Fluorescence-enhanced europium-diethylenetriaminepentaacetic (DTPA)-monoamide complexes for the assessment of renal function.

Real-time, noninvasive assessment of glomerular filtration rate (GFR) is essential not only for monitoring critically ill patients at the bedside, but also for staging and monitoring patients with chronic kidney disease. In our pursuit to develop exogenous luminescent probes for dynamic optical monitoring of GFR, we have prepared and evaluated Eu(3+) complexes of several diethylenetriamine pentaacetate (DTPA)-monoamide ligands bearing molecular "antennae" to enhance metal fluorescence via intramolecular ligand-metal fluorescence resonance energy transfer process. The results show that Eu-DTPA-monoamide complex 18b, which contains a quinoxanlinyl antenna, exhibits large (ca. 2700-fold) Eu(3+) fluorescence enhancement. Indeed, complex 18b exhibits the highest fluorescent enhancement observed thus far in the DTPA-type metal complexes. The renal clearance property was assessed using the corresponding radioactive (111)In complex 18a, and the data suggest that this complex clears via a complex mechanism that includes glomerular filtration.

Preparation, physico-chemical characterization, and relaxometry studies of various gadolinium(III)-DTPA-bis(amide) derivatives as potential magnetic resonance contrast agents.

Macroscopic protonation constants were measured for a series of DTPA mono- and bis-amide ligands using potentiometric titrations. Proton NMR pH titrations yielded protonation populations of the various nitrogen and oxygen basic sites of the ligands for the different protonation stages. Amide formation decreased the basicity of the backbone nitrogens of the ligands and the thermodynamic stability of the corresponding Gd3+ chelates. Nuclear magnetic relaxation dispersion (NMRD) profiles and ESR linewidths were measured for the Gd3+ chelates. Some of these exhibited an elevated high field relaxivity relative to Gd(DTPA)2-, in response to their high molecular weight. As opposed to Gd(DTPA)2-, at 5 degrees C the chemical exchange process of the single inner-sphere water molecule of the bis-amide complexes becomes so slow that it governs the paramagnetic relaxation process, causing the observed NMRD profiles to be close to those expected for the outer-sphere contribution. The chelates containing long alkyl side chains, such as Gd(DTPA-HPA2), showed increased relaxivity values in the presence of human serum albumin (HSA), indicative of noncovalent interaction with the protein. These chelates could be useful as nonionic hepatobiliary contrast agents.

A convenient method for the preparation of a variety of 13C-substituted D-fructose phosphates using readily available enzymes of the glycolytic pathway.

Methods are presented for the preparation of a variety of D-fructose phosphates, 13C-substituted at any single carbon site or at any two symmetrically disposed carbon sites, from either 13C-substituted pyruvate or L-alanine. It is demonstrated that millimole quantities of product can be obtained in good yield following a "one-pot" incubation of 13C-substituted precursors with commercially available enzymes and cofactors of the glycolytic pathway. Since it has previously been shown that a wide variety of aldehydes serve as acceptable substrates for the final rabbit muscle aldolase-catalyzed condensation step, the method can potentially be applied to prepare a wide variety of 13C-substituted sugars and sugar phosphates.

Stability constants for Gd3+ binding to model DTPA-conjugates and DTPA-proteins: implications for their use as magnetic resonance contrast agents.

Five DTPA-amide and ester derivatives have been synthesized and their Gd3+ stability constants have been measured using a simple spectrophotometric method. These results are compared to stability constants measured for Gd3+ binding to two different DTPA-conjugated proteins. Although the thermodynamic constants for Gd3+ binding to DTPA-monopropylamide and DTPA-monopropylester relative to Gd(DTPA)2- decrease by log K = 2.6 and 3.4, respectively, the blood pH conditional constants differ from Gd(DTPA)2- only by log K = 1.2 and 1.9, respectively. The corresponding dipropylamide and ester conjugates of DTPA show considerably lower thermodynamic and conditional constants. This has important implications in the covalent attachment of chelates to macromolecules for use in magnetic resonance imaging. The measured binding constants for Gd(DTPA)-IgG and Gd(DTPA)-BSA suggest that many of the DTPA molecules in these systems, prepared under our experimental conditions, are disconjugated. The model compound results indicate that it is important to use methods in attaching DTPA to macromolecules which preclude dionjugation of the chelate. Otherwise, their affinity for Gd3+ and consequently their usefulness as MRI contrast agents may be severely compromised.

Number of inner-sphere water molecules in Gd3+ and Eu3+ complexes of DTPA-amide and -ester conjugates.

The inner-sphere water coordination number for Eu3+ and Gd3+ complexed with five DTPA analogs, in which one or two terminal carboxylate groups are functionalized as propyl amides or propyl esters, have been studied using phosphorescence lifetime and nuclear magnetic relaxation dispersion (NMRD) measurements. Both methods show that the water coordination number does not increase above that observed for the analogous DTPA complexes. The phosphorescence lifetime results indicate that all five Eu3+ complexes have one inner-sphere water molecule at 25 degrees C. The NMRD profiles for three of the Gd3+ complexes at 25 degrees C are also consistent with one inner-sphere water molecule, whereas two complexes have profiles consistent only with a mixture of complexes, 50% containing a single water molecule and 50% with none. Lowering the temperature alters the population of these species such that all five Gd3+ complexes have significantly less bound water on average at 5 degrees C. These results explain the anomalous temperature dependencies of the NMRD curves reported previously for the Gd(DTPA)-protein conjugates. We suggest that the Gd(DTPA)-conjugate systems have a fluxional coordination sphere whereby the amount of inner-sphere coordinated water varies from near zero at 5 degrees C to a high of two near 37 degrees C.