Serum osteopontin concentration is decreased by exercise-induced fat loss but is not correlated with body fat percentage in obese humans

To evaluate the extent to which fat mass contributes to serum osteopontin (OPN) concentration, we investigated whether serum OPN levels are decreased by exercise-induced fat mass loss and whether they are associated with body fat percentage in obese humans. Twenty-three female college students were recruited to participate in an 8-week body weight control program. Body composition [body weight, soft lean mass, body fat mass, body fat percentage, waist-hip ratio and body mass index (BMI)] were assessed prior to and following the program. Serum lipid profiles and serum adiponectin, leptin and osteopontin levels were measured from serum collected prior to and following the program. To understand the effect of fat mass loss on the serum levels of adipokine, which is mainly produced in adipose tissue, the leptin and adiponectin levels were also measured prior to and following the program. Serum leptin levels (mean +/- standard error of the mean) decreased significantly following the program (from 9.82 +/- 0.98 to 7.23 +/- 0.67 ng/ml) and were closely correlated with body fat percentage. In addition, serum adiponectin levels were negatively correlated with body fat percentage, while serum adiponectin levels were not significantly altered. By contrast, serum OPN levels decreased significantly following the program (from 16.03 +/- 2.34 to 10.65 +/- 1.22 ng/ml). However, serum OPN levels were not correlated with body fat percentage, suggesting that serum OPN levels are controlled by several other factors in humans. In conclusion, a high expression of OPN in adipose tissues may not be correlated with serum OPN levels in obese humans. Thus, tissues or physiological factors other than fat mass may have a greater contribution to the serum OPN levels.