Lrpap1 (RAP) Inhibits Proximal Tubule Clathrin Mediated and Clathrin Independent Endocytosis, Ameliorating Renal Aminoglycoside Nephrotoxicity

Key Points

Proximal tubule endocytosis of toxins often leads to nephrotoxicity. Inhibition of endocytosis with receptor-associated protein may serve as a clinical approach to reduce or eliminate kidney damage from a potential nephrotoxin.

Background

Proximal tubules (PTs) are exposed to many exogenous and endogenous nephrotoxins that pass through the glomerular filter. This includes many small molecules, such as aminoglycoside and myeloma light chains. These filtered molecules are rapidly endocytosed by the PTs and lead to nephrotoxicity.

Methods

To investigate whether inhibition of PT uptake of filtered toxins can reduce toxicity, we evaluated the ability of Lrpap1 or receptor-associated protein (RAP) to prevent PT endocytosis. Munich Wistar Frömter rats were used since both glomerular filtration and PT uptake can be visualized and quantified. The injury model chosen was the well-established gentamicin-induced toxicity, which leads to significant reductions in GFR and serum creatinine increases. CKD was induced with a right uninephrectomy and left 40-minute pedicle clamp. Rats had 8 weeks to recover and to stabilize GFR and proteinuria. Multiphoton microscopy was used to evaluate endocytosis in vivo and serum creatinine, and 24-hour creatinine clearances were used to evaluate kidney functional changes.

Results

Studies showed that preadministration of RAP significantly inhibited both albumin and dextran endocytosis in outer cortical PTs. Importantly, this inhibition was found to be rapidly reversible with time. RAP was also found to be an excellent inhibitor of PT gentamicin endocytosis. Finally, gentamicin administration for 6 days resulted in significant elevation of serum creatinine in vehicle-treated rats, but not in those receiving daily infusion of RAP before gentamicin.

Conclusions

This study provides a model for the potential use of RAP to prevent, in a reversible manner, PT endocytosis of potential nephrotoxins, thus protecting the kidney from damage.

Proteomics profiling of kidney brush border membrane from rats using LC-MS/MS analysis

PURPOSE

Chronic kidney disease (CKD) is defined by a reduced renal function, that is, glomerular filtration rate, and the extent of kidney damage is assessed by determining serum creatinine levels and proteins in urine, diagnosed as proteinuria/albuminuria. Albuminuria increases with age and can result from glomerular and/or proximal tubule (PT) alterations. Brush border membranes (BBMs) on PT cells are important in maintaining the stability of PT functions.

EXPERIMENTAL DESIGN

An LC-MS/MS bottom-up proteomics analysis of BBMs from four groups of rat models was applied to investigate protein abundance alterations associated with CKD progression. Moreover, systems biology analyses were used to identify key proteins that can provide insight into the different regulated molecular pathways and processes associated with CKD.

RESULTS

Our results indicated that 303 proteins showed significantly altered expressions from the severe CKD BBM group when compared to the control. Focusing on renal diseases, several proteins including Ctnnb1, Fah, and Icam1 were annotated to kidney damage and urination disorder. The up-regulation of Ctnnb1 (β-catenin) could contribute to CKD through the regulation of the WNT signaling pathway.

CONCLUSION AND CLINICAL RELEVANCE

Overall, the study of protein abundance changes in BBMs from rat models helps to reveal protein corrections with important pathways and regulator effects involved in CKD. Although this study is focused on rat models, the results provided more information for a deeper insight into possible CKD mechanisms in humans.

Albumin Uptake and Processing by the Proximal Tubule: Physiologic, Pathologic and Therapeutic Implications

For nearly 50 years the proximal tubule (PT) has been known to reabsorb, process, and either catabolize or transcytose albumin from the glomerular filtrate. Innovative techniques and approaches have provided insights into these processes. Several genetic diseases, nonselective PT cell defects, chronic kidney disease (CKD), and acute PT injury lead to significant albuminuria, reaching nephrotic range. Albumin is also known to stimulate PT injury cascades. Thus, the mechanisms of albumin reabsorption, catabolism, and transcytosis are being reexamined with the use of techniques that allow for novel molecular and cellular discoveries. Megalin, a scavenger receptor, cubilin, amnionless, and Dab2 form a nonselective multireceptor complex that mediates albumin binding and uptake and directs proteins for lysosomal degradation after endocytosis. Albumin transcytosis is mediated by a pH-dependent binding affinity to the neonatal Fc receptor (FcRn) in the endosomal compartments. This reclamation pathway rescues albumin from urinary losses and cellular catabolism, extending its serum half-life. Albumin that has been altered by oxidation, glycation, or carbamylation or because of other bound ligands that do not bind to FcRn traffics to the lysosome. This molecular sorting mechanism reclaims physiological albumin and eliminates potentially toxic albumin. The clinical importance of PT albumin metabolism has also increased as albumin is now being used to bind therapeutic agents to extend their half-life and minimize filtration and kidney injury. The purpose of this review is to update and integrate evolving information regarding the reabsorption and processing of albumin by proximal tubule cells including discussion of genetic disorders and therapeutic considerations.

Changes in the Expression of Renal Brush Border Membrane N-Glycome in Model Rats with Chronic Kidney Diseases

Chronic kidney disease (CKD) is defined by a reduced renal function i.e., glomerular filtration rate (GFR), and the presence of kidney damage is determined by measurement of proteinuria or albuminuria. Albuminuria increases with age and can result from glomerular and/or proximal tubule (PT) alterations. Brush-border membranes (BBMs) on PT cells play an important role in maintaining the stability of PT functions. The PT BBM, a highly dynamic, organized, specialized membrane, contains a variety of glycoproteins required for the functions of PT. Since protein glycosylation regulates many protein functions, the alteration of glycosylation due to the glycan changes has attracted more interests for a variety of disease studies recently. In this work, liquid chromatography-tandem mass spectrometry was utilized to analyze the abundances of permethylated glycans from rats under control to mild CKD, severe CKD, and diabetic conditions. The most significant differences were observed in sialylation level with the highest present in the severe CKD and diabetic groups. Moreover, high mannose N-glycans was enriched in the CKD BBMs. Characterization of all the BBM N-glycan changes supports that these changes are likely to impact the functional properties of the dynamic PT BBM. Further, these changes may lead to the potential discovery of glycan biomarkers for improved CKD diagnosis and new avenues for therapeutic treatments.

Mechanism of how carbamylation reduces albumin binding to FcRn contributing to increased vascular clearance

Chronic kidney disease results in high serum urea concentrations leading to excessive protein carbamylation, primarily albumin. This is associated with increased cardiovascular disease and mortality. Multiple methods were used to address whether carbamylation alters albumin metabolism. Intravital two-photon imaging of the Munich Wistar Frömter (MWF) rat kidney and liver allowed us to characterize filtration and proximal tubule uptake and liver uptake. Microscale thermophoresis enabled quantification of cubilin (CUB7,8 domain) and FcRn binding. Finally, multiple biophysical methods including dynamic light scattering, small-angle X-ray scattering, LC-MS/MS and in silico analyses were used to identify the critical structural alterations and amino acid modifications of rat albumin. Carbamylation of albumin reduced binding to CUB7,8 and FcRn in a dose-dependent fashion. Carbamylation markedly increased vascular clearance of carbamylated rat serum albumin (cRSA) and altered distribution of cRSA in both the kidney and liver at 16 h post intravenous injection. By evaluating the time course of carbamylation and associated charge, size, shape, and binding parameters in combination with in silico analysis and mass spectrometry, the critical binding interaction impacting carbamylated albumin's reduced FcRn binding was identified as K524. Carbamylation of RSA had no effect on glomerular filtration or proximal tubule uptake. These data indicate urea-mediated time-dependent carbamylation of albumin lysine K524 resulted in reduced binding to CUB7,8 and FcRn that contribute to altered albumin transport, leading to increased vascular clearance and increased liver and endothelial tissue accumulation.

The Clinicopathological Study of Benign Lesions of Vocal Cords

Benign vocal lesions are non-malignant growths of abnormal tissue on the vocal cords. The common benign lesions of vocal cord are singer's nodule, polyps, papilloma, polypoidal degeneration and cysts. The aim of this study was to analyze the demographics such as age, sex, occupation, symptomatology, site of involvement. An objective evaluation of voice handicap was done pre and postoperatively using VHI-10 scale to see improvement in patient's symptoms. In this prospective study, a total of 50 cases were selected with benign lesions in regional hospital of India. The pre and post operative assessment for voice handicap was assessed by VHI-10. Chi square test (SPSS 20.0 version) used to analyze result; value of p < 0.05 was taken significant. In this study of 50 patients, the benign lesions were most common in 20-29 age group. Male (70%) outnumbered females (30%). Most common was Vocal polyp (56%), followed by nodule (32%), cyst (10%) and papilloma (2%) respectively. All patients showed improvement after phonosurgery and postoperative speech therapy, being assessed by VHI-10 scale. The benign lesions of vocal cords produces symptoms which can vary from hoarseness to stridor, affect social functioning, work performance. Speech therapy following microlaryngeal surgery forms an essential part of treatment, to avoid recurrence. VHI-10 scale as found to be a useful and convenient tool in measuring patient voice handicap and to see improvement after surgery.

Low-resolution SAXS and structural dynamics analysis on M. tuberculosis GmhB enzyme involved in GDP-heptose biosynthetic pathway

The M. tuberculosis GmhB protein converts the d-glycero-α-d-manno-heptose 1,7-bisphosphate (GMB) intermediate into d-glycero-α-d-manno-heptose 1-phosphate by removing the phosphate group at the C-7 position. To understand the structure and substrate binding mechanism, the MtbGmhB was purified which elutes as monomer on gel filtration column. The small angle x-ray scattering analysis shows that MtbGmhB forms fully folded monomer with shape profile similar to its modeled structure. The circular dichroism analysis shows 38% α-helix, 15% β-sheets and 47% random coil structures in MtbGmhB, similar to haloalkanoic acid dehalogenase (HAD) phosphohydrolase enzymes. The modeled MtbGmhB structure shows the catalytic site, which forms a concave, semicircular surface using the three loops around GMB substrate binding site. Dynamic simulation analysis on (i) Apo (ii) GMB bound (iii) GMB + Mg²⁺ bound (iv) Zn²⁺ +GMB + Mg²⁺ bound MtbGmhB structures show that Zn²⁺ as well as Mg²⁺ ions stabilize the loop conformation and trigger the changes in GMB substrate binding to active site of MtbGmhB. Upon demetallization, the large conformational changes occurred in ions binding loops, and leads to difference in GMB substrate binding to MtbGmhB. Our study provides information about structure and substrate binding of MtbGmhB, which may contribute in therapeutic development against M. tuberculosis.

Assessment and clinicopathological correlation of p16 expression in head and neck squamous cell carcinoma

INTRODUCTION

Oral squamous cell carcinoma is a major cause of death throughout the developed world. It is associated with smoking and alcohol consumption. Human papillomavirus (HPV) type 16 has also been suggested to play a role in etiology of head and neck squamous cell carcinoma (HNSCC). p16 expression is now being used as a surrogate marker of HPV infection in squamous cell carcinoma and provides important prognostic information and future therapy planning.

MATERIALS AND METHODS

In this prospective study, total of 75 cases of HNSCC were taken. Tumor grade was determined according to World Health Organization (WHO) criteria. p16 expression was determined by immunohistochemical staining. The obtained results were analyzed and evaluated using Chi-square test (Statistical Package for Social Sciences (SPSS) version 20), value of P <0.05 was taken significant.

RESULTS

Out of 75 cases, 78.7% cases were positive for p16 (inclusive of all grades), while 21.3% cases were negative. Expression of p16 was higher in nonsmokers and nonalcohol consumers and significantly associated with paan chewing habit. No significant correlation was seen with history of abnormal sexual habits, but p16 expression was significantly correlated in cases with multiple sexual partners (P = 0.003), with increasing histological grade (P = 0.045) and in cases with lymph node metastasis (P = 0.03).

CONCLUSION

As HPV integration with transcription of viral oncoprotein induces overexpression of p16, immunohistochemical expression of p16 can be used as a surrogate marker of HPV. This approach can be implemented in diagnostic laboratories and can provide support for vaccination program in high risk group.

Cystic acoustic neuromas

Predominantly cystic acoustic neuromas are rare and they usually present with clinical and radiological features different from their more common solid counterparts. Two cases of cystic acoustic neuromas are reported here.

Mucormycosis

A rare case of mucormycosis in a 58 years old healthy house-wife is reported which occurred without any predisposing factors like immuno-suppresion. Etiology, clinical features and treatment is outlined with the caution that the most effective drug i.e. amphotericin B may have very serious side effects as in this case. The disease is acutely fatal and treatment has potential hazards which may prove fatal. However, if the disease entity is kept in mind, with early diagnosis and treatment, the outcome would be quite favourable.

Endo-DCR: is it an end of the road for external DCR?

Endo-DCR is a safe, quick, less traumatic, with minimal blood loss and post-operative discomfort and last but not the least, avoids external scar. It has high success rate in both primary and secondary cases. Fifty two cases of chronic dacryocystitis were treated by the endoscopic technique including 33 females and 19 males in mean age group 35.8 year, 29 left eye and 23 right eye with 8 patients cannulated with nasolacrimal tube with very good results and few complications.

Obstructing mass lesion of epiglottis: it can be tubercular

We report a case of 60-year old male who had difficulty in breathing as well as in swallowing. On examination, he was found to be having proliferative growth of epiglottis and right aryepiglottic fold mimicking neoplasm. So emergency tracheostomy was performed and biopsy taken. He was found to be having asymptomatic miliary mottling on routine x-ray chest PA view. Further on HRCT, it turned out to be lesion suggesting tubercular etiology. Histopathology (epiglottic biopsy) report confirmed the whole process as tubercular. The patient recovered promptly in due course with anti-tubercular treatment. Point remains to be seen that if we can avoid tracheostomy and its complications in such cases.

Fatal pyothorax: a rare complication of retropharyngeal abscess

Fatal pyothorax following a massive acute retropharyngeal abscess in an adult is reported. Acute non-tuberculous retropharyngeal abscess usually develops following a penetrating injury due to a foreign body or endoscopy. Microbial isolates are mixed and consists of aerobic and anaerobic organisms. It may lead on to mediastinitis since there is a potential communication between the two spaces. Immediate cervical, pleural and mediastinal surgical drainage along with appropriate antibiotics can be life saving.

Serum selenium levels in patients with head and neck cancer

OBJECTIVE

The objective of this research was to estimate serum selenium levels in patients with head and neck cancer and to correlate them with tumour burden, as well as to study the effect of radiotherapy on serum selenium levels to determine its prognostic significance.

DESIGN

This prospective study was carried out by selection of head and neck cancer patients using periodic random numbers.

SETTING

This was a hospital-based study.

METHODS

Estimation of serum selenium was done using the Atomic Absorption Spectrophotometer (Model AAS 4129; Electronic Corporation of India Ltd., Hydrabad, India) with a hydride generator after digestion of the serum sample.

MAIN OUTCOME MEASURES

Patients were followed for 1 year postradiotherapy for any change in serum selenium level and its correlation with the outcome of the treatment.

RESULTS

All 30 patients had serum selenium levels significantly lower as compared with controls, and these levels decreased further as tumour burden increased. Levels came within normal range after 1 year of radiotherapy in 10 patients who were cured but in the remaining patients who had residual disease, levels remained persistently low.

CONCLUSIONS

The serum selenium level may serve as a useful marker in head and neck cancer.

Gallstone expectoration following laparoscopic cholecystectomy

Laparoscopic cholecystectomy is the treatment of choice for uncomplicated gallstone disease. Laparoscopic cholecystectomy may result in lost (spilled) gallstones. Such stones may precipitate various infective intra-abdominal complications. An unusual case of spilled gallstones eroding the diaphragm and eventually being expectorated out 12 months after laparoscopic cholecystectomy is reported.

Myringoplasty for chronic otitis media

METHODS

25 children in the age group of 8-14 years suffering from chronic suppurative otitis media were taken up for myringoplasty using onlay technique under general anaesthesia.

RESULTS

All selected cases had a central type of dry perforation, good cochlear reserve and healthy middle ear mucosa. Cases having enlarged adenoids, infection in nose or throat, any traumatic perforation or previous attempt at closure were excluded from the study. It was found that there was 76% take up of graft after two months who also had improvement in hearing.

CONCLUSION

We conclude that myringoplasty stands a good chance in children.