Neurotolerability of gadobenate dimeglumine. Evaluation of brain dopamine concentration in freely moving rats by microdialysis

Glucose-Receptor MR Imaging of Tumors: Study in Mice with PEGylated Paramagnetic Niosomes

PURPOSE

To evaluate a magnetic resonance (MR) imaging contrast agent for tumor detection based on paramagnetic nonionic vesicles (niosomes) bearing polyethylene glycol (PEG) and glucose conjugates for the targeting of overexpressed glucose receptors.

MATERIALS AND METHODS

Four gadobenate dimeglumine-loaded niosome preparations including nonconjugated niosomes, niosomes bearing glucose conjugates (N-palmitoyl glucosamine [NPG]), niosomes bearing PEG 4400, and niosomes bearing both PEG and NPG were tested. In vitro cellular uptake was measured at electron paramagnetic resonance (EPR) after incubation with human prostate carcinoma, PC3, cells. In vivo distribution was studied at MR imaging 6, 12, and 24 hours after injection, with assessment of tumor, brain, liver, and muscle signal intensity (SI) in 49 mice bearing PC3 cells. Efficiency of targeted contrast agents was assessed with tumor-to-muscle contrast-to-noise ratio (CNR). Testing for differences was performed with analysis of variance followed by a posteriori Fisher test.

RESULTS

In vitro, gadolinium could be detected at EPR only in cell pellets incubated with niosomes bearing glucose conjugates or niosomes bearing both glucose conjugates and PEG (4.9. 10(-15) and 4.5. 10(-15) mol gadolinium per PC3 cell). In vivo, marked predominant tumor enhancement was demonstrated 24 hours after injection of glycosylated PEG niosomes (P <.01); no significant differences were observed following injection of nonconjugated niosomes, glycosylated niosomes, or PEG 4400 niosomes. Twenty-four hours after injection, sole presence of NPG or PEG 4400 on the surface of the niosome led to higher tumor-to-muscle CNR than that observed after injection of nonconjugated niosomes (CNR of 3.3 +/- 0.7 [SD], 3.4 +/- 2.2, and 0 +/- 1.9). Combination of NPG and PEG led to even higher tumor-to-muscle CNR (6.3 +/- 2.2).

CONCLUSION

Combination of PEG and glucose conjugates on the surface of niosomes significantly improved tumor targeting of an encapsulated paramagnetic agent assessed with MR imaging in a human carcinoma xenograft model.

Pharmacokinetics and safety of gadobenate dimeglumine (multihance) in subjects with impaired liver function

RATIONALE AND OBJECTIVES

To characterize the pharmacokinetics of gadolinium and to evaluate the safety of gadobenate dimeglumine (Gd-BOPTA) compared with placebo, in subjects with impaired liver function.

METHODS

Volunteer adult subjects with hepatic impairment (Child-Pugh classification B or C) received, randomly and in double-blind fashion, either 0.1 mmol/kg gadobenate dimeglumine (n = 11) or placebo (n = 5) by intravenous injection. Blood and urine gadolinium concentrations were determined by ICP-AES and data were analyzed by compartmental and noncompartmental modeling. A full safety evaluation was performed. No magnetic resonance imaging was performed.

RESULTS

A bi-exponential model fit the gadolinium blood concentration-time data for 10 of 11 subjects administered Gd-BOPTA. The mean (CV%) distribution and elimination half-lives for these subjects were 0.18 (71.9) and 2.18 (44.2) hours, respectively. Non-parametric analysis of all 11 subjects revealed a mean (CV%) area under the curve [0-inf] of 138 (41.9) microg(Gd).h/mL. Mean (CV%) values for blood clearance, steady-state volume of distribution, and renal clearance were 172 (36.0) mL/minute, 22.9 (16.7) L, and 142 (49.0) mL/minute, respectively. A mean (CV%) of approximately 80% (24.5) of the administered dose was excreted in urine during 60 to 72 hours. No safety concerns were apparent.

CONCLUSION

Hepatic impairment did not modify the pharmacokinetics of gadobenate dimeglumine compared with values reported elsewhere for healthy subjects. The contrast agent was well tolerated and safe with an overall incidence of adverse events comparable to that of placebo.

Comparative study between gadobenate dimeglumine and gadobutrol in rats with brain ischemia: evaluation of somatosensory evoked potentials

RATIONALE AND OBJECTIVES

The present study had two main objectives: to validate a rat model of brain ischemia in terms of somatosensory evoked potentials (SEPs) and to compare, using the validated model, the potential activity on the somatosensory function of the new, approved contrast agent gadobenate dimeglumine with that of gadobutrol, a specific contrast agent, for magnetic resonance imaging of the brain.

METHODS

Rats were prepared for SEP recording at least 5 days before ischemia induction. Ischemia was induced by 30-minute right middle cerebral artery occlusion and 3-day reperfusion. The SEP responses, evoked contralaterally to the stimulated upper limb, were recorded from the primary somatosensory cortical area. Model validation, on day 3 after occlusion, was performed using iopromide, an iodinated contrast agent poorly neurotolerated in rats, intravenously injected at 7 g I/kg. The comparative study between gadobenate dimeglumine and gadobutrol was performed at an intravenously injected dose of 2 mmol/kg. Somatosensory evoked potential responses were measured as peak latencies (P2 and N2) and peak-to-peak amplitude (P2N2). The brain concentration of iopromide was measured by high-performance liquid chromatography, whereas that of the gadolinium contrast agent was measured by inductively coupled plasma-atomic emission spectrometry analysis; given the absence of metabolism for both contrast agents, the gadolinium content values can be interpreted as representing unmetabolized contrast agent.

RESULTS

In the ischemic rats, the SEP responses of the lesioned hemisphere showed significant increases in P2, N2, and interpeak N2-P2 latencies and a significant reduction in peak-to-peak (P2N2) amplitude. In the validation experiments, iopromide dramatically increased the P2N2 amplitude of the SEP responses recorded from both hemispheres of ischemic rats without affecting the P2, N2, and interpeak N2-P2 latencies. The iopromide effect was coupled with high concentrations of the contrast agent in the brain. Iopromide had no effect on healthy rats. In the comparative study, gadobenate dimeglumine did not induce any alteration in SEP components of either the lesioned or unlesioned hemisphere of ischemic rats. In fact, no significant difference was found between responses obtained before and after gadobenate dimeglumine injection. Gadobutrol, administered at the same dose, on the whole showed the same behavior as gadobenate dimeglumine, although a slight but significant decrease in the P2 latency, a sign of excitatory activity, was observed 2 hours after injection. Analytic data indicated higher levels of contrast agent in the lesioned hemisphere versus the unlesioned hemisphere 2 hours after injection.

CONCLUSIONS

Based on these results, three conclusions can be drawn: (1) the evaluation of SEPs in ischemic rats is a useful tool for assessing the potential neurological effects of a new contrast agent because ischemic and contrast agent effects can be clearly differentiated; (2) the experimental conditions used allow the contrast agents to penetrate into the brain, where their activity can be manifested and evaluated; and (3) the complete absence of neurological activity of gadobenate dimeglumine shows its safety profile and confirms its suitability for use in neurological diseases for which contrast-enhanced magnetic resonance imaging is indicated.

A review of contrast media research in 1999-2000

Contrast media research published during the years 1999 and 2000 is reviewed in this article, in terms of relevance to developments within the field of diagnostic radiology. The primary focus is on publications from the journal Investigative Radiology, which publishes much of the clinical and laboratory research performed in this field. The journals Radiology and the American Journal of Roentgenology are dominant in the field of diagnostic radiology and together publish more than 10 times the number of articles as appear each year in Investigative Radiology. However, in 1999 for example, these two journals together published fewer articles than did Investigative Radiology alone that concerned basic (animal) research with contrast media. Thirty-six percent of the articles in Investigative Radiology in 1999 had a primary focus on contrast media and 18% on basic (animal) research with contrast media. To make this review more complete, articles from other major journals are cited and discussed, as needed, to provide supplemental information in the few areas not well covered by articles in Investigative Radiology. The safety of contrast media is always an important topic and research continues to be performed in this area, both to explore fundamental issues regarding iodinated contrast media and also to establish the overall safety profile of new magnetic resonance (MR) and ultrasound agents. In regard to preclinical investigations, most of the work performed in the last 2 years has been with MR and ultrasound. In MR, research efforts continue to be focused on the development of targeted agents. In ultrasound, research efforts are split between studies looking at new imaging methods and early studies of targeted agents. In regard to the clinical application of contrast media, the published literature continues to be dominated by MR. Investigations include the study of disease in clinical trials and in animal models. A large number of studies continue to be published in regard to new techniques and applications within the field of contrast-enhanced magnetic resonance angiography. This field represents the single, largest new clinical application of contrast media in MR to emerge in the last decade. New clinical research continues to be published regarding the use of contrast media in computed tomography (CT), ultrasound, and x-ray angiography. The introduction of spiral CT (together with the multidetector scanners) has led to greater utilization of this modality, as well as intravenous iodinated contrast media. The number of publications regarding clinical applications of intravenously injected ultrasound contrast agents remains low, with the high expectations in regard to growth (in terms of number of exams using contrast) of the last decade yet to be fulfilled.

Neurotolerability of contrast agents in rats with brain ischemia induced by transient middle cerebral artery occlusion: EEG evaluation

RATIONALE AND OBJECTIVES

Because contrast agent (CA) formulations are injected intravenously to patients who may have a disrupted blood-brain barrier, their neurotolerability should be tested by using appropriate animal models. In the present study, a model of rat brain ischemia evaluated in terms of the electroencephalogram (EEG) was validated and then used to compare the neurotolerability of gadobenate dimeglumine to that of gadodiamide, a well-documented CA for brain MRI.

METHODS

Rats were prepared for EEG recording about 15 days before ischemia induction. Ischemia was induced in the right hemisphere by 2-hour middle cerebral artery (MCA) occlusion and 3-day reperfusion. Model validation in terms of EEG, on day 3 after MCA occlusion, was performed by using iopromide, a poorly neurotolerated iodinated CA in rats, intravenously injected at 7 g iodine/kg. The EEG recording was analyzed for pathological tracings and for changes in spectral content in terms of the frequency index (FI) at 1, 2, and 3 hours after test compound injection. The comparative study between gadobenate dimeglumine and gadodiamide was performed at 2.0 mmol/kg. D-Mannitol was used as a control compound. The presence of CA in the rat brain was verified by measuring the total gadolinium content by using inductively coupled plasma-atomic emission spectrometry analysis. Given the absence of metabolism for both CAs, the values of gadolinium content can be interpreted as representing unmetabolized CA.

RESULTS

On days 1, 2, and 3 after transient MCA occlusion, the lesioned hemisphere of rats presented a decreased FI value with respect to the basal value. The unlesioned hemisphere, after a slight, nonsignificant decrease in the FI value on the first 2 days, presented a normal FI value on day 3. Thus, ischemic rats on day 3 after transient MCA occlusion were chosen for these neurotolerability studies. Iopromide injected intravenously into ischemic rats at a dose 10 times higher than the maximum clinical dose caused bilateral spikes on the EEG and increases in FI values for the unlesioned hemisphere without affecting the lesioned hemisphere. Gadobenate dimeglumine, like gadodiamide when injected into ischemic rats, did not cause spikes or further changes in the FI value of the lesioned hemisphere and did not modify the normal FI value of the unlesioned hemisphere. Furthermore, no significant differences between gadobenate dimeglumine, gadodiamide, and D-mannitol were found when postinjection FI values were compared. Finally, higher levels of gadolinium were found in the lesioned hemisphere with respect to the unlesioned hemisphere after both gadobenate dimeglumine and gadodiamide administration.

CONCLUSIONS

We can therefore conclude that (1) on the EEG, ischemia induced by transient MCA occlusion is an appropriate model for evaluating CA neurotolerability because ischemic and CA effects can be clearly differentiated; (2) the higher level of CA in the lesioned hemisphere compared with the unlesioned one (two to three times), even 3 hours after injection, demonstrates that the CA effectively penetrated the brain; if it were neurotoxic, any negative effects would have been detected; and (3) gadobenate dimeglumine, like gadodiamide, injected intravenously at a dose 20 times higher than the intended clinical dose for brain MRI is well tolerated and, also like gadodiamide, is suitable for use in neurological diseases for which contrast-enhanced MRI is indicated.