Bilitranslocase localization and function in basolateral plasma membrane of renal proximal tubule in rat

Clinical Benefits of Indocyanine Green Fluorescence in Robot-Assisted Partial Nephrectomy

Background: To compare the intraoperative and postoperative outcomes of indocyanine green (ICG) administration in robot-assisted partial nephrectomy (RAPN) and report the differences in the results between patients with benign and malignant renal tumors. Methods: From 2017 to 2020, 132 patients underwent RAPN at our institution, including 21 patients with ICG administration. Clinical data obtained from our institution’s RAPN database were retrospectively reviewed. Intraoperative, postoperative, pathological, and functional outcomes of RAPN were assessed. Results: The pathological results indicated that among the 127 patients, 38 and 89 had received diagnoses of benign and malignant tumors, respectively. A longer operative time (311 vs. 271 min; p = 0.006) but superior preservation of estimated glomerular filtration rate (eGFR) at 3-month follow-up (90% vs. 85%; p = 0.031) were observed in the ICG-RAPN group. Less estimated blood loss, shorter warm ischemia time, and superior preservation of eGFR at postoperative day 1 and 6-month follow-up were also noted, despite no significant differences. Among the patients with malignant tumors, less estimated blood loss (30 vs. 100 mL; p < 0.001) was reported in the ICG-RAPN subgroup. Conclusions: Patients with ICG-RAPN exhibited superior short-term renal function outcomes compared with the standard RAPN group. Of the patients with malignant tumors, ICG-RAPN was associated with less blood loss than standard RAPN without a more positive margin rate. Further studies with larger cohorts and prospective designs are necessary to verify the intraoperative and functional advantages of the green dye.

Dietary Anthocyanins and Stroke: A Review of Pharmacokinetic and Pharmacodynamic Studies

Cerebrovascular accidents are currently the second major cause of death and the third leading cause of disability in the world, according to the World Health Organization (WHO), which has provided protocols for stroke prevention. Although there is a multitude of studies on the health benefits associated with anthocyanin (ACN) consumption, there is no a rigorous systematization of the data linking dietary ACN with stroke prevention. This review is intended to present data from epidemiological, in vitro, in vivo, and clinical studies dealing with the stroke related to ACN-rich diets or ACN supplements, along with possible mechanisms of action revealed by pharmacokinetic studies, including ACN passage through the blood-brain barrier (BBB).

Computational Approaches for Revealing the Structure of Membrane Transporters: Case Study on Bilitranslocase

The structural and functional details of transmembrane proteins are vastly underexplored, mostly due to experimental difficulties regarding their solubility and stability. Currently, the majority of transmembrane protein structures are still unknown and this present a huge experimental and computational challenge. Nowadays, thanks to X-ray crystallography or NMR spectroscopy over 3000 structures of membrane proteins have been solved, among them only a few hundred unique ones. Due to the vast biological and pharmaceutical interest in the elucidation of the structure and the functional mechanisms of transmembrane proteins, several computational methods have been developed to overcome the experimental gap. If combined with experimental data the computational information enables rapid, low cost and successful predictions of the molecular structure of unsolved proteins. The reliability of the predictions depends on the availability and accuracy of experimental data associated with structural information. In this review, the following methods are proposed for in silico structure elucidation: sequence-dependent predictions of transmembrane regions, predictions of transmembrane helix–helix interactions, helix arrangements in membrane models, and testing their stability with molecular dynamics simulations. We also demonstrate the usage of the computational methods listed above by proposing a model for the molecular structure of the transmembrane protein bilitranslocase. Bilitranslocase is bilirubin membrane transporter, which shares similar tissue distribution and functional properties with some of the members of the Organic Anion Transporter family and is the only member classified in the Bilirubin Transporter Family. Regarding its unique properties, bilitranslocase is a potentially interesting drug target.

Usage of invisible near infrared light (NIR) fluorescence with indocyanine green (ICG) and methylene blue (MB) in urological oncology. Part 1

INTRODUCTION

Near infrared (NIR) technology has recently garnered much interest as a tool for intraoperative image-guided surgery in various surgical sub-disciplines. In urology, although nascent, NIR technology is also fostering much enthusiasm. This review discusses the two major fluorophores, indocyanine green (ICG) and methlyene blue (MB), with NIR guidance in experimental and clinical urology. The authors aim to illustrate and analyze the currently available initial studies to better understand the potential and practicability of NIR-guided imaging in the diagnosis and surgical outcome improvement. In the first part of the study we analyzed problems associated with sentinel lymph node biopsy, NIR-guided detection and imaging of tumors.

MATERIAL AND METHODS

PubMed and Medline databases were searched for ICG and MB use in urological settings, along with data published in abstracts of urological conferences.

RESULTS

Although NIR-guided ICG and MB are still in their initial phases, there have been significant developments in major domains of urology, including uro-oncological surgery: 1) sentinel lymph node biopsy, 2) detection and imaging of tumors.

CONCLUSIONS

Much like in other fields of surgical medicine, the application of NIR technology in urology is at its early stages. Therefore, more studies are needed to assess the true potential and limitations of the technology. However, initial developments hint towards a pioneering tool that may influence various aspects of urology.

Development and characterization of a novel mAb against bilitranslocase - a new biomarker of renal carcinoma

Background

Bilitranslocase (TC 2.A.65.1.1) is a bilirubin-specific membrane transporter, found on absorptive (stomach and intestine) and excretory (kidney and liver) epithelia and in vascular endothelium. Polyclonal antibodies have been raised in rabbits in the past, using a synthetic peptide corresponding to AA65-77 of rat liver bilitranslocase, as an antigen. Affinity-purified antibodies from immune sera have been found to inhibit various membrane transport functions, including the bilirubin uptake into human hepatocytes and the uptake of some flavonoids into human vascular endothelial cells. It was described by means of immunohistochemistry using polyclonal antibodies that bilitranslocase expression is severely down-regulated in clear cell renal carcinoma. The aim of our work was development and characterization of high-affinity, specific mAbs against bilitranslocase, which can be used as a potential diagnostic tool in renal cell carcinoma as well as in a wide variety of biological assays on different human tissues.

Materials and methods

Mice were immunized with a multi-antigen peptide corresponding to segment 65–75 of predicted primary structure of the bilitranslocase protein. By a sequence of cloning, immune- and functional tests, we aimed at obtaining a specific monoclonal antibody which recognizes a 37 kDa membrane protein, and influences the transport activity of bilitranslocase.

Results

On the basis of previous results, specific IgM monoclonal antibodies were produced in BALB/c mice, in order to further improve and extend the immunological approach to the study of bilitranslocase in renal cancer cells as well as to develop its potential diagnostics use.

Conclusions

In this article we show an immunological approach, based on newly developed monoclonal antibodies, to a detailed biochemical and functional characterization of a protein whose gene and protein structure is still unknown. We were able to demonstrate our novel mAb as a tumor marker candidate of renal cell carcinoma, which may prove useful in the diagnostic procedures.

Expression and function of renal and hepatic organic anion transporters in extrahepatic cholestasis

Obstructive jaundice occurs in patients suffering from cholelithiasis and from neoplasms affecting the pancreas and the common bile duct. The absorption, distribution and elimination of drugs are impaired during this pathology. Prolonged cholestasis may alter both liver and kidney function. Lactam antibiotics, diuretics, non-steroidal anti-inflammatory drugs, several antiviral drugs as well as endogenous compounds are classified as organic anions. The hepatic and renal organic anion transport pathways play a key role in the pharmacokinetics of these compounds. It has been demonstrated that acute extrahepatic cholestasis is associated with increased renal elimination of organic anions. The present work describes the molecular mechanisms involved in the regulation of the expression and function of the renal and hepatic organic anion transporters in extrahepatic cholestasis, such as multidrug resistance-associated protein 2, organic anion transporting polypeptide 1, organic anion transporter 3, bilitranslocase, bromosulfophthalein/bilirubin binding protein, organic anion transporter 1 and sodium dependent bile salt transporter. The modulation in the expression of renal organic anion transporters constitutes a compensatory mechanism to overcome the hepatic dysfunction in the elimination of organic anions.

Role of BSP/bilirubin binding protein on p-aminohippurate transport in rat kidney

BSP/Bilirubin binding protein (BBBP) is a protein located on the sinusoidal membrane of the liver that transport several organic anions. The aim of this investigation was to determine whether BBBP is present in the kidney and its role in p-aminohippurate transport (PAH). Anti-BBBP antibodies inhibited PAH uptake in brush border membrane vesicles (BBMV) and Na(+)-independent PAH uptake in basolateral membrane vesicles (BLMV). Western blot studies revealed positivity to antiBBBP antibodies in both BBMV and BLMV. So BBBP is also expressed in the kidneys and accounts, at least in part, for the renal tubular transport of PAH.

Bilitranslocase and sulfobromophthalein/bilirubin-binding protein are both involved in the hepatic uptake of organic anions

The hepatic uptake of cholephilic organic anions is a carrier-mediated process. Three distinct proteins [bilitranslocase (BTL), sulfobromophthalein (BSP)/bilirubin-binding protein (BBBP), and organic anion-binding protein] have been isolated from the basolateral plasma-membrane domain of the hepatocyte. To investigate the relative role of the first two of them in accounting for the hepatic uptake of organic anions, we measured the initial rates of uptake of 35S-labeled BSP into rat liver plasma-membrane vesicles. Because transport by BTL is electrogenic but transport by BBBP is electroneutral, studies were done either with or without a positive-inside membrane potential produced by adding valinomycin in the presence of an inwardly directed K+ gradient (outside K+ > inside K+). Both electrogenic and electroneutral transport systems followed saturation kinetics. Electroneutral uptake showed an apparent Km of 20 +/- 3 microM (mean +/- SD) and a Vmax of 1.0 +/- 0.13 nmol.(mg of prot)-1.15 sec-1, whereas the electrogenic portion of BSP uptake exhibited a Km of 5.2 +/- 0.8 microM and a Vmax of 1.1 +/- 0.1 nmol.(mg of prot)-1.15 sec-1. In this case, an overshoot was observed 15 sec after valinomycin addition. Electroneutral BSP uptake was inhibited by incubation with anti-BBBP antibody, whereas anti-BTL antibody did not show any inhibitory effect. Conversely, the electrogenic uptake was inhibited by anti-BTL antibody at a BSP concentration of 5 microM; no inhibition was seen either at 20 microM BSP or upon addition of anti-BBBP antibody. From these data we conclude that the hepatic uptake of organic ions occurs via two immunologically distinct carrier proteins (BTL and BBBP) operating in parallel. BTL is a higher affinity electrogenic transporting system of organic ions, whereas BBBP is a lower affinity electroneutral transporter.

Difference in hepatic uptake of tetra- and di-bromosulfophthalein in rat. Role of hydrophobicity, binding to plasma proteins and affinity for plasma membrane carrier protein

The relative role of hydrophobicity, binding to plasma proteins and affinity for one of the plasma membrane transport proteins in the hepatic uptake of 3,4,5,6-tetra- (BSP) and 3,6-di- (DBSP) bromosulfophthalein was investigated in the rat. In terms of physicochemical characteristics, the two molecules show different pKa values and degrees of hydrophobicity, as determined from the n-octanol:water partition coefficient. In the intact animal, the plasma clearance and the plasma removal rate after a dose of 1.5 mumol/kg i.v. were significantly (P < 0.001) faster for BSP than DBSP, while no difference was found in the plasma distribution volume. The dissociation constant (Kd) of the high affinity binding sites of plasma proteins also differed for the two anions, being significantly lower for BSP than DBSP (0.95 +/- 0.02 vs 1.44 +/- 0.14 microM, P < 0.001). [35S]BSP uptake by liver plasma membrane vesicles was saturable with an apparent Km of 5.20 +/- 0.80 microM, and was competitively inhibited by DBSP (Ki 18.2 +/- 1.2 microM) indicating a common uptake system. The Kd value for binding of the organic anions to purified bilitranslocase, a plasma membrane protein involved in the electrogenic transport of pthaleins, was also significantly lower for BSP than DBSP (1.10 +/- 0.12 vs 3.02 +/- 0.27 microM, N = 3, P < 0.001), indicating a higher affinity of the former ligand for the carrier protein. No difference was observed in the capacity of the high affinity binding sites (32 +/- 3 vs 33 +/- 3 nmol/mg protein, BSP and DBSP, respectively). These data indicate that BSP and DBSP are two different cholephilic organic anions which share a common uptake mechanism, at least partly mediated by bilitranslocase. The greater affinity of BSP than DBSP for the carrier protein may account for the faster plasma disappearance rate of BSP observed in vivo, in spite of the higher plasma protein binding.