全反式维甲酸对酒精性肝损伤大鼠肝脏retinoids含量和CYP2E1表达的影响

目的:研究补充小剂量全反式维甲酸(ATRA)对酒精喂养大鼠肝脏维生素A类物质(reti- noids,主要是维生素A和RA)含量、维生素A类物质极性代谢产物(PRMs)形成,细胞色素P4502E1(CYP2E1)表达和肝细胞损伤的影响。方法:将30只SD大鼠随机分为A组(正常对照组),B组(单纯乙醇组)、C组(无水乙醇8 g/kg ig8wk+150μg/kg ATRA)、D组(无水乙醇8 g/kg ig 8 wk+1.5 mg/kg ATRA ig 4 wk)四组.光镜下观察肝组织病理变化,高效液相色谱(HPLC)技术测定肝组织中Vitamin A类物质(retinoids)的含量,Western blotting检测肝脏CYP2E1的表达.结果:B组大鼠肝脏RA、维生素A(Retinol)和维生素A棕榈酸酯(retinyl palmitate)与A组相比含量显著降低(0.077±0.029 nmol/g vs 0.183±0.037 nmol/g,8.13±1.379 nmol/g vs 21.43±2.944 nmol/g,132.6±6.472 nmol/g vs 221.1±10.35 nmol/g,P<0.01),且肝脏中出现明显的PRMs.C组RA和Retinol含量恢复至A组水平,retinyl palmitate含量也部分恢复.D组RA和retinyl Dalmilate完全恢复至正常水平,而Retinol水平较A组升高(27.26±3.149 nmol/g vs 21.43±2.944 nmol/g,P<0.05).两种剂量的ATRA均可完全阻止PRMs形成.病理组织学检查显示补充ATRA可明显减轻肝细胞肿胀、脂肪变性,但对CYP2E1的表达没有明显影响。结论:小剂量ATRA能恢复酒精性肝病(ALD)大鼠肝脏retinoids含量,阻止PRMs产生,从而减轻肝细胞损伤.

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

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

Effect of ATRA on Contents of liver Retinoids, Oxidative Stress and Hepatic Injury in Rat Model of Extrahepatic Cholestasis

The effects of all-trans-retinoic acid （ATRA） administration on the concentration of retinoids （RA and vitamin A） in liver, oxidative stress and the hepatic injury in a rat model of common bile duct ligation （CBDL）-induced liver injury were investigated. Female rats were subjected to a sham （n=5） or CBDL （n=48）. Two weeks after operation, rats undergoing CBDL were randomized to receive treatment with either ATRA at three different doses （0.1, 1.5, 7.5 mg/kg） dissolved in bean oil or only bean oil every day over a 4-week experimental period. Rats were killed and blood samples were collected from the heart for determination of the serum transaminase. The contents of retinoids in rat liver were detected by using HPLC. Malondialdehyde （MDA）, glutathione （GSH） and superoxide dismutase （SOD） levels in liver were determined by a spectrophotometric method according to the instruction of the kits. Liver pathologic changes were observed under the light microscopy and electron microscopy. The results showed that compared with sham-operated group, the levels of retinoids in the liver tissue were significantly decreased in the CBDL group （P〈0.01）. ATRA （0.1 mg/kg） administration in CBDL rats partially restored the contents of retinoids （P〈0.05）. Liver RA and vita- min A contents in CBDL group were significantly increased after ATRA （1.5 and 7.5 mg/kg） supplementation as compared with sham-operated group （P〈0.05）. However, in ATRA-treated CBDL group, hepatic GSH level and SOD activity, depressed by CBDL, and hepatic MDA level, increased by CBDL were returned to those in sham-operated group （P〈0.05）. The histologic observation of liver tissues indicated that ATRA treatment notably alleviated hepatocellular swelling, steatosis, the. swelling of mitochondria and proliferation of smooth endoplasmic reticulum （SER）. Treatment with ATRA could reduce levels of serum transaminase as compared with sham-operated group, more greatly in 1.5 and 7.5 mg/kg ATRA-treated groups than in 0.1 mg/kg ATRA-treated group. It was concluded that ATRA treatment can recover MDA and GSH levels and SOD activity in CBDL rat liver through restoring RA and vitamin A contents, and eventually ameliorate liver injury.

Role of retinoids in the prevention and treatment of colorectal cancer

Vitamin A and its derivatives, retinoids, have been widely studied for their use as cancer chemotherapeutic agents. With respect to colorectal cancer(CRC), several critical mutations dysregulate pathways implicated in progression and metastasis, resulting in aberrant Wnt/β-catenin signaling, gain-of-function mutations in K-ras and phosphatidylinositol-3-kinase/Akt, cyclooxygenase-2 over-expression, reduction of peroxisome proliferatoractivated receptor γ activation, and loss of p53 function. Dysregulation leads to increased cellular proliferation and invasion and decreased cell-cell interaction and differentiation. Retinoids affect these pathways by various mechanisms, many involving retinoic acid receptors(RAR). RAR bind to all-trans-retinoic acid(ATRA) to induce the transcription of genes responsible for cellular differentiation. Although most research concerning the chemotherapeutic efficacy of retinoids focuses on the ability of ATRA to decrease cancer cell proliferation, increase differentiation, or promote apoptosis; as CRC progresses, RAR expression is often lost, rendering treatment of CRCs with ATRA ineffective. Our laboratory focuses on the ability of dietary vitamin A to decrease CRC cell proliferation and invasion via RAR-independent pathways. This review discusses our research and others concerning the ability of retinoids to ameliorate the defective signaling pathways listed above and decrease tumor cell proliferation and invasion through both RAR-dependent and RAR-independent mechanisms.

Combination therapies improve the anticancer activities of retinoids in neuroblastoma

Most therapeutic protocols for child cancers use cytotoxic agents which have a narrow therapeutic index,and resulting in severe acute and chronic toxicities to normal tissues. Despite the fact that most child cancer patients achieve complete remission after chemotherapy,death still occurs due to relapse of persistent minimal residual disease(MRD) which remaining after initial cytotoxic chemotherapy. Advanced neuroblastoma(NB) is a leading cause of cancer deaths in young children. Retinoids are an important component of advanced NB therapy at the stage of MRD,yet half of all patients treated with 13-cis-retinoic acid still relapse and die. More effective combination therapies,with a lower side-effect profile,are required to improve outcomes for NB. Fenretinide or N-4-hydroxyphenyl retinamide is a synthetic derivative of retinoic acid which works on cancer cells through nuclear receptor-dependent and-independent signalling mechanisms. Moreover,several histone deacetylase inhibitors have entered early phase trials,and,suberoylanilide hydroxamic acid has been approved for use in adult cutaneous T cell lymphoma. A number of studies suggest that retinoid signal activation is necessary for histone deacetylase inhibitor activity. A better understanding of their mechanism of actions will lead to more evidence-based retinoid combination therapies.

Protective role of retinoid X receptor in H9c2 cardiomyocytes from hypoxia/reoxygenation injury in rats

BACKGROUND: Retinoid X receptor(RXR) plays a central role in the regulation of intracellular receptor signaling pathways. The activation of RXR has protective effect on H2O2-induced apoptosis of H9c2 ventricular cells in rats. But the protective effect and mechanism of activating RXR in cardiomyocytes against hypoxia/reoxygenation(H/R)-induced oxidative iniury are still unclear.METHODS: The model of H/R injury was established through hypoxia for 2 hours and reoxygenation for 4 hours in H9c2 cardiomyocytes of rats. 9-cis-retinoic acid(9-cis RA) was obtained as an RXR agonist, and HX531 as an RXR antagonist. Cultured cardiomyocytes were randomly divided into four groups: sham group, H/R group, H/R+9-cis RA-pretreated group(100 nmol/L 9-cis RA), and H/R+9-cis RA+HX531-pretreated group(2.5 μmol/L HX531). The cell viability was measured by MTT, apoptosis rate of cardiomyocytes by flow cytometry analysis, and mitochondrial membrane potential(ΔΨm) by JC-1 fluorescent probe, and protein expressions of Bcl-2, Bax and cleaved caspase-9 with Western blotting. All measurement data were expressed as mean±standard deviation, and analyzed using one-way ANOVA and the Dunnett test. Differences were considered signif icant when P was <0.05.RESULTS: Pretreatment with RXR agonist enhanced cell viability, reduced apoptosis ratio, and stabled ΔΨm. Dot blotting experiments showed that under H/R stress conditions, Bcl-2 protein level decreased, while Bax and cleaved caspase-9 were increased. 9-cis RA administration before H/R stress prevented these effects, but the protective effects of activating RXR on cardiomyocytes against H/R induced oxidative injury were abolished when pretreated with RXR pan-antagonist HX531.CONCLUSION: The activation of RXR has protective effects against H/R injury in H9c2 cardiomyocytes of rats through attenuating signaling pathway of mitochondria apoptosis.

Retinoid X receptor α downregulation is required for tail and caudal spinal cord regeneration in the adult newt

Some adult vertebrate species,such as newts,axolotls and zebrafish,have the ability to regenerate their central nervous system（CNS）.However,the factors that establish a permissive CNS environment for correct morphological and functional regeneration in these species are not well understood.Recent evidence supports a role for retinoid signaling in the intrinsic ability of neurons,in these regeneration-competent species,to regrow after CNS injury.Previously,we demonstrated that a specific retinoic acid receptor（RAR）subtype,RARβ,mediates the effects of endogenous retinoic acid（RA）on neuronal growth and guidance in the adult newt CNS after injury.Here,we now examine the expression of the retinoid X receptor RXRα（a potential heterodimeric transcriptional regulator with RARβ）,in newt tail and spinal cord regeneration.We show that at 21 days post-amputation（dpa）,RXRαis expressed at temporally distinct periods and in non-overlapping spatial domains compared to RARβ.Whereas RARβprotein levels increase,RXRαproteins level decrease by 21 dpa.A selective agonist for RXR,SR11237,prevents both this downregulation of RXRαand upregulation of RARβand inhibits tail and caudal spinal cord regeneration.Moreover,treatment with a selective antagonist for RARβ,LE135,inhibits regeneration with the same morphological consequences as treatment with SR11237.Interestingly,LE135 treatment also inhibits the normal downregulation of RXRαin tail and spinal cord tissues at 21 dpa.These results reveal a previously unidentified,indirect regulatory feedback loop between these two receptor subtypes in regulating the regeneration of tail and spinal cord tissues in this regeneration-competent newt.

Redox-sensitive micelles for targeted intracellular delivery and combination chemotherapy of paclitaxel and all-trans-retinoid acid

The application of paclitaxel(PTX) in clinic has been restricted due to its poor solubility.Several traditional nano-medicines have been developed to improve this defect,while they are still lack of tumor targeting ability and rapid drug release. In this work,an amphiphilic polymeric micelle of hyaluronic acid(HA) – all-trans-retinoid acid(ATRA) with a disulfide bond,was developed successfully for the co-delivery of PTX and ATRA. The combination chemotherapy of PTX and ATRA can strengthen the anti-tumor activity. Along with selfassembling to micelles in water,the delivery system displayed satisfying drug loading capacities for both PTX(32.62% ± 1.39%) and ATRA,due to directly using ATRA as the hydrophobic group. Rapid drug release properties of the PTX-loaded redox-sensitive micelles(HA-SS-ATRA) in vitro were confirmed under reducing condition containing GSH. Besides,HA-CD44 mediated endocytosis promoted the uptake of HA-SS-ATRA micelles by B16 F10 cells. Due to these properties,cytotoxicity assay verified that PTX-loaded HA-SS-ATRA micelles showed concentration-dependent cytotoxicity and displayed obvious combination therapy of PTX and ATRA. Importantly,HA-SS-ATRA micelles could remarkably prolong plasma circulation time after intravenously administration. Therefore,redox-sensitive HASS-ATRA micelles could be utilized and explored as a promising drug delivery system for cancer combination chemotherapy.

视黄素受体介导的视黄素(retinoids)抗癌作用

对近年来视黄素受体介导视黄素抗癌作用机理的研究进展作一综述 ,主要有 :1)视黄素受体 ;2 )视黄素受体与细胞生长 ;3)视黄素受体与孤生受体的相关性 ;4 )视黄素受体对 AP- 1活性的抑制作用 ;5)视黄素受体介导的信号转导途径 .通过研究 ,对于探讨视黄素受体的功能、阐明视黄素的抗癌机理、合成更多的受体选择性视黄素具有重要的现实意义 .

RETINOIDS AND THEIR APPLICATIONS IN CLINIC

This review provides an overview of relevant aspects of retinoid physiology and molecular biology, and summarizes the current status of clinical investigations on the use of retinoid for the treatment of malignancies. The mechanism underlying the anticarcinogenic activity of retinoids appears to be associated with the ability of retinoids to modulate the growth and induce differentiation, and apoptosis of normal, premalignant, and malignant cells in vitro and in vivo. Retinoid effects seem to be resulted from changes in gene expression mediated via specific nuclear receptors (termed retinoic acid receptors, RAR-a, -b and -g). Chromosome translocations play an important role in APL pathogenesis. In the classical translocation, RAR a gene is fused with PML gene to form PML-RAR a chimeric gene, which is expressed in over 95% of the APL patients with t (15; 17) (q22; q21). Therefore, PML-RAR a fusion gene is the molecular marker of APL. ATRA can induce relocalization of the PML and restore the normal structure of POD. Furthermore, it could cause a degradation of PML-RAR a. In addition to the very high clinical response rate for APL patients treated with ATRA, clinical responses have been observed for patients with myelodysplastic syndrome, cutaneous T-cell lymphoma and skin cancers. Applications of retinoids are reviewed in different malignancies: including skin cancer, head and neck carcinoma, neuroblastoma, lung cancer, breast cancer, prostate cancer, bladder cancer and ovarian cancer in vivo and in vitro studies. The results indicate that retinoids are potentially useful agents for cancer prevention. RA combined with IFNs or RA combined with G-CSF has synergistic effect in inducing differentiation of cell growth. From current clinical results at least four leads are expected to impact on clinical development of retinoids in future: (1) development of retinoid receptor-selective agents; (2) investigation on cross-talk among members of the steroid superfamily; (3) strategies for attaining sufficient tissue levels of retinoids; (4) combined use with other differentiation or chemotherapeutic agents.

INHIBITION OF TELOMERASE ACTIVITY DURING INDUCTIONOF HL-60 CELLS BY RETINOID Ro13-7410

Objective: To investigate the effects of Ro13-7410 on telomerase activity and cell cycle distribution. Methods: Telomerase activity of HL-60 cells induced by retinoid Ro13-7410 was detected by telomerase PCR-ELISA-kit. The cell cycle was analyzed by flow cytometry. Results: Telomerase activity declined gradually after 10?6 mol/L Ro13-7410 treatment, and the inhibition of telomerase activity at day 5 of treatment with Ro13-7410 was less effective than with Retinoid Acid (RA). DNA flow cytofluorimetric analysis revealed that Ro13-7410 caused partial cells arrest in the G2/M phase after 4-days treatment. Conclusion: Telomerase activity declined gradually and partial cells were arrested in the G2/M phase after Ro13-7410 treatment.

Mechanisms of a Synthetic Retinoid in Inhibiting Tumor-Repopulating Cells

Recently we have synthesized a novel small retinoid molecule WYC-209 that can effectively inhibit proliferation of malignant murine melanoma tumor-repopulating cells(TRCs).The molecule can induce 100%TRCs apoptosis at 10μM concentration.However,how WYC-209 induces TRCs apoptosis is still elusive.Here we demonstrate that WYC-209 at>6μM concentration started to induce TRCs apoptosis primarily via the caspase 3 pathway by releasing cytochrome c from mitochondria.Interestingly,we found that at concentrations<6μM WYC-209 induced TRCs to elevate dormancy marker COUP TF1 but induced no changes in apoptosis marker P53.Furthermore,proliferation markers Ki67 and PCNA decreased with the increase of WYC-209 concentrations,suggesting that low concentrations of WYC-209 inhibit TRCs growth by inducing cell dormancy instead of causing apoptosis.In addition,TRC traction forces were almost abolished when WYC-209 concentration was at 5μM,preceding the initiation of apoptosis.Our findings demonstrate that inhibition of TRCs by anti-cancer molecule WYC-209 is concentration-dependent and WYC-209 inhibits cellular force generation of the tumor-repopulating cells before inducing apoptosis.

RETINOIC ACID NUCLEAR RECEPTORα （RARα），A MAJORROLE IN MEDIATING RETINOIDS INHIBITION OF GROWTH IN HU

Retinoids mediate their actions via RARs(retinoic acid receptors)and RXRs(retinoid X receptors).Each classes of these nuclear retinoid receptor is further subdiviede into three species namelyα,βand γ.Recent studies demonstrate that ER-positive HBC cell lines are sensitive and ER-negative cell lines are resistant to growth inhibitory effects of retinoic acid(RA). In this study we look at the expresion of RARs and RXRs in 6 HBC cell lines, we found only RARαmRNA level was strong correlated with ER-status. To further inestigate the major role of RARαin retinoidmediated inhibition of growth, we transfected RARαcDNA in two RA-resistant ER-negative HBC cell lines.Analyses of different clonal populations of RARα transfectants from each cell line revealed growth inhibition by retinoids. Our results demonstrates that RARα Plays a major role in mediating retinoids inhibition of growth in HBC cells and adequate levels are required for such actions.

Identification and Characterization of Human Genomic Binding Sites for Retinoic Acid Receptor/Retinoid X Receptor Heterodimers

All-trans retinoic acid (ATRA) triggers a wide range of effects on vertebrate development by regulating cell proliferation, differentiation, and apoptosis. ATRA activates retinoic acid receptors (RARs) which heterodimerize with retinoid X receptors (RXRs). RAR/RXR heterodimers function as ATRA-dependent transcriptional regulators by binding to retinoic acid response elements (RAREs). To identify RAR/RXR heterodimer-binding sites in the human genome, we performed a modified yeast one-hybrid assays and identified 193 RAR/RXR heterodimer-binding fragments in the human genome. The putative target genes included genes involved in development process and cell differentiation. Gel mobility shift assays indicated that 160 putative RAREs could directly interact with the RAR/RXR heterodimer. Moreover, 19 functional regulatory single nucleotide polymorphisms (rSNPs) on the RAR/RXR-binding sequences were identified by analyzing the difference in the DNA-binding affinities. These results provide insights into the molecular mechanisms underlying the physiological and pathological actions of RAR/RXR heterodimers.

Retinoids——癌症化学预防剂

RetinoJds(RNDs)指天然或合成的各种维生素A(VA)的代谢物或类似物．包括维甲醇．维甲醛．维甲酸(rednoic acid．RA)及维胺酸维胺脂等．RA衍生物主要包括全反式RA(ATRA)．13-顺式RA(13CRA)．9-顺式RA(9CRA)、维胺酸维胺酷等：RNDs已有百年的历史．尤其近25年掀起了RNDs革命．

Retinoid and Ethanol-Sensitive Benzo(<i>α</i>)Pyrene Induction of Cytochrome P450 in Human Keratinocytes

Polycyclic aromatic hydrocarbons (PAHs) induce cytochrome P-450 monoxygenase enzymes that catalyze the formation of DNA adducts. We investigated the effects benzo(α)pyrene (B[α]P) alone or in combination with ethanol on normal human keratinocyte (NHK) growth, induction of cytochrome P-4501A1 (CYP1A1), and modulation of these treatments by retinoic acid (RA) in a serum-free culture medium. Growth-arrested confluent NHK serum-free cultures were treated with B[α]P alone or in combination with ethanol and RA. The effects on CYP1A1 enzyme activity were investigated. B[α]P treatment alone was not toxic to post-confluent cells;sub-toxic ethanol stimulated cell growth regardless B[α]P treatment. No CYP1A1 activity was detected in control or ethanol-treated NHK cell cultures. B[α]P alone induced CYP1A1 activity, and B[α]P plus ethanol treatment further enhanced B[α]P-induced CYP1A1 activity. Pretreatment with all-trans-RA (t-RA) abolished ethanol enhancement of CYP1A1 activity. There is a synergistic action of ethanol in combination with PAH on induction of P-450 cytochrome enzymes. By contrast, RA reverses ethanol enhancement implying a role for retinoid therapy in counteracting the risk posed by combined alcohol and PAH exposure on epidermal cell carcinogenesis.

Cancer Chemopreventive Retinoids: Validation and Analysis of in Vivo and in Vitro Bioassay Results

Several natural and synthetic retinoids (vitamin-A derived analogies) were examined for their potential anti-cancer activity in both in vivo animal models and a novel in vitro human keratinocyte clonal growth bioassay system. The natural retinoids included all-trans-retinoic (RA), 13-cis-retinoic acid, 4-oxoretinoic acid, and retinol. Among the synthetic retinoids tested were all trans N-(4-hydroxy(phenyl)retinamide, 3-substituted oxoretinoic acids, and 13 cis-N-ethylretinamide. The animal models employed were: 1) vitamin A-deficient hamster tracheal organ assay (HTOC);2) the benzo(α)pyrene-induced squamous metaplasia in a hamster tracheal organ system (BP-HTOC);3) the mouse skin tumor promoter (TPA)-induced ornithine decarboxylase enzyme assay(ODC);4) the mouse skin papilloma (MPA) assay;and 5) a novel retinoid bioassay in which retinoids display IC50 values to inhibit clonal growth of NHK. All-trans-RA, 4-oxoretinoic acid and retinol were consistently more active than any of the synthetic derivatives in all bioassays tested. A statistical model was developed and significant positive correlations were found between: 1) ED50 values in the HTOC system and reduction in TPA-induced ODC enzyme activity;2) tumors per animal in the MPA bioassay and suppression of TPA-induced ODC activity;and 3) a positive correlation between suppression of tumors per animal in the MPA assay, and retinoid inhibition of keratinocyte clonal growth. Test retinoids, were tested for their capacity to inhibit the clonal growth of a squamous carcinoma cell line (SCC-25), which were found to be 2 - 3 logs less sensitive for each tested retinoid than the corresponding activity against NHK cells. Antineoplastic retinoid drugs were reviewed.

EFFECT OF HYDROGEN BONDING ON DIRECTION OF PHOTOISOMERIZATION OF RETINOIDS:THE ORIGIN OF THE SOLVENT POLARITY EFFECT.

Studies of direction of photoisomerization of retinal,retinonitrile,a- retinonitrile and a trienenitrile analog in different solvents with varying wave- lengths of excitation and reaction temperature led to the conclusion that the well known solvent dependent photochemistry of retinoids is due to selective excitation of the hydrogen bonded species.

非环式retinoid对肝癌根治疗法后复发的抑制效果

压制人类癌症最佳手段是阻断癌发生的一级预防。进而，对具有致癌危险因素的高危人群，倾向于免疫预防和化学预防。后者的重点是消灭癌前病变（细胞），“阻断癌的萌芽”，防患于未然。提倡这一新概念的是美国国立癌研究所的Ｓｐｏｒｎ博士，并首先发起了利用维生素Ａ衍生...

Study on the Equivalent Conformation of Retinoids

具有诱导细胞分化作用及癌和皮肤病化学治疗作用的维甲类化合物，不仅要求分子一端有疏水性、另一端为极性羧基和整个分子的共轭性，而且分子的构象也起重要作用。本文合成的Ｎ（４羧基苯基）３，５双叔丁基４羟基苯甲酰胺（２）具有与全反式维甲酸（ＡＴＲＡ，１）相似性质的基团配置和构象，表现有维甲酸的生物活性。然而Ｎ甲基化合物３，由于构象的完全不同，丧失了活性。用Ｘ线晶体学、紫外和核磁共振等方法研究了化合物２、３和ＡＴＲＡ的结构异同。