Abstract
OBJECTIVE: Protection of the myocardium against ischemia/reperfusion
injury is a major challenge in cardiac surgery and cardiology. A
cardioprotective role of heat shock proteins (Hsp), in particular
Hsp 70, against ischemia has been demonstrated. A prerequisite for
clinical exploitation of high Hsp 70 levels in the heart during ischemia
is the determination of the efficacy and the kinetics of cardiac
Hsp synthesis in vivo. METHODS: We examined Hsp 70 and other immediate
early genes, that are induced by cardioplegia and reperfusion, in
right atrial biopsies taken from 15 patients during coronary artery
bypass grafting. Specimens were obtained before cardioplegia and
after ending of reperfusion and subsequently studied by immunohistochemistry
and Western blot analyses. RESULTS: Overall Hsp 70 increased 2.0+/-1.1-fold
(P<0.01) in the nucleus as well as in the cytosol of myocytes and
endothelial cells during open-heart surgery. As determined by comparison
to a dilution series of recombinant protein, Hsp 70 levels amounted
up to 6 per thousand of total cellular protein. The increase of Hsp
70 correlated well with the duration of cardioplegia and reperfusion
(P<0.005) showing a markedly accelerated increase at periods longer
than 2 h. Further, the immediate early gene c-Fos also increased
2.4+/-2.2-fold during open-heart surgery (P<0.05), whereas other
members of the Hsp family, like Hsp 27 and Hsp 90, showed no significant
changes in protein levels during cardioplegia and reperfusion. CONCLUSIONS:
These findings demonstrate that protein levels of Hsp 70 in the myocardium
increase to significant amounts within few hours after induction.
The optimum time point for induction of Hsp 70 appears to be at least
2 h before open-heart surgery.
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