PON1 and hepatocellular carcinoma: It is remarkable that, in turn, enhanced TNF-alpha levels have been shown to down-regulate PON1 expression in murine and human hepatoma cell lines as well as in vivo in mice, most probably via an NF-kappaB- and nuclear receptor peroxisome proliferator-activated receptor-alpha (PPAR-alpha)-dependent mechanism thereby diminishing the antioxidant and anti-atherogenic activity of HDLs [45,46].