Translational Medicine and Oncologists Meet

Background: Protein kinase C (PKC)-ε activation is a mechanism of preconditioning cardio-protection, but its role in repeated noninvasive

limb ischemic preconditioning (rNLIP) mediated cardio-protection against myocardial ischemia/reperfusion (I/R) injury in

diabetes is unknown.

Methods: Sprague–Dawley rats were induced diabetes with streptozotocin and subjected to coronary artery occlusion and reperfusion in the absence or presence of rNLIP (three cycles of 5 minutes occlusion/5 minutes reperfusion) in a hind limb daily for three days prior to inducing I/R. In vitro, cardiac H9C2 cells were cultured with normal or high glucose for 48 hours and subjected to hypoxia/re-oxygenation(H/R) with or without siRNAs of PKC-ε or signal transducers and activators of transcription 3(STAT3). Remote time hypoxia preconditioning (HPC) was achieved by three cycles of 5 minutes hypoxia followed by 5 minutes re-oxygenation 24 hours before inducing H/R.

Results: In eight week diabetic rats, post-ischemic myocardial infarct size and troponin-I release were significantly higher with concomitant cardiac PKC-E overexpression, while the phosphorylation of cardioprotective proteins STAT3 (p-STAT3) and Akt (p-Akt) were lower compared to non-diabetic rats (all P<0.05). rNLIP reduced infarct size and post-ischemic troponin release in

non-diabetic and diabetic rats and moderately but significantly reduced cardiac PKC-E expression and increased cardiac p-STAT3 and p-Akt. In H9C2 cells, high glucose increased PKC-E activation and exacerbated post-H/R injury, accompanied with reducing p-STAT3 and p-Akt, which were all reversed by HPC. The above HPC protective effects were abolished by either PKC-E or STAT3 gene-knockdown.

Conclusion: rNLIP may attenuate diabetic heart I/R injury by mitigating high glucose induced PKC-E overexpression and

subsequently activating STAT3.