Vitamin C Transporter Gene Discovery In Mice Suggests Possible Role for Ascorbic Acid in Preventing - Life-threatening Complications Seen in Premature Infants

Vitamin C Transporter Gene Discovery In Mice Suggests Possible Role for Ascorbic Acid in Preventing
Life-threatening Complications Seen in Premature Infants

Low Vitamin C Could Be Linked to Massive Brain Bleeding and Lung Failure in Premature Newborns

May 2002

BETHESDA, Md. - In what could provide new clues to the causes underlying the serious complications associated with premature birth, scientists at the National Human Genome Research Institute (NHGRI) have discovered a possible link between reduced vitamin C availability during pregnancy, and the devastating respiratory failure and massive cerebral bleeding that can occur immediately following premature birth.

The study, published today in the journal Nature Medicine by doctors and scientists from NHGRI's Genetic Disease Research Branch, the National Institute of Digestive and Kidney Diseases (NIDDK), and the division of Neonatology at the University of Pennsylvania School of Medicine and Children's Hospital, demonstrated that mice deprived of vitamin C during pregnancy and birth died almost immediately after birth from bleeding in the brain and respiratory failure.

In humans, intracerebral hemorrhage, lung complications and respiratory failure are frequent causes of serious morbidity and death in premature infants. Maturation of the lungs occurs during the final few months of human gestation. A child born before this maturation is at high risk for these complications in the immediate postnatal period.

"What I'm suggesting is that we need to take a look at whether vitamin C in human fetuses before birth, transported from the maternal circulation, is a normal physiological factor that helps to mature and protect the lungs and brain of newborn infants," said Dr. Robert Nussbaum, chief of the Genetic Disease Research Branch at NHGRI and co-author of the paper.

"There may be a link between sub-clinical deficiencies in vitamin C in the mother - that is, a deficiency not significant enough to cause scurvy - and the problems that can occur when the fetus prepares to leave the womb. We don't know for sure. What I'm suggesting is that the work in mice points to an area that needs to be investigated."

In the study, scientists created a mouse model - a "knockout mouse" - with a defective Slc23a1 gene, which encodes the transporter protein that gets vitamin C into cells. They discovered that this knockout model could not deliver vitamin C (ascorbic acid) from the blood to many fetal tissues nor transport it across the placental border. Hence, the Slc23a1gene-deficient mice had markedly reduced levels of ascorbic acid in their blood and very low or undetectable levels in their brains and other organs.

What surprised scientists was the discovery that the vitamin C-deprived mice died within minutes after birth due to massive cerebral hemorrhage (bleeding in the brain) and complete respiratory failure when their lungs failed to expand. These severe health problems occurred whether the newborn mice were delivered normally after 21 days gestation, or delivered early at 18.5 to 19.5 days by Caesarian section to avoid birth trauma.

Also, the abnormalities in lung function could not be explained by loss of surfactant protein production, since levels of a critical protein, surfactant B, were normal. And intracerebral hemorrhage due to vascular fragility, or a defect in collagen processing from low vitamin C levels - similar to the effects of scurvy - were ruled out since 4-hydoxyproline levels also were normal. And the mice had developed normally while in the womb, including normal weight gain.

"One could come back to the power of the "knockout" mouse," said Dr. Mark Levine, chief of the Molecular and Clinical Nutrition Section at the National Institute of Diabetes and Digestive and Kidney Diseases and senior staff physician at the National Institutes of Health (NIH) who co-authored the paper with Nussbaum. "It allows us to unveil and uncover new functions. These mice didn't breathe. That was a real surprise. The tests that we ran said that there was enough collagen [the structural "matrix" that holds tissues together]."

"We asked 'why didn't these mice breathe, what was different about their lungs?' " Levine continued, "and I think we may have unmasked a new function for vitamin C. It could have implications. We have more work to do."

The only proven human requirement for vitamin C, or ascorbic acid, is to prevent scurvy, a disease characterized by bleeding gums, anemia, skin hemorrhages, and death, first discovered in 18th century maritime sailors when their diet was found to be deprived of vitamin C-rich fruit.

The normal recommended daily allowance (RDA) for vitamin C for women is 75 mg daily, which is increased by 10 mg during pregnancy, a little more than the amount in the average-sized orange. Lactating (breast-feeding) women should take 95 mg. But overall vitamin C intake can vary greatly in the general public, ranging anywhere from 20 mg to 10,000 mg per day.

Knowing that 20 percent of the population consumes less than the recommended dietary allowance (RDA) for vitamin C intake, Levine said the study has greater implications for what happens when there's a vitamin C deficiency, rather than what occurs with the devastating effect in mice of a total absence of vitamin C. Since a low vitamin C level has no dramatic symptoms - at times only simple fatigue - the effects of that could remain undetected.

"What is the consequence of a low vitamin C level [during pregnancy]?" said Levine. "What is the consequence for prematurity and central nervous system function? The implication of this work is that potential new functions are revealed for vitamin C, especially for the lung and especially at birth.

"But the implication, too, is that if defects exist they can be fixed easily. For now, the message remains that fruits and vegetables containing vitamin C have health benefits - a decreased risk for infection, cancer, stroke, hypertension, maybe even diabetes. And pregnant women should strive for five servings of fresh fruits and vegetables daily in their diet."

Contact:
Geoff Spencer
NHGRI
(301) 402-0911

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