The scaffold protein PDZK1 modulates expression and function of the organic anion transporting polypeptide 2B1.

The protein family of Organic Anion Transporting Polypeptides (OATPs) summarizes various transporters known to facilitate cellular uptake of xenobiotics. One member of this family is OATP2B1. This transporter is ubiquitously expressed and possesses a PDZ-binding motif at the C-terminus. PDZK1 (PDZ domain-containing 1) is a scaffold protein that influences function of different membrane proteins by sorting/stabilization of their membrane localization. It was aim of the herein reported study to investigate whether there is an interaction between OATP2B1 and PDZK1, and to further characterize its impact on transport function. At first expression of both OATP2B1 and PDZK1 was evaluated in liver, kidney and intestine. Based on the existence of a C-terminal PDZ-class I binding motif in OATP2B1 and the co-expression in all tested tissues an interaction was likely. Testing the influence of PDZK1 on OATP2B1 transport function revealed enhanced transport capacity for estrone 3-sulfate, thereby suggesting a change in OATP2B1 amount in the membrane. This assumption was validated by Western blot analysis. Finally, deletion of the C-terminal PDZ-binding motif in OATP2B1 lowered the impact of PDZK1 on transport function. Taken together, we report an interaction of PDZK1 with OATP2B1, which influences localization and function of the transporter. Changes in PDZK1 expression may therefore be one factor contributing to interindividual differences in OATP2B1 mediated pharmacokinetic processes.

Neurosteroid Transport in the Brain: Role of ABC and SLC Transporters.

Neurosteroids, comprising pregnane, androstane, and sulfated steroids can alter neuronal excitability through interaction with ligand-gated ion channels and other receptors and have therefore a therapeutic potential in several brain disorders. They can be formed in brain cells or are synthesized by an endocrine gland and reach the brain by penetrating the blood-brain barrier (BBB). Especially sulfated steroids such as pregnenolone sulfate (PregS) and dehydroepiandrosterone sulfate (DHEAS) depend on transporter proteins to cross membranes. In this review, we discuss the involvement of ATP-binding cassette (ABC)- and solute carrier (SLC)-type membrane proteins in the transport of these compounds at the BBB and in the choroid plexus (CP), but also in the secretion from neurons and glial cells. Among the ABC transporters, especially BCRP (ABCG2) and several MRP/ABCC subfamily members (MRP1, MRP4, MRP8) are expressed in the brain and known to efflux conjugated steroids. Furthermore, several SLC transporters have been shown to mediate cellular uptake of steroid sulfates. These include members of the OATP/SLCO subfamily, namely OATP1A2 and OATP2B1, as well as OAT3 (SLC22A3), which have been reported to be expressed at the BBB, in the CP and in part in neurons. Furthermore, a role of the organic solute transporter OSTα-OSTß (SLC51A/B) in brain DHEAS/PregS homeostasis has been proposed. This transporter was reported to be localized especially in steroidogenic cells of the cerebellum and hippocampus. To date, the impact of transporters on neurosteroid homeostasis is still poorly understood. Further insights are desirable also with regard to the therapeutic potential of these compounds.

Magnetic Resonance Imaging of Parotid Gland Tumors: Dynamic Contrast-Enhanced Sequence Evaluation.

OBJECTIVE: The aim of the study was to evaluate dynamic contrast-enhanced magnetic resonance (MR) imaging in the characterization of parotid gland tumors. METHODS: Fifty-five parotid lesions in 55 patients were retrospectively included. Two observers interpreted 2 reading protocols derived from all MR imaging in 2 distinct sessions, independently and blinded. Benign versus malignant distinction was carried out for protocol 1 (without contrast administration) and protocol 2 (with dynamic contrast-enhanced sequence). Histopathological results after surgical resection were used as the criterion standard. Diagnostic accuracy was compared between protocols using McNemar test. A P values of less than 0.05 indicated significant difference. RESULTS: There was no intraobserver statistical discordance between protocols for both observers (P = 0.27 and P = 1). Interobserver reliability showed moderate agreement for protocol 1 (κ = 0.591; 95% confidence interval [CI], 0.376-0.806) and 2 (κ = 0.463, 95% CI, 0.226-0.701). Intraobserver reliability showed moderate agreement for observer 1 (κ = 0.507; 95% CI, 0.279-0.736) and 2 (κ = 0.477; 95% CI, 0.241-0.712). CONCLUSIONS: Magnetic resonance imaging protocol including dynamic sequence for the characterization of parotid gland lesion yielded nonsignificant increases in sensitivity, specificity, or positive predictive values, and negative predictive values over noninjected protocol.

Several adaptor proteins promote intracellular localisation of the transporter MRP4/ABCC4 in platelets and haematopoietic cells.

The multidrug resistance protein 4 (MRP4/ABCC4) has been identified as an important transporter for signalling molecules including cyclic nucleotides and several lipid mediators in platelets and may thus represent a novel target to interfere with platelet function. Besides its localisation in the plasma membrane, MRP4 has been also detected in the membrane of dense granules in resting platelets. In polarised cells it is localised at the basolateral or apical plasma membrane. To date, the mechanism of MRP4 trafficking has not been elucidated; protein interactions may regulate both the localisation and function of this transporter. We approached this issue by searching for interacting proteins by in vitro binding assays, followed by immunoblotting and mass spectrometry, and by visualising their co-localisation in platelets and haematopoietic cells. We identified the PDZ domain containing scaffold proteins ezrin-binding protein 50 (EBP50/NHERF1), postsynaptic density protein 95 (PSD95), and sorting nexin 27 (SNX27), but also the adaptor protein complex 3 subunit ß3A (AP3B1) and the heat shock protein HSP90 as putative interaction partners of MRP4. The knock-down of SNX27, PSD95, and AP3B1 by siRNA in megakaryoblastic leukaemia cells led to a redistribution of MRP4 from intracellular structures to the plasma membrane. Inhibition of HSP90 led to a diminished expression and retention of MRP4 in the endoplasmic reticulum. These results indicate that MRP4 localisation and function are regulated by multiple protein interactions. Changes in the adaptor proteins can hence lead to altered localisation and function of the transporter.

Fourth branchial pouch sinus: from diagnosis to treatment.

BACKGROUND: Fourth branchial pouch sinus (FBPS) is rare and frequently unknown to clinicians. Misdiagnosis is common and definitive surgery is often made difficult by previous episodes of infection and failed attempts at excision. The purpose of this paper is to clarify the diagnostic criteria and the methods used for the surgical management of FBPS. MATERIALS AND METHOD: From a series of 265 head and neck cysts and fistulae, 7 cases of FBPS were retrospectively reviewed. The surgical technique is detailed. RESULTS: Six cases were located on the left side and one on the right. CT scanning showed an air-filled structure on both sides of the lesser horn of the thyroid cartilage in 2 cases out of 4, and barium swallow found a FBPS in 1 case out of 3. Direct pharyngoscopy allowed confirmation of the diagnosis in all cases and permitted catheterization of the tract with the spring guidewire of a vascular catheter which helped surgical location and subsequent dissection. The recurrent laryngeal nerve was systematically dissected to avoid inadvertent damage. A hemi-thyroidectomy was performed in one case. A transient laryngeal paralysis (lasting 9 months) was noted in a 3-week-old newborn operated on. None of the 7 cases had a recurrence after complete resection of the FBPS (3.7 years average follow-up). CONCLUSION: Symptoms on the right side do not exclude the diagnosis of a FBPS. Endoscopy is the key investigation. It allows confirmation of the diagnosis and catheterization of the tract, which aids the surgical dissection. Total removal of the sinus tract tissue with dissection and preservation of the recurrent laryngeal nerve is recommended. EBM RATING: A-1.

Rehabilitation for high-frequency sensorineural hearing impairment in adults with the symphonix vibrant soundbridge: a comparative study.

OBJECTIVE: To assess and compare the benefits for patients with high-frequency hearing loss obtained from an implantable middle ear implant, the Symphonix Vibrant Soundbridge using the SIGNIA processing circuitry, to those derived from conventional amplification using the same integrated circuitry and to those derived from a variety of preoperatively worn hearing aids. STUDY DESIGN: A single-subject, repeated-measures study design was used for a comparative evaluation of the benefits derived from the Symphonix Vibrant Soundbridge and conventional amplification. Objective audiometric measures were performed postoperatively to compare the Symphonix Vibrant Soundbridge (404) and SIGNIA hearing aid, both using the SIGNIA processing chip. Tests were performed under three conditions: unaided, aided Symphonix Vibrant Soundbridge (404), and aided SIGNIA hearing aid. Subjective self-assessment scales, standardized and nonstandardized, were completed for the Symphonix Vibrant Soundbridge (404) and the preoperative hearing aid to compare the personally perceived benefits. Statistical comparison of the data sets with each device type was performed using the nonparametric Wilcoxon test. SETTING: One tertiary teaching hospital and one hearing aid specialist fitting office. SUBJECTS: Six patients displaying a high-frequency hearing loss who had the Symphonix Vibrant Soundbridge implanted for an average of 17 months. INTERVENTION: Rehabilitative. RESULTS: Aided thresholds with the Symphonix Vibrant Soundbridge (404) and the SIGNIA hearing aid showed no significant difference. Speech comprehension scores in quiet and in noise were significantly improved with each device type over the unaided condition scores. Individual performance on speech test measures was equivalent or superior with the Symphonix Vibrant Soundbridge (404) in comparison with that with the SIGNIA hearing aid. When using the Symphonix Vibrant Soundbridge (404) in quiet, the group achieved 50% speech comprehension at significantly softer presentation levels (p = 0.027) than when wearing the SIGNIA hearing aid. Similarly, in noise, 50% speech comprehension was achieved at significantly lower (more difficult) signal-to-noise ratios (p = 0.028) with the Symphonix Vibrant Soundbridge (404) than with the SIGNIA hearing aid. The level of satisfaction for various aspects of the device and performance and listening ease, particularly in the presence of aversive sounds and in reverberant conditions, was reported as significantly better with the Symphonix Vibrant Soundbridge (404) than with the preoperative hearing aid. CONCLUSIONS: Despite similar gain with each device type using the same SIGNIA processing technology, the patient group demonstrated significant advantages for speech comprehension in quiet and in noise when using the Symphonix Vibrant Soundbridge (404). Such an effect may be attributed to higher fidelity sound transmission by means of the direct-drive mechanism used by the implant. Subjective reports support the results from the objective assessments, both being in favor of the implant over conventional amplification. In conclusion, the Symphonix Vibrant Soundbridge (404) is a suitable treatment option offering advantages over conventional amplification to the hearing-impaired person with a high-frequency hearing loss.