Increased vigabatrin entry into the brain by polysorbate 80 and sodium caprate

Pharmacokinetics of Phytocannabinoid Acids and Anticonvulsant Effect of Cannabidiolic Acid in a Mouse Model of Dravet Syndrome

Cannabis sativa produces a complex mixture of many bioactive molecules including terpenophenolic compounds known as phytocannabinoids. Phytocannabinoids come in neutral forms (e.g., Δ⁹-tetrahydrocannabinol, THC; cannabidiol, CBD; etc.) or as acid precursors, which are dominant in the plant (e.g., Δ⁹-tetrahydrocannabinolic acid, THCA; cannabidiolic acid, CBDA; etc.). There is increasing interest in unlocking the therapeutic applications of the phytocannabinoid acids; however, the present understanding of the basic pharmacology of phytocannabinoid acids is limited. Herein the brain and plasma pharmacokinetic profiles of CBDA, THCA, cannabichromenic acid (CBCA), cannabidivarinic acid (CBDVA), cannabigerolic acid (CBGA), and cannabigerovarinic acid (CBGVA) were examined following intraperitoneal administration in mice. Next it was examined whether CBDA was anticonvulsant in a mouse model of Dravet syndrome (Scn1a^RX/+ mice). All the phytocannabinoid acids investigated were rapidly absorbed with plasma t_max values of between 15 and 45 min and had relatively short half-lives (<4 h). The brain-plasma ratios for the acids were very low at ≤0.04. However, when CBDA was administered in an alternate Tween 80-based vehicle, it exhibited a brain-plasma ratio of 1.9. The anticonvulsant potential of CBDA was examined using this vehicle, and it was found that CBDA significantly increased the temperature threshold at which the Scn1a^RX/+ mice had a generalized tonic-clonic seizure.

Mitochondria-Targeted Antioxidant SkQ1 (10-(6´-Plastoquinonyl)decyltriphenylphosphonium Bromide) Inhibits Mast Cell Degranulation in vivo and in vitro

The therapeutic effect of mitochondria-targeted antioxidant 10-(6´-plastoquinonyl)decyltriphenylphosphonium bromide (SkQ1) in experimental models of acute inflammation and wound repair has been shown earlier. It was suggested that the antiinflammatory activity of SkQ1 is related to its ability to suppress inflammatory activation of the vascular endothelium and neutrophil migration into tissues. Here, we demonstrated that SkQ1 inhibits activation of mast cells (MCs) followed by their degranulation and histamine release in vivo and in vitro. Intraperitoneal injections of SkQ1 in the mouse air-pouch model reduced the number of leukocytes in the air-pouch cavity and significantly decreased the histamine content in it, as well as suppressing MC degranulation in the air-pouch tissue. The direct effect of SkQ1 on MCs was studied in vitro in the rat basophilic leukemia RBL-2H3 cell line. SkQ1 inhibited induced degranulation of RBL-2H3 cells. These results suggest that mitochondrial reactive oxygen species are involved in the activation of MCs. It is known that MCs play a crucial role in regulation of vascular permeability by secreting histamine. Suppression of MC degranulation by SkQ1 might be a significant factor in the antiinflammatory activity of this mitochondria-targeted antioxidant.

Hypoxia-inducible factor stabilizers and other small-molecule erythropoiesis-stimulating agents in current and preventive doping analysis

Increasing the blood's capacity for oxygen transport by erythropoiesis-stimulating agents (ESAs) constitutes a prohibited procedure of performance enhancement according to the World Anti-Doping Agency (WADA). The advent of orally bio-available small-molecule ESAs such as hypoxia-inducible factor (HIF) stabilizers in the development of novel anti-anaemia therapies expands the list of potential ESA doping techniques. Here, the erythropoiesis-stimulating properties and doping relevance of experimental HIF-stabilizers, such as cobaltous chloride, 3,4-dihydroxybenzoic acid or GSK360A, amongst others, are discussed. The stage of clinical trials is reviewed for the anti-anaemia drug candidates FG-2216, FG-4592, GSK1278863, AKB-6548, and BAY85-3934. Currently available methods and strategies for the determination of selected HIF stabilizers in sports drug testing are based on liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS). For the support of further analytical assay development, patents claiming distinct compounds for the use in HIF-mediated therapies are evaluated and exemplary molecular structures of HIF stabilizers presented. Moreover, data concerning the erythropoiesis-enhancing effects of the GATA inhibitors K7174 and K11706 as well as the lipidic small-molecule ESA PBI-1402 are elucidated the context of doping analysis.

The effects of pharmaceutical excipients on drug disposition

Many new chemical entities are poorly soluble, requiring the use of co-solvents or excipients to produce suitable intravenous formulations for early pre-clinical development studies. There is some evidence in the literature that these formulation components can have significant physiological and physicochemical effects which may alter the distribution and elimination of co-administered drugs. Such effects have the potential to influence the results of pre-clinical pharmacokinetic studies, giving a false impression of a compound's intrinsic pharmacokinetics and frustrating attempts to predict the drug's ultimate clinical pharmacokinetics. This review describes the reported effects of commonly used co-solvents and excipients on drug pharmacokinetics and on physiological systems which are likely to influence drug disposition. Such information will be useful in study design and evaluating data from pharmacokinetic experiments, so that the potential influence of formulation components can be minimised.

Graded reversible opening of the rat blood-brain barrier by intracarotid infusion of sodium caprate

The fatty acid salt, sodium caprate (C10) is a well recognized drug absorption enhancer in intestine because of its ability to widen tight junctions in the epithelial cell lining. Caprate's potential usefulness to similarly alter the blood-brain barrier (BBB) tight junctions of brain vasculature and enhance CNS drug delivery has undergone little investigation. Adult SD rats were anesthetized and C10 was infused into the left internal carotid artery (dosing parameters: 10-30 mM, 1 or 2 ml min(-1), for 0.5-1.5 min). Beginning 5 or 60 min after infusion an i.v. bolus of [3H]mannitol was allowed to circulate for 30 min and degree of BBB leakiness measured as magnitude of the transfer constant (Ki, nl g(-1)s(-1)) for blood to brain mannitol permeation determined from brain and plasma samples. In initial experiments identical C10 infusions caused dramatic BBB opening in some rats, e.g., 10-fold increase in Ki, but not in others. Higher dosing produced consistent opening measured 5-35 or 60-90 min post-infusion but was also toxic as shown by severe brain edema and cardio-respiratory failure. The variable effect of moderate doses was attributed to the fact that arterial blood pressure markedly increased during C10 infusion and may have altered the flow dynamics of cerebrovascular caprate distribution from rat to rat. We modified the procedure by temporarily withdrawing blood to produce hypovolemia and systemic arterial hypotension during C10 infusion. Caprate infusions of 15-25 mM, 2 ml min(-1) for 1 min, produced reliable dose-related openings that lasted as much as an hour, were reversible, and accompanied by little or moderate edema, depending on dose. These findings confirm an earlier report showing that intracarotid caprate infusion opens the BBB but also show that control of the temporary hypertensive response produced by intracarotid caprate infusion is key to tailoring the dosage to consistently achieve graded, reversible BBB opening.

Limited P-glycoprotein mediated efflux for anti-epileptic drugs

A variety of anti-epileptic drugs (AEDs) were tested for their ability to be transported by P-glycoprotein (P-gp) through Caco-2 monolayers using bi-directional (apical (Ap) to basolateral (Bas), and Bas to Ap) studies. Transport rates were equivalent in both directions for vigabatrin, gabapentin, phenobarbitone, lamotrigine and carbamazepine, being 0.7 x 10- 6, 0.1 x 10- 6, 34 x 10- 6, 36 x 10- 6 and 55 x 10- 6 cm/s, respectively. Phenytoin displayed a 20% increase in Ap to Bas transport, while topiramate and ethosuximide each had greater transport in the uptake direction, with both drugs showing no efflux. None of the transport rates for these drugs were affected by P-gp inhibitors. However, the efflux rate for acetazolamide was 3-fold higher than its uptake and this was significantly reduced by P-gp inhibitors. Thus, only one anti-epileptic, acetazolamide, was shown to be weak P-gp substrate, suggesting that P-gp efflux may not be a factor in relation to the development of resistance of epilepsy therapy.

Elevated endogenous GABA level correlates with decreased fMRI signals in the rat brain during acute inhibition of GABA transaminase

Vigabatrin and gabaculine, both highly specific inhibitors of GABA (gamma-aminobutyric acid) transaminase, cause significant elevation of endogenous GABA levels in brain. The time course of GABA concentration after acute GABA transaminase inhibition was measured quantitatively in the alpha-chloralose-anesthetized rat brain using in vivo selective homonuclear polarization transfer spectroscopy. The blood oxygenation level-dependent (BOLD) effect in functional magnetic resonance imaging (fMRI) has been considered to be coupled tightly to neuronal activation via the metabolic demand of associated glutamate transport. Correlated with the rise in endogenous GABA level after vigabatrin or gabaculine treatment, the intensity of BOLD-weighted fMRI signals in rat somatosensory cortex during forepaw stimulation was found to be reduced significantly. These results are consistent with previous findings that inhibition of GABA transaminase leads to augmented GABA release and potentiation of GABAergic inhibition.

A new strategy for in vivo spectral editing. Application to GABA editing using selective homonuclear polarization transfer spectroscopy

A novel single-shot in vivo spectral editing method is proposed in which the signal to be detected, is regenerated anew from the thermal equilibrium magnetization of a source to which it is J-coupled. The thermal equilibrium magnetization of the signal to be detected together with those of overlapping signals are suppressed by single-shot gradient dephasing prior to the signal regeneration process. Application of this new strategy to in vivo GABA editing using selective homonuclear polarization transfer allows complete suppression of overlapping creatine and glutathione while detecting the GABA-4 methylene resonance at 3.02 ppm with an editing yield similar to that of conventional editing methods. The NAA methyl group at 2.02 ppm was simultaneously detected and can be used as an internal navigator echo for correcting the zero order phase and frequency shifts and as an internal reference for concentration. This new method has been demonstrated for robust in vivo GABA editing in the rat brain and for study of GABA synthesis after acute vigabatrin administration.

Pharmacological effects of formulation vehicles : implications for cancer chemotherapy

The non-ionic surfactants Cremophor EL (CrEL; polyoxyethyleneglycerol triricinoleate 35) and polysorbate 80 (Tween) 80; polyoxyethylene-sorbitan-20-monooleate) are widely used as drug formulation vehicles, including for the taxane anticancer agents paclitaxel and docetaxel. A wealth of recent experimental data has indicated that both solubilisers are biologically and pharmacologically active compounds, and their use as drug formulation vehicles has been implicated in clinically important adverse effects, including acute hypersensitivity reactions and peripheral neuropathy.CrEL and Tween 80 have also been demonstrated to influence the disposition of solubilised drugs that are administered intravenously. The overall resulting effect is a highly increased systemic drug exposure and a simultaneously decreased clearance, leading to alteration in the pharmacodynamic characteristics of the solubilised drug. Kinetic experiments revealed that this effect is primarily caused by reduced cellular uptake of the drug from large spherical micellar-like structures with a highly hydrophobic interior, which act as the principal carrier of circulating drug. Within the central blood compartment, this results in a profound alteration of drug accumulation in erythrocytes, thereby reducing the free drug fraction available for cellular partitioning and influencing drug distribution as well as elimination routes. The existence of CrEL and Tween 80 in blood as large polar micelles has also raised additional complexities in the case of combination chemotherapy regimens with taxanes, such that the disposition of several coadministered drugs, including anthracyclines and epipodophyllotoxins, is significantly altered. In contrast to the enhancing effects of Tween 80, addition of CrEL to the formulation of oral drug preparations seems to result in significantly diminished drug uptake and reduced circulating concentrations. The drawbacks presented by the presence of CrEL or Tween 80 in drug formulations have instigated extensive research to develop alternative delivery forms. Currently, several strategies are in progress to develop Tween 80- and CrEL-free formulations of docetaxel and paclitaxel, which are based on pharmaceutical (e.g. albumin nanoparticles, emulsions and liposomes), chemical (e.g. polyglutamates, analogues and prodrugs), or biological (e.g. oral drug administration) strategies. These continued investigations should eventually lead to more rational and selective chemotherapeutic treatment.