Cell Culture Experiments Link Florane to Dementia

BOSTON, Feb. 7 -- A commonly used general anesthetic creates a vicious cycle of cell death and deposits of Alzheimer's disease proteins -- at least in cell culture.

In laboratory experiments with cultured neuroglioma cells, Florane (isoflurane) was linked to increases in apoptosis as well as generation and aggregation of amyloid-?, whose deposits in the brain are characteristic of Alzheimer's, according to Zhongcong Xie, M.D., Ph.D., of the Massachusetts General Hospital Institute for Neurodegenerative Disease here.

Because the experiments were conducted in cell culture, Dr. Xie cautioned, it's too early to say whether the anesthetic acts the same way in people.

Nevertheless, "our studies have shown that isoflurane may induce a vicious cycle of apoptosis, amyloid-? generation, and further rounds of apoptosis leading to cell death," he said.

If research in vivo supports the results, he added, it would imply that "caution (should) be used in choosing this anesthetic for elderly patients, who already are at increased risk for Alzheimer's and for postoperative cognitive dysfunction."

In a series of experiments reported in the Feb. 7 issue of Journal of Neuroscience, Dr. Xie and colleagues attempted to tease out the relationship between Florane, apoptosis, and amyloid-?.

They had previously shown -- in H4 neuroglioma cells that expressed the precursor to amyloid-? (H4-APP cells) -- that exposure to Florane increased generation and aggregation of amyloid-?, as well as increasing apoptosis.

But in nave H4 cells -- which didn't express the precursor protein -- they found that exposure to 2% Florane for six hours had no effect on amyloid-?. On the other hand, Florane caused a 240% increased activation of the enzyme caspase-3, which is a key player in apoptosis.

Compared with control cells, the difference in caspase-3 was significant at P<0.01, Dr. Xie and colleagues said, implying that Florane can kick-start apoptosis without any effect on amyloid processing.

The finding was confirmed when they did the same experiment in H4-APP cells treated with a caspase inhibitor. Previously, Florane had caused increases in generation and aggregation of amyloid-?, but blocking the caspase pathway significantly diminished the effect (P<0.05).

The anesthetic also increase the levels of two enzymes that cleave the amyloid precursor protein, the researchers found.

Finally, Dr. Xie and colleagues said, adding amyloid-? to nave H4 cells and then treating them with 2% Florane for six hours markedly increased the activation of caspase-3 in a dose-dependent manner.

Specifically, the cells were incubated with amyloid-? for an hour in three concentrations -- 2.5, 5.0, and 7.5 ?M -- followed by treatment with Florane. Compared with controls, caspase activation was increased by 403%, 612%, and 1223%, respectively; the first two increases were significant at P<0.05, while the last was significant at P<0.01.

That last finding, combined with the link to caspase-3, implies that "increased (amyloid-?) generation induced by isoflurane can further potentiate the isoflurane-induced apoptosis, leading to a vicious cycle," the researchers said.

Rudolph Tanzi, Ph.D., of Massachusetts General Hospital, a co-author, said more research is needed before physicians will know what role Florane might play in the development of Alzheimer's or other dementias.

"We need to conduct in vivo studies before we can determine whether these results might be relevant to the development of delirium or Alzheimer's disease in human patients," he said.