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.

Nutrition transition and chronic diseases in China (1990-2019): industrially processed and animal calories rather than nutrients and total calories as potential determinants of the health impact.

OBJECTIVE: To extend analyses of nutrition transition in developed countries to China within the framework of the 3Vs rule considering degree of processing starting with plant/animal calorie ratio (Rule 1), industrially processed foods (IPFs, Rule 2), and food diversity through nutrient intakes (Rule 3). DESIGN: Total and main food group (n 13) calorie intakes, percentages of animal and IPF calories, adequacy of the Dietary Reference Intake (DRI) and prevalence of chronic diseases were retrieved from scientific literature and international databases. SETTING: China, 1990­2019. PARTICIPANTS: Overall population. RESULTS: The total calorie intake decreased by 9 % over 30 years while the prevalence of chronic diseases substantially increased. Percentages of IPFs (Rule 1) and animal (Rule 2) calorie intake shifted from 9 to 30 % and 2 to 30 %, respectively. Meanwhile, the overall DRI adequacy (Rule 3) did not improve, with calcium and retinol deficiencies in 2019, and, although remaining above DRI, iron, copper, magnesium, and vitamins E, C and B1­B9 intakes regularly decreased. Notably, the prevalence of obesity increased five-fold, paralleling the exponential increase in IPF calorie intake. Both sources of calories were highly correlated with prevalence of main chronic diseases. CONCLUSIONS: Despite a slight decreased of total calorie consumption and small variations of adequacy with DRI, the farther the Chinese population moved away from the 3Vs rule during the 1990­2019 period, the more the prevalence of chronic diseases increased. Further analyses on foods' transitions will be better assessed when advocating sources/quality of calories (Rules 1/2), rather than only nutrient composition (Rule 3).

Precipitated sdLDL: An easy method to estimate LDL particle size.

BACKGROUND: LDL-C lowering is the main measure in cardiovascular disease prevention but a residual risk of ischemic events still remains. Alterations of lipoproteins, specially, increase in small dense LDL (sdLDL) particles are related to this risk. OBJECTIVE: To investigate the potential use of sdLDL cholesterol concentration (sdLDL-C) isolated by an easy precipitation method and to assess the impact of a set of clinical and biochemical variables determined by NMR on sdLDL concentration. METHODS: sdLDL-C and NMR lipid profile were performed in 85 men samples. Association among them was evaluated using Pearson coefficients (rxy ). A multivariate regression was performed to identify the influence of NMR variables on sdLDL-C. RESULTS: A strong association between sdLDL-C and LDLLDL-P (rxy  = 0.687) and with LDL-Z (rxy  = -0.603) was found. The multivariate regression explained a 56.8% in sdLDL-C variation (P = 8.77.10-12). BMI, ApoB, triglycerides, FFA, and LDL-Z showed a significant contribution. The most important ones were ApoB and LDL-Z; a 1nm increase (LDL-Z) leads to decrease 126 nmol/L in sdLDL-C. CONCLUSION: The association between sdLDL-C, LDL-Z, and LDL-P is clear. From a large number of variables, especially LDL-Z and apoB influence on sdLDL-C. Results show that the smaller the LDL size, the higher their cholesterol concentration. Therefore, sdLDL-C determination by using this easy method would be useful to risk stratification and to uncover cardiovascular residual risk.

In vitro and in vivo antioxidant potential of milks, yoghurts, fermented milks and cheeses: a narrative review of evidence.

The antioxidant potential (AP) is an important nutritional property of foods, as increased oxidative stress is involved in most diet-related chronic diseases. In dairy products, the protein fraction contains antioxidant activity, especially casein. Other antioxidants include: antioxidant enzymes; lactoferrin; conjugated linoleic acid; coenzyme Q10; vitamins C, E, A and D3; equol; uric acid; carotenoids; and mineral activators of antioxidant enzymes. The AP of dairy products has been extensively studied in vitro, with few studies in animals and human subjects. Available in vivo studies greatly differ in their design and objectives. Overall, on a 100 g fresh weight-basis, AP of dairy products is close to that of grain-based foods and vegetable or fruit juices. Among dairy products, cheeses present the highest AP due to their higher protein content. AP of milk increases during digestion by up to 2·5 times because of released antioxidant peptides. AP of casein is linked to specific amino acids, whereas ß-lactoglobulin thiol groups play a major role in the AP of whey. Thermal treatments such as ultra-high temperature processing have no clear effect on the AP of milk. Raw fat-rich milks have higher AP than less fat-rich milk, because of lipophilic antioxidants. Probiotic yoghurts and fermented milks have higher AP than conventional yoghurt and milk because proteolysis by probiotics releases antioxidant peptides. Among the probiotics, Lactobacillus casei/acidophilus leads to the highest AP. The data are insufficient for cheese, but fermentation-based changes appear to make a positive impact on AP. In conclusion, AP might participate in the reported dairy product-protective effects against some chronic diseases.

Liposcale: a novel advanced lipoprotein test based on 2D diffusion-ordered 1H NMR spectroscopy.

Determination of lipoprotein particle size and number using advanced lipoprotein tests (ALTs) is of particular importance to improve cardiovascular risk prediction. Here we present the Liposcale test, a novel ALT based on 2D diffusion-ordered (1)H NMR spectroscopy. Our method uses diffusion coefficients to provide a direct measure of the mean particle sizes and numbers. Using 177 plasma samples from healthy individuals and the concentration of ApoB and ApoA from isolated lipoprotein fractions, our test showed a stronger correlation between the NMR-derived lipoprotein particle numbers and apolipoprotein concentrations than the LipoProfile(®) test commercialized by Liposcience. We also converted LDL particle numbers to ApoB equivalents (milligrams per deciliter) and our test yielded similar values of LDL-ApoB to the LipoProfile(®) test (absolute mean bias of 8.5 and 7.4 mg/dl, respectively). In addition, our HDL particle number values were more concordant with the calibrated values determined recently using ion mobility. Finally, principal component analysis distinguished type 2 diabetic patients with and without atherogenic dyslipidemia (AD) on a second cohort of 307 subjects characterized using the Liposcale test (area under the curve = 0.88) and showed concordant relationships between variables explaining AD. Altogether, our method provides reproducible and reliable characterization of lipoprotein particles and it is applicable to pathological states such as AD.

Does aging affect the immune status? A comparative analysis in 300 healthy volunteers from France, Austria and Spain.

BACKGROUND: As the European population is getting older, there is growing need in scientific data on how to achieve healthy and successful aging. A decline in immune function with age is unanimously supported by many epidemiological and clinical observations, with a decrease in T-cell mediated function encompassing a large part of this alteration. In the EU-funded VITAGE project, the effects of aging on biomarkers of immune status are being studied in three European countries. According to strict inclusion/exclusion criteria, a cohort of 300 healthy male non-smoking 20-75 years old volunteers were enrolled in France (n = 99), Spain (n = 100) and Austria (n = 101). In each country, the volunteers were classified as a function of age (one age group per decade). Biomarkers of immune status were determined including delayed-type hypersensitivity tests, measurement of lymphocyte surface markers, and serum determinations of interleukin-2, complement fractions and immunoglobulins. RESULTS: There were moderate differences in the biomarkers of immune status of the VITAGE study volunteers among the three European centres. The percentage of Natural Killer (NK) cells was 156% and 142% higher in Spain as compared to France and Austria, respectively (p < 0.0001), and this increase was observed at any age group above 30 years. Comparison between age-groups showed that in Spain, but not in France or Austria, older individuals had significantly a lower B lymphocyte distribution and conversely, a higher NK cell distribution. Moreover, the CD4/CD8 ratio was positively correlated with age in Austrian subjects (p < 0.0001). CONCLUSION: Our results provide evidence of an increased NK cell distribution in the elderly, especially in the Spanish population. NK cell status may predict morbidity and mortality in the elderly, emphasizing the importance of innate as well as adaptive immunity in ensuring healthy longevity and cancer resistance, possibly in link with the Mediterranean diet.

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.

Statistical mediation of the relationships between chronological age and lipoproteins by nonessential amino acids in healthy men.

Aging is a major risk factor for metabolic impairment that may lead to age-related diseases such as cardiovascular disease. Different mechanisms that may explain the interplay between aging and lipoproteins, and between aging and low-molecular-weight metabolites (LMWMs), in the metabolic dysregulation associated with age-related diseases have been described separately. Here, we statistically evaluated the possible mediation effects of LMWMs on the relationships between chronological age and lipoprotein concentrations in healthy men ranging from 19 to 75 years of age. Relative and absolute concentrations of LMWMs and lipoproteins, respectively, were assessed by nuclear magnetic resonance (NMR) spectroscopy. Multivariate linear regression and mediation analysis were conducted to explore the associations between age, lipoproteins and LMWMs. The statistical significance of the identified mediation effects was evaluated using the bootstrapping technique, and the identified mediation effects were validated on a publicly available dataset. Chronological age was statistically associated with five lipoprotein classes and subclasses. The mediation analysis showed that serine mediated 24.1% (95% CI: 22.9 - 24.7) of the effect of age on LDL-P, and glutamate mediated 17.9% (95% CI: 17.6 - 18.5) of the effect of age on large LDL-P. In the publicly available data, glutamate mediated the relationship between age and an NMR-derived surrogate of cholesterol. Our results suggest that the age-related increase in LDL particles may be mediated by a decrease in the nonessential amino acid glutamate. Future studies may contribute to a better understanding of the potential biological role of glutamate and LDL particles in aging mechanisms and age-related diseases.

Antioxidant status of elite athletes remains impaired 2 weeks after a simulated altitude training camp.

BACKGROUND: It has been shown that the antioxidant status was altered by the "live high-train low" (LHTL) method, however, no information is available regarding the antioxidant restoration during the recovery period. AIM OF THE STUDY: We tested the hypothesis that the antioxidant status is impaired by 18 days LHTL in elite athletes and remained altered after 14 days of recovery. METHODS: Eleven elite cross-country skiers from the French Skiing Federation were submitted to 18-day endurance training. Six (hypoxic group; HG) trained at 1,200 m and lived in hypoxia (simulated altitude of 2,500 m-3,000 m-3,500 m) and 5 (control group; CG) trained and lived at 1,200 m. Plasma levels of advanced oxidation protein products (AOPP), malondialdehydes (MDA), ferric reducing antioxidant power (FRAP), trolox equivalent antioxidant capacity (TEAC) lipid-soluble antioxidants (alpha-tocopherol, beta-carotene and lycopene) were measured at rest, before (PRE), the first day after (POST1) and again 2 weeks (POST14) after the training. Intakes of vitamins A and E were evaluated from the dietary recording. RESULTS: In POST1, FRAP and TEAC decreased in both groups, however, the TEAC decrease persisted in POST14 for HG only. Lycopene and beta-carotene decreased in POST1 for HG and remained lower in POST14. Finally, AOPP increased only for HG in POST1. The general decline of antioxidant status for both groups might result from insufficient intakes in vitamins A and E. CONCLUSION: This is the first study to show that the antioxidant status did not return to baseline 2 weeks after 18 days of LHTL training.

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.

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.

Thirteen days of "live high-train low" does not affect prooxidant/antioxidant balance in elite swimmers.

We investigated the impact of 13 days of "living high-training low" (LHTL) on the antioxidant/prooxidant balance in elite endurance swimmers. Eighteen elite swimmers from the French Swimming Federation were submitted to a 13-day endurance training and divided into two groups: one group trained at 1,200 m and lived in hypoxia (2,500-3,000 m simulated altitude) and the second group trained and lived at 1,200 m. The subjects performed an acute hypoxic test (10 min at 4,800 m) before and 1 day after the training period. Plasma levels of advanced oxidation protein products (AOPP), malondialdehydes (MDA), ferric reducing antioxidant power (FRAP), and lipid-soluble antioxidants were measured before and after the 4,800 m tests. After the training, MDA and AOPP responses to the 4,800 m test were lower than before training for both groups (+10 vs. +2%; P = 0.01 for MDA and +80 vs. +14%; P = 0.01 for AOPP). Thirteen days of LHTL did not modify antioxidant status (FRAP and lipid-soluble antioxidants) despite intakes in vitamins A and E below the recommended daily allowances. The LHTL did not affect the antioxidant status in elite swimmers; however, the normoxic endurance training induced preconditioning mechanisms in response to the 4,800 m test.

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.

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.

Inflammation interferes with the assessment of vitamin A status in magnesium deficiency.

Hyporetinemia is observed in several pathological conditions including a primary deficiency of vitamin A and has also been reported to accompany inflammatory diseases. Experimental magnesium (Mg) deficiency in rodents is accompanied by an inflammatory syndrome. The present study was designed to determine whether the acute phase response in Mg-deficient rats can modify vitamin A status. Clinical symptoms of acute phase response were observed in Mg-deficient rats and were accompanied by a reduction in plasma retinol and of plasma retinol binding protein (RBP). Mg deficiency in rats resulted in hyporetinemia without a significant decrease in liver retinol reserves. Consequently, the data strongly suggest that the decrease in plasma retinol concentration, resulting from the level of its binding protein, is related to the inflammatory effect of Mg deficiency. These results point to the possible interference of Mg deficiency on the use of plasma retinol as an indicator of vitamin A status.

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.

Progesterone-associated arginine decline at luteal phase of menstrual cycle and associations with related amino acids and nuclear factor kB activation.

BACKGROUND/OBJECTIVES: Given their role in female reproduction, the effects of progesterone on arginine and related amino acids, polyamines and NF-κB p65 activation were studied across the menstrual cycle. METHODS: Arginine, ornithine and citrulline as well as putrescine, spermidine, spermine, and N-acetyl-putrescine were determined in plasma, NF-κB p65 activation in peripheral blood mononuclear cells and progesterone in serum of 28 women at early (T1) and late follicular (T2) and mid (T3) and late (T4) luteal phase. RESULTS: Arginine and related amino acids declined from T1 and T2 to T3 and T4, while progesterone increased. At T3, arginine, ornithine, and citrulline were inversely related with progesterone. Changes (ΔT3-T2) in arginine, ornithine, and citrulline were inversely related with changes (ΔT3-T2) in progesterone. Ornithine and citrulline were positively related with arginine, as were changes (ΔT3-T2) in ornithine and citrulline with changes (ΔT3-T2) in arginine. At T2, NF-κB p65 activation was positively related with arginine. Polyamines did not change and were not related to progesterone. All results described were significant at P < 0.001. CONCLUSIONS: This study for the first time provides data, at the plasma and PBMC level, supporting a proposed regulatory node of arginine and related amino acids, progesterone and NF-κB p65 at luteal phase of the menstrual cycle, aimed at successful preparation of pregnancy.

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.

Reference values for plasma concentrations of asymmetrical dimethylarginine (ADMA) and other arginine metabolites in men after validation of a chromatographic method.

BACKGROUND: Owing to the growing number of reports in the literature on ADMA as a possibly useful marker of endothelial health, its use in the clinical laboratory is of increasing interest. Age dependency and the small, but statistically significant differences between healthy subjects and disease groups are difficult to interpret. Additionally, levels of ADMA in comparable patient groups of different studies vary widely, even when similar methods have been used. METHODS: After analytical evaluation of a chromatographic method according to international guidelines, we analysed asymmetrical (ADMA) and symmetrical dimethyl arginine (SDMA), homo-arginine and arginine in EDTA plasma of 292 healthy males aged 20 to 75 years (y) who had passed strict inclusion/exclusion criteria. For statistical analysis, 4 age groups were formed. Group differences were identified with the non-parametric Kruskal-Wallis test. RESULTS: Calibration curves were linear throughout the selected ranges; the standard deviation for the regression line, recovery, imprecision, and accuracy results were all highly satisfactory. The reference ranges of ADMA for the 4 age groups are presented as age (mean+/-SD of age group, y); number of subjects; median, 2.5th-97.5th percentile: group <35 y: 26.7+/-4.0 y; n=78; 0.58, 0.43-0.69 micromol/L; group 35-49 y: 41.6+/-4.0 y; n=93; 0.59, 0.45-0.73 micromol/L; group 50-65 y: 57.5+/-4.2 y; n=82; 0.61, 0.46-0.78 micromol/L; and group >65 y: 69.6+/-3.3 y; n=39; 0.64, 0.54-0.79 micromol/L. CONCLUSIONS: Only highly precise methods are able to detect small differences between groups. The application of an evaluated method to a well defined group of healthy subjects should provide a basis for comparison of ADMA concentrations in different patient populations of future studies.