A regulatory element is characterized by purine-mediated and cell-type-specific gene transcription

Nucleotide enrichment of live feed: a promising protocol for rearing of Atlantic cod Gadus morhua larvae

We investigated the effect of two commercial nucleotide products (NT1 and NT2), administered through live feed, on growth and stress tolerance of Atlantic cod larvae. Expression of genes related to muscle growth (igf-1, igf1r, igf-2, fst, fgf6, myod, and myhc) and nucleotide metabolism (uox, hprt, ndk, and uck) was evaluated during larval development. In addition, the expression of genes related to stress (hif-1α, hif-2α, hif-3α, and mb) was studied after an air exposure stress test. The enrichment of rotifers with nucleotides did not reveal any difference in nucleotide profiles, the exception being the RNA level of the NT1-enriched group that was significantly higher than the unenriched rotifer. Unenriched Artemia showed poor nucleotide profiles compared to enriched Artemia since 5' UMP, 5' GMP, and 5' AMP were observed only in the nucleotide groups. At 38 days post-hatch (dph), NT1 group had significantly higher dry weight (3.1 ± 0.1 mg) than the control (CON; 2.3 ± 0.1 mg). The treatments did not produce any significant differences in the expression of the key myogenic genes. Among the genes associated with nucleotide metabolism, ndk was down-regulated in NT1 at 38 dph. In the air exposure test, survival was significantly higher in the CON (77 ± 6 %) than in NT1 (48 ± 3 %) and NT2 (50 ± 3 %). After air exposure, mb was expressed at lower levels in NT2 group, hif-2α was induced in NT1 group, and hif-3α was upregulated in all groups. Our findings indicate that the improvement in the nucleotide profile of Artemia upon nucleotide enrichment could eventuate in the rapid growth of larvae.

Exogenous nucleosides modulate expression and activity of transcription factors in Caco-2 cells

Dietary nucleotides (NTs) have an important role in cellular and humoral immunity, intestinal growth, differentiation and recovery from tissue damage. Nucleosides (NSs) are the best-absorbed chemical form of NTs in the intestinal epithelium. The aim of this study was to evaluate the effects of NSs on the activity and expression of multiple transcription factors (TFs) in Caco-2 cells, as a possible molecular mechanism by which NSs modulate gene expression in human intestinal cells. The effects of NS-supplemented media on human Caco-2 cell proliferation, viability, protein and RNA concentration were determined, and the activity and expression profiles of multiple TFs were analyzed by using an array-based technology. Exogenous NSs did not affect Caco-2 cell proliferation or viability but increased the protein content in cytoplasm and nucleus and the nuclear protein/RNA ratio. The addition of NSs to the media increased the expression and activity of the TFs CCAAT displacement protein (CUX1), v-ets avian erythroblastosis virus E26 oncogene homolog 1 (ETS1) and SMAD family member 2. In contrast, NS addition decreased the expression and activity of the general upstream stimulatory factor 1 (USF1), glucocorticoid receptor (NR3C1), NFKB and tumor protein p53. In conclusion, our results suggest that exogenous NSs affect the expression and activity of several TFs involved in cell growth, differentiation, apoptosis, immune response and inflammation.

A balanced deoxyribonucleoside mixture increased the rate of DNA incorporation of 5-[125I]Iodo-2'-deoxyuridine in glioblastoma cells

Administration of nucleotide mixtures has been shown to restore and sustain the proliferation of leukocytes and enterocytes. Since it has been suggested that cancer cells use exogenous nucleotides more efficiently than normal cells, we hypothesized that administration of nucleotide mixtures would also stimulate the proliferation of cancer cells, thereby increasing the number of cells targeted by the thymidine analog 5-[(125)I]iodo-2'-deoxyuridine ([(125)I]IUdR). We first evaluated the influence of different deoxyribonucleoside mixtures on the DNA incorporation of [(125)I]IUdR in 3 human glioblastoma cell lines. Results showed that a 4-h coincubation with a mixture of identical concentration (10 microM) of deoxyadenosine, deoxyuridine, deoxyguanosine and deoxycytidine (AUGC) increased by 8.5-, 6.2-, and 2.0-fold the rate of DNA incorporation of [(125)I]IUdR in exponentially growing LN229, U87 and U251 cells, respectively. Replacing deoxyuridine by thymidine (ATGC) reversed the effect of the mixture, whereas removing deoxyuridine allowed a mixture of 10 microM AGC to increase by 2.2-fold the rate of DNA incorporation of [(125)I]IUdR in LN229 cells. Furthermore, the rate of DNA incorporation of [(125)I]IUdR in LN229 and U87 cells was increased up to 19.9- and 9.4-fold, respectively, by extending the coincubation time with 10 microM AUGC to 9 h, and up to 40.9- and 26.8-fold by incubating confluent cells for 4 h with 10 microM AUGC. Flow cytometry analysis showed that exposure of confluent cells to AUGC increased the percentage of cells in S phase of the cell cycle. Thus, co-administration of a balanced deoxyribonucleoside mixture may improve the use of radiolabeled nucleotide analogs, such as [(125)I]IUdR, for the targeting of cancer cells.

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.

Nutritional regulation of nucleoside transporter expression in rat small intestine

BACKGROUND & AIMS

Concentrative nucleoside transporters CNT1 (pyrimidine preferring) and CNT2 (purine preferring) may be involved in the uptake of nucleoside-derived drugs used in antiviral and chemical therapies. The possibility that nucleoside carrier isoform expression is modulated by nutrient availability has been studied.

METHODS

CNT1 and CNT2 tissue distribution was determined by Western blot analysis. The effect of 48-hour starvation on CNT expression was then studied. Nucleoside transporter expression and uptake activity were measured in jejunal brush border plasma membrane vesicles from fed and starved rats. The expression of nucleoside transporters was later determined in a second model of nutrient deficiency: rats fed a purified diet with or without nucleotides for 10 days.

RESULTS

CNT1 and CNT2 nucleoside transporters were expressed in a wider variety of tissues than expected from messenger RNA distribution analysis. CNT1 was sensitive to nutrient availability in small intestine and, accordingly, jejunal brush border membrane vesicles from 48-hour-fasted rats showed increased expression of CNT1 and enhanced Na(+)-dependent thymidine and gemcitabine uptake. This effect was mimicked by feeding semipurified diets lacking nucleotides.

CONCLUSIONS

Substrate availability modulates nucleoside transporter expression (CNT1) in rat jejunum in vivo.

Nucleotides and intestine

BACKGROUND

Dietary nucleotides play an important role in the growth and development of the intestine. Parenteral supplementation of nucleic acids may be necessary to maintain the mucosal proliferation and barrier functions during parenteral nutrition (PN).

METHODS

Male Wistar rats were divided into 3 groups: FED (food ad libitum with saline infusion); PN (a standard PN solution); and OG (OG-6, a mixture of nucleotide and nucleosides, in addition to the PN solution). The mucosal wet weight, protein, and DNA contents, villous height and crypt depth, electronmicroscopic examination of the intercellular junctions, proliferating activity of the mucosal cells, mucosal permeability, bacterial translocation, and mucosal cathepsin activities were examined.

RESULTS

The wet weight, protein, and DNA contents of the jejunal mucosa were significantly increased in the OG group, compared with those in the PN group. The morphometric examination revealed a significant increase in the villous height but not in the crypt depth in the OG group. The widths of both the tight and intermediate junctions were narrower in the OG group than those in the PN group. The activity of diamine oxidase was increased in the OG group, compared with that in the PN group. The ratio of proliferating cell nuclear antigen positive cells and the index of bromodeoxy uridine labeling index in the OG group were as high as in the FED group, and significantly higher than those in the PN group. The portal concentration of fluorescein isothiocyanate-dextran 70,000 after intragastric loading was significantly higher in the PN group than that in OG group. Likewise, the rate of urinary lactulose excretion after intragastric loading was higher in the PN group. The positive rate of bacteria cultured in mesenteric lymph nodes was higher in the PN group than in the OG group although the difference was not significant. The activities of mucosal cathepsins (B, H, and L), markers for phagocytic degradation of extrinsic substances and organisms, were higher in the PN group than those in the OG and FED groups.

CONCLUSIONS

Parenteral supplementation of nucleic acids supports the mucosal cell proliferation and functions.

Growth, development and differentiation: a functional food science approach

Few other aspects of food supply and metabolism are of greater biological importance than the feeding of mothers during pregnancy and lactation, and of their infants and young children. Nutritional factors during early development not only have short-term effects on growth, body composition and body functions but also exert long-term effects on health, disease and mortality risks in adulthood, as well as development of neural functions and behaviour, a phenomenon called 'metabolic programming'. The interaction of nutrients and gene expression may form the basis of many of these programming effects and needs to be investigated in more detail. The relation between availability of food ingredients and cell and tissue differentiation and its possible uses for promoting health and development requires further exploration. The course of pregnancy, childbirth and lactation as well as human milk composition and the short- and long-term outcome of the child are influenced by the intake of foods and particularly micronutrients, e.g. polyunsaturated fatty acids, Fe, Zn and I. Folic acid supplementation from before conception through the first weeks of pregnancy can markedly reduce the occurrence of severe embryonic malformations; other potential benefits of modulating nutrient supply on maternal and child health should be further evaluated. The evaluation of dietary effects on child growth requires epidemiological and field studies as well as evaluation of specific cell and tissue growth. Novel substrates, growth factors and conditionally essential nutrients (e.g. growth factors, amino acids, polyunsaturated fatty acids) may be potentially useful as ingredients in functional foods and need to be assessed carefully. Intestinal growth, maturation, and adaptation as well as long-term function may be influenced by food ingredients such as oligosaccharides, gangliosides, high-molecular-mass glycoproteins, bile salt-activated lipase, pre- and probiotics. There are indications for some beneficial effects of functional foods on the developing immune response, for example induced by antioxidant vitamins, trace elements, fatty acids, arginine, nucleotides, and altered antigen contents in infant foods. Peak bone mass at the end of adolescence can be increased by dietary means, which is expected to be of long-term importance for the prevention of osteoporosis at older ages. Future studies should be directed to the combined effects of Ca and other constituents of growing bone, such as P, Mg and Zn, as well as vitamins D and K, and the trace elements F and B. Pregnancy and the first postnatal months are critical time periods for the growth and development of the human nervous system, processes for which adequate substrate supplies are essential. Early diet seems to have long-term effects on sensory and cognitive abilities as well as behaviour. The potential beneficial effects of a balanced supply of nutrients such as I, Fe, Zn and polyunsaturated fatty acids should be further evaluated. Possible long-term effects of early exposure to tastes and flavours on later food choice preferences may have a major impact on public health and need to be further elucidated. The use of biotechnology and recombinant techniques may offer the opportunity to include various bioactive substances in special dietary products, such as human milk proteins, peptides, growth factors, which may have beneficial physiological effects, particularly in infancy and early childhood.

Dietary nucleotides correct plasma and liver microsomal fatty acid alterations in rats with liver cirrhosis induced by oral intake of thioacetamide

BACKGROUND/AIMS

Dietary nucleotides modulate a number of metabolic processes, including long-chain polyunsaturated fatty acid metabolism. In this study, we evaluated the effect of dietary nucleotides on plasma and liver microsomal fatty acid profiles in a rat model of liver cirrhosis induced by oral intake of thioacetamide.

METHODS

Fifty-four female Wistar rats were assigned to one of the following groups: rats in the thioacetamide group (n=45) were given 300 mg thioacetamide/l in their drinking water for 4 months, and rats in the control group (n=9) received water during the same period. After 4 months of treatment, 9 rats in each group were killed. The remaining rats in the thioacetamide group were divided into two new groups, and the animals in each were allowed to recover for 1 or 2 weeks on either a nucleotide-free diet or the same diet supplemented with 50 mg of each of the following: AMP, GMP, CMP, IMP and UMP per 100 g diet.

RESULTS

Saturated (mainly stearic acid), monounsaturated, and n-6 long-chain polyunsaturated fatty acids (mainly arachidonic acid), and also the unsaturation index decreased in plasma of rats with experimental cirrhosis. Administration of the diet supplemented with nucleotides to thioacetamide-treated rats corrected plasma levels of saturated, n-6 long-chain polyunsaturated fatty acids and the unsaturation index. In liver microsomes, the cirrhotic rats showed lower levels of protein and higher levels of palmitic, oleic, linoleic and arachidonic acids. Protein concentrations and levels of all the above-mentioned fatty acids were corrected with the nucleotide-enriched diet.

CONCLUSIONS

Dietary nucleotides contribute to correcting plasma and liver microsomal fatty acid alterations in rats with liver cirrhosis induced by chronic oral administration of thioacetamide.

Glutamine and nucleotide metabolism within enterocytes

Glutamine has an important role as a source of energy for enterocytes. However, it may also have a key role as a source of nitrogen for the synthesis of nucleotides. The relative contribution of de novo synthesis and salvage pathways seems to be affected by the position of enterocytes within the crypt-villus axis as well as the dietary intake of nucleic acids and glutamine. Nucleotides are especially important to enterocytes during intestinal development, maturation, and repair. Hence an understanding of nucleotide metabolism within enterocytes has important implications regarding both the composition and route of administration of nutrient solutions. Many important questions remain unanswered, in particular: Does glutamine stimulate intestinal de novo pyrimidine synthesis via the action of carbamoyl phosphate synthetase I? Can de novo purine synthesis maintain intestinal purine pools in the absence of dietary nucleic acids? And, what are the specific effects of parenterally administered nucleotides on the metabolism and well-being of enterocytes? A greater understanding of these issues will lead to a more rational approach toward the nutritional modulation of gut dysfunction.

Role of supplementation of a nucleic acid solution on the intestinal mucosa under total parenteral nutrition

Since dietary nucleotides play an important role in the growth and development of the intestine, supplementation of a nucleic acid solution (OG-VI) may support the optimal growth and integrity of the intestine under total parenteral nutrition (TPN). Supplementation of OG-VI to a TPN solution improved mucosal morphologic and functional changes, increased mucosal proliferation, and decreased mucosal permeability of the intestine. After 80% small bowel resection, OG-VI supplementation to a TPN solution attenuated the initial mucosal atrophy and improved intestinal cell turnover. Nucleic acid supplementation may be clinically beneficial in certain situations.

The role of glutamine, short-chain fatty acids, and nucleotides in intestinal adaptation to gastrointestinal disease

Important first steps have been taken towards establishing how some nutrients interact with genes and affect intestinal adaptation. These mechanisms may be typical of how other nutrients influence cell function and turnover and help to maintain intestinal integrity. The dietary effects of nucleotides on intestinal cell mucosa act at the gene transcription level. The dietary effects of nucleotides on immune suppression also may act through similar mechanisms. The effects of the other trophic agents may interact at this level or at other levels. Scientific interest in how the various tropic factors work to maintain and repair the gastrointestinal tract is manifested by a growing body of research that demonstrates potential mechanisms for nutrient-gene interaction and how much interactions affect intestinal development and turnover. It seems clear that intestinal gene transcription and the activity of transcription factors are at least sometimes directly related to nutrition. The techniques of molecular biology now permit the exploration and explanation of how dietary factors, such as glutamine, SCFAs, and nucleotides, affect normal and pathologic intestinal mucosal development, function, adaptation, and repair.

E2F-1 and a cyclin-like DNA repair enzyme, uracil-DNA glycosylase, provide evidence for an autoregulatory mechanism for transcription

The cell cycle-dependent transcription factor, E2F-1, regulates the cyclin-like species of the DNA repair enzyme uracil-DNA glycosylase (UDG) gene in human osteosarcoma (Saos-2) cells. We demonstrate, through the deletion of the human UDG promoter sequences, that expression of E2F-1 activates the UDG promoter through several E2F sites. The major putative downstream site for E2F, located in the first exon, serves as a target for E2F-1/DP1 complex binding in vitro. We also provide evidence for the functional relationship between the cyclin-like UDG gene product and E2F. High levels of UDG expression in a transient transfection assay result in the down-regulation of transcriptional activity through elements specific for E2F-mediated transcription. Overexpression of UDG in Saos 2 cells was observed to delay growth late in G1 phase and transiently arrest these cells from progressing into the S phase. This hypothetical model integrates one mechanism of DNA repair with the cell cycle control of gene transcription, likely through E2F. This implicates E2F as a multifunctional target for proteins and enzymes, possibly, responsive to DNA damage through the negative effect of UDG on E2F-mediated transcriptional activity.

Molecular analysis of APRT deficiency in mouse P19 teratocarcinoma stem cell line

We have used four gene probes specific for mouse chromosome 8, including adenine phosphoribosyltransferase (aprt), to demonstrate that the P19 teratocarcinoma stem cell line contains two distinct chromosome 8 homologs. One represents the common laboratory mouse C3H (Mus musculus domesticus) homolog while the second homolog was presumably contributed by a feral Mus musculus musculus animal. Six cell lines with APRT heterozygous deficiencies were isolated from P19 subclones. A molecular analysis of these heterozygotes demonstrated that three arose by deletion of the Mus musculus musculus aprt allele and three arose by aprt gene inactivation. APRT homozygous deficient cell lines were isolated from both classes of heterozygote; most contained little or no detectable APRT activity. When the heterozygous deficiency was due to deletion of the Mus musculus musculus aprt allele, the most frequent event yielding homozygous deficient cell lines was associated with loss of heterozygosity for all tested markers on the Mus musculus domesticus homolog indicating chromosome loss. In contrast, when the initial event resulting in APRT heterozygous deficiency was gene inactivation, homozygotes arose predominantly from gene deletion or a second inactivation event. These results suggest a potential relationship between the first- and second-step events resulting in APRT deficiencies.