Genesis of Eden Diversity Encyclopedia

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Ancient wisdom NS 22 Jan 2000

Age-old herbal remedies hold the promise of treating dementia

IN SHAKESPEARE's day, apothecaries treated memory loss in the elderly with sage and lemon bahn, while 2500 years ago the Greek physician Hippocrates recommended wormwood. They may have been on to something-all these herbs have similar effects to drugs used to treat Alzheimer's disease. And two of them are already undergoing clinical trials. The brains of Alzheimer's patients lose nicotinic receptors, one of the two types of receptor for the neurotransmitter acetylcholine. Increasing the levels of acetylcholine in the brain can help alleviate cognitive problems. Several drugs companies are now testing drugs that stimulate nicotinic receptors, which not only simulates a boost in acetylcholine levels but can also lead to the production of new receptors. Elaine Perry of the University of Newcastle wondered if the herbal remedies exploited the same mechanism. She and her colleagues made ethanol extracts of various species of sage, the related herb lemon balm (Melissa officinalis) and wormwood (Artemisia absinthium). They tested the extracts to see if they contained compounds that bound to acetylcholine receptors in the human brain. Wormwood contained chemicals that bound strongly to both types of acetylcholine receptors, the nicotinic and the muscarinic. Lemon balm bound to either or both, depending on the variety. Pineapple sage (Salvia elegans) bound strongly to the muscarinic receptors. Only common sage (S. officinalis) did not bind strongly to either receptor. The strength of the binding depended on the concentration of the extract, but some samples bound as strongly as carbamylcholine, a powerful drug that resembles acetylcholine. "The results are intriguing," says Alzheimer's expert Gareth Roberts, who heads Proteon, a biotechnology company in Cambridge. "Most of our pharmaceuticals were derived from plants." But he warns that licensing herbs for treatment can be difficult, as plants coktain varying quantities of active ingredients. Perry suspects plants make the compounds to poison plant-eating insects, whose nervous systems have similar receptors. Even before the results of Perry's work were known, varieties of sage and lemon balm were in the first stage of clinical trials at Newcastle. Lemon balm is being administered to volunteers as aromatherapy. "The active compounds are volatile, so that is an effective way to deliver the drug," says Perry. But she cautions against trying to protect your mental faculties by drinking absinthe, an especially potent spirit whose main flavouring is wormwood and which also contains lemon balm. It was banned in much of Europe in the 19th century, but has recently become available again. "Absinthe contains lots of toxic substances," says Perry. "It's not the best way to get your wormwood." Debora MacKenzie

Source: Journal of Ethnopharmacology (vol 69, p 105)

Relative values: Crossing rice with its wild cousins works wonders

NS Millennium edition

UNLIKELY marriages between scrawny wild species of rice and their commercial relatives are boosting rice yields by a staggering 10 to 20 per cent. Researchers say this approach has also produced other unexpected benefits, including protection against a virus. The news has prompted calls from environmental campaigners to adopt the technique as an alternative to genetic engineering. "If you do it by natural methods, we have no problem with that," says Benedikt Haerlin, Greenpeace's genetic engineering coordinator in Berlin. "Ibis could be extremely effective, and you don't need to get genes from daffodils or microorganisms." Susan McCouch of Cornell University, New York, explained the technique and unveiled her team's results on 16 November at a conference organised by Nature Biotechnology in London. There are many thousands of known strains of rice, McCouch says, of which only 25 per cent are used commercially. Normally, plant breeders only exploit a "wild" trait, such as disease resistance, if it is obvious in the wild relative. McCouch, however, reasoned that the huge number of genes present in wild species should include some that would be useful to their cultivated relatives. So in the early 1990s, she and her colleagues started crossing wild species with no outward signs of valuable traits with good breeding lines of Oryza sativa, the rice species grown commercially. All commercial varieties of rice derive from two sativa subspecies, japonica and indica. ilaponica varieties are favoured in China, japan and the rest of Southeast Asia. They produce stubby, sticky grains.

Indica varieties have longer grains and are generally grown elsewhere. "Mainstream colleagues told us it was preposterous to try crossing with wild relatives," says McCouch. But by the mid-1990s, she had boosted yields of a valuable Chinese breeding line of sativa by 18 per cent after crossing it with a bizarre-looking wild rice species, 0. rufipogon. "It's native to Malaysia, grows 2 metres tall, and shatters easily, spilling its grains," says McCouch. Since then, the programme has expanded, involving teams froin Korea, Indonesia, Colombia, Brazil and the Ivory Coast. Now, McCouch is awaiting the results of crosses between a dozen sativa varieties and three wild species, including 0. rufipogon. The other wild species0. glaberrina and 0. barthi are from Africa. Preliminary findings from five crosses suggest that yields have increased by 10 to 20 per cent, McCouch said. And one cross turned out to be resistant to the Hojablanca virus, which devastates rice crops in Latin America, despite the fact that neither parent was resistant. McCouch thinks that there must be new interactions occurring between proteins and genes from the different parents, even though they succumb to the virus individually. The team is combing through the DNA of the hybrid plants to identify the genes that imparted the improved traits. "If you know what the gene sequence is, you can go back in the wild populations and look for more beneficial variations," says McCouch. She says that using the library of genes available in the wild relatives of crop plants could make crop genetic engineering unnecessary. Andy Coghlan

Crunch time for cancer NS 13 Nov 99

WANTED: volunteers to eat a plate of raw broccoli every day for week. If you're willing to submit to this unusual diet, Brian Ratcliffe wants to hear from you. Ratcliffe, a food scientist at Robert Gordon University in Aberdeen, heads a team investigating whether broccoli can prevent colon cancer. So far, his experi- ments, suggest that the vegetable loses its potency if cooked. Only pigs eating raw broccoli appeared to reap any protective benefit, as measured by the amount of DNA damage in colon cells taken from the animals. "The level of damage was around half that in pigs eating cooked broccoli," says Ratcliffe. This suggests that cooking destroys chemicals called glucosinolates, which are metabolised in the colon to substances called isothiocyanates. These stimulate the production of enzymes that mop up free radicals that can damage DNA. Ratcliffe is now looking for people to continue the research. But even if cooked broccoli doesn't protect against colon cancer, Ratcliffe says it contains other beneficial ingredients such as vitamins A and C. "We're not saying everyone should eat only raw broccoli," he says. Andy Coghlan

The downside of liquorice

MEN who indulp their sweet tooth by eating liquorice may later find themselves unable to indulp their sweetheart, researchers in Italy have found. Decio Armanini of the University of Padua and his colleagues asked seven healthy young men to eat 7 grams of liquorice every day for a week. After only four days, the subjects' testos- terone levels had dropped by an average of 44 per cent. Glycyrrhizic acid-a compound in liquorice root extract- inhibits an enzyme involved in the production of the hormone (The New England Journal of Medicine, vol 341, p 11 58). The researchers suggest that doctors should consider liquorice as a potential culprit when treating men with sexual dysfunction.

Unpalatable truths
NS 17 Apr 99
FOCUS Demanding proof that genetically modified foods are safe is all very well, but without a rational system for testing conventional foods, we may never get it

EARLIER this year, Britain was rocked by claims that genetically modified foods are dangerous. Arpad Pusztai, a biochemist who used to work at the Rowett Research Institute in Scotland, said he had shown that GM potatoes were harmful to rats because of their genetic modification alone. Were the GM potatoes toxic? On the basis of Pusztai's evidence, it's impossible to say. In fact, his results support only one obvious conclusion: rats hate potatoes. Pusztai fed separate groups of rats on normal or GM potatoes to see if the GM food had different effects. That's good, basic toxicology. Unfortunately he couldn't make the animals eat enough potato, so they were malnourished no matter which kind they were eating. According to toxicologists who exam- ined the data, changes in their organ weights and immune reactivity showed no unambiguous association with genetic modification (This Week, 6 March, p 13). Starvation or known toxins in raw potato were the most likely culprits for any changes seen in the rats. These experiments reveal a serious problem that is only now being grasped by the biotechnology industry: standard toxicology tests don't work for food. It is often difficult to feed lab animals enough GM fodder, whether or not they find it palatable, to see if it has undesirable effects compared with unmodified food. Essen- tially, animal models are not sensitive enough to reveal small differences between modified and unmodified foods.


Even if you manage to get animals to eat enough test food, you risk changing their diet so profoundly that even those eating unmodified food will be abnormal. For all but the most blatantly toxic GM foods, this may make it impossible to draw meaning- ful conclusions from such experiments. Politicians, taken aback by huge public mistrust of "Frankenfoods", are also real- ising that safety testing of these foods is not straightforward. In Britain, the Cabi- net's biotechnology committee has com- missioned a report on the human health implications of GM foods from the gov- emment's Chief Medical Officer and Chief Scientific Adviser, due to be published this month. A Cabinet Office memo, leaked by Friends of the Earth, asks: "Why don't we require a pharmaceutical-type analysis of the safety of these foods, with proper trials?" But as the problems to date have shown, the proposition is a nonstarter. So how can we check the safety of GM food? Scientists from the 29 industrialised countries of the OECD concluded at a meeting in Paris in December that a whole new approach is needed. In September, they will meet again to start drawing up ways of carrying out such checks. They are up against some serious logis- tical problems. Harry Kuiper of the State Institute for Quality Control of Agricul- tural Products in Wageningen, Nether- lands, tested a GM tomato by freeze-drying it and feeding so much to rats that each got the equivalent of 13 of fresh tomatoes a day. Any more, and they would have been poi- soned by the basic nutrients, such as potas- sium, in the tomato powder. "But toxicologists still said we hadn't fed them enough to get a meaningful result," says Kuiper. The usual approach for testing a new food additive, for instance, is to feed it to a rat until a toxic effect is observed. That way, you get an idea of the nature and threshold of any toxicity. But with tomatoes, the researchers never man- aged to reach that threshold. In standard toxicological terms, says Kuiper, they have not been adequately tested. Others would argue that if such large amounts are harmless, the food cannot reasonably be called toxic. Nonetheless, these difficulties mean that GM food developers usually avoid testing whole foods. Instead, they try to isolate the changed portion and test that. As an example, Roy Fuchs, head of scientific affairs at Monsanto, one of the world's biggest developers of GM food, quotes potatoes carrying a gene for the Bt toxin, an insecticide normally produced by Bacillus thuringensis. Monsanto sells its Bt potatoes in the US and is applying for a European licence. Fuchs says that the potatoes, like afl genetically engineered plants so far, do not produce enough of the product of the novel gene for it to be isolated from the plants themselves and tested. "So we put the novel genes in bacteria, produce the gene product and test it by conventional methods." However, the protein made by the bacteria may not be the same as that made by the plant, especially in its poten- tial to cause allergy. The production of a novel protein is only one of the potentially harmful changes that occur in when a foreign gene is inserted into a plant. Because the positioning of the novel gene within the plant's DNA is essentially random, it may alter the plant's expression of its own genes-with unpre- dictable effects. It is this kind of change that stymies conventional toxicology. Food is a complex mixture of substances that occur in different quantities in different varieties of crops and in the same variety grown under even slightly different conditions. When is a change in one or several of those substances a problem? Unfortunately, says Keams, no one has ever tested conventional food for toxicity, so no one quite knows where to start. One exception is potatoes. Conventional plant breeders in the US and the Netherlands test new potato varieties for elevated levels of known toxins such as solenines. French breeders do not-and there are no legal requirements in any country to do so. And that still leaves toxins in GM foods that we may not yet know about. "We have to think through these things case by case," says Kearns, starting with a better understand- ing of what is in normal crops. Kuiper's institute is working on a screening test that detects differences in the pattem of messenger RNA molecules produced by normal and transgenic toma- toes. The hope it that this will provide a fast way to see if there have been large changes in gene expression. The method can reliably detect differences between red and green tomatoes-which is encourag- ing, says Kuiper, because green ones pro- duce more toxins.

Key differences

The team has also compared the chemicals synthesised by normal and transgenic plants by looking at their nuclear magnetic resonance (NMR) spectra. Nearly every chemical compound in the plant produces a characteristic "fingerprint" of peaks. The screening test revealed that there were up to eightfold differences in concentra- tions of sugars, amino acids and various unidentified compounds. Impressive as this sounds, it may not be significant: Kuiper notes that there were greater differences between unaltered tomatoes grown in different conditions than there were between GM and normal tomatoes grown in identical conditions. A better way of exploiting NMR might be to use it to find substances that differ in transgenic foods and then to test these substances in, for example, cell cultures, to see if the changes could be harmful. The need for such tests may be soon be pressing. But when crops are engineered to produce a number of desired nutrients or "nutraceuticals", changes in the plant's own gene expression could become much more complex and their potentially toxic effects harder to test. However, proponents of GM foods point out that whichever direction food testing goes, the subtly altered products on our plates will have been tested far more thor- oughly than any conventional food. After all, even ordinary kidney beans are poiso- nous if undercooked. Dozens of people die each year from cyanide from peach seeds. Manioc, the staple diet of millions, had to be grated, squeezed and cooked to drive off the cyanide before improved varieties became available. And some of the most notorious food-linked poisons, such as aflatoxins in grain, do not come from the food but moulds that infect it. In the com- parison between modified and urtmodified foods, nothing is clear cut. And testing is never simple. Debora MacKenzie

Red flag for green spray NS 29 May 99

Even organic farming is not immune to health scares

BACTERIAL spores sprayed on organic crops as a pesticide may damage the health of people who inadvertently breathe them in. French researchers have found that inhaling the spores can cause lung inflammation, internal bleeding and death in laboratory mice. Bacillus thuringiensis, or Bt, produces a toxin that kills insects. The dried spores of the bacteria have been used as a pesticide for more than 30 years and are one of the very few insecticides sanctioned for use on organic crops in Europe. Bt is also widely used to combat pest such as the spruce budworm, a caterpillar that attacks trees. Last year, French scientists isolated a strain of Bt that destroyed tissue in the wounds of a French soldier in Bosnia. The strain, known as H34, also infected wounds in immunosuppressed mice (This Week, 30 May 1998, p 7). Now the same team has found that H34 can kill mice with intact immune systems if they inhale the spores. Franqoise Ramisse of le Bouchet army research laboratories near Paris and her colleagues found that healthy mice inhaling 1011 spores of Bt H34 died within eight hours from internal bleeding and tissue damage. Spores from mutants of the same strain which did not produce the insecticide were equally lethal to mice, suggesting that it was not to blame. Ramisse and her colleagues presented their results at a conference in Paris last month. The researchers think that the symptoms are caused by other toxins. The bacterium's close cousin, Bacillus cereus, produces a toxin that ruptures cell membranes. And in 1991, Japanese researchers showed that B. thuringiensis produces the same toxin. In fact, when the French researchers ran samples from the soldier from Bosnia through an automated medical analyses it seemed to show that the bacterium was B. cereus. Ramisse suggest that companies producing Bt spores might make them safer by deleting the promoter sequence that activates the gene for the membranerupturing toxin. Although H34 is not used as a pesticide, commercial strains of Bt tested by the researchers also killed some mice or caused lung inflammation when inhaled. The team obtained these strains from Abbott Laboratories, a major supplier of Bt based in Chicago. Ramisse points out that the strains are sprayed on forest pests at concentrations of 1011 spores per square metre-and so might pose a danger to people in the immediate vicinity. But Abbott maintains that Bt issafe. "We stand by our products," says Linda Gretton, a company spokeswoman. The French researchers have not yet tested strains made by other companies. "I suspect Bt infection is more widespread than we realise," says Ramisse. Recorded infections by Bacillus pathogens are comparatively rare. Known pathogenic species can have very distinctive symptoms. Anthrax, for instance, is caused by B. anthracis. But where such tell-tale signs are absent, Ramisse suspects that doctors often fail to recognise that the bacteria are responsible, dismissing any Bacillus in patients' cultures as contamination. Consequently, the cultures are often discarded. "I wish they would start keeping them so we could check for Bt," she says. When Bt was sprayed in towns in Oregon in 1991 to combat gypsy moths, the bacterium was found in clinical samples from 55 patients who had been admitted to hospital for a variety of other reasons. Robert Haward of the Soil Association, which represents Britain's organic farmers, says that they may have to use masks and take more care when spraying the spores on crops. Debora MacKenzie

A clove a day keeps cancer at bay NS 29 May 99

EATING as little as half a clove of raw garlic per day in a salad might protect you against bowel cancer. Better known for helping you avoid heart disease, garlic also protects against bowel cancer. Rex and Christine Munday, a husband-and-wife team at the New Zealand government's Ruakura Agricultural Research Centre in Hamilton, wanted to find out how much garlic you needed to benefit. They fed rats for five days at a time with varying doses of diallyl disulfide, the substance in garlic reckoned to have the most potent anticancer properties. Disulfide makes the gut produce enzymes that purge it of cancer-causing substances.

The Mondays found that levels of these enzymes rose by 20 to 60 per cent at doses matching modest intakes in humans. "It's been recognised that garlic is an inducer of these enzymes, but previous studies have all been with doses at meaningless levels," says Rex Munday. "They implied you'd need to eat your own weight in garlic to achieve beneficial effects." In the rats, beneficial daily doses of disulfide were between 0-075 and 0-3 milligrams per kilogram of body weight. That's equivalent to about half a clove for humans-but you'd need to consume nine times as much if you cook it. The paper will appear in Nutrition and Cancer (vol 34, p 42). Andy Coghlan

Boiled is best NS 5 Jun 99

Soggy carrots and mushy broccoli could make you live longer

COOKED vegetables give you considerably more protection against heart disease and cancer than raw ones, according to a pan-European research team. Cooking softens up plant cells, the researchers say, improving gut absorption of carotenoidsantioxidants that combat tissue damage and the accumulation of plaque in arteries. "Absorption of carotenoids from raw carrots is about 3 or 4 per cent, but if you cook and mash them, absorption increares by four or fivefold," says Sue Southon, coordinator of the project at the Institute of Food Research in Norwich. Southon presented interim results last month in Brussels to officials from the European Commission and growers of fruit and vegetables. "One of the problems with getting carotenoids into your body is the structure of the food, particularly the tough-walled cells like those in carrots," says Southon. "Cooking helps to release them." Southon and her collaborators-drawn from Britain, the Netherlands, Spain, Ireland and France-have found that this applies to all vegetables and all carotenoids. The main carotenoid in carrots is betacarotene, a substance also abundant in green vegetables such as spinach and broccoli. Other important carotenoids linked with health benefits are lutein, found in many yellow and green vegetables, and lycopene, a constituent of tomatoes and watermelons.

With the help of an artificial gut developed at the Nutrition and Food Research Institute of TNO, the Dutch applied research organisation in Zeist (This Week, 30 January, p 4), Richard Faulks of the Institute of Food Research and his colleagues are trying to work out the precise amounts of carotenoids absorbed from standard portions of cooked or processed vegetables. "Then we can work out a recommended daily intake," says Faulks. He says the team's work builds on findings by Venket Rao and his colleagues at the University of Toronto, who discovered in 1997 that tomato pastes and purses are richer in lycopene than raw tomatoes. Likewise, Cheryl Rock and her colleagues at the University of Califon-da in San Diego found the first evidence last year that cooked carrots are richer in absorbable betacarotene. Southon says that the overall message from the programme is that people should eat more fruit and vegetables, and it doesn't matter whether they're cooked, mashed, fresh, frozen or canned. "Just pile your plate with colour," she says. The other important finding from the programme is that, for reasons that are not yet clear, carotenoids and nutrients such as vitamin E are more beneficial if eaten in foods rather than taken as supplements. 'It's my belief the supplement era for carotenoids is over," says Southon. Andy Coghlan

Too much too young
22 Apr 2000
More bad news for people who take dietary supplements

NUTRIENTS called flavonoids may occasionally trigger a deadly form of infant leukaemia which starts before birth, a new report suggests. This doesn't meant expectant mothers should avoid food containing flavonoids, however. "In whole foods, these chemicals are nutritionally very important," says study leader Janet Rowley of the University of Chicago in Illinois. "But taking too many supplements, and getting too much, might have untoward effects." Flavonoids are found in, among other things, beer, coffee, chocolate, herbs, wine, soya, and certain medicines, and there is overwhelming evidence that they can protect us against disease. Populations whose diets include high levels of flavonoids have substantially lower rates of breast and prostate cancer, for instance. But in the past decade, studies of a gene called MLL on chromosome 11 have provided hints that flavonoids can cause certain rare cancers. Leukaemias can arise as a side effect of cancer treatment with drugs such as VP16 (epipodophyllotoxin) which inhibit an enzyme called topoisomerase 11. Crippled topo 11 leaves breaks in DNA, and these kill rapidly dividing cancer cells. Unfortunately, this can also cause leukaemia by occasionally making nicks in, and ultimately rearranging the MLL gene. Nearly identical MLL rearrangements occur in more than two-thirds of infant leukaemias that start in the womb. Since some flavonoids also inhibit topo 11, Julie Ross of the University of Minnesota Cancer Center in Minneapolis and her colleagues suggested six years ago there might be a link. Rowley's team put the idea to the test I by comparing how well flavonoids could cut the MLL gene in human cells. Out of 20 flavonoids tested, 10 cut the gene in the same region as VP16 and two i quercetin, which is found in fruits and t vegetables, and fisetin, found in herbswere just as effective at cutting the gene S as the cancer drug. "It's quite amazing they're so potent," says Rowley. She adds that since infant leukaemias are exceedingly rare-37 cases per million births-and flavonoids are everywhere, a number of factors must conspire to turn these normally beneficial nutrients into a trigger for cancer. For instance, a genetically vulnerable fetus might only get leukaemia if it receives a surge of flavonoids at a time during development when it is particularly susceptible. Indeed, Rowley's team and other researchers are already looking for such genetic factors. "The message is not that fruit and vegetables are bad for you," says Ross. "It's much more complex." Ingested flavonoids might never reach a blood level where they could cut DNA, says nutrition and cancer specialist John Milner of Pennsylvania State University in University Park. "I just want to see it repeated in an animal model." But Rowley points out that some flavonoids are already being tested as cancer treatments at blood levels far in excess of those that will nick the MLL gene. Her work suggests that one unwelcome side effect of this treatment could be topo 11-induced leukaemias. "This is one reason I wanted to get this result out there now," she says. Philip Cohen

Source: Proceedings of the National Academy of Sciences, online Early Edition, 11 April 2000