Researchers at the University of Texas Medical Branch at Galveston ( UTMB ) have found a way to detect in blood the malformed proteins that cause “mad cow disease,” the first time such “prions” have been detected biochemically in blood.

The discovery, reported in the Nature Medicine, is expected to lead to a much more effective detection method for the infectious proteins responsible for brain-destroying disorders, such as bovine spongiform encephalopathy ( BSE ) in cattle and variant Creutzfeldt-Jakob disease ( vCJD ) in humans.

The blood test would make it much easier to keep BSE-infected beef out of the human food supply, ensure that blood transfusions and organ transplants do not transmit vCJD, and give researchers their first chance to figure out how many people may be incubating the disease.

“ The concentration of infectious prion protein in blood is far too small to be detected by the methods used to detect it in the brain, but we know it’s still enough to spread the disease,” said Claudio Soto at UTMB and senior author of paper. “ The key to our success was developing a technique that would amplify the quantity of this protein more than 10 million-fold, raising it to a detectable level.”

Researchers applied a method they call protein misfolding cyclic amplification ( PMCA ) to blood samples taken from 18 prion-infected hamsters that had developed clinical symptoms of prion disease.
PMCA uses sound waves to vastly accelerate the process that prions use to convert normal proteins to misshapen infectious forms.

Successive rounds of PMCA led to the discovery of prions in the blood of 16 of the 18 infected hamsters. No prions were found in blood samples that were taken from 12 healthy control hamsters and subjected to the same treatment.

“ The next step, which we’re currently working on, will be detecting prions in the blood of animals before they develop clinical symptoms and applying the technology to human blood samples,” Soto said.

Tests for infectious prions in cattle and human blood are badly needed. Because current tests require post-slaughter brain tissue for analysis, in the United States only cattle already showing clinical symptoms of BSE ( so-called “downer cows” ) are tested for the disorder. This is true even though vCJD potentially can be transmitted by animals not yet showing symptoms of the disease.
And although British BSE cases have been in decline since 1992, scientists believe the British BSE epidemic of the 1980s could have exposed millions of people in the UK and Europe to infectious prions.
The extent of the vCJD epidemic is yet unknown.
So far the disease has killed around 180 people worldwide, but numbers could reach thousands or even hundreds of thousands in the coming decades.
Prions have also been shown to be transmissible through blood transfusions and organ transplants.

Source: University of Texas Medical Branch at Galveston, 2005


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