Volumetric Portal Embolization: A New Concept to Improve Liver Regeneration and Hepatocyte Engraftment.

BACKGROUND: Hepatocyte transplantation has been proposed as an alternative to orthotopic liver transplantation to treat metabolic liver diseases. This approach requires preconditioning of the host liver to enhance engraftment of transplanted hepatocytes. Different methods are currently used in preclinical models: partial hepatectomy, portal ligature or embolization, and radiotherapy or chemotherapeutic drugs. However, these methods carry high risks of complications and are problematic for use in clinical practice. Here, we developed an innovative method called volumetric (distal, partial, and random) portal embolization (VPE), which preserves total liver volume. METHODS: Embolization was performed in the portal trunk of C57BL6 adult mice with polyester microspheres, to ensure a bilateral and distal distribution. The repartition of microspheres was studied by angiographic and histological analyses. Liver regeneration was evaluated by Ki67 labeling. Optimal conditions for VPE were determined, and the resulting regeneration was compared with that after partial hepatectomy (70%). Labeled adult hepatocytes were then transplanted, and engraftment was compared between embolized (n = 19) and nonembolized mice (n = 8). Engraftment was assessed in vivo and histologically by tracking labeled cells at day 5. RESULTS: The best volumetric embolization conditions, which resulted in the regeneration of 5% of total liver, were 8 × 10 ten-micron microspheres infused with a 29 G needle directly into the portal trunk at 3.3 µL/s. In these conditions, transplanted hepatocytes engraftment was significantly higher than that in control conditions (3 vs 0.65%). CONCLUSIONS: The VPE is a new, minimally invasive, and efficient technique to prepare the host liver for cell transplantation.

Dual SP/ALDH functionalities refine the human hematopoietic Lin-CD34+CD38- stem/progenitor cell compartment.

Identification of prevalent specific markers is crucial to stem/progenitor cell purification. Determinants such as the surface antigens CD34 and CD38 are traditionally used to analyze and purify hematopoietic stem/progenitor cells (HSCs/HPCs). However, the variable expression of these membrane antigens poses some limitations to their use in HSC/HPC purification. Techniques based on drug/stain efflux through the ATP-binding cassette (ABC)G2 pump (side population [SP] phenotype) or on detection of aldehyde dehydrogenase (ALDH) activity have been independently developed and distinguish the SP and ALDH(Bright) (ALDH(Br)) cell subsets for their phenotype and proliferative capability. In this study, we developed a multiparametric flow cytometric method associating both SP and ALDH activities on human lineage negative (Lin(-)) bone marrow cells and sorted different cell fractions according to their SP/ALDH activity level. We find that Lin(-)CD34(+)CD38(Low/-) cells are found throughout the spectrum of ALDH expression and are enriched especially in ALDH(Br) cells when associated with SP functionality (SP/ALDH(Br) fraction). Furthermore, the SP marker identified G(0) cells in all ALDH fractions, allowing us to sort quiescent cells regardless of ALDH activity. Moreover, we show that, within the Lin(-)CD34(+)CD38(-)ALDH(Br) population, the SP marker identifies cells with higher primitive characteristics, in terms of stemness-related gene expression and in vitro and in vivo proliferative potential, than the Lin(-)CD34(+) CD38(-)ALDH(Br) main population cells. In conclusion, our study shows that the coexpression of SP and ALDH markers refines the Lin(-)CD34(+)CD38(-) hematopoietic compartment and identifies an SP/ALDH(Br) cell subset enriched in quiescent primitive HSCs/HPCs.

Aminobisphosphonate stimulates bone regeneration and enforces consolidation of titanium implant into a new rat caudal vertebrae model.

Bisphosphonates are widely used as therapeutic agents in bone disorders including cancer metastasis due to their osteoclast inhibitory effect. Recent data shows that bisphosphonates may also induce bone-building by stimulating osteoblast activity. Clinical observations, however, have revealed that bisphosphonates may cause necrosis in the oral cavity which questions their usefulness in bone regeneration during the consolidation of inorganic implants. Here we report the investigation of bone neogenesis following chronic amine bisphosphonate (Zometa) treatment in a novel experimental model, using the rat tail vertebra as a support. This method involves (1) implantation of titan screw into the tail vertebrae, (2) systemic bisphosphonate treatment and (3) quantitative biophysical measurements which mirrors consolidation of implant, i.e. strength of fixation and changes in newly formed bone architecture using micro Computer Tomograph (micro-CT). The degree of fixation of titan implants (osseointegration) increased by 36% on the effect of Zometa and the structure of newly formed bone became robust. The mass of new bone increased 3.1-fold at 6 weeks of regeneration, as compared to controls. Thus, Zometa, a potent aminobisphosphonate used in therapy of cancer metastases, osteoporosis and bone marrow transplantation, significantly increased bone neogenesis and enforced osseointegration of titan implants as measured quantitatively in the rat tail vertebra. Our data support the usefulness of aminobisphosphonates in the rehabilitation of bone loss as well as in improvement osseointegration of implants. We emphasise that this novel method may open up new possibilities for screening the effects of local and systemic treatments.

Blood-forming potential of vascular endothelium in the human embryo.

Hematopoietic cells arise first in the third week of human ontogeny inside yolk sac developing blood vessels, then, one week later and independently, from the wall of the embryonic aorta and vitelline artery. To address the suggested derivation of emerging hematopoietic stem cells from the vessel endothelium, endothelial cells have been sorted by flow cytometry from the yolk sac and aorta and cultured in the presence of stromal cells that support human multilineage hematopoiesis. Embryonic endothelial cells were most accurately selected on CD34 or CD31 surface expression and absence of CD45, which guaranteed the absence of contaminating hematopoietic cells. Yet, rigorously selected endothelial cells yielded a progeny of myelo-lymphoid cells in culture. The frequency of hemogenic endothelial cells in the yolk sac and aorta reflected the actual blood-forming activity of these tissues, as a function of developmental age. Even less expected, a subset of endothelial cells sorted similarly from the embryonic liver and fetal bone marrow also exhibited blood-forming potential. These results suggest that a part at least of emerging hematopoietic cells in the human embryo and fetus originate in vascular walls.