Pramiracetam increases nitric oxide synthase (NOS) activity in the cerebral cortex of the rat [1]. NOS is the enzyme that catalyzes the formation of NO from oxygen and arginine is nitric oxide synthase [2]. NO has both positive and negative effects in the brain, as discussed in the following article [3]:
Scientists are finding evidence that NO participates in the brain cell damage that occurs in a variety of neurological ailments, such as stroke and Parkinson's disease. The new research is leading to:
• Targeted brain cell-protecting therapies that interfere with NO chemistry.
• Clearer insight into the complex behavior of NO.
• A better understanding of how gas compounds can impact biology.
For years, researchers were convinced that the tiny molecule consisting of a mere two atoms had no business in the body and brain. More complex compounds run many physiological processes so it made no sense that a gas could have an effect. Then in 1977 researchers determined that some of the drugs that are used to treat heart attacks by widening blood vessels, happen to release NO. Could NO naturally act to widen blood vessels in the body? Following a series of experiments, researchers concluded in 1986 that NO, indeed, regulates the widening of blood vessels. Research on NO snowballed. It turns out that NO influences a wide range of physiological functions. Among them, it appears to help the mechanisms that lead to memory and penile erection. Yes, NO mechanisms are behind the success of the well known impotence drug, Viagra.
Unfortunately you can get too much of a good thing.
Some researchers believe that many brain disorders can trigger an overproduction of NO. And the excess gas ends the life of brain cells known as neurons.
The first inkling of NO's sinister side came in 1991 when researchers found that they could block the neuron death that normally occurs in a cell model of stroke by inhibiting NO production. Specifically, they blocked the activity of an enzyme, known as nitric oxide synthase (NOS). This enzyme synthesizes the NO gas. Researchers have difficulty blocking NO directly because the gas has a very short lifespan in the neuron.
Additional research on animals also shows that NO is involved in neuron death. For example, studies determined that blocking NOS in the brain impedes the cell death that occurs from stroke as well as in other disorders such as Parkinson's disease.
Researchers now are actively investigating compounds that can derail NOS, in order to create new therapies that will control NO and protect human neurons in a range of brain ailments.
Scientists also are investigating other participants in NO's course of action in order to identify additional treatment targets. One participant that may hold promise is the enzyme called PARP. Some researchers believe that excess NO creates nicks and breaks in the DNA of neurons. The injuries in this important molecule activate PARP, which depletes energy sources in the cell, causing cell death. Scientists found that doses of small molecules that inhibit PARP reduce brain damage in a variety of animal stroke models. In addition, genetically-altered mice that do not produce PARP are protected from the damage of experimentally-induced stroke and Parkinson's disease.
Perhaps pramiracetam was taken off the market because it caused neuronal death, rather than protecting neurons.
References:
[1] Systemic administration of pramiracetam increases nitric oxide synthase activity in the cerebral cortex of the rat
by Corasaniti MT, Paoletti AM, Palma E, Granato T, Navarra M, Nistico G.
Faculty of Pharmacy, University of Reggio Calabria, Catanzaro, Italy.
Funct Neurol 1995 May-Jun;10(3):151-5
[2] http://www.aecom.yu....eau/nos/nos.htm
[3] http://www.sfn.org/c...tric.oxide.html