New Biomarkers in Acute Tubulointerstitial Nephritis: A Novel Approach to a Classic Condition

Effects of fourteen essential minerals and vitamins on acute and chronic tubulointerstitial nephritis: a multivariate Mendelian randomization study

OBJECTIVE

To investigate the causal relationship between minerals and vitamins and acute and chronic tubulointerstitial nephritis by Mendelian randomization.

METHODS

We selected fourteen minerals and vitamins from the GWAS database and acute tubulointerstitial nephritis and chronic tubulointerstitial nephritis from the Finnish database. Minerals and vitamins were first analyzed by two-sample Mendelian randomization for acute and chronic tubulointerstitial nephritis. The effects of minerals and vitamins on common acute and chronic tubulointerstitial nephritis were further explored by multivariate Mendelian randomization.

RESULTS

among fourteen minerals and vitamins by two-sample Mendelian randomization analysis, there was genetic causality for vitamin B6 and vitamin D on acute tubulointerstitial nephritis, and the results were vitamin B6 (β = -0.641; P = 0.049; OR = 0.527; 95% CI: 0.278-0.998); vitamin D (β = -3.165; P = 0.040; OR = 0.042; 95% CI: 0.002-0.861). Fourteen minerals and vitamins were not genetically causally associated with chronic tubulointerstitial nephritis. The presence of vitamin B6 was then analyzed by a multivariate Mendelian randomization study to independently affect acute tubulointerstitial nephritis and showed a negative correlation (P = 0.010; 95% CI: 0.021-0.159).

CONCLUSION

We genetically predicted the possible influence of minerals and vitamins on acute and chronic tubulointerstitial nephritis. Vitamin B6 deficiency in vivo was found to adversely affect acute and chronic tubulointerstitial nephritis. This suggests that we pay clinical attention to the different effects that nutrients such as minerals and vitamins bring to acute and chronic tubulointerstitial nephritis.

CLINICAL TRIAL NUMBER

Not applicable.

Tubulointerstitial nephritis in children and adolescents

The tubulointerstitial compartment comprises most of the kidney parenchyma. Inflammation in this compartment (tubulointerstitial nephritis-TIN) can be acute and resolves if the offending factor is withdrawn or may enter a chronic process leading to irreversible kidney damage. Etiologic factors differ, including different exposures, infections, and autoimmune and genetic tendency, and the initial damage can be acute, recurrent, or permanent, determining whether the acute inflammatory process will lead to complete healing or to a chronic course of inflammation leading to fibrosis. Clinical and laboratory findings of TIN are often nonspecific, which may lead to delayed diagnosis and a poorer clinical outcome. We provide a general review of TIN, with special mention of the molecular pathophysiological mechanisms of the associated kidney damage.

Urinary RANTES and MCP-1 as noninvasive biomarkers for differential diagnosis and prediction of treatment response in acute interstitial nephritis

Background

Although kidney biopsy is definitive for the diagnosis of acute interstitial nephritis (AIN) and acute tubular necrosis (ATN), its invasiveness limits its use. We aimed to identify urine biomarkers for differentiating AIN and ATN and to predict the response of patients with AIN to steroid treatment.

Methods

In this prospective cohort study, biopsy-proven ATN (n = 34) and AIN (n = 55) were included. Urinary cytokine/chemokine [interleukin-9, monocyte chemoattractant protein-1 (MCP-1), regulated on activation, normal T cell expressed and secreted (RANTES), tumor necrosis factor-α, tumor growth factor-β and vascular endothelial growth factor] levels and the proportion of immune cells [expressing cluster of differentiation (CD)45, CD3, CD20] and proliferating tubular cells (expressing Ki-67) were analyzed by immunohistochemistry. Cytokine/chemokine levels and intrarenal immunohistochemistry data according to the response to steroid treatment in the AIN patients were also analyzed.

Results

The urinary RANTES/creatinine ratio and the percentages of intrarenal CD45-, CD3-, CD20- and Ki-67-positive cells were significantly higher in the AIN group than in the ATN group (P < .05 for all). Among steroid-administered patients with AIN, renal function improved significantly in the steroid responder group. These patients had higher urinary MCP-1/creatinine and intrarenal CD45 and Ki-67 levels than those in the non-responder group.

Conclusions

The potential of the urinary RANTES/creatinine ratio as a noninvasive biomarker for differentiating AIN from ATN is highlighted. Urinary MCP-1/creatinine levels and the proportion of total intrarenal leukocytes and proliferating tubular cells may serve as indicators for predicting the response of patients with AIN to steroid treatment.

Urinary soluble PD-1 as a biomarker of checkpoint inhibitor-induced acute tubulointerstitial nephritis

Background

Acute interstitial nephritis (AIN) related to immune checkpoint inhibitors (ICI-AIN) has a not completely understood pathophysiology. Our objectives were to analyze possible biomarkers for the differentiation between acute tubular necrosis (ATN) and AIN, especially in cancer patients, and to study the participation of the immune checkpoint pathway in ICI-AIN.

Methods

We performed an observational study. We recruited patients with incident diagnosis of ICI-AIN (n = 19). We measured soluble PD-1 (sPD-1), sPD-L1, and sPD-L2 in serum and urine at diagnosis and compared to it patients with non-ICI-related AIN (non-ICI-AIN) (n = 18) and ATN (n = 21). The findings were validated in an independent cohort from another institution (n = 30). Also, we performed PD-L1 and PD-L2 immunostaining of kidney biopsies from patients with ICI-AIN and compared to patients with non-ICI-AIN.

Results

Urinary sPD-1 (usPD-1) was higher in patients with AIN compared to ATN (P = .03). Patients with AIN also showed higher serum sPD-1 (ssPD-1) than patients with ATN (P = .021). In cancer patients, usPD-1 <129.3 pg/ml had a 71.43% sensitivity and 94.44% specificity to differentiate ATN from ICI-AIN, with a likelihood ratio of 12.86. In the external validation cohort, the same cutoff showed a sensitivity of 80%. In kidney biopsies, patients with ICI-AIN showed higher density of PD-L1 positive tubules than patients with non-ICI-AIN (P = .02). The proportion of patients having >2.64/mm2 PD-L2 positive tubules was higher among patients with ICI-AIN compared to non-ICI-AIN (P = .034). There was a positive correlation (P = .009, r = 0.72) between usPD-1 and the number of PD-L1 positive tubules.

Conclusions

UsPD-1 and ssPD-1 are higher in AIN than ATN. Moreover, there was a strong correlation between usPD-1 and renal tubular PD-L1 expression. Our findings suggest a role of usPD-1 as non-invasive biomarker to differentiate ICI-AIN from ATN, especially in cancer patients, which has been confirmed in an external validation cohort.

Effect of Ultrasound-Guided Renal Biopsies on Urinary N-Acetyl-Beta-D-Glucosaminidase Index Activity in Dogs with Diffuse Parenchymal Nephropathies

BACKGROUND

Ultrasound-guided kidney biopsy is an essential diagnostics method that can increase the accuracy of the differential diagnosis between acute and chronic nephropathies. In addition, it will help clinicians perform an etiologic diagnosis, issue a prognosis, and orient therapy for the majority of parenchymal nephropathies. Due to the relative invasiveness and potential adverse effects, the use of kidney biopsies is limited among practitioners.

RESULTS

Twenty-eight dogs, of mixed breed and variable ages, of which 11 (39, 29%) were males and 17 (60, 71%) were females, were examined and underwent an ultrasound-guided kidney biopsy to establish a definitive diagnosis. The patients were presented with a variety of diffuse nephropathies, such as kidney lymphoma: 1 (3.57%), glomerulonephritis: 13 (46.43%), tubulointerstitial nephritis: 11 (39.29%), and nephrocalcinosis. A total of 3 (10.71%) of 18 (64.29%) were in acute kidney injury, and 10 (35.71%) were CKD patients. The type and the severity of the kidney lesions were correlated with changes in the urinary n-acetyl-beta-d-glucosaminidase index (iNAG. To quantify the side effects of percutaneous kidney biopsy, the magnitude of post-biopsy hematuria and changes in urinary iNAG activity were evaluated. The results indicate a significant post-biopsy increase in the urinary iNAG activity in all the patients that underwent this procedure (100.08 ± 34.45 U/g), with a pre-biopsy iNAG vs. 147.65 ± 33.26 U/g post-biopsy iNAG (p < 0.001), suggesting an intensification in the kidney tubular damage that comes consecutives to kidney puncture and sampling. Transitory macro- or microhematuria were constant findings in all the dogs that underwent ultrasound-guided kidney biopsy, but the magnitude and extent could not be associated with the platelet count (PLT 109/L), aPTT (s), and PT (s) levels in our patients, and they were also resolved after 12-24 h without therapeutic interventions.

CONCLUSIONS

Ultrasound-guided renal biopsy was shown to be a minimally invasive diagnostic procedure that causes transient and limited effects on kidney structures. Although these effects were minor and resolved without intervention, we feel that the benefit of obtaining higher-quality biopsied tissue outweighs the higher risks associated with this procedure.

The diagnosis of acute interstitial nephritis caused by infection versus antibiotic-induced interstitial nephritis: a narrative review

Acute interstitial nephritis (AIN) is a significant contributor to acute kidney injury and can be attributed to a variety of factors, including but not limited to allergens or drugs, infections, autoimmune or systemic diseases, and idiopathic forms of the disease. In some cases, AIN requires a therapeutic action according to a single specific etiology by handling the offending agent and applying an immunosuppressant. Although AIN can be diagnosed through renal biopsy, it is not able to pinpoint the precise cause when multiple causes are suspected to be present simultaneously. Such situations arise when a patient suffering from infection develops AIN during antibiotic therapy, the exact causative factor of which becomes a challenge for the clinicians to determine. This is attributed to the different approaches employed in different etiologies, wherein clinicians are required to maintain the current antibiotic therapy or augment the dose in cases of infection as AIN etiology, without resorting to immunosuppressant therapy as the primary objective is infection killing. In contrast, antibiotics as an etiology for AIN require an alternative drug from the antibiotics group, along with an immunosuppressant. In the interim, delaying the identification of the precise cause may result in interstitial fibrosis and chronic kidney disease. This narrative review highlights certain findings that can be typical of infection-associated ATIN compared with antibiotic-associated ATIN based on clinical history and physical examination, clinical presentation of different antibiotic drug classes, histopathological features, classical and novel biomarkers, serum and urine cytokines and chemokines, cellular biomarkers, and genetic biomarkers. Although these findings cannot provide conclusive and clear recommendations that can be useful in the clinical practice, they can entice researchers to conduct original research on these features to discover clear recommendations.

Overview of Antibiotic-Induced Nephrotoxicity

Drug-induced nephrotoxicity accounts for up to 60% of cases of acute kidney injury (AKI) in hospitalized patients and is associated with increased morbidity and mortality in both adults and children. Antibiotics are one of the most common causes of drug-induced nephrotoxicity. Mechanisms of antibiotic-induced nephrotoxicity include glomerular injury, tubular injury or dysfunction, distal tubular obstruction from casts, and acute interstitial nephritis (AIN) mediated by a type IV (delayed-type) hypersensitivity response. Clinical manifestations of antibiotic-induced nephrotoxicity include acute tubular necrosis (ATN), AIN, and Fanconi syndrome. Given the potential nephrotoxic effects of antibiotics on critically ill patients, the use of novel biomarkers can provide information to optimize dosing and duration of treatment and can help prevent nephrotoxicity when traditional markers, such as creatinine, are unreliable. Use of novel kidney specific biomarkers, such as cystatin C and urinary kidney injury molecule-1 (KIM-1), may result in earlier detection of AKI, dose adjustment, or discontinuation of antibiotic and development of nonnephrotoxic antibiotics.

A low BUN/creatinine ratio predicts histologically confirmed acute interstitial nephritis

INTRODUCTION

In hospitalized patients with acute renal injury (AKI), acute tubulointerstitial nephritis (AIN) constitutes one of the leading etiologies. The objective of this study was to identify clinical and biochemical variables in patients with AKI associated with kidney biopsy-confirmed AIN.

METHODS

For our prospective study, we recruited hospitalized patients aged 18 years and older who were diagnosed with AKI based on biochemical criteria. Prior to enrollment, each patient was assessed with a complete metabolic panel and a kidney biopsy.

RESULTS

The study consisted of 42 patients (with a mean age of 45 years) and equal numbers of male and female patients. Diabetes and hypertension were the main comorbidities. Nineteen patients had histological findings consistent with AIN. There was a correlation between histology and the BUN/creatinine ratio (BCR) (r = -0.57, p = 0.001). The optimal Youden point for classifying AIN via a receiver operating characteristic (ROC) curve analysis was a BCR ≤ 12 (AUC = 0.73, p = 0.024). Additionally, in diagnosing AIN, BCR had a sensitivity of 76%, a specificity of 81%, a positive predictive value of 81%, a negative predictive value of 76%, and OR of 14 (95% CI = 2.6 to 75.7, p = 0.021). In the multivariable analysis, BCR was the sole variable associated with AIN.

CONCLUSION

A BCR ≤ 12 identifies AIN in patients with AKI. This study is the first to prospectively assess the relationship between renal biopsy results and BCR.

Facing the Challenge of Drug-Induced Acute Interstitial Nephritis

BACKGROUND

Acute interstitial nephritis (AIN) is one of the chief causes of acute kidney injury (AKI). AIN might be produced by drugs, infections, autoimmune diseases, or can be idiopathic. Among these etiologies, drug-induced AIN (DI-AIN) is the dominant one in many countries. Even when DI-AIN is suspected, identification of the putative drug is challenging.

SUMMARY

DI-AIN is an increasingly common cause of AKI. Diagnosis continues to pose a challenge for physicians due to nonspecific clinical symptoms, and the fact that it can be triggered by a wide variety of medications. Furthermore, the gold standard for the diagnosis is kidney biopsy. All these aspects render the diagnosis more difficult. The withdrawal of the causative drug of DI-AIN is the centerpiece of the treatment, and if early restoration of original kidney function is not obtained, several studies support the treatment with steroids especially when they are started quickly.

KEY MESSAGES

Almost all drugs have the potential to produce drug-induced acute interstitial nephritis (DI-AIN); however, antibiotics, nonsteroidal anti-inflammatory agents, and proton pump inhibitors account for the majority of the reported cases. DI-AIN is produced by an idiosyncratic delayed type IV hypersensitivity reaction, but the precise pathophysiological mechanism remains to be elucidated. DI-AIN symptoms are nonspecific, and most of the patients will present mild symptoms including malaise, nausea, and vomiting. The classical triad, associating fever, rash, and eosinophilia, is seldom present. Nonoliguric acute kidney injury is the main renal manifestation of DI-AIN. Tubular nonnephrotic range proteinuria is usually present. Diagnosis of DI-AIN relies on maintaining a high index of suspicion in those patients at greater risk, but kidney biopsy is required to confirm diagnosis. Histologically, AIN is characterized by the presence of an extensive interstitial infiltrate, mainly composed of lymphocytes and monocytes, but eosinophils, plasma cells, histiocytes, and polymorphonuclear cells can also be found. The withdrawal of the presumed causative drug of DI-AIN is the mainstay of the treatment. When there is no evidence of kidney function recovery after an interval of 5-7 days since interrupting the treatment with the suspected drug, several studies support the treatment with steroids, especially when they are promptly started. Early corticosteroids would decrease the inflammatory infiltrates of the kidney interstitium, thus preventing the risk of subsequent fibrosis.

Pediatric uveitis: Role of the pediatrician

The challenges of childhood uveitis lie in the varied spectrum of its clinical presentation, the often asymptomatic nature of disease, and the evolving nature of the phenotype alongside normal physiological development. These issues can lead to delayed diagnosis which can cause significant morbidity and severe visual impairment. The most common ocular complications include cataracts, band keratopathy, glaucoma, and macular oedema, and the various associated systemic disorders can also result in extra-ophthalmic morbidity. Pediatricians have an important role to play. Their awareness of the various presentations and etiologies of uveitis in children afford the opportunity of prompt diagnosis before complications arise. Juvenile Idiopathic Arthritis (JIA) is one of the most common associated disorders seen in childhood uveitis, but there is a need to recognize other causes. In this review, different causes of uveitis are explored, including infections, autoimmune and autoinflammatory disease. As treatment is often informed by etiology, pediatricians can ensure early ophthalmological referral for children with inflammatory disease at risk of uveitis and can support management decisions for children with uveitis and possible underling multi-system inflammatory disease, thus reducing the risk of the development of irreversible sequelae.