Circulating levels of osteopontin are related with calcification parameters in patients with renal transplantations

Although osteopontin (OPN) is a local inhibitor of calcification, it may also be an indirect marker of ongoing systemic calcification. There are few data about clinical and laboratory parameters associated with serum OPN levels in renal transplant (RT) patients. We investigated the relationship between insulin resistance and calcification parameters as estimated with OPN after RT.

Between 1996 and 2006, the study enrolled 81 patients undergoing RT including 26 females and 55 males of overall mean age of 38±10 years. We evaluated demographic features, medications, smoking history, blood pressure values daily proteinuria as well as laboratory values of calcium-phosphate product (Ca×P), body mass index (BMI) and serum OPN. According to OPN values, we stratified patients as: group 1: OPN<8; group 2: OPN 8 to 45 and group 3: OPN≥45.

Serum OPN correlated with first month phosphorus (r=0.33, P=.00), Ca×product (r=0.41, P=.02), and proteinuria (r=0.34, P=.00) with negative relations to serum insulin (r=0.28, P=.04). Serum calcium, Ca×product, low-density lipoprotein cholesterol, alkaline phosphatase, Creactive protein and vitamin D values were significantly higher among group 3. Regression analysis showed only Ca×product to be an independent variable affecting serum OPN levels (β=0.68, P<.01).

OPN has been implicated in numerous physiological and pathological events including calcification, inflammation, and insulin resistance. Serum OPN may be a marker for increased cardiovascular risk in RT patients.