Aim: Small molecule glucokinase activators (GKAs) were developed as potential blood glucose lowering drugs for type 2 diabetes. However, some GKAs showed a decline in glycaemic efficacy during prolonged clinical trials. The proposed mechanisms remain speculative. We tested the hypothesis that GKAs induce hepatic adaptations that alter intra-hepatocyte metabolite homeostasis.
Methods: C57BL/6 mice on standard rodent diet were treated with a GKA (AZD1656) acutely or chronically. Hepatocytes were isolated from mice after 4 week or 8 week treatment for analysis of cellular metabolites and gene expression in response to substrate challenge.
Results: Acute exposure of mice to AZD1656 or a liver-selective GKA (PF-04991532), before a glucose tolerance test, or challenge of mouse hepatocytes with GKAs ex vivo induced various ChREBP target genes including ChREBP-β, Gckr and G6pc. Both glucokinase activation and ChREBP target gene induction by PF-04991532, were dependent on the chirality of the molecule confirming a mechanism linked to glucokinase activation. Hepatocytes from mice treated with AZD1656 for 4 weeks or 8 weeks had lower basal glucose 6-phosphate levels and improved ATP homeostasis during high substrate challenge. They also had raised basal ChREBP-β mRNA and AMPK-α mRNA (Prkaa1, Prkaa2) and progressively attenuated substrate-induction of some ChREBP target genes and Prkaa1 and Prkaa2.
Conclusions: Chronic GKA treatment of C57BL/6 mice for 8 weeks activates liver ChREBP and improves the resilience of hepatocytes to compromised ATP homeostasis during high-substrate challenge. These changes are associated with raised mRNA levels of ChREBP-β and both catalytic subunits of AMP-activated protein kinase.
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