Nanometric Chemical Speciation of Abnormal Deposits in Kidney Biopsy: Infrared-Nanospectroscopy Reveals Heterogeneities within Vancomycin Casts

FTIR Analysis of Renal Tissue for the Assessment of Hypertensive Organ Damage and proANP31–67 Treatment

The kidneys are one of the main end organs targeted by hypertensive disease. Although the central role of the kidneys in the regulation of high blood pressure has been long recognized, the detailed mechanisms behind the pathophysiology of renal damage in hypertension remain a matter of investigation. Early renal biochemical alterations due to salt-induced hypertension in Dahl/salt-sensitive rats were monitored by Fourier-Transform Infrared (FTIR) micro-imaging. Furthermore, FTIR was used to investigate the effects of proANP31–67, a linear fragment of pro-atrial natriuretic peptide, on the renal tissue of hypertensive rats. Different hypertension-induced alterations were detected in the renal parenchyma and blood vessels by the combination of FTIR imaging and principal component analysis on specific spectral regions. Changes in amino acids and protein contents observed in renal blood vessels were independent of altered lipid, carbohydrate, and glycoprotein contents in the renal parenchyma. FTIR micro-imaging was found to be a reliable tool for monitoring the remarkable heterogeneity of kidney tissue and its hypertension-induced alterations. In addition, FTIR detected a significant reduction in these hypertension-induced alterations in the kidneys of proANP31–67-treated rats, further indicating the high sensitivity of this cutting-edge imaging modality and the beneficial effects of this novel medication on the kidneys.

Determination of Secondary Structure of Proteins by Nanoinfrared Spectroscopy

Nanoscale infrared spectroscopy (AFMIR) is becoming an important tool for the analysis of biological sample, in particular protein assemblies, at the nanoscale level. While the amide I band is usually used to determine the secondary structure of proteins in Fourier transform infrared spectroscopy, no tool has been developed so far for AFMIR. The paper introduces a method for the study of secondary structure of protein based on a protein library of 38 well-characterized proteins. Ascending stepwise linear regression (ASLR) and partial least square (PLS) regression were used to correlate spectrum characteristic bands with the major secondary structures (α-helixes and β-sheets). ASLR appears to provide better results than PLS. The secondary structure predictions are characterized by a root mean square standard error in a cross validation of 6.39% for α-helixes and 6.23% for β-sheets.

Distinguishing active from quiescent disease in ANCA-associated vasculitis using attenuated total reflection Fourier-transform infrared spectroscopy

The current lack of a reliable biomarker of disease activity in anti-neutrophil cytoplasmic autoantibody (ANCA) associated vasculitis poses a significant clinical unmet need when determining relapsing or persisting disease. In this study, we demonstrate for the first time that attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy offers a novel and functional candidate biomarker, distinguishing active from quiescent disease with a high degree of accuracy. Paired blood and urine samples were collected within a single UK centre from patients with active disease, disease remission, disease controls and healthy controls. Three key biofluids were evaluated; plasma, serum and urine, with subsequent chemometric analysis and blind predictive model validation. Spectrochemical interrogation proved plasma to be the most conducive biofluid, with excellent separation between the two categories on PC2 direction (AUC 0.901) and 100% sensitivity (F-score 92.3%) for disease remission and 85.7% specificity (F-score 92.3%) for active disease on blind predictive modelling. This was independent of organ system involvement and current ANCA status, with similar findings observed on comparative analysis following successful remission-induction therapy (AUC > 0.9, 100% sensitivity for disease remission, F-score 75%). This promising technique is clinically translatable and warrants future larger study with longitudinal data, potentially aiding earlier intervention and individualisation of treatment.

Kidney biopsy findings in vancomycin-induced acute kidney injury: a pooled analysis

BACKGROUND

Acute kidney injury represents a major adverse effect of vancomycin administration. The aim of the present study is to accumulate all biopsy-proven cases of vancomycin nephrotoxicity and assess the association of histopathological features with renal prognosis.

METHODS

Medline, Scopus, CENTRAL, Web of Science, and Clinicaltrials.gov were systematically searched from inception to 29 September 2020. All case reports/series providing individual data of patients with biopsy-proven vancomycin nephrotoxicity were held eligible. A time-to-event analysis was performed evaluating the effects of histological diagnosis on renal recovery.

RESULTS

Overall, 18 studies were included, comprising 21 patients. Acute tubulointerstitial nephritis was the predominant pattern in 9 patients and was associated with a significantly higher risk of permanent renal dysfunction (HR: 5.08, 95% CI: [1.05-24.50)] compared to acute tubular necrosis. Tubulitis and eosinophilic infiltration were the most common histopathological findings, while interstitial fibrosis was linked to significantly worse renal prognosis (HR: 5.55, 95% CI: 1.13-27.27). Immunofluorescence and electron microscopy features were non-specific. Obstruction by tubular casts composed of vancomycin aggregates and uromodulin has been identified as a new mechanism of nephrotoxicity.

CONCLUSIONS

Acute tubular necrosis and tubulointerstitial nephritis represent the main histological patterns of vancomycin-induced acute kidney injury. The presence of fibrosis in the context of interstitial inflammation may be linked to lower recovery rates and worse long-term renal outcomes. A novel cast nephropathy obstructive mechanism has been suggested, necessitating further confirmation. Large-scale studies should define the exact indications of kidney biopsy in cases with suspected vancomycin nephrotoxicity.