Effects of ACE inhibitor on renal anemia in predialysis patients

A role for angiotensin-converting enzyme in the characterization, enrichment, and proliferation potential of adult murine pituitary colony-forming cells

Recently, we described a rare cell type within the adult murine pituitary gland with progenitor cell hallmarks (PCFCs). PCFCs are contained exclusively within a subpopulation of cells that import fluorescent beta-Ala-Lys-Nepsilon-AMCA (7-amino-4-methylcoumarin-3-acetic acid). Herein, we investigate the utility of cell surface molecules angiotensin-converting enzyme (ACE) and stem cell antigen-1 (Sca-1) to further enrich for PCFCs. ACE and Sca-1 were expressed on 61% and 55% of AMCA(+)CD45(-)CD31(-) cells, respectively, and coexpressed on 38%. ACE(+)Sca-1(+)AMCA(+) cells enriched for PCFCs by 195-fold over unselected cells. ACE(+)AMCA(+) cells enriched for PCFCs by 170-fold, and colonies were twofold larger than for AMCA(+) selection alone. Conversely, ACE(-)-selected cells reduced both colony-forming activity and size. Notably, colonies generated from AMCA(+) cells obtained from ACE(null) mice were 2.7-fold smaller than for wild-type mice. These data identify ACE as a previously unrecognized marker of PCFCs and suggest that ACE is functionally important for PCFC proliferation. Anatomically, the cells that imported AMCA and expressed ACE were situated in the marginal epithelial cell layer of the pituitary cleft and in the adjacent subluminal zone, thus supporting previous proposals that the luminal zone is a source of precursor cells in the adult pituitary.

Anemia and heart failure

Over the past few years, anemia has emerged as a powerful independent predictor of adverse outcomes in chronic heart failure (CHF). It affects up to 50% of patients with CHF, depending on the definition of anemia used and on the population studied. Even small reductions in hemoglobin are associated with worse outcome. However, the causes of anemia in CHF remain unclear, although impairment of renal function and inflammatory cytokines are proposed mechanisms. Both may act through impairment of the synthesis or action of erythropoietin. Preliminary studies have demonstrated improvement in symptoms, exercise tolerance, quality of life, and reductions in hospitalizations when patients with severe CHF were treated with erythropoietin. The benefits and the potential risks of such therapies will be further addressed in upcoming larger randomized trials. The recent interest in anemia reflects a new perspective in heart failure therapy, focusing on non-cardiovascular comorbidities.

Towards the understanding of the local hematopoietic bone marrow renin-angiotensin system

The classical view of the renin-angiotensin system (RAS) as a circulating endocrine system has evolved to organ- and tissue-based systems that perform paracrine/autocrine functions. Angiotensin II (Ang II), the dominant effector peptide of the RAS, regulates cellular growth in a wide variety of tissues in (patho)biological states. In 1996, we hypothesized that there exists a locally active RAS in the bone marrow affecting the growth, production, proliferation and differentiation of hematopoietic cells. Evidences supporting this hypothesis are growing. Ang II, through interacting with Ang II type 1 (AT1) receptor stimulates erythroid differentiation. This stimulatory effect of Ang II on erythropoiesis was completely abolished by a specific AT1 receptor antagonist, losartan. AT1a receptors are present on human CD34(+) hematopoietic stem cells. Ang II increases hematopoietic progenitor cell proliferation and this effect was also blocked by losartan. Angiotensin-converting enzyme (ACE) is involved in enhancing the recruitment of primitive stem cells into S-phase in hematopoietic bone marrow by degrading tetrapeptide AcSDKP. ACE inhibitors modified the circulating hematopoietic progenitors in healthy subjects. RAS may also affect pathological/neoplastic hematopoiesis. Renin has been isolated from leukemic blast cells. Higher bone marrow ACE levels in acute leukemic patients suggested that ACE is produced at higher quantities in the leukemic bone marrow. In this review, the 'State of the Art' of the local bone marrow RAS is summarized. A local RAS in the bone marrow can mediate, in an autocrine/paracrine fashion, some of the principal steps of hematopoietic cell production. To show a causal link between the components of RAS and the other regulatory hematopoietic growth factors is not only an academic curiosity. Elucidation of such a local bone marrow system may offer novel therapeutic approaches in pathologic/neoplastic conditions.

Renin expression in hematological malignancies and its role in the regulation of hematopoiesis

It has been demonstrated that some myeloid blasts express renin, but normal bone marrow (BM) does not display this expression. The aim of the present work was to analyze the renin expression in different hematological malignancies and different myeloid cell lines. We investigated the expression of renin by RT-PCR in BM from patients with hematological malignancies (106 patients), in nine normal BM from healthy donors and in leukemic cell lines (K562, KU812, MEG-01, U-937 and HL60), as well in K562 cell line subjected to differentiation treatments. We have observed renin expression in cells from acute myeloid leukemia (AML), chronic myelogenous leukemia (CML) and acute lymphoblastic leukemia (ALL) cases. The highest frequency was observed in AML-non acute promyelocytic leukemia(APL) cases (47.2% of the cases). The disappearance of this expression was associated with the status of complete remission of AML. Renin is expressed in some myeloid human leukemia cell lines such as K562, KU812 and MEG-01. However, when K562 cells were treated with inducers of growth inhibition and/or differentiation, the expression did not disappear, indicating that renin expression is associated with a blastic phenotype rather than with cell proliferation. The obtained findings suggest that the renin expression could have a role on the disease development and could be used as an aberrant marker of leukemia.

Serum erythropoietin in heart failure patients treated with ACE-inhibitors or AT(1) antagonists

BACKGROUND

Erythropoietin (Epo), a growth factor produced by the kidney, is important in heart failure patients to promote oxygen delivery to tissues. Seventy-two chronic heart failure (CHF) patients at our outpatient clinic were subjected to morning serum Epo-level measurements and classified according to NYHA criteria.

RESULTS

Forty-eight patients of classes III and IV had a significantly elevated serum Epo-level of 42.9+/-40.3 mIU/ml (mean+/-1 S.D.) when compared to the mean level of 24 patients of classes I and II who had a normal range mean value of 13.4+/-6.2 mIU/ml (P<0.05). Patients on angiotensin-converting enzyme (ACE) inhibitors showed a trend towards lower serum Epo-levels compared to patients treated with angiotensin-II type-1 receptor antagonists (AT(1) antagonists) (levels: 33.3+/-35.6 mIU/ml and 43.6+/-38.1 mIU/ml). This trend did not, however, reach statistical significance (P=0.36).

CONCLUSION

We suggest that a desirable Epo increase in class III and IV CHF patients could be achieved by either recombinant human Epo administration or, possibly, by appropriate selection of the concomitant medical therapy. A large prospective study shall investigate the possible advantage of AT(1) antagonists over ACE-inhibitors with regard to Epo effect.