Citrate enrichment in a Western diet reduces weight gain via browning of adipose tissues without resolving diet-induced insulin resistance in mice.

Citrate, a major component of processed foods, appears as either preservative or flavor enhancer. With no concentration limit, citrate is consumed in large quantities worldwide, principally in ultra-processed foods (UPF). UPF are encountered in Western diets (rich in saturated fat and sucrose), where consumption is directly associated with many conditions, such as obesity and diabetes, among others. Here, we administered a High-Fat, High-Sucrose (HFHS) diet to mice, enriched or not with citrate (67 mg g-1 diet), aimed to simulate UPF citrate consumption. Our results showed that citrate enrichment prevented the HFHS-induced lipid deposition in the liver and adipose tissues of the animals. Moreover, the treatment induced mitochondrial biogenesis in white adipose tissues, via upregulation of PCG1α. As a result, citrate enhancement upregulated UCP1, suggesting the browning of white adipose tissues. Nevertheless, the citrate-enhanced diet did not prevent HFHS-induced insulin resistance and causes further liver inflammation and injury. Altogether, our results clearly showed that, associated to UPF consumption, the excess of dietary citrate has caused harmful effects being associated to non-obesity related liver inflammatory diseases and insulin resistance.

Dietary citrate acutely induces insulin resistance and markers of liver inflammation in mice.

Citrate is widely used as a food additive being part of virtually all processed foods. Although considered inert by most of the regulatory agencies in the world, plasma citrate has been proposed to play immunometabolic functions in multiple tissues through altering a plethora of cellular pathways. Here, we used a short-term alimentary intervention (24 hours) with standard chow supplemented with citrate in amount corresponding to that found in processed foods to evaluate its effects on glucose homeostasis and liver physiology in C57BL/6J mice. Animals supplemented with dietary citrate showed glucose intolerance and insulin resistance as revealed by glucose and insulin tolerance tests. Moreover, animals supplemented with citrate in their food displayed fed and fasted hyperinsulinemia and enhanced insulin secretion during an oral glucose tolerance test. Citrate treatment also amplified glucose-induced insulin secretion in vitro in INS1-E cells. Citrate supplemented animals had increased liver PKCα activity and altered phosphorylation at serine or threonine residues of components of insulin signaling including IRS-1, Akt, GSK-3 and FoxO1. Furthermore, citrate supplementation enhanced the hepatic expression of lipogenic genes suggesting increased de novo lipogenesis, a finding that was reproduced after citrate treatment of hepatic FAO cells. Finally, liver inflammation markers were higher in citrate supplemented animals. Overall, the results demonstrate that dietary citrate supplementation in mice causes hyperinsulinemia and insulin resistance both in vivo and in vitro, and therefore call for a note of caution on the use of citrate as a food additive given its potential role in metabolic dysregulation.