Plant chemicals could help Alzheimer’s

Early trials of naturally-occurring chemicals in turmeric, blueberries, Gingko biloba and green tea suggest they may help prevent and treat Alzheimer’s disease, say experts. A new review of scientific evidence indicates these antioxidants may reduce inflammation, which is a possible cause of Alzheimer’s. However, this information is based largely on in vitro and animal studies, while studies in humans have been mixed, suggesting further work needs to be done. Alzheimer’s is a devastating disease that affects 10 to 15 per cent of people aged 65 or older, and as the population ages this number is expected to triple in the next 40 years. While the disease is characterised by amyloid beta plaques in the brain, attempts to remove amyloid have not slowed down the disease, says Dr Gerald Muench, a chemist working on Alzheimer’s drug discovery at the University of Western Sydney. There is no cure and current drugs only treat the symptoms of the disease, he says. Muench says a recent focus of research has been to target inflammation, which may be one of the driving forces behind Alzheimer’s. While non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen have been shown to prevent Alzheimer’s, these present problems, says Muench. “NSAIDs are actually quite dangerous,” he says. “Who wants to take NSAIDs 10 years pre-symptomatically when they get stomach ulcers and stomach bleeding.” In addition, NSAIDs do not slow down Alzheimer’s once it has started, says Muench. Epidemiological studies have shown diets rich in plant foods that are high in antioxidants lowers the risk or slows down progression against Alzheimer’s. So the search has been on to find plant chemicals that have the most powerful effect. “Just imagine, instead of eating healthy foods you could just take a pill. That would make prevention much much easier,” says Muench. During the new study, he and colleagues reviewed available evidence on the effects of chemicals called catechins and proanthocyanidins that occur in green tea, curcumin in turmeric, extracts enriched in bacosides from the Aryuvedic herb Brahmi (Bacopa monnieri), and flavone glycosides from Ginkgo biloba. The researchers also looked at omega-3 polyunsaturated fatty acids, which reduce inflammation in a different way to the plant chemicals. Their findings were published recently in the journal CNS & Neurological Disorders – Drug Targets. Muench says in vitro and animal evidence shows these chemicals suppress the production of cytokines and other inflammation markers present in the brains of people with Alzheimer’s. By contrast, he says, NSAIDs only suppress the production of prostaglandins, which are markers of inflammation in the periphery of the body. Muench says recent evidence suggests inflammation in Alzheimer’s begins in the periphery before it “spills over” to the brain, which probably explains why NSAIDs still show some effect in preventing Alzheimer’s. The chemicals studied also suppress production of prostaglandins, he says, which means they hold promise in both preventing and treating Alzheimer’s. In addition to their anti-inflammatory action, the chemicals have also been shown to enhance cognition in animal studies, he adds. Human trials, however, have yielded mixed results, says Muench, and many of these trials are not well-conducted. He says further human studies are required given their promise as a “safe strategy to delay the onset of Alzheimer’s disease”. Alzheimer’s researcher Dr Bryce Vissel from the Garvan Institute of Medical Research supports the call for further research. “People are aware of inflammation now as an increasingly important target to investigate,” he says. Vissel says each of the chemicals Muench and colleagues report on have a “good theoretical basis” for blocking inflammatory processes in the brain, and animal studies show they generally have a good effect. But he emphasises it is very unclear whether they are effective in humans. “There are some studies that suggest they might have a benefit, there are other studies that show there are no benefits,” says Vissel. He says the best available human evidence to date is for curcumin (in turmeric) but studies suggest the natural form of the chemical may need to be modified to increase its availability.

ABC Science News, 15 October 2014 ; ;