Josh: We must remember that not all inherited diseases are genetic in origin. Not only does the “genetic code”, the sequence of A, G, C, and T, matter but so do other modifications to that code. Examples are DNA methylation and histone modification.

A new study in the September issue of the Journal of Lipid Research suggests an unusual form of inheritance may have a role in the rising rate of diabetes, especially in children and young adults, in the United States.

DNA is the primary mechanism of inheritance; kids get half their genes from mom and half from dad. However, scientists are just starting to understand additional kinds of inheritance like metabolic programming, which occurs when an insult during a critical period of development, either in the womb or soon after birth, triggers permanent changes in metabolism.

In this study, the researchers looked at the effects of a diet high in saturated fat on mice and their offspring. As expected, they found that a high-fat diet induced type 2 diabetes in the adult mice and that this effect was reversed by stopping the diet.

However, if female mice continued a high-fat diet during pregnancy and/or suckling, their offspring also had a greater frequency of diabetes development, even though the offspring were given a moderate-fat diet. These mice were then mated with healthy mice, and the next generation offspring (grandchildren of the original high-fat fed generation) could develop diabetes as well.

In effect, exposing a fetal mouse to high levels of saturated fats can cause it and its offspring to acquire diabetes, even if the mouse goes off the high-fat diet and its young are never directly exposed.

The study used mice so it’s not time to warn women to eat differently during pregnancy and breastfeeding but earlier research has shown that this kind of inheritance is at work in humans. For example, there is an increased risk of hypertension and cardiovascular disease in children born of malnourished mothers.

Source: American Society for Biochemistry and Molecular Biology

“Effects of High Fat Diet Exposure During Fetal Life on Type 2 Diabetes Development in the Progeny”. Donatella Gniuli, Alessandra Calcagno, Maria Emiliana Caristo, Alessandra Mancuso, Veronica Macchi, Geltrude Mingrone, and Roberto Vettor. Journal of Lipid Research, Vol. 49, 1936-1945, September 2008

The largest genetic analysis of its kind to date for bipolar disorder has implicated machinery involved in the balance of sodium and calcium in brain cells. Researchers supported in part by the National Institute of Mental Health, part of the National Institutes of Health, found an association between the disorder and variation in two genes that make components of channels that manage the flow of the elements into and out of cells, including neurons.

“A neuron’s excitability – whether it will fire – hinges on this delicate equilibrium,” explained Pamela Sklar, M.D., Ph.D., of Massachusetts General Hospital (MGH) and the Stanley Center for Psychiatric Research at the Broad Institute of MIT and Harvard, who led the research. “Finding statistically robust associations linked to two proteins that may be involved in regulating such ion channels – and that are also thought to be targets of drugs used to clinically to treat bipolar disorder – is astonishing.”

Although it’s not yet known if or how the suspect genetic variation might affect the balance machinery, the results point to the possibility that bipolar disorder might stem, at least in part, from malfunction of ion channels.

Sklar, Shaun Purcell, Ph.D., also of MGH and the Stanley Center, and Nick Craddock, M.D., Ph.D., of Cardiff University and the Wellcome Trust Case Control Consortiuum in the United Kingdom and a large group of international collaborators report on their findings online Aug. 17, 2008 in Nature Genetics.

“Faced with little agreement among previous studies searching for the genomic hot spots in bipolar disorder, these researchers pooled their data for maximal statistical power and unearthed surprising results,” said NIMH Director Thomas R. Insel, M.D. “Improved understanding of these abnormalities could lead to new hope for the millions of Americans affected by bipolar disorder.”

In the first such genome-wide association study for bipolar disorder, NIMH researchers last fall reported the strongest signal associated with the illness in a gene that makes an enzyme involved the action of the anti-manic medication lithium. However, other chromosomal locations were most strongly associated with the disorder in two subsequent studies.

Since bipolar disorder is thought to involve many different gene variants, each exerting relatively small effects, researchers need large samples to detect relatively weak signals of illness association.

To boost their odds, Sklar and colleagues pooled data from the latter two previously published and one new study of their own. They also added additional samples from the STEP-BD study and Scottish and Irish families, and controls from the NIMH Genetics Repository. After examining about 1.8 million sites of genetic variation in 10,596 people – including 4,387 with bipolar disorder – the researchers found the two genes showing the strongest association among 14 disorder-associated chromosomal regions.

Variation in a gene called Ankyrin 3 (ANK3) showed the strongest association with bipolar disorder. The ANK3 protein is strategically located in the first part of neuronal extensions called axons and is part of the cellular machinery that decides whether a neuron will fire. Co-authors of the paper had shown last year in mouse brain that lithium, the most common medication for preventing bipolar disorder episodes, reduces expression of ANK3.

Variation in a calcium channel gene found in the brain showed the second strongest association with bipolar disorder. This CACNA1C protein similarly regulates the influx and outflow of calcium and is the site of interaction for a hypertension medication that has also been used in the treatment of bipolar disorder.

Source: NIH/National Institute of Mental Health

In a first, scientists from Weill Cornell Medical College and Columbia University Medical Center have described the specifics of how brain cells process antidepressant drugs, cocaine and amphetamines. These novel findings could prove useful in the development of more targeted medication therapies for a host of psychiatric diseases, most notably in the area of addiction.

Their breakthrough research, featured as the cover story in a recent issue of Molecular Cell, describes the precise molecular and biochemical structure of drug targets known as neurotransmitter-sodium symporters (NSSs), and how cells use them to enable neural signaling in the brain. A second study, published in the latest issue of Nature Neuroscience, pinpoints where the drug molecules bind in the neurotransmitter transporter — their target in the human nervous system.

“These findings are so clear and detailed at the level of molecular behavior that they will be most valuable to developing more effective therapies for mood disorders and neurologic and psychiatric diseases, and to direct effective treatments for drug addiction to cocaine and amphetamines,” says co-lead author Dr. Harel Weinstein, Chairman and Maxwell M. Upson Professor of Physiology and Biophysics, and director of the Institute for Computational Biomedicine at Weill Cornell Medical College. “This research may also open the door to the development of new therapies for dopamine-neurotransmitter disorders such as Parkinson’s disease, schizophrenia, and anxiety and depression.”

To make their observations, the research team led by Dr. Jonathan Javitch, senior author of the Molecular Cell study and contributing author to the Nature Neuroscience study, and professor of Psychiatry and Pharmacology in the Center for Molecular Recognition at Columbia University Medical Center, stabilized different structural states of the neurotransmitter-sodium-symporter molecule that relate to steps in its function. This allowed the team to study how substrates and inhibitors affect the transition between these different states, and thus to understand the way in which its function is accomplished.

“Crystallography had allowed the identification of only one structural form of the molecule, but our experiments and computations were able to identify how this form changes and thereby add an understanding of the functional role of the different forms that the molecule must adopt to accomplish transport activity,” says Dr. Javitch.

The main surprise was the realization that two binding sites on the transporter molecule need to be filled simultaneously and cooperate in order for transport to be driven across the cell membrane. For these studies, the scientists used the crystal structure of a bacterial transporter that is very similar to human neurotransmitter transporters. They performed computer simulations to reveal the path of the transported molecules into cells. Laboratory experimentation was used to test the computational predictions and validate the researchers’ inferences.

Together, these procedures revealed a finely-tuned process in which two sodium ions bind and stabilize the transporter molecule for the correct positioning of the two messenger molecules — one deep in the center of the protein, and the other closer to the entrance. Like a key engaging a lock mechanism, this second binding causes changes in the transporter throughout the structure, allowing one of the two sodium molecules to move inward, and then release the deeply bound messenger and its sodium partner into the cell.

In the bacterial transporter studied, antidepressant molecules bind in the outer one of two sites, and stop the transport mechanism, leaving the messenger molecule outside the cell.

The second team of researchers, involving a collaboration of the Weinstein and Javitch labs with colleagues in Denmark (the labs of Ulrik Gether and Claus Loland), found that in the human dopamine transporter cocaine binds in the deep site, unlike the antidepressant binding in the bacterial transporter. Therefore, the researchers conclude that anti-cocaine therapy will be more complicated, because interfering with cocaine binding also means interference with the binding of natural messengers.

“This finding might steer anti-cocaine therapy in a completely new direction,” says Dr. Weinstein.

Molecular understanding at this level of structural and dynamic detail is rare in the world of drug development, the authors note. Only about 15 percent of all drugs have a known molecular method-of-action, even though the effects of these drugs within the body — after very stringent and controlled laboratory testing — are well understood pharmacologically.

Source: New York- Presbyterian Hospital/Weill Cornell Medical Center/Weill Cornell Medical College

Josh: This is an extremely high penetrance mutation. More doctors and physicians need to be trained to order genetic tests for mutations such as this for their patients, especially those with a family history of colorectal cancer. If someone has this mutation, chances are they are going to get colorectal cancer, so routine screenings may be enough to save their life…preventative medicine at its best.

About one-third of colorectal cancers are inherited, but the genetic cause of most of these cancers is unknown. The genes linked to colorectal cancer account for less than 5 percent of all cases.

Scientists at Northwestern University’s Feinberg School of Medicine and colleagues have discovered a genetic trait that is present in 10 to 20 percent of patients with colorectal cancer. The findings strongly suggest that the trait is a major contributor to colorectal cancer risk and likely the most common cause of colorectal cancer to date.

If a person inherits this trait — which is dominant and clusters in families — the study found the lifetime risk of developing colorectal cancer is 50 percent, compared to 6 percent for the general population. The study will be published August 14 in an advanced on-line report in the journal Science.

“This probably accounts for more colorectal cancers than all other gene mutations discovered thus far,” said Boris Pasche, M.D., a lead author of the paper and director of the Cancer Genetics Program at the Feinberg School and the Robert H. Lurie Comprehensive Cancer Center of Northwestern University. Pasche also is a physician at Northwestern Memorial Hospital.

“The reasonable expectation is this finding will save some lives,” Pasche said. “We will be able to identify a larger number of individuals that are at risk of colorectal cancer and, in the long term, maybe decrease the cases of colorectal cancer and of people dying from it by being able to screen them more frequently.”

Colorectal cancer is the second leading cause of cancer death in the U.S.

The trait, which has been named TGFBR1 ASE, results in decreased production of a key receptor for TGF-beta, the most potent inhibitor of cell growth. With less of this vital protective substance to inhibit cell growth, colon cancer can more easily develop.

In 1998, Pasche and colleagues discovered the first mutation of this gene and in 1999 they showed that it was linked to a higher risk of colorectal cancer.

The results presented in this new study are the first to show that decreased production of this receptor for TGF-beta was present in 10 to 20 percent of patients with colorectal cancer. Decreased production of the same receptor was present in only 1 to 3 percent in healthy control groups.

The findings, which are based on a Caucasian population, need to be confirmed in other studies and may show strong variation between ethnic groups, Pasche said.

Pasche expects that a clinical test will soon be developed that could be offered to families with a history of colorectal cancer and other individuals to determine whether they carry this mutation.

Source: Northwestern University

Germline Allele-specific Expression of TGFBR1 Confers an Increased Risk of Colorectal Cancer. Laura Valle, Tarsicio Serena-Acedo, Sandya Liyanarachchi, Heather Hampel, Ilene Comeras, Zhongyuan Li, Qinghua Zeng, Hong-Tao Zhang, Michael J. Pennison, Maureen Sadim, Boris Pasche, Stephan M. Tanner, and Albert de la Chapelle. Science. Published online August 14 2008; 10.1126/science.1159397 (Science Express Reports)

In recent years, a class of small molecules known as microRNA have been found to play an important role in regulating gene products in most animal and plant species. A new study now indicates that microRNA may influence the development of alcohol tolerance, a hallmark of alcohol abuse and dependence. Researchers supported by the National Institute on Alcohol Abuse and Alcoholism (NIAAA) report the findings in the July 31 issue of the journal Neuron.

“This is an intriguing contribution to efforts aimed at identifying the molecular bases of alcohol tolerance,” noted NIAAA Director Ting-Kai Li, MD.

Tolerance is the decrease in sensitivity to alcohol that develops with repeated exposures to alcohol over time. Individuals who develop high tolerance (low sensitivity) to alcohol are at increased risk for becoming alcohol dependent. Thus, an important research objective has been to identify the adaptations within individual molecules that underlie tolerance.

In previous experiments, Steven N. Treistman, PhD, Professor of Psychiatry at the University of Massachusetts Medical School (UMMS), and colleagues at the university’s Brudnick Neurospychiatric Research Institute (BNRI), determined that a brain cell membrane structure known as the BK channel develops tolerance to alcohol, particularly in the supraoptic nucleus and the striatum, two brain regions important in alcohol’s effects. In both regions, alcohol tolerance was manifested as decreased alcohol sensitivity and reduced BK channel density. Previous studies have also shown that there are numerous variants of the BK channel gene.

In the current study, researchers led by Dr. Treistman, who is the director of the BNRI, examined whether microRNA might be involved in the alcohol tolerance observed in the BK channel.

In test tube experiments, the researchers showed that the amount of a specific microRNA molecule known as miR-9 increases in brain cells within minutes of exposure to alcohol. They also found that miR-9 blocks the expression of BK gene variants that contain a specific binding site for the molecule, while sparing those that lack a miR-9 binding site. Remarkably, the BK gene variants were destroyed exhibited high alcohol sensitivity, while those that remained showed significantly lower sensitivity, consistent with the development of tolerance.

“This represents a novel and elegant mechanism by which neurons are able to adapt to alcohol,” said Treistman. “Moreover, since adaptation, or tolerance, to the drug likely contributes to alcohol abuse, our findings identify a potential molecular target for therapeutic intervention.” Treistman credited his colleagues, especially Andrzej Z. Pietrzykowski, MD, PhD, research assistant professor of psychiatry, for their contributions to this important work.

A widely published expert on the molecular basis of addiction—in particular, the changes in the brain that occur as a function of drug exposure, which may make an individual prone to substance abuse and the compulsive behavior associated with drug addiction—Dr. Treistman noted that the microRNA process observed in this study may represent a general mechanism of neuronal adaptation to alcohol, with miR-9 playing a pivotal role in a complex regulatory network.

“This study demonstrates for the first time that alcohol exposure can cause rapid changes in microRNA levels, altering gene expression and perhaps behavior,” said Antonio Noronha, PhD, director of NIAAA’s Division of Neuroscience and Behavior. “In future studies, it will be interesting to determine if similar microRNA-based regulatory mechanisms influence alcohol problems in human populations.”

Source: University of Massachusetts Medical School

University of Florida College of Pharmacy researchers have discovered a marine compound off the coast of Key Largo that inhibits cancer cell growth in laboratory tests, a finding they hope will fuel the development of new drugs to better battle the disease.

The UF-patented compound, largazole, is derived from cyanobacteria that grow on coral reefs. Researchers, who described results from early studies today (Aug. 7) at an international natural products scientific meeting in Athens, Greece, say it is one of the most promising they’ve found since the college’s marine natural products laboratory was established three years ago.

An initial set of papers in the Journal of the American Chemical Society also has garnered the attention of other scientists, and the lab is racing to complete additional research. The molecule’s natural chemical structure and ability to inhibit cancer cell growth were first described in the journal in February and the laboratory synthesis and description of the molecular basis for its anticancer activity appeared July 2.

“It’s exciting because we’ve found a compound in nature that may one day surpass a currently marketed drug or could become the structural template for rationally designed drugs with improved selectivity,” said Hendrik Luesch, Ph.D., an assistant professor in UF’s department of medicinal chemistry and the study’s principal investigator.

Largazole, discovered and named by Luesch for its Florida location and structural features, seeks out a family of enzymes called histone deacetylase, or HDAC. Overactivity of certain HDACs has been associated with several cancers such as prostate and colon tumors, and inhibiting HDACs can activate tumor-suppressor genes that have been silenced in these cancers.

Although scientists have been probing the depths of the ocean for marine products since the early 1960s, many pharmaceutical companies lost interest before researchers could deliver useful compounds because natural products were considered too costly and time-consuming to research and develop.

Many common medications, from pain relievers to cholesterol-reducing statins, stem from natural products that grow on the earth, but there is literally an ocean of compounds yet to be discovered in our seas. Only 14 marine natural products developed are in clinical trials today, Luesch said, and one drug recently approved in Europe is the first-ever marine-derived anticancer agent.

“Marine study is in its infancy,” said William Fenical, Ph.D., a distinguished professor of oceanography and pharmaceutical sciences at the University of California, San Diego. “The ocean is a genetically distinct environment and the single, most diverse source of new molecules to be discovered.”

The history of pharmacy traces its roots back thousands of years to plants growing on Earth’s continents, used by ancient civilizations for medicinal purposes, Fenical added. Yet only in the past 30 years have scientists begun to explore the organisms in Earth’s oceans, he said. Fewer than 30 labs exist worldwide and research dollars have only become available in the past 15 years.

HDACs are already targeted by a drug approved for cutaneous T-cell lymphoma manufactured by the global pharmaceutical company Merck & Co. Inc. However, UF’s compound does not inhibit all HDACs equally, meaning a largazole-based drug might result in improved therapies and fewer side effects, Luesch said.

Since 2006, Luesch and his team of researchers have screened cyanobacteria provided by collaborator Valerie Paul, Ph.D., head scientist at the Smithsonian Marine Station in Fort Pierce. They check the samples for toxic activity against cancer cells and last year encountered one exceptionally potent extract — the one that ultimately yielded largazole.

To conduct further biological testing on the compound, Luesch and his team have been collaborating with Jiyong Hong, an assistant professor in the department of chemistry at Duke University, to replicate its natural structure and its actions in the laboratory.

Luesch said that within the next few months he plans to study whether largazole reduces or prevents tumor growth in mice.

Luesch has several other antitumor natural products from Atlantic and Pacific cyanobacteria in the pipeline.

“We have only scratched the surface of the chemical diversity in the ocean,” Luesch said. “The opportunities for marine drug discovery are spectacular.”

Source: University of Florida

Josh: This is certainly an interesting study. I suppose the primary question I have is why do cells decrease the expression of the lysosomal receptors with age? Knowing that would be helpful, I think not only for aging and neurodegenerative research, but also for cancer research. Too bad this won’t really be a realistic treatment in its current state…however, perhaps a drug could be used to increase expression.

As people age, their cells become less efficient at getting rid of damaged protein — resulting in a buildup of toxic material that is especially pronounced in Alzheimer’s, Parkinson’s disease, and other neurodegenerative disorders.

Now, for the first time, scientists at the Albert Einstein College of Medicine of Yeshiva University have prevented this age-related decline in an entire organ — the liver — and shown that, as a result, the livers of older animals functioned as well as they did when the animals were much younger. Published in the online edition of Nature Medicine, these findings suggest that therapies for boosting protein clearance might help stave off some of the declines in function that accompany old age. The study’s senior author was Dr. Ana Maria Cuervo, associate professor in the departments of developmental & molecular biology, medicine and anatomy & structural biology at Einstein.

The cells of all organisms have several surveillance systems designed to find, digest and recycle damaged proteins. Many studies have documented that these processes become less efficient with age, allowing protein to gradually accumulate inside cells. But aging researchers continue debating whether this protein buildup actually contributes to the functional losses of aging or instead is merely associated with those losses. The Einstein study was aimed at resolving the controversy.

One of these surveillance systems — responsible for handling 30 percent or more of damaged cellular protein — uses molecules known as chaperones to seek out damaged proteins. After finding such a protein, the chaperone ferries it towards one of the cell’s many lysosomes — membrane-bound sacs filled with enzymes. When the chaperone and its cargo “dock” on a receptor molecule on the lysosome’s surface, the damaged protein is drawn into the lysosome and rapidly digested by its enzymes.

In previous work, Dr. Cuervo found that the chaperone surveillance system, in particular, becomes less efficient as cells become older, resulting in a buildup of undigested proteins within the cells. She also detected the primary cause for this age-related decline: a fall-off in the number of lysosomal receptors capable of binding chaperones and their damaged proteins. Could replenishing lost receptors in older animals maintain the efficiency of this protein-removal system throughout an animal’s lifespan and, perhaps, maintain the function of the animal’s cells and organs as well?

To find out, Dr. Cuervo created a transgenic mouse model equipped with an extra gene — one that codes for the receptor that normally declines in number with increasing age. Another genetic manipulation allowed Dr. Cuervo to turn on this extra gene only in the liver and at a time of her choosing, merely by changing the animals’ diet.

To keep the level of the receptor constant throughout life, Dr. Cuervo waited until mice were six months old (the age that the chaperone system’s efficiency begins to decline) before turning on the added receptor gene. When the mice were examined at 22 to 26 months of age (equivalent to approximately 80 years old in humans), the liver cells of transgenic mice digested and recycled protein far more efficiently than in their normal counterparts of the same age — and, in fact, just as efficiently as in normal six-month old mice.

Does maintaining efficient protein clearance in liver cells of an older animal translate into better functioning for the liver as a whole? Since a key function of the liver is metabolizing chemicals, Dr. Cuervo answered this question by injecting a muscle relaxant into very old transgenic mice and very old normal mice. The very old transgenic mice metabolized the muscle relaxant much more quickly than very old normal mice and at a rate comparable to young normal mice.

“Our study showed that functions can be maintained in older animals so long as damaged proteins continue to be efficiently removed — strongly supporting the idea that protein buildup in cells plays an important role in aging itself,” says Dr. Cuervo. “Even more important, these results show that it’s possible to correct this protein ‘logjam’ that occurs in our cells as we get older, thereby perhaps helping us to enjoy healthier lives well into old age.”

Dr. Cuervo next plans to study animal models of Alzheimer’s, Parkinson’s and other neurodegenerative brain diseases to see whether maintaining efficient protein clearance in the brain might help in treating them. “Most people with these conditions are born with a mutation that gives rise to defective proteins, but they don’t experience symptoms until later in life,” says Dr. Cuervo. “We think that’s because their protein-clearance systems can handle abnormal proteins when the person is younger but get overwhelmed as their efficiency falls with age. By preventing this decline in protein clearance, we may be able to keep these people free of symptoms for a longer time.”

Dr. Cuervo will also investigate whether maintaining efficient protein clearance in all the body’s tissues will influence longevity and prevent the functional losses associated with growing old. “There’s reason to hope that drugs exerting a similar effect throughout the body may help us enjoy healthier lives well into old age,” says Dr. Cuervo. Meanwhile, she notes, evidence is mounting that two dietary interventions —low-fat and calorie-restricted diets — help cells to maintain efficient protein clearance.

Source : Albert Einstein College of Medicine

Restoration of chaperone-mediated autophagy in aging liver improves cellular maintenance and hepatic function. Cong Zhang & Ana Maria Cuervo. Nature Medicine. Published online: 10 August 2008; | doi:10.1038/nm.1851

If you’re a fan of habañero salsa or like to order Thai food spiced to five stars, you owe a lot to bugs, both the crawling kind and ones you can see only with a microscope. New research shows they are the ones responsible for the heat in chili peppers.

The spiciness is a defense mechanism that some peppers develop to suppress a microbial fungus that invades through punctures made in the outer skin by insects. The fungus, from a large genus called Fusarium, destroys the plant’s seeds before they can be eaten by birds and widely distributed.

“For these wild chilies the biggest danger to the seed comes before dispersal, when a large number are killed by this fungus,” said Joshua Tewksbury, a University of Washington assistant professor of biology. “Both the fungus and the birds eat chilies, but the fungus never disperses seeds – it just kills them.”

Fruits use sugars and lipids to attract consumers such as birds that will scatter the seeds. But insects and fungi enjoy sugars and lipids too, and in tandem they can be fatal to a pepper’s progeny.

However, the researchers found that the pungency, or heat, in hot chilies acts as a unique defense mechanism. The pungency comes from capsaicinoids, the same chemicals that protect them from fungal attack by dramatically slowing microbial growth.

“Capsaicin doesn’t stop the dispersal of seeds because birds don’t sense the pain and so they continue to eat peppers, but the fungus that kills pepper seeds is quite sensitive to this chemical,” said Tewksbury, lead author of a paper documenting the research.

“Having such a specific defense, one that doesn’t harm reproduction or dispersal, is what makes chemistry so valuable to the plant, and I think it is a great example of the power of natural selection.”

The paper is published the week of Aug. 11 in the online Proceedings of the National Academy of Sciences. Co-authors are Karen Reagan, Noelle Machnicki, Tomás Carlo, and David Haak of the University of Washington; Alejandra Lorena Calderón Peñaloza of Universidad Autonoma Gabriel Rene Moreno in Bolivia; and Douglas Levey of the University of Florida. The work was funded by the National Science Foundation and the National Geographic Society.

The scientists collected chilies from seven different populations of the same pepper species spread across 1,000 square miles in Bolivia. In each population, they randomly selected peppers and counted scars on the outer skin from insect foraging. The damage was caused by hemipteran insects – insects such as seed bugs (similar to aphids and leaf hoppers) that have sucking mouth parts arranged into a beaklike structure that can pierce the skin of a fruit.

The researchers found that not all of the plants produce capsaicinoids, so that in the same population fruit on one plant could be hotter than a jalapeño while fruit from other plants might be as mild as a bell pepper. But there was a much-higher frequency of pungent plants in areas with larger populations of hemipteran insects that attack the chilies and leave them more vulnerable to fungus.

The scientists also found that hot plants got even hotter, with higher levels of capsaicinoids, in areas where fungal attacks were common. But in areas with few insects and less danger of fungal attack, most of the plants lacked heat entirely. In those areas, chilies from the plants that did produce capsaicinoids had a lot less kick because they only produced about half the capsaicinoids as the plants did in areas where fungal attack was common.

Using chemical substances as a defense is not unique to peppers. Tomatoes, for example, are loaded with substances that give their unripened fruit a decidedly unpleasant taste, allowing the seeds a chance to mature and be dispersed. But unlike peppers, tomatoes and most other fruits lose their chemical defenses when the fruit ripens. That is a necessary step, scientists believe, because otherwise the fruit would not be consumed by birds and other animals that disperse the seed. The problem with that strategy, Tewksbury said, is that it leaves the fruit exposed to fungal attack.

“By contrast, peppers increase their chemical defense levels, or their heat, as they ripen. This is a very different model and peppers can get away with it because birds don’t sense pain when they eat capsaicin,” Tewksbury said. “I think a lot of plants would love to come up with this way of stopping fungal growth without inhibiting dispersers. It’s just very hard to do.”

The fact that chilies have capsaicin could be the reason humans started eating the peppers in the first place, he said. Chili peppers and corn are among the earliest domesticated crops in the New World.

“Before there was refrigeration, it was probably adaptive to eat chilies, particularly in the tropics,” Tewksbury said. “Back then, if you lived in a warm and humid climate, eating could be downright dangerous because virtually everything was packed with microbes, many of them harmful. People probably added chilies to their stews because spicy stews were less likely to kill them.”

All chilies originated in South America, and wild chilies now grow from central South America to the southwestern United States. Explorers carried the plants back to Europe, but they were not widely used there. From Europe, chilies made their way to Asia and Africa, where they have become a common ingredient in nearly every tropical cuisine.

“In the north, any adaptive benefit to using eating chilies would be much smaller than at the equator because microbial infection of food is less common and it’s easier to keep food cold. Maybe that’s why food in the north can be so boring,” Tewksbury said.

“Along the equator, without access to refrigeration, you could be dead pretty quickly unless you can find a way to protect yourself against the microbes you ingest every day.”

Source: University of Washington