Abstract
Renal clinical chemistry only detects kidney dysfunction after considerable damage has occurred and is imperfect in predicting long term outcomes. Consequently, more sensitive markers of early damage and better predictors of progression are being urgently sought, to better support clinical decisions and support shorter clinical trials. Transglutaminase 2 (TG2) is strongly implicated in the fibrotic remodeling that drives chronic kidney disease (CKD). We hypothesized that urinary TG2 and its ε-(γ-glutamyl)-lysine crosslink product could be useful biomarkers of kidney fibrosis and progression. Animal models: a rat 4-month 5/6th subtotal nephrectomy model of CKD and a rat 8-month streptozotocin model of diabetic kidney disease had 24-hour collection of urine, made using a metabolic cage, at regular periods throughout disease development. Patients: Urine samples from patients with CKD (n = 290) and healthy volunteers (n = 33) were collected prospectively, and progression tracked for 3 years. An estimated glomerular filtration rate (eGFR) loss of 2–5 mL/min/year was considered progressive, with rapid progression defined as > 5 mL/min/year. Assays: TG2 was measured in human and rat urine samples by enzyme-linked immunosorbent assay (ELISA) and ε-(γ-glutamyl)-lysine by exhaustive proteolytic digestion and amino acid analysis. Urinary TG2 and ε-(γ-glutamyl)-lysine increased with the development of fibrosis in both animal model systems. Urinary TG2 was 41-fold higher in patients with CKD than HVs, with levels elevated 17-fold by CKD stage 2. The urinary TG2:creatinine ratio (UTCR) was 9 ng/mmol in HV compared with 114 ng/mmol in non-progressive CKD, 1244 ng/mmol in progressive CKD and 1898 ng/mmol in rapidly progressive CKD. Both urinary TG2 and ε-(γ-glutamyl)-lysine were significantly associated with speed of progression in univariate logistic regression models. In a multivariate model adjusted for urinary TG2, ε-(γ-glutamyl)-lysine, age, sex, urinary albumin:creatinine ratio (UACR), urinary protein:creatinine ratio (UPCR), and CKD stage, only TG2 remained statistically significant. Receiver operating characteristic (ROC) curve analysis determined an 86.4% accuracy of prediction of progression for UTCR compared with 73.5% for UACR. Urinary TG2 and ε-(γ-glutamyl)-lysine are increased in CKD. In this pilot investigation, UTCR was a better predictor of progression in patients with CKD than UACR. Larger studies are now warranted to fully evaluate UTCR value in predicting patient outcomes.
Highlights
Proteinuria and albuminuria are the most frequently used predictors of renal function decline in kidney disease [1]
In the SNx model, 24-hour albuminuria was significantly elevated at all time points (S2E Fig in S1 File)
Urinary Transglutaminase 2 (TG2) levels were elevated by 83% compared with control animals as early as Day 7 post-surgery, this did not achieve statistical significance until Day 28, when levels were 9.3-fold higher than the time-matched controls (P = 0.0004)
Summary
Proteinuria and albuminuria are the most frequently used predictors of renal function decline in kidney disease [1]. Changes in urinary albumin:creatinine ratio (UACR), as well as estimated glomerular filtration rate (eGFR), are commonly used as surrogate endpoints in chronic kidney disease (CKD) clinical trials [2, 3] and recognized as important risk factors for cardiovascular disease [4, 5]. Microalbuminuria (30 to < 300 mg/day or 30–300 mg/L), typically measured as UACR (3–30 mg albumin/mmol creatinine), is often used as a gold standard for diagnosis of renal impairment and CKD development. Macroalbuminuria (300–3500 mg/day or UACR 30 to typically 9000 mg/mmol) is correspondingly used to estimate progression. Microalbuminuria is often transitory and irresolute; it is not a specific and reliable marker of CKD, especially in early disease
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
