Urinary Exosomal Cystatin C and Lipopolysaccharide Binding Protein as Biomarkers for Antibody−Mediated Rejection after Kidney Transplantation

Emerging roles of exosomes in the diagnosis and treatment of kidney diseases

The complex etiology and spectrum of kidney diseases necessitate vigilant attention; the focus on early diagnosis and intervention in kidney diseases remains a critical issue in medical research. Recently, with the expanding studies on extracellular vesicles, exosomes have garnered increasing interest as a promising tool for the diagnosis and treatment of kidney diseases. Exosomes are nano-sized extracellular vesicles that transport a diverse array of bioactive substances, which can influence various pathological processes associated with kidney diseases and exhibit detrimental or beneficial effects. Within the kidney, exosomes derived from the glomeruli and renal tubules possess the ability to enter systemic circulation or urine. The biomarkers they carry can reflect alterations in the pathological state of the kidneys, thereby offering novel avenues for early diagnosis. Furthermore, research studies have confirmed that exosomes originating from multiple cell types exhibit therapeutic potential in treating kidney disease; notably, those derived from mesenchymal stem cells (MSCs) have shown significant treatment efficacy. This comprehensive review summarizes the contributions of exosomes from different cell types within the kidneys while exploring their physiological and pathological roles therein. Additionally, we emphasize recent advancements in exosome applications for the diagnosis and treatment of various forms of kidney diseases over the past decades. We not only introduce the urinary and blood biomarkers linked to kidney diseases found within exosomes but also explore their therapeutic effects. Finally, we discuss existing challenges and future directions concerning the clinical applications of exosomes for diagnostic and therapeutic purposes.

Engineered Nanoparticles for Theranostic Applications in Kidney Repair

Kidney diseases are characterized by their intricate nature and complexity, posing significant challenges in their treatment and diagnosis. Nanoparticles (NPs), which can be further classified as synthetic and biomimetic NPs, have emerged as promising candidates for treating various diseases. In recent years, the development of engineered nanotherapeutics has focused on targeting damaged tissues and serving as drug delivery vehicles. Additionally, these NPs have shown superior sensitivity and specificity in diagnosis and imaging, thus providing valuable insights for the early detection of diseases. This review aims to focus on the application of engineered synthetic and biomimetic NPs in kidney diseases in the aspects of treatment, diagnosis, and imaging. Notably, the current perspectives and challenges are evaluated, which provide inspiration for future research directions, and encourage the clinical application of NPs in this field.

Forming a new perspective: Post-structural approaches to determination of donor compatibility and post-transplant assessment of allograft health

The purpose of this review is to encourage a new perspective on the question of donor-recipient compatibility and post-transplant assessment of graft health based on functional measures. The premise is that we should be better sighted on what (and how) the immune system responds toward rather than what is merely there. Continuance of the pursuit of further and better definition of antigens and antibodies is not however discouraged but seen as necessary to improved understanding of the structural correlates of functional immunity. There currently exists, in the opinion of the authors, an opportunity for histocompatibility and immunogenetics laboratories to develop and widen their scope of involvement into these new areas of laboratory activity in support and to the benefit of the transplant programmes they serve.

Advancing kidney transplant outcomes: the role of urinary proteomics in graft function monitoring and rejection detection

INTRODUCTION

Kidney transplantation significantly improves the lives of those with end-stage kidney disease, offering best alternative to dialysis. However, transplant success is threatened by the acute and chronic rejection mechanisms due to complex immune responses against the new organ.

AREAS COVERED

The ongoing research into biomarkers holds promise for revolutionizing the early detection and monitoring of the graft health. Liquid biopsy techniques offer a new avenue, with several diagnostic, predictive, and prognostic biomarkers showing promise in detecting and monitoring kidney diseases and an early and chronic allograft rejection.

EXPERT OPINION

Evaluating the protein composition related to kidney transplant results could lead to identifying biomarkers that provide insights into the graft functionality. Non-invasive proteomic biomarkers can drastically enhance clinical outcomes and change the way how kidney transplants are evaluated for patients and physicians if they succeed in this transition. Hence, the advancement in proteomic technologies, leads toward a significant improvement in understanding of the protein markers and molecular mechanisms linked to the outcomes of kidney transplants. However, the road from discovery to the use of such proteins in clinical practice is long, with a need for continuous validation and beyond the singular research team with comprehensive infrastructure and across research groups collaboration.

Extracellular vesicles as potential diagnostic markers for kidney allograft rejection

Kidney transplantation is a highly effective treatment for end-stage kidney disease. However, allograft rejection remains a significant clinical challenge in kidney transplant patients. Although kidney allograft biopsy is the gold-standard diagnostic method, it is an invasive procedure. Since the current monitoring methods, including screening of serum creatinine and urinary protein, are not of sufficient sensitivity, there is a need for effective post-transplant monitoring to detect allograft rejection at an early stage. Extracellular vesicles are vesicles with a lipid bilayer that originate from different cell types in pathological and physiological conditions. The content of extracellular vesicles reflects the status of cells at the time of their production. This review comprehensively summarizes clinical, in vivo, and in vitro reports that highlight the potential of extracellular vesicles as diagnostic biomarkers for kidney allograft rejection. Clarification would facilitate differentiation between rejection and non-rejection and identification of the mechanisms involved in the allograft rejection. Despite increasing evidence, further research is necessary to establish the clinical utility of extracellular vesicles in the diagnosis and monitoring of allograft rejection in kidney transplant recipients. Using extracellular vesicles as non-invasive biomarkers for diagnosis of kidney allograft rejection could have tremendous benefits in improving patient outcomes and reduce the need for invasive procedures.

Proteomic analyses of urinary exosomes identify novel potential biomarkers for early diagnosis of sickle cell nephropathy, a sex-based study

Sickle cell nephropathy (SCN) is a leading cause of morbidity and mortality in sickle cell disease (SCD). Early intervention is crucial for mitigating its effects. However, current diagnostic methods rely on generic tests and may not detect SCN until irreversible renal damage occurs. Therefore, specific biomarkers for early diagnosis of SCN are needed. Urinary exosomes, membrane-bound vesicles secreted by renal podocytes and epithelial cells, contain both common and cell type-specific membrane and cytosolic proteins, reflecting the physiologic and pathophysiologic states of the kidney. Using proteomics, we analyzed the proteomes of urinary exosomes from humanized SCD mice at 2 months (without albuminuria) and 4 months (with albuminuria) of age. Excretion of 164 proteins were significantly increased and 176 proteins was significantly decreased in the exosomes when mice developed albuminuria. Based on the relevance to SCD, chronic kidney disease and Western blot confirmation in mice, we analyzed protein abundance of heparanase, cathepsin C, α2-macroglobulin and sarcoplasmic endoplasmic Ca2+ ATPase-3 (SERCA3) in the urinary exosomes and urine of 18 SCD subjects without albuminuria and 12 subjects with albuminuria using Western blot analyses. Both male and female subjects increased or tended to increase the excretion of these proteins in their urinary exosomes upon developing albuminuria, but female subjects demonstrated stronger correlations between the excretion of these proteins and urine albumin creatinine ratio (UACR) compared to male subjects. In contrast, exosomal excretion of Tamm-Horsfall protein, β-actin and SHP-1 was independent of albuminuria. These findings provide a foundation for a time-course study to determine whether increases in the levels of these proteins precede the onset of albuminuria in patients, which will help determine the potential of these proteins as biomarkers for early detection of SCN.

Cystatin C alleviates unconjugated bilirubin-induced neurotoxicity by promoting bilirubin clearance from neurocytes via exosomes, dependent on hepatocyte UGT1A1 activity

There is an urgent need to identify effective drugs for the treatment of nerve injury caused by unconjugated bilirubin (UCB). Our previous research found that cystatin C (CST3) alleviates UCB-induced neurotoxicity by promoting autophagy in nerve cells, but that autophagy inhibitors did not completely inhibit the effects of CST3. This study investigated whether CST3 could alleviate the neurotoxicity of UCB by promoting the secretion and transport of exosomes containing UCB to the liver for metabolism. It demonstrated that hyperbilirubinemia mice treated with CST3 had a higher number of serum exosomes than those in hyperbilirubinemia mice treated with phosphate-buffered saline. CST3-mediated protection against UCB-induced damage was abolished when autophagy and extracellular vesicle inhibitors were used in combination. The number of exosomes in the CST3 overexpression group was higher than that in the control group. Molecular docking experiments showed that UCB and CST3 had high docking score (-8.2). These results suggest that UCB may be excreted from cells by exosomes, and CST3 may promote this process by binding to UCB and entering the exosomes. We demonstrated that the effect of CST3 relied on liver cells with normal UDP-glucuronyl transferase1A1 (UGT1A1) activity in a coculture system of HT22 and L02 cells. CST3 levels were lower in exosomes secreted by L02 cells than in those secreted by human umbilical vein endothelial cells (HUVECs), whereas CST3 levels were higher in the culture supernatants of L02 cells than in the culture supernatants of HUVECs. This suggests that UCB exosomes in L02 cells may be released and internalized by CST3 and that UCB is then processed by UGT1A1 to conjugate UCB, thus reducing its toxicity. These results suggest that CST3 might alleviate UCB-induced neurotoxicity by promoting the clearance of UCB from cells via exosomes and that these effects are dependent on UGT1A1 activity in liver cells.

Biomarker-Development Proteomics in Kidney Transplantation: An Updated Review

Kidney transplantation (KT) is the optimal therapeutic strategy for patients with end-stage renal disease. The key to post-transplantation management is careful surveillance of allograft function. Kidney injury may occur from several different causes that require different patient management approaches. However, routine clinical monitoring has several limitations and detects alterations only at a later stage of graft damage. Accurate new noninvasive biomarker molecules are clearly needed for continuous monitoring after KT in the hope that early diagnosis of allograft dysfunction will lead to an improvement in the clinical outcome. The advent of “omics sciences”, and in particular of proteomic technologies, has revolutionized medical research. Proteomic technologies allow us to achieve the identification, quantification, and functional characterization of proteins/peptides in biological samples such as urine or blood through supervised or targeted analysis. Many studies have investigated proteomic techniques as potential molecular markers discriminating among or predicting allograft outcomes. Proteomic studies in KT have explored the whole transplant process: donor, organ procurement, preservation, and posttransplant surgery. The current article reviews the most recent findings on proteomic studies in the setting of renal transplantation in order to better understand the effective potential of this new diagnostic approach.

Extracellular Vesicles: The Future of Diagnosis in Solid Organ Transplantation?

Solid organ transplantation (SOT) is a life-saving treatment for end-stage organ failure, but it comes with several challenges, the most important of which is the existing gap between the need for transplants and organ availability. One of the main concerns in this regard is the lack of accurate non-invasive biomarkers to monitor the status of a transplanted organ. Extracellular vesicles (EVs) have recently emerged as a promising source of biomarkers for various diseases. In the context of SOT, EVs have been shown to be involved in the communication between donor and recipient cells and may carry valuable information about the function of an allograft. This has led to an increasing interest in exploring the use of EVs for the preoperative assessment of organs, early postoperative monitoring of graft function, or the diagnosis of rejection, infection, ischemia-reperfusion injury, or drug toxicity. In this review, we summarize recent evidence on the use of EVs as biomarkers for these conditions and discuss their applicability in the clinical setting.