Targeting Oxygen-Sensing Prolyl Hydroxylase for Metformin-Associated Lactic Acidosis Treatment

Abstract

Metformin is one of the most widely used therapeutics for type 2 diabetes mellitus and also has anticancer and antiaging properties. However, it is known to induce metformin-associated lactic acidosis (MALA), a severe medical condition with poor prognosis, especially in individuals with renal dysfunction. Inhibition of prolyl hydroxylase (PHD) is known to activate the transcription factor hypoxiainducible factor (HIF) that increases lactate efflux as a result of enhanced glycolysis, but it also enhances gluconeogenesis from lactate in the liver that contributes to reducing circulating lactate levels. Here, we investigated the outcome of pharmaceutical inhibition of PHD in mice with MALA induced through the administration of metformin per os and an intraperitoneal injection of lactic acid. We found that the PHD inhibitors significantly increased the expression levels of genes involved in gluconeogenesis in the liver and the kidney and significantly improved the survival of mice with MALA. Furthermore, the PHD inhibitor also improved the rate of survival of MALA induced in mice with chronic kidney disease (CKD). Thus, PHD represents a new therapeutic target for MALA, which is a critical complication of metformin therapy.KEYWORDS CKD, Cori cycle, HIF, MALA, PHD, gluconeogenesis, hypoxia, lactic acidosis, metformin, prolyl hydroxylase T he hypoxic response is mainly regulated by the heterodimeric transcription factor hypoxia-inducible factor (HIF) composed of a stable ␤-subunit (HIF␤/ARNT) and labile ␣-subunit (HIF␣). The protein expression level of HIF␣ is negatively regulated by prolyl hydroxylase PHD1 to PHD3 (prolyl hydroxylase domain-containing proteins 1 to 3). Under normoxic conditions where oxygen is available, PHDs hydroxylate proline residues on HIF␣ targeted for von Hippel-Lindau (VHL) E3 ubiquitin ligase-dependent proteasomal degradation. On the other hand, enzymatic activities of PHDs are inhibited under the hypoxic conditions where available oxygen becomes limited as PHDs are 2-oxoglutarate-dependent dioxygenases which require molecular oxygen for their enzymatic activities. Thus, HIF␣ escapes from prolyl hydroxylation-dependent protein degradation, accumulates, binds to HIF␤/ARNT, and activates transcription of hypoxic mRNA, including that of Epo (erythropoietin [EPO] gene) or Vegf (vascular endothelial growth factor gene) under hypoxia (1). We previously reported that liver-specific inactivation of Phd2, the gene for the dominant prolyl hydroxylase for HIF␣, improved the survival rate of mice with lactic acidosis by activating hepatic gluconeogenesis from circulating lactate, which contributed to reducing the blood lactate level (2).

Hypoxia-Inducible Factor Prolyl 4-Hydroxylases and Metabolism

“…Similar results were obtained upon oral administration of the HIF-P4H inhibitors REC2923 or roxadustat, and these effects could be advantageous e.g. in T2D patients suffering from metformin-associated lactic acidosis [60]. In addition, liver-specific HIF-P4H-3 deletion in mice was shown to improve insulin signaling and to counteract diabetes [5].…”

Enhancement of glycolysis by inhibition of oxygen‐sensing prolyl hydroxylases protects alveolar epithelial cells from acute lung injury

“…PHD inhibition is potentially applicable for anemia (45, 46), ischemia‐reperfusion (47–49), colitis (50, 51), sepsis (43, 52), lactic acidosis (53), and lung injury (13, 15), and several PHD inhibitors have been developed (30, 54). Several clinical trials of orally bioavailable PHD inhibitors are being conducted for anemia in patients with chronic kidney diseases (30, 45, 46).…”

Metformin-Induced Lactic Acidosis: A Case Study

“…For example, a recent study by Oyaizu-Toramaru et al investigated the use of targeting oxygen-sensing prolyl hydroxylase (PHD) in patients with metformin-induced lactic acidosis. They found that inhibiting PHD activates a transcription factor, known as hypoxia-inducible factor (HIF), which promotes lactate efflux and gluconeogenesis by using lactate as the substrate; these all lower circulating lactate levels [ 8 ]. Even though there are many more treatment options for lactic acidosis, IV hydration therapy was effective in this case.…”