Osmotherapy With Hypertonic Saline Attenuates Global Cerebral Edema Following Experimental Cardiac Arrest via Perivascular Pool of Aquaporin-4

Abstract

Objectives: We tested the hypothesis that osmotherapy with hypertonic saline attenuates cerebral edema following experimental cardiac arrest and cardiopulmonary resuscitation by exerting its effect via the perivascular pool of aquaporin-4. We used mice with targeted disruption of the gene encoding α-syntrophin (α-Syn) that demonstrate diminished perivascular aquaporin-4 pool but retain the non-endfoot and ependymal pools.

Design: Laboratory animal study.

Setting: University animal research laboratory.

Interventions: Isoflurane-anesthetized adult male wild-type C57B/6 or α-Syn mice were subjected to cardiac arrest/cardiopulmonary resuscitation and treated with either a continuous IV infusion of 0.9% saline or various concentrations of hypertonic saline. Serum osmolality, regional brain water content, blood-brain barrier disruption, and aquaporin-4 protein expression were determined at 24 hours after cardiac arrest/cardiopulmonary resuscitation.

Measurements and main results: Hypertonic saline (7.5%) treatment significantly attenuated water content in the caudoputamen complex and cortex compared with 0.9% saline treatment in wild-type mice subjected to cardiac arrest/cardiopulmonary resuscitation. In contrast, in α-Syn mice subjected to cardiac arrest/cardiopulmonary resuscitation, 7.5% hypertonic saline treatment did not attenuate water content. Treatment with 7.5% hypertonic saline attenuated blood-brain barrier disruption at 24 hours following cardiac arrest/cardiopulmonary resuscitation in wild-type mice but not in α-Syn mice. Total aquaporin-4 protein expression was not different between 0.9% saline and hypertonic saline-treated wild-type mice.

Conclusions: Following experimental cardiac arrest/cardiopulmonary resuscitation: 1) continuous hypertonic saline therapy maintained to achieve serum osmolality of ≈ 350 mOsm/L is beneficial for the treatment of cerebral edema; 2) perivascular pool of aquaporin-4 plays a critical role in water egress from brain; and 3) hypertonic saline attenuates blood-brain barrier disruption via perivascular aquaporin-4 pool.

Figure 1

% Regional brain water contents in the caudoputamen (CP) complex, cortex, hippocampus, and cerebellum of WT mice treated with NS, 3% HS, 5% HS, or 7.5% HS for 24 hr following 8 min CA/CPR. * P < 0.05 versus surgical shams. †P < 0.05 versus CPR with NS treatment.

Figure 2

% Regional brain water contents in the caudoputamen (CP) complex, cortex, hippocampus, and cerebellum of α-Syn^-/- mice treated with NS or 7.5% HS for 24 hr following 8 min CA/CPR. * P < 0.05 versus surgical shams.

Figure 3

Blood brain barrier disruption as estimated by EB extravasation in various treatment groups at 24 hr following CA/CPR. * P < 0.05 versus NS treatment in WT mice.

Figure 4

Immunoblot of membrane protein isolated from the surgical shams or 8min CA mice treated with either NS or 7.5% HS for 24 hr. Naïve WT mice were used as controls. AQP4 was identified as a major band at ∼ 30 kDa. Densitometric analysis (intensity ratio) for the AQP4 protein was corrected to a standard protein (β–actin).

Figure 5

Mean arterial pressure in WT and α-Syn^-/- mice at baseline (B1), 8 min of CA (CA2 to CA8) and CPR (R 2.5 to R 30 in min).