Bioaccessibility of carotenoids from Chlorella vulgaris and Chlamydomonas reinhardtii.

Microalgae can contribute to a balanced diet because of their composition. Beside numerous essential nutrients, carotenoids are in the focus for food applications. The bioavailability of carotenoids from photoautotrophic-cultivated Chlorella vulgaris (C. vulgaris) and Chlamydomonas reinhardtii (C. reinhardtii) was compared. An in vitro digestion model was used to investigate carotenoid bioaccessibility. Furthermore, the effect of sonication on bioaccessibility was assessed. Lutein was the main carotenoid in both species. C. reinhardtii showed higher amounts of lutein and ß-carotene than C. vulgaris. In contrast to C. reinhardtii, no ß-carotene and only 7% of lutein were bioaccessible in nonsonicated C. vulgaris. Sonication increased the bioaccessibility of carotenoids from C. vulgaris to a level comparable with C. reinhardtii (ß-carotene: ≥ 10%; lutein: ≥ 15%). Thus, C. reinhardtii represents a good carotenoid source for potential use in foods without processing, while the application of processing methods, like sonication, is necessary for C. vulgaris.

Effect of sonication on bioaccessibility and cellular uptake of carotenoids from preparations of photoautotrophic Phaeodactylum tricornutum.

With regard to its cost-effective cultivation and the composition of high-value nutrients, the diatom Phaeodactylum tricornutum (P. tricornutum) attracts interest for the use in human nutrition. Besides a number of important nutrients, it is rich in carotenoids. Therefore, this study aimed to investigate the potential of P. tricornutum as a carotenoid source for human nutrition. In photoautotrophically produced P. tricornutum biomass the carotenoid constitution, bioaccessibility (in vitro digestion model) and cellular uptake in differentiated Caco-2 cells (Transwell model system) was determined. Furthermore, the influence of sonication on these parameters was investigated. The results indicate that ß-carotene, zeaxanthin and fucoxanthin were the main carotenoids found in P. tricornutum. Moreover, these carotenoids showed a good bioaccessibility (ß-carotene: 25%, zeaxanthin: 27%, fucoxanthin: 57%), which is further improved by sonication for ß-carotene and fucoxanthin. In line with the good bioaccessibility, fucoxanthin was the most abundant carotenoid in Caco-2 cells followed by zeaxanthin. In contrast, ß-carotene could not be detected in the cells. The present study demonstrated that P. tricornutum represents a good source of carotenoids, particularly fucoxanthin. Thus, this diatom can contribute to the intake of bioaccessible carotenoids, even without processing. In addition, sonication might be a useful tool to improve the carotenoid bioaccessibility.

Photoautotrophically Grown Chlorella vulgaris Shows Genotoxic Potential but No Apoptotic Effect in Epithelial Cells.

This study investigated the effect of Chlorella vulgaris (C. vulgaris) on genotoxicity, cytotoxicity, and apoptosis in Caco-2 and HT-29 cells. C. vulgaris significantly induced DNA damage in both cell lines at a concentration of 200 µg dry matter/mL (comet tail intensity CTI: 24.6 ± 4.7% for Caco-2, 16.6 ± 0.9% for HT-29). The application of processing (sonication, ball-milling) did not affect the genotoxicity negatively and lowered the lipid peroxidation in C. vulgaris preparations. C. vulgaris-induced intracellular formation of reactive oxygen species in human cell lines and might be responsible for the genotoxic effect. A solid fraction mainly triggered the observed DNA damage (CTI: 41.5 ± 1.9%), whereas a hydrophilic (CTI: 7.9 ± 1.7%) and lipophilic (CTI: 10.2 ± 2.1%) fraction revealed a significantly lower tail intensity. C. vulgaris significantly induced DNA damage in both cell lines possibly through intracellular formation of reactive oxygen species; however, it was repaired after a 2 h recovery time or was even avoided at lower concentrations. In addition, none of the preparations indicated an adverse effect on cell proliferation or revealed apoptotic activity.

A Lipophilic Fucoxanthin-Rich Phaeodactylum tricornutum Extract Ameliorates Effects of Diet-Induced Obesity in C57BL/6J Mice.

Phaeodactylum tricornutum (P. tricornutum) comprise several lipophilic constituents with proposed anti-obesity and anti-diabetic properties. We investigated the effect of an ethanolic P. tricornutum extract (PTE) on energy metabolism in obesity-prone mice fed a high fat diet (HFD). Six- to eight-week-old male C57BL/6J mice were switched to HFD and, at the same time, received orally placebo or PTE (100 mg or 300 mg/kg body weight/day). Body weight, body composition, and food intake were monitored. After 26 days, blood and tissue samples were collected for biochemical, morphological, and gene expression analyses. PTE-supplemented mice accumulated fucoxanthin metabolites in adipose tissues and attained lower body weight gain, body fat content, weight of white adipose tissue (WAT) depots, and inguinal WAT adipocyte size than controls, independent of decreased food intake. PTE supplementation was associated with lower expression of Mest (a marker of fat tissue expandability) in WAT depots, lower gene expression related to lipid uptake and turnover in visceral WAT, increased expression of genes key to fatty acid oxidation and thermogenesis (Cpt1, Ucp1) in subcutaneous WAT, and signs of thermogenic activation including enhanced UCP1 protein in interscapular brown adipose tissue. In conclusion, these data show the potential of PTE to ameliorate HFD-induced obesity in vivo.

Nuclear trapping of inactive FOXO1 by the Nrf2 activator diethyl maleate.

Diethyl maleate (DEM), a thiol-reactive α,ß-unsaturated carbonyl compound, depletes glutathione (GSH) in exposed cells and was previously shown by us to elicit a stress response in Caenorhabditis elegans that, at lower concentrations, results in enhanced stress resistance and longer lifespan. This hormetic response was mediated through both the Nrf2 ortholog, SKN-1, and the forkhead box O (FOXO) family transcription factor DAF-16. As FOXO signaling is evolutionarily conserved, we analyzed here the effects of DEM exposure on FOXO in cultured human cells (HepG2, HEK293). DEM elicited nuclear accumulation of GFP-coupled wild-type human FOXO1, as well as of a cysteine-deficient FOXO1 mutant. Despite the nuclear accumulation of FOXO1, neither FOXO1 DNA binding nor FOXO target gene expression were stimulated, suggesting that DEM causes nuclear accumulation but not activation of FOXO1. FOXO1 nuclear exclusion elicited by insulin or xenobiotics such as arsenite or copper ions was attenuated by DEM, suggesting that DEM interfered with nuclear export. In addition, insulin-induced FOXO1 phosphorylation at Thr-24, which is associated with FOXO1 nuclear exclusion, was attenuated upon exposure to DEM. Different from FOXO-dependent expression of genes, Nrf2 target gene mRNAs were elevated upon exposure to DEM. These data suggest that, different from C. elegans, DEM elicits opposing effects on the two stress-responsive transcription factors, Nrf2 and FOXO1, in cultured human cells.

Bioavailability and Safety of Nutrients from the Microalgae Chlorella vulgaris, Nannochloropsis oceanica and Phaeodactylum tricornutum in C57BL/6 Mice.

Microalgae are rich in macronutrients and therefore, they have been proposed as a potential future food source preserving natural resources. Here, we studied safety and bioavailability of algae nutrients in mice. Three microalgae species, Chlorella vulgaris, Nannochloropsis oceanica and Phaeodactylum tricornutum, were studied after ball mill disruption at different doses (5%, 15% and 25% dry weight) for 14 days. In response to all three algae diets, we observed a weight gain similar or superior to that in response to the control diet. No substantial differences in organ weights nor gut length occurred. Protein bioavailability from the algae diets did not differ from the control diet ranging from 58% to 77% apparent biological value. Fat absorption was lower for microalgae compared to soy oil in control diets, albeit still substantial. High liver eicosapentaenoic acid levels were measured following feeding with N. oceanica, the algae richest in omega-3 fatty acids. Neither histological nor serum analyses revealed any heart, kidney or liver toxicity induced by any of the algae diets. Algae-rich diets were thus well accepted, well tolerated and suitable for the maintenance of body weight and normal organ function. No toxicological effects were observed.

Modulation of cellular thiol status affects FoxO activity and life span.

Diethyl maleate (DEM) is a thiol-depleting agent frequently employed in cell culture analyses. Here, we investigated the effect of DEM exposure on insulin signaling at the level of FoxO transcription factor activity and its potential consequences for stress resistance and life span. Exposure of HepG2 human hepatoma cells to subcytotoxic concentrations of DEM resulted in nuclear accumulation of overexpressed EGFP-tagged FoxO1a. DEM-induced nuclear accumulation overrode insulin-induced nuclear exclusion of FoxO1a. Despite a slightly enhanced FoxO DNA binding activity in DEM-exposed cells, expression of FoxO-regulated genes (glucose 6-phosphatase, selenoprotein P) was downregulated, indicating that nuclear accumulation does not necessarily coincide with enhanced transcription factor activity. To test for an effect of DEM on organismal stress resistance, we exposed C. elegans roundworms to the thiol depletor. Survival in the presence of the redox cycler paraquat was significantly increased following exposure to DEM, implying that DEM pre-exposure induced cellular resistance against oxidative stress. Furthermore, in DEM-exposed C. elegans populations expressing a GFP-tagged version of the C. elegans FoxO ortholog, DAF-16, numbers of worms with predominantly nuclear DAF-16 increased - in line with the findings from HepG2 cells. In keeping with the known function of DAF-16 in stress resistance, C. elegans life span was elevated upon exposure to DEM in a concentration-dependent manner. A maximum extension of life span and deceleration of aging was achieved at 100 µ? of DEM. In summary, exposure to DEM caused a modulation of FoxO subcellular localization in both HepG2 cells and C. elegans roundworms, followed by a modulation of life span and stress resistance in C. elegans.