09 July 2010

Redeeming Older Brains: Possible New Alzheimer's Wonderdrugs

New nerve cells are constantly born in the hippocampus, but even in the normal adult brain, most of these newborn neurons die before they become functional.

And they fare much worse in the hippocampus of Alzheimer's patients.

Physical activity, an active social life and other intellectually and emotionally enriching experiences promote the birth and maturation of new neurons.

The scientists wanted to find compounds that can protect newborn neurons from dying.

P7C3 was selected from among about 1,000 compounds tested on mice.

The compound was found to help the survival of neurons in adult mice, which were genetically engineered to lack a gene that is crucial for the survival of newborn nerve cells. _IndiaToday

University of Texas Southwestern have reported in Cell the discovery of a molecule -- P7C3 -- that has the ability to protect brain cells, and trigger the production of new neurons. The scientists believe that new compounds in the same class as P7C3 may hold the key to slowing or temporarily reversing the progress of Alzheimer's Disease and other neurodegenerative conditions.
In a new study published today in the journal Cell, researchers screened 1000 molecules in mice to see which ones enhanced production of new neurons in a brain area involved in learning and memory. This region, known as the hippocampus, is one of two spots known to birth new neurons in the adult mammalian brain. It takes 2 to 4 weeks for the cells to migrate to the appropriate location and integrate into the existing neural circuitry, and many of them die along the way.

The researchers found that one compound, dubbed P7C3, protected these newborn neurons from dying. When given to mice genetically engineered to have very little new nerve cell growth, the compound seemed to repair the abnormal hippocampus. It could also increase birth and survival of new neurons in older rats, according to a press release from UT Southwestern Medical Center. The animals also had improved memory: they could better remember the location of a platform submerged in water, a standard test of learning and memory in rodents.

According to a release from the journal Cell, where the paper was published;

Two other drugs (Dimebon and Serono compounds) - both of which bear structural similarities to P7C3 -also encourage the growth of new neurons. It's tempting to think that all three compounds work in the same way.
In fact, Dimebon first came to the attention of researchers based on anecdotal reports by Russian physicians that the drug may ameliorate the symptoms of age-related cognitive decline. Unfortunately, unpublished reports from a phase 3 clinical trial have since failed to provide evidence that the drug could stave off the memory loss that comes with Alzheimer's disease.

In light of the new findings, it may be worth another look. "The speculative idea that these chemicals share a common mode of action will only be rigorously tested upon identification of their molecular target(s)."

Pieper, McKnight and colleagues tested more than 1000 small molecules in living mice. One of the compounds, designated P7C3, corrected deficits in the brains of adult mice engineered to lack a gene required for the survival of newborn neurons in the hippocampus. Giving P7C3 to the mice reduced programmed death of newborn cells -- normalizing stunted growth of branch-like neuronal extensions and thickening an abnormally thin layer of cells by 40 percent. Among clues to the mechanism by which P7C3 works, the researchers discovered that it protects the integrity of machinery for maintaining a cell's energy level.
To find out if P7C3 could similarly stem aging-associated neuronal death and cognitive decline, the researchers gave the compound to aged rats. Rodents treated with P7C3 for two months significantly outperformed their placebo-treated peers on a water maze task, a standard assay of hippocampus-dependent learning. This was traced to a threefold higher-than-normal level of newborn neurons in the dentate gyrus of the treated animals. Rats were used instead of mice for this phase of the study because the genetically engineered mice could not swim.
Prolonged treatment of aged rats with P7C3 also enhanced the birth of new neurons. "Aged rats normally show a decline in neurogenesis associated with an inability to form new memories and learn tasks," Pieper explained.

In their study, rats treated with P7C3 each day showed evidence of an increase in the formation of newborn neurons and significant improvements in their ability to swim to the location of a missing platform, a standardized test of learning and memory in rats.

The researchers pinpointed a derivative of P7C3, called A20, which is even more protective than the parent compound. They also produced evidence suggesting that two other neuroprotective compounds eyed as possible Alzheimer's cures may work through the same mechanism as P7C3. The A20 derivative proved 300 times more potent than one of these compounds currently in clinical trials for Alzheimer's disease. This suggested that even more potent neuroprotective agents could potentially be discovered using the same methods. Following up on these leads, the researchers are now searching for the molecular target of P7C3 -- key to discovering the underlying neuroprotective mechanism. _ScienceDaily
The study was two-tiered: First the scientists screened over a thousand small molecules in knockout mice, to find the one that provided the best protection for new hippocampal neurons. Then they tested the compound in senescent rats, looking for both behavioural improvements and better survival of new hippocampal neurons. They were successful on all counts.

H/T Brian Wang of NextBigFuture

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