Background
Remote ischaemic per-conditioning (RIC) in pre-clinical ischaemic stroke is neuroprotective and is achieved by repeated transient occlusion of the blood supply to a limb. The mechanisms of action are not fully understood, though release of numerous neuro-humeral chemical messengers have been implicated. 

Methods
We aimed to establish if plasma acquired four days post RIC (or sham) from participants of the Remote ischaemic Conditioning After Stroke Trial (RECAST [England Stroke 2017]) demonstrates neuroprotective properties. An in vitro 4-hour oxygen glucose deprivation (OGD) blood-brain-barrier (BBB) model (comprising human astrocytes, pericytes, brain microvascular endothelial cells and neurons) was treated with 70µL of plasma prior to OGD. Transepithelial resistance (TEER, reflecting BBB permeability), apical and basal lactate dehydrogenase (LDH) and interleukin 6 (IL-6) (markers of cell damage) were measured at time-points pre-OGD (baseline), immediately post-OGD and 24 hours.

Results
Over 24 hours, there was a significant reduction in TEER (i.e. increased permeability) in the control/sham group (n=4) compared to RIC (n=4), (mean difference in change from baseline 14.75%, p<0.001, repeated measures ANOVA). IL-6 production from apical and basal compartments was significantly lower at 24 hours in the RIC group (1061pg/mL versus 225pg/mL, p=0.004, n=4/group) but was not significantly different pre-OGD or post-OGD. LDH did not differ between groups at any time point.

Conclusions
Plasma obtained 4 days after a single ‘dose’ of RIC following ischaemic stroke displays neuroprotective properties, potentially through anti-inflammatory mechanisms. This ex-vivo in vitro method could be used to explore further mechanisms of action and optimal RIC dosing parameters.

REMOTE ISCHAEMIC PER-CONDITIONING PROVIDES PROLONGED NEUROPROTECTION 4 DAYS AFTER A SINGLE DOSE: DATA FROM AN EX-VIVO IN-VITRO BLOOD BRAIN BARRIER MODEL