Erythropoietin increases expression and function of vascular copper- and zinc-containing superoxide dismutase

Inactivation of BACE1 increases expression of endothelial nitric oxide synthase in cerebrovascular endothelium

Cerebrovascular effects of β-site amyloid precursor protein-cleaving enzyme 1 (BACE1) inactivation have not been systematically studied. In the present study we employed cultured human brain microvascular endothelial cells (BMECs), BACE1-knockout (BACE1^-/-) mice and conditional (tamoxifen-induced) endothelium-specific BACE1-knockout (eBACE1^-/-) mice to determine effect of BACE1 inhibition on expression and function of endothelial nitric oxide synthase (eNOS). Deletion of BACE1 caused upregulation of eNOS and glypican-1 (GPC1) in human BMECs treated with BACE1-siRNA, and cerebral microvessels of male BACE1^-/- mice and male eBACE1^-/- mice. In addition, BACE1siRNA treatment increased NO production in human BMECs. These effects appeared to be independent of amyloid β-peptide production. Furthermore, adenoviral-mediated overexpression of BACE1 in human BMECs down-regulated GPC1 and eNOS. Treatment of human BMECs with GPC1siRNA suppressed mRNA and protein levels of eNOS. In basilar arteries of male eBACE1^-/- mice, endothelium-dependent relaxations to acetylcholine and endothelium-independent relaxations to NO donor, DEA-NONOate, were not affected, consistent with unchanged expression of eNOS and phosphorylation of eNOS at Ser1177 in large cerebral arteries. In aggregate, our findings suggest that under physiological conditions, inactivation of endothelial BACE1 increases expression of eNOS in cerebral microvessels but not in large brain arteries. This effect appears to be mediated by increased GPC1 expression.

Role of superoxide ion formation in hypothermia/rewarming induced contractile dysfunction in cardiomyocytes

Rewarming following accidental hypothermia is associated with circulatory collapse due primarily to impaired cardiac contractile (systolic) function. Previously, we found that reduced myofilament Ca²⁺ sensitivity underlies hypothermia/rewarming (H/R)-induced cardiac contractile dysfunction. This reduced Ca²⁺ sensitivity is associated with troponin I (cTnI) phosphorylation. We hypothesize that H/R induces reactive oxygen species (ROS) formation in cardiomyocytes, which leads to cTnI phosphorylation and reduced myofilament Ca²⁺ sensitivity. To test this hypothesis, we exposed isolated rat cardiomyocytes to a 2-h period of severe hypothermia (15 °C) followed by rewarming (35 °C) with and without antioxidant (TEMPOL) treatment. Simultaneous measurements of cytosolic Ca²⁺ ([Ca²⁺]_cyto) and contractile (sarcomere shortening) responses indicated that H/R-induced contractile dysfunction and reduced Ca²⁺ sensitivity was prevented in cardiomyocytes treated with TEMPOL. In addition, TEMPOL treatment blunted H/R-induced cTnI phosphorylation. These results support our overall hypothesis and suggest that H/R disrupts excitation-contraction coupling of the myocardium through a cascade of event triggered by excessive ROS formation during hypothermia. Antioxidant treatment may improve successful rescue of accidental hypothermia victims.

Antioxidant and antiapoptotic effects of darbepoetin-α against traumatic brain injury in rats

INTRODUCTION

In this study, we tried to determine whether darbepoetin-α would protect the brain from oxidative stress and apoptosis in a rat traumatic brain injury model.

MATERIAL AND METHODS

The animals were randomized into four groups; group 1 (sham), group 2 (trauma), group 3 (darbepoetin α), group 4 (methylprednisolone). In the sham group only the skin incision was performed. In all the other groups, a moderate traumatic brain injury modelwas applied.

RESULTS

Following trauma both glutathione peroxidase, superoxide dismutase levels decreased (p < 0.001 for both); darbepoetin-α increased the activity of both antioxidant enzymes (p = 0.001 and p < 0.001 respectively). Trauma caused significant elevation in the nitric oxide synthetase and xanthine oxidase levels (p < 0.001 for both). Administration of darbepoetin-α significantly decreased the levels of nitric oxide synthetase and xanthine oxidase (p < 0.001 for both). Also, trauma caused significant elevation in the nitric oxide levels (p < 0.001); darbepoetin-α administration caused statistically significant reduction in the nitric oxide levels (p < 0.001). On the other hand, malondialdehyde levels were increased following trauma (p < 0.001), and darbepoetin α significantly reduced the malondialdehyde levels (p < 0.001). Due to the elevated apoptotic activity following the injury, caspase-3 activity increased significantly. Darbepoetin-α treatment significantly inhibited apoptosis by lowering the caspase-3 activity (p < 0.001). In the darbepoetin group, histopathological score was lower than the trauma group (p = 0.016).

CONCLUSIONS

In this study, darbepoetin-α was shown to be at least as effective as methylprednisolone in protecting brain from oxidative stress, lipid peroxidation and apoptosis.

Uncoupling of endothelial nitric oxide synthase in cerebral vasculature of Tg2576 mice

In this study, we tested the hypothesis that reduced bioavailability of tetrahydrobiopterin (BH4) is a major mechanism responsible for pathogenesis of endothelial dysfunction in cerebral microvessels of transgenic mice expressing the Swedish double mutation of human amyloid precursor protein (APP) (Tg2576 mice). Endothelial nitric oxide synthase (eNOS) protein expression was significantly increased in cerebral vasculature of Tg2576 mice. In contrast, bioavailability of BH4 was significantly reduced (p < 0.05). Moreover, superoxide anion production was increased in cerebral microvessels of Tg2576 mice (p < 0.05). Incubation with NOS inhibitor, Nω-nitro-L-arginine methyl ester, decreased superoxide anion indicating that uncoupled eNOS is most likely the source of superoxide anion. Increasing BH4 bioavailability either exogenously by BH4 supplementation or endogenously by treatment with the selective peroxisome proliferator-activated receptor--delta activator GW501516 (2 mg/kg/day, 14 days) attenuated eNOS uncoupling and decreased superoxide anion production in cerebral microvessels of Tg2576 mice (p < 0.05). Treatment with GW501516 restored the biological activity of endothelial nitric oxide in cerebral microvessels of Tg2576 mice, as indicated by the increased nitrite/nitrate content and 3,5-cyclic guanosine monophosphate levels (p < 0.05). Our studies indicate that sub-optimal BH4 bioavailability in cerebral vasculature is an important contributor to oxidant stress and endothelial dysfunction in Tg2576 mouse model of Alzheimer's disease. Existing evidence suggests that Aβ peptides-induced up-regulation of expression and activity of NADPH oxidase causes increased production of superoxide anion (.O2(-)). .O2(-) can also be converted to hydrogen peroxide (H2O2) by enzymatic activity of superoxide dismutase (SOD) or spontaneous dismutation. Elevation of .O2(-) and H2O2 might cause oxidation of tetrahydrobiopterin (BH4) to dihydrobiopterin (BH2) and subsequent uncoupling of endothelial nitric oxide synthase (eNOS) (a) thus reducing levels of nitric oxide (NO) and 3',5'-cyclic guanosine monophosphate (cGMP). Supplementation of BH4 or activation of PPARδ prevents detrimental effects of eNOS uncoupling by restoring bioavailability of BH4 and scavenging of .O2(-), respectively (b). Activation of PPARδ also increases expression of catalase thereby inactivating H2O2. Generation of H2O2 by uncoupled eNOS in cerebral microvessels of Tg2576 mice is hypothetical.

Erythropoietin prevents endothelial dysfunction in GTP-cyclohydrolase I-deficient hph1 mice

: In this study, we used the mutant hph1 mouse model, which has deficiency in GTP-cyclohydrolase I (GTPCH I) activity, to test the hypothesis that erythropoietin (EPO) protects aortic wall from oxidative stress induced by uncoupling of endothelial nitric oxide synthase (eNOS). Both GTPCH I activity and tetrahydrobiopterin (BH4) levels were reduced in hph1 mice, whereas 7,8-dihydrobiopterin (7,8-BH2) levels were significantly increased. Furthermore, BH4 deficiency caused increased production of superoxide anion and hydrogen peroxide in the aorta thus resulting in impairment of endothelium-dependent relaxations to acetylcholine. Treatment of hph1 mice with recombinant human EPO (1000 U/kg, subcutaneously for 3 days) significantly decreased superoxide anion production by eNOS and improved BH4 to 7,8-BH2 ratio in aortas. EPO also significantly decreased production of hydrogen peroxide and improved endothelium-dependent relaxations in aortas of hph1 mice. In addition, EPO treatment increased protein expressions of copper-/zinc-superoxide dismutase, manganese-superoxide dismutase, and catalase in the aorta of hph1 mice. Our findings demonstrate that treatment with EPO prevented oxidative stress and endothelial dysfunction caused by eNOS uncoupling. Increased vascular expressions of antioxidants seem to be an important molecular mechanism underlying vascular protection by EPO during chronic BH4 deficiency.

Erythropoietin increases bioavailability of tetrahydrobiopterin and protects cerebral microvasculature against oxidative stress induced by eNOS uncoupling

This study was designed to determine whether treatment with erythropoietin (EPO) could protect cerebral microvasculature against the pathological consequences of endothelial nitric oxide (NO) synthase uncoupling. Wild-type and GTP cyclohydrolase I (GTPCH-I)-deficient hph1 mice were administered EPO (1000 U/kg/day, s.c., 3 days). Cerebral microvessels of hph1 mice demonstrated reduced tetrahydrobiopterin (BH4) bioavailability, increased production of superoxide anions and impaired endothelial NO signaling. Treatment of hph1 mice with EPO attenuated the levels of 7,8-dihydrobiopterin, the oxidized product of BH4, and significantly increased the ratio of BH4 to 7,8-dihydrobiopterin. Moreover, EPO decreased the levels of superoxide anions and increased NO bioavailability in cerebral microvessels of hph1 mice. Attenuated oxidation of BH4 and inhibition of endothelial NO synthase uncoupling were explained by the increased expression of antioxidant proteins, manganese superoxide dismutase, and catalase. The protective effects of EPO observed in cerebral microvessels of hph1 mice were also observed in GTPCH-I siRNA-treated human brain microvascular endothelial cells exposed to EPO (1 U/mL or 10 U/mL; 3 days). Our results suggest that EPO might protect the neurovascular unit against oxidative stress by restoring bioavailability of BH4 and endothelial NO in the cerebral microvascular endothelium. We demonstrate that treatment with erythropoietin (EPO) could protect cerebral microvasculature against the pathological consequences of endothelial nitric oxide (NO) synthase uncoupling. Our results suggest that EPO might protect the neurovascular unit against oxidative stress by restoring bioavailability of tetrahydrobiopterin (BH4) and endothelial nitric oxide.

Autonomic neuropathy in experimental models of diabetes mellitus

Autonomic neuropathy complicates diabetes by increasing patient morbidity and mortality. Surprisingly, considering its importance, development and exploitation of animal models has lagged behind the wealth of information collected for somatic symmetrical sensory neuropathy. Nonetheless, animal studies have resulted in a variety of insights into the pathogenesis, neuropathology, and pathophysiology of diabetic autonomic neuropathy (DAN) with significant and, in some cases, remarkable correspondence between rodent models and human disease. Particularly in the study of alimentary dysfunction, findings in intrinsic intramural ganglia, interstitial cells of Cajal and the extrinsic parasympathetic and sympathetic ganglia serving the bowel vie for recognition as the chief mechanism. A body of work focused on neuropathologic findings in experimental animals and human subjects has demonstrated that axonal and dendritic pathology in sympathetic ganglia with relative neuron preservation represents one of the neuropathologic hallmarks of DAN but it is unlikely to represent the entire story. There is a surprising selectivity of the diabetic process for subpopulations of neurons and nerve terminals within intramural, parasympathetic, and sympathetic ganglia and innervation of end organs, afflicting some while sparing others, and differing between vascular and other targets within individual end organs. Rather than resulting from a simple deficit in one limb of an effector pathway, autonomic dysfunction may proceed from the inability to integrate portions of several complex pathways. The selectivity of the diabetic process appears to confound a simple global explanation (e.g., ischemia) of DAN. Although the search for a single unifying pathogenetic hypothesis continues, it is possible that autonomic neuropathy will have multiple pathogenetic mechanisms whose interplay may require therapies consisting of a cocktail of drugs. The role of multiple neurotrophic substances, antioxidants (general or pathway specific), inhibitors of formation of advanced glycosylation end products and drugs affecting the polyol pathway may be complex and therapeutic elements may have both salutary and untoward effects. This review has attempted to present the background and current findings and hypotheses, focusing on autonomic elements including and beyond the typical parasympathetic and sympathetic nervous systems to include visceral sensory and enteric nervous systems.

Effects of Erythropoietin on the Serum and Liver Tissue Levels of Copper and Zinc in Rats with Obstructive Jaundice / Efekti Eritropoetina Na Nivoe Bakra I Cinka U Serumu I Tkivima Jetre Kod Pacova Sa Opstruktivnom Žuticom

Background: Erythropoietin is an anti-apoptotic, anti-inflammatory, angiogenetic cytokine and has protective properties against oxidative stress. In this study we investigated the effects of erythropoietin on the levels (serum and liver tissue) of copper and zinc in cholestatic rats.

Methods: Thirty-two Wistar albino rats used in the study were divided into four groups - Group I: Sham; Group II: Erythropoietin; Group III: Obstructive Jaundice; Group IV: Obstructive Jaundice+Erythropoietin. After the first operation, rats were followed up for seven days and then operated for the second time. Rats were sacrificed by intracardiac blood taking, and the liver tissue samples were obtained immediately.

Results: Erythropoietin reduces copper, and increases zinc levels in serum and liver tissues after obstructive jaundice (p<0.05). Furthermore, it has been shown that the levels of alanine aminotransferase, aspartate aminotransferase, gamma glutamyl transferase, alkaline phosphatase and total bilirubin/direct bilirubin were significantly lower in Obstructive Jaundice+Erythropoietin group than Obstructive Jaundice group.

Conclusions: Erythropoietin affects the changes in copper and zinc levels, thus decreasing the liver damage biochemically in rats with obstructive jaundice. However, further investigations are needed to discover how erythropoietin therapy might reduce target organ damage in cholestatic liver cases by affecting copper and zinc levels.

Increased production of superoxide anion contributes to dysfunction of the arteriovenous fistula

Vascular access dysfunction causes morbidity in hemodialysis patients. This study examined the generation and pathobiological significance of superoxide anion in a rat femoral arteriovenous fistula (AVF). One week after AVF creation, there was increased production of superoxide anion accompanied by decreased total superoxide dismutase (SOD) and Cu/Zn SOD activities and induction of the redox-sensitive gene heme oxygenase-1. Immunohistochemical studies of nitrotyrosine formation demonstrated that peroxynitrite, a product of superoxide anion and nitric oxide, was present in increased amounts in endothelial and smooth muscle cells in the AVF. Because uncoupled NOS isoforms generate superoxide anion, and NOS coupling requires tetrahydrobiopterin (BH(4)) as a cofactor, we assessed NOS uncoupling by determining the ratio of BH(4) to dihydrobiopterin (BH(2)); the BH(4)-to-BH(2) ratio was markedly attenuated in the AVF. Because Src is a vasculopathic signaling species upstream and downstream of superoxide anion, such expression was evaluated; expression of Src and phosphorylated Src was both markedly increased in the AVF. Expression of NADPH oxidase (NOX) 1, NOX2, NOX4, cyclooxygenase (COX) 1, COX2, p47(phox), and p67(phox) was all unchanged, as assessed by Western analyses, thereby suggesting that these proteins may not be involved in increased production of superoxide anion. Finally, administration of tempol, a superoxide anion scavenger, decreased neointima formation in the juxta-anastomotic venous segment and improved AVF blood flow. We conclude that the AVF exhibits increased superoxide anion generation that may reflect the combined effects of decreased scavenging by SOD and increased generation by uncoupled NOS, and that enhanced superoxide anion production promotes juxta-anastomotic stenosis and impairs AVF function.

PPARδ agonist GW501516 prevents uncoupling of endothelial nitric oxide synthase in cerebral microvessels of hph-1 mice

Peroxisome proliferator-activated receptor delta (PPARδ) is ubiquitously expressed in the vasculature, including cerebral circulation. The role of PPARδ in metabolism of tetrahydrobiopterin (BH₄) has not been studied in the cerebral microvasculature. In the present study, the effects of PPARδ agonist GW501516 on uncoupling of endothelial nitric oxide synthase (eNOS) were determined in cerebral microvessels of BH₄-deficient hph-1 mice. Wild-type (B6CBA) and hph-1 mice were orally gavaged with a selective PPARδ activator, GW501516 (2 mg/kg/day) for 14 days, and thereafter, cerebral microvessels were isolated and studied. Treatment of hph-1 mice with GW501516 significantly reduced oxidation of BH₄ and increased the ratio of BH₄ to 7,8-BH₂ (P<0.05, n=6-9). Attenuation of L-NAME-inhibitable superoxide anion levels by GW501516 demonstrated that activation of PPARδ might prevent uncoupling of endothelial nitric oxide synthase (eNOS, P<0.05, n=6-9). Western blotting studies demonstrated that GW501516 selectively increased the endothelial expressions of CuZn superoxide dismutase (P<0.05, n=6-9) and catalase (P<0.05, n=6-8). PPARδ activation increased the total nitrite and nitrate (NO₂+NO₃) content in cerebral microvessels (P<0.05, n=6). Obtained results suggest that in vivo activation of PPARδ prevents eNOS uncoupling, restores bioavailability of NO and may help preserve endothelial function in the BH₄-deficient cerebral circulation.

Uncoupling of eNOS causes superoxide anion production and impairs NO signaling in the cerebral microvessels of hph-1 mice

In this study, we used the GTP cyclohydrolase I-deficient mice, i.e., hyperphenylalaninemic (hph-1) mice, to test the hypothesis that the loss of tetrahydrobiopterin (BH(4)) in cerebral microvessels causes endothelial nitric oxide synthase (eNOS) uncoupling, resulting in increased superoxide anion production and inhibition of endothelial nitric oxide signaling. Both homozygous mutant (hph-1(-/-)) and heterozygous mutant (hph-1(+/-) mice) demonstrated reduction in GTP cyclohydrolase I activity and reduced bioavailability of BH(4). In the cerebral microvessels of hph-1(+/-) and hph-1(-/-) mice, increased superoxide anion production was inhibited by supplementation of BH(4) or NOS inhibitor- L- N(G) -nitro arginine-methyl ester, indicative of eNOS uncoupling. Expression of 3-nitrotyrosine was significantly increased, whereas NO production and cGMP levels were significantly reduced. Expressions of antioxidant enzymes namely copper and zinc superoxide dismutase, manganese superoxide dismutase, and catalase were not affected by uncoupling of eNOS. Reduced levels of BH(4), increased superoxide anion production, as well as inhibition of NO signaling were not different between the microvessels of male and female mice. The results of our study are the first to demonstrate that, regardless of gender, reduced BH(4) bioavailability causes eNOS uncoupling, increases superoxide anion production, inhibits eNOS/cGMP signaling, and imposes significant oxidative stress in the cerebral microvasculature.

Erythropoietin attenuated vascular dysfunction and inflammation by inhibiting NADPH oxidase-derived superoxide production in nitric oxide synthase-inhibited hypertensive rat aorta

Erythropoietin (EPO), used clinically for renal anemia, reportedly exerts beneficial pleiotropic effects in various tissues. Recent studies suggest that nitric oxide (NO) plays an important role in EPO-induced tissue protection. The present study investigated whether recombinant human EPO (rHuEPO) exhibits vasoprotective effects even in the NO synthase-inhibited state. Rats that received a NO synthase inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME), in drinking water (0.7 mg/ml) were treated with rHuEPO (75 U/kg, s.c.) three times a week for 2 weeks. The administration of rHuEPO to L-NAME-treated rats had no effect on hematocrit values or increased blood pressure. Vasodilation in response to acetylcholine in the aortic ring was impaired in the L-NAME-treated rats, and improved by rHuEPO. Immunohistochemical staining revealed that infiltration by macrophages and expression of osteopontin were enhanced in the L-NAME-treated rat aorta, and the overexpression was suppressed by rHuEPO. rHuEPO also attenuated medial hyperplasia. Activation of Akt signaling was evident in rHuEPO-treated rats as the increased expression of phosphorylated Akt. rHuEPO enhanced the expression of antioxidant enzymes such as Cu/Zn-superoxide dismutase and heme oxygenase-1 in the aorta. In addition, rHuEPO reduced NADPH oxidase-dependent superoxide production and enhanced the expression of suppressor of cytokine signaling-1(SOCS-1) in the L-NAME-treated rat aorta. These results suggest that a low dose of rHuEPO results in the normalization of endothelial function and vascular inflammation beyond hematopoiesis even in a pharmacologically NO synthase-inhibited state. These effects might be due to the antioxidant properties of rHuEPO. SOCS-1 overexpression would play an important role in suppressing NADPH oxidase activation.

Reactive oxygen species signaling facilitates FOXO-3a/FBXO-dependent vascular BK channel β1 subunit degradation in diabetic mice

Activity of the vascular large conductance Ca(2+)-activated K(+) (BK) channel is tightly regulated by its accessory β(1) subunit (BK-β(1)). Downregulation of BK-β(1) expression in diabetic vessels is associated with upregulation of the forkhead box O subfamily transcription factor-3a (FOXO-3a)-dependent F-box-only protein (FBXO) expression. However, the upstream signaling regulating this process is unclear. Overproduction of reactive oxygen species (ROS) is a common finding in diabetic vasculopathy. We hypothesized that ROS signaling cascade facilitates the FOXO-3a/FBXO-mediated BK-β(1) degradation and leads to diabetic BK channel dysfunction. Using cellular biology, patch clamp, and videomicroscopy techniques, we found that reduced BK-β(1) expression in streptozotocin (STZ)-induced diabetic mouse arteries and in human coronary smooth muscle cells (SMCs) cultured with high glucose was attributable to an increase in protein kinase C (PKC)-β and NADPH oxidase expressions and accompanied by attenuation of Akt phosphorylation and augmentation of atrogin-1 expression. Treatment with ruboxistaurin (a PKCβ inhibitor) or with GW501516 (a peroxisome proliferator-activated receptor δ activator) reduced atrogin-1 expression and restored BK channel-mediated coronary vasodilation in diabetic mice. Our results suggested that oxidative stress inhibited Akt signaling and facilitated the FOXO-3a/FBXO-dependent BK-β(1) degradation in diabetic vessels. Suppression of the FOXO-3a/FBXO pathway prevented vascular BK-β(1) degradation and protected coronary function in diabetes.

Differential effects of eNOS uncoupling on conduit and small arteries in GTP-cyclohydrolase I-deficient hph-1 mice

In the present study, we used the hph-1 mouse, which displays GTP-cyclohydrolase I (GTPCH I) deficiency, to test the hypothesis that loss of tetrahydrobiopterin (BH(4)) in conduit and small arteries activates compensatory mechanisms designed to protect vascular wall from oxidative stress induced by uncoupling of endothelial nitric oxide synthase (eNOS). Both GTPCH I activity and BH(4) levels were reduced in the aortas and small mesenteric arteries of hph-1 mice. However, the BH(4)-to-7,8-dihydrobiopterin ratio was significantly reduced only in hph-1 aortas. Furthermore, superoxide anion and 3-nitrotyrosine production were significantly enhanced in aortas but not in small mesenteric arteries of hph-1 mice. In contrast to the aorta, protein expression of copper- and zinc-containing superoxide dismutase (CuZnSOD) was significantly increased in small mesenteric arteries of hph-1 mice. Protein expression of catalase was increased in both aortas and small mesenteric arteries of hph-1 mice. Further analysis of endothelial nitric oxide synthase (eNOS)/cyclic guanosine monophosphate (cGMP) signaling demonstrated that protein expression of phosphorylated Ser(1177)-eNOS as well as basal cGMP levels and hydrogen peroxide was increased in hph-1 aortas. Increased production of hydrogen peroxide in hph-1 mice aortas appears to be the most likely mechanism responsible for phosphorylation of eNOS and elevation of cGMP. In contrast, upregulation of CuZnSOD and catalase in resistance arteries is sufficient to protect vascular tissue from increased production of reactive oxygen species generated by uncoupling of eNOS. The results of our study suggest that anatomical origin determines the ability of vessel wall to cope with oxidative stress induced by uncoupling of eNOS.

Erythropoietin Increases Expression and Function of Transient Receptor Potential Canonical 5 Channels

Hypertension is a common complication in hemodialysis patients during erythropoietin (EPO) treatment. The underlying mechanisms of EPO-induced hypertension still remain to be determined. Increased transient receptor potential canonical (TRPC) channels have been associated with hypertension. Now, TRPC gene expression was investigated using quantitative real-time RT-PCR and immunoblotting in cultured human endothelial cells and in monocytes from hemodialysis patients. EPO dose-dependently increased TRPC5 mRNA in endothelial cells. EPO increased TRPC5 mRNA stability, that is, EPO prolonged the half-life period for TRPC5 mRNA from 16 hours (control) to 24 hours ( P <0.05). The poly(A) tail length was measured by rapid amplification of cDNA ends-poly(A) test. Increased TRPC5 mRNA stability was attributed to longer 3′ poly(A) tail lengths after EPO administration. EPO also significantly increased TRPC5 channel protein abundance by 70% ( P <0.05). Whole-cell patch clamp showed that angiotensin II–induced, TRPC5-mediated currents were dramatically increased in endothelial cells treated with EPO. Fluorescent dye techniques confirmed that increased calcium influx after EPO treatment was abolished after TRPC5 knockdown ( P <0.05). EPO also significantly increased intracellular reactive oxygen species production. Knockdown of TRPC5 alleviated EPO-induced reactive oxygen species generation in endothelial cells ( P <0.05). In vivo, EPO-treated hemodialysis patients showed significantly increased amounts of TRPC5 mRNA in monocytes compared with EPO-free hemodialysis patients (6.0±2.4 [n=12] versus 1.0±0.5 [n=9]; P <0.01). Patients undergoing EPO treatment also showed significantly elevated systolic blood pressure (160±7 versus 139±6 mm Hg; P <0.05). Our findings suggest that upregulated functional TRPC5 gene may be one cause of EPO-induced hypertension in patients with chronic kidney disease.

Darbepoetin alfa suppresses tumor necrosis factor-α-induced endothelin-1 production through antioxidant action in human aortic endothelial cells: role of sialic acid residues

Recombinant human erythropoietin (r-HuEPO) is widely used to correct anemia in end-stage renal disease patients, who commonly suffer from atherosclerosis. Endothelin-1 (ET-1) has been implicated in the pathogenesis of atherosclerosis. Here, we tested whether darbepoetin alfa, a hypersialylated analogue of r-HuEPO, regulates tumor necrosis factor-α (TNF-α)-induced ET-1 production in human aortic endothelial cells, and sought to identify the signal pathways involved. Darbepoetin alfa attenuated TNF-α-induced ET-1 production. It also diminished TNF-α-induced reactive oxygen species (ROS) accumulation and subsequent activation of c-Jun NH2-terminal kinase (JNK), which regulates the DNA-binding activities of both AP-1 and NF-κB required for ET-1 gene transcription. Like a JNK inhibitor, darbepoetin alfa did not affect IκBα degradation or p65 nuclear translocation, but did inhibit mitogen- and stress-activated protein kinase 1 (MSK1) activation and attenuated p65 phosphorylation (serine 276), effects that may account for the reduction in NF-κB DNA-binding activity. Desialylation completely abolished darbepoetin alfa's inhibitory effects on TNF-α-induced ROS accumulation, MSK1 activation, and ET-1 gene expression, without affecting its stimulation of STAT5 activity. These data demonstrate that darbepoetin alfa suppresses TNF-α-induced ET-1 production through its antioxidant action and suggest that the sialic acid residues of darbepoetin alfa are essential for its antioxidant effect, possibly by scavenging ROS.

Protecting against vascular disease in brain

Endothelial cells exert an enormous influence on blood vessels throughout the circulation, but their impact is particularly pronounced in the brain. New concepts have emerged recently regarding the role of this cell type and mechanisms that contribute to endothelial dysfunction and vascular disease. Activation of the renin-angiotensin system plays a prominent role in producing these abnormalities. Both oxidative stress and local inflammation are key mechanisms that underlie vascular disease of diverse etiology. Endogenous mechanisms of vascular protection are also present, including antioxidants, anti-inflammatory molecules, and peroxisome proliferator-activated receptor-γ. Despite their clear importance, studies of mechanisms that underlie cerebrovascular disease continue to lag behind studies of vascular biology in general. Identification of endogenous molecules and pathways that protect the vasculature may result in targeted approaches to prevent or slow the progression of vascular disease that causes stroke and contributes to the vascular component of dementia and Alzheimer's disease.

Cardiovascular effects of erythropoietin an update

Erythropoietin (EPO) is a therapeutic product of recombinant DNA technology and it has been in clinical use as stimulator of erythropoiesis over the last two decades. Identification of EPO and its receptor (EPOR) in the cardiovascular system expanded understanding of physiological and pathophysiological role of EPO. In experimental models of cardiovascular and cerebrovascular disorders, EPO exerts protection either by preventing apoptosis of cardiac myocytes, smooth muscle cells, and endothelial cells, or by increasing endothelial production of nitric oxide. In addition, EPO stimulates mobilization of progenitor cells from bone marrow thereby accelerating repair of injured endothelium and neovascularization. A novel signal transduction pathway involving EPOR--β-common heteroreceptor is postulated to enhance EPO-mediated tissue protection. A better understanding of the role of β-common receptor signaling as well as development of novel analogs of EPO with enhanced nonhematopoietic protective effects may expand clinical application of EPO in prevention and treatment of cardiovascular and cerebrovascular disorders.