Metformin inhibits Branched Chain Amino Acid (BCAA) derived ketoacidosis and promotes metabolic homeostasis in MSUD

Abstract

Maple Syrup Urine Disease (MSUD) is an inherited disorder caused by the dysfunction in the branched chain keto-acid dehydrogenase (BCKDH) enzyme. This leads to buildup of branched-chain keto-acids (BCKA) and branched-chain amino acids (BCAA) in body fluids (e.g. keto-isocaproic acid from the BCAA leucine), leading to numerous clinical features including a less understood skeletal muscle dysfunction in patients. KIC is an inhibitor of mitochondrial function at disease relevant concentrations. A murine model of intermediate MSUD (iMSUD) shows significant skeletal muscle dysfunction as by judged decreased muscle fiber diameter. MSUD is an orphan disease with a need for novel drug interventions. Here using a 96-well plate (liquid chromatography- mass spectrometry (LC-MS) based drug-screening platform we show that Metformin, a widely used anti-diabetic drug, reduces levels of KIC in patient-derived fibroblasts by 20–50%. This Metformin-mediated effect was conserved in vivo; Metformin-treatment significantly reduced levels of KIC in the muscle (by 69%) and serum (by 56%) isolated from iMSUD mice, and restored levels of mitochondrial metabolites (e.g. AMP and other TCA). The drug also decreased the expression of mitochondrial branched chain amino transferase (BCAT) which produces KIC in skeletal muscle. This suggests that Metformin can restore skeletal muscle homeostasis in MSUD by decreasing mitochondrial KIC production.

Effect of metformin on plasma metabolite profile in the Copenhagen Insulin and Metformin Therapy (CIMT) trial

“…Impact of metformin treatment on amino acid levels are, however, not yet clear. A recent study in mice with maple syrup urine disease suggests that metformin decreases the expression of mitochondrial branched-chain amino acid transaminase (BCAT) 2 in skeletal muscle leading to increased levels of leucine and decreased accumulation of its intermediate [22]. This could explain the increased levels of leucine/isoleucine in metformin-treated participants in the present study.…”

Effect of metformin on myotube BCAA catabolism

“…Second, our study did not determine if alterations in BCAA catabolic enzyme expression following metformin treatment result in a diminished capacity to oxidize BCAA. We selected 2 mM metformin because it has been used during previous experiments, 5,27 while other experiments used metformin concentrations ranging from 1-2.5 mM for various durations (up to 5 days) for in vitro experiments. Importantly, others have shown KLF15 is vital for the maintenance of blood glucose (using KLF15 KO mice), especially during times of low carbohydrate consumption.…”

“…[13][14][15][16][17][18][19][20] Reduced BCAA catabolism has been suggested as a likely contributor to the accumulation of circulating BCAAs in obese and diabetic populations. 27 One possible mechanism that explains an upregulation of PGC-1α by metformin, with a concurrent decrease in BCAA metabolism, is the simultaneous downregulation of Kruppel-like factor 15 (KLF15), which is recognized as a coordinating transcription factor in the metabolism of BCAA (including the expression of muscle BCAT2). 21 In fact, the activation of either PGC-1α or peroxisome proliferator-activator receptor α (PPARα) induces BCAA catabolic enzymes branched-chain aminotransferase (BCAT2) and branched-chain-alpha-keto acid dehydrogenase (BCKDH).…”

“…However, one report demonstrated metformin suppressed BCAT2 expression in both C2C12 myotubes and in a mouse model of maple syrup urine disease, however, the effects of metformin on BCKDH expression remains unknown. 4 The 2 mM supraphysiological concentration was selected because past reports have used 2 mM 5,29 in various cell culture models (including C2C12 myotubes 5,27 ) and have shown an induction of PGC-1α mRNA as early as 24 hours. 28 Interestingly, metformin was previously shown to significantly increase PGC-1α in primary mouse hepatocytes, and reduced PGC-1α acetylation (the indication of PGC-1α activation and Sirt1 activity), while suppressing KLF15 expression in HepG2 cells.…”

BCKDK of BCAA Catabolism Cross-talking With the MAPK Pathway Promotes Tumorigenesis of Colorectal Cancer

“…BCKDK plays an important role in many serious human diseases, including Huntington's disease (Mochel et al, 2007), Maple syrup urine disease (Beaudet, 2012, Sonnet et al, 2016), human autism with Epilepsy (Novarino et al, 2012), and Obesity (Burrage et al, 2014). However, the relationship between BCKDK and cancer is unknown.…”