Discovery and characterization of novel inhibitors of the sodium-coupled citrate transporter (NaCT or SLC13A5)

Abstract

Citrate is a key regulatory metabolic intermediate as it facilitates the integration of the glycolysis and lipid synthesis pathways. Inhibition of hepatic extracellular citrate uptake, by blocking the sodium-coupled citrate transporter (NaCT or SLC13A5), has been suggested as a potential therapeutic approach to treat metabolic disorders. NaCT transports citrate from the blood into the cell coupled to the transport of sodium ions. The studies herein report the identification and characterization of a novel small dicarboxylate molecule (compound 2) capable of selectively and potently inhibiting citrate transport through NaCT, both in vitro and in vivo. Binding and transport experiments indicate that 2 specifically binds NaCT in a competitive and stereosensitive manner, and is recognized as a substrate for transport by NaCT. The favorable pharmacokinetic properties of 2 permitted in vivo experiments to evaluate the effect of inhibiting hepatic citrate uptake on metabolic endpoints.

Mutations in the Na+/Citrate Cotransporter NaCT (SLC13A5) in Pediatric Patients with Epilepsy and Developmental Delay

“…Interestingly, heterozygotes may have some benefit relating to reduced liver citrate transport. A current focus in diabetes drug development targets the liver NaCT with small molecule inhibitors that do not penetrate the CNS (11,12). There is some evidence from other members of the SLC13 family that dimer formation can alter function, both homodimers (19) and heterodimers with other proteins (42).…”

“…A total of six NaCT mutants were prepared: four point mutations identified in this study, Y82C, G219R, T227M and L492P (Table 1 and Figure 1), and one mutation, L488P, identified previously (2). In addition, we prepared the DelG mutant of hNaCT, with a nucleotide deletion of hepatocytes, NaCT expression is correlated with lipid accumulation and triglyceride synthesis (10,11). Furthermore, inhibition of NaCT-mediated citrate transport by the liver is emerging as a therapeutic approach for the treatment of metabolic disorders, such as diabetes (11,12).…”

“…In addition, we prepared the DelG mutant of hNaCT, with a nucleotide deletion of hepatocytes, NaCT expression is correlated with lipid accumulation and triglyceride synthesis (10,11). Furthermore, inhibition of NaCT-mediated citrate transport by the liver is emerging as a therapeutic approach for the treatment of metabolic disorders, such as diabetes (11,12). Treatment of animals with small molecule NaCT inhibitors (that do not enter the central nervous system (CNS)) increased citrate excretion in urine, decreased hepatic lipid production and reduced plasma glucose (11).…”

“…Furthermore, inhibition of NaCT-mediated citrate transport by the liver is emerging as a therapeutic approach for the treatment of metabolic disorders, such as diabetes (11,12). Treatment of animals with small molecule NaCT inhibitors (that do not enter the central nervous system (CNS)) increased citrate excretion in urine, decreased hepatic lipid production and reduced plasma glucose (11). It is clear that NaCT in the liver plays an important metabolic role, but there is very little information on the role of NaCT in brain.…”

Determination of Unbound Partition Coefficient and in Vitro-in Vivo Extrapolation for SLC13A Transporter-Mediated Uptake

“…Inhibition of hepatic extracellular citrate uptake through SLC13A5 has been suggested as a potential therapeutic approach to treat metabolic diseases (Huard et al, 2015(Huard et al, , 2016Li et al, 2016). The SLC13A family contains five family members: SLC13A1 and SLC13A4 mainly transport sulfate, and SLC13A2, SLC13A3, and SLC13A5 transport di-and tri-carboxylates such as citrate (Lee et al, 2005;Bergeron et al, 2013).…”