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Biochemistry

Sugar for diabetics

A component of the cellular wall of a grass facilitates the absorption of glucose

eduardo cesarAt the roadside, the grass with purple flowers: a source of beta glucaneduardo cesar

A dogma has been knocked down. No longer can one say that diabetics must stay away from any type of sugar.  They must, for sure, stay clear of sugars that can rapidly cross the intestine walls and pile up in the blood stream, such as glucose, a molecule essential for any organism to produce the energy necessary to maintain itself. Researchers at the Botanic Institute of São Paulo and at the Federal University of Lavras (UFLA) have extracted from capim-favorito (Rhynchelytrum repens) – a grass that grows at the side of roads – a specific type of sugar called beta glucan, which can have a beneficial effect: it diminishes the quantity of glucose in the blood stream, as has been demonstrated by experiments with mice. Excessive glucose in the blood, a characteristic of diabetes, can lead to difficulties in wound healing, to blindness or even to heart problems, which, if not detected, can lead to a heart attack.

Studies carried out in Canada, Switzerland, France, Sweden and Japan with groups of human volunteers consider this sugar one more resource for treating a problem that reaches 150 million people throughout the world, 10 million of them in Brazil. A Swiss team have already proven that beta glucan, even in low concentrations, reduces the level of glucose in the blood, the so-called glycemia, by up to 50%. As well as this, three grams on a daily basis of this sugar would be enough to knock down the cholesterol level linked to the low density lipoproteins (LDL), a type of fat which promotes the formation of platelets in the walls of the veins and makes the circulation of the blood difficult.

In France, a recent study confirmed these gains for thirteen patients with diabetes type 2, when the organism does not make total use of the insulin that it produces, while in Canada another study with sixteen diabetic patients also of type 2 (10 men and 6 women) provided evidence of the value of a diet rich in cereals as a form of reducing glycemia – probably because the cereals contain beta glucan. Normally diabetics control the level of blood sugar through severe diets or daily insulin shots, the hormone that facilitates the capture of glucose by associating itself to a specific receptor of the muscle cells.

“The value of our discovery lies in the fact that we have studied a specific vegetal up until then unknown”, says Marcos Buckeridge, a research with the Botanic Institute and one of this study’s coordinators, which will be published in the Brazilian Journal of Medical and Biological Research. “We also noted the possibility that the interaction of beta glucan with another sugar found in grasses, named arabinoxylan, could be more powerful than beta glucan on its own.” According to him, as we eat cereals, we are ingesting beta glucans in interaction with arabinoxylans, “which could power up the action of retaining the glucose already during the diet, if our results come to be certified”. Beta glucan participated in the composition of fibers such as grasses, sugarcane, rice, wheat and corn or in cereals, for example, oatmeal, barley and rye, in levels that run from 1% to 7%. However, arabinoxylans is the most abundant type of sugar, varying between 20% to 30%.

Brazilian researchers entered onto the trail of beta glucan some three years ago when Rita de Cássia Leone Figueiredo Ribeiro, from the Botanic Institute, asked Marcos Buckeridge’s help, both being from the same laboratory, to understand the results of the doctorate student Ana Cardoso de Paula, whom she had been supervising. Ana Cardoso had verified the anti-diabetic effect of tea made from leaves of the capim-favorito (Rynchelytrum repens), a grass of African origin also called capim-natal or capim-gafanhoto in Brazil. At 30 centimeters in height, it has purple flowers and short and reddish leaves, when it is under continuous sunlight or green like that of the sugarcane, wider and longer if growing in the shade.

Repeated glucoses
As the effect of the reduction of glucose was due to the use of the precipitate from the tea – the insoluble material that deposits itself at the bottom of the tea cup -, Rita and Ana Cardoso suspected that they could be dealing with beta glucan, an insoluble sugar with which Buckeridge had worked for at least five years (see Pesquisa FAPESP No. 69). In 2001, in a special edition of the magazine Genetics and Molecular Biology dedicated to the results of the Sugarcane Genome, he had commented upon the genes of the sugarcane responsible for the production of this sugar.

Beta glucan forms part of the outer coating of the vegetable’s cellular structure – the cell wall -, participating in cellular growth and must constitute a reserve of energy for the germination of seeds, according to an article published last year in the magazine Cereal Chemistry, signed by Buckeridge and Nicholas Carpita, from Purdue University in the United States, with whom he had been working since 1998. Chemically speaking the beta glucan is a long molecule – a polymer – formed by units of glucose or glycopyranose, a closed or ring structure, as the specialists say, with six carbon atoms, which repeats itself, in this case, around 1,400 times. When isolated, it is a soluble sugar in hot water, forming a transparent solution; in an interaction with other molecules, beta glucan forms particles in suspension.

In the bloodstream
“We suspect that a polymer is what had formed the particles in suspension”, says Buckeridge. A further six months of work and they managed to purify fractions of beta glucan, whose effect became evident in an experiment with four groups of rats kept at the laboratory of Raimundo Souza, from the Veterinary Medical School of the University of Lavras, Minas Gerais. The first group was formed by normal animals (without diabetes), into which the researchers injected physiological serum – a solution of 0.9% sodium chloride, common salt – used as a placebo. In another group, made up of rats with diabetes induced by way of a chemical compound called streptozotocin, they also gave an injection of salty water. The two other groups of animals – both with induced diabetes – received injections of beta glucan from two distinct sources, one extracted from capim-favorito and the other pure, produced industrially starting from barley.

The diabetic mice of the third group were those who benefited most: the effect of the sugar extracted from capim-favorito lasted for twenty four hours, close to six times longer that the pure form. What’s the explanation? “My hypothesis is that the beta glucan takes longer to disappear in the blood stream because it must have remained linked, even partially, to the arabinoxylan, another sugar polymer from the cellular wall”, comments  Buckeridge.

“If this idea is correct, artificially we can make these linkages with the arabinoxylans, which could be extracted in large quantities from plants such as corn and sugarcane, and thus prolong the effect of the beta glucans.” For him, these results also suggest that the beta glucans or parts of their fragments, called oligosaccharides, pass through the intestine walls and are absorbed during the digestion of the grasses and cereals, in this manner controlling the quantity of glucose that gets to the organism after the gorging of the bread, cake or chocolate. Another idea, equally subject to confirmation, is that this sugar manages to act in an indirect manner, activating the production of insulin or even the molecules of this hormone that circulate in the bloodstream.

Mild taste
At  Buckeridge’s laboratory the work is progressing fast. One of his students, Ana Maria Silva, has found beta glucan in all parts of the sugarcane and in other grasses such as brachiaria sp (tanner grass), also very common in Brazil. And something unexpected happened. Some four years ago, the gardener Helena Leite Cirilo, who had accompanied step by step Ana Cardoso’s doctorate degree, decided to experiment tea made from capim-favorito and, when faced with the results, adopted it to control her diabetes. “I’d been taking insulin, but the glucose level hadn’t been going down very much”, said Helena, fifty three years of age, and a diabetic since the age of forty, today with a glucose level stabilized at 134 milligrams per 100 ml (it was almost 400, well above the band considered normal, from 70 to 110 milligrams).

“I don’t recommend this use and I explain that there were are enough studies to prove the tea’s safety”, says Buckeridge. His scientific curiosity has not yet motivated him to experiment the reasonably tasty tea, used at times in animal studies. “It could well be dangerous”, he alerts. Another day, someone else who frequents the laboratory – who is not suffering from diabetes – decided to take a chance. She was dizzy for two days, imagining that it was her blood pressure that had fallen, but probably the level of sugar in her blood stream had fallen very low.

The Project
Conservation and sustainable use of vegetal biodiversity of the Cerrado and Atlantic Rainforest: reserve carbohydrates and their role in establishing and maintaining plants in their natural environment; Modality Thematic Project; Coordinator Marcos Silveira Buckeridge – Botanic Institute; Investment R$ 309,845.00 and US$ 378,726.00

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