Structure of daunomycin complexed to d-TGATCA by two-dimensional nuclear magnetic resonance spectroscopy

The anthracycline antibiotic daunomycin, having four fused rings and an amino sugar, is being used in the treatment of acute leukemia. Binding to DNA is generally believed to be essential for its activity. We have studied the interaction of daunomycin with DNA hexamer sequence d-(TGATCA)2 by titrating up to two drug molecules per duplex using nuclear magnetic resonance spectroscopy. The solution structure of 2:1 drug to DNA complex based on two dimensional nuclear Overhauser enhancement (NOE) spectroscopy and molecular dynamics calculations has been studied. The change in conformation of drug molecule on binding to DNA, deoxyribose conformation and glycosidic bond rotation has been obtained. The absence of sequential NOE connectivities at d-T1pG2 and d-C5pA6 sites shows that the drug chromophore intercalates between these two base pairs. This is substantiated by intermolecular NOEs observed between nucleotide base protons and aromatic ring protons of drug molecule. A set of 17 intermolecular NOE interactions allowed the structure to be derived by restrained molecular dynamics simulations, which have been compared with that obtained by X-ray analysis. Several specific interactions between the drug and DNA protons are found to stabilize the formation of drug-DNA complex.     

Effects of cardiovascular lifestyle change on lipoprotein subclass profiles defined by nuclear magnetic resonance spectroscopy

Background  

Low-density lipoprotein (LDL) cholesterol lowering is a primary goal in clinical management of patients with cardiovascular disease, but traditional cholesterol levels may not accurately reflect the true atherogenicity of plasma lipid profiles. The size and concentration of lipoprotein particles, which transport cholesterol and triglycerides, may provide additional information for accurately assessing cardiovascular risk. This study evaluated changes in plasma lipoprotein profiles determined by nuclear magnetic resonance (NMR) spectroscopy in patients participating in a prospective, nonrandomized lifestyle modification program designed to reverse or stabilize progression of coronary artery disease (CAD) to improve our understanding of lipoprotein management in cardiac patients.     

Carbon-13 nuclear magnetic resonance spectra of vitamins D and related compounds.

1. The natural abundance carbon-13 nmr of vitamins D (D2 and D3) and several isomers (5, 6-trans-vitamin D2, isotachysterol2 and isovitamin D2) have been completely assigned by employing off-resonance noise-decoupling, acetylation shifts, and lanthanide-induced shifts experiments. The last two techniques were especially useful for the present study. 2. Carbon-13 nmr spectral characteristics of the three main conjugated triene moieties (SE-Z-SZ, SE-E-SZ, or SE-E-SE), involved in the molecules of vitamin D and its isomers, were revealed. Thus, the striking dependence of the shieldings on molecular geometries and high sensitivity of the resonances to the environments of conjugated systems were surveyed. 3. Conformational preferences in solutions of the hydroxyl groups in vitamins D2 and D3 as well as 5, 6-trans-vitamin D2 were conveniently determined.     

Characterization of buffalo milk by P-nuclear magnetic resonance spectroscopy

We report a ³¹P nuclear magnetic resonance (³¹P-NMR) investigation of buffalo milk, milk ultrafiltrate, and phospholipids from milk fat; for comparison corresponding data were also acquired for cow milk samples. In buffalo milk samples, we identified glycerophosphorylcoline, glycerophosphorylethanolamine and inorganic orthophosphate resonances, together with a broad peak assigned to serylphosphate residues of casein. Buffalo milk ultrafiltrate showed the presence of several phosporous signals, and ten of them (inorganic phosphate, phosphocreatine, glycerophosphorylcoline, glycerophosphorylethanolamine, N-acetylglucosamine-1-phosphate, glucose-6-phosphate, galactose-1-phosphate, phosphorylethanolamine, phosphorylcoline, and glycerol-1-phosphate) were unambiguously identified by addition of pure standards. In phospholipids fractions from buffalo milk, we clearly identified phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, sphingomyelin, and phosphatidylinositol. A preliminary estimation (mol%) of each phosphorylated compound was obtained. By comparing ³¹P-NMR data from milk samples from buffaloes and cows, we concluded that these milks are rather similar as far as the phosporous distribution in small molecules is concerned.     

The application of high-performance liquid chromatography humic acid columns in determination of Koc of polycyclic aromatic compounds

An improvement of a method for determination of the distribution coefficient for polycyclic aromatic compounds (PAC) between organic carbon and water (Koc) by high-performance liquid chromatography (HPLC) is presented in this paper. By use of silica-based HPLC columns with chemically immobilized humic acid (Aldrich, Zigma-Aldrich, Taufkirchen, Germany), the retention of PAC to humic acid can be measured, and the results can, when they are compared to those from a blank column, be used to a direct determination of Koc. These values agree quite well with literature Koc values for two- to four-ringed PAC. Our work has shown that it is possible to use this method to investigate how environmental parameters like electrolyte concentration, pH, and temperature affect the sorption of PAC to humic acid. Thermodynamic parameters can be estimated from variable temperature experiments. The advantage of the method is its cost and manpower effectiveness.     

磁共振成像和氢质子磁共振波谱在铅神经毒性研究中的应用

铅具有神经毒性，但是由于中枢神经系统的不可介入性，给临床诊断与治疗带来一定的困难。近年来，随着神经影像学在铅神经毒性研究中的应用，使人们对磁共振成像（MRI）和磁共振波谱（MRS）的认识不断加深，尤其是氢质子（^1H）核自然丰度最高，且氢质子磁共振波谱（^1H-MRS）灵敏度好，是目前研究活体组织器官、代谢、生化改变及化合物定量分析惟一的无创性方法，故其在神经变性疾病的研究中应用最广泛。     

磁共振成像和氢质子磁共振波谱在锰神经毒性研究中的应用

锰是维持人体正常生长发育以及中枢神经系统(CNS)正常功能的一种必需微量元素,但是长期吸入较高浓度的锰烟和锰尘,可引起锰中毒,晚期出现类似帕金森病等锥体外系神经受损的临床表现.肌张力是否增高是诊断慢性锰中毒的关键,但其判定缺乏客观灵敏的定量方法,且肯定的肌张力增高已非早期表现.     

Studies on self-aggregation of anthracycline drugs by restrained molecular dynamics approach using nuclear magnetic resonance spectroscopy supported by absorption, fluorescence, diffusion ordered spectroscopy and mass spectrometry

Self-association, a process that competes with binding to DNA and formation of hetero-complexes, is studied in anticancer drugs 4'-epiadriamycin, adriamycin and daunomycin by proton nuclear magnetic resonance spectroscopy. The 2D nuclear Overhauser enhancement spectra yield several intra-molecular and inter-molecular inter-proton connectivities suggesting specific stacking patterns of aromatic chromophores in parallel and anti-parallel orientation. Absorption, emission and diffusion ordered spectroscopy demonstrate the formation of self-aggregates. Electron spray ionization mass spectrometry gives a direct proof of the presence of dimer and absence of higher aggregates. The restrained molecular dynamics simulations show the structural differences between drugs, which have been correlated to the biological action. A clear evidence of reduced cardiotoxicity by 4'-epiadriamycin, as compared to daunomycin and adriamycin, is demonstrated by mass spectrometry data.     

Sorption of polar and nonpolar aromatic compounds to two humic acids with varied structural heterogeneity

The major objective of the present study was to evaluate the correlation between structural nature of humic acids (HAs) and sorption affinity of organic compounds with varied polarity. We compared the sorption behavior of three aromatic compounds-nonpolar phenanthrene (PHEN) and 1,2,4,5-tetrachlorobenzene (TeCB) and highly polar 2,4-dichlorophenol (DCP)-to a solid-phase coal humic acid (CHA) and a soil humic acid (SHA) suspended in aqueous solution. The structural nature of HAs was characterized using elemental analysis, ultraviolet absorbance, diffusive reflectance Fourier-transform infrared, and solid-state 13C nuclear magnetic resonance. The two tested HAs have very different structural properties: CHA consists primarily of poly(methylene)-rich aliphatics with high aromatic content and some COO/N-C=O but low polarity, while SHA consists of young materials of lignin, carbohydrates, and peptides with high polarity. In response to the structural heterogeneity of HAs, sorption of nonpolar and more hydrophobic solutes (PHEN, TeCB) to CHA is much greater than that to SHA because of the predominance of hydrophobic effects; however, disparities in sorption affinity between the two HAs become smaller for polar and less hydrophobic DCP because of the major role played by polar interactions. The influence of pH on the sorption of different solutes to the two HAs was also discussed. The results of the present work highlight the importance of structural heterogeneity of both solutes and HAs in the sorption process.     

Observation of intramyocellular lipids by means of 1H magnetic resonance spectroscopy

Magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) are being increasingly used for investigations of human muscle physiology. While MRI reveals the morphology of muscles in great detail (e.g. for the determination of muscle volumes), MRS provides information on the chemical composition of the tissue. Depending on the observed nucleus, MRS allows the monitoring of high-energy phosphates (31P MRS), glycogen (13C MRS), or intramyocellular lipids (1H MRS), to give only a few examples. The observation of intramyocellular lipids (IMCL) by means of 1H MRS is non-invasive and, therefore, can be repeated many times and with a high temporal resolution. MRS has the potential to replace the biopsy for the monitoring of IMCL levels; however, the biopsy still has the advantage that other methods such as those used in molecular biology can be applied to the sample. The present study describes variations in the IMCL levels (expressed in mmol/kg wet weight and ml/100 ml) in three different muscles before and after (0, 1, 2, and 5 d) marathon runs for a well-trained individual who followed two different recovery protocols varying mainly in the diet. It was shown that the repletion of IMCL levels is strongly dependent on the diet post exercise. The monitoring of IMCL levels by means of 1H MRS is extremely promising, but several methodological limitations and pitfalls need to be considered, and these are addressed in the present review.     

Interaction between carbamazepine and humic substances: a fluorescence spectroscopy study

Carbamazepine is a popular drug that has been detected in natural environments, but little is known about its biogeochemical cycling, influencing factors, and eco-environmental effects in aquatic ecosystems. Interaction between carbamazepine and humic substances, including fulvic and humic acids, was studied using three-dimensional excitation-emission matrix fluorescence spectroscopy and synchronous-scan fluorescence spectroscopy. The intrinsic fluorescence of humic substances was quenched on the addition of carbamazepine, and static quenching was the primary mechanism. The binding parameters on their interaction, including the conditional binding constants (log K) and binding capacities (C(L)), were estimated by the Ryan-Weber nonlinear theory equation. Log K ranged from 3.41 to 5.04 L/mol at 25 degrees C and pH 7.0. The influence of pH on the complexation and the competition between carbamazepine and Cu(II) for fluorescence-binding sites also were discussed. The present results would be helpful in understanding the fate and biogeochemical cycling of other pharmaceuticals and personal care products in aquatic ecosystems.     

Selective toxicity of gossypol against epithelial tumors and its detection by magnetic resonance spectroscopy

The antitumor toxicity of gossypol was measured in 6 human carcinoma cell lines and compared with its toxicity against human bone marrow stem cells. Marrow cells were more resistant than any of the tumor cell lines, and tumor cell sensitivity depended on the content of intracellular LDH-M. [31P]-Magnetic resonance spectroscopy showed decline in tumor ATP levels occurring within 24 hours of treatment, suggesting that this non-invasive technique may serve as an early biochemical monitor of gossypol toxicity.     

Iron and the brain: neurotransmitter receptors and magnetic resonance spectroscopy

Earlier studies show that in iron deficiency with anaemia and in latent iron deficiency neurotransmitters are altered. The changes induced in the fetal brain are irreversible on rehabilitation. The important alterations in glutamate metabolism in latent iron deficiency stimulated studies on gamma aminobutyric acid and glutaminate receptors. It was observed that binding of 3H-muscimol at pH 7.5 and 1 mg protein/assay increased significantly in synaptic vesicular membranes and under similar conditions 3H-glutamate binding showed reduction. Thus iron deficiency played a role in both excitatory and inhibitory neurotransmitter receptors. To elucidate the role of body iron status on the brain, anaemic children with thalassemia and iron deficiency were subjected to 'magnetic resonance spectroscopy' of globus pallidus, caudate and dentate nuclei and there was no change in iron content. The concentrations of creatinine and aspartate increased, with lowering of choline content. The findings were similar in thalassemia as well as iron deficiency anaemia, suggesting that in anaemia changes operate through reduced oxygen availability.     

Determination of intracellular free magnesium by nuclear magnetic resonance in human magnesium deficiency

Magnesium (Mg) deficiency is a common clinical problem. As Mg is predominantly an intracellular cation and Mg deficiency may exist despite normal serum Mg (sMg) concentrations, we have utilized nuclear magnetic resonance (NMR) techniques in an attempt to measure intracellular free Mg (Mg2+) in red blood cells (RBC). Twenty normal subjects, 22 hypomagnesemic patients, and 17 normomagnesemic alcoholic patients were studied. Mean RBC Mg2+ in normal subjects (178 +/- 6.3 microM) was significantly greater than in hypomagnesemic patients (146 +/- 7.1 microM, p less than 0.002). RBC Mg2+ correlated with sMg concentration (r = 0.54, p less than 0.001). In addition, four normal subjects were given a low Mg diet for 3 weeks. There was a progressive fall in both the sMg concentration and RBC Mg2+ during Mg depletion, with a concomitant rise in retention of a parenterally administered Mg load. These data suggest that the determination of intracellular Mg2+ by NMR may be a useful research tool in assessing the effect of changes in Mg2+ on intracellular processes. Its utility in the clinical evaluation of disorders of Mg deficiency remains to be determined.     

The use of non-invasive probes and (13)C nuclear magnetic resonance spectroscopy to assess liver metabolism in humans

Two new methods to assess liver metabolism in humans will be discussed, non-invasive probes and (13)C NMR (nuclear magnetic resonance) spectroscopy. Hepatic UDP-glucose and alpha-ketoglutarate can be sampled by non-invasive probes. This method has been used to quantitate the contribution of the indirect pathway to liver glycogen formation and to estimate relative flow rates and carbon exchange in the Krebs cycle. (13)C NMR spectroscopy has been developed to measure liver glycogen concentrations in vivo. Using this method in combination with measurements of whole body glucose production during fasting, the contribution of gluconeogenesis has been calculated.