How does the human body cure congenital vitamin C deficiency?

One study explained how humans, along with some high-level primates, guinea-pigs and fruit bats can live with the same innate metabolic defect: that the body is incapable. production of vitamin C from sugar.

According to the article published in the March 21, 2008 issue of Cell (a publication of Cell Press), unlike more than 4,000 mammal species capable of producing vitamin C blood cells of species without The ability to make vitamin C is specially equipped to absorb vitamins in the form of oxidation (L-dehydroascorbic acid - DHA). Once inside the blood cells, DHA is immediately converted back into ascorbic acid (vitamin C) and then transported through the bloodstream to parts of the body.

Naomi Taylor of Montpellier I and II (France) said: 'Evolution is amazing. Although people still consider it a congenital defect in metabolism that everyone has, there are still solutions to address this defect by using the most numerous cells' . She also pointed out that our bodies contain billions of blood cells. 'Through evolution, we have a system that captures oxidized vitamin C and transports the necessary non-oxidized form to the body . '

Ms. Taylor also said that blood cells in other mammals, if any, also take very little DHA. That explains why their bodies need to produce vitamin C many times more than we need from meals. The recommended dose of vitamin C for us is 1 mg / kg. But for example, goats, for example, can produce vitamin C at an amazing rate of 200 mg / kg a day.

In fact, the blood cells of animals that cannot produce vitamin C have cycle through the little things the body has. Previous studies have described this 'recycling' process. "Our contribution to the whole problem is to clarify that there is a special recycling process in mammals that cannot produce vitamin C," said Taylor.

Scientists found that the protein called Glut 1 in the membrane of cells in the body is the glucose transporter. At the same time they knew that Glut 1 could also transport DHA, thanks to the structural similarity between the two types of molecules. Biochemical experiments show that glucose transporters are interchangeable to transport both glucose and DHA.

But in a new study, Taylor's group made a surprising discovery: The Glut 1 protein in human blood cells particularly prioritizes DHA over glucose.

In fact, human blood cells contain more Glut 1 protein than any other cell type - there are more than 200,000 Glut 1 molecules on each cell's surface. However, the researchers also found that because blood cells are produced from the bone marrow, their ability to transport glucose is reduced even when the amount of Glut 1 protein rises.

The glucose transport process changes to DHA because of the presence of another membrane protein called stomatin. The rate of stomatin in the cell membrane is very low. Therefore, in patients with permeability disorders from hereditary blood cell membrane, the rate of transported DHA decreases by 50% while the amount of glucose collected increases significantly.

One more surprise: The researchers found that mouse blood cells - a species that can produce vitamin C - had no Glut 1 protein, instead Glut 4.

The researchers suggest that the difference in human blood cells is related to the inability to synthesize reduced form DHA (which is vitamin C) from our glucose. They investigated Glut 1 in blood cells of humans, guinea-pigs, and fruit bats but did not proceed with other mammalian blood cells; These include rabbits, mice, cats, dogs and sinsin squirrels. Later, they studied in detail the primates. The Haplorrhini sub-primates (including semifinals, neo-world monkeys, former world monkeys, humans and monkeys) have lost the ability to synthesize vitamin C, while primates belong to the Strepsirrhini set (including lemurs) is capable of producing this vitamin.

Remarkably, the researchers found Glut 1 in all tested blood cells of high-level primates, including long-tailed macaque, brown monkey, baboon and apes. . Glut 1 is not found in lemurs' blood cells. Furthermore, the rate of intracellular transport of 3 different lemur species is 10% lower than that of high-level primates.

The team concludes: 'The activity of Glut 1 in blood cells as well as DHA transport are special characteristics of species that cannot produce vitamin C but appear mainly in primates. High level, guinea pig and fruit bat. Blood cells of adult mice do not have Glut 1 protein nor transport DHA. But Glut 4 appears again. Therefore, simultaneous induction of Glut 1 and stomatin in blood cells acts as a compensation mechanism for mammals that cannot synthesize ascorbic acid metabolites , in other words, vitamin C. .