Article

Metabolomic and mass isotopomer analysis of liver gluconeogenesis and citric acid cycle - I. Interrelation between gluconeogenesis and cataplerosis; Formation of methoxamates from aminooxyacetate and ketoacids

Department of Nutrition, Case Western Reserve University, Cleveland, Ohio 44106, USA.
Journal of Biological Chemistry (Impact Factor: 4.6). 07/2008; 283(32):21978-87. DOI: 10.1074/jbc.M803454200
Source: PubMed

ABSTRACT We conducted a study coupling metabolomics and mass isotopomer analysis of liver gluconeogenesis and citric acid cycle. Rat livers were perfused with lactate or pyruvate +/- aminooxyacetate or mercaptopicolinate in the presence of 40% enriched NaH(13)CO(3). Other livers were perfused with dimethyl [1,4-(13)C(2)]succinate +/- mercaptopicolinate. In this first of two companion articles, we show that a substantial fraction of gluconeogenic carbon leaves the liver as citric acid cycle intermediates, mostly alpha-ketoglutarate. The efflux of gluconeogenic carbon ranges from 10 to 200% of the rate of liver gluconeogenesis. This cataplerotic efflux of gluconeogenic carbon may contribute to renal gluconeogenesis in vivo. Multiple crossover analyses of concentrations of gluconeogenic intermediates and redox measurements expand previous reports on the regulation of gluconeogenesis and the effects of inhibitors. We also demonstrate the formation of adducts from the condensation, in the liver, of (i) aminooxyacetate with pyruvate, alpha-ketoglutarate, and oxaloacetate and (ii) mercaptopicolinate and pyruvate. These adducts may exert metabolic effects unrelated to their effect on gluconeogenesis.

1 Follower
 · 
96 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Metformin is considered to be one of the most effective therapeutics for treating type 2 diabetes because it specifically reduces hepatic gluconeogenesis without increasing insulin secretion, inducing weight gain or posing a risk of hypoglycaemia. For over half a century, this agent has been prescribed to patients with type 2 diabetes worldwide, yet the underlying mechanism by which metformin inhibits hepatic gluconeogenesis remains unknown. Here we show that metformin non-competitively inhibits the redox shuttle enzyme mitochondrial glycerophosphate dehydrogenase, resulting in an altered hepatocellular redox state, reduced conversion of lactate and glycerol to glucose, and decreased hepatic gluconeogenesis. Acute and chronic low-dose metformin treatment effectively reduced endogenous glucose production, while increasing cytosolic redox and decreasing mitochondrial redox states. Antisense oligonucleotide knockdown of hepatic mitochondrial glycerophosphate dehydrogenase in rats resulted in a phenotype akin to chronic metformin treatment, and abrogated metformin-mediated increases in cytosolic redox state, decreases in plasma glucose concentrations, and inhibition of endogenous glucose production. These findings were replicated in whole-body mitochondrial glycerophosphate dehydrogenase knockout mice. These results have significant implications for understanding the mechanism of metformin's blood glucose lowering effects and provide a new therapeutic target for type 2 diabetes.
    Nature 05/2014; 510(7506). DOI:10.1038/nature13270 · 42.35 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Familial hypertrophic cardiomyopathy (HCM) is largely caused by dominant mutations in genes encoding cardiac sarcomeric proteins, and it is etiologically distinct from secondary cardiomyopathies resulting from pressure/volume overload and neurohormonal or inflammatory stimuli. Here, we demonstrate that decreased left ventricular contractile function in male, but not female, HCM mice is associated with reduced fatty acid translocase (CD36) and AMP-activated protein kinase (AMPK) activity. As a result, the levels of myocardial ATP and triglyceride (TG) content are reduced, while the levels of oleic acid and TG in circulating very low density lipoproteins (VLDLs) and liver are increased. With time, these metabolic changes culminate in enhanced glucose production in male HCM mice. Remarkably, restoration of ventricular TG and ATP deficits via AMPK agonism as well as inhibition of gluconeogenesis improves ventricular architecture and function. These data underscore the importance of the systemic effects of a primary genetic heart disease to other organs and provide insight into potentially novel therapeutic interventions for HCM.
    EMBO Molecular Medicine 04/2014; 6(4). DOI:10.1002/emmm.201302852 · 8.25 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Kidney proximal tubules subjected to hypoxia/reoxygenation develop a nonesterified fatty acid-induced energetic deficit characterized by persistent partial mitochondrial deenergization that can be prevented and reversed by citric acid cycle substrates. To further assess the role of competition between fatty acids and substrates on inner membrane substrate carriers in the deenergization and the contribution to deenergization of fatty acid effects on respiratory function, digitonin-permeabilized rabbit and mouse tubules were studied using either addition of exogenous oleate after control normoxic incubation or increases of endogenous fatty acids produced by hypoxia/reoxygenation. The results demonstrated major effects of matrix oxaloacetate accumulation on succinate-supported energization and respiration and their modification by fatty acids. Improvements of energization in the presence of fatty acids by glutamate were shown to result predominantly from lowering matrix oxaloacetate rather than from amelioration of transmembrane cycling of fatty acids and uncoupling. Mouse tubules had 2.5 fold higher rates of succinate utilization, which resulted in stronger effects of oxaloacetate accumulation than rabbit tubules. Hypoxia/reoxygenation induced respiratory inhibition that was more severe for complex I-dependent substrates. Fatty acids themselves did not acutely contribute to this respiratory inhibition, but lowering them during 60 min. reoxygenation to allow recovery of ATP during that period alleviated it. These data clarify the basis for the nonesterified fatty acid-induced mitochondrial energetic deficit in kidney proximal tubules that impairs structural and functional recovery and provide insight into interactions that need to be considered in the design of substrate-based interventions to improve mitochondrial function.
    PLoS ONE 04/2014; 9(4):e94584. DOI:10.1371/journal.pone.0094584 · 3.53 Impact Factor