Low Hepatic Mg²⁺ Content promotes Liver dysmetabolism: Implications for the Metabolic Syndrome

Metabolic Syndrome, a pathological condition affecting approximately 35% of the USA population, is characterized by obesity, insulin resistance, and hypertension. Metabolic syndrome is considered the single most common condition predisposing to the development of various chronic diseases including diabetes and hypertension. Hypomagnesaemia has been consistently observed in association with metabolic syndrome, but it is unclear whether reduced Mg²⁺ levels are the consequence or a possible cause for the development of the metabolic syndrome and/or its associated pathologies. Research performed in our laboratory showed that rats exposed for 2 weeks to a Mg²⁺ deficient diet presented decreased glucose accumulation into the hepatocytes together with low Mg²⁺ level in the circulation and within the liver cells. To better investigate the changes in glucose metabolism, HepG2 were used to mimic in vitro Mg²⁺ deficiency conditions. HepG2 cells cultured in low extracellular Mg²⁺ presented a 20% decrease in total cellular Mg²⁺ content, reduced glucose accumulation, and enhanced glucose 6-phosphate (G6P) transport into the endoplasmic reticulum (ER). The increased G6P transport was associated with its enhanced hydrolysis by the glucose 6-phosphatase, but also conversion to 6-phosphogluconolactone by the glucose 6-phosphate dehydrogenase. The latter process resulted in the increased generation of NADPH within the ER and the increased conversion of cortisone to cortisol by the 11-β-hydroxysteroid dehydrogenase type-1 (11-β-OHSD1). Taken together, our results provide compelling evidence that Mg²⁺ deficiency precedes and actually promotes some of the hepatic dysmetabolisms typical of the metabolic syndrome. The decrease in intrahepatic Mg²⁺ content up-regulates G6P entry into the hepatic endoplasmic reticulum and its routing into the pentose shunt pathway for energetic purposes. The associated increased in NADPH production within the ER then stimulates cortisol production, setting the conditions for hepatic insulin resistance and further altering liver metabolism.