Ischemic preconditioning as an adjunct to crystalloid or blood cardioplegia for myocardial protection in routine coronary surgery

Clinical cardioprotection and the value of conditioning responses

Adjunctive cardioprotective strategies for ameliorating the reversible and irreversible injuries with ischemia-reperfusion (I/R) are highly desirable. However, after decades of research, the promise of clinical cardioprotection from I/R injury remains poorly realized. This may arise from the challenges of trialing and effectively translating experimental findings from laboratory models to patients. One can additionally consider whether features of the more heavily focused upon candidates could limit or preclude therapeutic utility and thus whether we might shift attention to alternate strategies. The phenomena of preconditioning and postconditioning have proven fertile in identification of experimental means of cardioprotection and are the most intensely interrogated responses in the field. However, there is evidence these processes, which share common molecular signaling elements and end effectors, may be poor choices for clinical exploitation. This includes evidence of age dependence, limiting efficacy in target aged or senescent hearts; refractoriness to conditioning stimuli in diseased myocardium; interference from a variety of relevant pharmaceuticals; inadvertent induction of these responses by prior ischemia or commonly used drugs, precluding further benefit; and sex dependence of protective signaling. This review focuses on these features, raising questions about current research strategies, and the suitability of these widely studied phenomena as rational candidates for clinical translation.

Protection of myocardium by cyclosporin a and insulin: in vitro simulated ischemia study in human myocardium

BACKGROUND

The efficacy of myocardial protection by cyclosporin A (CSA) and insulin was tested in human right atrial myocardial slices subjected to simulated ischemia and reoxygenation.

METHODS

Slices of right atrial trabeculae were obtained from patients undergoing elective cardiac surgery. Trabeculae were incubated with oxygenated glucose containing phosphate buffered saline (O(2), G-PBS). After 30 minutes of stabilization the sections were exposed to 90 minutes of simulated ischemia (N(2), PBS without glucose) followed by 90 minutes reoxygenation (O(2), G-PBS). Cyclosporin A (0.2 micromol/L) or insulin (5 mU/mL) was added during the stabilization period prior the ischemia. Cell viability was measured by using 3-[4.5 dimethylthiazol 2-yl]-2,5-diphenyltetrazolium bromide (MTT), which is cleaved by active mitochondrial dehydrogenases of living cells.

RESULTS

The viability of untreated slices (control) was 30.45% +/- 2.5% versus 52.65% +/- 4.4% in the CSA treated slices, p less than 0.001. The extent of protection by CSA was affected by oral antiglycemic drugs (glibenclamide). The effect obtained by CSA was inhibited by 5-hydroxydecanoate (5HD), a specific blocker of mitochondrial K(ATP) channels. Protection of the myocardial slices with insulin appears to be superior and not affected by the medication before surgery. This protection was maximal when insulin was present during both preischemic equilibration and reoxygenation periods (68.9% +/- 9.3% viability with insulin versus 33.2% +/- 6.9% in the control, p < 0.001).

CONCLUSIONS

Protection of right atrial trabeculae slices with insulin is superior to that obtained with CSA and is independent of preoperative medication.