Single Exponential Fit Research Articles

Feasibility of Multiple Examinations Using (68)Ga-Labelled Collagelin Analogues: Organ Distribution in Rat for Extrapolation to Human Organ and Whole-Body Radiation Dosimetry.

Objectives: Fibrosis is involved in many chronic diseases. It affects the functionality of vital organs, such as liver, lung, heart and kidney. Two novel imaging agents for positron emission tomography (PET) imaging of fibrosis have previously pre-clinically demonstrated promising target binding and organ distribution characteristics. However, the relevant disease monitoring in the clinical setup would require multiple repetitive examinations per year. Thus, it is of paramount importance to investigate the absorbed doses and total effective doses and thus, the potential maximum number of examinations per year. Methods: Two cyclic peptide (c[CPGRVMHGLHLGDDEGPC]) analogues coupled via an ethylene glycol linker (EG2) to either 2-(4,7-bis(2-(tert-butoxy)-2-oxoethyl)-1,4,7-triazonan-1-yl)acetic acid (NO2A-Col) or 4-(4,7-bis(2-(tert-butoxy)-2-oxoethyl)-1,4,7-triazacyclononan-1-yl)-5-(tert-butoxy)-5-oxopentanoic acid (NODAGA-Col) were labelled with 68Ga. The resulting agents, [68Ga]Ga-NO2A-Col and [68Ga]Ga-NODAGA-Col, were administered in the tail vein of male and female Sprague–Dawley rats (N = 24). An ex vivo organ distribution study was performed at the 5-, 10-, 20-, 40-, 60- and 120-min time points. The resulting data were extrapolated for the estimation of human organ and total body absorbed and total effective doses using Organ Level Internal Dose Assessment Code software (OLINDA/EXM 1.1) assuming a similar organ distribution pattern between the species. Time-integrated radioactivity in each organ was calculated by trapezoidal integration followed by a single-exponential fit to the data points extrapolated to infinity. The resulting values were used for the residence time calculation. Results: Ex vivo organ distribution data revealed fast blood clearance and washout from most of the organs. Although the highest organ absorbed dose was found for kidneys (0.1 mGy/MBq), this organ was not the dose-limiting one and would allow for the administration of over 1460 MBq per year for both [68Ga]Ga-NO2A-Col and [68Ga]Ga-NODAGA-Col. The total effective dose was the limiting parameter with 0.0155/0.0156 (female/male) mSv/MBq and 0.0164/0.0158 (female/male) mSv/MBq, respectively, for [68Ga]Ga-NO2A-Col and [68Ga]Ga-NODAGA-Col. This corresponded to the total amount of radioactivity that could be administered per year of 643 and 621 MBq before reaching the annual limit of 10 mSv. Thus, up to six examinations would be possible. The residence time and organ absorbed doses in liver and spleen were higher for [68Ga]Ga-NODAGA-Col as compared to [68Ga]Ga-NO2A-Col. Conclusion: The limiting parameter for the administered dose was the total effective dose that would allow for at least six examinations per year that might be sufficient for adequate disease monitoring in longitudinal studies and a routine clinical setup.

Evaluation of low energy electron beam dose application by means of a portable optical device

We present our recent development concerning the evaluation of a low energy dose application to electron beam responding materials with a simple portable optical device. Electron beam irradiation is a promising option to sterilize sensitive and high performance products or surfaces at a low temperature and without moisture. Especially in the fields of the food industry and medicine, regulations regarding sterility are increasingly tightened. Because of this, a secure proof for electron-beam-assisted sterilization is required. However, no nondestructive and in situ method exists up until now. Our approach to provide a secure proof of sterilization is to place a suitable marker material based on rare-earth-doped phosphors inside or on the top of the packaging material of the respective product. Upon electron irradiation the marker material changes its luminescence properties as a function of the applied energy dose. We verified the energy dependence by means of time-resolved measurements of the luminescence decay of an upconversion phosphor with a portable optical device. In our experimental realization, short laser pulses in the near-infrared range are triggered by a microcontrol unit (MCU) and excite the marker material. The light emitted by the marker is collected in the range between 400 and 1100 nm via a silicon photodiode, processed by the MCU, and analyzed in a Labview program via a single-exponential fit. As a main result, we observe an increasing reduction of the luminescence lifetime with higher dose applications.

FPGA-based multi-channel fluorescence lifetime analysis of Fourier multiplexed frequency-sweeping lifetime imaging.

We report a fast non-iterative lifetime data analysis method for the Fourier multiplexed frequency-sweeping confocal FLIM (Fm-FLIM) system [Opt. Express 22, 10221 (2014)]. The new method, named R-method, allows fast multi-channel lifetime image analysis in the system's FPGA data processing board. Experimental tests proved that the performance of the R-method is equivalent to that of single-exponential iterative fitting, and its sensitivity is well suited for time-lapse FLIM-FRET imaging of live cells, for example cyclic adenosine monophosphate (cAMP) level imaging with GFP-Epac-mCherry sensors. With the R-method and its FPGA implementation, multi-channel lifetime images can now be generated in real time on the multi-channel frequency-sweeping FLIM system, and live readout of FRET sensors can be performed during time-lapse imaging.

Adequacy of a compartment model for CMRO₂ quantitation using ¹⁵O-labeled oxygen and PET: a clearance measurement of ¹⁵O-radioactivity following intracarotid bolus injection of ¹⁵O-labeled oxyhemoglobin on Macaca fascicularis.

We aimed at evaluating the adequacy of the commonly employed compartmental model for quantitation of cerebral metabolic rate of oxygen (CMRO2) using 15O-labeled oxygen (15O2) and positron emission tomography (PET). Sequential PET imaging was carried out on monkeys following slow bolus injection of blood samples containing 15O2–oxyhemoglobin (15O2–Hb), 15O-labeled water (H215O), and C15O-labeled hemoglobin (C15O–Hb) into the internal carotid artery (ICA). Clearance slopes were assessed in the middle cerebral artery territory of the injected hemisphere. The time–activity curves were bi-exponential for both 15O2–Hb and H215O. Single exponential fitting to the early (5 to 40 seconds) and late (80 to 240 seconds) periods after the peak was performed and the 15O2–Hb and H215O results were compared. It was found that a significant difference between the clearance rates of the 15O2–Hb and H215O injections is unlikely, which supports the mathematical model that is widely used to describe the kinetics of 15O2–Hb and H215O in cerebral tissues and is the basis of recent approaches to simultaneously assess CMRO2 and cerebral blood flow in a single PET session. However, it should be noted that more data are necessary to unequivocally confirm the result.

Determination of spent nuclear fuel assembly multiplication with the differential die-away self-interrogation instrument

We present a novel method for determining the multiplication of a spent nuclear fuel assembly with a Differential Die-Away Self-Interrogation (DDSI) instrument. The signal, which is primarily created by thermal neutrons, is measured with four 3He detector banks surrounding a spent fuel assembly. The Rossi-alpha distribution (RAD) at early times reflects coincident events from single fissions as well as fission chains. Because of this fact, the early time domain contains information about both the fissile material and spontaneous fission material in the assembly being measured. A single exponential function fit to the early time domain of the RAD has a die-away time proportional to the spent fuel assembly (SFA) multiplication. This correlation was tested by simulating assay of 44 different SFAs with the DDSI instrument. The SFA multiplication was determined with a variance of 0.7%.

Velocity storage mechanism in zebrafish larvae

The optokinetic reflex (OKR) and the angular vestibulo-ocular reflex (aVOR) complement each other to stabilize images on the retina despite self- or world motion, a joint mechanism that is critical for effective vision. It is currently hypothesized that signals from both systems integrate, in a mathematical sense, in a network of neurons operating as a velocity storage mechanism (VSM). When exposed to a rotating visual surround, subjects display the OKR, slow following eye movements frequently interrupted by fast resetting eye movements. Subsequent to light-off during optokinetic stimulation, eye movements do not stop abruptly, but decay slowly, a phenomenon referred to as the optokinetic after-response (OKAR). The OKAR is most likely generated by the VSM. In this study, we observed the OKAR in developing larval zebrafish before the horizontal aVOR emerged. Our results suggest that the VSM develops prior to and without the need for a functional aVOR. It may be critical to ocular motor control in early development as it increases the efficiency of the OKR.

Dynamic Stokes Shift of the Time-Resolved Phosphorescence Spectrum of ZnII-Substituted Cytochrome c

The dynamic phosphorescence Stokes shift (PSS) response of Zn(II)-substituted cytochrome c (ZnCytc) was detected using the time-resolved phosphorescence spectrum of the intrinsic Zn(II)-porphyrin chromophore, which senses the motions of the surrounding protein and hydration shell. The phosphorescence spectrum of ZnCytc exhibits resolved vibronic structure arising from in-plane deformations of the porphyrin macrocycle, as is also observed in the absorption and fluorescence spectra. As the emission time increases, the phosphorescence spectrum shifts to the red without incurring a significant change in vibronic structure or line shape, so the shift arises from dynamic solvation, the reorganizational motions of the protein and solvent that occur in response to formation of the first excited triplet state. A correlation time of 294 ± 14 μs was obtained from a single-exponential fit to the time dependence of the mean emission frequency of the T(0,0) peak in the phosphorescence spectrum. This time scale is consistent with a diffusive sampling of the native structure's minimum due to global or collective conformational fluctuations. We suggest that studies of the PSS response sensed in proteins by an intrinsic probe will be informative of protein and hydration-shell dynamics over the microsecond-millisecond time regimes associated with biological function.

Vibrational Energy Flow between Modes by Dynamic Mode Coupling in THIATS J-Aggregates

We performed ultrafast pump-probe spectroscopy of J-aggregates of 3,3'-disulfopropyl-5,5'-dichloro-9-ethyl thiacarbocyanine triethylammonium (THIATS), one of the most typical cyanine dyes, and detected excited molecular vibrations, using a sub-10 fs pulse laser. The time-resolved two-dimensional difference absorption (ΔA) spectra are observed between -314 and 1267 fs. By performing the Fourier transform and spectrogram analysis, vibrational modes in THIATS are observed at 285, 485, 555, 824, and 1633 cm(-1) and there was a modulation of the vibrational frequencies around 1633 cm(-1) which depend on the delay time, respectively. By the analysis of the modulation, energy flow is found to take place from other modes to the 1633 cm(-1) mode through the low frequency mode with ∼50 cm(-1). Also, by fitting the real-time traces of ΔA with the sum of two exponential functions and a constant term, the average lifetimes of three electronically excited states were found to be τ1 = 52 ± 5 fs and τ2 = 540 ± 78 fs. By performing single-exponential fitting around the stationary absorption peak at 1.990 eV, in the negative time range, the electronic dephasing time, T2(ele), is determined to be 18.30 fs.

Kinetic Characterization of the ATPase and Actin-activated ATPase Activities of Acanthamoeba castellanii Myosin-2

Phosphorylation of Ser-639 in loop-2 of the catalytic motor domain of the heavy chain of Acanthamoeba castellanii myosin-2 and the phosphomimetic mutation S639D have been shown previously to down-regulate the actin-activated ATPase activity of both the full-length myosin and single-headed subfragment-1 (Liu, X., Lee, D. Y., Cai, S., Yu, S., Shu, S., Levine, R. L., and Korn, E. D. (2013) Proc. Natl. Acad. Sci. U.S.A. 110, E23-E32). In the present study we determined the kinetic constants for each step in the myosin and actomyosin ATPase cycles of recombinant wild-type S1 and S1-S639D. The kinetic parameter predominantly affected by the S639D mutation is the actin-activated release of inorganic phosphate from the acto myosin·ADP·Pi complex, which is the rate-limiting step in the steady-state actomyosin ATPase cycle. As consequence of this change, the duty ratio of this conventional myosin decreases. We speculate on the effect of Ser-639 phosphorylation on the processive behavior of myosin-2 filaments.

Identification of a New Interaction Mode between the Src Homology 2 Domain of C-terminal Src Kinase (Csk) and Csk-binding Protein/Phosphoprotein Associated with Glycosphingolipid Microdomains

Proteins with Src homology 2 (SH2) domains play major roles in tyrosine kinase signaling. Structures of many SH2 domains have been studied, and the regions involved in their interactions with ligands have been elucidated. However, these analyses have been performed using short peptides consisting of phosphotyrosine followed by a few amino acids, which are described as the canonical recognition sites. Here, we report the solution structure of the SH2 domain of C-terminal Src kinase (Csk) in complex with a longer phosphopeptide from the Csk-binding protein (Cbp). This structure, together with biochemical experiments, revealed the existence of a novel binding region in addition to the canonical phosphotyrosine 314-binding site of Cbp. Mutational analysis of this second region in cells showed that both canonical and novel binding sites are required for tumor suppression through the Cbp-Csk interaction. Furthermore, the data indicate an allosteric connection between Cbp binding and Csk activation that arises from residues in the βB/βC loop of the SH2 domain.

A Novel Assay to Detect Fusion Pore Formation: Implication for Fluctuating Pore Formation

Membrane fusion is broadly envisioned as a three-step process proceeding from contacting bilayers through one or two semi-stable, nonlamellar lipidic intermediate states to a fusion pore. A true fusion event requires mixing of contents between compartments. Current content-mixing assays monitor movement of fairly small molecules. These assays seem to be unable to distinguish between passage of trapped contents through ‘fluctuating or transient pores’ that form in fusion intermediate states and passage through stable fusion pores. We report the use of fluorescence resonance energy transfer (FRET) between FAM and TAMRA probes covalently attached to complementary sequences of 10-base pair oligonucleotides to distinguish between formation of small pores and final fusion pores. These fluorescently labeled oligos were incorporated in two different populations of vesicles. Content mixing during PEG-mediated fusion of small, unilamellar vesicles was recorded over time, with a single exponential fit providing a rate constant. We also monitored fusion of similar vesicles using global fitting of the time courses of lipid mixing, and content mixing/content leakage followed by the more conventional Tb/DPA assay and obtained rate constants from a sequential model of membrane fusion (Biophys. J., 2007, 92; 4012). The rate constants of stable fusion pore formation were strikingly similar using the small-molecule and oligo assays but the extent of content mixing is always higher in the small molecule assay. We found similar correlations in the rates when peptides from natural fusion proteins were included in vesicles. These results provide strong support for the hypothesis that ‘fluctuating or transient pores’ are formed early in the fusion process (Biochemistry, 1997, 36; 6251).Supported by NIGMS grant 32707 to BRL.

Dual Effect of Phosphatidyl (4,5)-Bisphosphate PIP2 on Shaker K+ Channels

Dual Effect of Phosphatidyl (4,5)-Bisphosphate PIP2 on Shaker K+ Channels

Decomposition and change in N and organic composition of small-diameter Douglas-fir woody debris over 23 years

Managing second-growth forests for multiple benefits requires enhanced information on decomposition of woody debris generated during forestry operations. Experimental thinning and biomass sampling at the Shawnigan Lake Research Forest on southern Vancouver Island facilitated retrospective sampling of Douglas-fir ( Pseudotsuga menziesii (Mirb.) Franco) stem sections (4.9–21.5 cm diameter) from 0 to 23 years after cutting. A sigmoidal pattern of density loss was observed, while a single-exponential fit gave a decay rate (k) of 0.058 year–1. Initial N concentrations were higher in bark than in sapwood and heartwood, and all increased during decay, while C/N ratios declined to around 175 for wood and 70 for bark. Nitrogen contents initially increased but tended to decline after about 50% C loss. Solid-state 13C nuclear magnetic resonance spectroscopy showed little change in organic composition, consistent with white-rot fungal decay, with only a few 19-year samples showing large increases in lignin typical of extensive brown-rot decay. Hydrolyzable monosaccharides of wood and bark were dominated by glucose followed by mannose, xylose, galactose, and arabinose. For wood, the mole fraction of mannose decreased with decomposition, whereas those of glucose, arabinose, and galactose increased slightly and that of xylose remained constant for both brown and white rot. Our results support indications that decomposition of smaller diameter woody debris from managed conifer forests will likely be dominated by white-rot fungi, leaving residues high in cellulose rather than in lignin.

Direct simulation of magnetic resonance relaxation rates and line shapes from molecular trajectories.

We simulate spin relaxation processes, which may be measured by either continuous wave or pulsed magnetic resonance techniques, using trajectory-based simulation methodologies. The spin-lattice relaxation rates are extracted numerically from the relaxation simulations. The rates obtained from the numerical fitting of the relaxation curves are compared to those obtained by direct simulation from the relaxation Bloch-Wangsness-Abragam-Redfield theory (BWART). We have restricted our study to anisotropic rigid-body rotational processes, and to the chemical shift anisotropy (CSA) and a single spin-spin dipolar (END) coupling mechanisms. Examples using electron paramagnetic resonance (EPR) nitroxide and nuclear magnetic resonance (NMR) deuterium quadrupolar systems are provided. The objective is to compare those rates obtained by numerical simulations with the rates obtained by BWART. There is excellent agreement between the simulated and BWART rates for a Hamiltonian describing a single spin (an electron) interacting with the bath through the chemical shift anisotropy (CSA) mechanism undergoing anisotropic rotational diffusion. In contrast, when the Hamiltonian contains both the chemical shift anisotropy (CSA) and the spin-spin dipolar (END) mechanisms, the decay rate of a single exponential fit of the simulated spin-lattice relaxation rate is up to a factor of 0.2 smaller than that predicted by BWART. When the relaxation curves are fit to a double exponential, the slow and fast rates extracted from the decay curves bound the BWART prediction. An extended BWART theory, in the literature, includes the need for multiple relaxation rates and indicates that the multiexponential decay is due to the combined effects of direct and cross-relaxation mechanisms.

Evaluation of renal function in children with solid tumors: Comparison between estimation with Schwartz formula and EDTA clearance.

9560 Background: Using the [51Cr]-ethylenediamine tetra acetic acid ([51Cr]-EDTA) method provides an accurate measure of glomerular filtration rate (GFR) for each patient. However, this method is not always feasible in routine. Thus, several mathematical equations have been developed to predict creatinine clearance. The most widely used in pediatric patients is the Schwartz formula, based on patient height and serum creatinine. However, this method has not been validated in pediatric cancer patients. The aim of the present study was to compare GFR measured with the 51Cr-EDTA method to GFR estimated with the Schwartz formula in patients younger than 18 years of age and treated for solid tumors. Methods: Data have been retrospectively collected on consecutive children treated between 2001 and 2011 at Institut Gustave Roussy. All of the patients had undergone assessment of GFR via 51Cr-EDTA clearance and estimation of renal function by the Schwartz formula. Exclusion criteria were serum creatinine under 25µmol/L or no recent dosage available. GFR analysis was realized using the slope intercept method after a single injection of 51Cr-EDTA solution.. Values of the GFR were calculated by multiplying the volume of dilution by the slope of the single exponential fit to the three data points and then expressed in ml/min/1.73m². Student paired t-test (alpha = 0.05) was used to compare results obtained for each patient with the two methods. Results: 196 patients (120 males, 76 females), treated with various types of cancer (neuroblastoma, osteosarcoma, Ewing sarcoma, lymphoma…) Mean age was 6.7 years. Mean GFR was 127.5 ml/min/1.73m² with the 51Cr-EDTA method versus 148.1 ml/min/1.73m² with the Schwartz formula. Mean of difference was 20.7 ml/min/1.73m² with a confidence interval [-25.7 ; -15.6] (p < 0.0001). Conclusions: GFR estimated with the Schwartz formula is statistically different from the isotopic method. In most cases, GFR estimated with the Schwartz formula is overestimated. This study highlights the lack of accuracy of this equation in pediatric population with cancer. The 51Cr-EDTA method must be preferred when a reliable and accurate evaluation of renal function is needed.

Recruitment of resting vesicles into recycling pools supports NMDA receptor‐dependent synaptic potentiation in cultured hippocampal neurons

Most presynaptic terminals in the central nervous system are characterized by two functionally distinct vesicle populations: a recycling pool, which supports action potential-driven neurotransmitter release via vesicle exocytosis, and a resting pool. The relative proportions of these two pools are highly variable between individual synapses, prompting speculation on their specific relationship, and on the possible functions of the resting pool. Using fluorescence imaging of FM-styryl dyes and synaptophysinI-pHluorin (sypHy) as well as correlative electron microscopy approaches, we show here that Hebbian plasticity-dependent changes in synaptic strength in rat hippocampal neurons can increase the recycling pool fraction at the expense of the resting pool in individual synaptic terminals. This recruitment process depends on NMDA-receptor activation, nitric oxide signalling and calcineurin and is accompanied by an increase in the probability of neurotransmitter release at individual terminals. Blockade of actin-mediated intersynaptic vesicle exchange does not prevent recycling pool expansion demonstrating that vesicle recruitment is intrasynaptic. We propose that the conversion of resting pool vesicles to the functionally recycling pool provides a rapid mechanism to implement long-lasting changes in presynaptic efficacy.

The effect of coating of Fe3O4/silica core/shell nanoparticles on T2relaxation time at 9.4 T

Magnetic Resonance Imaging (MRI) that provides superior soft tissue contrast is commonly used for diagnosis of many diseases. However specificity of MRI cancer diagnosis can be further increased by application of target contrast agents comprising superparamagnetic nanoparticles (NPs) synthesised with biological objects, which deliver the contrast to the specific cancer cells. These superparamagnetic NPs shorten T 2 relaxation time thus change contrast to noise ratio for tumor tissues. Therefore the impact of Fe 3 O 4 size and silica coating for Fe 3 O 4 /silica core/shell superparamagnetic nanoparticles (NPs) on T 2 relaxation time was studied at 9.4 T. The magnetic resonance imaging (MRI) studies were performed using homogenous agar solution of NPs. Naked Fe 3 O 4 NPs with a mean core diameter of 10.0 ± 1.3 (mean ± SD), 15.0 ± 2.5 and 20.0 ± 0.9 nm were analyzed. Silica coated Fe 3 O 4 NPs with core size of 10.0 ± 1.3 nm and the shell thickness of 16.7 ± 1.8, 25.3 ± 2.7 and 33.9 ± 4.0 nm were also investigated. The T 2 values of agar solutions with different NPs were calculated using a single slice multi echo method and single exponential fitting of the echo train. The measurements showed linear correlation between T 2 and Fe 3 O 4 core diameter as well as shell thickness. Silica coating, while improving functionalization and potentially reducing toxicity of NPs, decreases the impact of the magnetic core on T 2 , thus decreasing MRI contrast efficacy.

The effect of coating of Fe3O4/silica core/shell nanoparticles on T2 relaxation time at 9.4 T

Magnetic Resonance Imaging (MRI) that provides superior soft tissue contrast is commonly used for diagnosis of many diseases. However specificity of MRI cancer diagnosis can be further increased by application of target contrast agents comprising superparamagnetic nanoparticles (NPs) synthesised with biological objects, which deliver the contrast to the specific cancer cells. These superparamagnetic NPs shorten T2 relaxation time thus change contrast to noise ratio for tumor tissues. Therefore the impact of Fe3O4 size and silica coating for Fe3O4/silica core/shell superparamagnetic nanoparticles (NPs) on T2 relaxation time was studied at 9.4 T. The magnetic resonance imaging (MRI) studies were performed using homogenous agar solution of NPs. Naked Fe3O4NPs with a mean core diameter of 10.0 ± 1.3 (mean ± SD), 15.0 ± 2.5 and 20.0 ± 0.9 nm were analyzed. Silica coated Fe3O4 NPs with core size of 10.0 ± 1.3 nm and the shell thickness of 16.7 ± 1.8, 25.3 ± 2.7 and 33.9 ± 4.0 nm were also investigated. The T2 values of agar solutions with different NPs were calculated using a single slice multi echo method and single exponential fitting of the echo train. The measurements showed linear correlation between T2 and Fe3O4 core diameter as well as shell thickness. Silica coating, while improving functionalization and potentially reducing toxicity of NPs, decreases the impact of the magnetic core on T2, thus decreasing MRI contrast efficacy.

Single-Molecule Fluorescence Measurements of Ribosomal Translocation Dynamics

We employ single-molecule fluorescence resonance energy transfer (smFRET) to study structural dynamics over the first two elongation cycles of protein synthesis, using ribosomes containing either Cy3-labeled ribosomal protein L11 and A- or P-site Cy5-labeled tRNA or Cy3- and Cy5-labeled tRNAs. Pretranslocation (PRE) complexes demonstrate fluctuations between classical and hybrid forms, with concerted motions of tRNAs away from L11 and from each other when classical complex converts to hybrid complex. EF-G⋅GTP binding to both hybrid and classical PRE complexes halts these fluctuations prior to catalyzing translocation to form the posttranslocation (POST) complex. EF-G dependent translocation from the classical PRE complex proceeds via transient formation of a short-lived hybrid intermediate. A-site binding of either EF-G to the PRE complex or of aminoacyl-tRNA⋅EF-Tu ternary complex to the POST complex markedly suppresses ribosome conformational lability.

Fluorescence Studies on a Designed Peptide of REIP as a Potential Hydrophobic Drug Carrier

Many hydrophobic drugs have limited or no activity in clinical application due to their poor aqueous solubility. In order to find fine delivery system, we designed a novel peptide REIP (Ac-RIEIRIEIAPAIEIRIEIR) and investigated its properties as a delivery system. Microcrystal of pyrene could be stabilized by the peptide REIP and suspended in aqueous solution. We used pyrene as a model hydrophobic drug and egg phosphatidylcholine (EPC) vesicles as model membranes to study the ability of REIP in hydrophobic drug encapsulation and transfer to EPC vesicles (liposome) by analyzing the fluorescence spectroscopy of pyrene. It was found that pyrene was present in the crystalline form when stabilized by REIP and was able to transfer into EPC vesicles in molecular form. The concentration of pyrene released into the EPC vesicles at a given time was quantified using a calibration curve. Double exponential curve fitting was better for the release profiles of REIP-Py solution than single exponential curve fitting.