Brassinosteroids and analogs as neuroprotectors: synthesis and structure-activity relationships

We have demonstrated previously that the brassinosteroid (BR) 24-epibrassinolide exerts neuroprotective effects deriving from its antioxidative properties. In this study, we synthesized 2 natural BRs and 5 synthetic analogs and analyzed their neuroprotective actions in neuronal PC12 cells, against 1-methyl-4-phenylpyridinium (MPP(+)), a neurotoxin known to induce oxidative stress and degenerescence of dopaminergic neurons characteristic of Parkinsonian brains. We also tested the neuroprotective potential of 2 commercially available BRs. Our results disclosed that 6 of the 9 BRs and analogs tested protected neuronal PC12 cells against MPP(+) toxicity. In addition, our structure-activity study suggests that the steroid B-ring and lateral chain play an important role for their neuroprotective action.     

Indirubin derivatives protect against endoplasmic reticulum stress-induced cytotoxicity and down-regulate CHOP levels in HT22 cells

Indirubin and its derivatives have been reported to exhibit anti-cancer and anti-inflammatory activities. Recently, some of its derived analogs have been shown to have neuroprotective potential. Endoplasmic reticulum (ER) stress has been demonstrated to contribute to the pathogenesis of various neurodegenerative diseases, whereas the effects of indirubin derivatives on ER stress-induced cell death have not been addressed. In the present study, a series of 44 derivatives of indirubin was prepared to search for a novel class of neuroprotective agents against ER stress-induced neuronal death. The MTT reduction assay indicated that tunicamycin (TM), an inducer of ER stress, significantly decreased the viability of hippocampal neuronal HT22 cells. Among the compounds tested, eight showed significant inhibitory activity against TM-induced cell death. Western blot analysis showed that application of these analogs to the cells simultaneously with TM reduced the TM-induced expression of CHOP, an established mediator of ER stress. Our results suggest that the preventive effect of these indirubin derivatives against ER stress-induced neuronal death may be due, at least in part, to attenuation of the CHOP-dependent signaling system.     

Generation of a locomotory rhythm by a neural network with recurrent cyclic inhibition

An oscillatory intersegmental neuronal network drives the swimming rhythm of the leech. This network consists of interneurons joined via inhibitory connections to form a series of segmentally iterated, concatenated rings. Recurrent cyclic inhibition in these rings produces a multiphasic activity rhythm. By theoretical analysis of such concatenated interneuronal rings and construction of their electronic analogs it is shown that the interneural network identified in the central nervous system of the leech has properties appropriate for generating the observed motor output.     

Design,synthesis, and evaluation of curcumin-derived arylheptanoids for glioblastoma and neuroblastoma cytotoxicity

Using an innovative approach toward multiple carbon–carbon bond-formations that relies on the multifaceted catalytic properties of titanocene complexes we constructed a series of C1–C7 analogs of curcumin for evaluation as brain and peripheral nervous system anti-cancer agents. C2-Arylated analogs proved efficacious against neuroblastoma (SK-N-SH & SK-N-FI) and glioblastoma multiforme (U87MG) cell lines. Similar inhibitory activity was also evident in p53 knockdown U87MG GBM cells. Furthermore, lead compounds showed limited growth inhibition in vitro against normal primary human CD34+hematopoietic progenitor cells. Taken together, the present findings indicate that these curcumin analogs are viable lead compounds for the development of new central and peripheral nervous system cancer chemotherapeutics with the potential for little effects on normal hematopoietic progenitor cells.     

Cyclohexane 1,3-diones and their inhibition of mutant SOD1-dependent protein aggregation and toxicity in PC12 cells

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by the progressive loss of motor neurons. Currently, there is only one FDA-approved treatment for ALS (riluzole), and that drug only extends life, on average, by 2-3 months. Mutations in Cu/Zn superoxide dismutase (SOD1) are found in familial forms of the disease and have played an important role in the study of ALS pathophysiology. On the basis of their activity in a PC12-G93A-YFP high-throughput screening assay, several bioactive compounds have been identified and classified as cyclohexane-1,3-dione (CHD) derivatives. A concise and efficient synthetic route has been developed to provide diverse CHD analogs. The structural modification of the CHD scaffold led to the discovery of a more potent analog (26) with an EC(50) of 700 nM having good pharmacokinetic properties, such as high solubility, low human and mouse metabolic potential, and relatively good plasma stability. It was also found to efficiently penetrate the blood-brain barrier. However, compound 26 did not exhibit any significant life span extension in the ALS mouse model. It was found that, although 26 was active in PC12 cells, it had poor activity in other cell types, including primary cortical neurons, indicating that it can penetrate into the brain, but is not active in neuronal cells, potentially due to poor selective cell penetration. Further structural modification of the CHD scaffold was aimed at improving global cell activity as well as maintaining potency. Two new analogs (71 and 73) were synthesized, which had significantly enhanced cortical neuronal cell permeability, as well as similar potency to that of 26 in the PC12-G93A assay. These CHD analogs are being investigated further as novel therapeutic candidates for ALS.     

Effects of fluorophore structure and hydrophobicity on the uptake and metabolism of fluorescent lipid analogs

Cellular transport and metabolism of fatty acids are integral components of lipid metabolism, but the mechanisms and regulation involved are poorly understood. A variety of commercially available fluorescent analogs of fatty acids, are potentially useful probes for the study of lipid metabolism by such techniques as cell sorting and fluorescence microscopy. We have screened a series of fluorescent fatty acids to identify analogs that would reliably simulate the metabolic behavior of natural fatty acids; i.e., similar kinetics of transport, of intracellular movement, and of metabolic fate. The metabolic behavior of these analogs was compared with those of some naturally occurring fatty acids in HepG2 cells, which are a good model of some aspects of hepatic function. Fluorescent analogs containing polar fluorophores yielded the lowest rates of cellular uptake and conversion to acylated lipid products. Similarly, fluorescent analogs with the fluorophore located near the carboxylic acid group were poorly metabolized. Fatty acid analogs containing anthracene or pyrene at the n-terminus of the acyl chain were the most extensively incorporated into cellular lipids. The types and amounts of labeled lipid products formed from these analogs and from natural fatty acids were similar. Pyrene-labeled analogs have spectral properties that can be measured fluorometrically at very low concentrations. Therefore, we compared the cellular metabolism of 12-(1-pyrenyl)dodecanoic acid with those of palmitic and oleic acids.(ABSTRACT TRUNCATED AT 250 WORDS)     

Endomorphin-1 analogs with enhanced metabolic stability and systemic analgesic activity: design, synthesis, and pharmacological characterization

We synthesized four new analogs of endomorphin-1 by systematic chemical modifications. To identify the best possible drug candidates for clinical pain management and to investigate the potential contribution of these alterations to the biological activity, their pharmacological properties were determined. All of the analogs showed significantly enhanced metabolic stability. The fact that centrally mediated analgesia following peripheral administration was observed with one of the analogs suggested the approach design undertaken here had validity in the development of endomorphin-1 as a successful opioid drug for the clinic.     

Sulfoximines as ATR inhibitors: Analogs of VE-821

The ATM- and Rad3-related (ATR) kinases play a key role in DNA repair processes and thus ATR is an attractive target for cancer therapy. Here we designed and synthesized sulfilimidoyl- and sulfoximidoyl-substituted analogs of the sulfone VE-821, a reported ATR inhibitor. The properties of these analogs have been investigated by calculating physicochemical parameters and studying their potential to specifically inhibit ATR in cells. Prolonged inhibition of ATR by the analogs in a Burkitt lymphoma cell line resulted in enhanced DNA damage and a substantial amount of apoptosis. Together our findings suggest that the sulfilimidoyl- and sulfoximidoyl-substituted analogs are efficient ATR inhibitors.     

Exenatide promotes cognitive enhancement and positive brain metabolic changes in PS1-KI mice but has no effects in 3xTg-AD animals

Recent studies have shown that type 2 diabetes mellitus (T2DM) is a risk factor for cognitive dysfunction or dementia. Insulin resistance is often associated with T2DM and can induce defective insulin signaling in the central nervous system as well as increase the risk of cognitive impairment in the elderly. Glucagone like peptide-1 (GLP-1) is an incretin hormone and, like GLP-1 analogs, stimulates insulin secretion and has been employed in the treatment of T2DM. GLP-1 and GLP-1 analogs also enhance synaptic plasticity and counteract cognitive deficits in mouse models of neuronal dysfunction and/or degeneration. In this study, we investigated the potential neuroprotective effects of long-term treatment with exenatide, a GLP-1 analog, in two animal models of neuronal dysfunction: the PS1-KI and 3xTg-AD mice. We found that exenatide promoted beneficial effects on short- and long-term memory performances in PS1-KI but not in 3xTg-AD animals. In PS1-KI mice, the drug increased brain lactate dehydrogenase activity leading to a net increase in lactate levels, while no effects were observed on mitochondrial respiration. On the contrary, exenatide had no effects on brain metabolism of 3xTg-AD mice. In summary, our data indicate that exenatide improves cognition in PS1-KI mice, an effect likely driven by increasing the brain anaerobic glycolysis rate.     

Modeling of ionic channel properties and its role in shaping neuronal spike activity

An electronic analog of a neuron operating in real time is presented. The sequence of signal formation in the analog follows that of processes occurring at the synapse, postsynaptic membrane, and soma of the cell. Concepts of the synapse as a "key" and of the postsynaptic membrane as ionic channel with conductance changing under the action of transmitter and intracellular potential having been put into effect in the physical model, the neuronal analog could be set up along the same lines as a spike generator in which operation of the synaptic apparatus and the structure of neuronal dendrites could be reproduced. Spike train transformation processes typical of different types of neurons (such as motoneurons and Renshaw cells) were modeled by changing the parameters of membrane resistance and capacitance. Findings from research on simple neuronal networks have made it possible to use the analogs suggested to study the principles governing organization of neuronal structures as well as mechanisms underlying neuronal interaction, particularly those of the motor control system.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 21, No. 3, pp. 379–389, May–June, 1989.     

Vitamin D analogs and bone

Vitamin D analogs increase intestinal calcium absorption, and have been shown to possess antiresorptive and also bone anabolic properties in vivo. Therefore, the pharmacological profile of vitamin D analogs would be well suited for the treatment of osteoporosis. However, the calcemic side effects of this compound class, especially at higher doses, have hampered their wide use in osteoporotic patients. Nevertheless, the clear potential for bone anabolic properties together with oral availability have stimulated the interest in this substance class, and there is an active search for bone selective vitamin D compounds. After an overview of the physiological functions of vitamin D in bone, this article focuses on the effects of acute and chronic administration of pharmacological doses of vitamin D analogs on bone in animal models and humans. Furthermore, the endocrinological, cellular, and microanatomical mechanisms involved in the skeletal actions of vitamin D analogs are discussed. The final section briefly reviews the available data on possible bone selective vitamin D analogs.     

9-(Adenylyl)alkylcobalamins as inhibitors of adenosylcobalamin-dependent glycerol dehydratase from Aerobacter aerogenes

The behavior of two coenzyme analogs, [(5-aden-9-yl)methoxyethyl] cob (III) alamin and [(5-aden-9-yl)pentyl] cob (III) alamin modified at the nucleoside ligand sugar moiety was studied in the system of adenosyl-cobalamin-dependent glycerol dehydratase from Aerobacter aerogenes. It was shown that neither of the analogs possesses coenzyme properties and that both are strong competitive inhibitors for adenosylcobalamin (AdoCbl). The affinity of the two analogs for the apoenzyme is higher than that of AdoCbl. The data obtained are indicative of the essential role of the ribofuranoside fragment of AdoCbl in the manifestation of the coenzyme activity. The apoenzyme interaction with the analogs under study is discussed in terms of the Dreiding stereomodels for AdoCbl and its analogs.     

3-Ketone-4,6-diene ceramide analogs exclusively induce apoptosis in chemo-resistant cancer cells

Multidrug-resistance is a major cause of cancer chemotherapy failure in clinical treatment. Evidence shows that multidrug-resistant cancer cells are as sensitive as corresponding regular cancer cells under the exposure to anticancer ceramide analogs. In this work we designed five new ceramide analogs with different backbones, in order to test the hypothesis that extending the conjugated system in ceramide analogs would lead to an increase of their anticancer activity and selectivity towards resistant cancer cells. The analogs with the 3-ketone-4,6-diene backbone show the highest apoptosis-inducing efficacy. The most potent compound, analog 406, possesses higher pro-apoptotic activity in chemo-resistant cell lines MCF-7TN-R and NCI/ADR-RES than the corresponding chemo-sensitive cell lines MCF-7 and OVCAR-8, respectively. However, this compound shows the same potency in inhibiting the growth of another pair of chemo-sensitive and chemo-resistant cancer cells, MCF-7 and MCF-7/Dox. Mechanism investigations indicate that analog 406 can induce apoptosis in chemo-resistant cancer cells through the mitochondrial pathway. Cellular glucosylceramide synthase assay shows that analog 406 does not interrupt glucosylceramide synthase in chemo-resistant cancer cell NCI/ADR-RES. These findings suggest that due to certain intrinsic properties, ceramide analogs’ pro-apoptotic activity is not disrupted by the normal drug-resistance mechanisms, leading to their potential use for overcoming cancer multidrug-resistance.     

The potential of fluorescent and spin-labeled steroid analogs to mimic natural cholesterol

Cholesterol analogs are often used to investigate lipid trafficking and membrane organization of native cholesterol. Here, the potential of various spin (doxyl moiety) and fluorescent (7-nitrobenz-2-oxa-1,3-diazol-4-yl (NBD) group) labeled cholesterol analogs as well as of fluorescent cholestatrienol and the naturally occurring dehydroergosterol to mimic the unique properties of native cholesterol in lipid membranes was studied in 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) membranes by electron paramagnetic resonance, nuclear magnetic resonance, and fluorescence spectroscopy. As cholesterol, all analogs undergo fluctuating motions of large amplitude parallel to the bilayer normal. Native cholesterol keeps a strict orientation in the membrane with the long axis parallel to the bilayer normal. Depending on the chemical modification or the position of the label, cholesterol analogs may adopt an "up-side-down" orientation in the membrane or may even fluctuate between "upright" and up-side-down orientation by rotational motions about the short axis not typical for native cholesterol. Those analogs are not able to induce a comparable condensation of phospholipid membranes as known for native cholesterol revealed by 2H nuclear magnetic resonance. However, cholesterol-induced lipid condensation is one of the key properties of native cholesterol, and, therefore, a well suited parameter to assess the potential of steroid analogs to mimic cholesterol. The study points to extreme caution when studying cholesterol behavior by the respective analogs. Among seven analogs investigated, only a spin-labeled cholesterol with the doxyl group at the end of the acyl chain and the fluorophore cholestatrienol mimic cholesterol satisfactorily. Dehydroergosterol has a similar upright orientation as cholesterol and could be used at low concentration (about 1 mol %), at which its lower potential to enhance lipid packing density does not perturb membrane organization.     

Synthesis, DNA binding, and cytotoxic evaluation of new analogs of diallyldisulfide, an active principle of garlic

Diallyldisulfide (DADS), an active principle of garlic (Allium sativum) is known for its antihyperlipidemic properties. However, its use is limited due to its extreme volatility. In the present study, we have synthesized and characterized a series of six new DADS analogs and investigated their interactions with different DNA duplexes. The spectroscopic and circular dichroism (CD) analyses revealed that DADS analogs bind preferentially with GC rich sequences. Thermodynamic parameters suggest that DADS analogs stabilize the calf thymus (CT) DNA and GC rich duplex by favorable enthalpic gains and follow the hierarchy, d(GC)(7)>CT DNA>d(AT)(10). Further, DADS analogs are less toxic and equally effective as the statins. The analogs therefore have a good potential to provide a new therapeutic approach for the treatment of cardiovascular and related diseases.     

Monocarbonyl Analogs of Curcumin with Potential to Treat Colorectal Cancer

Curcumin has a plethora of biological properties, making this compound potentially effective in the treatment of several diseases, including cancer. However, curcumin clinical use is compromised by its poor pharmacokinetics, being crucial to find novel analogs with better pharmacokinetic and pharmacological properties. Here, we aimed to evaluate the stability, bioavailability and pharmacokinetic profiles of monocarbonyl analogs of curcumin. A small library of monocarbonyl analogs of curcumin 1a–q was synthesized. Lipophilicity and stability in physiological conditions were both assessed by HPLC-UV, while two different methods assessed the electrophilic character of each compound monitored by NMR and by UV-spectroscopy. The potential therapeutic effect of the analogs 1a–q was evaluated in human colon carcinoma cells and toxicity in immortalized hepatocytes. Our results showed that the curcumin analog 1e is a promising agent against colorectal cancer, with improved stability and efficacy/safety profile.     

Understanding effects on excitability of simulated <Emphasis Type="Italic">I</Emphasis><Subscript>h</Subscript> modulation in simple neuronal models

The hyperpolarization-activated, inward, mixed cation current, I _h, appears in a wide variety of cells in the nervous system, contributes to diverse neuronal properties, and is up-regulated by a number of important neurotransmitters. Up-regulation of I _h is usually associated with an excitability-enhancing depolarization of resting membrane potential and an excitability-depressing shunting effect caused by a decrease in input resistance. In order to gain a better understanding of the interaction of these effects and their influence on excitability with I _h modulation, we systematically analyze changes in neuronal properties associated with excitability during I _h modulation in simplified, yet, biophysical neuron models based on a hippocampal pyramidal neuron. We simulate I _h modulation by varying both its maximal conductance and its half-activation voltage, mimicking the effects of cAMP-linked neurotransmitters, through ranges of physiologically realistic parameter regimes. Of particular interest is the contribution of the different effects of I _h up-regulation when membrane potentials are held at common levels and neuronal excitability is probed. Our modeling results suggest that, although holding potentials at common levels may compensate for changes in resting membrane potentials, this protocol may exaggerate the excitability-depressing influences of changes in input resistances with I _h up-regulation.     

Studies of synthetic peptide analogs of the amphipathic helix. Effect of charge distribution, hydrophobicity, and secondary structure on lipid association and lecithin:cholesterol acyltransferase activation

Four peptides capable of forming an amphipathic alpha-helix have been synthesized and their conformational and lipid-binding properties studied. These peptides have been designed to vary the alpha-helix-forming potential as well as the charge distribution of the model peptide. The resulting peptide analogs and their complexes with dimyristoyl phosphatidylcholine were studied by using right angle light scattering, negative stain electron microscopy, nondenaturing gradient gel electrophoresis, circular dichroism, intrinsic tryptophan fluorescence, and differential scanning calorimetry techniques. The four analogs, [Glu4,9, Leu11,17] (reverse-18A, [Glu4,9, Leu5,11,17] reverse-18A, [Glu1,8, Leu11,17] 18A, and [Glu1,8, Leu5,11,17] 18A were derived from a model amphipathic peptide Asp-Trp-Leu-Lys-Ala-Phe-Tyr-Asp-Lys-Val-Ala-Glu-Lys-Leu-Lys-Glu-Ala-Phe (18A) whose lipid-associating properties strongly mimic apolipoprotein A-I or derived from Lys-Trp-Leu-Asp-Ala-Phe-Tyr-Lys-Asp-Val-Ala-Lys-Glu-Leu-Glu-Lys-Ala-Phe (reverse-18A), a peptide with little affinity for lipid and having a reversed charge distribution compared to the 18A peptide. We have shown that by substituting glutamic acid and leucine for aspartic acid and alanine, respectively, in a weak lipid-associating amphipathic helix peptide, the lipid-associating ability can be increased. Thus, peptides with both kinds of charge distribution can associate with the lipid. The ability of the peptide to disrupt phospholipid bilayers, however, is higher for 18A analogs compared to the reverse-18A analogs even after increasing the helix-forming potential and hydrophobicity. In addition to forming smaller lipoprotein particles, the modified 18A analogs were much superior to the modified reverse-18A analogs in their ability to activate the enzyme lecithin:cholesterol acyltransferase. This demonstrates that the positions of charged residues in the amphipathic helix play an important role in lecithin:cholesterol acyltransferase activation.     

Cell lineage in the developing neural tube.

Acquisition of cell type specific properties in the spinal cord is a process of sequential restriction in developmental potential. A multipotent stem cell of the nervous system, the neuroepithelial cell, generates central nervous system and peripheral nervous system derivatives via the generation of intermediate lineage restricted precursors that differ from each other and from neuroepithelial cells. Intermediate lineage restricted neuronal and glial precursors termed neuronal restricted precursors and glial restricted precursors, respectively, have been identified. Differentiation is influenced by extrinsic environmental signals that are stage and cell type specific. Analysis in multiple species illustrates similarities between chick, rat, mouse, and human cell differentiation. The utility of obtaining these precursor cell types for gene discovery, drug screening, and therapeutic applications is discussed.     

Synthesis and surface activity of diether-linked phosphoglycerols: potential applications for exogenous lung surfactants

The synthesis of three phosphoglycerols is described, one of which contains the previously unknown phosphonoglycerol headgroup. The surface tension-lowering capabilities of synthetic lung surfactant mixtures containing the PG analogs were measured on the pulsating bubble surfactometer and compared to known controls. The PG-containing mixtures exhibited superior surface tension-lowering properties indicating the significant potential of these analogs as components in synthetic exogenous lung surfactants.