolites. Metabolites that have particular diagnostic value can be selected as candidates for chemical synthesis of standards.

Biotechnological Approach to the Synthesis of 9α‐Hydroxylated Steroids

The steroid 9alpha-hydroxylase gene has been cloned from Mycobacterium smegmatis into Escherichia coli BL21. Progesterone added to bioreactors was subjected to in vivo transformation into 9alpha-hydroxyprogesterone. In 7 days, 43.6 mg 9alpha-hydroxyprogesterone was formed from 53.8 mg/L progesterone. The enzyme also has shown evidence of processing 4-androstene-3,17-dione in vivo. An extensive analytical method development, including LLE, HPLC-DAD, MS, and NMR was performed to verify the product and to enable a quantitative analysis. Protocols for analytical and preparative separation have been developed, using binaphtol as internal standard. Both the growth pattern and the bioconversion rate were unaffected by the presence of binaphtol in the bioreactor. The enzyme was purified by immobilised metal affinity and ion exchange chromatography, resulting in low in vitro activity.

Cytochrome P450 3A4 mediated metabolism of 2,4-dichlorophenol

The metabolism of the environmental pollutant and hepatocarcinogen 2,4-dichlorophenol (2,4-DCP) was studied using microsomal fractions and whole-cells of Saccharomyces cerevisiae containing human cytochrome P450 3A4. 2,4-DCP exhibited a typical type I substrate binding spectrum with a K, of 75 microM. 2,4-DCP was metabolised into two major metabolites identified as 2-chloro-1,4-hydroxyquinone and 2-chloro-1,4-benzoquinone in microsomal fractions and whole cells of yeast expressing human cytochrome P450 3A4. A further metabolite, 1,2,4-hydroxybenzene, was also detected during biotransformation by whole cells, but was not observed in microsomal fractions. 2,4-DCP metabolism was dependent on NADPH in microsomal fractions and no activity was observed in microsomal fractions or whole cells of control transformants. Metabolites were identified by TLC followed by GC-MS.

Human cytochrome P450 3A4 is involved in the biotransformation of the herbicide 2,4-dichlorophenoxyacetic acid

2,4-Dichlorophenoxyacetic acid (2,4-D) is one of the most frequently used herbicides and is an environmental pollutant. Evidence exists that 2,4-D exposure results in an increased risk for certain malignant disorders such as nasal carcinoma and soft tissue sarcoma in humans and animals. The involvement of cytochrome P450 3A4 (CYP3A4), the major form of monooxygenase enzyme in human liver, in the metabolism of 2,4-D was studied using microsomal fractions and whole cells of Saccharomyces cerevisiae expressing cytochrome P450 3A4. 2,4-Dichlorophenol (2,4-DCP) was identified as the only product of metabolism by TLC followed by NMR and IR spectroscopy and a turnover of 0.13 nmol 2,4-DCP/min/nmol P450 was observed.

Metabolism of organochlorine pesticides: the role of human cytochrome P450 3A4

Organochlorine compounds are widely used as pesticides and are substantial environmental pollutants and carcinogens due to their extensive environmental release. In the present study biotransformation of these pesticides was observed in the microsomal fractions and whole cells of Saccharomyces cerevisiae expressing human cytochrome P450 3A4. In both in vitro and in vivo studies, hexachlorobenzene and pentachlorobenzene were metabolised into pentachlorophenol which was further transformed into tetrachlorohydroquinone. Metabolites were identified by thin layer chromatography and 13C-NMR spectroscopy. The formation of products was observed only in the presence NADPH in microsomal fractions and no activity was observed in control microsomal fractions, or in whole cells.

Metabolism of the herbicide chlortoluron by human cytochrome P450 3A4

Studies were carried out to investigate the metabolism of herbicide chlortoluron in the microsomal fractions and whole cells of Saccharomyces cerevisiae expressing human cytochrome P450 3A4. Both whole cells and microsomal fractions of yeast expressing human cytochrome P450 3A4 exhibited a typical dithionite-reduced, CO-difference absorbance spectrum with maximum absorbance at 448 nm. Chlortoluron produced a type I binding spectrum with cytochrome P450 3A4 with a Ks value of 200 microM. Chlortoluron was metabolised into four metabolites; hydroxylated-N-monodemethylated, hydroxylated ring methylated, N-didemethylated and N-monodemethylated products. Chlortoluron metabolism was absolutely dependent on NADPH and no metabolism was observed in control transformants.