Writing in the Pharmaceutical Biology journal, the researchers point to the extract’s efficacy in reducing inflammation in the brain – a key observation in the condition’s development.
“Our findings suggest that traditional medicines will provide new chemicals able to temper Alzheimer's disease progression," said Dr Wayne Carter, lead study author and lecturer at the University of Nottingham.
“As a population we are living longer, and the number of people with dementia is growing at an alarming rate.”
Traditional African remedy
The team took extracts from the leaves, stem and roots of the Carpolobia lutea, more commonly known as cattle stick.
It is a small shrub or tree found native to Central and West Africa. Traditionally, the root is used to ease genitourinary infections, gingivitis, and waist pains.
The use of plant extracts, as a potential source of disease-fighting polyphenols and flavonoids is not new. Herbal medicines have been used to address declining cognitive functions for many centuries.
Botanicals and derived preparations made from plants, algae, fungi or lichens have become widely available on the EU market in the form of food supplements.
While these food supplements, which include ginkgo, garlic, St. John’s Wort and ginseng, have a long history of use in Europe, worries still exist regarding their safety and quality.
These include the risk of chemical or microbiological contamination and the need to ensure that concentrations of bioactive agents are within safe limits.
Current EU rules governing botanical classification have hit choppy waters as the industry and regulators have argued over its classification as either a medicine or food.
The debate has been exacerbated by confusion as to what kind of evidence is needed to prove their safety.
The European Food and Safety Authority (EFSA) have been criticised for its indecision as how best to handle botanical evaluation.
It has overruled numerous botanical health claims as well as suspending hundreds more, some for as long as seven years, as it demands more stringent proof of efficacy.
This latest study began by taking the plant stem, leaves and roots and subjecting them to a series of solvent extractions.
The method is designed to isolate the phenolic and flavonoid contents that are most concentrated in these plant structures.
Along with anti-inflammatory activity, the team were also looking for anti-cholinesterase activity, which reduces the breakdown of the neurotransmitter acetylcholine (AChE).
In patients with Alzheimer's disease and other diseases such as Parkinson's disease the activity of the neurotransmitter acetylcholine, is reduced, leading to problems with memory and attention.
The team screened for anti-AChE activity across a concentration range of 0.02–200 micrograms per millilitre (μg/mL).
In addition to total phenolic and flavonoid content, plant free radical scavenging activity and reducing power were determined.
Cell toxicity was also assessed using human hepatocytes.
Results indicated the most potent inhibitory anti-AChE activity was located in the stem, where a crude ethanol extract and hexane stem fraction oil achieved a concentration of 140 μg/mL.
In addition, the leaves contained a chloroform leaf fraction concentration of 60 μg/mL.
The plant’s roots achieved a methanol, ethyl acetate and aqueous root fraction concentration of 0.3–3 μg/mL.
Dose-dependent free radical scavenging activity and reducing power were observed with increasing stem, leaf or root concentration.
Total phenolic contents were the highest in the stem, while total flavonoid content was the highest in the leaves.
At 1 μg/mL, only the crude ethanol extract oil was significantly cytotoxic to hepatocytes.
Less toxic than drugs?
What is IC50
The half maximal inhibitory concentration (IC50) measures the effectiveness of a chemical or compound in inhibiting a certain biological or biochemical function.
The figure represents the concentration of a drug that is required for 50% inhibition in vitro.
“Root extracts of C. lutea show particular promise for provision of a useful AChE inhibitor since in a partially purified state their IC50 was only an order of magnitude less potent than the anti-AChE drug eserine,” the team commented.
“By comparison, the anti-AChE drug tacrine has an IC50 value of less than 1 μM against human AChE.”
The team commented that the antioxidant capacity of certain stem and root extracts/fractions at 50 μg/mL was comparable with vitamin C (ascorbic acid).
They also said that at concentrations of 6.25–25 μg/mL, some of the stem and leaf extracts of C. lutea were oxidative in nature, indicative of the presence of pro- as well as anti-oxidant chemicals.
“C. lutea remains a potentially beneficial pharmacotherapy that could be further developed for the treatment of AD and/or other diseases such as Parkinson’s and myasthenia gravis that also require agents able to address cholinergic deficits,” the study concluded.
Source: Pharmaceutical Biology
Published online ahead of print: doi.org/10.1080/13880209.2017.1339283
“Anti-acetylcholinesterase activity and antioxidant properties of extracts and fractions of Carpolobia lutea.”
Authors: Wayne Carter et al