Human Plasma Esterase Research Articles

Modulation of the Activity of Human Plasma Esterases by Binary and Ternary Mixtures of Water Miscible Organic Solvents during In Vitro Drug Metabolism Studies

Modulation of the Activity of Human Plasma Esterases by Binary and Ternary Mixtures of Water Miscible Organic Solvents during In Vitro Drug Metabolism Studies

Studies on phytoenzymes as mimics of mammalian drug metabolising enzymes

Drug metabolism and pharmacokinetics is an integral part of the drug discovery and development process. The pharmacokinetic (absorption, distribution, metabolism and excretion) properties of a drug allow the drug development scientist to understand the safety and efficacy data required for regulatory approval. Further, the knowledge of mammalian enzymes involved in the metabolism of a new chemical entity is of prime importance. In this regard, plant metabolism of organic compounds is similar to the mammalian metabolism in terms of the processes for detoxification of contaminants, the specific enzymatic pathways, the structure of the enzymes involved and the removal of the compounds from the susceptible organelles. In our studies, we isolated phytoenzymes (esterases and glutathione-S-transferases, GSTs) from plant cells and investigated their applicability as tools for drug metabolism studies. A total of 32 plants were screened for esterases activity and 14 plants for GSTs activity. In case of esterases, the activity was compared to human plasma esterases and also the effect of esterase inhibitor on the activity was studied. Overall, the presence of phytoenzymes and their catalytic similarities to the mammalian drug metabolising enzymes suggest that plants can be potential models for mammalian drug metabolism. Further, phytoenzymes can be considered as a potential surrogate for reducing the number of animals utilized in the drug discovery process.

Contribution of human esterases to the metabolism of selected drugs of abuse

Human esterases such as the human carboxylesterases (hCES) are important for the catalytic ester hydrolysis of xenobiotics and they play an important role in the detoxification of drugs (e.g., cocaine) but also in the activation of prodrugs (e.g., ramipril). Therefore, the aim of the presented study was to characterize the enzyme-catalyzed ester hydrolysis of ten drugs (cocaine, dimethocaine, ethylphenidate, 4-fluoro-3α-tropacocaine, 4-fluoro-3β-tropacocaine, heroin, methylphenidate, mitragynine, ramipril, and thebacon) by different esterase-containing systems (recombinant hCES1b, hCES1c, and hCES2, pooled human liver microsomes, pooled human liver S9 fraction, and pooled human plasma). Michaelis–Menten kinetic studies were done using in vitro incubations with the aforementioned enzyme-containing systems and LC coupled to ion trap MS for analysis. Ramipril and heroin were used as known model substrates to ensure reliable incubation conditions. The hydrolysis reactions followed classic Michaelis–Menten kinetics with exception of cocaine and 4-fluoro-3α-tropacocaine, for which hydrolysis rate was too low for reliable modeling. The substrates were mainly metabolized by the following enzymes systems: cocaine, hCES1c; dimethocaine, human plasma esterases; ethylphenidate, hCES1c; 4-fluoro-3β-tropacocaine, human plasma esterases; heroin, hCES2; methylphenidate, hCES1c; mitragynine, hCES1c; ramipril, hCES1b; thebacon, hCES2. Compounds bearing a small alcohol part and a larger acyl part showed higher affinity to hCES1 while those with a large alcohol part showed higher affinity to hCES2. The collected data are important for prediction of drug–drug or drug–food interactions as well as for individual variations in metabolism of drugs of abuse due to enzyme polymorphisms.

Anandamide and its congeners inhibit human plasma butyrylcholinesterase. Possible new roles for these endocannabinoids?

Butyrylcholinesterase (BChE), a serine hydrolase biochemically related to the cholinergic enzyme Acetylcholinesterase (AChE), is found in many mammalian tissues, such as serum and central nervous system, but its physiological role is still unclear. BChE is an important human plasma esterase, where it has detoxifying roles. Furthermore, recent studies suggest that brain BChE can have a role in Alzheimer’s disease (AD). The endocannabinoid arachidonoylethanolamide (anandamide) and other acylethanolamides (NAEs) are almost ubiquitary molecules and are physiologically present in many tissues, including blood and brain, where they show neuroprotective and anti-inflammatory properties. This paper demonstrates that they are uncompetitive (oleoylethanolamide and palmitoylethanolamide) or non competitive (anandamide) inhibitors of BChE (Ki in the range 1.32–7.48 nM). On the contrary, NAEs are ineffective on AChE kinetic features. On the basis of the X-ray crystallographic structure of human BChE, and by using flexible docking procedures, an hypothesis on the NAE-BChE interaction is formulated by molecular modeling studies. Our results suggest that anandamide and the other acylethanolamides studied could have a role in the modulation of the physiological actions of BChE.

Stability of cucurbitacin E in human plasma: chemical hydrolysis and role of plasma esterases

It was shown previously that the anticancerous cytotoxic oxygenated triterpenes, cucurbitacin E (Cuc E) and its deacetylated form, cucurbitacin I (Cuc I), interacted differently with human serum albumin. In this study, the biochemical stability of Cuc E was investigated in vitro by reverse-phase high performance liquid chromatography. The hydrolysis rate in acidic and alkaline solutions, and in enzymatic conditions in human plasma and in purified plasma esterase solutions of butyrylcholinesterase and albumin, was compared with that measured in phosphate buffer saline (pH 7.4). Cuc E hydrolysis was detected in all the in vitro tests, but the extent of hydrolysis varied according to the different enzymatic and non-enzymatic conditions. A remarkable rapid hydrolysis of Cuc E was detected in acidic and alkaline solutions. A significant rate of hydrolysis of Cuc E was monitored in human plasma and was associated with the detection of Cuc I. The stability of Cuc E was greatly enhanced in the presence of albumin. However, purified butyrylcholinesterase had no effect on Cuc E stability. Among specific inhibitors of plasma esterases, only EDTA increased Cuc E stability, suggesting that paraoxonase is the human plasma esterase involved in the hydrolysis of Cuc E.

Liposomes loaded with lipophilic prodrugs of methotrexate and melphalan as convenient drug delivery vehicles

Abstract Liposomal formulations prepared by extrusion from natural phospholipids and 1,2-dioleoylglycerol conjugates of methotrexate and melphalan (egg phosphatidylcholine-phosphatidylinositol–prodrug, 8:1:1, by mol.) were characterized by size, composition and stability. Both prodrugs were shown to incorporate completely into unilamellar liposomes with the mean size below 100 nm and form stable dispersions containing the drug concentrations relevant for systemic injections in animals. For long-term storage, the dispersions can be subjected to deep freezing (- 196 °C) and stored at - 70 °C; before usage, they should be defrosted and treated shortly in an ultrasonic bath. According to the example of methotrexate conjugate, stability of prodrug ester bond in liposomal formulation towards hydrolysis by human plasma esterases during 24-h incubation were established. Also, liposomes bearing methotrexate conjugate were shown to overcome resistance of human leukemia cells related to impaired transport of initial drug across the membrane.

Substituted aminoalcohol ester analogs of indomethacin with reduced toxic effects

Synthesis and evaluation of five different N,N-disubstituted aminoethanol ester derivatives of indomethacin bearing structural resemblance to the aminoethanol ester class of anticholinergics are reported herein. The anticholinergic activity was incorporated into the intact esters to overcome the gastric toxicity of indomethacin, not only by blocking the acidic functionality but also by decreasing gastric secretions and motility. These derivatives exhibited in vitro stability in buffers of pH 2.0 and 7.4 for 6 h and were readily hydrolyzed by human plasma esterases to liberate the parent drug. All the derivatives were significantly less irritating to the gastric mucosa than the parent drug. Though only two esters showed antiinflammatory activity similar to that of the parent drug at equivalent dose levels, all the esters were equipotent to indomethacin in the mouse acetic acid–induced writhing assay for analgesic action. The present evaluation indicates that the combined pharmacological properties of these ester derivatives may prove useful for design and development of novel gastric sparing antiinflammatory molecules with potentially important therapeutic applications.

Human xenobiotic metabolizing esterases in liver and blood

Esterases in human liver microsomes hydrolysed fluazifop-butyl ( V max 9.8 ± 1.6 μmol/min/g tissue), paraoxon ( V max 47.4 ± 7.5 nmol/min/g tissue) and phenylacetate ( V max 57 ± 8 μnol/min/g tissue), whereas esterases found in the human liver cytosol hydrolysed fluazifop-butyl ( V max 10.0 ± 0.5 μmol/min/g tissue) and phenylacetate ( V max 37 ± 2.9 μmol/min/g tissue) but not paraoxon. Human plasma esterase hydrolysed fluazifop-butyl ( V max 0.09 ± 0.006 μmol/min/mL), paraoxon ( V max 210 ± 14 nmol/min/mL) and phenylacetate ( V max 250 ± 17 μmol/min/mL). Inhibitory studies using paraoxon, bis-nitrophenol phosphate and mercuric chloride indicated fluazifop-butyl hydrolysis involved carboxylesterase in liver microsomes and cytosol, and cholinesterase and carboxylesterase in plasma. Phenylacetate hydrolysis involved arylesterase in plasma, both arylesterase and carboxylesterase in liver microsomes and carboxylesterase in liver cytosol. Plasma hydrolysis is less important and overall esterase activity is lower in humans than in the rat which is therefore a poor model.