A uremic toxin, 3-carboxy-4-methyl-5-propyl-2-furanpropionate induces cell damage to proximal tubular cells via the generation of a radical intermediate

3-Carboxy-4-methyl-5-propyl-2-furanpropionate (CMPF), a furan fatty acid uremic toxin (UT) and a substrate for organic ion transporters, contributes to the accumulation of CMPF in renal tubular cells. Although oxidative stress induced by UTs has been proposed as a mechanism of its toxicity in chronic kidney disease, little information is available regarding the redox property of CMPF and its relation to renal cell damage. The findings herein show that CMPF enhances the production of reactive oxygen species (ROS) in HK-2 cells in the presence of angiotensin II (A-II), an inducer of O(2)(·-). When iron is also present, CMPF and A-II induce the Fenton reaction, resulting in a further increase in ROS production. Such CMPF-induced oxidative stress increases TGF-β1 secretion in HK-2 cells, and a positive correlation between CMPF-induced ROS production and the secretion of active TGF-β1 was observed. CMPF caused a reduction in cell viability which was negatively correlated with intracellular ROS production. These negative effects of CMPF in HK-2 cells were completely suppressed by probenecid, an inhibitor of organic anion transport. Interestingly, in vitro ROS assays indicate that CMPF directly interacts with superoxide anion radicals (O(2)(·-)) and peroxy radicals (LOO) to produce CMPF radicals. The subsequent interaction of CMPF radicals with dissolved oxygen leads to the overproduction of O(2)(·-). Based on these findings, we conclude that CMPF, which accumulates in the renal cells, appears to play a prominent role as a pro-oxidant which subsequently leads to renal cellular damage via the overproduction of O(2)(·-).

Preparation and evaluation of granules with pH-dependent release by melt granulation

This study had two objectives: (1) to prepare, by melt granulation in a high-shear mixer, granules containing acetaminophen (APAP) as a model drug and aminoalkyl methacrylate copolymer E (AMCE) as a pH-sensitive polymer that readily dissolves at pH values lower than 5, and (2) to investigate the effects of AMCE loading (5-15%) on granule properties and the in vitro release profile of drug from the granules. Compared with polymer-free granules, the granules containing 5% and 10% AMCE were found to have higher median diameters and wider particle size distributions. For the formulation containing 15% AMCE, on the other hand, the diameters and distribution were similar to those for polymer-free granules. From compression testing, load-displacement curves revealed that AMCE enhanced particle strength at ambient temperature and induced plastic strain, while suppressing fragmentation of the granules. In addition, from dissolution testing using media with pH 4.0 and pH 6.5, granules containing AMCE, except 15% AMCE loading, exhibited drug release with significant pH dependence. When the pH 4.0 and pH 6.5 dissolution profiles were further compared by calculating the difference factor (f(1)), the 5% AMCE granules showed the strongest pH dependence of drug release among all formulations in this study. Large cracks and breakage were observed on the surface of 10% AMCE granules after they were used in dissolution testing. The obtained results are attributed to the plastic strain properties of AMCE above its glass transition temperature, and to the irregular distribution of AMCE within granules. Hence, this study has demonstrated for the first time that the combination of melt granulation and AMCE incorporation enables the formulation of novel functional granules that exhibit pH-dependent release of the active ingredient.

Clarithromycin monohydrate: a synchrotron X-ray powder study

In the crystal structure of the title compound, clarithromycin (CAM) monohydrate, C(38)H(69)NO(13)·H(2)O, the water mol-ecule behaves as a proton donor and is hydrogen bonded to the hy-droxy O atom of the CAM cladinose ring. The hy-droxy O atom also behaves as a proton donor, forming an inter-molecular hydrogen bond with one of the hy-droxy groups of the 14-membered aglycone ring. The CAM mol-ecules are linked through these hydrogen bonds into chains running parallel to the c axis.

Clarithromycin form I determined by synchrotron X-ray powder diffraction

The structure of the metastable form I polymorph of the macrolide antibiotic clarithromycin, C38H69NO13, was determined by a powder diffraction method using synchrotron radiation. The space group of form I isP21212. The initial model was determined by a molecular replacement method using the structure of clarithromycin form 0 as a search model, and the final structure was obtained through Rietveld refinements. In the form I crystal structure, the clarithromycin molecules are aligned parallel along theaaxis in a head-to-tail manner with intermolecular hydrogen bonds between the hydroxy O atoms. The dimethylamine groups of the clarithromycin molecule interdigitate between neighbouring head-to-tail clarithromycin alignments. The novel crystal packing found in form I provides a mechanism that describes the transformation of form 0 to form I.

Preparation and evaluation of swelling induced-orally disintegrating tablets by microwave irradiation

A major challenge in the development of orally disintegrating tablets (ODTs) is to achieve a good balance between tablet hardness and disintegration time. In this study, an advanced method was demonstrated to improve these opposing properties in a molded tablet using a one-step procedure that exploits the swelling induced by microwave treatment. Wet molded tablets consisting of the delta form of mannitol and silicon dioxide were prepared and microwave-heated to generate water vapor inside the tablets. This induced either swelling or shrinking of tablets, in the extent of each being dependent on tablet formulation and manufacturing conditions. A two-level full factorial design method was used to evaluate the effects of several variables in formulation and manufacturing conditions on the tablet properties, hardness, disintegration time and change in shape. The variables investigated in this study were: ratio of silicon dioxide in formulation, water volume added in granulation, ratio of water absorbed by silicon dioxide prior to granulation, and microwave irradiation time. Swelling of tablet by microwave irradiation was observed in the batches with high ratio of silicon dioxide and low levels of water volume. The disintegration time was clearly shortened by induction of the swelling, while tablet hardness increased. We demonstrated that the water vapor generated by microwave irradiation promoted a change in the crystalline form of mannitol from delta to beta, and that this may have contributed to an increase in tablet hardness. Additionally, it was found that new solid bridges were formed between the granules in the tablet via the pathway from dissolution of mannitol in water vapor to congelation, resulting in an increase in tablet hardness. Thus, both tablet hardness and disintegration properties of the molded tablets were improved by the proposed one-step method and the appropriate ranges for variables are indicated. In addition, multiple regression modeling was used to optimize formulation and manufacturing conditions, and the tablets obtained under these optimized conditions showed both swelling and desirable tablet properties. Therefore, we concluded that this one-step method using microwave irradiation would be a useful method for preparing the ODTs.

Stabilization mechanism of clarithromycin tablets under gastric pH conditions

It has been reported that tablets of clarithromycin (CAM), a 14-membered macrolide antibiotic, are especially stable under low pH conditions such as in gastric fluid, and showed excellent antibacterial efficiency even though CAM molecules themselves are rapidly decomposed. Therefore, we aimed to clarify the stabilization mechanism of CAM tablets under low pH conditions. From the results of stability and dissolution tests, the optimal decomposition rate constant (K(dec)) and dissolution rate constant (K(dis)) at various pH values were calculated by curve-fitting to consecutive reactions. Consequently, log(K(dec)) increased as pH decreased. On the other hand, log(K(dis)) increased as pH decreased from 3.0 to 1.5, but decreased as pH decreased from 1.5 to 1.0. In addition, the disintegration time of commercially available tablets at pH 1.0 and 1.2 was found to be delayed, resulting in a decrease of K(dis). Furthermore, from powder X-ray diffraction, HPLC and elemental analysis, the delay in disintegration time might be attributable to the formation of a transparent gel, formed by the reaction between CAM molecule and hydrochloric acid under low pH conditions, on the surface of CAM tablet. On the basis of these results, this report can be considered the first case where a transparent gel prevents gastric fluid from penetrating the tablet, resulting in reduced decomposition of CAM following oral administrating.

A comparative study of glycerin fatty acid ester and magnesium stearate on the dissolution of acetaminophen tablets using the analysis of available surface area

To study the effect of glycerin fatty acid ester (Poem TR-FB) concentrations on the dissolution rate of acetaminophen (APAP), the dissolution and disintegration behaviors of APAP tablets formulated using various lubricants were examined. The change over time in the available surface area of APAP (S(t)), which is in direct contact with solvent, was also analyzed using these dissolution data. In the dissolution tests, a retarded dissolution of APAP was not observed with TR-FB, whereas magnesium stearate (Mg-St), which is widely used as a lubricant, retarded the dissolution. However, no significant difference in the disintegration time between the two lubricants was observed. With regard to the time course of the S(t), Mg-St at 0.1% gave a maximum surface area value at 9.19 min (peak time); however, the profiles for APAP with Mg-St at greater than 0.5% showed downward curvature indicating a gradual decrease in surface area over time. Conversely, with TR-FB, even when its concentration was increased, the S(t) profile for APAP had a maximum value that was more than twice that of APAP with that of 0.5-3.0% of Mg-St. Scanning electron microscopy (SEM) observations showed that the differences in the dissolution rate and S(t) patterns between Mg-St and TR-FB could be explained by differences in extensibility deriving from their morphology. Therefore, it was concluded that TR-FB does not cause retardation of drug dissolution and may prove to be a superior alternative lubricant to Mg-St.

Novel mathematical model for predicting the dissolution profile of spherical particles under non-sink conditions

A mechanistic mathematical model was designed to predict dissolution patterns under non-sink conditions. Sulfamethoxazole was used as a model drug, and its physico-chemical properties such as solubility, density, and intrinsic dissolution rate constant etc., were investigated in order to apply these experimental values to the proposed model. Dissolution tests were employed as a way of validating the mathematical model, and it was found that the predictions given by the model were surprisingly accurate for all particle sizes. In addition, a simulation focused on forecasting the fraction of the drug that was dissolved at a certain time point when various initial particle diameters were used was also particularly valuable. Therefore, these results demonstrated that the model enables dissolution profiles to be analyzed under non-sink conditions.

The uremic solute indoxyl sulfate acts as an antioxidant against superoxide anion radicals under normal-physiological conditions

The effect of the uremic solute indoxyl sulfate (IS) on scavenging superoxide anion radicals (O(2)(*-)) generated from both the xanthine/xanthine oxidase (X/XO) system and activated neutrophils was investigated by electron paramagnetic resonance spectroscopy, combined with 2-ethoxycarbonyl-2-methyl-3,4-dihydro-2H-pyrrole-1-oxide (EMPO). The findings show that the presence of normal-physiological serum concentrations of IS (0.1-10 microM) resulted in decreased formation of EMPO-superoxide adduct without affecting XO activity. Furthermore, IS showed scavenging activity against cell-derived O(2)(*-) generated from activated neutrophils. In addition, IS also eliminated hydroxyl radicals. These findings suggest that IS acts as a novel endogenous antioxidant under normal-physiological conditions.

Genetically engineered mannosylated-human serum albumin as a versatile carrier for liver-selective therapeutics

Human serum albumin (HSA), a non-glycosylated protein, is widely employed as carrier for drug delivery systems. A series of recombinant, mannosylated-HSA mutants (Man-rHSAs: D63N, A320T and D494N) and their triple mutant (TM-rHSA: D63N/A320T/D494N) were prepared, that can be selectively delivered to the liver via mannose receptor (MR) on the liver non-parenchymal cells. A pharmacokinetic analysis of (111)In-Man-rHSAs in mice showed that they were rapidly cleared from the blood circulation, and were largely taken up by the liver rapidly in the order: TM-rHSA>D494N>>A320T=D63N, consistent with their degree of mannosylation. In vivo competition experiments with an excess amount of chemically modified Man-BSA or mannan suggested that the hepatic uptake of TM-rHSA was selectively mediated by MR on Kupffer cells. Lastly, a TM-rHSA-NO conjugate, S-nitrosylated TM-rHSA, effectively delivered NO to the liver and then exhibited a significant inhibitory effect against hepatic ischemia/reperfusion injury model rats, accompanied by the induction of heme oxygenase-1.

Freeze-dried nifedipine-lipid nanoparticles with long-term nano-dispersion stability after reconstitution

Nifedipine (NI) is a poorly water-soluble drug and its oral bioavailability is very low. To improve the water solubility, NI-lipid nanoparticle suspensions were prepared by a combination of co-grinding by a roll mill and high-pressure homogenization without any organic solvent. The mean particle size and zeta potential of the NI-lipid nanoparticle suspensions were about 52.6 nm and -61.8 mV, respectively, and each parameter remained extremely constant during a period of 4 months under 6 degrees C and dark conditions, suggesting that the negative charge of the phospholipid, dipalmitoyl phosphatidylglycerol, is very effective in preventing coagulation of the particles. In order to assure the nano-order particle size of the suspensions in view of long-term stability, a freeze-drying technique was applied to the NI-lipid nanoparticle suspensions. The mean particle size of freeze-dried NI-lipid nanoparticles after reconstitution was significantly increased in comparison to that of the preparations before freeze-drying. It was found, however, that the addition of sugars (glucose, fructose, maltose or sucrose) to the suspensions before freeze-drying inhibited the aggregation of nanoparticles, suggesting that the long-term stability storage of freeze-dried NI-lipid nanoparticles after reconstitution would be overcome. In addition, freeze-dried nanoparticles with 100mg sugar (glucose, fructose, maltose or sucrose) showed excellent solubility (>80%), whereas without sugar, as a control, showed low solubility (<20%). It was found that negatively charged phospholipids and sugars prevent coagulation of NI nanoparticle suspensions, and reproduce the nanoparticle dispersion after reconstitution; and remarkably increase the apparent solubility of nifedipine.

CD36 is one of important receptors promoting renal tubular injury by advanced oxidation protein products

Chronic accumulation of plasma advanced oxidation protein products (AOPPs) promotes renal fibrosis. However, the mechanism at the cellular level has not been clarified. In the present study, endocytic assay of human proximal tubular cells (HK-2 cells) demonstrated that AOPPs-human serum albumin (HSA) (in vitro preparations of chloramine- modified HSA) were significantly endocytosed in a dose-dependent manner at a higher level than HSA. The expression of CD36, a transmembrane protein of the class B scavenger receptor, in HK-2 cells was confirmed in the immunoblot analysis. In a cellular assay using overexpressing human CD36 in Chinese hamster ovary (CHO) cells, AOPPs-HSA were significantly endocytosed by CD36-CHO cells but not by mock-CHO cells. Furthermore, the endocytic association and degradation of AOPPs-HSA by HK-2 cells was significantly inhibited by anti-CD36 antibody treatment, suggesting that CD36 is partly involved in the uptake of AOPPs-HSA by HK-2 cells. AOPPs-HSA upregulated the expression of CD36 in a dose-dependent manner. In addition, AOPPs-HSA upregulated the generation of intracellular reactive oxygen species and the secretion of transforming growth factor (TGF)-β1 in HK-2 cells, whereas anti-CD36 antibody neutralizes the upregulation of TGF-β1. These results suggest that AOPPs-HSA may cause renal tubular injury via the CD36 pathway.