Urinary matrix metalloproteinase activity in diabetic kidney disease: a potential marker of disease progression.

BACKGROUND: Progressive kidney fibrosis, associated with chronic kidney disease (CKD), results from an imbalance in extracellular matrix (ECM) homeostasis. Reduced matrix metalloproteinases (MMP) activity causing lower clearance of ECM proteins has been implicated mainly through an overproduction of tissue inhibitors of metalloproteinases (TIMP), but also by reduced MMP synthesis. We tested the hypothesis that MMP activity can be measured in human urine and can be used as a potential biomarker of the progression of diabetic kidney disease (DKD). METHODS: An observational prospective study was performed on 102 DKD patients using 21 diabetic patients without kidney disease and 21 healthy volunteers as controls. The Molecular Probes EnzChek Gelatinase/Collagenase Assay Kit were used to determine urinary MMP activity using DQ™ Gelatin (total MMPs), DQ™ Collagen I (interstitial collagenases) and DQ™ Collagen IV (gelatinises) substrates. A broad-spectrum synthetic inhibitor of all MMP, 1,10-phenanthroline, was used to confirm that the proteolytic activity is due to MMP activity. All MMP values were expressed per unit of urine creatinine. RESULTS: Overall urinary MMP activity (DQ Gelatin substrate) was significantly elevated in DKD patients (14.76 ± 3.65 Δ fl/h/mmol creatinine) compared to diabetes mellitus controls (7.09 ± 2.12 Δ fl/h/mmol creatinine) and healthy volunteers (1.87 ± 0.74 Δ fl/h/mmol creatinine) (ANOVA p = 0.01). Within the DKD cohort, there was an approximate threefold higher urinary MMP activity in nonprogressive DKD patients compared to those with progressive disease (p = 0.002). The urinary MMP activity:creatinine ratio was significantly higher in normoalbuminuric and microalbuminuric DKD compared to macroalbuminuric DKD. Positive correlations were observed between the rate of total MMP activity and interstitial collagenases (r = 0.75, p < 0.0001) and gelatinases (r = 0.59, p = 0.0001). The accuracy of MMP activity to predict the rate of annual eGFR decline (ROC analysis) was 77% compared to 64% for albuminuria. CONCLUSIONS: Total MMP activity can be easily measured in human urine. Surprisingly and in contrast to MMP activity in the kidney, urine MMP activity is elevated in DKD. However, there is a significantly lower MMP activity in patients with progressive DKD. ROC analysis demonstrates that single urine MMP activity estimation is superior to albuminuria in predicting DKD patients with progressive disease.

A study of the natural history of diabetic kidney disease (DKD).

BACKGROUND: In view of the alarming increase in the number of people with diabetes mellitus (DM), a rising number of patients with diabetic kidney disease (DKD), end-stage renal disease (ESRD) and cardiovascular disease (CVD) is forecasted. It is therefore imperative to re-visit the natural history of DKD and to identify potential risk factors, which may enhance the progression of the disease and its complications. METHODS: The medical records of 270 Type 2 diabetic chronic kidney disease patients followed up at the Sheffield Kidney Institute between 2000 and 2008 were reviewed. Various socio-demographic, clinical and biochemical parameters (baseline and follow-up parameters) were retrospectively collected from the patients' database. Progression of DKD was evaluated by evaluation of the rate of decline of estimated glomerular filtration rate (eGFR) as calculated from the simplified Modification of Diet in Renal Disease formula [progressors: loss of glomerular filtration rate (GFR) >2 mL/min/1.73m(2)/year] as well as by the progression pattern based on the slope of GFR changes. Variables associated with progression in univariate analysis were examined by multivariate analysis to determine the factors independently associated with DKD progression. RESULTS: The majority of the study populations were males (66.7%) and Caucasians (88%). Ninety-four patients (34.8%) had progressive, whereas 176 (65.2%) had non-progressive DKD. The rate of eGFR decline in progressors was -3.57 ± 1.45 mL/min/1.73m(2)/year compared to -1.31 ± 0.23 mL/min/1.73m(2)/year in non-progressors. The following parameters discriminated progressors from non-progressors by univariate analysis: baseline-blood pressure (BP) parameters, eGFR and proteinuria as well as serum uric acid. We also observed that area under the curve for follow-up systolic blood pressure (SBP), glycosylated haemoglobin (HbA1c) and proteinuria were significantly higher among the progressors (P = 0.043, P = 0.02 and P = 0.001, respectively). Independent determinants of DKD progression in this study in an adjusted logistic regression model were baseline HbA1c [odds ratio (OR), 2.27; 95% confidence interval (CI), 1.14-4.54], baseline SBP (OR, 1.23; 95% CI, 1.06-1.41), baseline proteinuria (OR, 3.24; 95% CI, 2.1-5.38), baseline serum uric acid (OR, 1.16; 95% CI, 1.09-1.39) and vascular co-morbidities (OR, 1.61; 95% CI, 1.02-2.54). Percentage changes in the key parameters (BP, HbA1c and proteinuria) during the first year of the study did not affect the rate of eGFR decline. CONCLUSIONS: Baseline HbA1c, SBP, proteinuria and serum uric acid together with the presence of vascular co-morbidities are strongly and independently associated with faster DKD progression. A further prospective observational study is currently undertaken to evaluate these findings and to determine the predictive value of other biochemical peptides and cellular markers on DKD outcome.