Antonio Sánchez-Pozo

Nucleotides as semiessential nutritional components

Dietary nucleotides are required nutrients for some tissues under certain circumstances. A lack of dietary nucleotides negatively influences protein synthesis in both the liver and the small intestine of rats. Ribosome degradation has been observed as being among the mechanisms responsible for this effect. Dietary nucleotides can also modulate gene expression by interaction with specific transcription factors, in both the liver and the small intestine.

Changes in the Protein Fractions of Human Milk during Lactation

The changes in the absolute and relative contents of alpha- and kappa-caseins, lactoferrin, alpha-lactalbumin, serum albumin and lysozyme in human milk have been studied through the period of lactation. Protein fractions of 209 samples were analyzed by a discontinuous polyacrylamide gel electrophoresis method. beta- and kappa-caseins decreased from colostrum to mature milk although their relative percentages remained constant. They accounted for 12-15 and 9-13% of the total protein in human milk, respectively. Lactoferrin decreased in absolute and relative amounts with advancing lactation. This protein represented 32-19% of the human milk proteins. alpha-Lactalbumin slightly decreased from colostrum to transitional milk but there was an increase in mature milk by 16-30 days. The percentages of this protein in colostrum and mature milk were approximately 23 and 30%, respectively. Serum albumin also decreased with advancing lactation, but the differences between transitional and mature milk were not statistically significant. Lysozyme increased from colostrum to mature milk both in relative and absolute amounts. Colostrum contained about 262 micrograms/ml, and mature milk 1,246 micrograms/ml, representing 1.5 and 12.1% of total milk proteins.

Maturation status of small intestine epithelium in rats deprived of dietary nucleotides.

We describe the changes of several brush-border enzymatic activities in different subpopulations of epithelial cells, separated sequentially from the villus tip-to-crypt axis of the small intestine, induced by deprivation of dietary nucleotides for different periods of time in adult rats. Deprivation of dietary nucleotides lead to a decrease in the content and specific activity of alkaline phosphatase, leucine-aminopeptidase, maltase, sucrase and lactase in the villus tip, but had little effect on the crypt zone. The effect of the nucleotide deprivation on the enzymatic activity progressively increased towards the tip of the villus. Since these enzymes are maturation markers of the intestinal cells, these results support the idea that dietary nucleotides affect the maturation status of small-intestine epithelium.

Characterization of human cd200 glycoprotein receptor gene located on chromosome 3q12-13

An immunomodulatory membrane protein, CD200R displays an expression pattern restricted to myeloid cells in mice. It is the receptor for a ligand, CD200, expressed by a broad range of cell types. In this study, we describe the cloning and characterization of the human homologue of the CD200R gene. This gene maps closely to the CD200 gene on human chromosome 3q12-13. The human CD200R gene spans a region of 52 kb, consists of nine exons, and encodes a 348-amino-acid cell-surface protein consisting of two IgFF domains in a typical V/C2 arrangement. The 59-amino-acid cytoplasmic domain has two tyrosine residues, one of which is contained within a NPXY motif. In common with other IgSF genes, the CD200R gene can generate different protein isoforms through alternative splicing. An alternative spliceout form, which has not yet been described in mice, encodes a 188-amino-acid truncated soluble polypeptide containing only the V immunoglobulin domain. In contrast to murine CD200R protein, the human membrane-bound and soluble CD200R proteins have an insertion of 23 amino acids at position 23, encoded by exon 2, which generates a putative dihydroxyacid dehydratase domain. The splicing of exon 2 generates two new isoforms, encoding the membrane and soluble proteins but lacking the dyhydroxyacid dehydratase domain. Northern-blot analysis shows that both membrane-bound and soluble isoforms are expressed in the thymus, liver, spleen and placenta. By RT-PCR, we have analyzed the expression of the four transcript variants in human placenta, spleen, liver, brain and kidney.

Morphological changes in hepatocytes of rats deprived of dietary nucleotides

The aim of the present study was to investigate the influence of dietary nucleotides on liver morphology. Adult rats were fed for 21 d on a nucleotide-containing diet or the same diet free of nucleotides. Liver sections were examined by light and transmission electron microscopy, as well as for nucleic acid and protein contents. Morphometric analysis was performed for different variables. Deprivation of dietary nucleotides resulted in a reduction in hepatocyte nuclear and nucleolar areas as well as in nuclear chromatin condensation. In addition, the rough endoplasmic reticulum was reduced, as were ribosome association and abundance, whereas fat accumulated. These findings portray dietary nucleotides as required nutrients for the liver under normal physiological conditions and suggest that an inadequate supply of nucleotides for a certain period of time has transient negative effects on liver ultrastructure and function.

Hepatotoxic agent thioacetamide induces biochemical and histological alterations in rat small intestine

We have assessed the effect of the oral ingestion of thioacetamide on small intestine structure and function. Thioacetamide-treated rats showed diminished mucosa weight; protein, DNA, and RNA content; and leucine aminopeptidase activity as compared to controls in both jejunum and ileum. In the jejunum, there was a reduction in the activities of alkaline phosphatase, ATPase, glucose-6-phosphatase, and myeloperoxidase, whereas in the ileum, maltase, lactase, and γ-glutamyltranspeptidase were reduced. In both jejunum and ileum we found enlarged intercellular spaces, dark epithelial enterocytes, and lymphocyte infiltration. Enterocytes showed lobulated nuclei, deranged mitochondria with loss of their cristae, dilated rough endoplasmic reticulum containing dense material, and vesiculation of the smooth endoplasmic reticulum and the Golgi apparatus. Smooth muscle cells of the intestine exhibited ultrastructural alterations. These findings indicate that chronic oral intake of thioacetamide mimics not only hepatic alterations but also small intestine alterations normally associated with human cirrhosis.

Lipoprotein changes in small-for-gestational-age infants fed nucleotide-supplemented milk formula

Morillas J, Moltó L, Robles R, Gil A, Sánchez‐Pozo A. Lipoprotein changes in small‐for‐gestational‐age infants fed nucleotide‐supplemented milk formula. Acta Prediatr 1994;83:481–5. Stockholm. ISSN 0803–5253

Lipoproteins in preterm and small‐for‐gestational‐age infants during the first week of life

Plasma lipoprotein levels and composition have been determined in preterm and small‐for‐gestational‐age (SGA) infants, and compared to full‐term infants, during the first week of life. Significantly lower levels of HDL and higher levels of VLDL were found in both preterm and SGA infants in comparison to full‐term healthy infants. These results suggest a low capacity to metabolize VLDL. Preterm infants showed a behaviour similar to full‐term infants with regard to the changes in lipoprotein composition. Small‐for‐gestational‐age infants showed a higher lipoprotein lipid content than preterm infants. A low ratio of cholesteryl ester to free cholesterol (CE/FC) was found in both preterm and SGA infants suggesting a reduced lecithin: cholesterol acyl transferase (LCAT) activity. In preterm infants we observed no changes in the CE/FC ratio during the first week of life, whereas in SGA infants this ratio increased after birth.

Age-Related Response of the Small Intestine to Severe Starvation and Refeeding in Rats

The impact of severe starvation and refeeding on the intestinal mucosa of rats of different ages has been studied in a diet-controlled model. Structural and functional alterations of the small intestinal mucosa were assessed by standard parameters including mucosal protein, DNA content as well as maltase, sucrase and leucine aminopeptidase enzymatic activities. Decreases in mucosal mass, DNA, protein and leucine aminopeptidase activity in both the jejunum and ileum caused by starvation, diminished with age. The depression of disaccharidase activities increased with age in the jejunum but not in the ileum. Except for jejunal protein and leucine aminopeptidase activity, the recovery from starvation, after refeeding, was complete for the other parameters studied, regardless of age.

Serum and Urine Amino Acid Patterns during the First Month of Life in Small-for-Date Infants

Prenatal nutrition is impaired in small-for-gestational-age infants. Serum amino acids may show some biochemical features related to the nutritional state of these children. We have carried out a study on serum and urine amino acids in 12 small-for-date infants (SFD) and 14 healthy newborns from birth to 1 month of life. SFD infants showed a high serum level of alanine and decreased concentrations of branched chain amino acids, aspartate, cystine and tryptophan at birth. The results are compatible with a protein malnutrition state. Levels of serum amino acids in SFD infants showed no differences in relation to normal infants after 1 month of rehabilitation with a diet consisting of an adapted milk formula.