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Scientists Use Animal Parts in Many Human Drugs
04/02/2008 - By International Herald Tribune
Oink, Oink, Oink
Chopped pig pancreas may not sound appetizing. But most cystic fibrosis patients eat a refined version of it each breakfast, lunch and dinner - five large capsules a meal - to supply enzymes that their bodies do not produce.
The pills are life-sustaining for most of the nearly 30,000 people in the United States with cystic fibrosis, a hereditary disease that attacks the lungs and digestive tract.
But partly because of the drug's source there have been longstanding concerns about those capsules, according to Leslie Hendeles, a University of Florida professor of pharmacy and pediatrics who has studied them.
"What would happen if there were a virus, a pig virus, something analogous to mad cow disease?" Hendeles asked.
The recent recall of the blood thinner heparin, which has been linked to 19 deaths and whose main ingredient comes from pig intestines, has raised public awareness that even in the age of sophisticated bioengineering, certain crucial medicines are still derived from animal parts.
The concerns remain, even though, as it turned out, the heparin problem had nothing to do with the pigs. Heparin made by Baxter International was recalled after samples were found to be contaminated with a substance from animal cartilage.
Scientific Protein Laboratories, which has plants in Waunakee, Wisconsin, and Changzhou, China, supplies the active ingredient in heparin to Baxter. It is also the supplier of much of the pig- derived pancreatic enzymes used by cystic fibrosis patients.
Medical and drug scientists have long worried about animal- derived drugs, but they also know that the search for synthetic alternatives has often ended in frustration.
"A number of pharmaceutical firms are trying to eliminate all animal-sourced products from their raw material streams," said Dr. Robert Rohwer, director of a neurovirology laboratory at the U.S. Department of Veterans Affairs. "It's a very demanding task."
In the case of cystic fibrosis, though, continued concern about the possibility of animal viruses, as well as a history of unusual variations and impurities in the pig-derived pills, have led the Cystic Fibrosis Foundation to work with Altus Pharmaceuticals to develop a synthetic version of the enzyme capsules. Altus has entered the final stages of clinical studies on its drug and is planning to seek approval from the U.S. Food and Drug Administration next year to market it in the United States.
Jonathan Lieber, chief financial officer of Altus, which is based in Cambridge, Massachusetts, said its drug uses enzymes derived from microbes that come not from animals but from bacteria and fungi. The enzymes are crystallized, then reproduced in large vats similar to those used to brew beer.
Synthetic replacements are also being sought for other medical products like pulmonary surfactants, the lung fluids that are used in neonatal wards, and for raw materials used in pharmaceutical production. There are also various efforts to find synthetic versions of heparin.
History has shown that the risk of transmitting disease from animal-based drugs, while small, is not merely theoretical, according to Paul Brown, a retired senior investigator for the U.S. National Institutes of Health.
"Anytime you take a tissue or an extract process from a tissue from one species and put it into another species or even another animal, you run the risk of unwanted pathogens that you didn't know were there," Brown said.
Even before the recall, efforts were under way to find synthetic alternatives to heparin. Millions of vials of heparin are used each year in the United States to prevent the formation of blood clots during major surgery and kidney dialysis. So far, no ideal synthetic version has been found.
Arixtra, a synthetic drug that is marketed by GlaxoSmithKline and copies the most active portion of heparin, has been successfully used for some types of surgery. But besides being about 10 times as expensive as heparin - the company said Arixtra sells for about $42 for a low dose and twice that for a higher dose - it has at least one major medical drawback. Unlike heparin, Arixtra has no specific antidote to enable doctors to reverse its anti-clotting properties if a patient develops bleeding problems.
Robert Linhardt, a heparin expert at Rensselaer Polytechnic Institute who has been working to develop another synthetic alternative, said the use of pigs for heparin was of less concern to him than the issue of where the pigs came from.
"There are 700 million pigs slaughtered each year, and 400 million are slaughtered in China," Linhardt said. "It makes us dependent. Basically 70 percent of the supply of heparin is coming from China. There's very little regulatory control in China. So the reason why synthetic heparins are appealing is that they could be made in places where there is stronger regulatory control."
In some cases, companies are managing risks of animal-derived products by using animals from specially controlled herds.
A herd of superpigs is being bred by scientists at the Mayo Clinic. The National Institutes of Health are helping finance the Mayo effort, which involves 200 genetically altered pigs housed in a disease-free environment. The hope is that those pigs and their offspring may provide a variety of useful parts, including entire pig hearts for human transplant, as an alternative to human hearts that are in short supply.
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