Circadian plasma citrate rhythms in juvenile diabetics

Model-Based Assessment of Plasma Citrate Flux Into the Liver: Implications for NaCT as a Therapeutic Target

Cytoplasmic citrate serves as an important regulator of gluconeogenesis and carbon source for de novo lipogenesis in the liver. For this reason, the sodium-coupled citrate transporter (NaCT), a plasma membrane transporter that governs hepatic influx of plasma citrate in human, is being explored as a potential therapeutic target for metabolic disorders. As cytoplasmic citrate also originates from intracellular mitochondria, the relative contribution of these two pathways represents critical information necessary to underwrite confidence in this target. In this work, hepatic influx of plasma citrate was quantified via pharmacokinetic modeling of published clinical data. The influx was then compared to independent literature estimates of intracellular citrate flux in human liver. The results indicate that, under normal conditions, <10% of hepatic citrate originates from plasma. Similar estimates were determined experimentally in mice and rats. This suggests that NaCT inhibition will have a limited impact on hepatic citrate concentrations across species.

The Role of INDY in Metabolic Regulation

Reduced expression of the Indy (I'm Not Dead Yet) gene in D. melanogaster and C. elegans extends longevity. Indy and its mammalian homolog mINDY (Slc13a5, NaCT) are transporters of TCA cycle intermediates, mainly handling the uptake of citrate via the plasma membrane into the cytosol. Deletion of mINDY in mice leads to significant metabolic changes akin to caloric restriction, likely caused by reducing the effects of mINDY-imported citrate on fatty acid and cholesterol synthesis, glucose metabolism and ß-oxidation. This review will provide an overview on different mammalian SLC1 3 family members with a focus on mINDY (SLCl3A5) in glucose and energy metabolism and will highlight the role of mINDY as a putative therapeutic target for the treatment of obesity, non-alcoholic fatty liver disease and type 2 diabetes.