Nitric oxide-dependent renal vasodilatation is not altered in rat with rHuEpo-induced hypertension

Erythropoietin-Induced Hypertension: A Review of Pathogenesis, Treatment, and Role of Blood Viscosity

Anemia is a common complication of certain chronic diseases and can be treated by stimulating hematopoietic cells to increase red blood cell count, and this action is achieved by recombinant human erythropoietin. In this review article, we have discussed about hypertension, which develops as a result of erythropoietin therapy. We have explored the pathogenesis of erythropoietin-induced hypertension and discussed some ways to prevent and treat this condition. Also, an attempt has been made to find out the role of blood viscosity in erythropoietin-induced hypertension. We conducted a comprehensive review of literature by collecting data from online databases like PubMed and Google Scholar. We mainly studied clinical trials that unraveled the mechanism of hypertension caused by erythropoietin. Hypertension is mainly caused due to enhanced vascular responsiveness to constrictors and impaired action of vasodilators. Role of blood viscosity in the pathogenesis of hypertension is doubtful due to the lack of consistency in the studies. Incidence of hypertension can be reduced by achieving slow correction of anemia and by switching to subcutaneous route of administration. Conventional anti-hypertensives have been found to be beneficial in the treatment. In some severe and persistent cases, temporary discontinuation of erythropoietin may be needed.

Erythropoietin for the Treatment of Subarachnoid Hemorrhage: A Feasible Ingredient for a Successful Medical Recipe

Subarachnoid hemorrhage (SAH) following aneurysm bleeding accounts for 6% to 8% of all cerebrovascular accidents. Although an aneurysm can be effectively managed by surgery or endovascular therapy, delayed cerebral ischemia is diagnosed in a high percentage of patients resulting in significant morbidity and mortality. Cerebral vasospasm occurs in more than half of all patients after aneurysm rupture and is recognized as the leading cause of delayed cerebral ischemia after SAH. Hemodynamic strategies and endovascular procedures may be considered for the treatment of cerebral vasospasm. In recent years, the mechanisms contributing to the development of vasospasm, abnormal reactivity of cerebral arteries and cerebral ischemia following SAH, have been investigated intensively. A number of pathological processes have been identified in the pathogenesis of vasospasm, including endothelial injury, smooth muscle cell contraction from spasmogenic substances produced by the subarachnoid blood clots, changes in vascular responsiveness and inflammatory response of the vascular endothelium. To date, the current therapeutic interventions remain ineffective as they are limited to the manipulation of systemic blood pressure, variation of blood volume and viscosity and control of arterial carbon dioxide tension. In this scenario, the hormone erythropoietin (EPO) has been found to exert neuroprotective action during experimental SAH when its recombinant form (rHuEPO) is administered systemically. However, recent translation of experimental data into clinical trials has suggested an unclear role of recombinant human EPO in the setting of SAH. In this context, the aim of the current review is to present current evidence on the potential role of EPO in cerebrovascular dysfunction following aneurysmal subarachnoid hemorrhage.

Prevention of Erythropoietin-Associated Hypertension

Hypertension is the most significant complication from treatment with erythropoietin (Epo). Can Epo-induced hypertension be eliminated? We examined systemic and local effects of our genetically engineered products, Epo-binding protein (Epo-bp) and anti–Epo-bp antibodies, on randomly assigned Sprague–Dawley rats at midnight, 4 am , 8 am , noon, 4 pm , and 8 pm . Blood pressure, hematocrit, and body weight were measured immediately before and after the completion of a 4-week, twice-weekly course of Epo (50 U/kg), Epo-bp, anti–Epo-bp antibodies, or physiological saline injections. Epo treatment increased hematocrit markedly overall as compared with the saline, Epo-bp, and anti–Epo-bp antibody groups (0.616 versus 0.427, 0.439, and 0.441, respectively) and at each of the 6 test times (all P <0.0001). Epo-bp and anti–Epo-bp antibody treatment with Epo had almost no effect on the Epo-induced hematocrit increase (0.616 versus 0.580 or 0.591, respectively). Circadian blood pressures for Epo versus saline, Epo-bp, and anti–Epo-bp antibody groups were 136.2±2.3 versus 116.2±1.7, 118.4±2.1, and 116.6±2.1 mm Hg, respectively (each P <0.0001). Significantly increased blood pressure was detected at noon, 4 pm , 8 pm , and midnight in Epo treatment. When Epo was given with Epo-bp or anti–Epo-bp antibodies, blood pressure was maintained at similar levels as in saline treatment (each P <0.0001) as compared with Epo treatment alone. Overall, body, brain, and heart weights were significantly lower in Epo treatment than those of other groups. Thus, Epo-bp and anti–Epo-bp antibodies eliminate Epo-induced hypertension without affecting hematocrit and blood volume.

Diabetic nephropathy and anaemia

Anaemia is a frequent complication of diabetic nephropathy. It has only recently been recognised that in diabetic patients anaemia is seen not only in preterminal renal failure, but also frequently in patients with only minor derangement of renal function. At any level of glomerular filtration rate (GFR) anaemia is more frequent and severe in diabetic compared to nondiabetic patients. A major cause of anaemia is an inappropriate response of erythropoietin to anaemia. Additional factors are iron deficiency and iatrogenic factors, e.g. ACE inhibitor treatment. When serum creatinine is still normal, the erythropoietin concentration is predictive of more rapid loss of glomerular function. When serum creatinine is elevated, the haemoglobin values are predictive of the rate of progression. It is currently under investigation whether reversal of anaemia attenuates the rate of progression. Because most of the late complications of diabetes (retinopathy, neuropathy, heart disease, peripheral arterial disease) involve ischaemic tissue damage, it would be intuitively plausible that treatment with human recombinant erythropoietin should be beneficial, but definite evidence for this hypothesis is currently not available.

Erythropoietin and hypoxia stimulate erythropoietin receptor and nitric oxide production by endothelial cells

Erythropoietin (EPO), a hypoxia-inducible cytokine, is required for survival, proliferation, and differentiation of erythroid progenitor cells. EPO can also stimulate proliferation and angiogenesis of endothelial cells that express EPO receptors (EPORs). In this study we investigated the EPO response of vascular endothelial cells at reduced oxygen tension (5% and 2%), in particular the effect of EPO on nitric oxide (NO) release. Endothelial nitric oxide synthase (eNOS) produces NO, which maintains blood pressure homeostasis and blood flow. We find that EPOR is inducible by EPO in primary human endothelial cells of vein (HUVECs) and artery (HUAECs) and cells from a human bone marrow microvascular endothelial line (TrHBMEC) to a much greater extent at low oxygen tension than in room air. We found a corresponding increase in eNOS expression and NO production in response to EPO during hypoxia. Stimulation of NO production was dose dependent on EPO concentration and was maximal at 5 U/mL. NO activates soluble guanosine cyclase to produce cyclic guanosine monophosphate (cGMP), and we observed that EPO induced cGMP activity. These results suggest that low oxygen tension increases endothelial cell capacity to produce NO in response to EPO by induction of both EPOR and eNOS. This effect of EPO on eNOS may be a physiologically relevant mechanism to counterbalance the hypertensive effects of increased hemoglobin-related NO destruction resulting from hypoxia-induced increased red cell mass.

An overview of new pharmacological treatments for cerebrovascular dysfunction after experimental subarachnoid hemorrhage

Cerebral vasospasm and the resulting cerebral ischemia occurring after subarachnoid hemorrhage (SAH) are still responsible for the considerable morbidity and mortality in patients affected by cerebral aneurysms. Mechanisms contributing to the development of vasospasm, abnormal reactivity of cerebral arteries and cerebral ischemia after SAH have been intensively investigated in recent years. It has been suggested that the pathogenesis of vasospasm is related to a number of pathological processes, including endothelial damage, smooth muscle cell contraction resulting from spasmogenic substances generated during lyses of subarachnoid blood clots, changes in vascular responsiveness and inflammatory or immunological reactions of the vascular wall. A great deal of experimental and clinical research has been conducted in an effort to find ways to prevent these complications. However, to date, the main therapeutic interventions remain elusive and are limited to the manipulation of systemic blood pressure, alteration of blood volume or viscosity, and control of arterial dioxide tension. Even though no single pharmacological agent or treatment protocol has been identified which could prevent or reverse these deadly complications, a number of promising drugs have been investigated. Among these is the hormone erythropoietin (EPO), the main regulator of erythropoiesis. It has recently been found that EPO produces a neuroprotective action during experimental SAH when its recombinant form (rHuEPO) is systemically administered. This topic review collects the relevant literature on the main investigative therapies for cerebrovascular dysfunction after aneurysmal SAH. In addition, it points out rHuEPO, which may hold promise in future clinical trials to prevent the occurrence of vasospasm and cerebral ischemia after SAH.

Effect of chronic and short-term erythropoietin treatment on random flap survival in rats: an experimental study

OBJECTIVE

The use of perioperative erythropoietin (EPO) therapy is gaining popularity to avoid blood transfusion and correct anemia in head and neck cancer surgery. The purpose of the study was to determine the effect of various doses and durations of EPO treatment on random flap survival.

STUDY DESIGN

A McFarlane type random and musculocutaneous (3 x 10 cm) flap were elevated on the dorsum of each rat.

METHODS

Eighty-four male Albino rats were randomly assigned into seven groups (2 animals in each group): group I, control animals receiving placebo; group II, chronic EPO injections (50 U/kg); group III, chronic EPO injections (100 mg/kg); group IV, chronic EPO injections (150 mg/kg); group V, short-term EPO injections (50 mg/kg); group VI, short-term EPO injections (100 mg/kg); and group VII, short-term EPO injections (150 mg/kg). Rats in groups II to IV began to receive EPO 3 weeks (thrice weekly) before the construction of flaps, and rats in groups V to VII received EPO after flap elevation for 1 week (thrice) subcutaneously. Following 7 days of recovery, the area of flap survival was measured. Hematocrit and systolic blood pressure were followed weekly in all groups.

RESULTS

Erythropoietin increased the hematocrit levels and systolic blood pressure in all groups, but significant increases were noted only in the long-term treatment groups. There was a significant increase in distal necrosis of random skin flaps after long-term EPO treatment (P <.05). However, short-term low and therapeutic doses of EPO improved flap survival significantly (P <.05).

CONCLUSIONS

Long-term EPO treatment might have impaired flap survival because of direct or prostaglandin-mediated vasoconstriction, endothelin-induced hypertension, increased peripheral vascular resistance, hyperviscosity, and increased thrombosis. However, EPO might have enhanced flap survival because of its antioxidant effect and modulation of nitric oxide levels. Effects of EPO are controversial, and further research is necessary to delineate the dose and duration relationship and the exact mechanism of action on flap viability.

Beneficial effects of systemic administration of recombinant human erythropoietin in rabbits subjected to subarachnoid hemorrhage

Cerebral vasospasm and ischemic damage are important causes of mortality and morbidity in patients affected by aneurysmal subarachnoid hemorrhage (SAH). Recently, i.p. administration of recombinant human erythropoietin (r-Hu-EPO) has been shown to exert a neuroprotective effect during experimental SAH. The present study was conducted to evaluate further the effect of r-Hu-EPO administration after SAH in rabbits on neurological outcome, degree of basilar artery spasm, and magnitude of neuronal ischemic damage. Experimental animals were divided into six groups: group 1 (n = 8), control; group 2 (n = 8), control plus placebo; group 3 (n = 8), control plus r-Hu-EPO; group 4 (n = 8), SAH; group 5 (n = 8), SAH plus placebo; group 6 (n = 8), SAH plus r-Hu-EPO. r-Hu-EPO, at a dose of 1,000 units/kg, and placebo were injected i.p. starting 5 min after inducing SAH and followed by clinical and pathological assessment 72 h later. Systemic administration of r-Hu-EPO produced significant increases in cerebrospinal fluid EPO concentrations (P < 0.001), and reduced vasoconstriction of the basilar artery (P < 0.05), ischemic neuronal damage (P < 0.001), and subsequent neurological deterioration (P < 0.05). These observations suggest that r-Hu-EPO may provide an effective treatment to reduce the post-SAH morbidity.

Nitric oxide-dependent pulmonary vasodilation in polycythemic rats

Polycythemia causes increased vascular production of nitric oxide (NO), most likely secondary to an effect of elevated vascular shear stress to enhance expression of endothelial nitric oxide synthase (eNOS). Because both polycythemia and increased eNOS expression are associated with chronic hypoxia-induced pulmonary hypertension, experiments were performed to test the hypothesis that increased hematocrit leads to upregulation of pulmonary eNOS and enhanced vascular production of NO independent of hypoxia. Rats were administered human recombinant erythropoietin (rEpo; 48 U/day) or vehicle for 2 wk. At the time of study, hematocrit was significantly greater in the rEpo-treated group than in the vehicle group (65.8 +/- 0.7% vs. 45.1 +/- 0.5%), although mean pulmonary artery pressure did not differ between treatments. Experiments on isolated, saline-perfused lungs demonstrated similar vasodilatory responses to the endothelium-derived NO-dependent agonist ionomycin in each group. Additional experiments showed that the vasoconstrictor response to the thromboxane mimetic U-46619 was diminished at lower doses in lungs from the rEpo group compared with the vehicle group. However, perfusate nitrite/nitrate concentration after 90 min of perfusion in isolated lungs was not different between groups. Additionally, no difference was detected between groups in lung eNOS levels by Western blot. We conclude that the predicted increase in shear stress associated with polycythemia does not result in altered pulmonary eNOS expression.