Cardioprotective effects of the MR contrast agent MnDPDP and its metabolite MnPLED upon reperfusion of the ischemic porcine myocardium

Purpose: To evaluate whether manganese dipyridoxyl diphosphate (MnDPDP) or its metabolite manganese dipyridoxyl ethyldiamine (MnPLED) reduces post-ischemic myocardial injury.

Material and Methods: Left anterior descending artery (LAD) in anesthetized pigs was occluded (30 min) followed by reperfusion (120 min) during hemodynamic monitoring and infarct assessment. Three μmol/kg MnDPDP, 1 μmol/kg MnPLED (or a mixture of both) or saline was injected i.v. 10 min before reperfusion followed by infusion of either 3 μmol/kg/h MnDPDP, 1 μmol/kg/h MnPLED (or a mixture of both) or saline. The plasma concentrations of MnDPDP, MnPLED and other metabolites (e.g., ZnDPDP and ZnPLED) were analyzed.

Results: Femoral blood flow was reduced by 60% during early reperfusion in controls, whereas only 23 and 31% reductions were seen in animals treated with MnDPDP and MnPLED. During that time, +LV/dP and -LV/dP (maximum rate of left ventricular isovolumic contraction and relaxation, respectively), systolic pressure and diastolic pressure fell significantly less in animals treated with MnDPDP or MnPLED. Three out of 5 control animals experienced ventricular fibrillation (VF) during reperfusion, whereas VF was not seen in any of the pigs treated with MnPLED or/and MnDPDP. The infarct sizes in saline- and MnPLED-treated animals were 39±6 and 16±5%, respectively, of the occluded areas. MnDPDP did not reduce the infarct size. A mixture of MnDPDP and MnPLED significantly reduced infarct size (10±4%). When reperfusion started and throughout reperfusion, almost all injected MnDPDP was present as Zn-metabolites.

Conclusion: MnPLED seems to reduce reperfusion-induced cardiac dysfunction and infarct size in pigs. MnDPDP does not reduce infarct size in the pig, probably because of the rapid exchange of Mn2+ for Zn2+ taking place in the pig.

Metabolism and pharmacokinetics of MnDPDP in man

Purpose: To study the metabolism and pharmacokinetics of mangafodipir trisodium injection, 0.01 mmol/ml (Teslascan), in healthy male volunteers.

Material and Methods: Eight volunteers received mangafodipir trisodium as an infusion over 20 min, and 5 received it as an injection (≤ min). Both groups received 5 and 10 μmol/kg b.w. with a wash-out period of 3 weeks between doses. Metabolites were measured in plasma, total manganese and zinc were measured in plasma and urine and total manganese was measured in faeces.

Results: The parent compound MnDPDP (manganese dipyridoxyl diphosphate) and 5 metabolites; MnDPMP (manganese dipyridoxyl monophosphate), MnPLED (manganese dipyridoxyl ethylenediamine) and the corresponding zinc compounds ZnDPDP, ZnDPMP and ZnPLED, were detected in plasma. ZnPLED was the only detectable metabolite 8 h after dosing. The apparent volume of distribution of manganese exceeded the interstitial body fluids. The volume of distribution of the ligand indicated distribution to the extracellular fluid only, with the plasma clearance close to the glomerular filtration rate. The manganese was incompletely excreted during the 4 days after treatment with the major part in faeces and less than 20% of the dose in the urine.

Conclusion: Dephosphorylation and simultaneous transmetallation with zinc are the main metabolic pathways of MnDPDP in man.

Tissue distribution and general safety of MnDPDP in male beagle dogs, with or without total common bile duct obstruction

Purpose: Evaluation of the tissue distribution of manganese (Mn) and general safety in normal and cholestatic male beagle dogs after i.v. administration of mangafodipir trisodium (MnDPDP, Teslascan).

Material and Methods: Male beagle dogs, with or without surgical obstruction of the common bile duct, received a single i.v. bolus injection of saline (control), or MnDPDP at doses of 10 or 50 μmol/kg b.w. and were sacrificed 1 or 7 days after treatment. Tox-icity was assessed and tissue concentrations of Mn were measured.

Results: Increased tissue Mn concentrations were found in all dogs treated with MnDPDP and were greatest in those with biliary obstruction. Although Mn concentrations decreased with time in most tissues in each of the treated groups, this was not the case for the brain and adrenal glands in dogs with total biliary obstruction in which further increases in Mn concentrations were seen at the later time point. This suggested a re-distribution of Mn from the major body depots such as the liver. There were no effects of MnDPDP on clinical sign/behaviour, organ weights, histomorphology or clinical biochemistry.

Conclusion: These findings indicate that a single clinical dose of 5 μmol/kg MnDPDP is likely to be well tolerated in patients with cholestasis.

Dephosphorylation of MnDPDP and related compounds by acid and alkaline phosphatase

The enzymatic dephosphorylation of the magnetic resonance imaging contrast agent Teslascan was studied in in vitro experiments with acid phosphatase (prostatic, from human semen) and alkaline phosphatase (from human placenta). The active component, MnDPDP (manganese (II)-N,N'-dipyridoxylethylenediamine-N,N'-diacetate-5,5'-bis(phosphate), was dephosphorylated by both enzymes to the monophosphate MnDPMP and the totally dephosphorylated compound MnPLED. The corresponding zinc compound, ZnDPDP (which is a result of in vivo metabolism), was also dephosphorylated by both enzymes to ZnDPMP and ZnPLED. In separate experiments, both enzymes dephosphorylated MnDPMP and ZnDPMP. With the same amount of enzyme units, alkaline phosphatase was almost four times more active than acid phosphatase in dephosphorylating MnDPDP and ZnDPDP with only minor differences whether the substrate contained Mn or Zn. A similar difference in enzymatic activity was seen with the monophosphates, MnDPMP and ZnDPMP. This, taken together with the approximately 50 times higher activity of alkaline phosphatase than acid phosphatase in serum shows that alkaline phosphatase is responsible for most of the dephosphorylation of MnDPDP and its metabolites in vivo.

Mangafodipir trisodium injection, a new contrast medium for magnetic resonance imaging: in vitro metabolism and protein binding studies of the active component MnDPDP in human blood

The binding to human serum proteins of MnDPDP (manganese(II) dipyridoxyl diphosphate), the active component of the magnetic resonance imaging contrast medium mangafodipir trisodium injection (Teslascan) was studied in ultrafiltration experiments. Sera from three males and three females were incubated with 86 microM [14C]MnDPDP for 60 min at room temperature (20-23 degrees C), followed by centrifugation through filters with a cut-off of 30 kDa. Analysis of the filtrates and the initial incubation mixtures for manganese, by ICP-AES, and for DPDP and its dephosphorylated metabolites DPMP (dipyridoxyl monophosphate) and PLED (dipyridoxyl ethylenediamine diacetate) by liquid scintillation counting, showed a clear difference in protein binding of manganese and the ligands under these conditions. Only 2.2 +/- 1.8% (mean +/- S.E.; n = 6) of DPDP, DPMP and PLED were bound to protein, whereas 26.9 +/- 2.9% (mean +/- S.E.; n = 6) of manganese was bound to protein. No binding of DPDP, DPMP or PLED to blood cells was observed when whole blood, containing either heparin or EDTA as anticoagulant, was spiked with [14C]MnDPDP and the cell-free fraction and the lysed cell fraction analysed by liquid scintillation counting. The extent of protein binding of manganese corresponded well with results from an in vitro metabolism study, in which MnDPDP was added to heparinized human whole blood, showing that approximately 25% of DPDP, DPMP or PLED were not bound to manganese. The in vitro metabolism study revealed that transmetallation with zinc was nearly complete within 1 min, and that dephosphorylation is a sequential process going from DPDP to the monophosphate DPMP, and then to the fully dephosphorylated compound PLED.

Mangafodipir trisodium injection, a new contrast medium for magnetic resonance imaging: detection and quantitation of the parent compound MnDPDP and metabolites in human plasma by high performance liquid chromatography

Manganese(II) dipyridoxyl diphosphate (MnDPDP) is the active component of mangafodipir trisodium injection (Teslascan), a new contrast medium for magnetic resonance imaging. A high performance liquid chromatography (HPLC) method was developed for the simultaneous determination of MnDPDP and its five major metabolites in human plasma, i.e. the dephosphorylation products MnDPMP (manganese(II) dipyridoxyl monophosphate) and MnPLED (manganese(II) dipyridoxyl ethylenediamine diacetate) and the corresponding substances obtained after transmetallation with zinc (ZnDPDP, ZnDPMP and ZnPLED). Heparinized blood samples from patients receiving mangafodipir trisodium injection were immediately mixed with solid trisodium phosphate dodecahydrate to obtain pH 10.0 +/- 0.2 in order to inhibit further in vitro dephosphorylation and transmetallation. The plasma thus obtained was ultrafiltrated prior to HPLC analysis. The chromatographic separation was obtained using a mixed-bed resin with both anion exchange and reversed-phase functions (OmniPac PAX-500) using isocratic elution and UV detection at 310 nm. With an injection volume of 50 microliters, the limit of quantitation (LOQ) values were 0.8-2.3 microM for the Mn compounds and 0.1-0.8 microM for the Zn compounds. The between-run accuracy of spiked plasma samples was in the range 97.5-106.7% with a precision in the range 3.1-9.0%. The best fit calibration curves were obtained using non-linear regression according to the equation Y = A + BXM in the concentration range from LOQ to 100 microM. Long-term storage of spiked plasma samples for three months at -20 degrees C demonstrated the required stability with recovery values within 85-115% of MnDPDP and its five metabolites.

Metabolism of mangafodipir trisodium (MnDPDP), a new contrast medium for magnetic resonance imaging, in beagle dogs

The metabolism of MnDPDP (manganese(II) N,N'-dipyridoxylethylenediamine-N,N'-diacetate-5,5'-bis(phosphate) was studied in dogs after intravenous infusion for 12.5 min with either 10, 30 or 100 mumol MnDPDP/kg b.w. HPLC analyses of plasma samples obtained 1, 5 and 30 min after the end of infusion revealed that MnDPDP was rapidly dephosphorylated to MnDPMP (manganese(II) N,N'-dipyridoxylethylenediamine-N,N'-diacetate-5-phosphate) and MnPLED (manganese(II) N,N'-dipyridoxylethylenediamine-N,N'-diacetate), with simultaneous transmetallation to the corresponding zinc metabolites ZnDPDP, ZnDPMP and ZnPLED. In the low-dose group, the parent compound MnDPDP was present at the lowest concentration compared to the metabolites at the first sampling time point, 1 min after the end of infusion, whereas MnPLED was the main metabolic. At 30 min post-infusion ZnPLED was the main metabolite. The medium- and high-dose groups showed a similar metabolic pattern. In the high-dose group, MnPLED was the main metabolite at all sampling time points. The estimated plasma half-life of total ligand was 20 min, and it was dose-independent with an apparent volume of distribution of 0.2 l/kg. The rate of dephosphorylation was similar to the rate of transmetallation, and both were dose-independent. However, calculations of the total Mn and Zn ligands indicated that the apparent plasma elimination was dose-dependent. The half-life for total Mn ligands which is a combination of both metabolism and elimination, were 10 and 20 min at 10 and 100 mumol/kg, respectively. The half-life for total Zn ligands which is the half-life for rate of formation of Zn ligands, were 40 and 65 min at 10 and 100 mumol/kg, respectively. No sex differences in metabolic pattern were observed in any of the three dosage groups.

The amino-acid sequence of the variable region of a carbohydrate-containing amyloid fibril protein EPS (immunoglobulin light chain, type lambda)

The amino-acid sequence of the variable region of a carbohydrate-containing amyloid fibril protein EPS of immunoglobulin lambda light chain origin has been elucidated. The protein was isolated from the liver of a patient (EPS) with an immunocyte dyscrasia of the IgM type. The molecular mass of this protein was found to be about 20 kDa including an oligosaccharide chain linked to it. The amino-acid sequence determination involved automatic Edman degradation of polypeptides obtained after cleaving the protein with BNPS-skatole, trypsin and thermolysin. The proposed sequence of the variable region of the protein showed that it may be assigned to the V lambda I subgroup. A tryptic and a thermolysinolytic peptide both containing the carbohydrate were isolated and characterized, and the localization of an oligosaccharide chain linked to asparagine was established.