Advancing the analysis of impurities in hydrogen by use of a novel tracer enrichment method

This paper presents and validates a novel hydrogen impurity enrichment method that can be used for concentrating the impurities in hydrogen to facilitate more routine and cost-effective purity analysis of fuel cell hydrogen.

Measurement of Fractional Synthetic Rates of Multiple Protein Analytes by Triple Quadrupole Mass Spectrometry

BACKGROUND Current approaches to measure protein turnover that use stable isotope-labeled tracers via GC-MS are limited to a small number of relatively abundant proteins. We developed a multiplexed liquid chromatography–selected reaction monitoring mass spectrometry (LC-SRM) assay to measure protein turnover and compared the fractional synthetic rates (FSRs) for 2 proteins, VLDL apolipoprotein B100 (VLDL apoB100) and HDL apoA-I, measured by both methods. We applied this technique to other proteins for which kinetics are not readily measured with GC-MS. METHODS Subjects were given a primed-constant infusion of [5,5,5-D3]-leucine (D3-leucine) for 15 h with blood samples collected at selected time points. Apolipoproteins isolated by SDS-PAGE from lipoprotein fractions were analyzed by GC-MS or an LC-SRM assay designed to measure the M+3/M+0 ratio at >1% D3-leucine incorporation. We calculated the FSR for each apolipoprotein by curve fitting the tracer incorporation data from each subject. RESULTS The LC-SRM method was linear over the range of tracer enrichment values tested and highly correlated with GC-MS (R2 > 0.9). The FSRs determined from both methods were similar for HDL apoA-I and VLDL apoB100. We were able to apply the LC-SRM approach to determine the tracer enrichment of multiple proteins from a single sample as well as proteins isolated from plasma after immunoprecipitation. CONCLUSIONS The LC-SRM method provides a new technique for measuring the enrichment of proteins labeled with stable isotopes. LC-SRM is amenable to a multiplexed format to provide a relatively rapid and inexpensive means to measure turnover of multiple proteins simultaneously.

Hyperinsulinemic euglycemic step clamping with tracer glucose infusion and labeled glucose infusate for assessment of acute insulin resistance in pigs

The present study aimed to establish hyperinsulinemic euglycemic step clamping with tracer glucose infusion and labeled glucose infusate (step hot-GINF HEC) for assessment of acute insulin resistance in anesthetized pigs and to arrange for combination with invasive investigative methods. Tracer enrichment was measured during d-[6,6-2H2]glucose infusion before and after surgical instrumentation ( n = 8). Insulin dose-response characteristics were determined by two step hot-GINF HEC procedures, with accordingly labeled glucose infusates performed at a total of six insulin infusion rates ranging from 0.2 to 2.0 mU·kg−1·min−1 ( n = 8). Finally, three-step hot-GINF HEC (0.4, 1.2, and 2.0 mU·kg−1·min−1) was performed subsequent to major surgical trauma ( n = 8). Tracer enrichment, basal glucose kinetics, and circulating levels of C-peptide, cortisol, glucagon, and catecholamines were not influenced by surgical instrumentation. Mean intraindividual coefficient of variance levels for glucose infusion rates and repeatedly measured insulin, glucose, and tracer enrichment indicated stable clamping conditions. Basal and maximal insulin-stimulated glucose utilization was twice as high as in humans at ∼5.5 and 21 mg·kg−1·min−1. Surgical trauma elicited pronounced peripheral and moderate hepatic insulin unresponsiveness (45% lower whole body glucose disposal and 19% less suppressed endogenous glucose release) and apparently diminished metabolic insulin clearance. Step hot-GINF HEC seems suitable for assessment of acute insulin resistance in anesthetized pigs, and combination with invasive investigative methods requiring surgical instrumentation can be accomplished without the premises for utilization of the technique being altered, but attention must be paid to alterations in metabolic insulin clearance.

Impaired lymphatic cerebrospinal fluid absorption in a rat model of kaolin-induced communicating hydrocephalus

It has been assumed that the pathogenesis of hydrocephalus includes a cerebrospinal fluid (CSF) absorption deficit. Because a significant portion of CSF absorption occurs into extracranial lymphatics located in the olfactory turbinates, the purpose of this study was to determine whether CSF transport was compromised at this location in a kaolin-induced communicating (extraventricular) hydrocephalus model in rats. Under 1–3% halothane anesthesia, kaolin ( n = 10) or saline ( n = 9) was introduced into the basal cisterns of Sprague-Dawley rats, and the development of hydrocephalus was assessed 1 wk later using MRI. After injection of human serum albumin (125I-HSA) into a lateral ventricle, the tracer enrichment in the olfactory turbinates 30 min postinjection provided an estimate of CSF transport through the cribriform plate into nasal lymphatics. Lateral ventricular volumes in the kaolin group (0.073 ± 0.014 ml) were significantly greater than those in the saline-injected animals (0.016 ± 0.001 ml; P = 0.0014). The CSF tracer enrichment in the olfactory turbinates (expressed as percent injected/g tissue) in the kaolin rats averaged 0.99 ± 0.39 and was significantly lower than that measured in the saline controls (5.86 ± 0.32; P < 0.00001). The largest degree of ventriculomegaly was associated with the lowest levels of lymphatic CSF uptake with lateral ventricular expansion occurring only when almost all of the lymphatic CSF transport capacity had been compromised. We conclude that lymphatic CSF absorption is impaired in a kaolin-communicating hydrocephalus model and that the degree of this impediment may contribute to the severity of the induced disease.