Dilution of oral D3 -Creatine to measure creatine pool size and estimate skeletal muscle mass: development of a correction algorithm.

BACKGROUND: Muscle mass can be measured directly in vivo by isotope dilution, using Creatine-(methyl-d3 ) monohydrate (D3 -Cr) by mouth followed by measurement of the steady-state enrichment of D3 -creatinine (D3 -Crn) in urine. Isotope dilution methods require knowledge of the amount of tracer delivered to the pool of interest. In a subset of human subjects, a small amount of orally administered D3 -Cr 'spills' into urine after absorption and prior to transport into skeletal muscle cells. The objectives were to develop a method to correct for spillage to compare the estimate of muscle mass by D3 -Cr dilution to other assessments of fat-free mass. METHODS: Subjects (19 males, 23-81 years old; 20 females, 20-77 years old) ingested a single dose of 60 mg D3 -Cr and urine was collected prior to and daily for 4 days following the dose. Fasting morning urine samples was assessed for D3 -Cr, total Cr, D3 -Crn, and total Crn concentrations, as well as isotopic enrichments of D3 -Crn, by LC/MS. The 24-h urine collections over 3 days after the dose of D3 -Cr were also performed to determine D3 -Cr spillage. Total body water, fat mass, and fat-free mass were assessed by bioelectrical impedance spectroscopy (BIS). RESULTS: Spillage of D3 -Cr in the urine was greater in women than men. D3 -Crn enrichment and the ratio of Cr/Crn were used in an algorithm to calculate Cr pool size and muscle mass. Specifically, an algorithm was developed for the estimation of spillage based on the relationship between the fasting Cr/Crn ratio and the cumulative proportion of the D3 -Cr dose excreted over 3 days based on 24-h urine collections. Muscle mass corrected using the algorithm based on fasting urine levels correlated (r = 0.9967, P < 0.0001) with that corrected by measuring D3 -Cr dose excreted. Muscle mass measured by D3 -Crn enrichment also correlated (r = 0.8579, P < 0.0001, algorithm corrected) with that measured by 24-h Crn excretion. Muscle mass measured by D3 -Cr dilution method correlated with intracellular water by BIS, whether using spillage corrected by the algorithm (r = 0.9041, P < 0.0001) or measured by 3 day D3 -Cr losses (r = 0.91, P < 0.0001) and similarly correlated with fat-free mass by BIA (r = 0.8857 and 0.8929, P < 0.0001, respectively). CONCLUSIONS: The D3 -Cr dilution method is further validated here as a non-invasive, easy-to-use test for measuring muscle mass. The technical issue of D3 -Cr spillage can be corrected for with a simple algorithm based on fasting spot urine samples. Muscle mass by Cr dilution potentially has broad applications in clinical and research settings.

Hyperdynamic microtubules, cognitive deficits, and pathology are improved in tau transgenic mice with low doses of the microtubule-stabilizing agent BMS-241027.

Tau is a microtubule (MT)-stabilizing protein that is altered in Alzheimer's disease (AD) and other tauopathies. It is hypothesized that the hyperphosphorylated, conformationally altered, and multimeric forms of tau lead to a disruption of MT stability; however, direct evidence is lacking in vivo. In this study, an in vivo stable isotope-mass spectrometric technique was used to measure the turnover, or dynamicity, of MTs in brains of living animals. We demonstrated an age-dependent increase in MT dynamics in two different tau transgenic mouse models, 3xTg and rTg4510. MT hyperdynamicity was dependent on tau expression, since a reduction of transgene expression with doxycycline reversed the MT changes. Treatment of rTg4510 mice with the epothilone, BMS-241027, also restored MT dynamics to baseline levels. In addition, MT stabilization with BMS-241027 had beneficial effects on Morris water maze deficits, tau pathology, and neurodegeneration. Interestingly, pathological and functional benefits of BMS-241027 were observed at doses that only partially reversed MT hyperdynamicity. Together, these data suggest that tau-mediated loss of MT stability may contribute to disease progression and that very low doses of BMS-241027 may be useful in the treatment of AD and other tauopathies.

Determination of mouth alcohol using the Dräger Evidential Portable Alcohol System.

Drivers suspected of alcohol intoxication are observed for a period of 15 min prior to quantitative breath alcohol testing. This is to preclude the interference of alcohol-based substances such as cough medicine, mouthwash, and breath spray just prior to actual evidential testing. To determine whether a 15 min observation period was necessary when performing evidential breath tests in the field, a mouth alcohol experiment was performed using the Dräger Evidential Portable Alcohol System (EPAS). Five types of alcohol beverages and the effects of expectorating versus swallowing were tested on twenty-five volunteer subjects. Serial measurements of breath and blood alcohol levels were performed at fixed time intervals. All alcohol beverage types gave two sequential measurements within 0.02 g/210 L of each other before 15 min had passed. Fifteen minutes was necessary to ensure there was no residual mouth alcohol. If the 15 min waiting period was not observed, the safety feature of the EPAS requiring two sequential measurements 2 min apart within 0.02 g/210 L would not ensure against mouth alcohol interference.