Shape of things to come in platelet mimicry

By mimicking the shape, size, flexibility and surface chemistry of real platelets, artificial platelets are pushed out of the main blood flow to vessel walls. There, the surface chemistry enables them to anchor on damaged cells and induce faster clotting at the site. Credit: Anirban Sen Gupta

Artificial platelet mimics developed by a research team from Case Western Reserve University and University of California, Santa Barbara, are able to halt bleeding in mouse models 65 percent faster than nature can on its own.

For the first time, the researchers have been able to integratively mimic the shape, size, flexibility and surface chemistry of real blood platelets on albumin-based particle platforms. The researchers believe these four design factors together are important in inducing clots to form faster selectively at vascular injury sites while preventing harmful clots from forming indiscriminately elsewhere in the body.

The new technology, reported in the journal ACS Nano, is aimed at stemming bleeding in patients suffering from traumatic injury, undergoing surgeries or suffering clotting disorders from platelet defects or a lack of platelets. Further, the technology may be used to deliver drugs to target sites in patients suffering atherosclerosis, thrombosis or other platelet-involved pathologic conditions.

Anirban Sen Gupta, an associate professor of biomedical engineering at Case Western Reserve, previously designed peptide-based surface chemistries that mimic the clot-relevant activities of real platelets. Building on this work, Sen Gupta now focuses on incorporating morphological and mechanical cues that are naturally present in platelets to further refine the design.

"Morphological and mechanical factors influence the margination of natural platelets to the blood vessel wall, and only when they are near the wall can the critical clot-promoting chemical interactions take place," he said.

These natural cues motivated Sen Gupta to team up with Samir Mitragotri, a professor of chemical engineering at UC Santa Barbara, whose laboratory has recently developed albumin-based technologies to make particles that mimic the geometry and mechanical properties of red blood cells and platelets.

Together, the team has developed artificial platelet-like nanoparticles (PLNs) that combine morphological, mechanical and surface chemical properties of natural platelets.

The researchers believe this refined design will be able to simulate natural platelet's ability to collide effectively with larger and softer red blood cells in systemic blood flow. The collisions cause margination -- pushing the platelets out of the main flow and closer to the blood vessel wall -- increasing the probability of interacting with an injury site.

The surface coatings enable the artificial platelets to anchor to injury-site-specific proteins, von Willebrand Factor and collagen, while inducing the natural and artificial platelets to aggregate faster at the injury site.

Testing in mouse models showed that intravenous injection of these artificial platelets formed clots at the site of injury three times faster than natural platelets alone in control mice.

The ability to interact selectively with injury site proteins, as well as the ability to remain mechanically flexible like natural platelets, enables these artificial platelets to safely ride through the smallest of blood vessels without causing unwanted clots.

Albumin, a protein found in blood serum and eggs, is already used with cancer drugs and considered a safe material. Artificial platelets that don't become involved in a clot and continue to circulate are metabolized within one to two days.

The researchers believe the new artificial platelet design may be even more effective in larger volume blood flows where margination to the blood vessel wall is more prominent. They expect to soon begin testing those capabilities.

This research was previously funded by American Heart Association and is currently funded by National Institutes of Health.

In addition to stemming bleeding, Sen Gupta believes the technology could also be useful in delivering clot-busting medicines directly to clots, to treat heart attack or stroke without having to systemically suspend the body's coagulation mechanism. The artificial platelets may also be used to deliver cancer medicines to metastatic tumors that have high platelet interactions. Sen Gupta is seeking grants to pursue that work.

Source: Case Western Reserve University

Genetic factors behind surviving or dying from Ebola shown in mouse study

In an emerging disease research lab at the University of Washington, Chris Williams, a research scientist who specializes in microbiology laboratory robotics, programs a piece of equipment that can be programmed to performs many lab tasks. Credit: Brian Donohue

A newly developed mouse model suggests that genetic factors are behind the mild-to-deadly range of reactions to the Ebola virus.

People exposed to Ebola vary in how the virus affects them. Some completely resist the disease, others suffer moderate to severe illness and recover, while those who are most susceptible succumb to bleeding, organ failure and shock.

In earlier studies of populations of people who have contracted Ebola, these differences are not related to any specific changes in the Ebola virus itself that made it more or less dangerous; instead, the body's attempts to fight infection seems to determine disease severity.

In the Oct. 30 edition of Science, scientists describe strains of laboratory mice bred to test the role of an individual's genetic makeup in the course of Ebola disease. Systems biologists and virologists Angela Rasmussen and Michael Katze from the Katze Laboratory at the University of Washington Department of Microbiology led the study in collaboration with the National Institutes of Health's Rocky Mountain Laboratories in Montana and University of North Carolina at Chapel Hill.

Research on Ebola prevention and treatment has been hindered by the lack of a mouse model that replicates the main characteristics of human Ebola hemorrhagic fever. The researchers had originally obtained this genetically diverse group of inbred laboratory mice to study locations on mouse genomes associated with influenza severity.

The research was conducted in a highly secure, state-of-the-art biocontainment safety level 4 laboratory in Hamilton, Mont. The scientists examined mice that they infected with a mouse form of the same species of Ebola virus causing the 2014 West Africa outbreak. The study was done in full compliance with federal, state, and local safety and biosecurity regulations. This type of virus has been used several times before in research studies. Nothing was done to change the virus.

Interestingly, conventional laboratory mice previously infected with this virus died, but did not develop symptoms of Ebola hemorrhagic fever.

In the present study, all the mice lost weight in the first few days after infection. Nineteen percent of the mice were unfazed. They not only survived, but also fully regained their lost weight within two weeks. They had no gross pathological evidence of disease. Their livers looked normal.

Eleven percent were partially resistant and less than half of these died. Seventy percent of the mice had a greater than 50 percent mortality. Nineteen percent of this last group had liver inflammation without classic symptoms of Ebola, and thirty-four percent had blood that took too long to clot, a hallmark of fatal Ebola hemorrhagic fever in humans. Those mice also had internal bleeding, swollen spleens and changes in liver color and texture.

The scientists correlated disease outcomes and variations in mortality rates to specific genetic lines of mice.

"The frequency of different manifestations of the disease across the lines of these mice screened so far are similar in variety and proportion to the spectrum of clinical disease observed in the 2014 West African outbreak," Rasmussen said.

While acknowledging that recent Ebola survivors may have had immunity to this or a related virus that saved them during this epidemic, Katze said, "Our data suggest that genetic factors play a significant role in disease outcome."

In general, when virus infection frenzied the genes involved in promoting blood vessel inflammation and cell death, serious or fatal disease followed. On the other hand, survivors experienced more activity in genes that order blood vessel repair and the production of infection-fighting white blood cells.

The scientists note that certain specialized types of cells in the liver could also have limited virus reproduction and put a damper on systemic inflammation and blood clotting problems in resistant mice. Susceptible mice had widespread liver infection, which may explain why they had more virus in their bodies and poorly regulated blood coagulation. The researchers also noticed that spleens in the resistant and susceptible mice took alternate routes to try to ward off infection.

"We hope that medical researchers will be able to rapidly apply these findings to candidate therapeutics and vaccines," Katze said. They believe this mouse model can be promptly implemented to find genetic markers, conduct meticulous studies on how symptoms originate and take hold, and evaluate drugs and that have broad spectrum anti-viral activities against all Zaire ebolaviruses, including the one responsible for the current West African epidemic.

Source: University of Washington Health Sciences/UW Medicine

Teeth, sex and testosterone reveal secrets of aging in wild mouse lemurs

A brown mouse lemur in the wild. Mouse lemurs, weighing a mere 30 to 80 grams, are the world's smallest primates. Credit: Jukka Jernvall

Mouse lemurs can live at least eight years in the wild -- twice as long as some previous estimates, a long-term longitudinal study finds.

PLOS ONE published the research on brown mouse lemurs (Microcebus rufus) led in Madagascar by biologist Sarah Zohdy, a post-doctoral fellow in Emory's Department of Environmental Sciences and the Rollins School of Public Health. Zohdy conducted the research while she was a doctoral student at the University of Helsinki.

"It's surprising that these tiny, mouse-sized primates, living in a jungle full of predators that probably consider them a bite-sized snack, can live so long," Zohdy says. "And we found individuals up to eight years of age in the wild with no physical symptoms of senescence like some captive mouse lemurs start getting by the age of four."

It is likely that starvation, predation, disease and other environmental stressors reduce the observed rate of senescence in the wild, Zohdy notes, but a growing body of evidence also suggests that captive conditions may affect mental and physical function.

"We focused on wild mouse lemurs because we want to know what happens naturally when a primitive primate is exposed to all of the extrinsic and intrinsic mortality factors that shaped them as a species," Zohdy says. "Comparing longevity data of captive and wild mouse lemurs may help us understand how the physiological and behavioral demands of different environments affect the aging process in other primates, including humans."

The study determined ages of wild mouse lemurs in Madagascar's Ranomafana National Park through a dental mold method that had not previously been used with small mammals. In addition to the high-resolution tooth-wear analysis for aging, fecal samples underwent hormone analysis.

The researchers found no difference between the longevity of male and female mouse lemurs, unlike most vertebrates where males tend to die first.

"And even more interestingly, we found no difference in testosterone levels between males and females," Zohdy says. Mouse lemurs are female dominant, which may explain why their testosterone levels are on a par with males.

"While elevated male testosterone levels have been implicated in shorter lifespans in several species, this is one of the first studies to show equivalent testosterone levels accompanying equivalent lifespans," Zohdy says.

A co-author of the study is primatologist Patricia Wright of the Centre ValBio Research Station in Madagascar and Stony Brook University. Other institutions involved in the study include Colorado State University, Duke University and the University of Arizona, Tucson.
Mouse lemurs, found only on the island of Madagascar, are the world's smallest primates. They are among nearly 100 species of lemurs that arrived in Madagascar some 65 million years ago, perhaps floating over from mainland Africa on mats of vegetation.

Mouse lemurs weigh a mere 30 to 80 grams but in captivity they live six times longer than mammals of similar body size, such as mice or shrews. Captive gray mouse lemurs (Microcebus murinus) can live beyond age 12. By age four, however, they can start exhibiting behavioral and neurologic degeneration. In addition to slowing of motor skills and activity levels, reduced memory capacity and sense of smell, the captive four-year-olds can start developing gray hair and cataracts, Zohdy says.

The wild brown mouse lemurs in the study were trapped, marked and released during the years 2003 to 2010. A total of 420 dental impressions were taken from the lower-right mandibular tooth rows of 189 unique individuals. Over the course of seven years, 270 age estimates were calculated. For 23 individuals captured three or more times during the duration of the study, the regression slopes of wear rates were calculated and the mean slope was used to calculate ages for all individuals.

"We found that wild brown mouse lemurs can live at least eight years," Zohdy says. "In the population that we studied, 16 percent lived beyond four years of age. And we found no physical signs of senescence, such as graying hair or cataracts, in any wild individual."

Limitations of the study include the inability to document gradual physiological symptoms of senescence in the wild. "Our results do not provide information about wild brown mouse lemurs that can be directly compared to senescence in captive gray mouse lemurs," Zohdy says. "Further research, using identical measures of senescence, will help to reveal whether patterns of physiological senescence occur consistently across the genus and in both captive and wild conditions."

Another confounding factor Zohdy cites is "the Sleeping Beauty effect," the fact that wild mouse lemurs hibernate for half the year, possibly boosting their life span.
"We now know that mouse lemurs can live a relatively long time in the wild," she says, "but we don't know the exact mechanisms behind why they live so long."

Source: Emory Health Sciences