NC100150 Injection, a preparation of optimized iron oxide nanoparticles for positive-contrast MR angiography.

A preparation of monocrystalline iron oxide nanoparticles with an oxidized starch coating, currently in clinical trials (NC100150 Injection; CLARISCAN), was characterized by magnetization measurements, relaxometry, and photon correlation spectroscopy. By combining the results with a measure of iron content, one can obtain the size and magnetic attributes of the iron cores, including the relevant correlation times for outer sphere relaxation (tau(SO) and tau(D)), and information about the interaction of the organic coating with both core and solvent. The results are 6.43 nm for the iron oxide core diameter, a magnetic moment of 4.38x10(-17) erg/G, and a water-penetrable coating region of oxidized oligomeric starch fragments and entrained water molecules. The latter extends the hydrodynamic diameter to 11.9 nm and lowers the average diffusivity of solvent about 64% (which increases tau(D) accordingly). The nanoparticles show little size-polydispersity, evidenced by the lowest value of r(2)/r(1) at 20 MHz reported to date, an asset for magnetic resonance angiography.

Nuclear magnetic relaxation dispersion profiles of substantia nigra pars compacta in Parkinson's disease patients are consistent with protein aggregation.

Nuclear Magnetic Relaxation field-cycling relaxometry is a technique, able to report on water mobility in tissues. By means of this technique, post-mortem specimens from both controls and idiopathic Parkinson's disease patients have been investigated. Results show different relaxometric behavior between the groups, which is consistent with protein aggregation in Parkinson's disease specimens.

1H-NMRD and 17O-NMR assessment of water exchange and rotational dynamics of two potential MRI agents: MP-1177 (an extracellular agent) and MP-2269 (a blood pool agent).

The parameters that govern water proton magnetic relaxation (e.g. water exchange rates, and rotational and electronic correlation times) of representatives of two classes of Gd(III) complexes have been estimated, using two different approaches and the results compared with those derived for known analogs. The complexes studied are: (i) the non-ionic GdDTPA-bis(-methoxyethyl-amide) [Gd(DTPA-BMEA)], a typical small-molecule extracellular MR agent, and (ii) the ionic Gd(III) complex of 4-pentylbicyclo[2.2.2]octane-1-carboxyl-di-L-aspartyl-lysine-deriv ed-DTPA [GdL]4-, a prototype MR blood pool agent, which binds to serum albumin in vivo through non-covalent hydrophobic interactions. An 17O-NMR study of [Gd(DTPA-BMEA)] gives a water exchange rate constant of k(ex)298 = (0.39 +/- 0.02) x 10(6) s(-1), identical to that for the bismethylamide analog [Gd(DTPA-BMA)]. Both approaches yield longer rotational correlation times for [Gd(DTPA-BMEA)], consistent with its higher molecular weight. An 17O-NMR study of [GdL]4- gives a water exchange rate constant of k(ex)298 = (4.2 +/- 0.1) x 10(6) s(-1), identical to that for [Gd(DTPA)]2-. The water exchange rate on [GdL]4- did not decrease considerably when bound to albumin, the lowest limit is k(ex,GdL-BSA) = k(ex,GdL)/2. Both approaches yield identical rotational correlation times for [GdL]4-, however, it was difficult to derive a consistent rotational constant for the albumin-bound [GdL]4- using the different approaches (values ranged between 1.0 and 23.0 ns).

'NC100150', a preparation of iron oxide nanoparticles ideal for positive-contrast MR angiography.

A laboratory-scale synthesis of NC100150 (iron oxide particles with an oxidized starch coating) was characterized by magnetization measurements (vibrating sample magnetometry, VSM), relaxometry (1/T1 NMRD profiles and 1/T2 at 10 and 20 MHz), and dynamic light scattering (photon correlation spectroscopy, PCS). The results were related to give a self-consistent physical description of the particles: a water-impenetrable part making up 12% of the total particle volume, 82% of this volume consisting of an iron oxide core and the remaining 18% consisting of an oxidized starch rind; and, a water-penetrable part making up 88% of the total particle volume, consisting of oxidized starch polymers and entrained water molecules. Relating the magnetization to the relaxometry results required that the oxidized starch coating slows the diffusivity of solvent water molecules in the vicinity of the iron oxide cores. The effect of the organic coating on water diffusivity, not previously considered in the application of relaxation theory to iron oxide nanoparticles, is supported by the much greater (factor of about 2) diameter obtained from the dynamic light scattering measurements in comparison to that obtained from the magnetization measurements. The present work shows that three physical techniques--VSM, relaxometry, and PCS--are needed for properly assessing iron oxide nanoparticles for use as contrast agents for magnetic resonance angiography (MRA). It is also shown that NC100150 has a narrow range of diameters and the smallest value of r2/r1 reported to date, an asset for MRA.

NMRD assessment of Gd-DTPA-bis(methoxyethylamide), (Gd-DTPA-BMEA), a nonionic MRI agent.

RATIONALE AND OBJECTIVES: Gd-DTPA-BMEA, a nonionic bis(methoxyethylamide) derivative of Gd-DTPA, is the active ingredient of OptiMARK, now awaiting FDA approval. In this study, we compare the relaxivities of Gd-DTPA-BMEA (OptiMARK) with those of the commercially available DTPA-based agents Gd-DTPA2- (Magnevist) and Gd-DTPA-BMA (Omniscan) at different field strengths (1/T1 nuclear magnetic relaxation dispersion (NMRD) profiles). In addition, we study how changes in structural attributes of small paramagnetic chelate complexes of Gd3+ ions influence 1/T1 NMRD profiles. METHODS: 1/T1 NMRD profiles of Gd-DTPA-BMEA (OptiMARK) were measured at 5 degrees and 35 degrees C and a set of values for the parameters that describe relaxation by Gd(3+)-proton magnetic dipolar interactions was obtained. The rotational (tau R) and the diffusional (tau D) correlation times for Gd-DTPA-BMA were adjusted for the 15% greater molecular weight of Gd-DTPA-BMEA. tau M (the resident lifetime of Gd(3+)-bound water) was obtained from available 17O NMR relaxation data. For tau S0 and tau V (the low-field relaxation time of the Gd3+ moment and its correlation time), Gd-DTPA-BMA values were taken as initial values and tau S0 refined as needed. RESULTS: Although, at 35 degrees C, tau M is comparable for the two neutral agents and an order of magnitude longer than that for Gd-DTPA2-, the 1/T1 NMRD profiles of Gd-DTPA-BMEA are indistinguishable from those of Gd-DTPA2- and Gd-DTPA-BMA. A 40% increase in the value of tau S0 from Gd-DTPA2- is required for agreement of data and theory for Gd-DTPA-BMEA. CONCLUSIONS: Based on their 1/T1 NMRD profiles, the efficacy of the three agents should be identical in typical clinical MRI applications. The data can be fit reliably to theory, and differences in the fit parameters (and structure) have no effect on the three profiles at 35 degrees C. The relatively long values of tau M for the two neutral agents would only be of importance at low temperatures.

Solvent relaxation by uniformly magnetized solute spheres. The classical-quantal connection.

RATIONALE AND OBJECTIVES: Large magnetic entities, with diameters in the range of 4 nm to 4 microns, are becoming of increasing interest for magnetic resonance imaging (MRI). The smaller are iron oxide nanoparticles, used for the RE system, and the larger are deoxygenated blood cells, for functional MRI. It can be useful to model such systems as magnetized solute spheres in water. Classical computations of 1/T2 have been reported for the larger particles, in the micron range, where the computational complexities are simplified by Monte Carlo methods. For smaller particles, the quantum mechanical (quantal) expressions for outer sphere relaxation, for both 1/T1 and 1/T2, have been available for some time, and are particularly simple to apply at MRI fields. The questions that arise, and which the author addresses, are how to interrelate the classical and quantal approaches and when to use which. METHODS: The author compares published results of Monte Carlo calculations of 1/T2 for diamagnetic polystyrene solute spheres of various sizes in water, made paramagnetic by addition of dysprosium-(DTPA)2-, with quantum mechanical outer sphere theory applied to the same system. The latter includes the usual assumption of motional narrowing and yields both 1/T1 and 1/T2. RESULTS: For particles with diameters less than about 1 micron, both approaches give identical results for 1/T2. For larger particles, the conditions for motional narrowing breakdown, and quantal theory overestimates 1/T2. In addition, in the particular system studied, relaxation becomes so effective near solute that there is insufficient time for all water molecules to experience their maximal effect. Classical theory handles this well whereas quantal theory does not. CONCLUSIONS: In comparing the classical and quantal approaches, one balances computational complexity but broader applicability with more limited but far simpler mathematics. In addition, because the quantal approach shows that 1/T1 and 1/T2 are intimately related, the author suggests, by analogy, how to extend classical methods to computation of 1/T1.

Magnetic field dependence of solvent proton relaxation by solute dysprosium (III) complexes.

RATIONALE AND OBJECTIVES: Many magnetic resonance imaging (MRI) agents are Gd(III)-based; its half-filled f-shell has an S-ground state and hence a long electronic relaxation time, leading to comparably large effects on 1/T1 and 1/T2 of water protons with no shift in the water-proton resonance frequency. 1/T1 and 1/T2 nuclear magnetic relaxation dispersion (NMRD) profiles of the Dy(III) aquo ion and its chelates have been reported recently. Dy(III) ions differ magnetically from Gd(III); the large spin-orbit interaction of its non-S-ground state reduces the electronic relaxation time 100-fold, and can have a large effect on proton 1/T2 and resonance frequency. Relaxation theory is well-developed and applicable to both ions but, for Dy(III), the phenomena are more wide-ranging. Recent interpretations have suggested that the data are anomolous, requiring a new mechanism for their explanation. The authors explain published Dy(III) data in terms of known theory, guided by experience with Gd(III) agents. METHODS: For fields below 1 T, the authors incorporate the shortened electronic relaxation time into the usual low-field theory for magnetic dipolar interactions between water protons and Dy(III) magnetic moments. Both inner- and outer-sphere relaxations are included. At higher fields (and unusual for small single-ion agents) one must include dipolar interactions of protons with the magnetization of the Dy(III) moments. This "Curie magnetization" causes a quadratic dependence of 1/T1 on field, and--through dipolar-induced shifts--an even greater quadratic dependence of 1/T2. RESULTS: All published data can be explained by magnetic dipolar interactions. For Dy(III), the Curie term has a longer correlation time than the low-field term, namely, the rotation of solute for 1/T1 and the even longer water exchange lifetime tau M for 1/T2. This exchange modulates the shift, producing phenomena not seen with Gd(III). CONCLUSIONS: Relaxation by Dy(III) chelates can be explained by the same well-established theory of dipolar interactions used for their Gd(III) analogs. Interestingly, for MRI applications, tau M should be long for Dy(III)-based agents and short for Gd(III)-based agents.

High relaxivity linear Gd(DTPA)-polymer conjugates: the role of hydrophobic interactions.

A series of linear copolymers of DTPA-class Gd3+ conjugates, linked by alpha, omega-alkyldiamides with a varying number (n) of methylenes separating the amide function, were synthesized. Surprisingly, their relaxivities at all fields increased with increasing n. At MRI fields and 35 degrees C, the relaxivities of the n = 10 and n = 12 polymers were unexpectedly high, similar to those of rigid dendrimer-based Gd3+ chelates. The magnetic field dependence of solvent proton 1/T1 was measured for aqueous urea-free and urea-containing polymer solutions. The results for urea-free solutions imply an increase of rigidity (required for high relaxivities) with increasing n, arising from hydrophobic interactions of the methylene groups with solvent. This hypothesis is supported by a large decrease in the relaxivities upon addition of urea, which is known to weaken hydrophobic interactions. The relaxivities are also independent of polymer concentration, indicating that the hydrophobic interactions are intramolecular.

Secretory and nonsecretory pituitary adenomas are distinguishable by 1/T1 magnetic relaxation rates at very low magnetic fields in vitro.

RATIONALE AND OBJECTIVES: The authors investigated whether hormonally active and inactive pituitary adenomas can be discriminated in vitro by magnetic resonance (MR) imaging-related data. METHODS: 1/T1 nuclear magnetic relaxation dispersion profiles were measured for 39 fresh surgical specimens of secreting and nonsecreting adenomas, classified using clinical criteria or preoperative serum hormone levels. Nonsecreting adenomas were subdivided into hormone-producing and nonhormone-producing by immunostains. At five fields (0.00024 to 1.2 tesla [T]), mean 1/T1 was analyzed for statistically significant differences among these three tumor categories. RESULTS: Mean 1/T1 was significantly higher (P < 0.02) for hormone-secreting than for nonsecreting adenomas at fields below 0.24 T; no significant difference existed at typical MR imaging fields (0.5 to 1.5 T). Mean 1/T1 for hormone-producing and nonhormone-producing, nonsecreting adenomas were not significantly different at any field. CONCLUSIONS: Because 1/T1 at low fields is related to 1/T2 at imaging fields, it may be possible to detect hormone secretion of pituitary adenomas noninvasively by MR imaging.

Relaxation of solvent protons by solute Gd3+-chelates revisited.

The magnetic field dependence (NMRD profile) of 1/T1 of solvent protons in an aqueous solution of Gd(DTPA)2- was remeasured at 5, 15, 25, 30, and 35 degrees C. The data were reanalyzed with the usual low-field theory, using recently published values for tauM, the residence lifetime of the single inner-coordinated waters of solute Gd(DTPA)2-. (These tauM values are significantly longer than earlier estimates). Values were obtained for three dynamic parameters: tauR, the rotational relaxation time of solute ions, and tauSo and tauV, the low-field relaxation time of the Gd3+ magnetic moment and the related correlation time. These Gd(DTPA)2- values, together with recent results for tauM for Gd(DTPA-BMA)--a nonionic structural analog of Gd(DTPA)2- with an unusually long tauM--were used to calculate NMRD profiles at 5 and 35 degrees C. These profiles agree very well with new data given here for a solution of Gd(DTPA-BMA). This reaffirms the importance of knowing the temperature-dependent values of tauM a priori in order to obtain unambiguous quantitative theoretical analyses of NMRD profiles of chelates of known structure. Additionally, the theory of inner sphere relaxation is extended to high fields, at which the magnetic energy of a solute moment is greater than its thermal energy.

Theory of 1/T1 and 1/T2 NMRD profiles of solutions of magnetic nanoparticles.

Organically coated iron oxide crystallites with diameters of 5-50 nm ("nanoparticles") are potential magnetic resonance imaging contrast agents. 1/T1 and 1/T2 of solvent water protons are increased dramatically by magnetic interactions in the "outer sphere" environment of the nanoparticles; subsequent diffusive mixing distributes this relaxation throughout the solvent. Published theory, valid for the solute magnetic energy small compared with thermal energy, is applicable to small magnetic solutes (e.g., gadolinium and manganese diethylenetriaminopentaacetic acid, and nitroxide free radicals) at generally accessible fields (< or = 50 T). It fails for nanoparticles at fields above approximately 0.05 T, i.e., at most imaging fields. The authors have reformulated outer sphere relaxation theory to incorporate progressive magnetic saturation of solute nanoparticles and, in addition, indicate how to use empirical magnetization data for realistic particles when their magnetic properties are not ideal. It is important to handle the effects of rapid thermally induced reorientation of the magnetization of the nanoparticles (their "superparamagnetism") effectively, including their sensitivity to particle size. The theoretical results are presented as the magnetic field dependence (NMRD profiles) of 1/T1 and 1/T2, normalized to Fe content, for three sizes of particles, and then compared with the limited data extant for well-characterized material.

Classes of hydration sites at protein-water interfaces: the source of contrast in magnetic resonance imaging.

Immobilized protein solute, approximately 20 wt %, alters the longitudinal and transverse nuclear magnetic relaxation rates 1/T1 and 1/T2 of solvent water protons in a manner that makes their values indistinguishable from those of a typical human tissue. There is now a quantitative theory at the molecular level (S.H. Koenig and R. D. Brown III (1993) Magn. Reson. Med. 30:685-695) that accounts for this, as a function of magnetic field strength, in terms of several distinguishable classes of water-binding sites at the protein-water interface at which significant relaxation and solute-solvent transfer of proton Zeeman energy occur. We review the arguments that these several classes of sites, characterized by widely disparate values of the resident lifetimes tau M of the bound waters, are associated with different numbers of hydrogen bonds that stabilize the particular protein-water complex. The sites that dominate relaxation-and produce contrast in magnetic resonance imaging (MRI), which derives from 1/T1 and 1/T2 of tissue water protons-have tau M approximately 10(-6)s. These, which involve four hydrogen bonds, occupy < or = 1% of the protein-water interface. Sites that involve three bonds, although more numerous, have < or = 20% smaller intrinsic effect on relaxation. The greater part of the "traditional" hydration monolayer, with even shorter-lived hydrogen-bonded waters, has little influence on solvent relaxation and is relatively unimportant in MRI. Finally, we argue, from the data, that most of the protein of tissue (a typical tissue is mostly protein) must be rotationally immobile (with Brownian rotational relaxation times slower than that of a 5 x 10(7) Da (very heavy) globular protein). We propose a functional basis for this immobilization ("cytoplasmic order"), and then indicate a way in which this order can break down ("cytoplasmic chaos") as a result of neoplastic transformation (cancer) and alter water-proton rates of pathological tissue and, hence, image contrast in MRI.

Calcification can shorten T2, but not T1, at magnetic resonance imaging fields. Results of a relaxometry study of calcified human meningiomas.

RATIONALE AND OBJECTIVES: Water content and water-proton relaxation rates are reported for fresh, histologically characterized, surgical specimens of calcified human intracranial meningiomas and compared with results for noncalcified meningiomas from an earlier study and with calcium hydroxyapatite (CaHA) suspensions to elucidate the influence of calcification on magnetic resonance imaging (MRI) signal intensity of calcified meningiomas. METHODS: The magnetic field dependence of 1/T1 of water protons (nuclear magnetic relaxation dispersion profile) and dry weights are reported for 38 calcified nonhemorrhagic and 3 hemorrhagic specimens of known histologic subtype, a subset of the 67 specimens measured earlier. Calcification was considered mild or heavy when the dry weight was within or above the range for noncalcified meningiomas. Preliminary 1/T1 profiles for pure CaHA and a single high-field 1/T2 value also are reported. RESULTS: The ranges of dry weights and of low-field 1/T1 values were twice as large for calcified as for noncalcified meningiomas. No correlation was found between low-field 1/T1 and either histologic subtype or dry weight. Mild calcification produced the highest low-field 1/T1 values; the most heavily calcified tumor had slightly increased low-field 1/T1. Calcium hydroxyapatite increases low-field 1/T1 significantly but not high-field 1/T1; high-field 1/T2 is large. For calcified hemorrhagic meningiomas, increases in both low-field and high-field 1/T1 were seen. CONCLUSION: For mild calcification, MRI signal voids result from an increased high-field 1/T2; for heavier calcification, reduced proton density (from excluded water) becomes of increasing importance. Cellular CaHA appears to brighten the signal in T1-weighted MRI in the presence of hemorrhage.

Relaxometry of noncalcified human meningiomas. Correlation with histology and solids content.

RATIONALE AND OBJECTIVES: Resected meningiomas were examined by relaxometry and light microscopy to evaluate the potential of magnetic resonance imaging (MRI) for identifying histologic subtypes and for discriminating among benign, radiation therapy-induced, and malignant meningiomas. METHODS: The magnetic field dependence of 1/T1 of water protons (nuclear magnetic relaxation dispersion [NMRD] profile) and the water content (dry weight) were measured for 67 specimens, and the data were compared with histology. Only noncalcified, nonhemorrhagic meningiomas are reported. RESULTS: No correlations were found between NMRD profiles, dry weight, and any histologic subtype, in contrast to an analogous study of astrocytomas. Rather, meningiomas have a broader variability of dry weight and 1/T1 than related parenchyma but a much narrower range than all grades of astrocytomas. The mean value of 1/T1, at all fields, is slightly higher in meningiomas--and the mean water content about the same--as adult cortical gray matter. CONCLUSION: Meningiomas are frequently isointense with cortex, and histologic subtypes cannot be differentiated at any magnetic field strength by MRI using only T1- or proton density-weighted MRI.

Studies of the binding specificity of concanavalin A. Nature of the extended binding site for asparagine-linked carbohydrates.

In the preceding paper [Mandal, D. K., Kishore, N., & Brewer, C. F. (1994) Biochemistry (preceding paper in this issue)] the trisaccharide 3,6-di-O-(alpha-D-mannopyranosyl)-D-mannose, which is present in all asparagine-linked carbohydrates, was shown by titration microcalorimetry to bind to the lectin concanavalin A (Con A) with nearly -6 kcal mol-1 greater enthalpy change (delta H) than methyl alpha-D-mannopyranoside (Me alpha Man). These results indicate that Con A possesses an extended binding site for the trisaccharide. In the present paper, we have investigated the binding of a series of synthetic analogs of the methyl alpha-anomer of the trisaccharide using hemagglutination inhibition, solvent proton magnetic relaxation dispersion (NMRD), near ultraviolet circular dichroism, and titration microcalorimetry measurements. Four of the analogs tested possess an alpha-glucosyl or alpha-galactosyl residue substituted at either the alpha(1-6) or alpha(1-3) position. Analysis of the data indicates that the alpha(1-6) residue of the parent trimannoside binds to the so-called monosaccharide site and the alpha(1-3) residue to a weaker secondary site. Binding at the secondary site involves unfavorable interactions of the 2-equatorial hydroxyl of the alpha(1-3) Glc derivative since this analog binds with 12-fold lower affinity and -3.4 kcal mol-1 lesser delta H than the trimannoside, whereas the alpha(1-3)-2-deoxyGlc analog possesses essentially the same affinity and delta H as the trimannoside.(ABSTRACT TRUNCATED AT 250 WORDS)

Variation of the magnetic relaxation rate 1/T1 of water protons with magnetic field strength (NMRD profile) of untreated, non-calcified, human astrocytomas: correlation with histology and solids content.

The magnetic relaxation rate 1/T1 of tissue water protons was measured over a wide range of magnetic field strengths (NMRD profile) for 92 fresh surgical specimens of astrocytomas to search for correlations of 1/T1 with tumor histology, as determined by light microscopy, and to assess the diagnostic potential of NMRD profiles for grading astrocytomas. A third goal was to elucidate the molecular determinants of 1/T1. Each specimen was histologically graded and inspected for evidence of mineral deposits (Ca, Fe); its dry weight was determined and expressed in % of original wet weight. To minimize variability not directly related to tumor grade, this initial report is limited to NMRD profiles of 47 non-calcified, non-hemorrhagic, untreated astrocytomas. For these, the mean value of 1/T1 at very low magnetic field strengths was found to increase with increasing grade of malignancy; no clear correlation could be demonstrated at high fields where most imaging is done. The spread of 1/T1 for different grades of malignancy is large, however, and the overlap significant, even at the lowest field, so that astrocytomas can not be graded by NMRD profiles alone. Average 1/T1 and average dry weight increase with grade of malignancy; but the variability of 1/T1 among specimens of the same dry weight is large, indicating that at least one other cellular parameter, not variable in normal tissue, influences 1/T1 strongly. We hypothesize that this parameter reflects changes at the molecular level in size distribution, mobility, or intermolecular interaction of cytoplasmic proteins. Which specific changes are induced by malignant transformation in astrocytomas remains to be investigated.