Jovan Adams

The Role of Tetrahydrobiopterin and Dihydrobiopterin in Ischemia/Reperfusion Injury When Given at Reperfusion

Reduced nitric oxide (NO) bioavailability and increased oxidative stress are major factors mediating ischemia/reperfusion (I/R) injury. Tetrahydrobiopterin (BH4) is an essential cofactor of endothelial NO synthase (eNOS) to produce NO, whereas dihydrobiopterin (BH2) can shift the eNOS product profile from NO to superoxide, which is further converted to hydrogen peroxide (H2O2) and cause I/R injury. The effects of BH4 and BH2 on oxidative stress and postreperfused cardiac functions were examined in ex vivo myocardial and in vivo femoral I (20 min)/R (45 min) models. In femoral I/R, BH4 increased NO and decreased H2O2 releases relative to saline control, and these effects correlated with improved postreperfused cardiac function. By contrast, BH2 decreased NO release relative to the saline control, but increased H2O2 release similar to the saline control, and these effects correlated with compromised postreperfused cardiac function. In conclusion, these results suggest that promoting eNOS coupling to produce NO and decrease H2O2 may be a key mechanism to restore postreperfused organ function during early reperfusion.

Protein kinase C (PKC) isoform peptide activator/inhibitors exert cardioprotective effects in polymorphonuclear leukocyte (PMN) induced ischemia/reperfusion (I/R) injury

Introduction Myocardial I/R injury is characterized by endothelial dysfunction, enhanced PMN infiltration into the myocardium, that results in sustained cardiac contractile dysfunction [1,2]. Enhancement of endothelial basal nitric oxide (NO) release or inhibition of PMN superoxide (SO) release reduces endothelial dysfunction and attenuates PMN/endothelial interaction. PKC is a key enzyme that regulates endothelial NO release and PMN SO release [1,2]. However, selective PKC isoforms mediating these responses are not well understood. Myristoylated PKC isoform peptides (MW=1130 to1928; Genemed Synthesis, Inc.) penetrate into cells by simple diffusion. The PKC beta II (βII) (N-MyrSLNPEWNET) and delta (δ) isoform (N-Myr-HDAPIGYD) inhibitors bind to its receptor-activated C kinase region attenuating PKC translocation. By contrast, the PKC δ peptide activator (N-Myr-MRAAEDPM) augments translocation. The PKC zeta (ζ) peptide inhibitor (N-Myr-SIYRRGARRWRKL) binds to the pseudosubstrate domain, attenuating interaction with cell membrane substrates, eNOS and NADPH oxidase [1,2]. We hypothesized that selective PKC peptide isoforms would attenuate PMNinduced contractile dysfunction (i.e., left ventricular developed pressure; LVDP) after I/R when given separately or in combination (i.e., βII /ζ) during reperfusion in the isolated perfused rat heart. We also wanted to determine the mechanism of action to account for any potential cardioprotective effects following I/R.