Branched-chain Alpha-keto Acid Dehydrogenase Research Articles

Partial suppression of BCAA catabolism as a potential therapy for BCKDK deficiency

Branched chain ketoacid dehydrogenase kinase (BCKDK) deficiency is a recently described inherited neurometabolic disorder of branched chain amino acid (BCAA) metabolism implying increased BCAA catabolism. It has been hypothesized that a severe reduction in systemic BCAA levels underlies the disease pathophysiology, and that BCAA supplementation may ameliorate disease phenotypes. To test this hypothesis, we characterized a recent mouse model of BCKDK deficiency and evaluated the efficacy of enteral BCAA supplementation in this model. Surprisingly, BCAA supplementation exacerbated neurodevelopmental deficits and did not correct biochemical abnormalities despite increasing systemic BCAA levels. These data suggest that aberrant flux through the BCAA catabolic pathway, not just BCAA insufficiency, may contribute to disease pathology. In support of this conclusion, genetic re-regulation of BCAA catabolism, through Dbt haploinsufficiency, partially rescued biochemical and behavioral phenotypes in BCKDK deficient mice. Collectively, these data raise into question assumptions widely made about the pathophysiology of BCKDK insufficiency and suggest a novel approach to develop potential therapies for this disease.

Cross-talk between BCKDK-mediated phosphorylation and STUB1-dependent ubiquitination degradation of BCAT1 promotes GBM progression

Branched-chain amino acid transferase 1 (BCAT1) is highly expressed in multiple cancers and is associated with poor prognosis, particularly in glioblastoma (GBM). However, the post-translational modification (PTM) mechanism of BCAT1 is unknown. Here, we investigated the cross-talk mechanisms between phosphorylation and ubiquitination modifications in regulating BCAT1 activity and stability. We found that BCAT1 is phosphorylated by branched chain ketoacid dehydrogenase kinase (BCKDK) at S5, S9, and T312, which increases its catalytic and antioxidant activity and stability. STUB1 (STIP1 homology U-box-containing protein 1), the first we found and reported E3 ubiquitin ligase of BCAT1, can also be phosphorylated by BCKDK at the S19 site, which disrupts the interaction with BCAT1 and inhibits its degradation. In addition, we demonstrate through in vivo and in vitro experiments that BCAT1 phosphorylation inhibiting its ubiquitination at multiple sites is associated with GBM proliferation and that inhibition of the BCKDK-BCAT1 axis enhances the sensitivity to temozolomide (TMZ). Overall, we identified novel mechanisms for the regulation of BCAT1 modification and elucidated the importance of the BCKDK-STUB1-BCAT1 axis in GBM progression.

Mitolnc controls cardiac BCAA metabolism and heart hypertrophy by allosteric activation of BCKDH.

Enzyme activity is determined by various different mechanisms, including posttranslational modifications and allosteric regulation. Allosteric activators are often metabolites but other molecules serve similar functions. So far, examples of long non-coding RNAs (lncRNAs) acting as allosteric activators of enzyme activity are missing. Here, we describe the function of mitolnc in cardiomyocytes, a nuclear encoded long non-coding RNA, located in mitochondria and directly interacting with the branched-chain ketoacid dehydrogenase (BCKDH) complex to increase its activity. The BCKDH complex is critical for branched-chain amino acid catabolism (BCAAs). Inactivation of mitolnc in mice reduces BCKDH complex activity, resulting in accumulation of BCAAs in the heart and cardiac hypertrophy via enhanced mTOR signaling. We found that mitolnc allosterically activates the BCKDH complex, independent of phosphorylation. Mitolnc-mediated regulation of the BCKDH complex constitutes an important additional layer to regulate the BCKDH complex in a tissue-specific manner, evading direct coupling of BCAA metabolism to ACLY-dependent lipogenesis.

Adipocytes Are the Only Site of Glutamine Synthetase Expression Within the Lactating Mouse Mammary Gland

BackgroundGlutamine in milk is believed to play an important role in neonatal intestinal maturation and immune function. For lactating mothers, glutamine utilization is increased to meet the demands of the enlarged intestine and milk production. However, the source of such glutamine during lactation has not been studied. ObjectivesWe aimed to assess the effects of lactation on the expression of glutamine synthetase (GS) in the mammary gland and other tissues of lactating mice. MethodsMouse tissues were sampled at 4 time points: 8-wk-old (virgin, control), postdelivery day 5 (PD5, early lactation), PD15 (peak lactation), and involution (4 d after weaning at PD21). We examined the gene expression and protein concentrations of GS and the first 2 enzymes of branched-chain amino acid catabolism: branched-chain aminotransferase 2 (BCAT2) and branched-chain ketoacid dehydrogenase subunit E1α (BCKDHA). ResultsThe messenger RNA expression and protein concentrations of GS in mammary glands were significantly lower at PD5 and PD15 compared with the control but were restored at involution. Within the mammary gland, GS protein was only detected in adipocytes with no evidence of presence in mammary epithelial cells. Compared with the control, messenger RNA and protein concentrations of BCAT2 and BCKDHA in mammary glands significantly decreased during lactation and involution. No changes in GS protein concentrations during lactation were found in the liver, skeletal muscle, and lung. In nonmammary adipose tissue, GS protein abundance was higher during lactation compared with the virgin. ConclusionsThis work shows that, within the mouse mammary gland, GS is only expressed in adipocytes and that the relative GS abundance in mammary gland sections is lower during lactation. This suggests that mammary adipocytes may be a site of glutamine synthesis in the lactating mouse. Identifying the sources of glutamine production during lactation is important for optimizing milk glutamine concentration to enhance neonatal and maternal health.

Exploration of bioactivation of a branched-chain ketoacid dehydrogenase kinase (BDK) inhibitor

Exploration of bioactivation of a branched-chain ketoacid dehydrogenase kinase (BDK) inhibitor

In Staphylococcus aureus, the acyl-CoA synthetase MbcS supports branched-chain fatty acid synthesis from carboxylic acid and aldehyde precursors.

In the human pathogen Staphylococcus aureus, branched-chain fatty acids (BCFAs) are the most abundant fatty acids in membrane phospholipids. Strains deficient for BCFAs synthesis experience auxotrophy in laboratory culture and attenuated virulence during infection. Furthermore, the membrane of S. aureus is among the main targets for antibiotic therapy. Therefore, determining the mechanisms involved in BCFAs synthesis is critical to manage S. aureus infections. Here, we report that the overexpression of SAUSA300_2542 (annotated to encode an acyl-CoA synthetase) restores BCFAs synthesis in strains lacking the canonical biosynthetic pathway catalyzed by the branched-chain α-keto acid dehydrogenase (BKDH) complex. We demonstrate that the acyl-CoA synthetase activity of MbcS activates branched-chain carboxylic acids (BCCAs), and is required by S. aureus to utilize the isoleucine derivative 2-methylbutyraldehyde to restore BCFAs synthesis in S. aureus. Based on the ability of some staphylococci to convert branched-chain aldehydes into their respective BCCAs and our findings demonstrating that branched-chain aldehydes are in fact BCFAs precursors, we propose that MbcS promotes the scavenging of exogenous BCCAs and mediates BCFA synthesis via a de novo alternative pathway.

The BCKDH kinase inhibitor BT2 promotes BCAA disposal and mitochondrial proton leak in both insulin-sensitive and insulin-resistant C2C12 myotubes.

Elevated circulating branched-chain amino acids (BCAAs) have been correlated with the severity of insulin resistance, leading to recent investigations that stimulate BCAA metabolism for the potential benefit of metabolic diseases. BT2(3,6-dichlorobenzo[b]thiophene-2-carboxylic acid), an inhibitor of branched-chain ketoacid dehydrogenase kinase, promotes BCAA metabolism by enhancing BCKDH complex activity. The purpose of this report was to investigate the effects of BT2 on mitochondrial and glycolytic metabolism, insulin sensitivity, and de novo lipogenesis both with and without insulin resistance. C2C12 myotubes were treated with or without low or moderate levels of BT2 with or without insulin resistance. Western blot and quantitative real-time polymerase chain reactionwere used to assess protein and gene expression, respectively. Mitochondrial, nuclei, and lipid content were measured using fluorescent staining and microscopy. Cell metabolism was assessed via oxygen consumption and extracellular acidification rate. Liquid chromatography-mass spectrometry was used to quantify BCAA media content. BT2 treatment consistently promoted mitochondrial uncoupling following 24-h treatment, which occurred largely independent of changes in expressional profiles associated with mitochondrial biogenesis, mitochondrial dynamics, BCAA catabolism, insulin sensitivity, or lipogenesis. Acute metabolic studies revealed a significant and dose-dependent effect of BT2 on mitochondrial proton leak, suggesting BT2 functions as a small-molecule uncoupler. Additionally, BT2 treatment consistently and dose-dependently reduced extracellular BCAA levels without altering expression of BCAA catabolic enzymes or pBCKDHa activation. BT2 appears to act as a small-molecule mitochondrial uncoupler that promotes BCAA utilization, though the interplay between these two observations requires further investigation.

Activation of Hepatic Branched-Chain α-Ketoacid Dehydrogenase Complex by Vitamin D Deficiency in Rats.

Branched-chain α-ketoacid dehydrogenase (BCKDH) complex is a rate-limiting enzyme in branched-chain amino acid catabolism and is subject to inactivation via phosphorylation by BCKDH kinase (BDK). In the present study, we examined the effects of vitamin D-deficiency on hepatic BCKDH and BDK activities in rats. Rats fed a vitamin D-deficient diet long-term showed a slight but significant decrease in plasma Ca concentration, which was associated with an elevation of BCKDH activity and a decrease in BDK activity. These results suggest that vitamin D deficiency promotes BCAA catabolism via BCKDH activation, which resulted from BDK suppression. It is proposed that Ca2+-dependent BDK inhibition by thiamine pyrophosphate may be involved in the BDK suppression.

Branched-chain amino acid catabolic defect promotes α-cell proliferation via activating mTOR signaling

Elevated circulating level of branched-chain amino acids (BCAAs) is closely related to the development of type 2 diabetes. However, the role of BCAA catabolism in various tissues in maintaining glucose homeostasis remains largely unknown. Pancreatic α-cells have been regarded as amino acid sensors in recent years. Therefore, we generated α-cell specific branched-chain alpha-ketoacid dehydrogenase E1α subunit (BCKDHA) knockout (BCKDHA-αKO) mice to decipher the effects of BCAA catabolism in α-cells on whole-body energy metabolism. BCKDHA-αKO mice showed normal body weight, body fat, and energy expenditure. Plasma glucagon level and glucose metabolism also remained unchanged in BCKDHA-αKO mice. Whereas, the deletion of BCKDHA led to increased α-cell number due to elevated cell proliferation in neonatal mice. In vitro, only leucine among BCAAs promoted aTC1-6 cell proliferation, which was blocked by the agonist of BCAA catabolism BT2 and the inhibitor of mTOR Rapamycin. Like Rapamycin, BT2 attenuated leucine-stimulated phosphorylation of S6 in αTC1-6 cells. Elevated phosphorylation level of S6 protein in pancreatic α-cells was also observed in BCKDHA-αKO mice. These results suggest that local accumulated leucine due to defective BCAA catabolism promotes α-cell proliferation through mTOR signaling, which is insufficient to affect glucagon secretion and whole-body glucose homeostasis.

Bckdk-Mediated Branch Chain Amino Acid Metabolism Reprogramming Contributes to Muscle Atrophy during Cancer Cachexia.

Branched chain amino acids (BCAAs) are essential amino acids and important nutrient signals for energy and protein supplementation. The study uses muscle-specific branched-chain α-keto acid dehydrogenase kinase (Bckdk) conditional knockout (cKO) mice to reveal the contribution of BCAA metabolic dysfunction to muscle wasting. Muscle-specific Bckdk-cKO mice are generated through crossbreeding of Bckdkf/f mice with Myf5Cre mice. Lewis lung cancer (LLC) tumor transplantation is used to establish the cancer cachexia model. The occurrence of cancer cachexia is accelerated in the muscle-specific Bckdk-cKO mice after bearing LLC tumor. Wasting skeletal muscle is characterized by increased protein ubiquitination degradation and impaired protein synthesis. The wasting muscle gastrocnemius is mechanized as a distinct BCAA metabolic dysfunction. Based on the atrophy phenotype resulting from BCAA metabolism dysfunction, the optimized BCAA supplementation improves the survival of cancer cachexia in muscle-specific Bckdk-cKO mice bearing LLC tumors, and improves the occurrence of cancer cachexia. The mechanism of BCAA supplementation on muscle mass preservation is based on the promotion of protein synthesis and the inhibition of protein ubiquitination degradation. Dysfunctional BCAA metabolism contributes to the inhibition of protein synthesis and increases protein degradation in the cancer cachexia model of muscle-specific Bckdk-cKO mice bearing LLC tumors. The reprogramming of BCAA catabolism exerts therapeutic effects by stimulating protein synthesis and inhibiting protein degradation in skeletal muscle.

Identification of putative allosteric inhibitors of BCKDK via virtual screening and biological evaluation

Abnormal accumulation of branched-chain amino acids (BCAAs) can lead to metabolic diseases and cancers. Branched-chain α-keto acid dehydrogenase kinase (BCKDK) is a key negative regulator of BCAA catabolism, and targeting BCKDK provides a promising therapeutic approach for diseases caused by BCAA accumulation. Here, we screened PPHN and POAB as novel putative allosteric inhibitors by integrating allosteric binding site prediction, large-scale ligand database virtual screening, and bioactivity evaluation assays. Both of them showed a high binding affinity to BCKDK, with Kd values of 3.9 μM and 1.86 μM, respectively. In vivo experiments, the inhibitors demonstrated superior kinase inhibitory activity and notable antiproliferative and proapoptotic effects on diverse cancer cells. Finally, bulk RNA-seq analysis revealed that PPHN and POAB suppressed cell growth through a range of signalling pathways. Taken together, our findings highlight two novel BCKDK inhibitors as potent therapeutic candidates for metabolic diseases and cancers associated with BCAA dysfunctional metabolism.

Branched-chain amino acid catabolic defect in vascular smooth muscle cells drives thoracic aortic dissection via mTOR hyperactivation

Metabolic reprogramming of vascular smooth muscle cell (VSMC) plays a critical role in the pathogenesis of thoracic aortic dissection (TAD). Previous researches have mainly focused on dysregulation of fatty acid or glucose metabolism, while the impact of amino acids catabolic disorder in VSMCs during the development of TAD remains elusive. Here, we identified branched-chain amino acid (BCAA) catabolic defect as a metabolic hallmark of TAD. The bioinformatics analysis and data from human aorta revealed impaired BCAA catabolism in TAD individuals. This was accompanied by upregulated branched-chain α-ketoacid dehydrogenase kinase (BCKDK) expression and BCKD E1 subunit alpha (BCKDHA) phosphorylation, enhanced vascular inflammation, and hyperactivation of mTOR signaling. Further in vivo experiments demonstrated that inhibition of BCKDK with BT2 (a BCKDK allosteric inhibitor) treatment dephosphorylated BCKDHA and re-activated BCAA catabolism, attenuated VSMCs phenotypic switching, alleviated aortic remodeling, mitochondrial reactive oxygen species (ROS) damage and vascular inflammation. Additionally, the beneficial actions of BT2 were validated in a TNF-α challenged murine VSMC cell line. Meanwhile, rapamycin conferred similar beneficial effects against VSMC phenotypic switching, cellular ROS damage as well as inflammatory response. However, co-treatment with MHY1485 (a classic mTOR activator) reversed the beneficial effects of BT2 by reactivating mTOR signaling. Taken together, the in vivo and in vitro evidence showed that impairment of BCAA catabolism resulted in aortic accumulation of BCAA and further caused VSMC phenotypic switching, mitochondrial ROS damage and inflammatory response via mTOR hyperactivation. BCKDK and mTOR signaling may serve as the potential drug targets for the prevention and treatment of TAD.

Regulation of the pleiotropic transcriptional regulator CodY on the conversion of branched-chain amino acids into branched-chain aldehydes in Lactococcus lactis.

Branched-chain aldehydes are the primary compounds that contribute to the nutty flavor in cheddar cheese. Lactococcus lactis, which is often applied as primary starter culture, is a significant contributor to the nutty flavor of cheddar cheese due to its ability of conversion of BCAAs into branched-chain aldehydes. In the present study, we found that the regulatory role of CodY is crucial for the conversion. CodY acts as a pleiotropic transcriptional regulator via binding to various regulatory regions of key genes. The results presented valuable knowledge into the role of CodY on the regulation and biosynthetic pathway of branched-chain amino acids and the related aldehydes. Furthermore, it provided new insight for increasing the nutty flavor produced during the manufacture and ripening of cheese.

Divergent Skeletal Muscle Metabolomic Signatures of Different Exercise Training Modes Independently Predict Cardiometabolic Risk Factors.

We aimed to understand the link between skeletal muscle metabolites and cardiometabolic health after exercise training. Although aerobic, resistance, and combined exercise training each enhance muscle insulin sensitivity as well as other cardiometabolic parameters, they disparately alter amino and citric acid metabolites as well as the lipidome, linking these metabolomic changes independently to the improvement of cardiometabolic risks with each exercise training mode. These findings reveal an important layer of the unique exercise mode-dependent changes in muscle metabolism, which may eventually lead to more informed exercise prescription for improving SI.

Mitophagy in Astrocytes Is Required for the Health of Optic Nerve.

Mitochondrial dysfunction in astrocytes has been implicated in the development of various neurological disorders. Mitophagy, mitochondrial autophagy, is required for proper mitochondrial function by preventing the accumulation of damaged mitochondria. The importance of mitophagy, specifically in the astrocytes of the optic nerve (ON), has been little studied. We introduce an animal model in which two separate mutations act synergistically to produce severe ON degeneration. The first mutation is in Cryba1, which encodes βA3/A1-crystallin, a lens protein also expressed in astrocytes, where it regulates lysosomal pH. The second mutation is in Bckdk, which encodes branched-chain ketoacid dehydrogenase kinase, which is ubiquitously expressed in the mitochondrial matrix and involved in the catabolism of the branched-chain amino acids. BCKDK is essential for mitochondrial function and the amelioration of oxidative stress. Neither of the mutations in isolation has a significant effect on the ON, but animals homozygous for both mutations (DM) exhibit very serious ON degeneration. ON astrocytes from these double-mutant (DM) animals have lysosomal defects, including impaired mitophagy, and dysfunctional mitochondria. Urolithin A can rescue the mitophagy impairment in DM astrocytes and reduce ON degeneration. These data demonstrate that efficient mitophagy in astrocytes is required for ON health and functional integrity.

Reactive nitrogen species inhibit branched chain alpha-ketoacid dehydrogenase complex and impact muscle cell metabolism

Branched chain α-ketoacid dehydrogenase complex (BCKDC) is the rate-limiting enzyme in branched chain amino acid (BCAA) catabolism, a metabolic pathway with great importance for human health. BCKDC belongs to the mitochondrial α-ketoacid dehydrogenase complex family, which also includes pyruvate dehydrogenase complex and oxoglutarate dehydrogenase complex. Here, we revealed that BCKDC can be substantially inhibited by reactive nitrogen species (RNS) via a mechanism similar to what we recently discovered with pyruvate dehydrogenase complex and oxoglutarate dehydrogenase complex-RNS can cause inactivating covalent modifications of the lipoic arm on its E2 subunit. In addition, we showed that such reaction between RNS and the lipoic arm of the E2 subunit can further promote inhibition of the E3 subunits of α-ketoacid dehydrogenase complexes. We examined the impacts of this RNS-mediated BCKDC inhibition in muscle cells, an important site of BCAA metabolism, and demonstrated that the nitric oxide production induced by cytokine stimulation leads to a strong inhibition of BCKDC activity and BCAA oxidation in myotubes and myoblasts. More broadly, nitric oxide production reduced the level of functional lipoic arms across the multiple α-ketoacid dehydrogenases and led to intracellular accumulation of their substrates (α-ketoacids), decrease of their products (acyl-CoAs), and a lower cellular energy charge. In sum, this work revealed a new mechanism for BCKDC regulation, demonstrated that RNS can generally inhibit all α-ketoacid dehydrogenases, which has broad physiological implications across multiple cell types, and elucidated the mechanistic connection between RNS-driven inhibitory modifications on the E2 and E3 subunits of α-ketoacid dehydrogenases.

Branched-chain keto-acid dehydrogenase kinase regulates vascular permeability and angiogenesis to facilitate tumor metastasis in renal cell carcinoma.

Branched-chain keto-acid dehydrogenase kinase (BCKDK) is the rate-limiting enzyme of branched-chain amino acid (BCAA) metabolism. In the last six years, BCKDK has been used as a kinase to promote tumor proliferation and metastasis. Renal cell carcinoma (RCC) is a highly vascularized tumor. A high degree of vascularization promotes tumor metastasis. Our objective is to explore the relationship between BCKDK and RCC metastasis and its specific mechanism. In our study, BCKDK is highly expressed in renal clear cell carcinoma and promotes the migration of clear cell renal cell carcinoma (ccRCC). Exosomes from ccRCC cells can promote vascular permeability and angiogenesis, especially when BCKDK is overexpressed in ccRCC cells. BCKDK can also augment the miR-125a-5p expression in ccRCC cells and derived exosomes, thereby decreasing the downstream target protein VE-cadherin level, weakening adhesion junction expression, increasing vascular permeability, and promoting angiogenesis in HUVECs. The novel BCKDK/Exosome-miR-125a-5p/VE-cadherin axis regulates intercellular communication between ccRCC cells and HUVECs. BCKDK plays a critical role in renal cancer metastasis, may be used as a molecular marker of metastatic ccRCC, and even may become a potential target of clinical anti-vascular therapy for ccRCC.

Abstract B003: Increasing branched-chain amino acid metabolism reduces clear cell renal cell carcinoma growth

Abstract North America has the highest incidence of renal cancer in the world with the most common subtype being clear cell renal cell carcinoma (ccRCC). Metabolic dysfunction is a hallmark of ccRCC based on molecular analysis and its clear cell histologic appearance due to significant cytoplasmic accumulation of lipid droplets and glycogen. Using publicly available RNA-Seq and proteomic datasets, we identified reduced expression of branched-chain amino acid (BCAA) enzymes BCAA transaminase 2 (BCAT2) and the branched-chain ketoacid dehydrogenase complex (BCKDH) in ccRCC compared to healthy kidney tissue. We validated these results by confirming that BCAT2 and the BCKDH complex are decreased at the mRNA and protein level in ccRCC tumors and cell lines compared to pair-matched normal adjacent kidney tissue. The reduced expression of the BCKDH complex was reinforced at the genome level by copy number loss of BCKDH subunits DBT and BCKDHB, underscoring the selection for suppression of this pathway. Metabolomics analysis then showed that the abundance of BCAAs were decreased in ccRCC tumors. Additionally, public datasets revealed that ccRCC patients presenting low mRNA expression of any of the four BCKDH subunits DBT, BCKDHB, BCKDHA, and DLD have a worse overall survival compared to patients with higher expression. To test if reactivating the BCAA pathway would impact ccRCC growth, I inhibited BCKDK, a kinase that inactivates the BCKDH complex, pharmacologically with BT2 and genetically with shRNA. Multiple ccRCC cell lines demonstrated reduced proliferation due to apoptosis after being treated with shRNA targeting BCKDK. Cell viability could be rescued by the antioxidant N-acetyl cysteine, suggesting loss of BCKDK increased the production of reactive oxygen species (ROS). Flow cytometry showed that knocking down BCKDK increases cellular ROS. Our data reveal that BCAA catabolism is decreased in ccRCC and reactivating the pathway reduces ccRCC growth in vitro by inducing apoptosis through increased production of ROS. This suggests that BCKDK could be a therapeutic target in ccRCC. Citation Format: Nathan J. Coffey, Romain Riscal, Nicolas Skuli, Nicholas P. Lesner, Michael Noji, Christine Jiang, Laura C. Kim, Xu Han, Megan C. Blair, Brian Keith, Zoltan Arany, M. Celeste Simon. Increasing branched-chain amino acid metabolism reduces clear cell renal cell carcinoma growth [abstract]. In: Proceedings of the AACR Special Conference: Advances in Kidney Cancer Research; 2023 Jun 24-27; Austin, Texas. Philadelphia (PA): AACR; Cancer Res 2023;83(16 Suppl):Abstract nr B003.

Small molecule branched-chain ketoacid dehydrogenase kinase (BDK) inhibitors with opposing effects on BDK protein levels

Branched chain amino acid (BCAA) catabolic impairments have been implicated in several diseases. Branched chain ketoacid dehydrogenase (BCKDH) controls the rate limiting step in BCAA degradation, the activity of which is inhibited by BCKDH kinase (BDK)-mediated phosphorylation. Screening efforts to discover BDK inhibitors led to identification of thiophene PF-07208254, which improved cardiometabolic endpoints in mice. Structure-activity relationship studies led to identification of a thiazole series of BDK inhibitors; however, these inhibitors did not improve metabolism in mice upon chronic administration. While the thiophenes demonstrated sustained branched chain ketoacid (BCKA) lowering and reduced BDK protein levels, the thiazoles increased BCKAs and BDK protein levels. Thiazoles increased BDK proximity to BCKDH-E2, whereas thiophenes reduced BDK proximity to BCKDH-E2, which may promote BDK degradation. Thus, we describe two BDK inhibitor series that possess differing attributes regarding BDK degradation or stabilization and provide a mechanistic understanding of the desirable features of an effective BDK inhibitor.

Abstract P3202: The Branched Chain α-Ketoacid Dehydrogenase Kinase (BCKDK) Inhibitor BT2 Is A Mitochondrial Uncoupler

Elevated levels of branched-chain amino acids (BCAAs) are associated with cardiovascular and metabolic disease including heart failure, diabetes, and obesity. BCAAs are first transaminated into their respective branched-chain α-ketoacids (BCKAs) by the mitochondrial branched-chain amino-transaminase (BCAT m ). The pharmacological agent BT2 (dichloropheno[b]thiophene-2-carboxylic-acid) was designed to induce catabolism of BCAAs by inhibiting the branched-chain α-ketoacid dehydrogenase kinase (BCKDK). The function of BCKDK is to phosphorylate and therefore deactivate the branched-chain α-ketoacid dehydrogenase (BCKDH), an enzymatic complex that converts the BCKAs into their respective R-CoAs. Although it has been shown that BT2 protects from heart failure and metabolic disease in animal models, recent studies have suggested that its protective effects may originate from a mechanism independent of targeting BCAA oxidation. The objective of this study was to investigate alternative molecular mechanisms by which BT2 may confer cardioprotection and protect from metabolic disease. We hypothesized that BT2 is a mitochondrial uncoupler based on its chemical structure as a lipophilic weak acid. We demonstrate BT2 is a mitochondrial uncoupler using a combination of respirometry, membrane potential, and patch-clamp electrophysiology. BT2 has 20% of the potency of the chemical uncoupler 2,4-dinitrophenol (DNP). The data suggest BT2 may exert some of its cardioprotective effects and protection from metabolic disease via mitochondrial uncoupling.