Tunable near-infrared Gires-Tournois resonators based on vanadium dioxide on gold film.

Vanadium dioxide (VO2) has been proposed as a phase-change material in tunable photonic and optoelectronic devices. In such devices, a thin layer of VO2 is typically deposited on metallic or insulating surfaces. In this Letter, we report the reflectance spectra of a subwavelength structure consisting of a thin layer of VO2 deposited on a gold film in the near-infrared spectral range, particularly near the wavelength of 1550 nm, which is significant for telecommunication applications. Our results indicate that in the insulating phase of VO2, the air/VO2/Au structure can be considered as a Gires-Tournois resonant cavity whose maximum absorption wavelength can be tuned by adjusting the thickness of the VO2 layer. In contrast, in the metallic phase of VO2, the reflectance of the structure increases by an amount of the order of a few tens of units. The proposed structure can prospectively lead to new design concepts in tunable photonic and optoelectronic devices.

Scanning diffracted-light microscopy.

Scanning the direction of the light that is diffracted by a sample permits the achievement of image diversity, which is necessary for implementing the Fourier ptychographic microscopy technique (FPM) using only perpendicular illumination. We also demonstrated that the same method allows for implementation of the illumination-direction-multiplexing FPM technique when the sample is illuminated using a ring-shaped condenser.

Subwavelength resolution scanning diffracted-light microscopy using plasmonic ultra-thin condensers.

We used a rotating slit placed at the back focal plane of the microscope's objective lens to scan the light diffracted by a plasmonic crystal, which had a period smaller than the resolution limit of the optical microscope. A set of images were collected at different orientations of the slit. A high-resolution image of the plasmonic crystal was obtained by processing the experimental images using a numerical Fourier ptychographic algorithm. Supporting simulations of the experiments are also presented.

Scanning diffracted-light photography using white-light and thermal radiation sources.

A 4-f imaging arrangement of lenses with a camera and a rotating slit placed at the Fourier plane of the system was used to obtain the optical disturbance produced by a macroscopic sample. The sample was illuminated by collimated beams from white-light and thermal radiation sources. The agreement between simulated and experimental results, obtained by processing the captured images using a Fourier ptychographic algorithm, demonstrates that scanning with the slit the direction of the light diffracted by the sample permits achieving the image diversity necessary for successful implementation of the scanning diffracted-light imaging technique.

Fourier ptychographic microscopy using an infrared-emitting hemispherical digital condenser.

Fourier ptychographic microscopy is demonstrated in the near-infrared spectral range using a computer-controlled hemispherical digital condenser comprising multiple 940 nm wavelength light emitting diodes. This technique was used to image periodic patterned samples (photonic crystals). Experimental and simulated results using a phase retrieval algorithm were found to be in excellent correspondence. We show that for samples with a single period in each direction, the resolution of the obtained high-resolution near-infrared images is limited by the Rayleigh criteria.

Versatile optical microscopy using a reconfigurable hemispherical digital condenser.

We present a computer-controlled hemispherical digital condenser and demonstrate that a single device can be used to implement a variety of both well established and novel optical microscopy techniques. We verified the condenser capabilities by imaging fabricated periodic patterned structures and biological samples.

Hemispherical digital optical condensers with no lenses, mirrors, or moving parts.

We present a simple method for obtaining direct non-scanning images in the far-field with subwavelength resolution. Our approach relies on the use of a digital optical condenser comprised of an array of light emitting diodes uniformly distributed inside of a hollow hemisphere. We demonstrate experimental observation of minimum feature sizes of the order of λ/6 with the proposed technique. Although our experiments were performed at visible frequencies, we anticipate that the proposed approach to subwavelength resolution can be extended to the ultraviolet and infrared spectral regions.

Tunable dual-band terahertz metamaterial bandpass filters.

We report metamaterial terahertz (THz) bandpass filters with tunable dual-band selectivity. The shift in the center frequency of the device is achieved by actively modifying the effective length of the resonators. This was realized by introducing vanadium dioxide (VO2) bridges interconnecting specific regions of each resonator. Raising the temperature across the phase transition shifted the resonance frequency by ~32% due to changes in the electrical conductivity of the VO2. Measured THz transmission response of the proposed dual-band filter was in good correspondence with simulations.

Fundaments of optical far-field subwavelength resolution based on illumination with surface waves.

We present a general discussion about the fundamental physical principles involved in a novel class of optical superlenses that permit to realize in the far-field direct non-scanning images with subwavelength resolution. Described superlenses are based in the illumination of the object under observation with surface waves excited by fluorescence, the enhanced transmission of fluorescence via coupling with surface waves, and the occurrence of far-field coherence-related fluorescence diffraction phenomena. A Fourier optics description of the image formation based on illumination with surface waves is presented, and several recent experimental realizations of this technique are discussed. Our theoretical approach explains why images with subwavelength resolution can be formed directly in the microscope camera, without involving scanning or numerical post-processing. While resolution of the order of λ/7 has been demonstrated using the described approach, we anticipate that deeper optical subwavelength resolution should be expected.

Imaging nanoscale features with plasmon-coupled leakage radiation far-field superlenses.

Optical images from nano-scale features were obtained by collection of leakage radiation coupled to surface plasmon polaritons excited by near-field fluorescence. Plasmonic crystals with spatial periods as small as 190 nm and non-periodic features separated by 80 nm, corresponding to ~λ/7, were clearly visible in the real plane images using this far-field technique. We show that the leaked light from the investigated samples carries detailed information to the far-field which is not present in the images obtained with conventional optical microscopy.

Terahertz bandpass filters using double-stacked metamaterial layers.

Bandpass filters are reported based on double-stacked metamaterial layers separated by an air gap for operation at terahertz frequencies. Several stacking configurations were investigated designed for a ~0.5 THz center frequency. The filters exhibited improved spectral transmission properties when compared with conventional ones based on single metamaterial layers. 3 dB bandwidth of ~78 GHz and sidelobe suppression ratio >16 dB were determined when symmetric or asymmetric double layers were stacked. We demonstrate that superior frequency selectivity can be achieved when metamaterial layers with different unit cells are used. Good agreement was found between measured and simulated transmission response.

Improvement in vesicoureteral reflux grade on serial imaging predicts resolution.

PURPOSE: When children are initially diagnosed with vesicoureteral reflux most undergo a period of antibiotic prophylaxis followed by serial imaging. Although improvement in reflux grade through time presumably predicts eventual resolution, the significance of changing grade through time is unknown. We examined whether improvement in reflux on serial imaging predicts resolution. MATERIALS AND METHODS: We retrospectively reviewed 1,761 children diagnosed with vesicoureteral reflux, of whom 965 had a minimum of 2 years of followup. We examined initial reflux grade and grade on serial imaging up to 5 years after the original diagnosis. For each child it was determined whether reflux was resolved, eventually resolved or never resolved. Groups were further stratified by clinical characteristics. RESULTS: Multivariate analysis revealed that male gender (HR 1.33, p = 0.05), age younger than 1 year at diagnosis (HR 1.35, p = 0.004), lower grade at presentation (grade I HR 2.2, grade II HR 1.96, grade III HR 1.33; p <0.001) and unilateral reflux (HR 1.39, p = 0.001) were all independent predictors of reflux resolution. Multivariate analysis also showed that reflux improvement on imaging 1 year after diagnosis (HR 3.14, p <0.0001) and improvement from the previous year at any point during followup (HR 1.8, p = 0.009) were independent predictors of reflux resolution. CONCLUSIONS: Consistent with previous findings, male gender, lower reflux grade at presentation, age less than 1 year at presentation and unilateral reflux were all predictive of reflux resolution. Our analysis also demonstrated that improvement in reflux grade on imaging study 1 year after diagnosis was predictive of resolution, and that reflux improvement from the previous year at any point during followup was an independent predictor of resolution. This information will prove valuable in clinical counseling and therapeutic decision making.

Role of transport proteins in drug discovery and development: a pharmaceutical perspective.

1. This review will explore, from a pharmaceutical industry perspective, the evidence and consequences of transport protein involvement in pharmacokinetic variability and safety of drugs in humans. With the preclinical and clinical evidence available, the transport proteins that are considered to be the most important in respect of pharmacokinetic variability and safety in humans will be highlighted. 2. A large number of transport proteins have been identified, at both the genetic and the cellular level, which have been suggested to play some role in the absorption, distribution or elimination of endogenous, xenobiotic or drug substrates. 3. The weight of evidence suggests that only a small number of transport proteins need to be routinely considered in the drug-discovery setting driven by the magnitude of their impact on tissue distribution, pharmacokinetic variability and drug-drug interactions. 4. For the majority of candidate drugs, an assessment of the role of transporter proteins in their disposition and safety need only be assessed if in vivo properties suggest that active transport is likely to be a significant factor, if transport proteins are implicated in a particular therapeutic target area or if the disposition and safety of a likely co-medication are known to be significantly modulated by transport proteins.

Relative receptor expression is a determinant in xenobiotic-mediated CYP3A induction in rat and human cells.

1. Species differences in xenobiotic-mediated transcriptional activation of CYP3A genes are known to exist. These differences are proposed to be due, in part, to host cell differences. 2. Host cell effects were investigated by trans-species transient transfection of reporter genes containing either the rat CYP3A23 or human CYP3A4 proximal promoters into human HepG2 and rat FaO and H4IIEC3 hepatoma cells. HepG2 and FaO cells supported activation of both CYP3A constructs by xenobiotics in a species-specific manner, whereas H4IIEC3 cells were non-permissive. 3. The mRNA complement of the cell lines was then quantified by semiquantitative RT-PCR for adult CYP3As (CYP3A23, CYP3A4/5), steroid hormone receptors (constitutive androstane receptor, glucocorticoid receptor-alpha, pregnane X receptor) and transcription factors (Hepatic nuclear factor 4alpha, retinoid X receptor). 4. Principal component analysis of absolute receptor levels demonstrated a wide scattering, with no coherent pattern. In contrast, PCA of relative receptor ratios segregated H4IIEC3 cells from all other samples. 5. The observation is confirmed that species differences in response to xenobiotics are a result of host cell environment. In addition, new evidence is provided to support the hypothesis that in addition to individual receptor activation profiles, the relative abundance of steroid hormone receptors that control CYP3A gene expression play an important role in this observed species difference.

Receptor-dependent transcriptional activation of cytochrome P4503A genes: induction mechanisms, species differences and interindividual variation in man.

1. The importance of CYP3A enzymes in drug metabolism and toxicology has yielded a wealth of information on the structure, function and regulation of this subfamily and recent research emphasis has been placed on the human forms, namely CYP3A4, CYP3A5, CYP3A7 and CYP3A43. 2. The current review will focus on the receptor-dependency of CYP3A regulation and includes consideration of the regulatory roles of the glucocorticoid (GR), pregnane X (PXR) and constitutive androstane (CAR) receptors. 3. Emphasis has been placed on the topics of expression and substrate specificity, assessment of induction, species differences in induction, CYP3A promoter sequences and regulation of gene expression, structural and functional aspects of receptor-mediated, CYP3A gene activation, receptor variants and interindividual variation in human CYP3A expression, the latter encompassing environmental, physiological and genetic aspects. 4. An outline of future research needs will be discussed in the context of receptor-mediated molecular mechanisms of CYP3A gene regulation and the impact on interindividual variations in CYP3A expression. 5. Taken collectively, this review highlights the importance of understanding the molecular mechanisms of CYP3A induction as a means of rationalizing human responses to many clinically used drugs, in addition to providing a mechanistically coherent platform to understand and predict interindividual variations in response and drug-drug interactions.

Expression, purification, and biochemical characterization of a human cytochrome P450 CYP2D6-NADPH cytochrome P450 reductase fusion protein.

Cytochrome P450 CYP2D6 metabolizes a wide range of pharmaceutical compounds. A CYP2D6 fusion enzyme (CYP2D6F), containing an amino-terminal human CYP2D6 sequence and a carboxyterminal human NADPH-cytochrome P450 oxidoreductase (CPR) moiety, was constructed. High levels of expression were achieved in Escherichia coli (60-100 nmol/liter) and the enzyme was catalytically active with optimal activities achieved in the presence of the antioxidant, GSH. Turnover values for bufuralol 1'-hydroxylation, metoprolol alpha-hydroxylation, O-desmethylation, and dextromethorphan O-demethylation, using membranes expressing the fusion enzyme, were 5.6, 0.4, 0.72, and 6.19 min(-1), respectively. These values were similar to E. coli membranes which coexpressed human CYP2D6 and CPR (CYP2D6/R). The K(m) and k(cat) values for bufuralol metabolism were estimated to be 10.2 microM and 4.1 min(-1), respectively. The enzyme was purified using ion-exchange chromatography, affinity chromatography (2'-5' ADP-Sepharose), and gel filtration. Estimated turnover rates for bufuralol 1'-hydroxylation, metoprolol alpha-hydroxylation, O-desmethylation, and dextromethorphan O-demethylation were 1.2, 0.52, 0.79, and 0.76 min(-1), respectively. Bufuralol 1'-hydroxylase activity by purified CYP2D6F was enhanced by phospholipids and added CPR. The CYP2D6F enzyme was able to stimulate CYP3A4 testosterone 6beta-hydroxylase activity in a reconstitution system indicating that electron transfer may be largely intermolecular. The catalytically self-sufficient CYP2D6F enzyme will facilitate investigations of P450-CPR interactions and the development of new biocatalysts.

Use of a reporter gene assay to predict and rank the potency and efficacy of CYP3A4 inducers.

Regulation of the CYP3A4 gene has been studied using an in vitro reporter gene assay. The effect of 17 xenobiotics on approximately 1 kilobase of the CYP3A4 proximal promoter, upstream of a secretory placental alkaline phosphatase reporter gene was investigated following transfection into the HepG2 cell line. Transfections were carried out either in the basal system or with cotransfection of expression plasmids for the human pregnane X receptor (hPXR) and the human glucocorticoid receptor (hGR), two important receptors in the regulation of CYP3A4 gene expression. Compounds were tested at four concentrations, and the resulting data were used to calculate maximal induction (I(max)) and EC(50) values. An "overall inductive ability" (IA) was derived by dividing I(max) by EC(50). Of the compounds tested seven were established transcriptional inducers, all of which were positive in the in vitro assay. The remaining 10 compounds represented a group with preliminary evidence for CYP3A transcriptional activation. Nine of these compounds produced statistically significant inductions in vitro, with only pravastatin failing to activate the reporter gene. This is of potential interest in light of the high IA values observed with the other structurally and functionally similar statins tested. We conclude that a four-concentration-point, in vitro model is capable of identifying CYP3A4 transcriptional inducers and yields an IA value allowing the ranking of compounds for their overall ability to induce CYP3A4 transcription. In addition, the majority of the compounds tested showed increased IA values in the hPXR/hGR cotransfected system, underpinning the importance of these receptors in CYP3A4 gene transcriptional regulation.

Role of transport proteins in drug absorption, distribution and excretion.

1. The molecular and functional characterization of transport proteins is emerging rapidly and significant numbers of drugs have been shown to be substrates or inhibitors. The purpose of this review is to highlight the in vivo preclinical and clinical evidence that supports a role for transport proteins in attenuating the absorption, distribution and excretion (ADE) of drugs. 2. For absorption, a clear role has emerged for P-glycoprotein in limiting permeability across the gastrointestinal tract. As a result, a wide variety of drugs suffer from incomplete, variable and non-linear absorption. Similarly, at the blood-brain barrier a range of drugs has limited brain penetration due to P-glycoprotein-mediated efflux, which can limit therapeutic effectiveness of CNS agents. In the liver, transport proteins are present on the sinusoidal membrane that can be the rate-limiting step in hepatic clearance for some drugs. Mechanistic studies clearly suggest a key role and broad substrate specificity for the OATP family of sinusoidal transporters. Mainly ATP-dependent transport proteins such as P-glycoprotein and MRP2 govern active biliary excretion. 3. Drug-drug interactions have been demonstrated involving inhibition or induction of transport proteins. Clinically significant interactions in the gastrointestinal tract and kidney have been observed with inhibitors such as ketoconazole, erythromycin, verapamil, quinidine, probenecid and cimetidine. Clinically significant inhibition at the blood-brain barrier is more difficult to demonstrate, relying on pharmacodynamic and toxicodynamic changes, but an example is quinidine increasing loperamide-induced central effects in humans. 4. This review highlights the emerging role of transport proteins in ADE of drugs and suggests these need to be considered, in drug discovery and development, with respect to variability in drug disposition and response.

Pharmacokinetics of the novel, high-affinity and selective dopamine D3 receptor antagonist SB-277011 in rat, dog and monkey: in vitro/in vivo correlation and the role of aldehyde oxidase.

1. In vitro studies with the selective dopamine D3 receptor antagonist SB-277011 were conducted in liver microsomes and homogenates from rat, dog, cynomolgus monkey and human to correlate the rate of metabolism with the in vivo pharmacokinetics of the compound in rat, dog and cynomolgus monkey. 2. In the presence of NADPH, SB-277011 was relatively stable in the presence of liver microsomes from rat, dog, cynomolgus monkey and human with an intrinsic clearance (CLi) of < 2 ml min(-1) g(-1) liver for all species. In total liver homogenates, SB-277011 was metabolized at a similar rate in rat and dog (CLi < 2 ml min(-1) g(-1) liver) to that in liver microsomes but in cynomolgus monkey and human (CLi = 9.9 and 45 ml min(-1) g(-1) liver, respectively) the intrinsic clearance was approximately 6- and 35-fold higher, respectively, than that in liver microsomes. 3. In the absence of NADPH, SR-277011 was rapidly cleared in liver homogenates from cynomolgus monkey and human (CLi = 7.4 and 27 ml min(-1) g(-1) liver, respectively) demonstrating that a significant pathway of metabolism of this compound was via an NADPH-independent non-microsomal oxidative route. This pathway was sensitive to inhibition with isovanillin suggesting that the enzyme responsible was aldehyde oxidase. 4. The in vivo pharmacokinetics showed that the plasma clearance of SB-277011 was low in rat (20 ml min(-1) kg(-1)), moderate in dog (14 ml min(-1) kg(-1)) and high in cynomolgus monkey (58 ml min(-1)kg(-1)), which is consistent with the in vitro findings and demonstrated a greater capacity for the monkey to metabolize this compound. The oral bioavailability of SB-277011 in rat, dog and cynomolgus monkey was 35, 43 and 2%, respectively. Given the high clearance of this compound in cynomolgus monkey, the low oral bioavailability is probably as a result of high first-pass elimination, specifically by aldehyde oxidase, rather than poor absorption. 5. The high in vitro clearance of SB-277011 in human liver homogenates and the involvement of aldehyde oxidase in the metabolism of SB-277011 indicates that the bioavailability of the compound is likely to be low in human.

Application of liquid chromatography-mass spectrometry(n) analyses to the characterization of novel glyburide metabolites formed in vitro.

The application of bench-top ion-trap atmospheric pressure ionization mass spectrometry in the characterization of in vitro metabolites of glyburide is discussed. The metabolites formed in vitro by rat, dog, monkey and human liver microsomes were separated by reversed-phase high-performance liquid chromatography (HPLC) and characterized by mass spectrometry (MS)n experiments. The utility of data dependent MS1-MS2-MS3 analyses, where the mass spectrometer makes "real-time" decisions about the experiment to be performed, are described using the characterization of two novel metabolites of glyburide as an example. The metabolite profiles from each species were similar. Six cyclohexyl hydroxylation products were detected, as well as two novel monooxygenation products formed via hydroxylation of the ethyl chain at the benzylic position, and alpha to the amide nitrogen. The ion-trap with electrospray ionization proved to be a sensitive and reliable HPLC detection system that provided important chemical structure information.