Functional Expression of Stereoselective Metabolism of Cephalexin by Exogenous Transfection of Oligopeptide Transporter PEPT1

The role of stereochemistry of antibiotic agents in the development of antibiotic resistance in the environment

Antibiotic resistance (ABR) is now recognised as a serious global health and economic threat that is most efficiently managed via a 'one health' approach incorporating environmental risk assessment. Although the environmental dimension of ABR has been largely overlooked, recent studies have underlined the importance of non-clinical settings in the emergence and spread of resistant strains. Despite this, several research gaps remain in regard to the development of a robust and fit-for-purpose environmental risk assessment for ABR drivers such as antibiotics (ABs). Here we explore the role the environment plays in the dissemination of ABR within the context of stereochemistry and its particular form, enantiomerism. Taking chloramphenicol as a proof of principle, we argue that stereoisomerism of ABs impacts on biological properties and the mechanisms of resistance and we discuss more broadly the importance of stereochemistry (enantiomerism in particular) with respect to antimicrobial potency and range of action.

A population pharmacokinetic approach to describe cephalexin disposition in adult and aged dogs

This study was conducted in order to characterize the pharmacokinetics of orally administered cephalexin to healthy adult and aged dogs, using a population pharmacokinetic approach. Two hundred and eighty-six cephalexin plasma concentrations obtained from previous pharmacokinetic studies were used. Sex, age, pharmaceutical formulation, and breed were evaluated as covariates. A one-compartment model with an absorption lag-time (Tlag) best described the data. The final model included age (adult; aged) on apparent volume of distribution (Vd/F), apparent elimination rate (ke/F), and Tlag; sex (female; male) on ke/F, and breed (Beagle; mixed-breed) on Vd/F. Addition of the covariates to the model explained 78% of the interindividal variability (IIV) in Vd/F, 36% in ke/F, and 24% in Tlag, respectively. Formulation did not affect the variability of any of the pharmacokinetic parameters. Tlag was longer, whereas Vd/F and ke/F were lower in aged compared to adult animals; in female aged dogs ke/F was lower than in male aged dogs; however, the differences were of low magnitude. Different disposition of cephalexin may be expected in aged dogs.

Targeting drug transporters - combining in silico and in vitro approaches to predict in vivo

Transporter proteins are expressed throughout the human body in different vital organs. They play an important role to various extents in determining absorption, distribution, metabolism, excretion, and toxicity (ADME/Tox) properties of therapeutic molecules. Over the past decade, numerous drug transporters have been cloned and considerable progress has been made toward understanding the molecular characteristics of individual transporters. In this chapter several in vitro and in silico techniques are described with applications to understand transporter behavior. These include employing new techniques to rapidly identify novel ligands for transporters. Ultimately these methods should lead to a greater overall appreciation of the role of transporters in vivo.

Absorption of lisdexamfetamine dimesylate and its enzymatic conversion to d-amphetamine

These studies investigated the absorption and metabolic conversion of lisdexamfetamine dimesylate (LDX), a prodrug stimulant that requires conversion to d-amphetamine for activity. Oral absorption of LDX was assessed in rat portal and jugular blood, and perfusion of LDX into isolated intestinal segments of anesthetized rats was used to assess regional absorption. Carrier-mediated transport of LDX was investigated in Caco-2 cells and Chinese hamster ovary (CHO) cells expressing human peptide transporter-1 (PEPT1). LDX metabolism was studied in rat and human tissue homogenates and human blood fractions. LDX was approximately10-fold higher in portal blood versus systemic blood. LDX and d-amphetamine were detected in blood following perfusion of the rat small intestine but not the colon. Transport of LDX in Caco-2 cells had permeability apparently similar to cephalexin and was reduced with concurrent PEPT1 inhibitor. Affinity for PEPT1 was also demonstrated in PEPT1-transfected CHO cells. LDX metabolism occurred primarily in whole blood (rat and human), only with red blood cells. Slow hydrolysis in liver and kidney homogenates was probably due to residual blood. The carrier-mediated absorption of intact LDX, likely by the high-capacity PEPT1 transporter, and subsequent metabolism to d-amphetamine in a high-capacity system in blood (ie, red blood cells) may contribute to the consistent, reproducible pharmacokinetic profile of LDX.

Inhibition of oligopeptide transporter suppress growth of human pancreatic cancer cells

Oligopeptide transporters are abundantly expressed in various types of cancer cells. We here synthesized two novel dipeptides, l-phenylalanyl sarcosine (Phe-Sar) and 4-(4-methoxyphenyl)-l-phenylalanyl sarcosine (Bip(OMe)-Sar), and examined their effect on the growth of human pancreatic cancer AsPC-1 cells, which are known to highly express oligopeptide transporter PEPT1/SLC15A1. Growth of AsPC-1 cells was inhibited by these two peptides and a typical PEPT1/SLC15A1 substrate Gly-Sar. Growth inhibition by Gly-Sar, Phe-Sar and Bip(OMe)-Sar was concentration-dependent with half-maximal inhibitory concentration of 50, 0.91 and 0.55mM, respectively. These peptides also inhibited PEPT1-mediated [(3)H]Gly-Sar uptake with half-maximal inhibitory concentration of 2.6, 0.81 and 0.27mM, respectively. Thus, the rank order of the tumor cell growth inhibition by these three peptides was the same as that of PEPT1-inhibitory activity. Growth of AsPC-1 cells was also inhibited by 2-aminobicyclo(2,2,1)heptane-2-carboxylic acid (BCH), which is a typical inhibitor of amino acid transporter system L. The growth inhibition by BCH and Gly-Sar was additive, suggesting that these compounds act at distinct loci. Oligopeptide transporters thus appear to be a promising target for inhibition of pancreatic cancer progression. These results also proposed the idea that oligopeptide transporter is required for growth of AsPC-1 cells.

Direct evidence for efficient transport and minimal metabolism of L-cephalexin by oligopeptide transporter 1 in budded baculovirus fraction

The oligopeptide transporter PEPT1 (SLC15A1) is responsible for absorption of peptidic nutrients in the small intestine. Although the L-diastereomer of the beta-lactam antibiotic cephalexin (L-cephalexin) is likely to be transported by PEPT1, there has been no direct demonstration of PEPT1-mediated L-cephalexin transport. Indeed, after the incubation with L-cephalexin, the intact form of L-cephalexin has not been identified inside vesicles/proteoliposomes prepared from brush border membrane of intestinal epithelial cells or cultured cell lines exogenously transfected with PEPT1 gene. Thus, it appears that L-cephalexin is rapidly metabolized by PEPT1 or PEPT1-associated proteins. Here, we attempted to verify whether L-cephalexin is transported by PEPT1 and whether it is hydrolyzed by PEPT1 itself, by using budded baculovirus expressing PEPT1 protein. Marked uptake of L-cephalexin in PEPT1-expressing budded baculovirus, compared with wild-type virus, indicated that L-cephalexin is a substrate for PEPT1. The uptake was found to be pH sensitive, and was strongly inhibited by the D-diastereomer of cephalexin and glycylsarcosine, but not by glycine. Thus, L-cephalexin is transported by PEPT1 itself. Upon the transport of both L- and D-cephalexin by PEPT1, dose-dependent membrane depolarization was observed; the EC(50) values of 0.18 and 2.9 mM, respectively, indicate that the affinity of L-cephalexin for PEPT1-mediated transport is much higher than that of the D-diastereomer. On the other hand, the L-cephalexin metabolite 7-aminodesacetoxycephalosporanic acid was not detected in PEPT1-expressing or wild-type virus at either pH 6.0 or 7.4. We conclude that L-cephalexin is transported by PEPT1 with high affinity, but is not metabolized by PEPT1 itself.

Carrier-mediated cellular uptake of pharmaceutical drugs: an exception or the rule?

It is generally thought that many drug molecules are transported across biological membranes via passive diffusion at a rate related to their lipophilicity. However, the types of biophysical forces involved in the interaction of drugs with lipid membranes are no different from those involved in their interaction with proteins, and so arguments based on lipophilicity could also be applied to drug uptake by membrane transporters or carriers. In this article, we discuss the evidence supporting the idea that rather than being an exception, carrier-mediated and active uptake of drugs may be more common than is usually assumed - including a summary of specific cases in which drugs are known to be taken up into cells via defined carriers - and consider the implications for drug discovery and development.