Development and Evaluation of EDTA-Treated Rabbits for Bioavailability Study of Chelating Drugs Using Levofloxacin, Ciprofloxacin, Hemiacetal Ester Prodrugs, and Tetracycline.

Laboratory rabbits are fed foods rich with cationic metals, and while fasting cannot empty gastric contents because of their coprophagic habits. This implies that, in rabbits, the oral bioavailability of chelating drugs could be modulated by the slow gastric emptying rates and the interaction (chelation, adsorption) with gastric metals. In the present study, we tried to develop a rabbit model with low amounts of cationic metals in the stomach for preclinical oral bioavailability studies of chelating drugs. The elimination of gastric metals was achieved by preventing food intake and coprophagy and administering a low concentration of EDTA 2Na solution one day before experiments. Control rabbits were fasted but coprophagy was not prevented. The efficacy of rabbits treated with EDTA 2Na was evaluated by comparing the gastric contents, gastric metal contents and gastric pH between EDTA-treated and control rabbits. The treatment with more than 10 mL of 1 mg/mL EDTA 2Na solution decreased the amounts of gastric contents, cationic metals and gastric pH, without causing mucosal damage. The absolute oral bioavailabilities (mean values) of levofloxacin (LFX), ciprofloxacin (CFX) and tetracycline hydrochloride (TC), chelating antibiotics, were significantly higher in EDTA-treated rabbits than those in control rabbits as follows: 119.0 vs. 87.2%, 9.37 vs. 13.7%, and 4.90 vs. 2.59%, respectively. The oral bioavailabilities of these drugs were significantly decreased when Al(OH)3 was administered concomitantly in both control and EDTA-treated rabbits. In contrast, the absolute oral bioavailabilities of ethoxycarbonyl 1-ethyl hemiacetal ester (EHE) prodrugs of LFX and CFX (LFX-EHE, CFX-EHE), which are non-chelating prodrugs at least in in vitro condition, were comparable between control and EDTA-treated rabbits irrespective of the presence of Al(OH)3, although some variation was observed among rabbits. The oral bioavailabilities of LFX and CFX from their EHE prodrugs were comparable with LFX and CFX alone, respectively, even in the presence of Al(OH)3. In conclusion, LFX, CFX and TC exhibited higher oral bioavailabilities in EDTA-treated rabbits than in control rabbits, indicating that the oral bioavailabilities of these chelating drugs are reduced in untreated rabbits. In conclusion, EDTA-treated rabbits were found to exhibit low gastric contents including metals and low gastric pH, without causing mucosal damage. Ester prodrug of CFX was effective in preventing chelate formation with Al(OH)3 in vitro and in vivo, as well as in the case of ester prodrugs of LFX. EDTA-treated rabbits are expected to provide great advantages in preclinical oral bioavailability studies of various drugs and dosage formulations. However, a marked interspecies difference was still observed in the oral bioavailability of CFX and TC between EDTA-treated rabbits and humans, possibly due to the contribution of adsorptive interaction in rabbits. Further study is necessary to seek out the usefulness of the EDTA-treated rabbit with less gastric contents and metals as an experimental animal.

Quantification of Risperidone Contained in Precipitates Produced by Tea Catechins Using Nuclear Magnetic Resonance.

A mixture of risperidone and eight major tea catechins: (-)-epicatechin-3-O-gallate (ECg), (-)-epigallocatechin-3-O-gallate (EGCg), (-)-catechin-3-O-gallate (Cg), (-)-gallocatechin-3-O-gallate (GCg), (-)-epicatechin (EC), (-)-epigallocatechin (EGC), (+)-catechin (CA), or (+)-gallocatechin (GC), in tartaric acid buffer (pH 3.0) afforded a precipitate. Amounts of risperidone and these catechins in the precipitate were measured by quantitative 1H-NMR (qNMR). About half or more of risperidone used was precipitated by gallated catechins ECg, EGCg, Cg, and GCg; on the other hand, it was precipitated little by non-gallated catechins EC, EGC, CA, and GC. Furthermore, risperidone was precipitated more by 2,3-trans gallated catechins Cg and GCg than 2,3-cis gallated catechins ECg and EGCg. Regarding the amount of tea catechins in the precipitate obtained by a mixture of risperidone and Catechin Mixture, the amounts of 2,3-cis gallated catechins EGCg and ECg were much larger than those of the other green tea catechins GCg, EC, EGC, CA, and GC. It was considered that risperidone was mainly precipitated by EGCg and ECg in Catechin Mixture. Therefore, it can be concluded that when patients take risperidone with catechin-rich beverages, the efficacy of risperidone reduces, mainly because the 2,3-cis gallated catechins EGCg and ECg form complexes with risperidone and precipitate.

Molecular Capture and Conformational Change of Diketopiperazines Containing Proline Residues by Epigallocatechin-3-O-gallate in Water.

The addition of an aqueous solution of diketopiperazine cyclo(Pro-Xxx) (Xxx: amino acid residue) to an aqueous solution of (-)-epigallocatechin-3-O-gallate (EGCg) led to precipitation of the complex of EGCg and cyclo(Pro-Xxx). The molecular capture abilities of cyclo(Pro-Xxx) using EGCg were evaluated by the ratio of the amount of cyclo(Pro-Xxx) included in the precipitates of the complex with EGCg to that of the total cyclo(Pro-Xxx) used. Stronger hydrophobicity of the side chain of the amino acid residue of cyclo(Pro-Xxx) led to a higher molecular capture ability. Furthermore, the molecular capture ability decreased when the side chain of the amino acid residue had a hydrophilic hydroxyl group. When diketopiperazine cyclo(Pro-Xxx), excluding cyclo(D-Pro-L-Ala), was taken into the hydrophobic space formed by the three aromatic A, B, and B' rings of EGCg, and formed a complex, their conformation was maintained in the hydrophobic space. Based on nuclear Overhauser effect (NOE) measurement, the 3-position methyl group of cyclo(D-Pro-L-Ala) in D2O was axial, whereas that of cyclo(L-Pro-L-Ala) was equatorial. When cyclo(D-Pro-L-Ala) was taken into the hydrophobic space of EGCg and formed a 2 : 2 complex, its 3-position methyl group changed from the axial position to the equatorial position due to steric hindrance by EGCg.

[Formation of oxalate in oxaliplatin injection diluted with infusion solutions].

Oxaliplatin use can cause acute peripheral neuropathy characterized by sensory paresthesias, which are markedly exacerbated by exposure to cold temperatures, and is a dose-limiting factor in the treatment of colorectal cancer.Oxalate is eliminated in a series of nonenzymatic conversions of oxaliplatin in infusion solutions or biological fluids.Elimination of oxalate from oxaliplatin has been suggested as one of the reasons for the development of acute neuropathy.In this study, we developed a high-performance liquid chromatography(HPLC)-based method to detect oxalate formation, and investigated the time dependent formation of oxalate in oxaliplatin diluted with infusion solutions.The results obtained showed that the amount of oxalate in the solution corresponded to 1.6% of oxaliplatin 8 h after oxaliplatin dilution with a 5% glucose solution. On the other hand, oxalate formation from oxaliplatin diluted with a saline solution was ten-fold higher than that from oxaliplatin diluted with the 5% glucose solution.Most patients who were intravenously injected with oxaliplatin experienced venous pain.As a preventive measure against venous pain, dexamethasone was added to the oxaliplatin injection.We measured the amount of oxalate formed in the dexamethasone-containing oxaliplatin injection diluted with a 5% glucose solution.The amount of oxalate formed when dexamethasone was added did not differ significantly from that formed when dexamethasone was not added.Thus, there are no clinical problems associated with the stability of oxaliplatin solutions.

[Comparison of hypersensitivity to branded and generic paclitaxel injections in rats].

The use of injectable generic antineoplastic agents has been increasing. Few studies have compared the quality and adverse reactions of generic and branded antineoplastic agents; and therefore, generic agents have not gained wide acceptance. Paclitaxel injections, which are used for treating solid cancers, are being marketed by some companies in Japan. The degree of hypersensitive reactions to these drugs may vary because of the differences in chemical properties of the polyoxyethylene castor oil that is used as a solvent in the paclitaxel preparations. Therefore, we investigated the incidence of pulmonary edema occurring as a hypersensitive reaction in rats administered branded and generic paclitaxel injections. Moreover, we compared the chemical properties of these preparations. We found that the pH of branded and generic paclitaxel preparations diluted with saline was different. This difference in pH may be attributed to a difference in chemical properties from the additive. We observed no significant differences in pulmonary vascular permeability, arterial partial pressure of oxygen, or leakage of protein in the pulmonary alveolus, between paclitaxel preparations administered to rats. These results suggest that both paclitaxel preparations induced pulmonary edema of a similar level in rats, irrespective of the differences in their chemical properties.

Ovariectomy aggravates hypersensitivity reactions to paclitaxel in rats.

The incidence of hypersensitivity reactions is still a matter of serious concern during chemotherapy with paclitaxel, particularly in patients with ovarian cancer. We recently reported that intravenous injection of paclitaxel causes acute lung injury characterized by vascular hyperpermeability, edema and respiratory dysfunction in rats. In the present study, we investigated the influence of ovariectomy on the paclitaxel-induced acute lung injury in rats. Ovariectomy worsened paclitaxel-induced acute lung injury, which was reversed by 17beta-estradiol. The mRNA expression for endothelial nitric oxide synthase was reduced in lungs of ovariectomized rats. To determine the role for nitric oxide, we examined the effects of several agents that modulate nitric oxide concentration on the pulmonary response to paclitaxel. In ovary-intact rats, a nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester exaggerated paclitaxel-induced acute lung injury, while nitric oxide donors such as sodium nitroprusside and isosorbide dinitrate attenuated the lung injury. Sodium nitroprusside was also effective in alleviating the paclitaxel-induced acute lung injury in ovariectomized rats. These findings suggest that ovariectomy enhances the susceptibility to paclitaxel hypersensitivity, in which decrease in estrogen and subsequent reduction in nitric oxide synthesis may be involved.

Similarity and difference in the acute lung injury induced by a radiographic contrast medium and an anticancer agent paclitaxel in rats.

Paclitaxel is one of the most frequently used anticancer agents but its use is sometimes limited because of the incidence of severe hypersensitivity reactions. The clinical symptoms of the reactions, including dyspnea and pulmonary edema, are similar to those induced by iodinated contrast medium during radiographic examination. Therefore, the premedication for the prophylaxis of hypersensitivity reactions to paclitaxel is carried out in accordance with that for radiographic contrast medium. In the present study, we compared the effects of paclitaxel and an iodinated radiocontrast medium ioxaglate on vascular permeability and pulmonary function in rats. Both paclitaxel (15 mg/kg) and ioxaglate (4 g iodine/kg) caused perivascular edema, plasma extravasation and decrease in arterial PaO2. Dexamethasone inhibited plasma extravasation induced by the two compounds. In contrast, histamine H1 and H2 antagonists attenuated the effects of ioxaglate without inhibiting those of paclitaxel. On the other hand, a neurokinin NK1 antagonist (LY303870: 0.5 mg/kg) significantly inhibited the pulmonary responses induced by paclitaxel but not by ioxaglate. Therefore, it is suggested that paclitaxel and ioxaglate cause similar acute lung injury but the mechanisms are different between the two compounds, in which histamine and substance P are involved in the pulmonary dysfunction induced by ioxaglate and paclitaxel, respectively. These findings also raise a possibility that more effective premedication is required for the prophylaxis of paclitaxel hypersensitivity.

Role of substance P in hypersensitivity reactions induced by paclitaxel, an anticancer agent.

The role of substance P in adverse pulmonary reactions induced by an anticancer agent paclitaxel was investigated in rats and humans who undertook post-operative chemotherapy for ovarian cancer. In rats, paclitaxel caused a marked plasma extravasation and edema in lungs with a concomitant decrease in arterial partial oxygen pressure, which were reversed by an NK1 antagonist LY303870. Substance P level in rat plasma and bronchoalveolar lavage fluid increased after paclitaxel injection. In 13 patients, plasma level of substance P but not histamine significantly (P < 0.05) increased during paclitaxel infusion. Therefore, substance P rather than histamine may be involved in paclitaxel hypersensitivity.

Pemirolast potently attenuates paclitaxel hypersensitivity reactions through inhibition of the release of sensory neuropeptides in rats.

The effects of anti-allergic agents on the hypersensitivity reactions to paclitaxel, an anti-cancer agent, were examined in rats. Intravenous injection of paclitaxel (15 mg/kg) caused a marked extravasation of plasma protein in lungs and a transient decrease in arterial partial oxygen pressure (PaO(2)). The paclitaxel-induced protein extravasation was inhibited by low doses (0.1-1 mg/kg) of pemirolast or high doses (30-100 mg/kg) of cromoglycate. However, ketotifen was not effective. The decrease in PaO(2) induced by paclitaxel was also significantly reversed by pemirolast. On the other hand, the paclitaxel-induced plasma extravasation was not attenuated by a histamine H(1) blocker diphenhydramine or an H(2) blocker famotidine, but was significantly reduced by a neurokinin NK(1) antagonist LY303870 (0.5 mg/kg) and an NK(2) antagonist SR48968 (1 mg/kg). The concentrations of proteins and sensory peptides such as substance P, neurokinin A and calcitonin gene-related peptide but not histamine in the rat bronchoalveolar lavage fluid were elevated by paclitaxel injection. Both cromoglycate and pemirolast reduced the paclitaxel-induced rise in proteins and sensory peptides. Therefore, we demonstrated for the first time that sensory nerve peptides are involved in paclitaxel hypersensitivity and that an anti-allergic agent pemirolast attenuates the paclitaxel response by inhibiting the release of sensory nerve peptides.

Role of sensory nerve peptides rather than mast cell histamine in paclitaxel hypersensitivity.

Paclitaxel is one of the most extensively used anticancer agents, however, its use is often limited by severe hypersensitivity reactions, including respiratory distress, bronchospasm, and hypotension, which can occur despite premedication with dexamethasone and histamine H1 and H2 antagonists. The present study was designed to determine the mechanisms of paclitaxel hypersensitivity. In rats, paclitaxel (15 mg/kg, intravenously) caused a marked increase in pulmonary vascular permeability and edema. PaO2 decreased, whereas PaCO2 increased, transiently after paclitaxel injection. The paclitaxel-induced pulmonary vascular hyperpermeability was blocked by dexamethasone but not by histamine H1 or H2 antagonists. Paclitaxel increased the vascular permeability in lungs of mast cell-deficient rats Ws/Ws(-/-) to almost the similar extent as that elicited in wild-type rats. On the other hand, the paclitaxel-induced pulmonary vascular hyperpermeability was reversed by sensory denervation with capsaicin or pretreatment with LY303870 and SR48968, NK1 and NK2 antagonists, respectively. Consistent with these findings, a marked elevation of sensory neuropeptides such as substance P, neurokinin A, and calcitonin gene-related peptide was observed in rat bronchoalveolar lavage fluid after paclitaxel injection. These findings suggest that sensory nerves rather than mast cells are implicated in the etiology of paclitaxel hypersensitivity.

Involvement of proteinase-activated receptor-2 in mast cell tryptase-induced barrier dysfunction in bovine aortic endothelial cells.

We report here a direct modulation by mast cell tryptase of endothelial barrier function through activation of proteinase-activated receptor-2 (PAR-2). In cultured bovine aortic endothelial cells (BAECs), tryptase, trypsin and PAR-2 activating peptide impaired the barrier function as determined by the permeability of protein-conjugated Evans blue. The tryptase-induced barrier dysfunction was completely blocked by U73122, and partially reversed by xestospongin C, calphostin C or Y27632. The intracellular Ca(2+) was elevated by tryptase. It was notable that ioxaglate, a contrast material that degranulates mast cells, markedly increased the permeability when applied to BAECs in combination with mast cells, an action that was blocked by nafamostat, a potent tryptase inhibitor. Immunofluorescence analysis showed that actin stress fibre formation and disruption of VE-cadherin were observed after exposure to tryptase or ioxaglate in combination with mast cells. Therefore, it is suggested that mast cell tryptase impairs endothelial barrier function through activation of endothelial PAR-2 in a manner dependent on the phospholipase C activity.

Roles of intracellular Ca2+ and cyclic AMP in mast cell histamine release induced by radiographic contrast media.

Mast cell histamine release is considered to be associated with the etiology of anaphylactoid reactions to iodinated radiographic contrast media (RCM). In the present study, the effects of various ionic and non-ionic RCM on histamine release from mast cells were compared, and the possible mechanisms of the histamine release were subsequently determined. Both ionic (ioxaglate and amidotrizoate) and non-ionic (iohexol, ioversol, iomeprol, iopamidol and iotrolan) RCM increased histamine release from the dissociated rat pulmonary cells, whereby ionic materials were more potent than non-ionic agents. There was no significant correlation between the extent of histamine release and the osmolarity of each RCM solution. In addition, hyperosmotic mannitol solution (1000 mOsm/kg) caused no marked histamine release. Thus, it is unlikely that the hyperosmolarity of RCM solutions contributes to the histamine release. RCM also stimulated, but to a lesser extent, the histamine release from rat peritoneal cells. The RCM-induced histamine release from both types of cells was inhibited by dibutyl cyclic AMP or combined treatment with forskolin and 3-isobutyl-1-methylxanthine. Corresponding to these results, RCM markedly reduced the cellular cyclic AMP content. On the other hand, the removal of intracellular but not the extracellular Ca2+ attenuated the RCM-induced mast cell histamine release. From these findings, it is suggested that the decrease in cellular cyclic AMP content and an increase in intracellular Ca2+ contribute at least in part to the RCM-induced mast cell histamine release.

A potent tryptase inhibitor nafamostat mesilate dramatically suppressed pulmonary dysfunction induced in rats by a radiographic contrast medium.

(1) Intravenous injection of ioxaglate (4 g iodine kg(-1)), an iodinated radiographic contrast medium, caused a marked protein extravasation, pulmonary oedema and a decrease in the arterial partial oxygen pressure in rats. (2) All of these reactions to ioxaglate were reversed by the pretreatment with gabexate mesilate (10 and 50 mg kg(-1), 5 min prior to injection) or nafamostat mesilate (3 and 10 mg kg(-1)), in which the inhibition was complete after injection of nafamostat mesilate (10 mg kg(-1)). (3) Both gabexate mesilate and nafamostat mesilate inhibited the activity of purified human lung tryptase, although the latter compound was far more potent than the former. (4) Ioxaglate enhanced the nafamostat-sensitive protease activity in the extracellular fluid of rat peritoneal mast cell suspensions. (5) Tryptase enhanced the permeability of protein through the monolayer of cultured human pulmonary arterial endothelial cells. Ioxaglate, when applied in combination with rat peritoneal mast cells, also produced the endothelial barrier dysfunction. These effects of tryptase and ioxaglate were reversed by nafamostat mesilate. (6) Consistent with these findings, immunofluorescence morphological analysis revealed that tryptase or ioxaglate in combination with mast cells increased actin stress fibre formation while decreasing VE-cadherin immunoreactivity. Both of these actions of tryptase and ioxaglate were reversed by nafamostat mesilate. (7) These findings suggest that tryptase liberated from mast cells plays a crucial role in the ioxaglate-induced pulmonary dysfunction. In this respect, nafamostat mesilate may become a useful agent for the cure or prevention of severe adverse reactions to radiographic contrast media.

Evidence for involvement of mast cell degranulation and subsequent stimulation of histamine H1 and H2 receptors in radiographic contrast media-increased vascular permeability in rats.

In the present study, the effects of systemic injection of radiographic contrast media (RCM) on vascular permeability was examined in various tissues of rats and the involvement of mast cell histamine in the RCM-induced vascular hyperpermeability subsequently determined. Both ionic (amidotrizoate) and non-ionic RCM (iohexol) enhanced vascular permeability specifically in lungs, as assessed by the extravasation of Evans blue (EB) dye. Another ionic RCM, ioxaglate, also markedly increased pulmonary vascular permeability and decreased pulmonary histamine content, whereby the extent of the reduction correlated well with the vascular hyperpermeability. Depletion of mast cells by prior treatment with compound 48/80 markedly attenuated the ioxaglate-induced enhancement of EB extravasation. The ioxaglate-increased extravasation was also inhibited by the mast cell stabilizer sodium cromoglicate and histamine H(1) and H(2) receptor antagonists. In isolated rat pulmonary mast cells, ioxaglate induced the concentration-dependent release of beta-hexosaminidase, an index of mast cell degranulation. The present findings thus show clearly that RCM causes the degradation of pulmonary mast cells and the resultant release of histamine that in turn increases vascular permeability by stimulating histamine H(1) and H(2) receptors.

Carbazochrome attenuates pulmonary dysfunction induced by a radiographic contrast medium in rats.

The effects of carbazochrome sodium sulfonate (AC-17), a capillary stabilizer, on pulmonary edema and dysfunction induced by ioxaglate, an ionic radiographic contrast medium, were evaluated in rats. The pulmonary edema was evaluated by the extravasation of intravenously injected Evans blue into lung tissues, while pulmonary dysfunction was determined by monitoring blood gasses including pO(2). Ioxaglate (4 g I/kg, i.v.) caused a marked increase in vascular permeability and a decrease in arterial pO(2). AC-17 reversed the ioxaglate-induced vascular hyperpermeability in a dose-dependent manner. In addition, AC-17 (10 mg/kg) significantly inhibited the decrease in arterial pO(2). In isolated rat pulmonary mast cells, ioxaglate markedly enhanced the histamine release, which was not affected by AC-17. On the other hand, AC-17 did significantly blocked the hyperpermeability induced in cultured bovine endothelial cells by tryptase, thrombin and proteinase-activated receptor-2 agonist peptide (SLIGKV-NH(2)). These findings suggest that AC-17 blocks radiographic contrast medium-induced pulmonary dysfunction by maintaining the endothelial barrier function. Thus, the compound is potentially useful for the prophylaxis of contrast media-induced acute pulmonary adverse events during angiography.