Oral manganese for liver imaging at three different field strengths

Oral Manganese Chloride Tetrahydrate: A Novel Magnetic Resonance Liver Imaging Agent for Patients With Renal Impairment: Efficacy, Safety, and Clinical Implication

ABSTRACT

Manganese-based contrast agents (MBCAs) show promise to complement gadolinium-based contrast agents (GBCAs) in magnetic resonance imaging (MRI) of the liver. Management of patients with focal liver lesions and severely impaired renal function uses unenhanced liver MRI or GBCA-enhanced MRI. However, unenhanced MRI risks reducing patient's survival.Gadolinium-based contrast agents, which help to detect and visualize liver lesions, are associated with increased risk of nephrogenic systemic fibrosis in renally impaired patients, a severe adverse event (AE) with potentially fatal outcome. Therefore, use of GBCA in patients with impaired renal function requires careful consideration. Other concerns are related to tissue deposition in the brain and other organs due to lack of gadolinium clearance, which could lead to concerns also for other patient populations, for example, those exposed to multiple procedures with GBCA. Of particular concern are the linear chelates that remain available for liver MRI, where there is no replacement technology. This has highlighted the urgency for safer alternatives.An alternative may be the drug candidate Ascelia-MBCA (ACE-MBCA, Orviglance), oral manganese chloride tetrahydrate. This candidate effectively visualizes and detects focal liver lesions, as demonstrated in 8 clinical studies on 201 adults (healthy or with known or suspected focal liver lesions). ACE-MBCA has a low and transient systemic exposure, which is likely the reason for its beneficial safety profile. The AEs were primarily mild and transient, and related to the gastrointestinal tract. This new, orally administered product may offer a simple imaging approach, allowing appropriate patient management in renally impaired patients when use of GBCA requires careful consideration.In this review, we highlight the clinical development of ACE-MBCA-a novel, liver-specific contrast agent. We begin with a brief overview of manganese properties, addressing the need for MBCAs and describing their optimal properties. We then review key findings on the novel agent and how this allows high-quality MRIs that are comparable to GBCA and superior to unenhanced MRI. Lastly, we provide our view of future perspectives that could advance the field of liver imaging, addressing the medical needs of patients with focal liver lesions and severe renal impairment.Our review suggests that ACE-MBCA is a promising, effective, and well-tolerated new tool in the radiologist's toolbox.

Manganese Exposure Aggravates β-Amyloid Pathology by Microglial Activation

Human epidemiological evidence and animal experimental data suggest that chronic manganese (Mn) exposure increases the risk of Alzheimer’s disease (AD) and amyloid plaques, a hallmark of AD brain pathology, but the underlying mechanisms were not fully understood. Using the transgenic APP/PS1/Tau triple transgenic AD (3×Tg-AD) mouse model and mouse-derived microglia and neuroblastoma cell lines, we found that chronic 5-month Mn treatment increased beta amyloid peptide (Aβ) expression and Aβ plaques in the cerebral cortex and hippocampus in these 3×Tg-AD mice. Furthermore, we found that the β- and γ-secretase cleavage activities were markedly increased, while α-secretase cleavage activity was reduced in the brain of Mn-treated AD mice; these effects increase Aβ production and thus are amyloidogenic. Equally important, Mn treatment alone did not alter β-secretase 1 (BACE1) gene expression or Aβ production in amyloidogenic mutant amyloid precursor protein (APP) gene hAPPsw-transfected N2a cells (APPsw-N2a), but in APPsw-N2a cells either co-cultured with microglia or cultured with microglia-conditioned media, Mn exposure increased BACE1 expression and amyloidogenesis. We further determined that Mn exposure promoted the activation of microglia both in 3×Tg-AD mouse brains and in cultured microglia cells, and increased the secretion of the inflammatory cytokines interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α). Taken together, these results suggest that Mn may increase the release of IL-1β and TNF-α from microglia that in turn stimulates the expression of BACE1 gene and protein and consequently Aβ production; this novel molecular mechanism not only advances our understanding about the amyloidogenic effect of chronic Mn exposure reported for special human populations but also indicates Mn dyshomeostasis as a potential contributor to AD pathogenesis.

Contribution of metals to brain MR signal intensity: review articles

Various metals are essential nutrients in humans, and metal shortages lead to a variety of deficiency diseases. Metal concentration abnormalities may cause metal deposition in the brain, and magnetic resonance imaging (MRI) is the most potent and sensitive technique now available for detecting metal deposition given the difficulties associated with performing brain tissue biopsy. However, the brain contains many kinds of metals that affect the signal intensity of MRI, which has led to numerous misunderstandings in the history of metal analysis. We reviewed the history of brain metal analysis with histologic findings. Typically, manganese overload causes high signal intensity on T1-weighted images (T1WI) in the globus pallidus, iron overload causes low signal intensity in the globus pallidus on T2-weighted images, and gadolinium deposition causes high signal intensity in the dentate nucleus, globus pallidus, and pulvinar of thalamus on T1WI. However, because nonparamagnetic materials and other coexisting metals also affect the signal intensity of brain MRI, the quantitative analysis of metal concentrations is difficult. Thus, when analyzing metal deposition using MRI, caution should be exercised when interpreting the validity and reliability of the obtained data.

A new manganese-based oral contrast agent (CMC-001) for liver MRI: pharmacological and pharmaceutical aspects

Manganese is one of the most abundant metals on earth and is found as a component of more than 100 different minerals. Besides being an essential trace element in relation to the metabolic processes in the body, manganese is also a paramagnetic metal that possesses similar characteristics to gadolinium with regards to T1-weighted (T1-w) magnetic resonance imaging (MRI). Manganese, in the form of manganese (II) chloride tetrahydrate, is the active substance in a new targeted oral contrast agent, currently known as CMC-001, indicated for hepatobiliary MRI. Under physiological circumstances manganese is poorly absorbed from the intestine after oral intake, but by the use of specific absorption promoters, L-alanine and vitamin D(3), it is possible to obtain a sufficiently high concentration in the liver in order to achieve a significant signal enhancing effect. In the liver manganese is exposed to a very high first-pass effect, up to 98%, which prevents the metal from reaching the systemic circulation, thereby reducing the number of systemic side-effects. Manganese is one of the least toxic trace elements, and due to its favorable safety profile it may be an attractive alternative to gadolinium-based contrast agents for patients undergoing an MRI evaluation for liver metastases in the future. In this review the basic pharmacological and pharmaceutical aspects of this new targeted oral hepatobiliary specific contrast agent will be discussed.

MRI of colorectal cancer liver metastases: comparison of orally administered manganese with intravenously administered gadobenate dimeglumine

OBJECTIVES

To compare the sensitivity of MRI to detect colorectal cancer liver metastases (CRLM) after ingestion of manganese-based contrast agent (CMC-001) with that of a comprehensive intravenous gadobenate dimeglumine protocol, and to assess the safety and acceptability of oral manganese.

METHODS

20 patients suspected of having 1-6 CRLM were included prospectively in this randomised cross-over study. Liver MRI was performed with a one-week interval at 1.5 T and included T1-w VIBE and T2-HASTE, before and after administration of 1.6 g CMC-001 or 0.1 mmol/kg gadobenate dimeglumine. The metastasis-to-liver signal intensity (SI) ratio was calculated. Standard of reference was histopathology after surgery, or combination of other imaging studies and/or follow up. Adverse events (AE) and clinicolaboratory tests were monitored.

RESULTS

Of 44 metastases, 41 were detected after CMC-001 (93%) and 42 after gadobenate dimeglumine (95%). Fifteen false-positive lesions were found after CMC-001 and 2 after gadobenate dimeglumine. The metastasis-to-liver SI ratio was significantly higher after CMC-001 than after gadobenate dimeglumine (0.51 and 0.21 respectively, P < 0.0001). More AE occurred after manganese compared to gadobenate dimeglumine.

CONCLUSIONS

CMC-001 is as sensitive as an extensive intravenous gadobenate dimeglumine protocol in detecting CRLM. It was relatively well tolerated but had higher rates of gastrointestinal AE.

KEY POINTS

• Liver MRI after ingestion of manganese is highly sensitive for detecting metastases • High false-positive rate necessitates further evaluation, in some cases • The MR examination time is short • Oral ingestion of manganese seems safe and relatively well tolerated by patients • Manganese compounds may be useful for liver metastasis surveillance after colorectal cancer.

Imaging liver metastases with a new oral manganese-based contrast agent

RATIONALE AND OBJECTIVES

The purpose of the study was a preliminary evaluation of a new oral, manganese-based, liver-specific contrast medium (CMC-001; CMC Contrast AB, Malmoe, Sweden) for magnetic resonance imaging (MRI) in patients with liver metastases.

MATERIALS AND METHODS

The study included 10 consecutive patients with known liver metastases. Patients underwent abdominal MRI as a supplement to routine diagnostics. Patients fasted for at least 10 hours before ingesting CMC-001 (1.6 g manganese chloride tetrahydrate, 1 g alanine, and 1,600 IU vitamin D3 were dissolved in water). MRI took place before and 2 hours after drinking CMC-001. The 1.5-T MRI protocol included two-dimensional T1w sequences to visualize metastases. T2w and diffusion weighted imaging (DWI) sequences were used to identify cysts and blood vessels correspondingly.

RESULTS

The intake of CMC-001 caused an increase in the signal intensity of the "healthy" liver tissue, making the internal structure of the liver significantly better visualized. Compared with our routine examinations, MRI showed more metastases in four patients and allowed determining a more precise outline of metastases.

CONCLUSION

CMC-001 improves imaging of liver metastases in comparison with computed tomography and with MRI without CMC-001.

Initial clinical experience with oral manganese (CMC-001) for liver MR imaging

Recently, a new oral liver-specific manganese-based MR agent (CMC-001) has been introduced. This contrast medium is delivered to the liver in high concentrations in the portal vein and very low doses in the hepatic artery, as only small amounts of manganese enter the general circulation. It is taken up by the hepatocytes and excreted in the bile. Our initial experience with the new MR contrast medium in a variety of patients is reported. A total of 20 patients (11 males and 9 females) were studied with MR imaging 2 h after oral ingestion of the contrast agent. Sixteen patients were referred for evaluation of focal liver lesion(s), whereas in the remaining four patients, evaluation of the biliary tract was requested. In the 17 patients without biliary obstruction, there was an increased signal intensity of the liver parenchyma, whereas in the three patients with biliary obstruction, the uptake was delayed. There was excellent visualization of the biliary system on the T1-weighted images in the 16 patients without biliary obstruction referred for evaluation of a focal liver lesion. In seven patients, the uptake was patchy. In patients with focal liver lesions or biliary tract diseases, it is possible to increase the signal intensity of the liver parenchyma after the oral intake of CMC-001. In patients without biliary tract obstruction, the biliary system is easily visualized. Oral manganese seems to be useful in hepatobiliary MRI. Further research is strongly warranted.

Safety of MR liver specific contrast media

Over the past few years a number of magnetic resonance (MR) liver specific contrast agents have been introduced. In this report the safety issues of these agents are addressed. A literature search was carried out. Based on the available information, simple guidelines on the safety issue of liver specific contrast agents have been produced by the Contrast Media Safety Committee of the European Society of Urogenital Radiology. The report and guidelines were discussed at the 11th European Symposium on Urogenital Radiology in Santiago de Compostela. Liver specific contrast agents appear in general to be safe and well tolerated. However, the incidence of adverse reactions with iron oxides and the intravenous manganese based agent seems to be slightly higher than with gadolinium based agents. However, no safety information from comparative clinical trials has been published. Guidelines on the safety aspects are presented.

Effect of new manganese contrast agent on tissue intensities in human volunteers: comparison of 0.23, 0.6 and 1.5 T MRI, a part of a phase I trial

To evaluate the effect of a new oral manganese contrast agent (CMC-001) on magnetic resonance imaging (MRI) intensities at different magnetic field strengths. Twelve healthy volunteers underwent abdominal MRI 1 week before and within 2.5-4.5 h after CMC-001 (MnCl(2) and absorption promoters dissolved in water) intake at three different MR scanners of 0.23, 0.6 and 1.5 T. Image contrast and intensity enhancement of liver and pancreas were analysed relatively to muscle and fat intensities. Manganese blood levels were followed for 24 h. Whole-blood manganese concentration levels stayed within the normal range. The liver intensities on T2w images decreased about 10% for the 1/2 contrast dose and about 20% for the full contrast dose independent of the field strength. The liver intensities on T1w images increased more than 30% for 1/2 contrast dose and over 40% for full contrast dose. The maximum T1 enhancement was achieved at the highest field. Pancreas intensities were not affected. Contrast between liver, muscle and fat intensities increased with magnetic field, as well as standard errors of the volunteer-averaged intensities. Oral intake of CMC-001 influences liver intensities and does not affect pancreas intensities at different magnetic field strengths.