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PubMed2005

Photodecomposition and phototoxicity of natural retinoids.

Sunlight is a known human carcinogen. Many cosmetics contain retinoid-based compounds, such as retinyl palmitate (RP), either to protect the skin or to stimulate skin responses that will correct skin damaged by sunlight. However, little is known about the photodecomposition of some retinoids and the toxicity of these retinoids and their sunlight-induced photodecomposition products on skin. Thus, studies are required to test whether topical application of retinoids enhances the phototoxicity and photocarcinogenicity of sunlight and UV light. Mechanistic studies are needed to provide insight into the disposition of retinoids in vitro and on the skin, and to test thoroughly whether genotoxic damage by UV-induced radicals may participate in any toxicity of topically applied retinoids in the presence of UV light. This paper reports the update information and our experimental results on photostability, photoreactions, and phototoxicity of the natural retinoids including retinol (ROH), retinal, retinoid acid (RA), retinyl acetate, and RP (Figure 1).

Animals↗
PubMedDate not supplied

Facial tolerability of topical retinoid therapy.

The facial tolerability of various topical retinoids was evaluated in 253 healthy volunteers in a series of split-face, randomized, investigator-masked studies-all conducted at the same site by the same investigator. Four variables were evaluated to determine if they influenced tolerability-retinoid concentration, formulation vehicle, skin sensitivity, and individual retinoid. Lower retinoid concentrations were associated with less irritation. Vehicle influenced tolerability but whether a gel or cream formulation was better tolerated varied from retinoid to retinoid. Tolerability was superior on normal skin than "sensitive skin." On normal skin, tazarotene cream was better tolerated than tretinoin cream whereas adapalene and tretinoin microsponge gels were better tolerated than tazarotene gel. On sensitive skin, tazarotene and adapalene creams were better tolerated than tretinoin cream whereas adapalene gel was better tolerated than tazarotene gel. Retinoid concentration, vehicle, skin sensitivity, and retinoid can all affect facial tolerability. Skin vulnerability may be the most important factor.

Adapalene↗
PubMedDate not supplied

Mechanisms of the comedolytic and anti-inflammatory properties of topical retinoids.

Retinoids comprise a family of compounds with structures and mechanisms of action that resemble those of vitamin A (retinol), an essential nutrient which plays a role in cell growth and differentiation. The retinoids, which interact with nuclear receptors and affect gene transcription, have enormous therapeutic potential, particularly if they are receptor- and function-selective. Tretinoin was the first topical retinoid employed for the treatment of acne. In recent years, other topical retinoids for the treatment of acne have been designed from a disease-specific approach, with enhanced receptor and function selectivity, which translates to improved therapeutic effects and more favorable tolerability. The properties that differentiate the topical retinoids tretinoin, adapalene, and tazarotene have permitted clinicians to tailor acne treatment regimens for maximum therapeutic outcomes. Tretinoin (all-trans-retinoic acid), considered a first-generation retinoid, acts by altering the milieu of the microcomedo and influences desquamation of abnormal epithelium. Two receptor-selective synthetic retinoids, adapalene and tazarotene, may be classified as third-generation retinoids. Adapalene, a derivative of naphthoic acid, has comedolytic, antiproliferative, and anti-inflammatory properties. Tazarotene is a prodrug metabolized to tazarotenic acid that modulates cellular differentiation, desquamation, and inflammation.

Adapalene↗
PubMed2005

Retinoid receptor mRNA expression profiles in human bladder cancer specimens.

Retinoids, which include vitamin A (retinol) and its derivatives, have previously been investigated as potential chemopreventive and chemotherapeutic agents in bladder cancer. We examined mRNA expression of the retinoid receptors RARalpha, RARbeta2, RARgamma and RXRalpha, as well as two putative RARbeta2 target genes, DAB2 and Midkine, in normal and malignant bladder tissue specimens from human patients. We evaluated 24 normal and malignant bladder specimens for retinoid receptor, DAB2 and Midkine mRNA expression using RT-PCR. We also examined the effects of retinoic acid and retinol on the expression of these genes in five human bladder cancer cell lines. Expression of RARalpha, RARbeta2, RARgamma and RXRalpha mRNA was detected in all of the non-neoplastic patient bladder specimens. RARbeta2 mRNA expression was undetectable in 7/13 tumors, RARalpha in 3/13, RARgamma in 1/13 and RXRalpha in 2/13. DAB2 mRNA was expressed in all non-neoplastic and all tumor specimens, while Midkine mRNA was detected in 8/11 non-neoplastic specimens versus 11/13 tumors. Two of the five bladder cancer cell lines expressed RARbeta2 independent of retinoid exposure; in three cell lines RARbeta2 expression was induced by retinoids. RARalpha, RARgamma and RXRalpha mRNA expression was detected in 5/5 cell lines, independent of retinoid exposure. We found a reduction in retinoid receptor mRNA expression, particularly for RARbeta2, in human bladder cancer specimens. We also demonstrated induction of RARbeta2 mRNA expression in some of the retinoid-treated bladder cancer cell lines. We suggest that restoration of RARbeta2 expression may be a reasonable biomarker for developing bladder cancer preventive and/or therapeutic drugs.

Aged↗
PubMedDate not supplied

Prescribing patterns for topical retinoids within NAMCS data.

OBJECTIVE: Fears of potentially costly use of topical retinoids for cosmetic treatment of photodamaged skin have resulted in many managed care organizations placing prior authorization requirements on this class of medications. The purpose of this investigation was to examine whether prescribing patterns of a nationally representative sample of US physicians shed light on the incidence of use of topical retinoids for indications other than acne. METHODS: A retrospective, cross-sectional study of data from the National Ambulatory Medical Care Survey (1996--2000) was used to examine the impact of physician specialty as well as patient diagnosis of acne on the probability of retinoid prescription in weighted multivariate logistic regression models. RESULTS: Topical retinoids were prescribed in 0.4% (14.7 million out of 3.67 billion) physician visits for any diagnosis in the 5-year period from 1996 to 2000, and in nearly 31% (12.0 million out of 38.7 million) of physician visits for a diagnosis of acne. Topical retinoids were prescribed for acne in 77.1% of the cases. This finding held when individual retinoids (tretinoin and adapalene) were examined separately. Clear age-related prescription trends are observed, with a significant decrease in prescriptions beyond the teen years. In older patients, tretinoin prescribing did not decrease as much as adapalene prescribing. CONCLUSIONS: These data suggest that managed care organizations may want to examine their own data to determine the optimum criteria for operation of prior authorization (PA) programs for retinoids. PA requirements for these medications appear unnecessary in young patients, given the very small probability of non-acne related use. PA in older patients might be targeted to those patients on topical retinoids (such as tretinoin) for which there is evidence of efficacy in treatment of cosmetic photoaging.

Acne Vulgaris↗
PubMedDate not supplied

Effects of retinoids on chick face development.

Local application of retinoic acid to chick embryos produces severe bilateral clefting of the primary palate but does not affect the lower beak. This paper reviews what is known about the basis and specificity of this retinoid-induced defect by examining three major developmental processes: morphogenesis, cell differentiation, and pattern formation. The conclusion reached is that neither cytotoxicity nor cartilage inhibition is the basis of the specific retinoid-induced defect. Retinoid treatment interferes with reciprocal epithelial-mesenchymal interactions in the upper beak. These interactions are involved in linking pattern formation--the spatial ordering of cell differentiation--to morphogenesis and outgrowth. These results suggest that retinoids are interfering with the process of pattern formation in the upper beak, a conclusion that is supported by the similarities between retinoid effects on face and limb development. Thus, it appears that retinoids may be acting as general signaling molecules throughout the developing embryo. In the lower beak, pattern-forming cues may occur earlier in development. Alternatively, the cells may be unresponsive to retinoids. The molecular basis for the specificity of the facial defect--as well as for the action of retinoids on developing systems--is discussed with reference to recent advances in molecular biology.

Animals↗
PubMed1991

Stimulation of tissue-type plasminogen activator synthesis by retinoids in cultured human endothelial cells and rat tissues in vivo.

Tissue-type plasminogen activator (t-PA) and its inhibitor, plasminogen activator inhibitor 1 (PAI-1), play an important role in regulating the fibrinolytic capacity of plasma. Both t-PA and PAI-1 are synthesized by the endothelium. We report that retinoic acid (vitamin A acid) and other retinoids rather specifically stimulate the production of t-PA by cultured human umbilical vein endothelial cells. Effective retinoids induced a dose-dependent (range: 0.01-50 microM) increase in the production of t-PA of maximally about six-fold, while simultaneously causing no or only a small increase (less than two-fold) of PAI-1. The effects on t-PA synthesis were apparent by 4-8 h, and reached maximal values after about 24-48 h of incubation with retinoid. The retinoid effect on t-PA production was accompanied by increased t-PA mRNA levels, without any parallel change in PAI-1 or GAPDH mRNA concentrations. The study also shows that modifications at the carboxyl group of retinoic acid are associated with a decrease in stimulatory potency. The stimulatory pathway appears to be identical for all retinoids but distinct from a pathway by which another strong inducer, sodium butyrate, induces t-PA synthesis in endothelial cells. The induction of t-PA by retinoids might involve protein kinase C (PKC) as judged by an experiment using a specific PKC inhibitor. The effect of retinoids on the fibrinolytic system in vivo was assessed by feeding rats with a vitamin A deficient diet or a diet with excess of vitamin A or other retinoids.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Interaction of phospholipids, retinoids and PMA with calcium, phospholipid-dependent protein kinase-catalyzed reaction in skin.

Previous investigations suggested that a mechanism independent of cAMP may be associated with the action of some retinoids. An alternative pathway involving calcium, phospholipid-dependent protein kinase (C-kinase), was therefore studied. In order to demonstrate this, C-kinase was partially purified from skin of hairless, Balb/c normal and Balb/c nude mouse. Interaction and effects of various response modifiers such as phospholipids, retinoids and phorbol ester tumor promoters showed both major and minor differences among these enzymes. In general, retinal, retinoic acid, 13-cis-retinoic acid and etretinate stimulated skin enzyme activity in the absence of the natural stimulants, phosphatidyl serine and diacylglycerol (DAG). However in their presence the C-kinases were inhibited by retinoids. Our data further indicated that the active retinoids may compete with DAG for binding sites on the enzyme. However, the high concentrations of retinoids needed to elicit these effects suggested a pharmacological role for retinoid action as a result of hydrophobic interaction with lipid domains on the enzyme. These investigations also revealed some of the complexity associated with retinoid effects on C-kinase. Tumor promoter, phorbol-12-myristate 13-acetate (PMA) interacted with its receptor (C-kinase) from hairless and normal mouse skin and stimulated enzyme activity. However, PMA-dependent stimulation of nude mouse C-kinase was about half of that noted with the other two C-kinases. Furthermore, unlike its effect on hairless and Balb/c normal C-kinases, PMA was unable to potentiate the retinoid-stimulated activity of nude mouse skin enzyme. This behavior suggested that nude mouse C-kinase may be a variant form of the normal enzyme. The presence of this variant C-kinase may, therefore, be responsible for the lack of phorbol ester-induced tumor promotion observed earlier in nude mouse skin by other investigators. Endogenous substrate phosphorylation catalyzed by C-kinase from hairless and Balb/c normal mice resulted in 32P incorporation into four target polypeptides of molecular weights 75-78, 47-50, 25-29 and 14-18 kilodaltons. However, with the nude mouse enzyme, only the 75- to 78-kilodalton protein served as the target supporting the suggestion that this may be a variant C-kinase. Neither retinoic acid (10(-3) M) nor PMA (10(-6) M) seemed to affect the phosphorylation of any of the four polypeptides.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1986

[Regulation of cell growth by retinoids and gene expression].

Retinoids are compounds that can elicit specific biological responses by virtue of their binding to and activating a specific receptor or a set of receptors. Retinoids produce various specific biological effects, including induction of terminal differentiation, regulation of cell proliferation, regulation of gene expression and regulation of the activity of specific enzymes in cells. In this article, the effects of retinoids on gene expression are reviewed. Among these effects suppression of myc expression and induction of EGF-receptor mRNA expression are considered to be closely related to regulation of cell proliferation. The effects of retinoids on cell growth are discussed on the basis of these two actions: myc mRNA suppression and EGFR mRNA induction. The mode of retinoidal action seems to be similar to that of steroids, as many investigators suggest. The molecular mechanism of retinoidal action is considered to be the formation of a retinoid-receptor complex and its interaction with regulatory elements of DNA. The possibility of application of the methodology used in the investigation of steroidal action to the study of retinoidal action is also discussed.

Animals↗
PubMed1988

[Recent advances in retinoids studies].

Retinoids are defined as the compounds which elicit the specific biological responses through binding or activating the specific receptor(s). Retinoids modulate the cellular differentiation and proliferation in many types of cells. A series of retinoidal benzoic acids, named retinobenzoic acids, have potent activities on human promyelocytic leukemia cells, HL-60, and other assay systems. Among them, Am80, AM580 and Ch55 are more active than retinoic acid in most cases. As these compounds possess quite different structures or physicochemical properties from retinoic acid or conventional retinoids, they are expected to be applied clinically for the treatments of the diseases in oncology and dermatology. Recently, progresses on the mechanistic studies on retinoidal actions have been reported. One of them is isolation and cloning of human retinoic acid-receptors and the mechanism of retinoidal action was concluded that the retinoid-receptor complex interact directly with DNA to regulate the expression of the gene, like steroid hormone. The other is the establishment of the presence of the retinoid-specific-binding protein (RSBP) by the use of our retinobenzoic acids as the probe.

Animals↗
PubMed1985

Computer-assisted correlation of structure and biological activity in a set of retinoids.

A computer-assisted pattern-recognition system (ADAPT) designed to elucidate structure-activity relationships was applied to a set of retinoids, potentially useful inhibitors of carcinogenesis. A data set of 67 retinoids was used as input to the ADAPT system; their structures were entered, and their 3-dimensional configurations were optimized by a molecular modelling algorithm. Forty of these retinoids were defined as the "more active" class based upon their ability to reverse keratinization in vitamin A-deficient hamster tracheal organ cultures at 10(-10) M or less. The remaining 27 retinoids were defined as the "less active" class due to their lack of ability to elicit this effect at 10(-8) M or more. Thirteen descriptors were generated by ADAPT for each of these retinoids based upon their structures, including: number of ring atoms; double bonds; del Ré sigma charges; and principal moments. Pattern recognition analysis techniques were applied to this data set to determine if information contained in these descriptors could generate a discriminant function equation which could separate more active from less active retinoids, successfully. Computer recognition of more active from less active retinoids was demonstrated by a number of pattern recognition techniques, and the discriminant function could predict correctly the relative activity of retinoids of "unknown" activity in 87% of trials. These results indicate the existence of distinct structure-activity relationships in this set of biologically important molecules.

Animals↗
PubMed1983

Induction of ornithine decarboxylase activity and DNA synthesis in hairless mouse epidermis by retinoids.

The ability of all-trans-retinoic acid (RA) and other retinoid derivatives to enhance DNA synthesis and to induce ornithine decarboxylase [L-ornithine carboxylyase; EC 4.1.1.17 (ODC)] activity has been investigated in normal and tape-stripped hairless mouse epidermis. Initial studies showed that the retinoids could inhibit the induction of epidermal ODC activity found 4.5 hr after tape stripping. Ten nmol RA, 13-cis-retinoic acid (13-cis-RA), ethyl-all-trans-9-(4-methoxy-2,3,6-trimethylphenyl)-3,7-dimethyl-2,4,6, 8-nonatetraenoate (aromatic retinoid), or ethyl-p-[(E)-2-(5,6,7,8-tetrahydro-5,5,8, 8,-tetramethyl-2-naphthyl)-1-propenyl]benzoate (arotinoid ethyl ester) applied topically to the skin at 1 hr before tape stripping inhibited the induction of ODC activity. Induction of epidermal ODC activity was inhibited by arotinoid ethyl ester but not by RA, 13-cis-RA, or aromatic retinoid when they were applied to the skin at 24 hr prior to tape stripping. RA applied topically to normal hairless mouse skin induced a dose-dependent increase in epidermal ODC activity, detectable 24 hr or more after treatment. RA induced epidermal ODC activity to levels only 15- to 30-fold less than found after treatment with the potent tumor promoter tetradecanoylphorbol-13-acetate. Epidermal ODC activity was also induced by topical 13-cis-RA, aromatic retinoid, and arotinoid ethyl ester at this time, although in lower amounts than after RA treatment. The induction of ODC activity by RA was itself inhibited by topical arotinoid ethyl ester treatment. RA, 13-cis-RA, and aromatic retinoid induced ODC activity at doses below those required to enhance epidermal DNA synthesis. In summary, we have shown that, in common with other proliferative stimuli, retinoids can induce ODC activity in hairless mouse epidermis per se. Our results suggest that, because of their ability to also inhibit the expression of ODC activity, the induced ODC activity is found only after the retinoids have been depleted. The ability both to inhibit and to induce ODC activity may be related to the action of RA as a weak tumor promoter under certain conditions and as an inhibitor of promotion under others.

Animals↗
PubMed1994

Lipoprotein lipase hydrolysis of retinyl ester. Possible implications for retinoid uptake by cells.

Adipose tissue contains substantial stores of retinoid (retinol+retinyl ester) that, quantitatively, are second only to retinoid stores in the liver. Our studies show that retinoid levels in adipose tissue are markedly influenced by dietary retinoid intake. Because lipoprotein lipase (LPL) increases the uptake of lipoproteins and lipid emulsion particles by many cell types including adipocytes, we investigated whether LPL also increases retinoid uptake by adipocytes from lipid-containing particles. Addition of LPL (10 micrograms/ml) to BFC-1 beta adipocytes produced a 2-fold increase in cellular uptake of [3H]retinoid from a lipid emulsion containing [3H]retinyl ester. Heparin, which displaces LPL from binding sites on cell surface proteoglycans, increased [3H]retinoid uptake by an additional 2-fold. High performance liquid chromatography analyses showed that greater than 75% of the media and 85% of the cellular radioactivity was present as retinol. The conversion of retinyl ester to retinol by LPL was then assessed using model retinyl ester containing lipid emulsions. Although triglyceride appears to be the preferred substrate for LPL, after greater than 25% of the triglyceride was hydrolyzed, significant amounts of retinyl ester were hydrolyzed by LPL. Retinyl ester hydrolysis was increased approximately 20-fold in the presence of a source of apolipoprotein C-II. The physiologically significant palmitate, stearate, oleate, and linoleate esters of retinol were all hydrolyzed by LPL. When LPL was incubated with [3H]retinyl ester containing rabbit mesenteric chylomicrons and in the presence of heparin and apolipoprotein C-II, the LPL was able to completely hydrolyze the retinyl ester to retinol. Thus, LPL is able to catalyze the hydrolysis of retinyl esters and, through the process of hydrolysis, may facilitate uptake of retinoid by adipocytes.

Adipocytes↗
PubMed1996

Retinoids as cancer-preventive agents.

Vitamin A and its metabolites play a crucial role in regulating the differentiation and proliferation of epithelial cells, and are potent inducers of apoptosis. The effects of retinoids are thought to be mediated through the metabolite retinoic acid, which binds to nuclear retinoic acid receptors that then interact with specific retinoic acid response elements. The development of cancers involves alterations in growth and differentiation of cells as a result of carcinogen-induced damage to DNA of regulatory genes. Most of the results from experimental animal studies indicate that retinoids are effective in preventing or suppressing cancers. Although the relationship between preformed vitamin A in the diet and epithelial cancers remains to be further clarified, a high intake of vegetables and fruits has been consistently associated with a lower risk of these cancers. This interesting biological activity profile of retinoids has prompted investigators to study them in the chemoprevention of epithelial cancers and in the treatment of advanced cancers. Although the therapeutic response of retinoids against advanced cancers is disappointing, they have emerged as promising chemopreventive agents, particularly in head and neck sites. Both natural and synthetic analogues of vitamin A have been shown to be effective in suppressing micronucleated cells, reversing oral leukoplakia, and preventing new and recurrent lesions in subjects with oral leukoplakia, as well as in reducing the occurrence of second primaries in treated head and neck cancer patients. They have not been consistently effective in suppressing either bronchial atypia or metaplasia, nor have they been proven effective in reducing the occurrence of recurrent lesions in treated skin cancer patients, although some activity has been demonstrated in reducing lesion counts in actinic keratoses. Vitamin A in combination with other micronutrients has not reduced incidence and mortality from oesophageal and stomach cancers. A synthetic retinoid, fenretinide, is currently being evaluated in preventing contralateral breast cancer in treated breast cancer patients. Toxicity has been a major concern with retinoids, as prolonged administration is required in chemoprevention studies. Available evidence indicates that natural analogues of retinoids are less toxic than synthetic compounds such as isotretinoin. Large studies are currently evaluating retinoids in the prevention of head and neck cancers and lung cancers. The outcome of these studies will be important in directing future research initiatives and in forming policies regarding the use of vitamin A compounds in the prevention of cancers.

Anticarcinogenic Agents↗
PubMed1997

Anticoagulant effects of synthetic retinoids mediated via different receptors on human leukemia and umbilical vein endothelial cells.

We recently found that retinoic acids (RAs) exert anticoagulant effects by upregulating thrombomodulin (TM) and downregulating tissue factor (TF) expression in acute promyelocytic leukemia (APL) cells and monoblastic leukemia cells. Two classes of nuclear RA receptors, termed retinoic acid receptors (RARs) and retinoid X receptors, have been identified. Each receptor class consists of three subtypes. In the present study, we have used several synthetic retinoids to determine which receptor subtypes are involved in the regulation of TM and TF expression in NB4 APL cells, U937 monoblastic leukemia cells, and human umbilical vein endothelial cells (HUVECs). Am80, which has no binding affinity for RAR gamma, and Ch55, which does not bind to cytoplasmic retinoic acid binding protein (CRABP), upregulated TM and downregulated TF in NB4 and U937 cells, similar to all-trans RA (ATRA). A specific RAR alpha antagonist, Ro41-5253, significantly suppressed the upregulation of TM by ATRA and Am80 in NB4 cells, U937 cells, and HUVECs. In contrast, only with preincubation with both RAR alpha and RAR beta antagonists was downregulation of TF by retinoids suppressed in NB4 cells. These findings indicate that the mechanism of transactivation and transrepression functions of RARs are distinct and also elucidate the major role of RAR alpha in TM upregulation by retinoids in leukemic cells and HUVECs and the cooperation of RAR alpha and RAR beta in TF downregulation by retinoids. They also indicate that binding to CRABP is not required for the anticoagulant effect of retinoids and that synthetic retinoids will prove very useful in controlling distinct targets, the TM and TF genes, at the level of transcription, and will permit the development of retinoids with a new type of anticoagulant effect.

Anticoagulants↗
PubMed1980

The effects of retinoids on proliferative capacities and macromolecular synthesis in human breast cancer MCF-7 cells.

The effects of various retinoids on the proliferative capacities and on the synthesis of DNA, RNA, and protein have been investigated in MCF-7 mammary carcinoma cells in culture. Of the various retinoids tested, retinoic acid revealed maximum activity in inhibiting cell proliferation and thymidine incorporation. The degree of inhibition of cell proliferation by the various retinoids paralleled their capacity to inhibit thymidine incorporation, suggesting suppression of DNA synthesis as a primary cause of restriction of cell growth by these compounds. Two nonepithelial human cell lines were tested for sensitivity to retinoids, and showed diminished responses compared with MCF-7 cells. This suggests a correlation between the ability of retinoids to exert control of differentiation and cell proliferation for a given cell type. Reversibility of the effect of retinoid treatment, high cell viability, and lack of retinoid-induced lysosomal enzyme release, as shown in our studies, indicate that cytotoxicity may be excluded as a cause of decreased cell proliferation and inhibition of thymidine incorporation by retinoids.

Breast Neoplasms↗
PubMed1981

Structure-activity relationship of retinoids in fetal rat bone cultures.

The structure-activity relationship of 29 retinoids was investigated in fetal rat bone organ cultures. Retinoids induced the release of proteoglycan followed by cartilage tissue breakdown. In this study the loss of RNA was used as a parameter for cartilage resorption. During 6 days of incubation RNA decreased up to 80% in presence of active retinoids. Thus the ED40 was determined from dose-response curves of the various retinoids. The new compounds, called arotinoids, which contained the retinoic acid carbon skeleton in a fixed cisoid geometric conformation, were up to 200 times more active than all-trans-beta-retinoic acid. The most active compound contained a tetramethylated tetralin ring and a second aromatic ring in the side chain. Several lines of evidence indicated that the carboxylic acid end group was essential for the activity of retinoids in fetal bone cultures. The new, highly active retinoids described here might be an excellent tool to investigate whether the retinoid action is mediated by specific cellular retinoid binding proteins.

Animals↗
PubMed1990

Synthetic retinoids, retinobenzoic acids, Am80, Am580 and Ch55 regulate morphogenesis in chick limb bud.

The retinobenzoic acids Am80, Am580 and Ch55 are synthetic stable analogs of retinoic acid (RA), and show very strong differentiation-inducing activity in human myelogeneous leukemia cell line HL-60. To examine the effects of these synthetic retinoids on limb pattern formation, AG1-X2 beads containing these retinoids were applied to the anterior margin of stage 19-20 chick wing buds. By implanting the beads with 1 microgram/ml retinoids, normal wings were formed and extra digits 2 or 32 were rarely formed. As the retinoid concentrations increased from 10 micrograms/ml to 100 micrograms/ml duplicated limbs 3234, 43234, 432234, 4334 were progressively produced. At higher concentrations, 1 mg/ml, the wings often truncated, although duplication occurred in some embryos. These synthetic analogs seem to have the same degree of morphogenetic potential as RA, since the activity index of these retinoids was similar to that of RA. Since these synthetic retinoids hardly bind to CRABP (cellular retinoic acid-binding protein), it may be possible that the retinoids and RA may affect limb-pattern formation without the interaction with CRABP. It is known that limb buds cannot develop distal structures when the posterior region including all ZPA (zone of polarizing activity) is removed. When beads containing the above mentioned retinoids were implanted to the anterior margin of wing buds from which the posterior one third region including all ZPA had been removed, distal growth of the wing buds and the formation of digit elements were observed. Some of the wing buds produced a completely reverse digit pattern 432. From these results, we discussed the roles of RA in limb development and pattern formation.

Animals↗