Relationship between antipyrine elimination rate constant, clearance and volume of distribution in the rat

While the relationship between the inverse of antipyrine half-life and clearance has been shown to be approximately linear in man, a recent report indicated that there was no significant relationship between antipyrine elimination rate constant (lambda) and clearance (CL) in the rat. Since this relationship is critical to the use of non-invasive methods to estimate drug metabolizing capacity, we have re-examined the relationship between lambda and CL in the rat. A significant correlation (r = 0.887) was found between antipyrine lambda and CL, while only a weak relationship (r = 0.442) was found between lambda and volume of distribution. These data support the use of non-invasive methods to estimate antipyrine elimination in the rat when invasive methods need to be avoided.     

常用肾功能测定方法与99mTc-DTPA清除率的关系探讨

目的为临床评估慢性肾功能衰竭患者的肾小球滤过率(GFR)提供依据.方法应用99mTc-DTPA清除率测定68例慢性肾功能衰竭患者的GFR(Tc-GFR),同时检测24小时内生肌酐清除率(24hCcr)和使用Ccockcroft-Gault公式计算肌酐清除率(Ccockcroft),然后进行分组比较和分析.结果①24hCcr、Ccockcroft与Tc-GFR的相关系数分别为0.91和0.83.②代偿期组的肌酐分泌率(TScr/Tc-GFR)高于对照组,失代偿期组、尿毒症前期组、尿毒症期组均低于对照组,并呈现出按代偿期组、失代偿期组、尿毒症前期组、尿毒症期组的顺序依次下降的趋势.结论①24hCcr、Ccockcroft能在一定程度上较为准确地反映GFR;但在代偿期、失代偿期和尿毒症前期都高于GFR,尤以失代偿期显著.②动态观察和比较TScr/Tc-GFR的变化可能对判断肾功能衰竭的程度和预后可能有一定的意义.     

常用肾功能测定方法与99mTc-DTPA清除率的关系探讨

目的 为临床评估慢性肾功能衰竭患的肾小球滤过率(GFR)提供依据。方法 应用99mTc-DTPA清除率测定68例慢性肾功能衰竭患的GFR(Tc-GFR)，同时检测24小时内生肌酐清除率(24hCer)和使用Ceoekeroft-Gault公式计算肌酐清除率(Ccockcroft)，然后进行分组比较和分析。结果 ①24hCer、Ceoekeroft与Tc-GFR的相关系数分别为0.9l和0．83。②代偿期组的肌酐分泌率(TScr／Tc-GFR)高于对照组，失代偿期组、尿毒症前期组、尿毒症期组均低于对照组，并呈现出按代偿期组、失代偿期组、尿毒症前期组、尿毒症期组的顺序依次下降的趋势。绪论 ①24hCer、Ccockcroft能在一定程度上较为准确地反映GFR；但在代偿期、失代偿期和尿毒症前期都高于GFR，尤以失代偿期显。② 动态观察和比较TScr／Tc-GFR的变化可能对判断肾功能衰竭的程度和预后可能有一定的意义。     

Permeability dominates in vivo intestinal absorption of P-gp substrate with high solubility and high permeability

Three purposes are presented in this study: (1) to study the in vivo regional dependent intestinal absorption of a P-gp substrate with high solubility and high permeability, (2) to study the gene expression difference in the various regions of the intestine, and (3) to study the contributions of P-gp or any other transporters for the absorption of a P-gp substrate. The in vivo permeability of verapamil and propranolol were determined by single-pass in situ intestinal perfusion in rat. The gene expression profiles were measured using Affymetrix GeneChip. Correlation analysis between drug in vivo permeability and expression of 3500 genes was performed with nonparametric bootstrap and ANOVA analysis. The permeability of verapamil and propranolol did not demonstrate regional dependency even though significant differences in gene expression were observed in various regions of the intestine. Verapamil permeability significantly correlates with propranolol permeability in both jejunum and ileum, but did not correlate with the permeability of other hydrophilic compounds (valacyclovir, acyclovir, and phenylalanine). Four different regions (duodenum, jejunum, ileum, and colon) showed distinct gene expression patterns with more than 70-499 genes showing at least 5-fold expression differences. Interestingly, P-gp expression is gradually increased by 6-fold from the duodenum to colon. Despite the distinct gene expression patterns in the various regions of the intestine, verapamil permeability did not correlate with any gene expression from 3500 expressed genes in the intestine. A 2-6-fold P-gp expression difference did not seem to associate verapamil permeability in the various intestinal regions in vivo. These data suggest that P-gp plays a minimal role in the in vivo intestinal absorption process of verapamil with high water solubility and high membrane permeability. The intestinal absorption of verapamil in vivo is primarily dominated by its high permeability. However, it is important to note that the findings in this paper do not undermine the importance of P-gp in oral drug bioavailability, drug disposition from the liver, drug efflux from the blood-brain barrier, and drug-drug interaction.     

Intestinal absorption of cephalosporin antibiotics: correlation between intestinal absorption and brush-border membrane transport

The absorption of seven cephalosporin antibiotics from the in-situ intestinal loop at pH 7.4 and their transport by brush-border membrane vesicles in the presence of an inward H+ gradient ([pH]i = 7.5, [pH]o = 6.0) were examined. A good correlation was found between the intestinal absorption rate and the initial uptake rate by brush-border membrane vesicles. The data suggest that the transport study using intestinal brush-border membrane vesicles is useful as a model system for the intestinal absorption of beta-lactam antibiotics.     

Prediction of in vivo intestinal absorption enhancement on P-glycoprotein inhibition, from rat in situ permeability

The purpose of this study is to determine the functional role of P-glycoprotein (P-gp) in intestinal absorption of drugs and to quantitatively predict the in vivo absorption enhancement on P-gp inhibition. In situ single-pass rat ileum permeability and aqueous solubility were measured for a set of 16 compounds. Permeability studies were also carried out in the presence of P-gp inhibitor to estimate the permeability enhancement on P-gp inhibition. A significant correlation was obtained between rat ileum permeability and the literature human intestinal absorption (HIA), F(a,human) (r = 0.891; p < 0.01). Compounds with permeability >0.2 x 10(-4) cm/s are completely absorbed; however, few practically insoluble compounds were overestimated with this relationship. Inhibition of P-gp increased the permeability (p < 0.05) of three moderately and three highly permeable compounds. Efflux inhibition ratio (EIR), the ratio of permeability due to P-gp-mediated efflux activity and passive permeability only, for these compounds was in the order of digoxin > paclitaxel > fexofenadine > quinidine > verapamil > cyclosporine. Integration of EIR with permeability versus F(a,human) predicted that modulation of P-gp has no significant effect on the absorption of highly permeable compounds (quinidine, verapamil, and cyclosporine A), while for moderately permeable compounds (digoxin, paclitaxel, and fexofenadine), P-gp profoundly influences the intestinal permeability. The in situ permeability in rat ileum may be used to predict the in vivo P-gp function and its quantitative contribution to intestinal drug absorption. Integration of the functional activity of P-gp with the characteristics of BCS may explain drug interactions and explore the possible pharmacokinetic advantage on P-gp inhibition.     

伐昔洛韦缓释片体外释放速率与人体内吸收速率的相关性

目的:研究伐昔洛韦缓释片体外释放速率与人体内吸收速率的相关性。方法:以水为释放介质,测定伐昔洛韦缓释片的体外释放速率;采用Wagner-Nelson法计算单剂量口服缓释片后体内吸收分数,考察吸收相体内吸收与体外释放的相关性。结果:伐昔洛韦缓释片体内吸收分数(f_a)与体外释放速率(f_r)的关系为:f_a=2.11f_r -20.12,r=0.994 0(n=5)。结论:伐昔洛韦缓释片人体内外相关性良好(P<0.001)。     

Relationship between total body clearance of caffeine and urine flow rate in elderly men

The total body clearance (CL), renal clearance (CLR), and nonrenal clearance (CLNR) of caffeine from plasma were determined following the intravenous administration of caffeine (4 mg kg-1) to ten healthy men (aged 66-86 years) on three separate occasions. Positive correlations were observed between CL and urine flow rate (UFR), between CLR and UFR, and between CLNR and UFR (r = 0.8947, p = 0.0002; r = 0.8832, p = 0.0003; and r = 0.8920, p = 0.0002, respectively). Previous studies have established similar relationships between CLR and UFR for caffeine and its initial dimethylxanthine metabolites; theophylline, theobromine, and paraxanthine. A relationship between CL and UFR has not been reported previously.     

Involvement of intestinal permeability in the oral absorption of clarithromycin and telithromycin

The involvement of intestinal permeability in the oral absorption of clarithromycin (CAM), a macrolide antibiotic, and telithromycin (TEL), a ketolide antibiotic, in the presence of efflux transporters was examined. In order independently to examine the intestinal and hepatic availability, CAM and TEL (10 mg/kg) were administered orally, intraportally and intravenously to rats. The intestinal and hepatic availability was calculated from the area under the plasma concentration–time curve (AUC) after administration of CAM and TEL via different routes. The intestinal availabilities of CAM and TEL were lower than their hepatic availabilities. The intestinal availability after oral administration of CAM and TEL increased by 1.3‐ and 1.6‐fold, respectively, after concomitant oral administration of verapamil as a P‐glycoprotein (P‐gp) inhibitor. Further, an in vitro transport experiment was performed using Caco‐2 cell monolayers as a model of intestinal epithelial cells. The apical‐to‐basolateral transport of CAM and TEL through the Caco‐2 cell monolayers was lower than their basolateral‐to‐apical transport. Verapamil and bromosulfophthalein as a multidrug resistance‐associated proteins (MRPs) inhibitor significantly increased the apical‐to‐basolateral transport of CAM and TEL. Thus, the results suggest that oral absorption of CAM and TEL is dependent on intestinal permeability that may be limited by P‐gp and MRPs on the intestinal epithelial cells. Copyright © 2014 John Wiley & Sons, Ltd.     

Relationship between phenol-induced cytotoxicity and experimental inhibition rate constant or a theoretical parameter

We synthesized various dimer forms of 2-methoxyphenols and 2-tert-butylphenols, as dimers such as curcumin exhibit potent antioxidant and anti-inflammatory activity. We investigated the QSARs between the cytotoxicity and independent variables; kinetic parameters (inhibition rate constant (kinh/kp), stoichiometric factor (n)) or DFT-based theoretical parameters (i.e. phenolic O-H bond dissociation enthalpy (BDE), ionization potential according to Koopman's theorem (IP), LUMO, absolute hardness (η), electronegativity (χ) and electrophilicity (ω)) for 2-methoxyphenols and 2- tert- or 2,6-di-tert-butylphenols. The cytotoxicity of these phenols against human tumor cells (HSG, HL60) and/or human gingival fibroblasts (HGF) showed a marked negative linear relationship to kinh/kp, suggesting that the cytotoxicity of phenols may be related to radical reactions. By contrast, a linear relationship between the cytotoxicity and η-term was demonstrated; 2-methoxyphenols showed a negative slope, whereas 2-tert- or 2,6-di-tert-butylphenols showed a positive slope. Also, the cytotoxicity of tert-butylphenols was linearly dependent on the LUMO-term, showing a positive slope. The cytotoxicity of methoxy-substituted monophenols toward both HSG and HGF cells was related to both log P and η- terms. Also, that of X-phenols toward murine L-1210 cells was related to both log P and η or IP-terms, determined from a dataset reported by Zhang et al., 1998. It was concluded that the phenol-induced cytotoxicity was attributable to radical reactions resulting from the terms (kinh/kp, IP, η, and LUMO) in QSAR. The LUMO-dependent cytotoxicity of 2-tert- or 2,6-di-tert-butylphenols may be related to their quinone oxidation products. Experimental and theoretical parameters provide a useful approach for analysis of the cytotoxicity for phenolic compounds.     

Enhanced permeability of insulin across the rat intestinal membrane by various absorption enhancers: their intestinal mucosal toxicity and absorption-enhancing mechanism of n-lauryl-beta-D-maltopyranoside

We have examined the in-vitro permeability characteristics of insulin in the presence of various absorption enhancers across rat intestinal membranes and have assessed the intestinal toxicity of the enhancers using an in-vitro Ussing chamber method. The absorption enhancing mechanism of n-lauryl-beta-D-maltopyranoside was studied also. The permeability of insulin across the intestinal membranes was low in the absence of absorption enhancers. However, the permeability was improved in the presence of enhancers such as sodium glycocholate and sodium deoxycholate in the jejunum, and sodium glycocholate, sodium deoxycholate, n-lauryl-beta-D-maltopyranoside, sodium caprate and ethylenediaminetetraacetic acid (EDTA) in the colon. Overall, the absorption enhancing effects were greater on the colonic membrane than on the jejunal membrane. The intestinal membrane toxicity of these enhancers was characterized using the release of cytosolic lactate dehydrogenase from the colonic membrane. A marked increase in the release of lactate dehydrogenase was observed in the presence of sodium deoxycholate and EDTA. The release of lactate dehydrogenase in the presence of these absorption enhancers was similar to that seen with sodium dodecyl sulphate (SDS), used as a positive control, indicating high toxicity of these enhancers to the intestinal membrane. In contrast, sodium glycocholate and sodium caprate caused minor releases of lactate dehydrogenase, similar to control levels, suggesting low toxicity. In addition, the amount of lactate dehydrogenase in the presence of n-lauryl-beta-D-maltopyranoside was much less than that seen with sodium deoxycholate, EDTA and SDS. Therefore, sodium glycocholate, sodium caprate and n-lauryl-beta-D-maltopyranoside are useful absorption enhancers due to their high absorption enhancing effects and low intestinal toxicity. To investigate the absorption enhancing mechanisms of n-lauryl-beta-D-maltopyranoside, the transepithelial electrical resistance (TEER), voltage clamp experiments and the circular dichroism spectra were studied. n-Lauryl-beta-D-maltopyranoside decreased the TEER values in a dose-dependent manner, suggesting that the enhancer may open the tight junctions of the epithelium, thereby increasing the permeability of insulin via a paracellular pathway. This speculation was supported by the findings that 20 mM n-lauryl-beta-D-maltopyranoside produced a greater increase in the paracellular flux rate than in the transcellular flux rate by the voltage clamp studies. Evaluating the circular dichroism spectra we found that insulin oligomers were not dissociated to monomers by the addition of n-lauryl-beta-D-maltopyranoside, but dissociation did occur with the addition of sodium glycocholate. Thus, the dissociation of insulin was not a major factor in the absorption enhancing effect of n-lauryl-beta-D-maltopyranoside. These findings provide basic information to select the optimal enhancer for the intestinal delivery of peptide and protein drugs including insulin.     

Ex vivo permeability experiments in excised rat intestinal tissue and in vitro solubility measurements in aspirated human intestinal fluids support age-dependent oral drug absorption

The possible influence of advanced age on intestinal drug absorption was investigated by determining the effects of aging on (i) solubility of model drugs in human intestinal fluids (HIF) obtained from two age groups (18–25 years; 62–72 years); and (ii) transepithelial permeation of model drugs across intestinal tissue excised from young, adult and old rats. Average equilibrium solubility values for 10 poorly soluble compounds in HIF aspirated from both age groups showed high interindividual variability, but did not reveal significant differences. Characterization of the HIF from both age groups demonstrated comparable pH profiles, while concentrations of individual bile salts showed pronounced variability between individuals, however without statistical differences between age groups. Transepithelial permeation of the transcellular probe metoprolol was significantly increased in old rats (38 weeks) compared to the younger age groups, while the modulatory role of P-glycoprotein in transepithelial talinolol transport was observed in adult and old rats but not in young rats. In conclusion, age-dependent permeability of intestinal tissue (rather than age-dependent luminal drug solubility) may contribute to altered intestinal drug absorption in older patients compared to young adults.     

Current methodologies used for evaluation of intestinal permeability and absorption

This review article will focus on the various techniques that are currently employed by drug discovery scientists in evaluating permeability/absorption of drug candidates during the drug candidate selection process. Various preclinical methodologies are available; each having advantages and disadvantages, but it is the judicious use of these techniques that can help identify drug candidates that will be well absorbed in humans. It is well recognized that the human intestinal permeability cannot be accurately predicted based on a single methodology (in vitro: tissue/cell culture, in situ, or in vivo).     

甘草素在体肠吸收及体外血脑屏障通透性研究

目的:研究甘草素(liquirtigenin)的肠吸收及血脑屏障(BBB)通透性.方法:利用大鼠单向肠灌流模型及联用高效液相色谱(HPLC)方法研究甘草素的吸收.分离鼠脑微血管内皮细胞(BMEC)和星形胶质细胞(AC),建立体外BBB模型,研究甘草素的BBB通透性.结果:在体肠灌流模型中甘草素在空肠处的有效渗透系数(Peff)为(101.1±4.7)×10-6cm·s-1,高于工具药盐酸普萘洛尔的Peff(77.4±15.2)×10-6cm·s-1.BBB通透实验中90 min时甘草素的BBB通透率为(29.73±6.83)％,工具药青霉素钠和氯霉素的BBB通透率分别为(1.64±0.17)％和(34.03±4.92)％.结论:甘草素肠壁通透性较好,也较易透过BBB.     

Dependence of intestinal absorption in vivo on the unstirred layer

Summary The appearance rate of butanol, antipyrine, salicylic acid, and urea in the venous blood of rat jejunal loops perfused in vivo is increased up to 64%, if the intraluminal solution is mixed more efficiently by the simultaneous perfusion of air. The enhancement of the absorption can be attributed partly to the enlarged absorbing area but mainly to the reduction of the effective unstirred layer thickness by about 500 m. The unstirred layer reduces the phenylalanine absorption at 0.1 mmol l^–1 but not at 100 mmol l^–1, since at high concentrations a full saturation of the transport system can be achieved in spite of the unstirred layer resistance. The interference of the unstirred layer increases with increasing absorbability of the substances.