How Tainted Heparin Slipped Through U.S. Safety Net

- MedPage Today

04/25/2008 -- Researchers here revealed today how the adulterated heparin from China evaded detection at the U.S. border and how it killed scores of patients.

Providing details of the episode that were previously disclosed by the FDA only in sweeping statements, the researchers confirmed that oversulfated chondroitin sulfate was the deadly culprit.

In companion papers published online in Nature Biotechnology and the New England Journal of Medicine, Ram Sasisekharan, Ph.D., of the Massachusetts Institute of Technology, and colleagues in the U.S. and elsewhere also explained why the tainted heparin originally passed muster.

The tainted heparin slipped past regulators because current tests look for contaminants such as protein, lipids, or DNA, Dr. Sasisekharan and colleagues said.

But oversulfated chondroitin sulfate, derived from animal cartilage, is a long sugar molecule that is structurally similar to heparin and thus was not detected, the researchers said.

To tease out the nature of the contaminant, the researchers used nuclear magnetic resonance techniques to determine its characteristics, which they described as "highly unusual" owing to the presence of both a 3-O-sulfated glucuronic acid and a tetrasulfated disaccharide repeat unit.

They compared the NMR spectrum of the contaminant, derived from studying tainted samples, to that of freshly synthesized oversulfated chondroitin sulfate and found the two spectra matched.

It is "highly unlikely that the contaminant reported here is produced naturally," they said in Nature Biotechnology.

The study "provides the scientific groundwork for critical improvements in screening practices that can now be applied to monitor heparin, thus ensuring patient safety," Dr. Sasisekharan said in a statement.

To understand the biological effects of the contaminant, the researchers studied 29 clinical lots of heparin, including 13 associated with adverse events. In blinded tests, the 13 associated with adverse events were shown to contain the contaminant, compared with none of the control lots, they said in the NEJM.

In vitro tests showed that the contaminated heparin activated kallikrein amidolytic activity in human plasma, while control samples did not. Also, when the researchers purified oversulfated chondroitin sulfate from a contaminated sample, it had the same effect.

The kinin-kallikrein pathway can lead to the generation of bradykinin, a powerful vasoactive mediator, Dr. Sasisekharan and colleagues said.

To test the possible effects in vivo, they gave pigs intravenous injections (at 5 mg/kg) of heparin, contaminated heparin, synthetic oversulfated chondroitin sulfate, or chondroitin sulfate A.

Two of the six animals treated with contaminated heparin suffered at least a 30% drop in blood pressure over the first 30 minutes after infusion, they found, while those treated with synthetic oversulfated chondroitin sulfate had even more profound drops in blood pressure.

In contrast, Dr. Sasisekharan and colleagues said, none of the pigs given control heparin had any substantive changes in blood pressure.

The physiological changes were mirrored by rapid induction of the amidolytic activity of kallikrein, they said.

The researchers also showed in vitro that the contaminant can induce the generation of C3a and C5 anaphylatoxins.

"These results provide a potential link between the presence of chemical contaminant in heparin and the clinical symptoms observed in affected patients," Dr. Sasisekharan said.

Jeremy Berg, Ph.D., director of the National Institute of General Medical Sciences, called the research "vital for public health" and a "chemical triumph."

"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," Dr. Berg said in a statement.