Dr Simon Avery and colleagues in the School of Biology used yeast genetics to examine the effects of quinine on a collection of 6000 yeast mutants, each one lacking exactly one of the yeast’s 6000 genes. While quite different from humans, yeast is comparable on a cellular level and yeast is frequently, and successfully, used as a front-line agent in testing chemicals and small molecule drugs.
This detailed screening process revealed that strains of yeast unable to make tryptophan were extremely susceptible to quinine poisoning, which led them to identify a tryptophan transporter as a key quinine target (yeast that cannot make their own tryptophan have to rely exclusively on external sources, and thus die if tryptophan transport is blocked).
This discovery fits in well with evidence that quinine reactions are more severe in malnourished individuals. Tryptophan is an essential amino acid which means the human body cannot produce it — we have to get it from the food we eat. Tryptophan is abundant in meat but limited in yams, a staple food crop in the tropics where malaria is prevalent. If quinine severely reduces tryptophan uptake, then it follows that people with preexisting tryptophan deficiency, a common occurrence in undernourished populations, would be especially at risk from this drug.
Each year there are an estimated 350 to 500 million cases of malaria — and every year it kills between one and three million people. In Africa, malaria is a leading cause of death in children. Estimates are that worldwide over three billion people are at risk of contracting the disease.
Dr Simon Avery said: “This finding could be a key step towards making quinine side-effects a thing of the past, so improving the quality of treatment for millions of malaria sufferers. It also highlights the benefits of collaborative research, in this case between my yeast group and the parasite immunology group of Dr. Richard Pleass.”
The body uses tryptophan to make the brain chemical serotonin — which is thought to produce healthy sleep and a stable mood - so a lack of tryptophan induced by quinine could also explain why many of quinine’s side effects are localized to the head region.
The researchers postulate that the toxic effects of quinine could be averted simply by taking dietary tryptophan supplements in conjunction with quinine treatments. Scientists now have to find out if tryptophan affects quinine action against the malaria parasite.
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Notes to editors: The University of Nottingham is ranked in the UK's Top 10 and the World's Top 100 universities by the Shanghai Jiao Tong (SJTU) and Times Higher (THE) World University Rankings.
More than 90 per cent of research at The University of Nottingham is of international quality, according to RAE 2008, with almost 60 per cent of all research defined as ‘world-leading’ or ‘internationally excellent’. Research Fortnight analysis of RAE 2008 ranks the University 7th in the UK by research power. In 27 subject areas, the University features in the UK Top Ten, with 14 of those in the Top Five.
The University provides innovative and top quality teaching, undertakes world-changing research, and attracts talented staff and students from 150 nations. Described by The Times as Britain's "only truly global university", it has invested continuously in award-winning campuses in the United Kingdom, China and Malaysia. Twice since 2003 its research and teaching academics have won Nobel Prizes. The University has won the Queen's Award for Enterprise in both 2006 (International Trade) and 2007 (Innovation — School of Pharmacy), and was named ‘Entrepreneurial University of the Year’ at the Times Higher Education Awards 2008.
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