An “extract from poisonous Foxglove can protect against high blood pressure and heart failure”, the Daily Mail has reported. It does this by enhancing the mechanism the body uses to protect itself against the conditions, the Mail says.
This story is based on laboratory research into the potential role of the drug digoxin (which is extracted from the foxglove plant) in treating heart conditions such as high blood pressure and heart failure. Digoxin is currently used to control heart rate in some patients with an irregular heartbeat, and has been shown to improve heart failure symptoms. However, the fact that it can be poisonous and needs to be monitored means that it is not commonly prescribed.
The current study identified a protein that is involved in the prevention of high blood pressure. The researchers scanned a library of thousands of existing drug compounds to identify ones that could potentially treat the condition. They found that digoxin was able to increase the presence of this protein in both cells in the lab and living mice. The researchers conclude that this may explain how digoxin improves heart failure symptoms, and suggest it may offer a new approach for treating heart conditions.
This was an early stage drug discovery study. It will probably take several years of continued research into the effectiveness and safety of digoxin for high blood pressure patients before the drug could be available for treating the condition.
Where did the story come from?
The study was carried out by researchers from the University of Michigan and the University of Toledo in the United States, and was funded by the US National Institutes of Health and the Swedish Heart and Lung Foundation.
The study was published in the peer-reviewed journal Molecular Pharmacology.
The Mail’s headline emphasising the poisonous nature of the foxglove extract is misleading, as is its discussion of the use of foxglove extract in the 13th century and Victorian times. While digoxin may have been used throughout history for various purposes and can be poisonous, it is a licensed treatment for certain heart conditions. However, it takes the body a long time to break down digoxin and, as such, treated patients, particularly the elderly, can be at risk of adverse effects due to toxic levels of digoxin building up in the body. Toxic levels of digoxin can cause heart problems, giving rise to symptoms similar to those it is used to treat. For this reason, digoxin can be a difficult drug to use, and levels in the blood sometimes have to be monitored to ensure that it is not building up to toxic levels.
What kind of research was this?
This research was carried out in cell cultures and animals. It aimed to identify an existing medicine that could target a specific protein, RGS2. This protein is important for normal heart function, and low levels of RGS2 are associated with high blood pressure (hypertension) and heart failure. The researchers thought that a drug that targets RGS2, increasing its production, could provide a new approach to treating these common conditions.
Cell and animal studies are a vital part of the drug discovery and drug development process. They can provide an early indication of the potential action of new drugs or, in this case, the potential action of old drugs in treating a new condition. They can also be useful in studying the specific mechanisms by which drugs work. However, they cannot tell us whether a drug will effectively and safely treat a condition in real patients. Further clinical trials in humans are required to assess these factors.
What did the research involve?
The researchers identified a protein, RGS2, which is found in low levels in some patients with high blood pressure and heart failure. They tested thousands of drugs to see whether or not they could increase the levels of RGS2 in cells.
The selected drug compounds were then tested in mice. The animals were given the drugs for seven days, and then their heart tissue was tested for RGS2 levels.
The researchers analysed the data to determine whether or not there was a dose-response relationship between drug treatment and RGS2 protein levels.
What were the basic results?
The researchers found that digoxin, and other similar drugs (digoxin was the only currently licensed medical drug used in the study), led to a two to three fold increase in RGS2 protein levels in cells. The change in RGS2 levels was both concentration and time dependent, with higher levels seen at greater digoxin levels, and the levels decreasing over time after exposure to the compound.
Mice treated with digoxin for seven days showed increased levels of RGS2 in both heart and kidney tissues compared with mice that were not treated with the drug.
How did the researchers interpret the results?
The researchers conclude that digoxin, a drug currently used to treat heart failure and certain heart rhythm problems, could be used for the treatment of high blood pressure.
This early stage drug discovery study suggests that digoxin may have potential use in the treatment of high blood pressure. However, much more research is needed to determine whether the drug is safe and effective for treatment of patients with hypertension.
Digoxin is a chemical found in the foxglove plant. It is a drug that increases the force of heart contraction, and also slows the conduction of electrical impulses through the heart. As such, digoxin is currently licensed to treat heart failure and certain heart rhythm problems. However, the risk of the drug building up to toxic levels in the body, which is particularly dangerous in the elderly, means that its use within the medical profession is often quite limited.
The exact mechanism by which digoxin improves heart function is not known. This research suggests that its role in increasing RGS2 levels may account for some of its clinical impact in the treatment of heart failure. Further research is required to determine whether this is the case, however.
The researchers say that, at this stage in the research, it is not possible to say whether the increased levels of RGS2 seen after treatment with digoxin will translate into a functional effect. They say that the effects of continuous digoxin treatment, and associated increases in RGS2 levels, are not known, and will need to be investigated in future studies.
Overall, this study provides additional knowledge that may be helpful in developing new drugs for heart conditions, and understanding how current cardiac therapies work. It has, however, little immediate relevance for patients with high blood pressure.
Analysis by Bazian
Edited by NHS Website
Links to the science
Molecular Pharmacology. Published online June 13 2012, doi:10.1124/mol.112.079293