A cellular model for screening neuronal nitric oxide synthase inhibitors

A reliable fluorimetric method to screen the nitric oxide synthase inhibitors in 96 well plate

In general, 4 amino-5-methylamino-2',7'-difluorescein diacetate (DAF-FM-DA) dye is used to detect nitric oxide in biological systems through cell imaging. In this study, we have used 96 well plate format to quantify nitric oxide using DAF-FM-DA through a multimode reader (or independently using fluorospectrometer) and could be visualized in a fluorescence microscope. Similar study otherwise will require a high-end instrument. The method has been validated to screen NOS inhibitors in the HEK 293T cell lines over-expressing the NOS isoforms. We observed that the method is very simple to use, adaptive, sensitive and most importantly it saves time. REAGENTS/TOOLS: Ethanol (70% [v/v] in distilled water), Nω-Nitro-l-arginine (l-NAME), 7-Nitro-Indazole (7-NI) (Sigma, St. Louis, MO), HEK 293T cell lines (National Centre for Cell Science (NCCS), Pune, India), DMEM (Himedia laboratories Pvt), Fetal Bovine Serum (FBS) (Invitrogen, Carlsbad, CA), 100 U/mL penicillin, and 0.1 mg/mL streptomycin in a 5% CO2 atmosphere. Hank's Balanced Salt Solution (HBSS) without Phenol Red of pH 7.4 was prepared with the following composition: NaCl, 8.0g, KCl, 0.4g, CaCl₂, 0.14g, MgSO₄⋅7H₂O, 0.1g, MgCl₂·6H₂O, 0.1g, Na₂HPO₄·2H₂O, 0.06g, KH₂PO₄, 0.06g, glucose, 1.0g, NaHCO₃, 0.35g, H₂O, to 1000 ml, Sterilized and refrigerated, Calcium Ionophore A23187 (Sigma Aldrich 52665-69-7) DAF-FM Di Acetate (Molecular Probes Life Technologies), and DAF-FM Di Aceatate was prepared as a stock solution (5 mM) in DMSO, divided into aliquots and stored at -20 °C, followed by dilution to the required concentration in HBSS buffer before use. EQUIPMENT: Neubauer chamber, Microtube centrifuges (1.5 mL), Micropipettors,10,100, and 1000 mL with corresponding tips, multimode reader (Tecan, Synergy-HT), inverted fluorescence microscope (Nikon, eclipse Ti-S), black flat bottom Microplates (96-well) (Corning 3603).

S-nitrosylation of UCHL1 induces its structural instability and promotes α-synuclein aggregation

Ubiquitin C-terminal Hydrolase-1 (UCHL1) is a deubiquitinating enzyme, which plays a key role in Parkinson’s disease (PD). It is one of the most important proteins, which constitute Lewy body in PD patient. However, how this well folded highly soluble protein presents in this proteinaceous aggregate is still unclear. We report here that UCHL1 undergoes S-nitrosylation in vitro and rotenone induced PD mouse model. The preferential nitrosylation in the Cys 90, Cys 152 and Cys 220 has been observed which alters the catalytic activity and structural stability. We show here that nitrosylation induces structural instability and produces amorphous aggregate, which provides a nucleation to the native α-synuclein for faster aggregation. Our findings provide a new link between UCHL1-nitrosylation and PD pathology.

Smooth muscle relaxation and activation of the large conductance Ca(++)-activated K+ (BK(Ca)) channel by novel oestrogens

BACKGROUND AND PURPOSE

Oestrogens can interact directly with membrane receptors and channels and can activate vascular BK(Ca) channels. We hypothesized that novel oestrogen derivatives could relax smooth muscle by an extracllular effect on the α and β1 subunits of the BK(Ca) channel, rather than at an intracellular site.

EXPERIMENTAL APPROACH

We studied the effects of novel oestrogens on the tension of pre-contracted isolated rat aortic rings, and on the electrophysiological properties of HEK 293 cells expressing the hSloα or hSloα+β1 subunits. Two of the derivatives incorporated a quaternary ammonium side-chain making them membrane impermeable.

KEY RESULTS

Oestrone, oestrone oxime and Quat DME-oestradiol relaxed pre-contracted rat aorta, but only Quat DME-oestradiol-induced relaxation was iberiotoxin sensitive. However, only potassium currents recorded in HEK 293 cells over-expressing both hSloα and hSloβ1 were activated by oestrone, oestrone oxime and Quat DME-oestradiol.

CONCLUSION AND IMPLICATIONS

The novel oestrogens were able to relax smooth muscle, but through different mechanisms. In particular, oestrone oxime required the presence of the endothelium to exert much of its effect, whilst Quat DME-oestradiol depended both on NO and BK(Ca) channel activation. The activation of BK(Ca) currents in HEK 293 cells expressing hSloα+β1 by Quat DME-oestradiol is consistent with an extracellular binding site between the two subunits. The binding site resides between the extracellular N terminal of the α subunit and the extracellular loop between TM1 and 2 of the β1 subunit. Membrane-impermeant Quat DME-oestradiol lacks an exchangeable hydrogen on the A ring obviating antioxidant activity.

Zhankuic acid A isolated from Taiwanofungus camphoratus is a novel selective TLR4/MD-2 antagonist with anti-inflammatory properties

TLR4, a membrane receptor that functions in complex with its accessory protein myeloid differentiation factor-2 (MD-2), is a therapeutic target for bacterial infections. Taiwanofungus camphoratus is highly valued as a medicinal mushroom for cancer, hypertension, and inflammation in traditional medicine. Zhankuic acid A (ZAA) is the major pharmacologically active compound of T. camphoratus. The mechanism of action of T. camphoratus or ZAA has not been fully elucidated. We analyzed the structure of human TLR4/MD-2 complex with ZAA by X-score and HotLig modeling approaches. Two Abs against MD-2 were used to verify the MD-2/ZAA interaction. The inflammation and survival of the mice pretreated with ZAA and injected with LPS were monitored. The modeling structure shows that ZAA binds the MD-2 hydrophobic pocket exclusively via specific molecular recognition; the contact interface is dominated by hydrophobic interactions. Binding of ZAA to MD-2 reduced Ab recognition to native MD-2, similar to the effect of LPS binding. Furthermore, ZAA significantly ameliorated LPS-induced endotoxemia and Salmonella-induced diarrhea in mice. Our results suggest that ZAA, which can compete with LPS for binding to MD-2 as a TLR4/MD-2 antagonist, may be a potential therapeutic agent for gram-negative bacterial infections.

Simplified 2-aminoquinoline-based scaffold for potent and selective neuronal nitric oxide synthase inhibition

Since high levels of nitric oxide (NO) are implicated in neurodegenerative disorders, inhibition of the neuronal isoform of nitric oxide synthase (nNOS) and reduction of NO levels are therapeutically desirable. Nonetheless, many nNOS inhibitors mimic l-arginine and are poorly bioavailable. 2-Aminoquinoline-based scaffolds were designed with the hope that they could (a) mimic aminopyridines as potent, isoform-selective arginine isosteres and (b) possess chemical properties more conducive to oral bioavailability and CNS penetration. A series of these compounds was synthesized and assayed against purified nNOS enzymes, endothelial NOS (eNOS), and inducible NOS (iNOS). Several compounds built on a 7-substituted 2-aminoquinoline core are potent and isoform-selective; X-ray crystallography indicates that aminoquinolines exert inhibitory effects by mimicking substrate interactions with the conserved active site glutamate residue. The most potent and selective compounds, 7 and 15, were tested in a Caco-2 assay and showed good permeability and low efflux, suggesting high potential for oral bioavailability.

On the selectivity of neuronal NOS inhibitors

Background and Purpose

Isoform-selective inhibitors of NOS enzymes are desirable as research tools and for potential therapeutic purposes. Vinyl-l-N-5-(1-imino-3-butenyl)-l-ornithine (l-VNIO) and N^ω-propyl-l-arginine (NPA) purportedly have good selectivity for neuronal over endothelial NOS under cell-free conditions, as does N-[(3-aminomethyl)benzyl]acetamidine (1400W), which is primarily an inducible NOS inhibitor. Although used in numerous investigations in vitro and in vivo, there have been surprisingly few tests of the potency and selectivity of these compounds in cells. This study addresses this deficiency and evaluates the activity of new and potentially better pyrrolidine-based compounds.

Experimental Approach

The inhibitors were evaluated by measuring their effect on NMDA-evoked cGMP accumulation in rodent hippocampal slices, a response dependent on neuronal NOS, and ACh-evoked cGMP synthesis in aortic rings of the same animals, an endothelial NOS-dependent phenomenon.

Key Results

l-VNIO, NPA and 1400W inhibited responses in both tissues but all showed less than fivefold higher potency in the hippocampus than in the aorta, implying useless selectivity for neuronal over endothelial NOS at the tissue level. In addition, the inhibitors had a 25-fold lower potency in the hippocampus than reported previously, the IC₅₀ values being approximately 1 μM for l-VNIO and NPA, and 150 μM for 1400W. Pyrrolidine-based inhibitors were similarly weak and nonselective.

Conclusion and Implications

The results suggest that l-VNIO, NPA and 1400W, as well as the newer pyrrolidine-type inhibitors, cannot be used as neuronal NOS inhibitors in cells without stringent verification. The identification of inhibitors with useable selectivity in cells and tissues remains an important goal.

Selective monocationic inhibitors of neuronal nitric oxide synthase. Binding mode insights from molecular dynamics simulations

The reduction of pathophysiologic levels of nitric oxide through inhibition of neuronal nitric oxide synthase (nNOS) has the potential to be therapeutically beneficial in various neurodegenerative diseases. We have developed a series of pyrrolidine-based nNOS inhibitors that exhibit excellent potencies and isoform selectivities (J. Am. Chem. Soc. 2010, 132, 5437). However, there are still important challenges, such as how to decrease the multiple positive charges derived from basic amino groups, which contribute to poor bioavailability, without losing potency and/or selectivity. Here we present an interdisciplinary study combining molecular docking, crystallography, molecular dynamics simulations, synthesis, and enzymology to explore potential pharmacophoric features of nNOS inhibitors and to design potent and selective monocationic nNOS inhibitors. The simulation results indicate that different hydrogen bond patterns, electrostatic interactions, hydrophobic interactions, and a water molecule bridge are key factors for stabilizing ligands and controlling ligand orientation. We find that a heteroatom in the aromatic head or linker chain of the ligand provides additional stability and blocks the substrate binding pocket. Finally, the computational insights are experimentally validated with double-headed pyridine analogues. The compounds reported here are among the most potent and selective monocationic pyrrolidine-based nNOS inhibitors reported to date, and 10 shows improved membrane permeability.

Establishment of a cell-based drug screening model for identifying agonists of human peroxisome proliferator-activated receptor gamma (PPARγ)

OBJECTIVES

Peroxisome proliferator-activated receptor gamma (PPARγ) plays a critical role in regulation of diverse biological processes, including lipid metabolism and adipogenesis, cell division and apoptosis, and is involved in variety of disease conditions, such as obesity, atherosclerosis, inflammation and tumour. Developing a cell-based reporter gene model targeting PPARγ would be useful to screen human PPARγ agonists that could be beneficial to patients with these diseases.

METHODS

We stably co-transfected human embryonic kidney (HEK) cell line 293T cells with phPPARγ-IRES2-EGFP vector to express human PPARγ (hPPARγ), a reporter vector pPPRE×3-TK-LUC, and control vector pRL-CMV. The efficiency of the co-transfection was evaluated with flow cytometry of hPPARγ expressing cells. Specificity of hPPARγ activity was determined by dual luciferase reporter assay of co-transfected cells exposed to PPARγ agonist rosiglitazone, PPARα agonist WY14643 and retinoic acid receptor alpha (RARα) agonist all-trans-retinoic acid (ATRA).

KEY FINDINGS

The phPPARγ-IRES2-EGFP co-transfected HEK293T cells showed concentration- and time-dependent luciferase induction upon exposure to the rosiglitazone, while WY14643 and ATRA were unable to activate the co-transfected HEK293T cells.

CONCLUSIONS

These data indicated that the HEK293T cells could be stably transfected with hPPARγ. This cell-based drug screening platform could be used targeting specific nuclear receptor of hPPARγ with effectiveness and specificity for hPPARγ agonists discovery.

Intramolecular hydrogen bonding: a potential strategy for more bioavailable inhibitors of neuronal nitric oxide synthase

Selective neuronal nitric oxide synthase (nNOS) inhibitors have therapeutic applications in the treatment of numerous neurodegenerative diseases. Here we report the synthesis and evaluation of a series of inhibitors designed to have increased cell membrane permeability via intramolecular hydrogen bonding. Their potencies were examined in both purified enzyme and cell-based assays; a comparison of these results demonstrates that two of the new inhibitors display significantly increased membrane permeability over previous analogs. NMR spectroscopy provides evidence of intramolecular hydrogen bonding under physiological conditions in two of the inhibitors. Crystal structures of the inhibitors in the nNOS active site confirm the predicted non-intramolecular hydrogen bonded binding mode. Intramolecular hydrogen bonding may be an effective approach for increasing cell membrane permeability without affecting target protein binding.

Symmetric double-headed aminopyridines, a novel strategy for potent and membrane-permeable inhibitors of neuronal nitric oxide synthase

We report novel neuronal nitric oxide synthase (nNOS) inhibitors based on a symmetric double-headed aminopyridine scaffold. The inhibitors were designed from crystal structures of leads 1 and 2 (Delker, S. L.; Ji, H.; Li, H.; Jamal, J.; Fang, J.; Xue, F.; Silverman, R. B.; Poulos, T. L. Unexpected binding modes of nitric oxide synthase inhibitors effective in the prevention of cerebral palsy . J. Am. Chem. Soc. 2010, 132, 5437-5442) and synthesized using a highly efficient route. The best inhibitor, 3j, showed low nanomolar inhibitory potency and modest isoform selectivity. It also exhibited enhanced membrane permeability. Inhibitor 3j binds to both the substrate site and the pterin site in nNOS but only to the substrate site in eNOS. These compounds provide a basis for further development of novel, potent, isoform selective, and bioavailable inhibitors for nNOS.

Potent and selective neuronal nitric oxide synthase inhibitors with improved cellular permeability

Recently, a series of potent and selective neuronal nitric oxide synthase inhibitors containing two basic nitrogen atoms was reported (Ji, H.; Stanton, B. Z.; Igarashi, J.; Li, H.; Martásek, P.; Roman, L. J.; Poulos, T. L.; Silverman, R. B. J. Am. Chem. Soc. 2008, 130, 3900-3914). In an effort to improve their bioavailability, three compounds (2a-c) were designed with electron-withdrawing groups near one of the basic nitrogen atoms to lower its pK(a). Inhibition studies with these compounds showed that two of them not only retained most of the potency and selectivity of the best analogue of the earlier series, but also showed improved membrane permeability based on data from a cell-based assay.

Roles of nitric oxide synthase isoforms in cutaneous vasodilation induced by local warming of the skin and whole body heat stress in humans

Nitric oxide (NO) participates in the cutaneous vasodilation caused by increased local skin temperature (Tloc) and whole body heat stress in humans. In forearm skin, endothelial NO synthase (eNOS) participates in vasodilation due to elevated Tloc and neuronal NO synthase (nNOS) participates in vasodilation due to heat stress. To explore the relative roles and interactions of these isoforms, we examined the effects of a relatively specific eNOS inhibitor, N(omega)-amino-l-arginine (LNAA), and a specific nNOS inhibitor, N(omega)-propyl-l-arginine (NPLA), both separately and in combination, on skin blood flow (SkBF) responses to increased Tloc and heat stress in two protocols. In each protocol, SkBF was monitored by laser-Doppler flowmetry (LDF) and mean arterial pressure (MAP) by Finapres. Cutaneous vascular conductance (CVC) was calculated (CVC = LDF/MAP). Intradermal microdialysis was used to treat one site with 5 mM LNAA, another with 5 mM NPLA, a third with combined 5 mM LNAA and 5 mM NPLA (Mix), and a fourth site with Ringer only. In protocol 1, Tloc was controlled with combined LDF/local heating units. Tloc was increased from 34 degrees C to 41.5 degrees C to cause local vasodilation. In protocol 2, after a period of normothermia, whole body heat stress was induced (water-perfused suits). At the end of each protocol, all sites were perfused with 58 mM nitroprusside to effect maximal vasodilation for data normalization. In protocol 1, at Tloc = 34 degrees C, CVC did not differ between sites (P > 0.05). LNAA and Mix attenuated CVC increases at Tloc = 41.5 degrees C to similar extents (P < 0.05, LNAA or Mix vs. untreated or NPLA). In protocol 2, in normothermia, CVC did not differ between sites (P > 0.05). During heat stress, NPLA and Mix attenuated CVC increases to similar extents, but no significant attenuation occurred with LNAA (P < 0.05, NPLA or Mix vs. untreated or LNAA). In forearm skin, eNOS mediates the vasodilator response to increased Tloc and nNOS mediates the vasodilator response to heat stress. The two isoforms do not appear to interact during either response.