Roughly half of all Americans drink coffee every day, and espresso is a popular way to consume it. To "pull" an espresso shot, hot water is forced through finely ground coffee beans, creating a concentrated extract. This is often used as a base for other drinks, including the trendy espresso martini. Recent research has suggested that coffee could also have beneficial effects against certain neurodegenerative diseases, including Alzheimer's disease. Although the exact mechanisms that cause these conditions are still unclear, it's thought that a protein called tau plays a significant role. In healthy people, tau proteins help stabilize structures in the brain, but when certain diseases develop, the proteins can clump together into fibrils. Some researchers propose that preventing this aggregation could alleviate symptoms. So, Mariapina D'Onofrio and colleagues wanted to see if compounds in espresso could prevent tau aggregation in vitro.

The researchers pulled espresso shots from store-bought beans, then characterized their chemical makeup using nuclear magnetic resonance spectroscopy. They chose caffeine and trigonelline, both alkaloids, the flavonoid genistein and theobromine, a compound also found in chocolate, to focus on in further experiments. These molecules, along with the complete espresso extract, were incubated alongside a shortened form of the tau protein for up to 40 hours. As the concentration of espresso extract, caffeine or genistein increased, fibrils were shorter and didn't form larger sheets, with the complete extract showing the most dramatic results. Shortened fibrils were found to be non-toxic to cells, and they did not act as "seeds" for further aggregation. In other experiments, the researchers observed that caffeine and the espresso extract could both bind pre-formed tau fibrils. Although much more research is needed, the team says that their preliminary in vitro findings could pave the way toward finding or designing other bioactive compounds against neurodegenerative diseases, including Alzheimer's.