Skeletal muscle ATP kinetics are impaired in frail mice

The interleukin-10 knockout mouse (IL10(tm/tm)) has been proposed as a model for human frailty, a geriatric syndrome characterized by skeletal muscle (SM) weakness, because it develops an age-related decline in SM strength compared to control (C57BL/6J) mice. Compromised energy metabolism and energy deprivation appear to play a central role in muscle weakness in metabolic myopathies and muscular dystrophies. Nonetheless, it is not known whether SM energy metabolism is altered in frailty. A combination of in vivo (31)P nuclear magnetic resonance experiments and biochemical assays was used to measure high-energy phosphate concentrations, the rate of ATP synthesis via creatine kinase (CK), the primary energy reserve reaction in SM, as well as the unidirectional rates of ATP synthesis from inorganic phosphate (Pi) in hind limb SM of 92-week-old control (n = 7) and IL10(tm/tm) (n = 6) mice. SM Phosphocreatine (20.2 ± 2.3 vs. 16.8 ± 2.3 μmol/g, control vs. IL10(tm/tm), p < 0.05), ATP flux via CK (5.0 ± 0.9 vs. 3.1 ± 1.1 μmol/g/s, p < 0.01), ATP synthesis from inorganic phosphate (Pi → ATP) (0.58 ± 0.3 vs. 0.26 ± 0.2 μmol/g/s, p < 0.05) and the free energy released from ATP hydrolysis (∆G ∼ATP) were significantly lower and [Pi] (2.8 ± 1.0 vs. 5.3 ± 2.0 μmol/g, control vs. IL10(tm/tm), p < 0.05) markedly higher in IL10(tm/tm) than in control mice. These observations demonstrate that, despite normal in vitro metabolic enzyme activities, in vivo SM ATP kinetics, high-energy phosphate levels and energy release from ATP hydrolysis are reduced and inorganic phosphate is elevated in a murine model of frailty. These observations do not prove, but are consistent with the premise, that energetic abnormalities may contribute metabolically to SM weakness in this geriatric syndrome.

Creatine kinase-overexpression improves myocardial energetics, contractile dysfunction and survival in murine doxorubicin cardiotoxicity

Doxorubicin (DOX) is a commonly used life-saving antineoplastic agent that also causes dose-dependent cardiotoxicity. Because ATP is absolutely required to sustain normal cardiac contractile function and because impaired ATP synthesis through creatine kinase (CK), the primary myocardial energy reserve reaction, may contribute to contractile dysfunction in heart failure, we hypothesized that impaired CK energy metabolism contributes to DOX-induced cardiotoxicity. We therefore overexpressed the myofibrillar isoform of CK (CK-M) in the heart and determined the energetic, contractile and survival effects of CK-M following weekly DOX (5mg/kg) administration using in vivo³¹P MRS and ¹H MRI. In control animals, in vivo cardiac energetics were reduced at 7 weeks of DOX protocol and this was followed by a mild but significant reduction in left ventricular ejection fraction (EF) at 8 weeks of DOX, as compared to baseline. At baseline, CK-M overexpression (CK-M-OE) increased rates of ATP synthesis through cardiac CK (CK flux) but did not affect contractile function. Following DOX however, CK-M-OE hearts had better preservation of creatine phosphate and higher CK flux and higher EF as compared to control DOX hearts. Survival after DOX administration was significantly better in CK-M-OE than in control animals (p<0.02). Thus CK-M-OE attenuates the early decline in myocardial high-energy phosphates and contractile function caused by chronic DOX administration and increases survival. These findings suggest that CK impairment plays an energetic and functional role in this DOX-cardiotoxicity model and suggests that metabolic strategies, particularly those targeting CK, offer an appealing new strategy for limiting DOX-associated cardiotoxicity.

Creatine kinase overexpression improves ATP kinetics and contractile function in postischemic myocardium

Reduced myofibrillar ATP availability during prolonged myocardial ischemia may limit post-ischemic mechanical function. Because creatine kinase (CK) is the prime energy reserve reaction of the heart and because it has been difficult to augment ATP synthesis during and after ischemia, we used mice that overexpress the myofibrillar isoform of creatine kinase (CKM) in cardiac-specific, conditional fashion to test the hypothesis that CKM overexpression increases ATP delivery in ischemic-reperfused hearts and improves functional recovery. Isolated, retrograde-perfused hearts from control and CKM mice were subjected to 25 min of global, no-flow ischemia and 40 min of reperfusion while cardiac function [rate pressure product (RPP)] was monitored. A combination of (31)P-nuclear magnetic resonance experiments at 11.7T and biochemical assays was used to measure the myocardial rate of ATP synthesis via CK (CK flux) and intracellular pH (pH(i)). Baseline CK flux was severalfold higher in CKM hearts (8.1 ± 1.0 vs. 32.9 ± 3.8, mM/s, control vs. CKM; P < 0.001) with no differences in phosphocreatine concentration [PCr] and RPP. End-ischemic pH(i) was higher in CKM hearts than in control hearts (6.04 ± 0.12 vs. 6.37 ± 0.04, control vs. CKM; P < 0.05) with no differences in [PCr] and [ATP] between the two groups. Post-ischemic PCr (66.2 ± 1.3 vs. 99.1 ± 8.0, %preischemic levels; P < 0.01), CK flux (3.2 ± 0.4 vs. 14.0 ± 1.2 mM/s; P < 0.001) and functional recovery (13.7 ± 3.4 vs. 64.9 ± 13.2%preischemic RPP; P < 0.01) were significantly higher and lactate dehydrogenase release was lower in CKM than in control hearts. Thus augmenting cardiac CKM expression attenuates ischemic acidosis, reduces injury, and improves not only high-energy phosphate content and the rate of CK ATP synthesis in postischemic myocardium but also recovery of contractile function.

Use of perfluorocarbon nanoparticles for non-invasive multimodal cell tracking of human pancreatic islets

In vivo imaging of engraftment and immunorejection of transplanted islets is critical for further clinical development, with (1)H MR imaging of superparamagnetic iron oxide-labeled cells being the current premier modality. Using perfluorocarbon nanoparticles, we present here a strategy for non-invasive imaging of cells using other modalities. To this end, human cadaveric islets were labeled with rhodamine-perfluorooctylbromide (PFOB) nanoparticles, rhodamine-perfluoropolyether (PFPE) nanoparticles or Feridex as control and tested in vitro for cell viability and c-peptide secretion for 1 week. (19)F MRI, computed tomography (CT) and ultrasound (US) imaging was performed on labeled cell phantoms and on cells following transplantation beneath the kidney capsule of mice and rabbits. PFOB and PFPE-labeling did not reduce human islet viability or glucose responsiveness as compared with unlabeled cells or SPIO-labeled cells. PFOB- and PFPE-labeled islets were effectively fluorinated for visualization by (19)F MRI. PFOB-labeled islets were acoustically reflective for detection by US imaging and became sufficiently brominated to become radiopaque allowing visualization with CT. Thus, perfluorocarbon nanoparticles are multimodal cellular contrast agents that may find applications in real-time targeted delivery and imaging of transplanted human islets or other cells in a clinically applicable manner using MRI, US or CT imaging.

Creatine kinase-mediated improvement of function in failing mouse hearts provides causal evidence the failing heart is energy starved

ATP is required for normal cardiac contractile function, and it has long been hypothesized that reduced energy delivery contributes to the contractile dysfunction of heart failure (HF). Despite experimental and clinical HF data showing reduced metabolism through cardiac creatine kinase (CK), the major myocardial energy reserve and temporal ATP buffer, a causal relationship between reduced ATP-CK metabolism and contractile dysfunction in HF has never been demonstrated. Here, we generated mice conditionally overexpressing the myofibrillar isoform of CK (CK-M) to test the hypothesis that augmenting impaired CK-related energy metabolism improves contractile function in HF. CK-M overexpression significantly increased ATP flux through CK ex vivo and in vivo but did not alter contractile function in normal mice. It also led to significantly increased contractile function at baseline and during adrenergic stimulation and increased survival after thoracic aortic constriction (TAC) surgery-induced HF. Withdrawal of CK-M overexpression after TAC resulted in a significant decline in contractile function as compared with animals in which CK-M overexpression was maintained. These observations provide direct evidence that the failing heart is "energy starved" as it relates to CK. In addition, these data identify CK as a promising therapeutic target for preventing and treating HF and possibly diseases involving energy-dependent dysfunction in other organs with temporally varying energy demands.

Fluorocapsules for improved function, immunoprotection, and visualization of cellular therapeutics with MR, US, and CT imaging

PURPOSE

To develop novel immunoprotective alginate microcapsule formulations containing perfluorocarbons (PFCs) that may increase cell function, provide immunoprotection for xenografted cells, and simultaneously enable multimodality imaging.

MATERIALS AND METHODS

All animal experiments were approved by an Institutional Animal Care and Use Committee. Cadaveric human islet cells were encapsulated with alginate, poly-l-lysine, and perfluorooctyl bromide (PFOB) or perfluoropolyether (PFPE). In vitro viability and the glucose-stimulation index for insulin were determined over the course of 2 weeks and analyzed by using a cross-sectional time series regression model. The sensitivity of multimodality (computed tomography [CT], ultrasonography [US], and fluorine 19 [(19)F] magnetic resonance [MR] imaging) detection was determined for fluorocapsules embedded in gel phantoms. C57BL/6 mice intraperitoneally receiving 6000 PFOB-labeled (n = 6) or 6000 PFPE-labeled (n = 6) islet-containing fluorocapsules and control mice intraperitoneally receiving 6000 PFOB-labeled (n = 6) or 6000 PFPE-labeled (n = 6) fluorocapsules without islets were monitored for human C-peptide (insulin) secretion during a period of 55 days. Mice underwent (19)F MR imaging at 9.4 T and micro-CT. Swine (n = 2) receiving 9000 PFOB capsules through renal artery catheterization were imaged with a clinical multidetector CT scanner. Signal intensity was evaluated by using a paired t test.

RESULTS

Compared with nonfluorinated alginate microcapsules, PFOB fluorocapsules increased insulin secretion of encapsulated human islets, with values up to 18.5% (3.78 vs 3.19) at 8-mmol/L glucose concentration after 7 days in culture (P < .001). After placement of the immunoprotected encapsulated cells into mice, a sustained insulin release was achieved with human C-peptide levels of 19.1 pmol/L ± 0.9 (standard deviation) and 33.0 pmol/L ± 1.0 for PFPE and PFOB capsules, respectively. Fluorocapsules were readily visualized with (19)F MR imaging, US imaging, and CT with research- and clinical-grade imagers for all modalities.

CONCLUSION

Fluorocapsules enhance glucose responsiveness and insulin secretion in vitro, enable long-term insulin secretion by xenografted islet cells in vivo, and represent a novel contrast agent platform for multimodality imaging.

Impaired ATP kinetics in failing in vivo mouse heart

BACKGROUND

The hypothesis that the failing heart may be energy-starved is supported in part by observations of reduced rates of adenosine 5'-triphosphate (ATP) synthesis through the creatine kinase (CK) reaction, the primary myocardial energy reservoir, in patients with heart failure (HF). Although murine models have been used to probe HF pathophysiology, it has not been possible to noninvasively measure the rate of ATP synthesis through CK in the in vivo mouse heart. The purpose of this work was to exploit noninvasive spatially localized magnetic resonance spectroscopy techniques to measure ATP flux through CK in in vivo mouse hearts and determine the extent of any reductions in murine HF.

METHODS AND RESULTS

The Triple Repetition Time Saturation Transfer (TRiST) magnetic resonance spectroscopy method of measuring ATP kinetics was first validated in skeletal muscle, rendering similar results to conventional saturation transfer magnetic resonance spectroscopy. In normal mouse hearts, the in vivo CK pseudo-first-order-rate constant, k(F), was 0.32±0.03 s(-1) (mean±SD) and the rate of ATP synthesis through CK was 3.16±0.47 μmol/g/s. Thoracic aortic constriction reduced k(F) by 31% (0.23±0.03 s(-1), P<0.0001) and ATP synthesis through CK by 51% (1.54±0.25 μmol/g/s, P<0.0001), values analogous to those in failing human hearts.

CONCLUSIONS

Despite the small size and high murine heart rate, the ATP synthesis rate through CK is similar in vivo in murine and human hearts and comparably reduced in HF. Because murine thoracic aortic constriction shares fundamental energetic similarities with human HF, this model and new magnetic resonance spectroscopy approach promise a powerful means to noninvasively probe altered energetics in HF.

Reduced in vivo high-energy phosphates precede adriamycin-induced cardiac dysfunction

Adriamycin (ADR) is an established, life-saving antineoplastic agent, the use of which is often limited by cardiotoxicity. ADR-induced cardiomyopathy is often accompanied by depressed myocardial high-energy phosphate (HEP) metabolism. Impaired HEP metabolism has been suggested as a potential mechanism of ADR cardiomyopathy, in which case the bioenergetic decline should precede left ventricular (LV) dysfunction. We tested the hypothesis that murine cardiac energetics decrease before LV dysfunction following ADR (5 mg/kg ip, weekly, 5 injections) in the mouse. As a result, the mean myocardial phosphocreatine-to-ATP ratio (PCr/ATP) by spatially localized (31)P magnetic resonance spectroscopy decreased at 6 wk after first ADR injection (1.79 + or - 0.18 vs. 1.39 + or - 0.30, means + or - SD, control vs. ADR, respectively, P < 0.05) when indices of systolic and diastolic function by magnetic resonance imaging were unchanged from control values. At 8 wk, lower PCr/ATP was accompanied by a reduction in ejection fraction (67.3 + or - 3.9 vs. 55.9 + or - 4.2%, control vs. ADR, respectively, P < 0.002) and peak filling rate (0.56 + or - 0.12 vs. 0.30 + or - 0.13 microl/ms, control vs. ADR, respectively, P < 0.01). PCr/ATP correlated with peak filling rate and ejection fraction, suggesting a relationship between cardiac energetics and both LV systolic and diastolic dysfunction. In conclusion, myocardial in vivo HEP metabolism is impaired following ADR administration, occurring before systolic or diastolic abnormalities and in proportion to the extent of eventual contractile abnormalities. These observations are consistent with the hypothesis that impaired HEP metabolism contributes to ADR-induced myocardial dysfunction.

Abnormal energetics and ATP depletion in pressure-overload mouse hearts: in vivo high-energy phosphate concentration measures by noninvasive magnetic resonance

(31)P magnetic resonance spectroscopy (MRS) offers a unique means to noninvasively quantify the major cardiac high-energy phosphates, creatine phosphate (PCr) and adenosine 5'-triphosphate (ATP), that are critical for normal myocardial contractile function and viability. Spatially localized (31)P MRS has been used to quantify the in vivo PCr-to-ATP ratio (PCr/ATP) of murine hearts, including those with pressure-overload hypertrophy induced by thoracic aortic constriction (TAC). To date, there has been no approach for measuring the absolute tissue concentrations of PCr and ATP in the in vivo mouse heart that promise a better understanding of high-energy metabolism. A method to quantify in vivo murine myocardial concentrations of PCr and ATP using an external reference is described, validated, and applied to normal and TAC hearts. This new method does not prolong the scan times in mice beyond those previously required to measure PCr/ATP. The new method renders an [ATP] of 5.0 +/- 0.9 (mean +/- SD) and [PCr] of 10.4 +/- 1.4 micromol/g wet wt in normal mouse hearts (n = 7) and significantly lower values in TAC hearts (n = 10) of 4.0 +/- 0.8 and 6.7 +/- 2.0 micromol/g wet wt for [ATP] (P < 0.04) and [PCr] (P < 0.001), respectively. The in vivo magnetic resonance [ATP] results are in good agreement with those obtained using an in vitro enzyme luminescent assay of perchloric acid extracts of the same hearts. In conclusion, a validated (31)P MRS method for quantifying [ATP] and [PCr] in the in vivo mouse heart using spatial localization and an external reference is described and used to demonstrate significant reductions in not only PCr/ATP but [ATP] in hypertrophied TAC hearts.

Neurological grading, survival, MR imaging, and histological evaluation in the rat brainstem glioma model

OBJECTIVE

Convection-enhanced delivery using carboplatin in brainstem glioma models was reported to prolong survival. Functional impairment is of additional importance to evaluate the value of local chemotherapy. We established a neurological scoring system for the rat brainstem glioma model.

MATERIAL AND METHODS

In 46 male Fisher rats stereotactically 10(5) F-98 cells were implanted at 1.4-mm lateral to midline and at the lambdoid suture using guided screws. Following 4 days local delivery was performed using Alzet pumps (1 microl/h over 7 days) with either vehicle (5% dextrose) or carboplatin via one or two cannulas, respectively. All rats were subsequently tested neurologically using a specified neurological score. In 38 animals survival time was recorded. Representative MR imaging were acquired in eight rats, respectively, at day 12 after implantation. HE staining was used to evaluate tumor extension.

RESULTS

Neurological scoring showed significantly higher impairment in the high dose carboplatin group during the treatment period. Survival was significantly prolonged compared to control animals in the high dose carboplatin-one cannula group as well as in both low dose carboplatin groups (18.6 +/- 3 versus 26.3 +/- 9, 22.8 +/- 2, 23.6 +/- 2 days; p < 0.05). Overall neurological grading correlated with survival time. MR imaging showed a focal contrast enhancing mass in the pontine brainstem, which was less exaggerated after local chemotherapy. Histological slices visualized decreased cellular density in treatment animals versus controls.

CONCLUSION

Local chemotherapy in the brainstem glioma model showed significant efficacy for histological changes and survival. Our neurological grading enables quantification of drug and tumor-related morbidity as an important factor for functional performance during therapy.

In vivo "hot spot" MR imaging of neural stem cells using fluorinated nanoparticles

To optimize (19)F MR tracking of stem cells, we compared cellular internalization of cationic and anionic perfluoro-15-crown-5-ether (PFCE) nanoparticles using cell culture plates with different surface coatings. The viability and proliferation of anionic and cationic PFCE-labeled neural stem cells (NSCs) did not differ from unlabeled cells. Cationic PFCE nanoparticles ((19)F T1/T2 = 580/536 ms at 9.4 Tesla) were superior to anionic particles for intracellular fluorination. Best results were obtained with modified polystyrene culture dishes coated with both carboxylic and amino groups rather than conventional carboxyl-coated dishes. After injecting PFCE-labeled NSCs into the striatum of mouse brain, cells were readily identified in vivo by (19)F MRI without changes in signal or viability over a 2-week period after grafting. These results demonstrate that neural stem cells can be efficiently fluorinated with cationic PFCE nanoparticles without using transfection agents and visualized in vivo over prolonged periods with an MR sensitivity of approximately 140 pmol of PFCE/cell.

Altered high-energy phosphate metabolism predicts contractile dysfunction and subsequent ventricular remodeling in pressure-overload hypertrophy mice

To study the role of early energetic abnormalities in the subsequent development of heart failure, we performed serial in vivo combined magnetic resonance imaging (MRI) and (31)P magnetic resonance spectroscopy (MRS) studies in mice that underwent pressure-overload following transverse aorta constriction (TAC). After 3 wk of TAC, a significant increase in left ventricular (LV) mass (74 +/- 4 vs. 140 +/- 26 mg, control vs. TAC, respectively; P < 0.000005), size [end-diastolic volume (EDV): 48 +/- 3 vs. 61 +/- 8 microl; P < 0.005], and contractile dysfunction [ejection fraction (EF): 62 +/- 4 vs. 38 +/- 10%; P < 0.000005] was observed, as well as depressed cardiac energetics (PCr/ATP: 2.0 +/- 0.1 vs. 1.3 +/- 0.4, P < 0.0005) measured by combined MRI/MRS. After an additional 3 wk, LV mass (140 +/- 26 vs. 167 +/- 36 mg; P < 0.01) and cavity size (EDV: 61 +/- 8 vs. 76 +/- 8 microl; P < 0.001) increased further, but there was no additional decline in PCr/ATP or EF. Cardiac PCr/ATP correlated inversely with end-systolic volume and directly with EF at 6 wk but not at 3 wk, suggesting a role of sustained energetic abnormalities in evolving chamber dysfunction and remodeling. Indeed, reduced cardiac PCr/ATP observed at 3 wk strongly correlated with changes in EDV that developed over the ensuing 3 wk. These data suggest that abnormal energetics due to pressure overload predict subsequent LV remodeling and dysfunction.

Xanthine oxidase inhibitors improve energetics and function after infarction in failing mouse hearts

After myocardial infarction, ventricular geometry and function, as well as energy metabolism, change markedly. In nonischemic heart failure, inhibition of xanthine oxidase (XO) improves mechanoenergetic coupling by improving contractile performance relative to a reduced energetic demand. However, the metabolic and contractile effects of XO inhibitors (XOIs) have not been characterized in failing hearts after infarction. After undergoing permanent coronary ligation, mice received a XOI (allopurinol or oxypurinol) or matching placebo in the daily drinking water. Four weeks later, 1H MRI and 31P magnetic resonance spectroscopy (MRS) were used to quantify in vivo functional and metabolic changes in postinfarction remodeled mouse myocardium and the effects of XOIs on that process. End-systolic (ESV) and end-diastolic volumes (EDV) were increased by more than sixfold after infarction, left ventricle (LV) mass doubled ( P < 0.005), and the LV ejection fraction (EF) decreased (14 ± 9%) compared with control hearts (59 ± 8%, P < 0.005) at 1 mo. The myocardial phosphocreatine (PCr)-to-ATP ratio (PCr/ATP) was also significantly decreased in infarct remodeled hearts (1.4 ± 0.6) compared with control animals (2.1 ± 0.5, P < 0.02), in agreement with prior studies in larger animals. The XOIs allopurinol and oxypurinol did not change LV mass but limited the increase in ESV and EDV of infarct hearts by 50%, increased EF (23 ± 9%, P = 0.01), and normalized cardiac PCr/ATP (2.0 ± 0.5, P < 0.04). We conclude that XOIs improve ventricular function after infarction and normalize high-energy phosphate ratio in heart failure. Thus XOI therapy offers a new and potentially complementary approach to limit the adverse contractile and metabolic consequences after infarction.

Regulation of murine myocardial energy metabolism during adrenergic stress studied by in vivo 31P NMR spectroscopy

Image-guided, spatially localized 31P magnetic resonance spectroscopy (MRS) was used to study in vivo murine cardiac metabolism under resting and dobutamine-induced stress conditions. Intravenous dobutamine infusion (24 mug. min-1. kg body wt-1) increased the mean heart rate by approximately 39% from 482 +/- 46 per min at baseline to 669 +/- 77 per min in adult mice. The myocardial phosphocreatine (PCr)-to-ATP (PCr/ATP) ratio remained unchanged at 2.1 +/- 0.5 during dobutamine stress, compared with baseline conditions. Therefore, we conclude that a significant increase in heart rate does not result in a decline in the in vivo murine cardiac PCr/ATP ratio. These observations in very small mammals, viz., mice, at extremely high heart rates are consistent with studies in large animals demonstrating that global levels of high-energy phosphate metabolites do not regulate in vivo myocardial metabolism during physiologically relevant increases in cardiac work.

Choline Phospholipid Metabolites of Human Vascular Endothelial Cells Altered by Cyclooxygenase Inhibition, Growth Factor Depletion, and Paracrine Factors Secreted by Cancer Cells

Magnetic resonance studies have previously shown that solid tumors and cancer cells in culture typically exhibit high phosphocholine and total choline. Treatment of cancer cells with the anti-inflammatory agent, indomethacin (INDO), reverted the phenotype of choline phospholipid metabolites in cancer cells towards a less malignant phenotype. Since endothelial cells form a key component of tumor vasculature, in this study, we used MR spectroscopy to characterize the phenotype of choline phospholipid metabolites in human umbilical vein endothelial cells (HUVECs). We determined the effect of growth factors, the anti-inflammatory agent INDO, and conditioned media obtained from a malignant cell line, on choline phospholipid metabolites. Growth factor depletion or treatment with INDO induced similar changes in the choline phospholipid metabolites of HUVECs. Treatment with conditioned medium obtained from MDA-MB-231 cancer cells induced changes similar to the presence of growth factor supplements. These results suggest that cancer cells secrete growth factors and/or other molecules that influence the choline phospholipid metabolism of HUVECs. The ability of INDO to alter choline phospholipid metabolism in the presence of growth factor supplements suggests that the inflammatory response pathways of HUVECs may play a role in cancer cell-HUVEC interaction and in the response of HUVECs to growth factors.

Choline phospholipid metabolites of human vascular endothelial cells altered by cyclooxygenase inhibition, growth factor depletion, and paracrine factors secreted by cancer cells

Magnetic resonance studies have previously shown that solid tumors and cancer cells in culture typically exhibit high phosphocholine and total choline. Treatment of cancer cells with the anti-inflammatory agent, indomethacin (INDO), reverted the phenotype of choline phospholipid metabolites in cancer cells towards a less malignant phenotype. Since endothelial cells form a key component of tumor vasculature, in this study, we used MR spectroscopy to characterize the phenotype of choline phospholipid metabolites in human umbilical vein endothelial cells (HUVECs). We determined the effect of growth factors, the anti-inflammatory agent INDO, and conditioned media obtained from a malignant cell line, on choline phospholipid metabolites. Growth factor depletion or treatment with INDO induced similar changes in the choline phospholipid metabolites of HUVECs. Treatment with conditioned medium obtained from MDA-MB-231 cancer cells induced changes similar to the presence of growth factor supplements. These results suggest that cancer cells secrete growth factors and/or other molecules that influence the choline phospholipid metabolism of HUVECs. The ability of INDO to alter choline phospholipid metabolism in the presence of growth factor supplements suggests that the inflammatory response pathways of HUVECs may play a role in cancer cell-HUVEC interaction and in the response of HUVECs to growth factors.

An increase in the myocardial PCr/ATP ratio in GLUT4 null mice

ATP and creatine phosphate (PCr) are prime myocardial high-energy phosphates. Their relative concentrations are conserved among mammalian species and across a range of physiologic cardiac workloads. The cardiac PCr/ATP ratio is decreased with several pathologic conditions, such as ischemia and heart failure, but there are no reports of an increase in the cardiac PCr/ATP ratio in any species or with interventions. We studied the in vivo energetics in transgenic mice lacking expression of the glucose transport protein GLUT4 (G4N) and observed a significant 60% increase in the myocardial PCr/ATP ratio in G4N that was confirmed in three different experimental settings including intact animals. The higher PCr/ATP in G4N is cardiac-specific and is due to higher total cardiac creatine (CR) concentrations in G4N than in wild-type (WT). However, [ATP], [ADP], and -DG(-ATP) did not differ between the strains. Expression of the creatine transport protein (CreaT) that is responsible for creatine uptake in myocytes was preserved in G4N cardiac tissue. These observations demonstrate, for the first time to our knowledge, that G4N manifest a unique increase in the cardiac PCr/ATP ratio, which suggests a novel genetic strategy for increasing myocardial creatine levels.

Hepatic hyperplasia in noncirrhotic fatty livers: is obesity-related hepatic steatosis a premalignant condition?

It is not known whether obesity increases the risk for hepatocellular carcinoma (HCC) simply because it promotes cirrhosis, a general risk factor for HCC, or via some other mechanism that operates independently of cirrhosis. If the latter occurs, then hepatocyte hyperplasia, an early event during the neoplastic process, might begin before liver cirrhosis develops. Genetically obese, leptin-deficient ob/ob mice are models for nonalcoholic fatty liver disease (NAFLD), a type of liver disease that is strongly associated with obesity and type 2 diabetes. Similar to obese, diabetic patients, ob/ob mice have an increased incidence of HCC. However, unlike humans with NAFLD, they rarely, if ever, develop cirrhosis spontaneously. To determine whether the noncirrhotic livers of ob/ob mice with NAFLD exhibit hepatocyte hyperplasia, parameters of proliferation and apoptosis were compared in adult ob/ob mice and their healthy litter mates. Adult ob/ob mice have an increase in liver mass relative to body mass. This hepatomegaly cannot be explained solely by lipid accumulation and is accompanied by significant increases in hepatocyte proliferative activity (as evidenced by increased Erk activation, cell-cycle related gene expression, bromodeoxyuridine incorporation, and hepatic DNA content) with concomitant inhibition of hepatocyte apoptosis (as evidenced by decreased numbers of apoptotic hepatocytes, induction of several antiapoptotic mechanisms, and decreased activation of procaspase 3). Thus, liver hyperplasia is evident at the earliest stage of NAFLD in ob/ob mice, which supports the concept that obesity-related metabolic abnormalities, rather than cirrhosis, initiate the hepatic neoplastic process during obesity.

Hepatic hyperplasia in noncirrhotic fatty livers: is obesity-related hepatic steatosis a premalignant condition?

It is not known whether obesity increases the risk for hepatocellular carcinoma (HCC) simply because it promotes cirrhosis, a general risk factor for HCC, or via some other mechanism that operates independently of cirrhosis. If the latter occurs, then hepatocyte hyperplasia, an early event during the neoplastic process, might begin before liver cirrhosis develops. Genetically obese, leptin-deficient ob/ob mice are models for nonalcoholic fatty liver disease (NAFLD), a type of liver disease that is strongly associated with obesity and type 2 diabetes. Similar to obese, diabetic patients, ob/ob mice have an increased incidence of HCC. However, unlike humans with NAFLD, they rarely, if ever, develop cirrhosis spontaneously. To determine whether the noncirrhotic livers of ob/ob mice with NAFLD exhibit hepatocyte hyperplasia, parameters of proliferation and apoptosis were compared in adult ob/ob mice and their healthy litter mates. Adult ob/ob mice have an increase in liver mass relative to body mass. This hepatomegaly cannot be explained solely by lipid accumulation and is accompanied by significant increases in hepatocyte proliferative activity (as evidenced by increased Erk activation, cell-cycle related gene expression, bromodeoxyuridine incorporation, and hepatic DNA content) with concomitant inhibition of hepatocyte apoptosis (as evidenced by decreased numbers of apoptotic hepatocytes, induction of several antiapoptotic mechanisms, and decreased activation of procaspase 3). Thus, liver hyperplasia is evident at the earliest stage of NAFLD in ob/ob mice, which supports the concept that obesity-related metabolic abnormalities, rather than cirrhosis, initiate the hepatic neoplastic process during obesity.

MRI/MRS assessment of in vivo murine cardiac metabolism, morphology, and function at physiological heart rates

Transgenic mice are increasingly used to probe genetic aspects of cardiovascular pathophysiology. However, the small size and rapid rates of murine hearts make noninvasive, physiological in vivo studies of cardiac bioenergetics and contractility difficult. The aim of this report was to develop an integrated, noninvasive means of studying in vivo murine cardiac metabolism, morphology, and function under physiological conditions by adapting and modifying noninvasive cardiac magnetic resonance imaging (MRI) with image-guided (31)P magnetic resonance spectroscopy techniques used in humans to mice. Using spatially localized, noninvasive (31)P nuclear magnetic resonance spectroscopy and MRI at 4.7 T, we observe mean murine in vivo myocardial phosphocreatine-to-ATP ratios of 2.0 +/- 0.2 and left ventricular ejection fractions of 65 +/- 7% at physiological heart rates ( approximately 600 beats/min). These values in the smallest species studied to date are similar to those reported in normal humans. Although these observations do not confirm a degree of metabolic scaling with body size proposed by prior predictions, they do suggest that mice can serve, at least at this level, as a model for human cardiovascular physiology. Thus it is now possible to noninvasively study in vivo myocardial bioenergetics, morphology, and contractile function in mice under physiological conditions.

Preservation of glucose metabolism in hypertrophic GLUT4-null hearts

GLUT4-null mice lacking the insulin-sensitive glucose transporter are not diabetic but do exhibit abnormalities in glucose and lipid metabolism. The most striking morphological consequence of ablating GLUT4 is cardiac hypertrophy. GLUT4-null hearts display characteristics of hypertrophy caused by hypertension. However, GLUT4-null mice have normal blood pressure and maintain a normal cardiac contractile protein profile. Unexpectedly, although they lack the predominant glucose transporter in the heart, GLUT4-null hearts transport glucose and synthesize glycogen at normal levels, but gene expression of rate-limiting enzymes involved in fatty acid oxidation is decreased. The GLUT4-null heart represents a unique model of hypertrophy that may be used to study the consequences of altered substrate utilization in normal and pathophysiological conditions.

Energy state, pH, and vasomotor tone during hypoxia in precontracted pulmonary and femoral arteries

To assess effects of smooth muscle energy state and intracellular pH (pH(i)) on pulmonary arterial tone during hypoxia, we measured ATP, phosphocreatine, P(i), and pH(i) by (31)P-NMR spectroscopy and isometric tension in phenylephrine-contracted rings of porcine proximal intrapulmonary arteries. Hypoxia caused early transient contraction followed by relaxation and late sustained contraction. Energy state and pH(i) decreased during relaxation and recovered toward control values during late contraction. Femoral arterial rings had higher energy state and lower pH(i) under baseline conditions and did not exhibit late contraction or recovery of energy state and pH(i) during hypoxia. In pulmonary arteries, glucose-free conditions abolished late hypoxic contraction and recovery of energy state and pH(i), but endothelial denudation abolished only late hypoxic contraction. NaCN had little effect at 0. 1 and 1.0 mM but caused marked vasorelaxation and decreases in energy state and pH(i) at 10 mM. These results suggest that 1) regulation of tone, energy state, and pH(i) differed markedly in pulmonary and femoral arterial smooth muscle, 2) hypoxic relaxation was mediated by decreased energy state or pH(i) due to hypoxic inhibition of oxidative phosphorylation, 3) recovery of energy state and pH(i) in hypoxic pulmonary arteries was due to accelerated glycolysis mediated by mechanisms intrinsic to smooth muscle, and 4) late hypoxic contraction in pulmonary arteries was mediated by endothelial factors that required hypoxic recovery of energy state and pH(i) for transduction in smooth muscle or extracellular glucose for production and release by endothelium.

Alterations in liver ATP homeostasis in human nonalcoholic steatohepatitis: a pilot study

CONTEXT

The mechanisms that drive progression from fatty liver to steatohepatitis and cirrhosis are unknown. In animal models, obese mice with fatty livers are vulnerable to liver adenosine triphosphate (ATP) depletion and necrosis, suggesting that altered hepatic energy homeostasis may be involved.

OBJECTIVE

To determine if patients with fatty liver disease exhibit impaired recovery from hepatic ATP depletion.

DESIGN

Laboratory analysis of liver ATP stores monitored by nuclear magnetic resonance spectroscopy before and after transient hepatic ATP depletion was induced by fructose injection. The study was conducted between July 15 and August 30, 1998.

SETTING

University hospital.

PATIENTS

Eight consecutive adults with biopsy-proven nonalcoholic steatohepatitis and 7 healthy age- and sex-matched controls.

MAIN OUTCOME MEASURE

Level of ATP 1 hour after fructose infusion in patients vs controls.

RESULTS

In patients, serum aminotransferase levels were increased (P = .02 vs controls); albumin and bilirubin values were normal and clinical evidence of portal hypertension was absent in both groups. However, 2 patients had moderate fibrosis and 1 had cirrhosis on liver biopsy. Mean serum glucose, cholesterol, and triglyceride levels were similar between groups but patients weighed significantly more than controls (P = .02). Liver ATP levels were similar in the 2 groups before fructose infusion and decreased similarly in both after fructose infusion (P = .01 vs initial ATP levels). However, controls replenished their hepatic ATP stores during the 1-hour follow-up period (P<.02 vs minimum ATP) but patients did not. Hence, patients' hepatic ATP levels were lower than those of controls at the end of the study (P = .04). Body mass index (BMI) correlated inversely with ATP recovery, even in controls (R = -0.768; P = .07). Although BMI was greater in patients than controls (P = .02) and correlated strongly with fatty liver and serum aminotransferase elevations, neither of the latter 2 parameters nor the histologic severity of fibrosis strongly predicted hepatic ATP recovery.

CONCLUSIONS

These data suggest that recovery from hepatic ATP depletion becomes progressively less efficient as body mass increases in healthy controls and is severely impaired in patients with obesity-related nonalcoholic steatohepatitis.

Nm23-transfected MDA-MB-435 human breast carcinoma cells form tumors with altered phospholipid metabolism and pH: a 31P nuclear magnetic resonance study in vivo and in vitro

Nm23 genes are involved in the control of the metastatic potential of breast carcinoma cells. To understand the impact of nm23 genes on tumor physiology and metabolism, a 31P nuclear magnetic resonance (NMR) spectroscopic study was performed on tumors formed in the mammary fat pad of severe combined immunodeficiency mice by MDA-MB-435 human breast carcinoma cells transfected with cDNA encoding wild type nm23-H1 and nm23-H2 proteins. Tumors formed by MDA-MB-435 cells transfected with vector alone were used as controls. All transgene tumors exhibited significantly higher levels of phosphodiester (PDE) compounds relative to phosphomonoester (PME) compounds in vivo compared with control tumors. Similar differences in PDE and PME also were observed for spectra obtained from cells growing in culture. Intracellular pH was significantly lower and extracellular pH was significantly higher for transgene tumors compared with control tumors. Histologic analysis of lung sections confirmed reductions in incidence, number, and size of metastatic nodules for animals bearing transgene tumors. These results suggest that nm23 genes may affect suppression of metastasis through phospholipid-mediated signaling and cellular pH regulation.

Nm23-transfected MDA-MB-435 human breast carcinoma cells form tumors with altered phospholipid metabolism and pH: a 31P nuclear magnetic resonance study in vivo and in vitro

Nm23 genes are involved in the control of the metastatic potential of breast carcinoma cells. To understand the impact of nm23 genes on tumor physiology and metabolism, a 31P nuclear magnetic resonance (NMR) spectroscopic study was performed on tumors formed in the mammary fat pad of severe combined immunodeficiency mice by MDA-MB-435 human breast carcinoma cells transfected with cDNA encoding wild type nm23-H1 and nm23-H2 proteins. Tumors formed by MDA-MB-435 cells transfected with vector alone were used as controls. All transgene tumors exhibited significantly higher levels of phosphodiester (PDE) compounds relative to phosphomonoester (PME) compounds in vivo compared with control tumors. Similar differences in PDE and PME also were observed for spectra obtained from cells growing in culture. Intracellular pH was significantly lower and extracellular pH was significantly higher for transgene tumors compared with control tumors. Histologic analysis of lung sections confirmed reductions in incidence, number, and size of metastatic nodules for animals bearing transgene tumors. These results suggest that nm23 genes may affect suppression of metastasis through phospholipid-mediated signaling and cellular pH regulation.

Three-dimensional tracking of axonal projections in the brain by magnetic resonance imaging

The relationship between brain structure and complex behavior is governed by large-scale neurocognitive networks. The availability of a noninvasive technique that can visualize the neuronal projections connecting the functional centers should therefore provide new keys to the understanding of brain function. By using high-resolution three-dimensional diffusion magnetic resonance imaging and a newly designed tracking approach, we show that neuronal pathways in the rat brain can be probed in situ. The results are validated through comparison with known anatomical locations of such fibers.

Effect of leptin deficiency on metabolic rate in ob/ob mice

Reduced metabolic rate may contribute to weight gain in leptin-deficient (ob/ob) mice; however, available studies have been criticized for referencing O2 consumption (VO2) to estimated rather than true lean body mass. To evaluate whether leptin deficiency reduces energy expenditure, four separate experiments were performed: 1) NMR spectroscopy was used to measure fat and nonfat mass, permitting VO2 to be referenced to true nonfat mass; 2) dietary manipulation was used in an attempt to eliminate differences in body weight and composition between ob/ob and C57BL/6J mice; 3) short-term effects of exogenous leptin (0.3 mg. kg-1. day-1) on VO2 were examined; and 4) body weight and composition were compared in leptin-repleted and pair-fed ob/ob animals. ob/ob animals had greater mass, less lean body mass, and a 10% higher metabolic rate when VO2 was referenced to lean mass. Dietary manipulation achieved identical body weight in ob/ob and C57BL/6J animals; however, despite weight gain in C57BL/6J animals, percent fat mass remained higher in ob/ob animals (55 vs. 30%). Exogenous leptin increased VO2 in ob/ob but not control animals. Weight loss in leptin-repleted ob/ob mice was greater than in pair-fed animals (45 vs. 17%). We conclude, on the basis of the observed increase in VO2 and accelerated weight loss seen with leptin repletion, that leptin deficiency causes a reduction in metabolic rate in ob/ob mice. In contrast, these physiological studies suggest that comparison of VO2 in obese and lean animals does not produce useful information on the contribution of leptin to metabolism.

Preservation of canine myocardial high-energy phosphates during low-flow ischemia with modification of hemoglobin-oxygen affinity

Conventional approaches for the treatment of myocardial ischemia increase coronary blood flow or reduce myocardial demand. To determine whether a rightward shift in the hemoglobin-oxygen saturation curve would reduce the metabolic and contractile effects of a myocardial oxygen-supply imbalance, we studied the impact of a potent synthetic allosteric modifier of hemoglobin-oxygen affinity, a 2-[4-[[(3,5-disubstituted anilino)carbonyl]methyl] phenoxy] -2-methylproprionic acid derivative (RSR13), during low-flow ischemia. Changes in myocardial high-energy phosphate levels and pH were studied by 31P nuclear magnetic resonance (NMR) spectroscopy in 12 open-chest dogs randomized to receive RSR13 or vehicle control during a reversible reduction of left anterior descending (LAD) coronary artery blood flow. Changes in cardiac metabolites and regional ventricular function studied by pressure segment-length relations were also investigated in additional animals before and after RSR13 administration during low-flow LAD ischemia. The intravenous administration of RSR13 before ischemia resulted in a substantial increase in the mean hemoglobin p50 and attenuated the decline in cardiac creatine phosphate/adenosine triphosphate (PCr/ATP), percent PCr, and pH during ischemia without a change in regional myocardial blood flow, heart rate, or systolic blood pressure. RSR13 given after the onset of low-flow ischemia also improved cardiac PCr/ATP ratios and regional function as measured by fractional shortening and regional work. Thus, synthetic allosteric reduction in hemoglobin-oxygen affinity may be a new and important therapeutic strategy to ameliorate the metabolic and functional consequences of cardiac ischemia.

Obesity induces expression of uncoupling protein-2 in hepatocytes and promotes liver ATP depletion

Uncoupling protein 2 (UCP2) uncouples respiration from oxidative phosphorylation and may contribute to obesity through effects on energy metabolism. Because basal metabolic rate is decreased in obesity, UCP2 expression is predicted to be reduced. Paradoxically, hepatic expression of UCP2 mRNA is increased in genetically obese (ob/ob) mice. In situ hybridization and immunohistochemical analysis of ob/ob livers demonstrate that UCP2 mRNA and protein expression are increased in hepatocytes, which do not express UCP2 in lean mice. Mitochondria isolated from ob/ob livers exhibit an increased rate of H+ leak which partially dissipates the mitochondrial membrane potential when the rate of electron transport is suppressed. In addition, hepatic ATP stores are reduced and these livers are more vulnerable to necrosis after transient hepatic ischemia. Hence, hepatocytes adapt to obesity by up-regulating UCP2. However, because this decreases the efficiency of energy trapping, the cells become vulnerable to ATP depletion when energy needs increase acutely.

Three-dimensional tracking of axonal projections in the brain by magnetic resonance imaging

The relationship between brain structure and complex behavior is governed by large-scale neurocognitive networks. The availability of a noninvasive technique that can visualize the neuronal projections connecting the functional centers should therefore provide new keys to the understanding of brain function. By using high-resolution three-dimensional diffusion magnetic resonance imaging and a newly designed tracking approach, we show that neuronal pathways in the rat brain can be probed in situ. The results are validated through comparison with known anatomical locations of such fibers.

Effects of hypoxia on energy state and pH in resting pulmonary and femoral arterial smooth muscles

To determine the effects of hypoxia on energy state and intracellular pH (pHi) in resting pulmonary and systemic arterial smooth muscles, we used 31P nuclear magnetic resonance spectroscopy and colorimetric and enzymatic assays to measure pHi; intracellular concentrations of ATP, phosphocreatine, creatine, and Pi; and phosphorylation potential in superfused tissue segments from porcine proximal intrapulmonary and superficial femoral arteries. Under baseline conditions (PO2 467 +/- 12.1 mmHg), energy state and total creatine (phosphocreatine + creatine) concentration were lower and pHi was higher in pulmonary arteries. During hypoxia (PO2 23 +/- 2.4 mmHg), energy state deteriorated more in femoral arteries than in pulmonary arteries. pHi fell in both tissues but was always more alkaline in pulmonary arteries. Reoxygenation reversed the changes induced by hypoxia. These results suggest that production and/or elimination of ATP and H+ was different in resting pulmonary and systemic arterial smooth muscles under baseline and hypoxic conditions. Because energy state and pHi affect a wide variety of cellular processes, including signal transduction, contractile protein interaction, and activities of ion pumps and channels, further investigation is indicated to determine whether these differences have functional significance.

Role of preischemic glycogen depletion in the improvement of postischemic metabolic and contractile recovery of ischemia-preconditioned rat hearts

BACKGROUND

Ischemic preconditioning (IPC) attenuates acidosis during prolonged ischemia and improves contractile and metabolic parameters during subsequent reperfusion. Glycogen depletion induced by IPC is proposed as a potential mechanism.

METHODS AND RESULTS

We studied the influence of manipulations of preischemic glycogen levels (Pre-G, micromol glucose/g wet wt) on contractile and metabolic (via 31P-nuclear magnetic resonance) parameters during 30 minutes of ischemia and recovery in four groups of isovolumic rat hearts: First, control (Con, n=18, mean Pre-G, 21.5+/-0.8); second, after two 5-minute IPC periods (IPC, n=12, Pre-G, 11.3+/-0.7); third, a control group in which Pre-G was depleted by glucose-free, acetate perfusion (Con-LowG, n=9, Pre-G, 7.9+/-1.2); and fourth, an IPC group in which Pre-G was raised by glucose and lactate perfusion such that Pre-G was similar to Con (IPC-HiG, n=11, Pre-G, 20+/-1.4). Manipulation of Pre-G significantly altered the pH fall during 30 minutes of ischemia (Con, 5.76+/-.03, Con-LowG, 6.26+/-.07; IPC-HiG, 5.91+/-.02, IPC, 6.05+/-.09). IPC-HiG hearts had significantly worse metabolic recovery (PCr, 70+/-7 versus 91+/-3% initial; IPC-HiG versus IPC, P<.05) and contractile recovery (end-diastolic pressure, 52+/-5 versus 29+/-5 mm Hg, P<.05) than IPC hearts but better recovery than Con (%PCr, 56+/-6% and end-diastolic pressure, 72+/-6 mm Hg). An ischemic rise in intracellular magnesium occurred and was atttenuated in preconditioned hearts.

CONCLUSIONS

Pre-G levels before ischemia influence but are not the sole determinants of the extent of acidosis during prolonged ischemia and of metabolic and contractile recovery during reperfusion in control and preconditioned hearts.

Attenuated glycogenolysis reduces glycolytic catabolite accumulation during ischemia in preconditioned rat hearts

Prior transient episodes of ischemia ("ischemic preconditioning") reduce lactate accumulation and attenuate acidosis during a subsequent prolonged ischemic insult. The mechanisms responsible for attenuated glycolytic catabolite accumulation have not been established but may include earlier exhaustion of glycogen stores, slowed glycogenolysis before complete glycogen depletion, and/or inhibition of glycolysis. Simultaneous repeated measures of myocardial glycogen and the rates of glycolysis, glycogenolysis, glucose utilization, and glycolytic ATP production were obtained during total ischemia by 13C nuclear magnetic resonance spectroscopy in control and ischemia-preconditioned isolated rat hearts. Both [13C]glycolytic and [13C]glycogenolytic rates were significantly lower during total ischemia in preconditioned compared with control hearts (0.77 +/- 0.04 versus 1.06 +/- 0.06 mumol/min per gram wet weight [P < .01] for glycolysis and 0.15 +/- 0.07 versus 0.78 +/- 0.12 mumol/ min per gram wet weight [P < .001] for glycogenolysis, respectively, at 2.5 minutes of ischemia). Slowed glycolysis was present even during the early minutes of ischemia, when significant amounts of available [13C]glycogen were still present. Importantly, the reduction in the rate of glycogenolysis was larger and out of proportion to the reduction in glycolysis and occurred despite an increase in glucose utilization in preconditioned hearts (2.23 +/- 0.15 versus 1.5 +/- 0.10 mumol/min per gram wet weight at 1.25 minutes, P < .01). During early ischemia, conversion of glycogen phosphorylase to the a or "active" form was less in preconditioned than in control hearts (29.1 +/- 2.6% versus 41.2 +/- 9.8%, respectively; P < .05). Taken together, these findings demonstrate that ischemic preconditioning significantly depresses glycolytic catabolite accumulation during sustained ischemia not by more severe glycolytic inhibition or exhaustion of glycogen stores but by depressed glycogenolysis from the onset of ischemia.

Consequences of altered aspartate aminotransferase activity on 13C-glutamate labelling by the tricarboxylic acid cycle in intact rat hearts

The appearance of 13C label in glutamate has been used to quantify cellular tricarboxylic acid (TCA) cycle activity using 13C-NMR spectroscopy. Glutamate is linked to the TCA cycle by the amino-transferase reactions, however the consequences of alterations in amino-transferase activity on glutamate labelling kinetics, at a constant total tricarboxylic acid cycle activity, have not been investigated. Aspartate amino-transferase activity in [2-13C]acetate-perfused beating rat hearts was found to be similar to total TCA cycle flux in the presence of normal perfusion conditions and was reduced by more than 50% with the subsequent administration of amino-oxyacetic acid (AOA). AOA did not reduce contractile or kinetic measures of total TCA cycle flux, but did slow the 13C labelling of glutamate, in accord with current mathematical predictions. The impact of similar reductions in amino-transferase activity on estimates of total TCA cycle flux derived from several previously reported methods was also evaluated. Because total TCA cycle and the amino-transferase activities both affect the kinetics of 13C-glutamate labelling and because the amino-transferase activities are often unknown under physiologic conditions and can be reduced under pathologic conditions, the calculation of total TCA cycle flux from 13C-NMR data in the future is probably best accomplished either with a sufficiently sophisticated mathematical model that assesses amino-transferase activity or with an empiric model that is relatively insensitive to variations in amino-transferase activity.

Detailed characterization of experimental acute alcoholic pancreatitis

BACKGROUND

With the ex vivo perfused canine pancreas preparation, the infusion of acetaldehyde, the primary metabolite of ethanol oxidation, plus a short period of ischemia to convert xanthine dehydrogenase to xanthine oxidase, results in the physiologic injury response of acute pancreatitis (edema, weight gain, hyperamylasemia). The free radical scavengers superoxide dismutase and catalase and a xanthine oxidase inhibitor, allopurinol, ameliorate this injury response, suggesting that toxic oxygen metabolites generated by xanthine oxidase play an intermediary role.

METHODS

The isolated ex vivo canine pancreas preparation was perfused for 4 hours, and weight gain of the preparation and amylase activity in the perfusate were monitored. Changes in pancreatic acinar cell architecture were characterized by light and electron microscopy, and intracellular phosphate metabolism was followed by magnetic resonance spectroscopy in control preparations and in glands simulating alcoholic pancreatitis.

RESULTS

Control preparations and preparations with a 1-hour period of ischemia before perfusion gained little weight (7 +/- 3 gm and 8 +/- 1 gm), amylase activity in the perfusate remained normal (933 +/- 513 units/dl and 1537 +/- 553 units/dl), and no changes in architecture were observed. Weight gain (5 +/- 6 gm) and amylase activity (1188 +/- 173 units/dl) were also normal in the preparations receiving acetaldehyde without preceding ischemia, but mild vascular and islet cell injury were observed on electron microscopy. One hour of ischemia followed by acetaldehyde infusion resulted in edema, increased weight gain (21 +/- 12 gm [p < 0.05]), and amylase activity (2487 +/- 1484 units/dl [p < 0.05]). Microscopy showed mild acinar cell damage and greater injury to the capillaries and the islets. The capillary and islet cell changes were reduced by superoxide dismutase and catalase. Intracellular adenosine triphosphate levels remained at baseline levels in the control preparations. Adenosine triphosphate decreased during ischemia but quickly recovered during perfusion without a significant difference whether acetaldehyde was infused after ischemia. An iron chelator desferoxamine ameliorated the injury response in the preparations simulating acute pancreatitis (weight gain, 13 +/- 6 gm [p = 0.09] and amylase activity, 1198 +/- 471 units/dl [p = 0.08]), but a cholecystokinin receptor antagonist L364,718 did not have an effect. A sulfhydryl group protector, dithiothreitol, decreased weight gain (10 +/- 7 gm [p = 0.06]), and amylase activity was not significantly increased over that of the control group (1582 +/- 641 units/dl), but a serine protease inhibitor phenylmethylsulphonylfluoride was ineffective.

CONCLUSIONS

In this model simulating acute alcoholic pancreatitis, both the early physiologic injury response and the early morphologic changes are mediated at least in part by free radicals, which are generated by xanthine oxidase converted reversibly from xanthine dehydrogenase. In addition to the superoxide radical, the hydroxyl radical may also be an important early intermediate step, but the cholecystokinin receptor is not.

Induction of anaerobic glucose metabolism during the development of acute pancreatitis

OBJECTIVE

Studies were performed with the ex vivo perfused canine pancreas preparation to characterize acinar cell metabolism during the development of acute pancreatitis.

SUMMARY BACKGROUND DATA

Acute pancreatitis can be initiated in the ex vivo perfused canine pancreas preparation by five different stimuli as follows: (1) the infusion of oleic acid (FFA), (2) partial obstruction of the pancreatic duct and secretin stimulation (POSS), (3) a 2-hour ischemic period before perfusion (ISCH 2), (4) a 1-hour ischemic period followed by acetaldehyde infusion (ISCH 1 + AA), and (5) supramaximal stimulation by cerulein (CER-HIGH). In each model, weight gain, edema formation, and hyperamylasemia occur, signifying the development of pancreatitis. Previously, the authors demonstrated that intracellular adenosine triphosphate (ATP) levels decline during the development of pancreatitis in the FFA model but not in the other four models.

METHODS

The ex vivo perfused canine pancreas preparation was used to study five different stimuli that result in the initiation of acute pancreatitis, as manifested by weight gain, edema formation, and hyperamylasemia during a 4-hour perfusion period. Glucose metabolism (using 13C-labeled glucose) and intracellular pH and ATP levels were monitored by magnetic resonance spectroscopy. Oxygen consumption and pancreatic secretion were measured directly.

RESULTS

In control preparations, a glucose signal appeared in the 13C-labeled spectra within 15 minutes, and a signal from glycogen appeared at the end of the 4-hour perfusion. In the preparations with an ischemic period (ISCH 2 and ISCH 1 + AA), a lactate signal appeared during the ischemia, disappeared during the early perfusion, and appeared again later during the perfusion as the physiologic injury response of pancreatitis developed. Similarly, in the POSS and CER-HIGH pancreatitis preparations, lactate accumulated in the pancreas during the perfusion period. In these four preparations, the intracellular pH did not differ significantly during the perfusion from that of the control preparations. Oxygen consumption was unchanged during the perfusion in the ISCH 2 and ISCH 1 + AA preparations and increased in the POSS and CER-HIGH preparations. In the FFA pancreatitis preparations, only a trace of glycogen was observed, and the metabolites of glucose were not detected. Intracellular pH and oxygen consumption both dropped significantly during the perfusion.

CONCLUSIONS

In four of the five acute experimental pancreatitis models, anaerobic glucose metabolism was induced, despite continuous oxygen extraction by the pancreas. This induction of anaerobic glucose metabolism may be important in maintaining normal levels of intracellular ATP early after the induction of pancreatitis because the absence of anaerobic glucose metabolism in the FFA model was associated with a remarkable decrease in intracellular ATP levels and pH. The FFA model of pancreatitis is the most severe of the five models.

Oxygenation in the rabbit myocardium: assessment with susceptibility-dependent MR imaging

PURPOSE

To determine the feasibility of using hemoglobin (Hb) desaturation as an indicator of myocardial oxygenation.

MATERIALS AND METHODS

High-resolution gradient-echo nuclear magnetic resonance (MR) images of isolated, blood-perfused rabbit hearts were obtained at various blood oxygenation levels. The hearts were perfused at 37 degrees C with a Langendorff apparatus modified for nuclear MR imaging. The perfusate contained bovine red blood cells in a cardioplegic solution that eliminated motion artifacts and minimized arteriovenous oxygenation differences. Hb saturation was varied (7%-100%) randomly. Perfusion pressure was continuously monitored, and blood samples were obtained.

RESULTS

There was a substantial correlation between image signal intensity in the myocardium and Hb saturation in the blood, believed to be due to susceptibility effects of the paramagnetic species deoxyhemoglobin.

CONCLUSION

Direct and noninvasive determination of regional Hb saturation with susceptibility-dependent MR imaging may provide information regarding regional myocardial O2 content.

Intracellular pH determination by 13C-NMR spectroscopy

A noninvasive method for the determination of pH by the 13C-nuclear magnetic resonance (NMR) chemical shift of the C-3 carbon of sn-glycerol 3-phosphate is described. Nonlinear least-squares analysis of the chemical shift variation of the C-3 resonance of sn-glycerol 3-phosphate with pH at 37 degrees C in solutions and in perchloric acid extracts of tissue yielded a pKa of 6.2, making it a very sensitive indicator of pH in the approximate range of 5-7. Intracellular pH determined by the present 13C-NMR method correlated well with simultaneous measurements of pH by 31P-NMR spectroscopy over a wide range during normal perfusion and ischemic conditions in intact rat hearts. These findings indicate that this approach is particularly suited for quantification of intracellular pH over the physiological range in intact tissues and that observed in ischemic myocardium.

Direct evidence that coronary perfusion affects diastolic myocardial mechanical properties in canine heart

OBJECTIVE

The effect of coronary perfusion on left ventricular chamber distensibility is only indirect evidence that perfusion alters the mechanical properties of the myocardium. The aim of this study was to demonstrate explicitly the effects of coronary perfusion on these mechanical properties.

METHODS

The effects of different levels of coronary perfusion were studied both on in-plane stress-strain relations and on transverse stiffness in an isolated, perfused canine interventricular septal preparation. Additionally, to determine the vascular compartment responsible for the mechanical effects of perfusion on tissue properties, we examined the in-plane stress-strain responses and transverse stiffness after embolisation of the vasculature with 15 microns microspheres.

RESULTS

The data show a clear dependence of tissue stress-strain properties on perfusion. The in-plane stress-strain relations were shifted to the left and transverse stiffness increased linearly as septal artery perfusion pressure increased. The dependence of both the in-plane stress-strain relations and transverse stiffness on perfusion was significantly decreased following embolisation.

CONCLUSIONS

Myocardial tissue stiffness is directly related to perfusion. The linear relationship between transverse stiffness and perfusion makes it easier to assess the effects of perfusion on tissue stiffness than with in-plane stress-strain relations. Perfusion of capillaries and/or venules is largely responsible for these alterations in myocardial stiffness.

Tricarboxylic acid cycle activity in postischemic rat hearts

BACKGROUND

Although myocardial oxidative tricarboxylic acid (TCA) cycle activity and contractile function are closely linked in normal cardiac muscle, their relation during postischemic reperfusion, when contractility often is reduced, is not well defined.

METHODS AND RESULTS

To test the hypothesis that oxidative TCA cycle flux is reduced in reperfused myocardium with persistent contractile dysfunction, TCA cycle flux was measured by analyzing the time course of sequential myocardial glutamate labeling during 13C-labeled substrate infusion with 13C nuclear magnetic resonance spectroscopy in beating isolated rat hearts at 37 degrees C. Total TCA cycle flux, indexed by both empirical and mathematical modeling analyses of the 13C data, was not reduced but rather increased in hearts reperfused after 17-20 minutes of ischemia (left ventricular pressure, 73 +/- 5% of preischemic values) compared with flux in developed pressure-matched controls (e.g., total flux, 2.5 +/- 0.4 versus 1.6 +/- 0.1 mumol.min-1.g wet wt-1, respectively; p < 0.01). No TCA cycle activity was detectable by 13C nuclear magnetic resonance in hearts reperfused after 40-45 minutes of ischemia, which lacked contractile recovery and had ultrastructural evidence of irreversible injury.

CONCLUSIONS

These results suggest that TCA cycle activity is not persistently decreased in dysfunctional reperfused myocardium after a brief ischemic episode and therefore cannot account for the reduced contractile function at that time.

Myocardial energetics during ventricular fibrillation investigated by magnetization transfer nuclear magnetic resonance spectroscopy

Ventricular fibrillation (VF) is known to produce alterations in myocardial energetics, but the mechanism of these changes remains unclear. To investigate energy metabolism during VF, phosphorus nuclear magnetic resonance spectroscopy and magnetization transfer were applied to isolated perfused ferret hearts. VF was induced either by perfusion with digitalis (strophanthidin, 30 microM) or by high-frequency electrical stimulation. We measured the flux in two critical reactions: from inorganic phosphate (Pi) to ATP (ATP synthesis rate) and from phosphocreatine (PCr) to ATP (energy transfer capacity). During digitalis-induced VF, energy-related phosphates showed changes similar to those during hypoxia: myocardial [Pi] increased and [PCr] decreased. Concomitantly, the ATP synthesis rate increased to levels about threefold higher than control, whereas oxygen consumption increased by only 16%. The ATP synthesis rate exhibited a strong negative correlation with left ventricular pressure during VF (r = -0.95, n = 5, p < 0.02), whereas oxygen consumption did not (r = 0.19, p > 0.05). On the other hand, energy transfer capacity catalyzed by creatine kinase was significantly smaller during VF than in the control condition but still higher than the simultaneous ATP synthesis rate. In contrast to the marked energetic deterioration during VF induced by digitalis, electrically induced VF led to only a small increase in [Pi] and a small decrease in [PCr], and there were no significant changes in the ATP synthesis rate, energy transfer capacity, or O2 consumption. These results indicate that the rundown in energy metabolism during VF induced by digitalis was mainly attributable to a limitation of energy production through oxidative phosphorylation as well as to a marked increase in energy consumption. In contrast, myocardial energy generation remained unimpaired during VF induced by electrical stimulation. Intracellular calcium overload is more severe during VF induced by digitalis than during electrically induced VF (Circ Res 1991;68:1378-1389); severe calcium overload would be expected to compromise the capacity for energy generation by mitochondria. Thus, we propose that known differences in cellular calcium loading underlie the discrepant energetic patterns of the two types of VF.

Indexing tricarboxylic acid cycle flux in intact hearts by carbon-13 nuclear magnetic resonance

Although the tricarboxylic acid (TCA) cycle is the prime means of carbon metabolism for energy generation in normal myocardium, the noninvasive quantification of TCA cycle flux in intact cardiac tissues is difficult. A novel approach for estimating citric acid cycle flux using 13C nuclear magnetic resonance (NMR) is presented and evaluated experimentally by comparison with measured myocardial oxygen consumption over a wide range of cardiac contractile function in intact, beating rat hearts. Continuous series of 13C NMR spectra, obtained after the introduction of [2-13C]acetate as substrate, quantified the time course of 13C appearance in the carbon positions of myocardial glutamate, which are sequentially enriched via citric acid cycle metabolism. A TCA cycle flux parameter was calculated using the premise that TCA cycle flux is inversely proportional to the time difference between 13C appearance in the C-4 and C-2 positions of glutamate (glutamate delta t50 [minutes]), which are enriched in subsequent "turns" of the TCA cycle. This TCA cycle flux parameter, termed KT, correlated strongly with myocardial oxygen consumption over a range of developed pressures in hearts perfused with 5 mM acetate (r = 0.98, p less than 0.001), as well as in separate studies in hearts perfused with 5 mM glucose and 0.5-0.8 mM acetate (r = 0.94, p less than 0.001). Results of numerical modeling of 13C glutamate kinetics suggest that this TCA cycle flux parameter, KT, is relatively insensitive to changes in metabolite pool sizes that could occur during metabolism of other substrates or during conditions of altered oxygen availability. Additional studies in separate hearts indicated that the time course of 13C appearance in citrate, which is predominantly mitochondrial in the rat heart, is similar to that in glutamate, further supporting the premise that the described 13C NMR parameters reflect mitochondrial citric acid cycle activity in intact cardiac tissues.

Regulation of myocardial glycogenolysis during post-ischemic reperfusion

Myocardial glycogen and the factors which primarily regulate its metabolism were studied during post-ischemic reperfusion. Myocardial [13C]glycogen was continuously monitored by 13C-NMR spectroscopy in beating rat hearts perfused with oxygenated solutions containing [1-13C]glucose (5 mM) and insulin, during normal flow at 15 ml/min (n = 5), and during reperfusion after 30 min of 1 ml/min (n = 5), or 0 ml/min (n = 4) ischemia. Mean myocardial [13C]glycogen fell during reperfusion from 1.1 +/- 0.6 at the end of zero-flow ischemia to 0.4 +/- 0.4 mumol of [13C]glucosyl units/g wet wt (P less than 0.02) over the first 7 min of reperfusion; it also fell during reflow following 1 ml/min ischemia, from 2.3 +/- 1.4 to 1.7 +/- 1.0 mumol (P less than 0.03) over the same interval. In parallel experiments, glycogen phosphorylase % a (GPA%) content was higher at the end of 30 min of 0 ml/min (37.3 +/- 7.3%, P less than 0.01), and trended higher after 1 ml/min flow (30.8 +/- 12.1%, P = 0.18) than under baseline conditions (20.1 +/- 7.4%). However GPA% returned to baseline values within 1 min of reflow after both 0 and 1 ml/min ischemic periods (20.6 +/- 3.0% and 19.0 +/- 8.0%, respectively). Inorganic phosphate, as determined by simultaneous 31P-NMR, remained elevated during early reperfusion relative to baseline, and significantly correlated with the extent of decline in [13C]glycogen during reperfusion (r = 0.79, P less than 0.01). Thus, glycogen breakdown continues to occur during early post-ischemic reperfusion, but the mechanism is not related to elevated GPA%, and may be due to persistently increased inorganic phosphate at that time.

Glycolytic inhibition and calcium overload as consequences of exogenously generated free radicals in rabbit hearts

Free radicals have been implicated in the pathogenesis of reperfusion injury, but it is unclear how they exert their deleterious effects on cellular metabolism. Several lines of indirect evidence suggest that free radicals elevate intracellular Ca2+ concentration ([Ca2+]i) and inhibit glycolysis as part of their mechanism of injury. We tested these ideas directly in hearts subjected to hydroxyl radicals produced by the Fenton and Haber-Weiss reactions. Nuclear magnetic resonance spectra were obtained from Langendorff-perfused rabbit hearts before, during, and after 4 min of perfusion with H2O2 (0.75 mM) and Fe(3+)-chelate (0.1 mM). Isovolumic left ventricular pressure exhibited progressive functional deterioration and contracture after exposure to H2O2 + Fe3+. Phosphorus nuclear magnetic resonance (NMR) spectra revealed partial ATP depletion and sugar phosphate accumulation indicative of glycolytic inhibition. To measure [Ca2+]i, fluorine NMR spectra were acquired in a separate group of hearts loaded with the Ca2+ indicator 5F-BAPTA [5,5'-difluoro derivative of 1,2-bis-(o-aminophenoxy)ethane- N,N,N',N'-tetraacetic acid]. Mean time-averaged [Ca2+]i increased from 347 +/- 14 nM in control to 1,026 +/- 295 nM 4 min after free radical generation (means +/- SEM, n = 7), and remained elevated thereafter. We conclude that free radicals induce clear-cut, specific derangements of cellular metabolism in the form of glycolytic inhibition and calcium overload. The observed increase in [Ca2+]i suggests that the deleterious effects of free radicals are at least partially mediated by secondary changes in cellular calcium homeostasis.

Changes in high-energy phosphate metabolism and cell morphology in four models of acute experimental pancreatitis

Previous studies using the isolated ex vivo perfused canine pancreatitis preparation showed that during a 4-hour perfusion pancreatitis (edema, weight gain, hyperamylasemia) can be induced by four different stimuli. The stimuli include the intra-arterial infusion of oleic acid (FFA), a 2-hour period of ischemia before perfusion (ISCH), partial obstruction of the pancreatic duct with secretin stimulation (POSS), and the intra-arterial infusion of cerulein at supramaximal doses (CER). In the present study, changes in high-energy phosphate metabolism, as determined by nuclear magnetic resonance spectroscopy, and changes in cellular structure, determined by light and electron microscopy, were documented for all four models of acute pancreatitis. The control preparations remained stable for the 4-hour perfusion period, with no decrease in adenosine triphosphate (ATP) levels. In the FFA preparations, ATP decreased to 36% of baseline levels during the 4-hour perfusion (p less than 0.001). In the ISCH preparations, ATP decreased to undetectable levels during the 2-hour period of ischemia, but recovered rapidly and remained at baseline levels during the perfusion. ATP levels remained stable in the remaining two models of pancreatitis (POSS, CER). Microscopy demonstrated that the initial injury was located chiefly in the capillaries (swollen endothelium, intravascular thrombi) in the FFA and ISCH preparations. In the POSS and CER preparations, capillary changes were minimal and the injury was located chiefly in the acinar cells (swollen endoplasmic reticulum, zymogen granule depletion, vacuolization). The POSS preparations also showed striking dilation of centroacinar lumens reflecting duct obstruction. In additional studies it was shown that the ATP decline in the FFA preparations could be significantly reduced by pretreatment with free radical scavengers. The morphologic changes could be reduced by free radical scavengers in the FFA and ISCH preparations. Any amelioration of morphologic injury in the POSS preparations was obscured by dilatation of centroacinar lumens in both treated and untreated groups. The morphologic changes in the CER preparations were reduced by treatment with a cholecystokinin inhibitor.

Coronary blood flow does not decrease during allograft rejection in heterotopic heart transplants

To evaluate changes in coronary blood flow during allograft rejection, 16 beagles with cervical cardiac allografts from mongrel donors were immunosuppressed postoperatively for 7 days with cyclosporine (20 mg/kg orally) and prednisone (0.5 mg/kg orally). They were weaned from immunosuppression over 3 days and then treated with methylprednisolone (30 mg/kg/day IV), cyclosporine (20 mg/kg orally), and prednisone (0.5 mg/kg orally) for 4 days. Previous experiments with this model have suggested the utility of phosphorus 31 nuclear magnetic resonance spectroscopy (31P NMR) in the diagnosis of rejection. Therefore in 10 dogs (NMR group) bioenergetic changes during rejection were assessed using the 31P NMR index of the ratio of phosphocreatine to inorganic phosphate (PCr/Pi). To correlate coronary blood flow and graft ischemia with allograft rejection, six dogs (FLOW group) underwent placement of a magnetic flow probe on the left anterior descending coronary artery to determine mean and peak coronary flow. In both NMR and FLOW groups, grafts were evaluated by endomyocardial biopsy (grading 0 to 8 for increasing rejection), and measurement of lactate production and left ventricular end-diastolic pressure. During the initial 7 days of immunotherapy, cellular rejection was effectively suppressed, and the bioenergetic status of the grafts remained stable (day 7: PCr/Pi = 70% of baseline, biopsy score = 2.0). During weaning of immunotherapy, however, the metabolic profile of the grafts decayed (day 10: PCr/Pi = 45% of baseline, biopsy score = 5.8; p less than 0.05 vs day 0). After 4 days of augmented immunosuppression, PCr/Pi recovered to 83% of baseline; this metabolic recovery corresponded with an improvement in mean biopsy score to 3.2.(ABSTRACT TRUNCATED AT 250 WORDS)

In vivo 31P NMR spectroscopic changes during liver regeneration

Liver regeneration following partial hepatectomy involves rapid cell division 24 to 72 hr postresection. This cell division would necessarily involve changes in intracellular energy stores and cell membrane phospholipid precursors. In tumor models 31P nuclear magnetic resonance (NMR) has been shown to identify intracellular substrate changes associated with cell growth. The ability to monitor early changes in adenosine triphosphate (ATP), inorganic orthophosphate (Pi), phosphomonoesters (PME), or phosphodiesters (PDE) after liver resection could indicate the intracellular changes necessary for hepatocellular regeneration. In vivo 31P NMR scans of the liver were performed in both normal rats and in rats at 24, 48, 72, and 120 hr after 70% hepatectomy. At 48 hr, total ATP fell to 18.9% (P less than 0.05) and both Pi/beta-ATP and PME/beta-ATP were significantly elevated (P less than 0.01) from controls. These changes correlate with the known mitotic peak in the rat following hepatectomy. We conclude that in vivo 31P NMR is a potentially valuable tool for studying hepatic regeneration. The data also suggest that hepatocellular regeneration may be critically dependent on cellular ATP stores.