Background and Objective
In microdose studies, the pharmacokinetic (PK) profile of a drug in blood after administration of a dose up to 100 μg is measured with sensitive analytical techniques, such as accelerator mass spectrometry (AMS). As most drugs exert their effect in tissue rather than blood, methodology is needed for extending PK analysis to different tissue compartments. In the present study, we combined, for the first time, AMS analysis with positron emission tomography (PET) in order to determine the PK profile of the model drug verapamil in plasma and brain of humans. In order to assess PK dose-linearity of verapamil, data were acquired and compared after administration of an intravenous (iv) microdose and an iv microdose dosed concomitantly with an oral therapeutic dose.
Six healthy male volunteers received an iv microdose (0.05 mg) (period 1) and an iv microdose dosed concomitantly with an oral therapeutic dose (80 mg) of verapamil (period 2) in a randomized, cross-over, two-period study design. The iv dose was a mixture of (R/S)-[14C]verapamil and (R)-[11C]verapamil and the oral dose was unlabelled racemic verapamil. Brain distribution of radioactivity was measured with PET whereas plasma PK of (R)- and (S)-verapamil was determined with AMS. PET data were analyzed by kinetic modeling to estimate the rate constants for transfer of radioactivity across the blood-brain barrier.
Most PK parameters of (R)- and (S)-verapamil as well as parameters describing exchange of radioactivity between plasma and brain (K1=0.030±0.003 and 0.031±0.005 mL·mL−1·min−1 and k2=0.099±0.006 and 0.095±0.008 min−1 for period 1 and 2, respectively) were not statistically different between the two periods although there was a trend for non-linear kinetics for the (R)-enantiomer. On the other hand, all PK parameters (except for t1/2) differed significantly between the (R)- and (S)-enantiomers for both periods. Cmax, AUC(0-24) and AUC(0-inf) were higher and CL, V and VSS were lower for the (R)- than for the (S)-enantiomer.
Combining AMS and PET microdosing allows long term PK data along with information on drug tissue distribution to be acquired in the same subjects thus making it a promising approach to maximize data output from a single clinical study.
Conspiracy theories (CTs) can take many forms and vary widely in popularity, the intensity with which they are believed and their effects on individual and collective behavior. An integrated account of CTs thus needs to explain how they come to appeal to potential believers, how they spread from one person to the next via communication, and how they motivate collective action. We summarize these aspects under the labels of stick, spread, and action. We propose the quasi-religious hypothesis for CTs: drawing on cognitive science of religion, social representations theory, and frame theory. We use cognitive science of religion to describe the main features of the content of CTs that explain how they come to stick: CTs are quasi-religious representations in that their contents, forms and functions parallel those found in beliefs of institutionalized religions. However, CTs are quasi-religious in that CTs and the communities that support them, lack many of the institutional features of organized religions. We use social representations theory to explain how CTs spread as devices for making sense of sudden events that threaten existing worldviews. CTs allow laypersons to interpret such events by relating them to common sense, thereby defusing some of the anxiety that those events generate. We use frame theory to explain how some, but not all CTs mobilize collective counter-conspiratorial action by identifying a target and by proposing credible and concrete rationales for action. We specify our integrated account in 13 propositions.
quasi-religion; social representations; frame theory; conspiracy theory; minimal counter-intuitiveness; sense making; beliefs
Tariquidar, a potent, nontoxic, third-generation P-glycoprotein (P-gp) inhibitor, is a possible reversal agent for central nervous system drug resistance. In animal studies, tariquidar has been shown to increase delivery of P-gp substrates into brain by several-fold. The aim of this study was to measure P-gp function at the human blood-brain barrier (BBB) after tariquidar administration using PET and the model P-gp substrate (R)–11C-verapamil. Methods: 5 healthy volunteers underwent paired (R)–11C-verapamil PET scans and arterial blood sampling, before and at 2 h 50 min after i.v. administration of tariquidar (2 mg/kg body weight). Inhibition of P-gp on CD56+ peripheral lymphocytes of each volunteer was determined by means of the rhodamine-123 efflux assay. Tariquidar concentrations in venous plasma were quantified using liquid chromatography/mass spectrometry. Results: Tariquidar administration resulted in significant increases (Wilcoxon test for paired samples) in the distribution volume (DV, +24±15%) and influx rate constant (K1, +49±36%) of (R)–11C-verapamil across the BBB (DV=0.65±0.13 and 0.80±0.07, p=0.043, K1=0.034±0.009 and 0.049±0.009, p=0.043, before and after tariquidar, respectively). A strong correlation was observed between change in brain DV after administration of tariquidar and tariquidar exposure in plasma (r=0.90, p=0.037). The mean plasma concentration of tariquidar achieved during the second PET scan (490±166 ng/mL) corresponded to 100% inhibition of P-gp function in peripheral lymphocytes. Conclusion: Tariquidar significantly increased brain penetration of (R)–11C-verapamil-derived activity, due to increased influx. As opposed to peripheral P-gp function, central P-gp inhibition appeared to be far from complete after the administered tariquidar dose.
PET; (R)-11C-verapamil; tariquidar; P-glycoprotein; blood-brain barrier
The aim of this study was to assess the influence of age on the functional activity of the multidrug efflux transporter P-glycoprotein (P-gp) at the human blood-brain barrier.
7 young (mean age: 27±4 years) and 6 elderly (mean age: 69±9 years) healthy volunteers underwent dynamic (R)-[11C]verapamil (VPM) positron emission tomography (PET) scans and arterial blood sampling. Parametric distribution volume (DV) images were generated using Logan linearisation and age groups were compared with statistical parametric mapping (SPM). Brain regions that SPM analysis had shown to be most affected by age were analysed by a region of interest (ROI)-based approach using a maximum probability brain atlas, before and after partial volume correction (PVC).
SPM analysis revealed significant clusters of DV increases in cerebellum, temporal and frontal lobe of elderly compared to younger subjects. In the ROI-based analysis, elderly subjects showed significant DV increases in amygdala (+30%), insula (+26%) and cerebellum (+25%), before PVC, and in insula (+33%), after PVC.
Increased VPM DV values in the brains of elderly subjects suggest a decrease in cerebral P-gp function with increasing age.
P-glycoprotein; blood-brain barrier; age; (R)-[11C]verapamil; positron emission tomography
Using positron emission tomography (PET) imaging we assessed in vivo the interaction between a microdose of (R)-[11C]verapamil, a P-glycoprotein (Pgp) substrate, and escalating doses of the Pgp inhibitor tariquidar (3, 4, 6 and 8 mg/kg) at the blood-brain barrier (BBB) of healthy human subjects. We compared the dose-response relationship of tariquidar in humans with data obtained in rats using similar methodology. Tariquidar was equipotent in humans and rats to increase (R)-[11C]verapamil brain uptake, expressed as whole brain volume of distribution (VT), with very similar half-maximum effect concentrations. Both in humans and rats, brain VTs approached plateau levels at tariquidar plasma concentrations >1,000 ng/mL. However, Pgp inhibition in humans only led to 2.7-fold increase in brain VT relative to baseline scans without tariquidar compared to 11.0-fold in rats. The results of this translational study add to the accumulating evidence of marked species-dependent differences in Pgp expression and functionality at the BBB.
P-glycoprotein; blood-brain barrier; drug-drug interaction; positron emission tomography; (R)-[11C]verapamil; tariquidar; human; rat
This study investigated the influence of P-glycoprotein (P-gp) inhibitor tariquidar on the pharmacokinetics of P-gp substrate radiotracer (R)-[11C]verapamil in plasma and brain of rats and humans by means of positron emission tomography (PET).
Data obtained from a preclinical and clinical study, in which paired (R)-[11C]verapamil PET scans were performed before, during, and after tariquidar administration, were analyzed using nonlinear mixed effects (NLME) modeling. Administration of tariquidar was included as a covariate on the influx and efflux parameters (Qin and Qout) in order to investigate if tariquidar increased influx or decreased outflux of radiotracer across the blood–brain barrier (BBB). Additionally, the influence of pilocarpine-induced status epilepticus (SE) was tested on all model parameters, and the brain-to-plasma partition coefficient (VT-NLME) was calculated.
Our model indicated that tariquidar enhances brain uptake of (R)-[11C]verapamil by decreasing Qout. The reduction in Qout in rats during and immediately after tariquidar administration (sevenfold) was more pronounced than in the second PET scan acquired 2 h after tariquidar administration (fivefold). The effect of tariquidar on Qout in humans was apparent during and immediately after tariquidar administration (twofold reduction in Qout) but was negligible in the second PET scan. SE was found to influence the pharmacological volume of distribution of the central brain compartment Vbr1. Tariquidar treatment lead to an increase in VT-NLME, and pilocarpine-induced SE lead to increased (R)-[11C]verapamil distribution to the peripheral brain compartment.
Using NLME modeling, we were able to provide mechanistic insight into the effects of tariquidar and SE on (R)-[11C]verapamil transport across the BBB in control and 48 h post SE rats as well as in humans.
Nonlinear mixed effects modeling; Positron emission tomography; (R)-[11C]verapamil; P-glycoprotein; Tariquidar; Pilocarpine-induced epilepsy; Species differences
Pronounced extracellular acidosis reduces both cardiac contractility and the β-adrenergic response. In the past, this was shown in some studies using animal models. However, few data exist regarding how the human end-stage failing myocardium, in which compensatory mechanisms are exhausted, reacts to acute mild metabolic acidosis. The aim of this study was to investigate the effect of mild metabolic acidosis on contractility and the β-adrenergic response of isolated trabeculae from human end-stage failing hearts.
Intact isometrically twitching trabeculae isolated from patients with end-stage heart failure were exposed to mild metabolic acidosis (pH 7.20). Trabeculae were stimulated at increasing frequencies and finally exposed to increasing concentrations of isoproterenol (0 to 1 × 10-6 M).
A mild metabolic acidosis caused a depression in twitch-force amplitude of 26% (12.1 ± 1.9 to 9.0 ± 1.5 mN/mm2; n = 12; P < 0.01) as compared with pH 7.40. Force-frequency relation measurements yielded no further significant differences of twitch force. At the maximal isoproterenol concentration, the force amplitude was comparable in each of the two groups (pH 7.40 versus pH 7.20). However, the half-maximal effective concentration (EC50) was significantly increased in the acidosis group, with an EC50 of 5.834 × 10-8 M (confidence interval (CI), 3.48 × 10-8 to 9.779 × 10-8; n = 9), compared with the control group, which had an EC50 of 1.056 × 10-8 M (CI, 2.626 × 10-9 to 4.243 × 10-8; n = 10; P < 0.05), indicating an impaired β-adrenergic force response.
Our data show that mild metabolic acidosis reduces cardiac contractility and significantly impairs the β-adrenergic force response in human failing myocardium. Thus, our results could contribute to the still-controversial discussion about the therapy regimen of acidosis in patients with critical heart failure.
The i-gel™, LMA-Supreme (LMA-S) and Laryngeal Tube Suction-D (LTS-D) are single-use supraglottic airway devices with an inbuilt drainage channel. We compared them with regard to their position in situ as well as to clinical performance data during elective surgery.
Prospective, randomized, comparative study of three groups of 40 elective surgical patients each. Speed of insertion and success rates, leak pressures (LP) at different cuff pressures, dynamic airway compliance, and signs of postoperative airway morbidity were recorded. Fibreoptic evaluation was used to determine the devices’ position in situ.
Leak pressures were similar (i-gel™ 25.9, LMA-S 27.1, LTS-D 24.0 cmH2O; the latter two at 60 cmH2O cuff pressure) as were insertion times (i-gel™ 10, LMA-S 11, LTS-D 14 sec). LP of the LMA-S was higher than that of the LTS-D at lower cuff pressures (p <0.05). Insertion success rates differed significantly: i-gel™ 95%, LMA-S 95%, LTS-D 70% (p <0.05). The fibreoptically assessed position was more frequently suboptimal with the LTS-D but this was not associated with impaired ventilation. Dynamic airway compliance was highest with the i-gel™ and lowest with the LTS-D (p <0.05). Airway morbidity was more pronounced with the LTS-D (p <0.01).
All devices were suitable for ventilating the patients’ lungs during elective surgery.
German Clinical Trial Register DRKS00000760
Laryngeal mask airway; Leak pressure; Laryngeal Tube
Adenosine monophosphate – activated kinase (AMPK) plays a key role in the coordination of the heart’s anabolic and catabolic pathways. It induces a cellular cascade at the center of maintaining energy homeostasis in the cardiomyocytes.. The activated AMPK is a heterotrimeric protein, separated into a catalytic α - subunit (63kDa), a regulating β - subunit (38kDa) and a γ - subunit (38kDa), which is allosterically adjusted by adenosine triphosphate (ATP) and adenosine monophosphate (AMP). The actual binding of AMP to the γ – subunit is the step which activates AMPK.
AMPK serves also as a protein kinase in several metabolic pathways of the heart, including cellular energy sensoring or cardiovascular protection. The AMPK cascade represents a sensitive system, activated by cellular stresses that deplete ATP and acts as an indicator of intracellular ATP/AMP. In the context of cellular stressors (i.e. hypoxia, pressure overload, hypertrophy or ATP deficiency) the increasing levels of AMP promote allosteric activation and phosphorylation of AMPK. As the concentration of AMP begins to increase, ATP competitively inhibits further phosphorylation of AMPK. The increase of AMP may also be induced either from an iatrogenic emboli, percutaneous coronary intervention, or from atherosclerotic plaque rupture leading to an ischemia in the microcirculation. To modulate energy metabolism by phosphorylation and dephosphorylation is vital in terms of ATP usage, maintaining transmembrane transporters and preserving membrane potential.
In this article, we review AMPK and its role as an important regulatory enzyme during periods of myocardial stress, regulating energy metabolism, protein synthesis and cardiovascular protection.
Adenosine monophosphate - activated protein kinase; AMPK; heart failure; cardiac energy metabolism.
We attempted to assess regional differences in cerebral P-glycoprotein (P-gp) function by performing paired positron emission tomography (PET) scans with the P-gp substrate (R)-[11C]verapamil in five healthy subjects before and after i.v. infusion of tariquidar (2 mg/kg). Comparison of tariquidar-induced changes in distribution volumes (DVs) in 42 brain regions of interest (ROIs) failed to detect significant differences among brain ROIs. Statistical parametric mapping analysis of parametric DV images visualized symmetrical bilateral clusters with moderately higher DV increases in response to tariquidar administration in cerebellum, parahippocampal gyrus, olfactory gyrus, and middle temporal lobe and cortex, which might reflect moderately decreased P-gp function and expression.
blood–brain barrier; P-glycoprotein; positron emission tomography (PET); (R)-[11C]verapamil; regional; tariquidar
The chromosome 22q11 region is proposed as a major candidate locus for susceptibility genes to schizophrenia. Recently, the gene ZDHHC8 encoding a putative palmitoyltransferase at 22q11 was proposed to increase liability to schizophrenia based on both animal models and human association studies by significant over-transmission of allele rs175174A in female, but not male subjects with schizophrenia.
Given the genetic complexity of schizophrenia and the potential genetic heterogeneity in different populations, we examined rs175174 in 204 German proband-parent triads and in an independent case-control study (schizophrenic cases: n = 433; controls: n = 186).
In the triads heterozygous parents transmitted allele G preferentially to females, and allele A to males (heterogeneity χ2 = 4.43; p = 0.035). The case-control sample provided no further evidence for overall or gender-specific effects regarding allele and genotype frequency distributions.
The findings on rs175174 at ZDHHC8 are still far from being conclusive, but evidence for sexual dimorphism is moderate, and our data do not support a significant genetic contribution of rs175174 to the aetiopathogenesis of schizophrenia.