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Protective effects of FK 506 against haemorrhagic shock‐induced microvascular hyperpermeability

Microvascular hyperpermeability, the excessive leakage of fluid and proteins from the intravascular space to the interstitium, is a devastating clinical concern in haemorrhagic shock (HS), sepsis, burn and so forth. Previous studies have shown that HS‐induced microvascular hyperpermeability is associated with activation of the mitochondria‐mediated ‘intrinsic’ apoptotic signalling cascade and caspase‐3 mediated disruption of the endothelial cell barrier. In this study, our objective was to test if FK506, an immunomodulator that is also known to protect mitochondria, would protect barrier functions and decrease vascular hyperpermeability following HS by acting on this pathway. FK506 (25 µM) was given 10 minutes before the shock period in a rat model of HS. The HS model was a non‐traumatic/fixed pressure model of hypovolemic shock developed by withdrawing blood to reduce the mean arterial pressure to 40 mm Hg for 60 minutes. The mesenteric post‐capillary venules were monitored for changes in permeability using intravital microscopic imaging. The changes in mitochondrial transmembrane potential (MTP) were determined using the cationic dye 5,5′,6,6′ tetrachoro‐1,1′,3,3′ tetraethyl benzimidazolyl carbocyanine iodide (JC‐1), that was superfused on the mesenteric vasculature followed by intravital imaging. The mesenteric caspase‐3 activity was measured fluorometrically. Haemorrhagic shock induced a significant increase in hyperpermeability compared to the sham‐control group and FK506 treatment decreased HS‐induced hyperpermeability significantly (P < .05). FK506 dampened HS‐induced loss of MTP and elevation of caspase‐3 activity significantly (P < .05). FK506 has protective effects against HS‐induced microvascular hyperpermeability. The maintenance of the MTP and protection against caspase‐3 mediated endothelial cell barrier disruption are possible mechanisms by which FK506 attenuates HS‐induced hyperpermeability. FK506, currently used in clinical settings as an immunomodulator, needs to be explored further for its therapeutic usefulness against HS‐induced vascular hyperpermeability and associated complications.