Hpx expression and consumption increased in HO-1^−/− mice. (A) mRNA expression of HPX was 5-fold higher (P < .001) in HO-1^−/− liver as measured by quantitative RT-PCR. Error bars represent SD of the mean. Western blot analyses of liver (B) and kidney (C) lysates showed higher levels of HPX protein in HO-1^−/− animals in these organs. Actin blots represent tissue protein loading controls. Albumin blots were used to indicate the level of blood contamination in the tissue. (D) Serum levels of Hpx in HO-1^−/− mice were on average lower than those of WT, consistent with intense usage of HPX for heme clearance and pointing to incomplete recycling of HPX. Serum was diluted for loading, and an equivalent of 0.5 μL of serum was loaded in each lane. (A-D) Mice were 8 months old, on average. Each panel represents one of 3 independent experiments performed on different groups of mice.