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Biomedical subjects

I Birlouez-Aragon

Publications and source records attributed to I Birlouez-Aragon.

At least 19 recordsLinked to original sources
PubMed2005

Evaluation of the maillard reaction in infant formulas by means of front-face fluorescence.

Foods are complex mixtures of macro- and micronutrients, which interact, leading to oxidation, glycation, and hydrolysis upon heating (e.g., sterilization, cooking) and storage. Their nutritional quality and safety are consequently affected, justifying the need for accurate monitoring of the evolution of the food composition during processing and shelf life. Classical chromatographic analysis as well as newly proposed rapid methods based on fluorescence spectrometry analyses were applied on whey powder-based models and commercial samples (in powdered form and ultrahigh temperature [UHT] sterilized), some of which had been previously submitted to protein hydrolysis. These samples were incubated for 48 h at 60 degrees C to mimic accelerated storage. Fluorescence fingerprints addressing modifications in the product composition during processing were recorded and analyzed by chemometric methods. Carboxymethyllysine (Nepsilon-[carboxymethyl]lysine; CML) was measured using an ELISA method. Fluorescence, recorded in a front-face mode on intact samples, is very sensitive to pertinent physicochemical changes induced by heat treatment, formulation (the moisture level in powders, presence of vitamin C and iron), and storage. Similar trends were observed between powders' fluorescence and CML-for example, a strong effect of protein hydrolysis and increasing water content. Addition of vitamin C was associated with an antioxidant effect despite the presence of iron. Good calibration models were obtained for predicting CML from fluorescence spectra both in food models and in commercial samples, although more work is needed to obtain accurate and robust calibration models. Results show the potential of nondestructively applied fluorescence spectrometry for measuring CML in formulas, a rapid, simple, and cost-effective method to monitor formula quality.

Fluorescence↗
PubMed2005

Effects of sterilization, packaging, and storage on vitamin C degradation, protein denaturation, and glycation in fortified milks.

Monitoring the nutritional quality of dietetic milk throughout its shelf life is particularly important due to the high susceptibility of some vitamins to oxidation, and the continuous development of the Maillard reaction during storage. The objective of this paper was to evaluate the vitamin C content and protein modification by denaturation and glycation on fortified milk samples (growth milks) destined for 1- to 3-yr-old children. The influences of the sterilization process, formulation, packaging, and storage duration at ambient temperature in the dark were studied. Vitamin C degradation was particularly influenced by type of packaging. The use of a 3-layered opaque bottle was associated with complete oxidation of vitamin C after 1 mo of storage, whereas in the 6-layered opaque bottle, which has an oxygen barrier, the vitamin C content slowly decreased to reach 25% of the initial concentration after 4 mo of storage. However, no significant effect of vitamin C degradation during storage could be observed in terms of Maillard reaction, despite the fact that a probable impact occurred during sterilization. Furosine content and the FAST (fluorescence of advanced Maillard products and soluble tryptophan) index-indicators of the early and advanced Maillard reaction, respectively-were significantly higher in the in-bottle sterilized milk samples compared with UHT samples, and in fortified milk samples compared with cow milk. However, after 1 mo, the impact of storage was predominant, increasing the furosine level and the FAST index at similar levels for the differently processed samples. The early Maillard reaction developed continuously throughout the storage period.In conclusion, only packaging comprising an oxygen and light barrier is compatible with vitamin C fortification of milk. Furthermore, short storage time or low storage temperature is needed to retard vitamin C degradation, protein denaturation, and development of the Maillard reaction.

Animals↗
PubMed2001

The FAST method, a rapid approach of the nutritional quality of heat-treated foods.

The FAST method is based on the determination of maximal fluorescence emission when exciting at 330-350 nm, which corresponds to molecular structures formed between reducing sugars or oxidizing lipids and lysine residues of proteins. This fluorescence is dependent on heat treatment and related to protein nutritional loss. Applied to a soluble extract of the food and corrected for the protein concentration of the solution obtained, using Trp fluorescence, the method allows to calculate the FAST index (FI), an indicator of the nutritional damage during heat process. The method, firstly validated on milk samples, is demonstrated here to well correlate with lysine damage on various food products, such as heat-treated milk and breakfast cereals, essentially modified by the Maillard reaction, and roasted soybean or cooked salmon, where interactions between oxidizing lipids and proteins better take place. Independently on the food product or the type of heat process, the FAST index appears always well correlated (r2: 0.84-0.98) to the lysine loss, the latter being estimated by determination of acid-released lysine, fluorescamine-reactive lysine or infrared. Shortly, roasted corn flakes appeared to be more damaged than extrudated flour (FI 100 and lysine blockage 40% instead of 55 and 30%), condensed milk more than UHT milk (FI 150 and 85% of acid-released lysine instead of 80 and 94%), and steam-cooked salmon much less than pan-fried (FI 28 instead of 372). Roasted soy can reach FI of more than 300 corresponding to chemical lysine loss of 40% and poultry-digestive lysine loss of 100%. As a conclusion, the FAST method, once precisely calibrated with pertinent nutritional indicators, should be of great interest for controlling or adapting a process in order to ensure a better nutritional quality for the food product.

Animals↗
PubMed2001

The fluorescence of advanced Maillard products is a good indicator of lysine damage during the Maillard reaction.

The objective of this study was to determine whether in heat-treated milk-resembling models or milk there is a lag phase, before lactulosyllysine (LL) is converted into advanced Maillard products (AMP), and if there is a step during the heat treatment where LL is actively degraded into AMP. For that purpose, a low temperature (60-85 degrees C) and a long heat treatment (15-90 h) were chosen. We observe that the heat treatment first induces a parallel increase in furosine and AMP fluorescence, confirming that AMP are produced very early during the heat treatment. At this step, both indicators are correlated with each other and precisely reflect the lysine damage. After a time, however, furosine reaches a steady-state concentration, whereas AMP fluorescence still increases, remaining correlated with the lysine blockage. Nevertheless, heat treatment applied to milk does not reach this step so that AMP fluorescence appears as a rapid alternative to furosine quantification.

Animals↗
PubMed2001

Associations of age, smoking habits and diabetes with plasma vitamin C of elderly of the POLA study.

The objective of this study was to determine the associations of age and sex with plasma vitamin C (vit C) concentration taking into account smoking habits and the presence of age-related pathologies, such as diabetes. The POLA study is a population-based study on age-related eye diseases and their risk factors, and plasma Vitamin C evaluation is part of the biological parameters measured in the 1987 volunteer subjects living in Sète (South of France) and aged more than 60 years. Men had lower average plasma vit C levels than women (31.6 microM.L-1 versus 40.3 microM.L-1, p = 0.001). Plasma vit C was stable as a function of age in women but decreased in men (p = 0.02), enhancing the difference in vit C concentration between men and women with advancing age. Smoking more than 10 cigarettes a day was associated to a lower plasma vit C concentration in men (p = 0.001) but not in women, and diabetic subjects tended to have lower vit C concentrations, the difference being significant only in women (p = 0.003). We conclude that there is a clear influence of sex on plasma vit C. This difference may be due to dietary habits, or metabolism, but may also be due to different sensitivity of age, smoking and to some pathologies.

Age Factors↗
PubMed2000

Riboflavin photodegradation and photosensitizing effects are highly dependent on oxygen and ascorbate concentrations.

Riboflavin (RF) is a normal component of the eye lens which triggers a strong photosensitizing activity when exposed to light. Upon irradiation with short wavelength radiations below 400 nm, RF-photosensitized damage may occur. However, vitamin C is present at high concentrations in the normal lens and plays an important role in inhibiting these photosensitization processes. An in vitro simple model was used with the objective of understanding better the relationships between vitamin C and oxygen concentrations on the mechanisms of RF-mediated photodegradation of tryptophan (Trp), a target particularly sensitive to photo-oxidation. Under nitrogen, the RF decomposition reached its maximal value, and vitamin C and Trp photo-oxidation was negligible. When increasing oxygen pressure, RF photodegradation dropped and vitamin C photo-oxidation strongly increased and was maximal at 100% O2. RF-induced photodegradation of Trp first increased with oxygen concentration, up to 40 microM O2, and then decreased. RF and Trp degradation were significantly protected by vitamin C so that no more than 20% of the substrates concentration were oxidized in the presence of vitamin C higher than 0.8 mM. From our results we conclude that in the specific conditions of the normal lens, the high vitamin C concentration (2 mM) is compatible with the UVA radiation hazard, despite the presence of RF. However, if lenticular vitamin C decreases below 0.8 mM, photodegradation of RF may occur and Trp may therefore be photo-oxidized by a Type-I mechanism.

Ascorbic Acid↗
PubMed1998

Low plasma vitamin C in Alzheimer patients despite an adequate diet.

OBJECTIVE: To compare the vitamin C and E plasma levels in patients with Alzheimer's disease (AD) and to assess the vitamin C intake and nutritional status. DESIGN: Case-control study. Four groups of sex- and age-matched subjects were compared: severe AD and moderate AD, in patients with moderate AD and controls. SETTING: Community and hospitalized patients in the region of Toulouse, France. PARTICIPANTS: Patients with dementia who fulfilled criteria for Alzheimer's disease: severe Alzheimer group (N = 20), Mini-Mental State Examination (MMSE) score range 0-9; moderate Alzheimer group (N = 24), MMSE 10-23; hospitalized Alzheimer group (N = 9), MMSE 10-23. Control group (N = 19), MMSE 24-30. MEASURES: Plasma vitamin E and C were quantified by HPLC-fluorescence. Consumption of raw and cooked fruit and vegetables was evaluated in order to determine the mean vitamin C intakes. Mini Nutritional Assessment (MNA) and plasma albumin were used to measure nutritional status. RESULTS: Institutionalized and community subjects were analysed separately. MNA scores were normal in home-living Alzheimer subjects with moderate dementia and significantly lower in those with severe disease, despite normal plasma albumin levels. In the home-living Alzheimer subjects, vitamin C plasma levels decreased in proportion to the severity of the cognitive impairment despite similar vitamin C intakes, whereas vitamin E remained stable. The hospitalized Alzheimer subjects had lower MNA scores and albumin levels but normal vitamin C intakes, but their plasma vitamin C was lower than that of community-living subjects. Institutionalized Alzheimer subjects had significantly lower MNA scores but normal vitamin C and albumin levels and vitamin C intakes compared with community-dwelling subjects of similar degree of cognitive impairment. CONCLUSION: Plasma vitamin C is lower in AD in proportion to the degree of cognitive impairment and is not explained by lower vitamin C intake. These results support the hypothesis that oxygen-free radicals may cause damage.

Aged↗
PubMed1998

Plasma protein glycation in Alzheimer's disease.

Recent studies have suggested that formation of advanced glycation end-products (AGEs) in some brain proteins could be associated with Alzheimer's disease. These AGEs can be produced by various sugars (hexose, pentose, glyceraldehyde and oxidative products of vitamin C). In this study, we quantified plasma protein glycation specifically derived from glucose in patients with Alzheimer's disease with different grades of cognitive disorders. Two groups of Alzheimer patients were studied: a group with moderate Alzheimer's disease (n = 6, 9 23) and a group of subjects with diabetes (n = 31). Protein glycation was evaluated in plasma with a highly specific HPLC-UV technique, using furosine, which is the acid hydrolysis product of epsilon-deoxy-fructosyl-lysine Plasma furosine was almost two times higher in subjects with Alzheimer's disease (p<.005) than in controls, but still 50% lower than in diabetic patients (P<.02). Fasting plasma glucose levels were significantly correlated to the furosine concentration. To explain these results, an eventual impairment in glucose peripheral use or an increase in protein glycation rate associated with Alzheimer's disease should be explored.

Adult↗
PubMed1998

Effect of pH, phosphate and copper on the interaction of glucose with albumin.

Protein glycation is believed to play an important role in the development of long-term disorders associated with diabetes. Previous studies have shown that copper could activate this process; however, these experiments were performed under non-physiological conditions. In this study, in vitro experiments were carried out at near-physiological conditions to examine the catalytic activity of copper on the interaction of albumin with glucose. Changes in pH and phosphate buffering capacity were shown to affect albumin glycation. Under stable pH conditions, copper activates albumin glycation only at low protein concentrations (< 30 g l(-1)). Copper had no effect on albumin glycation at higher protein concentrations probably because the metal is chelated by the protein.

Buffers↗
PubMed1998

Decrease in vitamin C concentration in human lenses during cataract progression.

Cataract formation is believed to result from an oxidative insult which decreases the antioxidant defense of the lens, particularly the vitamin C concentration. Upon oxidation, vitamin C contributes with glucose to protein glycation. It also favours tryptophan oxidation, resulting in fluorescent peptide cross-links and protein insolubilisation. The relationship between cataract and lenticular vitamin C was analysed in 48 cataractous lens nuclei classified into four severity grades, considering the sum of the colour and opacity. Ascorbic and dehydroascorbic acids were quantified by HPLC-fluorescence. The Amadori product was measured by means of furosine, advanced glycation end products by their fluorescence and tryptophan concentration by HPLC-UV. The lens vitamin C concentration significantly decreased with cataract severity, but mostly in severe brown cataracts (around 88 mumol/100 g lens in mild cataracts, and 50 mumol/100 g in dark brown lenses). The dehydroascorbic acid concentration was always low and stable (1.9 +/- 0.9 mumol/100 g), as was the furosine concentration (0.4 +/- 0.1 mumol/g). The fluorescence of insoluble advanced glycated end products was significantly higher in severe cataracts than in milder ones. The peptide tryptophan content was stable but the tryptophan to tyrosine ratio decreased and was highly correlated to the ascorbic acid concentration. Vitamin C content appears to be a good indicator of cataract severity, suggesting that oxidation could take part in cataract progression.

Ascorbic Acid↗
PubMed1996

Validation of a micromethod for determining oxidized and reduced vitamin C in plasma by HPLC-fluorescence.

An HPLC micro-method with fluorescence detection has been developed to determine total vitamin C (vit C) and dehydroascorbic acid (DHA) concentrations in human plasma samples. This method is based on the rapid, specific reaction of DHA with dimethyl-o-phenylenediamine (DMPD) to form a fluorescent quinoxaline derivative that is quantified by HPLC in less than 5 minutes. The method was assessed with reference to the direct 2,4-dinitrophenylhydrazine (DNPH) colorimetric method. They were well correlated (r3 = 0.879), but the DMPD-HPLC method had the limit of detection 6 times lower than the standard method and the relative error for a vitamin standard was 10 times better than that of the standard method. The plasma DHA to total vit C ratio varied from 10 to 60%, depending on sample processing. Plasma that were immediately analysed contained 10% DHA whatever the subject's age; frozen deproteinized samples kept 1 week (-67 degrees C) had 20%, and blood samples kept for one hour at room temperature before treatment had up to 60% DHA. The ratio in capillary samples taken from the finger was 11-42%. This rapid, specific and very sensitive micro-method is well suited to routine measurements of plasma vit C.

Adult↗
PubMed1995

Comparison of two levels of vitamin C supplementation on antioxidant vitamin status in elderly institutionalized subjects.

The concentrations of antioxidant vitamins, particularly vitamin C, are often low in the plasma of institutionalized elderly subjects, and could explain their susceptibility to oxidative stress. However, as such low levels were not always found in home-living healthy elderly persons, the antioxidant vitamin depletion in the formers could result from environmental conditions better than aging itself. The objective of this study was therefore to verify the antioxidant vitamin status in institutionalized elderly persons and to evaluate if a low vit C supplement could be sufficient to improve the plasma vit C concentration in those subjects. This study confirms that plasma vitamin C levels are in the scurvy range in 20 elderly institutionalized subjects and significantly lower than in healthy home-living elderly persons. Beta-carotene concentrations were found marginally low but alpha-tocopherol levels were in the normal range. All three vitamins were correlated. Fifteen days on a physiological vitamin C (150 mg/day) supplementation was sufficient to restore normal vit C levels (50 mumol/l). A further pharmacological vit C administration (750 mg/day) during 30 days only allowed a marginal increase in the plasma vit C concentrations.

Aged↗
PubMed1993

Relationship between lens protein glycation and membrane structure in human cataract.

Glycation, which begins with the spontaneous reaction between sugar and proteins by the formation of Schiff bases, is known to especially damage long-lived proteins such as lens crystallins, and has been implicated in the ageing process and particularly in cataract formation. In this study of human senile cataract, a specific method is used to measure the formation of Amadori compounds in control postmortem and cataractous lenses, but no difference was found. However, the fluorescence of proteins at 430 nm (exc 350 nm), which has been attributed to advanced glycation, increased with normal ageing of the lens (cortex versus nucleus, and as a function of subject's age for each type of fibres) and was further enhanced in cataractous lenses. The precise molecular origin of this fluorescence remains to be elucidated. In parallel to the accumulation of non-tryptophan fluorophores, a decrease in the membrane fluidity was observed with lens ageing and more acutely with cataract. Both parameters are positively correlated (P < 1%). The modification of the membrane structure with glycation could explain the strong permeability changes occurring during cataract, measured here in terms of cation concentration and inositol leakage, as shown by the negative relationship between the fluorescence signal and the sodium to potassium ratio or the inositol level.

Aged↗
PubMed1993

Disturbed galactose metabolism in elderly and diabetic humans is associated with cataract formation.

Lactose consumption has been associated with a high incidence of cataract in northern Indian and southern Italian populations. Galactose absorbed after hydrolysis of lactose from milk in individuals with normal lactase activity is considered responsible. However, lactase-deficient subjects who often avoid drinking milk are able to digest lactose and absorb free galactose in fermented milk and yogurt. This study was conducted to evaluate the relationships between milk and yogurt consumption, galactose metabolism and cataract risk. Milk ingestion was dose-related with cataract risk in lactose digesters (particularly in diabetics) but not in lactose maldigesters. Conversely, yogurt intake had a protective dose-effect on cataract formation for the whole population. Maximal galactose concentrations after an oral galactose test increased exponentially with age. Red blood cell galactokinase activity was significantly lower in elderly subjects (> 60 y) than in young individuals (P < 0.05), and galactose-1-phosphate uridyl-transferase activity was significantly lower in institutionalized subjects and in home-living elderly with cataract than in healthy elderly subjects (P < 0.05). We conclude that the cataractogenic action of milk lactose is dependent on the disturbance of galactose metabolism in elderly subjects and that yogurt is not cataractogenic, although the mechanism of the protective effect of yogurt remains unknown.

Adult↗
PubMed1990

Evidence for a relationship between protein glycation and red blood cell membrane fluidity.

This study examines the relationship between protein glycation and membrane fluidity in RBC membranes. Incubation of RBC membranes of healthy subjects with 25mM glucose or galactose at 37 degrees C induced a 38% (p less than 0.02) increase in protein glycation (using furosine determination by HPLC) and higher fluidity (p less than 0.05) in DPH polarization ratio). However, incubation of RBC membranes from diabetic subjects under the same conditions did not modify either membrane fluidity or protein glycation; protein glycation was above normal before incubation because of the high diabetic plasma glucose. There was no difference in the membrane fluidities of 21 healthy subjects and 32 diabetic subjects, despite a significantly elevated protein glycation in diabetics. Furthermore, there was no change with respect to age in either population. We conclude that other in vivo factors, such as membrane lipid changes (increase in CL/PL ratio) or formation of advanced Maillard products and peroxidation in the diabetic subjects, could be responsible for the difference between these in vitro results and the in vivo situation.

Adult↗
PubMed1990

Effect of prolonged galactose consumption on galactose tolerance in young healthy humans.

This study was carried out on two groups of healthy young subjects. One group (n = 8) was given a single oral dose of galactose (0.5 g/kg body weight), and a single measurement of blood galactose was made 40 min later. A second group (n = 16) was given a daily supplement of 0.5 g/kg galactose for 15 days, and blood galactose and galactitol were measured. On the first day of the test period, some subjects seemed to tolerate galactose less well than others: galactitol appeared in their plasmas and could be related to a significantly higher galactosaemia than that of subjects without detectable galactitol in the plasma. However, after 15 days of galactose intake, the less galactose-tolerant subjects appeared to have adapted, as indicated by the significant decrease in the blood galactose and the disappearance of galactitol. No change was found in the galactose-tolerant subjects. No significant difference was found between males and females.

Adult↗