Zhou et al. demonstrated a similar effect of co-treatment with SnPP on rapamycin-induced HO-1-mediated antiproliferative effects in vascular disease.[44] Interestingly, although SnPP administration in PH rats in the present study had no beneficial effect on pulmonary hypertension, the presence of SnPP still significantly increased HO-1 protein expression compared with that of untreated PH rats. This evidence concerns the gene HMOX1 and pulmonary arterial hypertension.