In vitro and in silico characterization of the transport of selected perfluoroalkyl carboxylic acids and perfluoroalkyl sulfonic acids by human organic anion transporter 1 (OAT1), OAT2 and OAT3.

Perfluoroalkyl carboxylic acids (PFCAs) and perfluoroalkyl sulfonic acids (PFSAs) belong to the group of poly- and perfluoroalkyl substances (PFASs), which may accumulate in humans due to their limited excretion. To provide more insight into the active renal excretion potential of PFASs in humans, this work investigated in vitro the transport of three PFCAs (PFHpA, PFOA, PFNA) and three PFSAs (PFBS, PFHxS and PFOS) using OAT1-, OAT2- or OAT3-transduced human embryonic kidney (HEK) cells. Only PFHpA and PFOA showed clear uptake in OAT1-transduced HEK cells, while no transport was observed for PFASs in OAT2-transduced HEK cells. In OAT3-transduced HEK cells only PFHpA, PFOA, PFNA, and PFHxS showed clear uptake. To study the interaction with the transporters, molecular docking and dynamics simulation were performed for PFHpA and PFHxS, for which a relatively short and long half-life in humans has been reported, respectively. Docking analyses could not always distinguish the in vitro transported from the non-transported PFASs (PFHpA vs. PFHxS), whereas molecular dynamic simulations could, as only a stable interaction of the PFAS with the inner part of transporter mouth was detected for those that were transported in vitro (PFHpA with OAT1, none with OAT2, and PFHpA and PFHxS with OAT3). Altogether, this study presents in vitro and in silico insight with respect to the selected PFASs transport by the human renal secretory transporters OAT1, OAT2, and OAT3, which provides further understanding about the differences between the capability of PFAS congeners to accumulate in humans.

Varieties of pictorial vision.

Pictorial awareness is addressed through experimental phenomenology involving over 90 naïve participants. Since one can't look at the "same" picture twice the study uses one-shot trials. The participant's fascination for the duration of a session is held through the artistic principle of theme and variation. Six variations focus on the theme of pictorial geometry, both two-dimensional and three-dimensional. Major findings are: Idiosyncratic deviations from veridical are huge as compared to common textbook "effects." Observers wield arbitrary heuristics for tasks that are "formally related." The assumption of a common formal framework is apparently unsound. The notion of "inverse optics" is misleading. A fair fraction of the population appears to lack monocular stereopsis as intuitive awareness. It suggests an as-yet unrecognized, but perhaps common variety of aphantasia.

The well-tempered color circle: A chromatic Gestalt.

The "Color Circle" is an important chromatic Gestalt in the visual arts. There is not really a formal equivalent in conventional colorimetry. The fact that the hues can be linearly ordered and that such an order is necessarily periodic was intuited by artists in the early 19th century, but only formally explained by Ostwald and later Schrödinger a century later. As with musical keys, various metrical orders are in common use. Is there such a thing as a "well tempered" order? We consider this an issue for experimental phenomenology. We discuss an attempt based on observations by 30 (nonartist) observers.

"Warm," "cool," and the colors.

Participants judged affective cooler/warmer gradients around a 12-step color circle. Each pair of adjacent colors was presented twice (left-right reversed), all in random order. Participants readily performed the task, but their settings do not correlate very well. Individual responses were compared with a small number of canonical templates. For a little less than one-half of the participants responses or judgements correlate with such a template. We find a warm pole (in the orange environment) and a cool pole (in the teal environment) connected with two tracks that tend to have one or more gaps or weak, even inverted links. We conclude that the common artistic cool-warm polarity is only weakly reflected in responses of our observers. If it does, the observers apparently use categorical warm and cool poles and may be uncertain in relating adjacent hue steps along the 12-step color circle.

Effects of allopurinol and febuxostat on uric acid transport and transporter expression in human umbilical vein endothelial cells.

Uric acid induces radical oxygen species formation, endothelial inflammation, and endothelial dysfunction which contributes to the progression of atherosclerosis. Febuxostat inhibits BCRP- and allopurinol stimulates MRP4-mediated uric acid efflux in human embryonic kidney cells. We hypothesized that endothelial cells express uric acid transporters that regulate intracellular uric acid concentration and that modulation of these transporters by febuxostat and allopurinol contributes to their different impact on cardiovascular mortality. The aim of this study was to explore a potential difference between the effect of febuxostat and allopurinol on uric acid uptake by human umbilical vein endothelial cells. Febuxostat increased intracellular uric acid concentrations compared with control. In contrast, allopurinol did not affect intracellular uric acid concentration. In line with this observation, febuxostat increased mRNA expression of GLUT9 and reduced MRP4 expression, while allopurinol did not affect mRNA expression of these uric acid transporters. These findings provide a possible pathophysiological pathway which could explain the higher cardiovascular mortality for febuxostat compared to allopurinol but should be explored further.

In vitro screening model for compound interactions with human and dairy animal BCRP orthologs.

Orthologs of breast cancer resistance protein (BCRP/ABCG2), an ATP-binding cassette (ABC) efflux transmembrane transporter, are present in several species. The list of compounds known to interact with BCRP is growing, and many questions remain concerning species-specific variations in substrate specificity and affinity and the potency of inhibitors. As the most abundant efflux transporter known to be present in the blood-milk barrier, BCRP can increase the elimination of certain xenobiotics to milk, posing a risk for suckling offspring and dairy product consumers. Here we developed a model that can be employed to investigate species-specific differences between BCRP substrates and inhibitors. Membrane vesicles were isolated from transiently transduced human embryonic kidney (HEK) 293 cells, overexpressing BCRP, with human, bovine, caprine, and ovine cDNA sequences. To confirm BCRP transport activity in the transduced cells, D-luciferin efflux was measured and to confirm transport activity in the membrane vesicles, [3H] estrone-3-sulfate ([3H]E1S) influx was measured. We also determined the Michaelis-Menten constant (Km) and Vmax of [3H]E1S for each species. We have developed an in vitro transport model to study differences in compound interactions with BCRP orthologs from milk-producing animal species and humans. BCRP transport activity was demonstrated in the species-specific transduced cells by a reduced accumulation of D-luciferin compared with the control cells, indicating BCRP-mediated efflux of D-luciferin. Functionality of the membrane vesicle model was demonstrated by confirming ATP-dependent transport and by quantifying the kinetic parameters, Km and Vmax for the model substrate [3H]E1S. The values were not significantly different between species for the model substrates tested. This model can be insightful for appropriate inter-species extrapolations and risk assessments of xenobiotics in lactating woman and dairy animals.

Pyruvate dehydrogenase is a potential mitochondrial off-target for gentamicin based on in silico predictions and in vitro inhibition studies.

During the drug development process, organ toxicity leads to an estimated failure of one-third of novel chemical entities. Drug-induced toxicity is increasingly associated with mitochondrial dysfunction, but identifying the underlying molecular mechanisms remains a challenge. Computational modeling techniques have proven to be a good tool in searching for drug off-targets. Here, we aimed to identify mitochondrial off-targets of the nephrotoxic drugs tenofovir and gentamicin using different in silico approaches (KRIPO, ProBis and PDID). Dihydroorotate dehydrogenase (DHODH) and pyruvate dehydrogenase (PDH) were predicted as potential novel off-target sites for tenofovir and gentamicin, respectively. The predicted targets were evaluated in vitro, using (colorimetric) enzymatic activity measurements. Tenofovir did not inhibit DHODH activity, while gentamicin potently reduced PDH activity. In conclusion, the use of in silico methods appeared a valuable approach in predicting PDH as a mitochondrial off-target of gentamicin. Further research is required to investigate the contribution of PDH inhibition to overall renal toxicity of gentamicin.

Exome sequencing of ATP1A3-negative cases of alternating hemiplegia of childhood reveals SCN2A as a novel causative gene.

Alternating hemiplegia of childhood (AHC) is a rare neurodevelopment disorder that is typically characterized by debilitating episodic attacks of hemiplegia, seizures, and intellectual disability. Over 85% of individuals with AHC have a de novo missense variant in ATP1A3 encoding the catalytic α3 subunit of neuronal Na+/K+ ATPases. The remainder of the patients are genetically unexplained. Here, we used next-generation sequencing to search for the genetic cause of 26 ATP1A3-negative index patients with a clinical presentation of AHC or an AHC-like phenotype. Three patients had affected siblings. Using targeted sequencing of exonic, intronic, and flanking regions of ATP1A3 in 22 of the 26 index patients, we found no ultra-rare variants. Using exome sequencing, we identified the likely genetic diagnosis in 9 probands (35%) in five genes, including RHOBTB2 (n = 3), ATP1A2 (n = 3), ANK3 (n = 1), SCN2A (n = 1), and CHD2 (n = 1). In follow-up investigations, two additional ATP1A3-negative individuals were found to have rare missense SCN2A variants, including one de novo likely pathogenic variant and one likely pathogenic variant for which inheritance could not be determined. Functional evaluation of the variants identified in SCN2A and ATP1A2 supports the pathogenicity of the identified variants. Our data show that genetic variants in various neurodevelopmental genes, including SCN2A, lead to AHC or AHC-like presentation. Still, the majority of ATP1A3-negative AHC or AHC-like patients remain unexplained, suggesting that other mutational mechanisms may account for the phenotype or that cases may be explained by oligo- or polygenic risk factors.

Transporter-Mediated Cellular Distribution of Tyrosine Kinase Inhibitors as a Potential Resistance Mechanism in Chronic Myeloid Leukemia.

Chronic myeloid leukemia (CML) is a hematologic neoplasm characterized by the expression of the BCR::ABL1 oncoprotein, a constitutively active tyrosine kinase, resulting in uncontrolled growth and proliferation of cells in the myeloid lineage. Targeted therapy using tyrosine kinase inhibitors (TKIs) such as imatinib, nilotinib, dasatinib, bosutinib, ponatinib and asciminib has drastically improved the life expectancy of CML patients. However, treatment resistance occurs in 10-20% of CML patients, which is a multifactorial problem that is only partially clarified by the presence of TKI inactivating BCR::ABL1 mutations. It may also be a consequence of a reduction in cytosolic TKI concentrations in the target cells due to transporter-mediated cellular distribution. This review focuses on drug-transporting proteins in stem cells and progenitor cells involved in the distribution of TKIs approved for the treatment of CML. Special attention will be given to ATP-binding cassette transporters expressed in lysosomes, which may facilitate the extracytosolic sequestration of these compounds.

The potential role of drug transporters and amikacin modifying enzymes in M. avium.

OBJECTIVES: Mycobacterium avium (M. avium) complex bacteria cause opportunistic infections in humans. Treatment yields cure rates of 60% and consists of a macrolide, a rifamycin, and ethambutol, and in severe cases, amikacin. Mechanisms of antibiotic tolerance remain mostly unknown. Therefore, we studied the contribution of efflux and amikacin modification to antibiotic susceptibility. METHODS: We characterised M. avium ABC transporters and studied their expression together with other transporters following exposure to clarithromycin, amikacin, ethambutol, and rifampicin. We determined the effect of combining the efflux pump inhibitors berberine, verapamil and CCCP (carbonyl cyanide m-chlorophenyl hydrazone), to study the role of efflux on susceptibility. Finally, we studied the modification of amikacin by M. avium using metabolomic analysis. RESULTS: Clustering shows conservation between M. avium and M. tuberculosis and transporters from most bacterial subfamilies (2-6, 7a/b, 10-12) were found. The largest number of transporter encoding genes was up-regulated after clarithromycin exposure, and the least following amikacin exposure. Only berberine increased the susceptibility to clarithromycin. Finally, because of the limited effect of amikacin on transporter expression, we studied amikacin modification and showed that M. avium, in contrast to M. abscessus, is not able to modify amikacin. CONCLUSION: We show that M. avium carries ABC transporters from all major families important for antibiotic efflux, including homologues shown to have affinity for drugs included in treatment. Efflux inhibition in M. avium can increase susceptibility, but this effect is efflux pump inhibitor- and antibiotic-specific. Finally, the lack of amikacin modifying activity in M. avium is important for its activity.

Physiologically-Based Pharmacokinetic Modelling to Predict the Pharmacokinetics and Pharmacodynamics of Linezolid in Adults and Children with Tuberculous Meningitis.

Linezolid is used off-label for treatment of central nervous system infections. However, its pharmacokinetics and target attainment in cranial cerebrospinal fluid (CSF) in tuberculous meningitis patients is unknown. This study aimed to predict linezolid cranial CSF concentrations and assess attainment of pharmacodynamic (PD) thresholds (AUC:MIC of >119) in plasma and cranial CSF of adults and children with tuberculous meningitis. A physiologically based pharmacokinetic (PBPK) model was developed to predict linezolid cranial CSF profiles based on reported plasma concentrations. Simulated steady-state PK curves in plasma and cranial CSF after linezolid doses of 300 mg BID, 600 mg BID, and 1200 mg QD in adults resulted in geometric mean AUC:MIC ratios in plasma of 118, 281, and 262 and mean cranial CSF AUC:MIC ratios of 74, 181, and 166, respectively. In children using ~10 mg/kg BID linezolid, AUC:MIC values at steady-state in plasma and cranial CSF were 202 and 135, respectively. Our model predicts that 1200 mg per day in adults, either 600 mg BID or 1200 mg QD, results in reasonable (87%) target attainment in cranial CSF. Target attainment in our simulated paediatric population was moderate (56% in cranial CSF). Our PBPK model can support linezolid dose optimization efforts by simulating target attainment close to the site of TBM disease.

Perfluoroalkyl substances (PFASs) are substrates of the renal human organic anion transporter 4 (OAT4).

Poly- and perfluoroalkyl substances (PFASs) are omnipresent in the environment and have been shown to accumulate in humans. Most PFASs are not biotransformed in animals and humans, so that elimination is largely dependent on non-metabolic clearance via bile and urine. Accumulation of certain PFASs in humans may relate to their reabsorption from the pre-urine by transporter proteins in the proximal tubules of the kidney, such as URAT1 and OAT4. The present study assessed the in vitro transport of 7 PFASs (PFHpA, PFOA, PFNA, PFDA, PFBS, PFHxS and PFOS) applying URAT1- or OAT4-transfected human embryonic kidney (HEK) cells. Virtually no transport of PFASs could be measured in URAT1-transfected HEK cells. All PFASs, except PFBS, showed clear uptake in OAT4-transfected HEK cells. In addition, these in vitro results were further supported by in silico docking and molecular dynamic simulation studies assessing transporter-ligand interactions. Information on OAT4-mediated transport may provide insight into the accumulation potential of PFASs in humans, but other kinetic aspects may play a role and should also be taken into account. Quantitative information on all relevant kinetic processes should be integrated in physiologically based kinetic (PBK) models, to predict congener-specific accumulation of PFASs in humans in a more accurate manner.

SLC7A8 coding for LAT2 is associated with early disease progression in osteosarcoma and transports doxorubicin.

Background: Despite (neo) adjuvant chemotherapy with cisplatin, doxorubicin and methotrexate, some patients with primary osteosarcoma progress during first-line systemic treatment and have a poor prognosis. In this study, we investigated whether patients with early disease progression (EDP), are characterized by a distinctive pharmacogenetic profile. Methods and Findings: Germline DNA from 287 Dutch high-grade osteosarcoma patients was genotyped using the DMET Plus array (containing 1,936 genetic markers in 231 drug metabolism and transporter genes). Associations between genetic variants and EDP were assessed using logistic regression models and associated variants (p <0.05) were validated in independent cohorts of 146 (Spain and United Kingdom) and 28 patients (Australia). In the association analyses, EDP was significantly associated with an SLC7A8 locus and was independently validated (meta-analysis validation cohorts: OR 0.19 [0.06-0.55], p = 0.002). The functional relevance of the top hits was explored by immunohistochemistry staining and an in vitro transport models. SLC7A8 encodes for the L-type amino acid transporter 2 (LAT2). Transport assays in HEK293 cells overexpressing LAT2 showed that doxorubicin, but not cisplatin and methotrexate, is a substrate for LAT2 (p < 0.0001). Finally, SLC7A8 mRNA expression analysis and LAT2 immunohistochemistry of osteosarcoma tissue showed that the lack of LAT2 expression is a prognostic factor of poor prognosis and reduced overall survival in patients without metastases (p = 0.0099 and p = 0.14, resp.). Conclusion: This study identified a novel locus in SLC7A8 to be associated with EDP in osteosarcoma. Functional studies indicate LAT2-mediates uptake of doxorubicin, which could give new opportunities to personalize treatment of osteosarcoma patients.

Eye contact avoidance in crowds: A large wearable eye-tracking study.

Eye contact is essential for human interactions. We investigated whether humans are able to avoid eye contact while navigating crowds. At a science festival, we fitted 62 participants with a wearable eye tracker and instructed them to walk a route. Half of the participants were further instructed to avoid eye contact. We report that humans can flexibly allocate their gaze while navigating crowds and avoid eye contact primarily by orienting their head and eyes towards the floor. We discuss implications for crowd navigation and gaze behavior. In addition, we address a number of issues encountered in such field studies with regard to data quality, control of the environment, and participant adherence to instructions. We stress that methodological innovation and scientific progress are strongly interrelated.

A Generative View of Rationality and Growing Awareness†.

In this paper we contrast bounded and ecological rationality with a proposed alternative, generative rationality. Ecological approaches to rationality build on the idea of humans as "intuitive statisticians" while we argue for a more generative conception of humans as "probing organisms." We first highlight how ecological rationality's focus on cues and statistics is problematic for two reasons: (a) the problem of cue salience, and (b) the problem of cue uncertainty. We highlight these problems by revisiting the statistical and cue-based logic that underlies ecological rationality, which originate from the misapplication of concepts in psychophysics (e.g., signal detection, just-noticeable-differences). We then work through the most popular experimental task in the ecological rationality literature-the city size task-to illustrate how psychophysical assumptions have informally been linked to ecological rationality. After highlighting these problems, we contrast ecological rationality with a proposed alternative, generative rationality. Generative rationality builds on biology-in contrast to ecological rationality's focus on statistics. We argue that in uncertain environments cues are rarely given or available for statistical processing. Therefore we focus on the psychogenesis of awareness rather than psychophysics of cues. For any agent or organism, environments "teem" with indefinite cues, meanings and potential objects, the salience or relevance of which is scarcely obvious based on their statistical or physical properties. We focus on organism-specificity and the organism-directed probing that shapes awareness and perception. Cues in teeming environments are noticed when they serve as cues-for-something, requiring what might be called a "cue-to-clue" transformation. In this sense, awareness toward a cue or cues is actively "grown." We thus argue that perception might more productively be seen as the presentation of cues and objects rather than their representation. This generative approach not only applies to relatively mundane organism (including human) interactions with their environments-as well as organism-object relationships and their embodied nature-but also has significant implications for understanding the emergence of novelty in economic settings. We conclude with a discussion of how our arguments link with-but modify-Herbert Simon's popular "scissors" metaphor, as it applies to bounded rationality and its implications for decision making in uncertain, teeming environments.

Prediction of Moxifloxacin Concentrations in Tuberculosis Patient Populations by Physiologically Based Pharmacokinetic Modeling.

Moxifloxacin has an important role in the treatment of tuberculosis (TB). Unfortunately, coadministration with the cornerstone TB drug rifampicin results in suboptimal plasma exposure. We aimed to gain insight into the moxifloxacin pharmacokinetics and the interaction with rifampicin. Moreover, we provided a mechanistic framework to understand moxifloxacin pharmacokinetics. We developed a physiologically based pharmacokinetic model in Simcyp version 19, with available and newly generated in vitro and in vivo data, to estimate pharmacokinetic parameters of moxifloxacin alone and when administered with rifampicin. By combining these strategies, we illustrate that the role of P-glycoprotein in moxifloxacin transport is limited and implicate MRP2 as transporter of moxifloxacin-glucuronide followed by rapid hydrolysis in the gut. Simulations of multiple dose area under the plasma concentration-time curve (AUC) of moxifloxacin (400 mg once daily) with and without rifampicin (600 mg once daily) were in accordance with clinically observed data (predicted/observed [P/O] ratio of 0.87 and 0.80, respectively). Importantly, increasing the moxifloxacin dose to 600 mg restored the plasma exposure both in actual patients with TB as well as in our simulations. Furthermore, we extrapolated the single dose model to pediatric populations (P/O AUC ratios, 1.04-1.52) and the multiple dose model to children with TB (P/O AUC ratio, 1.51). In conclusion, our combined approach resulted in new insights into moxifloxacin pharmacokinetics and accurate simulations of moxifloxacin exposure with and without rifampicin. Finally, various knowledge gaps were identified, which may be considered as avenues for further physiologically based pharmacokinetic refinement.

The Effect of Single Nucleotide Variations in the Transmembrane Domain of OATP1B1 on in vitro Functionality.

PURPOSE: Organic Anion Transporting Polypeptide 1B1 (OATP1B1) mediates hepatic influx and clearance of many drugs, including statins. The SLCO1B1 gene is highly polymorphic and its function-impairing variants can predispose patients to adverse effects. The effects of rare genetic variants of SLCO1B1 are mainly unexplored. We examined the impact of eight naturally occurring rare variants and the well-known SLCO1B1 c.521C > T (V174A) variant on in vitro transport activity, cellular localization and abundance. METHODS: Transport of rosuvastatin and 2,7-dichlorofluorescein (DCF) in OATP1B1 expressing HEK293 cells was measured to assess changes in activity of the variants. Immunofluorescence and confocal microscopy determined the cellular localization of OATP1B1 and LC-MS/MS based quantitative targeted absolute proteomics analysis quantified the amount of OATP1B1 in crude membrane fractions. RESULTS: All studied variants, with the exception of P336R, reduced protein abundance to varying degree. V174A reduced protein abundance the most, over 90% compared to wild type. Transport function was lost in G76E, V174A, L193R and R580Q variants. R181C decreased activity significantly, while T345M and L543W retained most of wild type OATP1B1 activity. P336R showed increased activity and H575L decreased the transport of DCF significantly, but not of rosuvastatin. Decreased activity was interrelated with lower absolute protein abundance in the studied variants. CONCLUSIONS: Transmembrane helices 2, 4 and 11 appear to be crucial for proper membrane localization and function of OATP1B1. Four of the studied variants were identified as loss-of-function variants and as such could make the individual harboring these variants susceptible to altered pharmacokinetics and adverse effects of substrate drugs.

Perception of the Potential for Interaction in Social Scenes.

In urban environments, humans often encounter other people that may engage one in interaction. How do humans perceive such invitations to interact at a glance? We briefly presented participants with pictures of actors carrying out one of 11 behaviors (e.g., waving or looking at a phone) at four camera-actor distances. Participants were asked to describe what they might do in such a situation, how they decided, and what stood out most in the photograph. In addition, participants rated how likely they deemed interaction to take place. Participants formulated clear responses about how they might act. We show convincingly that what participants would do depended on the depicted behavior, but not the camera-actor distance. The likeliness to interact ratings depended both on the depicted behavior and the camera-actor distance. We conclude that humans perceive the "gist" of photographs and that various aspects of the actor, action, and context depicted in photographs are subjectively available at a glance. Our conclusions are discussed in the context of scene perception, social robotics, and intercultural differences.

Differences in P-glycoprotein activity in human and rodent blood-brain barrier assessed by mechanistic modelling.

Variation in the efficacy and safety of central nervous system drugs between humans and rodents can be explained by physiological differences between species. An important factor could be P-glycoprotein (Pgp) activity in the blood-brain barrier (BBB), as BBB expression of this drug efflux transporter is reportedly lower in humans compared to mouse and rat and subject to an age-dependent increase. This might complicate animal to human extrapolation of brain drug disposition and toxicity, especially in children. In this study, the potential species-specific effect of BBB Pgp activity on brain drug exposure was investigated. An age-dependent brain PBPK model was used to predict cerebrospinal fluid and brain mass concentrations of Pgp substrate drugs. For digoxin, verapamil and quinidine, in vitro kinetic data on their transport by Pgp were derived from literature and used to scale to in vivo parameters. In addition, age-specific digoxin transport was simulated for children with a postnatal age between 25 and 81 days. BBB Pgp activity in the model was optimized using measured CSF data for the Pgp substrates ivermectin, indinavir, vincristine, docetaxel, paclitaxel, olanzapine and citalopram, as no useful in vitro data were available. Inclusion of Pgp activity in the model resulted in optimized predictions of their brain concentration. Total brain-to-plasma AUC values (Kp,brain) in the simulations without Pgp were divided by the Kp,brain values with Pgp. Kp ratios ranged from 1 to 45 for the substrates investigated. Comparison of human with rodent Kp,brain ratios indicated ≥ twofold lower values in human for digoxin, verapamil, indinavir, paclitaxel and citalopram and ≥ twofold higher values for vincristine. In conclusion, BBB Pgp activity appears species-specific. An age-dependent PBPK model-based approach could be useful to extrapolate animal data to human adult and paediatric predictions by taking into account species-specific and developmental BBB Pgp expression.