Treating hepatic steatosis and fibrosis by modulating mitochondrial pyruvate metabolism

A hepatic comorbidity of metabolic syndrome, known as nonalcoholic fatty liver disease (NAFLD), is increasing in prevalence in conjunction with the pandemics of obesity and diabetes. The spectrum of NAFLD ranges from simple hepatic fat accumulation to a more severe disease termed nonalcoholic steatohepatitis (NASH), involving inflammation, hepatocyte death, and fibrosis. Importantly, NASH is linked to a much higher risk of cirrhosis, liver failure, and hepatocellular carcinoma, as well as an increased risk for nonhepatic malignancies and cardiovascular disease. Interest in the understanding of the disease processes and search for treatments for the spectrum of NAFLD-NASH has increased exponentially, but there are no approved pharmacologic therapies. In this review, we discuss the existing literature supporting insulin-sensitizing thiazolidinedione compounds as potential drug candidates for the treatment of NASH. In addition, we put these results into new context by summarizing recent studies suggesting these compounds alter mitochondrial metabolism by binding and inhibiting the mitochondrial pyruvate carrier. Keywords: Nonalcoholic Steatohepatitis, Mitochondria, Pyruvate, Thiazolidinedion

The role and mechanisms of hexokinase-2-mediated protection against cardiac cell death and disease

Numerous cancer studies demonstrate that transformed cells exhibit both increased glucose metabolism and an increased propensity to survive in the face of stressful stimuli. These studies overwhelmingly correlate with overexpression of the rate-limiting glycolysis enzyme hexokinase-2 (HK2). However, the mechanisms linking increased glucose metabolism and survival are unknown. Additionally, there is limited evidence of increased glucose utilization being beneficial in normal cell cultures, as well as in vivo. Therefore, the current studies were designed to determine the mechanisms by which increased HK2 expression promotes cell survival, as well as investigate whether HK2 overexpression could attenuate a model of cardiac disease in vivo. Findings in AIM1 demonstrate that HK2 binding to the voltage-dependent anion channel 3 (VDAC3) on the mitochondria is important for protection against reactive oxygen species (ROS)-induced cell death. In AIM2, we show that cardiac HK2 overexpression limits cardiomyocyte hypertrophy and cell death in response to chronic isoproterenol administration in vivo. Results from these studies demonstrate that HK2 limits ROS accumulation during cardiac hypertrophy, and that this attenuation of ROS is mediated via the pentose-phosphate pathway. Collectively, our data establish several mechanisms by which HK2 overexpression and increased glucose utilization protect against cardiac cell death and disease. Additionally, these findings raise the possibility that activation of HK2 may be a therapeutic target in cardiac pathologies.Includes bibliographical references

Evaluation of urinary hydrogen peroxide as an oxidative stress biomarker in a healthy Japanese population

The usefulness of urinary hydrogen peroxide (H2O2) as an oxidative stress biomarker was evaluated in 766 healthy Japanese. The mean level of urinary concentrations of H2O2 was 5.66 +/- 8.27 mu mol/g creatinine, and was significantly higher in females than in males. Significant correlations of H2O2 were observed with age, aspartate aminotransferase (AST), alanine aminotransferase (ALT), total cholesterol (TC), low-density lipoprotein cholesterol (LDL-c), insulin, 8-hydroxy-2'-deoxyguanosine (8-OHdG), and exercise habit in females. In both sexes, H2O2 showed a significant correlation with 8-OHdG. By a multiple logistic regression analysis, urinary H2O2 was positively associated with urinary 8-OHdG and TC and was inversely associated with insulin. By stratification of sex and age, the association of urinary H2O2 with TC was positive in both sexes under 50 years old and was inverse in males over 50 years old, and that with insulin was inverse in males over 50 years old and in females under 50 years old. Moreover, by stratification of sex and age, a positive association of H2O2 with exercise and an inverse association of H2O2 with alcohol consumption became clear in males under 50 years old, although there were no significant odds for H2O2 after adjustment for covariates. In conclusion, the present results suggest that urinary H2O2 is a useful biomarker for oxidative stress, showing an association with 8-OHdG, TC, and insulin independently

Quantification of global myocardial oxygenation in humans: initial experience

<p>Abstract</p> <p>Purpose</p> <p>To assess the feasibility of our newly developed cardiovascular magnetic resonance (CMR) methods to quantify global and/or regional myocardial oxygen consumption rate (MVO₂) at rest and during pharmacologically-induced vasodilation in normal volunteers.</p> <p>Methods</p> <p>A breath-hold T₂quantification method is developed to calculate oxygen extraction fraction (OEF) and MVO₂rate at rest and/or during hyperemia, using a two-compartment model. A previously reported T₂quantification method using turbo-spin-echo sequence was also applied for comparison. CMR scans were performed in 6 normal volunteers. Each imaging session consisted of imaging at rest and during adenosine-induced vasodilation. The new T₂quantification method was applied to calculate T₂in the coronary sinus (CS), as well as in myocardial tissue. Resting CS OEF, representing resting global myocardial OEF, and myocardial OEF during adenosine vasodilation were then calculated by the model. Myocardial blood flow (MBF) was also obtained to calculate MVO₂, by using a first-pass perfusion imaging approach.</p> <p>Results</p> <p>The T₂quantification method yielded a hyperemic OEF of 0.37 ± 0.05 and a hyperemic MVO₂of 9.2 ± 2.4 μmol/g/min. The corresponding resting values were 0.73 ± 0.05 and 5.2 ± 1.7 μmol/g/min respectively, which agreed well with published literature values. The MVO₂rose proportionally with rate-pressure product from the rest condition. The T₂sensitivity is approximately 95% higher with the new T₂method than turbo-spin-echo method.</p> <p>Conclusion</p> <p>The CMR oxygenation method demonstrates the potential for non-invasive estimation of myocardial oxygenation, and should be explored in patients with altered myocardial oxygenation.</p

Resting myocardial perfusion quantification with CMR arterial spin labeling at 1.5 T and 3.0 T

<p>Abstract</p> <p>Background</p> <p>The magnetic resonance technique of arterial spin labeling (ASL) allows myocardial perfusion to be quantified without the use of a contrast agent. This study aimed to use a modified ASL technique and <it>T</it>₁regression algorithm, previously validated in canine models, to calculate myocardial blood flow (MBF) in normal human subjects and to compare the accuracy and repeatability of this calculation at 1.5 T and 3.0 T. A computer simulation was performed and compared with experimental findings.</p> <p>Results</p> <p>Eight subjects were imaged, with scans at 3.0 T showing significantly higher <it>T</it>₁values (<it>P </it>< 0.001) and signal-to-noise ratios (SNR) (<it>P </it>< 0.002) than scans at 1.5 T. The average MBF was found to be 0.990 ± 0.302 mL/g/min at 1.5 T and 1.058 ± 0.187 mL/g/min at 3.0 T. The repeatability at 3.0 T was improved 43% over that at 1.5 T, although no statistically significant difference was found between the two field strengths. In the simulation, the accuracy and the repeatability of the MBF calculations were 61% and 38% higher, respectively, at 3.0 T than at 1.5 T, but no statistically significant differences were observed. There were no significant differences between the myocardial perfusion data sets obtained from the two independent observers. Additionally, there was a trend toward less variation in the perfusion data from the two observers at 3.0 T as compared to 1.5 T.</p> <p>Conclusion</p> <p>This suggests that this ASL technique can be used, preferably at 3.0 T, to quantify myocardial perfusion in humans and with further development could be useful in the clinical setting as an alternative method of perfusion analysis.</p

The tuberculosis necrotizing toxin kills macrophages by hydrolyzing NAD.

Mycobacterium tuberculosis (Mtb) induces necrosis of infected cells to evade immune responses. Recently, we found that Mtb uses the protein CpnT to kill human macrophages by secreting its C-terminal domain, named tuberculosis necrotizing toxin (TNT), which induces necrosis by an unknown mechanism. Here we show that TNT gains access to the cytosol of Mtb-infected macrophages, where it hydrolyzes the essential coenzyme NAD(+). Expression or injection of a noncatalytic TNT mutant showed no cytotoxicity in macrophages or in zebrafish zygotes, respectively, thus demonstrating that the NAD(+) glycohydrolase activity is required for TNT-induced cell death. To prevent self-poisoning, Mtb produces an immunity factor for TNT (IFT) that binds TNT and inhibits its activity. The crystal structure of the TNT-IFT complex revealed a new NAD(+) glycohydrolase fold of TNT, the founding member of a toxin family widespread in pathogenic microorganisms

NADPH and glutathione redox link TCA cycle activity to endoplasmic reticulum homeostasis

Many metabolic diseases disrupt endoplasmic reticulum (ER) homeostasis, but little is known about how metabolic activity is communicated to the ER. Here, we show in hepatocytes and other metabolically active cells that decreasing the availability of substrate for the tricarboxylic acid (TCA) cycle diminished NADPH production, elevated glutathione oxidation, led to altered oxidative maturation of ER client proteins, and attenuated ER stress. This attenuation was prevented when glutathione oxidation was disfavored. ER stress was also alleviated by inhibiting either TCA-dependent NADPH production or Glutathione Reductase. Conversely, stimulating TCA activity increased NADPH production, glutathione reduction, and ER stress. Validating these findings, deletion of the Mitochondrial Pyruvate Carrier-which is known to decrease TCA cycle activity and protect the liver from steatohepatitis-also diminished NADPH, elevated glutathione oxidation, and alleviated ER stress. Together, our results demonstrate a novel pathway by which mitochondrial metabolic activity is communicated to the ER through the relay of redox metabolites