Impaired oxidative phosphorylation in hepatic mitochondria in growth-retarded rats

Intrauterine growth retardation (IUGR) has been linked to the development of type 2 diabetes in adulthood. We have developed an IUGR model in the rat whereby the animals develop diabetes between 3 and 6 mo of age that is associated with insulin resistance. Alterations in hepatic glucose metabolism are known to contribute to the hyperglycemia of diabetes; however, the mechanisms underlying this phenomenon have not been fully explained. To address this issue, intact liver mitochondria were isolated from IUGR and control offspring at different ages to examine the nature and time course of possible defects in oxidative metabolism. Phospho enolpyruvate carboxykinase (PEPCK) expression was also measured in livers of IUGR and control offspring. Rates of ADP-stimulated (state 3) oxygen consumption were increased for succinate in the fetus and for α-ketoglutarate and glutamate at day 1, reflecting possible compensatory metabolic adaptations to acute hypoxia and acidosis in IUGR rats. By day 14, oxidation of glutamate and α-ketoglutarate had returned to normal, and by day 28, oxidation rates of pyruvate, glutamate, succinate, and α-ketoglutarate were significantly lower than those of controls. Rotenone-sensitive NADH-O2 oxidoreductase activity was similar in control and IUGR mitochondria at all ages, showing that the defect responsible for decreased pyruvate, glutamate, and α-ketoglutarate oxidation in IUGR liver precedes the electron transport chain and involves pyruvate and α-ketoglutarate dehydrogenases. Increased levels of manganese superoxide dismutase suggest that an antioxidant response has been mounted, and hydroxynonenal (HNE) modification of pyruvate dehydrogenase E2-(catalytic) and E3-binding protein subunits suggests that HNE-induced inactivation of this key enzyme may play a role in the mechanism of injury. The level of PEPCK mRNA was increased 250% in day 28 IUGR liver, indicating altered gene expression of the gluconeogenic enzyme that precedes overt hyperglycemia. These results indicate that uteroplacental insufficiency impairs mitochondrial oxidative phosphorylation in the liver and that this derangement predisposes the IUGR rat to increased hepatic glucose production by suppressing pyruvate oxidation and increasing gluconeogenesis.

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Exogenous amino acids suppress glucose oxidation and potentiate hepatic glucose production in late gestation fetal sheep

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.00502.2016 ◽

2017 ◽

Vol 312 (5) ◽

pp. R654-R663 ◽

Cited By ~ 7

Author(s):

Laura D. Brown ◽

Jaden R. Kohn ◽

Paul J. Rozance ◽

William W. Hay ◽

Stephanie R. Wesolowski

Keyword(s):

Glucose Oxidation ◽

Hepatic Glucose Production ◽

Glucose Production ◽

Late Gestation ◽

Fetal Sheep ◽

Oxidation Rates ◽

Carbon Supply ◽

Hepatic Glucose ◽

Arterial Plasma ◽

Branched Chain

Acute amino acid (AA) infusion increases AA oxidation rates in normal late gestation fetal sheep. Because the fetal oxygen consumption rate does not change with increased AA oxidation, we hypothesized that AA infusion would suppress glucose oxidation pathways and that the additional carbon supply from AA would activate hepatic glucose production. To test this, late gestation fetal sheep were infused intravenously for 3 h with saline or exogenous AA (AA). Glucose tracer metabolic studies were performed and skeletal muscle and liver tissues samples were collected. AA infusion increased fetal arterial plasma branched chain AA, cortisol, and glucagon concentrations. Fetal glucose utilization rates were similar between basal and AA periods, yet the fraction of glucose oxidized and the glucose oxidation rate were decreased by 40% in the AA period. AA infusion increased expression of PDK4, an inhibitor of glucose oxidation, nearly twofold in muscle and liver. In liver, AA infusion tended to increase PCK1 gluconeogenic gene and PCK1 correlated with plasma cortisol concentrations. AA infusion also increased liver mRNA expression of the lactate transporter gene ( MCT1), protein expression of GLUT2 and LDHA, and phosphorylation of AMPK, 4EBP1, and S6 proteins. In isolated fetal hepatocytes, AA supplementation increased glucose production and PCK1, LDHA, and MCT1 gene expression. These results demonstrate that AA infusion into fetal sheep competitively suppresses glucose oxidation and potentiates hepatic glucose production. These metabolic patterns support flexibility in fetal metabolism in response to increased nutrient substrate supply while maintaining a relatively stable rate of oxidative metabolism.

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Non-steady state: error analysis of Steele's model and developments for glucose kinetics

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.1987.252.5.e679 ◽

1987 ◽

Vol 252 (5) ◽

pp. E679-E689 ◽

Cited By ~ 16

Author(s):

C. Cobelli ◽

A. Mari ◽

E. Ferrannini

Keyword(s):

Steady State ◽

Time Course ◽

Specific Activity ◽

Hepatic Glucose Production ◽

Glucose Production ◽

Glucose Kinetics ◽

New Model ◽

Average Value ◽

Hepatic Glucose ◽

Mean Glucose

The model proposed by Steele (Ann. NY Acad. Sci. 82: 420-430, 1959) to compute rates of appearance and disappearance in non-steady state is subjected to theoretical analysis. It is shown that this model introduces an error with two components, one dependent on the volume of the compartment, the other related to the complex configuration of the system. The errors depend on the time course of specific activity, change differently with time, and may take the opposite sign but they do not, in general, cancel each other. Corollaries of this analysis are the following: there is no single pool-fraction value satisfactory under all non-steady-state situations; keeping tracer specific activity as constant as possible during the experiment minimizes both errors; and non-steady-state analysis demands proper modeling of the system. Tracer experiments were carried out in five normal volunteers. Plasma [3-3H]glucose concentration was first brought to equilibrium by means of a primed constant 2-h infusion, and then the steady state was perturbed by a 2-h euglycemic insulin (1 mU X min-1 X kg-1) clamp, realizing a transition between a basal and a euglycemic hyperinsulinemic steady state. These data were analyzed with Steele's equation, the two compartment models of Radziuk et al. [Am. J. Physiol. 234 (Endocrinol. Metab. Gastrointest. Physiol. 3): E84-E93, 1978], and a new model based on a study on glucose kinetics carried out in the two steady states separately. Steele's equation yielded negative values for hepatic glucose production already 40 min into the clamp and throughout the study. The average value of glucose production during the 2nd h was -0.88 mg X min-1 X kg-1; the suppression of basal release over the 2-h period was 115%. In contrast, the new model calculated a mean glucose production of 0.37 mg X min-1 X kg-1 during the 2nd h and an overall suppression of 62%; no negative values were obtained.

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Enhanced gluconeogenesis from lactate in perfused livers after endurance training

Journal of Applied Physiology ◽

10.1152/jappl.1993.74.2.782 ◽

1993 ◽

Vol 74 (2) ◽

pp. 782-787 ◽

Cited By ~ 27

Author(s):

K. D. Sumida ◽

J. H. Urdiales ◽

C. M. Donovan

Keyword(s):

Endurance Training ◽

Hepatic Glucose Production ◽

Liver Perfusion ◽

Glucose Production ◽

Hepatic Gluconeogenesis ◽

Bicarbonate Buffer ◽

Hepatic Glucose ◽

14Co2 Production ◽

Glucose Output ◽

And Control

The effects of endurance training (running 90 min/day at 30 m/min, 10% grade) on hepatic gluconeogenesis were studied in 24-h-fasted rats with use of the isolated liver perfusion technique. After isolation, the liver was perfused (single pass) for 30 min with Krebs-Henseleit bicarbonate buffer and fresh bovine erythrocytes (hematocrit 22–24%) with no added substrate. Subsequent to the "washout" period, the reservoir was elevated with various concentrations of lactate and [U-14C]lactate (10,000 dpm/ml) to assess hepatic glucose production. Relative flow rates were not significantly different between trained (1.94 +/- 0.05 ml/g liver) and control livers (1.91 +/- 0.05 ml/g liver). Furthermore, no significant differences were observed in perfusate pH, hematocrit, bile production, or serum alanine aminotransferase effluxing from trained or control livers. At saturating arterial lactate concentrations (> 2 mM), the maximal rate (Vmax) for hepatic glucose production was significantly higher for trained (0.91 +/- 0.04 mumol.min-1 x g liver-1) than for control livers (0.73 +/- 0.02 mumol.min-1 x g liver-1). That this reflected increased gluconeogenesis is supported by a significant elevation in the Vmax for [14C]glucose production from trained (13,150 +/- 578 dpm.min-1 x g liver-1) compared with control livers (10,712 +/- 505 dpm.min-1 x g liver-1). Significant increases were also observed in the Vmax for lactate uptake (25%), O2 consumption (19%), and 14CO2 production (23%) from endurance-trained livers. The Km for hepatic glucose output, approximately 1.05 mM lactate, was unchanged after endurance training. These findings demonstrate that chronic physical activity results in an elevated capacity for hepatic gluconeogenesis, as assessed in situ at saturating lactate concentrations.

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Hepatic glucose production during the labeled IVGTT: estimation by deconvolution with a new minimal model

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.1993.264.5.e829 ◽

1993 ◽

Vol 264 (5) ◽

pp. E829-E841 ◽

Cited By ~ 15

Author(s):

A. Caumo ◽

C. Cobelli

Keyword(s):

Impulse Response ◽

Minimal Model ◽

Time Course ◽

Hepatic Glucose Production ◽

Glucose Production ◽

Intravenous Glucose Tolerance Test ◽

Glucose Kinetics ◽

Intravenous Glucose ◽

New Model ◽

Hepatic Glucose

A method for the estimation of hepatic glucose production during a labeled intravenous glucose tolerance test (IVGTT) is proposed. Stable-label IVGTT data in normal subjects have been considered. The method is based on deconvolution and uses a new two-compartment minimal model of glucose kinetics to describe the time-varying impulse response of the glucose system. A new model of glucose kinetics was needed because the available single-compartment minimal model, specifically developed to interpret labeled IVGTT data, provided a nonphysiological pattern of hepatic glucose production. The new minimal model has two novel features: glucose kinetics are described by a two-compartment structure, and insulin exerts its action on the irreversible loss of the slowly exchanging glucose pool. The deconvolution scheme used to reconstruct hepatic glucose production is described in detail both in terms of computational aspects and reliability. Confidence limits of the reconstructed hepatic glucose production in each individual are derived by taking into account both the measurement error of the data and the uncertainty associated with the description of the impulse response. Physiological plausibility of the time course of hepatic glucose production provided by this new method is discussed. The ability of the new model to reconstruct hepatic glucose production considerably enriches the kinetic portrait of glucose metabolism that can be obtained from the minimal-model analysis of labeled IVGTT data.

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Potential biomarker of metformin action

Journal of Endocrinology ◽

10.1530/joe-14-0084 ◽

2014 ◽

Vol 221 (3) ◽

pp. 363-369 ◽

Cited By ~ 13

Author(s):

Ling He ◽

Shumei Meng ◽

Emily L Germain-Lee ◽

Sally Radovick ◽

Fredric E Wondisford

Keyword(s):

Blood Cells ◽

Time Course ◽

Hepatic Glucose Production ◽

White Blood Cells ◽

Glucose Production ◽

First Line ◽

Potential Biomarker ◽

Hepatic Glucose ◽

Main Effect ◽

Time Course Experiment

Metformin is a first-line, anti-diabetic agent prescribed to over 150 million people worldwide. The main effect of metformin is to suppress glucose production in the liver; however, there is no reliable biomarker to assess the effectiveness of metformin administration. Our previous studies have shown that phosphorylation of CBP at S436 is important for the regulation of hepatic glucose production by metformin. In current study, we found that CBP could be phosphorylated in white blood cells (WBCs), and CBP phosphorylation in the liver and in WBCs of mice had a similar pattern of change during a fasting time course experiment. These data suggests that CBP phosphorylation in WBCs may be used as a biomarker of metformin action in the liver.

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