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Biomedical subjects

M Armand

Publications and source records attributed to M Armand.

At least 19 recordsLinked to original sources
PubMed2004

Physicochemical properties of lipids: new strategies to manage fatty acid bioavailability.

Fatty acid bioavailability can be managed through the physicochemical properties of lipid such as lipid-droplet size, lipid-droplet ultrastructure (lipids organization between core and surface), structure of triglycerides and of phospholipids. The lipid-droplet size exhibits a major effect on lipase activity during lipid digestion. The lipid-droplet ultrastructure is a dynamic factor controling lipase interaction at the lipid interface via the surface phospholipid layer, and also lipase activity via the proportion of triglyceride molecules able to locate at the surface. Triglyceride structure affects in a strong manner digestion, absorption and fatty acid metabolism. Finally, optimal fatty acid transport to specific tissues is dependent on the vehicle molecule (triglyceride or ethyl ester or phospholipid). All these aspects provide convincing support for the possibility of using biotechnologically remodeled lipids with specific physicochemical properties for health benefits.

Animals↗
PubMed2001

Issues and challenges facing rechargeable lithium batteries.

Technological improvements in rechargeable solid-state batteries are being driven by an ever-increasing demand for portable electronic devices. Lithium-ion batteries are the systems of choice, offering high energy density, flexible and lightweight design, and longer lifespan than comparable battery technologies. We present a brief historical review of the development of lithium-based rechargeable batteries, highlight ongoing research strategies, and discuss the challenges that remain regarding the synthesis, characterization, electrochemical performance and safety of these systems.

Journal Article↗
PubMed2001

The lung as a route for systemic delivery of therapeutic proteins and peptides.

The large surface area, good vascularization, immense capacity for solute exchange and ultra-thinness of the alveolar epithelium are unique features of the lung that can facilitate systemic delivery via pulmonary administration of peptides and proteins. Physical and biochemical barriers, lack of optimal dosage forms and delivery devices limit the systemic delivery of biotherapeutic agents by inhalation. Current efforts to overcome these difficulties in order to deliver metabolic hormones (insulin, calcitonin, thyroid-stimulating hormone [TSH], follicle-stimulating hormone [FSH] and growth hormones) systemically, to induce systemic responses (immunoglobulins, cyclosporin A [CsA], recombinant-methionyl human granulocyte colony-stimulating factor [r-huG-CSF], pancreatic islet autoantigen) and to modulate other biological processes via the lung are reviewed. Safety aspects of pulmonary peptide and protein administration are also discussed.

Absorption↗
PubMed2001

Gastric proteolysis in preterm infants fed mother's milk or formula.

Gastric proteolysis is assumed to be low in the newborn (Britton & Koldovsky 1989). Postprandial pepsin output is significantly lower in preterm infants than adults, 589 vs. 3352U/kg, respectively (Armand et al. 1995, 1996). We now report on gastric proteolysis in preterm infants (gestation age, 29 weeks; postnatal age, 5-6 weeks) gavage-fed mother's milk or preemie formula. The data show that a) the nonprotein component is higher in human milk than formula, b) net proteolysis amounts to 15% of protein, c) gastric proteolysis is lower than lipolysis and, contrary to the latter, is not enhanced by milk feeding (Armand et al. 1996). We suggest that stomach pH, enzyme output, and food structure are the reasons for differences in gastric digestion of protein and fat in infants.

Aging↗
PubMed2001

Processing of vitamin A and E in the human gastrointestinal tract.

We aimed to provide basic data on the processing of vitamin A and E in the human gastrointestinal tract and to assess whether the size of emulsion fat globules affects the bioavailability of these vitamins. Eight healthy men received intragastrically two lipid formulas differing in their fat-globule median diameter (0.7 vs. 10. 1 microm. Formulas provided 28 mg vitamin A as retinyl palmitate and 440 mg vitamin E as all-rac alpha-tocopherol. Vitamins were measured in gastric and duodenal aspirates, as well as in chylomicrons, during the postprandial period. The gastric emptying rate of lipids and vitamin A and E was similar. The free retinol/total vitamin A ratio was not significantly modified in the stomach, whereas it was dramatically increased in the duodenum. The proportion of ingested lipid and vitamins was very similar in the duodenal content. The chylomicron response of lipids and vitamins was not significantly different between the two emulsions. Our main conclusions are as follows: 1) there is no significant metabolism of vitamin A and E in the human stomach, 2) the enzyme(s) present in the duodenal lumen is significantly involved in the hydrolysis of retinyl esters, and 3) the size of emulsion fat globules has no major effect on the overall absorption of vitamin A and E.

Adult↗
PubMed2000

Green tea extract (AR25) inhibits lipolysis of triglycerides in gastric and duodenal medium in vitro.

In this study, we aimed to evaluate in vitro the inhibitory activity of a green tea extract (AR25 standardized at 25% catechins) on gastric and pancreatic lipase activities. We first used tributyrin as a substrate to evaluate the capability of AR25 to induce digestive lipase inhibition. Gastric lipase was totally inhibited by 40 mg AR25/g tributyrin whereas pancreatic lipase inhibition was maximum (78.8 +/- 0.7%) with 80 mg AR25/g tributyrin. We then used triolein, a long-chain triglyceride, to check whether AR25 could alter lipase activities on a physiologic substrate. AR25 60 mg/g triolein induced a dramatic inhibition of gastric lipase (96.8 +/- 0.4%) whereas pancreatic lipase activity was partially reduced (66.50 +/- 0.92%). Finally, the concerted action of gastric and pancreatic lipases was studied with an excess of enzymes to mimic the physiologic conditions observed in vivo. Incubation of AR25 with an excess of digestive lipases resulted in a drastic decrease in gastric lipolysis but the inhibitory effect on pancreatic lipase was less marked. On the whole, as compared to the control, lipolysis of triolein under the successive action of the two digestive lipases was reduced by 37 +/- 0.6% in the presence of AR25. Because a lipid/water interface is necessary for lipolysis to occur, lipid emulsification and emulsion droplet size were measured in gastric and duodenal media in the presence of AR25. In gastric and duodenal conditions, AR25 inhibited the lipid emulsification process. From these data we conclude that (1) in vitro, fat digestion is significantly inhibited by 60 mg AR25/g triolein, and (2) gastric as well as pancreatic lipase inhibition could be related to altered lipid emulsification in gastric or duodenal media. The green tea extract AR25 exhibiting marked inhibition of digestive lipases in vitro is likely to reduce fat digestion in humans.

Journal Article↗
PubMed1999

Protective function of human milk: the milk fat globule.

Human milk contains many components that protect the newborn against infection at a time when the infant's own defense mechanisms are poorly developed. Fat is one of the major nutrients in human milk. The fat is contained within milk fat globules composed of a core of triglyceride and a membrane consisting of phospholipids, cholesterol, proteins, and glycoproteins. Both the membrane and the core components can provide protection against microorganisms. The major protective membrane glycoproteins, mucin, and lactadherin are resistant to conditions in the newborn's stomach and maintain their structure and function even at low pH and in the presence of the proteolytic enzyme pepsin. The core triglycerides upon hydrolysis by digestive lipases (especially gastric lipase, which is well developed in the newborn) produce free fatty acids and monoglycerides, amphiphylic substances able to lyse enveloped viruses, bacteria, and protozoa. Therefore, in addition to its nutritional value, the fat in human milk has a major protective function.

Anti-Bacterial Agents↗
PubMed1999

Digestion and absorption of 2 fat emulsions with different droplet sizes in the human digestive tract.

BACKGROUND: The extent of fat emulsification affects the activity of digestive lipases in vitro and may govern digestion and absorption of dietary fat. OBJECTIVE: We investigated the effect of the fat globule size of 2 enteral emulsions on fat digestion and assimilation in humans. DESIGN: Healthy subjects received intragastrically a coarse (10 microm) and a fine (0.7 microm) lipid emulsion of identical composition in random order. Gastric and duodenal aspirates were collected throughout digestion to measure changes in fat droplet size, gastric and pancreatic lipase activities, and fat digestion. Blood lipids were measured postprandially for fat assimilation. RESULTS: Despite an increase in droplet size in the stomach (2.75-6.20 microm), the fine emulsion retained droplets of smaller size and its lipolysis was greater than that of the coarse emulsion (36.5% compared with 15.8%; P < 0.05). In the duodenum, lipolysis of the fine emulsion was on the whole higher (73.3% compared with 46.3%). The overall 0-7-h plasma and chylomicron responses given by the areas under the curve were not significantly different between the emulsions, but the triacylglycerol peak was delayed with the fine emulsion (3 h 56 min compared with 2 h 50 min). CONCLUSIONS: Fat emulsions behave differently in the digestive tract depending on their initial physicochemical properties. A lower initial fat droplet size facilitates fat digestion by gastric lipase in the stomach and duodenal lipolysis. Overall fat assimilation in healthy subjects is not affected by differences in initial droplet size because of efficient fat digestion by pancreatic lipase in the small intestine. Nevertheless, these new observations could be of interest in the enteral nutrition of subjects suffering from pancreatic insufficiency.

Absorption↗
PubMed1998

Effects of graded amounts (0-50 g) of dietary fat on postprandial lipemia and lipoproteins in normolipidemic adults.

Eight normolipidemic males ingested on separate days and in a random order five mixed meals containing 0, 15, 30, 40, or 50 g fat. Fasting and postprandial blood samples were obtained for 7 h and chylomicrons and lipoproteins were isolated. The nonfat and 15-g fat meals did not generate noticeable postprandial variations except for HDL phospholipids (P < 0.05). The serum and chylomicron triacylglycerol responses obtained after the meals correlated positively with the amount of fat ingested and peaked after 2-3 h. Serum free cholesterol and phospholipids increased and esterified cholesterol decreased postprandially in a dose-response manner. At the same time, triacylglycerol-rich-lipoprotein triacylglycerols, esterified cholesterol, LDL free cholesterol, HDL triacylglycerols, phospholipids, and free cholesterol increased whereas LDL and HDL esterified cholesterol decreased when the amount of ingested fat increased. The data showed that increasing the amount of fat in the usual range of ingestion (0-50 g) led to stepwise increases in the postprandial rise of chylomicron and serum triacylglycerols and induced marked changes in serum lipoproteins postprandially. The existence of a no-effect level of dietary fat (15 g) on postprandial lipemia and lipoproteins in healthy adults was shown.

Adult↗
PubMed1998

Stepping over obstacles during locomotion: insights from multiobjective optimization on set of input parameters.

In this study we investigate possible objectives that the central nervous system (CNS) may consider in planning a strategy for stepping over an obstacle. A link segment simulation model has been developed based on Lagrangian dynamics, with which muscle force inputs can be optimized to best satisfy the postulated objectives for landing stability, obstacle clearance, and efficiency of the movement. A direct optimization approach with multiobjective criteria based on the kinematic and kinetic characteristics of the swing phase of locomotion is used in the simulation. The role of initial conditions at toe-off and biarticular muscle forces during the swing phase was also investigated. The optimization was performed for both leading limb and the trailing limb during the swing phase. The simulation results demonstrate that the use of biarticular muscles is sufficient to clear a range of obstacles with the trailing limb (obstacle encountered during early swing). Stride length or landing stability objectives need not be specified suggesting a simpler control of trailing limb trajectory by the CNS (one of stride length or landing stability objectives were not necessary). In contrast while the use of biarticular muscles can be sufficient to clear obstacles with the leading limb (obstacle encountered during mid to late swing), a stable landing and smooth toe and knee trajectories are compromised without suitable initial conditions at toe-off. The results suggest that the set of postulated objectives for the lead limb is adequate, although not complete.

Biomechanical Phenomena↗
PubMed1998

Milk fat globule glycoproteins in human milk and in gastric aspirates of mother's milk-fed preterm infants.

Human milk fat globule (HMFG) glycoproteins can prevent infections by microorganisms in breast-fed infants; the MUC-1 mucin inhibits binding of S-fimbriated Escherichia coli to buccal mucosa, and lactadherin may prevent symptomatic rotavirus infections. In this study, the survival of these HMFG glycoproteins in the stomach of human milk-fed preterm infants (gestational age = 27.5 +/- 0.4 wk) was assessed, and levels in their mothers' milk determined, using specific RIAs. Butyrophilin, a major component of HMFG membrane that has no demonstrated antimicrobial activity, was studied for comparison. The levels of mucin, lactadherin, and butyrophilin in 41 milk samples of 20 mothers were 729 +/- 75, 93 +/- 10, and 41 +/- 3 microg/mL, respectively. Mucin and lactadherin were significantly higher in early milk samples (<15 d postpartum) than in later milk samples (15-90 d postpartum), whereas butyrophilin showed no such difference. Significant amounts of mucin and lactadherin were found in almost all gastric aspirates of human milk-fed infants, even 4 h after feeding (mucin, 270 +/- 30 microg/mL; lactadherin, 23.2 +/- 4.4 microg/mL), whereas butyrophilin was rapidly degraded in the majority of aspirates. Western blot analysis demonstrated that the immunoreactive mucin, lactadherin, and butyrophilin in the milk-fed gastric aspirates had the expected native molecular weights. Mucin and lactadherin survived at all gastric pH values, whereas butyrophilin was found only at pH > 4. Neither lactadherin nor butyrophilin were detected in gastric aspirates of formula-fed infants (gestational age = 27.8 +/- 0.5 wk), whereas the very low level of mucin (9.1 +/- 1.1 microg/mL) in this group is presumably cross-reacting gastric mucin. These results demonstrate that two HMFG glycoproteins implicated in prevention of infection, MUC-1 mucin and lactadherin, survive and maintain their integrity in the stomachs of human milk-fed preterm infants.

Anti-Infective Agents↗
PubMed1997

Postprandial chylomicron and plasma vitamin E responses in healthy older subjects compared with younger ones.

The effect of ageing on vitamin E bioavailability in humans was assessed by comparing chylomicron and plasma alpha-tocopherol postprandial concentrations after a dose of vitamin E (432 or 937 IU as d1-alpha-tocopherol acetate), in eight young (20-30 years old) and eight healthy elderly men (64-72 years old). The fasting plasma alpha-tocopherol concentration was significantly higher in the elderly (33 +/- 2 mumol L-1) than in the young (22 +/- 2 mumol L-1). In both groups, the plasma and chylomicron alpha-tocopherol postprandial concentrations were significantly, approximately twofold, higher after the 937-IU meal than after the 432-IU meal. For both test meals, the chylomicron alpha-tocopherol areas under the curve were significantly lower in the elderly than in the young subjects: 98.9 +/- 16.5 (young group) vs. 55.3 +/- 7.8 (elderly group) mumol L-1 h for the 937-IU test meal and 60.4 +/- 14.1 (young group) vs. 26.0 +/- 7.6 (elderly group) mumol L-1 h for the 432-IU test meal, whereas the plasma alpha-tocopherol area under the curve was significantly higher in elderly than in young subjects: 337.56 +/- 16.11 (937-IU test meal) vs. 159.81 +/- 35.55 (432-IU test meal) mumol L-1 h in the young group and 709.55 +/- 69.33 (937-IU test meal) vs. 436.39 +/- 41.08 (432-IU test meal) mumol L-1 h in the elderly group. We concluded that (a) the amount of vitamin E appearing in plasma is proportional to the dose ingested (up to 937 IU); (b) the intestinal absorption of vitamin E is not increased, even possibly decreased, in the elderly; and (c) the amount of vitamin E transported by non-chylomicron lipoproteins is apparently higher in the elderly. This suggests that vitamin E postprandial transport is affected by ageing, mainly as the consequence of age-related modifications of lipoprotein metabolism.

Adult↗
PubMed1996

Emulsification and lipolysis of triacylglycerols are altered by viscous soluble dietary fibres in acidic gastric medium in vitro.

This in vitro study was designed to test the hypothesis that soluble dietary fibres can alter the process of intragastric lipid emulsification and possibly subsequent triacylglycerol lipolysis. Three guar gums, two pectins and gum arabic were dissolved in acidic gastric medium in the concentration range 0.3-2.0% (w/v). Viscosities of fibre solutions were measured and apparent viscosities varied over a wide range (0.7-77 mPa/s). Emulsification of a lipid mixture (triolein/phosphatidylcholine/cholesterol) was performed under mild conditions in the presence of increasing concentrations of soluble fibres. The amount of emulsified lipid was not affected whereas the size of the emulsified droplets was increased by raising the concentration of viscous fibres only. The droplet size (r=0.75, P=0.006) and overall droplet surface area (r=-0.69, P=0.009) were strongly correlated with the medium viscosity in the range 0-20 mPa/s. The addition of solutions of viscous fibres to a preformed standard emulsion did not change the initial velocity of human gastric lipase reaction. Conversely, when emulsions prepared in the presence of fibres (i.e. with different droplet sizes) were incubated with excess gastric enzyme for 2 h, the high-viscosity guar gum significantly reduced the extent of triacylglycerol lipolysis, as compared with control and low- or medium-viscosity fibres. In conclusion, the data obtained show that reducing emulsification of dietary lipids in the mildly acid medium found in the stomach is a mechanism by which soluble viscous fibres can alter lipid assimilation.

Dietary Fiber↗
PubMed1996

Postprandial appearance of dietary deuterated cholesterol in the chylomicron fraction and whole plasma in healthy subjects.

This study examined the appearance of dietary cholesterol in the chylomicron fraction (chylomicrons plus chylomicron remnants) and whole plasma in healthy normolipidemic subjects during a 0-7-h postprandial period. Six adult males were given two diet sequences in random order: a low-fiber diet (standard Western diet for 14 d) followed by a labeled low-fiber test meal or a fiber-supplemented diet (40 g oat bran/d for 14 d) followed by a labeled oat bran (40 g) test meal. The test meals provided 192.5 mg cholesterol, including 80.1 mg octadeuterated cholesterol. Fasting and hourly postmeal blood samples were obtained for 7 h. Isotopic cholesterol ratios [tracer:(tracer+native cholesterol)] were determined by gas chromatography-mass spectrometry. Chylomicron triacylglycerol and cholesterol concentrations peaked after 2-3 h and returned to baseline after 7 h. After the low-fiber test meal, the isotopic cholesterol ratio continuously increased until 7 h in the chylomicron fraction (4.2 +/- 1.2 x 10(-3)) and whole plasma (1.04 +/- 0.39 x 10(-3)). At 7 h postprandial, the maximum dietary cholesterol concentration in the chylomicron fraction and plasma cholesterol was 1 in 99 and 1 in 397 cholesterol molecules, respectively. No marked differences were obtained after the high-fiber sequence compared with the low-fiber one; there was a comparable isotopic cholesterol ratio and concentration in the chylomicron fraction and a slightly lower (-44%, P < 0.10) 0-7 h area under the curve whole-plasma deuterated cholesterol concentration. Thus, dietary cholesterol supplied as a single meal does not simultaneously appear in the chylomicron fraction postprandially with endogenous cholesterol and triacylglycerols and fiber feeding does not markedly alter this process in healthy normolipidemic humans.

Adult↗
PubMed1996

Physicochemical characteristics of emulsions during fat digestion in human stomach and duodenum.

Seven fasting subjects were fitted with nasogastric and nasoduodenal tubes and received intragastrically a coarsely emulsified test meal. Gastric and duodenal aspirates were collected after 1, 2, 3, and 4 h. In the duodenum, most lipids (> 90%) were present as emulsified droplets 1-100 microns in size. Large droplets and unemulsified material present in the test meal (> 100 micron) disappeared, whereas smaller droplets (1-50 microns) were generated after 1 h of digestion. Thus the median lipid droplet diameter significantly decreased (19.6 vs. 56.5 microns in the test meal) and the droplet surface area significantly increased (1.58 vs. 0.70 micron2/g fat). Intermediate droplet diameters were 34.3, 46.3, and 27.6 microns after 2, 3, and 4 h, respectively. In the stomach, a comparable emulsion particle size pattern was observed, with median droplet diameters of 17.2, 37.9, 52.4, and 41.6 microns after 1, 2, 3, and 4 h, respectively. However, the extent of triglyceride hydrolysis was much lower in the stomach (6-16%) than in the duodenum (42-45%), where small droplets were enriched in lipolytic products, cholesterol, and phospholipids. The present findings show for the first time that most dietary lipids are present in the human duodenum as emulsified droplets 1-50 microns in size and that no further marked emulsification of dietary fat occurs in the duodenum compared with the stomach.

Adult↗
PubMed1996

Effect of human milk or formula on gastric function and fat digestion in the premature infant.

The effect of diet, human milk or formula, on gastric function (lipase and pepsin activity, pH, and volume) and intragastric digestion of fat was assessed in 28 appropriate for gestational age preterm infants (gestational age, 28.9 +/- 1.4, 29.1 +/- 0.9, 29.5 +/- 0.6 wk; birth weight, 1.00 +/- 0.14 to 1.18 +/- 0.07 kg). The infants were fed either human milk (n = 11), SMA Super Preemie formula (n = 9), or Similac, Special Care formula (n = 8). Fasting and postprandial activity of digestive enzymes, pH, and gastric volume (measured before or during 50 min after gavage feeding) did not differ as a function of diet among the three groups of infants. Gastric lipase output, 23.1 +/- 5.1, 28.3 +/- 6.6, and 22.5 +/- 6.4 (U/kg of body weight) in human milk-, SMA SP-, or Similac SC-fed infants was comparable to the gastric lipase output of healthy adults fed a high fat diet (22.6 +/- 3.0). Pepsin output was, however, significantly lower (597 +/- 77, 743 +/- 97, and 639 +/- 142 U/kg of body weight) in human milk-, SMA SP-, and Similac SC-fed infants) than in healthy adults (3352 +/- 753 U/kg). The hydrolysis of dietary fat was 1.7-2.5-fold higher (p < 0.01) in human milk-fed infants than in infants fed either formula. We conclude that differences in type of feeding, i.e. different fatty acid profiles (long chain or medium chain triglycerides), different emulsions (natural or artificial), and different fat particle sizes do not affect the level of activity of gastric enzymes. However, the triglyceride within milk fat globules appears to be more accessible to gastric lipase than that within formula fat particles. We suggest that the contribution of gastric lipase to overall fat digestion might be greater in the newborn (a period of pancreatic insufficiency) than in the adult.

Dietary Fats↗
PubMed1996

Carotenoids in biological emulsions: solubility, surface-to-core distribution, and release from lipid droplets.

Data on the physico-chemical properties of carotenoids in biological emulsions are essential to our knowledge of carotenoid metabolism. Therefore, we determined the behavior of carotenoids in phospholipid-stabilized triglyceride emulsions, a model for biological emulsions such as dietary emulsions, triglyceride-rich lipoproteins, and intracellular storage droplets. The solubility of beta-carotene (a model for apolar carotenoids, carotenes) in pure bulk triglycerides (0.112 to 0.141 wt % according to triglycerides) was significantly higher than zeaxanthin (a model for polar carotenoids, xanthophylls) (0.022 to 0.088 wt %). The solubility of both carotenoids increased when the chain-length of the triglycerides' fatty acids decreased. The amount of zeaxanthin associated with lipid droplet dramatically increased in phospholipid-triglyceride droplets as compared to the pure corresponding triglyceride droplets, whereas the amount of beta-carotene associated with lipid droplets increased only slightly beta-Carotene distributed almost exclusively in the core of triolein-lecithin-carotenoid droplets, while zeaxanthin distributed preferentially at the droplet's surface. A significant percentage (8.3%) of zeaxanthin was spontaneously transferred from lipid droplets to aqueous phase and the remaining part was transferred during triglyceride hydrolysis catalysed by pancreatic lipase, while beta-carotene absolutely required triglyceride lipolysis to be transferred to the aqueous phase. Our results show that polar and apolar carotenoids behave differently in biological emulsions. They further our understanding of the bioavailability of polar and apolar carotenoids and of their distribution between lipoprotein particles.

Animals↗