Direct enzyme-substrate affinity determination by real-time hyperpolarized (13)C-MRS.

A specialized kinetic analysis of real-time hyperpolarized [1,1,2,2-D4, 1-(13)C]choline (13)C-magnetic resonance spectroscopy enabled the determination of initial rates of metabolic enzyme activity (choline oxidase), enzyme-substrate affinity (Km), and inhibition. In a clinical MRI scanner, metabolite levels lower than 16 µM were detected at a temporal resolution of 1 s.

Remission of progressive multifocal leukoencephalopathy and primary central nervous system lymphoma in an HIV-infected patient.

The coexistence of progressive multifocal leukoencephalopathy (PML) and primary central nervous system lymphoma (PCNSL) is a rare event, usually associated with a fatal outcome. We report the case of a human immunodeficiency virus (HIV)-infected individual presenting with both PML and PCNSL who made a remarkable recovery after highly active anti retroviral therapy (HAART) and radiation therapy, and discuss diagnostic and therapeutic aspects of both conditions.

Differential routing of choline in implanted breast cancer and normal organs.

Choline is an essential nutrient participating as the initial substrate in major metabolic pathways. The differential metabolic routing of choline was investigated in MCF7 human breast cancer implanted in nude mice and in the kidney, liver, and brain of these mice. The distribution of metabolites following infusion of [1,2-(13)C]-choline was monitored by (13)C magnetic resonance spectroscopy. This infusion led to an 18-fold increase in plasma choline and to concomitant changes in the content and distribution of choline metabolites. In vivo kinetic studies of the tumor during the infusion demonstrated accumulation of choline in the interstitium and intracellular synthesis of phosphocholine. The amount of unlabeled choline metabolites was 7.1, 4.1, 3.5, and 1.4 micromol/g in the kidney, liver, tumor, and brain, respectively. The variations in the labeled metabolites were more pronounced with high amounts in the kidney and liver (8.0 and 4.3 micromol/g, respectively) and very low amounts in the tumor and brain (0.33 and 0.12 micromol/g, respectively). In the kidney and liver, betaine (unlabeled and labeled) was the predominant choline metabolite. The dominant unlabeled metabolite in breast cancer was phosphocholine and in the brain glycerophosphocholine. Magn Reson Med 46:31-38, 2001.

Choline metabolism in breast cancer; 2H-, 13C- and 31P-NMR studies of cells and tumors.

Choline metabolism in breast cancer cells and tumors has been investigated by multinuclear NMR in order to provide the biochemical basis for the presence of high phosphocholine in breast carcinoma relative to benign breast tumors and normal breast tissue. Choline was found to be transported into MCF7 human breast cancer cells and rapidly phosphorylated to phosphocholine which was then accumulated in the cells to high concentrations. The increased level of phosphocholine did not affect the rate of synthesis of phosphatidylcholine, indicating tight regulation of this pathway. The incorporation of [1,2-13C]choline (100 microM) into phosphocholine and phosphatidylcholine after 24 h was 69.5 and 36% of the total respective pools. Incorporation of 2H9-choline to tumors implanted in nude mice was achieved by infusing the deuterated choline to the blood circulation. The metabolism of deuterated choline was then monitored by 2H localized MRS. The blood level of choline before the infusion was 58.6 +/- 10.3 microM (measured by 1H-NMR of plasma samples) and increased approximately 5-fold during the infusion (measured by 2H-NMR). This increase in the blood level resulted in a gradual increase of a signal at 3.2 ppm due to deuterated choline metabolites. It appears that the increased availability of choline in the blood circulation leads to accumulation of phosphocholine in the tumors by the same mechanism as in the cells.

Kinetics of choline transport and phosphorylation in human breast cancer cells; NMR application of the zero trans method.

The mechanism and kinetics of choline transport and phosphorylation in MCF7 human breast cancer cells was studied by 31P, 13C and 2H NMR, applying the zero trans method. Choline was transported by a Michaelis-Menten like mechanism with a maximum transport rate T(max) = 13.5 +/- 2.6 nmol/hour/mg protein (3.06 +/- 0.6 fmol/cell/hour) and choline concentration at half maximal transport rate of Kt = 46.5 +/- 2.8 microM. The rate of choline phosphorylation was more than two orders of magnitude faster than the rate of its transport (T(max)) maintaining the ratio [phosphocholine]/[choline] higher than 100. The results demonstrated enhanced choline transport and choline kinase activity in breast cancer cells.