The Petri dish is a shallow, circular, glass or plastic dish with a loose-fitting cover over the top and sides, used for culturing bacteria and other microorganisms. The story of the Petri dish is an interesting one. Julius Richard Petri (1852-1921), a bacteriologist, worked for the master of “germ theory” in Germany in the late 1800s, Robert Koch (1843-1910). Initially, bacteria were cultured in liquid broth–a practice captured in famous images of experiments on spontaneous generation. Koch saw the advantage of growing bacteria on a solid medium instead. By spreading out mixtures of microorganisms on a solid surface, he could separate individual types in isolated colonies. With pure colonies, he could investigate the effects of each bacterium. The method allowed Koch to identify the specific organisms that cause tuberculosis, cholera, diphtheria, among many other diseases–and then to develop vaccines. At first, however, Koch used a “puddle” of gelatin on a flat piece of glass. Later, the gelatin was spread on the side of a flat bottle, accessed through a narrow opening at the end. Petri, however, realized that one could pour the gelatin in a shallow dish, and put a cover on it, making it easier to get at the bacterial cultures. Since then, of course, the Petri dish has become a staple in laboratory work–and not just in studying microbes. Koch’s work is certainly remembered (though oddly his name does not carry beyond the world of microbiologists, in the way that Pasteur’s has). However, at the same time, the name of Koch’s assistant has become a household word, though few know exactly who he was.
August 05, 2007
Genetically disabling the sensory organ that mice use to detect pheromones causes female mice to behave like males.
By short-circuiting the sensory organ that detects the chemical cues mice use to attract mates, a team of Howard Hughes Medical Institute (HHMI) researchers has prompted female mice to behave like male mice in the throes of courtship.
The finding, reported August 5, 2007, in the journal Nature, suggests that the neural circuits that govern gender-specific behaviors, such as aggression and courtship, are similar in the male and female brain. According to the new study, the sexual behaviors of female mice, at least, are ruled by a pheromone-detecting organ that engages a neural circuit that determines whether a mouse shows its feminine side or acts like a male.
Biologists have long searched for the root causes of sexually dimorphic behaviors—those that differ between the sexes. The new findings promise to redirect that quest.
“From a developmental standpoint, the finding is very satisfactory,” said Catherine Dulac, an HHMI investigator and Harvard University professor of molecular and cellular biology who led the new study. “It means you only have to build one brain in a species and that the one brain is built, more or less, the same in the male and the female.”
Dulac’s team, composed of first author Tali Kimchi, a postdoctoral fellow, and collaborator Jennings Xu, a Harvard undergraduate student, plumbed the neural depths of sexually dimorphic mouse behavior by engineering females to have functionally deficient vomeronasal organs. Also known as Jacobson’s organ, the vomeronasal organ is a pocket in the nasal cavity of many animals that is packed with receptor cells. It is the key detector of pheromones, chemical signals that elicit specific behavioral responses in certain animals, including mice.
The researchers found that female mice whose vomeronasal organs were genetically disabled behaved like males in the throes of courtship, exhibiting behaviors such as mounting, pelvic thrusts, solicitation and the complex ultrasonic vocalization characteristic of the male mouse. Correspondingly, female traits such as nursing behaviors and maternal aggression were diminished.
The findings provide strong evidence that male sexual behavior is hard wired into the female mouse brain and suggests, more broadly, that male and female courtship behaviors exist in the brains of both sexes and are switched on or off by the chemical cues mice use to initiate sex.
“The female behaves exactly like the male,” said Dulac. “In the big picture, it suggests that the female brain has a perfectly functional male behavioral circuit.”
“People who observe animal behavior have been struck by the fact that the biggest differences in behavior between animals of a given species are gender based,” Dulac explained, but little is known about the underlying differences in the brain that govern the characteristic patterns of gender-based behavior.
Scientists have explored many avenues to explain sexually dimorphic behavior. To try and ferret out its cause, they’ve looked at everything from the influences of hormones such as testosterone to anatomy, positing that there may be a region of the brain that organizes gender-based behavior.
The sensory-controlled neural switch that governs the circuit is most likely different in male and female mice, Dulac noted, but that may be the extent of gender differences in the brain.
The work of Dulac and her colleagues promises to open a new window to the neural mechanisms that underlie gender-based behavior in animals by bringing the senses and an animal’s ability to process what it sees, hears, and smells into the equation.
What occurs in humans and other animals may be quite different, Dulac noted, because the mouse depends largely on pheromones and its sense of smell, while humans and many other animals respond more to visual cues or a combination of sensory cues.
Scientists have been studying the vomeronasal organ for a century and know its role as a detector of pheromones well. While it is known that the organ is wired to the parts of the brain that govern reproductive behavior, its influence on gender-based behaviors was obscured in past studies because the surgical techniques used to ablate the organ flooded the nasal cavity with blood, disabling the olfactory system. To compare results from mice engineered to have a disabled vomeronasal organ, Dulac’s group surgically removed the organ and ensured the nasal cavity was clear and the olfactory system operational.
“When we removed the vomeronasal organ surgically, we found the animal had the same phenotype” as the engineered mice, Dulac explained.
The new insight into the mechanisms that govern sexual behavior in animals gives science a new avenue to explore the molecular and physiological pathways that lead to differences in sexual behavior, according to Dulac. “Now we can really approach things from a mechanistic point of view,” she said. “We can trace signaling events in the brain and see how brain areas controlling sex-specific behaviors are connected to each other.”
Sean J. Morrison, Ph.D.
Adult stem cells are the body’s ultimate repair system. These immature cells maintain a low profile within tissues and organs until activated by disease or injury. Stem cells then can morph into specialized cells within their tissue of origin, and they also have the remarkable ability to replenish themselves through a process called self-renewal. Sean Morrison is unraveling the mechanisms that regulate stem cell function in the blood and nervous systems, particularly those involved in stem cell self-renewal and aging. The Morrison laboratory also compares the mechanisms that regulate stem cell self-renewal and cancer cell proliferation. Ultimately, Morrison hopes to identify new treatments for diseases caused by stem cell defects, including cancer, degenerative disease, and birth defects.
Morrison began his pioneering stem cell work only after a brief stint as a biotech entrepreneur. For his high school science fair project, the Canadian native developed a hydroponically grown fungal fertilizer that dramatically increased the nutrient uptake in plants. The fertilizer attracted the interest and support of the Canadian government and Dalhousie University in Halifax, where he attended college. But when the project failed to garner enough venture capital at a critical point, Morrison shifted gears, opting instead for a career in medical research. He was fascinated by the process of discovery and the elegance he found in well-conceived research. “The best scientists are like artists in the sense that they are constantly motivated by the challenge of doing more and more beautiful work,” Morrison explains. “They push themselves to generate the most beautiful data and to perform the most elegant experiments. The best scientists find beauty and satisfaction in the process.”
As a graduate student, Morrison identified key markers that distinguish hematopoietic stem cells, which give rise to blood and immune system cells, from other immature hematopoietic cells. He determined that stem cells are fundamentally different from other immature cells, and his results also suggested that certain factors are involved in regulating stem cell self-renewal. Later, as a postdoctoral fellow in the Caltech laboratory of David Anderson, a fellow HHMI investigator, Morrison became the first to isolate uncultured neural crest stem cells, which give rise to the peripheral nervous system. This led to his discovery that stem cells persist throughout adult life in the peripheral nervous system, where they were not previously believed to exist.
Today, Morrison’s research focuses on neural crest stem cells and hematopoietic stem cells. By studying both, he hopes to understand the extent to which mechanisms that control self-renewal and other critical functions are conserved among stem cells in different tissues. Along those lines, Morrison in recent years has discovered that the gene Bmi-1 is required for the self-renewal of neural stem cells from the central nervous system and all other types of adult stem cell examined so far. He also has traced a potentially fatal birth defect that causes Hirschsprung disease to defects in the generation and migration of neural crest stem cells in the developing intestines. And, using techniques he developed as a graduate student, Morrison recently identified a family of cell surface receptors that scientists can use to separate hematopoietic stem cells from other, less primitive, hematopoietic progenitors. Each of these studies has the potential to change the way in which patients are treated.
Morrison strongly believes in the potential of medical research. “The greatest opportunities to change medicine arise from fundamental scientific discoveries, and I believe those opportunities exist in stem cell biology,” he says. “Stem cell biology is so central to a variety of important scientific and clinical questions that it commands a lot of attention from researchers in diverse fields. That attracted me, because if I invest years of my life answering a question, I really want people to care what the answer is.”
Dr. Morrison is also Henry Sewall Professor in Medicine at the University of Michigan Medical School, Research Associate Professor at the University of Michigan Life Sciences Institute, and Director of the University of Michigan Center for Stem Cell Biology.
RESEARCH ABSTRACT SUMMARY:
Sean Morrison is investigating the mechanisms that regulate stem cell function in the nervous and hematopoietic systems, particularly the mechanisms that regulate stem cell self-renewal and aging. Parallel studies of these mechanisms in stem cells from two different tissues will reveal the extent to which different types of stem cells employ similar or different mechanisms to regulate these critical functions.
Special To the Washington Post
Tuesday, August 7, 2007
By Eric Frederick Trump
Peter Molan holds a bandage treated with a type of honey that is being increasingly recognized for its therapeutic value. (Josephine Johnston)
For biochemist Peter Molan, honey’s ancient power to heal is not a matter of faith. So sure is he of the science behind it that he frequently applies the stuff of his research on himself — and on his wife.
“She had a persistent boil on her buttocks,” he explained. Since no standard salves had helped, he liquefied a dollop of a particular variety of honey known as manuka in the kitchen microwave, poured it over gauze and applied it.
The molten honey burned her.
“Fortunately, manuka is effective in treating burns as well as boils,” Molan said cheerfully. Within a short time, he said, both boil and burn healed.
Manuka honey — widely used for wound treatment in New Zealand, where Molan is co-director of Waikato University’s Honey Research Unit — is becoming increasingly accepted for this purpose around the world. Research over the past two decades, much of it conducted in Molan’s lab, has focused on the potential for manuka to be used as an antimicrobial that may one day stand alongside such standard wound treatments as silver dressings and penicillin.
Manuka has also attracted attention because, in an era when the efficacy of pharmaceutical antibiotics is under threat, it has shown some promise in the treatment of wounds infected with especially challenging bacteria, such as methicillin-resistant staphylococcus aureus (MRSA), the superbug whose incidence increased 32-fold in U.S. hospitals between 1976 and 2003, according to the Centers for Disease Control and Prevention.
Manuka dressings have been in use for some time in Great Britain and Australia as well as in New Zealand; earlier this year they were cleared for use as an antimicrobial dressing in Canada; and last month the Food and Drug Administration cleared them for use in wound and burn care — though not as an antimicrobial drug — making them the first honey-based products cleared for medical use in the United States.
The picture has not always been so bright for manuka, or its manufacturers. New Zealand’s scrubby manuka trees with their creamy blossoms used to be chopped down for farmland. Beekeepers regarded manuka honey as almost worthless, feeding it to their bees or simply discarding it: It was difficult to process, its taste too strong and bitter, its color too dark. In short, it seemed “medicinal.”
This began to change with Molan’s work. He had spent his career examining the possible antibacterial properties of various natural substances: milk, yeast, bull semen. At a colleague’s suggestion, he began looking into manuka honey, and for the past 25 years he has led the way in this particular aspect of apitherapy, the study of honey as a medicine.
Surrounded by the pipettes and petri dishes of his lab, and with a strip of manuka dressing wrapped around a cut finger, Molan says, “Manuka honey tastes like medicine because it is medicine.”
Today, New Zealand’s Active Manuka Honey Association estimates that 120 tons are sold each year, with sales of almost $10 million annually. Manuka is proving to be a moneymaker for many companies that market it online as “nature’s miracle” and “nature’s greatest secret,” claiming it can relieve everything from stomach ulcers to bedsores and sinus infections. Although Molan says he has no direct financial interests in honey, the honey research unit was set up with support from New Zealand’s Honey Industry Trust, and his work has resulted in his university’s signing a multimillion-dollar contract last year with New Zealand health-care products company Comvita.
An Extra Ingredient
All honey is medicinal to some extent. Its low water content allows it to draw fluid away from wounds; its high sugar content makes it difficult for microorganisms to grow. What’s more, worker bees secrete an enzyme, glucose oxidase, into nectar, which releases low levels of the disinfectant hydrogen peroxide when honey makes contact with a damp surface such as a wound. Because of a chemical reaction with tissue, honey also makes healing wounds smell good.
From the time of the ancient Sumerians, who prescribed a mix of river dust and honey for ailing eyes, until the early 20th century, honey was a conventional therapy in fighting infection, but its popularity waned with the advent in the mid-20th century of a potent, naturally occurring antibiotic: the blue-green mold penicillin.
Not all honeys are equal, though. Manuka appears to have a poorly understood antimicrobial ingredient, dubbed its Unique Manuka Factor (UMF). The level of UMF can vary, and each batch of manuka is ranked according to its UMF value: The higher the concentration, the darker, thicker and more expensive the manuka is. A 250-gram jar with UMF16, which is in the midrange, sells for about $28.95 on the Internet.
As with other natural health-care products, many of the claims for manuka’s efficacy are sweeping and scantily supported. Molan distances himself from the notion, for example, that, once ingested, manuka acts as a rejuvenator. The most promising research, he and many other scientists say, focuses instead on bioactive honey’s potency as a topical application.
The South African Medical Journal reported in 2006 on a trial among gold miners in which honey worked as well as, and was more cost-effective than, a standard gel on shallow wounds and abrasions.
The European Journal of Medical Research reported in 2003 that honey had an 85 percent success rate in treating infected post-op Caesarean wounds, compared with a 50 percent success rate for conventional interventions.
One reason for the heightened interest in honey is that traditional antibiotics are proving increasingly powerless against certain microbes. In 2000, a World Health Organization report warned: “Since 1970, no new classes of antibacterials have been developed to combat infectious diseases.” On average, the report said, “research and development of anti-infective drugs takes 10 to 20 years.” Today, according to the CDC, “nearly all significant bacterial infections in the world are becoming resistant to the most commonly prescribed antibiotic treatments.”
Hence the hope that a naturally occurring substance such as honey might help fill the void.
Molan offers anecdotal evidence from a ward at Waikato Hospital, where MRSA has been a persistent problem. The charge nurse, he says, began placing manuka on all wounds. “Not only did manuka clear up the infections, there were no cross-infections,” Molan says. “Now, whenever MRSA appears at Waikato Hospital, they choose honey dressings.”
At the May meeting of the European Wound Management Association, researchers presented the results of a small Irish study that compared the effects of manuka honey and a commonly used hydrogel dressing on 100 patients with chronic leg ulcerations. Those patients treated with manuka dressings experienced a higher rate of cleansing and faster healing than those who used the hydrogel dressing. Ten of the patients had ulcers colonized with MRSA. After four weeks, seven of those 10 wounds no longer showed the bacteria’s presence. The results have not yet been published.
‘Catching on Fast’
Even scientists who are intrigued by manuka’s promise recognize that more research needs to be done. (And there’s wide agreement among medical professionals that people should not test the treatment themselves by slathering their cuts and burns with honey from the pantry shelf.)
Andrew Jull, a research fellow at the University of Auckland’s Clinical Trials Research Unit and principal investigator in a trial in New Zealand of 368 patients into the use of honey as a therapy for leg ulcers, says that while “there is reasonable evidence for manuka honey’s antibacterial effect” in the lab, “there is still need for in vivo testing.”
Molan suggests there may be another reason the United States has been slower than some other countries to adopt medicinal honey: the scientific establishment’s resistance to traditional remedies.
He believes it’s not customers or patients who need convincing, “it’s the medical community. They find it difficult to accept anything that has an ancient lineage, whatever the scientific evidence,” he says. “But manuka is catching on fast.”
So much so that in July the FDA gave Derma Sciences, a manufacturer of wound-care products based in Princeton, N.J., clearance to sell manuka wound and burn dressings as medical devices. The company, which has been developing manuka products since 2005, buys medical-grade honey from Comvita, which receives unprocessed honey from beekeepers in New Zealand. The dressings should be available this fall.
Rose Cooper, a microbiologist and honey expert at the University of Wales Institute at Cardiff, remains cautiously optimistic that the increased use of honey dressings will help better information to emerge.
“Honey is not a panacea,” she said in a telephone interview, but it has been used by British doctors for several years, and with its growing use elsewhere in the world, “health-care professionals will be more likely to consider honey in treating wounds, and so more data will accumulate.” ·
Eric Frederick Trump is a science journalist and a research associate of the Trauma and Violence Interdisciplinary Studies Program at New York University. Comments:email@example.com.
An excellent educational video series regarding embryonic stem cells. Provided by the Howard Hughes Medical Institute, this lecture by Dr. Douglas Melton describes embryonic stem cells and their role in health and development. Lecture 1, part 1 of 6.
August 06, 2007
When it comes to generating neurons, researchers have found that not all embryonic stem (ES) cell lines are equal. In comparing neurons generated from two NIH-approved embryonic stem cell lines, scientists have uncovered significant differences in the mature, functioning neurons generated from each line. The discovery implies that culture conditions during ES cell generation — which have yet to be identified — can influence the developmental properties of human ES cells.
The report, which was published August 6, 2007, in the early online edition of the Proceedings of the National Academy of Sciences, also describes a new technique for producing functioning neurons from stem cells that will be important for creating models of human neurodegenerative diseases.
The research team was led by UCLA stem cell biologist Yi Sun and Howard Hughes Medical Institute investigator Thomas Südhof at the University of Texas Southwestern Medical Center at Dallas.
Embryonic stem cells are developmentally immature cells that are capable of self-renewal and of differentiating into any type of tissue in the body. Researchers believe they hold the potential for generating neural, cardiac and other cells that can be implanted to restored damaged tissue.
“To the best of my knowledge, until now there have been few functional studies of the neurons derived from embryonic stem cells,” said Südhof. “People in the field have traditionally been interested in whether they can make neurons and what molecular markers characterize those neurons. However, because different embryonic stem cell lines were derived under diverse conditions, the possibility existed that cell lines would produce neurons with distinct properties.”
The researchers compared mature neurons grown from two embryonic stem cell lines approved for research by the National Institute of Health. Sun and her colleagues developed procedures to differentiate the two stem cell lines first into neural progenitor cells, and then into mature neurons. They were also able to purify those neurons for study.
To probe how the neurons functioned, the researchers developed a culture technique that induced the newly produced neurons to establish synapses with one another. Synapses are the critical junctions between neurons where much of the signaling and communication between neural cells occurs.
Through functional analyses of these neurons, Sun, Südhof and their colleagues found that the two ES cell lines differentiated into two distinct types of neurons that are actually found in different parts of the brain.
The researchers next performed electrophysiological studies of the synaptic connections between the neurons. “We found that the neurons derived from the two cell lines have completely different properties in terms of what type of synapses they develop and at what time course this happens during culture,” said Südhof. Furthermore, the studies showed that the neurons derived from the two cell lines used different chemicals called neurotransmitters to communicate with one another, he said.
Sun and her colleagues compared the microRNAs produced by the two types of neurons. MicroRNAs are small snippets of genetic material that are believed to be significant regulators of stem cell differentiation.
“It’s been proposed that microRNAs might be part of the defining signatures for human ES cells, and many are expressed in the brain,” said Sun. “It was comforting that our analysis showed that as the ES cells matured into neural progenitors and neurons, the expression of the microRNAs genes specific to ES cells dropped thousands of times, and those specific to brain cells increased thousands of times. But on the other hand, when we compared the two lines, we found differences in microRNA gene expression that might contribute to this neuronal bias in the lines,” she said.
Südhof said that the differences among ES cell lines could have implications for potential treatments using the cells. “It’s clear that if you’re going to treat a motor neuron disease, you need those types of neurons; whereas if you want to treat a forebrain disease like Huntington’s, you need ES cells that differentiate into that type of neuron,” he said.
The differences in neurons produced by cell lines may offer both advantages and disadvantages for treatment, he said. “On the one hand, it may actually be good to have ES cells with a particular propensity for differentiation, because it may make it easier to get certain types of tissue. On the other hand, it may also limit the ability of these ES cells to fully replicate those types of tissues.”
Sun said that her technique for differentiating ES cells into mature neurons is likely to have important future research applications. “This technique enables us to produce pure cultures of functioning human neurons that we can genetically manipulate to mimic human disorders,” she said. “Before, it was only possible to use mouse or other animal cells to model neurodegenerative diseases, but the genetic background is so different from that of humans that key aspects of diseases such as Alzheimer’s could not be reproduced.”
Both Sun and Südhof said that their findings have implications for the production of ES cell lines. “There is absolutely no question that these findings mean that there need to be more embryonic stem cell lines for research purposes and for use in potential treatments,” said Südhof.
Sun said that developing more ES cell lines is important “because right now we still don’t know the causes for the functional differences we found. Understanding the causes will require more cell lines for study. And once we understand the causes, we can take them into account in generating new cell lines that will be better defined and enable more reproducible applications.”
“It may not seem a profound enough problem to dominate all the life sciences,” he observed, “but it contains, piece by piece, all the mysteries.””
How an organism recognizes a “vast universe” of odors is indeed “a fascinating problem in molecular recognition and perceptual discrimination,” agrees Richard Axel, an HHMI investigator at New York’s Columbia University.
Because of research by HHMI investigators Charles Zuker, University of California, San Diego, Linda Buck, Fred Hutchinson Cancer Center, and colleagues, we know a lot more about taste-sensing cells than we did a decade ago.
Put simply, how do we know what we’re smelling? Scientists are exploring this question in everything from worms to fruit flies to mice to humans, bringing a variety of new molecular tools and computational methods to bear.
Only in the last decade and a half, scientists, including Axel and HHMI investigator Linda Buck at Seattle’s Fred Hutchinson Cancer Research Center, have begun breaking the code the olfactory system uses to define different incoming odor molecules—the first step in recognizing them.
They have revealed how the coded information for a smell is represented or “mapped” in certain parts of the brain. Now the scientists are in hot pursuit of the next steps. “How does the brain transform that map into meaningful neural information so that odors will elicit appropriate cognitive responses and behaviors?” Axel says. “This is the central problem facing my laboratory.”
HHMI investigators Richard Axel, Columbia University, and Catherine Dulac,
Harvard University, are revealing the wiring of the systems involved in smell and
The nasal cavity and the tongue are laced with cells that detect chemical compounds—millions of neurons in the nose and specialized taste bud cells on the tongue. These cells are wired to relay stations and processing centers in the brain, which are thought to create sensory “images” of the perceived odors or flavors.
In parallel with the main olfactory system used for odor sensing, evolution has also spawned a separate, “accessory olfactory system” in some animals for detecting “pheromones”—chemical signals used by individuals of the same species to mark territory, warn of danger, identify close relations, and induce mating.
The lack of accessory olfactory structures in humans has suggested a corresponding lack of human pheromones. But interesting new discoveries are rewriting the textbook, demonstrating that in some mammals, at least, pheromones can be detected by the odor-sensing olfactory system as well.
Note: This story has been adapted from a news release issued by University of North Carolina at Chapel Hill.
Exenatide, a drug that is a synthetic form of a substance found in Gila monster saliva, led to healthy sustained glucose levels and progressive weight loss among people with type 2 diabetes who took part in a three-year study.
The hormone exendin-4 occurs naturally in the saliva of the Gila monster, a large venomous lizard native to the southwestern United States and northwestern Mexico. (Credit: iStockphoto/Rusty Dodson)
“The weight loss factor is important because being overweight and weight gain is an almost universal problem for people with diabetes,” said John Buse, M.D., Ph.D., lead researcher in the study and chief of endocrinology in the University of North Carolina at Chapel Hill School of Medicine.
“In that context, it is exciting that patients that continue exenatide injections continue to lose a bit of weight while maintaining blood sugar control, even in their third year of therapy,” Buse said.
“While this weight loss is encouraging, it’s important for people to understand that exenatide is not intended as a weight-loss drug and it is not approved for that purpose,” Buse said. “Only people with type 2 diabetes should take exenatide.”
Exenatide, marketed as Byetta, was approved by the Food and Drug Administration in April 2005 to treat type 2 diabetes in patients who were not able to get their high blood sugar under control in a combination with one or more of three other medications, metformin or sulfonylurea thiazolidinedione.
Weight loss was not the only significant finding. After three years of including exenatide in the drug regimen, 46 percent of participants achieved sustained glucose – or blood-sugar – levels of 7 percent, and 30 percent had levels of 6.5 percent. The ADA considers levels of 7 percent or lower to be healthy.
Exenatide, which is manufactured by Amylin Pharmaceuticals Inc. in collaboration with Eli Lilly and Company, comes in a prefilled pen that type 2 diabetics use to give themselves twice-daily injections within an hour before their morning and evening meals. It is typically given in addition to sulfonylurea, or with a combination of metformin and sulfonylurea.
Exenatide is a synthetic form of a hormone called exendin-4 that occurs naturally in the saliva of the Gila monster, a large venomous lizard native to the southwestern United States and northwestern Mexico. The lizard hormone is about 50 percent identical to a similar hormone in the human digestive tract, called glucagon-like peptide-1 analog, or GLP-1, that increases the production of insulin when blood sugar levels are high. Insulin helps move sugar from the blood into other body tissues where it is used for energy. The lizard hormone remains effective much longer than the human hormone, and thus its synthetic form helps diabetics keep their blood sugar levels from getting too high. Exenatide also slows the emptying of the stomach and causes a decrease in appetite, which is how it leads to weight loss.
The results being reported now come from following patients who took exenatide for three years. In the study, Buse and colleagues analyzed data from 217 diabetes patients. After three years of treatment, most patients showed sustained reductions in blood sugar levels, in blood biomarkers that indicate liver injury and sustained, progressive weight loss averaging 11 pounds.
The study’s co-authors are Leigh MacConell, Ph.D., Anthony H. Stonehouse, Ph.D., Xuesong Guan, James K. Malone, M.D., Ted E. Okerson, M.D., David G. Maggs, M.D. and Dennis D. Kim, M.D. All of the co-authors work for Amylin Pharmaceuticals except for Malone, who works for Eli Lilly and Company. Amylin has a global agreement with Eli Lilly and Company to collaborate on the development and commercialization of exenatide. Funding for this study was provided by Amylin and Eli Lilly and Company. Dr. Buse presented these results June 25, 2007 at the annual scientific sessions of the American Diabetes Association in Chicago.
You can try this experiment at home. Pour clean water onto a small plate. Wait for all the ripples to stop. Then mix a small amount of mineral oil with an even smaller amount of detergent. Squeeze a tiny drop of that mixture onto the water and watch in amazement as the oil appears to pump like a beating heart.
It’s a simple experiment, but explaining what makes the drop of oil throb–and then stop when deprived of fresh air–has long mystified the scientific community. Now, in work that could have applications in fields from biology to environmental engineering, an MIT team has cracked the case.
In the July 25 issue of the Journal of Fluid Mechanics, MIT Professors Roman Stocker of civil and environmental engineering and John Bush of mathematics explain what happens when an oil drop containing a water-insoluble surfactant (or material that reduces the surface tension of a liquid, allowing easier spreading) is placed on a water surface.
“It’s an easy experiment to make. But getting the theory for it was not straightforward,” Bush said. “Roman turned a microscope loose on the problem–which was key to finally understanding it.”
The question of the physical phenomenon of oil spreading on a surface has been around for some time. Benjamin Franklin wrote about it in 1774 in the Transaction of the American Philosophical Society, after he saw Bermuda spear fishermen use oil to damp waves so they could more easily see fish under the ocean surface.
The question Stocker and Bush examined had another dimension: why oil with an added surfactant doesn’t come to rest, but instead contracts and repeats the process in a periodic fashion.
The mechanism, they now know, is surface tension, or more precisely, evaporation-induced variations in surface tension. These changes in surface tension cause the drop to expand, then contract, and repeat the process every couple of seconds until it runs out of gas, which in this case, is surfactant. Covering the experiment stops the process because it prevents evaporation of the surfactant.
“We’re dealing with three interfaces: between the oil drop, the water in the Petri dish, and the air above it,” Stocker said, explaining surface tension. “A detergent is a surfactant, which reduces the surface tension of a liquid. The detergent molecules we added to the oil drop prefer to stay at the interface of the oil and water, rather than inside the oil drop.”
Think of the oil detergent drop as a small lens with a rounded bottom. The surfactant in the drop moves to the bottom surface of the lens, where it interacts with the water to decrease the surface tension where oil meets water. This change in tension increases the forces pulling on the outer edges of the drop, causing the drop to expand.
The center of the drop is deeper than the edges, so more surfactant settles there, reducing the surface tension correspondingly. This causes the oil and surfactant near the outer edges of the drop to circulate. This circulation creates a shear (think of it as two velocities going in opposite directions), which generates very tiny waves rolling outward toward the edge. When these waves reach the edge, they cause small droplets to erupt and escape onto the water surface outside the drop. Videomicroscopy – essentially, attaching a video camera to a microscope – was critical in observing this step in the process. Those droplets of oil and surfactant disperse on the water and decrease the surface tension of the water surface, so the drop contracts.
As the surfactant evaporates, the surface tension of the water increases again, and the system is reset. Forces pull at the outer edges of the lens, and the cyclical process begins again.
But the beating ceases instantly when Stocker and Bush put a lid over it. If the surfactant can’t evaporate, the oil drop remains stable. In the end, it was being able to stop the beating process that made it clear to the researchers that evaporation played a central role in the mechanism.
“This is a bizarre and subtle mechanism. Everybody was flummoxed,” said Bush, whose recent research includes understanding how some insects walk on water.
He first heard about the oil drop phenomenon from Professor Emeritus Harvey Greenspan of mathematics, who had pondered it for some time. Bush in turn talked to Stocker, who was then an instructor in the Department of Mathematics. It took about three years of sporadic work (without funding), and the help of two undergraduate students who carried out the lab repetitions–Margaret Avener and Wesley Koo–but Stocker and Bush finally solved it.
To what end, the researchers don’t yet know. “One rationalizes the physical world by understanding the mechanisms,” said Bush, explaining the importance of basic scientific research. “One can never predict which mechanisms will be important.”
“Oil contamination of water resources is a prominent problem in environmental engineering,” said Stocker. “Awareness of the fundamental mechanisms governing the interaction between the two phases is critical to devise sound engineering solutions for remediation.”
Spontaneous oscillations are observed in many natural systems, including nerve cells, muscle tissue, and the biological clocks responsible for circadian rhythms, the professors said. And previous work published on the oil drop problem had been carried out by scientists interested in seeing if the mechanism could explain biological oscillations.
Note: This story has been adapted from a news release issued by Massachusetts Institute of Technology.
Photo / Donna Coveney
Professors Roman Stocker, left, and John Bush display a mixture of oil, detergent and water. Their research explains what happens when an oil drop containing a water-insoluble surfactant is placed on a water surface.
The Human Heart
Anterior (frontal) view of the opened heart. White arrows indicate normal blood flow.
They have already been dubbed “master” heart cells, and hold the promise of treating patients with serious cardiovascular disease: Three US research groups claim that they can produce stem cells that give rise to different tissues found in the mammalian heart.
Each team has identified cardiovascular “precursor” cells from cultures of mouse embryonic stem cells (ESCs). It is very likely that these versatile cells will also be found in the embryonic human heart, the researchers say, raising hopes of one day repairing and “rejuvenating” damaged hearts by growing these embryonic stem cell lines in a lab.
Two of the groups, one led by Kenneth Chien of the Massachusetts General Hospital in Boston, the other by Gordon Keller of Mount Sinai School of Medicine in New York, say their precursors give rise to three types of cells in the heart. Cardiac muscle cells can be grown, as can the smooth muscle that makes up the blood vessels that supply the heart, and crucial endothelial cells that line the coronary blood vessels, they say.
The third team, led by Stuart Orkin of the Children’s Hospital in Boston, has identified precursors for cardiac and smooth muscle.
Being able to rebuild both cardiac muscle and blood vessels may be important for repairing hearts ravaged by cardiovascular disease. “Where there’s damage, there’s damage to more than one cell type,” notes Orkin.
Cell therapies for failing hearts have been hampered by the lack of a suitable stem cell. Some cardiologists have tried injecting bone marrow stem cells into patients’ coronary blood vessels or heart muscle. But there is no good evidence that injected marrow cells can differentiate into new heart tissue.
Trials with muscle cells taken from the legs have been even less successful, with some patients developing dangerous arrhythmias – where the heart does not beat to a correct rhythm.
These newly found precursor cells, discovered in culture, seem to correspond to cells present in the mouse embryo, which give rise to heart tissue during normal development, the three teams say. Mimicking natural developmental processes in culture boosts the prospects of successful cardiac repair, they argue.
“This is the beginning of science-based cardiovascular regenerative medicine,” claims Chien.
The researchers are now trying to work out if they are each studying cells on the same developmental pathway. “It’s hard to be absolutely dogmatic about that,” says Orkin, because each group identified their cells using different cell-surface marker molecules.
And each team wants to repeat the experiments with human ESCs, so that they can begin moving towards clinical trials. “We are following up very quickly with human cells,” says Keller.
The stem cell company, Geron of Menlo Park, California, also plans to treat heart disease using cells derived from human ESCs. It is concentrating on generating precursors for cardiac muscle, rather than “master” heart cells.
Geron’s CEO, Tom Okarma, says the company already has promising results from experiments in rodents with damage following a simulated heart attack. Okarma also hopes to avoid problems with immunological rejection by generating “tolerance” using immune cells derived from the same ESC lines.