Gaseous hydrogen sulfide protects against myocardial ischemia-reperfusion injury in mice partially independent from hypometabolism

Background

Ischemia-reperfusion injury (IRI) is a major cause of cardiac damage following various pathological processes. Gaseous hydrogen sulfide (H₂S) is protective during IRI by inducing a hypometabolic state in mice which is associated with anti-apoptotic, anti-inflammatory and antioxidant properties. We investigated whether gaseous H₂S administration is protective in cardiac IRI and whether non-hypometabolic concentrations of H₂S have similar protective properties.

Methods

Male C57BL/6 mice received a 0, 10, or 100 ppm H₂S-N₂ mixture starting 30 minutes prior to ischemia until 5 minutes pre-reperfusion. IRI was inflicted by temporary ligation of the left coronary artery for 30 minutes. High-resolution respirometry equipment was used to assess CO₂-production and blood pressure was measured using internal transmitters. The effects of H₂S were assessed by histological and molecular analysis.

Results

Treatment with 100 ppm H₂S decreased CO₂-production by 72%, blood pressure by 14% and heart rate by 25%, while treatment with 10 ppm H₂S had no effects. At day 1 of reperfusion 10 ppm H₂S showed no effect on necrosis, while treatment with 100 ppm H₂S reduced necrosis by 62% (p<0.05). Seven days post-reperfusion, both 10 ppm (p<0.01) and 100 ppm (p<0.05) H₂S showed a reduction in fibrosis compared to IRI animals. Both 10 ppm and 100 ppm H₂S reduced granulocyte-influx by 43% (p<0.05) and 60% (p<0.001), respectively. At 7 days post-reperfusion both 10 and 100 ppm H₂S reduced expression of fibronectin by 63% (p<0.05) and 67% (p<0.01) and ANP by 84% and 63% (p<0.05), respectively.

Conclusions

Gaseous administration of H₂S is protective when administered during a cardiac ischemic insult. Although hypometabolism is restricted to small animals, we now showed that low non-hypometabolic concentrations of H₂S also have protective properties in IRI. Since IRI is a frequent cause of myocardial damage during percutaneous coronary intervention and cardiac transplantation, H₂S treatment might lead to novel therapeutical modalities.

Renal effects of long-term darbepoetin alpha treatment in hypertensive TGR(mRen2)27 rats

INTRODUCTION

Erytropoietin (EPO) has cytoprotective and angiogenic properties and has a beneficial effect in ischaemic conditions. Since the development of renal interstitial abnormalities are often associated with ischaemia, we studied the effects of the long-acting EPO analogue darbepoetin alpha (DA) on kidney damage in TGR(mRen2)27 (Ren2) rats.

MATERIALS AND METHODS

Ren2 rats were randomised to DA or vehicle (VEH) or to DA + angiotensin converting enzyme inhibitor (ACEi) or VEH + ACEi. Sprague Dawley (SD) rats served as controls. Blood pressure was measured weekly and 24-h urine was collected to measure proteinuria. Blood samples were collected for creatinine and haematocrit. Kidneys were studied for inflammation and pre-fibrosis. Renal mRNA expression was studied for EPO, EPO-receptor, collagen-3α1 and kidney injury molecule-1 (KIM-1).

RESULTS

DA had no effect on SBP, serum creatinine and proteinuria. Interstitial and glomerular α-SMA expression was significantly increased in Ren2. ACEi but not DA improved the increased renal inflammatory and pro-fibrotic profile in Ren2 rats. DA on top of ACEi further reduced glomerular α-SMA and KIM-1 expression.

CONCLUSION

Long-term DA treatment has no beneficial effects on renal structural and functional changes in TGR(mRen2)27 rats in the time frame studied and the dose provided.

Heart failure-associated anemia: bone marrow dysfunction and response to erythropoietin

Heart failure (HF)-associated anemia is common and has a poor outcome. Because bone marrow (BM) dysfunction may contribute to HF-associated anemia, we first investigated mechanisms of BM dysfunction in an established model of HF, the transgenic REN2 rat, which is characterized by severe hypertrophy and ventricular dilatation and SD rats as controls. Secondly, we investigated whether stimulation of hematopoiesis with erythropoietin (EPO) could restore anemia and BM dysfunction. After sacrifice, erythropoietic precursors (BFU-E) were isolated from the BM and cultured for 10 days. BFU-E were quantified and transcript abundance of genes involved in erythropoiesis were assayed. Number of BFU-E were severely decreased in BM of REN2 rats compared to SD rats (50 ± 6.2 vs. 6.4 ± 1.7, p < 0.01). EPO treatment increased hematocrit in the SD-EPO group (after 6 weeks, 49 ± 1 vs. 58 ± 1%, p < 0.01); however, in the mildly anemic REN2 rats, there was no effect (43 ± 1 vs. 44 ± 1%). This was paralleled by a 67% decrease in BFU-E in BM of REN2 rats compared to SD (p < 0.01). EPO significantly improved BFU-E in both SD and REN2 but could not restore this to control levels in the REN2 rats. Expression of several genes involved in differentiation (LMO2), mobilization (SDF-1), and iron incorporation (transferrin receptor) of the BM were differentially expressed in REN2 rats compared to SD rats, and EPO did not normalize this. Altogether, these results suggest that BM dysfunction is an important contributor to HF-associated anemia and that EPO is not an effective agent to treat HF-associated anemia.

Erythropoiesis stimulation in acute ischemic syndromes

Erythropoietin (EPO) is a hematopoietic hormone with extensive nonhematopoietic properties. The discovery of an EPO receptor outside the hematopoietic system has fuelled research into the beneficial effects of EPO for various conditions, predominantly in cardiovascular disease. Experimental evidence has revealed the cytoprotective properties of EPO, and it seems that the EPO-EPO receptor system provides a powerful backbone against acute myocardial ischemia, gaining from the different properties of EPO. There is an ongoing discussion about possible discrepancy between preclinical and clinical effects of EPO on the cardiovascular system. Large, randomized, placebo-controlled clinical trials are underway to give a final verdict on EPO treatment for acute coronary syndromes.

Estradiol-induced, endothelial progenitor cell-mediated neovascularization in male mice with hind-limb ischemia

We investigated whether administration of estradiol to male mice augments mobilization of bone marrow-derived endothelial progenitor cells (EPC) and incorporation into foci of neovascularization after hind-limb ischemia, thereby contributing to blood flow restoration. Mice were randomized and implanted with placebo pellets or pellets containing low-dose estradiol (0.39 mg) or high-dose estradiol (1.7 mg). Hind-limb ischemia was induced by unilateral resection of the left femoral artery 1 week after pellet implantation, then EPC mobilization and functional recovery was evaluated. EPC recruitment was assessed in mice transplanted with bone marrow from transgenic donors expressing beta-galactosidase driven by the Tie-2 promoter. EPC culture assay performed 2 weeks after pellet implantation revealed a significantly greater (p<0.05) number of circulating EPCs in the high-dose estradiol group than in the low-dose estradiol and placebo groups. At 3 and 4 weeks after induction of hind-limb ischemia, perfusion was significantly greater (p<0.05) in high-dose estradiol mice than in mice implanted with the low-dose estradiol or placebo pellets. At 1 and 4 weeks after hind-limb ischemia surgery, more bone marrow-derived EPCs, identified as beta-galactosidase-positive cells, were observed in ischemic regions from high-dose estradiol animals than in low-dose (p<0.05) or placebo groups (p<0.05). These results indicate that estradiol dose-dependently increases the levels of EPCs in peripheral blood in male animals, improves the recovery of blood flow, and decreases limb necrosis after hind-limb ischemia, and that this enhancement occurs, in part, through augmentation of EPC mobilization and greater incorporation of bone marrow-derived EPCs into foci of neovascularization.

Therapeutic potential of erythropoietin in cardiovascular disease: Erythropoiesis and beyond

Erythropoietin (EPO) is a glycoprotein hormone implicated in the regulation of red blood cell production. Anemia is common in chronic heart failure (CHF) patients and associated with an inappropriately low EPO-production, suggesting a role for its recombinant human form (rhEPO) in treatment. Although safety concerns have been raised regarding treatment with rhEPO in patients with chronic kidney disease, treatment with rhEPO in patients with CHF has so far been safe and well tolerated. The effect of rhEPO on outcome in anemic CHF patients is under investigation in a phase III clinical trial. In addition to its erythropoietic effects, EPO has been detected in the cardiovascular system, fueling intense research into possible non-hematopoietic effects. EPO has been shown to exert protective effects on the heart during acute myocardial ischemia and improve cardiac function in experimental CHF. Acute protection is mediated through reduction of apoptotic cell death. Improvement of cardiac function in CHF is related to myocardial neovascularization. EPO exhibits a vast array of beneficial effects in cardiovascular disease. In addition to the correction of anemia in CHF, rhEPO might benefit patients with cardiovascular disease.

Erythropoietin in cardiac disease: new features of an old drug

Erythropoietin is a haematopoietic hormone with extensive non-haematopoietic effects. The discovery of an erythropoietin receptor outside the haematopoietic system has fuelled the research into the beneficial effects of erythropoietin for various conditions, predominantly in cardiovascular disease. Experimental evidence has revealed the cytoprotective and angiogenic properties of erythropoietin and it seems that the erythropoietin-erythropoietin receptor system provides a powerful backbone against acute and chronic myocardial ischemia, each gaining from the different properties of erythropoietin. Clinical trials in which erythropoietin was titrated to achieve certain haematocrit levels have generated equivocal results. It has been suggested that a (too) high haematocrit is undesirable in cardiovascular disease. We have shown that intermittent (low-dose) erythropoietin administration, that does not increase haematocrit substantially, suffices to activate the beneficial downstream pathways of erythropoietin. We postulate that intermittent administration or a lower than conventional dose of erythropoietin, not only aimed at increasing haemoglobin at high levels, will provide powerful cellular protection and will improve cardiac outcome, without the side effects of erythropoietin associated with increased haematocrit.