Identification of Phosphate-Containing Compounds as New Inhibitors of 14-3-3/c-Abl Protein-Protein Interaction.

The 14-3-3/c-Abl protein-protein interaction (PPI) is related to carcinogenesis and in particular to pathogenesis of chronic myeloid leukemia (CML). Previous studies have demonstrated that molecules able to disrupt this interaction improve the nuclear translocation of c-Abl, inducing apoptosis in leukemia cells. Through an X-ray crystallography screening program, we have identified two phosphate-containing compounds, inosine monophosphate (IMP) and pyridoxal phosphate (PLP), as binders of human 14-3-3σ, by targeting the protein amphipathic groove. Interestingly, they also act as weak inhibitors of the 14-3-3/c-Abl PPI, demonstrated by NMR, SPR, and FP data. A 37-compound library of PLP and IMP analogues was investigated using a FP assay, leading to the identification of three further molecules acting as weak inhibitors of the 14-3-3/c-Abl complex formation. The antiproliferative activity of IMP, PLP, and the three derivatives was tested against K-562 cells, showing that the parent compounds had the most pronounced effect on tumor cells. PLP and IMP were also effective in promoting the c-Abl nuclear translocation in c-Abl overexpressing cells. Further, these compounds demonstrated low cytotoxicity on human Hs27 fibroblasts. In conclusion, our data suggest that 14-3-3σ targeting compounds represent promising hits for further development of drugs against c-Abl-dependent cancers.

Epilepsy and hippocampal neurodegeneration induced by glutamate decarboxylase inhibitors in awake rats.

Glutamic acid decarboxylase (GAD), the enzyme responsible for GABA synthesis, requires pyridoxal phosphate (PLP) as a cofactor. Thiosemicarbazide (TSC) and γ-glutamyl-hydrazone (PLPGH) inhibit the free PLP-dependent isoform (GAD65) activity after systemic administration, leading to epilepsy in mice and in young, but not in adult rats. However, the competitive GAD inhibitor 3-mercaptopropionic acid (MPA) induces convulsions in both immature and adult rats. In the present study we tested comparatively the epileptogenic and neurotoxic effects of PLPGH, TSC and MPA, administered by microdialysis in the hippocampus of adult awake rats. Cortical EEG and motor behavior were analyzed during the next 2h, and aspartate, glutamate and GABA were measured by HPLC in the microdialysis-collected fractions. Twenty-four hours after drug administration rats were fixed for histological analysis of the hippocampus. PLPGH or TSC did not affect the motor behavior, EEG or cellular morphology, although the extracellular concentration of GABA was decreased. In contrast, MPA produced intense wet-dog shakes, EEG epileptiform discharges, a >75% reduction of extracellular GABA levels and remarkable neurodegeneration of the CA1 region, with >80% neuronal loss. The systemic administration of the NMDA glutamate receptor antagonist MK-801 30 min before MPA did not prevent the MPA-induced epilepsy but significantly protected against its neurotoxic effect, reducing neuronal loss to <30%. We conclude that in adult awake rats, drugs acting on PLP availability have only a weak effect on GABA neurotransmission, whereas direct GAD inhibition produced by MPA induces hyperexcitation leading to epilepsy and hippocampal neurodegeneration. Because this degeneration was prevented by the blockade of NMDA receptors, we conclude that it is due to glutamate-mediated excitotoxicity consequent to disinhibition of the hippocampal excitatory circuits.

Developmental hyperoxia alters CNS mechanisms underlying hypoxic ventilatory depression in neonatal rats.

Newborn mammals exhibit a biphasic hypoxic ventilatory response (HVR), but the relative contributions of carotid body-initiated CNS mechanisms versus central hypoxia on ventilatory depression during the late phase of the HVR are not well understood. Neonatal rats (P4-5 or P13-15) were treated with a nonselective P2 purinergic receptor antagonist (pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid, or PPADS; 125mgkg(-1), i.p.) to pharmacologically denervate the peripheral chemoreceptors. At P4-5, rats reared in normoxia showed a progressive decline in ventilation during a 10-min exposure to 12% O2 (21-28% decrease from baseline). No hypoxic ventilatory depression was observed in the older group of neonatal rats (i.e., P13-15), suggesting that the contribution of central hypoxia to hypoxic ventilatory depression diminishes with age. In contrast, rats reared in moderate hyperoxia (60% O2) from birth exhibited no hypoxic ventilatory depression at either age studied. Systemic PPADS had no effect on the ventilatory response to 7% CO2, suggesting that the drug did not cross the blood-brain barrier. These findings indicate that (1) CNS hypoxia depresses ventilation in young, neonatal rats independent of carotid body activation and (2) hyperoxia alters the development of CNS pathways that modulate the late phase of the hypoxic ventilatory response.

In vitro neurotoxicity of magnetic resonance imaging (MRI) contrast agents: influence of the molecular structure and paramagnetic ion.

Interest in contrast agent's (CA) neurotoxicity has greatly increased due to the growing need of new compounds dedicated to brain imaging. Magnetic resonance imaging (MRI) CA have been evaluated by means of different toxicological assays with cultured rat primary neurons (evaluation of neurite specific parameters via immunostaining of the cells and LDH leakage). To determine the potential neurotoxicity of a precise paramagnetic ion in a defined structure (architecture and molecular weight), novel hydrosoluble dendritic Manganese (II) and Gadolinium (III) complexes derived from diethylenetriamine pentaacetic acid (DTPA) have been studied and compared to a linear homologue (same molecular weight) and commercially available low molecular weight MRI CA like Mn-DPDP (Teslascan, GE Healthcare) and Gd-DTPA (Magnevist, Schering). The range of CA concentrations studied was 0.1-10mM, suitable for MRI examinations. This set of experiments allows a toxicity ranking of these reagents as a function of molecular structure and nature of the paramagnetic ion. We could determine that the architecture (linear vs. dendritic) does not play an important role in the in vitro neurotoxicity, whereas the structure of the chelating cage is of greater importance.

Beta-N-methylaminoalanine (BMAA): metabolism and metabolic effects in model systems and in neural and other tissues of the rat in vitro.

The non-protein amino acid, beta-N-methylaminoalanine (BMAA), is neurotoxic and has been implicated in the amyotrophic lateral sclerosis-Parkinsonism-dementia (ALS-PD) complex of Guam. This concept remains controversial, in part because of the lack of a convincing animal model. The neuropharmacology of BMAA is well established, but little is known of its metabolism. This paper reports aspects of the metabolism, and metabolic effects, of BMAA in rat tissues. BMAA changed the distribution of taurine, glycine and serine between rat brain slices and their incubation medium; the glutamate/glutamine cycle between neurones and glia was also compromised. In model experiments BMAA reacted non-enzymatically with pyridoxal-5'-phosphate, releasing methylamine. Rat liver and kidney homogenates, but not brain homogenates, also formed methylamine and 2,3-diaminopropanoic acid when incubated with BMAA. These results provide evidence that several biochemical mechanisms are involved in the neurotoxicity of BMAA. The novel discovery that methylamine is formed from BMAA in rat liver and kidney preparations may be significant since chronic administration of methylamine to rats causes oxidative stress. The extent to which this reaction occurs in different animal species might be a decisive factor in selecting an animal model.

Anticonvulsant characteristics of pyridoxyl-gamma-aminobutyrate, PL-GABA.

GABA is the major inhibitory neurotransmitter in the central nervous system, and its concentration in the brain in associated with a variety of neurological disorders, including seizures, convulsions, and epilepsy. The concentration of GABA is modulated by the pyridoxal-5'-phosphate (PLP)-dependent enzymes, GAD and GABA-T. In this study, we generated pyridoxyl-gamma-aminobutyrate (PL-GABA), a novel GABA analogue composed of pyridoxyl and GABA, and have also characterized its anticonvulsant and pharmacological functions in vitro. The results of biodistribution studies revealed that PL-GABA is capable of crossing the blood-brain barrier. PL-GABA evidenced anticonvulsant activity in a wide range of epilepsy models, some of which were electrically-based (MES seizures) and some chemically-based (bicuculline, pentylenetetrazol (PTZ), picrotoxine, 3-mercaptopropionic acid). Following a timed subcutaneous administration of PTZ to mice, PL-GABA consistently increased the latencies to first twitch and clonus. In addition, PL-GABA displayed no signs of tolerance after subchronic (10 day) treatment. PL-GABA appears to exert its anticonvulsant effects by influencing seizure spread and by raising the seizure threshold. Therefore, our results indicate that PL-GABA exerts a broad-spectrum anticonvulsant effect, and identify the potential for reduced PL-GABA tolerance as an additional positive profile for novel antiepileptic drugs.

Effect of pyridoxylidene aminoguanidine on human diploid cells B-HEF-2: in vitro cytotoxicity test and cytogenetic analysis.

BACKGROUND: Pyridoxylidene aminoguanidine is an appropriate inhibitor of protein glycation, respectively formation of advanced glycation products, which are connected with mechanism of pathogenesis in chronic diabetic complications. Moreover, it was found that in comparison with aminoguanidine, pyridoxylidene aminoguanidine does not influence the level of vitamin B6 in liver and kidneys in vivo. The aim of this study was to test cytotoxic effect of pyridoxylidene aminoguanidine in vitro, in regard to its potential use as inhibitor of advance protein glycation in diabetic patients. METHODS: The potential genotoxic activity of pyridoxylidene aminoguanidine in vitro was assessed by the micronucleus test and the karyological analysis. The direct contact method using diploid human cell line B-HEF-2 was performed to evaluate cytotoxicity. The concentrations of 5 x 10(-3), 2.5 x 10(-3) and 1 x 10(-3) ml/l were used in all tests. RESULTS: Microscopic analysis did not proved any changes in morphology of exposed fibroblasts. The inhibitive effect of pyridoxylidene aminoguanidine was increased with rising concentration. The proliferative activity of exposed cells to concentrations of 1 x 10(-3), 2.5 x 10(-3), 5 x 10(-3) mol/l was inhibited approximately by 30%, 60% and 80%, respectively. The frequency of micronuclei and rate of numerical or structural aberrations was not increased. CONCLUSION: Obtained results confirmed that pyridoxylidene aminoguanidine in selected concentrations has an inhibitive effect on the proliferation activity of exposed cells, but did not develop any cytotoxic effect on B-HEF-2 cells.

Cardiovascular safety of MnDPDP and MnCl2.

PURPOSE: To investigate the apparent discrepancy between expected basic physiological responses at the cellular level and the in vivo behaviour of both MnDPDP and MnCl2 administered i.v. prompted parallel investigations of these substances. MATERIAL AND METHODS: Studies were performed in isolated perfused rat hearts, isolated bovine mesenteric arteries, conscious dogs, and dogs with acute ischaemic heart failure. RESULTS: These studies confirmed that Mn+2 at high concentrations acted as a calcium antagonist inducing negative inotropy. Mn+2 at low concentrations was an effective superoxide scavenger, conserving nitric oxide and facilitating vasodilation. Mn+2 maintained or elevated heart rate (HR) and blood pressure (BP), and did not worsen existing cardiac failure. MnDPDP was about 10 times less potent than MnCl2 in eliciting these cardiovascular responses. CONCLUSION: The ex vivo properties of Mn+2, inducing vasodilation and negative inotropy, are counter-balanced in vivo through the action of 2 mechanisms: extensive plasma protein binding reducing active M+2, and the release of catecholamines which maintain or even raise HR and BP. Taken together with pharmacokinetic factors, including maximal plasma concentrations in humans given the recommended 5 mumol/kg dose, it is concluded that MnDPDP in normal clinical use represents no safety risk to the cardiovascular system.

The reproductive toxicology of intravenously administered MnDPDP in the rat and rabbit.

PURPOSE: The reproductive toxicology of mangafodipir trisodium (MnDPDP, Teslascan), a new hepatobiliary MR contrast agent, was evaluated in rats and rabbits. MATERIAL AND METHODS: Male and female fertility and post-natal development were examined in rats after repeated i.v. injections of MnDPDP. The developmental toxicity in rats was investigated after repeated daily i.v. injections during organogenesis with MnDPDP, MnCl2, or DPDP, as well as with MnCl2 administered orally. The developmental toxicity of i.v. injected MnDPDP was also investigated in rabbits. RESULTS: MnDPDP (100 mumol/kg) had no adverse effects on rat fertility. However, both MnDPDP (10-40 mumol/kg) and MnCl2 (30 mumol/kg) caused skeletal abnormalities in the rat, but not in the rabbit given 20 mumol MnDPDP/kg. Maternal treatment of rats with MnDPDP (40 mumol/kg) reduced survival and body weights of neonates, and adversely affected their functional, but not physical development. No skeletal abnormalities were seen in the rat after i.v. administered DPDP (40 mumol/kg) or MnCl2 (6 mumol/kg), or after MnCl2 (400 mumol/kg) given by oral gavage. Maternal toxicity was not seen in rats or rabbits given these doses. CONCLUSION: MnDPDP caused skeletal abnormalities in foetal rats, but not rabbits, and had no effects on rat fertility. Manganese appears to be the causative agent for inducing bone abnormalities in the rat.

General toxicology of MnDPDP.

PURPOSE: To investigate the general toxicology of mangafodipir trisodium (MnDPDP, Teslascan). MATERIAL AND METHODS: Studies were performed in accordance with standard methods and in compliance with regulations current at the time of conduct. RESULTS: Single-dose studies in rodents and dogs showed that MnDPDP was tolerated at doses of approximately 2000 mumol/kg, approximately 400 times a single imaging dose of 5 mumol/kg. The single dose tolerance of MnDPDP was approximately 10 times greater than MnCl2. A good safety profile of MnDPDP was also shown in repeat-dose studies (3 weeks), in which the no-observed-adverse-effect level for the rat, monkey and dog was 116, 29 and 10 mumol/kg, respectively. The local tolerance studies indicated that no adverse local tissue reactions are likely to occur after i.v. injection. Other studies indicate that accidental spillage of MnDPDP onto the skin is not expected to lead to significant systemic exposure, or to local irritation or hypersensitivity. MnDPDP was not genotoxic in a battery of several different tests. CONCLUSION: MnDPDP was shown to have a good safety profile suitable as an hepatobiliary MR contrast agent for i.v. administration.

The interaction of diadenosine polyphosphates with P2x-receptors in the guinea-pig isolated vas deferens.

1. The site(s) at which diadenosine 5',5"'-P1,P4-tetraphosphate (AP4A) and diadenosine 5', 5"'-P1,P5-pentaphosphate (AP5A) act to evoke contraction of the guinea-pig isolated vas deferens was studied by use of a series of P2-receptor antagonists and the ecto-ATPase inhibitor 6-N,N-diethyl-D-beta,gamma-dibromomethyleneATP (ARL 67156). 2. Pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS) (300 nM - 30 microM), suramin (3-100 microM) and pyridoxal-5'-phosphate (P-5-P) (3-1000 microM) inhibited contractions evoked by equi-effective concentrations of AP5A (3 microM), AP4A (30 microM) and alpha,beta-methyleneATP (alpha,beta-meATP) (1 microM), in a concentration-dependent manner and abolished them at the highest concentrations used. 3. PPADS was more potent than suramin, which in turn was more potent than P-5-P. PPADS inhibited AP5A, AP4A and alpha,beta-meATP with similar IC50 values. No significant difference was found between IC50 values for suramin against alpha,beta-meATP and AP5A or alpha,beta-meATP and AP4A, but suramin was more than 2.5 times more potent against AP4A than AP5A. P-5-P showed the same pattern of antagonism. 4. Desensitization of the P2xi-receptor by alpha,beta-meATP abolished contractions evoked by AP5A (3 microM) and AP4A (30 microM), but had no effect on those elicited by noradrenaline (100 microM). 5. ARL 67156 (100 microM) reversibly potentiated contractions evoked by AP4A (30 microM) by 61%, but caused a small, significant decrease in the mean response to AP5A (3 microM). 6. It is concluded that AP4A and AP5A act at the P2xi-receptor, or a site similar to the P2xi-receptor, to evoke contraction of the guinea-pig isolated vas deferens. Furthermore, the potency of AP4A, but not AP5A, appears to be inhibited by an ecto-enzyme which is sensitive to ARL 67156.

Developmental toxicity study of mangafodipir trisodium injection (MnDPDP) in New Zealand white rabbits.

Mangafodipir trisodium injection (MnDPDP) is an intravenously administered manganese chelate undergoing clinical evaluation for magnetic resonance imaging contrast enhancement of the hepatobiliary system. The anticipated single clinical dose for adults is 5 micromol/kg body wt. MnDPDP, as well as the inorganic salt, MnCl2, was previously shown to induce a specific syndrome of skeletal abnormalities in rats. The syndrome malformations included angulated or irregularly shaped clavicle, femur, fibula, humerus, ilium, radius, scapula, tibia, and/or ulna. The objective of the present study was to assess the developmental toxicity of MnDPDP in a second mammalian species, the New Zealand White rabbit. MnDPDP was intravenously administered daily to groups of rabbits (22 per group) on Days 6 through 18 of pregnancy at doses of 0 (saline), 5, 20, 40, and 60 micromol/kg MnDPDP. Fetuses were examined on Day 29 of pregnancy for external, visceral, and skeletal abnormalities. Treatment with MnDPDP did not result in overt symptoms of maternal toxicity, and there were no significant effects on maternal body weight gains or feed consumption. The maternal no-observed-adverse-effect level (NOAEL), therefore, was 60 micromol/kg MnDPDP. Treatment with MnDPDP resulted in a significant increase in postimplantation loss at 60 micromol/kg, but there was no significant increase in external, visceral, or skeletal abnormalities at any dose. The developmental NOAEL for MnDPDP, therefore, was 40 micromol/kg. These results indicate that the developmental toxicity profile of MnDPDP differs considerably in the rat and rabbit. In the rat, this compound induces specific skeletal abnormalities, whereas in the rabbit, embryo/fetal toxicity is the most sensitive developmental endpoint with no evidence for the induction of specific skeletal abnormalities.

Mice lacking tissue non-specific alkaline phosphatase die from seizures due to defective metabolism of vitamin B-6.

In humans, deficiency of the tissue non-specific alkaline phosphatase (TNAP) gene is associated with defective skeletal mineralization. In contrast, mice lacking TNAP generated by homologous recombination using embryonic stem (ES) cells have normal skeletal development. However, at approximately two weeks after birth, homozygous mutant mice develop seizures which are subsequently fatal. Defective metabolism of pyridoxal 5'-phosphate (PLP), characterized by elevated serum PLP levels, results in reduced levels of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) in the brain. The mutant seizure phenotype can be rescued by the administration of pyridoxal and a semi-solid diet. Rescued animals subsequently develop defective dentition. This study reveals essential physiological functions of TNAP in the mouse.

Developmental toxicity of mangafodipir trisodium and manganese chloride in Sprague-Dawley rats.

Mangafodipir trisodium (MnDPDP) is a manganese chelate being developed as a contrast agent for magnetic resonance imaging of the hepatobiliary system. The intended clinical dose is 5 mumol/kg. The potential for MnDPDP to induce embryotoxicity and/or teratogenicity in Sprague-Dawley rats was investigated. Twenty five inseminated rats/group were intravenously administered 0, 2, 5, or 20 mumol/kg MnDPDP from days 6-17 of gestation. Maternal toxicity was not observed at any dose of MnDPDP. There were no treatment-related effects on the numbers of fetuses, fetal viability, numbers of resorptions, implantations and corpora lutea, or the percent of pre- and post-implantation losses. However, at 20 mumol/kg, fetal body weights were significantly decreased (3.3 g vs. 3.9 g for control) and increased skeletal malformations were observed (141/270 vs. 0/285 in control). The malformations were of a specific type, which included angulated or irregularly shaped clavicle, femur, fibula, humerus, ilium, radius, scapula, tibia, and/or ulna. To better define the developmental stage that is most susceptible to the effects of MnDPDP, a segmented developmental study was conducted. Twelve inseminated rats were administered 0, 20, 40, or 80 mumol/kg MnDPDP on days 6-8, 9-11, 12-14, or 15-17 of gestation. Skeletal malformations, identical to those seen in the previous study, were increased in a dose-dependent manner with the highest incidence occurring in fetuses from females dosed from days 15-17 of gestation. A third study, in which 15 rats/group were dosed intravenously with 0, 5, 20, or 40 mumol/kg MnCl2 on days 6-17 of gestation, produced identical skeletal malformations to those seen with MnDPDP, indicating that manganese is the active moiety responsible for these specific malformations.

In vivo modification of GABAA receptor with a high dose of pyridoxal phosphate induces tonic-clonic convulsion in immature mice.

The biologic cofactor, pyridoxal-5'-phosphate (PLP), is responsible for tonic-clonic convulsion in immature mice. The mechanisms underlying such convulsive fits induced by administration of a single high dose of PLP were studied. The administration of PLP resulted in a 13% increase of PLP in the P2 fraction compared to control P2, and the calculated data suggested that membrane bound PLP increased over 31% (approximately 1 microM). The P2 fraction of administered mice was treated with [3H]NaBH4 and analyzed by SDS-polyacrylamide gel electrophoresis. The radioactivity was mainly incorporated into a 52 kDa protein which corresponded to a GABAA receptor subunit. The addition of PLP in vitro competitively inhibited [3H]GABA binding as well as [3H]flunitrazepam binding to synaptic membranes in a concentration-dependent manner, and 50% inhibition was achieved with 1 mM PLP. The results obtained in the present study demonstrate that PLP was rapidly permeable into the brain through the immature blood-brain barrier and then bound directly to GABAA receptor. It is probable that specific amino groups of lysine residues on the GABAA receptor react in vivo with PLP to form Schiff bases, and that the in vivo modification of the receptor produces a degeneration of GABAergic neurotransmission leading to the onset of a convulsive fit.

Effect of manganese dipyridoxal diphosphate on liver magnetic resonance imaging and serum bilirubin in rats with removable biliary obstruction.

RATIONALE AND OBJECTIVES: It is known that manganese dipyridoxal diphosphate (Mn-DPDP) causes persisting liver enhancement in cholestatic rats, that free Mn++ plus bilirubin induces intrahepatic cholestasis, and that free Mn++ is released in vivo after Mn-DPDP injection. Hence, there is a concern about potential secondary intrahepatic cholestasis in patients who have biliary obstruction. In this study, we further investigated this issue. METHODS: Removable total biliary obstruction (RTBO) was induced in 12 rats. Six of them (group A) received Mn-DPDP (25 mumol/kg). The others (group B) served as control animals. The data from serial magnetic resonance imaging and serum bilirubin tests were compared. RESULTS: Without Mn-DPDP, a minimal increase of the liver intensity was observed in both groups because of cholestasis. In group A, the intensity of the liver was strongly enhanced with Mn-DPDP but normalized within 48 hr after removal of the obstruction. In both groups, total bilirubin levels increased up to 131.67 mumol/l 2 days after RTBO but rapidly decreased within 4 hr and almost normalized within 24 hr after removal of the obstruction, suggesting a lack of Mn-DPDP influence on the bilirubin level. CONCLUSION: We found that Mn-DPDP did not cause secondary intrahepatic cholestasis. Retained Mn++ is likely eliminated after restoration of bile flow. These results indicate that Mn-DPDP can be used in patients who have obstructive jaundice as long as it is followed by successful bile drainage.

Preclinical evaluation of MnDPDP: new paramagnetic hepatobiliary contrast agent for MR imaging.

Manganese(II)-N,N'-dipyridoxylethylenediamine-N,N'-diacetate-5,5'-bis (phosphate) (MnDPDP) is a paramagnetic complex designed for use as a hepatobiliary agent. The T1 relaxivity of MnDPDP (2.8 [mmol/L]-1.sec-1 in aqueous solution) was similar to that of gadolinium diethylenetriaminepentaacetic acid (DTPA) (4.5 [mmol/L]-1.sec-1) and gadolinium tetraazocyclodecanetetraacetic acid (DOTA) (3.8 [mmol/L]-1.sec-1). However, in liver tissue the T1 relaxivity of MnDPDP (21.7 [mmol/L]-1.sec-1) was threefold higher than that reported for Gd-DOTA (6.7 [mmol/L]-1.sec-1). Maximum liver T1 relaxation enhancement occurred 30 minutes after injection of MnDPDP, at which time 54MnDPDP biodistribution studies indicated that 13% of total body activity was in the liver. Enhanced (MnDPDP, 50 mumol/kg) MR images showed a fivefold increase in tumor-liver contrast-to-noise ratio over baseline unenhanced images. Results of the authors' acute and subchronic toxicity studies suggest that MnDPDP will be safe at the doses necessary for clinical imaging; at 10 mumol/kg, the safety factor (LD50/effective dose) for MnDPDP is 540, significantly greater than the safety factor of Gd-DTPA (ie, 60-100).

Hepatobiliary MR imaging: first human experience with MnDPDP.

The first human MR imaging results for the hepatobiliary contrast agent manganese(II)N,N'-dipyridoxylethylenediamine-N,N'-diacetate 5,5'-bis(phosphate) (MnDPDP) are reported. MnDPDP is a paramagnetic contrast agent specific for hepatobiliary imaging. An imaging study was performed to investigate the presence of contrast enhancement or facilitated visualization of normal structures. Twelve healthy subjects receiving MnDPDP at doses of 3, 10, or 15 mumol/kg were imaged after injection for approximately 30 minutes at 1-5-minute intervals. Transaxial abdominal images were obtained at 1.5 T in a single breath-hold interval of 21 seconds with use of a spin-echo pulse sequence (repetition time = 150 msec, echo time = 20 msec). Liver parenchyma enhancement was observed 1 minute after injection and persisted for at least 30 minutes. Clearance into the gallbladder was visualized within 15 minutes. Enhancement was dose-dependent; a dose of 10 mumol/kg produced a 75%-100% signal enhancement of the liver at 10 minutes after injection.