Preventing cavities could one day involve the dental equivalent of a military surgical strike. A team of researchers supported by the National Institute of Dental and Craniofacial Research report they have created a new smart anti-microbial treatment that can be chemically programmed in the laboratory to seek out and kill a specific cavity-causing species of bacteria, leaving the good bacteria untouched.
The experimental treatment, reported online in the journal Antimicrobial Agents and Chemotherapy, is called a STAMP. The acronym stands for "specifically targeted antimicrobial peptides" and, like its postal namesake, STAMPs have a two-sided structure. The first is the short homing sequence of a pheromone, a signaling chemical that can be as unique as a fingerprint to a bacterium and assures the STAMP will find its target. The second is a small anti-microbial bomb that is chemically linked to the homing sequence and kills the bacterium upon delivery.
While scientists have succeeded in the past in targeting specific bacteria in the laboratory, this report is unique because of the STAMPs themselves. They generally consist of less than 25 amino acids, a relative pipsqueak compared to the bulky, bacteria-seeking antibodies that have fascinated scientists for years. Because of their streamlined design, STAMPs also can be efficiently and rapidly produced on automated solid-phase chemistry machines designed to synthesize small molecules under 100 amino acids, called peptides.
The first-generation STAMPs also proved extremely effective in the initial laboratory work. As reported in this month's paper, the scientists found they could eliminate the cavity-associated oral bacterium Steptococcus mutans within 30 seconds from an oral biofilm without any collateral damage to related but non pathogenic species attached nearby. Biofilms are complex, multi-layered microbial communities that routinely form on our teeth and organs throughout the body. According to one estimate, biofilms may be involved to varying degrees in up to 80 percent of human infections.
"We've already moved the S. mutans STAMP into human studies, where it can be applied as part of a paste or mouthrinse," said Dr. Wenyuan Shi, senior author on the paper and a scientist at the University of California at Los Angeles School of Dentistry. "We're also developing other dental STAMPs that target the specific oral microbes involved in periodontal disease and possibly even halitosis. Thereafter, we hope to pursue possible medical applications of this technology."
Shi said his group's work on a targeted dental therapy began about eight years ago with the recognition that everyday dental care had reached a crossroads. "The standard way to combat bacterial infections is through vaccination, antibiotics, and/or hygienic care," said Shi. "They represent three of the greatest public-health discoveries of the 20th century, but each has its limitations in the mouth. Take vaccination. We can generate antibodies in the blood against S. mutans. But in the mouth, where S. mutans lives and our innate immunity is much weaker, generating a strong immune response has been challenging."
According to Shi, a major limitation of antibiotics and standard dental hygiene is their lack of selectivity. "At least 700 bacterial species are now known to inhabit the mouth," said Shi. "The good bacteria are mixed in with the bad ones, and our current treatments simply clear everything away. That can be a problem because we have data to show that the pathogens grow back first. They're extremely competitive, and that's what makes them pathogenic."
To illustrate this point, Shi offered an analogy. "Think of a lawn infested with dandelions," he said. "If you use a general herbicide and kill everything there, the dandelions will come back first. But if you use a dandelion-specific killer and let the grass fill in the lawn, the dandelions won't come back."
Hoping to solve the selectivity issue, Shi and his colleagues began attaching toxins to the homing region of antibodies. They borrowed the concept from immunotherapy, an area of cancer research in which toxin-toting antibodies are programmed to kill tumor cells and leave the nearby normal cells alone.
Despite some success in killing specific bacteria in the oral biofilm, Shi said his group soon encountered the same technical difficulty that cancer researchers initially ran into with immunotherapy. Their targeting antibodies were large and bulky, making them unstable, therapeutically inefficient, and expensive to produce. "That's when we decided to get higher tech," said Dr. Randal Eckert, a UCLA scientist and lead author on the study.
Or, as Eckert noted, that's when they turned to the "power of genomics," or the comparative study of DNA among species. Eckert and colleagues clicked onto an online database that contains the complete DNA sequence of S. mutans. They identified a 21-peptide pheromone called "competence stimulating peptide," or CSP, that was specific to the bacterium. From there, they typed instructions into an automated solid-phase chemistry machine to synthesize at once the full-length CSP and a 16-peptide anti-microbial sequence, and out came their first batch of STAMPs.
After some trial and error, Eckert said he and his colleagues decided "to get even shorter." They ultimately generated a STAMP with the same anti-microbial agent but with a signature eight-peptide CSP sequence to target S. mutans. "We pooled saliva from five people and created an oral biofilm in the laboratory that included a couple hundred species of bacteria," said Eckert. "We applied the STAMP, and it took only about 30 seconds to eliminate the S. mutans in the mixture, while leaving the other bacteria in tact."
As dentists sometimes wonder, what would happen if S. mutans is eliminated from the oral biofilm? Does another equally or more destructive species fill its void, creating a new set of oral problems? Shi said nature already provides a good answer. "About 10 to 15 percent of people don't have S. mutans in their biofilms, and they do just fine without it," he said. "Besides, S. mutans is not a dominant species in the biofilm. It only becomes a problem when we eat a lot of carbohydrates."
Looking to the future, Shi said new STAMPs that seek out other potentially harmful bacterial species could be generated in a matter of days. He said all that is needed is the full DNA sequence of a microbe, a unique homing sequence from a pheromone, and an appropriate anti-microbial peptide. "We have a collection of anti-microbial peptides that we usually screen the bacterium through first in the laboratory," said Shi. "We can employ the anti-microbial equivalent of either a 2,000-ton bomb or a 200-pound bomb. Our choice is usually somewhere in the middle. If the anti-microbial peptide is too strong, it will also kill the surrounding bacteria, so we have to be very careful."
This research also was supported by a University of California Discovery Grant, Delta Dental of Washington, Delta Dental of Wisconsin, and C3 Jian Corporation. The National Institute of Dental and Craniofacial Research is the nation's leading funder of research on oral, dental, and craniofacial health.
Vegetables, Not Fruit, Help Fight Memory Problems in Old Age
CHICAGO - Eating vegetables, not fruit, helps slow down the rate of cognitive change in older adults, according to a study published in the October 24, 2006, issue of Neurology, the scientific journal of the American Academy of Neurology.
In determining whether there was an association between vegetables, fruit and cognitive decline, researchers from Rush University Medical Center studied 3,718 residents in Chicago, Illinois, who were age 65 and older. Participants completed a food frequency questionnaire and received at least two cognitive tests over a six-year period.
“Compared to people who consumed less than one serving of vegetables a day, people who ate at least 2.8 servings of vegetables a day saw their rate of cognitive change slow by roughly 40 percent, said study author Martha Clare Morris, ScD, associate professor at Rush University Medical Center in Chicago, Illinois. “This decrease is equivalent to about 5 years of younger age.”
Of the different types of vegetables consumed by participants, green leafy vegetables had the strongest association to slowing the rate of cognitive decline. The study also found the older the person, the greater the slowdown in the rate of cognitive decline if that person consumed more than two servings of vegetables a day. Surprisingly, the study found fruit consumption was not associated with cognitive change.
“This was unanticipated and raises several questions,” said Morris. “It may be due to vegetables containing high amounts of vitamin E, which helps lowers the risk of cognitive decline. Vegetables, but not fruits, are also typically consumed with added fats such as salad dressings, and fats increase the absorption of vitamin E. Further study is required to understand why fruit is not associated with cognitive change.”
Morris says the study’s findings can be used to simplify public health messages by saying people should eat more or less of foods in a specific food group, not necessarily more or less of individual foods.
The study was supported by grants from the National Institute on Aging.
Rush University Medical Center is an academic medical center that encompasses the more than 650 staffed-bed hospital (including Rush Children’s Hospital), the Johnston R. Bowman Health Center and Rush University. Rush University, with more than 1,270 students, is home to one of the first medical schools in the Midwest, and one of the nation’s top-ranked nursing colleges. Rush University also offers graduate programs in allied health and the basic sciences. Rush is noted for bringing together clinical care and research to address major health problems, including arthritis and orthopedic disorders, cancer, heart disease, mental illness, neurological disorders and diseases associated with aging.
Mayo Clinic study suggests that a central nervous system viral infection can lead to memory deficits
ROCHESTER, Minn. -- In one of the first known laboratory studies that explores memory deficits associated with a viral infection of the central nervous system, Mayo Clinic researchers have evidence that this infection can lead to memory loss late in life. The study, which was conducted in animal models, suggests that over the lifetime of an individual, a picornavirus-related infection could possibly have a permanent effect on memory late in life.
"Our study suggests that virus-induced memory loss could accumulate over the lifetime of an individual and eventually lead to clinical cognitive memory deficits," according to Charles L. Howe, Ph.D., a Mayo Clinic neuroscientist and corresponding author of the study that appears on the cover of the November issue of Neurobiology of Disease. The study's first author is Eric J. Buenz, Ph.D., a recent graduate of the molecular neuroscience program at Mayo Graduate School.
Picornaviruses are the most common infectious viral agents in humans. They are a family of viruses that include rhinoviruses, which is a virus associated with the common cold; enteroviruses, a virus associated with respiratory and gastrointestinal ailments; encephalitis, inflammation of the brain; myocarditis, inflammation of heart muscle; and meningitis.
Other viruses in this family include those that cause foot-and-mouth disease, polio and hepatitis A. Researchers were intrigued by the possibility of a link between picornavirus infections and memory loss. Little has been published in this area, Dr. Howe says.
In the study, mice were infected with Theiler's murine (mouse) encephalomyelitis virus (comparable to the human poliovirus). Researchers looked for signs of spatial memory loss in the mice. Mice that contracted the virus had difficulty learning to navigate a maze designed to test various components of spatial memory. The degree of memory impairment, which ranged from no discernable damage to complete devastation, was directly correlated to the number of dead brain cells in the hippocampus region of the mouse's brain.
Picornaviruses infect more than one billion people worldwide each year. Generally individuals contract two or three enterovirus and/or rhinovirus infections each year. In some cases the viruses get into the brain, and in some children these viruses can cause long-lasting brain injuries. "We think picornavirus family members cross into the brain and cause a variety of brain injuries. For example, the polio virus can cause paralysis. It can injure the spinal cord and different parts of the brain responsible for motor function. In the murine virus we studied, it did the same thing and also injured parts of the brain responsible for memory," Dr. Howe says.
Enteroviruses and rhinoviruses are among the most common in the picornavirus family. Certain enteroviruses (gastrointestinal illnesses among others), such as enterovirus 71, are common in Asia, particularly southeast Asia where many children are infected. Once the virus infects the host due to unsanitary conditions, it can cross over into the brain and cause encephalitis, which can lead to conditions ranging from lethargy to a coma. In recent years, scores of children have died from infection.
The degree of brain damage in humans infected with a picornavirus infection is not known, but the evidence from the mouse study suggests this is an area of research that should be explored further.
"Our findings suggest that picornavirus infections throughout the lifetime of an individual may chip away at the cognitive reserve, increasing the likelihood of detectable cognitive impairment as the individual ages. We hypothesize that mild memory and cognitive impairments of unknown etiology may, in fact, be due to accumulative loss of hippocampus function caused by repeated infection with common and widespread neurovirulent picornaviruses. Further analysis of such deficits and exploration of potential therapeutic interventions is clearly needed," the authors wrote.
Clinical case studies indicate that picornavirus infections in humans may be associated with inflammation of the brain and damage to the hippocampus -- the part of the brain responsible for forming, storing and processing memory. Inflammation-induced damage to the brain is believed to be associated with learning and memory deficits.
Because picornaviruses are widespread and infection is common, the potential for this family of viruses to damage the human brain presents a very real medical problem, Dr. Howe says.
In general, viruses that kill neurons in the hippocampus are not uncommon. For example infections caused by the herpes virus or human immunodeficiency virus (HIV) can lead to the loss of brain cells, but while brain damage from these viruses is based on a persistent infection, brain damage from a picornavirus infection occurs only during the acute phase of infection.
"Because they are all related, by studying one, we may learn something about all of them. My hope is that we will learn something about the virus and the serious illnesses associated with other viruses in this family," Dr. Howe says.
"Because hippocampus injury was correlated with reduced spatial memory formation across a range of damage and a range of memory performance, we suggest that picornavirus infection of the human central nervous system is likely to result in at least some degree of neurological deficit," the authors write.
The study was funded by grants from the National Multiple Sclerosis Society; National Institutes of Health; a gift from Donald and Francis Herdrich; and the Mayo Graduate School.
Diversity promotes cooperation among microbes
Understanding how cooperation evolves and is maintained represents one of evolutionary biology's thorniest problems. This stems from the fact that freeloading cheats will evolve to exploit any cooperative group that doesn't defend itself, leading to the breakdown of cooperation. New research using the bacterium Pseudomonas fluorescens has identified a novel mechanism that thwarts the evolution of cheats and broadens our understanding of how cooperation might be maintained in nature and human societies. The new findings are reported by Michael Brockhurst of the University of Liverpool and colleagues at the Université Montpellier and the University of Oxford in the October 24th issue of the journal Current Biology, published by Cell Press.
Pseudomonas fluorescens "wrinkly-spreader" colony. Credit: Andrew Spiers
Bacteria are known to cooperate in a wide variety of ways, including the formation of multicellular structures called biofilms. P. fluorescens biofilms are formed when individual cells overproduce a polymer that sticks the cells together, allowing the colonization of liquid surfaces. While production of the polymer is metabolically costly to individual cells, the biofilm group benefits from the increased access to oxygen that surface colonization provides. However, cheating types rapidly evolve that live in the biofilm but don't produce the polymer. The presence of cheats weakens the biofilm, imperiling its survival by causing it to sink.
In the new work, the researchers studied the effect of short-term evolution of diversity within the biofilm on the success of cooperation. The researchers found that within biofilms, diverse cooperators evolved to use different nutrient resources, thereby reducing the competition for resources within the biofilm. The researchers then manipulated diversity within experimental biofilms and found that diverse biofilms contained fewer cheats and can produce larger groups than non-diverse biofilms. The findings indicate that, as in ecological communities, biodiversity within biofilms is beneficial--moreover, the authors point out that this is the first time that such ideas have been applied in the context of social evolution, and it represents a new way in which cooperation can survive in the face of cheating. Furthermore, the new work sheds light on how division of labor within multicellular organisms may initially have evolved in order to minimize functional redundancy among cells and to increase efficiency.
The researchers include Michael A. Brockhurst of University of Liverpool in Liverpool, UK and Université Montpellier II in Montpellier, France; Michael E. Hochberg of Université Montpellier II in Montpellier, France; Thomas Bell and Angus Buckling of University of Oxford, South Parks Road in Oxford, UK.
This work was supported by grants from Les Fonds National de la Science, Programme Microbiologique (France), and the Royal Society (UK).
Brockhurst et al.: "Character Displacement Promotes Cooperation in Bacterial Biofilms." Publishing in Current Biology 16, 2030–2034, October 24, 2006 DOI 10.1016/j.cub.2006.08.068. www.current-biology.com
Healthy men who drink moderately have reduced risk of heart attack
For men with healthy lifestyle habits, drinking moderate amounts of alcohol may be associated with a lower risk of heart attack than drinking heavily or not drinking at all, according to a report in the October 23 issue of Archives of Internal Medicine, one of the JAMA/Archives journals.
Previous studies have found that adults who drink moderate amounts of alcohol have a lower risk of myocardial infarction (heart attack) than those who do not drink at all, according to background information in the article. Researchers suspect this is due to increased levels of HDL or "good" cholesterol in the blood. Because there are many risks associated with heavy drinking, physicians do not typically recommend that patients begin drinking alcohol to reduce their heart disease risk--instead, they focus on other proven lifestyle interventions, including diet and exercise. However, these habits are not mutually exclusive, the authors write. "For individuals who exercise, abstain from smoking, maintain optimal weight and adhere to an appropriate diet, there may be few other standard lifestyle interventions to lower risk," the authors write. "Whether alcohol intake is related to a lower risk for myocardial infarction in such individuals is unknown."
Kenneth J. Mukamal, M.D., M.P.H., M.A., Beth Israel Deaconess Medical Center, Boston, and colleagues assessed the connection between drinking alcohol and heart attack in 8,867 healthy men who were part of the Health Professionals Follow-up Study, which began in 1986 and included 51,529 dentists, pharmacists, veterinarians and other health care professionals age 40 to 75. At the beginning of the study and at regular intervals afterward, the participants filled out questionnaires about their diets and medical conditions, reported the frequency with which they consumed particular substances and specified the types of alcohol they drank. All of the men in the current study had healthy lifestyles, defined as not smoking, having a body mass index (BMI) of less than 25, getting at least 30 minutes of exercise per day and eating a healthy diet, including large amounts of fruits, vegetables, fish and polyunsaturated fats and low amounts of trans-fats and red meat.
Between 1986 and 2002, 106 men had heart attacks. This included eight of the 1,282 who drank 15 to 29.9 grams of alcohol per day (about two drinks), nine of the 714 who drank 30 grams or more per day, 34 of the 2,252 who drank .1 to 4.9 drinks per day and 28 of the 1,889 who did not drink at all. Those who drank 15 to 29 grams per day had the lowest risk for heart attack and those who did not drink at all had the highest. The researchers also performed an analyses comparing those who drank 5 grams per day or more and those who drank less than 5 grams a day. For the latter, "we estimate that 25 percent of the incidence cases of myocardial infarction in this population were attributable to consuming less than 5 grams per day," the authors write.
"There is a complicated mix of risks and benefits attributed to moderate drinking in observational studies, and the individual and societal complications of heavy drinking are well known," the authors conclude. "It is easy to understand why clinical guidelines encourage physicians and patients to concentrate on seemingly more innocuous interventions, despite the relative paucity of effective, straightforward and generalizable methods for encouraging regular physical activity, weight reduction and abstinence from smoking in clinical practice. Our results suggest that moderate drinking could be viewed as a complement, rather than an alternative, to these other lifestyle interventions, a viewpoint espoused by some authors."
(Arch Intern Med. 2006;166:2145-2150. Available pre-embargo to the media at www.jamamedia.org.)
Editor's Note: This study was supported by grants from the National Institutes of Health. Co-author Dr. Rimm has received honoraria for occasional speaking engagements at research conferences from industry-related organizations (Distilled Spirits Council and National Beer Wholesalers Association). Please see the article for additional information, including other authors, author contributions and affiliations, financial disclosures, funding and support, etc.
Steep oxygen decline halted first land colonization by Earth's sea creatures
Vertebrate creatures first began moving from the world's oceans to land about 415 million years ago, then all but disappeared by 360 million years ago. The fossil record contains few examples of animals with backbones for the next 15 million years, and then suddenly vertebrates show up again, this time for good.
The mysterious lull in vertebrate colonization of land is known as Romer's Gap, named for the Yale University paleontologist, Alfred Romer, who first recognized it. But the term has typically been applied only to pre-dinosaur amphibians, and there has been little understanding of why the gap occurred.
Now a team of scientists led by University of Washington paleontologist Peter Ward has found a similar gap during the same period among non-marine arthropods, largely insects and spiders, and they believe a precipitous drop in the oxygen content of Earth's atmosphere is responsible.
"These two groups acted exactly the same way. They proliferated, then they went away, and then they reappeared and multiplied like crazy," said Ward, a UW professor of biology and of Earth and space sciences.
He notes that atmospheric oxygen rose sharply at the end of the Silurian period about 415 million years ago, to reach a level of about 22 percent of the atmosphere, similar to today's oxygen content. But 55 million years later, atmospheric oxygen levels sank to 10 percent to 13 percent. The level remained low for 30 million years – during which Romer's Gap occurred – then shot up again, and vertebrates and arthropods again began moving from the sea to land.
"It matches two waves of colonization of the land," Ward said. "In the first wave the animals' lungs couldn't have been very good and when the oxygen level dropped it had to be hard for the vertebrates coming out of the water. I wonder if there is a minimum level of oxygen that has to be reached or nothing could ever have gotten out of the water."
Dinosaurs first appeared in the last part of the Triassic period, about 230 million years ago. That was during one of the lowest ebbs of atmospheric oxygen content of the last 500 million years, but he speculates that it took some time, until oxygen levels rose appreciably, before dinosaurs grew to their familiar gargantuan sizes.
"Dinosaurs thrived and nothing else did. There's an explanation for that, and it is that the air sac breathing system in dinosaurs and their descendants, modern birds, is more efficient than systems used by other organisms," Ward said.
He and his colleagues tested that hypothesis by examining the breathing system used by birds. They found that at sea level birds breathe 30 percent more efficiently than mammals and at 5,000 feet in elevation birds are 200 percent more efficient.
Ward pictures a world in which dinosaurs were able to adapt to low atmospheric oxygen content relatively easily, and when oxygen levels rose the dinosaurs developed into giant creatures that dominated the Earth.
"I think of dinosaurs as the high-altitude Denver athletes of their day. They ran rings around their prey," he said.
Ward also began to wonder whether respiratory needs dictated how other organisms' bodies developed. He thought that perhaps, rather than being based on feeding and movement, body shape and design might largely be determined by respiratory efficiency. For instance, a mollusk shell is typically thought of as protection for the marine creature, he said, but it turns out the shell actually channels water across the gill to deliver oxygen.
"An unshelled mollusk has a far greater respiratory problem than a shelled mollusk," Ward said. "In many groups the shell is an active part of the respiratory system."