METALS IN MEDICINE AND THE ENVIRONMENT

Magnets have been thought to have the ability to remedy many kinds of illnesses throughout history and across cultures, the first documented case in western culture being Hippocrates who used iron oxides to stop bleeding.  An even older example in India is known however from the writings of a Hindu surgeon Sucrata who used a magnet to remove an iron arrow tip from a patient (1).  Today, the new craze of alternative medicine has adopted magnets as a central focus in an attempt to provide treatment to patients with as little invasiveness, as few chemicals, and often using as little science as possible.  Alternative medicine practitioners claim magnets can cure diseases such as arthritis, diabetes, high blood pressure, osteoporosis, among many others  (2).  The purpose of this paper is to provide current scientific research using magnetic materials in medicine.

Iron oxide magnetic nanoparticles (MNPs) are being used for a wide range of applications.  Hyperthermia, or a rise in temperature, can be caused in a cell using magnetic nanoparticles or fluids in the presence of a quickly oscillating magnetic field.  The rapid change in orientation of this field causes the small magnetic particles to rapidly change their orientations resulting in heat loss to the surrounding environment.  This process generally is used to target tumor cells and uses weak temperature enhancement raising the intracellular temperature to somewhere between 40°- 50°C.  This temperature range can destroy some tumors via apoptosis pathways but is usually coupled with other therapies for maximum effectiveness (3).  These complexes can provide site-specific heating and greatly minimize damage to surrounding healthy tissue. Recent studies have shown almost complete regression of prostate cancer and melanoma in mice using these complexes (4,5).  See Figure 1.

tumor sizes

Figure 1. Tumor sizes of controls and experimental groups in prostate cancer mouse study (5).
 
Surface-modified magnetic nanoparticles have also been investigated for their ability to act as “smart” drug delivery systems as well as potential imaging agents.  One design uses a nanoparticle core and PEO-PPO-PEO block polymer with an interior polyethylene-imine block anchoring the polymer to the nanoparticle.  An advantage of this system is that the PPO interior region would be capable of holding a nonpolar drug while the outer PEO block would make ths system water soluble.  This system is known to undergo morphological variations as a function of temperature.  Dynamic light scattering results showed the hydrodynamic radius of the nanoparticle underwent a sharp decrease over the range of 20°-35°C.  Drug molecules could be loaded in at lower temperatures in the more relaxed state, frozen in place by raising the temperature and then again released by again lowering the temperature (6).  See Figure 2.

iron oxide particle polymer drug release

Figure 2.  Controlled drug release from PEI-PEO-PPO-PEO shell (6).

MNPs expressing specific binding sites are being used as detectors for proteins and nucleic acids.  One study sought to detect recombinant prion proteins using a short strand of nucleic acids showing high binding affinity, called an aptamer.  Iron oxide nanoparticles were coated in a thin layer of gold because of the easy functionalization of its surface using thiol chemistry.  To the gold layer was attached the short aptamer sequence and degree of binding was monitored using FTIR spectroscopy.  Binding was shown to occur and to be strongly concentration dependent (7).  It is unclear if such a method would be useful because it is not stated how strongly this aptamer sequence binds with proteins in general which would be ubiquitous in an in vivo environment.
  Retinal detachment is a serious medical problem associated with long recovery time.  Silicone based magnetic fluids have been developed for use in eye surgery to reattach the retina.  These fluids use sterically suspended iron oxide particles in a viscous polymer. An exterior scleral buckle behind the eye is used to direct the magnetic fluid, which is injected into the interior of the eye, to the desired location.  The pressure exerted from the fluid is enough to permanently reattach the retina (8).  See Figure 3.

retina reattachment


Figure 3.  Reattached retina using external magnet and sterically stabilized MNPs in a polysiloxane matrix.

References

(1) Andra, W., Nowak, H. ed. Magnetism in Medicine. Wiley-VCH, Berlin (1998).

(2) http://www.therionresearch.com.

(3) Glockl, G., Hergt, R., Zeisberger, M., Dutz, S., Nagel, S., Weitschies, W. Journal of Physics: Condensed Matter 18, S2935-S2949 (2006).

(4) Ito, A., Tanaka, K., Kondo, K., Shinkai, M., Honda, H., Matsumoto, K., Saida, T., Kobayashi, T. Cancer Science 94, 3, 308-313 (2003).

(5) Kawai, N., Ito, A., Nakahara, Y., Honda, H., Kobayashi, T., Futakuchi, M., Shirai, T., Tozawa, K., Kohri, K. The Prostate 66, 718-727 (2006).

(6) Chen, S., Li, Y., Guo, C., Wang, J., Ma, J. H., Liang, X. F., Yang, L. R., Liu, H. Z. Langmuir (2007).

(7) Kouassi, G. K., Wang, P., Sreevatan, S., Irudayaraj, J.  Biotechnology Progress 23, 1239-1244 (2007).

(8) Daily, J. P., Phillips, J. P., Riffle, J. S. Journal of Magnetism and Magnetic Materials 194, 140-148 (1999).

Author: Tyler St. Clair