Tumor pH and Protein Concentration Contribute to the Signal of Amide Proton Transfer Magnetic Resonance Imaging

Abnormal pH is a common feature of malignant tumors and has been associated clinically with suboptimal outcomes. Amide proton transfer magnetic resonance imaging (APT MRI) holds promise as a means to noninvasively measure tumor pH, yet multiple factors collectively make quantification of tumor pH from APT MRI data challenging. The purpose of this study was to improve our understanding of the biophysical sources of altered APT MRI signals in tumors. Combining in vivo APT MRI measurements with ex vivo histological measurements of protein concentration in a rat model of brain metastasis, we determined that the proportion of APT MRI signal originating from changes in protein concentration was approximately 66%, with the remaining 34% originating from changes in tumor pH. In a mouse model of hypopharyngeal squamous cell carcinoma (FaDu), APT MRI showed that a reduction in tumor hypoxia was associated with a shift in tumor pH. The results of this study extend our understanding of APT MRI data and may enable the use of APT MRI to infer the pH of individual patients' tumors as either a biomarker for therapy stratification or as a measure of therapeutic response in clinical settings.Significance: These findings advance our understanding of amide proton transfer magnetic resonance imaging (APT MRI) of tumors and may improve the interpretation of APT MRI in clinical settings

13C NMR studies of organic matter in whole soils: I. Quantitation possibilities

A detailed discussion of the quantitative nature of C-13 CPMAS NMR spectra as applied to solid samples, such as soil, is given. In particular, the influence of the cross-polarization (CP) time constant (T-CH), the relaxation time constant of protons in the rotating frame (T-1 rho H) and the contact time (t(c)) in the CPMAS experiment are considered. Three distinct quantitation regimes are numerically identified according to sample parameters T-CH and T-1 rho H, and the experimental choice of t(c): (i) quantitation obtainable from a single CPMAS spectrum; (ii) quantitation obtainable from a series of CPMAS spectra; and (iii) quantitation not possible using CPMAS. Strategies for the measurement of sample parameters T-CH and T-1 rho H are reviewed. When quantitation is not possible using CPMAS it is necessary to regress to the direct polarization (DP) of C-13 nuclei. The sensitivity problems of DPMAS are discussed, as too are general factors that affect the quantitation of C-13 data such as spinning sidebands. More specifically in relation to soil samples, the effects on quantitation arising from the presence of paramagnetics and the actual methods for the measurement of signal intensities are covered

13C NMR studies of organic matter in whole soils: II. A case study of some Rothamsted soils

Nuclear magnetic resonance (NMR) spectra were obtained for solid samples of whole soils from three long-term field sites at Rothamsted Experimental Station, UK. In all sites, soil organic matter content was either increasing or decreasing due to contrasted long-continued treatments. Two soils were from Highfield, one from under old grassland (47 g organic C kg(-1)) and one from an area kept as bare fallow following ploughing of grass 21 years previously (14 g organic C kg(-1)). Three soils were taken from Broadbalk, two from plots within the Broadbalk Continuous Wheat Experiment which had received no fertilizer or animal manure annually for 148 years (7 and 27 g organic C kg(-1), respectively) and one from Broadbalk Wilderness, wooded section (38 g organic C kg(-1)). Broadbalk Wilderness was arable until 1881 and has reverted to deciduous woodland in the subsequent 110 years. Two soils were from Geescroft, one from an arable field (9 g organic C kg(-1)) and one from Geescroft Wilderness (35 g organic C kg(-1)) which began reversion to deciduous woodland at the same time as Broadbalk Wilderness but is now acid (pH = 4.2) in contrast to Broadbalk which is calcareous (pH = 7.3). Solid-state C-13 NMR spectra were obtained on a 300-MHz instrument using cross polarization (CP) and magic angle spinning (MAS). All samples exhibited peaks in the following spectral regions: 0-45 ppm (alkyl), 45-60 ppm (methoxyl, carbohydrate and derivatives), 60-110 ppm (carbohydrates and derivatives, C-alpha of peptides), 110-160 ppm (aromatics) and 160-185 ppm (carboxyl groups and derivatives). Within the spectrum of a specific sample it was not possible to determine the relative proportions of soil organic carbon in the different forms identified because a range of factors can potentially alter the relative areas of peaks in different regions of the spectrum. However, from a comparison of relative peak areas within a set of soils from a given site, differing only in organic matter content, information can be deduced regarding the forms of C that are more or less subject to change in response to land use or management. At all sites carbohydrate C appears to be the form that is most subject to change, suggesting that it is an 'active' fraction compared with the other forms. It was greatest where organic matter inputs were greatest (due to inputs of farmyard manure or reversion to woodland) and declined relative to other forms following ploughing of old grassland. Alkyl C increased as total C accumulated but did not decline relative to other forms following ploughing of grass. One reason for the non-quantitative nature of the soil C-13 CPMAS spectra was a short (approximately 1 ms) component of the rotating-frame T-1 relaxation time for H nuclei (T-1 rho H). This problem was not overcome by acquiring data at -60 degrees C. In principle, solid-state spectra of soils obtained by direct polarization (i.e. without CP) might produce quantitative results, but the low C content of most mineral soils (10-50 g C kg(-1)) precludes this, given current instrumentation

13C NMR studies of organic matter in whole soils: II. A case study of some Rothamsted soils

Nuclear magnetic resonance (NMR) spectra were obtained for solid samples of whole soils from three long-term field sites at Rothamsted Experimental Station, UK. In all sites, soil organic matter content was either increasing or decreasing due to contrasted long-continued treatments. Two soils were from Highfield, one from under old grassland (47 g organic C kg(-1)) and one from an area kept as bare fallow following ploughing of grass 21 years previously (14 g organic C kg(-1)). Three soils were taken from Broadbalk, two from plots within the Broadbalk Continuous Wheat Experiment which had received no fertilizer or animal manure annually for 148 years (7 and 27 g organic C kg(-1), respectively) and one from Broadbalk Wilderness, wooded section (38 g organic C kg(-1)). Broadbalk Wilderness was arable until 1881 and has reverted to deciduous woodland in the subsequent 110 years. Two soils were from Geescroft, one from an arable field (9 g organic C kg(-1)) and one from Geescroft Wilderness (35 g organic C kg(-1)) which began reversion to deciduous woodland at the same time as Broadbalk Wilderness but is now acid (pH = 4.2) in contrast to Broadbalk which is calcareous (pH = 7.3). Solid-state C-13 NMR spectra were obtained on a 300-MHz instrument using cross polarization (CP) and magic angle spinning (MAS). All samples exhibited peaks in the following spectral regions: 0-45 ppm (alkyl), 45-60 ppm (methoxyl, carbohydrate and derivatives), 60-110 ppm (carbohydrates and derivatives, C-alpha of peptides), 110-160 ppm (aromatics) and 160-185 ppm (carboxyl groups and derivatives). Within the spectrum of a specific sample it was not possible to determine the relative proportions of soil organic carbon in the different forms identified because a range of factors can potentially alter the relative areas of peaks in different regions of the spectrum. However, from a comparison of relative peak areas within a set of soils from a given site, differing only in organic matter content, information can be deduced regarding the forms of C that are more or less subject to change in response to land use or management. At all sites carbohydrate C appears to be the form that is most subject to change, suggesting that it is an 'active' fraction compared with the other forms. It was greatest where organic matter inputs were greatest (due to inputs of farmyard manure or reversion to woodland) and declined relative to other forms following ploughing of old grassland. Alkyl C increased as total C accumulated but did not decline relative to other forms following ploughing of grass. One reason for the non-quantitative nature of the soil C-13 CPMAS spectra was a short (approximately 1 ms) component of the rotating-frame T-1 relaxation time for H nuclei (T-1 rho H). This problem was not overcome by acquiring data at -60 degrees C. In principle, solid-state spectra of soils obtained by direct polarization (i.e. without CP) might produce quantitative results, but the low C content of most mineral soils (10-50 g C kg(-1)) precludes this, given current instrumentation

Fertilization effects on organic matter in physically fractionated soils as studied by 13C NMR: results from two long-term field experiments

C-13-nuclear magnetic resonance (NMR) spectra taken using magic-angle spinning (MAS), cross polarization (CP) and with total suppression of side bands (TOSS) are reported for soils from two long-term field experiments. One set of soils was from the Broadbalk Experiment at Rothamsted, UK (monoculture of winter wheat since 1843) and the other was from the Lermarken site of the Askov Long-Term Experiment on Animal Manure and Mineral Fertilizers (arable rotation since 1894). At both sites soil samples were taken from three fertilizer treatments: nil, inorganic fertilizers, animal manure. Spectra were obtained from whole soil samples and from the size fractions clay (<2 mu m), silt (2-20 mu m) and, in some cases, sand (20-2000 mu m). Comparison of the total strengths of the C-13-NMR signal for each size separate in relation to its total organic C content shows that clay, particularly, contains large percentages of C not detected by NMR because of the large magnetic susceptibilities of the soil minerals. It is proposed that the bi observed signals come from the more labile pools of soil organic matter (SOM), on the presumption that these pools are less closely associated with soil minerals and iron oxides and are likely to be less protected from microbial or enzymic decomposition. For both Rothamsted and Askov, functional groups in the 45-110 ppm region (N- and O-alkyls) dominate in the spectra for whole soils, with aromatics (110-160 ppm) and alkyls (0-45 ppm) signals being the next prominent. In the Askov whole soil samples C-13-NMR revealed no differences between nil, inorganic fertilizer and animal manure treatments but in the Rothamsted whole soil there were some small differences. Clay and silt fractions from Askov contain more alkyls and less aromatics than those from Rothamsted. For both sites clay in enriched in alkyls and depleted in aromatics relative to silt. Clay from Askov, but not Rothamsted, contains more N-alkyls (45-65 ppm) and less acetals (90-110 ppm) than silt. O-alkyls (65-90 ppm) account for more than 20% of the total signal in clay and silt from both sites. Fertilization regimes have not significantly affected the chemical composition of SOM associated with clay- and silt-sized fractions in the soils at either site. We conclude that the chemical composition of SOM is determined primarily by the interaction between the organisms responsible for decomposition and the mineral soil matrix rather than the nature of substrate input