Guangwen Tang

Guangwen Tang
Tufts University | Tufts

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108
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Publications (108)
Article
Provitamin A carotenoids in plant foods provide more than 80% of vitamin A intake for people in developing countries. Therefore, the conversion efficiency of β-carotene to vitamin A is important, as it determines the effectiveness of plant foods as sources of vitamin A in humans. The objective of this study was to determine the effect of plant food...
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Background: Worldwide, an estimated 250 million children <5 y old are vitamin A (VA) deficient. In Mexico, despite ongoing efforts to reduce VA deficiency, it remains an important public health problem; thus, food-based interventions that increase the availability and consumption of provitamin A–rich foods should be considered. Objective: The objec...
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Isoflurane is a volatile halogenated anesthetic used especially for anesthesia maintenance whereas propofol is a venous anesthetic utilized for anesthesia induction and maintenance, and reportedly an antioxidant. However, there are still controversies related to isoflurane-induced oxidative stress and it remains unanswered whether the antioxidant e...
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Humans need vitamin A and obtain essential vitamin A by conversion of plant foods rich in provitamin A and/or absorption of preformed vitamin A from foods of animal origin. The determination of the vitamin A value of plant foods rich in provitamin A is important but has challenges. The aim of this paper is to review the progress over last 80 years...
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The mechanism of doxorubicin (DOX)-induced cardiotoxicity remains controversial. Wistar rats (n = 66) received DOX injections intraperitoneally and were randomly assigned to 2 experimental protocols: (1) rats were killed before (-24 h, n = 8) and 24 h after (+24 h, n = 8) a single dose of DOX (4 mg/kg body weight) to determine the DOX acute effect...
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Vitamin A (VA) deficiency (VAD) continues to be a major nutritional problem in developing countries, including Central America. In Mexico, milk is a well-accepted vehicle for the administration of micronutrients, including VA, to preschoolers. Thus, we conducted a randomized, controlled, clinical trial to investigate the efficacy of daily consumpti...
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Spirulina is an alga rich in high-quality protein and carotenoids. It is unclear whether spirulina can improve the total-body vitamin A stores of school-age children in China with a high prevalence of vitamin A malnutrition. We aimed to evaluate the efficacy of spirulina in improving the total-body vitamin A stores of school-age children in rural a...
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Phytochemicals are reported to provide various biological functions leading to the promotion of health as well as the reduced risk of chronic diseases. Fat-soluble plant pigments, carotenoids, are extensively studied micronutrient phytochemicals for their potential health benefits. It is noteworthy that specific carotenoids may be responsible for d...
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Dietary β-carotene is the most important precursor of vitamin A. However, the determination of the efficiency of in vivo conversion of β-carotene to vitamin A requires sensitive and safe techniques. It presents the following challenges: 1) circulating β-carotene concentration cannot be altered by eating a meal containing ≤6 mg β-carotene; 2) becaus...
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Various retinoic acid (RA) isomers (all-trans, 13-cis, 11-cis, and 9-cis) as well as retinol, carotenoids, and tocopherol concentrations were determined in both serum and breast adipose tissue of 22 benign breast disease patients and 52 breast cancer patients categorized into 4 stages by malignancy. Serum RA isomers were analyzed by a newly develop...
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Golden Rice (GR) has been genetically engineered to be rich in β-carotene for use as a source of vitamin A. The objective was to compare the vitamin A value of β-carotene in GR and in spinach with that of pure β-carotene in oil when consumed by children. Children (n = 68; age 6-8 y) were randomly assigned to consume GR or spinach (both grown in a n...
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Oxidative damage and inflammation are related to the pathogenesis of age-related macular degeneration (AMD). Epidemiologic studies suggest that insufficient dietary lutein and zeaxanthin intake or lower serum zeaxanthin levels are associated with increased risk for AMD. The objective of this work is to test the protective effects of lutein and zeax...
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Zeaxanthin is a predominant xanthophyll in human eyes and may reduce the risk of cataracts and age-related macular degeneration. Spirulina is an algal food that contains a high concentration of zeaxanthin. In order to determine the zeaxanthin bioavailability of spirulina for dietary supplementation in humans, spirulina was grown in nutrient solutio...
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Spirulina, chlorella, and dunalliella are unicellular algae that are commercially produced worldwide. These algae are concentrated sources of carotenoids (especially provitamin A carotenoids) and other nutrients, such as vitamin B12. Their health benefits as a complementary dietary source for macro and micro nutrients have been studied and confirme...
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Mallow (Corchorus olitorius) is a green vegetable, which is widely consumed either fresh or dry by Middle East population. This study was carried out to determine the contents of major carotenoids quantitatively in mallow, by using a High Performance Liquid Chromatography (HPLC) equipped with a Bischoff C30 column. Neoxanthin and violaxanthin in ma...
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Many animals convert β-carotene to retinol to meet their vitamin A (VA) requirement. However, this pathway is inefficient in many carnivores. This study quantified the plasma response to a single oral dose of [(2) H(8)]-β-carotene in adult domestic cats, including measurement of [(2) H(4)]-retinol derived from the dose. Cats were fed with either a...
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The bioconversion efficiency of yellow maize β-carotene to retinol in humans is unknown. The objective of this study was to determine the vitamin A value of yellow maize β-carotene in humans. High β-carotene-containing yellow maize was grown in a hydroponic medium with 23 atom% (2)H(2)O during grain development. Yellow maize β-carotene showed the h...
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Recent progress in the measurement of the bioconversion of dietary provitamin A carotenoids to vitamin A is reviewed in this article. Methods to assess the bioavailability and bioconversion of provitamin A carotenoids have advanced significantly in the past 10 y, specifically through the use of stable isotope methodology, which includes the use of...
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OSA is associated with increased incidence of cardiovascular diseases. Pathogenic mechanisms of vascular diseases include thickened vascular walls due to the increased number of smooth muscle cells (SMC). Retinoic acid (RA) suppresses the growth of SMC, and reduced retinoid levels are associated with vascular diseases. Oxidant signalling promotes S...
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Genetically engineered "Golden Rice" contains up to 35 microg beta-carotene per gram of rice. It is important to determine the vitamin A equivalency of Golden Rice beta-carotene to project the potential effect of this biofortified grain in rice-consuming populations that commonly exhibit low vitamin A status. The objective was to determine the vita...
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Spirulina is a high-protein food supplement that contains carotenoids. The objective of the study was to determine the vitamin A equivalence of spirulina beta-carotene in humans. Spirulina was grown in a 23 atom% (2)H(2)O cultural solution. Spirulina beta-carotene showed the greatest enrichment as [(2)H(10)]trans beta-carotene. Ten healthy Chinese...
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Maize is an important staple food consumed by millions of people in many countries. Yellow maize naturally contains carotenoids which not only provide provitamin A carotenoids but also xanthophylls, which are known to be important for eye health. This study was aimed at 1) evaluating the effect of saponification during extraction of yellow maize ca...
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Vitamin A (VA) kinetics, storage, and disposal rate were determined in well-nourished Chinese and U.S. adults using model-based compartmental analysis. [(2)H(8)]Retinyl acetate (8.9 micromol) was orally administered to U.S. (n = 12; 59 +/- 9 y; mean +/- SD) and Chinese adults (n = 14; 54 +/- 4 y) and serum tracer and VA concentrations were measured...
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Concentrations of 9-cis beta-carotene (9-cis betaC) and zeta-carotene (zetaC) in biological samples may provide crucial information on the biological activities of these carotenoids. However, in high-performance liquid chromatography (HPLC) these carotenoids are often co-eluted. Therefore, there is an urgent need to develop a method for 9-cis betaC...
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The mechanism of doxorubicin-induced cardiotoxicity remains controversial. Wistar rats (n=96) were randomly assigned to a control (C), lycopene (L), doxorubicin (D), or doxorubicin+lycopene (DL) group. The L and DL groups received lycopene (5 mg/kg body wt/day by gavage) for 7 weeks. The D and DL groups received doxorubicin (4 mg/kg body wt intrape...
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Doxorubicin is an excellent chemotherapeutic agent utilized for several types of cancer but the irreversible doxorubicin-induced cardiac damage is the major limitation for its use. Oxidative stress seems to be associated with some phase of the toxicity mechanism process. To determine if lycopene protects against doxorubicin-induced cardiotoxicity,...
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The metabolism of vitamin A and the diverse effects of its metabolites are tightly controlled by distinct retinoid-generating enzymes, retinoid-binding proteins and retinoid-activated nuclear receptors. Retinoic acid regulates differentiation and metabolism by activating the retinoic acid receptor and retinoid X receptor (RXR), indirectly influenci...
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The antioxidant activities of fruits (n = 21), vegetables (n = 67) and legumes (n = 7) commonly consumed in Korea were determined by both the lipophilic antioxidant performance assay (LAP) and the hydrophilic oxygen radical absorbance capacity assay (ORAC). The LAP assay used the lipophilic radical initiator MeO-AMVN [2,2′-azobis(4-methoxy-2,4-dime...
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beta-Carotene and its metabolites exert a broad range of effects, in part by regulating transcriptional responses through specific nuclear receptor activation. Symmetric cleavage of beta-carotene can yield 9-cis retinoic acid (9-cisRA), the natural ligand for the nuclear receptor RXR, the obligate heterodimeric partner for numerous nuclear receptor...
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Plant products are dietary sources of lutein and zeaxanthin. Lutein and zeaxanthin have been implicated in the protection of age related macular degeneration (AMD) and in cardiovascular diseases. However, xanthophylls and unidentified components (λmax=423 and 468nm) in plant products are often not separated well, and affect an accurate quantitative...
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Vitamin A deficiency is a major global public health problem. Among the variety of techniques that are available for assessing human vitamin A status, evaluating the provitamin A nutritional values of foodstuffs and estimating human vitamin A requirements, isotope dilution provides the most accurate estimates. Although the relative expense of isoto...
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The vitamin A value of spinach and carrots needs to be measured directly. The objective was to determine the vitamin A value of intrinsically labeled dietary spinach and carrots in humans. Spinach and carrots were intrinsically labeled by growing these plants in 25 atom% 2H2O nutrient solution. Growth in this medium yielded a range of trans beta-ca...
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Current knowledge of the bioavailability of lycopene in humans is limited due to the inability to distinguish newly administered lycopene from the body reserves of lycopene. A quantitative method to assess the absorption and relative bioavailability of newly absorbed synthetic or natural lycopene was developed using two deuterated lycopene sources,...
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Retinoic acid has antimitogenic effects on smooth muscle cells. Studies on the systemic circulation suggest that it may reduce vascular thickening. Relationships between retinoids and pulmonary hypertension/pulmonary vascular remodeling, however, have not been explored. Thus, the present study examined retinoid levels in plasma of patients with idi...
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The structures of biosynthetic deuterated carotenoids in labeled vegetables were investigated: (all-E)-lutein and (all-E)-beta-carotene from spinach, and (all-E)-beta-carotene and (all-E)-alpha-carotene from carrots. The vegetables were grown hydroponically using a nutrient solution enriched with deuterium oxide (D(2)O) and were extracted using mat...
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Using the post-mitochondrial fraction of rat intestinal mucosa, we have investigated lycopene metabolism. The incubation media was composed of NAD+, KCI, and DTT with or without added lipoxygenase. The addition of lipoxygenase into the incubation significantly increased the production of lycopene metabolites. The enzymatic incubation products of 2H...
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Using the post-mitochondrial fraction of rat intestinal mucosa, we have investigated lycopene metabolism. The incubation media was composed of NAD+, KCI, and DTT with or without added lipoxygenase. The addition of lipoxygenase into the incubation significantly increased the production of lycopene metabolites. The enzymatic incubation products of 2H...
Article
Using the post-mitochondrial fraction of rat intestinal mucosa, we have investigated lycopene metabolism. The incubation media was composed of NAD(+), KCl, and DTT with or without added lipoxygenase. The addition of lipoxygenase into the incubation significantly increased the production of lycopene metabolites. The enzymatic incubation products of...
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The present study was carried out to determine the conversion factor of synthetic 2H-labelled β-carotene to vitamin A in Chinese adults by using a stable-isotope dilution technique. Fifteen healthy volunteers aged 50–60 years were recruited for a 55 d experiment. The volunteers (nine males and six females) were each given a physiological dose of [2...
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The present study was carried out to determine the conversion factor of synthetic (2)H-labelled beta-carotene to vitamin A in Chinese adults by using a stable-isotope dilution technique. Fifteen healthy volunteers aged 50-60 years were recruited for a 55 d experiment. The volunteers (nine males and six females) were each given a physiological dose...
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The aim of the investigation was to assess a stable isotope method for determining the relative bioavailability of food-derived lutein in humans. Subjects were administered a single dose of deuterium-labeled carotenoids from intrinsically labeled spinach or collard green; 10 mL blood samples were drawn at various time points over a 34 days period....
Article
Quantitative information on the conversion of beta-carotene to vitamin A in humans is limited. We determined the short- and long-term conversion of labeled beta-carotene to vitamin A by using a stable-isotope reference method. [(2)H(8)]beta-Carotene (11,011 nmol, or 6 mg) in oil was given with a liquid diet (25% of energy from fat) to 22 adult volu...
Article
Using the post-mitochondrial fraction of rat intestinal mucosa, we have investigated lycopene metabolism. The incubation media was composed of NAD+, KCl, and DTT with or without added lipoxygenase. The addition of lipoxygenase into the incubation significantly increased the production of lycopene metabolites. The enzymatic incubation products of 2H...
Article
beta-carotene (beta-C) is a major and safe vitamin A source for a vast population in China. But there is little understanding on beta-C-vitamin A equivalence in Chinese population. This study was designed to evaluate intestinal and whole-body conversion of beta-C to vitamin A in some Chinese adults by using a stable isotope dilution technique. Fift...
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After a dose of labeled vitamin A is given to humans for estimating body stores of vitamin A, blood is customarily drawn at pseudo-equilibration times ranging from 11 to 26 d. The objective was to determine whether a shorter sample collection interval (6 h or 3 d), which would be more realistic in field settings, can be used. Correlations of enrich...
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Method for production of deuterated -carotene for the bioavailability studies of vitamin A has been developed using Spirulina platensis in culture. Suspension cultures of Spirulina in heavy water (99.4% D2O) medium produced maximum biomass and -carotene in 28 to 30 days. Of the total carotenoids, lutein constituted 30 to 35% while -carotene was abo...
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It is important to understand the factors affecting strategies to improve the vitamin A status of populations. We reported previously that a 3-d deuterated-retinol-dilution (DRD) procedure might be used to indicate total body stores of vitamin A. We studied the ability of 3-d DRD to detect changes in the body pool size of vitamin A and the effect o...
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A study of seasonal fluctuation of serum vitamin A concentrations in children in northern China showed that the prevalence of low serum levels of vitamin A was due to seasonal changes in the intakes of carotenoids. To determine whether plant carotenoids could sustain or improve children's vitamin A status during the fall and winter seasons, we perf...
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To assay the effect of green and yellow vegetables on serum carotenoid concentration and its relation to serum retinol level in children. A ten-week green and yellow vegetable intervention study was conducted in children aged 5.3 to 6.4 years of two classes in a kindergarten in Tai'an City of Shandong Province in early September 1996, one class of...