amudu

Thursday, September 1, 2011

Unfounded pesticide concerns adversely affect the health of low-income populations

The increasingly prevalent notion that expensive organic fruits and vegetables are safer because pesticides — used to protect traditional crops from insects, thus ensuring high crop yields and making them less expensive — are a risk for causing cancer has no good scientific support, an authority on the disease said here today. Such unfounded fears could have the unanticipated consequence of keeping healthful fruits and vegetables from those with low incomes.

Bruce N. Ames, Ph.D., developer of a widely used test for potential carcinogens that bears his name, spoke at the 242nd National Meeting & Exposition of the American Chemical Society (ACS), being held here this week. With more than 7,500 reports on new advances in science and more than 12,000 scientists and others expected in attendance, it will be one of 2011′s largest scientific gatherings.

Ames described his “triage theory,” which explains how the lack of essential vitamins and minerals from fruit and vegetables in the diet of younger people can set the stage for cancer and other diseases later in life. A professor emeritus of biochemistry and molecular biology at the University of California at Berkeley, Ames also is a senior scientist at Children’s Hospital Oakland Research Institute, where he works on healthy aging. He developed the Ames test, which uses bacteria to test whether substances damage the genetic material DNA and, in doing so, have the potential to cause cancer. He has received the U.S. National Medal of Science among many other awards.

In the presentation, Ames said that today’s animal cancer studies unfairly label many substances, including pesticides and other synthetic chemicals, as dangerous to humans. Ames’ and Lois Swirsky Gold’s research indicates that almost all pesticides in the human diet are substances present naturally in plants to protect them from insects.

“Animal cancer tests, which are done at very high doses of synthetic chemicals such as pesticides — the “maximum tolerated dose” (MTD) — are being misinterpreted to mean that minuscule doses in the diet are relevant to human cancer. 99.99 percent of the pesticides we eat are naturally present in plants to protect them from insects and other predators. Over half of all chemicals tested, whether natural or synthetic, are carcinogenic in rodent tests,” Ames said. He thinks this is due to the high dose itself and is not relevant to low doses.

At very low doses, many of these substances are not of concern to humans, he said. For example, a single cup of coffee contains 15-20 of these natural pesticides and chemicals from roasting that test positive in animal cancer tests, but they are present in very low amounts. Human pesticide consumption from fresh food is even less of a concern, according to Ames — the amount of pesticide residues that an average person ingests throughout an entire year is even less than the amount of those “harmful” substances in one cup of coffee. In fact, evidence suggests coffee is protective against cancer in humans.

Unfounded fears about the dangers of pesticide residues on fruit and vegetables may stop many consumers from buying these fresh, healthful foods. In response, some stores sell “organic” foods grown without synthetic pesticides, but these foods are much more expensive and out of the reach of low-income populations. As a result, people — especially those who are poor — may consume fewer fruits and vegetables.

But how does a lack of fresh produce lead to cancer and other aging diseases? That’s where Ames’ triage theory comes in.

In wartime, battlefield doctors with limited supplies and time do a triage, making quick decisions about which injured soldiers to treat. In a similar way, the body makes decisions about how to ration vital nutrients while experiencing an immediate moderate deficiency, but this is often at a cost.

“The theory is that, as a result of recurrent shortages of vitamins and minerals during evolution, natural selection developed a metabolic rebalancing response to shortage,” he said. “Rebalancing favors vitamin- and mineral-dependent proteins needed for short-term survival and reproduction while starving those proteins only required for long-term health.” Ames noted that the theory is strongly supported by recent work (Am J Clin Nutr. DOI: 10.3945/ajcn.2009.27930; FASEB J DOI:10.1096/fj.11-180885; J Nucleic Acids DOI:10.4061/2010/725071).

For example, if a person’s diet is low in calcium — a nutrient essential for many ongoing cellular processes — the body takes it from wherever it can find it — usually the bones. The body doesn’t care about the risk of osteoporosis 30 or 40 years in the future (long-term health) when it is faced with an emergency right now (short-term survival). Thus, insidious or hidden damage happens to organs and DNA whenever a person is lacking vitamins or minerals, and this eventually leads to aging-related diseases, such as dementia, osteoporosis, heart trouble and cancer.

And with today’s obesity epidemic, resulting largely from bad diets that lack healthful foods containing vitamins, minerals and fiber, aging-related diseases are likely to be around for some time to come.

Controlling cells’ environments: A step toward building much-needed tissues and organs

Posted by Biomechanism

With stem cells so fickle and indecisive that they make Shakespeare’s Hamlet pale by comparison, scientists today described an advance in encouraging stem cells to make decisions about their fate. The technology for doing so, reported here at the 242nd National Meeting & Exposition of the American Chemical Society (ACS), is an advance toward using stem cells in “regenerative medicine” — to grow from scratch organs for transplants and tissues for treating diseases.

Human embryonic stem cells offer the unique ability to not only renew themselves, but to also differentiate into any one of the more than 200 cell types found in the human body.

“Stem cells have great potential in regenerative medicine, in developing new drugs and in advancing biomedical research,” said Laura L. Kiessling, Ph.D., who presented the report. “To exploit that potential, we need two things: first, reproducible methods to grow human stem cells in the laboratory, and second, the ability to make stem cells grow into heart cells, brain cells or whatever kind of cell. Our technology takes a different approach to both of these problems, and the results are very encouraging.”

Biologically, so-called pluripotent human embryonic stem cells have not made up their minds about what to become. That’s essential because these cells, which are derived from embryos, have the agility to develop into the hundreds of different kinds of cells in a fully-formed human body. But controlling their differentiation has also stood as a major barrier to making the stem cell dream come true and using these all-purpose cells in medicine.

Past approaches to growing and scripting the fate of stem cells have involved adding growth-regulating and other substances to cultures of stem cells growing in the laboratory. These conditions left scientists guessing about exactly what wound up in the stem cells. Kiessling and colleagues are pioneering a new approach that involves using chemically controlled surfaces.

Kiessling previously developed chemically modified plastic and glass surfaces that take much of the guess work out of growing stem cells in laboratory cultures. In the past, scientists grew stem cells on surfaces that contained mouse cells. That left scientists with nagging questions about possible contamination of stem cells with disease-causing animal viruses — a stumbling block for using stem cells in potential medical applications. And that growth system was what scientists term “undefined.” There were variations from batch to batch of mouse cells, and scientists never really knew what the stem cells were coming into contact with and how it might be changing them. The synthetic, chemically-defined, surfaces ended that uncertainty. The approach was inexpensive, simple and a much-needed advance in producing stem cells, Kiessling explained.

With the ability to grow stem cells on the synthetic surfaces under chemically defined, or known, conditions, Kiessling’s group took an additional step in their latest research. It found that chemically defined surfaces can exert control over signaling pathways. “Signaling” is how molecules talk to one another and get things done inside a cell. It’s how an immune cell knows to fight an infection or how a pancreatic cell determines that more insulin is needed in the bloodstream, for example. By controlling how molecules inside a stem cell communicate, researchers could someday in the future nudge them to become one type of cell or tissue over another.

To see whether a new chemically defined surface could change signaling in a pilot experiment, Kiessling tested cancer cells. The research involved use of a signaling substance, transforming growth factor-beta (TGF-beta), which controls a range of activities, from cell growth to self-destruction.

“The new surfaces give scientists much more control over cells, opening up a wide range of possible future applications,” Kiessling explained. Building directly on the results of the pilot study, the surfaces could have applications in wound healing. TGF- beta can help wounds heal, but if it touches healthy skin, inflammation or even a cancerous tumor could develop. “We haven’t done this, but you could imagine a bandage that has a localized concentration of the special peptide surface that would recruit TGF-beta just to the wound site,” said Kiessling.

The surfaces also could make it easier to manufacture organs and tissues in the laboratory someday. “We think that this strategy, with different sets of peptides (building blocks of proteins) bound to the surface, could direct certain human embryonic stem cells on the surface to become one type of cell and other stem cells to become a second cell type, right next to each other. For the tissue engineering involved in growing replacement organs, you need to organize specialized cells in particular ways like this.”

Free radicals crucial to suppressing appetite

Posted by Biomechanism

Obesity is growing at alarming rates worldwide, and the biggest culprit is overeating. In a study of brain circuits that control hunger and satiety, Yale School of Medicine researchers have found that molecular mechanisms controlling free radicals—molecules tied to aging and tissue damage—are at the heart of increased appetite in diet-induced obesity.

Caption: This image shows satiety promoting melanocortin neurons (green) in the hypothalamus, some of which are activated (red nuclei) after treatment. Credit: Tamas Horvath, Yale University

Published Aug. 28 in the advanced online issue of Nature Medicine, the study found that elevating free radical levels in the hypothalamus directly or indirectly suppresses appetite in obese mice by activating satiety-promoting melanocortin neurons. Free radicals, however, are also thought to drive the aging process.

“It’s a catch-22,” said senior author Tamas Horvath, the Jean and David W. Wallace Professor of Biomedical Research, chair of comparative medicine and director of the Yale Program on Integrative Cell Signaling and Neurobiology of Metabolism. “On one hand, you must have these critical signaling molecules to stop eating. On the other hand, if exposed to them chronically, free radicals damage cells and promote aging.”

“That’s why, in response to continuous overeating, a cellular mechanism kicks in to suppress the generation of these free radicals,” added lead author Sabrina Diano, associate professor of Ob/Gyn, neurobiology and comparative medicine. “While this free radical-suppressing mechanism—promoted by growth of intracellular organelles, called peroxisomes—protects the cells from damage, this same process will decrease the ability to feel full after eating.”

After the mice ate, the team saw that the neurons responsible for stopping overeating had high levels of free radicals. This process is driven by the hormone leptin and glucose, which signal the brain to modulate food intake. When mice eat, leptin and glucose levels go up, as does free radical levels. However, in mice with diet-induced obesity, these same neurons display impaired firing and activity (leptin resistance); in these mice, levels of free radicals were buffered by peroxisomes, preventing the activation of these neurons and thus the ability to feel sated after eating.

According to Horvath and Diano, the crucial role of free radicals in promoting satiety as well as degenerative processes associated with aging may explain why it has been difficult to develop successful therapeutic strategies for obesity without major side effects. Current studies address the question of whether, under any circumstance, satiety could be promoted without sustained elevation of free radicals in the brain and periphery.

______________

Other authors on the study include Zhong-Wu Liu, Jin Kwoan Jeong, Marcelo O. Dietrich, Hai-Bin Ruan, Esther Kim, Shigetomo Suyama, Kaitlin Kelly, Erika Gyengesi, Jack L. Arbiser, Denise D. Belsham, David A. Sarruf, Michael W. Schwartz, Anton M. Bennett, Marya Shanabrough, Charles V. Mobbs, Xiaoyong Yang, and Xiao-Bing Gao.

The study was supported by grants form the National Institutes of Health and the American Diabetes Association.

Citation: Nature Medicine, DOI: 10.1038/nm.2421

Nano-thermometers show first temperature response differences within living cells

Posted by Biomechanism

Using a modern version of open-wide-and-keep-this-under-your-tongue, scientists today reported taking the temperature of individual cells in the human body, and finding for the first time that temperatures inside do not adhere to the familiar 98.6 degree Fahrenheit norm. They presented the research at the 242nd National Meeting & Exposition of the American Chemical Society (ACS), being held here this week.

Researchers are using quantum dots (shown in red) to take the temperature of living cells. Image Credit: Haw Yang, Ph.D.

Haw Yang and Liwei Lin, who collaborated on the research, did not use a familiar fever thermometer to check the temperature of cells, the 100 trillion or so microscopic packages of skin, nerve, heart, liver and other material that make up the human body. Cells are so small that almost 60,000 would fit on the head of a common pin. Yang is with Princeton University and Lin is with the University California-Berkeley.

“We used ‘nano-thermometers’,” Yang explained. “They are quantum dots, semiconductor crystals small enough to go right into an individual cell, where they change color as the temperature changes. We used quantum dots of cadmium and selenium that emit different colors (wavelengths) of light that correspond to temperature, and we can see that as a color change with our instruments.”

Yang said that information about the temperatures inside cells is important, but surprisingly lacking among the uncountable terabytes of scientific data available today.

“The inside of a cell is so complicated, and we know very little about it,” he pointed out. “When one thinks about chemistry, temperature is one of the most important physical factors that can change in a chemical reaction. So, we really wanted to know more about the chemistry inside a cell, which can tell us more about how the chemistry of life occurs.”

Scientists long have suspected that temperatures vary inside individual cells. Yang explained that thousands of biochemical reactions at the basis of life are constantly underway inside cells. Some of those reactions produce energy and heat. But some cells are more active than others, and the unused energy is discharged as heat. Parts of individual cells also may be warmer because they harbor biochemical power plants termed mitochondria for producing energy.

The researchers got that information by inserting the nano-thermometers into mouse cells growing in laboratory dishes. They found temperature differences of a few degrees Fahrenheit between one part of some cells and another, with parts of cells both warmer and cooler than others. Their temperature measurements are not yet accurate enough to give an exact numerical figure. Yang’s team also intentionally stimulated cells in ways that boosted the biochemical activity inside cells and observed temperature changes.

Yang says that those temperature changes may have body-wide impacts in determining health and disease. Increases in temperature inside a cell, for instance, may change the way that the genetic material called DNA works, and thus the way that the genes, which are made from DNA, work. Changing the temperature will also change how protein molecular machines operate. At higher temperatures, some proteins may become denatured, shutting down production.

“With these nano thermometer experiments, I believe we are the first to show that the temperature responses inside individual living cells are heterogeneous — or different,” said Yang. “This leads us to our next hypothesis, which is that cells may use differences in temperature as a way to communicate.”

Yang’s team is now conducting experiments to determine what regulates the temperature inside individual cells. One goal is to apply the information in improving prevention, diagnosis and treatment of diseases.

New skin test determines age of wild animals to help control nuisance animals

Posted by Biomechanism

A new skin test can determine the age of wild animals while they are still alive, providing information needed to control population explosions among nuisance animals, according to a report here today at the 242nd National Meeting & Exposition of the American Chemical Society (ACS).

Tigers (and all the Order Carnivora which consists of all cats, dogs, bears, seals, weasels, stoats, pinnipeds, etc.) are descended from the family of marten-like woodland animals called the miacidae. These small omnivores evolved during the late Cretaceous period (toward the end of the age of the dinosaurs), about 70-65 million years ago.

ACS, the world largest scientific society with more than 163,000 members, is holding the meeting through Thursday at the Colorado Convention Center and downtown hotels. With 7,500 reports on new advances in science and more than 12,000 scientists and others expected in attendance, it will be one of 2011’s largest scientific gatherings.

Randal Stahl, Ph.D., said that the improved method will provide important information about the health and stability of herds, flocks and other populations of wild animals, which lack the established birthdates of prized cattle, horses, and many household pets.

“Determining the age of wild animals is important for a number of reasons,” Stahl explained. “We are in the midst of population explosions of some animals that have negative impacts on people, property and other animals. Wildlife management programs have been established to cope with the situation. Some of these programs, for instance, seek to maintain healthy numbers of breeding pairs. The new skin test will help us tell how many animals in a wild population are of breeding age.”

Stahl is a scientist with the National Wildlife Research Center (NWRC) in Fort Collins, CO. The center is the research arm of the U.S. Department of Agriculture, Animal and Plant Health Inspection Service, Wildlife Services program.

The test detects pentosidine, a biomarker for so-called advanced glycation end products (AGEs), substances that form in the body as a result of aging; the amounts can indicate an animal’s age. Those substances also form in humans, and have been linked to a range of chronic disorders, including type 2 diabetes, cancer and Alzheimer’s disease.

Tests for AGEs already exist and have been used in both animals and humans. At the ACS meeting, Stahl and colleagues described development of a more sensitive version of the animal test. That test involves taking a biopsy, or sample, of the animal’s skin. In the past, scientists needed such a large skin sample — about the size of a postage stamp — that scientists usually could do the test only on dead animals. The new version of the test requires a skin sample only the size of a pea.

“We improved the sensitivity of the pentosidine test so we can detect very small amounts of it,” Stahl said. “The advance will enable scientists to capture a few individuals, take a small skin sample without harming the animal and then release it back into the wild. With this approach, we can sample a population repeatedly over time without having an effect on the size of the population.”

Stahl’s group is currently studying double-crested cormorants, large fish-eating birds that have become a nuisance due to population explosions. Federal and state agencies in the Great Lakes region, and other areas, are trying to manage cormorant populations to reduce the birds’ adverse impacts on vegetation, other water birds, private property, fish farming, sports fishing and risks of collisions with aircraft. Those efforts involve maintaining the number of breeding pairs of cormorants at environmentally healthy levels. And the new skin test will enable scientists to gauge the number of birds that are of breeding age.

Collaborating with the NWRC field station in Mississippi, the researchers also developed a technique of handling cormorants to obtain samples with little harm to the birds. They place a small hollow metal cylinder called a biopsy punch on the bird’s skin to remove the sample and then put an adhesive on the wound to prevent infection and promote healing, just like a Band-Aid. No anesthesia is needed.

Stahl plans to use the skin analysis method to study other wild populations, such as invasive species of snakes and lizards in Florida. And because of recent coyote attacks on humans in populated areas, such as the suburbs of New York City and in California, Stahl’s team also will use the method to determine the demographics of these urban coyote populations during management activities.

Scientists develop new technologies for understanding bacterial infections

Posted by Biomechanism

“New approach for studying molecules within their natural environment.”

Understanding how bacteria infect cells is crucial to preventing countless human diseases. In a recent breakthrough, scientists from the University of Bristol have discovered a new approach for studying molecules within their natural environment, opening the door to understanding the complexity of how bacteria infect people.

this development has enabled the research team to correlate intricate, atomic level detail of UspA1 obtained by X-ray crystallography of isolated fragments of the protein with delicate and previously unobservable physical changes of the bacterial cell as it binds to and infects its target human cells.

The research, led by a team of biochemists, microbiologists and physicists and published in the Proceedings of the National Academy of Sciences (PNAS), provides an unprecedented level of detail of the consequences of a bacterium approaching another cell, directly in situ.

Until now, traditional approaches to understanding infection have focused on either studies of the cells involved or dissection of individual molecules present within the cells. Leo Brady, Professor of Biochemistry and Mumtaz Virji, Professor of Molecular Microbiology, who led the research, have developed a novel method for bridging these, until now, separate approaches.

The team studied the common bacterium Moraxella catarrhalis, which causes middle ear infections in young children, and is a major cause of morbidity in those with heart disease. For many years, scientists approached this problem from the molecular medicine approach — through isolating and studying proteins from the Moraxella cell surface that initiate infection.

From these detailed studies the team have been able to develop an overview of one of the key proteins, called UspA1. However, as with the vast majority of molecular medicine approaches, this model has been based on studies of the UspA1 protein in isolation, rather than in its natural setting on the bacterium surface. A common worry for many biomedical scientists is how such understanding translates into the reality of these tiny molecules when they are part of a much larger cell. Understanding the increased complexity of individual molecules within the cellular mêlée is crucial to understanding why many promising drugs fail to live up to expectations.

To begin bridging this gap in our understanding, Professors Brady and Virji teamed up with Dr Massimo Antognozzi from the University’s School of Physics, whose group have been developing a novel form of atomic force microscope, termed the lateral molecular force microscope (LMFM).

Together, they have evolved the design of the LMFM microscope to optimise its ability to measure biological phenomena such as changes in UspA1 directly at the Moraxella cell surface. The LMFM differs from more conventional atomic force microscopes in tapping samples (in this case, individual cells) against an extremely fine lever, equivalent to the stylus of a record player, rather than moving the lever as is usually the case. Fabrication of extremely thin but stiff cantilevers together with exceptionally fine motor movements and a specialised visualisation system have all been combined in the device to tremendous effect. The sensitivity achieved has been further enhanced by its location within the extremely low vibration environment provided within the University’s innovative Nanoscience and Quantum Information building. The result has been a machine that can measure exquisitely fine molecular changes and forces in individual molecules directly on a living cell surface.

In the Moraxella study, this development has enabled the research team to correlate intricate, atomic level detail of UspA1 obtained by X-ray crystallography of isolated fragments of the protein with delicate and previously unobservable physical changes of the bacterial cell as it binds to and infects its target human cells.

Professor Brady said: “The findings have triggered the development of a novel technology that promises to open up a new approach for studying molecular medicine. This breakthrough will undoubtedly prove equally useful for the study of many other biological processes directly within their cellular environment, something that has long been needed in molecular medicine.”

This combined study has enabled the researchers to observe the very first responses as a bacterium binds to a human cell, hence opening the door to understanding the complexity of infection processes.
_________________
The UspA1 LMFM studies have been funded by the Wellcome Trust and the Biotechnology and Biological Sciences Research Council (BBSRC) and are published today [29 Aug] in the journal Proceedings of the National Academy of Sciences (PNAS).