Convection-Enhanced Drug Delivery: Experimental and Analytical Studies of Infusion Behavior in an In Vitro Brain Surrogate.

Convection-enhanced drug delivery (CED) directly infuses drugs with a large molecular weight toward target cells as a therapeutic strategy for neurodegenerative diseases and brain cancers. Despite the success of many previous in vitro experiments on CED, challenges still remain. In particular, a theoretical predictive model is needed to form a basis for treatment planning, and developing such a model requires well-controlled injection tests that can rigorously capture the convective (advective) and diffusive transport of an infusate. For this purpose, we investigated the advection-diffusion transport of an infusate (bromophenol blue solution) in the brain surrogate (0.2% w/w agarose gel) at different injection rates, ranging from 0.25 to 4 µL/min, by closely monitoring changes in the color intensity, propagation distance, and injection pressures. One dimensional closed-form solution was examined with two variable sets, such as the mathematically calculated coefficient of molecular diffusion and average velocity, and the hydraulic dispersion coefficient and seepage velocity by the least squared method. As a result, the seepage velocity was greater than the average velocity to some extent, particularly for the later infusion times. The poroelastic deformation in the brain surrogate might lead to changes in porosity, and consequently, slight increases in the actual flow velocity as infusion continues. The limitation of efficiency of the single catheter was analyzed by dimensionless analysis. Lastly, this study suggests a simple but robust approach that can properly capture the convective (advective) and diffusive transport of an infusate in an in vitro brain surrogate via well-controlled injection tests.

Biogenic and chemically synthesized Solanum tuberosum peel-silver nanoparticle hybrid for the ultrasonic aided adsorption of bromophenol blue dye.

This work was aimed at the synthesis of a hybrid (STpe-AgNP), obtained by impregnation of silver nanoparticles (AgNP) onto Solanum tuberosum peel (STpe), for the ultrasonic assisted adsorption of bromophenol blue (BB) dye. SEM, FTIR, XRD, EDX, TGA and BET techniques were used to characterize the adsorbents. The XRD, SEM and EDX confirmed successful impregnation of AgNPs onto STpe to form the hybrid. The AgNPs impregnated onto the hybrid were found to be water stable at various pH values of 2.0-9.0. Chi-square (χ2 < 0.024) and linear regression (R2 > 0.996) showed that the Freundlich model was best fitted among the isotherm models, corroborated by the oriented site model. Kinetic analysis conformed to the intraparticle diffusion and pseudo-first-order rate equations, while thermodynamics displayed a physical, spontaneous and endothermic adsorption process. The presence of competing Pb(II), Ni(II), Cd(II) and Zn(II) metal ions in solution interfered with the adsorption of BB onto the biosorbents. In terms of reusability, STpe and STpe-AgNP showed BB desorption of 91.3% and 88.5% respectively, using NaOH as eluent. Ultra-sonication significantly enhanced the adsorption of BB by both adsorbents, but the impregnation of AgNPs only slightly improved adsorption of the dye from the simulated wastewater. This study also illustrated that pristine STpe biomass waste is a cheap viable option for the decontamination of BB from water.

In Vitro Evaluation of Small Molecule Delivery into Articular Cartilage: Effect of Synovial Clearance and Compressive Load.

Intra-articular injection of drug depots is considered as a therapeutic strategy for the treatment of osteoarthritis. In this study, we designed an in vitro assay in a previously described bioreactor system to evaluate the uptake of a small molecule drug mimic as a function of drug clearance by the synovium and compressive load. Bromophenol blue (BPB) loaded hydrogels were placed on top of bovine articular cartilage explants and were compressed in a dual flow bioreactor. As a control, BPB was directly injected in the bioreactor compartment mimicking the synovial fluid. Subsequently, diffusion coefficients of the dye were estimated based on Fick's law. Mimicking synovial clearance revealed that dye penetration of BPB when released from a drug delivery system placed on top of a cartilage explant was enhanced compared to direct injection of BPB into a simulated synovial fluid. Furthermore, we show the synergistic effect of the amount of load and the frequency on drug uptake by the cartilage. In the described model, we have shown that, under compressive load, drug delivery from a depot was beneficial over conventional intra-articular drug administration. The assay mimics the complexity of the knee joint in several key aspects, which results in a more close representation of the expected drug outcome. In this study, we have evaluated the penetration of a model small molecule drug into articular cartilage under compressive conditions, and future development will focus on incorporating synovial(-like) fluid, synovium, and bone to increase the predictive potential of the assay further.

Bromophenol blue binding to mammalian albumins and displacement of albumin-bound bilirubin.

Interaction of bromophenol blue (BPB) with serum albumins from different mammalian species, namely, human (HSA), bovine (BSA), goat (GSA), sheep (SSA), rabbit (RbSA), porcine (PSA) and dog (DSA) was studied using absorption and absorption difference spectroscopy. BPB-albumin complexes showed significant differences in the spectral characteristics, i.e., extent of bathochromic shift and hypochromism relative to the spectral features of free BPB. Absorption difference spectra of these complexes also showed variations in the position of maxima and absorption difference (deltaAbs.) values. Absorption difference spectra of different bilirubin (BR)-albumin complexes showed a significant blue shift accompanied by decrease in deltaAbs. values in presence of BPB which were indicative of the displacement of bound BR from its binding site in BR-albumin complexes. These changes in the difference spectral characteristics of BR-albumin complexes were more marked at higher BPB concentration. However, the extent of these changes was different for different BR-albumin complexes. Taken together, all these results suggest that BPB partially shares BR binding site on albumin and different mammalian albumins show differences in the microenvironment of the BR/BPB binding site.

A realistic brain tissue phantom for intraparenchymal infusion studies.

OBJECT: The goal of this study was to validate a simple, inexpensive, and robust model system to be used as an in vitro surrogate for in vivo brain tissues in preclinical and exploratory studies of infusion-based intraparenchymal drug and cell delivery. METHODS: Agarose gels of varying concentrations and porcine brain were tested to determine the infusion characteristics of several different catheters at flow rates of 0.5 and 1 microl per minute by using bromophenol blue (BPB) dye (molecular weight [MW] approximately 690) and gadodiamide (MW approximately 573). Magnetic resonance (MR) imaging and videomicroscopy were used to measure the distribution of these infusates, with a simultaneous measurement of infusion pressures. In addition, the forces of catheter penetration and movement through gel and brain were measured. Agarose gel at a 0.6% concentration closely resembles in vivo brain with respect to several critical physical characteristics. The ratio of distribution volume to infusion volume of agarose was 10 compared with 7.1 for brain. The infusion pressure of the gel demonstrated profiles similar in configuration and magnitude to those of the brain (plateau pressures 10-20 mm Hg). Gadodiamide infusion in agarose closely resembled that in the brain, as documented using T1-weighted MR imaging. Gadodiamide distribution in agarose gel was virtually identical to that of BPB dye, as documented by MR imaging and videomicroscopy. The force profile for insertion of a silastic catheter into agarose gel was similar in magnitude and configuration to the force profile for insertion into the brain. Careful insertion of the cannula using a stereotactic guide is critical to minimize irregularity and backflow of infusate distribution. CONCLUSIONS: Agarose gel (0.6%) is a useful surrogate for in vivo brain in exploratory studies of convection-enhanced delivery.

Absorption of phenol red and bromphenol blue as model drugs from the peritoneal cavity around the liver surface in rats.

The importance of the injection site on the pharmacokinetics of phenol red and bromphenol blue as model drugs after intraperitoneal administration into rat was examined. Their absorption rate from the peritoneal cavity was faster after intraperitoneal administration to the liver surface than that after intraperitoneal administration to the distal small intestine, as shown by the increase in maximum concentration and decrease in mean residence time in plasma. A similar tendency was observed in the biliary excretion pattern. The enhanced absorption rate was supported by the significantly smaller amount of both drugs remaining in the peritoneal cavity at 15 min after liver surface administration than that after small intestine administration. The liver concentration of the model drugs at 15 min after liver surface administration was 1.5-2.0 times that after small intestine administration. Accordingly, liver surface administration was shown to be effective with good absorption and efficient drug delivery to the liver.

Effect of albumin on the absorption of phenol red, bromphenol blue and bromosulphonphthalein as model drugs from the liver surface membrane in rats.

The effect of bovine serum albumin (BSA) on drug absorption from the liver surface in rats was examined by using three organic anions (phenol red, bromphenol blue and bromosulphonphthalein) as model drugs which have a high affinity for albumin. The binding ratio of the model drugs (3 mg/ml in phosphate buffer) to BSA varied widely at a BSA concentration of 0.1--10% (w/v). The model drugs (3 mg/ml x 0.1 ml) with or without BSA were applied to the rat liver surface in vivo employing a cylindrical glass cell (i.d. 9 mm, area 0.64 cm2). The absorption ratios of the model drugs from the rat liver surface at 6h, calculated from the amount recovered from the glass cell, decreased with an increase in BSA concentration. A similar trend was observed with biliary recovery of the model drugs. A marked reduction in the absorption ratio was seen with bromosulphonphthalein, which has the highest binding activity to BSA among the three organic anions. Accordingly, protein binding appears to be a significant factor with respect to the drug absorption from the liver surface.

Absorption of organic anions as model drugs following application to rat liver surface in-vivo.

Absorption of organic anions (phenol red, bromphenol blue and bromosulphonphthalein) has been studied after their application to rat liver surface in-vivo, employing a cylindrical glass cell (i.d. 9 mm, area 0.64 cm2). Each drug appeared gradually in the blood with the peak level at about 1 h, after which its concentration declined slowly. Absorbed model drug was efficiently excreted into the bile. These observations appear to indicate the possibility of drug absorption from liver surface membrane. Absorption of model drugs was estimated to be more than 59% in 6 h. The biliary recovery and metabolism of phenol red did not change as compared with that after intravenous administration.