Nozik-Grayck and colleagues [174] found that eNOS activation and GTP cyclohydrolase-1 (GTPCH-1, a key enzyme for BH4 synthesis) levels are diminished in lungs from smooth muscle-specific SOD3 KO mice exposed to CH, while eNOS expression is unaltered. Here, SOD3 is linked to cyclic hematopoiesis.