Drug Metabolism Letters 

About: Drug Metabolism Letters is an academic journal published by Bentham Science Publishers. The journal publishes majorly in the area(s): Pharmacokinetics & Metabolite. It has an ISSN identifier of 1872-3128. Over the lifetime, 382 publications have been published receiving 4542 citations.

Esterase Activities in the Blood, Liver and Intestine of Several Preclinical Species and Humans

Abstract: Species and tissue differences in the activity of three major classes of esterases, carboxylesterase (CE), butyrylcholinesterase (BChE) and paraoxonase (PON), were studied. Substantial species differences in activity of these esterases were observed between the mouse, rat, dog monkey and human. Such species differences must be considered when using these preclinical species to optimize the pharmacokinetic properties of ester compounds intended for human use.

An examination of IC50 and IC50-shift experiments in assessing time-dependent inhibition of CYP3A4, CYP2D6 and CYP2C9 in human liver microsomes.

Abstract: The relationship between time-dependent inactivation (TDI) and IC50 is examined using a consolidated method for evaluating CYP450 inhibition during drug discovery. An IC50 fold-shift of >1.5 indicated significant TDI potency. Further, the "shifted IC50" could be used to estimate, the K(I) and TDI potency ratio k(inact)/K(I) to within 2-fold in most cases.

Efficiency in Drug Discovery: Liver S9 Fraction Assay As a Screen for Metabolic Stability

Abstract: Background A rapid and comprehensive metabolic stability screen at the top of a drug discovery flow chart serves as an effective gate in eliminating low value compounds. This imparts a significant level of efficiency and saves valuable resources. While microsomes are amenable to high throughput automation and are cost effective, their enzymatic make-up is limited to that which is contained in endoplasmic reticulum, thereby informing only on Phase I metabolism. Lack of Phase II metabolism data can become a potential liability later in the process, adversely affecting discovery projects' timelines and budget. Hepatocytes offer a full complement of metabolic enzymes and retain their cellular compartments, better representing liver metabolic function. However, hepatocyte screens are relatively expensive, labor intensive, and not easily automatable. Liver S9 fractions include Phase I and II metabolic enzymes, are relatively inexpensive, easy to use, and amenable to automation, making them a more appropriate screening system. We compare the data from the three systems and present the results. Results Liver S9 and hepatocyte stability assays binned into the same category 70-84% of the time. Microsome and hepatocyte data were in agreement 73-82% of the time. The true rate for stability versus plasma clearance was 45% for hepatocytes and 43% for S9. Conclusion In our opinion, replacing liver microsome and hepatocyte assays with S9 assay for high throughput metabolic screening purposes provides the combined benefit of comprehensive and high quality data at a reasonable expense for drug discovery programs.

Renal and Hepatic Transporter Expression in Type 2 Diabetic Rats

Abstract: Membrane transporters are critical for the uptake as well as elimination of chemicals and by-products of metabolism from the liver and kidneys. Since these proteins are important determinants of chemical disposition, changes in their expression in different disease states can modulate drug pharmacokinetics. The present study investigated alterations in the renal and hepatic expression of organic anion and cation transporters (Oats/Octs), multidrug resistance-associated proteins (Mrps), breast cancer resistance protein (Bcrp), P-glycoprotein (Pgp), and hepatic Na+-taurocholate cotransporting polypeptide (Ntcp) in type 2 diabetic rats. For this purpose, type 2 diabetes was induced by feeding male Sprague- Dawley rats a high fat diet followed by a single dose of streptozotocin (45 mg/kg, i.p., in 0.01 M citrate buffer pH 4.3) on day 14. Controls received normal diet and vehicle. Kidney and liver samples were collected on day 24 for generation of crude plasma membrane fractions and Western blot analysis of Oat, Oct, Mrp, Bcrp, Pgp, and Ntcp proteins. With regards to renal uptake transporters, type 2 diabetes increased levels of Oat2 (2.3-fold) and decreased levels of Oct2 to 50% of control kidneys. Conversely, efflux transporters Mrp2, Mrp4, and Bcrp were increased 5.4-fold, 2-fold, and 1.6-fold, respectively in type 2 diabetic kidneys with no change in levels of Mrp1, Mrp5, or Pgp. Studies of hepatic transporters in type 2 diabetic rats reveal that the protein level of Mrp5 was reduced to 4% of control livers with no change in levels of Bcrp, Mrp1, Mrp2, Mrp4, Ntcp, or Pgp. The changes reported in this study may have implications in type 2 diabetic patients.

Investigations Into the Drug-Drug Interaction Potential of Tapentadol in Human Liver Microsomes and Fresh Human Hepatocytes

Abstract: The new analgesic tapentadol was evaluated for induction and inhibition of several cytochrome P450 enzymes in vitro, and protein binding was assessed. It was concluded that no clinically relevant drug-drug interactions are likely to occur through either mechanism.