Tissue distribution of gallium following administration of the gallium-maltol complex in the rat: a model for an aluminium-maltol complex of neurotoxicological interest

The intestinal absorption and subsequent tissue distribution of aluminium-maltol, a potentially neurotoxic complex found in foods, was investigated using gallium as a marker for aluminium. Gallium or gallium-maltol labelled with 67Ga was administered orally to rats. The amount of gallium in 'blood-free' tissues was measured by correcting for gallium in residual blood and an estimate of intestinal absorption was then made by summing the values for all tissues examined. In both the test (gallium-maltol dosed) and control (gallium only dosed) experiments absorption of gallium was significantly increased in the fasted state when compared with that of the fed animals. In fasted but not in fed animals, administration of gallium-maltol doubled the amount of gallium absorbed when compared with administration of gallium alone.     

Tissue distribution of inhaled micro- and nano-sized cerium oxide particles in rats: results from a 28-day exposure study

In order to obtain more insight into the tissue distribution, accumulation, and elimination of cerium oxide nanoparticles after inhalation exposure, blood and tissue kinetics were investigated during and after a 28-day inhalation study in rats with micro- and nanocerium oxide particles (nominal primary particle size: < 5000, 40, and 5-10 nm). Powder aerosolization resulted in comparable mass median aerodynamic diameter (1.40, 1.17, and 1.02 μm). After single exposure, approximately 10% of the inhaled dose was measured in lung tissue, as was also estimated by a multiple path particle dosimetry model (MPPD). Though small differences in pulmonary deposition efficiencies of cerium oxide were observed, no consistent differences in pulmonary deposition between the micro- and nanoparticles were observed. Each cerium oxide sample was also distributed to tissues other than lung after a single 6-h exposure, such as liver, kidney, and spleen and also brain, testis, and epididymis. No clear particle size-dependent effect on extrapulmonary tissue distribution was observed. Repeated exposure to cerium oxide resulted in significant accumulation of the particles in the (extra)pulmonary tissues. In addition, tissue clearance was shown to be slow, and, overall, insignificant amounts of cerium oxide were eliminated from the body at 48- to 72-h post-exposure. In conclusion, no clear effect of the primary particle size or surface area on pulmonary deposition and extrapulmonary tissue distribution could be demonstrated. This is most likely explained by similar aerodynamic diameter of the cerium oxide particles in air because of the formation of aggregates and irrespective possible differences in surface characteristics. The implications of the accumulation of cerium oxide particles for systemic toxicological effects after repeated chronic exposure via ambient air are significant and require further exploration.     

Galanthamine: pharmacokinetics, tissue distribution and cholinesterase inhibition in brain of mice

Galanthamine was determined in plasma and tissue extracts of mice, after the application of 4, 6 and 8 mg/kg (i.v.), by reverse phase HPLC, with fluorescence detection. A biexponential decline of concentrations in plasma, with a terminal half-life of 43.3 min, was observed after the dose of 4 mg/kg. The volume of distribution (Vss) of 2.17 l/kg was similar to that found in other species, including man. Metabolism to the inactive diastereomer, epigalanthamine, was very limited. There was a rapid accumulation of galanthamine in tissues, which was most pronounced in the kidney (10-fold compared to plasma) and liver (5-fold). In brain, accumulation was similar to other parenchymatous organs (diaphragm, lung) and amounted to 2.10-fold. Red blood cells showed a concentration 1.34-fold greater than plasma. The accumulation of galanthamine in tissue, with the exception of liver and kidney, can be explained by passive distribution according to differences in pH, between intra- and extracellular compartments. Extraction of galanthamine from blood to brain tissue was complete, indicated by a clearance in the range of cerebral blood flow (1.05 ml min-1 g-1). The concentration-time course of galanthamine in brain tissue was parallel to that in plasma during the terminal elimination phase. Measurement of inhibition of acetylcholinesterase (AChE) in the same samples from brain revealed a maximum apparent inhibition of 43% in the homogenate of brain (1:4 w/v in phosphate buffer, 4 mg/kg, 5 min after injection).(ABSTRACT TRUNCATED AT 250 WORDS)     

A Population WB-PBPK Model of Colistin and its Prodrug CMS in Pigs: Focus on the Renal Distribution and Excretion

Purpose

The objective was the development of a whole-body physiologically-based pharmacokinetic (WB-PBPK) model for colistin, and its prodrug colistimethate sodium (CMS), in pigs to explore their tissue distribution, especially in kidneys.

Methods

Plasma and tissue concentrations of CMS and colistin were measured after systemic administrations of different dosing regimens of CMS in pigs. The WB-PBPK model was developed based on these data according to a non-linear mixed effect approach and using NONMEM software. A detailed sub-model was implemented for kidneys to handle the complex disposition of CMS and colistin within this organ.

Results

The WB-PBPK model well captured the kinetic profiles of CMS and colistin in plasma. In kidneys, an accumulation and slow elimination of colistin were observed and well described by the model. Kidneys seemed to have a major role in the elimination processes, through tubular secretion of CMS and intracellular degradation of colistin. Lastly, to illustrate the usefulness of the PBPK model, an estimation of the withdrawal periods after veterinary use of CMS in pigs was made.

Conclusions

The WB-PBPK model gives an insight into the renal distribution and elimination of CMS and colistin in pigs; it may be further developed to explore the colistin induced-nephrotoxicity in humans.

     

Pharmacokinetic disposition of the novel atypical anxiolytic CGS 9896 in the cynomolgus monkey

The intravenous pharmacokinetic disposition of the novel, atypical anxiolytic CGS 9896 was studied in six cynomolgus monkeys. CGS 9896 was infused at dose levels of approximately 60, 120, and 240 cro;g/h/kg for a duration of 12 h, resulting in steady-state plasma concentrations averaging 38.4, 51.8, and 124 ng/ml, respectively. The average total systemic clearance was 35.3 ml/min/kg which was independent of dose and totally attributable to nonrenal pathways. The hepatic clearance was determined to be blood flow-rate dependent and the first-pass extraction calculated as approximately 84%. Both the apparent elimination rate constant and volume of distribution exhibited dose-dependent changes. Even though the plasma protein bound fraction was high (98.6%), no concentration dependency was observed. Furthermore, no concentration dependency was observed in the plasma/blood distribution ratio indicating the observed dose-related reduction in the volume of distribution may be attributable to nonlinear tissue uptake of CGS 9896.     

Disposition of intact liposomes of different compositions and of liposomal degradation products

Small unilamellar liposomes containing bovine serum albumin were prepared by a new double-emulsion technique and administered to mice and rats in intravenous injections. The elimination of intact liposomes, the association of phospholipid marker with lipoproteins, and the appearance of released internal marker and its degradation products were followed by column chromatography of plasma samples. In vitro labelled lipoproteins were administered to the animals in intravenous injections together with free bovine serum albumin and the elimination of the two substances was studied by closely related techniques. The clearance of intact PC:PS (4:1) liposomes from plasma was biphasic and much faster than that of labelled lipoproteins and bovine serum albumin either originating from liposomes or injected as such. The second elimination phase for these liposomes was barely detectable by our analytical methods. In contrast, DSPC:CHOL (2:1) liposomes showed a very significant second-phase elimination, with a half-life of 12 hr for the intact liposomes. In tissue distribution studies in mice, the major accumulation of liposomal markers was found in the liver and spleen, and less in the kidneys and intestinal wall. Uptake into liver and spleen appeared to be due to the uptake of intact liposomes, whereas the uptake into kidneys and gut wall was caused by the uptake of liposomal degradation products. The uptake of PC:PS (4:1) liposomes into the liver was higher than that of DSPC:CHOL (2:1) liposomes; the opposite was the case with their uptake into the spleen. In rats, too, liposomes of different compositions showed significant variations in stability and in plasma half-lives of intact liposomes. Generally, there was a considerable increase in the liposomal stability in the presence of cholesterol and when use was made of a phospholipid with a high transition temperature.     

Formulating Paclitaxel in Nanoparticles Alters Its Disposition

Purpose Paclitaxel is active and widely used to treat multiple types of solid tumors. The commercially available paclitaxel formulation uses Cremophor/ethanol (C/E) as the solubilizers. Other formulations including nanoparticles have been introduced. This study evaluated the effects of nanoparticle formulation of paclitaxel on its tissue distribution.Methods We compared the plasma and tissue pharmacokinetics of paclitaxel-loaded gelatin nanoparticles and the C/E formulation. Mice were given paclitaxel-equivalent doses of 10 mg/kg by intravenous injection.Results The nanoparticle and C/E formulations showed significant differences in paclitaxel disposition; the nanoparticles yielded 40% smaller area under the blood concentration-time curve and faster blood clearance of total paclitaxel concentrations (sum of free, protein-bound, and nanoparticle-entrapped drug). The two formulations also showed different tissue specificity. The rank order of tissue-to-blood concentration ratios was liver > small intestine > kidney >> large intestine > spleen = stomach > lung > heart for the nanoparticles, and liver > small intestine > large intestine > stomach > lung kidney > spleen > heart for the C/E formulation. The nanoparticles also showed longer retention and higher accumulation in organs and tissues (average of 3.2 ± 2.3-fold), especially in the liver, small intestine, and kidney. The most striking difference was an 8-fold greater drug accumulation and sustained retention in the kidney.Conclusions These data indicate that formulation of paclitaxel affects its clearance and distribution into tissues, with preferential accumulation of nanoparticles in the liver, spleen, small intestine, and kidney.     

Physiologically based pharmacokinetic study on a cyclosporin derivative,SDZ IMM 125

The immunosuppressant, SDZ IMM 125 (IMM), is a derivative of cyclosporin A (CyA). The disposition kinetics of IMM in plasma, blood cells, and various tissues of the rat was characterized by a physiologically based pharmacokinetic (PBPK) model; the model was then applied to predict the disposition kinetics in dog and human. Accumulation of IMM in blood cell is high (equilibrium blood cell/plasma ratio=8), although the kinetics of drug transference between plasma and blood cell is moderately slow, taking approximately 10 min to reach equilibrium, implying a membranelimited distribution into blood cells. A local PBPK model, assuming blood-flow limited distribution and tissue/blood partition coefficient (K _P) data, failed to adequately describe the observed kinetics of distribution, which were slower than predicted. A membrane transport limitation is therefore needed to model dynamic tissue distribution data. Moreover, a slowly interacting intracellular pool was also necessary to adequately describe the kinetics of distribution in some organs. Three elimination pathways (metabolism, biliary secretion, and glomerular filtration) of IMM were assessed at steady statein vivo and characterized independently by the corresponding clearance terms. A whole-body PBPK model was developed according to these findings, which described closely the IMM concentration-time profiles in arterial blood as well as 14 organs/tissues of the rat after intravenous administration. The model was then scaled up to larger mammals by modifying physiological parameters, tissue distribution and elimination clearances;in vivo enzymatic activity was considered in the scale-up of metabolic clearance. The simulations agreed well with the experimental measurements in dog and human, despite the large interspecies difference in the metabolic clearance, which does not follow the usual allometric relationship. In addition, the nonlinear increase in maximum blood concentration andAUC with increasing dose, observed in healthy volunteers after intravenous administration, was accommodated quantitatively by incorporating the known saturation of specific binding of IMM to blood cells. Overall, the PBPK model provides a promising tool to quantitatively link preclinical and clinical data.     

Kinetic studies of the tissue binding tendency of the new vasodilator pildralazine

Studies of the binding and release of the new antihypertensive drug (+/-)-1-[(6-hydrazinopyridazin-3-yl)methylamino]-2-propanol (pildralazine, PD) were performed on isolated perfused guinea pig hearts according to the Langendorff technique. Extensive binding to and accumulation in the tissue were recorded. Even after 30 min of washout considerable PD concentrations were detected both in the myocardium (900 ng/g w.w.) and the effluent (17 ng/ml = 100 ng/min). The calculation of elimination half-life yielded a nearly identical value in the myocardial tissue and the effluent. Coronary vasodilation mediated by PD ran in close parallel to the drug concentrations. As the washout of [3H]-sucrose as an extracellular space marker was half-maximal already after 1.6 min rediffusion of PD originated from tissue sites and not only by dilution of the fluid in the extracellular space. In addition the results indicated that the observed binding of PD to cell structures prevented its normally rapid chemical destruction, already evident in aqueous solutions. The back diffusion of PD from the binding and storage sites into the coronary perfusate was very slow, explaining its long-lasting biological availability and action in vivo. The release kinetics may be described by an exponential function which obeys the criterions of a first order elimination process.     

Membrane Transport in Hepatic Clearance of Drugs II: Zonal Distribution Patterns of Concentration-Dependent Transport and Elimination Processes

Purpose. The objective of the present simulation study was to investigate the effects of hepatic zonal heterogeneity of membrane transporter proteins and intrinsic elimination activities on hepatic clearance (CL) and drug concentration gradient profiles in the sinusoidal blood and hepatocytes. Methods. The model used in the simulations assumes an apparent unidirectional carrier-mediated transport and a bidirectional diffusion of substrates in the hepatic sinusoidal membrane as well as a nonlinear intrinsic elimination. Three different distribution patterns of the transporter and the metabolizing enzyme along the sinusoidal flow path were used for the simulations. The effects of changes in the Michaelis-Menten parameters for those nonlinear processes, and in the unbound fractions of the drug in blood and tissue components were investigated. Results. Significant differences in CL occurred when the distribution patterns of the transporter and/or the metabolizing enzyme activities were altered under nonlinear conditions. The highest CL values were observed when the transporter and the metabolizing enzyme had similar distribution patterns within the liver acinus, while opposite distribution patterns produced the lowest CL values. Tissue concentration profiles were significantly affected by the distribution patterns of the transporter, but the changes in blood concentration profiles were relatively small. Altering protein binding in blood produced significant changes in CL, and blood and tissue concentration gradients, while altering protein binding in tissue affected only drug accumulation patterns within hepatocytes, regardless of the distribution patterns of the transporter or the metabolizing enzyme. Conclusions. The present simulations demonstrate that hepatic zonal heterogeneities in the transporter and the metabolizing enzyme activities can significantly influence hepatic clearance and/or drug concentration gradient profiles in the sinusoidal blood and hepatocytes.     

Toxicokinetics of methyl mercury in pigs

Toxicokinetics of methyl mercury were studied in pigs after intravenous (i.v.) administration of the compound. The distribution of methyl mercury was slow taking 3–4 days to be completed. Blood elimination half-life was found to be 25 days. The apparent volume of distribution was 9.8 l/kg indicating pronounced tissue accumulation of methyl mercury. Highest mercury levels were found in kidney and liver, with lower contents in muscle and brain and very little in adipose tissue. The results indicate that from organs like liver and kidney methyl mercury is eliminated much more slowly than from the blood. Over a period of 15 days 16% of the dose administered was excreted with faeces and 0.9% in the urine.     

Pharmacokinetics of propofol when given by intravenous infusion.

We have previously shown with i.v. bolus studies that the elimination of propofol is much slower than previously reported. Now we have studied the implications of this for prolonged i.v. infusion of propofol in seven patients who received continuous infusions of propofol for up to 9 h. Values of elimination half-life ranged from 13.1 to 44.7 h, systemic clearance from 1.02 to 1.63 l h-1 and volume of distribution from 1390 to 3940 l and these were similar to those obtained with bolus administration. The large volume of distribution is consistent with the high octanol/blood partition coefficient, which was found to be 72.0. Despite the very long elimination half-life, blood propofol concentrations appeared to approach steady state within 20 min rather than the 4-5 half-lives normally expected. This is because for this drug, which displays multicompartment pharmacokinetics, the rate of initial rise of blood concentrations is governed primarily by the very short distribution half-life of the drug. Therefore, the long elimination half-life of propofol is probably of little significance in designing infusions regimens, but the lower systemic clearance should be taken into account to avoid unwanted accumulation.     

Effect of the molecular weight of water-soluble polymers on accumulation at an inflammatory site following intravenous injection

The body distribution of noncharged, water-soluble polymers, e.g. poly(vinyl alcohol) (PVA), poly(ethylene glycol) (PEG), and dextran, was studied following their intravenous injection into mice with or without carrageenan-induced inflammatory lesions at the femoral muscle. Inflammation induction did not affect their distribution profile, although polymers of high molecular weight tended to remain in the blood circulation for a longer period than those of low molecular weight. Polymers exhibited longer accumulation at the inflammatory site than at the normal site, regardless of the polymer type and the molecular weight estimated by size exclusion chromatography. Maximum accumulation was observed for the polymer having a molecular weight around 200,000, regardless of the polymer type. Pharmacokinetic studies demonstrated that the accumulation rate of polymers at the inflammatory site was higher than at the normal site and decreased with increasing molecular weight. On the other hand, the higher the molecular weight of polymers, the longer the retention time in the blood circulation. Such trends were observed for all types of polymers used, indicating that the inflammatory site accumulation of polymers injected intravenously is governed solely by the polymer molecular weight. The balance between the accumulation rate of polymers and the blood retention seemed to determine the maximum accumulation of polymers having a certain range of molecular weight.     

Physiologic modeling of cyclosporin kinetics in rat and man

A physiologic pharmacokinetic model of cyclosporin has been developed in the rat aimed at predicting the time course of drug concentrations in blood, organs, and tissues. The model assumes that tissue distribution is perfusion-rate limited and that each tissue acts as a well-stirred compartment. The unbound equilibrium distribution ratios as well as the values of the fraction unbound and the distribution isotherm of cyclosporin between erythrocytes and plasma are included in the rate equations describing the time course of the drug concentration in each tissue. Parameter values for the rat were obtained experimentally from a continuous infusion study, in which 2.7 and 13.9 mg/kg per day doses of cyclosporin were administered subcutaneously to each of two groups of rats by osmotic pumps for 6 days. Steady-state cyclosporin concentrations in blood, CSF, and 18 different organs and tissues, were determined by a monoclonal antibody RIA. Differences in values of the unbound equilibrium distribution ratios in some tissues and unbound clearance indicated that both the processes of distribution and elimination may have elements of nonlinearity over the range of dosing rates tested. The model was evaluated in the rat with a kinetic experiment in which a 6-mg/kg dose of cyclosporin was infused intravenously over 15 min, with measurements of blood concentrations until 56 hr. Good agreement was obtained for the volume of distribution at steady state (blood), Vss, between the perfusion model and that calculated from the kinetic experiment. Also, the model prediction of the blood concentration temporal profile agreed closely with that observed except in the early moments, when distribution out of blood occurred considerably slower than predicted. On scaling the model up to humans, good agreement was found between the predicted plasma concentration-time profile and Vss and experimental data from the literature. Both rat and human data suggest that partition into adipose tissue plays an important role in the pharmacokinetics of cyclosporin.     

Distribution and elimination in vivo of polychlorinated biphenyl (PCB) isomers and congeners in the pigeon

1. Pigeons were injected with a single dose of commercial PCB mixtures (Aroclor 1248 plus Aroclor 1260), killed 120 h later and the abundance of individual PCBs was determined in adipose tissue, gonads, liver, brain, kidney, heart, muscle and blood. 2. Elimination factors for individual PCBs were calculated. Values of greater than 1 were obtained for PCBs with meta-para-unsubstituted carbon atoms in at least one ring, indicating that elimination exceeded accumulation in all or most tissues. By contrast, ortho-meta unsubstituted PCBs had elimination factors less than 1, thus indicating their impaired removal. 3. Tissues with high microsomal monooxygenase activity had the highest elimination factors for individual PCBs (i.e. liver greater than kidney greater than muscle greater than heart). 4. Distribution of individual PCBs was independent of sex and of ortho-chlorine substitution and showed that 90% of total PCBs in cadavers was present in adipose tissue, 2% in kidneys, 1% each in brain, muscle and heart and less than 0.1% in blood. 5. The distribution of the highly toxic non-ortho and mono-ortho substituted PCBs did not differ amongst all tissues analysed. 6. The present studies indicate that elimination of PCBs in vivo is favoured by the molecular feature of unsubstituted meta-para carbon atoms in the biphenyl moiety.     

Pharmacokinetics and distribution of a biodegradable drug-carrier

This paper describes tissue distribution, blood clearance and excretion of biodegradable cyanoacrylic nanoparticles.After intravenous administration, nanoparticles were rapidly cleared from the blood stream and concentrated mainly in the reticuloendothelial system. When administrated subcutaneously, nanoparticles seemed to avoid the liver and the spleen whereas they concentrated in the gut wall.Whole body autoradiography performed on Lewis Lung carcinoma-bearing mice showed progressive accumulation of the carrier in tumoral tissue. Furthermore a high level of radioactivity was found in the metastatic lungs of cancerous animals, whereas no lung accumulation was observed in healthy mice. Data are given concerning the enzymatic contribution to the degradation of the nanoparticles in vivo.     

头孢呋辛钠在小鼠体内的药代动力学及组织分布研究

目的：通过HPLC探讨注射用头孢呋辛钠在小鼠体内的药代动力学和组织分布。方法：小鼠单剂量背部推注头孢呋辛钠1000mg/kg,在不同时间取其血浆及各组织匀浆液经离心沉淀蛋白后,采用HPLC法测定其药代动力学及组织中药物浓度。结果：背部给药后血浆药—时曲线符合一室开放模型,头孢呋辛钠体内分布迅速,分布半衰期为0.6179h,消除半衰期为2.2098h,AUC为76.3199h.mg/mL,肺、肝脏及肾脏中药物浓度较高。结论：头孢呋辛钠在体内分布广、组织浓度高、消除半衰期。     

Pharmacokinetics of sulphadimethoxine in channel catfish (Ictalurus punctatus)

1. Plasma clearance, bioavailability, tissue disposition and elimination of 14C-sulphadimethoxine (SDM) were studied in channel catfish (Ictalurus punctatus) after intravenous (i.v.) and oral dosing (per os; p.o.) at 40 mg/kg body weight. 2. Analysis of blood SDM concentrations over time for intravascularly administered SDM showed that disposition and elimination were best described by a two-compartment pharmacokinetic model; estimated half-lives for SDM in blood were 0.09 and 12.6 h for the distribution and elimination phases, respectively. 3. SDM was found primarily in muscle tissue immediately after oral administration; however, clearance from muscle was rapid, with a half-life of 13.1 h. 4. With time, SDM-derived radioactivity became concentrated in the bile and was eliminated slowly (t 1/2 = 115.5 h). 5. Binding of SDM in channel catfish plasma was low (18%) and was non-specific and dose-independent. 6. With the exception of the initial, rapid clearance of SDM from blood, the pharmacokinetic parameters describing SDM distribution and elimination in channel catfish were similar to values reported for other vertebrate species; the rapid distribution of SDM from blood to the tissues in the catfish may be related to species differences in the plasma binding of SDM.     

Thalidomid-Analoga, 9. Mitt. Blutspiegelverlauf und Organverteilung von Biglumid (K-2004) bei der Maus

Blood Level Course and Organ Distribution of Biglumide (K-2004) in the Mouse The distribution of the total radioactivity in the blood, in various organs and tissues, and in the fetuses of mice after oral application of 140 mg/kg ³H-biglumide was determined, and the time course of the blood levels as well as the tissue concentrations in brain, liver, and kidney were measured. No appreciable accumulation of the compound and/or its metabolites takes place in any part of the organism. The calculated half-lives range between 0.28 and 0.40 h for the invasion and between 1.99 and 2.69 h for the elimination.     

Distribution and elimination in vivo of polychlorinated biphenyl (PCB) isomers and congeners in the pigeon

1. Pigeons were injected with a single dose of commerical PCB mixtures (Aroclor 1248 plus Aroclor 1260), killed 120 h later and the abundance of individual PCBs was determined in adipose tissue, gonads, liver, brain, kidney, heart, muscle and blood.

2. Elimination factors for individual PCBs were calculated. Values of >1 were obtained for PCBs with meta-para-unsubstituted carbon atoms in at least one ring, indicating that elimination exceeded accumulation in all or most tissues. By contrast, ortho-meta unsubstituted PCBs had elimination factors <1, thus indicating their impaired removal.

3. Tissues with high microsomal monooxygenase activity had the highest elimination factors for individual PCBs (i.e. liver> kidney > muscle > heart).

4. Distribution of individual PCBs was independent of sex and of ortho-chlorine substitution and showed that 90% of total PCBs in cadavers was present in adipose tissue, 2% in kidneys, 1% each in brain, muscle and heart and <0.1% in blood.

5. The distribution of the highly toxic non-ortho and mono-ortho substituted PCBs did not differ amongst all tissues analysed.

6. The present studies indicate that elimination of PCBs in vivo is favoured by the molecular feature of unsubstituted meta-para carbon atoms in the biphenyl moiety.