Transient changes in blood‐brain barrier integrity, thermotolerance, and heat shock protein expression following brief hyperthermia in an in vitro model

Abstract

Hyperthermia has potential as a means of opening the blood‐brain barrier (BBB) to enhance delivery of pharmaceuticals into the brain. An in vitro BBB model of porcine brain capillary endothelial cells was exposed to brief hyperthermia and transendothelial electrical resistance (TEER) was measured to assess BBB integrity. Hyperthermia for 10 s at 45, 48, and 51°C, and for 5 s at 54°C caused significant (P<0.0001) loss in BBB integrity compared to controls (10 s at 37°C). The relative loss of BBB integrity increased as the treatment temperature increased (r = 0.88, P<0.0001). All BBB models recovered their integrity (TEER) within 30 min. Thermotolerance was examined by applying a second hyperthermia (10 s at 51°C) 24 h afterward. All BBB models demonstrated thermotolerance by a significantly (P<0.001) less loss of BBB integrity. The degree of thermotolerance increased as the pre‐conditioning temperature increased (r = 0.42, P<0.0001). Heat shock protein (Hsp) 27 and Hsp70 were measured by Western blot analysis to test their role in this thermotolerance. The relative quantity of Hsp27 was not changed (P>0.10) by any of the heat treatments. Hsp70 increased (P<0.05) only after pre‐conditioning for 5 s at 54°C. In summary, heat treatment opened the BBB and induced thermotolerance to a subsequent heat treatment. However this thermotolerance cannot be completely explained by relative changes in Hsp27 and Hsp70 abundance.