The dynamics of urinary N-acetyl-β-D-glucosaminidase (NAG), a marker of renal tubular dysfunction, in patients with lupus nephritis undergoing oral prednisone therapy

Biomarkers Associated with Drugs for the Treatment of Lupus Nephritis

The constant updating of lupus drug treatment guidelines has led to a question. How can the efficacy of treatment be more effectively monitored? Systemic lupus erythematosus (SLE) is a complex autoimmune disease that often presents clinically with multi-organ involvement, and approximately 30% of patients with SLE develop lupus nephritis (LN). Therefore, it is important to better track disease progression and drug efficacy. Now, kidney biopsy is still the gold standard for diagnosing and guiding the treatment of LN, but it is invasive and expensive. If simple, non-invasive and effective biomarkers can be found, drug intervention and prognosis can be better monitored and targeted. In this review, we focus on LN and explore biomarkers related to LN therapeutics, providing clinicians with more possibilities to track the therapeutic effect of drugs, improve treatment options and assess patient outcomes.

Urinary biomarkers in lupus nephritis

Systemic lupus erythematosus (SLE) is the prototypical autoimmune disease that can affect any organ of the body. Multiple mechanisms may contribute to the pathophysiology of systemic lupus, including failure to remove apoptotic bodies, hyperactivity of self-reactive B and T lymphocytes, abnormal exposure to autoantigens, and increased levels of B-cell stimulatory cytokines. The involvement of the kidney, called lupus nephritis (LN), during the course of the disease affects between 30% and 60% of adult SLE patients, and up to 70% of children. LN is an immune-mediated glomerulonephritis that is a common and serious finding in patients with SLE. Nowadays, renal biopsy is considered the gold standard for classifying LN, besides its degree of activity or chronicity. Nevertheless, renal biopsy lacks the ability to predict which patients will respond to immunosuppressive therapy and is a costly and risky procedure that is not practical in the monitoring of LN because serial repetitions would be necessary. Consequently, many serum and urinary biomarkers have been studied in SLE patients for the complementary study of LN, existing conventional biomarkers like proteinuria, protein/creatinine ratio in spot urine, 24 ​h urine proteinuria, creatinine clearance, among others and non-conventional biomarkers, like Monocyte chemoattractant protein-1 (MCP-1), have been correlated with the histological findings of the different types of LN. In this article, we review the advances in lupus nephritis urinary biomarkers. Such markers ideally should be capable of predicting early sub-clinical flares and could be used to follow response to therapy. In addition, some of these markers have been found to be involved in the pathogenesis of lupus nephritis.

Lupus nephritis pathology prediction with clinical indices

Effective treatment of lupus nephritis and assessment of patient prognosis depend on accurate pathological classification and careful use of acute and chronic pathological indices. Renal biopsy can provide most reliable predicting power. However, clinicians still need auxiliary tools under certain circumstances. Comprehensive statistical analysis of clinical indices may be an effective support and supplementation for biopsy. In this study, 173 patients with lupus nephritis were classified based on histology and scored on acute and chronic indices. These results were compared against machine learning predictions involving multilinear regression and random forest analysis. For three class random forest analysis, total classification accuracy was 51.3% (class II 53.7%, class III&IV 56.2%, class V 40.1%). For two class random forest analysis, class II accuracy reached 56.2%; class III&IV 63.7%; class V 61%. Additionally, machine learning selected out corresponding important variables for each class prediction. Multiple linear regression predicted the index of chronic pathology (CI) (Q² = 0.746, R² = 0.771) and the acute index (AI) (Q² = 0.516, R² = 0.576), and each variable’s importance was calculated in AI and CI models. Evaluation of lupus nephritis by machine learning showed potential for assessment of lupus nephritis.

Urinary enzymatic markers (N-acetyl-beta-D-glucosaminidase) in assessing the tubulointerstitial compartment in chronic glomerulonephritis related to odontogenic foci

Chronic glomerulonephritis is related to focus infection. Odontogenic foci are frequently involved in glomerulonephritis. The relationship with the odontogenic focus infection can be demonstrated by the occurrence or aggravation of the symptoms of glomerulonephritis: proteinuria, haematuria, high blood pressure and oedema. Glomerular impairment in glomerulonephritis occurs together with inflammatory alterations of the tubulointerstitial compartment that can play an important part in the evolution of the disease. Tubular urinary markers can indicate the activation of this compartment during an infection of a focus, an odontogenic focus in our study.The paper aims at demonstrating the relationship between the odontogenic focus infection and tubulointerstitial lesions, assessed by a tubular urinary marker, N-acetyl beta-D glucosaminidase (NAG).We investigated the urinary N-acetyl beta-D glucosaminidase of 20 patients with chronic glomerulonephritis who presented odontogenic focus infections, comparing them with patients with chronic glomerulonephritis without odontogenic foci and of 20 controls, clinically healthy persons.Chronic glomerulonephritis patients with odontogenic focus infection presented clearly increased values as compared to clinically healthy control persons of urinary N-acetyl beta-D glucosaminidase.These patients underwent surgical intervention on the odontogenic focus under antibacterial prophylactic treatment. In 75% cases, the values of N-acetyl beta-D glucosaminidase diminished, indicating the favourable effect of the treatment of the odontogenic focus on the tubulointerstitial compartment in patients with chronic glomerulonephritis. In 25% cases this therapeutic treatment was associated with an increase of the values of urinary N-acetyl beta-D glucosaminidase, expressing its unfavourable effect on chronic glomerulonephritis.Urinary N-acetyl beta-D glucosaminidase indicated an etiopathogenetic relationship between the odontogenic focus and the tubulointerstitial compartment in chronic glomerulonephritis.

Urinary biomarkers in assessing the nephrotoxic potential of gentamicin in solitary kidney patients after 7 days of therapy

INTRODUCTION

The solitary kidney (SK) may present increased vulnerability to nephrotoxicity because of adaptive phenomena.

AIMS

Assessing the vulnerability of the SK with urinary tract infections (UTI) to gentamicin by means of urinary biomarkers (N-acetyl-beta-D-glucosaminidase (NAG) and urinary alpha-1-microglobulin), as well as glomerular filtration rate (GFR).

METHODS

We studied 14 patients with SK with UTI (group A) (mean age 58.07 ± 13.61 years, mean duration of SK 13.55 ± 12.33 years) who were administered gentamicin for 7 days. Group B consisted by 17 patients with SK without any other associated renal pathology (average age 51.17 ± 9.39 years, average existence period of a single kidney 33.23 ± 21.73 years). We also included a third group (group C) represented by nine healthy individuals, with two kidneys.

RESULTS

Increased values of urinary NAG were found in group B as compared to group C and alpha-1 microglobulin in group A as compared to group B. During treatment with gentamicin, increased values of both NAG and alpha-1-microglobulin in group A were found on day 7 as compared to values before treatment (day 7 NAG=18.99 ± 14.07 U/g creat versus day 0, NAG=5.15 ± 6.54 U/g creat, p=0.004; day 7 alpha-1-microglobulin=20.88 ± 18.84 mg/g creat versus day 0, urinary alpha-1-microglobulin=4.96 ± 6.57 mg/g creat, p=0.003). No statistically significant alterations of GFR were noticed after 7 days of treatment.

CONCLUSIONS

We found the nephrotoxic effects of gentamicin at tubular level, but not at glomerular level. The nephrotoxic potential of gentamicin in patients with a SK can be monitored by assessing urinary biomarkers during treatment of UTI.

Urinary immunoglobulin G to albumin ratio and N-Acetyl-Beta-D-Glucosaminidase as early predictors of therapeutic response in ANCA-associated glomerulonephritis

Background

The aim of our study was to evaluate the prognostic value of glomerular and tubular proteinuria and tubular enzymuria as early indicators of therapeutic response to induction therapy with i.v. pulse cyclophosphamide (CyC) and methylprednisolone (MP) in patients with antineutrophil cytoplasmic antibody (ANCA) associated glomerulonephritis.

Methods and Findings

An observational single-center study was conducted in 30 patients with ANCA-associated glomerulonephritis. Patients were divided into subgroups with good or poor response to CyC therapy according to clinical and laboratory parameters. The diagnosis of ANCA-associated glomerulonephritis was based on the Chapel-Hill disease definitions. Good response to induction therapy was significantly associated with higher absolute values of urine N-acetyl-beta-D-glucosaminidase (NAG) to creatinine ratio (above 14.83 microcat/mol) and urine immunoglobulin G (IgG) to albumin ratio (above 0.09) at the time of diagnosis, while albuminuria or proteinuria did not have any early predictive value. The remission of renal disease was anticipated as early as 3 months after introduction of induction therapy in patients with reduction of urine NAG to creatinine ratio below the baseline value and in patients with at least 24% rise in eGFR.

Conclusions

Urine IgG to albumin and urine NAG to creatinine ratio are better early predictors of treatment response in patients with ANCA-associated glomerulonephritis than proteinuria or albuminuria.