Desialylation of rat intraepithelial lymphocytes: effects on proliferation and dipeptidyl peptidase IV activity.
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Alkaline Phosphatase↗
Biomedical subjects
D Tomé
Publications and source records attributed to D Tomé.
Metabolism of enterostatin in rat intestine, brain membranes, and serum: differential involvement of proline-specific peptidases.
The degradation of enterostatin (VPDPR), a potent inhibitor of food intake, by intestinal brush-border membranes, brain membranes, and rat serum has been investigated in the presence of specific inhibitors. Hydrolysis by intestinal membranes was found to be 10 and 100 times faster than in serum and brain membranes, respectively. Enterostatin hydrolysis by intestinal and brain membranes involves the removal of C-terminal arginine by carboxypeptidase P, leading to the production of des-Arg-enterostatin, and the splitting of the Pro2-Asp3 bond by dipeptidyl aminopeptidase IV (DPP IV). A small amount of the potent anorectic peptide Pro2-Asp3-Pro4 was released during hydrolysis of des-Arg-enterostatin by brain membranes and rat serum. In rat serum, enterostatin degradation was mainly due to DPP IV.
Amino Acid Sequence↗
Transport of beta-lactoglobulin and alpha-lactalbumin in enterocyte-like Caco-2 cells.
The transport of [14C]-radiolabelled beta-lactoglobulin and alpha-lactalbumin through Caco-2 cell monolayers grown on permeable filters was studied in order to evaluate the different protein pathways through the intestinal epithelium. beta-Lactoglobulin or alpha-lactalbumin (0.25-3 mg/ml) was introduced on the apical side of the monolayer and both the transport and the release of labelled material from the cells were measured following different incubation times. The labelled material was analysed by either trichloroacetic acid precipitation or by high pressure liquid chromatography. Despite some differences between the 2 proteins, the overall mechanism followed approximately the same pattern. Part of the intact internalized protein was either recycled (10-15%) or transported via transcytosis (about 5%). Another pathway corresponded to the intracellular degradation of the protein. The calculation of the different routes followed by the proteins indicated that the main part of the degraded fraction (about 70%) was recycled whereas approximately 30% was transported to the other side. Moreover, 5-10% of the endocytosed material was retained intracellularly.
Biological Transport↗
15N-labeled immunoglobulins from bovine colostrum are partially resistant to digestion in human intestine.
To evaluate true ileal digestibility of bovine immunoglobulins, seven healthy human adults ingested a 15N-labeled preparation of an immunoglobulin concentrate. After fasting overnight, subjects drank 400 mL of immunoglobulin concentrate (77 mmol), and ileal effluents were collected for 8 h at 20-min intervals using a naso-intestinal intubation technique. In addition to osmolality and pH, the concentrations of exogenous and endogenous nitrogen and ions (Na+, K+, Cl-, Ca2+, Mg2+) in the effluents were measured. Bovine immunoglobulin concentrations (IgG, IgM, IgA) were estimated by a radial immunodiffusion technique. The mean flow rate of the liquid phase was 22.3 +/- 6.1 mL/20 min and did not vary significantly during the collection period. No change was observed for osmolality, pH or Na+, K+ and Cl- concentrations. Two hours after meal ingestion, Ca2+ and Mg2+ concentrations increased significantly (P < 0.05). The recoveries of nitrogen of ingested IgG and IgM still immunologically active were 19 +/- 3% and 19 +/- 4%, respectively. No IgA was detected in the ileum. Mean digestibility of the exogenous nitrogen fraction was 79 +/- 3%. In comparison to literature data, which show that other milk proteins have ileal digestibilities of > 90%, our results demonstrate a lower ileal digestibility of bovine immunoglobulins in humans.
Adult↗
Digestion patterns of endogenous and different exogenous proteins affect the composition of intestinal effluents in humans.
The purpose of this work was to determine if endogenous luminal proteins are stimulated differently by various dietary proteins and if their digestibility differs from that of dietary proteins. Intestinal effluents were collected from the jejunum of four volunteers who had previously fasted or ingested either casein or soybean proteins. After separating the jejunal digested fraction (nonprotein nitrogen) by dialysis, the protein nitrogen fractions of the effluents and of the protein sources were further hydrolyzed in vitro in a digestion cell with simultaneous dialysis of the digestion by-products. The results indicated a higher (P < 0.05) gastrojejunal absorption of casein (64.5 +/- 2.5%) compared with soybean protein (49.9 +/- 4.1%) in humans. Compared with fasting conditions, protein ingestion increased both the total nitrogen and protein nitrogen of the endogenous nitrogen fraction slightly (P < 0.05) but had no effect on the nonprotein nitrogen fraction. The amino acid profiles of the nonprotein nitrogen in the effluents differed from those of both the protein sources and their mixtures with endogenous secretions. This was attributed to the specific release of amino acids by pancreatic enzymes as measured in vitro. The hydrolysis patterns of amino acids were determined by the structure of food proteins and their interaction with endogenous proteins. Soybean and endogenous nitrogen had equivalent digestibilities when measured in vitro.
Adult↗
Transport and steady-state accumulation of putrescine in brush-border membrane vesicles of rabbit small intestine.
Absorption of polyamines from the lumen is essential for cell proliferation in small intestine but also in other rapidly growing body tissues and tumors. Intestinal uptake of polyamines is thought to involve one or more transport systems, but the characteristics of these systems have not yet been clearly elucidated. Because high levels of putrescine have been identified in intestinal lumen, we explored kinetic, physiochemical, and structural features of uptake of this diamine across rabbit intestinal brush-border membrane vesicles (IBBMV) prepared by CaCl2 or MgCl2 precipitation procedure. Initial rates of putrescine influx were measured during 5-min incubations at 25 or 37 degrees C (optimal temperature) for concentrations of 0.45-145 microM. At both temperatures, kinetics of putrescine transport fitted a model with a single Michaelis-Menten uptake component plus a nonsaturable uptake component. At 37 degrees C, the kinetic parameters for the saturable component of putrescine uptake, Km,app and Vmax,app, were 16.8 +/- 4.7 microM and 19.9 +/- 2.8 pmol.mg protein-1.min-1, respectively. The value of the constant for the nonsaturable component of putrescine uptake (P = 0.45 +/- 0.06 x 10(-8) l.mg protein-1.s-1) suggested this component represented essentially nonspecific binding of putrescine to IBBMV. Cadaverine, spermidine, and spermine were competitive inhibitors of putrescine transport, with inhibition constants equal to 47, 117, and 219 microM, respectively. When effects of a variety of alkyldiamines and structural analogues of polyamines (1 mM) on influx of 5.6 microM putrescine were compared, cadaverine, methylglyoxal bis(guanylhydrazone) (MGBG), and cyclic derivatives of MGBG were found to exhibit the highest inhibitory potencies.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Sparfloxacin secretion across Caco-2 cells involves a multidrug resistance-like mechanism.
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Anti-Infective Agents↗
Nitrogen movements in the upper jejunum lumen in humans fed low amounts of casein or beta-lactoglobulin.
OBJECTIVES AND METHODS: To compare the progression of milk proteins in the upper part of the digestive tract, gastro-jejunal nitrogen movements were studied in 6 healthy human volunteers after beta-lactoglobulin and casein ingestion. 400 mL of water (control), purified beta-lactoglobulin (20 g/L) or casein (20 g/L), each adjusted to 25 microCi with 14C-polyethylene glycol, were given per os. Samples were collected in the stomach and 20 cm below the Treitz ligament every 20 min for 2 hours and measured for volume, osmolarity, ions and nitrogen content. RESULTS: The jejunal flow rate peaked in the 0-20 min period following water and beta-lactoglobulin ingestion, and in the 20-40 min period after casein ingestion. The gastric half-emptying time (T1/2 min) of the liquid phase was significantly different (P < 0.05) for water (12.1 +/- 0.8), beta-lactoglobulin (14.5 +/- 3.3) and casein (26.5 +/- 9.3). Before ingestion of the test meals, the basal rate of nitrogen was 9.14 +/- 4.09 mmol/h in the jejunum. The total nitrogen content in the jejunum peaked significantly in the 0-20 min period after beta-lactoglobulin ingestion and the 20-40 min period after casein ingestion. The apparent gastro-jejunal protein absorption values were 63% for casein and 66% for beta-lactoglobulin in the 120 min period. CONCLUSIONS: These results show that beta-lactoglobulin and casein behave differently in the upper part of the digestive tract due to different gastric emptying rates.
Adult↗
The in vitro intestinal absorption of enterostatin is limited by brush-border membrane peptidases.
The intestinal metabolism and absorption of enterostatin was studied using brush-border membrane vesicles and an in vitro model of intestinal segments from rabbit ileum mounted in Sweetana-Grass diffusion chamber. Hydrolysis of enterostatin was observed with both epithelial sheets and brush-border membranes. The main metabolite was found to be des-arginine-enterostatin. Dipeptidylpeptidase IV was found to play a minor role in enterostatin degradation, whereas carboxypeptidase P activity accounted for the initial step of peptide hydrolysis. More than 50% of the amount of enterostatin added to the mucosal compartment of the Sweetana-Grass diffusion chamber was degraded after 30 min. Enterostatin was mainly absorbed as degradation products but a small transepithelial passage of des-arginine-enterostatin and immunoreactive enterostatin was also detected. Although immunoreactive enterostatin exhibits a low apparent permeability coefficient in rabbit ileum, the luminal production of this peptide may be of physiological importance in the control of appetite.
Amino Acid Sequence↗
Alterations in intestinal uptake of putrescine and tissue polyamine concentrations in tumor-bearing rats.
Intestinal absorption of putrescine and tissue metabolism of polyamines were investigated in rats grafted with the rapidly growing Mat-Lylu prostatic tumor. These animals exhibited a dramatic 21% decrease in weight and protein, but not DNA, content of their intestinal mucosa, relative to healthy rats reared under similarly controlled nutritional conditions. No significant variation in the specific activities of intestinal brush-border membrane enzymes was observed, however, suggesting a comparable differentiation state of intestinal cells exists in both groups. Putrescine uptake by brush-border membrane vesicles prepared from cancerous or healthy rat intestine was a time dependent process at 25 degrees C. Equilibrium uptake was much greater than could be explained by equilibration of the vesicle space with putrescine, indicating that the diamine was bound to membrane sites. Kinetics of putrescine uptake at 2 min revealed that the process involves two components, a saturable Michaelis-Menten carrier and passive diffusion. With respect to the kinetic parameters of putrescine transport, no significant changes were observed between the tumor-bearing and the control rats. After correction for nonspecific binding to the membranes, putrescine accumulation at equilibrium (75 min) was concentration-dependent and fit a single-site saturable model. Maximum accumulation of the diamine at equilibrium (Bmax) was increased by more than 46% in the cancerous rats relative to the controls, but the dissociation constant (Kd) was unchanged. Efflux of putrescine from the vesicles was slightly slower in the tumor-bearing group, but the differences were generally not significant. No change was observed with respect to the specific activity of ornithine decarboxylase and the concentration of polyamines in the intestinal mucosa. In Mat-Lylu grafted rats fed a standard diet supplemented with [14C]putrescine, about 19% of body radioactivity was recovered in the tumor within 24 h. This was concomitant with a decrease in the percentage of radioactivity retained in the intestinal, renal and hepatic tissues, relative to that retained in the same tissues of healthy rats. Our findings indicate that the presence of the tumor evolves an adaptive response in the small intestine of the rat, involving an increased capacity of the brush-border membrane to accumulate putrescine.
Adenocarcinoma↗
Rate of [15N]leucine incorporation and determination of nitrogenous fractions from gastro-jejunal secretion in fasting humans.
The aim of this study was to quantify the nitrogen fraction flow rates in gastro-jejunal secretions in fasting humans and to determine the [15N]leucine incorporation into the secreted proteins. A double lumen intestinal perfusion method was used in 5 healthy volunteers. Plasma and gastro-jejunal juices were collected during a 15-h intravenous [15N]leucine infusion. Total, soluble and insoluble nitrogen, amino acids and [15N]leucine enrichment were measured. The total nitrogen flow rate was 7.2 +/- 1.9 mmol.h-1 and 58% was ethanol soluble. The amino-acid composition remained constant and glycine was the most abundant. The plasma [15N]leucine enrichment at the isotopic plateau was 4.8 +/- 0.9 mol% excess. The [15N]leucine enrichment in the intestinal chyme increased asymptotically to reach a plateau after 5 h. The [15N]leucine enrichment at the plateau and the fractional synthesis rate of secreted proteins were 1.6 +/- 0.5 mol% excess and 21.5 +/- 3.3%.h-1, respectively. These results show that the composition of the basal gastro-jejunal secretion is very stable. A part of this secretion is composed of proteins with rapid synthesis rates.
Adult↗
Intestinal nitrogen and electrolyte movements following fermented milk ingestion in man.
The present study focuses on the digestion and absorption of milk and fermented milk (FM) reflected by gastro-ileal N and electrolyte movements in six healthy volunteers. The N and electrolyte content of the intestinal effluents were analysed both at the beginning of the jejunum and in the distal ileum. The gastric half-emptying time of the liquid phase was significantly (P < 0.05) shorter for milk (35 (SE 2) min) than for FM (60 (SE 2) min). The N balance showed that 58 and 50% of ingested proteins, milk and FM respectively were absorbed between the stomach and the proximal jejunum and that 91 and 90% respectively were absorbed between the stomach and the terminal ileum in 240 min. Evaluation of mineral absorption indicated that 44 and 67% of Ca was absorbed in the duodenum after milk and FM ingestion respectively, and 41 and 11% of Ca disappeared between the jejunum and the ileum respectively. With regards to N and Ca intestinal availability, the present study confirms that FM products represent an interesting source of N as well as minerals for man. This confers on FM a beneficial effect compared with milk especially for lactase (EC 3.2.1.108)-deficient subjects and children with persistent diarrhoea.
Adult↗
Gastric emptying regulates the kinetics of nitrogen absorption from 15N-labeled milk and 15N-labeled yogurt in miniature pigs.
Thirty-six miniature pigs divided into two groups of 18 animals were fed 15N-labeled milk or yogurt. Polyethylene glycol 4000 was added to the diets as a non-absorbable marker of the liquid phase. Animals were slaughtered 1, 2, 4, 8 and 12 h after meal ingestion, and the gastrointestinal tract was removed and divided into 10 parts. Polyethylene glycol, total nitrogen and 15N enrichment were measured in the digesta. Both the intestinal delivery of the liquid phase and the nitrogenous fraction of the chyme were delayed more in pigs fed yogurt than in pigs fed milk. No stimulatory effect of diet ingestion on endogenous nitrogen secretion was found. Both milk proteins and yogurt proteins were highly digestible: 93% of the exogenous nitrogen disappeared 12 h after feeding. The kinetics of exogenous nitrogen delivery into the intestine was correlated (r = 0.999 for milk and r = 0.974 for yogurt) with that of exogenous nitrogen absorption. These results suggest that milk proteins are rapidly absorbed after they reach the intestine. Gastric emptying is a major factor controlling the kinetics of milk nitrogen absorption.
Animals↗
True exogenous and endogenous nitrogen fractions in the human jejunum after ingestion of small amounts of 15N-labeled casein.
The purpose of this work was to determine exogenous and endogenous contributions to the overall nitrogen flux in the upper jejunum in humans. After the ingestion of water or 8 g of [15N]casein, the behavior of gastro-jejunal nitrogen and electrolyte (Na+, K+, Cl-) movements were studied in seven volunteers using the "slow marker" perfusion technique. The jejunal flow-rate of the chyme peaked during 0-20 min and 20-40 min periods following water and casein ingestion, respectively. Osmolarity, Cl- and Na+ concentrations decreased significantly (P < 0.05) during the first 20 min following meal ingestion and returned to the basal levels in the 20-60 min period. The gastric half-emptying times (min) of the liquid phase differed significantly (P < 0.05) for water (7.9 +/- 0.4) and casein (21.4 +/- 9.1). The basal flow rate of endogenous nitrogen was 9 +/- 3.3 mmol/h in the jejunum. After casein ingestion, the total nitrogen content reached maximum values in the 20-40 min period and then progressively returned to the initial level. The gastro-jejunal casein absorption was 58% and the remaining amount of casein in the jejunum was degraded more than 80% to alcohol-soluble compounds. After the ingestion of a low amount of casein no significant increase in the endogenous nitrogen fraction was observed. The 15N-dilution technique is an appropriate method in humans for the direct measurement of endogenous and exogenous contributions to the intestinal nitrogen fraction.
Adult↗
Modulation of beta-lactoglobulin transport in rabbit ileum.
This study was undertaken to investigate the mechanisms of beta-lactoglobulin transport and its regulation in rabbit intestinal mucosa. beta-Lactoglobulin, the major bovine milk whey protein, was slightly degraded by ileal brush-border membranes, indicating the presence of phosphoramidon-insensitive neutral endoproteases. Modulation of 14C-radiolabeled beta-lactoglobulin transport across rabbit ileum mounted in Grass diffusion cells was studied in Ringer solution in the presence and absence of (in mM) 25 glucose, 10 galactose, and 0.5 colchicine. The transport was also measured in Dulbecco's modified Eagle's medium as a more "balanced" medium. The transport of the degraded products and of [3H]polyethylene glycol-4000, which was used as an extracellular marker, was enhanced by addition of glucose, presumably indicating passage through the tight junctions. The transepithelial passage of intact protein was estimated to be 10-20% by trichloroacetic acid precipitation and high-performance liquid chromatography, thus indicating the effective transport of the intact protein. The passage of the intact protein was inhibited by both colchicine, a microtubule-depolymerizing agent, and galactose by 50 and 30%, respectively. Galactose-like glycoconjugates, known to be present on the membrane, might be involved in the interaction between the protein and the brush border.
Animals↗
Proton nuclear magnetic resonance spectroscopy of urine and plasma in renal transplantation follow-up.
Urine and plasma samples from 39 patients who underwent renal transplantation were analyzed by proton nuclear magnetic resonance (NMR) spectroscopy. The most relevant resonances for evaluating renal function after transplantation were those arising from citrate, trimethylamine-N-oxide (TMAO), alanine, and lactate when compared to creatinine. A resonance at 3.7 ppm was related to cyclosporine toxicity when associated with elevated levels of TMAO. The respective variations in these metabolites in urine could contribute to prognosis and diagnosis of renal function impairment related to cyclosporine toxicity or overdosage, or to rejection. Thus, NMR spectroscopy should improve the follow-up and management of renal transplantation patients.
Alanine↗
Identification of C-terminal peptides of bovine beta-casein that enhance proliferation of rat lymphocytes.
A casein polypeptidic fraction, obtained from a pepsin-chymosin digestion of caseins, showed a mitogenic effect on primed lymph node (LN) cells and unprimed spleen cells of rats. A biologically active C-terminal sequence of bovine beta-casein (residues 192-209) was characterized. The corresponding synthetic peptide had a stimulatory effect on primed LN cells but failed to enhance proliferation of spleen cells. We prepared two chymosin digests (PA and PB) of bovine beta-casein which contained, respectively, 80% and 95% of the sequence including residues 193-209. They induced a significant proliferative response in both LN and spleen cells. It is therefore possible that other active peptides in the PA preparation may be involved in mitogenic activity.
Amino Acid Sequence↗
Gastroileal nitrogen and electrolyte movements after bovine milk ingestion in humans.
Gastric emptying and flow rates of nitrogen and electrolytes (Na+, K+, Cl-, Mg2+, Ca2+) were studied in humans after bovine milk ingestion. With water as the control, intestinal effluents were collected after meal ingestion at the beginning of the jejunum or in the distal ileum. The flow rate of the effluent peaked in the first 40-min period after meal ingestion and returned to the initial amount within 100 min. After water ingestion the quantity of nitrogen recovered in the digesta remained unchanged both in the jejunum and in the ileum during the test period. After milk ingestion the nitrogen concentration in the jejunal digesta peaked in the first 20 min. Forty-two percent of milk nitrogen was absorbed before the jejunum and 93% was absorbed before the end of the ileum. These results showed that for the completion of the absorption of dietary proteins such as milk proteins, the lower part of the intestine is necessary.
Adult↗