Measuring local pH at interfaces from molecular tumbling: A concept for designing EPR-active pH-sensitive labels and probes.

Molecular probes and indicators are broadly employed for pH measurements in bulk media and at interfaces. The underlying physical principle of pH measurements of most of these probes is based on a change in the electronic structure that, for example, results in a shift of the emission peak of the fluorescence probes, changes in NMR chemical shifts due to the affected electronic shielding, or magnetic parameters of pH-sensitive nitroxides as measured by EPR. Here we explore another concept for measuring local protonation state of molecular tags based on changes in rotational dynamics of electron spin-bearing moieties that are readily detected by conventional continuous wave X-band EPR. Such changes are especially pronounced at biological interfaces, such as lipid bilayer membranes, due to the probe interactions with adjacent charges and polarizable dipoles. The concept was demonstrated by synthesizing a series of pH-sensitive nitroxides and spin-labelled phospholipids. EPR spectra of these newly synthesized nitroxides exhibit relatively small - about 0.5 G - changes in isotropic nitrogen hyperfine coupling constant upon reversible protonation. However, spin-labelled phospholipids incorporated into lipid bilayers demonstrated almost 6-fold change in rotational correlation time upon protonation, readily allowing for pKa determination from large changes in EPR spectra. The demonstrated concept of EPR-based pH measurements leads to a broader range of potential nitroxide structures that can serve as molecular pH sensors at the desired pH range and, thus, facilitates further development of spin-labelling EPR methods to study electrostatic phenomena at chemical and biological interfaces.

Renal Cell Carcinoma of Pelvic Kidney with Atypical Nodal Metastasis: A Diagnostic Challenge.

Ectopic pelvic kidney is a known congenital anomaly; however, the presence of renal cell carcinoma (RCC) in an ectopic kidney is rare with the evidence available in the form of a few case reports only. In this case report, we present a case of metastatic RCC in the pelvic kidney which became a diagnostic challenge because of atypical contrast-enhanced computed tomographic (CT) characteristics and unusual pattern of lymph node involvement including cervical lymph node in the absence of visceral metastasis. Because of its unusual location and uncertain vascular anatomy, ectopic kidney poses a surgical challenge. Owing to the rarity of this condition, optimal surgical approach, metastatic potential, routes of metastasis, and effectiveness of systemic agents in pelvic RCC compared to RCC in a normally located kidney, are largely unknown. Key Words: Renal cell carcinoma, Pelvic kidney, Lymph node metastasis.

Validation of a Bench-Top Training Model for Retrograde Intrarenal Surgery.

OBJECTIVE: To validate the in-house built Styrofoam box bench-top training model for retrograde intrarenal surgery (RIRS). MATERIALS AND METHODS: This study was performed in the setting of a half-day RIRS course. During the course, participants performed RIRS on a locally built bench-top model. We recruited 26 participants, comprising 20 trainees and 6 experts. Trainees and experts were asked to fill a self-administered questionnaire assessing various components of RIRS to assess the face and content validity. For construct validity, experts using Objective Structured Assessment of Technical Skills (OSATS) rated trainees and the mean OSATS score of junior versus senior residents was compared. RESULTS: As per trainees, the model was 86% (4.3/5) realistic, which was backed by experts who found this model to be 87.6% (4.38/5) realistic. The overall face validity of the model was 86.4% (4.32/5). The overall content validity of this model was 83.4% (4.17/5). Majority of the participants thought that this tool is useful for learning technique (4.38 ± 0.49) and safe-conduct (4.31 ± 0.73) of the procedure. The trainees concurred that the skills acquired are transferable to the operating room (4.23 ± 0.76). However, the construct validity by comparing mean OSATS score of junior versus senior residents was 19.5 ± 3.5 and 23 ± 4.5. A p value of 0.11 could not be established. CONCLUSION: This study has demonstrated the face, content, and construct validity of the bench-top training model for RIRS. Further evaluation is necessary to compare its effectiveness against other available models to demonstrate concurrent validity.