Featured Research

from universities, journals, and other organizations

How Humans Make Up For An 'Inborn' Vitamin C Deficiency

Date:
March 21, 2008
Source:
Cell Press
Summary:
A new study appears to explain how humans, along with other higher primates, guinea pigs and fruit bats, get by with what some have called an "inborn metabolic error": an inability to produce vitamin C from glucose.

A new study appears to explain how humans, along with other higher primates, guinea pigs and fruit bats, get by with what some have called an "inborn metabolic error": an inability to produce vitamin C from glucose.

Unlike the more than 4,000 other species of mammals who manufacture vitamin C, and lots of it, the red blood cells of the handful of vitamin C-defective species are specially equipped to suck up the vitamin's oxidized form, so-called L-dehydroascorbic acid (DHA), the researchers report in the March21st issue of Cell, a publication of Cell Press. Once inside the blood cells, that DHA--which is immediately transformed back into ascorbic acid (a.k.a. vitamin C)--can be efficiently carried through the bloodstream to the rest of the body, the researchers suggest.

"Evolution is amazing. Even though people talk about this as an 'inborn error'--a metabolic defect that all humans have--there is also this incredible manner in which we've responded to the defect, using some of the body's most plentiful cells," said Naomi Taylor of Université Montpellier I and II in France, noting that the body harbors billions of red blood cells. "[Through evolution], we've created this system that takes out the oxidized form of vitamin C and transports the essential, antioxidant form."

Meanwhile, the red cells of other mammals apparently take up very little, if any, DHA, which might explain why they need to produce so much more vitamin C than we need to get from our diets, Taylor said. The recommended daily dose of vitamin C for humans is just one mg/kg, while goats, for example, produce the vitamin at a striking rate of 200 mg/kg each day.

In essence, the red cells of animals that can't make vitamin C recycle what little they've got. Earlier studies had described the recycling process, Taylor said. "Our contribution to the whole story is to show that this process of recycling exists specifically in mammals that don't make vitamin C."

Scientists knew that the protein called Glut1, found in the membranes of cells throughout the body, is the primary transporter of glucose. They also knew that Glut1 can transport DHA too, thanks to the structural similarities between the two molecules. In biochemical assays, it appeared that the glucose transporter would move glucose and DHA interchangeably.

But, in the new study, Taylor's group made a surprising discovery: The Glut1 on human red blood cells strongly favors DHA over glucose. In fact, the human blood cells are known to carry more Glut1 than any other cell type, harboring more than 200,000 molecules on the surface of every cell. Nevertheless, the researchers found, as red blood cells develop in the bone marrow, their transport of glucose declines even as Glut1 numbers skyrocket.

The key to the glucose transporters switch to DHA, they show, is the presence of another membrane protein called stomatin. (Accordingly, in patients with a rare genetic disorder of red cell membrane permeability wherein stomatin is only present at low levels, DHA transport is decreased by 50% while glucose uptake is significantly increased, they report.)

Then, another surprise: The researchers found that the red cells of mice, a species that can produce vitamin C, don't carry Glut1 on their red blood cells at all. They carry Glut4 instead. They suspected that the differences in human red blood cells might be linked to our inability to synthesize the reduced form of DHA, vitamin C, from glucose. In fact, they confirmed Glut1 expression on human, guinea pig and fruit bat red blood cells, but not on any other mammalian red cells tested, including rabbit, rat, cat, dog and chinchilla. Next, they took a closer look at primates. Primates belonging to the Haplorrhini suborder (including prosimian tarsiers, new world monkeys, old world monkeys, humans and apes) have lost the ability to synthesize vitamin C, whereas primates in the Strepsirrhini suborder (including lemurs) are reportedly able to produce this vitamin, Taylor explained.

Notably, they detected Glut1 on all tested red blood cells of primates within the higher primate group, including long-tailed macaques, rhesus monkeys, baboons and magot monkeys. In marked contrast, Glut1 was not detected on lemur red blood cells. Moreover, they report, although DHA uptake in human and magot red cells was similar, the level of transport in cells from three different lemur species was less than 10% of that detected in higher primates.

"Red blood cell-specific Glut1 expression and DHA transport are specific traits of the few vitamin C-deficient mammalian species, encompassing only higher primates, guinea pigs and fruit bats," the researchers concluded. "Indeed, the red cells of adult mice do not harbor Glut1 and do not transport DHA. Rather, Glut4 is expressed on their cells. Thus, the concomitant induction of Glut1 and stomatin during red blood cell differentiation constitutes a compensatory mechanism in mammals that are unable to synthesize the essential ascorbic acid metabolite," otherwise known as vitamin C.

The researchers include Amelie Montel-Hagen, Institut de Genetique Moleculaire de Montpellier, CNRS, Universite´ Montpellier I and II, Montpellier, France; Sandrina Kinet, Institut de Genetique Moleculaire de Montpellier, CNRS, Universite´ Montpellier I and II, Montpellier, France; Nicolas Manel, Institut de Genetique Moleculaire de Montpellier, CNRS, Universite´ Montpellier I and II, Montpellier, France; Cedric Mongellaz, Institut de Genetique Moleculaire de Montpellier, CNRS, Universite´ Montpellier I and II, Montpellier, France; Rainer Prohaska, Max F. Perutz Laboratories, Department of Medical Biochemistry, Medical University of Vienna, Vienna, Austria; Jean-Luc Battini, Institut de Genetique Moleculaire de Montpellier, CNRS, Universite´ Montpellier I and II, Montpellier, France; Jean Delaunay, Hematologie, Hopital de Bicetre, APHP, INSERM U779, Faculte´ de Medecine Paris-Sud, Le Kremlin-Bicetre, France; Marc Sitbon, Institut de Genetique Moleculaire de Montpellier, CNRS, Universite´ Montpellier I and II, Montpellier, France; and Naomi Taylor, Institut de Genetique Moleculaire de Montpellier, CNRS, Universite´ Montpellier I and II, Montpellier, France.


Story Source:

The above story is based on materials provided by Cell Press. Note: Materials may be edited for content and length.


Cite This Page:

Cell Press. "How Humans Make Up For An 'Inborn' Vitamin C Deficiency." ScienceDaily. ScienceDaily, 21 March 2008. <www.sciencedaily.com/releases/2008/03/080320120726.htm>.
Cell Press. (2008, March 21). How Humans Make Up For An 'Inborn' Vitamin C Deficiency. ScienceDaily. Retrieved August 1, 2014 from www.sciencedaily.com/releases/2008/03/080320120726.htm
Cell Press. "How Humans Make Up For An 'Inborn' Vitamin C Deficiency." ScienceDaily. www.sciencedaily.com/releases/2008/03/080320120726.htm (accessed August 1, 2014).

Share This




More Health & Medicine News

Friday, August 1, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

House Republicans Vote to Sue Obama Over Healthcare Law

House Republicans Vote to Sue Obama Over Healthcare Law

Reuters - US Online Video (July 31, 2014) — The Republican-led House of Representatives votes to sue President Obama, accusing him of overstepping his executive authority in making changes to the Affordable Care Act. Mana Rabiee reports. Video provided by Reuters
Powered by NewsLook.com
Despite Health Questions, E-Cigs Are Beneficial: Study

Despite Health Questions, E-Cigs Are Beneficial: Study

Newsy (July 31, 2014) — Citing 81 previous studies, new research out of London suggests the benefits of smoking e-cigarettes instead of regular ones outweighs the risks. Video provided by Newsy
Powered by NewsLook.com
Dangerous Bacteria Kills One in Florida

Dangerous Bacteria Kills One in Florida

AP (July 31, 2014) — Sarasota County, Florida health officials have issued a warning against eating raw oysters and exposing open wounds to coastal and inland waters after a dangerous bacteria killed one person and made another sick. (July 31) Video provided by AP
Powered by NewsLook.com
Health Insurers' Profits Slide

Health Insurers' Profits Slide

Reuters - Business Video Online (July 30, 2014) — Obamacare-related costs were said to be behind the profit plunge at Wellpoint and Humana, but Wellpoint sees the new exchanges boosting its earnings for the full year. Fred Katayama reports. Video provided by Reuters
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins