CURRENT RESEARCH ON TREATMENTS AND VACCINES

Unfortunately, there are currently no treatments, cures or vaccines for any prion diseases. There are a few different medications that seem to slow its progress. Patients are often given opiates or painkillers to deal with the severe symptoms of CJD. There is, however, research happening regarding treatments and vaccines for prion diseases. This is happening more slowly than some would like, probably because the overall incidence is really rather low. It may be possible to develop a treatment in the future when testing for TSEs becomes easier and we know more about how to target infectious prions. In addition, it is believed that the build up of prions leads to toxicity, but according to a report by the Committee on Transmissible Spongiform Encephalopathies, 'it remains unclear whether the basis for nerve cell dysfunction and death in prion disease is related to the toxicity of PrPSc, to the loss of function of PrPC as a result of its conversion to PrPSc and its aggregation during a prion infection, or to other factors (2004, p. 68). Knowing the exact mechanism that leads to degeneration is very important in coming up with a treatment plan. Another problem with the development of treatment involves the administration of the drugs. It is necessary to treat TSEs with drugs that can cross the blood-brain barrier, or with drugs that can be administered directly into the cerebrospinal fluid in the brain, which is an invasive method of adminstration. Other issues are the potency of the drug to stop TSEs without being toxic to the living tissue, and the ability to find a treatment that can be transferred from working in cell cultures, where experimentation occurs, to actual organisms, especially humans.

There are many different places and times at which TSEs progress, so drugs may strategically target any of these spatial and temporal situations. Some of the sites for which treatments are being developed to prevent infectious prion spread at the site of introduction, lymphoid organs and their cells (digestive system, lymph nodes), from the peripheral nervous system to the central nervous system, and within the central nervous system. Furthermore, treatments to stop the spread within the brain involve preventing neuron death, allowing re-growth or new neuron growth, stopping infectious proteins from changing the conformaiton normal prions and creating ways to enhance and speed up the degradation of PrPSc (Cobb, 2009).

Riemer et al. (2008) conducted a treatment study with mice infected with diluted brain homogenates prepared with a strain of scrapie from terminally ill sheep. They treated the mice with five various potentially therapeutic drugs and later examined the results. They found that mice that were treated with low, but not high, doses of curcumin and mice treated with memantine survived significantly longer than control mice. Contrary to previous research, Riemer et al. (2008) also found that treatment with ibuprofen elicited adverse effects when compared to either control mice or mice without scrapie infection who were treated with ibuprofen. Their research showed promising leads, but more research must be done on these promising drugs before they can be used in actual treatment plans.

Other possible treatments based on researchers' knowledge of the prion mechanism have been proposed. One proposed method is to inject a peptide, which is a string of amino acids, with the same amino acid sequence as the internal part of the prion protein. This peptide will then bind to normal prion proteins and prevent the infectious prions from binding and transforming them. Other methods of preserving or stabilizing the normal prion structure by stabilizing the helices or by blocking interaction between it and the infectious protein so that it cannot change conformation are suggested. One of these other methods would be to use antibodies that target and attach to normal prions to prevent transformation by infectious prions. Another use of antibodies could be to target the infectious prion and destroy it. One method of preventing the interface between PrPSc and PrPC is to use gene therapy to genetically modify PrPC such that its function is preserved, but the point of interaction between it and the infectious protein is altered enough that it cannot be induced to misfold (Committee on Transmissible Spongiform Encephalopathies, 2004).

Current vaccine research is focusing on model organisms such as mice. In one study, the researchers determined that TSEs can be ameliorated by prion protein-specific antibodies and show early signs of promise for using active immunization to protect against TSEs (Fernandez-Borges, Brun, Whitton, Parra, Diaz-San Segundo, Salguero, Torres, & Rodriguez, 2006). They also noted that onset is slowed rather than prevented, which indicates more research needs to be conducted in this area. Bate, Salmona, Diomede and Williams (2004) performed in vitro experiments and found that the compound squalestatin cured prion-infected neurons and protected against further neurotoxicity. As exciting as these discoveries are, there is still a lot of work to be done in this area before this or other compounds can be used to treat infected humans and animals or prevent further transmissions.

As of now, patients can only be treated with drugs that are approved for other diseases in the hope that one of these may help slow the spread. Two of these drugs that seems to slow the progress of TSEs are chlorpromazine and quinacrine. Chlorpromazine is an antipsychotic drug that has been shown to slow down the disease, but the mechanism is not understood. Quinacrine is an anti-malarial drug that seems to work even better than chlorpromazine. A similar drug that has a dimeric structure (two subunits) of molecules similar to quinacrine, bisacridine, seems to be even more potent in preventing neurodegeneration. Different studies on the effectiveness of these drugs are often contradictory, so the evidence that any of them work is not very strong. Another drug that may be applied to fighting TSEs is the antibiotic tetracycline. Tetracycline seems to prevent the infectious prion buildup in the brain, and may make PrPSc more susceptible to protease breakdown (Committee on Transmissible Spongiform Encephalopathies, 2004).










 
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