Salivary and serum cystatin SA levels in patients with type 2 diabetes mellitus or diabetic nephropathy

Objective: To investigate putative salivary biomarkers for screening and diagnosis of type 2 diabetes mellitus and diabetic nephropathy. Design: Saliva and serum samples were collected from 29 patients with type 2 diabetes, 20 patients with diabetic nephropathy, eight patients with non-diabetic induced nephropathy, and 25 healthy subjects. Initially, pooled unstimulated saliva samples from six sex- and age-matched healthy subjects and six patients with type 2 diabetes were subjected to two-dimensional gel electrophoresis, followed by mass spectrometry. Protein expression of cystatin SA in the saliva of patients with type 2 diabetes was further examined in saliva and serum using enzyme-linked immunosorbent assay (ELISA). Results: Two-dimensional gel electrophoresis revealed upregulation of salivary cystatin SA in patients with type 2 diabetes. ELISA showed a weak trend of increasing salivary cystatin SA levels in patients with type 2 diabetes, compared with those levels in healthy subjects. When patients were stratified according to periodontal status, linear regression analyses revealed that salivary cystatin SA levels were associated with Periodontal Screening and Recording (PSR) index (beta = 0.297, p < 0.05) when the analysis was adjusted for age, sex, HbA(1C), estimated glomerular filtration rate (eGFR), and number of teeth. Serum cystatin SA levels were negatively associated with eGFR (beta = -0.534, p < 0.0001) when the analysis was adjusted for age, sex, HbA(1C), number of teeth, and PSR index. Conclusions: Salivary cystatin SA was associated with periodontal disease severity; moreover, serum cystatin SA levels could reflect kidney function.