Acetylation turns leucine into a drug by membrane transporter switching

Grant C Churchill,Mallory Factor,Michael Strupp,Cailley Factor,Tatiana Bremova-Ertl,Frances M Platt,Antony Galione,Marc C Patterson

doi:10.1038/s41598-021-95255-5

Abstract

Small changes to molecules can have profound effects on their pharmacological activity as exemplified by the addition of the two-carbon acetyl group to make drugs more effective by enhancing their pharmacokinetic or pharmacodynamic properties. N-acetyl-d,l-leucine is approved in France for vertigo and its l-enantiomer is being developed as a drug for rare and common neurological disorders. However, the precise mechanistic details of how acetylation converts leucine into a drug are unknown. Here we show that acetylation of leucine switches its uptake into cells from the l-type amino acid transporter (LAT1) used by leucine to organic anion transporters (OAT1 and OAT3) and the monocarboxylate transporter type 1 (MCT1). Both the kinetics of MCT1 (lower affinity compared to LAT1) and the ubiquitous tissue expression of MCT1 make it well suited for uptake and distribution of N-acetyl-l-leucine. MCT1-mediated uptake of a N-acetyl-l-leucine as a prodrug of leucine bypasses LAT1, the rate-limiting step in activation of leucine-mediated signalling and metabolic process inside cells such as mTOR. Converting an amino acid into an anion through acetylation reveals a way for the rational design of drugs to target anion transporters.

Highlights

Small changes to molecules can have profound effects on their pharmacological activity as exemplified by the addition of the two-carbon acetyl group to make drugs more effective by enhancing their pharmacokinetic or pharmacodynamic properties
Based on previous studies and our current results, we propose a mechanism of action of N-acetyl-leucine in which it is taken up and distributed by anion transporters, primarily monocarboxylate transporter type 1 (MCT1)
From the l-enantiomer, the l-leucine will be expected to be mostly utilized in the cell that deacetylates it, based studies on the uptake and utilization of 14C-l-leucine[56], with the important exception of the liver, which in contrast to all other amino acids does not metabolize leucine, but rather secretes it into the circulation for the use by other tissues, skeletal muscle and the central nervous s ystem[57]

Summary

Introduction

Small changes to molecules can have profound effects on their pharmacological activity as exemplified by the addition of the two-carbon acetyl group to make drugs more effective by enhancing their pharmacokinetic or pharmacodynamic properties. We show that acetylation of leucine switches its uptake into cells from the l-type amino acid transporter (LAT1) used by leucine to organic anion transporters (OAT1 and OAT3) and the monocarboxylate transporter type 1 (MCT1). MCT1-mediated uptake of a N-acetyl-l-leucine as a prodrug of leucine bypasses LAT1, the rate-limiting step in activation of leucine-mediated signalling and metabolic process inside cells such as mTOR. As the major barrier to membrane crossing is the hydrophobic interior[16], small, hydrophobic, neutral molecules can pass by passive diffusion (Fig. 1a), whereas hydrophilic molecules such as cations, anions and zwitterions, (including all α-amino acids) can only cross with the aid or solute carriers (SLC) transporters (Fig. 1a). Our calculations show that at physiological pH, l-leucine is a zwitterion, whereas N-acetyl-l-leucine

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