Michiko Narazaki

Analysis of Metabolic Remodeling in Compensated Left Ventricular Hypertrophy and Heart Failure

Background—Congestive heart failure (CHF) is associated with a change in cardiac energy metabolism. However, the mechanism by which this change is induced and causes the progression of CHF is unclear. Methods and Results—We analyzed the cardiac energy metabolism of Dahl salt-sensitive rats fed a high-salt diet, which showed a distinct transition from compensated left ventricular hypertrophy to CHF. Glucose uptake increased at the left ventricular hypertrophy stage, and glucose uptake further increased and fatty acid uptake decreased at the CHF stage. The gene expression related to glycolysis, fatty acid oxidation, and mitochondrial function was preserved at the left ventricular hypertrophy stage but decreased at the CHF stage and was associated with decreases in levels of transcriptional regulators. In a comprehensive metabolome analysis, the pentose phosphate pathway that regulates the cellular redox state was found to be activated at the CHF stage. Dichloroacetate (DCA), a compound known to enhance glucose oxidation, increased energy reserves and glucose uptake. DCA improved cardiac function and the survival of the animals. DCA activated the pentose phosphate pathway in the rat heart. DCA activated the pentose phosphate pathway, decreased oxidative stress, and prevented cell death of cultured cardiomyocytes. Conclusions—Left ventricular hypertrophy or CHF is associated with a distinct change in the metabolic profile of the heart. DCA attenuated the transition associated with increased energy reserves, activation of the pentose phosphate pathway, and reduced oxidative stress.

Constitutive SIRT1 overexpression impairs mitochondria and reduces cardiac function in mice.

Heart failure is associated with a change in cardiac energy metabolism. SIRT1 is a NAD(+)-dependent protein deacetylase, and important in the regulation of cellular energy metabolism. To examine the role of SIRT1 in cardiac energy metabolism, we created transgenic mice overexpressing SIRT1 in a cardiac-specific manner, and investigated cardiac functional reserve, energy reserve, substrate uptake, and markers of mitochondrial function. High overexpression of SIRT1 caused dilated cardiomyopathy. Moderate overexpression of SIRT1 impaired cardiac diastolic function, but did not cause heart failure. Fatty acid uptake was decreased and the number of degenerated mitochondria was increased dependent on SIRT1 gene dosage. Markers of reactive oxygen species were decreased. Changes in morphology and reactive oxygen species were associated with the reduced expression of genes related to mitochondrial function and autophagy. In addition, the respiration of isolated mitochondria was decreased. Cardiac function was normal in transgenic mice expressing a low level of SIRT1 at baseline, but the mice developed cardiac dysfunction upon pressure overload. In summary, the constitutive overexpression of SIRT1 reduced cardiac function associated with impaired mitochondria in mice.

Monitoring of biological one-electron reduction by 19F NMR using hypoxia selective activation of an 19F-labeled indolequinone derivative

Biological reduction of fluorine-labeled indolequinone derivative (IQ-F) was characterized by (19)F NMR for quantitative molecular understanding. The chemical shift change in (19)F NMR allowed monitoring of the enzymatic reduction of IQ-F. Upon hypoxic treatment of IQ-F with NADPH:cytochrome P450 reductase, IQ-F was activated via catalytic one-electron reduction to release nonafluoro-tert-butyl alcohol (F-OH), while the formation of F-OH was significantly suppressed under aerobic conditions. Similar hypoxia-selective reduction of IQ-F occurred within A549 cells, which expresses NADPH:cytochrome P450 reductase. The kinetic analysis was also performed to propose a reaction mechanism. The molecular oxygen slightly prevents the binding of IQ-F to reductase, while the rate of net reaction was decreased due to oxidation of a semiquinone anion radical intermediate generated by one-electron reduction of IQ-F. The disappearance of IQ-F and appearance of F-OH were imaged by (19)F fast spin echo, thus visualizing the hypoxia-selective reduction of IQ-F by means of MR imaging.

Size-Controlled and Biocompatible Gd2O3 Nanoparticles for Dual Photoacoustic and MR Imaging

The synthesis, characterization, and functional evaluation of new size-controlled and biocompatible Gd(2) O(3) nanoparticles as a bimodal contrast agent for use in photoacoustic (PA) and magnetic resonance (MR) imaging are reported. These nanoparticles show a clear PA image by themselves, without conjugation with gold, rare earth metals, or dyes. Relaxivity measurement by MR imaging clearly shows that their relaxivity, r(1) , is twice that of clinically available Gd-DTPA.

Construction of a 19F-lectin biosensor for glycoprotein imaging by using affinity-guided DMAP chemistry

In this study, assisted by affinity-guided DMAP strategy, we developed a novel (19)F-modified lectin as a biosensor for specific detection and imaging of glycoproteins. Exploited the large chemical shift anisotropy property of (19)F nuclei, glycoproteins detected by our (19)F-biosensor are signatured by broadened peaks in (19)F NMR, hence enabled the distinction between glycoproteins and small molecule saccharides. Such signal on/off switching was also applied to glycoprotein imaging by (19)F MRI.

Persistent Overexpression of Phosphoglycerate Mutase, a Glycolytic Enzyme, Modifies Energy Metabolism and Reduces Stress Resistance of Heart in Mice

Background Heart failure is associated with changes in cardiac energy metabolism. Glucose metabolism in particular is thought to be important in the pathogenesis of heart failure. We examined the effects of persistent overexpression of phosphoglycerate mutase 2 (Pgam2), a glycolytic enzyme, on cardiac energy metabolism and function. Methods and Results Transgenic mice constitutively overexpressing Pgam2 in a heart-specific manner were generated, and cardiac energy metabolism and function were analyzed. Cardiac function at rest was normal. The uptake of analogs of glucose or fatty acids and the phosphocreatine/βATP ratio at rest were normal. A comprehensive metabolomic analysis revealed an increase in the levels of a few metabolites immediately upstream and downstream of Pgam2 in the glycolytic pathway, whereas the levels of metabolites in the initial few steps of glycolysis and lactate remained unchanged. The levels of metabolites in the tricarboxylic acid (TCA) cycle were altered. The capacity for respiration by isolated mitochondria in vitro was decreased, and that for the generation of reactive oxygen species (ROS) in vitro was increased. Impaired cardiac function was observed in response to dobutamine. Mice developed systolic dysfunction upon pressure overload. Conclusions Constitutive overexpression of Pgam2 modified energy metabolism and reduced stress resistance of heart in mice.

Measurement of Technetium-99m Sestamibi Signals in Rats Administered a Mitochondrial Uncoupler and in a Rat Model of Heart Failure

Background Many methods have been used to assess mitochondrial function. Technetium-99m sestamibi (99mTc-MIBI), a lipophilic cation, is rapidly incorporated into myocardial cells by diffusion and mainly localizes to the mitochondria. The purpose of this study was to investigate whether measurement of 99mTc-MIBI signals in animal models could be used as a tool to quantify mitochondrial membrane potential at the organ level. Methods and Results We analyzed 99mTc-MIBI signals in Sprague-Dawley (SD) rat hearts perfused with carbonyl cyanide m-chlorophenylhydrazone (CCCP), a mitochondrial uncoupler known to reduce the mitochondrial membrane potential. 99mTc-MIBI signals could be used to detect changes in the mitochondrial membrane potential with sensitivity comparable to that obtained by two-photon laser microscopy with the cationic probe tetramethylrhodamine ethyl ester (TMRE). We also measured 99mTc-MIBI signals in the hearts of SD rats administered CCCP (4 mg/kg intraperitoneally) or vehicle. 99mTc-MIBI signals decreased in rat hearts administered CCCP, and the ATP content, as measured by 31P magnetic resonance spectroscopy, decreased simultaneously. Next, we administered 99mTc-MIBI to Dahl salt-sensitive rats fed a high-salt diet, which leads to hypertension and heart failure. The 99mTc-MIBI signal per heart tissue weight was inversely correlated with heart weight, cardiac function, and the expression of atrial natriuretic factor, a marker of heart failure, and positively correlated with the accumulation of labeled fatty acid analog. The 99mTc-MIBI signal per liver tissue weight was lower than that per heart tissue weight. Conclusion Measurement of 99mTc-MIBI signals can be an effective tool for semiquantitative investigation of cardiac mitochondrial membrane potential in the SD rat model by using a chemical to decrease the mitochondrial membrane potential. The 99mTc-MIBI signal per heart tissue weight was inversely correlated with the severity of heart failure in the Dahl rat model.

A motion tracking method that applies a spread spectrum communication technique to tagging MR imaging.

PURPOSE We propose a new motion tracking method that encodes an objects position information using tagging magnetic resonance (MR) images as digital codes, and we assess the methods feasibility in stationary and moving phantoms. The encoding and decoding of tag patterns employ principles of spread spectrum communication. METHODS We used a segmented fast low angle shot cine sequence (FLASH) with spatial modulation of magnetization (SPAMM) preparation pulses to encode position information as 7-bit code words and used this spread code to decode the position information. To make 7-bit code words using tag images, we adjusted the flip angle and phase of the 4 composite radiofrequency (RF) pulses and the gradient magnetic field strength in the SPAMM pulse to generate 7 types of tag patterns. The proposed method required 7 acquisitions with 7 types of tag patterns. We compared results with images obtained by conventional tagging in stationary and moving phantom experiments. RESULTS In a stationary phantom, the proposed method showed the same ability to identify pixel position as conventional tagging method using improved SNR images with the average of 7 acquisitions. In a moving phantom, pixel position was successfully decoded by the proposed method on a pixel-by-pixel basis. In this method, the motion of the phantom was detected by the simple calculation of the correlation coefficient of the code words. CONCLUSION We introduced a spread spectrum communication technique to tagging MR imaging that regards tag patterns as digital codes, and we demonstrated the methods potential to detect pixel position in sub-pixel resolution.