Scientists at Baylor University Medical Center in Texas, US, have developed a novel method of delivering an insulin gene into the pancreas of experimental rats in a potential breakthrough in diabetes research. The researchers injected the rats with microscopic spherical shells enclosing a gene that codes for insulin, which is not produced correctly in the pancreas of diabetes sufferers. The team then directed an ultrasonic pulse at the rats' pancreas, which broke the 'bubble' enclosing the new DNA. This method allows the gene to be delivered to a specific location, crucial in diabetes and until this point one of the biggest barriers to gene therapy.
Previous attempts at gene therapy have relied on the use of harmless viruses engineered to carry the healthy gene. These viruses are injected into the animal or person and the harmless virus and the new, desirable, gene become incorporated into the host's DNA. Gene therapy has a controversial history as this method has the potential for a dangerous immune response, thought to be responsible for the death of teenager Jesse Gelsinger in 1999 whilst undergoing gene therapy for a rare liver disorder. As well as the potential for a dangerous immune response this method does not allow the gene to be targeted to a particular location or organ. Pancreatic cells are the only cells in the body which are fine-tuned to release the correct levels of insulin in response to food intake. If other cells in the body were to pick up and start producing insulin the results could be disastrous. Speaking to the New Scientist, Mark Kay, from the Stanford University School of Medicine, explained that 'the results would be willy-nilly - you'd more likely die from hypoglycaemic shock than the high blood sugar levels' that characterise diabetes.
The team at Baylor injected the bubbles - made with a shell of water insoluble molecules - into rats. The bubbles that were initially injected contained an inert circular piece of DNA - known as a plasmid - engineered with a gene that codes for a fluorescent protein marker. The technique, known as 'ultrasound targeted microbubble destruction', involves using ultrasound waves directed at islet cells in the pancreas. These waves break bubbles in nearby blood vessels which consequently release the gene; the waves also break holes in the membranes of adjacent cells creating a passage for the genes to enter through. After breaking the bubbles in the rat pancreases using the directed ultrasound pulse, researchers dissected the animals and found higher levels of fluorescence in the pancreas than in other areas.
In further experiments the researchers injected bubbles containing a plasmid which had the human gene for insulin engineered into it. Again, after bursting the bubbles researchers dissected the rats and found significantly elevated levels of human insulin in the rodents. The animals' blood sugar levels also dropped compared with rats that were used as controls. 'This work shows that genes can be targeted to pancreatic islets in living, adult animals', commented Paul Grayburn, the cardiologist at Baylor who led the study, published in the Proceedings of the National Academy of Sciences. The next big challenge with this therapy will be developing it so that the effect lasts for a long time - currently the protein produced by the new gene can only be detected for around three weeks after treatment.
