Glenn A. Walter

Contribution of skeletal muscle atrophy to exercise intolerance and altered muscle metabolism in heart failure.

Background The purpose of this study was to investigate the prevalence of skeletal muscle atrophy and its relation to exercise intolerance and abnormal muscle metabolism in patients with heart failure (HF). Methods and Results Peak Vo2, percent ideal body weight (% IBW), 24-hour urine creatinine (Cr), and anthropometrics were measured in 62 ambulatory patients with HF. 31P magnetic resonance spectroscopy (MRS) and imaging (MRI) of the calf were performed in 15 patients with HF and 10 control subjects. Inorganic phosphorus (Pi), phosphocreatine (PCr), and intracellular pH were measured at rest and during exercise. Calf muscle volume was determined from the sum of the integrated area of muscle in 1-cm-thick contiguous axial images from the patella to the calcaneus. A reduced skeletal muscle mass was noted in 68% of patients, as evidenced by a decrease in Cr-to-height ratio of <7.4 mg/cm and/or upper arm circumference of <5% of normal. Calf muscle volume (MRI) was also reduced in the patients with HF (controls, 675±84 cm3/m2; HF, 567±112 cm3/m2; p < 0.05). Fat stores were largely perserved with triceps skinfold of <5% of normal and/or IBW of <80% in only 8% of patients. Modest linear correlations were observed between peak Vo2 and both calf muscle volume per meter squared (r = 0.48) and midarm muscle area (r = 0.36) (both p < 0.05). 31P metabolic abnormalities during exercise were observed in the patients with HF, which is consistent with intrinsic oxidative abnormalities. The metabolic changes were weakly correlated with muscle volume (r = −0.42, p<0.05). Conclusions These findings indicate that patients with chronic HF frequently develop significant skeletal muscle atrophy and metabolic abnormalities. Atrophy contributes modestly to both the reduced exercise capacity and altered muscle metabolism.

Rapid and effective labeling of brain tissue using TAT-conjugated CdS∶Mn/ZnS quantum dots

TAT (a cell penetrating peptide)-conjugated CdSratioMn/ZnS quantum dots (Qdots), intra-arterially delivered to a rat brain, rapidly (within a few minutes) labeled the brain tissue without manipulating the blood-brain-barrier (BBB). Qdot loading was sufficiently high that it allowed a gross fluorescent visualization of the whole rat brain using a low power hand-held UV lamp. Histological data clearly showed that TAT-conjugated Qdots migrated beyond the endothelial cell line and reached the brain parenchyma. Qdots without TAT did not label the brain tissue confirming the fact that TAT peptide was necessary to overcome the BBB. The present study clearly demonstrated the possibility of delivering a large amount of Qdot-based imaging agents to the brain tissue.

Resistance training improves strength and functional capacity in persons with multiple sclerosis

The purpose of this study was to evaluate the effect of an eight-week progressive resistance training programme on lower extremity strength, ambulatory function, fatigue and self-reported disability in multiple sclerosis (MS) patients (mean disability score 3.79-0.8). Eight MS subjects volunteered for twice weekly training sessions. During the first two weeks, subjects completed one set of 8 -10 reps at 50% of maximal voluntary contraction (MVC) of knee flexion, knee extension and plantarflexion exercises. In subsequent sessions, the subjects completed one set of 10 -15 repetitions at 70% of MVC. The resistance was increased by 2 -5% when subjects completed 15 repetitions in consecutive sessions. Isometric strength of the quadriceps, hamstring, plantarflexor and dorsiflexor muscle groups was assessed before and after the training programme using an isokinetic dynamometer. Magnetic resonance images of the thigh were acquired before and after the exercise programme as were walking speed (25-ft), number of steps in 3 min, and self-reported fatigue and disability. Knee extension (7.4%), plantarflexion (52%) and stepping performance (8.7%) increased significantly (PB-0.05). Self-reported fatigue decreased (PB-0.05) and disability tended to decrease (P -0.07) following the training programme. MS patients are capable of making positive adaptations to resistance training that are associated with improved ambulation and decreased fatigue.

Real-time imaging of de novo arteriovenous malformation in a mouse model of hereditary hemorrhagic telangiectasia

Arteriovenous malformations (AVMs) are vascular anomalies where arteries and veins are directly connected through a complex, tangled web of abnormal arteries and veins instead of a normal capillary network. AVMs in the brain, lung, and visceral organs, including the liver and gastrointestinal tract, result in considerable morbidity and mortality. AVMs are the underlying cause of three major clinical symptoms of a genetic vascular dysplasia termed hereditary hemorrhagic telangiectasia (HHT), which is characterized by recurrent nosebleeds, mucocutaneous telangiectases, and visceral AVMs and caused by mutations in one of several genes, including activin receptor-like kinase 1 (ALK1). It remains unknown why and how selective blood vessels form AVMs, and there have been technical limitations to observing the initial stages of AVM formation. Here we present in vivo evidence that physiological or environmental factors such as wounds in addition to the genetic ablation are required for Alk1-deficient vessels to develop to AVMs in adult mice. Using the dorsal skinfold window chamber system, we have demonstrated for what we believe to be the first time the entire course of AVM formation in subdermal blood vessels by using intravital bright-field images, hyperspectral imaging, fluorescence recordings of direct arterial flow through the AV shunts, and vascular casting techniques. We believe our data provide novel insights into the pathogenetic mechanisms of HHT and potential therapeutic approaches.

Cardiac Overexpression of Angiotensin Converting Enzyme 2 Protects the Heart From Ischemia-Induced Pathophysiology

Angiotensin converting enzyme 2 (ACE2) has been linked to cardiac dysfunction and hypertension-induced cardiac pathophysiology. In this study, we used a gene overexpression approach to investigate the role of ACE2 in cardiac function and remodeling after myocardial infarction. Rats received an intracardiac injection of 4.5×108 lentivirus containing ACE2 cDNA, followed by permanent coronary artery ligation (CAL) of the left anterior descending artery. At 24 hours and 6 weeks after surgery, cardiac functions, viability, and pathophysiology were assessed by MRI) and by histological analysis. At 24 hours post-CAL, left ventricular (LV) anterior wall motion was stunted to the same extent in control CAL and lenti-ACE2–treated CAL rats. However lenti-ACE2–treated CAL rats showed a 60% reduction in delayed contrast-enhanced LV volume after gadodiamide injection, indicating early ischemic protection of myocardium by ACE2. At 6 weeks after CAL, lenti-ACE2 rats demonstrated a complete rescue of cardiac output, a 41% rescue of ejection fraction, a 44% rescue in contractility, a 37% rescue in motion, and a 53% rescue in LV anterior (infracted) wall thinning compared with control CAL rats. No changes were observed in the LV posterior (noninfarcted) wall other than an 81% rescue in motion produced by ACE2 in CAL rats. Finally, infarct size measured by 2,3,5-triphenyl-tetrazolium chloride staining was not significantly different between the ligated groups. These observations demonstrate that cardiac overexpression of ACE2 exerts protective influence on the heart during myocardial infarction by preserving cardiac functions, LV wall motion and contractility, and by attenuating LV wall thinning.

Longitudinal study of skeletal muscle adaptations during immobilization and rehabilitation.

This study describes the metabolic, morphologic, neurologic, and functional adaptations observed in the plantar flexors during 8 weeks of lower leg immobilization and 10 weeks of physical therapy following ankle surgery. A combination of magnetic resonance imaging and spectroscopy, isokinetic and isometric muscle testing, and simple functional tests revealed many adaptive changes due to immobilization, including atrophy, loss of muscle strength, reduced central activation, increase in fatigue resistance, and an increase in inorganic phosphate content. After 10 weeks of physical therapy all alterations were reversed, with the exception of a remaining 5.5% deficit in total muscle cross‐sectional area.

Fluorescent Nanoparticle Probes for Cancer Imaging

Optical imaging technique has strong potential for sensitive cancer diagnosis, particularly at the early stage of cancer development. This is a sensitive, non-invasive, non-ionizing (clinically safe) and relatively inexpensive technique. Cancer imaging with optical technique however greatly relies upon the use of sensitive and stable optical probes. Unlike the traditional organic fluorescent probes, fluorescent nanoparticle probes such as dye-doped nanoparticles and quantum dots (Qdots) are bright and photostable. Fluorescent nanoparticle probes are shown to be very effective for sensitive cancer imaging with greater success in the cellular level. However, cancer imaging in an in vivo setup has been recently realized. There are several challenges in developing fluorescent nanoparticle probes for in vivo cancer imaging applications. In this review, we will discuss various aspects of nanoparticle design, synthesis, surface functionalization for bioconjugation and cancer cell targeting. A brief overview of in vivo cancer imaging with Qdots will also be presented.

In vivo ATP synthesis rates in single human muscles during high intensity exercise

1 In vivo ATP synthesis rates were measured in the human medial gastrocnemius muscle during high intensity exercise using localized 31P‐magnetic resonance spectroscopy (31P‐MRS). Six‐second localized spectra were acquired during and following a 30 s maximal voluntary rate exercise using a magnetic resonance image‐guided spectral localization technique. 2 During 30 s maximal voluntary rate exercise, ATPase fluxes were predominantly met by anaerobic ATP sources. Maximal in vivo glycogenolytic rates of 207 ± 48 mM ATP min−1 were obtained within 15 s, decreasing to 72 ± 34 mM ATP min−1 by the end of 30 s. In contrast, aerobic ATP synthesis rates achieved 85 ± 2 % of their maximal capacity within 9 s and did not change throughout the exercise. The ratio of peak glycolytic ATP synthesis rate to maximal oxidative ATP synthesis was 2.9 ± 0.9. 3 The non‐Pi, non‐CO2 buffer capacity was calculated to be 27.0 ± 6.2 slykes (millimoles acid added per unit change in pH). At the cessation of exercise, Pi, phosphomonoesters and CO2 were predicted to account for 17.2 ± 1.5, 5.57 ± 0.97 and 2.24 ± 0.34 slykes of the total buffer capacity. 4 Over the approximately linear range of intracellular pH recovery following the post‐exercise acidification, pHi recovered at a rate of 0.19 ± 0.03 pH units min−1. Proton transport capacity was determined to be 16.4 ± 4.1 mM (pH unit)−1 min−1 and corresponded to a maximal proton efflux rate of 15.3 ± 2.7 mM min−1. 5 These data support the observation that glycogenolytic and glycolytic rates are elevated in vivo in the presence of elevated Pi levels. The data do not support the hypothesis that glycogenolysis follows Michealis‐Menten kinetics with an apparent Km for [Pi]in vivo. 6 In vivo ‐measured ATP utilization rates and the initial dependence on PCr and glycolysis were similar to those previously reported in in situ studies involving short duration, high intensity exercise. This experimental approach presents a non‐invasive, quantitative measure of peak glycolytic rates in human skeletal muscle.

T₂ mapping provides multiple approaches for the characterization of muscle involvement in neuromuscular diseases: a cross-sectional study of lower leg muscles in 5-15-year-old boys with Duchenne muscular dystrophy.

Skeletal muscles of children with Duchenne muscular dystrophy (DMD) show enhanced susceptibility to damage and progressive lipid infiltration, which contribute to an increase in the MR proton transverse relaxation time (T2). Therefore, the examination of T2 changes in individual muscles may be useful for the monitoring of disease progression in DMD. In this study, we used the mean T2, percentage of elevated pixels and T2 heterogeneity to assess changes in the composition of dystrophic muscles. In addition, we used fat saturation to distinguish T2 changes caused by edema and inflammation from fat infiltration in muscles. Thirty subjects with DMD and 15 age‐matched controls underwent T2‐weighted imaging of their lower leg using a 3‐T MR system. T2 maps were developed and four lower leg muscles were manually traced (soleus, medial gastrocnemius, peroneal and tibialis anterior). The mean T2 of the traced regions of interest, width of the T2 histograms and percentage of elevated pixels were calculated. We found that, even in young children with DMD, lower leg muscles showed elevated mean T2, were more heterogeneous and had a greater percentage of elevated pixels than in controls. T2 measures decreased with fat saturation, but were still higher (P < 0.05) in dystrophic muscles than in controls. Further, T2 measures showed positive correlations with timed functional tests (r = 0.23–0.79). The elevated T2 measures with and without fat saturation at all ages of DMD examined (5–15 years) compared with unaffected controls indicate that the dystrophic muscles have increased regions of damage, edema and fat infiltration. This study shows that T2 mapping provides multiple approaches that can be used effectively to characterize muscle tissue in children with DMD, even in the early stages of the disease. Therefore, T2 mapping may prove to be clinically useful in the monitoring of muscle changes caused by the disease process or by therapeutic interventions in DMD. Copyright

Longitudinal measurements of MRI-T2 in boys with Duchenne muscular dystrophy: effects of age and disease progression.

Duchenne muscular dystrophy (DMD) is characterized by an increased muscle damage and progressive replacement of muscle by noncontractile tissue. Both of these pathological changes can lengthen the MRI transverse proton relaxation time (T2). The current study measured longitudinal changes in T2 and its distribution in the lower leg of 16 boys with DMD (5-13years, 15 ambulatory) and 15 healthy controls (5-13years). These muscles were chosen to allow extended longitudinal monitoring, due to their slow progression compared with proximal muscles in DMD. In the soleus muscle of boys with DMD, T2 and the percentage of pixels with an elevated T2 (⩾2SD above control mean T2) increased significantly over 1year and 2years, while the width of the T2 histogram increased over 2years. Changes in soleus T2 variables were significantly greater in 9-13years old compared with 5-8years old boys with DMD. Significant correlations between the change in all soleus T2 variables over 2years and the change in functional measures over 2years were found. MRI measurement of muscle T2 in boys with DMD is sensitive to disease progression and shows promise as a clinical outcome measure.