Friday, 20 May 2011

Extracts of Asparagus Show Antifungal Activity Against Aspergillus Fumigatus


Asphodelus tenuifolius

 Panghal and colleagues show in a new research paper that it is possible to extract crude compounds from a common weed of the Middle East (Asphodelus tenuifolius) and asparagus (A. racemosus) that will inhibit growth of a clinical sample of Aspergillus fumigatus in the laboratory.

The extraction must be carried out using organic solvents e.g. benzene, chloroform as other solvents failed to extract active compounds e.g. water. Note: boiling this material in water isn't going to result in an 'antifungal brew'.

The microbial isolates were taken from a series of patients undergoing treatment for cancer and who were known to be vulnerable to infection i.e. they were at least partially neutropenic, so any antimicrobial activity found could at least be said to be effective against organisms selected for their ability to infect patients - an important distinction.

Clear zones around antimicrobial discs
The authors carefully extracted material from several different plant species and tested them in the laboratory for activity against A. fumigatus and a series of other fungal & bacterial clinical isolates by growing the isolates on nutrient agar in the presence of discs of absorbant material impregnated with the extracted compounds. If the microbe was sensitive to any compound a clear region would develop around the disc. Three or four extracts were shown to be at least partially active against Aspergillus fumigatus.

Given the need for as many new antifungals as we can find this is an encouraging result but it isn't the first time antifungal substances have been found in plant extracts by any means. Nor does it mean that eating parts of the plants mentioned is likely to have a marked effect on an existing fungal infection as we know little about the properties of the substances being investigated. The human body is a very different place compared with a nutrient agar plate in a laboratory.

But perhaps we are asking too much of these remedies via that route of administration anyway. Herbalists seem to use the antifungal characteristics of their remedies as a treament for superficial infections rather than deep infections, much as in the same way we use creams and ointments containing antifungal drugs.

To develop new antifungals to treat infections deep in our bodies we need to look at how the compounds in plant material work, and then try to develop those compounds into one that we can get deep into body tissues.

It is notable that when the authors of this paper compared the strength of their new compounds with that of commercial antifungals such as ketoconazole they were weaker. That might be because the concentration of the substance was weaker and simply grinding up more plant material would increase the strength of the plant compound, or it might be the antifungal mechanism of the plant compound just doesn't work as well as the commercial compound.

Here again we come across problems caused by trying to use these herbal remedies by eating parts of the plant. The active ingredient is dispersed around our bodies after eating and is heavily diluted, so imagine how much you would have to eat to have any beneficial antifungal effect. Consider that the antifungal you are taking is intended to prevent infection of a plant that might weight a few hundred grammes. If you dilute that compound it will reduce in effectiveness. You are a thousand times bigger therefore you are going to have to eat a thousand plants! If you had to eat a large amount of plant material you are increasing the chances of 'side effects' as there are thousands of other substances in that material.

For these reasons and more it is much better that we isolate and purify the active ingredient.

To summarise
  1. These plants are not cheap alternatives to commercial drugs if you are treating aspergillosis or any other deep fungal infection
  2. These observations are good starting points for investigation into new antifungal drugs, but are not the end product in themselves. The antifungal activity is likely to be too dilute, too inaccessible or unsuitable for use in animals (they are after all intended to be active in plants)

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