Brisbane Rainforest Action & Information Network


Pharmaceutical properties of some south-east Queensland rainforest plants

Dr. Merv Hegarty has 40 years experience as a plant chemist with CSIRO in tropical crops and pastures, advising on the toxicology of plants. Dr. Hegarty now runs a consultancy (Plantchem) with his wife, Dr. Elwyn Hegarty, (a botanist, specialising in vines and rainforest ecology) which advises on the use of native plants in 'bush tucker' and pharmaceutical products.

Compounds in plants can be considered as primary or secondary. Primary compounds, such as proteins, fats and oils are essential to the physical structure and workings of the plant. Secondary compounds are not common to all plants and are not essential for the life of the plant. Indeed, it was originally thought that alkaloids found in bark were waste products. Now they are recognised as playing important roles in the ecology of the plant, such as its defence or insect attraction.

These compounds are generally small molecules, especially when compared to proteins and carbohydrates. The most potent perfumes, insecticides, flavours and poisons can be found amongst them.

Castanospermum australe - Black Bean

The compound Castanospermine is an alkaloid extracted from the seed of the Black Bean tree. It is found in all parts of the Black Bean tree but the content of the seed is especially high. It is easy to extract the alkaloid from the seed, as it is water soluble - the aboriginal people found this out a long time ago. The compound inhibits the actions of the enzyme that breaks down the sugar, glucose.

The molecule has been found to affect the workings of the Human Immunodeficiency Virus by preventing the 'docking' of the virus's glycoproteins to human lymphocytes. Two years ago the first clinical trials were held but pharmaceutical companies later dropped castanospermine to concentrate on 'cocktails' including the compound AZT. Who knows when/if castanospermine will be resurrected?

A different isomer (molecule with same components but different shape) is being used in research against nematodes. In New Zealand researchers are using castanospermine as the starting point from which to develop other compounds. A possible use is in improving tissue grafting (because of the way in which it affects 'docking' to sites) in surgery.

Swainsona greyana - Hairy Darling Pea

The molecule Swainsonine prevents the action of the enzyme that breaks down the sugar manose. Overseas this compound is being tested for its anti-tumour properties.

Duboisia sp. - Corkwood

Although there are plantations of Duboisia around Proston, with Queensland producing 50-70% of the world's supply, most extraction occurs overseas. Hyoscyamine is used in optometry to dilate pupils. Hyoscine is used as a muscle relaxant and as a transdermal patch to treat motion sickness. A derivative of the compound is used to treat gastric disorders. At the University of Queensland research on Duboisia hybrids, to produce uniform material, is being undertaken.

Bursaria spinosa - Blackthorn

From this unassuming plant, the water-soluble compound escolin is easy to isolate. It has anti-inflammatory and anti-oxidant properties but is a low value pharmaceutical. It can absorb Ultraviolet light and has therefore been used in sunscreen creams. It has also been used to treat dermatitis.

Sarcomelicope

This plant contains a water-insoluble alkaloid. A laboratory in the US is looking at its anti-cancer potential.

Advances in technology now allow sites in the body to be modelled and the shape of the molecule required to do a particular job to be deduced. Molecules of these shapes/types can then be searched for in plants that are known to contain these types of compounds. Previously many plants were looked at, all manners of compounds extracted and identified and all manners of uses found for them, with a golden age of discovery during the war years. With the new technology there is less scope for spin-offs and the most high profile diseases (cancer and HIV aids) are most likely to benefit.

Many thanks to Dr. Hegarty for his interesting (and as that terrible punster Jim Johnston said, 'eye-opening') talk.