Simulation of human xenobiotic metabolism in microorganisms. Yeast a good compromise between E. coli and human cells

Dimerization of kringle 1 domain from hepatocyte growth factor/scatter factor provides a potent MET receptor agonist

We designed and characterized a potent full MET receptor agonist consisting of two recombinantly linked HGF/SF kringle 1 domains and demonstrated its potential in epithelial tissue regeneration.

Hepatocyte growth factor/scatter factor (HGF/SF) and its cognate receptor MET play several essential roles in embryogenesis and regeneration in postnatal life of epithelial organs such as the liver, kidney, lung, and pancreas, prompting a strong interest in harnessing HGF/SF-MET signalling for regeneration of epithelial organs after acute or chronic damage. The limited stability and tissue diffusion of native HGF/SF, however, which reflect the tightly controlled, local mechanism of action of the morphogen, have led to a major search of HGF/SF mimics for therapy. In this work, we describe the rational design, production, and characterization of K1K1, a novel minimal MET agonist consisting of two copies of the kringle 1 domain of HGF/SF in tandem orientation. K1K1 is highly stable and displays biological activities equivalent or superior to native HGF/SF in a variety of in vitro assay systems and in a mouse model of liver disease. These data suggest that this engineered ligand may find wide applications in acute and chronic diseases of the liver and other epithelial organs dependent of MET activation.

Comparison of microbial hosts and expression systems for mammalian CYP1A1 catalysis

Mammalian cytochrome P450 enzymes are of special interest as biocatalysts for fine chemical and drug metabolite synthesis. In this study, the potential of different recombinant microorganisms expressing rat and human cyp1a1 genes is evaluated for such applications. The maximum specific activity for 7-ethoxyresorufin O-deethylation and gene expression levels were used as parameters to judge biocatalyst performance. Under comparable conditions, E. coli is shown to be superior over the use of S. cerevisiae and P. putida as hosts for biocatalysis. Of all tested E. coli strains, E. coli DH5α and E. coli JM101 harboring rat CYP1A1 showed the highest activities (0.43 and 0.42 U g⁻¹(CDW), respectively). Detection of active CYP1A1 in cell-free E. coli extracts was found to be difficult and only for E. coli DH5α, expression levels could be determined (41 nmol g⁻¹(CDW)). The presented results show that efficient expression of mammalian cyp1a1 genes in recombinant microorganisms is troublesome and host-dependent and that enhancing expression levels is crucial in order to obtain more efficient biocatalysts. Specific activities currently obtained are not sufficient yet for fine chemical production, but are sufficient for preparative-scale drug metabolite synthesis.

Extending the capabilities of nature's most versatile catalysts: directed evolution of mammalian xenobiotic-metabolizing P450s

Cytochrome P450 enzymes are amongst the most versatile enzymatic catalysts known. The ability to introduce a single atom of oxygen into an organic substrate has led to the diversification and exploitation of these enzymes throughout nature. Nowhere is this versatility more apparent than in the mammalian liver, where P450 monooxygenases catalyze the metabolic clearance of innumerate drugs and other environmental chemicals. In addition to the aromatic and aliphatic hydroxylations, N- and O-dealkylations, and heteroatom oxidations that are common in drug metabolism, many more unusual reactions catalyzed by P450s have been discovered, including reductions, group transfers and other biotransformations not typically associated with monooxygenases. A research area that shows great potential for development over the next few decades is the directed evolution of P450s as biocatalysts. Mammalian xenobiotic-metabolizing P450s are especially well suited to such protein engineering due to their ability to interact with relatively wide ranges of substrates with marked differences in structure and physicochemical properties. Typical characteristics, such as the low turnover rates and poor coupling seen during the metabolism of xenobiotics, as well as the enzyme specificity towards particular substrates and reactions, can be improved by directed evolution. This mini-review will cover the fundamental enabling technologies required to successfully engineer P450s, examine the work done to date on the directed evolution of mammalian forms, and provide a perspective on what will be required for the successful implementation of engineered enzymes.

Recombinant Production of Human Microsomal Cytochrome P450 2D6 in the Methylotrophic Yeast Pichia pastoris

Microsomal cytochrome P450 monooxygenases of groups 1-3 are mainly expressed in the liver and play a crucial role in phase 1 reactions of xenobiotic metabolism. The cDNAs encoding human CYP2D6 and human NADPH-P450 oxidoreductase (CPR) were transformed into the methylotrophic yeast Pichia pastoris and expressed with control of the methanol-inducible AOX1 promoter. The determined molecular weights of the recombinant CYP2D6 and CPR closely matched the calculated values of 55.8 and 76.6 kDa. CPR activity was detected by conversion of cytochrome c by using isolated microsomes. Nearly all of the recombinant CYP was composed of the active holoenzyme, as confirmed by reduced CO difference spectra, which showed a single peak at 450 nm. Only by coexpression of human CPR and CYP was CYP2D6 activity obtained. Microsomes containing human CPR and CYP2D6 converted different substrates, such as 3-cyano-7-ethoxycoumarin, parathion and dextrometorphan. The kinetic parameters of dextrometorphan conversion closely matched those of CYP2D6 from other recombinant expression systems and human microsomes. The endogenous NADPH-P450 oxidoreductase of Pichia pastoris seems to be incompatible with human CYP2D6, as expression of CYP2D6 without human CPR did not result in any CYP activity. These recombinant strains provide a novel, easy-to-handle and cheap source for the biochemical characterisation of single microsomal cytochromes, as well as their allelic variants.

Eicosapentaenoic Acid Suppresses Basal and Insulin-Stimulated Endothelin-1 Production in Human Endothelial Cells

cis-Polyunsaturated fatty acids such as eicosapentaenoic acid (EPA) are the major fatty acids contained in fish oil, and are known to affect the various physiological properties of cell membranes in humans. The present study investigated the effects of polyunsaturated fatty acids on endothelin-1 (ET-1) production in human umbilical vein endothelial cells (HUVECs) and on insulin activity. After addition of various concentrations of EPA, docosahexaenoic acid, arachidonic acid, or linoleic acid to a culture medium, the concentration of ET-1 was measured using ELISA, and that of ET-1 mRNA was determined by RT-PCR. The results showed that EPA had the strongest inhibitory effect (p<0.05) on both basal ET-1 production and ET-1 mRNA levels. In addition, insulin (1 micromol/l) markedly increased ET-1 production, and EPA also significantly decreased the effect induced by insulin. Pretreatment with Ca2+ chelator EGTA (1 mmol/l), NOS inhibitor L-NAME (300 micromol/l), or calmodulin antagonist W-7 (300 micromol/l) inhibited NO production by EPA (100 micromol/l), but these pretreatments had no effect on ET-1 production by EPA. These findings suggest that EPA reduces basal and insulin-enhanced ET-1 production by inhibiting ET-1 mRNA production. These effects of EPA may contribute to its vasorelaxant and anti-atherosclerotic effects.

The 'biodrug' concept: an innovative approach to therapy

Cell engineering technology using recombinant microorganisms has created new opportunities in the development of innovative drugs. This article presents the use of living genetically engineered microorganisms, such as bacteria or yeasts, as a new delivery vehicle to the gastrointestinal tract. This 'biodrug' concept was demonstrated using recombinant Saccharomyces cerevisiae expressing the plant cytochrome P450 73A1. This enzyme provides a relevant model for potential therapeutic applications, such as 'biodetoxication' in the digestive environment. An artificial gastrointestinal tract simulating human digestion was chosen as a powerful tool to validate the biodrug concept. This approach offers a novel strategy for drug discovery and testing.

High efficiency family shuffling based on multi-step PCR and in vivo DNA recombination in yeast: statistical and functional analysis of a combinatorial library between human cytochrome P450 1A1 and 1A2

The design of a family shuffling strategy (CLERY: Combinatorial Libraries Enhanced by Recombination in Yeast) associating PCR-based and in vivo recombination and expression in yeast is described. This strategy was tested using human cytochrome P450 CYP1A1 and CYP1A2 as templates, which share 74% nucleotide sequence identity. Construction of highly shuffled libraries of mosaic structures and reduction of parental gene contamination were two major goals. Library characterization involved multiprobe hybridization on DNA macro-arrays. The statistical analysis of randomly selected clones revealed a high proportion of chimeric genes (86%) and a homogeneous representation of the parental contribution among the sequences (55.8 +/- 2.5% for parental sequence 1A2). A microtiter plate screening system was designed to achieve colorimetric detection of polycyclic hydrocarbon hydroxylation by transformed yeast cells. Full sequences of five randomly picked and five functionally selected clones were analyzed. Results confirmed the shuffling efficiency and allowed calculation of the average length of sequence exchange and mutation rates. The efficient and statistically representative generation of mosaic structures by this type of family shuffling in a yeast expression system constitutes a novel and promising tool for structure-function studies and tuning enzymatic activities of multicomponent eucaryote complexes involving non-soluble enzymes.

Drug-induced liver diseases

Drug-induced liver injuries make up a persisting and challenging problem for physicians, health agencies and pharmaceutical firms. The clinical expression is polymorphous, acute hepatitis being predominant. The diagnosis is frequently difficult because of the absence of specific signs in most cases and mainly relies on the exclusion of other causes. The diagnosis should be particularly evoked in patients over 50 yr who are taking many drugs, after viral infections have been ruled out. Acute hepatocellular hepatitis is particularly severe because of the risk of fulminant hepatitis or of a more insidious course leading to cirrhosis. Cross hepatotoxicity can sometimes occur. One should avoid re-administration of not only the causative agents but also of other drugs belonging to the same family or having a related chemical structure. The prediction of the hepatotoxicity of new drugs must be improved. Investigations would be particularly useful for drugs having critical chemical structures and belonging to families with an established history of hepatotoxicity.