Production of deuterated lutein by Chlorella protothecoides and its detection by mass spectrometric methods

Cultivation of the microalgae Chlamydomonas reinhardtii and Desmodesmus quadricauda in highly deuterated media: Balancing the light intensity

The production of organic deuterated compounds in microalgal systems represents a cheaper and more versatile alternative to more complicated chemical synthesis. In the present study, we investigate the autotrophic growth of two microalgae, Chlamydomonas reinhardtii and Desmodesmus quadricauda, in medium containing high doses of deuterated water, D₂O. The growth of such cultures was evaluated in the context of the intensity of incident light, since light is a critical factor in the management of autotrophic algal cultures. Deuteration increases the light sensitivity of both model organisms, resulting in increased levels of singlet oxygen and poorer photosynthetic performance. Our results also show a slowdown in growth and cell division processes with increasing D₂O concentrations. At the same time, impaired cell division leads to cell enlargement and accumulation of highly deuterated compounds, especially energy-storing molecules. Thus, considering the specifics of highly deuterated cultures and using the growth conditions proposed in this study, it is possible to obtain highly deuterated algal biomass, which could be a valuable source of deuterated organic compounds.

To Divide or Not to Divide? How Deuterium Affects Growth and Division of Chlamydomonas reinhardtii

Extensive in vivo replacement of hydrogen by deuterium, a stable isotope of hydrogen, induces a distinct stress response, reduces cell growth and impairs cell division in various organisms. Microalgae, including Chlamydomonas reinhardtii, a well-established model organism in cell cycle studies, are no exception. Chlamydomonas reinhardtii, a green unicellular alga of the Chlorophyceae class, divides by multiple fission, grows autotrophically and can be synchronized by alternating light/dark regimes; this makes it a model of first choice to discriminate the effect of deuterium on growth and/or division. Here, we investigate the effects of high doses of deuterium on cell cycle progression in C. reinhardtii. Synchronous cultures of C. reinhardtii were cultivated in growth medium containing 70 or 90% D2O. We characterize specific deuterium-induced shifts in attainment of commitment points during growth and/or division of C. reinhardtii, contradicting the role of the "sizer" in regulating the cell cycle. Consequently, impaired cell cycle progression in deuterated cultures causes (over)accumulation of starch and lipids, suggesting a promising potential for microalgae to produce deuterated organic compounds.

Stable isotope compounds - production, detection, and application

Stable isotopes are used in wide fields of application from natural tracers in biology, geology and archeology through studies of metabolic fluxes to their application as tracers in quantitative proteomics and structural biology. We review the use of stable isotopes of biogenic elements (H, C, N, O, S, Mg, Se) with the emphasis on hydrogen and its heavy isotope deuterium. We will discuss the limitations of enriching various compounds in stable isotopes when produced in living organisms. Finally, we overview methods for measuring stable isotopes, focusing on methods for detection in single cells in situ and their exploitation in modern biotechnologies.

Carrot solution culture bioproduction of uniformly labeled 13C-lutein and in vivo dosing in non-human primates

Lutein is a xanthophyll abundant in nature and most commonly present in the human diet through consumption of leafy green vegetables. With zeaxanthin and meso-zeaxanthin, lutein is a component of the macular pigment of the retina, where it protects against photooxidation and age-related macular degeneration. Recent studies have suggested that lutein may positively impact cognition throughout the lifespan, but outside of the retina, the deposition, metabolism, and function(s) of lutein are poorly understood. Using a novel botanical cell culture system ( Daucus carota), the present study aimed to produce a stable isotope lutein tracer for use in future investigations of dietary lutein distribution and metabolism. Carrot cultivars were initiated into liquid solution culture, lutein production conditions optimized, and uniformly labeled ¹³C-glucose was provided as the sole media carbon source for four serial growth cycles. Lutein yield was 2.58 ± 0.24 µg/g, and mass spectrometry confirmed high enrichment of ¹³C: 64.9% of lutein was uniformly labeled and 100% of lutein was labeled on at least 37 of 40 possible carbons. Purification of carrot extracts yielded a lutein dose of 1.92 mg with 96.0 ± 0.60% purity. ¹³C-lutein signals were detectable in hepatic extracts of an adult rhesus macaque monkey ( Macaca mulatta) dosed with ¹³C-lutein, but not in hepatic samples collected from control animals. This novel botanical biofactory approach can be used to produce sufficient quantities of highly enriched and pure ¹³C-lutein doses for use in tracer studies investigating lutein distribution, metabolism, and function.

Rational design of a culture medium for the intensification of lipid storage in Chlorella sp. Performance evaluation in air-lift bioreactor

An optimal medium to culture Chlorella sp., microalgae capable of storage intracellular lipids was obtained. This culture medium consists of a saline base plus carbon-energy and nitrogen sources. Significant factors exerting influence on the culture parameters were selected. Then, by applying response surface methodology coupled to desirability function, an optimal formulation, specific for the heterotrophic growth of Chlorella sp. that allows maximizing lipid concentration was obtained. During the experimental verification, the possibility of replacing commercial glucose by hydrolysates obtained from lignocellulosic materials was evaluated. Biochemical hydrolysate of corn bran allowed obtaining important improvements in lipid concentration. Finally, the optimal formulation was evaluated in an air-lift bioreactor performing a fed-batch culture. Culturing the strain in these conditions allowed rising lipid concentrations.

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.

Retinal carotenoids can attenuate formation of A2E in the retinal pigment epithelium

A2E, an important constituent of lipofuscin in human retinal pigment epithelium (RPE), is thought to mediate light-induced oxidative damage associated with aging and other ocular disorders. Ocular carotenoids in overlying retinal tissues were measured by HPLC and mass spectrometry and were correlated with levels of RPE A2E. We observed a statistically significant increase in total A2E levels in human RPE/choroid with age, and A2E levels in macular regions were approximately 1/3 lower than in peripheral retinal regions of the same size. There was a statistically significant inverse correlation between peripheral retina carotenoids and peripheral RPE/choroid A2E. Prospective carotenoid supplementation studies in Japanese quail demonstrated nearly complete inhibition of A2E formation and oxidation. These findings support current recommendations to increase dietary intake of xanthophyll carotenoids in individuals at risk for macular degeneration and highlight a new potential mechanism for their protective effects-inhibition of A2E formation and oxidation in the eye.

Identification and metabolic transformations of carotenoids in ocular tissues of the Japanese quail Coturnix japonica

As in humans and monkeys, lutein [(3R,3'R,6'R)-beta,epsilon-carotene-3,3'-diol] and zeaxanthin [a mixture of (3R,3'R)-beta,beta-carotene-3,3'diol and (3R,3'S-meso)-beta,beta-carotene-3,3'-diol] are found in substantial amounts in the retina of the Japanese quail Coturnix japonica. This makes the quail retina an excellent nonprimate small animal model for studying the metabolic transformations of these important macular carotenoids that are thought to play an integral role in protection against light-induced oxidative damage such as that found in age-related macular degeneration (AMD). In this study, we first identified the array of carotenoids present in the quail retina using C30 HPLC coupled with in-line mass spectral and photodiode array detectors. In addition to dietary lutein (2.1%) and zeaxanthin (11.8%), we identified adonirubin (5.4%), 3'-oxolutein (3.8%), meso-zeaxanthin (3.0%), astaxanthin (28.2%), galloxanthin (12.2%), epsilon,epsilon-carotene (18.5%), and beta-apo-2'-carotenol (9.5%) as major ocular carotenoids. We next used deuterium-labeled lutein and zeaxanthin as dietary supplements to study the pharmacokinetics and metabolic transformations of these two ocular pigments in serum and ocular tissues. We then detected and quantitated labeled carotenoids in ocular tissue using both HPLC-coupled mass spectrometry and noninvasive resonance Raman spectroscopy. Results indicated that dietary zeaxanthin is the precursor of 3'-oxolutein, beta-apo-2'-carotenol, adonirubin, astaxanthin, galloxanthin, and epsilon,epsilon-carotene, whereas dietary lutein is the precursor for meso-zeaxanthin. Studies also revealed that the pharmacokinetic patterns of uptake, carotenoid absorption, and transport from serum into ocular tissues were similar to results observed in most human clinical studies.