The mRNA levels of atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP), as essential markers for cardiac hypertrophy that indicates heart injury [28], were significantly up-regulated by PM2.5 in Nrf2+/+ mice, and these effects were further accelerated in Nrf2-/- mice after PM2.5 exposure (Figure 2C). Here, NPPB is linked to cardiac hypertrophy.