Objective: To explore the significance of urinary smad3(usmad3) protein level change in diabetic nephropathy (DN) in type 2 diabetes mellitus and examine its relationship with the progression of DN.
Methods: From May 2010 to August 2011, a total of 282 patients with type 2 diabetes were selected for the experimental group according to instant urine specimen albumin-creatinine ratio (UACR). Another 100 healthy subjects were taken as the control group. Then the diabetics were divided into 3 groups, including 110 with normal albuminuria (NA group), 114 with microalbuminuria (MA group) and 58 with macroalbuminuria (DN group). Enzyme-linked immunosorbent assay (ELISA) was used to detect the content of usmad3. The parameters of age, systolic blood pressure, body mass index (BMI), blood glucose, blood lipids, urinary albumin/creatinine (ACR), estimated glomerular filtration rate (eGFR) and glycosylated hemoglobin were measured. And non-mydriatic fundus camera was used to evaluate retinopathy, the DN group (n = 58) was then divided into two groups of those without retinopathy (n = 25) and with retinopathy (n = 33).
Results: (1) The usmad3 level in type 2 diabetes group was significantly higher than that in the control group (489(273,1193) vs 311 (179, 497) ng/mmol Cr (P < 0.01). (2) According to UACR, type 2 diabetes group was divided into 3 different groups to compare the relative level differences of usmad3 in different groups: MA group versus NA group, 552 (316,1338) vs 317 (200,594), DN group versus NA group, 1035 (503,3035)vs 317 (200,594), DN group versus MA group, 1035(503,3035)vs 552(316,1338), all P < 0.01. (3) Pearson correlation test showed the level of usmad3 was significantly correlated with age, SBP, HbA1c, blood urea nitrogen, creatinine, total cholesterol, low density lipoprotein, eGFR and UACR (r = 0.57, P < 0.01). And multiple linear regression analysis showed that usmad3 and UACR were independently correlated (β = 0.754, P < 0.01). (4) The usmad3 level in DN with retinopathy were significantly higher than that in DN without retinopathy (1905(806,4303) vs 595 (331,1183), P < 0.01). No significant difference existed in uACR level between DN with retinopathy and DN without retinopathy(P > 0.05).
Conclusions: Urinary level of smad3 is significantly elevated in type 2 diabetics and it is significantly associated with ACR. It suggests that usmad3 is a potential marker in the diagnosis of DN and may be used to predict the severity of DN.