Biomedical subjects

Maili Liu

Publications and source records attributed to Maili Liu.

12 recordsLinked to original sources

PubMed2006

Metabolic changes in rat prefrontal cortex and hippocampus induced by chronic morphine treatment studied ex vivo by high resolution 1H NMR spectroscopy.

Ex vivo(1)H NMR spectroscopy was used to measure changes in the concentrations of cerebral metabolites in the prefrontal cortex (PFC) and hippocampus of rats subjected to repeated morphine treatment known to cause tolerance/dependence. The results show that repeated morphine exposure induces significant changes in the concentrations of a number of cerebral metabolites, and such changes are region specific. After 10 days of repeated morphine treatment, the concentration of gamma-aminobutyric acid (GABA) increased significantly in the PFC (20+/-11%), but decreased in the hippocampus (-31+/-12%), compared to control. In contrast, the glutamate (Glu) concentrations in both the PFC (-15+/-8%) and hippocampus (-13+/-4%) decreased significantly. Significant changes were also observed in the concentrations of hippocampal glutamine (Gln), myo-inositol, taurine, and N-acetyl aspartate. These morphine-induced changes were reversed during a subsequent 5-day withdrawal period. It is suggested that the observed concentration changes for Glu, Gln and GABA are most likely the result of a shift in the steady-state equilibrium of the Gln-Glu-GABA metabolic cycle. Changes in the metabolism of this neurotransmitter system might be part of the adaptive measures taken by the central nervous system in response to repeated morphine exposure and subsequent withdrawal.

Animals↗

PubMed2006

High-resolution magic-angle spinning (13)C spectroscopy of brain tissue at natural abundance.

High-resolution magic-angle spinning (MAS) (1)H and (13)C magnetic resonance spectroscopy (MRS) has recently been applied to study the metabolism in intact biological tissue samples. Because of the low natural abundance and the low gyromagnetic ratio of the (13)C nuclei, signal enhancement techniques such as cross-polarization (CP) and distortionless enhancement by polarization transfer (DEPT) are often employed in MAS (13)C MRS to improve the detection sensitivity. In this study, several sensitivity enhancement techniques commonly used in liquid- and solid-state NMR, including CP, DEPT and nuclear Overhauser enhancement (NOE), were combined with MAS to acquire high-resolution (13)C spectra on intact rat brain tissue at natural abundance, and were compared for their performances. The results showed that different signal enhancement techniques are sensitive to different classes of molecules/metabolites, depending on their molecular weights and mobility. DEPT was found to enhance the signals of low-molecular weight metabolites exclusively, while the signals of lipids, which often are associated with membranes and have relatively lower mobility, were highly sensitive to CP enhancement.

Animals↗

PubMed2005

Realization of a decoherence-free subspace using multiple quantum coherences.

This Letter presents a two-dimensional nuclear magnetic resonance (NMR) approach for constructing a two-logical-qubit decoherence-free subspace (DFS) by using four multiple-quantum coherences of a CH3 spin system as logical qubits. The three protons in this spin system are magnetically equivalent and can only be used as a single qubit in one-dimensional NMR. We have experimentally demonstrated that our DFS can protect against more types of decoherences than those of the one composed of four noisy physical qubits all with different chemical shifts. This idea may provide new insights into extending qubit systems in the sense that it effectively utilizes the magnetically equivalent nuclei.

Journal Article↗

PubMed2005

A competitive low-affinity binding model for determining the mutual and specific sites of two ligands on protein.

A competitive low-affinity binding model was proposed for determining the number of mutual (overlapped) and specific binding sites of two ligands (A, B) on a protein (P). To use the model, one needs to carry out a titration experiment by adding either ligand A or B into a three-component system (A-B-P), and to monitor the spectroscopic parameter changes. Fitting the titration curve to the proposed model, one can get the mutual and specific binding sites of the two ligands on the protein. The model was examined by using human serum albumin (HSA) as a receptor and tolmetin (TOL) and salicylic acid (SAL) as ligands. Proton longitudinal relaxation rates (R1) were measured on a 500-MHz NMR spectrometer during the titration and used to derive the mutual binding sites. It was found that among the binding sites of 32+/-4 for SAL and 28+/-2 for TOL on HSA, there were 17+/-5 mutual sites for the two ligands. This result indicates that, although HSA has large binding capacities for most ligands, there are still a reasonable amount of the low-affinity binding sites that are structure selective.

Algorithms↗

PubMed2004

"Spectral implementation" for creating a labeled pseudo-pure state and the Bernstein-Vazirani algorithm in a four-qubit nuclear magnetic resonance quantum processor.

A quantum circuit is introduced to describe the preparation of a labeled pseudo-pure state by multiplet-component excitation scheme which has been experimentally implemented on a 4-qubit nuclear magnetic resonance quantum processor. Meanwhile, we theoretically analyze and numerically investigate the low-power selective single-pulse implementation of a controlled-rotation gate, which manifests its validity in our experiment. Based on the labeled pseudo-pure state prepared, a 3-qubit Bernstein-Vazirani algorithm has been experimentally demonstrated by spectral implementation. The "answers" of the computations are identified from the split peak positions in the spectra of the observer spin, which are equivalent to projective measurements required by the algorithms.

Journal Article↗

PubMed2004

1H NMR spectroscopic evidence of interaction between ibuprofen and lipoproteins in human blood plasma.

Recent studies have suggested that ibuprofen inhibits low-density lipoprotein oxidation in a high dose-dependent manner and is a promising drug for treatment of the conditions associated with atherosclerosis. In this article, we present the NMR spectroscopic evidence for the interaction between ibuprofen and phospholipids in lipoprotein particles in intact human plasma. Ibuprofen caused chemical shift upfield drifts for the protons of -N(+)(CH(3))(3) moieties of phosphatidylcholine and sphingomyelin, olefinic chains (-CH[double bond]CH[bond], [bond]CH[triple bond]CHCH(2)CH[triple bond]CH[bond], [bond](CH(2))(n)CH(2)CH[double bond]), and (CH(2))(n) and CH(3) groups, from unsaturated lipids in lipoprotein particles. The ibuprofen may interact directly with the above-mentioned groups of phospholipids or induce structural changes in the lipoproteins. This may shed light on the mechanism by which the drug protects against oxidative modification of lipoproteins.

Binding Sites↗

PubMed2003

Comparison between Gd-DTPA and several bisamide derivatives as potential MRI contrast agents.

Four neutral gadolinium complexes of diethylenetriaminepentaacetic acid (DTPA)-bisamide derivatives have been synthesized and characterized. Their potential application as tissue-specific and low-osmolarity MRI contrast agents has been evaluated by in vitro and in vivo experiments. Their measured relaxivities in D(2)O, bovine serum albumin and human serum transferrin solutions showed favorable relaxation ability. In vivo studies have proven that Gd(DTPA-BDMA), Gd(DTPA-BIN), and Gd(cyclic-DTPA-1,2-pn) could be promising liver-specific MRI contrast agents and Gd(DTPA-BDMA), and Gd(cyclic-DTPA-1,2-pn) have favorable renal excretion capability. Among them, Gd(cyclic-DTPA-1,2-pn) is a more powerful hepatic contrast agent and Gd(DTPA-BIN) provides the stable imaging contrast for several hours. They also show a lower toxicity.

Amides↗

PubMed2003

Interaction between calcium-free calmodulin and IQ motif of neurogranin studied by nuclear magnetic resonance spectroscopy.

The interaction of Ca(2+)-free calmodulin (apoCaM) with the IQ motif corresponding to the calmodulin-binding domain of neurogranin has been studied by nuclear magnetic resonance (NMR) methods. The NMR spectra of uncomplexed apoCaM and apoCaM in complex with the IQ motif recorded at 750 MHz were studied and the backbone assignments of the protein in both forms were obtained by triple-resonance multidimensional NMR experiments. Chemical shift perturbations were used to map the binding surfaces. Only a single set of resonances was observed throughout the titration, indicating that the binding interaction is under fast exchange. Analysis of chemical shift changes indicates that (a) the main interaction and conformational changes occur in the C-terminal domain of calmodulin and (b) linker-1 (residues 40-44) between EF-1 and EF-2, linker-3 (residues 112-117) between EF-3 and EF-4, and the end of the alpha-helix H (residues 145-148) may be involved in the binding process. The dissociation constant (K(d)), estimated by fitting the chemical shift changes against the IQ peptide concentration, ranged from about 1.2 x 10(-5) to 8.8 x 10(-5) M. This result demonstrates that the interaction falls into the weak binding regime.

Amino Acid Motifs↗

PubMed2003

Quantitative estimation of property parameters of crude oil using two-dimensional 13C-1H J-resolved nuclear magnetic resonance spectroscopy (HET-JRES).

The physical and chemical properties of crude oil depend on the type and relative amount of hydrocarbons present. When it is not possible to elucidate the exact composition of the oil, "average structural information" may be a meaningful description of the bulk properties of the oil. In this paper, the application of NMR for this purpose has been extended by the use of two-dimensional (2D) 13C-1H J-resolved spectroscopy (HET-JRES) to obtain the average structural information of a set of crude oils. This makes it possible to estimate the molar concentration of the different CHn (n = 0, 1, 2, 3) spin systems in the sample. It is demonstrated here that structural information, derived from HET-JRES, correlates with the density and viscosity of the crude oils. Hence this new approach, which is rapid, may represent a useful method for crude oil characterization.

Carbon↗

PubMed2002

Comparison between GdDTPA and two gadolinium polyoxometalates as potential MRI contrast agents.

Two gadolinium polyoxometalates, Gd(2)P(2)W(18)O(62) and K(15)[(GdO)(3)(PW(9)O(34))(2)], have been evaluated by in vivo as well as in vitro experiments as the candidates of tissue-specific magnetic resonance imaging (MRI) contrast agents. T(1)-relaxivities of 28.4 mM(-1).s(-1) for Gd(2)P(2)W(18)O(62) and 11.2 mM(-1).s(-1) for K(15)[(GdO)(3)(PW(9)O(34))(2)] (400 MHz, 25 degrees C) were higher than that of the commercial MRI contrast agent (GdDTPA). Their relaxivities in bovine serum albumin and human serum transferrin were also reported. The favorable liver-specific contrast enhancement and renal excretion capability in in vivo MRI with Sprague-Dawley rats after i.v. administration of K(15)[(GdO)(3)(PW(9)O(34))(2)] was demonstrated. In vivo and in vitro assay showed that K(15)[(GdO)(3)(PW(9)O(34))(2)] is a promising liver-specific MRI contrast agent. However, Gd(2)P(2)W(18)O(62) did not show the favorable quality in vivo as expected from its high relaxivity in vitro, which was attributed to low bioavailability, indicating that it is of limited value as tissue-specific MRI contrast agent.

Animals↗

PubMed2002

1H-NMR study of the effect of acetonitrile on the interaction of ibuprofen with human serum albumin.

The effect of acetonitrile (ACN) on the low-affinity interaction between human serum albumin (HSA) and ibuprofen (IBP) was studied using 1H-NMR techniques. Both chemical shift and relaxation measurements showed the addition of ACN to the solutions decreased the binding affinity of IBP to HSA and reduced the hydrophobic interaction between them. The self-diffusion coefficients of IBP were measured as a function of the drug concentration at different ACN concentrations. The association constant, K(a), for ligand-HSA complexes and the number of binding sites, n, are evaluated by the application of Langmuir isotherm. The results indicated that the value of n was about 38 without ACN, and about 26 with ACN concentration 12% (v/v%). The decreased binding capacity of IBP to HSA in the presence of ACN was mainly attributed to the competition of ACN with IBP to the low-affinity binding sites of HSA molecule.

Acetonitriles↗

PubMed2002

An evaluation of gadolinium polyoxometalates as possible MRI contrast agent.

Two gadolinium polyoxometalates, K(9)GdW(10)O(36) and K(11)[Gd(PW(11)O(39))(2)], have been evaluated both in vivo and in vitro as candidates for tissue-specific MRI contrast agents. T(1)-relaxivities of 6.89 mM(-1). s(-1) for K(9)GdW(10)O(36) and 5.27 mM(-1). s(-1) for K(11)[Gd(PW(11)O(39))(2)] are slightly higher than that of the commercial MRI contrast agent (Gd-DTPA). Both compounds bind with bovine serum albumin and human serum transferrin and favorable liver-specific contrast enhancement in in vivo MRI with Sprague-Dawley rats after i.v. administration has been demonstrated. Imaging studies demonstrate that the two agents have a long residence time, showing MR signal enhancement in the liver for more than 40 min, longer than commercially available contrast agents. In vivo and in vitro assays showed that GdW(10) and Gd(PW(11))(2) are promising liver-specific MRI contrast agents and GdW(10) may be used in the diagnosis of the pathological state. However, with the higher acute toxicity, the two gadolinium polyoxometalates need to be modified and studied further before clinical use.

Animals↗