23 March 2012

Research Points to Developments in Dengue Prevention and Treatment

Dengue infection is a leading cause of illness and death in the tropics and subtropics. The Center for Disease Control and Prevention (CDC) estimates that 100 million people are infected yearly. Dengue is caused by viruses transmitted by female mosquitoes. Vaccines to prevent infection with dengue virus (DENV) have not yet been discovered to counteract the spread and the most effective protective measures are those that avoid mosquito bites. When infected, early recognition and prompt supportive treatment can substantially lower the risk of developing severe disease.

Symptoms for dengue include high fever, headaches, joint and muscle pain, vomiting and rashes. The recovery time for dengue is around 2 weeks. During the treatment time, drinking lots of fluids, resting and taking non-aspirin fever-reducing medicines might help. Sometimes dengue turns into dengue hemorrhagic fever, which causes bleeding from the nose, gums or under the skin. It can also become dengue shock syndrome, which causes massive bleeding and shock. These forms of dengue are life-threatening.

Researchers have identified enzymes and biochemical compounds called lipids that are targeted and modified by the dengue virus during infection, suggesting a potential new approach to control the aggressive mosquito-borne pathogen.

Findings also suggest that medications used to treat high cholesterol and other lipid-related conditions might also inhibit dengue's replication and could represent a potential new therapy. The researchers have identified how infected mosquito cells undergo changes to certain lipids in membranes and in biochemical sensors that alert cells of invading viruses.

"The virus reorganizes the internal architecture of the cell to support its own needs," said Purdue University research scientist Rushika Perera. "Many details are unknown. This is our first attempt to understand how the virus alters lipids as part of the infection process. Part of what we looked at in this work was how the virus changes the cell, and the next step will be to figure out why."

Video: Controlling Dengue

The researchers uncovered new details of how the virus alters lipids in membranes surrounding structures inside cells called organelles, including the mitochondria, which provide energy critical for a cell to function, and the endoplasmic reticulum, where proteins and lipids are synthesized.

"Findings also show that important host enzymes are used by the virus and may be targets for future antiviral drugs," said Richard J. Kuhn, a professor and head of Purdue's Department of Biological Sciences and director of the Bindley Bioscience Center. "It turns out, the pills you take to control your cholesterol might have some capability to control dengue."

The work was led by Perera in collaboration with researchers at Purdue's Bindley Bioscience Center and the Pacific Northwest National Laboratory. Findings are detailed in a research paper to appearing in the journal PLoS Pathogens.

The findings could apply to viruses similar to dengue, including the West Nile virus, yellow fever and hepatitis C.

Dengue causes 50 million to 100 million infections per year and is considered one of the most aggressive mosquito-borne human pathogens worldwide. It is a leading cause of serious illness and death among children in some Asian and Latin American countries.

"Identifying pathways of infection will help us understand how these viruses work," Kuhn said. "Many viruses, including dengue, dramatically alter a host cell upon infection, and in this paper we begin to dissect the precise changes that occur. Ultimately, we are trying to understand how the virus subverts and exploits the host and uses it for its own purpose, which is to replicate."

The team learned specifically that an enzyme called fatty acid synthase, which cells use to synthesize lipids, is affected by the virus. Researchers showed that compounds inhibiting production of the enzyme also inhibit virus replication, suggesting drugs already on the market to treat diseases related to lipid synthesis and storage, including diabetes and cancer, also might be used to treat dengue, Kuhn said.

The research paper was written by Perera; Kuhn; Bindley researchers Catherine Riley, Amber S. Hopf-Jannasch and Jiri Adamec; and PNNL researchers Giorgis Isaac, Ronald J. Moore, Karl W. Weitz, Ljiljana Pasa-Tolic and Thomas O. Metz.

The researchers had previously studied a compound that inhibits the production of fatty acid synthase in human cells. In the new findings, the researchers showed that the virus commandeers some of the same enzymes in both mosquito and human cells, meaning the same compound could work to attack the virus in mosquito cells.

"This is important because it may be easier to control the virus in mosquitoes than in humans," Kuhn said.

Globally, dengue has grown dramatically in recent decades, placing about half the world's population at risk of infection. The infection causes flulike illness and occasionally develops into a potentially lethal complication called dengue hemorrhagic fever. Prompt medical care for this severe form of dengue virus infection has been shown to decrease mortality rates from more than 20 percent to less than 1 percent, according to the World Health Organization.

The research hinges on recent advances in two areas: high-resolution mass spectrometry and "informatics," or using computers to process volumes of information.

"You generate a large quantity of data that has to be interpreted in terms of what molecules you are looking at," Perera said. "The mass spectrometer takes hundreds of lipids and breaks them apart, and then a computer is needed to put it all back together and identify them. It's only in the past five years or so that we've had the capability to do this with the required accuracy."

The researchers also detail changes in the curvature of membranes, using another technique called cryoelectron microscopy, and pinpointed an isolated part of the cell where most of the virus replication takes place, a complex of membranes modified by the infection. The virus is thought to commandeer enzymes, relocating them to this region where virus replication factories are situated.

Because the research tools enable scientists to see how changes in membranes and signaling lipids alter how a cell functions, a long-term benefit of the research is learning how to use a virus as a tool to better understand cellular processes, Perera said.


Purdue University
Bindley Bioscience Center
Pacific Northwest National Laboratory
PLoS Pathogens
World Health Organization
National Institutes of Health
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