Rare Earths for Medical Applications

Lanthanides are used in many medicinal applications, such as in anti- tumor agents and kidney dialysis medicine. One of the most known application of these elements is the use of Gadolinium in Magnetic Resonance Imaging (MRI). (1)

The first medical applications in this field became reality shortly after the development of magnetic resonance imaging and the introduction of this technique in medical diagnosis. MRI is an NMR technique that visualizes, with a very high resolution, the morphology of the body. The intensity of each voxel in a three-dimensional image reflects the intensity of the 1H NMR signal of the water in the corresponding part of body. The intensities of these signals and, consequently, the contrast of the images are dependent on magnetic relaxation of the nuclei. Relaxation can be enhanced by paramagnetic compounds, and the lanthanide ion Gd(III) with its seven unpaired electrons is the paramagnetic champion of the periodic table. This ion is ideal for improving the contrast in MRI scans. Gd(III) chelates such as Gd(DTPA) and Gd(DOTA) have been developed that have a very low toxicity, even at the relatively high doses in which they are applied. These contrast agents are as safe as an aspirin, and they have contributed to the success of MRI in clinical diagnostics. Nowadays, about 30% of MRI scans are performed after administration of a Gd(III)-based contrast agent.The luminescent properties of the lanthanides also have been utilized in medical diagnosis. A variety of luminescent bioassays and sensors have been developed that take advantage of the unique luminescent properties of these elements, such as a relatively long-lived emission. (2)

 

MRI-scan-room

Fig 1. Magnetic resonance imaging (MRI)

Europium compounds, for example are often used in molecular genetics to mark specific strands of DNA. Europium oxide was also used in cathode ray television sets as the red glowing dye in the trichromatic setup. (3)

The¬†treatment for high blood phosphate uses compounds called phosphate binders; in the gut these prevent phosphate uptake from the diet. ‘The ideal phosphate binder should have low solubility and little or no systemic adsorption. It should be non-toxic and available in a palatable oral dosage form. Aluminium and calcium based phosphate binders can cause problems due to metal ion absorption, he said. Fosrenol¬†(lantnanum carbonate chewable tablets) avoids the adverse effects associated with earlier drugs because it cannot cross the gut lining and so is not transmitted to the rest of the body. (4)

A new focus nowadays has been put on the anti-cancer treatment use of lanthanides, because of their therapeutic radioisotopes. The dominant pharmacological applications of lanthanides are as agents in radioimmunotherapy and photodynamic therapy. (5)

(1) http://nuclearweaponarchive.org/Usa/Med/Lbfm.htm

(2) http://pubs.acs.org

(3) Shriver and Atkins Inorganic Chemistry

(4) http://www.rsc.org

(5) Kostova, I. Current Medicinal Chemistry РAnti-Cancer Agents, Lanthanides as Anticancer Agents, Volume 5, Number 6, November 2005, pp. 591-602(12)

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