Plasma Concentration Rate Research Articles

Development and validation of a sensitive LC/MS/MS method for the determination of γ‐tocotrienol in rat plasma: application to pharmacokinetic studies

γ-Tocotrienol has attracted much attention owing to its multiple health benefits. This study developed and validated a simple, specific, sensitive and reliable LC/MS/MS method to analyze γ-tocotrienol in rat plasma. Plasma samples (50 μL) were extracted with internal standard solution (25 ng/mL of itraconazole) in acetonitrile (200 μL) with an average recovery of 44.7% and an average matrix effect of -2.9%. The separation of γ-tocotrienol and internal standard from the plasma components was achieved with a Waters XTerra® MS C(18) column with acetonitrile-water as mobile phase. Analysis was performed under positive ionization electrospray mass spectrometer via the multiple reaction monitoring. The standard curve was linear over a concentration range of 10-1000 ng/mL with correlation coefficient values >0.997. The method was validated with intra- and inter-day accuracy (relative error) ranging from 1.79 to 9.17% and from 2.16 to 9.66%, respectively, and precision (coefficient of variation) ranged from 1.94 to 9.25% and from 2.37 to 10.08%, respectively. Short-term stability, freeze-thaw stability and the processed sample stability tests were performed. This method was further applied to analyze γ-tocotrienol plasma concentrations in rats at various time points after administration of a 2 mg/kg single intravenous dose, and a pharmacokinetic profile was successfully obtained.

Effect of oral administration of glycyrrhetinic acid on six metal elements in rat serum

To determine glycyrrhetinic acid concentration in rat plasma and concentration of calcium (Ca), copper (Cu), iron (Fe), potassium (K), magnesium (Mg) and sodium (Na) in rat serum after oral administration by LC-MS/MS and the flame atomic absorption method, and analyze the effect of glycyrrhetinic acid on the six elements in serum. A similar variation trend between the concentration of glycyrrhetinic acid in plasma and that of Na, Cu elements in serum after oral administration of glycyrrhetinic acid was observed. Glycyrrhetinic acid in plasma at 2 h after administration reached the peak. Meanwhile, the concentration of Na and Cu at 4 h after the administration of glycyrrhetinic acid exhibited a significant increase (P < 0.05). Moreover, an increasing glycyrrhetinic acid dosage could result in the accumulation of Cu and Na in rat serum. Compared with the control group, the concentration of Cu and Na in the the glycyrrhetinic acid administration group with doses of 200 and 400 mg x kg(-1) revealed a significant increase (P < 0.05). However, glycyrrhetinic acid did not exhibit the great impact on the concentration of other elements in serum. This study focuses on the effect of oral administration of glycyrrhetinic acid on six metal elements in rat serum and provides an experimental basis for the adverse effect of glycyrrhetinic acid in clinical-applications.

Determination of a novel TAZ modulator, 2-butyl-5-methyl-6-(pyridine-3-yl)-3-[2′-(1H-tetrazole-5-yl)-biphenyl-4-ylmethyl]-3H imidazo[4,5-b]pyridine] (TM-25659) in rat plasma by liquid chromatography–tandem mass spectrometry

TM-25659 compound, a novel TAZ modulator, is developed for the control of bone loss and obesity. TAZ is known to bind to a variety of transcription factors to control cell differentiation and organ development. A selective and sensitive method was developed for the determination of TM-25659 concentrations in rat plasma. The drug was measured by liquid chromatography-tandem mass spectrometry after liquid-liquid extraction with ethyl acetate. TM-25659 and the internal standard imipramine were separated on a Hypersil GOLD C18 column with a mixture of acetonitrile-ammonium formate (10 mM) (90:10, v/v) as the mobile phase. The ions m/z 501.2→207.2 for TM-25659 and m/z 281.0→86.0 for imipramine in multiple reaction monitoring mode were used for the quantitation. The calibration range was 0.1-100 μg/ml with a correlation coefficient greater than 0.99. The lower limit of quantitation of TM-25659 in rat plasma was 0.1 μg/ml. The percent recoveries of TM-25659 and imipramine were 98.6% and 95.7% from rat plasma, respectively. The intra- and inter-batch precisions were 3.17-15.95% and the relative error was 0.38-10.82%. The developed assay was successfully applied to a pharmacokinetic study of TM-25659 administered intravenously (10 mg/kg) to rats.

Metabolism and Pharmacokinetic Study of Ardipusilloside I in Rats

Ardipusilloside I, extracted from ARDISIA PUSILLA A.DC, effectively inhibits the progression of several cancers in animal models and is a potential anti-cancer drug candidate. However, the metabolism and pharmacokinetic characteristics of ardipusilloside I remain unknown. In this study, we developed a highly sensitive liquid chromatography-tandem MS method to determine the ardipusilloside I concentration in rat plasma using ginsenoside Re (whose structure is similar to ardipusilloside I) as the internal standard. After oral administration of ardipusilloside I, its four possible metabolites (M1, M2, M3, and M4, whose structures were determined by MS) were detected in the content from rat small intestine. In rat plasma, however, only M3 and M4 were detected after oral administration of ardipusilloside I. None of the metabolites were detected in plasma samples after intravenous administration of ardipusilloside I to rats. These results indicated that the metabolites, but not the drug itself, were absorbed into plasma after oral administration of ardipusilloside I to rats and that M3 and M4 may be responsible for the antitumor activity of orally administered ardipusilloside I in rat models of cancer.

Determination of aripiprazole in rat plasma and brain using ultra‐performance liquid chromatography/electrospray ionization tandem mass spectrometry

Aripiprazole is an important antipsychotic drug. A simple, sensitive and rapid ultra-performance liquid chromatography/electrospray ionization tandem mass spectrometry (UPLC-ESI-MS/MS) method was developed and validated for the simultaneous quantification of this compound in rat plasma and brain homogenate. The analyte was extracted from rat plasma and brain homogenate using a weak cation exchange mixed-mode resin-based solid phase extraction. The compound was separated on an Agilent Eclipse Plus C(18) (2.1 × 50 mm, 1.8 µm) column using a mobile phase of (A) 0.1% formic acid aqueous and (B) acetonitrile with gradient elution. The analyte was detected in positive ion mode using multiple reaction monitoring. The method was validated and the specificity, linearity, limit of quantitation (LOQ), precision, accuracy, recoveries and stability were determined. The LOQ was 0.5 ng/mL for aripiprazole in plasma and 1.5 ng/g in brain tissue. The MS response was linear over the concentration range 0.5-100 ng/mL for aripiprazole in plasma and 1.5-300 ng/g in brain tissue. The precision and accuracy for intra-day and inter-day were better than 14%. The relative and absolute recoveries were above 72% and the matrix effects were low. This validated method was successfully used to quantify the rat plasma and brain tissue concentrations of the analyte following chronic treatment with aripiprazole.

Pharmacokinetics of Cimifugin in Rat Plasma after Oral Administration of the Extract of Saposhnikovia divaricatae Root

High performance liquid chromatography (HPLC) coupled with the solid phase extraction method was developed for determining cimifugin (a coumarin derivative; one of Saposhnikovia divaricatae's constituents) in rat plasma after oral administration of Saposhnikovia divaricatae extract (SDE), and the pharmacokinetics of cimifugin either in SDE or as a single compound was investigated. The HPLC analysis was performed on a commercially available column (4.6 mm x 200 mm, 5 pm) with the isocratic elution of solvent A (Methanol) and solvent B (Water) (A:B=60:40) and the detection wavelength was set at 250 nm. The calibration curve was linear over the range of 0.100-10.040 microg/mL. The limit of detection was 30 ng/mL. At the rat plasma concentrations of 0.402, 4.016, 10.040 microg/mL, the intra-day precision was 6.21%, 3.98%, and 2.23%; the inter-day precision was 7.59%, 4.26%, and 2.09%, respectively. The absolute recovery was 76.58%, 76.61%, and 77.67%, respectively. When the dosage of SDE was equal to the pure compound calculated by the amount of cimifugin, it was found to have two maximum peaks while the pure compound only showed one peak in the plasma concentration-time curve. The pharmacokinetic characteristics of SDE showed the superiority of the extract and the properties of traditional Chinese medicine.

Development and validation of a liquid chromatography–tandem mass spectrometric method for the quantification of 5-thio-d-glucose in rat and human plasma

A highly selective, sensitive, and robust liquid chromatography–tandem mass spectrometric method for the determination of 5-thio-d-glucose concentrations in rat and human plasma was developed and validated. The sample preparation procedure involved protein precipitation and solid phase extraction, which efficiently removed sources of interference present in the plasma. Chromatographic separation was obtained using an NH2-column with distilled water and acetonitrile as the mobile phase under gradient conditions. Detection was performed using tandem mass spectrometry equipped with an electrospray ionization interface in negative ion mode. The selected reaction monitoring (SRM) transitions for 5-thio-d-glucose and an internal standard (5-thio-d-glucose-13C6) were m/z 195→m/z 105 and m/z 201→m/z 108, respectively. The correlation coefficients of the calibration curves ranged from 0.9997 to 0.9999 over a concentration range from 10 to 3000ng/mL plasma. The validated method was successfully applied to a pharmacokinetic study in rats.

Determination of strontium in rat plasma and plasma ultrafiltrate by Zeeman Furnace atomic absorption spectroscopy and its application to a pharmacokinetic study

A rapid and sensitive analytical assay for the determination of total strontium concentrations in rat plasma was developed and validated. The total strontium levels were determined by use of graphitefurnace atomic-absorption spectrometry (GF-AAS) with Zeeman correction, 1000°Ci n ashing temperatures and 2700°C in atomization temperatures after 3.5% HNO 3 protein precipitation. The accuracy was between 95.46 and 102.24% (intra-day variation), and 101.74 and 102.15% (inter-day variation). The precision was between 1.86 and 8.24% (intra-day variation), and 1.27 and 11.20% (interday variation). Linear calibration curves were obtained over the concentration range 0.2 to 10 μg/ml(r = 0.9993). Validation data were within the acceptable limits for analytical methods. This assay was successfully applied to evaluate the pharmacokinetics of strontium fructose 1, 6-diphosphate (Sr-FDP), a new compound in rats and free strontium after plasma ultrafiltrate was also performed by direct determination. Significantly different pharmacokinetics between total and free strontium were observed that provided more information for the pharmacokinetic study of Sr-FDP. Key words : Graphite furnace atomic-absorption spectrometry (GFAAS), strontium fructose 1, 6-diphosphate, strontium, ultrafiltrate, anti-osteoporosis.

Anticancer activity of an extract from needles and twigs of Taxus cuspidata and its synergistic effect as a cocktail with 5-fluorouracil

BackgroundBotanical medicines are increasingly combined with chemotherapeutics as anticancer drug cocktails. This study aimed to assess the chemotherapeutic potential of an extract of Taxus cuspidata (TC) needles and twigs produced by artificial cuttage and its co-effects as a cocktail with 5-fluorouracil (5-FU).MethodsComponents of TC extract were identified by HPLC fingerprinting. Cytotoxicity analysis was performed by MTT assay or ATP assay. Apoptosis studies were analyzed by H & E, PI, TUNEL staining, as well as Annexin V/PI assay. Cell cycle analysis was performed by flow cytometry. 5-FU concentrations in rat plasma were determined by HPLC and the pharmacokinetic parameters were estimated using 3p87 software. Synergistic efficacy was subjected to median effect analysis with the mutually nonexclusive model using Calcusyn1 software. The significance of differences between values was estimated by using a one-way ANOVA.ResultsTC extract reached inhibition rates of 70-90% in different human cancer cell lines (HL-60, BGC-823, KB, Bel-7402, and HeLa) but only 5-7% in normal mouse T/B lymphocytes, demonstrating the broad-spectrum anticancer activity and low toxicity to normal cells of TC extract in vitro. TC extract inhibited cancer cell growth by inducing apoptosis and G2/M cell cycle arrest. Most interestingly, TC extract and 5-FU, combined as a cocktail, synergistically inhibited the growth of cancer cells in vitro, with Combination Index values (CI) ranging from 0.90 to 0.26 at different effect levels from IC50 to IC90 in MCF-7 cells, CI ranging from 0.93 to 0.13 for IC40 to IC90 in PC-3M-1E8 cells, and CI < 1 in A549 cells. In addition, the cocktail had lower cytotoxicity in normal human cell (HEL) than 5-FU used alone. Furthermore, TC extract did not affect the pharmacokinetics of 5-FU in rats.ConclusionsThe combinational use of the TC extract with 5-FU displays strong cytotoxic synergy in cancer cells and low cytotoxicity in normal cells. These findings suggest that this cocktail may have a potential role in cancer treatment.

VALIDATION OF A RAPID AND SIMPLE LC-MS/MS METHOD TO DETERMINE TRIMETAZIDINE IN RAT PLASMA

A rapid, simple, and sensitive LC-MS/MS method was developed and validated for the determination of trimetazidine in rat plasma, using lidocaine as the internal standard (IS). The chromatographic separation was accomplished on a Atlantis dC18 column (150 × 2.1 mm, 5 µm) with the mobile phase consisting of acetonitrile and 10 mM ammonium formate (3:7, v/v) (pH 3.05, adjusted with formic acid). Plasma samples were deproteined with acetonitrile (1:3) and 3 μL of the supernatant was injected into the system. The retention times of trimetazidine and IS were approximately 1.45 min and 2.10 min, respectively. Calibration curves were linear over the concentration range of 0.5–500 ng/mL (1000 fold). The intra- and inter-batch precision, accuracy, and the relative standard deviation were all <15%. This method was successfully applied to determine trimetazidine concentrations in rat plasma.

Study on pharmacokinetics of borneol in rats injected with novel-Xingnaojing by GC-FID

To develop a GC-FID method for the determination of borneol concentration in rat plasma and to investigate the pharmacokinetics after injection of novel-Xingnaojing. Novel-Xingnaojing was injected via by caudal vein injection. The blood samples were collected by posterior orbital venous plexus approach at 0.5, 1, 3, 5, 8, 12, 20, 30, 45 min. The drug in plasma was extracted with ethyl acetate and then detected by GC-FID, octadecane was used as the internal standard. The pharmacokinetic parameters were calculated by the software of Kinetica. The calibration curve was good linear in the range of 1.67-16.67 mg x L(-1). The extraction recoveries of low, medium and high concentration were (92.81 +/- 1.11)%, (85.38 +/- 0.86)% and (84.58 +/- 0.58)%, respectivley. And the RSDs of within-day and between-day were below 3.00%. Plasma concentration of borneol was consistent with the two-compartment open model. The pharmacokinetic parameters were that the t1/2alpha was (1.18 +/- 0.20) min, the t1/2beta was (22.27 +/- 6.85) min, the C(max)(Calc) was (18.76 +/- 2.10) mg x L(-1), the MRT was (23.84 +/- 7.67) min(-1), and the AUC was (100.00 +/- 15.85) mg x min x L(-1). The GC-FID method developed can be applied to determination and pharmacokinetics. The borneol in novel-Xingnaojing is distributed and metabolized fast after being administrated.

4-Methylmethcathinone (Mephedrone): Neuropharmacological Effects of a Designer Stimulant of Abuse

The designer stimulant 4-methylmethcathinone (mephedrone) is among the most popular of the derivatives of the naturally occurring psychostimulant cathinone. Mephedrone has been readily available for legal purchase both online and in some stores and has been promoted by aggressive Web-based marketing. Its abuse in many countries, including the United States, is a serious public health concern. Owing largely to its recent emergence, there are no formal pharmacodynamic or pharmacokinetic studies of mephedrone. Accordingly, the purpose of this study was to evaluate effects of this agent in a rat model. Results revealed that, similar to methylenedioxymethamphetamine, methamphetamine, and methcathinone, repeated mephedrone injections (4× 10 or 25 mg/kg s.c. per injection, 2-h intervals, administered in a pattern used frequently to mimic psychostimulant "binge" treatment) cause a rapid decrease in striatal dopamine (DA) and hippocampal serotonin (5-hydroxytryptamine; 5HT) transporter function. Mephedrone also inhibited both synaptosomal DA and 5HT uptake. Like methylenedioxymethamphetamine, but unlike methamphetamine or methcathinone, repeated mephedrone administrations also caused persistent serotonergic, but not dopaminergic, deficits. However, mephedrone caused DA release from a striatal suspension approaching that of methamphetamine and was self-administered by rodents. A method was developed to assess mephedrone concentrations in rat brain and plasma, and mephedrone levels were determined 1 h after a binge treatment. These data demonstrate that mephedrone has a unique pharmacological profile with both abuse liability and neurotoxic potential.

Simple, Sensitive, High-Throughput Method for the Quantification of Mitragynine in Rat Plasma Using UPLC-MS and Its Application to an Intravenous Pharmacokinetic Study

A simple, sensitive and rapid ultra-performance liquid chromatography-mass spectrometry (UPLC-MS) method was developed and validated for the quantification of mitragynine in rat plasma using amitriptyline hydrochloride as an internal standard. Sample preparation involved a one-step liquid–liquid extraction using methyl t-butyl ether. Mitragynine was separated on an Acquity UPLC™ BEH HILIC column using isocratic elution with a mobile phase of 10 mM ammonium formate buffer containing 0.1% formic acid:acetonitrile (15:85, v/v). At a flow rate of 0.2 mL min−1, the retention time of mitragynine was found to be 1.3 min. Ionization was performed in the positive ion electrospray mode. The selected mass-to-charge (m/z) ratio transition of mitragynine ion [M + H]+ used in the selected ion recording (SIR) was 399.1. The calibration curve was found to be linear over a concentration range of 1–5,000 ng mL−1 (r = 0.999) with a lower limit of quantification (LLOQ) of 1 ng mL−1. Intra- and inter-day assay variations were found to be less than 15%. The extraction recoveries ranged from 85–93% at the three concentrations (2, 400 and 4,000 ng mL−1) in rat plasma. This method was successfully used to quantify mitragynine in rat plasma following intravenous administration of the compound.

Pharmacological Blockade of Serotonin 5-HT7 Receptor Reverses Working Memory Deficits in Rats by Normalizing Cortical Glutamate Neurotransmission

The role of 5-HT7 receptor has been demonstrated in various animal models of mood disorders; however its function in cognition remains largely speculative. This study evaluates the effects of SB-269970, a selective 5-HT7 antagonist, in a translational model of working memory deficit and investigates whether it modulates cortical glutamate and/or dopamine neurotransmission in rats. The effect of SB-269970 was evaluated in the delayed non-matching to position task alone or in combination with MK-801, a non-competitive NMDA receptor antagonist, and, in separate experiments, with scopolamine, a non-selective muscarinic antagonist. SB-269970 (10 mg/kg) significantly reversed the deficits induced by MK-801 (0.1 mg/kg) but augmented the deficit induced by scopolamine (0.06 mg/kg). The ability of SB-269970 to modulate MK-801-induced glutamate and dopamine extracellular levels was separately evaluated using biosensor technology and microdialysis in the prefrontal cortex of freely moving rats. SB-269970 normalized MK-801 -induced glutamate but not dopamine extracellular levels in the prefrontal cortex. Rat plasma and brain concentrations of MK-801 were not affected by co-administration of SB-269970, arguing for a pharmacodynamic rather than a pharmacokinetic mechanism. These results indicate that 5-HT7 receptor antagonists might reverse cognitive deficits associated with NMDA receptor hypofunction by selectively normalizing glutamatergic neurotransmission.

Perturbation of Mitosis through Inhibition of Histone Acetyltransferases: The Key to Ochratoxin A Toxicity and Carcinogenicity?

Ochratoxin A (OTA) is one of the most potent rodent renal carcinogens studied to date. Although controversial results regarding OTA genotoxicity have been published, it is now widely accepted that OTA is not a mutagenic, DNA-reactive carcinogen. Instead, increasing evidence from both in vivo and in vitro studies suggests that OTA may promote genomic instability and tumorigenesis through interference with cell division. The aim of the present study was to provide further support for disruption of mitosis as a key event in OTA toxicity and to understand how OTA mediates these effects. Immortalized human kidney epithelial cells (IHKE) were treated with OTA and monitored by differential interference contrast microscopy for 15 h. Image analysis confirmed that OTA at concentrations ≥ 5 μM, which correlate with plasma concentrations in rats under conditions of carcinogenesis, causes sustained mitotic arrest and exit from mitosis without nuclear or cellular division. Mitotic chromosomes were characterized by aberrant condensation and premature sister chromatid separation associated with altered phosphorylation and acetylation of core histones. To test if OTA directly interferes with histone acetyltransferases (HATs) which regulate lysine acetylation of histones and nonhistone proteins, a cell-free HAT activity assay was conducted using total nuclear extracts of IHKE cells. In this assay, OTA significantly blocked HAT activity in a concentration-dependent manner Overall, results from this study provide further support for a mechanism of OTA carcinogenicity involving interference with the mitotic machinery and suggest HATs as a primary cellular target of OTA.

Pharmacokinetics of verapamil in diabetic rats induced by combination of high-fat diet and streptozotocin injection

The aim of this study was to investigate effects of type 2 diabetes on the pharmacokinetics of verapamil after intravenous administration.Diabetes mellitus (DM) rats were induced by combination of high-fat diet (HFD) and streptozotocin. Plasma concentrations of verapamil in DM rats, rats fed with HFD, and control (CON) rats were measured after intravenous administration of 1 mg/kg verapamil and corresponding pharmacokinetic parameters were estimated. Area under the plasma concentration in DM rats was significantly smaller than that in CON rats.In vitro microsomal study showed that intrinsic clearance of verapamil in DM rats was significantly higher than those in CON rats. Compared to CON rats, higher intrinsic clearance was also observed in HFD rats. Western blot results demonstrated higher levels of CYP3A2 in DM and HFD rats, which was in line to activity of CYP3A.All the results gave a conclusion that diabetes may enhance metabolism of verapamil in rat, and the enhancement may partly result from induction of CYP3A.

Abstract 2599: RP3035, a potent cytostatic anti-cancer agent, reduces NCI-H460 tumor growth in mice via inhibition of Orai1

Abstract Background: Non-small cell lung cancer (NSCLC) is the most prevalent form of lung cancer and is one of the leading causes of cancer-related mortality across the globe. Majority of the NSCLC are characterized by the presence of ras mutation thereby rendering the subject relatively insensitive to treatment by known kinase inhibitors. Current treatment regimes for NSCLC are therefore limited to cytotoxic drugs besides surgery and radiation therapy. Herein, we describe the pharmacological profile of RP3035, a novel and potent cytostatic agent that inhibits tumor growth in xenograft models via a Calcium Release Activated Calcium (CRAC) channel pathway. Methods: Inhibition of thapsigargin induced calcium influx into Fluo-8 loaded NCI-H460 cells was determined fluorometrically. Viability assay (MTT) was conducted to determine the growth inhibitory effect of the compound on NCI-H460, a NSCLC cell line. Lactate dehydrogenase (LDH) release into the medium was determined colorimetrically. In vivo efficacy of the compound was determined using a mouse NCI-H460 xenograft model. Briefly, Balb/c mice were inoculated with NCI-H460 cells to induce tumor growth. Animals were treated with 30 mg/kg/po RP3035 BID for 15 d. Total RNA was extracted from tumors and evaluated for Orai1 expression by Real-Time PCR. Metabolic stability of the compound was evaluated in microsomes. Pharmacokinetic behaviour of RP3035 in plasma after single dose oral administration or IV injection was determined in female Balb/c mice and male Wistar rats. Results: RP3035 demonstrated remarkable potency at inhibiting thapsigargin-induced calcium influx into NCI-H460 cells (IC50 = 66.4 nM). Growth inhibition studies indicated that the compound suppressed proliferation in NCI-H460 cells with IC50 values of 230.4 nM without any noticeable cytotoxicity even at the highest dose. Xenograft studies, representative of NSCLC, demonstrated that RP3035 inhibited tumor growth by 42%, comparable with the reduction observed with paclitaxel. Real-time expression analysis revealed &amp;gt;90% reduction in Orai1 mRNA implicating its role in NSCLC progression and growth. Pharmacokinetic studies indicated good oral bioavailability of RP3035 with a favourable half-life and peak plasma concentrations in mouse and rat. Further, RP3035 was metabolically stable across species studied besides showing no significant CYP inhibition in human liver microsomes. Conclusions: Results demonstrate the efficacy and therapeutic potential of RP3035 in NCSLC. Targeting NSCLC through inhibition of Orai1 represents a novel approach primarily aimed at bypassing the resistance due to ras mutations besides alleviating the deleterious effects associated with cytotoxic agents. Dose-response studies for RP3035 are currently underway in NSCLC xenograft models. Besides lung cancer, studies are planned to test the efficacy of the compound in various other cancers as well. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2599. doi:10.1158/1538-7445.AM2011-2599

A comparison of the effects on blood glucose and ketone-body levels, and of the toxicities, of pent-4-enoic acid and four simple fatty acids.

Abstract Some effects of the hypoglycaemic compound pent-4-enoic acid in rats and mice, are described. Pent-2-enoic acid, pentanoic acid, cyclopropanecarboxylic acid and cyclobutanecarboxylic acid, which were shown to be non-hypoglycaemic, were used as controls. Pent-4-enoic acid and cyclopropanecarboxylic acid caused ketosis in rats, with a lowering of the blood β-hydroxybutyrate/acetocetate (βHB/AcAc) ratio; some ketosis was caused by the other fatty acids but the βHB/AcAc ratio was not changed. Pent-4-enoic acid caused an increase in free fatty acid concentration in rat plasma. The acute toxicities of these compounds in mice were determined. The mechanism of the hypoglycaemic action of pent-4-enoic acid is discussed in relation to that of hypoglycin.

Dependency of salivary excretion of mexiletine on the plasma concentration in rats.

The effect of steady-state plasma concentrations on the salivary excretion of mexiletine was investigated following simultaneous bolus intravenous injection of the loading dose (2.7 or 16.1 mg kg-1) and constant-rate intravenous infusion of the maintenance dose (15 or 102 micrograms min-1 kg-1) in male Wistar rats. Parotid and mandibular saliva was collected separately by stimulating salivation with a constant-rate infusion of pilocarpine (50 micrograms kg-1 min-1) in each rat. The low and high steady-state levels of mexiletine in blood plasma were attained at 0.259 +/- 0.123 and 1.616 +/- 0.475 micrograms mL-1, respectively, within the first 1-2 h after drug administration. Similarly, the two different steady-states in both parotid and mandibular saliva were attained. Although the mexiletine levels in both types of saliva were lower than that in plasma, the drug level in parotid saliva was always higher than that in mandibular saliva at any steady-state (P < 0.001 or 0.01). In parotid saliva, the high steady-state produced greater saliva to plasma drug concentration ratios (S/P ratio, 0.475 +/- 0.160) than that (0.386 +/- 0.131) at the low steady-state (P < 0.05). The S/P ratio for mandibular saliva at the high (0.204 +/- 0.060) steady-state was also greater than that at the low (0.158 +/- 0.050) steady-state (P < 0.01). These changes in the S/P ratio could not be explained by the pH for either parotid or mandibular saliva, but partially by the change in the unbound fraction of the drug which tended to be consistent with that in the ratio for both salivary glands. These findings suggest that the salivary excretion of mexiletine may be dependent on the plasma unbound concentration in rats.

Tissue and blood concentrations of chloroquine following chronic administration in the rat.

The antimalarial drug, chloroquine, is extensively distributed in tissue and slowly eliminated such that after a single dose, a plasma half-life of 3-5 days has been found (McChesney & McAuliff 1961; McChesney et al 1967). A peak tissue/plasma concentration ratio greater than 300 is obtained in many tissues and after a single dose the drug can be found in the liver and urine for up to five years (Gaudette & Coatney 1961; Rubin et al 1963; Zvaifler et al 1963). Chronic administration of chloroquine for the treatment of rheumatoid arthritis has revealed an ocular toxicity due to accumulation of the drug in the pigmented layers of the eye, particularly the choroid (Fuld & Horwish 1958; Fuld 1959). A more recent indication for chronic administration of chloroquine is in the prophylaxis of malaria, for which the drug is administered at a dose of 300-600 mg weekly to adults. The long term toxic effects of chloroquine when administered in this way are unknown but no ocular toxicity has been reported even after five years of such use. Since tissue toxicity and other untoward effects are largely determined by tissue stores (Fuld & Horwish 1958; Fuld 1959) and blood levels (Laaksonen et al 1974; Frisk-Holmberg et al 1979) of the drug, it is useful to know the changes occurring in tissue and plasma concentrations during chronic administration. Previous studies in animals have given conflicting results. McChesney et al (1965) found a steady increase in the tissue and plasma concentrations in rats throughout a 3-month period although the increase was fastest in the first month. Grundmann et al (1972) found that most rat tissues were saturated with chloroquine between the 10th and the 16th weeks. Plasma concentrations were not measured hence the effect of tissue saturation on blood levels was not determined, yet saturation of tissue stores would be expected to lead to a rapid increase in plasma concentration that could affect the pattern and incidence of adverse reactions to the drug. We have reinvestigated the uptake of chloroquine by rat tissues during chronic administration of the drug and in particular to relate the tissue levels to plasma concentrations.