Analysis of retinoids and carotenoids: problems resolved and unsolved

Label-Free Assessment of Key Biological Autofluorophores: Material Characteristics and Opportunities for Clinical Applications

Autofluorophores are endogenous fluorescent compounds that naturally occur in the intra and extracellular spaces of all tissues and organs. Most have vital biological functions - like the metabolic cofactors NAD(P)H and FAD+, as well as the structural protein collagen. Others are considered to be waste products - like lipofuscin and advanced glycation end products - which accumulate with age and are associated with cellular dysfunction. Due to their natural fluorescence, these materials have great utility for enabling non-invasive, label-free assays with direct ties to biological function. Numerous technologies, with different advantages and drawbacks, are applied to their assessment, including fluorescence lifetime imaging microscopy, hyperspectral microscopy, and flow cytometry. Here, the applications of label-free autofluorophore assessment are reviewed for clinical and health-research applications, with specific attention to biomaterials, disease detection, surgical guidance, treatment monitoring, and tissue assessment - fields that greatly benefit from non-invasive methodologies capable of continuous, in vivo characterization.

A Scoping Review on Carotenoid Profiling in Passiflora spp.: A Vast Avenue for Expanding the Knowledge on the Species

The Passiflora genus is recognised for its ethnopharmacological, sensorial, and nutritional significance. Yet, the screening of its dietary and bioactive molecules has mainly targeted hydrophilic metabolites. Following the PRISMA-P protocol, this review assessed the current knowledge on carotenoid composition and analysis within Passiflora, examining 968 records from seven databases and including 17 studies focusing on carotenoid separation and identification in plant parts. Those publications originated in America and Asia. P. edulis was the most frequently examined species of a total of ten, while pulp was the most studied plant part (16 studies). Carotenoid analysis involved primarily high-performance liquid chromatography separation on C18 columns and detection using diode array detectors (64.71%). Most studies identified the provitamin A β-carotene and xanthophylls lutein and zeaxanthin, with their geometric configuration often neglected. Only one study described carotenoid esters. Besides the methodology's insufficient description, the lack of use of more accurate techniques and practices led to a high risk of bias in the carotenoid assignment in 17.65% of the articles. This review highlights the opportunity to broaden carotenoid studies to other species and parts within the diverse Passiflora genus, especially to wild, locally available fruits, which may have a strategic role in enhancing food diversity and security amidst climatic changes. Additionally, it urges the use of more accurate and efficient analytical methods based on green chemistry to better identify Passiflora carotenoids.

The quantum mechanics of skincare: A context for the biochemistry curriculum

Designing a relevant and engaging curriculum for biochemistry undergraduates can be challenging for topics which are at the periphery of the subject. We have used the framework of context-based learning as a means of assessing understanding of quantum theory in a group of students in their junior year. Our context, the role of retinol in skincare, provides a basis for the simple application of quantum mechanical principles to a biological context in an adaptation of the polyene in a box concept. As part of the learner journey, they gain experience of practical computational chemistry, which provided an in silico alternative to traditional laboratory work during the SARS-CoV-19 pandemic. Student feedback was overwhelmingly positive, and this approach is now firmly embedded in the undergraduate curriculum.

Fabrication, Physical-Chemical and Biological Characterization of Retinol-Loaded Poly(vinyl Alcohol) Electrospun Fiber Mats for Wound Healing Applications

Nowadays, there exists a huge interest in producing innovative, high-performance, biofunctional, and cost-efficient electrospun biomaterials based on the association of biocompatible polymers with bioactive molecules. Such materials are well-known to be promising candidates for three-dimensional biomimetic systems for wound healing applications because they can mimic the native skin microenvironment; however, many open questions such as the interaction mechanism between the skin and the wound dressing material remain unclear. Recently, several biomolecules were intended for use in combination with poly(vinyl alcohol) (PVA) fiber mats to improve their biological response; nevertheless, retinol, an important biomolecule, has not been combined yet with PVA to produce tailored and biofunctional fiber mats. Based on the abovementioned concept, the present work reported the fabrication of retinol-loaded PVA electrospun fiber mats (RPFM) with a variable content of retinol (0 ≤ Ret ≤ 25 wt.%), and their physical-chemical and biological characterization. SEM results showed that fiber mats exhibited diameters distribution ranging from 150 to 225 nm and their mechanical properties were affected with the increasing of retinol concentrations. In addition, fiber mats were able to release up to 87% of the retinol depending on both the time and the initial content of retinol. The cell culture results using primary mesenchymal stem cell cultures proved the biocompatibility of RPFM as confirmed by their effects on cytotoxicity (low level) and proliferation (high rate) in a dose-dependent manner. Moreover, the wound healing assay suggested that the optimal RPFM with retinol content of 6.25 wt.% (RPFM-1) enhanced the cell migratory activity without altering its morphology. Accordingly, it is demonstrated that the fabricated RPFM with retinol content below the threshold 0 ≤ Ret ≤ 6.25 wt.% would be an appropriate system for skin regenerative application.

Spectroscopy of Retinoic Acid at the Air-Water Interface

The spectroscopy of all-trans-retinoic acid (ATRA), an important molecule of biological origin that can be found in nature, is investigated at the air-water interface using UV-Vis and IR reflection spectroscopy. We employ a UV-Vis reflection absorption spectroscopy (RAS) experiment along with infrared reflection absorption spectroscopy (IR-RAS) to probe ATRA at the air-water interface. We elucidate the factors influencing the spectroscopy of ATRA at the air-water interface and compare its spectra at the water surface with results of bulk samples obtained with conventional spectroscopic methods and computational chemistry. Monolayers of pure ATRA as well as mixed ATRA with stearic-d₃₅ acid were prepared, and the spectroscopy reveals that ATRA forms J-aggregates with itself, causing a significant redshift of its S₀ to S₁ electronic transition. Pure ATRA monolayers are found to be unstable at the air-water interface and are lost from the surface over time due to the formation of aggregates. The mixture of ATRA and stearic-d₃₅ acid has been shown to stabilize the monolayers and inhibit the loss of surface ATRA. On the basis of our observations, we propose that ATRA could be a significant photosensitizer in natural aqueous environments.

Separation and Concentration of Astaxanthin and Lutein from Microalgae Liquid Extracts Using Magnetic Nanoparticles

The downstream processing of natural active molecules remains the most significant cost in the production pipeline. This considerable cost is largely attributed to rigorous chromatographic purification protocols. In an ongoing effort to abate the dependence on chromatography in downstream processing, alternative affinity matrices in the form of magnetic particles (e.g., iron oxide) have emerged as viable candidates. Nevertheless, biotechnological applications of iron oxide particles are still confined to the research level or for low-throughput clinical applications. Herein, we describe an efficient, quick, and environmentally friendly method for the isolation of astaxanthin and lutein, two carotenoids with very similar chemical structure, from extracts of the microalga Haematococcus pluvialis. The technology proposed, named Selective Magnetic Separation (SMS), is based on the use of magnetic materials carrying affinity ligands that bind carotenoids and is applied as second step of purification. The method, thanks to functionalized magnetic nanoparticles, reduces the use of organic or toxic solvents. In the present work, we examined the most efficient binding conditions such as temperature, magnetic nanoparticles concentration, and elution time, as well as their effects on carotenoids recovery, with the aim to improve the non-covalent binding between the ligand (amines) and astaxanthin/lutein. Our initial results clearly showed that it is possible to use magnetic separation as an alternative to chromatography to isolate important and valuable compounds.

HPLC-MS/MS Shows That the Cellular Uptake of All-Trans-Retinoic Acid under Hypoxia Is Downregulated by the Novel Active Agent 5-Methoxyleoligin

All-trans-retinoic acid (atRA) is the essential derivative of vitamin A and is of interest due to its various biological key functions. As shown in the recent literature, atRA also plays a role in the failing heart during myocardial infarction, the leading cause of death globally. To date insufficient mechanistic information has been available on related hypoxia-induced cell damage and reperfusion injuries. However, it has been demonstrated that a reduction in cellular atRA uptake abrogates hypoxia-mediated cell and tissue damage, which may offer a new route for intervention. Consequently, in this study, the effect of the novel cardio-protective compound 5-methoxyleoligin (5ML) on cellular atRA uptake was tested in human umbilical-vein endothelial cells (HUVECs). For this purpose, a high-performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS) method was developed to assess intra-cellular levels of the active substance and corresponding levels of vitamin A and its derivatives, including potential cis/trans isomers. This work also focused on light-induced isomerization and the stability of biological sample material to ensure sample integrity and avoid biased conclusions. This study provides evidence of the inhibitory effect of 5ML on cellular atRA uptake, a promising step toward a novel therapy for myocardial infarction.

Characterization of Retinol Stabilized in Phosphatidylcholine Vesicles with and without Antioxidants

Retinol stability has been reported to be improved by encapsulation in liposomes, both with and without cholesterol. However, this improvement is limited because of lipid peroxidation. In this study, we compare the stability of retinol in phosphatidylcholine liposomes under ultraviolet (UV) light or standard room air, with and without the addition of antioxidants. Both butylated hydroxytoluene (BHT) and a proprietary mix (StoppOx) improved the shelf stability from <10 to over 30 d. The addition of cholesterol had no effect. Fluorescence imaging showed a heterogeneous distribution of retinol within the vesicles, including within the aqueous layer. Fluorescence lifetimes were equally heterogeneous. Under UV irradiation, StoppOx protected retinol for significantly longer than BHT and via different mechanisms. This suggests that natural antioxidants work well to improve the retinol stability, but that further work to determine the optimal vesicle structure remains to be performed.

Retinol deficiency in animals: Etiopathogenesis and consequences

Infertility is widespread for all species of animals and causes significant economic losses to livestock due to the loss and shortage of offspring, their reduced viability and, consequently, increased morbidity and mortality. Alimentary-deficiency factors are among the commonest causes of infertility, from which A-vitamin deficiency should be singled out. The precursor of vitamin A in the body is carotene, which is an unstable compound which is easily destroyed even under the influence of moderate factors of influence, in connection with which its deficiency is global, especially at the end of the winter – stall period of keeping animals. Accordingly it is the leading etiological factor of retinol deficiency infertility. As a result, the body has two negatives that act in parallel: carotene / vitamin A deficiency adversely affects the organs, the constituent and major functional unit of which is the secretory epithelial cell, and the free radical oxides formed in high concentration are extremely effective in destroying the cells, weakening antioxidant protection. Vitamin A has a significant effect on the reproductive function of animals both directly and indirectly. It is necessary to ensure the structure and functioning of the epithelial tissues of the organs of regulation and performance of sexual function, and therefore the physiological development of the fetus and the course of pregnancy, parturition and postpartum period, ovo- and spermiogenesis, the manifestation of sexual reflexes. Instead, its deficiency underlies the etiology and pathogenesis of retinol deficiency infertility of animals, causing changes in individual indices of homeostasis and prooxidate-antioxidant system, morphostructure of the reproductive and endocrine organs, hormonal status, sperm quality and reproductive function. The consequence is the emergence and development of gynecological, andrological, mammological and perinatal (ante-, intra-, post- and neo-) pathologies. At the same time, the addition of carotene or retinol to the diets of animals or their oral administration in cases of deficiency of vitamin A prevents impaired reproductive function. The study of the features of the etiopathogenesis of retinol deficiency infertility of animals allows programs of complex diagnostics, therapy and prevention to be developed which provide determination of carotene and vitamin A content and replenishment of the organism in cases of their deficiency.

Retinol and α-tocopherol in pregnancy: Establishment of reference intervals and associations with CBC

Profound physiological changes during pregnancy may affect the requirement of retinol and tocopherol, which are essential micronutrients for the maintenance of maternal health and foetal development. However, the current reference intervals (RIs) of retinol and tocopherol are based on non‐pregnant population. In the present study, a liquid chromatography–tandem mass spectrometry quantitation method for serum retinol and α‐tocopherol was established and validated. In addition, we established trimester‐specific RIs of retinol and α‐tocopherol using the data from paired screening test for 31,301 outpatients who participated in the prenatal vitamins A/E evaluation program at our hospital using the Hoffmann method, which is a simple indirect RI estimation method that does not require the recruitment of healthy subjects. Further, to explore the associations between the levels of retinol and α‐tocopherol and the parameters of complete blood count (CBC), the results of retinol, α‐tocopherol, and CBC of 1,977 pregnant outpatients in the third trimester were analysed. The testing interval between the levels of vitamins and CBC was no more than 7 days. Although no significant changes were noticed in the levels of retinol, the α‐tocopherol levels continuously increased with normal physiological changes throughout pregnancy. Lower retinol levels were associated with the higher incidence of anaemia, whereas higher levels of retinol and lower levels of α‐tocopherol were associated with higher platelet count.

Vitamin A and Pregnancy: A Narrative Review

Vitamin A is a crucial micronutrient for pregnant women and their fetuses. In addition to being essential for morphological and functional development and for ocular integrity, vitamin A exerts systemic effects on several fetal organs and on the fetal skeleton. Vitamin A requirements during pregnancy are therefore greater. Vitamin A deficiency (VAD) remains the leading cause of preventable blindness in the world. VAD in pregnant women is a public health issue in most developing countries. In contrast, in some developed countries, excessive vitamin A intake during pregnancy can be a concern since, when in excess, this micronutrient may exert teratogenic effects in the first 60 days following conception. Routine prenatal vitamin A supplementation for the prevention of maternal and infant morbidity and mortality is not recommended; however, in regions where VAD is a public health issue, vitamin A supplementation is recommended to prevent night blindness. Given the importance of this topic and the lack of a complete, up-to-date review on vitamin A and pregnancy, an extensive review of the literature was conducted to identify conflicting or incomplete data on the topic as well as any gaps in existing data.

Potential therapeutic roles of retinoids for prevention of neuroinflammation and neurodegeneration in Alzheimer's disease

All retinoids, which can be natural and synthetic, are chemically related to vitamin A. Both natural and synthetic retinoids use specific nuclear receptors such as retinoic acid receptors and retinoid X receptors to activate specific signaling pathways in the cells. Retinoic acid signaling is extremely important in the central nervous system. Impairment of retinoic acid signaling pathways causes severe pathological processes in the central nervous system, especially in the adult brain. Retinoids have major roles in neural patterning, differentiation, axon outgrowth in normal development, and function of the brain. Impaired retinoic acid signaling results in neuroinflammation, oxidative stress, mitochondrial malfunction, and neurodegeneration leading to progressive Alzheimer's disease, which is pathologically characterized by extra-neuronal accumulation of amyloid plaques (aggregated amyloid-beta) and intra-neurofibrillary tangles (hyperphosphorylated tau protein) in the temporal lobe of the brain. Alzheimer's disease is the most common cause of dementia and loss of memory in old adults. Inactive cholinergic neurotransmission is responsible for cognitive deficits in Alzheimer's disease patients. Deficiency or deprivation of retinoic acid in mice is associated with loss of spatial learning and memory. Retinoids inhibit expression of chemokines and neuroinflammatory cytokines in microglia and astrocytes, which are activated in Alzheimer's disease. Stimulation of retinoic acid receptors and retinoid X receptors slows down accumulation of amyloids, reduces neurodegeneration, and thereby prevents pathogenesis of Alzheimer's disease in mice. In this review, we described chemistry and biochemistry of some natural and synthetic retinoids and potentials of retinoids for prevention of neuroinflammation and neurodegeneration in Alzheimer's disease.

Fluorescing fatty acids in rat fatty liver models

The autofluorescence (AF) of NAD(P)H and flavins has been at the basis of many in-situ studies of liver energy metabolism and functionality. Conversely, few data have been so far reported on fluorescing lipids. In this work we investigated the AF of liver lipid extracts from two fatty liver models, Wistar rats fed with MCD diet for 12 days (Wi-MCD), and obese (fa/fa) Zucker rats. Among the most abundant fatty acids in the lipid extracts, indicated by mass spectrometry, arachidonic acid (AA) exhibited higher quantum yield than the other fluorescing fatty acids (FLFA), and red shifted AF spectrum. This allowed to estimate the AA contribution to the overall emission of lipid extracts by curve fitting analysis. AA prevailed in obese Zucker livers, accounting for the different AF spectral profiles between the two models. AF and mass spectrometry indicated also a different balance between the fluorescing fraction and the overall amount of AA in the two models. The ability of AF to detect directly AA and FLFA was demonstrated, suggesting its supportive role as tool in wide-ranging applications, from the control of animal origin food, to experimental investigations on liver fat accumulation, lipotoxicity and disease progression, with potential translation to the clinics.

Molecular Signaling Mechanisms of Natural and Synthetic Retinoids for Inhibition of Pathogenesis in Alzheimer's Disease

Retinoids, which are vitamin A derivatives, interact through retinoic acid receptors (RARs) and retinoid X receptors (RXRs) and have profound effects on several physiological and pathological processes in the brain. The presence of retinoic acid signaling is extensively detected in the adult central nervous system, including the amygdala, cortex, hypothalamus, hippocampus, and other brain areas. Retinoids are primarily involved in neural patterning, differentiation, and axon outgrowth. Retinoids also play a key role in the preservation of the differentiated state of adult neurons. Impairment in retinoic acid signaling can result in neurodegeneration and progression of Alzheimer's disease (AD). Recent studies demonstrated severe deficiencies in spatial learning and memory in mice during retinoic acid (vitamin A) deprivation indicating its significance in preserving memory function. Defective cholinergic neurotransmission plays an important role in cognitive deficits in AD. All-trans retinoic acid is known to enhance the expression and activity of choline acetyltransferase in neuronal cell lines. Activation of RAR and RXR is also known to impede the pathogenesis of AD in mice by inhibiting accumulation of amyloids. In addition, retinoids have been shown to inhibit the expression of chemokines and pro-inflammatory cytokines in microglia and astrocytes, which are activated in AD. In this review article, we have described the chemistry and molecular signaling mechanisms of natural and synthetic retinoids and current understandings of their therapeutic potentials in prevention of AD pathology.

Characterization of carotenoids in soil bacteria and investigation of their photodegradation by UVA radiation via resonance Raman spectroscopy

A soil habitat consists of an enormous number of pigmented bacteria with the pigments mainly composed of diverse carotenoids. Most of the pigmented bacteria in the top layer of the soil are photoprotected from exposure to huge amounts of UVA radiation on a daily basis by these carotenoids. The photostability of these carotenoids depends heavily on the presence of specific features like a carbonyl group or an ionone ring system on its overall structure. Resonance Raman spectroscopy is one of the most sensitive and powerful techniques to detect and characterize these carotenoids and also monitor processes associated with them in their native system at a single cell resolution. However, most of the resonance Raman profiles of carotenoids have very minute differences, thereby making it extremely difficult to confirm if these differences are attributed to the presence of different carotenoids or if it is a consequence of their interaction with other cellular components. In this study, we devised a method to overcome this problem by monitoring also the photodegradation of the carotenoids in question by UVA radiation wherein a differential photodegradation response will confirm the presence of different carotenoids irrespective of the proximities in their resonance Raman profiles. Using this method, the detection and characterization of carotenoids in pure cultures of five species of pigmented coccoid soil bacteria is achieved. We also shed light on the influence of the structure of the carotenoid on its photodegradation which can be exploited for use in the characterization of carotenoids via resonance Raman spectroscopy.

Pathways of retinoid synthesis in mouse macrophages and bone marrow cells

In vivo pathways of natural retinoid metabolism and elimination have not been well characterized in primary myeloid cells, even though retinoids and retinoid receptors have been strongly implicated in regulating myeloid maturation. With the use of a upstream activation sequence-GFP reporter transgene and retrovirally expressed Gal4-retinoic acid receptor α in primary mouse bone marrow cells, we identified 2 distinct enzymatic pathways used by mouse myeloid cells ex vivo to synthesize retinoic acid receptor α ligands from free vitamin A metabolites (retinyl acetate, retinol, and retinal). Bulk Kit(+) bone marrow progenitor cells use diethylaminobenzaldehyde-sensitive enzymes, whereas bone marrow-derived macrophages use diethylaminobenzaldehyde-insensitive enzymes to synthesize natural retinoic acid receptor α-activating retinoids (all-trans retinoic acid). Bone marrow-derived macrophages do not express the diethylaminobenzaldehyde-sensitive enzymes Aldh1a1, Aldh1a2, or Aldh1a3 but instead, express Aldh3b1, which we found is capable of diethylaminobenzaldehyde-insensitive synthesis of all trans-retinoic acid. However, under steady-state and stimulated conditions in vivo, diverse bone marrow cells and peritoneal macrophages showed no evidence of intracellular retinoic acid receptor α-activating retinoids, despite expression of these enzymes and a vitamin A-sufficient diet, suggesting that the enzymatic conversion of retinal is not the rate-limiting step in the synthesis of intracellular retinoic acid receptor α-activating retinoids in myeloid bone marrow cells and that retinoic acid receptor α remains in an unliganded configuration during adult hematopoiesis.

Carotenoids and Retinoids: Nomenclature, Chemistry, and Analysis

Carotenoids are polyenes synthesized in plants and certain microorganisms and are pigments used by plants and animals in various physiological processes. Some of the over 600 known carotenoids are capable of metabolic conversion to the essential nutrient vitamin A (retinol) in higher animals. Vitamin A also gives rise to a number of other metabolites which, along with their analogs, are known as retinoids. To facilitate discussion about these important molecules, a nomenclature is required to identify specific substances. The generally accepted rules for naming these important molecules have been agreed to by various Commissions of the International Union of Pure and Applied Chemistry and International Union of Biochemistry. These naming conventions are explained along with comparisons to more systematic naming rules that apply for these organic chemicals. Identification of the carotenoids and retinoids has been advanced by their chemical syntheses, and here, both classical and modern methods for synthesis of these molecules, as well as their analogs, are described. Because of their importance in biological systems, sensitive methods for the detection and quantification of these compounds from various sources have been essential. Early analyses that relied on liquid adsorption and partition chromatography have given way to high-performance liquid chromatography (HPLC) coupled with various detection methods. The development of HPLC coupled to mass spectrometry, particularly LC/MS-MS with Multiple Reaction Monitoring, has resulted in the greatest sensitivity and specificity in these analyses.

A fast isocratic liquid chromatography method for the quantification of xanthophylls and their stereoisomers

A fast isocratic liquid chromatography method was developed for the simultaneous quantification of eight xanthophylls (13-Z-lutein, 13'-Z-lutein, 13-Z-zeaxanthin, all-E-lutein, all-E-zeaxanthin, all-E-canthaxanthin, all-E-β-apo-8'-carotenoic acid ethyl ester and all-E-β-apo-8'-carotenal) within 12 min, compared to 90 min by the conventional high-performance liquid chromatography method. The separation was achieved on a YMC C30 reversed-phase column (100 mm x 2.0 mm; 3 μm) operated at 20°C using a methanol/tert-butyl methyl ether/water solvent system at a flow rate of 0.8 mL/min. The method was successfully applied to quantify lutein and zeaxanthin stereoisomers in egg yolk, raw and cooked spinach, and a dietary supplement. The method can be used for the rapid analysis of xanthophyll isomers in different food products and for quality control purposes.

Retinoic acid signaling pathways in development and diseases

Retinoids comprise a group of compounds each composed of three basic parts: a trimethylated cyclohexene ring that is a bulky hydrophobic group, a conjugated tetraene side chain that functions as a linker unit, and a polar carbon-oxygen functional group. Biochemical conversion of carotenoid or other retinoids to retinoic acid (RA) is essential for normal regulation of a wide range of biological processes including development, differentiation, proliferation, and apoptosis. Retinoids regulate various physiological outputs by binding to nuclear receptors called retinoic acid receptors (RARs) and retinoid X receptors (RXRs), which themselves are DNA-binding transcriptional regulators. The functional response of RA and their receptors are modulated by a host of coactivators and corepressors. Retinoids are essential in the development and function of several organ systems; however, deregulated retinoid signaling can contribute to serious diseases. Several natural and synthetic retinoids are in clinical use or undergoing trials for treating specific diseases including cancer. In this review, we provide a broad overview on the importance of retinoids in development and various diseases, highlighting various retinoids in the drug discovery process, ranging all the way from retinoid chemistry to clinical uses and imaging.

Physiological and genomic consequences of adrenergic deficiency during embryonic/fetal development in mice: impact on retinoic acid metabolism

Adrenergic hormones are essential for early heart development. To gain insight into understanding how these hormones influence heart development, we evaluated genomic expression changes in embryonic hearts from adrenergic-deficient and wild-type control mice. To perform this study, we used a mouse model with targeted disruption of the Dopamine β-hydroxylase (Dbh) gene, whose product is responsible for enzymatic conversion of dopamine into norepinephrine. Embryos homozygous for the null allele (Dbh(-/-)) die from heart failure beginning as early as embryonic day 10.5 (E10.5). To assess underlying causes of heart failure, we isolated hearts from Dbh(-/-) and Dbh(+/+) embryos prior to manifestation of the phenotype and examined gene expression changes using genomic Affymetrix 430A 2.0 arrays, which enabled simultaneous evaluation of >22,000 genes. We found that only 22 expressed genes showed a significant twofold or greater change, representing ~0.1% of the total genes analyzed. More than half of these genes are associated with either metabolism (31%) or signal transduction (22%). Remarkably, several of the altered genes encode for proteins that are directly involved in retinoic acid (RA) biosynthesis and transport. Subsequent evaluation showed that RA concentrations were significantly elevated by an average of ~3-fold in adrenergic-deficient (Dbh(-/-)) embryos compared with controls, thereby suggesting that RA may be an important downstream mediator of adrenergic action during embryonic heart development.

Two-photon microscopy for non-invasive, quantitative monitoring of stem cell differentiation

Background

The engineering of functional tissues is a complex multi-stage process, the success of which depends on the careful control of culture conditions and ultimately tissue maturation. To enable the efficient optimization of tissue development protocols, techniques suitable for monitoring the effects of added stimuli and induced tissue changes are needed.

Methodology/Principal Findings

Here, we present the quantitative use of two-photon excited fluorescence (TPEF) and second harmonic generation (SHG) as a noninvasive means to monitor the differentiation of human mesenchymal stem cells (hMSCs) using entirely endogenous sources of contrast. We demonstrate that the individual fluorescence contribution from the intrinsic cellular fluorophores NAD(P)H, flavoproteins and lipofuscin can be extracted from TPEF images and monitored dynamically from the same cell population over time. Using the redox ratio, calculated from the contributions of NAD(P)H and flavoproteins, we identify distinct patterns in the evolution of the metabolic activity of hMSCs maintained in either propagation, osteogenic or adipogenic differentiation media. The differentiation of these cells is mirrored by changes in cell morphology apparent in high resolution TPEF images and by the detection of collagen production via SHG imaging. Finally, we find dramatic increases in lipofuscin levels in hMSCs maintained at 20% oxygen vs. those in 5% oxygen, establishing the use of this chromophore as a potential biomarker for oxidative stress.

Conclusions/Significance

In this study we demonstrate that it is possible to monitor the metabolic activity, morphology, ECM production and oxidative stress of hMSCs in a non-invasive manner. This is accomplished using generally available multiphoton microscopy equipment and simple data analysis techniques, such that the method can widely adopted by laboratories with a diversity of comparable equipment. This method therefore represents a powerful tool, which enables researchers to monitor engineered tissues and optimize culture conditions in a near real time manner.

The acute and chronic toxic effects of vitamin A

The acute and chronic effects of vitamin A toxicity are well documented in the literature. Emerging evidence suggests that subtoxicity without clinical signs of toxicity may be a growing concern, because intake from preformed sources of vitamin A often exceeds the recommended dietary allowances (RDA) for adults, especially in developed countries. Osteoporosis and hip fracture are associated with preformed vitamin A intakes that are only twice the current RDA. Assessing vitamin A status in persons with subtoxicity or toxicity is complicated because serum retinol concentrations are nonsensitive indicators in this range of liver vitamin A reserves. The metabolism in well-nourished persons of preformed vitamin A, provided by either liver or supplements, has been studied by several research groups. To control vitamin A deficiency, large therapeutic doses are administered in developing countries to women and children, who often are undernourished. Nevertheless, little attention has been given to the short-term kinetics (ie, after absorption but before storage) of a large dose of vitamin A or to the short- and long-term effects of such a dose given to lactating women on serum and breast-milk concentrations of retinol and its metabolites. Moreover, appropriate dosing regimens have not been systematically evaluated to ascertain the quantitative improvement in vitamin A status of the women and children who receive these supplements. The known acute and chronic effects of vitamin A toxicity have been reported previously. However, further research is needed to ascertain the areas of the world in which subclinical toxicity exists and to evaluate its effects on overall health and well-being.

Aging affects the retinoic acid and the triiodothyronine nuclear receptor mRNA expression in human peripheral blood mononuclear cells

BACKGROUND

Inadequate retinoid status has often been described as occurring with aging. Moreover, subclinical hypothyroid status has also been evoked in the elderly. Several studies performed in animals have described the crucial incidence of age-related hypo-functioning of retinoid and thyroid signalling pathways, particularly in the brain.

OBJECTIVE

The aim of the present study was to clarify whether aging modifies retinoid and thyroid signalling in humans.

METHODS

Using real-time RT-PCR the relative amount of mRNA of the retinoid (RARalpha, RARgamma and RXRalpha) and thyroid (TRalpha and TRbeta) nuclear receptors in peripheral blood mononuclear cells (PBMC) of young (24-57 years old, n = 22) compared with elderly (69-90 years old, n = 24) healthy subjects was quantitated. Classical plasma parameters used to characterize the retinoid and thyroid status - retinol (ROH), retinol-binding protein (RBP), free triiodothyronine (FT3) and thyroxine (FT4), thyroid-stimulating hormone (TSH) and transthyretin (TTR) - were also assessed.

RESULTS

RARgamma expression was significantly decreased in elderly versus young subjects while no modification of the retinoid-related plasma parameters ROH and RBP were emphasized by aging. Concerning thyroid criteria, the elderly exhibited an increase in TSH concentration (+39%) without significant modifications of FT3 and FT4, which indicated an age-related sub-clinical hypothyroidism. Concurrently, the amount of TR mRNA (alpha as well as beta subtypes) was significantly decreased in the elderly.

CONCLUSION

These data constitute the first evidence of an age-related hypo-activation of the retinoid and thyroid nuclear pathways in PBMC. Further study of the possible association between the expression of the retinoid and thyroid nuclear receptors and age-related cognitive alterations in humans would be interesting.