Endothelial dysfunction as a result of ischemia/reperfusion (I/R) injury contributes to local organ damage in heart attack patients. In vascular cells, NADPH oxidase (NOX) and the mitochondrial electron transport chain are initiating sources of reactive oxygen species (ROS) during I/R injury. Protein kinase C beta II (PKCβII) is an attractive therapeutic target due to its phosphorylation of p66Shc to enhance mitochondrial-derived ROS production and p47 phox to promote ROS release from NOX. In previous studies, a cell-permeable myristoylated PKCβII peptide inhibitor (N-myr-SLNPEWNET; myr-PKCβII-) has been shown to improve post-reperfusion cardiac function and reduce infarct size in rat myocardial I/R injury. The decrease in myocardial I/R injury with myr-PKCβII- may in part be attributed to improved vascular endothelial function. Due to myr-PKCβII- peptide sequence being highly conserved among mammalian species, we hypothesize that myr-PKCβII- will confer protection by directly inhibiting ROS production from NOX and mitochondria in human umbilical endothelial cells (HUVECs) subjected to hypoxia/reoxygenation (H/R) mediated injury. HUVECs, cultured in gelatin-coated 96-well plates, were subjected to 24h hypoxia and 24h reoxygenation in a Billups-Rothenburg chamber with 1% O 2 , 5% CO 2 , and balance nitrogen. Myr-PKCβII- (20 μM) was administered at the beginning of the 24h reoxygenation period. Cell viability was assessed using tetrazolium-salt (WST-8) colorimetric assay with a microplate reader (450 nm) and normalized against the normoxia control group. Data were analyzed using Student-Newman-Keuls post-hoc analysis. At the 24h reoxygenation period, cell viability (%) was significantly reduced to 78±2% (n=5; p<0.05) in the non-treated H/R group compared to normoxia controls (n=5). Myr-PKCβII- significantly improved HUVEC survival (95±4%; n=5) compared to non-treated H/R controls (n=5; p<0.01) which were not significantly different from normoxia controls. The data suggest that PKCβII inhibition promotes cell survival possibly due to directly attenuating NOX and mitochondrial derived ROS in cells subjected to H/R conditions. Further studies are needed to determine cell survival potential under more severe H/R mediated injury.

Endothelial dysfunction as a result of ischemia/reperfusion (I/R) injury is known to contribute to damage in myocardial infarction and organ transplant patients. In vascular cells, NADPH oxidase (NOX) and the mitochondrial electron transport chain are primary sources of reactive oxygen species (ROS) during I/R injury resulting in reduced nitric oxide bioavailability. Protein kinase C beta II (PKCβII) is an attractive therapeutic target due to its regulation of these downstream mediators of ROS production. PKCβII phosphorylates p66Shc to enhance mitochondrial‐derived ROS production and p47 phox to promote ROS release from NOX. We have previously shown that myristoylated PKCβII peptide inhibitor (N‐myr‐SLNPEWNET; myr‐PKCβII‐) improved post‐reperfusion cardiac function and reduced infarct size in rat myocardial I/R injury compared to non‐treated controls. The decrease in myocardial I/R injury with myr‐PKCβII‐treatment may be attributed to improved vascular endothelial function. The myristoylated peptide sequence (cargo sequence) targets a highly conserved peptide sequence among mammalian species and inhibits PKCβII translocation to protein substrates (e.g. NOX and p66Shc) after second messenger activation. We hypothesize that myr‐PKCβII‐ will confer protection by directly inhibiting ROS production from NOX and mitochondria in human umbilical vein endothelial cells (HUVECs) subjected to hypoxia/reoxygenation (H/R) injury. HUVECs were cultured in gelatin‐coated 96‐well plates and subjected to 24h hypoxia and 24h reoxygenation in Billups‐Rothenburg hypoxia chamber with 1% O2, 5% CO2, and balanced nitrogen. Myr‐PKCβII‐ (20 mM) treatment was administered at the beginning of the 24h reoxygenation period. Cell viability was assessed using tetrazolium‐salt (WST‐8) colorimetric assay with a microplate reader (450 nm) and normalized against the normoxia control group. Data were analyzed using Student‐Newman‐Keuls post‐hoc analysis. At the end of the 24h reoxygenation period, cell viability (%) was significantly reduced to 78±2% (p<0.05; n=5) in the non‐treated H/R group compared to normoxia controls (n=5). Myr‐PKCβII‐significantly improved HUVEC survival (95±4%; p<0.01; n=5) compared to non‐treated H/R controls and was not significantly changed compared to normoxia controls. The data suggests that PKCβII inhibition promotes cell survival subjected to H/R possibly due to directly attenuating NOX and mitochondrial derived ROS. Further studies are needed to control for the myristoylated acid conjugation of the peptide cargo. Support or Funding Information This research was supported by the Division of Research, Department of Biomedical Sciences, and the Center for Chronic Disorders of Aging at the Philadelphia College of Osteopathic Medicine. Current license is supported by Young Therapeutics, LLC.

Endothelial dysfunction is a major consequence of ischemia‐reperfusion (I/R) injury, such as during the re‐establishment of blood flow after endovascular thrombus removal. It is characterized by limited nitric oxide (NO) bioavailability and production of superoxide (SO) instead of NO, in part from uncoupled endothelial NO synthase (eNOS) activity when the dihydrobiopterin (BH2) to tetrahydrobiopterin (BH4) ratio is elevated during reperfusion following prolonged ischemia. The protein kinase C epsilon (PKCɛ) isoform is known to participate in pre‐conditioning (PKCɛ activation treatment prior to ischemia) and post‐conditioning (PKCɛ inhibition treatment during reperfusion) to attenuate rat myocardial I/R injury. Normally following diacylglycerol‐dependent activation, PKCɛ binds to isoform‐specific receptors for activated C‐kinase (RACK) and translocates from the cytosol to the cell membrane to phosphorylate its targets, such as eNOS at Ser‐1177 to augment NO release when the BH2 to BH4 ratio is reduced to promote coupled eNOS activity that is normally seen prior to prolonged ischemia. Cell permeable myristic acid conjugated PKCɛ peptide activator (myr‐HDAPIGYD; myr‐PKCɛ+) and inhibitor (N‐myr‐EAVSLKPT; myr‐PKCɛ‐) has been shown to increase and decrease NO release, respectively, in rat aortic tissue by regulating PKCɛ translocation to eNOS. However, modulation of PKCɛ‐mediated NO release with these peptides in human cells remains undetermined. We hypothesize that myr‐PKCɛ+ will augment and myr‐PKCɛ‐ will attenuate NO release in cultured human umbilical vein endothelial cells (HUVECs). Real‐time HUVEC NO release (pmol) was measured using a calibrated NO electrode following administration of myr‐PKCɛ+ or myr‐PKCɛ‐ ± acetylcholine (Ach; positive control). Data were analyzed by ANOVA using Fishers post‐hoc analysis. Basal NO levels (66±6; n=35) were determined as the pmol difference between cell‐populated (106 cells/well) and reagent only wells. Control Ach (10 μM) enhanced NO release (102±7; n=37), myr‐PKCɛ+ (10 μM) enhanced NO release with Ach (107±16; n=8) and without Ach (107±13; n=7), and myr‐PKCɛ‐ (10 μM) attenuated NO release with Ach (37±9; n=13) and without Ach (7±29; n=9) compared to basal levels (all p<0.05). Results suggest that myr‐PKCɛ +/− effects on NO release is translational across mammalian species, presumably through activation and inhibition of PKCɛ‐mediated phosphorylation of eNOS. Thus, therapeutic intervention that targets inhibition of PKCɛ to reduce uncoupled eNOS activity during reperfusion may yield protective effects via attenuating the extent of I/R injury seen in clinical myocardial infarction, coronary bypass, coronary angioplasty, and organ transplantation. Support or Funding Information This research was supported by the Division of Research, Department of Biomedical Sciences, and the Center for Chronic Disorders of Aging at Philadelphia College of Osteopathic Medicine. Current research license is supported by Young Therapeutics, LLC.