The molecular specificity of action of the tetrapeptide acetyl-N-Ser-Asp-Lys-Pro (AcSDKP) in the control of hematopoietic stem cell proliferation

Investigating the antifibrotic potential of N-acetyl seryl-aspartyl-lysyl-proline sequence peptides

N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP) is a physiological antifibrotic peptide that is hydrolysed by angiotensin I-converting enzyme (ACE). The beneficial antifibrotic effects of ACE inhibitors have been attributed, in part, to its inhibition of Ac-SDKP cleavage. There is indirect evidence that the SDK fragment of Ac-SDKP is the main component required for its antiproliferative action. However, the exact component of the physiological peptide that is responsible for its antifibrotic effect has yet to be determined. Ac-SDKP-derived analogues that are resistant to ACE degradation may provide a new avenue for fibrosis therapy. We tested the antifibrotic potential of various Ac-SDKP peptide sequences and an analogue resistant to ACE degradation in lung fibroblasts. We investigated the contribution and molecular mechanism of action of the amino acid residues in the Ac-SDKP sequence to its antifibrotic effects, and the effects of Ac-SDKP peptides in the prevention of collagen deposition in cells. The Ac-DKP fragment moderately inhibited endothelin-1 (ET-1) mediated transforming growth factor-β (TGF- β) expression, and could be slowly cleaved by ACE, revealing a different sequence requirement for the antifibrotic action of Ac-SDKP. The Ac-SDψKP analogue (where the peptide bond between the aspartate and lysine is reduced) inhibited TGF-β/small mother against decapentaplegic (Smad)-3 signalling and collagen deposition. The Ac-SDKP peptide, in combination with ACEi, demonstrated a greater inhibition of hydroxyproline as compared to Ac-SDKP alone.

Elevation of the antifibrotic peptide N-acetyl-seryl-aspartyl-lysyl-proline: a blood pressure-independent beneficial effect of angiotensin I-converting enzyme inhibitors

Blockade of the renin-angiotensin system (RAS) is well recognized as an essential therapy in hypertensive, heart, and kidney diseases. There are several classes of drugs that block the RAS; these drugs are known to exhibit antifibrotic action. An analysis of the molecular mechanisms of action for these drugs can reveal potential differences in their antifibrotic roles. In this review, we discuss the antifibrotic action of RAS blockade with an emphasis on the potential importance of angiotensin I-converting enzyme (ACE) inhibition associated with the antifibrotic peptide N-acetyl-seryl-aspartyl-lysyl-proline (AcSDKP).

Novel anti-inflammatory mechanisms of N-Acetyl-Ser-Asp-Lys-Pro in hypertension-induced target organ damage

High blood pressure (HBP) is an important risk factor for cardiac, renal, and vascular dysfunction. Excess inflammation is the major pathogenic mechanism for HBP-induced target organ damage (TOD). N-acetyl-Ser-Asp-Lys-Pro (Ac-SDKP), a tetrapeptide specifically degraded by angiotensin converting enzyme (ACE), reduces inflammation, fibrosis, and TOD induced by HBP. Our hypothesis is that Ac-SDKP exerts its anti-inflammatory effects by inhibiting: 1) differentiation of bone marrow stem cells (BMSC) to macrophages, 2) activation and migration of macrophages, and 3) release of the proinflammatory cytokine TNF-alpha by activated macrophages. BMSC were freshly isolated and cultured in macrophage growth medium. Differentiation of murine BMSC to macrophages was analyzed by flow cytometry using F4/80 as a marker of macrophage maturation. Macrophage migration was measured in a modified Boyden chamber. TNF-alpha release by activated macrophages in culture was measured by ELISA. Myocardial macrophage activation in mice with ANG II-induced hypertension was studied by Western blotting of Mac-2 (galectin-3) protein. Interstitial collagen deposition was measured by picrosirius red staining. We found that Ac-SDKP (10 nM) reduced differentiation of cultured BMSC to mature macrophages by 24.5% [F4/80 positivity: 14.09 +/- 1.06 mean fluorescent intensity for vehicle and 10.63 +/- 0.35 for Ac-SDKP; P < 0.05]. Ac-SDKP also decreased galectin-3 and macrophage colony-stimulating factor-dependent macrophage migration. In addition, Ac-SDKP decreased secretion of TNF-alpha by macrophages stimulated with bacterial LPS. In mice with ANG II-induced hypertension, Ac-SDKP reduced expression of galectin-3, a protein produced by infiltrating macrophages in the myocardium, and interstitial collagen deposition. In conclusion, this study demonstrates that part of the anti-inflammatory effect of Ac-SDKP is due to its direct effect on BMSC and macrophage, inhibiting their differentiation, activation, and cytokine release. These effects explain some of the anti-inflammatory and antifibrotic properties of Ac-SDKP in hypertension.

Effects of Palladacycle Complex on Hematopoietic Progenitor Cells Proliferation In Vivo and In Vitro and Its Relation with the Inhibitory Properties of This Compound on the Angiotensin‐I Converting Enzyme Activity

In the present study, we introduce a new class of organometallic compound, the Biphosphinic Palladacycle Complex [Pd (C2, N-S(-)(dmpa)(dppf)] Cl (BPC), as an angiotensin-I converting-enzyme inhibitor (ACEI) with hematological regulation properties. When BPC was assayed as a competitive inhibitor over the hydrolysis of Abz-YRK (Dnp)-P-OH (Km = 7.0 microM), it showed a Kiapp = 0.2259 ng and a Ki value of 94.12 pg. Using murine long-term bone marrow cultures (LTBMCs) and clonal culture techniques, we also evaluated the capacity of this drug (1.18 microM) to module haematopoietic progenitor cells proliferation in vitro and in vivo. Our results demonstrated that BPC produces no toxicity to bone marrow cells, as determined by the unchanged cell number in the non-adherent layer at weeks 1, 2, and 8 and the increased number of adherent cells present in the BPC-treated LTBMCs. However, the proportion of CFU-Cs in the non-adherent cell layer was reduced at weeks 5, 6, 8, and 9. In vivo studies using the dose of 1 mg/kg of BPC, administered by subcutaneous route, presented similar result as those found in vitro, in the number of CFU-Cs. This latter finding may be explained by the inhibitory effects of this drug on the ACE activity, which probably result in increased levels of its substrate AcSDKP, a negative regulator of hematopoiesis.

Synthesis and biological evaluation of analogues of the tetrapeptide N-Acetyl-Ser-Asp-Lys-Pro (AcSDKP), an inhibitor of primitive haematopoietic cell proliferation

The tetrapeptide N-Acetyl-Ser-Asp-Lys-Pro (AcSDKP), an inhibitor of haematopoietic stem cell proliferation, reduces in vivo and in vitro the damage to the stem cell compartment resulting from treatment with chemotherapeutic agents or ionizing radiations. In order to provide new molecules likely to improve the myeloprotection displayed by this tetrapeptide, we have prepared a set of analogues of AcSDKP. These compounds are derived from the parent peptide by substitution or modification of the N- or of the C-terminus, or substitution of side chains. We report here that almost all investigated analogues retain the antiproliferative activity reducing in vitro the proportion of murine Colony-Forming Units Granulocyte, Macrophage (CFU-GM) in S-phase and inhibiting the entry into cycle of High Proliferative Potential Colony-Forming Cells (HPP-CFC). This shows that the polar groups of Ser, Asp or Lys are critical for the expression of biological activity, but that the modification of the N- or C-terminus mostly yielded compounds still retaining antiproliferative activity and devoid of toxicity. The efficacy of AcSDKP analogues in preventing in vitro the primitive haematopoietic cells from entering into cycle makes these molecules new candidates for further in vivo investigations.

Bone marrow as multidimensional orbit oscillator after autologous bone marrow transplantation

The local renin-angiotensin system (RAS) in bone marrow is probably involved in the control of hematopoiesis. Earlier observations suggest the relationship between the frequency of sodium and potassium concentration changes in urine and bone marrow recovery after chemotherapy. The purpose of this study was to prove the relationship between sodium and potassium excretion changes in urine and granulocyte counts in peripheral blood after autologous bone marrow and peripheral blood stem cell transplantation. The correlation between amplitude maximum FFmax of F=d[Na]/d[K], where d[Na] and d[K] are changes of sodium and potassium excretions in 24 h, and granulocytes, recorded k days later, was found in 12 patients with autologous bone marrow transplantation (BMT) and/or PBSCT. In patients with successful engraftment, k ranged from 4 to 7 days. In the patient with unsuccessful BMT, k was 12 days. The results imply the interaction between systemic and bone marrow RAS.

In vitro effect of acetyl-N-Ser-Asp-Lys-Pro (AcSDKP) analogs resistant to angiotensin I-converting enzyme on hematopoietic stem cell and progenitor cell proliferation

The tetrapeptide Acetyl-N-Ser-Asp-Lys-Pro (AcSDKP), an inhibitor of hematopoietic stem cell proliferation, is known to reduce in vivo the damage resulting from treatment with chemotherapeutic agents or ionizing radiation on the stem cell compartment. Recently, AcSDKP has been shown to be a physiological substrate of the N-active site of angiotensin I-converting enzyme (ACE). Four analogs of the tetrapeptide expressing a high stability towards ACE degradation in vitro have been synthesized in order to provide new molecules likely to improve the myeloprotection displayed by AcSDKP. These analogs are three pseudopeptides with a modified peptidic bond, Ac-Serpsi(CH2-NH)Asp-Lys-Pro, Ac-Ser-Asppsi(CH2-NH)Lys-Pro, Ac-Ser-Asp-Lyspsi(CH2-N)Pro, and one C-terminus modified peptide (AcSDKP-NH2). We report here that these analogs reduce in vitro the proportion of murine colony-forming units-granulocyte/macrophage in S-phase and inhibit the entry into cycle of high proliferative potential colony-forming cells. The efficacy of AcSDKP analogs in preventing in vitro primitive hematopoietic stem cells from entering into cycle suggests that these molecules could be new candidates for the powerful inhibition of hematopoietic stem and progenitor cell proliferation in vivo.

Inhibitory action of the peptide AcSDKP on the proliferative state of hematopoietic stem cells in the presence of captopril but not lisinopril

The effect of Angiotensin I-converting enzyme (ACE) inhibitors on their own and in combination with the peptide AcSDKP on the proliferation of hematopoietic stem cells has been investigated. Hematopoietic stem cells from murine bone marrow induced into cell cycle following exposure to 2 Gy gamma-irradiation were incubated in vitro for up to 24 h in the presence of medium, captopril/lisinopril, AcSDKP, and AcSDKP with either ACE inhibitor. Hematopoietic stem cells were monitored using the high proliferative potential-colony forming cell-1 (HPP-CFC-1) population cloned in the presence of human IL-1 beta, murine IL-3, and murine M-CSF. No significant inhibitory effect was observed in the presence of AcSDKP on its own and AcSDKP in combination with lisinopril. However, there was a significant inhibition of stem cell cycling when AcSDKP and captopril were combined. This suggests that captopril inhibits AcSDKP breakdown better than lisinopril. The combination of AcSDKP and captopril also had an inhibitory effect on cell recruitment into S phase. The fact that a combination of AcSDKP and captopril switches cycling hematopoietic stem cells out of cycle indicates the importance of the N-active catalytic site of ACE in AcSDKP hydrolysis in vitro. Thus, AcSDKP in combination with appropriate ACE inhibitors may be of use in regulating the proliferation of hematopoietic stem cells in vitro.

Growth inhibitors in haemopoiesis and leukaemogenesis

The haemopoietic stem cell occupies a central position in the hierarchy of the haemopoietic system and it is at this cellular level that all haemopoietic function can be ultimately regulated. Much efforts has thus gone into characterizing regulators of stem cell proliferation with a view to enhancing our understanding of the regulation of this important cell, and in addition to examining the potential clinical roles of such stem cell active factors. We focus on inhibitors of haemopoietic stem cell proliferation and review their molecular and cellular biology and potential clinical usefulness in cancer therapy. The potential roles of inhibitory molecules in the pathogenesis of leukaemias are also discussed.

Catabolism of the hemoregulatory peptide N-Acetyl-Ser-Asp-Lys-Pro: a new insight into the physiological role of the angiotensin-I-converting enzyme N-active site

The tetrapeptide N-Acetyl-Ser-Asp-Lys-Pro (AcSDKP) was first isolated from bone marrow extracts and shown to be involved in the negative control of hematopoiesis by preventing the recruitment of primitive stem cells into S-phase. In vitro studies on AcSDKP catabolism in human plasma revealed that AcSDKP was cleaved by plasmatic angiotensin-I converting enzyme (ACE). The evaluation of the respective involvement of the two active sites of ACE in AcSDKP degradation in vitro revealed that the N-active site was preferentially involved in this catabolism. Moreover, an in vivo study on healthy volunteers of the catalytic efficiency of ACE towards AcSDKP after administration of Captopril demonstrated that AcSDKP was a physiological substrate of ACE. AcSDKP might represent the first natural specific substrate of the N-active site of the enzyme. These results pose the question of a potential role of ACE in the control of hematopoiesis as well as possible applications of ACE inhibitors to cope with dysfunctions in which AcSDKP might exert physiological control.