Free Retinol Research Articles

Retinol-Loaded Deep Eutectic Solvent emulsion: Improved Stability and Therapeutic Efficiency

Retinol is used to manage epidermal and keratin metabolism, promote collagen formation, erase wrinkles for firmer skin, and restore suppleness and smoothness. Retinol can be difficult to store and use owing to the potential for skin irritation, oxidation, and biological ineffectiveness. The linolenic acid and phosphatidylcholine deep eutectic solvent (DES) had a low melting point, high bioactivity, and integrated capsule technology for retinol encapsulation. Safety evaluation tests revealed that the formulated DES-retinol emulsion was less cytotoxic than free retinol, as well as less irritant toward chicken embryos, pig skin, and human patches. In a keratinocyte inflammatory factor inhibition assay, the DES-retinol emulsion reduced monocyte chemoattractant protein-1 expression, indicating the potential to reduce the inflammatory response of the skin to retinol-induced irritation. The DES-retinol emulsion exhibited pro-permeability, anti-wrinkle, firming, and antioxidant characteristics in cellular, skin, and clinical investigations. The DES-retinol emulsion promoted type I collagen production, suppressed matrix metalloproteinase-1 activity, and reduced the release of reactive oxygen species. Consequently, the quantity, size, and depth of wrinkles were substantially improved, along with an enhanced anti-aging effect, heightened skin hydration, increased collagen intensity and flexibility, and diminished retinol-induced irritation. In conclusion, the retinol-loaded linolenic acid and phosphatidylcholine DES emulsion exhibited improved stability, enhanced transdermal efficiency, and notable therapeutic effects.

Silica Microparticles from Sugarcane By-Products as an Encapsulation System for Retinoids Aimed at Topical Sustained Release.

The encapsulation of retinol within silica microparticles has emerged as a promising opportunity in the realm of cosmetic and pharmaceutical formulations, driven by the need to reinforce the photoprotection and oxidation stability of retinol. This work examines the process of encapsulating retinol into silica microparticles. The association efficiency, microparticle size, molecular structure, morphology, oxidation, and release profile, as well as biocompatibility and skin sensitization, were evaluated. Results showed that 0.03% of retinol and 9% of emulsifier leads to an association efficiency higher than 99% and a particle size with an average of 5.2 µm. FTIR results indicate that there is an association of retinol with the silica microparticles, and some may be on the surface. Microscopy indicates that when association happens, there is less aggregation of the particles. Oxidation occurs in two different phases, the first related to the retinol on the surface and the second to the associated retinol. In addition, a burst release of up to 3 h (30% free retinol, 17% associated retinol) was observed, as well as a sustained release of 44% of retinol up to 24 h. Encapsulation allowed an increase in the minimal skin cytotoxic concentrations of retinol from 0.04 μg/mL to 1.25 mg/mL without skin sensitization. Overall, retinol is protected when associated with silica microparticles, being safe to use in cosmetics and dermatology.

Retrospective Observational Analysis of Free Serum Retinol in a Cohort of Pediatric Patients with Short Bowel Syndrome and Intestinal Failure

Retrospective Observational Analysis of Free Serum Retinol in a Cohort of Pediatric Patients with Short Bowel Syndrome and Intestinal Failure

Development and validation of a method to deliver vitamin A to macrophages.

Macrophages are critical players in the development of atherosclerotic lesions, where they promote local and systemic inflammation. Macrophages engulf lipoproteins and cell debris upon entry into the arterial wall, becoming lipid-laden foam cells. While most lipids found in foam cells are triglyceride and cholesterol, these cells accumulate several other lipids with bioactive properties, such as vitamin A and carotenoids. Vitamin A has strong immunomodulatory actions in macrophages and other immune cells. For example, macrophages release vitamin A as retinoic acid to modulate T cell differentiation, but the implication of intracellular vitamin A stores in this process remains elusive due to the lack of an adequate experimental model to load vitamin A into macrophages. The purpose of this study was to develop a reliable method to deliver vitamin A to cultured murine macrophages. Our results show that thioglycolate-elicited peritoneal macrophages fail to take up significant levels of vitamin A when provided as free retinol. Cultured macrophages and macrophages in the peritoneal cavity can take up retinyl esters, either as retinyl ester-loaded serum or retinyl esters infused directly into the peritoneal cavity. HPLC analyses in macrophage lysates revealed that the intraperitoneal injection method results in a fourfold greater vitamin A loading efficiency than retinyl ester-loaded serum added to cultured cells. These two alternative methods provide an efficient and reliable methodology to load macrophages with vitamin A for downstream applications such as studies of gene regulation trafficking of intracellular vitamin A, and vitamin A release from macrophages.

β-Carotene Bioavailability and Conversion Efficiency Are Significantly Affected by Sex in Rats: First Observation Suggesting a Possible Hormetic Regulation of Vitamin A Metabolism in Female Rats.

To study the effect of variation in dietary vitamin A (VA) content on its hepatic and intestinal metabolism. Adult female and male rats are fed with diets containing 400, 2300, or 9858IU kg-1 VA for 31-33 weeks. VA concentrations are measured in plasma and liver. Bioavailability and intestinal conversion efficiency of β-carotene to VA are assessed by measuring postprandial plasma β-carotene and retinyl palmitate concentrations after force-feeding rats with β-carotene. Expression of genes involved in VA metabolism, together with concentrations of RBP4, BCO1, and SR-BI proteins, are measured in the intestine and liver of female rats. Plasma retinol concentrations are lower and hepatic free retinol concentrations are higher in females than in males. There is no effect of dietary VA content on β-carotene bioavailability and its conversion efficiency, but bioavailability is higher and conversion efficiency is lower in females than in males. The expression of most genes exhibited a U-shaped dose response curve depending on VA intake. β-Carotene bioavailability and conversion efficiency to VA are affected by the sex of rats. Results of gene expression suggest a hormetic regulation of VA metabolism in female rats.

Combining Raman imaging and MCR-ALS analysis for monitoring retinol permeation in human skin.

Monitoring the transcutaneous permeation of exogenous molecules using conventional techniques generally requires long pre-analytical preparation or labelling of samples. However, Raman spectroscopy is a label-free and non-destructive method which provides spatial distribution of tracked actives in skin. The aim of our study was to prove the interest of Raman imaging coupled with multivariate curve resolution alternating least square (MCR-ALS) analysis in monitoring retinol penetration into frozen and living human skin. After topical treatment of skin samples by free or encapsulated retinol, thin cross sections were analysed by Raman imaging (up to 100µm depth). Mann-Whitney test was used to identify retinol spectroscopic markers in skin. MCR-ALS was used to estimate retinol contribution in Raman spectral images. Heat maps were constructed to compare the distribution of free and encapsulated retinol in skin models. We identified the bands at 1158, 1196 and 1591cm-1 as specific features for monitoring retinol in skin. Moreover, our MCR-ALS results showed an improvement of retinol penetration (up to 30µm depth) with the encapsulated form as well as storage reservoir formation in stratum corneum, for each skin model. Finally, greater retinol penetration into living skin was observed. This study shows a proof of concept for the evaluation of retinol penetration in skin using Raman imaging coupled with MCR-ALS. This concept needs to be validated on more subjects to include inter-individual variability but also other factors affecting skin permeation (age, sex, pH, etc). Our study can be extended to other actives.

Development and Validation of a Method to Deliver Vitamin A in Cell Culture

ObjectivesTo develop a method by which vitamin A is delivered to cultured eukaryotic cells MethodsThe multifaceted role of vitamin A in numerous physiological processes critical to energy metabolism, growth and development is well established. There is epidemiological evidence linking vitamin A levels to a reduced risk of metabolic diseases, suggesting that it plays a vital role at the cellular level. Our strategy was based on reports that retinoid uptake in adipocytes occurs possibly by the hydrolytic actions of lipoprotein lipase on retinyl esters and that retinyl esters are the predominant form in which Vitamin A is stored in hepatic stellate cells. Our preliminary studies show that cultured cells do not take up significant amounts of free retinol delivered in DMSO. To determine whether cells take up vitamin A when present in lipoproteins, we gavaged mice with 300 mg/kg of retinyl esters. Mice were sacrificed four hours later. ResultsHPLC analyses showed that the predominant form of vitamin A in serum was retinyl esters and that this concentration reached approximately 8 μM. We used this plasma to treat cells and observed a significant increase in intracellular vitamin A stores. ConclusionsIn conclusion, this study demonstrated that, vitamin A enriched serum treatment of eukaryotic cells, but not otherwise, increase their vitamin A load, and offer vitamin A packed cells for therapeutic applications. Further experiments are being performed to optimize the process, which has potential applications in furthering disease research on vitamin A in cell culture models. Funding SourcesNational Institutes of Health (NIH).

A Rapid Method to Measure Serum Retinol Concentrations in Japanese Black Cattle Using Multidimensional Fluorescence

Vitamin A levels in fattening Japanese Black cattle affect meat quality; therefore, it is important to monitor serum retinol concentrations. To simplify and accelerate the evaluation of serum retinol concentrations in cattle, we developed a new predictive method using excitation-emission matrix (EEM) fluorescence spectrophotometry. For analytical comparison, the concentration of serum retinol was also measured using the conventional HPLC method. We examined excitation (Ex) and emission (Em) wavelengths of cattle serum, which were 250–450 and 250–600 nm, respectively. Parallel factor analysis separated four components from EEM data, one of which was related to retinol. Next, a partial least square regression model was created using the obtained EEMs as explanatory variables and accrual measurement values as objective variables. The determination coefficient value (R2), root mean squared error of prediction (RMSEP), and the ratio of performance to deviation (RPD) of the model were determined. A comparison with reference values found that R2, RMSEP, and RPD of the calibration model were 0.95, 6.4 IU/dl, and 4.2, respectively. This implies that EEM can estimate the serum retinol concentration with high accuracy. Additionally, the fluorescent peaks that contributed to the calibration, which were extracted from the regression coefficient and variable importance in projection plots, were Ex/Em = 320/390 and 330/520 nm. Thus, we assume that this method observes not only free retinol, but also retinol-binding protein. In conclusion, multidimensional fluorescence analysis can accurately and quickly determine serum retinol concentrations in fattening cattle.

Retinyl esters are elevated in progeny of retinol dehydrogenase 11 deficient dams

Retinol dehydrogenase 11 (RDH11) is an NADPH-dependent retinaldehyde reductase that was previously reported to function in the visual cycle. Recently, we have shown that RDH11 contributes to the maintenance of retinol levels in extraocular tissues under conditions of vitamin A deficiency or reduced vitamin A availability. RDH11 is also expressed in the embryo. Rdh11 knockout animals do not display embryonic defects and appear to develop normally to the adult stage, but the exact function of RDH11 during development is not yet known. In contrast to RDH11-null mice, animals that lack dehydrogenase/reductase 3 (DHRS3), the enzyme that functions as a retinaldehyde reductase and is essential for the maintenance of retinoid homeostasis during embryogenesis, rarely survive until birth. Here, we investigated whether inactivation of RDH11 together with DHRS3 exacerbates the severity of retinoid homeostasis disruption in embryos that lack both enzymes compared to DHRS3-null mice. The results of this study indicate that in vitamin A sufficient animals, the loss of RDH11 in addition to DHRS3 does not appear to significantly impact the total levels of retinoic acid, free retinol, or retinyl esters in Rdh11−/−/Dhrs3−/−embryos in comparison to Dhrs3−/− embryos. Surprisingly, Rdh11−/− single gene knockout embryos obtained from breeding of Rdh11−/− dams display elevated levels of embryonic retinyl esters compared to wild type embryos. The mechanism of the maternal effect of Rdh11 status on fetal retinoid stores remains to be elucidated.

High-Performance Liquid Chromatography with Fluorescence Detection for Simultaneous Analysis of Retinoids (Retinyl Palmitate, Retinyl Acetate, and Free Retinol) and α-, β-, γ-, and δ-Tocopherols in Foods

A method based on high-performance liquid chromatography with fluorescence detection for the simultaneous analysis of retinoids (vitamin A) and tocopherols (vitamin E) was developed. This method consists of an isocratic solution using hexane/ethyl acetate (85:15, v/v) as the mobile phase and fluorescence detection using a time program that sets the excitation (Ex) and emission (Em) wavelengths at adequate elution times for retinoids (Ex 342 nm, Em 476 nm) and tocopherols (Ex 298 nm, Em 325 nm), respectively. The separation of three retinoids (retinyl palmitate, retinyl acetate, and free retinol) and four tocopherol homologs was achieved with sufficient reproducibility and quantitative ability. Additionally, the necessity of saponification was considered. As a result, saponification was not used in this method because of the complexity of the procedure and the loss of free retinol. The retinoid and tocopherol contents of various foods were evaluated using the developed method. Our method could evaluate the retinoid and tocopherol contents of fish (eel, Anguilla japonica, and amberjack, Seriola dumerili) muscle and liver, roasted soybean (Glycine max) flour, and Japanese torreya seed (Torreya nucifera). Additionally, our method could be applied to the determination of retinoids and tocopherols not only in foods but also in supplements and cosmetics.

Analysis of microsamples of human faeces: a non-invasive approach to study the bioavailability of fat-soluble bioactive compounds.

Bioavailability is a critical feature in the assessment of the role of micronutrients in human health. Poorly bioavailable micronutrients like carotenoids may reach significant concentrations in the gastrointestinal tract where they may exert biological actions. We evaluated a simple collection protocol to determine vitamin A, E and carotenoids in microsamples of human faeces as a non-invasive approach for nutritional studies. Microsamples of human faeces were collected using a commercially available device, extracted and analysed on two LC systems. Suitability of the protocol was assessed by evaluating several factors including the effect of simulated colonic conditions and two nutritional scenarios with different dietary components, chemical forms, nutritional goals and target groups. The protocol was reproducible and representative of a faeces sample. The major dietary and serum carotenoids, and several "unidentified" compounds (possibly metabolites) could be detected, and cis-/trans-β-carotene profile reflected dietary intervention. In faeces of neonates, free retinol, retinyl and α-tocopheryl acetate (from infant formula), long-chain fatty acid retinyl esters (from human milk), free γ-tocopherol and α-tocopherol could be detected. Our results show that the analysis of vitamin A, E and carotenoids in microsamples of human faeces is a suitable, non-invasive approach that may provide relevant information regarding responsiveness, nutrient stability and metabolism and may help assess adequacy of chemical forms and delivery systems reaching the colon.

Downregulation of STRA6 Expression in Epidermal Keratinocytes Leads to Hyperproliferation-Associated Differentiation in Both In Vitro and In Vivo Skin Models

Retinoids are known to affect skin cell proliferation and differentiation and are key molecules that target retinoid and retinoic acid receptors (RXRs and RARs), leading to physiological and pharmacologic effects. Our aim was to elucidate the role of the retinol-binding protein receptor STRA6, mediating cellular uptake of retinol, on skin structure and function. Our results indicate that STRA6 is constitutively expressed in human epidermal keratinocytes and dermal fibroblasts and is regulated via RAR/RXR-mediated pathways. HaCaT (Human adult low Calcium high Temperature) cells with stable STRA6 knockdown (STRA6KD) showed increased proliferation. Consistently, human organotypic 3D skin models using stable STRA6KD HaCaT cells showed a significantly thicker epidermis and enhanced expression of activation, differentiation, and proliferation markers. The effects were reversible after treatment with free retinol. Human skin reconstitution employing STRA6KD HaCaT cells leads to massive epithelial thickening under in vivo conditions in SCID mice. We propose that STRA6KD could lead to cellular vitamin A deficiency in keratinocytes. Consequently, STRA6 has a role for regulating retinoid homeostasis and in helping to program signaling that drives proliferation and differentiation of human skin cells. By its influence on hyperproliferation-associated differentiation, STRA6 could also have a role in skin regeneration and could be a target for pharmacological approaches to improve wound healing.

How Free Retinol Behaves Differently from RBP-Bound Retinol in RBP Receptor-Mediated Vitamin A Uptake

How Free Retinol Behaves Differently from RBP-Bound Retinol in RBP Receptor-Mediated Vitamin A Uptake

Free fatty acid binding protein-4 and retinol binding protein-4 in polycystic ovary syndrome: response to simvastatin and metformin therapies

Free fatty acid binding protein-4 (FABP4) and retinol binding protein-4 (RBP4) contribute to metabolic syndrome. We investigated serum FABP4 and RBP4 responses to insulin sensitizing and lipid lowering therapies in polycystic ovary syndrome (PCOS). Sixty-two healthy, untreated women with PCOS (age 25.1 ± 3.6 years, BMI: 24.0 ± 4.7 kg/m2) were randomized to metformin (n = 24), simvastatin (n = 20) or metformin plus simvastatin (n = 18) for 3 months. Anthropometric measures, fasting blood tests and oral glucose tolerance tests (OGTT) were obtained at the baseline and the end. At the baseline serum FABP4 correlated with obesity (BMI: r = 0.63, p < 0.001), insulin resistance (fasting insulin: r = 0.44, p = 0.0002; QUICKI: r = −0.30, p = 0.02; OGTT-insulin sensitivity index: r = −0.27, p = 0.04), dyslipidemia (HDL: r = −0.26, p = 0.03) and hyperandrogenemia (free-testosterone: r = 0.23, p = 0.03; SHBG: r = −0.28, p = 0.03); while RBP4 correlated with total-cholesterol (r = 0.33, p = 0.009). Multiple regression analysis indicated that t best predictors of serum FABP4 and RBP4 were BMI (β = 1.02, p = 0.0003) and total cholesterol (β = 2326, p = 0.01), respectively. Simvastatin, alone or with metformin did not affect serum FABP4 or RBP4. Serum FABP4 related to the obesity, insulin resistance and inflammation while RBP4 related to lipids. Insulin sensitizing and lipid lowering therapies did not affect FABP4 or RBP4 levels in PCOS.

Chronic effects of lead (Pb) on bone properties in red deer and wild boar: Relationship with vitamins A and D3

Here we study the occurrence of abnormalities on bone tissue composition and turnover mechanisms through the Pb-mediated disruption of vitamins A and D in wild ungulates living in a lead (Pb)-polluted mining area. Red deer (Cervus elaphus) and wild boar (Sus scrofa) from the mining area had significantly higher liver and bone Pb levels than controls, which were associated with the depletion of liver retinyl esters and the corresponding increase of free retinol levels both in deer and boar from the mining area. Pb-exposed adult deer had lower carbonate content in bone mineral than controls, which was associated with the increased free retinol percentage. In wild boar, the degree of bone mineralization was also positively associated with higher burdens of retinyl esters. These results suggest that Pb-associated changes in bone composition and mineralization is likely influenced by the depletion of vitamin A in wildlife exposed to environmental Pb pollution.

STRA6-Catalyzed Vitamin A Influx, Efflux, and Exchange

Vitamin A has diverse biological functions and is essential for human survival. STRA6 is the high-affinity membrane receptor for plasma retinol binding protein (RBP), the principle and specific carrier of vitamin A (retinol) in the blood. It was previously shown that STRA6 couples to lecithin retinol acyltransferase (LRAT) and cellular retinol binding protein I (CRBP-I), but poorly to CRBP-II, for retinol uptake from holo-RBP. STRA6 catalyzes both retinol release from holo-RBP, which is responsible for its retinol uptake activity, and the loading of free retinol into apo-RBP, which can cause retinol efflux. Although STRA6-catalyzed retinol efflux into apo-RBP can theoretically deplete cells of retinoid, it is unclear to what extent this efflux happens and in what context. We show here that STRA6 can couple strongly to both CRBP-I and CRBP-II for retinol efflux to apo-RBP. Strikingly, pure apo-RBP can cause almost complete depletion of retinol taken up by CRBP-I in a STRA6-dependent manner. However, if STRA6 encounters both holo-RBP and apo-RBP (as in blood), holo-RBP blocks STRA6-mediated retinol efflux by competing with apo-RBP's binding to STRA6 and by counteracting retinol efflux with influx. We also found that STRA6 catalyzes efficient retinol exchange between intracellular CRBP-I and extracellular RBP, even in the presence of holo-RBP. STRA6's retinol exchange activity may serve to refresh the intracellular retinoid pool. This exchange is also a previously unknown function of CRBP-I and distinguishes CRBP-I from LRAT.

Lipid Peroxidation in Judoists Using Oral Contraceptives

12 female judoists using oral contraceptives (OCU) containing 0.03 mg ethinylestradiol and 3 mg drospirenone for 20 ± 12 months (mean ± SD) were compared with a control group of 14 judoist noncontraceptive users (NCU) in order to evaluate resting (T1) and postexercise (T2) lipid peroxidation (LPO) and antioxidant parameters. Data were collected 20 min before and 10 min after a morning session of judo training and included determination of lag phase (Lp) before free radical-induced oxidation, glutathione peroxidase (GPx), α-tocopherol, retinol, and oxidative stress markers related to LPO. Significantly higher resting oxidative stress (+125.8 and +165.2% for malondialdehyde and lipid peroxides, respectively) and lower values of Lp and GPx (-23.4 and -12.1%, respectively) were observed in the OCU compared with NCU. The judo training session induced an increase in plasma LPO whatever the treatment. We noted significant increases in Lp (+14.7%; p<0.05 vs. preexercise) and GPx (22.1%; p<0.05 vs. preexercise) only in the NCU group. We suggest that a judo training session favourably altered some antioxidants in NCU but not in OCU. As excessive oxidative stress is linked to the development of several chronic diseases, the use of agents to reduce antioxidants may be reasonable in OCU.

Antioxidant Status in Hyperthyroid Cats before and after Radioiodine Treatment

Reversible antioxidant depletion is found in hyperthyroid humans, and antioxidant depletion increases the risk of methimazole toxicosis in rats. To determine whether abnormalities in concentrations of blood antioxidants or urinary isoprostanes were present in hyperthyroid cats, and were reversible after radioiodine treatment. To determine whether or not antioxidant abnormalities were associated with idiosyncratic methimazole toxicosis. Hyperthyroid cats presented for radioiodine treatment (n = 44) and healthy mature adult control cats (n = 37). Prospective, controlled, observational study. Red blood cell glutathione (GSH), plasma ascorbate (AA), plasma free retinol (vitamin A), α-tocopherol (vitamin E), and urinary free 8-isoprostanes in hyperthyroid cats were compared to healthy cats and to hyperthyroid cats 2 months after treatment. Blood antioxidants were not significantly different in hyperthyroid cats (mean GSH 1.6 ± 0.3 mM; AA 12.8 ± 4.9 μM, and vitamin E, 25 ± 14 μg/mL) compared to controls (GSH 1.4 ± 0.4 mM; AA 15.0 ± 6.6 μM, and vitamin E, 25 ± 17 μg/mL). Urinary isoprostanes were increased in hyperthyroid cats (292 ± 211 pg/mg creatinine) compared to controls (169 ± 82 pg/mg; P = .006), particularly in hyperthyroid cats with a USG < 1.035. Plasma free vitamin A was higher in hyperthyroid cats (0.54 ± 0.28 μg/mL versus 0.38 ± 0.21 in controls; P = .007). Both abnormalities normalized after radioiodine treatment. No association was found between oxidative status and prior idiosyncratic methimazole toxicosis. Increased urinary isoprostane could reflect reversible renal oxidative stress induced by hyperthyroidism, and this requires additional evaluation.

Critical difference applied to exercise-induced oxidative stress: the dilemma of distinguishing biological from statistical change

Even though intense exercise has traditionally been associated with a statistically significant accumulation of blood-borne biomarkers of free radical-mediated lipid peroxidation, it remains to be determined if the oxidative stress response is biologically significant. To examine biological significance, we calculated the critical difference of selected biomarkers of oxidants-antioxidants in the peripheral circulation of ten male subjects aged 24±3 years. Venous blood was drawn in the resting supine position every hour over an 8-h period (Study 1). As proof-of-concept, supine venous blood was also obtained at rest and following maximal cycling exercise in a separate group of 13 males, mean age 22±3 years (Study 2). The critical difference of electron paramagnetic resonance spin-trapped alkoxyl free radicals, lipid hydroperoxides, malondialdehyde, ascorbic acid, retinol, lycopene, α-tocopherol, β-carotene and α-carotene was calculated as 121%, 28%, 50%, 9%, 29%, 106%, 13%, 28% and 107%, respectively (Study 1). Maximal exercise was associated with a statistically significant (P<0.05 vs. rest) reduction in α-tocopherol and retinol, and a corresponding rise in alkoxyl free radicals and lipid hydroperoxides (Study 2). However, these changes were all within the critical difference percentage value. In conclusion, these findings highlight the importance of distinguishing biological from statistical significance when assessing the physiological and clinical impact of exercise-induced oxidative stress.

Changes in broiler chick tissue concentrations of lipid-soluble antioxidants immediately post-hatch

The antioxidant protection of the chicken ( Gallus gallus) embryo during incubation and early postnatal development plays an important role in chick viability. To assess the antioxidant capacity of the newly hatched chick, we determined the concentrations of vitamin A, vitamin E, carotenoids and coenzyme Q 10 in the major tissues of chicks which had been held in an incubator for up to 36 h post-hatch. Concentrations of total carotenoids and free retinol and retinol esters in the tissues did not differ significantly over the 36 h period post-hatch ( p > 0.05 ). In contrast concentrations of vitamin E (α-tocopherol, γ-tocopherol, and α-tocotrienol and γ-tocotrienol) in various tissues (liver, heart, brain and leg muscle) decreased significantly in chicks that had been held in the incubator for 36 h when compared to younger chicks that were held for up to 18 h. Comparatively high concentrations of coenzyme Q 10 were detected in the yolk sac membrane, liver and heart, the concentrations being dependent on age of chicks, the highest value being recorded 18 h post-hatch. In most of the tissues studied, coenzyme Q 10 concentrations decreased substantially between 18 and 36 h post-hatch. This study demonstrated that there are tissue-specific changes in the concentrations of the major antioxidants (vitamin E and coenzyme Q 10) during the 36 h post-hatch.