Prediction of dissolution-absorption relationships from a dissolution/Caco-2 system

While the analysis of in vitro dissolution-in vivo absorption relationships from oral solid dosage forms provides biopharmaceutical insight and regulatory benefit, no well developed method exists to predict dissolution-absorption relationships a priori to human studies. The objective was to develop an integrated dissolution/Caco-2 system to predict dissolution-absorption relationships, and hence the contributions of dissolution and intestinal permeation to overall drug absorption for fast and slow formulations of piroxicam, metoprolol, and ranitidine. Dissolution studies were conducted on fast and slow dissolving immediate-release formulations of piroxicam, metoprolol tartrate, and ranitidine HCl. Dissolution samples were treated with concentrated buffers to render them suitable (i.e., isotonic and neutral pH) for Caco-2 monolayer permeation studies. The dissolution/Caco-2 system yielded a predicted dissolution-absorption relationship for each formulation which matched the observed relationship from clinical studies. The dissolution/Caco-2 system's prediction of dissolution or permeation rate-limited absorption also agreed with the clinical results. For example, the dissolution/Caco-2 system successfully predicted the slow piroxicam formulation to be dissolution rate-limited, and the fast piroxicam formulation to be permeation rate-limited. Moreover, the system predicted this change from dissolution rate-limited absorption for slow piroxicam to permeation rate-limited absorption for fast piroxicam, in spite of piroxicam's high permeability and low solubility. The dissolution/Caco-2 system may prove to be a valuable tool in formulation development. Broader evaluation of such a system is warranted.     

Examination of metformin hydrochloride in a continuous dissolution/HDM system

A continuous dissolution/absorption system using a hexadecane membrane (HDM) as the permeation measurement has been examined for three distinct formulations of metformin hydrochloride. This system was used to correlate the absorption rate of metformin through the membrane after release from the dosage form to rate of appearance of metformin in the plasma from the same formulations. These correlations were then used to make predictions of the in vivo plasma profile for each formulation. Successful predictions of AUC were accomplished for both immediate release and extended release formulations of metformin hydrochloride.     

Towards Prediction of In Vivo Intestinal Absorption Using a 96-Well Caco-2 Assay

We systematically validated a robust 96-well Caco-2 assay via an extended set of 93 marketed drugs with diverse transport mechanisms and quantified by LC/MS/MS, to investigate its predictive utility while dealing with challenging discovery compounds. Utilizing nonlinear fit, the validation led to a good correlation (R² = 0.76) between absorptive permeability, log-P_app(A–B), from in vitro Caco-2 assay and reported human fraction of dose absorbed. We observed that paracellular compounds could be flagged by log P_app(A–B) (<?5.5 cm/s) and physicochemical property space (c log P < 1). Of 8000 Novartis discovery compounds examined 13% were subject to low recovery (< 30%). Compound loss was investigated by comparing cell monolayer and artificial membrane, while 0.5% bovine serum albumin (in both donor and acceptor compartments) was utilized to improve recovery. The second focus of this study was to investigate the advantages and limitations of the current Caco-2 assay for predicting in vivo intestinal absorption. Caco-2 measurements for compounds with high aqueous solubility and low in vitro metabolic clearance were compared to 88 in vivo rat bioavailability studies. Despite the challenges posed by discovery compounds with suboptimal physicochemical properties, Caco-2 data successfully projected low intestinal absorption. This platform sets the stage for mechanistically evaluating compounds towards improving in vitro–in vivo correlations.     

Assessment of fexofenadine hydrochloride permeability and dissolution with an anionic surfactant using Caco-2 cells

The purpose of this study was to estimate the effect of the anionic surfactant sodium dodecyl sulphate (SDS) on the permeability and dissolution of fexofenadine hydrochloride (FEX) and the transepithelial electrical resistance (TEER) with Caco-2 cells. The dissolution profile of FEX was evaluated at different pH values (1.2, 3.2, 4.2, 4.5, 5.2 and 6.8) at 37 +/- 0.5 degrees C and chracterized in presence of SDS. The dissolution of FEX was increased in the presence of SDS. For permeability studies, apical to basolateral and basolateral to apical permeability was assesed with various concentrations of FEX (50, 100, 500, 1000 and 5000 microM) and in the presence of SDS. The FEX transport changed with 10 and 50 microM of SDS and the TEER values, after 120 min, decreased. In conclusion, a low and concentration-dependent permeability was found for FEX across the Caco-2 cells. FEX transport increased and TEER decreased with increasing SDS concentrations. These results supports the use of SDS as anionic surfactant in these concentration; SDS can be used safely as permeation and dissolution enhancer for the oral delivery of FEX.     

New and better protocols for a short-term Caco-2 cell culture system

The aim of the present study was to develop new and better protocols for a short-term Caco-2 cell culture system for use in rapid screening of intestinal drug absorption. Caco-2 cells were cultured according to several protocols for short-term cell culture to obtain monolayers. The effects of serum (fetal bovine serum, FBS) in the culture medium and of the period of cell culture on the barrier function and transporter activities of the monolayers were examined. The barrier function was estimated both from the transepithelial electrical resistance (TEER) and the permeability of [(14)C]mannitol. Transporter activities were monitored by measuring the permeability of [(14)C]glycylsarcosine for oligopeptide transporter (PepT1) and of rhodamine 123 for P-glycoprotein (P-gp). Caco-2 monolayers obtained by 3-day culture in the BIOCOAT HTS Caco-2 Assay System, developed by Becton Dickinson Bioscience, showed much higher permeability to hydrophilic compounds, such as mannitol, compared with those obtained by the standard 21-day culture system, due to the leaky structure of cell junctions. The newly developed 3-day protocol, which includes 10% FBS in the culture medium during the first day of culture, markedly enhanced TEER and lowered mannitol permeability of the monolayers. This protocol allowed us to better determine the rank order of permeability of compounds, giving results equivalent to those in the 21-day culture system. The longer culture period gave tighter monolayers, and the maximum value of TEER was obtained with 5 days in culture. However, after 5 days in culture, the integrity of monolayers decreased gradually. The highest activities of transporters, PepT1 and P-gp, in monolayers were obtained at days 5 or 6 of culture by the new protocol with FBS-containing medium. These results indicate that by a simple modification of the short-term culture protocol, it is possible to obtain Caco-2 monolayers with better barrier properties and higher activity of transporters that are equivalent to those found in the 21-day Caco-2 culture system.     

布洛芬/羟丙基-β-环糊精体系的Caco-2细胞转运研究

目的:考察羟丙基-β-环糊精(HP-β-CD)超分子体系对布洛芬细胞转运的影响.方法:运用相溶解度法考察超分子体的表观稳定常数(K);运用Caco-2细胞模型考察各类超分子体中布洛芬的表观渗透系数(P<,app>)以及跨膜电阻(TEER)的变化.结果:随HP-β-CD的浓度增加,布洛芬的溶解度不断提高;在0%～5%HP-β-CD的范围内,布洛芬的表观渗透系数随HP-β-CD的浓度增加逐渐下降;布洛芬三元体系表观稳定常数的变化趋势与布洛芬的表观渗透系数变化趋势相反.结论:布洛芬的细胞转运与体系中HP-β-CD浓度、超分子体系的稳定常数有密切关系.HP-β-CD浓度升高可显著增加布洛芬的溶解度,但过量的HP-β-CD不利于布洛芬的渗透转运;布洛芬、HP-β-CD通过与适量泊洛沙姆188(Poloxamer 188)、聚山梨酯-80(Tween-80)、十二烷基硫酸钠(SDS)组成的三元体系,可影响布洛芬、HP-β-CD之间的相互作用,改善布洛芬的表观渗透系数.     

Prediction of drug dissolution from tablets using near-infrared diffuse reflectance spectroscopy as a nondestructive method

The goal of this study is to use near-infrared (NIR) reflectance spectroscopy to measure the percentage drug dissolution from a series of tablets compacted at different compressional forces, calibrate NIR data vs. laboratory equipment data, develop a model equation, validate the model, and test the model predictive ability. Seven theophylline tablet formulations of the same composition but with different dissolution profiles were prepared. Laboratory dissolution profiles were compared with NIR diffuse reflectance data. Linear regression, quadratic, cubic, and partial least-square techniques were used to determine the relationship between dissolution profiles data and NIR spectra. The results demonstrated that a decrease in the amount of drug dissolution produced an increase in NIR absorbance. A series of model equations, depending on the mathematical technique used for regression, were developed from the calibration of the percentage of drug dissolution by using laboratory equipment vs. the NIR diffuse reflectance for each formulation. The results of NIR dissolution data were similar to laboratory tests. The NIR diffuse reflectance spectroscopy method is an alternative, nondestructive method for measurement of drug dissolution from tablets.     

Structure-activity relationships for enhancement of paracellular permeability by 2-alkoxy-3-alkylamidopropylphosphocholines across Caco-2 cell monolayers

The oral route is the preferred route of delivery for a large number of drug molecules. However, the intestinal epithelium presents a formidable barrier for delivery of drugs into systemic circulation. Phospholipids are among compounds that enhance the absorption of drugs across the intestinal epithelium. In this paper, we describe structure-activity relationships for phospholipid derivatives as enhancers of paracellular permeability across Caco-2 cell monolayers. In a series of 2-alkoxy-3-alkylamidopropylphosphocholine derivatives, compounds with a long chain at C-3 (R3) and short chain at C-2 (R2) were potent in causing a decrease in transepithelial electrical resistance (TEER) and an increase in mannitol transport, but also showed significant cytotoxicity. Compounds with 9-11 carbons at C-3 and 6-10 carbons at C-2 provided good separation (up to 2.7-fold) between activity and cytotoxicity. Notably, a good correlation (r2 = 0.93) was observed between EC(50) (TEER) [concentration that caused a drop in TEER to 50% of its control (untreated) value] and EC10x (mannitol) [concentration that caused 10-fold increase in mannitol transport over the control (untreated) value], confirming that a decrease in TEER is associated with enhanced permeability of the hydrophilic compounds across Caco-2 cell monolayers. Compounds with medium to long carbon chains at C-2 and C-3, and the total carbons in the alkyl chains > 20, showed poor activity and no cytotoxicity.     

两种阿仑膦酸钠片的崩解度和溶出度及在Caco-2细胞模型上的转运比较

目的：建立9-氯甲酸芴甲酯（FMOC）柱前衍生化高效液相色谱法测定阿仑膦酸钠片含量的方法,比较两种阿仑膦酸钠片的崩解度、溶出度和转运特性,为该药物制剂开发和临床应用提供参考。方法：采用Kromasil-C18色谱柱（4.6mm×150mm,5μm）;以甲醇-乙腈-柠檬酸与焦磷酸钠混合液为流动相,梯度洗脱;流速为1mL·min-1;柱温为35℃;紫外检测波长为265nm。结果：阿仑膦酸钠在2-200μg·mL-1范围内线性关系良好（r=0.9998）,回收率、日内和日间精密度RSD均小于15%。两种阿仑膦酸钠片的崩解度、溶出度均有一定的差异,而在Caco-2细胞模型的转运量没有显著的差异。结论：两种阿仑膦酸钠片的生物利用度、药代动力学可能存在差异。     

Permeability assessment for solid oral drug formulations based on Caco-2 monolayer in combination with a flow through dissolution cell.

The aim of our study was to develop an apparatus assessing in vitro permeation through Caco-2 monolayers of oral solid dosage forms as a possible tool to forecast in vivo performance. Therefore, flow through dissolution and permeation modules were connected by means of a stream splitter. Permeation was measured in a specially designed cell, dissolution took place in the apparatus 4, USP. In order to test the apparatus for its reproducibility and conclusiveness, different tablet strengths and varying release profiles of propranolol HCl tablets were produced and evaluated. It was shown that for both tablet species, immediate and extended release, the apparatus was able to measure permeation through Caco-2 monolayer as well as dissolution simultaneously with high precision and reproducibility. The permeated amount of the three immediate release tablets with increasing dosage strength showed linear dependency on the dosage strength. Furthermore, the effect of retarded release on permeation could be detected and conclusive data for dissolution and permeation were obtained. In summary, connecting cell culture based permeability assessment with compendial flow through dissolution equipment led to promising results and poses the base for more advanced studies for detecting influences of dosage forms on permeation process.     

Transport of alkamides from Echinacea species through Caco-2 monolayers

To gain more insights into the human intestinal absorption of alkamides from Echinacea species, transport studies were performed with the human adenocarcinoma colonic cell line Caco-2 (ATCC) as a model to assess the epithelial transport of dodeca-2 E,4 E,8 Z,10 E/ Z-tetraenoic acid isobutylamides (1/ 2). 30 minutes after apical loading of 25 microg/ml 1/ 2, about 15 % of these alkamides were detectable on the basolateral side. Close monitoring of the transport during 6 hours revealed a nearly complete transport to the basolateral side after 4 hours and no significant metabolism was observable. Transport experiments performed at 4 degrees C showed only a slight decrease in transport, which is a strong hint that dodeca-2 E,4 E,8 Z,10 E/ Z-tetraenoic acid isobutylamides (1/ 2) cross biological membranes by passive diffusion. Nearly the same results were obtained after preincubation of the Caco-2 cells with lipopolysaccharides (LPS) or phorbol 12-myristate-13-acetate (PMA) to mimic an inflammatory status. These results support the assumption that the alkamides can be easily transported from the intestinum and hence may contribute to the in vivo effects of Echinacea preparations.     

Effects of continuous exposure to digoxin on MDR1 function and expression in Caco-2 cells

The Caco-2 cell line has been used widely for studying intestinal permeability and several transport functions, and express the multidrug resistance transporter MDR1/P-glycoprotein. Previously, the transient exposure to digoxin for 24 h was found to induce MDR1 mRNA in Caco-2 cells. Here, a digoxin-tolerant Caco-2 subline (Caco/DX) was newly established by the continuous exposure of Caco-2 cells to digoxin, and the effects of continuous exposure to digoxin on MDR1 were examined. The 50% growth inhibitory concentration (IC(50)) values for digoxin in Caco-2 and Caco/DX cells were 17.2 and 81.4 nM, respectively. The IC(50) values for paclitaxel, an MDR1 substrate, were 1.0 and 547 nM, respectively, whereas the cytotoxicity of 5-fluorouracil was comparable in both cells. The uptake and efflux of Rhodamine123, an MDR1 substrate, in Caco/DX cells were significantly less and greater, respectively, than those in Caco-2 cells, and these transports were affected by the addition of ciclosporin. The expression of MDR1 mRNA in Caco/DX cells was approximately 2- and 1.7-fold compared with Caco-2 cells and Caco-2 cells treated with 100 nM digoxin for 24 h, respectively. On the other hand, MRP1 mRNA in Caco/DX cells was unchanged. These observations confirmed that the continuous exposure to digoxin, as well as the transient exposure, induced MDR1 in Caco-2 cells.     

Influence of chitosan and its glutamate and hydrochloride salts on naproxen dissolution rate and permeation across Caco-2 cells

Chitosan and its glutamate and hydrochloride salts were evaluated for their efficacy in improving the dissolution behaviour of naproxen (a poorly water-soluble antiinflammatory drug) and its transport in vitro across Caco-2 cell monolayers. Drug-polymer physical mixtures and coground products, prepared at two different w/w ratios (30/70 and 10/90), were characterized by differential scanning calorimetry, X-ray powder diffractometry, scanning electron microscopy, and tested for dissolution properties. Coground systems were more effective than physical mixtures in improving drug dissolution and chitosan base, in spite of its lower water solubility, showed higher solubilizing power than its salts. According to the solid state analyses results, this effect was directly related to its stronger amorphizing power. Transport studies showed that only coground mixtures with chitosan glutamate salt allowed a significant drug apparent permeability improvement; however, they did not exhibit appreciable effects on the Caco-2 tight junctions (measured by the trans-epithelial electrical resistance variations), thus indicating that their enhancer effect was mainly due to an improved naproxen transport by transcellular passive diffusion rather than through the paracellular route. The direct compression properties and antiulcerogenic activity together with the demonstrated dissolution and permeation enhancer abilities toward naproxen make chitosan glutamate an optimal carrier for developing fast-action oral solid dosage forms of this drug.     

Controlled flow-through dissolution methodology: a high-performance system

Measuring release rates using compendial systems, especially for sparingly soluble compounds, often produces complex results with less than desired precision and lacks relevance to key formulation or biological parameters. A flow-through approach was used by focusing on convective diffusion and controlling certain key physical-chemical factors. Results are presented for an automated multisample flow-through system that displays significant advantages over compendial (1) stirred and (2) flow-through systems. Advantages include precision, physicochemical, and in vivo relevance, along with analytical and formulation sensitivity. The convective diffusion/dissolution process was also simulated by using finite element modeling with predictions agreeing with measurements to within a few percent.     

Prediction of drug dissolution profiles from tablets using NIR diffuse reflectance spectroscopy: a rapid and nondestructive method

A comparison between dissolution profiles obtained by using a dissolution apparatus (conventional method) and the NIR diffuse reflectance spectra of a series of clonazepam-containing batches is reported. Ten different formulations with fixed amount of clonazepam and varying proportions of excipients were analyzed at seven dissolution times and three different media. The percentages of dissolution of each sample were correlated with the NIR spectra of three tablets of each batch, through a multivariate analysis using the PLS regression algorithm. The squared correlation coefficients for the plots of percentages of dissolution from the equipment laboratory (dissolution apparatus and HPLC determination) versus the predicted values, in the leave-one-out cross-validation, varied from 0.80 to 0.92, indicating that the NIR diffuse reflectance spectroscopy method is an alternative, nondestructive tool for measurement of drug dissolution from tablets.     

应用光纤药物溶出仪对硝苯地平缓释片释放度的考察

目的:对硝苯地平缓释片进行全程的实时、原位在线释放度测定,并与该品种已有国标[1]释放度测定结果进行比较.方法:运用FODT-601光纤药物溶出仪,选择237/550 nm双波长法,消除赋形剂干扰,按该品种已有国标释放度检查项溶出条件,测试该药物溶出曲线,并与按国标方法测得的溶出曲线进行比较.结果:在3.37μg·mL-1～17.83μg·mL-1范围内,浓度(C)与吸光度(A)呈良好的线性关系,浓度对应的溶出量(Q)% 与吸光度(A)也呈良好的线性关系,相关系数均在0.9990以上;3个浓度各3份样在6个通道的平均回收率分别为98.52%、99.22%、98.78%;对应的RSD(n=18)分别为1.1%、0.7%、0.7%,溶出曲线与国标方法测定的溶出曲线无显著性差异(P>0.05).结论:硝苯地平缓释片光纤药物溶出仪测定结果与按常规国标方法测定结果基本一致,而且该法具有操作简便,测定快速,获取信息量更大的优点.     

Short term Caco-2/TC7 cell culture: comparison between conventional 21-d and a commercially available 3-d system

The Caco-2 cell model is a valuable tool for studying intestinal biotransformation of xenobiotics and to evaluate the potential of human intestinal absorption of new compounds. These properties were evaluated with Caco-2/TC7 cells in accelerated conditions to reduce maturation lag time from 21-d to 3-d in order to increase time and labor efficiency. Transmission electron and fluorescent microscopy were used for morphological characterization. Alkaline phosphatase and lactate dehydrogenase activities were assessed within time. Cytochrome P450 expression was studied by RT-PCR. Apparent permeabilities of a set of passively absorbed molecules across Caco-2/TC7 cell monolayers were determined to evaluate potential of both systems for prediction of human intestinal absorption. Microscopic images revealed that cells under both conditions differentiated as enterocyte-like cells but did so heterogeneously in the 3-d model. TEER values have shown that the 3-d model is a leakier cell system with higher mannitol Papp (cm/s). Biochemical characterization (hydrolase activities, CYP450 expression) suggested that the 3-d model was at a lower maturation level than the 21-d model. Carrier-mediated uptake of L-Phe was lower in the 3-d model suggesting that this model has limited application for mechanistic studies. Reasonable correlation was obtained between the two models (r2=0.88, p>0.01) for 11 passively absorbed compounds with high potential of rank ordering of compounds. Although results suggested that the 3-d cells are under-differentiated, they could be usable to estimate the oral absorption of passively absorbed compounds.