Longitudinal Follow-Up of Serum and Urine Biomarkers Indicative of COVID-19-Associated Acute Kidney Injury: Diagnostic and Prognostic Impacts.

In patients hospitalized for severe COVID-19, the incidence of acute kidney injury (AKI) is approximately 40%. To predict and understand the implications of this complication, various blood and urine biomarkers have been proposed, including neutrophil gelatinase-associated lipocalin (NGAL), chemokine (C-C motif) ligand 14 (CCL14), cystatin C, leucine aminopeptidase (LAP), and soluble urokinase plasminogen activator (suPAR). This study, conducted between mid-January and early May 2021, aimed to assess the diagnostic and prognostic capabilities of these biomarkers in a cohort of COVID-19 patients monitored during the initial two weeks of hospitalization. Among the 116 patients included in this study, 48 developed AKI within the first three days of hospitalization (41%), with 29 requiring intensive care unit (ICU) admission, and the overall mortality rate was 18%. AKI patients exhibited a statistically significant increase in urinary LAP levels, indicating acute tubular injury as a potential mechanism underlying COVID-19-related renal damage. Conversely, urinary NGAL and CCL-14 excretion rates did not differ significantly between the AKI and non-AKI groups. Importantly, elevated plasma suPAR and cystatin C levels upon admission persisted throughout the first week of hospitalization and were associated with unfavorable outcomes, such as prolonged ICU stays and increased mortality, irrespective of AKI development. In conclusion, this study underscores the early predictive value of urinary LAP levels in identifying acute tubular injury in COVID-19-induced AKI. Moreover, elevated plasma suPAR and cystatin C levels serve as valuable prognostic markers, offering insights into the short-term morbidity and mortality risks among COVID-19 patients, regardless of AKI occurrence. These findings shed light on the complex interplay between COVID-19, renal injury, and biomarkers with diagnostic and prognostic potential.

Experimental Aristolochic Acid Nephropathy: A Relevant Model to Study AKI-to-CKD Transition.

Aristolochic acid nephropathy (AAN) is a progressive tubulointerstitial nephritis caused by the intake of aristolochic acids (AA) contained in Chinese herbal remedies or contaminated food. AAN is characterized by tubular atrophy and interstitial fibrosis, characterizing advanced kidney disease. It is established that sustained or recurrent acute kidney injury (AKI) episodes contribute to the progression of CKD. Therefore, the study of underlying mechanisms of AA-induced nephrotoxicity could be useful in understanding the complex AKI-to-CKD transition. We developed a translational approach of AKI-to-CKD transition by reproducing human AAN in rodent models. Indeed, in such models, an early phase of acute tubular necrosis was rapidly followed by a massive interstitial recruitment of activated monocytes/macrophages followed by cytotoxic T lymphocytes, resulting in a transient AKI episode. A later chronic phase was then observed with progressive tubular atrophy related to dedifferentiation and necrosis of tubular epithelial cells. The accumulation of vimentin and αSMA-positive cells expressing TGFß in interstitial areas suggested an increase in resident fibroblasts and their activation into myofibroblasts resulting in collagen deposition and CKD. In addition, we identified 4 major actors in the AKI-to-CKD transition: (1) the tubular epithelial cells, (2) the endothelial cells of the interstitial capillary network, (3) the inflammatory infiltrate, and (4) the myofibroblasts. This review provides the most comprehensive and informative data we were able to collect and examines the pending questions.

The impact of p53 on aristolochic acid I-induced nephrotoxicity and DNA damage in vivo and in vitro.

Exposure to aristolochic acid (AA) is associated with human nephropathy and urothelial cancer. The tumour suppressor TP53 is a critical gene in carcinogenesis and frequently mutated in AA-induced urothelial tumours. We investigated the impact of p53 on AAI-induced nephrotoxicity and DNA damage in vivo by treating Trp53(+/+), Trp53(+/-) and Trp53(-/-) mice with 3.5 mg/kg body weight (bw) AAI daily for 2 or 6 days. Renal histopathology showed a gradient of intensity in proximal tubular injury from Trp53(+/+) to Trp53(-/-) mice, especially after 6 days. The observed renal injury was supported by nuclear magnetic resonance (NMR)-based metabonomic measurements, where a consistent Trp53 genotype-dependent trend was observed for urinary metabolites that indicate aminoaciduria (i.e. alanine), lactic aciduria (i.e. lactate) and glycosuria (i.e. glucose). However, Trp53 genotype had no impact on AAI-DNA adduct levels, as measured by 32P-postlabelling, in either target (kidney and bladder) or non-target (liver) tissues, indicating that the underlying mechanisms of p53-related AAI-induced nephrotoxicity cannot be explained by differences in AAI genotoxicity. Performing gas chromatography-mass spectrometry (GC-MS) on kidney tissues showed metabolic pathways affected by AAI treatment, but again Trp53 status did not clearly impact on such metabolic profiles. We also cultured primary mouse embryonic fibroblasts (MEFs) derived from Trp53(+/+), Trp53(+/-) and Trp53(-/-) mice and exposed them to AAI in vitro (50 µM for up to 48 h). We found that Trp53 genotype impacted on the expression of NAD(P)H:quinone oxidoreductase (Nqo1), a key enzyme involved in AAI bioactivation. Nqo1 induction was highest in Trp53(+/+) MEFs and lowest in Trp53(-/-) MEFs; and it correlated with AAI-DNA adduct formation, with lowest adduct levels being observed in AAI-exposed Trp53(-/-) MEFs. Overall, our results clearly demonstrate that p53 status impacts on AAI-induced renal injury, but the underlying mechanism(s) involved remain to be further explored. Despite the impact of p53 on AAI bioactivation and DNA damage in vitro, such effects were not observed in vivo.

CD4+ and CD8+ T Cells Exert Regulatory Properties During Experimental Acute Aristolochic Acid Nephropathy.

Experimental aristolochic acid nephropathy is characterized by transient acute proximal tubule necrosis and inflammatory cell infiltrates followed by interstitial fibrosis and tubular atrophy. The respective role of T-cell subpopulations has never been studied in the acute phase of the mouse model, and was heretofore exclusively investigated by the use of several depletion protocols. As compared to mice injected with aristolochic acids alone, more severe acute kidney injury was observed after CD4+ or CD8+ T-cells depletion. TNF-alpha and MCP-1 mRNA renal expressions were also increased. In contrast, regulatory T-cells depletion did not modify the severity of the aristolochic acids induced acute kidney injury, suggesting an independent mechanism. Aristolochic acids nephropathy was also associated with an increased proportion of myeloid CD11bhighF4/80mid and a decreased proportion of their counterpart CD11blowF4/80high population. After CD4+ T-cell depletion the increase in the CD11bhighF4/80mid population was even higher whereas the decrease in the CD11blowF4/80high population was more marked after CD8+ T cells depletion. Our results suggest that CD4+ and CD8+ T-cells provide protection against AA-induced acute tubular necrosis. Interestingly, T-cell depletion was associated with an imbalance of the CD11bhighF4/80mid and CD11blowF4/80high populations.

Early detection of acute cisplatin nephrotoxicity: interest of urinary monitoring of proximal tubular biomarkers.

BACKGROUND: Renal toxicity induced by cisplatin (CisPt) is a clinical issue in patients with or without chronic kidney disease (CKD). Proximal tubular injury can result in acute kidney injury (AKI), which may compromise the course of chemotherapy and the prognosis. The purpose of this study was to investigate the time course of urinary markers of acute tubulotoxicity and to assess the usefulness of such monitoring in a routine clinical setting. METHODS: This work is an open prospective pilot study carried out among 23 patients receiving a platinum-based chemotherapy. Individual comorbidities, plasma parameters of kidney function (urea, creatinine) and estimated glomerular filtration rate were registered. Urinary excretion of leucine aminopeptidase, neutrophil gelatinase-associated lipocalin, cystatin C, liver fatty acid-binding protein and interleukin-18 were monitored during successive chemotherapy cycles. Episodes of AKI were identified according to KDIGO (Kidney Disease Improving Global Outcomes) 2012 guidelines. RESULTS: A total of 28 patients were recruited; among them 23 agreed to be part of the study, of whom 18 received CisPt and 5 carbo- or oxaliplatin. Of the 18 CisPt patients, 12 had a preexisting CKD. Sixteen AKI episodes were observed in 13 patients receiving CisPt with a pejorative evolution in seven cases (partial recovery of the renal function); a transient but dramatic increase in urinary biomarkers was observed 3 h after chemotherapy initiation, whereas plasma creatinine rise appeared 72 h after the end of CisPt treatment. Identified precipitating factors included: dehydration due to lack of fluid intake or diuretic use, exposure to high CisPt doses, regular use of nonsteroidal anti-inflammatory drugs and/or iodinated contrast agents and sepsis. CONCLUSION: Even if numerous precipitating factors could be avoided, the monitoring of urinary markers seemed helpful for the early detection of subclinical AKI induced during CisPt chemotherapy.

Blocking TGF-ß Signaling Pathway Preserves Mitochondrial Proteostasis and Reduces Early Activation of PDGFRß+ Pericytes in Aristolochic Acid Induced Acute Kidney Injury in Wistar Male Rats.

BACKGROUND: The platelet-derived growth factor receptor ß (PDGFRß)+ perivascular cell activation becomes increasingly recognized as a main source of scar-associated kidney myofibroblasts and recently emerged as a new cellular therapeutic target. AIMS: In this regard, we first confirmed the presence of PDGFRß+ perivascular cells in a human case of end-stage aristolochic acid nephropathy (AAN) and thereafter we focused on the early fibrosis events of transforming growth factor ß (TGFß) inhibition in a rat model of AAN. MATERIALS AND METHODS: Neutralizing anti-TGFß antibody (1D11) and its control isotype (13C4) were administered (5 mg/kg, i.p.) at Days -1, 0, 2 and 4; AA (15 mg/kg, sc) was injected daily. RESULTS: At Day 5, 1D11 significantly suppressed p-Smad2/3 signaling pathway improving renal function impairment, reduced the score of acute tubular necrosis, peritubular capillaritis, interstitial inflammation and neoangiogenesis. 1D11 markedly decreased interstitial edema, disruption of tubular basement membrane loss of brush border, cytoplasmic edema and organelle ultrastructure alterations (mitochondrial disruption and endoplasmic reticulum edema) in proximal tubular epithelial cells. Moreover, 1D11 significantly inhibited p-PERK activation and attenuated dysregulation of unfolded protein response (UPR) pathways, endoplasmic reticulum and mitochondrial proteostasis in vivo and in vitro. CONCLUSIONS: The early inhibition of p-Smad2/3 signaling pathway improved acute renal function impairment, partially prevented epithelial-endothelial axis activation by maintaining PTEC proteostasis and reduced early PDGFRß+ pericytes-derived myofibroblasts accumulation.

Human bone morphogenetic protein-7 does not counteract aristolochic acid-induced renal toxicity.

Aristolochic acids (AA) are nephrotoxic and profibrotic agents, leading to chronic kidney disease. As some controversial studies have reported a nephroprotective effect of exogenous recombinant human bone morphogenetic protein (rhBMP)-7 in several models of renal fibrosis, we investigated the putative effect of rhBMP-7 to prevent progressive tubulointerstitial damage after AA intoxication in vitro and in vivo. In vitro, the toxicity of AA on renal tubular cells was demonstrated by an increase in vimentin as well as a decrease in ß-catenin expressions, reflecting a dedifferentiation process. Increased fibronectin and interleukin-6 levels were measured in the supernatants. Enhanced α-SMA mRNA levels associated to decreased E-cadherin mRNA levels were also measured. Incubation with rhBMP-7 only prevented the increase in vimentin and the decrease in ß-catenin expressions. In vivo, in a rat model of AA nephropathy, severe tubulointerstitial lesions induced by AA after 10 and 35 days (collagen IV deposition and tubular atrophy), were not prevented by the rhBMP-7 treatment. Similarly, rhBMP-7 did not ameliorate the significant increase in urinary concentrations of transforming growth factor-ß. In summary, our in vitro data demonstrated a poor beneficial effect of rhBMP-7 to reverse cell toxicity while, in vivo, there was no beneficial effect of rhBMP-7. Therefore, further investigations are needed to confirm the exact role of BMP-7 in progressive chronic kidney disease.

Evaluation of diagnostic criteria for endemic nephropathy.

Diagnosis of endemic nephropathy (EN) is based on the combination of several clinical and laboratory criteria. Despite extensive research no specific diagnostic biomarker for EN has yet been identified. The aim of the study was to evaluate the diagnostic significance of the variables previously proposed as diagnostic criteria, but also new ones. After an extended questionnaire, the clinical and laboratory examination population in EN villages was classified according to the modified WHO criteria. The urinary active form of TGF-ß was measured with a bioassay using a cell line which expresses luciferase activity. In the study we used ROC analysis to examine the predictive value of the tested variables. In the study there was no difference in haemoglobin level between the study subgroups. Leucine aminopeptidase (LAP) in urine and active urinary TGF-ß levels were increased in the EN diseased group when compared to other subgroups, but they did not fulfil the statistical criteria needed for differentiating a diseased form from other study subgroups. Both kidney length and parenchima thickness, alfa1-microglobulinuria, and kidney function assessed by MDRD formula were the variables that differentiated the study subgroups well. Based on our results the cut-off value of alfa1-microglobulin for screening should be 23.5 mg/g creatinine instead of 15 mg/g creatinine in the present criteria, and for making a diagnosis of EN 31,5 mg/g creatinine. Persons with a positive family history for EN had a 5.8 times greater risk of developing EN when compared to a negative one. Taken together, the above-mentioned variables should be implemented in new uniform diagnostic criteria for EN.

Probenecid prevents acute tubular necrosis in a mouse model of aristolochic acid nephropathy.

Experimental aristolochic acid nephropathy is characterized by early tubulointerstitial injury followed by fibrosis, reproducing chronic lesions seen in humans. In vitro, probenecid inhibits aristolochic acid entry through organic anion transporters, reduces specific aristolochic acid-DNA adduct formation, and preserves cellular viability. To test this in vivo, we used a mouse model of aristolochic acid nephropathy displaying severe tubulointerstitial injuries consisting of proximal tubular epithelial cell necrosis associated to transient acute kidney injury followed by mononuclear cell infiltration, tubular atrophy, and interstitial fibrosis. Treatment with probenecid prevented increased plasma creatinine and tubulointerstitial injuries, and reduced both the extent and the severity of ultrastructural lesions induced by aristolochic acid, such as the loss of brush border, mitochondrial edema, and the disappearance of mitochondrial crests. Further, the number of proliferating cell nuclear antigen-positive cells and total aristolochic acid-DNA adducts were significantly reduced in mice receiving aristolochic acid plus probenecid compared with mice treated with aristolochic acid alone. Thus, we establish the nephroprotective effect of probenecid, an inhibitor of organic acid transporters, in vivo toward acute proximal tubular epithelial cell toxicity in a mouse model of aristolochic acid nephropathy.

Early proximal tubule injury in experimental aristolochic acid nephropathy: functional and histological studies.

BACKGROUND: Aristolochic acid (AA), the plant extract of Aristolochia species, is involved in the onset of progressive tubulointerstitial renal fibrosis in humans. Clinical and in vitro findings have previously suggested that the proximal tubule was the target of AA. METHODS: Using a rat model of AA nephropathy, the proximal tubular lesions induced by daily subcutaneous injections of AA for 35 or 5 days were characterized biochemically and histologically. Urinary excretion of proteins, albumin, low molecular weight proteins, N-acetyl-beta-d-glucosaminidase, alpha-glutathione S-transferase, leucine aminopeptidase and neutral endopeptidase (NEP) was determined and related to histological conventional findings and immunostainings of NEP and megalin. RESULTS: In both protocols, an acute phase of release of urinary markers was observed within the first 3 days of AA treatment in parallel with a significant increase of specific AA-related DNA adducts reflecting early tubular intoxication. A dramatic loss of the proximal tubule brush border was histologically confirmed, while the expression of megalin decreased at the damaged apical epithelium (mainly of the S3 segment). CONCLUSION: Proximal tubule injury occurs early after AA intoxication in rats, with a link between specific AA-DNA adduct formation, decreased megalin expression and inhibition of receptor-mediated endocytosis of low molecular weight proteins, bringing in vivo confirmation of previous in vitro studies.

The renin-angiotensin system blockade does not prevent renal interstitial fibrosis induced by aristolochic acids.

BACKGROUND: Experimental aristolochic acid nephropathy (AAN), characterized by interstitial fibrosis, tubular atrophy, and chronic renal failure, was reported after 35-day injections of aristolochic acids (AA) to salt-depleted male Wistar rats. The link between renal fibrosis and the renin-angiotensin system (RAS) in this model remains unknown. METHODS: We investigated the impact of sodium diets (low and normal), of RAS inhibition with enalapril (ENA) alone, or combined with candesartan (CSN) for 35 days, and ENA + CSN for 65 days on AAN development. At the end of each observation period, blood pressure and renal angiotensin-converting enzyme activity were measured, as well as renal functional impairment (plasma creatinine increase, proteinuria) and histologic lesions (interstitial fibrosis, monocytes/macrophages infiltration, myofibroblasts collagens type I and IV, proliferating cells). RESULTS: Sodium intake did not modify renal functional and morphologic impairment induced by AA. The RAS blockade by ENA or ENA + CSN in rats receiving AA did not result in any statistical difference in terms of renal failure, proteinuria, and interstitial fibrosis on day 35 or 65. On day 35, the monocytes/macrophages infiltration was significantly decreased by two-fold when ENA (P < 0.01) or ENA + CSN (P < 0.01) was given from day 0. CONCLUSION: Our data demonstrate that RAS modulation by salt depletion and pharmacologic blockade do not influence renal failure and interstitial fibrosis in the rat model of AAN. We suggest that pathways of interstitial renal fibrosis may be independent of RAS at least in some conditions.

Effects of dexfenfluramine on aristolochic acid nephrotoxicity in a rat model for Chinese-herb nephropathy.

Chinese-herb nephropathy (CHN) is a progressive renal interstitial fibrosis initially reported after concomitant intake of an anorexigen, (dex)fenfluramine, and a Chinese herb ( Aristolochia fangchi) containing nephrotoxic and carcinogenic aristolochic acid (AA). We thus tested the possible enhancing effect of the active enantiomer dexfenfluramine (DXF) on AA nephrotoxicity in a rat model for CHN. Groups of 12 salt-depleted male Wistar rats received daily subcutaneous injections of 7 mg/kg body weight DXF (DXF group), 7 mg/kg body weight AA (AA group), a combination of the same doses of AA and DXF (AA+DXF group), or vehicle (control group) for up to 35 days. Six animals per group were killed on day 10 and the remaining six on day 35. Renal function was evaluated by determining serum creatinine and urinary leucine aminopeptidase activity. Histological evaluation of kidney samples was performed and tubulointerstitial injuries were semiquantified. The DXF group did not differ from controls for any parameter. Similarly elevated serum creatinine levels, decreased leucine aminopeptidase enzymuria, and renal lesions were observed in the AA and the AA+DXF groups after both 10 and 35 days. The formation of specific AA-DNA adducts in liver and renal tissue samples was assessed by the (32)P-postlabelling method. Specific AA-DNA adduct levels were significantly increased in kidney tissues from AA+DXF rats compared with AA rats. These functional and histological data suggest that DXF does not enhance AA nephrotoxicity in a rat model for CHN. Further investigations are needed to clarify the mechanism by which DXF may enhance AA-DNA adduct formation.

Aristolochic acids induce chronic renal failure with interstitial fibrosis in salt-depleted rats.

Chinese-herb nephropathy (CHN) is a rapidly progressive renal fibrosis associated with the intake of a Chinese herb (Aristolochia fangchi) containing nephrotoxic and carcinogenic aristolochic acids (AA). This study attempted to reproduce the main features of human CHN (renal failure, tubular atrophy, and interstitial fibrosis) in a rat model similar to that of cyclosporin-induced nephropathy. Salt-depleted male Wistar rats received daily subcutaneous injections of either 1 mg/kg body wt AA (low-dose AA group), 10 mg/kg body wt AA (high-dose AA group), or vehicle (control group) for 35 d. On days 10 and 35, assessment of renal function, measurements of urinary excretion of glucose, protein, and leucine aminopeptidase, and histologic analyses were performed (six rats euthanized/group). High-dose AA induced glucosuria, proteinuria, and elevated serum creatinine levels and reduced leucine aminopeptidase enzymuria on days 10 and 35, whereas low-dose AA had no significant effect. Tubular necrosis associated with lymphocytic infiltrates (day 10) and tubular atrophy surrounded by interstitial fibrosis (day 35) were the histologic findings for the high-dose AA-treated rats. In both AA groups, urothelial dysplasia was also observed, as well as fibrohistiocytic sarcoma at the injection site. A short-term model of AA-induced renal fibrosis was established in salt-depleted Wistar rats. These results support the role of AA in human CHN and provide a useful model for examination of the pathophysiologic pathways of renal fibrosis.