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Last Updated: Dec 27th, 2006 - 19:07:47 |
US scientists have genetically engineered pigs in a way that they increase production of heart healthy omega-3 fatty acids in their bodies, according to a new study scheduled to appear in the April 6 issue of the prestigious journal Nature Biotechnology.
The cloned transgenic pigs created in the study produce high levels of omega-3 fatty acids from omega-6 analogs while keeping the total and other types of fatty acids unchanged.
Pigs and other animals such as sheep, cows, goats, rabbits, horses and dogs have been cloned, but cloned pigs that produce omega-3 fatty acids have not been reported previously.
Because of the study, pork products such as bacon, ham and others that are loaded with artery-clogging s aturated fats and c holesterol may become beneficial to cardiovascular health in the future.
Omega-3 fatty acids, particularly the long chain n-3 such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) found mainly in oily fish such as salmon, mackerel, sardines and albacore tuna, have been well known to boost the brain development in children and prevent cardiovascular disease in a dults. American Heart Association recommends eating f ish at least twice a week.
The concern, however, is that f ish gets increasingly polluted with mercury, d ioxin, P CBs and other environmental t oxins. The f ish supplies are also diminishing. Because of this, quality fish that can provide high amounts of omega-3 fats is quite limited.
The current study may help people, at least those who enjoy pork products, to improve the ratio of omega-6 to omega 3 fatty acids in their diet. Cloned pigs as those created for the current study may even become an alternative and safe source of omega-3 fatty acids. But for now, the only way for humans to have the benefits of omega-3 fatty acids is by taking dietary supplements or by eating a few types of oily fish.
"While fish, especially salmon and tuna, is one of the best food sources of omega-3 fatty acids, we have been warned to limit consumption because of high mercury levels," said Yifan Dai, MD, Ph.D., one of the two corresponding authors, professor of the University of Pittsburgh School of Medicine. "These animals (cloned pigs) could represent an alternative source as well as be an ideal model for studying cardiovascular disease and autoimmune disorders,"
As the first step of the study, Dr. Dai and colleagues transferred a worm gene known as fat-1 into pig primary fetal fibroblasts, the cells that give rise to connective tissue. The gene encodes an n-3 fatty acid desaturase that converts the more abundant, yet less desirable omega-6 fatty acids into omega-3 fatty acids.
Afterwards, Randy Prather, Ph.D. professor of the University of Missouri-Columbia (MU) National Swine Resource and Research Center and colleagues, created the cloned pigs from the cells with the worm fat-1 gene inserted using a method called nuclear transfer cloning.
Tissues from the pigs were then analyzed for omega-3 fatty acids by the laboratory of Jing X. Kang at Massachusetts General Hospital (MGH), and the laboratories of Dr. Dai and Rhobert Evans, Ph.D., at the University of Pittsburgh.
High levels of omega-3 fatty acids are formed in some parts of pigs examined.
Researchers found that in the tail tissues, the total of omega-3 fatty acids in the cloned piglets is four times higher than that in the wild type, 8.59 percent versus 2.18 percent. The ratio of n-6 to n-3 in the cloned pigs was five times lower than that for the wild type, 1.69 versus 8.52, a sign that the fats of the n-3 pigs are much heart healthier for human consumption, according to the study paper.
"Livestock with a health ratio of omega-3 to omega-6 fatty acids may be a promising way to re-balance the modern diet without relying solely on diminishing fish supplies or supplements," said Dr. Kang.
The ratio of omega-3 to omega-6 fatty acids in the American diet is well known to be dangerously low, which is believed to attribute to many diseases including c oronary a rtery disease, d iabetes, c ancer, a rthritis and d epression.
The conventional method to increase omega-3 fatty acids in pigs is to increase omega-3 in the pig feed with flaxseed, f ish oil or f ish meal. But such a method, despite increasing the n-3 fatty acids in pigs to 6 percent from normally 1 percent, would increase alpha-l inolenic acid (ALA), which alone would affect the pork f lavor. The increase of n-3 fatty acids in the cloned pigs would not affect the pork flavor, researchers say in their paper.
Although the cloned pigs still produce same amounts of saturated fats, which are not as healthy as omega-3 fatty acids, people who have a habit of eating pork or pork products will still benefit from the n-3 rich products even if the pork fats are not as good as f ish oil.
"If these animals are put into the food chain, there could be other potential benefits. First, the pigs could have better cardiovascular function and therefore live longer, which would limit livestock loss for farmers. Second, they could be healthier animals for human consumption," said Dr. Prather.
But consumer groups fear that cloning techniques may not always create healthy a nimals. In their paper, researchers disclosed that a few piglets developed symptoms of heart failure a couple of weeks after birth, which the researchers believe was caused primarily by an interatrial septal defect commonly associated with the cloning process.
Another question that remains to be answered is, would consumers accept the cloned pork even after the cloned pigs prove safe in the end? Previous public opinion surveys have showed the majority of consumers would not buy cloned cow and pig products. But no one knows for sure how the consumers' attitude will change in the future.
The Food and Drug Administrating has not yet approved any genetically engineered a nimals as foods even though the FDA tends to believe the cloned a nimals are as safe as their conventional counterparts.
The agriculture industry has still observed a voluntary FDA moratorium on using cloned a nimals as human foods. It may take years for the genetically engineered a nimals such as the omega-3 producing pigs to get into the human food chain.
Another way to generate omega-3 fatty acids might be cultivating genetically engineered plants. Some scientists have been exploring the possibility of using genetically m odified plants to produce long chain n-3 fatty acids. Natural plant sources such as f laxseed, c anola, and n uts offer only short chain n-3 fats, which are viewed as inferior to the long chain n-3.
Regardless, the cloned pigs may offer an opportunity for scientists to study the effect of omega-3 fatty acids on the cardiovascular health.
"Pigs and humans have a similar physiology," said Dr. Prather, one of the two corresponding authors, distinguished professor of reproductive biology in MU's College of Agriculture, Food and Natural Resources.
"We could use these animals as a model to see what happens to heart health if we increase the omega-3 levels in the body. It could allow us to see how that helps cardiovascular function," Prather added.
The omega-3 pigs will now provide researchers with opportunities to conduct studies that were previously impossible. Harold Laughlin, Ph.D., char of Department of Biomedical Sciences at MU's College of Veterinary Medicine plans to use the n-3 pigs for his research to determine how higher levels of omega-3 fatty acids and exercise could affect the cardiovascular system.
Source: Liangxue Lai et al. 2006 Generation of cloned transgenic pigs rich in omega-3 fatty acids, published online on March 26, 2006.
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