Retinoid receptors (RARs)

Retinol is the fat soluble vitamin retinol. Vitamin A binds to and activates retinoid receptors (RARs), thereby inducing cell differentiation and apoptosis of some cancer cell types and inhibiting carcinogenesis. Vitamin A plays an essential role in many physiologic processes, including proper functioning of the retina, growth and differentiation of target tissues, proper functioning of the reproductive organs, and modulation of immune function.

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In this study, it remains unclear which is the exact molecule that induced the enhancement of GSH production in RAW264 cells. However, one possibility is that β‐carotene is metabolized into retinol, and then retinol actually exerts the effect on enhancement of GSH synthesis. It is well‐known that β‐carotene is pro‐vitamin A, and that retinol (vitamin A) converted from β‐carotene has potential for physiological functions, the representative one of which is the sense of vision. It was reported that retinol was not detected in RAW264 cells after incubation with culture medium supplemented with β‐carotene in the previous study (Katsuura et al., 2009). Likewise, it was also reported there that the mRNA for β‐carotene‐15,15′‐monooxygenase (BCMO1), which catalyzes the production of retinoids from β‐carotene or β‐cryptoxanthin, was not detected in RAW264 cells. In contradiction to that, Zolberg et al. reported that BCMO1 protein and its product retinol were detected in RAW264.7 cells after the incubation with 9‐cis β‐carotene (Zolberg Relevy et al., 2015). Another possibility is that both β‐carotene and retinol may, at least in part, have almost the same effect on the enhancement of GSH synthesis in RAW264 cells[1].

IMQ-treated mice developed erythema, scales, and skin thickening. Compared with the control groups, IMQ-treated groups had the following changes: 1) interleukin (IL)-17A, IL-23, and tumor necrosis factor (TNF)-α levels were raised significantly in both serum and lesional skin (all p < 0.001); 2) retinol levels in lesional skin increased slightly (p = 0.364), but no change was evident in serum retinol levels; 3) STRA6 was upregulated in both lesional skin (p = 0.021) and serum (p = 0.034); 4) RBP4 levels were elevated in serum (p = 0.042), but exhibited only an increasing trend (p = 0.273) in lesional skin; and 5) proteins and enzymes that mediate retinoic acid formation and transformation were upregulated in lesional skin.[2]
Conclusions: As the demand for vitamin A in psoriatic mice increased, retinol underwent relocation from the circulation to target tissues. RBP4, STRA6, and the transformation from retinol to retinoic acid were upregulated, which may be part of the mechanism of psoriasis skin lesion formation. We propose that a positive feedback mechanism was formed that maintained the severity of psoriasis[2].

In this study, researchers evaluated the potential of retinol and retinoic acid (RA) to enhance intracellular glutathione (GSH) levels in a murine cultured macrophage cell line, RAW264, to investigate whether the RA signaling pathway is involved in the β-carotene-induced GSH enhancement. [1]
Methods and results: We examined GSH levels in RAW264 cells cultured in media supplemented with β-carotene and various inhibitors (ER50891 for RA receptor (RAR)α, CD2665 for RARβ/γ, or HX531 for all subtypes of retinoid X receptor (RXR)), to verify each inhibitor's activity against β-carotene, as well as in media supplemented with various stimulants (AM80 for RARα, CD2314 for RARβ, CD437 for RARγ, or SR11237 for RXR), to compare their activity with that of β-carotene. We also examined the GSH level and glutamate-cysteine-ligase (GCL) expression in RAW264 cells cultured in all-trans RA- or retinol-supplemented media. Enhanced GSH production was not inhibited by any tested antagonist, and, apart from β-carotene, no agonist induced GSH production. Retinol, but not all-trans RA, enhanced GSH synthesis and increased GCL expression, similar to that observed with β-carotene. [1]
Conclusion: The RA signaling pathway may not be involved in the β-carotene-induced enhancement of GSH levels in RAW264 cells, whereas, like β-carotene, retinol can enhance the GSH level and GCL expression.[1]

Thirty mice were divided into four study groups: two groups underwent IMQ application for 3 or 6 days (groups A and B, respectively), and two groups underwent Vaseline application for 3 or 6 days (groups C and D, respectively). Blood and skin samples from both lesional and non-lesional areas of the mice were analyzed using enzyme-linked immunosorbent assays, hematoxylin and eosin staining, immunochemistry, real-time reverse transcription polymerase chain reaction, and RNA sequencing.[2]

Absorption, Distribution and Excretion
Readily absorbed from the normal gastrointestinal tract
Vitamin A is distributed into breast milk ... .
Less than 5% of circulating vitamin A is bound to lipoproteins in blood (normal), but may be up to 65% when hepatic stores are saturated because of excessive intake. The amount of vitamin A bound to lipoproteins may be increased in hyperlipoproteinemia. When released from liver, vitamin A is bound to retinol-binding protein (RBP). Most vitamin A circulates in the form of retinol bound to RBP.
Storage: Hepatic (approximately 2 years' adult requirements), with small amounts stored in kidney and lung tissues. Zinc is required for mobilization of vitamin A reserves in the liver.
More than 90% of the intake of preformed vitamin A is in the form of retinol esters, usually as retinyl palmitate. ... When a large excess is ingested, some of the vitamin escapes in the feces. ... Absorption ... is related to that of lipid and is enhanced by bile. ... Aqueous dispersions ... are absorbed more rapidly than are oily solution.
For more Absorption, Distribution and Excretion (Complete) data for VITAMIN A (9 total), please visit the HSDB record page.

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Metabolism / Metabolites
Hepatic. Retinol is conjugated with glucuronic acid; the B-glucuronide undergoes enterohepatic circulation and oxidation to retinol and retinoic acid. Retinoic acid undergoes decarboxylation and conjugation with glucuronic acid.
Retinol is converted to retinyl phosphate in epithelial tissues, and this intermediate is in turn metabolized to mannosylretinylphosphate in a reaction that is catalyzed by a microsomal enzyme and requires guanosine diphosphomannose as a glycosyl donor. ... /the vitamin A/ mediates transfer of mannose to specific glycoproteins.
Retinol is in part conjugated to form a beta-glucuronide, which undergoes enterohepatic circulation and is oxidized to retinal and retinoic acid.
Within the retina, all-trans-retinol is oxidized to retinal by alcohol dehydrogenases, and is then Isomerized to the 11-cis-isomer which combines with opsin in the rod to yield rhodopsin, and with different opsins in human cones to yield three different iodopsin pigments.
Retinoic acid (RA) is the bioactive metabolite of vitamin A (retinol) which acts on cells to establish or change the pattern of gene activity. Retinol is converted to RA by the action of two types of enzyme, retinol dehydrogenases and retinal dehydrogenases. In the nucleus RA acts as a ligand to activate two families of transcription factors, the RA receptors (RAR) and the retinoid X receptors (RXR) which heterodimerize and bind to the upstream sequences of RA-responsive genes.
Retinol has known human metabolites that include retinal and 4-Hydroxyretinol.
Hepatic. Retinol is conjugated with glucuronic acid; the B-glucuronide undergoes enterohepatic circulation and oxidation to retinol and retinoic acid. Retinoic acid undergoes decarboxylation and conjugation with glucuronic acid.
Half Life: 1.9 hours

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Biological Half-Life
1.9 hours
Hepatic reserves of vitamin A decrease with a half-life of about 50 days in animals ...

Toxicity Summary
Vision:Vitamin A (all-trans retinol) is converted in the retina to the 11-cis-isomer of retinaldehyde or 11-cis-retinal. 11-cis-retinal functions in the retina in the transduction of light into the neural signals necessary for vision. 11-cis-retinal, while attached to opsin in rhodopsin is isomerized to all-trans-retinal by light. This is the event that triggers the nerve impulse to the brain which allows for the perception of light. All-trans-retinal is then released from opsin and reduced to all-trans-retinol. All-trans-retinol is isomerized to 11-cis-retinol in the dark, and then oxidized to 11-cis-retinal. 11-cis-retinal recombines with opsin to re-form rhodopsin. Night blindness or defective vision at low illumination results from a failure to re-synthesize 11-cis retinal rapidly.
Epithelial differentiation: The role of Vitamin A in epithelial differentiation, as well as in other physiological processes, involves the binding of Vitamin A to two families of nuclear retinoid receptors (retinoic acid receptors, RARs; and retinoid-X receptors, RXRs). These receptors function as ligand-activated transcription factors that modulate gene transcription. When there is not enough Vitamin A to bind these receptors, natural cell differentiation and growth are interrupted.

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Interactions
Insulin antagonizes the /teratogenic/ effects /of vitamin A/.
The antithyroid compound methylthiouracil increases teratogenic effect /of vitamin A/.
Thyroxine antagonizes the teratogenic action of vitamin A.
In rats, the incidence of congenital abnormalities in the head due to hypervitaminosis A was increased greatly by appropriate administration of cortisone to the dams.
For more Interactions (Complete) data for VITAMIN A (19 total), please visit the HSDB record page.

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Non-Human Toxicity Values
LD50 Mouse ip 1510 mg/kg (10 day)
LD50 Mouse oral 2570 mg/kg (10 day)
LD50 Hen oral 3.15 - 3.7 g/kg body weight

[1]. Retinol but not retinoic acid can enhance the glutathione level, in a manner similar to β-carotene, in a murine cultured macrophage cell line. Food Sci Nutr . 2018 Jul 20;6(6):1650-1656.
[2]. Retinol and vitamin A metabolites accumulate through RBP4 and STRA6 changes in a psoriasis murine model. Nutr Metab (Lond) . 2020 Jan 13:17:5.

Therapeutic Uses
Vitamin A is indicated only for prevention or treatment of vitamin A deficiency states. Vitamin A deficiency may occur as a result of inadequate nutrition or intestinal malabsorption but does not occur in healthy individual receiving an adequate balanced diet. For prophylaxis of vitamin A deficiency, dietary improvement, rather than supplementation, is advisable. For treatment of vitamin A deficiency, supplementation is preferred. /Included in US product labeling/
Recommended intakes may be increased and/or supplementation may be necessary in infants receiving unfortified formula or in individuals with the following conditions (based on documented vitamin A deficiency): Diarrhea; gastrectomy; hyperthyroidism; infections, chronic; intestinal diseases: celiac, diarrhea, topical sprue, regional enteritis; malabsorption syndromes associated with pancreatic insufficiency: pancreatic disease, cystic fibrosis; measles; protein deficiency, severe, stress, prolonged; xerophthalmia. /Included in US product labeling/
Some unusual diets (e.g., reducing diets that drastically restrict food selection, especially the fat-containing foods) may not supply minimum daily recommended intakes of vitamin A. Supplementation is necessary in patients receiving total parenteral nutrition (TPN) or undergoing rapid weight loss or in those with malnutrition, because of inadequate dietary intake.
Recommended intakes for most vitamins and minerals are increased during pregnancy. Many physicians recommend that pregnant women receive multivitamin and mineral supplements, especially those pregnant women who do not consume an adequate diet and those in high-risk categories (i.e., women carrying more than one fetus, heavy cigarette smokers, and alcohol and drug abusers). Taking excessive amounts of a multivitamin and mineral supplement may be harmful to the mother and/or fetus and should be avoided.
For more Therapeutic Uses (Complete) data for VITAMIN A (7 total), please visit the HSDB record page.

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Drug Warnings
Pregnancy risk category: X /CONTRAINDICATED IN PREGNANCY. Studies in animals or humans, or investigational or post-marketing reports, have demonstrated positive evidence of fetal abnormalities or risk which clearly outweights any possible benefit to the patient./ /Parenteral vitamin A/
Doses of vitamin A that do not exceed the physiologic requirement are usually nontoxic.
There are insufficient data to show that vitamin A may reduce the occurrence of certain types of cancer.
... Vitamin A has not been proven effective for treatment of renal calculi, hyperthyroidism, anemia, degenerative conditions of the nervous system, sunburn, lung diseases, deafness, osteoarthritis, inflammatory bowel disease, or psoriasis.
For more Drug Warnings (Complete) data for VITAMIN A (9 total), please visit the HSDB record page.

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Pharmacodynamics
Vitamin A is effective for the treatment of Vitamin A deficiency. Vitamin A refers to a group of fat-soluble substances that are structurally related to and possess the biological activity of the parent substance of the group called all-trans retinol or retinol. Vitamin A plays vital roles in vision, epithelial differentiation, growth, reproduction, pattern formation during embryogenesis, bone development, hematopoiesis and brain development. It is also important for the maintenance of the proper functioning of the immune system.

C20H30O

286.45

286.229

C, 83.86; H, 10.56; O, 5.59

68-26-8

445354

Solvated crystals from polar solvents, such as methanol or ethyl formate

1.0±0.1 g/cm3

421.2±14.0 °C at 760 mmHg

61-63 °C(lit.)

147.3±16.4 °C

0.0±2.3 mmHg at 25°C

1.549

6.84

1

1

5

21

496

0

CC1=C(C(CCC1)(C)C)/C=C/C(=C/C=C/C(=C/CO)/C)/C

FPIPGXGPPPQFEQ-OVSJKPMPSA-N

InChI=1S/C20H30O/c1-16(8-6-9-17(2)13-15-21)11-12-19-18(3)10-7-14-20(19,4)5/h6,8-9,11-13,21H,7,10,14-15H2,1-5H3/b9-6+,12-11+,16-8+,17-13+

(2E,4E,6E,8E)-3,7-dimethyl-9-(2,6,6-trimethylcyclohexen-1-yl)nona-2,4,6,8-tetraen-1-ol

Prepalin; Testavol; Vitamin A; alcohol All-trans-retinol; all-trans-3,7-Dimethyl-9-(2,6,6-trimethyl-1-cyclohexen-1-yl)-2,4,6,8-nonatetraen-1-ol; Axerophthol; Vafol; Avibon; Afaxin; Retinol; Aoral; Biosterol; Vitamin A Chocola A; Alphasterol;

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

May dissolve in DMSO (in most cases), if not, try other solvents such as H2O, Ethanol, or DMF with a minute amount of products to avoid loss of samples

Note: Listed below are some common formulations that may be used to formulate products with low water solubility (e.g. < 1 mg/mL), you may test these formulations using a minute amount of products to avoid loss of samples.

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Injection Formulation 1: DMSO : Tween 80： Saline = 10 : 5 : 85 (i.e. 100 μL DMSO stock solution → 50 μL Tween 80 → 850 μL Saline)
*Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH ₂ O to obtain a clear solution.
Injection Formulation 2: DMSO : PEG300 ：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL DMSO → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)
Injection Formulation 3: DMSO : Corn oil = 10 : 90 (i.e. 100 μL DMSO → 900 μL Corn oil)
Example: Take the Injection Formulation 3 (DMSO : Corn oil = 10 : 90) as an example, if 1 mL of 2.5 mg/mL working solution is to be prepared, you can take 100 μL 25 mg/mL DMSO stock solution and add to 900 μL corn oil, mix well to obtain a clear or suspension solution (2.5 mg/mL, ready for use in animals).

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Injection Formulation 4: DMSO : 20% SBE-β-CD in saline = 10 : 90 [i.e. 100 μL DMSO → 900 μL (20% SBE-β-CD in saline)]
*Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.
Injection Formulation 5: 2-Hydroxypropyl-β-cyclodextrin : Saline = 50 : 50 (i.e. 500 μL 2-Hydroxypropyl-β-cyclodextrin → 500 μL Saline)
Injection Formulation 6: DMSO : PEG300 : castor oil : Saline = 5 : 10 : 20 : 65 (i.e. 50 μL DMSO → 100 μLPEG300 → 200 μL castor oil → 650 μL Saline)
Injection Formulation 7: Ethanol : Cremophor : Saline = 10： 10 : 80 (i.e. 100 μL Ethanol → 100 μL Cremophor → 800 μL Saline)
Injection Formulation 8: Dissolve in Cremophor/Ethanol (50 : 50), then diluted by Saline
Injection Formulation 9: EtOH : Corn oil = 10 : 90 (i.e. 100 μL EtOH → 900 μL Corn oil)
Injection Formulation 10: EtOH : PEG300：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL EtOH → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)

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Oral Formulation 1: Suspend in 0.5% CMC Na (carboxymethylcellulose sodium)
Oral Formulation 2: Suspend in 0.5% Carboxymethyl cellulose
Example: Take the Oral Formulation 1 (Suspend in 0.5% CMC Na) as an example, if 100 mL of 2.5 mg/mL working solution is to be prepared, you can first prepare 0.5% CMC Na solution by measuring 0.5 g CMC Na and dissolve it in 100 mL ddH2O to obtain a clear solution; then add 250 mg of the product to 100 mL 0.5% CMC Na solution, to make the suspension solution (2.5 mg/mL, ready for use in animals).

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Oral Formulation 3: Dissolved in PEG400
Oral Formulation 4: Suspend in 0.2% Carboxymethyl cellulose
Oral Formulation 5: Dissolve in 0.25% Tween 80 and 0.5% Carboxymethyl cellulose
Oral Formulation 6: Mixing with food powders

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Note: Please be aware that the above formulations are for reference only. InvivoChem strongly recommends customers to read literature methods/protocols carefully before determining which formulation you should use for in vivo studies, as different compounds have different solubility properties and have to be formulated differently.

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 (Please use freshly prepared in vivo formulations for optimal results.)