Discrepancies in the P-glycoprotein-Mediated Transport of 18F-MPPF: A Pharmacokinetic Study in Mice and Non-human Primates

Purpose

Several in vivo studies have found that the 5-HT_1A PET radioligand ¹⁸F-MPPF is a substrate of rodent P-glycoprotein (P-gp). However, in vitro assays suggest that MPPF is not a substrate of human P-gp. We have now tested the influence of inhibiting P-gp on the brain kinetics of ¹⁸F-MPPF in mice and non-human primates.

Methods

We measured the peripheral kinetics (arterial input function, metabolism, free fraction in plasma (f_P)) during ¹⁸F-MPPF brain PET scanning in baboons with or without cyclosporine A (CsA) infusion. We measured ³H-MPPF transport at the mouse BBB using in situ brain perfusion in P-gp/Bcrp deficient mice and after inhibiting P-gp with PSC833.

Results

There was an unexpected 1.9-fold increase in brain area under the curve in CsA-treated baboons (n?=?4), with no change in radiometabolite-corrected arterial input. However, total volume of distribution corrected for f_P (V_T/f_P) remained unchanged. In situ brain perfusion showed that P-gp restricted the permeability of the mouse BBB to ³H-MPPF while Bcrp did not.

Conclusion

These and previous in vitro results suggest that P-gp may not influence the permeability of human BBB to ¹⁸F-MPPF. However, CsA treatment increased ¹⁸F-MPPF free fraction, which is responsible for a misleading, P-gp unrelated enhanced brain uptake.     

Dyadic OPTION: Measuring perceptions of shared decision-making in practice

Background

Current models of the medical consultation emphasize shared decision-making (SDM), whereby the expertise of both the doctor and the patient are recognised and seen to equally contribute to the consultation. The evidence regarding the desirability and effectiveness of the SDM approach is often conflicting. It is proposed that the conflicts are due to the nature of assessment, with current assessments from the perspective of an outside observer.

Aims

To empirically assess perceived involvement in the medical consultation using the dyadic OPTION instrument.

Method

36 simulated medical consultations were organised between general practitioners and standardized- patients, using the observer OPTION and the newly developed dyadic OPTION instruments.

Results

SDM behaviours observed in the consultations were seen to depend on both members of the doctor and patient dyad, rather than each in isolation. Thus a dyadic approach to measurement is supported.

Conclusions

This current study highlights the necessity for a dyadic approach to assessment and introduces a novel research instrument: the dyadic OPTION instrument.     

Word-finding difficulties in French-speaking children with SLI: a case STUDY

This study presents the case of a 9-year-old boy, Jeoffrey, with word-finding difficulties. In an attempt to investigate the cause(s) of these difficulties, an in-depth evaluation of his semantic and phonological skills was carried out, in which lexical and phonological variables such as age of acquisition or phonological complexity were controlled. Jeoffrey's performance was compared to a child matched for age. Although Jeoffrey showed no apparent phonological deficit, our results revealed deficits in semantic processes. We argue that this boy's word-finding difficulties are the result of imprecise and unspecified semantic representations. Therefore, as this case demonstrates, it is essential to determine the origin(s) of children's word-finding difficulties, which could be different and specific for each child presenting such a lexical deficit.     

High hepatic glutathione stores alleviate Fas-induced apoptosis in mice

BACKGROUND/AIMS: The agonistic Jo2 anti-Fas antibody reproduces human fulminant hepatitis in mice. We tested the hypothesis that enhancing hepatic glutathione (GSH) stores may prevent Jo2-induced apoptosis. METHODS: We fed mice with a normal diet or a sulfur amino acid-enriched (SAA(+)) diet increasing hepatic GSH by 63%, and challenged these mice with Jo2. RESULTS: The SAA(+) diet markedly attenuated the Jo2-mediated decrease in hepatic GSH and the increase in the oxidized glutathione (GSSG)/GSH ratio in cytosol and mitochondria. The SAA(+) diet prevented protein kinase Czeta (PKCzeta) and p47(phox) phosphorylations, Yes activation, Fas-tyrosine phosphorylation, Bid truncation, Bax, and cytochrome c translocations, the mitochondrial membrane potential collapse, caspase activation, DNA fragmentation, hepatocyte apoptosis, and mouse lethality after Jo2 administration. The protective effect of the SAA(+) diet was abolished by a small dose of phorone decreasing hepatic GSH back to the levels observed in mice fed the normal diet. Conversely, administration of GSH monoethyl ester after Jo2 administration prevented hepatic GSH depletion and attenuated toxicity in mice fed with the normal diet. CONCLUSIONS: The SAA(+) diet preserves GSSG/GSH ratios, and prevents PKCzeta and p47(phox) phosphorylations, Yes activation, Fas-tyrosine phosphorylation, mitochondrial permeabilization, and hepatic apoptosis after Fas stimulation. GSH monoethyl ester is also protective, suggesting possible clinical applications.     

Neurogenic stunned myocardium following hemorrhagic cerebral contusion

Neurogenic stunned myocardium (NSM) is a well-known complication of subarachnoidal hemorrhage, but has been reported rarely in association with other central nervous system disorders. A case of NSM is described in a patient with hemorrhagic brain contusion associated with cerebral edema. An 18-year-old man was admitted with severe cranial trauma following a car roll-over. Six days after admission, he developed findings suggestive for NSM. The troponin T and creatine kinase-MB level were elevated and echocardiogram showed apical and inferoposterior hypokinesis and diffuse left ventricular akinesis with severely reduced ejection fraction (18%). Invasive measurements confirmed low cardiac output. His cardiac function resolved completely within 6 days after decompressive craniotomy. This case supports the presumed unifying role of the increased intracranial pressure, probably triggering a vigorous sympathetic outflow hyperactivity leading to NSM.     

Influenza A Virus Neuraminidase Enhances Meningococcal Adhesion to Epithelial Cells through Interaction with Sialic Acid-Containing Meningococcal Capsules

The underlying mechanisms of the epidemiological association between influenza virus infections and Neisseria meningitidis invasive infections are not fully understood. Here we report that adhesion of N. meningitidis to human Hec-1-B epithelial cells is enhanced by influenza A virus (IAV) infection. A potential role of the viral neuraminidase (NA) in facilitating meningococcal adhesion to influenza virus-infected epithelial cells was examined. Expression of a recombinant IAV NA in Hec-1-B human epithelial cells increased the adhesion of strains of N. meningitidis belonging to the sialic acid-containing capsular serogroups B, C, and W135 but not to the mannosamine phosphate-containing capsular serogroup A. Adhesion enhancement was not observed with an inactive NA mutant or in the presence of an NA inhibitor (zanamivir). Furthermore, purified IAV NA was shown to cleave sialic acid-containing capsular polysaccharides of N. meningitidis. On the whole, our findings suggest that a direct interaction between the NA of IAV and the capsule of N. meningitidis enhances bacterial adhesion to cultured epithelial cells, most likely through cleavage of capsular sialic acid-containing polysaccharides. A better understanding of the association between IAV and invasive meningococcal infections should help to set up improved control strategies against these seasonal dual viral-bacterial infections.Neisseria meningitidis is commonly found in the human naso-oropharynx, among other commensal bacterial species. Asymptomatic carriers represent about 10% of the population (41). In Europe and North America, cases of invasive infection leading to meningococcal disease (MD), mainly septicemia and meningitis, occur sporadically. The annual incidence of MD varies between 0.3 and 4.35 per 100,000 inhabitants (36). Both bacterial virulence factors (32) and host susceptibility factors (34, 38) contribute to the development of invasive infections, but the exact mechanisms involved remain largely unknown. The serogroups of N. meningitidis, which are defined by the nature of the capsular polysaccharide, are distributed differently among carried and disease-associated isolates (42). Serogroups B and C (whose capsules are composed of polymers of sialic acids) and serogroups Y and W135 (whose capsules are composed of repeated units of sialic acid with d-glucose and d-galactose, respectively [4]) are prominent in MD in Europe and North America. Serogroup A, whose capsule is composed of α1,6-linked N-acetylmannosamine-1-phosphate (18), is most frequently involved in MD epidemics in Africa.A number of clinical observations of MD occurring in patients with influenza have been reported (6, 13, 43). Epidemiological studies clearly showed a spatiotemporal association between influenza and N. meningitidis invasive infections (2, 14, 25). Recent data from the French National Reference Center for Meningococci and from the Sentinelles Network confirmed the overlap between the winter peaks of incidence of bacteriologically confirmed MD cases and influenza-like illnesses during the period from 2000 to 2008 (Fig. ​(Fig.1),1), in agreement with data published previously (14).Open in a separate windowFIG. 1.Invasive meningococcal infections and influenza-like illnesses recorded in France by the Reference Center for Meningococci and the Sentinelles Network from January 2000 to May 2008. Reporting of invasive meningococcal infections is mandatory. All invasive meningococcal isolates in France are sent to the National Reference Center for Meningococci for full characterization and typing. The general practitioners of the Sentinelles Network report on influenza-like illnesses on a weekly basis by sending patient deidentified data via the Internet to a GIS database (11). The monthly incidence of MD (right axis) and the weekly incidence of influenza-like illnesses (left axis) during the period of January 2000 to May 2008 are represented on the same graph.The mechanisms by which influenza virus infection may favor bacterial superinfection with N. meningitidis, as well as with staphylococci, pneumococci, streptococci, and Haemophilus influenzae, have been investigated using cellular and animal models (15, 19, 22, 33). Virus-induced immune dysregulation, such as impairment of phagocytic functions or alterations in the production of cytokines, can be involved (12). In mice convalescing from influenza A virus (IAV) infection, the production of interleukin-10 in the lungs enhanced susceptibility to meningococcal (3) and to pneumococcal (37) superinfection. Influenza virus infection can also enhance bacterial adhesion by disrupting the respiratory epithelium or by increasing the accessibility or expression of membrane receptors (26). Conflicting results about the effects of influenza virus infection on meningococcal adherence to epithelial cells have been reported. One study reported that meningococci bind IAV-infected epithelial cells more efficiently than uninfected cells (10), whereas another concluded that coinfection with influenza B virus does not affect the association of meningococci with cultured human nasopharyngeal mucosa (29). Adhesion to epithelial cells in the nasopharynx is the early step enabling N. meningitidis to colonize the upper respiratory tract before it possibly goes through the epithelial barrier into the blood to induce bacteremia and reaches the meningeal spaces to induce meningitis. The adhesion process is associated with a downregulation of the capsule (9). We hypothesized that sialic acid-containing capsules could be a substrate for the neuraminidase (NA) of IAV and that this direct virus-bacterium interaction could play a major role in enhancing meningococcal adhesion to the respiratory epithelium. This hypothesis was tested on isolates belonging to various serogroups of N. meningitidis, using an in vitro model of adhesion to epithelial cells transiently expressing IAV-derived recombinant NAs.     

In vitro susceptibility of various genotypic strains of Toxoplasma gondii to pyrimethamine, sulfadiazine, and atovaquone

Sulfadiazine, pyrimethamine, and atovaquone are widely used for the treatment of severe toxoplasmosis. Their in vitro activities have been almost exclusively demonstrated on laboratory strains belonging to genotype I. We determined the in vitro activities of these drugs against 17 strains of Toxoplasma gondii belonging to various genotypes and examined the correlations among 50% inhibitory concentrations (IC50s), growth kinetics, strain genotypes, and mutations on drug target genes. Growth kinetics were determined in THP-1 cell cultures using real-time PCR. IC50s were determined in MRC-5 cell cultures using a T. gondii-specific enzyme-linked immunosorbent assay performed on cultures. Mutations in dihydrofolate reductase (DHFR), dihydropteroate synthase (DHPS), and cytochrome b genes were determined by sequencing. Pyrimethamine IC50s ranged between 0.07 and 0.39 mg/liter, with no correlation with the strain genotype but a significant correlation with growth kinetics. Several mutations found on the DHFR gene were not linked to lower susceptibility. Atovaquone IC50s were in a narrow range of concentrations (mean, 0.06 +/- 0.02 mg/liter); no mutation was found on the cytochrome b gene. IC50s for sulfadiazine ranged between 3 and 18.9 mg/liter for 13 strains and were >50 mg/liter for three strains. High IC50s were not correlated to strain genotypes or growth kinetics. A new mutation of the DHPS gene was demonstrated in one of these strains. In conclusion, we found variability in the susceptibilities of T. gondii strains to pyrimethamine and atovaquone, with no evidence of drug resistance. A higher variability was found for sulfadiazine, with a possible resistance of three strains. No relationship was found between drug susceptibility and strain genotype.     

The speed of orthographic processing during lexical decision: electrophysiological evidence for independent coding of letter identity and letter position in visual word recognition

Adults can decide rapidly if a string of letters is a word or not. However, the exact time course of this discrimination is still an open question. Here we sought to track the time course of this discrimination and to determine how orthographic information -- letter position and letter identity -- is computed during reading. We used a go/no-go lexical decision task while recording event-related potentials (ERPs). Subjects were presented with single words (go trials) and pseudowords (no-go trials), which varied in orthographic conformation, presenting either a double consonant frequently doubled (i.e., "ss") or never doubled (i.e., "zz") (identity factor); and a position of the double consonant was which either legal or illegal (position factor), in a 2 x 2 factorial design. Words and pseudowords clearly differed as early as 230 msec. At this latency, ERP waveforms were modulated both by the identity and by the position of letters: The fronto-central no-go N2 was the smallest in amplitude and peaked the earliest to pseudowords presenting both an illegal double-letter position and an identity never encountered. At this stage, the two factors showed additive effects, suggesting an independent coding. The factors of identity and position of double letters interacted much later in the process, at the P3 level, around 300-400 msec on frontal and central sites, in line with the lexical decision data obtained in the behavioral study. Overall, these results show that the speed of lexical decision may depend on orthographic information coded independently by the identity and position of letters in a word.