NEW YORK (Reuters Health) - Researchers have shown that a common anesthetic gas can cause fragments of a normal brain protein called amyloid-beta to clump together, which is thought to be the main problem underlying Alzheimer's disease. Intravenous anesthetics have less of an effect, the team reports in the journal Biochemistry.

"Physicians should pay attention to the type of anesthetics they use, especially for a long surgery," Dr. Pravat K. Mandal from Western Psychiatric Institute and Clinic, Pittsburgh, told Reuters Health. "Our biophysical study shows clearly with the help of the state-of-the-art technology that inhaled anesthetics isoflurane and halothane are not good."

Mandal and colleagues conducted a series of lab experiments using nuclear magnetic resonance to investigate the reaction of amyloid-beta peptides to the inhaled anesthetic isoflurane and the intravenous anesthetics propofol and thiopental.

The team found that the peptides aggregated together after 10 to 30 hours' exposure to isoflurane, depending on the concentration of the gas and the size of the protein fragments.

The effect was seen with propofol after exposure for 48 hours, but no clumping was seen with thiopental, the researchers report.

"A number of clinical reports have suggested a possible link between anesthesia and the subsequent onset of senile dementia," the investigators say in their article. However, they note, "epidemiological studies have failed to demonstrate a relationship between frequency and/or duration of exposure to anesthesia and increased risk of Alzheimer's disease."

It seems more research is needed to see if anesthesia is a concern with regard to dementia in real life. "There is no clinical database at present for documentation of post-operative cognition, type of anesthesia used, duration of anesthesia, occurrence of dementia on follow-up," Mandal said. "We need funding for this database."