Immobilization of microsomes into alginate beads is a convenient method for producing glucuronides from drugs

Use and engineering aspects of immobilized cells in biotechnology

A short review of the research in the past two years (1990-1991) on immobilized whole cells, such as microbial, plant, and animal cells, is presented including a discussion from an engineering point of view. Recent works concerning the intraparticle mass transfer effect on immobilized microbial cells by the authors and their co-workers are also introduced. Finally, future prospects of the immobilized cell system will be discussed.

The covalent immobilization of microsomal uridine diphospho-glucuronosyltransferase (UDPGT): initial synthesis and characterization of an UDPGT immobilized enzyme reactor for the on-line study of glucuronidation

The microsomal fraction of rat liver containing uridine diphospho-glucuronosyltransferase (UDPGT; EC 2.4.1.17) has been covalently immobilized on a high performance chromatographic support. In this study Nucleosil Si-500 silica was converted into diol-bonded silica and subsequently converted into an aldehyde form through oxidation with sodium periodate. The microsomal fraction was immobilized via Schiff base formation followed by reduction with sodium cyanoborohydride. The resulting immobilized enzyme reactor (IMER) was placed in a multi-dimensional chromatographic system which utilized a mixed mode (C18 and anion exchange) column to trap the parent compound and glucuronide and a C18 column to separate the substrate and product. The IMER system was used for the online glucuronidation of 4-methylumbelliferone (4Me7OHC) and acetaminophen (APAP). The Michaelis-Menten kinetic parameters (Km and Vmax) associated with the formation of 4Me7OHC and APAP glucuronides demonstrated that the immobilization had not significantly affected the enzymatic activity of the UDPGT relative to the non-immobilized enzyme. The IMER retained enzymatic activity for more than 6 weeks. The results of this study demonstrate an easy and convenient way to identify compounds which may be glucuronidated and to synthesize and characterize the resulting products.

Plant Glycosyltransferases: Their Potential as Novel Biocatalysts

The potential application of glycosyltransferases in glycoconjugate synthesis has attracted considerable interest from the biotechnology community in recent years. This concept article focuses on the current understanding of the chemistry of a family of plant enzymes capable of glycosylating small lipophilic molecules. These enzymes are discussed in terms of their regio- and enantioselective substrate recognition, sugar-donor selectivity and their utility as biocatalysts in whole-cell systems.

Use of a plant-derived enzyme template for the production of the green-note volatile hexanal

Hexanal is a key organoleptic element of green-note that is found in both fragrances and flavors. We report a novel process for the production of hexanal using immobilized enzyme templates extracted from different plant sources in combination with hollow-fiber ultrafiltration for in situ separation. Enzyme templates, known to be responsible for the synthesis of hexanal from linoleic acid (18:2), were isolated from naturally enriched tissues including carnation petals, strawberry and tomato leaves. These templates were immobilized in an alginate matrix and used as a biocatalyst in a packed-bed bioreactor. Continuous product recovery was achieved using a hollow-fiber ultrafiltration unit. The effects of pH, reaction temperature, and substrate and enzyme concentrations were studied and their effects on hexanal generation identified and optimized. Utilizing optimized conditions, hexanal production 112-fold higher than endogenous steady-state levels in a corresponding amount of plant tissue could be achieved over a 30-minute period. Based on the reactor studies, product inhibition also appears to be an important factor for bioreactor-based hexanal production.

Synthesis of acylglucuronides of drugs using immobilized dog liver microsomes octadecylsilica particles coated with phospholipid

Immobilized dog liver microsome octadecylsilica (ODS) particles coated with phospholipid were developed for the synthesis of acylglucuronides of drugs. The phospholipid-coated ODS particles were readily prepared by stirring a solution containing L-alpha-dipalmitoylphosphatidylcholine with the ODS particles, in which the phospholipid was absorbed on the ODS surfaces by hydrophobic interaction between the acyl group of phospholipid and the otcadecyl group of the ODS particles. Similarly, the microsome-immobilized particles were readily prepared by stirring a buffer solution containing dog liver microsomes with the phospholipid-coated ODS particles, in which the microsomes were immobilized on the phospholipid-coated ODS particles by hydrophobic binding. The microsome-immobilized particles exhibited UDP-glucuronosyltransferase activity which catalyzed the glucuronidation of ketoprofen and a nonpeptide endothelin receptor antagonist, S-1255 ([R]-[+]-2-[benzo(1,3)dioxol-5-yl]-6-isopropyl-4-[4-methoxyphenyl]-2H-chromene-3-carboxylic acid), to the corresponding acylglucuronide in the presence of uridine 5(')-diphosphate (UDP)-glucuronic acid, and two acylglucuronides of ketoprofen and S-1255 were synthesized using the microsome-immobilized particles. These acylglucuronides were synthesized by simply shaking the microsome-immobilized particles adsorbed on the substrate in a buffer solution containing UDP-glucuronic acid with a thermostated mixer. The molecular weights and chemical structures of the synthesized acylglucuronides were identified by mass spectrometry and nuclear magnetic resonance, respectively. The productivity of S-1255 acylglucuronide using microsome-immobilized particles was approximately threefold higher than that observed with free microsomes, whereas the ketoprofen acylglucuronide productivity was slightly lower than that observed with free microsomes. The present method should be very useful for the synthesis of acylglucuronides of drugs, which are slightly soluble aqueous solutions in the drug development stage.

An enzymatic synthesis of glucuronides of azetidinone-based cholesterol absorption inhibitors

Two derivatives, 1 and 3, of a novel cholesterol absorption inhibitor, Sch 58235, were glucuronidated with the help of glucuronyl transferases derived from bovine and dog liver microsomes. An efficient procedure for the iodination of 4 was developed on an analytical scale to be used for the preparation of a 125I-labeled radioactive glucuronide 5.

Glycation of human serum albumin by acylglucuronides of nonsteroidal anti-inflammatory drugs of the series of phenylpropionates

The covalent binding to human serum albumin (HSA), of acylglucuronides from carboxylic nonsteroidal anti-inflammatory drugs (NSAIDs) was investigated. The adduct formation was followed and quantitated by HPLC and by radiometric detection. Three types of albumin adducts were evidenced. The acylglucuronide or the drug itself was bound to 0.2 up to 9% of the albumin molecules, depending on the drug, whereas the majority of adducts (23-49% of albumin molecules) retained the glucuronic acid moiety. The possible involvement of specific Lys located in site I of albumin in the formation of these main adducts was demonstrated, using a series of HSA whose specific Lys residues have been modified chemically. This study shows that acylglucuronides from NSAIDs can significantly contribute to the glycation of proteins, such as albumin.

Enzymatic glucuronidation of a novel cholesterol absorption inhibitor, Sch 58235

A glucuronide of a novel cholesterol absorption inhibitor was synthesized on a 200-mg scale in one step via bovine liver glucuronyltransferase-catalyzed coupling of the glucuronyl moiety of UDP-glucuronic acid with the phenolic hydroxyl of Sch 58235. It was shown that the product yield is limited by the hydrolysis of UDP-glucuronic acid by impurities present in the commercial microsomal preparation of the transferase. This detrimental effect of UDPGluA hydrolysis could be diminished by the presence of high concentration of glucuronlytransferase. Optimization of reaction conditions and purification procedure resulted in a process that proceeded with 95% conversion and 88% isolated product yield. The 13C6-glucuronide of Sch 58235 was prepared with the help of a cascade of eight enzymes operating concurrently in one pot.

Stereoselective binding of the glucuronide of ketoprofen enantiomers to human serum albumin

Since acyl glucuronides are known to undergo deconjugation, especially in the presence of human serum albumin (HSA), only a few reports have described their reversible binding to plasma proteins. The aim of this study was to investigate the reversible binding of R and S ketoprofen glucuronides to HSA by a rapid technique, such as ultraviolet circular dichroism. Binding of R ketoprofen glucuronide only induced an extrinsic Cotton effect at 340 nm. Scatchard plot analysis revealed that R ketoprofen and its glucuronide are bound to one site of albumin with an association constant of 28.1 x 10(4) and 6.1 x 10(4) M-1, respectively. Modification of one tyrosine residue by diisopropylfluorophosphate prevented the access of ligands to sites I and II of albumin, and also fully inhibited the binding of R ketoprofen and that of its conjugate. Displacement experiments with specific probes of albumin binding sites suggested that R ketoprofen and the glucuronide are bound to site II rather than site I. However, R ketoprofen was not displaced by its conjugate. S ketoprofen glucuronide is also bound to HSA, since it decreased the binding of the antipode conjugate. However, the binding of this metabolite to albumin did not induce an extrinsic Cotton effect large enough to determine the binding constants. D-Glucuronic acid did not bind to sites I or II of albumin. This moiety is likely responsible for the lower affinity of HSA for the R ketoprofen glucuronide when compared to that for R ketoprofen, due to the hydrophilicity and/or the bulkiness of this group.

High-performance liquid chromatographic enantioselective assay for the measurement of ketoprofen glucuronidation by liver microsomes

A stereoselective high-performance liquid chromatographic (HPLC) method was developed to study the in vitro glucuronidation of ketoprofen enantiomers by liver microsomes. The HPLC system consisted of a Superspher 100 RP 18 end-capped column eluted with a mixture of acetonitrile and 10 mM tetrabutylammonium bromide in 1 mM potassium phosphate adjusted to pH 4.3 (30:70, v/v). Ultraviolet detection was performed at a wavelength of 254 nm. The capacity factors of S-ketoprofen glucuronide, R-ketoprofen glucuronide and R,S-ketoprofen were 12.8, 14.5 and 18.1, respectively. Sample pretreatment consisted of protein precipitation in microsomal incubation suspensions and further purification on a Sep Pak C18 cartridge before injection onto the HPLC system. Quantitation was performed with standard glucuronides biosynthetized with immobilized microsomes and purified by semi-preparative HPLC. The linearity of the method between 1.25 and 25.0 micrograms ml-1 (coefficient of correlation greater than 0.999), the repeatability (coefficient of variation = 1.2%; n = 5), and recovery (within 85%) were tested. The limit of detection was 10 ng for each glucuronide injected. The in vitro glucuronidation of R- and S-ketoprofen was measured in liver microsomes from man and from various animal species (dog, rat, rabbit). For both enantiomers, dog presented the highest specific activity. In contrast, the lowest activity was found in rabbit. On the other hand, the formation ratio of the S- and R-glucuronides of ketoprofen was close to 1 in man, rat and rabbit, but was 4.5 in dog, thus indicating that the reaction was stereoselective in this species.