Cardioprotection by a nonerythropoietic, tissue-protective peptide mimicking the 3D structure of erythropoietin

The protective effect of erythropoietin and its novel derived peptides in peripheral nerve injury

Peripheral nerve injury seriously endangers human life and health, but there is no clinical drug for the treatment of peripheral nerve injury, so it is imperative to develop drugs to promote the repair of peripheral nerve injury. Erythropoietin (EPO) not only has the traditional role of promoting erythropoiesis, but also has a tissue-protective effect. Over the past few decades, researchers have confirmed that EPO has neuroprotective effects. However, side effects caused by long-term use of EPO limited its clinical application. Therefore, EPO derivatives with low side effects have been explored. Among them, ARA290 has shown significant protective effects on the nervous system, but the biggest disadvantage of ARA290, its short half-life, limits its application. To address the short half-life issue, the researchers modified ARA290 with thioether cyclization to generate a thioether cyclized helical B peptide (CHBP). ARA290 and CHBP have promising applications as peptide drugs. The neuroprotective effects they exhibit have attracted continuous exploration of their mechanisms of action. This article will review the research on the role of EPO, ARA290 and CHBP in the nervous system around this developmental process, and provide a certain reference for the subsequent research.

Peptides derived from growth factors: Exploring their diverse impact from antimicrobial properties to neuroprotection

Growth factor-derived peptides are bioactive molecules that play a crucial role in various physiological processes within the human body. Over the years, extensive research has revealed their diverse applications, ranging from antimicrobial properties to their potential in neuroprotection and treating various diseases. These peptides exhibit innate immune responses and have been found to possess potent antimicrobial properties against a wide range of pathogens. Growth factor-derived peptides have demonstrated the ability to promote neuronal survival, prevent cell death, and stimulate neural regeneration. As a result, they hold immense promise in the treatment of various neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, and multiple sclerosis, as well as in the management of traumatic brain injuries. Moreover, growth factor-derived peptides have shown potential for supporting tissue repair and wound healing processes. By enhancing cell proliferation and migration, these peptides contribute to the regeneration of damaged tissues and promote a more efficient healing response. The applications of growth factor-derived peptides extend beyond their therapeutic potential in health; they also have a role in various disease conditions. For example, researchers have explored their influence on cancer cells, where some peptides have demonstrated anti-cancer properties, inhibiting tumor growth and promoting apoptosis in cancer cells. Additionally, their immunomodulatory properties have been investigated for potential applications in autoimmune disorders. Despite the immense promise shown by growth factor-derived peptides, some challenges need to be addressed. Nevertheless, ongoing research and advancements in biotechnology offer promising avenues to overcome these obstacles. The review summarizes the foundational biology of growth factors and the intricate signaling pathways in various physiological processes as well as diseases such as cancer, neurodegenerative disorders, cardiovascular ailments, and metabolic syndromes.

Cyclic helix B peptide alleviates proinflammatory cell death and improves functional recovery after traumatic spinal cord injury

BACKGROUND

Necroptosis and pyroptosis, two types of proinflammatory programmed cell death, were recently found to play important roles in spinal cord injury (SCI). Moreover, cyclic helix B peptide (CHBP) was designed to maintain erythropoietin (EPO) activity and protect tissue against the adverse effects of EPO. However, the protective mechanism of CHBP following SCI is still unknown. This research explored the necroptosis- and pyroptosis-related mechanism underlying the neuroprotective effect of CHBP after SCI.

METHODS

Gene Expression Omnibus (GEO) datasets and RNA sequencing were used to identify the molecular mechanisms of CHBP for SCI. A mouse model of contusion SCI was constructed, and HE staining, Nissl staining, Masson staining, footprint analysis and the Basso Mouse Scale (BMS) were applied for histological and behavioural analyses. qPCR, Western blot analysis, immunoprecipitation and immunofluorescence were utilized to analyse the levels of necroptosis, pyroptosis, autophagy and molecules associated with the AMPK signalling pathway.

RESULTS

The results revealed that CHBP significantly improved functional restoration, elevated autophagy, suppressed pyroptosis, and mitigated necroptosis after SCI. 3-Methyladenine (3-MA), an autophagy inhibitor, attenuated these beneficial effects of CHBP. Furthermore, CHBP-triggered elevation of autophagy was mediated by the dephosphorylation and nuclear translocation of TFEB, and this effect was due to stimulation of the AMPK-FOXO3a-SPK2-CARM1 and AMPK-mTOR signalling pathways.

CONCLUSION

CHBP acts as a powerful regulator of autophagy that improves functional recovery by alleviating proinflammatory cell death after SCI and thus might be a prospective therapeutic agent for clinical application.

The cytokine receptor CRLF3 is a human neuroprotective EV-3 (Epo) receptor

The evolutionary conserved orphan cytokine receptor-like factor 3 (CRLF3) has been implicated in human disease, vertebrate hematopoiesis and insect neuroprotection. While its specific functions are elusive, experimental evidence points toward a general role in cell homeostasis. Erythropoietin (Epo) is a major regulator of vertebrate hematopoiesis and a general cytoprotective cytokine. Erythropoietic functions mediated by classical Epo receptor are understood in great detail whereas Epo-mediated cytoprotective mechanisms are more complex due to involvement of additional Epo receptors and a non-erythropoietic splice variant with selectivity for certain receptors. In the present study, we show that the human CRLF3 mediates neuroprotection upon activation with the natural Epo splice variant EV-3. We generated CRLF3 knock-out iPSC lines and differentiated them toward the neuronal lineage. While apoptotic death of rotenone-challenged wild type iPSC-derived neurons was prevented by EV-3, EV-3-mediated neuroprotection was absent in CRLF3 knock-out neurons. Rotenone-induced apoptosis and EV-3-mediated neuroprotection were associated with differential expression of pro-and anti-apoptotic genes. Our data characterize human CRLF3 as a receptor involved in Epo-mediated neuroprotection and identify CRLF3 as the first known receptor for EV-3.

STUDY OF THE PHARMACOLOGICAL ACTIVITY OF NOVEL EPOR/CD131 HETERORECEPTOR AGONISTS IN MICE WITH ENDOTHELIAL-SPECIFIC EXPRESSION OF MUTANT POLG GENE

The aim of the research was to study antiatherosclerotic and endothelial kinds of a protective activity of peptides mimicking an erythropoietin a-helix B tertiary structure with laboratory codes EP-11-1 (UEHLERALNSS), EP-11-2. (UEQLERALNCS), EP-11-3 (UEQLERALNTS).

Materials and methods. The study was conducted on 96 C57Bl/6J male double transgenic Polgmut/mut/Cdh5-CRE mice. Atherosclerosis was induced by a balloon injury accompanied by Western diet. Then, for 27 days, the drugs under study were administered once per 3 days at the dose of 20 μg/kg. On the 28th day, the animals were euthanized and the area of atherosclerotic plaques was collected for an assessment. The expression of genes associated with the processes of inflammation, apoptosis, and angiogenesis was determined in the tissues of the aorta. In addition, the endothelial protective effect of peptides in isolated segments of the thoracic aorta of wild and transgenic ransgenic Polgmut/mut mice was studied.

Results. The assessment of the plaque size in the animals with the Polgmut/mut/Cdh5-CRE genotype against the background of the peptides under study did not reveal statistically significant differences in comparison to control. However, a quantitative PCR showed a statistically significant decreased expression of pro-apoptotic factors p-53 and Bax, and also increase the expression of anti-apoptotic factor Bcl-2 against the background of the peptides EP-11-1 and EP-11-2 administration. The administration of EP-11-1 and the original peptide pHBSP resulted in a statistically significant decrease in the Bax/Bcl-2 ratio. Compounds EP-11-1, EP-11-2, and EP-11-3 were more effective than the original peptide pHBSP, in reducing the increased expression of genes for inflammatory markers iNos, intercellular adhesion molecules Icam-1, Vcam-1 and E-selectin. The use of EP-11-1 led to a more efficient, in comparison with pHBSP, restoration of endothelial-dependent vasodilation of the aortic segments in mice with endothelial-specific overexpression of the mutant Polg gene.

Conclusion. The study carried out on a murine model of the endothelial-specific expression of mutant gamma polymerase has shown that derivatives of the pHBSP peptide with laboratory codes EP-11-1, EP-11-2, EP-11-3, obtained by BLAST-searching for groups of pHBSP related peptides, have atheroprotective and endothelial protective kinds of a protective activity, which is more pronounced in comparison with the original peptide pHBSP.

Multifaceted roles of a bioengineered nanoreactor in repressing radiation-induced lung injury

Radiation-induced lung injury (RILI) is a potentially fatal and dose-limiting complication of thoracic cancer radiotherapy. However, effective therapeutic agents for this condition are limited. Here, we describe a novel strategy to exert additive effects of a non-erythropoietic EPO derivative (ARA290), along with a free radical scavenger, superoxide dismutase (SOD), using a bioengineered nanoreactor (SOD@ARA290-HBc). ARA290-chimeric nanoreactor makes SOD present in a confined reaction space by encapsulation into its interior to heighten stability against denaturing stimuli. In a RILI mouse model, intratracheal administration of SOD@ARA290-HBc was shown to significantly ameliorate acute radiation pneumonitis and pulmonary fibrosis. Our investigations revealed that SOD@ARA290-HBc performs its radioprotective effects by protecting against radiation induced alveolar epithelial cell apoptosis and ferroptosis, suppressing oxidative stress, inhibiting inflammation and by modulating the infiltrated macrophage phenotype, or through a combination of these mechanisms. In conclusion, SOD@ARA29-HBc is a potential therapeutic agent for RILI, and given its multifaceted roles, it may be further developed as a translational nanomedicine for other related disorders.

Erythropoietin Receptor/β Common Receptor: A Shining Light on Acute Kidney Injury Induced by Ischemia-Reperfusion

Acute kidney injury (AKI) is a health problem worldwide, but there is a lack of early diagnostic biomarkers and target-specific treatments. Ischemia-reperfusion (IR), a major cause of AKI, not only induces kidney injury, but also stimulates the self-defense system including innate immune responses to limit injury. One of these responses is the production of erythropoietin (EPO) by adjacent normal tissue, which is simultaneously triggered, but behind the action of its receptors, either by the homodimer EPO receptor (EPOR)₂ mainly involved in erythropoiesis or the heterodimer EPOR/β common receptor (EPOR/βcR) which has a broad range of biological protections. EPOR/βcR is expressed in several cell types including tubular epithelial cells at low levels or absent in normal kidneys, but is swiftly upregulated by hypoxia and inflammation and also translocated to cellular membrane post IR. EPOR/βcR mediates anti-apoptosis, anti-inflammation, pro-regeneration, and remodeling via the PI3K/Akt, STAT3, and MAPK signaling pathways in AKI. However, the precise roles of EPOR/βcR in the pathogenesis and progression of AKI have not been well defined, and its potential as an earlier biomarker for AKI diagnosis and monitoring repair or chronic progression requires further investigation. Here, we review biological functions and mechanistic signaling pathways of EPOR/βcR in AKI, and discuss its potential clinical applications as a biomarker for effective diagnosis and predicting prognosis, as well as directing cell target drug delivery.

Locust Hemolymph Conveys Erythropoietin-Like Cytoprotection via Activation of the Cytokine Receptor CRLF3

The cytokine receptor-like factor 3 (CRLF3) is an evolutionary conserved class 1 cytokine receptor present in all major eumetazoan groups. Endogenous CRLF3 ligands have not been identified and the physiological responses mediated by mammalian CRLF3 are poorly characterized. Insect CRLF3 is activated by erythropoietin (Epo) and several related molecules that protect mammalian neurons from stress-induced apoptosis. However, insects neither express Epo nor “classical” Epo receptor. Cell-protective effects of insect hemolymph have been described for several species. In this study, we explored the possibility that the endogenous CRLF3 ligand is contained in locust hemolymph. PCR analyses confirmed expression of crfl3-transcripts in neurons and hemocytes of Locusta migratoria and Tribolium castaneum. Survival of locust hemocytes in primary cultures was significantly increased by supplementation of culture medium with locust hemolymph serum. Locust primary neuron cultures were also protected by locust hemolymph, though preceding exposure to fetal bovine serum changed the hemolymph dose-dependency of neuroprotection. Direct comparison of 10% hemolymph serum with recombinant human Epo in its optimal neuroprotective concentration revealed equivalent anti-apoptotic effects on hypoxia-exposed locust neurons. The same concentration of locust hemolymph serum also protected hypoxia-exposed T. castaneum neurons. This indicates that the neuroprotective factor in locust hemolymph is sufficiently conserved in insects to allow activation of neuroprotective receptors in different species. Locust hemolymph-induced neuroprotection in both L. migratoria and T. castaneum was abolished after RNAi-mediated suppression of crlf3-expression. In summary, we report the presence of a conserved endogenous cytokine in locust hemolymph that activates CRLF3 and connected anti-apoptotic processes in hemocytes and neurons. Identification and characterization of the CRLF3 ligand will promote knowledge about cytokine evolution and may unravel cell-protective agents with potential clinical application.

Technetium-99 m-PEGylated dendrimer-G2-(Dabcyle-Lys6,Phe7)-pHBSP: A novel Nano-Radiotracer for molecular and early detecting of cardiac ischemic region

In cardiac ischemic disorder, pyroglutamate helix B surface peptide (pHBSP) which derived from erythropoietin causes to increase cell stability. To improve the serum stability of pHBSP, two lipophilic amino acids Arg⁶, Ala⁷ were replaced with Fmoc-(Dabcyle)-Lys-OH and Fmoc-Phe-OH during the peptide synthesis. This peptide was subsequently conjugated to PEGylated dendrimer-G₂ and labeled with ^99mTcO₄^- to detect cardiac ischemic region. Radiochemical purity (RCP) of ^99mTc-PEGylated dendrimer-G₂-(Dabcyle-Lys⁶,Phe⁷)-pHBSP was evaluated by ITLC method. In addition, the radiopeptide was investigated for stability in human serum and binding affinity to hypoxic cells in myocardium H9c2 cell lines. Biodistribution and SPECT/CT scintigraphy were assessed in cardiac ischemic rats. Radiochemical yield indicated that the anionic dendrimer has a very high potential to complex formation with ^99mTcO^-₄ (RCP > 94%) which was stable in human serum with RCP 89% up to 6 h. The binding of ^99mTc- nanoconjugate to hypoxic cells was significantly more than normoxic cells (3-fold higher compared to normoxic cells at 1 h). In biodistribution studies, erythropoietin receptor-Beta common receptor (EPO-BcR)-positive uptake in the cardiac ischemic region was 3.62 ± 0.44% ID/g 30 min post injection. SPECT imaging showed a prominent uptake of ^99mTc-nanoconjugate in EPO-BcR expressing ischemic heart.

Erythropoietin and its derivatives: from tissue protection to immune regulation

Erythropoietin (EPO) is an evolutionarily conserved hormone well documented for its erythropoietic role via binding the homodimeric EPO receptor (EPOR)₂. In past decades, evidence has proved that EPO acts far beyond erythropoiesis. By binding the tissue-protective receptor (TPR), EPO suppresses proinflammatory cytokines, protects cells from apoptosis and promotes wound healing. Very recently, new data revealed that TPR is widely expressed on a variety of immune cells, and EPO could directly modulate their activation, differentiation and function. Notably, nonerythropoietic EPO derivatives, which mimic the structure of helix B within EPO, specifically bind TPR and show great potency in tissue protection and immune regulation. These small peptides prevent the cardiovascular side effects of EPO and are promising as clinical drugs. This review briefly introduces the receptors and tissue-protective effects of EPO and its derivatives and highlights their immunomodulatory functions and application prospects.

Cyclic helix B peptide ameliorates acute myocardial infarction in mice by inhibiting apoptosis and inflammatory responses

Cyclic helix B peptide (CHBP) is a peptide derivant of erythropoietin with powerful tissue-protective efficacies in a variety of organ injuries, but without erythropoietic effect. However, the role of CHBP in acute myocardial infarction (AMI) and related mechanisms are not studied yet. In this study, we found in a murine AMI model that the administration of CHBP could ameliorate cardiac injury, increase the survival rate, inhibit cardiomyocyte apoptosis, improve cardiac function and remodeling, and reduce the expression of inflammatory cytokines in the serum and kidney tissue both at 24 h and 8 weeks following AMI. This study suggests that CHBP has the potential to be used as an effective drug in the treatment of AMI.

The vasoreparative potential of endothelial colony-forming cells in the ischemic retina is enhanced by cibinetide, a non-hematopoietic erythropoietin mimetic

PURPOSE

Retinal ischemia remains a common sight threatening end-point in blinding diseases such as diabetic retinopathy and retinopathy of prematurity. Endothelial colony forming cells (ECFCs) represent a subpopulation of endothelial progenitors with therapeutic utility for promoting reparative angiogenesis in the ischaemic retina. The current study has investigated the potential of enhancing this cell therapy approach by the dampening of the pro-inflammatory milieu typical of ischemic retina. Based on recent findings that ARA290 (cibinetide), a peptide based on the Helix-B domain of erythropoietin (EPO), is anti-inflammatory and tissue-protective, the effect of this peptide on ECFC-mediated vascular regeneration was studied in the ischemic retina.

METHODS

The effects of ARA290 on pro-survival signaling and function were assessed in ECFC cultures in vitro. Efficacy of ECFC transplantation therapy to promote retinal vascular repair in the presence and absence of ARA290 was studied in the oxygen induced retinopathy (OIR) model of retinal ischemia. The inflammatory cytokine profile and microglial activation were studied as readouts of inflammation.

RESULTS

ARA290 activated pro-survival signaling and enhanced cell viability in response to H₂O₂-mediated oxidative stress in ECFCs in vitro. Preconditioning of ECFCs with EPO or ARA290 prior to delivery to the ischemic retina did not enhance vasoreparative function. ARA290 delivered systemically to OIR mice reduced pro-inflammatory expression of IL-1β and TNF-α in the mouse retina. Following intravitreal transplantation, ECFCs incorporated into the damaged retinal vasculature and significantly reduced avascular area. The vasoreparative function of ECFCs was enhanced in the presence of ARA290 but not EPO.

DISCUSSION

Regulation of the pro-inflammatory milieu of the ischemic retina can be enhanced by ARA290 and may be a useful adjunct to ECFC-based cell therapy for ischemic retinopathies.

MEPO promotes neurogenesis and angiogenesis but suppresses gliogenesis in mice with acute ischemic stroke

Previously study has proved the non-erythropoietic mutant erythropoietin (MEPO) exerted neuroprotective effects against ischemic cerebral injury, with an efficacy similar to that of wild-type EPO. This study investigates its effects on neurogenesis, angiogenesis, and gliogenesis in cerebral ischemic mice. Male C57BL/6 mice were subjected to middle cerebral artery occlusion (MCAO) and reperfusion. EPO (5000 U/kg), MEPO (5000 U/kg) or equal volume of normal saline was injected intraperitoneally. Neurological function was evaluated by Rota-rod test, Neurological severity scores (NSS) and Adhesive removal test. After ischemia and reperfusion (I/R), the survival rate, brain tissue loss, neurogenesis, angiogenesis and gliogenesis were detected by Nissl staining, Immunofluorescence and Western blot, respectively. The results shown that MEPO significantly increased survival rate, reduced brain tissue loss, and improved neurological function after MCAO (P < 0.05). Furthermore, MEPO obviously enhanced the proliferation of neuronal precursors (DCX) and promoted its differentiation into mature neurons (NeuN) (P < 0.05). In addition, compared to normal saline treatment mice, MEPO increased the number of BrdU-positive cells in the cerebral vasculature (P < 0.05). Whereas, MEPO treatment also reduced the numbers of newly generated astrocytes (GFAP) and microglia (Iba1) (P < 0.05). Among all the tests in this study, there was no significant difference between EPO group and MEPO group. Taken together, MEPO promoted the regeneration of neurons and blood vessels in peripheral area of infarction, and suppressed the gliogenesis, thus promoting neurogenesis, improving neurological function and survival rate. Our findings suggest that the MEPO may be a therapeutic drug for ischemic stroke intervention.

Testosterone-mediated upregulation of delayed rectifier potassium channel in cardiomyocytes causes abbreviation of QT intervals in rats

Men have shorter rate-corrected QT intervals (QTc) than women, especially at the period of adolescence or later. The aim of this study was to elucidate the long-term effects of testosterone on cardiac excitability parameters including electrocardiogram (ECG) and potassium channel current. Testosterone shortened QT intervals in ECG in castrated male rats, not immediately after, but on day 2 or later. Expression of Kv7.1 (KCNQ1) mRNA was significantly upregulated by testosterone in cardiomyocytes of male and female rats. Short-term application of testosterone was without effect on delayed rectifier potassium channel current (IKs), whereas IKs was significantly increased in cardiomyocytes treated with dihydrotestosterone for 24 h, which was mimicked by isoproterenol (24 h). Gene-selective inhibitors of a transcription factor SP1, mithramycin, abolished the effects of testosterone on Kv7.1. Testosterone increases Kv7.1-IKs possibly through a pathway related to a transcription factor SP1, suggesting a genomic effect of testosterone as an active factor for cardiac excitability.

Autophagy and Akt in the protective effect of erythropoietin helix B surface peptide against hepatic ischaemia/reperfusion injury in mice

Helix B surface peptide (HBSP) is an erythropoietin (EPO)-derived peptide that protects tissue from the risks of elevated blood pressure and thrombosis. This study focused on the protection of HBSP in hepatic ischaemia/reperfusion (I/R) by enhancing the level of autophagy. In detail, we randomly divided C57BL/6 mice into sham-operated, hepatic ischaemia/reperfusion (I/R), I/R + HBSP, I/R + HBSP + 3-methyladenine (autophagy inhibitor), I/R + HBSP + rapamycin (mTOR inhibitor), and I/R + HBSP + Ly294002 (Akt inhibitor) groups. We assessed alanine aminotransferase (ALT), aspartate aminotransferase (AST) and lactate dehydrogenase (LDH) levels in mouse sera, and performed haematoxylin/eosin (HE) staining, immunohistochemistry, electron microscopy, immunofluorescence microscopy, and western blotting on liver tissue to detect the degree of liver injury, liver apoptosis, autophagy, and the expression of microtubule associated protein 1 light chain 3 alpha (Map1lc3, or LC3), Beclin 1, phospho-mTOR, mTOR, phospho-Akt (P-Akt), and Akt. HBSP relieved hepatic I/R injury in a concentration-independent manner. The expression of LC3II, LC3I, and Beclin 1, and the formation of autophagosomes, in the I/R + HBSP group were higher than those in the I/R group. The protective effects of HBSP were abolished by 3-methyladenine and, to a lesser extent, Ly294002, but enhanced by rapamycin. Furthermore, In vivo, HBSP also protected against hypoxia injury induced by cobalt chloride (CoCl₂) through improving the level of autophagy. Therefore, HBSP protected against hepatic I/R injury, mainly via regulating autophagy by targeting mTOR.

The role of PI3-K/Akt signal pathway in the antagonist effect of CEPO on CHF rats

The possible role of phosphoinositide 3-kinase (PI3-K)/protein kinase B (Akt) signal pathway in the antagonist effect of carbamylated erythropoietin (CEPO) on chronic heart failure (CHF) in rats was investigated. Twenty of 120 rats were randomly selected as the control group, and the remaining rats as the model group. Rats in the model group received intraperitoneal injection of isoproterenol, those in the control group underwent intraperitoneal injection of equivalent normal saline. Rats with successful model establishment were divided into 4 groups, i.e. CHF group, CEPO group, LY294002 (LY) group and CEPO + LY group. Rats in the CEPO group underwent intraperitoneal injection of CEPO, while those in the CHF group received intraperitoneal injection of equivalent normal saline at the same time, those in the LY group received intraperitoneal injection of LY after model establishment, and those in the CEPO + LY group received the combined intraperitoneal injection of CEPO and LY simultaneously. Indicators for hemodynamics were determined using BL-410S bio-functional experiment system, including heart rate (HR), left ventricular end-diastolic pressure (LVEDP), left ventricular systolic pressure (LVSP) and maximal increased rate of left ventricular pressure (LVP)/maximal reduced rate of LVP (±dp/dt_max). Western blotting assay was utilized to determine the changes in activity of PI3-K/Akt signal pathway. LVSP and ±dp/dt_max in the CHF, the CEPO, the CEPO + LY and the LY groups were significantly lower than those in the control group (P<0.05); LVSP and ±dp/dt_max in the CEPO group were also elevated significantly compared with CHF, LY and CEPO + LY groups (P<0.05) with significant decreases in LVEDP and HR (P<0.05); compared with the CHF group, LVSP and ±dp/dt_max in the LY group were each significantly decreased (P<0.05), in the LY group, pAkt level was significantly lower than that in the CHF group (P<0.05). In conclusion, CEPO can generate the antagonist effect on CHF in rats through activation of PI3-K/Akt signal pathway.

Synergistic Reduction of Apoptosis With Diazoxide and Erythropoietin in Spinal Cord Ischemic Injury

BACKGROUND

Paraplegia remains a devastating complication of thoracoabdominal aortic intervention. Metabolic stress induces expression of beta common receptor subunit of erythropoietin (EPO) receptor (βcR) to exert a neuroprotective effect in spinal cord ischemia reperfusion injury (SCIR). Diazoxide (DZ) has been shown to induce ischemic tolerance. We previously reported that DZ upregulated βcR expression and enhanced the neuroprotective effects of EPO through the upregulation of βcR. We hypothesize that βcR expression induced by DZ before ischemia amplifies the antiapoptotic effects of EPO in a murine model of SCIR.

METHODS

Experimental groups included phosphate-buffered saline (PBS) pretreatment + PBS immediately before the operation, PBS+EPO, DZ+PBS, DZ+EPO, and sham. Spinal cord ischemia was induced by a 4-minute thoracic aortic cross-clamp. Functional scoring (Basso Mouse Score) was done at 12-hour intervals for 48 hours. Spinal cords were harvested for histologic analysis, and antiapoptotic factors (caspase 3, 8, and 9, B-cell lymphoma-2, and neuroglobin) were evaluated by Western blot analysis.

RESULTS

The motor function of DZ+EPO group was significantly preserved compared with all other groups. The levels of cleaved caspase 8 and 3 in DZ+EPO were significantly lower than in the other groups. Mice treated with DZ+EPO had significantly fewer terminal deoxynucleotide transferase-mediated deoxy uridine triphosphate nick-end labeling-positive cells than other groups.

CONCLUSIONS

Optimized upregulation of βcR by DZ can increase the extrinsic antiapoptotic effects of EPO. Better understanding of this synergetic mechanism may serve to help prevent ischemic complications caused by aortic intervention.

Cyclic helix B peptide protects HK‑2 cells from oxidative stress by inhibiting ER stress and activating Nrf2 signalling and autophagy

Renal ischemia-reperfusion injury (IRI) is present in numerous diseases and is observed following certain treatments, including renal transplantation. Preventing tubular epithelial cells (TECs) from undergoing apoptosis is vital for treatment of renal IRI. Cyclic helix B peptide (CHBP) is a novel agent that has a protective effect on renal IRI in vivo. In the present study, the effect and underlying mechanism of CHBP on TECs was investigated. The HK-2 human renal proximal tubular epithelial cell line was treated with 500 µmol/l H₂O₂ for 4 h prior to determining the effect of CHBP pretreatment for 1 h on cell viability, caspase 3 activity and expression levels, expression levels of oxidative stress markers, endoplasmic reticulum (ER) stress markers, NF-E2-related factor 2 (Nrf2), heme oxygenase-1 (HO-1) and autophagy markers. This was investigated using a Cell Counting kit 8, a terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling assay, western blotting, reverse transcription-quantitative polymerase chain reaction and immunocytochemistry. Results revealed that pretreatment with CHBP enhanced HK-2 cell viability, the glutathione/glutathione disulphide ratio, activation of Nrf2 and mRNA expression levels of HO-1 and the expression levels of beclin-1 and light chain 3 A/B-II/I. Conversely, CHBP pretreatment reduced the expression levels of reactive oxygen species, the activity and protein expression levels of capase-3, the mRNA and protein expression levels of C/EBP homologous protein and binding immunoglobulin protein, and the expression levels of phosphorylated (p)-mechanistic target of rapamycin (mTOR) Ser2448 and p62 during oxidative stress. However, the expression of p-mTOR Ser2481 was enhanced after CHBP pretreatment. CHBP pretreatment reduced the expression levels of reactive oxygen species, the activity and protein expression levels of capase-3, the mRNA and protein expression levels of C/EBP homologous protein and binding immunoglobulin protein, and the expression levels of phosphorylated (p)-mechanistic target of rapamycin (mTOR) Ser2481, p62 and p-mTOR Ser 2448 during oxidative stress. In conclusion, CHBP pretreatment protected HK-2 cells from H₂O₂-induced injury, inhibited ER stress and pro-apoptotic pathways, and activated the Nrf2 signalling pathway and autophagy. These results provide a potential mechanism of how CHBP protects against renal IRI.

Helix B Surface Peptide Protects Cardiomyocytes Against Hypoxia/Reoxygenation-induced Apoptosis Through Mitochondrial Pathways

BACKGROUND

Helix B surface peptide (HBSP), a newly developed tissue-protective erythropoietin derivative, has beneficial effects on myocardial ischemia. This study aimed to investigate the cardio-protective effects of HBSP against hypoxia/reoxygenation (H/R) injury and its possible mechanism.

METHODS

A rat-derived cardiomyocyte cell line (H9C2 cells) were established and pretreated with HBSP. The pretreated primary cultures were subjected to H/R and monitored for cell viability using the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide assay. Intracellular reactive oxygen species (ROS) levels, apoptosis, and mitochondrial membrane potential (ΔΨm) were detected by flow cytometry. The expression of cytochrome C and Bcl-2 family proteins, as well as the activities of caspases 3 and 9 were determined by Western blot analysis and a colorimetric method, respectively.

RESULTS

HBSP reduced apoptotic cells in cardiomyocytes subjected to H/R. In HBSP-treated cardiomyocytes, the H/R-induced mitochondrial ROS production, ΔΨm collapse, and cytochrome C release from mitochondria to the cytosol significantly decreased. Moreover, HBSP inhibited the activation of caspases 9 and 3, as well as the alteration of Bcl-2 family proteins, which were induced by H/R.

CONCLUSIONS

These results indicated that HBSP has protective effects against H/R-induced apoptosis by regulating the mitochondrial pathway. This mechanism involves inhibiting mitochondrial ROS generation, inhibiting caspase-3 activity, reducing ΔΨm collapse, reducing cytochrome release, and balancing anti and proapoptotic Bcl-2 family proteins.

The Protective Effects of Helix B Surface Peptide on Experimental Acute Liver Injury Induced by Carbon Tetrachloride

BACKGROUND

To investigate the protective effects of helix B surface peptide (HBSP) on acute liver injury induced by carbon tetrachloride (CCl₄).

METHODS

HBSP (8 nmol/kg) was intraperitoneally injected into C57 BL/6 mice 2 h after CCl₄ administration. Serum and liver tissue samples were collected 24 h after injury. Liver function and histological injuries were evaluated. Inflammatory cell infiltration and cytokines were examined and hepatocytes apoptosis was measured. The human liver cell line LO2 and murine primary hepatocytes were stimulated by CCl₄ with and without HBSP treatment and glutathione peroxidase activity, cell survival, and apoptosis were evaluated. In addition, we examined the PI3K/Akt/mTORC1 pathway to elucidate the mechanism underlying HBSP-mediated protection in acute liver injury.

RESULTS

HBSP significantly decreased serum alanine aminotransferase, aspartate aminotransferase, lactate dehydrogenase, and pro-inflammatory cytokines in liver tissues after CCl₄ injection compared with those in the control group. Immunohistochemical staining indicated that the number of CD3-, CD8-, and CD68-positive cells and the expression of cleaved caspase-3 were significantly decreased by HBSP treatment. Additionally, HBSP reduced apoptosis in vivo. In an in vitro study, the glutathione peroxidase activity and survival rate increased, while the total apoptotic rate was reduced in the HBSP-treated group compared with that in the control group after CCl₄ treatment. HBSP activated the PI3K/Akt/mTORC1 pathway, which was confirmed by the PI3K inhibitor LY294002 both in vivo and in vitro. Furthermore, HBSP increased the survival of mice with acute liver injury, and this effect was abolished by LY294002.

CONCLUSIONS

HBSP is a potential therapeutic agent against acute liver injury induced by CCl₄.

Beneficial Effect of Erythropoietin Short Peptide on Acute Traumatic Brain Injury

There is currently no effective medical treatment for traumatic brain injury (TBI). Beyond the immediate physical damage caused by the initial impact, additional damage evolves due to the inflammatory response that follows brain injury. Here we show that therapy with JM4, a low molecular weight 19-amino acid nonhematopoietic erythropoietin (EPO) peptidyl fragment, containing amino acids 28-46 derived from the first loop of EPO, markedly reduces acute brain injury. Mice underwent controlled cortical injury and received either whole molecule EPO, JM4, or sham-treatment with phosphate-buffered saline. Animals treated with JM4 peptide exhibited a large decrease in number of dead neural cells and a marked reduction in lesion size at both 3 and 8 days postinjury. Therapy with JM4 also led to improved functional recovery and we observed a treatment window for JM4 peptide that remained open for at least 9 h postinjury. The full-length EPO molecule was divided into a series of 6 contiguous peptide segments; the JM4-containing segment and the adjoining downstream region contained the bulk of the death attenuating effects seen with intact EPO molecule following TBI. These findings indicate that the JM4 molecule substantially blocks cell death and brain injury following acute brain trauma and, as such, presents an excellent opportunity to explore the therapeutic potential of a small-peptide EPO derivative in the medical treatment of TBI.

Helix B Surface Peptide Protects against Acute Myocardial Ischemia-Reperfusion Injury via the RISK and SAFE Pathways in a Mouse Model

OBJECTIVE

This study explores the effects of helix B surface peptide (HBSP) on myocardial infarct size (IS), cardiac function, cardiomyocyte apoptosis and oxidative stress damage in mouse hearts subjected to myocardial ischemia-reperfusion injury (MIRI) and also the mechanisms underlying the effects.

METHOD

Male adult mice were subjected to 45 min of ischemia followed by 2 h of reperfusion; 5 min before the reperfusion, they were treated with HBSP or vehicle. MIRI-induced IS, cardiomyocyte apoptosis and cardiac functional impairment were determined and compared. Western blot analysis was then conducted to elucidate the mechanism of HBSP after treatment.

RESULTS

HBSP administration before reperfusion significantly reduced the myocardial IS, decreased cardiomyocyte apoptosis, reduced the activities of superoxide dismutase and malondialdehyde and partially preserved heart function. As demonstrated by the Western blot analysis, HBSP after treatment upregulated Akt/GSK-3β/ERK and STAT-3 phosphorylation; these inhibitors, in turn, weakened the beneficial effects of HBSP.

CONCLUSION

HBSP plays a protective role in MIRI in mice by inhibiting cardiomyocyte apoptosis, reducing the MIRI-induced IS, oxidative stress and improving the heart function after MIRI. The mechanism underlying these effects of HBSP is related to the activation of the RISK (reperfusion injury salvage kinase, Akt/GSK-3β/ERK) and SAFE (STAT-3) pathways.

A novel proteolysis-resistant cyclic helix B peptide ameliorates kidney ischemia reperfusion injury

Helix B surface peptide (HBSP), derived from erythropoietin, displays powerful tissue protection during kidney ischemia reperfusion (IR) injury without erythropoietic side effects. We employed cyclization strategy for the first time, and synthesized thioether-cyclized helix B peptide (CHBP) to improve metabolic stability and renoprotective effect. LC-MS/MS analysis was adopted to examine the stability of CHBP in vitro and in vivo. The renoprotective effect of CHBP in terms of renal function, apoptosis, inflammation, extracellular matrix deposition, and histological injury was also detected in vivo and in vitro. Antibody array and western blot were performed to analyze the signal pathway of involvement by CHBP in the IR model and renal tubular epithelial cells. In this study, thioether-cyclized peptide was significantly stable in vivo and in vitro. One dose of 8nmol/kg CHBP administered intraperitoneally at the onset of reperfusion improved renal protection compared with three doses of 8nmol/kg linear HBSP in a 48h murine IR model. In a one-week model, the one dose CHBP-treated group exhibited remarkably improved renal function over the IR group, and attenuated kidney injury, including reduced inflammation and apoptosis. Interestingly, we found that the phosphorylation of autophagy protein mTORC1 was dramatically reduced upon CHBP treatment. We also demonstrated that CHBP induced autophagy via inhibition of mTORC1 and activation of mTORC2, leading to renoprotective effects on IR. Our results indicate that the novel metabolically stable CHBP is a promising therapeutic medicine for kidney IR injury treatment.

STAT transcription in the ischemic heart

All seven STAT proteins are expressed in the heart, and in this review we will focus on their contribution to cardiac physiology and to ischemic heart disease and its consequences. A substantial literature has focused on the roles of STAT1 and STAT3 in ischemic heart disease, where, at least in the acute phase, they appear to have a yin-yang relationship. STAT1 contributes to the loss of irreplaceable cardiac myocytes both by increasing apoptosis and by reducing cardioprotective autophagy. In contrast, STAT3 is cardioprotective, since STAT3-deficient mice have larger infarcts following ischemic injury, and a number of cardioprotective agents have been shown to act, at least partly, through STAT3 activation. STAT3 is also absolutely required for preconditioning—a process where periods of brief ischemia protect against a subsequent or previous prolonged ischemic episode. Prolonged activation of STAT3, however, is strongly implicated in the post-infarction remodeling of the heart which leads to heart failure, where, possibly together with STAT5, it augments activation of the renin-angiotensin system.

In vitro protection of adipose tissue-derived mesenchymal stem cells by erythropoietin

Mobilization of stem cells and their differentiation into cardiomyocytes are known to have protective effects after myocardial infarction. The integrity of transplanted mesenchymal stem cells for cardiac regeneration is dependent on cell-cell or cell-matrix interaction, which is adversely affected by reactive oxygen species in an ischemic environment. Treatment with erythropoietin was shown to protect human adipose tissue derived mesenchymal stem cells in an ischemic injury in vitro model. The analyses indicated that expression of erythropoietin receptors played a pivotal role in erythropoietin mediated cell survival. In this study, the anti-apoptotic effect of erythropoietin on stem cells was analyzed in apoptosis-induced human mesenchymal stem cells. Apoptosis was induced in cultured adult human adipose tissue derived mesenchymal stem cells by hydrogen peroxide. A group of cultured cells was also treated with recombinant human erythropoietin in a concentration of 50 ng mL(-1). The degree of apoptosis was analyzed by flow-cytometry and immunohistochemical staining for Caspase 3. The average percentages of apoptotic cells were significantly higher in H2O2-induced stem cells than in cells co-cultured with erythropoietin (63.03 ± 4.96% vs 29 ± 3.41%, p<0.01). We conclude that preconditioning with erythropoietin suppresses apoptosis of mesenchymal stem cells and enhances their survival.

Protective effects of HBSP on ischemia reperfusion and cyclosporine a induced renal injury

Ischemia reperfusion (IR) and cyclosporine A (CsA) injuries are unavoidable in kidney transplantation and are associated with allograft dysfunction. Herein, the effect and mechanism of a novel tissue protective peptide, helix B surface peptide (HBSP) derived from erythropoietin, were investigated in a rat model. The right kidney was subjected to 45 min ischemia, followed by left nephrectomy and 2-week reperfusion, with or without daily treatment of CsA 25 mg/kg and/or HBSP 8 nmol/kg. Blood urea nitrogen was increased by CsA but decreased by HBSP at 1 week and 2 weeks, while the same changes were revealed in urinary protein/creatinine only at 2 weeks. HBSP also significantly ameliorated tubulointerstitial damage and interstitial fibrosis, which were gradually increased by IR and CsA. In addition, apoptotic cells, infiltrated inflammatory cells, and active caspase-3+ cells were greatly reduced by HBSP in the both IR and IR + CsA groups. The 17 kD active caspase-3 protein was decreased by HBSP in the IR and IR + CsA kidneys, with decreased mRNA only in the IR + CsA kidneys. Taken together, it has been demonstrated, for the first time, that HBSP effectively improved renal function and tissue damage caused by IR and/or CsA, which might be through reducing caspase-3 activation and synthesis, apoptosis, and inflammation.

Experimental acute myocardial infarction in rats: HIF-1α, caspase-3, erythropoietin and erythropoietin receptor expression and the cardioprotective effects of two different erythropoietin doses

The cardioprotective effects of two different doses of erythropoietin administration were analyzed in rats with experimental myocardial infarction. None, saline, standard-dose (5000Ukg(-1)) and high-dose (10,000Ukg(-1)) of human recombinant erythropoietin alpha were administered intraperitoneally in Wistar rats with myocardial infarction induced by coronary artery ligation. Infarct sizes measured after triphenyltetrazolium chloride staining, levels of biochemical markers, histopathology examined by light and electron microscopy, and immunohistochemical expressions of erythropoietin, erythropoietin receptor, hypoxia inducible factor-1α and caspase-3, were analyzed. Lower scores of infarction and hemorrhage, lower number of macrophages and higher score of vascularization surrounding the infarct area were observed in the erythropoietin administered groups (p<0.05). Erythropoietin administration after myocardial infarction reduced the area of infarction and hemorrhage. There were hypoxia inducible factor-1α and caspase-3 expressions in the marginal area, and erythropoietin and erythropoietin receptor expression in both marginal and normal areas (p<0.001). Vascularization, erythropoietin expression in the normal area and vascular erythropoietin expression were positively correlated with human erythropoietin levels. The cardioprotective effects of erythropoietin treatment were independent of endogenous erythropoietin/erythropoietin receptor activity. Moreover exogenous erythropoietin treatment did not suppress endogenous erythropoietin. Erythropoietin administration after myocardial infarction reduced caspase 3 expression (apoptotic activity) and induced neovascularization around the infarct area. Higher erythropoietin administration did not provide an additional benefit over the standard-dose in myocardial protection.

Suppression of coronary atherosclerosis by helix B surface Peptide, a nonerythropoietic, tissue-protective compound derived from erythropoietin

Erythropoietin (EPO), a type I cytokine originally identified for its critical role in hematopoiesis, has been shown to have nonhematopoietic, tissue-protective effects, including suppression of atherosclerosis. However, prothrombotic effects of EPO hinder its potential clinical use in nonanemic patients. In the present study, we investigated the antiatherosclerotic effects of helix B surface peptide (HBSP), a nonerythropoietic, tissue-protective compound derived from EPO, by using human umbilical vein endothelial cells (HUVECs) and human monocytic THP-1 cells in vitro and Watanabe heritable hyperlipidemic spontaneous myocardial infarction (WHHLMI) rabbits in vivo. In HUVECs, HBSP inhibited apoptosis (≈70%) induced by C-reactive protein (CRP), a direct mediator of atherosclerosis. By using a small interfering RNA approach, Akt was shown to be a key molecule in HBSP-mediated prevention of apoptosis. HBSP also attenuated CRP-induced production of tumor necrosis factor (TNF)-α and matrix metalloproteinase-9 in THP-1 cells. In the WHHLMI rabbit, HBSP significantly suppressed progression of coronary atherosclerotic lesions as assessed by mean cross-sectional stenosis (HBSP 21.3 ± 2.2% versus control peptide 38.0 ± 2.7%) and inhibited coronary artery endothelial cell apoptosis with increased activation of Akt. Furthermore, TNF-α expression and the number of M1 macrophages and M1/M2 macrophage ratio in coronary atherosclerotic lesions were markedly reduced in HBSP-treated animals. In conclusion, these data demonstrate that HBSP suppresses coronary atherosclerosis, in part by inhibiting endothelial cell apoptosis through activation of Akt and in association with decreased TNF-α production and modified macrophage polarization in coronary atherosclerotic lesions. Because HBSP does not have the prothrombotic effects of EPO, our study may provide a novel therapeutic strategy that prevents progression of coronary artery disease.

Helix B surface peptide administered after insult of ischemia reperfusion improved renal function, structure and apoptosis through beta common receptor/erythropoietin receptor and PI3K/Akt pathway in a murine model

Erythropoietin (EPO) has been well recognized as a tissue protective agent by inhibiting apoptosis and inflammation. The tissue protective effect of EPO, however, only occurs at a high dosage, which may elicit severe side-effects at the meantime. Helix B surface peptide (HBSP), a novel peptide derived from the non-erythropoietic helix B of EPO, plays a specific role in tissue protection. We investigated effects of HBSP and the expression of its heterodimeric receptor, beta common receptor (βcR)/EPO receptor ( ), in a murine renal ischemia reperfusion (IR) injury model. HBSP significantly ameliorated renal dysfunction and tissue damage, decreased apoptotic cells in the kidney and reduced activation of caspase-9 and -3. The βcR/EPOR in the kidney was up-regulated by IR, but down-regulated by HBSP. Further investigation revealed that the expression and phosphorylation of Akt was dramatically enhanced by HBSP, but strongly reversed by wortmannin, the PI3K inhibitor. Wortmannin intervention improved βcR/EPOR expression, promoted caspase-9 and -3 activation, and increased active caspase-3 positive cells, while renal function and structure, and apoptotic cell counts scarcely changed. This result indicates a significant contribution of PI3K/Akt signaling pathway in the renoprotection of HBSP. The therapeutic effects of HBSP in this study suggest that HBSP could be a better candidate for renal protection.

Erythropoietin attenuates cardiac dysfunction in experimental sepsis in mice via activation of the β-common receptor

There is limited evidence that the tissue-protective effects of erythropoietin are mediated by a heterocomplex of the erythropoietin receptor and the β-common receptor (‘tissue-protective receptor’), which is pharmacologically distinct from the ‘classical’ erythropoietin receptor homodimer that is responsible for erythropoiesis. However, the role of the β-common receptor and/or erythropoietin in sepsis-induced cardiac dysfunction (a well known, serious complication of sepsis) is unknown. Here we report for the first time that the β-common receptor is essential for the improvements in the impaired systolic contractility afforded by erythropoietin in experimental sepsis. Cardiac function was assessed in vivo (echocardiography) and ex vivo (Langendorff-perfused heart) in wild-type and β-common receptor knockout mice, that were subjected to lipopolysaccharide (9 mg/kg body weight; young mice) for 16–18 hours or cecal ligation and puncture (aged mice) for 24 hours. Mice received erythropoietin (1000 IU/kg body weight) 1 hour after lipopolysaccharide or cecal ligation and puncture. Erythropoietin reduced the impaired systolic contractility (in vivo and ex vivo) caused by endotoxemia or sepsis in young as well as old wild-type mice in a β-common-receptor-dependent fashion. Activation by erythropoietin of the β-common receptor also resulted in the activation of well-known survival pathways (Akt and endothelial nitric oxide synthase) and inhibition of pro-inflammatory pathways (glycogen synthase kinase-3β, nuclear factor-κB and interleukin-1β). All the above pleiotropic effects of erythropoietin were lost in β-common receptor knockout mice. Erythropoietin attenuates the impaired systolic contractility associated with sepsis by activation of the β-common receptor, which, in turn, results in activation of survival pathways and inhibition of inflammation.

ARA290, a non-erythropoietic EPO derivative, attenuates renal ischemia/reperfusion injury

Background

In contrast with various pre-clinical studies, recent clinical trials suggest that high dose erythropoietin (EPO) treatment following kidney transplantation does not improve short-term outcome and that it even increases the risk of thrombotic events. ARA290 is a non-erythropoietic EPO derivative and does not increase the risk of cardiovascular events, but potentially has cytoprotective capacities in prevention of renal ischemia/reperfusion injury.

Methods

Eight female Dutch Landrace pigs were exposed to unilateral renal ischemia for 45 minutes with simultaneous cannulation of the ureter of the ischemic kidney. ARA290 or saline was administered by an intravenous injection at 0, 2, 4 and 6 hours post-reperfusion. The animals were sacrificed seven days post-reperfusion.

Results

ARA290 increased glomerular filtration rate during the observation period of seven days. Furthermore, ARA290 tended to reduce MCP-1 and IL-6 expression 15 minutes post-reperfusion. Seven days post-reperfusion ARA290 reduced interstitial fibrosis.

Conclusions

The improvement in renal function following renal ischemia/reperfusion and reduced structural damage observed in this study by ARA290 warrants further investigation towards clinical application.

Erythropoietin and cytoprotective cytokines in experimental traumatic brain injury

The various biochemical cascades that follow primary brain injury result in secondary brain injury which can adversely affect the clinical outcome. Over the last few years it has been well established that molecules like erythropoietin (Epo) have a neuroprotective role in experimental traumatic brain injury (TBI). Epo is shown to produce this effect by modulating multiple cellular processes, including apoptosis, inflammation, and regulation of cerebral blood flow. Derivatives of Epo, including asialo Epo and carbamylated Epo, have been developed to separate the neuroprotective properties from the erythropoiesis-stimulating activities of Epo which may have adverse effects in clinical situations. Peptides that mimic a portion of the Epo molecule, including Helix B surface peptide and Epotris, have also been developed to isolate the neuroprotective activities. The TBI model in rodents most commonly used to study the effect of Epo and these derivatives in TBI is controlled cortical impact injury, which is a model of focal contusion following a high velocity impact to the parietal cortex. Following TBI, rodents are given Epo or an Epo derivative vs. placebo and the outcome is evaluated in terms of physiological parameters (cerebral blood flow, intracranial pressure, cerebral perfusion pressure), behavioral parameters (motor and memory), and histological parameters (contusion volumes, hippocampus cell counts).

Treatment of mild traumatic brain injury with an erythropoietin-mimetic peptide

Mild traumatic brain injury (mTBI) results in an estimated 75-90% of the 1.7 million TBI-related emergency room visits each year. Post-concussion symptoms, which can include impaired memory problems, may persist for prolonged periods of time in a fraction of these cases. The purpose of this study was to determine if an erythropoietin-mimetic peptide, pyroglutamate helix B surface peptide (pHBSP), would improve neurological outcomes following mTBI. Sixty-four rats were randomly assigned to pHBSP or control (inactive peptide) 30 μg/kg IP every 12 h for 3 days, starting at either 1 hour (early treatment) or 24 h (delayed treatment), after mTBI (cortical impact injury 3 m/sec, 2.5 mm deformation). Treatment with pHBSP resulted in significantly improved performance on the Morris water maze task. Rats that received pHBSP required 22.3±1.3 sec to find the platform, compared to 26.3±1.3 sec in control rats (p=0.022). The rats that received pHBSP also traveled a significantly shorter distance to get to the platform, 5.0±0.3 meters, compared to 6.1±0.3 meters in control rats (p=0.019). Motor tasks were only transiently impaired in this mTBI model, and no treatment effect on motor performance was observed with pHBSP. Despite the minimal tissue injury with this mTBI model, there was significant activation of inflammatory cells identified by labeling with CD68, which was reduced in the pHBSP-treated animals. The results suggest that pHBSP may improve cognitive function following mTBI.

Bench-to-bedside review: Erythropoietin and its derivatives as therapies in critical care

Erythropoietin (EPO) is known to have numerous biological functions. Its primary function in the body is to increase red blood cell numbers by way of preventing the apoptosis of erythroid progenitor cells via the homodimeric EPO receptor. The discovery that the local production of EPO within the brain in response to hypoxia or ischemia protects neurons against injury via an anti-apoptotic effect formed the basis of the hypothesis that the local generation of EPO limits the extent of injury. Although the hypothesis proved to be true in pre-clinical models of ischemia/reperfusion injury and inflammation, the randomized, controlled clinical trials that followed demonstrated serious adverse events of EPO due to activation of the hematopoietic system. Consequently, derivatives of EPO that lacked erythropoietic activity were discovered to reduce injury in many pre-clinical models associated with ischemia and inflammation. Unfortunately, there are no published clinical trials to determine the efficacy of non-erythropoietic derivatives of EPO in humans.

Delayed administration of pyroglutamate helix B surface peptide (pHBSP), a novel nonerythropoietic analog of erythropoietin, attenuates acute kidney injury

In preclinical studies, erythropoietin (EPO) reduces ischemia-reperfusion-associated tissue injury (for example, stroke, myocardial infarction, acute kidney injury, hemorrhagic shock and liver ischemia). It has been proposed that the erythropoietic effects of EPO are mediated by the classic EPO receptor homodimer, whereas the tissue-protective effects are mediated by a hetero-complex between the EPO receptor monomer and the β-common receptor (termed "tissue-protective receptor"). Here, we investigate the effects of a novel, selective-ligand of the tissue-protective receptor (pyroglutamate helix B surface peptide [pHBSP]) in a rodent model of acute kidney injury/dysfunction. Administration of pHBSP (10 μg/kg intraperitoneally [i.p.] 6 h into reperfusion) or EPO (1,000 IU/kg i.p. 4 h into reperfusion) to rats subjected to 30 min ischemia and 48 h reperfusion resulted in significant attenuation of renal and tubular dysfunction. Both pHBSP and EPO enhanced the phosphorylation of Akt (activation) and glycogen synthase kinase 3β (inhibition) in the rat kidney after ischemia-reperfusion, resulting in prevention of the activation of nuclear factor-κB (reduction in nuclear translocation of p65). Interestingly, the phosphorylation of endothelial nitric oxide synthase was enhanced by EPO and, to a much lesser extent, by pHBSP, suggesting that the signaling pathways activated by EPO and pHBSP may not be identical.

The receptor that tames the innate immune response

Tissue injury, hypoxia and significant metabolic stress activate innate immune responses driven by tumor necrosis factor (TNF)-α and other proinflammatory cytokines that typically increase damage surrounding a lesion. In a compensatory protective response, erythropoietin (EPO) is synthesized in surrounding tissues, which subsequently triggers antiinflammatory and antiapoptotic processes that delimit injury and promote repair. What we refer to as the sequelae of injury or disease are often the consequences of this intentionally discoordinated, primitive system that uses a "scorched earth" strategy to rid the invader at the expense of a serious lesion. The EPO-mediated tissue-protective system depends on receptor expression that is upregulated by inflammation and hypoxia in a distinctive temporal and spatial pattern. The tissue-protective receptor (TPR) is generally not expressed by normal tissues but becomes functional immediately after injury. In contrast to robust and early receptor expression within the immediate injury site, EPO production is delayed, transient and relatively weak. The functional EPO receptor that attenuates tissue injury is distinct from the hematopoietic receptor responsible for erythropoiesis. On the basis of current evidence, the TPR is composed of the β common receptor subunit (CD131) in combination with the same EPO receptor subunit that is involved in erythropoiesis. Additional receptors, including that for the vascular endothelial growth factor, also appear to be a component of the TPR in some tissues, for example, the endothelium. The discoordination of the EPO response system and its relative weakness provide a window of opportunity to intervene with the exogenous ligand. Recently, molecules were designed that preferentially activate only the TPR and thus avoid the potential adverse consequences of activating the hematopoietic receptor. On administration, these agents successfully substitute for a relative deficiency of EPO production in damaged tissues in multiple animal models of disease and may pave the way to effective treatment of a wide variety of insults that cause tissue injury, leading to profoundly expanded lesions and attendant, irreversible sequelae.

Erythropoietin produced by the retina: its role in physiology and diabetic retinopathy

Erythropoietin (Epo) is the principal regulator of erythropoiesis by inhibiting apoptosis and by stimulating the proliferation and differentiation of erythroid precursor cells. However, Epo also performs extra-erythropoietic actions of which the neuroprotective effects are among the most relevant. Apart from kidney and liver, Epo is also produced by the brain and the retina. In addition, Epo receptor (Epo-R) expression has also been found in the brain and in the retina, thus suggesting an autocrine/paracrine action which seems essential for the physiological homeostasis of both brain and retina. In this review, we will give an overview of the current concepts of the physiology of Epo and will focus on its role in the retina in both normal conditions and in the setting of diabetic retinopathy. Finally, the reasons as to why Epo could be contemplated as a potential new treatment for the early stages of diabetic retinopathy will be given.

EPO and super-EPO: erythropoietins direct neoangiogenesis by cardiac progenitor cells

Erythropoietin, the red blood cell-making cytokine, is also a potential cytoprotective agent in heart disease. In this issue of Cell Stem Cell, Hoch et al. (2011) use two heart failure models, including chemotherapeutic cardiotoxicity, to reveal a mechanistic connection between reduced cardiomyocyte production of erythropoietin and neoangiogenesis by cardiac progenitors.

Erythropoietin preserves the endothelial differentiation capacity of cardiac progenitor cells and reduces heart failure during anticancer therapies

Anticancer therapies, such as targeting of STAT3 or the use of anthracyclins (doxorubicin), can induce cardiomyopathy. In mice prone to developing heart failure as a result of reduced cardiac STAT3 expression (cardiomyocyte-restricted deficiency of STAT3) or treatment with doxorubicin, we observed impaired endothelial differentiation capacity of Sca-1(+) cardiac progenitor cells (CPCs) in conjunction with attenuated CCL2/CCR2 activation. Mice in both models also displayed reduced erythropoietin (EPO) levels in the cardiac microenvironment. EPO binds to CPCs and seems to be responsible for maintaining an active CCL2/CCR2 system. Supplementation with the EPO derivative CERA in a hematocrit-inactive low dose was sufficient to upregulate CCL2, restore endothelial differentiation of CPCs, and preserve the cardiac microvasculature and cardiac function in both mouse models. Thus, low-dose EPO treatment could potentially be exploited as a therapeutic strategy to reduce the risk of heart failure in certain treatment regimens.

Erythropoietin neuroprotection with traumatic brain injury

Numerous experimental studies in recent years have suggested that erythropoietin (EPO) is an endogenous mediator of neuroprotection in various central nervous system disorders, including TBI. Many characteristics of EPO neuroprotection that have been defined in TBI experimental models suggest that it is an attractive candidate for a new treatment of TBI. EPO targets multiple mechanisms known to cause secondary injury after TBI, including anti-excitotoxic, antioxidant, anti-edematous, and anti-inflammatory mechanisms. EPO crosses the blood-brain barrier. EPO has a known dose response and time window for neuroprotection and neurorestoration that would be practical in the clinical setting. However, EPO also stimulates erythropoiesis, which can result in thromboembolic complications. Derivatives of EPO which do not bind to the classical EPO receptor (carbamylated EPO) or that have such a brief half-life in the circulation that they do not stimulate erythropoiesis (asialo EPO and neuro EPO) have the neuroprotective activities of EPO without these potential thromboembolic adverse effects associated with EPO administration. Likewise, a peptide based on the structure of the Helix B segment of the EPO molecule that does not bind to the EPO receptor (pyroglutamate Helix B surface peptide) has promise as another alternative to EPO that may provide neuroprotection without stimulating erythropoiesis.

Neuroprotection with an erythropoietin mimetic peptide (pHBSP) in a model of mild traumatic brain injury complicated by hemorrhagic shock

Pyroglutamate helix B surface peptide (pHBSP) is an 11 amino acid peptide, designed to interact with a novel cell surface receptor, composed of the classical erythropoietin (EPO) receptor disulfide linked to the beta common receptor. pHBSP has the cytoprotective effects of EPO without stimulating erythropoiesis. Effects on early cerebral hemodynamics and neurological outcome at 2 weeks post-injury were compared in a rat model of mild cortical impact injury (3m/sec, 2.5 mm deformation) followed by 50 min of hemorrhagic hypotension (MAP 40 mm Hg for 50 min). Rats were randomly assigned to receive 5000 U/kg of EPO, 30 μg/kg of pHBSP, or an inactive substance every 12 h for 3 days, starting at the end of resuscitation from the hemorrhagic hypotension, which was 110 min post-injury. Both treatments reduced contusion volume at 2 weeks post-injury, from 20.8±2.8 mm(3) in the control groups to 7.7±2.0 mm(3) in the EPO-treated group and 5.9±1.5 mm(3) in the pHBSP-treated group (p=0.001). Both agents improved recovery of cerebral blood flow in the injured brain following resuscitation, and resulted in more rapid recovery of performance on beam balancing and beam walking tests. These studies suggest that pHBSP has neuroprotective effects similar to EPO in this model of combined brain injury and hypotension. pHBSP may be more useful in the clinical situation because there is less risk of thrombotic adverse effects.

A nonerythropoietic peptide that mimics the 3D structure of erythropoietin reduces organ injury/dysfunction and inflammation in experimental hemorrhagic shock

Recent studies have shown that erythropoietin, critical for the differentiation and survival of erythrocytes, has cytoprotective effects in a wide variety of tissues, including the kidney and lung. However, erythropoietin has been shown to have a serious side effect-an increase in thrombovascular effects. We investigated whether pyroglutamate helix B-surface peptide (pHBSP), a nonerythropoietic tissue-protective peptide mimicking the 3D structure of erythropoietin, protects against the organ injury/ dysfunction and inflammation in rats subjected to severe hemorrhagic shock (HS). Mean arterial blood pressure was reduced to 35 ± 5 mmHg for 90 min followed by resuscitation with 20 mL/kg Ringer Lactate for 10 min and 50% of the shed blood for 50 min. Rats were euthanized 4 h after the onset of resuscitation. pHBSP was administered 30 min or 60 min into resuscitation. HS resulted in significant organ injury/dysfunction (renal, hepatic, pancreas, neuromuscular, lung) and inflammation (lung). In rats subjected to HS, pHBSP significantly attenuated (i) organ injury/dysfunction (renal, hepatic, pancreas, neuromuscular, lung) and inflammation (lung), (ii) increased the phosphorylation of Akt, glycogen synthase kinase-3β and endothelial nitric oxide synthase, (iii) attenuated the activation of nuclear factor (NF)-κB and (iv) attenuated the increase in p38 and extracellular signal-regulated kinase (ERK)1/2 phosphorylation. pHBSP protects against multiple organ injury/dysfunction and inflammation caused by severe hemorrhagic shock by a mechanism that may involve activation of Akt and endothelial nitric oxide synthase, and inhibition of glycogen synthase kinase-3β and NF-κB.

Erythropoietic and non-erythropoietic functions of erythropoietin in mouse models

As the basic function of erythropoietin (Epo) is stimulation of red blood cell production, systemic overexpression of Epo results in erythrocytosis. The patho-physiological consequences of chronically elevated red blood cell counts have been studied in Epo overexpressing mice. Genetically modified mice, however, have also played an important role in discovering multiple additional functions of Epo besides stimulating erythrocyte production. Non-erythropoietic functions of Epo are widespread and play a role in organogenesis during early embryonic development and in tissue protection in ischaemic diseases. Future work in the field will most likely focus on these additional functions of Epo, which have great clinical potential.

A small nonerythropoietic helix B surface peptide based upon erythropoietin structure is cardioprotective against ischemic myocardial damage

Strong cardioprotective properties of erythropoietin (EPO) reported over the last 10 years have been difficult to translate to clinical applications for ischemic cardioprotection owing to undesirable parallel activation of erythropoiesis and thrombogenesis. A pyroglutamate helix B surface peptide (pHBP), recently engineered to include only a part of the EPO molecule that does not bind to EPO receptor and thus, is not erythropoietic, retains tissue protective properties of EPO. Here we compared the ability of pHBP and EPO to protect cardiac myocytes from oxidative stress in vitro and cardiac tissue from ischemic damage in vivo. HBP, similar to EPO, increased the reactive oxygen species (ROS) threshold for induction of the mitochondrial permeability transition by 40%. In an experimental model of myocardial infarction induced by permanent ligation of a coronary artery in rats, a single bolus injection of 60 μg/kg of pHBP immediately after coronary ligation, similar to EPO, reduced apoptosis in the myocardial area at risk, examined 24 h later, by 80% and inflammation by 34%. Myocardial infarction (MI) measured 24 h after coronary ligation was similarly reduced by 50% in both pHBP- and EPO-treated rats. Two wks after surgery, left ventricular remodeling (ventricular dilation) and functional decline (fall in ejection fraction) assessed by echocardiography were significantly and similarly attenuated in pHBP- and EPO-treated rats, and MI size was reduced by 25%. The effect was retained during the 6-wk follow-up. A single bolus injection of pHBP immediately after coronary ligation was effective in reduction of MI size in a dose as low as 1 μg/kg, but was ineffective at a 60 μg/kg dose if administered 24 h after MI induction. We conclude that pHBP is equally cardioprotective with EPO and deserves further consideration as a safer alternative to rhEPO in the search for therapeutic options to reduce myocardial damage following blockade of the coronary circulation.