Mystery Solved: How Sickle Hemoglobin Protects Against Malaria

ScienceDaily (Apr. 28, 2011) — The latest issue of the journal Cell carries an article that is likely to help solve one of the long-standing mysteries of biomedicine. In a study that challenges currently held views, researchers at the Instituto Gulbenkian de Ciência (IGC), in Portugal, unravel the molecular mechanism whereby sickle cell hemoglobin confers a survival advantage against malaria, the disease caused by Plasmodium infection. These findings, by the research team lead by Miguel P. Soares, open the way to new therapeutic interventions against malaria, a disease that continues to inflict tremendous medical, social and economic burdens to a large proportion of the human population.

These are normal and sickle red blood cells. 

Sickle cell anemia is a blood disease in which red blood cells reveal an abnormal crescent (or sickle) shape when observed under a conventional microscope. It is an inherited disorder -- the first ever to be attributed to a specific genetic modification (mutation), in 1949 by Linus Pauling (two-times Nobel laureate, for Chemistry in 1954, and Peace, in 1962). The cause of sickle cell anemia was attributed unequivocally to a single base substitution in the DNA sequence of the gene encoding the beta chain of hemoglobin, the protein that carries oxygen in red blood cells.

Only those individual that inherit two copies of the sickle mutation (one from their mother and the other from their father) develop sickle cell anemia. If untreated, these individuals have a shorter than normal life expectancy and as such it would be expected that this mutation would be rare in human populations. This is however, far from being the case. Observations made during the mid-20th century and building on Pauling's findings, revealed that the sickle mutation is, in fact, highly, selected in populations from areas of the world were malaria is very frequent, with sometimes 10-40% of the population carrying this mutation.

Individuals carrying just one copy of the sickle mutation (inherited from either the father or mother) were known not to develop sickle cell anemia, leading rather normal lives. However, it was found that these same individuals, said to carry the sickle cell trait, were in fact highly protected against malaria, thus explaining the high prevalence of this mutation in geographical areas where malaria is endemic.

These findings lead to the widespread believe in the medical community that understanding the mechanism whereby sickle cell trait protects against malaria would provide critical insight into developing treatment or a possible cure for this devastating disease, responsible for over a million premature deaths in sub-Saharan Africa. Despite several decades of research, the mechanism underlying this protective effect remained elusive. Until now.

Several studies suggested that, in one way or another, sickle hemoglobin might get in the way of the Plasmodium parasite infecting red blood cells, reducing the number of parasites that actually infect the host and thus conferring some protection against the disease. The IGC team's results challenge this explanation.

In painstakingly detailed work, Ana Ferreira, a post-doctoral researcher in Miguel Soares' laboratory, demonstrated that mice obtained from Prof. Yves Beuzard's laboratory, that had been genetically engineered to produce one copy of sickle hemoglobin similar to sickle cell trait, do not succumb to cerebral malaria, thus reproducing what happens in humans.

When Prof. Ingo Bechman observed the brains of these mice he confirmed that the lesions associated with the development of cerebral malaria where absent, despite the presence of the parasite.

Ana Ferreira went on to show that the protection afforded by sickle hemoglobin in these mice, acts without interfering directly with the parasite's ability to infect the host red blood cells. As Miguel Soares describes it, "sickle hemoglobin makes the host tolerant to the parasite."

Through a series of genetic experiments, Ana Ferreira was able to show that the main player in this protective effect is heme oxygenase-1 (HO-1), an enzyme whose expression is strongly induced by sickle hemoglobin. This enzyme, that produces the gas carbon monoxide, had been previously shown by the laboratory of Miguel Soares to confer protection against cerebral malaria. In the process of dissecting further this mechanism of protection Ana Ferreira demonstrated that when produced in response to sickle hemoglobin the same gas, carbon monoxide, protected the infected host from succumbing to cerebral malaria without interfering with the life cycle of the parasite inside its red blood cells.

Miguel Soares and his team believe that the mechanism they have identified for sickle cell trait may be a general mechanism acting in other red blood cell genetic diseases that are also know to protect against malaria in human populations: "Due to its protective effect against malaria, the sickle mutation may have been naturally selected in sub-Saharan Africa, where malaria is endemic and one of the major causes of death. Similarly, other clinically silent mutations may have been selected throughout evolution, for their ability to provide survival advantage against Plasmodium infection."

This research was carried out the at the IGC in collaboration with the Team of Prof. Yves Beuzard (Université Paris VII et XI, France), an expert in sickle cell anemia, and Prof. Ingo Bechman an expert in neuropathological diseases (Institute of Anatomy, University of Leipzig, Germany). Other IGC researchers involved in this study are Ivo Marguti, Viktória Jeney, Ângelo Chora, Nuno Palha and Sofia Rebelo. This project was funded by Fundação para a Ciência e a Tecnologia (Portugal), GEMI Fund Linde Healthcare and the European Commission's Framework Programme 7.

Vacina contra malária tem ''pais'' brasileiros

Produto com ótimos resultados na África é fruto da pesquisa do casal Nussenzweig, que atua na New York University desde 1964

Em fevereiro, cientistas anunciaram resultados de uma promissora vacina contra malária. Milhares de crianças foram imunizadas na África. Quase metade (45,8%) ficou protegida, um recorde nos testes de larga escala. Pouca gente sabe, mas os pais da vacina são brasileiros.

"O trabalho de Ruth e Victor Nussenzweig fundamentou a concepção e o desenvolvimento da vacina", afirma Joe Cohen, da farmacêutica GSK Bio, autor do artigo no The Lancet que descreve os resultados na África. O casal Ruth e Victor vive nos EUA desde 1964. Eles trabalham na New York University (NYU).

A comunidade científica não acreditava em uma vacina para malária. Todos sabiam que, depois de sucessivas infecções, pessoas que vivem em áreas endêmicas não costumam adquirir imunidade. Daí seguia um raciocínio tão simples quanto incorreto: se a natureza não gera uma resposta imune eficaz, a técnica não pode almejar resultado melhor.

Ruth desafiou o consenso. Utilizou esporozoítos - estágio do plasmódio na glândula salivar dos mosquitos inoculado durante a picada. O primeiro passo foi esterilizá-los com Raios X, estratégia para tornar os esporozoítos inofensivos. Depois, injetou-os em camundongos. Os roedores desenvolveram imunidade, comprovando a viabilidade de uma vacina. Os resultados mereceram publicação na Nature em 1967 e foram, depois, confirmados em macacos e humanos.

Mesmo assim, a vacina permanecia distante: não seria viável dissecar mosquitos para produzir, em escala industrial, a forma atenuada do esporozoíto.

Infecção. Na década de 80, a equipe de Victor identificou a proteína na superfície do esporozoíto que, ao ser neutralizada pelo sistema imune, impossibilitava a infecção: a proteína circunsporozoíto (CSP, na sigla em inglês). Era a chave para uma vacina sintética e economicamente viável.

A descoberta rendeu uma honra incomum: a visita de Sir John Maddox, da Nature. O lendário editor da maior revista científica do mundo viajou de Londres a Nova York para garantir que o brasileiro publicaria a descrição do gene da CSP na sua revista.

As farmacêuticas ficaram eufóricas. No dia 3 de agosto de 1984, o New York Times estampou uma foto de Ruth sob o título "Uma vacina iminente contra malária".

A NYU estabeleceu uma parceria com a suíça Hoffmann-La Roche e criou uma vacina que recolhia o pedaço mais importante da CSP. Nos testes clínicos, em 1987, 35 indivíduos receberam o composto. Três tiveram ótima reação do sistema imunológico e foram expostos a picadas do mosquito infectado. Um ficou completamente protegido e os outros dois, parcialmente.

Foi um balde de água fria na opinião pública, mas, para Victor, representava um grande avanço: comprovava a viabilidade da vacina. Pouca gente concordou na época e quase todas as farmacêuticas desistiram.

Com uma exceção: Joe Cohen, da GSK Bio, sabia que os resultados eram sólidos e bastaria um bom adjuvante - substância que amplifica a resposta imune - para aumentar a eficácia. A aposta foi premiada. A vacina da GSK deve começar a proteger crianças na África em 2015.

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Fighting Malaria With African Plant Extracts

ScienceDaily (Apr. 8, 2011) — Plants used in traditional African medicine may have an effect on the malaria parasite as well as the mosquitoes that spread the disease. A Norwegian pilot project is now indexing and testing these plants.

Various herbal medicines are used to combat malaria. In Uganda, Torunn Stangeland and her colleagues collected plants to analyze.

The malaria parasite has gradually developed resistance to the most commonly used medicines. To make matters worse, several mosquito species that host and transmit the parasite have become resistant to insecticides, making it difficult to eliminate them from populated areas.

Now researchers at the Norwegian University of Life Sciences (UMB) in Ås, south of Oslo, are studying and testing plant extracts that have been used in traditional African medicine to fight malaria. Ultimately, the researchers hope to find supplements and replacements for today's conventional medicines.

Plants used in traditional African medicine may have an effect on the malaria parasite as well as the mosquitoes that spread the disease. A Norwegian pilot project is now indexing and testing these plants.

Malaria is caused by the parasite Plasmodium falciparum, which is transmitted to its human hosts via various mosquito species of the genus Anopheles. The disease can cause fever high enough to be fatal. In tropical and subtropical regions such as sub-Saharan Africa, malaria remains a major cause of illness and death as well as a contributing factor to poverty.

Each year, 300 million people contract malaria. And each year, the disease kills one million of them -- mostly children under five years of age. Pregnant women are also highly vulnerable.

New solutions to thwart resistance

The malaria parasite has gradually developed resistance to the most commonly used medicines. To make matters worse, several mosquito species that host and transmit the parasite have become resistant to insecticides, making it difficult to eliminate them from populated areas.

Now researchers at the Norwegian University of Life Sciences (UMB) in Ås, south of Oslo, are studying and testing plant extracts that have been used in traditional African medicine to fight malaria. Ultimately, the researchers hope to find supplements and replacements for today's conventional medicines.

The pilot project "Malaria control using plant extracts" has been granted funding under the Research Council's National Programme for Research in Functional Genomics in Norway (FUGE).

Effects and side effects

"There are several plants that have been shown to kill the malaria parasite," explains Researcher Torunn Stangeland of UMB. "Other plants are toxic to malaria-transmitting mosquitoes and could perhaps be utilised as insecticides." She and her colleague Hans Overgaard head the project.

The plants in question have never been scientifically tested for efficacy. Another unknown factor is whether they cause detrimental side effects for humans.

Early results promising

The Norwegian researchers have begun by testing the effectiveness of selected plant extracts against the parasite and mosquitoes. Next they will check for potential toxins to make sure the plants are safe to use. So far the trials look promising, but the results will not be finalised for some time.

The researchers will also investigate if there are synergistic effects of different compounds in the plant extracts. It may be more difficult for the malaria parasite and mosquitoes to develop resistance to the medicines or insecticides if the entire plant is used, because of the many different chemical components that are present in varying concentrations.

"The fact that both the sweet wormwood plant (Artemisia annua) and the bark of the cinchona tree have been used for centuries against malaria -- and the parasite has yet to become resistant -- indicates some support for this theory," says Dr Stangeland.

Medicines owned and produced by Africa?

"If we can find plants that prove effective against malaria," says Dr Stangeland, "we hope that African authorities and countries will register the tested medicines and produce them themselves."

An African herbal medicine could be a vital supplement to costly, imported medicines -- and could even replace some of them. Producing medicines in Africa would boost local industries and the economies of countries involved.

Prelude to a larger study

Parallel to experimenting with previously untested plants, the UMB researchers will also produce an overview of plants from nearby areas in Africa that are already mentioned in the scientific literature and may be effective against malaria. An added benefit of the pilot project is that it strengthens cooperation with African universities and scientists working on malaria.

"And this is only the beginning," asserts Dr Stangeland. "We hope the pilot project will lead to a larger, more comprehensive study with clinical tests of the plant-based medicines and insecticides as a main element."

Teste de vacina contra malária mostra proteção de longa duração

Uma vacina experimental contra a malária da GlaxoSmithKline oferece a crianças africanas uma proteção duradoura, embora sua eficácia diminua ligeiramente ao longo do tempo, de acordo com dados de um estudo inacabado, publicado na sexta-feira (14). Os experimentos foram conduzidos no Instituto de Pesquisa Médica do Quênia.

Segundo os pesquisadores, os resultados mostram que a vacina oferece 46% de proteção por 15 meses.

A malária é uma doença infecciosa transmitida por mosquitos que ameaça mais da metade da população mundial. A maioria das vítimas são crianças menores de 5 anos que vivem em países pobres da África subsaariana.

O último relatório da OMS (Organização Mundial de Saúde) sobre a doença encontrou avanços na última década, como a queda da estimativa de mortes, de quase um milhão em 2000 para 781.000 em 2009.

O estágio avançado de testes da vacina da GSK --conhecido como RTS, S ou Mosquirix-- está em andamento com 16.000 crianças em sete países da África. A imunização termina no próximo mês.

Se os dados mostrarem que a vacina é realmente eficaz, ela poderá ser licenciada e lançada em 2015.

O estudo, realizado entre março de 2007 e outubro de 2008, envolveu 894 crianças com idade superior a cinco meses, no Quênia e na Tanzânia.

Os primeiros resultados, publicados em 2008, mostraram que a vacina deu 53% de proteção contra a malária, pelo menos por oito meses, mas pesquisadores liderados por Ally Olotu, no instituto em Kilifi, Quênia, querem averiguar se a proteção durararia mais tempo.

Os resultados publicados na revista "The Lancet" mostraram que após 15 meses de acompanhamento, a eficácia da vacina não tinha diminuído muito. As crianças vacinadas ainda tinham 46% menos probabilidade de contrair a doença em relação àquelas que não tinham sido imunizadas.

"Mais estudos são necessários para estabelecer a eficácia da vacina, por exemplo, em crianças infectadas pelo HIV ou desnutridas", disse Olotu no estudo. Ele ainda acrescentou que devem ser feitos novos testes em locais com intensidade diferente de transmissão para confirmar os resultados.

O diretor do laboratório GSK (GlaxoSmithKline) Andrew Witty, disse que, se a eficácia da vacina for demonstrada, ela será vendida a um preço acessível a quem mais precisa dela. A empresa informou que está planejando uma margem de lucro de 5% sobre o custo de fabricação, que seriam reinvestidos em novas vacinas contra a malária e outras doenças negligenciadas.

Pinning Down a Deadly Shape Shifter: Progress against the Malaria Parasite

A parasite's genome is yielding clues to how malaria kills

ONE STEP AHEAD: P. FALCIPARUM(purple) attacking red blood cells (yellow).

More people have died from malaria than from any other disease in history. If we look at the African parasite that causes its most severe form, it is obvious why the pathogen is so deadly. Plasmodium falciparum has a multistage life cycle and highly mutable genes. It’s already widely resistant to one of the most common medications used to treat it, chloroquine, and it is starting to evolve around a newer drug, artemisinin.Falciparum is also a shape shifter, presenting different proteins on its surface as it develops in the body and remaining one step ahead of the immune system.

All this complexity is bad news for victims. But, in a sense, it may be good news for scientists, who sequenced the organism’s genome in 2002 and are starting to figure out what malaria’s intricate biology says about its natural history. Until recently, for instance, researchers thought falciparumhad jumped into humans from chimps. But in September a team from Alabama—known for its work on the origin of HIV—showed that all falciparum parasites are descended from a single lineage that jumped from gorillas millions of years ago. Since then, the parasite has been furiously evolving. Drug resistance is part of that. But a much more important factor, according to researchers at the Broad Institute of M.I.T. and Harvard, is the human body itself. The malarial genes under the most intense selection pressure—those with the most variation, generated over a millennium-long cat-and-mouse game with the immune system’s antibody response—are the ones that encode the identifying proteins on the surface of the parasite. Scientists have struggled to explain why some people get very sick from falciparum, whereas others suffer only mild symptoms; early work suggests that some of these “var” genes are behind serious cases in children.

One of the crucial next steps in understanding malaria’s genome will be assessing how it differs from parasite to parasite and region to region. “Knowing the amount of variation within an individual is crucial,” says Dominic Kwiatkowski, who leads malaria genomics research at the Wellcome Trust Sanger Institute near Cambridge, England. “Fortunately, we can quantify that with extraordinary precision.” Kwiatkowski’s group and others recently built MapSeq, an interactive database of genotyped samples from several hundred patients around the world. Researchers can use it to look for mutations unique to their areas—and to tailor their control strategies around them.

Cientista desenvolve novo método para bloquear transmissão de malária

Um novo método para bloquear a transmissão de malária foi revelado pelo pesquisador John Quigley durante o encontro anual da Sociedade de Hematologia norte-americana, realizado em Orlando, na Flórida, a partir deste sábado (4) até 7 de dezembro. O cientista é membro da Universidade de Illnois em Chicago.

A técnica consiste na redução da produção de uma proteína conhecida como FLVCR, encontrada no interior de mosquitos que carregam o protozoário Plasmodium, responsável pela doença. A inibição deste componente torna o inseto resistente ao micro-organismo. A explicação é o aumento do "estresse oxidativo" dentro do mosquito, condição que diminui as chances de reprodução do protozoário.

Os pesquisadores da equipe de Quigley conseguiram identificar e isolar o gene ligado à produção de FLVCR em dois dos mais conhecidos mosquitos que transmitem a malária.

Mosquitos fêmeas consomem grandes quantidades de hemoglobina, proteína encontrada no sangue humano, que é necessária para o desenvolvimento dos ovos do inseto. Ao consumir sangue contaminado pelo micro-organismo Plasmodium, o protozoário consegue se reproduzir e infestar o mosquito inteiro.

Quando pica um humano, o inseto irá gerar um novo ciclo de transmissão da doença. A pesquisa de Quigley ainda está em andamento e outros estudos são necessários para saber se a inibição de FLVCR pode mesmo bloquear a transmissão do Plasmodium. Para o pesquisador, a técnica ainda poderia ser aplicada para o combate de outras doenças infecciosas causadas por insetos que se alimentam de sangue como dengue e leishmaniose.

A malária infecta cerca de 300 milhões de pessoas por ano, matando quase 1 milhão delas no mesmo período. No Brasil, o número de contaminados em 2009 ultrapassou 300 mil. Dentro do humano, o protozoário causa a destruição dos glóbulos vermelhos do sangue, as hemácias, responsáveis pelo transporte de oxigênio aos tecidos do corpo, e também de células do fígado.