Nitric Oxide Plays Key Role in Defense Against Malaria

Utah is a long way from malaria country-but a disease that kills more than 1 million children a year is powerful incentive for medical researchers to bridge the distance.

University of Utah School of Medicine specialists in infectious diseases are searching for ways to better treat or even prevent malaria, a major killer of children in many tropical countries. And their work is paying off.

Since August, U researchers, along with U.S. and international colleagues, have published the findings of three important studies on the biochemical, genetic, and immunological aspects of the disease. The studies focus on the production of nitric oxide (NO), a molecule the human body produces to fight infection and that appears to be critical in the ability of children to fend off malaria.

Findings of the studies appear in the international medical journal, The Lancet, with the latest article being published in the February 22 issue.

"Our goal is to try to understand malaria to help children who are at risk of dying," said Donald L. Granger, M.D., U professor of internal medicine overseeing the research. Granger came to the U of U in 1995 from Duke University after studying malaria in Tanzania.

Along with Granger, U of U researchers involved in the studies include infectious diseases fellow Bert K. Lopansri, M.D., Maurine R. Hobbs, Ph.D., research assistant professor of internal medicine, and David L. Pombo, M.D., internal medicine instructor.

They collaborated on the studies with J. Brice Weinberg, M.D., and Marc C. Levesque, Ph.D., M.D., Duke University School of Medicine, Nicholas M. Anstey, M.D., Menzies School of Health Research, Darwin, Australia, and Esther Mwaikambo, M.D., a pediatrician from the Muhimbili Medical Center and Hubert Kairuki Memorial University in Dar es Salaam, Tanzania.

In the February 22 issue of The Lancet, Lopansri is lead author on a study that found Tanzanian children faced a fourfold higher risk of dying from cerebral malaria when their bodies lacked sufficient levels of arginine. Arginine is an amino acid that plays a critical role in the production of nitric oxide by the enzyme nitric oxide synthase (NOS2). Without arginine, the human body cannot make nitric oxide.

Lopansri, Granger, and their colleagues found the median arginine level of coastal Tanzanian children was less than half of normal. If the lack of arginine affects the body's ability to fight malaria by shutting down the production of nitric oxide, that may be treatable by increasing the levels of arginine in children through their diets. It also may lead to the development of malaria treatments that don't rely solely on anti-parasitic drugs, medicines that are failing because of resistance developing in malarial organisms.

But it's also possible reduced arginine levels are the result of malaria, so more research will be needed to nail down what role the amino acid plays in the body's response to the disease. Nonetheless, the U researchers believe they've made progress in understanding how the disease develops in people.

"We feel this is another piece of the puzzle," Lopansri said.

The Thrasher Research Fund, a Salt Lake City nonprofit organization that funds medical research on child health issues, provided support for the study. Lopansri's research may be an important step in developing cost-effective mechanisms for managing the disease, according to the Thrasher Research Fund president.

"The Fund hopes the groundbreaking discoveries on malaria, such as those made by Dr. Granger and Dr. Lopansri, can be swiftly applied to help save the lives of children," said A. Dean Byrd, Ph.D., M.B.A., M.P.H.

The National Institutes of Health also funds the research.

The need for malaria research is becoming increasingly important. The disease, caused by parasites transmitted through mosquito bites, strikes more than 500 million people and kills more than 1 million children annually, mostly in tropical countries. But more adults also are dying as drug resistance worsens globally. Approximately 1,000 Americans contract the disease from traveling in foreign countries every year.

The arginine article followed one in the November Lancet about a genetic variation that protects African children from cerebral malaria and severe malarial anemia, two of the severest forms of the disease. Hobbs was lead author of this study, which found that children with a variant form of the gene that makes nitric oxide synthase are up to 88 percent less likely to contract either of the two deadly forms of malaria.

The researchers examined the same Tanzanian children Lopansri studied and also assayed the DNA of Kenyan children. Those with the variant NOS2 gene often displayed no symptoms, despite infection, and showed higher levels of nitric oxide in their bodies.

"This is exciting because it confirms the importance of nitric oxide in the immune response to malaria," Hobbs said.

While Lopansri and Hobbs looked at biochemical and genetic mechanisms that produce nitric oxide, a third study, published in The Lancet in August, showed conclusively that the human body responds to malaria by dramatically increasing nitric oxide synthase, the enzyme responsible for nitric oxide production.

David J. Pombo, M.D., internal medicine instructor in infectious diseases at the U of U and LDS Hospital, and a group of colleagues conducted a trial with five Australians who volunteered to be infected with low levels of malaria. (The volunteers were cured with antibiotics before symptoms of the disease developed.)

After being infected, the volunteers' NOS2 activity climbed markedly, while there was no evidence of anti-malaria antibody formation. This led the researchers to believe cell-mediated immune responses (including nitric oxide production) may provide the main protection against malaria. The study was the first in humans to demonstrate nitric oxide formation in response to a controlled malaria infection and may lead to new strategies for developing malaria vaccines.

The latest studies continue the U's internationally regarded nitric oxide research. John B. Hibbs, Jr., M.D., infectious diseases division chief and distinguished professor of internal medicine, discovered nitric oxide in the immune system in the 1980s. Hibbs was the first researcher to clearly demonstrate the role of nitric oxide in protection against cancer and other infections.

Esther Mwaikambo, the Tanzanian physician who worked with the Utah researchers, said finding the link between nitric oxide and protection from malaria is one that may save many lives. She looks forward to working more with the U team and the other researchers.

"I would like to say that the Tanzanian team and myself are proud to have been involved in the original work that led to the discovery of the role of nitric oxide in cerebral malaria," Mwaikambo said. "Who knows? We may be the ones to discover a cure or prevention of cerebral malaria."