Empirico-inductive and/or hypothetico-deductive methods in food science and nutrition research: which one to favor for a better global health?

Scientific research generally follows two main methods: empirico-inductive (EI), gathering scattered, real-world qualitative/quantitative data to elaborate holistic theories, and the hypothetico-deductive (HD) approach, testing the validity of hypothesized theory in specific conditions, generally according to reductionist methodologies or designs, with the risk of over simplifying the initial complexity empirically perceived in its holistic view. However, in current food and nutrition research, new hypotheses are often elaborated from reductionist data obtained with the HD approach, and aggregated to form (ultra)reductionist theories, with no application of EI observations, limiting the applicability of these hypotheses in real life. This trend and the application of the EI method are illustrated as regards with the global health issue through the examples of food classifications/scoring, clinical studies, the definition of a sustainable diet, the "matrix effect"-related hypothesis, the concept of healthy core metabolism, and obesity prevention within the perspective of social sciences. To be efficient for producing food and nutritional data appropriable by the society, it finally appears that not only both approaches are necessary, starting with the EI method then the HD one, but also a back and forth between the two, this being not always realized, potentially leading to confusion and misunderstanding in society.

Exclusive reductionism, chronic diseases and nutritional confusion: the degree of processing as a lever for improving public health.

Exclusive reductionism in nutritional science consists of viewing foods as only the sum of nutrients. This position paper argues that the extreme application of this paradigm since 1950 has greatly contributed to confusion about a healthy diet among consumers and to the development of chronic diseases worldwide. First, history of nutritional sciences in Western countries shows that by approximately 1850, laboratory research had mainly been conducted by reducing foods to nutrients that were interchangeable from one food to another. Second, descriptive and experimental studies show that the increased prevalence of chronic diseases mainly derive from ultra-processed foods. With such foods being representative of a final output in the degree of food processing, the relevance of reformulating food versus developing less unstructured processed foods is discussed. Third, the reductionist validation of food additives, randomized controlled trials, and food scoring is also questioned. Additionally, epidemiological studies that associate dietary patterns with the risk of chronic diseases and that aggregate approaches in nutrition, technology, food science and food scoring appear to be more adapted for nutritional recommendations in society. It is concluded that a complementary holistic perspective is needed to communicate to society about diet/food health potential and to efficiently prevent populations from chronic diseases.

Perspective: Reductionist Nutrition Research Has Meaning Only within the Framework of Holistic and Ethical Thinking.

Today, it seems that nutrition is in a state of great confusion, especially for the general public. For decades, some nutrients (e.g., cholesterol, saturated fats, sugars, gluten, salt) and food groups (e.g., dairy, cereals, meats) have been regularly denigrated. In this position paper, we hypothesize that such a state of confusion is mainly the result of the reductionist paradigm applied to nutrition research for more than a century, and by being pushed to its extreme, this perspective has led to accusations about some nutrients and foods. However, the real issue is about foods taken as a whole and therefore about their degree of processing, which affects both the food matrix and composition. Indeed, we eat whole foods, not nutrients. Therefore, the objectives of this article are to emphasize the need for more holistic approaches in nutrition to preserve our health, animal welfare, and planet. We propose to first redefine the food health potential on a holistic basis and then to show that reductionism and holism are interconnected approaches that should coexist. Then, we try to explain how extreme reductionism has been disconnected from reality and ethical considerations and has ultimately led to environmental degradation and loss of biodiversity, notably through very specific crops, and to an increased prevalence of chronic diseases. Furthermore, to address the confusion of the general public and to simplify nutritional messages, we propose 3 holistic golden rules based on scientific evidence to protect human health, animal welfare, and the environment (climate and biodiversity). Finally, we try to show how these 3 rules can be easily applied worldwide while respecting the environment, cultural traditions, and heritage.

From a Reductionist to a Holistic Approach in Preventive Nutrition to Define New and More Ethical Paradigms.

This concept paper intends to define four new paradigms for improving nutrition research. First, the consequences of applying a reductionist versus a holistic approach to nutrition science will be discussed. The need for a more focused preventive nutrition approach, as opposed to a curative one, will then be presented on the basis of the 'healthy core metabolism' concept. This will lead us to propose a new classification of food products based on processing for future epidemiological studies. As a result of applying the holistic approach, health food potential will be redefined based on both food structure and nutrient density. These new paradigms should help define a more ethical preventive nutrition for humans to improve public recommendations while preserving the environment.

Proteomic analysis identifies cytoskeleton-interacting proteins as major downstream targets of altered folate status in the aorta of adult rat.

SCOPE: Mild folate deficiency and subsequently elevated plasma level of homocysteine are associated with an increased risk for vascular diseases in adults. Conversely, high intakes of folic acid (FA) may have beneficial effects on vascular function, presumably in part through homocysteine lowering. However, these effects have not yet been translated in terms of prevention or treatment of vascular pathologies. Besides, the complex biologic perturbation induced by variations of the folate supply is still not fully deciphered. We thus carried out a proteomic analysis of the aorta of adult rats after a dietary FA depletion or supplementation. METHODS AND RESULTS: Nine month-old rats were fed a FA-depleted, FA-supplemented or control diet for 8 weeks. Total proteins from adventitia-free aortas were separated by 2DE and differentially expressed proteins were identified by MS. FA depletion or supplementation resulted in significantly changed abundance of 29 spots (p < 0.05), of which 20 proteins were identified. Bioinformatic analysis revealed that most of these proteins are involved in cytoskeleton-related processes important to cell function/maintenance, assembly/organization, and movement. CONCLUSION: Our proteomic study supports that expression of proteins essential to vascular structure and, presumably, function is modulated by high intake as well as deprivation of FA.

Toward a new philosophy of preventive nutrition: from a reductionist to a holistic paradigm to improve nutritional recommendations.

The reductionist approach has been predominant to date in human nutrition research and has unraveled some of the fundamental mechanisms at the basis of food nutrients (e.g., those that involve deficiency diseases). In Western countries, along with progress in medicine and pharmacology, the reductionist approach helped to increase life expectancy. However, despite 40 y of research in nutrition, epidemics of obesity and diabetes are growing each year worldwide, both in developed and developing countries, leading to a decrease in healthy life years. Yet, interactions between nutrition-health relations cannot be modeled on the basis of a linear cause-effect relation between 1 food compound and 1 physiologic effect but rather from multicausal nonlinear relations. In other words, explaining the whole from the specific by a bottom-up reductionist approach has its limits. A top-down approach becomes necessary to investigate complex issues through a holistic view before addressing any specific question to explain the whole. However, it appears that both approaches are necessary and mutually reinforcing. In this review, Eastern and Western research perspectives are first presented, laying out bases for what could be the consequences of applying a reductionist versus holistic approach to research in nutrition vis-à-vis public health, environmental sustainability, breeding, biodiversity, food science and processing, and physiology for improving nutritional recommendations. Therefore, research that replaces reductionism with a more holistic approach will reveal global and efficient solutions to the problems encountered from the field to the plate. Preventive human nutrition can no longer be considered as "pharmacology" or foods as "drugs."

Immune status is more affected by age than by carotenoid depletion-repletion in healthy human subjects.

Prospective studies have indicated an age-related impairment of the immune response. Carotenoids have been hypothesised to enhance immune cell function. The aim of the present study was to describe the age-related effects and the impact of in vivo dietary carotenoid depletion and repletion on specific and non-specific immunity. A total of ninety-eight healthy male subjects (aged 20-75 years) received a carotenoid-depleted diet for 3 weeks and were then supplemented daily for 5 weeks with 30 mg ß-carotene, 15 mg lycopene and 9 mg lutein. Blood samples were collected at study entry, after depletion and supplementation, and biomarkers of immune status were determined. We found that serum IgA levels were positively correlated with ageing. Lymphocyte phenotyping indicated an increase with age in the memory T-helper cell subpopulation (CD4⁺CD45RO⁺) concomitantly with a decrease in naive T-helper cells (CD4⁺CD45RA⁺). A significant increase in the natural killer cells subpopulation and a small decrease in B lymphocytes were also observed, especially for the oldest volunteers. From ex vivo cell function exploration, a positive correlation was observed between age and IL-2 production of phytohaemagglutinin-stimulated lymphocytes. Neutrophils' bactericidal activity was significantly impaired with age (from 50 years) and was modulated by carotenoid status. An age effect was found on neutrophils' spontaneous migration but not on directed migration. Immune response in healthy human subjects is mostly affected by age rather than by dietary carotenoid depletion and repletion. Even in carefully selected healthy volunteers, some age-related immune changes occur predominantly from 50 years onwards. This immunosenescence could generate a loss in the immune system adjustment capacity.

Neutrophils are immune cells preferentially targeted by retinoic acid in elderly subjects.

BACKGROUND: The immune system gradually deteriorates with age and nutritional status is a major factor in immunosenescence. Of the many nutritional factors implicated in age-related immune dysfunction, vitamin A may be a good candidate, since vitamin A concentrations classically decrease during aging whereas it may possess important immunomodulatory properties via its active metabolites, the retinoic acids. This prompted us to investigate the immune response induced by retinoids in adults and elderly healthy subjects. Before and after oral supplementation with 13cis retinoic acid (0.5 mg/kg/day during 28 days), whole blood cells were phenotyped, and functions of peripheral blood mononuclear cells (PBMC) and polymorphonuclear cells (PMN) were investigated by flow cytometry and ELISA tests. RESULTS: In both young adults (n = 20, 25 ± 4 years) and older subjects (n = 20, 65 ± 4 years), retinoic acid supplementation had no effect on the distribution of leukocyte subpopulations or on the functions of PBMC (Il-2 and sIl-2R production, membrane expression of CD25). Concerning PMN, retinoic acid induced an increase in both spontaneous migration and cell surface expression of CD11b in the two different age populations, whereas bactericidal activity and phagocytosis remained unchanged. CONCLUSIONS: We demonstrated that retinoic acid induces the same intensity of immune response between adult and older subjects, and more specifically affects PMN functions, i.e. adhesion and migration, than PBMC functions.

Differential effects of lycopene consumed in tomato paste and lycopene in the form of a purified extract on target genes of cancer prostatic cells.

BACKGROUND: Prospective studies indicate that tomato consumers are protected against prostate cancer. Lycopene has been hypothesized to be responsible for tomato health benefits. OBJECTIVE: Our aim was to differentiate the effects of tomato matrix from those of lycopene by using lycopene-rich red tomatoes, lycopene-free yellow tomatoes, and purified lycopene. DESIGN: Thirty healthy men (aged 50-70 y old) were randomly assigned to 2 groups after a 2-wk washout period. In a crossover design, each group consumed yellow and red tomato paste (200 g/d, which provided 0 and 16 mg lycopene, respectively) as part of their regular diet for 1 wk separated by 2 wk of washout. Then, in a parallel design, the first group underwent supplementation with purified lycopene (16 mg/d) for 1 wk, whereas the second group received a placebo. Sera collected before and after the interventions were incubated with lymph node cancer prostate cells to measure the expression of 45 target genes. RESULTS: Circulating lycopene concentration increased only after consumption of red tomato paste and purified lycopene. Lipid profile, antioxidant status, prostate-specific antigen, and insulin-like growth factor I were not modified by consumption of tomato pastes and lycopene. We observed significant up-regulation of IGFBP-3 and Bax:Bcl-2 ratio and down-regulation of cyclin-D1, p53, and Nrf-2 after cell incubation with sera from men who consumed red tomato paste when compared with sera collected after the first washout period, with intermediate values for yellow tomato paste consumption. Cell incubation with sera from men who consumed purified lycopene led to significant up-regulation of IGFBP-3, c-fos, and uPAR compared with sera collected after placebo consumption. CONCLUSION: Dietary lycopene can affect gene expression whether or not it is included in its food matrix. This trial was registered by the French Health Ministry at http://www.sante-sports.gouv.fr as 2006-A00396-45.

High-magnesium concentration and cytokine production in human whole blood model.

The potential influence of magnesium (Mg) on inflammatory responses was assessed using an ex vivo model--human whole blood incubated with and without lipopolysaccharide (LPS). Addition of LPS leads to higher levels of cytokines including TNF-alpha and IL-6. No significant effect of Mg was observed following LPS stimulation whereas high concentration of Mg inhibited the baseline level (without LPS) of TNF-alpha and IL-6 production. This observation contrasts with that of a previous one on Mg-deficient animals. Therefore, the weak efficiency of increasing Mg concentration in this study on the whole blood from healthy volunteers suggests that the efficiency of Mg supplementation on cytokine production induced by endotoxin challenge depends on Mg status.

Digestive stability of xanthophylls exceeds that of carotenes as studied in a dynamic in vitro gastrointestinal system.

Epidemiological studies have suggested that high consumption of tomato products is associated with a lower risk for chronic diseases. To exert their health effect, the phytochemicals of tomatoes have to be bioavailable and therefore it implies their stability through the digestion process. Here, we assessed the digestive stability of the red-pigmented lycopene and other carotenoids brought in nutritional quantity within different food matrixes, using the TNO gastrointestinal tract model (TIM). This multicompartmental dynamic system accurately reproduces the main parameters of gastric and small intestinal digestion in human. In vitro digestions of a standard meal containing red tomato (RT), yellow tomato (devoid of lycopene), or lycopene beadlets were performed. Zeaxanthin and lutein were stable throughout artificial digestions, whereas beta-carotene and all-trans lycopene were degraded (approximately 30 and 20% loss at the end of digestion, respectively) in the jejunal and ileal compartments. The recovery of beta-carotene in the digesta of the RT meal was significantly lower than that in the yellow one, showing a food matrix effect. In the same way, until 180 min of digestion, the recovery percentages of all-trans lycopene from RT were significantly lower than those issued from the supplement. Isomeric conformation also influenced the stability of carotenoids, 5-cis lycopene being the most stable isomer followed by all-trans and 9-cis. No trans-cis isomerization of lycopene occurred in the TIM. By using a relevant dynamic in vitro system, this study allowed us to gain further insight into the parameters influencing the digestive stability of carotenoids, and therefore their bioavailability, in humans.

Wheat germ supplementation of a low vitamin E diet in rats affords effective antioxidant protection in tissues.

BACKGROUND: Oxidative stress is implicated in the etiology of many diseases, but most of clinical trials failed to demonstrate beneficial effects of antioxidant supplementation. METHODS: In the present experiment, we assessed the mean-term effect of wheat germ supplementation, as a dietary source of vitamin E, on antioxidant protection in rat. RESULTS: Feeding rats a 20% wheat germ diet significantly increased plasma and liver vitamin E levels, compared to the low vitamin E basal diet. Concurrently, wheat germ diet consumption strongly decreased the susceptibility of heart and liver lipids to oxidation, as well as the plasma. Wheat germ feeding did not change triglycerides (TG) nor total cholesterol concentrations in plasma or liver, resulting in higher vitamin E/TG ratio compared to controls. Similar results were found with a diet in which wheat germ oil provided the same amount of vitamin E. CONCLUSIONS: Wheat germ appears thus very effective to improve antioxidant defense status, especially in tissues, irrespective of modifications of lipids status.

Inulin supplementation prevents high fructose diet-induced hypertension in rats.

BACKGROUND & AIMS: The aim of this experiment was to evaluate the potential beneficial effect of supplementation with different inulin-type fructan fractions against common features of the metabolic syndrome in a rat model of this syndrome (fructose-fed rat). METHODS: Forty Wistar rats were randomly divided into five groups and the animals received for 4 weeks either a semi-purified starch or fructose-based diet, or diets in which fructose was partially substituted with various fructans: 10 g/100 g of long-chain inulin or oligofructose, or an oligofructose-enriched inulin. After this period, blood pressure was measured and samples of blood and tissues were collected for selected biochemical analyses. RESULTS: As compared to the starch-fed group, the fructose-fed rats presented: hypertriglyceridemia, hypertension, increased susceptibility to heart peroxidation and renal damages. Long-chain inulin and oligofructose-enriched inulin supplementation prevented fructose induced elevated blood pressure, susceptibility to heart peroxidation and renal damages. All inulin-type fructans containing diets prevented fructose induced hypertriglyceridemia. CONCLUSIONS: These results suggest that supplementation with inulin-type fructans is efficient against fructose induced hypertension and that effects are most pronounced for long-chain inulin and oligofructose-enriched inulin. We hypothesize that the anti-hypertensive effect of inulin could be explained by the reduction of the high fructose induced oxidative stress.

Serum from rats fed red or yellow tomatoes induces Connexin43 expression independently from lycopene in a prostate cancer cell line.

Epidemiologic studies suggested a protective effect of tomatoes against prostate cancer brought by lycopene, a carotenoid conferring the red colour of tomatoes. However, intervention studies on patients have shown that the preventive effect of tomato was more potent than that of lycopene. The aim of this study was to compare the effects of red tomato, yellow tomato (devoid of lycopene) and lycopene on Connexin43 (Cx43) expression, a protein regulating cell growth, on a prostate cancer cell line expressing the androgen receptor. Cells were incubated with serum from rats fed a control diet (CS) or control diet supplemented with red tomato (RTS), yellow tomato (YTS) or lycopene beadlets (LBS). After exposure of the cells to RTS or YTS for 48h, the expression of Cx43 was significantly increased compared to cells exposed to CS. Whereas LBS effect was not significantly different. The cells incubated with RTS and LBS had similar levels of lycopene, while those incubated with YTS contained no lycopene. These data first show that serum nutritionally enriched with red and yellow tomatoes could up-regulate Cx43 turn-over in PC3AR cells independently from lycopene level. Within the physiological approach used in the present study, it can be concluded that compounds other than lycopene contribute to the preventive effect of tomatoes.

Preferential response of glutathione-related enzymes to folate-dependent changes in the redox state of rat liver.

BACKGROUND: Oxidative stress likely constitutes an important contributing factor in the onset of degenerative diseases associated with folate deficiency. Direct, as well as homocysteine-linked, antioxidant properties of folate could explain its preventive effect on these pathologies. AIM OF THE STUDY: Our study aimed at determining the changes in the redox status of adult rats as a function of folate intake. METHODS: Adult male rats were pair-fed for 4 weeks with a semi-synthetic diet containing 0, 0.5, 1.5, 8 or 20 mg of folic acid/kg. Folate and homocysteine concentrations, redox status markers and antioxidant enzyme activities were measured in the plasma and/or liver of the rats. A principal component analysis of the overall data was performed to draw a general scheme of the changes observed between the conditions. RESULTS: Folate deficiency caused increased homocysteinemia and features of oxidative stress including reduced plasma antioxidant capacity together with increased lipid peroxidation in liver and heart. This was associated with an increase in the specific activity of several enzymes involved in liver glutathione metabolism (glutathione peroxidase, glutathione reductase and glutathione S-transferase), suggesting an adaptive tissue response to the oxidative stress induced by folate deficiency. In contrast, no such variation was observed for hepatic superoxide dismutase and catalase. CONCLUSION: Despite no changes in hepatic levels of total glutathione, our findings indicate that glutathione-dependent antioxidant pathways could be particularly involved in the compensatory mechanism committed by liver to counteract the oxidative stress induced by folate deficiency. They also suggest that folate supplementation may not be associated with a better antioxidant protection of rats.

In vivo antioxidant activity of procyanidin-rich extracts from grape seed and pine (Pinus maritima) bark in rats.

BACKGROUND: In vitro evidence exists for the potential antioxidant benefits of procyanidin-rich extracts, but in vivo studies are scarce. We have evaluated the effects of selected procyanidin-rich extracts on oxidative stress in rats in condition of prolonged consumption of these compounds and also after single administration i.e. in postprandial conditions. METHODS: Rats were fed for 8 weeks with diets supplemented with either a grape seed extract (GE), a pine bark extract (PE), or a high-degree polymerized pine bark extract (HPE). An additional study was performed in order to assess the postprandial effect of these extracts on plasma antioxidant capacity. The ferric-reducing antioxidant power (FRAP) and thiobarbituric acid-reactive substances (TBARS) were determined in plasma. For lipid peroxidation study of heart tissue, homogenates were prepared and TBARS were measured after lipid peroxidation induced by FeSO4-ascorbate. RESULTS: After 8 weeks of dietary treatment, total antioxidant capacity in plasma was significantly higher in the GE and PE groups as compared with the other two groups. Plasma TBARS concentrations and heart susceptibility to peroxidation were not significantly different between the groups. In the postprandial state, by comparing plasma antioxidant capacity 2 hours after ingestion of the different procyanidin-rich extracts (500 mg/kg body weight), we observed that FRAP values were higher in the procyanidin-rich extracts groups as compared with the control group. Moreover, plasma FRAP concentration was significantly higher in the GE group as compared with the other groups. CONCLUSION: The results of the present experiment constitute positive evidence for an in vivo antioxidant effect at the plasma level of procyanidin-containing plant extracts.

Entire potato consumption improves lipid metabolism and antioxidant status in cholesterol-fed rat.

BACKGROUND: Vegetables and fruits are rich sources of a variety of nutrients, including vitamins (E and C), trace minerals, and dietary fibers, and many other classes of biologically active compounds such as carotenoids and polyphenols, which are often assumed to protect against degenerative pathologies such as cardiovascular diseases. Although potato is considered as a starchy food, it is also included in the category of vegetables by its micronutrient content. AIM OF THE STUDY: In the present study, we investigated in the rat the effect of a potato-enriched diet on lipid metabolism and antioxidant protection. RESULTS: Feeding rats a potato-enriched diet for 3 weeks led to a significant decrease in cholesterol and triglyceride levels in plasma (respectively, -30%, P<0.0001 and -36%, P<0.05) and cholesterol level in liver (-42%, P<0.0001). Antioxidant status was also improved by potato consumption. TBARS levels in heart were decreased and vitamin E/triglycerides ratio in plasma was improved. CONCLUSIONS: Our present results suggest that consumption of cooked potatoes (consumed with skin) may enhance antioxidant defense and improve the lipid metabolism. These effects could be interesting for prevention of cardiovascular disease.

Proteomic analysis reveals changes in the liver protein pattern of rats exposed to dietary folate deficiency.

Epidemiologic and experimental studies showed that folate deficiency is associated with increased risk of degenerative diseases by enhancing abnormal one-carbon metabolism. We studied the changes in the proteome of liver, the main tissue of folate storage and metabolism, in a rat model of dietary folate depletion. Four-month-old rats were fed for 4 wk an amino acid-defined diet without folate and compared with pair-fed rats given the same diet adequately supplemented with folic acid. Folate deprivation decreased plasma and hepatic folate concentrations dramatically, while increasing homocysteinemia significantly. Using 2-dimensional electrophoresis and matrix-assisted laser desorption/ionization time-of-flight MS, we identified 9 spots corresponding to differentially expressed proteins in the liver of folate-deficient rats compared with controls. Among those spots, 4 had a significantly increased volume, whereas the volume of the 5 other spots was decreased. Upregulated proteins included glutathione peroxidase (GPx) 1 and peroxiredoxin 6, 2 enzymes involved in the response to oxidative stress, and MAWD binding protein (MAWDBP), which has been associated with cancer. MAWDBP was simultaneously identified as a second spot with a lower isoelectric point (pI) that vanished almost completely after folate deficiency. Decreased abundance was also observed for cofilin 1, a protein linked to tumorigenesis, and for the GRP 75 precursor and preproalbumin, both of which are responsive to oxidative stress and/or inflammation. Moreover, an enzyme activity assay and/or Western blot analysis of GPx-1 and MAWDBP confirmed the proteomic findings. Our results show that folate deficiency modifies the abundance of several liver proteins consistently with adaptive tissue responses to oxidative and degenerative processes.

Effect of copper supplementation on indices of copper status and certain CVD risk markers in young healthy women.

Western diets containing suboptimal Cu concentrations could be widespread. A link between marginal Cu deficiency and CVD has been suggested. The objective of the present study was to investigate the effect of Cu supplementation on both Cu status and CVD risk factors in healthy young women. Sixteen women with a mean age of 24 (sd 2) years participated in a randomised crossover study of three 4-week periods with 3-week washouts between periods. During each intervention period, subjects received 0, 3 or 6 mg elemental Cu/d as CuSO4 in addition to their habitual diet. Blood samples were taken to assess the effect of supplementation on putative markers of Cu status. The content of plasma lipids, lipoprotein (a), apo and certain haemostatic factors, as putative indices of CVD, was also analysed. Daily supplementation with 3 mg Cu significantly increased (P < 0.05) serum Cu concentration and the activity of erythrocyte superoxide dismutase, although there was no further significant increase after an intake of 6 mg Cu/d. The concentration of the fibrinolytic factor plasminogen activator inhibitor type 1 was significantly reduced (P < 0.05) by about 30 % after supplementation with 6 mg Cu/d. No other marker of Cu status or CVD risk factor was affected by Cu supplementation. The results indicate that supplementation with 3 or 6 mg Cu/d may improve Cu status in these healthy young women. Increased Cu intake could reduce the risk of CVD and atherosclerosis in man by promoting improved fibrinolytic capacity.

In vivo and in vitro evidences that carotenoids could modulate the neutrophil respiratory burst during dietary manipulation.

BACKGROUND: The primary role of polymorphonuclear neutrophils (PMNs) is to destroy pathogenic microorganisms after phagocytosis by producing reactive oxygen species (ROS) and toxic molecules. However, PMNs produce sufficient amounts of ROS during an oxidative burst to be autotoxic and detrimental to their own functions and to possibly cause DNA damage, protein and lipid oxidation and cell membrane destructuration. OBJECTIVE: The aim of this study was to investigate in vivo the role of the antioxidant capacities of carotenoids in modulating ROS content in PMNs during oxidative burst. Moreover to investigate the direct or indirect effect of carotenoids, the modification of PMN ROS content was explored after in vitro supplementation with beta-carotene or lycopene, chosen taking account of their vitamin A and no vitamin A precursor effect, respectively. DESIGN: In vivo study: Venous blood was collected from 10 healthy male volunteers and ROS production from phorbol myristate acetate (PMA)-stimulated PMNs was determined, by flow cytometry using the fluorescent dye dihydrorhodamine 123, at baseline, after 3 weeks of carotenoid depletion (carotenoid intake limited to 25% of usual intake) and after 5 weeks of carotenoid repletion (30 mg beta-carotene, 15 mg lycopene and 9 mg lutein per day). In vitro study: ROS content in PMA-stimulated PMNs isolated from carotenoid depleted subjects and controls was quantified after an in vitro enrichment with beta-carotene (1 micromol/L) or lycopene (0.3 micromol/L). RESULTS: In vivo carotenoid depletion increased PMN H2O2 content after PMA activation by 38% (p < 0.05 vs baseline),while supplementation for 5 weeks restored basal H2O2 generation (p < 0.05 vs depletion). Although H2O2 measurement in PMNs from non-depleted subjects was not affected by an in vitro supply with beta-carotene or lycopene, a significant decrease in H2O2 content by 78.9 % and 81.2%, respectively, was observed in PMNs from carotenoid depleted subjects (p < 0.01 vs depleted control subjects). CONCLUSIONS: The carotenoid ROS quenching capacities control both in vivo and in vitro the PMNs ROS generation and probably protect these cells against DNA, membrane lipid and protein damages during oxidative burst. Moreover, these effects appear independent from the metabolic conversion of carotenoids to vitamin A.