Functional studies of newly synthesized benzoic acid derivatives: identification of highly potent retinoid-like activity

Regulating the Uptake of Viral Nanoparticles in Macrophage and Cancer Cells via a pH Switch

Controlling the uptake of nanomaterials into phagocytes is a challenging problem. We describe an approach to inhibit the cellular uptake by macrophages and HeLa cells of nanoparticles derived from bacteriophage Qβ by conjugating negatively charged terminal hexanoic acid moieties onto its surface. Additionally, we show hydrazone linkers can be installed between the surface of Qβ and the terminal hexanoic acid moieties, resulting in a pH-responsive conjugate that, in acidic conditions, can release the terminal hexanoic acid moiety and allow for the uptake of the Qβ nanoparticle. The installation of the "pH switch" did not change the structure-function properties of the hexanoic acid moiety and the uptake of the Qβ conjugates by macrophages.

Molecular Anti-inflammatory Mechanisms of Retinoids and Carotenoids in Alzheimer's Disease: a Review of Current Evidence

Alzheimer's disease (AD) is considered as one of the most prevalent neurodegenerative disorders characterized by progressive loss of mental function and ability to learn. AD is a multifactorial disorder. Various hypotheses are suggested for the pathophysiology of AD including "Aβ hypothesis," "tau hypothesis," and "cholinergic hypothesis." Recently, it has been demonstrated that neuroinflammation is involved in the pathogenesis of AD. Neuroinflammation causes synaptic dysfunction and neuronal death within the brain. Excessive production of pro-inflammatory mediators induces Aβ peptide production/accumulation and hyperphosphorylated tau generating inflammatory molecules and cytokines. These inflammatory molecules disrupt blood-brain barrier integrity and increase the production of Aβ42 oligomers. Retinoids and carotenoids are potent antioxidants and anti-inflammatory agents having neuroprotective properties. They are able to prevent disease progression through several mechanisms such as suppression of Aβ peptide production/accumulation, oxidative stress, and pro-inflammatory mediator's secretion as well as improvement of cognitive performance. These observations, therefore, confirm the neuroprotective role of retinoids and carotenoids through multiple pathways. Therefore, the administration of these nutrients is considered as a promising approach to the prevention and/or treatment of AD in the future. The aim of this review is to present existing evidences regarding the beneficial effects of retinoids and carotenoids on AD's risk and outcomes, seeking the mechanism of their action.

Retinoid signaling is necessary for, and promotes long-term memory formation following operant conditioning

Retinoic acid, a metabolite of vitamin A, is proposed to play an important role in vertebrate learning and memory, as well as hippocampal-dependent synaptic plasticity. However, it has not yet been determined whether retinoic acid plays a similar role in learning and memory in invertebrates. In this study, we report that retinoid signaling in the mollusc Lymnaea stagnalis, is required for long-term memory formation following operant conditioning of its aerial respiratory behaviour. Animals were exposed to inhibitors of the RALDH enzyme (which synthesizes retinoic acid), or various retinoid receptor antagonists. Following exposure to these inhibitors, neither learning nor intermediate-term memory (lasting 2 h) was affected, but long-term memory formation (tested at either 24 or 72 h) was inhibited. We next demonstrated that various retinoid receptor agonists promoted long-term memory formation. Using a training paradigm shown only to produce intermediate-term memory (lasting 2 h, but not 24 h) we found that exposure of animals to synthetic retinoids promoted memory formation that lasted up to 30 h. These findings suggest that the role of retinoids in memory formation is ancient in origin, and that retinoid signaling is also important for the formation of implicit memories, in addition to its previously demonstrated role in hippocampal-dependent memories.

Retinoids ameliorate insulin resistance in a leptin-dependent manner in mice

Transgenic mice expressing dominant-negative retinoic acid receptor (RAR) α specifically in the liver exhibit steatohepatitis, which leads to the development of liver tumors. Although the cause of steatohepatitis in these mice is unknown, diminished hepatic expression of insulin-like growth factor-1 suggests that insulin resistance may be involved. In the present study, we examined the effects of retinoids on insulin resistance in mice to gain further insight into the mechanisms responsible for this condition. Dietary administration of all-trans-retinoic acid (ATRA) significantly improved insulin sensitivity in C57BL/6J mice, which served as a model for high-fat, high-fructose diet-induced nonalcoholic fatty liver disease (NAFLD). The same effect was observed in genetically insulin-resistant KK-A(y) mice, occurring in concert with activation of leptin-signaling pathway proteins, including signal transducer and activator of transcription 3 (STAT3) and Janus kinase 2. However, such an effect was not observed in leptin-deficient ob/ob mice. ATRA treatment significantly up-regulated leptin receptor (LEPR) expression in the livers of NAFLD mice. In agreement with these observations, in vitro experiments showed that in the presence of leptin, ATRA directly induced LEPR gene expression through RARα, resulting in enhancement of STAT3 and insulin-induced insulin receptor substrate 1 phosphorylation. A selective RARα/β agonist, Am80, also enhanced hepatic LEPR expression and STAT3 phosphorylation and ameliorated insulin resistance in KK-A(y) mice.

CONCLUSION

We discovered an unrecognized mechanism of retinoid action for the activation of hepatic leptin signaling, which resulted in enhanced insulin sensitivity in two mouse models of insulin resistance. Our data suggest that retinoids might have potential for treating NAFLD associated with insulin resistance.

Tyrosinase inhibitory effect of benzoic acid derivatives and their structure-activity relationships

A series of benzoic acid derivatives 1-10 have been synthesised by two different methods. Compounds 1-6 were synthesised by a facile procedure for esterification using N,N'-dicyclohexylcarbodiimide (DCC) as a coupling agent, methylene chloride as a solvent system and dimethylaminopyridine (DMAP). While 7-10 were synthesised by converting benzoic acid into benzoyl chloride by treating with thionyl chloride in the presence of benzene and performing a further reaction with amine in dried benzene. The structures of all the synthesised derivatives of benzoic acid (1-10) were assigned on the basis of extensive NMR studies. All of them showed inhibitory potential against tyrosinase. Among them, compound 7 was found to be the most potent (1.09 μM) when compared with the standard tyrosinase inhibitors of kojic acid (16.67 μM) and L-mimosine (3.68 μM). Finally in this paper, we have discussed the structure-activity relationships of the synthesised molecules.

Towards retinoid therapy for Alzheimer's disease

Alzheimer's disease(AD) is associated with a variety of pathophysiological features, including amyloid plaques, inflammation, immunological changes, cell death and regeneration processes, altered neurotransmission, and age-related changes. Retinoic acid receptors (RARs) and retinoids are relevant to all of these. Here we review the pathology, pharmacology, and biochemistry of AD in relation to RARs and retinoids, and we suggest that retinoids are candidate drugs for treatment of AD.

2-(2-Methyl-5-nitro-1H-imidazol-1-yl)ethyl 3-bromo-benzoate

The mol-ecule of the title compound, C(13)H(12)BrN(3)O(4), is non-planar, as indicated in the dihedral angle of 59.5 (4)° formed between the least-squares planes through the imidazole and benzene rings. In the crystal, mol-ecules are connected via C-H⋯O contacts, forming a supra-molecular chain.

Synergistic potentiation of thiazolidinedione-induced ST 13 preadipocyte differentiation by RAR synergists

Peroxisome proliferator-activated receptor gamma (PPAR gamma) belongs to a nuclear receptor super family that functions as a master regulator of adipocyte differentiation. PPAR gamma binds its DNA response element together with a partner, retinoid X receptor (RXR), in fat cells. Five RXR ligands (HX600, HX630, DA022, DA124, LGD1069, referred to as retinoid synergists) by themselves exhibit weak transactivation activity on the PPAR gamma response element. However, addition of PPAR gamma-specific ligand in this assay gave rise to a 5- to 13-fold increase, indicating a strong synergy between these ligands. LGD1069 was the most effective activator of the RXR/PPAR gamma heterodimer on the transactivation of the reporter gene. But, in contrast to the other four RXR ligands, LGD1069 did not show synergistic induction of ST 13 preadipocytes to adipocytes. This apparent contradiction may result from the ligand-binding property of LGD1069. In this article we discuss the fact that retinoid synergists also act as PPAR gamma synergists.

Depletion of arylhydrocarbon receptor during adipose differentiation in 3T3-L1 cells

Arylhydrocarbon receptor (AhR) is the receptor for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and related compounds. Although a physiological ligand for AhR has yet to be identified, several lines of evidence suggest that AhR may play an important role not only in the regulation of xenobiotic metabolism but also in the maintenance of homeostatic functions. When TCDD is administrated in vivo, this compound is primarily deposited in adipose tissue. Therefore, it is critical to know the states of AhR in adipose cells for assessing the expression of toxicities of TCDD and related compounds in vivo. In this report, we examined the levels of AhR protein and its associated protein (Arnt) during the adipose differentiation in 3T3-L1 cells. The level of AhR protein was found to decrease with ongoing adipose differentiation in 3T3-L1 cells. The binding activity to the xenobiotic response element and the cellular response to TCDD were also lowered as a result of adipose differentiation. These results indicate that the depletion of AhR is a novel event associated with adipose differentiation in 3T3-L1 cells and that the magnitude of the depletion of AhR is sufficient for 3T3-L1 cells to lose the functional response to xenobiotics. We also found a population of 3T3-L1 cells which have an adipose differentiation capability in the presence of high doses of TCDD. These cells lack nuclear AhR but not cytoplasmic AhR, suggesting a possible negative role of liganded nuclear AhR in adipose differentiation. The level of the Arnt protein also decreased as a result of the differentiation. However, the pattern of the depletion of the Arnt protein was distinct from that of the AhR protein. The data presented in this study will provide opportunities to carry out studies to better understand the roles of AhR in adipose cells which are the primary targets of TCDD.

Biotransformation of a new synthetic retinoid, 4-[(5,6,7, 8-tetrahydro-5,5,8,8-tetramethyl-2-naphthyl)carbamoyl] benzoic acid (Am-80), in the rat. Structure elucidation of the metabolites by mass and nmr spectrometry

1. The major metabolites of Am-80 in rat bile were examined by tlc-radiochromatography and hplc-radiochromatography after the intravenous administration of 14C-Am-80, and > 15 metabolites were detected. 2. Intact and Glusulase-treated bile were analysed by both tlc-radiochromatography and hplc-radiochromatography. As both samples gave similar patterns in both chromatography systems, we have concluded that neither glucuronide nor sulphate conjugates were present. 3. 2H3-Am-80 and 2H6-Am-80 were administered to rats, and the major metabolites in bile were detected and their structures elucidated by GC-MS. 4. The chemical structures of seven major biliary metabolites, including unchanged Am-80, were identified by mass and two-dimensional nmr spectrometry, and included 6-hydroxy-Am-80 (M-3), 7-hydroxy-Am-80 (M-4), 6-oxo-Am-80 (M-5), unchanged Am-80 (M-0) and the taurine conjugates of M-3 (M-1), M-4 (M-2) and M-0 (M-6).

Retinoids are positive effectors of adipose cell differentiation

Retinoids, especially all-trans retinoic acid (t-RA), have been reported in the last decade to inhibit the differentiation of preadipose cells. In those studies, however, the concentrations of t-RA were supraphysiological (0.1-10 microM range). In contrast we show that, when present at concentrations below or close to the Kd values of retinoic acid receptors, retinoids behave as potent adipogenic hormones (1 pM to 10 nM range). As shown by the use of specific ligands for each RAR subtype, these positive effects on adipose differentiation involve in particular the RAR alpha subtype, and have been observed in Ob17 cells exposed to serum-supplemented or serum-free medium, and in rat preadipocytes exposed to serum-free medium. Among the two classes of retinoid acid receptors (RARs) and retinoid X receptors (RXRs), RAR alpha, RAR gamma, RXR alpha and RXR beta mRNAs could be detected in growing adipoblasts and were found to be increased in committed preadipocytes and differentiated cells upon retinoid treatment. Like other adipogenic hormones, retinoids were only effective in the terminal differentiation process leading from preadipocytes to adipocytes.

Radicicol, a microbial cell differentiation modulator, inhibits in vivo angiogenesis

Angiogenesis plays a significant role in various pathological states, including the progressive growth of solid tumors, rheumatoid arthritis, psoriasis, and diabetic retinopathy, in addition to its crucial role in embryonic development. Recent studies have revealed that an angiogenesis inhibitor is efficacious for these so-called angiogenic diseases. In the previous studies, we found that retinoids and vitamin D3 analogs, which are known to exhibit cell differentiation-modulating activity, effectively inhibit angiogenesis in vivo, thus forming the basis of our working hypothesis that a modulator of cell differentiation is capable of affecting angiogenesis. In this study, to verify this hypothesis further, radicicol (syn. monorden; 5-chloro-6-(7,8-epoxy-10-hydoxy-2-oxo-3,5-undecadienyl)-beta -resorcylic acid mu-lactone), a microbial cell differentiation modulator from a fungus, a strain of Neocosmospora tenuicristata, was examined for its anti-angiogenic activity in a bioassay system involving chorioallantoic membranes of growing chick embryos. The microbial cell differentiation modulator dose dependently inhibited embryonic angiogenesis, the ID50 value being 200 ng/egg. Radicicol also inhibited both the proliferation of and plasminogen activator production by vascular endothelial cells in the nM concentration range in a concentration-dependent manner, suggesting the possible involvement of these inhibitory effects in the anti-angiogenic action of the microbial product. These results indicate that radicicol might be a potential drug for treating different angiogenesis-dependent diseases, such as solid tumors, psoriasis, rheumatoid arthritis, and diabetic retinopathy.

Characterization of environmental regulators of Bordetella pertussis

Bordetella pertussis suppresses transcription of its virulence genes in response to specific environmental conditions, a response called modulation. The organism responds to high concentrations of SO4 and CIO4 ions, nicotinic acid, and nicotinic acid analogs in vitro; however, the in vivo modulator has not been identified. We investigated which chemical structures of the nicotinic acid molecule are important for modulation by testing various analogs for their ability to modulate. The ring nitrogen of nicotinic acid was not required, since benzoic acid was a modulator. In contrast, the carboxyl group was required, since derivatives like ethylnicotinate, 3-pyridylcarbinol, 3-acetyl pyridine, and 6-chloronicotinamide with altered carboxyl groups were not modulators. The planar ring structure or resonance in the ring was required for modulation, since nipecotic acid failed to modulate. The most potent modulators were nicotinic acid derivatives with electron-withdrawing substituents in the meta or para position relative to the carboxyl group. Relative hydrophilicity of substituents did not appear to contribute to modulation. Although these modulators elicited a clear biological response, the mechanism of modulation remains unclear, because no binding of the modulator 35SO4 or [14C]4-chlorobenzoic acid to whole B. pertussis was detected. However, modulation appears to involve a charge-charge interaction, since the response was blocked by chlorine ions.

The respecification of limb pattern by new synthetic retinoids and their interaction with cellular retinoic acid-binding protein

We describe here experiments to examine the role of cellular retinoic-acid-binding protein (CRABP) during the induction of limb duplication in the chick limb bud and regenerating axolotl limb by retinoids. A newly synthesised class of retinoic acid analogues have been used because among them, some have been specifically designed with the property of binding to the retinoic acid receptors, but not to CRABP. We can thus test whether binding to CRABP is an obligatory step during limb respecification. The binding of four of these compounds to chick limb bud and axolotl CRABP was tested in sucrose density gradient assays and then their potencies at inducing limb duplications tested. Two of the four compounds do not bind to limb CRABP and yet are able to induce limb duplications, suggesting that an interaction with CRABP is not an obligatory step in the process. However, the two compounds which do bind to CRABP are more potent than the two which do not, suggesting that an interaction with CRABP may, nevertheless, increase the potency of a retinoid.

A highly potent antiangiogenic activity of retinoids

Four retinoids, i.e. retinol (vitamin A), retinoic acid, retinyl acetate and synthetic chalcone carboxylic acid (Ch 55), were examined for their effects on embryonic angiogenesis using 4.5-day chorioallantoic membranes of chick embryo. The effects of these retinoids were compared with that of antibiotic herbimycin A, which was the most powerful inhibitor of the angiogenesis reported previously. The four retinoids strongly inhibited embryonic angiogenesis; the order of inhibitory activity was Ch 55 greater than retinoic acid greater than herbimycin A greater than retinyl acetate based on the dose required for the half-maximal inhibitory effect. The present results suggest that retinoids are effective inhibitors of angiogenesis, and can be applied for the management of certain diseases accompanied by aberrant angiogenesis, particularly that which occurs during progressive growth of solid tumors.

Sodium butyrate selectively antagonizes the inhibitory effect of retinoids on cornified envelope formation in cultured human keratinocytes

Sodium butyrate affects cell differentiation in confluent epidermal keratinocyte cultures by considerably increasing the spontaneous formation of cross-linked envelopes in normal human keratinocytes (NHK). It also favors the development of envelope competence in the Simian virus-40 (SV-40)-transformed human foreskin keratinocyte line SV-K14. It completely abolishes the inhibitory effect of serum and retinoic acid on the expression of plasma membrane-associated transglutaminase. However, other markers of epidermal differentiation that are also under the control of retinoids such as keratins or the enzyme cholesterol sulfotransferase are not affected by butyrate. The level of the cellular retinoic acid binding protein (CRABP) is considerably increased in its presence. Butyrate does not interfere with the binding of retinoids to their cellular binding proteins. Our observations suggest that sodium butyrate stimulates cornified envelope formation via the induction of the plasma membrane-associated transglutaminase required for cornified envelope synthesis and, additionally, by abolishing the inhibitory effect of retinoids on the expression of this enzyme.

Specific uptake of retinoids into human promyelocytic leukemia cells HL-60 by retinoid-specific binding protein: possibly the true retinoid receptor

The uptake of all-trans-retinoic acid (RA) and two new retinoids [4-(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthalenylcarbamoyl )benzoic acid (Am80) and (E)-4-[3-(3,5-di-tert-butylphenyl)-3-oxo-1-propenyl]benzoic acid (Ch55)] by HL-60 human promyelocytic leukemia cells was investigated. For the investigation, [3H]RA and [3H]Am80 with high specific radioactivities (more than 50 Ci/mmol) were used. [3H]Am80 was prepared by hydrogenolysis of the corresponding chlorinated derivative of Am80 with tritium gas. The retinoids RA, Am80 and Ch55 were efficiently taken up by HL-60 cells, and induced differentiation of the cells into mature granulocytes. The specific bindings (uptake) of RA, Am80 and Ch55 (the bindings inhibited competitively by the other two retinoids) by HL-60 cells were due to a newly detected binding protein. The protein that bound specifically to RA appeared identical to that which bound specifically to Am80 by high-performance liquid chromatography (HPLC), and was named retinoid-specific binding protein (RSBP). One HL-60 cell was found to contain about 1500 molecules of RSBP distributed between the nuclear fraction and cytosolic fraction in proportions of about 4:1. The bindings of the three retinoids (RA, Am80 and Ch55) to RSBP (i.e., formation of retinoid-RSBP complexes) greatly enhanced the affinity of RSBP for the nuclei. The apparent molecular weight of RSBP was estimated to be 95,000 daltons by size exclusion HPLC. The association constants (Ka) of RSBP were calculated to be 2.4 X 10(10) M-1 for RA and 4.4 X 10(10) M-1 for Am80 from Scatchard plots. The bindings of RA, Am80 and Ch55 to RSBP were mutually competitive, indicating that the binding sites for RA, Am80 and Ch55 were identical. The very high affinities of these retinoids for RSBP (Ka's of the order of 10(10) M-1) correspond to the effective concentrations of these retinoids in HL-60 cell culture medium for induction of differentiation of the cells. The mutually competitive bindings of these retinoids strongly support the idea that RSBP is the true receptor of retinoids.