Urinary Smad1 is a new biomarker for diagnosis and evaluating the severity of diabetic nephropathy.

The aim of this study was to analyze urinary Smad1 level in patients with type 2 diabetes, explore the possibility of Smad1 being a biomarker for early diagnosis and evaluation of severity of diabetic nephropathy, and explore the impact factors affecting urinary Smad1 concentration. In this study, 132 subjects with type 2 diabetes and 50 healthy volunteers were enrolled. Subjects were grouped according to urine albumin to creatinine ratio (ACR) into: normal albumin in urine (NAU), low albumin in urine (LAU), high albumin in urine (HAU), and very high albumin in urine (VHAU). Among those, LAU, HAU, and VHAU were regarded as the diabetic nephropathy group (DN group), NAU was regarded as nondiabetic nephropathy (non-DN group), and the healthy volunteers were the controls. Enzyme-linked immunosorbent assay was used to detect the urinary Smad1 concentration, urinary Smad1 to creatinine ratio (SCR) was used as the standard reference. Compared with non-DN group, SCR of DN group was higher (P < 0.05), while there was no difference between the non-DN group and controls (P > 0.05). There was no significant difference for SCR between LAU and NAU groups (P > 0.05). The SCR was higher in VHAU group than those in HAU and LAU groups, and higher in HAU than that in LAU group (P < 0.05). Pearson correlation analysis showed that SCR measures were positively correlated to ACR, duration and diabetic retinopathy of the disease (r = 0.285, 0.230, 0.202; P = 0.001, 0.008, 0.019, respectively). Multiple linear regression analysis showed that ACR and duration were independent impact factors for SCR (P < 0.05). This is the first known study examining the correlation of Smad1 and DN in clinical practice. It suggested that the urinary Smad1 may be a potential diagnostic parameter for DN and may be used to evaluate the severity of DN. However, it cannot predict those in patients with the earliest DN and low urine albumin concentration. Furthermore, ACR and duration may be independent impact factors for urinary Smad1.