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1.  Mitochondrial Respiratory Capacity and Content Are Normal in Young Insulin-Resistant Obese Humans 
Diabetes  2013;63(1):132-141.
Considerable debate exists about whether alterations in mitochondrial respiratory capacity and/or content play a causal role in the development of insulin resistance during obesity. The current study was undertaken to determine whether such alterations are present during the initial stages of insulin resistance in humans. Young (∼23 years) insulin-sensitive lean and insulin-resistant obese men and women were studied. Insulin resistance was confirmed through an intravenous glucose tolerance test. Measures of mitochondrial respiratory capacity and content as well as H2O2 emitting potential and the cellular redox environment were performed in permeabilized myofibers and primary myotubes prepared from vastus lateralis muscle biopsy specimens. No differences in mitochondrial respiratory function or content were observed between lean and obese subjects, despite elevations in H2O2 emission rates and reductions in cellular glutathione. These findings were apparent in permeabilized myofibers as well as in primary myotubes. The results suggest that reductions in mitochondrial respiratory capacity and content are not required for the initial manifestation of peripheral insulin resistance.
PMCID: PMC3868052  PMID: 23974920
2.  Inhibiting Myosin-ATPase Reveals Dynamic Range of Mitochondrial Respiratory Control in Skeletal Muscle 
The Biochemical journal  2011;437(2):10.1042/BJ20110366.
Assessment of mitochondrial ADP-stimulated respiratory kinetics in permeabilized skeletal myofibres (PmFB) is increasingly used in clinical diagnostic and basic research settings. However, estimates of the Km for ADP vary considerably (∼20-300 μM) and tend to overestimate respiration at rest. Noting PmFBs spontaneously contract during respiration experiments, we systematically determined the impact of contraction, temperature and oxygenation on ADP-stimulated respiratory kinetics. Blebbistatin (BLEB), a myosin II ATPase inhibitor, blocked contraction under all conditions and yielded high Km values for ADP of >∼250 and ∼80 μM in red and white rat PmFB, respectively. In the absence of BLEB, PmFB contracted and the Km for ADP decreased by ∼2 to 10-fold in a temperature-dependent manner. PmFB were sensitive to hyperoxia (increased Km) in the absence of BLEB (contracted) at 30°C but not 37°C. In PmFB from humans, contraction elicited high sensitivity to ADP (m <100 μM) whereas blocking contraction (+BLEB) and including PCr:Cr = 2 to mimic the resting energetic state yielded a Km for ADP = ∼1560 μM, consistent with estimates of in vivo resting respiratory rates of <1% maximum. These results demonstrate the sensitivity of muscle to ADP varies over a wide range in relation to contractile state and cellular energy charge, providing evidence that enzymatic coupling of energy transfer within skeletal muscle becomes more efficient in the working state.
PMCID: PMC3863643  PMID: 21554250
bioenergetics; creatine kinase; blebbistatin; N-benzyltoluene sulphonamide; metabolism; skeletal muscle contraction
3.  Iodine-131—Metaiodobenzylguanidine Double Infusion With Autologous Stem-Cell Rescue for Neuroblastoma: A New Approaches to Neuroblastoma Therapy Phase I Study 
Journal of Clinical Oncology  2009;27(7):1020-1025.
Iodine-131—metaiodobenzylguanidine (131I-MIBG) provides targeted radiotherapy with more than 30% response rate in refractory neuroblastoma, but activity infused is limited by radiation safety and hematologic toxicity. The goal was to determine the maximum-tolerated dose of 131I-MIBG in two consecutive infusions at a 2-week interval, supported by autologous stem-cell rescue (ASCR) 2 weeks after the second dose.
Patients and Methods
The 131I-MIBG dose was escalated using a 3 + 3 phase I trial design, with levels calculated by cumulative red marrow radiation index (RMI) from both infusions. Using dosimetry, the second infusion was adjusted to achieve the target RMI, except at level 4, where the second infusion was capped at 21 mCi/kg.
Twenty-one patients were enrolled onto the study at levels 1 to 4, with 18 patients assessable for toxicity and 20 patients assessable for response. Cumulative 131I-MIBG given to achieve the target RMI ranged from 22 to 50 mCi/kg, with cumulative RMI of 3.2 to 8.92 Gy. No patient had a dose-limiting toxicity. Reversible grade 3 nonhematologic toxicity occurred in six patients at level 4, establishing the recommended cumulative dose as 36 mCi/kg. The median time to absolute neutrophil count more than 500/μL after ASCR was 13 days (4 to 27 days) and to platelet independence was 17 days (6 to 47 days). Responses included two partial responses, eight mixed responses, three stable disease, and seven progressive disease. Responses by semiquantitative MIBG score occurred in eight patients, soft tissue responses occurred in five of 11 patients, but bone marrow responses occurred in only two of 13 patients.
The lack of toxicity with this approach allowed dramatic dose intensification of 131I-MIBG, with minimal toxicity and promising activity.
PMCID: PMC2738616  PMID: 19171714

Results 1-3 (3)