Bioavailability of synthetic and biosynthetic deuterated lycopene in humans

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, in conjunction with an advanced LC/APCI-MS (liquid chromatography/atmospheric pressure chemical ionization-mass spectrometry) to analyze newly absorbed lycopene in blood samples of study subjects. Two subjects (1 male and 1 female) consumed hydroponically grown tomatoes containing deuterium-enriched lycopene (80-84 g wet weight tomato containing 16.3 and 17.4 micromol lycopene, respectively) and two subjects (1 male, and 1 female) consumed 11 micromol synthetic (2)H(10) lycopene in 6 g of corn oil. Tomatoes were steamed and pureed. The doses were given together with a liquid formulated drink with 25% energy from fat. Our results showed that up to 34 days after taking an oral (2)H(10) lycopene dose (synthetic or from tomato) with a liquid formula drink, the area under the curve of the average serum percent enrichment response of synthetic lycopene reached 33.9 (+/-1.7) nmol-day/micromol lycopene in the dose, whereas that of lycopene from the tomato dose was 11.8 (+/-0.3) nmol-day/mumol lycopene in the dose. Our study provides evidence that the absorption of physiological levels of lycopene in intrinsically labeled tomatoes can be studied in humans. From these preliminary investigations, we find that the bioavailability of synthetic lycopene in oil appears to be about three times higher than that of lycopene from steamed and pureed tomatoes.     

Processing of vegetable-borne carotenoids in the human stomach and duodenum

Carotenoids are thought to diminish the incidence of certain degenerative diseases, but the mechanisms involved in their intestinal absorption are poorly understood. Our aim was to obtain basic data on the fate of carotenoids in the human stomach and duodenum. Ten healthy men were intragastrically fed three liquid test meals differing only in the vegetable added 3 wk apart and in a random order. They contained 40 g sunflower oil and mashed vegetables as the sole source of carotenoids. Tomato purée provided 10 mg lycopene as the main carotenoid, chopped spinach (10 mg lutein), and carrot purée (10 mg beta-carotene). Samples of stomach and duodenal contents and blood samples were collected at regular time intervals after meal intake. all-trans and cis carotenoids were assayed in stomach and duodenal contents, in the fat and aqueous phases of those contents, and in chylomicrons. The cis-trans beta-carotene and lycopene ratios did not significantly vary in the stomach during digestion. Carotenoids were recovered in the fat phase present in the stomach during digestion. The proportion of all-trans carotenoids found in the micellar phase of the duodenum was as follows (means +/- SE): lutein (5.6 +/- 0.4%), beta-carotene (4.7 +/- 0.3%), lycopene (2.0 +/- 0.2%). The proportion of 13-cis beta-carotene in the micellar phase was significantly higher (14.8 +/- 1.6%) than that of the all-trans isomer (4.7 +/- 0.3%). There was no significant variation in chylomicron lycopene after the tomato meal, whereas there was significant increase in chylomicron beta-carotene and lutein after the carrot and the spinach meals, respectively. There is no significant cis-trans isomerization of beta-carotene and lycopene in the human stomach. The stomach initiates the transfer of carotenoids from the vegetable matrix to the fat phase of the meal. Lycopene is less efficiently transferred to micelles than beta-carotene and lutein. The very small transfer of carotenoids from their vegetable matrices to micelles explains the poor bioavailability of these phytomicroconstituents.     

Irradiance levels affect growth parameters and carotenoid pigments in kale and spinach grown in a controlled environment

Carotenoids play critical roles in both light harvesting and energy dissipation for the protection of photosynthetic structures. However, limited research is available on the impact of irradiance on the production of secondary plant compounds, such as carotenoid pigments. Kale ( Brassica oleracea L.) and spinach ( Spinacia oleracea L.) are two leafy vegetables high in lutein and β-carotene carotenoids. The objectives of this study were to determine the effects of different irradiance levels on tissue biomass, elemental nutrient concentrations, and lutein β-carotene and chlorophyll (chl) pigment accumulation in the leaves of kale and spinach. 'Winterbor' kale and 'Melody' spinach were grown in nutrient solution culture in growth chambers at average irradiance levels of 125, 200, 335, 460, and 620 μmol m⁻² s⁻¹. Highest tissue lutein β-carotene and chls occurred at 335 μmol m⁻² s⁻¹ for kale, and 200 μmol m⁻² s⁻¹ for spinach. The accumulations of lutein and β-carotene were significantly different among irradiance levels for kale, but were not significantly different for spinach. However, lutein and β-carotene accumulation was significant for spinach when computed on a dry mass basis. Identifying effects of irradiance on carotenoid accumulation in kale and spinach is important information for growers producing these crops for dry capsule supplements and fresh markets.     

Plasma appearance of labeled beta-carotene, lutein, and retinol in humans after consumption of isotopically labeled kale

The bioavailability of carotenoids from kale was investigated by labeling nutrients in kale with 13C, feeding the kale to seven adult volunteers, and analyzing serial plasma samples for labeled lutein, beta-carotene, and retinol. Ingested doses of labeled carotenoids were 34 micromol for beta-carotene and 33 micromol for lutein. Peak plasma concentrations, areas under the plasma concentration-time curves (AUCs), and percentages of dose recovered at peak plasma concentrations were calculated. Average peak plasma concentrations were 0.38, 0.068, and 0.079 microM for [13C]lutein, [13C]beta-carotene, and [13C]retinol, respectively. Average AUC values (over 28 days) were 42.8, 13.6, 13.2 microM h for [13C]lutein, [13C]beta-carotene, and [13C]retinol, respectively. Percentages of dose recovered at peak plasma concentrations were 3.6, 0.7, and 0.7% for [13C]lutein, [13C]beta-carotene, and [13C]retinol, respectively. A positive relationship was observed between baseline plasma retinol levels and [13C]retinol plasma response. It is possible that this relationship was mediated either through some aspect of beta-carotene absorption or via the common pathways of metabolism for postdose and endogenous retinoid.     

Lutein bioavailability from lutein ester-fortified fermented milk: in vivo and in vitro study

We assessed the bioavailability of lutein from lutein-fortified fermented milk using in vivo and in vitro approaches. Twenty-four volunteers were randomized to take lutein-fortified fermented milk at two levels of fortification. Single-dose bioavailability study (2×100 ml, ca. 8 or 16 mg of lutein) was performed using a three-point approach (baseline, 3.5 and 6.5 h). Multiple-dose study consisted of consuming one serving/day (ca. 4 or 8 mg/100 ml) for 14 days. Blood samples for biochemical, hematological and lutein analysis were drawn at baseline, Day 7 and Day 14. In vitro bioaccessibility was assessed by a static gastrointestinal digestion model. Lutein content, in vitro ester hydrolysis and micellarization, and lutein concentrations achieved in serum were analyzed by HPLC. In vivo, post-prandial response was higher using the high content fermented milk, but the percentage of absorption was not different according to the dose consumed. Net increments at Day 7 and Day 14 were significantly higher on consuming the high-dose milk as well. In vitro, lutein ester hydrolysis was incomplete regardless of the amount initially present. Free lutein released was higher using the high-dose fermented milk, but the percentage of hydrolysis was similar at both levels of fortification. In the micellar phase, the percentage of free and total lutein was not different according to the dose. Our results support the suitability of the fermented milk as a carrier of lutein esters and an in vivo dose-dependent effect upon regular consumption and suggest the usefulness of in vitro models to provide relevant information to predict in vivo responses.     

Enhanced lutein bioavailability by lyso-phosphatidylcholine in rats

The bioavailability of lutein solubilized in mixed micelles containing either phosphatidylcholine (PC) or lysophosphatidylcholine (lysoPC) was evaluated in male rats. Mixed micelles contained 2.5 mM monooleoylglycerol, 7.5 mM oleic acid, 12 mM sodium taurocholate and 200 μM lutein either with 3 mM PC or lysoPC. To study lutein bioavailability, single and repeated dose experiments were conducted. For single dose study, group of rats (n = 30/group) were fed single dose of lutein solubilized in lysoPC (LPC group), PC (PC group) and no phospholipids (NoPL group) in micellar form. Each group was further divided in to five sub-groups (n = 6/sub group) to measure lutein bioavailability over time up to 9 h. For repeated dose study, group of rats (n = 6/group) were fed daily for 10 days a dose of lutein in mixed micelles with NoPL, PC and LPC. A separate group (n = 6) not fed mixed micelles was considered as zero-time control. In both the experiments, mixed micelles (0.2 ml/rat) were fed to the rat by direct intubation to the stomach. Results of single dose studies showed that the mean lutein levels in the plasma and liver of the PC group was significantly lower (p < 0.05) than those of the other two groups. Moreover, the average lutein level in the plasma and liver was significantly (p < 0.05) different among the groups in the order LPC > NoPL > PC. But, repeated dose experiment followed the order LPC > PC > NoPL. The level of lutein excreted through urine and feces of PC group was significantly higher (p < 0.05) than those of the other two groups. Thus, the results indicate that the PC in the mixed micelles suppressed the intestinal uptake of lutein after single dose but not after repeated dose and that lysoPC enhanced the absorption. In both the experiments, plasma and liver level of lutein was higher in LPC compared with PC group. Results also suggest that the luminal hydrolysis of PC to lysoPC is necessary for intestinal uptake of lutein solubilized in mixed micelles.     

Epimerisation of lutein to 3'-epilutein in processed foods

Lutein can convert to 3'-epilutein and anhydrolutein I in acidic medium as well as during different cooking methods. To our knowledge, this is the first demonstration of the epimerisation and dehydration of lutein in native samples. During different cooking processes the lutein content of the processed vegetables and fruits dramatically decreases, thus the bioavailability of processed plant food may also decrease. The occurrence of 3'-epilutein in processed food may be important regarding the application of synthetic lutein as food additive.     

Resonance Raman spectroscopy of carotenoids in Photosystem I particles

Low-temperature resonance Raman (RR) spectroscopy was used for the first time to study the spectral properties, binding sites and composition of major carotenoids in spinach Photosystem I (PSI) particles. Excitation was provided by an argon ion laser at 457.9, 476.5, 488, 496.5, 502 and 514.5 nm. Raman spectra contained the four known groups of bands characteristic for carotenoids (called from nu(1) to nu4). Upon 514.5, 496.5 and 476.5 nm excitations, the nu(1)-nu(3) frequencies coincided with those established for lutein. Spectrum upon 502-nm excitation could be assigned to originate from violaxanthin, at 488 nm to 9-cis neoxanthin, and at 457.9 nm to beta-carotene and 9-cis neoxanthin. The overall configuration and composition of these bound carotenoid molecules in Photosystem I particles were compared with the composition of pigment extracts from the same PSI particles dissolved in pyridine, as well as to configuration in the main chlorophyll a/b light-harvesting protein complex of photosystem II. The absorption transitions for lutein, violaxanthin and 9-cis neoxanthin in spinach photosystem I particles are characterized, and the binding sites of lutein and neoxanthin are discussed. Resonance Raman data suggest that beta-carotene molecules are also present in all-trans and, probably, in 9-cis configurations.     

Bioavailability of carotenoids and tocopherols from broccoli: in vivo and in vitro assessment

Fruits and vegetables are the major sources of biologically active compounds, and carotenoids and tocopherols constitute important groups in human diets. Bioavailability is a critical feature in the assessment of the role of micronutrients in human health, and the approaches to this issue include in vitro and in vivo methods. Our aim was to evaluate the bioavailability of carotenoids and tocopherols present in broccoli and to compare in vitro and in vivo approaches. Fourteen apparently healthy volunteers consumed 200 g broccoli once a day for seven days. Blood samples were drawn at baseline and after intervention to determine changes in lutein, beta-carotene, and alpha- and gamma-tocopherol as relevant phytochemicals provided with this vegetable. Broccoli also was subjected to simulated gastrointestinal digestion to assess changes related to preabsorptive processes. Analytes in serum and at each phase of the digestion were assayed by high-performance liquid chromatography. During the intervention, the amounts supplied daily ranged from 2.4 to 3.1 mg lutein, 1.4 to 1.8 mg beta-carotene, 4.5 to 6.8 mg alpha-tocopherol, and 0.8 to 1.8 mg gamma-tocopherol. Significant changes in serum in both men and women were observed only for lutein, whereas for gamma-tocopherol a significant change was detected in women. No changes were observed for alpha-tocopherol, beta-carotene, retinol, the alpha-tocopherol-to-cholesterol ratio, or serum lipids. Using the in vitro model, more than 75% of lutein, beta-carotene, gamma-tocopherol, and alpha-tocopherol remained at the duodenal phase, whereas incorporation into the supernatants accounted for <20% of the initial content in food. Regular consumption of broccoli at dietary levels increased serum concentrations of lutein and gamma-tocopherol without affecting alpha-tocopherol or beta-carotene status in serum. The behavior of these phytochemicals under in vitro gastrointestinal conditions does not fully explain the changes observed in vivo.     

Occurrence of thermotolerant campylobacters in fresh vegetables sold at farmers' outdoor markets and supermarkets.

A total of 1564 fresh samples of 10 vegetable types from two different retail levels (533 samples from farmers' outdoor markets and 1031 samples from supermarkets) were surveyed for the occurrence of thermotolerant campylobacters. In samples from the outdoor markets, campylobacters were detected on six types of vegetables; the detection rates were spinach, 3.3; lettuce, 3.1; radish, 2.7; green onions, 2.5; parsley, 2.4; and potatoes, 1.6%. Campylobacter jejuni was the predominant species (88%), with the remainder being C. lari (8%) and C. coli (4%). When the outdoor market samples were thoroughly washed with chlorinated water, all were negative for campylobacters. Of the samples from supermarkets, all were negative for campylobacters whether purchased in summer or winter. These results suggest that vegetables sold at farmers' outdoor markets are produced and (or) stored under less sanitary conditions than those sold at supermarkets, and they could constitute health hazards. Therefore, vegetables (e.g., potatoes and spinach) from farmers' markets must be decontaminated by washing with chlorinated water or cooked thoroughly before consumption.     

Supplementation with lutein or lutein plus green tea extracts does not change oxidative stress in adequately nourished older adults

Epigallocatechin gallate, a major component of green tea polyphenols, protects against the oxidation of fat-soluble antioxidants including lutein. The current study determined the effect of a relatively high but a dietary achievable dose of lutein or lutein plus green tea extract on antioxidant status. Healthy subjects (50–70 years) were randomly assigned to one of two groups (n=20 in each group): (1) a lutein (12 mg/day) supplemented group or (2) a lutein (12 mg/day) plus green tea extract (200 mg/day) supplemented group. After 2 weeks of run-in period consuming less than two servings of lightly colored fruits and vegetables in their diet, each group was treated for 112 days while on their customary regular diets. Plasma carotenoids including lutein, tocopherols, flavanols and ascorbic acid were analyzed by HPLC-UVD and HPLC-electrochemical detector systems; total antioxidant capacity by fluorometry; lipid peroxidation by malondialdehyde using a HPLC system with a fluorescent detector and by total hydroxyoctadecadienoic acids using a GC/MS. Plasma lutein, total carotenoids and ascorbic acid concentrations of subjects in either the lutein group or the lutein plus green tea extract group were significantly increased (P<.05) at 4 weeks and throughout the 16-week study period. However, no significant changes from baseline in any biomarker of overall antioxidant activity or lipid peroxidation of the subjects were seen in either group. Our results indicate that an increase of antioxidant concentrations within a range that could readily be achieved in a healthful diet does not affect in vivo antioxidant status in normal healthy subjects when sufficient amounts of antioxidants already exist.     

Tagging of biomolecules with deuterated water (D2O) in commercially important microalgae

To understand the effect of any biomolecules in specific metabolic pathways in humans, bioavailability and for other basic understanding, stable isotopically-labelled biomolecules (preferably deuterated) is the fundamental pre-requisite. Production of deuterated biomolecules such as, astaxanthin, β-carotene, lutein, chlorophyll-a, and eicosapentaenoic acid (EPA, 20:5n-3) by metabolic tagging have been shown in commercially important microalgae, Haematococcus pluvialis and Phaeodactylum tricornutum. These microalgae were grown in appropriate optimized medium supplemented with 25 % (v/v) deuterated water. LC–MS analysis showed a maximum of 20, 25, 23, 24, and 27 % replacement of hydrogen by deuterium atoms respectively in astaxanthin, β-carotene, lutein, chlorophyll-a, and EPA. To our knowledge, this is the first report on the production of deuterated astaxanthin, chlorophyll-a and EPA by these microalgae.     

Comparison of dietary supplementation with lutein diacetate and lutein: a pilot study of the effects on serum and macular pigment

The responses of subjects taking a 20 mg/day lutein diacetate supplement were compared with that for a 20 mg/day crystalline lutein or a placebo. Ten subjects, assigned to each of three groups, lutein diacetate (group 1), lutein (group 2), and a placebo (group 3), were supplemented for 24 weeks. Groups 1 and 2 consumed a dose equivalent to 20 mg per day of free lutein. Serum samples, collected at baseline, and at weeks 6, 12, 18, and 24 were analyzed by HPLC. Macular Pigment Optical Density (MPOD) was obtained by heterochromatic flicker photometry at baseline and weeks 6, 12, 18 and 24. Results: The average serum lutein concentrations for weeks 6 to 24 expressed as a ratio to the baseline value (±S.D.) were 5.52 ± 2.88 for group 1, 4.43 ± 1.61 for group 2, and 1.03 ± 0.25 for group 3. The median rate of macular pigment increase (milli-absorbance units/week) for groups 1, 2, and 3 were 2.35, 1.55, and 0.19 mAU/wk, respectively. P-values for these serum and MPOD increases are both highly significant when compared to placebo. The average serum response was about 25% higher for group 1 compared with group 2 and, the median MPOD response was 52% higher for group 1 than group 2. P-values calculated for the differences in these increases were, p = 0.066, marginally significant, for serum, and p = 0.09 approaching significance, for MPOD.     

Dose-dependent response of serum lutein and macular pigment optical density to supplementation with lutein esters

We conducted a study to determine the effect of different doses of a lutein supplement on serum lutein concentration and macular pigment optical density (MPOD). Lutein is one of the major components of human macular pigment. Eighty-seven subjects received daily doses of 5, 10, or 20 mg of lutein, or a placebo, over a 140 day period. Serum lutein concentration was determined by HPLC and MPOD by heterochromatic flicker photometry (HFP). Serum lutein responded positively, except in the placebo group, reaching a plateau that, averaged for each dosage group, was linearly dependent on dose. Likewise MPOD, on average, increased at a rate that varied linearly with dose. For subjects deemed more proficient at HFP, approximately 29% of the variability in MPOD response could be attributed to a linear dependence on the fractional change in serum lutein concentration. We did not detect any significant influence of age on serum lutein uptake or MPOD response.     

Lutein and cataract: from bench to bedside

Cataract is one of the most important leading causes of blindness in the world. Extensive research showed that oxidative stress may play an important role in the initiation and progression of a cataract and other age-related eye diseases. Extra-generation of reactive oxygen and nitrogen species in the eye tissue has been shown as one of the most important risk factors for cataracts and other age-related eye diseases. With respect to this, it can be hypothesized that dietary antioxidants may be useful in the prevention and/or mitigation of cataract. Lutein is an important xanthophyll which is widely found in different vegetables such as spinach, kale and carrots as well as some other foods such as eggs. Lutein is concentrated in the macula and suppresses the oxidative stress in the eye tissues. A plethora of literature has shown that increased lutein consumption has a close correlation with reduction in the incidence of cataract. Despite this general information, there is a negligible number of review articles considering the beneficial effects of lutein on cataracts and age-related eye diseases. The present review is aimed at discussing the role of oxidative stress in the initiation and progression of a cataract and the possible beneficial effects of lutein in maintaining retinal health and fighting cataract. We also provide a perspective on the chemistry, sources, bioavailability and safety of lutein.     

A Rare Dirhamnosyl Flavonoid and Other Radical-Scavenging Metabolites from Cynophalla mollis (Kunth) J. Presl and Colicodendron scabridum (Kunt) Seem. (Capparaceae) of Ecuador

The phytochemistry of Cynophalla mollis (Kunth) J. Presl and Colicodendron scabridum (Kunth), both belonging to the family Capparaceae, were investigated in this study for the first time. Lupeol, betulin, lutein, stachydrine and quercetin-3,4’-di-O-rhamnoside were isolated from C. mollis, whereas C. scabridum afforded lupeol, lutein, stachydrine, β-sitosterol, stigmasterol, betonicine and narcissoside. All these compounds were purified by preparative liquid chromatography, in both open column and instrumental (MPLC) separation systems. Preparative TLC was also applied. They were all identified by ¹H- and ¹³C-NMR experiments. The complete structure of the very rare flavonoid quercetin-3,4’-di-O-rhamnoside was fully elucidated through DEPT-135, COSY, HMQC and HMBC experiments, together with UV/VIS and FT-IR spectrophotometry. Complete NMR data for quercetin-3,4’-di-O-rhamnoside in deuterated methanol were presented here for the first time. All the extracts did not exert antioxidant activity at the maximum tested dose of 1 mg/mL. Three out of the nine isolated compounds exerted a good spectrum of antioxidant capacity, being narcissoside the most active against ABTS radicals, with SC₅₀=12.43 μM. It was followed by lutein and quercetin-3,4’-di-O-rhamnoside, with 40.92 μM and 46.10 μM, respectively.     

HPLC and GC/MS determination of deuterated vitamin K (phylloquinone) in human serum after ingestion of deuterium-labeled broccoli

The ability to intrinsically label plant constituents with stable isotopes has the potential to advance the study of vitamin K-absorption and metabolism in humans. Broccoli, a primary food source of phylloquinone (VK-1), was grown hydroponically using 31 atom % deuterium oxide in order to label VK-1 within the food matrix. Deuterium-labeled broccoli (115 g; 168 &mgr;g VK-1) was fed to one male subject in a single serving. Multiple serum samples were drawn throughout the subsequent 24-hr period. Reversed-phase HPLC was used to extract and purify VK-1 in both broccoli and serum. Ion abundances of the deuterium-labeled and unlabeled (endogenous) VK-1 were determined using GC/MS in negative chemical ionization mode. No sample derivatization was required. Endogenous VK-1 produced isotopomers from m/z 450 to m/z 453. The labeled VK-1 isotopomers in the broccoli were from m/z 452 to m/z 467, with the most abundant isotopomer being m/z 458 (14.1% of total labeled VK-1). The GC/MS chromatograms from serum revealed both endogenous VK-1 and VK-1 derived from the deuterium-labeled broccoli. The profile of labeled VK-1 isotopomers in serum was identical to the VK-1 isotopomer profile in labeled broccoli, indicating that no deuterium was lost due to exchange either in the body or in sample preparation. At 4 hr following broccoli intake, there was an 81.1% enrichment of phylloquinone in serum; labeled VK-1 was no longer detectable in serum at 24 hr. Use of isotope labeled vegetables enables one to discriminate exogenous intake of VK-1 from endogenous pools and ultimately to determine bioavailability of VK-1 from foods.     

Determination of imipramine in plasma by high pressure liquid chromatography and field ionization mass spectrometry: increased sensitivity in comparison with gas chromatography mass spectrometry

A quantitative method is reported for the determination of imipramine in plasma samples in the low nanogram and subnanogram range. The sensitivity and precision of the technique, which involves high pressure liquid chromatography and direct probe field ionization mass spectrometry, are approximately an order of magnitude greater than are offered by gas chromatography mass spectrometry with selected ion monitoring using deuterated or other types of internal standards. [2H6]Imipramine, labeled in the ethylene bridge and in the aromatic rings, serves as the isotopic diluent. The method has been used for the determination of the comparative bioavailabilities of two different commercial preparations of imipramine. In these tests, subjects ingested a 25 mg tablet of one or the other drug preparation together with a solution containing an equivalent amount of imipramine deuterated in the ethylene bridge ([2H2]imipramine). The latter served as an internal check for intrasubject variability in absorption of the imipramine tablets. Typical results from one of the subjects are presented.     

Calcium bioavailability and kinetics of calcium ascorbate and calcium acetate in rats

The objective was to investigate the bioavailability and mechanism of calcium absorption of calcium ascorbate (ASC) and calcium acetate (AC). A series of studies was performed in adult Sprague-Dawley male rats. In the first study, each group of rats (n = 10/group) was assigned to one of the five test meals labeled with (45)Ca: (i) 25 mg calcium as heated ASC or (ii) unheated ASC, (iii) 25 mg calcium as unheated AC, (iv) 3.6 mg Ca as unheated ASC, or (v) unheated AC. Femur uptake indicated better calcium bioavailability from ASC than AC at both calcium loads. A 5-min heat treatment partly reduced bioavailability of ASC. Kinetic studies were performed to further investigate the mechanism of superior calcium bioavailability from ASC. Two groups of rats (n = 10/group) received oral doses of 25 mg Ca as ASC or AC. Each dose contained 20 micro Ci (45)Ca. Two additional groups of rats (n = 10/group) received an intravenous injection (iv) of 10 micro Ci (45)Ca after receiving an unlabeled oral dose of 25 mg calcium as ASC or AC. Sequential blood samples were collected over 48 hrs. Urine and fecal samples were collected every 12 hrs for 48 hrs and were analyzed for total calcium and (45)Ca content. Total calcium and (45)Ca from serum, urine, and feces were fitted by a compartment kinetics model with saturable and nonsaturable absorption pathways by WinSAAM (Windows-based Simulation Analysis and Modeling). The difference in calcium bioavailability between the two salts was due to differences in saturable rather than passive intestinal absorption and not to endogenous secretion or calcium deposition rate. The higher bioavailability of calcium ascorbate was due to a longer transit time in the small intestine compared with ASC.     

A high sensitivity iron-dependent bioreporter used to measure iron bioavailability in freshwaters

A Nostoc sp. PCC 7120 iron bioreporter containing iron-regulated schizokinen transporter gene alr0397 promoter fused to the luxAB genes was examined to optimize its response to bioavailable iron. Dose-response relationships between luciferase activity and free ferric ion (Fe(3+) ) concentrations pFe (-lg [Fe(3+) ]) were generated by measuring luciferase activities of the bioreporter in trace metal-buffered Fraquil medium with various incubation times. The results were best demonstrated by sigmoidal curves (pFe 18.8-21.7, Fe(3+) =?10(-18.8) -10(-21.7) M) with the linear range extending from pFe 19.6-21.5 (Fe(3+) =?10(-19.6) -10(-21.5) M) after a 12-h incubation time. Optimal conditions for the use of this bioreporter to sense the iron bioavailability were determined to be: a 12-h exposure time, initial cell density of OD(730?nm) =?0.06, high nitrate (100?μM), high phosphate (10?μM), moderate Co(2+) (0.1-22.5?nM), Zn(2+) (0.16-12?nM), Cu(2+) (0.04-50?nM), and wide range of Mn(2+) concentration (0.92-2300?nM). The applicability of using this iron bioreporter to assess iron availability in the natural environment has been tested using water samples from eutrophic Taihu, Donghu, and Chaohu lakes. It is indicated that the bioreporter is a useful tool to assess bioavailable iron in various water quality samples, especially in eutrophic lakes with high bioavailable iron.