Benorylate hydrolysis by human plasma and human liver

Exploring acetaminophen prodrugs and hybrids: a review

This critical review highlights the advances in developing new molecules for treating pain syndrome, an important issue for human health. Acetaminophen (APAP, known as paracetamol) and nonsteroidal anti-inflammatory drugs (NSAIDs) are commonly used in clinical practice despite their adverse effects. Research is being conducted to develop innovative drugs with improved pharmaceutical properties to mitigate these effects. A more practical way to achieve that is to study well-known and time-tested drugs in their molecular combinations. Accordingly, the present work explores APAP and their combined chemical entities, i.e., prodrugs (soft drugs), codrugs (mutual prodrugs), and hybrids. Due to their molecular structure, APAP prodrugs or codrugs could be considered merged or conjugated hybrids; all these names are very fluid terms. This article proposed a structural classification of these entities to better analyze their advances. So, the following: carrier-linked O-modified APAP, -linked N-modified APAP derivatives (prodrugs), and direct- and spacer-N,O-linked APAP hybrids (codrugs) are the central parts of this review and are examined, especially ester and amide NSAID-APAP molecules. The C-linked APAP and nitric oxide (NO)-releasing APAP hybrids were also briefly discussed. Prime examples of APAP-based drugs such as propacetamol, benorylate, acetaminosalol, nitroparacetamol, and agent JNJ-10450232 weave well into this classification. The proposed classification is the first and original, giving a better understanding of the SAR studies for new pain relievers research and the design development for the analgesic APAP-(or NSAID)-based compounds.

Conversion and pharmacokinetics profiles of a novel pro-drug of 3-n-butylphthalide, potassium 2-(1-hydroxypentyl)-benzoate, in rats and dogs

Potassium 2-(1-hydroxypentyl)-benzoate (dl-PHPB) is a novel pro-drug of 3-n-butylphthalide (dl-NBP) that is used to treat ischemic stroke. Currently, dl-PHPB is in phase II-III clinical trials in China. In this study, we investigated the conversion and pharmacokinetics profiles of dl-PHPB in vitro and in vivo. The conversion of dl-PHPB to dl-NBP was pH- and calcium-dependent, and paraoxonase was identified as a major enzyme for the conversion in rat plasma. The pharmacokinetics, tissue distribution and excretion of dl-PHPB were studied and compared with equal-molar doses of dl-NBP in rats and dogs. The in vivo studies showed that dl-PHPB could be quickly and completely converted to dl-NBP. The plasma concentration-time course of converted dl-NBP after intravenous dl-PHPB administration was nearly the same as that after equal-molar dl-NBP. The C_max and AUC of dl-NBP after oral dl-PHPB administration in rats and dogs were higher by 60% and 170%, respectively, than those after oral dl-NBP administration. Analysis of the tissue distribution of dl-PHPB revealed that converted dl-NBP was primarily distributed in fat, the brain and the stomach. In the brain, the levels of dl-NBP were relatively higher after dl-PHPB treatment by orally than after treatment with equal-molar dl-NBP. Approximately 3%-4% of dl-NBP was excreted within 72 h after dosing with dl-PHPB or dl-NBP, but no dl-PHPB was detected in urine or feces excrements. Our results demonstrate that the conversion of dl-PHPB is fast after oral or intravenous administration. Furthermore, the bioavailability of dl-PHPB was obviously better than that of dl-NBP.

In vitro stability and metabolism of O2', O3', O5'-tri-acetyl-N6-(3-hydroxylaniline) adenosine in rat, dog and human plasma: chemical hydrolysis and role of plasma esterases

O2', O3', O5'-tri-acetyl-N(6)-(3-hydroxylaniline)adenosine (WS070117), a new structure-type lipid regulator, is being developed in pre-clinical study. In order to monitor drug kinetics it is essential to understand pre-analytical factors that may affect drug assay. In vitro stability and metabolism were investigated using high-performance liquid chromatography (HPLC) method in this study. The hydrolysis products were identified by HPLC-mass spectrometry (MS)/MS method. The esterases involved in WS070117 hydrolysis was assigned via inhibition rate assay. It was found that WS070117 was chemically unstable in alkaline solutions compared to acidic and near neutral solutions. Enzymatic hydrolysis was even more rapid. Hydrolytic rate constants differ between species, being 4.24, 5.96 × 10(-3) and 6.85 × 10(-2) min(-1) in rat, dog and human plasma at 37°C, respectively. The hydrolysis was catalyzed by plasma esterase because NaF (sodium fluoride: a general esterase inhibitor) inhibited WS070117 hydrolysis and metabolite production. Hydrolysis was fast in rat plasma and was catalysed by carboxylesterase and butyrylcholinesterase. In dog plasma, carboxylesterase, butyrylcholinesterase and paraoxonase were mainly responsible. Butyrylcholinesterase was the major esterase involved in WS070117 hydrolysis in human plasma. The WS070117 hydrolysis in plasma proceeded by gradual loss of acetyl groups. The knowledge of in vitro drug stability and metabolic pathways identified in this study will be essential for future pre-clinical and clinical pharmacokinetics studies.

Isosorbide-based aspirin prodrugs. II. Hydrolysis kinetics of isosorbide diaspirinate

Aspirin prodrugs have been intensively investigated in an effort to produce compounds with lower gastric toxicity, greater stability or enhanced percutaneous absorption, relative to aspirin. This report describes the hydrolysis kinetics and aspirin release characteristics of isosorbide diaspirinate (ISDA), the aspirin diester of isosorbide. ISDA underwent rapid hydrolysis when incubated in phosphate buffered human plasma solutions (pH 7.4) at 37 degrees C, producing appreciable quantities of aspirin. In 30% human plasma solution the half-life was 1.1 min and 61% aspirin was liberated relative to the initial ester concentration. The hydrolysis kinetics of ISDA were monitored in aqueous solution at 37 degrees C over the pH range 1.03-9.4. The aqueous hydrolysis followed pseudo-first-order kinetics over several half-lives at all pH values, resulting in a U-shaped pH rate profile. Salicylate esters and salicylic acid were formed during these processes. The hydrolysis characteristics of ISDA were also investigated in pH 7.4 phosphate buffered solutions containing alpha-chymotrypsin [EC 3.1.1.1] (t(1/2)=200.9 min), carboxyl esterase [EC 3.1.1.1] (t(1/2)=31.5 min), human serum albumin (t(1/2)=603 min), purified human serum butyrylcholinesterase [EC 3.1.1.8] (80 micro g/ml; t(1/2)=9.4 min; 55% aspirin), purified horse serum butyrylcholinesterase (100 micro g/ml; t(1/2)=1.85 min;11% aspirin) and in 10% human plasma solution in the presence of physostigmine (3 micro M). The results indicate that a specific enzyme present in human plasma, probably human butyrylcholinesterase, catalyses aspirin release from isosorbide diaspirinate.

Evaluation of hepatic metabolism of salicylic acid in perfused rat liver

Hepatic metabolism of salicylic acid was studied using a single-pass liver perfusion technique. Livers obtained from male, Sprague-Dawley rats (200-300 g) were perfused with Krebs-Henseleit bicarbonate buffer containing the drug (50-100 micrograms/mL) and glycine (0.5 or 5 mM) or glucose (5.5 mM) or bovine serum albumin (0.33%). Effluent samples over a 30-50 min interval were analyzed for salicylic acid and its metabolites (gentisic acid, salicyluric acid, and salicyl acyl and salicyl phenolic glucuronides). Effluent concentrations of salicylic acid did not differ from those in the perfusate, indicating that the liver is not a site for the metabolism of this drug. Hepatic uptake studies are needed to confirm this finding.

Esterase activity in rat hepatocytes

Hydrolysis of acetylsalicylate, benorylate, phenetsal, fluazifop butyl and paraoxon has been studied with freshly isolated rat hepatocytes maintained as a monolayer. Acetylsalicylate and paraoxon were the poorest substrates for hydrolysis whereas benorylate was hydrolysed one hundred times faster. Phenetsal and fluazifop butyl were both hydrolysed at one-tenth of the rate of benorylate. Inhibitor studies with paraoxon, BNPP and physostigmine indicated the involvement of different carboxylesterase isozymes. Studies with acetylsalicylate indicated that uptake of the substrate into the hepatocyte may influence the rate of formation of the hydrolysis product. Studies of hydrolysis in hepatocytes more closely reflect in vivo hepatic hydrolysis than subcellular fractions as cytosolic and microsomal esterases can act in parallel.