AQP4 and ischemic stroke: Studied indicated that HBOP has positive effects on traumatic brain injury,1, 20 ischemic stroke,21, 22 and spinal cord injury.2, 3 Recently, there is also discovered that HBOP provides neuroprotective effect on ICH.6, 7 HBOP‐induced activation of ribosomal protein S6 kinases (p70 S6 K), an important enzyme in protein synthesis, causes HO‐1 upregulation and reduces brain edema.5 Also, HBOP attenuated ICH‐induced brain edema by downregulation of aquaporin‐4 (AQP‐4) expression at days 1, 2, and 7 after ICH.6