Living autologous heart valves engineered from human prenatally harvested progenitors

BACKGROUND

Heart valve tissue engineering is a promising strategy to overcome the lack of autologous growing replacements, particularly for the repair of congenital malformations. Here, we present a novel concept using human prenatal progenitor cells as new and exclusive cell source to generate autologous implants ready for use at birth.

METHODS AND RESULTS

Human fetal mesenchymal progenitors were isolated from routinely sampled prenatal chorionic villus specimens and expanded in vitro. A portion was cryopreserved. After phenotyping and genotyping, cells were seeded onto synthetic biodegradable leaflet scaffolds (n=12) and conditioned in a bioreactor. After 21 days, leaflets were endothelialized with umbilical cord blood-derived endothelial progenitor cells and conditioned for additional 7 days. Resulting tissues were analyzed by histology, immunohistochemistry, biochemistry (amounts of extracellular matrix, DNA), mechanical testing, and scanning electron microscopy (SEM) and were compared with native neonatal heart valve leaflets. Fresh and cryopreserved cells showed comparable myofibroblast-like phenotypes. Genotyping confirmed their fetal origin. Neo-tissues exhibited organization, cell phenotypes, extracellular matrix production, and DNA content comparable to their native counterparts. Leaflet surfaces were covered with functional endothelia. SEM showed cellular distribution throughout the polymer and smooth surfaces. Mechanical profiles approximated those of native heart valves.

CONCLUSIONS

Prenatal fetal progenitors obtained from routine chorionic villus sampling were successfully used as an exclusive, new cell source for the engineering of living heart valve leaflets. This concept may enable autologous replacements with growth potential ready for use at birth. Combined with the use of cell banking technology, this approach may be applied also for postnatal applications.

Preserved placental oxygenation and development during severe systemic hypoxia

Local tissue oxygenation profoundly influences placental development. To elucidate the impact of hypoxia on cellular and molecular adaptation in vivo, pregnant mice at embryonic days 7.5–11.5 were exposed to reduced environmental oxygen (6–7% O2) for various periods of time. Hypoxia-inducible factor (HIF)-1α mRNA was highly expressed in the placenta, whereas HIF-2α was predominantly found in the decidua, indicating that HIF-1 is a relevant oxygen-dependent factor involved in placental development. During severe hypoxia, HIF-1α protein was strongly induced in the periphery but, however, not in the labyrinth layer of the placenta. Accordingly, no indication for tissue hypoxia in this central area was detected with 2-(2-nitro-1 H-imidazol-1-yl)- N-(2,2,3,3,3-pentafluoropropyl)acetamide staining and VEGF expression as hypoxic markers. The absence of significant tissue hypoxia was reflected by preserved placental architecture and trophoblast differentiation. In the search for mechanisms preventing local hypoxia, we found upregulation of endothelial nitric oxide synthase (NOS) expression in the labyrinth layer. Inhibition of NOS activity by Nω-nitro-l-arginine methyl ester application resulted in ubiquitous placental tissue hypoxia. Our results show that placental oxygenation is preserved even during severe systemic hypoxia and imply that NOS-mediated mechanisms are involved to protect the placenta from maternal hypoxia.

Umbilical cord blood derived endothelial progenitor cells for tissue engineering of vascular grafts

BACKGROUND

A substantial limitation regarding present pediatric cardiac surgery is the lack of appropriate materials for the repair of congenital defects. To address this shortcoming, tissue engineering is a scientific field that aims at in vitro fabrication of living autologous grafts with the capacity of growth, repair, and regeneration. Here we focused on tissue engineered vascular grafts using human umbilical cord blood derived endothelial progenitor cells (EPCs), as a noninvasive cell source for pediatric applications.

METHODS

EPCs were isolated from 20 ml fresh human umbilical cord blood by Ficoll gradient centrifugation and cultured in endothelial basal medium containing growth factors. After proliferation and differentiation cells were analyzed by immunohistochemistry and seeded onto three-dimensional (3D) biodegradable vascular scaffolds (porosity > 95%, n = 22). Twenty-four hours after seeding the vascular grafts were positioned into a pulse-duplicator-in vitro system and grown for 48 hours under biomimetic conditions. A second group was grown 6 days statically and an additional 6 days biomimetically. Controls were cultured statically. Analysis of the grafts included immunohistochemistry, histology, and scanning electron microscopy.

RESULTS

Preseeding differentiated EPCs indicated constant endothelial phenotypes including acetylated low-density lipoprotein, cluster of differentiation 31, von Willebrand factor, and endothelial nitric oxide synthetase. Seeded EPCs established favorable cell-to-polymer attachment and proliferation into the 3D tubular scaffolds. Both conditioned and static cellular constructs demonstrated positive staining for cluster of differentiation 31, von Willebrand factor, and expression of endothelial nitric oxide synthase.

CONCLUSIONS

Human umbilical cord derived EPCs indicated exceptional growth characteristics used for tissue engineering of vascular grafts. These cells demonstrated a constant endothelial phenotype and related functional features. Based on these results EPCs seem to be a promising autologous cell source with regard to cardiovascular tissue engineering, particularly for the repair of congenital defects.

Effect of postpartum iron supplementation on red cell and iron parameters in non-anaemic iron-deficient women: a randomised placebo-controlled study

OBJECTIVE

To investigate the effect of oral iron on postpartum red cell and iron parameters in non-anaemic women with iron deficiency.

DESIGN

Randomised study of supplementation with oral iron sulphate 80 mg daily or placebo for 12 weeks starting 24-48 hours after delivery, with visits antepartum and 1, 4, 6 and 12 weeks postpartum.

SETTING

Swiss university hospital obstetric unit.

PARTICIPANTS

Fifty-two women with antenatal iron deficiency (serum ferritin <15 microg/L) and no antenatal or postnatal anaemia (haemoglobin >11 g/dL up to 48 hours before delivery, and >10 g/dL postpartum), divided into two groups comparable in antenatal iron status.

METHODS

Supplementation was started 24-48 hours after delivery (visit 1:V1). Additional tablets were issued one week after V1 (V2), four weeks after V1 (V3) and six weeks after V1 (V4). The last visit took place 12 weeks after visit 1 and 6 weeks after visit 4 (V5). Patients were required to return blisters and boxes whether they were used and unused at each visit and compliance was assessed by counting the tablets. Blood samples for haematology and iron status testing were taken before delivery and at each visit.

MAIN OUTCOME MEASURES

Iron status (serum ferritin, hypochromic red cells, iron, transferrin saturation, soluble transferrin receptor concentration); erythropoiesis (standard parameters, including reticulocyte indices); and inflammatory response (serum neopterin, C-reactive protein, white cell count) in five-datapoint profiles.

RESULTS

Increased ferritin (P= 0.0004) and transferrin saturation (P= 0.03), decreased soluble transferrin receptors (P= 0.02); increased haemoglobin (P= 0.02) and decreased hypochromic red cells (P= 0.04) compared with placebo at 12 weeks, with no differences in other red cell or reticulocyte parameters. There was a positive correlation between C-reactive protein and postpartum ferritin. No correlation was observed in the puerperium between C-reactive protein and hypochromic red cells or soluble transferrin receptors.

CONCLUSIONS

Haemoglobin levels and iron stores in women with term gestational iron deficiency benefit significantly from iron supplementation compared with placebo, even in an industrialised population.

Living patches engineered from human umbilical cord derived fibroblasts and endothelial progenitor cells☆

OBJECTIVE

A major shortcoming in contemporary congenital heart surgery is the lack of viable replacement materials with the capacity of growth and regeneration. Here we focused on living autologous patches engineered from human umbilical cord derived fibroblasts and endothelial progenitor cells (EPCs) as a ready-to-use cell source for paediatric cardiovascular tissue engineering.

METHODS

EPCs were isolated from 20 ml fresh umbilical cord blood by density gradient centrifugation and myofibroblasts were harvested from umbilical cord tissue. Cells were differentiated and expanded in vitro using nutrient media containing growth factors. Before seeding, cell-phenotypes were assessed by immuno-histochemistry. Biodegradable patches fabricated from synthetic polymers (PGA/P4HB) were seeded with myofibroblasts followed by endothelialization with EPCs. All patches were cultured in a perfusion bioreactor. A subgroup of patches was additionally stimulated by cyclic strain. Analysis of the neo-tissues comprised histology, immuno-histochemistry, extracellular matrix (ECM) analysis and biomechanical testing.

RESULTS

Endothelial phenotypes of EPCs before seeding were confirmed by Ac-Dil-LDL, CD 31, von-Willebrand-Factor and eNOS staining. Histology of the seeded patches demonstrated layered viable tissue formation in all samples. The cells in the newly formed tissues expressed myofibroblast markers, such as desmin and alpha-SMA. The EPCs derived neo-endothelia showed constant endothelial phenotypes (CD 31, vWF). major constituents of ECM such as collagen and proteoglycans were biochemically detected. Stress-strain properties of the patches showed features of native-analogous tissues.

CONCLUSIONS

Living tissue engineered patches can be successfully generated from human umbilical cord derived myofibroblasts and EPCs. This new cell source may enable the tissue engineering of versatile, living, autologous replacement materials for congenital cardiac interventions.

Sequence analysis of bile salt export pump (ABCB11) and multidrug resistance p-glycoprotein 3 (ABCB4, MDR3) in patients with intrahepatic cholestasis of pregnancy

Intrahepatic cholestasis of pregnancy (ICP) is a liver disorder associated with increased risk of intrauterine fetal death and prematurity. There is increasing evidence that genetically determined dysfunction in the canalicular ABC transporters bile salt export pump (BSEP, ABCB11) and multidrug resistance protein 3 (MDR3, ABCB4) might be risk factors for ICP development. This study aimed to (i). describe the extent of genetic variability in BSEP and MDR3 in ICP and (ii). identify new disease-causing mutations. Twenty-one women with ICP and 40 women with uneventful pregnancies were recruited between April 2001 and April 2003. Sequencing of BSEP and MDR3 spanned 8-10 kb per gene and comprised the promoter region and 100-350 bp of the flanking intronic region around each exon. DNA sequencing of polymerase chain reaction fragments was performed on an ABI3700 capillary sequencer. MDR3 promoter activity of promoter constructs carrying different ICP-specific mutations was studied using reporter assays. A total of 37 and 51 variant sites were detected in BSEP and MDR3, respectively. Three non-synonymous sites in codons for evolutionarily conserved amino acids were specific for the ICP collective (BSEP, N591S; MDR3, S320F and G762E). Furthermore, four ICP-specific splicing mutations were detected in MDR3 [intron 21, G(+1)A; intron 25, G(+5)C and C(-3)G; and intron 26, T(+2)A]. Activity of the mutated MDR3 promoter was similar to that observed for the wild-type promoter. Our data further support an involvement of MDR3 genetic variation in the pathogenesis of ICP, whereas analysis of BSEP sequence variation indicates that this gene is probably less important for the development of pregnancy-associated cholestasis.

Oxygen-regulated expression of TGF-beta 3, a growth factor involved in trophoblast differentiation

The transforming growth factor-beta 3 (TGF-beta 3) is involved in oxygen-dependent differentiation processes during placental development and pregnancy disorders. However, the importance of oxygen partial pressure for the regulation of TGF-beta 3 expression is presently unclear. We and others presented preliminary evidence that the hypoxia-inducible factor-1 (HIF-1) confers TGF-beta 3 transcription but it was unknown whether this occurred directly or indirectly. To analyze how HIF-1 regulates TGF-beta 3 gene transcription, we cloned and sequenced the mouse TGF-beta 3 promoter region. Multiple putative HIF-1 binding sites (HBSs) were identified, many of which co-localized with two G+C rich CpG islands 5' to the TGF-beta 3 transcription start site. A 6.8 kb fragment of the TGF-beta 3 promoter induced reporter gene expression under hypoxic conditions or when treated with an iron chelator known to stabilize and activate the HIF-1 alpha subunit. Deletion of a 2.4 kb fragment upstream of the distal CpG island abolished inducibility of reporter gene expression. Two HBSs (HBS1 and HBS6) that bound the HIF-1 protein could be identified within this 2.4 kb fragment. These results suggest that TGF-beta 3 gene expression is directly regulated by HIF-1.

Human umbilical cord cells for cardiovascular tissue engineering: a comparative study

OBJECTIVE

Tissue engineering of viable, autologous cardiovascular replacements with the potential to grow, repair and remodel represents an attractive approach to overcome the shortcomings of available replacements for the repair of congenital cardiac defects. Currently, vascular myofibroblast cells represent an established cell source for cardiovascular tissue engineering. Cell isolation requires the invasive harvesting of venous or arterial vessel segments prior to scaffold seeding, a technique which may not be preferable, especially in pediatric patients. This study evaluates cells isolated from human umbilical cord artery, umbilical cord vein and whole cord as alternative autologous cell sources for cardiovascular tissue engineering.

METHODS

Cells were isolated from human umbilical cord artery (UCA), umbilical cord vein (UCV), whole umbilical cord (UCC) and saphenous vein segments (VC), and were expanded in culture. All three expanded cell groups were seeded on bioabsorbable copolymer strips and grown in vitro for 28 days. Isolated cells were characterized by flow cytometry, histology, immunohistochemistry, proliferation assays and compared to VC. Morphological analysis of the seeded polymer strips included histology, immunohistochemistry, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and uniaxial stress testing.

RESULTS

UCA, UCV and UCC demonstrated excellent cell growth properties comparable to VC. Following isolation, all three cell groups showed myofibroblast-like morphology and characteristics by staining positive for alpha-smooth muscle actin (ASMA) and vimentin. Histology and immunohistochemistry of seeded polymers showed good tissue and extracellular matrix formation containing collagen I, III and elastin. TEM showed viable myofibroblasts and the deposition of collagen fibrils and progressive growing tissue formation, with a confluent surface, was observed in SEM. No difference was found among the mechanical properties of UCA, UCV, UCC and VC tissue engineered constructs.

CONCLUSIONS

Tissue engineering of cardiovascular constructs by using UCA, UCV and UCC is feasible in an in vitro environment. Cell growth, morphology, characteristics and tissue formation were comparable between UCA, UCV, UCC and VC. UCC represent an attractive, readily available autologous cell source for cardiovascular tissue engineering offering the additional benefits of utilizing juvenile cells and avoiding the invasive harvesting of intact vascular structures.

Impact of parturition on iron status in nonanaemic iron deficiency

BACKGROUND

Iron-deficient nonanaemic parturients risk underdiagnosis as a result of the reliance on postpartum ferritin and haemoglobin as markers of iron status. Ferritin is an acute-phase protein whose levels increase during the inflammatory response, as occurs after delivery. Our aims were to evaluate the impact of parturition on iron status, erythropoiesis and the inflammatory response, and identify the optimal parameters and timing for diagnosing iron deficiency in the presence of postpartum inflammation.

MATERIALS AND METHODS

Conventional parameters of iron status, erythropoiesis and the inflammatory response (serum ferritin, serum iron, transferrin saturation, C-reactive protein) were compared with more recent parameters [soluble transferrin receptors (sTfR), hypochromic red cells, reticulocyte indices] within 48 h either side of delivery in 64 iron-deficient nonanaemic women (defined by a prepartum serum ferritin < or =15 microg L(-1), and a pre- and postpartum haemoglobin of > or =11.0 g dL(-1) and > or =10.0 g dL(-1), respectively).

RESULTS

Mean sTfR decreased pre to postpartum from 7.3 to 5.8 microg mL(-1) (P<0.01), while mean serum ferritin increased from 9.7 to 16.9 microg L(-1) (P<0.01). Serum ferritin did not correlate with haemoglobin pre or postpartum (r=0.04, P=0.7; r=0.2, P=0.09), but a correlation persisted postpartum between hypochromic red blood cells and haemoglobin (r=-0.26; P<0.05). The percentage of hypochromic red cells remained virtually unchanged pre- and postpartum (4.0% vs. 3.8%; NS). Postpartum mean reticulocyte haemoglobin content (CHr) was 27.1 +/- 1.6 pg.

CONCLUSION

Iron status should be tested prepartum, in the absence of an inflammatory response, rather than in the early postpartum. A valuable additional parameter, where available, might be the hypochromic red cell percentage, which is virtually uninfluenced by the inflammatory response. Furthermore, hypochromic red cell percentage, CHr and sTfR can be helpful to differentiate between functional iron deficiency and depleted iron stores.

Hypertension in a pregnancy with renal anemia after recombinant human erythropoietin (rhEPO) therapy

Management of renal anemia in pregnancy remains a major issue. We report the use of human recombinant erythropoietin (rhEPO) combined with parenteral iron sucrose in a pregnancy with chronic glomerulonephritis, progressive anemia and initially normal blood pressure. Therapy from 32 weeks gestation increased the hematocrit by 0.4% daily and the hemoglobin from 8.6 to 10.3 g/dL within 2 weeks. Despite the improvement of anemia, Cesarean section had to be performed at 34 weeks due to acute hypertension, preeclampsia and worsening renal function. Blood pressure remained elevated postpartum. Because of symptomatic postpartum anemia with a hemoglobin of 7.5 g/dL on the 5th postoperative day rhEPO in combination with parenteral iron sucrose was readministered over 3 following days. Blood pressure reached a maximum of 210/130 mm Hg 3 weeks later. Possible causes include advancing preeclampsia and renal disease, but also rhEPO (due to its intrinsic vascular effects and/or the rapid response of the hematocrit), and a combination of both.

Iron deficiency and anaemia in pregnancy: modern aspects of diagnosis and therapy

The prevalence of iron-deficiency anemia in different regions of the world ranges from 12 to 43%. The increased iron requirement in pregnancy and the puerperium carry with it an increased susceptibility to iron deficiency and iron-deficiency anemia and perioperative or peripartal blood transfusion. Prevention and correction presuppose reliable laboratory parameters and a thorough understanding of the mechanisms of iron therapy. The Hb level alone is insufficient to guide management. A complete work-up (ferritin, transferrin saturation) is essential, preferably with hematological indices such as hypochromic and microcytic red cells and reticulocytes, classified by degree of maturity, in particular, before parenteral therapy is given. Since ferritin acts as both an iron-storage and acute-phase protein, it cannot be used to evaluate iron status in the presence of inflammation. A high ferritin level thus requires the presence of an inflammatory process to be eliminated before it can be taken at face value. If the C-reactive protein level is also raised, the soluble TfR concentration can be used, since it is unaffected by inflammation. Inadequate understanding of the complex chemistry of parenteral iron administration was previously responsible for serious side effects, such as toxic and allergic reactions, and even anaphylactic shock, in particular with dextran preparations. However, the current type II iron complexes that release iron to the endogenous iron-binding proteins with a half-life of about 6 hours are not only effective but carry a minimal risk of allergic accident and overload, especially after a comprehensive pretreatment work-up. Our departmental data collected over 8 years and backed by postmarketing experience in 25 countries indicate that iron sucrose complex therapy is a valid first-line option for the safe and rapid reversal of iron-deficiency anemia.