(Updates throughout with New England Journal of Medicine study)
By Maggie Fox, Health and Science Editor
WASHINGTON, April 23 Researchers said they had identified a chemical contaminating the blood-thinner heparin from China and also shown how it could cause a sometimes fatal allergic reaction in people.
The contaminant is oversulfated chondroitin sulfate, the researchers said, confirming earlier U.S. Food and Drug Administration findings.
It appears to activate two inflammatory pathways, causing severe allergic reactions and low blood pressure, Ram Sasisekharan of the Massachusetts Institute of Technology and colleagues reported in the New England Journal of Medicine.
"These results provide a potential link between the presence of chemical contaminant in heparin and the clinical symptoms observed in affected patients," Sasisekharan said in a statement.
Sasisekharan and another team also used a standard analytical method to find the contamination, which had been difficult to pinpoint before, and said it might be used to screen other batches.
The tainted heparin had been used by at least 81 U.S. patients who died soon afterwards. They had classic allergic reactions, with plummeting blood pressure, swelling of the larynx and other severe symptoms.
Their cases forced manufacturer Baxter International (BAX.N) to recall the commonly used blood-thinner and caused a diplomatic squabble between U.S. and Chinese officials.
The chondroitin contaminant, derived from animal cartilage, has a structure very similar to that of heparin, taken from pig intestines. It thus cannot be identified with the tests normally used to inspect batches of heparin.
NEW SCREENING METHODS
"Our analysis suggests effective screening methods that can be used to determine whether or not heparin lots contain the contaminant reported here," Sasisekharan and colleagues wrote in the journal Nature Biotechnology.
They tested oversulfated chondroitin sulfate taken from FDA samples and found it directly activated an extreme allergic reaction, called anaphylaxis, in pigs .
They also freeze-dried the heparin and used a combination of nuclear magnetic resonance imaging and liquid chromatography-mass spectrometry to analyze its structure.
Oversulfated chondroitin sulfate is derived from a popular supplement used to treat arthritis, among other things. It can resemble heparin's active ingredient but is much cheaper, leading some experts to suspect it was added deliberately.
Chinese officials said on Monday they had tested batches of heparin used by patients who reported health problems and only some of these batches contained the contaminant. But the FDA countered this.
"In addition to being vital for public health, identifying the recent impurity in heparin was a chemical triumph," said Dr. Jeremy Berg, director of the National Institute of General Medical Science, which helped pay for the study.
"The research team accomplished this difficult task by using a unique combination of scientific techniques that might in the future be used to detect other impurities in pharmaceutical materials."
(Editing by Cynthia Osterman)