Every day, in Alzheimer’s labs and clinics around the world, researchers conduct target practice. One of their targets is beta amyloid, the sticky protein many scientists think causes Alzheimer’s. This target practice is somewhat of a trial and error process, involving educated guesses about which weapons might work against beta amyloid and other substances and conditions implicated in Alzheimer’s.
One such target practice is directed from the Roskamp Institute, only thirty miles south of where I live. Working with the Trinity College Institute of Neuroscience in Dublin, Ireland, Dr. Michael Mullan and his colleagues are conducting a clinical trial of the calcium channel blocker Nilvadipine to see whether it reduces beta amyloid and improves memory in Alzheimer’s patients.
Calcium channel blockers are drugs used to treat high blood pressure and other diseases. Some studies have shown that these medications might be useful in preventing or treating dementia. A follow-up to the Systolic Hypertension in Europe trial showed that for people with high blood pressure, long term use of a calcium channel blocker may cut the risk of developing dementia by 55%. This makes sense, because scientists have observed toxic levels of calcium in Alzheimer’s brains. “Calcium overload in cells is lethal, says Dr. Mullan, “and this is the final pathway by which cells may die in Alzheimer’s.”
It’s not clear whether calcium channel blockers as a group help preserve memory. Results from the Canadian Study of Health and Aging showed that people taking these drugs were more likely to suffer from cognitive decline. Another study concluded that patients taking blood pressure medicines, including calcium channel blockers, performed worse on cognitive tests than did those taking other drugs. The conflicting results of these studies might be because each drug in this class has different effects.
The fact that Nilvadipine is a calcium channel blocker may be irrelevant anyway. “Nilvadipine's anti-amyloid effects do not seem to be due to the calcium channel blocking of drugs,” says Dr. Mullan. It’s not clear how Nilvadipine might reduce amyloid in Alzheimer’s brains, but it may be related to increased blood flow.
“This drug increases cerebral blood flow in rodents and humans, and we wonder whether there is a link between the two,” Dr. Mullan says. “It could be that there is increased clearance of amyloid from the brain due to increased blood flow. If that is the case, we don't know what the mechanism would be. However, the most likely reason that we see reduced amyloid in the brains of mice is that Nilvadipine directly reduces amyloid production. We've seen this effect in a number of cell types.”
The trial of Nilvadipine in 150 people diagnosed with mild to moderate Alzheimer’s is being carried out in Ireland, where the drug is available by prescription [it’s not currently approved for use in the US]. Doctors will measure the level of amyloid in these patients’ blood. If the levels of amyloid are higher in the blood of patients taking Nilvadipine compared with those not taking the drug, this may mean that it is clearing amyloid from the brain. Doctors will also monitor any changes in blood flow in the brains of trial participants, as well as blood pressure and performance on cognitive tests.
In the US, the Roskamp Institute is also looking for volunteers who have been diagnosed with Alzheimer’s. These volunteers won’t receive any medication, but will give blood to provide data to be used in the trial.
When my father had mild dementia, I wondered whether increased blood flow to his brain would help his memory. I asked Dr. Mullan if Dad would have been eligible for this trial, given that his pulse rate and blood pressure were low, not high. “It's possible (although there are many alternative reasons why your father may have had his cardiovascular signs) that increasing cerebral blood flow would have been beneficial. However, the blood pressure lowering effect of Nilvadipine would probably have precluded him from the study,” he says.
Dad also had cerebral amyloid angiopathy (CAA), and it’s not clear how Nilvadipine and other drugs thought to reduce amyloid would affect CAA patients. In CAA, beta amyloid similar to that in Alzheimer’s plaques is deposited on the walls of the blood vessels in the brain. The protein deposits cause the vessel walls to crack, allowing blood to leak out. Every hemorrhage, large or small, damages brain cells and can cause dementia as well as major hemorrhagic strokes like the one Dad had. “The vessel walls are weakened by amyloid and removing it (depending on how it is removed) might weaken them further,” says Dr. Mullan. “This is a very difficult area to predict, and clinically we will see when we have potent anti-amyloid drugs.”
Memory Pharmaceuticals is testing a similar drug called Mem 1003, and this trial is currently recruiting patients in the US. The company hasn’t responded to my request for information. [11/01/06 Note: Memory Pharmaceuticals says that Mem 1003 works by modulating the amount of calcium that enters neurons in the brain. This seems to be a different mechanism for treating dementia than the potential anti-amyloid action of Nilvadipine.]
It’s too late for my father, but I hope all this target practice means that multiple treatments for Alzheimer’s and dementia will be ready in time to help others who have dementia now. With its established safety record, Nilvadipine could be available fairly quickly. But first it must be proven effective in this study and in future trials.