HMOX1 and cyclic hematopoiesis: Sardana et al. also demonstrated that HO-1 levels increased strongly in rat liver after SnPP application while HO-1 activity was significantly inhibited.[47] Based on these findings, we hypothesize that HO-1 activity rather than HO-1 protein over-expression is the key factor underlying the beneficial effects of simvastatin treatment in MCT- and CH-PH.