Tissue Uptake Mechanism Research Articles

Pharmacokinetics of cucurbitacin B from Trichosanthes cucumerina L. in rats

BackgroundCucurbitacin B is the major bioactive constituent in Trichosanthes cucumerina L. fruits, which the pharmacological properties have been studied for decades particularly an anti-tumor activity. The pharmacokinetic profile of this compound is still limited and investigation is needed for further phytopharmaceutical product development. This study aimed to investigate the pharmacokinetic profile of cucurbitacin B after administering the compound at different doses and routes to rats.MethodsMale Wistar rats (n = 6) were treated by cucurbitacin B extracted from Trichosanthes cucumerina L. The cucurbitacin B was administered at 0.1 mg/kg intravenously or by oral gavage at 2–4 mg/kg. Blood samples and internal organs were collected serially within 24 h after administration. Urine and feces were collected from time 0 to 48 h. The level of cucurbitacin B in biological samples was determined by liquid chromatography-tandem mass spectrometry.ResultsThe absolute oral bioavailability of cucurbitacin B was approximately 10%. The maximum concentration in plasma after normalization by dose ranged from 4.85–7.81 μg/L and the time to reach maximum value was approximately within 30 min after oral dosing. The level of cucurbitacin B in plasma increased proportionally to the given dose. After intravenous administration, cucurbitacin B had a large volume of distribution of about 51.65 L/kg and exhibited a high tissue to plasma concentration ratio, approximately 60 to 280-fold in several organs. Negligible amount of unchanged cucurbitacin B could be detected in urine and feces and accounted less than 1% of administered dose.ConclusionCucurbitacin B had low oral bioavailability, but could be distributed extensively into internal organs with a high volume of distribution and tissue to plasma ratio. Only negligible amounts of unchanged cucurbitacin B were excreted via urine and feces suggesting that the compound might be biotransformed before undergoing an excretion. Further studies of the metabolic pathway and tissue uptake mechanism are required to strategize the future development of cucurbitacin B into clinical studies.

Tissue Uptake Mechanisms Involved in the Clearance of Non-Protein Nanoparticles that Mimic LDL Composition: A Study with Knockout and Transgenic Mice.

Lipid core nanoparticles (LDE) resembling LDL behave similarly to native LDL when injected in animals or subjects. In contact with plasma, LDE acquires apolipoproteins (apo) E, A-I and C and bind to LDL receptors. LDE can be used to explore LDL metabolism or as a vehicle of drugs directed against tumoral or atherosclerotic sites. The aim was to investigate in knockout (KO) and transgenic mice the plasma clearance and tissue uptake of LDE labeled with 3H-cholesteryl ether. LDE clearance was lower in LDLR KO and apoE KO mice than in wild type (WT) mice (p<0.05). However, infusion of human apoE3 into the apoE KO mice increased LDE clearance. LDE clearance was higher in apoA-I KO than in WT. In apoA-I transgenic mice, LDE clearance was lower than in apoA-I KO and than in apoA-I KO infusion with human HDL. Infusion of human HDL into the apoA-I KO mice resulted in higher LDE clearance than in the apoA-I transgenic mice (p<0.05). In apoA-I KO and apoA-I KO infused human HDL, the liver uptake was greater than in WT animals and apoA-I transgenic animals (p<0.05). LDE clearance was lower in apoE/A-I KO than in WT. Infusion of human HDL increased LDE clearance in those double KO mice. No difference among the groups in LDE uptake by the tissues occurred. In conclusion, results support LDLR and apoE as the key players for LDE clearance, apoA-I also influences those processes.

Sunitinib tissue distribution changes after coadministration with ketoconazole in mice.

Sunitinib is a multitargeted tyrosine kinase inhibitor approved for gastrointestinal stromal tumor (GIST), advanced renal cell carcinoma (RCC) and pancreatic neuroendocrine tumors. It is metabolized via CYP3A4 and has low brain penetration due to efflux transporters ABCB1B and ABCG2. We studied the interaction with ketoconazole (50mg/kg), antifungal drug which shares metabolic pathways and efflux transporters, in ICR female mice after oral coadministration (30min apart) of 60mg/kg sunitinib (study group) versus sunitinib alone (control group). Plasma, liver, kidney and brain sunitinib concentrations were measured by HPLC at 2, 5, 10, 20, 40min, 1, 2, 4, 6, 12h post-sunitinib administration, and non-compartmental pharmacokinetic parameters estimated. In plasma, ketoconazole coadministration increased plasma maximum concentration (C MAX) 60%, delayed time to C MAX (T MAX); 1.6-fold greater area under the curve AUC0→∞ (p<0.001); lower apparent steady-state volume of distribution (V SS/F) and oral clearance (Cl/F) 40 and 61%, respectively; and shorter elimination half-life (t 1/2). Sunitinib exhibited extensive tissue distribution which increased after ketoconazole coadministration: total area under the curve (AUC0→∞) increased 1.8-, 2.8- and 1.2-fold in kidney, liver and brain, respectively (all p<0.001). Sunitinib presented high tissue-to-plasma AUC0→∞ ratio in liver (17.8±1.2), kidney (14.6±1.52) and brain (2.25±0.18) which was modified after coadministration: AUC0→∞ ratio increased in liver (31.4±4.7; p<0.001), kidney (17.1±2.2; p>0.05) and decreased in brain (1.70±0.23, p>0.05). The results showed a significant ketoconazole-sunitinib interaction that affected plasma, tissue pharmacokinetics and tissue uptake mechanisms. The study portrays the risk to increase toxicity and potential clinical translatability to treat tumors in tissues.

WE-A-342-01: Contrast Agents in MRI

Drugs, known as “Magnetic Resonance (MR) Contrast Agents (CA)” are firmly established in current clinical practice. According to recent data, MR CAs are administered in about 25–30% of all MR Imaging(MRI) procedures; it is estimated that in 2005 about 20 million procedures involving injected CAs were performed worldwide. In standard applications, they are administered intravenously with the intent to modify the Nuclear Magnetic Resonance (NMR)characteristics of tissues. Since the extent of contrast agent impact varies with tissue type, the differential effect of drug action on imaged lesions modifies their appearance on MR images. This phenomenon is used to aid the clinical diagnosis. Physical principles governing the behavior of CAs are discussed first, with emphasis on mechanisms that play a major role in MRI applications. CA's main role is to modify the NMR relaxation properties (longitudinal relaxation time T1, transverse relaxation time T2, or both) of its molecular environment. Since the effect is proportional to CA's concentration in the tissue, the biodistribution of CA has a major impact on the overall efficacy of the drug. Thus, in addition to NMR relaxation processes, fundamentals of compartmental analysis are discussed. The segment is concluded with taxonomy of CAs currently available for clinical use. The second part of the presentation describes clinical applications of MR CAs. Currently, routine applications explore non‐organ targeted relaxation enhancement mechanisms of action. In this method, a bolus of CA is injected intravenously and data collection for MRI begins a few minutes later, after tissue uptake mechanisms have established stationary conditions throughout the patient's body. Abnormalities within organs accumulate higher concentrations of CA, which shortens their T1 relaxation time and makes them appear brighter (relative to their background) on T1‐weighted MR images. However, two major off‐label areas of use have emerged already: contrast‐enhanced MR Angiography (MRA) examinations and Dynamic Contrast Enhancement (DCE) studies of tissue perfusion. Strengths and weaknesses of these techniques are reviewed. The segment ends up with a discussion of tissue‐specific CAs, such as superparamagnetic iron oxides (SPIO) used in imaging of the liver. The last part of the lecture focuses on the safety issues associated with the use of MR CAs. Despite rigorous pre‐market evaluations (MR CAs are considered drugs and are subject to FDA regulations) some side effects emerge only after the drug has been on the market for considerable time, when the large volume of available clinical records reveals patterns that remain hidden within smaller data pools. The recent alarm caused by emergence of the Nephrogenic Systemic Ribrosis (NSF) syndrome as a serious consequence of using Gadolinium‐based CA during MR studies in patients with acute or chronic kidney disease is used to describe and analyze safety issues related to the use of MR CAs. Educational Objectives: 1. Understand the physical mechanisms governing the action of contrast agents used in MR Imaging. 2. Become acquainted with the taxonomy of contrast agents used in current clinical practice. 3. Learn about safety issues related to the use of contrast agents in MRI practice.

Triglycerides in fish oil affect the blood clearance of lipid emulsions containing long- and medium-chain triglycerides in mice.

Lipid emulsions containing long-chain triglycerides (LCT) and medium chain triglycerides (MCT) are widely used in parenteral nutrition. Recently, fish oil (FO) triglyceride (TG)-derived emulsions are considered therapeutic because of their many beneficial biological modulatory actions. We investigated in mice whether adding 10% FO to an intravenous lipid emulsion with MCT and LCT (MCT:LCT:FO -50:40:10% by wt) would affect particle blood clearance and tissue targeting in comparison to LCT (100% by wt) and MCT:LCT (50:50% by wt) emulsions. The 3 emulsions were labeled with [3H] cholesteryl oleoyl ether and administered by bolus injection (400 microg TG/mouse) to C57BL/6J mice. Contributions of LDL receptor (LDL-R) and LDL-R-related protein to emulsion catabolism were assessed using LDL-R-deficient mice and preinjection of lactoferrin, and the effects of lipoprotein lipase (LPL) were determined by preinjection of heparin and Triton WR 1339. Although fractional catabolic rates did not differ among the 3 emulsions, blood removal at each time point after injection was greater for MCT:LCT:FO particles due to their higher initial margination volume. Compared with MCT:LCT and LCT emulsions, patterns of tissue uptake of the MCT:LCT:FO emulsions were different, e.g. MCT:LCT:FO emulsion particle uptake was lower in heart, adipose tissue, and muscle, and higher in lung, and the removal of MCT:LCT:FO emulsion particles was less dependent on LPL, LDL-R, and lactoferrin-sensitive pathways. These data suggest that the addition of a low percentage of FO to MCT:LCT emulsions substantially changes their particle clearance and tissue uptake mechanisms.

Vascular responses of ophthalmic arteries to exogenous and endogenous norepinephrine

A participation of neuronal and tissue uptake mechanism in responses to periarterial electrical sympathetic nerve stimulation (ES) and intra-arterial applications of norepinephrine (NE) was investigated in the isolated and perfused canine ophthalmic arteries (OA), using key pharmacological drugs such as imipramine, tyramine, cocaine, cortisol and diltiazem. Results were as follows: 1. (1) NE, KCl and ES induced marked vasoconstrictions in a dose- and frequeney-related manner, but tyramine induced only a slight constriction even at large doses; 2. (2) cortisol, an uptake, blocker, did not significantly modify KCl- and ES-induced vasoconstrictions, but significantly enhanced NE-induced responses; 3. (3) small doses of imipramine, a neuronal uptake, blocker, did not modify NE-induced vasoconstrictions, but large doses decreased them. On the other hand, the ES-induced response was slightly increased by a relative small dose of imipramine; 4. (4) cocaine, another uptake, blocker, slightly enhanced NE- and ES-induced responses; 5. (5) ES-induced response was reduced by not only diltiazem, but also Ca 2+-free solution with EGTA (1 m m l −1). The NE-induced response was not affected by diltiazem (Ohkubo and Chiba, 1987, Exp. Eye Res. 45, 263–270), and slightly but significantly depressed by Ca 2+-free solution with EGTA. These results suggest that tissue and neuronal uptake mechanisms exist in responses to ES and NE 1, the response to ES was markedly dependent on Ca 2+ influx to the cell membrane 2, and exogenous NE may induce Ca 2+ movement mainly from the intracellular store site.

Dose-Independent Pharmacokinetics of Fentanyl

Fentanyl is used as an analgesic in small doses (1-2 micrograms X kg-1) and as an anesthetic in very large doses (greater than 150 micrograms X kg-1). It has been demonstrated that the effects of fentanyl correlate with its concentrations in plasma. It is important, therefore, to know whether or not the pharmacokinetics of fentanyl vary with dose size in order to predict the plasma concentrations and effects produced by various dosage regiments. The authors studied the pharmacokinetics of fentanyl in dogs. 3H-fentanyl (2.5-640 micrograms X kg-1) was injected intravenously in dogs anesthetized at a stable level with enflurane-O2. Arterial plasma and urine were analyzed for unchanged 3H-fentanyl. Kinetic indices were derived by nonlinear least-squares analysis of log concentration of fentanyl in plasma (ng X ml-1) versus time after a bolus injection. The terminal elimination half-time (t 1/2 beta = 211 min), the apparent volume of distribution (9.5 l X kg-1), the volume of the central compartment (1.14 l X kg-1), and the clearance (37 ml X kg-1 X min-1) of fentanyl were independent of dose over the 6.4-640 micrograms X kg-1 dose range. The distribution volume and distribution half-times were lower for the 2.5 micrograms X kg-1 than for some of the larger doses; this was attributed to differences in experimental conditions. The authors conclude that the pharmacokinetics of fentanyl are dose independent certainly over the 6.4-640 micrograms X kg-1 dose range. There is no evidence of saturation of biotransformation or tissue uptake mechanisms for doses in the range of 2.5 to 640 micrograms X kg-1.

Dose-independent pharmacokinetics of fentanyl.

Fentanyl is used as an analgesic in small doses (1-2 micrograms X kg-1) and as an anesthetic in very large doses (greater than 150 micrograms X kg-1). It has been demonstrated that the effects of fentanyl correlate with its concentrations in plasma. It is important, therefore, to know whether or not the pharmacokinetics of fentanyl vary with dose size in order to predict the plasma concentrations and effects produced by various dosage regiments. The authors studied the pharmacokinetics of fentanyl in dogs. 3H-fentanyl (2.5-640 micrograms X kg-1) was injected intravenously in dogs anesthetized at a stable level with enflurane-O2. Arterial plasma and urine were analyzed for unchanged 3H-fentanyl. Kinetic indices were derived by nonlinear least-squares analysis of log concentration of fentanyl in plasma (ng X ml-1) versus time after a bolus injection. The terminal elimination half-time (t 1/2 beta = 211 min), the apparent volume of distribution (9.5 l X kg-1), the volume of the central compartment (1.14 l X kg-1), and the clearance (37 ml X kg-1 X min-1) of fentanyl were independent of dose over the 6.4-640 micrograms X kg-1 dose range. The distribution volume and distribution half-times were lower for the 2.5 micrograms X kg-1 than for some of the larger doses; this was attributed to differences in experimental conditions. The authors conclude that the pharmacokinetics of fentanyl are dose independent certainly over the 6.4-640 micrograms X kg-1 dose range. There is no evidence of saturation of biotransformation or tissue uptake mechanisms for doses in the range of 2.5 to 640 micrograms X kg-1.

Release of endogenous noradrenaline from an isolated elastic artery

1. The overflow of noradrenaline following field stimulation of vasoconstrictor nerves has been studied in isolated preparations of the guineapig thoracic aorta.2. Stimulation with trains of 3000 pulses at 5 and 25 pulses.s(-1) resulted in mean overflows of 0.15 and 0.17 (ng.g(-1)).pulse(-1) respectively.3. These overflows were not affected by pre-treatment of the aortae with the inhibitor of neuronal amine re-uptake desmethylimipramine (10(-5)M) or with the inhibitors of extraneuronal amine uptake metanephrine (5 x 10(-4)M) or desoxycorticosterone (2.5 x 10(-5)M).4. In contrast, inhibition of monoamine oxidase and catechol-O-methyl transferase with pargyline (1 x 10(-4)M) and tropolone (2.5 x 10(-4)M) caused the mean overflows to be increased to 0.27 and 0.31 (ng.g(-1)).pulse(-1) in response to stimulation at 5 and 25 pulses.s(-1) respectively. Inhibition of either enzyme alone had little effect.5. It is concluded that in the guinea-pig aorta nervously released noradrenaline is inactivated primarily by enzymic metabolism, while neural re-uptake is insignificant. This situation is the reverse of that existing in the uterine artery of the same species.6. Phenoxybenzamine (10(-5)M) also caused pronounced increases in overflow at both high and low frequencies of stimulation. This could be due to an effect of phenoxybenzamine on release of noradrenaline or on some tissue uptake mechanism distinct from the normal neuronal and extraneuronal pathways.7. Calculations based on the overflow at 5 pulses.s(-1) following total enzyme inhibition indicated that a single stimulating pulse liberated 2.1 x 10(-4) of the total transmitter store.