β-Actin as a loading control for plasma-based Western blot analysis of major depressive disorder patients

Western blot analysis is a commonly used technique for determining specific protein levels in clinical samples. For normalization of protein levels in Western blot, a suitable loading control is required. On account of its relatively high and constant expression, beta-actin has been widely employed in Western blot of cell cultures and tissue extracts. However, beta-actin's presence in human plasma and this protein's putative role as a plasma-based loading control for Western blot analysis remain unknown. In this study, an enzyme-linked immunosorbent assay was used to determine the concentration of beta-actin in human plasma, which is 6.29 +/- 0.54 ng/ml. In addition, the linearity of beta-actin immunostaining and loaded protein amount was evaluated by Western blot, and a fine linearity (R-2 = 0.974 +/- 0.012) was observed. Furthermore, the expression of plasma beta-actin in major depressive disorder subjects and healthy controls was compared. The data revealed no statistically significant difference between these two groups. Moreover, the total coefficient of variation for beta-actin expression in the two groups was 9.2 +/- 1.2%. These findings demonstrate that beta-actin is present in human plasma and may possibly be used as a suitable loading control for plasma-based Western blot analysis in major depressive disorder. (C) 2012 Elsevier Inc. All rights reserved.