Organic Chemists Fighting Blindness

Researchers converted a natural compound into an effective anti-parasitic medicine, Ivermectin. It has gone on to be a key part of a hugely successful campaign to fight onchocerciasis, one of the leading infectious causes of blindness.

River blindness

Onchocerciasis, or river blindness, causes debilitating skin disease as well as severe itching of the eyes and eventually destruction of eye tissue, leading to blindness. More than 25 million people are infected globally, over 99% of whom live in sub-Saharan Africa. Some 300,000 people have been blinded by the disease, and another 800,000 are visually impaired.

The disease is caused by parasitic bacteria which live within the nematode worm Onchocerca volvus. The worm larvae are transmitted to humans by the bites of infected blackflies, which live in fast-flowing rivers, hence the common name for the disease: river blindness. Once inside a person, the worms die and release bacteria.

Improving a natural product

A breakthrough in treatment was made during the 1970s, with the development of the drug Ivermectin (Mectizan^TM), which is effective against the infection when taken twice a year for 10-15 years. Ivermectin (Mectizan^TM) is a broad-spectrum anti-parasitic drug, and it was developed from a compound, called Avermectin which is made by bacteria found in a soil sample from Japan. It works by killing the worm larvae before they develop into adults and begin to cause damage.

Avermectin was not effective enough to be used as a drug to cure river blindness. Organic chemists converted it into Ivermectin by changing one carbon-carbon double bond into a single bond. This altered the 3D shape of the molecule, making it safer and more effective as a medicine.

The double bond was turned into a single bond by catalytic hydrogenation, using a specific organometallic catalyst called Wilkinson’s catalyst. This catalyst is named after the British chemist and 1973 Nobel Laureate, Sir Geoffrey Wilkinson and is used to add hydrogen to alkenes to form alkanes – a reaction that is used heavily in organic synthesis and pharmaceutical research. This was crucial, because in order for Ivermectin to work effectively, none of the other carbon-carbon double bonds in the structure could be altered. Research into catalysis is vital for designing new organic synthesis pathways, which will allow the creation of new drugs for a wide range of diseases.

Tackling a public health problem

Since the discovery of Ivermectin, a large scale public health programme to tackle the disease in West Africa has made a significant impact. Ivermectin, under the name Mectizan, has been given free of charge to aid agencies working in developing countries under the Mectizan Donation Program (MDP).

Distribution of Ivermectin formed a key part of this programme, along with spraying insecticides into the rivers where blackflies breed. It is estimated that the programme has prevented 600,000 cases of blindness and made 25 million hectares of land safe for living and farming.

Programmes are still ongoing to tackle onchocerciasis in other parts of the world, and it is estimated that 76 million Ivermectin treatments were distributed in 2010.

Also of Interest

Neglected Diseases and Drug Discovery

Copyright: 2011
Michael J Palmer
An invaluable guide to successful practice in neglected tropical diseases (NTDs) and highlights best practice to guide the ongoing drug discovery effort.

Sightsavers work with partners to eliminate avoidable blindness in the developing world.

The Merck (Mectizan) Donation Program provides free treatment for river blindness (onchocerciasis) in endemic countries worldwide.

UNICEF partners with Merck & Co. to fight onchocerciasis, a neglected tropical disease.