Trials of what was the most promising vaccine against Alzheimer鈥檚 disease have been dropped, after 15 patients developed symptoms of brain inflammation.
Elan Corporation鈥檚 experimental vaccine, AN-1792, had been shown to clear amyloid beta plaques in animals. The plaques are characteristic of the brains of patients with Alzheimer鈥檚 disease. Human safety tests conducted in 2000 suggested the vaccine was safe, and an international trial to investigate its effects on the immune system of patients with mild to moderate Alzheimer鈥檚 disease was launched.
But, as reported by 快猫短视频 in January 2002, the trial was suspended after four of 97 patients developed central nervous system inflammation. Symptoms typically appeared several weeks after the second injection, and since January, another 11 patients have become ill.
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鈥淥ur decision to first suspend dosing, and now permanently discontinue dosing, remains in the best interests of the health and safety of patients,鈥� says Ivan Lieberburg, Elan鈥檚 chief scientific officer. 鈥淲e are hopeful that our alternative Alzheimer鈥檚 approaches will continue to advance in development.鈥�
David Smith, professor of pharmacology at Oxford University and chairman of the UK鈥檚 Alzheimer鈥檚 Research Trust, says the abandonment of the trial is 鈥渧ery disappointing. I know of no other treatment being developed that will actually attempt to reverse the disease process, which is basically what Elan was hoping to do.鈥�
Inflammatory response
AN-1792 contains a synthetic form of beta amyloid protein 鈥� the main component of the protein plaques that form in the brains of Alzheimer鈥檚 patients. In animals, the vaccine worked by stimulating an immune response to the protein.
Some Alzheimer鈥檚 researchers feared that vaccinating against a protein that exists in the brain might produce the kind of side-effects found in the 15 patients. 鈥淚n any vaccination, there鈥檚 a risk of some inflammatory response,鈥� says Smith. 鈥淎nd when you鈥檙e doing vaccinating against something that鈥檚 already present in the brain, there鈥檚 the worry that inflammation could happen.鈥�
Richard Harvey, director of research at the UK鈥檚 Alzheimer鈥檚 Society says he remains optimistic that stimulating the immune system to target amyloid beta could work safely.
Lieberburg speculates that the vaccine might have over-stimulated the immune response in some people. Injecting specific doses of beta amyloid antibodies, rather than stimulating the body to produce its own antibodies, might be a solution, he says.
Preventing Alzheimer鈥檚
Preventing Alzheimer鈥檚 disease developing in the first place might be a more promising long-term approach, says Smith.
A recent prospective study of more than 1000 people in the US found that those with high blood levels of an amino acid called homocysteine had double the risk of developing Alzheimer鈥檚 between eight and 11 years later. A high level of homocysteine indicates a low intake of B12 and folate. Previous work has shown that homocysteine can be toxic to nerve cells.
The US National Institute on Aging is now planning a trial of homocysteine-lowering vitamins in people with Alzheimer鈥檚.
But Smith thinks trials on people with mild memory impairment but without full-blown dementia should now be conducted. Each year, about one million older people in Europe develop memory problems that do not significantly impact on everyday life. Up to 80 per cent of these people develop Alzheimer鈥檚 within five years, he says.