Study shows the effects of nutritional restriction during pregnancy

Unesp scientists reveal alterations of enzymes and nutrient transporters in the intestines of rats whose mothers underwent protein restriction during pregnancy

By Karina Toledo

Agência FAPESP – A study carried out at the Universidade Estadual Paulista (Unesp) has shown that nutritional restriction to the mother during pregnancy causes changes in her offspring’s intestines that persist into adulthood. These changes might lead to the obesity observed in animals born under these conditions.

The results of the study, which was performed in rats, support the so-called fetal programming hypothesis, already established in other studies in the literature, which proposes that a fetus adapts its metabolism to an adverse intrauterine environment. These metabolic adaptations are maintained after birth, making the individual more likely to become overweight when caloric intake improves.

The study, coordinated by Professor Maria de Lourdes Mendes Vicentini Paulino from the Unesp Botucatu Biosciences Institute, focused on the effects of low protein intake during pregnancy on the expression of intestinal enzymes and on the gene expression and immunolocalization of intestinal transporters in the offspring, which are fundamental for the absorption of nutrients in the intestine.

“In order for nutrients to be absorbed, they must first be digested by enzymes until they are small enough to cross the membrane of intestinal cells. Furthermore, for this crossing to happen, the molecules must connect to proteins that act as transporters,” explained Paulino.

The activity and gene expression of the enzymes invertase, lactase and maltase—which are responsible for the digestion of carbohydrates—were studied. “In order to know how much the synthesis of these enzymes was being stimulated, we measured the amount of their messenger RNAs,” said Paulino.

To measure the quantity of enzymes present in intestinal cells, a mucous scraping was incubated with the carbohydrate to be ingested.

“If the intention is to measure the quantity of invertase for example, the mucous is placed in a tube with a sucrose solution. The enzyme present in the mucous breaks down the carbohydrate into glucose and fructose. Finally, the glucose from the reaction is quantified to determine how much of the enzyme is present,” explained the researcher.

The team evaluated the presence and gene expression of two glucose transporters, SGLT1 and GLUT2, and of the peptide transporter PEPT1.

“Through an immunohistochemistry study of intestinal cells, we verified the presence of these transporters. We also measured the proliferation of intestinal cells and the height of the villi to determine whether the surface for nutrient absorption was increased,” said Paulino.

Step by step

The Unesp experiment began with two groups of pregnant female rats. During the gestational period, the rats in the control group were fed a 17% protein diet. The other group received only 6% protein in their feed.

As soon as the baby rats were born and began to nurse, the nursing mothers were given identical diets containing 23% protein. The first analyses were made when the babies were three weeks old, the point at which they stopped nursing.

“Of the three enzymes studied, we perceived a statistically significant increase in lactase (the enzyme responsible for the digestion of milk sugar) in the group that suffered the nutritional restriction. There was also an increase in the gene expression of the enzyme,” affirmed Paulino.

After the nursing period had ended, the babies from the two groups were fed identical normal protein diets. At 16 weeks of age (adulthood for rats), a second analysis was conducted. This experiment showed increased invertase activity and gene expression in the group whose mothers had been protein deprived during pregnancy.

“We didn’t measure the activity of lactase in the adult phase, because the synthesis of this enzyme normally diminishes in mammals after nursing ends,” she explained.

In both analyses—at 3 and 16 weeks of age—the scientists found greater intestinal cell proliferation, greater gene expression and greater levels of the SGLT1, GLUT2 and PEPT1 transporters, which directly affect nutrient absorption. These results were mainly found in the duodenum, the first part of the small intestine.

“The results show us that the differences in the small intestine that are seen among adults can be programmed during pregnancy and that the response can be attributed, at least partially, to the gene expression of enzymes and transporters. These alterations, which allow for greater nutrient absorption, may lead to the accumulation of fat observed in other studies,” evaluated Paulino.

The team now intends to investigate whether the enzymatic activity and gene expression of pancreatic enzymes, which are responsible for the initial digestion of nutrients, are affected by nutritional restriction.

“We will study the phase before the digestive process. Pancreatic enzymes are also connected to the energy supply of the organism,” said Paulino. Paulino highlighted the important contributions of Daniela Felipe Pinheiro, who is carrying out her post-doctoral research at the Unesp Biosciences Institute as a FAPESP fellow.