Solubility of drugs in the presence of gelatin: effect of drug lipophilicity and degree of ionization

Lysosomal Targeted Cyclometallic Iridium(Ⅲ) Salicylaldehyde-Coumarin Schiff Base Complexes and Anticancer Application

Natural coumarin derivatives and cyclometallic iridium (Ⅲ) (Ir^Ⅲ) complexes have attracted much attention in the field of anticancer. In this study, six coumarin-modified cyclometallic Ir^Ⅲ salicylaldehyde Schiff base complexes ([(ppy)₂Ir(O^N)]/[(ppy-CHO)₂Ir(O^N)]) were designed and synthesized. Compared with coumarin and Ir^Ⅲ complex monomers, target complexes exhibited favorable cytotoxic activity toward A549 and BEAS-2B cells. These complexes could induce extensive apoptosis of A549 cell (late apoptosis), which was represented by the disturbance of cell cycle (G₁-phase) and the accumulation of intracellular reactive oxygen species, exhibiting an anticancer mechanism of oxidation. With the help of suitable fluorescence of these complexes, no conflict with the probes, confocal detection confirmed that complexes showed an energy-dependent cellular uptake mechanism and triggered lysosome-mediated apoptosis in A549 cell line. Above all, our findings reveal the design of a lysosomal targeting cyclometallic Ir^Ⅲ Schiff base complexes and provide a new idea for the design of integrated drugs for diagnosis and treatment.

Maresin 1 Promotes Wound Healing and Socket Bone Regeneration for Alveolar Ridge Preservation

Tooth extraction results in alveolar bone resorption and is accompanied by postoperative swelling and pain. Maresin 1 (MaR1) is a proresolving lipid mediator produced by macrophages during the resolution phase of inflammation, bridging healing and tissue regeneration. The aim of this study was to examine the effects of MaR1 on tooth extraction socket wound healing in a preclinical rat model. The maxillary right first molars of Sprague-Dawley rats were extracted, and gelatin scaffolds were placed into the sockets with or without MaR1. Topical application was also given twice a week until complete socket wound closure up to 14 d. Immediate postoperative pain was assessed by 3 scores. Histology and microcomputed tomography were used to assess socket bone fill and alveolar ridge dimensional changes at selected dates. The assessments of coded specimens were performed by masked, calibrated examiners. Local application of MaR1 potently accelerated extraction socket healing. Macroscopic and histologic analysis revealed a reduced soft tissue wound opening and more rapid re-epithelialization with MaR1 delivery versus vehicle on socket healing. Under micro-computed tomography analysis, MaR1 (especially at 0.05 μg/μL) stimulated greater socket bone fill at day 10 as compared with the vehicle-treated animals, resulting in less buccal plate resorption and a wider alveolar ridge by day 21. Interestingly, an increased ratio of CD206⁺:CD68⁺ macrophages was identified in the sockets with MaR1 application under immunohistochemistry and immunofluorescence analysis. As compared with the vehicle therapy, local delivery of MaR1 reduced immediate postoperative surrogate pain score panels. In summary, MaR1 accelerated extraction wound healing, promoted socket bone fill, preserved alveolar ridge bone, and reduced postoperative pain in vivo with a rodent preclinical model. Local administration of MaR1 offers clinical potential to accelerate extraction socket wound healing for more predictable dental implant reconstruction.

Drug Distribution to Human Tissues: Prediction and Examination of the Basic Assumption in In Vivo Pharmacokinetics-Pharmacodynamics (PK/PD) Research

The tissue:plasma partition coefficients (Kp ) are good indicators of the extent of tissue distribution. Therefore, advanced tissue composition-based models were used to predict the Kp values of drugs under in vivo conditions on the basis of in vitro and physiological input data. These models, however, focus on animal tissues and do not challenge the predictions with human tissues for drugs. The first objective of this study was to predict the experimentally determined Kp values of seven human tissues for 26 drugs. In all, 95% of the predicted Kp values are within 2.5-fold error of the observed values in humans. Accordingly, these results suggest that the tissue composition-based model used in this study is able to provide accurate estimates of drug partitioning in the studied human tissues. Furthermore, as the Kp equals to the ratio of total concentration between tissue and plasma, or the ratio of unbound fraction between plasma (fup ) and tissue (fut ), this parameter Kp would deviate from the unity. Therefore, the second objective was to examine the corresponding relationships between fup and fut values experimentally determined in humans for several drugs. The results also indicate that fup may significantly deviate to fut ; the discrepancies are governed by the dissimilarities in the binding and ionization on both sides of the membrane, which were captured by the tissue composition-based model. Hence, this violated the basic assumption in in vivo pharmacokinetics-pharmacodynamics (PK/PD) research, since the free drug concentration in tissue and plasma was not equal particularly for the ionizable drugs due to the pH gradient effect on the fraction of unionized drug in plasma (fuip ) and tissue (fuit ) (i.e., fup × fuip × total plasma concentration = fut × fuit × total tissue concentration, and, hence, the free drug concentration in plasma and tissue differed by fuip/fuit). Therefore, this assumption should be adjusted for the ionized drugs, and, hence, a mathematical correction to the basic assumption of similar free drug concentration in plasma and tissues can be derived from the tissue composition-based model. Note that this assumption will be further challenged in a dynamic in vivo system in a companion manuscript. Overall, this study was a first attempt to predict the in vivo Kp values for specific human tissues by considering separately the effect of fup and fut , with the aim of facilitating the use of physiologically-based PK (PBPK) model in PK/PD studies.

In vivo degradability of hydrogels prepared from different gelatins by various cross-linking methods

This study is an investigation to evaluate the in vivo degradation of gelatin hydrogels in terms of their number of cross-links. Various hydrogels were prepared from acidic gelatin, extracted from bovine bone, porcine skin or fish scale, and basic gelatin, extracted from porcine skin, through four types of cross-linking methods, i.e., glutaraldehyde (GA) or dehydrothermal treatment and ultraviolet (UV) or electron beam irradiation. The water content of hydrogels and their number of cross-links, calculated from the tensile modulus of hydrogels, were evaluated as the measure of hydrogel cross-linking extent. Following subcutaneous implantation of 125I-labeled gelatin hydrogels into mice, the radioactivity remaining was measured at different time intervals to assess the in vivo degradability of hydrogels. Irrespective of the gelatin type and cross-linking method, a good correlation was found between the in vivo degradability of hydrogels and their number of cross-links, which is different from the correlation to their water content. This finding indicates that the degradability of hydrogels is governed by their number of cross-links.

Crosslinking of gelatin-based drug carriers by genipin induces changes in drug kinetic profiles in vitro

Hydrogels are extensively studied as carrier matrices for the controlled release of bioactive molecules. The aim of this study was to design gelatin-based hydrogels crosslinked with genipin and study the impact of crosslinking temperature (5, 15 or 25°C) on gel strength, microstructure, cytocompatibility, swelling and drug release. Gels crosslinked at 25°C exhibited the highest Flory-Rehner crosslink density, lowest swelling ratio and the slowest release of indomethacin (Idn, model anti-inflammatory drug). Diffusional exponents (n) indicated non-Fickian swelling kinetics while drug transport was anomalous. Hydrogel biocompatibility, in vitro cell viability, cell cycle experiments with AH-927 and HaCaT cell lines indicated normal cell proliferation without any effect on cell cycle. Overall, these results substantiated the use of genipin-crosslinked hydrogels as a viable carrier matrix for drug release applications.

A practical deuterium-free NMR method for the rapid determination of 1-octanol/water partition coefficients of pharmaceutical agents

A simple and rapid NMR method is described to determine the logP of pharmaceutical agents. This method is highly versatile and efficient, because it does not require the use of deuterated solvents or the addition of any internal/external standards to the sample. We demonstrate that logP can be accurately measured using NMR for pharmaceutical agents with known logP values. Our proposed method is made possible by the combination of state-of-the-art NMR techniques including the solvent concentration reference and robust solvent suppressions.

Cellular pharmacokinetics of the novel biaryloxazolidinone radezolid in phagocytic cells: studies with macrophages and polymorphonuclear neutrophils

Radezolid (RX-1741) is the first biaryloxazolidinone in clinical development. It shows improved activity, including against linezolid-resistant strains. Radezolid differs from linezolid by the presence of a biaryl spacer and of a heteroaryl side chain, which increases the ionization and hydrophilicity of the molecule at physiological pH and confers to it a dibasic character. The aim of this study was to determine the accumulation and subcellular distribution of radezolid in phagocytic cells and to decipher the underlying mechanisms. In THP-1 human macrophages, J774 mouse macrophages, and human polymorphonuclear neutrophils, radezolid accumulated rapidly and reversibly (half-lives of approximately 6 min and 9 min for uptake and efflux, respectively) to reach, at equilibrium, a cellular concentration 11-fold higher than the extracellular one. This process was concentration and energy independent but pH dependent (accumulation was reduced to 20 to 30% of control values for cells in medium at a pH of <6 or in the presence of monensin, which collapses pH gradients between the extracellular and intracellular compartments). The accumulation at equilibrium was not affected by efflux pump inhibitors (verapamil and gemfibrozil) and was markedly reduced at 4 degrees C but was further increased in medium with low serum content. Subcellular fractionation studies demonstrated a dual subcellular distribution for radezolid, with approximately 60% of the drug colocalizing to the cytosol and approximately 40% to the lysosomes, with no specific association with mitochondria. These observations are compatible with a mechanism of transmembrane diffusion of the free fraction and partial segregation of radezolid in lysosomes by proton trapping, as previously described for macrolides.

Haemolytic fungi isolated from sago starch in Papua New Guinea

Sago haemolytic disease (SHD) is a rare but often fatal illness linked to consumption of stale sago starch in Papua New Guinea. Although the aetiology of SHD remains unknown, mycotoxins are suspected. This study investigated whether fungi isolated from Papua New Guinean sago starch were haemolytic. Filamentous fungi and yeasts from sago starch were grown on sheep blood agar and some on human blood agar. Clear haemolytic activity was demonstrated by 55% of filamentous fungal isolates, but not by yeasts. A semi-quantitative bioassay was developed involving incubation of human erythrocytes with fungal extracts. Extracts of cultures of Penicillium, Aspergillus and Fusarium all caused rapid haemolysis in the bioassay. Partial fractionation of extracts suggested that both polar and non-polar haemolytic components had haemolytic activity in vitro. Further work is warranted to identify these metabolites and determine if they play a role in SHD.

In vitro evaluation of the dissolution behaviour of itraconazole in bio-relevant media

Drugs in the gastrointestinal tract are exposed to a medium of partially digested food, comprising mixtures of fat, protein and carbohydrate. The dissolution behaviour of itraconazole was evaluated in bio-relevant media which were developed to take this into account. Media containing milk with different fat contents, protein (albumin, casein, gluten and gelatin), carbohydrates (glucose, lactose and starch) and amino acids (lysine, glycine, alanine and aspartic acid) to mimic a digested meal and bile components (sodium taurocholate and lecithin) to represent a key endogenous digestive material were investigated. The effect of medium composition on the intrinsic dissolution rate of itraconazole was evaluated as this drug has extremely poor solubility and its bioavailability is affected by food. Dissolution tests were carried out in simple compendial media based on dilute solutions of hydrochloric acid or neutral solutions of phosphate buffer and in more complex media containing the dietary components. The data obtained showed that most of the dietary components enhanced the solubility compared to simulated gastric fluid (SGF) but to differing extents. The greatest increase in dissolution was observed with the addition of milk and albumin although an increase was also seen with other proteins, amino acids and simulated gastrointestinal fluids.

Enhancement of the dissolution rate and gastrointestinal absorption of pranlukast as a model poorly water-soluble drug by grinding with gelatin

The effect of grinding with gelatin on the dissolution behavior and gastrointestinal absorption of a poorly water-soluble drug was evaluated using the antiasthmatic agent, pranlukast, as a model poorly water-soluble drug. A ground pranlukast-gelatin mixture was prepared by grinding equal quantities of pranlukast and gelatin. In the dissolution testing, the dissolution rate of pranlukast in the suspension of the ground pranlukast-gelatin mixture under conditions of pH 3.0, 5.0 and 7.0 was markedly faster than that in the suspension of pranlukast. According to powder X-ray diffractometry (PXRD) and differential scanning calorimetry (DSC) analysis, the enhanced dissolution rate of pranlukast produced by grinding with gelatin was caused by changing the crystalline state of pranlukast into an amorphous state. In an animal experiment, the bioavailability of pranlukast following oral administration of the ground pranlukast-gelatin mixture to rats was threefold greater than that following administration of pranlukast. In the in vitro permeation experiment, the amount of permeated pranlukast through Caco-2 cell monolayers after application of the ground pranlukast-gelatin mixture was greater than that after application of pranlukast. These results suggest that the enhancement of the gastrointestinal absorption of pranlukast by grinding with gelatin is due to enhancement of the dissolution rate. Grinding a poorly water-soluble drug with gelatin is a useful method of enhancing its gastrointestinal absorption.

Development of a partially automated solubility screening (PASS) assay for early drug development

A medium-throughput, compound-saving, thermodynamic solubility assay for early drug development was developed. Solid compound suspended in heptane was used for simple, time-saving, and flexible compound distribution into 96-well plates, with minor risk to generate new physical forms during dispensing. Low volume, well-stirred incubation vessels were generated by using a combination of V-shaped wells, well caps, and vertically inserted stir bars. This allowed solubility determination up to 100 mg/mL in 40-80 microL volumes in aqueous and nonaqueous, low- and high-viscosity solvents. After removal of residual solid through syringe filters mounted on microtiter plates, the filtrate was quantified by ultra performance liquid chromatography (UPLC) using a 1.2 min gradient. Combined with a robotic liquid handling system, throughput was 45 samples per hour and >600 solubility measurements per week. Results from the partially automated solubility screening (PASS) assay correlated well with reported solubility values (r2 = 0.882). The PASS assay is useful for compound-saving, thermodynamic solubility measurement at the discovery-development interface where maximal solubility in many commonly used solvents needs to be determined. PASS results provide a basis for the identification of formulation strategies, the selection of appropriate excipients, and for the prediction of the potential in vivo behavior of compounds.

Solubility of silybin in aqueous poly(ethylene glycol) solution

Silybin is a main component in silymarin, which is an antihepatotoxic polyphenolic substance isolated from the milk thistle plant, Silybum marianum. A major problem in the development of an oral solid dosage form of this drug is the extremely poor aqueous solubility. In present work, the solubility of silybin in aqueous poly(ethylene glycol) 6,000 (PEG 6,000) solution at the temperature range from 293.15 to 313.15K was measured by a solid liquid equilibrium method. The aim of this study is to investigate the possible effect of poly(ethylene glycol) concentration and temperature on the solubility of the drug, and to reveal the solubilization capacity of the polymer for the drug. Experimental results reveal that the solubility of silybin increases with the increase both in PEG's concentration and temperature. With the increase in PEG's concentration, the transfer enthalpy and entropy for silybin from water to aqueous PEG solution increases first in a positive region, and then decreases to a negative region. The transfer enthalpy is lower than the entropy term. A modified Universal Quasi Chemical (UNIQUAC) model was used to correlate solubility data.

High variation of tioguanine absorption in patients with chronic active Crohn's disease

BACKGROUND

Tioguanine (thioguanine) has been suggested as a therapeutic alternative for patients with Crohn's disease resistant or intolerant to azathioprine or mercaptopurine. However, pharmacokinetic data on tioguanine in inflammatory bowel disease are missing.

AIM

To determine the disposition of three different 40 mg tablet preparations of tioguanine in patients with Crohn's disease.

METHODS

Six patients with chronic active Crohn's disease were included in a randomized, cross-over, single-dose study. Pharmacokinetic analysis was based on plasma concentrations of tioguanine during 6 h after dosing. Tioguanine was measured by a validated high-pressure liquid chromatographic method.

RESULTS

The areas under the curve (AUC) varied 4-7-fold between patients. In two patients, tioguanine was not detected in plasma following the intake of one of the three tablets; another patient did not absorb tioguanine in two of the three different preparations. No significant differences were found in the AUC and Cmax values between the three tablets. In all patients, there was a second peak in plasma concentration following a meal 3 h after drug administration.

CONCLUSIONS

The absorption of tioguanine is highly variable in patients with Crohn's disease, which may be responsible for treatment failure. Therapy with tioguanine may be improved by monitoring tioguanine nucleotides as a surrogate parameter of efficacy.