All-trans-retinoic acid distribution and metabolism in vitamin A-marginal rats

LX-2 Stellate Cells Are a Model System for Investigating the Regulation of Hepatic Vitamin A Metabolism and Respond to Tumor Necrosis Factor α and Interleukin 1β

Hepatic stellate cells (HSCs) are the major site of vitamin A (retinol) esterification and subsequent storage as retinyl esters within lipid droplets. However, retinyl esters become depleted in many pathophysiological states, including acute and chronic liver injuries. Recently, using a liver slice culture system as a model of acute liver injury and fibrogenesis, a time-dependent increase and decrease in the apparent formation of the bioactive retinoid all-trans-retinoic acid (atRA) and retinyl palmitate was measured, respectively. This coincided with temporal changes in the gene expression of retinoid-metabolizing enzymes and binding proteins, that preceded HSC activation. However, the underlying mechanisms that promote early changes in retinoid metabolism remain unresolved. We hypothesized that LX-2 cells could be applied to investigate differences in quiescent and activated HSC retinoid metabolism. We demonstrate that the hypermetabolic state of activated stellate cells relative to quiescent stellate cells may be attributed to induction of STRA6, RBP4, and CYP26A1, thereby reducing intracellular concentrations of atRA. We further hypothesized that paracrine and autocrine cytokine signaling regulates HSC vitamin A metabolism in both quiescent and activated cells. In quiescent cells, tumor necrosis factor α dose-dependently downregulated LRAT and CRBP1 mRNA, with EC50 values of 30-50 pg/mL. Likewise, interleukin-1β decreased LRAT and CRBP1 gene expression but with less potency. In activated stellate cells, multiple enzymes were downregulated, suggesting that the full effects of altered hepatic vitamin A metabolism in chronic conditions require both paracrine and autocrine signaling events. Further, this study suggests the potential for cell type-specific autocrine effects in hepatic retinoid signaling. SIGNIFICANCE STATEMENT: HSCs are the major site of vitamin A storage and important determinants of retinol metabolism during liver fibrogenesis. Here, two LX-2 culture methods were applied as models of hepatic retinoid metabolism to demonstrate the effects of activation status and dose-dependent cytokine exposure on the expression of genes involved in retinoid metabolism. This study suggests that compared to quiescent cells, activated HSCs are hypermetabolic and have reduced apparent formation of retinoic acid, which may alter downstream retinoic acid signaling.

Quantification of All-Trans Retinoic Acid by Liquid Chromatography-Tandem Mass Spectrometry and Association with Lipid Profile in Patients with Type 2 Diabetes

Retinoic acids are vitamin A metabolites that have numerous essential functions in humans, and are also used as drugs to treat acne and acute promyelocytic leukemia. All-trans retinoic acid (atRA) is the major occurring metabolite of retinoic acid in humans. This study provides a sensitive and specific liquid chromatography-tandem mass spectrometry approach in order to quantify atRA in human plasma samples. The isolation of atRA by hyperacidified liquid-liquid extraction using hexane and ethyl acetate resulted in a recovery of 89.7 ± 9.2%. The lower limit of detection was 20 pg·mL^-1, and 7 point calibration displayed good linearity (R² = 0.994) in the range of 50-3200 pg mL^-1. Selectivity was guaranteed by the use of two individual mass transitions (qualifier and quantifier), and precision and accuracy were determined intraday and interday with a coefficient variation of 9.3% (intraday) and 14.0% (interday). Moreover, the method could be used to isolate atRA from hyperlipidemic samples. Applying this method to plasma samples from patients with poorly controlled Type 2 diabetes significantly decreased atRA plasma levels as compared to those of the healthy controls. In addition, atRA concentrations were highly associated with increased low-density lipoprotein (LDL) and decreased high-density lipoprotein (HDL) cholesterol levels.

MiR-30a and miR-379 modulate retinoic acid pathway by targeting DNA methyltransferase 3B in oral cancer

BACKGROUND

Epigenetic silencing of retinoic acid (RA) signaling-related genes have been linked with the pathogenesis and clinical outcome in oral squamous cell carcinoma (OSCC) carcinogenesis. However, the precise mechanisms underlying the abnormal silencing of RA signaling-related genes in OSCC have not been well investigated.

METHODS

Using combined analysis of genome-wide gene expression and methylation profile from 40 matched normal-tumor pairs of OSCC specimens, we found a set of retinoid signaling related genes are frequently hypermethylated and downregulated in OSCC patient samples, including alcohol dehydrogenase, iron containing 1 (ADHFE1) and aldehyde dehydrogenase 1 family, member A2 (ALDH1A2), which are the important rate-limiting enzymes in synthesis of RA. The expression of ADHFE1 and ALDH1A2 in OSCC patients was determine by quantitative real-time PCR (qRT-PCR) and immunohistochemistry. The binding sites of miR-30a and miR-379 with DNA methyltransferase 3B (DNMT3B) were predicted using a series of bioinformatic tools, and validated using dual luciferase assay and Western blot analyses. The functions of miR-30a, miR-379, and DNMT3B were accessed by growth and colony formation analyses using gain- and loss-of-function approaches. Chromatin immunoprecipitation (ChIP) was performed to explore the molecular mechanisms by arecoline and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) treatment.

RESULTS

We demonstrated that deregulated miR-30a and miR-379 could represent a mechanism for the silencing of ADHFE1 and ALDH1A2 in OSCC through targeting DNMT3B. Ectopic expression of miR-30a and miR-379 could induce re-expression of methylation-silenced ADHFE1 and ALDH1A2, and lead to growth inhibition in oral cancer cells. Furthermore, the dysregulation of the miRNAs and DNMT-3B may result from exposure to tobacco smoking and betel quid chewing.

CONCLUSIONS

Our results demonstrate that tobacco smoking and betel quid chewing could repress miR-30a and miR-379, which upregulate the DNMT3B expression, in turn, lead to the hypermethylation of ADHFE1 and ALDH1A genes, consequently, promote the oncogenic activity. These findings highlight the potential use of retinoids in combination with epigenetic modifiers for the prevention or treatment of oral cancer.

Efficacies of rosiglitazone and retinoin on bleomycin-induced pulmonary fibrosis in rats

The present study investigated the intervention efficacies of rosiglitazone (ROS) and retinoin (RET) on bleomycin-induced pulmonary fibrosis in rats. A total of 48 rats were randomly divided into the control group (group C), the model group (group M), the dexamethasone group (group D), the ROS group (group R), the RET group (group W) and the ROS + RET group (group L). Group M and the treatment groups were intratracheally injected with 5 mg/kg bleomycin, while group C was injected with saline. The lungs of rats in each group were inspected using high resolution computed tomography (HRCT), lung tissue hematoxylin and eosin staining and Masson staining; furthermore, lung L-hydroxyproline (Hyp) content and the concentration of transforming growth factor β1 (TGF-β1) serum of each group were also determined. The fibrosis score, Hyp content and TGF-β1 concentration of each treatment group were significantly lower when compared with group M (P<0.01), while the imaging results were improved when compared with group M, with lower alveolitis and fibrosis scores. Group L, R and W exhibited significantly lower fibrosis scores, Hyp content and TGF-β1 concentrations when compared with group D (P<0.05). Imaging results for group L, R and W indicated that while the imaging results were superior to group D, group L was lower than groups R and W (P<0.05). No significant difference in the fibrosis score, Hyp content and TGF-β1 concentration was exhibited between groups R and W (P>0.05). Findings from the present study conclude that ROS and RET are able to suppress bleomycin-induced pulmonary fibrosis with improved efficacies when compared with dexamethasone; furthermore, the combination of these two pharmacological agents may exert synergistic effects.

Metabolic Effects of Inflammation on Vitamin A and Carotenoids in Humans and Animal Models

The association between inflammation and vitamin A (VA) metabolism and status assessment has been documented in multiple studies with animals and humans. The relation between inflammation and carotenoid status is less clear. Nonetheless, it is well known that carotenoids are associated with certain health benefits. Understanding these relations is key to improving health outcomes and mortality risk in infants and young children. Hyporetinolemia, i.e., low serum retinol concentrations, occurs during inflammation, and this can lead to the misdiagnosis of VA deficiency. On the other hand, inflammation causes impaired VA absorption and urinary losses that can precipitate VA deficiency in at-risk groups of children. Many epidemiologic studies have suggested that high dietary carotenoid intake and elevated plasma concentrations are correlated with a decreased risk of several chronic diseases; however, large-scale carotenoid supplementation trials have been unable to confirm the health benefits and in some cases resulted in controversial results. However, it has been documented that dietary carotenoids and retinoids play important roles in innate and acquired immunity and in the body's response to inflammation. Although animal models have been useful in investigating retinoid effects on developmental immunity, it is more challenging to tease out the effects of carotenoids because of differences in the absorption, kinetics, and metabolism between humans and animal models. The current understanding of the relations between inflammation and retinoid and carotenoid metabolism and status are the topics of this review.

Inflammation rapidly modulates the expression of ALDH1A1 (RALDH1) and vimentin in the liver and hepatic macrophages of rats in vivo

Background

Members of the ALDH1 protein family, known as retinal dehydrogenases (RALDH), produce retinoic acid (RA), a metabolite of vitamin A, and may also oxidize other lipid aldehydes. Of three related ALDH1 genes, ALDH1A1 is most highly expressed in liver. ALDH1A1 is also rapidly gaining importance as a stem cell marker. We hypothesized that ALDH1A1 may have a broad cellular distribution in the liver, and that its expression may be regulated by RA and perturbed by inflammation.

Methods

Studies were conducted in vitamin A-deficient and –adequate rats that were further treated with all-trans-RA or lipopolysaccharide (LPS) to induce a state of moderate inflammation. RALDH1A1 expression was determined by quantitative PCR and RALDH1, as well as marker gene expression, was determined by immunocytochemical methods.

Results

Inflammation reduced ALDH1A1 mRNA in whole liver regardless of the level of vitamin A in the diet (P < 0.05), while treatment with RA reduced ALDH1A1 expression only in chow-fed rats. ALDH1A1 protein exhibited diffuse staining in hepatocytes, with greater intensity in the periportal region including surrounding bile ducts. Six h after administration of LPS, portal region macrophages were more numerous and some of these cells contained ALDH1A1. Vimentin, which was used as a marker for stellate cells and fibroblasts, was increased by LPS, P = 0.011 vs. without LPS, in both ED1 (CD68)-positive macrophages and fibroblastic stellate-like cells in the parenchyma as well as portal regions. Alpha-smooth muscle actin staining was intense around blood vessels, but did not change after LPS or RA, nor overlap with staining for vimentin.

Conclusions

Acute inflammation rapidly downregulates ALDH1A1 expression in whole liver while increasing its expression in periportal macrophages. Changes in ALDH1A1 expression appear to be part of the early acute-phase inflammatory response, which has been shown to alter the expression of other retinoid homeostatic genes. In addition, the rapid strong response of vimentin expression after treatment with LPS suggests that increased vimentin may be a useful marker of early hepatic inflammation.

Periadventitial atRA citrate-based polyester membranes reduce neointimal hyperplasia and restenosis after carotid injury in rats

Oral all-trans retinoic acid (atRA) has been shown to reduce the formation of neointimal hyperplasia; however, the dose required was 30 times the chemotherapeutic dose, which already has reported side effects. As neointimal formation is a localized process, new approaches to localized delivery are required. This study assessed whether atRA within a citrate-based polyester, poly(1,8 octanediolcitrate) (POC), perivascular membrane would prevent neointimal hyperplasia following arterial injury. atRA-POC membranes were prepared and characterized for atRA release via high-performance liquid chromatography with mass spectrometry detection. Rat adventitial fibroblasts (AF) and vascular smooth muscle cells (VSMC) were exposed to various concentrations of atRA; proliferation, apoptosis, and necrosis were assessed in vitro. The rat carotid artery balloon injury model was used to evaluate the impact of the atRA-POC membranes on neointimal formation, cell proliferation, apoptosis, macrophage infiltration, and vascular cell adhesion molecule 1 (VCAM-1) expression in vivo. atRA-POC membranes released 12 μg of atRA over 2 wk, with 92% of the release occurring in the first week. At 24 h, atRA (200 μmol/l) inhibited [(3)H]-thymidine incorporation into AF and VSMC by 78% and 72%, respectively (*P = 0.001), with negligible apoptosis or necrosis. Histomorphometry analysis showed that atRA-POC membranes inhibited neointimal formation after balloon injury, with a 56%, 57%, and 50% decrease in the intimal area, intima-to-media area ratio, and percent stenosis, respectively (P = 0.001). atRA-POC membranes had no appreciable effect on apoptosis or proliferation at 2 wk. Regarding biocompatibility, we found a 76% decrease in macrophage infiltration in the intima layer (P < 0.003) in animals treated with atRA-POC membranes, with a coinciding 53% reduction in VCAM-1 staining (P < 0.001). In conclusion, perivascular delivery of atRA inhibited neointimal formation and restenosis. These data suggest that atRA-POC membranes may be suitable as localized therapy to inhibit neointimal hyperplasia following open cardiovascular procedures.

Overexpression of miR-122 promotes the hepatic differentiation and maturation of mouse ESCs through a miR-122/FoxA1/HNF4a-positive feedback loop

BACKGROUND & AIMS

microRNA-122 is the only identified liver-specific miRNA and plays a crucial role in liver development, maintenance of hepatic homeostasis as well as tumourigenesis. In our previous differentiation of ESCs into hepatocytes, microRNA-122 (miR-122) was expressed at a relatively low level. Here, we aim to elucidate the effect and underlying mechanisms of miR-122 during differentiation of ESCs into hepatocytes.

METHODS

Mouse ESCs were initially induced towards HPCs by activin A, FGF-4 and sodium butyrate and were subsequently transfected with a recombinant adenovirus expressing vector pAV.Ex1d-CMV>miR-122/IRES/eGFP 9 days after induction. Cells were analysed by real-time PCR, immunofluorescence, flow cytometry, microscopy and functional assays. Furthermore, microarray analysis was performed.

RESULTS

We demonstrated that overexpression of miR-122 could effectively promote hepatic differentiation and maturation, as assessed by morphological and functional tests. The microarray analysis revealed that 323 genes were down-regulated, whereas 59 were up-regulated. Particularly, two liver-specific transcription factors, FoxA1 and HNF4a, were significantly up-regulated. Moreover, the expression of E-cadherin was dramatically increased and the proliferation of HPCs was suppressed, whereas knockdown of FoxA1 reduced E-cadherin expression and increased the proliferation of HPCs. In addition, the expression levels of FoxA1, HNF4a and E-cadherin in time-course transfection experiments with miR-122 were not significantly increased except in cells in which transfection with miR-122 occurred 9 days after induction.

CONCLUSION

Overexpression of miR-122 at an appropriate stage could promote hepatic differentiation and maturation by regulating the balance between proliferation and differentiation, as well as the balance between EMT and MET, partially through a miR-122/FoxA1/HNF4a-positive feedback loop.

Inflammation induced by lipopolysaccharide does not prevent the vitamin A and retinoic acid-induced increase in retinyl ester formation in neonatal rat lungs

Vitamin A (VA) plays an important role in post-natal lung development and maturation. Previously, we have reported that a supplemental dose of VA combined with 10% of all-trans-retinoic acid (VARA) synergistically increases retinol uptake and retinyl ester (RE) storage in neonatal rat lung, while up-regulating several retinoid homeostatic genes including lecithin:retinol acyltransferase (LRAT) and the retinol-binding protein receptor, stimulated by retinoic acid 6 (STRA6). However, whether inflammation has an impact on the expression of these genes and thus compromises the ability of VARA to increase lung RE content is not clear. Neonatal rats, 7- to 8-d-old, were treated with VARA either concurrently with lipopolysaccharide (LPS; Expt 1) or 12 h after LPS administration (Expt 2); in both studies, lung tissue was collected 6 h after VARA treatment, when RE formation is maximal. Inflammation was confirmed by increased IL-6 and chemokine (C–C motif) ligand 2 (CCL2) gene expression in lung at 6 h and C-reactive protein in plasma at 18 h. In both studies, LPS-induced inflammation only slightly reduced, but did not prevent the VARA-induced increase in lung RE. Quantitative RT-PCR showed that co-administration of LPS with VARA slightly attenuated the VARA-induced increase of LRAT mRNA, but not of STRA6 or cytochrome P450 26B1, the predominant RA hydroxylase in lung. By 18 h post-LPS, expression had subsided and none of these genes differed from the level in the control group. Overall, the present results suggest that retinoid homeostatic gene expression is reduced modestly, if at all, by acute LPS-induced inflammation and that VARA is still effective in increasing lung RE under conditions of moderate inflammation.

DHRS3, a retinal reductase, is differentially regulated by retinoic acid and lipopolysaccharide-induced inflammation in THP-1 cells and rat liver

Both retinoid status and inflammation have been shown to control the level of expression of retinoid homeostatic genes. In the present study, DHRS3, previously shown to possess retinal reductase activity, was identified by microarray analysis of THP-1 monocytes as a possible gene target of all-trans-retinoic acid (RA). In these cells, DHRS3 mRNA increased 30- to 40-fold after treatment with ≤20 nM RA for 24 h, while DHRS3 protein also increased. Of several synthetic retinoids tested, only Am580, a RA receptor-α-selective retinoid, increased DHRS3 mRNA expression. The full-length DHRS3 cDNA was cloned from rat liver and subjected to in vitro transcription-translation. Two major ∼30- and 35-kDa proteins were detected. In adult rat tissues, DHRS3 mRNA was most abundant in the adrenal gland, liver, and ovary. In the liver, DHRS3 is expressed in hepatocytes and possibly in all liver cells. To evaluate whether DHRS3 is regulated in the liver by RA and/or inflammatory stimuli, we treated rats for 6 h with RA or LPS or both. DHRS3 mRNA was doubled by RA but reduced by >90% after treatment with LPS in the absence and presence of RA. On the basis of our results, DHRS3 mRNA expression is regulated by RA in a tissue- or cell-type specific manner; the RA-induced increase in DHRS3 may contribute to retinoid storage; and a reduction of DHRS3 expression in the liver during inflammation may contribute to the perturbation of whole body vitamin A metabolism that has previously been shown to occur in conditions of inflammatory stress.

Multiple cytochrome P-450 genes are concomitantly regulated by vitamin A under steady-state conditions and by retinoic acid during hepatic first-pass metabolism

Vitamin A (retinol) is an essential precursor for the production of retinoic acid (RA), which in turn is a major regulator of gene expression, affecting cell differentiation throughout the body. Understanding how vitamin A nutritional status, as well as therapeutic retinoid treatment, regulates the expression of retinoid homeostatic genes is important for improvement of dietary recommendations and therapeutic strategies using retinoids. This study investigated genes central to processes of retinoid uptake and storage, release to plasma, and oxidation in the liver of rats under steady-state conditions after different exposures to dietary vitamin A (deficient, marginal, adequate, and supplemented) and acutely after administration of a therapeutic dose of all-trans-RA. Over a very wide range of dietary vitamin A, lecithin:retinol acyltransferase (LRAT) as well as multiple cytochrome P-450s (CYP26A1, CYP26B1, and CYP2C22) differed by diet and were highly correlated with one another and with vitamin A status assessed by liver retinol concentration (all correlations, P < 0.05). After acute treatment with RA, the same genes were rapidly and concomitantly induced, preceding retinoic acid receptor (RAR)β, a classical direct target of RA. CYP26A1 mRNA exhibited the greatest dynamic range (change of log 2(6) in 3 h). Moreover, CYP26A1 increased more rapidly in the liver of RA-primed rats than naive rats, evidenced by increased CYP26A1 gene expression and increased conversion of [(3)H]RA to polar metabolites. By in situ hybridization, CYP26A1 mRNA was strongly regulated within hepatocytes, closely resembling retinol-binding protein (RBP)4 in location. Overall, whether RA is produced endogenously from retinol or administered exogenously, changes in retinoid homeostatic gene expression simultaneously favor both retinol esterification and RA oxidation, with CYP26A1 exhibiting the greatest dynamic change.

Multiple retinoic acid response elements cooperate to enhance the inducibility of CYP26A1 gene expression in liver

CYP26A1, which catalyzes the oxidation of all-trans (at)-retinoic acid (RA), is induced moderately by RA in numerous tissues, but is highly responsive in liver. To understand this difference, we have examined the CYP26A1 gene sequence, identified multiple RA response elements (RAREs) and tested them functionally in HepG2 cells as model hepatocytes, and in the liver of vitamin A (VA)-adequate and -deficient rats. Analysis of a 2.2 kbp 5'-flanking region upstream of the CYP26A1 transcription start site (TSS) identified 3 conserved hexameric direct repeat-5 elements, RARE1, -2 and -3, and a half site, RARE4. The full-length promoter containing all 4 elements was sufficient and necessary to increase promoter activity similar to levels of endogenous CYP26A1 mRNA produced in HepG2 cells treated with at-RA. In DNA binding and chromatin immunoprecipitation assays, the binding of RARs to the proximal RARE1 and distal RARE2, -3, and -4 regions of the CYP26A1 promoter was increased in RA-treated HepG2 cells, and greater in VA-sufficient than VA-deficient liver. Moreover, RA increased the binding of RNA polymerase-II in the distal as well as the proximal region, indicating that the distal region may be looped to become positioned close to the TSS, a process favored by retinoic acid receptors. The results support a cooperative model in which the functioning of multiple RAREs may account for the strong inducibility of CYP26A1 in liver, which, in turn, may be important physiologically for restoring retinoid homeostasis when the concentration of RA rises.

Liver-specific cytochrome P450 CYP2C22 is a direct target of retinoic acid and a retinoic acid-metabolizing enzyme in rat liver

Several cytochrome P450 (CYP) enzymes catalyze the C4-hydroxylation of retinoic acid (RA), a potent inducer of cell differentiation and an agent in the treatment of several diseases. Here, we have characterized CYP2C22, a member of the rat CYP2C family with homology to human CYP2C8 and CYP2C9. CYP2C22 was expressed nearly exclusively in hepatocytes, where it was one of the more abundant mRNAs transcripts. In H-4-II-E rat hepatoma cells, CYP2C22 mRNA was upregulated by all-trans (at)-RA, and Am580, a nonmetabolizable analog of at-RA. In comparison, in primary human hepatocytes, at-RA increased CYP2C9 but not CYP2C8 mRNA. Analysis of the CYP2C22 promoter region revealed a RA response element (5'-GGTTCA-(n)5-AGGTCA-3') in the distal flanking region, which bound the nuclear hormone receptors RAR and RXR and which was required for transcriptional activation response of this promoter to RA in CYP2C22-luciferase-transfected RA-treated HepG2 cells. The cDNA-expressed CYP2C22 protein metabolized [3H]at-RA to more polar metabolites. While long-chain polyunsaturated fatty acids competed, 9-cis-RA was a stronger competitor. Our studies demonstrate that CYP2C22 is a high-abundance, retinoid-inducible, hepatic P450 with the potential to metabolize at-RA, providing additional insight into the role of the CYP2C gene family in retinoid homeostasis.

Retinoids synergize with insulin to induce hepatic Gck expression

Hepatic GK (glucokinase) plays a key role in maintaining glucose homoeostasis. Many stimuli regulate GK activity by controlling its gene transcription. We hypothesized that endogenous lipophilic molecules modulate hepatic Gck expression. Lipophilic molecules were extracted from rat livers, saponified and re-constituted as an LE (lipophilic extract). LE synergized with insulin to induce primary hepatocyte, but not beta-cell, Gck expression in an SREBP-1c (sterol-regulatory-element-binding protein-1c)-independent manner. The dramatic induction of Gck mRNA resulted in a significant increase in GK activity. Subsequently, the active molecules were identified as retinol and retinal by MS after the purification of the active LE fractions. Retinoids synergized with insulin to induce Gck expression by the activation of both RAR [RA (retinoic acid) receptor] and RXR (retinoid X receptor). Inhibition of RAR activation completely abolished the effect of retinal. The hepatic GK specific activity and Gck mRNA levels of Zucker lean rats fed with a VAD [VA (vitamin A)-deficient] diet were significantly lower than those of rats fed with VAS (VA-sufficient) diet. Additionally, the hepatic Gck mRNA expression of Sprague-Dawley rats fed with a VAD diet was lower than that of rats fed with VA-marginal, -adequate or -supplemented diets. The reduced expression of Gck mRNA was increased after an intraperitoneal dose of RA in VAD rats. Furthermore, an intravenous injection of RA rapidly raised hepatic Gck expression in rats fed with a VAS control diet. Understanding the underlying mechanism that mediates the synergy may be helpful for developing a treatment strategy for patients with diabetes.

Vitamin A concentrations in piglet extrahepatic tissues respond differently ten days after vitamin A treatment

Periodic supplementation to infants and young children is encouraged in developing countries by the WHO. We investigated vitamin A (VA) in extrahepatic tissues of piglets after supplementation with retinyl acetate to determine long-term storage. 3, 4-Didehydroretinyl acetate (DRA) as a tracer was used to evaluate uptake from chylomicra in 4 h. Sows were fed a VA-depleted diet throughout pregnancy and lactation. Male castrated piglets (n = 28, 11.6 +/- 0.5 d) from these sows were weaned onto a VA-free diet for 1 wk, assigned to 4 groups, and dosed orally with 0, 26.2, 52.4, or 105 micromol VA. After 10 d, 5.3 micromol DRA was administered to determine short-term uptake of 3, 4-didehydroretinol (DR). Four hours later, piglets were killed; adrenal glands, kidney, lung, and spleen were collected and analyzed for retinol and DR. Retinol concentrations of kidney and adrenal gland were higher than control, but treated groups did not differ. Retinol concentration was highest in kidney (1.70-2.52 nmol/g), followed by adrenal gland (0.30-0.48 nmol/g), lung (0.15-0.21 nmol/g), and spleen (0.11-0.15 nmol/g). Total retinol in kidney and spleen was different among the groups (P < 0.05). Unesterified retinol was the major VA form; the percent retinol of total VA was lowest in adrenal glands. DR did not differ among the groups. In 4 h, the minimum estimated chylomicron contribution to tissue DR was 63-280% higher than the maximum DR exposure from retinol-binding protein. Constant dietary intake may be important in maintaining VA concentrations in extrahepatic tissues.

Liposomal retinoic acids modulate asthma manifestations in mice

Signaling of all-trans retinoic acid (ATRA) through nuclear retinoid acid (RA) receptors regulates several biological functions in airway epithelial cells, eosinophils, and immune cells, yet its impact on different in vivo aspects of pulmonary allergic reaction remains elusive. We compared the effect of a treatment with liposomally encapsulated ATRA (Lipo-ATRA) in a mouse model of ovalbumin (OVA)-induced T helper (Th) 2-type responses and airway remodeling. Daily intraperitoneal injections of 10 mg/kg Lipo-ATRA, at the time of each of the 2 systemic sensitizing injections, increased OVA-induced Immunoglobulin E synthesis, bronchoalveolar lavage (BAL) eosinophilia, and accumulation of IL-5, transforming-growth factor beta1, fibronectin, eotaxin/chemokine (C-C motif) ligand 11 (eotaxin/CCL11) and regulated upon activation, normal T expressed and secreted chemokine (C-C motif) ligand 5. In contrast, Lipo-ATRA, administered during each of the 4 intranasal OVA challenges, did not affect these variables. Regardless of the treatment regimen, Lipo-ATRA augmented mucin levels in BAL fluid and reduced lung total collagen content. In vitro incubation of mouse splenocytes or purified spleen cluster of differentiation (CD) 4-positive T lymphocytes, with ATRA, increased, respectively, OVA- and anti-CD 3 antibody-induced IL-4 and IL-5 production and inhibited IFNgamma release. These findings demonstrate that, when given during systemic sensitization, Lipo-ATRA exacerbates allergic immune and inflammatory responses, most likely by promoting Th2 development.

Lipopolysaccharide opposes the induction of CYP26A1 and CYP26B1 gene expression by retinoic acid in the rat liver in vivo

Retinoic acid (RA), a principal metabolite of vitamin A (retinol), is an essential endogenous regulator of gene transcription and an important therapeutic agent. The catabolism of RA must be well regulated to maintain physiological concentrations of RA. The cytochrome P450 (CYP) gene family CYP26, which encodes RA-4-hydroxylase activity, is strongly implicated in the oxidation of RA. Inflammation alters the expression of numerous genes; however, whether inflammation affects CYP26 expression is not well understood. We investigated the regulation of CYP26A1 and CYP26B1 mRNA levels by RA and LPS in the rat liver, as the liver is centrally involved in retinoid metabolism and the acute-phase response to LPS. Both CYP26A1 and CYP26B1 mRNA were induced in <4 h by a single oral dose of all-trans-RA. RA-induced responses of both CYP26A1 and CYP26B1 were significantly attenuated in rats with LPS-induced inflammation whether LPS was given concurrently with RA or after the RA-induced increase in CYP26A1 and CYP26B1 mRNA levels. When RA and LPS were administered simultaneously (6-h study), LPS alone had little effect on either CYP26A1 or CP26B1 mRNA, but LPS reduced by 80% the RA-induced increase in CYP26A1 mRNA (P<0.02), with a similar trend for CYP26B1 mRNA. When LPS was administered 4 h after RA (16-h study), it abrogated the induction of CYP26A1 (P<0.02) and CYP26B1 (P<0.01). Overall, these results suggest that inflammation can potentially disrupt the balance of RA metabolism and maintenance of RA homeostasis, which may possibly affect the expression of other RA-regulated genes.

Chronic vitamin A status and acute repletion with retinyl palmitate are determinants of the distribution and catabolism of all-trans-retinoic acid in rats

The relation between vitamin A (VA) nutritional status and the metabolism of all-trans-retinoic acid (RA) is not well understood. In this study, we determined the tissue distribution and metabolism of a test dose of [(3)H]-RA in rats with graded, diet-dependent, differences in VA status. The design included 3 groups, designated VA-deficient, VA-marginal, and VA-adequate, with liver total retinol concentrations of 9.7, 35.7 and 359 nmol/g, respectively, (P < 0.05), and an additional group of VA-deficient rats treated with a single oral dose of retinyl palmitate (RP) 20 h before the injection of [(3)H]-RA. Plasma, liver, lung, and small intestines, collected 30 min after [(3)H]-RA, were analyzed for total (3)H, unmetabolized [(3)H]-RA, polar organic-phase metabolites of [(3)H]-RA, and aqueous phase [(3)H]-labeled metabolites. In all groups, [(3)H]-RA was rapidly removed from plasma and concentrated in the liver. VA deficiency did not prevent the oxidative metabolism of RA. Nevertheless, the quantity of [(3)H]-RA metabolites in plasma and the ratio of total [(3)H]-polar metabolites to unmetabolized [(3)H]-RA in liver varied directly with VA status (VA-adequate > VA-marginal > VA-deficient, P < 0.05). Moreover, supplementation of VA-deficient rats with RP reduced the metabolism of [(3)H]-RA, similar to that in VA-adequate or VA-marginal rats. Liver retinol concentration, considered a proxy for VA status, was correlated (P < 0.05) with [(3)H]-RA metabolites in liver (R(2) = 0.54), plasma (R(2) = 0.44), lung (R(2) = 0.40), intestine (R(2) = 0.62), and all combined (R(2) = 0.655). Overall, the results demonstrate close linkage between dietary VA intake, hepatic storage of VA, and the degradation of RA and suggest that measuring plasma retinoid metabolites after a dose of RA may provide insight into the metabolism of this bioactive retinoid by visceral organs.

The components of VARA, a nutrient-metabolite combination of vitamin A and retinoic acid, act efficiently together and separately to increase retinyl esters in the lungs of neonatal rats

Retinoic acid (RA), produced from vitamin A (VA, retinol), is required for normal lung development and postnatal lung maturation. The concentration of retinyl ester (RE), the major storage form of retinol, decreases in the lungs in the perinatal period. Previously, we tested VARA, a nutrient-metabolite combination of VA and RA (10:1 molar ratio), on lung RE formation in postnatal rats and showed that the components of VARA acted synergistically to increase lung RE, as compared with the effects of equal amounts of VA and RA given alone. In this study, we first determined the equivalency of orally administered VARA in comparison to a standard oral supplement of VA, with respect to lung and liver RE storage. In a dose-dilution study, VARA was 4 times as effective as the standard dose of VA (VARA-25% did not differ from VA-100%). The synergistic effect of VARA was selective for the lungs, compared with the liver, in which VA and VARA had equal effects. Secondly, we tested whether the 2 components of VARA must be coadministered to exert their synergistic effect on lung RE content. RA and VA and were administered separately and together as VARA. Although RA alone had no effect on lung RE in this 24-h experiment, RA synergized with VA administered either 12 h before RA or 12 h after RA, as well as when coadministered as VARA. We infer that VA and RA are both limiting for lung RE formation in neonates. Given the importance of bioactive retinoids in cell differentiation and lung development, assuring an adequate lung RE content postnatally could be of benefit for lung maturation.