Assessment of Peripheral Serotonin Synthesis Using Stable Isotope-Labeled Tryptophan.

Serotonin (5-HT) is synthesized from dietary tryptophan (Trp) and plays an important role in numerous diseases of the central nervous system and periphery. Stable isotope tracers enable safe monitoring of metabolic rates. Here we demonstrate measurement of peripheral 5-HT synthesis in healthy subjects by monitoring the produced [13 C10 ]-5-HT (h-5-HT) in EDTA-whole blood from three doses of orally administered [13 C11 ]-Trp (h-Trp) tracer. h-Trp was rapidly absorbed and distributed in a multiphasic manner, followed by a slower terminal elimination phase. The h-5-HT synthesis rate was dependent on h-Trp dose, appeared linear up to 12 hours postdose, and could be reliably assessed for the two highest doses. The human data was compared to similar studies in rats and dogs, finding larger interspecies differences in the h-5-HT synthesis rate than in 5-HT levels. In future studies, the h-5-HT synthesis rate can be used to assess disease-dysregulated 5-HT synthesis or quantify the pharmacodynamics of 5-HT synthesis inhibitors.

Clinical assessment of the lag-time and tmax of pellets with controlled release of glucose: in vitro/in vivo comparison using 13 C-breath test.

Maintaining a stable glycaemia in diabetes mellitus type 1 requires flexible insulin administration and carbohydrate intake to affected individuals. In real life, there might be some situations limiting the insulin-sugar balance control, e.g. night sleep or prolonged sporting activities. Glucose pellets with a pre-determined time lag between the pellet administration and glucose release were developed to mimic a 'snack eaten in advance'. In this article, a 13 C-glucose breath test was introduced to translate laboratory dissolution testing to clinical confirmation of the glucose release pattern using 5% δ abundance to differentiate the appearance of in 13 C exhaled breath. An independent two-sample t-test (p = 0.20) confirmed an average clinical lag time of 300 min and an in vitro time of 338 min to be identical at a level of significance of α = 0.05. Moreover, using the same statistical method, the clinical tmax (564 min) and the in vitro t50 (594 min) were also considered identical (p = 0.34). It was concluded that dissolution testing is a relevant method to determine the time lags of dosage forms with controlled release of glucose and that the 13 C-glucose breath test is a suitable clinical tool for lag time verification in clinical studies.

Combining hyperpolarized 13 C MRI with a liver-specific gadolinium contrast agent for selective assessment of hepatocyte metabolism.

PURPOSE: Hyperpolarized 13 C MRI is a powerful tool for studying metabolism, but can lack tissue specificity. Gadoxetate is a gadolinium-based MRI contrast agent that is selectively taken into hepatocytes. The goal of this project was to investigate whether gadoxetate can be used to selectively suppress the hyperpolarized signal arising from hepatocytes, which could in future studies be applied to generate specificity for signal from abnormal cell types. METHODS: Baseline gadoxetate uptake kinetics were measured using T1 -weighted contrast enhanced imaging. Relaxivity of gadoxetate was measured for [1-13 C]pyruvate, [1-13 C]lactate, and [1-13 C]alanine. Four healthy rats were imaged with hyperpolarized [1-13 C]pyruvate using a three-dimensional (3D) MRSI sequence prior to and 15 min following administration of gadoxetate. The lactate:pyruvate ratio and alanine:pyruvate ratios were measured in liver and kidney. RESULTS: Overall, the hyperpolarized signal decreased approximately 60% as a result of pre-injection of gadoxetate. In liver, the lactate:pyruvate and alanine:pyruvate ratios decreased 42% and 78%, respectively (P < 0.05) following gadoxetate administration. In kidneys, these ratios did not change significantly. Relaxivity of gadoxetate for [1-13 C]alanine was 12.6 times higher than relaxivity of gadoxetate for [1-13 C]pyruvate, explaining the greater selective relaxation effect on alanine. CONCLUSIONS: The liver-specific gadolinium contrast-agent gadoxetate can selectively suppress normal hepatocyte contributions to hyperpolarized 13 C MRI signals. Magn Reson Med 77:2356-2363, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Renal ischemia and reperfusion assessment with three-dimensional hyperpolarized 13 C,15 N2-urea.

PURPOSE: The aim of this work was to investigate whether hyperpolarized 13 C,15 N2 -urea can be used as an imaging marker of renal injury in renal unilateral ischemic reperfusion injury (IRI), given that urea is correlated with the renal osmotic gradient, which describes the renal function. METHODS: Hyperpolarized three-dimensional balanced steady-state 13 C magnetic resonance imaging (MRI) experiments alongside kidney function parameters and quantitative polymerase chain reaction measurements were performed in rats subjected to unilateral renal ischemia for 60-minute and 24-hour reperfusion. RESULTS: We revealed a significant reduction in the intrarenal gradient in the ischemic kidney in agreement with cortical injury markers neutrophil gelatinase-associated lipocalin and kidney injury molecule 1, as well as functional kidney parameters. CONCLUSION: Hyperpolarized functional 13 C,15 N2 urea MRI can be used to successfully detect changes in the intrarenal urea gradient post-IRI, thereby enabling in vivo monitoring of the intrarenal functional status in the rat kidney. Magn Reson Med 76:1524-1530, 2016. © 2016 International Society for Magnetic Resonance in Medicine.

Role of the ¹³C-methacetin breath test in the assessment of acute liver injury in a rat model.

AIM: To evaluate the role of the (13)C-methacetin breath test ((13)C-MBT) in the assessment of acute liver injury in a rat model. METHODS: Acute liver injury in rats was induced by a single intraperitoneal injection of D-galactosamine (D-GalN). Forty-eight male Sprague-Dawley rats were randomly assigned to a control group (n = 8) and five model groups (each n = 8), and acute liver injury was assessed at different time points (6, 12, 24, 48 and 72 h) after D-GalN injection. The (13)C-MBT, biochemical tests, 15-min retention rate of indocyanine green (ICGR15), and liver biopsy were performed and compared between the control and model groups. Correlations between parameters of the (13)C-MBT (Tmax, MVmax, CUM120 and DOBmax), biochemical tests, ICGR15 and liver necrosis score were also analyzed using Spearman's correlation analysis. RESULTS: Tmax, MVmax, CUM120 and DOBmax, as well as most of the traditional methods, correlated with the liver necrosis score (r = 0.493, P < 0.05; r = -0.731, P < 0.01; r = -0.618, P < 0.01; r = -0.592, P < 0.01, respectively). MVmax, CUM120 and DOBmax rapidly decreased and were lower than those in the controls as early as 6 h after D-GalN injection (3.84 ± 0.84 vs 5.06 ± 0.78, P < 0.01; 3.35 ± 0.72 vs 4.21 ± 1.44, P < 0.05; 52.3 ± 20.58 vs 75.1 ± 9.57, P < 0.05, respectively) and reached the lowest point 24 h after D-GalN injection. MVmax, CUM120 and DOBmax returned to normal levels 72 h after D-GalN injection and preceded most of the traditional methods, including liver biopsy. CONCLUSION: The (13)C-MBT is a sensitive tool for the timely detection of acute liver injury and early prediction of recovery in a rat model. Further clinical studies are warranted to validate its role in patients with acute liver injury.

Multimodal assessment of in vivo metabolism with hyperpolarized [1-13C]MR spectroscopy and 18F-FDG PET imaging in hepatocellular carcinoma tumor-bearing rats.

UNLABELLED: Abnormalities of tumor metabolism can be exploited for molecular imaging. PET imaging of (18)F-FDG is a well-established method using the avid glucose uptake of tumor cells. (13)C MR spectroscopic imaging (MRSI) of hyperpolarized [1-(13)C]pyruvate and its metabolites, meanwhile, represents a new method to study energy metabolism by visualizing, for example, the augmented lactate dehydrogenase activity in tumor cells. Because of rapid signal loss, this method underlies strict temporal limitations, and the acquisition of data-encoding spatial, temporal, and spectral information within this time frame-is challenging. The object of our study was to compare spectroscopic images with (18)F-FDG PET images for visualizing tumor metabolism in a rat model. METHODS: (13)C MRSI with IDEAL (Iterative Decomposition of water and fat with Echo Asymmetry and Least-squares estimation) chemical shift imaging in combination with single-shot spiral acquisition was used to obtain dynamic data from 23 rats bearing a subcutaneous hepatocellular carcinoma and from reference regions of the same animals. Static and dynamic analysis of (18)F-FDG PET images of the same animals was performed. The data were analyzed qualitatively (visual assessment) and quantitatively (magnitude and dynamics of (18)F-FDG uptake, (13)C MRSI dynamics, and physiologic parameters). RESULTS: In most animals increased [1-(13)C]lactate signals in the tumor could be detected by simple display of integrated [1-(13)C]lactate images with corresponding enhanced (18)F-FDG uptake. Low [1-(13)C]pyruvate or [1-(13)C]lactate signals did not correlate with histologic or physiologic parameters. Significantly less pyruvate reached the tumors than the gastrointestinal tract, but in tumors a significantly higher amount of pyruvate was converted to lactate and alanine within seconds after intravenous administration. CONCLUSION: This study reveals that PET and (13)C MRSI can be used to visualize increased glycolytic flux in malignant tissue. The combination of signals will allow the quantitative dissection of substrate metabolism, with respect to uptake and downstream metabolic pathways. Although hyperpolarized [1-(13)C]pyruvate increases the sensitivity of MR imaging, signal-to-noise ratio constraints still apply for spatially and temporally resolved (13)C MRSI, emphasizing the need for further MR methodologic development. These first imaging data suggest the feasibility of (13)C MRSI for future clinical use.

Liver function assessment with three (13)C breath tests by two-point measurements.

In this study, we performed three breath tests - l-[1-(13)C ]phenylalanine breath test (PBT), l-[1-(13)C ] methionine breath test, and [(13)C]methacetin breath test (MethaBT) - in patients with chronic liver disease to determine the optimal timing of expired air collection for diagnosing chronic liver disease and evaluating the grade of fibrosis. The subjects were 61 adults with normal livers, 98 chronic hepatitis patients, and 91 liver cirrhosis patients. We investigated the relationships of breath test results with routine biochemical tests and the Child-Pugh score, as well as the diagnostic capacities of the breath tests for liver dysfunction/cirrhosis and grade of liver fibrosis. For the diagnosis of liver cirrhosis and correlations with liver fibrosis, the accuracy of the PBT at 30 min (PBT30) was similar to that of the MethaBT at 15 min (Metha15). For liver function assessment by two-point measurement with (13)C breath tests, we recommend the PBT30 and the Metha15.

A non-invasive, low-cost study design to determine the release profile of colon drug delivery systems: a feasibility study.

PURPOSE: Conventional bioavailability testing of dosage forms based on plasma concentration-time graphs of two products in a two-period, crossover-design, is not applicable to topical treatment of intestinal segments. We introduce an isotope dual-label approach ((13)C- and (15)N(2)-urea) for colon drug delivery systems that can be performed in a one-day, non-invasive study-design. METHODS: Four healthy volunteers took an uncoated or a ColoPulse-capsule containing (13)C-urea and an uncoated capsule containing (15)N(2)-urea. In case of colon-release (13)C-urea is fermented and (13)C detected as breath (13)CO(2). Absorbed (13)C-urea and (15)N-urea are detected in urine. RESULTS: C and (15)N in urine released from uncoated capsules showed a ratio of 1.01 ± 0.06. The (13)C/(15)N-recovery ratio after intake of a ColoPulse-capsule was constant and lower >12 h post-dose (median 0.22, range 0.13-0.48). The (13)C/(15)N-ratio in a single urine sample at t ≥ 12 h predicted the 24 h non-fermented fraction (13)C of <26 %. Breath (13)CO(2) indicated delayed (>3 h) release and a fermented fraction (13)C >54 %. CONCLUSIONS: Breath and urine (13)C and (15)N data describe the release-profile and local bioavailability of a colon delivery device. This allows non-invasive bioavailability studies for evaluation of colon-specific drug delivery systems without radioactive exposure and with increased power and strongly reduced costs.

Resting energy expenditure and protein turnover are increased in patients with severe chronic obstructive pulmonary disease.

The mechanisms leading to weight loss in patients with chronic obstructive pulmonary disease (COPD) are poorly understood. Changes in protein metabolism and systemic inflammation may contribute to increased resting energy expenditure (REE) in COPD, leading to an energy imbalance and loss of fat and fat-free mass. The objective of this study was to determine first whether REE was increased in patients with COPD and, second, whether this was associated with increased protein turnover and/or systemic inflammation. Resting energy expenditure was determined using indirect calorimetry in 14 stable outpatients with severe COPD (7 with low and 7 with preserved body mass indices) and 7 healthy controls. Endogenous leucine flux, leucine oxidation, and nonoxidative disposal, indices of whole-body protein breakdown, catabolism, and synthesis, were measured using intravenous infusions of (13)C-bicarbonate and 1-(13)C-leucine. Total body water, from which fat-free mass and fat mass were calculated, was determined using an intravenous bolus of deuterated water. Plasma markers of systemic inflammation were also measured. As a group, subjects with COPD had increased REE adjusted for fat-free mass (P < .001) and faster rates of endogenous leucine flux (P = .006) and nonoxidative leucine disposal (P = .002) compared with controls. There was a significant correlation between REE and both endogenous leucine flux (P = .02) and nonoxidative leucine disposal (P = .008). Plasma concentrations of the inflammatory markers C-reactive protein and interleukin-6 were not different between COPD subjects and controls. Increased rates of protein turnover are associated with increased REE and loss of fat-free mass in COPD.