Epidemic Proportions

3 10 2013

The fight against infectious diseases increasingly links discovery with care

 

A WAR WITH LITTLE PEACE: The incidence of extensively drug-resistant tuberculosis continues to grow in Russia. This young man is a patient in a tuberculosis ward in a psychiatric hospital in the North Caucasus region of that nation.

 

 When Mycobacterium tuberculosis invades a person’s body, it doesn’t just settle into the lungs and look for a spot from which to eke out a living. It hijacks that person’s macrophages—cells that attack invading bacteria—and uses the mechanisms of inflammation to manipulate the environment around it, remodeling its new home to suit its needs.

 

Salmaan Keshavjee knew about Mycobacterium’s penchant for makeovers, and thought that this knowledge might be useful in the fight against tuberculosis. So he was intrigued when he learned of an unusual approach that researchers at Sweden’s Karolinska Institutet were taking to control these bacteria-orchestrated renovations.

To understand this twist in the body’s normal path of self-defense, and to find ways to get the immune response back on track, the Sweden-based team, led by Markus Maeurer, a professor of clinical immunology at the institute, had cultured the mesenchymal stem cells from patients with extensively drug-resistant tuberculosis (XDR TB), then reinfused the patients with those cultured stem cells. Because mesenchymal stem cells help suppress inflammation, the researchers wanted to see if they could safely dampen and refocus the inflammatory response without  compromising immune function.

“Their preliminary data suggested that the stem cells didn’t suppress immunity in an adverse way, and surprisingly, the patients who received the transplanted cells did much better on their XDR TB treatment than typical patients in their condition,” says Keshavjee, an HMS associate professor in the Department of Global Health and Social Medicine and a physician in the Division of Global Health Equity at Brigham and Women’s Hospital. With the treatments now in use, fewer than a third of patients with XDR TB recover, but in this small initial study, all the participants appeared to recover.

Keshavjee is developing a partnership with the institute’s team, laying a foundation for more-extensive trials of the treatment in Russia and Peru. “Saving lives from a disease that’s killing people—that’s always good,” Keshavjee says. “But this work also opens the door to thinking about tuberculosis differently. If the mycobacterium is manipulating its environment by modulating T cells and other immune cells, we need to ask, ‘What if we unmodulate that environment?’ ”

“Inside our bodies, the bugs are living in an ecosystem,” he adds. “As humans, we also have our own ecology, which plays out in society. Recognizing the complex biosocial nature of infectious diseases moves you toward some crucial insights about how these diseases work and how to fight them.”

To fight infectious diseases worldwide, biomedical researchers and clinicians are joining efforts to apply laboratory-based discoveries to the challenge of saving the lives of people with tuberculosis, cholera, and other age-old ravages. These international collaborations are increasingly considering such diseases in context, as integrated parts of complex interconnected systems that involve humans.

 

“We now have genomic and proteomic platforms that are beginning to have immediate relevance to the challenges of diagnosing and treating infectious disease in poor communities,” says Paul Farmer ’90, the Kolokotrones University Professor at Harvard, head of the Department of Global Health and Social Medicine at HMS, and a cofounder of Partners In Health, an international nonprofit that brings health care to the poor. “Many of these new technologies are more portable, scalable, and affordable than ever before.”

 

In Black and White

Tuberculosis is a global public health issue that is unevenly distributed: the burden of the disease is highest in Asia and Africa, with India and China accounting for almost 40 percent of cases. Africa has 24 percent of the world’s cases and the highest rates of disease and death per capita. In the Russian Federation, XDR TB is a particular concern: it has rapidly spread through prison populations. In Peru, while the incidence of tuberculosis is decreasing, the incidence of multidrug-resistant tuberculosis is on the rise. Overall, according to a 2012 report from the World Health Organization, there were an estimated 8.7 million new cases of tuberculosis and 1.4 million deaths worldwide from the disease in 2011.

Similar sobering statistics can be found for cholera. Although up to 80 percent of cholera cases can be successfully treated with low-cost oral rehydration salts, the WHO estimates that annually more than 100,000 people succumb to the disease.The impact of cholera is most acute in regions with poor sanitation and unsafe supplies of drinking water, conditions that annually spawn three to five million cases worldwide. The entire country of Bangladesh is considered at high risk for this disease, the only country with this designation from the WHO.

 

Delete Buttons

Like tuberculosis, cholera elicits a complex immune response. The infection takes place in the mucosal membrane of the small intestine, where billions of beneficial bacteria live. Our gut microbiota perform welcome chores such as fermenting carbohydrates to release their useful energy. Although our gut mucosa is always on the alert for foreign bacteria, killing every newcomer would be imprudent, as some may be useful in maintaining the health of their human host. Yet when a pathogen is identified, the mucosal cells mount a vigorous immune response.

 

Unfortunately, the basic mechanisms of that response are still poorly understood. This knowledge gap has hindered the development of effective, durable vaccines for diseases such as cholera. In fact, current vaccines offer only partial protection that lasts for just a few years.

To extend this protection, or perhaps even block the disease permanently, researchers, including John Mekalanos, the Adele H. Lehman Professor of Microbiology and Molecular Genetics and head of the Department of Microbiology and Immunobiology at HMS, are tweaking the genetic makeup of Vibrio cholerae. The trick has been determining how to eliminate the genes that turn off the disease without disturbing the ones that elicit an immune reaction. Mekalanos, along with Mike Levine at the University of Maryland, has pioneered the use of a live oral cholera vaccine. This vaccine uses a genetically altered version of the organism that is unable to cause disease.

In addition to learning which genes halt the cholera bacterium, it is necessary to understand which ones are activated during its transmission and infection. Stephen Calderwood ’75, the Morton N. Swartz, M.D. Academy Professor of Medicine (Microbiology and Immunobiology) at HMS and Massachusetts General Hospital, is looking at gene expression at different points in V. cholerae’s life cycle to determine which genes are expressed by the pathogen during infection, as well as which trigger immune responses in the human host.

For this research, Calderwood is collaborating with clinicians and researchers at the International Centre for Diarrhoeal Disease Research in Dhaka, Bangladesh. Calderwood’s team has collected thousands of samples from patients who have been hospitalized with severe cholera.

 

The Sniff Test

The insights from such molecular biology studies can also lead to some surprising diagnostic tools for infectious disease. The tubercle bacterium, for example, can be insidious; it can lurk in the lungs of a mildly infected patient for years. Active infections of the bacterium, however, release a detectable signature of volatile organic compounds. This airborne fingerprint may be useful in diagnosing the disease, particularly in children; not only is it difficult for them to produce sufficient sputum for analysis, their sputum contains relatively few of the organisms.

“A baby’s exhalation could be captured,” says Ed Nardell, an HMS associate professor of medicine at Brigham and Women’s, “so she wouldn’t need to produce a sputum sample.”

 

Nardell is part of a team that’s investigating the effectiveness of a new gas chromatography technology that can detect the chemical signature of M. tuberculosis in a few puffs of human breath. In some parts of the world, giant Gambian rats, trained to sniff out the bacterium’s signature compounds, are already being used to detect M. tuberculosis in sputum samples. Unlike humans using microscopes, these trained rats accurately examine specimen after specimen without fatigue—and all for the fee of a sweet treat.

 

Phase Shifts

Another complicating factor in the fight against these diseases is that the causal agents change throughout their life cycles. The tubercle bacterium modifies its environment to suit its needs. By contrast, the cholera bacterium acclimates itself to the environment it inhabits. Many cholera microbes spend their lives in water, feeding on plankton to derive energy. During this aquatic phase, the adaptations that help them survive in water make them much less infectious in humans. Calderwood and his team, however, have discovered that the cholera microbes found in the fecal matter of infected humans—before the microbes adapt to the aquatic environment—are hyperinfectious for a brief period following their evacuation from the host.

Because this human ecology is important to the transmission of the disease, Calderwood’s collaborators in Bangladesh dispatch research teams to patients’ homes. To study disease transmission in a household, the team invites all family members, sick or well, to participate. While visiting, the team can survey a patient’s living conditions and, if needed, provide medical care to other family members.

 

“These diseases are perfect examples of how knowing the social context of an infection can be crucial,” says Mercedes Becerra, an HMS associate professor of global health and social medicine. “It’s not some vague notion of social context; it’s actually seeing the physical setting where people live and testing the strains that have infected different members of a family or community. The household is a really important unit for analysis and for medical interaction.”

Just as it is crucial to see how the bacteria operate—at the chemical and genetic levels—in human hosts, it is important to understand how the illness plays out in the context of specific human populations, according to Becerra.

 

Knit One, World View

These diseases also interact in another key ecosystem: the community of HMS researchers working on global health and infectious disease. Some may be community health workers with knowledge of the lives of their neighbors. Some are social scientists measuring the clinical effectiveness of different approaches to preventing and treating these diseases, or mapping the social, political, and historical aspects of health. Geneticists, immunologists, engineers, and architects—each play a role in teasing out the intricacies of these diseases and the pathogens that cause them.

“To beat these diseases, somebody has to understand the immune system and the bugs at different levels,” Becerra says, “while others have to work on understanding the impact on patients and families. That’s why it’s so important to work together from multiple angles, linking discovery with care delivery—and then turn around to look for new discoveries.”

Jake Miller is a science writer in the HMS Office of Communications and External Relations.

 

by Jake Miller

 

 

 

Hms.harvard.edu [en línea] Cambridge, MA (USA)

hms.harvard.edu, 03 de octubre de 2013 [ref. Summer 2013] Disponible en Internet: http://hms.harvard.edu/news/harvard-medicine/harvard-medicine/how-bugs-are-built/epidemic-proportions



Secrets of trail-blazing bacteria revealed

22 07 2013

Bacteria in slimy biofilms are able to spread rapidly over surfaces such as catheters by building a transport network with DNA for tracks, say Australian researchers.

Microbiologist Associate Professor Cynthia Whitchurch from the University of Technology, Sydney and colleagues report their findings today in the journal Proceedings of the National Academy of Sciences.

Extracellular DNA (yellow) organises traffic flow of individual bacteria (blue) as a biofilm expands and spreads infection (Source: E. Gloag and L. Turnbull/The ithree institute and University of Technology Sydney)

Extracellular DNA (yellow) organises traffic flow of individual bacteria (blue) as a biofilm expands and spreads infection (Source: E. Gloag and L. Turnbull/The ithree institute and University of Technology Sydney)

“By following each other along this network and behaving the rules they can move quite efficiently through the system and out to the front of the biofilm,” says Whitchurch.

“We believe this is the equivalent to how a bacterial biofilm would expand up a catheter.”

Bacteria colonise the surfaces of our body, and the environment, in communities held together with slime.

These “biofilms” are a real problem because they make the bacteria resistant to antibiotics and disinfectants, and to the immune systems of organisms.

“They’re really resistant to everything we can throw at them, pretty much,” says Whitchurch.

“Probably half of hospital-acquired infections are due to biofilms forming on implanted medical devices … like catheters.”

If a biofilm establishes on a catheter, it can migrate and spread infection up to the bladder and kidneys, says Whitchurch.

To investigate how biofilms form and expand into new areas she and colleagues studied Pseudomonas aeruginosa, a bacteria that commonly causes urinary tract and respiratory infections.

 

Virtual tracking

The researchers used a technique called high-resolution phase-contrast time-lapse microscopy to track the movement of thousands of individual bacterial cells on computer.

“For the first time we could get quantitative data of individual cell movements during the process of biofilm expansion,” says Whitchurch. 

She and colleagues were able to show the cells lining up in co-ordinated fashion to blaze new trails.

Atomic force microscopy revealed that the advancing bacteria were forging furrows, which constituted the edges of the network.

Fluorescence microscopy revealed that DNA excreted by the bacteria provided the network “tracks” that organised the flow of bacterial traffic.

“You have long ropes of DNA that the bacteria are aligning themselves to,” says Whitchurch.

To demonstrate the role of the DNA the researchers used an enzyme to chew up the DNA.

“When we remove the DNA, the bacteria completely lose their ability to co-ordinate their behaviours. They start bouncing around as individual cells and end up in traffic jams and the whole rate of expansion of the biofilm seizes up.”

 

Bulldozing bacteria

Importantly, Whitchurch and colleagues also found that the DNA was also helping to glue together individual bacteria, called “bulldozer aggregates”, which collectively forged new furrows ahead of them. 

“They can’t move out into new territory individually. They have to act as a collective to do that,” says Whitchurch.

She says if this is indeed how bacterial biofilms colonise, it suggests ways of controlling biofilms on medical devices such as catheters.

“One opportunity is to build our own networks that tell the bacteria to go in a way that doesn’t enable their biofilm to expand,” says Whitchurch.

Whitchurch suggests it might be possible to insert small furrows on the devices using microfabrication that would limit the spread of the biofilm.

“We could build our own furrows and get the bacteria running around in futile circles instead of co-ordinating themselves to move along the device,” she says.

 

 

Abc.net.au [en línea] Sydney (AUS): abc.net.au, 22 de julio de 2013 [ref. 25 de junio de 2013] Disponible en Internet: http://www.abc.net.au/science/articles/2013/06/25/3788443.htm?topic=health



Aplicaciones médicas de las proteínas adhesivas del mejillón.

25 02 2013

Cuando se trata de energía para adherirse en condiciones de humedad, los mejillones marinos son difíciles de superar, ya que pueden pegarse a prácticamente todas las superficies inorgánicas y orgánicas y mantenerse en agua salada, incluyendo entornos turbulentos de marea. Esa proteína adhesiva del mejillón ha servido de fuente de inspiración a los científicos para aplicaciones biomédicas, como la entrega de medicamentos de reparación quirúrgica y fármacos contra el cáncer.

Foto: TAMORLAN

Foto: TAMORLAN

En concreto, se han creado nuevos materiales que imitan las proteínas adhesivas del mejillón para tres aplicaciones médicas: selladores para la reparación de la membrana fetal, la autoconfiguración de hidrogeles antibacterianos y polímeros para la entrega de fármacos contra el cáncer y la destrucción térmica de las células cancerosas.

Phillip B. Messersmith, profesor de Ingeniería Biomédica en la Escuela McCormick de Ingeniería y Ciencias Aplicadas de la Universidad Northwestern, en Estados Unidos, hablará de su investigación en este sentido en el simposio ‘La traducción de Adhesión Mejillón beneficiosos a nuevos conceptos y materiales’ que se celebrará en la reunión anual de la Asociación Americana para el Avance de la Ciencia (AAAS) que tiene lugar estos días en Boston.

“La adhesión del mejillón es un proceso notable que implica la secreción de una proteína de pegamento líquido que se endurece rápidamente en un sólido, adhesivo resistente al agua– explica Messersmith–. Varios aspectos de este proceso inspiran nuestro desarrollo de materiales sintéticos para aplicaciones prácticas. Una oportunidad inusualmente convincente para la traducción de los conceptos de adhesión de mejillón es en la reparación o reconstrucción de tejidos en el cuerpo humano, donde el agua es ubicua y su presencia representa un desafío para alcanzar los resultados deseados”.

El pie del mejillón común (Mytilus edulis) produce un pegamento pegajoso para adherirse a las rocas y otros objetos y su clave es una familia de proteínas especiales, denominadas proteínas adhesivas del mejillón, que contienen una alta concentración de DOPA catecólico ácido amino (dihidroxifenilalanina). Todos los materiales biomédicos creados por Messersmith contienen una forma sintética de DOPA, un polímero sintético con una DOPA sencilla que desarrolló por primera vez en 2002.

Para la reparación de la membrana fetal, que puede romperse prematuramente de forma espontánea o por un procedimiento quirúrgico, que a menudo conduce a un parto prematuro, nacimiento prematuro y otras complicaciones graves, el polímero sintético de Messersmith se formula como un pegamento líquido que se solidifica rápidamente al adherirse al tejido húmedo y sella los defectos fetales membrana. Su grupo está colaborando con investigadores en Europa para llevar a cabo pruebas in vivo de sus sellantes médicos inspirados en el mejillón para la reparación de la membrana fetal.

En el caso de los hidrogeles antibacterianos de autoajuste, Messersmith emplea plata tanto para inducir hidrogel de reticulación por vía de oxidación de catecol y como un precursor para la formación de nanopartículas de plata, que se incrustan dentro de la estructura del hidrogel y libera iones de plata para producir un efecto antibacteriano. Los iones de plata poseen actividad antibacteriana en concentraciones bajas, y esto ha conducido a un interés en la incorporación de plata en los dispositivos médicos.

El adhesivo sintético para la administración de fármacos contra el cáncer y la eliminación destrucción de las células cancerosas consiste en que el polímero forma vehículos sensibles al pH para suministro de fármacos que son estables e inactivos en el torrente sanguíneo, pero se activan en el ambiente del tumor ácido, liberando el fármaco.

Un segundo diseño consiste en modificar la superficie de nanorods de oro con un recubrimiento del polímero que ayuda a las células diana y que, una vez en el destino, los nanorods se irradian con luz de infrarrojo cercano para producir un calentamiento muy localizado que destruye térmicamente las células cancerosas.

 

 

Europapress.es [en línea] Madrid (ESP): europapress.es, 25 de febrero de 2013 [ref. 16 de febrero de 2013] Disponible en Internet: http://www.europapress.es/salud/noticia-pegamento-mejillon-inspira-cientificos-reparacion-quirurgica-20130216153202.html