Effect of erythropoietin on blood pressure and on the vascular endothelial ET-1/ETB receptor system

Protective effects of PPAR-γ against pregnancy-induced hypertension by differential ETR expression in rat models

This study aims to investigate the effects of PPAR-γ on rats with pregnancy-induced hypertension (PIH) by regulating endothelin receptor (ETR). A total of 60 pregnant Wistar rats were selected, and 50 rats were used to establish endotoxin induced PIH rat models. Rats were equally assigned into PIH-NS, PIH-5 mg/kg RM, PIH-10 mg/kg RM, PIH-100 mg/kg ETR, and PIH-200 mg/kg ETR groups, and the rest 10 rats were assigned to a the control group. Reverse transcription quantitative polymerase chain reaction (RT-qPCR) and Western blotting were used for determining mRNA and protein expressions of PPAR-γ and ET_A R, respectively. Protein expression of ET-1 was detected by immunohistochemistry. Results show that On the 22nd day of pregnancy, compared with the PIH-NS group, SBP decreased in other groups, and platelet concentration increased most significantly in the PIH-10 mg/kg RM and PIH-200 mg/kg ETR groups. Compared with the control, PIH-10 mg/kg RM and PIH-200 mg/kg ETR groups, the increase in the expression of ET-1 and ET_A R was most significant in the PIH-NS group. Compared with the control and PIH-10 mg/kg RM groups, expression of PPAR-γ was lower in the PIH-NS, PIH-5 mg/kg RM, PIH-100 mg/kg ETR, and PIH-200 mg/kg ETR groups. Compared with the PIH-NS, PIH-100 mg/kg ETR and PIH-200 mg/kg ETR groups, PPAR-γ expression was significantly higher in the PIH-5 mg/kg RM group (all P < 0.05). Based on our findings, we conclude that PPAR-γ activation inhibits ETR expression and reduces the effect of ET-1 on vascular contraction thereby delaying PIH progression.

Advanced heart failure and nocturnal hypoxaemia due to central sleep apnoea are associated with increased serum erythropoietin

AIMS

Central sleep apnoea (CSA) and increased serum erythropoietin (EPO) concentration have each been associated with adverse prognosis in heart failure (HF) patients. The aim of this study was to examine the relationship between nocturnal hypoxaemia due to CSA and the serum EPO concentration in patients with HF.

METHODS AND RESULTS

Heart failure subjects (n = 33) and healthy controls (n = 18) underwent polysomnography (PSG) for diagnosis of CSA and identification and quantification of hypoxaemia. Blood collection for measurement of EPO was performed immediately post-PSG. For the analysis, HF subjects were dichotomized into subgroups defined by the presence or absence of CSA and by HF severity. Multivariate analyses were performed to evaluate the relationships of hypoxaemia and advanced HF to EPO concentration. Mean EPO concentration was 62% higher for HF subjects with CSA than for healthy controls (P = 0.004). The magnitude of nocturnal hypoxaemia was significantly and positively related to EPO concentration (r = 0.45, P = 0.02). Advanced HF was also significantly and positively related to EPO concentration (r = 0.43, P = 0.02). On multivariate analysis, the presence of combined nocturnal hypoxaemia and advanced HF yielded greater correlation to EPO concentration than either factor alone (r = 0.57, P = 0.04 and P = 0.05, respectively). Linear regression demonstrated that the combination of New York Heart Association Class and CSA was strongly associated with EPO concentration (P < 0.0001).

CONCLUSION

In non-anaemic HF patients, advanced HF and hypoxaemia due to CSA may each be independently associated with increased serum EPO concentration.

Human recombinant erythropoietin alters the flow-dependent vasodilatation of in vitro perfused rat mesenteric arteries with unbalanced endothelial endothelin-1 / nitric oxide ratio

Chronic use of human recombinant erythropoietin (r-HuEPO) is accompanied by serious vascular side effects related to the rise in blood viscosity and shear stress. We investigated the direct effects of r-HuEPO on endothelium and nitric oxide (NO)-dependent vasodilatation induced by shear stress of cannulated and pressurized rat mesenteric resistance arteries. Intravascular flow was increased in the presence or absence of the NO synthase inhibitor NG-nitro-l-arginine methyl ester (L-NAME; 10−4 mol/L). In the presence of r-HuEPO, the flow-dependent vasodilatation was attenuated, while L-NAME completely inhibited it. The association of r-HuEPO and L-NAME caused a vasoconstriction in response to the rise in intravascular flow. Bosentan (10−5 mol/L), an inhibitor of endothelin-1 (ET-1) receptors, corrected the attenuated vasodilatation observed with r-HuEPO and inhibited the vasoconstriction induced by flow in the presence of r-HuEPO and L-NAME. r-HuEPO and L-NAME exacerbated ET-1 vasoconstriction. At shear stress values of 2 and 14 dyn/cm2 (1 dyn = 10–5 N), cultured EA.hy926 endothelial cells incubated with r-HuEPO, L-NAME, or both released greater ET-1 than untreated cells. In conclusion, r-HuEPO diminishes flow-induced vasodilatation. This inhibitory effect seems to implicate ET-1 release. NO withdrawal exacerbates the vascular effects of ET-1 in the presence of r-HuEPO. These findings support the importance of a balanced endothelial ET-1:NO ratio to avoid the vasopressor effects of r-HuEPO.

Role of oxidative stress in erythropoietin-induced hypertension in uremic rats

BACKGROUND

Erythropoietin (EPO) administration in uremic rats leads to an increase in blood pressure (BP). Because chronic renal failure has been associated with oxidative stress, we hypothesize that EPO treatment could accentuate this condition and contribute to hypertension. The present study was designed to investigate the role of reactive oxygen species in EPO-induced hypertension and the effect of tempol, a superoxide dismutase-mimetic.

METHODS

Renal failure was induced by a two-stage 5/6 nephrectomy followed by a 3-week stabilization period. Uremic rats were divided into four groups and received for 4 weeks: vehicle; EPO (100 U/kg, subcutaneously, three times per week); vehicle + tempol (1 mmol/l in drinking water); and EPO + tempol. Systolic BP and biochemical parameters were assessed before and at the end of the treatment. Renal histology, creatinine clearance rate, endothelin-1 (ET-1) concentrations and superoxide anion production were assessed at the end of the study.

RESULTS

The uremic rats developed anemia and hypertension. ET-1 concentrations and superoxide anion production were increased. EPO administration corrected anemia, but accentuated hypertension and renal injuries such as glomerulosclerosis, interstitial fibrosis, and inflammation. EPO therapy further increased tissue levels of ET-1 and superoxide anion production. Tempol treatment improved hypertension and renal injury, and reduced ET-1 concentrations and superoxide anion production.

CONCLUSION

Oxidative stress contributes to the development of hypertension and to the progression of renal injuries in uremic rats. EPO administration further increases oxidative stress, which might partly account for the accentuation of hypertension and renal injury.

Intravenously administered darbepoetin alfa once a week could maintain hemoglobin level more efficiently than once every 2 weeks in patients on hemodialysis

BACKGROUND

Darbepoetin alfa, which has a much longer half-life than recombinant human erythropoietin, is used to treat renal anemia. However, there are few reports investigating the efficacy of darbepoetin alfa administered every 2 weeks (Q2W).

METHODS

We performed the single-center, prospective, and randomized study in chronic hemodialysis patients. Clinically stable patients on hemodialysis were recruited, and darbepoetin alfa 15-40 microg/week was administered intravenously once a week (QW) to achieve a hemoglobin (Hb) level of 10.5-12.0 g/dl for 8 weeks prior to randomization. The patients were randomly assigned to 2 different dosing frequency groups: once a week (QW) or every 2 weeks (Q2W). We switched to a double dose in the Q2W group. We measured Hb level every 2 weeks and administered darbepoetin alfa to achieve an Hb level of 10.5-11.5 g/dl. The primary endpoints were the weekly dose of darbepoetin alfa administered at week 24.

RESULTS

We assigned 19 and 20 patients into QW and Q2W, respectively. There were no significant differences between the groups in Hb, transferrin saturation, ferritin, and weekly dose of darbepoetin alfa at end of the baseline period. There was no significant difference in Hb level at week 24, at which time the weekly dose requirement and dose per dry body weight were much higher in the Q2W than in the QW group.

CONCLUSION

Administration of darbepoetin alfa Q2W could maintain Hb level similarly to to that obtained QW, but we did not confirm efficiency at a higher dose requirement or blood pressure elevation.

Hypertension in dialysis and kidney transplant patients

For the first time, the Canadian Hypertension Education Program has studied the evidence supporting blood pressure control in people requiring renal replacement therapy for end-stage kidney disease, including those on dialysis and with renal transplants. According to the Canadian Organ Replacement Registry's 2008 annual report, there were an estimated 33,832 people with end-stage renal disease in Canada at the end of 2006, an increase of 69.7% since 1997. Of these, 20,465 were on dialysis and 13,367 were living with a functioning kidney transplant. Thus, it is becoming more likely that primary care practitioners will be helping to care for these complex patients. With the lack of large controlled clinical trials, the consensus recommendation based on interpretation of the existing literature is that blood pressure should be lowered to below 140/90 mmHg in hypertensive patients on renal replacement therapy and to below 130/80 mmHg for renal transplant patients with diabetes or chronic kidney disease.