Separation of some fatty ointment excipients by gradient elution HPTLC

A very simple gradient elutionTlc system for the separation of some common fatty excipients of rather varying polarities in one run is presented. WhenHptlc precoated plates are used, run times are as short as 10 minutes. The system is useful as a simple quality control for fatty excipients, ointment bases and complete ointments.     

Analysis of creams

A standard procedure, consisting of twotlc systems, for the qualitative control of creams is presented. All common cream excipients, except those of very high polarity, are separated in a simple gradient elution system, using diethyl ether as the eluent in a chromatographic chamber saturated withn-pentane. The very polar cream base components are separated usingn-butanol-glacial acetic acid-water (20+2+5) as the eluent. The chromatographic behaviour of common cream excipients as well as threefna cream bases and four commercial cream bases is discussed.     

Triterpenoid saponins from the root of Anemone tomentosa

Three new triterpenoid saponins, tomentoside A (1), B (2) and C (3), along with four known saponins (4?C7) were isolated from the root of Anemone tomentosa. The structures of the new compounds were elucidated as 3-O-??-d-ribopyranosyl-(1??3)-??-l-rhamnopyranosyl-(1??2)-[??-d-glucopyranosyl-(1??4)]-??-l-arabinopyranosyl hederagenin 28-O-??-l-rhamnopyranosyl-(1??4)-??-d-glucopyranosyl-(1??6)-??-d-glucopyranoside (1), 3-O-??-d-ribopyranosyl-(1??3)-??-l-rhamnopyranosyl-(1??2)-[??-d-glucopyranosyl-(1??4)]-??-d-xylopyranosyl hederagenin 28-O-??-l-rhamnopyranosyl-(1??4)-??-d-glucopyranosyl-(1??6)-??-d-glucopyranoside (2) and 3-O-??-d-galactopyranosyl-(1??3)-??-l-rhamnopyranosyl-(1??2)-??-d-xylopyranosyl oleanolic acid 28-O-??-l-rhamnopyranosyl-(1??4)-??-d-glucopyranosyl-(1??6)-??-d-glucopyranoside (3) on the basis of chemical and spectral evidence. In the oligosaccharide chains of compound 3, the characteristic d-galactose residue is a rare structural feature and secondly encountered among triterpenoid saponins from Anemone.     

(−)-Catechin glycosides from Ulmus davidiana

Extensive chromatographic separation of the n-BuOH soluble fraction obtained from the stem and root barks of U. davidiana resulted in five hitherto unknown compounds together with a known one (?)-catechin 1. Structures of the five compounds were elucidated by chemical and spectroscopic analyses, to be (?)-catechin-7-O-gallate-5-O-(5″″-trans-caffeoyl)-β-d-apiofuranoside-3-O-β-d-apiofuranosyl-(1 → 2)-β-d-glucopyranoside 2, (?)-catechin-7-O-gallate-5-O-(5″″-trans-caffeoyl)-β-d-apiofuranoside-3-O-β-d-glucopyranoside 3, (?)-catechin-7-O-gallate-5-O-β-d-apiofuranoside-3-O-(2″-O-galloyl)-β-d-glucopyranoside 4, (?)-catechin-7-O-gallate-5-O-(5″″-trans-caffeoyl)-β-d-apiofuranoside 5, and (?)-catechin-7-O-gallate-5-O-(5″″-trans-feruloyl)-β-d-apiofuranoside 6.     

Correlations between phototoxicity of some 7-chloro-I,4-benzodiazepines and their (photo)chemical properties

In relation to the phototoxicity of 7-chloro-1,4-benzodiazepine-N-oxides the photostability of some of theseN-oxides and the thermostability of their photoproducts, the oxaziridines, were studied. Rather than a consequence of a direct phototoxic effect by theN-oxides the ultimate toxic effect in the test systemSalmonella typhimurium appeared to be caused by products formed during and after the irradiation. For chlordiazepoxide (Cdz) and its main metabolites in man desmethylchlordiazepoxide (Des) and demoxepam (Dem) the formation of an oxaziridine is indeed a crucial factor for the onset of the toxic effect. However,Dem oxaziridine (Dem Ox.) being very thermolabile in protic medium forms non-toxic conjugates with the solvent,Cdz Ox. andDes Ox. are thermally converted into theirN-oxide, althoughDes Ox. partly decomposes into 6-chloro-4-phenylquinazoline-2-carboxaldehyde as well. This compound proved to be an important factor in the toxic action ofDes after irradiation.     

Analysis of creams

The uv absorbing properties of the components of the cream bases as described in the Formulary of the Dutch Pharmacists were investigated. Directuv spectrophotometric determinations without any clean-up steps appeared to be possible for a number of drugs (e.g. tripelennamine HCl, tretinoin, salicylic acid, methyl salicylate, resorcinol, clioquinol), with the help of a solvent mixture in which the cream samples dissolved completely to yield clear solutions. Correcting for the contribution to theuv absorbance by the preservative is sometimes necessary and can be achieved by measuring the absorbance at two wavelengths. The determination of chlorhexidine, as an example of a basic drug withuv absorbing properties which prevent direct measurements of the solution of the cream samples, could be achieved after removal of the interfering compounds by a simple liquid-liquid extraction.     

A novel saponin from Manilkara hexandra seeds and anti-inflammatory activity

Chromatographic separation of acetone precipitate of the seeds of Manilkara hexandra has resulted in a novel saponin, 3-O-(β-d-apiofuranosyl-(1 → 3)-β-d-glucopyranosyl)-28-O-(α-l-rhamnopyranosyl(1 → 3)-β-d-xylopyranosyl(1 → 4)-α-l-rhamnopyranosyl(1 → 2)-α-l-arabinopyranosyl)-16-α-hydroxyprotobassic acid (Saponin 3), together with two known saponins isolated for the first time from the family Sapotaceae, viz, 3-O-β-d-glucopyranosyl(1 → 6)[(β-d-apiofuranosyl-(1 → 3)]-β-d-glucopyranosyl)-28-O-(α-l-rhamnopyranosyl(1 → 3)-β-d-xylopyranosyl(1 → 4)-α-l-rhamnopyranosyl(1 → 2)-α-l-arabinopyranosyl)-16α-hydroxyprotobassic acid (Saponin 1), 3-O-(β-d-glucopyranosyl)-28-O-(α-l-rhamnopyranosyl(1 → 3)-β-d-xylopyranosyl(1 → 4)-α-l-rhamnopyranosyl(1 → 2)-α-l-arabinopyranosyl)-protobassic acid, and 3-O-(β-d-glucopyranosyl)-28-O-(α-l-rhamnopyranosyl(1 → 3)-β-d-xylopyranosyl(1 → 4)-α-l-rhamnopyranosyl(1 → 2)-α-l-arabinopyranosyl)-protobassic acid (Saponin 2). Also, three known phenolic compounds were isolated for the first time from the species hexandra, viz, gallic acid, myrecetin, and quercetin. The chemical structures of the isolated saponin compounds were established by spectral techniques (UV, ¹H, ¹³C NMR, and MS). The acetone fraction containing the crude saponin mixture possessed a significant inhibitory effect on LPS-induced nitric oxide to the extent of 60 % compared to the LPS-stimulated cells and to the extent of 20 % compared to the control level showing significant anti-inflammatory activity. Acetone and MeOH seed extracts as well as the crude saponin fraction of M. hexandra showed no antioxidant activity as measured by DPPH assay (SC₅₀ = 217.65, 496.68, and 562.38 μg/ml, respectively) compared to that of ascorbic acid (SC₅₀ = 12.9). The MeOH seed extract showed no cytotoxic activity against three different human cancer cell lines, viz, colon carcinoma (HCT-116), hepatocellular carcinoma (Hep-G2), and breast adenocarcinoma (MCF-7), estimated by MTT assay (IC₅₀ = 95.20, 73.39, and 79.15 μg/ml, respectively).     

The release of endogenous dopamine and its metabolites from rat striatum as detected in push-pull perfusates: effects of systemically administered drugs

The release of dopamine (Da) and its metabolites 3,4-dihydroxyphenylacetic acid (Dopac) and homovanillic acid (Hva) was determined in push-pull perfusates from the striatum of the anaesthetized rat with high pressure liquid chromatography and electrochemical detection. Striking differences were found between the released amounts ofDa (less than 7 fmol/min) and those of the metabolites (approx 0.5 pmol/min). It was calculated that 5% of theDa metabolites left the striatum via the push-pull cannula. The effects of systemic application of apomorphine, (+)-amphetamine, haloperidol or haloperidol in combination with amfonelic acid on the release ofDa and its metabolites, were investigated. The release rate ofDopac correlated well with the drug-induced changes of these metabolites in striatal tissue, however, this was not the case forHva. The increase of striatal levels ofDopac andHva induced by the anaesthesia is a serious limitation of the method. To enable reliable estimation of the release ofDa, 1μM (+)-amphetamine had to be added to the perfusion medium (which may have modified the origin ofDopac andHva in the perfusates). (+)-Amphetamine (5 mg/kg, intravenous) induced a two- to threefold increase in the release ofDa. Systemic administration of apomorphine, haloperidol or haloperidol in combination with amfonelic acid did not change the output of the neurotransmitter in the push-pull cannula. This implies that neuroleptics cause only a small and transient rise inDa release, whereas the pronounced and persisting increase inDopac andHva seen after neuroleptics is the result of enhanced metabolism related to increased synthesis ofda.     

Evaluation of antioxidant activity of new constituents from the fruits of Lycium chinense

Two new compounds as labd-7,11-dien-3β, 13α-diol-3α-l-arabinopyranosyl-(2a → 1b)-α-l-arabinopyranosyl-(2b → 1c)-α-l-arabinopyranosyl-(2c → 1d)-α-l-arabinopyranosyl-(2d → 1e)-α-l-arabinopyranosyl-(2e → 1f)-α-l-arabinopyranosyl-(2f → 1g)-α-l-arabinopyranoside (1), and 5 (6), 11 (12), 15 (15′), 5′ (6′), 11′ (12′)-decadehydro-β-carotenyl-4β,4′β-diol-4-α-l-arabinopyranosyl-(2a → 1b)-α-l-arabinopyranosyl-(2b → 1c)-α-l-arabinopyranosyl-(2c → 1d)-β-l-arabinopyranosido-4′-α-l-arabinopyranosyl-(2e → 1f)-α-l-arabinopyranosyl-(2f → 1g)-α-l-arabinopyranosyl-(2g → 1h)-α-l-arabinopyranosyl-(2h → 1i)-β-l-arabinopyranoside (2) along with known compound have been isolated from the methanol extract of fruits of Lycium chinense. Their chemical structures were established with the help of physical, chemical, and spectroscopic methods. The compounds 1 and 2 were investigated for scavenging of the diphenylpicrylhydrazyl (DPPH) radical scavenging activity, reducing power, and the phosphomolybdenum activity, and the results demonstrate that the compound (1) has potential as a natural antioxidant whereas the compound (2) exhibited moderate antioxidant activity.     

New cycloartane glycosides from the aerial part of Thalictrum fortunei

Four new cycloartane glycosides, 3-O-β-d-xylopyranosyl-(1 → 6)-β-d-glucopyranosyl-(1 → 4)-β-d-fucopyranosyl (22S,24Z)-cycloart-24-en-3β,22,26-triol 26-O-(6-O-acetyl)-β-d-glucopyranoside (1), 3-O-α-l-arabinopyranosyl-(1 → 6)-β-d-glucopyranosyl-(1 → 4)-β-d-fucopyranosyl (22S,24Z)-cycloart-24-en-3β,22,26-triol 26-O-(6-O-acetyl)-β-d-glucopyranoside (2), 3-O-β-d-glucopyranosyl (24S)-cycloartane-3β,16β,24,25,30-pentaol 25-O-β-d-glucopyranosyl-(1 → 6)-β-d-glucopyranoside (3) and 3-O-β-d-glucopyranosyl (24S)-cycloartane-3β,16β,24,25,30-pentaol 25-O-β-d-glucopyranosyl-(1 → 4)-β-d-glucopyranoside (4), were isolated from the aerial parts of Thalictrum fortunei. Their structures were established on the basis of extensive NMR and HR-ESI-MS analyses, along with acid hydrolysis.     

Antihepatotoxic, nephroprotective, and antioxidant activities of phenolic compounds from Satureja macrostema leaves against carbon tetrachloride-induced hepatic damage in mice

Satureja macrostema (SM) is used with culinary and medicinal purposes. Methanol extract from SM was investigated for its phenolic content, antioxidant, hepatoprotective, and kidney protective activities. Liver and kidney damage were induced in rats with CCl₄. Hepatoprotective efficacy was measured by the activity of aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, total bilirubin, cholesterol, high density lipoprotein and total protein, and lipid peroxidation. Kidney function was evaluated by measuring plasma urea and creatinine. Antioxidant activity was evaluated by measuring blood glutathione content, superoxide dismutase and catalase activities, and malondialdehyde equivalent; their activity was comparable to that of silymarin, a well-known hepatoprotective agent. Methanol extracts of S. macrostema showed potent antioxidant, kidney protective, and hepatoprotective activities; in-depth chromatographic investigation resulted in the identification of six new flavonoid glycosides: 5-hydroxy-3,6,4′-trimethoxyflavonol-7-C-α-l-rhamnopyranosyl-(1 → 3)-β-d-glucopyranoside (2), 4′-methoxy-5,7,3′,5′-tetra-hydroxyflavanone-3-O-β-d-rhamnopyranosyl-(1 → 2)-β-d-rhamnopyranoside (3), 5,4′-dimethoxy-7,3′,5′-trihydroxyflavanone-3-O-β-d-rhamnopyranoside (4), 5,3′,4′,5′-tetrahydroxyflavanone-7-O-β-d-rhamnopyranoside (5), 5,3′,4′,5′-tetramethoxyflavanone-7-O-β-d-rhamnopyranoside (6), and 5,4′-dimethoxy-3′-hydroxyflavone-7-β-d-rhamnopyranoside (8) along with three known compounds: 5-hydroxy-7,4′-dimethoxyflavone (1), prunin (7), and diosmin (9) that were isolated. Structural elucidation of the new compounds was established based on the spectral data. The present study revealed that S. macrostema leaves have a significant radical scavenging and hepatoprotective activity.     

Novel quercetin glucosides from Helminthostachys zeylanica root and acceleratory activity of melanin biosynthesis

Two novel quercetin glucosides, namely 4′-O-β-d-glucopyranosyl-quercetin-3-O-β-d-glucopyranosyl-(1→4)-β-d-glucopyranoside (compound 1) and 4′-O-β-d-glucopyranosyl-(1→2)-β-d-glucopyranosyl-quercetin-3-O-β-d-glucopyranosyl-(1→4)-β-d-glucopyranoside (compound 2), were isolated from Helminthostachys zeylanica root 50 % EtOH extract. Structural analysis of isolated compounds was achieved mainly by 600 MHz and 800 MHz NMR, UPLC–TOFMS and GC–MS. Of the two quercetin glucosides, compound 1 showed a high melanogenic acceleratory effect, 2.7 times higher than control, at 10 μM concentration in murine B16 melanoma cells, with no cytotoxic effect.     

Inotropic effects of l-lysine in the mammalian heart

We studied the effects of l-lysine in cardiac preparations of mice and men. Of note, l-lysine increased force of contraction in a concentration- and time-dependent manner in isolated electrically paced left atrium of mouse and in human right atrium. It further increased heart rate and left ventricular pressure in the isolated perfused mouse heart. In isolated adult mouse cardiomyocytes, the contractility as assessed by edge detection was increased as well as the Ca²⁺ transients after electrically pacing by field stimulation. However, using the patch clamp technique, no effect of l-lysine on action potential duration from a constant holding potential or on current through l-type calcium channels could be observed. However, l-lysine led to a depolarization of unclamped cells. Furthermore, effects of l-lysine were stereospecific, as they were not elicited by d-lysine. The inotropic effects of l-lysine were not abrogated by additionally applied l-ornithine or l-arginine (known inhibitors of lysine transport). However, l-lysine (5 mM) shifted the concentration–response curve for a positive inotropic effect of 5-hydroxytryptamine (5-HT; serotonin) in atrium of transgenic mice (with cardiac specific overexpression of 5-HT₄ receptors) to higher concentrations. In summary, we describe a novel positive inotropic effect of an essential amino acid, l-lysine, in the mammalian heart. One might speculate that l-lysine treatment under certain conditions could sustain cardiac performance. Moreover, l-lysine is able to block, at least in part, cardiac 5-HT₄ receptors.     

Biosynthesis of β-lactam antibiotics by cell-free extract fromLysobacter lactamgenus

Using cell-free extract ofLysobacter lactamgenus, enzymatic conversion of δ-l-(α-aminoadipyl)-l-cysteinyl-d-valine (ACV), the first substrate of β-lactam biosynthesis, into antibiotic compounds was attempted. In high performance liquid chromatographic (HPLC) analysis, the biosynthetic intermediates for cephalosporin antibiotics including isopenicillin N, deacetoxycephalosporin C, deacetylcephalosporin C and unknown cephem compound were detected in reaction mixtures. It implies that cephabacin compounds fromL. lactamgenus could be produced by biosynthetic routes through penicillin ring formation and its expansion to cephalosporin ring, likely as cephalosporin C fromCephalosporium or cephamycin C fromStreptomyces. Among biosynthetic enzyme in cell-free extract, the ring formation activity (isopenicillin N synthetase activity) was separated in 50–60% of ammonium sulfate fraction, and ring expansion activity (deacetoxycephalosporin C synthetase activity) was found to be in 40–50% fraction. The partially purified isopenicillin N synthetase could convert as much as 90% ACV to isopenicillin N during 6-hour reaction.     

Isolation and analytical aspects of Valeriana compounds

Valepotriates are considered as one of the main groups of compounds responsible for the sedative activity of Valeriana preparations. An extraction method for valepotriates is given and the isolation of (iso) valtrate, didrovaltrate andIvhd-valtrate by means of column chromatography on silicagel was shown to be a fast method without giving much decomposition. Toluene-ethyl acetate-methyl ethyl ketone (80+15+5) as a mobile phase gives an excellent indication of the presence of the various valepotriates in Valeriana preparations. For the quantitative determination of valepotriates a direct spectrophotometric scanning onTlc plates was compared with aHplc     

Ionically Fixed Polymeric Nanoparticles as a Novel Drug Carrier

Purpose

In this study, we have prepared a novel polymeric drug delivery system comprised of ionically fixed polymeric nanoparticles (IFPN) and investigated their potential as a drug carrier for the passive targeting of water-insoluble anticancer drugs.

Materials and Methods

For this purpose, the physicochemical characteristics of the IFPN were investigated by comparing them with conventional polymeric micelles. IFPN containing paclitaxel were prepared and evaluated for in vitro stability and in vivo pharmacokinetics.

Results

The IFPN were successfully fabricated using a monomethoxypolyethylene glycol-polylactide (mPEG-PLA) diblock copolymer and a sodium salt of d,l-poly(lactic acid) (d,l-PLACOONa) upon the addition of CaCl₂. The transmittance of the IFPN solution was much lower than that of a polymeric micelle solution at the same polymer concentration implicating an increase in the number of appreciable particles. The particle size of the IFPN was approximately 20～30 nm which is in the range of particle sizes that facilitate sterile filtration using a membrane filter. The IFPN also have a regular spherical shape with a narrow size distribution. The zeta potential of the IFPN was almost neutral, similar to that of the polymeric micelles. In contrast, mixed micelles with a combination of mPEG-PLA and d,l-PLACOONa prior to the addition of Ca²⁺ showed a negative charge (?17 mV), possibly due to the carboxyl anion of polylactic acid exposed on the surface of the micelles. The IFPN formulation was highly kinetically stable in aqueous medium compared to the polymeric micelle formulation. The molecular weight of d,l-PLACOONa in the IFPN and the mPEG-PLA/d,l-PLACOONa molar ratio had a great influence upon the kinetic stability of the IFPN. Pharmacokinetic studies showed that the area under the concentration vs time curve (AUC) of IFPN in blood was statistically higher (about two times) when compared with that of Cremophor EL-based formulation (Taxol^® equivalent) or polymeric micelle formulation.

Conclusions

The results suggests that the IFPN were retained in the circulation long enough to play a significant role as a drug carrier in the bloodstream, possibly resulting in improved therapeutic efficiency. Therefore, the IFPN are expected to be a promising novel polymeric nanoparticulate system for passive tumor targeting of water-insoluble anticancer drugs including paclitaxel.     

Effects of coincident 5-HT1A receptor stimulation and NMDA receptor antagonism on l-DOPA-induced dyskinesia and rotational behaviors in the hemi-parkinsonian rat

Rationale

Serotonin 1A receptor (5-HT1AR) agonists reduce l-DOPA-induced dyskinesia and enhance motor function in experimental and clinical investigations of Parkinson’s disease (PD). While the mechanism(s) by which these effects occur are unclear, recent research suggests that modulation of glutamate neurotransmission contributes.

Objective

To further delineate the relationship between 5-HT_1A receptors and glutamate, the current study examined the effects of the 5-HT_1AR agonist, ±8-OH-DPAT and the N-methyl-d-aspartic acid receptor (NMDAR) antagonist, MK-801, on l-DOPA-induced motor behavior.

Materials and methods

Unilateral 6-hydroxydopamine lesioned male Sprague–Dawley rats were rendered dyskinetic with 1 week of daily l-DOPA (12 mg/kg, i.p.) + benserazide (15 mg/kg, i.p.). On test days, one group of rats received pretreatments of: ±8-OH-DPAT (0, 0.03, 0.1, 0.3 mg/kg, i.p.) or MK-801 (0, 0.03, 0.1, 0.3 mg/kg, i.p.). A second group was administered combined ±8-OH-DPAT (0, 0.03 or 0.1 mg/kg, i.p.) + MK-801 (0, 0.1 mg/kg, i.p.). Pretreatments were followed by l-DOPA administration, after which, abnormal involuntary movements (AIMs) and rotations were monitored. To investigate effects on motor performance, subthreshold doses of ±8-OH-DPAT (0.03 mg/kg, i.p.) + MK-801 (0.1 mg/kg, i.p.) were administered to l-DOPA-naïve hemiparkinsonian rats before the forepaw adjusting steps test.

Results

Individually, both ±8-OH-DPAT and MK-801 dose-dependently decreased l-DOPA-induced AIMs without affecting rotations. Combined subthreshold doses of ±8-OH-DPAT+MK-801 reduced l-DOPA-induced AIMs and potently enhanced contralateral rotations without altering l-DOPA-induced motor improvements.

Conclusions

The current results indicate a functional interaction between 5-HT_1AR and NMDAR that may improve pharmacological treatment of PD patients.     

Effect of d-amphetamine on emotion-potentiated startle in healthy humans: implications for psychopathy and antisocial behaviour

Rationale

An emerging literature associates increased dopaminergic neurotransmission with altered brain response to aversive stimuli in humans. The direction of the effect of dopamine on aversive motivation, however, remains unclear, with some studies reporting increased and others decreased amygdala activation to aversive stimuli following the administration of dopamine agonists. Potentiation of the startle response by aversive foreground stimuli provides an objective and directional measure of emotional reactivity and is considered useful as an index of the emotional effects of different drugs.

Objective

We investigated the effects of two doses of d-amphetamine (5 and 10 mg), compared to placebo, for the first time to our knowledge, using the affect–startle paradigm.

Method

The study employed a between-subjects, double-blind design, with three conditions: 0 mg (placebo), and 5 and 10 mg d-amphetamine (initially n?=?20/group; final sample: n?=?18, placebo; n?=?18, 5 mg; n?=?16, 10 mg). After drug/placebo administration, startle responses (eyeblinks) to intermittent noise probes were measured during viewing of pleasant, neutral and unpleasant images. Participants’ general and specific impulsivity and fear-related personality traits were also assessed.

Results

The three groups were comparable on personality traits. Only the placebo group showed significant startle potentiation by unpleasant, relative to neutral, images; this effect was absent in both 5- and 10-mg d-amphetamine groups (i.e. the same effect of d-amphetamine observed at different doses in different people).

Conclusions

Our findings demonstrate a reduced aversive emotional response under d-amphetamine and may help to account for the known link between the use of psychostimulant drugs and antisocial behaviour.     

Semi in vitro labelling of red blood cells with99mTc: a comparison with the in vivo labelling

A method ofsemi in vitro labelling of red blood cells (Rbc) is described.Rbc, ‘pre-tinned’ in the body, were labelledin vitro with99mTc. The labelling efficiency, expressed as the percentage of the administered activity found in the blood, appeared to be higher with this preparation method compared toin vivo labelling ofRbc, respectively 91.3±3.6 and 71.3±3.5 (mean±Sem). There was no difference between both methods in elimination of the label in the urine up to one hour (4.6% of the administered activity). The data here presented, show that thesemi in vitro method provides a preparation with a high cell-bound activity of 96%. Because of a better labelling efficiency, application of thesemi in vitro method results in more circulating activity and a higher left ventricle to background ratio.     

Mechanistic Modeling of Monocarboxylate Transporter-Mediated Toxicokinetic/Toxicodynamic Interactions Between γ-Hydroxybutyrate and l-Lactate

Overdose of γ-hydroxybutyrate (GHB) can result in severe respiratory depression. Monocarboxylate transporter (MCT) inhibitors, including l-lactate, increase GHB clearance and represent a potential treatment for GHB intoxication. GHB can also affect l-lactate clearance, and l-lactate has been reported to affect respiration. In this research, we characterize these toxicokinetic/toxicodynamic interactions between GHB and l-lactate using mechanistic modeling. Plasma, urine, and respiration data were taken from our previous study in which GHB and sodium l-lactate were administered alone and concomitantly in rats. A model incorporating active renal reabsorption for both agents fit GHB and l-lactate toxicokinetic data. The K_m for renal reabsorption of GHB (650 μg/mL) was close to its K_m for the proton-dependent MCT1 and that for l-lactate (13.5 μg/mL) close to its K_m for the sodium-dependent SMCT1. Inhibition of reabsorption by both agents was necessary to model concomitant drug administration. The metabolic K_m for l-lactate closely resembled that for MCT-mediated hepatic uptake in vitro, and GHB inhibited this process. l-lactate significantly inhibited respiration at a high dose, and an indirect response model was used to fit these data. GHB toxicodynamics was modeled as a direct effect delayed by nonlinear transport into the brain extracellular fluid, with a K_m value of 1,865 μg/mL for brain uptake which is similar to the in vitro K_m value determined in rat brain endothelial cells. This model was useful for characterizing multiple MCT-mediated interactions. Incorporation of many parameters that can be determined in vitro may allow for clinical translation of these interactions.