Past research has suggested that a common spice in Asian and Middle Eastern cuisine may improve mental performance in elderly people. Now, scientists have discovered a mechanism by which this spice, called turmeric, could help the body clear plaque deposits associated with Alzheimer’s disease.
Those deposits consist of a protein called amyloid-beta. Healthy people’s bodies make the protein, but immune system cells called macrophages regularly identify, engulf, and remove it. In the new study, a team led by Milan Fiala of the Greater Los Angeles Veteran’s Affairs Medical Center found that macrophages in blood samples from people with Alzheimer’s couldn’t destroy amyloid-beta.
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Fiala’s team then compared the gene activity of these impaired macrophages with that of macrophages from healthy people. The researchers identified several genes that were less active in the impaired cells.
When they exposed these dysfunctional macrophages to a chemical in turmeric, the subdued genes switched on, restoring the ability of some of the cells to destroy amyloid-beta.
“These genes are critical for the function of macrophages, so if these genes aren’t being expressed, then macrophages wouldn’t function properly,” says Fiala.
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Many of the genes identified as vulnerable belong to a family that makes cell parts called toll-like receptors, which enable immune cells to recognize foreign microbes and other disease-causing agents.
The gene apparently most impaired by Alzheimer’s was MGAT3, which was more than 300 times as active in the healthy macrophages as in those from Alzheimer’s patients.
In separate experiments, the researchers blocked the function of MGAT3 in lab-cultured monocytes, immune cells that are similar to macrophages. The procedure prevented the cells from engulfing amyloid-beta, a critical step in clearing the plaque-forming protein.
Exposure to the turmeric chemical increased activity of MGAT3 and the receptor genes in blood samples from all 73 Alzheimer’s patients. However, only about half the samples showed a full recovery of gene activity, the team reports in the July 31 Proceedings of the National Academy of Sciences. Differences in the causes of the disease among patients could account for the variation in response, Fiala says.
“I think [the study] is very fascinating,” says Bharat Aggarwal of the M.D. Anderson Cancer Center in Houston, who has also done research on chemicals in turmeric. “There is definitely something interesting going on here.”
Whether the chemical in turmeric will affect macrophages in Alzheimer’s patients remains to be seen. The researchers didn’t test whether the compound might influence the patients’ immune systems or clear any amyloid-beta plaques from their brains. Fiala notes that the experiments involved higher doses of the compound than a person would get by eating foods prepared with turmeric.
Further studies would be needed to investigate why the macrophages of people with Alzheimer’s become impaired in the first place.