Histopathology and laser autofluorescence of ischemic kidneys of rats

Therapeutic α-1-microglobulin ameliorates kidney ischemia-reperfusion injury

α-1-Microglobulin (A1M) is a circulating glycoprotein with antioxidant, heme-binding, and mitochondrial protection properties. The investigational drug RMC-035, a modified therapeutic A1M protein, was assessed for biodistribution and pharmacological activity in a broad set of in vitro and in vivo experiments, supporting its clinical development. Efficacy and treatment posology were assessed in various models of kidney ischemia and reperfusion injury (IRI). Real-time glomerular filtration rate (GFR), functional renal biomarkers, tubular injury biomarkers (NGAL and KIM-1), and histopathology were evaluated. Fluorescently labeled RMC-035 was used to assess biodistribution. RMC-035 demonstrated consistent and reproducible kidney protection in rat IRI models as well as in a model of IRI imposed on renal impairment and in a mouse IRI model, where it reduced mortality. Its pharmacological activity was most pronounced with combined dosing pre- and post-ischemia and weaker with either pre- or post-ischemia dosing alone. RMC-035 rapidly distributed to the kidneys via glomerular filtration and selective luminal uptake by proximal tubular cells. IRI-induced expression of kidney heme oxygenase-1 was inhibited by RMC-035, consistent with its antioxidative properties. RMC-035 also dampened IRI-associated inflammation and improved mitochondrial function, as shown by tubular autofluorescence. Taken together, the efficacy of RMC-035 is congruent with its targeted mechanism(s) and biodistribution profile, supporting its further clinical evaluation as a novel kidney-protective therapy.NEW & NOTEWORTHY A therapeutic A1M protein variant (RMC-035) is currently in phase 2 clinical development for renal protection in patients undergoing open-chest cardiac surgery. It targets several key pathways underlying kidney injury in this patient group, including oxidative stress, heme toxicity, and mitochondrial dysfunction. RMC-035 is rapidly eliminated from plasma, distributing to kidney proximal tubules, and demonstrates dose-dependent efficacy in numerous models of ischemia-reperfusion injury, particularly when administered before ischemia. These results support its continued clinical evaluation.

Renal Artery Catheterization for Microcapsules' Targeted Delivery to the Mouse Kidney

The problem of reducing the side effects associated with drug distribution throughout the body in the treatment of various kidney diseases can be solved by effective targeted drug delivery. The method described herein involves injection of a drug encapsulated in polyelectrolyte capsules to achieve prolonged local release and long-term capillary retention of several hours while these capsules are administered via the renal artery. The proposed method does not imply disruption (puncture) of the renal artery or aorta and is suitable for long-term chronic experiments on mice. In this study, we compared how capsule size and dosage affect the target kidney blood flow. It has been established that an increase in the diameter of microcapsules by 29% (from 3.1 to 4.0 μm) requires a decrease in their concentration by at least 50% with the same suspension volume. The photoacoustic method, along with laser speckle contrast imaging, was shown to be useful for monitoring blood flow and selecting a safe dose. Capsules contribute to a longer retention of a macromolecular substance in the target kidney compared to its free form due to mechanical retention in capillaries and slow impregnation into surrounding tissues during the first 1-3 h, which was shown by fluorescence tomography and microscopy. At the same time, the ability of capillaries to perform almost complete "self-cleaning" from capsular shells during the first 12 h leads to the preservation of organ tissues in a normal state. The proposed strategy, which combines endovascular surgery and the injection of polymer microcapsules containing the active substance, can be successfully used to treat a wide range of nephropathies.

Enhancing in vivo renal ischemia assessment by high-dynamic-range fluorescence molecular imaging

Fluorescence imaging has been used to evaluate the physiological features of renal ischemia in animal model. However, the fluorophore distribution details of the ischemia model could not be fully represented due to the limited dynamic range of the charged-couple device. A high-dynamic-range (HDR) strategy was adopted in renal ischemia fluorescence imaging, both ex vivo and in vivo. The HDR strategy successfully combined ischemia relevant biological features that could only be captured with different exposure times, and then presented these features in the HDR results. The HDR results effectively highlighted the renal ischemic areas with relatively better perfusion and diminished the saturation that resulted from long exposure time. The relative fluorescence intensities of the ischemic kidneys and the image entropy values were significantly higher in the HDR images than in the original images, therefore enhancing the visualization of the renal ischemia model. The results suggest that HDR could serve as a postprocessing strategy to enhance the assessment of in vivo renal ischemia, and HDR fluorescence molecular imaging could be a valuable imaging tool for future studies of clinical ischemia detection and evaluation.

Fluorescence spectroscopy in renal ischemia and reperfusion: noninvasive evaluation of organ viability

BACKGROUND

Damage provoked by ischemia in renal transplants is difficult to quantify. To determine whether a donated organ is fit for transplantation. We sought to correlate the findings of fluorescence spectroscopy (FS) with histologic evidence of ischemic injury and organ viability.

METHODS

Kidneys of 33 rats were submitted to FS of the upper and lower poles as well as the middle third. Excitation was generated by the laser's wavelengths of 408, 442, and 532 nm. Rats were randomized into groups with the 30, 60, and 120 minutes warm ischemia before analysis by FS, that was repeated at 5 minutes after reperfusion.

RESULTS

FS results in the reperfusion phase correlated with ischemia time and degree of histologic injury. After 60 or 120 minutes of ischemia, the excitation lasers of 532 and 442 nm resented a significant negative correlation coefficient with the histological grade (r = -0.61 and r = -0.73, respectively).

CONCLUSIONS

There was a strong correlation between FS and histologic changes only in the reperfusion phase after renal ischemia. The method was thus unable to assess the viability of organs before transplantation.

Evaluation by fluorescence spectroscopy of the most appropriate renal region for obtaining biopsies: a study in the rat

INTRODUCTION

Renal puncture biopsies are directed at the lower poles of the organ to decrease the risk of hemorrhage and complications.

OBJECTIVES

To evaluate by fluorescence spectroscopy (FS) the most appropriate renal region (in terms of metabolic changes) to obtain a biopsy.

MATERIALS AND METHODS

The kidneys of 33 Rattus norvegicus rats were submitted to FS detection in the upper and lower poles and in the middle third. Excitations were generated with lasers at wavelengths of 408, 442, and 532 nm. Animals were divided at random into groups of warm ischemia (30, 60, and 120 minutes), whose kidneys were again analyzed by FS, as well as after 5 minutes of reperfusion using the same excitation beams in the same renal regions. Then the kidneys underwent histologic preparation and examination.

RESULTS

The middle third area of the rat's kidneys proved to be significantly more sensitive to ischemic and reperfusion changes than the renal poles, as determined by FS (P < .001).

CONCLUSIONS

The middle third of the kidney was the most appropriate site for a renal biopsy to monitor a transplanted organ.

Sudan black B reduces autofluorescence in murine renal tissue

CONTEXT

Renal tissue emits intense autofluorescence, making it difficult to differentiate specific immunofluorescence signals and thus limiting its application to clinical biopsy material.

OBJECTIVE

To identify and minimize autofluorescence of renal tissue and demonstrate a simple, efficient method to reduce autofluorescence using Sudan black B.

DESIGN

In this study, the sources and features of autofluorescence emitted from kidney tissue were examined. Broad autofluorescence was visualized in both frozen and paraffin kidney sections of normal mice and mice with Adriamycin-induced nephropathy using confocal laser scanning microscopy. Autofluorescence appeared in commonly used 4',6-diamidino-2-phenylindole, fluorescein isothiocyanate, and Texas Red channels but not in far-red channel, and emitted extensively from red cells, injured tubulointersitial cells, and protein casts in diseased kidney. To eliminate autofluorescence, Sudan black B was used on formaldehyde-fixed paraffin sections and frozen sections of mouse kidney. The effects of Sudan black B in various concentrations were tested on kidney tissue.

RESULTS

The 0.1% Sudan black B effectively blocked autofluorescence from both paraffin and frozen sections without adversely affecting specific fluorescence signals. Interestingly, the solvent for Sudan black B, 70% ethanol, was also shown to reduce autofluorescence on frozen sections, but not on paraffin sections.

CONCLUSIONS

This study demonstrates a simple, efficient, and cost-effective method to reduce autofluorescence using Sudan black B, and also provides a comprehensive approach to identify and minimize autofluorescence of renal tissue.