General anesthetic binding to neuronal alpha4beta2 nicotinic acetylcholine receptor and its effects on global dynamics

The neuronal alpha4beta2 nicotinic acetylcholine receptor (nAChR) is a target for general anesthetics. Currently available experimental structural information is inadequate to understand where anesthetics bind and how they modulate the receptor motions essential to function. Using our published open-channel structure model of alpha4beta2 nAChR, we identified and evaluated six amphiphilic interaction sites for the volatile anesthetic halothane via flexible ligand docking and subsequent 20-ns molecular dynamics simulations. Halothane binding energies ranged from -6.8 to -2.4 kcal/mol. The primary binding sites were located at the interface of extracellular and transmembrane domains, where halothane perturbed conformations of, and widened the gap among, the Cys loop, the beta1-beta2 loop, and the TM2-TM3 linker. The halothane with the highest binding affinity at the interface between the alpha4 and beta2 subunits altered interactions between the protein and nearby lipids by competing for hydrogen bonds. Gaussian network model analyses of the alpha4beta2 nAChR structures at the end of 20-ns simulations in the absence or presence of halothane revealed profound changes in protein residue mobility. The concerted motions critical to protein function were also perturbed considerably. Halothane's effect on protein dynamics was not confined to the residues adjacent to the binding sites, indicating an action on a more global scale.

Anesthetic effects on the structure and dynamics of the second transmembrane domains of nAChR alpha4beta2

Channel functions of the neuronal alpha4beta2 nicotinic acetylcholine receptor (nAChR), one of the most widely expressed subtypes in the brain, can be inhibited by volatile anesthetics. Our Na(+) flux experiments confirmed that the second transmembrane domains (TM2) of alpha4 and beta2 in 2:3 stoichiometry, (alpha4)(2)(beta2)(3), could form pentameric channels, whereas the alpha4 TM2 alone could not. The structure, topology, and dynamics of the alpha4 TM2 and (alpha4)(2)(beta2)(3) TM2 in magnetically aligned phospholipid bicelles were investigated using solid-state NMR spectroscopy in the absence and presence of halothane and isoflurane, two clinically used volatile anesthetics. (2)H NMR demonstrated that anesthetics increased lipid conformational heterogeneity. Such anesthetic effects on lipids became more profound in the presence of transmembrane proteins. PISEMA experiments on the selectively (15)N-labeled alpha4 TM2 showed that the TM2 formed transmembrane helices with tilt angles of 12 degrees +/-1 degrees and 16 degrees +/-1 degrees relative to the bicelle normal for the alpha4 and (alpha4)(2)(beta2)(3) samples, respectively. Anesthetics changed the tilt angle of the alpha4 TM2 from 12 degrees +/-1 degrees to 14 degrees +/-1 degrees , but had only a subtle effect on the tilt angle of the (alpha4)(2)(beta2)(3) TM2. A small degree of wobbling motion of the helix axis occurred in the (alpha4)(2)(beta2)(3) TM2. In addition, a subset of the (alpha4)(2)(beta2)(3) TM2 exhibited counterclockwise rotational motion around the helix axis on a time scale slower than 10(-4) s in the presence of anesthetics. Both helical tilting and rotational motions have been identified computationally as critical elements for ion channel functions. This study suggested that anesthetics could alter these motions to modulate channel functions.

Effect of siRNA targeting HIF-1alpha combined L-ascorbate on biological behavior of hypoxic MiaPaCa2 cells

The aim of the study was to observe the effect of small interference RNA (siRNA) targeting hypoxia-inducible factor 1alpha (HIF-1alpha) combined L-ascorbate on proliferation, migration, and apoptosis of hypoxic MiaPaCa2 human pancreatic cancer cells. A cassette encoding siRNA targeting HIF-1alpha mediated by recombinant adeno-associated virus (rAAV) was constructed, giving rAAV-siHIF. rAAV-siHIF and L-ascorbate, which were used alone or in combination, were delivered to exponentially growing MiaPaCa2 cells under hypoxic conditions. Then, we observed the expression of HIF-1alpha mRNA and protein, the proliferation, apoptosis, and migration of MiaPaCa2 cells by real-time PCR, Western blot, MTT, TUNEL, and Transwell assay, respectively. Under hypoxic conditions, rAAV-siHIF inhibited the expression of HIF-1alpha mRNA in MiaPaCa2 cells but L-ascorbate did not. However, rAAV-siHIF and L-ascorbate both inhibited the expression of HIF-1alpha protein and the proliferation and migration of MiaPaCa2 cells and induced MiaPaCa2 cell apoptosis. The effect in the combined group was more efficient than that seen when rAAV-siHIF or L-ascorbate was used separately. rAAV-siHIF and L-ascorbate both affect biological behavior of hypoxic MiaPaCa2 cells through modulating HIF-1alpha protein expression and rAAV-siHIF and L-ascorbate have synergy under hypoxic conditions.

Anionic lipid and cholesterol interactions with alpha4beta2 nAChR: insights from MD simulations

Anionic lipids and cholesterols (CHOL) are critical to the function of nicotinic acetylcholine receptors (nAChR). We investigated their interactions with an open- and closed-channel alpha4beta2 nAChR by over 10 ns molecular dynamics simulations in a ternary lipid mixture of 1-palmitoyl-2-oleoyl phosphatidylcholine (POPC), 1-palmitoyl-2-oleoyl phosphatidic acid (POPA), and CHOL with a ratio of 3:1:1 (Haddadian et al., J. Phys. Chem. B 2008, 112, 13981). On average there were 65 and 74 interfacial lipids around the closed- and open-channel alpha4beta2 nAChR, respectively, in the equilibrated simulation systems. In the open-channel system, 42% of the interfacial POPA had acyl chains partially inserted into intra- or intersubunit cavities, as compared to only 7% in the closed-channel alpha4beta2. No CHOL was found in cavities within single subunits, though some CHOL infiltrated into the gaps between subunits. Because of its smaller headgroup, POPA could access some nonannular sites where POPC could not easily reach due to steric exclusion. Furthermore, POPA acted not only as an acceptor for hydrogen bonding (H bonding) as POPC did, but also as a donor through its hydroxyl group for H bonding with the backbone of the protein. The charged headgroup of POPA allowed the lipid to form stable salt bridges with conserved Arg and Lys residues at the interfaces of the transmembrane (TM) and extracellular (EC) or intracellular (IC) domains of the alpha4beta2. A higher number of salt bridges and hydrogen bonds (H bonds) between POPA and the alpha4beta2 nAChR were found in the open system than in the closed system, suggesting a potential role of POPA in the equilibrium between different channel states. Most interfacial POPA molecules showed lower order parameters than the bulk POPA due to the mixed effect of gauche defects, hydrophobic mismatch, and the lipid orientations near the magic angle. These unique properties enable the interfacial POPA to achieve what POPC cannot with regard to specific interactions with the protein, thereby making POPA essential for the function of nAChR.

Faster recovery of cerebral perfusion in SOD1-overexpressed rats after cardiac arrest and resuscitation

BACKGROUND AND PURPOSE

Protracted hypoperfusion is one of the hallmarks of secondary cerebral derangement after cardiac arrest and resuscitation (CAR), and reactive oxygen species have been implicated in reperfusion abnormalities.

METHODS

Using transgenic (Tg) rats overexpressing copper zinc superoxide dismutase (SOD1), we investigated the role of this intrinsic antioxidant in the restoration of cerebral blood flow (CBF) after CAR. Nine Tg and 11 wild-type (WT) rats were subjected to a nominal 15-minute cardiac arrest, and CBF was measured using the noninvasive arterial spin labeling MRI method before and during cardiac arrest, and 0 to 2 hours and 1 to 5 days after resuscitation.

RESULTS

The SOD1-Tg rats showed rapid normalization of CBF 1 day after the insult, whereas CBF in WT animals remained abnormal for at least 5 days, showing a progressive increase in CBF from hypo- to hyperperfusion on postresuscitation days 1 to 5. The long-term outcome, as measured by survival time, change in body weight, and mapping of apparent diffusion coefficient (ADC) for ion/water homeostasis, was significantly better in the SOD1-Tg rats.

CONCLUSIONS

Our results support the notion that reactive oxygen species are at least partially responsible for microvascular reperfusion disorders.

A phase II study of Halichondrin B analog eribulin mesylate (E7389) as second-line therapy for patients with advanced pancreatic cancer

e15634

Background: Eribulin mesylate is a halichondrin B analog that inhibits microtubule dynamics by a mechanism that is distinct from other tubulin-targeted agents. Preclinical studies suggest that Eribulin may be effective in pancreatic cancer. The primary objective of this study was to determine the objective response rate (complete and partial) to Eribulin in patients with advanced, pancreatic adenocarcinoma that had progressed after gemcitabine based therapy. Methods: Eligibility criteria included histologically confirmed pancreatic adenocarcinoma; measurable locally advanced, or metastatic disease; disease progression after gemcitabine; and ECOG performance status 0–2. Patients (pts) received Eribulin mesylate 1.4 mg/m2 IV on days 1 and 8. Treatment was repeated every 3 weeks in the absence of disease progression or unacceptable toxicity. Response was assessed by CT scans every 6 weeks while on treatment. Initially 12 pts were to be accrued, if 1 or more pt(s) had an objective response the accrual would increase to a total of 37. Results: 15 pts were accrued,14 received treatment and 12 were evaluable for response. Median age 61; M:F = 8:7; ECOG 1:2 = 11:4; Median number of cycles 2 (1–15). Grade 3+ adverse events included neutropenia (29%), fatigue (14%), peripheral neuropathy (7%) and thrombosis (7%). There were no complete or partial responses, and therefore the study was closed at the first accrual cut off. The best response was stable disease (SD) in 5/12 (42%) pts. Of these 5 pts, 3 (42%) had SD for 12 cycles or greater. Survival data is pending. Conclusions: Eribulin was well tolerated and did not result in any objective responses in refractory pancreatic cancer. However, 42% of pts had stable disease and for 3 pts this was maintained for more than 9 months. Further studies of eribulin in pancreatic cancer may be warranted.

No significant financial relationships to disclose.

Phase II trial of erlotinib in advanced pancreatic cancer (PC)

4609

Background: The epidermal growth factor receptor (EGFR) is a potentially important target in PC. Benefit from erlotinib (Tarceva), an oral EGFR tyrosine kinase inhibitor has been associated with the presence of a skin rash. The purpose of this study was to determine the efficacy of erlotinib, dosed to achieve a rash, in patients (pts) with PC. Methods: Erlotinib was given at an initial dose of 150 mg/day to eligible pts with locally advanced (LA) or metastatic PC who had progressed or were unable to tolerate gemcitabine-based chemotherapy. The dose of erlotinib was increased by 50mg every 2 weeks (maximum 300 mg/day) until > grade 1 rash (CTCAE v 3.0) or other dose-limiting toxicities occurred. Erlotinib pharmacokinetic (PK) studies were performed. Baseline tumor tissue was collected for analysis of Kras mutations, EGFR by IHC and FISH. The primary endpoint of this two- stage phase II trial was prolonged disease control (PR + SD > 8 wks) with a rate of >20% assumed to be significant . Results: Fifty pts were accrued (median age 61, M:F = 25:25, ECOG 0:1:2 = 5:41:4, LA:Metastatic = 5:45, prior gemcitabine none:adjuvant:palliative = 2:16:35). 47 and 40 pts were evaluable for toxicity and response, respectively. Dose-escalation to 200–300 mg of erlotinib was possible in 9 pts. Most common treatment adverse events (TAEs) of any grade were: rash (35 pts, 74.5%), diarrhea (18 pts, 38.3 %), and fatigue (8 pts, 17%). Grade 3+ TAEs were rash in 2 pts and diarrhea in 2 pts. Best response was SD in 14 pts, 0.35 (95% CI: 0.2–0.5). Prolonged disease control (SD > 8 wks) was observed in 10/40 evaluable pts, 0.25 (95% CI: 0.12–0.38), which met the primary study endpoint. Median TTP was 1.6 mo (95% CI:1.6–2.1), mOS 4.1 mo (95% CI:3.2–7.3), and 6 mo OS rate was 39% (95%CI: 24–61%). PK and correlative data are being analyzed and will be presented. Conclusions: Erlotinib is associated with prolonged stable disease in a subset of pts with advanced refractory PC. Dose escalation in the absence of toxicity is feasible and safe.

[Table: see text]

In silico models for the human alpha4beta2 nicotinic acetylcholine receptor

The neuronal alpha4beta2 nicotinic acetylcholine receptor (nAChR) is one of the most widely expressed nAChR subtypes in the brain. Its subunits have high sequence identity (54 and 46% for alpha4 and beta2, respectively) with alpha and beta subunits in Torpedo nAChR. Using the known structure of the Torpedo nAChR as a template, the closed-channel structure of the alpha4beta2 nAChR was constructed through homology modeling. Normal-mode analysis was performed on this closed structure and the resulting lowest frequency mode was applied to it for a "twist-to-open" motion, which increased the minimum pore radius from 2.7 to 3.4 A and generated an open-channel model. Nicotine could bind to the predicted agonist binding sites in the open-channel model but not in the closed one. Both models were subsequently equilibrated in a ternary lipid mixture via extensive molecular dynamics (MD) simulations. Over the course of 11 ns MD simulations, the open channel remained open with filled water, but the closed channel showed a much lower water density at its hydrophobic gate comprised of residues alpha4-V259 and alpha4-L263 and their homologous residues in the beta2 subunits. Brownian dynamics simulations of Na+ permeation through the open channel demonstrated a current-voltage relationship that was consistent with experimental data on the conducting state of alpha4beta2 nAChR. Besides establishment of the well-equilibrated closed- and open-channel alpha4beta2 structural models, the MD simulations on these models provided valuable insights into critical factors that potentially modulate channel gating. Rotation and tilting of TM2 helices led to changes in orientations of pore-lining residue side chains. Without concerted movement, the reorientation of one or two hydrophobic side chains could be enough for channel opening. The closed- and open-channel structures exhibited distinct patterns of electrostatic interactions at the interface of extracellular and transmembrane domains that might regulate the signal propagation of agonist binding to channel opening. A potential prominent role of the beta2 subunit in channel gating was also elucidated in the study.

Residual dipolar coupling measurements of transmembrane proteins using aligned low-q bicelles and high-resolution magic angle spinning NMR spectroscopy

Bicelles are a major medium form to produce weak alignment of soluble proteins for residual dipolar coupling (RDC) measurements. The obstacle to using the same type of bicelles for transmembrane proteins with solution-state NMR spectroscopy is the loss of signals due to the adhesion or penetration of the proteins into large bicelles, resulting in slow protein tumbling. In this study, weak alignment of the second and third transmembrane domains (TM23) of the human glycine receptor (GlyR) was achieved in low-q bicelles (q = DMPC/DHPC). Although protein-free bicelles with such low q would likely show isotropic properties, the insertion of TM23 induced weakly preferred orientations so that the RDC of the embedded protein can be measured. The extent of the alignment increased but the TM23 signal intensity decreased when q was varied from 0.19 to 0.60. A q of 0.50 was found to be an optimal compromise between alignment and the signal-to-noise ratio. In each pair of NMR experiments for RDC measurements, the same sample and pulse sequence were used, with one being performed at high-resolution magic-angle spinning to obtain pure J-couplings without RDC. A meaningful structure refinement in bicelles was possible by iteratively fitting the experimental RDCs to the back-calculated RDCs using the high-resolution NMR structure of GlyR TM23 in trifluoroethanol as the starting template. Combination of this method with the conventional high-resolution NMR in membrane mimicking mixtures of water and organic solvents offers an attractive way to derive structural information for membrane proteins in their native environment.

Anesthetic modulation of protein dynamics: insight from an NMR study

Mistic (membrane integrating sequence for translation of integral membrane protein constructs) comprises the four-alpha-helix bundle scaffold found in the transmembrane domains of the Cys-loop receptors that are plausible targets for general anesthetics. Nuclear magnetic resonance (NMR) studies of anesthetic halothane interaction with Mistic in dodecyl phosphocholine (DPC) micelles provide an experimental basis for understanding molecular mechanisms of general anesthesia. Halothane was found to interact directly with Mistic, mostly in the interfacial loop regions. Although the presence of halothane had little effect on Mistic structure, (15)N NMR relaxation dispersion measurements revealed that halothane affected Mistic's motion on the microsecond-millisecond time scale. Halothane shifted the equilibrium of chemical exchange in some residues and made the exchange faster or slower in comparison to the original state in the absence of halothane. The motion on the microsecond-millisecond time scale in several residues disappeared in response to the addition of halothane. Most of the residues experiencing halothane-induced dynamics changes also exhibited profound halothane-induced changes in chemical shift, suggesting that dynamics modification of these residues might result from their direct interaction with halothane molecules. Allosteric modulation by halothane also contributed to dynamics changes, as reflected in residues I52 and Y82 where halothane introduction brought about dynamics changes but not chemical shift changes. The study suggests that inhaled general anesthetics could act on proteins via altering protein motion on the microsecond-millisecond time scale, especially motion in the flexible loops that link different alpha helices. The validation of anesthetic effect on protein dynamics that are potentially correlated with protein functions is a critical step in unraveling the mechanisms of anesthetic action on proteins.

Characterisation and aerosolisation of mannitol particles produced via confined liquid impinging jets

Mannitol particles, produced by spray drying (SD), have been used commercially (Aridol) in bronchial provocation test. In this study, we propose an alternative method to produce inhalable mannitol powders. The elongated mannitol particles (number median length 4.0microm, and axial ratio of 3.5) were prepared using a confined liquid impinging jets (CLIJs) followed by jet milling (JM). Spray dried and jet milled raw mannitol particles were compared in an attempt to assess the performance of the particles produced by the new method. Aerosol performance of the three different powders (CLIJ, SD, and JM) was relatively poor (fine particle fraction or FPF(loaded) below 15%) when dispersed by the Rotahaler. Dispersion through the Aeroliser led to better aerosol performance of the CLIJ mannitol (FPF(loaded) 20.3%), which is worse than the JM (FPF(loaded) 30.3%) and SD mannitol particles (FPF(loaded) 45.7%) at 60 L/min, but comparable (FPF(loaded) 40.0%) with those of the JM (FPF(loaded) 40.7%) and SD (FPF(loaded) 45.5%) powders at 100L/min. Hence, the optimum use of these elongated mannitol particles can be achieved at increased air flow with a more efficient inhaler. In addition to crystallinity, morphology, and particle size distribution, the surface energies of these powders were measured to explain the differences in aerosol performance. A major advantage of using the CLIJ method is that it can be scaled up with a good yield as the precipitate can be largely collected and recovered on a filter, compared with spray drying which has a low collection efficiency for fine particles below 2microm.

Volatility of heavy metals during incineration of tannery sludge in the presence of chlorides and phosphoric acid

Knowledge of the behaviour of heavy metals in the combustion process is a most important factor in selecting disposal alternatives for waste materials. Accordingly, in this work, the vaporization behaviour of highly concentrated heavy metals (Pb, Zn, Cu and Cr) in tannery sludge were investigated experimentally. The sludge was spiked with various chlorine compounds (i.e. PVC, FeCl3, CaCl2 and NaCl) and pre-treated with phosphoric acid in order to evaluate the capacity of enhancement and weakening of the volatility of the heavy metals contained in tannery sludge. The experimental results show that the vaporization percentages increased with increasing ratio of Cl/sludge and temperature, and the accelerating and increasing effect of the addition of chlorides on the vaporization percentage of heavy metals was dependent on the release capacity of chlorine radicals. The vaporization percentages of lead and zinc increased by 15-20%, whereas those of copper and chromium increased by only about 3 and 10% at 800 degrees C. However, heavy metals were not expected to be completely released in the combustion process in spite of the high ratio of Cl/sludge. Alternately, heavy metals contained in tannery sludge can be immobilized effectively by pre-treatment with phosphoric acid. When the 85% phosphoric acid accounted for 10% of dry basis of tannery sludge, the phosphate-treated sludge showed the lowest vaporization percentage of about 3-15% with formation of Ca18Cu3(PO4)14, Ca9Cr(PO4)7, Ca19Zn2(PO4)14 and PbMgP2O7 in the bottom ash.