Treatment Prion Diseases

There are no treatments available that have been shown to alter the course of prion diseases in humans. Currently, medical treatment is directed at controlling the neurologic and psychiatric symptoms, providing palliative care for patients and support for their families. For example, myoclonus and seizures can be controlled with anticonvulsant medications such as valproic acid and benzodiazepines. Severe hyperkinetic movement disorders such as chorea or dyskinesias and psychotic behavioral symptoms can be controlled with neuroleptic medications. Other psychiatric symptoms can be improved with medications that are used for behavioral symptoms in other patients with dementia. Quality nursing care is very important and can limit pain and the complications of being bedridden. Finally, and most importantly, patients and their families need a tremendous amount of emotional and social support to cope with these devastating diseases.

One goal of medical management is to prevent the infectious spread of prion diseases. Prions can be transmitted from one organism to another if nervous system tissue containing PrPSc from an infected patient is transferred to another patient. Thus, the equipment used in neurosurgery, corneal transplants, and depth electrodes must be decontaminated by methods that inactivate prions if they have come in contact with a patient with a prion disease. Procedures for decontaminating operating and autopsy rooms have been developed and are unique for prions (Committee on Health Care Issues, American Neurological Association, 1986; Steelman, 1999) Universal precautions should be used when handling cerebrospinal fluid, optic tissue, blood, and urine. Cerebrospinal fluid and optic tissue have the highest titers of infectious prions, but small amounts of infectious prions have been found in other tissues, blood, and urine (Committee on Health Care Issues, American Neurological Association, 1986). Secretory and excretory products such as saliva, sweat, and stool have not been found to contain infectious prions. Procedures for handling and deactivating tissue from patients with prion disease have been developed for pathologists (Committee on Health Care Issues, American Neurological Association, 1986). Patients with known prion disease are prevented from donating blood or other tissue although there have been no documented cases of the spread of prion disease by blood transfusions. Brown et al. suggests that transmission of prion diseases via blood transfusion is unlikely because of the absence of significant infectivity until symptomatic disease, a reduction of infectivity during plasma processing, and a need for the presence of five to seven times more infectious prions to transmit disease by the intravenous route as compared to the intracerebral route (Brown et al., 1999).

In the past several years, tremendous advances have been made in developing disease-altering therapies for prion diseases (Korth, May,

Cohen, & Prusiner, 2001; Perrier et al., 2000; Priola, Raines, & Caughey, 2000; Supattapone, Nguyen, Cohen, Prusiner, & Scott, 1999). This research suggests PrPSc production can be blocked at multiple steps, including stabilizing the PrPC molecule to prevent the conformational change to PrPSc, destabilizing PrPSc so that it becomes protease sensitive, preventing PrPSc from serving as a template for replication, and blocking the interaction of protein X with PrPC in the process of forming a complex with PrPSc (Perrier et al., 2000). Using scrapie-infected neuroblastoma cells to screen for inhibition of formation of PrPSc and clearance of preexisting PrPSc, researchers have found two effective antiprion compounds that have been used in humans for many years (Korth et al., 2001). The two compounds—chlorpromazine, an antipsychotic agent, and quinacrine, an antimalarial drug—were effective in inhibiting the accumulation of PrPSc. The mechanism by which these and related compounds are effective as antiprion agents is unclear. However, because both agents have been used safely in humans for more than 50 years, development of human trials is underway. Dosage required to produce antiprion effects and whether one agent will be more effective or better tolerated at therapeutic doses in humans is unknown. However, identification of these agents and development of the in vitro methods used to screen for an-tiprion agents are tremendous breakthroughs in the search for safe and effective treatments for the prion diseases.

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